Screw of injection molding machine for foam molding, and injection molding machine

A screw of an injection molding machine for foam molding in a heating cylinder in which an inside of the heating cylinder is partitioned into a first stage and a second stage from a rear side to a front side of the screw due to a shape of the screw, the first stage being formed with a first compression section, comprising a compression portion and a measurement portion, in which a resin is to be compressed, the second stage being formed with a starvation section in which a pressure of the resin is to be lowered and an inert gas is to be introduced, and with a second compression section in which the resin is to be compressed, the screw comprising:

• a barrier flight, including a combination of a main flight and a sub-flight having a lead angle larger than that of the main flight, provided in a portion of the screw corresponding to the first compression section;
• and
• a multi-start flight provided in a portion of the screw corresponding to the second stage,
• wherein the multi-start flight of the second stage is located on the front side of the screw after the first stage,
• wherein the multi-start flight comprises a plurality of spiral flights protruding from an outer surface of a main body of the screw, and the plurality of flights are disposed in parallel with each other, and
• wherein the heating cylinder is provided with an introduction port for introducing an inert gas at a predetermined position corresponding to the starvation section, and a first constant groove depth of the screw corresponding to the starvation section is larger than a second constant groove depth of the screw corresponding to the main flight in the measurement portion of the first compression section, such that
• the pressure of the resin is lowered, and
• a gas phase is formed in the starvation section.