GB1583037A

GB1583037A - Hydrocarbon/silicone oil lubricating compositions

Info

Publication number: GB1583037A
Application number: GB13792/77A
Authority: GB
Original assignee: Union Carbide Canada Ltd
Current assignee: Union Carbide Canada Ltd
Priority date: 1976-04-02
Filing date: 1977-04-01
Publication date: 1981-01-21
Also published as: DE2714135A1; SE426843B; NO144775B; DK147377A; NO771162L; BE853183A; NO144775C; JPS52135307A; DE2714135B2; SE7703608L; FR2346441B1; FI770987A; FR2346441A1; NL7703604A; DE2714135C3; CA1067887A

Description

(54) HYDROCARBON/SILICONE OIL LUBRICATING COMPOSITIONS (71) We, UNION CARBIDE CANADA LIMITED, a company incorporated under the laws of Canada, of 123 Eglinton Avenue East, Toronto, Province of Ontario, Canada, M4P lJ3, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to low temperature lubricant compositions having improved viscosity-temperature properties, lubricating properties, and pour point.

Lubricating oil compositions are often employed as speciality oils, power transmission fluids, or heat transfer fluids, such as in automatic transmissions, pumps, and hydraulic equipment. Most equipment of this sort is rendered inoperable if the viscosity of the functional fluid changes dramatically between extremes of operating temperature. The problem is particularly acute in arctic regions where the ambient temperature can vary from 750F to 1000 F, and the operating temperature of the equipment may vary from -750F to 3000F; similar operational temperature ranges are frequency encountered in heat exchange equipment.

In order to achieve the required viscosity stability (high viscosity index) the fluids are provided with additives such as polyalkyl methacrylate polymers and copolymers, polyisobutylenes, polyalkyl styrenes, and copolymers of methacrylates or fumaric-acid esters with polar monomers; typical of the last type is vinyl pyrrolidine. These additives, however, are not always completely satisfactory; in many cases their thermal stability, stability under load, or both, are insufficient to provide the modified fluid with an extended or useful life.

Where conventional viscosity index improvers have not been successful in providing adequate viscosity index along with other properties, common practice has been to operate equipment continually to maintain the operating temperature, or to frequently change the fluid to conform with changing ambient conditions and operating temperature. Clearly, such routes are economically and conservationally unsound.

It is well known that certain liquid poly(organosiloxanes) exhibit a very high viscosity index which enables them to be used as functional fluids over a broad temperature range. Poly(dimethylsiloxane) in particular, shows a performance in this area which is superior to virtually all known materials. Unfortunately, these socalled silicone oils, especially poly(dimethylsiloxane), are incompatible with most other materials and are economically unattractive; moreover, they have poor lubricating properties when used as lubricants for metal on metal, particularly steel on steel applications. Their incompatibility makes it difficult to improve their performance with additives.

In order to take advantage of the good viscosity-temperature properties of silicone oils, it is desirable to dissolve them in lubricating oil carriers. This has been carried out with various poly(organo-siloxanes) as described in German Patent 1,806,445. However, the solubility characteristics of poly(dimethylsiloxane) generally prevent its dispersion in liquid media, except with the aid of dispersing agents or emulsifiers, such as described in U.S. Patent 3,445,385 and U.S. Patent 2,466,642.

It is well known that the higher the molecular weight of the polymer or solvent, the more difficult it becomes to effect dissolution. Thus, in those few cases where poly(dimethylsiloxane) oil has been successfully incorporated into a homogeneous composition, the molecular weight of the silicone has been such that its viscosity has been limited to around 1,000 cS or less as shown in U.S. Patent 2,652,364 and U.S. Patent 2,618,601. The solubility characteristics, viscosity-temperature behaviour, and lubricating properties of such low molecular weight polymers of dimethylsiloxane are markedly different from those exhibited by the higher liquid polymers. In fact, it is generally accepted that high polymers of any polymeric material possess very different properties from their lower molecular weight counterparts. Clearly, the behaviour of plastic polyethylene cannot be predicted from the properties of hexane or octane. It has been the experience of workers in the field that solutions of high viscosity (i.e. high molecular weight) poly(dimethylsiloxane) are temperature sensitive, and solution components separate at temperatures significantly above those at which lower polymers become incompatible. For this reason, it has, heretofore, been impossible to utilize hydrocarbon lubricants containing significant amounts of high viscosity dimethyl silicone oil in applications where even nominally low temperatures are encountered.

It is an object of this invention to provide a low temperature lubricant oil composition containing poly(dimethylsiloxane) having a relatively high viscosity, said composition exhibiting good lubricity and pour point characteristics.

