Patent ID: 6375876
Filing Date: 2002-04-23
Classification: B01D,C08J

Abstract:
Process for producing an integrally asymmetrical hydrophobic membrane having a sponge-like, open-pored, microporous support structure and a separation layer with a denser structure compared to the support structure, the process comprising:a) preparing a homogeneous solution of 20-90% by weight of a polymer component comprising at least one polyolefin in 80-10% by weight of a solvent system containing a compound A and a compound B that are liquid and miscible with each other at a dissolving temperature, wherein the solution of the polymer component, compound A and compound B has a critical demixing temperature and a solidification temperature and has a miscibility gap in a liquid state of aggregation below the critical demixing temperature, wherein compound A comprises a solvent for the polymer component, and compound B raises a demixing temperature of a solution consisting of the polymer component and compound A, b) rendering the solution to form a shaped object, with a first and a second surface, in a die having a temperature above the critical demixing temperature, c) cooling the shaped object using a cooling medium, tempered to a cooling temperature below the solidification temperature, at such a rate that a thermodynamic non-equilibrium liquid-liquid phase separation into a high-polymer-content phase and a low-polymer content phase takes place and solidification of the high-polymer-content phase subsequently occurs when the temperature falls below the solidification temperature, and d) optionally removing compound A and compound B from the shaped object, wherein compound A is a weak solvent for the polymer component, for which a demixing temperature of a solution of 25% by weight of the polymer component in this solvent is less than 10% below a melting point of pure polymer component, wherein compound B is a non-solvent for the polymer component that does not dissolve the polymer component to form a homogeneous solution when heated to a boiling point of the non-solvent, and wherein, for cooling, the shaped object is brought into contact with a solid or liquid cooling medium that does not dissolve or react chemically with the polymer component at temperatures up to the die temperature.