MXPA02001684A - Tissue products having increased absorbency. - Google Patents

Abstract

A tissue product containing a cellulosic fibrous material and less than about 10 wt. % of a superabsorbent material (e.g., fibers, particles, etc.) is provided. In some instances, the superabsorbent material can absorb between about 100 to about 350 grams of an aqueous solution per gram of superabsorbent material. In some embodiments, the superabsorbent material can be applied at the stock preparation stage of a papermaking process, and can be provided in a dry or preswollen state.

Description

TISU PRODUCTS THAT HAVE INCREASED ABSORBANCE Related Requests The present application is based on the additional application filed on August 23, 1999, which has serial number 60 / 150,325.

BACKGROUND OF THE INVENTION Tissue products, such as facial tissues, paper towels, bath tissues, and the like, are designed to include several important properties. For example, the products should have good volume, a smooth feeling and should have good integrity. Furthermore, it is often desirable to provide such tissues with high absorbency characteristics, particularly when used in certain applications such as paper towels.

In the past, superabsorbent materials have been applied to paper products to increase their absorbency characteristics. For example, superabsorbents have been applied to dry leaves. In addition, superabsorbents have also been applied to wet base sheets. For example, the European patent EP 0 359 615 Al describes a method for applying a superabsorbent material to a wet base sheet. However, a problem associated with applying a superabsorbent material to a dry sheet or a wet base sheet in a conventional manner is that the superabsorbent material is not uniformly distributed through the paper fabric. As a result of this, only parts of the tissue of the paper can have sufficient absorbent capacities.

As such, there is presently a need for an improved method for uniformly incorporating a superabsorbent material into a tissue product.

SYNTHESIS OF THE INVENTION The present invention is generally directed to a method for forming tissue products having improved absorbency properties. In particular, a tissue product formed in accordance with the present invention is typically formed of a cellulose fibrous material and a superabsorbent material in an amount of less than about 10% by weight of the tissue product.

The tissue product of the present invention can generally be produced from a paper fabric having one or multiple layers. In addition, depending on the desired characteristics of the tissue, the tissue product may be a tissue of single stratum or a multiple stratus tissue. Normally, the basis weight of the tissue product is less than about 100 grams per square meter, particularly less than 70 grams per square meter, and more particularly from about 10 to about 40 grams per square meter. In addition, any of a variety of materials can be used to form the tissue product. For example, the material used to make a tissue product in the present invention may include pulp fibers either alone or in combination with other types of fibers, such as synthetic fibers.

In addition, as stated above, a superabsorbent material ("SAM") is also included within the tissue product of the present invention. A superabsorbent material can provide excellent absorption capabilities to the tissue product. In general, a "superabsorbent material of the present invention can absorb at least about 10 times its weight, and in some embodiments at least about 30 times its weight of an aqueous solution, such as water. The superabsorbent material of the present invention can generally absorb at least about 20 grams of an aqueous solution per gram of the superabsorbent material, particularly at least about 50 grams, and more particularly between about 100 grams to about 350 grams of a aqueous solution per gram of superabsorbent material.

In general, the amount of the superabsorbent material used may vary. In some embodiments, the superabsorbent material can be applied in an amount of less than about 10% by weight of the tissue, in particular, the concentrations of superabsorbent material of between about 0.1% by weight to about 10% by weight , particularly between about 0.1% by weight to about 5% by weight, and more particularly between about 0.1% to about 3% by weight, can be used.A variety of superabsorbent materials may also be used within a tissue product formed in accordance with the present invention. For example, in one embodiment, fibrous superabsorbent materials such as • OASIS 101 (available from Technical Absorbent Ltd., "of the United Kingdom of Great Britain) may be used." In another embodiment, particulate superabsorbent material may be used. , such as FAVOR 880 (available from Stockhausen).

When incorporated into a tissue product of the present invention, the superabsorbent material can be combined with the fibers to make paper at any stage of tissue formation. For example, in some embodiments the superabsorbent material can be combined with the fibers of the "supply preparation stage" of a process to make paper. As used herein, the phrase "supply preparation step" generally refers to which step or step of a papermaking process that occurs prior to the formation of a fabric, such as, but not limited to, pulp reduction, the machine chest, the head box and the like. The superabsorbent material can be applied in one or more steps during the supply preparation phase.

In general, the superabsorbent material can be applied in either a "dry state" or "a pre-swollen state". A dry-state euperabsorbent material can be entrained when mixed with a liquid suspension of fibrous material. This swelling of superabsorbent material can have a variety of beneficial effects on tissue formation. For example, cellulosic fibers typically dry faster than swollen superabsorbent materials. Therefore, during the tissue drying step, the partially wetted and swollen superabsorbent material may allow the structure of the fibrous tissue to remain open, thereby resulting in a tissue product having an increased volume, permeability and void volume. The superabsorbent materials can be particularly useful when applied in certain steps, such as in the pulp reducer or in the chest of the machine.

