Patent ID: 8727136
Filing Date: 2014-05-20
Classification: B01D

Abstract:
1. A method for producing an integrally asymmetric membrane for microfiltration in the form of a flat sheet, based on a film forming hydrophobic first polymer from the group of aromatic sulfone polymers, the integrally asymmetric membrane having a membrane wall with a first porous surface and a second porous surface and an interior situated between the surfaces, possessing a porous structure with a pore size distribution over the membrane wall, and having a separating layer in the wall's interior with a minimum pore size, and also having, in the direction from this separating layer towards the first porous surface, a first asymmetrical region, and towards the second porous surface, a second asymmetrical region, with pore sizes increasing towards the surfaces, the second porous surface having pores with a mean diameter of at least 1 μm and having a diameter of maximum separating pores of 0.1-5 μm in the separating layer, whereby the method comprises the following steps: a. producing a homogeneous casting solution from a polymer component and a solvent system, the polymer component consisting of 10-25 wt.%, relative to the weight of the solution, of the hydrophobic first polymer from the group of aromatic sulfone polymers and 2-20 wt. %, relative to the weight of the solution, of a hydrophilic second polymer, and the solvent system consisting of 5-80 wt. %, relative to the weight of the solvent system, of a solvent for the polymer component, 0-80 wt. %, relative to the weight of the solvent system, of a latent solvent for the polymer component, as well as 0-70 wt. %, relative to the weight of the solvent system, of a non-solvent for the polymer component, b. conditioning the homogeneous casting solution to a molding temperature, c. pouring the homogeneous casting solution onto a carrier to form a film, which carrier is temperature controlled and has a temperature that is at least 15° C. higher than the molding temperature of the casting solution, and which carrier has a speed v d. conveying the film located on the carrier through a climate-controlled zone with a temperature in the range from 35 to 55° C. and a relative humidity in the range from 40 to 75%, e. introducing the film located on the carrier into a coagulation medium and initiating the coagulation of the film for the formation of a membrane structure, f. withdrawing the membrane structure from the carrier within the coagulation medium by means of withdrawal device moving with a speed of v g. stabilizing the membrane structure in the coagulation medium, h. extracting the resulting membrane and subsequently drying the membrane.