White polyester film and surface light source therewith

Abstract

[Problems] To provide: a white polyester film excellent in whiteness, reflecting properties, lightweight properties, and dimensional stability to heat; and a surface light source employing the film and having excellent luminance characteristics. [Means for Solving Problems] The white polyester film comprises a white polyester layer (layer W) which comprises a polyester resin ingredient (A) and an ingredient (B) incompatible with the resin ingredient (A) and has bubbles therein. The incompatible ingredient (B) is a cycloolefin resin (b) having a glass transition temperature of 110° C. or higher, and the content (Z) of the cycloolefin resin (b) in the white polyester layer (layer W) is 5-50 wt. % based on the white polyester layer (layer W).

Dependencies are inferred from the claim text.