US3653949A - Coated fabrics and methods for applying coatings thereto - Google Patents

Abstract

Glass fibers in the form of yarns and fabrics are provided with a surface treatment to improve their resistance to abrasion and flammability by coating the yarns and fabrics with a thickened dispersion of very fine particles of a solid organic polymeric material, drying and sintering this coating through various heating zones, and optionally padding the treated yarns and fabric with a lubricant to ensure flexibility thereof.

Description

United States Patent Dillon [45] Apr. 4, 1972 [54] COATED FABRICS AND METHODS FOR APPLYING COATINGS THERETO [72] Inventor: James J. Dillon, Providence, R1.

[73] Assignee: Owens-Corning Fiberglas Corporation [22] Filed: Sept. 5, 1969 21 Appl. No.: 855,513

2,712,509 7/l955 Biefeld ..28/75 R 2,731,367 1/1956 Caroselli. 17/126 GS 2,754,223 7/1956 Caroselli.... 17/126 GB 2,907,677 10/1959 Hochberg.. 17/126 GB 3,434,875 3/1959 Smith et al. ..l17/126 GS Primary Examiner-William D. Martin Assistant ExaminerD. Cohen Attorney-Statelin & Overman and Robert E. Witt [57] ABSTRACT Glass fibers in the form of yarns and fabrics are provided with a surface treatment to improve their resistance to abrasion and flammability by coating the yarns and fabrics with a thickened dispersion of very fine particles of a solid organic polymeric material, drying and sintering this coating through various heating zones, and optionally padding the treated yarns and fabric with a lubricant to ensure flexibility thereof.

5 Claims, 2 Drawing Figures Patented April 4, 1972 3,653,949

' INVENTOR.

(/4145; J 5/4 1 av COATED FABRICS AND METHODS FOR APPLYING COATINGS Tl-IERETO The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of section 305 of the National Aeronautics and Space Act of l958, Public Law 85 568 (72 Statute 435; 42 U.

This invention relates to glass fibers characterized by a marked increase in resistance to deterioration by abrasion and it relates more particularly to glass fiber fabrics having improved abrasion and flammability resistance and to a method and composition for use in the preparation of the same.

Glass fibers are employed extensively in the manufacture of fabrics of high strength, high resistance to wrinkling, good washability, excellent appearance, and in which one or more of the important characteristics is resistance to heat and flammability. One of the barriers to the more widespread usage of glass fibers as a textile material resides in the relatively low abrasion resistance of the glass fibers whereby the fibers fray or break down in response to mutual abrasion or other surface abrasions to which the glass fiber fabric might be exposed during use.

Substantial inroads have been made in overcomingthe relatively poor abrasion resistance of the glass fibers and fabrics formed thereof whereby glass fiber fabrics have found increased utilization as atextile material in applications where 'fire resistance, strength, wrinkle proofness, flexibility and appearance constitute one or more of the factors in the selection of a textile material.

Because of the many outstanding properties ofglass fibers as a textile material, extensive research and development has been expended towards the further increase of the abrasion resistance of glass fibers and fabrics formed thereof, and in the same regard to maintain or further increase the fire resistance properties of glass fibers and fabrics formed thereof.

It is an object of this invention to provide a method for producing glass fibers and fabrics formed thereof having greatly improved resistance to abrasion and greatlyimproved resistance to flammability, in which the improved properties are achieved without loss of other desirable properties possessed by glass fibers or fabrics formed thereof.

It is another object of this invention to provide a method and composition for use in the treatment of glass fibers and fabrics formed thereof whereby the same are highly resistant to deterioration by mutual or other abrasion and are self extinguishing in an oxygen atmosphere and it is a related object to provide a treatment of the type described which makes use of relatively low cost and readily available materials; which can be applied in a simple and efficient manner during the processing of the fibers and fabrics formedthereof; which does not interfere with the processing of the glass fibers during formation of the glass fiber filaments in yarns, cords and fabrics formed thereof; which does not interfere with the fuller utilization of the desirable properties of the glass fibers and glass fiber fabrics and which results in a glass fiber fabric of high strength, good appearance and long life.

