US2521438A - Grease composition - Google Patents

Description

Patented Sept. 5, 1950 GREASE COMPOSITION John C. Zimmer, Union, and Arnold J. Morway,

Rahway, N. J assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 6, 1947,

Serial No. 790,220

6 Claims.

The present invention relates to lubricating greases and more particularly to low temperature lubricating greases which include dibasic acid esters as substantial elements. The present ap-' plicaticn is a continuation-in-part of application Serial No. 570,784, filed December 30, 1944, now Patent No. 2,436,347, issued February '17,

In the usual methods of manufacturing low temperature greases, low boiling mineral oil fractions with resultant low flash points and low viscosities are compounded with metallic soaps to form plastic masses, or semi-solid grease compositions. It has been observed that the torque necessary to turn a bearing lubricated by grease is directly proportional to the viscosity of the oil used in the grease at the particular temperature. Therefore, it has been necessary in the manufacture of low temperature greases to use low boiling mineral oil fractions since these fractions have low viscosities at extremely low temperatures (-100 F.) However, since the equipment, for instance the shutter on an aerial reconnaissance camera, on which this grease is to be used may at times be subjected to relatively high temperatures (150 F.), the low boiling mineral oil present. The use of extremely-low boiling, mineral oil fractions is feasible in the manufacture of low temperature greases, but such use is subject to drastic restrictions because of the high volatility of such fractions at higher-temperatures. In addition, their use creates operational difiiculties due to fire hazards encountered in manufacture and use. Also, when the lubricant of volatile characteristics is subjected to high temperatures, loss of the liquid element by evaporation may soon render it deficient for low temperature operations. Hence it is desirable to avoid high volatility without impairing low temperature fluidity.

It has now been found that the esters of allphatic dibasic acids, particularly those esters in which the esterifying radical is a branched chain alkyl radical, may be used to replace a part of the resulting mixtures, as set forth hereinafter, have excellent lubricating properties at low temperatures, but are not soexpensive as the greases claimed in the parent application which employ esters as the entire liquid lubricating element. As stated in the application referred to above, these esters possess unusually high boiling points and resulting low vapor pressures at ordinary room temperatures, high viscosity indices, or low viscosity-temperature coefiicient, extremely low pour points and. are relatively stable chemically.

Among the aliphatic dicarboxylic acids suitable for the preparation of the esters used in making the grease compositions of the present invention, there may be mentioned malonic, succinic, isosuccinic, glutaric, ethyl malonic, pyro tartaric, adipic, pimelic, suberic, azelaic and sebacic acids. Instead of one of the enumerated acids, any acid or mixture of acids having the formula HOOC (R) COOH where R is a bivalent aliphatic hydrocarbon radical-for example synthetic acids produced by polymerization 0r dimerization of unsaturated fatty acids or their estersmay be used.

The esters which may be used in making the grease compositions of the present invention have the general formula R1OOCR COOR2, where R, is a bivalent aliphatic hydrocarbon radical such as methylene, polymethylene, ethylidene, propylidene, methyl dimethylene, butenylidene and the like; R1 and R are hydrocarbon radicals such as branched chain alkyl, alkaryl and cycle alkyl radicals of which secondary butyl, benzyl, cyclo hexanol and secondary octyl phenyl are representative- These are generally derived from the corresponding alcohols. Isobutyl Z-ethylhexyl sebacate is an example of a mixed ester. These esters may containadditional constituents or functional groups, such as Cl, Br, NHz, NHR, NRIRZ, CHO,

CO, SH, SR, RSSR, ROR, ROMetal. The esters may be made by any of the methods for producing esters known to the art.

One suitable method of preparing the esters consists of reacting the alcohol with the acid at elevated temperatures in the presence of an esterification catalyst such as sulfuric acid sulfosalicylic acid, etc. The reaction is facilitated by a continuous removal of water formed during the reaction by azeotropie distillation with a solvent such as benzene, toluene, etc., or by passing inert gas through the reaction mixture to remove water of reaction. The product is washed with dilute alkali to remove the catalyst and any traces of unreacted acid and, if necessary, is heated under reduced pressure with or without blowing with an inert gas to remove any unreacted alcohol or other low boiling material. If necessary .the prod- I uct can be clay-treated, and 1t 15 desirable a l f f i i gg f g f lit f ifgf though notrabsolutely necessary, that the finished f. 101 examp e o with esters as described above in quantities of 80 ester have a neutralization number not higher th b t 0 2 KOH m f e ter to to o@% of the weight of ilquld meolum are quite t on t t g i satisfactory and possess certain advantages over am fsulta'ble f y 0 a smce S lubricants prepared using only the ester. Thus a m the fimshed matelrlal P grease prepared with a liquid base-stock contion of the product, particularly 1n the presence taming 70% by Weight of di 2 ethy1heXy1 Sabaof materials such as copperor brass at: elevated. Gate and 5 f mineral lubricating 1 a highly mp ratures acid treated oil of about 58 s. s. U. at 100 F. de-

