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Sept. 9, 1941. . , H, R. FIFE .. HYDRAULIC " BRAKE FLUID ' _ 2,255,208 ' Filed April 15, 1939 Q N v m z 9 O 3 % L 5-) a 2 . '\,_ 5 I d 8 c L U 2 .... 6 O z O l‘n I: U l 3 3 s ‘2’ < F < 5 ° 1: E ,1: mil 9 é ' s |- *8 a: u- u (I E ‘$4 i “- i u 3< \ q o q- m Gin-Id JO SBWO‘IOA OOI N N ' > N 83d HBlVM d0 SEWFHOA "3.02 .LV EDNVHHWOJ. HHlVM INVENTOR HARVEY R. FIFE BY / ATN 2,255,208 Patented Sept. 9, 1.941.’ UNITED STATES PATENT 'OFFlClE‘." HYDRAULIC BRAKE FLUID Harvey R. Fife, Mount Lebanon, Pa., assiznor to Carbide and Carbon Chemicals Corporation, a corporation of New York ’ Application April 15, 1939, Serial No. 268,100 7 Claims. This invention 'is concerned with improve (Cl, 252-79) tendency which is also accentuated at'low tem peratures. In such case‘ the separated castor oil ments in hydraulic brake ?uids and it is par ticularly directed to making improved substances _ phase may congeal. ~ to use as the lubricating elements of these ?uids. This application is a continuation-in-part of my The object of the present invention is to cor rect such disadvantageous features accompany copending application Serial No. 111,682, ?led November 19, 1936, now Patent No. 2,200,494, is ing the use of castor oil in brake ?uids as are sued May 14, 1940. _ . . It is essential that a brake ?uid contain a v lubricating element to insure proper operation 10 of the moving parts of the system. However, all known hydraulic brake systems contain rubber parts as essential parts of the system, and the vast majority of both mineral and vegetable outlined above and yet retain all the present de sirable characteristics of castor oil, such as its lubricity and its low swelling action for rubber. It has been found that this object can be suc cessfully achieved by appropriate chemical modi ?cation of castor oil. This chemical modi?cation comprises reacting castor oil, by heating it in the presence of a substantially non-volatile alkaline lubricating oils are characterized by excessive 15 catalyst, with a substantial excess of polypropyl ene glycol above that stoichiometrically required to form the monoricinoleate ester of the poly erty makes them entirely unsuited for use in glycol by complete radical interchange with the brake ?uids. 0f the lubricating oils, castor oil glyceryl triricinoleate constituent of the castor is practically the only oil which is su?iciently inert toward rubber to permit its use in brake 20 oil. It is an important feature of this invention that unreacted polypropylene glycol resulting ?uids. Unfortunately, castor oil alone cannot be from the use of such excess, which must also be used as a hydraulic brake ?uid because it pos su?icient to make up for polypropylene glycol sesses a relatively high freezing point and con swelling or solvent action on rubber. This prop consumed in any incidental side reaction, is re 25 tained as a miscible constituent of the reaction products._ It has been found that such a mixture Consequently, it is necessary to add diluents to geals at temperatures normally encountered in the operation of the brake system. ' ‘ is particularly desirable as the lubricating'ele ment of hydraulic ‘brake ?uid. The polypropyl ene glycol used in this invention" may be pre requisites for such diluents are that the diluent is sumciently non-volatile; that it does not va- ,_30 pared by the reaction of propylene oxide with propylene glycol and may consist of substantially porize unduly at the highest temperatures en 95% dipropylene glycol, the ‘remainder being countered in the operation of the brake system; higher homologs of dipropylene glycol. The term that it be non-corrosive to aluminum and other “polypropylene glycol,” as used the speci?ca metals used in constructing the brake system; and that it does not exert an excessive swelling 35 tion andv claims, is intended to include such mix the castor oil in order to reduce its viscosity to working limits at low temperatures. Among the action on rubber. However, many diluents are known which ful?ll these requirements, and yet > they fail to meet the primary requisite for such 7 tures. ‘ It is acknowledged that the use of ricinoleate esters of glycerine and glycols in brake ?uids has diluents namely, miscibility with castor oil, par 40 previously been suggested. The distinguishing attribute of this invention is that“ a‘ homogeneous ticularly at low temperatures. Thus, a disad vantageous characteristic of castor oil in brake - mixture of the reacted and modi?ed castor oil with the excess polypropylene glycol is employed ?uids is ‘its relative lack of miscibility with as the lubricating element of the brake fluid. It diluents, especially at low temperatures. Such has been found that when castor oil is modi?ed low temperature