US20060144541A1

US20060144541A1 - Softening agent pre-treated fibers

Info

Publication number: US20060144541A1
Application number: US11/027,617
Authority: US
Inventors: Deborah Joy Nickel; Troy Runge
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 2004-12-30
Filing date: 2004-12-30
Publication date: 2006-07-06
Also published as: WO2006073536A1; MX2007008101A

Abstract

A paper product includes fibers, such as cellulosic fibers, that are pre-treated with a softening agent. The softening agent is added to a fiber slurry and then is allowed to cure onto the fibers, typically by drying. The pre-treated fibers are then diluted, re-slurried, and incorporated into the fiber stream of a paper machine to form a fibrous web. The fibrous web can then be converted into a paper product, such as a personal care paper product, which exhibits improved softness with minimized slough.

Description

BACKGROUND

The invention generally concerns paper products and properties thereof. More particularly, in the manufacture of personal care paper products, such as facial tissues, bath tissues, napkins, wipes, and paper towels, it is often desired to optimize various aesthetic and performance related properties. For example, personal care products should generally exhibit a soft feel, low slough, good bulk, and sufficient strength to perform the desired functions.
Unfortunately, when steps are taken to increase one of these properties, other such properties may also be adversely affected. For instance, softness is an important aesthetic property of many personal care paper products, so it is desirable in the art to develop products which exhibit improved softness. One conventional method for improving softness in such products is to apply a chemical debonder to the fiber-water suspension in the wet-end section of a paper machine. Another conventional method is to spray such a chemical debonder directly onto the fibrous web in the forming section of a paper machine. In either case, the chemical debonder interrupts the bonding which would normally take place between the fibers, which reduces the overall strength of the fibrous web. This reduction in strength corresponds directly to an increase in softness.
However, this same reduction in strength also leads to an increase in slough, which is generally undesirable for personal care products. For example, during processing and/or use, the loosely bound (i.e., debonded) fibers can be freed from the paper product, thereby creating airborne fibers and fiber fragments. Moreover, zones of fibers that are poorly bound to each other but not to adjacent zones of fibers may be created which can break away from the paper surface and then can deposit onto other surfaces, such as human skin or clothing. Therefore, there is a desire for a paper product which exhibits improved softness while minimizing the level of slough.

SUMMARY

The invention concerns a paper product and properties thereof. More particularly, the invention concerns a soft, low slough paper product which comprises at least a quantity of cellulosic fibers which have been pre-treated with a softening agent, then allowed to cure, and then diluted and incorporated into a paper machine's fiber stream. In one embodiment, the pre-treated fibers exhibit a Water Retention Value below 0.9 g/g. In another embodiment, the fibers have a degree of curl that is less than 1.3.
The resulting paper product can comprise about 10% to about 100% pre-treated fibers, such as about 10% to about 50% pre-treated fibers. The paper product can also comprise a single layer or multiple layers of pre-treated and/or untreated fibers. In one embodiment, the tensile strength of a fibrous web comprising pre-treated fibers is reduced by 50% as compared to the same fibrous web consisting of untreated fibers.
Numerous other features and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which help illustrate exemplary embodiments of the invention. Such embodiments do not represent the full scope of the invention. Reference should therefore be made to the claims herein for interpreting the full scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where:
FIG. 1 illustrates one embodiment of a dry-lap machine that can be used for pre-treating fibers with a softening agent;
FIG. 2 illustrates one embodiment of a paper machine that can be used to form a fibrous web comprising at least pre-treated fibers made in accordance with the present invention;
FIG. 3 illustrates one embodiment of a headbox that can be used in accordance with the present invention;
FIG. 4 a illustrates an apparatus for testing slough; and
FIG. 4 b is a perspective view of the abrasive spindle of FIG. 4 a.
Repeated use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.
Definitions
It should be noted that, when employed in the present disclosure, the terms “comprises,” “comprising” and other derivatives from the root term “comprise” are intended to be open-ended terms that specify the presence of any stated features, elements, integers, steps, or components, and are not intended to preclude the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof.
The terms “additive” and “chemical additive” refer to a single treatment compound or to a mixture of treatment compounds.
The terms “cure,” “cured,” “curing” and other derivatives of the term “cure” refer to the drying of fibers that have been pre-treated with a softening agent of the present invention such that the softening agent substantially adheres to and retains to such fibers through a papermaking process and paper converting process. The dryness required to cure the softening agent(s) onto the fibers will vary depending on the softening agent(s) utilized. However, in general, the pre-treated fibers may be dried to a consistency of at least about 80% by weight.
The term “nits” refers to fiber/polymer bundles that create the appearance of white spots within a fibrous web and/or paper product. These white spots will generally be on the order of one square millimeter in size or greater. A “nit count” refers to the number of nits counted in a 7.5 inch by 7.5 inch sample of a fibrous web and/or paper product made from pre-treated pulp fibers. The fibrous web and/or paper product should have a nit count of about 10 or less, more specifically about 5 or less, and still more specifically about 3 or less.
The term “personal care paper product” is used herein to broadly include tissue such as bath tissue, facial tissue, napkins, wipers, and towels, along with other cellulose structures including absorbent pads, intake webs in absorbent articles such as diapers, bed pads, wet wipes, meat and poultry pads, feminine care pads, and the like made in accordance with any conventional process for the production of such products. The term “paper” as used herein includes any fibrous web containing cellulosic fibers alone or in combination with other fibers, natural or synthetic. A paper product can be layered or unlayered, creped or uncreped, and can comprise a single ply or multiple plies. In addition, the paper product can contain reinforcing fibers for integrity and strength.
The term “slough” refers to the loss of paper particles from the surface of the paper due to surface abrasion. Slough tends to increase when conventional softening techniques, such as the use of chemical debonders, are utilized in the wet-end section of a paper machine. In general, slough is an undesirable property for personal care paper products. For example, many consumers react negatively to paper that exhibits a high level of slough. Therefore, it is a desire to provide a paper product that exhibits a minimal amount of slough.
The term “softening agent” refers to chemical additives that can be incorporated into paper products to provide improved softness and tactile feel. These chemical additives can also act to reduce paper stiffness and paper strength, and can act solely to improve the surface characteristics of tissue, such as by reducing the coefficient of friction between the paper surface and a person's hand.
The term “water” refers to water or a solution containing water and other treatment additives desired in the papermaking process.
These terms may be defined with additional language in the remaining portions of the specification.

