US2566793A - Grease compositions - Google Patents

Description

Patented Sept. 4, 1951 UNITED STATES PATENT OFFICE GREASE COMPOSITIONS Raymond Glyn Davies, Teddington, and Reginald William Noad, New Malden, England, assignors to Shell Development Company, San Francisco, Califi, a corporation of Delaware No Drawing. Application July 5, 1949, Serial No. 103,164." In Great Britain October 18, 1948 13 Claims. (Cl. 252-41) This invention relates to improved lubricating rease compositions. More particularly this invention pertains to novel grease compositions which resist oxidation, bleeding, age-hardening and which possess outstanding mechanical stability, storage stability as well as good stability when subjected to static heating and thermal reversibility.

It is well established that oxidation has a profound deteriorating effect upon lubricants and lubricating compositions. The rapidity of this deterioration varies with diffeernt lubricants and depends in part upon the source of the base oil, the presence of additives therein as well as on the conditions to which the lubricant is exposed. ()nce oxidation has started in a lubricant the deterioration caused thereby appears to be an autocatalytic phenomenon which results in further deterioration of the lubricant.

Bleeding is another phenomenon which is frequently encountered in grease compositions. Bleeding is primarily due to the fact that the soaps present in grease compositions have a marked tendency to synergize, thereby causing a separation of the soap from the oil or synthetic base lubricant in which it is dispersed.

Generally, to inhibit bleeding and improve the texture of greases special precautionary measures are taken, such as employing slow or rapid means of cooling, or extensively working the grease in special homogenizers, e. g. the Cornell homogenizer and the like. Such procedures are usually time consuming and add greatly to the cost of the grease. Other ways of producing stable, non-bleeding greases have been attempted by either reducing the soap content generally to less than about by weight or by increasing the soap content to a maximum. These methods of stabilizing greases again-st bleeding have also proved to be unsatisfactory because in the case of reducing the soap content to less than 5% such greases become limited in their use due to the low soap content, while increasing the soap content to a maximum makes the grease too costly and such products generally possess an undesired consistency.

The cause or causes of age-hardening of greases at present is not understood. It is be lieved to be caused by the soap fibers which in storage tend to form cross layers the to the presence of active group associated with the soap micelles, and thereby increase the consistency of the grease. Such hardening is extremely undesirable for it introduces numerous lubricating difiiculties such as in pumping equipment and thelike.

Another deficiency generally encountered in greases is their lack of resistance to shear as well as other types of mechanical forces which are generally exerted upon greases under various working conditions.

2 Thus in the lubrication of ball and roller bearing greases are generally subjected to high shearing stresses which gradually break down their grease structure to aliquid or semi-liquid state. Once this has occurred they are incapable of adhering to the lubricating surfaces and bearingfailure results. It is essential of good greases therefore to resist shearing stresses, particularly over wide temperature ranges.

It is an object of this invention to produce grease compositions having outstanding mechanical stability, good stability when subjected to static heating and good-storage stability. It is another object of this invention to produce greases having good thermal reversibility and which are capable of resisting shearing stresses over wide temperature ranges. Still another object of this invention is to produce non-b1eed ing greases. Still another object of this invention is to produce novel greasesoi this invention by conventional grease-making techniques. Furthermore, it is an object of this invention to produce an all-purpose industrial grease of outstanding lubricating quality.

The above and other objects of this invention may be attained by admixing or blending with a suitable base oil under conventional grease forming conditions, a mixture of two different alkali metal soaps the cationic or s aponifiable portions of said soaps being dissimilar but each being of a specific type. Essentially, grease compositions of thisinvention are dependent on two features which are: (1) one of the soaps must be a lithium soap of hydroxy fatty acids and/or their glycerides and the other soap can be a non-lithium alkali metal soap of fatty acids or its glycerides, such as sodium or potassium soaps. Additionally the ratio of the two soaps is critical and should be within the weight ratio limits of lithium soap to the non-lithium alkali metal soap of from :10 to :5 and (2 the hydroxy content of the soap mixture should be between the limits of 3.2

and 4.0% by weight and preferably between 3:3

' and 3.9% by weight.

