US20170370036A1

US20170370036A1 - Towel having improved wet performance

Info

Publication number: US20170370036A1
Application number: US15/542,582
Authority: US
Inventors: Michael Alan Hermans; Maurizio Tirimacco; Jeffrey James Timm
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 2015-01-28
Filing date: 2015-01-28
Publication date: 2017-12-28
Also published as: BR112017015120A2; KR20170106985A; AU2015380641A1; WO2016122477A1; MX2017009066A

Abstract

The present invention provides a creped tissue web having a CD Wet/Dry ratio that meets or exceeds satisfactory levels without the excess use of a wet strength resin. The satisfactory level of CD Wet/Dry ratio is generally greater than about 0.40, more preferably greater than about 0.42 and still more preferably greater than about 0.44, such as from about 0.40 to about 0.45. The satisfactory level of CD Wet/Dry ratio is surprisingly achieved by treating the tissue making furnish with a relatively modest amount of non-wood synthetic fibers, preferably fibrillated acrylic fiber.

Description

BACKGROUND OF THE DISCLOSURE

In the development and manufacture of paper products, particularly paper towels for the consumer market, it is a continual objective to improve the absorbent characteristics of the product. For cleaning up some spills, the consumer needs high absorbent capacity. For some uses, consumers want a fast rate of absorbency. For other uses, a combination of high absorbent capacity and fast absorbent rate is desired. At the same time, constraints on achieving this objective include the need to maintain or reduce costs in order to provide the consumer with the highest possible value, which in part means minimizing the amount of fiber in the product.

SUMMARY OF THE DISCLOSURE

It has now been surprisingly discovered that absorbency may be increased, even at higher basis weights and tensile strengths, by manufacturing a tissue sheet using synthetic fibers and more specifically acrylic pulp fibers. Even at low levels of addition, such as less than 20 percent by weight of the total fiber furnish, and even when incorporated into only one layer of a multi-layer web, the use of acrylic pulp fibers greatly improves towel wet performance.
Generally the absorbent and wet strength properties demonstrated by the inventive tissues could only be achieved by manufacturing the tissue product with a binder, such as a latex binder. Now however, the inventors have discovered that by employing a relatively small amount of synthetic fibers, binders may be omitted without sacrificing absorbency and wet strength properties. As such, the tissue products of the present invention are generally manufactured without the use of a binder. Rather, the tissue products generally employ synthetic fibers, and in certain instances conventional wet strength agents.
Accordingly, in certain aspects the present disclosure provides a tissue product free from latex binder, the tissue product having an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.
In other aspects the present disclosure provides a single-ply through-air dried tissue product free from latex binder, the tissue product having a basis weight from about 36 to about 50 gsm, such as from about 36 to about 45 gsm, and an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.
In still other aspects the present disclosure provides an uncreped through-air dried tissue product having a CD Wet/Dry Ratio greater than about 0.40 and a Wet CD Durability greater than about 2.0.
In yet other aspects the present disclosure provides an uncreped through-air dried tissue product comprising from about 5 to about 10 kg of a polyamide-epichlorohydrin wet strength resin per ton of furnish, the tissue web having a CD Wet/Dry Ratio greater than about 0.40 and a Wet CD Durability greater than about 2.0.
In other aspects the present disclosure provides a through-air dried tissue product comprising from about 1 to about 20 percent, by weight of the product, fibrillated acrylic fibers, the tissue product having an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.
In still other aspects the present disclosure provides a layered through-air dried tissue product comprising at least one tissue web comprising a first fibrous layer and a second fibrous layer, the first fibrous layer comprising wood pulp fibers and the second layer comprising fibrillated acrylic fibers, wherein the first fibrous layer is substantially free of fibrillated acrylic fibers and wherein the fibrillated acrylic fibers comprise from about 1 to about 20 percent of the total weight of the through-air dried web, the tissue product having a CD Wet/Dry Ratio greater than about 0.40.

