Resin sheet having porous layered structure useful as electrode separator for electric cells. [olefin resin with finely divided inorganic substace and surfactant]

A resin sheet having a porous layered structure useful as an electrode separator for electric cells is described. The sheet comprises an olefin resin, a finely divided inorganic substance, and at least one substance selected from the group consisting of a water-swellable thermoplastic resin, a water-insoluble or difficultly water-soluble hydrophilic nonionic surface active agent, and a water-insoluble or difficultly water-soluble hydrophilic anionic surface active agent. The sheet includes fine pores arranged throughout its cross section in a plurality of layers, at least some of them forming open cells. This sheet is prepared by a process comprising fabricating a mixture containing the above components into a sheet, and stretching the sheet in at least one direction. 2 figures.