Document JJbZbnG1a2aq6G6r7V8Z95ReX

FILE NAME: Phenolic Resins (PHR) DATE: 1985 Sept 3 DOC#: PHR062 DOCUMENT DESCRIPTION: US Patent - Asbestos Free Friction Element; from Borg-Warner File United States Patent m Wargin [li]. Patent Numben [45] Date of Patent: 4,539,240 Sep. 3,1985 [54] ASBESTOS FREE FRICTION ELEMENT [75] Inventor: Robert V. Wargin, Sao Paulo, Brazil [73] Assignee: Borg-Warner Corporation, Chicago, III. [21] Appi. No.: 676,144 [22] Filed: Nov. 29,1984 [51] I n t C U ...............................................B32B3/02 [52] U.S. a ......................................... 428/64; 57/238; 57/240; 192/107 M; 428/222; 428/292; 428/294; 428/377 [58] Field of Search................ 57/237, 238, 239, 240; 428/375, 377, 432, 379, 64, 292, 294; 192/107 M; 428/222 [56] References Cited U.S. PATENT DOCUMENTS 3,756,910 9/1973 Peters et al. 428/222 3,967,037 6/1976 Marzocchi et al............... 428/375 Primary Examiner--James J. Bell Attorney, Agent, or Firm--R. J. Schlott [57] ABSTRACT Friction elements, particularly those employed in clutch elements, which incorporate fiber strands im pregnated with a binder resin wound into a friction element and cured are markedly improved in wear characteristics and burst strength when the fiber strands are formed of a combination of glass, acrylic fiber and metallic filament. The fiber strands, twisted into a yam and plied to form a composite yam of opposing twist, contribute greatly to improved performance, particu larly better fade resistance and engagement response, together with high burst strength. 5 Claims, No Drawings 1 4, 539,240 2 ASBESTOS FREE FRICTION ELEMENT shown for example in U.S. Pat. Nos. 3,756,910 and 3,967,037. The glass fibers are said not only to improve BACKGROUND OF THE INVENTION burst stength and wear-resistance, particularly at ele vated temperatures, but also to serve as the active fric This invention relates to an improved composition 5 tion ingredient. Generally, such friction elements are for use in forming shaped friction elements such as fabricated by known techniques using a conventional, clutch facings and the like. More particularly, the in heat-curable organic binder to bond the glass fibers vention relates to friction elements incorporating a spe together in a mass. cific combination of fibers in the form of twisted and It has been stated that glass, as the active friction plied yarns which provides improved friction charac 10 ingredient of a friction element, is too "aggressive" in teristics and burst strengths. Such friction elements most commercial applications in comparison with con possess properties comparable with known friction ele ventional asbestos-containing friction facings. This ag ments yet, consonant with the increased demand to gressiveness is often manifested during simulated or protect the environment against exposure to airborne actual operating conditions as noise, vibration and/or substances that are deleterious to health, eliminates 15 erratic friction effects when the friction element is en asbestos as the conventional component of such friction gaged with a mating surface, none of which manifesta elements. tions can be tolerated by the highly-competitive auto The mineral asbestos has been long associated with motive industry. One method for overcoming this ag the manufacture of articles whose use requires that they gressiveness is disclosed in U.S. Pat. No. 4,418,115, withstand heat. Cloth woven from the fibrous substance 20 describing the use of a combination of glass fibers and was known, even in the 12th century, to remain incom acrylic or modacrylic fibers. bustible when thrown into fire. It is not surprising, A variety of other methods for improving or modify therefore, that asbestos has been the major component ing the friction and/or wear characteristics of asbestos- of friction elements such as those used m the brake and free friction materials are also known and further meth clutch assemblies of automotive vehicles where severe 25 ods for modifying the properties of asbestos-free fric operating temperatures and pressures must be with tion compositions are constantly being sought to widen stood. For more than 50 years, asbestos dominated as the principal active friction ingredient in friction mate the commercial applications for such materials. rials. SUMMARY OF THE INVENTION When the asbestos used m friction elements is in the 30 form of a yam, the yam is commonly provided with a A composition for use in forming an improved asbe core of fine metal wire to provide the tensile strength stos-free friction element is comprised of organic fiber, needed in handling the yam during fabrication of a metallic filaments and glass fiber reinforcing constitu friction element. Asbestos fibers are commonly rein ents, and a cross-linkable polymeric binder. The organic forced with a stronger fibrous substance such as cotton 35 fiber, metallic filaments and glass fiber are formed into in order to spin the asbestos into a yam. The introduc a plied yam before being impregnated with the binder tion of cotton or some other fiber into the asbestos was resin and winding into a clutch element. The binder, to improve its spinability or the tensile strength of the when cross-linked, forms a matrix for the glass fibers, yam, and thus the addition was to be tolerated rather metallic filaments and organic fibers in the friction ele than encouraged. The need for including a limited 40 ment. amount of other fibers such as cotton in asbestos yam intended for use in friction elements has become so well accepted that in recent years, such yams are commonly DETAILED DESCRIPTION OF THE INVENTION described only as "asbestos yam" without specifically The cross-linkable polymeric binder useful in the mentioning such other fibers. 