US2983680A - Lubricating greases thickened with mixtures of lithium fatty acid soaps and lithium dilinoleate - Google Patents

Description

States George W. Eckert, Wappingers Falls, and Paul R. Thomas, Beacon, N.Y., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed June 5, 1957, Ser. No. 663,587

6 Claims. (Cl. 252-421) This invention relates to improved lubricating greases, and more particularly to lithium base greases containing the lithium soap of an unsaturated fatty acid dimer.

In accordance with this invention, improved lithium base greases are obtained by employing as the thickening agent a mixture of a lithium soap of a monomeric higher fatty acid and the lithium soap of dilinoleic acid. We have found that lubricating greases are obtained by employing this combination of lithium soaps having superior shear stability and other advantages as compared with greases obtained from lithium soaps of the conventional fatty acids as .the sole thickening agent. In addition, the use of a saponifiable material comprising a mixture of monomeric higher fatty acid and dilinoleic acid permitsthe grease preparation to be carried out by the convenient low temperature method, wherein the grease mixture is maintained at a temperature below the melting point of the soap during both the saponification and dehydration steps.

Dilinoleic acid is considered to have the formula:

It is obtained by the heat polmerization of linoleic acid acid or of the methyl ester or glyceridc of linoleic acid, followed by hydrolysis. The polmerization may be carried out as described, for example, in US. 2,482,761, by heating an unsaturated fatty acid material comprising linoleic acid as the chief polyunsaturated fatty acid component at about 260-360 C. for about 3-8 hours under a steam pressure of about 80-400 pounds per square inch. The unpolymerized fatty acids are then removed by distillation under reduced pressure. The product obtained in this manner consists chiefly of the linoleic acid dimer in admixture with small amounts, up

to about percent based on the weight of the product,

of the trimer. "It may also contain minor amounts of other materials, such as other unsaturated acid polymers, as impurities. Such a product may be employed directly in the preparation of the lithium soap.

The monomeric high molecular weight fatty acid materials employed for forming the other soap component of these greases are those employed conventionally in grease making, suitably fatty acids containing about 12 to 32 carbon atoms per molecule and their glycerides or other esters. The preferred materials of this character are substantially saturated fatty acids containing about 14-22 carbon atoms per molecule and the glycerides or other esters thereof, such as myristic acid, palmitic acid, stearic acid, tallow, and hydrogenated fish fatty oils.

The lithium soap of the high molecular weight conventional fatty acids and the lithium soap of dilinoleic acid are employed in a ratio of about 1:2 to about 2:1 by weight. With higher proportions of the conventional lithium soap the shear stability of the grease falls ofi rapidly, whereas with higher proportions of the dimer acid soap the yield becomes unsatisfactory, a grease struc- Z ture being unobtainable with the dimer acid soap alone. The two soaps are preferably employed in a. ratio of about 1:1 by Weight, with sufiicient of the mixture employed to give a grease consistency. Ordinarily the grease will contain from about 5 to about 50 percent by weight of the combined soaps. With particular advantage, the grease may contain a small excess of free alkali, preferably from about 0.2 to about 1.0 percent by weight of lithium hydroxide. We have found that such an excess of lithium hydroxide in these greases produces both improved yields and increased dropping points, dropping points of 500 or higher being obtained with an excess of about 0.5 percent or more of lithium hydroxide.

The oleaginous liquids employed in these greases may be any oils suitable for use in grease making generally, such as mineral oils obtained by any of the conventional refining processes in the lubricating oil viscosity range, preferably those having viscosities from about seconds Saybolt Universal at F. to about 225 seconds at 210 F. For certain purposes, such as for producing greases suitable for high temperature operations, various synthetic oils may be employed with advantage, such as high molecular weight ethers, esters, and silicone polymer oils. Particularly suitable synthetic esters are dicarboxylic acid esters, such as, for example, di-Z-ethylhexyl sebacate, di(secondary amyl) sebacate, and di-2-ethylhexyl azelate.

The greases may also contain various additives of the usual types employed in lubricating greases, such as corrosion inhibitors, oxidation inhibitors. antiwear agents, etc. Preferably, they contain an oxidation inhibitor, which may suitably be an oxidation inhibitor of the amine type, such as diphenylamine, phenyl naphthylamine or tetramethyl diamino diphenyl methane.

The grease preparation may be carried out by any suitable grease making procedure. It is preferably carried out by the method involving saponification in situ, wherein a mixture of dilinoleic acid and conventional saponifiable material as described above is saponified in a portion of the lubricating oil employed as the liquid base, preferably in a mineral oil. Following the saponification, the saponification mass is heated at a higher temperature, such as a temperature in about the range 300-350 F., to dehydrate, and the main portion of the oleaginous liquid component and any additives employed are mixed in while the grease is allowed to cool.

The following examples are illustrative of the lubricating greases of this invention.

