US3556919A

US3556919A - Water-dispersible fabric

Info

Publication number: US3556919A
Application number: US653540A
Authority: US
Inventors: Martha Marie Johns; John Andrew Lynch Jr
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1967-07-14
Filing date: 1967-07-14
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19

Abstract

SOFT, WATER-DISPERSIBLE FABRICS ARE PREPARED BY MODIFYING ONE SIDE OF A WOVEN FABRIC OR NONWOVEN FABRIC OF ENTANGLED FIBERS, THROUGH A DEPTH OF A LEAST 40% BUT LESS THAN 95% OF ITS THICKNESS TO CONVERT FIBERS IN SUCH MODIFIED SIDE TO A HIGH-SWELLING FORM.

Description

WATER-DISPERSIBLB FABRIC Filed July 14, 1967 FIG.

INVEN'IOR MARTHA M. JOHNS JOHN A. LYNCH, JR.

' ATTORNEY United States Patent 3,556,919 WATER-DISPERSIBLE FABRIC Martha Marie Johns, Wilmington, Del., and John Andrew Lynch, Jr., Chadds Ford, Pa., assignors to E. I. du

Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed July 14, 1967, Ser. No. 653,540 Int. Cl. D03d 15/00; A61f 13/16; B32b 7/00 US. Cl. 161-70 Claims ABSTRACT OF THE DISCLOSURE Soft, water-dispersible fabrics are prepared by modifying one side of a woven fabric or nonwoven fabric of entangled fibers, through a depth of at least 40% but less than 95% of its thickness to convert fibers in such modified side to a high-swelling form.

DETAILED DESCRIPTION This invention relates to disposable woven and nonwoven fabrics and to a process for making fabrics and fabric-like materials disposable in sewage systems. More particularly, the present invention is concerned with woven and nonwoven fabrics which have adequate strength, durability and a firm surface while wet with body fluids, but which are dispersible in the flushing water of an ordinary toilet.

Single use devices intended for the absorption of body fluids such as diapers. bandages, sanitary napkins and the like are generally constructed of an absorbing body and a cover. Such covers must have suflicient wet strength to maintain their integrity in use. In general, conventional covers have a sufficient wet strength to maintain their integrity in turbulent water and, hence, make disposal in a home sewer line a risky experiment.

It has been found that flushable woven and nonwoven fabrics composed of certain high-swelling fibers, such as, for example, those formed in the rapid high-temperature carboxymethylation of a rayon fabric to a certain degree of substitution, maintain a useful degree of strength and integrity when wet with body fluids. This invention is concerned with a further advance in this area of technology particularly as to the hand or feel as well as the abrasion resistance of the surface of such fabrics when Wet with urine, menstrual fluid and the like. The invention provides a modified water-dispersible woven or nonwoven fabric having a surface of improved hand and abrasion resistance when wet with body fluids. The invention further provides a process for the modification of woven and nonwoven fabrics to yield water-dispersible products having an improved hand and abrasion resistance when wet with body fluids.

This invention comprises a soft, water-dispersible woven fabric, or nonwoven fabric with entangled fibers, said fabric having a dry tensile strength of at least 1.0 lb./in. (178.6 g./cm.), a water-wet tensile strength of less than 0.1 lb./in. (17.86 g./cm.), a synthetic urine-Wet tensile strength of over 0.05 lb./in. (8.9 g./cm.), a dispersibility of over 20%, and a bending length of less than 3.0 cm. The fabric consists of a water-sensitive and a water-insensitive layer. The former comprises between 40 and 95% of the fabric thickness while the latter constitutes the remainder. The boundary between these layers is not necessarily flat so that the actual thickness of the watersensitive layer may vary. However, on the average, it will be present in the proportions indicated.

As described in more detail below, the fibers of the fabrics under consideration will pass up and down through the fabric thickness at regular or irregular intervals. The water-insensitive layer of the fabric consists essentially 3,556,919 Patented Jan. 19, 1971 of the low swelling segments of fibers, while the watersensitive layer consists essentially of the high-swelling segments of the same fibers. The water-sensitive layer may contain some fibers that are entirely high-swelling. At least and preferably above of the fibers of the fabric are segmented, that is, they are constituted by both high-swelling and low-swelling segments.

The invention further comprises, in the process of modifying the low-swelling fibers of a woven fabric or a nonwoven fabric and entangled fibers to a high-swelling form, the improvement of applying a reagent liquid having a viscosity of 20 to 35,000 centipoises, in an amount of 100% to 300% of the dry weight of the fabric, so that the reagent penetrates through at least 40% but less than of the thickness of the fabric, causing the reagent to bring about reaction only with the portion of the fabric which it contacts, and where necessary removing excess reagent and by-products. Care should be taken to avoid reagent penetration through the entire fabric thickness, although complete penetration in small areas though not preferred, would not be detrimental to the purpose of the invention. The process preferably also includes the steps of treating the fabric with a deswelling salt solution and drying, and also may include the step of mechanically working the fabric during or after drying to soften it and remove excess salt.

