Patent ID: 7563516

Claim:
An intermediate sheet having a laminated structure including a first polyvinyl acetal resin layer (A) and a second polyvinyl acetal resin layer (B), characterized in that: said first polyvinyl acetal resin layer (A) contains a plasticizer and a first polyvinyl acetal resin obtained via acetalization of polyvinyl alcohol with at least one aldehyde (a) selected from the group consisting of aldehydes having 4-6 carbon atoms; said second polyvinyl acetal resin layer (B) contains a plasticizer and a second polyvinyl acetal resin in the form of a coacetalized product obtained via coacetalization of polyvinyl alcohol with at least one aldehyde (a) selected from the group consisting of aldehydes having 4-carbon atoms and with at least one aldehyde (b) selected from the group consisting of aldehydes having 1-3 carbon atoms; and a polymer unit (X) and a polymer unit (Y), in total, account for at least 55% by mole while the first polymer unit (X) alone accounts for 0.5-80% by mole of the total of said coacetalized product, wherein the polymer unit (X) is an acetalized unit derived from the first aldehyde (a) and the polymer unit (Y) is an acetalized unit derived from the second aldehyde (b) the plasticizer content of the second polyvinyl acetal resin layer (A) is generally in the range of 30-45 parts by weight, the plasticizer content of the second polyvinyl acetal resin layer (B) is generally in the range of 10-40 parts by weight, the plasticizer content (A)/plasticizer content (B) is in the range of 1.0-3, wherein the plasticizer content (A) is a plasticizer content of the first polyvinyl acetal resin layer (A) and the plasticizer content (B) is a plasticizer content of the second polyvinyl acetal resin layer (B).