US2844537A - Homogeneous lithium base lubricating grease compositions - Google Patents

Description

HOMOGENEOUS LITHIUM BASE LUBRICATING GREASE COMPOSITIONS Paul R. McCarthy, Allison Park, and Thomas R. ()rem,

Blawnox, Pa, assignors to Gulf Research & Developmerit (Jompany, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application January 19, 1956 Serial No. 560,061

8 Claims. (Cl. 252-411) This invention relates to lubricating grease compositions. More particularly, it is concerned with stable lithium base greases which do not require milling or-homogenization to produce a finished grease.

This application is a continuation-in-part of our prior copending application Serial No. 376,966, new abandoned, filed August 27, 1953, and assigned to the same assignee as the present application.

Generally speaking, lithium base greases prepared from lithium soaps of saturated fats or fatty acids are water resistant and possess a high melting point. However, difficulties are encountered in the preparation of such greases, particularly a lack of homogeneity in structure as evidenced by graininess and bleeding. Accordingly, in order to obtain a homogeneous and relatively stable grease, some type of homogenization or milling of the grease has been found to be essential. Homogenization or milling of such lithium base greases is attended by the disadvantage of costly special equipment such as homogenizers and deaerators. The prior art has been cognizant of this problem and has proposed the incorporation of certain additives in the grease, for example, high molecular weight esters, to obtain a grease requiring no milling. However, since such additives are themselves relatively expensive, the cost advantage obtained by not milling the grease is materially reduced.

We have now discovered that homogeneous, mechanically stable lithium base greases can be prepared from a suitable lubricating oil thickened to a grease with a lithium soap of a mixture of saturated, unsubstituted fatty acids having at least 12 carbon atoms, said mixture containing acids having at least 20 carbon atoms and acids having less than 20 carbon atoms, to obtain a finished grease without the necessity of homogenization or milling and without requiring the use of special additives. In accordance with our discovery, we have found that by properly proportioning the mixture of the above-described fatty acids used to prepare the lithium soap of our greases to provide a ratio of acids having at least 20 carbon atoms to acids having less than 20 carbon atoms in the range of from 1:10 to 1:1, we obtain excellent finished lithium base greases requiring no milling or homogenization.

As has been stated, the fatty acids employed to obtain the greases of our invention are saturated, unsubstituted fatty acids having at least 12 carbon atoms, and include such acids as lauric, myristic, palmitic, stearic, arachidic, behenic, lignoceric, cerotic, montanic, melissic and the like. Since the use of pure saturated fatty acids to obtain the required content of C or higher saturated fatty acids nited States Pate F 2044,53? Patented July 22, 195% in the mixture of acids is generally too expensive, it is preferred to employ mixtures of commercially available saturated fatty acids such as are obtainable, for example, in hydrogenated fish oil fatty acids. These acids represent distilled cuts of mixtures of acids containing variable amounts of C 'to C acids. The following table shows the percentage composition of some commercially available hydrogenated fish oil fatty acids.

It will be noted that of the fatty acids having at least 20 carbon atoms, arachidic acid and behenic acid are present in relatively large amounts in the Hydrofol AB and Hydrofol 53 acids. For this reason these hydrogenated fish oil fatty acids form a preferred source of these materials. However, hydrogenated rapeseed oil fatty acids contain about to percent behenic acid and 10 to 15 percent stearic acid and can also be used in preparing the greases of our invention. The long chain aliphatic monocarboxylic acids derived from the oxidation of the high molecular weight paraffin wax obtained in the Fischer-Tropsch process also furnish a suitable source of fatty acids having at least 20 carbon atoms. Any one of the saturated fatty acids having at least 20 carbon atoms, or mixtures of such acids, can be employed in accordance with the invention. The specific number of carbon atoms in such acids, that is, whether the acid is a C C C C or higher acid, is immaterial. However, considerations of cost and availability will usually dictate the choice of the arachidic (C and behenic (C acids found in hydrogenated fish oils. In accordance with our invention, the various fatty acids are suitably blended to obtain in the resulting grease the required amount of C or higher fatty acids.

