JP5291372B2 - Ink composition - Google Patents

Description

  The present invention relates to an ink composition used for preparing a printing plate using an ink jet printer, and more particularly to an ink composition for forming an image portion of a printing plate using an ink jet printer.

  Conventionally, a so-called PS plate having an oleophilic photosensitive resin layer on a hydrophilic support has been used for producing a printing plate. After exposing an image or the like to the PS plate, a non-printed plate is prepared with an alkali developer. A method of forming an image by dissolving an image forming portion has been performed. However, this method has various problems such as the need for processing of a used alkaline developer, or the developability varies depending on the frequency of use of the developer, and stable image reproducibility cannot be obtained.

  Therefore, in recent years, there is an increasing expectation for a so-called processless printing plate that does not require such a special alkaline developer. As an image forming method for a processless printing plate, an ink jet method is disclosed in which an image is directly formed on a hydrophilic support using an ink jet printer. While this inkjet system has the advantage that the apparatus is relatively inexpensive, it is difficult to obtain high-quality images because the ink tends to bleed after the ink has landed on the support, and the printing durability is practical. There was a problem that the level was not right.

As a method for solving these problems, ink that is solid at room temperature is melted and discharged by a heating head, and the ink is cured when the ink lands on the support. A technique is disclosed in which the printing durability is improved by eliminating UV and then irradiating the image portion with ultraviolet rays to cure (see, for example, Patent Document 1). In addition, using ink that cures upon irradiation with actinic radiation, the time from ink landing to irradiation with actinic radiation is controlled to an extremely short time, preventing ink from bleeding before curing and curing with high sensitivity. Thus, a technique for improving printing durability is disclosed (for example, see Patent Document 2).
JP-A-11-256085 JP 2007-169364 A

  However, in the case of the above heat-soluble ink, a heating head and an ultraviolet irradiation device for use in curing are required for the printer head, and in the case of a radiation curable ink, a radiation irradiation device for use in curing is required, Furthermore, since a heater or the like is required in the head in order to keep the ink viscosity constant, the apparatus becomes expensive and the advantage of the ink jet printer that it is relatively inexpensive is reduced. In general, ink compositions containing a resin as a curing component tend to clog the nozzles of the printer head.

  The object of the present invention is to solve the above-mentioned problems, and there is no nozzle clogging in the printer head despite the fact that the ink composition contains a resin as a curing component, so that a printing plate can be prepared with a simpler apparatus than before. An object of the present invention is to provide an ink composition that can be produced and that can produce a printing plate having improved printing durability and resolution.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by using a rosin-modified phenolic resin in combination with a specific organic solvent, thereby completing the present invention.

That is, the ink composition of the present invention is an ink composition used for producing a printing plate using an ink jet printer, and has a softening point of 160 to 200 ° C. and a mass average molecular weight of 80,000 to 200. A rosin-modified phenolic resin, a colorant and an organic solvent, and the organic solvent is at least one compound selected from the group consisting of glycol ether ester compounds, glycol ether compounds and glycol ester compounds. It is characterized by.

  By using the ink composition of the present invention, a printing plate excellent in resolution and printing durability can be obtained with a simple device that does not cause clogging of the nozzles of the printer and does not require a special device for curing the ink discharge portion and the image. Can be produced.

Hereinafter, the ink composition of the present invention will be described in detail.
The ink composition of the present invention is an ink composition used for producing a printing plate using an ink jet printer, and contains a rosin-modified phenolic resin, a colorant and an organic solvent. Any rosin-modified phenolic resin can be used in the present invention. However, the rosin-modified phenolic resin preferably has a softening point (measured according to JIS K 5903) of 160 to 200 ° C, particularly preferably 170 to 190 ° C. When the softening point is less than 160 ° C., there is a tendency that the printing durability is deteriorated. Further, the rosin-modified phenolic resin preferably has a mass average molecular weight of 80,000 to 200,000, particularly preferably 100,000 to 150,000. When the mass average molecular weight is less than 80,000, the printing durability tends to be reduced, and when it exceeds 200,000, there is a tendency that nozzle clogging is likely to occur. The blending amount of the rosin-modified phenolic resin is determined in consideration of the viscosity, dischargeability and the like of the ink composition, but preferably occupies 5 to 30% by mass of the ink composition, and occupies 10 to 20% by mass. It is particularly preferred.

