Document RaeZvbBGgo0XXROE1LXdxNxOa

fl6Qf Patented Sept 30,1947 2,428,299 UNITED STATES PATENT OFFICE 2,428,299 . FRICTION ELEMENTS BONDED WITH A RE ACTION PRODUCT OF POLYMERIZED LIN SEED OIL, SULFUR AND PHENOL-ALDE HYDE RESIN MIXED WITH A BUTADIENEACRYLONITRILE COPOLYMER Ray E. Spokes, Ann Arbor, and Emil C. Keller, Detroit, Mich., assignors to American Brake Shoe Company, Wilmington, Del., a corporation of Delaware Original application November 16,1942, Serial No. 465,734. Divided and this application February 27,1947, Serial No. 731,274 - 8 Claims. (CL 260--19) 12 This invention relates to friction elements and ments containing finely divided dispersed and to making the same and more particularly, the dust-like particles heretofore employed may re present Invention relates to friction elements of sult from the heat decomposition of such or the type which are employed in the brakes of ganic bonding and other agents and the conse- automotive vehicles, including trucks, buses, and 5 quent formation of a high percentage of benzol passenger cars, as well as for clutch facings and - extractable material, and accompanying forma the like. tion of a glazed surface, or may be enhanced by This application is a division of our copending carbonization of such organic bonding agents and application. Serial No. 465,734, filed November other materials or by both of such causes. It 16,1942, on "Friction dements." 10 may be said, however, that such loss of friction Friction elements of the aforesaid character, stability results largely from the baking on the as now made, are composed, in general, of fric friction surface of the products resulting from tion material, such, for example, as asbestos, to the heat decomposition of the organic bonding gether with an organic binder and other organic agent or agents and other materials employed or mineral friction-controlling or imparting 15 in such friction elements. ` agents, together with other materials which may be employed for imparting specific properties Moreover, the glazed film thus formed on the friction surface of friction elements bonded with or characteristics to such friction elements, such, for example, as greater heat resistance, greater organic bonding agents, and which friction ele ments may contain finely divided and dispersed coefficient of friction, and the like. Friction elements which are intended for heavy duty use upon heavy automotive trucks, buses and the like are commonly subjected to severe service conditions, that is to say, they are sub jected in use to repeated and often prolonged braking operations which develop high tempera tures in such friction elements, such tempera tures frequently approaching 1000* F. on the friction surface of the friction elements, and pro gressively lower temperatures inwardly of the 20 dust-like particles composed of the materials re ferred to hereinbefore, cannot readily be removed and is not self-removing since it decreases subse quent friction and heat formation so that a fric tion element with such a surface not only loses 25 stability of friction characteristics but tends to retain the undesirable glazed film which causes this instability. Hence/ it will be seen that a fric tion element so affected cannot recover desired 30 frictional stability through normal use of the fric friction surfaces thereof. Such high tempera tion element. Moreover, this is also true when tures, especially when occurring or, repeated fre the organic bonding agents or the finely divided quently, tend to depolymerize or .'otherwise de friction-controlling organic particles dispersed in compose organic bonding materials, as well as sUch/Diction elements undergo carbonization due other organic bonding materials which may be in 35 to tne heat of friction Incidental to the use of corporated in friction elements, including finely friction elements embodying such materials. divided granulated or so-called dispersed discrete These conditions are commonly known in the art particles of vulcanized natural soft scrap rubber, as "fade" and "recovery." finely divided particles of cashew nut shell liquid Furthermore,' the heat decomposition of or- polymer, or finely divided particles of heat poly 40 ganlc bonding and friction-controlling agents in merized drying oils, which have been employed friction elements is attended by a softening there in friction elements for the purpose of impart of and results in loss of volatile matter which ing desirable characteristics to such friction ele causes the structure of the friction element to ments, including greater or more stable coeffi become Impaired. When the structure is so im- cient of friction, improved wear, and the like. 45 paired, it has been observed that there is an in Accordingly, there is a consequent tendency of crease in friction and that the friction element such friction elements to exhibit,loss of stability wears away at a comparatively rapid rate, which of friction characteristics due to heat decomposi obviously is undesirable inasmuch as it mate tion or due to carbonization of the organic bond rially shortens the life of the element. ing and other agents therein and due/ to the re SO Moreover, when the glazed condition, which sulting presence on the friction surface or within is referred to hereinbefore, occurs, it is neces such friction elements of depolymerized and oth sary to apply much greater braking forces than erwise liquefied products of heat decomposition normally employed, and under such, conditions, of such organic bonding and other materials. and with a softened bond or friction-controlling The loss of stability, as aforesaid, in friction ele- 55 agent, greater shearing forces are exerted within ABEX 024.025 SCF-ABEX-0425 34 the structure of the friction element, likewise re practice of the present Invention the hardness sulting In rapid wear. ' and heat-resistance of the finely divided or dust Hence, It will be seen that It Is important and like friction-stabilizing particles may be easily desirable that the bonding and friction-control and readily controlled and varied by employing in ling agents employed In friction elements, and 6 the making of said particles material having a especially In heavy duty friction elements which selected and predetermined composition. Stated are subjected to the severe service conditions and otherwise, in the practice of the present inven high temperatures referred to above, be able to tion there Is employed in making said finely di withstand such severe usage and high tempera vided friction-stabilizing particles a copolymer tures without undergoing excessive heat decom 10 material, which will be referred to hereinafter, position or carbonization of such organic braid and the hardness and heat resistance and related ing or friction-controlling agents employed there properties of said finely divided or dust-like par in and resulting loss of stable friction charac ticles may be varied and controlled by employing teristics under varying operating conditions. in the making thereof a copolymer material which Various attempts have heretofore been made to 15 contains a selected and predetermined percentage overcome the foregoing and other difficulties of one component thereof inasmuch as the hard which have been experienced in the use of fric ness and heat resistance and related properties tion elements embodying organic bonding and of said finely divided or dust-like particles vary friction-controlling agents and among such at directly, that is. increase or decrease, in direct tempts have been the use of the various materials 20 relationship to tbe percentage of said compo referred to above, namely, vulcanized soft scrap nent in said copolymer material. rubber, cashew nut shell liquid polymer, heat Other materials have also been employed in polymerized vegetable drying oils, and sulphur friction elements in an endeavor to control and ized oils, in the form of finely divided granules stabilize the coefficient of friction and other fric- or so-called dispersed discrete particles, for con 25 tion characteristics thereof and to prevent de trolling the friction characteristics of such fric crease in coefficient of friction under varying and tion elements or for preventing or inhibiting or continuous service conditions, and such materials compensating for decrease In the coefficient of have Included small amounts of harsh abrasive friction in such friction elements. Incidental to materials. However, such harsh abrasive mate- Increasing temperatures, and so as to endeavor to 55 rials have not been entirely satisfactory Inasmuch maintain a substantially constant coefficient of as such harsh abrasive materials sometimes exert friction under continuous service conditions. an undesirable scoring effect upon brake drums While such finely divided friction controlling and the like with which friction elements are granules or so-called dispersed discrete particles, used. Moreover, there Is a tendency for such composed of the materials referred to hereinbe 55 