US2721845A - Metal soap grease containing alkaline earth metal alkyl phenol sulfide - Google Patents

Description

United States PatentO METAL SOAP GREASE C(DNTAINING ALKALINE EARTH METAL ALKYL PHENOL SULFIDE John P. Dilworth, Fishkill, N. Y., Charles H. Culnane, Grosse Ile, Mich, and Harry V. Ashburn, deceased, late of Beacon, N. Y., by Evelyn L. Ashburn, administratrix, Beacon, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Original application April 18, 1951, Serial No. 221,742. Divided and this application February 19, 1953, Serial No. 337,874

4 Claims. (Cl. 25242.1)

This invention relates to a lubricating grease composition, and particularly to such a composition which is inhibited against copper corrosion.

This is a division of our co-pending application Serial No. 221,742, filed April 18, 1951, now'Patent Number 2,690,998.

Lithium base lubricating grease compositions have found substantial use in aircraft controls and for other purposes where operation over a wide temperature range, and particularly operation at extremely low temperatures, is encountered. U. S. Patent No. 2,450,221, Ashburn, Barnett and Puryear, is typical of a superior lithium base grease of this type prepared from a lithium soap of a hydroxy fatty acid or the glyceride thereof, such as hydrogenated castor oil, and containing as the major proportion of the liquid lubricating base an oil soluble high molecular weight high boiling liquid aliphatic dicarboxylic acid ester within the lubricating oil viscosity range and possessing lubricating properties. As disclosed therein, the lithium soap may be formed from a major proportion of the hydroxy fatty acid or glyceride thereof, and a minor proportion of a saturated fatty acid, the grease containing a small excess of free fatty acid. Such greases have exceptional shear and texture stability over a wide temperature range and excellent low temperature properties.

Whilethe lithium base greases of the aforesaid type have proved eminently satisfactory in service, the increased use of copper and copper alloys in certain applications particularly in aircraft and artillery control instruments, has introduced an additional problem of rendering the grease non-corrosive to copper in long time service. For this purpose, U. S. Army Specification 2134 has prescribed a rigorous copper corrosion test for qualification under this specification. In attempting to meet this specification, it has been found that corrosion inhibitors heretofore employed in greases are ineffective. f

One of the principal objects of the present invention is to provide a lubricating grease which satisfactorily meets the copper corrosion test of U. S. Army Specification 2-134.

Another object of the present invention is to provide a lithium base grease which retains all the desirable properties of the previously known greases of this type, including shear and texture stability over a wide temperature range and excellent low temperature properties, and at the same time is eifectively inhibited against corrosion of copper and copper alloys in long time service.

In accordance with the present invention, the foregoing objects have been attained by incorporating in the grease about 0.25 to 5% by weight of an oil-soluble alkaline earth metal salt of an alkyl phenol sulfide having a total of to 30 carbon atoms in the alkyl substituents on each benzene nucleus. Salts of this type have heretoforebeen suggested as detergent additives for mineral lubricating oils; but it was entirely unexpected that such salts would function in the present greases as copper corrosion inhibitors, since this action is completely remote from detergency.

The alkaline earth metal salts which are effective copper corrosion inhibitors for purposes of the present invention, are prepared from thealkyl phenol sulfides having the structural formula where R is an alkyl group containing 5 to 30 carbon atoms, )1 represents the number 'of alkyl substituents on each benzene nucleus and is generally 1 or 2, with the proviso that the total number of carbon atoms of the alkyl substituents on each benzene nucleus is at least 10, and x is either 1 or 2. The alkaline earth metal salts may be either normal salts wherein the alkaline earth metal completely neutralizes the OH groups of 2 molecules of the alkyl phenol, producing the compound having the formula -Sz- Rn Rn where M represents the alkaline earth metal, or may be the basic salt having the formula OMOH OMOH These various compounds may be prepared in known manner by the alkylation of a phenol sulfide with a selected olefin or olefin polymer of the proper chain length, namely from 5 to 30 carbon atoms, in the presence of a suitable alkylation catalyst, such as HF, BFs, and the like. The .olefin polymer is preferably prepared by polymerizing propylene under pressure, using for example a BFs-HzO catalyst. Likewise butylene polymer can be used. Depending upon the conditions of the alkylation, the phenol sulfide may be monoor dialkylated. Where a lower molecular weight olefin, such as amylene is employed for alkylation, the phenol sulfide is dialkylated to provide a total of at least 10 carbon atoms in the substituent alkyl groups. Where a high molecular weight olefin is employed, such for example as a propylene polymer fraction having olefins of 15 to 30 carbon atoms in the molecule, the product is generally monoalkylated. In addition to simple phenol sulfide, other sulfides of monohydroxy mononuclear aromatic compounds'having the hydroxyl group attached to the ring can be employed as the starting material, such for example as the cresols, xylenols and other alkyl phenols. In the following description and claims, all of these various alkylated compounds will be referred to as alkyl phenol sulfides.

