Most plastic protoplasts are extruded or pressed. During hot extrusion, trace air or volatile impurities in the raw materials may escape to the surface, forming many micro defects such as "volcanic craters", resulting in reduced surface gloss and poor aesthetics. In addition, most conventional plastic parts have poor wear resistance and solvent resistance, and are easy to scratch, fog, and surface damage. Therefore, surface decoration and protection of plastic parts are required. Plastic materials with poor light aging performance can also be protected by light stabilized UV coating to prevent or delay the aging of plastic substrate, which is particularly important for occasions often used outdoors and exposed to sunlight and artificial short wave light sources (such as fluorescent lamps) for a long time. There are many kinds of plastic substrates with different chemical and physical properties. In terms of mechanical properties, they can be divided into hard and soft plastics; The surface properties can be divided into polarity and weak polarity. Common plastic materials include polystyrene, polymethyl methacrylate, PVC, polyethylene, polypropylene, polyester, polycarbonate, ABS plastics, etc. The physical properties of plastics with the same or similar components may be different. In addition to ordinary brittle varieties, polystyrene also includes high impact polystyrene; Polyethylene materials also include hard high-density polyethylene and soft low-density polyethylene. The plastic surface of polyester, polymethyl methacrylate, polycarbonate and other materials has certain polarity, and the adhesion problem of UV coating on it is easy to solve; The surface polarity of polyethylene and polypropylene materials is very low, and their adhesion to UV coatings is generally poor. It is often necessary to conduct spark discharge, corrosion and other polar treatment on plastics first, or add adhesion promoter in the formulation of UV coatings, for example, chlorinated resin can improve the adhesion of polypropylene. The formulation of UV curable coatings will be different due to different properties of plastic materials.
The plastic coatings in China started from the early 1980s. With the rapid development of the plastic products industry, the development of plastic coatings is rapid, especially in the automotive industry, household appliances and other fields. In 2007, China's demand for plastic products reached 35 million tons, and the consumption of plastic coatings used exceeded 120000 tons, with an average annual growth rate of 10% - 15%. The consumption of plastic coatings in China ranks first in the coating industry, and its consumption ranks only behind architectural coatings, automotive coatings, anti-corrosion coatings and wood coatings. The market prospect is promising. The plastic coatings in China have developed rapidly from general decoration to special functionality, from solvent based to water based. They have developed and produced plastic coatings that can be used to coat ABS, HIPS, PS, PP and other substrates, and their application fields have been continuously expanded.