The main material components of polyurethane adhesives

The core components of polyurethane adhesives are mainly isocyanates and polyols, supplemented by chain extenders, catalysts, and additives. Through chemical reactions, amino carbamate bonds (-NHCOO-) are formed, thereby achieving bonding performance. The component system can be divided into three major categories: main resin, reaction monomers, and functional additives. 

 

Among the main raw materials, isocyanates are the most crucial reactive monomers. Commonly used are aromatic MDI (diphenylmethane diisocyanate) and TDI (toluene diisocyanate), as well as aliphatic HDI, IPDI, etc. The former has high bonding strength and moderate cost, and is mostly used for general soft packaging, sheets, and foam bonding; the latter has good resistance to yellowing and weathering, and is suitable for outdoor and high-end transparent products. The other core component is polyol compounds, including polyether polyols, polyester polyols, and polybutyl ester polyols, etc. Polyether polyols are resistant to hydrolysis and have good flexibility, while polyester polyols have strong cohesion, good heat resistance and oil resistance. These two determine the elasticity, strength and medium resistance of the adhesive layer. 

 

The reaction supporting components include chain extenders and crosslinking agents, such as small molecule diols and diamines (ethylene glycol, MOCA), which are used to regulate the length of molecular chains and the crosslinking density, thereby enhancing hardness and bonding strength; catalysts (organic tin, tertiary amines) accelerate the reaction between isocyanates and hydroxyl groups and water, shortening the curing time, and are suitable for different construction processes. 

In addition, functional additives will also be added: plasticizers to improve low-temperature toughness, antioxidants and light stabilizers to enhance aging resistance, defoamers and leveling agents to optimize workability, and fillers (calcium carbonate, silica) to reduce costs, adjust viscosity and cohesion. 

 

Polyurethane adhesives, through precise ratios of isocyanate and polyol, combined with various additives, can be applied in multiple fields such as flexible packaging, composite films, shoe materials, automobiles, and wood, and possess high adhesive strength, flexibility, fatigue resistance, and good process adaptability.