US2628949A - Stabilized lithium base grease - Google Patents

Description

Patented Feb. 17, 1953 STABILIZED LITHIUM BASE GREASE Richard. A. Butcosk, East Hempst'ead', N. Y., assignor to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing.v Application February 14, 1951, Serial No. 210,984

21 Claims. (01.252-325) This invention relates to lubricating grease compositions suitable for use over a'wide' range of operating temperatures. More specifically,

'-thepresent invention is concerned with-lithium base greases of excellent lubricating character and stable when used at temperatures varying from about 70 F. to about 250 F;

In recent years, a demand has been created for greases of outstanding lubricating character which retain their grease structure during use over a wide range of operating temperatures. Typical of such a demand is" that created by the aircraft industry; For efficient aircraft operation, greases should havelow temperature torque properties such that they will flow properly at temperatures as low as about 70 F. In addition, the greases should be of low vo1atility and retainv their grease structure at temperatures at least high as 250 F. Failure to retain grease structure results in high consumption of grease and frequent servicing. Other desirable features of such greases are: homogeneity and smooth, unctuous consistency; water resistant; resistant to oxidation; resistant to oil separation; and resistant to sheer or breakdown upon working or milling.

The demand for greases of the foregoing specification has not been satisfied to date, except by dation stability. One approach takento effect improvement of these lithium base greases involves a special film-cooling technique to obtain satisfactory grease structure. As will be evident to those skilled in the art, film-cooling is a slow and expensive procedure requiring special equipment. Another approach taken to effect such improvement involves the use of a lithium soap of lz-hydroxy stearic acid and. quick cooling. Still another approach involves the use of a very high soap content grease. Still another means adopt-f. ed toimprove grease structure. is the use of a mixed: soap, namely the use of a calcium soap in' acid; n-octadecyl phosphonic acid;

provide a grease effective over a wide temperature range, particularly from about '-70 F. to about 250 F; A further object is to provide 'a grease which retains its original character over a wide range of operating conditions. Another object is to provide a grease of desired character which can be manufactured by conventional grease procedures in conventional grease-making equipment. Other objects of the invention will be apparent from the following description.

It has now been discovered that lithium base greases containing vehicles comprising esters of polybasi'c organic acids "are greatly enhanced by the incorporation therein of small amounts of certain lithium phosphonates and/or lithium phosphinates, such that the foregoing objects are realized.

The lithium phosphonates contemplated herein are lithium salts of the phosphonic acids represented by general Formula I:

a-rio wherein R is an aliphatic group containing from about four to about 22 carbon atoms per molecule, a mono-cyclic aryl group, an alkylated mono-cyclic aryl group, a mono-cyclic n-aphthyl group or an alkylated mono-cyclic naphthyl group. a

Typical of such phosphonate soaps" are the monoand di-lithium salts, and mixtures of such monoand di-lithium salts, of the following acids: n-butyl phosphonic acid; iso-butyl phosphonic acid; amyl phosphonic acids; 2-ethyl-nhexyl phosphonic acid; tetradecyl phosphonic eicosanyl phosphonic acid; docosanyl phosphonic acid; phenyl phosphonic acid; cresyl phosphonic acid; dodecyl benzene phosphonic acid; cyclohexyl phosphonic acid, etc. Particularly effective of such soaps are the di-lithium salts of the. following acids: Z-ethyl-hexyl phosphonic acid; tetrad'ecyl phosphonic acid; n-octadecyl phosphonic acid; phenyl phosphonic acid; and dodecyl benzene phosphonic acid.

As. indicated above, it has also been discoveredthat the closely related lithium phosphinates admixture with the lithium soap. However, calciumt-lithium base greases are deficient in. me-

chanical stability and have lower melting points, I thus requiring their use. at lower operating, temperatures (e. g. below. 250 R).

are effective when incorporated in corresponding lithium base greases. The lithium phosphinates of thisv invention are lithium soaps of; the phosphinic acids represented by general Formula II: (Ii) t R1-P*R2 generally used in soap type greases.

