DE29624263U1 - Water-dispersible, fibrous coform composite nonwovens - Google Patents

Description

GRÜNECKER KINKELDE/· SCWW&NHÄUSSER

LAW FIRM

GKS & S MAXIMILIANSTRASSE 58 D-80536 MUNICH GERMANY LAWYERS
LAWYERS

MUNICH

DR. HELMUT EICHMANN

GERHARD BARTH

DR. ULRICH BLUMENRÖDER, LLM.

CHRISTA NIKLAS-FALTER

OR. MAXIMILIAN KiNKEiJDPf, LLM.

SONJA SCHAEFFLER

DR. KARSTEN BRANDT

ANJA FRANKE, LL.M.

UTE STEPHANI

DR. BERNDALLEKOTTE, LLM.

PATENT ATTORNEYS PATENT ATTORNEYS

EUROPEAN PATENT AHORNEYS EUROPEAN PATENT ATTORNEYS

MUNICH

DR. HERMANN KINKELDEY

PETER H. JAKOB

WOLFHARD MEISTER

HANS HILGERS

DR. HENNING MEYER-PLATH

ANNELIE EHNOLD

THOMAS SCHUSTER

DR. KLARA GOLDBACH

MARTIN AUFENANGER

GOHFRIED KUTZSCH

DR. HEIKE VOGELSANG-WENKE

REINHARD KNAUER

DIETMAR KUHL

DR. FRANZ-JOSEF ZIMMER

BETTINA K. REICHELT

DR. ANTON K. PFAU

DR. UDO WEIGELT

RAINER BERTRAM

JENS KOCH. M.S. (U of PA) M.S.

BERND ROTHAEMEL

DR. DANIELA KINKELDEY

DR.

COLOGNE

OR. MARTIN DROPMANN

CHEMNITZ MANFRED SCHNEIDER

BERLIN

DIETER JANDER

OF COUNSEL PATENT ATTORNEYS

AUGUST GRUNECKER DR. GUNTER BEZOLD OR. WALTER LANGHOFF

DR. WILFRIED STOCKMAIR (-1996)

YOUR REF / YOUR REF OUR REF.

DATE I DATE

G4518-00983/CO

21-03.2001

Water-dispersible fibrous coform composite nonwovens

KIMBERLY-CLARK WORLDWIDE INC. 401 NORTH LAKE STREET

NEENAH, Wisconsin 54957-0349

USA

GRÜNECKER KINKELDEY STOCKMAIR & SCHWANHÄUSSER MAXIMILIANSTR. 58 D-80538 MUNICH GERMANY

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e-mail: postmaster@grunecker.de

WATER-DISPERSIBLE FIBROUS COFORM COMPOSITE NONWOVEN FABRICS

FIELD OF INVENTION

The invention relates to water-dispersible fibrous composite nonwoven structures comprising at least two different components, wherein the composite is water-dispersible. In particular, the invention relates to fibrous composite nonwoven structures, referred to as "coform" materials, which are water-dispersible.

BACKGROUND OF THE INVENTION

Fibrous nonwovens and fibrous composite nonwovens are widely used as products or as components of products because they can be inexpensively manufactured and endowed with specific properties. One method has been to blend thermoplastic polymer fibers with one or more types of fibrous material and/or particles. The blends are collected in the form of fibrous nonwoven web composites that can be bonded or treated to create coherent composite nonwoven materials that exploit at least some of the properties of each component. For example, U.S. Patent No. 4,100,324, issued July 11, 1978 to Anderson et al., discloses a fibrous nonwoven generally composed of a uniform blend of wood pulp and meltblown thermoplastic polymer fibers. From US Patent No. 3,971,373, issued to Braun on July 7, 1976, a nonwoven material is known which contains meltblown thermoplastic polymer fibers and discrete solid particles. According to this patent, the particles are evenly dispersed and mixed with the meltblown fibers in the nonwoven material. From US Patent No. 4,429,001, issued to Kolpin et al. on January 31, 1984, an absorbent web material is known which contains a combination of meltblown thermoplastic polymer fibers and solid

superabsorbent particles. The superabsorbent particles are disclosed as being uniformly dispersed and incorporated into a web of meltblown thermoplastic polymer fibers. European Patent No. 0080382 to Minto et al., published June 1, 1983, and European Patent No. 0156160 to Minto et al., published October 25, 1985, also disclose combinations of particles such as superabsorbents and meltblown thermoplastic polymer fibers. U.S. Patent No. 5,350,624 to Georger et al., issued September 27, 1994, discloses an abrasion-resistant fibrous nonwoven structure comprising a matrix of meltblown fibers having a first outer surface, a second outer surface, and an inner portion having at least one other fibrous material incorporated into the meltblown fiber matrix. The concentration of meltblown fibers disposed adjacent to each outer surface of the nonwoven structure is at least about 60 weight percent and the concentration of meltblown fibers in the inner portion is less than about 40 weight percent. Many of the above blends are referred to as "coform" materials because they are formed into a single structure by combining two or more materials in the forming step.

Composites produced by coform techniques offer a wide range of applications, including absorbent media for aqueous and organic liquids, filtration media for wet and dry applications, insulation materials, protective cushioning materials, containment and discharge systems, and wipers for both wet and dry applications. Many of the above applications can be realized to a greater or lesser extent due to the use of simplified structures, such as absorbent structures using only wood pulp fibers. This was widely true, for example, for the absorbent cores of absorbent hygiene products such as diapers. Wood pulp fibers, when formed as such, tend to form nonwoven web structures with very low mechanical integrity and a high rate of collapse upon wetting. The advent of coform structures incorporating thermoplastic meltblown fibers even in small amounts greatly improved the properties of such structures, including

Both wet and dry tensile strength. The same improvements were observed with the advent of coform wipes.

