Additive for lubricating oil and lubricating oil composition

Abstract

The present invention is intended to provide a lubricating oil additive having high viscosity index improvability and shear stability and a lubricating oil composition containing the additive and having excellent viscosity index and excellent shear stability. The lubricating oil additive comprises an ethylene/α-olefin random copolymer having the following properties: (i) said copolymer is a copolymer of ethylene and at least one α-olefin selected from α-olefins of 3 to 20 carbon atoms and contains at least constituent units derived from ethylene in amounts of 10 to 75% by mol and constituent units derived from at least one α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 20 to 80% by mol, (ii) the kinematic viscosity at 100 ° C. is in the range of 500 to 1,000,000 mm 2 /s, (iii) the intrinsic viscosity [η] is in the range of 0.15 to 11.0 dl/g, (iv) the molecular weight distribution (Mw/Mn), as measured by GPC, is not more than 4, and (v) the number-average molecular weight is in the range of 5,000 to 30,000.

What is claimed is:  
     
         1 . A lubricating oil additive comprising an ethylene/α-olefin random copolymer having the following properties: 
 (i) said copolymer is a copolymer of ethylene and at least one α-olefin selected from α-olefins of 3 to 20 carbon atoms and contains at least constituent units derived from ethylene in amounts of 10 to 75% by mol and constituent units derived from at least one α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 20 to 80% by mol,  
 (ii) the kinematic viscosity at 100° C. is in the range of 500 to 1,000,000 mm 2 /s,  
 (iii) the intrinsic viscosity [η], as measured in decalin at 135° C., is in the range of 0.15 to 1.0 dl/g,  
 (iv) the molecular weight distribution (Mw/Mn, Mw:  
 weight-average molecular weight, Mn: number-average molecular weight), as measured by gel permeation chromatography, is not more than 4, and  
 (v) the number-average molecular weight is in the range of 5,000 to 30,000.  
 
     
     
         2 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 30 to 75% by mol and constituent units derived from at least one α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 25 to 70% by mol.  
     
     
         3 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 30 to 75% by mol and constituent units derived from at least one α-olefin selected from α-olefins of 10 to 16 carbon atoms in amounts of 25 to 70% by mol.  
     
     
         4 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 35 to 70% by mol and constituent units derived from 1-decene in amounts of 30 to 65% by mol.  
     
     
         5 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 10 to 75% by mol., constituent units derived from at least one lower α-olefin selected from α-olefins of 3 to 6 carbon atoms in amounts of 5 to 50% by mol, and constituent units derived from at least one higher α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 20 to 85% by mol.  
     
     
         6 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 10 to 70% by mol, constituent units derived from at least one lower α-olefin selected from α-olefins of 3 to 6 carbon atoms in amounts of 10 to 40% by mol, and constituent units derived from at least one higher α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 20 to 80% by mol.  
     
     
         7 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 10 to 70% by mol, constituent units derived from at least one lower α-olefin selected from α-olefins of 3 to 4 carbon atoms in amounts of 10 to 40% by mol, and constituent units derived from at least one higher α-olefin selected from α-olefins of 10 to 14 carbon atoms in amounts of 20 to 80% by mol.  
     
     
         8 . The lubricating oil additive as claimed in  claim 1 , wherein the ethylene/α-olefin random copolymer contains constituent units derived from ethylene in amounts of 10 to 70% by mol, constituent units derived from propylene in amounts of 10 to 40% by mol, and constituent units derived from 1-decene in amounts of 20 to 80% by mol.  
     
     
         9 . A lubricating oil additive containing constituent units derived from ethylene in amounts of 30 to 75% by mol and constituent units derived from at least one α-olefin selected from α-olefins of 8 to 20 carbon atoms in amounts of 25 to 70% by mol, and having the following properties: 
 the shear stability (A (%)) and the viscosity index (B) satisfy the following formula:  
   B≧ 0.4 ×A+ 155,  
  and  
 A is a number satisfying the condition of A≦30.  
 
     
     
         10 . The lubricating oil additive as claimed in  claim 9 , wherein the shear stability (A (%)) and the low-temperature viscosity (C (mPa·s)) as measured at −26° C. satisfy the following formula:  
         C≦− 50 ×A+ 15,000.  
     
     
         11 . A lubricating oil composition comprising: 
 (A) at least one base oil selected from a synthetic hydrocarbon, a mineral oil and an ester, which has a kinematic viscosity at 100° C. of 1 to 20 mm 2 /s, in an amount of 50 to 99.8 parts by weight,    (B) the lubricating oil additive of-any one of  claims 1  to  10 , in an amount of 0.2 to 50 parts by weight, with the proviso that the total of the component (A) and the component (B) is 100 parts by weight, and optionally,    (C) at least one additive selected from the group consisting of a dispersant, a viscosity index improver, an antioxidant, a corrosion inhibitor, an anti-wear agent, a pour point depressant, a rust preventive, an anti-foaming agent and an extreme pressure agent.