US3316122A

US3316122A - Process of bonding nonwoven fabric with chlorinated atactic polypropylene and the bonded fabric

Info

Publication number: US3316122A
Authority: US
Inventors: Walter B Armour; Gerald H Brown; Emil D Mazzarella
Original assignee: National Starch and Chemical Corp
Current assignee: Ingredion Inc
Priority date: 1964-02-20
Filing date: 1964-02-20
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25

Description

United States Patent 3,316,122 PROCESS OF BONDING NONWOVEN FABRIC WITH CHLORINATED ATACTIC POLYPRO- PYLENE AND THE BONDED FABRIC Walter B. Armour, Plainfield, N.J., Gerald H. Brown, Syracuse, N.Y., and Emil D. Mazzarella, Plainfield, NJ., assignors to National Starch and Chemical Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Feb. 20, 1964, Ser. No. 346,092 8 Claims. (Cl. 117-136) 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 which are characterized by their excellent fire retardancy as well as by their unusual degree of softness and strength.

Nonwoven 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 to gether 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. These machines produce a web or flimsy sheet of fibers which will not remain in one piece by itself, but has to be sup ported 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 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 mixture or by using them as the sole component of the web. Application of heat causes these fibers to become tacky and thus stick to each other and/or to other non-thermoplastic fibers,

The formation of a nonwoven gauze difiers, in some 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 calendar stack.

Various materials have been employed as binding agents for nonwoven fabric and gauze, including such binders as polyvinyl acetate, polyacrylates, polyvinyl chloride, ureaformaldehyde 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.

Thus, for example, it is well known that many of the binding agents heretofore utilized have provided nonwoven fabrics with very little, if any, resistance to fire and flame propagation and, in some cases, these binders have even served to increase the flammability of the fabric. Fire resistance is, of course, of great importance in nonwoven fabrics which are to be used in either consumer or industrial applications wherein they may tend to become accidentally ignited. Unfortunately, in at tempting to provide binders which successfully imparted fire retardancy, it was found that the binders which were desirable in this respect were often deficient with regard to their adhesive an-d/ or processing characteristics.

In addition to the above described fire retardency problem, water resistance, tensile strength, edge tear, and elongation of nonwoven products have often proved deficient when binders heretofore known have been utilized. Moreover, since nonwoven fabrics are widely use-d in wearing apparel, upholstery, floor and wall coverings, and similar applications, it is often desirable that such fabrics possess a degree of softness, or, as it is commonly referred to, a good hand or feel. This latter property has often lacking in nonwoven products when the binding agents of the prior art have been used in their manufacture.

Thus, it is an object of this invention to provide binding compositions for nonwoven fabrics and gauze, the use of which results in no nwoven materials which are characterzed by their outstading resistance to fire and flame propagation as well as by their desirable characteristics of wear and feel. Other objects and advantages of this invention will be apparent from the discussion which follows hereinafter.

We have now discovered that the use of chlorinated atactic polypropylene as a binder for nonwoven fabrics provides the resulting products with outstanding fire retardancy properties. In addition, the use of this novel binder imparts highly desirable properties of water resistance, tensile strength, edge tear, and elongation to said fabrics and also provides them with a remarkable degree of softness. Moreover, the latter chaarcteristic of softness of 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 chlorinated atactic polypropylene which may be in the form of either a lacquer or an aqueous emulsion.

Polyproplylene 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 late 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 propypropylene molcules will exhibit a socalled isotactic structure wherein the methyl groups will be regularly distributed on the same side of the polymer a a a; chain in a manner analogous to that shown in the folintroduced therein. The sulfuryl chloride is then slowly lowing diagram: added with the solution being maintained at reflux for a CH2 CH CH2 On the other hand, polypropylene which is not crystalperiod which may range from about 5 to hours, thereline will exhibit a so-called atactic structure wherein the by yielding the desired chlorinated atactic polypropylene.

methyl groups are randomly distributed on either side It may be noted that the above described chlorination of the polymer chain in a manner analogous to that shown procedure may also be utilized with thionyl chloride.

