US3284233A - Bonded nonwoven fabrics and binders for the manufacture thereof - Google Patents

Description

United States Patent Ofiice 3,284,233 Patented Nov. 8, 1966 3,284,233 BONDED NDNWGVEN FABRlCfi AND BINDERS FOR THE MANUFACTURE THEREOF Fred H. Sexsmith, Passaic, Ni, assignor to Johnson &

Johnson, a corporation of New Jersey No Drawing. Filed Mar. 4, 1965, Ser. No. 437,257 15 Claims. (Cl. 11714tl) This application is a continuation-in-part of my copendin-g application Serial No. 28,867, filed May 13, 1960, now abandoned.

The present invention relates to bonded nonwoven fabrics, to methods of making such bonded nonwoven fabrics, and to binders for use in such bonding methods. More particularly, the present invention relates to bonded nonwoven fabrics comprising cellulosic fibers and to binders of cellulosic origin for use in bonding such cellulosic fibers.

Bonded nonwoven fabrics are generally produced by forming a base fibrous layer or web of loosely assembled, overlapping and intersecting fibers, and depositing an adhesive bonding material thereon to bond the base fibrous web into an integral, self-sustaining nonwoven fabric. Such fabrics exhibit various interdependent and inversely proportionate levels of physical strength and softness and it has always been a primary purpose of the industry to provide a nonwoven fabric which combines good physical strength and softness.

Among the adhesive bonding materials employed in the nonwoven fabric industry are the water insoluble and alkali soluble binders of cellulose derivatives such as hydr-oxyethyl cellulose, carboxymethyl cellulose, and regenerated cellulose or viscose. The use of such cellulose derivative binder materials is particularly applicable for bonding nonwoven fabrics containing cellulosic fibers because of the chemical affinity between the cellulosic binder and the cellulosic fiber. They are also desirable because of their insensitivty to water in the regenerated state.

Polyolefins have many desirable properties known to the art and these properties could enhance the properties of an alkali soluble, water insoluble cellulose binder if a means of bringing the two together in a bonding solution could be developed. This has not been possible in the past because of the non-existence of one known solvent for both of these constituents.

This has been overcome by the instant invention which provides a colloidal dispersion of polyolefin particles in an alkaline solution having dispersed therein a member selected from the group consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xantha-te, said dispersion being adapted to be app-lied to fibrous webs, to bind the individualized fibers of said web, the bonded nonwoven fabric which results therefrom having increased softness, flexibility, drapeability and pliability, reduced stiffness, along with increased elongation to break.

The particular colloidal polyolefin which is selected to be incorporated in the cellulose solution may be selected from a broad group of such polyolefin materials. Representative examples of such a group are polyethylene, commonly identified by the chemical formula {-CH CH H- polypropylene, comm-only identified by the chemical for mula {CH CI-HCH H poly-l-butene, commonly identified by the chemical formula CH CH(C H poly-2- butene, commonly identified by the chemical formula {CH(CH )CH(CH and p olyisobutylene, commonly identified by the chemical formula -ECH O(CH It is to be noted that the polyolefinic materials used in applying the principles of the present invention are actually saturated chemical compounds and do not contain any canbon-to-carbon double bonds, even though they have been polymerized from monomeric materials such as ethylene (high and low density), propylene, l-butene,

2-butene, isobutylene,.etc., which are unsaturated and contain carbon-t-o-canbon double bonds. Such saturation and absence of carbon-to-carbon double bonds in the polyolefinic materials creates excellent stability and chemical inertness and avoids the main causes of discoloration, and resinification on ageing. There is no necessity to stabilize these polyolefins against oxidation, such .as there is in the case of rubber which requires a vulcanization treatment, and, consequently, the development of objectionable odors is avoided. Additionally, the polyolefins are nontoxic and innocuous. In this way, the use of the-polyolefins in the present invention renders the finalproducts particularly attractive for surgical, medical and sanitary purposes.

The polyolefins are available commercially in aqueous emulsion form and may be used as such or, if available initially as a finely divided powder, may be dispersed in aqueous media with traces of a wetting agent to furnish stable emulsions of desired solids content.

