Paper products and methods for applying chemical additives to fibers in the manufacture of paper

Abstract

In the manufacture of tissue products from cellulose fibers, it is often desirable to enhance physical properties by the addition of chemical additives, including for example debonding agents. These additives serve to prevent or disrupt interfiber or intrafiber hydrogen bonding. Depending upon the nature of the chemical additive, debonding agents may also act as softening agents. During the papermaking process, chemical additives of this type can be added to fiber slurries in the wet end of a papermaking machine. Alternately, such additives may be sprayed upon tissue layers during manufacture, prior to assembly into multi-ply tissue structures. The chemical additives may include quaternary ammonium salts or organofunctional polysiloxanes. The chemical additives may include quaternary ammonium salts or organofunctional polysiloxanes or polysiloxanes. Some of the quaternary salts which may be used include salts comprised in part of imidazoline heterocyclic nitrogen ring structures.

Description

RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application of U.S. Ser. No. 09/589,450 filed on Jun. 7, 2000.

BACKGROUND OF THE INVENTION

[0002] In the manufacture of paper products from cellulose fibers, such as facial tissue, bath tissue, paper towels, dinner napkins and the like, it is often desirable to enhance product properties by the addition of chemical additives. Properties that may be enhanced using additives include: dry strength, wet strength, softness, absorbency, opacity, brightness and color.

[0003] Additives provided during papermaking, such as debonding agents, may provide a softening effect by reducing inter-fiber bonding within the tissue structure. However, using such additives often undesirably increases the amount of lint or sloughing of particles from the surface of the tissue during use by a consumer. Also, many additives or debonding agents undesirably reduce the strength of tissues.

[0004] Softness is a key attribute in tissue products. A feeling of softness imparts to human skin a clean and soothing effect. Improving the balance of tissue softness and strength is a continuous effort in tissue making. Tissue product designers attempt to maximize the strength and softness of tissues. It has been recognized as a general rule of tissue manufacture that the greater the strength of a given tissue, the lower the softness of that tissue. There is usually an inverse relationship between strength and softness. In general, prior efforts have been directed at achieving softness using chemicals directed at reducing the inter-fiber bonding within the tissue structure or coating the tissue surface with such chemicals. Mechanical means have been used in the art of tissue making to increase the softness of tissue paper. Many tissues are creped with a doctor blade to increase softness. Uncreped tissues sometimes are subjected to a rush transfer step to increase softness.

[0005] During the papermaking process, additives are commonly added to fiber slurries in the wet end of a papermaking machine. Wet end chemical addition may provide a relatively uniform distribution of chemical additives on the fiber surfaces of a tissue product. Additionally, wet end chemical addition sometimes facilitates the selection of a particular fraction to be treated with a specific chemical additive in order to enhance the performance of the paper, or to enhance the performance of a chemical additive. Wet end chemical addition enables multiple additives of various types to be added to a fiber slurry, either simultaneously or sequentially, prior to formation of the paper web. Topical spraying, printing or size press are other methods for chemical addition.

[0006] Compositions comprising about 80% imidazoline quaternary ammonium compound and about 10% polyethylene glycol have been used as debonders in tissue manufacture. Witco C-6027 produced by the Witco Chemical Company is one product that has been used in tissue manufacture to improve the softness of tissue. PCT International Publication WO 99/34057 discloses using Witco C-6092 as a softener/debonder in tissue manufacture.

[0007] Two component chemical softening compositions also have been used to soften tissue. In one process, chemical debonders which include mixtures of (1) quaternary ammonium compounds, and (2) polysiloxane, have been used in the manufacture of tissue. U.S. Pat. No. 5,573,637 shows the use of such a two-component quaternary/polysiloxane system in tissue manufacture. Binder materials also are described as being used in connection with such processes. A first step includes forming a papermaking aqueous furnish of fibers, including a mixture of at least one quaternary ammonium compound, with binder materials and a wetting agent. Then, in a second step, a solution comprising a polysiloxane compound is sprayed on the dry tissue web after creping. This two-step procedure, which uses quaternary compounds and a polysiloxane, has been reported to improve tissue characteristics.

[0008] What is needed in the industry is a chemical softening composition and technique of manufacture that will result in a softer, stronger tissue. A system that will provide to a final tissue product a desirable strength, with good tactile sensory softness characteristics in a process of manufacture that is relatively simple to apply at a reasonable cost would be highly desirable.

SUMMARY OF THE INVENTION

[0009] Tissues may be manufactured which exhibit softness and strength improvement using additives that can be applied into the wet end of a papermaking machine, or topically sprayed on the tissue web during manufacture. In one aspect of the invention, a tissue product is shown which comprises cellulosic fibers and an adsorbable chemical debonding additive. The additive includes, in some embodiments, a quaternary ammonium salt and a surfactant. The tissue product may employ an additive comprised of between about 10% and about 60% imidazoline quaternary ammonium salt. The tissue product also may be used in which the additive is comprised of or contains a lubricant.

