Injecting the gas for blowing agent inside the thermoplastics melting inside the gas supply device for blowing agent, the formation device of the thermoplastics

摘要

PROBLEM TO BE SOLVED: To provide a supply apparatus for a gas for a foaming agent capable of supplying the gas for the foaming agent by keeping a constant pressure difference between the molten resin and the gas independently of the state of the injected gas, a molding apparatus for a thermoplastic resin foamed item and a molding method for the thermoplastic resin molded item by use of it. SOLUTION: The supply source 12 of a gas for a foaming agent injects the gas for the foaming agent into a molten thermoplastic resin in a screw cylinder 5 to form a thermoplastic resin foamed item wherein it is provided with pressure difference detecting means (18, 19, 21, 22 and 23) detecting pressure difference between the pressure of the thermoplastic resin and the pressure of the injected gas and pressure difference controlling means (24 and 20) controlling at least one of the pressure of the thermoplastic resin and the pressure of the injected gas so that the pressure difference detected by the pressure difference detecting means meets a predetermined relation.