WO2015036812A1

WO2015036812A1 - Ink formulations and film constructions thereof

Info

Publication number: WO2015036812A1
Application number: PCT/IB2013/002571
Authority: WO
Inventors: Benzion Landa; Gregory Nakhmanovich; Galia Golodetz; Sagi Abramovich; Gal AVIDOR; Dan AVITAL; Jose Kuperwasser
Original assignee: Landa Corporation Ltd.
Priority date: 2013-09-12
Filing date: 2013-09-12
Publication date: 2015-03-19

Abstract

There are provided aqueous inkjet ink formulations comprising a solvent comprising water and a co-solvent, a water soluble or water dispersible polymeric resin and a colorant. Other embodiments are also described.

Description

INK FORMULATIONS AND FILM CONSTRUCTIONS THEREOF

FIELD AND BACKGROUND

[0001] The presently claimed invention relates to ink formulations suitable for ink jet printing systems, and more particularly for indirect printing systems.

[0002] Digital printing techniques have been developed that allow a printer to receive instructions directly from a computer without the need to prepare printing plates. Amongst these are color laser printers that use the xerographic process. Color laser printers using dry toners are suitable for certain applications, but they do not produce images of a photographic quality acceptable for publications, such as magazines.

[0003] A process that is better suited for short run high quality digital printing is used in the HP -Indigo printer. In this process, an electrostatic image is produced on an electrically charged image bearing cylinder by exposure to laser light. The electrostatic charge attracts oil-based inks to form a color ink image on the image bearing cylinder. The ink image is then transferred by way of a blanket cylinder onto paper or any other substrate.

[0004] Inkjet and bubble jet processes are commonly used in home and office printers. In these processes droplets of ink are sprayed onto a final substrate in an image pattern. In general, the resolution of such processes is limited due to wicking by the inks into paper substrates. Fibrous substrates, such as paper, generally require specific coatings engineered to absorb the liquid ink in a controlled fashion or to prevent its penetration below the surface of the substrate. Using specially coated substrates is, however, a costly option that is unsuitable for certain printing applications, especially for commercial printing. Furthermore, the use of coated substrates creates its own problems in that the surface of the substrate remains wet and additional costly and time consuming steps are needed to dry the ink, so that it is not later smeared as the substrate is being handled, for example stacked or wound into a roll. Furthermore, excessive wetting of the substrate by the ink causes cockling and makes printing on both sides of the substrate (also termed perfecting or duplex printing) difficult, if not impossible.

[0005] Furthermore, inkjet printing directly onto porous paper, or other fibrous material, results in poor image quality because of variation of the distance between the print head and the surface of the substrate.

[0006] Using an indirect or offset printing technique overcomes many problems associated with inkjet printing directly onto the substrate. It allows the distance between the surface of the intermediate image transfer member and the inkjet print head to be maintained constant and reduces wetting of the substrate, as the ink can be dried on the intermediate image member before being applied to the substrate. Consequently, the final image quality on the substrate is less affected by the physical properties of the substrate.

[0007] The use of transfer members which receive ink droplets from an ink or bubble jet apparatus to form an ink image and transfer the image to a final substrate have been reported in the patent literature. Various ones of these systems utilize inks having aqueous carriers, non-aqueous carrier liquids or inks that have no carrier liquid at all (solid inks).

[0008] The use of aqueous based inks has a number of distinct advantages. Compared to non-aqueous based liquid inks, the carrier liquid is not toxic and there is no problem in dealing with the liquid that is evaporated as the image dries. As compared with solid inks, the amount of material that remains on the printed image can be controlled, allowing for thinner printed images and more vivid colors.

[0009] Generally, a substantial proportion or even all of the liquid is evaporated from the image on the intermediate transfer member, before the image is transferred to the final substrate in order to avoid bleeding of the image into the structure of the final substrate. Various methods are described in the literature for removing the liquid, including heating the image and a combination of coagulation of the image particles on the transfer member, followed by removal of the liquid by heating, air knife or other means.

[0010] Generally, silicone coated transfer members are preferred, since this facilitates transfer of the dried image to the final substrate. However, silicone is hydrophobic which causes the ink droplets to bead on the transfer member. This makes it more difficult to remove the water in the ink and also results in a small contact area between the droplet and the blanket that renders the ink image unstable during rapid movement of the transfer member.

[0011] Surfactants and salts have been used to reduce the surface tension of the droplets of ink so that they do not bead as much. While these do help to alleviate the problem partially, they do not solve it. Hence, ink formulations suitable for ink jetting in particular on the intermediate transfer member of an indirect printing system are desired.

BRIEF DESCRIPTION

[0012] The presently claimed invention pertains to a particular aspect of a novel printing process and system for indirect digital inkjet printing using aqueous inks, other aspects of which are described and claimed in other applications of the same Applicant which have been filed or will be filed at approximately the same time as the present application. Further details on examples of such printing systems are provided in co-pending PCT application Nos. PCT/IB2013/051716, PCT/IB2013/051717 and PCT/IB2013/051718. A non-limitative description of such printing systems will be provided below.

[0013] Briefly, the printing process shared in particular, but not exclusively, by the above- mentioned systems, comprises directing droplets of an aqueous inkjet ink onto an intermediate transfer member having a hydrophobic release layer to form an ink image on the release layer, the ink including an organic polymeric resin and a colorant in an aqueous carrier, and the transfer member having a hydrophobic outer surface. Upon impinging upon the intermediate transfer member, each ink droplet in the ink image spreads to form an ink film. The ink is then dried while the ink image is being transported by the intermediate transfer member, by evaporating the aqueous carrier from the ink image to leave a residue film of resin and coloring agent. The residue film is then transferred to a substrate. Without wishing to be bound by theory, it is presently believed that mutually attractive intermolecular forces between molecules in the outer region of each ink droplet nearest the surface of the intermediate transfer member and molecules on the surface of the intermediate transfer member itself (e.g. , between negatively charged molecules in the ink and positively charged molecules on the surface of the intermediate transfer member), counteract the tendency of the ink film produced by each droplet to bead under the action of the surface tension of the aqueous carrier, without causing each droplet to spread by wetting the surface of the intermediate transfer member.

[0014] There is provided in accordance with an embodiment of the invention a water- based inkjet ink formulation comprising: (a) a solvent containing water and, optionally, a co-solvent, said water constituting at least 8 wt.% of the formulation; (b) at least one colorant dispersed or at least partly dissolved within the solvent, the colorant constituting at least 1 wt.% of the formulation; and (c) an organic polymeric resin, which is dispersed or at least partially dissolved within the solvent, the resin constituting 6 to 40 wt.% of the formulation, wherein the average molecular weight of the resin is at least 8,000, the ink formulation having at least one of (i) a viscosity of 2 to 25 centipoise (cP) at at least one temperature in the range of 20-60°C and (ii) a surface tension of not more than 50 milliNewton/m (mN/m) at at least one temperature in the range of 20-60°C; and wherein at least one of the following two statements is true: (1) the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90°C to 195°C, the dried ink has a first dynamic viscosity in the range of 1 ,000,000 (1 x 10⁶) cP to 300,000,000 (3 x 10⁸) cP, and (b) at at least one temperature in the range of 50°C to 85°C, the dried ink has a second dynamic viscosity of at least 80,000,000 (8 x 10⁷) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity; and (2) the weight ratio of the resin to the colorant is at least 1 : 1.

[0015] In some embodiments, the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90°C to 195°C, the dried ink has a first dynamic viscosity in the range of 1,000,000 (1 x 10⁶) cP to 300,000,000 (3 x 10⁸) cP, and (b) at at least one temperature in the range of 50°C to 85°C, the dried ink has a second dynamic viscosity of at least 80,000,000 (8 x 10⁷) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity. In some embodiments, the first dynamic viscosity is at most 25^»10⁷cP, at most 20^»10⁷cP, at most 15^»10⁷cP, at most 12^»10⁷cP, at most 10^»10⁷cP, at most 9^»10⁷cP, at most 8^»10⁷cP, or at most 7^»10⁷cP. In some embodiments, the first dynamic viscosity is at least 2 x 10⁶ cP, at least 4 x 10⁶ cP, at least 5 x 10⁶ cP, at least 6 x 10⁶ cP, at least 7 x 10⁶ cP, at least 8 x 10⁶ cP, at least 9 x 10⁶ cP, at least 1 x 10⁷ cP, at least 1.1 x 10⁷ cP, at least 1.2 x 10⁷ cP, at least 1.3 x 10⁷ cP, at least 1.4 x 10⁷ cP, at least 1.5 x 10⁷ cP, at least 1.6 x 10⁷ cP, at least 2.5 x 10⁷ cP, or at least 4 x 10⁷ cP. In some embodiments, the first dynamic viscosity is within a range of 10⁶cP to 2.5^»10⁸cP, 10⁶cP to 2.0^»10⁸cP, 10⁶cP to 10⁸cP, 3^»10⁶cP to 10⁸cP, 5^»10⁶cP to 3^»10⁸cP, 5^»10⁶cP to 3^»10⁸cP, 8^»10⁶cP to 3^»10⁸cP, 8^»10⁶cP to 10⁸cP, 10⁷cP to 3^»10⁸cP, 10⁷cP to 2^»10⁸cP, 10⁷cP to 10⁸cP, 2^»10⁷cP to 3^»10⁸cP, 2^»10⁷cP to 2^»10⁸cP, or 2^»10⁷cP to 10⁸cP.

[0016] In some embodiments, when the ink when substantially dried has a first dynamic viscosity as previously mentioned, at at least one temperature in the range of 125°C to 160°C, the first dynamic viscosity of the substantially dried ink is in the range of 10⁷ cP to 3 xlO⁸ cP. In some of these embodiments, the first dynamic viscosity is at least 1.1 x 10⁷ cP, at least 1.2 x 10⁷ cP, at least 1.3 x 10⁷ cP, or at least 1.4 x 10⁷ cP; in some of these embodiments the first dynamic viscosity is at most 25^»10⁷cP, at most 20^»10⁷cP, at most 15^»10⁷cP, at most 12^»10⁷cP, at most 10^»10⁷cP, at most 9^»10⁷cP, at most 8^»10⁷cP, or at most 7^»10⁷cP; in some of these embodiments, the first dynamic viscosity is within a range of 10⁷cP to 3^»10⁸cP, 10⁷cP to 2^»10⁸cP, 10⁷cP to 10⁸cP, 2^»10⁷cP to 3^»10⁸cP, 2^»10⁷cP to 2^»10⁸cP, or 2^»10⁷cP to 10⁸cP.

[0017] In some embodiments, the formulation further comprises a dispersant. In some embodiments, the dispersant constitutes not more than 3.5 wt.%, not more than 3 wt.%, not more than 2.5 wt.%, not more than 2 wt.%, not more than 1.5 wt.%, not more than 1 wt.% or not more than 0.5 wt.% of the formulation. [0018] In some embodiments in which the formulation comprises a dispersant and, when substantially dried, has a first dynamic viscosity as mentioned above, at at least one temperature in the range of 90°C to 125°C the first dynamic viscosity of the substantially dried ink is in the range of 4 x 10⁷ cP to 2 x 10⁸ cP. In some of these embodiments the first dynamic viscosity is at least 5 x 10⁷ cP or 6 x 10⁷ cP; in some of these embodiments the first dynamic viscosity is at most 5 x 10⁷ cP or 6 x 10⁷ cP; in some of these embodiments the dispersant is selected from the group consisting of a high molecular weight aminourethane (Disperbyk^® 198), a modified polyacrylate polymer (EFKA^® 4560, EFKA^® 4580), or acrylic block copolymer made by controlled free radical polymerisation (EFKA^® 4585, EFKA^® 7702), or an ethoxylated non-ionic fatty alcohol (Lumiten^® N-OC 30).

[0019] In some embodiments in which the inkjet ink formulation when substantially dried has a second dynamic viscosity as mentioned above, the second dynamic viscosity is at least 9·10⁷ cP, at least 10⁸ cP, at least 1.1-10⁸ cP, at least 1.2-10⁸ cP, at least 1.3Ί0⁸ cP, at least 1.4·10⁸ cP, at least 1.5Ί0⁸ cP, at least 2.0Ί0⁸ cP, at least 2.5Ί0⁸ cP, at least 3.0Ί0⁸ cP, at least 3.5Ί0⁸ cP, at least 4.0Ί0⁸ cP, at least 5.0Ί0⁸ cP, at least 6·10⁸ cP, at least 7.5Ί0⁸ cP, at least 10⁹ cP, at least 2·10⁹ cP, at least 4·10⁹ cP, or at least 6·10⁹ cP.

[0020] In some embodiments in which the inkjet ink formulation when substantially dried has a first dynamic viscosity and a second dynamic viscosity as mentioned above, the ratio of the second dynamic viscosity to the first dynamic viscosity is at least 1.2: 1, at least 1.3:1, at least 1.5:1, at least 1.7:1, at least 2: 1, at least 2.5: 1, at least 3:1, at least 3.5:1, at least 4: 1, at least 4.5: 1, at least 5: 1, at least 6: 1, at least 7: 1, at least 8: 1, at least 10:1, at least 15: 1, at least 20: 1, at least 25:1, at least 50: 1, at least 100: 1, at least 500: 1, or at least 1000: 1. In some embodiments, a ratio of said second dynamic viscosity, at 90°C, to said first dynamic viscosity, at 60°C, is at least 1.2: 1, at least 1.3: 1, at least 1.5:1, at least 1.7: 1, at least 2:1, at least 2.5: 1, at least 3:1, at least 4: 1, at least 4.5 :1, at least 5: 1, at least 6: 1, at least 7: 1, or at least 8: 1. In some embodiments, the ratio of the first dynamic viscosity to the second dynamic viscosity is at most 30: 1, at most 25: 1, at most 20: 1, at most 15: 1, at most 12: 1, or at most 10: 1.

[0021] In some embodiments, the weight ratio of the polymeric resin to the colorant is at least 1 : 1. In some embodiments, the weight ratio of the polymeric resin to the colorant is at least 1.25: 1, at least 1.5: 1, at least 1.75: 1, at least 2: 1, at least 2.5: 1, at least 3: 1, at least 3.5:1, at least 4: 1, at least 5: 1, at least 7: 1, or at least 10: 1. In some embodiments, the weight ratio of the polymeric resin to the colorant is at most 15: 1, at most 12: 1, at most 10: 1, at most 7: 1, at most 5: 1, at most 4: 1, at most 3: 1, at most 2.5: 1, at most 2: 1, or at most 1.7: 1.

[0022] In some embodiments, the inkjet ink formulation, when substantially dried, has a glass transition temperature (T_g) of at most 50°C, at most 47°C, at most 45°C, at most 44°C, at most 43°C, at most 42°C, at most 40°C, at most 39°C, at most 37°C, at most 35°C, at most 32°C, at most 30°C or at most 28°C.

[0023] In some embodiments, the polymeric resin is an acrylic-based polymer selected from an acrylic polymer and an acrylic-styrene copolymer.

[0024] In some embodiments, the inkjet ink formulation comprises a co-solvent. In some embodiments, the co-solvent is miscible with the water. In some embodiments the co- solvent is miscible with water at the at least one particular temperature in the range of 20°C to 60°C, whereby the solvent is a single-phase solvent. In some embodiments, the co- solvent is selected to provide the single-phase solvent with a reduced vapor pressure relative to water at the at least one particular temperature in the range of 20°C to 60°C. In some embodiments, the co-solvent is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, glycerol, PEG 400, N-methyl pyrrolidone, and mixtures thereof. In some embodiments, the co-solvent is not a water-soluble polymer. In various embodiments, the co-solvent is not a water-soluble polymer having an average molecular weight greater than 1000, greater than 750, or greater than 500. In various embodiments, the co-solvent constitutes at least 5 wt.%, at least 10 wt.%, at least 15 wt.%>, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, or at least 40 wt.% of the formulation. In some embodiments, the co-solvent constitutes not more than 40 wt.%, not more than 35 wt.%, not more than 30 wt.%, not more than 25 wt.%, not more than 20 wt.%, not more than 15 wt.%, not more than 10 wt.%, or not more than 5 wt.% of the formulation. In some embodiments, the ratio of co-solvent to water, on a weight-weight basis, is within the range of 0.2: 1 to 1.5 : 1.

[0025] In some embodiments, the inkjet ink formulation further comprises a surfactant, in addition to the polymeric resin, colorant, water and optional co-solvent. In some embodiments, the surfactant is present in an amount of not more than 2 wt.%, not more than 1.5 wt.%, not more than 1 wt.%, or not more than 0.5 wt.%. In some embodiments, the surfactant is a non-ionic surfactant. In some embodiments, the surfactant is an anionic surfactant. In some embodiments, the surfactant is a cationic surfactant. [0026] In some embodiments, the polymeric resin has a T_g below 50°C. In various embodiments, the polymeric resin has a T_g that is at most 48°C, at most 47°C, at most 45°C, at most 40°C, at most 35°C, or at most 30°C.

[0027] In some embodiments, the average molecular weight of the polymeric resin is not more than 70,000, not more than 65,000, not more than 60,000, not more than 55,000, not more than 50,000, not more than 45,000 or not more than 40,000. In some embodiments, the average molecular weight of the polymeric resin is at least 10,000, at least 15,000, at least 20,000, at least 25,000 or at least 30,000.

[0028] In some embodiments, the average molecular weight of the polymeric resin is at least 70,000, at least 80,000, at least 100,000, at least 120,000, at least 140,000, at least 160,000, at least 180,000, or at least 200,000.

[0029] In some embodiments, the colorant comprises a pigment or a mixture of pigments. In some embodiments, the average particle size (D₅₀) of the at least one pigment is not more than 120 nm, not more than 110 nm, not more than 100 nm, not more than 90 nm, not more than 80 nm, not more than 70 nm, not more than 65 nm, or not more than 60 nm. In some embodiments, the average particle size (D₅₀) of the pigment is at least 20 nm, at least 25 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, at least 50 nm, at least 55 nm, at least 60 nm, at least 65 nm, or at least 70 nm. In various embodiments, the average particle size (D₅₀) of the pigment is in the range of 20-120 nm, in the range of 20- 110 nm, in the range of 20-100 nm, in the range of 20-90 nm, in the range of 20-80 nm, in the range of 20-70 nm, in the range of 30-120 nm, in the range of 30-110 nm, in the range of 30-100 nm, in the range of 30-90 nm, in the range of 30-80 nm, in the range of 30-70 nm, in the range of 35-120 nm, in the range of 35-110 nm, in the range of 35-100 nm, in the range of 35-90 nm, in the range of 35-80 nm, in the range of 35-70 nm, in the range of 40-120 nm, in the range of 40-110 nm, in the range of 40-100 nm, in the range of 40-90 nm, in the range of 40-80 nm, or in the range of 40-70 nm.

[0030] In some embodiments, water constitutes at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 45 wt.%, at least 50 wt.%, at least 55 wt.%, at least 60 wt.%, at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, or at least 80 wt.% of the formulation. In some embodiments, water constitutes not more than 85 wt.%, not more than 80 wt.%, not more than 75 wt.%, not more than 70 wt.%, not more than 65 wt.%, not more than 60 wt.%, not more than 55 wt.%, not more than 50 wt.%, not more than 45 wt.%, or not more than 40 wt.% of the formulation. [0031] In some embodiments, the polymeric resin is a negatively chargeable resin. In some embodiments, the polymer resin is negatively charged.

[0032] In some embodiments, the ink when substantially dried contains at least 1.2 wt.%, at least 1.5 wt.%, at least 2 wt.%, at least 3 wt.%, at least 4 wt.%, at least 6 wt.%, at least 8 wt.%, or at least 10 wt.% of the colorant.

[0033] In some embodiments, the ink when substantially dried contains at least 5 wt.%, at least 7 wt.%, at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 30 wt.%, at least 40 wt.%), at least 50 wt.%, at least 60 wt.%, or at least 70 wt.% of the polymeric resin.

[0034] In some embodiments, a solubility of the resin in water, at a temperature within a temperature range of 20°C to 60°C, and at a pH within a pH range of 8.5 to 10, is at least 3%), at least 5%, at least 8%, at least 12%, at least 18%, or at least 25%, by weight of dissolved resin to weight of solution.

[0035] In some embodiments, the inkjet ink formulation comprises a pH-raising compound. In some embodiments, the pH-raising compound constitutes not more than 2 wt.%, not more than 1.5 wt.%, or not more than 1 wt.% of the formulation.

[0036] There is also provided, in accordance with an embodiment of the invention, an inkjet ink concentrate comprising: (a) a solvent containing water and, optionally, a co- solvent; at least one colorant dispersed or at least partly dissolved within said solvent; and an organic polymeric resin, which is dispersed or at least partially dissolved within said solvent, wherein the average molecular weight of said resin is at least 8,000, and (d) optionally, at least one of a surfactant, a dispersant, and a pH raising compound; wherein the concentrate, when diluted with a solvent comprising water and a co-solvent, yields an aqueous inkjet formulation as described herein. In some embodiments, the concentrate must be diluted with at least 50%, at least 100%), at least 150%, at least 200%), at least 250%), at least 300%), least 350%> or at least 400%) solvent on a weight/weight basis relative to the concentrate to yield the aqueous inkjet ink formulation. In some embodiments, the co-solvent is selected from the group consisting of glycerol, propylene glycol, ethylene glycol, diethylene glycol, N-methyl pyrrolidone, PEG 400, and mixtures thereof.

[0037] In some embodiments the inkjet ink formulation has both a viscosity of 2 to 25 cP at at least one temperature in the range of 20-60°C and a surface tension of not more than 50 (mN/m) at at least one temperature in the range of 20-60°C.

[0038] In various embodiments, the second dynamic viscosity is not more than 6 x 10⁹ cP, not more than 5 x 10⁹ cP, not more than 4 x 10⁹ cP, not more than 3 x 10⁹ cP, not more than 2 x 10⁹ cP, not more than 1 x 10⁹ cP, not more than 9 x 10⁸ cP, not more than 8 x 10⁸ cP, not more than 7 x 10 cP, not more than 6 x 10 cP, not more than 5 x 10 cP, not more than 4 x 10⁸ cP, not more than 3 x 10⁸ cP, or not more than 2 x 10⁸ cP.

[0039] In some embodiments, the polymeric resin comprises primarily or exclusively one or more negatively chargeable polymers, such as polyanionic polymers. By a "negatively chargeable polymer" or "negatively chargeable polymer resin" is meant a polymer or polymeric resin which has at least one proton which can easily be removed to yield a negative charge; as used herein, the term refers to an inherent property of the polymer, and thus may encompass polymers which are in an environment in which such protons are removed, as well as polymers in an environment in which such protons are not removed. In contrast, the term "a negatively charged polymer resin" refers to a resin in an environment in which one or more such protons have been removed. Examples of negatively chargeable groups are carboxylic acid groups (-COOH), including acrylic acid groups (-CH₂=CH-COOH) and methacrylic acid groups (-CH₂=C(CH₃)-COOH), and sulfonic acid groups (-S0₃H). Such groups can be covalently bound to polymeric backbones; for example styrene-acrylic copolymer resins have carboxylic acid functional groups which readily lose protons to yield negatively-charged moieties. Many polymers suitable for use in embodiments of the invention, when dissolved in water, will be negatively charged; others may require the presence of a pH raising compound to be negatively charged. Commonly, polymers will have many such negatively chargeable groups on a single polymer molecule, and thus are referred to as polyanionic polymers. Examples of polyanionic polymers include, for instance, polysulfonates such as polyvinylsulfonates, poly(styrenesulfonates) such as poly(sodium styrenesulfonate) (PSS), sulfonated poly(tetrafluoroethylene), polysulfates such as polyvinylsulfates, polycarboxylates such as acrylic acid polymers and salts thereof (e.g., ammonium, potassium, sodium, etc.), for instance, those available from BASF and DSM Resins, methacrylic acid polymers and salts thereof (e.g., EUDRAGIT^®, a methacrylic acid and ethyl acrylate copolymer), carboxymethylcellulose, carboxymethylamylose and carboxylic acid derivatives of various other polymers, polyanionic peptides and proteins such as homopolymers and copolymers of acidic amino acids such as glutamic acid, aspartic acid or combinations thereof, homopolymers and copolymers of uronic acids such as mannuronic acid, galacturonic acid and guluronic acid, and their salts, alginic acid and its salts, hyaluronic acid and its salts, gelatin, carrageenan, polyphosphates such as phosphoric acid derivatives of various polymers, polyphosphonates such as polyvinylphosphonates, as well as copolymers, salts, derivatives, and combinations of the preceding, among various others. In some embodiments, the polymeric resin comprises an acrylic-based polymer, viz. a polymer or copolymer made from acrylic acid or an acrylic acid derivative (e.g. methacrylic acid or an acrylic acid ester), such as polyacrylic acid or an acrylic acid- styrene copolymer. Nominally, the polymeric resin may be, or include, an acrylic styrene co-polymer. In some embodiments the polymeric resin comprises primarily or exclusively an acrylic-based polymer selected from an acrylic polymer and an acrylic-styrene copolymer. In some embodiments, the polymeric resin comprises an aliphatic polyurethane. In some instances, the polymeric resin is at least partly water soluble; in some instances, the polymeric resin is water dispersible, and may be provided as an emulsion or a colloid. Examples of such materials that are available commercially that have been found suitable for use in embodiments of the present invention include Joncryl 142-E, Joncryl 637, Joncryl 638, Joncryl 8004, Joncryl HPD 296, Neocryl BT-26, Neocryl BT-100, Neocryl BT-102, and Neocryl BT-9. (Joncryl® and Neocryl® are registered trademarks of BASF Corporation and DSM, respectively.)

[0040] In various embodiments, taken together the water, co-solvent if present, colorant, and polymeric resin constitute at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, at least 80 wt.%, at least 85 wt.%, at least 90 wt.% or at least 95 wt.% of the formulation.

[0041] In some embodiments, the colorant contains less than 5% dye. In some embodiments, the colorant is substantially free of a dye.

[0042] In some embodiments, the colorant comprises a dye. In some embodiments, the colorant contains less than 5% pigment. In some embodiments, the colorant comprises a dye and is substantially free of pigment.

[0043] In various embodiments, the polymeric resin constitutes not more than 20 wt.%, not more than 19 wt.%, not more than 18 wt.%, not more than 17 wt.%, not more than 16 wt.%, not more than 15 wt.%, not more than 14 wt.%, not more than 13 wt.%, not more than 12 wt.%, not more than 1 1 wt.%, not more than 10 wt.%, not more than 9 wt.%, or not more than 8 wt.% of the formulation.

[0044] In some embodiments, the polymeric resin is at least partially soluble in the solvent. In some embodiments, the polymeric resin is partially soluble in the solvent at a pH of 8.5-10. In various embodiments, at at least one temperature in the range of 20- 60 ° C, the solubility of the polymeric resin in water is at least 2%, at least 3%, at least 5%, at least 7.5%, or at least 10% on a resin-to-water weight- weight basis. [0045] In some embodiments, at at least one temperature in the range of 60 to 100°C, the polymeric resin has a viscosity of less than 10¹¹ cP, of 5 x 10¹⁰ cP or less, of 10¹⁰ cP or less, of 5 x 10⁹ cP or less, of 10⁹ cP or less, or of 5 x 10⁸ cP or less.

[0046] In some embodiments, at at least one temperature in the range of 125 to 170°C, the polymeric resin has a viscosity of 5 x 10⁸ cP or less, of 10⁸ cP or less, or of 5 x 10⁷ cP or less.

[0047] In some embodiments, the polymeric resin consists predominantly of acrylic styrene copolymer. In some embodiments, the polymeric resin consists essentially of acrylic styrene copolymer. In various embodiments, the weight ratio of the acrylic styrene copolymer to the total amount of polymeric resin is at least 0.5, at least 0.6, at least 0.7, at least 0.8, at least 0.9, at least 0.95, or substantially 1.

[0048] In some embodiments, at a temperature in the range of 20-60°C the viscosity of the formulation is within a range of 2-25 cP. In some embodiments, the viscosity in this temperature range is at least 2 cP, at least 3 cP, at least 4 cP, at least 5 cP, or at least 6 cP. In some embodiments, the viscosity in this temperature range is not more than 25 cP, not more than 22 cP, not more than 20 cP, not more than 18 cP, or not more than 15 cP.

[0049] In various embodiments, the surface tension of the formulation at at least one particular temperature within a temperature range of 20°C to 60°C is not more than 50 milliNewton/m, not more than 45 mN/m, or not more than 40 mN/m. In various embodiments, the surface tension of the formulation at this temperature is at least 18 mN/m, at least 20 mN/m, or at least 22 mN/m.

[0050] In some embodiments, other than the polymeric resin and, if present, the dispersant, the formulation is substantially free of water soluble polymer. In some embodiments, the formulation is substantially free of saccharide. In some embodiments, the formulation is substantially free of wax. In some embodiments, other than a pH-controlling agent, the formulation is substantially free of salt. In some embodiments, other than salts having the polymeric resin and/or the dispersant, if present, as one of the ions in the salt, the formulation is substantially free of salt. In some embodiments, the formulation is substantially free of precipitant. In some embodiments, the formulation is substantially free of a dye insolubilizing agent. In some embodiments, the formulation is substantially free of a coagulating agent. In various embodiments, the formulation contains less than 5 wt.% inorganic filler particles (such as silica particulates, titania particulates and alumina particulates), less than 3 wt.% inorganic filler particles, less than 2 wt.% inorganic filler particles, less than 1 wt.% inorganic filler particles, less than 0.5 wt.% inorganic filler particles, or less than 0.1 wt.% filler particles. In some embodiments, the formulation is substantially free of inorganic filler particles. In various embodiments, the formulation is substantially free of a co-solvent having a molecular weight of 1000 or higher, having a molecular weight of 750 or higher, or having a molecular weight of 500 or higher. In some embodiments, the co-solvent of which the formulation is substantially free is a polymer having a plurality of hydroxyl groups. In some embodiments, the polymer having a plurality of hydroxyl groups is selected from a polyethylene glycol and a polypropylene glycol. In some embodiments, the formulation is devoid or substantially devoid of oils such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil), or other oils used in offset ink formulations, and thus contains at most 1%, at most 0.5%, at most 0.1%, or at most 0%), by weight, of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air-drying.

[0051] In various embodiments, the total amount of material in the formulation which remains as solids when the formulation is substantially dried constitutes less than 20 wt.%, less than 19 wt.%, less than 18 wt.%, less than 17 wt.%, less than 16 wt.%, less than 15 wt.%), less than 14 wt.%, less than 13 wt.%, or less than 12 wt.% of the formulation.

[0052] In various embodiments, the colorant and the polymeric resin together constitute at least 50 wt.%, at least 55 wt.%, at least 60 wt.%, at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, at least 80 wt.%, at least 85 wt.%, at least 90 wt.%, at least 95 wt.% or at least 97 wt.% of the material in the formulation which remains as solids when the formulation is substantially dried.

[0053] In accordance with an embodiment of an invention described in a co-pending PCT application No. PCT/IB2013/000757, the contents of which are incorporated herein by reference, in a printing process such as that described above or as will described in more detail hereinbelow, in which an aqueous inkjet ink containing a negatively chargeable polymeric resin is jetted onto a hydrophobic release layer prior to being transferred to a substrate, there is provided a method for treating the release layer prior to the jetting of the aqueous ink onto the release layer, the method comprising contacting the release layer with an aqueous solution or dispersion of a positively chargeable polymeric chemical agent. The chemical agent used in the pre -treatment of the release layer prior to ink jetting may be referred to as a conditioning agent. In some embodiments of that invention, the chemical agent has at least one of (1) a positive charge density of at least 3 meq/g of chemical agent and an average molecular weight of at least 250, and (2) a nitrogen content of at least 1% and a molecular weight of at least 10,000. In some embodiments of that invention, the chemical agent has a positive charge density of at least 3 meq/g and an average molecular weight of at least 5,000; or a positive charge density of at least 6 meq/g and an average molecular weight of at least 1 ,000; or a nitrogen content of at least 1 wt.% and an average molecular weight of at least 50,000; or a nitrogen content of at least 18 wt.% and an average molecular weight of at least 10,000. In some embodiments of that invention, the chemical agent comprises nitrogen atoms in functional groups selected from primary amines and linear, branched and cyclic secondary and tertiary amines, as well as quaternized ammonium groups and combinations of such groups.

