Patent ID: 8535585

Claim:
A process for preparing expandable granules based on thermoplastic polymers through a granulation die, comprising: i) bringing a stream of molten vinyl aromatic polymer to a selected temperature, wherein said selected temperature ranges from a critical temperature of an expanding system minus 25′C and a critical temperature of the expanding system plus 25° C.; ii) incorporating into a second stream of molten polymeric material, from 0 to 60% by weight, with respect to the weight of a resulting stream of inorganic and organic additives containing, less than 10 percent by weight of particles having a size larger than half of the diameter of holes of the die; iii) incorporating an expanding system in a polymeric composition in a molten state (ii) at a selected pressure, wherein said selected pressure is higher than a critical pressure of the expanding system; iv) incorporating the polymeric composition (iii) in the stream of vinyl aromatic polymer (i); vii) granulating the expandable polymeric composition thus obtained in a cutting chamber of a device for hot granulation of thermoplastic polymers, comprising: a) a die comprising a cylindrical body including to series of extrusion holes on an external surface and polymer adduction channels positioned inside the cylindrical body, in correspondence with and connected to the holes; b) a set of knives situated in correspondence with the die holes, rigidly connected to a rotating shaft; c) a set of nozzles situated behind the set of knives which generates a liquid jet directed against the die; d) an inlet from which a stream of gas is fed; and in which the stream of gas coming from said inlet (d) prevents flooding of the cutting chamber.