abrasive particles to pulverize upon the surface fore, have, in certain Instances, Imparted desira of friction elements embodying the same with ble characteristics to friction elements in which consequent undesirable Increase in abrasiveness such finely divided particles have been incorpo and greater tendency toward scoring of brake rated, we have found that such materials, are not drums and the like with which such friction ele- always or entirely satisfactory and have bad ob 40 ments are used. jectionable properties and undesirable charac Accordingly, an object of the present invention teristics including those hereinafter indicated. is to afford a new and Improved friction element, Thus, for example, we have found that such and method of making the same, which is sub finely divided particles undergo either substan stantially free from the foregoing and other dls- tial and excessive heat decomposition or disinte 45 advantages and objectionable features which have gration and softening, or excessive carbonization, been experienced heretofore in the use of fric as a result of the high temperatures developed tion elements containing organic bonding agents in the use of friction elements under severe service and embodying finely divided dust-llke particles conditions and for prolonged periods of time, as or so-called dispersed discrete particles composed will be referred to more specifically hereinafter, 50 essentially of tbe various materials hereinbefore with consequent decrease in coefficient of fric referred to and which have been employed here tion and loss of other friction-controlling char tofore as friction-controlling or friction-stabi acteristics in friction elements employing snch lizing agents. materials. A further object of the invention is to afford a Moreover, the only way in which it is possible 55 new and improved friction element and method to control and vary the hardness and related of making the same which imparts substantially properties and characteristics of finely divided uniform friction characteristics to such friction particles of vulcanized'soft scrap natural rubber, elements under continuous and varying and se mid tbe properties Imparted thereby to friction vere service conditions and prevents substantial elements In which such particles may be employed 50 loss of or decrease In tbe coefficient of friction as a friction-controlling or friction-stabilizing in therein, due to break-down of the bonding agent gredient. is by controlling the degree or extent to or friction-controlling agent employed therein by which such particles of soft scrap rubber are vul reason of the heat of friction Incidental to the canized. Farther, the only way in which it is severe usage of such friction elements, thereby possible to control the hardness of finely divided 45 maintaining the coefficient of friction in such particles of cashew nut shell liquid polymer, and friction elements substantially constant, while, at the properties and characteristics Imparted the same time, being substantially free from or thereby to friction elements in which such parti highly resistant to carbonization at the high cles may be employed as a friction-controlling or temperatures to which such friction elements are friction-stabilizing Ingredient, is by the use of a TO subjected in use. resin of the phenolic-aldehyde type in conjunc Another object of the present invention, an tion with such finely divided particles of cashew cillary to the foregoing objects, is to afford a new nut shell liquid polymer particles to render said and Improved friction element which is adapted particles harder and more heat-resistant. How for heavy duty use upon heavy trucks, buses and ever, as will be pointed out hereinafter. In the 11 the like, as well as for use upon passenger cars ,8 488,888 5 and light trucks, particularly when they may fie In the form of finely divided dust-llke particles or operated under severe conditions, and which em so-called dispersed discrete particles composed of bodies as a friction-controlling agent finely di the materials heretofore employed for this pur vided dust-like particles which resist heat decom pose, while at the same time being free from the position and heat depolymerization and excessive 6 aforesaid and other objectionable characteristics softening and loss of friction stability resulting of harsh abrasive materials. from such decomposition, and which are also More speclficalhCwe have ascertained that fric highly resistant to carbonization at the high tem tion elements embodying as a friction-controllings' peratures to which such friction elements are sub or friction-stabilizing ingredient finely divided jected in use. 10 dust-llke particles composed essentially of one An additional object of the present invention or more vulcanlzable synthetic rubber elasto is to afford a new and Improved friction element, prenes or so-called synthetic rubbers of the buta and method of making the same, employing finely diene-acrylonitrile copolymer type, compounded divided particles of a synthetic rubber-like elasto- with a relatively low sulphur content, are highly prene of the butadiene-acrylonitrile copolymer 15 resistant to heatfiecompositlon and heat depolytype as a friction-controlling or friction-stabiliz merizatlon and.carbonization even at the high ing ingredient therein and in which the desired temperatures to which heavy duty friction ele degree of hardness and heat resistance and re ments are subjected in use upon heavy duly lated properties and characteristics which It may trucks and buses and the like. Moreover, we be desired to Impart to said finely divided par ticles, and( to a friction element containing said 20 have ascertained that friction elements embody ing the finely divided dust-llke materials which particles, may be readily controlled and varied by have been found useful and advantageous as fric employing In the making of said finely divided tion-controlling agents in the practice of tire particles a butadiene-acrylonitrile copolymer con present invention do not tend to form a relatively taining a selected and predetermined percentage of acrylonitrile as a component of the copolymer 25 high percentage of benzol-extractable material upon being subjected to relatively high braking material. temperatures and hence do not tend to exhibit A further object of the present Invention, an cillary to the immediately preceding object, is to the consequent loss of friction stability which is exhibited by friction elements embodying the afford a new and improved friction element, and 30 finely divided dust-llke materials which have been method of making the same, containing as a employed heretofore. as friction-controlling friction-controlling or friction-stabilizing ingre agents in friction elements, but retain substan dient finely divided particles of a synthetic rub tially their original friction stability and other ber-like elastoprene of the butadiene-acrylonitrile desirable characteristics. '" copolymer type and which particles possess im 35 Hence, it will be seen that the present inven proved properties and characteristics as com tion is primarily concerned with friction ele pared to finely divided particles of vulcanized ments containing as a friction-controlling in soft scrap rubber including markedly superior gredient finely divided particles or dust-like ma heat resistance and the additional desirable ad terials composed essentially of one or more vul vantage which resides in the fact that the degree 40 canlzable synthetic vulcanized rubbery butadi of such increased or superior heat resistance pos ene-acrylonitrile copolymer elastoprenes, com sessed by the new friction-stabilizing particles pounded with a low sulphur content, and which may be predetermined and controlled and varied may be subjected to severe service conditions by employing in the making of said new friction- without exhibiting objectionable heat decompo stabilizing particles a butadiene-acrylonitrile co 45 sition or heat depolymerization and softening or polymer containing a selected and predetermined carbonization resulting from or incidental to the percentage of acrylonitrile, thus enabling friction high temperatures and severe service conditions elements containing said friction-stabilizing par to which friction elements are frequently sub ticles to be readily adapted or adjusted to par jected in use, and as may occur In the use of ticular and varying requirements and uses. 50 friction elements embodying as a friction-con Other and further objects of the present inven trolling ingredient therein the finely divided par tion will be apparent from the following descrip ticles or dust-like materials heretofore employed tion and claims and from the accompanying for this purpose while being, at the same time, drawings. - substantially free from the objectionable char In the drawings,' 55 acteristics of the harsh finely divided abrasive Figs. 1 and 2 are graphs illustrating certain materials which have been employed heretofore