Importance

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Abstract

Disclosed is a process for producing a polypropylene-based resin foam by subjecting a linear polypropylene-based resin, which has a melt tension at 230° C. of from 5 to 30 g and satisfies the below-described formula (1) in which MFR stands for a melt flow rate of the linear polypropylene-based resin at 230° C. and MT stands for the melt tension at 230° C., to melt extrusion through an extruder while injecting carbon dioxide into the resulting molten resin to foam the molten resin. The process includes subjecting the extruder to temperature control such that the extruder has a temperature of from 200 to 240° C. at a position of a cylinder barrel thereof, where the carbon dioxide is to be introduced, and the cylinder barrel has a temperature of from 175 to 190° C. at a position before the foaming; and then discharging the molten resin into atmospheric pressure with a discharge rate of the molten resin per opening area of a die being controlled to give a resin pressure of from 5 to 20 MPa at a position immediately proximal to an opening of the die, thereby foaming the molten resin. The process of the present invention can provide a polypropylene-based resin foam having a high expansion ratio, uniformly dispersed foam cells and a good surface appearance.Log(MT)>−1.33 Log(MFR)+1.2   (1)

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First Claim