Porous film and method for producing same

Abstract

Provided are a porous film having excellent surface smoothness and a method for producing the same. The surface roughness of a porous film of polyvinylidene fluoride, polyethersulfone, polyimide and/or polyamide-imide is Ra 30,000 Å or less. The opening diameter of the porous film is preferably from 100 nm to 5000 nm. The method for producing a porous film preferably includes a step for kneading a varnish containing fine particles and at least one resin selected from the group consisting of polyvinylidene fluoride, polyether sulfone, polyamic acid, polyimide, polyamide-imide precursor, and polyamide-imide. The varnish preferably has a viscosity at 25° C. of 0.1-3 Pa·s, a solids fraction concentration of 10-50 mass %, and a fine particle average particle size of 10-5000 nm.

1 . A porous film of polyvinylidene fluoride, polyethersulfone, polyimide and/or polyamide-imide,
 wherein surface roughness Ra is 30000 Å or less.   
     
     
         2 . The porous film according to  claim 1 , wherein an opening diameter in a surface is 10 nm to 5000 nm. 
     
     
         3 . The porous film according to  claim 1 , wherein the surface roughness Ra is surface roughness Ra on a surface opposite to a surface facing a substrate during production. 
     
     
         4 . A porous film of polyvinylidene fluoride, polyethersulfone, polyimide and/or polyamide-imide,
 wherein the porous film includes a structure in which spherical pores communicate with each other,   no waviness is deeper than a recess formed by an opening portion, and   a diameter of the opening portion is 10 nm to 5000 nm.   
     
     
         5 . A method for producing a porous film of polyvinylidene fluoride, polyethersulfone, polyimide and/or polyamide-imide, the method comprising:
 kneading a varnish containing fine particles and resin such that surface roughness Ra of an unburned composite film containing the fine particles and the resin that is at least one resin selected from the group consisting of polyvinylidene fluoride, polyethersulfone, polyamide acid, polyimide, a polyamide-imide precursor and polyamide-imide, is 30000 Å or less.   
     
     
         6 . A method for producing a porous film of polyvinylidene fluoride, polyethersulfone, polyimide and/or polyamide-imide, the method comprising:
 kneading a varnish containing fine particles, and at least one resin selected from the group consisting of polyvinylidene fluoride, polyethersulfone, polyamide acid, polyimide, a polyamide-imide precursor and polyamide-imide,   wherein the varnish has a viscosity at 25° C. of 0.1 to 3 Pa·s, a solid content concentration of 10 to 50% by mass, and an average particle diameter of the fine particles of 10 to 5000 nm, and   the kneading is carried out for 2 minutes to 10 hours.   
     
     
         7 . The porous film according to  claim 2 , wherein the surface roughness Ra is surface roughness Ra on a surface opposite to a surface facing a substrate during production.