| 摘要 |
PROBLEM TO BE SOLVED: To obtain a uniform high-strength microporous film by laminating a micropore forming precursor layer comprising a thermoplastic resin A and an inert organic liquid substance B with a subsidiary layer comprising a thermoplastic resin C, etc., by coextrusion, solidifying the precursor layer by rapid curing with a heating medium, uniaxially stretching the laminate under specified temperature conditions, peeling the subsidiary layer from the laminate and extracting substance B from the remaining layer. SOLUTION: At least one micropore-forming precursor layer (layer M) made from a composition based on 15-90 pts.vol. thermoplastic resin A and 85-10 pts.vol. inert organic liquid substance B which is extractible and having a viscosity of 1,000 cP or below at 200 deg.C is laminated with a subsidiary layer (layer S) being different from layer M and based on a thermoplastic resin C by coextrusion through a multilayer die, and the laminate is solidified by rapid cooling with a heating medium, and the laminate is uniaxially stretched at a draw ratio of at least 2 under conditions including a temperature equal to the Vicat softening point of the resin A plus 50 deg.C to obtain a multilayer film. Layer S is removed from the laminate, and substance B is extracted from the remaining layer. |