DETAILED DESCRIPTION

The present invention concerns a paper product, such as a personal care paper product, and properties thereof. Generally stated, the present invention is directed to a paper product that, among other things, exhibits an improved level of softness and which minimizes slough. In particular, the paper product includes fibers that are pre-treated with a softening agent wherein the softening agent has been cured onto the fibers, and wherein the fibers are then diluted and incorporated into the fiber stream of a paper machine.
Personal care paper products can generally be formed in accordance with the present invention from at least one fibrous web. For example, in one aspect, the paper product can contain a single-layered fibrous web formed from a blend of pre-treated and untreated fibers. In another aspect, the paper product can contain a multi-layered (i.e., stratified) fibrous web wherein at least one layer comprises at least pre-treated fibers, and at least one layer comprises at least untreated fibers. Furthermore, the paper product itself can be constructed from a single fibrous web or from multiple fibrous webs. In one particular aspect, at least one fibrous web in the paper product comprises pre-treated fibers according to the present invention.
In general, the basis weight of a fibrous web of the present invention is less than about 200 grams per square meter (gsm), such as between about 5 and about 120 gsm or between about 10 and about 70 gsm. Fibers that are suitable for the invention include cellulosic fibers such as hardwood fibers, softwood fibers, recycled fibers, and the like, as well as synthetic fibers. Such fibers can be formed by a variety of pulping processes, including Kraft, sulfite, mechanical, thermomechanical, and chemithermomechanical pulping processes, and the like. In one example, the paper product includes a fibrous web having at least one layer formed primarily from pre-treated Kraft hardwood fibers.
Hardwood fibers such as Eucalyptus, maple, birch, and aspen typically have an average fiber length of about 0.5 mm to about 1.5 mm and exhibit relatively large diameters (as compared to softwood fibers). As such, hardwood fibers may be more useful for enhancing the softness of a fibrous web than softwood fibers. Therefore, it may be desirable to provide at least one outer surface of a paper product which comprises substantially hardwood fibers. However, when conventional methods are utilized to enhance softness, such as through the addition of a chemical debonder in the wet-end section of a paper machine, fibrous webs containing hardwood fibers tend to result in substantially higher levels of slough.
In contrast, softwood fibers such as northern softwood, southern softwood, redwood, cedar, hemlock, pine, and spruce typically have an average fiber length of about 1.5 mm to about 3 mm with relatively small diameters (as compared to hardwood). As such, softwood fibers may be more useful for enhancing the strength of a fibrous web than hardwood fibers. However, softwood fibers substantially reduce the softness of a fibrous web. In addition, softwood fibers can also result in increased levels of slough when conventional methods are used to enhance softness. Therefore, softwood fibers are typically blended with hardwood fibers, or may be used as an inner layer in a multi-layered fibrous web.
If desired, secondary fibers obtained from recycled materials may also be utilized in a paper product of the invention. Such secondary fibers can be obtained from sources including old newsprint, reclaimed paperboard, envelopes, and mixed office waste. Additionally, other natural fibers can be utilized in the present invention, such as abaca, sabai grass, milkweed floss, pineapple leaf, and the like. Furthermore, in some instances, synthetic fibers can also be utilized, such as rayon fibers, ethylene vinyl alcohol copolymer fibers, polyolefin fibers, polyesters, and the like.
Suitable cellulosic fibers for the present invention can include, for example, ARACRUZ ECF, a Eucalyptus hardwood Kraft pulp available from Aracruz, a business having offices located in Rio de Janeiro, RJ, Brazil; LONGLAC-19, a northern softwood Kraft pulp available from Neenah Paper Incorporated, a business having offices located in Alpharetta, Ga., U.S.A.; NB 416, a bleached southern softwood Kraft pulp, available from Weyerhaeuser Co., a business having offices located in Federal Way, Wash., U.S.A.; CR 54, a bleached southern softwood Kraft pulp, available from Bowater Inc., a business having offices located in Greenville, S.C., U.S.A.; SULPHATATE HJ, a chemically modified hardwood pulp, available from Rayonier Inc., a business having offices located in Jesup, Ga., U.S.A.; NF 405, a chemically treated bleached southern softwood Kraft pulp, available from Weyerhaeuser Co.; and CR 1654, a mixed bleached southern softwood and hardwood Kraft pulp, available from Bowater Inc.
As referenced above, a paper product of the present invention can be formed from one or more fibrous webs, each of which can be single-layered or multi-layered. For instance, in one aspect, the paper product can comprise a single-layered paper web that is formed from a blend of fibers. For example, in some instances, Eucalyptus and softwood fibers can be homogeneously blended to form the single-layered paper web. In another aspect, the paper product can contain a multi-layered paper web that is formed from a stratified pulp furnish having various principal layers. In one particular aspect, the fibrous web can comprise three layers wherein at least one of the outer layers includes pre-treated Eucalyptus fibers, while at least the inner layer includes untreated northern softwood Kraft fibers. In another aspect, the fibrous web can comprise two layers wherein one layer comprises pre-treated hardwood Kraft fibers, while the remaining outer layer comprises a blend of untreated northern softwood Kraft fibers and untreated synthetic fibers. In still another aspect, the fibrous web can comprise three layers wherein at least one of the outer layers includes a blend of pre-treated hardwood fibers and untreated softwood fibers, while the inner layer comprises untreated recycled fibers. It should be understood that a multi-layered paper web can include any number of layers and can be made from various types of fibers.
In accordance with the present invention, various properties of a paper product such as described above, can be optimized. For instance, softness, slough level, strength (e.g., tensile index), bulk and the like, are some examples of properties which may be optimized in accordance with the present invention. However, it should be understood that not every property mentioned above needs be optimized in every instance. For example, in certain applications, it may be desired to form a paper product that has optimized softness without regard to strength.
For purposes of the invention, the process of pre-treating fibers with a suitable softening agent can be accomplished by first adding a softening agent to a slurry or a web of fibers, then allowing the combination to dry to at least about 80% consistency such that the softening agent cures onto the fibers, and then diluting the fibers with water, re-slurrying the fibers, and incorporating the pre-treated fibers into the fiber stream of a papermaking process. The result is a paper product which exhibits an increased level of softness while minimizing the level of slough. Without being bound by a particular theory, it is believed that pre-treating fibers with a softening agent in accordance with the invention results in fibers that can have areas of high strength while decreasing the overall bonded area between the fibers. More particularly, it is believed that the overall bonded area is decreased due to the pre-treated fibers' inability to conform to neighboring fibers (i.e., less flexibility), thus creating more voids between the fibers during the papermaking process.
Suitable softening agents should have the ability to cure onto the fibers, and should allow the fibers to be re-slurried substantially without nits. In some aspects, the softening agent can decrease the contact angle of the fiber and/or prevent the fiber from swelling through mechanisms such as cross-linking. In other aspects, the softening agent can decrease the overall bonding potential of the fibers without decreasing the surface fiber tension of the fiber-water suspension. In still other aspects, the softening agent can decrease the strength of a fibrous web formed from the pre-treated fibers by at least about 30%, such as at least about 50%, as compared to a similar web consisting of untreated fibers. In yet other aspects, fibrous webs comprising pre-treated fibers can exhibit a Water Retention Value of about 0.9 g/g or less.
Without being held to a particular theory, it is believed that suitable softening agents used for pre-treating fibers in accordance with the present invention result in fibers that are more resilient to compression when wet. This, in turn, can prevent full bonding of such fibers to neighboring fibers in a fiber-water suspension, and thus increases softness of a resulting paper product. Additionally, higher bulk may be obtained in wet-pressed webs because such pre-treated fibers can resist compression from a pressure roll on a paper machine. Furthermore, it is believed that the pre-treated fibers tend not to debond through reduction of surface tension, thus unretained resin would tend not to have an adverse effect on other fibers, such as those used for the purpose of increasing strength.
Suitable softening agents include wet strength resins, sizing agents, latex emulsions, cross-linking agents, and thermoplastics, as well as other additives. In general, wet strength resins are typically used to impart mechanical strength to a paper product under wet conditions without adversely affecting absorbency properties. However, as used in accordance with the present invention, wet strength resin can result in a personal care paper product which exhibits improved softness while minimizing slough. Suitable wet strength resins can be temporary or permanent, and can be cationic, anionic, or nonionic.
Examples of suitable temporary wet strength resins include, but are not limited to, cationic glyoxylated polyacrylamides such as those under the trade name PAREZ 631 NC and PAREZ 725, available from Cytec Industries Inc., a business having offices located in West Paterson, N.J., U.S.A. and HERCOBOND 1366, available from Hercules Inc., a business having offices located in Wilmington, Del., U.S.A. Other similar resins are described in U.S. Pat. No. 3,556,932 to Williams et al., herein incorporated by reference in a manner consistent with the present disclosure. Still other suitable temporary wet strength resins include dialdehyde starches, such as those under the trade name COBOND 1000, available from National Starch and Chemical Company, a business having offices located in Bridgewater, N.J., U.S.A. as well as those described in U.S. Pat. No. 6,224,714 to Schroeder et al.; U.S. Pat. No. 6,274,667 to Shannon et al.; U.S. Pat. No. 6,287,418 to Schroeder et al.; U.S. Pat. No. 6,365,667 to Shannon et al. U.S. Pat. No. 4,675,394 to Solarek et al., and Japanese Kokai Tokkyo Koho JP 03,185,197, all of which are herein incorporated by reference in a manner consistent with the present disclosure. Still other suitable temporary wet strength resins include, but are not limited to, dialdehyde starch, polyethylene imine, mannogalactan gum, glyoxal, and dialdehyde mannogalactan. Other suitable temporary wet-strength agents are described in U.S. Pat. No. 3,556,932 to Coscia et al.; U.S. Pat. No. 5,466,337 to Darlington, et al.; U.S. Pat. No. 3,556,933 to Williams et al.; U.S. Pat. No. 4,605,702 to Guerro et al.; U.S. Pat. No. 4,603,176 to Bjorkquist et al.; U.S. Pat. No. 5,935,383 to Sun, et al.; and U.S. Pat. No. 6,017,417 to Wendt, et al., all of which are herein incorporated by reference in a manner consistent with the present disclosure.
Examples of suitable permanent wet strength resins include, but are not limited to, cationic oligomeric or polymeric resins, as well as those described in U.S. Pat. No. 2,345,543 to Wohnsiedler et al.; U.S. Pat. No. 2,926,116 to Keim; and U.S. Pat. No. 2,926,154 to Keim. Other suitable permanent wet strength agents include polyamine-epichlorohydrin, polyamide epichlorohydrin or polyamide-amine epichlorohydrin resins, which are collectively termed “PAE resins.” These materials have been described in U.S. Pat. No. 3,700,623 to Keim; U.S. Pat. No. 3,772,076 to Keim; U.S. Pat. No. 3,855,158 to Petrovich et al.; U.S. Pat. No. 3,899,388 to Petrovich et al.; U.S. Pat. No. 4,129,528 to Petrovich et al.; U.S. Pat. No. 4,147,586 to Petrovich et al.; and U.S. Pat. No. 4,222,921 to Van Eenam, all of which are herein incorporated by reference in a manner that is consistent with this disclosure. Still other suitable permanent wet strength resins included polyethyenimine resins and aminoplast resins obtained by reaction of formaldehyde with melamine or urea. In one example of the present invention KYMENE 6500, a polyamide-polyamine-epichlorohydrin commercially available from Hercules Inc. is utilized as the softening agent. Other commercially available resins include KYMENE 557H and KYMENE 557LX, also from Hercules Inc. In some aspects, it is advantageous to utilize both permanent and temporary wet strength resins for pre-treating the fiber.
As mentioned above, sizing agents can also be utilized as the softening agent. In general, sizing agents are typically used in non-absorbent paper products, such as fine paper, to control excess penetration of coating formulations and ink, reduce bleed-through for improved print quality, and improve opacity. However, when used in accordance with the present invention, sizing agents can result in a personal care paper product which exhibits improved softness while minimizing slough. Suitable sizing agents can be natural or synthetic, and can be cationic, anionic, or nonionic. Suitable natural sizing agents include, but are not limited to, rosins and modified and unmodified natural starches such as reserve polysaccharides found in plants (e.g., corn, wheat, potato and the like) that can have linear (amylose) and/or branched (amylopectin) polymers of alpha-D-glucopyranosyl units. Suitable synthetic sizing agents include, but are not limited to, synthetic copolymers such as polyvinyl alcohol and styrene, as well as other cellulose-reactive sizes including alkenyl succinic anhydride and alkyl ketene dimer. In one example of the invention, HERCON 70 sizing agent, an alkyl ketene dimer commercially available from Hercules Inc., is utilized as the softening agent.