properties or characteristics of finely divided as friction-controlling Ingredients in friction ele particles composed of materials heretofore em ments. - ' ployed as friction-controlling ingredients In fric The class of finely divided particles or dust-llke tion elements and illustrating comparable prop erties or characteristics of the friction-controlling 60 materials which may be employed as friction controlling or friction-stabilizing agents In fric materials which are employed In the practice of tion elements, in the practice of the present In the present invention. vention, is that class of vulcanlzable synthetic We have found, among other things, that rubbery elastoprenes or so-called synthetic rub friction elements embodying as friction-control 65 bers which are essentially copolymers of the bu ling or friction-stabilizing agents finely divided tadiene-acrylonitrile type and which are exem dust-like materials or so-called dispersed discrete plified by, but not limited to, the disclosure of particles composed essentially of certain vulcan- United States Letters Patent No. 1,973,000, grant izable synthetic rubbery elastoprenes or so-called ed September 11,1934. synthetic rubbers, which are referred to herein 70 We have found that such materials have de after, overcome or are substantially free from the sirable properties as friction-controlling agents foregoing and other difficulties and objectionable In friction elements in the practice of the pres features which have been experienced heretofore ent Invention including resistance to heat decom in the use of friction elements embodying fric position and heat depolymerization and soften tion-controlling or friction-stabilizing materials 76 ing, as well as resistance to carbonization, under ,3 498,990 8 the high temperatures experienced In the severe usage of such friction elements, while still pos which are referred to above and which I have found to be useful as friction-controlling or fric sessing a substantial degree or amount of resili tion-stabilizing agents in friction elements, in the ency and even after prolonged and severe usage practice of the present invention, may be lllus- and exposure to the high temperatures inciden 6 trated as follows (J. L E. C., vol. 34, No. 2, pp. tal thereto. Moreover, resiliency in such finely 245-251, and News edition. Am. Chem. Soc., 19, divided and dispersed particles is of particular 750 (1941), and revision, Chem. and Eng. News, significance, in that it enables the finely divided vol. 20, No. 8, April 25, 1942, pp. 536, 537, 538): particles which are employed as friction-con H H H H H H trolling agents in friction elements to compen sate for such loss of friction stability and de 10 0=0--C=C HH + H0=0T - ON [ IH H H H H H --C-C----- C--C=C--C- HI H H ON crease in coefficient of friction which might otherwise occur if it were not for the resiliency Butadiene -f acrylonitrile or vinyl cyanide > which is Inherent In the finely divided or dust particles composed essentially of one or more _15_ ""PBeurnbatmNa"n" Product: synthetic vulcanizable rubbery elastoprenes of the butadiene-acrylonitrile copolymer type which are "HycarOR"or ... "Hycar Nincne B" (Goodrich) "Chemlgizm'* (MX" or *T') (Goodyear) employed as friction controlling agents In fric f "Blanco1' (Standard OU ol New Jersey) tion elements In the practice of the present In It will be understood In connection with the vention; 20 general type of synthesis or copolymerization il While a certain degree or amount of resiliency lustrated above that certain of the materials Is inherent in the finely divided particles of soft which are employed in or are necessary in such scrap rubber, and in the finely divided particles syntheses. Including the emulsifying, wetting, of heat polymerized drying oils and, to a some modifying and catalytic agents which are em- what greater degree In the particles of cashew 25 pioyed-in the synthesis of the above mentioned nut shell liquid polymer, which have been em butadiene-acrylonitrile copolymer type synthetic ployed heretofore in friction .elements as friction rubber-like elastoprenes, are trade secrets, al controlling agents, such resiliency as is possessed though all of these materials are known to be by these materials Is present therein only In the essentially copolymers of the butadiene-acrylo- earlier stages of the use of such materials In fric 30 nitrile type. tion elements and the resiliency of such materials All of the synthetic elastoprenes or so-called is substantially lost or decreased either by heat synthetic rubbers referred to above, and which decomposition or carbonization of such materials are known to be useful as friction-controlling or Incidental to the use thereof as friction-control friction-stabilizing materials, in the practice of ling agents in friction elements, as referred to 35 the present Invention, are currently available hereinbefore. upon the market in commercial quantities, un Other types of synthetic elastoprenes or so- der the trade names referred to. called synthetic rubbers are, of course, known, It will be seen, therefore, from the foregoing and among these are those of the butadiene-sty description, and from the disclosures referred rene copolymer type which are exemplified by 40 to therein, that the present invention is primarily the disclosure of United States Letters Patent concerned with friction elements containing or No. 1,938,731, granted December 12,1933, and the ganic bonding agents and which friction elements non-vulcanizable chloro-butadiene or chloro- contain as an ingredient thereof a friction-con prene type of polymers, which have been referred trolling agent in the form of dust-like materials to above, and which are known as "Neoprene," 45 or so-called finely divided dispersed discrete par "Duprene," and the like. ticles composed essentially of one or more vul We have found, however, that finely divided or canizable synthetic rubber-like elastoprenes or dust-like particles composed essentially of syn so-called synthetic rubbers of the character ob thetic elastoprenes of the butadiene-styrene co tained by copolymerization (under conditions and polymer type, as well as those of the chloro-buta 60 in the presence of other materials, such, for ex diene type, do not possess or impart to friction ample, as those which are disclosed in Patent No. elements the desirable characteristics, including 1,973,000) of an unsaturated dlolefinic or butadi friction stability, and resistance to heat decom ene hydrocarbon of the type position and carbonization, which are imparted to friction elements by finely divided particles 55 composed essentially of synthetic elastoprenes of HH c=c--c=i the butadiene-acrylonitrile copolymer type com H1 pounded with a relatively low sulphur content, as in the practice of the present invention. The where * represents either hydrogen or an alkyl present invention is, therefore, primarily con Q0 group, and a compound (an acrylonitrile) of the cerned with friction elements embodying as fric type tion-controlling or friction-stabilizing agents therein finely divided dust-like materials or so- called dispersed discrete particles composed es sentially of vulcanizable synthetic rubber-like 65 1=0--C=N [R elastoprenes or so-called synthetic rubbers of the butadiene-acrylonitrile copolymer type, com where R represents either hydrogen, as in acrylic add nitrile, per se, or an alky] group, as in metha- pounded with preferably from about five percent crylic acid nitrile, to form a synthetic rubber-like to about ten percent, by weight, of sulphur, and high molecular weight elastoprene of the butadi- to which more specific reference will now be 70 ene-acrylonitrile copolymer type, followed by made. compounding the product thus obtained with a The relationship of the monomer components relatively low percentage of sulphur and which and the general type of synthesis of the copolymer is preferably not substantially less than five per nuclei of the group of class of vulcanizable syn cent nor substantially more than ten percent, thetic elastoprenes or so-called synthetic rubbers 75 by weight, of the copolymer, and then finely ,3 428,389 9 10 dividing the sulphurized product thus obtained The compositions Illustrated in the foregoing Into relatively small particles or granules which Examples Nos. 1 and 2 may be converted into may be dispersed with substantial uniformity heavy duty type friction elements by intimately throughout friction elements' of the character mixing the ingredients thereof and forming the herein contemplated. 