PROCESS FOR PRODUCING ORIENTED THERMOPLASTIC RESIN FILM, APPARATUS THEREFOR AND BASE FILM FOR OPTICAL FILM

摘要

In longitudinally drawing a formed polyester film (18) while heating one of the obverse and reverse surfaces of the film by means of a radiant heating system heater (30), the radiated electromagnetic waves consist of those of wavelength band effecting transmission of 20 to 50% of the total thermal energy radiated on the one surface of the polyester film (18) from the one surface to the other surface. Accordingly, even in the event of longitudinal drawing while heating one surface of the film in the longitudinal drawing step, curling of the film can be suppressed.