| 摘要 |
A coating liquid containing a polymer and a hydrophobic solvent is applied to a support to form a coating layer. In a humidifying process with high humidity, the coating layer is set under an atmosphere having a first dew point higher than a surface temperature of the coating layer. Then, in a humidifying process with low humidity, the coating layer is set under an atmosphere having a second dew point higher than the surface temperature of the coating layer and lower than the first dew point. Thereby, water vapor is condensed from ambient air on the coating layer to generate minuscule water drops. Thereafter, the coating layer is dried to form a porous film having plural pores made by the minuscule water drops as a template. Since the humidifying process with high humidity is performed for a short period of time and then the humidifying process with low humidity is performed, the minuscule water drops are prevented from growing up, to obtain a porous film having minute pores.
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