5 resulting mixture into friction element shapes A suitable formula which may be followed in and then effecting the cure of the ,organlc bond making friction elements for normal heavy duty service, in the practice of the present invention, is the following, in which all parts indicated are ing agent, as by the Application of heat alone, or by the application of' both heat and pressure. Thus, in the manufacture of friction elements by weight: 10 employing, the composition which is illustrated , Example No. 1 \ in the foregoing Example No. 2, a temperature of from about 300 F. to about 325 F., and the Parts by weight application of a pressure of about two thousand Beat polymerized vegetable drying oil (lin pounds per square inch, for about four hours, seed) 8.4 Oil modified phenol-formaldehyde resin___ 8.4 15 are suitable, it being understood that the pre ferred or optimum temperature, pressure and ap Lead formate- 9.0 plication time stated above may be varied some Potassium dlchromate 1.0 what depending in part upon the particular com Vulcanized butadiene-acrylonitrile copoly position and the specific temperature, pressure mer synthetic rubber-like elastoprene (finely divided dust-like particles, vulcan- 20 and application time employed. However, in the manufacture of friction elements employing either lzed with ten percent sulphur, by weight) -- 4.0 the composition which is illustrated in the fore Pyrobitumlnous material (soft coal, finely going Example No. 1, or the composition which divided) ------------------------------------------------ 15.0 is illustrated in the foregoing Example No. 3, the Asbestos fiber _65.0 Sulphur--------------------------------------------------- 2.5 25 application of heat alone is sufficient to effect the cure of the bond and a typical example of A suitable formula which may be followed, in suitable progressively Increasing temperatures the practice of the present invention, in making and application times which may be employed Is friction elements which may be subjected to ex ceptionally severe heavy duty service, is the fol lowing, in which all parts indicated are by weight: 30 as follows: Three hours at 225 F.; three hours at 275 F.; three hours at 300 F.; and three hours at 315 F. As pointed out hereinbefore, the hardness and Example No. 2 heat resistance and related properties and char Parts by weight Crude (natural) rubber--------------------------- 5.76 Reclaimed rubber 8.00 35 acteristics of the finely divided or dust-like par ticles of the butadiene-acrylonitrile copolymer friction-stabilizing material, which are referred Sulphur 3.25 Rubber accelerator (benzothlazyl disul phide) ----------------------------------------------Zinc oxide 2.0 Carbon black 4.0 Graphite----------------------------------------------Lead sulphate16.0 to in the foregoing Examples Nos. 1 to 3, inclu sive, may ba readily varied and controlled by 0.25 40 selecting and employing in the making of said finely divided friction-stabilizing particles, for a given sulphur content, a synthetic rubber-like 7.0 elastoprene material of the butadiene-acryloni trile copolymer type containing a predetermined Blanc fixe----------------------------------------------- 7.5 Phenol-formaldehyde resin------------------------- 12.0 Vulcanized butadiene-acrylonitrile copoly mer synthetic rubber-like elastoprene (finely divided dust-like particles, vul canized with ten per cent sulphur, by weight)______ 3.0 , Powdered lead_j'_______________________ 8.0 45 t 60 or preselected percentage of acrylonitrile as a component of the copolymer material. Thus, the relative hardness and heat resistance of said finely divided or dust-like particles of friction-stabi lizing material may be Increased by employing in, the making of said particles a butadiene-acrylo-' nitrile copolymer containing a relatively high percentage of acrylonitrile as a component of Brass chips110.0 the copolymer material as is true, for example, Asbestos fiber___________________________ 28.0 in the case of "Hycar OR" (5-15 or 25), "Chenii- gum" (X and I), and in certain of the mate A suitable formula which may be followed, in the practice of the present invention, in making 55 rials known as "Stanco" and in the materials known as "Standard" and "Perbunan." On the friction elements for use as brake linings upon other hand, if desired, the relative hardness and passenger automobiles, light trucks, and the like, heat resistance of said finely divided particles of is the following, in which all parts indicated are friction-stabilizing material may be decreased by by weight: Example No. 3 60 employing in the making thereof a butadieneacrylonitrile copolymer containing a relatively Parts by weight low percentage of acrylonitrile as a component of Crude (natural) rubber cement13.25 the copolymer material as in the case, for ex Oil modified phenol-formaldehyde flexible ample, of "Hycar Nlnene B," and in certain of resin12.0 65 the materials known as "Stanco." White lead 7.5 It may be added, at this point, that the Per Pyrobitumlnous material (soft coal, finely centage of acrylonitrile in the vattous butadiene- divided) _______________________ 10.0 acrylonitrile copolymer materials or elastoprenes Sulphur 1.5 referred to above, varies from a lower range of Vulcanized butadiene-acrylonitrile copoly 70 the order of approximately fifteen per cent, by mer synthetic rubber-llke elastoprene weight, in the case of "Hycar Ninene B" and in (finely divided, dust-like particles, vul certain of the materials known as "Stanco," to an canized with ten per cent sulphur, by upper range of this order of approximately fifty weight)3.0 per cent, or slightly less, by weight, in the case of Asbestos fiber_________65,0 T6 "Hycar OR" (5) and in certain of the materials 2,428,280 11 12 known as "Stanco." It Is to be understood, how ployed in the form of dust-like materials or finely ever, that the aforesaid ranges are merely Illus trative and not critical and that butadiene-acry divided dispersed discrete particles as friction controlling agents in friction elements, namely, lonitrile copolymers containing, a percentage of finely divided particles composed assentially of acfylonitrile below or above these ranges may be 5 cashew nut shell liquid polymer, finely divided employed within the scope and contemplation of particles composed essentially of a heat polymer the present invention. ized vegetable drying oil such, for example, as It will thus be seen that the hardness and heat linseed, or finely divided particles composed of resistance and related properties and character soft scrap rubber dust, as well as the results of istics of said finely divided or dust-like particles 10 corresponding heat tests made upon materials of friction-stabilizing material may be easily and which have been found useful as friction-con readily controlled, in the practice of the present trolling agents in friction elements in the prac Invention, and suited to the particular needs, re tice of the present invention, namely, finely di quirements and uses of friction elements in which vided or dust-like particles of vulcanizable syn said finely divided or dust-like friction-stabilizing particles are to be employed. 15 thetic rubber-like elastoprenes of the butadieneacrylonitrile copolymer type. It will be noted, in this connection, however, The abscissae In Fig. 1 represent the loss in that strength is not an essential property or char terms of per cent by weight of the specimens acteristic of the aforesaid finely divided or dust tested and the nature of the materials tested and like friction stabilizing particles and hence in making such particles a butadiene-acrylonitrile 20 the times and temperatures involved in the tests are shown at the left in Fig. 1. copolymer may be employed which contains a Ip making the tests which are illustrated in relatively low percentage of acrylonitrile. How the graphs shown in Pigs. 1 and 2, synthetic vul ever, in those instances wherein the butadiene- canized rubbery elastoprenes of the butadiene- acrylonitrile copolymer material is to be employed as a bonding agent in friction elements, strength 25 acrylonitrile "Perbunan") copolymer type C'Hycar were compounded in one Or" and instance, is a highly desirable and important property and with five per cent by weight of sulphur and in an characteristic and hence for such purposes and uses a butadiene-acrylonitrile copolymer material is preferred which contains a relatively high per centage of acrylonitrile in the copolymer. In other words, in such instances, the hardness, heat resistance, and strength of the bonding agent may be easily and readily controlled and increased by selecting therefor a butadiene-acrylonitrile co polymer containing a relatively high percentage of acrylonitrile since, as pointed out hereinbefore, the hardness, heat resistance, and strength of such a bonding agent Increase in direct rela tionship to the percentage of the acrylonitrile in the copolymer material. Moreover, this is true regardless of the particular brand of synthetic 30 35 40 other instance with ten per cent by weight of sulphur, and the materials were sheeted, vulcan ized by heat, chilled, cured and pulverized to a particle size of approximately 40 mesh. A one gram specimen of each of the finely divided or dust-like materials thus formed was then heated and tested under carefully controlled conditions including the controlled conditions of time and temperature which are shown in