Definitions

As used herein, the term “tissue product” refers to products made from tissue webs and includes, bath tissues, facial tissues, paper towels, industrial wipers, foodservice wipers, napkins, medical pads, and other similar products.
As used herein, the terms “tissue web” and “tissue sheet” refer to a fibrous sheet material suitable for use as a tissue product.
As used herein, the term “layer” refers to a plurality of strata of fibers, chemical treatments, or the like, within a ply.
As used herein, the terms “layered tissue web,” “multi-layered tissue web,” “multi-layered web,” and “multi-layered paper sheet,” generally refer to sheets of paper prepared from two or more layers of aqueous papermaking furnish which are preferably comprised of different fiber types. The layers are preferably formed from the deposition of separate streams of dilute fiber slurries, upon one or more endless foraminous screens. If the individual layers are initially formed on separate foraminous screens, the layers are subsequently combined (while wet) to form a layered composite web.
As used herein, the term “ply” refers to a discrete product element. Individual plies may be arranged in juxtaposition to each other. The term may refer to a plurality of web-like components such as in a multi-ply facial tissue, bath tissue, paper towel, wipe, or napkin.
As used herein the term “basis weight” generally refers to the bone dry weight per unit area of a tissue and is generally expressed as grams per square meter (gsm). Basis weight is measured using TAPPI test method T-220.
As used herein the term “CD Wet/Dry Ratio,” refers to the ratio of the wet CD tensile strength to the dry CD tensile strength, measured as described in the Test Methods Section, below. While the CD Wet/Dry Ratio may vary, tissue products prepared as described herein generally have a CD Wet/Dry Ratio greater than about 0.40, more preferably greater than about 0.42 and still more preferably greater than about 0.44, such as from about 0.40 to about 0.50. Generally the foregoing ratios are achieved at a Wet CD Tensile greater than about 400 g/3′, more preferably greater than about 425 g/3′ and still more preferably greater than about 450 g/3″, such as from about 400 to about 550 g/3″ and still more preferably from about 425 to about 500 g/3″.
As used herein the term “Wet CD Durability,” refers to the CD Wet Stretch multiplied by 100, divided by the CD Wet Tensile, and is a measurement of the wet CD extensibility of a product at a given wet tensile strength. At CD Wet Tensile strengths greater than about 400 g/3″ the inventive tissue products of the present invention generally have a Wet CD Durability greater than about 2.0 and still more preferably greater than about 2.1 and still more preferably greater than about 2.2, such as from about 2.0 to about 2.5.
As used herein the term “Wet Strength Efficiency.” refers to the CD Wet/Dry Ratio divided by the add-on amount of wet strength resin (measured in kilograms per dry metric ton of fiber) multiplied by 100 and is a measure of the amount of wet strength generated relative to dry strength normalized by the amount of wet strength added.
As used herein, the terms “geometric mean tensile” and “GMT” refer to the square root of the product of the machine direction tensile strength and the cross-machine direction tensile strength, measured as described in the Test Methods section, below.
As used herein, the term “Absorbent Capacity” is a measure of the amount of water absorbed by the paper towel product in the vertical orientation and is expressed as grams of water absorbed per gram of fiber (dry weight). Absorbent Capacity is measured as described in the Test Methods section and generally has units of grams per gram (g/g).
As used herein the term “ton of fumish” refers to one thousand kilograms (1,000 kg) of air dried papermaking furnish having a moisture content less than about ten percent (10%).
As used herein, the term “Stiffness Index” refers to the quotient of the geometric mean slope (having units of g/3′) divided by the geometric mean tensile strength (having units of g/3″).
As used herein the term “substantially free” refers to the composition of one layer of a multi-layered web which comprises less than about 0.25 percent by weight, synthetic fiber. The foregoing amounts of fiber are generally considered negligible and do not affect the physical properties of the layer. Moreover the presence of negligible amounts of synthetic fibers in a given layer generally arise from synthetic layers applied to an adjacent layer, and have not been purposefully disposed in a given layer.

