Patent ID: 8426522

Claim:
A method for producing a copolymer rubber composition comprising: a copolymer rubber (1); and a copolymer rubber (2), as a rubber component, wherein the content of the copolymer rubber (1) is 60% by weight or more and 75% by weight or less, and the content of the copolymer rubber (2) is 40% by weight or less and 25% by weight or more, based on 100% by weight of the total of the copolymer rubber (1) and the copolymer rubber (2); and [iodine value of the copolymer rubber (1)−iodine value of the copolymer rubber (2)] is 5 or more and 30 or less, and wherein, the copolymer rubber (1) is an ethylene-α-olefin-nonconjugated polyene copolymer rubber wherein the molar ratio of monomer units based on ethylene to monomer units based on α-olefin is 50/50 or more and 70/30 or less; and the iodine value is 15 or more and 45 or less, and the copolymer rubber (2) is an ethylene-α-olefin-nonconjugated polyene copolymer rubber wherein the molar ratio of monomer units based on ethylene to monomer units based on α-olefin is more than 70/30 and 95/5 or less; and the iodine value is 10 or more and 30 or less, the method comprising manufacturing one of the copolymer rubber (1) and the copolymer rubber (2) in a first reaction tank, feeding the one copolymer rubber manufactured in the first reaction tank to a second reaction tank, and manufacturing the other copolymer rubber in the second reaction tank, wherein the two tanks are coupled in series, and wherein the manufacturing of the copolymer rubber (1) is conducted in the presence of a polymerization catalyst containing a vanadium compound represented by formula (1) and an organoaluminum compound represented by formula (2) as polymerization catalyst components, formula (1): VO(OR) m X 3−m wherein R denotes a straight chain hydrocarbon group having 1 to 8 carbon atoms; X denotes a halogen atom: an m denotes a number satisfying 0≦m≦3; formula (2): R″ j AlX″ 3−j wherein R″ denotes a hydrocarbon group; X″ denotes a halogen atom; and j denotes a number satisfying 0<j≦3; and wherein the manufacturing of the copolymer rubber (2) is conducted in the presence of a polymerization catalyst containing a vanadium compound represented by formula (3) and the organoaluminum compound represented by formula (2) as polymerization catalyst components, formula (3): VO(OR′) n X′ 3−n wherein R′ denotes a secondary or tertiary hydrocarbon group having 3 to 8 carbon atoms; X′ denotes a halogen atom; and n denotes a number satisfying 0<n≦3.