US2755250A

US2755250A - Extreme pressure lubricant

Info

Publication number: US2755250A
Application number: US497404A
Authority: US
Inventors: Forrest J Watson; Paul H Williams
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1955-03-28
Filing date: 1955-03-28
Publication date: 1956-07-17
Anticipated expiration: 1973-07-17

Description

v H 1m .1

acidic extreme pressure additives.

United States Patent 2,755,250 EXTREME PRESSURE LUBRICANT Forrest J. Watson, Berkeley, and Paul H. Williams,

Orinda, Califi, as'signors to Shell Development Company, New York, N. Y., a corporation of Delaware No Drawing. Application March 28, 1955, Serial No. 497,404

8 Claims. 01. 252-56) This invention relates to lubricants particularly suitable for lubrication under extreme operating conditions, such as under extreme pressure, high speed and high temperature conditions.

It is well known that the high pressures occurring in certain types of gears and bearings may cause a film of lubricant to rupture with the consequent damage to the machinery. It has been shown that base lubricants, such as mineral oil, can be improved with regard to their protective effect, particularly on rubbing surfaces by the addition of certain substances, so that excessive wear, scuffing and seizure (which normally follow a break in the film of lubricant) can be prevented even under the most unfavorable pressure and speed conditions. Lubricants possessing this highly desirable property are called extreme pressure lubricants.

It is known that elements or certain compounds of elements of the type of chlorine, sulfur, phosphorus and lead are capable of imparting extreme pressure properties to lubricants which may be lubricating oils or greases. Among the compounds heretofore used are notably the lead soaps, phosphoric acid esters, free or loosely bound sulfur, and certain chlorinated organic compounds. Two principal objections have been encountered in the use of these and like materials. Firstly, they are highly reactive with the contacting metal surfaces causing etching, corrosion and discoloration of said surfaces; because of this, these additives alter the original chemical nature of the contacting surface and result in the rapid depletion from the lubricant of the extreme pressure additive. The second'objection or defect is of substantial importance with respect to the maintenance of a uniform extreme pressure lubricating composition: This defect resides in the tendency of many of the materials known to be useful for their extreme pressure imparting function to separate from the lubricating medium. In overcoming the latter disadvantage, it has been found that a limited amount of the material may be kept in colloidal suspension in a luene fluids as a solvent type base for certain water-soluble I In the latter system it was found possible to dissolve amounts in the order of about 2% of the acidic substances in the base lubricant without the aid of the surface active materials necessary when mineral oil is the base employed- However, even here there is a limiting concentration which will dissolve in the base fluid and consequently a limit placed upon the pressures which suchlubricants can stand before rupturing.

It is an object of the present invention to provide improved extreme pressure lubricating compositions. It is a further object of the present invention to provide ho-' mogeneous extreme pressure lubricating compositions exhibiting outstanding extreme pressure properties. Other objects will become apparent during the following discussion.

Now, in accordance with the present invention, it has been found that substantially greater proportions of extreme pressure agents can be used and much greater effectiveness of the extreme pressure limitations can be obtained by forming homogeneous solutions in water-miscible polyoxyalkylene fluids of the heat condensation products formed between water-soluble aliphatic hydroxy carboxylic acids and the lower aliphatic polyhydric alcohols.

The subject compositions referred to above have been found to possess the advantageous property of complete miscibility even in the absence of dispersing agents and when the composition is anhydrous or contains only small amounts of water (e. g. less than 5% by Weight of the polyoxyalkylene fluid) in higher concentrations than can be obtained by the use of the acids per se in the same fluid. It is preferred that the presence of water be held at a maximum not exceeding 2% by Weight if possible and in most cases the presence of water is found to be entirely unnecessary in order tov form homogeneous solutions between the heat condensation products and the water-soluble polyoxyalkylene fluids. By water-soluble acids is meant those acids of the recited class having a solubility of at least 0.5% by weight in Water at 20 C. Preferably the solution is in the order of about at least 2% by weight in water.

