US2508741A - Lubricating grease composition - Google Patents

Description

Patented May 23, 1950 LUBBJOATING GREASE COMPOSITION Harry V. Ashburn, Waynesburg, Pa... and Robert 8. Barnett, Beacon, and Oney P. Puryear, Fishkill, N. Y., assilnors to The Texas Company,

New York, N. Y., a corporation of Delaware No Drawing. Application April 12, 1948, Serial No. 20,606

* teams. (01. ass-42.1)

This invention relates to improved lubricating crease compositions and particularly to texturestable grease compositions in which a synthetic liquid polyorganosiloxane comprises part or all oi the oil component.

This is a continuation-in-part of our copending application Serial No. 611,908, filed August 21, 1945, now Patent No. 2,450,221 dated September 28, 1948.

Recent developments in the production of lubricating greases and particularly those designed for specialty equipment employing shielded and/or sealed bearings and operating over wide temperature ranges, have led to the use of a number of organic chemical compounds as substitutes for the conventional mineral lubricating oils. For this purpose the synthetic liquid polyorganosiloxanes, also known as silicones, have been proposed for use as the lubricant base in greases. These'oleaginous compounds offer a marked advantage over the mineral oils in that they possess a comparatively uniform viscosity over a wide temperature range and are not as susceptible to evaporation loss as a comparable viscosity mineral oil. These features are particularly desirable and have been used to advantage in the production of greases used in shielded and/or sealed life-time bearing installations and low temperature greases used in aircraft controls and the like. However, one undesirable characteristic of these so-called synthetic greases is their lack of resistance to shear. Under conditions of operation where high shearing stresses are involved, such as in ball and roller-bearing lubrication and magneto gear boxes, the structure of these greases gradually breaks down and their consistency falls off until they become liquid or semi-liquid. At a certain point fluidity becomes pronounced enough to induce serious leakage resulting both in starved lubrication and in the lubricant reaching such objectionable locations as magneto breaker points.

In accordance with the present invention it has been found possible to produce a synthetic grease composition which possesses not only the desirable characteristics imparted by the polyorganosiloxane compounds, but is also resistant to shear. The synthetic greases previously proposed and accepted by the industry have been prepared from the metal soaps of the conventional iatty acid sources, such as stearic acid and other soap-forming fatty acids or their 2 glycerides. It has been component of the metal soap is an important factor in the production of synthetic greases and that synthetic greases produced from metal soaps of soap-forming hydroxy fatty acids or their glycerides possess exceptional texture-stability and maintain their structure with little change in consistency even after extensive working at either high or low temperatures.

This unusual characteristic of the metal soaps of hydroxy fatty acids is applicable to those grease compositions in which a synthetic polyorganosiloxane compound comprises part or all of the oil component. The term "polyorganosiloxane as used herein embraces those organic polymers having the unit structure:

wherein the units are attached through the silicon and oxygen atoms and wherein R and R represent alkyl, aryl, alkaryl, aralkyl, and cycloalkyl groups. The method of producing these polymers is well known, and may involve the reaction of a silicon halide witha Grignard reagent to form the corresponding organo silicon halide, followed by hydrolysis of the organo silicon halide to form a silicol, and then condensation of the silicol in the presence of air or oxygen, with the aid of a catalyst or heat to form the polyorganosiloxane or silicone polymer (Kipping,l?roc. Chem. Soc. 20, 15-16 (1904)). Depending upon the extent of condensation or polymerization, the resulting products vary from relatively light liquids to solid resins and are reported to be both chain-like (U. S. Patent No. 2,352,974Rochow) and cyclic (U. S. Patent No. 2,371,050Hyde) in structure. For purposes of the present invention, only those polymers which are high boiling liquids within the lubricating oil viscosity range are suitable, these generally possessing a viscosity of 100 F. within the range of about 10-600 centistokes. These polyorganosiloxane liquids within this viscosity range are generally colorless, odorless and relatively inert, have very low 'volatility, such that vapor pressure within the discovered that the acidpolymers within the foregoing definition are contemplated for purposes of the present invention, the preferred polymers, from the standpoint of cost, are those which have achieved the greatest commercial production, namely, the dimethyl silicone polymers, the diethyl silicone polymers, and the ethylphenyl or methylphenyl silicone polymers. However, it is contemplated that the silicone polymers produced from higher molecular weight alkyl groups, such as butyl, amyl and above, when economically available, will constitute valuable lubricant bases for purposes of the present invention. In general, these silicone polymers are adapted to specialized lubrication outside the conventional lubricating temperature ranges, such as ultra low temperature operation found in refrigerator systems and arctic service, or to general purpose lubrication over a wide lubricating temperature range which was previously unattainable through the use of a single mineral lubricating oil because of the latters high viscosity change over such a wide temperature range. In addition, these silicone materials are more resistant at high temperatures where hydrocarbons, esters of carbon chain compounds, and similar synthetic lubricant bases of essentially organic structure are subject to carbonization such that they eventually become dry and hard.

