US3758407A

US3758407A - Lithium soap grease containing monolithium borate

Info

Publication number: US3758407A
Application number: US00201140A
Authority: US
Inventors: G Harting
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1971-11-11
Filing date: 1971-11-22
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: DE2235098A1; JPS5747235B2; JPS4856203A; GB1370947A; FR2159251B2; FR2159251A2; DE2235098C2; CA971545A; MY7500155A

Abstract

A GREASE COMPOSITION THAT COMBINES GOOD WATER RESISTANCE, GOOD MECHANICAL STABILITY AND HIGH OIL RETENTION WITH EXCELLENT OXIDATION STABILITY AND HIGH DROPPING POINT IS PREPARED BY THE USE OF A NOVEL THICKENER SYSTEM WHOSE ESSENTIAL COMPONENTS INCLUDE A COMBINATION OF THE MONOLITHIUM SALT OF BORIC ACID; AND A LITHIUM SOAP OF A 9-, 10-, OR 12-HYDROXY C12 TO C24 FATTY ACID, E.G., LITHIUM 12HYDROXYSTEARATE. FURTHER IMPROVEMENT IN THIS TYPE OF GREASE RESULTS WHEN A THIRD THICKENER COMPONENT IS INCLUDED, THIS BEING A LITHIUM SALT FORMED IN SITU IN THE GREASE FROM A SECOND HYDROXY CARBOXYLIC ACID OF FROM 3 TO 14 CARBON ATOMS WHEREIN THE OH GROUP IS ATTACHED TO A CARBON ATOM NOT MORE THAN 6 CARBON ATOMS REMOVED FROM THE CARBOXYL GROUP, AND WHEREIN EITHER OF THOSE GROUPS MAY BE ATTACHED TO EITHER ALIPHATIC OR AROMATIC PORTIONS OF A MOLECULE.

Description

United States Patent 01 nee 3,758,407 Patented Sept. 11, 1973 3,758,407 LITHIUM SOAP GREASE CONTAINING MONOLITHIUM BORATE Gary L. Harting, Westfield, N.J., assiguor to Esso Research and Engineering Company No Drawing. Filed Nov. 22, 1971, Ser. No. 201,140

Int. Cl. C10m 5/14 U.S. Cl. 252-18 6 Claims ABSTRACT OF THE DISCLOSURE A grease composition that combines good water resistance, good mechanical stability and high oil retention with excellent oxidation stability and high dropping point is prepared by the use of a novel thickener system whose essential components include a combination of the monolithium salt of boric acid; and a lithium soap of a 9-, 10-, or 12-hydroxy C to C fatty acid, e.g., lithium 12- hydroxystearate. Further improvement in this type of grease results when a third thickener component is included, this being a lithium salt formed in situ in the grease from a second hydroxy carboxylic acid of from 3 to 14 carbon atoms wherein the OH group is attached to a carbon atom not more than 6 carbon atoms removed from the carboxyl group, and wherein either of those groups may be attached to either aliphatic or aromatic portions of a molecule.

BACKGROUND OF THE INVENTION This invention concerns a modified lithium soap grease of premium quality with outstanding properties which include a high dropping point, excellent oxidation stability, long lubrication life and water resistance.

Lithium greases have been known and widely used for many years. The lithium soaps that are used as thickening agents for these greases are ordinarily prepared by reaction of lithium hydroxide or other suitable lithium base with a conventional high molecular weight acid or acids. The principal advantages of lithium greases have been high water resistance and ease of dispersion of the soaps in all types of lubricating oil base stocks. Particularly useful have been greases prepared from lithium hydroxystearate, since the soaps of the hydroxystearic acids and related hydroxy fatty acids have been found to be more mechanically stable than the corresponding soaps of the conventional fatty acids.

There are many fields of application of grease compositions where a high dropping point is required, as, for example, in the lubrication of traction motor bearings. The bearings of these locomotives may be required to operate for periods of as much as three years without any maintenance, and temperatures as high as 250 F. can be reached in such bearings.

