| abstract |
The invention relates to expanded porous thermoplastic polymer membranes which are characterised by a proportion of at least 80 % open cells and a pore volume of at least 75 %. The invention also relates to a method and a device for producing said membranes. The membranes can be used for microfiltration and macrofiltration of fluids in industry, laboratories and protection of the environment. According to the inventive method, a polymer melt is conveyed through an extruder under pressure, whereby it is loaded in an injection stage with cell builders with different diffusion rates in comparison with said polymer melt, and it is pressed through a die to form a membrane. In an additional mixing step which occurs upstream from the die, the temperature of the single-phase melt is reduced to a temperature which is lower than the original processing temperature and/or the pressure thereof is increased. The cell builders enable the polymer melt to be expanded when it is passed through the die to form a predominantly open cell structure. |