In the accompanying drawing, FIG. 1 shows a magnified cross-sectional view of one of the preferred products of this invention, made from a nonwoven fabric with entangled fibers. Modified, high-swelling fiber 1 and highdwelling fiber segments 2 are cross-hatched. Low-swelling fibers 3 and fiber segments 4 are left clear. The process of preparing the modified fabric is such that substantially all of the low-swelling fiber 3, and low-swelling fiber segments 4, are on one side of the center plane of the fabric, indicated by center line 5 of the drawing.

FIG. 2 shows a product of the invention made of a plain woven fabric. Again, the high-swelling fiber segments 6 are cross-hatched and the low-swelling fiber segments 7, are left clear. Substantially all of the low-swelling fiber segments are on one side of the center plane of the fabric, indicated by center line 8.

FIG. 3 is a diagram of a preferred process for the manufacture of the products shown in FIGS. 1 and 2 The original woven or nonwoven fabric 9, is passed between backing roller, 10, and etched print roller, 11, which revolves with its lower surface dipping into a viscous reagent liquid, 12, contained in trough, 13. Excess reagent is removed from the engraved print roller by scraper blade, 14. The fabric carrying the reagent liquid is next passed through chamber, 15, where it is treated with hot air, gaseous reagents or irradiation to bring about chemical modification of that portion of the fabric already contacted by the viscous reagent liquid from the print roller. The fabric is then passed under sprays, 16, which may neutralize excess reagents, and wash out impurities with water or salt solutions. The final spray, 17, is an aqueous salt spray which dewaters the swollen fibers so that they may be dried without sticking and harshenin-g. The liquids sprayed on the fabric are caught in pans, 18, from which they may be sent to the sewer or to recovery facilities for reuse. The deswollen fabric is now passed between squeeze rollers, 19, to remove as much liquid as possible before it is dried by passing over heated rollers, 20, and wound up on collecting roll 21. Before use, the fabric may be subjected to additional softening treatments such as mechanical working.

The process of this invention consists essentially of the conversion of a portion of a woven fabric or of a nonwoven fabric with entangled fibers, to a high-swelling, low-wet-strength form, while maintaining one surface of the fabric substantially unchanged. By woven fabric is meant any conventional over-and-under interlaced construction such as is made on a loom. Plain weaves in which no surface thread skips for long distances before returning to the other side of the fabric are especially suitable for the practice of this invention.

Especially suitable as starting materials for the process of this invention are nonwoven fabrics with entangled fibers. Nonwoven fabrics are products made from textile fibers without the use of conventional weaving or knitting operations.

The usual starting material for nonwoven fabrics is a basic web of staple-length fibers. The basic web has little or no integrity or strength and the alignment of the fibers with one another may vary from complete randomness to complete unidirectionality. Such webs are made by carding, air deposition or liquid deposition of the fibers. Webs suitable for use in the practice of this invention will have weights of about 0.4 to 5.0 oz./yd. (13.6 to 16915 g./m. and preferably from about 0.6 to 2.5 oz./ yd. (20.3 to 84.8 g./m. The fibers usually have an average length of from 0.5 to 2.5 inches (1.27 to 6.35 em.) but some processes may use fibers as short as 0.25 inch (0.635 cm.) or as long as 6 inches (15 cm.). Starting webs can also be made from continuous filaments by a direct lay-down process. The fibers will generally be of from 0.75 to denier per filament. The single webs can be combined to form a composite of different fiber alignment, different composition or different type, such as the combination of a continuous filament web and a staple fiber web.

To make a useful nonwoven fabric, the starting webs must be treated to provide restraining junctions or bonds for the individual fibers. A preferred method of providing the restraining junctions in the nonwoven fabrics to be used in this invention, is the use of fine, essentially columnar liquid streams at relatively high pressure, traversing the web which is supported on an apertured pattering member such as a wire screen. The method is described in detail in Luxembourg Patent 46,703.

By the use of these methods of entanglement, nonwoven fabrics may be given sufiicient integrity for all textile uses. If, however, it is desired to give the fibers a less firm degree of entanglement for reasons of economy, the entangled fibers may be further reinforced by adhesive bonding in isolated spots of various shapes and patterned dispositions such as described in US. Pats. 2,705,686 or 3,120,449. Generally, the distance between bonded areas must be at most slightly less than the average length of the fibers but must be greater than the average length of the low-swelling fiber segments to ensure dipersibility in water. The discrete area bonding of nonwoven fabrics may be accomplished by means of an added hinder or by means of self-bonding through the application of elevated temperature or activating liquids. The preparation of nonwoven webs and bonding of them is Well known in the art. The book Nonwoven Fabrics by F. M. Buresh, published by tReinhold Publishing Corporation, New York, N.Y. in 1962, provides a basic teaching and a large bibliography.

By nonwoven fabric with entangled fibers is meant a fabric in which the fibers pass up and down through the thickness of the fabric at regular or irregular intervals. Such structures will allow most or all of the fibers in the unmodified portion to pass, in one or more places, through the portion of the fabric made high-swelling by chemical modification. It is the modified high-swelling segments of the fibers which are most affected by the water in the flushing operation, and which break or slip apart allowing the fabric to disintegrate in the turbulent Water.

