VERFAHREN ZUR HERSTELLUNG GESCHAEUMTER PROFILE AUS THERMOPLASTISCHEN KUNSTSTOFFEN

摘要

1439805 Extruding foamed resin NIPPON PETROCHEMICALS CO Ltd 6 June 1973 26972/73 Heading B5A [Also in Division C3] Foamed continuously extruded thermoplastic resin articles having a foamed inner portion and a non-foamed surface layer are made by melting and mixing a mixture of a thermoplastic resin and a foaming agent having a decomposition temperature (for a chemical foaming agent) or boiling point (for a physical foaming agent) above the m.p. of the resin by heating the mixture to a temperature below the activation temperature of the foaming agent and above the m.p. of the resin, heating the melt to above the activation temperature of the foaming agent without further mixing and under sufficient pressure to suppress substantial foaming (i.e. keeping the gas bubbles produced at a minimum size and uniformly distributed), causing the melt to expand by feeding it into a die held at a temperature and pressure below that of the preceding step but above the m.p. of the resin, the expansion being confined to the inner portion of the mixture. Fig. 2 shows an apparatus for carrying out the above foaming wherein a hopper 1b, feeds a mixture of resin and foaming agent to an extruder having cylinder, 1a, provided with external heater (not shown), screw, 1d, outlet, 1c, and a screen pack, 1e. The melted mixture is fed to a heated pressurized chamber, 2a, connected to the extruder by a flange, 5, where the foaming agent is gasified without substantial foaming and the melt is then fed into a foaming die, 3a, 3b, 3c, at a lower pressure and temperature than 2a and where a skinned foamed material is formed and then solidified in sizing die 4a, 4b, 4c which is disposed in water in a trough, 8, having inlet 8a, and outlet, 8b, and also guide rollers, 8d and 8e, to guide the product, 10, to take-off rollers 9. Fig. 6 shows a heater, 3e, in the melt passage, 3d, of the foaming die, 3a; a throttle plate, 6c, being located between two flanges 6 and 7 being flanges between the foaming, 3a, and sizing, 4a, dies.