High-bulk Tissue Laminates for Building Materials and Other Purposes

Introduction

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 Tissue

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 Materials

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:

• 25 layers of a 40 gram per square meter (gsm) basis weight UCTAD web comprising 1% permanent wet strength adhesive and a sizing agent, joined by applying about 5 to 10 gram per square meter of binder fibers between adjacent layers and then heating the stack with heated air passing through the assembly to fuse the binder fibers and join the plies. The stack of layers may be maintained in a flat, board-like state or may be bent or molded into a three-dimensional shape, either before, during, or after thermal treatment. Examples of shaped products include a curved corner panel or any of the shapes shown in Figures 6-12 below.

• 10 layers of an 80 gsm UCTAD web comprising refined softwood with a Canadian Standard Freeness (CSF) of less than 600 ml and sufficient wet strength resin to impart a wet:dry CD tensile strength ration of at least 0.1 or at least 0.2

• 20 layers alternating between 30 gsm UCTAD webs and 50 gsm UCTAD webs, joined by hot melt adhesive having a basis weight of about 20 gsm per UCTAD layer, applied heterogeneously with a patterned spray.

Figure 6. Board comprising multiple layers of 3-D tissue
laminated together with a smooth facing layer.

Figure 7. Curved panel formed by molding a tissue laminate.	Figure 8. Curved panel of laminated tissue for placement in corners.
Figure 9. Curved tissue laminate for wrapping a pipe or pole (insulation, cushioning, etc.).	Figure 10. Cylinder formed by stacking disks of flat tissue laminates.
Figure 11. Sinuous board (possible upright barrier, sound insulator, etc.).	Figure 12. Figure 12. Cross-shaped tissue laminate.

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 Uses

Further Details

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:

• Large panels of thermal insulating material such as 4-feet by 8-feet panels, one to four inches thick, formed from multiple layers of high basis-weight UCTAD tissue impregnated with hydrophobic binder resin that imparts water resistance and strength to the multi-layered assembly.

• Custom curved panels that are formed by placing a partially bonded or unbonded panel in a desired configuration, and then applying heat to fuse binder material between layers. The applied heat may be applied by convective heating (e.g., a blow dryer), by application of radiofrequency energy, ultrasonic energy, and the like, for sufficient time to fuse the materials together.

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 1

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 2

Example 3

Example 4

Conclusion