Water-absorption Fibrous Materials And Method Of Making The Same

Abstract

A readily disposable water absorbent product, such as a diaper, bed napkin or catamenial device, and process of making the same, the product comprising a supporting sheet of cellulose fiber and a layer of dry, flexible fibers which on contact with 20 times their weight of water at 25.degree. C. lose their fibrous character and form a soft plastic gel, said flexible fibers consisting essentially of a polysaccharide gum or starch and the weight ratio of said cellulose fibers to said gel-forming fibers being in the range of 20:1 to 1:1.

Description

This invention relates to novel fibrous materials, their manufacture and their use.

In accordance with one aspect of this invention there is produced a dry flexible fibrous material which on contact with water (e.g., on contact with 20 times its weight of water at 25.degree. C.) loses its fibrous character within a very short period of time (e.g., less than a minute) and forms a soft plastic gel.

This fibrous material is suitable for use in structures designed for absorbing body fluids, e.g., diapers, catamenial devices such as sanitary napkins or vaginal tampons, pads for protecting the bed against wetting, and surgical and medical applications. In such cases the fibers are on a supporting sheet or between supporting sheets or they may be present in a self-supporting sheet. The supporting sheet or sheets may be of the disposable type (e.g., of soft paper), so that the diaper or other structure may be disposed by flushing it down toilet.

In a preferred form of the invention there is prepared a dry flexible fibrous mass comprising intertangled fibers which on contact with water, (e.g., 10 or 20 times its weight of water at 25.degree. C.) forms a soft plastic gel having a pH of about 5 to 8, which gel retains its water content under mechanical pressure such as is exerted by the body when the gel is present as an intermediate layer in a diaper. Thus, unlike ordinary diapers made wholly of cellulose, which can give up their absorbed urine when pressed or squeezed, diapers containing the fibers of this invention retain the moisture in the form of the soft nonfibrous gel and are therefore more comfortable in use. The gel is harmless and inert to the body of the water.

In one preferred form of the invention the fibers are made of guar, which is a natural gum of polysaccharide character, soluble in cold water. Chemically guar is a galactomannan and is believed to consist essentially of a straight chain of d-mannose units, linked to each other by means of beta (1-4) glycosidic linkages, the chain having single-membered d-galactose side branches; the branches are found on alternate mannose units. The guar may be the natural product or a chemically modified type such as the self-complexing guars. The guar may be admixed with other hydrophilic materials; good results have been obtained with fibrous products made from mixture of guar gum and a proportion of a cold-water-swelling starch such as pregelatinized starch or a chemically modified starch. In place of, or in admixture with, the guar other suitable water-soluble materials, including polysaccharide gums or starches, may be used. For example, the guar may be mixed with natural gums such as locust bean gum, gum karaya, and gum tragacanth, as such or chemically modified, or with proteinaceous water-soluble materials such as egg albumin or blood albumin; gums or other polymers, other than guar, when formed into dry flexible fibers of the type described herein, may be employed alone. Plasticizing agents may be present in admixture; thus, the fibers may contain one half or 1 percent of water-soluble polyvinyl alcohol which may improve the adhesion of the fibers to the sheet on which they are supported in the final product. The fibrous material may be prepared by mixing a well hydrated mass of the gum with a water-miscible nonsolvent for the gum while agitating. Thus a smooth syrupy or thick honeylike aqueous solution of the gum may be added to the water miscible nonsolvent, or the nonsolvent may be added to the aqueous solution, while agitating the resulting mixture (as by means of a rapidly rotating stirrer or by blowing air bubbles through the mixture) to form a fibrous mass which can then be freed of surface water and dried under such conditions that a soft flexible fibrous mass, not hard or horny, is obtained. In experimental work thus far moderate drying temperatures, well below 60.degree. C. have given best results.