According to the present invention a lubricating oil composition comprises a homogeneous mixture of (A) from lV to 500/, by weight of poly(siloxane) having the general formula:

wherein R is a methyl group in substantially all cases and n has a value such that the average viscosity of the poly(siloxane) at 1000F is between 10,000 cS and 1,000,000 cS, and (B) a hydrocarbon oil having a viscosity of less than 40,000 cS at -65 F, and a flashpoint higher than 175"F, said hydrocarbon oil being at least one selected from (a) alkenes, (b), isoparaffins, and (c) naphthenes having a single ring which has many alkyl substituents.

More preferably, R in the polysiloxane is always a methyl group, and n has values such that the viscosity of the poly(siloxane) at 1000F is between 10,000 cS and 500,000 cS and the poly(siloxane) is present in the composition in concentrations from 5 to 300/, by weight. It will be appreciated by those skilled in the art of polymer chemistry that in polymers of the size described above, the possibility exists that R might be other than a methyl group in one or more of the positions along the polymer chain. Some slight deviation from R being a methyl group in the poly(dimethylsiloxane) would therefore be acceptable without departing from the present invention so long as the extent of deviation does not significantly affect the viscosity, temperature behaviour, or solubility. For this reason the formula given above is described wherein R is a methyl group in substantially all of the cases.

The hydrocarbon oil of the invention may be of either synthetic or natural origin, and is selected from the classes known as naphthenic, paraffinic, alkene, or a combination of these. By naphthenic species, we mean any non-aromatic ring structure comprised solely of carbon and hydrogen. By paraffinic species, we mean all those hydrocarbons that do not contain cyclic structures, or double or triple bonds. By alkene species, we include only those hydrocarbons not containing cyclic structures, hut which contain non-conjugated double bonds.

The hydrocarbon oils of the invention have a viscosity less than 40,000 cS at -65"F, and a flashpoint higher than 175"F.

More specifically, the paraffinic hydrocarbons must be multi-branched hydrocarbons, commonly known as iso-paraffins, wherein at least 500/, of the primary branches are located on carbon atoms which are immediately adjacent to each other, or on carbon atoms which are separated by only one carbon atom. We have also discovered that the degree and type of branching is critical to the solvent power of the isoparaffins. While it is permissible for the primary branches to be higher alkyl groups, where they exceed 3 carbon atoms, they must also be branched, e.g. isobutyl radicals are acceptable, whereas n-butyl radicals are not.

Examples of petroleum distillates corresponding to this description include Esso Univolt 40, and Imperial Oil Isopar M products. The words Esso, Univolt and Isopar are registered Trade Marks.

The entire range of the above described paraffins may correspond identically to, and may be obtained directly by hydrogenation of polymers, oligomers, or copolymers of hydrocarbons of twelve carbons or less. Said small hydrocarbons include, propylene, butenes, pentenes and hexenes.

The present invention will now be further described by means of the following Examples 1 to 6, 10 to 19, 25, 27-31, and 33 to 36. The other Examples which follow are for comparative purposes.

EXAMPLE 1 15% by weight of poly(dimethylsiloxane), having a viscosity of 750,000 cS at 100"F, was dissolved in Esso Univolt 40, a petroleum oil fraction very high in isoparaffin content, which has a flashpoint of 210 F and viscosities of 750 cS and 1.4 cS at -65"F and 210 F respectively. (Esso and Univolt are registered Trade Marks). The resulting composition was homogeneous at --650F, and had viscosities of 8,792.2 cS and 53.9 cS at -650F and 210"F.

EXAMPLE 2 50% by weight of poly(dimethylsiloxane), having a viscosity of 10,000 cS at 100"F, was dissolved in Univolt 40 (Univolt is a registered Trade Mark). The resulting composition was homogeneous at -650F, and had viscosities of 17,000 cS and 187.5 cS at -650F and 210 F respectively.

EXAMPLE 3 10% by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cS at 100"F was dissolved in 2,2,4,4,6,8,8 heptamethylnonane, a material obtainable by hydrogenating a random polymer of isobutylene. Other methods for the synthesis of this hydrocarbon also exist of course and are known to those skilled in the art.

Heptamethylnonane has a flashpoint of 240"F and viscosities at -650F and 210 F of 160 cS and 1.42 cS respectively. The resulting composition was homogeneous at -65"F, and had viscosities of 750 cS and 12.5 cS at -650F and 210 F respectively.