These and other objects and advantages of this invention will hereinafter appear, and for purposes ofillustration but not of limitation embodiments of the invention are shown in the accompanying drawings, in which FIG. I is a schematic view showing the arrangement of elements for the treatment of glass fibers in conjunction with a glass fiber forming operation, and

FIG. 2 is an enlarged sectional view across a woven glass fiber fabric treated in accordance with the practice of this invention.

Continuous glass fiber filaments are formed by rapid attenuation of molten streams of glass 12 issuing from hundreds of orifices in the bottom side of a glass melting furnace 14. The bare surfaces of the formed glass fiber filaments are wet at a coating station 16 with a conventional sizing composition. Application to the individual filaments may be made by means of a roller coater 18 schematically illustrated in FIG. 1, in position to engage the glass fiber filaments before they are brought together to form a glass fiber bundle 20. The roller makes contact with a reservoir of the coating composition whereby the surfaces of the roller become wet for transfer to the filaments as they pass thereover. The sized filaments are subsequently gathered together in the form of a strand or bundle and wound upon a rapidly rotating collet or drum 22 which operates to pull the fibers to effect the described attenuation. The treated strands can thereafter be twisted and plyed into yarns and woven into fabric and then treated by the inventive concept. However, the treated strands can be further subjected to additional finishing operations. in accordance with the inventive concept, prior to beingwoven into fabric.

It has been found that the abrasion resistance and selfextinguishing characteristics of theftreated glass fibers or fabric formed thereof in an oxygen atmosphere can be increased many fold when they are coated with a thickened dispersion of polytetrafluoroethylene. The thickened dispersion is applied to glass fibers and fabrics formed thereof preferably prior to any heat cleaning of the fibers or fabrics, i.e. the dispersion is applied to greige yarns and fabrics. By coating the glass fiber yarns andfabrics prior to heat cleaning, only one heat cycle is required to burn off or expel unwanted volatiles and to obtain a uniform coating of the polytetrafluoroethylene thereon.

It has been observed thatby first heat cleaning the yarns or fabrics prior to coating thesame with the thickened dispersion and subsequently exposing the same to another heat cycle, other desirable properties and characteristics of the glass fibers, especially the strength properties, are adversly affected.

When the glass fibers or fabric are treated according to the inventive concept three objects are accomplished: l organic matter or volatiles are distilled off; (2) the polytetrafluoroethylene is sintered slowly; and (3) when the glass fibers are in fabric form the fabric is heat set, i.e. a permanent crimp is established in the glass fibers of the fabric to help give dimensional stability thereto. Furthermore, when the volatiles are distilled off by the inventive concept hereinafter described in *greater detail the fabric remains very white in color.

It was observed during the development of this invention that when the yarns are twisted and subsequently coated with polytetrafluoroethylene and exposed to high temperatures ranging up to 750F. for periods up to 1 minute the resultant yarn is brown in color, probablybecause not all of the organic material has had a chance to be expelled, thereby making the treated yarns susceptible to flammability in an oxygen atmosphere. Furthermore the treated yarn may have bumpy characteristics due to an uneven flow of the polytetrafluoroethylene coating thereby making subsequent weaving operations difficult and inefficient. From this obser vation it was determined that a gradual build up of temperature over an extended time period would be desirable in order to overcome the above deficiencies.

The inventive process is applied to glass fibers that have been twisted and/or plied into yarns, wherein the fibers have a forming size thereon. A dispersion of polytetrafiuoroethylene is subsequently coated onto the yarns arid the coated yarns are merely dried so that the coating on the yarns is not immediate ly melted nor sintered. This is accomplished by heating the coated yarns at a temperature of from 300 to 350 F. for preferably 30 seconds to 5 minutes, however exposure of up to 24 hours will not adversely affect the properties. This dried yarn is then woven into fabric form and the fabric is subsequently heat cleaned to expel volatile organic materials therefrom and at the same time to make the polytetrafluoroethylene flow, and to weave set the yarns in the fabric thereby yielding a smooth, uniform coating on the fabric. With this process, it has been noticed that (1) this yields an efficient coatirtg operation of the yarns, and (2) the coating is smooth and uniform for easy harlcllirig and further operations, and when woven into fabric form and heat treated, the fabric possesses good hand, flexibility, strength, and is white in color. Additionally, subsequent to heat cleaning, a

