US3472775A - Synthetic ester lubricant base fluid containing a polyester thickener - Google Patents

Description

United States Patent Int. Cl. C10m N28 US. Cl. 25257 7 Claims ABSTRACT OF THE DISCLOSURE Synthetic ester lubricating fluid containing thickening amounts of a polyester formed from a polymerized higher 'fatty acid and a glycol, said polyester having been refined with a glycidyl ester of an aliphatic acid.

BACKGROUND OF THE INVENTION This invention is concerned with lubricant compositions and, more particularly, with synthetic lubricant compositions containing a polyester thickening agent that has been refined with a glycidyl ester of an aliphatic acid having from to 22 carbon atoms.

Synthetic ester lubricants have been used in gas turbine and internal combustion engines and are well known in the art. The viscosity of synthetic ester lubricants tends to thin out excessively at high temperatures. Since lubricants are'subjected to a wide range of temperatures in the operation of an engine, it is desirable that the viscosity should only slightly vary with the temperature of the fluid. The resistance of a lubricant to viscosity change is referred to as the V.I. (viscosity index) of the lubricant. The V.I. is determined by a method described by Dean and Davis, Ind. and Eng. Chem, vol. 32, p. 104 (1940). The greater the V.I. the more ideal the lubricant is, that is, the greater is the resistance of the lubricant to thicken at low temperatures and to thin out at high temperatures.

v.A number of additives have been used in the past in an attempt to make lubricants act like ideal fluids, that is, fluids in which the viscosity does not vary with temperature (a high V.I.). Included among these additives have been a number of polymeric materials, such as polyisobutenes, polymethacrylates, polyvinyl acetates, and polyacrylates. These long chain polymers improve the V.I. by changing size and shape when the temperature is increased. At low temperatures the polymer is insoluble in the synthetic ester lubricant due to the molecule coiling up or collapsing. These coils or spheres contribute slightly to the viscosity of the lubricating fluid. As the temperature increases, the polymers open up and extend into the fluid with the result that they contribute significantly to the, viscosity of the base fluid. The overall effect is to reduce the rate of change of viscosity with temperature.

The polymeric V.I. improving compounds mentioned above have been unsatisfactory in engines in which there is great shear since under high shear conditions they tend to break apart and lose their ability to thicken the lubricatjng fluid. Polyester additives prepared from glycols and long chain dicarboxylic acids, such as polymerized unsaturated fatty acids, commonly referred to as dimer acids, have been found to resist shear and has as a result been used to some extent as lubricant V.I. improvers. One problem with these esters is that they generally contain an excessive amount of acidity in the form of unreacted acids used in the preparation of the ester. The excess acidity results from (1) incomplete esterification caused by the discontinuance of the esterification reaction before completion can be achieved, it being uneconomical and unfeasible from a time standpoint to allow "Ice the reaction to go to virtually completion, (2) the hydrolysis of the esters after they have been formed by the water by-product of the esterification reaction (water is removed during the esterification reaction; however, it is not economically or technically feasible to remove it entirely and thus the residual water causes hydrolysis of the esters to the original glycol and acid reactants), and (3) the use of unequal equivalents of acid and glycol. Because of the reaction kinetics, it is sometimes desirable to use an excess of acid in order to drive the reaction toward completion. The excess acid above that which can be easily distilled off remains in solution. If an attempt is made to remove all of the acid by distillation, excessive losses of the ester product often result and the ester product frequently undergoes some decomposition resulting in an undesirable darkened product.

A number of methods have been attempted in the past to reduce the acidity of esters. One of the most popular methods has been the treatment of the acid/ glycol reaction'product with an aqueous alkali solution, such as potassium carbonate or sodium hydroxide, or the percolating of the ester reaction product through an alkaline bed. While being effective in reducing the acid value, the alkali treatment has not been entirely satisfactory. The dimer acid, which is prepared from polymerized fatty acids, such as polymerized oleic or linoleic acid, forms a salt (or soap) which is more soluble in the ester than in water and thus cannot be removed when conventional alkali refining is attempted.

