Method of making resilient battery separator media

Abstract

Resilient battery separator media, especially adapted for use as battery separators for starved electrolyte batteries, are formed from air laid, fibrous mats of randomly oriented, entangled microfibers which may be needled to further entangle the fibers. The fibrous mats may be essentially uniform in density throughout their thickness or may include one or two relatively high density, high tensile strength fibrous surface layer(s) and a relatively low density, more resilient fibrous layer integral with and, in one embodiment, intermediate the two surface layers wherein the fibers in the surface layer(s) of the mats are more entangled than the fibers in the resilient layer. The fibrous mats, with one or two surface layers, are formed from the air laid fibrous mats by further entangling the fibers at and adjacent one or both surfaces of the mats, e.g. through hydroentanglement, relative to the entanglement of the fibers in the resilient fibrous layer. The fibrous mats with substantially uniform densities may be made by flooding the air laid mats with a liquid and drawing a vacuum though the mats. Preferably, no organic binders are used in the mats. However, the fibers of the mats may be treated with an acid solution to hydrolyze the surfaces of the fibers and bond the entangled fibers together at their points of intersection.