45 practice of the invention is that usually employed in Since the passage of the Occupational Safety and friction elements and referred to as "binder" or "binder Health Act of 1970, the standards for occupational ex cement". posure to asbestos have become increasingly rigid to the The binder contains a cross-linkable or curable resin point where zero exposure may be required. The impo such as a phenolic resin. The term "phenolic resin", as sition of such standards was brought about by evidence 50 used herein, is intended to mean and include thermoset that exposure to asbestos may be carcinogenic to man. ting resins based on the condensation of an aldehyde It is thus a worthy (and perhaps in the future a manda and a phenol. The aldehydes useful in forming the phe tory) objective to eliminate asbestos as a component of nolic resins are, but not limited to, formaldehyde, acet friction materials. aldehyde, acrolein, and the like. The phenols useful in The use of glass fibers in friction products has been 55 forming the phenolic resin are those phenols capable of suggested. Some of the earlier of these suggestions in electrophilic aromatic substitution; for example, phenol, volved the use of glass fibers to reinforce asbestos-con resorcinol, catechol, aminophenol, and the like. Both taining friction elements, first as backing materials for the resole and novalac type phenolic aldehyde resins are conventionally produced friction elements and then as contemplated to be within the scope of the term "phe part of the friction facing itself. The stated purpose for 60 nolic resin". The resole resins are characterized by their the use of glass fibers was to increase the burst strength formation with base catalysis and the novalac resins are of the friction elements (Burst strength is an index of the characterized by their formation with acid catalysis. centrifugal forces which can be withstood by a friction Generally, the resole resins are more highly methylol- element without disintegrating. The test of burst ated than the novalacs. The choice between the resole strength is usually carried out at elevated temperatures). 65 and the novolac resin in a particular system is contin More recently, it has been suggested that glass fibers alone or together with metal wire or chips may be used to form friction elements containing no asbestos, as gent on the other materials present in the system. In the binder, phenol formadehyde novalac resins are among the most commonly used and preferred. 4, 539,240 3 4 In addition to the phenolic resin the binder cement ous materials. The glass fiber surface must be treated may and usually does contain an elastomer, such as a with a bridging composition to effectively bond (chemi natural or synthetic rubber. "Synthetic rubber" as used cally and/or physically) the glass to the matrix of the herein is intended to mean and include the hydrocarbon friction element. chain rubbers which are based upon a diene monomer. 5 During formation, the individual glass filaments are The diene monomers which are used in the preparation treated with a size which contains a coupling agent that of suitable synthetic rubbers include chloroprene, buta links the glass surface to the matrix. These coupling diene, isoprene, cyclopentadiene, dicyclopentadiene agents include both the silane coupling agents and the and the like. Other olefins capable of free radical, ani Werner complex type coupling agents. Typical silane onic, or cationic interpolymerization with the conju 10 coupling agents are the vinyl, alkyl, betachloropropyl, gated unsaturated monomer are useful in forming the phenyl, thio-alkyl, thio-alkaryl, methacrylate, epoxy, synthetic rubbers. These olefins include the acrylic and mercaptosilanes, their hydrolysis products, poly monomers such as methacrylic acid, acrylic acid, acry mers of their hydrolysis products and mixtures of any of lonitrile, methacrylonitrile, methyl methacrylate, meth these. Werner type coupling agents are those which ylacrylate, ethylacrylate, ethylmethacrylate and the 15 contain a trivalent nuclear atom such as chromium, like; mono-olefmic hydrocarbons such as ethylene, coordinated with an organic acid such as methacrylic propylene, styrene, alphamethylstyrene and the like; acid. Such agents are well-known in the art and are and other functional monounsaturated monomers such