US3159577A - Grease containing polytetrafluoroethylene - Google Patents

Description

United States Patent 3,159,577 GREASE CGNTAINING PDLYTETRAFLUORO- 'ETHYLENE Henry A. Ambrose, Penn Hills, and Paul R. McCarthy,

Allison Park, Pa, assignors to Gulf Research 8: Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Dec. 23, 1959, Ser. No. 861,449 1 Claim. (CL 252-28) This invention relates to lubricating compositions and more particularly to thickened lubricants suitable for use on bearings operating at high temperatures and high rotational speeds.

The trend in design of modern engines has accentuated 'the need for lubricants which will lubricate anti-friction bearings operating at high rotational speeds and high temperatures. While considerable progress has been made in producing lubricants which will effectively lubricate bear ngs operating at high temperatures, some difiiculty has been experienced in producing a lubricant which will also etfectively lubricate bearings operating at high rotational speeds for prolongedperiods of time. Conventional liquid lubricants because of their tendency to be thrown from a fast rotating bearing 'by centrifugal force have failed to meet the stringent requirements on such lubricants.

We have'discovered that a lubricating composition having satisfactory lubricating characteristics for an extended period of time when used to lubricate bearings operating at an elevated'temperature and 'a hi'gh rota-. tional speed canbe obtained by incorporating a small amount ofa tetrafluoroethylene polymer into an oil thickens/d to a consistency of a grease with an oil thickening agent. The improved lubricating composition of our invention therefore comprises a'major amount of alubricating oil thickened to a grease consistency with an oil thickening agent and having incorporated therein a small amount of a tetrafluoroethylene polymer.

The lubricating oil in which the thickening agent and the tetrafiuoroethylene polymer are incorporated is preferably a lubricant of the type best suited for the particular use for which the ultimate composition isdesigned. Since many of the properties possessed by thelubricating oil are imparted to the ultimate lubricating composition, we advantageously employ an oil which is thermally stable at the contemplated lubricating temperature. Some mineral oils, especially hydrotreated mineral oils, 'are sufliciently stable to provide alubricating base for preparing lubricants to be used under moderately elevated-ternpreferred class of lubricating bases because of their high thermal stability. By the term synthetic oil we mean an oil of nommineral origin. The synthetic oil can be an organic ester which has a majority of the properties of a hydrocarbon oil of lubricatinggradesuch as di-Z-ethylhexyl sebacate, dioctyl .phthalate and dioctyl azelate. Instead of an organic ester, we can use polymerized olefins, copolymers'of alkylene glycols and alkylene oxides, polyorgano siloxanes and the like. 7 ,1

The liquid polyorgano siloxanes because of their exceedingly high thermal stability form a preferred group of synthetic oils to which the oil thickening agent and thetetrafluoroethylene polymer are added. These polyorgano siloxanes are known commercially as silicones and are made up of silicon and oxygen ,atomswherein 3,5 9,577 Patented Dec. 1, 1964 compounds are the dimethyl silicone polymers, diethyl silicone polymers, ethyl-phenyl silicone polymers and methyl-phenyl silicone polymers.

In those instances where'a mineral oil is used as the base 011, it may be a refined or semi-refined paratfin'io,

naphthenic-, or asphalt-base oil having a viscosity of about 50 to 4000 'SUS at 100 .F. The viscosity of the oil has little effect on the dropping point of the ultimate lubricating composition, but the more viscous oils produce compositions having greater stickiness and adhesive properties than do the lighter viscosity oils. If desired, a blend of oils of suitable viscosity may be employed as the lubricating oil base instead of a single oil by means of which any desired viscosity may be secured. Therefore, depending upon the particular use for which the ultimate composition is designed, the lubricating oil base may be a mineral oil, a synthetic oil, or a mixture of mineral and/or synthetic oils. Although the lubricating oil content of the compositions prepared according to this invention preferably comprises about 80 to about 95 percent by weight of the total composition, it can be present in amounts as low as 50 percent and as high as 97 percent.

