Two-component polyurethane adhesives were developed relatively early. Since their introduction, due to their advantages such as adjustable performance, high bonding strength and wide bonding range, they have become the most diverse and widely produced products among polyurethane adhesives.
The categories of two-component polyurethane adhesives can be classified based on the presence or absence of solvents, including solvent-based two-component polyurethane adhesives, solvent-free polyurethane adhesives, and water-based two-component polyurethane adhesives. In terms of application, there are also many varieties, such as general-purpose polyurethane adhesives, two-component polyurethane adhesives for composite films, two-component polyurethane adhesives for shoes, two-component polyurethane sealants, polyurethane potting compounds, polyurethane structural adhesives, etc. The following are the characteristics of two-component polyurethane adhesives.
1. It is a reactive adhesive. When the two components are mixed, a chemical reaction occurs, generating a cured product.
2. The formula is flexible, with a wide range of applications and a variety of adhesive products.
3. It usually cures at room temperature and can be accelerated by heating. The initial adhesion and final bonding strength of two-component polyurethane adhesives are usually higher than those of one-component wet-curing adhesives, which can meet the requirements of structural adhesives.
4. The dosages of the two components can be adjusted within a certain range, and there is generally a certain tolerance. The molar ratio of NCO/OH of the two components is generally greater than 1 or equal to 1. For solvent-based two-component adhesives, the main agent has a relatively large molecular weight and good initial adhesion performance. The dosage of the two components can be adjusted within a wide range, and the isocyanate component can be greatly excessive. The molar ratio of NCO/OH can even be less than 1. In cases where the NCO component is in excess, the polyisocyanate self-polymerizes to form a tough adhesive layer, which is suitable for bonding hard materials. In cases where the amount of NCO component is small, the adhesive layer is soft and can be used for bonding soft materials such as leather and fabric.