in the following diagram. However, when gaseous clflorine is used, this procedure CH3 CH3 CH3 I l I CH CH CH CH CH CH CH CH CH C 2 CH CH CH In manufacturing polypropylene, the processes curis modified somewhat in that the reaction temperatures rently employed make use of so-called stereospecific are maintained below reflux levels. catalysts which are chosen for their ability to provide In using chlorinated atactic polypropylene as the bindthe resulting polypropylene with an isotactic structure ing agent in the manufacture of nonwoven fabrics, there and thereby impart a maximum degree of crystallinity to are several possible techniques for their application to the polymer. However, despite the use of these catalysts, the fiber web. These include saturation bonding, wet-roll present polymerization techniques still produce a product bonding, spray bonding, and segmental bonding. Saturawith a significant proportion of atactic polypropylene. tion bonding, which is also referred to as continuous, im-

The presence of this non-crystalline fraction would, of mersion, solution or impregnation bonding, is the most course, detract from the strength of any articles manucommonly used bonding method and consists simply of factured from such polypropylene. Therefore, it is the passing the fragile fiber web through a liquid binder bath.

practice in the art to separate this atactic portion from The web is then passed through squeeze rolls to remove the crystalline material and this is readily accomplished the excess binding agent. Wet-roll bonding is similar by means of a solvent extraction technique. To date, to the saturation process, the main difference being that very few, if any, applications have been found for this the web does not go through the liquid bath. Instead, a atactic polypropylene residue. Its inherent lack of crystalseries of mechanical rolls pick up the binder and translinity obviates its use in the preparation of films, fibers, fer it to the moving web. Spray bonding applies the and molded products; while any use of this material as liquid binding agent by spraying a fine mist of binder over an adhesive base is similarly precluded since the resultthe surface of the web. And, segmental bonding, which ing adhesive films are exceeding soft and display relatively is also referred to as discontinuous, patterned, print, enlittle strength. graved, intermittent, and spot bonding, is the process The chlorinated atactic polypropylene which is used as wherein the binding agent is applied to the web in a unithe binding agent in the process of our invention is preform pattern, resulting in definite bonded and unbonded pared by dissolving the atactic polypropylene in a nonreactive organic solvent such as carbon tetrachloride,

portions upon the web surface.

With the above described application techniques, or

methylene chloride, chlorobenzene, or chloroform. The with any other procedures which may be devised by the atactic polypropylene is then chlorinated in the presence practitioner, it is desirable that the finished nonwoven of a suitable catalyst which may be a solvent soluble orfabric or gauze contain from about 3% to 2 80% of ganic peroxide, such as benzoyl peroxide or lauroyl perbinding agent, i.e., chlorinated atactic polypropylene oxide, or a metal salt, such as ferric chloride or aluminum solids, as based on the weight of the dry fibers in the finchloride. :The latter catalysts are usually present in the ished nonwoven product. Particularly effective fabrics reaction mixture in a concentration of about 0.1 to 1.0%, were obtained wherein the finished product contained by weight, of the atactic polypropylene undergoing chlorifrom about to 200% of binding agent. The desired nation. Chlorination may be accomplished by bubbling binder content can be realized by proper adjustment of chlorine gas directly onto the reaction mixture or by rethe solids content of the binding agent lacquer or emulfluxing the latter in the presence of a chlorination agent sion and/or by varying by means well known to those such, for example, as sulfuryl chloride or thionyl chloskilled in the art, the initial pickup by the fiber Web or ride. warp yarns of the binding agent.

