Patent ID: 7794818

Claim:
A process for preparing transparent adhesive polyvinyl butyral interlayer, the process comprising: a. providing a continuous web of self-supporting adhesive polyvinyl butyral sheet; b. slitting the web at or near its mid-point to form two slit webs; and c. winding the slit webs onto separate rolls; wherein the continuous web of self-supporting adhesive polyvinyl butyral sheet comprises: (i) two areas of uniform thickness profile across at least 20% of its width extending from the edges of the web toward the center such that by splitting the web at or near its midpoint between the outer edges, two pieces of sheet can be obtained each having an area of at least 20% uniform thickness, and (ii) an area of non-uniform thickness profile wherein the thickness of the web is continuously increasing starting at or near the center of the web and increasing in the direction of both edges to the areas of uniform thickness along the edges of the web, wherein a vertex is formed at each juncture where an area of uniform thickness meets an area of non-uniform thickness, and wherein the vertices are curved such that a sharp edge is not detectable by physical inspection of the vertex.