Abstract: A multi-layer microfiltration membrane having an integrated prefiltration layer. Pursuant to a phase inversion process, several layers are successively poured out onto one another prior to phase separation of a lower layer, with the viscosity for the pour solution decreasing toward the upper layers. This produces a microporous, multi-layer, integral filtration membrane having a homogenous symmetrical pore structure for the final filtration layer and an open-pored structure for the prefiltration layer disposed therebelow. Even with small pore diameters, this membrane can be easily pleated for installation in filter cartridges without the formation of damage at the crease edges. High throughput rates are possible at a low tendency to clog.

Abstract: A permanently hydrophilic membrane on an aromatic polysulphone basis and a method for its production. Due to their chemical and thermal resistivity and also because they are unobjectionable with respect to their contacting foodstuffs, membranes on an aromatic polysulphone basis represent a preferred filtration material. But since they are hydrophobic, they would have to be hydrophilated before they are used. Known hydrophilation methods were insufficient to maintain the hydrophilic properties of the membranes, especially after repeated sterilization. The new method aims at making the membranes permanently hydrophilic under sterilization conditions. In an aftertreatment step, the membranes on an aromatic polysulphone basis are conducted, before or after drying, through an impregnating bath of polyvinylpyrrolidone, a copolymer of vinylpyrrolidone and one or more hydrophobic monomers and peroxodisulphate, then heated to 70 to 150.degree. C. and cooled down again.