For use as a binding agent in the Process of 6p Subsequent to the application of our chlorinated Vention, the chlorinated atactic P yp p y 0 atactic polypropylene binding agent, the sheet or web of lain from about 8 to about 35%, by Weight, of chlorillenonwoven fabric may be dried at room or elevated tem- A typical procedure, in this case employing sulfuryl peratures. The drying cycles used in this process depend chloride, which may be utilized for the chlorination of upon the temperature employed, the rate and amount of atactic polypropylene would involve first preparing an orair flow, and other factors inherent in the practitioners ganic solvent solution of the atactic polypropylene with facilities and method of operation. In any case, temthe process of solution being assisted by subjecting the peratures varying from room temperature to about 350 mixture to mechanical agitation as Well as by heating it P, may the used to remove the solvent or water that is to reflux. While the thus prepared solution is mainpresent in the wet web.

tained under reflux and agitation, the selected catalyst is 7 When the binders of our invention are utilized in the form of laquers, it is possible to use various solvents in their preparation. Thus, for example, chlorinated atactic polypropylene may be dissolved in a variety of solvents, including: aromatic hydrocarbons, such as toluene and xylene; cyclic hydrocarbons, such as 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, tirichloroethylene, 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 combina tions of any of the above listed solvents. The resin solids content of these chlorinated atactic polypropylene lacquers should usually range from about 1% to about 50% by weight.

When the chlorinated atactic polypropylene is employed in our invention in the form of an aqueous emulsion, the latter may be prepared by adding an aqueous solution of an emulsifying agent, such as polyvinyl alcohol, morpholine-oleic acid mixtures, and the like, to an organic solvent solution of chlorinated atactic polypropylene; the latter solution having been prepared by the use of any of the above listed solvents. Water is then added with vigorous agitation, the amount of water added depending upon the solids content desired in the ultimate emulsion. In those cases where the organic solvent has a boiling point less than that of water, it can be removed from the emulsion by distillation or other appropriate means. The resin solids content of these chlorinated atactic polypropylene emulsions usually ranges from about 2 to 65%, by weight.

It should be mentioned that various additives, such as defoamers, lubricants, antioxidants, and the like, may be added to our chlorinated atactic polypropylene binder formulations in order to enhance the properties imparted to the nonwoven fabrics to which said binders are applied. It may also be noted that our chlorinated atactic polypropylene binders may be used in combination with various thermosetting and thermoplastic resin binders.

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 fire retardant nonwoven fabrics using lacquers and emulsions of chlorinated 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 chlorinated atactic polypropylene having a chlorine content of by weight. 85 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 chlorinated atactic polypropylene solids. A nonwoven sheet composed of 95/5 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 yield a finished fabric containing 3%, by weight, of chlorinated atactic polypropylene solids, as based. on the dry fiber weight.

(b) A nonwoven sheet composed of /5 rayon/cellulose fibers was passed through a 2%, by weight, hexane lacquer of chlorinated atactic polypropylene having a chlorine content of 30%, by weight. The sheet was thereafter squeezed between rollers, and dried at room temperature. In this case, the nip pressure was adjusted so as to yield a finished fabric containing 3%, by weight, of chlorinated atactic polypropylene solids, as based on the dry fiber weight.

Example II Medium for Percent resin Percent resin solids Binding Agent solids or" medium content of resulting nonwoven fabric Aqueous emulsion 1 3 Hexane lacqueL 2 8 Aqueous emulsiom 40 20 Hexane lacquer: 50 25 Aqueous emulsion. 65 280 Hexane lacquer 50 280 The nonwoven fabrics produced by using each of the formulations given above exhibited outstanding properties of fire retardancy 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 in addition to fire retardancy, obtained by using chlorinated 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 different binding agent. In each case, the binding agent solids 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 prop erties 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 T-470M-54, wherein higher readings indicate a proportionately stronger fabric. The percent elongation was determined by means of TAPPI test T457-M-46.

The test for stiffiness 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 stilr'er and less desirable fabric.

Medium for Gurley Finch Percent Binding Agent Binding Agent I'Iand Stifiness Edge Elontnig.) Tear gation (lb/in.)

Polyvinyl acetate Emulsion Poor I, 400 2. 3 18 Polyvinylidene chloride d 824 4.3 22 :80 vinyl acetate :ethyl aerylate coploymer 444 6.8 44 75:25 butadienezacrylonitrile oopolyiner 380 7. 8 55 Chlorinated atactic polypropylene (10%, by 230 13.0 84

weight chlorine content).