EXAMPLE 4 10% by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cS at 1000 F, was dissolved in a cut of hydrogenated polyisobutylene that had a flashpoint of 260"F and viscosities at-650F and 210 F of 1,150 cS and 1.8 cS respectively; the isobutylene polymer was formed exclusively by head to tail monomer addition. The resulting composition was homogeneous at 650 F, and had viscosities of 5,000 cS and 10.34 cS at --650F, and 210"F respectively.

EXAMPLE 5 1% by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cS at 100"F, was dissolved in Esso Univolt 40 (Esso and Univolt are registered Trade Marks). The resulting composition was homogeneous at -650F and had viscosities at -65"F and 210"F of 740 cS and 1.75 cS respectively.

The alkene hydrocarbons used in the invention must have a structure such that their saturated analogues correspond to the suitable paraffins described above.

These alkenes may correspond identically to, and may be obtained directly from polymers, oligomers, or copolymers of hydrocarbons of twelve carbons or less.

Such small hydrocarbons include propylene, butenes, pentenes and hexenes. An example of a composition that contains such an olefinic compound follows.

EXAMPLE 6 10 by weight of poly(dimethylsiloxane), having a viscosity of 100,000 cS at 100"F, was dissolved in polypropylene, a polymerization product having a flashpoint of 240"F, and a viscosity at -650F of 433 cS. The resulting composition was homogeneous at -650F and had viscosities of 1,624 cS and 9.55 cS at -650F and 2l00F respectively.

The naphthenics used in the invention do not contain more than one ring; furthermore, the rings contain many substituent alkyl groups, and that where said substituent groups exceed four carbons, they must correspond to structures defined above for olefins or iso-paraffins.

To illustrate the advantage of compositions of the invention over compositions comprising quantities of high molecular weight poly(dimethylsiloxane) and known solvents for low molecular weight poly(dimethylsiloxane), the following examples are offered. It is to be understood that Examples 7-9 are provided for illustrative purposes, and in no way constitute or simulate compositions of the invention.

EXAMPLE 7 A naphthenic oil, Sunoco Circosol304, having a pour point of -50"F (i.e. a viscosity at -500F > 90,000 cS) was combined with 10% by weight of poly(dimethylsiloxane), having a viscosity at 100"F of 100,000 cS. (Sunoco is a registered Trade Mark). The admixture was observed to separate at temperatures below 40"F.

EXAMPLE 8 Polyisobutylene, of the type described in U.S. Patent 2,446,642, having a flashpoint > 360 F, and viscosity at -650F > 40,000 cS, was combined with 10% by weight of poly(dimethylsiloxane) having a viscosity at 1000F of 100,000 cS. The admixture became non-homogeneous and separated at temperatures below 20"F.

EXAMPLE 9 A highly refined paraffin oil (Sunpar 106H) having a pour point of 150F, was combined with 100/, by weight of poly(dimethylsiloxane) having a viscosity at 1000 F of 100,000 cS. The admixture separated at 750 F.

To illustrate the great improvement in viscosity properties obtained when using poly(dimethylsiloxane) instead of another viscosity improver, the following example is offered for comparison with Example 1.

EXAMPLE 10 Two compositions were prepared using quantities of poly(dimethylsiloxane) having a viscosity at 1000F of 60,000 cS, and a commercial viscosity improver, TLA-407, which when dissolved in Univolt 40 gave initial viscosities which were approximately equal: 9.7 cS and 9.6 cS respectively at 1000C (Univolt is a registered Trade Mark). The viscosities of the same solutions at -67"F were 990 cS and 1,390 cS respectively. The relative difference in viscosity change favours the use of the silicone viscosity improver by a wide margin.

It is a characteristic and great advantage of the compositions of the invention that they are compatible with selected antiwear additives. Wear of system components moving with respect to, and in contact with each other is a serious problem and limits the life and usefulness of all machinery. Thus for lubricating fluids, utilized in environments where other than hydrodynamic lubrication is required, commonly referred to as boundary or extreme pressure lubrication conditions, industry and military specifications have been set on the lubricating, or antiwear, or load bearing properties of the fluid. Under these so-called boundary or extreme pressure conditions, one or more of the components of the lubricant composition interact with each other and/or interact or chemically react with the surfaces to be lubricated to provide the fluid with certain measurable and unique lubricating antiwear, and/or load bearing properties. Numerous examples exist in the literature where so-called lubricity or antiwear additives have been included in lubricant compositions to provide the desired properties. Among the more common antiwear additives are: polyalkyl and polyaryl phosphates such as tricresyl phosphate, organic acids such as adipic acid, various amines, diesters, thiophosphates and thiocarbamates.

