The following article was published October 6, 2003 on IP.com as Article 19880D.
High-bulk Tissue Laminates for Building Materials and Other PurposesJeffrey D. Lindsay, Fung-Jou Chen, and Julie Bednarz
IntroductionA wide variety of novel uncreped tissue products have been developed in recent years at Kimberly-Clark Corporation. In the past, it was generally believed that creping was needed to produce high-bulk tissue, but creping introduced many limitations. Advances in through-drying technology combined with other operations in novel ways have allowed soft, high bulk tissue to be made without the need to crepe the web. By eliminating the physical and chemical restraints imposed by creping, uncreped through-air dried (UCTAD) tissue has provided new possibilities in the degree of texture, bulk, resiliency, and other properties that can be achieved. Some forms of UCTAD tissue are suitable for creating thick structures with bulk and rigidity laminating to form high bulk multi-ply structures that can be used for many purposes previously outside the scope of conventional tissue. For example, multiple layers of uncreped tissue can be laminated together and optionally coated or impregnated to create board-like materials suitable as a lightweight construction material, thermal insulating material, sound proofing material, customized wall contouring, absorbent ground panels, and so forth.
In this paper, we discuss the physics and properties of UCTAD tissue compared to conventional creped tissue, and disclose how laminated multi-ply structures of UCTAD tissue can be used for building materials. We also note that some other forms of tissue can also be used to make related products.
Physics of Uncreped and Creped TissuePaper towel and other tissue products made with creping has long been limited in terms of the bulk and mechanical properties that can be achieved. This is partly because the creped tissue web must first be dried in a flat, densified state. In creping, a wet, embryonic tissue web is pressed into a flat, dense, moist state onto a large heated drum known as a Yankee dryer, the surface of which is continuously sprayed with a solution of chemicals containing adhesive compounds and often one or more release agents, as shown in Figure 1. The tissue dries rapidly from conductive heat transfer from the drum and from convective drying due to hot air impinging on the exposed side of the tissue. As the tissue dries, hydrogen bonds form between the fibers, creating a bond-defined web morphology that is flat and dense.
Figure 1. Tissue web being dried and creped on a Yankee dryer.
The creped web can be soft and bulky, but when the web is wetted, the cellulose fibers swell and straighten out, relaxing the stresses in the fibers and partially returning the morphology of the web to its bond-defined state prior to creping, which was flat and thin. This is depicted in Figure 2, which schematically depicts the structure of a group of fibers on a Yankee dryer before creping, after creping, and then after rewetting, showing the transition from a dense state to a bulky creped state characterized by kinks or deformations in individual fibers, followed by a return to a dense state when the kinks and deformations have been largely relaxed by the wetting and swelling of the fibers. In general, when a creped sheet is wetted, the structure imparted by creping to the dry web is substantially lost and the sheet tends to flatten out and lengthen in the machine direction by an amount approximately equal to the degree of foreshortening imparted during creping.. If parts of the web are constrained and prevented from expanding uniformly in the machine direction, regions of the web may become coarsely wrinkled upon wetting, as one can readily demonstrate by pouring a small quantity of water in the middle of a dry creped sheet as it rests on a flat surface. Capillary forces between the wetted region and the flat surface can prevent some expansion, causing the web to buckle, or dry regions around a wetted region can impose restraint and cause the wetted region to buckle or warp as it tries to expand in the machine direction.
Figure 2. Schematic representation of fiber changes as a web on
a Yankee dryer is creped and subsequently wetted.
In addition to limitations imposed by the dense state of the tissue web prior to creping, creping also imposes restraints in the chemistry of the web. During drying, the adhesive materials bond the web to the drum. A creping blade pressed against the Yankee dryer then removes the tissue, suddenly fracturing the adhesive bonds and forcing the tissue to become foreshortened, with disruption to some fiber-fiber bonds and bulking of the sheet with numerous small peaks and valleys in its structure, often associated with kinks and compressions in individual fibers. The art of creping depends on carefully maintaining the right level of adhesion between the tissue and the Yankee dryer. If the level of adhesion is too great, the sheet may break, and if it is too low, the sheet may be removed with little foreshortening or softening of the web. Many efforts are made to adjust the balance between adhesion and releasability of the web, and great care is also taken to find the right balance of web dryness at the crepe blade, blade angle, and other parameters that govern creping. Because the physics of creping is intimately tied to the chemistry binding the web to the surface of the Yankee, the tissue maker is greatly constrained regarding the chemistry of the web itself. Changes in papermaking additives at any point prior to the creping operation made modify the adhesion of the web to the Yankee, and some otherwise desirable additives may make creping nearly impossible.
