Importance

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Abstract

A void-containing composite film including (A) a polyester base layer containing voids composed mainly of a polymer mixture of a polyester and a thermoplastic resin which is not compatible with the polyester and is selected from the group of polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, cellulose resins, polysiloxane resins and silicone resins, and (B) at least one outer surface layer composed mainly of polyethylene terephthalate and formed on at least one side of the polyester base layer (A), the polyester base layer (A) and the at least one outer surface layer (B) being formed into a composite film by co-extrusion, followed by orientation in at least one direction, the void percentage of a surface portion having 3 .mu.m thickness from the surface of the polyester base layer (A) is 8% by volume or less, the average void percentage of the composite film is 10% to 50% by volume, and the composite film has substantially no voids at the interface between the polyester base layer (A) and the outer surface layer (B).

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First Claim