[0010] In one alternative embodiment, the tissue product employs an additive comprising about 19-24% low to medium charge density imidazoline quaternary ammonium salts, about 15-20% high charge density dialkyl imidazoline quaternary ammonium salts, about 12-19% surface fiber lubricant, about 47-52% nonionic surfactants and wetting agents, and about 2% emulsion particle size control additives.

[0011] A multilayered product may be used, and the tissue may comprise a center layer consisting essentially of softwood fibers and two outer layers comprising about 50% or greater hardwood fibers. The product may be a layered tissue.

[0012] In one aspect of the invention, at least one outer layer of the tissue is capable of absorbing an additive which is applied to the tissue by spraying following assembly of the layers of the tissue. In one embodiment, the quaternary ammonium salt comprises in part a nitrogen ring compound. In other aspects of the invention, the quaternary ammonium salt comprises in part a dinitrogen ring compound. The quaternary ammonium salt may comprise a heterocyclic compound having more than one type of atom in a ring structure, which may or may not be aromatic.

[0013] A method of making a tissue product is also disclosed. The method may include: providing a fiber furnish comprising water, cellulosic fibers, and an adsorbable chemical additive, wherein the chemical additive comprises an imidazoline quaternary ammonium salt and a surfactant. Then, in a next step, the fiber furnish is dewatered. Next, the fiber furnish is dried.

[0014] In another aspect of the invention, a method of making a tissue product is shown as follows:

[0015] (a) providing a fiber furnish of water and cellulosic fibers,

[0016] (b) dewatering the fiber furnish to form a first tissue layer, and(c) spraying upon the surface of a first tissue layer an adsorbable chemical additive, the chemical additive comprising a quaternary ammonium salt and a surfactant. It is possible to apply an additive to one or more outer layers, and then assemble the layers with one or more other layers in a multi-layer structure. That is, one may combine the first tissue layer with additional tissue layers to form a layered tissue product.

[0017] A tissue product also is presented in which the product includes cellulosic fibers and an adsorbable aminofunctional polysiloxane which is provided as a debonding agent. A method of making a tissue product also is shown, which includes providing a fiber furnish comprising water, cellulosic fibers, and an adsorbable chemical additive, the chemical additive comprising an aminofunctional silicone; dewatering the fiber furnish, and then drying the fiber furnish. In some applications, hydraulic spraying of a silicone softener may be utilized. In some applications, the silicone may be applied by spraying.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A full and enabling disclosure of this invention, including the best mode shown to one of ordinary skill in the art, is set forth in this specification.

[0019] FIG. 1 shows in graphical form sample data prepared as provided below in the Examples.

[0020] FIG. 2 is a plan view of one embodiment of a system and process for producing uncreped through-air dried paper webs.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in this invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present invention are disclosed in or are obvious from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

[0022] A "debonding agent" or "debonder" refers to any chemical that can be incorporated into paper products, such as tissue, to prevent or disrupt interfiber or intrafiber hydrogen bonding. In general, a debonder stops the hydrogen bonding and reduces the strength of the tissue by breaking down bonds. As a general rule, use of a debonder softens the tissue. However, a debonding agent also can cause the tissue to lint or slough, which is undesirable. Therefore, softness is normally inversely proportional to strength when it comes to tissue.

[0023] Depending upon the nature of the chemical, debonding agents may also act as softening agents. A softening agent is generally any chemical additive that can be incorporated into paper products, such as tissue, to provide improved tactile feel. These chemicals can also act as debonding agents or can act solely to improve the surface characteristics of tissue, such as by reducing the coefficient of friction between the tissue surface and the skin on the hand.

[0024] In contrast, the term "bonding agent" refers to any chemical that can be incorporated into tissue to increase or enhance the level of interfiber or intrafiber bonding in the sheet. The increased bonding can be either ionic, hydrogen or covalent in nature.

[0025] The current invention is geared towards the addition of a debonder or softening agent during the manufacture of a paper product, such as a tissue. Typically, the debonder is added to the tissue at an add-on rate of from about 0.01 to about 10 weight percent of the fiber. For instance, the add-on rate may be from about 0.4 to about 7 weight percent of the fiber.

[0026] According to the present invention, various debonders can be used. For instance, the debonder can be a blend of imidazoline quaternary ammonium salts, one or more non-ionic silicones, or one or more aminofunctional siloxanes. The above debonders can be used alone or in combination. Further, the debonders can be added during the formation of the paper web by being combined with an aqueous slurry of fibers used to form the web or can be applied topically to the web after the fibers have been applied to a forming fabric. Whether or not the debonder is added at the wet end of the papermaking process or after the web has been formed on the forming fabric depends upon various circumstances including the debonders chosen.

