Waterborne polyurethane coating
In 1942, Shlack successfully prepared cationic waterborne polyurethane for the first time. Industrial production of waterborne polyurethane began in the 1970s, and now the annual output of waterborne polyurethane tree ester in the world is about 50,000 ~ 60,000 T. Choose water as dispersion medium coating, waterborne polyurethane coating organic solvent in the structure of polyurethane coating system is less, with the current environmental protection energy conservation and emissions reduction requirements for the proposed coating field, and the application of waterborne polyurethane coating in the related field and development problem is becoming more and more attention by the industry and attention. Up to now, although in our country whole coating domain, the application proportion of concerned polyurethane coating is only in 4% or so, but the engineering application of waterborne polyurethane coating is maintaining the growth rate of nearly 10% in recent years. In general, there is no need to add dispersants or emulsifiers to waterborne polyurethane coatings, and the molecular size and structure can be adjusted appropriately according to the situation. In view of this, waterborne polyurethane coatings have better low temperature film-forming properties than latex coatings which are widely used in the traditional sense. There is no need to add the plasticizer and film-forming auxilaries. Compared with other coatings, waterborne polyurethane coatings not only have a good appearance, but also short drying time, showing a unique advantage in the field of wood coatings. The traditional solvent-based acrylic leather coatings have been gradually replaced by waterborne polyurethane leather coatings. With their advantages in chemical resistance and low temperature resistance, they have attracted much attention from leather coating personnel. In addition, this kind of material also plays a very specific application value in plastic, vehicle, industry and anticorrosion and other related fields, and has quite broad development space.
The properties of waterborne polyurethane coatings still have some limitations. The lack of water resistance is one of the main factors affecting the application of waterborne polyurethane coatings in practice. In addition, there are also certain problems in the application of waterborne polyurethane coatings during the construction period. For example, for the two-component waterborne polyurethane coatings, the drying rate after incorporation into the construction materials is relatively slow and requires a long time for maintenance. Carbon dioxide bubbles generated during the reaction of waterborne polyurethane coating with water may remain in the film and affect its properties. Moreover, the high cost has become one of the main factors affecting the industrial application of waterborne polyurethane coatings. More importantly, in the waterborne polyurethane coating, the addition of a large number of waterborne coatings may have an impact on the iron base material in engineering buildings, leading to the emergence of flash erosion, and even affect the wettability and appearance performance of the surface coating. Aiming at these problems, in order to promote the further development of water-borne polyurethane coatings, subsequent composite modified water dispersible polyurethane coating shall be as a key development direction and research, try to some function is relatively special molecular structure, such as containing silicon polymer chains, containing fluorine polymer chain in the polyurethane chain, in order to improve the comprehensive performance of coating film, exert its in the advantage of high temperature resistance, water resistance and weatherability. Low VOC and high performance two-component waterborne polyurethane coatings can also be the focus of research and development to reduce the cost of polyurethane coatings and improve the efficiency of use.