Reasons why flexible packaging polyurethane laminating adhesive can not be mixed at will

Flexible packaging polyurethane laminating adhesives are the core materials in laminated packaging production. Many people mistakenly believe that similar polyurethane laminating adhesives have similar properties and can be mixed at will. However, in fact, there are significant quality risks involved. Different models and brands of adhesives must not be mixed at will. 

 

The first issue is the incompatibility of chemical formulations. The resin structures, active groups, and additive ratios of different polyurethane laminating adhesives are all different. When some adhesives containing special additives and solvents are mixed together, uncontrollable chemical reactions will occur, resulting in sudden increases in viscosity, delamination, precipitation, gelation, and other problems, which directly undermine the stability of the adhesive and cause it to fail and be scrapped. 

Secondly, it will disrupt the equilibrium of the curing reaction. For flexible packaging, most commonly used are two-component polyurethane adhesives, where the main agent and the curing agent are in a dedicated ratio system. Mixing different adhesives will disrupt the reaction ratio between hydroxyl groups and isocyanates, resulting in incomplete curing, sticky surfaces, soft collapse inside, or excessive cross-linking leading to brittle cracking of the adhesive layer, significantly reducing the lamination bonding strength. 

 

Furthermore, the mixture can lead to quality defects in the final product. Glue with an imbalanced formula will have problems such as packaging delamination, blistering, and detachment after curing. Its temperature resistance, moisture resistance, and aging resistance will significantly decrease, and food packaging may also have safety issues such as off-flavors and excessive impurities. At the same time, the mixed glue is prone to clogging the gluing equipment, increasing production failures and losses. Therefore, in production, it is necessary to exclusively use the corresponding model of adhesive and strictly prohibit random mixing.