DETAILED DESCRIPTION OF THE DISCLOSURE

Generally, the present invention provides a creped tissue web having a CD Wet/Dry ratio that meets or exceeds satisfactory levels without the excess use of a wet strength resin. The satisfactory level of a CD Wet/Dry ratio is generally greater than about 0.40, more preferably greater than about 0.42 and still more preferably greater than about 0.44, such as from about 0.40 to about 0.45. The satisfactory level of CD Wet/Dry ratio is surprisingly achieved by treating the tissue making furnish with a relatively modest amount of non-wood synthetic fibers, preferably fibrillated acrylic fiber. Generally CD Wet/Dry ratios may be achieved with the addition of less than about 20 percent, by weight of the tissue product, such as from about 1 to about 20 percent and more preferably from about 5 to about 15 percent. The addition of synthetic fibers surprisingly improves the CD Wet/Dry ratio without negatively affecting the absorbency of the tissue product. For example, tissue products of the present invention generally have an Absorbent Capacity greater than about 6.0 g/g, such as from about 6.0 to 7.0 g/g. As such the tissue products are durable when wet, but are still sufficiently absorbent. This balance of absorbency and wet strength is not found in the prior art without resorting to adding latex binders or the like to the tissue product.
Further, the aforementioned wet-strength properties may be achieved with only modest additions of conventional wet-strength resin. For example, in certain embodiments the tissue products comprise less than about 10 kg of wet-strength resin per metric ton of furnish, such as from about 3 to about 10 kg, and more preferably from about 3 to about 5 kg. Rather than employ an excessive amount of wet-strength resin, the improved wet-strength properties are achieved by the addition of relatively modest amounts of synthetic fibers during the manufacture of the tissue product, such as from about 1 to about 20 percent, by weight of the product, synthetic fibers and more preferably from about 5 to about 15 percent, by weight.
Accordingly, in certain embodiments the tissue products generally comprise synthetic fibers and still more preferably hydrophobic synthetic fibers and still more preferably fibrillated acrylic fibers. Particularly preferred fibrillated acrylic fibers are polyacrylonitrile (PAN) fibers or copolymers containing at least 85 percent PAN. Other synthetic fibers that may be used include polypropylene, modacrylic fiber (having 35-80 percent PAN content), polyester, olefin or polyethylene, polyamide (nylon) and polylactide. A number of other synthetic hydrophobic fibers may be useful, such as commercially available specialty fibers, including PVC (vinyon), polyvinylidene chloride (Saran™ resins from Dow Chemical Company), polytetrafluoroethylene (Teflon® fibers from E.I. du Pont de Nemours and Company (DuPont)), polyurethane-polyethylene glycol (PU-PEG) block copolymer (spandex, e.g., Lycra® fibers from Invista), aramids (aromatic polyamide, including Kevlar® and Nomex® fibers from DuPont), polybenzimidazole (PBI), aromatic polyester (vectran fibers from Kuraray Co., Ltd.), thermoset polyurethane (Zylon® fibers from Toyobo Corp.), and polyetheretherketone (PEEK, available from Zyex Ltd.).
In certain embodiments the tissue products comprise from about 1 to about 20 percent, by weight of total fiber furnish, fibrillated acrylic fibers and more preferably from about 3 to about 15 percent and still more preferably from about 5 to about 10 percent. The fibrillated acrylic fibers generally have a solids content from about 20 to about 50 percent, a freeness (measured as Canadian Standard Freeness, CSF) from about 100 to about 700 ml and an average fiber length from about 3 to about 7 mm and more preferably from about 4 to about 6 mm. Exemplary fibrillated acrylic fibers are commercially available from Sterling Fibers (Shelton, Conn.) under the trade name CFF®.
In addition to the use of relatively modest amounts of synthetic fiber the tissue products of the present invention are preferably prepared without the addition of binders, particularly latex binders and more specifically carboxyl-functional latex emulsion polymers, such as those described in U.S. Pat. Nos. 6,187,140 and 7,462,258. Latex binders, such as those disclosed in the foregoing references, have been used previously in the manufacture of tissue products to improve wet performance. These binders, however, add manufacturing complexity and cost Therefore, it is desirable to produce a tissue product, such as the inventive tissues, without the use of binders and more especially latex binders.
Further, tissues prepared according to the present disclosure are not treated with a sizing agent, such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA), either during the tissue manufacturing process or after formation and drying of the tissue web. Rather, the tissue webs are prepared by adding synthetic fibers and in certain embodiments a wet strength resin, to the papermaking furnish prior to formation of the web, to enhance the wet-strength properties of the finished web. Unlike conventional sizing agents, which reduce the adsorption rate of water into the sheet, synthetic fibers and conventional wet-strength resins allow the sheet to adsorb water as intended during the end use but maintain sheet integrity and strength when wetted.
Rather than employ latex binders or sizing agents, the tissue products typically comprise a conventional wet-strength resin. Useful conventional wet strength resins include diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), epichlorhydrin resin(s), polyamide-epichlorohydrin (PAE), or any combinations thereof, or any resins to be considered in these families of resins. Particularly preferred wet strength resins are polyamide-epichlorohydrin (PAE) resins. Commonly PAE resins are formed by first reacting a polyalkylene polyamine and an aliphatic dicarboxylic acid or dicarboxylic acid derivative. A polyaminoamide made from diethylenetriamine and adipic acid or esters of dicarboxylic acid derivatives is most common. The resulting polyaminoamide is then reacted with epichlorohydrin. Useful PAE resins are sold under the trade name Kymene® (commercially available from Ashland, Inc., Covington, Ky.).
Generally the conventional wet-strength resin is added to the fiber furnish prior to formation of the tissue web. The amount of the wet-strength resin can be less than about 10 kg per ton of furnish, more preferably less than about 8 kg per ton of furnish and still more preferably less than about 5 kg per ton of furnish. Generally the add-on level of wet-strength resin will be from about 1 to about 10 kg per ton of furnish and more preferably from about 3 to about 8 kg per ton of furnish and still more preferably from about 3 to about 5 kg per ton of furnish.
Although such low add on levels of wet strength are generally not considered to be suitable for achieving exceptional wet performance, such as a CD Wet/Dry Ratio greater than about 0.40, it has now been discovered that combining low levels of wet strength with non-wood synthetic fibers yields tissue products having a CD Wet/Dry Ratio greater than about 0.40 and in certain embodiments greater than about 0.42, such as from about 0.40 to about 0.45. The combination of conventional wet strength resin, such as PAE resins, and synthetic fiber have a synergistic effect. Accordingly, when the CD Wet/Dry Ratio and Wet CD Durability are concerned, the combination of wet-strength resin addition and synthetic fiber according to the invention provides a synergistic effect which has not been disclosed previously. This synergistic effect is valuable, since it makes it possible to achieve a higher wet-strength level without the excessive use of wet-strength resin.
Table 1 illustrates the desirable increase in wet-strength properties that can be achieved via the combination of acrylic fibers and a conventional wet-strength resin. As the table illustrates, at a constant level of wet-strength addition, a higher wet/dry tensile level can be achieved via the addition of the acrylic fiber. The examples of table 1 are tissue samples made via the conventional wet-pressed process.

TABLE 1

Synthetic Fiber	Wet	CD	Delta CD	Wet
(amount by	Strength	Wet/Dry	Wet/Dry	Strength	BW	GMT	MD/CD
weight)	(kg/MT)	Ratio	Ratio (%)	Efficiency	(gsm)	(g/3″)	Ratio

—	3	0.255	—	8.52	39.2	1536	2.13
CFF ® 106-3	3	0.284	11%	9.46	38.9	1680	2.00
(5.1%)
CFF ® 106-3	3	0.303	18%	10.11	39.2	1846	1.87
(17%)

Even more surprising is that the greatest benefit, measured as the relative increase in CD Wet/Dry Ratio, may be achieved by manufacturing the tissue web without compressive dewatering. For example, as illustrated in the table below, the greatest increase in CD Wet/Dry Ratio may be achieved by manufacturing the tissue web by a through-air drying and more specifically uncreped through-air drying.

