US 3361670 A
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United States Patent Office 3,3615% Patented Jan. 2, 1958 3,361,675) LUBRICANTS AND ANTIGXIDANTS THEREFQR Bruce W. Hotter], Orinda, Calih, assignor to Chevron Research Company, San Francisco, Calif., a corporation of Delaware N Drawing. Filed Sept. 20, 1965, Ser. No. 488,780 Claims. (Cl. 252-421) This invention relates to grease compositions and as antioxidant additives therefor, novel polyaryl ureas. More particularly, it relates to greases which are thickened by metal-soap type thickeners which tend to promote oxidation, these greases being inhibited from oxidation by the polyaryl polyureas.
Lubricants which are employed in present-day machinery, such as automobiles, etc., are becoming increasingly subject to attack by oxidation due to the severe operating conditions encountered in the machines. In particular, the increased speeds, pressures, and correspondingly high temperatures at which the machines are operated produce these results. The consequences of oxidative attack, a buildup in oxidative products in the lubricant and a loss in lubricity result in increasing Wear upon parts being lubricated and often in early failure of the equipment.
The aforementioned effects of oxidation are particularly pronounced in the case of greases, and, more specifically in the case of greases which are thickened by metal ion-containing substances, such as soaps, etc. A most particular case in point are the greases which are gelled by lithium soaps. These greases are most often employed in high temperature applications, due to their extremely high dropping points. Thus, the combination of high temperature and the presence of metallic ion in the compositions subjects the lubricant base to extreme conditions of oxidation. Many conventional anti-oxidants are ineffective in these applications. For example, phenolic and sulfur-containing antioxidants which are often used to inhibit oxidation in lubricating oils are of little effectiveness in these compositions. While diaryl amines have been used in inhibiting metal-containing greases, and they are effective antioxidants, they are usually quite toxic and are often corrosive to copper parts with which the grease is contacted.
It has now been found that metallic-soap thickened grease compositions, highly resistant to oxidation and greatly reducing wear of lubricated surfaces, result from the inclusion in said composition of a minor amount of a polyaryl polyurea of the formula:
wherein n is 3 to 8; R R and R are hydrocarbyl radicals of 1 to 24 carbon atoms; and x, y and z are 0 to 1. Thus, the antioxidant compounds of this invention are ring-substituted aryl carbamido derivatives of a compound having alternate methylene and phenylene radicals in a chain-like structure. Thus, the compounds may be prepared by reacting a suitable amine with a ring-substituted pol-yisocyanate or by reacting an isocyanate wlth a polyamine in which the amino groups are on a suitable poly- (phenylmethylene) chain. It is preferred that there be from about 3 to 8 phenylene groups in the chain.
The additives of this invention are most conveniently prepared by the reaction of aniline or hydrocarbyl-substituted aniline with a poly(phenylmethyleneisocyanate). An example of a suitable and preferred isocyanate is a material designated poly(alkylphenyl) polyisocyanate, or PAPI, sold by the Carwin Company is a material having an average of 4 to 5 phenylmethylene groups per molecule. The amines which are reacted with the isocyanate are aryl amines, either unsubstituted or substiuted on the rings by hydrocarbyl groups of from 1 to 24 carbon atoms. Illustrative materials are aniline, and various alkyl-substitued anilines, such as methyl, ethyl, propyl, dodecyl, tridecyl, etc. anilines. An example of preferred material is dodecyl aniline. Also suitable are polyalkylsubstitued analines such as dimethylaniline, di(dodecyl) aniline, etc.
The polyaryl polyureas are prepared by reacting the isocyanates and amines. This reaction can be effected by simply mixing the materials together; however, heating will speed the reaction. The materials are reacted in such proportions that at least one amine group is present for each isocyanate group. Thus, molar ratios of from about 3 to 1 up to about 8 to 1 are employed.
The materials are employed in the grease compositions in amounts sufiicient to inhibit oxidation. Amounts of from 0.01% to 5% by weight are preferred. Examples of the grease thickeners which are employed in the compositions of this invention include the metallic soaps which are usually the salts of saturated fatty acids containing more than 10 carbon atoms (stearic, palmitic, lauric, etc.) and the salts of oleic acid, an unsaturated fatty acid. The metallic ions which are employed include aluminum, barium, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, nickel, silver, strontium, thallium, tin, and zinc. The materials which are especially useful in the compositions of this invention are the soaps of lithium, often employed because the soaps are high melting and are thus useful in high temperature application, and where susceptibility to oxidation becomes quite important. An example of a highly useful soap is a lithium stearate soap.
The oleaginous lubricants which comprise the bases for the compositions of this invention are those oily or greasy materials most commonly employed in lubrication. Examples of these materials are natural and synthetic oils and greases made from these oils. Base materials which are not suitable for the compositions of this invention and are not classified as oleaginous lubricants are those inorganic substances sometimes used in lubrieating functions, such as molybdenum disulfide, tungsten disulfide, graphite, ground glass, ground basalt, etc.
