The curing process of the flexible packaging polyurethane laminating adhesive is the core step in the lamination production process. Its essence is to achieve molecular cross-linking through chemical reactions, transforming the liquid adhesive layer into a high-strength and high-toughness solid adhesive film. This directly determines the bonding strength, temperature resistance and sealing performance of the flexible packaging composite film, and is widely used in lamination scenarios involving plastics and aluminum foil.
Currently, the mainstream in the industry is divided into single-component and dual-component curing systems. The dual-component adhesive is composed of a main agent containing hydroxyl groups and a curing agent containing isocyanate. When mixed, the hydroxyl groups and isocyanate groups undergo cross-linking reactions, gradually forming a three-dimensional network structure. After curing, it has strong cohesion and high bonding stability, making it the preferred choice for high-end flexible packaging. The single-component adhesive does not require mixing and is triggered to cure by water vapor in the air. The isocyanate reacts with water to form a cross-linked structure, which is simple to operate and suitable for lightweight packaging production.
The curing effect is significantly influenced by temperature, humidity and the ratio. In industrial production, the curing temperature is usually controlled at 40-50℃. An appropriate temperature can accelerate the molecular reaction and shorten the curing cycle; too low humidity will delay the curing of single-component, while too high humidity may cause blistering of the adhesive layer. At the same time, for two-component, the ratio of groups must be strictly controlled. An unbalanced ratio will result in incomplete curing and detachment of the bond. The cured adhesive layer after complete curing has good flexibility and can meet the subsequent processing requirements such as bending and heat sealing of soft packaging, ensuring the performance and shelf life of the packaging product.