The water-miscible polyoxyalkylene fluids are distinguished from the corresponding classes ofpolyoxyalkylene fluids which are miscible in aliphatic hydrocarbons including mineral oils. Water miscibility is taken to mean the formation of clear uniphase mutual solutions when the fluid and water are mixed at room temperature (20 C.) in any proportions. The classes of materials with which this invention is concerned are those having an average molecular Weight of at least abou 250 and usually below about 1500. Polyoxyalkylene fluids of lower molecular weight such as the tripropylene glycol monoethers, are suitable solvents for the subject classes of additives but do not exhibit proper lubricating characteristics or extreme pressure properties. For the most part the polyoxyalkylene fluids which are miscible with Water comprise mixtures of polymers of lower molecular weight epoxides and glycols. Polyethylene glycols having average molecular weights between about 250 and 750 are suitable. Monoestersof said glycols with fatty acids having less than about eight carbon atoms per molecule and monoethers of alcohol having less than about ten carbon atoms also may be utilized.

The preferred classes of water-miscible fluids for use in the present compositions comprise the copolymers of ethylene oxide and 1,2-propylene oxide, as well as the monoethers thereof, particularly when the oxide ratio is 25 to 10-90 ethylene oxide-1,2-propylene oxide. By the ratio from 7525 to 10-90 is meant that, in the oxide mixture which may be used in forming the copolymers the amount of 1,2-propylene oxide in the mixture is from /3 to 9 times the amount of ethylene oxide present, by weight, the parts or proportion of the 1,2-propylene oxide being given last. These materials are described in two United States patents, namely, U. S. 2,425,755 to Roberts et a1. and U. S. 2,425,845 to Toussaint et al. The

materials preferred for use in the subject compositions are those having molecular weights of at least about 250 and preferably below about 1500. The unmodified diols falling within these limitations may be employed or the monoethers thereof may be used. In the preparation of the monoethers, alcohol having from 1 to about carbon atoms are preferred, and still more preferably these are aliphatic monohydric alcohols having the above carbon chain.

The subject polyoxyalkylene fluids may be prepared by polymerization of low molecular weight alkylene glycols to form a closely similar class of polymers. The epoxides and glycols are preferably those having from 1 to 4 carbon atoms each and it is further preferred that the epoxide linkage or the glycol radicals be attached to adjacent carbon atoms. Suitable glycols for use in the formation of water-miscible polymers include ethylene glycol, 1,2- propylene glycol, trimethylene glycol and butylene glycol.

The heat condensation products to be employed as dissolved additives in the above class of water-soluble polyoxyalkylene fluids comprise those formed between water-soluble aliphatic hydroxy carboxylic acids and lower aliphatic polyhydric alcohols. The term heat condensation product appears to be the best way of describing the products to be used, since the products are somewhat indeterminate in composition. The following acids comprise those most preferred in the preparation of the subject heat condensation products:

Hydroxy acids:

Monohydroxy fatty acids:

Glycollic acid Lactic acid l-ethylidene lactic acid 2-ethylidene lactic acid Ethylene lactic acid Hydroxy caproic acid a-Hydroxy butyric acid Acetonic acid Leucic acid e-Hydroxy crotonic acid u-Hydroxy valeric acid Polyhydroxy fatty acids:

Glyceric acid Arabonic acid Gluconic acid Gulonic acid Galactonic acid Talonic acid Mannonic acid Hydroxy polycarboxylic acids:

Citric acid Tartaric acid Trihydroxyglutaric acid Saccharic acid Tartronic acid Malic acid The polyhydric alcohols which may be employed in the preparation of the subject heat condensation products are preferably the lower alkylene glycols containing from 2 to 6 carbon atoms per molecule, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and the like. While these glycols are preferred, carbohydrates may be employed, such as sugars and derivatives thereof. The pentoses and hexoses are favored including ribose, arabinose, glucose, fructose, galactose and mannose, as well as hexitols, such as sorbitol or mannitol. The mixtures to be heat treated should predominate on a weight basis with respect to the hydroxy carboxylic acids and it is preferred that the mixture to be treated contain from 75 to 90% by Weight based on the mixture of the subject class of acids.

