Injection molding method and injection mold

An injection mold comprising:

• a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate;
• and
• a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir,
• wherein when the molten resin material is being charged into the cavity, a distal end of the cut punch which extends in a moving direction of the cut punch that is toward the resin reservoir is located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir;
• wherein when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir, the cut punch moves toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,
• wherein the runner contacts the resin reservoir, and the gate is disposed at the point where the runner contacts the resin reservoir, such that the gate does not protrude into the resin reservoir, and
• wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening.(6)

An injection mold comprising:

• a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate;
• and
• a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir,
• wherein when the molten resin material is being charged into the cavity, a distal end of the cut punch which extends in a moving direction of the cut punch that is toward the resin reservoir is located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir;
• wherein when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir, the cut punch moves toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,
• wherein the runner contacts the resin reservoir, and the gate is disposed at the point where the runner contacts the resin reservoir, such that the gate does not protrude into the resin reservoir, and
• wherein a depth as viewed in a moving direction of the cut punch in the resin reservoir is 1.5 to 10 times an opening distance of the communicating portion. (11)

An injection mold comprising:

• a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate;
• a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch is operative to be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir, and
• a communicating portion, formed between the resin reservoir and the cavity when the cut punch is not in slidable contact with the resin reservoir, the communication portion allowing the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir,
• wherein a molded resin product is formed when the cut punch device moves through the resin reservoir towards the gate to close the communication portion, which cuts the resin material at the communication portion so that the resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir,
• wherein the cut punch moves at a time when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir and
• wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening. (15)

An injection mold comprising:

• a fixed die and a movable die which form a cavity into which a molten resin material is injected via both a runner and a gate provided in the fixed die, the gate being connected to the cavity through a resin reservoir formed by recessing the fixed die toward the gate;
• and
• a cut punch provided on the side of the movable die that confronts the gate through the resin reservoir, the cut punch being movable so that the cut punch can be inserted into the resin reservoir so as to be in slidable contact with the resin reservoir and having a distal end which extends in a moving direction of the cut punch that is toward the resin reservoir, the distal end located between the resin reservoir and the cavity at such a position as to open a communicating portion that allows the resin reservoir and the cavity to communicate with each other so that the molten resin material is introduced into the cavity via the resin reservoir;
• and
• means for driving the cut punch when an inner portion of the resin material that is present in the resin reservoir is still molten and a portion of the resin material thereof that is in direct contact with the cooled dies is gradually solidified after the molten resin material has been charged into the cavity and the resin reservoir,
• wherein the cut punch is driven toward the gate so that the cut punch is inserted into the resin reservoir, whereby the cut punch not only closes the communicating portion while forcibly pushing the still molten resin material present in the resin reservoir back into the gate, but also cuts the resin material at the communicating portion so that a resin molded product formed in the cavity is separated from a resin solidified portion formed in the resin reservoir, and
• wherein an undercut portion is provided at a periphery of the distal end of the cut punch, disposed closer to an edge portion of the distal end than a center portion of the distal end, the undercut portion serving to hold the resin solidified portion formed in the resin reservoir at the time of mold opening.(18)