commercially available. Glass filaments are also widely as vinyl pyridine, vinyl pyrrolidone and the like func available commercially having been sized during the tional vinylic monomers. Also within the scope of the 20 manufacture, and these filaments are suitable for use in term synthetic rubber are the non-hydrocarbon chain the practice of this invention. rubbers such as silicone rubbers. In selecting an elasto The physical form of the glass fibers may vary ac mer for use in the binder composition, care should be taken to ensure that the chemical composition of the cording to the particular method of fabricating the fric tion element. Thus, fiber glass in the form of strand, particular elastomer does not interfere with the func 25 yam, roving or the like may be used in forming the tioning or lifetime of the friction element and apparatii associated therewith. friction element. Preferably, in the fabrication of clutch In addition to the polymeric constituents of the facings, the glass fibers are in continuous form and sized binder, other known materials for forming binders may to improve the burst strength of the friction element be used. For example, vulcanizing agents may be added 30 while, at the same time, permitting convenient friction to the binder to cross-link the unsaturated rubbers. Ex element fabrication techniques. emplary of such vulcanizing agents are sulphur, zinc The organic fibers useful in the practice of the inven oxide (for vulcanizing neoprene), peroxides, dinitroso- tion are those generally described as acrylic fibers, in benzene and the like. Vulcanization accelerators may be cluding modacrylic fibers. These fibers are widely used such as zinc oxide, stearic acid and the like. Poly 35 available commercially in the form of staple fiber and amines may also be added to the binder to promote the yam. The metallic filament may be formed of copper or cross-linking and interraction of the phenolic resin and copper alloy such as brass or bronze. the elastomer. Typical polyamines are hexamethylene The proportion of acrylic fiber, glass fiber and metal tetraamine, diethylene triamine, tetraethylene pent- lic filament employed and their combination into a amine, diphenylguanidine and the like. 40 twisted yam are important to achieving good frictional Fillers may be added to the binder to modify the final properties and burst strength. In the practice of this physical properties and reduce the expense of the fric invention the fibers are formed into a twisted composite tion element. Common fillers including carbon black, yam. For example, the fiber glass component may first clay, graphite, lead sulphate, aluminum silicate, wollas- be formed into a yam having a left-handed or "z" twist. tomte rottenstone, mica, lime, gypsum and the like may 45 The z-twisted glass yam may then be combined with be used. A wide variety of commercial phenolic resins the requisite acrylic yam and metallic filament and plied and phenolic binder compositions are readily available to form a yam having a right-handed or "s" twist. It commercially. Such resins may be employed as ob will be apparent that the first yam may have an "s" tained or be further modified by addition of one or more twist and the final yam a "z" twist, the essential feature of the aforementioned materials to provide binder resins 50 being that the final structure is formed by plying the suitable for use in the practice of this invention. twisted yarns in the opposite helical direction from the Typically, the binder composition with all attendant helical twist of the twisted yams. A variety of alterna ingredients is dissolved and/or dispersed in a solvent for tives exist, including for example combining the fiber the soluble polymeric constituents. Sufficient solvent is glass and acrylic components into a z-twisted yam, provided to obtain the proper binder solution/disper- 55 followed by plying a plurality of these composite yams sion viscosity for combination with the glass and the with .the metallic filament into an s-twisted cabled yarn, organic fiber to obtain the proper ratio of binder to or z-twisting fiberglass, acrylic and copper wire to reinforcing constituents. The infusible organic fibers gether to form a yam, then s-twisting two or more of and the glass fibers taken together are preferably pres these yarns to form a plied or cabled yarn. The propor ent in the range of 20 to 75 percent by weight based on 60 tion of metallic filament, acrylic yam and glass fiber in the total weight of the final friction element and more the cabled composite yam or cord will vary from about preferably in the range of 30 to 65 percent by weight. If 30 to about 70 wt. % glass fiber, from about 15 to about the level of organic, metallic and glass components is 25 wt. % acrylic yam and from about 45 to about 15 wt. too low, inadequate reinforcement of the friction ele % metallic filament. ment will result. If the level of fibers is too high, exces 65 In addition to improving the performance of friction sive wear will be demonstrated by the friction element. elements, many combinations of glass and acrylic fibers The glass fibers useful in the practice of the invention and metallic filament reduce the weight of the friction are those typically utilized for reinforcing cured resin element, improve responsiveness during engagement, 4, 539,240 - 5 increase fade resistance at high temperatures, and pro vide high burst strength. 