As mentioned above, latex emulsions can also be utilized as the softening agent. In general, latex emulsions are typically used in coatings for fine paper, publication paper and coated paperboard used in packaging, such as for improved printing performance. However, when used in accordance with the present invention, latex emulsions can result in a personal care paper product which exhibits improved softness while minimizing slough. For purposes of the present invention, latex emulsions can be used on there own, or in conjunction with another polymer to form a latex emulsion complex. Suitable latex emulsions include AIRFLEX 124, AIRFLEX 426, and AIRFLEX EN1165, all available from Air Products, a business having offices in Allentown, Pa., U.S.A., and RESYN 225A, available from National Starch, a business having offices in Chicago, Ill., U.S.A. In one example of the present invention, a latex emulsion complex containing an anionic styrene butadiene latex emulsion at a solids content of about 50% by weight under the trade name LATRIX 6300, available from Nalco Company, a business having offices in Naperville, Ill., U.S.A. combined with a quaternary amine imidazoline softener at a solids content of about 80% by weight under the trade name PROSOFT TQ-1003, available from Hercules Inc., is utilized as the softening agent.
As mentioned above, cross-linking agents can also be utilized as the softening agent. In general, cross-linking agents are typically used to impart high strength in paper products which may be subjected to rigorous wet conditions, such as filtering paper. However, when used in accordance with the present invention, cross-linking agents can result in a personal care paper product which exhibits improved softness while minimizing slough. Suitable cross-linking agents include, but are not limited to, styrene-butadiene copolymers, polyvinyl acetate copolymers, vinyl-acetate acrylic copolymers, ethylene-vinyl chloride copolymers, acrylic polymers, nitrile polymers, dispersed polyolefins, diols, polyols, diamines, polyamines, dicarboxylic acids, polycarboxylic acids, dialdehydes, polyaldehydes, butandiol, diethylene triamine, citric acid, glutaric dialdehyde and ethylene glycol diglycidyl ether, tri-valent or tetra-valent metal ions, and combinations thereof.
The amount of softening agent added for pre-treating fibers in accordance with the present invention will vary depending upon the softening agent chosen. For example, in one aspect, a wet strength resin such as KYMENE 6500 can be utilized in an amount ranging from about 0.1 to about 10 dry kilograms/oven dry metric-ton (kg/ODMT) of fiber, such about 1 to about 2 dry kg/ODMT of fiber. Alternatively, the same KYMENE 6500 can be utilized in a pre-treatment amount which results in about 0.01 to about 5 dry kg/ODMT, such as about 0.2 to about 1 dry kg/ODMT of KYMENE 6500 on the treated fibers in the finished product. In another aspect, a sizing agent such as HERCON 70 can be utilized in an amount ranging from about 1 to 10 dry kg/ODMT of fiber. In still another aspect, a latex emulsion complex can be utilized in an amount ranging from about 1 to 10 dry kg/ODMT of fiber. In yet another aspect, a cross-linking agent can be utilized in an amount ranging from about 0.1 to 10 dry kg/mt of dry fiber. Additionally combinations of these agents are considered within the scope of this invention.
Numerous methods can be utilized for pre-treating fibers with a softening agent in accordance with the present invention. Such methods should include the ability for the softening agent to be cured onto the fibers, such as by drying, and should allow for the fibers to be diluted with water and re-slurried substantially without nits. For example, in one aspect, the softening agent can be added to dry-lap pulp during a dry-lap pulp manufacturing process either in the wet-end stock or onto the formed sheet such as before the dryer section. In another aspect, the softening agent can be added in a side-stream process as part of a papermaking system where the pre-treated fibers are allowed to dry and then re-slurried and incorporated into the papermaking fiber system.
An exemplary process for pre-treating fibers with a softening agent in accordance with the present invention is described below. With reference to FIG. 1, dry-lap pulp manufacturing equipment 20 is illustrated in which a softening agent can be applied to pulp fibers according to one aspect of the present invention. A fiber slurry 10 is prepared and thereafter transferred through suitable conduits (not shown) to the headbox 28 where the fiber slurry 10 is injected or deposited onto a fourdrinier section 30 thereby forming a wet fibrous web 32. The wet fibrous web 32 may be subjected to mechanical pressure to remove process water. It is understood that the process water may contain process chemicals used in treating the fiber slurry 10 prior to a web formation step.
In the illustrated example, the fourdrinier section 30 precedes a press section 44, although alternative dewatering devices such as a nip thickening device, or the like may be used. The fiber slurry 10 is deposited onto a foraminous fabric 46 such that the fourdrinier section filtrate 48 is removed from the wet fibrous web 32. The fourdrinier section filtrate 48 comprises a portion of the process water. The press section 44 or other dewatering device known in the art suitably increases the fiber consistency of the wet fibrous web 32 to about 30% by weight or greater, such as about 40% by weight or greater, thereby creating a dewatered web 33. The process water removed as fourdrinier section filtrate 48 during the web forming step may be used as dilution water for dilution stages in the pulp processing or may be discarded.
The dewatered fibrous web 33 may be further dewatered in additional press sections or other dewatering devices known in the art. The suitably dewatered fibrous web 33 may be transferred to a dryer section 34 where evaporative drying is carried out on the dewatered fibrous web 33 to a consistency of about 80% by weight or greater, thereby forming a dried fibrous web (i.e., dry-lap) 36. The dry-lap 36 is thereafter wound on a reel 37 or slit, or cut into sheets, and allowed to sufficiently cure before delivery to a paper machine.
The softening agent 24 may be added or applied to the dewatered fibrous web 33 or the dry-lap 36 at a variety of addition points 35 a, 35 b, 35 c, and 35 d as shown in FIG. 1. It is understood that while only four addition points 35 a, 35 b, 35 c, and 35 d are shown in FIG. 1, the application of the softening agent 24 may occur at any point between the point of initial dewatering of the wet fibrous web 32 to the point the dry-lap 36 is wound on the reel 37 or baled for transport to the paper machines. The addition point 35 a shows the addition of the softening agent 24 within press section 44. The addition point 35 b shows the addition of the softening agent 24 between the press section 44 and the dryer section 34. The addition point 35 c shows the addition of the softening agent in the dryer section 34. The addition point 35 d shows the addition of the softening agent 24 between the dryer section 34 and the reel 37.
Once the softening agent has sufficiently cured onto the fibers, the dry-lap 36 can be diluted with water and re-slurried to form a softening agent pre-treated fiber slurry. The pre-treated fiber slurry can then be incorporated into the fiber stream of a paper machine and processed to form a finished product.
A paper product made in accordance with the present invention can generally be formed according to a variety of papermaking processes known in the art. In fact, any process capable of making a paper web can be utilized in the present invention. For example, a papermaking process of the present invention can utilize wet-pressing, creping, through-air-drying, creped through-air-drying, uncreped through-air-drying, single recreping, and double recreping. Also, calendering, embossing, as well as other steps in processing the paper web may also be utilized. By way of illustration, various suitable papermaking processes are disclosed in U.S. Pat. No. 5,667,636 to Engel et al.; U.S. Pat. No. 5,607,551 to Farrington, Jr. et al.; U.S. Pat. No. 5,672,248 to Wendt et al.; and, U.S. Pat. No. 5,494,554 to Edwards et al., all of which are herein incorporated by reference in a manner that is consistent with the present disclosure.
An exemplary paper making process which could be utilized for the present invention is described below. In general, one or more fiber furnishes are provided. For instance, in one aspect, two fiber furnishes can be utilized. Although other fibers may be utilized, at least one fiber furnish should comprise pre-treated fibers. Moreover, by way of example, a second fiber furnish can be utilized containing pre-treated or untreated softwood fibers. In still other aspects, by way of example, the second fiber furnish or a third fiber furnish can contain pre-treated or untreated hardwood, softwood, recycled fibers, synthetic fibers, or combinations thereof.
The above exemplary fiber furnishes can then be fed to separate pulpers that disperse the fibers into individual fibers. The pulpers can run continuously or in a batch format to supply fibers to the papermaking machine. Once the fibers are dispersed, the furnishes can then, in some embodiments, be pumped to a dump chest and diluted to about a 3% to about a 4% by weight consistency. For example, in one aspect, a fiber furnish containing pre-treated fibers can be transferred to a dump chest. Thereafter, the fiber furnish can be transferred directly to a clean stock chest, where it is diluted to a consistency of about 2% to about a 3% by weight. If desired, additional chemical additives can also be added to the dump chest and/or clean stock chest to improve various properties of the finished product. The furnish(es) can further be diluted, if desired, to about 0.1% by weight consistency at the fan pump prior to entering the headbox of a paper machine.
With reference to FIG. 2, an exemplary fibrous web forming process (i.e., papermaking machine) is described. In this example, a tissue web 64 is formed by feeding a fiber slurry 42 comprising pre-treated fibers into a 2-layer headbox 50. The headbox 50 deposits the fiber slurry 49 between a forming fabric 52 and a conventional wet press papermaking (or carrier) felt 56 which wraps at least partially about a forming roll 54 and a press roll 58 to create a tissue web 64. The tissue web 64 is then transferred from the papermaking felt 56 to the Yankee dryer 60 by applying the vacuum press roll 58. An adhesive mixture is optionally sprayed using a spray boom 59 onto the surface of the Yankee dryer 60 just before the application of the tissue web 64 onto the Yankee dryer 60 from the press roll 58. In some aspects, certain additives can be applied to the paper web as the web traverses over the dryer 60. A natural gas heated hood (not shown) may partially surround the Yankee dryer 60, assisting in drying the tissue web 64. The tissue web 64 can then be removed from the Yankee dryer by a creping doctor blade 62.
The fibrous web 64 may optionally be calendered, and is then wound into a hard roll. The substrate can then be converted using various means known in the art to produce a paper product, such as a personal care paper product, which exhibits enhanced softness and minimized slough due to the retention of the softening agent by the pre-treated pulp fibers.
Although the exemplary embodiment discussed above relates to a multi-layered paper web having two layers, it should be understood that the paper web can contain any number of layers greater than or equal to one. For example, FIG. 3 illustrates a particular aspect wherein a paper machine comprises a 3-layer headbox. As shown, an endless traveling forming fabric 76, suitably supported and driven by rolls 78 and 80, receives the layered paper making stock issuing from the headbox 70. Once retained on the fabric 76, the fiber suspension passes water through the fabric as shown by the arrows 82. In one aspect, at least one of the outer layers 72,74 can contain pre-treated fibers and at least the inner-layer 73 can contain strength enhancing fibers. Water removal can then be achieved as described above.
In addition, it should also be understood that the layers of the multi-layered paper web can also contain more than one type of fiber. For example, in some aspects, one of the layers can contain a blend of pre-treated hardwood fibers and untreated hardwood fibers, a blend of pre-treated hardwood fibers and untreated softwood fibers, a blend of untreated hardwood fibers and pre-treated softwood fibers, a blend of pre-treated hardwood fibers and recycled fibers, a blend of pre-treated hardwood fibers and synthetic fibers, and the like.
It should be further understood that a paper product of the present invention can comprise single or multiple fibrous webs. At least one of these webs is formed in accordance with the present invention. For instance, in one aspect, a two-ply paper product can be formed. The first and second ply, for example, can be a multi-layered paper web formed according to the present invention. The configuration of the plies can also vary. For instance, in one embodiment, one ply can be positioned such that a layer comprising pre-treated hardwood fibers can define a first outer surface of the paper product to provide a soft feel with minimized slough to consumers. If desired, another ply can also be positioned such that a layer comprising pre-treated hardwood fibers can define a second outer surface of the paper product.
The plies may be similarly configured when more than two plies are utilized. For example, in some embodiments, when forming a paper product from three plies, fibrous webs comprising pre-treated fibers can be positioned to define first and second outer surfaces of the paper product to provide a soft feel with minimized slough to consumers. Additionally, a third fibrous web comprising untreated softwood fibers can be positioned to define an inner ply to provide enhanced strength of the paper product to consumers. However, it should also be understood that any other ply configuration may be utilized in the present invention.
The present invention may be better understood with reference to the following examples.