[0027] In one embodiment of this invention, an additive comprising 10-60% imidazoline quaternary ammonium salts, about 7-25% surface fiber lubricant, about 20%-70% nonionic surfactants and wetting agents, and about 1-5% emulsion particle size control additives is used as the debonder. For instance, this debonder composition can comprise between about 40% and 60% quaternary ammonium salts by weight, and in still another embodiment the composition comprises about 50% quaternary ammonium salts by weight.

[0028] The quaternary ammonium salt may comprise in part a nitrogen ring compound. For instance, the quaternary ammonium salt may comprise a dinitrogen ring compound. The salt may comprise a heterocyclic compound having more than one type of atom in a ring structure, which may or may not be aromatic.

[0029] In one embodiment, the composition may be comprised of a blend of quaternary ammonium salts with differing charge densities. For instance, the composition can comprise about 15-30% of a low to medium charge density imidazoline quaternary ammonium salt and about 10-25% of a high charge density dialkyl imidazoline quaternary ammonium salts, about 7-25% surface fiber lubricant, about 20-70% nonionic surfactants and wetting agents, and about 1-5% emulsion particle size control additives.

[0030] For instance, in one embodiment of the current invention, QuaSoft 229 may be used as the debonder. QuaSoft 229 is a composition that is manufactured and distributed by the Quaker Chemical Corporation of Conshohocken, Pennsylvania ("QuaSoft 229" is believed to be a trademark of the Quaker Chemical Company).

[0031] QuaSoft 229 is believed to comprise about 19-24% low to medium charge density imidazoline quaternary ammonium salts, about 15-20% high charge density dialkyl imidazoline quaternary ammonium salts, about 12-19% surface fiber lubricant, about 47-52% nonionic surfactants and wetting agents, and about 2% emulsion particle size control additives. The nonionic surfactants in the QuaSoft 229 are polyethylene glycol and polypropylene glycol esters and the lubricant is a lanoline derivative.

[0032] The low to medium charge density imidazoline quaternary ammonium salts described above have a charge density of less than about 0.7 meq/g. For instance, in one embodiment the charge density is less than about 0.5 meq/g, such as from about 0.25 meq/g to about 0.42 meq/g when present in a neat or concentrated form. The molecular weight of the low to medium charge density imidazoline quaternary ammonium salts, in one embodiment, can be from about 1250 to about 1300.

[0033] The high charge density imidazoline quaternary ammonium salts can have a charge density greater than about 0.9 meq/g. For instance, in one embodiment, the charge density can be greater than about 1.2 meq/g, such as from about 1.22 meq/g to about 1.23 meq/g when present in the neat form. In one embodiment, the high charge density imidazoline quaternary ammonium salts can have a molecular weight of from about 650 to about 700.

[0034] As described above, the above charged density ranges are for the components in a neat form. When contained in a debonder composition, however, the charge densities can be diluted. For example, if a low to medium charge density imidazoline quaternary ammonium salt is present in the composition in an amount of 21% by weight, the charge density of the salt in the solution can be from about 0.07 meq/g to about 0.09 meq/g. If a high charge density imidazoline quaternary ammonium salt is present in an amount of 17% by weight, the salt can have a charge density of from about 0.20 meq/g to about 0.21 meq/g.

[0035] In the QuaSoft 229 product, the difference in charge densities in the quaternary ammonium salts is believed to be due to the amount of converted tertiary amines present. For example, the high charge density quaternary ammonium compounds show a high degree of conversion of the tertiary amines to the quaternary positively charged amines. The low/medium density quaternary amines contain more unconverted tertiary amines. However, tertiary amines do not carry any charge, and thus the overall charge density is less for that reason. Including in the composition a certain amount of tertiary amines has been observed to improve handfeel. Therefore, in a preferred composition of the invention, quaternary amines having both relatively high and relatively low charge densities are provided.

[0036] QuaSoft 229 applied at the wet end of the papermaking process may increase surface softness while maintaining an acceptable base sheet strength. It has been discovered by the present invention, however, that topically applying the composition directly on the sheet will provide increased surface softness at similar strength levels. In addition, increasing the amount of chemical softener in the sheet of tissue, either by wet end addition or topical application, improves the surface softness at similar strength levels when compared to other debonding agents. This may be due to the increased amount of composition that is retained on the tissue surface.

[0037] In another embodiment of the current invention, a non-ionic silicone emulsion may be used as the debonder. This emulsion may be used in conjunction with an imidazoline quaternary ammonium salt composition as described above or another debonder.

[0038] In one embodiment, one such non-ionic silicone emulsion additive is Dow Corning DC-2-5304. This additive is a white liquid comprising (by weight) about 40-70% water; 30-60% polydimethylsiloxane (molecular weight of from 8,000 to 12,000); 5-10% dimethyl, methylhydroxypropyl, ethoxylated propoxylated siloxane; 3-7% polyethylene oxide, propylene oxide) monoallyl ether; and 1-5% alkoxy polyethoxy ethanol.

