US2351384A - Lithium soap grease - Google Patents

Description

Patented June 13,1944

umrao STATES, PATENT 'OFFICE LITHIUM. soar cams]:

poration of Delaware No Drawing. Application November 15, 1942, Serial N0. 468,068

12 Claims.

This invention relates to a stable low temperature grease. More particularly, it deals with a lithium soap grease comprising a small amount of an oxidation inhibitor, and a low viscosity and low pour point mineral oil having a viscosity gravity constant (V. G. C.) of greater than .84.

The V. G. C. is an arbitrary constant calculated from the Saybolt Universal viscosity of an oil and its specific gravity, the value of which constant increases with the naphthenicity, and decreases with the paraihnicity of the oil (see the article by Hill and Coats in vol. 22, 1928, pp. 641-4, Ind. Eng. Chem, entitled Viscosity Gravity Con stant of Petroleum Lubricating Oils). Pennsylvania oils, typical of parafiinic oils, have V. G. C.s of about .80, while typical naphthenic oils have V. G. C.s above about .84 up to about .90.

Investigations into the flow properties of greases at low temperatures have revealed in the past that the flow of greases is primarily a function of the viscosity of the oil at that temperature and, to a lesser extent, of the amount and type of soap employed. Since oils of low V. G. C. change less in viscosity of a given temperature range than oils of higher V. G. C., such oils have in the past been employed for low temperature operation. Concerning the influence of the soap, it is known that relatively small amounts of soap are preferred to preserve the flow properties of the oil, and that lithium soap greases have better flow properties at low temperatures than comparable greases made with other soaps.

Lithium soap greases must contain free fatty acid to prevent excessive gelling. Such low temperature greases as were produced heretofore employing oils having S. U. viscosities below 100 sec. at 100 F. normally contain at least about .5% free acid calculated as stearic acid.

It is usually considered that low temperature greases should have consistencies of between about 200 and 370 A. S. T. M. penetration at 77 F. By low temperatures as herein stated, we mean temperatures low as about -100 F.

It has now been discovered that an improved low temperature lithium soap grease can be produced by using a naphthenic oil rather than a parafiinic oil. The new lithium soap grease of this invention differs from the previous lithium soap greases having the same consistency and equally good physical properties in that the grease of this invention requires only about /2 the amount of soap and less than A the amount of free fatty acid used in previous lithium soap low temperature greases.

The reduced amount of lithium soap employed Ill in the grease of this invention is of material economic advantage, since lithium soap is very expensive. Also, the reduced amount of soap counteracts the advantage of low V. G. C. oils employed in other lithium soap greases, because the more soap a grease contains the less it preserves the flow properties of the oil contained in it.

Furthermore, the amount of free fatty acid in this new grease is critical in that an excess of acid over the amount later specified causes the grease to become too soft, and when the grease is too soft, more soap must be added-which defeats one of the main advantages of this invention, namely, that of employing a smaller amount of soap.

These differences and advantages of the lithium soap grease of this invention are based upon the peculiar and unexpected influence of naphthenic mineral oils having a V. G. C. greater than .84 on the ability of the lithium soap to produce a grease of a given consistency.

It is a primary purpose of this invention to produce an economical low temperature lithium soap grease which meets the rigid Army and Navy Aeronautical Specification AN-G-3. Another purpose is to produce a stable lithium soap grease having an efiective lubricating temperature range of between about 100 F. and +300 F. A further purpose is to produce a smooth homogeneous lithium soap grease having a low soap content and a low free fatty acid content.

The composition of the grease of this invention may be summarized as follows:

Greases of the above composition have consistencies as measured by the A. S. T. M. penetrometer of between about 200 and 370+.

Suitable lithium soaps consist essentially of or comprise predominantly salts of lithium with fatty acids having 12 or more carbon atoms. In

addition, the lithium soap may contain minor amounts of fatty acid salts of other metals, particularly Na, K, Ca, Ba, Zn, Al, etc.

Saturated fatty acids preferred in the manu facture of the lithium soap, as well as for making up the free fatty acid content of the grease, are, for example, lauric, myristic, palmitic,

stearic, arachlc, behenic, hydroxy stearic, etc. Unsaturated fatty acids which may be present comprise oleic, ricinoleic, etc.

