US3126297A - Treatment of nonwoven fabric with - Google Patents

Description

United States Patent 3,126,297 TREATMENT OF N (ENWOVEN FABRIC WITH ATACTIC POLYPROPYLENE Michael P. Diamantopoulos, North Plainfield, Walter B.

Armour, Pia-infield, and Gerald Brown, Bound Brook,

NJ, assign'ors to National Starch and Chemical Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed May 22, 1962, Ser. No. 196,589

2 Claims. (Cl. 117-140) This invention relates to novel binding compositions for use in the preparation of nonwoven fabrics. More particularly, it relates to the preparation of nonwoven fabrics that exhibit an unusual degree of softness, strength, and flexibility.

N onwoven fabrics are fabrics which are neither woven, knitted spun nor made by conventional wool felting processes. They are, instead, built up through the interlocking of fibers by means of chemical bonding agents or fusible fibers. This is accomplished by any combination of mechanical means, chemical action, or heat. Nonwoven fabrics may thus be broadly defined as a textile structure consisting of a web or mat of fibers held together with a binding material.

In preparing these nonwoven fabrics it is possible to use either natural or synthetic fibers. Thus, among the fibers which may be used in nonwoven fabrics are cotton, rayon, cellulose acetate, and triacetate, nylon, acrylic, polyester, glass, vinyl polymer and copolymer fibers, as well as paper fibers, wood pulp fibers, and fibers derived from waste paper. Generally, different types of fibers are blended in order to achieve the desired end product properties. After being blended, the individual fibers are then picked or shredded so as to obtain a more uniform distribution. These initial operations serve to prepare the fibers for the web forming process which employs various complex web forming machines. machines produce a web or flimsy sheet of fibers which will not remain in one piece by itself, but has to be supported by conveyors.

At this point in the process, the web must be bonded and this may be accomplished by mechanical means which entangle the fibers and thus give strength to the web. However, binding is more usually accomplished by the use of a chemical binding agent which may be in the form of an emulsion, a powder, a solvent, or a solution. These binding agents can be applied to the nonwoven web by immersion, spraying, in the form of a foam, by rolls or pads, or by the sprinkling of dry thermoplastic resins. The web can be completely covered with the binding agent or the binding agent may be applied so as These to form a discontinuous pattern by processes similar to printing. Thermoplastic fibers may also be used to accomplish binding by being blended into the fiber mixl i l l l l H H H CH CK CH CH X ture or by using them as the sole component of the web.

CH3 cs 3,l2b,27 Patented Mar. 24, 1364':

respects, from the preparation of a nonwoven fabric. Rather than being formed into a web, the fibers'are, instead, made into yarns which are aligned parallel to each other. These yarns, which represent the warp yarns of the gauze, are then run through a saturation bath wherein a series of steel cones mechanically meter the amount of binding agent that is applied to the warp yarns. The wet warp yarns are thereupon adhered to a series of fill yarns which comprise parallel aligned yarns positioned perpendicularly with respect to the wet warp yarns. The complete gauze is then dried by any suitable means such as by being passed over a drying drum or a heated calender stack.

Various materials have been employed as binding agents for nonwoven fabric and gauze, including such binders as polyvinyl acetate, polyacrylates, polyvinyl chloride, urea-formaldehyde resins, and the like. None of these binding agents, however, have been entirely satisfactory, primarily because of prohibitive costs and/or unsatisfactory properties imparted to the resulting nonwoven products. In particular, flexibility, Water resistance, tensile strength, edge tear, and elongation of the nonwoven products have often proven deficient when binders heretofore known to the practitioner have been utilized. Moreover, since nonwoven fabrics are widely used in wearing apparel, upholstery, floor and wall coverings, and similar applications, it is desirable that such fabrics possess a degree of softness, or, as it is commonly called, a good hand or feel. This latter property has often been lacking in nonwoven products when binding agents heretofore known have been used in the manufacture thereof.

