Lubricating oil composition

Abstract

An object of the present invention is to obtain a lubricating oil for machine tools, which has good lubricating properties and abrasion resistance and also exhibits a high flash point and a low pour point. A lubricating oil composition comprises, as a base oil, a base oil which includes an oil containing 20 mass % to 49 mass % of n-paraffin components and 51 mass % to 80 mass % of i-paraffin components at a quantity of 90 mass % or more of the total quantity of the base oil and which has a kinematic viscosity at 40° C. of 1 to 5 mm2/s. By blending a small quantity of β-dithiophosphorylated propionic acid and/or an acidic phosphoric acid ester in this base oil, a lubricating oil composition suitable for use for a main shaft of a machine tool is obtained. The lubricating oil composition for a main shaft of a machine tool has a flash point of 100° C. or more, a pour point of −10° C. or less, and a Shell four-ball wear mark diameter of 0.7 mm or less.

1 . A lubricating oil composition for a main shaft of a machine tool, the composition comprising a base oil, which includes an oil containing 20 mass % to 49 mass % of n-paraffin components and 51 mass % to 80 mass % of i-paraffin components at a quantity of 90 mass % or more of the total quantity of the base oil, and which has a kinematic viscosity at 40° C. of 1 to 5 mm 2 /s, wherein the base oil contains at least one component selected from among β-dithiophosphorylated propionic acid represented by formula 1 below and an acidic phosphoric acid ester represented by formula 2 below: 
       
         
           
           
               
               
           
         
       
       wherein, in formula 1, R 1  represents a branched alkyl group having 3 to 8 carbon atoms, and R 2  represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms and in formula 2, m denotes an integer of 1 or 2, and R represents a straight chain or branched chain hydrocarbon having 6 to 22 carbon atoms. 
     
     
         2 . The lubricating oil composition for a main shaft of a machine tool according to  claim 1 , wherein the β-dithiophosphorylated propionic acid is 3-(O,O-diisobutyl-dithiophosphoryl)-2-methyl-propionic acid and is contained at a quantity of 0.01 mass % or more and less than 2 mass % relative to the total quantity of the composition. 
     
     
         3 . The lubricating oil composition for a main shaft of a machine tool according to  claim 1 , wherein the acidic phosphoric acid ester is a compound in which R in formula 2 is a straight chain or branched chain hydrocarbon having 8 to 18 carbon atoms and is contained at a quantity of 0.01 mass % or more and less than 2 mass % relative to the total quantity of the composition. 
     
     
         4 . The lubricating oil composition for a main shaft of a machine tool according to  claim 1 , wherein the base oil is a base oil derived from Fischer-Tropsch polymerization. 
     
     
         5 . The lubricating oil composition for a main shaft of a machine tool according to  claim 1 , which further comprises an oxygen-containing organic compound as a solubilizing agent at a quantity of 0.01 to 5 mass % relative the total quantity of the composition. 
     
     
         6 . The lubricating oil composition for a main shaft of a machine tool according to  claim 1 , wherein the flash point (COC) of the composition is 100° C. or higher.