| abstract |
A porous polyimide film having a three-layer structure that comprises two surface layers (a) and (b) and a macrovoid layer sandwiched between the surfaces layers (a) and (b). The macrovoid layer has a partition wall bonding to the surface layers (a) and (b), and multiple macrovoids each surrounded by the partition wall and the surface layers (a) and (b) and having a mean pore size in the film plane direction of from 10 to 500 μm. The partition wall of the macrovoid layer has a thickness of from 0.1 to 50 μm and has multiple pores having a mean pore size of from 0.01 to 50 μm. The surface layers (a) and (b) each have a thickness of from 0.1 to 50 μm, at least one of the surface layers has multiple pores having a mean pore size of from more than 5 μm to 200 μm, and the other surface layer has multiple pores having a mean pore size of from 0.01 to 200 μm. The pores in the partition wall of the macrovoid layer as well as in the surface layers (a) and (b) communicate with each other and further communicate with the macrovoids. The film has a total thickness of from 5 to 500 μm and a porosity of from 60 to 95%. |