US2690429A - Grease compositions containing an aryl oxy alkyl salt as a stabilizer - Google Patents

Description

Patented Sept. 28, 1954' GREASE COMPOSITIONS CONTAINING ARYL OXY ALKYL SALT AS A STABILIZER Arnold J. Morway,

Clark Township,

Union County, and Paul V. Smith, Jr., Westfield, N. J., assignors to Standard Oil Development Company, a. corporation of Delaware No Drawing. Application April 7, 1952, Serial No. 281,046

6 Claims. 1

This invention relates to lubricating grease compositions and more particularly to anti-friction bearing lubricating greases which are suitable for high temperature use. More particularly, the invention relates to high temperature greases prepared from lubricating oil thickened with an alkali metal soap of a higher fatty acid, in conjunction with an alkali metal salt of a lower molecular weight oxy acid.

It has been suggested in the prior art that for some purposes, it is advantageous to combine certain metal salts, particularly the metal salts of organic acids of low molecular weight, with the metal soaps which are ordinarily employed as thickeners for lubricating grease compositions. Various investigators have found that the addition of metal salts of the character referred to have utility for improving stability and high temperature properties, and the like. There ap pear to be several theories as to the operation of such metal salts in conjunction with the metal soaps. One such theory is that the addition of salts of low molecular weight acids to soaps of relatively high molecular weight results in the formation of a complex with superior grease thickening effect and improved stability.

Whatever may be the phenomena involved, the addition of salts of low molecular weight compounds appears to be particularly advantageous in connection with greases of alkali and alkaline earth metal soap bases. The low molecular weight salts appear in many cases to improve the physical structure of the grease. Compositions of this character are particularly receptive to the action of oxidation inhibitors and it is possible that the compositions themselves are more stable against oxidation than greases thickened with soaps of high molecular weight carboxylic acids alone, for example.

Suggestions in the prior art have included the use of metal salts of low molecular weight carboxylic acids which are saturated, such as acetic and propionic acids, and even more recently it has been suggested that certain of the lower unsaturated acids, such as acrylic acid, crotonic acid, and the like may be used as soap thickener adjuncts.

According to the present invention, the salts of certain low molecular weight oxy acids are highly useful as ingredients of lubricating greases.

It is the object of this invention, therefore, to prepare an improved grease suitable for antifriction bearing and related surfaces at elevated temperatures, i. e., temperatures in the neighborhood of from 300 F. to 350 F. and even higher. A further object of the invention is to provide a lubricating grease composition comprising a lubricating oil thickened to a grease consistency with a combination of the alkali metal soaps of high molecular weight aliphatic acids and alkali metal salts of lower molecular weight oxy acids, hereinafter to be described.

The low molecular weight oxy acids which are employed in this invention contain an ether linkage and in this respect are similar to furoic acid, which is a heterocyclic unsaturated acid containing an ether linkage in a 5-membered ring. In fact, greases prepared by employing salts of alkoxy acids such as ethoxypropionic acid, methoxybenzoic acid, and the like, are, in many re spects, similar to the excellent high dropping point greases prepared from furoic acid. Other acids containing oxygen are apparently quite different. For example, when the soap of levulinic acid is employed, as the thickening agent alone or in combination with high molecular weight acid soaps, greases are formed of relatively low dropping point and poor structural characteristics. This would appear to be due to the oxygen atom of ketonic linkage contained in the levulinic acid molecule. The soaps of saturated straight chain acids of 6 to 10 carbon atoms having no oxygen in the hydrocarbon chain, such as caproic acid, do not form greases due to their diificulty of satisfactory dispersion. In addition, mixtures of soaps of levulinic acid and straight chain aliphatic acids are difiicult to disperse in mineral oil even at elevated temperatures, whereas the mixtures of the grease soaps and the salts of the oxy acids of this invention have a high degree of dispersability.

Grease formulations containing the salts of the oxy aromatic acids such as p-methoxybenzoic acid, have the added advantage of a low degree of water solubility and will wet metallic surfaces covered with water. These grease iormulations are also much more adhesive to metal surfaces than other type greases.

The structure of some of the oxy acids mentioned above are shown below:

Molecular Weight 118 CH3-CHr-O-CHzCH2COOH Ethoxypropioic acid 112 OCH=CHOH=OCOOH Furoic acid 116 CHa-( 3CH2CHz-COOH Levulinic acid 116 CH3-CHzGH2-OH1CH2-COOH Caproic acid 152 oH3oC co0H Anisic acid Ethoxypropionic acid may be prepared from beta-propiolactone by reaction with ethyl alcohol. The beta-propiolactone may be prepared from formaldehyde and ketone. The preparation of this acid is described in the Journal of American Chemical Society, vol. 70, pages 998-1006 (1943) It may also be prepared by adding ethanol to acrylonitrile or acrylic esters followed by hydrolysis or by the reaction of an alkali ethoxide with beta-halopropionic acid.