In some cases the effectiveness of common lubricity additives is diminished by their interaction with certain components of the fluid. Specifically, it is well documented that fluids containing or comprised of liquid poly(organosiloxanes), particularly poly(dimethylsiloxane), inhibit the action of such lubricity additives; examples include "Antiwear and Antifriction Properties of Poly (organosiloxanes and Their Mixtures with Hydrocarbons", G. V. Vinogradov et al, Paper No. 64-Lub8, Transactions of the ASME, 1964; "Influence of Additives on the Antiabrasion and Antifriction Properties of Polysiloxarres", M. I. Nosov and G. V. Vinogradov, Khim i Topliv i Masel 9 (8), 50-3, (1964); "Effects of Chemically Active Additives on Boundary Lubrication of Steel by Silicones", S. F. Murray, R. L. Johnson, Natl. Advisory Comm. Aeronaut. Tech. Note 3257, (1954). With these fluid compositions, it is necessary to utilize excessive concentrations of antiwear additives or alternatively, to use highly reactive materials to replace common additives in order to provide wear protection meeting common standards. Either of these approaches produce adverse effects, including damaging corrosion and/or decomposition of the other materials contained in the fluid. It is also known that additional problems are encountered when using additives in fluids containing silicone oils. Poly (organosiloxane) molecules are sensitive to the presence of certain chemical functionalities, most notably acids, which act to decompose the silicone molecule. Also, certain additives will cause silicone oil to be precipitated from solution, thereby degrading the properties of the fluid.

We have discovered that the inclusion of selected antiwear additives in the compositions of the invention overcomes the problems outlined above, and that said additives show unexpected and advantageous activity in the presence of silicone oil as found in said compositions. The additives are not essential to the composition of the invention but if used are selected from three general classes, the first being certain metal salts of thiophosphates, corresponding to the general formula:

in which R is selected from an alkyl group and an aryl group and M is selected from among cadmium, lead, or zinc. Most preferably, R is an alkyl group of less than 20 carbons, and M is zinc. The compositions may contain said thiophosphate salts to the extent that the concentration of the metal in the final formulation is between 0.02 weight percent and 0.5 weight percent, and preferably between 0.06 weight percent and 0.3 weight percent. These compounds are commonly referred to as zinc dialkyl dithiophosphates, and are well known in the industry. Examples of effective dithiophosphate salts available in industry include: Lubrizol 1395, available from Lubrizol Corp.; Elco 116 and Elco 124, available from Elco Corp.; Oloa 267 and Oloa 269 available from the Oronite division of Chevron Chemical Co.; and Hitec E-522, available from Edwin Cooper Inc. Lubrizol, Elco and Hitec are registered Trade Marks.

Additionally, it has been discovered that certain metal salts of thiocarbamates are also useful at normal levels in the presence of silicones. These are of the general formula:

in which R may be an alkyl group or an aryl group. More preferably, R is an alkyl group, and most preferably R is a 5 carbon alkyl group.

The compositions may contain said thiocarbamate salts in concentrations such that the concentration of the metal in the final formulation is between 0.02 weight percent and 0.5 weight percent, and preferably between 0.06 weight percent and 0.3 weight percent. Examples of effective dithiocarbamate salts available in industry include: Cadmium diamyl dithiocarbamate, marketed as Vanlube 61, and Antimony dialkyl dithiocarbamate marketed as Vanlube 73; both are available from the R. T. Vanderbilt Corp. Vanlube is a registered Trade Mark.

Further, for applications where corrosion is required to be negligible, thus precluding the use of sulphur, it has been discovered that, in contrast to the performance of other known organic esters, certain alkyl esters of 4-isopropyl benzoic acid, commonly known as cumic acid, provide excellent antiwear properties when used in conjunction with silicone oils. These esters are of the general formula:

where R is an alkyl group containing from I to 10 carbon atoms and preferably from 3 to 5 carbon atoms. Concentrations between 0.1 to 20/, by weight, and especially 0.5 to 1% by weight of the named esters are preferred in the final formulation to meet rigorous industry specifications.

An example of an effective ester is isobutyl cumate which has the structure:

Wear Additive Product Performance Small concentrations of the above named anti-wear additives are effective in maintaining wear at or below common specifications. The wear properties of lubricating fluids are commonly determined with a four-ball wear tester. In this test, one steel ball is rotated in the interstice formed by three other immobilized balls immersed in the oil. The wear scars on the three immobilized balls are measured to give an indication of the lubricating properties of the oil. One such test, described in the U.S.A. Military Specification Mil-H-5606-C and commonly utilized by industry to approximate boundary or moderate E.P. conditions, (henceforth referred to as test condition A) is conducted under the following conditions: Test Condition A Temperature 75"C Speed of Rotation of Ball 1200 RPM Pressure 40 kg Time 1 hour The average diameter of the wear scar produced on the three immobilized balls must be less than 1 mm for the lubricating fluid to pass the specification. Examples 12-19 which follow illustrate the superior performance of the selected antiwear additives when tested according to test condition A. Example 11 illustrates a composition according to the inventioh but without the addition of the selected antiwear additive.

