resin, and b) a hydrolysate of at least one alkoxysilane represented by formula (1) or formula (2), or a mixture thereof: R1 --Si(OR2)3. ( 1) Si(OR2)4 ( 2) wherein R1 is a methyl group, an ethyl group or an organic group containing at least one group selected from the group consisting of a vinyl group, an acryloyl group, a methac