[0039] In a further embodiment of the current invention, an aminofunctional siloxane in a cationic emulsion may be used as the debonding agent. In one particular embodiment, DC-2-8050, a cationic emulsion manufactured by Dow Corning Corp. of Midland, Mich., may be used as the debonder. DC-2-8050 debonder includes from about 15% to about 40% by weight of an aminofunctional siloxane (molecular weight of from 30,000 to 40,000), from about 7% to about 13% by weight of polyoxyethylated tridecyl alcohol, from about 7% to about 13% by weight hexadecyltrimethyl ammonium chloride, and from about 3% to about 7% by weight octamethyl cyclotetrasiloxane.

[0040] Any of the debonders mentioned above are added during the manufacture of the tissue. The addition may be at the wet end or applied to the surface of a formed sheet. When applied to the surface of a paper product, the debonder composition can be applied by spraying, rotogravure printing, trailing blade coating, flexographic printing, and the like.

[0041] In general, the debonder composition of the present invention can be applied to any suitable paper product, such as bath tissue, facial tissue, paper towels, industrial wipers, and the like. The paper product can be made in any suitable manner. For instance, paper products utilized in the present invention can be made utilizing 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 known in the paper art. By way of illustration, various tissue making processes are disclosed in U.S. Pat. No. 5,607,551 issued Mar. 4, 1997 to Farrington and U.S. Pat. No. 5,667,636 issued Sep. 16, 1997 to Engel et al., which are incorporated herein by reference.

[0042] A variety of conventional papermaking apparatus may be used in the application of this invention, as they are known by persons of skill in the art. Conventional operations may be used with respect to the stock preparation, headbox, forming fabrics, web transfers, and creping and drying.

[0043] Stock preparation equipment may be used to apply chemical additives to papermaking fibers according to one embodiment of the present invention. The stock preparation equipment may include a first stock chest, a second stock chest, and a dewatering device between the stock chests. Papermaking fibers and water are added to the first stock chest to form a fiber slurry. The fiber slurry in the first stock chest typically has a consistency of about 20% or lower, and particularly about 5% or lower, such as about 3 to about 5%. The fiber slurry in the first stock chest is desirably under agitation using a mixing blade, rotor, recirculation pump, or other suitable device for mixing the fiber slurry.

[0044] When the debonding agent is added in the wet end of the papermaking apparatus, one or more chemical additives are supplied from a reservoir and added to the fiber slurry in the first stock chest. The amount of chemical additive may range from about 5 to about 20 kg./metric ton in the outer layer of the web. In particular embodiments, the chemical additive comprises a blend of imidazoline-based debonding agents and is added to one layer of the fiber furnish in an amount from about 7.5 to about 15 kg./metric ton, or more. The range provided is simply a workable range, and in no way is intended to be limiting of the scope of the invention. The fiber slurry and chemical additive are desirably allowed to remain together in the first stock chest under agitation for a residence time sufficient to allow the papermaking fiber to absorb a substantial portion of the chemical additive. A residence time of about 15 to about 30 minutes, for instance, may be sufficient.

[0045] The fiber slurry is thereafter transferred through suitable conduits and a pump to the dewatering device. In this illustrated embodiment, the dewatering device can comprise a belt press, although alternative dewatering devices such as a centrifuge, a nip thickening device or the like may be used. The fiber slurry is injected between a pair of foraminous fabrics such that press filtration is removed from the slurry. The press filtrate comprises a portion of the process water along with unabsorbed chemical additives in the water. The belt press or other dewatering device suitably increases the fiber consistency of the slurry to about 20% or greater, and particularly about 30% or greater. The unabsorbed chemical additive can be removed from the process or used as dilution water in prior stock preparation steps, but importantly it is not sent forward with the chemically treated finish.

[0046] In those applications for which two stock chests are used, the thickened fiber slurry is then transported through conduits to a second stock chest. The fiber slurry is then re-diluted with fresh water from a suitable reservoir and optionally agitated using a mixing device. The fiber consistency of the slurry is suitably decreased to about 20% or less, and particularly about 5% or less, such as about 3 to about 5%. The fiber slurry may then be removed from the second stock chest through suitable conduits and a pump for subsequent processing. Alternatively, the fiber slurry may be processed through the foregoing procedure again in an effort to further increase the chemical additive retention level.

[0047] In an alternative embodiment of the present invention, the stock preparation equipment may be used to apply chemical additives to papermaking fibers and to mechanically treat the fibers. Thus, the equipment used may optionally comprise three stock chests, two dewatering devices, two dilution water chests, and a disperser for mechanically treating the papermaking fibers.

