Abstract: A co-casting of plural dopes is made to form a casting film (80) of a multi-layer structure having a base layer and at least one outer layer overlapping to the base layer. A viscosity of the dope forming the outer layer is at most 35 Pa·s. Just after the formation of the casting film (80), a drying air is fed out almost in parallel to the belt 73 from an outlet 82a directed in the running direction of the belt (73), while a temperature of the drying air is controlled in the range of 70° C. to 130° C. A heater 84 heats the casting film (83) from a rear side of the belt 73 such that the temperature of a rear surface of the casting film (83) may be controlled in the range of 40° C. to 80° C. Thus the production speed can be increased and the produced film is excellent in planarity.

Abstract: In a solution casting system, a casting die causes dope containing polymer and solvent to flow. A casting support belt is disposed movably under the casting die, for forming cast film from the dope being cast. A stripping roller strips the cast film having a self-supporting property to form self-supporting cast film. A first dryer stretches the self-supporting cast film, and while the self-supporting cast film is stretched, applies first gas with temperature T2 to the self-supporting cast film containing the solvent, to evaporate the solvent therefrom. A second dryer, after the self-supporting cast film is stretched, applies second gas with temperature T3 to the self-supporting cast film containing the solvent, to evaporate the solvent therefrom for obtaining polymer film. The first and second dryers satisfy a condition of: 0<T2?T3<50. Also, a tentering machine contains the first and second dryers to stretch the self-supporting cast film.