HETEROGENEOUS MEMBRANE AND PROCESS FOR PRODUCTION THEREOF

摘要

A heterogeneous membrane of a thermoplastic crystalline polymer composed of a microporous layer and a nonporous layer and having excellent properties, for example as a diaphragm for separating a gaseous mixture; and a process for production thereof. The heterogeneous membrane is in the form of, for example, a flat film or a tubular film (preferably a hollow fiber). The microporous layer contains pores with a diameter of 0.01 to 50 microns, whereas the nonporous layer does not substantially contain pores having a diameter of at least 30 ANGSTROM and has a thickness of 0.01 to 1 micron. The heterogeneous membrane is characterized by having at least 3 times as high an apparent oxygen permeability coefficient P(O2) at 25 DEG C. as a nonporous homogeneous membrane of the same material and an oxygen-nitrogen separation coefficient alpha (O2/N2) at 25 DEG C., i.e. the ratio of the apparent oxygen permeability coefficient P(O2) to the apparent nitrogen permeability coefficient P(N2), of at least 1.2. The heterogeneous membrane can be industrially produced easily and conveniently with a high efficiency by a melt-extrusion film-forming step, a stretching step and a heat-setting step under specified conditions.