Patent ID: 8827086

Claim:
A hydrophilic, integrally asymmetric, semi-permeable hollow-fibre membrane for ultrafiltration made from a hydrophobic aromatic sulfone polymer and at least one hydrophilic polymer, the membrane exhibiting an inner surface facing towards its lumen, an outer surface facing outwards and an intermediate wall with a wall thickness, whereby in its wall on the inner surface the hollow-fibre membrane has an open-pore separating layer, adjoining the separating layer towards the outer surface a subsequent supporting layer with asymmetric, sponge-like pore structure without finger pores and adjoining the supporting layer towards the outer surface an outer layer, characterised in that a. The separating layer has a cutoff in the range between 20,000 and 200,000 daltons and a thickness of no greater than 10% of the wall thickness and the pore structure in the area of the separating layer is essentially isotropic, b. The size of the pores in the supporting layer initially increases from the separating layer up to a zone with maximum pore size, then decreases beyond this zone towards the outer layer, c. The outer layer has a thickness of 10 to 25% of the wall thickness, the pore structure in the area of the outer layer is essentially isotropic and the mean size of the pores in the outer layer is larger than the mean pore size in the separating layer, but smaller than the mean pore size in the supporting layer, d. The wall thickness lies in the range from 100 to 450 μm, and e. The hollow-fibre membrane has a transmembrane flow for water of at least 0.5 ml/(cm 2 ·min·bar) and a breaking strength σ B of at least 500 cN/mm 2 , wherein the breaking strength σ B is defined as a breaking force BK of the membrane referred to the cross-sectional area A Q of the wall of the membrane.