Bridgestone Corporation

Honda Motor Co., Ltd.

Japan Synthetic Rubber Co., Ltd.

Hideaki Yokoyama

Koichi Sato

Tadashi Shibata

Iwakazu Hattori

Ryuji Nakagawa

Tatsuro Hamada

Kiyoshi Shibata

Uchu Mukai

Yoshitaka Yamakawa

Toshiyuki Ishikuro

Kyouyuu Yasuda

Kuniko Itoh

A water jacket core () includes a base part () and is provided with an intermediate female thread part () in that base within a region surrounded by tangent lines () that are parallel to a center line () passing through the centers of a plurality of bore pin insertion bores () for forming cylinder bores and are in contact with the bore pin insertion bores and by an intermediate position for the adjacent bore pin insertion bores.

Water jacket core

Rubber composition

A tire having a portion formed of a rubber composition which comprises a high-molecular-weight polymer component which contains bound styrene in an amount not greater than 30% by weight, is a styrene-butadiene copolymer or a conjugated diene polymer such as polybutadiene, and has a weight-average molecular weight of at least 30.times.10.sup.4 ; and a low-molecular-weight polymer component which contains bound styrene in an amount not greater than 30% by weight, is a styrene-butadiene copolymer or a conjugated diene polymer such as polybutadiene, and has a weight-average molecular weight of from 0.2.times.10.sup.4 to 8.times.10.sup.4. The rubber composition contains 30 parts by weight of the low-molecular-weight polymer component relative to 100 parts by weight of the high-molecular-weight polymer component. The ratio between the amount of bound styrene and the vinyl linkage content falls within specific ranges. When the vulcanized rubber composition was extracted by chloroform, an amount of the extract is not less than 15% by weight of the low-molecular-weight polymer component.

Rubber composition having both high and low molecular weight polymer

A rubber composition for tire tread has a considerably improved rolling resistance without degrading wet-skid resistance, fracture resistance and wear resistance and comprises a particular styrene-isoprene copolymer as a rubber ingredient, in which a part or whole of the copolymer is a terminal-modified copolymer coupled at its active terminal with a particular halogenated tin compound.

Rubber compositions for tire tread

A pneumatic tire comprises a tread of cap and base structure, in which a rubber composition comprising a particular amount of a specified rubber-reinforcing thermoplastic resin containing not less than 10% by weight of a conjugated diene rubber component and the balance being a resin component and having a particular glass transition temperature is used in a tread base rubber of the tread and has excellent chipping resistance, cut resistance and durability to heat build-up.

Pneumatic tire with cap and base structure

A process for producing a diolefin polymer or copolymer, comprising the steps of polymerizing 55-100 wt % of a conjugated diolefin with 0-45 wt % of an aromatic vinyl compound as monomers in a hydrocarbon as a solvent, by using initiators: a reaction product [a1] between at least one secondary amine compound (A) and an organic lithium compound and/or a lithium amide compound [a2] of the at least one secondary amine compound (A) as well as a reaction product [b1] between at least one alcohol (B) and an organic lithium compound and/or a lithium alkoxide compound of the at least one alcohol (B). A rubber composition containing not less than 30 wt % of such a diolefin polymer or copolymer with respect to an entire rubber component is also disclosed. This rubber composition exhibits excellent abrasion resistance, high tensile strength, steering stability and low rolling resistance, and is suitable for tires, particularly, as treads of low fuel consumption tires.

Process for producing a diolefin polymer or copolymer and a rubber

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Tokyo, Japan

Hideaki Yokoyama