PROCESS AND APPARATUS FOR PRODUCING POROUS FILM

摘要

First and second solutions which comprise an organic solvent and a polymer and differ in viscosity are cast on a casting belt to form a cast film having a two-layer structure composed of a first layer (25) and a second layer (26). When the viscosity of the first solution, which forms the first layer (25), i.e., that layer in the cast film which is exposed to the air, is expressed by ?1 and the viscosity of the second solution, which forms the second layer (26) underlying the first layer, is expressed by ?2, then ?1 is lower than ?2 and ?1 is in the range of 1x10-4 to 1 Pa s. Thus, a porous film (17) having a large thickness (L) can be obtained irrespective of the pore diameter (D) of pores (35).