The oxy acids which are employed in the greases of this invention have the following general formula:

R representing a saturated aliphatic radical having from 1 to 5 carbon atoms such as methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, sec. y -b y yl, etc., or an aromatic radical having from 6 to 10 carbon atoms such as phenyl, tolyl, Xylyl, t-butylphenyl, etc., R representing a divalent radical as selected from the group above.

Specific mention may be made of such compounds as methoxypropionic acid, ethoxypropicnic acid, nand isopropoxypropionic acid, nand isopropoxyacetic acid, seccndarybutoxyacetic acid, p-methoxybenzoic acid, p-ethoxybenzoic acid, phenoxyacetic acid, beta-phenoxypropionic acid, phencxybenzoic acid, and the like.

As has been stated before, the grease compositions of this invention are formed by combining with the desired lubricating oil an alkali metal salt of a low molecular weight oxy acid with an alkali metal salt of a high molecular weight substantially saturated aliphatic acid. In general, the metallic element of the salts as well as of the soaps may be any of the alkali metals. Sodium, however, is the preferred embodiment of the invention. It is within the concept of the invention, however, to use mixtures of sodium and lithium, i. e., the sodium salt of the low molecular weight oxy acid may be used in conjunction with the lithium soap of the high molecular weight saturated fatty acid and vice versa.

The relative proportions of the high molecular weight soap and of the low molecular weight salt may be varied rather widely. In molecular proportions, it is preferred to use 1 to 3 parts of the soap with about 1 to 2 parts of the salt. In general, however, it is preferable that the molecular proportions be more nearly equal and specifically, proportions of about 1 to 1 appear to be the most satisfactory. Further, the quantity of the soap and salt ingredients to be used in a given grease composition vary with the type of grease which is desired and also with the kind and the viscosity of the oil which is used as a liquid base.

For a stifi grease composition, the total quantity of soap and salt may approach 50% of the weight of the final composition. On the other hand, for a soft grease, the total proportion of soap and salt may be as low as about 5% based on the weight of the entire composition.

In general, the grease should consist of a lubricating oil having a viscosity of about 35 to 200 SUS at 210 F. containing about 3 to 20 Or 30% by weight of the metal soap of a C12 to C22 fatty acid or glyceride along with 2 to 15 or 20% by weight of the metal salt of the low molecular weight oxy acid. In general, ethoxypropionic acid is preferred to form the low molecular weight oxy acid portion. However, as it was pointed out above, other oxy acids, such as methoxypropionic acid, propoxypropionic acid, pmethoxybenzoic acid, and the like, may be used.

For ordinary anti-friction bearing greases, the sodium soap and the sodium salt of ethoxypropicnic acid are specifically preferred.

In the preferred embodiment of this invention a substantially saturated fatty acid having an average chain length in the range of 12 to 22 carbon atoms is utilized, however, any of the fatty acids known in the art of grease manufacture may be employed. For ease of dispersion, generally the higher molecular weight acids are preferred. These preferred acids consist predominantly of acids having a carbon chain length of 18 or slightly higher. They may be natural products such as stearic, arachidic, or the hydrogenated acids obtained from tallow or fish oil acid fractions.

For the liquid phase of the grease, mineral base lubricating oils are preferred but the invention is not necessarily limited to the mineral base oils. Various synthetic oils may also be used. As is well known in the art of grease making, certain synthetic esters, especially the dibasic acid esters, such as di-2-ethylhexyl sebacate and homologous and analogous esters are preferred for certain purposes in grease making. According to this invention, the lithium soap grease of such compounds, modified with the sodium or lithium salts of ethoxypropionic acid, and the like, are particularly useful for lubrication at very low temperatures. Other synthetic oil base greases such as those employing the polyglycols or the glycol others are also contemplated as being within the scope of this invention. The combined soaps and salts may be used to thicken mixtures of mineral oil and synthetic oil as well as being useful with either type of oil alone.