The average particle size of the colloidal polyolefinic particles must fall within a predetermined particle size range in order that the purposes of the present invention be realized. It has been established that particles having an average diameter of less than about microns are suitable. More finely divided microdispersions, having an average particle diameter on the order of less than about 1 micron, have been found particularly useful where such finer size is more suitable for the particular fabric being treated. The lower limit of the particle size of the polyolefinic particles will depend upon the particular purpose in mind. Within the more commercial aspects of the present invention, an average particle size of down to about 0.1 micron has been found satisfactory. One specific commercially available polyisobutylene colloidal dispersion having an average particle size of about 0.5 micron and an average size distribution within the range of from about 0.05 to about 1 micron has beenfound very satisfactory. Even finer particle size ranges may be employed when desired or required, depending upon the particular circumstances involved.

The term cellulose derivatives as used herein .is restricted to those cellulose derivatives which. are soluble in alkaline solutions and most solvents for cellulose, yet insoluble in water and almost all of the other organic solvents. These cellulose derivatives include hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xanthate.

While cellulose itself is virtually insoluble in all solvents, the solubility of its derivatives is dependent upon both the kind and degree of substitution or addition effected with respect to the OH groups present in the cellulose monomer. This is true with respect to hydroxyethyl cellulose and canboxymethyl cellulose as is readily appreciated by those skilled in the art of cellulose chemistry. Thus the solubility of hydroxyethyl cellulose or canboxymethyl cellulose in an. alkaline solution is dependent upon the degree of substitution or the extent to which all three OH groups of the cellulose monomer, i.e.

are reacted. This is also true as to their insolubilityin Water.

Carboxymethyl cellulose is available commercially in the form of the sodium salt which is certainly applicable here.

Viscose as used herein is meant to define the cellulose xanthate or, more particularly, the sodium xanthate which is formed in the process where cellulose is treated with caustic soda and a soda cellulose is formed which is shredded, aged under controlled temperature and humidity to break down the original high chain polymer and treated with carbon disulfide followed by an aqueous solution of sodium hydroxide. The resultant viscoussolution is known as viscose, or chemically as sodium xanthate which is soluble in aqueous alkaline solutions. Sodium xanthate can be dissolved in water but this is due to the presence of the sodium which provides the alkaline medium. Regeneration of cellulose from this viscous solution is well understood by the art.

The colloidal polyolefin dispersion may be incorporated into the alkali solution containing the alkali soluble, water insoluble cellulose derivative by any desired means, such as a simple addition accompanied by stirring. Complete compatibility has been established for substantially all proportions of the two, with no signs of polyolefin coagulation. The polyolefin particles are in the dispersed phase, whereas the cellulose derivative is dissolved in the continuous phase. There is no reaction between the cellulose derivative and the polyolefin.

The colloidal polyolefin-cellulose derivative solution may be applied to the fibrous web as an over-all impregnant, such as by dipping, spraying or immersing processes, or it may be applied by intermittent binder printing or other predetermined or random binder deposition techniques. If the solution is applied by printing techniques in the form of discrete binder areas, such areas may be in the form of continuous or discontinuous straight or wavy lines, circles, annuli, rectangles, squares, diamonds, triangles, ellipses, ovals, or like rectilinear or curvilinear figures or other similar regular or irregular figures.

Subsequent to the application of such solution to the fibrous web, the dissolved cellulose derivative is insolubilized or coagulated and regenerated to the water insoluble cellulose derivative form preferred as a binder material.

The final binder constitutes a composite of the additive properties of the alkali soluble cellulose derivative and the particular polyolefin used. Increasing the amount of the polyolefin in the binder of this invention will enhance the softness and flexibility contributed by the binder to the final product. With a major proportion of polyolefin and a very minor amount of cellulose derivative, the latter would tend to enhance the film-forming propensity of the mixture and, because of its high efficiency, contribute to the strength without deleteriously affecting the softness of the polyolefin.

