Mfg. thin bottom, thicker rim polystyrene packing trays - from granules by hot moulding and cooling in mould using granules coated and part-expanded pref. immediately before moulding

摘要

Polystyrene in granular form is pre-treated and the treated material is fed into a two-part moulding die in which it is heated so that the granules expand to form a tray which is then cooled and, when stable, removed from the die. Prepn. and moulding is pref. carried out in-line. The starting material pref. consists of (5 wt.%) pentane-contg. 0.4-0.6mm polystyrene granules which are coated, pref. with 0.5% Zn-stearate, at raised temp., then pre-foamed with steam to 0.8-1.2mm and size-graded before being fed into the moulding machine.