EXAMPLE 11 A silicone hydrocarbon composition was formulated as follows: Poly(dimethylsiloxane) 100,000 cS 10 by weight Esso Univolt 40 90% by weight (Esso and Univolt are registered Trade Marks).

This oil was tested in the four-ball tester according to test condition A, and an average scar diameter of 1.16 mm was obtained.

EXAMPLES 12-19 The anti-wear additives were combined with a base oil described in Example 11. Since, with the exception of isobutyl cumate, they are available in industry in dilute form, higher concentrations of the diluted commercial products have been used in a manner consistent with the preceding discussion.

Example Wt. %; Blended with Average No. Additive Base Oil of Example 11 Wear Scar mm 12 Lubrizol 1395 5% .61 13 Elco 116 5%; .69 14 Elco 124 50/, .64 15 Oloa 267 5%; .75 16 Oloa 269 5% .64 17 Hitec E-522 5% .62 18 Vanlube 61 5% .78 19 Isobutyl Cumate 1% .82 (Lubrizol, Elco, Hitec and Vanlube are registered Trade Marks).

EXAMPLES 224 The exceptional and surprising performance of the selected additives is appreciated by comparing their performance with that of other common additives of the same general class which are shown to be ineffective. Such a comparison is provided by examining the following data which were obtained from the testing of several common additives under conditions identical to Examples 12-19. It is to be understood that the antiwear additives described in Examples 22-26 are not suitable for addition to the composition of the invention.

Example Wt. %; Blended With Average No. Additive Base Oil of Example 11 Wear Scar mm 20 TCP 5% 1.07 21 Non-Metallic Thiophosphate (Vanlube 73) 5%; Weld 22 Zinc Dibutyl Dithiocarbamate 1 /O 1.08 23 Sulphur (Elco 217) 5% 1.01 24 Antimony Dialkyl 3%; 1.09 Dithiophosphate (Oloa 254) The concentrations given in Examples 21, 23 and 24 refer to percentages of commercial products rather than pure active ingredient.

Vanlube and Elco are registered Trade Marks.

A significant aspect of the invention is the apparent complementary action between silicone-containing fluids and the selected antiwear additives. Illustrative of this is the positive or neutral effect that the selected antiwear additives have with respect to the antiwear properties of unimproved solutions of poly(dimethylsiloxane), as described in Example 11. It is well known that solutions of silicone oil show antiwear properties superior to those of either the silicone or the other component and publications describing this synergistic phenomenon are plentiful; examples include: "Polysiloxanes as Additives for Increasing the Lubricating Action of Petroleum Oils and Hydrocarbons". M. I. Nosov; Teoriya Smaz. Diestviya i Novye Materialy, Akad. Nauk SSSR; 1965. 68-72. "Antiwear and Antifriction Properties of Poly (organosiloxane)s and their Mixtures with Hydrocarbons". G. V. Vinogradov et al Wear, 8 (12), 92-111, 1965.

The conditions under which this effect occurs are commonly encountered in industry, and they can be approximated by the following four-ball test which is given in the Canadian Government Specification Board, specification 3 GP-59 (henceforth referred to here as test condition B): Test Condition B Temperature 75"C Speed of Rotating Ball 600 RPM Pressure 15 kg Time 2 hours TESTS 1--3 The solution described in Example 13 was prepared and tested along with the individual components, according to test condition B.

Test Description Average Scar Diam.

Solution described in Example 13 .48 2 Univolt 40 .82 3 Poly(dimethylsiloxane) weld Univolt is a registered Trade Mark.

TESTS 4--7 The following tests were made on the four-ball tester according to test B.

Many of the selected additives are not designed to improve the lubricating properties under conditions as mild as those of test B (e.g. tests 6 and 7), as is seen by the following tests. Such limited usefulness with respect to severity of conditions is common to many materials used by industry for antiwear additives. Nevertheless, it is indicative of their utility in conjunction with silicone, that the selected additives do not adversely affect the antiwear action of silicone solutions, whereas other additives do. Comparing the following tests with Test 1 illustrates the neutral or beneficial effects of additives of the invention with regard to silicone induced antiwear scar diameters s0.35 mm.