These p lyorganosiloxanes may be used as the sole oil component of the grease, or they may be blended with a mineral lubricating oil or other synthetic lubricating oil, as desired. In some instances, where the soap component is to be formed in situ, it is desirable to conduct the saponiflcation in the presence of mineral oil and then add the silicone polymer. This results in the combination of mineral oil and silicone polymer as the lubricant base or oil component of the finished grease. Furthermore, various addition agents may be incorporated in the grease with the silicone polymer to impart other desirable characteristics. Thus, an extreme pressure agent may be incorporated to improve the antiwear characteristics, or an anti-oxidant may be incorporated to improve the anti-oxidant properties of the finished grease.

The metal soaps which have l'ien found to contribute to the desirable attributes of the synthetic greases are those in which a soapforming hydroxy fatty acid constitutes at least part of the acid component. The soap-forming hydroxy fatty acids contemplated herein are those containing at least 12 carbon atoms in the molecule and one or more hydroxyl groups separated from the carboxyl group by at least one carbon atom, as well as mixtures thereof. These hydroxy fatty acids may be obtained from natural sources, such as castor oil, or may be prepared by the classical synthetic methods, such as oxidation of unsaturated fatty acids or catalytic oxidation of petroleum oils and waxes with extraction and fractionation to the desired molecular range. In the practice of the invention, as described herein, 12-hydroxy stearic acid and hydrogenated castor oil will be used as the representative types of hydroxy fatty acids and their glycerides. These acids are preferred because of their advantage of availability and cost which renders them competitive to the conventional fats and fatty acids.

The soap-forming hydroxy fatty acids may be used as the sole acidic component of the metal soaps or they may be blended or combined with the conventional fats or fatty acids in such proportions that at least 50% of the total acidic component is comprised of the hydroxy fatty acids. The choice of fats or fatty acids and the specific proportion thereof which may be blended or combined with the hydroxy fatty acids depends upon the particular metallic constituent and the type of service for which the synthetic grease is intended. In general, any of. the recognized fatty acid materials normally used in grease manufacture may be used providing they are essentially saturated in character. These fats and fatty acids include mixtures of fatty acid glycerides found in naturally-occurring fats and oils, together with fractionated components thereof. The fatty acids may be a mixture of acids split on from these fats or prepared from hydrogenation of fish oils, etc., or individual acids themselves.

The metallic constituent of the scans of hydroxy fatty acids may be any of the metals normally used in the production of thickening agents for lubricating oils, such as Na, Li, Ca, Ba, Al, etc., as well as mixtures thereof. In many respects, the choice of the metallic constituent is dependent upon the physical properties desired in the finished grease, such as dropping point, water resistance, texture, etc. For the purpose of the present invention the metals preferred are the alkali metals, sodium and lithium.

The choice of the particular methods of manufacture applicable to the production of the synthetic greases of the invention will depend upon the type of silicone polymer used and whether or not mineral oil is to be used as part of the oil component. The conventional method of preparing synthetic greases is the gelling method in which the preformed metal soap and the silicone polymer a. e heated to a homogeneous solution and rapidly cooled to form the grease gel. This method of preparation possesses certain disadvantages in that it requires a preformed metal soap which in and of itself raises the cost of the grease because of the separate saponification step required and extensive milling equipment to work the grease gel to a homogeneous consistency. However, in preparing the greases of the invention other methods of manufacture, conventional to the grease industry, may be usedv A particular advantage in the use of metal soaps of hydroxy fatty acids is the fact that the high temperatures required by the conventional gelling methods may be avoided and the preparation conducted at temperatures around 300 F. or at least those attained in a steam-heated kettle and the finished grease drawn from the kettle without requiring homogenization. Furthermore, saponification in situ is possible either in the presence of mineral oil or a silicone polymer, or a mixture thereof.

The following example is presented as illustrating the preparation of a representative synthetic grease falling within the scope of the present invention:

Example A grease base consisting of the lithium soaps of the combination of by weight of hydrogenated castor oil, and 25% by weight of triple pressed stearic acid, together with mineral lubricating oil, was first prepared as follows:

A steam-heated kettle equipped with stirring mechanism was charged with 16.8 pounds of 10.4% lithium hydroxide solution and 9.0 pounds 75 of water. Stirring was started at 35 R. P. M. and

I the lithium hydroxide solution heated to about 180 F. 16.2 pounds of hydrogenated castor oil (Titer74.'6 C., Sap. No.-183, Hydroxyl value- 165) and 15.0 pounds of a mildly refined mineral lubricating distillate having a BUS viscosity at 100 F. of about 50 were then added. The kettle contents were held at 170-190 F. for about 4 hours with continued stirring, and 5.52 pounds of melted triple pressed stearic acid were added. The temperature was then maintained at 180-184 F. for an additional hour and the kettle shut down over night. The next day stirring at 35 R. P. M.,