In carrying out the heat condensation, the physical mixture is simply heated to a temperature between about 100 and 200 C. for a period varying from about onehalf to about 4 hours. Under these conditions, it has been found that a complex series of reactions occur, the

two predominating comprising polymerization of the acids and simultaneous esterification of the acids or of the polymerization products thereof. The course of the condensation can be followed by measuring the quantity of Water evolved during the condensation process, since both the polymerization and esterification reactions result in the formation of water. It is preferred that the proportion of water formed during the process be between about 5 and about 12% by weight of the original mixture. Under these conditions, the product has been found to be most readily soluble in the subject class of water-miscible polyoxyalkylene fluids. Still more preferably, the proportion of water evolved during the heat condensation period is between about 6.5 and 9.5% by weight of the original mixture. It is a preferred practice to remove this water as it is formed but limited amounts may be permitted to remain in the product to assist in dissolving the latter in the water-miscible polyoxyalkylene fluids.

The act of solution of the heat condensation product is to be carried out subsequent to heat condensation and normally will comprise simple stirring, possibly aided by mild heating or warming to hasten the dissolving. Preferably the period of heating is between about threequarters and 1% hours at temperatures between about 50 C. and about C.

In accordance with one phase of the present invention, it has been discovered that the subject heat condensation products will dissolve in the above described watermiscible polyoxyalkylene fluids to a much larger extent than the corresponding acids themselves. While acids such as tartaric acid are soluble in the subject class of fluids to the extent of about 2% by weight, it has been ascertained that the subject heat condensation products formed for example between tartaric acid and propylene glycol will dissolve in amounts up to about 10-12% by weight of the polyoxyalkylcne fluid, dependent upon the proportion of acid to glycol and upon the extent to which the complex condensation heat treatment has been carried out.

In further accordance with the present invention, it has been ascertained that not only is it possible to incorporate far greater proportions of the heat condensation products in the subject class of fluids than is pos sible with the acids themselves, but also the resulting compositions have wider applicability than do the same fluids containing only the unmodified acids. More specifically, it has been found by extensive testing that water-soluble polyoxyalkylene fluids modified by the presence of acids such as tartaric acid and other acids as listed hereinbefore are not satisfactory for the op eration of gears wherein intensive high pressures and rubbing action occur, as in hypoid gears. Under these conditions, the last described compositions cause seizure after onlya short period of operation. As opposed to this, the compositions of the present invention have been found to provide extremely satisfactory operation in bypoid gears as further described in the working examples appearing hereinafter. The following examples illustrate the present invention:

Example 1 Fifteen parts by weight of propylene glycol and 85 parts by weight of tartaric acid are heated for one hour from room temperature to about C. and thereafter for another hour at about 150 C. During this time water was lost due to polymerization of the acid and/or esterification of the acid by the glycol. 6.8% by weight of water was lost during this period. The product was a viscous resin which upon cooling became solid.

Another condensation product can be prepared by heating the same proportion of the same reactants for about one-half hour to a temperature of 150 C. and thereafter for an hour at a temperature between 150 and C. to cause a water loss of 9.2% based on the original ingredients of the mixture. This product had a w st higher molecular weight than that described above and did not dissolve as readily in the subject polyoxyalkylene water-soluble fluids. v

A third product was prepared by heating the same proportions of reactants and the same reactants for a period of about one hour to a temperature of 150 C. and thereafter for about one-half hour to a temperature of 162 C. This caused a water formation of 7.3% which was eliminated from the reaction mixture.

Four per cent by weight of the reaction product can be dissolved in a high viscosity polyoxyalkylene oxy-1,2- propylene glycol trade named Ucon 50 HB 660. When tested in a four-ball test machine at 1800 R. P. M. for a period of ten seconds under various loadings, it was found that the composition had an initial seizure load of 178 kg. anda Weld load of 200 kg. The unmodified polyoxyalkylene fluid had an initial seizure load of about 79 kg. and a weld load of about 141 kg.

Example 2 Eighty-five parts by weight of tartaric acid and 15 parts by weight of propylene glycol were heated together at a temperature between about 160 and 170 C. for a period of 75 minutes. This caused a water loss of about 6.5% from the reaction product. One hundred sixty grams of the product can be dissolved in 1440 grams of the polyoxyalkylene fluid identified in the previous ex ample. The product obtained when tested in the fourball test machine had an initial seizure load (10 seconds) of 224-251 kg. and a weld load of 251 kg.

