Bipolare Membran und Verfahren zu deren Herstellung

The invention relates to a bipolar diaphragm, comprising an anion-selective and a cation-selective layer and a process for its manufacture, by manufacturing a first ion-selective layer from the liquid phase and applying a second ion-selective layer of opposite charge on the first layer. From a polymer solution L1, an ion-selective layer is produced by expanding the solution L1 into a more or less thick film, and during expansion, the resulting polymer film is exposed to an inert gas or gas mixture containing water vapour or saturated with water vapour, a gas or gas mixture is used with such a high content of water vapour that firstly, a condensation of the water is avoided and secondly, the mixing gap in the phase diagram of polymer-solvent-water is attained, the solvent is removed and, on the side of the resulting ion-selective layer which was exposed to the gas or gas mixture containing water vapour, a second ion-selective layer with opposite charge is produced from a polymer solutio n L2.