Many of the items or products incorporating coform materials are generally considered to have a limited life as disposable products. This means that the product or products are used only a few times or in some cases only once before being discarded. With increasing concern about waste disposal, the search is now intensifying for materials that can be either recycled or disposed of using mechanisms other than landfill. One possible waste disposal alternative for many products, particularly in the area of absorbent hygiene products and wipes, is flushing them into the sewer system.

The underlying reason why many coform materials are more beneficial than traditional materials, i.e. the meltblown thermoplastic fiber matrix, is also the same reason why such materials are more difficult to recycle or flush away. Many wood pulp fiber-based products can be recycled by hydrating and reprocessing the recovered pulp fibers. However, in coform structures, the thermoplastic meltblown fibers do not break down easily. The meltblown fibers are difficult to separate from the wood pulp fibers and remain essentially cohesive, which can clog or otherwise damage recycling equipment, such as reprocessors. As regards flushability, it is currently believed that for a product to be flushable, it must be made of very small and/or very weak fibres so that the material breaks easily into smaller pieces when exposed to water volumes such as those found in toilets, and when flushed away - again due to the nature of the fibres - does not become entrained or trapped in the pipework of conventional private and public sewerage systems. Many of these systems, particularly sewer laterals, may have protruding parts such as tree roots within the pipes, which may cause any kind of still

relatively intact material. This would be the case with conventional, non-water-degradable, meltblown thermoplastic fibers in coform materials. At least for the reasons mentioned above, there is therefore a need for a coform material that promises greater user-friendliness with regard to recycling processes and disposal alternatives to landfill, such as flushing. Therefore, it is an object of the invention to provide such a material.

SUMMARY OF THE INVENTION

The invention relates to a water-dispersible fibrous composite nonwoven structure which utilizes at least two different components and wherein the composite is water-dispersible. Such structures are commonly referred to as "coform" materials. The water-dispersible, fibrous composite nonwoven structure comprises a matrix of melt-spun, water-degradable reinforcing fibers and a plurality of discrete absorbent fibers disposed within the matrix of melt-spun, water-degradable reinforcing fibers. The absorbent fibers may comprise, for example, staple fibers having average fiber lengths of about 18 mm or less and wood pulp fibers. In addition, the water-dispersible, fibrous composite nonwoven structure may also comprise particulate material within the matrix as such as a superabsorbent and/or odor-reducing agent, such as activated carbon. Examples of melt-spun, water-degradable reinforcing fibers include, but are not limited to, water-degradable polyamides and poly(vinyl alcohol). Instead of or in addition to the plurality of discrete absorbent fibers, the water-dispersible, fibrous composite nonwoven structure may comprise a plurality of particles disposed within and held by the matrix of melt-spun, water-degradable reinforcing fibers. The materials of this invention offer a variety of applications, e.g., absorbent personal care articles such as wipes, diapers, training pants, panty liners, sanitary napkins, incontinence aids, wound dressings, bandages and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic side view, partly in section, of a

possible method and a possible device for producing water-dispersible, fibrous composite nonwoven structures according to the invention;

Figure 2 is a perspective view of a portion of a fibrous composite nonwoven structure made by the method and apparatus of Figure 1;

Fig. 3 shows a schematic partial side view of another possible

A method and an apparatus for producing water-dispersible, fibrous composite nonwoven structures according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a fibrous composite nonwoven structure comprising at least two different components which are water dispersible. The term "fibrous composite nonwoven structure" as used herein refers to a structure of individual fibers or filaments with or without particles interposed therebetween, but not in a recognizable, repeating manner. Nonwoven structures as such, such as fibrous nonwoven webs, have previously been produced by various processes known to those skilled in the art, for example by meltblowing and melt spinning processes, spunbonding processes and carded nonwoven web processes.

The term "water dispersible" as used here refers to a fibrous composite nonwoven structure that, when placed in an aqueous environment for a sufficient period of time, breaks down into smaller pieces. Consequently, once the structure is dispersed, it may be more easily processed in recycling processes or used in septic tanks and municipal

If desired, such fibrous nonwoven structures can be made more water dispersible or dispersion can be accelerated by the use of agitators and/or certain initiators as described below. The actual time required will depend at least in part on the particular design criteria of the end use. For example, in the sanitary napkin embodiments described below, the fibers break apart in less than one minute. In other applications, longer times may be desirable.

The fibrous nonwoven structure of the present invention comprises a melt-spun reinforcing fiber of a water-degradable polymer and one or more other components which are mixed with the reinforcing fiber to form a composite fibrous nonwoven structure of the invention. "Melt-spun" as used herein means a fiber formed by a fiber forming process which produces longer and more continuous fibers (generally greater than 7.5 cm) such as those produced by the meltblown and spunbond processes. "Water-degradable" means a polymer which, when formed into a fiber and placed in sufficient amounts of water for a sufficient period of time, breaks down into smaller pieces. In some cases, stirring or agitation may be required to break the fibers apart. Again, the actual time may vary or may be varied to meet a particular end-use need. Many of today's polymers can be designed or selected to break apart in minutes or even less. The most common form of the fibrous composite nonwoven structure of the invention is commonly referred to as a "coform" material which comprises longer and more coherent melt-spun reinforcing fibers mixed with shorter absorbent fibers such as staple fibers and wood pulp fibers or particles such as superabsorbents. Staple fibers generally have lengths up to about 7.5 cm. Currently, there are many short cut thermoplastic staple fibers which typically have lengths of less than about 18 mm and are made from a variety of thermoplastic extrudable polymers.

including, but not limited to, polyolefins and polyesters, as well as homopolymers, copolymers and blends of such polymers.