DESCRIPTION OF THE INVENTION In accordance with the present invention, a lithium base grease having excellent oxidation and mechanical stability and desirably high dropping points is prepared from a 9-hydroxy, 10-hydroxy, or 12-hydroxy C to C preferably C to C fatty acid, and boric acid. Additionally, for further improvement in dropping point, there may advantageously be used a second hydroxycarboxylic acid of from 3 to 14 carbon atoms, wherein the hydroxy group is attached to a carbon atom not more than 6 carbon atoms removed from the carboxyl group.

It has already been taught in US. Pat. 2,940,930 that high dropping point greases (500 F. or greater) can be prepared from mixtures of monocarboxylic and dicarboxylic acids. However, in preparing the greases described in that patent, it was necessary to also include a glycol.

The presence of a glycol is undesirable because it renders the grease prone to oxidation and makes the water resistance of the grease undesirably low in some applications. The present invention makes possible the preparation of high dropping point greases from hydroxy fatty acids without the necessity of incorporating a glycol.

While U.S. Pats. 3,223,633 and 3,223,624 teach the preparation of high dropping point greases from a 3-component mixture of acids, the presence of a C to 0., fatty acid salt, which is an esesntial component of those greases, is frequently undesirable because of the tendency of such greases to undergo surface hardening on standing.

The hydroxy fatty acid employed in preparing the greases of this invention will have from about 12 to 24, or more usually about 16 to 20 carbon atoms, and will preferably be a hydroxystearic acid, e.g., 9-hydroxy, 10- hydroxy, or l2-hydroxystearic acid, more preferably the latter. Ricinoleic acid, which is an unsaturated form of 12-hydroxystearic acid, having a double bond in the 9- 10 position, can also be used. Other hydroxy fatty acids include 12-hydroxybehenic acid and IO-hydroxypalmitic acid.

When a second hydroxycarboxylic acid is used along with the boric acid and hydroxy fatty acid, it will be one having an OH group attached to a carbon atom that is not more than 6 carbon atoms removed from the carboxyl group. This acid has from 3 to 14 carbon atoms and can be either an aliphatic acid such as lactic acid, -hydroxydecanoic acid, 3-hydroxybutanoic acid, l-hydroxycaproic acid, 4 hydroxybutanoic acid, 6-hydroxy-alphahydroxystearic acid, etc. or an aromatic acid such as parahydroxybenzoic acid, salicylic acid, 2-hydroxy-4-hexylbenzoic acid, metahydroxybenzoic acid, 2,5-dihydroxybenzoic acid (gentisic acid); 2,6-dihydroxybenzoic acid (gamma resorcylic acid); (4-hydroxy-4-methoxybenzoic acid, etc. or a hydroxyaromatic aliphatic acid such as orthohydroxyphenyl, metahydroxyphenyl, or parahydroxyphenyl acetic acid. A cycloaliphatic hydroxy acid such as hydroxycyclopentyl carboxylic acid or hydroxynaphthenic acid could also be used. Particularly useful hydroxy acids are lactic acid, salicylic acid, and parah'ydroxybenzoic acid.

In place of the free hydroxy acid of the latter type when preparing the grease, one can use a lower alcohol ester, e.g., the methyl, ethyl, or propyl, isopropyl, or sec-butyl ester of the acid, e.g., methyl salicylate, to give a better dispersion when the salt is insoluble. The amount of lithium salt of the hydroxy acid will range from about 0.1 to about 10 wt. percent of the finished grease, or preferably from about 0.2 to about 5 wt. percent. The monolithium salt or the dilithium salt of the second hydroxy acid can be used, but the dilithium salt is preferred.

