US2486805A - Diapers and like sheetlike materials - Google Patents

Description

Patented Nov. 1, 1949 DIAPERS AND LIKE SHEETLIKE MATERIALS Raymond B. Seymour and George M. Schroder, Chattanooga, Tenn., assignors to Henry H. Frede and Company, Chattanooga, Tom a corporation of Tennessee No Drawing. Application October 8, 1947, Serial No. 778,717

8 Claims. 1 This invention relates to diapersand sheets and more particularly to articles of this character which may be disposed of after a single use.

There is a considerable demand for disposable diapers because of the convenience of their use.

: As they are discarded after they have been used once, they completely eliminate the objectionable handling and washing of soiled diapers. They have the added advantage that it is generally unnecessary to have on hand as many disposable diapers as would be required of the customary cloth diapers which are reused.

Despite the acknowledged benefits of disposable diapers the ones now available have not had complete public acceptance because of certain undesirable properties. They have either been expensive or they have lacked the qualities requisite of a satisfactory diaper. If they have had desirable physical properties, they have been costly to manufacture and their consequent high selling price has limited their sales.

The disposable diapers which have been sold at an acceptable low price have not been satisfactory because they have not been sufficiently ab sorptive or have been so bulky or harsh in texture that their use has been avoided. They frequently have formed wrinkles and creases when folded about the infant and consequently lack the desired smoothness. Or, their surfaces have been of such a coarse or rough material that they have chafed the infants skin.

These objectionable properties of the prior disposable diapers have arisen because a satisfactory diaper presents a somewhat conflicting set of conditions. It is of course preferable that it be thin so that it will not be bulky, but this requires that it have exceptional absorption capacity. Also, if it is thin it must be highly absorptive on one side and be water repellent on its other side. In addition it must be strong even when wet and this is especially difficult toobtain in a thin diaper. The diaper of the present invention can be made at low cost. It is thin and therefore it is not bulky when applied to the infant; it is soft and therefore does not chafe when wrinkled and creased; Despite its thinness it has a satisfactory strength even when wet and has a high absorptive capacity. It is made water repellent on one side by a moisture resistant coating, but this does not detract from either the highly pliable character of the product or from its soft and smooth texture. I

Generally considered, the diaper of the invention consists of a base material which is a sheet of loose, unwoven fibers having a random distribution. To one side of this fibrous sheet is applied a coating which retains the surface fibers against movement but which readily absorbs and transmits moisture to the inner fibers. To the other side of the fibrous sheet is applied a coating which serves as a binder for the surface fibers. and also serves as a water proofing material.

The fibrous sheeting employed to carry out the invention is preferably that obtained by garnetting picked, woven, knitted or felted materials of virgin cotton or other cellulosic fibrous materials In this process, an especially designed machine of known type called a picker picks apart the woven, knitted or felted materials and these materials, virgin cotton, viscose rayon, or other cellulosic fibrous materials, are formed into a batting or felt of substantially uniform thickness of an especially designed machine of known type called a garnett. This fibrous sheet is economically produced, particularly if it is made from waste or rejected cellulosic or wool cloth. The cellulosic fibers may be either natural or synthetic.

The resulting sheet of fibrous material has the advantage over felt or batting produced by a carding process because its fibers are distributed in all directions in a random fashion. The fibrous sheet consequently has substantially no tensile strength in any direction, but what strength it does possess is nearly uniform in all directions due to the irregular disposition of the fibers. This would not be true of a carded felt as there the fibers are all lined up in the same direction.

To one side of this sheet of fibrous material is applied the material which is to form the coating which is to bind the surface fibers together and also transmit moisture to the interior of the felt. Although the sheet of irregularly arranged fibers is weak, it has sufiicient strength to be handled during application of this fiber binding material.

One suitable coating material for this purpose is applied as a dilute aqueous solution of a sodium salt of carboxy methyl cellulose and this may, for example, be a sodium salt of an ether formed by the reaction of alkali cellulose and monochloro acetic acid in such manner as to obtain a product having from 0.2 to 1.0 glycolate groups per anhydro glucose unit of cellulose at a pH of 3 to 8.5. One suitable product of this character is that having a molecular weight such that a 2% aqueous solution will have a viscosity of from 10 to 1,000 centipoises. It is preferable to employ a medium molecular weight of the cellulose ether i .l. A... l wwmnwwanah.

derivative, but a blendof high and low molecular weight products may be used.

