Stabilizing compositions for lubricants
View Patent ↗A lubricant composition is disclosed that comprises lubricating oil and a mixture of at least two antioxidants, the first antioxidant being a substituted diphenylamine and/or a heterocyclic amine and the second antioxidant being a substituted phenol. Also disclosed is a method of increasing the oxidation stability of a lubricating oil comprising adding thereto at least two antioxidants, the first antioxidant being a substituted diphenylamine and/or a heterocyclic amine and the second antioxidant being a substituted phenol.
1. A lubricant composition comprising:
(A) at least one lubricating oil selected from the group consisting of natural and synthetic lubricating base oils;
(B) 0.1 to 5.0 weight percent based on the weight of the composition of at least one diphenylamine of the formula:
wherein R 1 and R 2 are independently selected from the group consisting of hydrogen, alkyl of 1 to 12 carbon atoms, styryl, and α-alkyl styryl, provided that at least one of R 1 and R 2 is not hydrogen; and
(C) 2,2′-thiobis(4-methyl-6-tert-butyl-phenol) wherein the weight ratio of the diphenylamine to 2,2′-thiobis(4-methyl-6-tert-butyl-phenol) is greater than 3:1.
2. The composition of claim 1 which also comprises an additional component selected from the group consisting of triaryl phosphate esters, tri-alkyl phosphate esters, alkyl mono-acide phosphates, alkyl di-Acid phosphates, alkyl phosphites, aryl phosphites, liquid phenolic antioxidants, aminic antioxidants, carboxylate esters, aromatic hydrocarbons, and liquid glycols.
3. A method of increasing the oxidation stability of a lubricant comprising adding thereto
(A) 0.1 to 5.0 weight percent based on the weight of the composition of at least one diphenylamine of the formula:
wherein R 1 and R 2 are independently selected from the group consisting of hydrogen, alkyl of 1 to 12 carbon atoms, styryl, and α-alkyl styryl, provided that at least one of R 1 and R 2 is not hydrogen; and
(B) 2,2′-thiobis(4-methyl-6-tert-butyl-phenol)
wherein the weight ratio of the diphenylamine to 2,2′-thiobis(4-methyl-6-tert-butyl-phenol) is greater than 3:1 and the lubricant is selected from the group consisting of natural and synthetic lubricating base oils.
4. The composition of claim 1 wherein the weight ratio of the diphenylamine to 2,2′-thiobis(4-methyl-6-tert-butyl-phenol) ranges from about 3:1 to about 4:1.
5. The method of claim 3 wherein the weight ratio of the diphenylamine to 2,2-thiobis(4-methyl-6-tert-butyl-phenol) ranges from about 3:1 to about 4:1.
6. The composition of claim 1 wherein R 1 and R 2 are independently selected from the group consisting of hydrogen methyl, ethyl and isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.
7. The composition of claim 1 wherein the diphenylamine is selected from the group consisting of nonylated diphenylamine; butylated, octylated diphenylamine; and octylated, styrenated diphenylamine.
8. The composition of claim 1 wherein the lubricating oil is selected from the group consisting of Group I, Group II and Group III API Base Oil Category base stocks.
9. The method of claim 3 wherein R 1 and R 2 are independently selected from the group consisting of hydrogen methyl, ethyl and isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.
10. The method of claim 3 wherein the diphenylamine is selected from the group consisting of nonylated diphenylamine; butylated, octylated diphenylamine; and octylated, styrenated diphenylamine.
11. The method of claim 3 wherein the lubricant is selected from the group consisting of Group I, Group II and Group III API Base Oil Category base stocks.