It should be understood that a few fibers in the unmodified portion of the fabric may remain unmodified and low-swelling over their entire (unsegmented) length without destroying the fiushability of the fabric. In nonwoven fabrics containing no bonding elements other than 4 entanglement, a minor portion, for example 10% or less, of fiber up to /2 in. long and of a different and less reactive composition than the fiber to be modified, may be used. For example, cotton or synthetic fibers such as nylon or polyester fibers may be added.

The major portion of the fibers, of which the fabrics are woven or otherwise made up, must be of such a composition as to allow chemical conversion to a high-swelling from, or if originally high-swelling, to a low-swelling form.

Although it is not essential to the operation of the process of the invention, it is desirable to bring about the chemical modification reaction as rapidly as possible after application of the reagent liquid in order to minimize further spread of the reagent through the fabric as by wicking. A particularly preferred system for accomplishing this is the rapid, high-temperature carboxymethylation of fabrics composed of rayon fibers or suitably degraded cotton fibers as set forth in detail in the examples. In this process, a solution containing sodium chloroacetate and sodium hydroxide is applied to one side of the fabric, and the reaction is brought to completion in a matter of minutes or even seconds by the application of heat or hot air.

Fabrics composed of either cotton or rayon fibers may be made water sensitive on one side by conversion to the hydroxyethyl ether. In this process, a thickened solution of sodium hydroxide preferably of 15 to 21% concentration is substituted for the etherification mixture used in the examples. The fabric carrying the alkali on one side is then treated in a chamber by a process such as is described in US. Patent 2,847,411, wherein gaseous ethylene oxide is passed through the fabric. The device is preferably arranged so that the ethylene oxide enters the fabric from the dry, untreated side, thus, discouraging the spread of the alkali to the untreated fiber segments. At the end of the reaction, the modified fabric is acidified in a deswelling solution such as 15% sodium sulfate solution containing 5% sulfuric acid. Excess solution may be squeezed out between rolls, and the fabric is neutralized in a buffered salt solution such as 17% sodium sulfate containing 3% disodium phosphate. The fabric is again squeezed free of excess liquid and dried with mechanical working as described for the carboxymethylated fabrics in the examples.

Cellulosic fabrics may be converted to a water-sensitive ester derivative on one side by treatment with the sulfamic acid-urea sulfating reagent described in US. Patent 2,511,229. The reagent, preferably thickened as described below, is applied to one side of the fabric by one of the methods illustrated in the examples. When the reaction has been completed by the method in the patent referred to, the dried fabric is washed with 18% sodium sulfate solution while supported on a moving wire screen. It is then converted to the sodium salt form in a buffered salt bath containing 17% sodium sulfate and 3% disodium phosphate. The fabric is finally squeezed free of excess liquid and dried with mechanical working as before.

Cellulosic fabrics which have been fully modified to one of the above ionic-derivative forms may be converted to the surface-modified forms of this invention by a variety of means. For example, the fully-modified carboxymethyl ether or half-succinate ester may be converted to the low-swelling free-acid form by treating with dilute sulfuric acid, washing with water and drying. One side of the fabric is then treated with a buffered salt solution to convert the fibers contacted to the high-swelling salt form.

Alternatively, a fully-modified ionic-form fabric may be converted to the high-swelling sodium salt form and dried. One surface of this fabric is then treated with a solution of a calcium or aluminum salt, thus, converting the fibers contacted to a low-swelling ion-cross-linked form. In this case, the penetration by the reagent should preferably be limited to about 50% of the fabric thickness.

Still another method is to convert the entire fully-modified ionic-form fabric to the low-swelling calcium salt form by treating the modified fabric with a 1% solution of calcium acetate, washing with water, and drying. One surface of the fabric is then treated with a solution of sodium hexametaphosphate sequestering agent (the Calgon of commerce). The fibers contacted by the reagent are converted to the high-swelling sodium-salt form.

An example of a noncellulose fiber useful in the practice of this invention is the partial half-succinate ester of polyvinyl alcohol (PVA). The PVA succinate may be made by the method described in US Patent 2,484,415. A useful improvement of this process is to use dimethyl sulfoxide as a solvent and precipitate the product by pouring the solution into acetone with stirring. The modified PVA is dissolved in dimethyl sulfoxide to form a 20% solution which is spun into yarn by extruding it through a spinneret into an evaporative atmosphere by methods well known in the art. The dried filaments are cut into staple fibers and converted into an entangled nonwoven fabric by the method given in the examples. The fibers are then cross-linked and insolubilized by soaking the fabric in a 1% solution of aluminum sulfate, rinsing in water, and drying. This fabric is then treated on one side with a solution containing 1% sodium hydroxide and sodium sulfate. The fabric, with the untreated side up, is then passed under a shower of 17% sodium sulfate solution until excess caustic is removed. Excess washing liquid is squeezed out between rollers, and the fabric is dried with mechanical working. Other chemical fiber compositions and chemical modification reactions will be apparent to those skilled in the art.

A thickening agent may be used in the reagent liquid to retard wicking and help control depth of penetration into the fabric. The thickener must be selected to be soluble or dispersible in the solvent used, and to be compatible with the other components of the mixture. It is desirable to use a low concentration of a high molecular weight polymeric compound to attain the viscosity needed.