Test Composition Average Scar Diam.

4 As described in Example 12 .34 5 As described in Example 13 .32 6 As described in Example 17 .50 7 As described in Example 18 .40 TESTS 8-13 The effects of other additives on the antiwear action of silicone solutions tested according to test B show marked contrast to the selected additives (Examples 12-18). Note also the deterioration occurring in Tests 8-13 from the results of Test 1. It is to be understood that the antiwear additives described in Tests 8-13 are not suitable for addition to the compositions of the invention.

Test Composition Average Scar Diam.

8 5%; TPSA in blend of Example 11 .62 9 As described in Example 20 .72 10 5%; organic acids and esters in blend of Example 11 .75 11 As described in Example 21 .78 12 As described in Example 22 .80 13 As described in Example 24 .88 The foregoing tests 4--7 illustrate the exceptional antiwear performance of lubricating compositions of the invention, to which the selected antiwear additives have been added. The large wear scars observed for compositions containing common additives other than the selected additives illustrate the unexpected and important improvement realized by adding the selected additives to compositions of the invention To qualify silicone-containing speciality oils for use under extreme pressure or boundary conditions requires improved performance such as that shown by compositions of the invention to which the selected antiwear additives have been added.

It is a further advantage of compositions of the invention that they are compatible with many common additives such as pour point depressants, e.g. low viscosity ( < 500 cS at 1000 F) polydimethylsiloxane, viscosity improvers, e.g.

polymethacrylates, oxidation or corrosion inhibitors, and dyes. It is also an advantage of the invention that the compositions thereof may be diluted with materials which would not normally be compatible with dimethyl silicone oil. Such materials may include mineral oils, for example distillate oils and residual oils, common synthetic hydrocarbons, alcohols, and other speciality oils. To illustrate the valuable compatibility characteristics, the following test is offered.

TEST 14 A composition as described in Example 3 was diluted with 20% by weight of Imperial H-515, a commercial hydraulic fluid. The mixture was compatible.

Poly(dimethylsiloxane) having a viscosity of 100,000 cS at 1000F is not miscible in H-515 alone.

It is an additional characteristic of compositions of the invention that they are prone to foaming. This foaming is caused by the entrainment and subsequent release of air from the liquid, a phenomenon which frequently occurs in conjunction with vigorous agitation, decompression, or circulation of the lubricant.

It is recognized throughout industry that foam is in a speciality oil can be highly detrimental to the operation of an automatic transmission or hydraulic device; thus, in order to ensure the commercial utility of compositions of the invention under such conditions, it was desirable to identify a foam controlling additive.

The foaming tendency of many hydrocarbon fluids is controlled by the use of silicone oils, e.g. U.S. Patent 2,416,503, or alternatively by using various halogenated materials, e.g. U.S. Patent 2,394,595, and U.S. Patent 2,515,115, or dispersed metal complexes, or surfactants. However, because the compositions of the invention contain large quantities of silicone oil, their properties are inherently different from those of compositions previously known, and their foaming tendencies are not controlled by the addition of most conventional additives.

It is an additional but optional feature of this invention that a certain species of perfluoroalkylpolyether in contrast to the behaviour of other known types of antifoam agents, and in contrast to the behaviour of other well known foamcontrolling perfluoroalkylpolyethers, has been discovered to be an effective antifoam agent in compositions of the invention.

Specifically, the lubricating compositions may contain a minor foam inhibiting amount of perfluoroalkylpolyether.

More specifically, the compositions as described above may contain from about 1 to 500 parts per million by weight and preferably 5 to 100 parts per million by weight, of a perfluoroalkvlpolyether corresponding to the formula: F-[CF (CF3)CF2O]x C2Fs in which x has a value providing an average molecular weight for the perfluoroalkylpolyether in the range from 2,000 to 7,000. This molecular weight range will correspond to values for x of about 11 to 41. The preferred perfluoroalkylpolyethers are those in which the average molecular weight in the range from 2,000 to 5,500 which molecular weights correspond to values for x of about 11 to 32, respectively. Some effective perfluoroalkylpolyethers are described below.

(a) A perfluoroalkylpolyether having the formula: F-[CF(CF3)CF2O]x C2F5 and having an average molecular weight of 4,500 corresponding to a value for x of about 26. This perfluoroalkylpolyether has a viscosity in centistokes at 1000F of 85 and at OOF of 6,900, and an approximate boiling range at 0.8 mm. Hg of 440 485"F.

