Lubricating Oil Composition

Abstract

A lubricating oil composition comprising: (A) an oil of lubricating viscosity in a major amount, comprising a Group III base stock; (B) as an additive component in a minor amount, a viscosity index improver comprising a linear or star-shaped polymer which is derivable, at least in part, from the polymerisation of one or more conjugated diene monomers; and, wherein the lubricating oil composition is contaminated with at least 0.3 mass %, based on the total mass of the lubricating oil composition, of a biofuel or a decomposition product thereof and mixtures thereof.

1 . A lubricating oil composition comprising:
 (A) an oil of lubricating viscosity in a major amount, comprising a Group III base stock;   (B) as an additive component in a minor amount, an oil-soluble or oil-dispersible viscosity index improver comprising a linear or star-shaped polymer which is derivable, at least in part, from the polymerisation of one or more conjugated diene monomers; and,   
       wherein the lubricating oil composition is contaminated with at least 0.3 mass %, based on the total mass of the lubricating oil composition, of a biofuel or a decomposition product thereof and mixtures thereof. 
     
     
         2 . A lubricating oil composition as claimed in  claim 1 , wherein the one or more conjugated diene monomers comprises 1,3-butadiene, isoprene, or mixtures thereof. 
     
     
         3 . A lubricating oil composition as claimed in  claim 1 , wherein the viscosity index improver comprises at least one star-shaped, at least partially hydrogenated, polymer. 
     
     
         4 . A lubricating oil composition as claimed in  claim 3 , wherein the star-shaped, at least partially hydrogenated, polymer includes one or more arms, said arms comprising a homopolymer derived from a single said conjugated diene monomer, a copolymer derived from two or more of said conjugated diene monomers, or a copolymer derived from one or more of said conjugated diene monomers and predominantly from at least one vinyl aromatic hydrocarbon monomer. 
     
     
         5 . A lubricating oil composition as claimed in  claim 4 , wherein the vinyl aromatic hydrocarbon monomer comprises styrene. 
     
     
         6 . A lubricating oil composition as claimed in  claim 4 , wherein said arms of the star-shaped, at least partially hydrogenated, polymer comprises a copolymer derived from 70 to 90 mass % isoprene monomers and 30 to 10 mass % 1,3-butadiene monomers. 
     
     
         7 . A lubricating oil composition as claimed in  claim 4 , wherein said arms of the star-shaped, at least partially hydrogenated, polymer comprises a copolymer derived essentially from isoprene monomers, 1,3-butadiene monomers and a vinyl aromatic hydrocarbon monomer. 
     
     
         8 . A lubricating oil composition as claimed in  claim 7 , wherein the vinyl aromatic hydrocarbon monomer comprises styrene. 
     
     
         9 . A lubricating oil composition as claimed in  claim 7 , wherein the copolymer of said arms includes up to 35 mass % of the vinyl aromatic hydrocarbon monomer. 
     
     
         10 . A lubricating oil composition as claimed in  claim 9 , wherein the vinyl aromatic hydrocarbon monomer comprises styrene. 
     
     
         11 . A lubricating oil composition as claimed in  claim 1 , wherein the star-shaped polymer includes one or more arms, said arms comprising a linear diblock copolymer comprising at least one diblock copolymer comprising at least one block derivable predominantly from a vinyl aromatic hydrocarbon monomer and at least one block derivable predominantly from one or more conjugated diene monomers. 
     
     
         12 . A lubricating oil composition as claimed in  claim 11 , wherein the linear diblock copolymer is at least one diblock copolymer comprising at least a polystyrene block and a block derived from isoprene, butadiene or a mixture thereof. 
     
     
         13 . A lubricating oil composition as claimed in  claim 12 , wherein the linear diblock copolymer is at least one diblock copolymer selected from the group consisting of hydrogenated styrene/butadiene diblock copolymers, hydrogenated styrene/isoprene diblock copolymers and hydrogenated styrene/isoprene-butadiene diblock copolymers. 
     
     
         14 . A lubricating oil composition as claimed in  claim 4 , wherein the arms of the star-shaped, at least partially hydrogenated, polymer comprises a homopolymer derived from isoprene monomers or 1,3-butadiene monomers. 
     
     
         15 . A lubricating oil composition as claimed in  claim 1 , wherein the star-shaped polymer comprises a core derived from a polyolefinic linking agent. 
     
     
         16 . A lubricating oil composition as claimed in  claim 1 , wherein the viscosity index improver comprises a linear diblock copolymer comprising at least one block derivable predominantly from a vinyl aromatic hydrocarbon monomer and at least one block derivable predominantly from said one or more conjugated diene monomers. 
     
     
         17 . A lubricating oil composition as claimed in  claim 16 , wherein the linear diblock copolymer is at least one diblock copolymer comprising at least a polystyrene block and a block derived from isoprene, butadiene or a mixture thereof. 
     
     
         18 . A lubricating oil composition as claimed in  claim 17 , wherein the linear diblock copolymer is at least one diblock copolymer selected from the group consisting of hydrogenated styrene/butadiene diblock copolymers and hydrogenated styrene/isoprene diblock copolymers. 
     
     
         19 . A lubricating oil composition as claimed in  claim 1 , further comprising one or more co-additives in a minor amount, other than additive component (B), selected from ashless dispersants, metal detergents, corrosion inhibitors, antioxidants, pour point depressants, antiwear agents, friction modifiers, demulsifiers, antifoam agents and viscosity modifiers. 
     
     
         20 . A method of lubricating a spark-ignited or compression-ignited internal combustion engine which is fuelled at least in part with a biofuel, comprising operating the engine with a lubricating oil composition comprising: (A) an oil of lubricating viscosity in a major amount, comprising a Group III base stock; and, (B) as an additive component in a minor amount, an oil-soluble or oil-dispersible viscosity index improver as defined in  claim 1 .