[0048] Papermaking fibers and water are added to the first stock chest to form a fiber slurry. The fiber slurry in the first stock chest desirably has a consistency of about 20% or lower, and particularly about 5% or lower. One or more chemical additives are supplied from a reservoir and added to the fiber slurry in the first stock chest while under agitation.

[0049] After a sufficient residence time, the fiber slurry is transferred through suitable conduits and a pump to a belt press or other suitable dewatering device. Unabsorbed chemical additives in the water are removed with the press filtrate during the pressing operation and stored in the first dilution water chest. The contents of the first dilution water chest may be used as either pulper make-up water or dilution water or may be discarded. The dewatering device suitably increases the fiber consistency of the slurry to about 20% or greater, and particularly about 30% or greater.

[0050] The thickened fiber slurry is then transported through suitable conduits to the disperser for mechanical treatment of the fibers. Dispersers suitable for use in the present method are disclosed in U.S. Pat. Nos. 5,348,620 and 5,501,768 which are incorporated herein by reference.

[0051] After dispersing, the fiber slurry may be transported via conduits to a second stock chest. A second chemical additive or second group of chemical additives may be supplied from a reservoir and added to the fiber slurry in the second stock chest while under agitation. Additionally, the fiber slurry may optionally be diluted with filtrate from a source described hereinafter. The fiber consistency of the slurry suitably decreases to about 20% or lower, and particularly about 5% or lower, such as about 3 to about 5%. In particular embodiments, the second chemical additive comprises a softening agent and/or a debonding agent, and the fiber slurry is not subjected to high shear refining forces such as those generated in a disperser once the softening and/or debonding agent is added to the fiber slurry.

[0052] One suitable process for making paper products from the fiber slurries is the uncreped through-air drying method (UCTAD). One or more embodiments of the uncreped through-air drying method is disclosed in U.S. Pat. 5,656,132 to Farrington, Jr. et al., which is incorporated herein by reference.

[0053] As shown in FIG. 2, a twin wire former having layered papermaking headbox 10 injects or deposits a stream 11 from the fiber slurry onto the forming fabric 13 to form a cellulosic web. The web is then transferred to fabric 17 which serves to support and carry the newly-formed wet web downstream in the process as the web is partially dewatered to a consistency of about 10 dry weight percent. Additional dewatering of the wet web can be carried out, such as by vacuum suction, while the wet web is supported by the fabrics.

[0054] The transfer fabric 17 travels at a slower speed than the forming fabric in order to impart increased MD (machine direction) stretch into the web. A so-called "kiss" transfer is completed in many embodiments to avoid compression of the wet web, preferably with the assistance of a vacuum shoe. The transfer fabric may be a fabric having impression knuckles or it may be a smoother fabric such as Asten 934, 937, 939, 959 or Albany 94M, which are fabrics known to persons of skill in the art.

[0055] If the transfer fabric is of the impression knuckle type described herein, it can be utilized to impart some of the same properties as the through-air drying fabric and can enhance the effect when coupled with a through-air drying fabric also having the impression knuckles. When a transfer fabric having impression knuckles is used to achieve the desired CD (cross direction) stretch properties, it provides the flexibility to optionally use a different through-air drying fabric, such as one that has a decorative weave pattern, to provide additional desirable properties not otherwise attainable.

[0056] The web then may be transferred from the transfer fabric to a through-air drying fabric 19 with the aid of a vacuum transfer roll 20 or a vacuum transfer shoe. The through-air drying fabric typically travels at about the same speed or a different speed relative to the transfer fabric. If desired, the through-air drying fabric may be run at a slower speed to further enhance MD (machine direction) stretch. Transfer is preferably carried out with vacuum assistance to ensure deformation of the sheet to conform to the through-air drying fabric, thus yielding desired bulk, flexibility, CD stretch and appearance. The through-air drying fabric is preferably of the impression knuckle type, but it is not necessary that it be of that type.

[0057] The level of vacuum used for the web transfers can be from about 3 to about 15 inches (about 75 to about 380 millimeters) of mercury, such as from about 10 to about 15 inches (about 254 to about 380 millimeters) of mercury. The vacuum shoe (negative pressure) used in the rush transfer step 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 addition to or as a replacement for sucking it onto the next fabric with vacuum. Also, a vacuum roll or rolls can be used to replace the vacuum shoes.

[0058] While supported by the through-air drying fabric, the web is final dried to a consistency of about 94% or greater by the throughdryer 21 and thereafter transferred to a carrier fabric 22. The dried base 23 sheet is transported to the reel 24 using carrier fabric 22 and an optional carrier fabric 25. An optional pressurized turning roll 26 can be used to facilitate transfer of the web from carrier fabric 22 to fabric 25.

[0059] Many fiber types may be used in the practice of the present invention including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like. Numerous different types of papermaking fibers may be employed, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulosic fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers), some component portion of synthetic fibers (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulping processes), thermomechanically pulped, chemithermomechanically pulped, and the like.

