Coated composite high voltage electrical insulator

Abstract

The present invention relates to a one-part room temperature vulcanizable organopolysiloxane rubber composition which crosslinks in the presence of moisture to form a coating for the high voltage insulators including composite insulators. The one-part organopolysiloxane rubber composition comprises the product which is obtained by mixing the following: a) from about 20 to about 60 weight percent of one or more polydiorganosiloxane fluids of the formula R″ [(R)2SiO]n(R)2SiR′ in which R is a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical, R′ and R″ which may be the same or different are OH or a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical and n has an average value such that the viscosity is from about 10 to about 100,000 centipoise at 25° C., wherein at least one of the polyorganosiloxane fluid has at least one of R′ and R″ equal to OH and n has an average value such that the viscosity is in the range from 100 to 100,000 centipoise at 25° C., preferably from 1,000 to 40,000 centipoise at 25° C.; b) from 0 to about 40 weight percent of a cyclo-organosiloxane of the formula [(R)2SiO]n in which R is a monovalent alkyl or alkylene radical having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms and n has an average value of 3 to 10 c) from 0 to about 40 weight percent of an inorganic extending or non-reinforcing filler c) from about 0.5 to about 15 weight percent of an amorphous SiO2 reinforcing filler having a surface area of between about 100 to 250 m2/g and a particle size range between about 0.01 and 0.03 microns; e) from about 1 to about 10 weight percent of an oximinosilane cross-linking agent of the formula; RSi(ON═CR′2)3 in which R and R′ are independently selected from monovalent alkyl or alkylene radicals having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms; f) from about 0.2 to about 3 weight percent of an adhesion promoter of the formula 1 in which R2 and R3 are independently selected from monovalent alkyl or alkylene radicals having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms, b is an integer between 0 and 3, and R1 is a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 10 carbon atoms which may optionally contain a functional group; g) from about 0.02 to about 3 weight percent of an organotin salt as a condensation catalyst; and h) from about 20 to about 50 weight percent of alumina trihydrate, the alumina trihydrate having a median particle size of 10 μm to 30 μm, containing 65.1 percent Al2O3, 34.5 percent combined H2O, 0.3 percent Na2O, 0.02 percent CaO, 0.01 percent SiO2 and having a specific gravity of 2.42.

Dependencies are inferred from the claim text.