GB1012277A - Foamable polystyrene and process for moulding it - Google Patents

Abstract

Foamable polystyrene particles consisting of polystyrene, a volatile hydrocarbon blowing agent and from 0.1 to 10% of a wax by weight of the polystyrene are produced by a process in which the wax is incorporated before or after the polymerization of the styrene. The preferred hydrocarbon is pentane in amounts of up to 10% by weight of the polystyrene. Suitable waxes are those having a melting-point less than the softening point of the polystyrene, e.g. beeswax, paraffin wax, ozokerite, carnauba wax, microcrystalling wax and especially polyethylene wax. The wax may be incorporated by steeping polystyrene particles containing blowing agent in a molten wax, but a preferred method is to coagulate an aqueous dispersion of a wax in the presence of the foamable particles at a temperature above the melting-point of the wax if necessary under pressure. The wax may also be incorporated during the later stages of the suspension polymerization of styrene, the blowing agent being added during or after polymerization. Heating of the foamable particles may be by steam, hot water or hot air, or by an infra-red heater to produce foamed beads which are exposed to the atmosphere for a day or two before moulding. The moulding takes place by injecting steam through inlets in the mould walls to produce a foamed article which requires a cooling time between 30% and 80% of the time necessary when ordinary polystyrene particles containing blowing agent only are employed.