This composition, when used for the lubrication of hypoid gears at a pinion speed of about 2250 R. P. M. forward and 4000 rev. permitted running in either forward or reverse direction at the maximum load (about 100 p. s. i. forward, 50 p. s. i. rev.). The same fluid, omitting the condensation product, caused scoring at low loads in the order of about p. s. i.

Example 3 Example 4 By heating about by weight of ethylene glycol and 90% by weight of lactic acid for a period of about one hour at a temperature of 110 C., a product is obtained having a water loss of about 29%. The heat condensation product, which is a syrupy resin, when dissolved in a low viscosity polyoxyethylene oxy-1,2-propylene glycol fluid having water-soluble properties to the extent of 10% by weight forms a lubricating composition having a four-ball initial seizure load of 178 kg.

We claim as our invention:

1. A lubricant composition comprising a major amount of a water-miscible mixture of heteric oxyethylene oxy- 1,2-propylene diols in which the ethylene oxide and 1,2- propylene oxide are combined therein as oxyethylene and oxy 1,2-propylene groups in a ratio which is at least onethird part of 1,2-propylene oxide for each part of ethylene oxide by Weight, said diols containing in a single molecule both oxyethylene and oxy 1,2-p1'opylene groups, said mixture having an average molecular weight of at least 300 attributable to said groups, and a minor amount sufficient to improve the extreme pressure properties thereof of a heat condensation product of a mixture of tartaric acid and propylene glycol, said mixture prior to condensation comprising a predominating proportion by Weight of tartaric acid said heat condensation being carried outby heating the acid and glycol at a temperature between about 125 and 175 C. for a period between about 0.5 and about 4 hours until between about 6.5 and about 9.5% by weight of water, based on the mixture, is formed.

2. A composition according to claim 1 wherein the mixture of tartaric acid and propylene glycol prior to heat condensation thereof, comprises between about and about by weight of tartaric acid.

3. A lubricant composition comprising a major amount of a water-miscible mixture of heteric oxyethylene oxy- 1,2propylene diols in which the ethylene oxide and 1,2- propylene oxide are combined therein as oxyethylene and oxy 1,2-pr0pylene groups in a ratio which is at least onethird part of 1,2-propylene oxide for each part of ethylene oxide by weight, said diols containing in a single molecule both oxyethylene and oxy 1,2-propylene groups, said mixture having an average molecular weight of at least 300 attributable to said groups, and a minor amount sufficient to improve the extreme pressure properties thereof of a heat condensation product of a mixture of a watersoluble monohydroxy fatty acid having 2-6 carbon atoms per molecule and a lower alkylene glycol having between 2 and 6 carbon atoms per molecule formed by heating for a period between about 0.5 and about 4 hours at a temperature between about and 200 C. until between about 5 and about 12% by weight of Water, based on the mixture, is formed.

4. A composition according to claim 3 containing in addition between about 0.5% and about 5% by weight of water.

5. A lubricant composition comprising a major amount of a water-miscible mixture of heteric oxyethylene oxy 1,2-propylene diols in which the ethylene oxide and 1,2- propylene oxide are combined therein as oxyethylene and oxy 1,2-pr0pylene groups in a ratio which is at least onethird part of 1,2-propylene oxide for each part of ethylene oxide by weight, said diols containing in a single molecule both oxyethylene and oxy 1,2-propylene groups, said mixture having an average molecular weight of at least 300 attributable to said groups, and a minor amount sufficient to improve the extreme pressure properties thereof of a heat condensation product of a mixture of a watersoluble aliphatic carboxylic acid containing 3-6 carbon atoms per molecule and having at least one hydroxy substituent and propylene glycol formed by heating for a period between about 0.5 and about 4 hours at a temperature between about 100 and about 200 C. until between about 5 and about 12% by weight of water, based on the mixture, is formed.

