초록 ▼

A molded resin product can be produced without shrinkage on the surface by providing a hollow part and foam cells therein. Before molten resin containing a foaming gas is introduced into a cavity between molds, the cavity is preliminarily filled with a gas with pressure high enough to prevent the fo

A molded resin product can be produced without shrinkage on the surface by providing a hollow part and foam cells therein. Before molten resin containing a foaming gas is introduced into a cavity between molds, the cavity is preliminarily filled with a gas with pressure high enough to prevent the foaming gas from beginning to foam or expand. While the molten resin is injected into the cavity or after its injection is over, another high-pressure gas is injected through at least one gas injection nozzles into the resin where a hollow part is desired. As the nozzle is retracted from the cavity, the high-pressure gas is removed from the cavity, allowing the foaming gas to begin to foam and expand, forming a hollow part and foam cells inside the molded product.

대표청구항 ▼

[ What is claimed is:] [1.] A method of producing a molded resin product by using a injection molding apparatus having a pair of molds with a cavity therebetween, said method comprising the steps of:preliminarily filling said cavity with a counter-pressure gas with pressure greater than the atmosphe

[ What is claimed is:] [1.] A method of producing a molded resin product by using a injection molding apparatus having a pair of molds with a cavity therebetween, said method comprising the steps of:preliminarily filling said cavity with a counter-pressure gas with pressure greater than the atmospheric pressure, said counter-pressure gas comprising air;controlling the oxygen concentration of said counter-pressure gas by controllingly adding an inactive gas to said air;thereafter injecting into said cavity molten resin containing a foaming gas;forming a hollow space inside said molten resin by injecting a hollowness-creating gas with pressure greater than the atmospheric pressure into said molten resin at a specified position inside said product; andremoving said counter-pressure gas and said hollowness-creating gas from said cavity and from within said product, thereby allowing said foaming gas to begin to foam and expand and causing foam cells to be formed in said product.