permanganate is used, aqueous sulfurous acid is added to dissolve the precipitated manganese dioxide. t o from the precipitate by treatment with a suitable solvent such as a low boiling naphtha. The .unk

dissolved hydroxy acids can'be removed with the aid of ether and recoveredtherefrom and purified by repeated recrystalliz ation with alcohol. hydroxy acids remaining in the filtrate can be recovered by neutralizing it, evaporating it down The hydroxy acids can be recovered to abouthalf its volume and acidifying it. The hydroxy acids are then recovered using ether and alcohol in the manner described. Other methods of producing hydroxy fatty acids may be used such as digesting bromo derivatives of unsaturated fatty acids with silver hydroxide or by droxy palmitic acid, linusic acid, sativic acid,

lanoceric acid, dihydroxy gadoleic, dihydroxy benhenic acid, quince oil acid and the like. The preferred hydroxy fatty acids are those in which the hydroxy group is at least 12 carbon atoms removed from the carboxyl group. Also, it is preferable to use hydroxy fatty acids having at least carbon atoms and up to about 32 carbon atoms and preferably those having between 14 and 32 carbon atoms in the molecule. Instead of using the free fatty acids containing a hydroxy radical their glycerides can be used such as castor oil or hydrogenated castor oil or mixtures of free hydroxy fatty acids and their glycerides can be used.

The other soap of this invention may be a nonlithium alkali metal soap of substituted and unsubstituted saturated or unsaturated fatty acids (1. e., acyclic monocarboxylic acids) and/ or their glycerides having at least 10 carbon atoms and preferably from 12 to 24 carbon atoms in the molecule. The preferred fatty acids are capric, lauric, myristic, palmitic, stearic, arachidic, behenic, lignoceric; myristoleic, palmitoleic, oleic, ricinoleic, erucic acids and their mixtures and/ or their glycerides, such as lard, beef, rape seed, palm, menhaden, herring oils, etc.

Lublicating greases of this invention, therefore, comprise a grease forming lubricant base and a mixture of lithium and other dissimilar alkali metal soaps such as sodium soaps of particular fatty materials as defined above wherein the ratio of the lithium soaps to the other alkali metal soaps in said mixtures lies between the limits 95:5 and 90:10; wherein the lithium soaps comprise or consist of lithium soaps of one or more hydroxy or polyhydroxy fatty acids and/or their glycerides; and wherein the hydrcxyl content of the soap mixture falls between the limits of 3.2 and 4.0% and preferably between 3.3 and 3.9% by weight. It has been found that by controlling the soap ratioand the hydroxy content, greases can be produced which have optimum mechanical stability. Moreover, the general physical nature of the resulting grease compositions are such that during'the cooling stage of the preparation of these compositions well-defined greasy characteristics appear and make the subsequent plasticising of the product a simple task leading to a uniform stable grease structure.

In order to secure a total hydroxyl content of the soap mixture within the limits with which one feature of this invention is concerned, the lithium soap content may consist of a suitable blend of a lithium soafp' of one or more hydroxy or polyhydroxy stearic acids, and some other lithium soap free from substituent 7 hydroxy groups, as for instance, the lithium soap of stearic, palmitic, oleic, lauric' or myristic acid.

Havin regard to the weight ratio of sodium what blend, if any, of lithium soap of hydroxi or polyhydroxy stearic'acid and lithium, soap of other fatty acid is a requisite for any given percentage hydroxyl content in the proposed soap mixture. Insofar as it may be desired to use starting materials for the preparation of the soap mixture forming an essential feature of the lubri- -eating greases of the present invention, hydroxy or polyhydroxy stearic acids adulterated by undefined amounts of non-hydroxylated fatty acids, the hydroxyl content of the soap or soap mixture can be readily determined by conventional analytical technique.- Thus, a Weighed amount of the sample under test is heated with a weighed amount of a mixture of three parts by weight of dry pyridine and one .part by weight of acetic anhydride, the excess acetic anhydride hydrolyzed, cooled," and the acetic acid produced determined by titration with alcoholic potash, a blank determination being carried out simultaneously identical with the actual determination except that the sample is omitted. The reduction in the acetic acid content due to the presence of the sample is a measure of the hydroxyl content of the sample, due allowance being made for the acidity of the sample itself.

The soap content of grease composition of this invention may vary over wide limits and may be eral oil of wide viscosity range varying from about 150 Saybolt Universal viscosity at 100 F. to about 2000 Saybolt Universal viscosity at 100? F. The viscosity index of the oil can vary'from below zero to about and have an average molecular weight ranging from about 250 to about 600. It may be highly refined and solvent.

treated by any known means. A preferred min eral oil is one which has a viscosity between about, 300 to 700 SUS at F., a viscosity index of from about 40 to '70 and an average molecular weight of between about 350 and 550.