lubricant may be padded on the fabric to insure or increase flexibility thereof. The lubricant may be an organosilicon compound selected from the group consisting of a silane, its hydrolysis product, and its polymerization product wherein the silane has from one to three highly hydrolyzable groups attached to the silicon atom and at least one organic group attached to the silicon atom. The organosilicon compound should be applied to the treated glass fiber surfaces in a very dilute solution or dispersion in an aqueous medium or in organic solvents containing less than 2 percent by weight of the organosilicon compound sufficient to form at least a monomolecular layer. An example of such an organosilicon compound is XEC-4-2l02 commercially available from the Dow-Corning Corporation.

Other lubricants that may be suitably used are cationic softeners, such as quarternary ammonium salts of amides or imidazolines and acetate salts of tetraethylene pentamine mono-, di-, poly-stearate, or non-ionic softeners such as polyethylene dispersions or emulsions, glycerine monostearates and amino and imide derivatives of high molecular weight fatty alcohols. Also, chromium complexes, such as stearato chromic chloride, and methacrylato chromic chloride have been found to maintain the flexibility of fabrics treated in accordance with the inventive concepts.

Advantages possessed by the yarns and fabrics treated by the concepts of the subject invention include; (1) their whiteness, (2) their high tensile properties, (3) their high abrasion resistance, (4) their excellent flexibility and hand, and (5) their non-flammability, even in an oxygen atmosphere at 16 psia.

It was further observed that when techniques other than the inventive concept were employed to apply a polytetrafluoroethylene dispersion to greige glass fabric, such as by impregnation, serious drawbacks developed, i.e. a dirty brown color appeared on the fabric after oven drying and sintering and the fabric was stiff and its resistance to flammability was adversely affected.

Fabrics treated by the inventive concept find increased utility in applications where protective clothing is necessitated, i.e. protection from heat, fire and chemicals.

Other materials other than polytetrafluoroethylene that are suitable to coat glass fiber fabrics by the inventive concept are KEL-F and Fluorels, polyflorinated polymers manufactured by the Minnesota Mining Company. These above materials also appear to provide increased wrinkle recovery and better hand to the treated fabrics.

A commercially available polytetrafluoroethylene (Teflon 30) dispersion was thickened with commonly known thickening agents such as Carbopol, Methocel, and Superclear (natural or synthetic gum or modifications thereof).

Knife coating the thickened polytetrafluoroethylene dispersion onto the glass fiber fabrics is accomplished with a knifeover roll, floating knife, reverse roller or other suitable means. When the polytetrafluoroethylene is applied to a glass fiber yarn, a wiping die, wiping rod, or dip coating is sufficient to apply the coating thereon.

By controlling the time and temperature that the coated yarns or fabrics are exposed to, caramelization or brownish color is avoided on the yarns or fabrics because all of the organic volatile materials are distilled off. A suitable method for accomplishing this follows. The thickened polytetrafluoroethylene dispersion is coated onto glass yarn or glass fabric at room temperature. The amount of polytetrafluoroethylene applied to the glass yarn or the glass fabric is dependent upon the desired properties and end uses of the glass yarns and fabric. For example, if the treated glass fabric is to be used as protective clothing wherein the fabric is exposed to dynamic use a lesser amount is applied than if it is to be used in a static situation such as a wall curtain. However, amounts of polytetrafluoroethylene in the range of from about 0.5 to about 40,0 percent by weight per weight of the fabric is sufficient. Preferably, when glass fabric is coated, the amount of polytetrafluoroethylene is from about-2.0 to about 15.0 percent by weight per weight of the fabric for each surface of the fabric. Depending upon the end use of the treated fabric, it is usually preferred to coat only one surface of the fabric. Subsequently the coated yarns woven into fabric, or coated fabrics are exposed to temperatures ranging from 300-750" F. over a period ranging from 12-60 hours. This temperature range has been determined to be that at which the volatiles distil off the coated yarns or fabrics without exothermic decomposition. At this temperature range sintering of the polytetrafluoroethylene, and weave setting and heat cleaning of the yarns and fabric occur simultaneously.

