Microporous film and method for producing the same

A method for producing a microporous film, comprising the steps of (A) to (D) below:

• (A) a step of taking off a thermoplastic resin composition in a molten state at a draw ratio of 10 to 300 to obtain a film, the thermoplastic resin composition comprising (a) 100 parts by mass of a polypropylene resin and (b) 5 to 90 parts by mass of a polyphenylene ether resin;
• (B) a step of heat-treating the film obtained at the step (A) at a temperature of not less than 100° C. and not more than 160° C.;
• (C) a cold stretching step of stretching the film obtained at the step (B) at a temperature of not less than −20° C. and less than 100° C.;
• and
• (D) a hot stretching step of stretching the film obtained at the step (C) at a temperature of not less than 100° C. and less than 170° C.