US3520807A - Grease thickened with fibers coated with a soap - Google Patents

Description

United States Patent 3,520,807 GREASE THICKENED WITH FIBERS COATED WITH A SOAP Edward A. Cross, Beaumont, Tex., and Richard L. Frye, Baton Rouge, La., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 580,900, Sept. 21, 1966. This application June 26, 1968, Ser. No. 740,084

Int. Cl. Cm 5/14, 5/16, 7/20 US. Cl. 25213 11 Claims ABSTRACT OF THE DISCLOSURE A shear stable, water resistant grease composition thickened with a soap-wettable fiber which is coated with soap and a method of preparing said composition.

The application is a continuation-in-part application of application Ser. No. 580,900, filed Sept. 21, 1966 and now abandoned.

This invention relates to a process for preparing a grease thickened with fibers coated with soap. This invention also relates to the grease so prepared. More particularly, this invention relates to mineral fibers, e.g., asbestos fibers coated with a soap, e.g., lithium 12-hydroxystearate.

There are many different processes for preparing greases thickened with soaps and there are also processes for preparing greases thickened with fibers such as asbestos. However, processes heretofore known generally do not provide asbestos thickened greases having all of the desired properties of a grease thickened with soap. Heretofore, greases thickened with asbestos have not been shear stable and generally they are extremely water sensitive. Furthermore, these known greases generally do not have a good dispersion of the asbestos fiber in the grease and hence they are characterized by poor yields as determined by standard ASTM 217-48 penetration tests.

It is an object of the invention, therefore, to provide a lubricating grease thickened with asbestos characterized by high shear stability and lack of water sensitivity.

It is still another object of this invention to provide such a grease having good shear stability and water resistance wherein the asbestos fibers are evenly dispersed without substantial coherence of the fibers together throughout the grease composition.

It is another object of this invention, therefore, to provide a process for preparing such a grease thickened with fiber coated with a soap.

These and other objects of this invention will become apparent from the following more complete description of our invention and appended claims.

Broadly, this invention contemplates a process for preparing a grease thickened with a soap-fiber mixture which comprises forming a mixture of soap and fiber in lubricating oil, heating the mixture to a temperature in the range of from about 50 -F. below the soap melting point temperature up to about 30 F. above the soap melting point temperature, cooling the mixture and shearing the resultant mixture.

In a particularly desirable embodiment of this invention, the mixture of soap and fiber in the lubricating oil is between 3 and 25% by weight, depending upon the grade of grease being manufactured, the mixture is heated to a temperature within the above prescribed range, the so-heated mixture is cooled and sheared at a temperature between 350 and 150 F., most suitably 200 F.

In accordance with the process of our invention any soap-wettable fiber heretofore known can be employed.

We can in our process utilize organic polymers such as polyethylene fiber, polypropylene fiber, polyester fiber, polymethacrylate fiber, polyacrylonitrile fiber, polyvinylchloride fiber and nylon fiber. Nonorganic fibers such as asbestos fiber, wollastonite fiber, graphite fiber, quartz microfiber and glass microfiber can be used. The inorganic type is preferred, with asbestos being the prime example, particularly the chrysotile asbestos fibers.

The soaps which can be used in accordance with the process of our invention are soaps of any of the following metals: lithium, sodium, calcium, manganese, cobalt, zinc, potassium, barium, magnesium and aluminum. Preferably the metal is lithium, calcium or sodium. Mixed soaps can also be employed. These metals as metal saponifying agents can be in the form of a metal hydroxide, a metal oxide, or a metal carbonate.

Suitable saponifiable materials employed in these grease preparations are higher fatty acids containing from 12 to 32 carbon atoms per molecule and hydroxy-substituted higher fatty acids and glycerides, and other esters and mixtures thereof. In the grease preparations wherein the method of our invention is employed most advantageously, the saponifiable material comprises at least about 35% and preferably at least about 50% by weight of a hydroxy-fatty acid material. A particularly suitable class of saponifiable materials for this purpose are the lower alkyl (C -C esters of 12-hydroxystearic acid. We can also use, especially in minor amounts, fatty components derived from tallow, animal fat, etc.