[0054] In some embodiments of that invention, the chemical agent is selected from the group consisting of linear polyethylene imine, branched polyethylene imine, modified polyethylene imine, poly(diallyldimethylammonium chloride), poly(4-vinylpyridine), polyallylamine, a vinyl pyrrolidone-dimethylaminopropyl methacrylamide co-polymer (e.g., Viviprint 131), a vinyl caprolactam-dimethylaminopropyl methacryamide hydroxy- ethyl methacrylate copolymer (e.g., Viviprint 200), a quaternized copolymer of vinyl pyrrolidone and dimethylaminoethyl methacrylate with diethyl sulfate (e.g., Viviprint 650), a guar hydroxypropyltrimonium chloride, and a hydroxypropyl guar hydroxypropyl- trimonium chloride. In some embodiments of that invention, the chemical agent is a polyethylene imine.

[0055] In some embodiments of that invention, the chemical agent is applied as a dilute solution, resulting in a very thin layer of chemical agent on the release layer and a low concentration of the chemical agent on the release layer after evaporation of the solvent.

[0056] According to some teachings of the present invention there is provided an ink film construction including: (a) a printing substrate; and (b) a plurality of continuous ink films, fixedly adhered to a surface of the printing substrate, the ink films containing at least one colorant dispersed in an organic polymeric resin; the ink films having a first dynamic viscosity within a range of 10⁶cP to 5^»10⁷cP for at least a first temperature within a first range of 60°C to 87.5°C, the ink films having a second dynamic viscosity of at least 6^» 10⁷cP, for at least a second temperature within a second range of 50°C to 55°C.

[0057] According to another aspect of the present invention there is provided an ink film construction including: (a) a printing substrate; and (b) a plurality of continuous ink films, fixedly adhered to a surface of the printing substrate, the ink films containing at least one colorant dispersed in an organic polymeric resin, and a softening agent selected to improve a flowability of the polymeric resin; the ink films having a first dynamic viscosity within a range of 10⁶cP to 5^»10⁷cP for at least a first temperature within a first range of 60°C to 100°C, the ink films having a second dynamic viscosity of at least 6^»10⁷cP, for at least a second temperature within a second range of 50°C to 55°C, the softening agent having a vapor pressure of at most 0.40 kPa at 150°C.

[0058] According to another aspect of the present invention there is provided a water- based inkjet ink formulation including: (a) a solvent containing water; (b) at least one colorant dispersed or at least partly dissolved within the solvent; and (c) at least one organic polymeric resin, dispersed within the solvent; the ink formulation forming, when dried, a dried ink residue having: (i) a first dynamic viscosity within a range of 10⁶cP to 5^»10⁷cP at at least a first temperature within a first range of 60°C to 87.5°C; and (ii) a second dynamic viscosity of at least 6^»10⁷cP, for at least a second temperature within a second range of 50°C to 55°C.

[0059] According to further features in the described preferred embodiments, the first dynamic viscosity is at most 4^»10⁷cP, at most 3^»10⁷cP, at most 2.5^»10⁷cP, at most 2^»10⁷cP, at most 1.5^»10⁷cP, or at most M0⁷cP.

[0060] According to still further features in the described preferred embodiments, the first dynamic viscosity is at least 2^»10⁶cP, at least 4^»10⁶cP, at least 6^»10⁶cP, at least 7^»10⁶cP, at least 8^»10⁶cP, at least 9^»10⁶cP, or at least M0⁷cP.

[0061] According to still further features in the described preferred embodiments, the first dynamic viscosity is within a range of 10⁶cP to 4^»10⁷cP, 10⁶cP to 3^»10⁷cP, 10⁶cP to 2^»10⁷cP, 3^»10⁶cP to 4^»10⁷cP, 3^«10⁶cP to 3^«10⁷cP, 5^«10⁶cP to 3^«10⁷cP, 7^«10⁶cP to 3^«10⁷cP, 8^»10⁶cP to 3^»10⁷cP, 9^»10⁶cP to 3^»10⁷cP, 10⁷cP to 5^»10⁷cP, 10⁷cP to 5^»10⁷cP, 10⁷cP to 4^»10⁷cP, 10⁷cP to 3^»10⁷cP, 1.5^»10⁷cP to 3^»10⁷cP, or 10⁷cP to 3^»10⁷cP.

[0062] According to still further features in the described preferred embodiments, the second dynamic viscosity is at least 8^»10⁷cP, at least 9^»10⁷cP, at least 10⁸cP, at least 1.2^»10⁸cP, at least 1.5^»10⁸cP, at least 2.0^»10⁸cP, at least 2.5^»10⁸cP, at least 3.0^»10⁸cP, at least 3.5'10⁸cP, at least 4.0^»10⁸cP, at least 5.0^»10⁸cP, or at least 7.5^»10⁸cP.

[0063] According to still further features in the described preferred embodiments, the second dynamic viscosity is at most 6^»10⁹cP, at most 4^»10⁹cP, at most 3^»10⁹cP, at most 2^»10⁹cP, at most 1.5^»10⁹cP, or at most 10⁹cP.

[0064] According to still further features in the described preferred embodiments, the second dynamic viscosity is within a range of 7^»10⁷cP to 5^»10⁹cP, 7^»10⁷cP to 3^»10⁹cP, 7'10⁷cP to 2^»10⁹cP, 7^»10⁷cP to M0⁹cP, 8^»10⁷cP to 5^»10⁹cP, 9^»10⁷cP to 5^»10⁹cP, 9^»10⁷cP to 3^»10⁹cP, 9^»10⁷cP to 2^»10⁹cP, 9^»10⁷cP to 1.5^»10⁹cP, M0⁸cP to 5^»10⁹cP, M0⁸cP to 3^»10⁹cP, M0⁸cP to 2'10⁹cP, or 1.5^»10⁸cP to 1.5^»10⁹cP.

[0065] According to still further features in the described preferred embodiments, the upper temperature limit of the first range is 87°C, 86°C, 85°C, 84°C, 82°C, 80°C, 78°C, 76°C, 74°C, 72°C, 70°C, or 68°C.

[0066] According to still further features in the described preferred embodiments, the lower temperature limit of the first range is 61°C, 62°C, 63°C, 64°C, or 65°C.

[0067] According to still further features in the described preferred embodiments, the average single ink-film thickness or height of the films is at most 2,000nm, at most l,800nm, at most l,600nm, at most l,400nm, at most l,200nm, at most Ι,ΙΟΟηηι, or at most Ι,ΟΟΟηηι.

[0068] According to still further features in the described preferred embodiments, the average single ink-film thickness or height of the films is at most 900nm, at most 800nm, at most 700nm, at most 650nm, at most 600nm, or at most 550nm.

[0069] According to still further features in the described preferred embodiments, the ink films or dried ink residue have a glass transition temperature (T_g) of at least 52°C, at least 54°C, at least 56°C, or at least 58°C.

[0070] According to still further features in the described preferred embodiments, the ink films or dried ink residue have a glass transition temperature (T_g) of at least 60°C, at least 65°C, at least 70°C, or at least 75°C.

[0071] According to still further features in the described preferred embodiments, the plurality of ink films or dried ink residue contain at least one water-soluble material or at least one water-dispersible material.

[0072] According to still further features in the described preferred embodiments, the at least one water-soluble material includes an aqueous dispersant.

[0073] According to still further features in the described preferred embodiments, the ink films or dried ink residue contain at least 2%, at least 3%, at least 5%, or at least 8%, by weight, of the water-soluble material. [0074] According to still further features in the described preferred embodiments, the ink films or dried ink residue contain at least 30%, at least 40%, at least 50%>, at least 60%>, or at least 70%>, by weight, of the water dispersible material.

[0075] According to still further features in the described preferred embodiments, the ink films or dried ink residue contain at most 10%, at most 7%, at most 5%, at most 3%, at most 2%>, at most 1%, or at most 0.5%> inorganic filler particles, by weight.

[0076] According to still further features in the described preferred embodiments, the ink films are laminated onto the surface of the printing substrate.

[0077] According to still further features in the described preferred embodiments, the ink films or dried ink residue contain at least 1.2%, at least 1.5%, at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 12%, at least 15%, or at least 20% of the colorant, by weight.

[0078] According to still further features in the described preferred embodiments, the ink films or dried ink residue contain at least 20%, at least 30%, at least 40%, at least 50%, at least 60%), or at least 70%> of the resin, by weight.

[0079] According to still further features in the described preferred embodiments, the colorant includes at least one pigment.

[0080] According to still further features in the described preferred embodiments, the weight ratio of the resin to the colorant within the plurality of ink films or dried ink residue is at least 1 : 1, at least 1.25: 1, at least 1.5: 1, at least 1.75: 1, at least 2: 1, at least 2.5: 1, at least 3: 1, at least 3.5: 1, at least 4: 1, at least 5: 1, at least 7: 1, or at least 10:1.

[0081] According to still further features in the described preferred embodiments, ΔΤ defines a temperature differential between a temperature (T_F) at which the ink films or dried ink residue begin to exhibit a particular degree of flowability, and a baseline temperature (T_B):

ΔΤ = T_F - T_B

[0082] the degree of flowability being defined by a critical viscosity (μοι at which the degree of flowability is achieved, and wherein, when the baseline temperature equals 50°C, and the critical viscosity equals 10⁸cP, the temperature differential is at least 3°C, at least 4°C, at least 5°C, at least 7°C, at least 12°C, at least 15°C, at least 18°C, at least 20°C, or at least 25°C. [0083] According to still further features in the described preferred embodiments, the printing substrate is a fibrous printing substrate.

[0084] According to still further features in the described preferred embodiments, the fibrous printing substrate is a commodity coated printing substrate.

[0085] According to still further features in the described preferred embodiments, the fibrous printing substrate is an uncoated printing substrate.

[0086] According to still further features in the described preferred embodiments, the continuous ink film of the continuous ink films is defined as an ink dot, a dimensionless aspect ratio (R_aspect) is defined by:

Raspect ⁼ Ddot Hdot

[0087] wherein: D_dot is an average diameter of the dot; H_dot is an average thickness of the dot; the dimensionless aspect ratio being at least 15, at least 20, at least 25, or at least 30, at least 40, at least 50, at least 60, at least 75, at least 85, at least 95, at least 110, or at least 120.

[0088] According to still further features in the described preferred embodiments, the dimensionless aspect ratio is at most 200 or at most 175.

[0089] According to still further features in the described preferred embodiments, the plurality of continuous ink films are fixedly adhered directly on the surface of the printing substrate.

[0090] According to still further features in the described preferred embodiments, the colorant constitutes at least 0.3%, at least 0.5%, at least 0.7%>, at least 0.85%>, at least 1%, at least 1.2%, at least 1.4%, at least 1.6%, at least 1.8%, or at least 2%, by weight, of the formulation.

[0091] According to still further features in the described preferred embodiments, the formulation further includes a softening agent.

[0092] According to still further features in the described preferred embodiments, the softening agent has a vapor pressure of at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa, at 150°C. [0093] According to still further features in the described preferred embodiments, the softening agent is stable up to a temperature of at least 170°C, at least 185°C, at least 200°C, or at least 220°C.

[0094] According to still further features in the described preferred embodiments, the formulation contains at most 10%, at most 8%, at most 6%, at most 4%, at most 2%, at most 1%), or at most 0.2% glycerol, by weight.

[0095] According to still further features in the described preferred embodiments, the formulation or the at least one organic polymeric resin further includes an aqueous dispersant.

[0096] According to still further features in the described preferred embodiments, the dispersant constitutes at most 5%, at most 4.5%, at most 4%, at most 3.5 wt.%, at most 3 wt.%, at most 2.5 wt.%, at most 2 wt.%, at most 1.5 wt.%, at most 1 wt.% or at most 0.5 wt.% of the formulation.

[0097] According to still further features in the described preferred embodiments, the dispersant is selected from the group consisting of high molecular weight polyurethanes or aminourethanes, styrene-acrylic copolymers, modified polyacrylate polymers, acrylic block copolymer made by controlled free radical polymerization, sulfosuccinates, acetylenic diols, ammonium salts of carboxylic acid, alkylol ammonium salts of carboxylic acid, aliphatic polyethers with acidic groups, and ethoxylated non-ionic fatty alcohols.

[0098] According to still further features in the described preferred embodiments, the polymeric resin includes, mainly includes, or consists essentially of an acrylic-based polymer selected from the group consisting of an acrylic polymer and an acrylic-styrene copolymer; or includes, mainly includes, or consists essentially of linear or branched resins of polyester or co-polyester.

[0099] According to still further features in the described preferred embodiments, the formulation is adapted such that when diluted by at least 50%, at least 100%, at least 150%, at least 200%, at least 250%, at least 300%, at least 350%, or at least 400%, on a weight/weight basis by a diluting solvent or water, a resultant mixture is an aqueous inkjet ink having: (i) a viscosity of 2 to 25 cP at at least one particular temperature in a range of 20-60°C; and (ii) a surface tension of at most 50 milliNewton/m at at least one particular temperature within the range. DETAILED DESCRIPTION

[00100] The presently claimed invention pertains to aqueous inkjet ink formulations. These formulations may be used in indirect printing systems having an intermediate transfer member. In particular the present formulations may be used as part of and in conjunction with, respectively, a novel printing process and system for indirect digital inkjet printing, other novel aspects of which are described and claimed in other applications of the same applicant being filing at the same time as the present patent application. Briefly, the printing process comprises directing droplets of an aqueous inkjet ink onto an intermediate transfer member having a hydrophobic release layer to form an ink image on the release layer, the ink including an organic polymeric resin and a colorant in an aqueous carrier. The term "release layer" is used herein to denote the hydrophobic outer surface of the intermediate transfer member, and while in some instances that outer surface may be part of a layer that is readily distinguishable from the rest of the intermediate transfer member, in theory it is possible that the intermediate transfer member has a uniform construction, in which case the outer surface will not, strictly speaking, be part of a separate layer. As previously explained, the release layer may be pretreated with a conditioning agent. Upon impinging upon the intermediate transfer member, each ink droplet in the ink image spreads to form an ink film having a pancake-like structure. The ink is then dried while the ink image is on the intermediate transfer member, generally while being transported by the intermediate transfer member, by evaporating the aqueous carrier from the ink image to leave a residue film of resin and coloring agent. The residue film is then transferred to a substrate.

[00101] As stated, upon impinging upon the surface of the intermediate transfer member, each ink droplet tends to spread out into a pancake-like structure due to the kinetic energy of the droplet itself. However, because the ink used in the process described above is aqueous, but the release layer of the intermediate transfer member is hydrophobic, the ink droplets tend to bead on the transfer member. The term "to bead" is used herein to describe the action of surface tension to cause a pancake or disk-like film to contract radially and increase in thickness so as to form a bead, that is to say a near-spherical globule. Thus the chemical compositions of the ink and of the release layer or of the chemical agent which is applied to the surface of the intermediate transfer member are selected, inter alia, so as to counteract the tendency of the ink film produced by each droplet to bead under the action of the surface tension of the aqueous carrier, without causing each droplet to spread by wetting the surface of the intermediate transfer member. Without wishing to be bound by theory, it is presently believed that this is due to mutually attractive intermolecular forces between molecules in the region of each droplet nearest the surface of the intermediate transfer member and molecules on the surface of the intermediate transfer member itself.

[00102] A hydrophobic outer surface on the intermediate transfer member is desirable as it assists in the eventual transfer of the residue film to the substrate. Such a hydrophobic outer surface or release layer is however undesirable during ink image formation, among other reasons because bead-like ink droplets cannot be stably transported by a fast moving intermediate transfer member and because they result in a thicker film with less coverage of the surface of the substrate. In some embodiments, the hydrophobic release layer may comprise positively chargeable molecules or moieties, such as amino silicones as further detailed in a co-pending PCT application No. PCT/IB2013/051751. However, when the hydrophobic release layer does not contain positively chargeable groups, the contacting of the release layer with a positively chargeable polymeric chemical agent prior to the jetting of the aqueous ink facilitates the preservation, or freezing, of the thin pancake shape of each ink droplet, that is caused by the flattening of the ink droplet on impacting the surface of the intermediate transfer member, despite the hydrophobicity of the surface of the intermediate transfer member. By a "positively chargeable polymer" or "positively chargeable group" is meant a polymer or chemical moiety which either can readily add a proton (e.g., -NH₂) or has a permanent positive charge (e.g., -N(CH₃)₃ ⁺); as used herein, the term refers to an inherent property of the polymer or moiety, and thus may encompass polymers or moieties which are in an environment in which such protons are added, as well as polymers in an environment in which such protons are not added. In contrast, the term "a positively charged" polymer or group refers to a polymer or group in an environment in which one or more such protons have been added or which has a permanent positive charge.

[00103] Briefly, the invention described and claimed in PCT/IB2013/000757 facilitates printing using an aqueous ink and an intermediate transfer member having a hydrophobic surface, by applying to the surface of the transfer member to which the ink is applied - i.e. by applying to the hydrophobic release layer - a small amount, preferably in the form of a thin layer, of chemical agent that reduces the tendency of the aqueous inkjet ink droplet that has been printed onto the release layer to contract. Measurements show that the contact angle of water on a hydrophobic release layer so treated remains high, indicating that, in contrast to wetting agents, treatment with the chemical agent does not result in a loss of surface tension. Therefore, the chemical agent advantageously reduces droplet contraction, without causing an undesired spreading of the droplet much beyond its initial impact pancake shape. Electron micrographs of aqueous inkjet inks in accordance with embodiments of the present invention, printed onto a release layer so treated, then dried while still on the release layer and then transferred to a paper substrate show that the edges of such ink droplets are sharper than the edges of ink droplets transferred to paper by other means. The chemical agent thus fixes the ink film to the release layer, although it will be appreciated that such fixation is weaker than the subsequent adhesion of the resin in the ink film to the substrate.

[00104] Whether the positively chargeable functional groups of the molecules on the release layer are part of the release layer itself (e.g., if the release layer has protonatable elastomers such as amino silicones) or whether they are part of the chemical agent applied on the electrically neutral hydrophobic release layer (e.g., silanol terminated silicones), such positive groups may interact with negatively charged functional groups of molecules of the ink. Suitable negatively charged or negatively chargeable groups include carboxylic acid groups (-COOH), including acrylic acid groups (-CH₂=CH-COOH) and methacrylic acid groups (-CH₂=C(CH₃)-COOH), and sulfonic acid groups (-SO3H). Such groups can be covalently bound to polymeric backbones; for example styrene-acrylic copolymer resins have carboxylic acid functional groups which readily lose protons to yield negatively- charged moieties.

[00105] As noted above, the hydrophobic release layer of the intermediate transfer member may be silicone-based. In one embodiment of the aforementioned inventions pertaining to intermediate transfer members having a hydrophobic outer surface, the release layer can be the product of cross-linking a silanol-terminated polydialkylsiloxane, such as a polymer of formula (I):

where Rl to R6 are each independently a Ci to C₆ hydrocarbon group (linear or branched, saturated or unsaturated), R7 is selected from the group consisting of OH, H or a Ci to C₆ hydrocarbon group (linear or branched, saturated or unsaturated), and n is an integer from 50 to 400. In some cases, n is an integer between 200 and 350. In some instances, the silicone has a molecular weight of between 15,000 to 26,000 g/mole, e.g., 16,000 to 23,000 g/mol, prior to crosslinking. In one example of such a material, the silicone is a silanol- terminated polydimethylsiloxane, i.e. Rl to R6 are all C¾ and R7=OH. The crosslinker, which may be present in an amount between e.g., 5 to 20 wt.%, such as 9 to 12 wt.%, relative to the polymer prior to crosslinking, may be a oligomeric condensate of a polyethylsilicate monomer, such as Silopren E 0.7 (Momentive), PSI023 (Gelest) and Ethylsilicate 48 (Colcoat). The silicon polymer may be made by condensation curing.

[00106] Release layers so prepared are amenable to pre-treatment with a conditioning agent as afore mentioned. Although in principle the aqueous ink may be jetted onto the chemical agent-treated release layer while the chemical agent is still wet in solution, it is preferable that the chemical agent generally be dry prior to the jetting of the ink, and in practice this is the the conditioning agent may be immediately removed following application {e.g., by air flow) and release layer will generally be heated, resulting in drying of the chemical agent solution before jetting of the ink occurs, so that the ink droplets are directed onto a substantially dry surface.

[00107] Aqueous inkjet inks in accordance with embodiments of the present invention, which are suitable for use in the process and with the system described above and hereinbelow, contain water-soluble or water-dispersible colorants, e.g., nano pigments, and a water-dispersible or water-soluble polymeric resin. As noted above, such resins, including for instance styrene-acrylic copolymers, contain moieties such as free carboxyl groups that are negatively charged under the conditions of use {e.g., at alkaline pH). In addition to being suitable for jetting from an inkjet printhead, the inks should also be formulated so as to transfer well from the intermediate transfer member to the substrate under the conditions of use, and preferably should be susceptible to having most or substantially all of the solvent and, if present, other volatiles removed therefrom prior to the transfer.

[00108] The ratio of charges in the ink droplet to the charges in the region of the release layer upon which the ink droplet rests may be small, but this need not be the case, and often there will be a significantly larger number of negative charges in an ink droplet relatively the area of the release layer upon which the ink is jetted.

[00109] It is believed that the concentration and distribution of the charged resin particles in such an ink droplet is not substantially changed as a result of contact with the release layer per se, if positively chargeable, or with the positively chargeable chemical agent that may have been applied upon the release layer. [00110] In some instances, the intermediate transfer member is a flexible blanket of which the outer surface is the hydrophobic outer surface upon which the ink image is formed. The blanket may be looped to form a continuous belt when mounted in suitable printing systems. It is however alternatively possible for the intermediate transfer member to be constructed as a drum.

[00111] In some instances, prior to transferring the residue film onto the substrate, the ink image is heated to a temperature at which the residue film of resin and coloring agent that remains after evaporation of the aqueous carrier is rendered tacky (e.g. , by softening of the resin). The temperature of the tacky residue film on the intermediate transfer member may be higher than the temperature of the substrate, whereby the residue film cools during adhesion to the substrate.

[00112] By suitable selection of the thermo-rheological characteristics of the residue film, the effect of the cooling may be to increase the cohesion of the residue film, whereby its cohesion exceeds its adhesion to the transfer member so that, when brought into contact with the substrate e.g., at an impression station (see below), for which it has greater affinity than for the release layer, substantially all of the residue film is separated from the intermediate transfer member and impressed as a film onto the substrate. In this way, it is possible to ensure that the residue film is impressed on the substrate without significant modification to the area covered by the film nor to its thickness.

[00113] As noted, inks in accordance with embodiments of the invention, which may be used if desired in conjunction with a chemical agent on the release layer, preferably utilize an aqueous carrier, which reduces safety concerns and pollution issues that occur with inks that utilize volatile hydrocarbon carrier. In general, the ink must have the physical properties that are needed to apply very small droplets close together on the transfer member.

[00114] Other effects that may contribute to the shape of the droplet remaining in the flattened configuration are, quick heating of the droplets to increase their viscosity, a barrier (a polymer coating or a conditioning agent) that reduces the hydrophobic effect of the silicone layer and a surfactant that reduces the surface tension of the ink.

[00115] In general, ink jet printers require a trade-off between purity of the color, the ability to produce complete coverage of a surface and the density of the ink-jet nozzles. If the droplets (after beading) are small, then, in order to achieve complete coverage, it is necessary to have the droplets close together. However, it is very problematic (and expensive) to have the droplets closer than the distance between pixels. By forming relatively flat droplet films that are held in place in the manner described above, the coverage caused by the droplets can be close to complete.

[00116] In some instances, the carrier liquid in the image is evaporated from the image after it is formed on the transfer member. Since the colorant in the droplets is distributed within the droplet, either as a solution (e.g., in the case of a dye) or as a dispersion (e.g., in the case of a pigment), a preferred method for removal of the liquid is by heating the image, either by heating the transfer member or by external heating of the image after it is formed on the transfer member, or by a combination of both. In some instances, the carrier is evaporated by blowing a heated gas (e.g. air) over the surface of the transfer member.

[00117] In some instances, different ink colors are applied sequentially to the surface of the intermediate transfer member and a heated gas is blown onto the droplets of each ink color after their deposition but before deposition on the intermediate transfer member of the next ink color. In this way, merging of ink droplets of different colors with one another is reduced.

[00118] In some instances, the polymer resin used in the ink is a polymer that enables the ink to form a residue film when it is heated (the term residue film is used herein to refer to the ink droplets after evaporation of the liquid carrier therefrom). Acrylic-styrene copolymers with an average molecular weight around 60,000, for example, have been found to be suitable. Preferably all of the liquid in the ink is evaporated, however, a small amount of liquid, that does not interfere with the forming of a residue film may be present. The formation of a residue film has a number of advantages. The first of these is that when the image is transferred to the final substrate all, or nearly all, of the image can be transferred. This allows in some cases for a system without a cleaning station for removing residues from the transfer member. It also allows for the image to be attached to the substrate with a nearly constant thickness of the image covering the substrate. Additionally, it prevents the penetration of the image beneath the surface of the substrate.

[00119] In general, when an image is transferred to or formed on a substrate while it is still liquid, the image penetrates into the fibers of the substrate and beneath its surface. This causes uneven color and a reduction in the depth of the color, since some of the coloring agent is blocked by the fibers. In some instances, the residue film is very thin, preferably between 10 nm and 800 nm and more preferably between 50 nm and 500 nm. Such thin films are transferred intact to the substrate and, because they are so thin, replicate the surface of the substrate by closely following its contours. This results in a much smaller difference in the gloss of the substrate between printed and non-printed areas.

[00120] When the residue film reaches a transfer or impression station at which it is transferred from the intermediate transfer member to the final substrate, it is pressed against the substrate, having preferably previously been heated to a temperature at which it becomes tacky in order to attach itself to the substrate.

[00121] Preferably, the substrate, which is generally not heated, cools the image so that it solidifies and transfers to the substrate without leaving any of residue film on the surface of the intermediate transfer member. For this cooling to be effective, additional constraints are placed on the polymer in the ink.

[00122] The fact that the carrier is termed an aqueous carrier is not intended to preclude the presence of certain organic materials in the ink, in particular, certain innocuous water miscible organic material and/or co-solvents, such as ethylene glycol or propylene glycol.

[00123] As the outer surface of the intermediate transfer member is hydrophobic, there may be little or substantially no swelling (e.g., less than 1.5%) of the transfer member due to absorption of water from the ink; such swelling is known to distort the surface of transfer members in commercially available products utilizing silicone coated transfer members and hydrocarbon carrier liquids. Consequently, the process described above and hereinbelow may achieve a highly smooth release surface, as compared to intermediate transfer member surfaces of the prior art.

[00124] As the image transfer surface is hydrophobic, and therefore not water absorbent, substantially all the water in the ink should be evaporated away if wetting of the substrate is to be avoided. It will be appreciated that the inclusion of certain co-solvents, such as ethylene glycol or propylene glycol, which have higher boiling points than water, may reduce the rate at which the solvent evaporates relative to the situation in which water is the only solvent. However, the ink droplets on the transfer member are of sufficiently small thickness relative to their surface area, and are usually heated at a temperature for a time, sufficient to allow for evaporation of substantially all of the solvent prior to transfer to the substrate.

Brief Description of the Drawings

[00125] Embodiments of the present invention will now be described further, by way of examples, and with reference to the accompanying drawings showing the operation of a printing system in which the presently claimed invention may be practiced, in which: [00126] Figure 1 is an exploded schematic perspective view of a printing system in accordance with which an embodiment of the invention may be used;

[00127] Figure 2 is a schematic vertical section through the printing system of Fig.1, in which the various components of the printing system are not drawn to scale;

[00128] Figure 3 is a schematic representation of a printing system of the invention in accordance with which an embodiment of the invention may be used;

[00129] Figures 4 and 5 are scans of paper onto which ink was transferred from a hydrophobic release layer, illustrating the effects of contacting the release layer with different (or no) chemical agents prior to jetting of the ink onto the release layer;

[00130] Figure 6 is a ramped-down temperature sweep plot of dynamic viscosity as a function of temperature, for several ink formulations of the present invention;

[00131] Figure 7 is a ramped-down temperature sweep plot of dynamic viscosity as a function of temperature, for several ink formulations of the present invention, vs. several commercially available inkjet inks; and

[00132] Figure 8 is a magnified view of the plot of Figure 8, for lower viscosities;

[00133] Figure 9A provides temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of various ink formulations, including ink formulations according to the present invention;

[00134] Figure 9B provides temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of inventive ink formulations containing various polyester resins;

[00135] Figure 10 provides temperature sweep plots of dynamic viscosity as a function of temperature, for representative dried ink dried residues of various ink formulations provided in Figures 9 A and 9B;

[00136] Figure 11 provides temperature sweep plots of dynamic viscosity as a function of temperature, for representative dried ink residues of ink formulations of the present invention, vs. dried ink residues of several commercially available inkjet inks;

[00137] Figure 12A provides a first plurality of temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of five ink formulations having identical components, and a varying ratio of softening agent, using a first thermoplastic resin and a first softening agent; [00138] Figure 12B provides a second plurality of temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of five ink formulations having identical components, and a varying ratio of softening agent, using a different thermoplastic resin and a different softening agent with respect to those used in Figure 17 A;

[00139] Figures 18A-18D are temperature sweep plots of dynamic viscosity as a function of temperature, for residue films of ink formulations having different softening agents, and varying concentrations of those agents;

[00140] Figure 14 provides temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of four ink formulations having different colorants (C, M, Y, K) but otherwise identical formulation components;

[00141] Figures 15A-F display two-dimensional (Figures 15A-C) and three- dimensional (Figures 15D-F) laser-microscope acquired magnified images of ink films on coated paper substrates, obtained using various printing technologies, wherein: Figures 15A and 15D are magnified images of a liquid electro-photography film (LEP); Figures 15B and 15E are magnified images of an offset splotch; and Figures 15C and 15F are magnified images of an inkjet ink film construction according to the present invention;

[00142] Figures 16A-F display two-dimensional (Figures 16A-C) and three- dimensional (Figures 16D-F) laser-microscope acquired magnified images of ink films on uncoated paper substrates, obtained using various printing technologies, wherein: Figures 16A and 16D are magnified images of a liquid electro-photography film (LEP); Figures 16B and 16E are magnified images of an offset splotch; and Figures 16C and 16F are magnified images of an inkjet ink film construction according to the present invention;

[00143] Figures 17A-1 to 17E-1 provide a magnified view of a field of ink dots or films on commodity-coated fibrous substrates (Figures 17A-1 to 17C-1) and uncoated fibrous substrates (Figures 17D-1 and 17E-1), produced using an ink formulation of the present invention;

[00144] Figures 17A-2 to 17E-2 provide further magnified views of a portion of the frames of Figures 17A-1 to 17E-1, in which the ink films disposed on commodity-coated paper are provided in Figures 17A-2 to 17C-2, and in which the ink films disposed on uncoated paper are provided in Figures 17D-2 and 17E-2; corresponding optical uniformity profiles are provided in Figures 17A-3 to 17E-3; [00145] Figures 17A-4 to 17E-4 provide magnified views of ink films disposed on coated paper (Figures 17A-4 to 17C-4) and un coated paper (Figures 17D-4 and 17E-4), along with corresponding image-processor computed contours and convexity projections thereof, the ink films produced using an ink formulation of the present invention;

[00146] Figure 18A provides a magnified view of a field of ink dots on a commodity-coated fibrous substrate, produced using a commercially available, aqueous, direct inkjet printer;

[00147] Figure 18B provides a magnified view of a field of ink dots on an uncoated fibrous substrate, produced using the identical, commercially available, aqueous, direct inkjet printer;

[00148] Figures 19A-2 to 19F-2 provide images of ink splotches or films obtained using various prior-art printing technologies on uncoated (Figures 19A-2 to 19C-2) and coated (Figures 19D-2 to 19F-2) paper, and optical uniformity profiles (19A-1 to 19F-1) therefor;

[00149] Figure 20A shows a two-dimensional shape having the mathematical property of a convex set;

[00150] Figure 20B shows a two-dimensional shape having the mathematical property of a non-convex set;

[00151] Figure 20C is a schematic top projection of an ink film having a rivulet and an inlet, the schematic projection showing a smoothed projection of the ink image;

[00152] Figures 21 A and 2 IB provide respective schematic cross-sectional views of an inventive ink film construction and an inkjet ink dot construction of the prior art, wherein the substrate is a fibrous paper substrate; and

[00153] Figures 22A and 22C each show an image of the surface of the outer layer of an intermediate transfer member; Figures 22B and 22D are corresponding images of the surface of the ink films produced using those outer layers, in accordance with the present invention.

