Process for producing uncrosslinked polypropylene-based resin foam sheets and uncrosslinked polypropylene-based resin foam sheets

摘要

The present invention provides a process for producing uncrosslinked polypropylene-based resin foam sheets which is characterized by using an extrusion foaming apparatus having a gear pump which is interposed between the extruder and the die and which is linked by means of adapters, wherein the pressure (Pg) at the inlet of the gear pump is within the range specified by the following formula (Formula 1) and the extruder is controlled so that the value of Pg is constant.;Formula 1; ; ;: theoretical expansion ratio when the foaming agent added is 100% held;H: coefficient of solubility of the foaming gas in the resin at the resin temperature in the gear pump inlet (cm³(STP)/cm³atm) and the like.;The present invention makes it possible to produce uncrosslinked polypropylene-based resin foam sheets having fine foam cells and good appearance and being excellent in productivity and extrusion stability as well as in productivity improving effect in the production of high-expansion thin sheets with reducing wavy or corrugated defects at ends of sheets.