A preferred dilution of the sodium salt of carboxy methyl cellulose for application to the fibrous sheet, is a 1% aqueous solution. Excelby bringing the fibrous sheet into contact with a rotating roller upon which the solution is continuously sprayed. A film of the solution is thereby formed upon the roller and this film is transferred to the fibrous sheet as the sheet continuously comes into contact with the rotating roller.

After a film of the aqueous solution of the cellulose derivative is applied to the fibrous sheet, heat is applied to remove the water of solution. This heat is preferably applied by advancing the coated sheet to a rotating roller maintained at a temperature of from 300 to 450 F. This heated roller also serves to drive the coating material into the surface of the fibrous sheet.

It is important to heat the coating film to a temperature of from 300 to 450 F. to obtain the full benefits of the use of this substance. By applying this moderately high heat the cellulose derivative becomes quite water insoluble but does not lose its capacity'to absorb moisture. It is not definitely known why this heat changes the water soluble compound to an essentially water insoluble compound but one explanation is that the carboxyl group on the carboxymethyl cellulose reacts with a free hydroxyl group in an adjacent carboxymethyl cellulose molecule to form a compound having an apparent high molecular weight. This result is not obtained if heat of only 250 F. is applied. 7

It is preferable that the cellulose derivative be applied in such quantity that it will be present in the range of from 0.1 to 0.4 pound per thousand square feet. This film thickness may be obtained by properly relating the quantity of coating material being delivered by the spray to the speed of travel of the fibrous sheet.

As a result of the application of this coating to one side of the fibrous sheet, the portions of the fibers at the surface are held against relative movement. The water absorbability of the fibers is not impaired as the water rapidly penetrates through the coating. Due to the formation of a substantially continuous film of the binding material, all, or nearly all of the surface fiber portions are interconnected both at their points of intersection and along their intervening sections. Also, as the binding material penetrates somewhat into the sheet, it binds together the fibers below the surface.

Although the solution of the sodium salt of carboxy methyl cellulose. which has been described, is a preferred coating material, the invention can be practiced by employing other materials which will form a coating which will bind. the surface fibers against relative movement and which will transmit moisture through the coating to the inner fibers of the sheet. One such material which can be employed is hydroxy ethyl cellulose.

This coatingmaterial is applied in much the same way as the sodium salt of carboxy methyl cellulose. In this application there must be sufficient hydroxyethyl groups present to permit the product to be soluble in aqueous alkali. Those cellulose derivatives having additional hydroxyethyl groups are also satisfactory. These materials are prepared by reacting aqueous solutions of alkali cellulose with ethylene oxide at temperatures ranging from 10 to 60 C. and both the alkali soluble and water soluble types are commercially available.

A preferred dilution o hydroxyethyl cellulose is a 2% aqueous solution but excellent results are obtained with aqueous solutions of 0.5 to 5%.

The method of application is essentially the same as that used in the previous example. However. it has been found advantageous to dry the fibrous sheet impregnated with hydroxyethyl cellulose at about 220 F. before subjecting it to the elethis material is essentially impervious to water.

A preferred proportion is to have the styrenemaleic anhydride constitute of the combined weight.

The hetero-polymer of styrene and maleic acid may be obtained, for example. in accordance with the disclosure of Patent 2,047,398 to Voss et al. and it should have a molecular weight such that a 0.2% aqueous solution will have a viscosity of from 0.5 to 50 centipoises. The ammonium salt of this polymer is used in making up the aqueous solution for application to the fibrous sheet. This aqueous solution also contains a solid polyethylene glycol and these solid polyethylene glycols may vary in average molecular weight from 1000 to 7000. These materials are very water-soluble and are highly hygroscopic.

It may be observed that to obtain the waterrepellent coating, some consideration should be given to the molecular weight of the solid polyethylene glycol. Thus, with the lower molecular weights, it is possible to obtain a water-repellent coating by use of larger proportions of solid polyethylene glycol than in the case when higher molecular weight polyethylene glycol is used.

