| 摘要 |
PURPOSE: To obtain a hollow part having a foam wall of a rough inner surface by extending a preform in a foaming mold by an externally operating negative pressure, and generating an overpressure existing therein. CONSTITUTION: The synthetic resin hollow unit having a foam wall made of many layers including different void fractions is manufactured by extruding at least one type of foamable thermoplastic resin by a multiple layer extruder, and foaming its preform by a negative pressure operating at an outside of the preform in the mold. An overpressure higher by 0.1 to 0.8 bar than a pressure of an outside of the hollow unit is generated in the preform. To manufacture the foam synthetic resin hollow unit, a thermoplastic resin to be foamed by a foaming agent is suitable. For example, a low density, intermediate density and high density polyethylenes, polypropylenes, polystyrenes, polyvinyl chlorides, polyacetal or the like are used. Preferably, the low density, intermediate density and high density polyethylenes, and polypropylene are used. Among them, the polypropylene is preferably used. |
