Since the beginning of the 21st century, the application fields of PU have been continuously expanding. Especially with the increasingly high environmental protection requirements worldwide, the development pace of waterborne polyurethane industry has been further accelerated. After decades of development, PU products have approached or reached the level of solvent-based products in fields such as automotive coatings and adhesives, and the production of raw materials has achieved large-scale.
The development speed of waterborne polyurethane adhesives abroad is significantly faster than that of other adhesive products, and they have a wide variety and large output. These adhesives generally have good initial adhesion, water resistance and temperature resistance, etc. In recent years, the pressure of environmental protection has forced some traditional products to gradually fade out of the market, while water-based high-solid content and powder products have gradually become mainstream products. Waterborne polyurethane adhesives, with their unique and outstanding properties, are facing unprecedented development opportunities. The demand for them is growing at a rate of 16% to 30%, more than twice that of other adhesive products, and is moving towards high performance, functionalization, and further expansion of application fields.
China began its research on waterborne polyurethane in the early 1970s. PU was first used in China to prepare electrophoretic paint. Later, people developed water-soluble PU for fabric finishing and PU emulsion as a leather finishing agent. After entering the 1980s, the research speed of WP adhesives in China has accelerated. However, compared with the level of series and industrialization abroad, it is still in its infancy, with problems such as single raw materials and preparation methods, few varieties, insufficient theoretical research and not in-depth enough application research.
From the perspective of product structure, the main type is emulsion type, followed by water-soluble latex type, which is less common. From the perspective of raw materials, polyether type polyols are mainly used, followed by polyester type. Other types such as polycarbonate are extremely rare, and the varieties of isocyanates are even rarer [only TDI(toluene diisocyanate) is commonly used, while HDI(hamethylene diisocyanate) and MDI(diphenylmethane diisocyanate) have only been reported]. From the perspective of preparation methods and types, the general ones are self-emulsifying carboxylic acid type and anionic system, while the quaternary ammonium salt self-emulsifying system is relatively rare. Methods such as melt dispersion and solid self-dispersion have not yet been involved. From both theoretical and application perspectives, emphasis is placed on application development, while theoretical research is relatively scarce. Domestic research on waterborne polyurethane adhesives focuses on modification studies. The modified waterborne polyurethane adhesives possess specific properties in certain aspects and can play different advantageous roles in different application environments.
