| abstract |
A microporous membrane is produced by coolingna solution comprising a vinylidene fluoride homopolymernor copolymer having a weight average molecular weight ofn1 x 10 5 or more and a solvent therefor, to form a two-phasengel, said microporous membrane comprising anpolymer phase comprising said vinylidene fluoridenhomopolymer or copolymer, and intercommunicating voidsnwhich have an average pore size measured by the half-drynmethod of 0.005 to 5 µm and range from one side of thenmembrane to the other side, and said microporousnmembrane having as its internal structure a percolationnstructure in which the polymer phase forms an isotropicnnetwork structure by three-dimensional branching innarbitrary directions, the voids are formed bynsurrounding by said polymer phase of the networknstructure and intercommunicate with one another, and thenratio of the maximum pore size measured by the bubblenpoint method to the average pore size measured by thenhalf-dry method is 2.0 or less. |