EXAMPLES

Pulpsheets
Twenty-four grams of oven dry fiber from various dry-lap samples was used to prepare pulpsheets each having a basis weight of approximately 460 grams per square meter (gsm). The pulpsheets were prepared by diluting the fiber with water in a BRITISH PULP DISINTEGRATOR (commercially available from Lorentzen and Wettre AB, a business having offices located in Atlanta, Ga., U.S.A.) to a consistency of 1.2% by weight.
Each sample was allowed to soak in the disintegrator for a total of 5 minutes. After about 2.5 minutes, a particular amount of desired softening agent was introduced into the fiber-water mixture and was pulped in the disintegrator for 5 seconds before stopping and resuming the soaking period. After the soaking period was completed, the sample was pulped in the disintegrator for 5 minutes at ambient temperature (i.e., about 25° C.). A control sample was also made using the same procedure, but eliminating the step of adding the softening-agent.
An appropriate amount of the fiber slurry required to make a 460 gsm sheet was measured into a graduated cylinder. The slurry was then poured from the graduated cylinder into an 9-inch by 9-inch VALLEY handsheet mold, commercially available from Voith Inc., a business having offices located in Appleton, Wis., U.S.A.) that had been pre-filled to the appropriate level with water.
After pouring the slurry into the mold, the mold was then completely filled with water, including water used to rinse the graduated cylinder. The slurry was then agitated gently with a standard perforated mixing plate that was inserted into the slurry and moved up and down seven times, then removed. A valve was then opened to allow the water-fiber slurry to drain from the mold through a 90×90 mesh stainless-steel wire cloth with a 14×14 mesh backing wire at the bottom of the mold that retained the fibers to form a fibrous web. The web was allowed to dewater using the vacuum formed by the water drop of 31.5 inches.
One 360 gsm reliance grade blotter sheet (commercially available from Curtis Fine Papers, a business having offices located in Guardbridge, Scotland) was then placed on top of the web with the smooth side of the blotter contacting the web. The web was then couched from the mold wire by using a 10 kg roller and passing over the sheets several times. The top blotter sheet and fibrous web were lifted from the screen. The blotter sheet was then positioned with the fibrous web facing up and was placed on top of two dry blotter sheets. Two additional dry blotter sheets were then placed on top of the fibrous web to make a total of five blotter sheets.
The stack of blotter sheets, including the fibrous web, was placed in a VALLEY hydraulic press (commercially available from Voith, Inc.) and pressed for one minute at a pressure of 100 psi. The pressed web was then removed from the blotter sheets and dried, wire-side up, for 2 minutes to absolute dryness using a VALLEY STEAM HOTPLATE (commercially available from Voith, Inc.) heated with saturated steam at a pressure of 2 pounds per square inch and a standard weighted canvas cover having a weighted tube (4.75 pounds) at one end to maintain constant tension.
Handsheets
Twenty-four grams of oven dry fiber from the pulpsheet samples described above was used to prepare handsheet strip samples having a basis weight of 60 grams per square meter (g/m²). The twenty-four grams of pulp sheet sample was placed into the BRITISH PULP DISINTEGRATOR and was diluted with water to a consistency of 1.2% by weight. The pulp fiber sample was again allowed to soak for 5 minutes in the disintegrator, and then was re-slurried in the disintegrator for 5 minutes at ambient temperature (i.e., about 25° C.).
An appropriate amount of the fiber slurry required to make a 60 gsm sheet was measured into a graduated cylinder. The slurry was then poured from the graduated cylinder into the 9-inch by 9-inch VALLEY handsheet mold (described above) that had been pre-filled to the appropriate level with water.
After pouring the slurry into the mold, the mold was then completely filled with water, including water used to rinse the graduated cylinder. The slurry was then agitated gently with a standard perforated mixing plate that was inserted into the slurry and moved up and down seven times, then removed. A valve was then opened to allow the water-fiber slurry to drain from the mold through a 90×90 mesh stainless-steel wire cloth with a 14×14 mesh backing wire and at the bottom of the mold that retained the fibers to form a fibrous web. The web was allowed to dewater using the vacuum formed by the water drop of 31.5 inches.
One 360 gsm reliance grade blotter sheet (commercially available from Curtis Fine Papers) was then placed on top of the web with the smooth side of the blotter contacting the web. The web was then couched from the mold wire by using a 10 kg roller, passing over the sheets several times. The top blotter sheet and fibrous web were lifted from the screen. The blotter sheet was then positioned with the fibrous web facing up and was placed on top of two dry blotter sheets. Two additional dry blotter sheets were then placed on top of the fibrous web to make a total of five blotter sheets.
The stack of blotter sheets, including the fibrous web, was placed in the VALLEY hydraulic press (described above) and pressed for one minute at a pressure of 100 psi. The pressed web was then removed from the blotter sheets and dried, wire-side up, for 2 minutes to absolute dryness using the VALLEY STEAM HOTPLATE (described above) which was heated with saturated steam at a pressure of 2 pounds per square inch and utilized a standard weighted canvas cover having a weighted tube (4.75 pounds) at one end to maintain constant tension. The resulting handsheet was then conditioned in a humidity controlled room at 23° C. and 50% relative humidity prior to preparation as a handsheet strip sample for testing.

