| 摘要 |
PURPOSE:To improve the durability of a tire by providing on the outer periphery of a crown section of a tire a laminated tread layer which consists of a styrene- butadiene-type cap rubber having predetermined physical properties and a polybutadiene-type base rubber of a predetermined microcrystalline structure. CONSTITUTION:A cap rubber 9 is placed on a base rubber 10 so as to be united to the outer periphery of a crown section 5 of a tire. The cap rubber 9 contains as a principal component a blended rubber which contains 60 percent by weight of styrene-butadiene rubber among the entire rubber components thereof. The cap rubber has, after vulcanization, a restitution coefficiency of 50% or less. The base rubber 10 contains as a principal component a polybutadiene rubber consisting principally of a block or graft polymer of cis-1,4- and syn-1,2-polybutadienes. The polymer contains 6-20wt% of a microcrystalline syn-1,2-structure, and 40 wt% or more thereof is crystalline. The polymer is further in short filaments having the average diameter of 0.05-1mum and the average length of 0.8-10mum. The base rubber 10 has, after vulcanization, a restitution coefficiency of 70% or more and an elastic modulus of 25kg/cm<2> or more at a temperature of 100 deg.C. Thus, the provision of a cap-base laminated tread layer can improve the durability of a tire. |