When aqueous solutions are used, polymeric carbohydrates such as natural gums and pectic substances, as well as starch and water-soluble cellulose and starch derivatives may be used. In the preferred alkaline sodium chloroacetate carboxymethylating reagent, high-viscosity commercial sodium carboxymethyl cellulose has been found to be especially suitable as a thickening agent. An-

other especially suitable thickener for the carboxymethylating solution is Kelzan, a complex bacterial polysaccharide manufactured by the Kelco Co. of Chicago, Ill. Reagent solutions containing about 0.3 to 1.0% of this thickener have been found effective when used with the light weight nonwoven fabrics preferred for the practice of this invention. Such solutions have viscosities in the range of 50 0 to 50,000 centipoises. It is preferred to use solutions having viscosities of 100030,000 centipoises, but considerable variation in solution viscosity may be accommodated by proper adjustment of the method of application and speed of operation. At relatively high speeds, no added thickener at all is required.

The thickened reagent liquid is most easily applied to the fabric to be modified by means of an etched print-roller such as is used in the color printing of textiles. This device provides a means for applying an exactly predetermined amount of reagent liquid to the fabric so that the proper degree of penetration is obtained. The reagent liquid may also be applied from smooth-surfaced rolls such as are used for the distribution of ink in a printing press. The thickened reagent liquid may be applied through a silk screen of the type used in silk screen printing but with the opaque filling material removed over all of the useful surface. Other methods of application such as spraying or padding through a wire screen will be apparent to those skilled in the art.

By high-swelling fibers or high-swelling segments is meant fibers or fiber segments having an absorbency in distilled water of at least 8 grams/gram, by the test to be described. By low-swelling fibers or low-swelling segments is meant fibers or segments having an absorbency in distilled water of less than 5 grams/gram.

Preferably, the high-swelling segments should have an abso;bency of 10 to l5 g./g. in distilled water, or even higher, to ensure quick and easy flushability in the water of domestic water supplies, which may contain dissolved salts of calcium and the like. The high-swelling segments of the fabric of Example I are almost soluble in distilled water, but the fabric has adequate strength in use when wet with body fluids. The untreated fiber segments, on the other hand, should have as low an absorbency as possible to give a more desirable hand or feel when wet. Rayon fibers, for example, have an absorbency of about 3 g./ g. In composite structures, the low-absorbency side of the fabric should be used on the outside. This will result in a more pleasant feel when the fabric is wet, as well as tending to keep the skin of the wearer more dry, when used as a diaper for example.

In order to produce a functionally significant difference in the tactile and abrasion-resistant properties of the surfaces of any one fabric, the low-swelling and high-swelling fibers and fiber segments should differ in absorbency by at least 4 grams/gram.

The absorbency of the segments of a segmented fiber cannot be measured directly by the standard test, but is inferred to be the same as the absorbency of a mass of fibers which have received treatment over their whole length similar to that accorded the segment. The existence of high-swelling and low-swelling segments can easily be observed by direct microscopic examination of the fibers swollen in water. The segments may also be made visible in the dry fiber by differential dyeing techniques. The high-swelling segments in the fibers of the preferred prod uct made by carboxymethylation of rayon fabric, for example, are colored deep blue by a solution of methylene blue, whereas the low-swelling unmodified segments are only lightly tinted by the dye.

Although the absorbency of the high-swelling fiber segments or high-swelling fabric layers cannot be measured directly, the absorbency test can be applied to the composite finished fabric using the same procedure used for uniformly high-swelling or low-swelling fibers and fabrics. In the case of the layered fabrics, the apparent absorbency will be an average value for the proportions of high and low-swelling fibers or fiber segments present. The fiushable layered fabrics of this invention will always have at least 40% of high-swelling fibers and fiber segments with an absorbency of at least 8 grams/gram. The measured apparent absorbency of the composite fabric will be at least (3.2+0.6A) grams/gram where A is the absorbency of the fibers in the low-swelling portions of the fab ric. flushable layered fabrics based on the surface carboxymethylation of rayon, for example, will have a composite absorbency of at least 3.2+0.6 3:5 grams/gram. Preferred products will have a composite absorbency of 7 grams/gram or more as illustrated in the examples.

Following the process for chemical modification of the desired portion of the woven or nonwoven fabric, the fabric usually must be treated to remove unreacted materials and by-products. The water sensitivity of the modified fibers and fiber segments must be considered in selecting the purification process. Generally, a deswelling medium such as a strong salt solution, or an aqueous mixture containing a water miscible organic compound such as acetone or alcohol may be used to prevent damage during processing and hornification during drying.

Sodium sulfate is an efficient and economical source of the above mentioned salt solution. Other alkali metals or ammonium may serve as the cation of the salt in combination with sulfate, citrate, borate, phosphate and less preferably acetate as the anion. The salt solution should preferably be at least 0.3 molar.

In the treatment of the preferred product obtained by the partial carboxymethylation of rayon fabrics, the modified fibers may be temporarily rendered relatively insensitive to water by the application of a dilute solution of a strong acid such as H 50 The acid form of carboxymethyl cellulose so obtained may be safely washed free of impurities with water. The fibers are then converted back to their high swelling sodium salt form by the application of a salt solution containing a mild alkali, or preferably a buffered salt solution.

