Shin-etsu Chemical Co., Ltd.

Yutaka Hagiwara

Minoru Igarashi

Masaharu Takahashi

Keiji Shibata

Kenji Tawara

Yoshio Tomizawa

A method for producing a silicone rubber compound in a reduced blending time, and which imparts excellent resistance to plasticity reversion and the cured silicone rubber prepared without heat treatment has excellent resistance to compression set. (A) an organopolysiloxane with polymerization degree of at least 100 represented by the following average compositional formula (I):RSiO&#x2003;&#x2003;(I)(R: a substituted or unsubstituted monovalent hydrocarbon group, a: 1.95 to 2.05), (B) a reinforcing silica having a specific surface area (BET) of at least 50 m/g, and (C) a preliminary hydrolysis product of (C-1) an alkoxysilane represented by the following formula (II):RSi(OR)&#x2003;&#x2003;(II)(R: hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, R: a substituted or unsubstituted alkyl group, m: 0, 1, 2, or 3), and (C-2) water at a molar amount 0.3 to 5 times the alkoxy group in the alkoxysilane of component (C-1) are mixed and heated.

Method for producing silicone rubber compound and silicone rubber composition

A silicone rubber composition comprising an organopolysiloxane containing at least two alkenyl radicals and having a degree of polymerization of at least 100, an organopolysiloxane or organosilane, reinforcing silica, and an alkali metal salt of phosphoric acid has minimized plasticity recovery with time and improved storage stability and cures with an organic peroxide or addition reaction curing agent into a silicone rubber having improved compression set and yellowing resistance.

Silicone rubber compositions

An organopolysiloxane gum is prepared by polymerizing a cyclic organopolysiloxane with a low molecular weight linear organopolysiloxane end-blocked with a triorganosilyl group in the presence of a thermally decomposable catalyst. After the polymerization reaction, the catalyst is deactivated by heating the reaction product under a subatmospheric pressure of typically up to 500 mmHg.

Preparation of organopolysiloxane gum

An organopolysiloxane gum is continuously prepared by (I) mixing at least one cyclopolysiloxane with an end capping agent, (II) feeding the mixture to a self-cleaning reactor along with an alkaline polymerization catalyst, and effecting polymerization at a temperature of 100 to 250&deg; C. and under subatmospheric pressure, (III) continuously adding a neutralizing agent to the reaction mixture of step (II), thereby terminating the polymerization reaction, and (IV) continuously removing the cyclopolysiloxane and volatile components from the reaction mixture.

An organopolysiloxane gum is continuously prepared by (I) mixing at least one cyclopolysiloxane with an end capping agent, (II) feeding the mixture to a self-cleaning reactor along with a polymerization catalyst of thermal decomposition type, and effecting polymerization at a temperature of 80-130&deg; C., (III) heating the reaction mixture of step (II) at a temperature of 130-200&deg; C. under subatmospheric pressure for deactivating the catalyst, thereby terminating the polymerization reaction, and (IV) continuously removing the cyclopolysiloxane and volatile components from the reaction product.

In a first step, basic components including (A) 100 parts by weight of an organopolysiloxane gum, (B) 5-100 parts by weight of a reinforcing silica filler, and (C) 0.1-30 parts by weight of a processing aid are fed batchwise to a closed mixer for mixing them until uniform. In a second step, the mixture is continuously fed into a kneader/extruder for heat treating. The first step achieves quick dispersion and cooperates with the second step for the efficient production of a heat-curable silicone rubber compound.

Method for preparing heat-curable silicone rubber compounds

In a first step, basic components including (A) 100 parts by weight of an organopolysiloxane gum, (B) 5-100 parts by weight of a reinforcing silica filler, and (C) 0.1-30 parts by weight of a processing aid are fed batchwise to a closed mixer for mixing them at a temperature of room temperature to 150.degree. C. In a second step, the mixture is fed into a kneader/mixer for heat treating at a temperature of 150-250.degree. C. The first step achieves quick dispersion and cooperates with the second step to form a heat-curable silicone rubber compound in an efficient manner.

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Annaka, Japan

Yutaka Hagiwara