Process for the partial modification of porous, hydrophilic filter membranes, post-treated filter membranes and filtration modules fitted therewith, in particular filter candles

In the embedding of hydrophilic filter membranes into hydrophobic fixing elements of filtration modules, the membrane filters are made hydrophobic in a rim zone over the embedding region so that this rim zone which can no longer be wetted by water represents an air bypass when the filtration modules are tested and thus makes the filtration modules untestable. The novel process is to modify these rim regions in such a manner that, even after embedding part-regions into hydrophobic polymer material, these rim regions remain continuously porous and hydrophilic over the entire region of their active surface. The porous filter membranes, in the regions provided for embedding, are impregnated with a solution of a composition rendering them hydrophilic, so that the filter membranes saturate with solution in the regions in question and the filter membranes thus treated are then washed and dried. By means of this process the modified rim regions are several times more hydrophilic than the untreated regions in the filter membranes so that the membrane regions immediately adjoining the fixing elements in the filtration modules still remain sufficiently hydrophilic.