| 摘要 |
PROBLEM TO BE SOLVED: To provide a porous film by casting a solution, in a filmy shape, over a substrate and drying the obtained filmy material while generating a fluctuation of polyamide density in the filmy material in the in-plane direction of the film. SOLUTION: A polyamide solution of a polyamide and an alcoholic solvent is adjusted by dissolving both polyamide and alcoholic solvent in such a ratio of 0.5-7 wt.% of the former and 99.5-93 wt.% of the latter. In addition, a filmy material is formed on a substrate by a method for casting the solution over a platelike material which is a substrate or over the surface of a movable belt or a method for soaking the substrate into the solution. The filmy material of the polyamide solution formed on the substrate is dried on condition that the fluctuation of polyamide density be generated in the in-plane direction of a film during drying process. In order to make sure that the fluctuation is generated, the filmy material needs to be dried at a temperature of 40 deg.C or less and for a drying time of one minute or more. Thus it is possible to obtain the polyamide porous film by peeling the dried film from the substrate.
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