The buffering action is afforded by a mixture of a weak acid or a weak base and its salt. Suitable systems will be obvious to those skilled in the art and include the following to mention a few: potassium acid phthalate-dipotassium phthalate (pH 5.0 to 6.2), sodium dihydrogenphosphate-disodium hydrogenphosphate (pH 5.9-8.0), boric acid-borax (pH 6.8 to 9.0), disodium hydrogenphosphatecitric acid (pH 5 to 8), citric acid-sodium citrate, and sodium bicarbonate. Such systems are normally made by titrating one of the components with a strong base or acid to the desired pH level.

It is preferred in most cases that the modified fabric be treated with a large excess of an aqueous agent at some time following the modification treatment in order to remove by-products of the reaction and the thickening agent used to impart high viscosity to the reagent liquid, which may cause the dried fabric to be stiff or harsh or brittle. The final aqueous treatment of the fabric containing the high-swelling fibers must be made with a deswelling solution as described above.

The final washed product, preferably wet with a deswelling salt solution, is pressed to remove excess liquid and dried. It may be softened by mechanical working which also serves to remove excess salt.

When the high-swelling fibers and fiber segments of this invention are cellulose ethers, they should have a degree of substitution of at least 0.2 to about 0.8. When the etherified fibers and fiber segments are carboxymethylated rayon, they should have a degree of substitution of between 0.2 and 0.6 and preferably between about 0.25 and 0.4. These values of degree of substitution delineate materials that withstand the effects of body fluids while swelling in water with marked loss of strength. It will be understood that due to the diffusion of even the high viscosity etherifying reagent solution along the fibers there may be a gradient of decreasing degree of substitution as one moves from the side of the fabric on which the reagents were applied towards the unmodified side of the fabric.

The products of this invention are useful as diapers, covers for catamenial devices such as sanitary napkins and tampons, as single use undergarments, bandages and the like. They may be used alone or in combination with absorbing elements such as wood fluff, batts or nonwoven structures of highly hydrophilic fibers.

TESTING PROCEDURES Samples used for tensile tests, and fabric weight are conditioned at 70 F. (21 C.) and 65% relative humidity for at least 24 hours before testing under these conditions.

Tensile strengths and elongations are measured on 1.0 x 2 inch (2.54 x 5.08 cm.) samples at an elongation of 50% per minute on an Instron testing machine. The results are in pounds/inch (grams per centimeter) hereafter designated as lbs/in. (g./cm.).

Samples are soaked for 5 minutes in distilled water or other liquid at 21 C. and then clamped in the tester and broken in air to determine w t tensile strength in water. In determining wet tensile strength in synthetic urine, the soaking is done in synthetic urine.

Fabric weights are expressed in ounces/square yard 8 (grams per square meter), hereafter designated as oz./yd. (g./m. and are based on the weight of the air-dry fabric.

For the purposes of this invention and to evaluate the effects of body fluids on the fabrics a salt solution termed synthetic urine with a composition similar to human urine [10 g. NaCl, 24 g. urea, 0.6 g. MgSO and 0.7 g. calcium acetate monohydrate per 964.7 g. distilled water I is employed.

A test related to durability in use is termed work to break in synthetic urine. In this test, strips of fabric one inch (2.54 cm.) wide are first soaked 5 minutes in synthetic urine. Each soaked strip is placed between 100 x 100 mesh per inch (2.54 cm.) wire screens which are then placed between bleached sulfite blotters under a pressure of about 0.5 1b./in. (35.8 g./cm. for 5 minutes. The test strips are then removed and tested at once in the Instron tensile tester. The work to break is measured as the area under the stress-strain curve and is expressed in inch pounds per square inch (gram centimeters per square centimeter) hereafter designated as in lb./in. (g. cm./cm.

A solution termed synthetic hard water containing 0.4 g. of calcium acetate monohydrate and 0.175 g. of MgSO in 999.4 g. of distilled water is used in some tests.

The dispersibility is determined in a 250 ml. filter flask having an added side arm at the bottom of the conical wall and containing a magnetically rotated bar. The bar is 3.8 cm. long by 8 mm. in diameter, weighs 11.73 grams and is rotated at 500 revolutions per minute. A 3 x 3-inch (7.62 x 7.62 cm.) sample is folded in half and inserted under the surface of the Water (at the topside arm). Tap water at about 25 C. is added through the bottom tube at a rate of 0.70 liter/minute for a period of 2 minutes. The effluent liquid from the upper side arm is filtered and the residue dried to constant weight at 100 C. to give the weight of fibers dispersed. The contents of the filter flask are filtered after the test and dried to yield the weight of undispersed fibers. The percent dispersibility is equal to 100 times the weight of fibers dispersed divided by the total weight of fibers recovered. Conventional toilet tissues have a dispersibility of 7%.

