BORAMIDE COATINGS FOR FRICTION MATERIALS

Abstract: A method for using alkanolamide borates as a coating for friction materials which during use contact, at least part of the time, rustable metals. The method comprises contact­ ing the friction material with an aqueous solution comprising at least about 0.05 weight alkanolamide borates selected from the group consisting of compounds having the for­ mula: wherein X and X′ are selected from any of H, R-OH or R′ - O - B(OH)₂, and wherein R, R′, and R″ are each selected from any same or different C₁ - C₅ alkyl group, preferably ethyl groups, and thereafter evaporating water from the aqueous coating on the friction material so as to leave the friction material with a coating comprising alkanolamide borates. Friction materials coated by above method are also claimed.

Description: BORAMIDE COATINGS FOR FRICTION MATERIAL Technical Field Thc method of this invention relates to the use of aikanolamid- borates as coatings for friction materials which during use, contact rustable metals. rlorb particularly. the friction material is contacted with an aqueous solution comprising at least about 0.05 weight percent, based on the weight of the solution, alkanolanide borates and sobsequently dried to remove water, leaving a coating comprising alkanolamide borates on the triction material. background Art During use, friction materials, such as brake lining or clutch tracings, come in contact with metals, e.g., cast iron. Corrosion of such ferrous metals may cause adhesion (stiction) ot the triction material to the metal when they are allowed to contact one another for a period of time. Generally, such corrosion and stictinn occur before the metal and friction material have received substantial sustained wear. One longstanding approach to preventing clutch facing stiction comprises coating the friction material with sodium nitrite. However, recent and anticipated agency recommendations have created a need to replace sodium nitrite which is ecologically less than desirable. It also does not aFpear to retain its corrosion resistant properties longer than a few weeks (often before the friction material is operating on the vehicle), oxidizing at ambient temperatures to the nitrate. However, we have found that coatinos comprising alkanolamide borates on friction material S arc. significantly more offective in preventiog such corrosion honding and tha: they maintain these properties after Application and during friction material use tor a substantially greater period of time. Alkanolamide botates have been used as flame retardents in cotton batting, however more usually as corrosion inhibitors and lubricants -in cutting fluids. U.S. Patent 4,022,713 to Waldstein teaches a conposition comprising a liquid carrier constituting water dtlJ an alkandlamide borate, which is the reaction product of boric acid dod a primary C1 - C3 alkanolanine, usefal as a corrosion inhibitor in making cutting fluids. Disclosure of the Invention The invention is directed to a method for using altanolamide borates as a coating for friction materials which during use contact suitable metals. The coating on the friction material acts to prevent corrosion or corrosion product bailed up on the metal contacting -the friction material. The method of this application comprises: (A) contacting the friction material with an aqueous solution comprising at least about 0.05, preferably between about 0.1 and about 10.0, most preferably between about 0.2 and about 5.9 weight percent, based on the weight of the- solution, of alkanolanide borates; and (B) evaporating water from aqueous coating on the friction material so as to leave the friction material with a coating comprising alkanolamide borates. The alkanolamide borates are selected from the group of compounds having the formula: EMI3.1 wnerein X and X' are each selected trom any oi H, R-Ofl or R'-O-B(OH)2, and wherein R, R',and R" are cach selected trom any C1 - C5 aliphatic group. Preferably, X and X' of said formula are selected from any of R-OH or R' - 0 - B(OH)2, wherein, on the average, greater than about 50% of X and X' of the formula are R' - 0 - B(OH)2. More preterably, X is H,and X' is selected from any of ti-OH or R' - O - B(OH)2, wherein on the average greater than 50% of X' ot the formula is R' - 0 - ss(OH)2. Mest preferably,additionally R, r;', and P are ethyl groups. The invention is also directed to friction materials coated according to the method disclosed above. Advantageously, the borates can be applied to the friction material at very low concentrations and provide superior prevention of such corrosion related phenomena as stiction. The alkanolamide borates ot this invention also exhibit excellent compatibility with dust suppressants commonly employed for use with friction materials. Best ode tor Carrying Out the Invention The method of this invention can be used with any friction material. In general, friction materials contain a matrix of binder, such as thermosetting resin or vulcanized rubber, a tibrous reintorcement, and friction modifiers. Commonly employed fibers include asbestos, glass and steel wool while metals, metal oxides, cashew