6 EXAMPLE 2 Friction elements embodying the present invention may be fabricated in accordance with procedures Two fiberglass rovings formed of H glass (type E) filament and having a weight of tex 200 were combined known to those skilled in the art. In general, the cabled 5 with 1 acrylic yarn and 1 copper filament (approxi yarns are impregnated with the formulated cross-linka mately 8 mil) and given a left hand z-twist of approxi ble polymeric binder solution to form an imprgnant. mately 70 turns per meter. Two of these z-twisted yams The binder solution should be of sufficiently low viscos were then combined and plied into a composite cord ity to wet the fibers. The imprgnant is dried by evapo having a right-handed or s-twist of about 70 turns per rating the binder solvent to form a "B" stage. The B 10 meter. stage composition is molded under heat and pressure to cross-link the cross-linkable polymeric binder. The molded article may then be machined into its final form. Impregnating and Clutch Plate Preparation EXAMPLE 3 eleOmneentcso, manmdoenslpyecuiaselldy tcelcuhtcnhiqfuaecinfogrs,fiosrtmoicnognsfrtircutciot na 15 imFproeugrncaotemdpwosiitthe acocrodnsvpernetpioanreadl pasheinnoElxicambipnldee1r wreesrine preform. A "preform" is a loosely structured article in solution comprising 25.7 wt. % phenolic resin, 24.9% the B stage, composed of woven or wound reinforcing rubber and rubber accelerators, 15.5 wt. % sulfur, 5.5 constituents impregnated with a cross-linkable binder, wt. % carbon and 28.4 wt. % fillers. which roughly resembles the configuration of the final 20 A tape was formed by gathering the four composite friction element. The preform is molded under heat and cords together into a flat parallel configuration, passing pressure to give it a final shape and cross-link the the cords through a dip tank containing the binder resin, binder. then through a drying oven maintained at 80 C. The One particular method for constructing a preform resin pick-up was approximately 38.5 wt. %, based on involves the formation of a tape composed of one or 25 tporteaplarweedigihnt thoef tchoenvreesnitnio-cnoaaltemdantanpeer. bPyrewfoinrmdisngwethree more continuous strands of cabled yam arranged in parallel relationship and impregnated with binder and tape in an undulating fashion onto a revolving mandrel. The preforms were then molded in a clutch facing mold cured to a B stage. The continuous cabled yams of at 5000 psi and 160 C. for 31 mins., and cured at fibrous material are passed through a dip tank contain 180260 C. for 7J hours to provide clutch plates for ing the cross-linkable organic binder solution which is 30 testing. adjusted to a viscosity sufficient to provide for adequate impregnation of the fibrous components and pickup of EXAMPLE 4 the binder. The proper binder pickup is adjusted by a Four composite cords of Example 2 are similarly die, and the imprgnant is passed through a drying impregnated, formed into a tape, wound into a preform, tower maintained at a temperature sufficient to evapo 35 molded and cured as in Example 3 to provide clutch rate the solvent of the binder solution to form a B stage plates for testing. The B stage imprgnant is stored in drums for further processing. Control Examples A -E In fabricating a preform, one or more B stage impreg A variety of cabled yarns, prepared by substantially nated tapes are wound in an undulating manner to a 40 the same method employed in Example 1, were formed revolving mandrel using methods conventional in the into clutch facings using the procedures of Example 3. clutch-facing art, to produce a preform of the desired The cabled yams of these control examples, together size, shape and weight The preform is subjected to heat with clutch performance test data, are summarized in acnodrdipnrgestsourme ettohopdrsodwueclle kanocwurnedinftrhicetiaornt. element ac 45 TaTbhleeIc. lutch plates were assembled into clutch assem A particular advantage of the present invention is blies for dynamometer testing to determine friction and that it provides a composition for preparing friction wear characteristics. The fade characteristics were elements by using existing commercial practices and measured in a standard Krauss testing machine, and equipment. 50 burst strength were determined in a centrifugal burst The following is a specific embodiment of the present machine to establish the rotational speed at burst for elevated (500 F.) temperatures. These test data are invention; however, the invention is not to be construed summarized in Table I. as being limited to this embodiment for there are numer ous possible variations and modifications. TABLE I Preparation of Composite Cord 55 E x No Cord Comp Ave W ear Fade *C. M ax *C. Burst rpm EXAMPLE 1 3 4 gV 2A c/2 cu 4 4 gl/2A c/2 cu Fiberglass roving formed of H glass (type E) filament A 6 g !