One type of gate in plastic injection molding is a submarine gate. Submarine gates are available in two types, elliptical or D-shaped, depending on how the gate is processed into the mold. Generally, there are many mold manufacturers that manufacture molds with an elliptical cross section. However, if an elliptical mold is used for the submarine gate, the mold processing is easy, but the gate may not be easily cut because resin residue may be generated depending on the plastic due to the large cross-sectional area during releasing. As a result, the quality of the finished surface of the injection molded product may be poor.

When a submarine gate is used in plastic molding for medical use, the D-shaped gate shape cuts the finished surface of the plastic injection molded product neatly, which leads to improved quality of the molded product. Since the shape of the submarine gate is type, stress concentrates on the corners of the gate, so that the resin is more likely to be cut during release and the quality of the release surface is improved. In addition, since the cross-sectional area can be reduced with the D-type gate, resin orientation is less likely to occur, so that the generation of resin residue can be suppressed.