Factors Affecting Flexible Packaging Polyurethane Lminating Adhesives

Polyurethane laminating adhesives are the core materials in the production of flexible packaging lamination. Their bonding strength, curing effect, and product stability are influenced by multiple factors, directly determining the lamination quality and service life of flexible packaging products. The key influencing factors mainly lie in the formulation, environment, substrate, and construction process. 

 

The formulation ratio of the adhesive itself is the fundamental key. The ratio of the main agent to the curing agent in the two-component polyurethane laminating adhesive, as well as the NCO content, directly affect the effect of the cross-linking reaction. An imbalanced ratio will lead to incomplete curing and a decrease in adhesion force. At the same time, the viscosity and solid content of the adhesive determine the uniformity of coating. An excessively high viscosity is prone to cause uneven coating, while an excessively low viscosity will result in insufficient coating volume, thereby affecting the firmness of the lamination. 

 

The environmental temperature and humidity have a significant impact on the curing process. The curing of polyurethane relies on the cross-linking reaction of isocyanates. In a high-humidity environment, the moisture in the air will react with the curing agent, consuming the effective components and causing problems such as bubbles, whitening, and re-adhesion, which will damage the stability of the composite layer. Low temperatures will significantly slow down the curing rate and prolong the curing time; high temperatures will shorten the opening time of the glue and cause coating defects. 

The condition of the base material and the construction process are equally crucial. If the surface energy of the base material such as films and aluminized films is insufficient, or if dust and oil stains are adhered to the surface, it will reduce the wetting property and adhesion of the glue, and pre-treatment with corona discharge and plasma can effectively improve the bonding effect. In addition, improper process parameters such as coating thickness, compounding speed, and curing conditions can cause uneven bonding, delamination and detachment, significantly reducing the quality of the finished flexible packaging products.