Example I A grease was prepared having the following composition in percent by weight:

Lithium stearate -a 12.5 Lithium dilinoleate 12.5 Phenyl alpha naphthylamine 0.5 Mineral lubricating oil Remainder The mineral lubricating oil was a refined naphthene base distillate oil having a Saybolt Universal viscosity of about 312 seconds at 100 F.

The lithium stearate was obtained by saponification of a commercial triple-pressed stearic acid having a neutralization number of 201, a saponiiication number of 211, an iodine number of 2 and a titer of 54.6 C. The lithium dilinoleate was obtained by saponification of a commercial dilinoleic acid having an apparent molecular weight of about 600, a neutralization number of 183, a saponification number of 188, an iodine number of 73 and a hydroxyl number of 6.

The grease preparation was carried out in the following manner: A laboratory grease kettle was charged with with 245 grams of stearic acid, 245 grams of the dimer mass was maintained at 310 F. and 500 grams more Dropping point, F. 376 Penetration, AST M, at 77 F.:

Worked, 60 strokes 332 Worked, 100,000 strokes 354 Dynamic water resistance test, percent loss Norma-Hoffman oxidation test, 210 F., 100 hours, pressure drop, lbs. Dynamic shear test:

Miniature penetration- Original 70 After test 189 The dynamic shear test is conducted in an apparatus consisting of a perforated piston reciprocating within a closed cylinder maintained at a constant temperature.

'The results given in the table were obtained in the test carried out at a temperature of 225 F., with the piston reciprocated at 49 strokes per minute for eight hours.

As shown by the data, the grease of this invention gave an increase of 119 points in miniature penetration, which the severe conditions of this test. This represents a 'very considerable improvement in shear stability over greases thickened with lithium stearate alone, which break down to liquid or semi-liquid products under these conditions.

Example II Another grease was prepared having the following composition in percent by weight:

Lithium stearate 9.9 Lithium dilinoleate 9.9 Phenyl alpha naphthylamine 0.5 Excess LiOH I v 0.5 Mineral lubricating oil Remainder The mineral lubricating Mind the saponifiable materials employed were the same as those described in Example I. The grease preparation was carried out in the same manner as described in Example I except that the,

dehydration was carried out at 325 F.

The product obtained was a brown, uniform grease of slightly stringy texture which gave the following tests.

is considered only a moderate amount of softening under 4 Dropping point, F. 500+? Penetration, ASTM, at 77 F.:

Unworked 358 Worked 360 Dynamic water resistance test, percent loss 0 Norma-Hoffman oxidation test, 210 F., 100

hours, pressure drop, lbs. 2 Torque breakdown machine test, -250 F.,

rating Good As shown by the data, the grease of the above example, containing 0.5 percent of excess lithium hydroxide, had a dropping point above 500 F. and softened only two points upon working, in addition to having excellent oxidation resistance and resistance to water washing. This grease also maintained good lubrication under actual service conditions in the torque breakdown machine test, giving no leakage from a Federal Precision ball bearing rotated at 1750 r.p.m. upon a shaft for 3 hours at 80 F. to 250 F. s

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 shear stable and substantially water insoluble lubricating grease composition consisting essentially of a lubricating oil thickened to a grease consistency with a mixture in about a 1:2 to 2:1 ratio by weight of a lithium soap of a high molecular weight fatty acid and lithium dilinoleate.

2. The grease composition of claim 1 wherein the said lubricating oil is a mineral lubricating oil.

3. The grease composition of claim 1 wherein the said soaps are employed in a ratio of about 1:1 by weight.

4. The grease composition of claim 1 wherein the said lithium soap of high molecular weight fatty acid is the lithium soap of a substantially saturated fatty acid containing 14-22 carbon atoms per molecule.

5. The grease composition of claim 1 wherein'the said composition contains about 0.5-1.0 percent by weight of excess lithium hydroxide.

6. A shear stable and substantially water insoluble lubricating grease composition consisting essentially of a mineral lubricating oil thickened to a grease consistency by about 5 to 50 percent by weight of a mixture in about a 1:1 ratio by weight of lithium stearate and lithium dilinoleate and containing about 0.2-1.0 percent by weight of excess lithium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,555,104 Ashley et a1. May 29, 1951 2,585,321 ,Butcosk Feb. 12, 1952 2,699,428 Lux et al. Ian. 11, 1955 2,710,838 'Morway et a1. June 14, 1955 2,737,497 Wasson et a1. Mar. 6, 1956 2,883,342 Sprouleet al. Apr. 21, 1959 FOREIGN PATENTS 736,921 Great Britain Sept. 14. 1955

Claims (1)

1. A SHEAR STABLE AND SUBSTANTIALLY WATER INSOLUBLE LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKNED TO A GREASE CONSISTENCY WITH A MIXTURE IN ABOUT A 1:2 TO 2:1 RATIO BY WEIGHT OF A LITHIUM SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID AND LITHIUM DILINOLEATE.