Forming polyolefin-filler film with rugged pattern and stretching to obtain porosity

Abstract From the Canadian patent

A gas-permeable porous film which is prepared by stretching a film made from a mixture containing a polyolefin resin and an inorganic filler at least uniaxially and possesses a rugged pattern on its surface. One process for producing the film comprises forming the aforesaid mixture into a film providing on the surface of the film a rugged pattern stretching the resulting film at least uniaxially and forming on the stretched film thus-formed a rugged pattern by means of a heated emboss roll and simultaneously allowing the stretched film to contract.