Injection molding method and injection molding machine

An injection molding method which uses an injection molding machine including a first mold part which is provided with a first cavity, and a second mold part which is provided with a second cavity and is arranged in tandem with the first mold part, the method comprising:

• a first molding step of injecting a second material into the first cavity and compressing the second material in the first cavity;
• and
• a second molding step of injecting a first material into the second cavity,
• wherein in the first molding step and the second molding step, the first mold part and the second mold part are clamped together by mold clamping means,
• wherein in the second molding step, while a pressure generated in the second mold part by injecting the material into the second cavity in the second molding step acts on the first mold part so that a compressive force is applied to the second material in the first cavity, a mold clamping force generated by the mold clamping means is decreased at a predetermined timing,
• wherein a molding cycle is defined by including the first molding step and the second molding step,
• wherein the second material is laminated on a primary molded body formed of the first material to form a secondary molded body formed of the first material and the second material,
• wherein in the first molding step, the second material is injected in a state where the primary molded body is accommodated in the first cavity to form the secondary molded body, the primary molded body being formed during the second molding step in an earlier molding cycle than a current molding cycle, and
• in the second molding step, the first material is injected into the second cavity to form a different primary molded body used in the first molding step in a later molding cycle.