General overview of a printing apparatus

[00154] The printing system shown in Figs. 1 and 2 essentially comprises three separate and mutually interacting systems, namely a blanket system 100, an image forming system 300 above the blanket system 100 and a substrate transport system 500 below the blanket system 100.

[00155] The blanket system 100 comprises an endless belt or blanket 102 that acts as an intermediate transfer member and is guided over two rollers 104, 106. An image made up of dots of an aqueous ink is applied by image forming system 300 to an upper run of blanket 102 at a location referred herein as the image forming station. A lower run selectively interacts at two impression stations with two impression cylinders 502 and 504 of the substrate transport system 500 to impress an image onto a substrate compressed between the blanket 102 and the respective impression cylinder 502, 504. As will be explained below, the purpose of there being two impression cylinders 502, 504 is to permit duplex printing. In the case of a simplex printer, only one impression station would be needed. The printer shown in Figs. 1 and 2 can print single sided prints at twice the speed of printing double sided prints. In addition, mixed lots of single and double sided prints can also be printed.

[00156] In operation, ink images, each of which is a mirror image of an image to be impressed on a final substrate, are printed by the image forming system 300 onto an upper run of blanket 102. In this context, the term "run" is used to mean a length or segment of the blanket between any two given rollers over which the blanket is guided. While being transported by the blanket 102, the ink is heated to dry it by evaporation of most, if not all, of the liquid carrier. The ink image is furthermore heated to render tacky the film of ink solids remaining after evaporation of the liquid carrier, this film being referred to as a residue film, to distinguish it from the liquid film formed by flattening of each ink droplet. At the impression cylinders 502, 504 the image is impressed onto individual sheets 501 of a substrate which are conveyed by the substrate transport system 500 from an input stack 506 to an output stack 508 via the impression cylinders 502, 504. Though not shown in the figures, the substrate may be a continuous web, in which case the input ant output stacks are replaced by a supply roller and a delivery roller. The substrate transport system needs to be adapted accordingly, for instance by using guide rollers and dancers taking slacks of web to properly align it with the impression station.

Image Forming System

[00157] The image forming system 300 comprises print bars 302 which may each be slidably mounted on a frame positioned at a fixed height above the surface of the blanket 102. Each print bar 302 may comprise a strip of print heads as wide as the printing area on the blanket 102 and comprises individually controllable print nozzles. The image forming system can have any number of bars 302, each of which may contain an aqueous ink of a different color.

[00158] As some print bars may not be required during a particular printing job, the heads can be moved between an operative position (at which the bar remains stationary), in which they overlie blanket 102 and an inoperative position (at which the bar can be accessed for maintenance).

[00159] Within each print bar, the ink may be constantly recirculated, filtered, degassed and maintained at a desired temperature and pressure, as known to the person skilled in the art without the need for more detailed description.

[00160] As different print bars 302 are spaced from one another along the length of the blanket, it is of course essential for their operation to be correctly synchronized with the movement of blanket 102.

[00161] If desired, it is possible to provide a blower following each print bar 302 to blow a slow stream of a hot gas, preferably air, over the intermediate transfer member to commence the drying of the ink droplets deposited by the print bar 302. This assists in fixing the droplets deposited by each print bar 302, that is to say resisting their contraction and preventing their movement on the intermediate transfer member, and also in preventing them from merging into droplets deposited subsequently by other print bars 302.

Blanket and Blanket Support System

[00162] The blanket 102, in one variation, is seamed. In particular, the blanket is formed of an initially flat strip of which the ends are fastened to one another, releasably or permanently, to form a continuous loop often referred to as a belt. A releasable fastening may be a zip fastener or a hook and loop fastener that lies substantially parallel to the axes of rollers 104 and 106 over which the blanket is guided. A permanent fastening may be achieved by the use of an adhesive or a tape. Alternatively, the belt may be seamless.

[00163] In order to avoid a sudden change in the tension of the blanket as the seam passes over rollers or other parts of the support system, it is desirable to make the seam, as nearly as possible, of the same thickness as the remainder of the blanket.

[00164] The primary purpose of the blanket is to receive an ink image from the image forming system and to transfer that image dried but undisturbed to the impression stations. To allow easy transfer of the ink image at each impression station, the blanket has a thin upper release layer that is hydrophobic, suitable examples of which have been above described.

[00165] The strength of the blanket can be derived from a support or reinforcement layer. In one instance, the reinforcement layer is formed of a fabric. If the fabric is woven, the warp and weft threads of the fabric may have a different composition or physical structure so that the blanket should have, for reasons to be discussed below, greater elasticity in its widthways direction (parallel to the axes of the rollers 104 and 106) than in its lengthways direction.

[00166] The blanket may comprise additional layers between the reinforcement layer and the release layer, for example to provide conformability and compressibility of the release layer to the surface of the substrate. Other layers provided on the blanket may act as a thermal reservoir or a thermal partial barrier and/or to allow an electrostatic charge to the applied to the release layer. An inner layer may further be provided to control the frictional drag on the blanket as it is rotated over its support structure. Other layers may be included to adhere or connect the aforementioned layers one with another or to prevent migration of molecules therebetween.

[00167] The blanket support system may comprise thermally conductive support plates 130 forming a continuous flat support surface both on the top side and bottom side of the support frame. Electrical heating elements can be inserted into transverse holes of the plates to apply heat to the plates 130 and through plates 130 to the blanket 102. Other means for heating the blanket will occur to the person of skill in the art and may include heating from below, above, or within the blanket itself.

[00168] Also mounted on the blanket support frame are two pressure or nip rollers 140, 142 which can be raised and lowered from the lower run of the blanket. The pressure rollers are located on the underside of the support frame in gaps between the support plates 130 covering the underside of the frame. The pressure rollers 140, 142 are aligned respectively with the impression cylinders 502, 504 of the substrate transport system. Each impression roller and corresponding pressure roller, when both are engaged with the blanket passing therebetween, form an impression station.

[00169] In some instances, the blanket support system further comprises a continuous track which can engage formations on the side edges of the blanket to maintain the blanket taut in its width ways direction. The formations may be spaced projections, such as the teeth of one half of a zip fastener sewn or otherwise attached to the side edge of the blanket. Alternatively, the formations may be a continuous flexible bead of greater thickness than the blanket. The lateral track guide channel may have any cross-section suitable to receive and retain the blanket lateral formations and maintain it taut. To reduce friction, the guide channel may have rolling bearing elements to retain the projections or the beads within the channel.

[00170] In order for the image to be properly formed on the blanket and transferred to the final substrate and for the alignment of the front and back images in duplex printing to be achieved, a number of different elements of the system must be properly synchronized. In order to position the images on the blanket properly, the position and speed of the blanket must be both known and controlled. For this purpose, the blanket can be marked at or near its edge with one or more markings spaced in the direction of motion of the blanket. One or more sensors 107 sense the timing of these markings as they pass the sensor. The speed of the blanket and the speed of the surface of the impression rollers should be the same, for proper transfer of the images to the substrate from the transfer blanket. Signals from the sensor(s) 107 are sent to a controller 109 which also receives an indication of the speed of rotation and angular position of the impression rollers, for example from encoders on the axis of one or both of the impression rollers (not shown). Sensor 107, or another sensor (not shown) also determines the time at which the seam of the blanket passes the sensor. For maximum utility of the usable length of the blanket, it is desirable that the images on the blanket start as close to the seam as feasible.

Blanket Pre-treatment

[00171] Fig.l shows schematically a roller 190 positioned on the external side of the blanket immediately before roller 106. Such a roller 190 may be used optionally to apply a thin film of pre-treatment solution containing a conditioning chemical agent, as above described.

[00172] While a roller can be used to apply an even film, the pre-treatment or conditioning material can alternatively be sprayed onto the surface of the blanket and optionally spread more evenly, for example by the application of a jet from an air knife. Independently of the method used to apply the optional conditioning solution, if needed, the location at which such pre-print treatment can be performed may be referred herein as the conditioning station. The alternative printing system illustrated in Figure 3 may also include a conditioning station.

[00173] As noted, when the ink droplet impinges on the transfer member, the momentum in the droplet causes it to spread into a relatively flat volume. In the prior art, this flattening of the droplet is almost immediately counteracted by the combination of surface tension of the droplet and the hydrophobic nature of the surface of the transfer member.

[00174] In some instances, the shape of the ink droplet is "frozen" such that at least some and preferably a major part of the flattening and horizontal extension of the droplet present on impact is preserved. It should be understood that since the recovery of the droplet shape after impact is very fast, the methods of the prior art would not effect phase change by agglomeration and/or coagulation and /or migration.

[00175] Without wishing to be bound by theory, it is believed that, on impact, the positive charges which have been placed on the transfer member attract the negatively charged polymer resin particles of the ink droplet that are immediately adjacent to the surface of the member. It is believed that, as the droplet spreads, this effect takes place along a sufficient area of the interface between the spread droplet and the transfer member to retard or prevent the beading of the droplet, at least on the time scale of the printing process, which is generally on the order of seconds.

[00176] As the amount of charge is too small to attract more than a small number of charged resin particles in the ink, it is believed that the concentration and distribution of the charged resin particles in the drop is not substantially changed as a result of contact with the chemical agent on the release layer. Furthermore, since the ink is aqueous, the effects of the positive charge are very local, especially in the very short time span needed for freezing the shape of the droplets.

[00177] The efficacy of this method and of the water-based treating solutions associated therewith, also termed "conditioning solutions", was established in laboratory experimental setups and in preliminary pilot printing experiments. As disclosed in the above-mentioned application the use of such solutions was highly beneficial, as assessed by the print quality of the image following its transfer from the intermediate transfer member to the printing substrate. The optical density of the printed matter was considered of particular relevance and the use of such method of blanket treatment prior to ink jetting clearly improved the measured outcome on the printing substrate.

[00178] According to our originally developed (and as yet unpublished) method, a very thin coating of conditioning solution was applied to the transfer member, immediately removed and evaporated, leaving no more than few layers of the suitable chemical agent. Ink droplets were jetted on such pre -treated blanket, dried and transferred to the printing substrate. Typically, the ink film image so printed could be identified by the presence on their outer surface of the conditioning agent. In other words, the dried ink droplet upon transfer ripped the underlayer of conditioning agent and was impressed on the final substrate in inversed orientation.

[00179] It was expected that untransferred residues of conditioning agents (e.g., in areas where no ink was jetted), would readily redissolve in the next cycle, upon the application of a fresh coating of conditioning solution. The operating temperature of the process, which may vary at the different stations along the path the jetted image would follow, but would typically be above 50°C, was expected to facilitate such resolubilization of the residual conditioning agents, if any, in the freshly applied solution. In addition, any such residue was expected to be readily eliminated during cleaning of the transfer member that could take place, if desired, to remove dirt or traces of ink residues that may gather on such member following repeated printing cycles.

[00180] In the field, numerous operative parameters were tested, such that the number of runs being performed under a given set of variables was relatively limited, i.e., up to 1,500- 3,000 impression repeats. However, upon repeated use of this method in pilot experiments of longer runs (e.g., at least 5,000-10,000 impressions), various undesirable phenomena were found to occur. Perhaps most significantly, the inventors discovered that various above-provided conditioning agents, though based on water-soluble polymers, did not— once dried on the ITM — resolubilize satisfactorily when subjected to a subsequent application of the conditioning solution.

[00181] In addition, the inventors have found that low-temperature operation of the image forming station may appreciably complicate or increase the difficulty of the conditioning duty. Without wishing to be limited by theory, the inventors believe that at higher temperatures, the evaporation of the carrier of the ink formulation proceeds at a relatively high rate, which reduces the requisite duty of the conditioning agents with respect to the retardation of droplet beading. However, at lower operating temperatures, the evaporation kinetics may be significantly slower, as are the kinetics for the attraction process between the positively-charged conditioning agents and the negatively-charged functional groups in the ink (typically in the resin).

[00182] Moreover, the inventors believe that the kinetics of resolubilization may also be appreciably reduced at lower temperatures, which as elaborated hereinabove, may detract from print image quality. [00183] The inventors have surprisingly discovered aqueous formulations that act as a conditioning solution, and that facilitates resolubilization of residual conditioning agents. In some embodiments, the aqueous conditioning formulation may be sufficiently active, at low temperatures (Image Forming Station temperatures within a range of 40°C to 95°C, 60°C to 95°C, 75°C to 95°C, 60°C to 90°C, or 60°C to 85°C) to efficaciously interact with various negatively charged molecules in the ink, within the requisite time frame (at most a few seconds), such that beading of the droplet is sufficiently retarded.

[00184] The inventive aqueous conditioning formulation may include: a positively chargeable polymeric conditioning agent, typically having an amine functional group, such as a polyethylene imine (PEI), and a resolubilizing agent selected to improve resolubilization of the conditioning agent, both disposed within an aqueous carrier liquid. Typically, the PEI has an average molecular weight of at least 5,000 and a positive charge density of at least 10 meq/g. The resolubilizing agent may advantageously have, in a pure state, a vapor pressure of less than 0.025, less than 0.020, less than 0.015, less than 0.012, less than 0.010, or less than 0.008 bar at 90°C.

[00185] The weight ratio of the resolubilizing agent to the PEI, within the conditioning formulation, is typically within a range of 1 : 10 to 20: 1, within a range of 1 :5 to 20: 1, within a range of 1 :5 to 15: 1, and more typically, within a range of 1 :3 to 10: 1, within a range of 1 :3 to 7: 1, within a range of 1 :3 to 5: 1, within a range of 1 :2 to 5: 1, or within a range of 1 : 1 to 5 : 1.

[00186] The resolubilizing agent may have a solubility in water of at least 1%, at least 3%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at 25°C and a pH of 7. The PEI, resolubilizing agent, and carrier liquid may make up at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 97%, or at least 99% of the formulation, by weight.

[00187] The PEI may be a linear polyethylene imine, a branched polyethylene imine, a modified (e.g., ethoxylated) polyethylene imine, or combinations thereof. The average molecular weight of the PEI may be at least 25,000, at least 50,000, at least 100,000, at least 150,000, at least 200,000, at least 250,000, at least 500,000, at least 750,000, at least 1,000,000, or at least 2,000,000. [00188] The charge density of the PEI may be at least 11 meq/g, at least 12 meq/g, at least 13 meq/g, at least 14 meq/g, at least 15 meq/g, at least 16 meq/g, at least 17 meq/g, at least 18 meq/g, at least 19 meq/g, or at least 20 meq/g.

[00189] The concentration of PEI within the formulation may be not more than 5 wt.%, not more than 4 wt.%, not more than 3 wt.%, not more than 2 wt.%, not more than 1 wt.%, not more than 0.5 wt.%, not more than 0.4 wt.%, not more than 0.3 wt.%, not more than 0.2 wt.%, not more than 0.1 wt.%, not more than 0.05 wt.%, or not more than 0.01 wt.%.

[00190] The resolubilizing agent may be stable at a temperature of up to at least 100°C, at least 125°C, at least 150°C, at least 175°C, at least 200°C, or at least 225°C.

[00191] The resolubilizing agent may include, mainly include, or consist essentially of at least one sugar, at least one alcohol, at least one amine, or combinations thereof.

[00192] Exemplary conditioning solutions that can be used to treat an ITM upon which ink formulations of the present invention can be deposited are provided hereinbelow the amount of the respective ingredients being provided in weight percent (wt.%) of the complete conditioning formulation:

Conditioning Solution A

PEI Lupasol® PS (BASF)

Sucrose

Water

Conditioning Solution B

PEI Lupasol® P (BASF)

Glycerol

Water

Conditioning Solution C

PEI Lupasol® HF (BASF)

Triethanolamine

Water

Conditioning Solution D PEI Lupasol® WF (BASF) Pentaerythritol 1 Water 97

Conditioning Solution E

PEI branched, MW 25,000 (Aldrich) 3

Polyethylene glycol 400 6

Water 91

Conditioning Solution F

PEI, 80 % ethoxylated MW 111 ,000, 37% water solution (Aldrich) 4

Glycerol 4

Water 92

[00193] Such conditioning solutions were typically prepared by mixing the conditioning agent with most of the water, subsequently adding the resolubilizing agent and further stirring the mixture. Water was then added to complete the conditioning formulation up to 100 weight parts and the resulting formulation was optionally filtered through a 0.5 μιη filter.

[00194] Such conditioning solutions can be prepared as concentrated stock to be diluted to the final concentration desired in operation of a relevant printing system. Exemplary concentrated stock of conditioning solutions that can be diluted used to treat an ITM upon which ink formulations of the present invention can be deposited are provided hereinbelow, the amount of the respective ingredients being provided in weight percent (wt.%) of the stock:

Conditioning Stock Solution G

PEI Lupasol® P (BASF) 40

Glycerol 40

Water 20

Conditioning Stock Solution H

PEI, Lupasol PN-50 30

Triethanolamine 20

Water 50 Conditioning Solution I

Viviprint 131 2 %

Glycerol 2 %

Water 96 %

Conditioning Solution J

PEI Lupasol® PS (BASF) 1 %

Water 98%

Glycerol 2 %

The re-solubility of Solution I and Solution J was tested according to the following procedure: each sample (50 ml) was dried for 3 days at 100°C. The dried residue was resuspended with 50 ml of hot water (with heating to 60°C to accelerate the experiment and to approximate the temperature of the ITM).

Results: the residue of Solution I dissolved almost immediately (in less than 1 second). By contrast, dissolution of Solution J, which was devoid of a resolubilization agent, required 1 minute of intensive shaking.

Solution K

PEI Lupasol® HF (BASF)

3%

Ethyl alcohol

94%

Triethanol amine

3%

Solution L

PEI Lupasol® PS (BASF) 1% Isopropyl alcohol

97%

Glycerol

2%

Inks

[00195] Inks in accordance with embodiments of the presently claimed invention, which are suitable for use in the process and in conjunction with the system described herein are, for example, aqueous inkjet inks that contain (i) a solvent comprising water and optionally a co-solvent, (ii) a negatively chargeable polymeric resin (the ink may include a small amount of a pH-raising substance to ensure that the polymer is negatively charged), and (iii) at least one colorant. Preferably, water constitutes at least 8 wt.% of the ink; the at least one colorant is dispersed or at least partly dissolved within the solvent and constitutes at least 1 wt.% of the ink; the polymeric resin is dispersed or at least partially dissolved within the solvent and constitutes 6 to 40 wt.% of the ink; the average molecular weight of the polymeric resin is at least 8,000 and in some cases not more than 70,000; and prior to jetting the ink has at least one of (i) a viscosity of 2 to 25 cP at at least one temperature in the range of 20-60°C and (ii) a surface tension of not more than 50 milliNewton/m at at least one temperature in the range of 20-60°C. The colorant may contain a pigment, preferably a nanopigment, for example having an average particle size (D₅₀) of not more than 120 nm.

[00196] Preferably, either (1) the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90°C to 195°C, the dried ink has a first dynamic viscosity in the range of 1,000,000 (1 x 10⁶) cP to 300,000,000 (3 x 10⁸) cP, and (b) at at least one temperature in the range of 50°C to 85°C, the dried ink has a second dynamic viscosity of at least 80,000,000 (8 x 10⁷) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity; or (2) the weight ratio of the resin to the colorant is at least 1 : 1.

[00197] With respect to the ink, "substantially dried" or "substantially dry" refers to ink that has no more solvent and other volatile compounds than does a layer of the ink of 1 mm initial thickness after such a layer is dried in an oven for 12 hours at 100°C.

[00198] As noted, the polymer resins, such as acrylic-based polymers, may be negatively charged at alkaline pH. Consequently, in some embodiments, the polymeric resin has a negative charge at pH 8 or higher; in some embodiments the polymeric resin has a negative charge at pH 9 or higher. Furthermore, the solubility or the dispersability of the polymeric resin in water may be affected by pH. Thus in some embodiments, the formulation comprises a pH-raising compound. Examples of such are diethyl amine, monoethanol amine, and 2-amino-2-methyl propanol. Such pH-raising compounds, when included in the ink, are generally included in small amounts, e.g., about 1 wt.% of the formulation and usually not more than about 2 wt.% of the formulation.

[00199] It will also be appreciated that acrylic-based polymers having free carboxyl groups may be characterized in terms of their charge density or, equivalently, the acid number, viz. the number of mg of KOH needed to neutralize one g of dry polymer. Thus, in some embodiments, the polymeric resin has an acid number in the range of 70-144. [00200] As noted, the ink formulation contains at least one colorant. As used herein in the specification and in the claims section that follows, the term "colorant" refers to a substance that is considered, or would be considered to be, a colorant in the art of printing. The concentration of the at least one colorant within the ink formulation when substantially dry may be at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, or at least 22%, by weight. Typically, the concentration of the at least one colorant within the ink film is at most 40%, at most 35%, at most 30%, or at most 25%. More typically, the ink formulation when substantially dry may contain 2-30%, 3- 25%, or 4-25% of the at least one colorant. The colorant may include at least one pigment. Alternatively or additionally, the colorant may include at least one dye.

[00201] As used herein in the specification and in the claims section that follows, the term "pigment" refers to a finely divided solid colorant. The pigment may have an organic and/or inorganic composition. Typically, pigments are insoluble in, and essentially physically and chemically unaffected by, the vehicle or medium in which they are incorporated. Pigments may be colored, fluorescent, or pearlescent. Pigments may alter appearance by selective absorption, interference and/or scattering of light. They are usually incorporated by dispersion in a variety of systems and may retain their crystal or particulate nature throughout the pigmentation process.

[00202] As used herein in the specification and in the claims section that follows, the term "dye" refers to at least one colored substance that is soluble or goes into solution during the application process and imparts color by selective absorption of light.

[00203] As used herein in the specification and in the claims section that follows, the term "average particle size", or "D50", with reference to the particle size of pigments, refers to an average particle size, by weight, as determined by a laser diffraction particle size analyzer (e.g., Mastersizer™ 2000 of Malvern Instruments, England), using standard practice.

[00204] A variety of pigments are suitable for use in the inks in accordance with embodiments of the invention, although it has been found that results are best when the average particle size (D₅₀) of the pigment is from 10 nm to 300 nm, such as 120 nm or less, for example on the order of 70-80 nm. The pigments may thus be nanopigments; the particle size of the nanopigments may depend on the type of pigment and on the size reduction methods used in the preparation of the pigments. For example, the particle size for magenta and yellow pigments may be in the range of 10 nm to 100 nm, while blue or green pigments may be in the range of 75 nm to 200 nm. Generally the D50 of the pigment particles may be within a range of 10 nm to 270 nm. Pigments of various particle sizes, utilized to give different colors, may be used for the same print. Some pigments having such particle sizes are commercially available, and may be employed as-is in embodiments of the invention; in other cases, the pigments may be milled to the appropriate size. It will be appreciated that in general, the pigments are dispersed (or at least partly dissolved) within the solvent along with the polymeric resin, or are first dispersed within the polymeric resin (e.g., by kneading) to obtain colored resin particles which are then mixed with the solvent.

[00205] In some applications, particularly when it is desirable to have an ultra-thin ink film laminated onto the printing substrate, the weight ratio of the polymeric resin to the colorant may be at most 7: 1, at most 5: 1, at most 3: 1, at most 2.5: 1, at most 2: 1 , or at most 1.7:1.

[00206] Examples of suitable co-solvents which are miscible with water are ethylene glycol, diethylene glycol, propylene glycol, glycerol, and N-methyl pyrrolidone. Another example is polyethylene glycol 400 (PEG 400), although in some embodiments, the ink formulation is substantially free of water soluble polymers. In some embodiments the ink formulation is substantially free of saccharides. The co-solvent may be present as a mixture of co-solvents.

[00207] In some embodiments, it may be desirable to include, in addition to the polymeric resin, colorant, water and co-solvent, a small amount of a surfactant, e.g., 0.5- 1.5 wt.% of the ink. In some embodiments, the surfactant is a non-ionic surfactant.

[00208] In some embodiments, the ink formulation is devoid or substantially devoid of wax. Typically, the ink formulation contains less than 30 wt.% wax, less than 20 wt.% wax, less than 15 wt.%> wax, less than 10 wt.%> wax, less than 7 wt.%> wax, less than 5 wt.%) wax, less than 3 wt.%> wax, less than 2 wt.%> wax, or less than 1 wt.%> wax. In other embodiments, wax is included in the ink formulation in order to impart greater abrasion resistance in the printed ink. Such waxes may be natural or synthetic, e.g. , based on esters of fatty acids and fatty alcohols or long-chain alkanes (paraffin waxes), or mixtures thereof. In such cases, the formulation may comprise for example 0.1-10 wt.% wax, e.g., up to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7. 0.8, 0.9, 1.0, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9 or 10 wt.% wax. The wax may be incorporated into the formulation as an aqueous dispersion of small wax particles, e.g., having average size of 10 micron or smaller, preferably having average size of 1 micron or smaller. [00209] In some embodiments, the ink formulation is devoid or substantially devoid of oils such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil). Typically, the ink formulation contains at most 20 wt.%, at most 12 wt.%, at most 8 wt.%, at most 5 wt.%), at most 3 wt.%, at most 1 wt.%, at most 0.5 wt.%, or at most 0.1 wt.%, by weight, of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air- drying. In some embodiments, the formulation is substantially free of a plasticizer.

[00210] In some embodiments, the ink formulation is devoid or substantially devoid of one or more salts, including salts used to coagulate or precipitate ink on a transfer member or on a substrate (e.g., calcium chloride). Typically, the ink formulation contains at most 8 wt.%), at most 5 wt.%, at most 3 wt.%, at most 1 wt.%, at most 0.5 wt.%, at most 0.1 wt.%, or substantially 0 wt.% of one or more salts. Such salts may be referred to herein as "precipitants", and it will be appreciated that when it is stated that a formulation does not include a salt or contains salt in an amount less than a certain weight percentage, this does not refer to salts that may form between the polymer(s) of the polymeric resin and pH modifiers, such as alcohol amines, or that may be present in the polymeric resin itself if the polymeric resin is provided as a salt. As discussed above, it is presently believed that the presence of negative charges in the polymeric resin is beneficial to the print process.

[00211] In some embodiments, the ink formulation is devoid or substantially devoid of inorganic particulates, e.g., silica particulates, titania particulate or alumina particulates, containing less than 2 wt.%, less than 1 wt.%, less than 0.1 wt.% or substantially no inorganic particulates. By "silica particulates" is meant fumed silica, silica chips, silica colloids, and the like. Specific examples of such silica particulates include those available from DuPont Company under the names: Ludox AM-30, Ludox CL, Ludox HS-30; and those available from Nyacol Nanotechnologies Company under the names: NexSil 12, NexSil 20, NexSil 8, Nexsil 20, Nexsil 85. In the context of the present application, the term "silica particulates" does not include colorants.

Ink Image Heating

[00212] The heaters, either inserted into the support plates 130 or positioned above the blanket as intermediate drying system 224 and drying station 214, are used to heat the blanket to a temperature that is appropriate for the rapid evaporation of the ink carrier and compatible with the composition of the blanket. For blankets comprising for instance silanol- modified or terminated polydialkylsiloxane silicones in the release layer, heating is typically of the order of 150°C, though this temperature may vary within a range from 70°C to 180°C, depending on various factors such as the composition of the inks and/or of the conditioning solutions if needed. Blankets comprising amino silicones may generally be heated to temperatures between 70°C and 130°C. When using beneath heating of the transfer member, it is desirable for the blanket to have relatively high thermal capacity and low thermal conductivity, so that the temperature of the body of the blanket 102 will not change significantly as it moves between the optional pre -treatment or conditioning station, the image forming station and the impression station(s). When using top heating of the transfer member, the blanket would preferably include a thermally insulating layer to prevent undue dissipation of the applied heat. To apply heat at different rates to the ink image carried by the transfer surface, independently of the architecture of a particular printing system, additional external heaters or energy sources (not shown) may be used to apply energy locally, for example prior to reaching the impression stations to render the ink residue tacky (see 231 in Figure 3), prior to the image forming station to dry the conditioning agent if necessary and at the printing station to start evaporating the carrier from the ink droplets as soon as possible after they impact the surface of the blanket.

[00213] The external heaters may be, for example, hot gas or air blowers 306 (as represented schematically in Figure 1) or radiant heaters focusing, for example, infrared radiation onto the surface of the blanket, which may attain temperatures in excess of 175°C, 190°C, 200°C, 210°C, or even 220°C.

[00214] The residue film left behind may have an average thickness below 1500 nm, below 1200 nm, below 1000 nm, below 800 nm, below 600 nm, below 500 nm, below 400 nm, or below 300 nm.

[00215] As explained above, temperature control is of paramount importance to the printing system if printed images of high quality are to be achieved. This is considerably simplified in the embodiment of Figure 3 in that the thermal capacity of the belt is much lower than that of the blanket 102 in the embodiments of Figures 1 and 2.

[00216] It has also been proposed above in relation to the embodiment using a thick blanket 102 to include additional layers affecting the thermal capacity of the blanket in view of the blanket being heated from beneath. The separation of the belt 210 from the blanket 219 in the embodiment of Figure 3 allows the temperature of the ink droplets to be dried and heated to the softening temperature of the resin using much less energy in the drying section 214. Furthermore, the belt may cool down before it returns to the image forming station which reduces or avoids problems caused by trying to spray ink droplets on a hot surface running very close to the inkjet nozzles. Alternatively and additionally, a cooling station may be added to the printing system to reduce the temperature of the belt to a desired value before the belt enters the image forming station. Cooling may be effected by passing the belt 210 over a roller of which the lower half is immersed in a coolant, which may be water or a cleaning/treatment solution, by spraying a coolant onto the belt of by passing the belt 210 over a coolant fountain.

[00217] Printing systems as described herein may be produced by modification to existing lithographic printing presses. The ability to adapt existing equipment, while retaining much of the hardware already present, considerably reduces the investment required to convert from technology in common current use. In particular, in the case of the embodiment of Figure 1 , the modification of a tower would involve replacement of the plate cylinder by a set of print bars and replacement of the blanket cylinder by an image transfer drum having a hydrophobic outer surface or carrying a suitable blanket. In the case of the embodiment of Figure 3, the plate cylinder would be replaced by a set of print bars and a belt passing between the existing plate and blanket cylinders. The substrate handling system would require little modification, if any. Color printing presses are usually formed of several towers and it is possible to convert all or only some of the towers to digital printing towers. Various configurations are possible offering different advantages. For example each of two consecutive towers may be configured as a multicolor digital printer to allow duplex printing if a perfecting cylinder is disposed between them. Alternatively, multiple print bars of the same color may be provided on one tower to allow an increased speed of the entire press.

[00218] The following examples illustrate inkjet ink formulations in accordance with embodiments of the invention, and in some cases their performance in a printing method as described above.

[00219] A general procedure for preparing inks in accordance with embodiments of the invention is as follows: first, a pigment concentrate is prepared by mixing distilled water, at least a portion of the polymeric resin or dispersant, if used, and colorant, and milling until a suitable particle size is reached; if a pH-raising compound is used it may be included in this step. Thereafter, the remaining ingredients, including additional polymeric resin, are mixed in, and then the ink is filtered.