. terials thereof. -oil acids, oleic acid, palmitic acid, myristie acid, l2-hydroxy stearic acid, hydrogenated fish oils such as Hydrogenated Fish ()il, Iodine No. 77

L phatic fatty acids.

wherein R1 and R2 can be the same or difierent and are selected from the groups represented by the symbol ,R in general Formula I above.

Representative of such soaps are the lithium salts, and mixtures thereof, of the following acids: dWn-butyl) phosphinic acid; diamyl) phosphinic acids; n-butyl, amyl phosphinic acid; di 2.-

ethyl hexyl) phosphinic acid; di{tetradecyl) phosphinic acid; methyl, n-octadecyl phosphinic acid; diphenyl) phosphinic acid; ditcyclohexyl) phosphinic acid, etc. Lithium di42-ethyl hexyl) phosphinate and lithium diphenyl) phosphinic acid are two salts which have proven particularly satisfactory.

The lithium salts of the phosphonic and phosphinic acids represented above by the general formulae can be prepared by any of the methods vknown in the art. An excellent review of methods of preparation of phosphonic and phosphinic acids and their corresponding metal salts, is pro- -vided by the recent text of G. M. Kosolapoff 'Organophosphorus Compounds; Wiley; York; 1950.

New

As shown above, the metal component of the phosphonate and/or phosphinate 'salt is lithium. It will be apparent that the lithium soap can be prepared by reacting lithium hydroxide, for example, with a phosphonic or phosphinic acid.

" It will be noted also that the metal used in the soap component of the grease and also in the 1 modifier, that is the phosphonate and/or phosphinate, is the same.

This is a decided advantage in preparing the grease, and avoids the difl'lculties normally encountered in balancing the proportions of mixed metals in a mixed base grease.

The lithium phosphonates and/or phosphinates are used in amounts of the order of from about 0.25 to about 5%, by weight of the grease. Generally, however, particularly advantageous behav ior is realized with from about 0.75 to about 2.5% of a lithium phosphonate; similarly, excellent results have been obtained with from about 0.5

p to about 1.5% of a lithium phosphinate.

The lithium fatty acid soaps constituting the major soap component of the greases of this invention are prepared with fats and fatty acids Such fatty materials contain from about eight to about 1' twenty-two carbon atoms per molecule. Representative of such materials are vegetable, animal and fish fatty oils, and hydrogenated fatty ma- Stearin, stearic acid, cottonseed and Hydrofol are typical. Preferred soaps, however, are lithium stearate and the lithium soap of 12-hydroxy stearic acid. Methods of preparation of lithium soaps are well known in I the art and discussion of the same is believed to be unnecessary.

It is also contemplated that the greases can contain relatively minor amounts of other soaps,

such as soaps of alkaline earth metals and ali- Typical of such soaps are calcium stearate, strontium stearate and barium stearate, calcium palmitate and the like.

The oils of the greases contemplated herein include synthetic vehicles comprising esters of aliphatic dibasic acids.

Suitable acids from which the esters are derived are: sebacic, glutaric, azelaic, succinic, malonic, phthalic, adipic, pimelic and suberic. Typical alcohols used in preparing the esters are: butyl, iso-butyl, hexyl, octyl,

4 2-ethyl hexyl, cyclohexyl, Z-ethyl butyl, 3-methyl butyl. Accordingly, esters of the type suitable herein include: diZ-ethyl hexyl) sebacate, dibutyl glutarate, dihexyl azelate, diamyl succinate, didecyl malonate, dibutyl phthalate, diQ-ethyl hexyl) adipate. It will be understood, that, in accordance with present day knowledge of such synthetic vehicles, simple or mixed esters are contemplated, as are esters containing one or more substituent groups such as halogen, phosphorus, sulfur, nitrogen.