In one preferred form of the invention the nonsolvent is isopropanol. Other water-miscible alcohols, e.g., volatile alkanols of lower molecular weight such as methanol, ethanol or n-propanol, may also be used alone or in admixture with the isopropanol. It is also within the scope of this invention to use such materials as volatile ketones, e.g., acetone, or to use nonvolatile ketones, alcohols or other organic liquids, or suitable aqueous salt solutions where appropriate.

One typical fibrous product according to this invention comprises a mass of fine fibers of various thicknesses and lengths which are intertangled and also, at spaced points, adhered together, having an appearance like that of loose well-opened blotting paper. The mass is flexible; it is limp and gives substantially no resistance to bending with one's fingers and its individual fibers are easily pulled apart, torn, broken or disintegrated, as by a light pull with one's fingers. In one form the fibers are present as small clumps of tangled and adhered fibers, with each clump having a length in the range of, say, about one quarter inch to 2 inches, the clumps having on their surfaces a multiplicity of projecting individual fine fiber ends or loops (bends), and the thickness of these individual fine fibers being on the order of a thousandth of an inch or so, the fibers of the mass generally having thicknesses in the range of, say, about 0.0005 to 0.02 inch.

Any suitable technique may be employed for distributing the fibers or clumps thereof onto the supporting sheet. Thus the material may be rolled onto the supporting sheet, or the fibers may be chopped up easily, to short lengths (e.g., one quarter inch) if desired, and then, for example, sprinkled onto the supporting sheet. The supporting sheet may be dampened with moisture to aid in anchoring the fibers thereto without destroying their fibrous character. The chopped fibers may be united to the sheet of cellulose fibers by mixing them with paper fibers, or other cellulose fibers, in varying proportions (such as a weight ratio of the cellulose fibers to the water-absorption fibers of 20:1, 10:1, 5:1, 2:1, 1:1 or 1.2) and forming the mixture into a soft sheet in which the water-absorption fibers are interspersed among the cellulose fibers. It is also within the broad scope of the invention to mix the water-absorption fibers with other natural or synthetic fibers.

In another aspect of this invention the fibrous material, which as stated, is easily torn or broken, can be protected by a removable coating of film-forming strengthening agent, the coating being removed in whole or in part before the fibers are finally positioned in the finished product whereby the fibers can be effective in that finished product substantially unhindered by that coating. For example, long discontinuous fibers of guar gum may be made by extruding an aqueous syrupy solution of the gum through a spinneret having fine orifices into a water-miscible nonsolvent for the gum (e.g., isopropanol). The collected fibers are dried in air and sprayed with a solution of a high polymer such as a cellulose derivative (e.g., a solution of carboxymethyl cellulose or methyl cellulose) or polyvinyl acetate and then formed into yarns (as by conventional spinning methods which are thereafter woven, or knitted, into fabric (e.g., a fabric of relatively open weave). The coating can then be removed by passing the fabric through a bath of a solvent for the coating which does not affect the fibers e.g., aqueous alcohol). The use of the coating facilitates the mechanical operations of yarn-forming, weaving or knitting and helps avoid fiber-breakage during these operations.

In one type of product utilizing the fibers of this invention there is a body-touching sheet or ply and a second, strength-giving, sheet. The body touching ply may be a thin, soft, absorbent cellulose-type sheet. It is advantageously made of a fine soft paper of a quality at least such as in a good grade of facial tissue. It is of such quality so that in the dry state it does not abrade or irritate the skin. It is beneficially relatively loosely textured, for example, as in a soft quality facial or toilet tissue, but yet of sufficient wet strength to retain its continuity and not tear while in the wet state on the wearer. This is desirable because, for example, it is not uncommon that when a diaper-wearing child only wets the diaper, the wet diaper is not replaced and the child continues to wear it and will wet it again one or more times.

