Pre-treatment: Injection molded parts are usually molded by injection molding process, and the mold is coated with a layer of mold release agent, which can significantly affect the adhesion of the coating and easily cause defects such as paint shrinkage. Therefore, the crucial pre-treatment must be carried out to remove the mold release agent. Pre-treatment methods, including the water washing, organic solvent, and snow treatment methods, are not just options but essential steps. The purpose is to adjust the tension of the plastic surface, improve the surface wetting properties, and complete the removal of oil and mold release agents. Internal Stress Relief: In the injection molding process of plastic products, internal stress is a common problem, which may lead to stress concentration and cracks during painting. Internal stress relief can be accomplished through annealing or finishing techniques. Annealing involves heating the plastic part below the heat deflection temperature and holding it, whereas full-face treatment uses a solution that removes internal stresses at room temperature. Surface cleaning: The surface of the plastic part can be contaminated with oils, sweat from hands, and mold-releasing agents, which can weaken the adhesion of the paint. Therefore, cleaning treatment must be carried out; the standard method is to use gasoline or alcohol cleaning, followed by chemical degreasing, to ensure that the lye residue on the surface of the workpiece is thoroughly cleaned and rinsed with pure water, and finally, air dry or dry. Dust removal: Since the plastic parts are insulators, their surface resistance is high. They are prone to generating static electricity and adsorbing tiny dust in the air. Using high-pressure ionized airflow to remove electricity and dust is more effective. Paint adhesion enhancement: Nylon, PP, and other plastic materials often lack adhesion between the substrate and paint due to their high surface crystallinity and low polarity, leading to paint fall problems. This can be solved by spraying a layer of adhesion promoter to change the molecular arrangement on the substrate’s surface and improve the dyne value, thus enhancing the adhesion. Spraying: Spraying uses compressed air flow through the spray gun spray paint to form a paint mist. Spray the body to the surface of the coated parts to create a uniform paint film. This method can produce a uniform paint film, coating delicate and smooth, suitable for the more hidden parts of the spray coating. Inspection: After spraying, inspection is required to ensure the quality of the coating. The inspection includes a film thickness test, adhesion test, water resistance test, color difference measurement, and appearance evaluation. Through the above steps, the quality and effectiveness of the painting process for injection-molded parts can be ensured to meet the needs of protection, decoration, and other special applications.