TABLE 2

	Synthetic
	Fiber	Wet	CD	Delta CD	Wet
Manufacturing	(amount by	Strength	Wet/Dry	Wet/Dry	Strength	BW	GMT	MD/CD
Mode	weight)	(kg/MT)	Ratio	Ratio (%)	Efficiency	(gsm)	(g/3′)	Ratio

CTEC	CFF ® 106-3	10	0.373	28%	3.73	38.4	1968	1.63
	(17%)
UCTAD	CFF ® 106-3	10	0.442	41%	4.42	37.8	1290	1.71
	(17%)

The improvement in wet tensile properties is further evident when the inventive tissue products are compared to commercially available tissue products. As illustrated in the table below, the inventive tissue products display both wet durability, such as a CD Wet/Dry Ratio greater than about 0.40 and good absorbency, such as an Absorbent Capacity greater than about 6.0. In certain aspects the inventive tissue products also have improved Wet CD Durability relative to commercially available tissue products, such as a Wet CD Durability greater than about 2.0.

TABLE 3

				CD
		Wet CD	Wet CD	Wet/		Absorbent
		Tensile	Stretch	Dry	Wet CD	Capacity
Product	Plies	(g/3″)	(%)	Ratio	Durability	(g/g)

Invention	1	436	9.7	0.44	2.22	6.5
Scott	1	855	7.5	0.34	0.88	5.5
Scott Naturals	1	811	11.3	0.33	1.39	4.7
Viva Vantage	1	969	8.2	0.34	0.85	3.9
Bounty	2	1096	10.1	0.35	0.92	8.0
Bounty Dura	2	1062	11.8	0.37	1.11	8.0
Towel
Bounty Basic	1	1040	7.2	0.47	0.69	4.9
Brawny	2	884	5.0	0.34	0.57	9.0
Sparkle	2	611	3.7	0.29	0.61	4.7
Ology	2	160	3.1	0.18	1.94	4.0
Great Value	2	1006	6.0	0.30	0.60	14.1
Up&Up	2	906	5.9	0.30	0.65	14.4
Kirkland	2	956	5.9	0.31	0.62	15.0
Signature