Qther synthetic vehicles suitable herein are esters of poly alcohols and monocarboxylic acids. These synthetic ester vehicles can be represented by general Formula III:

wherein R9. and Rh are either the same or different aliphatic groups, such as amyl, isooctyl. 2-

ethyl hexyl, etc., and A represents an alkyl ether group such as ethylene oxide, propylene oxide,

' butylene oxide and the like.

Particularly advantageous of such esters of poly alcohols and monocarboxylic acids are those represented by general Formula IV below:

wherein Ra and Rb are described above in connection with general Formula III and a: is an integer from 1 to 8.

Representative of such esters is polyethylene glycol di{2-ethyl hexoate), also referred to as polyglycol, dioctoate. lowing Formula V:

This material has the fol- The latter material is marketed under the designation Ucon Brand Fluid 818, or Flexol Plasticizer 4G0.

The synthetic vehicles described above and contemplated for use in the reases of this invention generally have a viscosity from about 40 seconds to about 300 seconds, S. U. V., at F. Particularly desirable are those having a viscosity of the order of 60- 0 seconds, S. U. V., at 100 F.

The proportions of the lithium soap, lithium phosphonate and/or phosphinate, and synthetic ester lubricant are balanced in order to-provide greases of the desired character. The lithium soap or soaps-comprise from about 8 to about 20 per cent (.by' weight) of the finished grease, and preferably from about 10.0 to about 17.0 per cent. For: example, when: more .than 20% of a lithium soap is used in the .grease, the grease becomes hard and unsuited for use over a wide range of temperatures such as contemplated herein. The lithium phosphonate and/or phosphinate, as in- :dicated above is present in the finished grease in amounts ranging from 0.25 to about 5 per cent. The ester lubricant constitutes the balance of thegrease. Accordingly, the various constituents (on a dry basis) of the new greases can vary "within the following limits:

. General. Preferred Lithium's a s -c 8-20 10-17 Lithium 'Phosphon'at 0. 25 -5; 0. 75-2. 5 Lithium .Phosphinates. 0.25-5 0. 5-1;.5 ZEster Lubricant; Balance to'lGDgpercent It is to: be understood that the greases of this invention can'also contain other characterizing materials. For example, the greases can contain grease antioxidants such as amines, phenols, sul .fides, etc., and lubricity improving agents such as :free fat, free fatty acids, esters of alkyl and/or :aryl acids, sulfurized fats, lead soaps, etc. These [characterizing materials do not detract from the lubricating value of the greases contemplated Iherein nor do they :detract from the beneficial properties imparted %by the phosphonate and/or 'phosphinate .salt; rather, these characterizing materials serve to impart their customary properties to the grease.

By way of illustration, the greases of this in- 'vention can be formed in the following manner. .A phosphonic acid in water, or low molecular weight aliphatic alcohol, is neutralized'with suffi- -cient lithium hydroxide to phenolphthalein end point, thereby forming a lithium phosphonate. 'The phosphonate is mixed with lithium soap, such as lithium stearate, and with approximately one half of the diester vehicle to be used. The ingredients are mixed thoroughly and, while agitated constantly, are heated to a temperature of; about 380-390 F. for about 20-39 minutes. The bala-nce of the diester vehicle is then added and the resulting mixture is heated to 400-410" F. for -20 minutes. The product is withdrawn from the vessel in which .it is prepared and is poured into a-suitable mold, as a pan. The grease product is allowed to cool to room temperature, about -25 C., whereupon it solidifies. The

solidi-grease is then cut into cakes of the desired size, andmilled to desired consistency.

litis to be understood that the lithium phosphonate can be used as a pre-formed product, rather than formed in situ through reaction of lithium hydroxide and alkyl or aryl phosphonic acid. Similarly, the lithium soap or soaps used can be pro-formed as shown above or can be prepared in situ by reaction of a suitable lithium A note of caution should be given iinconnection with the preparation of the greases. Inasmuch as esters are susceptible to saponincation, they should not be used in the preparation of the grease until the formation of the lithium soap is complete, if a lithium soap is formed in situ. If they re formed in the diesters, they should be reacted at relatively low temperatures such as 80 to 200 F.

