| abstract |
A process for preparing a porous sheet material, comprises impregnating and/or coating on a substrate a water-in-oil polyurethane emulsion (d) comprising a hydrophobic polyurethane (a), a hydrophilic polyurethane (b), an organic solvent (c) and water, and drying it, characterized in that said hydrophobic polyurethane (a) is a hydrophobic polyurethane dispersion (e) obtained by reacting a hydrophobic polyol, an organic diisocyanate and a chain extender in an organic solvent (c) which has a limited compatibility with water and in which the polyurethane thereby formed is substantially insoluble; said hydrophilic polyurethane (b) is a polyurethane containing about 20 to about 40% by weight, based on the total polymer, of polyoxyethylene groups and the weight ratio of (a): (b) is about 90-99: about 10-1. |