Another method which has been used for the removal of excess acidity has been the treatment of the unrefined ester lubricant which short chain alkylene oxides, such as propylene oxide or ethylene oxide. One of the drawbacks to this process is that the reaction product of alkylene oxides, particularly the lower alkylene oxides, and the free acid is a material which is generally unstable under high temperature operating conditions and either decomposes resulting in the contamination of the lubricant composition or gives a lubricant having excessive volatility. Another problem connected with the use of alkylene oxides is their tendency to polymerize causing materials which are difficult to remove.

This invention is concerned with a new and improved method for reducing the acid value of polyester thickeners and thus making them more suitable for use in lubricant systems.

DESCRIPTION OF THE INVENTION This invention concerns lubricant compositions containing novel thickeners. The thickeners are high molecular weight polyesters which have been refined with a glycidyl ester of an aliphatic acid having from 5 to 22 carbon atoms.

The polyester thickeners used in the lubricant compositions of this invention may be prepared from long chain dicarboxylic acids and glycols. The preferred acids used in the preparation of the polyesters are polymerized unsaturated fatty acids, such as linoleic and oleic acid. The glycols may be short chain glycols, such as propylene glycol and ethylene glycol, preferably hindered glycols, such as neopentyl glycol, and 2,2,4-trimethylpentanediol- 1,3. After the polyester is prepared, it contains excess acid which cannot be introduced into a lubricant composition. Thus, the glycidyl ester is added in excess of the amount needed to neutralize the excess acidity of the polyester and acts as an acid scavenger.

The glycidyl esters which may be used in the practice of the present invention include the glycidyl esters of aliphatic acids having from 5 to about 22 carbon atoms. The acids may be normal or branched. The preferred compounds forming the acid moiety of the glycidyl esters which may be used are neo-acids, that is, acids in which the alpha carbon atoms are completely substituted with alkyl groups.

The glycidyl esters used in this invention may be formed by the reaction of epichlorohydrin and an alkali metal salt of the acid used and should have the following formula:

I! RCOCHzCH-CH2 wherein R is a branched or straight chain alkyl group having from 4 to 21 carbon atoms.

The preferred acid scavenging glycidyl ester is a compound havin the general formula:

wherein R R and R are all saturated alkyl groups and contain a total of about 7 to 9 carbon atoms. The glycidyl esters having this structure produce, when reacted with the free acid of the ester thickener, materials which are particularly stable and compatible with the lubricant system. Among the other glycidyl esters which may be used as an acid scavenger in addition to the neo-acid esters are the gylcidyl esters of pelargonic acid, heptanoic acid, valeric acid, isostearic acid, and oleic acid.

In performing the refining operation on the polyester thickeners used in the lubricant compositions of this invention, the excess glycol used in preparation of the polyester is removed by heating the reation mixture to about 260 C. with a pressure of about 1 to 2 torr. The polyester is then cooled. The acid value of the polyester is measured and then a 100% excess of the stoichiometric amount of the glycidyl ester needed to neutralize the acid still present is added to the polyester. The reactants are further reacted until the acid value of the polyester is reduced to a value lower than 0.05. The excess glycidyl ester is removed by heating the ester to 245 C. and applying vacuum.