Example 1

ARACRUZ ECF in the form of a 1000 gsm dry-lap sheet were used to create a first set of pulp sheets, which was used to create a set of handsheets. The Pulpsheet and Handsheet methods described above for making the handsheets were utilized. This first set of comparative handsheets, hereinafter referred to as Control 1, represents a paper product without any type of chemical treatment for improving aesthetic properties, such as softness. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 2

ARACRUZ ECF was used to create a set of pulpsheets, which were then used to create a set of handsheets. The Pulpsheet and Handsheet methods described above for making comparative handsheets were again utilized, except that PROSOFT TQ-1003 debonder (commercially available from Hercules Inc.) was added in an amount equal to 0.075% on a dry fiber basis during the pulp re-slurrying step of the Handsheet procedure above. This second set of comparative handsheets, hereinafter referred to as Control 2, represents a paper product in which a debonder is added to the fiber without curing, such as through addition in the wet end of a paper machine. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 3

ARACRUZ ECF was used to create a set of pulpsheets which were used to create a set of handsheets. The same procedure was utilized as in EXAMPLE 2 above, except that the addition of PROSOFT TQ-1003 debonder was in an amount of 0.15% on a dry fiber basis. This third set of comparative handsheets, hereinafter referred to as Control 3, represents a paper product in which a debonder is added to the fiber without curing, such as through addition in the wet end of a paper machine. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 4

ARACRUZ ECF was used to create a set of pulp sheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing a polyamide-polyamine-epichlorohydrin (PAE) type resin under the trade name KYMENE 6500 in an amount equal to 0.2% on a dry fiber basis. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This first set of pre-treated fibers, hereinafter referred to as Sample 1, represents fibers which are pre-treated with a softening agent in the form of a permanent wet strength resin, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream for a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 5

ARACRUZ ECF was used to create a set of handsheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing KYMENE 6500 in an amount equal to 0.5% on a dry fiber basis. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This second set of pre-treated fibers, hereinafter referred to as Sample 2, represents fibers which are pre-treated with a softening agent in the form of a permanent wet strength resin, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream for a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 6

ARACRUZ ECF was used to create a third set of pulpsheets representing pre-treated fibers of the present invention identical to Sample 1 above using the Pulpsheet procedure described above. Additionally, ARACRUZ ECF was used to create a set of comparative pulpsheets identical to Control 1 above using the Pulpsheet procedure described above. A 1:1 mixture of the treated and untreated dried fiber sheets were diluted with water to a consistency of 1.2% and slurried, and then made into standard handsheets utilizing the Handsheet procedure described above. This first set of blended pre-treated/untreated fiber pulp sheets, hereinafter referred to as Sample 3, represents fibers which are pre-treated with a softening agent in the form of a permanent wet strength resin, then cured, and then diluted with water and re-slurried and incorporated into the fiber stream of a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

The resulting properties for the Control 1-3 comparative examples, as well as the Samples 1-3 invention examples are shown in Table 1 below.

TABLE 1


Pretreated Pulp Properties with PAE resin

Control 1

Control 2

Control 3

Sample 1

Sample 2

Sample 3

Description

				Pretreated	Pretreated	1:1 Euc and
		Euc w/0.075%	Euc w/0.15%	Euc. w/0.2%	Euc. w/0.5%	Pretreated
Physical Properties	Eucalyptus	ProSoft	ProSoft	PAE	PAE	Euc w/0.2% PAE

Tensile Index	8.74	5.71	4.98	2.73	0.67	5.45
Average (Nm/g)
Tensile Index	0.37	0.32	0.61	0.10	0.11	0.39
Standard Deviation
Caliper Average	6.29	6.46	6.63	7.06	8.09	6.88
(in 10-3)
Caliper Standard	0.25	0.29	0.35	0.22	0.39	0.22
Deviation
Slough Average (mg)	12.83	17.6	18.23	16.83	too weak	15.2
					to test for
					slough
Slough Standard	1.97	1.19	2.48	2.25	n/a	1.2
Deviation

* Note, samples that are identified as “Control #” represent comparative examples, while samples that are identified as “Sample #” represent examples of the invention.

The results in Table 1 show that fibers in Samples 1 and 2 that were pre-treated with a polyamide-polyamine-epichlorohydrin permanent wet strength resin have a substantial debonding effect compared to Control 1 resulting in a reduced tensile index for the pre-treated samples, which equates to increased softness (i.e., as the tensile index decreases, softness increases). In fact the tensile index reduction for Samples 1 and 2 is significantly greater for the pre-treated samples than with the PROSOFT debonder samples of Control 2 and 3. Furthermore, it can be surmised that the pre-treated fibers show a potential to reduce slough at equal tensile strengths as compared to a traditional wet-end softener such as PROSOFT imidazoline debonder. This can be illustrated when comparing the properties between Control 2, which was prepared with 0.075% PROSOFT debonder and Sample 3, which was prepared using a 1:1 ratio of 0.2% PAE resin treated fiber and untreated fiber. Additionally, the pre-treated fiber in Sample 3 has higher caliper and lower slough than Control 2 at approximately the same tensile index. In general, the increased caliper for each of the pre-treated samples equates to an increase in bulk for the resulting paper product.

Example 7

ARACRUZ ECF was used to create a set of handsheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing HERCON 70 in an amount equal to 0.15% on a dry fiber basis. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This set of pre-treated handsheets, hereinafter referred to as Sample 4, represents fibers which are pre-treated with a softening agent in the form of a sizing agent, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream of a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 8

ARACRUZ ECF was used to create a set of handsheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing HERCON 70 in an amount equal to 0.50% on a dry fiber basis. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This set of pre-treated handsheets, hereinafter referred to as Sample 5, represents fibers which are pre-treated with a softening agent in the form of a sizing agent, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream of a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

The resulting properties for the Control 1-3 comparative examples, as well as the Samples 4-5 invention examples are shown in Table 2 below.

TABLE 2


Pretreated Pulp Properties with AKD sizing agent

Control 1

Control 2

Control 3

Sample 4

Sample 5

Description

				Pretreated	Pretreated
		Euc w/0.075%	Euc w/0.15%	Euc. w/0.15%	Euc. w/0.5%
Physical Properties	Eucalyptus	ProSoft	ProSoft	Hercon	Hercon

Tensile Index	8.74	5.71	4.98	6.53	3.87
Average (Nm/g)
Tensile Index	0.37	0.32	0.61	0.73	0.08
Standard Deviation
Caliper Average	6.29	6.46	6.63	6.59	6.70
(in 10-3)
Caliper Standard	0.25	0.29	0.35	0.34	0.20
Deviation
Slough Average (mg)	12.83	17.6	18.23	12.53	16.23
Slough Standard	1.97	1.19	2.48	1.29	1.05
Deviation

* Note, samples that are identified as “Control #” represent comparative examples, while samples that are identified as “Sample #” represent examples of the invention.