The foregoing alkyl phenol sulfides in solution in a suitable aromatic solvent, such as toluene, are then reacted with the alkaline earth metal compound to produce the corresponding alkaline earth metal salt. Any of the alkaline earth metals, including calcium, barium, strontium and magnesium can be employed, although barium and magnesium are generally preferred. In the manufacture of a magnesium alkyl phenolate sulfide, for example, the alkyl phenol sulfide in toluene solution may bereactedwithmagnesium methylate dissolved in excess methyl alcohol at a temperature-of about 40-50 C., using slightly less than one mol of the magnesium methylate per mol of the alkyl'phenol sulfide. The temperature is then'increased and the-methyl alcohol distilled off. The resulting toluene solutionof magnesium alkyl phenolate sulfide, which is the normal salt represented-byformula No. 2 above, is-filtered while hot; and then sufficient mineral lubricating oil, such as a distillate oil having an SUS viscosity at 100 F. of about 300, is added to produce an ultimate -to 50% concentrate of the magnesium alkyl phenolate sulfide in the lubricating oil. The toluene solvent is then stripped from the lubricating oil concentrate.

In preparing a basic alkaline earth metal salt of the foregoing alkyl phenol sulfides, the latter are preferably reacted with a substantial excess of an aqueous solution of a watersoluble alkaline earth metal salt. For example, inzpreparinga basic barium alkylphenolate sulfide, an aqueous-solution of barium chloride with the latter in excess of that'required'for neutralization is added to a lubricatingoil solution of the alkyl phenol sulfide. The reaction mix is subjected to steaming with agitation for a substantial period of time, such as about 1-4 hours. Following separation of the aqueous.phase,'the lubricating oil solution of the basic barium alkyl phenolate sulfide is washed and then heated to remove residual mixture to obtain a lubricating oil concentrate of the desired additive in about 25-50% concentration. The basic salts may also be prepared by reacting an oil solution of the alkyl phenol sulfide witha methanolsolution of an excess of barium hydroxide, and then removing the methanol.

. Typical compounds prepared as outlined above and which are useful for purposes of the present invention are barium diamyl phenolate monosulfide, barium diamyl phenolate disulfide, basic barium cardanolate sulfide formed from hydrogenated cardanol, magnesium alkyl phenolate monosulfide or disulfide wherein the alkyl group contains from 15 to carbon atoms and is preferably C18 to Czs, and similar compounds of the other alkaline earth metals. Instead of preparing the alkylphenol sulfide by alkylation as described above, suitable .alkyl phenol sulfides containing at least 10 carbon atoms in the alkyl substituentson each benzene nucleus can be used, such as the hydrogenated cardanolate sulfide as specified above.

The above described alkaline earth metal salts of alkyl phenol sulfides may be employedin lithium base greases formed from any saturated fatty material, such as the conventional saturated fatty acids or glycerides thereof, to provide copper corrosion inhibition.

Preferably, the lithium base greases formed from hydroxy fatty acids or their corresponding glycerides, such as hydrogenated castor oil, are employed to obtain the improved shear and texture stability. Suitable types of soap-forming hydroxy fatty acids and glycerides thereof are disclosed in said Patent No. 2,450,221. While the soapforming hydroxy fatty acids or their glycerides may be used as the sole acidic component of the lithium soap, they may be blended or combined with the conventional saturated fatty acids or fats in such proportions that at least 50% of the total acidic component iscomprised of the hydroxy fatty acids or glyceridesthereof. In general, any of the recognized fatty acid materials normally used in grease manufacture may be employed providing they are essentially saturated in character. These fats'and fatty acids include mixtures of fatty acid glycerides found in naturally occurring fats and oils, together with fractionated components thereof. The fatty acids may be a mixture of acids split oif from these fats or prepared by hydrogenation of fish oils, or the individual acids themselves. Verysatisfactory results are secured by employing as the. saturated fatty material for the formation of the lithium soap a mixture'of about 60-80% of. hydrogenated castor nil or 12-hydroxy :stearic :acid, with-40- 20% of a saturated fatty acid such as stearic acid. The

1 grease may contain about lO-30% by weight of the lithium soap.