/2 A c /2 cu 0.0130 410 460 0.012 350 450 0.021 300 350 10,688 13,292 9.000 having a silone coupling agent and having a weight of 60 B C 4 g]/2A c/l cu 4 gl/2C t/2 cu 0.0186 310 350 -- 450 510 9,600 11,070 tex 200 (200 g/1000 meters) was given a left-hand or D 6 g !/2 R a y o n /2 cu 0.0204 310 340 9,250 z-twist of approximately 70 turns per meter. Four z- E 4 g]/2 R ayon/2 cu 0.015 270 330 9,565 twisted rovings were then combined with two acrylic Notes: yarns and two copper filaments, each of about 8 mil Cord Comp: Composition o f cabled yarn; gl = glass filament, Ac = acrylic yam, ct diameter, and plied with a right-handed or s-twist at 65 = cotton yarn, cu --copper filament Fade, Fade Max -- Krauss data, fourth cycle Burst = rpm a t burst, 232 mm diameter clutch facings. approximately 70 turns per meter to provide a compos ite cord comprising 47.3 wt. % fiberglass, 17.5 wt. % It will be apparent from these data that the burst acrylic yarn and 35.2 wt. % copper filament strengths of facings are substantial when cabled com- 4, 539,240 7 8 posite yams are employed in their manufacture accord variety of friction elements without departing from the ing to the practice of this invention. The form of yam spirit and scope of the invention. fabrication contributes further to the burst strength, as I claim: . shown by a comparison of Examples 3 and 4. It will also 1. In a friction element adapted for use in a clutch, be seen that a reduction in the copper content, Control 5 said friction element comprising fiber strands impreg B, or an increase in glass content, Control A affects fade nated with a binder, resin composition and disposed in resistance and wear properties. When assembled into a clutch, installed into a Ford Escort automobile and run on a test track, clutch plates prepared substantially as in an undulating fashion and then cured to form a disc shaped facing, the improvement wherein said fiber strands are in the form of a plied yarn comprising from Example 3 exhibited substantially less aggressiveness as 10 about 30 to about 70 wt. % glass fiber, from about 15 to determined by pressure plate wear, compared with about 25 wt. % acrylic fiber and from about 15 to about clutch plates prepared from glass fiber and rayon yam. 45 wt. % metallic filament. The invention will thus be seen to be an improved 2. In the friction element of claim 1, the improvement friction element which includes a resin binder and a wherein said plied yarn comprises a plurality of twisted plurality of fiber strands wherein the fiber strands are in 15 yarns, said twisted yams having a helical twist of From the form of a plied yam comprising from 30 to 70 wt. % 50 to 120 turns per meter and said plied yarn having a glass fiber, from 15 to 25 wt. % acrylic fiber and from helical twist of from 50 to 120 turns per meter opposite 15 to 45 wt. % metallic filament Preferably, the plied in direction to the twist direction of the twisted yams. yam is formed from a plurality of twisted yams, each 3. In the friction element of claim 1, the improvement having a helical twist of from 50 to 120 turns per meter 20 wherein said plied yam comprises at least two twisted in the same direction, the twisted yams being formed yams having a helical twist of from 50 to 120 turns per into a plied yam having a helical twist o f from 50 to 120 meter and at least one copper wire, said plied yam turns per meter opposite in direction to the twist direc having a helical twist of from 50 to 120 turns per meter tion o f the twisted yams. The plied yam may be made opposite in direction to the twist direction of the twisted up entirely of twisted yams formed of metallic, acrylic 25 yams. and glass components, or of a combination of twisted 4. A plied yam adapted for use in the manufacture of yams and metallic and/or acrylic fibers. The friction friction elements, said plied yam comprising from about elements of this invention exhibit markedly improved 30 to about 70 wt. % glass fiber, from about 15 to about strength, fade resistance and wear characteristics over 25 wt. % acrylic fiber and from about 15 to about 45 wt. similar structures formed from other fiber combina- 30 % metallic filament, wherein said plied yam having a tions. These skilled in the art will recognize that the helical twist of from 50 to 120 turns peT meter and com non-limiting examples are provided by way of illustra prising a plurality of twisted yams having a helical twist tion and it will be apparent that many further variations of from 50 to 120 turns per meter opposite in direction may be made, particularly in the use of fillers, friction to the twist direction of the plied yarn. modifying additives, alternative resin binder composi- 35 5. The plied yam of claim 4 comprising at least two tions and the like, and that the compositions of this invention may be further adapted for use in producing a twisted yams and at least one copper wire. ***** 40 45 50 55 60 65