The total soap and salt content of the grease will be in the range of from about 2 to 30 wt. percent and preferably about 5 to 20 wt. percent. The proportion of the C to C hydroxy fatty acid to boric acid will be in the range of a weight ratio of about 3 to 100 parts, or more usually about 5 to parts, of hydroxy fatty acid per part by weight of boric acid. There will be a weight ratio of about 0.1 to 10, or more usually about 0.5 to about 5 parts of said second hydroxycarboxylic acid per part by weight of boric acid in the case of the greases made from 3 acid components.

The lubricating oil base that is used in preparing the grease compositions of this invention can be any of the conventionally used mineral oils, synthetic hydrocarbon oils, or synthetic ester oils, and will generally have a viscosity within the range of about 35 to 200 SUS at 210 F. Synthetic lubrictaing oils that can be used include esters of dibasic acids such as di-Z-ethylhexyl sebacate, esters of glycols' such as the C oxo acid diester of tetraethylene glycol, or complex esters such as a complex ester formed by reacting l mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Other synthetic oils that can be used include synthetic hydrocarclude the polyphenyl ethers, e.g., those having from about 3 to 7 ether linkages and about 4 to 8 phenyl groups. (See US. Pat. 3,424,678, column 3.)

The greases can be prepared by coneutralizing all three types of acid, or alternatively by first neutralizing the boric acid and hydroxy fatty acid together and then forming the lithium salt of the second hydroxycarboxylic acid.

The following examples, which include preferred embodiments, are presented to illustrate the preparation and various characteristics of greases manufactured according to this invention. Comparative examples are also included to show that inferior results are obtained if boric acid is omitted or if the boric acid is neutralized beyond the monolithium salt stage.

Example 1 (including comparative greases) A grease designated grease A was prepared using as the thickener system a combination of lithium 12-hydroxystearate and monolithium borate. The base oil used in preparing this grease was a solvent-refined Mid-Continent lubricating oil distillate known as Solvent 450 Neutral, having a viscosity at 100 F. of about 450 SUS. The 12- hydroxystearic acid was added to a portion of the base oil (about /2 of the total oil used in the complete grease) and the mixture was heated to a temperature sufliciently high to melt the 12-hydroxystearic acid, this temperature being about 180 F. to 190 F. Then the boric acid and the lithium hydroxide monohydrate were added as an aqueous solution, and the resulting mixture was stirred and heated to a final temperature of about 380 F. to 390 P. Then the remaining portion of the base oil was added and the mixture was cooled to ambient temperature and milled in a conventional grease mill. A comparative grease corresponding to A but omitting the boric acid was also prepared.

Two additional greases were prepared using in each case the same proportion of l2-hydroxystearic acid and boric acid to base oil as in grease A but increasing the amount of lithium hydroxide monohydrate so as to form dilithium borate and trilithium borate instead of monolithium borate.

Each of the greases thus prepared was measured for dropping point and for ASTM penetration at 77. F. The composition of the greases and the inspections are shown in Table I which follows:

Example 2 Two greases were prepared using as the thickener system a combination of dilithium salicylate, lithium 12-hydroxy-stearate and monolithium borate, the proportions of the thickener components being varied as between the two greases. The base oil used in preparing these greases was a solvent refined Mid-Continent lubricating oil distillate known as Solvent 600 Neutral, having a viscosity at F. of about 600 SUS. Methyl salicylate and 12-hydroxystearic acid were added to a portion of the base oil and the mixture was heated. After it was observed that the 12-hydroxystearic acid had melted, the temperature being then about F. to F., all of the lithium hydroxide that was to be used in forming the various lithium salts was added in the form of a 10% aqueous solution to which had also been aded the boric acid that was to be used in making the grease. The resulting mixture was stirred and heated to a final temperature of about 380 F. to 390 F. Then the remaining portion of the base oil was added and the mixture was cooled to about 250 F. at which point an antioxidant and other components of the grease such as rust inhibitors were incorporated. The grease was then milled in a conventional grease mill.

