POROUS FILMS, PROCESS FOR PRODUCING THE SAME, AND LAMINATE FILMS AND RECORDING SHEETS MADE WITH THE USE OF THE POROUS FILMS

摘要

Porous films each having a structure consisting of separated microphases and a light transmittance at 400 nm of at least 30 % are obtained by the dry phase transition method comprising drying a coating film of a dope containing a polymer, a good solvent for the polymer and a poor solvent for the polymer having a boiling point higher than that of the good polymer. Examples of the above polymer include cellulose derivatives, vinyl polymers such as acrylonitrile polymers and (meth)acrylate polymers, and polysulfone polymers. The films have a void content of from 10 to 60 %, an average pore size of from about 0.002 to about 0.35 mu m, and a maximum pore size of not more than 0.4 mu m. These films are excellent in transparency and can be obtained in high yields.