The base fluids for the lubricant compositions of this invention may be either pariffins or synthetic esters. When the base fluid is an ester it may be prepared from various combinations of aliphatic monocarboxylic acids and dicarboxylic acids having from about 6 to 36 carbon atoms, and monohydric and polyhydric aliphatic alcohols having from about 4 to about 20 carbon atoms. Specific examples of these esters that may be used are: di-iso-octyl adipate, di-2-ethylhexyl azelate, didecyl azelate, di-isodecyl azelate, di-isodecyl adipate, ditridecyl adipate, di-iso-octyl sebacate, di-isodecyl sebacate, di-Z-ethylhexyl sebacate, diiso-octyl dodecanedioate, di-Z-ethylhexyl brassylate, and di-iso-octyl brassylate. Other esters may also be used as synthetic lubricants that are made from hindered polyols and monoand polycarboxylic acids of about 5 to 13 carbon atoms. Specific examples of these esters are: esters of monopentaerythritol and an acid blend comprised of 70% by weight of isovaleric acid and 30% by weight pelargonic acid; monopentaerythritol and an acid blend of 50% by weight of isovaleric acid, 25% by weight of pelargonic acid, and 25 by weight of a mixture of acids with an average of C chain length; trimethylol pentane and two moles of pelargonic acid and one mole of a mixture of monocarboxylic acids with C chain length; and trimethylol pentane and three moles of a mixture of monocarboxylic acids with an average of C chain length. Among other complex esters used are those having a structural formula such as XYZYX, wherein X is a monohydric alcohol radical, Ynis a dibasic acid radical, and Z is a glycol radical, or a structural formula such as ABCBA, wherein A is a monocarboxylic acid radical, B is a glycol radical, and C is a dicarboxylic acid radical. Examples of these complex esters are the reaction products of 2-ethyl-l,3-hexanediol, sebacic acid, and 2- ethylhexanoic acid; adipic acid, diethylene glycol, and pelargonic acid; sebacic acid, trimethylolethane, and hexamole acid; and sebacic acid, l,3,5,7-octanetetr0l and pentanoic acid.

The molecular weight of the polyester thickeners used in the lubricant compositions of this invention have a range of about 2000 to 12,000 and preferably from about 2000 to 6000.

The polyester thickeners may be used in an amount of about 0.5 to 30.0 percent by weight of the composition and preferably from about 1.0 to 10.0 weight percent based on the total lubricant composition weight.

To further illustrate the lubricant compositions of the present invention, the following examples are provided. It is to be understood that these examples are illustrative only and are not to be considered limitative of the scope of this invention.

EXAMPLE I A preferred polyester thickener for use in preparing the lubricant compositions of this invention was prepared by reacting 2760 gms. of dimer acid, a polymerized oleic acid sold under the trademark Empol 1010, 490 gms. of neopentyl glycol, and 57 gms. of propylene glycol. The esterification was continued until the acid value was determined to be 11.2, then 159 gms. of the glycidyl ester of a neo-acid, sold under the trademark Cardura E, and having a molecular weight of 245, were added. The 159 gms. represented a excess over the stoichiometric amount required to react with all of the free acid contained in the polyester thickener. The reaction vessel was heated to a temperature of 210-220 C. for a period of 6 hours after which the excess glycidyl ester was stripped off at a temperature of about 230 C. while subjecting the reaction vessel to a pressure of 1 to 2 torr. The resulting polyester had an acid value of 0.034, and a molecular weight of about 3500.

EXAMPLE II A lubricant composition was prepared using 57.2% by weight of di-isodecyl azelate, 24.52% by weight di-isodecyl pelargonate, and 12.21% by weight of a commercial thickener, methyl acrylate, sold under the trademark Acryloid 710. The remaining portion of the composition was a combination of commerical antioxidants and metal deactivators. This composition was tested for sonic shear stability using ASTM Standard Test Appendix III (1961 Edition). After the test was run, the fluid had a 51.3% viscosity loss at 100 F.

EXAMPLE III A composition was made in accordance with Example I except that 2.51% by weight of a methyl acrylate sold under the trademark Acryloid 710 and 4.25% by weight of the glycidyl ester refined polyester prepared in Example I was substituted for the thickener used in Example II. This composition was tested for sonic shear stability as in Example II. It showed a viscosity loss of 24.3% at 100 F.