In addition, several different types and/or sizes of such fibers can be used in the coform structure. Another example of absorbent fibers is wood pulp fibers. Wood pulp fibers are generally obtained from natural sources, e.g., woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute and bagasse. In addition, synthetic wood pulp fibers are also available and can be used in the present invention. Wood pulp fibers typically have lengths of about 0.5 to 10 mm and a length to maximum width ratio of about 10/1 to 400/1. A typical cross-section has an irregular width of about 30 pm and a thickness of about 5 pm. A wood pulp suitable for use in the invention is Kimberly-Clark CR-54 wood pulp from Kimberly-Clark Corporation of Neenah, Wisconsin.

The water-degradable reinforcing fibers typically have lengths greater than those of the absorbent fibers, including staple and wood pulp fibers. Examples of two such water-degradable reinforcing fibers are meltblown fibers and spunbond fibers. Meltblown fibers are formed by extruding molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a heated high-velocity gas stream, such as air, which attenuates the filaments of molten thermoplastic material, thereby reducing their diameter. The meltblown fibers are then carried by the high-velocity gas stream and deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. The meltblowing process is well known and described in various patents and publications, such as NRL Report 4364, "Manufacture of Super-Fine Organic Fibers" by B. A. Wendt, E. L. Boone and C. D. Fluharty, NRL Report 5265, "An Improved Device for the Formation of Super-Fine Thermoplastic Fibers" by K. D. Lawrence, R. T. Lukas, J.

A. Young in U.S. Patent No. 3,676,242 issued to Prentice on July 11, 1972 and in U.S. Patent No. 3,849,241 issued to Buntin et al. on November 19, 1974. The above documents are hereby incorporated by reference in their entirety. Such meltblown fibers can be made in a wide variety of diameters. Typically, such fibers have an average diameter of no more than about 100 microns and usually no more than 15 microns.

Spunbond fibers are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries in a spinneret, with the diameter of the extruded filaments then being rapidly reduced, for example, by non-absorbent or aspirating fluid withdrawal devices or other well-known spunbond mechanisms. The manufacture of spunbonded webs is shown in patents such as Appel et al., U.S. Patent No. 4,340,563, Matsuki et al., U.S. Patent No. 3,802,917, Dorschner et al., U.S. Patent No. 3,692,61, Kinney, U.S. Patent Nos. 3,338,992 and 3,341,394, Levy, U.S. Patent No. 3,276,944, Peterson, U.S. Patent No. 3,502,538, Hartman, U.S. Patent No. 3,502,763, Dobo et al., U.S. Patent No. 3,542,615, and Harmon, Canadian Patent No. 803,714. Reference is hereby made to the above-mentioned literature in its entirety.

In addition to the water-degradable reinforcing fibers and absorbent fibers, such as staple fibers and wood pulp fibers, the fibrous nonwoven structure of the present invention may also utilize superabsorbent materials. Superabsorbent materials are absorbent materials that can absorb at least 10 grams of an aqueous liquid (e.g., distilled water) per gram of absorbent material while immersed in a liquid for four hours, and that hold substantially all of the absorbed liquid while subjected to a compressive force of up to about 10 kilopascals (kPa). Superabsorbent materials are manufactured in many different forms, including, but not limited to, particles, fibers, and flakes. Such superabsorbent materials may be used in the present invention in combination with the water-degradable reinforcing fibers and shorter absorbent fibers, or in place of the staple fibers.

Because the fibers formed by the above meltblown and spunbond processes are longer and more cohesive, such fibers and the resulting nonwoven webs, including coform webs, do not break apart easily due to the inherent toughness of the meltblown and/or spunbond fibers. As a result, the coform materials, which are predominantly wood pulp fibers but still contain longer fibers such as meltblown polyolefin fibers, are difficult to reclaim in equipment such as reprocessors. In addition, these longer and more cohesive fibers also tend to become entangled in or on projections in wastewater side channels, making transportation of such composite materials through the wastewater treatment system difficult. The fibrous composite nonwoven structures of the present invention utilize a water-degradable reinforcing fiber, which can be made, for example, by the above-mentioned and described meltblown and spunbond processes.

Water-degradable polymers are polymers that can be used to form fibers, for example, by the melt-blown and spunbond processes. When formed into fibers and blended with absorbent materials, such as staple and/or wood pulp fibers and/or particles such as superabsorbents, these water-degradable polymers can form fibrous nonwoven structures called coform materials. These coform materials can have subsequent end uses where the structures are exposed to aqueous liquids, including but not limited to normal tap water, waste water, and body fluids such as blood and urine. Conventional coform fibrous nonwoven structures are used as absorbent products either alone, such as in the form of wipes, or as components of other absorbents such as absorbent hygiene articles, including but not limited to diapers, training pants, incontinence garments, sanitary napkins, tampons, wound dressings, bandages, and others. Therefore, it is desirable that the inventive coform fibrous nonwoven structures withstand the harsh conditions of their intended uses, and the coform fibrous nonwoven web structures must

then become water-dispersible after the particular uses have been terminated. To achieve this, water-degradable polymers that employ a variety of triggering mechanisms can be used as polymers for forming the water-degradable reinforcing fibers of the fibrous composite nonwoven structure of the present invention.

