Effect of humidity on flexible packaging polyurethane laminating adhesive

Polyurethane laminated adhesive is the core material of flexible packaging composite production, and environmental humidity is the key factor affecting its curing effect, bonding strength and finished product quality. High humidity environment can easily lead to various composite quality defects, which is the key link of flexible packaging production control.

 

The curing core of polyurethane laminating adhesive depends on the cross-linking reaction between isocyanate and main agent, and the moisture in the air will preferentially react with isocyanate groups in curing agent, which will greatly consume curing agent components and break the original proportion balance of glue, resulting in incomplete curing of adhesive, large residual viscosity, and problems such as back adhesion and softness of finished composite film. At the same time, the reaction will generate carbon dioxide gas, forming fine bubbles and white spots inside the adhesive layer, destroying the compactness of the adhesive layer, directly reducing the peeling strength of the film, and causing delamination and delamination failures.

Long-term high humidity environment will also cause hydrolysis and fracture of polyurethane molecular chain, damage the structural stability of adhesive layer, and greatly reduce the temperature resistance and durability of finished products during storage and use. On the other hand, if the humidity is too low, the curing rate of glue will be too fast, resulting in poor leveling and uneven bonding, which will affect the composite flatness.

 

In actual production, it is necessary to control the humidity in the workshop in a reasonable range, strictly control the moisture content of solvents and substrates, and adjust the glue ratio and curing process to avoid the quality hidden danger caused by humidity and ensure the stability and qualified rate of flexible packaging composite products.