separation of the components 45 by heating with an excess of such substances as of brake ?uids is very undesirable because a free ethylene glycol, glycerine or diethylene glycol, castor oil phase is formed and the castor oil may ' the resulting reaction products, are not miscible, congeal at temperatures usually encountered in especially at low temperatures. This effect, in the operation of a brake system. _ Another disadvantage of the present brake 50 contrast to that obtained in the present inven tion, may be illustrated, in part, by the following ?uids containing castor oil is that, upon absorp example : tion of small amounts of water, either acciden Example I ‘ tally or promoted by any hygroscopicity oi the A sample of castor oil was reacted in the pres diluent, the ?uids have a tendency to separate into a castor oil phase and a diluent phase, a 55 ence of 0.2% by weight of a 50% ‘solution of Q 2,255,208 caustic soda at a temperature of 200° C. with Table B equal proportions by weight of (1) glycerine, (2) ethylene glycol, and (3) polypropylene glycol. In each case, the polyhydroxy substance was Added diluent, 1-. present in excess of that stoichiometrlcally re cent of total ?ulrfgy quired to form its monoricinoleate ester. The resulting reaction products were compounded in equal proportions by weight with each of three diluents, as shown. Water, in amounts shown below, was then added and the separation tem perature of the different ?uids determined. The separation temperature is obtained by cooling the ?uid from a temperature at which the ?uid is homogeneous to the point at which the com volume , o excess polypro Excess polypropylw? Npylene glycol glycol used, 1 part 3 parts castor oil by volume ' Ethylene glygol Immlsciblc. 9%.... Mlsclble. immiscible. Do. Gl cerine: W ______ __ ponents begin to separate. This point is detected . o. immiscible. Do. water, be below minimum operating tempera tures normally encountered, this test is determi 20 native of one of the most vital characteristics of the ?uids. The separation temperature of the , Example II The value of the present invention in increas ing the tolerance of brake ?uids for water with out separation of the components may be better understood by reference to the attached draw~ ing. The composition of the original ?uid by 25 volume was castor oil, 15 parts; propylene gly col 15 parts; polypropylene glycol, ‘ 15 parts; Table A Separation temperature, ° 0., diluent-diacetone alcohol, Castor oil reacted with excess propylene glycol. by vo ume by the appearance of cloudiness in the ?uid. Since it is requisite in a brake ?uid that its sep aration temperature, even in the presence of di?erent ?uids was as follows: used, 1 part poly- ' polypropylene sly col, 1 art castor oil added water’ percent’ 0 l l l Glycerlne ____________________ _- +153 2 3 Ethylene glycol _____________ -. Polypropylene glycol ________ .. —l3 -35 2 3 butanol, 55 parts. Its water tolerance was 23.8 expressed in volumes of water absorbed without separation of the components per 100 volumes 30 of ?uid tested. Since both propylene and poly propylene glycol are quite hygroscopic, the ?uid 4 has a tendency to~absorb water, which may cause separation and it is therefore essential that the ?uid have high water tolerance. ____________________ _. —l2 ~—35 —l2 -—33 —l1 —33 —9 —3() 35 The polypropylene glycol and the castor oil, in the same amounts as above, were then reacted together but separate from the other ingredients Separation temperature, ° 0., diluent-ethylene glycol Castor oil reacted with excess monoethyl ether, added wa tor, percent 0 1 Glycerine _____________ -_,.___'... +108 2 3 Ethylene glycol _____________ __ Polypropylene glycol ........ __ —l6 —30 1 2 3 ‘ 4 at about 200° C. for the times shown in the draw ing and both with and without the presence of 40 caustic soda as a catalyst. The reaction products were then diluted with the same amounts of butanol and propylene glycol as above and the separation temperature determined. The results as set forth graphically in the drawing, show the pronounced increase in water tolerance obtained in both instances. However, the time required _____________________ __ ~14 —30 —12 -—30 —12 -—28 ~10 —28 for reaction is excessive when a catalyst,‘ such as caustic soda, is not used. The reaction products, when caustic soda was Cnstor oil reacted with excess Separation temperature, “ 0., diluent-butanol, added wa 50 employed, were believed principally to consist of tel" percent - polypropylene glycol mono-ricinoleate, unreacted 0 I 1 2 l 3 polypropylene glycol, and small amounts of sodium ricinoleate and free glycerine. In this 4 instance the amount of polypropylene glycol l Glycerinc ____________________ _. +73.5 2 3 Ethylene glycol _____________ .. —l8.5 Polypropylene