Improvements in or relating to the compression-moulding of thermoplastic compositions

摘要

A thermoplastic composition containing a predominating proportion of thermoplastic material is heated by means of a high-frequency electrostatic field and transferred to a mould. Direct moulding pressure is then applied thereto and the moulded article is cooled or allowed to cool below the softening point while still in the mould and then removed from the mould. The heating is effected at a power input which heats the material to moulding temperature substantially uniformly throughout its mass within a time which is sufficient to bring about substantial breakdown or discoloration of the material. The mould may be kept cool. Fillers may be selected to aid the high frequency heating. Specifications 517,798 and 572,425 are referred to. The Specification as open to inspection under Sect. 91 comprises drawings showing simple moulds for use in the invention. There drawings do not form part of the Specification as accepted.