Injection compression molding method for optically formed product

A method of producing an optically molded product of a thermoplastic resin by injection compression molding, the method comprising the steps:

• (1) expanding the volume of a cavity more than the volume of the optically molded product of interest;
• (2) injecting a molten thermoplastic resin into the cavity through an injection cylinder;
• (3) compressing the expanded cavity to a prescribed thickness of a center portion of the molded product or a thickness 200 μm smaller than the prescribed thickness;
• (4) changing resin pressure in the injection cylinder and compression pressure in the cavity in limits that the change width does not exceed 100 μm from the prescribed thickness of center portion of the molded product to achieve the prescribed thickness of the molded product in the end;
• (5) keeping the molten thermoplastic resin in the cavity until the molded product of interest is formed;
• and
• (6) taking out the obtained molded product from the cavity.