It is an object of this invention to provide binding compositions for nonwoven fabrics and gauze whose use results in nonwoven materials which are characterized by their desirable characteristics of wear and feel. Other objects and the advantages of this invention will be apparent from the discussion that appears hereinafter.

Polypropylene is a synthetic resin which, of late, has enjoyed greatly increased usage in the preparation of molded articles, fibers and films. For use in the latter applications it is desirable that the polypropylene should have a highly crystalline structure which thereby serves to increase the strength of this versatile plastic. The inherent crystallinity of polypropylene is, in turn, dependent upon its molecular structure or configuration. Thus, crystalline polypropylene molecules will exhibit a socalled isotactic structure wherein the methyl groups will be regularly distributed on the same side of the polymer chain in a manner analogous to that shown in the following diagram:

CH3 CH3 On the other hand, polypropylene which is not crystalline will exhibit a so-called atactic structure wherein the methyl groups are randomly distributed on either side of the polymer chain in a manner analogous to that shown in the following diagram:

slug (1H H H C I C C l C C H ClxMH CH (iii l'lz CH2 C12 CH2 C2 C2 CH2 C2 CH2 C12 C2 In manufacturing polypropylene, the processes currently employed make use of so-called stereospecific catalysts which are chosen for their ability to provide the resulting polypropylene with an isotactic structure and thereby impart a maximum degree of crystallinity to the polymer. However, despite the use of these catalysts, present polymerization techniques still produce a product with a significant proportion of atactic polypropylene. The presence of this non-crystalline fraction would, of course, detract from the strength of any articles manufactured from such polypropylene. Therefore, it is the practice in the art to separate this atactic portion from the crystalline material and this is readily accomplished by means of a solvent extraction technique. To date, very few, if any, applications have been found for this atactic polypropylene residue. Its inherent lack of crystallinity obviates its use in the preparation of films, fibers, and molded products; while any use of this material as an adhesive base is similarly precluded since the resulting adhesive films are exceedingly soft and display relatively little strength.

\Ve have now discovered that the use of atactic polypropylene as a binder for nonwoven fabrics not only imparts highly desirable properties of flexibility, water resistance, tensile strength, edge tear, and elongation to said fabrics, but also imbues these fabrics with a remarkable degree of softness. Moreover, the latter characteristic of softness or hand is realized without any sacrifice in the strength of the resulting nonwoven products.

In accordance with the invention, nonwoven products are prepared by means of a process involving the application, to a nonwoven sheet or web of fibers, of a binder composition comprising atactic polpropylene either in the form of a lacquer or an aqueous emulsion.

In using atactic polypropylene as the binding agent in the manufacture of nonwoven fabrics, there are several possible techniques for their application to the fiber web. These include saturation bonding, wet-roll bonding, spray bonding, and segmental bonding. Saturation bonding, which is also referred to as continuous, immersion, solution or impregnation bonding, is the most commonly used bonding method and consists simply of passing the fragile fiber web through a liquid binder bath. The web is then passed through squeeze rolls to remove the excess binding agent. Wet-roll bonding is similar to the saturation process, the main difference being that the web does not go through the liquid bath. Instead, a series of mechanical rolls pick up the binder and transfer it to the moving web. Spray bonding applies the liquid binding agent by spraying a fine mist of binder over the surface of the web. And, segmental bonding, which is also referred to as discontinuous, patterned, print, engraved, intermittent, and spot bonding, is the process wherein the binding agent is applied to the web in a uniform pattern, resulting in definite bonded and unbonded portions upon the web surface.

With the above described application techniques, or with any other procedures which may be devised by the practitioner, it is desirable that the finished nonwoven fabric or gauze contain from 3% to 280% of binding agent, i.e., atactic polypropylene solids, as based on the weight of the dry fibers in the finished nonwoven product. Particularly effective fabrics were obtained wherein the finished product contained from 50% to 200% of binding agent. The desired binder content can be realized by proper adjustment of the solids content of the binding agent lacquer or emulsion and/or by varying the initial pickup by the fiber web or warp yarns of the binding agent, i.e., atactic polypropylene solids plus solvent. Thus, the initial pickup of the liquid binding agent may be in the range of from 4% to 500%, as based on the weight of the web or warp yarns.

