US2820008A - Lubricating grease composition - Google Patents

Description

United LUBRICATING GREASE COMPOSITION No Drawing. Application April 22, 1955 Serial No. 503,340

9 Claims. (Cl. 25233.3)

This invention is concerned with improved grease compositions. More particularly, it is directed to grease compositions conferring markedly improved corrosion protection and bearing life, and having greater mechanical stability.

Grease compositions comprising a lubricating oil and soap are subject to two primary degrading influences, namely, oxidation and the deleterious effects of products produced thereby, as well as due to thermal degradation and the resulting decomposition products thereof. A great variety of additive materials have been studied for their efiect upon the several properties of greases such as maintenance of consistency, depression of corrosion characteristics, stabilization against oxidation and resistance to thermal decomposition. One property which most greases are subject to in addition to those discussed above is the sensitivity of the composition with respect to water.

Most soaps and therefore soap-based greases are sensitive to a lesser or greater degree to emulsification 'or solution in water. Since wheel bearings and similar lubrication points are subject to the washing action of water especially in wet weather it is imperative that greases be constructed so as to be resistant to excessive emulsification or solution thereof in water or similar solvents.

In addition to the sensitivity of a grease with respect to water, other situations occur in which the machinery to be lubricated is subject to corrosive agents such as organic acids and the like. Such is the case in cannery equipment, an aggravated example of which is equipment utilized for the canning or freezing of spinach and similar vegetables. Many food juices, such as spinach juice are corrosive to metal. In addition, they are often preserved in weak brines. The combination of the food juices and the brines is often extremely corrosive to the equipment. Consequently, greases must be designed to protect cannery equipment from corrosion, especially for the processing of such materials.

It is an object of the present invention to provide greases especially suitable for operation of machinery in the presence of water. It is another object of the present invention to provide grease compositions which will afford protection against corrosion by aqueous brine and food juices such as those just described. It is a further object of the present invention to provide grease compositions not only improved in the two respects just mentioned but also having greatly prolonged mechanical stability. Other objects will become apparent during the following discussion.

Now, in accordance with the present invention,'soap ,base greases comprising a major amount of a lubricating oil thickened to a grease consistency with a minor proportion of a metallic soap have been unexpectedly improved by the synergistic-combination of mono (aliphatic carboxylic acid) esters of polyoxyalkylene glycols (wherein each oxyalkylene radical contains 2-6 carbon atoms) and alkaline earth metal hydrocarbyl sulfonates. It has been t'tznlnd'that the'combination of these particular additives,

tates Pater p 2,820,008 Patented J an.- "14,1958

tween about 0.1% and about 5%, by weight, based on the total grease composition, provides an unexpected prolongation in the useful bearing life of the grease, are

unexpectedly resistant to the washing or emulsification action of water, and provide excellent resistance against corrosion for metallic surfaces lubricated thereby.

The polyalkylene glycol monoesters have the general formula wherein R is an alkylene radical having between about 2 and about 6 carbon atoms, preferably between 2 and 4 carbon atoms. R, is an alkyl radical having between about 8 and about 24 carbon atoms, preferably between about 12 and about 20 carbon atoms, and n is a whole integer between about 5 and about 20. Preferably the polyoxyalkylene glycols from which the subject monoesters are formed have molecular weights between about 150 and about 2000, and the monoesters derived therefrom are of high enough molecular weight to be oil-soluble. Suit-' able glycols from which the monoesters may be prepared include polyethylene glycol, polypropylene glycol, polybutylene glycol, polyamylene glycol, and polyhexylene glycol, as well as combinations thereof including the heteric polymers of ethylene glycol and propylene glycol, for example. Acids which may be utilized in accordance with the present invention to form the subject monoesters comprise both saturated and unsaturated aliphatic monocarboxylic acids, including both fatty acids and hydroxy fatty acids. lncluded expressly are capric, lauric, myristic, palmitic, and stearic acids, and the corresponding unsaturated acids of which oleic acid is typical and preferred. Also the corresponding hydroxy fatty acids may be utilized such as 12-hydroxy stearic acid, or the corresponding mixtures derived by the hydrogenation of castor oil or similar naturally occurring oils. Typical species of suitable monoesters comprise the oleic acid esters of polyethylene glycol, the stearic acid esters of polypropylene glycol, polyethylene glycol monolaurate, and the like.