Typical esters together with some. of their more i ed from naphthenic type crude, passes the significant properties are given in the following copper corrosion test satisfactorily and is sutable. perior. in the bleeding test to a grease containing TABLE I Oentistokes Viscosity at- Slope on ASftIMTVis- P igpjqroxnatte C051 yemp'. 01.11 0 mg 0111 Name of Ester thCl1IaI,1rl; for 1 Pglgnt, F. agAtl e terva mosp eric F 1000 F mm!) F of 210 F. Pressure to -i0 F.

Di-secondary butyl sebacate 2. 09 6.42 320 O 752 136 Di-2-ethylhexyl sebacatm- 3.31 12.64 1.532 O 707 152i Di-lm'decanyl sehacate 4.66 22. 83 8,000 0 716 13815 Di-Z-ethylhexyl allzylated sebacate 5. 56- 42.72: 200,000 0.812 68:5 Di-2-ethy lhexylaze1ate 1 3.05 11.25 1,200 0 729 147 1 Alcohol-Sethyl nonanol 2 C4HCHGzH4CH-CH3- 2 Extrapolated fromthe 100 and 210 F. values.

As disclosed in the parent application referred only t t d th soap. The percentages to jg Sultable 9 'ff m i i i given above refer to the. liquid constituent only 53: is g g i t g r F PE and not to thefinished grease.

a y y Se m W n mm D In general, the mineral oil tobe used should 0f soap of a metal selected from the have a viscosit of to se" Sa bolt at 100 F group consisting of alkali and alkaline earth metv I d f -g 0 L" als together with a stabilizer consisting of an 1 Y z y m s g f a o asn amphoteric metal compound, specifically an oxa g 27 O 4 O an ide, carbonate or soap of zinc or aluminumv As point of about to 30 andmay be further examples,- the composition may consist of derlYed-ilrom naphthemc Daraffimc type a major proportion, for example 65% or more, of The fellewme table e v h o pl f di-secondary butyl adipate and' di' isopropyl'sebmulas o wo COmDOSiGiOHS S g Comparative acate with 6 to 30% of soap and stabilizer as-re- P p es of reases W th and W thout m al cited above. oil'replacing part of the ester.

TABLE II.

Composition Per cent P233311 24 hogtrgzl" F. C oplgBlegding Weight (60 Strokes) 0 l3 Ingredients Per cent 2.15212 F.

1ithiun1st%arate i1 fi1 1 20.0

en} a p a nap y amine 0.5 n Example I Zinc naphthenate 0. 5 202 Pass (N0 Stammg) 3.2

Di-Z-Ethyl Hexyl Selig-"ate" 79.0 Hydrogenated fish oil acids 17.00 ll lgzhiuin lhyidroxidfflrlnrlmohydrate 2. 8g

eny a p anap y amine 0.5 Example Zinc naphthanate 0. 50 261 Mineral oil 58 SSU at 100 F 23.00 Di-2-ethy1l1exyl sebacate 56.12

The lubricating greases described in the above mentioned application, of which the present is a continuation-inpart, have proved to be very sat- Table III shows the results obtained upon sucmission of the greases of Examples I and II to the tests outlined in the Government Specificaisfactory for. use at temperatures as low as tion AN-G-25.

. TABLE III Conformation of experimental greases with test requirements of Government Specification AN-G-25 Tests AN-G 25 Spec. Requirements Example I Example II Odnr None other than that of ester None None. Homogeneity" Completely homogeneous Homogeneous- Homogeneous. Corrosion on Copper Slight brown Stain, only Slight brown Pass.

s am. Dropping Point, F 325 Minimum Worked Penetration at 77 F., m. m../ 260- Water Resistance at 120 F., Per Cent Washed Out Low Temperature Torque Test at 67 F., See/Rev maximum 5 maximum The composition containing mineral oil (Extating. When the soap concentrate was approximately dry, the temperature was raised to 300 F. and a sample was taken for a free alkalinity determination. The percent free alkali should be in the range of 0.15 to 0.25%, calculated as NaOI-l. Any adjustments of the free alkali content were made, and thereafter residual water was removed by holding the grease at the elevated temperature of 300 F. The di-2-ethyl hexyl sebacate was next added and the temperature was raised further to 400 to 420 F. The phenyl alpha naphthylamine and the zinc naphthenate were then added. The hot molten grease was pumped to a continuous type grease cooler and cooled to 90 to 100 F. in one pass. The finished grease was then ready to be filtered'and packaged.

