Process for the preparation of biaxially oriented polyester film

摘要

A biaxially oriented polyester film with excellent levelling property is produced by the inventive process which comprises: (a) melt-extruding and extending biaxially a polyester resin to shape it into a film; (b) treating the film thermally under a condition that formulae (1), (2) and (3) are satisfied; and (c) relaxing the film at a temperature range of Tm-60 DEG C. to Tm-140 DEG C. during the step (b): Tm-60 DEG C.<T1<Tm-10 DEG C.(1) 50<T1-T2<100(2) 5<(T1-T2)/t<25(3) wherein: Tm represents the melting point of the film ( DEG C.), T1 represents the initial temperature for the thermal treatment of the film ( DEG C.), T2 represents the terminal temperature for the thermal treatment of the film ( DEG C.), and t represents time for the thermal treatment (sec.).