[0060] Mixtures of any subset of the above mentioned or related fiber classes may be used. The fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties.

[0061] Further, a single headbox or a plurality of headboxes may be used in the practice of the invention. The headbox or headboxes may be stratified to permit production of a multilayered structure from a single headbox jet in the formation of a web. In particular embodiments, the web may be produced with a stratified or layered headbox to preferentially deposit shorter fibers on one side of the web for improved softness, with relatively longer fibers on the other side of the web or in an interior layer of a web having three or more layers. The web is desirably formed on an endless loop of foraminous forming fabric which permits drainage of the liquid and partial dewatering of the web. Multiple embryonic webs from multiple headboxes may be couched or mechanically or chemically joined.

[0062] In one embodiment, the formed paper web contains three layers of fibers. In particular, the web may contain a middle layer of softwood fibers surrounded by two outer layers of hardwood fibers. Paper broke can also be added to the outer layers in an amount less than about 25% by weight of the layer, for instance, in an amount of less than about 10% by weight of the layer. In this embodiment, each of the outer layers can comprise from about 20% to about 40% of the total weight of the web.

[0063] The debonder may also be applied using topical application, such as spraying, as opposed to addition at the wet end. In fact, the present invention has discovered that, in some embodiments, certain debonders may yield better results from topical application than wet end addition. Spraying is performed using a spray nozzle which adds the debonder to the tissue. In one embodiment, the debonder may be applied to the top layer of the tissue, or upon the layer that will ultimately become the top layer of the tissue. The debonder may also be applied to the outer layers of a multi-layer tissue. The debonder may require dilution with water when applying using a spraying method. For example, the debonder may be present in an aqueous composition in an amount less than about 30% by weight, such as in an amount less than about 20% by weight. For example, in one embodiment, the debonder can be present in an aqueous composition in an amount less than about 10% by weight, such as less than 5% by weight. In one particular embodiment, the debonder can be present in an aqueous composition in an amount less than about 3% by weight.

[0064] In applying a debonder topically, the amount of moisture contained in the debonder composition and contained within the web can be adjusted to optimize results. For instance, in a three layer tissue containing a softwood layer surrounded on each side by a hardwood layer, the softwood layer serves as the strength layer. In this embodiment, the debonder can be added topically such that it does not substantially migrate to the softwood layer. In particular, the less moisture added to the outer layers or present in the outer layers, the less chance there is of migration to the inner softwood layer. Further, the less migration, the more debonder remains on the outer layers that actually contact the user.

[0065] The amount of moisture contained within the web when the debonder composition is applied to the web can vary depending on the particular application and process conditions. In general, the consistency of the web can be from about 20% to about 80%. More particularly, the consistency of the web can be from about 25% to about 60%.

[0066] In one embodiment, application of the debonder is performed between a rush transfer step and a through-air drying step. Prior to the through air drying step, the consistency of the web in one embodiment is less than about 40% such as from about 25% to about 29%. For instance, in one embodiment, the consistency is from about 26% to about 29% after rush transfer and prior to drying.

[0067] In an alternative embodiment, the papermaking process can include a first through-air dryer and a second consecutive through-air dryer. Application of the debonder can be performed in between the through-air dryers. In this embodiment, the consistency of the web can be from about 40% to about 80%.

[0068] Other chemical additives may be used in conjunction with the present invention. These additives include: dry strength aids, wet strength aids, softening agents, debonding agents, absorbency aids, sizing agents, dyes, optical brighteners, chemical tracers, opacifiers, dryer adhesive chemicals, and the like. Additional forms of chemical additives may include: pigments, emollients, humectants, virucides, bactericides, buffers, waxes, fluoropolymers, odor control materials and deodorants, zeolites, perfumes, debonders vegetable and mineral oils, humectants, sizing agents, superabsorbants, surfactants, moisturizers, UV blockers, antibiotic agents, lotions, fungicides, preservatives, aloe-vera extract, vitamin E, or the like. Suitable chemical additives are adsorbable by the cellulosic papermaking fiber and are usually water soluble or water dispersible.

[0069] The following Examples serve to illustrate possible approaches pertaining to the present invention. The particular amounts, proportions, compositions, and parameters are meant to be exemplary, and are not intended to specifically limit the scope of the invention.

EXAMPLES 1-3

[0070] An uncreped through air dried tissue product was used in this Example. The chemicals screened included the three following examples:

[0071] 1) QuaSoft 229 (i.e. codes QS-2, QS-3, QSWE-2) (applied at either the wet end or by spraying)

[0072] 2) aminofunctional siloxane, DC-2-8050, a cationic emulsion manufactured by Dow Corning of Midland, Mich. (codes AFS-2 and AFS-3) (applied at the wet end)

[0073] 3) nonionic silicone emulsion, DC-2-5304, manufactured by Dow Corning of Midland, Mich. (codes SC-2 and SC-3) (applied by hydraulic spraying after rush transfer and before through air drying).

