Membrane production as developed at 3M is principally based on three different technologies:
- Solvent induced phase separation SIPS
- Thermally induced phase separation TIPS
- Dry stretch process
In the SIPS process, phase separation is induced by a non-solvent into which the polymer solution is spun, whereas in the TIPS process, quenching by a cooling bath is responsible for the phase separation of the polymer solution. As a result, in both technologies the polymer re-solidifies and the solvent is extracted from the pores. The membrane formation has to be controlled precisely to yield the desired structure as well as pore size.
In the dry stretch process, a dense capillary or flat sheet is produced by melt extrusion. This capillary or foil is subjected to consecutive annealing and stretching steps at different temperatures, which lead to a specified porosity of the membrane wall.
As experts in membrane manufacturing over many years and as a result of extensive research into all parameters relevant to the pore and surface morphology, 3M is able to incorporate special features like S.E.T. Sieving Enhancing Technology during the membrane formation process.