1476791-A is referenced by 1 patents.
1476791 Stretched porous polymer films MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 7 June 1974 [11 June 1973 6 Feb 1974] 25489/74 Heading C3C Porous polymer films are made by the separate sequential steps of (a) forming voids in a stretchable polymer composition having a phase separation structure (i.e. in which the same or different compounds form two or more phases) and having the property of forming voids on deformation at a temperature below its m.p. (b) heating the polymer composition concontaining the voids to its stretching temperature (which is lower than the m.p. and higher than the temperature at which voids are formed on deformation) under tension of at least 0À1 Kg/mm2 in one direction so that the voids do not disappear and (c) enlarging the voids by multi-axial stretching of the polymer composition at the stretching temperature.; In the examples sheets of isotactic polypropylene which was connected to let crystalline particles grow high impact polystyrene (containing butadiene) and blends of polyethylene isotactic and atactic polypropylene nylon 6, polystyrene, ethylene vinyl acetate copolymer, polyethylene terephthalate, nylon 12, polyvinyl chloride, polyacetal and/or polycarbonate were cracked by bending along a bar in liquid nitrogen or at room temperature, by pressing a metal bar against the sheet placed on a rubber plate, by winding the sheet around a metal bar or by stretching the sheet by rolling between belts; the cracked sheets were then heated under tension and then stretched biaxially in one or two stages.