The regenerated cellulose in the final product, or rather in the binding composition of this invention on the nonwoven fabric as a binder, contributes its water insensitivity, the fact that it print bonds with very little binder migration, the fact that the human body is not sensitive to cellulose, and the fact that it is an extremely efficient binder for nonwovens, i.e. low solids add-on is required to develop adequate strengths. The undesirable property of harshness which is characteristic of cellulose is modified by the polyolefin which contributes softness, but also its water insensitivity and its inertness to the human body. In combination then, the better qualities of both are obtained, i.e. a softening of the viscose by the rubber, or, at the other extreme, an improvement in the rubber strength by the viscose. In addition, the addition of the polyolefin is a means of obtaining controlled restriction of fluid spread on the surface of a fabric bonded with the composition of this invention.

Restricting fluid spread is of obviously great importance in sanitary napkins and surgical bandages and sponges where the fluid should contact the fabric, go through it and become absorbed by the absorbent media provided, rather than spread along the surface of the fabric.

The amount of binder material (dry solids basis) to be applied to the fibrous starting layer or web may range from as little as about 1% to about 100% or more by weight of the starting web (dry basis) and preferably from about 10% to about by weight. The surface area of the web covered by the binder will naturally be about 100% in the case of the over-all impregnated type. In the case of the intermittent pattern variety, the surface area of the web covered by the binder may be between about 7% to about of the total area of the web. However, in general, it is preferred that the binder-containing areas cover at least about 12% and not more than about 30% of the total surface area of the fabric.

The proportions by weight (dry basis) of the cellulosic binder material and the colloidal polyolefin in the bonded nonwoven fabric may be varied within relatively wide limits. From about 5 parts to about 95 parts by weight of the cellulosic binder material may be employed with from about 95 parts to about 5 parts by weight of the polyolefin. Within the more commercial aspects of the present invention, it has been found preferable to use from about 25 parts to about 75 parts by weight of the cellulosic binder material and from about 75 parts to about 25 parts by weight of the polyolefin. It is to be noted that these proportions are those existing in the dry bonded nonwoven fabric and that care must be exercised in the initial blending or combining of the cellulose solution and the colloidal polyolefin inasmuch as they are normally commercially available in solutions of widely varying solids content. For example, a viscose solution normally contains only between 6 and 7% by weight of cellulose whereas a microdispersion of polyisobutylene, which may contain up to or more by weight solids content.

The layer of overlapping and intersecting fibers, i.e. individualized fibers, which is processed to form the bonded nonwoven fabric of the present invention may be formed by any one of a number of conventional techniques for depositing, arranging, or rearranging fibers in a web. These techniques include carding, garnetting, airlaying, papermaking methods and the like. Individual webs or thin layers formed by one or more of these techniques may be laminated to provide a thicker layer for conversion into a fabric. In general, the individual fibers extend in a plurality of diverse directions in general alignment with the major plane of the fabric, overlapping, intersecting and supporting one another to form an open porous fibrous structure. The degree of fiber orientation in any particular direction will depend primarily. upon the method of formation of the web. Webs formed by. airlaying techniques normally have very little orientation in any particular direction and are basically isotropic. On the other hand, webs formed by carding and garnetting techniques are more or less predominantly oriented in the long direction of the web. Each type of web has its own properties and characteristics and each is useful for particular purposes. Reference is made to US. Patents 2,862,251; 2,705,687; 2,705,688; and 2,676,363 which disclose typical methods and apparatus for making such fibrous webs.

The fibrous web may contain natural or synthetic, vegetable, animal or mineral fibers such as cotton, silk, wool, vicuna, mohair, alpaca, flax, ramie, jute, etc.; synthetic or man-made fibers such as the cellulosic fibers, notably cuprammonium, viscose or regenerated cellulose fibers; cross-linked cellulosic fibers such as Corval and Topel; cellulose ester fibers such as cellulose acetate (Celanese) and cellulose tri-acetate (Arnel); the saponified cellulose ester fibers such as Fortisan and Fortisan-36; the polyamide fibers such as nylon 420, nylon 6 (polycaprolactam), nylon 66 (hexamethylene diamine-adipic acid), nylon 610 (hexamethylene diaminesebacic acid), nylon 11 (ll-amino undecanoic acid Rilsan); protein fibers such as Vica-ra; halogenated hydrocarbon fibers such as Teflon ('polytetrafluoroethylene); hydrocarbon polyolefin fibers such as polyethylone and polypropylene; polyester fibers such as Kodel and Dacron, vinyl fibers such as Vinyon and Saran;

tail by the following specificexamples.

acrylic fibers such as Orlon, Acrilan, Creslan, etc.; modacrylic fibers such as Dynel and Vcrel; mineral fibers such as glass, metal, etc.

