Patent ID: 8529813

Claim:
A method for producing a poly(vinyl butyral) interlayer comprising: forming a first poly(vinyl butyral) melt, a second poly(vinyl butyral) melt, and a third poly(vinyl butyral) melt; coextruding said first poly(vinyl butyral) melt, said second poly(vinyl butyral) melt, and said third poly(vinyl butyral) melt to form said interlayer comprising, in order, a first low plasticizer content poly(vinyl butyral) layer, a high plasticizer content poly(vinyl butyral) layer with 50 to 80 phr by weight plasticizer, and a second low plasticizer content poly(vinyl butyral), wherein the low plasticizer content poly(vinyl butyral) layers differ from the high plasticizer content poly(vinyl butyral) layer by at least 25 phr by weight in plasticizer content; and controlling melt fracture during coextruding such that both surfaces of said interlayer have an R z of 20-50 microns and an R sm of less than 800 microns that is imparted by melt-fracture; wherein the first low plasticizer content poly(vinyl butyral) layer has a tensile break stress that is at least 15 kilograms per square centimeter greater than the tensile break stress of said high plasticizer content poly(vinyl butyral) layer, and said second low plasticizer content poly(vinyl butyral) layer has a tensile break stress that is at least 15 kilograms per square centimeter greater than the tensile break stress of said high plasticizer content poly(vinyl butyral) layer.