Rubber composition for tread, and pneumatic tire
Rubber composition for a tread, which enables not only improving handling stability, abrasion resistance, and fuel economy in a balanced manner, but also improving wet grip performance and processability in a balanced manner, in a pneumatic tire formed from the rubber composition. The rubber composition comprises a terminally-modified solution-polymerized styrene-butadiene rubber, a butadiene rubber synthesized in the presence of a rare earth catalyst, and a particular type of reinforcing agent.
1. A pneumatic tire comprising a cap tread formed from a rubber composition comprising:
a rubber component comprising
(a) a terminally-modified solution-polymerized styrene-butadiene rubber which has been modified with a compound represented by the following formula (1):
wherein R 1 , R 2 , and R 3 are the same as or different from each other and each represent a C1- to C4-alkoxy group; R 4 and R 5 are the same as or different from each other and each represent a hydrogen atom or a C1- to C4-alkyl group; and n represents an integer of 1 to 5,
(b) a butadiene rubber synthesized in the presence of a rare earth catalyst, and
(c) a non-modified styrene-butadiene rubber; and
a reinforcing agent comprising 3 to 15 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 m 2 /g to 140 m 2 /g and 50 to 90 parts by mass of silica having a nitrogen adsorption specific surface area of 150 m 2 /g to 220 m 2 /g,
wherein the rubber component of the rubber composition contains, based on 100% by mass of the rubber component, 40 to 70% by mass of the terminally-modified solution-polymerized styrene-butadiene rubber and 10 to 30% by mass of the butadiene rubber synthesized in the presence of a rare earth catalyst.
2. The pneumatic tire according to claim 1 ,
wherein the rubber component contains, based on 100% by mass of the rubber component, 10 to 40% by mass of non-modified styrene-butadiene rubber (c), which has a styrene content of 20% by mass or more, a weight average molecular weight (Mw) of 800,000 or more, and a ratio of weight average molecular weight to number average molecular weight (Mw/Mn) of 0.9 to 2.5.
3. The pneumatic tire according to claim 1 , comprising, per 100 parts by mass of the rubber component,
1 to 8 parts by mass of an aromatic vinyl polymer polymerized from at least one of α-methylstyrene and styrene.
4. The pneumatic tire according to claim 1 ,
wherein an amount of the reinforcing agent and an acetone-extractable content satisfy the following relation:
3.0≦[(the amount of the reinforcing agent)/(the acetone-extractable content)]≦10.0.