In addition, as stated, the superabsorbent material can also be "pre-swollen" before being incorporated into the tissue product. The amount of pre-swelling can vary, depending on factors such as the nature of the solution and the time in which the superabsorbent material is allowed to remain there. For example, in some embodiments, the superabsorbent material may be pre-inflated in an amount of at least about 30% of its total swelling capacity, in some embodiments of at least about 50%, in some embodiments of at least about 70%, and in some embodiments, at least about 90% of its inflation capacity. Pre-swelling can also be particularly useful when the superabsorbent material is applied in certain steps such as the headbox.

In addition to the materials mentioned above, various other additives or materials may also be used to form a tissue product of the present invention. For example, various softening agents, wet strength agents, binders, etc. may be applied. In fact, by using a superabsorbent material in conjunction with a wet strength agent, it has been found that the strength of the tissue product can also be increased. In particular, a swollen superabsorbent material can reduce the number of fiber crossover points as indicated previously. As a result of the reduced number of crossing points, the wet strength agent can have a greater effect on a smaller number of points, thereby resulting in a paper fabric that is strong but is soft.

Other features and aspects of the present invention are discussed in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS A complete and enabling description of the present invention, including the best mode thereof for one with ordinary skill in the art is more particularly set forth in the remainder of the description, including reference to the accompanying figure in which: Figure 1 illustrates an embodiment of the present invention for forming a tissue product with a superabsorbent material.

The repeated use of the reference characters in the present description and drawings is intended to represent the same or analogous features or elements of the present invention. --d-fc- DETAILED DESCRIPTION OF THE REPRESENTATIVE INCORPORATIONS Reference will now be made in detail 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 and not of limitation of said invention. In fact, it will be apparent to one skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of an embodiment may be used over another embodiment to give an additional incorporation. Therefore, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

In general, the present invention is directed to tissues that have improved absorption capacities. In particular, it has been discovered that a superabsorbent material can be incorporated into a tissue product so that the resulting product is strong, smooth and has excellent absorption capabilities. As used herein, a "tissue product" generally refers to various paper products, such as facial tissue, bath tissue, paper towels and the like. A tissue product of the present invention can generally be produced from a tissue of paper having a or multiple layers. In addition, depending on the desired characteristics of the tissue, the tissue product may be a single stratum or multiple layer tissue. In one embodiment, for example, a three-layer tissue may contain two layers containing superabsorbent material of the present invention. Normally, the basis weight of a tissue of the present invention is less than about 100 grams per square meter, particularly less than about 70 grams per square meter, and more particularly between about 10 to about 40 grams per square meter. square meter.

Regardless of the overall structure of the tissue product, any of a variety of materials can be used to form the tissue product. For example, the material used to make a tissue product of the present invention may include pulp fibers either alone or in combination with other types of fibers. The pulp fibers may be soft wood fibers having an average fiber length greater than one millimeter and particularly from about 2 to about 5 millimeters based on the average of heavy length. Such fibers may include soft northern wood kraft, southern softwood kraft, cedar, red cedar, spruce, pine (southern pines for example) pinabete (for example black pinabete), combinations thereof and the like. Exemplary commercially available pulp fibers suitable for the present invention include those available from Kimberly-Clark Corporation under the trade designations "Longlac-19". Hardwood fibers such as eucalyptus, maple, birch, aspen and the like may also be employed. In addition, secondary fibers obtained from recycled materials can be used such as fiber pulp from sources such as, for example, newsprint, reclaimed paperboard, and office waste. In addition, other natural fibers may also be used in the present invention such as abaca, fan dwarf palm grass, benzene fiber silk thread, pineapple leaf and the like. In addition, synthetic fibers can also be used as long as such fibers do not have a substantial effect on the absorbency of the resulting tissue product. Some suitable synthetic fibers may include, but are not limited to, rayon fibers, ethylene vinyl alcohol copolymer fibers, polyolefin fibers, polyesters, and the like.

In some embodiments, the fibers can also be curled or enchiladas. As is known in the art, the fibers may be crimped, for example by adding a chemical agent to the fibers or subjecting the fibers to a mechanical process. The crimped fibers can create more entanglement and hollow volume within the fabric and also increase the amount of fibers oriented in the -z direction as well as increasing the strength properties of the fabric.

In accordance with the present invention, a "superabsorbent material" is also generally incorporated into a tissue product of the present invention. By using a "superabsorbent" material, the tissue product can be provided with a number of benefits, including excellent absorption capabilities. As used herein, the term "superabsorbent material" ("SAM") refers to any material which is insoluble in water, and substantially swellable in water capable of absorbing, swelling or gelling at least about 10 times its weight, and in some additions at least about 30 times their weight, in an aqueous solution such as water. In addition, a superabsorbent material of the present invention can generally absorb at least about 20 grams of an aqueous solution per gram of superabsorbent material, particularly at least about 50 grams, more specifically at least about 75 grams, and more particularly between about 100 grams to about 350 grams of the aqueous solution per gram of superabsorbent material. In contrast, pulp fibers, for example, can typically only absorb about 6 grams of water per gram of pulp.

