Patent ID: 8431047

Claim:
A polyvinyl acetal resin composition, which comprises a polyvinyl acetal resin A and a polyvinyl acetal resin B incompatible with said polyvinyl acetal resin A, which is formed by acetalizing a mixed polyvinyl alcohol containing two or more kinds of polyvinyl alcohols having different saponification degrees, and wherein said mixed polyvinyl alcohol contains main two kinds of polyvinyl alcohols in which X and Y satisfy the relationship of the following equation (1): [Formula 1] | X−Y|≧ 10 (1) in which X represents the saponification degree of any one polyvinyl alcohol a of the polyvinyl alcohols contained in the mixed polyvinyl alcohol and Y represents the saponification degree of a polyvinyl alcohol b other than the polyvinyl alcohol a, and wherein in denoting, by M, the polymerization degree of one polyvinyl alcohol having a higher polymerization degree of said main two kinds of polyvinyl alcohols and denoting the polymerization degree of the other polyvinyl alcohol by N, M and N have the relationship of the following equation (2): [Formula 2] M/N≧ 3 (2) and a phase composed of said polyvinyl acetal resin A and a phase composed of said polyvinyl acetal resin B form a sea-island structure.