Patent ID: 6623864
Filing Date: 2003-09-23
Classification: B32B,C08G,C08K,C08L,C09D,Y10T

Abstract:
A silicone composition comprising:(A) 0.50 to 4.50 weight percent of a liquid dimethylvinyl end blocked polydimethylsiloxane polymer having an average molecular weight in the range of 9300 to 12,600 and a vinyl group content in the range of 0.35 to 0.60 weight percent; (B) 2.00 to 10.00 weight percent of a blend of from 55:45 to 65:35 of a liquid dimethylvinyl end blocked polydimethylsiloxane polymer having an average molecular weight in the range of 27,000 to 36,800 and having a vinyl group content in the range of 0.18 to 0.25 weight percent and, an organopolysiloxane resin consisting essentially of (i) R12(CH2&boxH;CH)SiO0.5 units (ii) R23SiO0.5 units and (iii) SiO4/2 units wherein the molar ratio of the combination of (i) and (ii) units to (iii) units is from 0.6 to 1.1, and the concentration of (i) units is from 0.2 to 8 weight percent based on the weight of said organopolysiloxane resin, and R1 and R2 are each selected from the group consisting of alkyl groups containing from 1 to 4 carbon atoms and phenyl, with the proviso that at least 95 percent of the R1 and R2 groups are methyl groups and the total mixture has a weight percent vinyl content in the range of from 0.40 to 0.60; (C) 14.00 to 55.00 weight percent of a blend of from 60:40 to 70:30 of a liquid dimethylvinyl end blocked polydimethylsiloxane polymer having an average molecular weight in the range of 48,000 to 65,000 and having a vinyl group content in the range of 0.075 to 0.10 weight percent and, an organopolysiloxane resin consisting essentially of (i) R12(CH2&boxH;CH)SiO0.5 units (ii) R23SiO0.5 units and (iii) SiO4/2 units wherein the molar ratio of the combination of (i) and (ii) units to (iii) units is from 0.6 to 1.1, and the concentration of (i) units is from 0.2 to 8 weight percent based on the weight of said organopolysiloxane resin, and R1 and R2 are each selected from the group consisting of alkyl groups containing from 1 to 4 carbon atoms and phenyl, with the proviso that at least 95 percent of the R1 and R2 groups are methyl groups and the total mixture has a weight percent vinyl content in the range of from 0.40 to 0.60; (D) 0 to 0.45 weight percent of a silanol endblocked methylvinyl/dimethyl polysiloxane copolymer containing in the range of 8.0 to 14.0 weight percent vinyl groups; (E) 1.00 to 4.00 weight percent of a crosslinker in the form of a liquid organohydrogensiloxane in an amount sufficient to provide from 1 to 3 silicon-bonded hydrogen atoms per vinyl group present in components (A), (B), (C), and (D) combined, said organohydrogensiloxane having an average of at least three silicon-bonded hydrogen atoms per molecule and consisting essentially of units selected from the group consisting of methylhydrogensiloxy, dimethylsiloxy, dimethylhydrogensiloxy, trimethylsiloxy and SiO4/2 units; (F) 1.50 to 35.0 weight percent of hollow ceramic spheres having a mean particle size of 5 to 500&mgr; and a bulk density in the range of 0.35 g/cm3 to 0.45 g/cm3; (G) 8.0 to 30.00 weight percent of a filler having at least 90% of the particles with an average mesh size of 270 or greater selected from the group consisting of (i) quartz and (ii) magnesium oxide; (H) 0.05 to 0.40 weight percent of a catalyst, wherein the weight percent of components (A), (B), (C), (D), (E), (F), (G), and (H) are based on the total weight of components (A), (B), (C), (D), (E), (F), (G), and (H) in the composition.