Instead of using straight mineral oil as the base, synthetic oils and lubricants may be substituted in part or wholly for the mineral oil. Among the synthetic lubricants which can be used are: polymerized olefins; copolymers of alkylene glycol and alkylene oxides; organic esters, e. g. 2 ethyl hexyl sebacate; dioctyl phthalate, trioctyl phosphate, polymeric tetrahydrofuran; polyalkyl silicon polymers, e. g. di-. methyl silicon-polymer, etc. Under'some conditions of lubrication minor amounts of a fixed oil such as castor oil, lard oil and the like, may be admixed with the hydrocarbon oil, and/ or syn-1 thetic oil used in making a grease composition of this invention. I

Grease compositions of this invention may be prepared from preformed soapsor the soaps may be made in situ in a grease-forming base as described above. The soap-formin'g ingredients of pre-formed soaps and base oil are heated above the melting point of the rease (as, for example, to 425 F.), and thereafter cooled from a liquid to a semi-solid or solid state. to carry out the heating and cooling down to aroundabout .275? F. or 200? F. under agitation;

It is preferably The'grease is then dumped into pans or on a suitable conveyor and allowed to cool in thin layers to room temperature. The grease can be improved in appearance and texture by milling by any suitable means.

The following examples illustrate grease compositions falling within the'scope of the present invention, percentages being by Weight unless otherwise stated.

Example I -A grease was prepared from an edeleanized mineral oil base stock of specific gravity Gil/60 F. of 0.906, a Saybolt Universal seconds at 100 F. of 194496 and the following mixture of soap; lithium hydroxy stearate, prepared from hydrogenated castor oil fatty acidby neutralization mixture of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate. In this soap mixture the sodium soap: lithium soap ra tio was 8:92 and the total hydroxyl content of the soap was 3.6 per cent. Manufacture of the grease followed the technique prescribed in th above Example I and in the finished grease composition the soap content was approximately 8 per cent.

The above grease compositions of this inven- 10 tion were compared with a conventional straight lithium hydroxy stearate grease by subjecting said grease to the Shell roll mechanical stability test and the bleeding test as described in specification D. T. D. 577 appendix III, and the results as tabulated below clearly indicate the marked improvement of composition of this invention over a conventional lithium grease.

8% Li Hydroxy Mechanlcal Stability Example I Example 11 Example III Stearate Grease Rolling test (a) Penetration at 77 F. (approximately) after rolling. at room temperature for:

Initial Worked Initial Worked Initial Worked Initial Worked (b) Penetration at 77 F. (apiroximately) after rolling at 100 for indlicated period and allowedto recoo: I 5 hrs 271 326 292 324 274 297 273 323 10 hrs"; 282 332 285 325 275 298 286 338 l5.hrs 297 341 270 325 264 299 291 350 Bleeding 50 hrs. at 100 0., per cent weight l. 7 2. 4 2. 4 5. 0

with lithium hydroxide, lithium stearate and sodium hydroxy stearate.

This mixture of soaps was so chosen that the sodium soap: lithium soap ratio was 6:94 and the hydroxyl content of the soap mixtur was 3.6 per cent.

The mixture of soaps amounting. in ,all to 8 Per cent of the total composition was. compounded with the oil base stock. andth mixture heated; to about 428 F, with agitation until completely homogenized. After cooling the grease to. about 275 it was then poured in thin layers into trays where the cooling operationwas completed overnight, the composition being finally milled in'a triple roll mill to procure the finished grease. During the coolingoperation following homogenization the composition assumed well defined greasycharacteristics at about295 F.

' Example II Example III I grease was prepared from the lubricating base stock specified in Example 1 above and a In the case Of the foregoing examples, the product obtained was characterized by uniform consistency, high mechanical stability, very good stability under conditions of static heating and under storage, and in these respects the products were superior to the corresponding greases having the same total soap content of a soap mixture consisting of the three specified soaps, but wherein the sodium lithium soap ratio lies outside the aforementioned limits, or where the hydroxyl content of the soap mixture falls outsid the above-described limits of hydroxyl content. It is, however, to be noted that variation of the hydroxyl content of the soap mixture above the upper limit already specified does not yield products so markedly different in consistency and stability as is the cas when hydroxyl content is varied below the lower limit already indicated. In the case of variations of the sodium soap c0 lithium soap ratio outside the limits already specified, it is found that such variations have an adverse effect on the mechanical stability at room temperatures, and in the absence of a sodium soap in the grease, the bleeding characteristics Of the resultin lubricating greas compositions compare unfavorably with the corresponding characteristics of the compositions of the present invention. I