An example of the concept of this invention, a grease composition containing the ethoxyprcpicnic acid and its properties are described below:

EXAMPLE I a. Formulation Ingredients: Per cent weight Ethoxypropionic acid 6.0 Hydrogenated fish oil acids 15.0 Sodium hydroxide 4.4 Phenyl alpha naphthylamine 1.0

Mineral lub. oil of 500 SUS vis. at F. (55 at 210 F.) 73.6

1). Method of preparation The hydrogenated fish oil acids and A; of the mineral oil were charged to a fire heated grease kettle and the temperature raised to F. The ethoxypropicnie acid was charged and the acids immediately coneutralized with a 30% aqueous Properties:

Percent free alkali 0.12 as NaOH. Appearance yellow-smooth short fiber. Dropping point F 446. Worked penetration mm./ 306. Structure stability to mechanical 339 mm./l0.

working penetration after 100,000 strokes fine hole worker plate.

Water washing test-Percent loss (125 0.0.

F. water temperature). Wheel bearing test, 6 hours at 220 F.... Pass, conditions and lubrication excellent. High temperature spindle test 204 400 hours before bearbearing, 10,000 R. P. M.300 F. ing failure Grease still in good condition.

EXAMPLE II a. Formulation Percent Ingredients: weight Anisic acid 5.00 Hydrogenated fish oil acids 10. 00

Sodium hydroxide Phenyl-alpha-naphthylamine Mineral lubrication oil of 50 (50 SUS at 210 F.)

b. Method of manufacture The anisic acid, fish oil acid and /3 of the mineral oil were charged to a fire heated grease kettle and heated While agitating to 150 F. The sodium hydroxide as a 30% aqueous solution was added and the soaps formed dehydrated while heating to 300 F. The balance of the mineral oil was then gradually added while continuing to heat to 450 F. At this temperature the phenylalpha-naphthylamine Was added and the grease drawn into pans for cooling. (It may be left in the kettle to cool.) When cool the grease was broken down by stirring in the kettle and homogenized. The free reaction of the grease may vary from 0.5% as oleic acid to 0.5% as NaOH. Greases varyin between these limits are of excellent structure and stability.

water; unaffected at temp. up to 185 F. Tendency to displace water on a wet Displaces water and metal surface. clings to metal surfaces. Norma-Hoffman bomb, oxidation hours 385.

to 5 p. s. i. drop at 210 F. (hours).

EXAMPLE III a. Formulation Percent Ingredients: weigf t Anisic acid 3. 45

Hydrogenated fish oil acids 7. 50 Sodium hydroxide Phenyl-alpha-naphthylarninc 75 0 Mineral lubrication oil of 500 SUS visc. at 100 F. (50

SUS at 210 F.) 85.60

b. Method of manufacture The anisic acid, fish oil acid and A; of the mineral oil were charged to a fire heated grease kettle and heated while agitating to 150 F. The sodium hydroxide as a 30% aqueous solution was added and. the soaps formed dehydrated while heating to 300 F. The balance of the mineral oil was then gradually added while continuing to heat to 450 F. At this temperature the phenyl-alphanaphthylamine was added and the grease drawn into pans for cooling. (It may be left in the kettle to cool.) When cool the grease was broken down by stirring in the kettle and homogenized. The free acidity of the grease may vary from 0.5% as oleic acid to 0.5% as NaOH. Greases varying between these limits are of excellent structure and stability.

Properties:

Penetrations, mm./10 77 F UnworkecL 220. Worked 60 strok 225. Worked 100,000 strokes (fine hole 275.

worker plate) Dropping Point, F 500+. Water resistance Soluble in boiling water; unafiected at temp. up to 185 F. Tendency to displace water on a wet Displaces water and metal surface. clings to metal surfaces. Norma-Hofiman bomb,oxidationhours 385.

to 5 p. s. i. drop at 210 F. (hours).

EXAMPLE IV a. Formulation Percent Ingredients: weight gethoxy benzoic acid... 5.0 ydrogenated fish oil ac 10. 0 Sodium hydroxide 3. 0 Phenyl-alpha-naphthylam 1. 0 Mineral lubricating oil of 500 SUS viscosity at F. (50

SUS at 210 F.) 81.0

b. Method of manufacture This grease composition was prepared according to the procedure described in Example III(b) above.

EXAMPLE V a. Formulation Percent Ingredients: weight Phenoxy acetic acid 5. 0 Stearic acid Sodium hydroxide 3. 2 Phenyl-alpha-naphthylarnine Minegall lpbricating oil of 500 SUS at 100 F. (50 SUS at 210 b. Method of manufacture The grease of this example was prepared by the procedure detailed in Example III(b) above.

Properties:

Penetrations, 111111.]10, 77 F.:

Unworked 200. Worked 60 strokes 210 Worked 100,000 strokes (fine worker plate) Dropping point, Water resistance Norma-Hellman oxidation test rs to 5 p. s. i. pressure drop at 210 F) 295.

