Lubricating oil composition

Abstract

The object of this invention is to offer a lubricating oil composition which has superior extreme pressure properties (ability to prevent welding), which generates a small amount of sludge and which also has a high viscosity index. The invention provides a lubricating oil composition to which has been added a copolymer of specified olefins and alkyl methacrylates.

1 . A lubricating oil composition comprising:
 (A) 50 to 90% by mass of a base oil selected from the group consisting of a Group II base oil, a Group III base oil, a Group IV base oil, and any combination thereof;   (B) 10 to 50% by mass of a copolymer of an olefin having from 2 to 20 carbons and an alkyl methacrylate having alkyl groups with from 1 to 20 carbons, wherein the copolymer has a molecular weight of from 1,200 to 50,000; and   (C) 5 to 15% by mass of a carboxylic acid ester compound.   
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the base oil is a polyalphaolefin or a GTL (gas-to-liquid) oil. 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the copolymer has a weight average molecular weight of from 7,000 to 20,000. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the carboxylic acid ester compound is a polyol ester. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein the lubricating oil composition has a kinematic viscosity at 40° C. of from 140 to 320 mm 2 /s, a viscosity index of not less than 150, and produces no more than 1,200 mg/kg of sludge in a Dry TOST test. 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . A method of lubrication comprising:
 supplying a lubricating oil composition to a surface in relative movement to another surface, wherein the lubricating oil composition comprises:   (A) 50 to 90% by mass of a base oil selected from the group consisting of a Group II base oil, a Group III base oil, a Group IV base oil, and any combination thereof;   (B) 10 to 50% by mass of a copolymer of an olefin having from 2 to 20 carbons and an alkyl methacrylate having alkyl groups with from 1 to 20 carbons, wherein the copolymer has a molecular weight of from 1,200 to 50,000; and   (C) 5 to 15% by mass of a carboxylic acid ester compound.   
     
     
         9 . The method according to  claim 8 , wherein the base oil is a polyalphaolefin or a GTL (gas-to-liquid) oil. 
     
     
         10 . The method according to  claim 8 , wherein the copolymer has a weight average molecular weight of from 7,000 to 20,000. 
     
     
         11 . The method according to  claim 8 , wherein the carboxylic acid ester compound is a polyol ester. 
     
     
         12 . The method according to  claim 8 , wherein the lubricating oil composition has a kinematic viscosity at 40° C. of from 140 to 320 mm 2 /s, a viscosity index of not less than 150, and produces no more than 1,200 mg/kg of sludge in a Dry TOST test. 
     
     
         13 . The method according to  claim 8 , wherein the surface is a gear. 
     
     
         14 . The method according to  claim 13 , wherein the gear is in an apparatus for wind-power generation of electricity. 
     
     
         15 . A method of lubrication comprising:
 supplying a lubricating oil composition to a surface of a gear, wherein the lubricating oil composition comprises:   (A) 50 to 90% by mass of a base oil selected from the group consisting of a Group II base oil, a Group III base oil, a Group IV base oil, and any combination thereof; and   (B) 10 to 50% by mass of a copolymer of an olefin and an alkyl methacrylate, wherein the copolymer has a molecular weight of from 1,200 to 50,000.   
     
     
         16 . The method according to  claim 15 , wherein the gear is in an apparatus for wind-power generation of electricity. 
     
     
         17 . The method according to  claim 15 , wherein the base oil is a polyalphaolefin or a GTL (gas-to-liquid) oil. 
     
     
         18 . The method according to  claim 15 , wherein the copolymer has a weight average molecular weight of from 7,000 to 20,000. 
     
     
         19 . The method according to  claim 15 , wherein the lubricating oil composition further comprises: (C) 5 to 15% by mass of a carboxylic acid ester compound. 
     
     
         20 . The method according to  claim 15 , wherein the lubricating oil composition has a kinematic viscosity at 40° C. of from 140 to 320 mm 2 /s, a viscosity index of not less than 150, and produces no more than 1,200 mg/kg of sludge in a Dry TOST test.