Accordingly, in one embodiment tissue products comprise at least one multi-layered tissue web. Preferably the web comprises three layers where synthetic fibers, and more preferably fibrillated acrylic fibers, are selectively disposed in the middle layer, the tissue product having a CD Wet/Dry Ratio greater than about 0.40 an Absorbent Capacity greater than about 6.0. While in one embodiment it is preferred that the tissue web comprise a three-layered tissue having synthetic fibers selectively incorporated into the middle layer, it should be understood that tissue products made from the foregoing multi-layered web can include any number of plies and the plies may be made from various combinations of single and multi-layered tissue webs. Further, tissue webs prepared according to the present invention may be incorporated into tissue products that may be either single or multi-ply, where one or more of the plies may be formed by a multi-layered tissue web having synthetic fibers selectively incorporated in one of its layers.
As noted previously, the instant tissue products have a high degree of absorbent capacity such as an Absorbent Capacity greater than about 6.0 g/g, such as from about 6.0 to about 7.0 g/g and more preferably from about 6.5 to about 7.0 g/g, while also having a CD Wet/Dry Ratio greater than about 0.40, such as from about 0.40 to about 0.50. Generally the foregoing absorbent capacities and wet strengths are achieved at basis weights from about 30 to about 60 grams per square meter (gsm) and more preferably from about 35 to about 50 gsm and still more preferably from about 40 to about 50 gsm.
In addition to having satisfactory absorbent properties, the tissue products generally have improved wet CD performance. For example, in certain embodiments the tissue products have a Wet CD Durability greater than about 2.0, such as from about 2.0 to about 2.6 and more preferably from about 2.2 to about 2.5. At the foregoing Wet CD Durability levels the tissue products may have a Wet CD Stretch greater than about 8.0 percent, such as from about 8.0 to about 10.0 percent and more preferably from about 9.0 to about 10.0 percent.
While having improved properties, the tissue products prepared according to the present disclosure continue to be strong enough to withstand use by a consumer. For example, inventive tissue products generally have a geometric mean tensile (GMT) greater than about 1200 g/3″, such as from about 1200 to about 3000 g/3″, and more preferably from about 1200 to about 2500 g/3″.
Not only are the instant tissue products absorbent and strong enough to withstand use, they are generally flexible and have good hand feel. As such the tissue products may have a GM Slope less than about 10 kg, such as from about 4 to about 10 kg and more preferably from about 4 to about 6.5 kg. The foregoing GM Slopes are generally achieved at relatively modest GMT, such as from about 1200 to about 2500 g/3″, and more preferably from about 1200 to about 2200 g/3″. At these GM Slopes and GMT, the tissue products may have a Stiffness Index less than about 8.0, such as from about 4.0 to about 8.0 and more preferably from about 4.0 to about 6.0.
In one particularly preferred embodiment the inventive tissue product comprises a single-ply, multi-layered, through-air-dried web, wherein a first layer comprises wood pulp fibers and a second layer comprises fibrillated acrylic fibers, the first layer being substantially free of fibrillated acrylic fibers and the product comprising from about 1 to about 20 percent, by weight, fibrillated acrylic fibers. The tissue product generally has a CD Wet/Dry Ratio greater than about 0.40 an Absorbent Capacity greater than about 6.0, while having a Stiffness Index less than about 6.0, such as from about 4.0 to about 6.0.
Webs useful in preparing tissue products according to the present disclosure can vary depending upon the particular application. In general, in addition to synthetic fibers, the webs can be made from any suitable type of fiber. For instance, the base web can be made from cellulosic fibers, and more preferably cellulosic pulp fibers. Suitable cellulosic fibers for use in connection with this invention include secondary (recycled) papermaking fibers and virgin papermaking fibers in all proportions. Such fibers include, without limitation, hardwood and softwood fibers.
Tissue webs made in accordance with the present disclosure can be made with a homogeneous fiber furnish or can be formed from a stratified fiber fumish producing layers within the single- or multi-ply product. Stratified base webs can be formed using equipment known in the art, such as a multi-layered headbox. Both strength and softness of the base web can be adjusted as desired through layered tissues, such as those produced from stratified headboxes.
For example, in certain embodiments, the tissue products may be prepared from multi-layered webs having a first outer layer and a second outer layer containing primarily hardwood fibers. The hardwood fibers can be mixed, if desired, with paper broke in an amount up to about 10 percent by weight and/or softwood fibers in an amount up to about 10 percent by weight. The web further includes a middle layer positioned in between the first outer layer and the second outer layer. The middle layer can contain a mixture of softwood fibers and synthetic fibers, and more preferably a mixture of northern softwood kraft pulp fibers and fibrillated acrylic fibers. In a particularly preferred embodiment the synthetic fibers are generally selectively incorporated into a single layer and the other layers of the multi-layered web are substantially free from synthetic fibers.
When constructing a web from a stratified fiber furnish, the relative weight of each layer can vary depending upon the particular application. For example, in one embodiment, when constructing a web containing three layers, each layer can be from about 15 to about 40 percent of the total weight of the web, such as from about 25 to about 35 percent of the weight of the web. Generally the synthetic fibers, and more preferably the fibrillated acrylic fibers, will comprise from about 1 to about 20 percent, by weight, of the web.
The tissue products of the present disclosure can generally be formed by any of a variety of papermaking processes known in the art. Preferably the tissue web is formed by through-air drying and be either creped or uncreped. For example, a papermaking process of the present disclosure can utilize adhesive creping, wet creping, double creping, embossing, wet-pressing, air pressing, through-air drying, creped through-air drying, uncreped through-air drying, as well as other steps in forming the paper web. Some examples of such techniques are disclosed in U.S. Pat. Nos. 5,048,589, 5,399,412, 5,129,988 and 5,494,554 all of which are incorporated herein in a manner consistent with the present disclosure. When forming multi-ply tissue products, the separate plies can be made from the same process or from different processes as desired.
In a particularly preferred embodiment at least one web of the tissue product is formed by an uncreped through-air drying process, such as the process described, for example, in U.S. Pat. Nos. 5,656,132 and 6,017,417, both of which are hereby incorporated by reference herein in a manner consistent with the present disclosure.
In one embodiment the web is formed using a twin wire former having a papermaking headbox that injects or deposits a furnish of an aqueous suspension of papermaking fibers onto a plurality of forming fabrics, such as the outer forming fabric and the inner forming fabric, thereby forming a wet tissue web. The forming process of the present disclosure may be any conventional forming process known in the papermaking industry. Such formation processes include, but are not limited to, Fourdriniers, roof formers such as suction breast roll formers, and gap formers such as twin wire formers and crescent formers.
The wet tissue web forms on the inner forming fabric as the inner forming fabric revolves about a forming roll. The inner forming fabric serves to support and carry the newly-formed wet tissue web downstream in the process as the wet tissue web is partially dewatered to a consistency of about 10 percent based on the dry weight of the fibers. Additional dewatering of the wet tissue web may be carried out by known paper making techniques, such as vacuum suction boxes, while the inner forming fabric supports the wet tissue web. The wet tissue web may be additionally dewatered to a consistency of greater than 20 percent, more specifically between about 20 to about 40 percent, and even more specifically between about 20 to about 30 percent.
The forming fabric can generally be made from any suitable porous material, such as metal wires or polymeric filaments. For instance, some suitable fabrics can include, but are not limited to, Albany 84M and 94M available from Albany International (Albany, N.Y.); Asten 856, 866, 867, 892, 934, 939, 959, or 937; Asten Synweve Design 274, all of which are available from Asten Forming Fabrics, Inc. (Appleton, Wis.); and Voith 2164 available from Voith Fabrics (Appleton, Wis.).
The wet web is then transferred from the forming fabric to a transfer fabric while at a solids consistency of between about 10 to about 35 percent, and particularly, between about 20 to about 30 percent. As used herein, a “transfer fabric” is a fabric that is positioned between the forming section and the drying section of the web manufacturing process.
Transfer to the transfer fabric may be carried out with the assistance of positive and/or negative pressure. For example, in one embodiment, a vacuum shoe can apply negative pressure such that the forming fabric and the transfer fabric simultaneously converge and diverge at the leading edge of the vacuum slot. Typically, the vacuum shoe supplies pressure at levels between about 10 to about 25 inches of mercury. As stated above, the vacuum transfer shoe (negative pressure) can be supplemented or replaced by the use of positive pressure from the opposite side of the web to blow the web onto the next fabric. In some embodiments, other vacuum shoes can also be used to assist in drawing the fibrous web onto the surface of the transfer fabric.
Typically, the transfer fabric travels at a slower speed than the forming fabric to enhance the MD and CD stretch of the web, which generally refers to the stretch of a web in its cross (CD) or machine direction (MD) (expressed as percent elongation at sample failure). For example, the relative speed difference between the two fabrics can be from about 30 to about 70 percent and more preferably from about 40 to about 60 percent. This is commonly referred to as “rush transfer”. During rush transfer many of the bonds of the web are believed to be broken, thereby forcing the sheet to bend and fold into the depressions on the surface of the transfer fabric. Such molding to the contours of the surface of the transfer fabric may increase the MD and CD stretch of the web. Rush transfer from one fabric to another can follow the principles taught in any one of the following patents, U.S. Pat. Nos. 5,667,636, 5,830,321, 4,440,597, 4,551,199, 4,849,054, all of which are hereby incorporated by reference herein in a manner consistent with the present disclosure.
The wet tissue web is then transferred from the transfer fabric to a through-air drying fabric. Typically, the transfer fabric travels at approximately the same speed as the through-air drying fabric. However, a second rush transfer may be performed as the web is transferred from the transfer fabric to the through-air drying fabric. This rush transfer is referred to as occurring at the second position and is achieved by operating the through-air drying fabric at a slower speed than the transfer fabric.
In addition to rush transferring the wet tissue web from the transfer fabric to the through-air drying fabric, the wet tissue web may be macroscopically rearranged to conform to the surface of the through-air drying fabric with the aid of a vacuum transfer roll or a vacuum transfer shoe. If desired, the through-air drying fabric can be run at a speed slower than the speed of the transfer fabric to further enhance MD stretch of the resulting absorbent tissue product. The transfer may be carried out with vacuum assistance to ensure conformation of the wet tissue web to the topography of the through-air drying fabric.
While supported by a through-air drying fabric, the wet tissue web is dried to a final consistency of about 94 percent or greater by a through-air dryer. The web then passes through the winding nip between the reel drum and the reel and is wound into a roll of tissue for subsequent converting.

