The curing agent for flexible packaging two-component PU glue is mainly composed of modified products of polyisocyanates. It is selected in three major systems: solvent-based, non-solvent-based, and dedicated for boiling treatment. The main types are aromatic and aliphatic.
The most commonly used solvent-based dry bonding adhesive is the TMP-TDI addition product, which is formed by the addition of toluene diisocyanate and trimethylolpropane. It is diluted with ethyl acetate to a solid content of 75%, featuring high cost-effectiveness and moderate curing speed. It is suitable for normal PET, BOPP, and CPP temperature-composite packaging. The ratio is mainly masterbatch: curing agent = 100:5-8. After 36-72 hours of curing, it is ready for molding. It is the standard curing agent for ordinary snack packaging bags. For products that can withstand boiling water and high-temperature steaming, the TMP-MDI addition product is used. Its molecular structure is regular, with a higher crosslinking density, and it is resistant to media and high temperatures. It is suitable for aluminum foil and nylon steaming bag composites.
The solvent-free soft packaging adhesive curing agent is a high NCO aromatic MDI prepolymer. It is 100% solvent-free, has high viscosity at room temperature and excellent flowability when heated for coating. When combined with polyester polyol as the main agent, it is suitable for high-speed solvent-free laminating machines. It is mainly used for food aluminum-coated film laminating. The low free monomer grade can meet the food-grade compliance requirements.
The high-end transparent and yellow-resistant packaging uses HDI tri-functional aliphatic curing agent, which does not yellow and is resistant to aging. It is mainly used in daily care products and high-end transparent soft packaging, and its cost is higher than that of the aromatic system. The water-based soft packaging adhesive is paired with hydrophilic modified isocyanate curing agent, which is mixed in water for use. It focuses on being environmentally friendly and low in VOC.