the graphs; comparable specimens composed essentially of cashew nttt shell liquid polymer, heat polymer ized drying oil (glycerol ester of fatty acid poly mer known as "Neofat"), and finely divided par ticles composed of soft scrap rubber dust, all hav rubber-like clastoplastic of the butadiene-acry ing the same particle size, were heated and tested lonitrile copolymer type which may be employed under identical conditions, with the results in and regardless of the particular catalytic and emulsifying and other agents which may be em 45 dicated in the Figs. 1 and 2. graphs which are illustrated in ployed in the process of making the particular or selected butadiene-acrylonitrile copolymer It may be added, at this point, that the heat polymerized drying oil employed in making cer 1 material. tain of the specimens was the most stable and It may be desirable and advantageous, In cer tain instances, and for particular uses or pur 50 most completely heat polymerized drying oil cur rently available commercially, and is known by poses, to employ in making said finely divided or the trade name "Neofat," and is a product re dust-like friction-stabilizing particles a mixture .or mixtures of two or more butadiene-acryloni sulting from substantially complete heat, poly merization of a glycerol ester of a fatty acid of trile copolymer materials of the character herein before referred to so as to combine selected de 55 animal origin so that the heat tests made show, among other things, the results of comparative sirable characteristics thereof. heat resistance and other properties of finely di It will be noted, in this connection, that a typi vided particles of a relatively highly stable and cal and suitable manner of effecting substantially completely polymerized drying oil and the corre uniform distribution of the finely divided particles of the material found useful as a friction-con 60 sponding properties of the materials which have been found useful as friction-controlling agents trolling and friction-stabilizing agent throughout in friction elements in the practice of the present the resulting friction elements is to intimately invention. mix said particles with the organic bonding agent While, as pointed out above, the new finely di prior to the time the organic bonding agent is 65 vided or dust-like friction-controlling materials intimately mixed with the friction material. may be compounded with either five per cent However, the invention is not limited to this pro or ten per cent, by weight, of sulphur, about ten cedure and said finely divided particles may, if per cent, by weight, of sulphur Is preferred be desired, be intimately mixed with the friction cause approximately this percentage of sulphur material and bonding agent after the friction ma 70 assures sufficient hardness in the resulting vul terial and bonding agent have been mixed canized material to enable it to be granulated together. or formed into finely divided or dust-like particles The graphs illustrated in Pigs. I and 2 of the while also assuring that such particles will pos drawings show, among other things, the results sess sufficient resiliency to render them useful as of heat tests made upon materials heretofore em- 75 friction-controlling agents or ingredients in frlc- 2,428,390 13 14 tlon elements In the practice of the present in material and its resistance to heat decomposi vention. ' tion or heat depolymerization. The graphs in Figs. 1 and 2 show, among other As Indicated at 12 in Fig. 1, a specimen of things, the percentage of acetone-soluble or un finely divided particles of butadiene-acrylonitrile polymerized monomer fraction or material pres- g copolymer synthetic vulcanized rubbery elasto ent In the specimens prior to their being sub prene, vulcanized with five per cent, by weight, jected to the heat tests; the loss in weight in terms of per cent in the specimens tested as measured by the percentage of acetone-soluble of sulphur, showed a loss of only about 5.26 per cent, by weight, as measured in terms of vola tile material, after having been subjected to a monomer or depolymerized material, and other 10 substantially constant temperature of 260 C. for acetone-soluble material resulting from the heat a period of 19.5 hours. Moreover, as indicated at decomposition of the heat' polymerized oils em 13 in Hg. 1, a specimen of this material showed ployed in preparing certain of the specimens, due a loss of only 0.21 per cent by weight, as meas to the heat tests made thereon; the loss in weight ured in terms of benzol-soluble material, after in terms of per cent in the specimens tested as IS having been subjected to a substantially constant measured by the percentage of benzol-soluble temperature of 260 C. for 19.5 hours, thus indi material formed in certain of the specimens and cating the high degree of resistance to heat de resulting from heat decomposition thereof dur composition possessed by this material. ing the heat tests; and the loss in weight in As indicated at 14 in Fig. 1, a specimen of finely terms of per cent in the specimens tested as 20 divided.particles composed essentially of buta ^measured by the percentage of volatile materials diene-acrylonitrile copolyiner vulcanized with five , given oft by the specimens during and as a result per cent, by weight, of sulphur contained about of the heat tests. . eight per cent by weight, of acetone-soluble or It will be noted, in this connection, that the monomer material, and a specimen of the same percentage of acetone-soluble material which was 28 material showed a loss of about. 6.5 per cent, by present in the specimens tested after they had weight, as measured in terms of loss of volatile been subjected to the heat tests, is a measure of material, after having been subjected to a sub the percentage of monomer fraction or beat de stantially constant temperature of 315 C. for a polymerized material, and other products of heat period of one hour, as indicated at IS in Fig. 1. decomposition, in general, present in such sped- 30 As indicated at 16 in Fig. 1, a specimen of finely mens after they had been subjected to the heat tests. This test is also a measure of the per divided particles composed essentially of buta diene-acrylonitrile copolymer type synthetic vul centage of the products of heat polymerization and heat decomposition, in general, formed in friction elements containing such materials when said friction elements are subjected to the tem peratures to which such friction elements are subjected in use. Similarly, the percentage of benzol-soluble ma terial present in certain of the specimens, after they had been subjected to the heat tests, is a 35 40 canized rubbery elastoprene, vulcanized with ten per cent, by weight, of sulphur, when tested at atmospheric temperature, contained about 4.58 per cent, by weight, of acetone-soluble or depoly merized material. . A specimen of finely divided particles composed essentially of butadiene-acrylonitrile copolymer compounded with ten per cent, by weight, of sul phur, showed a loss of about 5.60 per cent, by weight, as measured in terms of volatile material, measure of the extent to which such specimens after having been subjected to a substantially tested had undergone heat decomposition during constant temperature of 260 C. for a period of and as a result of the heat tests, and this test 19.5 hours, as indicated at 38 in Fig. 1. is employed as a measure of the extent to which As Indicated at 17 in Fig. 1, a similar specimen the friction-controlling materials referred to in of this material after having been subjected to certain of the graphs have undergone heat de- .. a substantially constant temperature of 260 c. terioratlon or decomposition. - for a period of 19.5 hours showed a loss by weight, The percentage of volatile material present in .. as measured in terms of acetone-soluble material, the specimens, after they had been subjected to of only about 0.27 per cent, thereby exhibiting the heat tests, is also a measure of the compara the marked resistance to heat depolymerization tive stability of such materials when used as possessed by this material. friction-controlling agents or ingredients in fric A specimen of finely divided particles composed tion elements, and further indicates the extent 65 essentially of butadiene-acrylonitrile copolymer or degree of heat decomposition of the materials type synthetic vulcanized rubbery elastoprene, tested. compounded or vulcanized with ten per cent, by As indicated at 10,- in Fig, 1, a specimen of weight, of sulphur, showed a loss in weight, as finely divided granules or particles composed es measured in terms of benzol-soluble material, of sentially of butadiene-acrylonitrile copolymer go only 0.22 per cent, after having been subjected to synthetic vulcanized rubbery elastoprene, vulcan a substantially constant temperature of 260 C. for ized with five per cent, by weight, of sulphur a period of 19.5 hours, as Indicated at 18 in Fig. 1.' when tested at atmosphere temperature con