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Abstract

A method of making a battery separator useful in flooded cell type lead acid batteries comprising providing a sheet of microporous polyolefin material having two planar surfaces, forming at least one hollow rib extending from one of the planar surfaces, and wholly or partially filling the hollow rib with a rib core material. The forming of the hollow rib and the filling of the hollow rib with rib core material may be effected in separate steps or simultaneously. Where the formation and filling of the hollow rib take place simultaneously, the process involves applying at least one bead of a rib core material to one planar surface of the sheet of microporous polyolefin material, pressing the bead of rib core material into said microporous polyolefin sheet to thereby displace the microporous polyolefin material located thereunder outwardly from the other planar surface to thereby form a rib member projecting from said other planar surface. The separator thus produced is a sheet of microporous polyolefin material having at least one rib projecting from one planar surface thereof, the rib having an outer surface of the microporous polyolefin material and a core of a rib core material. The microporous polyolefin material is preferably microporous polyethylene. The rib core material is a polymeric material selected from the group consisting of thermoplastics, thermosetting polymers and reactive hot melts.

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