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

Example IV The following example illustrates the actual preparation of a number of samples of chlorinated atactic polypropylene lacquers wherein each of the respective samples had a different chlorine content. These lacquers were then converted to aqueous emulsions which were used for the preparation of fire retardant nonwoven fabrics by means of the basic procedure described in Example I. It may also be noted that the various samples of chlorinated atactic polypropylene whose use was described in Examples I, II and III were all prepared by means of the process described below.

Using gaseous chlorine and sulfuryl chloride as chlorination agents, We prepared several chlorinated atactic polypropylene lacquers each of which had a resin solids content of by weight. In preparing these lacquers, the chlorination procedure described earlier in the specification was utilized. The resulting lacquers were then converted into aqueous emulsions by adding an aqueous solutiOn of an emulsifier to the lacquer while subjecting the latter to vigorous agitation. In each case, we used 6%, of emulsifier as based on the weight of chlorinated atactic polypropylene in the respective lacquers. These emulsions, each of which had a resin solids content of 5%, by weight, were then used as binding agents for the preparation of nonwoven fabrics by means of the basic procedure described in Example I.

In the following table are presented details relating to the preparation of the various chlorinated atactic polypropylene lacquers and their subsequent conversion to Summarizing, this invention provides the practitioner with fire retardant nonwoven products through the use of novel binders comprising chlorinated atactic polypropylene. Variations may be made in proportions, procedures and materials without departing from the scope of the invention which is limited only by the following claims.

We claim:

1. The process of making a bonded nonwoven fabric characterized by its resistance to fire, softness and strength, said process comprising applying to a web of fibers a binding agent consisting essentially of chlorinated atactic polypropylene dispersed in a liquid medium.

2. The process of claim 1, wherein said chlorinated atactic polypropylene has a chlorine content of from about 8 to by weight.

3. The process of claim 1, wherein said binding agent is in the form of an organic solvent solution.

4. The process of claim 1, wherein said binding agent is in the form of an aqueous emulsion.

5. A bonded nonwoven fabric characterized by its fire retardancy, softness and strength, said fabric comprising a web of fibers bonded solely with a chlorinated atactic polypropylene binding agent.

6. The nonwoven fabric of claim 5, wherein said chlorinated atactic polypropylene has a chlorine content of from about 8 to 35%, by weight.

7. A bonded nonwoven fabric characterized by its fire retardancy, softness and strength, said fabric comprising a web of fibers bonded solely with the dried residue of an organic solvent solution of chlorinated atactic polypropylene.

8. A bonded nonwoven fabric characterized by its fire retardancy, softness and strength, said fabric comprising a web of fibers bonded solely with the dried residue of an aqueous emulsion of chlorinated atactic polypropylaqueous emulsions. ene.

Parts of 4 Parts of i Chlorine in l Formulation No. Atactic Catalyst Used (Parts) Chlorination Agent Chlorinating Chlorinated Emulsifying Agent Polypro Agent Polymer pylcne 1 -s 100 Lauroylperoxide (0.3). 2 0 35 Polyvinyl alcohol.

100 Ferric chloride (0.3). 94 26 Do. 100 Ferric chloride and I 18 Do. Ferric chloride (0.3). 45 11 Oleic acidmorpholine. 100 0 30 S Polyvinyl alcohol.

References Cited by the Examiner UNITED STATES PATENTS 3,126,297 3/1964 Diamantopoulos et al. l17-140 3,192,188 6/1965 Orthner of al 260-882 3,228,791 1/1966 Armour et a1 117--138.8

WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner.

Claims

1. THE PROCESS OF MAKING A BONDED NONWOVEN FIBRIC CHARACTERIZED BY ITS RESISTANCE TO FIRE, SOFTNESS AND STRENGTH, SAID PROCSS COMPRISING APPLYING TO A WEB OF FIBERS A BINDING AGENT CONSISTING ESSENTIALLY OF CHLORINATED ATACTIC POLYPROPYLENE DISPERSED IN A LIQUID MEDIUM.