Patent ID: 7597815

Claim:
A process for producing a porous track membrane useful in the separation of materials from a fluid comprising the steps of: a) exposing a film of polyvinylidene fluoride to a bombardment of heavy ions to provide the film with a track density, wherein heavy ions are defined to have a mass greater than or equal to argon ions; and b) etching pores into the resulting tracked film with an etching solution at temperatures in a range of 100° to 150°C., said etching solution is an alkaline solution of potassium permanganate and containing at least one non-basic salt of alkali metals in sufficient concentration to increase the boiling point of the resulting alkali metal-containing solution, and circulating the etching solution over and in contact with the etching film at a flow rate to produce a Reynolds Number in the range from 100 to 500 to provide the film with a density of the pores corresponding to the track density.