glycol ________ _. —45 present was about two times as much as that _____________________ .. —l8 —45 —l8 ---42 —l6 —-42 —l6 —40 stoichiometrically required to form its mono ricinoleate ester. The reaction product of the castor oil with the excess polypropylene glycol is also character In each of the cases marked 1 and 2 above, high separation temperatures are obtained ap 60 ized by greatly increased miscibility with dilu ents as compared with castor oil itself. ‘This in parently because the ricinoleate ester formed is I ‘only partially miscible with the unreacted glycer . creased miscibility with a variety of diluents is . ine or ethylene glycol. ' Further experiments have also shown the de a very important improvement, especially from a practical viewpoint, because a number of di? erent brake ?uids are available and are very ' sirability of using an excess polypropylene glycol to react with the castor oil. The results of these“ experiments are presented in tabulated form below; The reaction mixtures were prepared by likely to become intermixed during re?lling of following the procedure speci?ed precedingly. would occur on such intermixing. By using an excess of the polypropylene glycol, the objects of this invention are more satisfac torily achieved, as is illustrated by the improved . miscibility of the lubricating element with dilu ents when an excess polypropylene glycol is used. 75 a given hydraulic brake system. The increased miscibility of the new ?uid lessens the danger that separation of the components of the ?uids The following table shows the improved'mis clbility at ordinary'temperatures and at low tem peratures of the new lubricating element with di luents as compared to unreacted mixtures of castor oil and polypropylene glycol. The reacted 2,255,209 g _ 3 ' mixture was prepared by following the procedure parts byweight otbutanol in order to. form a‘ speci?ed in ExampleI. ?uid'suitable for use in hydraulic brake ?uids. The new ?uid possessed a water tolerance. or 38. volumes of water per 100 volumes of ?uid, where as ,a‘?uid oi the same empirical composition which had not received the heat treatment de scribed had a water tolerance of only 11- in the . " Table 0 React'ed mum _ Added diluent, per- . A cent of total ?uid by volume C same units. In other respects, the new?uid showed operating features decidedly superior to > , 1 part poly- 1 part poiy1 part poly ropy en propylene gly- propylene gly gycolandl col andlpart col and Sifmrts oil by volume Ethylene glycol: B , castor Glyoerine: 9% .... ._ Unreacted mixtures Miscible_ ___ 9%"; _____________ __do ____ __ castor oil by by volume Immlscible_-__ Miscible______ Immiscible___-_ the unreacted ?uid oi the‘ same empirical compo sition andtov many ?uids now in use. by volume example, may, of course, be varied. Do. - Do. D0. ____ _do ______ __ Do. For in- f stance, other substantially non-volatile alkaline. catalysts, such as potassium'hydroxide and tri ethanolamine, may be used. Also, as shown in the drawing, the catalyst may be omitted al-' though longer reaction times are then required. When a catalyst is used, the temperature may be Immiscible. ____ -do ______ _. , The‘vexact ‘conditions speci?ed in the above castor o by widely varied from about 70° C. to about 300° C. depending largely on the time of heating. Incarrying out the reaction between castor oil and the excess polypropylene glycol,‘ it is desirable .to observe certain precautions. For 25 instance, the caustic should be addedslowly and uniformly with vigorous agitation. Otherwise, up. Methyl ether of diethylene glycol: 50% __________ __ the caustic solution separates to the bottom of the reaction vessel and solid sodium ricinoleate . _ Miscible at tempera- immiscible at tempera- . _ immiscible at tempera t u r e s tures below tures above —-23°G. —4°C. below > 30 —38° C. is deposited. This is undesirable and promotes discoloration and high alkalinity in the reaction products. The pH of the reaction products pro duced under these conditions 'may be as high as' 9 and this is sometimes su?‘icient to cause severe A wide range of diluents may thus be employed alkaline corrosion of the aluminum pistons in with the new lubricating element. As examples 35 the brake system. In contrast, by using vigorous may be mentioned butanol, secondary butyl al > agitation and slow addition of the caustic, a pH ‘ cohol, tertiary butyl alcohol, the methyl, ethyl as low as 7.4 to 7.8'may beobtained and the and butyl monoethers of ethylene glycol and of propylene glycol. possibility of alkaline corrosion by the ?uid thus avoided. ' Another outstanding advantage of the newl - 40 In addition, it is desirable to use several times bricating element is its lower viscosity at reduced the amount of caustic required for neutralization