EXAMPLE VI a. Formulation Ingredients:

Beta-phenoxy propionic acid Hydrogenated fish oil acids Sodium hydroxide Phenyl-alpha-naphthylamme Mineral lubricating oil of 500 SUS at 81.0

100 F. (50 SUS at 210 F.).

Percent weiahot b. Method of manufacture The grease sample was prepared in accordance with Example III(b) above.

Properties:

Penetrations, rum/10, 77 F;

Unworked 205. Worked 60 strokes 215. Worked 1000,000 strokes (fine hole 265.

Worker plate). Dropping point, F 500+. Water resistance Insoluble at 210 F.

Norma-Hoffman oxidation test (hours 265.

to p. s. i. drop at 210 F.).

The greases of Examples IV through VI were all dark brown, smooth uniform compositions and had free alkalinity values ranging from 0.25 to 0.31% as NaOH.

The grease compositions of Examples I through VI above were compared with similar formulations employing furoic, levulinic and caproic acid and comparative data are set out in the table below. The formulation for the three greases using furoic, levulinic and caproic acid is as follows:

Basic formulation:

6.0% low molecular weight acid. 15.0% hydrogenated fish oil acids. 4.4% sodium hydroxide. 1.0% henyl-alpha-naphthylamine. 73.6 o mineral oil, viscosity 500 SUS at 100 F., 50 SUS at 210 F.

phenoxy acetic acid, beta-phenoxy propionic acid, and the like are contemplated herein.

What is claimed is:

1. A lubricating grease composition consisting essentially of a lubricating oil thickened to grease consistency with from 5% to 20% by weight of a mixture of from one to three parts of an alkali metal soap of a high molecular weight fatty acid and from one to two parts of an alkali metal salt of a material having the formula Table COMPARATIVE DATA ON GREASES EMPLOYING LOW MOLECULAR WEIGHT ACID SALTS Ethoxy P-methoxy P-ethoxy Phenoxy B-phenoxy F Propionic Benzolc Benzoic Acetic Prcpionic Lewltmlc Ca roic Acid Acid Acid Acid Acid Acid Acld A019 p Percent FreeAlkalinity 0.12 0.3 0.29 0.25 0.31 0 25 worked t m narr. c 200 0 210 215 Grease did not form. Structural Stability Penetration 100,000 Strokes) 339 272 a 275 280 265 Dropping Point F.) 44c 45 500+ 500+ 500+ Dispersibility of Soap Excellent Excellent, Excel e t Excellent. Excellent Wheel Bearing Test (6 hours at 220 F.) Pass 1. Pass Pass Pass Pass The above results show that the sodium soap or low molecular weight oxy acids according to this invention in combination with the sodium soap of hydrogenated fish oil acids are easy to disperse and give excellent greases of high dropping point and structural stability.

In a copending application, Serial No. 182,886, filed for the same inventors on September 1, 1950, now Patent No. 2,623,854 issued December 30, 1952, there is claimed grease compositions containing low molecular weight oxy acid salts, that is, alkyl oxy alkyl acid salts. This application, a continuation-in-part of that application is directed toward the carboxyl derivatives of an alkyl aryl ether corresponding to the formula where R and R are either aliphatic radicals containing from 1 to 5 carbon atoms or aromatic radicals containing from 6 to 10 carbon atoms. In other words there is claimed herein grease compositions containing an alkali metal salt of a carboxyl derivative of an alkyl aryl ether wherein the alkyl portion of the ether contains from 1 to 5 carbon atoms and the aryl portion contains from 6 to 10 carbon atoms. Compounds such as p-methoxy benzoic acid p-ethoxy benzoic acid,

of aliphatic substantially saturated fatty acids, having an average carbon chain length within a range of from 12 to 22 carbon atoms and from 2% to 15% by weight of an alkali metal salt of a material having the formula wherein R is an alkyl group, containing from one to two carbon atoms.

5. A lubricating composition according to claim 4 wherein said material of the formula is phenoxyacetic acid.

6. A lubricating grease composition according to claim 4 wherein said material of the formula is beta phenoxy propionic acid.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO GREASE CONSISTENCY WITH FROM 5% TO 20% BY WEIGHT OF A MIXTURE OF FROM ONE TO THREE PARTS OF AN ALKALI METAL SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID AND FROM ONE TO TWO PARTS OF AN ALKALI METAL SALT OF A MATERIAL HAVING THE FORMULA