UNG UND SEKUNDÄRZELLE

摘要

An improved wet-laid nonwoven fabric for a battery separator wherein 20 to 95% by weight of thermoplastic staple fibers having a single fiber diameter of 20 mu m or less are three-dimensionally entangled with hot-melt fibers having a melting point lower by 20 DEG C than that of the thermoplastic staple fibers so that a mean fiber entangling point interval is 300 mu m or less, wherein at least part of the hot-melt fibers is fused to bond the fibers with each other to fix the nonwoven structure. The nonwoven fabric has a basis weight in a range from 10 to 350 g/m<2>, a thickness in a range from 30 to 1000 mu m and an apparent density in a range from 0.26 to 0.7 g/cm<3>, and excellent in uniformity and mechanical strength. The wet-laid nonwoven fabric is particularly excellent in air permeability, liquid holding capability, liquid retention capability and liquid absorption rate and satisfies the requirement for a battery separator. Therefore, it is useful for the production of a high performance secondary battery having favorable overcharging characteristic and cycle characteristic. The wet-laid nonwoven fabric according to the present invention is prepared by subjecting a wet-laid web of staple fibers having a ratio L/D of a fiber length L to a single fiber diameter D in a range 0.5 x 10<3> to 2.0 x 10<3> to a hydroentangling treatment while taking a care not to leave a mark from a water jet on the web.