temperatures as compared to castor oil alone or of the free fatty acid contained in the castor oil. simple mixtures of castor oil and polypropylene The excess caustib serves as a catalyst and also glycol. The lubricating element of this invention produces an equivalent amount of sodium ricino is also characterized by improved chemical sta 45 leate which acts as a .bu?er salt in maintaining bility in service. For instance, castor oil is un the proper alkalinity to avoid corrosion. Conse stable in , service in the presence of sodium quently, the use of a corrosion inhibitor with the ricinoleate, since it tends to decompose and form new ?uid is not essential. It is also desirable to carbon dioxide, whereas the new ?uid is extreme carry out the reaction in the absence of air and ly stable in the presence of this salt and it is not in a closed system. necessary to remove it from the reaction prod 59 Example IV ucts before use. Finally, the lubricating element of this invention is substantially as inert toward Following these precautions, a large scale ex rubber as is castor oil and it does not promote periment was conducted in which ~15 parts by corrosion of the metallic parts of the system nor volume of castor oil and 15 parts by volume of does it separate from diluents at temperatures polypropylene glycol were reacted'by pumping above zero Fahrenheit in any case. .the reactants through a heating coil. Uniform Further examples to illustrate the manner of heating was carried out at a temperature within, making the improved lubricating element will now be given. Example III A mixture consisting. of 31% by weight of castor oil, 67% by weight of a mixture of poly the range of 160°- to 215° C. and for a period of 60 about 45 minutes. ‘. , - On cooling, the reaction products were mixed with 55 parts of butanol and‘ 15 parts of pro ; pylene glycol, all by volume. This fluid was not discolored; it had a pH range of 7.4 to 8.2; and propylene glycols consisting of dipropylene glycol a water tolerance of 38 to 44 volumes per 100 and a small amount of its higher homologs, and 65 volumes of ?uid. The separation temperature of 0.2% by weight of a 36% aqueous solution of the-?uid was far below zero Fahrenheit, the sodium hydroxide was heated for about 2 hours actual test value being 4-60“ F. After a year's at a\ temperature of about 200° C. In this case service, this ?uid had caused no corrosion, did the polypropylene glycols present were about ?ve 70 not gum, maintained a pH range of 7.4 to 8.2, times the amount stoichiometrically required to form the mono-ricinoleate ester of the respective polyglycols. and retained its high water tolerance; and the original separation temperature remained un changed. _ ‘ After cooling, 66 parts by weight of the modi Other modi?cations of the invention other lied and homogeneous oil were mixed with 34 75 than those disclosedtwill be readily apparent to 4 2,2553% 5.- A hydraulic brake ?uid comprising a lubri »' those skilled in the art and are intended to be included within the invention as de?ned by the appended claims. eating element, which comprises a homogeneous mixture of polypropylene glycol mono-rlcinoleate and-polypropylene glycol, combined with a dilu ent of the group of aliphatic alcohols and mono alkyl ethers of alkylene and polyalkylene glycols. lubricating element comprising polypropylene 6. A hydraulic brake ?uid comprising a homo glycol mono-ricinoleate and polypropylene glycol; geneous mixture of polypropylene glycol mono 2. In a hydraulic brake fluid, ‘a homogeneous ricinoleate and polypropylene glycol, as a lubri lubricating element comprising polypropylene glycol and the polypropylene glycol mono-esters '10 cating element, combined with an organic liquid diluent; said polypropylene glycol in each in of the fatty acids derived from castor oil. stance being substantially identical with that 3. A hydraulic brake fluid comprising a homo resulting from the reaction of propylene glycol geneous mixture of polypropylene glycol mono with propylene oxide. ricinoleate and polypropylene glycol, as a lubri I claim: 1. In a hydraulic brake ?uid, a homogeneous eating element, combined with an organic liquid diluent. ' 4. A’ hydraulic brake ?uid comprising a lubri cating element and an organic liquid diluent, said lubricating element being a homogeneous mix U. '7. A hydraulic “brake ?uid’ comprising, by vol ume, about six parts of a homogeneous mixture of polypropylene glycol with the polypropylene glycol mono-esters of the fatty acids derived from castor oil, about three parts of monopropylene ture of polypropylene glycol and an ester ex '20 glycol, and about eleven parts of butanol. change product of castor oil and polypropylene glycol containing polypropylene glycol mono riclnoleate. ' HARVEY lit’. FIFE.