Preferably, the solid polyethylene glycol and the styrene-maleic anhydride, in the above range of proportions, are used in an amount to make up a 1% aqueous solution. Excellent results are however obtained with an aqueous solution of from 0.5 to 4.0%. This aqueous solution may be applied in the same manner that the solution of the sodium carboxy methyl cellulose is applied to the other side of the fibrous sheet, as described above. This involves the use of an applying roller upon which the solution is sprayed, and a heated roller maintained at a temperature of from 250 to 450 F.

The heated roller not only serves to remove the water of solution, but also serves to drive oil the' ammonia from its salt of the styrene-maleic anhydride. As a result, a water repellent coating mo'nia is driven ofl. Since only two hydroxyl groups are present in molecules of the polyethylene glycol having molecular weights of 1000 to 7000, it is surprising that a soft flexible film which is essentially insoluble, results. v

This coating of solid polyethylene glycol and styrene-maleic acid, like the coating, for example, of sodium carboxy methyl cellulose 0n the other side of the fibrous sheet, is continuous or substantially continuous. As a consequence, all, or practically all of the fiber portions at the surfaces are retained in these coatings and thereby held against displacement. It is this structure, as distinct from a structure in which the binding material is localized at the intersections of the fibers, which accounts for the high strength of the present product. A strong interconnection exists between the fibers not only at their surface points of intersection but along their intervening portions at the surface of the sheet, aswell.

It is preferable that the mixture of the solid polyethylene glycol and the styrene-maleic anhydride be applied in such quantity that it will be present in the range of 0.25 to 2.0 pounds per thousand square feet. A film of corresponding thickness can be readily applied by adjusting the speed of rotation of the applying roller and the quantity delivered by the spray.

As has been noted, the coating of sodium carboxy methyl cellulose or other material having a like function on the one side of the fibrous sheet, is water absorptive and freely transmits it to the inner fibers, and this makes it possible to deposit this as a continuous film. The coating of the solid polyethylene glycol and styrenemalelc anhydride, is however water resistant and not only serves to bind the fibers but produces a water resistant barrier.

In its broader aspects, therefore, the invention involves a sheet of unwoven fibers having a random distribution, on one side of which is the interpolymer of solid polyethylene glyocol and styrene-maleic acid to produce a water-repellant coating, andon the other side of which is a coating which will bind together the surface fibers and transmit moisture to the interior fibers of the sheet. Because of the high strength of the water-repellent coating which has been described it is not absolutely essential that the coating on the other side impart a high strength to the sheet.

By using this coating of solid polyethylene glycol, and styrene-maleic acid interpolymer, a highly satisfactory water-proofing coating is formed. It performs a two-fold function as has been noted, thus making it unnecessary to add an additional water-proofing coating. The coating is flexible and will not crack when bent, it

is not tacky, and it presents a smooth surface which is not unpleasant. Moreover, it has no deleteriousefiect on the infants skin. It acts as a barrier to prevent the passage of absorbed water through thematerial but does not impair the absorbalbility of the fibrous sheet.

' Th resulting diaper not only possesses this considerable capacity to absorb moisture, but it retains considerable strength even after becoming wet. As a consequence, safety pins used to hold the diaper in place, will not pull through the material after it becomes wet. As has been stated. because the diaper is thin it can easily be folded in place and does not form objectionable creases and It is soft and flexible and is no more annoying to the infant than cloth diapers.

Although the invention has been described with particular reference to diapers, it is to be understood that the product of this invention may be applied to equivalent uses. Thus, the sheet material of the invention may be used in situations where its absorbent properties are desired, such as for bibs, table cloths, surgical sheets, and the like.

The invention may be further illustrated by the following examples:

Example 1.Rejected cotton cloth is picked apart in a picker and felted in a garnetting machine and the resulting felt having a weight of 1 to 2 ounces per running yard is sprayed on one side of the garnetted material with a 2% aqueous solution of sodium carboxy methyl cellulose. The other side is sprayed with a 2% aqueous solution made up of 0.6 pound of dissolved solid polyethylene glycol having an average molecular weight of 1540, and 1.4 pounds of the ammonium salt of styrene-maleic acid in 98 pounds of water. The treated material is passedthrough drum rollers to dry the coatings. The roll drying the water absorptive carboxy methyl cellulose film has a temperature of 400 to 420 F., while the other roll used to remove the water from the polyethylene glycol styrene-maleic anhydride has a temperature of 400 to 450 F. The resulting sheet is cut to a trapezoidal shape.

