PURPOSE:To manufacture a film with very fine pores in high density and with narrow width of pore diameter distribution by mixing a block copolymer and a hydrophilic polymer, manufacturing a film, and then removing the hydrophilic polymer by means of a solvent. CONSTITUTION:A block copolymer containing a component polymer compatible with a hydrophilic polymer such as plystyrene-polytutadiene or the like and a component polymer non-compatible with said hydrophilic polymer and a hydrophilic polymer such as polyvinyl ether are mixed, and a film is formed by the casting method or the like. At that time, size, shape and the like of a micro-phase separation organization are adjusted. Then, said polymer film is immersed in a hydrophilic solvent such as water, alcohol, and the hydrophilic polymer is removed by the supersonic washing method or the like, and further the same is dried to manufacture a film with 50-100Angstrom pores. The pore diameter distribution at that time is as small as the maximum pore diameter/manimum pore diameter =1.5-50. Thus, a film with very fine pores in high density and narrow width of pore diameter distribution can be manufactured easily and inexpensively.
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