In general, the amount of the superabsorbent material used may vary depending on the desired characteristics of the resulting tissue product. In most embodiments, the superabsorbent material can be applied in amounts of less than about 3.0% by weight of the tissue. In some embodiments, the superabsorbent material concentrations of between about 0.1% by weight to about 10% by weight, particularly from about 0.1% by weight to about 5% by weight, and more particularly, from about 0.1% to around 3% by weight can be used. In fact, it has been discovered that even minimal amounts of a superabsorbent material can significantly improve the absorbent capacity of the tissue product when used in accordance with the present invention. For example, a superabsorbent material present in an amount of only about 1% by weight the tissue absorbent capacity can increase by about 15%.

Some suitable superabsorbent materials that can be used in the present invention include inorganic and organic materials. For example, suitable inorganic superabsorbent materials may include sorbent clays and silica gels. In addition, some suitable organic superabsorbent materials include natural materials, such as agar, pectin, guar gum, etc., as well as synthetic materials such as synthetic hydrogel polymers.

Such hydrogel polymers include, for example, the alkali metal salts of polyacrylic acids, polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride copolymers, polyvinyl ethers, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl morpholinone; and polymers and copolymers of sulfonic acid vinyl, polyacrylates, polyacrylamides, polyvinyl pyridine, and the like. Other suitable polymers include hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch and isobutylene maleic anhydride polymers and mixtures thereof. The hydrogel polymers can be crosslinked slightly to make the materials essentially insoluble in water. The cross-linking can, for example, be achieved by irradiation or by covalent, ionic, Van der Waals, or hydrogen bonding.

The superabsorbent materials of the present invention can be provided in any form suitable for use in the absorbent composites including particles, fibers, flakes, filaments, spheres and the like. For example, a suitable fibrous superabsorbent material is available from Technical Absorbents Ltd., of the United Kingdom of Great Britain under the trade name "OASIS 101". In addition, an example of a suitable particulate superabsorbent material is FAVOR 880 available from Stockhausen, Inc., located in Greensboro, North Carolina. Although not required, particulate superabsorbent materials generally have particle sizes ranging from about 20 to --Í .--- M-- --É -____ a ._- »- ai --- t-- > --to-------.."..-. < »» * • ---- < - ** • - around 2000 micras.

A tissue product containing a superabsorbent material according to the present invention can generally be formed by any of a variety of papermaking processes known in the art. In particular, it should be understood that the present invention is not limited to any particular papermaking process. In fact, any process capable of forming a paper web can be used in the present invention. For example, a papermaking process of the present invention can use adhesive creping, wet creping, double creping, etching, wet pressing, air pressing, air drying, drying through of creped air, non-creped continuous drying as well as other steps for the formation of paper tissue. Some examples of such techniques are discussed in the Patents of the United States of America Nos. 5,048,589 granted to Cook et al .; 5,399,412 granted to Suda11 and others; 5,129,988 issued to Farrington, Jr.; 5,494,554 issued to ~ Edwards and others; ~ which are incorporated here in their entirety by reference to them.

In this regard, referring to Figure 1 an embodiment of a process for making paper that can be used in the present invention is illustrated. For simplicity, the various tensioning rollers used schematically for define the various cloth runs are shown but not numbered. Initially, a fibrous material is placed in a pulp reducer or paper supply fiber puncher (not shown) that contains a liquid, such as water. If the fibers are of a cellulose nature, for example, the fibers can be refined in the pulper or the pulp reducer until they are hydrated with water. The supply of fibrous material is typically maintained in continuous agitation so that it forms a liquid suspension.

In some embodiments, a superabsorbent material may be combined with the fibers either before or upon formation of the liquid suspension within the pulp reducer. After having intermixed, optionally with a euperabsorbent material, the fibrous suepension can then be diluted and bound for formation in a fibrous tissue layer using conventional papermaking techniques. In this aspect, the fibrous suspension (for example the delivery solution) can be stored in any apparatus, such as a machine chest (not shown) prior to tissue formation. In some embodiments, the superabsorbent material may also be combined with the fibrous material in the machine chest, prior to tissue formation. If desired, the pH of the supply solution can also be adjusted for equipment compatibility.

As shown, a head box for making paper 10 can then be used to inject or deposit a stream 11 of an aqueous fiber suepeneion to make paper on the forming fabric 12. The head box 10 can be any forming head box of tissue used in the art, such as a stratified headbox capable of producing a multi-layered fabric. For example, it may be desirable to provide straight or relatively short fibers in one layer of the base sheet to give the layer a high capillary pressure, while the other layer comprises relatively longer, bulkier or more crimped fibers for superior permeability and a high absorbent capacity and a high pore volume. It may also be desirable to apply different chemical agents to separate layers of a base fabric to optimize dry and wet strength, pore space, wetting angle, appearance or other properties of a fabric. In addition, multiple head boxes can be used to create a layered structure as is known in the art.