The flushability of a sample is determined by dropping a 10 x 26-inch (25.4 x 66 cm.) sample that has been folded to 10 x 13 inches (25.4 x 33 cm.) into the bowl of a household toilet (Model F-2122 made by the American Radiator and Standard Sanitary Corporation of New York, N.Y.) and flushing. The discharge from the toilet is passed through a length of glass pipe 2.33 feet (71 cm.) long and of 10.8 cm. inside diameter containing an artificial obstruction. The obstruction is constructed of standard flattened expanded metal with 0.5 inch (1.27 cm.) wide diamond perforations, formed into a cylinder 1 foot (30.5 cm.) long and about 10.8 cm. in diameter and provided with 41 inside projections randomly distributed and made by making parallel pairs of cuts about 0.25 to 0.75 inch (0.63 to 1.9 cm.) long and about 0.3 inch (0.76 cm.) apart, and bending the cut sections to stand perpendicular to the Walls of the cylinder. One flushing gives a flow of 18 to 20 liters of water in 20 seconds. The toilet is flushed 3 times for each sample. The percentage of the sample that passes the hooks in the glass pipe is estimated and recorded after each flush. A sample is termed Flushable if at least passes by the hooks after 2 flushes. At least of a sample of the preferred products passes by the hooks after 2 flushes.

It has been observed that samples termed Flushable by the above test have a dispersibility of at least about 20% in the small-scale dispersion test. Preferred products have a dispersibility of at least 40%.

Bending length is 0.5 the length of a strip of sample that bends under its own weight to a 45 angle. It is determined on a l x 6-inch (2.54 x 15.2 cm.) sample on a Drape-Flex Stiffness Tester (made by Fabric Development Tests, Brooklyn 32, N.Y.). The test is performed according to ASTM Standard Method D1388-55T. Unless otherwise stated, the value measured in the cross direction of the fabric is given.

The liquid absorbency of a sample of fiber is determined by soaking a small sample in an excess of the liquid at 25 C. unless otherwise designated (1 g. in 3000 g. liquid). The sample is removed from the liquid and spread over a x 5 cm. area on a bleached sulfite blotter paper. The sample is placed between layers of blotter paper and loaded -with a 3 kilogram weight to give a pressure of 120 g./cm. Pressure is applied for five minutes after which the sample is removed and weighed, giving the wet weight. Then the sample is dried to constant weight using a Noble and Woods sheet dryer at 100 C. Absorbe-ncy equals the water absorbed (wet weight minus dry weight) divided by the dry weight. In the case of absorbency determinations in body fluids or synthetic urine, the dry weight must be corrected for solids dissolved in the liquid absorbed. All absorbencies are measured in distilled water unless otherwise noted.

In order to determine the depth of penetration of the modifying agent, it is desirable to use a differential staining technique on the final fabric. For polymers whose modified portion contains acidic groups, for example carboxymethyl cellulose, staining with methylene blue is preferred. The fabric is first converted to the free acid form by soaking it 5 minutes in 5% sulfuric acid, and washing it free of acid in distilled water. The fabric is then soaked for /2 hour in 0.1% methylene blue solution and rinsed in distilled water until the rinsings are colorless. (Tap water must NOT be used at any point in this procedure.) The modified fabric surface is dyed deep blue in this procedure. The unmodified surface is scarcely tinted by the dye. The dried fabric is imbedded in paraffin, and cross sections are cut and mounted on slides by methods well known in the art. (The use of polymeric imbedding media must be avoided because the organic liquid causes the stain to bleed to unmodified fiber segments). Under the microscope, the dark, modified fiber sections are easily distinguished from the light, unmodified fiber sections.

EXAMPLE I Rayon fibers of 1.56 inches (3.94 cm.) length and 1.5 d.p.f. are made into a batt of randomly oriented fibers by an air deposition process using a Rando-Webber machine (made by Curlator Corp. of East Rochester, N.Y.). The batt has a weight of 2.53 oz./yd. (85.8 g./m. The fibers are entangled and the batt given integrity by supporting it on a 16 x 16 mesh per inch (16 X 16 mesh per 2.54 cm.) wire screen having 19% open area and passing it twice at 3 feet (92 cm.) per minute under a row of columnar water streams. The streams are formed by water at 200 lbs./in. (14 kg./cm. on the first pass and 500 pounds per square inch (35 kg./ cm?) on the second pass, flowing through a row of orifices spaced 20/inch (20/2.54 cm.) and located about 2.5 cm. above the fibers. The orifices are conical and have a diameter of 7 mils (0.18 mm.). The dried structure has an averaged tensile strength of 7.5 lbs./in. (1340 g./cm.).

A thickened reagent solution is prepared containing 20% sodium chloroacetate, 4% NaOH and 0.4% Kelzan (thickener). The solution has a viscosity of 2050 centipoises. A piece of the nonwoven fabric is covered with a piece of very fine open-mesh Dacron polyester screen, of the type used in silk screen printing, from which the opaque filling material has been removed from the entire area of the screen. The thickened alkaline sodium chloroacetate solution is forced through the screen by means of a straight rubber blade until an amount of solution equal to about 280% of the dry weight of the fabric has been transferred to one side of the fabric.

The reagent liquid penetrates more than half way through the fabric but does not wet the other side. The reagent is then caused to react with the portion of the fabric which it has contacted by heating the fabric on a Noble and Woods hot plate at C. for 5 minutes. The fabric is next soaked for 2 minutes in an aqueous bath containing 5% H SO and 15% Na SO squeezed out, ,and neutralized in an aqueous bath containing 3% Na HPO and 17% Na SO adjusted to a pH of about 8.5. Excess liquid is squeezed out of the fabric which is dried and softened by tumbling in a house laundry drier at about 60 C. with a baseball 9.7 cm. in diameter.