Example 1A

[00220] An inkjet ink formulation was prepared containing: Ingredient Function Wt.%

Jet Magenta DMQ pigment 2

(BASF)

Joncryl HPD 296 (BASF) polymeric resin (acrylic styrene co10.6** (solid resin polymer solution, ave. MW content)

-11,500)

Glycerol (Aldrich) Water-miscible co-solvent 20

BYK 345 (BYK) surfactant (silicone) 0.5

Water - Balance to 100%

**The polymeric resin was provided in a 35.5 wt.% water solution; 30 wt.% of the final formulation consisted of this solution, i.e. 10.6 wt.% in the final ink formulation consisted of the polymeric resin itself.

[00221] To prepare this ink formulation, a pigment concentrate containing pigment (10%)), water (70%>) and resin - in the present case Joncryl HPD 296 - (20%>) was made by mixing and milling them until the particle size (D₅₀) reached about 70 nm. The remaining materials were then added to the pigment concentrate and mixed. After mixing, the ink was filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained was about 9 cP, and the surface tension was approximately 25 mN/m.

Examples 2A and 2B

[00222] An inkjet ink formulation was prepared containing:

**The BT-9 resin was provided in a 40 wt.% water dispersion, the HPD 296 was provided in a 35.5 wt.% water solution. 16.5% and 9%, respectively, of the final formulation consisted of these two components, i.e. 6.6 wt.% of the final ink formulation consisted of BT-9 itself and 3.2 wt.% consisted of HPD 296 itself.

[00223] Another inkjet ink formulation was prepared containing:

**The BT-9 resin was provided in a 40 wt.% water dispersion, the HPD 296 was provided in a 35.5 wt.% water solution. 17.25%) and 9%, respectively, of the final formulation consisted of these two components, i.e. 6.9 wt.% of the final ink formulation consisted of

BT-9 itself and 3.2 wt.% consisted of HPD 296 itself.

[00224] To prepare these formulations, pigment concentrates containing pigment (14%), water (79%) and Joncryl HPD 296 296 (7%) was prepared by mixing these ingredients and milling them until the particle size (D₅₀) reached 70 nm, as described in Example 1. Then the remaining materials were added to the pigment concentrate and mixed. After mixing the inks were filtered through 0.5 micron filter. At 25°C, the viscosity of the inks thus obtained was about 13 cP, the surface tension about 27 mN/m, and the pH 9-10.

Examples 3A and 3B

[00225] An inkjet ink formulation was prepared containing:

Neocryl BT-26 (40% water polymeric resin (acrylic 17.25 (6.9 solid resin)** dispersion) (DSM resins) polymer, ave. MW 25,000)

Monoethanol amine pH raiser 1.5

Propylene glycol Water-miscible co-solvent 20

N-methylpyrrolidone Water-miscible co-solvent 10

BYK 349 (BYK) surfactant (silicone) 0.5

Water - Balance to 100%

**The polymeric resin was provided in a 40 wt.% water dispersion; the final ink formulation consisted of 17.25 wt.% of this dispersion, i.e. 6.9 wt.% in the final ink formulation consisted of the polymeric resin itself

[00226] Another inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 40 wt.% water dispersion; the final ink formulation consisted of 17.5 wt.% of this dispersion, i.e. 7 wt.% in the final ink formulation consisted of the polymeric resin itself

[00227] To prepare these ink formulations, first a pigment concentrate was made by mixing the pigment (10%), water (69%), Neocryl BT-26 (20%) and monoethanolamine (1%) and milling as described in Example 1 until the particle size (D₅₀) reached 70 nm. Then the rest of materials were added to the pigment concentrate and mixed. After mixing the ink was filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained was about 8 cP, and the surface tension was approximately 24 mN/m, and the pH 9-10. Example 4A

[00228] An inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 40 wt.% water dispersion; the final ink formulation consisted of 25 wt.% of this dispersion, i.e. 10 wt.% of the final ink formulation was polymeric resin itself

[00229] A pigment concentrate was formed by mixing the pigment (12.3%), water (84.4%o) and Joncryl 683 fully neutralized with KOH (3.3%) and milling as described in Example 1 until the particle size (D₅₀) reached 70 nm. Then the rest of materials were added to the pigment concentrate and mixed. After mixing the ink was filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained was about 7 cP, and the surface tension was approximately 24 mN/m, and the pH 7-8.

Example 5A

[00230] An inkjet ink formulation was prepared containing:

Ingredient Function Wt.%

NeoRad R-440 (40% water polymeric resin (aliphatic 30 (12 solid resin)** emulsion) (DSM resins) polyurethane, MW 25,000)

Propylene glycol Water-miscible co-solvent 40

2-Amino-2-Methyl- 1 - pH raiser 1

Propanol

Glycerol Water-miscible co-solvent 5

BYK 349 (BYK) surfactant (silicone) 0.5

Water - Balance to 100%

**The polymeric resin was provided in a 40 wt.% water emulsion; the final ink formulation consisted of 30 wt.% of this emulsion, i.e. 12 wt.% in the final ink formulation was polymeric resin itself

[00231] A pigment concentrate was formed by mixing the pigment (14.6%), water (81.5%)) and Joncryl 671 fully neutralized with KOH (3.9%>) and milling as described in Example 1A until the particle size (D₅₀) reached 70 nm. Then the rest of materials were added to the pigment concentrate and mixed. After mixing the ink was filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained was about 10 cP, the surface tension was approximately 26 mN/m, and the pH 9-10.

Example 6A

[00232] In a manner similar to those described in the preceding examples, an inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 40 wt.% water dispersion; this dispersion constitute 18% of the final product, so that the 7.2 wt.% in the final ink formulation refers to the concentration of the polymeric resin itself, without water

[00233] The above-provided formulation contains approximately 9.6% ink solids, of which 25% (2.4% of the total formulation) is pigment, and about 75% (40%* 18% = 7.2% of the total formulation) is resin, by weight.

Example 7A

[00234] In a manner similar to those described in the preceding examples, an inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 35.5 wt.% water solution; this solution constitutes 20% of the final product, so that the 7.1 wt.% in the final ink formulation refers to the concentration of the polymeric resin itself

Example 8A

[00235] An inkjet ink formulation was prepared containing:

Glycerol Water-miscible co-solvent 15

Zonyl FSO-100 (DuPont) fluorosurfactant 0.2

Water - Balance to 100%

**The polymeric resin was provided in a 35.5 wt.% water solution; the 12.5 wt.% in the final ink formulation refers to the concentration of the polymeric resin itself

[00236] A pigment concentrate was formed by mixing the pigment (14 wt.%), Joncryl HPD 296 (7 wt.%) solids), and water (79 wt.%, triple distilled) and milling until the particle size (D₅₀) reached 70 nm. Then the rest of materials were then added to the pigment concentrate and mixed. After mixing the ink was filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained was about 9 cP and the surface tension was approximately 24 mN/m.

Example 9A

[00237] An inkjet ink formulation may be prepared containing:

**The polymeric resin was provided in a 40 wt.% water emulsion; this constitutes 17.5 wt.% of the final ink formulation, i.e. 7 wt.% in the final ink formulation is 142E resin itself. [00238] A pigment concentrate is formed by mixing the pigment (10 wt.%), water (83.6 wt.%) and Disperbyk-198 (6.4 wt.%) and milling. The progress of milling is controlled on the basis of particle size measurement (Malvern, Nanosizer). The milling is stopped when the particle size (D₅₀) reaches 70 nm. Then the rest of materials are added to the pigment concentrate and mixed. After mixing the ink is filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained is about 15 cP, the surface tension is approximately 26 mN/m, and the pH 9-10.

Example 10A

[00239] An inkjet ink formulation may be prepared containing:

**The polymeric resin was provided in a 40 wt.% water emulsion; this constitutes 17.5 wt.% of the final ink formulation, i.e. 7 wt.% in the final ink formulation is BT-9 resin itself.

[00240] A pigment concentrate is formed by mixing the pigment (10 wt.%), water (87.6 wt.%) and EFKA 4580 (5.5 wt.%) and milling. The progress of milling is controlled on the basis of particle size measurement (Malvern, Nanosizer). The milling is stopped when the particle size (D₅₀) reaches 70 nm. Then the rest of materials are added to the pigment concentrate and mixed. After mixing the ink is filtered through a 0.5 micron filter. At 25°C, the viscosity of the ink thus obtained is about 9 cP, the surface tension is approximately 24 mN/m, and the pH 9-10. [00241] Formulations similar to those of Examples 9 A and 10A may be prepared using EFKA^® 4560, EFKA^® 4585, EFKA^® 7702 or Lumiten^® N-OC 30 as the dispersant.

Example 11 A

[00242] An inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 40 wt.% water emulsion; this constituted 20 wt.% of the final ink formulation, i.e. 8 wt.% in the final ink formulation was BT-102 resin itself.

[00243] Preparation: a pigment concentrate was formed by mixing pigment (14 wt.%), water (72 wt.%) and Disperbyk 198 (14 wt.%) and milling. The progress of milling was controlled on the basis of particle size measurements (Malvern, Nanosizer). The milling was stopped when the average particle size (D₅₀) reached 70 nm. The remaining materials were then added to the pigment concentrate and mixed. After mixing, the ink was filtered through a 0.5 μιη filter. At 25°C, the viscosity of the ink thus obtained was about 5.5 cP, the surface tension about 25 mN/m, and the pH 6.5.

Example 12A

[00244] In a manner similar to those described in the preceding examples, an inkjet ink formulation was prepared containing:

monoethanolamine pH raiser 1.5

Propylene glycol Water-miscible co-solvent 20

N-methylpyrrolidone Water-miscible co-solvent 10

BYK 348 (BYK) surfactant (silicone) 0.5

Water - Balance to 100%

**The polymeric resin was provided in a 40 wt.% water dispersion; this dispersion constituted 10% of the final product, i.e. 4 wt.% of the final ink formulation was Joncryl 142E resin per se

Example 13A

[00245] In a manner similar to those described in the preceding examples, an inkjet ink formulation was prepared containing:

**The polymeric resin was provided in a 46.5 wt.% water dispersion; this dispersion constituted 15% of the final product, i.e. 7 wt.% of the final ink formulation was Joncryl 537E resin per se

[00246] A pigment concentrate was prepared by mixing pigment (10%), water (72.5%) and Disperbyk 198 (17.5%) and milling until the average particle size (d₅₀) reached 70 nm. The remaining materials were then added to the pigment concentrate and mixed. After mixing, the ink was filtered through a 0.5 μιη filter. At 25°C, the viscosity of the ink thus obtained was about 7.5 cP, the surface tension about 27 mN/m, and the pH 8-9. [00247] With respect to the foregoing examples, various milling procedures and apparati will be apparent to those of ordinary skill in the art. Various commercially available nano- pigments may be used in the inventive ink formulations. These include pigment preparations such as Hostajet Magenta E5B-PT and Hostajet Black O-PT, both from Clariant, as well as pigments demanding post-dispersion processes, such as Cromophtal Jet Magenta DMQ and Irgalite Blue GLO, both from BASF.

[00248] One of ordinary skill in the art may readily recognize that various known colorants and colorant formulations may be used in the inventive ink or inkjet ink formulations. In some embodiments, such pigments and pigment formulations may include, or consist essentially of, inkjet colorants and inkjet colorant formulations.

[00249] Alternatively or additionally, the colorant may be a dye. Examples of dyes suitable for use in the ink formulations of the present invention include: Duasyn Yellow 3GF-SF liquid, Duasyn Acid Yellow XX-SF, Duasyn Red 3B-SF liquid, Duasynjet Cyan FRL-SF liquid (all manufactured by Clariant); Basovit Yellow 133, Fastusol Yellow 30 L, Basacid Red 495, Basacid Red 510 Liquid, Basacid Blue 762 Liquid, Basacid Black X34 Liquid, Basacid Black X38 Liquid, Basacid Black X40 Liquid, Basonyl Red 485, Basonyl Blue 636 (all manufactured by BASF).

[00250] It will also be appreciated that it is possible to formulate an ink concentrate. This is similar to the procedure described above, differing in that, after forming the pigment (or dye) concentrate, the remaining ingredients are added and mixed, except that most or all of the additional solvent (water and co-solvent) is not added. The additional solvent may be mixed into such a concentrate at a later time, for example after the concentrate has been shipped to an end-user, to yield an inkjet ink formulation in accordance with embodiments of the invention. The concentrate may be diluted by addition of, for example, at least 50%, at least 100%, at least 150%), at least 200%), at least 250%o, at least 300%>, least 350%> or at least 400%> solvent on a weight/weight basis relative to the concentrate to yield the aqueous inkjet ink formulation

Example 14A

[00251] The purpose of the experiment was to check the suitability of candidate chemical agents for the treatment of the release layer. Other than polyethylene imine (PEI), which was supplied as an aqueous solution (Lupasol^® PS, BASF) and diluted 1 : 100 to a concentration of about 0.3 wt.%, each chemical agent (N-Hance™ BF 17 cationic guar, N-Hance™ CCG 45 cationic guar, N-Hance™ HPCG 1000 cationic guar, N- Hance BF 13 cationic guar, N-Hance CG 13 cationic guar, N-Hance 3196 cationic guar, all from Ashland Specialty Ingredients) was provided as a powder and dissolved in deionized water on a weight per weight basis to prepare a conditioning solution, which was used "as is" without modification of the resulting pH. Each conditioning solution was manually applied to a release layer surface of a blanket of approximately 20 cm x 30 cm size, the release layer comprising a silanol-terminated polydimethylsiloxane silicone and being at a temperature of 150°C. The conditioning solution was applied by moistening a Statitech 100% polyester cleanroom wiper with the solution and wiping the release layer surface. The conditioning solution was then allowed to dry spontaneously on the heated blanket. Thereafter, a black ink as per Example 8 above (containing Carbon Black Mogul L (Cabot), 1.3 wt.%, Joncryl HPD 296 35.5% water solution (BASF), 35% (12% solids), glycerol 15%, Zonyl FSO-100 (DuPont) 0.2% and balance water) was jetted at a resolution of 600 dpi x 600 dpi onto the conditioned release layer while still at 150°C, using conventional Kyocera inkjet print heads. It will be appreciated that during printing the heated release layer was moved relative to the print heads at a rate of 75 cm/s. The test file printed for the experiment printed a gradient of ink coverage, from a less to more dense population of ink dots. The drop size was set to 3 or 4, which corresponds to 13 pi or 18 pi respectively of ink. The ink film formed was allowed to dry for at least 5 seconds and then while still hot was transferred to Condat Gloss^® 135 gsm paper using manual pressure, using one of two methods, either by the Paper On Blanket (POB) method, or the Roll method. In POB, the sheet of paper was placed directly onto the inked blanket, then manual pressure was applied. In Roll, the paper was tightly fixed with tape to a metal cylinder and the ink image was transferred to the paper by manually rolling this paper (with pressure) over the inked blanket. Representative printouts obtained by the POB method are shown in Fig. 4, wherein the areas of lower ink coverage are omitted and in some cases the area of 100% coverage is truncated. The diameters of several ink dots in two of the less dense regions of the printed area (not shown in the Figures), having drop size 3 or 4, as reported in the tables below, were then determined using a Lext Confocal Microscope at X20 magnification. The measures were repeated for 5 representative round dots on areas of adequate conditioner coverage and the results in each area were averaged. The diameters of the various dots were compared. Results are presented in the Tables 1 and 2 below; PEI = polyethylene imine, GHPTC = guar hydroxypropyltrimonium chloride, HGHPTC = hydroxyl guar hydroxypropyltrimonium chloride; viscosities and charge densities are as reported by the manufacturer. A larger diameter suggests retention of the spreading of ink on the release layer and good transfer therefrom.

[00252] Table 1 - Results for POB

[00253] Table 2 - Results for Roll Chemical Material Viscosity Charge Ave. Ave. diameter, agent, wt.% density diameter, drop size 4 drop size 3

Lupasol PS PEI Very high

0.3% 43.2656 54.7352

GHPTC

CG 13 0.1% High Medium 43.0544 54.3544

GHPTC

CG 13 0.5% High Medium 48.2376 58.5096

GHPTC

BF 13 0.1% High Medium 47.6172 57.9916

GHPTC

BF 13 0.5% High Medium 45.4408 57.0412

GHPTC

3196 0.1% High Medium 49.1352 61.2340

GHPTC

3196 0.5% High Medium 47.5316 56.8892

GHPTC

BF 17 0.1% High Very High 46.5030 57.5252

GHPTC

BF 17 0.5% High Very High 48.4056 58.3452

GHPTC

CCG 45 0.1% Low Medium 44.2352 57.1564

GHPTC

CCG 45 0.5% Low Medium 44.8136 56.2856

Hpcg 1000 HGHPTC

0.1% Medium Medium 46.6876 57.9184

Hpcg 1000 HGHPTC

0.5% Medium Medium 46.1952 58.1752

[00254] The optical densities of these prints, in the region of 100% ink coverage, were also measured, using an X-rite 500 series spectrodensitometer using a 0.5 cm optical probe. The results are presented in Table 3 (numbers are the average of three measurements; the numbers in parenthesis indicate the OD of the tested agent as a % of OD of Lupasol PS):

[00255] Table 3

PEI 2.00 (100%) 1.95 (100%)

CG 13 0.1% 1.49 (75%) 1.44 (74%)

CG 13 0.5% 1.82 (91%) 1.72 (88%)

BF 13 0.1% 2.06 (103%) 1.91 (98%)

BF 13 0.5% 1.57 (79%) 1.78 (91%)

3196 0.1% 2.06 (103%) 2.16 (111%)

3196 0.5% 2.10 (105%) 2.01 (103%)

BF 17 0.1% 1.72 (86%) 1.52 (78%)

BF 17 0.5% 2.12 (106%) 1.69 (87%)

CCG 45 0.1% 1.42 (71%) 1.42 (73%)

CCG 45 0.5% 1.25 (63%) 1.59 (82%)

Hpcg 1000 0.1% 2.18 (109%) 1.86 (95%)

Hpcg 1000 0.5% 1.88 (94%) 1.72 (88%)

[00256] The above results show that cationic guars are suitable chemical agents to serve for the conditioning of release layers of printing blankets.

[00257] In a manner similar to Example 14 A, solutions of various chemical agents were applied to a 10 square cm (cm²) area of a heated silanol-terminated polydimethylsiloxane silicone release layer and dried prior to printing thereon in a gradient pattern with the aqueous ink described in Example 8A, this time using a Fujifilm Dimatix DMP-2800 printer jetting 10 pi droplets. See Fig. 5. It was found that a vinyl pyrrolidone- dimethylaminopropyl methacrylamide co-polymer (Viviprint 131, a copolymer of N-[3- (dimethylamino)propyl]-2-methyl-2-propeneamide and l-ethenyl-2-pyrrolidone), a vinyl caprolactam-dimethylaminopropyl methacryamide hydroxyethyl methacrylate copolymer (Viviprint 200, a copolymer of of 2-methyl-2-hydroxyethyl ester-2-propenoic acid and N- [3-(dimethylamino)propyl]-2-methyl-2-propenamide and 1 -ethenylhexahydro-2H-azepin- 2-one), and a quaternized copolymer of vinyl pyrrolidone and dimethylaminoethyl methacrylate with diethyl sulfate (Viviprint 650, a copolymer of copolymer of 2-methyl-2- (dimethylamino)ethyl ester-2-propenoic acid and l-ethenyl-2-pyrrolidinone with diethyl sulfate) were suitable. Other tests showed that linear polyethylene imine, branched polyethylene imine, modified polyethylene imine, poly(diallyldimethylammonium chloride), poly(4-vinylpyridine), and polyallylamine were all suitable for use as conditioning agents for the release layer of the intermediate transfer member. Example 15A

[00258] Tack (or tackiness) may be defined as the property of a material that enables it to bond with a surface on immediate contact under light pressure. Tack performance may be highly related to various viscoelastic properties of the material (polymeric resin, or ink solids). Both the viscous and the elastic properties would appear to be of importance: the viscous properties at least partially characterize the ability of a material to spread over a surface and form intimate contact, while the elastic properties at least partially characterize the bond strength of the material. These and other thermo-rheological properties are rate and temperature dependent.

[00259] By suitable selection of the thermo-rheological characteristics of the residue film which is formed by jetting an ink in accordance with embodiments of the invention onto a hydrophobic release layer and drying the jetted ink, the effect of cooling may be to increase the cohesion of the residue film, whereby its cohesion exceeds its adhesion to the release layer of the intermediate transfer member so that all or substantially all of the residue film is separated from the image transfer member and impressed as a film onto a substrate. In this way, it is possible to ensure that the residue film is impressed on the substrate without significant modification to the area covered by the film nor to its thickness.

[00260] Viscosity temperature sweeps — ramp and step — were performed using a Thermo Scientific HAAKE RheoStress® 6000 rheometer having a TM-PE-P Peltier plate temperature module and a P20 Ti L measuring geometry (spindle).

[00261] Samples of dried ink residue having a 1mm depth in a 2cm diameter module were tested. The samples were dried overnight in an oven at an operating temperature of 100°C. A volume of sample (pellet) was inserted into the 2cm diameter module and softened by gentle heating. The sample volume was then reduced to the desired size by lowering the spindle to reduce the sample volume to the desired depth of 1mm.

[00262] In temperature ramp mode, the sample temperature was allowed to stabilize at low temperature (typically 25°C to 40°C) before being ramped up to a high temperature (typically 160°C to 190°C) at a rate of approximately 0.33°C per second. Viscosity measurements were taken at intervals of approximately 10 seconds. The sample temperature was then allowed to stabilize at high temperature for 120 seconds before being ramped down to low temperature, at a rate of approximately 0.33°C per second. Again, viscosity measurements were taken at intervals of approximately 10 seconds. Oscillation temperature sweeps were performed at a gamma of 0.001 and at a frequency of 0.1 Hz.

[00263] Figure 6 provides ramped-down temperature sweep plots of dynamic viscosity as a function of temperature, for several dried ink formulations suitable for the ink film construction of the present invention. After reaching a maximum temperature of approximately 160°C, and waiting 120 seconds, the temperature was ramped down as described.

[00264] The lowest viscosity curve is that of a dried residue of an inventive yellow ink formulation, containing about 2% pigment solids, and produced according to the procedure described hereinabove. At about 160°C, the rheometer measured a viscosity of about 6.7· 10⁶ cP. As the temperature was ramped down, the viscosity steadily and monotonically increased to about 6·10⁷ cP at 95°C, and to about 48·10⁷ cP at 58°C.

[00265] The intermediate viscosity curve is that of a dried residue of an inventive cyan ink formulation, containing about 2% pigment solids, and produced according to the procedure described hereinabove. At about 157°C, the rheometer measured a viscosity of about 86· 10⁶ cP. As the temperature was ramped down, the viscosity increased to about 187Ί0⁶ cP at 94°C, and to about 8·10⁸ cP at 57°C.

[00266] The highest viscosity curve is that of a dried residue of an inventive black ink formulation, containing about 2% pigment solids, and produced according to the procedure described hereinabove. At about 160°C, the rheometer measured a viscosity of about 196·10⁶ cP. As the temperature was ramped down, the viscosity steadily and monotonically increased to about 763·10⁶ cP at 95°C, and to about 302·10⁷ cP at 59°C.

[00267] Figure 7 is a ramped-down temperature sweep plot of dynamic viscosity as a function of temperature, for several dried ink formulations of the present invention, vs. several ink residues of prior art ink formulations. The viscosity curves of the prior art formulations are labeled 1 to 5, and are represented by dashed lines; the viscosity curves of the inventive formulations are labeled A to E, and are represented by solid lines. The ink formulations of the present invention include the three previously described in conjunction with Figure 6 (A = black; C= cyan; and E = yellow), and two ink formulations ("B"; "D") containing about 2%, by weight of solids, of a magenta pigment [Hostajet Magenta E5B- PT (Clariant)], along with about 6% of various styrene-acrylic emulsions. The residues of the prior art inks were prepared from various commercially available inkjet inks, of different colors. [00268] A magnified view of the plot of Figure 7, for viscosities of less than 36· 10 , is provided in Figure 8. Only the viscosity curves of the inventive formulations A to E, and that of prior-art formulation 5, may be seen in Figure 8.

[00269] It is evident from the plots, and from the magnitude of the viscosities, that the dried ink residues of the various prior art ink formulations exhibit no or substantially no flow behavior over the entire measured range of temperatures (up to at least 160°C). The peaks observed at extremely high viscosities in some plots of the prior-art formulations would appear to have no physical meaning. The lowest measured viscosity for each of the prior art residue films was within a range of at least 135Ί0⁷ cP to at least 33Ί0⁸ cP. The lowest value within this range, 135· 10⁷ cP, is well over 6 times the highest viscosity value of any of the residues of the inventive ink formulations, at about 160°C.

[00270] Moreover, during the ramp-down phase of the experiment, Samples 1 to 5 of the prior art exhibited viscosity values that exceeded the viscosity measured at about 160°C, and/or appear sufficiently high so as to preclude transfer of the film. In practice, the inventors of the present invention successfully transferred all five of the inventive ink films to a printing substrate, but failed to transfer any of the five prior-art ink films to a printing substrate, even after heating to over 160°C.

[00271] Numerous organic polymeric resins exist and many recognized to serve for the preparation of ink compositions are commercially available and known to persons skilled in this industry. Generally such polymers, whether well established ink resins or less typical to this field, serve to entrap (e.g., encapsulate) or otherwise immobilize or associate with the coloring agent of relevance through physical, covalent or ionic interactions, ultimately also enabling the ink image to attach to the printed substrate. Such polymeric resins are therefore often referred to as binders. Some polymers may alternatively or additionally serve as dispersants, maintaining the ink formulations in desired suspension or emulsion form. Though the exact function of an organic polymeric resin may vary in the context of a specific formulation or may include more than one function, it is used herein to refer to the predominant binder function which typically account for most of such polymers presence in a final ink composition.

[00272] Water dispersible thermoplastic resins include, but are not limited to linear and branched acrylic polymers, acrylic styrene copolymers, styrene polymers, polyesters, co-polyesters, polyethers, polyamides or polyester amides, polyurethanes and polyamines. Such polymers are typically supplied with basic data on their average molecular weight (MW), their glass transition (T_g) or softening temperature, their minimal film forming temperature (MFFT), their hardness, their ability to contribute to the gloss of the final printed inks, or to their adherence to the printed substrate, or to their resistance to abrasion. Some polymers may be defined by their reactivity or by the density of their functional groups, the acid number or the hydroxyl number being but examples of such qualifications.

[00273] Ink formulators are familiar with such parameters and will readily appreciate that the selection of a suitable organic polymeric resin may depend on the intended purpose. For instance, binders need not provide high gloss if the printed image is intended to be matte or if the ink image is to be further laminated or coated with a varnish that would independently provide the desired optical effect. Such gloss-related information is generally provided by the supplier, but can be independently measured, for example by using a gloss meter at a fixed angle of incidence. Using a Micro-gloss (BYK-Gardner, Germany) single-angle gloss meter at 75°, prints displaying a gloss above 65-70 are regarded as glossy, whereas prints having a gloss below 65 are regarded as matte.

[00274] Similarly, the presence of a laminate or varnish may reduce the need to select polymers providing good to excellent abrasion resistance. Each supplier may use variations of the standard resistance test ASTM D5264 to assess this property. In absence of coating protection and if the printed product is intended or may be subjected to scrub, then polymers having higher abrasion resistance should be preferred. It can be appreciated that the hardness of the polymer can correlate with its ability to form ink film images that may have the desired resistance to abrasion, if needed. Therefore, for certain purposes, resins having a good to high hardness are preferred.

[00275] Such a coating may also improve the adhesion of the ink image to certain substrates. Understandingly, the degree of adherence a polymer would need to have would depend on the intended substrate. Some organic resins provide good adherence to coated or synthetic substrates typically having a relatively low surface roughness. Other resins have superior abilities and can additionally or alternatively adhere to substrates having a higher surface roughness, such as most of the uncoated printing substrates. The resins may also be selected to suit cellulose-based, cellulose-free, plastic-based or metal-based printing substrates, as commonly used in the field of commercial printing. Advantageously, though not necessary, a suitable organic polymeric resin shall be appropriate for a broad range of possible substrates. This capability to adhere to the substrate of choice, if not provided by the resin manufacturer, can be readily assessed using a tape adherence test on the intended printing substrate.

[00276] The acid number, also termed the acid value or neutralization number, relates to the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of a chemical substance. The acid number is usually provided by the manufacturer, but readily measurable as per its definition. Resins having a high acid number are expected to yield ink films less stable when exposed to water (water fastness) and should therefore be avoided when the intended use of the printed matter may expose it to conditions that would be deleterious to films comprising such resins. Resins suitable for the present invention generally have an acid number below 100, or below 90. In some embodiments, the organic polymeric resins have an acid number between 60 and 100, and in particular, between 70 and 90.

[00277] In some embodiments, and in particular, for various embodiments employing a polyester or polyester-based resin, the acid number may be below 15, below 12, below 10, below 7, below 5, or below 2.5. Such polymeric resins may have an acid number between 0 and 15, between 0 and 10, and in particular, between 0 and 5 or between 1 and 5.

[00278] The polymer resins, such as acrylic-based polymers, may be negatively charged at alkaline pH. Consequently, in some embodiments, the polymeric resin has a negative charge at a pH above 7.5, above 8 or above 9. Furthermore, the solubility or the dispersability of the polymeric resin in water may be affected by pH. Thus, in some embodiments, the formulation comprises a pH-raising compound. Examples of such are diethyl amine, monoethanol amine, and 2-amino-2-methyl propanol. Such pH-raising compounds, when included in the ink, are generally included in small amounts, e.g., about 1 wt.% of the formulation and usually not more than about 2 wt.% of the formulation.

[00279] Some resins are characterized by a hydroxyl number, also termed the hydroxyl value, which is a measure of the content of free hydroxyl groups in a compound, hence typically used in connection with esters. This value, if not provided, can be determined by acetylation of the free hydroxyl groups of the compound of interest and standard titrations and calculations known in the art. As other functional groups, such as primary or secondary amines, may take part in the chemical reactions used to assess this number, they can also be reported as hydroxyl. Hence the hydroxyl number may serve to assess the more general reactivity / functionality of the resin. It is expressed as the mass of potassium hydroxide (KOH) in milligrams equivalent to the hydroxyl content of one gram of the chemical substance, corrected for carboxyl hydroxyl groups by titration of an unacetylated sample of the same material. Some suitable resins, e.g., polyester or polyester-based resins, including co-polyester resins, linear and branched polyester or co- polyester resins, can have a hydroxyl value between 15 and 60, between 25 and 55, or between 35 and 50.

[00280] Additionally, a suitable resin needs to satisfy the thermo-rheological conditions to be described in more detail in the following sections. Again, such rheological patterns can be adapted to the intended purpose. For instance, for use with printing substrates having low surface roughness, the viscosity of the dried ink film at a high temperature may be higher than the viscosity of the dried ink film intended to adhere on a substrate having a higher surface roughness. In other words, the ink composition to be suited for uncoated substrates would require a relatively lower viscosity of the dried film that would allow the image to better follow the contour of the surface topography, hence increasing area of contact for better adherence. Generally stated, for use in the printing process herein described, the selection of the organic polymeric (binder) resin to be included in the ink formulations of the present disclosure may further take into account the temperature at which the ink is jetted at the image forming station, the type of inkjet head (such as continuous ink jet (CD) or drop-on-demand (DOD)), the temperature at which it contacts the intermediate transfer member, the temperature at which it is dried upon the transfer member and the temperature at which it is transferred from the transfer member to the intended printing substrate at the impression station.