The lengths of the individualized fibers in the starting fibrous web may vary from about /8 inch or /2 inch up to about 2 /2 inches or more in length, depending upon the particular properties and characteristics required or desired in the resulting fibrous web. If desired, the fibrous layer may have added thereto, by a subsequent processing step, if necessary, from about 1 or 2% by weight up to about 100% by weight of fibers other than those of textile length. In special cases, all of the textile length fibers may be replaced by fibers other than of textile length. These other fibers may be of papermaking length, which extend from about 78 inch in length down to about of an inch or less in length, which shorter fibers normally are not used in conventional methods of producing fibrous webs.

Illustrative of these short papermaking fibers are the natural cellulosic fibers such as woodpulp and wood fibers, cotton linters, cotton hull shavings fibers, mineral fibers such as asbestos, glass, rock wool, et-c., or any of the herein-before-mentioned natural or synthetic fibers in lengths less than about inch and down to about of an inch or less.

The denier of the individual synthetic fibers referred to above is preferably in the range of the approximate thickness of the natural fibers mentioned and consequently deniers in the range of from about 1 to about 5 are preferred. Where greater opacity or greater covering power is desired, special fiber deniers of down to about A. or even about Mr may be employed. Where desired, deniers of up to about 8, 10, 15, or higher may be used. The minimum and maximum denier are naturally dictated by the desires or requirements for producing a particular fibrous Web, by the machines and methods for producing the same, and so forth.

The weight of the fibrous web of starting material may 'be varied within relatively wide limits above a predetermined minimum value, depending upon the requirements of the intermediate or the final products. A single, thin web of fibers, such as produced by a card, may have a weight of from about to about 250 or more grains per square yard and may be used in the application of the principles of the present invention. Within the more commercial aspects of the present invention, however, web weights of from about 90 grains per square yard to about 800 grains per square yard .are contemplated. If heavier web weights are desired, such as up to 2000 grains, for example, several of the individual webs may be combined into a laminated structure to obtain the desired weight. The product of one card may be folded,

doubled, tripled, etc., on itself to reach the heavier weight,

or a plurality of cards may be used and the individual .products stacked or laminated'for a similar purpose.

The invention will be further illustrated in greater de- It should be understood, however, that although these examples may features of the invention, they are givenprimarily for purposes of illustration and the invention in its broader aspects is not to be construed as limited thereto.

Example I The starting fibrous material is a card web Weighing about 400 grains per square yard and containing 1 /2 denier, 1%; inches staple length viscose rayon fibers (regenerated cellulose). The improvement in softness, flexibility and dimensional stability is determined as follows: Test samples of the cardweb measuring approximately 18 inches long (45.72 cms.) and. 8 inches wide (20.32 cms.) are selected and are lightly prebonded with polyvinyl alcohol binder.

The viscose (sodium cellulose xanthate) used to treat describe in particular detail some of the more specific the card web test samples is a standard 7% caustic, 7% cellulose solution. The polyolefin added to the viscose is polyisobutylene used as an elastomer emulsion, 55% solids, average particle size about 0.5 micron, particle size distribution from about 0.05 micron diameter (minimum) to about 1 micron diameter (maximum). The elastomer emulsion has a specific gravity of about 0.96, a weight per gallon of about 8.1 pounds, and a pH of 5-6.

