Membrane film for batteries, having a shut-off function

摘要

The invention relates to a biaxially oriented microporous film composed of at least two coextruded layers encompassing an external shut-off layer and another layer, wherein both layers contain a mixture of propylene homopolymer and propylene block copolymer andβ-nucleation agent. The propylene block copolymer I of the other layer has a melting point exceeding 140° C. and the propylene block copolymer II of the external shut-off layer has a melting range starting at a temperature ranging from 50 to 120° C. The melting point of the propylene block copolymer I is greater than the melting point of the propylene block copolymer II. The film can be used as a separator in a primary or secondary battery.