For the lubricating oil component of the grease prepared in accordance with the invention we can employ any suitable oil having lubricating characteristics, including the conventional mineral lubricating oils as well as synthetic lubricating oils including oils prepared by cracking and polymerization, and other synthetic oleaginous compounds such as high molecular weight polyethers and polyesters having viscosities within the lubricating oil viscosity range. The dicarboxylic acid esters such as di-2-ethylhexyl sebacate, di-secondary amyl sebacate, di-2-ethylhexyl azelate, diisooctyl adipate, etc., are a particularly suitable class of synthetic oils. They can be employed as the sole oleaginous component of the grease mixture or in blends with other synthetic oils or mineral oils. However the oil employed in the saponification mixture is preferably one which is substantially inert under the saponification conditions if the soap is formed in situ during the process of our invention as more fully discussed below. Preferably, therefore, the lubricating oil component is a mineral lubricating oil. Suitable mineral oils for use in the greases prepared by our process are those having viscosities in the range from about seconds to about 2,000 seconds Saybolt Universal at 100 F. and can be either naphthenic, or paraffinic in type, or blends thereof.

Additives of the usual types employed in lubricating compositions may also be present, such as oxidation inhibitors, corrosion inhibitors, tackiness agents, such as various high polymer materials, extreme pressure agents, etc. Suitable oxidation inhibitors include particularly those of the amine type, such as phenylalphanaphthylamine, diphenylparaphenylenediamine, tetramethyldiaminodiphenyl methane and bis(2-hydroxy-3-tbutyl-5-methylphenyl)- methane. With particular advantage, a surface active agent of the type which imparts water resistant properties to inorganic solids may be employed, such as quaternary ammonium salts of fatty acids, polyglycol ethers, metal alkyl sulfates or sulfates or sulfonates, etc.

As indicated above, the process of our invention can be performed by forming the soap which coats the fiber in situ. This is done simply by providing a suitable saponifiable material, e.g., 12-hydroxystearic acid and a suitable metal saponifying agent, e.g., lithium hydroxide and including them in the mixture of lubricating oil.

During the heating of this mixture saponification will occur and, as this temperature is in excess of the boiling point of water, dehydration will also occur. After dehydration, the fiber is added and the mixture heated to a temperature within the range of from about 50 F. below up to about 30 F. above the melting point of the soap. When the mixture is cooled down by addition of additional lubricating oil to a temperature of about 200 F., and the mixture sheared, as by milling, there is provided a grease composition having excellent shear stability, excellent dispersion of fiber through the grease composition, and good water resistance. The grease is characterized particularly in its novelty by having the fiber coated with the soap. This same result is provided when the grease making process is performed using a preformed soap, e.g., lithium 12 hydroxy stearate, sodium 12- hydroxystearate or calcium 12-hydroxystearate. Electron photomicrographs of greases prepared by our process reveal soap fibers appearing curved and twisted together and coating the fibers. It is theorized that this coating renders the fibers oleophilic, resulting in a thickening agent which produces a shear stable, water resistant grease. The grease also retains a high dropping point typical of greases thickened with uncoated fibers, particularly in the case of asbestos thickened greases prepared by our process.

In carrying out the process of the present invention, it is necessary to heat the mixture of fiber, soap and oil to a temperature in the range of from about 50 F. below the soap melting point temperature up to about 30 F. above the soap melting point temperature for satisfactory results in terms of shear stability and water resistance. The use of temperatures below this range results in unsatisfactory grease compositions in relation to shear stability and water resistance.

The ratio of fiber to soap utilized in our invention is not particularly critical. One can, for instance, employ a ratio of fiber to soap between say 111-15 :1. Naturally, the ratio of fiber to soap will have some effect upon the yield, shear stability, water resistance and other properties of the finished grease. We have found that a fiber: soap ratio of from 2 to 7:1 provides excellent greases.

