US2771422A

US2771422A - Polymethylpolysiloxane thickened phenylmethyl silicone oil

Info

Publication number: US2771422A
Application number: US285080A
Authority: US
Inventors: George V Browning; Cecil G Brannen
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1952-04-29
Filing date: 1952-04-29
Publication date: 1956-11-20
Anticipated expiration: 1973-11-20

Description

United States Patent POLYMETHYLPOLYSILOXANE THICKENED PHENYLMETHYL SILICONE OIL George V. Browning, Schenectady, N. Y., and Cecil Brannen, Munster, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana No Drawing. Application April29, 1952, Serial No. 285,080

8 Claims. (Cl. 252-49.6)

The present invention relates to novel lubricant greases and to the method of preparing same. More particularly it relates to novel greases wherein both the lubricant-vehicle and the thickening agent comprise organosilicon compounds.

Very high temperatures resulting from high speed operation of machines, engines, etc. have resulted in a great need for lubricant greases which are stable at such temperatures, and the requirements of lubricants of this type are more and more difficult to fulfill as the temperatures encountered become progressively higher. The art has progressed from the use of petroleum lubricant vehicles in such greases to silicone polymer oils which are capable of withstanding much higher temperatures and since the thickening agents heretofore employed, e. g. lithium soaps of high molecular weight carboxylic acids and the like cannot withstand such temperatures, more stable thickeners are likewise required. Lubricant greases have been produced recently by milling a thickener gel prepared from dimethyldichlorosilane and methyltrichlorosilane with dimethyl silicone liquids having lubricating properties, but certain problemshave been encountered therewith, viz., a difiiculty in obtaining a smooth homogeneous product and relative stability at high temperatures. Thus, despite the chemical similarity of the gel and the silicone polymer vehicle, such materials cannot be combined readily to produce a smooth homogeneous product by usual milling operations and it appears that unreacted--OH groups in such a gel and the consequent residual functionality resulting therefrom are responsible for the instability thereof at elevated temperatures, e. g. 200 F. and above.

It is a primary object of the present inventionto provide an improved method of preparing lubricant greases wherein both the thickening agent and the lubricant vehicle are organo-silicon compounds. A further object is to provide a method of preparing an organo-silicon thickening agent, for use in grease manufacture, which can readily be milled with organo silicon lubricant vehicles to yield smooth greases having excellent high temperature stability. A still further object is to provide novel organo-silico-n greases which are stable and retain effective lubricating properties at elevated temperatures. Additional objects will be apparent from the ensuing description of the present invention.

Greases of the present invention are prepared by thickening liquid organo-silicon polymers having lubricating properties to grease consistency by means of novel organo-silicon thickening agents. Such thickening agents or gels, as they may be referred to alternatively, are prepared by heating polymethylpolysiloxanes having substantially no residual functionality to a temperature in the range of from about 400 F. to about 550 F. in the presence of a stable liquid organo-silicon polymer, e. g. phenylmethylsilicone oil, for a period of time which is dependerit upon temperature and other factors which will hereinafter be more fully described. A polysiloxane has nolresidual functionality, for purposes of the present.

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invention, when it has substantially no tendency to react further with itself or other siloxa-nes because of the presence of unreacted -OH groups in the polymer. The polymethylpolysiloxanes, which may be heated to form thickener gels suitable for use in accordance herewith, may be either linear or branched, i. e. they may comprise essentially straight chain polymers derived principally from dimethyldichlorosilane or dimethyldiethoxysilane, or they may be cross-linked polymers resulting from the cohydrolysis of two or more methylchloroor methylethoxysilan-es. Such chains are freed from residual functionality by cohydrolyzing therewith a relatively small amount of a mono-functional silane, viz. trimethylchlorosilane or trimethylethoxysilane.