(b) A perfluoroalkylpolyether having the formula: F-[CF(CF3)CF2Oix C2Fs and having an average molecular weight of approximately 2,000 corresponding to a value for x of about 11. This perfluoroalkylpolyether has a viscosity in centistokes at 100"F of 18 and at OOF of 550 and an approximate boiling range at 0.8 mm. Hg of 290--365"F. It is commercially available as Krytox AZ (where Krytox is a registered Trade Mark).

(c) A perfluoroalkylpolyether having the formula: F-[CF(CF3)CF2O]x C2Fs and having an average molecular weight of about 7,000 corresponding to a value for x of about 41. This perfluoroalkylpolyether has a viscosity in centistokes at 100"F of 495 and at 2100F of 43, and a vapor pressure at 7000F of about 80 mm of Hg. It is commercially available as Krytox AD (where Krytox is a registered Trade Mark).

Commercial perfluoroalkylpolyether products corresponding to the foregoing description are Krytox fluids manufactured by E. I. duPoint de Nemours & Company, Krytox being a registered Trade Mark.

To illustrate the surprising effectiveness of the perfluoroalkylpolyethers when added to compositions of the invention, the antifoam properties of a series of lubricant compositions, both with and without antifoams, were determined in a modified ASTM Foam Test, D-892. According to this test, the foam volume is determined at the end of five (5) minutes blowing with air, and again after standing for an additional ten (10) minutes, the test being conducted at room temperature.

EXAMPLES 25-30 The significance of the presence of dimethyl silicone oil in compositions of the invention is demonstrated by comparing foaming properties of hydrocarbons before and after the addition of said silicone oil. The effectiveness of perfluoroalkylpolyethers when added to compositions of the invention is also unambiguously demonstrated. Results appear in Table I.

EXAMPLES 31-32 The promotion of foaming due to the presence of substantial concentrations of poly(organosiloxanes) as a class is demonstrated by comparing the corresponding data in Table I with that of Examples 25-26. The foam controlling effectiveness of the perfluoroalkylpolyethers when added to compositions of the invention is again demonstrated.

EXAMPLES 33-35 As an illustration of the outstanding and unexpected performance of the perfluoroalkylpolyether antifoams when added to the compositions of the invention, they may be compared (especially Example 25) with the performance of various conventional antifoams, and other fluorinated antifoams (shown in these examples). Results appear in Table I. It is understood that the antifoam agents described in Examples 33-35 are presented for comparative purposes. In the Table, Univolt, and Krytox are registered Trade Marks.

TABLE I Foam Volume ASTM D892 75 F Without Antifoam With Antifoam After After After After 5' 10' 5' 10' Example Composition Antifoam Aeration Settling Aeration Settling 25 10 100,000 cS 2.5 ppm Krytox AZ, 400 ml 20 ml 30 ml 0 ml dimethylsilicone as described oil, 90 Univolt in (b) above 40, as described in Example 11 26 Univolt 40 10 ppm Krytox AZ 95 ml 0 ml 35 ml 0 ml 27 25% poly(dimethyl- 10 ppm Krytox AZ 450 ml 40 ml 25 ml 0 ml siloxane) (10,000 cS) 75 Univolt 40 28 10/, 750,000 cS 1 ppm Krytox AD, 200 ml 0 ml 140 ml 0 ml dimethyl silicone as described in oil, 99% Univolt (c) above 40 29 As described in 400 ppm Krytox AZ 400 ml 20 ml 0 ml 0 ml Example 25 30 As described in 400 ppm Krytox AD 400 ml 20 ml 10 ml 0 ml Example 25 31 50%; alkylpoly- 10 ppm Krytox AZ 170 ml 5 ml 35 ml 0 ml siloxane, 50% Univolt 40 32 25%; poly(phenyl- 10 ppm Krytox AZ 560 ml 260 ml 185 ml 0 ml methysiloxane), 75 Univolt 40 33 As described in 112 ppm FC-43 400 ml 20 ml 345 ml 0m1 Example 25 (heptacosafluoro- tributyl amine) 34 As described in 100 ppm 100,000 cS 400 ml 20 ml No No Example 25 silicone antifoam Change Change L-45 35 As described in 132 ppm FS-1265 400 ml 20 ml 175 ml 0 ml Example 25 (300) (trifluoro propylpolysiloxane) The foregoing examples illustrate the exceptional foam resistant tendencies of compositions of the invention when the perfluoroalkylpolyether antifoam additive is added thereto. This outstanding improvement over other foam controlled compositions is essential to qualify compositions of the invention for certain rigorous applications.

