| abstract |
The method is intended for the production of expanded polyolefin materials, having a coefficient of thermal conductivity below 40 mW/°K*m and a density below 50 kg/m3, by the extrusion of a polymeric material with the addition of a physical expansion agent. The extrusion is carried out in a twin-screw extruder with co-rotating, interpenetrating screws (12), with a ratio between axial separation (I) and diameter (D) of between 0.7 and 0.8 and a length/diameter ratio (L/D) between 22 and 30, and in which the said screws (12) have a plurality of mixing areas (back mixing) (18a-c) and a plurality of alternating pumping areas (16a-d) with a length ratio between mixing areas (18a-c) and pumping areas (16a-d) of between 65% and 75%. During extrusion, the screws are rotated at less than 50 rpm. |