As indicated at 19 in Fig. 1, a similar specimen tained about 4.67 per cent acetone-soluble un of this material when subjected to a substantially polymerized or monomer material. However, as gg constant temperature of 315 C. for a period of may likewise be seen by reference to Fig. 1, and one hour, showed a loss of only about 7.6 per cent, as therein indicated at II, a specimen of finely by weight, as measured in terms of loss of vola divided particles or granules of butadiene-acrylo tile material, and, as indicated at 20 in Fig. 1, nitrile copolymer synthetic vulcanized rubbery a similar specimen of the same material showed elastoprene, vulcanized with five per cent, by 70 a loss of only about 7.4 per cent, by weight, as weight, of sulphur, after having been heated for measured in terms of acetone-soluble material, 19.6 hours at a substantially constant tempera when subjected to a substantially constant tem ture of 260 C,, contained only about 0.28 per cent, perature of 315 C. for a period of one hour, by weight, of acetone-soluble or monomer mate thereby further demonstrating the marked re rial, thus Indicating the marked stability of this 75 sistance possessed lor this material to heat deteri- 9 2,428,209 15 16 oration and heat depolymerization, and its conse acetone-soluble material, thus indicating the rela quent desirable characteristics for use as a fric tion controlling ingredient in friction elements, in tively very high percentage of unpolymerized or acetone-extractable monomer fraction present in "the practice of the present invention. this material as compared to the relatively very As may be seen by reference to Fig. 1, and as 5 low percentage of unpolymerized or acetonetherein indicated at 21, a specimen of finely di soluble monomer fraction which is present, at at vided particles or granules composed essentially mospheric temperatures, in the materials which of cashew nut shell liquid polymer, when tested have been found useful as friction-controlling or at atmospheric temperature, showed about 14.20 friction-stabilizing agents in friction elements, in per cent, by weight, of acetone-soluble material, 10 the practice of the present invention. This com thereby exhibiting the presence in this material parative relationship may be seen by comparing of a substantially greater amount or percentage graphs 10 and 16 with graph 27 in Fig. 1. of unpolymerized material or monomer fraction Graph 28 in Fig. 1 shows that a specimen of than is present in the finely divided particles finely divided particles composed essentially of a composed essentially of butadiene-acrylonitrile 15 heat polymerized drying; oil (the glycerol ester copolymer type synthetic vulcanized rubbery of fatty acid polymer which is referred to in the elastoprene, compounded with either five per cent, preceding paragraph) showed a loss in weight by weight, of sulphur (see graph 10 in Fig. 1) or of 28.72 percent, as measured in terms of loss of with ten per cent of sulphur (see graph 16 in volatile material, after having been subjected to Fig. 1). As may also be seen by reference to Fig. 1, and 20 a substantially constant temperature of 260 C. for a period of 19.5 hours, thus indicating the as therein indicated at 2, a specimen of finely relatively poor or low resistance of this material divided particles composed essentially of cashew to heat decomposition, as compared to the rela nut shell liquid polymer, when heated for a period tively high heat resistance possessed by the ma of 19.5 hours at a substantially constant tem perature of 260 C,, showed a loss in weight of 25 terials which have been found useful as friction controlling or friction-stabilizing ingredients in 16.87 per cent, as measured in terms of loss of volatile material. , A specimen of finely divided particles com friction elements, in the practice of the present invention.' This comparative relationship may be seen by comparing graphs 12 and 18 with graph posed essentially of cashew nut shell liquid pol ymer showed a loss of 2.72 percent, by weight, as 30 28 in Fig. 1. , Graph 29 in Fig. 1 shows that a specimen of measured in terms of acetone-soluble material, finely divided particles composed essentially of after having been exposed to a substantially con the heat polymerized drying oil which is' referred stant temperature of 260 C. for a period of 19.5 to above in connection with graphs 27 and 28, hours, as indicated at 23 in fig. 1, as compared to losses of only 0.28 and 0.27 percent, by weight, 35 showed a loss in weight of 1.76 percent, as meas ured in terms of acetone-extractable material, in the case of specimens of finely divided parti after having been subjected to a substantially cles composed essentially of butadiene-acryloni constant temperature of 260 C. for a period of trile copolymer synthetic elastoprene compounded 19.5 hours. It will be noted, in this connection, with five percent and ten percent, by weight, re spectively, of sulphur (see graphs 11 and 17, re 40 however, that while this materia] exhibited a rela tively small percentage of acetone-soluble depol- spectively, in Fig. 1), when heat tested under ymerlzed or monomer fraction, and other ace identical conditions. This demonstrates the su tone-soluble products resulting from the heat de perior resistance to heat depolymerization and composition of the oil employed in preparing this heat decomposition, in general, which is pos 45 specimen, after having been subjected to the heat sessed by the materials found useful as friction test described, its relatively low percentage of controlling ingredients in friction elements in the acetone-extractable material was due, not to any practice of the present invention compared to high degree of resistance of this material to heat- friction-controlling material composed essentially depolymerization and heat decomposition, in of finely divided particles of cashew nut shell 50 general, but to the fact that this material under liquid polymer. went a high degree of carbonization during this As indicated at 24 in Fig. 1, a specimen of finely heat test. Moreover, the relatively poor resist divided particles composed essentially of cashew ance of this material to heat decomposition is nut shell liquid polymer showed a loss of 0.22 per shown by graph 28 in Fig. 1 which shows the rel cent, by weight, as measured in terms of benzol- 55 atively high percentage of volatile matter lost extractable material, after having been exposed by this material after having been subjected to to a substantially constant temperature of 260 C. the heat test Just described. for a period of 19.5 hours. Graph 30 in Fig. 1 shows that a specimen of Graph 25 in Fig. 1 shows that a specimen of finely divlf'.ed particles composed essentially of finely divided particles composed essentially of 00 the heat polymerized drying oil, which has been cashew nut shell liquid polymer, when heated for referred to above in connection with graphs 28 a period of one- hour at a substantially constant and, 29, showed a loss of only about 0.34 percent, temperature of 315 C.. showed a loss of about by weight, as measured in terms of benzol-ex twelve percent, by weight, as measured in terms tractable material, after having been exposed to of loss of volatile material and graph 26 in Fig. 1 65 a substantially constant temperature of 260 C. shows that a specimen of the same material when for a period of 19.5 hours. HoweveT, the rela subjected to the same conditions or heat test tive^ low percentage of benzol-extractable ma showed a loss of about 3.40 percent, by weight, as terial developed by this specimen in the heat test measured in terms of acetone-soluble material. Just described was not due to good or high re Graph 27 in Fig. 1 shows that a specimen of 70 sistance of this material to beat decomposition finely divided particles of a heat-polymerized dry but was due to the fact that the specimen un ing oil (glycerol ester of fatty acid polymer known derwent a high degree of carbonization during by and commercially available under the trade the heat test. Moreover, the relatively poor re name "Neofat") when tested at atmospheric tem sistance of this material to heat decomposition is perature contained 47.28 percent, by weight, of 75 shown by the relatively high degree of percentage 3,428,269 17 18 of loss by weight, as measured in terms of loss or low resistance possessed by this material to of volatile material, shown by graph 28 in Fig. 1, heat-depoiymerization and heat decomposition, and sis described hereinbefore. in general, at temperatures encountered by fric Graph 31 in Fig. 1 shows,that a specimen of tion elements in use, compared to the relatively finely divided particles composed essentially of 6 high resistance to heat-depolymerization and the heat polymerized drying oil, which has been heat decomposition, in general, which is pos referred to hereinbefore in combination with sessed by the materials which have been found graphs 21, 28, 29 .and 30, showed a loss by weight useful as friction-controlling