It has been discovered that tissue with many of the commercially desirable properties of creped tissue can be made without creping. Principles for producing soft UCTAD tissue have been disclosed in a series of patents issued to Kimberly-Clark Corporation (US Patent No. 5,932,068, issued Aug. 3, 1999 to Farrington, Jr. et al.; U.S. Patent No. 5,672,248 issued to Wendt et al.; US Pat. No. 5,048,589, issued Sept. 17, 1991 to Cook and Westbrook; and US Pat. No. 6,436,234, issued Aug. 20, 2002 to Chen et al.). In general, an uncreped tissue web is foreshortened while still moist in a process called rush transfer, which is transfer of the web from one fabric to a second slower-moving fabric under carefully controlled conditions (e.g., US Patent No. 5,888,347, issued Mar. 30, 1999 to Engel et al.), and the moist web is placed on advanced three-dimensional through-drying fabrics (US Patent No. 5,429,686, issued July 4, 1995 to Chiu et al.; US Patent No. 6,120,642, issued Sept. 19, 2000 to Lindsay and Burazin; US Patent No. 6,398,910, issued June. 4, 2002 to Burazin et al.; and PCT publications WO 03/40464, and WO 03/40470, both published May 15, 2003 by Burazin and Lindsay) after which hot air passes through the web to dry it in a morphology corresponding to that of the fabric. Figure 3 depicts one configuration for a through dryer, showing a moist web that has been transferred to a through-drying fabric which then passes over a porous through dryer, such as a honeycomb roll, through which heated air passes from a drying hood. The hot air passing through the web provides high heat transfer rates and effective drying without significant compression of the web.
Figure 3. Tissue web being dried on a through dryer.
Through-air drying does not densify the web, unlike Yankee drying, and helps maintain bulk at the microscopic level as well as imparting high macroscopic bulk from the texture of the fabric. Because the web is in a bulky, three-dimensional state as hydrogen bonds are formed during drying, the bond-defined morphology of the web is inherently three-dimensional. Thus, when a textured UCTAD web is wetted, the morphology of the web remains relatively unchanged, as shown in Figure 4.
Figure 4. Schematic representation of fiber changes as a web
through-dried on a 3-D TAD fabric is subsequently wetted.
An UCTAD web can be compressed, embossed, or creped after production, if desired, imparting kinks and microcompressions to the dry fibers, but when the web is subsequently wetted, the tissue tends to return to its original three-dimensional form. Thus, a highly calendered UCTAD web can increase in bulk when wet, moving from a dense state to a high-bulk, textured state when wetted (US Patent No. 5,779,860, issued July 14, 1998 to Hollenberg et al.), quite contrary to the behavior of conventional creped tissue.
The machine direction stretch and bulk from creping are now imparted by rush transfer and through-air drying on novel fabrics. Tactile softness can be enhanced, if desired, by using layered structures with short hardwood fibers such as eucalyptus on the outer layers of the tissue. The use of chemical debonders in the outer layers, or specially treated fibers, can also be considered (US Patent No. 5,932,068, issued Aug. 3, 1999 to Farrington, Jr. et al). However, for the present paper, the issue of softness is typically not an important consideration.
In a related patent (US Pat. No. 6,436,234, issued Aug. 20, 2002), Chen et al. discovered that very high bulk and wet resiliency can be obtained in tissue through a combination of high-yield fibers such as bleached chemi-thermo-mechanical pulp (BCTMP), chemical wet strength agents such as epichlorohydrins, and through-air drying on high-bulk fibers. Such structures were shown to maintain high bulk under compressive loads, demonstrating measures of wet resiliency well above that of previously known tissue materials or other high-bulk cellulosic products. Such materials appear to have particularly interesting potential as laminated multi-ply materials.
