Method of producing microporous thermoplastic resin membrane

Abstract

A method of producing a microporous thermoplastic resin membrane of excellent permeability having uniform and fine micropores without filling stress concentrators to the thermoplastic resin is provided. Namely, there is provided a method of producing a microporous thermoplastic resin membrane, in which a thermoplastic resin foam incorporating fine cells having a ratio B/A between a cell size (A) and a wall thickness (B) of the cells of less than 0.5 and having a void ratio of not less than about 50% is subjected to plastic deformation of the boundaries of the cells themselves sufficient to cause shape deformation of the cells, thereby breaking the boundaries of the cells. Also there is provided a microporous thermoplastic resin membrane of excellent permeability having uniform and fine micropores produced by the method as described above.

Dependencies are inferred from the claim text.