Co-injection molding apparatus, method for controlling same, and injection product by co-injection molding

A co-injection molding apparatus to mold an injection product that includes a skin layer to form an outer surface and a core layer having an interior to be surrounded by the skin layer, the skin layer to be formed by a first material, and the core layer to be formed by a second material, the co-injection molding apparatus comprising:

• an injection mold configured to be injection molded by the first material and the second material, and to provide the injection product;
• a runner configured to provide the first material and the second material to the injection mold;
• a first injector configured to inject the first material to the runner;
• a second injector configured to inject the second material, different from the first material, to the runner and the second injector provided between the first injector and the injection mold,
• wherein the runner includes:
• a runner main body configured to connect to the first injector and to the second injector,
• a bypass runner configured to connect the second injector and the injection mold, and including at least one bend so as to increase a retention amount of the first material, and
• a backflow prevention part formed on the runner main body between the first injector and the second injector, and having a diameter smaller than a diameter of the runner main body.