A major technological breakthrough in solvent-free polyurethane (PU) adhesives has been achieved, specifically tailored for high-temperature retort plastic packaging, marking a significant leap in the flexible packaging industry. The innovation, developed through in-depth research on prepolymer optimization, solves the long-standing problem of poor adhesion and delamination of traditional solvent-free PU adhesives under high-temperature and high-humidity retort conditions.
Researchers optimized the formula of two-component solvent-free PU adhesives by adjusting key parameters, including the isocyanate mass fraction (ωNCO) of the prepolymer, the molecular weight of polyols, and the molar ratio (r value) of –OH to –NCO groups. The results show that when the ωNCO is 17%, the prepolymer maintains low viscosity, ensuring smooth coating, while the adhesive achieves high peel strength after boiling treatment.
Under the optimal conditions – polyol molecular weight of 1609 g/mol, ωNCO of 17% and r value of 2.5 – the peel force of the retort cast polypropylene (RCPP) layer reaches 6.30 N before boiling and 4.37 N after boiling, far exceeding national standards. The adhesive also meets the requirements of GB/T 41168-2021 for the retort resistance of aluminum-plastic composite films, eliminating safety hazards such as solvent residues.
Compared with traditional solvent-based PU adhesives, the new solvent-free technology achieves zero VOC emissions, reducing energy consumption by more than 60% as it eliminates the need for drying processes. It also improves production efficiency, with the production line speed increased from 8000 meters per hour to 12000 meters per hour in practical applications.
Industry experts point out that this breakthrough will accelerate the replacement of solvent-based adhesives in the retort packaging field, especially in food and pharmaceutical packaging. It not only ensures the safety and integrity of packaged products during high-temperature sterilization but also aligns with the global trend of green and sustainable packaging. It is expected that the market share of solvent-free PU adhesives in the flexible packaging industry will rise to over 70% by 2028.
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