[0074] The speed of the continuous sheet former machine used in the testing was about 50 ft./minute.

[0075] FIG. 1 shows a graph of softness (designated as IHR) versus Product Strength. Product strength refers to tissue strength, as measured in GMT (geometric mean tensile strength). Positive IHR scores indicate that more of the attribute is present, while negative scores indicate that less of the attribute is present. For purposes of this testing, the designations on FIG. 1 are as follows:

[0076] AFS=aminofunctional silicone;

[0077] QS=QuaSoft 229;

[0078] QSWE=QuaSoft 229 applied at the wet end of the papermaking process;

[0079] C6027=Witco's C-6027 product;

[0080] SC=nonionic silicone composition

[0081] Numerals following a letter designation indicate different run numbers.

[0082] Samples containing a non-ionic silicone, an aminofunctional silicone and QuaSoft 229 showed surprisingly good results in this test, especially as compared to the control (C-6027). FIG. 1 illustrates the product results for the control (C-6027) and seven test variants (hereafter called "codes"). The chemicals applied by spraying are represented by codes QS2, QS3, SC2, SC3, the others were added at the wet-end (AFS2, AFS3, QSWE2 and C-6027).

[0083] All codes were showed greater softness characteristics than the control (C-6027; Witco product) even though the control had the lowest GMT. These results represent a surprising and unexpected departure from the regular softness/strength curve. That is, although one usually sees an inverse correlation between strength and softness, no such inverse correlation is seen in the codes as compared to the control in these results.

[0084] Of particular interest, the results in FIG. 1 show that when the debonder composition containing the blend of the imidazoline quaternary ammonium salts is applied to the paper product, an increase in softness occurs when the composition is applied topically as opposed to being applied at the wet end.

[0085] Samples are shown below in Table 1.

1TABLE 1 Codes for Samples Used in Testing Type of Target add-on rate Code Softener Application on total basesheet Control C-6027 Wet-end 0.48% actives AFS-2 2-8050 Wet-end 0.48% actives AFS-3 2-8050 Wet-end 1.3% actives SC-2 2-5304 Hydraulic spray 0.75% actives SC-3 2-5304 Hydraulic spray 1.75% actives QS-2 QuaSoft 229 Hydraulic spray 2.92% total solids QS-3 QuaSoft 229 Hydraulic spray 5.1% total solids QSWE-2 QuaSoft 229 Wet-end 5.1% total solids

[0086] The spraying equipment used comprised Quick Veejet Spray Nozzles: #650017 capacity/size with a 40 psi/0.017 gal/min nozzle. The model machine was set up to simulate the uncreped through-air drying process for the trial. Headbox #1 was used to form the outer layer of the sheet with Headbox #2 adding the middle layer of sheet.

[0087] The spray boom was located on the #3 fabric run between rolls, just after the vacuum slot on the fabric. The spray fans were aimed directly at the sheet. Given the configuration of the machine, this resulted in the chemistry being sprayed at the outer layer (which was also the layer supported by the fabric). This is consistent for topical application for a normal three strata tissue structure, since the outer strata are comprised predominantly of eucalyptus fiber.

[0088] Two nozzles were placed to improve uniformity. A plastic tent and evacuation system was arranged. The concentration of the chemical solutions was adjusted accordingly to obtain the desired target add-on. Water, tinted with food coloring was used to visually set the spray distance at approximately 12 inches. For this trial, the geometry and pressure were maintained constant.

[0089] In the tests using a wet end application, a Parez 631-NC product manufactured by Cytec is a glyoxylated polyacrylamide temporary wet strength resin. The glyoxylated polyacrylamide wet strength resin was added to the machine chest and mixed for 15-20 min. Softener was added afterwards to the machine chest and mixed for about 20 min. Sheet strength target was set at 750 @50 GMT.

[0090] It is understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. The invention is shown by example in the appended claims.

Claims

What is claimed:

1. A tissue product, comprising: (a) cellulosic fibers, and (b) an adsorbable chemical debonding additive, wherein the additive comprises at least two quaternary ammonium salts, the quaternary ammonium salts comprising a first imidazoline quaternary ammonium salt having a first charge density and a second imidazoline ammonium salt having a second charge density, the first charge density being greater than about 0.9 meq/g and the second charge density being less than about 0.7 meq/g when the ammonium salts are in a neat form, and wherein the quaternary ammonium salts comprise between about 10% and 60% by weight of the additive when water is not present.

2. The tissue product of claim 1, wherein the quaternary ammonium salts comprise between about 40% and about 60% by weight of the additive when water is not present.

3. The tissue product of claim 1, in which the debonding additive comprises by weight, (i) about 19-24% of the first imidazoline quaternary ammonium salt; and (ii) about 15-20% of the second imidazoline quaternary ammonium salt.

