To obtain a coating film which closely adheres to a substrate and having a low refractive index and a large angle of contact with water by heat- curing a coating film of a solution of a polysiloxane prepared by cocondensing an alkoxy organosilicon having a specified composition in the absence of water on the surface of a substrate.
A reaction mixture is formed by mixing a silicon compound (A) represented by formula I (wherein R is a 1-5 C alkyl) with a silicon compound (B) represented by formula I (wherein R1 is a 1-5 C alkyl; and (n) is 0-12), a 1-13 C alkyl alcohol (C) and oxalic acid (D) in such amounts that 0.05-0.43mol of B is present per mol of A, 0.5-100mol of C and 0.2-2mol of D are present per mol of the total alkoxyls of A and B, and 0.5-10wt.% (in terms of the Si atom) SiO2 is present. This solution is heated to 50-180°C in the absence of water until the total residual amount of A and B decreases to 5mol% or below to form a polysiloxane solution. A coating fluid containing this solution is applied, and the coating film is heat-cured at 80-450°C to obtain a coating film having a refractive index of 1.28 and an angle of contact with water of 90-115 degrees. This film is useful as an antireflection film.
NAKADA TAKAKAZU
SAKAI RIE
HOSOYA TAKESHI