Subsequent to the application of our atactic polypropylene binding agent, the sheet or web of nonwoven fabric may be dried at room or elevated temperatures. The drying cycles used in this process depend upon the temperature employed, the rate and amount of air flow, and other factors inherent in the practitioners facilities and method of operation. In any case, temperatures varying from room temperature to about 350 F. may be used to remove the solvent or water that is present in the wet web.

When the binders of our invention are utilized in the form of lacquers, it is possible to use various solvents in their preparation. Thus, for example, atactic polypropylene may be dissolved in a variety of solvents, including: aromatic hydrocarbons, such as toluene, xylene, decahydronaphthalene and tetrahydronaphthalene; aliphatic hydrocarbons containing from 5 to 11 carbon atoms, such as pentane, hexane, and nonane; and, chlorinated hydrocarbons, such as methylene chloride, carbon tetrachloride, trichloroethylene, perchloroethylene, and also chlorinated aromatic hydrocarbons such as chlorobenzene. It should be noted that, Where so desired by the practitioner, it is possible to prepare these lacquers with various combinations of any of the above listed solvents. The resin solids content of these atactic polypropylene lacquers should usually range from about 1% to about 50% by weight.

When the atactic polypropylene is employed in our invention in the form of an aqueous emulsion, the latter may be prepared by adding an emulsifying agent to an organic solvent solution of atactic polypropylene, the solution being prepared by the use of any of the above listed solvents. Water is then added with vigorous agita tion, the amount of water added depending on the solids content desired in the resulting emulsion. The organic solvent can then be removed from the emulsion by distillation or other appropriate means. The resin solids content of these atactic polypropylene emulsions usually ranges from about 2% to about 65% by weight.

It should be mentioned that various additives, such as defoamers, resins to impart wet strength, lubricants, and the like, may be added to our atactic polypropylene binder formulations in order to enhance the properties imparted to the nonwoven fabrics to which said binders are applied.

In the following examples, which further illustrate the embodiment of our invention, all parts given are by weight unless otherwise indicated.

Example I This example illustrates the preparation of nonwoven fabrics using lacquers and emulsions of atactic polypropylene as the binding agents therefor.

In this example, and in the examples that follow, the same basic procedure was utilized in preparing the nonwoven fabric. In this basic procedure, a web was bonded as it passed through the nip of a padder, the binding agent being applied by a stainless steel transfer roll which dipped into a pan containing the binding agent and transferred the impregnant to the passing web. The amount of binding agent picked up by the web was determined by the pressure at the nip as well as by the initial solids content of the binding agent. The wet web was then passed into a forced draft oven and dried at 300 F. for a period of 3 minutes. This drying operation effected a complete removal of water or solvent and the web was thereupon cooled to room temperature.

(a) 4 parts of oleic acid and 4 parts of morpholine were added to 100 parts of a 40% hexane solution of atactic polypropylene. parts of water were then added with vigorous agitation. The hexane was removed from the emulsion by distillation, and the solvent-free emulsion was diluted with water to a final concentration of 1%, by weight, of atactic polypropylene solids. A nonwoven sheet composed of /5 rayon/cellulose fibers was passed through this emulsion, squeezed between rollers, and dried at room temperature. In this case, the nip pressure was adjusted so as to give a total binding agent pickup of thus yielding a finished fabric containing 3%, by weight, of atactic polypropylene solids, as based on the dry fiber weight. The finished fabric exhibited outstanding properties of flexibility and strength and was remarkably soft to the touch.

(b) A nonwoven sheet composed of 95/5 rayon/ cellulose fibers was passed through a 2%, by weight, solids lacquer of atactic polypropylene in hexane, the sheet thereafter being squeezed between rollers, and dried at room temperature. In this case, the nip pressure was adjusted so as to give a total binding agent pickup of 100%, thus yielding a finished fabric containing 3%, by weight, of atactic polypropylene solids, as based on the dry fiber weight. The finished fabric exhibited outstanding properties of flexibility and strength and was remarkably soft to the touch.