Comparative example Using the same procedure as in Examaple 2, comparative greases were prepared in which one case the methyl salicylate was omitted, in a second case the boric acid was omitted and in the third case both the boric acid and methyl salicylate were omitted. In each instance the corresponding quantity of lithium hydroxide needed to form the soap or salt of the omitted component was also omitted.

Each of the greases prepared as in Example 2 and in comparative example was measured for dropping point and for ASTM penetration at 77 F. The composition of each of the greases and the inspections are shown in Table II which follows.

TABLE II Greases of invention Comparative greases M N X Y Z Composition, weight percent:

IAOH'HZO 4. 0 1. 9 2. 5 2. 9 1. 8 12-hydroxystearic acid 12. 9 10. 4 12. 9 11. 5 12. 9 Boric acid 1. 1 0. 5 1. 1 Methyl salicylate 2. 7 0. 5 2. 5 Base oil 78. 3 84. 7 82. 5 81. 1 85. 3 Phenyl alpha naphthyline 1.0 1.0 1 0 1.0 Na-Sul-B SN 1. 0 1. 0 Inspections:

Dropping point, F 500+ 500+ 437 415 405 ASTM penetration at 77 Unworked--. 252 275 262 217 261 60 strokes... 201 280 255 240 250 10,000 strokes 293 299 291 242 277 The phenyl alpha naphthylamine referred to was used as an antioxidant. The Na-Sul-BSN is a trademarked product which serves as a rust inhibitor; it is a 50 wt. percent concentrate, in a light mineral oil, of a neutral bar-' ium salt of dinonyl naphthalene sulfonic acid derived from naphthalene alkylated with tripropylene.

Referring to the data in Table II, comparison of grease X with grease Z and with grease M shows that while incorporation of monolithium borate into a lithium hydroxystearate grease increases the dropping point somewhat, much greater increase in dropping point results when lithium saiicylate is also used. Comparison of greases Y and Z shows that incorporation of the lithium salicylate without the monolithium borate does not improve the dropping point significantly.

Various other conventional additives can be incorporated into the grease compositions of this invention, as is understood by those skilled in the art. Such additives include antioxidants, rust inhibitors, tackiness agents, odor modifiers, dyes, extreme pressure agents, etc.

It wilrl be understood that the specific examples herein presented are by way of illustration and not limitation. The scope of this invention is to be determined by the appended claims.

What is claimed is:

1. A lubricating grease composition of high dropping point which comprises a major proportion of a lubricating oil and from about 2 to 30 wt. percent of a thickener system whose essential components include a lithium soap of a C to C hydroxy fatty acid and a monolithium salt of boric acid, wherein there are from 3 to 100 parts by weight of hydroxy fatty acid per part by weight of boHc acid.

2. Composition as defined by claim 1 wherein the thickener system also includes as a third component a lithium salt of a second hydroxycarboxylic acid of from 3 to 14 carbon atoms, wherein the hydroxy group is attached to a carbon atom not more than 6 carbon atoms removed from the carboxy group, and wherein there is a weight ratio of from about 0.1 to about 10 parts of said second hydroxycarboxylic acid per part of boric acid.

3. Grease composition as defined by claim 1 wherein said hydroxy fatty acid is 12-hydroxystearic acid.

4. Grease composition as defined by claim 2 wherein said second hydroxycarboxylic acid is salicylic acid.

5. Grease composition as defined by claim 2 wherein said second hydrocarboxylic acid is lactic acid.

6. Grease composition as defined by claim 2 wherein said second hydroxycarboxylic acid is parahydroxybenzoic acid.

References Cited UNITED STATES PATENTS 2,614,076 10/ 1952 Moore et al 252-42.1

2,951,808 9/1960 Norton et al. 25218 2,987,476 6/ 1961 Hartley et a1 25218 FOREIGN PATENTS 778,468 7/1957 Great Britain 25218 PATRICK P. GARVIN, Primary Examiner A. H. METZ, Assistant Examiner US. Cl. X.R. 2s2-25, 42.1