Mold-releasable curable organopolysiloxane composition
AssigneeShin-Etsu Chemical Co., Ltd.
InventorsHironao Fujiki, Morio Oohasi, Mitsuaki Igarashi
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Abstract
A mold-releasable curable organopolysiloxane composition suitable for use as a material of a matrix mold having excellent durability of mold releasability in the preparation of replicas by resin casting is disclosed. The composition comprises, in addition to the conventional ingredients including a vinyl-containing diorganopolysiloxane, an organohydrogenpolysiloxane as a crosslinking agent of the diorganopolysiloxane, a reinforcing silica filler and a platinum compound as a catalyst, a strongly alkaline compound of an alkali metal such as potassium hydroxide, potassium siliconate, lithium siliconate and the like in a limited amount.
Claims17
A mold-releasable curable organopolysiloxane composition which comprises, as a blend:
- (a) 100 parts by weight of a diorganopolysiloxane represented by the average unit formula
- R.sub.a SiO.sub.(4-a)/2,
- in which R is an unsubstituted or substituted monovalent hydrocarbon group and the subscript a is a positive number 1.9 to 2.4, and mainly consisting of difunctional siloxane units of the formula R.sub.2 SiO, at least two of the groups denoted by R per molecule being alkenyl groups;
- (b) an organohydrogenpolysiloxane having, in a molecule, at least three hydrogen atoms directly bonded to the silicon atoms, in an amount sufficient to provide from 0.4 to 4.0 moles of the silicon-bonded hydrogen atoms per mole of the alkenyl groups in the component (a);
- (c) an alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal oxides, alkali metal carboxylates, alkali metal alcoholates and alkali metal siliconates, in an amount of 5 to 5000 ppm by weight as alkali metal based on the amount of the component (a);
- (d) 5 to 50 parts by weight of a finely divided silica filler having a specific surface area of at least 50 m.sup.2 /g;
- and
- (e) a catalytic amount of a platinum compound.
A process for the production of a cured silicone rubber comprising:
- (i) uniformly blending together:
- (a) 100 parts by weight of a diorganopolysiloxane represented by the average unit formula
- R.sub.a SiO.sub.(4-a)/2,
- in which R is an unsubstituted or substituted monovalent hydrocarbon group and the subscript a is a positive number 1.9 to 2.4, at least two of the groups denoted by R per molecule being alkenyl groups, and said diorganopolysiloxane having a linear molecular structure;
- (b) an organohydrogenpolysiloxane having, in a molecule, at least three hydrogen atoms directly bonded to silicon atoms, in an amount sufficient to provide 0.4 to 4.0 moles of the silicone-bonded hydrogen atoms per mole of the alkenyl groups in component (a);
- (c) an alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal oxides, alkali metal carboxylates, alkali metal alcoholates and alkali metal siliconates, in an amount of 5 to 5,000 ppm by weight as alkali metal based on the amount of component (a);
- (d) 5 to 50 parts by weight of a finely divided silica filler having a specific surface area of at least 50 m.sup.2 /g;
- and
- (e) a catalytic amount of a platinum compound;
- and
- (ii) curing the resultant composition at room temperature to 150.degree. C. for 30 minutes to 3 days.
A mold-releasable curable organopolysiloxane composition which comprises, as a blend:
- (a) 100 parts by weight of a diorganopolysiloxane represented by the average unit formula
- R.sub.a SiO.sub.(4-1)/2,
- in which R is an unsubstituted or substituted monovalent hydrocarbon group and the subscript a is a positive number 1.9 to 2.4, at least two of the groups denoted by R per molecule being alkenyl groups, and said diorganopolysiloxane having a linear molecular structure;
- (b) an organohydrogenpolysiloxane having, in a molecule, at least three hydrogen atoms directly bonded to silicon atoms, in an amount sufficient to provide 0.4 to 4.0 moles of the silicon-bonded hydrogen atoms per mole of the alkenyl groups in component (a);
- (c) an alkali metal compound selected from the group consisting of alkali metal hydroxides, alkali metal oxides, alkali metal carboxylates, alkali metal alcoholates and alkali metal siliconates, in an amount of 5 to 5,000 ppm by weight as alkali metal based on the amount of component (a);
- (d) 5 to 50 parts by weight of a finely divided silica filler having a specific surface area of at least 50 m.sup.2 /g;
- and
- (e) a catalytic amount of a platinum compound.
Dependencies are inferred from the claim text.