Patent ID: 8435432

Claim:
A method for producing a transparent polymer film, which comprises heat-treating a polymer film selected from the group consisting of cellulose ester films, polycarbonate films, cyclo-olefin polymer films, poly alylate films, poly sulfone films, vinyl polymer films, polyamide films, polyimide films, cyclo-olefin copolymer films and poly norbornene films at a temperature T (unit, ° C.) satisfying a condition of the following formula (1): Tc≦T<Tm 0 Formula (1) wherein Tc represents the crystallization temperature (unit, ° C.) of the polymer film before the heat treatment; and Tm 0 represents the melting point (unit, ° C.) of the polymer film before the heat treatment, wherein the method is for producing a transparent polymer film satisfying the following formula (2): | Rth|/Re< 0.5 Formula (2) wherein Re represents the retardation (unit, nm) in the in-plane direction; and Rth means the retardation (unit, nm) in the film-thickness direction.