When wet with water or synthetic urine, the unreacted side of the fabric has the feel of an unmodified fabric. When the acidified fabric is dyed with a hot 0.1% solution of methylene blue and rinsed out in distilled water, the unreacted side of the fabric is only lightly tinted, but the remainder of the fabric is dyed deep blue. Fibers removed from the fabric contain lightly-tinted segments and-deeply-dyed segments. Some of the fibers are dark blue over their entire length. The fabric has the following physical properties:

MD-l-CD Dry tensile strength 7.5 lbs/in. (1340 glam.)

Wet tensle Strength (MD) 0.053 lbs/in. 9.5 g./crn.)

(hard water) (MD) 0.204 lbs/in. (36.4 g./c1n.)

) 0.075 in. lbs/in? Depth of penetration by the modifying reagent was determined to be 54%, by counting the light and dark fibers in a cross section of the fabric stained with methylene blue. Fibers were pulled at random from both sides and various parts of the stained fabric. Because of the thoroughness of the entanglement and the fineness of the individual filaments, the fibers broke in lengths of about 10 to 15 mm. Eleven of the fibers were examined closely under a microscope whose eyepiece contained a calibrated reticule. Six of the fibers contained between 7 and 13 segments, each, of alternating modified and unmodified areas. The segments ranged in length from 0.05 to 2.40 mm. for modified areas and from 0.10 to 4.50 mm. for unmodified areas. Five fibers, ranging in length from 8 to 12.7 mm., were modified over their entire length. There were no totally unmodified fibers. The composite absorbency of the entire fabric in distilled water was 13.9 grams/gram.

To determine the absorbency and degree of substitution of the fiber segments in the modified portion of the fabric, an analogous composite fabric was made up of two layers of entangled rayon fabric in close contact. The two thicknesses had a total fabric weight of about 2.5 =oz./yd. (34 g./m. This composite was modified in exactly the same way as the original single fabric had been, with the use of 298% of the fabric weight in added reagent. After being heated, acidified, neutralized, and squeezed out, the two layers were separated and dried. The layer from the side to which the reagent had been applied had an average degree of substitution of 0.44 carboxymethyl groups per glucose unit of the cellulose. The fabric was almost completely soluble in distilled water and had an absorbency of 13.2 g./g. in ordinary tap water.

EXAMPLE II An entangled nonwoven fabric with a weight of 1.3 oz./yd. (44.1 g./m. was made from the rayon fibers of Example I, using a 20 x 20 mesh/inch (20 x 20 mesh/ 1 l 2.54 cm.) screen with 36% open area. The fabric was passed at 15 feet/min. (7.62 cm./sec.) under five rows of oscillating columnar streams of water issuing from 7 mil (0.18 mm.) dia. conical holes spaced 20 holes/inch (2O holes/2.54 cm.), and supplied with water at 200, 400, 700, 800 and 800 p.s.i. (14, 28, 49, 56 and 56 kg./cm. pressure respectively.

A thickened reagent solution containing 20% sodium chloroacetate, 4.28% NaOH and 0.4% Kelzan, and having a viscosity of 1000 centipoises, is prepared and applied using the method of Example I, until an amount of the solution equal to 260% of the dry weight of the fabric has been transferred to one side of the fabric. The partially wet fabric is baked, washed and dried as an Example I.

When wet with Water or synthetic urine, the unmodified side of the fabric has a substantially firmer and dryer hand than the modified side. When dyed with methylene blue, most of the unmodified side of the fabric is only lightly tinted. Fibers removed from the fabric contain lightly-tinted segments and deeply-dyed segments. Many of the fibers are dark blue over their entire length. The fabric has the following physical properties (MD only):

Dry tensile strength: 3.71lb./in. (663 g./cm.) Wet tensile strength (hard water): 0.033 lb./in.

(5.9 g./om.)

Wet tensile strength (synthetic urine): 0.103 lb./in.

(18.4 g./cm.)

Dispersibility: 20.2%

EXAMPLE III An entangled nonwoven rayon fabric having a weight of 0.9 oz./yd. (30.5 g./m. is prepared by a method similar to that used in Example II. A thickened reagent I liquid containing 20% sodium chloroacetate, 4.5% NaOH, and 0.6% Kelzan and having a viscosity of 2850 centipoises at 26 C. is applied to the fabric, moving at 8 feet/min. (0.41 cm./sec). The thickened liquid is applied by means of a printing roll etched over its entire surface with 80-100 lines per inch (80-100 lines/2.54 cm.) at a depth of 1-2 mils (0.025 to 0.050 mm.) In this manner an amount of reagent liquid equal to 153% of the fabric Weight is applied to one side of the fabric. The fabric is then passed continuously through a circulating hot air oven 2 feet (0.6 meter) long at a temperature of 160 C. after which the fabric is passed successively under a shower of a solution of H 50 and Na SO through a running-water Wash tank, squeze rolls, a neutralizing bath containing 17% Na SO and 3% Na HPO at pH 8.5, and a final set of squeeze rolls. The damp fabric is cut into pieces and dried with mechanical working as in Example I. The final fabric has the following physical properties:

M D X 1) Dry tensile strength: w

(Lbs/in) 2. 89 1. 87 516. 2 334. 0 0.055 0. 091 Hard water, g./cm 9. 82 16. 3 Wet tensile strength, 1 0. 11 0.011 Synthetic urine, g./cm 10. 16. 1 Work to break, in. lbs/in. 0. 05d 0. 1345 Synthetic urine, g. cur/cm. Dispersibility, percent. Bending length (en1.) Flushability, percnnt Depth, penetration of cross-section, percent. Composite absorbency (g./g.)