Certain polymers are only water-degradable when exposed to sufficiently large amounts of an aqueous liquid within a certain pH range. Outside of that range, they do not degrade. Thus, it is possible to select a pH-sensitive, water-degradable polymer that will not degrade in an aqueous liquid or liquids within a pH range of, for example, 3 to 5, but will degrade in an excessive amount of tap water. See, for example, U.S. Patent No. 5,102,668 to Eichel et al., which is hereby incorporated by reference in its entirety. Thus, when fibrous composite nonwovens are exposed to body fluids such as urine, the water-degradable reinforcing fibers will not degrade. After use, such a fibrous composite nonwoven structure can be placed in an excess amount of a higher pH liquid, such as tap water, which causes the degradation of the water-degradable polymer forming the reinforcing fibers. Consequently, the longer and more coherent reinforcing fibers begin to break apart either on their own or with sufficient agitation so that the discrete fibrous components, e.g., wood pulp fibers, can be recovered, reused, or eliminated by flushing. Examples of polymers that could be used to form this type of fiber include acrylate ester/acrylic acid or methylacrylic acid copolymers and blends such as those supplied by Findley Adhesives, Incorporated, Milwaukee, Wisconsin, under the designation N-10, H-10, or X-10. These materials are stable under body pH conditions (or when buffered against body fluids), but break apart quickly in toilet water during the flushing process (excessive water).

Another mechanism that can be used to trigger water degradability is ion sensitivity. Certain polymers contain acid-based components (R-COO or R-SO3) that are held together by hydrogen bonding. When dry, these polymers remain solid. In an aqueous solution with a relatively high cation concentration, such as urine, the polymers remain relatively intact. However, when the same polymers are later exposed to larger amounts of water with dilute ion content, such as in a toilet bowl, the cation concentration becomes diluted and the hydrogen bond begins to break apart. When this occurs, the polymers themselves begin to break apart in the water. See, for example, U.S. Patent No. 4,419,403 to Varona, which is hereby incorporated by reference in its entirety. Polymers that are stable in solutions with high cation concentrations (for example, baby or adult urine and menstrual bleeding) would be sulfonated polyesters such as those supplied by Eastman Chemical Company, Kingsport, Tennessee, under the codes AQ29, AQ38 or AQ55. The Eastman AQ38 polymer is composed of 89 mole percent isophthalic acid, 11 mole percent sodium sulfoisophthalic acid, 78 mole percent diethylene glycol and mole percent 1,4-cyclohexanedimethanol. It has a nominal molecular weight of 14,000 daltons, an acid number of less than 2, a hydroxyl number of less than 10 and a glass transition temperature of 38°C. Other examples would be blends of poly(vinyl alcohol) copolymers blended with polyacrylic or methylacrylic acid or polyvinyl methyl ether blended with polyacrylic or methylacrylic acid. The Eastman polymers are stable in solutions with high cation concentrations, but break down rapidly when introduced into sufficient excess water, e.g. tap water, to dilute the cation concentration.

Yet another means of making a polymer water-degradable is the application of temperature changes. Certain polymers have a cloud point temperature. As a result, these polymers will precipitate from a solution at a certain temperature, the cloud point. These polymers can be used to form fibers that are water-degradable above a

· · ·

certain temperature, but become soluble and hence water-degradable at a lower temperature. Thus, it is possible to select or mix a polymer that will not decompose in body fluids such as urine at or near body temperature (37 ⁰ C), but will degrade when placed in water at temperatures below body temperature, e.g. at room temperature (23 ⁰ C) _1. An example of such a polymer is polyvinyl methyl ether, which has a cloud point of 34 ° C. If this polymer is exposed to body fluids such as urine at 37 ⁰ C, it will not degrade because this temperature is above its cloud point (34 ⁰ C). However, if the polymer is placed in water at room temperature (23 ° C), then over time the polymer will go back into solution because it is now exposed to water at a temperature below its cloud point. As a result, the polymer will begin to decompose.

Mixtures of polyvinyl methyl ether and copolymers may also be considered. Other cold water soluble polymers include poly(vinyl alcohol) graft copolymers with codes Ecomaty AX2000, AX10000 and AX300G supplied by Nippon Synthetic Chemical Company, Ltd., Osaka, Japan.

Other polymers are only water-degradable when exposed to sufficiently large amounts of water. Thus, these types of polymers may be suitable for use in environments with a low water volume, e.g. for panty liners, light incontinence products and wipes for babies or adults. Examples of such materials could be the aliphatic polyamides NP2068, NP2075 or NP2120, as supplied by H. B. Fuller Company, Vadnais Heights, Minnesota.

Having described the various components that can be used to form a water-dispersible, fibrous composite nonwoven structure according to the invention, examples of several processes that could be used to form such materials are now illustrated below. One process for forming the water-dispersible, fibrous nonwoven web structures of the invention is shown in Figure 1 of the drawings. In this

In the drawing, a water-degradable polymer is extruded through a die 10 into a high velocity primary gas stream 11, heated gas (usually air) is supplied from nozzles 12 and 13 to attenuate the molten polymer into long, somewhat coherent fibers. In forming these water-degradable reinforcing fibers, the primary gas stream 11 mixes with a secondary gas stream 14 containing discrete wood pulp fibers or other materials, including particles, to combine the two different fibrous materials into a single fibrous composite nonwoven structure. The apparatus for forming and supplying the secondary gas stream 14 including the wood pulp fibers may be apparatus of the type described and claimed in U.S. Patent No. 3,793,678 to Appel. This apparatus includes a conventional picker roller 20 having plucking teeth for tearing the pulp webs 21 into individual fibers. The pulp webs 21 are fed to the picker roller 20 by means of rollers 22 radially, i.e. along a picker roller radius. As the teeth on the picker roller 20 tear the pulp webs 21 into individual fibers, the resulting separated fibers are transported downward to the primary air stream through a forming nozzle or channel 23. A housing 24 encloses the picker roller 20 and creates a passage 25 between the housing 24 and the picker roller surface. Process air is supplied to the picker roller in the passage 25 via channel 26 in sufficient quantity as a medium for transporting the fibers through the forming channel 23 at a speed approximating the speed of the picker teeth. The air can be supplied by a conventional device, e.g. a blower.

