Improved multilayer porous membranes and methods of making same

A multilayer film comprising at least two co-extruded layers wherein the two co-extruded layers comprise different polymers and one of the two co-extruded layers comprises an extrusion additive. Examples of useful extrusion additives may include nucleating agents or pore-forming particles. Methods of making the films are also disclosed. The use of extrusion additives when co-extruding two different polymers avoids some drawbacks associated with processes involving co-extrusion of different polymers, particularly processes in which the co-extruded non-porous precursor is subsequently stretched to form pores. For example, the defects of lower permeability, difficulty in manufacturing lower Gurley, cracking and the like can be improved. 多层膜，包含至少两个共挤出的层，其中，两个共挤出的层包含不同的聚合物，并且两个共挤出的层中的一个含挤出添加剂。有用的挤出添加剂的例子可以包括成核剂或成孔颗粒。还公开了制造该膜的方法。当共挤出两种不同的聚合物时使用挤出添加剂避免了与涉及不同聚合物的共挤出的工艺相关的一些缺点，特别是其中共挤出的无孔前体随后被拉伸以形成孔的工艺。例如，渗透性较低、难以制成较低的Gurley、开裂等缺点可以得到改善。