When polymethylpolysiloxanes are heated to a temperature in the above indicated range it appears to result in their oxidation and thermal rearrangement, with gels prepared from either linear or branched chain polysiloxanes being substantially cross-linked. Such cross-linking is potentially desirable inasmuch as the lattice thus formed should serve as an excellent framework into which the lubricant vehicle may be imbibed, but it has been found, surprisingly enough, that unless the gel is prepared in the presence of a stable silicone liquid such as phenylmethyl silicone polymer the manufacture of smooth greases is ditficult if not impossible. A silicone lubricant vehicle and a thickener gel prepared in the absence of a stable silicone liquid cannot be milled together satisfactorily, apparently because the lubricant vehicle is not readily imbibed into the gel. When, however, a stable liquid polymer is uniformly distributed throughout the lattice structure during formation thereof, imbibition of the lubricant vehicle into the gel is effectively promoted during the milling operation. A liquid polymer must be employed for this purpose which is not oxidized or thermally rearranged to any substantial extent under the conditions encountered and which will serve to promote the rapid and smooth admixture of gel and lubricant vehicle by uniformly blending with such lubricant vehicle and promoting its inhibition. For this purpose, a phenylmethylsilicone liquid in the lubricant viscosity range is preferred, although other organo-silicon liquids which are stable at the elevated temperatures may likewise be employed. The liquid organo-silicon polymer may be mixed with the polysiloxane to be gelled just prior to heating same or it may be combined in the initial hydrolysis of the various silanes.

An amount from about 2% to about 60% and preferably from about 10% to about 30% by weight of the mixture subjected to heating should comprise stable silicone, e. g. phenylmethylsilicone. l-f phenylmethylsilicone liquid or other suitable stable silicone liquid is to be employed as the total lubricant vehicle, it may be present in its entirety during the heating step, but it is preferred from the standpoint of economy, both of time and energy, to prepare the gel with a lesser quantity and then to mill same with the remaining portion of the vehicle. The insulating efiect of a large quantity of thermally stable liquid, such as phenylmethylsilicone, greatly retards the formation of the gel and consequently requires longer heating times.

Although the present invention does not reside in either th method of preparation of the polysiloxanes from which our thickener gels are prepared or the composition of such polymers, it is preferred to employ an aqueous-ether medium for carrying out the hydrolysis of the silanes because of proven excellent results obtainable therewith. Furthermore, it is essential that minimum quantities of certain silanes be present during hydrolysis in order to obtain sufficient chain formation; thus, it is necessary, in accordance herewith, to employ at least a minimum amount of dimethyldichlorosilane or dimethyldiethoxysilane as the primary chain former along with a minimum quantity of trimethylchlorosilane or trimethylethoxysilane to inhibit chain formation and assure substantial elimination of residual functionality. Varying amounts of methyltrichloroor methyltriethoxysilane may or may not be present as well. Rochows Chemistry of the Silicones (Wileyl95l), which goes into considerable detail with respect to preparative techniques, coupled with the illustrative examples hereinafter set forth eliminates the necessity for further detailed discussion thereof.

In accordance with the present invention, therefore, the thickener gel is prepared by heating in the presence of a stable liquid organo-silicon polymer, polysiloxanes resulting from the hydrolysis of a mixture comprising about 30% to about 90% and preferably from about 45 to about 70%, of dimethyldichlorosilane or dimethyldiethoxysilane, from to about 70% and preferably from about 25% to about 50% of methyltrichlorosilane or methyltriethoxysilane, and from about to about 70% and preferably from about to about 30% of trimethylchlorosilane or tn'methylethoxysilane. Such polysiloxanes should be heated to a temperature in the range of from about 400 F. to about 550 F. for a period of from about 2 hours to about 72 hours depending upon the temperature employed and preferably for a period of from about hours to about 40 hours at temperatures in the range of from about 450 F. to about 500 F. in order to produce a suitable gel for use in accordance herewith. It should be understood that longer time is required at lower temperatures and that at the higher temperatures the gels are formed more quickly. Furthermore, the larger th percentage of stable silicone present, the longer the time required at any given temperature.

The amount of gel, prepared in accordance herewith, which is required to thicken a silicone lubricating viscosity range oil to grease consistency varies over a relatively wide range depending upon the consistency of the grease desired and the composition of the particular gel. If, for example, the gel is prepared from a mixture comprising a relatively large amount of stable phenylmethylsilicone liquid, a greater percentage of that gel is required to produce a grease in admixtures with a silicone oil inasmuch as such a gel already embodies a rather large part of the lubricant vehicle in its lattice. In accordance herewith, therefore, greases of the present invention may be prepared by milling an amount of from about 10% to about 80% and preferably from about 20% to about 60% of a gel prepared in accordance with the present invention with a silicone liquid in the lubricating viscosity range of the type hereinafter more fully defined.