In some embodiments, the superabsorbent material can be added to the fibrous material in the headbox. For example, the superabsorbent material can be injected into the liquid suspension stream 11 just before entering the head box 10. Furthermore, when incorporated into a paper fabric having multiple layers, the Super absorbent material can generally be incorporated in any of the layers, either alone or in combination with the cellulosic fibers. For example, in one embodiment, one of the layers may contain a mixture of a superabsorbent material and a cellulose fibrous material. In another embodiment, a multilayer paper fabric including a layer of a euperabiebent material contained between the cellulosic fiber layers which acts to essentially prevent the superabsorbent material from migrating from the fabric may also be provided. It should be understood, however, that the multilayer paper fabric, as described above, can be formed without the use of multiple or stratified head boxes, and that it can be formed generally according to any process known in the art. .

In some embodiments, the superabsorbent material may be applied in either a "dry state" or a "previously swollen state". For example, pre-swelling can be especially desired when the superabsorbent material is applied to certain stages of a papermaking process, such as a headbox. In particular, at least some pre-swelling can be ensured so that the superabsorbent material has sufficient time to adequately swell during the process.

The extent of pre-swelling can vary from only a small amount of swelling to full swelling. To achieve the desired amount of pre-swelling, the superabsorbent material can be placed in an aqueous solution, such as water, for a certain period of time. The amount of pre-swelling can vary, depending on a variety of factors, such as the time in which the superabsorbent material is allowed to remain in the solution, the type of superabsorbent material, the amount of superabsorbent material, the phase of the process in the which material is applied, the desired amount of absorbency of the tissue and the like. For example, in some embodiments, the superabsorbent material may be previously swollen by at least about 30% of its total swelling capacity, in some incorporations by at least about 50%, in some incorporations by at least about 70% , and in some additions at least about 90% of its total inflation capacity. In addition, in some cases, the nature of the aqueous solution in which the superabsorbent material is dissolved can also be varied. For example, water can be provided with different amounts of dissolved solids to control the amount of swelling of the superabsorbent material there.

As stated, the superabsorbent material can also be applied in a dry state. The application of Super absorbent in a dry state can be particularly useful in certain steps of the papermaking process. For example, in some embodiments, a superabsorbent material in the dry state can be combined with the fibrous suepension in the pulp reducer or in the machine chest to ensure that the superabsorbent material of dry state has a sufficient time to swell. A superabsorbent material of dry state may, as in some circumstances, swell when mixed with a liquid suspension of the fibrous material. This swelling of the superabsorbent material can have a variety of beneficial effects on tissue formation. For example, cellulosic fibers typically dry faster than swollen euperabsorbent materials. Therefore, during the wet drying step (described below), the partially wet and swollen superabeorbent material may allow the structure of the fibrous tissue to remain open, thereby resulting in a tissue product having a volume, permeability and volume upper hollow.

From the supply preparation phase, the fibroea solution can then be transferred to the tissue formation phase. For example, in one embodiment, with the help of a roller 14, the fibrous stream 11 can then be transferred to a cloth 13, which serves to support and bring the newly formed humerus downward from the process by being partially dewatered the fabric 15 at a consistency of about 10% by dry weight. Additional drainage of the wet fabric can be carried out, such as by suction with vacuum while the wet fabric is supported by the forming fabric.

The wet fabric 15 is then transferred to the fabric 13 to a transfer fabric 17, which typically travels at a slower speed than that of the fabric 13 in order to impart an increased stretch to the fabric. This is commonly referred to as a "quick" transfer. A useful method of carrying out the rapid transfer is taught in U.S. Patent No. 5,667,636 issued to Engel et al. Which is hereby incorporated by reference in its entirety. The relative speed difference between the two fabrics can be from 0% to about 80%, particularly greater than about 10%, more particularly from about 10% to about 60% and more particularly from about 10%. % to around 40%. The transfer can be carried out with the help of a vacuum shoe 18 so that the forming fabric and the transfer fabric converge simultaneously and diverge at the leading end of the vacuum slot.

Then, any of a variety of papermaking techniques, such as drying, creping, etching, etc., can be used. For example, the fibrous tissue 15 ^^^ .--- 3-a - * .--- ^ .____ "•. ^ Fc fca ....

It can be dried. The drying processes that incorporate infrared radiation, Yankee dryers, dryers through air, vacuum with vacuum, microwave, ultrasonic energy, etc., can be used. Further thermal treatments may also be used, either alone or in combination with drying to melt a part of any of the thermally fusible fibers that may be present in the material.

For example, as shown in Figure 1, in one embodiment, the fabric 15 is transferred from the transfer fabric 17 to a continuous drying cloth 19 with the help of a shoe or transfer roller with vacuum 20. The dryer fabric continuous 19 can be moved around the same speed or at a different speed relative to the transfer fabric 17. For example, if desired, the continuous drying fabric 19 can run at a slower speed to help increase the stretch. The vacuum transfer shoe or roller 20 (negative pressure) can be supplemented or replaced by the use of positive pressure from the opposite side of the fabric to blow the fabric onto the next fabric.