EXAMPLE IV A lubricant was made using 91.43 parts by weight of di-isodecyl azelate, 2.5 parts by weight of the glycidyl ester refined polyester prepared in Example I, and the composition was tested for sonic shear stability as in Example II. It showed a 4.0% viscosity loss at 100 F.

It can be seen from the sonic shear stability test results in Examples II to IV that the use of a polyester thickener in the lubricant compositions vastly improve the shear stability of the lubricant compositions over the shear stability achievable with the conventional thickeners shown for comparative purposes.

EXAMPLES V-VII Lubricant compositions were prepared in accordance with the formulations shown in Table I below. These compositions were evaluated using Federal Test 791, Corrosion and Oxidation Stability, Method 5308, run

at 425 F. for 72 hours. This test subjects lubricant compositions to heat and aeration in the presence of five metals; copper, silver, steel, magnesium, and aluminum. The data in Table II shows that the change in metal weight was not great, and that the change in metal weight was within the specifications of Pratt and Whitney PWA 521-B, which allows a maximum change in metal Weight of $0.30 mg./em. and a maximum increase in viscosity at 100 F. of 50%.

Lubricant compositions containing polyesters which have not been refined have excess acidity and consequent corrosive propensities which render them of marginal utility.

TABLE I Example No V VI VII Pentaerythrltol ester 93. 73 Pentaerythritol ester 2 93. 73 Trimethylol propane ester 46. 50 Trirnethylol propane ester 4 46. 50 Polyester 5 r 1. 20 4. 48 1. 20 Commercial Anti-oxidants 2. O 2. 0O 2. 00 Commercial Metal Deactivator- 0. 0. 05 0. 05 Quinizarin 0. 02 0. 02 0. 02 TOP 3. 00 3. 00 3. O0

1 An ester prepared from monopentaerythritol and a mixture of C and C monobasic acids.

2 An ester prepared from monopentaerythritol and a mixture of O to C monobasic acids.

3 An ester prepared from trimethylol propane and a mixture of C to C9 monebasio acids.

4 An ester prepared from trimethylol propane and a mixture of C to C monobasic acids.

5 Prepared in Example I.

TABLE II Example No- Viscosity change at 100 F. (Percent). Sludge (mg) Acid value Copper corrosion (mg./cm. Steel corrosion (mg/cm?) Silver corrosion (mg/cm!) Magnesium corrosion (mg/emi Aluminum corrosion (mg/cm?) We claim:

1. A lubricant composition comprising a major amount of a synthetic ester base, fluid and a thickening amount of a polyester formed from a polymerized higher fatty acid and a glycol, said polyester having a molecular weight between about 2,000 and 12,000 and having been refined with a glycidyl ester of an aliphatic acid by reacting said glycidyl ester with free acid contained in said polyester.

2. The composition of claim 1 wherein said glycol is selected from the group consisting of ethylene glycol, propylene glycol, neopentyl glycol, and mixtures thereof.

3. The composition of claim 2 wherein said glycol is neopentyl glycol.

4. The composition of any of claims 1 to 3 wherein said glycidyl ester is selected from the group consisting of glycidyl esters of neo-acids, pelargonic acid, valeric acid, isostearic acid, heptanoic acid, and mixtures thereof.

5. The composition of any of claims 1 to 3 wherein said glycidyl esters of neo-acids have the formula:

wherein R R and R are all saturated alkyl groups and contain a total of 7 to 9 carbon atoms.

6. The composition of any of claims 1 to 3 wherein said thickener comprises from about 0.5 to 30 percent by weight of said lubricant composition.

7. The composition of any of claims 1 t0 3 wherein said polyester thickener has an acid value of not more than 0.05

References Cited UNITED STATES PATENTS 1,786,248 12/1930 Jordan et al 260-421 2,424,588 7/1947 Sparks et a1. 252--56 DANIEL E. WYMAN, Primary Examiner W. CANNON, Assistant Examiner U.S. Cl. X.R.