The results in Table 2 show that fibers pre-treated with an alkyl ketene dimer type sizing agent resin have a substantial debonding effect compared to Control 1 resulting in a reduced tensile index for the pre-treated samples, which equates to increased softness (i.e., as the tensile index decreases, softness increases). Furthermore, it can be surmised that the pre-treated fibers show a potential to reduce slough at equal tensile strengths as compared to a traditional wet-end softener such as the PROSOFT imidazoline debonder used in Control 2 and 3. Additionally, the increased caliper of the pre-treated samples equates to an increase in bulk for the resulting paper product.

Example 9

ARACRUZ ECF was used to create a set of handsheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing a complex of hydrophobic polymer anionic emulsion and a cationic surfactant at a 2:1 mass ratio in an amount equal to 0.3% on a dry fiber basis. The complex was prepared by mixing LATRIX 6300 emulsion at a solids content of about 50% by weight with PROSOFT TQ-1003 at a solids content of about 80% by weight. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This set of pre-treated handsheets, hereinafter referred to as Sample 6, represents fibers which are pre-treated with a softening agent in the form of a polymer emulsion, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream of a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

Example 10

ARACRUZ ECF was used to create a set of handsheets representing pre-treated fibers of the present invention. The fibers were treated according to the Pulpsheet procedure described above utilizing a complex of hydrophobic polymer anionic emulsion and a cationic surfactant at a 2:1 mass ratio in an amount equal to 1.0% on a dry fiber basis. The complex was prepared by mixing LATRIX 6300 emulsion at a solids content of about 50% with PROSOFT TQ-1003 at a solids content of about 80%. The fibers were then diluted and re-slurried to form handsheets according to the Handsheet procedure described above. This set of pre-treated handsheets, hereinafter referred to as Sample 7, represents fibers which are pre-treated with a softening agent in the form of a latex emulsion complex, then cured, and then diluted with water, re-slurried and incorporated into the fiber stream of a paper machine to enhance aesthetic properties such as softness while minimizing slough. The handsheets were then tested for various properties in accordance with the test procedures set forth below.

The resulting properties for the Control 1-3 comparative examples, as well as the Samples 6-7 invention examples are shown in Table 3 below.

TABLE 3


Pretreated Pulp Properties with Polymer complex

Control 1

Control 2

Control 3

Sample 6

Sample 7

Description

				Pretreated	Pretreated
		Euc w/0.075%	Euc w/0.15%	Euc. w/0.3%	Euc. w/1.0%
Physical Properties	Eucalyptus	ProSoft	ProSoft	Complex	Complex

Tensile Index	8.74	5.71	4.98	5.21	4.43
Average (Nm/g)
Tensile Index	0.37	0.32	0.61	0.38	0.41
Standard Deviation
Caliper Average	6.29	6.46	6.63	6.61	6.75
(in 10-3)
Caliper Standard	0.25	0.29	0.35	0.41	0.16
Deviation
Slough Average (mg)	12.83	17.6	18.23	15.63	10.37
Slough Standard	1.97	1.19	2.48	0.83	1.01
Deviation

* Note, samples that are identified as “Control #” represent comparative examples, while samples that are identified as “Sample #” represent examples of the invention.

The results in Table 3 show that fibers pre-treated with the complex formed from hydrophobic polymer anionic emulsion with a cationic surfactant at a 2:1 ratio have a substantial debonding effect compared to the untreated control, which equates to increased softness (i.e., as the tensile index decreases, softness increases). Further, the samples containing fibers pre-treated with the polymer complex exhibit lower slough at equal or lower tensile strengths compared to the PROSOFT debonder controls. Additionally, the increased caliper of the pre-treated samples equates to an increase in bulk for the resulting paper product.

Example 11

A 90% ARACRUZ ECF Eucalyptus/10% LL-19 northern softwood pulp sheet was produced on a pilot scale tissue machine at a speed of 18 feet per minute. The pulp sheet was dried to 85% solids with a basis weight of 160 grams per square meter. The pulp sheet was re-slurried for 30 minutes at 120° F. (hereinafter, the “Untreated Fibers”) and used to make a comparative example Control 4.
A layered fibrous web having a basis weight of about 7.0 pounds per 2880 square feet of oven dried tissue web was then produced on the pilot scale tissue machine by utilizing a 3 layer headbox to form a sheet having two outer layers and one inner layer. The first outer layer comprised 66% ARACRUZ ECF and 34% of the Untreated Fibers from above. The inner layer comprised 70% LL-19 and 30% of the Untreated Fibers from above. A 0.1% solution of strength additive under the tradename HERCOBOND 1366, available from Hercules Inc., was also added to the center layer to control the final strength of the layered fibrous web to a geometric mean tensile of 2.41 Nm/g. The dilute solution of HERCOBOND 1366 was added continuously through a pump to the stock pipe prior to the headbox. The remaining outer layer comprised 66% ARACRUZ ECF and 34% of the Untreated Fibers from above. Additionally, a solution of wet strength additive, under the tradename KYMENE 6500, available from Hercules Inc., was added to all 3 layers at an amount of 2 dry kg/dry metric ton of tissue to provide wet strength to the product. The KYMENE 6500 was added in to the pulp storage vat and allowed to mix for 10 minutes before the pulp was transported to the headbox.
The layered fibers were deposited from the headbox onto a forming fabric and dewatered with vacuum. The tissue web was then transferred to a papermaking felt which carried the wet web at approximately 20% solids content from the formic fabric to a press roll which pressed additional water from the web to approximately a 45% solids content and transferred the web to a Yankee dryer. An adhesive mixture was sprayed using a spray boom onto the surface of the Yankee dryer just before the application of the tissue web by the press roll. The adhesive mixture contained about 40% by weight polyvinyl alcohol, about 40% by weight polyamide resin and about 20% by weight quaternized polyamido amine, such as disclosed in U.S. Pat. No. 5,730,839 to Wendt et al. which is herein incorporated by reference in a manner that is consistent with the present disclosure. The application rate of the adhesive mixture was about 6 pounds of dry adhesive per metric ton of oven dry pulp fiber in the tissue web.
The sheet was dried on the Yankee dryer which was heated with 23 psi pressure saturated steam. Additionally, a natural gas heated hood partially surrounding the Yankee dryer had a supply air temperature of about 600° F. to assist in drying the tissue web. The temperature of the tissue web after the application of the creping doctor was about 225° F. as measured with a handheld infrared temperature gun. The sheet was creped off of the dryer using a steel blade with a 10 degree bevel. The blade was held in a chamber with a ¾ inch extension, which was pressed against the dryer with enough force to allow the tissue to be scraped uniformly from the dryer. The tissue was wound onto a reel that was traveling 27% slower than the Yankee dryer. The machine speed of the 16 inch wide tissue web was about 50 feet per minute.
Two rolls of the creped tissue were then rewound and plied together in a fashion to allow both creped sides to be on the outside of the 2-ply structure. The plied structures were calendered at approximately 40 pounds per linear inch, mechanically crimped on the edges to hold the plies together, and slit on the edges to achieve a width of approximately 8.5 inches to form a two-ply facial tissue product. The product was then tested for various properties in accordance with the test procedures set forth below. The results can be seen in Table 4.

Example 12

A 90% ARACRUZ ECF Eucalyptus/10% LL-19 northern softwood pulp sheet was produced on a pilot scale tissue machine at a speed of 18 feet per minute. In this example, the fibers were pre-treated with KYMENE 6500 PAE resin controlled to achieve an addition amount of 0.1% on a dry fiber basis. The resin treatment involved mixing the resin with the pulp fibers for 30 minutes pulping time at 120° F. before forming and drying the pulpsheet. The pulpsheet was dried to 85% solids with a basis weight of 160 grams per square meter. The pulpsheet was then re-slurried for 30 minutes at 120° F. (hereinafter, the “Pre-Treated Fibers”) and used as a fiber source to produce Sample 8, a two-ply facial tissue product produced in the same manner as Control 4 above, with the exception that the amounts of Untreated Fibers were replaced with Pre-Treated Fibers made in this example. The product was then tested for various properties in accordance with the test procedures set forth below. The results can be seen in Table 4.

TABLE 4


Two-ply Facial Tissue using PAE resin pre-treated pulp.

Code	Control 4	Sample 8
Description	Average (Std. Dev.)	Average (Std. Dev.)

BW, (gsm)	32.2 (0.15)	31.7 (0.14)
Caliper	9.01 (0.12)	9.72 (0.22)
(0.001 in)
Slough mg	6.78 (0.93)	4.62 (0.72)
MD Tensile	3.56 (0.24)	3.36 (0.23)
(Nm/g)
CD Tensile	1.64 (0.08)	1.61 (0.10)
(Nm/g)
GMT (Nm/g)	2.42	2.33

* Note, samples that are identified as “Control #” represent comparative examples, while samples that are identified as “Sample #” represent examples of the invention.