Eight different binder formulations having varying proportions of viscose and polyisobutylene are prepared as follows:

Polyiso- Polyiso- 'lotal Sample No. Viscose butylene butylene Binder (Grams) (Grams) (Percent (Percent Solids) Solids) 200 0 0 7. 0 175 25 42 10. 7 150 50 G4 14. 4 125 75 7G 18. 1 100 84 21. 8 75 90 25. 4 50 94 29. O 25 97 32. 9

These viscose-polyisobutylene binder formulations all mixed well and are smooth and creamy. They are applied substantially uniformly to the oriented card web test samples to about 300% wet pick-up by weight by hand mangling procedures. Standard acid coagulation andregeneration techniques are used to coagulate and regenerate the viscose, followed by prolonged washing in water and subsequent air drying. The processing takes place with the card web test samples in a relatively relaxed condition. The physical evaluations of the resulting products are as follows:

Final Tear Sample No. Dry Weight Gurley Final Strength (Grains/ Stiffness Width (Long) Yard The Gurley Stifiness Tester is described on page 43 in The Paper Trade Journal, December 20, 1934; its readings as well as the tear strength readings are relative and show trends or improvements over the control sample (No. 1) which does not contain polyisobutylene. improvement in softness and flexibility is shown by the steady decrease in Gurley Stiffness readings as the percent of polyisobutylene in the binder formulation increases. The increase in dimensional stability is noted in the decrease of shrinkage in width of the test samples as the percent of polyisobutylene in the binder formulation increases. Theincrease in dry tear strength is also to be noted. The reduced stiffness, the increased softness and flexibility, and the reduced shrinkage without any apparent serious loss of wet strength, dry strength or color stability make the bonded nonwoven fabrics suitable for use as a wiping cloth.

Example II The starting fibrous material is a 600 grain per square yard card web containing 100% bright viscose rayon fibers (regenerated cellulose) having a denier of 1 /2 and a staple length of 1% inches.

Four different binder systems are used to bond the card webs: (1) 100% standard viscose solution containing 7% caustic, 7% cellulose, diluted with one part of 6% caustic solution for three parts of viscose solution; (2) a viscose-polyisobutylene emulsion in which the polyiso- The The physical evaluations of the resulting products are as follows:

Final Dry Cross Percent Percent Weight Elongation Gurley Sample Cellulose Polyethyl- (Grains/ Stiffness Solids one Solids Yard Dry Wet The reduced stiffness, the increased softness and drapeterms of material transfer and low wet migration. The fabricidentrficatrons and evaluations follow: ability and the increased cross elongation without any Final Percent Elongation Sample Binder Fabric Dry Weight Gurley (Grains/ Stiffness Yard Long Cross 640 22 7 28 664 is 0 49 696 6 10 59 712 12 83 696 18 9 25 70s 11 9 28 723 5 12 25 672 11 70 712 9 10 74 688 s 11 53 608 6 12 59 695' 6 14 91 640 5 9 36 696 5 11 37 582 4' 12 as 576 4 12 44 The improvement in softness and flexibility is shown by the relatively constant decrease in Gurley Stiffness readings, as the percent of polyisobutylene in the binder formulation increases. Gurley Stiffness readings at low levels are not completely reliable or reproducible and are omitted from the above table. The increase in the percent elongation to break in the long and cross direction is also to be noted. The reduced stiffness, increased softness and flexibility and increased elongation to break without any apparent serious loss of wet strength, dry strength or stability color make the bonded nonwoven fabrics suitable for use as a hospital wash cloth.

As used herein, the term Masslinn nonwoven fabric (occasionally identified by the letter M) is intended to cover bonded nonwoven fabrics such as disclosed in US. Patents 2,705,6862,705,688, issued April 5, 1955. The term Keybak bundled fabric (occasionally identified by the letter K) is intended to cover nonwoven fabrics disclosed in US. Patents 2,862,251, 3,081,514 and 3,081,515.

Example III The starting fibrous material is a 600 grain per square yard Keybak bundled fabric containing 100% viscose rayon fibers (regenerated cellulose) having a denier of 1 /2 and a staple length of 1% inches.

Three different binder systems are used to bond the card webs: (l) 3 parts of standard viscose solution containing 7% caustic, 7% cellulose, diluted with 1 part water but no added polyolefin; (2) 3 parts of standard viscose solution and 1 part of solids by weight polyethylene aqueous dispersion; and (3) 2% parts of standard viscose solution and 1% parts of 40% solids by weight polyethylene aqueous dispersion. The polyethylene has a high molecular weight and is a very finely divided, dispersible powder having a particle size of 90 microns (diameter) or less.