The lubricating bases used in our greases can be any suitable lubricating oil such as mineral lubricating oils, or synthetic lubricating oils, such as the diester lubricants, e. g., di-Z-ethylhexyl sebacate or adipate, polyalkylene glycol or polyalkylene oxide polymers and polymerized olefins.

The total soap content of the greases of our invention will vary with the consistency desired, the lubricant base employed, etc., as is known in the art. In general, the soap content can vary from about 5 percent to about 25 percent by weight of the grease, and preferably-from about 10 percent to 15 percent by weight of the grease.

In the following table, there are set forth illustrative examples of the greases of this invention. For the purpose of comparison, there is also included (Example III) a grease not containing the C or higher fatty acids. Each of the greases in the table was prepared as follows. Forty (40) percent of the lubricating oil base, together with the fatty acids and the lithium hydroxide were added to a 5, conventional pressure saponification kettle. Saponification was carried out at a pressure of 90'to 100 p. s. i. g. at a temperature ranging from about 320 to 350 F. for a period of one hour. The mass was then discharged to an open kettle where the temperature was raised to 350 F. for dehydration. After dehydration, the remainder of the mineral lubricating oil base was added, the temperature was raised to 400 F. until the grease was completely liquid and the grease was held at this temperature for /2 hour. The grease was then cooled and discharged from the kettle. Except where indicated (Example 111), the

greases Were not milled but were Withdrawnfrom theiket tie as a final product.

The 500/3 Texas Oil employed inthe greases. of the antioxidants such as alpha naphthylamine, phenyl alpha naphtliylamine, diphenylamine, 2,4-ditertiarybutyl-6-methyl phenyl, and the like. If desired, conventional additives, such as corrosion inhibitors, extreme pressure agents, oiliness agents, dyes or other coloring matter, and the like can also be added without departing from the spirit of the invention. Although the specific examples show the preparation of the lithium soap in situ in the oil, the lithium soap containing the required amount of C or higher fatty acids can be preformed and. dispersed in the oil by well known methods.

Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

table was a naphthenic oil having the following typical. We claim: inspections: 1. A lubricating grease composition comprising a 111- V bricatingoil thickened to a grease with a lithium soap o I V 1 o of a mixture of saturated, unsubstituted fatty acids hav- 31 F 510 ing at least 12 carbon atoms, said mixture containing 54 9 acids having at least 20 carbon atoms and acids having Fla h 0 C 3- less than 20 carbon atoms, the ratio of acids having at j 20, least 20 carbon atoms to acids having less than 20 carbon T atoms ranging from 1:10 to 1:1. COIOTASTM Union 2. A lubricating grease in accordance with claim 1, It will be understood that other lubricating oil bases can wherein the acid having at least 20 carbon atoms is be employed. arachidic acid.

Table II Composition, Percent by Wt. Ex. I Ex. II Ex. III Ex. IV Ex. V Ex. VI

500/3 TexasOil s4. 90 84. 90 84. 90 84. 90 84. 90 84.- 90 Hydrofol A-B Acids 6.20 9. 2v 48 6. 20 4.13 H no 410 e20 3.10 12. 9.91 Hydroiol Acids 15 6. 20 8; 26' .1120 2.00 1.90 2.00 1.96 2.00 2.00 ater 0. 0. 80. 0. 70 0. 0. 71 0. 71 Ratio A B Acids to other Acids 1:1 3:1 1:4 1:1 1:2 Inspection:

Appearance Smooth Smooth Grainy Smooth Smooth Smooth Penetration, ASTM D21748- Unworked 309 317 l 261 280 295 337 Worked 315 324 1 278 304 309 340 Dropping Point, F., AS'IM D566-42 382 391 Wheel Bearing Test, 0rd. Spec. AXS- T1ma24brs. Temp-240 F. Percent Leakage 0. 53 1.9 0.42 0.18 Water Resistance, 500 cc. water/min. for

15 minutes sprayed on test panels coated with grease- Percent Grease retained on panels:

92 78 63 31 180 F 1 5 Adhesion to Metal-Grease spun on concave disc at 1800 R. P. M. for 7 minutes Percent Grease retained:

1 Data obtained on milled sample; milled at20G240 F. excessively.

As will be seen from the above examples, all of the greases with the exception of the grease; of Example III presented a smooth homogeneous appearance and an excellent mechanical stability. The' grease of Example III, which was made from hydrogenated. fish oil fatty acids consisting essentially of palmitic and steanic acids, was grainy and required milling in order to obtain a homogeneous grease.

