Water-based polyurethane adhesive (PU adhesive) is a kind of adhesive which is made from water-based polyurethane as base material. It is an important kind of water-based adhesive. It has been developed rapidly in recent years with its excellent adhesion, outstanding oil resistance, impact resistance, wear resistance and low temperature resistance.
1. Most of the aqueous polyurethane adhesives do not contain-NCO groups, and thus are mainly cured by the internal cohesion and the adhesion of the polar groups in the molecule. And the solvent-based or solvent-free one-component and two-component polyurethane adhesive can make full use of the reaction of-NCO and enhance the bonding property during the bonding and curing process. The water-based polyurethane contains the groups such as the base group, the hydroxyl group and the like, and can participate in the reaction under the appropriate conditions, so that the adhesive can be crosslinked.
2. In addition to the addition of the high-molecular thickening agent, the important factors that affect the viscosity of the aqueous polyurethane are the ionic charge, the core-shell structure, the particle size of the emulsion, etc. the more ions and counter-ions in the polymer molecule (the free ions in the solution that are opposite to the ion groups contained in the polyurethane main chain and the side chain), the higher the viscosity, the solid content (concentration), the molecular weight of the polyurethane resin, The effect of cross-linking agent and other factors on the viscosity of the water-based polyurethane is not obvious, which is beneficial to the polymer quantification of the polyurethane, so as to improve the cohesive strength of the adhesive. the main influencing factors of the viscosity of the solvent-based polyurethane adhesive are the molecules of the polyurethane, The amount, the degree of branching, the concentration of the glue, and the like. The same solid content, the viscosity of the water-based adhesive is smaller than that of the solvent-based adhesive.
3. The viscosity is an important parameter of the performance of the adhesive. The viscosity of the aqueous polyurethane is generally adjusted by a water-soluble thickener and water. The solvent-based adhesive can be adjusted by increasing the solid content, the molecular weight of the polyurethane, or the selection of a suitable solvent.
4. Because the volatility of water is worse than that of organic solvent, the drying of waterborne polyurethane adhesive is slow, and the wetting ability to surface hydrophobic substrate is poor because of the large surface tension of water. If most of the moisture is not evaporated from the adhesive layer, the coating evaporates into the air, or is absorbed by the porous substrate, it is difficult to obtain a continuous adhesive layer.
5. Waterborne polyurethane adhesive can be mixed with a variety of waterborne resins to improve performance or reduce cost. At this time, attention should be paid to the ion properties and acidity and alkalinity of the ionic waterborne adhesive, otherwise it may cause condensation. Due to the compatibility between polymers or the solubility in some solvents, solvent polyurethane adhesive can only be mixed with a limited number of other resin adhesives.
6. The water-based polyurethane adhesive has the advantages of small odor, convenient operation and easy cleaning of the residual glue, and in the solvent-based polyurethane adhesive, a large amount of solvent is also required to be consumed, and the cleaning is not convenient.