Test Methods

Wet and Dry Tensile

Samples for tensile strength testing are prepared by cutting a 3 inches (76.2 mm) by 5 inches (127 mm) long strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (Thwing-Albert Instrument Company, Philadelphia, Pa., Model No. JDC 3-10, Ser. No. 37333). The instrument used for measuring tensile strengths is an MTS Systems Sintech 11S, Serial No. 6233. The data acquisition software is MTS TestWorks™ for Windows Ver. 4 (MTS Systems Corp., Research Triangle Park, N.C.). The load cell is selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, such that the majority of peak load values fall between 10 and 90 percent of the load cell's full scale value. The gauge length between jaws is 4±0.04 inches. The jaws are operated using pneumatic-action and are rubber coated. The minimum grip face width is 3 inches (76.2 mm), and the approximate height of a jaw is 0.5 inches (12.7 mm). The crosshead speed is 10±0.4 inches/min (254±1 mm/min), and the break sensitivity is set at 65 percent. The sample is placed in the jaws of the instrument, centered both vertically and horizontally. The test is then started and ends when the specimen breaks. The peak load is recorded as either the “MD tensile strength” or the “CD tensile strength” of the specimen depending on the sample being tested. At least six (6) representative specimens are tested for each product, taken “as is,” and the arithmetic average of all individual specimen tests is either the MD or CD tensile strength for the product.
Wet tensile strength measurements are measured in the same manner, but after the center portion of the previously conditioned sample strip has been saturated with distilled water immediately prior to loading the specimen into the tensile test equipment. More specifically, prior to performing a wet CD tensile test, the sample must be aged to ensure the wet strength resin has cured. Two types of aging were practiced: natural and artificial. Natural aging was used for older samples that had already aged. Artificial aging was used for samples that were to be tested immediately after or within days of manufacture. For natural aging, the samples were held at 73° F., 50 percent relative humidity for a period of 12 days prior to testing. Following this natural aging step, the strips are then wetted individually and tested. For artificially aged samples, the 3-inch wide sample strips were heated for 4 minutes at 105±2° C. Following this artificial aging step, the strips are then wetted individually and tested. Sample wetting is performed by first laying a single test strip onto a piece of blotter paper (Fiber Mark, Reliance Basis 120). A pad is then used to wet the sample strip prior to testing. The pad is a green, Scotch-Brite brand (3M) general purpose commercial scrubbing pad. To prepare the pad for testing, a full-size pad is cut approximately 2.5 inches long by 4 inches wide. A piece of masking tape is wrapped around one of the 4-inch long edges. The taped side then becomes the “top” edge of the wetting pad. To wet a tensile strip, the tester holds the top edge of the pad and dips the bottom edge in approximately 0.25 inches of distilled water located in a wetting pan. After the end of the pad has been saturated with water, the pad is then taken from the wetting pan and the excess water is removed from the pad by lightly tapping the wet edge three times across a wire mesh screen. The wet edge of the pad is then gently placed across the sample, parallel to the width of the sample, in the approximate center of the sample strip. The pad is held in place for approximately one second and then removed and placed back into the wetting pan. The wet sample is then immediately inserted into the tensile grips so the wetted area is approximately centered between the upper and lower grips. The test strip should be centered both horizontally and vertically between the grips. (It should be noted that if any of the wetted portion comes into contact with the grip faces, the specimen must be discarded and the jaws dried off before resuming testing.) The tensile test is then performed and the peak load recorded as the CD wet tensile strength of this specimen. As with the dry CD tensile test, the characterization of a product is determined by the average of at least six, but in the case of the examples disclosed, twenty representative sample measurements.