As shown in Figure 1, the primary and secondary gas streams 11 and 14 preferably move perpendicularly towards each other at the fusion point, although other fusion angles can be used if desired to vary the degree of mixing and/or to form concentration gradients through the structure. The velocity of the secondary stream 14 is substantially lower than that of the primary stream 11, so that the integrated stream 15 resulting from the fusion flows in the same direction as the primary stream 11. The fusion of the two streams resembles a suction effect, whereby the fibers in the

secondary stream 14 into primary stream 11 as it passes the exit of duct 23. If a uniform structure is desired, it is important that the velocity difference between the two gas streams be such that the secondary stream is integrated with the primary stream by turbulence so that the fibers in the secondary stream are completely mixed with the meltblown fibers in the primary stream. Generally, increasing velocity differences between the primary and secondary streams result in more homogeneous integration of the two materials, while lower velocities and smaller velocity differences cause concentration gradients of the components in the fibrous composite nonwoven structure. For maximum production speeds, it is generally desirable for the primary air stream to initially be at sonic speed within nozzles 12 and 13 and for the secondary air stream to be at subsonic speed. On exiting nozzles 12 and 13, the air stream immediately expands with a resulting reduction in velocity.

Slowing down the high velocity gas flow carrying the water-degradable meltblown fibers frees the fibers from the pulling forces that initially form them from the water-degradable polymer mass. As the water-degradable reinforcing fibers relax, they are better able to follow tiny eddies and entangle and capture the relatively short wood pulp fibers or other absorbent fibers while dispersing and suspending both types of fibers in the gaseous medium. The resulting combination is an intimate blend of wood pulp fibers and water-degradable reinforcing fibers that is integrated by physical entrapment and mechanical entanglement.

Weakening of the water-degradable reinforcing fibers occurs both before and after entanglement of these fibers with the pulp fibers. To convert the fiber mixture in the integrated stream 15 into a fibrous nonwoven structure, the stream 15 is introduced into the gap of a pair of vacuum rollers 30 and 31 with foraminous surfaces, which continuously rotate over a pair of fixed vacuum nozzles 32 and 33. Upon entry of the integrated stream

15 into the gap between the rollers 31 and 33, the carrier gas is sucked into the two vacuum nozzles 32 and 33, while the fiber mixture is supported and slightly compressed by the opposing surfaces of the two rollers 30 and 31. This creates an integrated, self-supporting fibrous composite nonwoven structure 34 which is sufficiently intact so that it can be pulled out of the vacuum roller gap and transported to a take-up roll 35.

The inclusion of the wood pulp fibers in the integrated reinforcing fiber matrix is achieved without further processing or treatment of the airlaid composite structure. However, if it is desired to improve the strength of the fibrous composite nonwoven structure 34, e.g., for use as a wiper, the composite web or structure 34 can be embossed or bonded using heat and/or pressure. Embossing can be achieved, for example, using ultrasonic bonding and/or by mechanical bonding, e.g., using smooth and/or patterned bonding rolls which may or may not be heated. Such bonding techniques are well known to those skilled in the art. In Figure 1, the composite structure 34 is passed through an ultrasonic bonding station having an ultrasonic calendering head 40 which oscillates against a patterned anvil roll 41. The bonding conditions (e.g. pressure, speed, power input) as well as the bonding pattern can be selected appropriately to create the desired properties in the final product. See Figure 2.

The relative weight percentages of the water-degradable reinforcing fibers and the absorbent fibers can be varied according to the particular end use. In general, as the weight percentage of the water-degradable reinforcing fibers increases, the overall tensile strength and the integrity of the resulting fibrous composite nonwoven structure increases.

Another forming process that can be used to form the water-dispersible fibrous composite nonwovens according to the invention is shown in Figure 3 of the drawings. In Figure 3, an exemplary device for

Formation of an abrasion-resistant fibrous composite nonwoven structure is illustrated, generally designated by the reference numeral 110. In forming the abrasion-resistant fibrous composite nonwoven structure of this invention, pellets or chips, etc., of a thermoplastic polymer (not shown) are introduced into a petlet hopper 112 of one or more extruders 114.

The extruders 114 are equipped with extrusion screws (not shown) that are driven by a conventional drive motor (not shown). As the polymer is advanced through the extruders 114, it is progressively heated to the melt state due to the rotation of the extrusion screw by the drive motor. Heating the thermoplastic polymer to the melt state may be carried out in several discrete steps, with its temperature gradually increasing as it is advanced through the discrete heating zones of the extruder 114 to the two meltblowing nozzles 116 and 118, respectively. The meltblowing nozzles 116 and 118 may also form yet another heating zone, maintaining the temperature of the thermoplastic resin for extrusion at an elevated level.

Each meltblowing nozzle is designed so that two streams of the normally heated diluent gas per nozzle converge to form a single gas stream which entrains and attenuates the molten filaments of the water-degradable gas as the filaments exit from the small holes or orifices 124 in the meltblowing nozzle. The molten filaments are attenuated into fibers 120 or, depending on the degree of attenuation, into microfibers having a small diameter which is normally less than the diameter of the orifices 124. Thus, each meltblowing nozzle 116 and 118 has a corresponding single gas stream 126 and 128 containing entrained and attenuated polymer fibers. The gas streams 126 and 128 containing the polymer fibers are directed to converge at an impingement zone 130.