Example 2.Discarded viscose rayon and cotton cloth are picked apart simultaneously on pickers, the materials are conveyed to difierent garnetting machines and the products from these materials are conveyed to a common apron so that the long, staple, soft rayon forms one surface of the garnetted sheet. This sheet is coated as in Example 1, the water-proofing coating being applied to the cotton side.

Example 3.--Virgin cotton is used instead of picked and garnetted cloth as in Example 1.

Example 4.-To garnetted cotton fiber in mat form is applied on one side a 2% aqueous solution of hydroxyethyl cellulose and on the other side is applied a 2% aqueous solution of solid polyethylene glycol having an average molecular weight of 4000 and an ammonium salt of styrene maleic acid using a ratio of 67.5 to 22.5.

The impregnated batting is dried at 210 to 230 F. and then passed through rolls at 375 to 450 F. The product is cut and placed in packages.

Diapers made in accordance with this invention possess excellent properties as shown by the following tests:

A piece of felt 1" in cross section and processed according to Example l,was placed between clamps and weights were added and the length of time i for break was determined, the distance between the clamps being 2". The untreated felt broke immediately when a 20 gram weight was added. The treated product was not broken in 10 seconds after the addition of a 1500 gram weight. The sample was immersed in water and the test was repeated. Under these conditions the sample did not break in 10 seconds after the addition of the 1500 gram weight. The tests were repeated using strips cut at right angles to the previously described test pieces, and under these conditions similar results were obtained.

A piece of bonded cotton felt, measuring 3" x 4" and weighing 1 gram, was immersed in water for 10 seconds, placed on blotting paper for 5 seconds and reweighed. The total weight after this procedure was 11 grams, indicating that the material had absorbed times its own weight of water. This test was repeated using a piece or absorbent woven cloth weighing 1 gram and the woven material gained 4 grams'in weight due to the absorption of water.

A section of the diaper type material was clamped to a glass cylinder in which was placed 50 ml. water, the column of water being 6 centimeters above the coated cloth. At the end oi} ten minutes no water had passed through the material.

What is claimed is:

l. A diaper having one side water-repellant comprising a sheet of unwoven fibers having a random distribution, a substantially continuous moisture transmitting coating on one side thereof of sodium carboxy methyl cellulose having a thickness corresponding to from 0.1 to 0.4 pound per thousand square feet and which has been rendered essentially water-insoluble by heat treatment to a temperature of from 300 to 450 F., and on the other side of the fibrous sheet, a water-repellent coating of a water insolubilized composition consisting f 25 to 40 parts of a solid polyethylene glycol having an average molecular weight of 1000 to 7000 and 60 to 75 parts of a styrene-maleic anhydride interpolymer, the latter coating having been subjected to a temperature of from 250 to 450 F. l

2. A diaper having one side water-repellent comprising a sheet of unwoven fibers having a random distribution, a substantially continuous moisture transmitting coating on one side thereof of sodium carboxy methyl cellulose which has been rendered essentially water-insoluble by heat treatment to a temperature 01 from 300 to 450 F., and on the other side of the fibrous sheet, a water-repellent coating of a water insolubilized composition consisting of 25 to 40 parts of a solid polyethylene glycol having an average molecular weight of 1000 to 7000 and to 75 parts of a styrene-maleic anhydride interpolymer, the latter coating having been subjected to a temperature of from 250 to 450 F. and having a thickness corresponding to from 0.25 to 2.0 pounds per thousand square feet.

3. A diaper having one side water-repellan comprising a sheet of unwoven fibers having a random distribution, a substantially continuous moisture-transmitting coating on one side thereof of sodium carboxy methyl cellulose which has been subjected to a temperature of from 300 to 450 F., and on the other side of the fibrous sheet, a water-repellent coating of a composition consisting of 25 to 40 parts of a solid polyethylene glycol having an average molecular weight of 1000 to 7000 and 60 to '75 parts of a styrenemaleic anhydrlde interpolymer, said composition having been subjected to a temperature of from 250 to 450 F.