So long as it has the required softness, the body-touching ply need not be restricted to a felted sheet, which is the preferred form; it may be a loose weave, for example, a fine grade gauze treated for softness. It can be made of cellulose, cotton, paper cotton, rayon, or even synthetic celluloselike fiber, all of which and others like them are embraced by the expression "cellulose-type." In thickness, it can range from about one one-thousandth to about two one-hundredths or even about three one-hundredths of an inch.

The second sheet likewise can be composed of a cellulose type sheet such as used for the body-touching ply. However, the second sheet need not have the relatively open texture. It can be of fuller texture to provide somewhat greater strength, for it generally is the strongest of the three requisite component parts of the product. The second sheet may also be coated with a moisture resistant material on one or both sides, if desired.

Water-imperviousness is imparted to this sheet by application to one or both sides of it of a water-repellant coating that is inert or harmless to the skin of the wearer. Such coating can be of any suitable natural or synthetic wax, such as paraffin wax, and applied in known manner; or natural or synthetic resin, either rolled on or applied dissolved in a volatile solvent, or of lacquer.

However, whatever coating material is used should be applied preferably only in quantity sufficient to impart the water-imperviousness and should be one that leaves the coated sheet sufficiently flexible. While this second sheet can be as thin as the body-touching sheet, it desirably can be thicker. The water-impervious coating, when employed, is applied to prevent wetting, and particularly soiling, of any other garment worn next to the napkin. Ordinarily, the coated side of this sheet can be the exposed surface of it in the assembled finished napkin.

The surface of the second sheet and also of the body touching sheet that is not an exposed surface in the assembled finished napkin is conveniently referred to as the unexposed side of the second sheet or of the body-touching sheet respectively.

The multiply products of this invention can be readily prepared by continuous manufacturing processes. For example, the body-touching sheet can be made available rolled up on a roller, and the second sheet can be similarly set up. These rolls can be mounted spaced apart from one another, e.g., one above the other, and arranged so that both of the sheets can be rolled off toward a common meeting point. If woven or knitted fibers are to be used as the intermediate layer, sheets formed therefore can also be rolled up on a roller and fed to the common meeting point between the body-touching sheet and the second sheet to form the multiply product of this invention. If nonwoven fibers are employed, they can be sprayed or sprinkled on to the unexposed surface of either of the two sheets at any time prior to the common meeting point and the resulting combination passed to a set of rollers for pressing operation. Alternatively, the fibers can be supported on a separate cellulose-type sheet, a roll of which is so mounted that the sheet coming off it can be fed toward the common meeting point between the body-touching sheet and the second sheet feeding off their respective rolls. In either case the body-touching sheet or the second sheet may be premoistened with water (e.g., so that they are damp to the touch) to aid in anchoring the fibers thereto without destroying their fibrous character; the assembly may thereafter be dried in any suitable way, e.g., with hot air. It should be understood, however, that the exact manner of manufacturing the multiply products, such as a napkin capable of being flushed away by a toilet stream, is not one of the essential features of this invention and that various known procedures for manufacturing multiply products can be utilized with equal effectiveness. The use of the fibrous material of this invention, instead of a powder or flake, overcomes the problem of migration of the water-absorption material, by which migration areas that have reduced moisture absorption are formed during manufacture, shipment, storage, or use of the multilayer product.

For the preparation of disposable diapers, the width of the sheets can be the same as the width of the diapers. These can be sold on rollers from which can be cut off any desired length, or they can be cut into selected lengths, for example, separated by suitable perforations or scoring. In the case of diapers or bed pads the product may be scored the entire width and length of the product for more simple disposition.

The edges of the two or three sheets pressed together can be sealed by any suitable innocuous adhesive or heat sealable polymer, either of which can be applied in known manner.

Bedpads to protect a bed surface against wetting can be prepared in substantially the same way as are the disposable diapers.

Catamenial pads can be prepared in relatively the same way by cutting them from sheets of suitable width, for example, a strip of any suitable width cut from a wide sheet, or may be stamped out by suitable dies from the sheets or wound around a core.

