Patent ID: 6290884
Filing Date: 2001-09-18
Classification: B29C

Abstract:
A process for producing uncrosslinked polypropylene-based resin foam sheets which is characterized by using an extrusion foaming apparatus having an extruder, a die and a gear pump,wherein the gear pump is interposed between the extruder and the die and is linked by means of adapters,wherein the extrusion foaming apparatus has at least one kind of means for reduction of pressure loss, said means comprising said die or said extruder in which the die in the means has a form specified by 5.ltoreq.L/t.ltoreq.12 where L (mm) stands for the length of lip land and t (mm) stands for the lip gap or in which the extruder in the means has a form specified by 1/4.ltoreq.A/B.ltoreq.1 and C/A.ltoreq.10 where B (mm) stands for the barrel diameter, C (mm) stands for the length of the adapter, and A (mm) stands for the adapter diameter,wherein a pressure (Pg) at the inlet of the gear pump is within a range specified by the following Formula 1 and the extruder is controlled so that the value of Pg is constant:Formula 1:Pc.ltoreq.Pg(atm).ltoreq.Pc+90Pc=(.chi.-1)/H.chi.: theoretical expansion ratio when the foaming agent added is 100% heldH: coefficient of solubility of the foaming gas in the resin at the resin temperature in the gear pump inlet (cm.sup.3 (STP)/cm.sup.3.multidot.atm).