Method of in-mold coating

A method of in-mold coating, comprising steps of:

• forming a molded product by applying a clamping pressure to a mold including a fixed mold half and a movable mold half to mold a synthetic resin molding material in the mold according to an injection molding method, an injection compression molding method or an injection press molding method;
• then reducing the clamping pressure to a reduced pressure value or parting the fixed mold half and the movable mold half;
• injecting a coating material into a space formed between an inner surface of the mold and a surface of the molded product in the mold;
• and
• coating the surface of the molded product with the coating material, clamping the mold again,
• wherein the coating material is injected in such a state that the molded product has cured or solidified to such an extent that the surface of the molded product can withstand an injection pressure and a flow pressure of the coating material,
• wherein the clamping of the mold after injection of the coating material is carried out such that the clamping pressure is changed from the reduced pressure value to and maintained at a first pressure value and then further changed from the first pressure value to and maintained at a second pressure value,
• wherein the clamping of the mold after the injection of the coating material is carried out such that the clamping pressure is further changed from the second pressure value to and maintained at a third pressure value,
• wherein the first pressure value is 10 Kgf/cm2-100 Kgf /cm2 with respect to a projected area of the molded product, a clamping pressure transitional period of time during which the clamping pressure is changed from the reduced pressure value to the first pressure value is 0.5 sec-10 sec and a clamping pressure maintaining period of time during which the clamping pressure is maintained at the first pressure value is 0.5 sec-20 sec in an initial stage,
• wherein the second pressure value is 20%-80% of the first pressure value, a clamping pressure transitional period of time during which the clamping pressure is changed from the first pressure value to the second pressure value is 0.1 sec-5 sec and a clamping pressure maintaining period of time during which the clamping pressure is maintained at the second pressure value is 0.5 sec-20 sec in an intermediate stage, and
• wherein the third pressure value is lower than the first pressure value in the initial stage, and 40%-200% of the second pressure value in the intermediate stage, a clamping pressure transitional period of time during which the clamping pressure is changed from the second pressure value to the third pressure value is 0.1 sec-5 sec and a clamping pressure maintaining period of time during which the clamping pressure is maintained at the third pressure value is not less than 1 sec in a final stage.