Envelope type separator for storage battery and manufacturing process therefor

A process for preparing an envelope type separator for a storage battery which comprises:

• (a) forming a wet microporous paper layer from an aqueous slurry of a mixture of an inorganic powder material, a synthetic organic fiber material, and a synthetic organic pulp material;
• (b) forming a wet course paper layer from an aqueous slurry of a mixture of a synthetic organic fiber material, and a synthetic organic pulp material that contains no inorganic powder material;
• (c) combining said wet microporous paper layer and said wet coarse paper layer together by a paper making process;
• (d) heating the resultant combination-paper type wet sheet to effect drying and binding the two paper layers thereof together through fusion of the synthetic pulp materials thereby producing a combination-paper type separator sheet, said combination-paper type separator sheet being an integral combination of the microporous paper layer containing the inorganic powder material and the coarse paper layer containing no inorganic powder material, said course paper layer being comparatively large in pore diameter and thus in porosity;
• (e) arranging said separator sheet so that the mutually inward facing surfaces of the coarse paper layer are placed one upon another;
• and
• (f) adhering the mutually inward facing surfaces of the coarse paper layer together by melting the synthetic pulp materials by thermal fusion at predetermined locations thereof so that the separator sheet is formed into the shape of an envelope.