Spherical PET or PBT bead production from prepolymer or polymer melts involves a precrystallization stage where falling melt droplets are swirled around by a vibrated cloth in a hopper

摘要

Polymer melt droplets fall through a falling tower(12) with an opposing fluid flow to a precrystallizing stage(45). In the latter stage the droplets are swirled by a gas-vibrated cloth-like element and/or are fed to a hopper shaped area at the end of the falling zone which is supplied with gas to induce turbulence for moving droplets towards the central area and/or outlets. An Independent claim is also included for a plant for manufacturing the beads which includes a nozzle plate(10) for dropping polymer through a falling zone with a hopper-shaped lower end. The hopper periphery is bordered by a vibrating cloth(50) and/or a self supporting sheet with openings and the hopper base leads to a crystallizing unit and a post condensation stage. Preferred Features: Gas inlets in the hopper area ensure that melt droplets are swirled tangentially along the inner face of the hopper area. Gas pulses for vibrating the cloth follow a sine wave and have frequency of 1-30Hz, preferably 1-10Hz. Maximum gas speed is <= 2m/sec, preferably <= 0.3m/sec, more preferably <= 0.1m/sec and gas pressure is 0-200 mbar, preferably 0-150 mbar above atmospheric. The cloth or self-supporting sheet openings whose diameter is <= 0.2mm, preferably <= 0.1mm.