The weight ratio of the mixture of fiber and soap to lubricating oil is not particularly critical either, as the amount of fiberzsoap mixture in the total grease composition can range from say 3 to 25% by weight, preferably in the range of 4 to 15%. Consistency of the resultant grease is dependent to a large extent upon the type of shearing used in the final step in the preparation procedure. Much shear, such as milling, gives greatest yield (hardest consistency per amount of thickener), whereas shear by circulating through a partially closed valve gives poorer yield (softer consistency) but somewhat better shear stability.

In order to illustrate the nature of our invention, and the manner of practicing the same the following examples are presented. These examples include the best mode contemplated by us for carrying out our invention. Following these examples are tests which show the criticality of performing the grease making process according to the teachings of our invention.

EXAMPLE 1 An asbestos grease wherein the asbestos fibers were coated with lithium 12-hydroxystearate was prepared by mixing 14.3 parts by weight asbestos, 2 parts by weight of preformed lithium l2-hydroxystearate soap and 66.9 parts of a refined parafiinic residual mineral oil having an API gravity of 27.50 and an SUS viscosity at 100 F. of 118. This mixture was heated with stirring to 405 F., about 15 above the melting point of the soap, lithium l2-hydroxystearate, and held for minutes. Application of heat to the vessel containing the mixture was discontinued and 16.8 parts of additional mineral oil was poured into the vessel to quench-cool the composition to a temperature of about 350 F. It took about minutes to cool the composition to this temperature. The composition was then further cooled to 200 F. and milled to disperse the soap-fiber thickener and achieve a grease consistency. The resultant grease had good yield, shear stability and water resistance. Electron micrograph examination of the grease showed excellent dispersion of the asbestos fibers and indicated that they were coated with lithium l2-hydroxystearate. The improved shear stability, yield and water resistance of this grease indicate formation of a new thickener system formed by the interaction of the asbestos fiber and the lithium 12-hydroxystearate soap.

EXAMPLE 2 The grease thickened with an asbestoszsoap mixture was prepared as follows: 29.3 parts of the refined paraffinic residual mineral lubricating oil of Example 1, 5.0 parts asbestos fiber and 0.7 part lithium 12-hydroxystearate were charged to a grease kettle and heated with mixing to 405 F. The mixture was stirred for five minutes at 405 F. and then cooled at a rate of about 2 F. per minute. At 220 F., 20.4 parts of the same mineral lubricating oil was added over a 30 minute period. The batch was then milled with a Premier mill set at a 0.003 inch clearance. The properties of the grease S0 prepared are set forth in the table below.

EXAMPLE 3 A grease containing asbestos fiber and a mixed soap was prepared by mixing together 200 parts by weight asbestos fiber, 800 parts of the same refined, paraffinic residual lubricating oil, as in Example 1, and one hundred forty parts of a grease mixture prepared from 16.63% hydrogenated castor oil, 3.66% caustic soda, 0.32% hydrated lime and 0.50% diphenylamine and 78.89% of a blend of highly refined parafiinic distillate lubricating oils. The above mentioned ingredients were mixed together at room temperature. The mixture was heated to 325 F. to melt the sodium-calcium soap and 256 parts of the residual oil mentioned above was added to quench the batch and precipitate the soap. Fourteen parts of N-phenylalpha-naphthylamine was added when the grease had cooled to 250 F. The batch was then milled and the resultant grease was comparable in quality and properties to the grease of Example 1.

In contrast to these greases several other greases were made using different procedures:

COMPARATIVE EXAMPLE A Five parts of asbestos were mixed with 30 parts of the mineral oil of Example 1 at room temperature and the mixture was milled in a Premier Colloid mill at 0.033 inch clearance. The resultant grease was shear unstable and exhibited poor water resistance. The asbestos fibers cohered together and were not satisfactorily dispersed throughout the composition.