It is recognized in the art that lithium base greases are not equivalent to sodium base greases. This non-equivalence extends to the lithium greases of the present invention. Thus when a grease was prepared exactly as in Example I, above, with the exception that an equivalent amount of sodium hydroxide was used in place of the lithium hydroxide, the sodium base grease obtained was grainy and required milling to obtain a homogeneous grease.

As will be understood -by those skilled in the art,,,the greases of our invention can contain minor amounts of Unmilled grease was very granular and bled 3. A lubricating grease in accordance with claim 1, wherein the acid having at least 20 carbon atoms is behenic acid.

4. A lubricating grease in accordance with claim 1, wherein the acid having at least 20 carbon atoms is part of the mixture of fatty acids present in a hydrogenated fish oil fatty acid.

5. A lubricating grease in accordance with claim 1,, wherein the lubricating oil is a mineral lubricating oil.

6. A lubricating grease composition comprising a lubricating oil thickened to a grease with a lithium soap of a mixture of saturated,unsubstituted fatty acids having from 12 to 22 carbon atoms, the ratio, in said mixture, of acids having at least 20 carbon atoms to acids having less than 20 carbon atoms ranging from 1:10 to 1:1.

7. ,A lubricating grease in accordance with claim 6, wherein the mixture of acids is a mixture of hydrogenated fish oil fatty acids.

8. In the manufacture of a homogeneous, mechanically stable lithium base grease from a lubricating oil and a lithium soap of a mixture of saturated, unsubstituted fatty acids having at least 12 carbon atoms wherein said soap is dispersed in the oil at an elevated temperature and then cooled, the improvement which comprises forming said lithium soapfrom said mixture of acids containing acids having at least 20 carbon atoms and acids having less than 20 carbon atoms, the ratio of acids having at least 20 carbon atoms to acids having less than 20 carbon atoms ranging from 1:10 to 1:1, whereby the cooled grease is obtained as a final product not requiring homogenization.

6 References Cited in the file of this patent UNITED STATES PATENTS 2,229,042 Brunstrum et a1. Jan. 21, 1941 2,588,280 OHalloran et a1. Mar. 4, 1952 2,590,801 Teter et a1 Mar. 25, 1952 2,626,896 Dilworth et a1. Jan. 27, 1953 2,626,898 Dilworth et al Jan. 27, 1953 OTHER REFERENCES Manufacture and Application of Lubricating Greases, Boner, Reinhold Pub. 00., N. Y. (1954), pages 434 and 435.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nor. 2,844,537 July 22, 1958 Paul Rn McCarthy et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columns 3 and 4,, Table II, fifth column thereof under the heading "EX, IV", last number, for "4" read -=-=9=-=,,

Signed and sealed this 7th day of October 1958 (SEAL) Attest:

KARL 5 AXLINE ROBERT C. WATSON Attesting Oificer Commissioner of Patents

Claims (1)

1. A LUBRICATING GREASE COMPOSITION COMPRISING A LUBRICATING OIL THICKENED TO A GREASE WITH A LITHIUM SOAP OF A MIXTURE OF SATURATED, UNSUBSTITUTED FATTY ACIDS HAVING AT LEAST 2 CARBON ATOMS, SAID MIXTURE CONTAINING ACIDS HAVING AT LEAST 20 CARBON ATOMS AND ACIDS HAVING LESS THAN 20 CARBON ATOMS, THE RATIO OF ACIDS HAVING AT LEAST 20 CARBON ATOMS TO ACIDS HAVING LESS THAN 20 CARBON ATOMS RANGING FROM 1:10 TO 1:1.