Abstract: A process for the production of extruded sheets of expanded polystyrene, which only uses expanding agents with low environmental impact, comprising the steps of: a) heating polystyrene or a mixture composed of polystyrene and at least one component selected from the group consisting flame retardants, coloring agents, plasticizers, heat stabilizers and lubricants at a temperature in the range of 180-2500 C thus obtaining a polymer melt, which is subjected to homogenization; b) adding to the polymer melt a mixture of expanding agents comprising carbon dioxide and water; c) homogenizing the polymer melt including said expanding agents; d) homogeneously cooling the polymer melt to a temperature lower than or equal to 1400 C; e) extruding the cooled polymer melt through a die to obtain an expanded polystyrene sheet.

Abstract: This invention relates to a process for extruding particular shapes in thermoplastic material and, more precisely, flat plates, corrugated plates and the like or, in general, shapes having one section much larger than the other; said process being suited to eliminate the uneven feed of the molten material coming out from a die. This invention relates also to an improved extrusion machine which is particularly useful for carrying out the aforementioned process.