COMPARATIVE EXAMPLE B Five parts asbestos were mixed with 25 parts of the mineral oil of Example 1. The mixture was then heated to approximately 400 F., the heat turned off and 6 additional parts of the mineral oil added for rapid cooling or quenching. The batch was allowed to cool to 200 F. and then milled. This procedure resulted in a grease having improved water resistance over the grease prepared according to Comparative Example A. This improvement resulted in better dispersion of the asbestos fibers in the grease composition as revealed by electron micrograph but the grease had poor shear stability as shown by the high yields, particularly after 100,000 strokes and was unsatisfactory in the Shell Roll Test results.

COMPARATIVE EXAMPLE C Twelve parts asbestos and 1 part lithium 12-hydroxystearate were mixed with parts of the mineral oil of Example 1 containing 1.2% N-phenyl-alpha-naphthylamine oxidation inhibitor. The mixture was then milled. The resultant grease showed some improvement in water resistance over the grease made with asbestos alone at roorntemperature (Comparative Example A). However, no improvement in shear stability was achieved.

COMPARATIVE EXAMPLE D Modifying the grease preparation procedure of Comparative Example C by increasing the concentration of lithium 12-hydroxystearate to 2 parts did not significantly affect the properties of the grease. An electron micrograph of this grease composition and of the grease composition prepared according to Comparative Example A shows that the incorporation of lithium soap into the asbestos thickened grease had little if any beneficial effect on the dispersion of the asbestos fibers.

Table A below shows the comparative results of the greases prepared according to Examples 1 and 2 versus the greases obtained by the procedures of Comparative Examples A-D.

From the results in Table A it will be seen that the grease compositions of Examples land 2 are significantly better greases than the greases of the prior processes, particularly with respect to their shear stability and water resistance. The present process enables the preparation of a shear stable, water resistant high dropping point grease having inherent extreme pressure (EP) properties and hence is more economical than greases heretofore used containing additional chemical additives to provide extreme pressure properties thereto.

6 worked grease was determined using half scale cone and shaft.

The Percent Water Absorption test was performed as follows:

Known increments of water (e.g., 2 ml.) were added under stipulated conditions to gram sample of grease which was being stirred at a specific rate of 1200 rpm. The end point (Percent Water Absorption) was taken as that point at which free water was observed at the end of one minute stirring. Color, texture and/ or consistency was taken on the grease at the end point and compared with value of the original sample.

The criticality of the processing temperature in the preparation of the grease composition is shown by the following examples.

COMPARATIVE EXAMPLE E AND EXAMPLES 4 AND 5 A series of grease compositions were prepared from a mixture of 1.1% lithium 12-hydroxystearate soap, 8.0% asbestos fibers, and 90.9% by weight of a refined paraffinic mineral oil having an API gravity of 27.5 and an SUS viscosity at 100 F. of 118. The above components were charged to a grease kettle and heated with stirirng to a selected processing temperature shown in Table B, below, and then cooled with continued stirring to a temperature of 120 F. below the upper processing temperature. The cooled grease was spread on a tray, allowed to further cool to room temperature, and finished by milling through a colloid mill.

TABLE A Compar- Compar- Compar- Comparative ative ative ative Example 1 Example 2 Ex. A Ex. B Ex. 0 Ex. D

Grease of composition, wt. percent:

As estos 14. 3 9. 02 14. 3 14.3 14. 3 14. 3 Lubricating oil 83. 7 89. 71 85. 7 85. 7 83. 5 82. 4 Lithium 12-hydroxy stearate 2. 0 1. 1.2 2. 3 N-phenyl-alpha-naphthylamine r 1. 0 1. 0

Preparation temperature, F Tests, (ASTM 217-48), Penetration:

Unworked Worked strokes.

100,000 strokes (ASTM D2265-64T) Dropping point, F. Shell roll, 4 lir., room temperature:

Point change Percent water absorption Penetration before Penetration end point Percent water washout at 100 F.. Mean Hertz load i 4-ballllvear, 75, 1 hr., 600 r.p.m.:

1 Room temperature. 2 Described below.

3 Soup.

4 None.

5 Trace oil.

The Shell Roll test was used to determine the shear 65 grease. At the end of 4 hours, the consistency of the 75 TABLE B Example No.