The lubricating greases of this invention may include additives frequently incorporated in grease manufacture as currently practiced, for instance, oxidation inhibitors may be incorporated in minor amounts such as: N -butyl para phenylene diamine. Also effective as oxidation inhibitors are alpha or :beta naphthylamine,

awe/res phenyl-alpha or beta naphthylamine, a1pha-a1-g pha, beta-beta or alpha-beta dinaphthylamine, diphenylamine, tetramethyl diamino diphenyl methane, phenylene diamine, petroleum alkyl phenols, and ZA-ditertiary butyl 6 methyl phenol.

. Corrosion inhibitors which are particularly ap- 'plicable with compositiOns of this invention are N-primary amines containing at least 6 and more than 18 carbon atoms in the molecule such as hexylamine, octylamine, decylamine, dodecylamine, octadecylamine, heterocyclic nitrogen containing organic compounds such as alkyl substituted oxazolines and oxazoline salts of fatty acids.

Extreme pressure agents can be added to such grease and the preferred comprise esters of phosphorus acids such as triaryl, alkylhydroxy, alkyl, or aralykyl phosphates, thiophosphates or phosphites, etc., neutral aromatic sulfur compounds such as diaryl sulfides and polysulfides, e. g. diphenyl sulfide, dicresol sulfide, dibenzyl sulfide, methyl butyl diphenol sulfide, etc., diphenyl selenide and diselenide; dicresol selenide and polyselenide, etc.: sulfurized fatty oils or esters'of fatty acids and monohydric alcohols, e. g. sperm oil, jojoba oil, etc., in which the sulfur is tightly bound: sulfurized long-chain olefins obtained by dehydrogenation or cracking of'waxz' sulfurized phosphorized fatty oils, acids, esters and ketones,

phosphorus acid esters having sulfurized organic radicals, such as esters of phosphoric or phosphorus acids with hydroxy fatty acids; chlorinated hydrocarbons such as chlorinated paraffins, aromatic hydrocarbons, terpenes, mineral lubricating oils, etc.: or chlorinated ester of fatty acids containing the chlorine in positions other than alpha position.

Additional ingredients which can be added are anti-wear agents such as oil-soluble urea or thio-urea derivatives, e. g. urethanes, allophanates, carbazides, carbazones, etc.; or rubber, polyisobutylene, polyvinyl esters, etc.; VI improvers such as polyisobutylene having a molecular, weight above about 800, volatilized paraffin wax, unsaturated polymerized esters of fatty acids and monohydric alcohols, etc.: oiliness agents such as stearic and oleic acids and pour point depressors such as chlorinated naphthaline to further lower the pour point of the lubricant.

The amount of the above additives can be added to grease compositions of this invention in a round about 0.01% to less than 10% by weight, and preferably 0.1 to 5.0% by weight.

.LGreases of this invention are applicable for general automotive uses, and are excellent aircraft greases, industrial greases and the like. :We claim as our invention:

1. A lubricating grease comprising a major proportion of a mineral oil and minor amounts sufficient to form a grease of a mixture of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate, the ratio of the lithium soaps to be sodium soap being 94:6 and the hydroxyl content of the entire soap mixture being 3.6 per cent.

2. A lubricating grease comprising a major proportion of a mineral oil and minor amounts sufficient to form a grease of a mixture of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate, the ratio of the lithium soaps to the sodium soap varying from 90:10 to 95:5, respectively, and the hydroxyl content of the entire soap mixture varyingfrom 3.2 to 4.0 per cent.

3.. A lubricating grease comprising a major proportion of a lubricating oil base: and minor" amounts sufficient to form a grease of a mixture of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate, the ratio of the lithium soaps to the sodium soap varyingfrom 90 1 0.'to 95:5, respectively, and the hydroxyl content o'f the entire soap. mixture varying from 3.2to'4 0. per cent. V

4. A lubricating grease comprising a-majorpro: portion of a, lubricating oil base and minor amounts sufiicient to form a grease of a mixture of lithium soap of a hydroxy fatty acid-of high molecular weight and sodium soap of fatty acids; of high molecular weight, the ratio of the lithium; soap to the sodium soap varying from.90: 10 to; 95:5 andthe hydroxyl content of the entiresoap; mixture varying from 3.23to 4.0 per cent.