4. The tissue product of claim 1, in which the additive further comprises of between about 12-19% lubricant by weight.

5. The tissue product of claim 1, in which the additive further comprises about 20-70% by weight nonionic surfactants.

6. The tissue product of claim 1, in which the additive comprises between about 34% and about 44% by weight of the imidazoline quaternary ammonium salts.

7. The tissue product of claim 1, in which the tissue product is multi-layered.

8. The tissue product of claim 7, in which the tissue product includes a middle layer positioned in between a first outer layer and a second outer layer of fibers, the first and second outer layers comprising hardwood fibers, the middle layer comprising softwood fibers.

9. The tissue product of claim 8, in which the debonding additive is applied to the tissue product such that the additive is substantially only present in the first and second outer layers.

10. The tissue product of claim 1, wherein the debonding additive has been applied to at least one surface of the tissue product.

11. The tissue product of claim 10, in which the debonding additive has been applied to both sides of the tissue product.

12. The tissue product of claim 1, wherein the first charge density is from about 1.22 meq/g to about 1.23 meq/g.

13. The tissue product of claim 1, wherein the second charge density is from about 0.35 meq/g to about 0.42 meq/g.

14. A method of making a tissue product, comprising: (a) providing a fiber furnish of water and cellulosic fibers, (b) forming the fiber furnish into a tissue layer, and (c) applying to the surface of the tissue layer an adsorbable chemical additive, the chemical additive comprising a mixture of quaternary ammonium salts, the mixture comprising a first imidazoline quaternary ammonium salt, and a second imidazoline quaternary ammonium salt.

15. The method of claim 14 further comprising the step of: (d) combining the tissue layer with additional tissue layers to form a layered tissue product.

16. The method of claim 14 further comprising the steps of: (d) providing a second fiber furnish to form a second tissue layer, (e) spraying upon the surface of the second tissue layer the adsorbable chemical additive, and (f) forming the tissue product using the tissue layers as outer plies.

17. The method of claim 14, wherein the first imidazoline quaternary ammonium salt has a first charge density and the second imidazoline quaternary ammonium salt has a second charge density, the first charge density being greater than about 0.9 meq/g, the second charge density being less than about 0.7 meq/g.

18. The method of claim 17, wherein the first charge density is from about 1.22 meq/g to about 1.23 meq/g.

19. The method of claim 17, wherein the second charge density is from about 0.35 meq/g to about 0.42 meq/g.

20. The method of claim 14, wherein the additive is applied to the tissue layer when the tissue layer has a consistency of greater than about 20%.

21. The method of claim 14, wherein the additive is applied to the tissue layer when the tissue layer has a consistency of greater than about 25% and less than about 80%.

22. The method of claim 14, wherein the additive is applied to the tissue layer in between a rush transfer operation and a through-air drying operation.

23. The method of claim 14, wherein the additive is applied to the tissue layer in between a first through-air drying operation and a second through-air drying operation.

24. The method of claim 14, wherein the tissue layer comprises a stratified fiber furnish including a first layer and a second layer, the first layer comprising hardwood fibers, the second layer comprising softwood fibers.

25. The method of claim 24, wherein the additive is applied to the first layer containing hardwood fibers, the additive being applied in a manner such that substantially all of the additive is contained within the first layer containing the hardwood fibers.

26. The method of claim 14, wherein the tissue layer comprises a stratified fiber furnish including a middle layer positioned between a first outer layer and a second outer layer, the first and second outer layers comprising hardwood fibers, the middle layer comprising softwood fibers.

27. The method of claim 26, wherein the additive is applied to the first outer layer and the second outer layer, the additive being applied in a manner such that the additive remains substantially within the first and second outer layers without migrating to the middle layer.

28. The method of claim 14, wherein the additive further comprises a lubricant and a surfactant.

29. The method of claim 28, wherein the lubricant comprises a lanolin derivative.

30. The method of claim 28, wherein the surfactant comprises a polyethylene glycol ester, a polypropylene glycol ester, or mixtures thereof.

31. A tissue product comprising: a paper web comprising cellulosic fibers; and an adsorbable chemical debonding additive topically applied to the paper web, the debonding additive being present in the web in an amount of from about 0.01% to about 10% by weight, the debonding additive comprising an aminofunctional siloxane or a nonionic siloxane, the debonding additive being applied to the paper web while the web has a consistency of less than about 80%.

32. A tissue product as defined in claim 31, wherein the non-ionic silicone comprises polydimethylsiloxane.

33. A tissue product as defined in claim 31, wherein the debonding additive is applied to the paper web when the paper web is at a consistency of less than about 60%.

34. A tissue product as defined in claim 31, wherein the debonding additive is applied to the paper web when the paper web is at a consistency of less than about 40%.