Polyurethane laminating adhesive is the core supporting material for the lamination of flexible packaging films. Relying on the action of amine carbamate bonds and hydrogen bonds in the molecular chain, it can achieve high-strength composites of different substrates such as plastic films, aluminum foil, and paper, and is widely used in the flexible packaging fields of food, medicine, and daily chemicals. It is a key material for ensuring the stability of the interlayer composite of packaging.
From the perspective of the product technology system, the current industry is divided into three main categories: solvent-based, water-based, and solvent-free. The solvent-based PU glue has mature technology and excellent wetting performance, and is suitable for various high and low temperature composite processes. However, it has the shortcomings of high VOC emissions and heavy environmental pressure. The water-based PU glue uses water as the dispersion medium and has no organic solvents, which has excellent environmental performance. However, its water resistance and initial adhesion are relatively weak, and it is only suitable for ordinary normal temperature packaging. The solvent-free two-component PU glue is the current mainstream upgraded direction. It has a solid content of 100% and zero VOC emissions. It does not require a drying process, has lower production energy consumption, and can be adapted to high-speed composite production lines.
In terms of core application performance, performance customization can be achieved through modification of the molecular structure. By adjusting the ratio of polyether and polyester polyols, the adhesive's resistance to media can be enhanced, protecting it from erosion by substances such as sauces and oils. Using aliphatic isocyanate raw materials can solve the problem of yellowing during high-temperature cooking, meeting the production requirements for sterilization bags at temperatures of 121℃ and above. At the same time, compliant products can meet the national standards for food contact materials, with low migration and low odor, and are suitable for packaging for direct food contact.
At present, the technical challenges in the industry mainly lie in two issues: the slow low-temperature curing of solvent-free adhesives and the failure of adhesion after the surface corona decay of the film. Future research and development will focus on low-viscosity, rapid-curing solvent-free systems, single-component PU adhesives without mixing, and high-weatherability modified products. It will balance production efficiency, environmental indicators, and end-use performance of packaging, promoting the green and low-carbon upgrade of the flexible packaging composite industry.
