Lubricating oil composition

Abstract

Provided is a lubricating oil composition containing (A) 70 mass % or more and 95 mass % or less of a poly-α-olefin base oil, (B) 5 mass % or more and 20 mass % or less of an ester-based base oil, and (C) an ester-based defoaming agent, the poly-α-olefin base oil (A) being a polymer of an α-olefin having 8 to 12 carbon atoms. The lubricating oil composition is able to keep excellent defoaming performance over a long period of time and is suitable as a step-up gear oil composition for wind power generation.

1 . A lubricating oil composition, comprising
 (A) 70 mass % or more and 95 mass % or less of a poly-α-olefin base oil,   (B) 5 mass % or more and 20 mass % or less of an ester-based base oil, and   (C) an ester-based defoaming agent,   wherein the poly-α-olefin base oil (A) is a polymer of an α-olefin comprising 8 to 12 carbon atoms.   
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein a sum total of the poly-α-olefin base oil (A) and the ester-based base oil (B) is 90 mass % or more based on a total amount of the composition. 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the ester-based defoaming agent (C) comprises a (meth)acrylate polymer having a weight average molecular weight of 10,000 or more and 100,000 or less. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the poly-α-olefin base oil (A) is a decene oligomer. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein the ester-based base oil (B) is a polyol ester. 
     
     
         6 . The lubricating oil composition according to  claim 1 , which is a step-up gear oil composition for wind power generation.