In order to obtain the improved wide temperature range and low temperature properties, the liquid lubricating base of the lithium grease composition is preferably formed of a major proportion of a synthetic oleaginous lubricating compound or condensation product, many types of which are now known in the art. Very satisfactory synthetic lubricants of this character are represented by the high molecular weight high boiling liquid aliphatic dicarboxylic acid esters which are within the lubricating oil viscosity range and possess lubricating properties. The compounds within this particular class are the esters of such acids as sebacic, adipic, pimelic, azelaic, alkenyl succinic, alkylmaleic, etc. The esters thereof are preferably the aliphatic esters and particularly the branched chain aliphatic diesters. Specific examples of the preferred oleaginous compounds are di- 2ethyl hexyl-sebacate, di-Z-ethyl hexyl azelate, di-2-ethyl hexyl adipate, di-sec-amyl sebacate, di-2-ethyl hexyl alkenyl succinate, di-2-ethoxyethyl sebacate, di-2-(2'- methoxyethoxy) ethyl sebacate, di-2-(2'-ethyl butoxy) ethyl sebacate, di-2-butoxy ethyl azelate, di-2 (2-butoxy ethoxy) ethyl alkenyl succinate, etc.

These oleaginous compounds may be used as the sole oil component of the grease or they may be blended with a mineral lubricating oil. Where a blend is em- I ployed, and low temperature properties are required, the

mineral lubricating oil is preferably a light refined distillate mineral lubricating oil, such as a naphthene or parafiin base distillate, having an SUS viscosity at F. of about 50130 and preferably about 100 secs. The

' mineral lubricating oil will generally constitute less than 50% of-the blend, and ordinarily about 40-20% thereof. The mineral lubricating oil blend is advantageous where the lithium soap is formed in situ. In such case, the saponification of the fatty material with the lithium hydroxide and dehydration of the resulting soap are'conveniently carried out in the presence of a portion of the mineral lubricating oil, and the synthetic lubricant together with the additives employed in the grease are then added following dehydration and as the agitated soap mix cools.

The following examples are given toillustrate the present invention:

EXAMPLE 1 A lithium base grease was prepared from a fatty material consisting of about 75 by weight of hydrogenated castor oil and 25% by weight of stearic acid. The lubricating base used was a mixture of about 75% by weight of di-Z-ethyl hexyl azelate with about 25% by weight of a paraffin base mineral lubricating oil having an SUS viscosity at 100 F. of about 100. The method of preparation-involved charging a steam heated kettle with the required amount of 10.3% lithium hydroxide solution together with a small amount of water, the hydrogenated castor oil and a small proportion of the parafiin base mineral lubricating oil, the latter being less than the amount of hydrogenated castor oil and generally about /2. to of the latter. The kettle contents were held at -190 F. for about 4 hours with agitation, and then the stearic acid was added and the temperature maintained with stirringfor'another 1-2 hours to complete saponification. Following saponification, a 25% concentrate of an octyl methacrylate ester polymer in a mineral lubricating oil, which is sold commercially by Rohm and Haas under the name Acryloid HF-600, was added in an amount to provide 2% by weight of the concentrate in the final grease composition. The feature of adding methacrylate ester polymers of this type to a lithium base ball and roller bearing grease for the purpose of noise suppression in bearings operated at high speeds is disclosed and claimed in the co-pending application of Dilworth, Finn and Puryear, Serial No. 220,538, filed April I1,

1951." The saponified mix was then heated with stirring at 290 to 330 F. for about 4 hours to effect dehydration. The balance of the mineral lubricating oil was then added with stirring as the kettle contents cooled 6 for no pressure drop during the test, and this item is not separately listed in the table.