[00281] In some embodiments, suitable organic polymeric resins include acrylic polymers, acrylic styrene copolymers, styrene polymers, polyesters. In additional embodiments, the resins are one or more polymers selected from the group comprising Joncryl® 90, Joncryl® 530, Joncryl® 537E, Joncryl® 538, Joncryl® 631, Joncryl® 1158, Joncryl® 1180, Joncryl® 1680E, Joncryl® 1908, Joncryl® 1925, Joncryl® 2038, Joncryl® 2157, Joncryl® Eco 2189, Joncryl® LMV 7051, Joncryl® 8055, Joncryl® 8060, Joncryl® 8064, Joncryl® 8067, all acrylic-based polymers available from BASF; Dynacoll® 7150, Desmophen® XP2607 and Hoopol® F-37070, all polyester-based polymers respectively available from Evonik, Bayer and Synthesia International, and any other commercially available chemical equivalents thereof. For convenience, the data concerning these materials as provided by their respective suppliers is reproduced below. It should be noted that some information reported below under the MFFT characteristic of a compound may correspond to a softening temperature as assessed by the resin manufacturer. The dispersant Joncryl HPD 296 is included for comparative purposes.

Material MW Tg MFFT Acid No. OH No.

Joncryl® 90 >200,000 1 10 °C >85 °C 76

Joncryl® 530 75 °C 95 °C 50

Joncryl® 537E >200,000 50 °C 43°C 52

Joncryl® 538 >200,000 64 °C 60 °C 70

Joncryl® 631 >200,000 107 °C >85 °C 70

Joncryl® 1158 103 °C

Joncryl® 1180 >200,000 107 °C >85 °C

Joncryl® 1680 E >200,000 56 °C 49 °C 28

Joncryl® 1908 98 °C > 70 °C 55

Joncryl® 1925 75 °C > 70 °C 50

Joncryl® 2038 >200,000 > 85 °C > 85 °C 76

Joncryl® 2157 >200,000 105 °C > 85 °C 36

Joncryl® Eco 2189 >200,000 98 °C > 85 °C 65

Joncryl® LMV 7051 >200,000 98 °C 56°C 115

Joncryl® 8055 >200,000 110 °C > 85 °C

Joncryl® 8060 >200,000 110 °C 84 °C 150

Joncryl® 8064 >200,000 97 °C 58 °C 158

Joncryl® 8067 >200,000 1 10 °C > 90 °C 78

Joncryl® HPD 296 11,500 15 °C 141

Dynacoll® 7150 2600 50 °C 85 °C < 2 38-46

Desmophen® XP2607 2670 - 50 °C < 2 42 Material MW T_g MFFT Acid No. OH No.

Hoopol® F-37070 2650 51 °C < 2 38-46

The molecular weight of the resin need not be limited. In some embodiments, the resin has an average molecular weight of at least 1 ,200, at least 1 ,500, at least 2,000, or at least 5,000, at least 25,000, at least 50,000, at least 100,000, at least 150,000, or at least 200,000. In some embodiments, suitable organic polymeric resins, and particularly polyester or polyester-based resins, including co-polyester resins, linear and branched polyester or co-polyester resins, may have an average molecular weight of at most 12,000, at most 10,000, at most 8,000, at most 6,000, at most 5,000, at most 4,000, at most 3,500, or at most 3,000.

EXAMPLES

The following examples illustrate inkjet ink formulations according to the teachings of the present disclosure.

Materials and chemicals were purchased from various manufacturers, including:

Air Products Air Products and Chemicals Inc., USA

BASF BASF Schweiz AG, Basel, Switzerland

BYK BYK-Chemie GmbH, Wesel, Germany

Cabot Cabot Corporation, Billerica MA, USA

Clariant Clariant International Ltd, Muttenz, Switzerland

Dupont DuPont de Nemours, France

Dow Dow Chemical Company, Midland MI, USA

Evonik Evonik Industries AG, Essen, Germany

Huntsman Huntsman, TX, USA

Sigma-Aldrich Sigma-Aldrich Corporation, St. Louis MO, USA

SKC SKC, Seoul, Korea.

Though the below formulations were prepared using materials supplied under the indicated trademarks of their respective manufacturer, such ingredients can be replaced by other commercially available compounds having similar chemical formulas.

For brevity, the below formulations are presented using Carbon Black as pigment to serve for black (K) color inks. Some of the below formulations were prepared with cyan pigments (e.g., PV Fast Blue BG), magenta pigments (e.g., Cromophtal® Jet Magenta DMQ) or yellow pigments (e.g., Hansa Brilliant Yellow 5GX03) at the same concentrations as indicated for the black pigment, to yield respectively cyan (C), magenta (M) and yellow (Y) inks. Results obtained with black inks will be referred to by their appropriate example number. If such results are displayed or discussed with reference to colors other than black, the one letter code of the specific color is indicated. For instance, 'Ex. 4 C will correspond to the Cyan version of the formulation disclosed in Example 4. Similarly, some of the below formulations were prepared with dyes instead of pigments. Tested dyes in conjunction with the inventive ink formulations included Basonyl® Red 485 and Basonyl® Blue 636. Alternative coloring agents (whether pigments or dyes) that may be suitable for such formulations are readily known to persons skilled in the art of formulating printing inks.

Polymeric binder resins are commercially available in many forms, including various solid forms, such as amorphous or crystalline structures. The resins may be available as free-flowing powders, and pellets. The resins may be available in liquid form, as emulsions or dispersions, typically blended with suitable additives. Additionally, each such commercially available resins may have a particular, characteristic particle size distribution.

As known, the viscosity of a composition can be affected by the type of ingredients it contains, their respective inherent rheological properties and their concentration. As appreciated by persons skilled in the art of ink formulation, the particle size may also affect the viscosity, to some degree, since the same amount of a material having a lower particle size, provides a higher surface area available for interactions capable of modifying some of its original physico-chemical properties. The particle size is, however, but one parameter, and need therefore not be limited.

In some embodiments, the resins have an average particle size d₅o of 3 micrometer (μιη) or less, or of less than 1 μιη, or of less than 0.5 μιη, or of less than 400 nm, or of less than 300 nm, or of less than 200 nm, or of less than 100 nm.

A general procedure for preparing inks in accordance with embodiments of the invention for resins available in liquid form is as follows: first, a pigment or dye concentrate is prepared by mixing distilled water, at least a portion (typically about 20%) of the polymeric resin or dispersant, if used, and colorant, and milling by procedure known in the art using any appropriate apparatus until a suitable particle size is reached. If a dispersant was used in this step, it was typically at a 1 : 1 ratio with the colorant. Alternatively, commercially available nano-pigments (e.g., having a d₅o below 1 μιη) or sub-micron to low micronic range resins (e.g., having a d₅o below 5 μιη) may be readily used in the preparation of the ink formulations of the present disclosure. If a pH-raising compound is used it may be included in this step. The milling process was monitored on the basis of particle size measurements using a dynamic light scattering particle size analyzer (e.g., ZETASIZER™ Nano-S, ZEN 1600 of Malvern Instruments, England), using standard practice. Unless otherwise stated, the process was stopped when the average particle size (d₅o) reached about 70 nm.

The remaining materials were then added to the pigment concentrate and mixed. After mixing, the ink was filtered through a 0.5 μιη filter. The viscosity of the inks thus obtained was measured at 25°C using viscometer (DV II + Pro by Brookfield) and was typically in the range of about 2 cP to 25 cP. The surface tension was measured using a standard liquid tensiometer (EasyDyne by Kruss) and was generally in the range of approximately 20 to 30 mN/m. The resulting pH was usually in the range of 6.5 to 10.5 range, and more typically, in the range of 7.0 to 9.0.

In other embodiments, when the polymeric resin is available in solid form, an alternative procedure can be used. Typically, the resin is thoroughly milled with a dispersant, before being admixed with the coloring agent and any other ingredient of the ink formulation. For the preparation of some formulations herein-disclosed, a slurry consisting of 37.5g Dynacoll® 7150 (Evonik, flakes), 93.75g Dispex Ultra PX 4575 (BASF) and 131.25 ml of distilled water was milled at 5°C for 48 hours in a ball mill (Atrittor OS, Union Process, USA), having a ceramic inner surface and 0.8 mm Zirconia beads. The ground slurry was then mixed at desired ratio with a concentrate of coloring agent (e.g., a black pigment dispersed in a standard milling apparatus with a dispersant). In the present examples, the pigment was dispersed with the same Dispex Ultra PX 4575 so that the final ratio of resin to dispersant was 1 :0.35. As desired, a softening agent was added to the resin - pigment mix, and water was added if needed to achieve the final formulation. The fully formulated ink was then mixed and filtered through a 0.5 μιη filter. Viscosity, surface tension and pH were measured as mentioned hereinabove.

A partial list of the ink formulations prepared by these exemplary methods is presented below, the content of each ingredient being indicated in weight percent (wt. %) of the stock material, whether a liquid or solid chemical or a diluted solution, dispersion or emulsion comprising the material of interest, the weight percent being relative to the total weight of the final formulation. Concentrated versions having a solid content of at least 45% (see Example 42) and of about 80% are also provided (see Examples 40 and 41). Persons skilled in the art to which this invention pertains will readily appreciate that other methods of preparation may be equally suitable.

Example 1

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0

Joncryl® 1680E, 43.5 % emulsion

Resin 18.4 water

Softening Agent PEG 8,000 8.0 Humectant Propylene glycol 30.0

Joncryl® HPD 296, 35.5 % solution

Dispersant 5.6 water

Wetting Agent BYK® 348 0.2 Carrier Water 35.8

Example 2

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.2

Joncryl® 1680E, 43.5 % emulsion

Resin 11.0 water

Softening Agent PEG 8,000 9.6 Humectant Ethylene glycol 20.0

Joncryl® HPD 296, 35.5 % solution

Dispersant 3.4 water

Wetting Agent BYK® 345 0.2 Carrier Water 54.6

Example 3

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0 Resin Joncryl® 1680E, 43.5 % emulsion in 13.8 water

Softening Agent PEG 8,000 6.0 Humectant Ethylene glycol 30.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent BYK® 345 0.2 Carrier Water 42.4

Example 4

Type of Material Name

Pigment Carbon Black, Monarch® 700

Joncryl® 1680E, 43.5 % emulsion

Resin

water

Softening Agent PEG 8,000

Humectant Propylene glycol

Joncryl® HPD 296, 35.5 % solution

Dispersant

water

Wetting Agent BYK® 345

Carrier Water

Example 5

Type of Material Name

Pigment Carbon Black, Monarch® 700

Joncryl® 1680E, 43.5 % emulsion

Resin

water

Softening Agent PEG 20,000

Humectant Propylene glycol

Joncryl® HPD 296, 35.5 % solution

Dispersant

water

Wetting Agent BYK® 348

Carrier Water Example 6

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.8

Joncryl® 1680E, 43.5 % emulsion

Resin 12.4 water

Softening Agent PEG 20,000 5.4 Humectant Ethylene glycol 20.0

Joncryl® HPD 296, 35.5 % solution

Dispersant 5.1 water

Wetting Agent BYK® 345 0.2 Carrier Water 55.1

Example 7

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.8

Joncryl® 1680E, 43.5 % emulsion

Resin 18.4 water

Softening Agent PEG 20,000 8.0 Humectant Ethylene glycol 15.0

Joncryl® HPD 296, 35.5 % solution

Dispersant 2.3 water

Wetting Agent BYK® 345 0.2 Carrier Water 55.4

Example 8

Type of Material Name

Pigment Carbon Black, Monarch® 700 0.7 Resin Joncryl® 2038, 43.5 % emulsion in water 6.4

Softening Agent PEG 8,000 5.6 Humectant Propylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.0 water

Wetting Agent BYK 345 0.2 Carrier Water 60.1

Example 9

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0 Resin Joncryl® 2038, 43.5 % emulsion in water 18.4

Softening Agent Tween® 60 8.0 Humectant Propylene glycol 22.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent Capstone® FS-65 0.01 Carrier Water 43.97

Example 10

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.9 Resin Joncryl 2038, 43.5 % emulsion in water 8.3

Softening Agent Tween® 60 7.2 Humectant Propylene glycol 17.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.5 water

Wetting Agent BYK® 345 0.2 Carrier Water 63.9

Example 11

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.4 Resin Joncryl® 8064, 43.5 % emulsion in water 22.1

Softening Agent Span® 20 2.4 Humectant Propylene glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 6.8 water

Wetting Agent BYK® 345 0.2 Carrier Water 51.2

Example 12

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.5 Resin Joncryl® 8064, 43.5 % emulsion in water 13.8

Softening Agent Span® 20 3.0 Humectant Ethylene glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 4.2 water

Wetting Agent BYK® 345 0.2 Carrier Water 62.3

Example 13

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0 Resin Joncryl® 8064, 43.5 % emulsion in water 18.4

Softening Agent PEG 8,000 8.0 Humectant Propylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent BYK® 348 0.2 Carrier Water 40.8

Example 14

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.0 Resin Joncryl® 8064, 43.5 % emulsion in water 9.2

Softening Agent PEG 8,000 8.0 Humectant Ethylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.8 water

Wetting Agent BYK® 345 0.2 Carrier Water 53.8

Example 15

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.8

Joncryl® 1680E, 43.5 % emulsion in

Resin 18.4 water

Softening Agent PEG 8,000 16.0 Humectant Ethylene glycol 5.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.3 water

Wetting Agent BYK® 345 0.2 Carrier Water 57.4

Example 16

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0 Resin Joncryl® 8060, 45 % emulsion in water 17.8

Softening Agent PEG 8,000 8.0 Humectant Propylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent BYK® 348 0.2 Carrier Water 41.4

Example 17

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.0 Resin Joncryl® 8060, 45 % emulsion in water 8.9

Softening Agent PEG 8,000 8.0 Humectant Ethylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.8 water Wetting Agent BYK® 345 0.2

Carrier Water 54.1

Example 18

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.3

Joncryl® 1680E, 43.5 % emulsion in

Resin 29.9 water

Softening Agent PEG 8,000 13.0

Humectant Ethylene glycol 10.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 3.7 water

Wetting Agent BYK® 345 0.2

Carrier Water 42.0

Example 19

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 2.0

Resin Joncryl® 2038, 43.5 % emulsion in water 18.4

Softening Agent Span® 20 8.0

Humectant Propylene glycol 22.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent Capstone® FS-65 0.01

Carrier Water 43.97

Example 20

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.9

Resin Joncryl® 2038, 43.5 % emulsion in water 8.3

Softening Agent Span® 20 7.2

Humectant Propylene glycol 17.0

Dispersant Joncryl® HPD 296, 35.5 % solution in 2.5 water

Wetting Agent BYK® 345 0.2 Carrier Water 63.9

Example 21

Type of Material Name Wt. %

Softening Agent PEG 8,000 10.0 Humectant Ethylene glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.8 water

Wetting Agent BYK® 345 0.2 Carrier Water 52.1

Example 22

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.9 Resin Joncryl® 8060, 45 % emulsion in water 8.0

Softening Agent PEG 8,000 9.9 Humectant Propylene Glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.5 water

Wetting Agent BYK® 348 0.2 Carrier Water 53.5

Example 23

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.2 Resin Joncryl® 8060, 45 % emulsion in water 10.7

Softening Agent PEG 8,000 14.4

Humectant Propylene Glycol 25.0

Dispersant Joncryl® HPD 296, 35.5 % solution in 3.4 water

Wetting Ag BYK® 345 0.2 Carrier Water 45.2

Example 24

Type of Material Name Wt. %

Dye Basonyl Red 485 (BASF) 1.2 Resin Joncryl® 2038, 43.5 % emulsion in water 11.0

Softening Agent PEG 8,000 9.9 Humectant Ethylene Glycol 25.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 3.4 water

Wetting Agent BYK® 345 0.2 Carrier Water 49.3

Example 25

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.8

Joncryl® 1680E, 43.5 % emulsion

Resin 4.6 water

Softening Agent PEG 20,000 2.0 Humectant Ethylene glycol 15.0

Joncryl® HPD 296, 35.5 % solution

Dispersant 2.3 water

Wetting Agent BYK® 345 0.2 Carrier Water 75.1

Example 26

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.0

Joncryl® 1680E, 43.5 % emulsion in

Resin 11.5 water

Softening Agent PEG 20,000 5.0 Humectant Propylene Glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.8 water

Wetting Agent BYK® 348 0.2 Carrier Water 64.5

Example 27

Type of Material Name Wt. %

Softening Agent Tween® 20 8.0 Humectant Propylene Glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent Capstone® FS-65 0.01 Carrier Water 50.97

Example 28

Type of Material Name Wt. %

Softening Agent Tween® 20 16.0 Humectant Ethylene Glycol 20.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 5.6 water

Wetting Agent BYK® 345 0.5 Carrier Water 37.48

Example 29

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.5 Resin Joncryl® 2038, 43.5 % emulsion in water 13.8

Softening Agent Tween® 40 3.0 Humectant Ethylene Glycol 15.0 Joncryl® HPD 296, 35.5 % solution in

Dispersant 4.2 water

Wetting Agent Capstone® FS-65 0.01 Carrier Water 62.47

Example 30

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.8 Resin Joncryl® 2038, 43.5 % emulsion in water 7.4

Softening Agent Tween® 40 3.2 Humectant Propylene Glycol 18.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.3 water

Wetting Agent BYK® 348 0.30 Carrier Water 68.1

Example 31

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 0.9 Resin Joncryl® 2038, 43.5 % emulsion in water 8.3

Softening Agent Tween® 40 7.2 Humectant Propylene Glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.5 water

Wetting Agent BYK® 345 0.20 Carrier Water 65.9

Example 32

Type of Material Name Wt. %

Softening Agent Tween® 80 1.4 Humectant Ethylene Glycol 15.0 Joncryl® HPD 296, 35.5 % solution in

Dispersant 2.0 water

Wetting Agent Capstone® FS-65 0.01 Carrier Water 74.48

Example 33

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.2 Resin Joncryl® 2038, 43.5 % emulsion in water 11.0

Softening Agent Tween® 80 9.6 Humectant Ethylene Glycol 15.0

Joncryl® HPD 296, 35.5 % solution in

Dispersant 3.4 water

Wetting Agent BYK® 345 0.20 Carrier Water 59.6

Example 34

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.0

Dynacoll® 7150 milled with EFKA®

Resin 18.5

4575 1 :1 (14.38% total solids)

Humectant Ethylene Glycol 15.0 Dispersant EFKA® 4575 1.7 Wetting Agent BYK® 345 0.70 Carrier Water 63.0

Example 35

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.1

Dynacoll® 7150 milled with EFKA®

Resin 43.7

4575 1 :1 (14.38% total solids)

Softening Ag Tween® 20 12.6 Humectant Propylene Glycol 15.0 Dispersant EFKA® 4575 1.9 Wetting Agent BYK® 348 0.70 Carrier Water 25.0

Example 36

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.5

Dynacoll® 7150 milled with EFKA®

Resin 59.6

4575 1 :1 (14.38% total solids)

Softening Agent Tween® 20 12.9 Humectant Propylene Glycol 15.0 Dispersant EFKA® 4575 2.6 Wetting Agent BYK® 345 0.70 Carrier Water 7.8

Example 37

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.2

Dynacoll® 7150 milled with EFKA®

Resin 47.7

4575 1 :1 (14.38% total solids)

Softening Agent Tween® 20 6.9 Humectant Ethylene Glycol 20.0 Dispersant EFKA® 4575 2.1 Wetting Agent BYK® 348 0.50 Carrier Water 21.7

Example 38

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.0

Dynacoll® 7150 milled with EFKA®

Resin 39.7

4575 1 :1 (14.38% total solids)

Softening Ag PEG 8,000 11.4 Humectant Propylene Glycol 15.0 Dispersant EFKA® 4575 1.7 Wetting Agent BYK® 348 0.70 Carrier Water 30.4

Example 39

Type of Material Name Wt. %

Pigment Carbon Black, Monarch® 700 1.3

Dynacoll® 7150 milled with EFKA®

Resin 51.7

4575 1 :1 (14.38% total solids)

Softening Agent PEG 8,000 7.4 Humectant Ethylene Glycol 20.0 Dispersant EFKA® 4575 2.2 Wetting Agent BYK® 348 0.50 Carrier Water 16.9

Example 40

Type of Material Name Wt. %

Heliogen® Blue D7092 milled with

Pigment

EFKA® 4575 1 :0.6 (30% total solids) 8.0

Resin Joncryl® ECO 2189 (48% nvs) as is 27.0

Softening Agent Tween® 80 64.8 Wetting Agent BYK® 345 0.20

Example 41

Type of Material Name Wt. %

Carbon Black, Monarch® 700 milled with

Pigment

EFKA® 4575 1 :0.6 (30% total solids) 10.0

Resin Joncryl® ECO 2189 (48% nvs) as is 26.2

Softening Agent Span® 20 62.8 Wetting Agent BYK® 348 1.00

Example 42

Type of Material Name Wt. % Heliogen® Blue D7092 milled with

Pigment

EFKA® 4575 1 :0.6 (30% total solids) 30.0

Resin Joncry®! ECO 2189 (48% nvs) as is 41.0

Softening Agent Tween® 20 19.6 Wetting Agent BYK® 348 1.00

Carrier Water 8.40

Various commercially available nano-pigments may be used in the inventive ink formulations. These include pigment preparations such as CAB-O-JET® 352K by Cabot, Hostajet Magenta E5B-PT and Hostajet Black O-PT, both by Clariant as well as pigments demanding post-dispersion processes, such as Cromophtal Jet Magenta DMQ and Irgalite Blue GLO, both by BASF.

One of ordinary skill in the art may readily recognize that various known colorants and colorant formulations may be used in the inventive ink or inkjet ink formulations. In one embodiment, such pigments and pigment formulations may include, or consist essentially of, inkjet colorants and inkjet colorant formulations.

Alternatively or additionally, the colorant may be a dye. Examples of dyes suitable for use in the ink formulations of the present invention include: Duasyn Yellow 3GF-SF liquid, Duasyn Acid Yellow XX-SF, Duasyn Red 3B-SF liquid, Duasynjet Cyan FRL-SF liquid (all manufactured by Clariant International Ltd.); Basovit Yellow 133, Fastusol Yellow 30 L, Basacid Red 495, Basacid Red 510 Liquid, Basacid Blue 762 Liquid, Basacid Black X34 Liquid, Basacid Black X38 Liquid, Basacid Black X40 Liquid (all manufactured by BASF).

Various suitable dispersants may be selected by those of skill in the art, including commercially available products. Such dispersants may include high molecular weight polyurethane or aminourethane (e.g., Disperbyk® 198), a styrene-acrylic copolymer (e.g., Joncryl® HPD 296), a modified polyacrylate polymer (e.g., EFKA® 4560, EFKA® 4580), an acrylic block copolymer made by controlled free radical polymerization (e.g., EFKA® 4585, EFKA® 7702), a sulfosuccinate (e.g., Triton GR, Empimin OT ), an acetylenic diol (e.g., Surfynol CT), an ammonium salt of carboxylic acid (e.g., EFKA 7571), an alkylol ammonium salt of carboxylic acid (e.g., EFKA 5071), an aliphatic polyether with acidic groups (e.g., EFKA 6230), or an ethoxylated non-ionic fatty alcohol (e.g., Lumiten® N-OC 30).

In some embodiments, it may be desirable to include, in addition to the polymeric resin, colorant, water and optional co-solvent, a small amount of a surfactant, e.g., 0.5-1.5 wt.% of the ink. Such surfactants may serve as wetting agents and/or as leveling agents. In some embodiments, the surfactant is a non-ionic surfactant. Exemplary types of wetting agents and/or leveling agents include silicones, modified organic polysiloxanes and polyether modified siloxanes (e.g., BYK^® 307, BYK^® 333, BYK^® 345, BYK^® 346, BYK^® 347, BYK^®-348, or BYK^®-349, from BYK, or Hydropalat WE 3240 from BASF). Fluorosurfactants such as Capstone FS-10, Capstone FS-22, Capstone FS-31 , Capstone FS- 65 (DuPont), Hydropalat WE 3370, and Hydropalat WE 3500, may also be suitable. Hydrocarbon surfactants such as block copolymers (e.g., Hydropalat WE 31 10, WE 3130), sulfosuccinates (e.g., Hydropalat WE 3475), and acetylene diol derivatives (e.g., Hydropalat WE 3240) can be used as wetting and/or leveling agents.

In some embodiments, it may be desirable to include at least one humectant. Examples of humectants that are miscible with water are ethylene glycol, diethylene glycol, propylene glycol, glycerol, N-methyl pyrrolidone, and polyethylene glycol 400 (PEG 400).

Various other, or additional, dispersants, humectants, and wetting and leveling agents, which may be suitable for use in the ink formulations of the present invention, will be apparent to those of ordinary skill in the art.

Thermo-Rheological Properties

The inventive process in which the ink formulations can be used may include the heating of the ink film or image, during transport on the surface of the image transfer member, to evaporate the aqueous carrier from the ink image. The heating may also facilitate the reduction of the ink viscosity to enable the transfer conditions from the ITM to the substrate. The ink image may be heated to a temperature at which the residue film of organic polymeric resin and colorant that remains after evaporation of the aqueous carrier is rendered tacky (e.g., by softening of the resin).

Immediately prior to the transfer to the printing substrate, the residue ink film on the surface of the image transfer member may be dry or substantially dry. The film includes the resin and the colorant from the ink formulation. The residue film may further include small amounts of one or more surfactants or dispersants, which are typically water soluble at the pH of the ink (i.e., prior to jetting).

The ink residue film may be rendered tacky before it reaches the impression cylinder. In this case, the film may cool at the impression station, by its contact with the substrate and exposure to the environment. The already tacky ink film may adhere immediately to the substrate onto which it is impressed under pressure, and the cooling of the film may be sufficient to reduce film adhesion to the image transfer surface to the point that the film peels away neatly from the image transfer member, without compromising adhesion to the substrate.

Tack (or tackiness) may be defined as the property of a material that enables it to bond with a surface on immediate contact under light pressure. Tack performance may be highly related to various viscoelastic properties of the material (polymeric resin, or ink solids). Both the viscous and the elastic properties would appear to be of importance: the viscous properties at least partially characterize the ability of a material to spread over a surface and form intimate contact, while the elastic properties at least partially characterize the bond strength of the material. These and other thermo-rheological properties are rate and temperature dependent.

Some of the significant difficulties associated with low-temperature operation of the Image Forming Station have been described hereinabove. Briefly, though a lower temperature at the image forming station may reduce nozzle clogging resulting from ink carrier evaporation and prolong the lifespan of the blanket subjected then to less stringent operating conditions, lowering the temperature of the blanket section underneath this station to be below the temperature of evaporation of the carrier creates its own problems. While the inks need to retain jettability from the print head nozzles, the deposited droplets need to readily adhere to the outer surface of the ITM at a viscosity that would be lower than the one obtainable with the same formulation at a higher temperature, largely due to the much reduced rate of evaporation. Such ink droplets need to be able to form instantaneously, once on the ITM surface, a skin preventing disturbance of droplet position and shape on the blanket, as long as the ink carrier is not fully evaporated. If the adhesion needs to be facilitated by the treatment of the blanket with a conditioning solution prior to ink jetting and image formation, the type of interaction with the optional conditioning agents may also be affected by temperature.

• The resultant ink drops subsequently undergo heating, drying, and transfer to the printing substrate, to produce the residue ink films. These residue films, which are obtained from the ink formulations of the present invention, and may be processed substantially as described herein, may have several salient features, including:

• ultra-thin film thickness (typically about 0.5 ιη for a single-layer film);

• temperature gradients: temperature variations as a function of position along the Z- axis (thickness direction) of the film;

• substantially or completely dry films, including the interface between the ITM and the film surface proximal thereto; and

• an inventive conditioning layer that may advantageously peel off the ITM to form an integral part of the residue film.

Moreover, the process may require the inventive residue films to have sufficient fiowability to readily transfer from the ITM to the printing substrate at low temperatures (e.g., below 140°C, below 120°C, below 100°C or below 90°C). The process may also require the inventive residue films to have sufficiently low fiowability at lower temperatures (e.g., below 55°C) such that the residue films "permanently" adhere to the printing substrate at such temperatures, without developing a tendency to adhere to other surfaces.

By suitable selection of the thermo-rheological characteristics of the residue film, the effect of the cooling may be to increase the cohesion of the residue film, whereby its cohesion exceeds its adhesion to the transfer member so that all or substantially all of the residue film is separated from the image transfer member and impressed as a film onto the substrate. In this way, it is possible to ensure that the residue film is impressed on the substrate without significant modification to the area covered by the film nor to its thickness.

The inventors have found that the dried or substantially dried ink residue or ink residue film may advantageously have a first dynamic viscosity within a range of 10⁶cP to 5^» 10⁷cP for at least a first temperature within a first range of 60°C to 87.5°C. The inventors have found that such a first dynamic viscosity may be correlated with efficacious low- temperature transfer of the dried ink film from the ITM to various fibrous (e.g. , coated and uncoated papers and cardboards) and non- fibrous (e.g., various types of plastic) substrates. The inventors have further found that the ink residue film may advantageously have a second dynamic viscosity of at least 7^»10⁷cP, for at least a second temperature within a second temperature range of 50°C to 55°C. At such viscosities and temperatures, the residue films may display good adhesion to the printing substrate, while surface tack is sufficiently low to discourage adhesion to other surfaces.

Thermo-rheological Measurements

Viscosity temperature step sweeps were performed using a Thermo Scientific HAAKE Mars III rheometer having a TM-PE-P Peltier plate temperature module and a P20 Ti L measuring geometry or PP20 disposable (spindle).

Samples of dried ink residue having a 1mm depth in a 2cm diameter module were tested. The samples were dried in an oven at an operating temperature of 110°C until the weight of the sample did not further change (and typically reached the weight expected on the basis of the non-volatile materials). Typically, the samples were dried for one hour or more and up to overnight (i.e., up to 18 hours). A volume of sample (pellet) was inserted into the 2cm diameter module and softened by gentle heating (typically at 80°C for less than one minute) to ensure adequate contact between the surface of the sample and the spindle. The sample volume was then reduced to the desired size by lowering the spindle to reduce the sample volume to the desired depth of 1mm.

In temperature ramp mode, the sample temperature was allowed to stabilize for 120 seconds at low temperature (typically 45°C to 55°C, in particular circa 50°C) before being ramped up to a high temperature (typically 150°C to 190°C, in particular circa 180°C).

The measurements were performed under two regimens, termed, respectively, the "long method" and "short method". In the long method, the temperature was set to increase at a rate of approximately 0.08°C per second up to about 110°C and at a rate of approximately 0.04°C per second at higher temperature (above 110°C). Viscosity measurements were taken at intervals of approximately 10°C, 20 repeat measurements being carried out at each time point. The sample temperature was then allowed to stabilize at high temperature for 120 seconds before being ramped down to low temperature, at the same rates. Oscillation temperature sweeps were performed at a frequency of 1 Hz (Ω = 6.2832 rad/sec) under a stress of 1-500 Pa up to 110°C and at 5 Pa between 110°C and 180°C. In the short method, the temperature was set to increase at a rate of approximately 0.11°C per second up to about 110°C and at a rate of approximately 0.07°C per second at higher temperature. In the range of up to about 110°C, viscosity measurements were taken at intervals of approximately 90 seconds, ten repeat measurements being carried out at each time point. The sample temperature was then allowed to increase to the target high temperature during 940 seconds, at which time the viscosity was last measured without ramping down back to lower temperature. The spindle was set to oscillate at a frequency of 1 Hz.

The rheometer used in the present experimental setup provided up to ten repeat measurements for a given temperature and for temperatures of up to 100°C, the rheometer ranked the quality of each of the measurements, allowing trained operators to manually select, if needed, the most representative values in the linear viscous elastic range (typically at least the last three measurements in a series performed at a given temperature). Above 110°C, the samples were generally viscous and generally had a sufficient linear viscous elastic range to permit automatic measurement.

In the specification and in the claims section that follows, values for dynamic viscosity are quantitatively determined by the "short method" described hereinabove.

Various experiments were performed in which the frequency of oscillation was reduced from 1.0 Hz to 0.1 Hz, and/or in which the rate of increase of temperature was raised from about 2°C per minute, to about 10°C per minute. Such modifications did not appreciably affect the observed thermo-rheo logical behavior of the samples.