One or more types of secondary fibers 132 and/or particles are added to the two streams 126 and 128 of the water-degradable thermoplastic

Polymer fibers or microfibers 120 are added at the impact zone 130. The introduction of the secondary fibers 132 into the two streams 126 and 128 of the water-degradable thermoplastic polymer fibers 120 is designed to achieve a graded distribution of the secondary fibers 132 within the combined streams 126 and 128 of the thermoplastic polymer fibers. This can be achieved by fusing a secondary gas stream 134 containing the secondary fibers 132 between the two streams 126 and 128 of the water-degradable thermoplastic polymer fibers 120 so that all three gas streams converge in a controlled manner.

One means for achieving such fusion may be a conventional arrangement of the picker roller 136 having a plurality of teeth 138 capable of breaking down a mat or batt 140 of secondary fibers into the individual secondary fibers 132. The mat or batt of secondary fibers 140 fed to the picker roller 136 may be a web of pulp fibers (if a two-component blend of water-degradable thermoplastic polymer fibers and secondary pulp fibers is desired), a mat of staple fibers (if a two-component blend of water-degradable thermoplastic polymer fibers and secondary staple fibers is desired), or both a web of pulp fibers and a mat of staple fibers (if a three-component blend of water-degradable thermoplastic polymer fibers, secondary staple fibers, and secondary pulp fibers is desired). In embodiments where, for example, an absorbent material is desired, the secondary fibers 132 are absorbent fibers. The secondary fibers 132 can generally be selected from the group comprising one or more of polyester fibers, polyamide fibers, cellulosic fibers such as rayon fibers, wood pulp fibers and superabsorbent fibers, multicomponent fibers such as sheath/core multicomponent fibers, natural fibers such as silk fibers, wool fibers or cotton fibers, or electrically conductive fibers or mixtures of two or more such secondary fibers. Other types of secondary fibers 132 such as polyethylene fibers and polypropylene fibers and mixtures of two or more other types of secondary fibers 132

can be used. The secondary fibers 132 can be microfibers or macrofibers with an average diameter of about 300 pm to about 1,000 [im .

The webs or mats 140 of secondary fibers 132 are fed to the picker roller 136 by means of a roller assembly 142. After the teeth 138 of the picker roller 136 separate the mat of secondary fibers 140 into separate secondary fibers, the individual secondary fibers 132 are transported to the stream of thermoplastic polymer fibers or microfibers 120 through a nozzle 144. A housing 146 encloses the picker roller 136 and creates a passage or gap 148 between the housing 146 and the surface of the teeth 138 of the picker roller 136. A gas, such as air, is fed to the passage or gap 148 between the surface of the picker roller 136 and the housing 146 by means of a gas channel 150. The gas channel 150 may enter the passage or gap 148 generally at the intersection 152 of the nozzle 144 and the gap 148. The gas is supplied in sufficient quantity to serve as a medium for transporting the secondary fibers 132 through the nozzle 144. The gas supplied from the channel 150 also serves to aid in the removal of the secondary fibers 132 from the teeth 138 of the picker roller 136. The gas may be supplied by any conventional means such as an air blower (not shown). It is also contemplated that additives and/or other materials may be added to or entrained in the gas stream to treat the secondary fibers 132 or to provide desired properties in the resulting web.

Generally, the individual secondary fibers 132 are transported through the nozzle 144 at approximately the speed at which the secondary fibers 132 exit the teeth 138 of the picker roller 136. In other words, the secondary fibers 132 generally maintain their speed, both in magnitude and direction, as they exit the teeth 138 of the picker roller 136 and enter the nozzle 144 from the point at which they exit the teeth 138 of the picker roller 136. Such an arrangement, which is described in more detail in U.S. Patent No. 4,100,324

to Anderson et al., contributes significantly to the reduction of fiber flocculation.

The width of the nozzle 144 should be oriented in a direction generally parallel to the width of the meltblowing nozzles 116 and 118. Desirably, the width of the nozzle 144 should be approximately the same width as the meltblowing nozzles 116 and 118. Typically, the width of the nozzle should not exceed the width of the webs or mats 140 fed to the picker roll 136. In general, the length of the nozzle 144 separating the picker from the impingement zone 130 should desirably be as short as the equipment configuration allows.

The picker roller 136 may be replaced by a conventional particulate injection system for forming a fibrous composite nonwoven structure 154 containing various secondary particles. A combination of secondary particles as well as secondary fibers could be added to the water-degradable thermoplastic polymer fibers 120 prior to forming the fibrous composite nonwoven structure 154 if a conventional particulate injection system was added to the system shown in Figure 3. The particles may be, for example, activated carbon, clay, starches and/or hydrocolloid (hydrogel) particles, commonly referred to as superabsorbents.

Due to the fact that the water-degradable thermoplastic polymer fibers in the fiber streams 126 and 128 are normally still in a semi-molten and sticky state when the secondary fibers 132 are incorporated into the fiber streams 125 and 128, the secondary fibers 132 usually become not only mechanically entangled within the matrix formed by the water-degradable fibers 120, but also thermally bonded or bonded to the water-degradable fibers.

To convert the composite stream 156 of water-degradable fibers 120 and secondary fibers 132 into a fibrous composite nonwoven structure 154 consisting of a coherent matrix of the water-degradable fibers 120 with the

secondary fibers 132, a collector is disposed in the path of the composite stream 156. The collector may be an endless belt 158 conventionally driven by rollers 160 and rotating in the direction of arrow 162 indicated in Figure 3. Other collectors are well known to those skilled in the art and may be used in place of the endless belt 158. For example, a porous rotating drum assembly could be used. The fused streams of water-degradable fibers and secondary fibers are collected as a coherent fibrous matrix on the surface of the endless belt 158 to form the fibrous composite nonwoven structure or web 154. Vacuum boxes 164 assist in retaining the matrix on the surface of the belt 158. The vacuum may be set at about 2.5 to about 10 cm of water.

