Preparation of semi-permeable composite membranes

A process for producing semipermeable composite membranes from at least one porous support and at least one semipermeable layer formed on the porous support, characterized in that an at least bifunctional amine having primary or secondary amino groups and an at least bifunctional bisulfite-capped isocyanate are reacted on the surface of the porous support in which the amine and the capped isocyanate are applied separately in dissolved form to the porous support and, as solvents for the amine and the capped isocyanate, water or aqueous mixtures are used, the solvents for the amine or the capped isocyanate being miscible with one another and the membranes thus obtained and their use in pressure filtration and reverse osmosis.