Thermo-rheological Results

Figure 9A provides a temperature sweep plot of dynamic viscosity as a function of temperature, for residue films of various ink formulations, including ink formulations of the present invention. The twenty plots provided correspond to dried ink residues of the ink formulations of Example Nos. 1-4, 7-15, 18, 20, 23, 24, 28, 31 and 33, and the viscosity axis spans from l^»10⁶cP to l^»10⁹cP. The dried ink residues were obtained using the drying procedure provided hereinabove.

As described above, it may be advantageous for the dried ink residues to exhibit a dynamic viscosity of at least 7^»10⁷cP, within a temperature range of 50°C to 55°C. The dried ink residues may advantageously exhibit a dynamic viscosity of at least 8^»10⁷cP, at least 9^»10⁷cP, at least l^»10⁸cP, or at least 1.5^»10⁸cP. At such viscosities and temperatures, the residue films may display good adhesion to the printing substrate, while surface tack is sufficiently low to discourage adhesion to other surfaces.

A first rectangular window (Wl), plotted in Figure 9A, shows suitable viscosities for dried ink residues at 60°C to about 87.5°C, within the temperature sweep. The inventors have found that residue films exhibiting good transfer properties at low temperature generally display temperature sweep viscosity curves that fall within this window.

A rectangular window (W2), also plotted in Figure 9A, shows suitable viscosities for dried ink residues at 50°C to 55°C, within the temperature sweep. Of course, the dried ink residues may advantageously have a viscosity in excess of the upper bound of the plot, i.e., M0⁹cP.

In the ink film constructions of the present invention, and in the ink formulations of the present invention, the temperature sweep plot of dynamic viscosity as a function of temperature, for residue films, may fall within both windows (Wl, W2).

Figure 9B provides temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of inventive ink formulations containing various polyester resins. The plots provided correspond to dried ink residues of the ink formulations of Example Nos. 34-39 and the viscosity axis spans from l^»10⁷cP to l^»10⁸cP to magnify the area of interest. The dried ink residues were obtained using the drying procedure provided hereinabove.

In the ink film constructions of the present invention, and in the ink formulations of the present invention, the temperature sweep plot of dynamic viscosity as a function of temperature, for residue films containing polyester based resins, may fall within both windows (Wl, W2), both shown in truncated form in Figure 9B.

This may be more clearly demonstrated using Figure 10, which provides temperature sweep plots of dynamic viscosity as a function of temperature, for representative dried ink residues of various ink formulations, some of which were provided in Figure 9A and 9B. Near the top left-hand corner of the graph, the temperature sweep of residue #16 (of formulation #16 from Example 16) passes through W2 at a viscosity of approximately l^»10⁹cP. At temperatures above 55°C, the viscosity of residue #16 drops monotonically. However, the slope (or negative slope) is far from sufficient for the thermo-rheological plot of residue #16 to pass through Wl. Similarly, the temperature sweep of residue #19 (from Example 19) appears to pass through W2 at a viscosity above l^»10⁹cP. At temperatures above 55°C, the viscosity of residue #19 drops more steeply than the viscosity of residue #16. However, the slope is still insufficient for the thermo-rheo logical plot of residue #19 to pass through Wl.

The temperature sweep of residue #2 (from the inventive ink formulation provided in Example 2) passes through W2 at a viscosity of close to l^»10⁹cP, and at temperatures above 55°C, the viscosity drops monotonically. However, in contrast to the thermo- rheological behavior exhibited by the previous examples, the slope is easily sufficient for the thermo-rheo logical plot of residue #2 to pass through Wl.

The temperature sweep of residue #34 (from the inventive ink formulation provided in Example 34) passes through W2 at a viscosity of about 7^»10⁷cP, and at temperatures above 55°C, the viscosity drops monotonically. However, the slope is low with respect to residue #2 and residue #19.

With reference now to residue #8 (from the inventive ink formulation provided in Example 8), the temperature sweep passes through W2 at a viscosity approaching 2^»10⁸cP. At temperatures above 55°C, the viscosity drops monotonically, the slope being comparable to that of residue #2. The temperature sweep passes through a central area of W2.

Like residue #8, the temperature sweep of residue #7 (from the inventive ink formulation provided in Example 7) passes through W2 at a viscosity of around 2^»10⁸cP. At temperatures above 55°C, the viscosity drops sharply, such that the sweep passes through Wl near the bottom, left-hand corner, attaining a viscosity of l^»10⁶cP at around 70°C.

The temperature sweep of residue #15 (from the ink formulation provided in Example 15) has a slope that is similar to that of residue #7, however, the residue has sufficiently-high flowability at low temperatures such that the temperature sweep falls outside the bounds of both Wl and W2.

The temperature sweep of residue #14 (from the ink formulation provided in Example 14) passes through Wl, but at lower temperatures of 50°C to 55°C, fails to develop the requisite viscosity for dry ink residues according to the present invention.

Figure 11 provides temperature sweep plots of dynamic viscosity as a function of temperature, for representative dried ink residues of ink formulations of the present invention, vs. dried ink residues of several commercially available inkjet inks. The dried ink residues of inventive ink formulations 2, 7 and 8 are those described hereinabove with reference to Figure 12; residue #35 was obtained by drying the inventive ink formulation provided in Example 35. The commercially available inkjet inks are black inks of Canon, Epson, HP, and Toyo, and are labeled accordingly.

It is evident from the plots, and from the magnitude of the viscosities, that the dried ink residues of the various prior art ink formulations exhibit no or substantially no flow behavior over the entire measured range of temperatures. The peaks observed at extremely high viscosities in some plots of the prior-art formulations would appear to have no physical meaning. Significantly, within the temperature range of 60°C to 87.5°C, all of the prior art residue films exhibit a minimum viscosity exceeding 1 · 10¹⁰ cP, two and a half orders of magnitude above the top boundary of 5·10⁷ cP for W2.

In practice, the inventors of the present invention successfully transferred all of the inventive ink residues to a printing substrate, but failed to transfer any of the prior-art ink films to a printing substrate, even after heating to over 160°C.

The transferability to printing substrates of ink formulations prepared as described in previous examples was assessed as follows: the formulations being tested were applied to the outer surface of a printing blanket of approximately 20 cm x 30 cm size pre -heated to a desired temperature, typically between 70 and 90°C. Unless otherwise stated, this surface comprised a silanol-terminated polydimethyl-siloxane silicone release layer. A conditioning solution, generally comprising 0.3wt.% of polyethylenimine (PEI) (e.g., Lupasol® PS) in water, was manually applied to the release layer surface by moistening a Statitech 100% polyester cleanroom wiper with the solution and wiping the release layer surface. The conditioning solution was then allowed to dry spontaneously on the heated blanket and the temperature of the release layer was monitored using an IR Thermometer Dual Laser by Extech Instruments.

Thereafter, the ink formulation was applied and evened on the surface of the heated and optionally pre-conditioned blanket using a coating rod (e.g. , Mayer rod) yielding a wet layer having a characteristic thickness of approximately 12 micrometers. The ink film so formed was allowed to dry for at least 5 seconds and then, while still hot, was transferred to the desired printing substrate, such as Condat Gloss® 135 gsm coated paper. The paper was placed on the surface of the dried ink and the transfer was performed using a metal roller by applying manual pressure. The quality of the transferred image was visually assessed. The surface of the release layer was observed in the event of partial transfer. For each formulation, the transferability test was performed at least three times for each temperature of transfer and/or printing substrate.

Softening Agents

The inventors have found that certain softening agents may be introduced to the ink formulations according to the present invention. In some embodiments of the inventive ink formulations, the addition of such softening agents may enable the use of various resins exhibiting characteristically poor flowability at low temperatures.

By way of example, Figure 12A displays a first plurality of temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of five ink formulations having identical components, and a varying ratio of softening agent, using a first thermoplastic resin (Joncryl® 1680E), and a first softening agent (polyethylene glycol (PEG) 20,000). The dried residues were obtained from the ink formulations corresponding to Examples 5, 6, 7, 25 and 26.

Figure 12B provides a second plurality of temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of five ink formulations having identical components, and a varying ratio of softening agent, using a second thermoplastic resin, namely, Joncryl® 8060, and a second softening agent, namely, PEG 8,000. The dried residues were obtained from the ink formulations corresponding to Examples 16, 17, 21, 22 and 23.

Figures 13A-13D are temperature sweep plots of dynamic viscosity as a function of temperature, for residue films of ink formulations having different softening agents, and varying concentrations of those agents. For convenience of comparison, the pigment and the polymeric resin were the same black pigment and Joncryl® 2038, and were kept at a 1 :4 ratio for all samples. Figure 13A provides the thermo-rheological behavior of dried residues of ink formulations comprising Tween® 20 (Examples 27-28); Figure 13B displays sweep plots observed for formulations comprising Tween® 40 (Examples 29-31); Figure 13C for formulations comprising Tween® 60 (Examples 9-10); and Figure 13D for formulations comprising Tween® 80 (Examples 32-33).

In some embodiments, the softening agent may have a vapor pressure of at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa, at 150°C. In some embodiments, the softening agent may be stable up to a temperature of at least 170°C, at least 185°C, at least 200°C, or at least 220°C.

In some embodiments, the weight ratio of the softening agent to the resin within the formulation may be at least 0.05: 1, at least 0.10: 1, at least 0.15: 1, at least 0.2: 1, at least 0.25:1, at least 0.35: 1, at least 0.4: 1, at least 0.5: 1, at least 0.6: 1, at least 0.75: 1, at least 1 :1, at least 1.25: 1, at least 1.5: 1, at least 1.75: 1, at least 2: 1, at least 2.5: 1, at least 3:1 , at least 3.5:1, at least 4: 1, at least 5: 1, at least 6: 1, or at least 7: 1.

In some embodiments, this weight ratio may be at most 15: 1, at most 12: 1, at most 10: 1, at most 9: 1, at most 8: 1, or at most 7.5: 1.

Coloring Agents

The term "colorant" or "coloring agent", as used herein in the specification and in the claims section that follows, refers to a substance that is considered, or would be considered to be, a colorant in the art of printing. The colorant may include at least one pigment. Alternatively or additionally, the colorant may include at least one dye.

As used herein in the specification and in the claims section that follows, the term "pigment" refers to a solid colorant, typically finely divided. The pigment may have an organic and/or inorganic composition. Typically, pigments are insoluble in, and essentially physically and chemically unaffected by, the vehicle or medium in which they are incorporated. Pigments may be colored, fluorescent, metallic, magnetic, transparent or opaque. Pigments may alter appearance by selective absorption, interference and/or scattering of light. They are usually incorporated by dispersion in a variety of systems and may retain their crystal or particulate nature throughout the pigmentation process.

As used herein in the specification and in the claims section that follows, the term "dye" refers to at least one colored substance that is soluble or goes into solution during the application process and imparts color by selective absorption of light.

Although a wide range of average particle sizes (d₅o) or particle size distributions (PSDs) may be suitable for pigments utilized in various embodiments of the inventive inks, the inventors believe that best results may be attained when the d₅o of the pigment is within the range of 20 nm to 300 nm, (e.g., at most 120 nm, at most lOOnm, or 40-80 nm). The pigments may thus be nanopigments; the particle size of the nanopigments may depend on the type of pigment and on the size reduction methods used in the preparation of the pigments. Pigments of various particle sizes, utilized to give different colors, may be used for the same print. Some pigments having such particle sizes are commercially available, and may be employed as-is in embodiments of the invention; in other cases, the pigments may be milled to the appropriate size. It will be appreciated that in general, the pigments are dispersed (or at least partly dissolved) within the solvent along with the polymeric resin, or can be first dispersed within the polymeric resin (e.g., by kneading) to obtain colored resin particles that are then mixed with the solvent.

The concentration of the at least one colorant within the ink formulation, when the formulation is substantially dry, may be at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%>, or at least 22%, by weight. Typically, the concentration of the at least one colorant within the ink film is at most 40%, at most 35%, at most 30%, or at most 25%. More typically, the dry ink residue may contain 2-30%, 3- 25%, or 4-25% of the at least one colorant.

In some applications, particularly when it is desirable to have an ultra-thin ink film laminated onto the printing substrate, the weight ratio of the polymeric resin to the colorant may be at most 10: 1 , at most 7: 1 , at most 5 : 1 , at most 3 : 1 , at most 2.5 : 1 , at most 2: 1 , or at most 1.7: 1.

Figure 19 provides temperature sweep plots of dynamic viscosity as a function of temperature, for dried ink residues of four ink formulations having different colorants (C, M, Y, K) but otherwise identical formulation components. The black formulation is as disclosed in Example 4.

It will be appreciated by those of skill in the art that the inventive formulations may be modified in a fairly predictable manner to achieve desired formulation properties, and in particular, thermo-rheological properties. To this end, a large number of exemplary formulations, and thermo-rheological plots thereof, have been provided. Moreover, the plots have been arranged within the Figures to provide guidance on the effect of resin to pigment ratio on the thermo-rheological behavior. Figure 12A and Figure 12B demonstrate the effect of the softening agent to resin ratio on thermo-rheological behavior, for 2 different thermoplastic resins and 2 different softening agents. Higher softening agent to resin ratios are generally associated with lower viscosities. Relatively hard resins may be made suitable for low-temperature transfer by the softening agents. Figures 13A-13D demonstrate the effect of different softening agents on thermo-rheological performance, combined with varying softening agent to resin ratio, while keeping other formulation parameters constant. From the similarity of the curves in Figure 19 it is evident that the colorants play a thermo-rheological role, but that that role is generally of secondary importance.

The first, "high-temperature" viscosity (associated with Wl) provides a general indication of film transfer properties, which is important in the transfer of the film from the release layer of the ITM. The maximum viscosity value associated with that physical property may be represented by the top line or area of Wl .

The second, "low-temperature" viscosity (associated with W2 at 50-55°C) provides a general indication of how the film will behave on the printing substrate. The minimum viscosity value associated with that physical property may be represented by the bottom of W2.

With respect to the ink, the terms "substantially dried" or "substantially dry", with regard to an ink-containing sample, refer to a sample dried according to the following conditions (or substantially identical conditions): samples of ink formulations (5 g) are placed on an aluminum crucible and dried in a vacuum oven (VT 6025, Thermo Scientific) at a temperature of 110°C and under a pressure of 1 mbar (absolute). The level of dryness is gravimetrically checked every hour, and the drying procedure is stopped when the difference in weight loss between immediately adjacent weighings (1 hour apart) of the sample is less than 2%. For low vapor pressure materials such as glycerol, the weight loss between immediately adjacent weighings (1 hour apart) of the sample is less than 0.5%. Thus, if, for a 5 gram sample, the weight loss in the current weighing was 0.0330 grams, and the weight loss in the immediately previous weighing was 0.0335 grams, the difference in weight loss between immediately adjacent weighings would be about 1.5%. For samples having known composition, the target stable weight can be estimated on the basis of the amount of solids or other non-volatile materials in the formulation.

In some embodiments, the ink formulation is devoid or substantially devoid of wax. Typically, the ink formulation contains less than 30 wt.% wax, less than 20 wt.% wax, less than 15 wt.% wax, less than 10 wt.% wax, less than 7 wt.% wax, less than 5 wt.% wax, less than 3 wt.% wax, less than 2 wt.% wax, or less than 1 wt.% wax. In other embodiments, wax is included in the ink formulation in order to impart greater abrasion resistance in the printed ink. Such waxes may be natural or synthetic, e.g. , based on esters of fatty acids and fatty alcohols or long-chain alkanes (paraffin waxes), or mixtures thereof. In such cases, the formulation may comprise, for example, 0.1-10 wt.% wax, e.g., up to 0.1, 0.3, 0.5, 0.7, 1.0, 1.5, 2, 3, 4, 6, 8, or 10 wt.%> wax. The wax may be incorporated into the formulation as an aqueous dispersion of small wax particles, e.g., having an average size of 10 micrometers or smaller, preferably having average size of 1 μιη or smaller.

In some embodiments, the ink formulation is devoid or substantially devoid of oils such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil). Typically, the ink formulation contains at most 20 wt.%, at most 12 wt.%, at most 8 wt.%, at most 5 wt.%, at most 3 wt.%), at most 1 wt.%>, at most 0.5 wt.%>, or at most 0.1 wt.%>, by weight, of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air-drying.

In some embodiments, the ink formulation is devoid or substantially devoid of glycerol. Typically, the ink formulation contains at most 10%, at most 8%, at most 6%, at most 4%), at most 2%>, at most 1%>, at most 0.5%>, or at most 0.2%> glycerol, by weight.

In some embodiments, the ink formulation is devoid or substantially devoid of one or more salts, including salts used to coagulate or precipitate ink on a transfer member or on a substrate (e.g., calcium chloride). Typically, the ink formulation contains at most 8 wt.%, at most 5 wt.%>, at most 3 wt.%>, at most 1 wt.%>, at most 0.5 wt.%>, at most 0.1 wt.%>, or substantially 0 wt.% of one or more salts. Such salts may be referred to herein as "precipitants", and it will be appreciated that when it is stated that a formulation does not include a salt or contains salt in an amount less than a certain weight percentage, this does not refer to salts that may form between the polymer(s) of the polymeric resin and pH modifiers, such as alcohol amines, or that may be present in the polymeric resin itself if the polymeric resin is provided as a salt. As discussed above, it is presently believed that the presence of negative charges in the polymeric resin is beneficial to the print process.

In some embodiments, the ink formulation is devoid or substantially devoid of inorganic particulates, e.g., silica particulates, titania particulate or alumina particulates, containing less than 2 wt.%>, less than 1 wt.%>, less than 0.1 wt.%> or substantially no inorganic particulates. By "silica particulates" is meant fumed silica, silica chips, silica colloids, and the like. Specific examples of such silica particulates include those available from DuPont Company under the names: Ludox® AM-30, Ludox® CL, Ludox® HS-30; and those available from Nyacol Nanotechnologies Company under the names: NexSil™ 12, NexSil™ 20, NexSil™ 8, NexSil™ 85. In the context of the present application, the term "silica particulates" does not include colorants.

INK FILM CONSTRUCTIONS

In the ink film constructions of the present invention, the ink dot may essentially be laminated onto a top surface of the printing substrate. As described herein, the form of the dot may be determined or largely determined prior to the transfer operation, and the dot is transferred as an integral unit to the substrate. This integral unit may be substantially devoid of solvent, such that there may be no penetration of any kind of material from the blanket transfer member into, or between, substrate fibers. The continuous dot, which may largely contain organic polymeric resin and colorant, adheres to, or forms a laminated layer on, the top surface of the fibrous printing substrate.

Printing tests employing the afore-disclosed ink compositions show good transfer to various and varied paper and plastic substrates, as will be illustrated in some of the following Figures.

Figures 15A-F display two-dimensional (Figures 15A-C) and three-dimensional (Figures 15D-F) laser-microscope acquired magnified images of ink films on commodity- coated paper substrates, obtained using various printing technologies, wherein: Figures 15A and 15D are magnified images of a liquid electro-photography film (LEP); Figures 15B and 15E are magnified images of an offset splotch; and Figures 15C and 15F are magnified images of an inkjet ink film construction according to the present invention. The laser microscopy imaging was performed using an Olympus LEXT 3D measuring laser microscope, model OLS4000.

Figures 16A-F display two-dimensional (Figures 16A-C) and three-dimensional (Figures 16D-F) laser-microscope acquired magnified images of ink films on uncoated paper substrates, obtained using various printing technologies, wherein: Figures 16A and 16D are magnified images of a liquid electro-photography film (LEP); Figures 16B and 16E are magnified images of a lithographic offset splotch; and Figures 16C and 16F are magnified images of an inkjet ink film construction according to the present invention.

The ink dots in the ink dot constructions of the present invention may exhibit consistently good shape properties (e.g., roundness, edge raggedness, and the like), irrespective, to an appreciable degree, of the particular, local topographical features of the substrate, and irrespective, to an appreciable degree, of the type of printing substrate (coated or uncoated printing substrates, plastic printing substrates, etc.). By contrast, the quality of ink dots in various known printing technologies, and in direct aqueous inkjetting technologies in particular, may vary significantly with the type of printing substrate, and with the particular, local topographical features of the substrate. It will be readily appreciated that, by way of example, when an ink drop is jetted onto a particularly flat local contour having a relatively homogeneous substrate surface (such as a broad fiber), the ink dot obtained may display significantly better shape properties, with respect to the other, or average ink dots disposed elsewhere on the substrate.

In these prior art ink and substrate constructions, the inkjet ink drops have penetrated the surface of the paper, as may be best seen in Figures 16D-16F. Such penetration may be typical of various printing technologies using uncoated or commodity-coated paper, in which the paper may draw ink carrier solvent and pigment within the matrix of the paper fibers.

In contrast to these prior art ink constructions, the inventive inkjet ink film constructions may be characterized by well-defined individual ink films, disposed generally above, and adhering to, the fibrous substrates, both coated (Figures IOC, 10F) and uncoated (Figures 16C, 16F).

The inventive inkjet single-drop ink film (or individual ink dot) construction was produced using the inventive system and method described herein, using an ink formulation Example 29 according to the present invention.

Dot Perimeter Characterization

The perimeter of the offset ink splotch and the perimeter of the LEP ink splotch have a plurality of protrusions or rivulets, and a plurality of inlets or recesses. These ink forms may be irregular, and/or discontinuous. By contrast, the inkjet ink dot produced according to the present invention, best seen in Figures IOC and 16C, has a manifestly rounded, convex, shape. The perimeter of the ink film is relatively smooth, regular, continuous and well defined.

More particularly, projections of the ink film of the invention against the substrate surface (i.e., projections from a top view) tend to be rounded, convex projections that form a convex set, i.e., for every pair of points within the projection, every point on the straight line segment that joins them is also within the projection. Such a convex set is shown in Figure 20 A. By sharp contrast, the rivulets and inlets in the projections of various prior-art define those projections as a non-convex sets, i.e., for at least one straight line segment within a particular projection, a portion of that straight line segment is disposed outside the projection, as illustrated in Figure 20B.

It must be emphasized that ink images may contain an extremely large plurality of individual or single ink films. For example, a 5mm by 5mm ink image, at 600 dpi, may contain more than 10,000 of such single ink films. Therefore, it may be appropriate to statistically define the ink film constructions of the present invention: at least 10%, at least 20%), or at least 30%>, and more typically, at least 50%>, at least 70%>, or at least 90%>, of the single ink dots (selected at random), or projections thereof, may be convex sets.

It must be further emphasized that ink images may not have crisp boundaries, particularly when those boundaries are viewed at high magnification. Therefore, it may be appropriate to relax the definition of the convex set whereby non-convexities (rivulets or inlets) having a radial length L_r (as shown in Figure 20C) of up to 3,000nm, up to l,500nm, up to Ι,ΟΟΟηηι, up to 700nm, up to 500nm, up to 300nm, or up to 200nm, are ignored, excluded, or are "smoothed", whereby the ink film or ink film projection is considered to be a convex set. The radial length L_r is measured by drawing a radial line L from the center point C of the ink film image, through a particular rivulet or inlet. The radial length L_r is the distance between the actual edge of the rivulet or inlet, and a smoothed projection P_s of the ink image, devoid of that rivulet or inlet, and matching the contour of the ink film image.

In relative terms, it may be appropriate to relax the definition of the convex set whereby non-convexities (rivulets or inlets) having a radial length of up to 15% of the film/drop/splotch diameter or average diameter, up to 10%>, and more typically, up to 5%, up to 3%o, up to 2%o, or up to 1%, are ignored, excluded, or are "smoothed", as above, whereby the ink film or ink film projection is considered to be a convex set.

The perimeter of various ink dots or films of the prior art may characteristically have a plurality of protrusions or rivulets, and a plurality of inlets or recesses. These ink forms may be irregular, and/or discontinuous. By sharp contrast, the inkjet ink dot produced according to the present invention characteristically has a manifestly rounded, convex, circular shape. The perimeter of the ink dot of the invention may be relatively smooth, regular, continuous and well defined. Ink dot roundness, convexity, and edge raggedness are structural parameters used to evaluate or characterize shapes, or optical representations thereof. It can readily be observed, by comparing the magnified images of the prior-art ink forms of Figures 10A and 10B with the inventive ink dot construction of Figure IOC, or by comparing the magnified images of the prior-art ink forms of Figures 16A and 16B with the inventive ink dot construction of Figure 16C, that the appearance of the ink dots of the present invention is manifestly distinct from these prior-art ink forms. That which is readily observed by the human eye may be quantified using image-processing techniques. Various characterizations of the ink forms are described hereinbelow, after a description of the image acquisition method.

Acquisition Method

(1) For each of the known printing technologies to be compared in the study, single dots, splotches, or film images printed on coated paper and on uncoated paper were used, including numerous coated and uncoated fibrous substrates, and various plastic printing substrates.

(2) With regard to the printing technology according to the present invention, single drop dot images were printed on coated paper and on uncoated paper. Care was taken to select substrates having similar characteristics to the substrates of the known ink-dot constructions used in (1).

(3) The acquisition of the dot images was performed using an OLS4000 (Olympus) microscope. Those of ordinary skill in the art know how to adjust the microscope to achieve the requisite focus, brightness and contrast, so that the image details will be highly visible. These image details include the dot contour, the color variance within the dot area, and the fibrous structure of the substrate surface.

(4) The images were taken with an XI 00 optical zoom lens having a resolution of 129micrometersX129micrometers. This high resolution may be essential in obtaining fine details of the dot and of the fibrous structure of the substrate surface.

(5) The images were saved in uncompressed format (Tiff) having a resolution of 1024x1024 pixels, as image data may be lost in compression.

(6) Generally, a single dot or splotch was evaluated for each printing technology. From a statistical point of view, however, it may be advantageous to obtain 15 dot images (at least) for each type of hard-copy print being analyzed, and to manually select the 10 (at least) most representative dot images for image processing. The selected dot images should be representative in terms of dot shape, contour and color variation within the dot area. Another approach to print dot sampling, termed "field of view", is described hereinbelow.

Dot Contour Computation

The dot images were loaded to the image-processing software (ImageXpert). Each image was loaded in each of the Red, Green and Blue channels. The processing channel was selected based on a highest visibility criterion. For example, for cyan dots, the Red channel typically yielded the best dot feature visibility, and was thus selected for the image processing step; the Green channel was typically most suitable for a magenta dot. The dot edge contour was detected (automatically computed), based on a single threshold. Using a "full screen view" mode on a 21.5" display, this threshold was chosen manually for each image, such that the computed edge contour would best match the real and visible dot edge. Since a single image-channel was processed, the threshold was a gray value (from 0 to 255, the gray value being a non color value).

A computed perimeter value was obtained from the image-processing software (e.g. , ImageXpert), the perimeter value being the sum of all distances between the adjacent, connected pixels at the edge of the dot or splotch. If, for example, the XY coordinates for adjacent pixels are (xl, yl) and (x2, y2), the distance is V[(x2-xl)² + (y2-yl)²], while the perimeter

+ (yi+i-yi)²] } -

In various embodiments of the invention, it is desired to measure the length of the perimeter of an ink dot. An alternative method for measuring the perimeter length will now be described. As a first step, an image comprising an ink dot is used as input for an algorithm that outputs perimeter length. The pixel dimension MxN of the image may be stored in a two-element array or an ordered pair image _pixel_size. An example of the value of the image _pixel_size is 1280,760 - in this example M=1280 and N=760. This corresponds to an image 1280 pixels in the horizontal axis and 760 pixels in the vertical axis. Subsequently, the image magnification ratio or scale is obtained and stored in variable image jnagnification. One example of variable image jnagnification is 500. When comparing perimeters between ink dots in first and second images it is mandatory that the variables image_pixel_size and image magnification of the two images are equal. It is now possible to calculate the corresponding length of one square pixel - i.e. the side length in a real-world length units (e.g., micrometers) or a pixel. This value is stored in a variable pixel _pitch. One example of the variable pixel _pitch is 0.05 μιη. The image is now converted to grayscale by methods known to the skilled artisan. One proposed method is converting the input image, the image typically in an sRGB color space, to the L*a*b* color space. Once the image is in the Lab color space, the values for the variables a and b are changed to zero. It is now possible to apply an edge detection operator to the image. The preferred operator is a Canny edge detection operator. However, any operator known in the art may be applied. The operators are not limited to first order derivatives, such as the canny operator, but rather open to second derivatives as well. Furthermore, a combination of operators may be used in order to obtain results that may be compared between operators and subsequently remove "unwanted" edges. It may be favorable to apply a smoothing operator such as a Gaussian blur prior to applying the edge detection operator. The threshold level applied when applying the edge detection operator is such that an edge that forms an endless loop is first obtaining in the area between the formerly described minimal circumference Ink dot engulfing circle and the maximal circumference ink dot enclosed circle. A thinning operator is now implemented to render the endless loop edge substantially one pixel wide. Any pixel that is not a part of the endless loop edge has its L* value change to zero, while any pixel that is part of the endless loop edge has its L* value change to 100. The endless loop edge is defined as the perimeter of the ink dot. A pixel link is defined as a straight line connecting to pixels. Each pixel along the perimeter incorporates two pixel links, a first pixel link and a second pixel link. These two pixel links define a pixel link path within a single pixel. In this method of computing perimeter length, each pixel is a square pixel. Therefore, each pixel link may form a line from the center of the pixel to one of eight possible nodes. The possible nodes being the corners of the pixel or a midpoint between two neighboring corners of the pixel. Nodes at the corners of the pixels are of the type node_l one nodes at the midpoint between two corners are of type node_2. As such, there are six possibilities of pixel link paths within a pixel. These can be categorized into three groups. Group A, B, and C. Each group has its own corresponding coefficient, namely, coefficient _A, coefficient _B, and coefficient _C. The value of coefficient_A is 1, the value of coefficient _B is the sqrt(2), and the value of coefficient _C is (l+sqrt(2))/2. Group A contains pixels whose pixel link path coincides with nodes of type node_2. Group B contains pixels whose pixel link path coincides with nodes of type node l . Group C contains pixels whose pixel link path coincides with nodes of type node l and type node_2. It is now possible to calculate the pixel length of the perimeter. The pixel length of the perimeter is calculated by summing all of the pixels in the perimeter multiplied by their corresponding coefficient. This value is stored in variable perimeter _pixel_length. It is now possible to calculate the actual length of the ink dot perimeter. This is done by multiplying perimeter _pixel_length by pixel _pitch. Roundness

A dimensionless roundness factor (ER), may be defined by:

ER = Ρ²/(4π·Α)

wherein P is the measured or calculated perimeter, and A is the measured or computed area within the ink film, dot or splotch. For a perfectly smooth and circular ink dot, ER equals 1.

The deviation from a round, smooth shape may be represented by the expression (ER - 1). For a perfectly circular, idealized ink dot, this expression equals zero.

The R-square of the roundness factor may be computed for each of the 10 most representative dot images selected for each type of printing technology, and averaged into a single value.

For ink film constructions in which the fibrous substrate {e.g., paper) is uncoated, or for ink film constructions in which the fibrous substrate is coated with a coating such as the commodity coating in coated offset paper (or such as coatings which enable the carrier from traditional water-based inkjet ink to reach the paper fibers), the deviation from a round, smooth round shape [(ER - 1), henceforth, "deviation"] for the ink dots of the present invention is not ideal, and will exceed 0.

In Figures 14A-2 to 14F2, exemplary magnified ink film images disposed on uncoated and coated substrates are provided for the following printers: direct inkjet: HP DeskJet 9000 (uncoated: Figure 14A-2; coated: Figure 14D-2); digital press: HP Indigo 7500 (uncoated: Figure 14B-2; coated: Figure 14E-2); and lithographic offset: Ryobi 755 (uncoated: Figure 14C-2; coated: Figure 14F-2).

Figures 12A-2 to 12E-2 provide magnified views of ink films disposed on coated paper (12A-2 to 12C-2) and uncoated paper (12D-2 and 12E-2), according to the present invention. These ink film images were obtained generally according to the image acquisition method detailed hereinabove.

Quantitative analysis of the deviation from roundness (ER - 1) is provided hereinbelow.

Convexity As previously described, the ink dots or films of the prior art may characteristically have a plurality of protrusions or rivulets, and a plurality of inlets or recesses. These ink forms may be irregular, and/or discontinuous. By sharp contrast, the inkjet ink film produced according to the present invention characteristically has a manifestly rounded, convex, circular shape. Dot convexity, or deviation therefrom, is a structural parameter that may be used to evaluate or characterize shapes, or optical representations thereof.