EXAMPLE IV El Paso combed cotton was processed on the Rando- Webber to a randomly-oriented batt having a nominal weight of 1 oz./yd. (33.9 g./m. The fibers are entangled and the batt given integrity by supporting it on a 24 x 24 mesh per inch (24 x 24 mesh per 2.54 cm.) wire screen with 16% open area and passing it four times at 20 feet (6.10 m.) per minute under a row of columnar 12 Water streams. The streams are formed by water at 200 lbs./in. (14.3 kg./cm. on the first pass and 400 lbs/in. (28.6 kg./cm. on the last 3 passes, flowing through a row of orifices spaced 40/inch (40/ 2.54 cm.) and located about 2.5 cm. above the fibers. The orifices are conical and have a diameter of 5 mils (0.127 mm.).

The entangled cotton fibers are dewaxed by heating the fabric for 1 hour at 90-100 C. in water containing 0.1% trisodium phosphate and 0.1% Tide, a commercial home laundry detergent, and the fabric is rinsed. The cotton cellulose is degraded by submerging it in 18.5% HCl at C. for 60 seconds and washing in cold water. The dried fabric may be treated with a thickened carboxymethylating reagent liquid containing 25% sodium chloroacetate, 10% sodium hydroxide and 0.6% commercial high-viscosity sodium CMC in essentially the same manner as is used in Example II. The final fabric will have substantially the same properties as the fabric of Example III, but will be somewhat less soft in the dry condition.

EXAMPLE V A batt of 1.56 inch (3.96 cm.), 1.5 denier per filament rayon staple fiber is hydraulically entangled to give a fabric with a weight of 0.93 oz./yd. A thickened reagent solution is prepared containing 20% sodium chloroacetate, 4.0% NaOH and 0.75% Kelzan. The solution has a viscosity of 30,800 centipoises at 18 C. The reagent solution is applied to one side of the fabric at a rate of 2 grams of liquid per gram of fabric using a printing roll etched over its entire working surface with to lines per inch (80 to 100 lines per 2.54 cm.) at a depth of 0.002 inch (0.050 mm.). The fabric is then processed essentially as in Example III.

The final dried fabric is dyed with methylene blue and is found to be substantially unmodified on one side. The unmodified side has the feel of a normal fabric when wet with water or synthetic urine. The modified fabric has the following physical properties:

An examination of 25 individual fibers pulled from the stained fabric at random parts of both sides was made, as described in Example I. Twenty-two of the fibers contained from 3 to 12 segments, each, of alternating modified and unmodified areas. The modified segments were 0.10 to 6.50 mm. long, and the unmodified segments ranged from 0.10 to 9.90 mm. Three fibers were modified over their entire length. There were no totally unmodified fibers.

What is claimed is:

1. The improvement in woven and nonwoven fabrics for use in contact with body fluids, of a fabric having adequate strength and durability for such use which is also dispersible in the flushing water of an ordinary toilet after use, wherein the improvement comprises a fabric consisting essentially of fibers which are high swelling in a watersensitive layer on one side of the center plane of the fabric and which are low swelling in a water-insensitive layer on the other side of the fabric, the absorbency in said water-sensitive layer being at least 8 grams of distilled water per gram of dry fiber and the absorbency in said water-insensitive layer being less than 5 grams per gram, said fabric being characterized by a strip tensile strength of at least 1.0 lb./inch when dry, of less than 0.1 1b./inch when wet with distilled water, and of greater than 0.05

13 lb./inch when soaked in synthetic urine, the fabric having a dispersibility of over 20% when tested for dispersibility in Water.

2. The fabric defined in claim 1 wherein said watersensitive layer constitutes between 40% and 95% of the fabric thickness.

3. The fabric defined in claim 1 wherein said watersensitive layer consists essentially of carboxymethylated rayon and said water-insensitive layer consists essentially of rayon.

4. The fabric defined in claim 1 which is a nonwoven fabric with entangled fibers providing restraining junctions for the individual fibers.

5. The fabric defined in claim 1 characterized by a bending length of less than 3.0 centimeters.

References Cited UNITED STATES PATENTS 3,083,118 3/1963 Bridgeford 8-128X 14 FOREIGN PATENTS 3,924,856 11/1964 Japan 8-120 3,923,814 10/1964 Japan 8-120 3,924,856 11/1964 Japan 8-120 OTHER REFERENCES Reinhardt, Robert M. Ferner, Terrence W., Pad-Bake Carboxymethylation of Cotton Textile Materials, I & EC Product Research and Development, vol. 4, pp. 82-86. June 1965.

ROBERT F. BURNETT, Primary Examiner L. M. CARLIN, Assistant Examiner US. Cl. X.R.