or friction-stabiliz of about 23.5 per cent, as measured in terms of ing ingredients in friction elements, in the prac loss of volatile material, after having been sub 10 tice of the present invention. This comparative jected to a substantially constant temperature of relationship may be seen by comparing graphs 315 C. for a period of one hour, thereby indicat 11 and i 1 With graph 36 in Fig. 1. ing the relatively poor or low resistance of this The specimens of finely divided particles com material to heat decomposition at temperatures posed essentially of soft scrap rubber dust, vul encountered by friction elements in use, and as 16 canized with a relatively low percentage of sul compared to the relatively high heat resistance phur (2 to 6 per cent), and the results of heat possessed by the materials found useful as fric tests upon which are illustrated in graphs 35 and tion-controlling or friction-stabilizing ingredi 36 in Fig. 1, all liquefied during these heat tests ents in friction elements, in the practice of the and when exposed to a substantially constant present invention. This comparative relation 0 temperature of 260 C. for a period of 19.5 hours. ship may be seen by comparing graphs IS and Hence, it was impossible to subject specimens 19 with graph 31 in rig. 1. of this material to heat tests at the higher tem Graph 32 in Fig. 1 shows that a specimen of perature of 315 C., as was done in the case of finely divided particles composed essentially of the specimens composed of the other materials the heat polymerized drying oil. Which has been 6 which are referred to in Fig. 1. This further in referred to above in connection with graphs 2T, dicates the poor or low heat resistance possessed - 28, 29, 30 and 31, showed a loss by weight of by finely divided particles of soft scrap rubber, approximately 6.5 per cent, as measured in terms vulcanized with a relatively low percentage of of acetone-extractable material, after having sulphur, such as from 2 to 6 per cent, and the been subjected-to a substantially constant tem SO consequent unsuitability of this material for use perature of 315 C. for a period of one hour. It as a friction-controlling or friction-stabilizing In will again be noted, however, that the relatively gredient in friction elements, as evidenced by the low percentage of acetone-extractable material exhibited by this specimen, after the heat test fact that this material liquefies at temperatures which are frequently encountered in the use of just described, was not due to its resistance to 86 such friction elements. heat-depolymerization or to heat decomposition, It is to be noted) in connection with the mate in general, but was due to a marked degree of rials which have been found useful as friction carbonization of the specimen at the temperature controlling and friction-stabilizing ingredients m involved in the test. Moreover, the relatively friction elements, m the practice of the present poor resistance of this material to heat decom invention, that the flneiy divided particles com position, as shown by the relatively high per posed essentially of butadiene-acrylonitrile co centage of loss by weight, as measured in terms polymer compounded with ten per cent, by weight, of loss of volatile matter, exhibited by this ma of sulphur, are somewhat harder than the same terial, compared to the materials employed as materials compounded with five per cent, by friction-controlling or friction-stabilizing ingre 46 weight, of sulphur. Moreover, the variations or dients in friction elements, in the practice of the present invention, has been pointed out herein before in connection with graph 31 and may be seen by comparing graphs 15 and 19 with graph 31 in Fig. 1. Graph 33 in Fig. 1 shows that a specimen com posed essentially of finely divided particles of soft scrap rubber, vulcanized with a relatively low percentage of sulphur (from 2 to 6 per cent), contained approximately 431 per cent of unpoly merized or acetone-soluble monomer fraction when tested at atmospheric temperatures. Graph 35 in Fig. 1 shows that a specimen of flneiy divided particles composed essentially of soft scrap rubber dust, vulcanized with a rela tively low percentage of sulphur (from 2 to 6 per cent), showed a loss by weight of 5.76 per 60 66 60 gradations in hardness of these materials corre spond, in a general way, or are analogous to, the various gradations of hardness in finely divided particles composed essentially of cashew nut shell liquid polymer, and the hardness of which latter particles depends largely upon the degree of poly merization of the cashew nut shell liquid polymer of which such materials are composed. A sig nificant difference, however, between the mate rials which have been found useful as fnctioncontrolling or friction-stabilizing agents in fric tion elements, in the practice of the present in vention and finely divided particles composed es sentially of cashew nut shell liquid polymer re sides in the fact that the softer forms of flneiy divided particles of cashew nut shell liquid poly cent, as measured in terms of loss of volatile ma terial, when subjected to a substantially constant mer are substantially less resistant to heat-depolymerizatlon and heat decomposition, in gen temperature of 260 C. for a period of 19.5 hours. 66 eral, and give off substantially more volatile ma Graph 36 in Fig. 1 shows that a specimen of terial than harder forms of flneiy divided par flneiy divided particles composed essentially of ticles composed essentially of cashew nut shell soft scrap rubber dust, vulcanized with a rela liquid polymer. It Is to be noted, however, that tively low percentage of sulphur (2 to 6 per cent), a comparable or like situation does not exist in showed a less by weight of 21.0 per cent, as meas ured in terms of acetone-extractable material, 70 regard to the materials employed as friction-con trolling or friction-stabilizing agents in friction when subjected to a substantially constant tem elements in the practice of the present invention perature of 260 C. for a period of 19.5 hours. since the finely divided particles composed es The high percentage of acetone-extractable ma sentially of butadiene-acrylonitrile copolymer terial exhibited by this specimen shows the poor 76 compounded with five per cent, by weight,' of sul- 2,428,209 19 20 phur.possess substantially the same degree or order of heat resistance that Is possessed by finely measured in terms of benzol-extractable ma terial. ' divided particles of the same material compound* As shown in Fig. 2, the specimen of finely di ed with ten per cent, by weight, of sulphur. vided particles composed essentially of heat poly However, since, as pointed out elsewhere herein, 6 merized drying oil (glycerol ester of fatty acid the particles of this material compounded with polymer) showed a substantial percentage of loss ten per cent, by weight, of sulphur are somewhat by weight, as measured in terms of benzol-ex harder and hence easier to break up into the de tractable material, namely, approximately 18 per sired particle size, the material compounded with cent, when heated for only a relatively short pe ten per cent, by weight, of sulphur is preferred. 10 riod of between 1 and 2 hours at a substantially It is desirable that finely divided particles of constant temperature of 500 F. As shown by friction-controlling or friction-stabilizing materi graph I in Fig. 2 this specimen showed a further als. In friction elements, be at least as heat-re Increase in loss of weight, up to about 33 per cent, sistant as the organic bonding agents which are - as measured in terms of benzol-extractable ma employed in suchfrictionelements. Itispreferred, 15 terial, during the remainder of the heat test, however, that such finely divided particles of fric thereby indicating its poor resistance to heat de tion-controlling and friction-stabilizing materi composition at temperatures to which friction als preferably have substantially greater resist elements are frequently subjected in use. ance to heat depolymerization and heat decom Graph 2 in Fig. 2 shows that a specimen of position, in general, than is possessed by the 20 finely divided particles composed essentially of organic bonding agents which are employed in cashew nut shell liquid polymer also exhibited friction elements and in which such finely di substantially greater loss by weight, as measured vided particles of friction-controlling or friction- in terms of loss of benzol-extractable material, stabilizing materials may be dispersed. than was exhibited by the specimen of finely di It is significant to note, however, and we have 25 vided particles of material found useful as a fric so ascertained, that finely divided particles com tion-controlling and stabilizing agent in friction posed essentially of soft scrap rubber, vulcanized elements in the practice of the present invention, with a low percentage of sulphur, such as from namely, finely divided particles composed essen 2 to 6 per