The tetrafluoroethylene polymer employed in the lubricating composition of the present invention is itself wellknown 'in the art. Polymerized' tetrafluoroethylene and a method of preparing it, for example, are disclosed and claimed in'U.S. Patent No. 2,230,654 which issued on February l, 1941, to Roy J. Plunkett. Polymerized tetrafluoroethylene is generally obtained as a white or brown powder or jelly which rapidly changes to a powder. The polymer is insoluble in the usual solvents including hot and cold water, acetone, ether, petroleum ether, ethyl alcohol, isoamyl alcohol, carbon tetrachloride, C F Cl dichlorobenzene, ethyl acetate, pyridine, nitro- V benzene, 30 percent aqueous sodium hydroxide, petroperatures. Where temperatures in the order of 400 and above are to be encountered, synthetic oils form .a.

thesilicon atoms may be substituted with alkyl, aryl, -al- '1 leum oil, glacial acetic acid, concentrated sulfuric acid and concentrated nitric acid. It is inert to the usual chemical reagents and does not burn. It is a crystalline material which undergoes a reversible transition at temperatures above about325 F.

In preparing the lubricating com-position of the invention, we can use either powdered polymerized .tetrafiuoroethylene or aqueous polytetrafiuc-roethylene dispersions containing from about 25 percent to about percent by weight of polytetrafluoroethylene. Suitable concentrated aqueous colloidal dispersions and a process for. preparing them are disclosed and claimed in US. Patent No. 2,478,229, which issued to Kenneth L. Berry on August 9, 1949. According tothe patent concentrated aqueous colloidal dispersions of polytetrafiuoroethylene may be obtained by polymerizing tetrailuoroethylene in the presence of water, adding a surface-active agent to the dilute suspension, fiocculating the polymer by insolubilizing the surface-active agent, separating the-flocculated polymer and a small proportion of the aqueous phase from the bulk of the aqueous phase and then peptizing the fiocculated polymer. While the polytetrafluoroethylene may comprise about 0.5 to about 45 percent by weight of the total composition, We prefer to use amounts in the order of about 0.5 toabout 10 percent by weight. should be understood, however, that 'dependingupon the properties desired inthe ultimate composition less than 0.5 percent or more than 45 percent'of the polytetr'afluord 3 selves known in the art and do not, per se, constitute a part of the invention. These agents, for example, are exemplified by soaps of fatty acids and organophilic siliceous materials. employed may vary over wide limits depending upon the thickening agent which is used, the particular oil with which the thickening agent is blended and upon the properties desired in the ultimate composition. While the oil thickening agent may comprise about 0.5 to about 45 percent by weight of the total composition, we prefer to use amounts in the order of about 2 to about 25 percent by weight. In any case, the thickening agent is dispersed in the oil in an amount sufiicient to produce a composition having the consistency of a grease.

The weight ratio of thickening agent to polytetrafluoroethylene is advantageously between about 0.5 :1 and about 20:1. In some instances the ratio of thickening agent to polymer may be as much as 50:1. However, for optimum improvement the ratio of thickening agent to polymer in any particular case depends upon the characteristics of the oil used and the characteristics desired in the final composition. When the oil thickening agent is an organophilic siliceous material such as, for example, dimethyldicetyl ammonium bentonite, a particularly advantageous lubricating composition results when the weight ratio of the bentonite compound to polytetrafluoroethylene is between about 1:1 and about 4:1. Thickened lubricants having superior performance lives in bearing tests are obtained when the weight ratio of the bentonite compound to polymer is about 2:1 to about 3:1.