Multi-ply UCTAD Structures as Construction MaterialsWe propose a class of products comprising multi-layered laminates of high-bulk, textured through-air dried tissue, particularly UCTAD tissue. Generally, tissue layers are joined with an inter-ply adhesive such as a hotmelt, a thermosetting adhesive, a glue, resin, or other curable adhesive component, or thermoplastic particles that have been at least partially fused to join adjacent tissue layers together. Thermoplastic particles can include binder fibers such as sheath-core bicomponent fibers with a low-melting-point sheath around a high-melting-point core, wherein heat is applied to fuse the sheath but not the core. Principles for forming a multi-layered laminate of UCTAD tissue are disclosed in PCT publication WO 03/59139, "Sponge-Like Pad Comprising Paper Layers and Method of Manufacture," by Chen et al., published July 24, 2003, in which low-cost sponge substitute materials are disclosed. Figure 5 depicts a cross-section of a similar multi-ply bonded structure comprising resilient, three-dimensional through-dried webs.
Figure 5. Cross-section of a board comprising multiple
layers of resilient tissue bonded together.
For construction materials, much larger sheets than those one might use for a cleaning tool. The tissue laminated may be large enough to provide large panels or boards suitable for use in construction. For example, the laminate may have a width and a length independently selected from any of the following ranges: at least 4 inches, at least 8 inches, at least 12 inches, at least 16 inches, at least 24 inches, at least 36 inches, at least 48 inches, at least 60 inches, and at least 80 inches. For example, panels may have a width from 12 to 36 inches, and a length from 24 to 160 inches or greater. Thickness of the board may be at least any of the following: 0.3 inches, 0.6 inches, 1 inch, 1.5 inches, 2 inches, 4 inches, 8 inches, and 12 inches. Exemplary materials could include any of the following:
Figure 6. Board comprising multiple layers of 3-D tissue
laminated together with a smooth facing layer.
Such shapes may be formed from one stack of tissue that is molded, or from multiple stacks that are joined together to create the desired geometry.
Other UsesThe laminates described herein can be used for many purposes, such as forming a portion of a wall (e.g., a temporary cubicle wall in an office), serving as insulation (either thermal or acoustic) for rooms or objects such as pipes, serving as a cushion to reduce impact or prevent injury, absorbing fluids and spills (e.g., hazardous wasters, oil, etc.), serving as temporary barriers or walls, serving as biodegradable soil stabilizers or erosion inhibitors, collecting oil or other liquids on a garage floor (a mat made from tissue laminates could serve as a disposable surface over which automobiles could drive, for example), serving as a shock-absorbing and sweat-absorbing mat, an exercise mat, etc. Panels of the laminates could also serve as disposable, absorbent mats for cleaning feet, or for use as floor mats in pet shelters, tents, etc. For construction purposes, the panels could augment or replace drywall, especially in areas where complex contours are needed or where high strength is not critical. Laminates could also serve as liners or pads to protect the body in contact sports. Bulletin boards could also be constructed from such material. Multiple panels may be combined in foldable form to have large boards that can be unfolded from smaller assemblies.
Further DetailsThe UCTAD tissue may have a basis weight from about 10 to about 200 gsm, such as from about 20 gsm to about 100 gsm, or from about 30 gsm to about 150 gsm. The ratio of adhesive materials to cellulose mass may be greater than any of the following: about 2%, about 5%, about 10%, about 20%, and about 30%, and may range from about 3% to about 75%, from about 5% to about 50%, or from about 10% to about 50%.
In one embodiment, the tissue layers are substantially impregnated with the adhesive material that joins the plies together, with continuous paths of adhesive material extending from one side the multi-layered assembly to the other. In one embodiment, at least 20% of the non-cellulose volume of the sample is occupied by adhesive material; in other embodiments, at least 40%, at least 60%, or at least 80% of the non-cellulose volume of the sample is occupied by adhesive material, which may be a resin suitable for impregnating multiple layers of tissue. (Vacuum-assisted impregnation or forced flow impregnation may be used, for example.). In one embodiment, a composite material is formed by impregnating substantially all of the void volume of the multi-layer assembly with a resin, such as a hot melt, an epoxy resin, a urethane, a thermosetting polymer, a silicone adhesive, and the like.