The silicone polymer oils useful as th lubricant vehicles in accordance with the present invention, as distinguished from the thermally stable phenylmethyl silicone or the like, which must be heated with the gel, have the following unit structure:

B one] it wherein R and R represent alkyl, aryl, alkylaryl, aryalkyl and cycloalkyl groups. Such compounds may be produced by well-known methods, e. g. the hydrolysis of dialkyldichlorosilanes or dialkyldiethoxysilanes. For purposes of the present invention, only those polymers which are high boiling liquids within th lubricating oil viscosity range are suitable, these generally possessing a viscosity at 100-F. which is within the range of from about 10 to about 600 centistokes. Such products are generally colorless and inert, have very low volatility and undergo relatively slight change in viscosity for a given change in temperature. Relatively common oils of this type are dimethylsilicone polymer, phenylmethylsilicone polymer, chlorophenylmethylsiliconepolymer, etc., it being preferred to employ the phenylmethylsilicone polymer in accordance herewith. Methods of preparing such compounds are taught in numerous patents, e. g. U. S. 2,410,346, U. S. 2,456,496, and in the literature such as Chemistry of the Silicones by Rochow, page 61, et seq. A particularly desirable phenylmethylsilicone polymer for use in accordance with the present invention is Dow-Corning 550 silicon fluid, a product of Dow- Corning, Inc., which has a viscosity at 77 F. of about 100 to 150 centistokes. As indicated above, it is preferred that the organo-silicon polymer oil employed as promoter and which is incorporated with the polysiloxanes during the heating step be the same as that with which the resulting gel is milled to produce a grease, but this is not necessary and different polymers may be employed. Thus, for example, phenylmethylsilicone oil may be employed as the promoter liquid and after formation of the gel, under conditions hereinabove set forth, the gel may be milled with a methylsilicone oil to produce a grease.

As indicated in the Chemistry of the Silicones by Rochow (1951), page 78 et seq., various theoretical and practical possibilities exist for th preparation of crosslinked polysiloxanes of the type herein described and whereas the initial reactants are preferably the methylchlorosilanes, the methylethoxysilanes may likewise be used to produce the desired gel.

In order that those skilled in the art may better understand how th present invention may be carried into efiect, the following illustrative examples are given. In the following examples the temperatures given are those determined by means of a thermocouple attached to the electrical heating mantles employed and are known to be substantially higher than the temperature of the material being heated, particularly in those cases where a short period of time was employed and opportunity for equilibrium is not available.

Example 1 A mixture of 100 g. of methyltrichlorosilane, 100 g. of dimethylchlorosilane, 20 g. of trimethylchlorosilane, 80 g. of Dow-Corning 550 silicone fluid, and 500 ml. of ethyl ether was poured onto about 500 g. of ice and the layers were separated. The volatile material was distilled olf and the residue baked at a thermocouple reading of 600 F. for two hours to give a white gel. Previous experience with the heating mantle would indicate that a pot temperature of about 550 existed. This gel and 50 additional grams of Dow-Corning 550 silicone fluid were mixed and passed through a colloid mill to give a smooth white grease. When passed through a mesh screen in a Hain microworker, the following micropenetrations were measured:

Worker strokes: Penetration 0 254 Example 2 Example 3 g. of dimethyldichlorosilane, 100 g. of methyltrichlorosilane, 50 g. of trimethylchlorosilane and 12.5 g. of Dow-Corning 550 oil were hydrolyzed in a manner similar to that set forth in Example 1 and after removing the ether the resulting hydrolysis product was heated to 400 F. for a period .of about 70 hours to produce a white gel. This gel was then milled with 30 g. of DC 550 oil and milled in a roller mill to produce a smooth homogeneous grease.

