| 摘要 |
Provided is a method for producing a separator which has uniform and dense pores on the negative electrode surface side. A method for producing a porous polyimide film according to the present invention comprises: a first un-burned composite film forming step wherein a first un-burned composite film is formed on a substrate using a first varnish that contains (A1) a polyamide acid or a polyimide and (B1) fine particles at a volume ratio (A1):(B1) of from 19:81 to 45:65; a second un-burned composite film forming step wherein a second un-burned composite film is formed on the first unburned composite film using a second varnish that contains (A2) a polyamide acid or a polyimide and (B2) fine particles at a volume ratio (A2):(B2) of from 20:80 to 50:50 and has a lower fine particle content ratio than the first varnish; a burning step wherein an un-burned composite film composed of the first un-burned composite film and the second un-burned composite film is burned, thereby obtaining a polyimide-fine particle composite film; and a fine particle removal step wherein the fine particles are removed from the polyimide-fine particle composite film. |
