Patent ID: 7846360
Filing Date: 2010-12-07
Classification: B29B,B29C,B29K

Abstract:
1. A process for the production of granules of expandable thermoplastic polymers by means of extrusion which comprises: i) bringing the polymer to a temperature higher than the melting point, in a single- or multi-screw extruder; ii) incorporating at least one expanding agent in the polymer in the molten state; iii) granulating the polymer thus obtained in a device for the hot granulation of thermoplastic polymers comprising: a die, positioned at the head of the extruder, consisting of a cylindrical body containing on the outer surface a series of small plates, equipped with a series of extrusion holes, and a plurality of feeding ducts of the molten polymer, situated inside the cylindrical body in correspondence with and connected to the perforated small plates, lined with a material having a high thermal conductivity; a cutting chamber comprising a set of spraying nozzles which create a jet of drops of a thermostat-regulating liquid, used for cooling and removing the cut granules, nebulized and sprayed against the die; a cutting system comprising a cutting plate, firmly constrained to a rotating shaft, supporting a set of knives arranged so that the cutting profile of the knife is radial with respect to the surface of the die which faces said cutting system; iv) annealing the granules thus obtained by heating to a temperature higher than or equal to the glass transition temperature (Tg); v) cooling the annealed granules to room temperature.