Example 4 In comparison to the grease of Example 2, 100 g. of Dow-Corning 200 were heated to a temperature of 500 F. for a period of 30 hours during which time air was continuously bubbled therethrough. The white gel which resulted had essentially the same appearance as that of Example 2 but could not be readily milled With 50 g. of Dow-Corning 550 oil and the product resulting therefrom a grainy, lacked homogeneity, and was extremely lumpy.

It should be understood, with respect to the temperature range in which the gels of the present invention may be prepared, that below about 400 F. any gelation which might occur would take too long to be practical and that above about 550 F. the possibility of incipient decomposition of the organo-silicon constituents exists, particularly the thickened polymethylpolysiloxane.

The percentages recited in the above description and appended claims are by weight unless otherwise indicated.

Having thus described the present invention, what we claim as new and desire to secure as Letters Patent of the United States is:

l. The method of preparing a homogeneous thermally stable organo-silicone polymer grease consisting essentially of a thermally stable organo-silicone polymer having a viscosity in the lubricating oil range of from about to about 600 centistokes at 100 F. thickened to grease consistency with a gelled polymethylpolysiloxane, comprising mixing from about 40% to 98% of a liquid polymethylpolysiloxane substantially free of unreacted OH groups with from about 2% to about 60% of a liquid organo-silicone polymer, other than said polymethylpolysiloxane, thermally stable at temperatures up to about 550 F. and having a viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., heating said mixture to a temperature in the range of from about 400 F. to about 550 F. for a period of from about 1 hour to about 72 hours to form a gelled mixture, and milling the resultant gelled mixture with a sufiicient amount of a thermally stable organo-silicone polymer having a viscosity in the lubricating oil viscosity range of from about 10 to about 600 centistokes at 100 F. to form a homogeneous grease containing from about 10% to about 80% of said gelled mixture. I

2. A homogeneous thermally stable grease prepared by the method of claim 1.

3. The method of preparing a homogeneous thermally stable organo-silicone polymer grease consisting essentially of a phenylmethyl silicone polymer having a viscosity in the lubricating oil viscosity range of from about 10 to about 600 centistokes at 100 F. and a polymethylpolysiloxane, comprising mixing from about 40% to about 98% of aliquid polymethylpolysiloxane substantially free of unreacted OH groups with from about 2% to about 60% of a phenylmethyl silicone liquid stable at a temperature of about 550 F. and having a viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., heating said mixture to a temperature in the range of from about 400 F. to about 550 F. for a time sutficient to form a gelled mixture, and milling the resultant gelled mixture with a suflicient amount of a thermally stable organo-silicone polymer having a viscosity in the lubricating oil viscosity range of from about 10 to about 600 centistokes at 100 F. to form a homogeneous grease composition containing from about 10% to 80% of said gelled mixture.

4. A homogeneous thermally stable grease prepared by the method of claim 3.

5. The method of preparing a homogeneous thermally stable organo-silicone polymer grease, consisting essentially of a thermally stable organo-silicone polymer, havinga viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., thickened to grease consistency with a gelled liquid polymethyl-polysiloxane, comprising mixing from about 2% to about 60% of a liquid or'gano-silicone polymer, thermally stable at a temperature up to about 550 F. and having a viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., with from about 40% to 98% of a mixture comprising, from about 30% to about 90% of a silane selected from the group consisting of dimethyldichlorosilane and dimethyldiethoxysilane, from 0% to about 70% of a silane selected from the class consisting of methyl trichlorosilane and methyl triethoxysilane, and from about 10% to about 70% of a silane selected from the group consisting of trimethyl chlorosilane and trimethylethoxysilane, cohydrolyzing said mixture in an aqueous-ether medium to obtain a resultant mixture of a polymethylpolysiloxane substantially free of unreacted --OH groups, and said organosilicone polymer, heating said resultant mixture to a temperature in the range of from about 400 F. to about 550 F. for a time suflicient to form a gelled mixture, and milling said gelled mixture with a sufiicient amount of a liquid organo-silicone polymer, having a viscosity in the lubricating oil viscosity range of from about 10 to about 600 centistokes at 100 F. and thermally stable at a temperature up to about 550 F., to forma homogeneous grease composition containing from about 10% to of said gelled mixture.

