Patent GB-701636-A (GB)
Title: Improvements in and relating to lubricating greases
Filed: 1950-09-15
Abstract: A lubricating grease comprises a lubricating oil base and between 4 and 25 per cent. based on the weight of the grease, of a mixture of a metal soap of a "defined fatty acid" and a metal salt as a stabilising additive, the metal salt constituting from 4 to 14 mole. per cent. of the total soap plus salt content.  The "defined fatty acid" is an aliphatic monocarboxylic acid having 10 to 24 carbon atoms in the molecule and bearing no non-hydrocarbon groups closer than 9 carbon atoms to the carboxyl group and bearing no hydroxyl groups at all, such as the acids derived from vegetable, animal and fish oils.  Hydrogenated vegetable oil acids, oleic acid, stearic acid, linoleic and linolenic acids, and the acids derived from beef fat and tallow may be used.  Preferably an alkali metal soap may be used, but calcium, barium, aluminium and other metal soaps are permissible. Mixtures of different metal soaps of the defined fatty acids may be employed.  Specified soaps are sodium stearate, lithium oleate, calcium stearate, aluminium oleate, and barium linoleate. The stabilising additive is a metal salt of an organic monocarboxylic acid having 3 to 18 carbon atoms in the molecule and bearing a hydroxy, mercapto, amino, keto, thioketo, nitro or sulpho group less than 9 carbon atoms removed from the carboxyl group.  The acid may be of the alkane, cycloalkane or moncyclic aromatic series.  The preferred additives are the salts of hydroxy alkane, hydroxy cycloalkane, hydroxy monocyclic aromatic, monoketo alkane, monothioketoalkane, and monoaminoalkane monocarboxylic acids, the hydroxy, keto, thioketo or amino substituent group being attached less than 9 carbon atoms removed from the carboxyl group. Preferably the alkane monocarboxylic acids have substantially no branching in the hydrocarbon portion of the molecule, and the cycloalkane and aromatic acids are substantially free from branched chain substituents.  Lithium salts are preferred, but other metal salts, especially alkali metal salts, (sodium and potassium) may be used. The preferred stabilizing additives are the lithium salts of C3 to C18 monohydroxy alkane monocarboxylic acids wherein the hydroxyl group is in the beta, gamma or delta position to the carboxyl group. Such acids are the appropriate hydroxy substituted propionic, butyric, valeric, caproic, enanthic, caprylic, lauric, myristic, palmitic and stearic acids.  The corresponding mercapto acids may be used. Other specified additives are the lithium salts of 3-aminopropionic acid, 3-aminohexanoic acid, 3-aminopentanoic acid, 4-aminohexanoic acid, 5-aminodecanoic acid; the lithium, sodium, potassium, calcium and aluminium salts of pyruvic acid, propionyl carboxylic acid, acetoacetic acid, levulinic acid, acetobutyric acid and the corresponding thioketo acids; the metal salts of hydroxy naphthenic acids derived from petroleum such as p  the hydroxy derivatives of (3-ethyl-4-methyl-1-cyclopentanyl) - acetic, -butyric and -valeric acids; and the lithium, sodium, potassium, calcium and aluminium salts of o-, m- or p-nitrobenzoic acid, o-, m- or p-aminobenzoic acid, o-, m- or pmercaptobenzoic acid, o-, m- or p-hydroxybenzoic acid, mandelic acid, tropic acid, benzoyl formic acid and benzoylacetic acid.  Mixtures of the additives may be employed.  The lubricating oil may be a mineral oil, a natural oil (vegetable or animal) or a synthetic lubricant such as a polymerised olefin, polyalkylene oxide such as polypropylene oxide, polymerized sulphide such as polypropylene sulphide, polymerized glycol such as polypropylene glycol, an ester of a dicarboxylic acid such as bis-(2-ethylhexyl) sebacate or a phosphate such as tributyl and tricresyl phosphates. Mixtures of these lubricants may be employed. For high temperature greases, fluoro compounds and silicone oils may be used as part or all of the lubricating oil base.  Mineral oils having an aromatic content of 0 to 25 per cent. and especially between 0.1 and 1.0 per cent. are preferred.  Further the nitrogen content of the refined oil should be as low as possible.  Other additives such as anti-bleeding agents (glycol, glycerine) and antioxidants (p-phenylene diamine) may be present.  It is preferred to prepare the grease by the quench method as follows:- the acids are mixed with about one third of the oil, lithium hydrate added at about 100 DEG C. and raising the temperature to about 200 DEG C. to dehydrate the mixture.  The concentrate so formed is quenched by the addition of the remainder of the cold oil.  The mixture is reheated to about 190 DEG C. and cooled to room temperature with working.  In example 1 greases prepared from the lithium salts of hydrogenated fish oil acids, a turbine oil of viscosity 100 centistokes at 100 DEG F. and viscosity index of 55 and lithium 4-hydroxyvalerate, lithium 4-ketovalerate and lithium 3-hydroxypropionate are prepared and tested by the roll stability method.  Example II describes the preparation of a grease from mineral lubricating oil and the potassium salts of hydrogenated fish oil acids and a-amino-isocaproic acid.  Specification 701,637 is referred to.