and rubber particles are molten employed as friction modifiers. Fillers or extenders may be included to modify physical characteristics and ioduce cost. The method of the present invention is d.sected to coating any friction material which during use contacts, at least tor a time fustable metals. The corrosion of such metals may result,- tor exanple, trom exposure to salt water, high humidity, etc. One such embodiment, which was mentioned above, comprises coating clutch facing materials in order to prevent stiction which may occur when the clutch Lacing rests aqainst the clutch pressure plate or engine flywheel, particularly- as mentioned above, at a time betore -the triction material and metal have received sustained wear. It appears that with sustained wear, surtace characteristics ot the friction material and the metal are modified so as to significantly decrease the likelihood ot stiction occurring. Another embodiment of the method of the present invention comprises providing a coating comprising alkanolamide borates on brake linings, for example, to prevent corrosion build up (also known as rust-3acking) on the portion of the shoe adjacent to the lining. Other applications ot the method ot this invention to prevent corrosion would be apparent to those skilled in the art. The inhibitor ester compounds employed in the method of this application, i.e., the alkanolamide berates are selected trom the group consisting ot compounds having the formula: EMI4.1 wherein X and X' are each selected trom any of H, R-OH or R'-O(OH)2, and wherein R, R and R are eacn selected trom any C1 - C5 aliphatic group. Preterably, the alkanolamide borate is a tri- or (more preferably) a aialkanolamide borate, l.e., wherein, X and X' ot the tormula are selected froa any of R - Oil or R - 0 - t3(OH)2. wherein, on the average, greater than 50% oL X ano X' ot the formula are R' - 0 - a(OH)2, or mort-- preferably, wherein X is H and X' oL the formula is selected trom any ot R-Oll or R' - O - 8(0H)2, and wrercin on the average, greater than about 50% of X of the formula is R' - 0 - B(OH)2. Most preferably, addltionally R, R' and R" are ethyl groups. Most preferably, the alkanolamide borate Is a dialkanolamide borate having the formula: EMI5.1 wherein at least about 50 percent ot the dialkanolamide borate component comprises the borate ot formula (1). It is to be noted that in the most general embodiment of the alkanolamide, R, R' and P can be the same or different C1 - Cg aliphatic groups. As would be apparent to.one skilled in the art, mixtures ot suitable alkanolamide borates, preferably mixtures ot di- anci trialkanolamide borates, could also be used in the method ot the subject invention. The aqueous solution ot the alkanolamide borate comprises at least about 0.05, preferably between about 0.1 and about 10,0, most preferably between about 0.2 and about b.0 weight percent borate. in embodiments ot the subject invention wherein, tor example, clutch pacings are coated to prevent stiction, it is generally preferable to employ aqueous solutions comprising between about 0.1 and about 5.0, more preferably between about U.2 and about 2.u weright percent botate, based on the weight ot the solution. It has beer, found that Lnr such applications, concentrations that give a reactive corate concentretion of about 1-10 gms/mê are particularly uselui. However, in coatin brake friction materials so as. to prevent corrosion build up on the attached metal ( to eliminate rust-jacking), it is preferable to employ an aqueous solution comprising between about S. u and lo.U weiqht percent alkanolamide borate, based on the weight ot the aqueous solution. As would be apparent to one skilled in the art, optimal concentration of tf boramide solution to be employed would depend, in part, on the particular intended use of the coating, as well as application techniques, etc. Selection ot optimal solution coating concentration would be within the skill of those in the art. Representative of the various alkanolamide borates falling within the above formula are, [or example, those commercially available trom Keil Chemical Division, ferro Corp., (hammond, indians) under the trademane Synkad-2UZ or trom Mazer Chemical Industries tGurnee Illinois), as a concentrate of the borJte in water generally comprising about 20-95 weight percent borate. The concentrate may be suitably diluted for use in the method of the invention of this application. The aqueous solution containing the alkanolamide borates ot this method may also .clude other materials conventionally employed in such coating. These may include wetting agents, e.g., non-ionics or organic phosphate esters. dyes, and antioxidants, e.g., amines, which additives are generally employed at up to about 1 weight percent, based on solution weight. Other materials such as bust suppressants, e.g., acrylates, sodium silicates or polyvinyl alcohol (PVA) may be included, generally in amounts up to about IS weight percent, based on solution weight. While the dust suppressant may be included in the aqueous borato solution, thi- dast s! ressant Tay also be employed as a separate coating composition to be employed before. however