Injection molding method and injection molding apparatus

An injection molding apparatus, comprising:

• an injection mold comprising a gate, a cavity connected with the gate, and a flow channel having an opening which opens toward a back surface of a molded product,
• wherein the injection mold further comprises a columnar area for forming a hole in the molded product;
• a molten resin injection device for injecting molten resin from the gate into the cavity, wherein the opening of the flow channel is formed in a vicinity of a boundary where the molten resin that has passed a right side of the columnar area and the molten resin that has passed a left side of the columnar area merge together;
• a pressure keeping device for applying pressure from the gate against the injected resin within the cavity after the cavity has been filled with the molten resin;
• and
• a pressurized fluid injection device for injecting a pressurized fluid toward the back surface of the molded product via the flow channel while the molten resin injection device injects molten resin from the gate into the cavity,
• wherein the pressure applied by the pressure keeping device is lower than injection pressure applied by the molten resin injection device,
• fluid pressure applied by the pressurized fluid injection device is lower than the pressure applied by the pressure keeping device,
• the pressure applied by the pressure keeping device is pressure that would not be sufficient to prevent a design surface of the molded product from separating from a surface of the cavity unless injecting the pressurized fluid by the pressurized fluid injection device, and
• the fluid pressure applied by the pressurized fluid injection device is pressure that would not be sufficient to prevent the design surface of the molded product from separating from the surface of the cavity unless applying the pressure by the pressure keeping device.