The results in Table 4 show that a tissue product made from fibers pre-treated with the 20% PAE resin inclusion in the furnish have, at approximately the same geometric mean tensile strength (GMT), an increase in caliper with less slough.

Example 13

Samples were produced in a similar manner as Control 1-3, and Samples 1-2 and 4-7 above. However, prior to the step of re-slurrying the samples, the fibers were tested to determine water retention values using the procedure described below. In the case of Control 2 and Control 3, the PROSOFT chemistry was added during the Pulpsheet procedure, rather than during the re-slurrying step of the Handsheet procedure. The results are shown in Table 5. Additionally, these same samples were used to measure Length Weighted Curl Index using the procedure described below. The Curl Index values are also shown in Table 5.

TABLE 5


Pulpsheet Water Retention Values

	Water
Water	Retention
Retention	Value		Curl Index
Value	Standard	Curl Index	Standard
Average (g/g)	Deviation	Average	Deviation

Control 1	1.24	0.03	0.087	0.004
Control 2	1.14	0.02	0.083	0.001
Control 3	1.15	0.05	0.086	0.003
Sample 1	0.87	0.04	0.090	0.001
Sample 2	0.82	0.03	0.093	0.002
Sample 4	0.96	0.08	0.087	0.002
Sample 5	0.83	0.01	0.079	0.004
Sample 6	0.86	0.01	0.084	0.002
Sample 7	0.79	0.07	0.082	0.001

* Note, samples that are identified as “Control #” represent comparative examples, while samples that are identified as “Sample #” represent examples of the invention.

The data in Table 5 suggest a potential mechanism describing why pulp pre-treatment of the present invention creates a paper product having increased softness while minimizing slough. Without being held to a particular theory, it appears that by having low water retention, an inventive debonding mechanism is created which differs from the use of typical debonder chemistries. For example, it is believed that the pre-treated fibers, which have less water in them, are less flexible and create a lower density fibrous mat in a wet formation process. It can be surmised that the lower density fibrous mat diminishes fiber to fiber contact, thus making the mat weaker. This contrasts with chemical debonders which are believed to adsorb to fibers and reduce hydrogen bonding of fibers through covering hydroxyl and carboxyl sites as well as reducing surface tension which draws fibers together. Therefore, it is believed that the invention reduces fiber to fiber contact but allows strong bonds to form where contact is made, whereas traditional debonder chemistries reduce the strength of all bonds through adsorption to cellulose.
Test Procedures
Tensile Test
Unless otherwise specified, tensile strengths were measured according to TAPPI Test Method T 494 om-88 for tissue, modified in that the tensile tester used a crosshead speed of 10 inches per minute. The samples were conditioned at 23° C.+/−1° C. and 50%+/−2% relative humidity for a minimum of 4 hours. The handsheets were cut into 1-inch wide strips using a Precision sample cutter model JDC 15M-10, commercially available from Thwing-Albert Instruments, a business having offices located in Philadelphia, Pa., U.S.A.
Each strip was then placed into the tensile frame at a gauge length of 5 inches. The tensile frame used in these experiments was an ALLIANCE RT/1 frame run with TESTWORKS 4 software, available from MTS Systems Corporation, a business having offices located in Cary, N.C., U.S.A. Each strip was then subjected to a strain of 0.5 inches per minute and the resulting stress was recorded with an appropriate load cell.
The Tensile Index (TI) is a measure of tensile strength normalized for basis weight of the web tested. The tensile strength as measured above may be converted to tensile index using the following formula:
Tensile Index=Peak Load (N)/[Sample basis weight (g/m²)×Sample width (m)]
where peak load is expressed in Newtons (N), the sample basis weight is expressed in grams per square meter (g/m²), the sample width is expressed in meters (m), and the tensile index is expressed in Newton meter per gram (Nm/g).
The Geometric Mean Tensile (GMT) was also calculated for the samples to provide an average strength independent of test direction. The GMT was calculated using the following formula:
GMT=Square Root (MD tensile value×CD tensile value)
The Tensile Test procedure for the tissue samples of Control 4 and Sample 8 was modified slightly. These particular tissue samples were conditioned at 23° C.+/−1° C. and 50%+/−2% relative humidity for a minimum of 4 hours. The samples were cut into 3 inch wide strips using the Precision sample cutter model JDC 15M-10. Two strips, to represent a 2-ply product, were then placed into the tensile frame at a gauge length of 4 inches. The tensile frame used in these experiments was the ALLIANCE RT/1 frame run with TESTWORKS 4 software described above. Each strip was then subjected to a strain of 10 inches per minute and the resulting stress was recorded with an appropriate load cell. The Tensile Index and the Geometric Mean Tensile were then calculated as described above.
Caliper Test
The term “caliper” as used herein refers to the thickness of a single tissue sheet. Caliper may either be measured as the thickness of a single tissue sheet or as the thickness of a stack of ten tissue sheets where each sheet within the stack is placed with the same side up and dividing the measurement by ten. Caliper is expressed in microns or 0.001 inches. Caliper was measured in accordance with TAPPI test methods T402 “Standard Conditioning and Testing Atmosphere For Paper, Board, Pulp Handsheets and Related Products” and T411 om-89 “Thickness (caliper) of Paper, Paperboard, and Combined Board” optionally with Note 3 for stacked tissue sheets. The micrometer used for carrying out T411 om-89 was a MODEL 49-72-00 BULK MICROMETER (available from TMI Company, a business having offices located in Amityville, N.Y. U.S.A.) or equivalent having an anvil diameter of 4 1/16 inches (103.2 millimeters) and an anvil pressure of 220 grams/square inch (3.3 kiloPascal).
Slough Test
The Slough Test determines the abrasion resistance or tendency of the fibers to be rubbed from the web when handled. More particularly, this test measures the resistance of tissue material to abrasive action when the material is subjected to a horizontally reciprocating surface abrader. Each sample was measured by abrading the tissue specimens via the following method.
All samples were conditioned at 23+ C.+/−1° C. and 50%+/−2% relative humidity for a minimum of 4 hours. The slough of each handsheet was measured using a 3-inch wide by 8-inch long strip fastened by weighted clamps allowing a rough, slow-rotating mandrel to pass back and forth under the tissue strip for a pre-determined number of cycles. This instrument was designed by the Kimberly-Clark Corporation in Neenah, Wis. Weights to the nearest 0.0001 gram are recorded for each sample strip before and after testing to determine the amount of sloughing measured in milligrams.
With reference to FIG. 4, the abrading spindle 94 contained a stainless steel rod 96, 0.5″ in diameter with the abrasive portion 84 having a 0.005″ deep diamond pattern extending 4.25″ in length around the entire circumference of the rod 96. The spindle 94 was mounted perpendicularly to the face of the instrument such that the abrasive portion 84 of the rod 96 extends out its entire distance from the face of the instrument 100. Guide pins 102,104 with magnetic clamps 86,88 are located on each side of the spindle 94, one movable 86 and one fixed 88, spaced 4 inches apart and centered about the spindle 94. The movable clamp 86 and guide pins 102 were allowed to slide freely in the vertical direction, providing the means for insuring a constant tension of the sample over the spindle 94 surface.
Using a die press with a die cutter, the specimens 92 were cut into 3+/−0.05 inch wide by 8 inch long strips with two holes (not shown) at each end of the sample 92 for the guide pins 102,104 to fit through. For the tissue samples 92, the MD direction corresponds to the longer dimension. Each test strip 92 was then weighed to the nearest 0.0001 gram. Each end of the sample 92 was slid onto the guide pins 86,88 and magnetic clamps 86,88 held the sheet 92 in place. The movable jaw 86 was then allowed to fall providing constant tension across the spindle 94.
The spindle 94 was then moved back and forth at an approximate 15 degree angle from the centered vertical centerline in a reciprocal horizontal motion 90 against the test strip 92 for 40 cycles (each cycle is a back and forth stroke), at a speed of 80 cycles per minute, removing loose fibers from the web surface. Additionally, the spindle 94 rotated counter clockwise 98 (when looking at the front of the instrument) at an approximate speed of 5 RPMs. The magnetic clamps 86,88 were then removed from the sample 92 and the sample 92 was slid off of the guide pins 102,104 and any loose fibers on the sample 92 surface were removed by blowing compressed air (approximately 5-10 psi) on the test sample 92. The test sample 92 was then weighed to the nearest 0.0001 gram and the weight loss was calculated. Ten test samples per tissue sample were tested and the average weight loss value in grams (or milligrams) was recorded.
Water Retention Value
Each dried pulp sample was disintegrated by diluting in deionized water to a consistency of 1.2% by weight in a BRITISH PULP DISINTEGRATOR (described above). The pulp fiber sample was allowed to soak for 5 minutes before being pulped at 15,000 revolutions for 5 minutes at ambient temperature (i.e., about 25° C.). A sheet of a Whatman No. 1 filter paper (available from Whatman Inc., a business having offices located in Clifton, N.J. U.S.A.) used to gravity filter approximately 100 mL of the fiber suspension was supported on a 50 mesh wire screen in a plastic centrifuge tube with a drainage hole on the bottom. Four samples were prepared in this manner and placed into metal centrifuge tubes with a space of approximately 3 mm to allow water to drain from the samples. The assembly was placed into a centrifuge where the samples where accelerated to achieve 900 gravities of centrifugal force on the pulp specimens. The samples were spun at this speed for 30 minutes after which time the samples were removed utilizing a dissecting needle.
The filter papers were quickly separated from the dewatered fiber samples and each sample was placed onto a pre-weighed drying dish. Each wet sample was weighed, subtracting the weight of the dish, recorded as the wet fiber weight (Wwet). The sample was then dried in an oven at approximately 105 degrees C. for 12 hours and weighed again with the weighing dish. This dish weight was subtracted and recorded as the dry fiber weight (Wdry). The water retention value (WRV) was calculated from the following equation:
WRV=(Wwet−Wdry)/Wdry
where Wwet and Wdry are expressed in grams (g), and WRV is expressed as g water/g fiber.
Curl Index
“Curl” or “curl index” of a fiber is the measure of fractional shortening of a fiber due to kinks, twists, and/or bends in the fiber. For the purposes of this invention, a fiber's curl value is measured in terms of a two-dimensional plane, determined by viewing the fiber in a two-dimensional plane. To determine the curl index of a fiber, the projected length of a fiber as the longest dimension of a two-dimensional rectangle encompassing the fiber (I), and the actual length of the fiber (L), are both measured. An image analysis method may be used to measure “L” and “I”. A suitable image analysis method is described in U.S. Pat. No. 4,898,642 to Moore et al., which is incorporated herein by reference in a manner that is consistent with this disclosure. The curl value of a fiber can then be calculated from the following equation:
Curl index=(L/l)−1
The Wet Curl value for fibers was determined by using a FIBER QUALITY ANALYZER, OPTEST PRODUCT CODE LDA 96, available from OpTest Equipment Inc., a business having offices located in Hawkesbury, Ontario, Canada. The sample was placed into a 600 milliliter plastic sample beaker to be used in the Fiber Quality Analyzer. The fiber sample in the beaker was diluted with tap water until the fiber concentration in the beaker was about 10 to about 25 fibers per second for evaluation by the Fiber Quality Analyzer. An empty plastic sample beaker was filled with tap water and placed in the Fiber Quality Analyzer test chamber. The <System Check> button of the Fiber Quality Analyzer was then pushed. If the plastic sample beaker filled with tap water was properly placed in the test chamber, the <OK> button of the Fiber Quality Analyzer was then pushed. The Fiber Quality Analyzer then performed a self-test. If a warning was not displayed on the screen after the self-test, the machine was ready to test the fiber sample.
The plastic sample beaker filled with tap water was removed from the test chamber and replaced with the fiber sample beaker. The <Measure> button of the Fiber Quality Analyzer was then pushed. The <New Measurement> button of the Fiber Quality Analyzer was then pushed. An identification of the fiber sample was then typed into the Fiber Quality Analyzer. The <OK> button of the Fiber Quality Analyzer was then pushed. The <Options> button of the Fiber Quality Analyzer was then pushed. The fiber count was set at 3,000. The parameters of scaling of a graph to be printed out was set to automatic. The <Previous> button of the Fiber Quality Analyzer was then pushed. The <Start> button of the Fiber Quality Analyzer was then pushed. If the fiber sample beaker was properly placed in the test chamber, the <OK> button of the Fiber Quality Analyzer was then pushed.
The Fiber Quality Analyzer then began testing and displayed the fibers passing through the flow cell. The Fiber Quality Analyzer also displayed the fiber frequency passing through the flow cell, which was about 10 to about 20 fibers per second. If the fiber frequency is outside of this range, the <Stop> button of the Fiber Quality Analyzer should be pushed and the fiber sample should be diluted or have more fibers added to bring the fiber frequency within the desired range. If the fiber frequency is sufficient, the Fiber Quality Analyzer tests the fiber sample until it has reached a count of 3000 fibers at which time the Fiber Quality Analyzer automatically stops. The <Results> button of the Fiber Quality Analyzer was then pushed. The Fiber Quality Analyzer calculated the Wet Curl value of the fiber sample, which printed out by pushing the <Done> button of the Fiber Quality Analyzer.
It will be appreciated that details of the foregoing examples, given for purposes of illustration, are not to be construed as limiting the scope of this invention. Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the examples without materially departing from the novel teachings and advantages of this invention. For example, features described in relation to one example may be incorporated into any other example of the invention.
Accordingly, all such modifications are intended to be included within the scope of this invention, which is defined in the following claims and all equivalents thereto. Further, it is recognized that many embodiments may be conceived that do not achieve all of the advantages of some embodiments, particularly of the preferred embodiments, yet the absence of a particular advantage shall not be construed to necessarily mean that such an embodiment is outside the scope of the present invention. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A paper product comprising at least one fibrous web which comprises pre-treated cellulosic fibers, wherein said pre-treated cellulosic fibers have been cured with a softening agent prior to incorporation into said paper product.