The dryer continues can achieve the removal of moisture from the fabric 15 by passing the air through the fabric without applying any mechanical pressure, for example ^? uaAa Á MAá ^ i? ? t- ^ ^^? áisÉ no compressive drying. Non-compressive drying can also increase the volume and softness of the fabric. In one embodiment, for example, the continuous dryer may contain a perforated and rotating cylinder and a cover (not shown) for receiving the hot air blown through the cylinder bores by bringing the continuous drying fabric 19 to the fibrous tissue 15 on the euperior part of the cylinder. The heated air is forced through the perforations in the cylinder of the continuous dryer 21 and removes the remaining water from the fibrous tissue 15. The temperature of the forced air through the fibrous tissue 15 by the dryer continues may vary, but is typically from about 148.88 ° C (300 ° F) to around 315.55 ° C (600 ° F).

When the fabric 15 contains a euperabsorbent material, the drying step may provide additional benefits to the resulting tissue product. In particular, during the drying step, the cellulosic fibers normally dry at a faster rate than the superabsorbent materials. Therefore, the cellulosic fibers can be completely dried while the euperabbruent material may possess some replenishing moisture content. For example, in some embodiments, the superabsorbent material is dried to have a moisture content of less than about 50% by weight of the superabsorbent material, and particularly less than about 25%. In addition, the moisture content of the tissue After drying, it can be between about 5% to about 20%, in some embodiments between about 5% to about 15% by weight of the fabric, and in some additions between about 5% to about 10% by weight of the fabric.

The remaining moisture content can provide a number of benefits. For example, because it is not generally necessary to completely dry the superabsorbent material, the process can be made more efficient by using less energy to dry the fabric. In addition, the tissue product may have a higher basis weight due to the added moisture content. In addition, the remaining moisture content can act as a "liquid reservoir" to increase the equilibrium moisture content of the final tissue product.

Although this additional moisture content is generally beneficial to the tissue forming process, it may in some cases promote the growth of some indented microbes, particularly when the moisture content becomes eignificantly greater than about 20% by weight of the fabric. Notwithstanding this, to further ensure against such microbial growth, various known antimicrobial agents can be applied to the paper fabric. In addition, in some embodiments, the superabsorbent material itself can be modified so that it possesses the desired antimicrobial characteristics.

In addition to the above-mentioned benefits, the drying of the paper fabric can also provide various other benefits according to the present invention. In particular, the euperabsorbent material can also be firmly attached to the cellulosic fibers as the fabric is dried. It is believed that this binding may be due to the hydrogen bonds and ester bonds formed between the carboxyl functionalities of the superabsorbent material and the hydroxyl groups of the cellulose fibers, as well as the actual physical entrapment of the superabsorbent material within the fibrous matrix. Because the superabsorbent material can be firmly attached to the cellulosic fibers, its separation from the tissue with the wetting can be minimized.

The dried fabric 23 can then be transported to a carrier fabric 22 to a spool 24, where it can be wound. An optional flip roll 26 or a cloth 25 may be used to facilitate tranending the fabric from the carrier fabric 22 to the spool 24. Even if it does not move, the reel calendering or subsequent off-line calendering may be used to improve the smoothness and the softness of the base sheet. In addition to calendering, any of a variety of other determined steps can also be used. For example, the fabric may be brushed to provide a uniform outer appearance and / or certain tactile properties. The material can also be wet creped, dry creped and / or mechanically smoothed through other methods to improve softness and feel. Such processes can be done online before the roll of the fabric on a roll or this can be done offline. Adhesive with adhesive can also be used to improve the resistance to volume properties. In addition, printed finishes can be applied to improve aesthetics.

In some embodiments, the superabsorbent material may also be applied during the tissue formation phase. The tissue forming phase generally refers to steps in a papermaking process that occur after the fibers are deposited on the fabric or forming wire, and before the fabric is dried. For example, in one embodiment, the superabsorbent material can be applied to the wet fabric 15 as it is formed on the forming fabric 12 or on the fabric 13. For example, in one embodiment, the superabsorbent material can be sprayed onto the wet fabric 15 using any of a variety of known spray techniques. In other embodiments, the superabsorbent material can additionally be applied in the conversion phase. The conversion phase generally refers to any phase of the process to make paper that It happens after tissue drying. When applied to these faee, it may be desirable for the superabsorbent material to be added in a previously swollen state or a dry state. Once applied to a dry tissue, the tissue can be connected with an aqueous solution such as water to initiate swelling. For example, in one embodiment, the superabsorbent material can be exposed to high humidity using, for example, a vapor blister. In other cases, however, the superabsorbent material may be maintained in its previously dry or swollen state. In such cases, the superabsorbent material can be completely swollen with the moistening of the tissue product by a consumer, thereby effecting the desired increase in the absorbency capacity of the tissue. In addition, in one embodiment, the superabsorbent material can be metered into the dried paper fabric 23 before it is wound onto a roll 24. "In some embodiments, the euperabiebent material can also be measured in two or more layers of the fabric 23.

