A mold device where a pressurized fluid is injected into a clearance between a resin injected into a cavity and a cavity wall surface, the mold device including: a shaft body provided on at least one of a first mold and a second mold, the first mold and the second mold forming a molding space, the shaft body ejecting a molded article molded from the resin injected into the molding space; a ring-shaped elastic member for supporting and sealing the shaft body, an opening of a groove formed in the ring-shaped elastic member along a circumferential direction of the ring-shaped elastic member being oriented toward the molding space, a load being applied on the ring-shaped elastic member to improve adhesion to the shaft body; and an injection portion provided on at least one of the first mold and the second mold for injecting the pressurized fluid into the molding space.

[Problem] The present invention relates to a manufacturing method for obtaining a molded article having an expanded layer in the molded article, wherein an expanding agent and device used to manufacture a resin having expansion properties, and a means for increasing expansion ratio are provided.

[Solution] In the present invention, an expanding agent placed in a heating cylinder of a molding machine is configured as a liquid, the volume of the expanding agent is controlled, and the expanding agent is injected into a molten resin in the heating cylinder of the molding machine. The volume of the injected expanding agent can thereby be accurately measured each time. When a low-boiling liquid such as water, an alcohol, or an ether is used as the injected expanding agent, all of the liquid is vaporized by the temperature of the heating cylinder of the molding machine, and no residue thereof is therefore left in the molded article. When sodium bicarbonate water is used as the injected expanding agent, solvent water vaporizes and water vapor also becomes expandable gas, which is less expensive than using sodium bicarbonate as the expanding agent for a master batch using the resin that is to be molded.

Wings are provided on mold components and linear ways are provided below these wings. A pad rides on each linear way below each wing. A force generator, such as a spring, is disposed between each wing and underlying pad. In this way the weight of the mold components is borne, at least in part, by the linear ways so that the weight on components that might otherwise sag is lessened.