| 摘要 |
A mixture of polystyrenes with different melting points is pumped(8) into an extruder and liquid carbon dioxide blowing agent (9) added. Melt strands are extruded, foamed, granulated and cooled and then fed into an automatic molding machine. Steam is supplied to the machine at a temperature suited to the PS with higher melting point. A mixture of PS(polystyrenes) with different melting points is pumped(8) into an extruder and liquid carbon dioxide blowing agent(9) added to give an apparent foam particle density of /}50kg/cu m. Blowing agent added ensures a cell size of /}0.3mm, more preferably /}0.1mm. Melt strands are extruded, foamed, granulated and cooled and then fed into an automatic molding machine. Steam is supplied to the machine at a temperature suited to the PS with higher melting point so that the PS with lower melting point forms a skin on the particles and a skin on the component. The melting point difference between the different PS granules is >= 5, more preferably >= 10 deg C. Carbon dioxide is added to melt in or prior to the dispersion zone of a twin screw extruder. Blowing agent may be added via an annular nozzle or several nozzles around the extruder barrel. Melt pressure prior to the extrusion nozzle is 80-120bar, preferably 110/!5bar. Nozzle diameter is 0.6-1.5mm, preferably 0.9-1.1mm and lip length 1-10mm, preferably 4-6mm. Melt temperature in the nozzles is within a range10 deg C above or below the melt temperature. Melt pressure can be varied by changing the number of nozzles, e.g. by replacing the nozzle plate or by shutting off individual nozzles. Melt flow in each nozzle is 0.25-2.5kg, more preferably 0.4-0.6kg for each 0.8sq mm of nozzle opening.
|