Absorbency

As used herein, “vertical absorbent capacity” is a measure of the amount of water absorbed by a paper product (single ply or multi-ply) or a sheet, expressed as grams of water absorbed per gram of fiber (dry weight). In particular, the vertical absorbent capacity is determined by cutting a sheet of the product to be tested (which may contain one or more plies) into a square measuring 100 millimeters by 100 millimeters (±1 mm.) The resulting test specimen is weighed to the nearest 0.01 gram and the value is recorded as the “dry weight.” The specimen is attached to a 3-point clamping device and hung from one corner in a 3-point clamping device such that the opposite corner is lower than the rest of the specimen, then the sample and the clamp are placed into a dish of water and soaked in the water for 3 minutes (±5 seconds). The water should be distilled or de-ionized water at a temperature of 23±3° C. At the end of the soaking time, the specimen and the clamp are removed from the water. The clamping device should be such that the clamp area and pressure have minimal effect on the test result. Specifically, the clamp area should be only large enough to hold the sample and the pressure should also just be sufficient for holding the sample, while minimizing the amount of water removed from the sample during clamping. The sample specimen is allowed to drain for 3 minutes (±5 seconds). At the end of the draining time, the specimen is removed by holding a weighing dish under the specimen and releasing it from the clamping device. The wet specimen is then weighed to the nearest 0.01 gram and the value recorded as the “wet weight”. The vertical absorbent capacity in grams per gram=[(wet weight−dry weight)/dry weight]. At least five (5) replicate measurements are made on representative samples from the same, roll or box of product to yield an average vertical absorbent capacity value.

Examples

Base sheets were made using a through-air dried papermaking process commonly referred to as “uncreped through-air dried” (“UCTAD”) and generally described in U.S. Pat. No. 5,607,551, the contents of which are incorporated herein in a manner consistent with the present invention. Inventive base sheets were produced from a furnish comprising northern softwood kraft, eucalyptus kraft and fibrillated acrylic fibers using a layered headbox fed by three stock chests such that the webs having three layers (two outer layers and a middle layer) were formed. The outer layers comprised 100 percent eucalyptus kraft fiber for both the control and inventive samples. The center layer was 100 percent northern softwood kraft fiber for the control sample; for the inventive sample, the center layer was a 50/50 blend of northern softwood kraft and fibrillated acrylic fibers. The layer splits, by weight of the web, are detailed in Table 4, below. Fibrillated acrylic fibers were CFF® 106-3 (commercially available from Sterlingfibers Shelton, Conn.).
The tissue web was formed on a Voith Fabrics TissueForm V forming fabric, vacuum dewatered to approximately 25 percent consistency and then subjected to rush transfer when transferred to the transfer fabric. The layer splits, by weight of the web, are detailed in Table 4, below. The transfer fabric was the fabric described as t1207-11 (commercially available from Voith Fabrics, Appleton, Wis.). The web was then transferred to a through-air drying fabric. Transfer to the through-drying fabric was done using vacuum levels of greater than 10 inches of mercury at the transfer. The web was then dried to approximately 98 percent solids before winding.

TABLE 4

	Layer Split	Synthetic Fiber	Wet Strength
Sample	(Air/Middle/fabric Wt %)	(Wt %)	(kg/MT)

Control	33/34/33	—	10
Inventive 1	33/34/33	17%	10

The base sheet webs were converted into rolled towel products by calendering using a conventional polyurethane/steel calender comprising a 4 P&J polyurethane roll on the air side of the sheet and a standard steel roll on the fabric side. The finished product comprised a single ply of base sheet. The finished products were subjected to physical testing, the results of which are summarized in Table 5.