The alkaline earth metal hydrocarbyl sulfonates are preferentially oil-soluble and preferably are obtained from petroleum sources and are known as petroleum sulfonates. These are ordinarily obtained in the treatment of petroleum oils to obtain highly refined products of the type of electrical insulating oils, turbine oils and the like, in which the petroleum oils are treated successively with a number of portions of concentrated sulfuric acid or fuming sulfuric acid. A variety of compounds'are formed by the chemical reactions of sulfuric acid upon the oil including sulfonic acid, organic esters of sulfuric acid, partial esters of sulfuric acid, etc. Most of these compounds are relatively insoluble in the oil under the treating conditions and separate from the oil together with unreacted sulfuric acid as a sludge, which is separated from the oil after each treatment. The sulfuric acid is usually added in dumps of about /2 lb. per gallon of the oil, the total quantity of the acid added depending upon the oil being treated and the desired final product. Usually from about 3 pounds to about 9 pounds of sulfuric acid per gallon of especially when they are present in amounts each of beoil are used. Some of the sulfonic acids resulting from the treatment of the oil with the sulfuric acid are preferentially oil-soluble and remain in the oil layer after removal of the acid sludge These can be removed'from the oil by neutralizing the acid-treated oil with an alkaline agent such as oxides, hydroxide, or carbonate of an alkaline earth, for example, calcium oxide, to form sulfonic acid soaps or sulfonates which are then extracted from the oil by treatment with 50% to %aqueous ales),- hol solutions or other suitable means. Because of the Preferably the sulfonic acids agent such as lime are combined with sulfonic acid radicals, or the so-called pane sulfonates may be employed .whereinthe metallic radical has one valence attached to .a;sulfouic acid radical and the dtli'er'being a hydroxyl sub's'tituent.

,fThe preferred sulfonates are the soj-called"ba'sic sul- "fonates'i believed to "have the [general formula repres ented 'by wherein R a 'hydrocarbyl radical, M is an alkaline earth radical, R usually being. a 'na-phthenyl, alkyl naphthenyL alkaryI or naphthe'nylearyl radical, such that the weight of the sulfonic acid 'is that stipulated hereinbetore. The-possibilityrexists that the "basic-lsulfonate cornprises a colloidal mixtureofthe neutralsulfonate and alkaline earth metal hydroxide.

.Thesoapgreases {to be benefitted-by the presence of this combination or improving substances cornprise those *whereinthe lubricating oil isof mineral oil origin or of synthetic origin as given-in greater detail hereinafter. -.The'soaps utilized for thickening these oils to' a:.;grease consistency comprisethe alkali metal or alkaline earth .metal soaps of fatty acids or hydroxy fatty'acids, including especially the calciumor lithium soaps'ofstearic acid or of lZ-hydroxy stearic. acid. Other soaps utilized :for .the formation ofsuitable greases to beineluded 'within 'thepresentinvention are well known in the art. Calcium and-lithium stearates or hydroxystearates havea. certain amount of inherent water'resistance and are preferred for this reason. However, the invention contemplates the use ofniore water-sensitive soaps asWell, such as the sodium soaps of suitable fatty acids. The fatty (or hyxlroxy fatty) acids which may be employed are those havingbetween about 12 and about 24 carbonatoms per molecule, preferably between about 16 and 20 carbon atoms per .moleculc. Ordinarily, :sources of acids are utilized whichpreponderate in acids having an average or aboutlS carbon atoms per moleculesuch as those obtainedfromcastor oil or fromanirnal fats, and the like.

Fln addition to the ordinary mineral oils utilized as is fllknown in the art for the preparation of greases,synthetic lubricants maybe utilized including the aliphatic esters 30f dicarboxylic acids, the liquid polyoxya lkylene glycols and oxides, liquid phosphorus esters, silicates, and similar materials. Typical species of these classes include tricresyl phosphate, tri (2-ethylhexyl) phosphate, bis(2- ethylhexyl) sebacate, adipate, tetrahexyl silicate,.heteric copolymers of ethylene oxide andpropylene oxide, and similar substances.

