A process comprising the steps of: (i) providing an elongated porous web, said elongated porous web comprising two outermost surfaces; (ii) transporting said elongated porous web downwards between two impregnating heads and said impregnation heads each comprising a slot with an upper and a lower slot face, said faces having a vertical orientation or an orientation which may deviate from vertical by no more than 10°, parallel to said elongated porous web providing simultaneously to both surfaces of said elongated porous web metered quantities of a dope, said quantities on both surfaces are identical or may deviate from identical by no more than 5%, comprising at least one membrane polymer and at least one solvent therefor; (iii) thereby impregnating said elongated porous web completely with said dope and providing dope layers on each surface of said outermost surfaces of said elongated porous web with an equally thickness or a thickness which may deviate from equally by no more than 5%, said thickness being independent of the gap between one of said lower slot faces and the surface of said elongated porous web nearest thereto; (iv) subjecting said dope associated with said elongated porous web to phase inversion with at least one non-solvent wherein said phase inversion of said dope layer is symmetrical on each surface of said web, thereby forming a membrane; and (v) removing residues of said at least one solvent for said at least one membrane polymer from said membrane thereby producing an ion-permeable web-reinforced separator, characterized in that said dope has a ratio of viscosity at a shear of 1 s -1 to the viscosity at a shear of 100 s -1 at the impregnation temperature of at least 2.5 and the distance between the lower faces of the slots of the impregnation heads is greater than the distances between the upper faces of the slots of the impregnation heads. (i) providing an elongated porous web, said elongated porous web comprising two outermost surfaces; (ii) transporting said elongated porous web downwards between two impregnating heads and said impregnation heads each comprising a slot with an upper and a lower slot face, said faces having a vertical orientation or an orientation which may deviate from vertical by no more than 10°, parallel to said elongated porous web providing simultaneously to both surfaces of said elongated porous web metered quantities of a dope, said quantities on both surfaces are identical or may deviate from identical by no more than 5%, comprising at least one membrane polymer and at least one solvent therefor; (iii) thereby impregnating said elongated porous web completely with said dope and providing dope layers on each surface of said outermost surfaces of said elongated porous web with an equally thickness or a thickness which may deviate from equally by no more than 5%, said thickness being independent of the gap between one of said lower slot faces and the surface of said elongated porous web nearest thereto; (iv) subjecting said dope associated with said elongated porous web to phase inversion with at least one non-solvent wherein said phase inversion of said dope layer is symmetrical on each surface of said web, thereby forming a membrane; and (v) removing residues of said at least one solvent for said at least one membrane polymer from said membrane thereby producing an ion-permeable web-reinforced separator,