Top processing temperature F 325 350 400 Penetration:

60 strokes 375 308 298 100,000 strokes 300 336 324 Water absorption, percent... 150 180 Water washout, percent 6. 6 2. 9 l. 1

(Melting point of lithium lzhydroxystearate, about 400 F.)

Table B above shows that grease compositions of Examples 4 and thickened by lithium 12-hydroxystearate coated asbestos fibers exhibited good yields (penetration values at 60 strokes) with consistencies between a NLGI No. 1 and No. 2 grade. They also showed good shear stability by maintenance of a NLGI No. 1 grade consistency after being worked 100,000 strokes. In contrast, the grease of Comparative Example E exhibited a worked penetration at least 20% softer than the grease of Examples 4 and 5.

The water resistance of the grease compositions of the present invention is shown in the Table B to be superior to that of Comparative Example E, by the results of the Water Absorption and Water Washout tests. In particular the results shown for Example 5 are outstanding in comparison to the results in Example E.

Similar results are obtained by variations in the procesing procedure, i.e., by omitting the milling step and also by cooling the greases statically to room temperature before milling.

COMPARATIVE EXAMPLES F AND G AND EXAMPLES 6 AND 7 Another series of grease compositions were prepared in the manner described above (Comparative Example E and Examples 4 and 5) employing 1.4% lithium 12-hydroxystearate, 10% asbestos and 88.6% by weight of the same mineral oil. The top processing temperatures are shown in Table C below. These greases were not milled 2 Unable to obtain results.

The above Table C demonstrates that the grease compositions of Examples 6 and Z were satisfactory since they softened only 8 and 12 points respectively, in penetration after 100,000 strokes whereas the greases of Comparative Examples F and G were unsatisfactory, having become too soft to measure after 100,000 strokes.

Additional evidence to support the shear stability of the greases of the present invention is found in the Shell Roll test results.

The grease of Example 6 hardened 22 points and in Example 7 13 points while no measurable results could be obtained for the greases of Examples F and G.

COMPARATIVE EXAMPLES H TO K AND EXAMPLE 8 A series of grease compositions were prepared from a mixture of 1.1% sodium stearate, 8% asbestos fibers and 90.9% by weight of the same mineral oil of Example 1. The various mixtures were heated to the processing temperatures shown in Table D, cooled statically to room temperature then milled in a colloid mill. The results of penetration tests are shown in Table D.

The data in the above table for 100,000 stroke penetration show that only the grease composition of Ex- 8 ample 8 is shear stable. The remaining greases have 100,000 stroke penetrations of 440+ or indicating the grease had been reduced to a pourable soupand consequently were unsatisfactory greases.

COMPARATIVE EXAMPLES L AND M AND EXAMPLES 9 TO ll Following the procedure of Examples H-K and 8 above, a series of grease compositions were prepared using magnesium stearate as the soap. These greases were cooled statically and milled in a colloid mill.

The processing temperatures and test results are shown in Table E.

The penetration results shown above for Examples 9-11 show the magnesium stearate greases prepared by the process of the invention are shear stable as is evidenced by the very small differences in penetration values 5, 12 and 8 points, respectively, as compared to the 25 and 66 points in increased penetration for the greases of Comparative Examples L and M. These latter greases are of inferior shear stability.

The terms and expressions which have been employed are used as terms of description and not of limitation as there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

We claim:

1. A process for the preparation of lubricating grease composition having improved shear stability and water resistance which comprises forming in an oil of lubricating viscosity a dehydrated admixture of 3 to 25% by weight of the composition of a metal soap and a soap wettable uncoated fibrous inorganic material wherein the weight ratio of uncoated fiber to soap is 1 to 15 parts of fiber per part of soap, heating said admixture to an elevated temperature in the range of from about 50 F. below the melting point temperature of the soap up to about 30 F. above the melting point temperature of the soap, then cooling said heated admixture by the addition of a portion of said lubricating oil in the finished grease composition to coat said fibers with said soap and shearing the resulting cooled admixture.