One of the unexpectedffeatures of/theprescnt invention comprises the very substantial increase inthe mechanical stability of the greases containing the recited combination of additive substances. This is especially unexpected-in view .of the fact that the single substances utilized in the absence of the other even in the-same type of grease compositions results in no increase in roll stability or at leastfin an improvement of only a minor amount. {This feature is especiallyevident 'inEEXample -given*hereinafter, and the 'efiect is most pronounced dt elevated temperature,"in the order of' at :least "about i 50 Tsan'd' shave. Even 'atroom temperature, however, rrt--'has b'een found thatilthe-useef the combination of additives results in substantially doubling the efiective .life .of thevgrease composition under mechanical stress.

In studying the various possible aspects of the general class of compositions considered herewith, the use of the corresponding sodium sulfonates was considered. However, as the comparative data given in Example I demonstrates, the alkali *rnetal-sulfonates are highly undesirable,.since whenutilized in amounts efifective to promote even a mild degree of corrosion protection in the g'reasecompositio'ns, 'their'tpresenc'e creates a substantial "amount or ivater sensitivity as evidenced by the percent of the grease lostby means of emulsificationor otherwise inastandardwater resistance test. As the proportion of sodium sulfonate'isincrea-sed for the purpose of providing furtherprotectiou against corrosion, the water resistance of the grease *dra'sticetllydecreases. Thus, by increasing the proportion of sodium sulfonate from about 2% to about 2 /2% in the same lithium 12-hydroxystearate-mineral oil grease, the percent loss ofgrease in "a-water resistancetestincreasedfrom 32% to about 5 5%. Thus it was determined that sodium 'sulfonates could not be used in the present compositions due to their disadvantageous tendency to create water sensitivity of the grease. For-thisreason, as well'as because of the *Sup'eriorme'chanical stabilizing properties of the alkaline earth rne'tal sulfonates, the alkali metal sulfonates are noti'ncl'uded within the scope of the present invention.

Example 1 14 days Hours to 230 per "glass jar roll stability Water corrosion v washout, testpercent 0.05% 3 loss NaCl- Room number 212 F. temp. of rollers corroded l3 ase grease +2% 'Na sul ionates +25% polytethylene glycol) mono-oleate- 32 4 48 300 Base grease +2% Co. sultonates' +12% poly(ethylene glycol) mono-oleate 11 N one 290 550 Base grease 5 121 36 300 The base Y grease employed m the above example comprised the lithium 12-hydroxystearate soap in gelling amounts and a medium viscosity mineral lubricating oil .in a major :amount.

.Further investigation of the subject grease composi- 'tions disclosedthe factthat'the combination of monoesters and alkaline earth metal sulfonates, while providing in highly unexpected increase in the mechanical stabilityof the grease, atthe'same time caused the grease 'torbecomesomewhat'more sensitive to oxidation. While thisproperty isof h'o-importance when thegreaseis utilized in applications where attacked by oxygen is-of amin'ororder, itwould -behighly desirable to overcome 'this property if it is p'ossibletodo so. Thefurther prepara'tio'nbf polyvalent 'rnet-al salts of'dithiocarbamicacid has been found to notonly restore the original stability 0f the grease butaetually can cause anunexpected-increase-in the oxidation-resistance thereof. Typical membe'rsof'this class 'of additivesc'omprise the zinc, aluminum,'1ead, iron, icalcium, barium, and-sodium salts of dialkyldithi-ocarbamatessuch as the zinc salt of 'dibutyl-j "dithiocarbamate, the calcium :salt of diethyldithiq carbamate, the barium salt of dimethyldithiocarbamat thelead salt --'of "dimetliyldithiocarbamate, the zinc sa of:dihexyldithiocarbamate, -the bariurn salt of diamyld thiocarba'm'ate, and the corresponding salts -"of-dioct di'propyl, propyh butyl and-ethylphenyl dithi'ocarbamat These rriaterials shouldljbe uu'liz'ed in 1 an amount betwe abou't .01 'a'nd -ab'outI l.-5'% by weight oi -the total' gr'e composition. 'AEEXmplelIfgiVen helo'wish-ows, the use (if the -dibutyldithiocarbamate .n'ot only irestored "the oxidati stability of the grease composition after it had been somewhat degraded in this respect by the addition of the combined calcium petroleum sulfonate and polyethylene glycol monooleate, but actually improved the composition in this property.

1 33.3% concentrate.

Still further improvements may be made by the addition of other types of ingredients such as aromatic amines including the phenyl-alpha-naphthylamine and other naphthylamines as well as guanadine derivatives and the like.