Tampons can be prepared, for example, by selecting sheets of suitable width or cutting such widths from wider sheets, and rolling the resulting strips into suitable tampon form; or by rolling any number of turns of the moisture-absorption layer about a tampon core, to either of which these can be attached in any convenient known manner the strings for their removal after use.

The products of the invention are not limited to the several herein described uses. The combination can be applied to other uses wherein their water absorbency serves effectively. Thus they can serve to absorb any other moisture, blood or aqueous exudation from any body opening, natural or otherwise, for example, as a bandage over any form of open wound.

The intermediate layer of the multiply product can also be provided with a minor amount of a suitable, capillary penetrating agent or surfactant that is inert to the water-absorbent fibers or filaments, the fibers of the other sheets and harmless to the body in use. The capillary-penetrating agent may either be incorporated into the water absorption fibers or admixed therewith in particulated form.

While the products of the invention may be more generally embodied in a disposable diaper their particular combination lends itself to their being embodied also as sanitary napkins, vaginal tampons or pads for protecting beds or cots or other surfaces against wetting by children who have not yet develop control of their elimination and voiding or by older people who during illness or otherwise have temporary extended loss of such control.

The water-absorption fibers may also be used with other materials, for example, in paper trays used for commercial packaging or frozen foods such as chickens, meat, fish, etc., as in paper and fabric wrapping of shipped products where high humidity may be a factor.

The following Examples are given to illustrate this invention further. All temperatures in the Examples are room temperature (e.g., 25.degree. C) and pressures are atmospheric pressure, unless otherwise indicated.

EXAMPLE 1

5 grams of guar gum ("Jaguar 315-CM" is added gradually to 325 ml. of water with vigorous stirring until an apparently homogeneously solution is obtained. The mixture is then allowed to stand, with occasional stirring for 1 hour to hydrate more fully. Then one liter of anhydrous isopropanol is added with stirring, forming a fibrous precipitate, which was allowed to settle. After the supernatant material is decanted off the fibrous precipitate is washed with an additional 500 ml. of anhydrous isopropanol after which the isopropanol is filtered off and a current of room temperature air is drawn through the fibrous material until it has a dry appearance. The fibrous material is then dried overnight in air in a forced draft oven set at 40.degree.-50.degree. C.

Similar results are obtained when the aqueous solution is allowed to stand for periods of 2, 3 or 4 hours instead of 1 hour.

The guar gum used in this Example 1 is of the well-known chemically modified self-complexing type which shows exceptionally high viscosity and forms solid gels at very low concentrations in water.

EXAMPLE 2

200 grams of powered guar gum ("Jaguar 806" are wet with 400 ml. of isopropanol and then dispersed in 20 liters of tapwater with the aid of a mechanical stirrer. The mixture is allowed to stand for 2-3 days for further dehydration of the gum to occur, forming a smooth moderately viscous dispersion. This dispersion is added slowly in a continuous stream (at the rate of 10-15 ml. per minute) to a bath of isopropanol which is mechanically stirred. As the gum precipitates in the isopropanol it is feathered into a fibrous white mass by the rotary mechanical stirrer. The white fibrous precipitate is removed periodically during the process, gently squeezed by hand to remove excess liquid and washed in fresh isopropanol, then collected on an aluminum screen, dispersed in fresh isopropanol for a second washing and spread out to dry at room temperature (e.g., 25.degree. C.) overnight, and then fluffed by whipping with a thin flexible tube attached to a rotary mechanical stirrer.

EXAMPLE 3

Example 2 is repeated, using the guar gum sold under the designation "A-20-D" (Stein Hall) with similar results.

EXAMPLE 4

Example 2 is repeated using a mixture of 190 grams of the guar gum and 10 grams of pregelatinized starch (or of 180 or 170 grams of guar and 20 or 30 grams, respectively, of pregelatinized starch) in place of the 200 grams or guar gum.