2. A process as claimed in claim 1 wherein the mixture of soap and fiber in said lubricating grease composition in between 5 and 15% by weight, the mixture is heated to a temperature in the range from 50 F. below to 10 F. above the soap melting point temperature, and the resulting cooled mixture is sheared at a temperature between F. and 350 F.

3. A process according to claim 2 wherein said fiber is asbestos fiber.

4. A process according to claim 2 wherein said soap is lithium l2-hydroxystearate.

5. A process according to claim 2 wherein said soap is a mixture of calcium and sodium soap of hydrogenated castor oil.

6. A process according to claim 2 wherein a mixture of lithium 12-hydroxystearate and asbestos fiber in lubricating oil is heated to a temperature of from about 20 F. below up to about 15 F. above the melting point of the lithium 12-hydroxystearate, the so-heated mixture is cooled and the resulting mixture is sheared at a temperature of about 200 F.

7. A process for the preparation of an anhydrous grease composition having improved shear stability and water resistance comprising the steps of:

(a) forming in a dehydrated oil of lubricating viscosity an admixture of 3 to 25% by weight of the grease composition, of a metal soap and uncoated fibrous asbestos wherein the weight ratio of asbestos to metal soap is from 1 to 15 parts of fiber per part of metal soap, and

(b) heating said admixture to a temperature ranging from about 50 F. below the melting point of the metal soap to about 30 F. above the melting point of the soap, until said asbestos fibers are coated with said metal soap, and

(c) cooling said heated admixture by the addition of at least a portion of said lubricating oil and shearing the resulting lubricating oil of grease viscosity to its desired consistency.

8. The grease product produced by the process of claim 7.

9. A process for the preparation of dehydrated lubricating grease compositions thickened with metal soapcoated, fibrous chrysotile asbestos, said soap having been prepared in situ from its component parts in the absence of said asbestos, comprising the steps of:

(l) forming in the presence of oil of lubricating viscosity, a mixture of:

(a) at least one metal saponifying agent selected from the group consisting of hydroxides, oxides and carbonates of alkali metals and alkaline earth metals, and mixtures of these metal saponifying agents,

(b) at least one saponifiable material selected from the group consisting of stearic acid, hydrogenated castor oil, l2-hydroxystearic acid, the lower alkyl esters of 12hydroxystearic acid and mixtures of these saponifiable materials, said metal saponifying agent and saponifiable material being present in amounts suflicient to comprise 10 from about 1 to 13% by Weight of the final weight of said grease composition as soap,

(2) heating the mixture of oil, metal saponifying agents and saponifiable material at a temperature and for a time suflicient to produce the corresponding metal soap in situ in a dehydrated environment.

(3) adding uncoated fibrous chrysotile asbestos to said heated, dehydrated oil-soap mixture, said asbestos being added in amounts sufiicient to result in a weight ratio of asbestos to soap from 1 to 15 parts 'by weight of fiber per part of metal soap.

(4) heating said dehydrated mixture of oil-metal soapasbestos to a temperature within the range of from about 50 F. below the melting point of the soap, up to about 30 F. above the melting point of the soap, until said fibrous asbestos is coated with said metal soap,

(5) adding sufiicient oil of lubricating viscosity with cooling to produce a dehydrated mixture having a final oil concentration of from about 3 to 97% by weight, and

(6) shearing the resultant cooled lubricating compositions to produce the desired dehydrated grease composition.

10. The grease product produced by the process of claim 1.

11. The grease product produced by the process of claim 9.

References Cited UNITED STATES PATENTS 2,028,155 1/1936 Hodson 252-21 3,010,896 11/1961 Odell et a1. 252-13 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R. 252-2l