Prodn. of foamed thermoplastics - by mixing into polymer in or on discharge from extruder specific non-toxic gases which are not harmful to ozone layer

摘要

Polystyrene and/or polyethylene foam or similar foams are produced by processing the polymer in an extruder and/or during discharge and/or after discharge from the extruder mixing foaming agent with it, using only or essentially N2 and/or CO2 and/or H2O and/or N2O as the foaming agent. The extruder die lips are pref. coated with "Teflon" (RTM). The temp. of the mixed material must be lowered to prevent the occluded cells from bursting, the surface must be densified to prevent loss of the gas used, and the foaming agent must be bonded in to the polymer. The cooling is best conducted in an initial air cooling phase followed by water cooling. The foaming agents can be used as liquids. and pumped in metered proportions into the polymer, but feeding in a measured volume of pressurised gas can also be used. The distribution of the gas is aided by the addition of emulsifier, e.g. glycerol monostearate. ADVANTAGE - The method replaces the foaming agents which are harmful to the ozone layer. The new types of foaming agents are reasonable in cost; they are non-toxic, their functional etc. properties are at least as good as those of former agents, and their disposal is environmentally favourable.