pereferably after, coating ot the traction material with the aqueous solution comprising the alkanolamine borate. It has also been tound preferable, when employing separate coatings (two step) of a dust suppressant solution and a borate solution, to subject the friction material to the dust suppressant coating solution for a shorter period of time than that ot the borate solution coating during respective coating applications thereof. The aqueous solution comprising the alkanolamide borate may be applied as. a coating to the friction material by any known method such as spraying, flow coating, roll coating or immersion or like techniques. Selection ot optimal coating technique would he well within the skill of those in the art, and depends, for example, on triction material size. porosity crocessln:3 parameters, etc. The coating may be applied so as to be adsorbed on and absorbed into the. friction material in any desired amount. Penetration (absortion) of the coating into the friction material to between about D.5 1.0 mm of depth for clutch facings, for example, has been found suitable to prevent stiction. Coatings applied, on the other hand, to prevent rust-jacking are generally suitably applied to lower penetration depths. Penetration into the friction material would depend, in part, on the physical properties ot the friction materials, including its porosity, a condition of manufacture (e.g., molding conditions). After coating the traction material according to the method of this invention, water is allowed to evaporate from the aqueous coating on the friction material so as to leave a coating of alkanolamide borate on the friction material. This tray be dor. " drying the trii=tion material at ambient temFeratures or at elevated tamperatures, or by a combination of both aajicnt and elevated temperature drying operations. while it is preferable to allow evaporation of essentially all oL the water present in the aqueous coating on the friction material, it is not necessary to do so. The optimal amount oL water to be evaporated would depend on intended application, processing conditions, etc., oE the coated friction material and thus selection or this optimal amount of water to be removed would be within the skill or those in the art. These alkanolamide borates may we prepared by reacting a mixture ot (ortho) boric acre (H3BO3) and alkanolamine under conditions so as to esterify at least some ol hydroxyl groups present on the alkanol moiety with the boric acid. the alkamolamine employed in the esteritication may be a mono-, dl-, trialkonolamine or suitable mixtures thereof, wherein the alkanol moiety is a C1 - C5 aliphatic group which may be unsubstitutec or substituted with non-interfering functionality. Preterably, the alkanolamine is a di- or Tralkanolamine or suitable mixtures thereof. Typical alkanol moieties include but are not limited to, ethanol, l-lsopropanol, 2-amino-2-methyl propanol and butanol, with ethanol being most preferred. Waldstein, in U.S. Patent 4,022,71t, teaches a method for making monoalkanolamide borates, by reaction of suitable monoalkanolamines - and boric acid at mildly elevated temperatures, which patent is hereby incorporated by reterence tor these teachings. In the esterilication reaction, the water formed may be removed by means oL a reflux condenser or solvent extraction. Any excess of unreacted alkanolamine can be left in the reaction product (the alkanolamide $bo(ate) inasmuch es it does not interfere with the rust inhibiting action of tY: borate product. Excess boric acid may be noutralized with bases, such as sodium hydroxide, to raintain desired pH. The reaction conditions described above are merely meant as exemplary of one such formulation, and are not neant to be limitin.3 to the method of this invention. The following examples are presented by my ot description of the process of the invention and set forth the best mode contemplated by the inventors but are not to be construed as limiting. Example 1 4 1. O by weight solution of Keil Synkad 202 (approximately 30% by weight alkanolamide horate) is prepared oy adding 10 grams of the material to 990 g or water. 25 mm square samples ot Beral R208-1 142K-81, a non-asbestos clutch friction material, are then coated utilizing the lollowing process cycle: Cycle I @ 1.08 by weight keil Synkad 202 -0.3 minute immersion ambient temperature o Air dry approximately 15 minutes at ambient temperature Oven dry 30 minutes at 135 C The samples are evaluated tor stiction using a rust adhesion test procedure developed at Ford rotor company Scientitic Research Laboratories. The test procedure is as folloçs: 25 mn. square clutch facing samples are clamped (35-50 lbs pressure) into 1.0 ml Fools of a 5-! by weight aqueous sodium chloride (NaCl) solution on a precleaned cast icon test plate (the sat solution is delivered Sy syringe). The- entire assembly is sealed in 3 polyethylene bag with an open breaker containing approximately 100 ml of a 5.0% by Naol solution and lett overnight (16 hours) The assembly is carefully removed from the bag and gently dried at cast iron temperatures at or below 439C until dry (approximately) 2 