Typical soap-type thickening agents include the metal soaps of fatty acids such as, for example, the sodium, lithium, copper, magnesium, calcium, zinc, strontium, barium, aluminum and lead soaps of fatty acids having 12 to 24 carbon atoms. The. acids may be saturated or unsaturated and may contain substituents such as hydroxyl groups. Aliphatic acids are generally preferred. Examples of the aliphatic acids are lauric, myristic, palmitic, stearic, hydroxystearic, oleic, linoleic, linolenic, arachidic, behenic, lignoceric and selacholeic acids. Mixtures of these acids or mixtures obtained by saponification of natural fats such as cottonseed oil, lard, tallow, castor oil, fish oil, hydrogenated fatty oils, especially the fatty acids derived from hydrogenated animal, vegetable and marine oils known commercially as the Hydrofol acids may be used. The soap is formed by saponifying the acid or the fat with a base such as, for example, sodium, lithium, calcium, barium or strontium hydroxide.

Typical non-soap oil thickening agents which can be employed in the lubricating composition of the invention are exemplified by bentonite-organic base compounds known commercially as Bentones and finely divided organo-siliceous solids such as the esterified siliceous solids known commercially as Estersils.

Typical bentonite-organic base compounds employed in accordance with the invention are compounds composed of a montmorillonite mineral in which at least a part of the cation content of the mineral has been replaced by an organic base. Clays that swell at least to some extent on being contacted with water and contain as a primary constituent a mineral of the group known as montmorillonites are generally referred to as bentonites. Such clays, which contain exchangeable alkali metal atoms either naturally or after treatment, constitute the raw materials employed in making the bentonite-organic base compounds used in the compositions of this invention. So far as known, all naturally occurring montmorillonites contain some magnesium and certain of them, as exemplified by Hector clay, contain such a high percentage of magnesium that they largely have magnesium in place of the aluminum content characteristic of the more typical montmorillonites.

The bentonite-organic base compounds are preferably prepared as described in US. Patent No. 2,033,856, issued March 10, 1936, to Claude R. Smith, by bringing together the bentonite and the organic base in the presence of aque- The amount of the oil thickening agent ous mineral acid to elfect base exchange. The organic bases should preferably be titratable with mineral acids. Among these reactive bases are many alkaloids, and cyclic, aliphatic, and heterocyclic amines. The bentonite-organic base compounds used in preparing the lubricating compositions of this invention are preferably those prepared by bringing together a bentonite clay and such organic bases as aliphatic amines, their salts, and quaternary ammonium salts. Examples of such amines and salts are: decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, hexadecyl ammonium acetate, octadecyl ammonium acetate, dimethyldioctyl ammonium acetate, dimethyldidodecyl ammonium acetate, dimethyldodecylhexadecyl ammonium acetate, dimethyldicetyl ammonium acetate, dimcthylhexadecyloctadecyl ammonium acetate, dimethyldioctadecyl ammonium acetate, and the corresponding chlorides and quaternary ammonium chlorides. The organic bases employed should be such as to impart substantial organophilic properties to the resulting compounds. The preferred bentonite compounds are prepared from quaternary ammonium compounds in which the N- substituents are aliphatic groups containing at least one alkyl group with a total of at least 10 to 12 carbon atoms. When aliphatic amines are used they preferably contain at least one alkyl group containing at least 10 to 12 carbon atoms.

While the long chain aliphatic amine bentonite compounds are readily dispersible in practically all oil bases, dispersion of the short or single chain aliphatic amine bentonite compounds, in the oil, particularly mineral oils and synthetic oils other than ester lubricants, can be facilitated by the use of one or more solvating agents. Suitable solvating agents are polar organic compounds such as organic acids, esters, alcohols, ethers, ketones, and aldehydes, especially low molecular weight compounds of these classes. Examples of suitable solvating agents are: ethyl acetate, acetic acid, acetone, methyl alcohol, ethyl alcohol, benzoyl chloride, butyl stearate, cocoanut oil, cyclohexanone, ethylene dichloride, ethyl ether, furfural, isoamyl acetate, methyl ethyl ketone, and nitrobenzene. In cases where the use of a solvating agent is desirable for effecting more rapid and more complete dispersion of the organic bentonite compound in the oil, ordinarily only a relatively small amount of such agent may be necessary. However, as much as about 50 percent by weight based on the amount of the bentonite compound can be used.