The image acquisition method may be substantially identical to that described hereinabove.

Convexity Measurement

A MATLAB script was created to compute the ratio between the area of the minimal convex shape that bounds the dot contour and the actual area of the dot. For each ink dot image, the (X,Y) set of points of the dot edge contour, created by ImageXpert, was loaded to MATLAB.

In order to reduce the sensitivity of measurement to noise, the dot edge was passed through a Savitzky-Golay filter (image-processing low-pass filter) to slightly smooth the edge contour, but without appreciably modifying the raggedness characteristic thereof. A window frame size of 5 pixels was found to be generally suitable.

Subsequently, a minimal-area convex shape was produced to bound the smoothed edge contour. The convexity ratio between the convex shape area (CSA) and the actual (calculated) dot or film area (AA) was then computed as follows:

CX = AA/CSA

The deviation from this convexity ratio, or "non-convexity", is represented by 1-CX, or DCdot-

Quantitative analysis of this non-convexity is provided hereinbelow. Field of View

On both commodity-coated and uncoated fibrous substrates, the ink dots in the ink dot constructions of the present invention may exhibit consistently good shape properties (e.g., convexity, roundness, edge raggedness, and the like), irrespective, to a large degree, of the particular, local topographical features of the substrate, and irrespective, to some degree, of the type of printing substrate (coated or uncoated printing substrates, plastic printing substrates, etc.). By contrast, the quality of ink dots in various known printing technologies, and in direct aqueous inkjetting technologies in particular, may vary appreciably with the type of printing substrate, and with the particular, local topographical features of the substrate.

Using a more robust, statistical approach, however, may better distinguish between the inventive ink dot constructions with respect to ink dot constructions of the art. Thus, in some embodiments of the present invention, the ink dot constructions may be characterized as a plurality of ink dots disposed on the substrate, within a representative field of view. Assuming the characterization of the dot is obtained through image processing, a field of view contains a plurality of dot images, of which at least 10 dot images are suitable for image processing. Both the field of view and the dot images selected for analysis are preferably representative of the total population of ink dots on the substrate (e.g. , in terms of dot shape).

Procedure

A printed sample, preferably containing a high incidence of single ink dots, is scanned manually on the LEXT microscope, using a X20 magnification to obtain a field that includes at least 10 single dots in a single frame. Care should be taken to select a field whose ink dot quality is fairly representative of the overall ink dot quality of the printed sample.

Each dot within the selected frame is analyzed separately. Dots that are "cleaved" by the frame margins (which may be considered a square geometric projection) are considered to be part of the frame, and are analyzed. Any satellites and overlapping dots are excluded from the analysis. A "satellite" is defined as an ink dot whose area is less than 25% of the average dot area of the dots within the frame, for frames having a generally homogeneous dot size, or as an ink dot whose area is less than 25% of the nearest adjacent dot, for non- homogeneous frames.

Each distinct ink dot is subsequently magnified with a XI 00 zoom, and image processing may be effected according to the procedure provided hereinabove with respect to the convexity and roundness procedures.

Results

Figure 13A provides a magnified view of a field of ink dots on a commodity-coated fibrous substrate (Arjowiggins coated recycled gloss, 170gsm), produced using a commercially available, aqueous, direct inkjet printer. Figure 13B provides a magnified view of a field of ink dots on an uncoated fibrous substrate (Hadar Top uncoated-offset 170gsm), produced using the identical, commercially available, aqueous, direct inkjet printer. Although technically, the frame of Figure 13A does not qualify as a "field" of ink dots, such fields requiring at least 10 single dots within a single frame, the frames are provided, and the dots are characterized, for illustrative purposes.

In Figure 13 A, ink image A is a satellite, and is excluded from the analysis. Dot B is cleaved by the frame margin, and is included in the analysis (i.e., the full ink dot is analyzed). Tail or projection C is considered to be part of the ink dot disposed to its left. Thus, the field contains only 6 ink dots for image processing.

With regard to Figure 13B, it became evident, only at high magnification, that dots E and F are distinct individual dots. While several splotches are reasonably round and well- formed, most of the splotches display poor roundness and convexity, have poorly-defined edges, and appear to contain multiple ink centers that are associated or weakly associated.

Figures 12A-1 to 12E-1 provide a magnified view of a field of ink dots or films on commodity-coated fibrous substrates (Figures 12A-1 to 12C-1) and uncoated fibrous substrates (Figures 12D-1 and 12E-1), produced in accordance with the present invention. The printed image was prepared by jetting an ink, corresponding to Example 29, on a blanket having a release layer comprising a condensation cured silanol terminated polydimethylsiloxane. The blanket was heated to about 70°C and was pre-treated with a conditioning solution comprising PEI subsequently removed and evaporated, as already described for the basic transferability test. A black ink corresponding to Example 29 was jetted upon the treated release layer using a traditional ink jet head at a resolution of 600 x 1200 dpi (providing an average drop volume of 9pL) to form an ink image of varying ink coverage / dot density. The relative speed of the blanket relative to the print bars was 0.5m/sec. The ink image was dried at 200°C for up to 5 seconds and the dried image transferred to the substrates indicated in the table below and in Figures 12A-1 to 12E-3, by application of manual pressure.

Figures 12A-2 to 12E-2 provide further magnified views of a portion of the frames of Figures 12A-1 to 12E-1, in which the magnified views of the ink films disposed on commodity-coated paper are provided in Figures 12A-2 to 12C-2, and the magnified views of the ink films disposed on uncoated paper are provided in Figures 12D-2 and 12E-2.

It is manifest from a comparison of the figures that the fields of ink dots in the inventive ink constructions exhibit superior dot shape (roundness, convexity, and edge definition) and average dot shape, with respect to the prior-art fields provided in Figures 13A and 13B. In fact, the field of ink dots provided in Figure 12D-1, in which the uncoated substrate is the most coarse and challenging, the inventive ink construction exhibits superior dot shape and average dot shape, relative to the prior-art field (Figure 13 A) in which the substrate is a relatively smooth, coated substrate.

That which is readily observed by the human eye may be quantified using the image- processing techniques and field-of-view processing procedures provided above.

TABLE 1 : Inventive Ink Dot Constructions— Field of View

TABLE 2: Prior Art Ink Dot Constructions— Field of View

(Standard Deviation)

Coated Paper 0.943 0.085 4.0

Uncoated Paper 3.347 0.253 19.1

These exemplary results have been confirmed on several additional fibrous substrates, both commodity-coated and uncoated.

For all tested commodity-coated fibrous substrates, fields of the ink dot construction according to the present invention exhibited a mean non-convexity of at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, at most 0.009, or at most 0.008.

For all tested uncoated fibrous substrates, fields of the ink dot construction according to the present invention exhibited a mean non-convexity of at most 0.085, at most 0.07, at most 0.06, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.018, or at most 0.015.

In some embodiments, the field non-convexity is at least 0.0005, at least 0.001, at least 0.002, at least 0.003, or at least about 0.004. In some cases, and particularly for uncoated fibrous substrates, the field or mean non-convexity may be at least 0.05, at least 0.07, at least 0.10, at least 0.12, at least 0.15, at least 0.16, at least 0.17, or at least 0.18.

For all tested commodity-coated fibrous substrates, fields of the ink dot construction according to the present invention exhibited a mean deviation from roundness of at most 0.60, at most 0.50, at most 0.45, at most 0.40, at most 0.35, at most 0.30, at most 0.25, at most 0.20, at most 0.17, at most 0.15, at most 0.12, or at most 0.10.

For all tested uncoated fibrous substrates, fields of the ink dot construction according to the present invention exhibited a mean deviation from roundness of at most 0.85, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.22, or at most 0.20.

In some embodiments, the mean deviation from roundness is at least 0.010, at least 0.02, at least 0.03, or at least about 0.04. In some cases, the deviation from roundness may be at least 0.05, at least 0.07, at least 0.10, at least 0.12, at least 0.15, at least 0.16, at least 0.17, or at least 0.18.

While the above-described non-convexity and deviation from roundness values are for fields having at least 10 dots suitable for evaluation, they further apply to fields having at least 20, at least 50, or at least 200 of such suitable dots. Moreover, the inventors have found that the distinction between both the non-convexity values and deviation from roundness values of the inventive ink dot constructions vs. the prior-art ink dot constructions becomes even more statistically significant with increasing field size.

For plastic substrates, the fields of the ink dot construction according to the present invention can exhibit a mean non-convexity of at most 0.075, at most 0.06, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, at most 0.009, or at most 0.008; the fields of the ink dot construction according to the present invention may exhibit a mean deviation from roundness of at most 0.8, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, or at most 0.15. Smooth plastics, such as atactic polypropylene and various polyesters, typically exhibit a mean deviation from roundness of at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.

Optical Uniformity

The ink film images provided in Figures 5A and 5B are not optically uniform. Generally, the ink film images disposed on uncoated paper are less optically uniform than the corresponding ink film images disposed on coated paper.

Furthermore, it can be observed that the inventive ink dots exhibit superior optical uniformity in comparison with the various prior-art ink forms. This appears to hold for both uncoated and coated printed substrates. That which is readily observed by the human eye may be quantified using image-processing techniques. The method of measuring ink dot uniformity is provided below.

Optical Uniformity Measurement

The dot images are loaded to the ImageXpert Software, preferably using the statistical rules provided hereinabove. Each image is loaded in each of the Red, Green and Blue channels. The channel selected for the image processing is the channel exhibiting the highest visible details, which include the dot contour and color variance within the dot area, and the substrate surface fibrous structure. For example, the Red channel is typically most suitable for a cyan dot, while the Green channel is typically most suitable for a magenta dot. For each of the selected dots, a line profile (preferably 3 line profiles for each of the at least 10 most representative dots) is measured across the dot area, crossing through the center of the dot. Since the line profile is measured on a single channel, gray values (0-255, non color values) are measured. The line profiles are taken across the center of the dot and cover only the inner two thirds of the dot diameter, to avoid edge effects. The standard for sampling frequency is about 8 optical measurements along the line profile (8 measured gray values evenly spaced along each micrometer, or 125 nanometers +/- 25 nanometers per measurement along the line profile), which was the automatic frequency of the ImageXpert Software, and which was found to be suitable and robust for the task at hand.

The standard deviation (STD) of each of the line profiles is computed, and multiple line-profile STDs for each type of printed image are averaged into a single value.

Figures 14A-1 to 14F-2 provide images of ink splotches or dots obtained using various printing technologies, and optical uniformity profiles therefor. More specifically, Figures 14A-2 to 14C-2 provide ink dot images disposed on uncoated paper, for the following printing technologies: HP DeskJet 9000 (Figure 14A-2); Digital press: HP Indigo 7500 (Figure 14B-2); and Offset: Ryobi 755 (Figure 14C-2). Similarly, Figures 14D-2 to 14F-2 provide ink dot images disposed on commodity coated paper, for those printing technologies.

Figures 14A-1 to 14F-1 provide the (non-color) gray relative value as a function of the position on the line passing through the center of the ink dot image, for each of the ink dot images provided by Figures 14A-2 to 14C-2 (on uncoated paper), and by Figures 14D- 2 to 14F-2 (on coated paper), for those printing technologies.

Figures 14A-3 to 14-F3 provide the contour analysis of these dots on uncoated and coated substrates as obtained by the afore-mentioned printing technology of the art. The contour profile are used for the calculation of the convexity characteristics of the printed dots.

Figures 22A-3 to 22E-3, respectively, provide graphs plotting the (non-color) gray relative value as a function of the position on the line passing through the center of the ink dot image, for each of the ink dot images provided by Figures 22A-3 to 22C-3 (on coated paper), and by 22D-3 to 22E-3 (on uncoated paper). A relatively flat linear profile for a particular ink dot image indicates high optical uniformity along the line.

The results would appear to confirm that the ink dots disposed on the uncoated fibrous printing substrates exhibit poorer uniformity with respect to the corresponding ink dots disposed on the coated fibrous printing substrates.

Moreover, for uncoated substrates, the line profile of the inventive ink film produced by the inventive system and process had an average STD of about 4.7, which compares favorably to the STD achieved using the prior art technology (19). For coated substrates, the line profile of the inventive ink dot produced by the inventive system and process produced an STD of about 2 to 2.7, which compares favorably, though less strikingly so, to the STD achieved using the prior art technology (4).

When comparing between films or dots on coated papers, the average of each of the standard deviations (STD) of the dot profiles of the present invention was always below 3.5. More generally, the STD of the dot profiles of the present invention is less than 3.2, less than 3.0, less than 2.9, or less than 2.8.

In comparing between films or dots on uncoated papers, the standard deviation (STD) of the dot profiles of the present invention was always below 6. More generally, the STD of the dot profiles of the present invention is less than 15, less than 12, less than 10, less than 8, less than 7, or less than 6.

Because, as noted above, ink images may contain an extremely large plurality of individual or single ink dots (at least 20, at least 100, at least 1,000, at least 10,000, or at least 100,000), it may be meaningful to statistically define the inventive ink dot constructions wherein at least 10%, at least 20%, or at least 30%>, and in some cases, at least 50%), at least 70%>, or at least 90%>, of the inventive ink dots (or inventive single-drop ink dots), disposed on any uncoated or coated (or commodity-coated) fibrous substrate, exhibit the above-mentioned standard deviations for uncoated papers and for commodity- coated papers.

Penetration

Such continuous dots are typically produced by various inkjetting technologies, such as drop-on-demand and continuous jetting technologies.

Referring again to the drawings, Figures 16A and 16B provide schematic cross- sectional views of an inventive ink film construction 300 and an inkjet ink splotch or film construction 370 of the prior art, respectively. Referring now to Figure 16B, inkjet ink film construction 370 includes a single-drop ink splotch 305 adhering to, or laminated to, a plurality of substrate fibers 320 in a particular continuous area of a fibrous printing substrate 350. Fibrous printing substrate 350 may be, by way of example, an uncoated paper such as bond, copy, or offset paper. Fibrous printing substrate 350 may also be one of various commodity coated fibrous printing substrates, such as a coated offset paper.

A portion of ink splotch 305 is disposed below the top surface of substrate 350, between fibers 320. Various components of the ink, including a portion of the colorant, may penetrate the top surface along with the ink carrier solvent, to at least partially fill a volume 380 disposed between fibers 320. As shown, a portion of the colorant may diffuse or migrate underneath fibers 320, to a volume 390 disposed beneath fibers 320. In some cases (not shown), some of the colorant may permeate into the fibers.

By sharp contrast, inventive ink film construction 300, provided in Figure 16A, includes an integral continuous ink dot such as individual ink dot 310, disposed on, and fixedly adhering (or laminated) to, a top surface of a plurality of substrate fibers 320, in a particular continuous area of fibrous printing substrate 350. The adhesion or lamination may be, primarily or substantially, a physical bond. The adhesion or lamination may have little, or substantially no, chemical bonding character or more specifically, no ionic bonding character.

Ink dot 310 contains at least one colorant dispersed in an organic polymeric resin. Within the particular continuous area of fibrous substrate 350, there exists at least one direction (as shown by arrows 360— several directions) perpendicular to the top surface of printing substrate 350. With respect to all the directions normal to this top surface over all of the dot area, ink dot 310 is disposed entirely above the area. The volume 380 between fibers 320 and the volume 390 underneath fibers 320 are devoid, or substantially devoid, of colorant, resin, and any and all components of the ink.

The extent of penetration of an ink into a printing substrate may be quantitatively determined using various analytical techniques, many of which will be known to those of ordinary skill in the art. Various commercial analytical laboratories may perform such quantitative determination of the extent of penetration.

These analytical techniques include the use of various staining techniques such as osmium tetroxide staining (see Patrick Echlin, "Handbook of Sample Preparation for Scanning Electron Microscopy and X-Ray Microanalysis" (Springer Science + Business Media, LLC 2009, pp.140-143).

One alternative to staining techniques may be particularly suitable to inks containing metals such as copper. Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was performed using a TOF-SIMS V Spectrometer [Ion-ToF (Munster, Germany)]. This apparatus provides elemental and molecular information with regard to the uppermost layer of organic and inorganic surfaces, and also provides depth profiling and imaging having depth resolution on the nanometric scale, submicrometer lateral resolution and chemical sensitivity on the order of 1 ppm.

Translation of the raw data of the TOF-SIMS into concentration may be performed by normalizing the signals obtained to the carbon (C+) concentration measured by X-ray Photoelectron Spectroscopy (XPS), in the sample. The XPS data was obtained using a Thermo VG Scientific Sigma Probe (England). Small area chemical analysis of solid surfaces with chemical bonding information was obtained by using a microfocused (from 15 to 400 μιη) monochromated x-ray source. Angle resolved information is obtained with and without tilting the sample. This enables depth profiling with good depth resolution.

As a baseline, the atomic concentration of copper within a fibrous paper substrate was measured, as a function of depth. The atomic concentration of copper was found to be substantially zero at the surface, down to a depth of several micrometers. This procedure was repeated for two cyan-colored inkjet ink film constructions of the prior art, and for a cyan-colored ink film construction of the present invention.

Measurements of the atomic concentration of copper [Cu] within the ink dot and within the fibrous paper substrate, as a function of the approximate depth, within a first cyan-colored inkjet ink film construction of the prior art, were performed as described above. The initial [Cu], measured near the top surface of the cyan-containing ink film construction, was approximately 0.8 atomic %. Within a depth of about lOOnm, [Cu] dropped steadily to about 0.1 atomic %. Over a depth range of about lOOnm - Ι,ΟΟΟηηι, [Cu] dropped from about 0.1 atomic % to about zero. Thus, it is evident that the inkjet ink pigment has penetrated into the fibrous paper substrate, possibly attaining a penetration depth of at least 700nm, at least 800nm, or at least 900nm.

Additional measurements of the atomic concentration of copper within the ink dot construction, as a function of the approximate depth, within a second cyan-colored inkjet ink film construction of the prior art, led to the following findings: the initial atomic concentration of copper [Cu] within the ink dot construction, measured near the top surface, was approximately 0.02 atomic %. This concentration was generally maintained over a depth of about 3,000nm. Over a depth range of about 3,000nm to almost 6,000nm, [Cu] dropped very gradually to about 0.01 atomic %. It would appear that this prior-art construction has little or no ink film on the surface of the substrate, and that penetration of the pigment into the substrate was pronounced (at least 5-6 micrometers).

In view of the fundamental nature of the inventive laminated film transfer technology, described hereinabove (particularly with regard to Figures 21 A and 2 IB) and in view of atomic concentration of copper [Cu] measurements performed by the inventors on similar ink film constructions, it is would appear manifest that the ink films of the inventive constructions are substantially solely disposed on the surface of the substrate, and that pigment penetration into the substrate is substantially negligible, both in terms of penetration depth and in terms of the penetration quantity or fraction.

Film Height or Thickness

Instrumentally measured heights (H) or thicknesses of single-film ink dots or splotches were obtained using a measuring laser microscope (Olympus LEXT 3D, model OLS4000). The LEP specimens typically had a height or thickness within a range of 900- 1150 nm; the lithographic offset specimens typically had a height or thickness within a range of 750-1200 nm.

With regard to ink dots or films produced from jetted ink drops, we have found that the maximum average supra-substrate thickness of the ink dot may be calculated from the following equation:

TAVG(MAX) ⁼ VDROP /[AFILM * RVOL] (I) wherein:

T_AVG(_MAX) is the maximum average supra-substrate thickness;

V_DROP is the volume of the jetted drop, or a nominal or characteristic volume of a jetted drop (e.g., a nominal volume provided by the inkjet head manufacturer or supplier);

AFILM is the measured or calculated area of the ink dot; and

RVOL is a dimensionless ratio of the volume of the original ink to the volume of the dried ink residue produced from that ink.

By way of example, an ink dot disposed on a plastic printing substrate has an area of 1075 square micrometers. The nominal size of the jetted drop is 10.0 ± 0.3 picoliters. RVOL was determined experimentally: a vessel containing 20.0ml of the ink was heated at 130°C until a dry residue was obtained. The residue had a volume of 1.8ml. Plugging into Equation (I), TAVG(MAX) = 10ρίΰθ1ίΐεΓ8 /[1075μιη² * (20.0/1.8)] = 837 nanometers.

For generally round ink dots, the area of the ink dot may be calculated from the ink dot diameter. Moreover, it was found that the dimensionless ratio RVOL is generally about 10 for a wide variety of inkjet inks.

While for inks that penetrate into the substrate, the actual average thickness may be somewhat less than T_AVG(MAX), this calculation may reliably serve as an upper bound for the average thickness. Moreover, in the case of various plastic substrates, and in the case of various premium coated substrates, the maximum average supra-substrate thickness may substantially equal the average supra-substrate thickness. In the case of various commodity-coated substrates, the maximum average supra-substrate thickness may approach the average supra-substrate thickness, often within 100 nanometers, 200 nanometers, or 300 nanometers.

With regard to ink dots or films produced from jetted ink drops, it was found that the maximum average supra-substrate thickness of the ink dot may be calculated from the following equation:

TAVG(MAX) ⁼ [VDROP * PINK * F_nREsiDUE ] / [AFILM * PFILM] (Π) wherein:

PINK is the specific gravity of the ink;

FnREsiDUE is the weight of the dried ink residue divided by the weight of the original ink; and

PFILM is the specific gravity of the ink.

Typically, the ratio of PINK to PFILM is approximately 1 , such that Equation (II) may be simplified to: TAVG(MAX) - [VDROP * FnRESIDUE ] / ApiLM (HI)

For a wide variety of aqueous ink jet inks, F_nRESiDUE roughly equals the weight fraction of solids in the ink jet ink.

Using the above-described Olympus LEXT 3D measuring laser microscope, the height of above the substrate surface was measured for various ink dot constructions.

Atomic Force Microscopy (AFM) is another, highly accurate measurement technique for measuring height and determining ink dot thickness on a substrate. AFM measurements may be performed using commercially available apparatus, such as a Park Scientific Instruments Model Autoprobe CP, Scanning Probe Microscopy equipped with ProScan version 1.3 software (or later). The use of AFM is described in depth in the literature, for example, by Renmei Xu, et al., "The Effect of Ink Jet Papers Roughness on Print Gloss and Ink Film Thickness" [Department of Paper Engineering, Chemical Engineering, and Imaging Center for Ink and Printability, Western Michigan University (Kalamazoo, MI)].

With regard to the ink film constructions of the present invention, the inventors have found that the thickness of the dry ink film on the substrate may be adjusted by modifying the inkjet ink formulation. To obtain a lower dot thickness, such modifying may entail at least one of the following:

• reducing the resin to pigment ratio;

• selecting a resin or resins enabling adequate film transfer, even with a reduced resin to pigment ratio;

• utilizing finer pigment particles;

• reducing the absolute quantity of pigment.

To obtain thicker dots, at least one of the opposite modifications (e.g., increasing the resin to pigment ratio) may be made.

Such changes in the formulation may necessitate, or make advantageous, various modifications in the process operating conditions. The inventors have found that lower resin to pigment ratios may require a relatively high transfer temperature.

For a given inkjet ink formulation, an elevated transfer temperature may reduce ink film thickness. Increased pressure of the pressure roller or cylinder toward the impression cylinder during the transfer of the residue film to a substrate at the impression station may also reduce ink film thickness. Also, ink film thickness may be reduced by increasing the time of contact between the substrate and the intermediate transfer member, interchangeably termed herein an "image transfer member" and both abbreviated ITM.

All this notwithstanding, a practical minimum characteristic (i.e., median) thickness or average thickness for ink films produced according to the present invention may be about lOOnm. More typically, such ink films are single-drop ink films having a dot thickness, average dot thickness, or height (of the top surface of the dot) with respect to the substrate of at least 125nm, at least 150nm, at least 175nm, at least 200nm, at least 250nm, at least 300nm, at least 350nm, at least 400nm, at least 450nm, or at least 500nm.

Using the above-provided film thickness guidelines, the inventors are able to obtain inventive film constructions having an average thickness of at least 600nm, at least 700nm, at least 800nm, at least Ι,ΟΟΟηηι, at least l,200nm, or at least l,500nm. The characteristic thickness or average thickness of a single drop film (or an individual ink dot) may be at most about 2,000nm, at most l,800nm, at most l,500nm, at most l,200nm, at most Ι,ΟΟΟηηι, or at most 900nm. More typically, the characteristic thickness or average thickness of a single drop film may be at most 800nm, at most 700nm, at most 650nm, at most 600nm, at most 500nm, at most 450nm, at most 400nm, or at most 350nm.

Using the film thickness guidelines delineated hereinabove, the inventors are able to obtain inventive film constructions in which a characteristic thickness or average thickness of the ink film may be within a range of lOOnm, 125nm or 150nm up to l,800nm, l,500nm, l,200nm, l.OOOnm, 800nm, 700nm, 600nm, 550nm, 500nm, 450nm, 400nm, or 350nm. More typically, the characteristic thickness or average thickness of the ink film may be within a range of 175nm, 200nm, 225nm or 250nm up to 800nm, 700nm, 650nm, 600nm, 550nm, 500nm, 450nm, or 400nm. Suitable optical density and optical uniformity may be obtained, using the system, process, and ink formulations of the present invention.

The thickness (Hdot) of single-drop ink film or individual ink dot (shown schematically as dot 310 in Figure 21A) may be at most l,800nm, at most l,500nm, at most l,200nm, at most Ι,ΟΟΟηηι, or at most 800nm, and more typically, at most 650nm, at most 600nm, at most 550nm, at most 500nm, at most 450nm, or at most 400nm. The thickness (Hdot) of single-drop ink dot 310 may be at least 50nm, at least lOOnm, or at least 125nm, and more typically, at least 150nm, at least 175nm, at least 200nm, or at least 250nm.

Aspect Ratio The inventors have found that the diameter of an individual ink dot in the ink film constructions of the present invention may be adjusted, inter alia, by selection of a suitable ink delivery system for applying the ink {e.g., jetting) onto the ITM, and by adjusting the ink formulation properties {e.g., surface tension) to the requirements of the particular ink head.

This ink film diameter, Ddot, or the average dot diameter on the substrate surface, Ddot avera e, may be at least 10 micrometers, at least 15 μιη, or at least 20 μιη, and more typically, at least 30 μιη, at least 40 μιη, at least 50 μιη, at least 60 μιη, or at least 75 μιη. Ddot or Ddot average may be at most 300 micrometers, at most 250 μιη, or at most 200 μιη, and more typically, at most 175 μιη, at most 150 μιη, at most 120 μιη, or at most 100 μιη.

Generally D_dot or D_dot average may be in the range of 10-300 micrometers, 10-250 μιη, 15-250 μιη, 15-200 μιη, 15-150 μιη, 15-120 μιη, or 15-100 μιη. More typically, with the currently used ink formulations, and a particular ink head, D_dot or D_dot average may be in the range of 20-120 μιη, 25-120 μιη, 30-120 μιη, 30-100 μιη, 40-120 μιη, 40-100 μιη, or 40-80 μιη.

Each single-drop ink film or individual ink dot is characterized by a dimensionless aspect ratio defined by:

Raspect ⁼ Ddot Hdot

wherein Ra_Spect is the aspect ratio; Ddot is the longest diameter of the dot; and Hd₀t is the average height of the top surface of dot with respect to the substrate.

The aspect ratio may be at least 15, at least 20, at least 25, or at least 30, and more typically, at least 40, at least 50, at least 60, at least 75. In many cases, the aspect ratio may be at least at least 95, at least 110, or at least 120. The aspect ratio is typically below 200 or below 175.

Surface Roughness

Using laser microscopy imaging and other techniques, the inventors have observed that the top surface of the ink dots in the ink film constructions of the present invention may be characterized by a low surface roughness, particularly when the substrates of those constructions have a high paper (or substrate) gloss.

Without wishing to be limited by theory, the inventors believe that the relative flatness or smoothness of the ink film constructions of the present invention may largely be attributed to the smoothness of the release layer on the surface of the ITM, and to the inventive system and process in which the emerging ink film surface substantially complements that of that surface layer, and in which the developing ink film image may substantially retain or completely retain that complementary topography through the transfer onto the printing substrate.

Referring now to Figure 17A, Figure 17A is an image of the surface of a release layer of an ITM or blanket used in accordance with the present invention. While the surface may be nominally flat, various pockmarks (recesses) and protuberances, typically of the order of 1-5 μιη, may be observed. Many of these marks have sharp, irregular features. An image of an ink dot surface produced using this blanket, provided in Figure 17B, displays topographical features that are strikingly similar in nature to those shown in Figure 17A. The dot surface is peppered with a large plurality of marks having sharp, irregular features, which strongly resemble (and are within the same size range as) the irregular marks in the blanket surface.

A smoother blanket was installed; Figure 17C provides an image of the release layer of this blanket. The irregular pockmarks of Figure 17A are conspicuously absent. Dispersed on the highly smooth surface are highly circular surface blemishes, perhaps made by air bubbles, typically having a diameter of about 1-2 μιη. An image of an ink dot surface produced using this blanket, provided in Figure 17D, displays topographical features that are strikingly similar in nature to those shown in Figure 17C. This image has virtually no distinctive pockmarks, but has a number of highly circular surface blemishes that are strikingly similar in size and form to those shown of the blanket surface.

Plastic Substrates

In view of the afore-mentioned results as observed on various fibrous substrates, and in view of the fundamental nature of the inventive transfer technology, the ink dots of the present invention are expected to exhibit superior optical and shape properties, including roundness, convexity, edge raggedness, and surface roughness, on plastic printing substrates as well.

The non-convexity, or deviation from convexity for ink dots printed on a wide variety of plastic printing substrates, may typically be at most 0.020, at most 0.018, at most 0.016, at most 0.014, at most 0.012, or at most 0.010. At least some of the ink dots, can exhibit non-convexities of at most 0.008, at most 0.006, at most 0.005, at most 0.004, at most 0.0035, at most 0.0030, at most 0.0025, or at most 0.0020. On some substrates (e.g., polyester and atactic polypropylene substrates), typical ink dots may exhibit non- convexities of at most 0.006, at most 0.004, at most 0.0035, and even more typically, at most 0.0030, at most 0.0025, or at most 0.0020.

On all plastic substrates, individual ink dots in the ink dot constructions according to the present invention may exhibit a typical deviation from roundness of at most 0.8, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, or at most 0.15. On various smooth plastics, such as atactic polypropylene and various polyesters, individual ink dots may exhibit a typical deviation from roundness of at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.

Glass Transition Temperature of the Resin

The inventors have found that in selecting resins, and combinations of resins, for use within the formulations supporting the ink film constructions of the present invention, the softening temperature (or glass transition temperature for at least partially amorphous resins) may be a useful indicator of resin suitability. Specifically, the resins used in the ink formulations (and disposed in the ink films of the present invention) may have a glass transition temperature (T_g) of at least 42°C, at least 44°C, at least 46°C, at least 48°C, at least 50°C, and more typically, at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, at least 75°C, or at least 80°C. The glass transition temperature is typically at most 110°C, at most 105°C, at most 100°C, at most 95°C, or at most 90°C.

More generally, from a process standpoint, the ink formulations disposed on the ITM, after becoming devoid or substantially devoid of water, any co-solvent, and any other vaporizable material that would be vaporized under process conditions, e.g., pH adjusting agents, (producing "ink solids", a "dried ink residue", or the like), and/or the resins thereof, may have a T_g of at least 42°C, at least 44°C, at least 46°C, at least 48°C, or at least 50°C.

In the event that multiple glass transition temperatures are observed, the term T_g, as used in the claims, refers to the glass transition temperature of the predominant resin, on a weight basis.

