Bridgestone Corporation

Ube Industries, Inc.

Japan Synthetic Rubber Co., Ltd.

Yoshiyuki Morimoto

Noboru Oshima

Tatsuo Fujimaki

Mitsuhiko Sakakibara

Fumio Tsutsumi

Eiji Yamanaka

Tatsuro Hamada

Seiichiro Iwafune

Masanori Aoyama

Koji Yamauchi

Koichi Nagakura

Mitsuru Araki

Koji Ishiguchi

Akio Iakashima

A rubber composition includes a rubber component and particulates of a crystalline syndiotactic-1,2-polybutadiene resin dispersed therein. The particulates have an average particle diameter of 1 to 500 .mu.m, and the melting point of the crystalline syndiotactic-1,2-polybutadiene resin is not less than 110.degree. C. The compounding ratio of the resin is 5 to 60 parts by weight relative to 100 parts by weight of the rubber component. The rubber composition is useful for tires, other rubber articles, etc. With respect to tires in particular, a pneumatic tire includes a rubber composition used for a tread, wherein the rubber composition includes a rubber component and particulates of crystalline syndiotactic-1,2-polybutadiene resin. The matrix portion of the tread rubber other than the above particulates is preferably a foamed rubber.

Rubber composition and all season type pneumatic tires made from a

A pneumatic tire has a tread with a rubber composition produced by blending a rubber component with a styrene based thermoplastic elastomer. The rubber component is composed mainly of a diene based rubber, and the elastomer is so preliminarily internally crosslinked that tensile stress at a 100% elongation is increased to 10 to 1,000% of that of the styrene based thermoplastic elastomer not internally crosslinked. A pneumatic tire is also disclosed, having a tread portion with a rubber composition blended with a vinyl aromatic hydrocarbon thermoplastic elastomer in an amount of 5-80 parts by weight relative to 100 parts by weight of the rubber component. The vinyl aromatic hydrocarbon thermoplastic elastomer satisfying the following requirements: (1) the elastomer is a vinyl aromatic hydrocarbon-conjugated diene based block type thermoplastic elastomer; (2) the elastomer has a weight ratio between a vinyl aromatic hydrocarbon and a conjugated diene as constituent monomer units thereof being 40/60 to 95/5; (3) a content percentage of the vinyl aromatic hydrocarbon in vinyl aromatic hydrocarbon based segments in the elastomer is not less than 50% by weight; and (4) a weight average molecular weight of the elastomer is not less than 1.times.10.sup.5.

Pneumatic tires

A rubber composition containing at least 20% by weight of a styrene-butadiene block copolymer consisting of a block (A) and a block (B) characterized in that: (i) the block (A) is a styrene-butadiene copolymer block having the content of styrene of 10-80% by weight and the average content of the vinyl bonds in the butadiene portion of 30-70% by weight; (ii) the block (B) is a polybutadiene block with the average content of the vinyl bonds in the butadiene portion being not more than 60% by weight (iii) the styrene-butadiene block copolymer contains at least 20% by weight of each of the block (A) and the block (B); (iv) the average content of the vinyl bonds in the butadiene portion of the block (A) is greater by at least 5% by weight than that of the block (B); (v) the glass transition temperature of the block (A) is higher by at least 30.degree. C. than that of the block (B); (vi) the whole content of the bound styrene in the above block copolymer is 5-40% by weight; (vii) the ratio Mw/Mn between the weight average molecular weight Mw and the number average molecular weight Mn of the block copolymer is 1.8-5.0 when calculated as polystyrene according to the gel permeation chromatogram; and (viii) the Mooney's viscosity (ML.sub.1+4.sup.100.degree. C.) of the block copolymer is 20-150.

Rubber composition comprising a styrene-butadiene block copolymer having

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Tokyo, Japan

Yoshiyuki Morimoto