Lithium soaps may be manufactured by conventional methods, e. g. by saponification of vari- An oxidation inhibitor is essential to produce an oxidation-stable grease. Some lubricating oil oxidation inhibitors are more efiective than others in this grease. Specifically, it has been discovered that N-alkyl para-phenylene diamine inhibitors and condensed polynuclear aromatic mono-amine inhibitors are the most effective.

The N-alkyl para-phenylene diamine inhibitors have the advantage of very materially increasing the oxidation stability and life of the grease. Such inhibitors are N-butyl para-phenylene diamine, N-N'-dibutyl para-phenylene diamine, etc. The condensed polynuclear aromatic monoamine inhibitors do not produce a grease having quite so long a life as the same amount of the N-alkyl para-phenylene diamine. Such inhibitors are pha or beta naphthylamine, alpha-alpha, betabeta, or alpha-beta dinaphthylamine, etc. er'al of these inhibitors have the advantage of slightly increasing the consistency of the grease. Other suitable inhibitors are mixed petroleum alkyl phenols boiling from about 200 C.-240 C.

Some oxidation inhibitors which are less effective in the grease of this invention are: diphenyl amine, t-etra-methtyl-aminol diphenyl methane, 2.4-di-tertiary butyl G-methyl phenol, and some sulfurand phosphorus-containing inhibitors.

The naphthenic mineral oils suitable for making the low temperature lithium soap grease of this invention, as stated above, are those having a low viscosity, low pour point and a V. G. C. of greater than .84. Such oils are generally lubricating oils obtained from Gulf Coast, California, Venezuela and similar crudes. The pour point must be below about 60 F. and the S. U. V. at 100 F. usually less than 100 seconds and preferably between about 50 and 90 seconds. Oils of S. U. V. of about 30 seconds at 100 F. are too light to be considered lubricating oils.

Other ingredients which may be added include various corrosion inhibitors, extreme pressure additives, anti-wear agents, stabilizers, V. 1. improvers, and the like, provided they do not interfere with the low temperature operation and oxidation stability of the grease.

Some extreme pressure additives which may be used comprise: esters of phosphorus acids such as triaryl, alkyl hydroxy aryl, or aralkyl phosphates, thiophosphates, or phosphites, etc.; neutral aromatic sulfur compounds of relatively high boiling temperatures such as diaryl sulfides, diaryl disulfides, alkyl aryl disulfides, e. g. diphenyl sulfide, diphenol sulfide, dicresol sulfide, dixylenol sulfide, methyl butyl diphenol sulfide, dibenzyl sulfide, corresponding diand tri-sulfides, etc.; sulfurized fatty oils or esters of fatty-acids and monohydric alcohols, e. g. sperm oil, jojoba oil, etc., in which the sulfur is strongly bonded; sulfurized long-chain olefins such as may be obalpha or beta naphthylamine', phenyl altained by dehydrogenation or cracking of wax; sulfurized phosphorized fatty oils or acids, phosphorus acid esters having sulfurized organic radicals, such as esters of phosphoric or phosphorus acids with sulfurized hydroxy fatty acids; chlorinated hydrocarbons as chlorinated parailins, aromatic hydrocarbons, terpenes, mineral lubricating oils, etc.; or chlorinated esters of fatty acids containing the chlorine in position other than alpha position.

Additional ingredients other than extreme pressure additives may comprise anti-wear agents such as oil-soluble urea or thio-urea derivatives, e. g. urethanes, allophanates, carbazides, carbazones, etc.; or rubber, poly-isobutylene, polyvinyl esters, or other high molecular weight oil-soluble polymers to improve the stability of the grease;

or pour point depressors to further lower the pour 7 point of the oil; or stabilizer to reduce bleeding such as glycerine (less than .1% by weight); and V. I. improvers such as poly-isobutylenes of molecular weights-above about 800, volatilized paraflin wax, unsaturated polymerized esters of fatty acids, and monohydric alcohols and other high molecular weight oil-soluble compounds.