Typical estersils employed in acordance with the invention are described in US. Patent No. 2,657,149, issued October 27, 1953 to R. K. Iler. The estersils are organophilic solids made by chemically reacting primary or secondary alcohols with certain siliceous solids. In brief, the estersils are powders or pulverulent materials the internal structure or .subStrate" of which have an average specific surface area of from 1 to 900 square meters per gram. The substrate has a surface of silica which is coated with OR groups, the coating of OR' groups being chemically bound to the silica. R is a hydrocarbon radical of a primary or secondary alcohol containing from 2 to 18 carbon atoms. The carbon atom attached to the oxygen is also attached to hydrogen.

The estersil substrates are solid inorganic siliceous materials which contain substantially no chemically bound organic groups prior to esterification. The substrates are in a supercolloidal state of subdivision, indicating that whatever discrete particles are present are larger than colloidal size. In general, the supercolloidal substrates have at least one dimension of at least millimicrons. The supercolloidal particles may be aggregates of ultimate units which are colloidal in size.

The estersils which we employ are advantageously those in which the ultimate units have an average diameter of 8 to 10 millimicrons. The substrates advantageously have specific surface areas of at least 25 square meters per gram and preferably at least 200 square meters per gram.

comes in contact with water. When C to C alcohols are used in preparing the estersils, the estersils may contain from 300 to 400 ester groups per 100 square millirnicrons of substrate surface. Thus, a preferred group of estersils are those prepared from the C to C alcohols. The estersils, as noted above, are powders or pulverulent materials. The estersil powders are exceedingly fine, light and flufiy. The bulk density of preferred estersils is in the order of 0.15 to 0.20 gram per cubic centimeter at 3 pounds per square inch and in the order of about 0.30 gram per cubic centimeter at 78 pounds per square inch. The-estersils are available commercially and thus the este'rsils per se andtheir preparation constitute nopart of this invention.

In compounding the compositions of the present invention, various mixing and blending-procedures may be used. In preparing a soap-thickened lubricant, the soap may be prepared and then added to the oil, or the soap may be preparedin situ. According to one embodiment, for example, the tats and/or fatty acids are charged to an atmospheric or pressure type vessel and intimately mixed at a temperature below 200 F. After thorough 1 intermixture, the temperature is raised to between about 300 and about 400 F. to efiect saponification. After complete dehydration of the soap base, the soap is admixed with mineral oil While cooling to a temperature of 150 to 250 F. The polytetrafiuoroethylene in-the desired proportion is then added to the grease composition. The

product is adjusted to the desired consistency and then about 300 F. under a pressure of about 80 to about 90. pounds per square inch until saponification is complete.

The kettle contents are then transferred'to'an open kettle Where stirring is continued and the temperature raised to about 400 F. over a period of about one hour. The'ternpera'ture is maintained for an additional 30 minutes or until dehydration is substantially complete. The remainder of the oil and the polytetrafiuoroethyleneare then added and the mixture stirred and heated atabout 400 F. for an additional period to remove any water introduced with the'polytetrafluoroethylne. The" grease composition thus formed is cooled to about 200 to about 250 F. 'The cooled grease 'is'then'pmnpeatohomcgsnne or otherwise treated as in a colloid mill or similar device to give the desired degreeof dispersion. When the soap is prepared in situ, 'a small amount, i.e.', 1 to 3 percent by weight, of glycerin, particularly when an excess of saponifyi ng base is employed,increases the dropping point of the final grease composition.

In preparing a non-soap'thickened lubricant, the lubricating oil, the polytetrafluoroethylene and the organophilic siliceous thickener togethenwith a solvating agent 3 and conventional lubricantadditives, if .desired,:are mixed together at room temperature for a period of 10 to 30 period some thickening-is evidenced. Some lumps may be formed. I The slurry'thus formed is then subjected Thus, the products which contain "100 ester to-a conventional milling operation in a ball mill, a; colloid mill, 'homogenizer or similar device used in compounding greases to give the desired degree of dispersion.