Samples 1-3 inclusive of the foregoing table represent the base grease of Example 1, and the base grease comdown to about 280 F. The di-2-ethyl hexyl azelate was 5 pounded with 1% and 3% respectively of Paranox 56. then slowly added with stirring as the mix continued to As will be noted from the calculated composition of the cool to about 220 F. Phenyl alphanaphthylamine in an base grease, a calculated excess of 0.2% by weight of amount of about 0.5% by weight based on the grease was lithium hydroxide was employed in preparing this grease; then added as an oxidation inhibitor, and a small amount and, as shown by the table the greases of samples 1-3 of a dye was introduced. The resulting base grease was analyzed to a free alkali content, calculated as lithium drawn at a temperature below 200 F. hydroxide, of 0.09%. It is to be noted that the base The resulting base grease had the following calculated grease of sample 1 produced a grey stain on the copper composition: strip and a pink discoloration on the grease, and thus failed the test. Samples 2 and 3 containing the Paranox Lithium Soap of hydrogenated Castor oil Welght fg 56 successfully passed this rigorous copper corrosion Lithium Stearate test. In this 0011212111011, a??? a}; giscloged 11113116 2233132- u ing app ication o eorge c ert, eria o. lg t z iin ee om saponification of hydrogenated 0.2 l February 5 Patent Castor on) 1.3 nized copper corrosion inhibitors Wl'llCh are eifective 1n Paraffin base lubricating oil 19.7 20 other relationships are completely ineffective for purposes Di z ethyl hexyl azelate 59 2 of the present invention. It was entirely unexpected that Phenyl alphanaphthylam'irlg a material, such as an alkaline earth metal salt of an Acryloid alkylphenol sulfide, wh ch is recognized as a detergent Dye d addit ve for lubricating 0115, such as motor OllS, should be effective as a copper corrosion inhibitor in the new en- To different portions of the foregoing base grease, varvironment of a lithium base grease. ious amounts of barium diamyl phenolate sulfide, which In the aforementioned Eckert application, the use of a is solid commercially by the Enjay Company, Inc. as different type of copper corrosion inhibitor, namelyabasic Paranox 56, were added as shown in samples 2 and 3 alkaline earth metal sulfonate, in a lithium base grease in the following table. The said greases were then subof this character is disclosed and claimed; and, further, jected to the copper corrosion test of the 2134 specifiit is pointed out that the grease should be prepared to cation with the results as shown in the table. a calculated excess alkalinity in order for this different Table 2-134 Cu Corrosion Test Additive, wt. Rating Copper Grease 1. Base Grease- Grey stain Pintk discolor- Fail. 2. Base Grease-.. +1%Paranox56 Very slight N3 ch ngeun Pass. 3. Base Grease.-- +3%Paranox 56- ol e r l i do D0. 4. Base Grease--. +1%Paranox56 Borderline to 5. Base Grease--. +0.7%Paranox56 Sta P l 6. Base Grease-.. +0. 1%Paranox56- 7. Base Grease... +3.0%Paranox 56- (1), (2) and (3) Free alkali (LiOH). (4) Free fatty acid (oleic) (5) Free alkali (LiOH) (6) Free alkali (LiOH) (7) Prepared with di-2-ethyl hexyl sebacateiree fatty acid (oleic) The 2-134 corrosion test of the foregoing table was run by placing a copper strip in a Norma-Hofiman bomb so as to be partially immersed in the sample of the grease under test, and then maintaining the bomb under oxygen pressure (110 pounds per sq. in. initial pressure) at 210 F. for 20 hours. During that period, no pressure drop due to oxygen absorption must occur. Then, at the completion of the 20-hour period, both the sample of grease and copper strip are inspected. In addition to the requirement for no pressure drop during the test, there must be no more than a very faint stain on the copper strip and no more than a slight stain on the grease in order to be rated as passing. Slightly inferior products which do not merit a full pass rating are given a rating of borderline to pass where there is no more than a light strain on the grease and no pressure drop; and a rating of borderline to fail where there is a stain on the copper with or without a stain on the grease and no type of copper corrosion inhibitor to be uniformly effective in the said 2-134 test. Samples 47 of the foregoing table show that this requirement of excess alkalinity is obviated by the copper corrosion inhibitors of the present invention. Thus sample 4 represents a grease prepared in accordance with Example 1 above except that a slight excess of stearic acid was used so that the grease analyzed to a free fatty acid content, calculated as oleic, of 0.23% by weight. As shown, 1% of Paranox 56 in this grease gave a borderline to pass rating in the 2-134 copper corrosion test. Sample 7 of the table represents a grease prepared in accordance with Example 1 above, except that di-Z-ethyl hexyl sebacate was employed as the major portion of the lubricant base instead of the corresponding azelate, and also an excess of stearic acid was again used in the formulation. 3% of Paranox 56" in this particular grease gave a clear pass rating. Samples 5 and 6 of the table were prepared in accordance with Example 1 above, using a calculated excess of lithium hydroxide of 0.3% and 0.2% respectively. It will be noted that as little as 0.4% by weight of Paranox 56 in this grease gas a pass rating.

While the additives of the present invention have been specifically described above in connection with lithium base greases because these are representative of the type generally employed for specialty wide temperature range, and particularly low temperature service, it is to be understood that the invention is not limited thereto. Rather, the invention is also applicable to the improvement of the copper corrosion properties of other metal base greases, including those of sodium, calcium, aluminum, barium, and mixed base greases. For example, a grease comprising an oleaginous liquid lubricating base, such as a mineral lubricating oil or a synthetic lubricant base or mixture thereof, thickened to a grease-like consistency with about 10-30% of calcium 12-hydroxy stearate, may have added thereto for copper corrosion inhibition about 0.25-% by weight of an alkaline earth metal salt of a phenol sulfide of the type described above. The invention is particularly applicable to various metal base greases wherein the soap-forming fatty material of the metal soap consists of at least 50% by weight of hydroxy fatty acids or the glycerides thereof, such as 12-hydroxy stearic acid and hydrogenated castor oil.