hours at 43 C, 4 hours at 27"C), Care is taken to avoid thermally or mechanically shocking the assembly. The clamps are cautiously removed to avoid disturbing the samples. Shear stress measurements are taken utilizing a force gage (compression type, 500 N capacity, in 5 N or smaller increments). These measurements are made by placing the push rod which is attached to the force gauge against a side of the triction material. Force is applied until lateral displacement of the test sample occurs along the test plate. This torce Is recorded in N. Stiction Shear Stress Values (S.S.S.) are subsequently determined in Pa for the samples. Beral X 2Q8-1 142K-81 from Cycle I tested utilizing the afocementioned procedure has average stiction shear strr-ss (S.S.S.) values of 14 kPa. Untreated samples exhibit average S.S.S. values of 56 kPa. Note: Test Plate Cleaning Procedure The.cast iron test plate is cleaned by low Speed sanding with 150 grit, followed by 32U grit abrasives. It is then wiped clean with anhydrous alcohol (ethanol), then acetone, and air dried. Example 2 25 mm square Nuturn FB-2 NAFC la non-asScstes clutch friction material samples are treated according to the following cycle: Cycle 11 o Keil Synkad 202 1.0 weight percent 60 selond immersion ambient temperature Air Dry approximately 15 minutes at ambient temperature Oven Dry 25 minutes at 103 C Utilizing the rust adhesion test procedure described in Example 1, average stiction shear stress (S.S.S.) values of 24 kPa are obtained tor the treated samples. Samples similarly prepared and tested, except utilizing the Xeil Synkad 202 concentrations ot 0.1% and 0.5 wt. %, have average S.S.S. values of 35 kPa and 42 kPa, respectively. Untreated Nuturn FB-2 MAFC 18 samples have average S.S.S. values of 280 kPa. Example 3 25mm square samples of Raybestos Manhatten (R-M) US X 96yx, an asbestos bcaring -clutch friction material ar treated and tested as in Example 1. The average S.S.S. values are 21 kPa for the above samples. Untreated RsT US H969X samples are similarly tested and have average S.S.S. values of 98 kPa. Example 4 (a) Utilizing a two step coating process, an alkanolamide borate corrosion inhibitor solution and a sodium silicate (water glass) dust suppressant solution are applied to 25 mm square R-M US 9bYX clutch traction material samples by the process descrilbed below: Cycle III Keil Synkad 202 1.0 weight percent 60 second immersion ambient temperature @ Air Dry-approximately 10 minutes at ambient temperatuce Oven Dry 25 minutes at 105 C Air Cool 15 minutes at ambient temperature Sodium Silicate 40-42 Baume 10t by volume 30 second immersion ambient temperature Air Dry approximately 10 minutes Oven Dry 25 minutes at 105 C. Sodium silicate solution was preparcd by addin', 40 ml 40-429 Baume sodium silicate (available from M.C.B. Mnautacturing Chemists Corp., Cincinatti, Ohio) (@5% by weight) to 360 ml of water. After testing as described in Example 1, the average s.s.s. values-for the above samples is 17 Kpa. (b) A single solution (Solution II) was utilized which comprised the dust surppressant and corrosion inhibitor used in Example 4A. solution II was prepred by adding 40.0 ml 40-42 aaume sodium silicate (¯ 5,0 wt. t) and 4.5 ml Synkad @@@ (¯1.0 wt. %) to 356 ml water. 1" square samples ot R'i US 969X clutch friction material are treated according to the following cycle: Cycle IV e Solution II - 60 second immersion ambient temperature Air Dry - 10 minutes at ambient temperature Oven Dry - 25 minutes at 105 C The clutch samples are then tested as in Example 1. The average S.S.S. values are 10 kPa. Untreated R-M US 969X samples have average 5.S.S. values of 98 kpa. Example 5 25 mm square samples cf Thermoid 219 X 146 CL bTL 549C ANF clutch Kiction material are treated with konwn corrosion inhibitors utilizing the following cycle: Cycle V - Corrosion inhibitor - tU sec. immersion ambient temperature Oven Dry - 10 minutes at 1000C The corrosion inhibitors utilized along with the average S.S.S. values observed during testing are listed below. When the corrosion inhibitor was: Sodium tetraborate decahydrate 10 by wt. agueous solution, average S.S.S. values were 71 kPa o sodium nitrite aqueous solutions ot b% and 15 by wt. average 5.5.5 values were 85 and 125 kPa, respectively Example 6 Thiokol 1959 4715 and Bendix 7161A semimetallic disc brake traction materials were treatea using the following cycle. o Keil Synkad 202 - 1% by weight 30 second immersion ambient temperature Air Dry- 10 minutes Oven Dry - 25 minutes at 100 "C. The pads were then riveted to. coid rolled steel brake shoes and corrosion testec (modified Ford Arizona Proving Ground Test) in a humidity cabinet with p-riodic application of 5.0 wt. % aqueous sodium chloride solution to the friction material/shoe interface. The brake shoe assemblies were attorded excellent corrosion protection at the interface, after 5 we-ks accelerated testing. In view of this disclosure, many modifications of this invention will be apparent to those skilled in the art. It is intended that all such modifications which fall within the true scope of this invention be included within the terms of the appended claims.

