Patent ID: 7135064

Claim:
A silica-based coating film formed on the surface of a substrate, which film has a dielectric constant not exceeding 2.5, said film being produced by applying to the surface of said substrate, a uniform solution comprising: (A) an organic solvent; and (B) an organopolysiloxane, which is a hydrolysis-condensation product of a polyalkoxy silane compound represented by the general formula R 1 4-n Si(OR 2 )n, in which R 1 is a hydrogen atom or a monovalent hydrocarbon group, R 2 is an alkyl group and the subscript n is 2, 3 or 4, said uniform solution being produced by steps comprising: (a) dissolving said polyalkoxy silane compound in a first organic solvent, which is an alcohol solvent, to give a solution, in a concentration in the range from 1 to 5% by weight calculated as SiO 2 ; (b) admixing the solution with a basic compound and water to effect hydrolysis of the polyalkoxy silane compound so as to give said organopolysiloxane as a hydrolysis-condensation product thereof; and (c) replacing the first organic solvent in the solution with a second organic solvent, which is an aprotic polar organic solvent, in such an amount that the concentration of the organopolysiloxane in the solution is in the range from 5 to 25% by weight calculated as SiO 2 .