The greases of this invention are illustrated by the following examples tabulated in Table I below. Provided also in Table I are comparable examples in which lithium base greases other than those contemplated herein are illustrated. Each of the greases shown in Table I was prepared according to the procedure first described above.

In Table .I, the appearance and. performance characteristics of thegreases are recited. salient tests, other than visual inspection, are those which. demonstrate the resistance of the grease to disintegration by shearing stresses.

The Shell Roll Test used is that. which is described in The Institute Spokesman; March 1, 1943; pages 1, 4. and '5; thispublication is the official organ of the National Lubricating Grease Institute. This test reveals mechanical stability or sheer resistance of the grease.

Another significant test is the resistance of mination of worked penetration. However, for

the purpose of this investigation, thef'fgrease sample under test was subjected to 100,000 double strokes (using holes), instead of the so double strokes (using 4" holes) prescribed fora conventional work penetration test. Accordingly, the test conditions used in this investigation were more rigorous than those customarily used.

The oil separation test used is that whioh is normally used for lithium base greases, and measures oil separated from grease during a 24 hour period, with the grease sample maintained at 210 F. in a constant temperature oven. (U. S. Government Specification ANG25.)

In reviewing the results set forth in Table I, it will be noted that greases '1 through 4, 8 and 10, represent various combinations of lithium base greases without lithium phosphionate or phosphinate. All of these greases are deficient in structure and suffer from excessive oil separation.

Greases 5, 6, 7, 9,v and 11 through 15, represent novel compositions of the present invention. These greases form firm blocks or cakes upon cooling in the pans. Without the phosphonate or phosphinate salt, the center of the greases in the pans are semi-fluid and the sides are extremely firm. The lithium phosphonates and phosphinates cooperate in the greases to impart the property of "easy milling; they'also provide a mechanically stable buttery grease with low bleeding or oil separation in storage. The greases retain their properties at elevated temperatures, that is, they do not change materially in consistency at elevated temperatures.

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3. A lubricating grease comprising: a dibasic acid ester vehicle selected from the group consisting of esters of aliphatic dibasic acids and of alcohols having from about four to about ten carbon atoms per molecule and esters represented by general formula wherein Ra and Rb are aliphatic groups each having from about five to about eight carbon atoms and A represents an alkyl ether group, a lithium soap in quantity sufiicient to substantially thicken said vehicle, and a minor amount, sufiicient to increase the stability of said grease, of a lithium salt of a phosphonic acid represented by the general formula wherein R is selected from the group consisting of an aliphatic hydrocarbon group containing from about four to about twenty-two carbon atoms, a monocyclic aryl group, and an alkylsubstituted aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group.

4. The grease defined by claim 3 wherein the lithium phosphonate is present in an amount from about 0.75 per cent to about 2.5 per cent by weight, of the grease.

5. A lubricating grease comprising: a lithium soap content from about 8 to about 20 per cent by weight, about 0.25 to about per cent by weight of a lithium salt of a phosphonic acid represented by the general formula wherein R is selected from the group consisting of an aliphatic hydrocarbon group containing from about four to about twenty-two carbon atoms, a monocyclic aryl group, and an alkylsubstituted aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group, and the balance a dibasic acid ester vehicle selected from the group consisting of esters of all-- phatic dibasic acids and of alcohols having from about four to about ten carbon atoms per molecule and esters represented by general formula wherein Re. and Rb are aliphatic groups each having from about five to about eight carbon atoms and A represents an alkyl ether group.

6. A grease as defined by claim 5 wherein the ester is difZ-ethyl hexyl) sebacate.

' '7. A grease as defined by claim 5 wherein the phosphonate is lithium tetradecyl phosphonate. 8. A lubricating grease comprising: about 15 per cent by weight of lithium stearate, about 2 per cent by weight of lithium tetradecyl phosphonate and the balance difi2-ethyl hexyl) sebacate.

