What is Polyurethane (PU) and its application?
Polyurethane (PU), whose full name is polyurethane, is a polymer compound. It was produced in 1937 by Otto Bayer and others. Polyurethane has two categories: polyester type and polyether type. They can be made into polyurethane plastic (mainly foam), polyurethane fiber (called spandex in China), polyurethane rubber and elastomers.
Soft polyurethane mainly has a thermoplastic linear structure. It has better stability, chemical resistance, resilience and mechanical properties than PVC foam materials, and has less compression deformation. Good heat insulation, sound insulation, anti-vibration and anti-virus performance. Therefore, it is used as packaging, sound insulation, and filter material.
Rigid polyurethane plastic is light in weight, excellent in sound insulation, heat insulation, chemical resistance, good electrical properties, easy to process, and low water absorption. It is mainly used as a structural material for construction, automobile, aviation industry, and thermal insulation. The properties of polyurethane elastomer are between plastic and rubber, oil resistance, abrasion resistance, low temperature resistance, aging resistance, high hardness and elasticity. Mainly used in the shoe industry and medical industry. Polyurethane can also be used to make adhesives, coatings, synthetic leather, etc.
Polyurethane appeared in the 1930s. After nearly eighty years of technological development, this material has been widely used in the field of home furnishing, construction, daily necessities, transportation, and home appliances.
(1) Waterborne polyurethane coating
In 1942, Shlack successfully prepared cationic water-based polyurethane for the first time. In the 1970s, the industrial production of water-based polyurethane began. Up to now, the world's annual output of water-based polyurethane resin is about 50,000 to 60,000 tons. Waterborne polyurethane coatings use water as the coating dispersion medium. There are fewer organic solvents in the entire polyurethane coating structure system, which meets the current environmental protection requirements for energy saving and emission reduction in the coating field. Therefore, the application of waterborne polyurethane coatings in related fields is related to Development issues have received increasing attention and attention from industry insiders. Up to now, although the application proportion of polyurethane coatings in my country's entire coatings field is only about 4%, the engineering application of water-based polyurethane coatings has maintained a growth rate of nearly 10% in recent years. Under normal circumstances, waterborne polyurethane coatings do not need to add dispersants or emulsifiers, and the molecular size and molecular structure can be adjusted appropriately according to the situation. In view of this feature, compared with the more widely used latex coatings in the traditional sense, waterborne polyurethane coatings can have better low-temperature film-forming properties, without the need to add plasticizers and film-forming aids in proportion to the profit. Compared with other coatings, waterborne polyurethane coatings not only have a good appearance, but also have a short drying time, which shows a unique advantage in the field of wood coatings. Solvent-based acrylic leather coatings in the traditional sense have gradually been replaced by water-based polyurethane leather coatings. With their advantages in chemical resistance and low temperature resistance, they have attracted the attention and attention of people in the leather coatings field. In addition, this type of material also plays a very precise application value in related fields such as plastics, vehicles, industry, and anti-corrosion, and has a considerable space for development.
The performance of waterborne polyurethane coatings still has certain limitations. Insufficient water resistance is one of the most important factors affecting the application of waterborne polyurethane coatings in practice. In addition, during the construction period, there are also certain problems related to the application of water-based polyurethane coatings. For example, for two-component water-based polyurethane coatings, the drying speed after being incorporated into construction materials is relatively slow and requires a long time for maintenance. . The carbon dioxide bubbles generated during the reaction of the waterborne polyurethane coating with water may remain in the coating film in large quantities, affecting its performance. Moreover, the high cost has become one of the main factors affecting the industrial application of waterborne