PURPOSE: To obtain a microporous film of a thermoplastic resin which is water- repellent and has a strength sufficient for practical use and a high porosity, by a method wherein a porous film of a thermoplastic resin having a specified construction and specified properties is stretched and heat-treated in specified conditions.
CONSTITUTION: A porous film having three-dimensional network skeleton structure consisting of open pores having a porosity of 30W70% and an average pore diameter of 0.05W1μm is formed from a thermoplastic resin having a critical surface tension of not higher than 35dyn/cm. The film is stretched in space between a temperature of lower than the melting point or the sofetening point of the resin by 5°C and a temperature of lower than the melting point or the softening point by 50°C, and is heat-treated in space at a temperature between the stretching temperature and the melting or softening point, inclusive. Accordingly, a microporous film having an open-pore porosity of at least 60% with an average pore diameter of 0.1W2.0μm and sufficient strength and flexibility for practical use can be obtained.
KOUNO MITSUO
MATSUDA KAZUO
| JPS56159128A | 1981-12-08 |