Example II This example illustrates the preparation of nonwoven fabrics by the process of our invention whereby the fabrics contain varying amounts of atactic polypropylene solids.

The basic procedure of Example I was employed to prepare nonwoven fabrics of various fiber types, including polyamide, polyacrylonitrile, rayon, and glass fibers.

formulations given above exhibited outstanding properties of flexibility and strength and were remarkably soft to the touch.

Example III This example illustrates the vastly improved results with respect to a number of different properties obtained by using atactic polypropylene as the binding agent for nonwoven fabrics, as compared to the results obtained by using a number of conventional binding agents under the same conditions.

(a) The basic procedure of Example I was employed to prepare a number of viscose fiber nonwoven fabrics, each of which was bound with a diiferent binding agent. In each case, the binding agent constituted about 50% by weight of the resulting fabric, as based on the weight of the dry fibers. The table appearing below sets forth the binding agents used, along with certain properties exhibited by the fabrics thereby bound.

In determining the edge tear and percent elongation of the fabrics tested, test procedures established by the Technical Association of the Pulp and Paper Industry (TAPPI) were followed. The Finch edge tear was determined by means of TAPPI test T470M54, wherein higher readings indicate a proportionately stronger fabric. The percent elongation was determined by means of TAPPI test T-457-M-46.

The test for stiffness was carried out on an instrument called the Gurley stiffness tester. In using this instrument, a sample of the fabric 1 inch wide and 1.5 inches long was clamped centrally on the projected arm of the machine with the length of the sample being in a vertical position. This sample extended parallel to a freely swinging pointer to which various weights were fastened. As weights were added, the arm with the clamped sample pressed against and moved the pointer, thereby giving a reading in milligrams which comprises the Gurley stiffness, wherein a higher reading indicates a proportionately stiffer and less desirable fabric.

From the results represented in the above table, it can be seen that the use of atactic polypropylene as the binding agent for nonwoven fabrics presents a sig nificant advantage over the use of any of the conventional binding agents listed above.

(b) The basic procedure of Example I was employed to prepare a number of nonwoven fabrics, each comprising 95/5 acrylic/ glass fibers, and each being bound with a different binding agent. In each case, the binding agent constituted about 50%, by weight, of the resulting fabric, as based on the weight of the dry fibers. The table appearing below sets forth the binding agents used, along with certain properties exhibited by the fabrics thereby bound.

In determining the discoloration and flexibility of the fabrics tested, test procedures established by the Technical Association of the Pulp and Paper Industry (TAPPI) were followed. The discoloration was determined by means of TAPPI test T-452-M-48, and flexibility was determined by means of TAPPI test T-451- M-60.

Binding Agent Discolora- Residual Odor Flexibility tion 60:40 butadienezstyrene co- Poor Slight Good.

polymer latex.

Polyehylacrylatelatex(46% Good do Do.

so 1 s :15 vinyl aeetatezbutyl do Very Slight Fair.

acrylate latex (47% solids).

Atactic polypropylene do None Excellent.

From the results represented in the above table, it can be seen that the use of atactic polypropylene as the binding agent for nonwoven fabrics presents significant advantages over the use of any of the conventional binding agents listed above.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the invention as defined by the following claims.

References Cited in the file of this patent UNITED STATES PATENTS 2,927,047 Schulde et al. Mar. 1, 1960 2,992,149 Drelich July 11, 1961 3,049,466 Erlich Aug. 14, 1962

Claims (1)

1. THE PROCESS OF MAKING A BONDED NONWOVEN FABRIC CHARACTERIZED BY GREAT SOFTNESS, FLEXIBILITY, AND STRENGTH WHICH COMPRISES APPLYING TO A WEB OF FIBERS A BINDING AGENT COMPRISING ATACTIC POLYPROPYLENE DISPERSED IN A LIQUID MEDIUM, AND DRYING THE SAME.