The fibrous composite nonwoven structure 154 is coherent and can be removed from the tape 158 as a self-supporting nonwoven material. In general, the fibrous composite nonwoven structure 154 has sufficient strength and integrity to be usable without post-processing such as pattern bonding and the like. If desired, a pair of nip rolls or pattern bonding rolls (not shown) can be used to bond portions of the material. Although such processing may improve the integrity of the fibrous composite nonwoven structure 154, it tends to compress and compact the structure.

In addition to the above methods, there are numerous other methods suitable for producing various types of coform materials. For example, McFarland et al., U.S. Patent No. 4,604,313, issued August 5, 1986, deals with a method for forming a multilayer coform material comprising meltblown fibers and wood pulp fibers in one layer and a second layer containing meltblown fibers, wood pulp fibers and superabsorbent particles. Another method is disclosed in Eschwey et al., U.S. Patent 4,902,559, issued February 20, 1990. From this patent, a method is known in which continuous filaments are spun through a long spinneret into a passage for forming fibers, which are generally referred to as

Spunbond fibers are referred to as spunbond fibers. At the same time, smaller hydrophilic or oleophilic fibers are added to the stream of spunbond fibers. Optionally, superabsorbent particles can also be introduced into the above fiber mixture. The patent by McFarland et al. and the patent by Eschwey et al. are hereby incorporated by reference in their entirety.

Having described various components and methods useful in forming water-dispersible fibrous composite nonwoven structures according to the invention, a series of examples have now been prepared to illustrate the present invention.

EXAMPLES Example I

In Example I, water-dispersible fibrous composite nonwoven structures were prepared using a water-soluble meltblown poly(vinyl alcohol) copolymer and fluffy wood pulp in weight percent ratios (meltspun/pulp) of 20/80, 30/70, and 40/60 based on the total weight of the fibrous composite nonwoven structure. The polyvinyl alcohol copolymer was codenamed Ecomaty AX10000 and was manufactured by Nippon-Gohsei, Osaka, Japan. The melt flow rate of this AX10000 copolymer was 100 g per 10 minutes at a temperature of 190 ⁰ C under a load of 2.16 kg using ASTM Test Method D-1238. The softening temperature of the AX10000 copolymer was 18O ⁰ C, but it was better processed at 21O ⁰ C to produce meltblown microfibers. The fluffy wood pulp was coded NF405, supplier: Weyerhauser Corporation, Federal Way, Washington. The absorbent structure was made using a dual extruder and pulping line as shown in Figure 3. The co-molded composites were formed on either a porous fabric backing or a spunbonded polypropylene nonwoven web backing. Optionally,

the coform composites can also be formed directly on a forming wire. The basis weights of the coformed absorbent structures were 190 grams per square ^meter (gm ² ). The absorbent structures were then pattern bonded in a separate operation using a heated calendering nip with a total bonding area of approximately 20%. When the formed absorbent was placed in room temperature water and shaken, the meltblown fibers dissolved and the web broke apart in less than one minute and usually in less than 30 seconds. The 20/80 web was subjected to an intermenstrual panty liner test in a consumer study with adult women and the coformed absorbent was found to be able to withstand low fluid loads from urine and menstrual bleeding for periods of up to six hours.

Example II

In Example II, a water-dispersible, fibrous nonwoven structure was prepared using a water-soluble meltblown polyamide polymer and wood pulp flakes in a 30 to 70 weight ratio (meltblown/fluffy). The polyamide polymer was coded NP 2068, supplied by HB Fuller Company of St. Paul, Minnesota. The viscosity of the NP-2068 polymer was 95 Pascal seconds at a temperature of 204 ^° C. The softening temperature range of the NP-2068 polymer was 128°-145°C, but it processed best at 210 ^° C to produce meltblown microfibers. The fluffy wood pulp was coded NF405, supplied by Weyerhauser Corporation, Federal Way, Washington. The absorbent structure was prepared in the same manner as in Example I. The co-molded composite was formed on a porous fabric carrier layer. The basis weight of the co-molded absorbent structure was 190 g per m ² . When the molded absorbent was placed in room temperature water and stirred, the meltblown fibers dissolved and the web broke apart in less than one minute and typically less than 30 seconds.

Example III

In Example III, a water-dispersible, fibrous composite nonwoven structure was prepared using a water-soluble meltblown polyamide polymer and wood pulp flakes in a weight ratio of 30 to 70 (meltspun/fluffed). The polyamide polymer was coded NP 2074, supplied by HB Fuller Company, St. Paul, Minnesota. The viscosity of the NP-2074 polymer was 290 Pascal seconds at a temperature of 204 ^° C. The softening temperature range of the NP-2074 polymer was 133-145 ^° C, but it processed best at 210 ^° C to produce meltblown microfibers. The fluffed wood pulp was coded NF405, supplied by Weyerhauser Corporation, Federal Way, Washington. The absorbent structure was prepared in the same manner as in Example I. The co-molded composite was formed on a porous fabric carrier layer, and the basis weight of the co-molded absorbent structure was 190 g per m ² . When the molded absorbent was placed in room temperature water and stirred, the meltblown fibers dissolved and broke apart in less than one minute and typically in less than 30 seconds.

