Silicone rubber compositions for high-voltage electrical insulators

A liquid silicone rubber composition for use as a high-voltage electrical insulator and for injection molding comprising

• (1) 100 parts by weight of at least one organopolysiloxane of the following average compositional formula:
• R.sup.6.sub.f SiO.sub.(4-f)/2
• wherein R.sup.6 is a halo- or cyano- substituted or unsubstituted monovalent hydrocarbon group and letter f is a number of 1.85 to 2.10, said organopolysiloxane being blocked with a trivinylsilyl, divinylmethylsilyl or vinyldimethylsilyl group at either end of the molecular chain thereof, 80-100% by weight of the organopolysiloxane being blocked with a trivinylsilyl or divinylmethylsilyl group at either end of a molecular chain, said organopolysiloxane having a viscosity of about 400 to 100,000 centipoise at 25.degree. C.,
• (2) about 1 about 100 parts by weight based on 100 parts by weight of component (1) of an inorganic filler,
• (3) about 50 to 300 parts by weight based on 100 parts by weight of component (1), of aluminum hydroxide having the formula Al.sub.2 O.sub.3.3H.sub.2 O and a mean particle size of up to 30 .mu.m,
• (4) 0 to about 20 parts by weight based on 100 parts by weight of component (1), of an organopolysiloxane of the following average compositional formula:
• R.sup.7.sub.g SiO.sub.(4-g)/2
• wherein R.sup.7 is an unsubstituted monovalent hydrocarbon group exclusive of an aliphatic unsaturated hydrocarbon group and letter g is a number of 1.85 to 2.2, blocked with a (CH.sub.3).sub.3 SiO.sub.1/2 unit at either end of its molecular chain, and having a viscosity of about 30 to 100,000 centipoise at 25.degree. C., and
• (5) about 0.1 to about 10 parts by weight based on 100 parts by weight of component (1), of an organic peroxide.