When thickeners are added to a commercially available polytetrafluoroethylene dispersion its consistency or viscosity should be suitable for knife coating, or other conventional means for coating. The amount of thickener that is added to the polytetrafluoroethylene dispersion ranges from about 10 to about 60 percent by weight, ofa 3-5 percent aqueous solution of solids, per weight of polytetrafluoroethylene dispersion.

Organic solids, present in forming sizes etc.', when not given a chance to escape during the heat treatment, caramelize or turn the fabric an undesirable brown color and impair its nonflammability properties. Furthermore, if the fabric is exposed to a padding operation or is impregnated with the polytetrafluoroethylene dispersion there is a more complete coating of the internal fibers making up the body of the yarns thereby inducing caramelization, and on flexing, the fabric cracks and crazes. Cracking and crazing of the fabric finish adversely affects the purpose of the inventive concept, i.e. to improve abrasion resistance, fire resistance, hand, et al.

Any fusing of the polytetrafluoroethylene coating that occurs at the yarn cross-over points in a woven fabric, formed by the intersection of warp and fill yarns, during the heat treatment process may be eliminated by flexing or washing the fabric, without deleteriously affecting the fabric finish.

Having described the basic concepts of this invention and the theoretical considerations believed to be involved, illustrations will now be made of the practice of this invention.

EXAMPLE I [n the following example, the inventive treatment is carried out with fabrics woven ofglass yarns in which glass fibers making up these yarns have previously been sized with a conventional size composition in the forming operation to enable the fibers to be processed into strands, yarns, and fabrics and in which the original size has not been removed from the fabric by conventional means such as by washing or by burning off in response to heating the fabric in an oxidizing atmosphere.

A woven fabric 28 as pictured in FIG. 2 is produced by subjecting it to a knife coating operation with a thickened polytetrafluoroethylene aqueous dispersion 34 having a consistency suitable for knife coating, i.e. analogous to the thickness of whipped cream. Knife coating only one surface of the fabric increases flexibility and hand because there is no interlocking of the yarns Warp yarns 32 and fill yarns 30 are generally not bonded together such as by fusing, but any fusing that may occur at the cross-over points 36 of the warp and fill yarns may be subsequently eliminated by flexing the fabric, without deleteriously affecting the finish.

The treated fabric is placed in an oven at room temperature wherein gas burners are subsequently turned on in order to controllably reach a temperature ranging from 300-750 F. The controlled build-up of temperature is a necessary feature so that the volatiles will not be locked therein. The tempera ture should increase from room temperature to about 450 F. slowly (5-30 minutes) and held at the latter temperature for a period ranging from 1 to 15 hours. The volatile organic materials distil off without exothermic decomposition. Subsequently the temperature is slowly raised (over a 30 minute period) to about 650-750 F. and held for an additional 15-35 hours at which temperature sintering of the polytetrafluoroethylene and heat cleaning and weave setting of the fabric occurs.

The heat treated fabric is white in color, shows excellent strength properties, shows that it is self-extinguishing in an oxygen atmosphere up to 16.5 psia and furthermore possesses good flexibility and hand.

EXAMPLE 11 Glass yams previously treated with a protective sizing were coated with a thickened aqueous dispersion of polytetrafluoroethylene by means of a wiping die. Subsequently, the yarns were dried and woven into fabric. The treated fabric was exposed to a heat cycle wherein the temperature was slowly increased from room temperature to about 400-500 F. and held at the latter temperature fro about 5 hours. Subsequently the temperature was increased to about 750 F. and held there for an additional hours, in order to heat clean and weave set the fabric and to sinter the polytetrafluoroethylene thereon. Optionally, the fabric was treated with an aqueous solution of an organo silicon, such as XEC 4-l02, manufactured by the Dow-Corning Corporatron.

EXAMPLE Ill Glass yarns, treated with a protective sizing but not heat cleaned, were coated with a thickened aqueous dispersion of polytetrafluoroethylene by means of squeeze pads and subsequently dried very slowly at a temperature of about 350 F. for about 1 hour. The glass yarns with the dried coating thereon were then sintered at a temperature of about 65070 0 F. for about 12 hours in order to obtain a uniform film of polytetrafiuoroethylene thereon and to distill off unwanted volatiles from the yarns.

