The hazards of ratio errors in flexible packaging polyurethane laminating adhesives and precise control methods

The flexible packaging two-component polyurethane laminating adhesive consists of a main agent and a curing agent. Precise ratio matching is the foundation for the normal cross-linking and stable formation of the adhesive layer. In production, imbalanced ratios are common latent problems. Even a slight deviation from the standard ratio can lead to a series of lamination quality defects, and most of these defects will only be exposed after curing or during the storage period of the finished product, resulting in extremely high rework costs. 

 

When the curing agent is in excess, there are too many free isocyanate groups inside the adhesive layer. The excess components cannot participate in the cross-linking reaction and will easily absorb water vapor from the air and continue to react, resulting in the laminated film turning white, bubbling, and the surface becoming sticky. At the same time, it will aggravate the problem of residual solvents and unpleasant odors, seriously affecting the safety of food packaging. Long-term storage will also cause the adhesive layer to become brittle and the peel strength to decrease.

 

Insufficient curing agent is more common. The hydroxyl groups in the main agent cannot fully cross-link, resulting in insufficient cross-linking density of the adhesive layer, and forming a soft bond. The finished product shows poor adhesion, significant reduction in water boiling resistance and low-temperature resistance, and is prone to delamination when bent or pulled during packaging, failing to meet the end-user standards. 

 

The deviation in proportion is mainly caused by calibration errors of the mixing equipment, mistakes in manual weighing, residual substances in the pipelines, etc. During production, it is necessary to regularly calibrate the automatic mixing machine, standardize the manual proportioning process, remove residual glue, eliminate uneven mixing, strictly control the proportioning error range, and ensure the stable cross-linking effect of Polyurethane Glue and the quality stability of laminated products from the source.