| 摘要 |
In a process for manufacturing from a thermoplastic material shaped articles having a substantially closed-cell structure, the pre-foamed particles obtained by heating thermoplastic material particles containing an inflating agent are first aged for at least one hour at substantially atmospheric pressure and then at elevated gas pressure, and the final working up into shaped articles takes place before the super-atmospheric pressure in the pre-foamed material is reduced to atmospheric pressure by permeation. Doubly pre-expanded particles, which have been aged (suitably at least partly at elevated pressure) between the first and second pre-expansion treatments, can be treated. The pressure in the ageing step is preferably 2 to 8 atm. abs. but may be higher. The mould or matrix used in the shaping need only be partly filled, e.g. to 75%, with the aged particles. Oxygen, nitrogen, carbon dioxide, helium, lower hydrocarbons, halogenated hydrocarbons, but preferably air, are suitable for the ageing at elevated pressure. When air is used the resulting treated particles have an air content higher than that required for equilibrium with air at atmospheric pressure. the treated particles slowly lose their internal gas pressure and are preferably moulded within 10 hours of manufacture. The process in applicable to polystyrene beads, foam waste having a closed cell structure and reduced to particles (of size 0.2 to 1.0 cm.), styrene acrylonitrile copolymers, and polystyrene flame-proofed, e.g. by chlorinated paraffin wax and antimony oxide. |
