US3000821A - Grease composition containing lithium salt of an ester of an acid phosphate - Google Patents

Description

No Drawing. Filed June 24, 1959, Ser. No. 822,436 6 Claims. (Cl. 252-325) This invention relates to lubricating oil compositions containing metal salts or organic substituted phosphoric acid. Particularly, the invention relates to solid grease compositions formed by thickening lubricating oils with alkali metal salts of esters of phosphoric acid.

This application is a continuation-in-part of our prior application, Serial No. 644,710, filed March 8, 1957 and now abandoned.

The phosphorus containing salts of the invention are prepared from alkali metals such as lithium and sodium. These salts impart fire retardency to the lubricant because of their high phosphorus content. In addition, they can form high dropping point greases, even in the case of lithium. Thus, while lithium salts and soaps have found widespread use as grease thickeners because of their excellent water insolubility, their application has been somewhat limited because of inability to form suitable high dropping point greases. This disadvantage is overcome by the present invention. On the other hand, salts of the alkaline earth metals, e.g. calcium, do not have the thickening etfect of the corresponding alkali metal salts and form lower dropping point greases.

The thickeners of the invention are metal salts of aliphatic hydrocarbon esters of acid phosphate having the general formula OX RO-i wherein R is a hydrocarbon radical such as an alkyl or alkenyl radical, and contains about 2 to 6, preferably 3 to 5, carbon atoms; Y is an alkali metal; and X is R, hydrogen or an alkali metal. The total number of carbon atoms in the compound will be about 2 to 10, preferably 3 to 8. Examples of such salts include dilithiurn isopropy'lphosphate, dilithium n-amyl phosphate, lithium npropyl amylphosphate, sodium amyl acid phosphate, sodium diethylenephosphate, sodium hydrogen ethylenephosphate, sodium-lithium isopropylphosphate, etc.

Because of their general oil-insolubility and the difficulty of dispersing into oil, the metal salts of the acid phosphate esters are best prepared in situ in the lubricating oil. This is done by reacting metal base with an acid phosphate ester directly in the lubricating oil. The commercially available acid phosphate-esters are generally equilibrium mixtures of monoand di-esters which are formed by the reaction of one mole of phosphoric anhydride with 3 to moles of an alcohol. A typical such reaction using 6 moles of alcohol per mole of P 0 is shown by the following equations:

The weight percentages of the mono-ester and the diabout 20 .to 90 wt. percent of mono-ester to about '10 to added 'to form the final grease product. grease may also be homogenized by passing it through a Patented Sept. 19, 1961 ice the monoor di-ester may be used alone as well as mixtures in'any proportions of the monoand di-ester.

The metal base used to form the salt may be a hydroxide, oxide, or a carbonate of an alkali metal such as lithium, potassium and sodium. The metal base may be added inthe form of an aqueous solution, if desired, to the mixture of oil and acid phosphate ester; however, the use of water is not necessary to stabilize the dispersion of the thickening agent in the oil.

In general, the grease composition of the invention will have an A.S.T.M. penetration of 100 to 350 mm./ 10, when worked 60 strokes at 77 F. and a dropping point of about 400 to 500+ F. These greases will comprise a major proportion such as to 90 wt. percent, preferably to wt. percent of a lubricating oil, and a grease thickening amount, such as about 10 to 30 wt. percent, preferably 15 to 25 wt. percent, of the metal salt of the acid phosphate ester. The lubricating oil may be either a mineral oil or a synthetic oil.

Synthetic lubricating oils which may be used include esters of monobasic acids (e.g. C Oxo alcohol ester of C Oxo acid); esters of dibasic acids (e.g. di-2-ethyl hexyl sebacate); esters of glycols (e.g. C Oxo acid diester of tetraethylene glycol); complex esters (e.g. the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2- ethyl hexanoic acid); esters of phosphoric acid (e.g., the ester formed by contacting three molesof the mono methyl ether of ethylene glycol with one mole of phosphorus o'xychloride, etc.); halocarbon oils e.g., the polymer of chlorotrifluoroethylene containing twelve recurring units of chlorotrifluoroethylene); alkyl silicates -e.g. methyl polysiloxanes, ethyl polysiloxanes, methyloils known to the art.

The grease will generally be prepared as follows: A portion or all of the lubricating oil is mixed with the acid phosphate ester and the mixture is heated to about to 250 F. At this point, the alkali metal base is added. The mixture is then further heated to about 260 to 300 F. and maintained at this temperature for about /2 to 3 hours to form the thickener and to dehydrate the grease. Additional lubricating oil and additives may be If desired, the

Manton-Gaulin homogenizer, or a similar type of homogenizer.