  The rosin-modified phenolic resin that can be used in the ink composition of the present invention can be produced by a known production method. For example, a method in which rosins are esterified with polyhydric alcohols and then a resole resin synthesized with phenol and formaldehyde in the presence of a basic catalyst is reacted; It can be produced by a method of esterification with alcohols. Examples of rosins that are the above raw materials include gum rosin, wood rosin, polymerized rosin, tall oil rosin, disproportionated rosin and the like, and phenols such as phenol, butylphenol, amylphenol, octylphenol, nonylphenol, dodecylphenol, cresol, Examples thereof include phenylphenol and bisphenol A, and examples of polyhydric alcohols include glycerin, pentaerythritol, trimethylolpropane, and diethylene glycol. In addition, dibasic acids such as phthalic acid, adipic acid, maleic acid and the like can be added during the above esterification reaction, and further, oistica oil, linseed oil, safflower oil, cottonseed oil, soybean oil, tall oil, dehydrated castor oil Vegetable oils such as dry oils such as tung oil and semi-dry oils, and polymers thereof can also be used. Examples of the basic catalyst include sodium hydroxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, ethylamine, triethanolamine, and triethylenediamine.

  In the ink composition of the present invention, a rosin-modified phenolic resin and another binder resin can be used in combination. The binder resin that can be used in combination is a binder resin commonly used in ordinary ink-jet ink compositions, such as vinyl chloride-vinyl acetate copolymer resin, epoxy resin, phenol resin, novolac resin, acrylic resin. , Polyester resins, amino resins such as melamine, benzoguanamine, polyamide resins, cellulose diacetate, cellulose triacetate, cellulose ester resins such as nitrocellulose, cellulose nitrate, cellulose propionate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, Cellulose ether resins such as benzylcellulose, tritylcellulose, cyanethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, etc. It can be mentioned. These resins can be added in such an amount that does not impair printing durability and nozzle clogging, and for example, can be added in an amount that occupies 0.5 to 30% by mass of the ink composition.

  In the ink composition of the present invention, at least one compound selected from the group consisting of glycol ether ester compounds, glycol ether compounds and glycol ester compounds is used as the organic solvent.

  Specific examples of glycol ether ester compounds that can be used in the ink composition of the present invention include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, and diethylene glycol. Monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate , Dipropylene glycol monobutyl ether Teruasetato and their mixtures and the like.

  Specific examples of glycol ether compounds that can be used in the ink composition of the present invention include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether. , Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, etc. Ethylene glycol ethers, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene Examples thereof include propylene glycol ethers such as glycol dimethyl ether and dipropylene glycol diethyl ether, and mixtures thereof.

  Specific examples of glycol ester compounds that can be used in the ink composition of the present invention include ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoacetate, diethylene glycol diacetate, triethylene glycol monoacetate, triethylene glycol. Examples thereof include ethylene glycol diacetate, propylene glycol monoacetate, propylene glycol diacetate, dipropylene glycol monoacetate, dipropylene glycol diacetate, and mixtures thereof.

  In the ink composition of the present invention, ethylene glycol monobutyl ether acetate or propylene glycol monoethyl ether acetate is particularly preferable as the organic solvent from the viewpoint of ejection stability of the ink composition and ink drying property.

  In the ink composition of the present invention, alcohols such as methanol, ethanol and isopropanol, ketones such as methyl ethyl ketone, cyclohexanone and acetone, aromatics such as toluene and xylene, γ-butyrolactone, γ- Lactone compounds such as valerolactone, γ-caprolactone, and ε-valerolactone can also be used. Further, water, ethylene glycol, diethylene glycol, propylene glycol are used as a solvent for preventing drying of the ink composition at the nozzle portion, preventing solidification of the ink composition, and preventing ejection of the stable ink composition and drying of the nozzle over time. Triethylene glycol, polyethylene glycol, glycerin, tetraethylene glycol, dipropylene glycol and the like can also be used.

  The blending amount of the solvent in the ink composition of the present invention is determined in consideration of the viscosity, surface tension and the like of the ink-jet ink composition, and preferably accounts for 50 to 94.5% by mass of the ink composition. It is particularly preferred to account for ~ 89.5% by weight.

  In the ink composition of the present invention, it is preferable to use a colorant that is compatible with the above-mentioned mixture of rosin-modified phenolic resin and an organic solvent and is soluble in the solvent, and particularly an oily dye. Is preferred. Examples of oil-based dyes that can be used in the ink composition of the present invention include carbonium dyes, indigo dyes, metal complex dyes, naphthol dyes, azo dyes, anthraquinone dyes, nitroso dyes, quinoimine dyes, cyanine dyes, quinoline dyes, nitro dyes, and naphthoquinones. Examples thereof include dyes, benzoquinone dyes, naphthalimide dyes, phthalocyanine dyes, and perinone dyes.

