Injection molding apparatus for molding multi-layered article and method of injection-molding multi-layered article

An injection molding apparatus for injection molding a multi-layered article, which comprises; (a) a mold having a cavity block provided with a cavity and a hot runner block, (b) at least a first injection cylinder and a second injection cylinder, (c) a first resin-flow-passage for connecting an inside of the first injection cylinder and the cavity, and (d) a second resin-flow-passage for connecting an inside of the second injection cylinder and the cavity, the injection molding apparatus having a structure in which those portions of the first and second resin-flow-passages which are located within the mold are provided in the hot runner block, and the first resin-flow-passage and the second resin-flow-passage meet with each other in a junction portion upstream to a gate portion opened to the cavity, the injection molding apparatus being provided with back flow means for letting first molten resin in the first resin-flow-passage flow into the second resin-flow-passage after second molten resin is injected into the cavity through the second resin-flow-passage, the back flow means being operable with a pressure which the first molten resin in the first resin-flow-passage exerts on second molten resin in the second resin-flow-passage.