The oils which can be used as base oils for the compositions of this invention include a Wide variety of luricating oils, such as naphthenic-base, paraffin-base and mixed-base lubricating oils, other hydrocarbon lubricants, e. g., lubricating oils derived from coal products, and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and the mixtures thereof), alkylene oxide-type polymers (e.g., alkylene oxide polymers prepared by polymerizing alkylene oxide, e.g., propylene oxide polymers, etc., in the presence of water or alcohols, e.g., ethyl alcohol), carboxylic acid esters (e.g., those which were prepared by esterifying such carboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenylsuccinic acid, fumaric acid, maleic acid, etc., with the alcohols such as butyl alcohol, hexyl alcohol, 2-ethylhexy1 alcohol, pentaaerythritol, etc.), liquid esters of acids of phosphorus, alkylbenzenes, polyphenyls (e.g., biphenyls and terphenyls), alkylbiphenyl ethers, polymers of silicon, e.g., tetraethyl silicate, tetraisopropyl a silicate, tetra(4-methyl-2-tetraethyl) silicate, hexyl(4- methyl-Z-pentoxy) disiloxane, poly(methyl) siloxane, and poly(methylphenyl) siloxane, etc.
The base oils can be used individually or in combinations, whenever miscible or wherever made so by use of mutual solvents.
The following examples illustrate the preparation of In addition to the subject inhibitors described in this application, the lubricating compositions of this invention may also contain other lubricating oil and grease additives, such as oiliness agents, extreme pressure agents, oxidation inhibitors, rust inhibitors, corrosion inhibitors, viscosity index improving agents, dyes, lubricating oil detergents, etc.
the polyurea antioxidants of this invention. The examples are only illustrative and are non-limiting.
Example 1 A 65 g. portion (0.5 equivalent) of poly(phenylmethyleneisocyanate) having an average of four to five phenylmethylene units was mixed at room temperature with 131 g. (0.5 mol) of dodecylaniline. An exothermic reaction resulted, and the material was heated with mixing to 180 C. and held for 60 minutes until completed. The resultant product was 184 g. of a resinous material having a melt- TABLE I Concentra- Bomb Bearing Life Antioxidant Additive tion, Weight Oxidation, (Geometric Mean) Percent p.s.i. drop None 27 53; 236; 376 (170). Zinc dibutyltlliocarbamat 2 -3. 3 196; 76 (132). Plwnyl-anaphthylamlnm 2 (79 Polyarylpolyurea 2 1,183; 746 (940).
I claim: I. A polyarylpolyurea of the formula: H cH. H
NHGQNH ing temperature in the range of 130 to 160 C.
In order to demonstrate the effectiveness of the compounds of this invention in reducing oxidation of a grease and increasing bearing life of bearings lubricated by the grease, greases containing small quantities of the material were subjected to a bomb oxidation test and a hearing life test.
The mob oxidation test, ASTM D-942-50, briefly involves placing a 20 g. sample of the grease in a bomb, and subjecting the sample to an initial pressure of 110 p.s.i. of oxygen at 200 F. for 100 hours and then measuring the pressure loss at the end of the period. In general, the higher absorption of oxygen indicates greater oxidation of the sample.
The bearing life test used is known as the Navy High Speed Bearing Test and is described in Federal Test Method No. 331.1. In this test, a ball hearing was operated at 10,000 r.p.rn. continuously for approximately 22 hours at 300 F. while being lubricated with the subject grease sample. The apparatus was then cooled to room temperature during a period of two hours. This procedure of operating and cooling was repeated until there was hearing failure. The number of hours to bearing failure is indicated as Bearing Life.
The table following shows the results of the abovementioned test. The base grease was a synthetic oil (bis- 2-ethylhexyl sebacate) thickened with 15% by weight of a lithium stearate soap. The Bearing Life for each sample and the geometric mean of the Bearing Life are given. Comparative data for an uninhibited grease and greases inhibited with conventional antioxidants, zinc dithiocarbamate and phenyl-a-naphthylamine, are included (see Table I).
As noted from these data, the zinc dibutylthiocarbamate actually gave a lower bearing life than uninhibited grease, and the polyaryl polyurea of this invention gave a Bearing Life significantly higher than either the thiocarbamate or the phenyl-ix-naphthylamine, which, as previously mentioned, is a highly toxic material.
In addition to the particular usefulness of the polyarylureas as oxidation inhibitors in greases, they are also useful as antioxidants in other lubricants such as in lubricating oils used in machinery and automotive applications. Examples of such oils are those previously described as suitable bases for the greases of this invention.
wherein n is 3 to 8; R R and R are hydrocarbyl radicals of l to 24 carbon atoms and x, y, and z are 0 to 1.
2. The polyarylpolyurea of claim 1, wherein n is 4 to 5 and R R and R are alkyl groups.
3. The polyarylpolyurea of claim 2, wherein x is 1, y and z are 0.
4. The polyarylpolyurea of claim 3, wherein R is an alkyl group of 6 to 20 carbon atoms.
5. The polyarylpolyurea of claim 4, wherein R is a dodecyl group.
6. A lubricating composition comprising an oleaginous lubricant base and in an amount sufiicient to inhibit oxidation a polyarylpolyurea of the formula:
wherein n is 3 to 8; R R and R are hydrocarbyl radicals of 1 to 24 carbon atoms and x, y, and z are 0 to 1.
7. The composition of claim 6, wherein R R and R are alkyl groups.
8. The composition of claim 7, wherein x is 1 and y and z are 0 and R is an alkyl group of 6 to 20 carbon atoms.
9. The composition of claim 6, in which the oleaginous lubricant base is a metal soap thickened grease.
10. The composition of claim 9, in which the grease is a lithium soap thickened grease.
References Cited UNITED STATES PATENTS 7/1954 Hill et al. -a 25251.5 5/1959 Katz 26O77.5