5. A lubricating grease comprising a major proportion of a lubricating oil base and minor amounts sufiicient to form a grease of a mixture of lithium soap of a hydroxy fatty acid of high molecular Weight and potassium soap of fatty acids of high molecular weight, the ratio of the lithium soap to the potassium soap varying from 90:10 to 95:5, and the hydroxyl content of the entire soap mixture varying from 3.2 to 4.0 per cent.

6. A lubricating grease comprising a major proportion of a lubricating oil base and minor amounts sufficient to form a grease of a mixture of lithium soap of a hydroxy fatty acid of high molecular weight and non-lithium alkali metal soap of fatty acids of high molecular weight, the ratio of the lithium soap to the non-lithium alkali metal soap varying from 90:10 to 95:5 and the hydroxyl content of the entire soap mixture varying from 3.2 to 4.0 per cent.

7. A lubricating grease comprising a major proportion of a lubricating oil base and minor amounts sufiicient to form a grease of a mixture of lithium hydroxy stearate, lithium stearateand sodium stearate, the ratio of the lithium'soaps to the sodium soap varying from :10 to :5, respectively, and. the hydroxyl content of the entire soap mixture varying from 3.2 to 4.0 peri cent. l,

8. A lubricating grease comprising a major proportion of a lubricating oil base and minor; amounts sufiicienttoform a grease of a-mixture. of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate, the ratio of the lithium soaps to the sodium soap varying from 90:10.120' 95:5, respectively, and the hydroxyl content of the entire soap mixture varying from 3.2 to- 4.0 per cent and an antioxidant amount of phenyl-; beta-naphthylamine. 1 z- 9. A lubricating grease comprisinga major proportion of a lubricating oil base and minor amounts sufi'icient to form a grease of a mixture of lithium hydroxy stearate, lithium stearate and sodium stearate, the ratio of the lithium soaps to the sodium soap varying from 90:10 to 95.'5;

respectively, and the hydroxyl content of the entire soap mixture varying from 3.2 to 4.0"per cent and an antioxidant amount of phenyl-beta naphthylamine.

10. A lubricating grease comprising a major proportion of a lubricating oil base and minor amounts sufficient to form a grease of a mixture of lithium soap of a hydroxy fatty acid of high molecular weight and non-lithium alkali "metal soap of acyclic monocarboxylic acids of high molecular weight, the ratio of the lithium soap to the non-lithium alkali metal soap varyingv from 90:10 to 95:5 and the hydroxyl content'of the entire soap mixture varying from 3.2 to 4.0 per cent and an antioxidant amount of phenylbeta-naphthylamine.

11. A lubricating grease comprising a major proportion of a lubricating oil base and minor amounts sufiicient to form a grease of a mixture of lithium soap of a hydroxy fatty acid of high molecular weight and non-lithium alkali metal soap of acyclic monocarboxylic acids of high molecular weight the ratio of the lithium soap to the non-lithium alkali metal soap varying from 90:10 to 95:5 and the hydroxyl content of the entire soap mixture varying from 3.2 to 4.0 per cent and an antioxidant amount of an organic amine.

12. A lubricating grease comprising a major proportion of a mineral oil and minor amounts sufiiclent to form a grease of a mixture of lithium hydroxy stearate, lithium stearate and sodium hydroxy stearate, the ratio of the lithium soaps to the sodium soap varying from 90:10 to 95:5, respectively, and the hydroxyl content of the entire soap mixture being 3.6% by weight.

13. A lubricating grease comprising a major REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,397,956 Fraser Apr. 9, 1946 2,403,104 Lien July 2, 1946 2,450,219 Ashburn Sept. 28, 1948 2,450,220 Ashburn Sept. 28, 1948 2,450,255 Puryear Sept. 28, 1948 2,475,589 Bondi July 12, 1949

Claims (1)

1. A LUBRICATING GREASE COMPRISING A MAJOR PROPORTION OF A MINERAL OIL AND MINOR AMOUTS SUFFICIENT TO FORM A GREASE OF A MIXTURE OF LITHIUM HYDROXY STEARATE, LITHIUM STEARATE AND SODIUM HYROXY STEARATE, THE RATIO OF THE LITHIUM SOAPS TO BE SODIUM SOAP BEING 94:6 AND THE HYDROXYL CONTENT OF THE ENTIRE SOAP MIXTURE BEING 3.6 PER CENT.