Abstract: For a cap tread layer of a pneumatic tire, a rubber composition is used, which contains from 60 to 90 parts by mass of silica per 100 parts by mass of a diene rubber containing from 15 to 30 mass % of a natural rubber, from 40 to 70 mass % of a terminal-modified styrene-butadiene rubber having a vinyl content of from 35 to 45 mass %, and from 15 to 30 mass % of a modified butadiene rubber obtained by modifying an active terminal of a conjugated diene polymer with at least a hydrocarbyloxysilane compound, the total of these being 100 mass %. A hardness Hu of the undertread Layer and a hardness Hc of the cap tread layer satisfy the relationship of Hu>Hc. The hardness Hc is 63 or greater and 67 or less. A difference ?H between the hardness Hu and the hardness Hc is 10 or more.

Abstract: A rubber composition for a tire contains a diene rubber, silica, and a specific modified butadiene polymer, wherein the diene rubber contains an aromatic vinyl-conjugated diene rubber A and at least one rubber component B selected from an aromatic vinyl-conjugated diene rubber b1 other than the rubber A and a butadiene rubber b2 having a weight average molecular weight of ?15000. A content of the aromatic vinyl-conjugated diene rubber A is from 30 to 90% by mass, and a content of the rubber component B is from 10 to 70% by mass, an average TG of the diene rubber is lower than ?20° C., a content of the silica is from 80 to 200 parts by mass per 100 parts by mass of the diene rubber, and a content of the modified butadiene polymer is from 1.0 to 25.0% by mass with respect to content of the silica.

Abstract: The present invention provides a rubber composition for a tire, the rubber composition containing: a diene rubber; silica; and a heterocyclic compound (where, the heterocyclic compound does not have a silicon atom) having a hydrocarbon group having from 3 to 30 carbons and at least one type of heterocycle selected from the group consisting of a piperazine ring, a morpholine ring, and a thiomorpholine ring; an average glass transition temperature of the diene rubber being ?50° C. or higher; a content of the silica being from 80 to 200 parts by mass per 100 parts by mass of the diene rubber; and a content of the heterocyclic compound being from 0.5 to 20% by mass with respect to the content of the silica. Such rubber composition has excellent processability, exhibits excellent wet grip performance and has low rolling resistance when the rubber composition is formed into a tire.

Abstract: An object of the present invention is to provide a method of producing a copolymer that produces an aromatic vinyl-diene copolymer having a low glass transition temperature, and a method of producing a rubber composition using the method. The subject method produces an aromatic vinyl-diene copolymer having a content of repeating units derived from an aromatic vinyl in an amount of 18 mass % or greater, and among repeating units derived from a diene, a proportion of a vinyl structure of 8 mol % or less, a proportion of a 1,4-trans structure of 60 mol % or less, and a proportion of a 1,4-cis structure from 40 to 95 mol %, the method including copolymerizing a monomer containing an aromatic vinyl and a diene using an initiator prepared with an organolithium compound, an alkylaluminum, a metal alcoholate, and at least one polar compound selected from the group consisting of water and an alcohol.

Abstract: A rubber composition for a tire contains a diene rubber, silica, and a specific modified butadiene polymer, wherein the diene rubber contains an aromatic vinyl-conjugated diene rubber A and at least one rubber component B selected from an aromatic vinyl-conjugated diene rubber b1 other than the rubber A and a butadiene rubber b2 having a weight average molecular weight of ?15000. A content of the aromatic vinyl-conjugated diene rubber A is from 30 to 90% by mass, and a content of the rubber component B is from 10 to 70% by mass, an average TG of the diene rubber is lower than ?20° C., a content of the silica is from 80 to 200 parts by mass per 100 parts by mass of the diene rubber, and a content of the modified butadiene polymer is from 1.0 to 25.0% by mass with respect to content of the silica.

Abstract: The present invention provides a rubber composition for a tire, the rubber composition containing: a diene rubber; silica; and a heterocyclic compound (where, the heterocyclic compound does not have a silicon atom) having a hydrocarbon group having from 3 to 30 carbons and at least one type of heterocycle selected from the group consisting of a piperazine ring, a morpholine ring, and a thiomorpholine ring; an average glass transition temperature of the diene rubber being ?50° C. or higher; a content of the silica being from 80 to 200 parts by mass per 100 parts by mass of the diene rubber; and a content of the heterocyclic compound being from 0.5 to 20% by mass with respect to the content of the silica. Such rubber composition has excellent processability, exhibits excellent wet grip performance and has low rolling resistance when the rubber composition is formed into a tire.