Analysis of Ink Films on Printed Substrates 3 sheets of printed matter (based on B2, 750x530 mm) are subjected to the following procedure: after 1 week, the sheets are cut into 3x3 cm pieces and introduced into 300 grams of a solution containing 1% 2-amino-2-methyl-l-propanol dissolved in water, which is able to sufficiently dissolve ink images printed using various water-soluble inks. If, however, the solution remains colorless, the water is separated off and an identical weight of a less polar solvent, ethanol, is introduced. Again, if the solution remains colorless, the solvent is separated off, and an identical weight of a less polar solvent, methyl ethyl ketone, is introduced. The procedure continues with successfully less polar solvents: ethyl acetate, toluene, and Isopar™ (synthetic mixture of isoparaffins). After 5 hours stirring at room temperature with the most appropriate solvent, the mixture is filtered through a 5 micrometer filter. The filtrate or filtrates containing the dissolved ink is dried using a rotary evaporator. The residues are then dissolved in 5 grams of DMSO (or one of the above-listed solvents) and dried in an oven at 1 10°C for 12 hours to yield the "recovered residue".

The thermo-rheological behavior of the recovered residue may then be characterized (e.g., by performing a viscosity "sweep" as a function of temperature, as described above) and compared with the thermo-rheological behavior of a dried sample of the original ink, when available. The inventors have found this procedure to provide a strong correlation between the thermo-rheological behavior of the recovered residue and the thermo- rheological behavior of a dried sample of the original ink. The inventors believe that this correlation may be attributed to both the increase in residence time and the use of additional solvents of varying polarity.

This procedure may advantageously be used to produce and thermo-rheologically characterize dry ink residues recovered from printed matter such as magazines and brochures.

One of ordinary skill in the art will readily appreciate that other, potentially superior, procedures may be used to de-ink a printed substrate and produce the recovered ink residue for rheological, thermo-rheological and/or chemical analysis.

Ink Formulations and Ink Film Compositions

Among other things, the present inkjet inks are aqueous inks, in that they contain water, usually at least 30 wt.% and more commonly around 50 wt.% or more; optionally, one or more water-miscible co-solvents; at least one colorant dispersed or at least partly dissolved in the water and optional co-solvent; and an organic polymeric resin binder, dispersed or at least partly dissolved in the water and optional co-solvent.

It will be appreciated that acrylic-based polymers may be negatively charged at alkaline pH. Consequently, in some embodiments, the resin binder has a negative charge at pH 8 or higher; in some embodiments the resin binder has a negative charge at pH 9 or higher. Furthermore, the solubility or the dispersability of the resin binder in water may be affected by pH. Thus in some embodiments, the formulation includes a pH-raising compound, non-limiting examples of which include diethyl amine, monoethanol amine, and 2-amino-2-methyl propanol. Such compounds, when included in the ink, are generally included in small amounts, e.g., about 1 wt.% of the formulation and usually not more than about 2 wt.% of the formulation.

The ink film of the inventive ink film construction contains at least one colorant. The concentration of the at least one colorant within the ink film may be at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, or at least 22%, by weight of the complete ink formulation. Typically, the concentration of the at least one colorant within the ink film is at most 40%, at most 35%, at most 30%, or at most 25%.

More typically, the ink film may contain 2-30%, 3-25%, or 4-25% of the at least one colorant.

The particle size of the pigments may depend on the type of pigment and on the size reduction methods used in the preparation of the pigments. Generally, the d₅o of the pigment particles is expected to be within a range of 20nm to 300nm. Pigments of various particle sizes, utilized to give different colors, may be used for the same print.

The ink film contains at least one resin or resin binder, typically an organic polymeric resin. The concentration of the at least one resin within the ink film may be at least 10%, at least 15%, at least 20%, at least 25%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 80%, by weight.

The total concentration of the colorant and the resin within the ink film may be at least 10%, at least 15%, at least 20%, at least 30%, or at least 40%, by weight. More typically, however, the total concentration of the colorant and the resin within the ink film may be at least 50%, at least 60%, at least 70%, at least 80%, or at least 85%. In many cases, the total concentration of the colorant and the resin within the ink film may be at least 90%, at least 95%, or at least 97% of the ink film weight.

Nominally, the resin dispersion may be, or include, a polyester (including co- polyester) or an acrylic styrene co-polymer (or co(ethylacrylate metacrylic acid) dispersion. The acrylic styrene co-polymer from the ink formulation ultimately remains in the ink film adhering to the printing substrate.

In one embodiment, the ink film in the ink film constructions according to the present invention is devoid or substantially devoid of wax. Typically, the ink film according to the present invention contains less than 30%> wax, less than 20%> wax, less than 15%) wax, less than 10%> wax, less than 7% wax, less than 5% wax, less than 3% wax, less than 2% wax, or less than 1% wax.

In one embodiment, the ink film according to the present invention is devoid or substantially devoid of oils such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil), or various oils used in offset ink formulations. Typically, the ink film according to the present invention contains at most 20%, at most 12%, at most 8%, at most 5%, at most 3%, at most 1%, at most 0.5%, or at most 0.1%, by weight, of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air-drying.

In one embodiment, the ink film according to the present invention is devoid or substantially devoid of one or more salts, including salts used to coagulate or precipitate ink on a transfer member or on a substrate (e.g., calcium chloride). Typically, the ink film according to the present invention contains at most 8%, at most 5%, at most 4%, at most 3%), at most 1%, at most 0.5%, at most 0.3%, or at most 0.1% of one or more salts.

In one embodiment, the ink film according to the present invention is devoid or substantially devoid of one or more photoinitiators. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%, at most 0.3%, at most 0.2%, or at most 0.1% of one or more photoinitiators.

In one embodiment, the printing substrate of the inventive ink film construction is devoid or substantially devoid of one or more soluble salts, including salts used for, or suitable for coagulating or precipitating ink, or components thereof, on the substrate (e.g. , calcium chloride). In one embodiment, the printing substrate of the inventive ink film construction contains, per 1 m² of paper, at most 100 mg of soluble salts, at most 50 mg of soluble salts, or at most 30 mg of soluble salts, and more typically, at most 20 mg of soluble salts, at most 10 mg of soluble salts, at most 5 mg of soluble salts, or at most 2 mg of soluble salts.

In one embodiment, the ink film and formulation are substantially free of saccharides. Typically, the concentration of saccharides, by weight, within the inventive ink is at most 6%, at most 4%, at most 3%, at most 1%, at most 0.5%, at most 0.3%, or at most 0.1%.

In one embodiment, the ink film according to the present invention is devoid or substantially devoid of one or more priming agents (such as a coagulating agent or viscosity-building agent). Such priming agents may be jetted onto the surface of the substrate, or otherwise applied, as will be appreciated by those of ordinary skill in the art. The priming agents may be applied solely in the vicinity of the subsequently jetted drops, or may be applied substantially on the entire printing surface of the substrate. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%), at most 0.3%>, at most 0.2%>, or at most 0.1 % of such priming agents.

It will be appreciated that such a priming agent may chemically interact with the printing substrate, or, more commonly, with a component of an ink jet ink, to produce a "bonded priming agent". Thus, in one embodiment, the ink film according to the present invention is devoid or substantially devoid of one or more bonded priming agents. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%), at most 0.3%>, at most 0.2%>, or at most 0.1 % of such priming agents.

In one embodiment, the ink film in the ink film constructions according to the present invention contains at most 5%, at most 3%, at most 2%, at most 1%, or at most 0.5%), by weight, of inorganic filler particles such as silica.

In one embodiment, the dried resins present in the ink film of the invention may have a solubility of at least 3%, at least 5%, or at least 10% in water, at at least one particular temperature within a temperature range of 20°C to 60°C, at a pH within a range of 8 to 10 or within a range of 8 to 11.

In one embodiment, the recovered ink film of the invention may have a solubility of at least 3%, at least 5%, or at least 10% in water, at at least one particular temperature within a temperature range of 20°C to 60°C, at a pH within a range of 8 to 10 or within a range of 8 to 11.

Waterfastness of Print Images ASTM Standard F2292 - 03 (2008), "Standard Practice for Determining the Waterfastness of Images Produced by Ink Jet Printers Utilizing Four Different Test Methods— Drip, Spray, Submersion and Rub", may be used to assess the waterfastness of ink dots and films printed on various substrates. The waterfastness of ink constructions according to the present invention can be evaluated by three of these test methods: drip, spray, and submersion.

In all three tests, several inventive ink film constructions exhibited complete waterfastness; no ink bleeding, smearing or transfer was observed.

Identification of nitrogen-based conditioners in a printed image on a substrate

When, prior to printing, the outer surface of the ITM is pre-treated or conditioned with a chemical agent that is, or contains, at least one nitrogen-based conditioning agent such as a polyethylene imine (PEI), transfer of the printed image to a substrate may typically result in at least some of the nitrogen-based conditioner being transferred as well. This conditioner may be detected using X-ray photoelectron spectroscopy (XPS) or by other means that will be known to those of ordinary skill in the art of polymer analysis or chemical analysis of polymers or organic nitrogen-containing species.

In one exemplary demonstration, two printed paper substrates were prepared under substantially identical conditions (including: inkjetting aqueous inkjet ink having nanopigment particles onto a transfer member; drying the ink on the transfer member; and transferring the ink film produced to the particular substrate), except that the first substrate was printed without preconditioning of the transfer member, while for the second substrate the ITM was conditioned with a polyethylene imine. XPS analysis of the printed images was conducted using a VG Scientific Sigma Probe and monochromatic Al Ka x-rays at 1486.6eV having a beam size of 400 μιη. Survey spectra were recorded with a pass energy of 150eV. For chemical state identification of nitrogen, high energy resolution measurements of Nls were performed with a pass energy of 50eV. The core level binding energies of the different peaks were normalized by setting the binding energy for the Cls at 285. OeV. Deconvolution of the observed peaks revealed that the PEI pre-treated sample contained a unique peak at about 402 eV, which corresponds to a C-NH₂ ⁺-C group.

Thus, in some embodiments of the invention, there is provided a printed ink image having an XPS peak at 402.0 ± 0.4 eV, 402.0 ± 0.3 eV, or 402.0 ± 0.2 eV.

The inventors have found that at the top or upper surface of the film, distal to the top surface of the substrate, the surface concentration of nitrogen may appreciably exceed the concentration of nitrogen within the bulk of the film. The concentration of nitrogen within the bulk of the film may be measured at a depth of at least 30 nanometers, at least 50 nanometers, at least 100 nanometers, at least 200 nanometers, or at least 300 nanometers below the upper film surface.

In some embodiments, the ratio of the surface nitrogen concentration to a nitrogen concentration within the bulk of the film is at least 1.1 : 1, at least 1.2: 1, at least 1.3: 1, at least 1.5 : 1 , at least 1.75 : 1 , at least 2: 1 , at least 3 : 1 , or at least 5: 1.

In some embodiments, the ratio of nitrogen to carbon (N/C) at the upper film surface to a ratio of nitrogen to carbon (N/C) within the bulk of the film is at least 1.1 : 1, at least 1.2: 1 , at least 1.3 : 1 , at least 1.5 : 1 , at least 1.75 : 1 , or at least 2: 1.

In some embodiments, the concentration of a secondary amine group at the upper film surface exceeds a concentration of a secondary amine group within the bulk of the film.

In some embodiments, the concentration of a tertiary amine group at the upper film surface exceeds a concentration of a tertiary amine group within the bulk of the film.

In some embodiments, the concentration of secondary and tertiary amine groups at the upper film surface exceeds a concentration of secondary and tertiary amine groups within the bulk of the film.

In some embodiments, the upper film surface contains at least one PEL

In some embodiments, the upper film surface contains at least one poly quaternium cationic guar, such as a guar hydroxypropyltrimonium chloride, and a hydroxypropyl guar hydroxypropyltrimonium chloride.

In some embodiments, the upper film surface contains a polymer having quaternary amine groups, such as an HC1 salt of various primary amines.

As used herein in the specification and in the claims section that follows, the term "average particle size", or "d₅o", with reference to the particle size of pigments, refers to an average particle size, by volume, as determined by a laser diffraction particle size analyzer (e.g., Mastersizer 2000 of Malvern Instruments, England) or by a dynamic light scattering particle size analyzer (e.g., Zetasizer™ Nano-S, ZEN1600, also of Malvern Instruments, England), using standard practice.

As used herein in the specification and in the claims section that follows, the term "geometric projection" refers to an imaginary geometric construct that is projected onto a printed face of a printing substrate.

As used herein in the specification and in the claims section that follows, the term "distinct ink dot" refers to any ink dot or ink dot image, at least partially disposed within the "geometric projection", that is neither a "satellite", nor an overlapping dot or dot image.

As used herein in the specification and in the claims section that follows, the term "mean deviation", with respect to the roundness, convexity, and the like, of a plurality of "distinct ink dots", refers to the sum of the individual distinct ink dot deviations divided by the number of individual distinct ink dots.

As used herein in the specification and in the claims section that follows, the term "weight" or "weight ratio", with respect to a resin in a formulation or dried ink residue, is meant to include the entire resin content within that formulation or residue, including, by way of example, the resin "binder" and any resin dispersant.

As used herein in the specification and in the claims section that follows, the term "softening agent" is used as the term would normally be understood by those of skill in the art of polymeric resins. Thus, by way of example, a material added to a particular polymeric resin in a ratio of 1 : 1 by weight, and attained insignificant softening of the resin (e.g., the Tg was lowered by less than 1°C), would not be considered a "softening agent" with respect to that particular polymeric resin.

With regard to fibrous printing substrates, persons skilled in the printing arts will appreciate that coated papers used for printing may be generally classified, functionally and/or chemically, into two groups, coated papers designed for use with non-inkjet printing methods (e.g., offset printing) and coated papers designed specifically for use with inkjet printing methods employing aqueous inks. As is known in the art, the former type of coated papers utilize mineral fillers not only to replace some of the paper fibers in order to reduce costs, but to impart specific properties to paper, such as improved printability, brightness, opacity, and smoothness. In paper coating, minerals are used as white pigments to conceal the fiber, thereby improving brightness, whiteness, opacity, and smoothness. Minerals commonly used to this end are kaolin, calcined clay, ground calcium carbonate, precipitated calcium carbonate, talc, gypsum, alumina, satin white, blanc fixe, zinc sulfide, zinc oxide, and plastic pigment (polystyrene).

Coated papers designed for use in non-inkjet printing methods have hitherto been unsuitable for use with aqueous inkjet inks, or produce print dots or splotches that may be manifestly different from the printed ink film constructions of the present invention.

In contrast, specialty coated papers designed for use with inkjet inks, which in some cases may have layer of filler pigment as with other types of coated papers, may also include a layer of highly porous mineral, usually silica, in combination with a water- soluble polymer such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP), which acts as a binder, upon which the ink is printed. Such coated inkjet papers are designed to quickly remove the water from the printed ink, facilitating the printing of ink droplets with good uniformity and edge roughness. The present invention encompasses ink droplets printed on uncoated paper as well as coated paper not designed for inkjet use, but some embodiments of the present invention are not intended to encompass ink droplets printed on special coated inkjet paper.

Thus, in some embodiments, the substrate is an uncoated paper. In other embodiments, the substrate is a coated paper that does not contain a water-soluble polymer binder in a layer upon which the ink is printed.

As used herein in the specification and in the claims section that follows, the term "commodity coated fibrous printing substrate" is meant to exclude specialty and high-end coated papers, including photographic paper and coated inkjet papers.

In a typical paper coating of a commodity coated fibrous printing substrate, the coating formulation may be prepared by dispersing pigments, such as kaolin clay and calcium carbonate into water, then adding in binder, such as polystyrene butadiene copolymer and/or an aqueous solution of cooked starch. Other paper coating ingredients, such as rheological modifiers, biocides, lubricants, antifoaming compounds, crosslinkers, and pH adjusting additives may also be present in small amounts in the coating.

Examples of pigments that can be used in coating formulations are kaolin, calcium carbonate (chalk), China clay, amorphous silica, silicates, barium sulfate, satin white, aluminum trihydrate, talcum, titanium dioxide and mixtures thereof. Examples of binders are starch, casein, soy protein, polyvinylacetate, styrene butadiene latex, acrylate latex, vinylacrylic latex, and mixtures thereof. Other ingredients that may be present in the paper coating are, for example, dispersants such as polyacrylates, lubricants such as stearic acid salts, preservatives, antifoam agents that can be either oil based, such as dispersed silica in hydrocarbon oil, or water-based such as hexalene glycol, pH adjusting agents such as sodium hydroxide, rheology modifiers such as sodium alginates, carboxymethylcellulose, starch, protein, high viscosity hydroxyethylcellulose, and alkali-soluble lattices.

As used herein in the specification and in the claims section that follows, the term "fibrous printing substrate" of the present invention is specifically meant to include:

• Newsprint papers including standard newsprint, telephone directory paper, machine-finished paper, and super-calendered paper;

• Coated mechanical papers including light-weight coated paper, medium- weight coated paper, high-weight coated paper, machine finished coated papers, film coated offset;

• Woodfree uncoated papers including offset papers, lightweight papers;

• Woodfree coated papers including standard coated fine papers, low coat weight papers, art papers;

• Special fine papers including copy papers, digital printing papers, continuous stationery;

• Paperboards and Cartonboards; and

• Containerboards.

As used herein in the specification and in the claims section that follows, the term "fibrous printing substrate" of the present invention is specifically meant to include all five types of fibrous offset substrates described in ISO 12647-2.

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

It will be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification, including PCT Applications Nos. PCT/IB2013/051716, PCT/IB2013/000757, PCT/IB2013/051743 and PCT/IB2013/051751, are hereby incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

[00282] The contents of all of the above mentioned applications of the Applicant are incorporated by reference as if fully set forth herein.

[00283] The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons skilled in the art to which the invention pertains.

[00284] In the description and claims of the present disclosure, each of the verbs, "comprise" "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a colorant" or "at least one colorant" may include a plurality of colorants.

Claims

WHAT IS CLAIMED IS:

1. A water-based inkjet ink formulation comprising:

(a) a solvent containing water and, optionally, a co-solvent, said water constituting at least 8 wt.% of the formulation;

(b) at least one colorant dispersed or at least partly dissolved within said solvent, said colorant constituting at least 1 wt.% of the formulation; and

(c) an organic polymeric resin, which is dispersed or at least partially dissolved within said solvent, the resin constituting 6 to 40 wt.% of the formulation,

wherein the average molecular weight of said resin is at least 8,000,

the ink formulation having at least one of (i) a viscosity of 2 to 25 cP at at least one temperature in the range of 20-60°C and (ii) a surface tension of not more than 50 milliNewton/m at at least one temperature in the range of 20-60°C;

and wherein at least one of the following two statements is true:

(1) the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90°C to 195°C, the dried ink has a first dynamic viscosity in the range of 1,000,000 (1 x 10⁶) cP to 300,000,000 (3 x 10⁸) cP, and (b) at at least one temperature in the range of 50°C to 85°C, the dried ink has a second dynamic viscosity of at least 80,000,000 (8 x 10⁷) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity; and

(2) the weight ratio of the resin to the colorant is at least 1 : 1.

2. The inkjet ink formulation according to claim 1, wherein the ink is such that, when substantially dried, (a) at at least one temperature in the range of 90°C to 195°C, the dried ink has a first dynamic viscosity in the range of 1,000,000 (1 x 10⁶) cP to 300,000,000 (3 x 10⁸) cP, and (b) at at least one temperature in the range of 50°C to 85°C, the dried ink has a second dynamic viscosity of at least 80,000,000 (8 x 10⁷) cP, wherein the second dynamic viscosity exceeds the first dynamic viscosity.

3. The inkjet ink formulation of claim 2, wherein the first dynamic viscosity is at most 25^»10⁷cP, at most 20^»10⁷cP, at most 15^»10⁷cP, at most 12^»10⁷cP, at most 10^»10⁷cP, at most 9^»10⁷cP, at most 8^»10⁷cP, or at most 7^»10⁷cP.

4. The inkjet ink formulation of claim 2 or 3, wherein the first dynamic viscosity is at least 2 x 10⁶ cP, at least 4 x 10⁶ cP, at least 5 x 10⁶ cP, at least 6 x 10⁶ cP, at least 7 x 10⁶ cP, at least 8 x 10⁶ cP, at least 9 x 10⁶ cP, at least 1 x 10⁷ cP, at least 1.1 x 10⁷ cP, at least 1.2 x 10⁷ cP, at least 1.3 x 10⁷ cP, at least 1.4 x 10⁷ cP, at least 1.5 x 10⁷ cP, at least 1.6 x 10⁷ cP, at least 2.5 x 10⁷ cP, or at least 4 x 10⁷ cP.

5. The inkjet ink formulation claims 2 or 3, wherein said first dynamic viscosity is within a range of 10⁶cP to 2.5^»10⁸cP, 10⁶cP to 2.0^»10⁸cP, 10⁶cP to 10⁸cP, 3^»10⁶cP to 10⁸cP, 5^»10⁶cP to 3^»10⁸cP, 5^»10⁶cP to 3^»10⁸cP, 8^»10⁶cP to 3^»10⁸cP, 8^»10⁶cP to 10⁸cP, 10⁷cP to 3^»10⁸cP, 10⁷cP to 2^»10⁸cP, 10⁷cP to 10⁸cP, 2^»10⁷cP to 3^»10⁸cP, 2^»10⁷cP to 2^»10⁸cP, or 2^»10⁷cP to 10⁸cP.

6. The inkjet ink formulation of claim 2, wherein at at least one temperature in the range of 125°C to 160°C, the dried ink has a first dynamic viscosity in the range of 10⁷ cP to 3 xlO⁸ cP.

7. The inkjet ink formulation of claim 6, wherein the first dynamic viscosity is at least 1.1 x 10⁷ cP, at least 1.2 x 10⁷ cP, at least 1.3 x 10⁷ cP, or at least 1.4 x 10⁷ cP.

8. The inkjet ink formulation of claim 6 or 7, wherein the first dynamic viscosity is at most 25^»10⁷cP, at most 20^»10⁷cP, at most 15^»10⁷cP, at most 12^»10⁷cP, at most 10^»10⁷cP, at most 9^»10⁷cP, at most 8^»10⁷cP, or at most 7^»10⁷cP.

9. The inkjet ink formulation of any of claims 6 to 8, wherein said first dynamic viscosity is within a range of 10⁷cP to 3^»10⁸cP, 10⁷cP to 2^»10⁸cP, 10⁷cP to 10⁸cP, 2^»10⁷cP to 3^»10⁸cP, 2^»10⁷cP to 2^»10⁸cP, or 2^»10⁷cP to 10⁸cP.

10. The inkjet ink formulation of any of claims 1 to 9, wherein the formulation further comprises a dispersant.

11. The inkjet ink formulation of claim 10, wherein the dispersant constitutes not more than 3.5 wt.%, not more than 3 wt.%, not more than 2.5 wt.%, not more than 2 wt.%, not more than 1.5 wt.%, not more than 1 wt.% or not more than 0.5 wt.% of the formulation.

12. The inkjet ink formulation of claim 10 or claim 11 wherein at at least one temperature in the range of 90°C to 125°C, the dried ink has a first dynamic viscosity in the range of 4 x 10⁷ cP to 2 x 10⁸ cP.

13. The inkjet ink formulation of claim 12 wherein said first dynamic viscosity is at least 5 x 10⁷ cP or 6 x 10⁷ cP.

14. The inkjet ink formulation of claim 12 or claim 13 wherein said first dynamic

7 7

viscosity is at most 5 x 10 cP or 6 x 10' cP.

15. The inkjet ink formulation of any of claims 12 to 14 wherein the dispersant is selected from the group consisting of high molecular weight aminourethane, a modified polyacrylate polymer, an acrylic block copolymer made by controlled free radical polymerisation, or an ethoxylated non-ionic fatty alcohol.

16. The inkjet ink formulation of any one of claims 1 to 15, wherein said second dynamic viscosity is at least 9^»10⁷cP, at least 10⁸cP, at least l .l^»10⁸cP, at least 1.2^»10⁸cP, at least 1.3^»10⁸cP, at least 1.4^»10⁸cP, at least 1.5^»10⁸cP, at least 2.0^»10⁸cP, at least 2.5'10⁸cP, at least 3.0^»10⁸cP, at least 3.5^»10⁸cP, at least 4.0^»10⁸cP, at least 5.0^»10⁸cP, at least 6^»10⁸cP, at least 7.5^»10⁸cP, at least 10⁹cP, at least 2^»10⁹cP, at least 4^»10⁹cP, or at least 6^»10⁹cP.

17. The inkjet ink formulation of any of claims 1 to 16, wherein the ratio of the second dynamic viscosity to the first dynamic viscosity is at least 1.2: 1, at least 1.3: 1, at least 1.5:1, at least 1.7: 1, at least 2: 1, at least 2.5: 1, at least 3: 1, at least 3.5: 1, at least 4: 1, at least 4.5:1, at least 5: 1, at least 6: 1, at least 7: 1, at least 8: 1, at least 10: 1, at least 15: 1, at least 20: 1, at least 25: 1, at least 50: 1, at least 100: 1, at least 500: 1, or at least 1000: 1.

18. The inkjet ink formulation of any one of claims 1 to 17, wherein a ratio of said second dynamic viscosity, at 90°C, to said first dynamic viscosity, at 60°C, is at least 1.2: 1, at least 1.3:1, at least 1.5: 1, at least 1.7:1, at least 2: 1, at least 2.5: 1, at least 3: 1, at least 4: 1, at least 4.5: 1, at least 5: 1, at least 6: 1, at least 7: 1, or at least 8: 1.

19. The inkjet ink formulation of claim 17 or 18, wherein said ratio is at most 30:1, at most 25: 1, at most 20: 1, at most 15: 1, at most 12: 1, or at most 10: 1.

20. The inkjet ink formulation of any of claims 1 to 19, wherein the weight ratio of the polymeric resin to the colorant is at least 1 : 1.

21. The inkjet ink formulation of claim 20, wherein the weight ratio of the polymeric resin to the colorant is at least 1.25: 1, at least 1.5: 1, at least 1.75: 1, at least 2:1, at least 2.5:1, at least 3: 1, at least 3.5: 1, at least 4: 1, at least 5: 1, at least 7: 1, or at least 10: 1.

22. The inkjet ink formulation of any of claims 1 to 21, wherein the weight ratio of the polymeric resin to the colorant is at most 15: 1, at most 12: 1, at most 10: 1, at most 7: 1, at most 5 : 1 , at most 4: 1 , at most 3 : 1 , at most 2.5 : 1 , at most 2: 1 , or at most 1.7: 1.

23. The inkjet ink formulation of any one of claims 1 to 22, which, when substantially dried, has a glass transition temperature (T_g) of at most 50°C, at most 47°C, at most 45°C, at most 44°C, at most 43°C, at most 42°C, at most 40°C, at most 39°C, at most 37°C, at most 35°C, at most 32°C, at most 30°C or at most 28°C.

24. The inkjet ink formulation of any of claims 1 to 23, wherein the polymeric resin is an acrylic-based polymer selected from an acrylic polymer and an acrylic-styrene copolymer.

25. The inkjet ink formulation of any one of claims 1 to 24 which comprises a co- solvent.

26. The inkjet ink formulation of claim 25 wherein the co-solvent is miscible with said water at said at least one particular temperature in the range of 20°C to 60°C, whereby said solvent is a single-phase solvent.

27. The inkjet ink formulation according to any one of claims 1 to 26, wherein the formulation further comprises a surfactant, in addition to the polymeric resin, colorant, water and optional co-solvent.

28. The inkjet ink formulation of claim 27, wherein said surfactant is present in an amount of not more than 2 wt.%, not more than 1.5 wt.%, not more than 1 wt.%, or not more than 0.5 wt.%.

29. The inkjet ink formulation of any one of claims 1 to 20, wherein said polymeric resin has a T_g below 50°C.

30. The inkjet ink formulation of any one of claims 1 to 29, wherein said average molecular weight of said polymeric resin is not more than 70,000, not more than 65,000, not more than 60,000, not more than 55,000, not more than 50,000, not more than 45,000 or not more than 40,000.

31. The inkjet ink formulation of any one of claims 1 to 30, wherein said average molecular weight of said polymeric resin is at least 10,000, at least 15,000, at least 20,000, at least 25,000 or at least 30,000.

32. The inkjet ink formulation of any one of claims 1 to 29, wherein the average molecular weight of said polymeric resin is at least 70,000, at least 80,000, at least 100,000, at least 120,000, at least 140,000, at least 160,000, at least 180,000, or at least 200,000.

33. The inkjet ink formulation of any one of claims 1 to 32, wherein the colorant comprises a pigment or a mixture of pigments.

34. The inkjet ink formulation of claim 33 wherein the average particle size (D₅₀) of the at least one pigment is not more than 120 nm, not more than 110 nm, not more than 100 nm, not more than 90 nm, not more than 80 nm, not more than 70 nm, not more than 65 nm, or not more than 60 nm.

35. The inkjet ink formulation of claim 33, wherein the average particle size (D₅₀) of the pigment is at least 20 nm, at least 25 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, at least 50 nm, at least 55 nm, at least 60 nm, at least 65 nm, or at least 70 nm.

36. The inkjet ink formulation according to any one of claims 1 to 35, wherein water constitutes at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 45 wt.%, at least 50 wt.%, at least 55 wt.%, at least 60 wt.%, at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, or at least 80 wt.% of the formulation.

37. The inkjet ink formulation of claim 36, wherein water constitutes not more than 85 wt.%, not more than 80 wt.%, not more than 75 wt.%, not more than 70 wt.%, not more than 65 wt.%, not more than 60 wt.%, not more than 55 wt.%, not more than 50 wt.%, not more than 45 wt.%, or not more than 40 wt.% of the formulation.

38. The inkjet ink formulation of any of claims 1 to 37, wherein the polymeric resin is a negatively chargeable resin.

39. The inkjet ink formulation of any of claims 1 to 38, wherein the polymeric resin is negatively charged.

40. The inkjet ink formulation of any one of claims 1 to 39, wherein the ink when substantially dried contains at least 1.2%, at least 1.5%, at least 2%, at least 3%, at least 4%), at least 6%, at least 8%, or at least 10% of said colorant, by weight.

41. The inkjet ink formulation of any one of claims 1 to 39, wherein the ink when substantially dried contains at least 5%, at least 7%, at least 10%, at least 15%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, or at least 70% of said resin, by weight.

42. The inkjet ink formulation of any one of claims 1 to 41, wherein a solubility of said resin in water, at a temperature within a temperature range of 20°C to 60°C, and at a pH within a pH range of 8.5 to 10, is at least 3%, at least 5%, at least 8%, at least 12%, at least 18%), or at least 25%, by weight of dissolved resin to weight of solution.

43. The inkjet ink formulation of any one of claims 1 to 42, wherein the formulation comprises a pH-raising compound.

44. An inkjet ink concentrate comprising:

(a) a solvent containing water and, optionally, a co-solvent;

(b) at least one colorant dispersed or at least partly dissolved within said solvent;

(c) an organic polymeric resin, which is dispersed or at least partially dissolved within said solvent, wherein the average molecular weight of said resin is at least 8,000, and

(d) optionally, at least one of a surfactant, a dispersant, and a pH raising compound, wherein the concentrate, when diluted with a solvent comprising water and a co-solvent, yields an aqueous inkjet formulation according to any one of claims 1 to 43.

45. An inkjet ink concentrate according to claim 44, wherein the concentrate must be diluted with at least 50%, at least 100%, at least 150%, at least 200%, at least 250%, at least 300%), least 350%> or at least 400%> solvent on a weight/weight basis relative to the concentrate to yield the aqueous inkjet ink formulation.

46. An inkjet ink concentrate according to claim 44 or 45, wherein the co-solvent is selected from the group consisting of glycerol, propylene glycol, ethylene glycol, diethylene glycol, N-methyl pyrrolidone, PEG 400, and mixtures thereof.

47. A water-based inkjet ink formulation comprising:

(a) a solvent containing water;

(b) at least one colorant dispersed or at least partly dissolved within said solvent; and

(c) at least one organic polymeric resin, dispersed within said solvent;

the ink formulation forming, when dried, a dried ink residue having:

(i) a first dynamic viscosity within a range of 10⁶cP to 5^»10⁷cP at at least a first temperature within a first range of 60°C to 87.5°C; and

(ii) a second dynamic viscosity of at least 6^»10⁷cP, for at least a second temperature within a second range of 50°C to 55°C.