Abstract: The present invention relates to a process for the preparation of a bi-layer coated steel substrate comprising an inner inorganic ceramic layer and an external sol-gel layer, or alternatively an inner sol-gel layer and an external inorganic ceramic layer and to the bi-layer coated steel substrate obtainable by this process.

Abstract: The present invention relates to a process for preparing an anti-reflective sol-gel coating composition comprising: a) mixing a hydrolysable silicon alkoxide, (C1-C8)alcohols, an aqueous solution of one acid catalyst; and one or more surfactants of formula (II) wherein: R9 is (C1-C30)alkyl, and m is an integer selected from 2 to 40; the concentration of the surfactant of formula (II) is from 150 to 300 g/L; the molar ratio hydrolysable silicon alkoxide and aqueous solution of acid catalyst is from 0.15 to 1; the molar ratio hydrolysable silicon alkoxide and (C1-C8)alcohol is from 0.15 to 0.30, and molar ratio hydrolysable silicon alkoxide and the surfactant of formula (II) is from 7 to 11.5; b) preparing a second mixture by mixing (C1-C8)alcohols, and an aqueous solution of one acid catalyst; c) adding the second mixture to the mixture of step a); and adding (C1-C8)alcohols until the molar ratio hydrolysable silicon alkoxide and (C1-C8)alcohol is from 0.025 to 0.100 and the composition thus obtained.