The foregoing data and discussion serve to reveal the exceptional properties and characteristics of speciality oil compositions containing high molecular weight silicone oil, and in some cases specific and surprisingly effective additives for the control of wear and foaming tendencies. For use in extreme and rigorous environments, speciality oils are required which possess properties such as those exhibited by compositions of the invention. As a final illustration of such a composition the following example is presented.

EXAMPLE 36 To a composition containing 100/, by weight poly(dimethylsiloxane), (100,000 cS) and 90% by weight Esso Univolt 40, was added: 2% by weight of Elco 116, 7.9 ppm Krytox AZ, 10/, by weight of an oxidation inhibitor; and a minor concentration of coloring dye. The resulting composition was homogeneous at -65 F, and had viscosities of 2,241 cS and 10.19 cS at -650F and 210 F respectively. The formulation gave good wear properties on a Shell four-ball wear test, and performed outstandingly when run in a Vickers type V-104-A hydraulic pump for 40 hours under high pressure conditions (Esso, Univolt, Elco, Krytox, Shell and Vickers are registered Trade Marks).

Van Lube is a trade mark of R. T. Vanderbilt Inc.

Elco is a trade mark of Elco Corporation.

Oloa is a trade mark of Chevron Corporation.

Claims

WHAT WE CLAIM IS:-

1. A lubricating oil composition comprising a homogeneous mixture of (A) from 1 to 500/, by weight of the total composition of polysiloxane having the general formula

wherein R is a methyl group in substantially all cases and n has a value such that the average viscosity of the polysiloxane at 1000F is between 10,000 cS and 1,000,000 cS, and (B) a hydrocarbon oil having a viscosity less than 40,000 cS at --650F, and a flashpoint higher than 175"F, said hydrocarbon oil being at least one selected from (a) alkenes, (b) isoparaffins, and (c) naphthenes having a single ring which has many alkyl substituents.

2. A composition as claimed in Claim I also comprising a minor amount of an antiwear additive (C) selected from (I) metal salts of thiophosphates corresponding to the formula:

in which each R is an alkyl group or an aryl group and M is cadmium, lead, or zinc; (2) metal salts of thiocarbamates corresponding to the formula:

in which each R is an alkyl group or an aryl group and (3) esters of 4-isopropyl benzoic acid, commonly known as cumic acid, corresponding to the formula:

where R is an alkyl group; wherein the proportion of component (C), is sufficient to give antiwear properties to the composition.

3. A composition as claimed in claim 2 wherein (C) is a metal salt of a thiophosphate wherein M is zinc and wherein each R is an alkyl group of no more than 18 carbon atoms, and wherein the proportion of component (C) is in a range from a concentration such that the weight percent of zinc is 0.020/, of the total composition to a concentration such that the weight percent of zinc is 0.5% of the total composition.

4. A composition as claimed in claim 2 wherein (C) is a metal salt of a thiocarbamate wherein each R is an alkyl group of no more than 18 carbon atoms, and wherein the proportion of component (C) is in a range from a concentration such that the weight percent of Cd or Sb is 0.02 of the total composition to a concentration such that the weight percent of Cd or Sb is 0.5 of the total composition.

5. A composition as claimed in Claim 2 wherein (C) is an ester of cumic acid, wherein each R is an alkyl group of no more than 10 carbon atoms, and wherein the proportion of (C) is in a range from 0. I weight percent to 2 weight percent of the total composition.

6. A composition as claimed in Claim 5 wherein each R is an isobutyl group.

7. A composition as claimed in any one of the preceding claims which also comprises (D) I to 500 parts per million of the total composition of perfluoroalkylpolyether of the general formula F-1CF(CF3)CF2O]x C2Fs in which x has a value which provides an average molecular weight for the perfluoroalkylpolyether in a range from 2,000 to 7,000.

8. A composition as claimed in Claim 7 wherein x has a value which provides an average molecular weight for the perfluoroalkylpolyether of 2,000 to 5,500 and wherein the proportion of (D) is from 5 to 100 parts per million by weight of the total composition.

9. A composition as claimed in any one of the preceding claims wherein n has values such that the viscosity of the polysiloxane at 1000F is between 10,000 cS and 500,000 cS.

10. A composition as claimed in any one of Claims 1 to 9 wherein said hydrocarbon oil is an iso-paraffin or an alkene, and wherein the amount of component (A) in said mixture of components is from 5% to 30% by weight.

11. A composition as claimed in any one of Claims 1 to 9 wherein the hydrocarbon oils (B) are saturated or unsaturated copolymers of propylene or isobutylene.

12. A lubricating oil composition as claimed in Claim 1 and substantially as hereinbefore described with reference to any one of Examples 1 to 6, 10 to 19, 25, 27 to 31 and 33-36.