The invention "will be further understood by the following illustrations which include preferred embodiments of the invention.

EXAMPLE I parts by weight of the mono-n-propyl dihydrogen phosphate and 7 parts by weight of the di-n-propyl monohydrogen phosphate. The mixture of these esters and oil was then heated to a temperature of 250 F. The temperature was allowed to drop to 225 F. and then 6.4 parts by weight of lithium hydroxide in the form of an aqueous solution was added to the oil-phosphate ester mixture. The resulting mixture was then further heated to a temperature of about 300 F. and maintained at this temperature for about 1 hour. The grease was then cooled to room temperature.

EXAMPLES II TO IV 4 EXAMPLE v 18 parts by weight of isopropyl acid phosphate (same phosphate mixture as used in Example 11) was mixed with 73.8 parts by weight of a mineral lubricating oil having a viscosity at 100 F. of 300 S.U.S. and a V1. of 70. This mixture was heated to a temperature of about 250 F. and 6.4 parts by weight of lithium hydroxide in an aqueous solution was then added. The mixture was further heated to a temperature of about 300 -F. for about one hour. The base grease thus formed was cooled to about 200 F. and 1.8 parts by weight was then added of a surface active agent sold under the trade name of Victamine C. The mixture was cooled to room temperature and tested. Victamine C has the formula:

For comparison purposes, several greases similar to that of Example V were prepared but containing different Table I GREASES PREPARED FROM LITHIUM SALTS OF ALKYL ACID PHOSPHATES A.S.'I.M. Penetration at 77 F. Alkyl Radical Wt. Ratio of Micro Dropping A.S.T.M. Example of Acid mono-ester Pene- Point, F. Wheel Bear- Phosphate to di-ester tration Wogtllred 18%? mg Test Strokes Strhkes I n-propyl 3/7 134 425 340 decomposed isopropyl 2.8/7.2 54 500+ 180 210 no leakage. n-butyl 3/7 l 116 480 310 n-amyl 3/7 125 460 330 ethyl, lauryl- 100% diester 800 230 As seen by the preceding table, Examples I to IV resulted in high dropping point greases, while Grease A prepared from a higher molecular weight acid phosphate (total of 14 carbon atoms per molecule) formed a grease having a much lower dropping point.

Various other additives may also be added to the grease composition of the invention, such as oxidation inhibitors, dyes, metal deactivators, corrosion inhibitors, and surface active agents.

Certain surface active agents are particularly desirable in some cases in obtaining a fine: dispersion of the thickener in the grease, thereby making a more efficient use of the grease thickener. The preferred surface active agents which may be used have the general formula:

wherein R is an alkyl or substituted alkyl radical of 1 to 4 carbon atom-s and R and R" are alkyl or substituted alkyl radicals of 8 to 20 carbon atoms. Examples of such compounds include the stearyl amine salt of the stearyl amide of ethyl orthophosphoric acid, the lauryl amine salt of the lauryl amide of n-propyl orthophosphoric acid, the lauryl amine salt of the stearyl amide of ethyl orthophosphoric acid, etc. Surface active agents of the above type have been described in U.S. Patent 2,406,423.

The above-described type of surface active agent may be used in the compositions of the invention in amounts of 0.1 to 3.0 wt. percent, e.g. 0.2 to 2.0 wt. percent, based on the total weight of the grease composition, as illustrated by the following example:

surface active agents.

The effect of these surface active agents is illustrated in the following table:

Table II Surface Active Agent incorporated A.S.T. Example 1n the Grease 1 Penetration None 190 V 1.8 wt. percent Victamine C 159 1.8 wt. percent N-dodecyl-B-alanine... 1.8 wt. percent Lithium salt of laur- 236 alkyl phosphate 1.8 wt. percent Ethomeen 18/5 232 1.8 wt. percent Stearlc Acid 216 Mineral oil grease thickened with the lithium salt of isopropyl acid phosphate 1 The lithium salt of lauralkyl phosphate had the formula:

CnHz50-P O EXAMPLES VI to X The effect of varying the concentration of the thickener in the oil was also investigated in these examples which were prepared in a manner similar to the procedure of Example V.

Grease B.For comparison purposes, a calcium grease was prepared in a manner similar to Example V, except that calcium hydroxide was used in place of the lithium hydroxide.

The formulation of the above greases in weight percent and their characteristics are summarized in Table HI.