The greases of this invention may be produced in various other ways. For example, the soap may b prepared in situ in the mineral oil by reaction of a fatty material with an alkali or alkaline earth hydroxide, the soap concentrate dried, and the ester then added to the dry oilsoap mixture. Alternatively, the soap may be preformed separately either by direct reaction-of a fatty material with an alkali or alkaline earth hydroxide or in the case of lithium, calcium, magnesium or aluminum soaps, by precipitation from water according to well-known procedures. After being dried, the soap may be powdered, if desired, to facilitate dispersion in the estermineral oil medium. The soap is then added to the cold ester-oil solution. Once an ester-oil-soap mixture has been obtained, it is heated to a temperature of about 400-450" F. until the soap is completely melted in the liquid ingredients. The molten grease is then cooled either slowly in pans or rapidly in a continuous type grease cooler. The rapid cooling is to be preferred, inasmuch as greases prepared in this manner are more resistant to shear breakdown than those prepared by a slow cooling process. For example, the penetration of a pan-cooled grease rises from 260 mm./10 to 375 mm./10 after only 60 strokes Apparent Viscosity, Poises at 67 F. (20 sec. shear rate) 15,000 maximum .Bleeding, 30 Hours at 212 F., Per Cent Loss 5 maximum Evaporation, 20 Hours at 210 F., Per Cent Tms 2 max Norma Hoffman Bomb Oxidation at 210 F., PSI Pressure 5 maximum 1.0 3

Drop in Hours.

Storage Stability (4 months at loo- F.), Penetration in- 30 maximum 10 5 crease, mm./10. Wgrkmg Sta/balmy (100,000 Strokes Fine Hole Plate), Penetra- 375 maximum 316 305,

ion, mm.

Aeration Test (Per Cent Increase in Volume) 15 m m 4.5 5.0.

High temperature Performance: No. of Hours run in a ball 1000 Eours (minimum) more than 1000 more than 1000 bcarlng at 10,000 R. P. M. and 250 F. hours hours of an ASTM worker, while a rapidly cooled grease having the same unworked penetration shows a pentration of only 305 mm./10 after 100,000 strokes of the worker. It may be pointed out that in the preparation of the greases of this invention it is not desirable to form the soap in situ in the ester because hydrolysis of the ester occurs and an unsatisfactory product results.

In general, from 4 to 25 parts of fatty material are combined with 1 to 5 parts of saponifying agent, either before or after the fatty material is added to 20 to 40 parts of lubricating oil. After saponification the temperature is raised well above the boiling point of water to dry the soap and thereafter 45 to 65 parts of the ester are added. An oxidation inhibitor, such as 0.01 to 1 part of naphthylamine may be added after the ester. 0.1 to 5 parts of amphoteric metal soap may be added at any stage of the process, preferably after formation of the principal soap.

While lithium hydroxide is the preferred medium, because of the temperature stability properties of lithium soap greases, any of the alkali or alkaline earth metal oxides or hydroxides may be used for neutralizing or saponifying the fatty fatty oils, from which they are derived such as stearic acid, oleic, erucic, lauric, palmitic acid, tallow, lard oil, animal fats, etc., may be used to form the soaps with which to make the grease. The saturated acids derived from hydrogenated fish oil are especially suitable. On formulating the greases of the present invention they will contain in general 5 to 30% of alkali or alkaline earth soaps, 65 to 93.5% of the ester-mineral oil mixture or mixture of several esters with mineral oil, and preferably 0.1 to 5% of a stabilizer, preferably an amphoteric metal soap such as zinc or aluminum stearate and related materials. The use of a stabilizer smooths out the texture of the grease and further aids in the actual production of the grease. It is not always essential but is preferably used. The oxides, carbonates, or soaps of metals forming amphotericoxides such as the soaps of zinc, tin and aluminum, have been found to be very beneficial in their use as stabilizers, particularly in the case of greases containing free alkali. Mixtures of these soaps may also be used, a particularly effective combination being 0.5% aluminum stearate and 0.5% zinc naphthenate.

light hydrocarbon.

Greases prepared using a lithium soap and containing mineral lubricating oil of the general character described above in lieu of part of the ester have obvious economic advantages over lu-- bricants of the type described and claimed in the above-mentioned application, Serial No. 570,784.