Claims: We claim 1. A method for using alkanolanide borates as a coating for friction materials which during use compact rustable metals, which method comprises: (A) contacting said friction material with an aqueous solution comprising at least about 0.05 weight percent said alkanolamide borate selected from the group consisting of compounds having the formula: EMI16.1 wherein X and X' are each selected from any of d, R-OH or P.' - 0 - B(OP)2, and wherein R, R', and R" are each selected trom any C1 - C5 alkyl group; and (B) evaporating water from the aqueous coating on said friction material so as to leave said friction material with a coating comprising said alkanolamide borates. 2. A method according to claim 1, wherein said aqueous solution comprises between about 0.1 and about 10.0 weight percent said alkanolamide borate. 3 A method accordiny to clain: 1. wherein said aqueous solution comprises between stout U.2 and about b.0 weight percent said alkanolamide borate. 4. A method according to claim 1, wherein X of said formula is H and X' is selected from any of R-OH or R' - O-- B(OH32, and wherein, on the average, greater than SUt ot. X' ot said formula is R' - 0 - B(OH)2. 5. A method according to claim I, wherein X and X' of said formula are selected trom any of R-OH or R' - O - B(OH)2, and wherein, on the average, greater than about 50% of X and X' o@ said formula are R'- O-n(ON)2. 6. A method according to claim 4 or b, wherein in said formula R, R' and R" are ethyl groups. 7. A method according to claim 1, wherein said aqueous solution further comprises up to about 15 weight percent dust suppressants based on the weight ot said aqueous solution. 8. A method according to claim 1; wherein said method further comprises coating said friction material with a dust suppressant composition. 9. A method according to claim 1, wherein said. friction materials are selectea from clutch tacings and brake friction materials. 10. A method according to claim 9, wherein said friction 'rateriaL is a clutch facing which is coated with said solution comprising elkanolamide borates toa depth ct between about 0,5 and about l.0 mm. - 11. A friction material having a coating comprising alkanolamide borates selected trom the group consisting of compounds having the-formula: EMI18.1 wherein X and X' are each selected trom any of H, R-OH, or R - O - B(OH)Z, and wherein R, R' -ano R" are each selected from any C1 - C5 alkyl group. 12. A friction material according to claim lU, wherein said alkanolamide borates are applied to said friction material in an aqueous solution comprising greater than about 0.05 weight percent alkanolamide borates based on the iieight of said aqueous solution. 13. A friction materialaccording to claim II, wherein X of said formula is H and X'.-is selected trom any of R-OH or R' - 0 - B(OH)2 and wherein, on the average, greater than but at X' ot said formula is R' - 0 - B(OH)2. 14. A friction material according to clam 11, wherein X and X' of said formula are selected from any of R-OH or R. - 0 - B(OH)2, and wherein, on the average, greater than about 50% of X and x of said formula are R -O-B(OH)2. 15. A friction material accordiny to claim 1' or 14 wherein, R, R' and P ot said formula are ethyl groups. 16. A friction material according to claim 11, wherein said friction materials are selected trom clutch facings and brake friction material. 17. A friction material according to claim 16, wherein said friction material is a clutch facing which has been coated with said alkanolamide borates to a depth ot between about 0.5 and about 1.0 mm. 18. A friction material according to claim 1 or 16, wherein said coating on said friction material further comprises dust suppressants.

Inventors: ANDERSON, ARNOLD ERIC, MELOTIK, DONALD JOSEPH, WEINTRAUB, MARVIN HARRIS
Applicants: FORD FRANCE SOCIETE ANONYME, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1983
Main classification: F16D69
IPC codes: F16D69, C23F11, C23F15