cent, not only possess relatively poor tially of butadiene-acrylonitrile copolymer type or low resistance to heat depolymerization and 80 synthetic vulcanized rubbery elastoprenes, com- heat decomposition, in general, at temperatures ponded with about ten per cent, by weight, of to which friction elements are commonly sub rubber, as may be seen by comparing graphs I jected in use, but such finely divided particles of and 2 with graph 3 in Fig. 2. soft rubber scrap are, in fact, substantially less It will thus be seen from the foregoing descrip , resistant to heat depolymenzation and heat de 85 tion, considered in conjunction with the graphs composition, in general, at such temperatures which are shown in Figs. 1 and 2, that finely di than are the organic bonding agents which are vided particles of material found useful as a fric commonly employed in friction elements and such, tion-controlling and friction-stabilizing agent in for example, as an oil modified phenol resin, or friction elements, in the practice of the present natural hard rubber vulcanized with a high per 40 invention, namely, finely divided particles com centage of sulphur and protected by means of a posed essentially of butadiene-acrylonitrile co phenol resin. Moreover, as shown In the graphs polymer type synthetic vulcanized rubbery elasto- Illustrated in Figs. 1 and 2, the heat resistance prene, compounded with preferably not in excess of such finely divided particles of soft scrap rub of about ten per cent, by weight, of sulphur, ber, vulcanized with a low percentage of sul 45 possess substantially greater resistance to heat phur, is not substantially superior to the heat depolymerization, and to heat decomposition, in resistance of finely divided particles of polymer general, than is possessed by finely divided parti ized drying oils which, in turn, cure substantially cles of the materials heretofore employed as fric inferior in heat resistance to finely divided par tion-controlling and friction-stabilizing agents in ticles of the materials which have been found 50 friction elements, and which have been referred useful as friction-controlling and friction-stabi to hereinbefore. lizing materials in friction elements in the prac It will be seen, therefore, from the foregoing de tice of the present invention. scription, considered in conjunction with the ac Fig. 2 is a graph illustrating the results of tests companying drawings, that the present invention made upon specimens of certain of the friction 55 affords a new and improved friction element, and controlling materials which were employedinmak a new and substantially superior friction-con ing the heat tests, the results of which are shown trolling and friction-stabilizing agent for friction in Fig. 1, namely, a specimen of finely divided elements. It will also thus be seen that friction particles composed essentially of heat polymer elements containing the material found useful as ized drying oil (glycerol ester of fatty acid poly 60 a friction-controlling agent in the practice of mer) (graph I in Fig. 2); a specimen of finely the present Invention have the desirable proper divided particles composed essentially of cashew ties and characteristics, which have hereinbefore nut shell liquid polymer (graph 2 in Fig. 2); and been pointed out, as well as others which are in a specimen of finely divided particles of the ma herent in the invention, and including greater terial which has been found useful as a friction 65 friction stability, greater resistance to heat de- controlling ingredient in friction element in the polymerizatlcm, and to heat decomposition, in practice of the present invention, namely, buta general, and to softening, and greater resiliency, diene-acrylonitrile copolymer type synthetic vul at temperatures to which friction elements are canized rubbery elastoprenes, compounded with subjected in use, than is possessed by the mate ten per cent by weight of sulphur. 70 rials heretofore employed as friction-controlling The abscissae in Fig. 2 represent the number agents in friction elements. of hours at which the specimens were subjected It will thus be seen that friction elements made to heat tests at a substantially constant tem according to the practice of the present invention perature of 500 F,, and the ordinates represent possess the desirable characteristics hereinbefore the per cent loss by weight of the specimens as 75 mentioned, as well as others which are inherent 2,428,389 21 22 In the invention, and that the invention thus divided, dust-like, resilient, friction-stabilizing accomplishes its Intended objects Including those particles being employed as a component of the hereinbefore specifically set forth, as well as said bond in the amount of 17.2 per cent of the others which are Inherent in the invention and said bond, by weight, and the said friction ele in the practice thereof. . 5 ment being characterized by friction stability and It will likewise be seen, from the foregoing de high resistance of the said finely divided, dust scription, considered in conjunction with the ac like, resilient, friction-stabilizing particles to companying drawings, that the Present invention heat-depolymenzation and resulting heat-decom affords a new and improved method of making position when the said friction element is sub friction elements and that said method results in 10 jected to elevated temperatures m use. friction elements or products having the advan 2. A friction element as defined in claim 1 in tages and desirable characteristics hereinbefore which the said heat-resistant phenol-aldehyde set forth and others inherent therein. resin is a heat-resistant phenol-formaldehyde While we have illustrated and described se resin. lected embodiments of our invention, and of the IS 3. A friction element as defined in claim 1 in new friction elements made in the practice there which the said heat-resistant phenol-aldehyde of, it is to be understood that these are capable resin is a heat-resistant oil-modified phenol-fonn- of variation and modification and we do not, aldebyde resin. therefore, wish to be limited to the precise details 4. A friction element as defined in claim 1 in of the friction elements, composition and method 20 which the hydrocarbon component of the said which are set forth but desire to avail ourselves copolymer of which the said finely divided, dust of such changes and modifications as come with like, resilient, friction-stabilizing particles are in the purview of the following claims. formed is 1,3 butadiene. - We claim: . 5. A friction element as defined in claim 1 in 1. A friction element for use upon vehicular 28 which the hydrocarbon component of the said brakes, and upon clutches, comprised of a mass copolymer of which the said finely divided, dust of friction material, inert filler, and a friction like, resilient, friction-stabilizing particles are modifying agent, bonded with the heat-reaction formed is 2-methyl 1,3 butadiene. product of a mixture of a sulphurlzable heat- 6. A friction element as defined in claim l in polymerized linseed oil, together with a heat-re 30 which the acrylonitrile component of the unvul sistant phenol-aldehyde resin, and sulphur, the canized butadiene 1,3 acrylonitrile copolymer of said sulphurizable heat-polymerized linseed oil which the said finely divided, dust-like, resilient, and the said heat-resistant phenol-aldehyde resm fnction-stabilizing particles are formed is acrylic and the said sulphur being employed as compo acid nitrile. - nents of the said bond in the ratios relative to 35 7. A friction element as defined in claim 1 in each other of 8.4 parts of heat-polymenzed lin which the acrylonitrile component of the unvul seed oil to 8 4 parts of heat-resistant phenol- canized butadiene 1,3 acrylonitrile copolymer of aldehyde resin and 2.5 parts of sulphur, all of whicb the said finely divided, dust-llke, resilient, said parts being by weight; the said bond having friction-stabilizing particles are formed is meth- dispersed therethrough finely divided, dust-like, 40 acrylic acid nitrile. resilient, friction-stabilizing particles of a co 8. A friction element 'as defined In claim 1 in polymer of a member of the group consisting of which the acrylonitrile component of the said butadiene 1,3 and 2 methyl butadiene 1,3 and a butadiene 1,3 acrylonitrile of which the said finely member of the group consisting of acrylic acid divided, dust-Uke, resilient, friction-stabilizing nitrile and methacrylic acid nitrile, the said finely 45 particles are formed "'constitutes not less than divided dust-like resilient, friction-stabilizing par fifteen per cent nor more"than fifty per cent of ticles being employed as a component of the said the said unvulcanized butadiene 1,3 acrylonitrile bond m a partially vulcanized condition as com copolymer, by weight. . pounded with not less than five per cent nor RAY E. SPORES. more than ten per cent of the unvulcanized co 60 EMIL C. KELLER. polymer, by weight, of sulphur, the said finely