DE3342823

Processes for the production of filter elements based on aromatic polyamide in which a semi-finished filter element is produced from a solution of the polyamide in aprotic solvent and the polyamide is then coagulated by immersion in a liquid bath containing precipitating agent may be used for the production of filter elements with a pore size of from 0.05 mu m to 10 mu m for the separation of particles from filtrates by microfiltration if pore formers are added to the solution mixture for the preparation of the semi-finished filtering agent in a quantity of from 20 to 35% by weight and precipitating agents are added in quantity ranging from 1% by weight to the limit of solution stability of the polyamide and if the same solvent is added to the precipitation and coagulation bath as to the solution mixture in a quantity of from 35 to 55% weight and if the same pore former as that used in the solution mixture is added in a quantity of from 1% by weight to 40% by weight, to be specific, in a quantity ranging form 1% by weight to the same percentage pore former content as in the solution mixture if filter elements having an asymmetric cell structure and a pore size of from 0.05 mu m to 10 mu m are to be produced or in a quantity ranging from the same percentage pore former content as in the solution mixture to 40% by weight if filter elements having a symmetric cell structure and a pore size of from 0.05 to 10 mu m are to be produced. The polyamide content of the solution mixture used for the semi-finished filter element, the temperature of the precipitation and coagulation bath and the water content of the precipitation and coagulation bath may then be used as controllable process parameters for obtaining the desired membrane density.