~~ In addition to the superabsorbent materials, additional chemical treatments can also be used at any stage of the papermaking process. For example, the application of liquid treatments such as dyes, wet strength agents, binders, brighteners, flame retardants, germicides, smoothing agents, starches, correction inhibitors, textile finishes, acid citric, ethylenediamine, etc., can be achieved using spraying, embedding, tightening techniques, vacuum extraction, liquid curtains, saturation techniques and the like.

For example in order to reinforce the tissue, various wet reinforcing agents may be applied according to the present invention. Particular wet strength agents that can be used in the present invention include latex compositions, such as acrylates, vinyl acetates, vinyl chlorides and methacrylates. Some water-soluble wet strength agents can also be used including polyacrylamides (for example glyoxylated polyacrylamides), polyvinyl alcohols, and carboxymethyl cellulose. In one embodiment, the wet strength agent used in the present invention contains an ethylene vinyl acetate copolymer. In particular, the ethylene vinyl acetate copolymer can be crosslinked with n-methylacrylamide groups using an acid catalyst. Suitable acidic catalysts include ammonium chloride, citric acid and maleic acid.

When used, the wet strength agent can increase the strength of a fabric by fortifying the bonds of the cellulosic fibers at points where they cross each other. In addition, by using a superabsorbent material in conjunction with an agent of tissue reinforcement, it has been found that the strength of the tissue product can also be increased. In particular, the swollen superabsorbent material can reduce the number of fiber crossing points. As a result of the reduced number of crossing points, the wet strength agent can have a greater effect on a small number of points, resulting therefore in a paper fabric that is strong, but soft. Furthermore, as stated, a tissue product of the present invention may also include a chemical softening or debranching agent to further increase the "soft feel" of the tissue product. Some softening agents are also believed to act as lubricants or friction reducers. Any material that has some affinity with fibers and that is capable of reducing fiber bonding and / or reducing friction, can generally be used as a softening agent. Some examples of suitable softening agents may include, but are not limited to, quaternary ammonium compounds, imidazolinium compounds, bis-imidazolinium compounds, phospholipid derivatives, polydimethylsiloxanes and non-silicone compounds. ionic and cationic related, to the fatty and carboxylic derivatives, to the mono- and poly-saccharide derivatives, to the polyhydroxy hydrocarbons, etcetera. Still other suitable softening agents are disclosed in U.S. Patent Nos. 5,529,665 issued to Kaun and 5,558,873 issued to Funk and others which are hereby incorporated by reference in their entirety. For example, Kaun defines the use of various silicone compositions as softening agents.

In alternating incorporations the softening agent may also contain antimicrobial agents to destroy germs that come into contact with the tissue of paper. For example, a commercially available softening agent having antimicrobial properties is DOW 5700 marketed by Dow-Corning Corporation of Midland, Michigan. The DOW 5700 is a quaternary silicone spray containing antimicrobial agents. In other embodiments, the softening agent may also include a fragrance or an odor masker.

In addition to the above mentioned materials, it should be understood that any other additive, agent or material may be added to a tissue product of the present invention, if desired. For example, additives and / or additional softening agents are described in the patents of the United States of America Noe. 5,814,188 granted to Vinson and others and 5,830,317 granted to Vinson and others which are incorporated here in their entirety by reference to them.

In some embodiments, to further ensure that the superabsorbent material is contained within the tissue product, a variety of containment mechanisms can be used. For example, one or more of the layers may be separated from a tissue wrapping sheet, a high density fiber layer, or another similar layer to prevent a substantial dry migration of the superabsorbent material between the two layers. In addition, in one embodiment, the cellulosic fibers can be crimped so that the superabsorbent material can be trapped within the curls of the paper fabric. In another embodiment, a multi-strand tissue product may be pressed lightly between the calendering rollers to further ensure that a superabsorbent material contained within the strata is sufficiently contained therein.

In addition, various additives, such as binders, can also be used to further ensure that the superabsorbent material is contained within the tissue product. The binders can help the superabsorbent material to adhere to the fibrous material, particularly when the fibers and the material form a mixture. For example, in one embodiment, the polymeric binding fibers can also be added to the liquid suspension in the supply preparation phase or in any other stage of the papermaking process. Some suitable binder fibers that can be used in the present invention are adhesives. Examples of the adhesives that can be used in the present invention include but are not limited to acrylates, styrene butadiene, vinyl chloride, methacrylates, acrylics (such as carboxylated acrylics), and vinyl acetates (such as cross-linked ethyl vinyl acetate, hydrolyzed polyvinyl acetate, or crosslinked unlinked ethyl vinyl acetate) . In certain embodiments, the adhesive may be carboxylated acrylic, such as a carboxylated acrylic latex of the HYCAR brand. For example, in one embodiment, the binders can be printed on a fabric that is then double-folded.