To further illustrate the invention, experimental panty liners were prepared using the water-degradable coform materials as shown in Examples I through III above and compared to a conventional coform-containing panty liner. The conventional panty liner construction comprised a polyethylene protective film, a 13 g/ ^m2 heat-embossed spunbonded polypropylene liner, and a 190 g/ ^m2 coform material as the absorbent core. The coform material contained 30% by weight of polypropylene meltblown fibers having an average fiber diameter of about 5 μm and 70% by weight, based on the weight of the absorbent core, of wood pulp fibers. The polypropylene meltblown fibers and the wood pulp fibers were intimately mixed together to form the absorbent core. To assemble the

To form the panty liner structure, a water-based adhesive was used to laminate the polyethylene film to one side of the coform material, and the spunbonded polypropylene liner was heat embossed to the other side of the coform material.

A garment adhesive strip was applied to the outside of the polyethylene film protector to secure the product to the wearer's undergarments. This laminate served as a control because it did not contain any water-degradable reinforcing fibers, but instead utilized the meltblown polypropylene fibers as the reinforcing agent. Further description of such products can be found in U.S. Patent No. 3,881,490 to Whitehead et al. and U.S. Patent No. Des. 247,368 to Whitehead, both of which are incorporated herein by reference in their entirety.

The materials of the present invention from Examples I to III were also formed into pantiliners of the same general type as described above. Instead of the 190 gm ² polypropylene coform material in the control, 190 gm ² coform composites of 30 wt.% water-degradable reinforcing fibers to wt.% wood pulp fibers according to Examples I, II and III were used. In addition, the polyethylene protector was replaced with a water-degradable film and the protector was applied to the coform absorbent core using a hot melt adhesive instead of a water-based adhesive.

Twenty samples of each of the four panty liners, including the control, were each subjected to a toilet flush test. In the test, individual samples were randomly placed in a 3.5 gallon toilet and allowed to remain in the toilet for 30 seconds before flushing. The control, which contained regular coform material, only flushed six of the twenty samples; this means that only 30% of these panty liners would be flushable in a 3.5 gallon toilet. In contrast, for the three types of panty liners using the water dispersible materials of the invention, all twenty samples of each material flushed away. Thus, these materials were 100% flushable. Visual observation during the test revealed that the panty liners of the invention absorbed water almost immediately and therefore

sank directly to the bottom of the toilet bowl. In contrast, the control panty liners, which contained polypropylene fibres (which have a density of less than 1 g per cm ³ and a polyethylene protective film with a density of less than 1 g per m ³ ), floated on the surface of the water in the toilet bowl. The hydraulic driving force exerted on the control product was therefore much lower than that exerted on the test products. This demonstrated the non-flushability of the control product, as it could not exploit the driving force of the filling jet in the toilet.

In addition, five samples each of the control and the pantiliners containing the inventive materials were separately introduced into a moving water system at a rate of about 0.6 meters per second. In less than one minute, the inventive absorbent core material completely broke apart to the extent that it was no longer recognizable. In contrast, the control absorbent core remained substantially intact even after a 30 minute exposure period. Thus, it is apparent that the inventive water-dispersible fibrous composite nonwoven structures allow for a variety of applications requiring products that readily disperse in water after their intended use cycle.

Having described the invention in detail, it should now be apparent that numerous modifications and variations of the present invention are possible without departing from the spirit and scope of the following claims.

Claims (20)

1. A water-dispersible fibrous composite nonwoven structure comprising a matrix of melt-spun, water-degradable reinforcing fibers and a plurality of discrete absorbent fibers disposed within the matrix of melt-spun, water-degradable reinforcing fibers. 2. The water-dispersible fibrous composite nonwoven structure of claim 1, wherein the absorbent fibers are staple fibers having average fiber lengths of about 18 mm or less. 3. The water-dispersible fibrous composite nonwoven structure of claim 1, wherein the absorbent fibers are wood pulp fibers. 4. The water-dispersible fibrous composite nonwoven structure of claim 1 further comprising a particulate material within the matrix. 5. The water-dispersible fibrous composite nonwoven structure of claim 4, wherein the particulate material is a superabsorbent. 6. The water-dispersible fibrous composite nonwoven structure of claim 4, wherein the particulate material is an odor reducing agent. 7. The water-dispersible fibrous composite nonwoven structure of claim 1, wherein the melt-spun water-degradable reinforcing fibers contain water-degradable polyamides. 8. The water-dispersible fibrous composite nonwoven structure of claim 1, wherein the melt-spun, water-degradable reinforcing fibers comprise poly(vinyl alcohol). 9. A personal care absorbent article comprising a water-dispersible fibrous composite nonwoven structure according to claim 1. 10. The absorbent hygiene article of claim 9, wherein the article is a wipe. 11. The sanitary absorbent article of claim 9, wherein the article is a diaper. 12. The absorbent hygiene article of claim 9, wherein the article is a training pant. 13. An absorbent hygiene article according to claim 9, wherein the article is a panty liner. 14. The sanitary absorbent article of claim 9, wherein the article is a sanitary napkin. 15. The absorbent hygiene article of claim 9, wherein the article is an incontinence device. 16. An absorbent hygiene article according to claim 9, wherein the article is a wound dressing. 17. The absorbent hygiene article of claim 9, wherein the article is a bandage. 18. A water-dispersible fibrous composite nonwoven structure comprising: a matrix of melt-spun, water-degradable reinforcing fibers and a plurality of particles disposed within and retained by the matrix. 19. The water-dispersible fibrous composite nonwoven structure of claim 18, wherein the particles contain a superabsorbent. 20. The water-dispersible fibrous composite nonwoven structure of claim 18, wherein the particles contain an odor-reducing material.