Integral skin foamed thermoplastic mouldings - made by injecting gaseous medium into charge of molten expandable thermoplastic in mould cavity

摘要

In the prodn. of foamed plastics articles with an integral skin surrounding the foamed core, a charge of an expandable thermoplastic material contg. a blowing agent is injected into the hollow cavity of a mould. The vol. of the charge is less than the vol. of the mould cavity. During and/or after introducing the plastified plastic into the mould, a gaseous medium is introduced into the charge at a pressure, greater than of equal to the pressure of the blowing agent at the prevailing temp., and the plastic is moulded under the pressure of the gas. As soon as the skin layer has formed on the moulding, the pressure on the mould cavity is relaxed. The process allows the prodn. of thick-walled sandwich type mouldings with a foamed core using a single plastifying unit in place of the twin plastifying units. This allows more economical single stage prodn. processes to be used and reduces equipment investment costs.