Thereafter the treated yarns were collected on a drum for shipping to weavers for fabrication into fabric. Some of the treated yarns were woven into fabric, and the fabric was optionally heat cleaned in order to achieve some weave setting of the yarns within the fabric.

When glass yarns are treated with a aqueous dispersion of polytetrafluoroethylene, the dispersion may be thickened or unthickened, depending upon the method of application to the glass fibers and the intended end-use of the treated fibers.

lclaim:

l. A method for improving abrasion resistance and flammability resistance of glass fabric, said glass fabric comprising glass fibers in the form of bundles, said bundles comprising a multiplicity of the glass fibers sized with a protective material, comprising the steps of applying a thickened dispersion of very fine particles of a polyfluorinated polymer onto the glass fabric, heating the glass fabric having the polyfluorinated polymer thereon by subjecting it to a first heat zone wherein the temperature is gradually increased from about 72 F. to about 450 F. so that volatile material from the sizing on' the glass fibers is not entrapped therein and maintaining the temperature at about 450 F. for about 12-18 hours, and subsequently subjecting the heated glass fabric to an additional heat zone ranging from about 640 F. to about 750 F. for approximately 15-35 hours, in order to sinter the polyfluorinated polymer and to weave set the glass fabric, applying an organosilicon material to the heat-treated glass fabric and drying the organosilicon on the glass fabric.

2. The method as claimed in claim 1 in which the polyfluorinated polymer is polytetrafluoroethylene.

3. The method as claimed in claim 1 in which the thickened dispersion is applied via knife coating to only one surface of the glass fabric.

4. A method for improving abrasion resistance and flammability resistance of glass fabric, said glass fabric comprising glass yarn, wherein said yarn comprises a multiplicity of bundles of glass fibers, which glass fibers are sized with a protective material, comprising the steps of applying a thickened dispersion of very fine particles of a polyfluorinated polymer onto the glass yarn, drying the yarn, weaving the yarn into fabric, heating the glass fabric by subjecting it to a first heat zone wherein the tern erature is gradually increased from about 72 F. to about 4 0 F. so that volatile material from the sizing on the glass fiber is allowed to escape therefrom maintaining the temperature at about 450 F. for about 12-18 hours, and subsequently subjecting the heated glass fabric to an additional heat zone ranging from about 650 F. to about 750 F. for approximately 15-35 hours in order to sinter the polyfluorinated polymer and to weave set the glass yarns in the fabric, applying a lubricant to the heat treated glass fabric and drying the lubricant on the glass fabric.

5. The method as claimed in claim 4 wherein the polyfluorinated polymer is polytetrafluoroethylene.

Claims (4)

1. 2. The method as claimed in claim 1 in which the polyfluorinated polymer is polytetrafluoroethylene.
2. 3. The method as claimed in claim 1 in which the thickened dispersion is applied via knife coating to only one surface of the glass fabric.
3. 4. A method for improving abrasion resistance and flammability resistance of glass fabric, said glass fabric comprising glass yarn, wherein said yarn comprises a multiplicity of bundles of glass fibers, which glass fibers are sized with a protective material, comprising the steps of applying a thickened dispersion of very fine particles of a polyfluorinated polymer onto the glass yarn, drying the yarn, weaving the yarn into fabric, heating the glass fabric by subjecting it to a first heat zone wherein the temperature is gradually increased from about 72* F. to about 450* F. so that volatile material from the sizing on the glass fiber is allowed to escape therefrom maintaining the temperature at about 450* F. for about 12-18 hours, and subsequently subjecting the heated glass fabric to an additional heat zone ranging from about 650* F. to about 750* F. for approximately 15-35 hours in order to sinter the polyfluorinated polymer and to weave set the glass yarns in the fabric, applying a lubricant to the heat-treated glass fabric and drying the lubricant on the glass fabric.
4. 5. The method as claimed in claim 4 wherein the polyfluorinated polymer is polytetrafluoroethylene.

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