The Importance of the Ratio of Two-Component Polyurethane Laminating Adhesive

The two-component polyurethane laminating adhesive consists of the main agent and the curing agent. The ratio directly determines the degree of cross-linking reaction and is the core factor affecting the bonding quality. An imbalanced ratio will damage the performance of the adhesive layer in terms of curing, bonding, and weather resistance. 

 

The amount of curing agent is insufficient, resulting in a lack of crosslinking groups. The resin cannot fully react and cure. The adhesive layer remains sticky for a long time and does not dry completely. The internal cohesion significantly decreases, and it is prone to delamination under force. At the same time, the water resistance and solvent resistance of the adhesive layer deteriorate. It is also prone to softening and peeling when heated. When the amount of curing agent is excessive, the excess curing agent remains in the gel and slowly precipitates later, causing the adhesive layer to crack and shrink, develop wrinkles, and create gaps at the bonding interface, thereby reducing the peel strength. 

Precise proportioning enables the hydroxyl groups and isocyanate groups to react chemically in a complete manner according to the stoichiometry, forming a dense and stable network molecular structure. The hardness and toughness of the adhesive layer are balanced, making it suitable for composite substrates such as soft plastics and aluminum foil, meeting the requirements for high-speed composite production of packaging materials. Deviation in the proportion will also affect the curing rate. Imbalance in the proportion or excessive curing can result in bubbles, pinholes, or prolonged curing time, delaying the production process. 

 

Furthermore, if the ratio is out of control, it can release small molecular by-products. The composite product may experience bubbling and have an unpleasant smell, which does not meet the safety standards for food and pesticide packaging. Only by strictly following the manufacturer's ratio for material addition can the bonding effect be stabilized, the loss of defective products be reduced, and the long-term stability of the product be guaranteed.