Patent ID: 8414803

Claim:
A method for producing a transparent polymer film, comprising heat-treating a polymer film containing a polymer and a plasticizer having a number-average molecular weight of from 500 to 10000 and having a repetitive unit, at a temperature T (unit, ° C.) satisfying the following formula (1) to obtain a film satisfying the following formula (2): Tc≦T<Tm 0 (1) wherein Tc means crystallization temperature (unit, ° C.) of the polymer film before heat-treatment, and Tm 0 means melting point (unit, ° C.) of the polymer film before heat treatment, | Rth|/Re< 0.5 (2) wherein Re means in-plane retardation (unit, nm) of the film; and Rth means thickness-direction retardation (unit, nm), and wherein the polymer is a cellulose acylate.