Patent ID: 8361362

Claim:
A method for production of expandable polystyrene beads comprising the steps of supplying a polymer melt flow and an expanding agent flow to a mixing zone, dispersing the expanding agent in the polymer melt under simultaneous thorough shear mixing in a first static mixer, holding a resulting mixture in a second static mixer with simultaneous thorough shear mixing, cooling the mixture in a third static mixer with simultaneous mixing to an intermediate temperature with subsequent cooling of the mixture down to a temperature required for granulation, and extruding polymer filaments on a shock cooling and a resulting granulation, maintaining a weight ratio between the melt flow Gp and the expanding agent flow G EA within a range of 13 to 19 and a temperature in the first static mixer being [200+56(1−G EAcurrent /G EA max )]° C., in the second static mixer being [175+70(1−G EAcurrent /G EA max )]° C., and in the third static mixer being [150+70(1−G EAcurrent /G EA max )]° C. where G EAmax is a maximum possible expanding agent flow rate, and G EAcurrent is a flow rate of the expanding agent and where a second ratio between a melt flow index (MFI) of the polymer melt and a weight-average molecular weight (M w ) is maintained within a range of (0.8 to 12.0)×10 −5 .