6. A lubricating composition adapted for extreme pressure use comprising a major amount of a water-miscible mixture of monohydroxy oxyethylene oxy 1,2-propylene aliphatic monoethers in which the ethylene oxide and 1,2- propylene oxide are combined therein as oxyethylene and oxy 1,2-propylene groups in a ratio which is at least onethird part of 1,2-propylene oxide for each part of ethylene oxide by weight, said mixture having an average molecular weight of at least 300 attributable to said groups, the aliphatic monoethers of said mixture containing in a single molecule both the oxyethylene and oxy 1,2-propylene groups and a minor amount sufiicient to improve the extreme pressure properties thereof of a heat condensation product of a mixture of an aliphatic hydroxy polycarboxylic acid having 2-3 carboxyl radicals, 1-2 hydroxyl groups, and a total of 3-6 carbon atoms per molecule and a lower alkylene glycol having between 2 and 6 carbon atoms per molecule formed by heating for a period between about 0.5 and about 4 hours at a temperature between about 100 and 200 C. until between about 5 and about 12% by weight of water, based on the mixture, is formed.

7. A lubricating composition comprising a major amount of a water-miscible polyoxyalkylene fluid and a minor amount suflicient to improve the extreme pressure properties thereof of a mixture of a heat condensation product or a mixture of a water-soluble aliphatic carboxylic acid containing 36 carbon atoms per molecule and having at least one hydroxy substituent and a lower aliphatic glycol having between 2 and 6 carbon atoms per molecule forrned by heating for a period between about 0.5 and about 4 hours at a temperature between about 100 and about 200 C. until between about 5 and about 12% by weight of water, based on the mixture, is formed.

8. A lubricant composition comprising a major amount of a water-miscible mixture of heteric oxyethylene oxy 1,2 '-propylene diol's in which the ethylene oxide and 1,2- propylerie oxide are combined therein as oxyethylene and oxy 1,2-prop'ylene groups in a ratio which is at least onethird part of 1,2-propy1ene oxide for each part of ethylene oxide by weight, said diols containing in a single molecule both oxyethylene and oxy 1,2-propylene groups, said mixture having an average molecular weight of at least 300 attributable to said groups, and a minor amount sufficient to improve the extreme pressure properties thereof of a heat condensation product of a mixture of tartaric acid and propylene glycol formed by heating for a period between about 0.5 and about 4 hours at a temperature between about C. and about C. until between about 6.5 and about 9.5% by weight of water, based on the mixture, is formed.

References Cited in the file of this patent UNITED STATES PATENTS 2,147,647 Gleason Feb. 21, 1939 2,152,683 Eichwald Apr. 4, 1939 2,370,300 Farrington Feb. 27, 1945 2,430,842 Young Nov. 11, 1947 OTHER REFERENCES Ucon"-Fluids and Lubricants-Carbide and Carbon Chem. Corp., New York, May 31, 1948; page 3 pertinent.

Claims

3. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A WATER-MISCIBLE MIXTURE OF HETERIC OXYETHYLENE OXY1.2-PROPYLENE DIOLS IN WHICH THE ETHYLENE OXIDE AND 1,2PROPYLENE OXIDE ARE COMBINED THEREIN AS OXYETHYLENE AND OXY 1,2-PROPYLENE GROUPS IN A RATIO WHICH IS AT LEAST ONETHIRD PART OF 1,2-PROPYLENE OXIDE FOR EACH PART OF ETHYLENE OXIDE BY WEIGHT, SAID DIOLS CONTAINING IN A SINGLE MOLECULE BOTH OXYETHYLENE AND OXY 1,2-PROPYLENE GROUPS, SAID MIXTURE HAVING AN AVERAGE MOLECULAR WEIGHT OF AT LEAST 300 ATTRIBUTABLE TO SAID GROUPS, AND A MINOR AMOUNT SUFFICIENT TO IMPROVE THE EXTREME PRESSURE PROPERTIES THEREOF OF A HEAT CONDENSATION PRODUCT OF A MIXTURE OF A WATERSOLUBLE MONOHYDROXY FATTY ACID HAVING 2-6 CARBON ATOMS PER MOLECULAR AND A LOWER ALKYLENE GLYCOL HAVING BETWEEN 2 AND 6 CARBON ATOMS PER MOLECULE FORMED BY HEATING FOR A PERIOID BETWEEN ABOUT 0.5 AND ABOUT 4 HOURS AT A TEMPERATURE BETWEEN ABOUT 100 AND 200* C. UNTIL BETWEEN ABOUT 5 AND ABOUT 12% BY WEIGHT WATER, BASED ON THE MIXTURE, IS FORMED.