The lubricating composition of this invention can contain conventional lubricant additives, if desired, to-improve other specific properties of the lubricant without departing-from the scope of the invention. Thus, the lubricating composition can contain a filler, a corrosion and rustinhibitor, an extreme pressure agent, an antioxidant, a metal deactivator, a dye, and the like. Whether or not such additives are employed and the amounts thereof depend to a large extent upon the severity of the-conditions to which the composition is subjected and upon the stability of the lubricating oil base in the first instance. Since the polyorgano siloxanes, for example, are in general more stable than mineral oils, they require theaddition of very little, if any, oxidation inhibitor. When such conventional additives are used they are generally added in amounts between about 0.01 and about 5 percent by weight based on the weight of the total composition.

In order to illustrate the lubricating characteristics at an elevated temperature and a high rotational speed, grease compositions of the invention were subjected to the'test procedure outlined by the Coordinating Research Council Tentative Draft (July 1954 Research Technique for the Determination of Performance Characteristics of Lubricating Grease in An-tifriction Bearings at Elevated Temperatures, C'RC Designation L-35. According to this procedure, 3 grams of the grease to be tested are placed in a bearing assembly containing an -ei'ght-ball 'SAE No. 204 ball hearing. The hearing asthis meansrhe temperature of the bearing can be main- "tained at a desired elevated temperature which. in'the tests reported hereinafter was 300 and 350 F. The

spindle is driven by a constant belt-tension motor drive assembly, capable of giving spindle speeds up to 10,000

- input power increases to a value approximately 300 peradded to the grease and homogenized.

' lubricating composition with a non-soap thickening agent, -theoi1, the .polytetrafluroethylene and the thickener were 'minutes to forrna slurry.. During this initial mixing cent above the steady state condition at the test temperature; '(2) an increase in temperature at the test hearing of 20 F. over the test temperature during any portion of a cycle; or (3) the test bearing locks or the drive belt slips at the start or during the test cycle.

The lubricating oil used in preparing illustrative lubricating compositions of the invention, comprised a'highly refined parafiinic mineral oil having as typical properties an APIgravity of 30.2, a viscosity of 303 SUS at F. and 53.9 SUS at 210 F., a viscosity index of 107, a fiashpoint of 420 F., a fire point of 530 F., and a pour point of +5 F. In preparing the lubricating composition with a soap-type thickening agent, the soap was prepared in situ. The polytetrafiuoroethylene was then In preparing the percent C and 90 percent C 'straight chain fatty acids.

As typical properties, Hydrofol has a titer of 64-65 'C.,-and iodine numberfof 3, an acid number of -199 and a saponification number of 196-200. The thickened lubricating compositions which were It has a viscosity at 65 F. of 3487 centistokes, at F. of 390 centistokes, at 100 F. of 71.3 centistokes, at 210 Table 1 Composition, percent By Weight A B C D E F Mineral lubricating oil 66.85 89.1 85.72 88 85.5 83 Polytetrafiuorethylcne powder 6.41 Aqueous colloidal dispersion of po ytetrafluorethylene (53.6% polytetrafluoroethylene) 1.0 4. 76 7.5 Dimethyldicetyl ammonium bentonite 9.9 9. 52 7 7.0 7 Hydrofol acids 150 21. 73 a Sodium hydroxide 3. 48 Glycerin 1. 63 Approximate ratio of thickener to polytetrafluoroethylene 4:1 18:1 4:1 3:1 2:1 1:1 Inspection:

Penetration (AS'IM D217-52T):

Unworked 220 210 207 2 275 256 Worked 300 223 255 249 282 268 Dropping Point, F. (ASTM D5664 387 450+ 450+ 450+ 450+ 450+ Performance Life, hours 10,000

r.p.m.:

At 300 F 808 1, 596 2, 544 775 At 350 F 240 140 384 95 103 The long performance life of the compositi ns f t F. of 22 centistokes and at 700 F. of 1.9 centistokes. invention at high temperatures and a g rotational speed Estersil GT is marketed by E. I. du Pont de Nemours lsilself-evldent from UR q f P li i 111 f i i and Company and consists of an amorphous silica coated W f t i fi P gl l 2 I b l l d with approximately 340 butoXy groups per 100 square i l g s gcg'g gga gf g g g iizi g 23 millimicrons of surface. The product is a White granular a P y g P Solid comprising 88 to 89 percent Si0 having an ultimate that the compositions wherein the ratio of thickener to particle Sizp of 8 to 10 minimicrons Th u f polytetrafiuoroethylene is about 2:1 to 3:1 (Compositions com rises a 285 to 335 S r ace area B and D, respectively) have superior performance lives at p Square meters Per F. The product has a pH in a -50 methanol-water mixture Other lubricating compositions within the scope of the of to and a bulk density of 19 to 20 Pounds 1 invention are illustrated in Table II. 35 cubic foot.

Table II Composition, Percent By Weight G H I J K L M N Mineral lubricating oil 93 92 91 88 9 9 8S Dimethyldioetyl ammonium bentonite 4 4 4 4 4 4 4 4 Polytetrailuoroethylene powder 1 3 6 Aqueous colloidal dispersion oi poly-tetrafluoroethylcne (53.6% polytctrafluoroethylene) 1 2 3 4 6 Methanol 1 1 1 1 1 1 1 1 Octylated diphenylamines dant) 1 1 1 1 1 1 1 1 Approximate ratio of thickener to polytetrafiuoroethylene 7:1 4:1 2:1 2:1 1:1 4:1 1:1 0.711 Inspection:

Penetration (ASTM D217-52T):

Unworked 314 330 309 333 338 316 318 295 Wor e 328 335 309 342 356 291 301 304 Dropp' g Point, F. (ASTMD5G6- Other lubricating compositions Within the scope of the DC 550 Fluid is a synthetic oil marketed by Dowinvention are illustrated in Table III. G. E. Silicone 81717 is marketed by General Electric Company and is 55 a water-White to amber liquid polymer of the general formula [-Si(CH OSi(CH OSi(CH O] Corning Corporation. This fluid is a methylphenyl-siloxane polymer having as typical characteristics a viscosity at F. of 300 to 400 SUS, a viscosity-temperature coeilieient of 0.75, a freezing point of 54 F., a flash point of 600 F. and a specific gravity 25 C./25 C. of 1.08.

Table III Composition, Percent By Weight Lubricating Oil:

DC 550 Fluid G.E. Silicone 81717- Di-2-ethylhexy1 sebacate.

Mineral oil.

Thickener:

Dimethyldicetyl ammonium hentonite Dimethyldidodecyl ammonium bentonite Dimethyldioetyl ammonium bentonite. Ditmetgilydioctadeeyl ammonium ben- Barium stearate Strontium stcarate Polytetrafluoroethylen Ratio of thickener t ethylene 9 i While our invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously practiced within the scope of the claimhereinafter made.

We claim:

A lubricating composition capable of functioning at 0.5 to about 45 percent by weight of an aqueous colloidal V dispersion of polytetrarfluoroethylene, said aqueous colloidal dispersion consisting of about 25 to about 75 per- 10 cent by weight of polytetrafiuoroethylene and about 75 to about 25 percent by weight of water, the weight ratio of the bentonite compound to the tetrafiuoroethylene polymer being about 2:1 to about 3:1.

References Cited in the file of this patent I UNITED STATES PATENTS 2,230,654 Plunkett Feb. 4, 1941 2,510,112 Holbr-ook June 6, 1950 2,679,479 Peterson et al May 25, 1954 2,742,428 Agens Apr. 17, 1956 3,011,975 Nitzsche et a l. Dec. 5, 1961 3,069,387 Allen et a1 Dec. 18, 1962