Peel strength is the core indicator for evaluating the reliability of adhesion in flexible packaging composite films. It directly determines the sealing performance, weather resistance and service life of polyurethane laminating adhesive composite products, and is widely used in flexible packaging fields such as food, cosmetics and medicine. The higher the peel strength value, the stronger the interlayer bonding force of the lamination film, and the less likely the packaging is to have quality defects such as delamination, glue separation and edge warping.
The peel strength of polyurethane laminating adhesive is mainly influenced by three factors: raw material formula, substrate condition, and lamination process. At the formula level, the molecular weight of polyols and the content of NCO directly affect the cohesion of the adhesive layer. Reasonable combination of soft and hard segments can balance the toughness of the adhesive layer and the bonding strength, and enhance the peel strength at normal temperature and after boiling. In terms of the substrate, insufficient corona treatment of the film will reduce the surface tension, and the adhesive cannot fully wet the substrate interface, directly resulting in a significant reduction in peel strength. The release agents and other additives in the film will also disrupt the interface bonding effect.
The production process is the key link in controlling the peel strength. If the curing temperature is too low, it will cause incomplete cross-linking reaction of the adhesive and insufficient curing of the adhesive layer. If the temperature is too high, internal stress will be generated, making the adhesive layer brittle and reducing the peel strength as well. At the same time, the temperature and humidity in the workshop, the amount of coating, and the compounding pressure will also affect the bonding effect. A high humidity environment is prone to cause the polyurethane laminating adhesive to fail when exposed to water, reducing the effective cross-linking points.
In actual production, it is necessary to match the substrate type with the adhesive, standardize the corona treatment procedures, precisely control the curing temperature and the amount of glue application, and isolate the interference of water vapor. Through comprehensive optimization, the peel strength of the lamination film can be stably enhanced, meeting the requirements of different working conditions such as normal temperature packaging and high-temperature boiling, and ensuring the overall performance of the flexible packaging products.
