The performance characteristics of water-based polyurethane catalyst: compared with solvent-based polyurethane Compared with adhesives, water-based polyurethane adhesives not only have the advantages of being non-flammable, solvent-free, and not polluting the environment, but also have the following characteristics:
1. Solvent-based two-component adhesive makes full use of the reaction of NCO groups to enhance bonding performance during the curing process; Since water-based polyurethane adhesive does not contain NCO groups, the adhesion mainly relies on the cohesion generated by polar groups in the polymer. Water-based polyurethane contains carboxyl, hydroxyl and other groups, which can also participate in the reaction under appropriate conditions, causing the adhesive to interact. linked reaction.
2. The important factors that affect the viscosity of water-based polyurethane include ionic charge, core-shell structure, emulsion particle size, etc. The more ions and counterions in the polymer molecules, the The greater the viscosity. However, the molecular weight, solid content, cross-linking agent and other factors of polyurethane resin have no obvious impact on the viscosity of water-based polyurethane. This is conducive to increasing the molecular weight of polyurethane to increase the cohesive strength of the adhesive. For polymers with the same solid content, the viscosity of water-based polyurethane adhesives is smaller than that of solvent-based adhesives.
3. Viscosity is an important indicator that determines the performance of adhesives. According to Coating Online, the viscosity of water-based polyurethane is generally adjusted through water-based thickeners or water, while solvent-based polyurethane adhesives can be adjusted by increasing the solid content, molecular weight or selecting an appropriate solvent.
4. Since the evaporation rate of water is lower than that of organic solvents, water-based polyurethane adhesives dry slowly. Because the surface tension of water is large, it has poor wetting ability on the hydrophobic surface of the substrate. If most of the water has not evaporated from the adhesive into the air, or is suddenly heated and dried before being absorbed by the porous substrate, it will not be easy to obtain continuous results. sexual coating. Since the main solid component of water-based polyurethane is hydrophilic, the dried film will have poor water resistance if it does not undergo a certain degree of cross-linking.
