Toshiba Silicone Co., Ltd.

Japan Synthetic Rubber Co., Ltd.

Bridgestone Corporation

Hitachi Industrial Equipment Systems Co., Ltd.

Hironori Matsumoto

Junichiro Watanabe

Kazuo Sugiura

Yuichi Funahashi

Seisuke Tomita

Yasuhiko Takemura

Takatsugu Hashimoto

Yoji Mori

Yoshiaki Kawamura

Akihiro Maehara

Atsushi Ootake

An oil-resistant rubber composition comprising (A) 90 to 10 parts by weight of an unsaturated nitrile-conjugated diene rubber having a .DELTA.Tg of 58.degree. C. or more and an average bound nitrile content of 15 to 50% by weight, (B) 10 to 90 parts by weight of at least one rubber selected from the group consisting of an ethylene-propylene type copolymer rubber, a natural rubber and a polyisoprene and (C) 0 to 50 parts by weight, per 100 parts by weight of the total of (A) and (B), of at least one component (C) selected from the group consisting of a styrene polymer and a polyalkenamer. Said rubber composition is oil-resistant and excellent in mechanical properties such as tear strength, resistance to crack growth, etc.

Oil-resistant rubber composition

A vulcanizable silicone elastomer composition which has novel crosslinking points comprises (A) 100 parts by weight of a polyorganosiloxane having a polymerization degree of at least 100, wherein the organic groups are selected from monovalent substituted and unsubstituted hydrocarbon groups and are attached to silicon atoms at a rate, on average, in the range of 1.98 to 2.02 per silicon atom and at least two of the organic groups are monovalent hydrocarbon groups possessing at least five carbon atoms and a carbon-carbon double bond issuing from a silicon atom through at least one carbon atom, (B) 5 to 200 parts by weight of an inorganic filler having a specific surface area of at least 50 m.sup.2 /g, and (C) 0.05 to 15 parts by weight of an organic peroxide.

Silicone elastomer composition

Rubber compounds comprising a specific type of polyorganosiloxane of the following formula ##STR1## in which R and R' independently represent a hydrocarbon substituent and n is an integer of not smaller than 3 provided that at least 6 mole % of the substituents R and R' consists of a hydrocarbon group having Small's molecular attraction constant not smaller than 350. Carbon black is added to the polyorganosiloxane whereby various physical properties are improved including breaking strength, water and hot water resistances. The rubber compound may further comprise at least one organic rubber other than the above polyorganosiloxane.

Rubber compounds

A silicone elastomer composition which has novel crosslinking points comprises (A) 100 parts by weight of a polyorganosiloxane of a polymerization degree of at least 20, wherein the organic groups are selected from monovalent substituted and unsubstituted hydrocarbon groups and are attached to silicon atom, and at least two of the organic groups are monovalent hydrocarbon groups possessing at least five carbon astoms and a carbon-carbon double bond bonded to a silicon atom via at least one carbon atom, (B) 5 to 200 parts by weight of an inorganic filler having a specific surface area of at least 50 m.sup.2 /g, and (C) 0.1 to 25 parts by weight of a vulcanizer selected from the group consisting of sulfur, sulfur donor, substituted or unsubstituted alkylphenol resins, and quinoids.

A polysiloxane containing an ethylidene norbornyl group possesses a terminal group represented by the formula: ##STR1## wherein R.sup.1 stands for a monovalent hydrocarbon group, a hydroxyl group, an alkoxy group, or at least one of the hydrocarbon groups represented by Y, and each R.sup.2 stands for the same or different groups selected from the class consisting of hydrogen, monovalent hydrocarbon groups, and a group represented by R.sup.1 wherein R.sup.1 has the same meaning as defined above, and being substantially in the form of a straight chain, 0 to 100 mol %, providing that 100 mol % is excluded where neither of the R.sup.1 's in the terminal groups is a hydrocarbon group represented by Y of the component units being represented by the formula: ##STR2## wherein each R.sup.3 's stand for the same or different groups selected from the class consisting of hydrogen and monovalent hydrocarbon groups and 100 to 0 mol %, providing that 0 mol % is excluded where neither of the R.sup.1 's in the terminal groups is a hydrocarbon group represented by Y of the component units being represented by the formula: ##STR3## wherein R.sup.4 stands for a monovalent hydrocarbon group of 1 to 8 carbon atoms and Y stands for ##STR4## so as to bond a silicon atom to the neighboring silicon atom through an oxygen atom.

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Tokyo, Japan

Hironori Matsumoto