What are the descriptions of water-based two-component polyurethane resins?

Compared with the solvent-based two-component polyurethane wood coating, the water-based resin of the two-component water-based polyurethane coating has a very low V O C content, which can be reduced by 70% to 90%, and the drying speed is fast. Gloss, physical and chemical properties and service life can all meet the requirements of water-based wood coatings, so making room temperature curing two-component water-based wood coatings is an important way to significantly improve the performance of the coating film. The water-based two-component polyurethane is cured into a film after a series of processes of two-component fusion, particle coagulation, competitive reaction between hydroxyl and water and polyisocyanate, and the escape of carbon dioxide. Generally speaking, the composition of water-based hydroxyl groups is designed to have a certain number of carbonyl groups, which can avoid resin flocculation after the carbonyl groups are formed into salts. ester, water-based alkyd and water-based polyurethane), the relative molecular mass and T g value of the hydroxyl dispersion are generally higher than those of the hydroxyl emulsion, and the hydroxyl content is too high or the glass transition temperature is too high will make the acrylic dispersion too hydrophilic and The curing agent cannot be effectively emulsified in water, and the small particle size of the acrylic dispersion is beneficial to improve the hardness and appearance of the coating film. When the particle size is small, the specific surface area of ​​the particles increases, and the distance for the curing agent to disperse into the particles is shortened, thereby improving the utilization rate of hydroxyl groups.

In addition, as the particle size decreases, capillary action occurs in the film-forming process, and these actions are also conducive to the coalescence of the two components; the pot life of water-based two-component polyurethane is usually short, and the viscosity increases after adding the curing agent. The incompatibility of the pot life will affect the performance of the coating, such as leveling, gloss, transparency, solvent resistance, water resistance and durability; there are reactions between isocyanates and polyols in the system, urethanes and urea and isocyanates As well as the reaction between isocyanate and water, there is also the reaction between isocyanate and hydroxyl, which is slower than the reaction with water, because the reaction between isocyanate and water forms a viscous urea layer, which hinders the agglomeration of hydroxyl particles and affects the In the final film forming process, the escape of carbon dioxide generated by the reaction will cause defects such as shrinkage, bubbles and loss of light in the coating film. The limit thickness for forming pinholes becomes smaller, the longer the flashing time, the better the leveling, and the limit thickness for forming pinholes is also larger, but the hardness, solvent resistance and chemical resistance of the coating film are slightly reduced; High temperature and low humidity are also conducive to the volatilization of water, and lower humidity will increase the limit thickness and sag resistance of the coating film to form pinholes.