The present invention can also be better understood with reference to the following examples: EXAMPLE 1 The ability to form a tissue with a superabsorbent material was demonstrated. Initially a liquid pulp fiber suepeneion ("Longlac-19") was dispersed using a British disintegrator to form a liquid suspension. Then, a dry superabsorbent material (OASIS 101 of technical absorbers) was added to the suspension so that the resulting fiber supply contained 95% pulp fibers and 5% superabsorbent material.

After the formation of the supply, a paper web having a basis weight of 14 grams per square meter was formed using a TAPPI hand sheet mold and conventional tissue forming techniques, as described above. Once the tissue was formed, it was then placed on a stainless steel rack and dried in a conventional oven at 105 ° C. After drying, the formed tissue was then removed from the dryer and examined. Subjectively, the euperabsorbent material was retained within the dried fabric.

EXAMPLE 2 The ability to form a tissue with superabsorbent material was demonstrated. Initially, the pulp fibers ("Longlac-19") and the superabsorbent material (OASIS 101 from Technical Absorbent) were blended and disperse using a British disintegrator to form a liquid suspension - containing 95% pulp fibers and 5% superabsorbent material.

- After the formation of the supply, the paper fabric had a basis weight of 14 grams per square meter and was formed using a TAPPI hand sheet mold and conventional tissue forming techniques, as described above. Once the tissue was formed, it was then placed on a stainless steel rack and dried in a convection oven at 105 ° C. After drying, the tissue was formed and was then removed from the dryer and examined. It was subjectively determined that the superabsorbent material was retained within the dried fabric.

EXAMPLE 3 The ability to form a tissue with a superabsorbent material was demonstrated. Initially, a liquid slurry of pulp fibers ("Longlac-19") was dispensed using a British disintegrator to form a liquid suspension. Then, a dry superabsorbent material (OASIS 101 from Technical Absorbents) was then applied to the suspension so that the resulting fiber furnish contained 95% pulp fibers and 5% superabsorbent material.

After forming the furnish, a paper web having a basis weight of 40 grams per square meter was formed using a TAPPI hand sheet mold and conventional tissue-forming techniques, as described above. Once the tissue was formed, it was then placed on a stainless steel rack and dried in a convection oven at 105 ° C. After drying, the formed fabric was then removed from the dryer and examined. It was subjectively determined that the superabsorbent material was retained within the wet tissue.

EXAMPLE 4 The ability to form a tissue with superabsorbent material was demonstrated. Initially, the pulp fibers ("Longlac-19") and the superabsorbent material (Favor 880 of Stockhausen) were mixed and dispersed using a British disintegrator to form a liquid suspension containing 95% pulp fibers and 5% superabsorbent material .

After forming the supply, a paper web having a basis weight of 40 grams per square meter was formed using a TAPPI hand sheet mold and conventional tissue forming techniques, as described above. - Once the fabric was formed, it was then placed on a stainless steel rack and dried in a convection oven at 105 ° C. After drying, the formed fabric was then removed from the dryer and examined. Subjectively it was determined that the superabsorbent material was retained in the dried fabric.

Although several embodiments of the invention have been described using specific terms, devices and methods, such a description is for illustrative purposes only. The words used are words of description rather than limitation. It should be understood that changes and variations may be made by that of an ordinary skill in the art without departing from the spirit or scope of the present invention which is set forth in the following claims. In addition, it should be understood that the aspects of the various incorporations can be exchanged in whole or in part. Therefore, the spirit of scope of the appended claims should not be limited to the description of the preferred versions contained therein.

Claims (35)

1. A process for forming a tissue product having a basis weight of less than about 100 grams per square meter, said process comprising the steps of: providing a superabsorbent material that is capable of absorbing at least about 20 grams of an aqueous solution per gram of said superabsorbent material; provide a cellulosic fibrous material; forming a paper web of said cellulosic fibrous material and said superabsorbent material, said superabsorbent material comprising less than about 10% by weight of said tissue product; Y at least partially drying said tissue.

2. A process as described in clause 1 characterized in that said superabsorbenffee material is provided in a dry state.

3. A process as claimed in clause 1 further characterized in that it comprises the step of partially pre-inflating at least said superabsorbent material before forming said paper web.

4. A process as claimed in clause 3 characterized in that said superabsorbent material is pre-inflated to at least about 30% of the total swelling capacity of said superabsorbent material.

5. A process as claimed in clause 3 characterized in that said superabsorbent material is pre-inflated to at least about 50% of the total swelling capacity of said superabsorbent material.

6. A process as claimed in clause 3 characterized in that said superabsorbent material is pre-inflated to at least about 70% of the total swelling capacity of said material superabsorbent

7. A process as claimed in clause 3 characterized in that said superabsorbent material is pre-inflated to at least about 90% of the total swelling capacity of said superabsorbent material.

8. A process as claimed in clause 1 characterized in that the superabsorbent material comprises between about 0.1% by weight to about 5% by weight of said tissue product.

9. A process as claimed in clause 1 characterized in that the superabsorbent material comprises between about 0.1% by weight to about 3% by weight of said tissue product.

