Lubricating oil composition

Abstract

The present invention relates to a lubricating oil composition containing a base oil (A) and a viscosity index improver (B) such that in X-ray small-angle scattering spectra obtained through measurement at 40° C. and 100° C., a ratio [Δ|α(40)|/Δ|α(100)|] between Δ|α(40)| and Δ|α(100)|, each of which is an absolute value of a slope of a straight line calculated in a range of the scattering vector q as the x axis of from 0.1 nm −1 to 1 nm −by the least-squares method, is 1.5 or more.

1 . A lubricating oil composition comprising a base oil (A) and a viscosity index improver (B) in which a ratio [Δ|α(40)|/Δ|α(100)|] between Δ|α(40)| and Δ|α(100)| as calculated through the following operations (i) to (iii) is 1.5 or more:
 Operation (i): a sample oil comprising the viscosity index improver (B) dissolved in a mineral oil is prepared, and X-ray small-angle scattering measurement is performed under a temperature condition at 40° C. to acquire X-ray small-angle scattering spectra (x axis: scattering vector q (nm −1 ), y axis: common logarithm log (I) of scattering intensity I) at 40° C. and 100° C., respectively; 
 Operation (ii): in the X-ray small-angle scattering spectrum at 40° C. obtained in Operation (i), an absolute value Δ|α(40)| of a slope of a straight line is calculated in a range of the scattering vector q as the x axis of from 0.1 nm −1  to 1 nm −1  by the least-squares method; and 
 Operation (iii): in the X-ray small-angle scattering spectrum at 100° C. obtained in Operation (i), an absolute value Δ|═(100)| of a slope of a straight line is calculated in a range of the scattering vector q as the x axis of from 0.1 nm −1  to 1 nm −1  by the least-squares method. 
 
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the base oil (A) comprises a mineral oil. 
     
     
         3 . The lubricating oil composition according to  claim 2 , wherein the mineral oil is a mineral oil classified into Group 2 or Group 3 of the base stock categories of the API (American Petroleum Institute). 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the viscosity index improver (B) comprises a polymer (B1) having a structural unit (β1) derived from a monomer selected from butadiene and hydrogenated butadiene. 
     
     
         5 . The lubricating oil composition according to  claim 4 , wherein a content of the structural unit (β1) is 0.1 to 70 mol % relative to a total amount of structural units of the polymer (B1). 
     
     
         6 . The lubricating oil composition according to  claim 4 ., wherein the polymer (B1) is at least one selected from a styrene-isoprene-butadiene copolymer (B11) and a comb-shaped polymer (B12). 
     
     
         7 . The lubricating oil composition according to  claim 1 , wherein a weight average molecular weight of the viscosity index improver (B) is 100,000 to 900,000. 
     
     
         8 . The lubricating oil composition according to  claim 1 , wherein a content of the viscosity index improver (B) expressed in terms of a resin component is 0.5 to 8.0% by mass relative to a total amount of the lubricating oil composition. 
     
     
         9 . (canceled) 
     
     
         10 . An engine, comprising the lubricating oil composition according to  claim 1 . 
     
     
         11 . A method of lubricating an engine, the method comprising contacting the engine with the lubricating oil composition according to  claim 1 .