Rubber composition for treads and pneumatic tire
Provided are a rubber composition for treads which achieves a balanced improvement in fuel economy, abrasion resistance, and wet grip performance while offering good processability, and a pneumatic tire formed from the rubber composition. The present invention relates to a rubber composition for treads containing: a polybutadiene; and a terpene resin having a glass transition temperature (Tg) of 40° C. to 90° C., the polybutadiene satisfying the following conditions (A), (B) and (C): (A) a ratio (Tcp/ML 1+4 , 100° C.) of 5% by mass toluene solution viscosity (Tcp) to Mooney viscosity (ML 1+4 , 100° C.) is 0.9 to 2.3; (B) a stress relaxation time (T80) is 10.0 to 40.0 seconds, which is a time required for torque to decay by 80%, where 100% represents torque at the end of a ML 1+4 , 100° C. measurement; and (C) a molecular weight distribution (Mw/Mn) is 2.50 to 4.00.
1. A pneumatic tire, comprising a tread formed from a rubber composition for treads, the rubber composition comprising:
a polybutadiene; and
a terpene resin having a glass transition temperature (Tg) of 50° C. to 70° C.,
the polybutadiene satisfying the following conditions (A), (B), and (C): (A) a ratio (Tcp/ML 1+4 , 100° C.) of 5% by mass toluene solution viscosity (Tcp) to Mooney viscosity (ML 1+4 , 100° C.) is 0.9 to 2.3; (B) a stress relaxation time (T80) is 10.0 to 40.0 seconds, which is a time required for torque to decay by 80%, where 100% represents torque at the end of a ML 1+4 , 100° C. measurement; and (C) a molecular weight distribution (Mw/Mn) is 2.50 to 4.00,
wherein the rubber composition comprises the polybutadiene in an amount of 10% to 40% by mass based on 100% by mass of a rubber component in the rubber composition, and the terpene resin in an amount of 5 to 15 parts by mass per 100 parts by mass of the rubber component,
wherein the rubber composition further comprises silica in an amount of 50 to 90 parts by mass per 100 parts by mass of the rubber component,
wherein the rubber composition further comprises styrene-butadiene rubber terminally modified with N-methylpyrrolidone in an amount of 10% to 95% 60% to 90% by mass based on 100% by mass of the rubber component.
2. The pneumatic tire according to claim 1 ,
wherein the rubber composition comprises the polybutadiene in an amount of 15% to 40% by mass based on 100% by mass of the rubber component.
3. The pneumatic tire according to claim 1 ,
wherein the polybutadiene satisfies the following conditions (A), (B), and (C): (A) a ratio (Tcp/ML 1+4 , 100° C.) of 5% by mass toluene solution viscosity (Tcp) to Mooney viscosity (ML 1+4 , 100° C.) is 1.4 to 1.7; (B) a stress relaxation time (T80) is 12.0 to 20.0 seconds, which is a time required for torque to decay by 80%, where 100% represents torque at the end of a ML 1+4 , 100° C. measurement; and (C) a molecular weight distribution (Mw/Mn) is 2.70 to 3.20.
4. The pneumatic tire according to claim 1 ,
wherein the terpene resin is at least one selected from the group consisting of polyterpene resin, aromatic modified terpene resin, and hydrogenated product thereof.