10. A process as claimed in clause 1 characterized in that said superabsorbent material is capable of absorbing at least about 50 grams of an aqueous solution per gram of superabsorbent material.

11. A process as claimed in clause 1 characterized in that said superabsorbent material is capable of absorbing between about 100 to about 350 grams of aqueous solution per gram of said superabsorbent material.

12. A process as claimed in clause 1 further characterized in that it comprises the step of applying a wet strength agent to said paper web.

13. A process as claimed in clause 1 characterized in that said paper fabric is dried to have a moisture content of less than about 20% by weight of said fabric.

14. A process as claimed in clause 1 characterized in that said paper tissue is dried - to have a moisture content of between about 5% "to about 20% by weight of said fabric.

15. A process as claimed in clause 1 characterized in that said paper web is dried to have a moisture content of between about 5% to about 15% by weight of said fabric.

16. A process as claimed in clause 1 characterized in that said paper fabric is dried to have a moisture content of between about 5% a about 10% by weight of said fabric.

17. A process as claimed in clause 1 characterized in that it comprises the step of combining said superabsorbent material with said cellulosic fibrous material before forming said paper tissue.

18. A process for forming a tissue product having a basis weight of less than about 100 grams per square meter, said process comprising the steps of: providing a superabsorbent material that is capable of absorbing at least about 20 grams of an aqueous solution per gram of said superabsorbent material. pre-inflating said superabsorbent material to at least about 30% of the total swelling capacity of said superabsorbent material; provide a cellulosic fibrous material; forming a paper web of said cellulosic fibrous material and said superabsorbent material, said superabsorbent material comprises between about 0.1% to about 5% by weight of said tissue product; and at least partially drying said tissue.

19. A process as claimed in clause 18 characterized in that said paper web is dried to have a moisture content of between about 5% to about 20% by weight of said fabric.

20. A process as claimed in clause 18 characterized in that said superabsorbent material comprises between about 0.1% by weight to about 3% by weight of said tissue product.

21. A process as claimed in clause 18 characterized in that said superabsorbent material is capable of absorbing at least about 50 grams of an aqueous solution per gram of said superabsorbent material.

22. A process as claimed in clause 18 characterized in that said superabsorbent material is capable of absorbing between about 100 to about 350 grams of an aqueous solution per gram of said superabsorbent material.

23. A process as claimed in clause 18, characterized in that it also comprises the step of combining said super-absorbent material with said cellulosic fibrous material before forming said paper tissue.

24. An absorbent tissue product comprising: a fibrous cellulosic material; a superabsorbent material, said superabsorbent material comprises up to about 10% by weight of said absorbent tissue product, said superabsorbent material is capable of absorbing at least about 20 grams of water per gram of superabsorbent material; Y wherein said absorbent tissue product has a basis weight of less than about 100 grams per square meter.

25. An absorbent tissue product as claimed in clause 24 characterized in that said superabsorbent material comprises between about 0.1% by weight to about 5% by weight of said absorbent tissue product.

26. An absorbent tissue product as claimed in clause 24 characterized in that said superabsorbent material comprises between 0.1% by weight to about 3% by weight of said absorbent tissue product.

27. An absorbent tissue product as it is claimed in clause 24 characterized in that said superabsorbent material has a moisture content of less than about 50% of the weight of said superabsorbent material. _? i

28. An absorbent tissue product as claimed in clause 24 characterized in that said superabsorbent material has a moisture content of less than about 25% by weight of said superabsorbent material.

29. An absorbent tissue product as claimed in clause 24 characterized in that said superabsorbent material is capable of absorbing at least about 50 grams of an aqueous solution per gram of said superabsorbent material.

30. An absorbent fabric product as claimed in clause 24 characterized in that said superabsorbent material is capable of absorbing between about 100 to about 350 grams of an aqueous solution per gram of said superabsorbent material.

31. An absorbent tissue product comprising: a fibrous cellulosic material; a superabsorbent material, said superabsorbent material comprises between about 0.1% to about 5% by weight of said absorbent tissue product, said mater_S |, superabsorbent is capable of absorbing at least about 20 grams of water per gram of said material superabsorbent, wherein said superabsorbent material has a moisture content of about 50% by weight of said superabsorbent material; Y wherein said absorbent tissue product has a basis weight of less than about 100 grams per square meter.

32. An absorbent tissue product as claimed in clause 31 characterized in that said superabsorbent material has a moisture content of less than about 25% by weight of said superabsorbent material.

33. An absorbent tissue product as claimed in clause 31 characterized in that said superabsorbent material is capable of absorbing at least about 50 grams of an aqueous solution per gram of said superabsorbent material.

34. An absorbent tissue product as claimed in clause 31 characterized in that the absorbent material is capable of absorbing between about 100 a about 350 grams of an aqueous solution per gram of said superabsorbent material.

35. An absorbent tissue product as claimed in clause 31 characterized in that said superabsorbent material comprises between about 0.1% to about 3% by weight of said absorbent tissue product.