Table III Example Components VI VII VIII IX Grgaso Isopropyl acid phosphate (same as in Example II) percent 18.0 15.2 13. 9 9. 5 19. Lithium hydroxide. .d0 6. 4 5. 3 4. 4 3. 4 LimeCa(OH)z do 3.8 Victamine C 1 do 1. 8 3.0 2. 8 1.9 Mineral lubricating oil (300 S.U.S. vis. at 100 F., V.I. 0t 70) percent 73.8 77. 2 Mineral lubricating oil (150 S.U.S. viS. at 100 F., V.I. of 90) percent 76. 78. 9 85. 2 A.S.T.M. Penetration at 77 F. (worked 60 strokes)- 159 202 238 350 3 0 Dropping Point F 44 Boiling Water Test Pass Pass Pass 0l 1 C1zH2 NH-P=O a n ns Decomposed at 425 F.

As seen by the preceding table, a much larger quantity of thickener was required in the case of the calcium grease (Grease B) and even this resulted in a relatively soft grease. On the other hand, about half as much thickener was required to obtain the same Worked penetration in the corresponding lithium grease (Example IX).

What is claimed is:

1. A lubricating grease composition having an ASTM penetration of 100 to 350 mm./ when worked 60 strokes at 77 F. and having a dropping point of about 400 F. to 500+ F. comprising a major proportion of a lubricating oil and about 10 to 30 wt. percent of a lithium salt of an ester of an acid phosphate which contains a total of 2 to 10 carbon atoms having the formula O/O-X R.O-

wherein R is a C to C aliphatic hydrocarbon radical, Y is lithium, and X is selected from the group consisting of R, hydrogen and lithium.

2. A lubricating grease composition according to claim 1, wherein said ester of an acid phosphate is a mixture of monoand di-esters.

3. A lubricating grease composition according to claim 1, wherein said lubricating oil is a mineral oil.

4. A lubricating grease composition according to claim 1, wherein said composition also contains 0.1 to 3.0 wt. percent of a surface active agent of the formula:

(])11 RNHP=O ONHQR wherein R is an alkyl radical of 1 to 4 carbon atoms and R and R" are alkyl radicals of 8 to 20 carbon atoms.

5. A method of lubricating metal bearings Which comprises maintaining on said bearings a lubricating grease composition having an ASTM penetration of 100 to 350 mrn./l0 when Worked strokes at 77 F. and having a dropping point of about 400 F. to 500+ F. comprising a major proportion of a lubricating oil and about 10 to 30 wt. percent of an alkali metal salt of an ester of an acid phosphate which contains a total of 2 to 10 carbon atoms having the formula H/ R0-P wherein R is a C to C aliphatic hydrocarbon radical, Y is lithium, and X is selected from the group consisting of R, hydrogen and lithium.

6. A process of preparing a lubricating grease having an ASTM penetration of to 350 mm./ 10 when worked 60 strokes at 77 F. and a dropping point of about 400 F. to 500+ F. consisting essentially of a mineral lubricating oil and about 10 to 30 Wt. percent of lithium salt of an ester of an acid phosphate having the formula:

wherein R is a C to C aliphatic hydrocarbon radical, Y is lithium and X is selected from the group consisting of R, hydrogen, and lithium, wherein the total number of carbon atoms in the compound is about 2 to 10, said method comprising dispersing in at least a portion of said lubricating oil acid phosphate ester, heating the mixture to about 100 to 250 F., adding lithium hydroxide sufficient to form the salt and further heating at a temperature of 260 to 300 F. for a time sufficient to dehydrate the grease.

References Cited in the file of this patent UNITED STATES PATENTS 2,167,867 Benning Aug. 1, 1939 2,224,695 Prutton Dec. 10, 1940 2,228,659 Farrington et al. Jan. 14, 1941 2,274,302 Mulit Feb. 24, 1942 2,406,423 Woodstock Aug. 27, 1946

Claims (1)

1. A LUBRICATING GREASE COMPOSITION HAVING AN ASTM PENETRATION OF 100 TO 350 MM./10 WHEN WORKED 60 STROKES AT 77*F. AND HAVING A DROPPING POINT OF ABOUT 400*F. TO 500+*F. COMPRISING A MAJOR PROPORTION OF A LUBRICATING OIL AND ABOUT 10 TO 30 WT. PERCENT OF A LITHIUM SALT OF AN ESTER OF AN ACID PHOSPHATE WHICH CONTAINS A TOTAL OF 2 TO 10 CARBON ATOMS HAVING THE FORMULA