4. A diaper having one side water-repellant comprisin a sheet of unwoven fibers having a random distribution, a substantially continuous moisture transmitting coating on one side thereof of sodium carboxy methyl cellulose which has been subjected to a temperature of from 300 to 450 F., said coating having a thickness corresponding to from 0.1 to 0.4 pound per thousand square feet, and on the other side of the fibrous sheet, a water-repellant coating of a composition consisting of 25 to 40 parts of a solid polyethylene glycol having an average molecular weight of 1000 to 7000 and 60 to 75 parts of a styrenemalelc anhydrlde interpolymer, said composition having been subjected to a temperature of from 250 to 450 F., the latter coating having a thickness corresponding to from .25 to 2.0 pounds per thousand square feet.

5. A diaper having one side water-repellent comprising a sheet of unwoven fibers having a random distribution, a substantiall continuous moisture transmitting coating on one side thereof of sodium carboxy methyl cellulose having a medium molecular weight and which has been subjected to a temperature of from 300 to 450 F., and on the other side of the fibrous sheet, a water-repellant coating of a composition consisting of 25 to 40 parts of a solid polyethylen glycol having an average molecular weight of from 1,000 to 7,000, and 60 to '75 parts of a styrene-maleic anhydride interpolymer having a molecular weight such that a 0.2% aqueous solution will have a viscosity of from 0.5 to 50 centipolses, the latter coating having been subjected to a temperature of from 250 to 450 F. to render it substantf ally water insoluble.

6. The process of making a diaper having one side water-repellant which comprises applying to one side ofa sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of sodium carboxy methyl cellulose, applyin heat to said coating on the order of 300 to 450 F. whereby a moisture transmitting coating is obtained, applying to the other side of the sheet a substantially continuous coating of a 0.5 to 4.0% aqueous. solution of 25 to 40 parts of a solid polyethylene glycol having an average molecular weight of 1000 to 7000 and .60 to parts of an ammonium salt of styrene-maleic anhydride interpolymer, and applying heat to the latter coating on the order of 250 to 450 F, to expel the water of solution and convert the coating to an essentially water insoluble and water-repellant product.

I. The process of making a diaper having one side water-repellent which comprises applying to one side of a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of sodium carboxy methyl cellulose, applying heat to said coating on the order of 300 to 450 F. whereby a moisture transmitting coating is obtained, applying to the other side of the sheet a substantially continuous coating of a 0.5 to 4.0% aqueous solution of 25 to 40 parts of solid polyethylene glycol having an average molecular weight of 1000 to 7000 and 60 to '75 parts of an ammonium salt of styrene-maleic anhydride interpolymer, and applying heat to the latter coating on the order of 300 to 450 F. to expel the water of solution and convert the coating to an essentially water insoluble and water-repellant product, the solution of sodium carboxy methyl cellulose being applied to yield a driedcoating in the range of from 0.1 to 0.4 pounds per thousand square feet.

8. The process of making adiaper having one side water-repellent which comprises applying to one side of a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of sodium carboxy methyl cellulose, applying heat to said coating on the order of 300 to 450 F. whereby a moisture transmitting coating is obtained, applying to the other side of the sheet a substantially continuous coating of a 0.5 to 4.0% aqueous solution of 25 to 40 parts of a solid poly- 75 ethylene glycol having an averag molecular weight of 1000 to 7000 and 60 to 75 parts of an ammonium salt 0! styrene-maleic anhydride interpolymer, and applying heat to the latter coating on the order of 250 to 450 F. to expel the water of solution and convert the coating to an essentially water insoluble and water-repellent product, the solution containing said interpoly mer being applied to yield a. dried coating in the range of from 0.25 to 2.0 pounds per thousand square feet.

RAYMOND B. SEYMOUR. GEORGE M. SCHRODER.

10 nmmces ormn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Loomis Sept. 26, 1933 Leguillon Dec. 3, 1935 Stoops July 20. 1943 Schwartz Sept. 28, 1943 Wallach Feb. 18, 1947