	TABLE 5

	Control	Inventive 1

BW (gsm)	38.4	37.8
Wet CDT (g/3″)	482	436
Wet CDS (%)	8.46	9.69
Wet CD TEA (g*cm/cm²)	2.92	2.77
Wet CD Durability	1.76	2.22
CD Wet/Dry	0.313	0.442
Absorbent Capacity (g/g)	6.64	6.49
Wet Strength Efficiency	3.13	4.42
GMT (g/3″)	1968	1290
Dry CDT (g/3″)	1541	986
Dry MDT (g/3″)	2513	1688
Dry CD Slope (kg)	5.68	4.02
Dry MD Slope (kg)	9.26	8.68
Dry GM Slope (kg)	7.25	5.91
Stiffness Index	3.68	4.58

The foregoing is one example of an inventive tissue product prepared according to the present disclosure. In other embodiments the disclosure provides a tissue product, free from latex binder, having an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.
In another embodiment the disclosure provides a tissue product of the foregoing embodiment having a Wet CD Durability of greater than about 2.0.
In yet another embodiment the disclosure provides a tissue product of any one of the foregoing embodiments having an Absorbent Capacity from about 6.5 to about 7.0 g/g and a CD Wet/Dry Ratio from about 0.42 to about 0.50.
In still another embodiment the disclosure provides a tissue product of any one of the foregoing embodiments having a GMT from about 1200 to about 2600 g/3″.
In yet another embodiment the disclosure provides a tissue product of any one of the foregoing embodiments having a Stiffness Index from about 4.0 to about 6.0.
In another embodiment the disclosure provides a tissue product of any one of the foregoing embodiments having a basis weight from about 36 to about 50 gsm.
In still other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments having wet CD stretch greater than about 8.0 percent, such as from about 8.0 to about 10.0 percent.
In other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments wherein the tissue product comprises a single-ply multi-layered web having a first, a second and a third layer.
In still other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments wherein the tissue product comprises from about 1 to about 20 percent, by weight of the tissue product, hydrophobic synthetic fiber. In certain embodiments the hydrophobic synthetic fiber comprises fibrillated acrylic fiber and more specifically a fiber comprising at least about 85 percent PAN.
In other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments wherein the tissue product comprises at least one through-air dried tissue web.
In yet other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments wherein the tissue product comprises at least one multi-layered through-air dried tissue web.
In still other embodiments the disclosure provides a tissue product of any one of the foregoing embodiments wherein the tissue product comprises at least one multi-layered through-air dried tissue web comprising a first fibrous layer and a second fibrous layer, the first fibrous layer comprising wood pulp fibers and the second layer comprising fibrillated acrylic fibers, wherein the first fibrous layer is substantially free of fibrillated acrylic fibers and wherein the fibrillated acrylic fibers comprise from about 1 to about 20 percent of the total weight of the through-air dried web.

Claims

What is claimed is:

1. A tissue product, free from latex binder, having an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.

2. The tissue product of claim 1 having a Wet CD Durability of greater than about 2.0.

3. The tissue product of claim 1 having an Absorbent Capacity from about 6.5 to about 7.0 g/g and a CD Wet/Dry Ratio from about 0.42 to about 0.50.

4. The tissue product of claim 1 having a GMT from about 1200 to about 2600 g/3″.

5. The tissue product of claim 4 having a Stiffness Index from about 4.0 to about 6.0.

6. The tissue product of claim 1 wherein the tissue product comprises a single-ply multi-layered web having a first, a second and a third layer.

7. The tissue product of claim 6 wherein at least one layer comprises from about 1 to about 20 percent, by weight of the tissue product, hydrophobic synthetic fiber.

8. The tissue product of claim 7 wherein the hydrophobic synthetic fiber comprises fibrillated acrylic fiber.

9. The tissue product of claim 8 wherein the fibrillated acrylic fiber comprises at least about 85 percent PAN.

10. A through-air dried tissue product comprising from about 1 to about 20 percent, by weight of the product, fibrillated acrylic fibers, the tissue product having an Absorbent Capacity greater than about 6.0 g/g and a CD Wet/Dry Ratio greater than about 0.40.

11. The tissue product of claim 10 having a Wet CD Durability of greater than about 2.0.

12. The tissue product of claim 10 having an Absorbent Capacity from about 6.5 to about 7.0 g/g and a CD Wet/Dry Ratio from about 0.42 to about 0.50.

13. The tissue product of claim 10 having a GMT from about 1200 to about 2600 g/3″.

14. The tissue product of claim 10 having a Stiffness Index from about 4.0 to about 6.0.

15. The tissue product of claim 10 wherein the tissue product comprises a single-ply multi-layered web having a first, a second and a third layer.

16. The tissue product of claim 15 wherein the first and third layers consist essentially of wood pulp fibers and are substantially free from fibrillated acrylic fibers and the fibrillated acrylic fibers are selectively disposed in the second layer.

17. The tissue product of claim 10 wherein the fibrillated acrylic fiber comprises at least about 85 percent PAN.

18. A layered through-air dried tissue product comprising at least one tissue web comprising a first fibrous layer and a second fibrous layer, the first fibrous layer comprising wood pulp fibers and the second layer comprising fibrillated acrylic fibers, wherein the first fibrous layer is substantially free of fibrillated acrylic fibers and wherein the fibrillated acrylic fibers comprise from about 1 to about 20 percent of the total weight of the through-air dried web, the tissue product having a CD Wet/Dry Ratio greater than about 0.40.

19. The layered through-air dried tissue product of claim 18 having a Wet CD Durability of greater than about 2.0.

20. The layered through-air dried tissue product of claim 18 having an Absorbent Capacity from about 6.5 to about 7.0 g/g and a CD Wet/Dry Ratio from about 0.42 to about 0.50.