The binders are applied to the card webs in an intermittent print pattern comprising wavy lines extending across the width of the card web, with four wavy lines to the inch as measured in the long direction. Standard coagulation and regeneration procedures are employed.

apparent serious loss of wet strength, dry strength, or color stability make the bonded nonwoven fabric suitable for use as a disposable wash cloth.

Although several specific examples of the inventive concept have been described, the same should not be construed as limited thereby nor to the specific features mentioned therein but to include various other equivalent features as set forth in the claims appended hereto. It is understood that any suitable changes, modifications and variations may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A colloidal dispersion of polyolefin particles in an alkaline solution having dispersed therein a member selected from the group of alkaline soluble cellulosic derivatives consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xanthate, said dispersion being adapted to be applied to nonwoven fibrous webs to bind together the individualized fibers of said webs.

2. The dispersion of claim 1 wherein said polyolefin is polyethylene.

3. The dispersion of claim 1 wherein said polyolefin is polypropylene.

4. A colloidal dispersion of from about parts to about 5 parts by weight of polyolefin in the form of particles having an average diameter of less than about microns, suspended in an alkaline solution having dispersed therein from about 5 parts to about 95 parts, based on the total parts of the dispersion, of a member selected from the group of alkaline soluble cellulosic derivatives consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xanthate, said dispersion being adapted to be applied to a nonwoven fibrous web to bind together the individualized fibers of said web.

5. The dispersion of claim 4 wherein said polyolefin is polyethylene.

6. The dispersion of claim 4 wherein said polyolefin is polypropylene.

The Persion of claim 4 wherein said polyolefin is polyisobutylene,

8. The dispersion of claim 4 wherein said polyolefin is poly-l-butene.

9. A bonded nonwoven fabric of overlapping, intersecting individualized fibers bonded together by binder areas constituting from about 7% to about 100% of the total surface area of the fabric, said binder areas comprising a film of from about parts to about 95 parts by Weight of a member selected from the group of alkaline soluble cellulosic derivatives consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xanthate and from about 95 parts to about 5 parts by Weight of polyolefin.

The fabric of claim 9 wherein the polyolefin is pol ethylene.

11. The fabric of claim 9 wherein the polyolefin is polypropylene.

12. The fabric of claim 9 wherein the polyolefin is polyisobutylene.

13. The fabric of claim 9 wherein the polyolefin is poly-l-butene.

14. A bonded nonwoven fabric of overlapping, intersecting individualized fibers bonded together by binder areas constituting from about 7% to about 35% of the total surface area of the fabric, said binder areas comprising a film of from about 5 parts to about 95 parts by Weight of a member selected from the group of alkaline soluble cellulosic derivatives consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cel lulose Xanthate and from about 95 parts to about 5 parts by Weight of polyolefin.

15. The fabric of claim 14 wherein said binder areas comprise a film of from about parts to about parts by weight of a member selected from the group of alkaline soluble cellulosic derivatives consisting of hydroxyethyl cellulose, carboxymethyl cellulose and cellulose xanthate and from about 75 parts to about 25 parts by weight of a polyolefin.

References Cited by the Examiner UNITED STATES PATENTS 2,372,713 4/1945 Curado et al 11714O 2,653,919 9/1953 Hunter 117161 2,868,742 1/1959 Burnham 260-17 FOREIGN PATENTS 491,199 8/1938 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

S. W. ROTHSTEIN, Assistant Examiner.

Claims (1)

1. 9. A BONDED NONWOVEN FABRIC OF OVERLAPPING INTERSECTING INDIVIDUALIZED FIBERS BONDED TOGETHER BY BINDER AREAS CONSTITUTING FROM ABOUT 7% TO ABOUT 100% OF THE TOTAL SURFACE AREA OF THE FABRIC, SAID BINDER AREAS COMPRISING A FILM OF FROM ABOUT 5 PARTS TO ABOUT 95 PARTS BY WEIGHT OF A MEMBER SELECTED FROM THE GROUP OF ALKALINE SOLUBLE CELLULOSIC DERIVATIVES CONSISTING OF HYDROXYETHYL CELLULOSE, CARBOXYMETHYL CELLULOSE AND CELLULOSE XANTHATE AND FROM ABOUT 95 PARTS TO ABOUT 5 PARTS BY WEIGHT OF POLYOLEFIN.