Patent ID: 7829186

Claim:
A porous film comprising a film base and a coat of a chemical-resistant polymeric compound, the film base produced by a phase conversion method in which mixtures containing polymers are cast as films and then introduced to solidifying liquids, the coat of the chemical-resistant polymeric compound forming a thin solid layer over cell wall surfaces throughout the porous structure of the film base, and formed by subjecting a solution of a chemical-resistant polymeric compound or a precursor thereof dissolved in a solvent which can dissolve the polymeric compound or a precursor thereof to a coat forming procedure, with or without further subjecting the coat formed to treatment with at least one selected from the group consisting of heat, ultraviolet rays, visible radiations, electron beams, and radioactive rays, wherein: the porous film includes a multiplicity of communicating micropores having an average pore size of 0.01 μm or more and 5 μm or less; an average rate of open pores inside the porous film (porosity) is 30% to 80%; the porous film maintains the properties of the film base; an amount of the coal of the chemical-resistant polymeric compound is 0.01 to 50 percent by weight relative to the porous film; the film base comprises amide-imide polymers or imide polymers, and the coat of the chemical-resistant polymeric compound comprises at least one selected from the group consisting of phenolic resins, epoxy resins, fluororesins, and ethylene/vinyl alcohol copolymers.