'with heating, was resumed to bring the mix up Wt. per cent Lithium soap Glycerine 3.5 Mineral oil 750 grams of the grease base were charged to a kettle and heated with stirring at 234 F. The heat was then reduced and 1020 grams of a dimethyl silicone polymer possessing a flash point above 600 F., with a kinematic viscosity of 82 cs. at 100 F. and 32 cs. at 210 F. were slowly added over a period of 6 hours. At this point the temperature was 147 F. and the ASTM control penetration at 77 F. was 203-210 unworked and 221- 223 worked. 1000 grams of additional dimethyl silicone polymer were then added slowly until a control worked penetration of 345 at 78 F. was obtained. The batch was then drawn at 'a temperature of 176 F. The product was a smooth, light-colored, buttery grease having the following calculated composition:

Per cent Lithium soap 12.8 Glycerine 0.9 Mineral oil 13.4 Dimethyl silicone polymer 72.9

The subject grease was tested in a so-called grease-breakdown machine wherein a No. 204 anti-friction bearing was packedwith the grease and mounted on a motor-driven shaft operating at 3450 R. P. M. and surrounded by a heating jacket. The test was started at room temperature and the bearing radually heated, while running at a constant speed, until the temperature reached 300 F., about one hour being required to complete the test. During the period of the test the performance of the grease was noted. At the conclusion of the test the grease was removed from the bearing and examined as to change in texture and consistency. The results obtained on the subject grease indicated excellent performance, with no appreciable change in texture or consistency of the grease at the conclusion of the test.

In comparison therewith a commercial dimethyl silicone grease was also tested and, although showing excellent performance on antifriction bearings while running, the grease became semi-fluid toward the end of the test and drained from the bearing when the test was stopped.

. 0 Other typical tests obtained on the foregoing grease are listed in the following table:

ASTM penetration at 77' E:

Unworked 279 Worked 330 Dropping point F. 356 Water absorption (AN-G-3a) per cent 40 Oil bleeding and evaporation test hrs. at

250 F.; mesh cones):

Oil bleeding, per cent 5.8 Evaporation loss, per cent 4.3

The foregoing tests show the grease to possess a fairly high dropping point, to be low in evaporation loss (loss attributable to the mineral oil component) and low in oil bleeding for the tem-- perature of the test, and to meet torque requirenients at minus 67 F. for a low temperature grease. In addition, the grease-breakdown test is outstanding, since it shows the product to behave excellently up to 800 1''. without breakdown or change in texture or body.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only'such limitations should be imposed as are indicated in the appended claims.

1. A lubricating grease composition comprising as thelubricant base and the major constituent of the composition a synthetic high boiling liquid polyorganosiloxane within the lubricating oil viscosity range, and suiilcient metal soap of a soapforming fatw material selected from the group consisting of hydroxy fatty acids and hydroxy fatty acid glycerides to thicken said lubricant base, said grease composition being texture stable under high shearing stress.

2. A lubricating grease composition according to claim 1, wherein the said synthetic high boiling liquid polyorganosiloxane is a dimethyl silicone polymer.

3. A lubricating grease composition according to claim 1, wherein the said metal soap is lithium soap.

4. A lubricating grease composition comprising as the lubricant base and the major constituent of the composition a. synthetic high boiling liquid polyorganosiloxane within the lubricating oil viscosity range, and suflicient metal soap of soap-forming fatty material to thicken said lubricant base, said soap-forming fatty ma- I swam 7 -6. A lubricating grease composition according to claim 4, wherein said polyorganosiloxane is a dimethyl silicone polymer, and said metal soap is a mixture of a major proportion of the lithium soap of hydrogenated castor oil and a minor proportion of lithium stearate.'

7. A lubricating grease composition comprising as the major constituent a lubricant base consistlng primarily of a high boiling liquid dimethyl silicone polymer mixed with a small proportion of a mineral lubricating oil, sufllcient lithium soap of a mixture of about 75% by weight of hydrogenated castor oil and about 25% by weight of stearic acid to thicken said lubricant base, and glycerine resulting from the saponiflcation of said hydrogenated castor oil.

HARRY V. ASHBURN. ROBERT S. BARNETT. om P. PURYEAR.

8 REFERENCES crrnn The following references are of record in the tile 0! this patent:

UNITED STATES PATENTS Number Name a Date 2,283,602 Fiero May 19, 1942 2,308,599 Fraser Jan. 19, 1948 2,351,384 -Wo0ds et a1. June 13, 1944 2,397,956 Fraser Apr. 9, 1946 2,446,177 Hain et al Aug. 3, 1948 2,450,219 Ashburn et al. Sept. 28, 1948 2,450,221 Ashburn et al Sept. 28, 1948

Claims (1)

1. A LUBRICATING GREASE COMPOSITION COMPRISING AS THE LUBRICANT BASE AND THE MAJOR CONSTITUENT OF THE COMPOSITION A SYNTHETIC HIGH BOILING LIQUID POLYORGANOSILOXANE WITHIN THE LUBRICATING OIL VISCOSITY RANGE, AND SUFFICIENT METAL SOAP OF A SOAPFORMING FATTY MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROXY FATTY ACIDS AND HYDROXY FATTY ACID GLYCERIDES TO THICKEN SAID LUBRICANT BASE, SAID GREASE COMPOSITION BEING TEXTURE STABLE UNDER HIGH SHEARING STRESS.