Example I A low temperature grease according to this invention was prepared by a process comprising making a slurry in an open kettle of lithium stearate and distillate oil having a Saybolt Universal viscosity at F. of 62 sec., a pour point of 75 F. and a V. G. C. of .8468. The slurry was continuously agitated and heated to a temperature of about 375 F. At this temperature phenyl alpha naphthylamine was added to the grease. The temperature of the resulting mixture was then brought up to between about 385 F. and 400 F. for a period of about 15 minutes and then the grease was drawn from the kettle and cooled as quickly as possible in open pans one inch deep. The cooled grease was then worked to remove any lumps that might be present therein. Amounts of the ingredients were such that the composition of this grease was as follows:

Per cent by weight Lithium stearate 7.00 Free stearic acid .02 Phenyl alpha naphthylamine .20 Mineral oil 92.78

This grease was a smooth, non-corrosive, lightcolored, homogeneous grease having a consistency of about 275 as measured by the A. S. T. M. grease penetrometer. At the end of 50 hours it bled less than 1.5% and was tested to be an effective lubricant at temperatures as low as -67 F.

Example II Eight other samples of such lithium soap greases were similarly prepared, containing (1 no amine, (2) .1% and (3) .25% phenyl alpha naphthylamine; (4) .1% and (5) 25% phenyl beta naphthylamine; (6) .1% N-N-dibutyl paragauge measures the pressure. The time required is recorded for the pressure to drop due to adsorption of the oxygen by the grease. The following table shows the results obtained on these samples:

Per cent Sample (lonsist- Lbs./m. Hours N o. mhlbltopused ency pres. drop time I 290 5 3 2 Phony] alpha 1 266 100 naphthylamine. 2g g 238 a 262 450 4 Phenyl beta .1 282 5 85 naphthylamine. 0 100 S ti t 5 u y gara-phenyiene .l 241 1 8 e. c 7 Alkyl phenols, .l 250 5 78 $321, 12. 200 C.- s ..do .25 279 The oxidation stability limits allowed by the Army and Navy Aeronautic Specification AN-Gqi for low temperature grease are 5 pounds p. s. i. drop in pressure after 100 hours of oxidation. Thus, samples 2, 3, 5, 6 and 8 meet these requirements.

The low temperature greases of this invention are particularly applicable for lubricating mechanisms, including ball bearings, that are used in cold climates as well as mechanisms of transportation including aircraft which operate within short periods of time between tropical temperatures at sea level and subzero temperatures at high altitudes.

We claim as our invention:

' .1% and 1% by weight 1. A low temperature grease consisting essentially of a hydrocarbon oil having a V. G. C. greater than .84 and a, pour point below 60 F., and containing between about 3% and 10% by weight of a lithium soap of a fatty acid of 12 or more carbon atoms, between about .01% and .5% by weight of free fatty acid having 12 or more carbon atoms and between about .01% and 2% by weight of an oxidation inhibitorxselected from the class consisting of N-alkylated para-phenylene diamines and polynuclear aromatic amines.

2. The grease of claim 1 wherein the soap is lithium stearate.

3. The grease of claim 1 containing between about 6% .and 9% by weight of said lithium soap.

4. The grease of claim 1 containing between .03% and .2% by weight of said free fatty acid.

5. A low temperature grease stable to oxidation consisting essentially of a hydrocarbon oil having a V. G. C. greater than .84, a pour point below -60 F. and an S. U. V. at 100 F. of less than 100 seconds, and containing between about 3% and 10% by weight of a'lithium soap of a fatty acid of 12 or more carbon atoms, between .01% and .5% by weight of free fatty acid having 12 or more carbon atoms. and between about .01% and 2% by weight or an oxidation inhibitor.

6. The grease of claim-5 wherein the oxidation inhibitor is selected from the class of N -a1kylated para-phenylene diamines and polynuclear aromatic amines.

7. The grease of claim 5 wherein the oxidation inhibitor is phenyl alpha naphthylamine.

8. The grease of claim 5 wherein the oxidation inhibitor is phenyl beta naphthylamine.

9. The grease of claim 5 wherein the oxidation inhibitor is N-N'-dibutyl para-phenylene diamine.

10. The grease of claim 5 containing between of said oxidation inhibitor.

11. The grease of claim 5 wherein the hydrocarbonoil has an S. U. V. at 100 F. of between about and 90 seconds.

12. A low temperature grease consisting essentially of a hydrocarbon oil having a V. G. C. reater than .84 and a pour point below F., and containing between about 6% and 9% by weight of a lithium soap of a fatty acid of 12' or more carbon atoms and between about .01% and .5% by weight of free fatty acid having 12 or more carbon atoms.

HAROLD A. WOODS. JACOBUS M. PLAN'IFEBER.