Multilayer microporous films and methods of making

摘要

Multilayer microporous films comprise first and second microporous film layers. The first film layer has a first maximum pore size and the second film layer has a second maximum pore size different from the first maximum pore size. In a more specific embodiment, the multilayer microporous films comprise coextruded first, second and third microporous film layers. One of the first, second and third film layers has a maximum pore size smaller than the respective maximum pore sizes of the remaining layers of the multilayer film or larger than the respective maximum pore sizes of the remaining layers of the multilayer film, and the one layer does not have an unconstrained surface in the multilayer film. Methods for producing multilayer microporous films provide a first film layer having a maximum pore size upon stretching which is different from that of a second film layer upon stretching.