The multi-layered assembly can be substantially planar or may have a three-dimensional form such as a curved panel, two straight regions joined at an angle such as a panel with a 90-degree angle bend, and the like, and may have any shape such as a rectangle, an oval, a panel with cut-out elements of any shape, a panel with a sinuous cross-section, and the like. The panel or regions thereof may be apertured, slit, stamped, and the like.
The multi-layered assembly formed by laminating multiple bulky webs of textured tissue with adhesive materials can have almost any desired thickness and can have high rigidity. be used to create construction materials such as any of the following examples:
Alternatively, the layers can be joined together by non-adhesive means, either alone or in combination with some level of adhesive attachment. Non-adhesive means may include stitches applied by sewing, mechanical entanglement by needle punching, crimping, or other means, the use of hook and loop materials as mechanical fasteners to join one or more adjacent layers (or to join one multi-layered assembly to another), rivets, bolts, grommets, and the like.
The tissue layers can also vary throughout the structure in terms of fiber composition (e.g., some layers rich in high-yield fibers, with others predominantly softwood), degree of refining, basis weight, chemical additives (e.g., selectively higher wet strength levels or sizing levels in outer layers), filler content, web texture, web bulk, color, stiffness, etc. Some layers may be UCTAD tissue, while other materials can be use elsewhere. The other materials can include layers of polymeric films as outer layers or inner layers, spunbond or meltblown cover or internal layers, layers of untextured paper such as linerboard, corrugated medium, wax paper, silicone-treated paper, bag paper, and the like. Other forms of tissue can also be used, such as creped tissue, conventional paper towel materials such as BOUNTY® paper towel (Procter and Gamble Corporation, Cincinnati, Ohio), VIVA® paper towel (Kimberly-Clark Corporation, Houston, Texas), other through-dried materials, and the like.
The laminated multi-ply assembly can comprise an impervious or water resistant outer surface, which can be provided by any known method, either by pretreatment of layers for use as outer layers, or by treatment of outer surfaces of an existing multi-layer assembly, before or after activation of adhesive bonds between the layers. For example, a shrink-wrapped polymeric film can serve as a moisture barrier. Other materials, such as TYVEK® film or other films can be added to the entire outer surface or to one or more exposed surfaces of the multi-layered assembly. Alternatively, all or a portion of the outer surfaces of the assembly may be sprayed, printed, or coated with water resistant materials such as a film-forming emulsion, sizing agents, molten polyolefins (application of one or more meltspun layers to the multi-layer assembly or to one or more outer layers prior to forming the multi-layer assembly can be considered), etc.
The assembly can also comprise reinforcement means in selected locations, such as scrim materials between layers, patches between layers or on outside layers, strings or tow, stitches sewn along edges or other regions for reinforcement, and the like.
In one embodiment, the multi-layered assembly comprises three-dimensional tissue layers joined with a tacky water-soluble adhesive applied in a spaced-apart pattern on a surface of the tissue for joining to adjacent layers or for joining the entire multi-layer assembly to another multi-layer assembly or to another surface.
In another embodiment, an adhesive-treated portion of an outside layer of the tissue stack is covered with a release layer that can be removed to allow placement of the adhesive-treated region onto a surface, permitting the multi-layered assembly to be held in place, where it may also serve as a temporary absorbent layer than can be placed, for example, within a cabinet, drawer, refrigerator, or microwave. Such an attachable absorbent layer can be removed using water to wash away any residual adhesive. In another embodiment, the assembly is adhesively attached to a thin film, wherein the assembly can then provide mechanical strength or absorbent properties not provided by the film. An adhesive such as a tacky, water-soluble compound comprising polyvinyl alcohol and a plasticizing agent such as sorbitol, may be applied heterogeneously (e.g., in a printing step to print fine adhesive dots).
Adhesive matter may be preferentially applied to the most elevated portions of a surface of UCTAD tissue for good attachment to an adjoining surface, following the general principles and structures disclosed in U.S. Patent 5,990,377, "Dual-zoned Absorbent Webs," issued Nov. 23, 1999 to Fung-Jou Chen et al. In one embodiment, adhesive is applied to an UCTAD tissue, and then joined to another sheet or web as an outer layer. In another embodiment, no additional layer is joined to the UCTAD tissue after treatment with adhesive, in which case the adhesive may serve as pressure-sensitive adhesive for joining the laminate to a wall or other surface.
