A PROCESS FOR THE PRODUCTION OF EXPANDABLE GRANULES OF THERMOPLASTIC POLYMERS AND RELATIVE APPARATUS

摘要

A process for the production of expandable granules of thermoplastic polymers comprising: (a) the extrusion of the polymer in which an expanding agent is incorporated, through a die-head in order to obtain an expandable polymer; (b) immediate cooling of this polymer in water, kept at a temperature at which the polymer remains in the non-expanded state, but not lower than the Tg of the expandable polymer; (c) cutting of the polymer to granules in water immediately at the outlet of the die-head, and (d) annealing of the thus obtained granules, by slow cooling in a temperature range comprised between at least +5 DEG C. and at least -5 DEG C. the Tg of the expandable polymer, wherein the cooling and the cutting of the polymer to granules and the annealing thereof are carried out under pressure. The apparatus comprises an extruder; a means for injecting the expanding agent into the extruder; a die-head; a chamber fastened to said die-head and provided with cutter and pipes for feeding water under pressure; a tower for the annealing of the granules and a means for maintaining the pressure in the chamber and in the tower.