Patent ID: 7704423
Filing Date: 2010-04-27
Classification: B29C

Abstract:
1. An injection-foaming molding process for manufacturing a formed article by injecting a molten resin containing a foaming agent into a cavity of a mold being retained in an openable state and then expanding the cavity by opening the mold to allow the resin to foam, consisting of: i) a step of presetting a back pressure to a positive value, in a resin-reserving section of an injection device located at a front end of a screw of the injection device connected to the cavity of the mold, during a charging of the resin into the resin-reserving section, the back pressure being a minimum pressure on the resin in the resin-reserving section during the entire molding process; ii) a step of injecting the resin into the cavity and increasing the pressure in the resin-reserving section during the injecting step; iii) a step of discontinuing access to the cavity of the mold from the resin-reserving section immediately after a completion of injection of a molten resin containing a foaming agent into the mold cavity wherein the pressure decreases in the resin-reserving section; and iv) a step of keeping the resin-reserving section located at the front end of the screw under pressure equal to the preset back pressure for charging during a period from the completion of injection to a start of charging the molten resin containing the foaming agent for a next injection, and then starting a charging, wherein the resin-reserving section is discontinued with the mold cavity by using a shutoff nozzle or a valve gate after completion of injection of the molten resin into the mold cavity, and pressure in the resin-reserving section is kept at a same level as that of the preset back pressure, and wherein said preset back pressure for charging prevents a foaming gas from being released in the molten resin containing a foaming agent.