  In the ink composition of the present invention, a pigment can also be used as a colorant. Examples of such pigments include inorganic or organic pigments such as titanium oxide, carbon black, zinc sulfide, oil smoke, yellow lead, bengara, phthalocyanine blue, phthalocyanine green, brilliant carmine 6B, and lake red C. However, when an insoluble dye or pigment is used, it is preferable that the particle diameter is 1 μm or less, particularly 0.25 μm or less in order to prevent clogging of the nozzle. These dyes and pigments may be used alone or in appropriate combination.

  In addition, in the ink composition of this invention, it is preferable to use in the quantity which occupies 0.5-20 mass% of an ink composition from the point of the ejection stability of an ink.

  In the ink composition of the present invention, additives such as a conductivity adjusting agent, a surfactant, an ultraviolet absorber, an antifoaming agent, a dispersing agent, and an antiseptic can be blended as necessary. Examples of the conductivity adjusting agent that can be used in the ink composition of the present invention include lithium nitrate, lithium nitrite, ammonium sulfite, ammonium formate, ammonium acetate, lithium halide, and sodium thiocyanate. Furthermore, surfactants, ultraviolet absorbers, antifoaming agents, dispersants, preservatives, and the like that can be used in the ink composition of the present invention are those commonly used in ink jet printing compositions. The ink composition of the present invention can contain these additives in an amount occupying 0.01 to 5% by mass of the ink composition.

  The ink composition of the present invention can be prepared by mixing and stirring the respective components. The mixing and stirring can be performed by a high-speed disperser, an emulsifier or the like in addition to stirring by a stirrer using a normal stirring blade. The mixed ink composition is filtered through a filter having a pore diameter of 3 μm or less, preferably 1 μm or less, before or after dilution. Prior to filtration with a filter, filtration by centrifugation can also be used, thereby reducing clogging during filtration with the filter and extending the usable period of the filter.

  The ink composition of the present invention is required to have characteristics adapted to the ink jet printing method. Therefore, the viscosity at 20 ° C. is preferably 1 to 20 mPa · s, and preferably 5 to 15 mPa · s. Particularly preferred. Moreover, it is preferable that the surface tension in 20 degreeC is 20-70 mN / m, and it is especially preferable that it is 20-40 mN / m.

  The ink composition of the present invention can be used in any conventionally known ink jet printer. Examples of such an ink jet printer include a load control method, an ink-on-demand method, and a method in which ink is ejected by a thermal head. Ink jet-printed ink can form a dry film at room temperature. From the viewpoint of improving resolution, the substrate is heated and dried to the extent that nozzle clogging does not occur before printing, during printing, or after printing. Things are desirable.

  As a substrate used for producing a printing plate using the ink composition of the present invention, a known substrate whose surface is subjected to a hydrophilic treatment can be used. Examples of the base material of the substrate include a metal plate, water-resistant paper, a plastic film, a composite base material of a metal plate and a plastic film, and the like. Examples of the metal plate include aluminum, zinc, stainless steel, iron, and the like, but aluminum is particularly preferable in terms of specific gravity and rigidity. An aluminum substrate with a hydrophilic surface is obtained by graining by a mechanical polishing method such as brush polishing or ball polishing, or an electrochemical method such as etching using an electrolytic solution such as sulfuric acid or hydrochloric acid. Can do. Furthermore, in order to increase the strength of the aluminum substrate, improve the ink fixability, and increase the printing durability, it is desirable to perform an anodizing treatment that forms an aluminum oxide film on the surface after graining.

  Examples of plastic films include polyethylene naphthalate, polyethylene terephthalate, polycarbonate, etc., and a hydrophilic image obtained by applying and drying a coating containing inorganic pigments such as silica, kaolin, clay, calcium carbonate on the surface. A formation layer can be formed. Furthermore, in order to suppress plate elongation at the time of printing, a composite base material in which the metal plate and a plastic film are appropriately bonded can also be used.

  In the ink composition of the present invention, a dry film is formed in which the contact angle of water with respect to the surface of the dry film after uniformly applying the ink composition of the present invention on the substrate is 60 ° or more after 1 minute of dropping. It is preferable to obtain. If the angle is less than 60 °, the inking property of the offset printing ink tends to deteriorate.

Hereinafter, the present invention will be described in more detail with reference to Examples, Reference Examples and Comparative Examples.
Examples 1-3, Reference Examples 4, 5, Examples 6, 7 and Comparative Example 1
A commercially available rosin-modified phenol resin having a softening point and a weight average molecular weight shown in Table 1 as the rosin-modified phenol resin, and an organic solvent A: propylene glycol monomethyl ether acetate,
Organic solvent B: ethylene glycol monobutyl ether acetate,
Organic solvent C: diethylene glycol ethyl methyl ether,
Organic solvent D: propylene glycol diacetate,
Organic solvent E: cyclohexanone,
Organic solvent F: γ-butyrolactone,
C., which is an oil-based dye as a colorant. I. Solvent Black 3 was used.