6. The method of claim 5 in which the organo-silicone polymer is a phenylmethyl silicone.

7. The method of preparing a homogeneous thermally stable organo-silicone polymer grease, consisting essentially of a thermally stable organo-silicone polymer, having a viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., thickened to grease consistency with a gelled liquid polymethyl-polysiloxane, comprising mixing from about 2% to about 60% of a liquid organo-silicone polymer, thermally stable at a temperature up to about 550 F. and having a viscosity in the lubricating oil range of from about 10 to about 600 centistokes at 100 F., with from about 40% to 98% of a mixture comprising from about 30% to about of dimethyldichlorosilane, from 0% to about 70% of methyltrichlorosilane, and from about 10% to about 70% of trimethylchlorosilane, cohydrolyzing said mixture in an aqueous-ether medium to obtain a resultant mixture of a polymethyl polysiloxane substantially free of unreacted OH groups, and said organo-silicone polymer, heating said resultant mixture to a temperature in the range of from about 400 F. to about 550 F. for a time sufiicient to form a gelled mixture, and milling said gelled mixture with a sufficieut amount of a liquid organosi-licone polymer having a viscosity in the lubricating oil viscosity range of from about 10 to about 600 centistokes at 100 F. and thermally stable at a temperature up to about 550 F., to form a homogeneous grease composition containing from about 10% to 80% of said gelled mixture.

8. A homogeneous thermally stable grease prepared by the method of claim 7.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,218 Rochow Oct. 7, 1941 2,397,727 Daudt Apr. 2, 1946 2,407,181 Scott Sept. 3, 1946 2,443,353 Hyde et al. June 15, 1948 2,460,457 Hyde Feb. 1, 1949 2,460,795 Warrick Feb. 1, 1949 (Other references on following page) UNITED STATES PATENTS I 2,561,178

Daudt May 3, 1949 2, 45,5 3 Hyde Oct. 25, 1949 Pederson Nov. 1, 1949 Daudt Apr. 24, 1951 365,3

, Burkhard July 17, 1951 Hunter et a1 Oct. 21, 1952 Barry' July 14, 1953 FOREIGN PATENTS Germany Feb. 2, 1953

Claims

1. THE METHOD OF PREPARING A HOMOGENEOUS THERMALLY STABLE ORGANO-SILICONE POLYMER GREASE CONSISTING ESSENTIALLY OF A THERMALLY STABLE ORGANO-SILICONE POLYMER HAVING A VISCOSITY IN THE LUBRICATING OIL RANGE OF FROM ABOUT 10 TO 600 CENTISTOKES AT 100* F. THICKENED TO GREASE CONSISTENCY WITH A GELLED POLYMETHYLPOLYSILOXANE, COMPRISING MIXING FROM ABOUT 40% TO 98% OF A LIQUID POLYMETHYLPOLYSILOXANE SUBSTANTIALLY FREE OF UNREACTED -OH GROUPS WITH FROM ABOUT 2% TO ABOUT 60% OF A LIQUID ORGANO-SILICONE POLYMER, OTHER THAN SAID POLYMETHYLPOLYSILOXANE, THERMALLY STABLE AT TEMPERATURES UP TO ABOUT 550* F. AND HAVING A VISCOSITY IN THE LUBRICATING OIL RANGE OF FROM ABOUT 10 TO ABOUT 600 CENTISTOKES AT 100* F., HEATING SAID MIXTURE TO A TEMPERATURE IN THE RANGE OF FROM ABOUT 400* F. TO ABOUT 550* F. FOR A PERIOD OF FROM ABOUT 1 HOUR TO ABOUT 72 HOURS TO FORM A GELLED MIXTURE, AND MILLING THE RESULTANT GELLED MIXTURE WITH A SUFFICIENT AND MILLING THE RESULTANT GELLED MIXTURE WITH A POLYMER HAVING A VISCOSTIY IN THE LUBRICATING OIL VISCOSITY RANGE OF FROM ABOUT 10 TO ABOUT 600 CENTISTOKES AT 100* F. TO FORM A HOMOGENEOUS GREASE CONTAINING FROM ABOUT 10% TO ABOUT 80% OF SAID GELLED MIXTURE.