Patent ID: 7858002

Claim:
An injection-foaming method for a thermoplastic resin which comprises: providing a molding machine provided with two stage screw injection unit having a resin feeding part and a resin plasticizing part which can increase a foaming agent pressure at the fore-end of the two stage screw wherein a thermoplastic resin fed from the feeding part is plasticized at the plasticizing part, a plasticizing cylinder and a screw, under increasing pressure and the resultant resin is injected as a foaming-agent-containing melted resin containing the foaming agent and the molding machine also having a mold being provided with a mold cavity capable of expanding and contracting and being filled with the foaming-agent-containing melted resin injected from the injection unit and a clamp-controlling part capable of maintaining a position of the mold until a completion of a foaming process, injecting the foaming agent into a thermoplastic resin by using a mixture of a foam nucleating agent and a foaming gas, consisting of compressed nitrogen gas or compressed air, as a foaming agent, feeding the mixture to a feeding part or a plasticizing part of an injection unit at a pressure of 0.1 MPa or more and less than 1.0 MPa, contacting the mixture with a thermoplastic resin before or after the plasticization in the feeding part or the plasticizing part and increasing the pressure of the foaming agent at the fore end of the two stage screw; and filling the mold cavity with a foaming-agent-containing melted resin by injecting it from the injection unit, detecting a completion of filling the mold cavity with the resin, decreasing a clamping force of the mold cavity, and then enlarging the mold cavity for allowing the foaming-agent-containing melted resin to expand.