Polyurethane adhesive refers to an adhesive containing a urethane group (-NHCOO-) or an isocyanate group (-NCO) in the molecular chain. It has excellent performance and should be widely used. According to Gunter Festel, a polyurethane adhesive specialist at Bayer in Germany, the diversity of polyurethane adhesives is almost a solution to every bonding problem.
Polyurethane adhesives are classified into two major categories: polyisocyanates and polyurethanes. They contain highly polar, highly chemically reactive isocyanate (-NCO) and urethane (-NHCOO-) groups, and materials that contain active hydrogen, such as Porous materials such as foam plastics, wood, leather, fabrics, paper, and ceramics, and materials with smooth surfaces such as metal, glass, rubber, and plastics all have excellent chemical adhesion. The effect of hydrogen generated between the polyurethane and the adhered material increases the cohesive force of the polymer. This will make the bond stronger. In addition, polyurethane adhesives also have the characteristics of adjustable toughness, simple bonding process, excellent low temperature resistance and excellent stability. In recent years, they have become the fastest growing adhesives at home and abroad.
Waterborne polyurethane adhesive
Waterborne polyurethane adhesive refers to the adhesive formed when polyurethane is dissolved in water or dispersed in water. In practical applications, waterborne polyurethanes are mostly based on polyurethane emulsions or dispersions, and the aqueous solution type is less.
In Europe, the earliest research and development of polyurethane water dispersion system, after the 70's formed several more mature preparation methods, such as acetone, prepolymer dispersion, melt dispersion method, ketimine ketone nitrogen and so on. The product types mainly include self-emulsifying and forced emulsifying types.
In recent years, a lot of research has been done on the problems of slow drying speed of aqueous polyurethane adhesives, poor wettability on non-polar substrates, low initial viscosity, and poor water resistance, and significant progress has been made. The research results show that if the solid content is increased to more than 50%, the drying rate is similar to that of common solvent type polyurethane adhesive at a drying temperature of 40-60°C. Blending with other emulsions (such as EVA, acrylate emulsions, etc.) to form an interpenetrating network or a grafted structure improves initial tack and adhesion performance, while reducing costs. The cross-linking method can improve the water resistance and heat resistance. For example, BASF's anionic polyether waterborne polyurethane composite film adhesives have reached the level of two-component solvent-based polyurethane adhesives.