9. A lubricating grease comprising: a vehicle comprising an ester of a polyhydric alcohol and a monocarboxylic acid represented by the general wherein Ra and Rb are aliphatic groups each having from about five to about eight carbon atoms and a: is an integer from 1 to 8, a lithium soap in quantity sufiicient to substantially thicken said vehicle, and a minor amount, sufiicient to increase the stability of said grease, of a lithium salt of a phosphonic acid represented by the general formula wherein R is selected from the group consisting of an aliphatic hydrocarbon group containing from about four to about twenty-two carbon atoms, a monocyclic aryl group, and an alkylsubstituted aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group.

10. A grease as defined by claim 9 wherein the phosphonate is lithium tetradecyl phosphonate.

11. A grease as defined by claim 9 wherein the vehicle is polyethylene glycol dir2-ethyl-hexanoate) having a molecular weight of about 446.

12. A lubricating grease comprising: a dibasic acid ester vehicle selected from the group consisting of esters of aliphatic dibasic acids and of alcohols having from about four to about ten carbon atoms per molecule and esters represented by general formula wherein R1 and R2 are selected from the group consisting of an aliphatic hydrocarbon group containing from about four to about twenty-two carbon atoms, a monocyclic aryl group, an alkyl substituted monocyclic aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group.

13. The grease defined by claim 12 wherein the lithium phosphinate is present in an amount from about 0.5 per cent to about 1.5 per cent of the grease.

14. A lubricating grease comprising: a lithium soap content from about 8 to about 20 per cent by weight, about 0.25 to about 5 per cent by weight of a lithium salt of a phosphinic acid represented by the general formula wherein R1 and R2 are selected from the group ,consisting of an aliphatic hydrocarbon group containing from about four to about twenty-two carbon atoms, a monocyclic aryl group, an alkylsubstituted monocyclic aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group, and the balance of a dibasic acid ,ester vehicle selected from the group consisting of esters of aliphatic dibasic acids and of alcohols having from about four to about ten carbon atoms per molecule and esters represented by general formula sebacate.

18. A lubricating grease comprising: a vehicle comprising an ester of a polyhydric alcohol and a monocarboxylic acid represented by the general formal R.-( ,O-CHz-- (EH1) Rv-(fi-O-CHr- Ha wherein Ra and Rh are aliphatic groups each having from about five to about eight carbon atoms and a: is an integer from 1 to 8, a lithium soap in quantity suflicient to substantially thickwherein R1 and R2 are selected from the group consisting of an aliphatic hydrocarbon group containing from about four to about twentytwo carbon atoms, a monocyclic aryl group, an alkyl-substituted monocyclic aryl group, a monocyclic naphthene group and an alkyl-substituted naphthene group.

19. A grease as defined by claim 18 wherein the phosphinate is lithium difiZ-ethyl hexyl) phosphinate.

20. A grease as defined by claim 18 wherein the vehicle is polyethylene glycol diZ-ethylhexanoate) having a molecular weight of about 21. A lubricating grease comprising: about 15 per cent by weight of lithium stearate, about 2 per cent by Weight of lithium dHZ-ethyl hexyl) phosphinate and the balance polyethylene glycol di2-ethyl hexanoate) having a molecular weight of about 446.

RICHARD A. BUTCOSK.

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

UNITED STATES PATENTS Number Name Date 2,228,659 Farrington et a1. Jan. 14, 1941 2,311,306 Ritchey Feb. 16, 1943 2,497,133 Morway et al. Feb. 14, 1950 2,521,438 Zimmer et a1 Sept. 5, 1950

Claims (1)

1. IN A LITHIUM BASE GREASE COMPRISING A LUBRICATING LIQUID COMPRISING AN ESTER OF AN ORGANIC ACID AND AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ESTERS OF ALIPHATIC DIABASIC ACIDS AND OF ALCOHOLS HAVING FROM ABOUT FOUR TO ABOUT TEN CARBON ATOMS PER MOLECULE AND ESTERS REPRESENTED BY GENERAL FORMULA