Polyurethane is one of the six major synthetic materials in the world. It is “The Fifth Plastic”. And PU has promising prospects. Polyurethane(PU) coating serves as one of the main varieties occupying significant positions in the coating industry, with pleasant cohesiveness, abrasion resistance, and high glossiness. For this reason, this article reviews the research progress of polyurethane coating monomer, prepolymer and environmentally friendly polyurethane coating. It gives an account of the performance and application of environmentally friendly polyurethane coating. And also indicates its development trend.
Polyurethane coating is a kind of new material. It did not spring up until the second half of the 20th century. And PU has both properties similar to those of acylamino. Such as strength, abrasion resistance, oil resistance, and heat resistance & solvent resistance of polyester. It also has water resistance & flexibility of polyether. As polyurethane coating contains. Besides urethane bond, ester bond, ether bond, urea bond, diuretic bond, urea formate bond, acyl urea bond and unsaturated bond of grease. In 1937, German Professor Bayer from German synthesized polyurethane for the first time. Since then people recognize it gradually due to its major characteristics. Such as the wide adjustable extent of hardness and low temperature resistant and good flexibility and strong adhesion. Its elastomer, foam plastic, coating, and adhesive have been widely utilized.
Furthermore, the main raw material of polyurethane is quite active. Isocyanate can not only combine with hydroxyl resin but with hydroxide radical in the substrate. It forms a firm chemical bond and hydrogen bond and enhances adhesive power with the substrate. That makes it a good combination of coating advantages. Polyurethane possesses excellent versatility and outstanding effect. Acts as one of the fastest growing varieties of paints, all countries globally widely studied the polyurethane coating because of its high value. And its proportion and growth reflect the coating industry level of a country.
Polyurethane automotive paint
Automobile coatings include automobile primer, intermediate coat, and finishing paint. According to the coating process, 92% of primer uses cathodic electric deposit (CED). It includes 90% cathode electrophoretic paint. Polyurethane electrophoretic paint has excellent comprehensive performance. Such as thick coating, fairly smooth surface and chipping resistance. It also can be applied to rust protection steel plates perfectly. The proportion of polyurethane electrophoretic paint is becoming increasingly large.
In China, paint manufacturers have successively introduced thick film type polyurethane cathode electrophoretic paint from Japan Kansai Paint Company as car primer. Its main ingredient being epoxy polyamide polyurethane two-component electrophoretic paint. It is principally used in home-made autos like FAW Audi, Tianjin Xiali, and Chongqing Isuzu.
The intermediate coating has quite a high requirement for stone hit resistance. While polyurethane coating is the best in this regard and thus valued greatly. So some famous enterprises in the world have the patent of polyurethane anti-stone coating. They are Sanyo Chemical, BASF, PPG, and Bayer, etc. As to the automobile finishing coat, polyurethane coating is characterized by metallic effect and the use of the paint is the development trend.
At present, two-component acrylic polyurethane varnish has been extensively used in European automobile production line. This kind of varnish has outstanding acid resistance. In China, acrylic polyurethane finishing coat has been developed by many enterprises. Thermosetting acrylic paint is widely used in the coating of cars, buses, and trucks as it is low-temperature drying, self-drying, and non-yellowing, with fatty polyisocyanate as cross-linking agent.