The invention claimed is:

1. A grease composition comprising a mineral lubricating oil thickened to a grease consistency with an alkali metal soap of a hydroxy fatty acid having from 12 to 24 carbon atoms per molecule and between about 0.25% and about 5% by Weight each of an oil-soluble alkaline earth metal basic sulfonate and a mono(unsaturated fatty acid) ester of a polyalkylene glycol said glycol having 5-20 alkylene radicals, said fatty acid having from about 12 to about 24 carbon atoms per molecule.

2. A grease according to claim 1, containing in addition from about 0.01% to about 5% by weight of an oil soluble zinc salt of a dialkyl dithiocarbamate.

3. A grease according to claim 1, containing in addition from about 0.01% to about 5% by weight of an oil-soluble metal salt of a dialkyl dithiocarbamic acid.

4. A grease composition comprising a major amount of a mineral lubricating oil thickened to a grease consistency with a minor amount of lithium soap of 12- hydroxystearic acid, and from about 0.25% to about 5% by weight each of basic oil-soluble calcium petroleum sulfonates and a polyethylene glycol mono-oleate said glycol having 5-20 ethylene radicals.

5. A grease composition according to claim 4 containing in addition between about 0.1% and about 5% by weight of zinc dibutyl dithiocarbamate.

6. A grease composition comprising a major amount of a mineral lubricating oil, a minor proportion sufiicient to thicken said oil to grease consistency of an alkali metal soap, and between about 0.25% and about 5% by weight each of an oil-soluble alkaline earth metal basic sulfonate and a mono fatty acid ester of a polyalkylene glycol said glycol having 5-20 alkylene radicals, said fatty acid having from about 12 to about 24 carbon atoms per molecule.

7. A grease composition comprising a major amount of a mineral lubricating oil, a minor proportion sufficient to thicken said oil to a grease consistency of an alkali metal soap and between about 0.25% and about 5% by weight each of an oil-soluble alkaline earth metal petroleum sulfonate and a polyalkylene glycol monoester having the general formula wherein n is an integer between 5 and 20, R is an alkylene radical having 2-6 carbon atoms and R is an aliphatic hydrocarbon radical having 8-24 carbon atoms.

8. A grease composition comprising a major amount of a mineral lubricating oil, a minor proportion suflicient to thicken said oil to a grease consistency of an alkali metal soap, and between about 0.25% and about 5% by weight each of an oil-soluble alkaline earth metal hydrocarbyl sulfonate and a polyalkylene glycol monoestcr having the general formula wherein n is an integer between 5 and 20, R is an alkylene radical having 2-6 carbon atoms and R is an aliphatic hydrocarbon radical having 8-24 carbon atoms.

9. A grease composition comprising a major proportion of a lubricating oil, a minor proportion, suflicient to thicken said oil to a grease consistency, of a soap of the group consisting of alkali metal fatty acid soaps, alkaline earth metal fatty acid soaps, alkali metal hydroxy fatty acid soaps and alkaline earth metal hydroxy fatty acid soaps, and between about 0.25% and about 5% by weight each of an alkaline earth metal hydrocarbyl sulfonate and a polyalkylene glycol monoester having the general formula H H 0 R (0 Bl" C 1 wherein n is an integer between 5 and 20, R is an alkylene radical having 2-6 carbon atoms and R is an aliphatic hydrocarbon radical having 8-24 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,243 Bondi June 20, 1950 2,352,811 Swenson July 4, 1944 2,450,633 Clayton Oct. 5, 1948

Claims (1)

1. A GREASE COMPOSITION COMPRISING A MINERAL LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH AN ALKALI METAL SOAP OF A HYDROXY FATTY ACID HAVING FROM 12 TO 24 CARBON ATOMS PER MOLECULE AND BETWEEN ABOUT 0.25% AND ABOUT 5% BY WEIGHT EACH OF AN OIL-SOLUBLE ALKALINE EARTH METAL BASIC SULFONATE AND A MONO(UNSATURATED FATTY ACID) ESTER OF A POLYALKYLENE GLYCOL SAID GLYCOL HAVING 5-20 ALKYLENE RADICALS, SAID FATTY ACID HAVING FROM ABOUT 12 TO ABOUT 24 CARBON ATOMS PER MOLECULE.