FOAMED POROUS DIAPHRAGMS MADE OF THERMOPLASTIC POLYMERS AND METHOD AND DEVICE FOR MAKING SUCH DIAPHRAGMS Russian patent published in 2003 - IPC

FIELD: technology of polymers. SUBSTANCE: invention relates to foamed porous diaphragms made of thermoplastic polymers featuring large volume of voids and large share of open pores and to method and device for making such diaphragms. Foamed porous diaphragms contain at least 80% of open pores with volume of voids not less than 75% with distribution of open pores according to sizes at standard deviation from average diameter of pores being ±10%. According to proposed method of manufacture, polymeric melt is forced under pressure through extruder. Excess amount of foamer featuring different diffusion speeds relative to melt is delivered into melt at injection stage. Polymeric melt is mixed at first zone passing from injection stage to end of extruder cylinder. Then melt is moved through additional mixing stage limited by first and second pumps where temperature of obtained single-phase melt is reduced to level lower than initial machining temperature and/or melt pressure is increased. Single-phase melt is forced through head at adjustable pressure by means of second pump for melt. Invention contains description of device for implementing the method. Invention makes it possible to obtain foamed diaphragms which have no defects and feature large volume of voids and large share of open pores at narrow pore size limits. EFFECT: improved quality of foamed porous diaphragms. 16 cl, 1 dwg