As described more fully in the above mentioned application, of which the present is a continuation-in-part, there is considerable drag on bearings at low temperatures when ordinary low temperature greases are used. This drag becomes particularly objectionable at extremely low temperatures such as -40 to 70 F. or lower. While very light mineral oils are fairly satisfactory at such low temperatures they evaporate excessively at temperatures of 120 to 150 F. Such extremes of temperature are commonly encountered in the use of aircraft, and when lubricating greases are subjected to considerable evaporation they are no. longer entirely suitable for low temperature lubrication.

Grease compositions comprising substantial quantities of esters of the type described above,

in combination with comparable or preferably somewhat smaller quantities of light mineral oils, are not so readily evaporated as those wherein the lubricating fluid consists entirely of a very Somewhat heavier hydrocarbons may be used in combination with esters such as di-2-ethylhexyl sebacate, secondary butyl sebacate and the like without encountering undue torque or drag at very low temperature. By the use of amphoteric metal soap as a stabilizer, excess alkali is absorbed or taken up and thus prevented from reactin with the esters, the composition at the same time retaining the improved oxidation and structural characteristics of the alkaline type greases.

What is claimed is:

l. A low temperature grease composition consisting essentially of 20 to 40% by weight of mineral lubricatin oil, 45 to 65% of an ester having the general composition COOR1(R)COOR2 wherein R is a bivalent aliphatic hydrocarbon radical and R1 and R2 are branched chain hydrocarbon radicals, 5 to 30% of a soap selected from the group consisting of the alkali and alkaline earth metal soaps, and 0.1 to 5% of amphoteric metal soap as a stabilizer.

2. Composition according to claim 1 in which the amphoteric metal soap stabilizer is a mixture of aluminum stearate and zinc naphthenate.

3. A lubricating grease composition suitable for low temperature use consisting essentially of approximately 56% by weight of di-2-ethylhexyl sebacate, 23% mineral lubricatin oil, 19% lith- 5 ium soap, and less than 1% each of an oxidation inhibitor and. an amphoteric metal soap as a stabilizer.

4. Composition according to claim 1 wherein said mineral oil is an oil of 45 to 70 S. S. U. viscosity at 100 F., having a flash point of 275 to 400 F.

5. Process of preparing a low temperature lubricating grease which comprises adding 4 to 25 parts of fatty material to 20 to 40 parts of mineral lubricating oil, heating said fatty material and. lubricating oil to 125 to 200 F., adding 1 to 5 parts of a saponifying agent selected from the class consisting of the alkali and alkaline earth metal oxides and hydroxides, the quantity of saponifying agent used being adjusted to yield a free alkalinity of 0.15 to 0.25, calculated as NaOI-I, thereafter heating above the boiling point of water to dry the soap, adding 45 to 65 parts of an ester having the general formula COOR1 (R) COORz wherein R is a bivalent aliphatic hydrocarbon radical, and R1 and R2 are branched chain hydrocarbon radicals, and adding a small amount of an amph-oteric metal soap to take up excess alkali and stabilize the grease.

6. Process according to claim 5 wherein to 1 part of an oxidation inhibitor and 0.1 to parts of an amphoteric metal soap are added during processing.

JOHN C. ZIMMER. ARNOLD J. MORWAY.

REFERENCES CITED The followingreferences are of record in the file of this patent:

* UNITED STATES PATENTS Number Name Date 2,363,013 Morway et al. Nov. 21, 1944 2,383,147 Morgan Aug. 21, 1945 2,391,113 Zimmer et a1 Dec. 18, 1945 2,436,347 Zimmer et al Feb. 17, 1948 2,448,567 Zisman et a1 Sept. 7, 1948 2,450,221 Ashburn et al Sept. 28, 1948 2,450,222 Ashburn et al. Sept. 28, 1948

Claims (1)

1. A LOW TEMPERATURE GREASE COMPOSITION CONSISTING ESSENTIALLY OF 20 TO 40% BY WEIGHT OF MINERAL LUBRICATING OIL, 45 TO 65% OF AN ESTER HAVING THE GENERAL COMPOSITION COOR1(R)COOR2 WHEREIN R IS A BIVALENT ALIPHATIC HYDROCARBON RADICAL AND R1 AND R2 ARE BRANCHED CHAIN HYDROCARBON RADICALS, 5 TO 30% OF A SOAP SELECTED FROM THE GROUP CONSISTING OF THE ALKALI AND ALKALINE EARTH METAL SOAPS, AND 0.1 TO 5% OF AMPHOTERIC METAL SOAP AS A STABLIZER.