It will be understood that the grease of the present invention may also contain other additives in small proportions which are compatible with the essential ingredients and do not interfere with the desirable properties thereof. Such additional additives include extreme pressure or lubricity agents, such as dibenzyl disulfide and tricresyl phosphate, materials for improving resistance in the salt spray humidity cabinet test, such as sorbitan mono-oleate, and the like.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A lubricating grease composition comprising as the essential constituents an oleaginous liquid lubricating base of. which at least the major proportion is a high boiling liquid aliphatic dicarboxylic acid ester, about -30% by weight of a lithium soap of a saturated soap-forming fatty material, said grease normally being corrosive to copper, and from 0.25 to 5% by weight based on said composition of barium diamyl phenolate sulfide in sutficient proportion to enable said grease composition to pass the copper corrosion test of U. S. Army specification 2-134.

2. A lubricating grease composition comprising as the essential and a major proportion of the lubricating base an oil-soluble high molecular weight high-boiling liquid aliphatic dicarboxylic acid ester within the lubricating viscosity range and possessing lubricating properties, sufficient lithium soap of soap-forming fatty material to thicken said lubricant base, said soap-forming fatty material consisting of more than 50% by weight of a hydroxy soap-forming fatty material selected from the group consisting of hydroxy fatty acids and hydroxy fatty acid glycerides, said grease normally being corrosive to copper, and from 0.5 to 3% by weight based on said composition of barium diamyl phenolate sulfide in sufiicient proportion to enable said grease composition to pass the copper corrosion test of U. S. Army specification 2-134.

3. A lubricating grease composition comprising as the lubricant base a mixture of substantial proportions each of mineral lubricating oil and a branched chain aliphatic diester of a dicarboxylic acid selected from the group consisting of sebacic, azelaic and adipic acids, with said diester being in major proportion of the said mixture, about 10-30% by weight based on the composition of lithium soap of a mixture of a major proportion of hydrogenated castor oil and a minor proportion of stearic acid, said grease normally being corrosive to copper, and from 0.5 to 3% by weight based on said composition of barium diamyl phenolate sulfide in sufficient proportion to enable said grease composition to pass the copper corrosion test of U. S. Army specification 2-134.

4. A lubricating grease composition consisting essentially of the following constituents in the approximate percentages by Weight:

Di-2-ethyl hexyl sebacate 50-85 Lithium soap of a 2:1 to 4:1 weight mixture of hydrogenated castor oil and stearic acid 10-30 Phenyl alpha naphthyl amine 0.3-1.0 Barium diamyl phenolate sulfide 0.5-3.0 Mineral lubricating oil Balance References Cited in the file of this patent UNITED STATES PATENTS 2,351,384 Woods et al June 13, 1944 2,362,289 Mikeska Nov. 7, 1944 2,362,291 Winning Nov. 7, 1944 2,362,292 McNab Nov. 7, 1944 2,397,956 Fraser Apr. 9, 1946 2,409,303 Morris et al Oct. 15, 1946 2,450,222 Ashburn Sept. 13, 1948 2,461,335 Mikeska Feb. 8, 1949 2,480,664 McNab et al Aug. 30, 1949 2,483,505 Rogers Oct. 4, 1949 2,518,379 Rogers Aug. 8, 1950

Claims (1)

1. A LUBRICATING GREASE COMPOSITION COMPRISING AS THE ESSENTIAL CONSTITUENTS AN OLEAGINOUS LIQUID LUBRICATING BASE OF WHICH AT LEAST THE MAJOR PROPORTION IS A HIGH BOILING LIQUID ALIPHATIC DICARBOXYLIC ACID ESTER, ABOUT 10-30% BY WEIGHT OF A LITHIUM SOAP OF A SATURATED SOAP-FORMING FATTY MATERIAL, SAID GREASE NORMALLY BEING CORROSIVE TO COPPER, AND FROM 0.25 TO 5% BY WEIGHT BASED ON SAID COMPOSITION OF BARIUM DIAMYL PHENOLATE SULFIDE IN SUFFICIENT PROPORTION TO ENABLE SAID GREASE COMPOSITION TO PASS THE COPPER CORROSION TEST OF U. S. ARMY SPECIFICATION 2-134.