2. The paper product of claim 1 comprising about 10% to about 50% of said pre-treated cellulosic fibers.

3. The paper product of claim 1 wherein said at least one fibrous web comprises pre-treated cellulosic fibers having a Water Retention Value below 0.9 g/g.

4. The paper product of claim 1 wherein said at least one fibrous web has a tensile strength that is reduced by at least 50% compared to the same fibrous web comprising untreated cellulosic fibers.

5. The paper product of claim 1 wherein said softening agent is selected from the group consisting of wet strength resins, sizing agents, latex emulsions, cross-linking agents, and combinations thereof.

6. The paper product of claim 5 wherein said wet strength resin is selected from the group consisting of glyoxylated polyacrylamide, dialdehyde starch, aldehyde containing, polyamide-polyamine-epichlorohydrin, polyethylenimine resins, aminoplast, and combinations thereof.

7. The paper product of claim 5 wherein said sizing agent is selected from the group consisting of alkenyl succinic anhydride, alkyl ketene dimer, amylopectin starch, and combinations thereof.

8. The paper product of claim 5 wherein said latex emulsion is a complex formed from a hydrophobic polymer anionic styrene butadiene latex emulsion at a solids content of about 50% by weight and a quaternary amine imidazoline softener at a solids content of about 80% by weight.

9. The paper product of claim 5 wherein said cross-linking agent is chosen from the group consisting of styrene-butadiene copolymers, polyvinyl acetate copolymers, vinyl-acetate acrylic copolymers, ethylene-vinyl chloride copolymers, acrylic polymers, nitrile polymers, dispersed polyolefins, and combinations thereof.

10. The paper product of claim 1 further comprising a debonding agent.

11. The paper product of claim 1 wherein said pre-treated cellulosic fibers are not distributed uniformly throughout said soft paper product.

12. The paper product of claim 1 wherein said pre-treated cellulosic fibers are distributed discretely within said soft paper product.

13. The paper product of claim 1 wherein said pre-treated cellulosic fibers have a curl index less than 0.2.

14. The paper product of claim 1 wherein said pre-treated cellulosic fibers comprise substantially hardwood fibers.

15. The paper product of claim 14 wherein said hardwood fibers comprise Eucalyptus fibers.

16. The paper product of claim 1 wherein said at least one fibrous web is a multi-layered fibrous web having two outer layers, wherein at least one of said two outer layers comprises said pre-treated cellulosic fibers.

17. A method for making a paper product comprising:

providing a fiber slurry comprising water and cellulosic fibers;

adding a softening agent to said cellulosic fibers;

allowing said softening agent to cure with said cellulosic fibers to form pre-treated fibers;

diluting said pre-treated fibers with water;

re-slurrying said pre-treated fibers and water to form a pre-treated fiber slurry;

incorporating said pre-treated fiber slurry into a fiber stream of a papermaking machine;

forming a fibrous web comprising said pre-treated fibers on said papermaking machine; and

converting said fibrous web into a paper product.

18. The method of claim 17 further comprising adding a debonding agent to said fiber stream.

19. The method of claim 17 wherein said paper product comprises about 10% to about 50% of said pre-treated cellulosic fibers.

20. The method of claim 17 wherein said fibrous web further comprises synthetic fibers.