The moisture content of dry guar gum is about 10-13 percent. Its ash content is less than about 1 percent. (e.g.,

As will be seen in the Examples, it is often desirable to permit the gum solution to stand for some time to hydrate fully before forming it into fibers. In the case of guar, particularly if a slow-hydrating type is used, a number of hours may be needed for the solution to attain its full viscosity. The viscosity of solutions of guar in water, after full hydration (e.g., after 24 hours) is often on the order of 3000-3500 centipoises (measured with a Brookfield Viscometer Synchro Electric Model RVO at 20 r.p.m. at 25.degree. C. using spindle No. 3) for a 1 percent solution; for a 3 percent solution it is over 50,000 centipoises which is substantially a gel. The solutions are nonNewtonian, if measured at 12 r.p.m. the viscosity of a 1 percent solution is about 5,000 rather than 3,500 centipoises. For the self-complexing type of guar gel-formation is attained at lower concentrations. It will be seen that while the fibrous character of the product can be destroyed very quickly on contact with water, full hydration and gel formation is a slower process.

In general, the polysaccharide materials of this invention preferably have viscosities (measured at 20 r.p.m. as described above) of over 2,000 centipoises, more preferably at least 2,500 centipoises for a 1 percent aqueous solution, and well above 20,000 centipoises for a 3 percent solution.

Small amounts of borax or other materials may be present with the fibrous material of this invention or in a separate layer of the product (e.g., the second sheet or the body-contacting ply) to modify the surface tension of the aqueous body fluid or the effect thereof on the gum.

It is understood that the foregoing detailed description is given merely by way of illustration and that variations may be made therein without departing from the spirit of the invention. The "Abstract" given above is merely for the convenience of technical searchers and is not to be given any weight with respect to the scope of the invention.

Claims

I claim:

1. A readily disposable water adsorbent product comprised of a supporting sheet of cellulose fiber said supporting sheet having united therewith dry flexible fibers which on contact with 20 times their weight of water at 25.degree. C. lose their fibrous character rapidly and form a soft plastic gel, said flexible fibers consisting essentially of a polysaccharide gum or starch and the weight ratio of said cellulose fibers to said gel-forming fibers being in the range of 20:1 to 1:1.

2. A product as in claim 1, such as a disposable diaper, bed napkin or catamenial device, having a body-touching layer and an outer layer, said fibers being positioned between said layers.

3. A product as in claim 1 in which said fibers are nonaligned.

4. A product as in claim 1 in which said fibers are of guar.

5. Product as in claim 1 in which said soft plastic gel has a pH of about 5 to 8 and retains its water content under mechanical pressure.

6. Product as in claim 5 in which said gel-forming fibers are nonwoven.

7. A process for the manufacture of readily disposable water absorbent products which comprises the steps of forming a dry flexible fibrous material which fibrous material on contact with 20 times its weight of water at 25.degree. C. loses its fibrous character rapidly and forms a soft plastic gel, and uniting said fibrous material with a supporting sheet of cellulose fibers in a weight ratio of said cellulose fibers to said fibrous material in the range of 20:1 to 1:1, said fibrous material consisting essentially of a polysaccharide gum or a starch.

8. A process as in claim 7 in which said dry flexible fibrous material is made by bringing an aqueous solution of said gum or starch into contact with a water-miscible nonsolvent therefor while agitating, and then drying the resulting fibrous precipitate to produce a dry flexible fibrous mass.

9. A process as in claim 8 in which said fibrous precipitate is dried in air at a temperature below 60.degree. C.

10. A process as in claim 9 in which said uniting step forms a length of sheet material, said process including the step of cutting said length with individual diapers.

11. Process as in claim 7 in which said soft plastic gel has a pH of about 5 to 8 and retains its water content under mechanical pressure.

12. Process as in claim 11 in which said gel-forming fibers are nonwoven.