Example 1A structural panel having good rigidity was made by laminating 23 layers of UCTAD tissue and an additional top layer consisting of a sheet of commercial white photocopy paper with dimensions of 11 x 17 inches. The tissue was made substantially according to Example 4 of Kimberly-Clark's US Pat. No. 6,436,234, "Wet-Resilient Webs and Disposable Articles Made Therewith," issued Aug. 20, 2002 to Fung-Jou Chen et al. The tissue so made has a basis weight of 30 gsm and comprises 100% Temcel Tembec 525/80 spruce BCTMP pulp, with Kymene 557-LX wet strength agent of Hercules Chemical (Wilmington, DE) added to the fibrous slurry prior to web formation, at a dosage of 26 kg Kymene per ton of dry fibers (kg/ton). The through-drying fabric used to mold the three-dimensional sheet was a Voith I 10 Fabrics (formerly Lindsay Wire, Appleton, Wisconsin) T-116-3 TAD fabric. The transfer fabric (used to transfer the embryonic web from the forming fabric to the TAD fabric) was a Voith Fabrics T-216-3 fabric. A 27% rush transfer level was used when the web was transferred to the TAD fabric to impart machine direction stretch and to improve molding to the TAD fabric.
Tissue webs were cut to 11-inch by 18-inch rectangles and stacked, with binder fibers applied substantially uniformly across the upper surface of all tissue layers in the stack, such that binder fibers were between the uppermost photocopy paper layer and the underlying stack of tissue layers. The binder fiber was KOSA T-255 Bicomponent Fiber, 2.8 denier, cut to a fiber length of 0.25 inches and applied at a basis weight of 3 grams per square meter for each layer that received binder fibers. The binder fiber was applied pneumatically, wherein a predetermined quantity of binder fiber was dispersed and entrained in an air stream that passed through the tissue layer to uniformly deposit the entrained binder fibers over the exposed surface of the web, as described in PCT publication WO 03/59139, "Sponge-Like Pad Comprising Paper Layers and Method of Manufacture," by Chen et al., published July 24, 2003. The stack with binder fiber was placed under 0.03 psi load and then heated in a convection oven at 172°C for 60 minutes to cure the assembly (though much shorter curing times could be used). The stack was then removed and allowed to cool at room temperature. The resulting stack had a thickness of 0.685inches. The stack had a stiffness that imparted board-like properties, such that it did not bend or substantially deflect under its own weight when held horizontally from a spot on a side of the stack.
Example 2A stack similar to that of Example 1 was made, but with curing under a load of 0.06 psi, resulting in a board-like stack with a thickness of 0.65 inches.
Example 3A stack similar to that of Example 1 was made, but with 25 plies, 3 gsm of binder fibers per ply, curing under a load of 0.03 psi for 45 minutes at 172°C, resulting in a board-like stack with a thickness of 0.66 inches. No additional sheet of paper was attached to the stack. A portion of this stack was compressed under a high mechanical load to form a densified stack 0.25 inches in thickness, which was then cut and shaped to form two insoles for placement in a pair of shoes. These were inserted into the shoes and worn.
Example 4To illustrate the three-dimensional molding that can be done with a multilayer stack of UCTAD tissue, the tissue described in Example 1 was stacked as four plies with 3 gsm layers of binder fiber applied therebetween, and the stacked plies where then molded under the weight of loose, dry particles creating a load of about 0.03 psi to conform the stack to the shape of a pie plate. The assembly was then heated at 172°C for 50 minutes and cooled, resulting in a stack having a bowl-like contour.
ConclusionTextured, three-dimensional through-dried tissue can serve as a useful component of multi-layered laminates suitable for use as a board-like material or a molded material with many functions based on the inherent resiliency and other properties of the tissue. Such materials can provide useful low-cost alternatives to commonly used materials, and may offer new advantages in some embodiments due to other properties that can be achieved, such as absorbency, biodegradability, wet resiliency, breathability, porosity, lightness, etc.
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