| 摘要 |
A process for the production of expanded or foamed articles in a mould comprises placing a mass of a solid, particulate, thermoplastic polymer composition, which is capable of thermal foaming or expansion by virture of a contact of a volatile organic expanding agent which is not a solvent for the polymer, into the mould and subjecting the mass of the polymer composition to a first heating by passing a liquid gaseous or vaporous heating medium through the mass until the individual particles in the polymer composition are heated throughout to a temperature above the boiling point of the volatile organic expanding agent, which temperature is lower than that at which the polymer composition softens or at which the individual particles flow together or adhere to one another and thereafter subjecting the polymer composition to a second heating at a higher temperature at which foaming or expansion and fusion between the particles takes place. The method is particularly effective when the particulate thermoplastic polymer composition has been partially prefoamed and is capable of further foaming or expansion. Suitable polymers are polystyrene, polyvinyl chloride, copolymers of vinyl and vinylidene chloride, polyacrylic esters and copolymers of styrene and methyl methacrylate, acrylonitrile or natural or synthetic rubber, and especially polymers or copolymers of monovinyl aromatic compounds. The gaseous heating medium may be saturated or superheated steam or steam in admixture with inert gases such as air, carbon, dioxide, nitrogen, methane, ethane, propane, butane and/or helium. In examples the process is applied to beads of styrene and styrene-acrylonitrile copolymer containing pentane. Heating is effected by evacuating the mould and then using steam first at an absolute pressure of 150 mm. and than at 3 lbs. s.i. guage. After moulding the chamber surrounding the mould is again evacuated to cause drying and cooling of the moulded body by vaporization and removal of the water. |