In Table 1, Tamanol is the trade name of rosin modified phenolic resin manufactured by Arakawa Chemical Industries, Ltd., Tespol is the trade name of rosin modified phenolic resin manufactured by Hitachi Chemical Polymer Co., Ltd., and the softening point is a value measured by the ring and ball method. The mass average molecular weight is a polystyrene equivalent value.

After above rosin-modified phenolic resin, a colorant and an organic solvent were blended so that the composition shown in Table 2 (wt%), were uniformly mixed, Examples 1 3 were filtered through a membrane filter having a pore size 1μm The ink compositions of Reference Examples 4, 5, Examples 6, 7 and Comparative Example 1 were prepared.

The viscosity, storage stability, nozzle clogging property, printing plate image quality, printing durability and contact angle of the obtained ink composition were measured and evaluated by the following methods. The results were as shown in Table 2.
<Viscosity measurement>
It measured at 20 degreeC using the Ostwald viscometer.

<Storage stability>
The viscosity after storing the ink composition at 60 ° C. and −5 ° C. for 1 month was measured at 20 ° C. using an Ostwald viscometer.
◎: Change in viscosity after storage for 1 month within ± 5% each
○: Viscosity change after storage for 1 month is more than 5% and 10% or less,
X: Any change in viscosity after storage for 1 month is more than 10%.

<Nozzle clogging>
After printing for several minutes with an ink jet printer, printing was stopped and left for 5 minutes. When printing was started again, the number of nozzles that could not eject ink to a predetermined position was counted and evaluated according to the following criteria.
A: The number of nozzles that cannot be discharged to a predetermined position is 1/60 or less of the total number of nozzles,
○: The number of nozzles that cannot be discharged at a predetermined position is more than 1/60 of the total number of nozzles, and less than 2/60
X: The number of nozzles that cannot be discharged to a predetermined position is more than 2/60 of the total number of nozzles.

<Print quality>
A drawing image of the obtained printing plate was observed with an optical microscope at a magnification of 200 times and evaluated according to the following judgment.
◎: There is no problem with the drawn image and the fine lines and characters are very good.
○: There is no problem with the drawn image, and fine lines and fine characters are good.
X: The thin line or fine character has a defect or blur and is defective.

  A composite material of a plastic film having a hydrophilic surface and aluminum was used as the base material of the printing plate. Each of the ink compositions described above was printed on the hydrophilically treated printing plate surface with an on-demand printer. Printing was performed with an offset printing machine using the obtained printing plate, and printing durability was evaluated by the following method. Further, the contact angle of water on the dry film surface of the ink was measured by the following method. The results were as shown in Table 2.

<Print durability>
The printed image portion was checked visually every time 5000 sheets were printed. The stage in which the background stain of the printed matter, the missing image, and the decrease in the density of the solid portion were confirmed was terminated, and the evaluation was performed with the following number of sheets.
A: More than 20,000 sheets
○: 10,000 or more, less than 20,000 sheets,
X: Less than 10,000 sheets.

<Contact angle>
Distilled water (0.03 ml) was dropped onto the surface of the dried ink film, and the contact angle of water one minute after dropping was measured at 20 ° C. with a contact angle meter (image processing type CA-X, manufactured by Kyowa Interface Science Co., Ltd.). It was measured.

Claims (5)

A rosin-modified phenolic resin having a softening point of 160 to 200 ° C. and a weight average molecular weight of 80,000 to 200,000, which is used for producing a printing plate using an inkjet printer, coloring An ink composition comprising an agent and an organic solvent, wherein the organic solvent is at least one compound selected from the group consisting of glycol ether ester compounds, glycol ether compounds and glycol ester compounds.   2. The ink composition according to claim 1, wherein the colorant is an oily dye. The ink composition according to claim 1 or 2 , wherein the amount of the rosin-modified phenol resin is 10 to 20% by mass . A mixture of a compound selected from glycol ether ester compounds and a compound selected from glycol ether compounds, a compound selected from glycol ether ester compounds and a compound selected from glycol ester compounds; The ink composition according to any one of claims 1 to 3, wherein the ink composition comprises at least one compound selected from a mixture of the above and a glycol ether ester compound .   The ink composition according to claim 1, wherein a dry film having a contact angle with water of 60 ° or more can be formed.