Key points for controlling the compatibility between flexible packaging polyurethane laminating adhesives and printing inks

In the production of flexible packaging color printing lamination, the compatibility between polyurethane laminating adhesives and printing inks is a key factor determining the appearance, adhesion, and weather resistance of the lamination products. Many abnormal phenomena such as white spots, blistering, delamination, ink migration, and blackening in the lamination are not due to individual quality issues of the adhesives or inks, but rather are caused by the incompatibility of the two systems, resulting in a failure in compatibility matching. This is a key control point in color printing packaging production.

 

Solvent-based and alcohol-soluble inks are most prone to compatibility issues with polyurethane laminating adhesives. Residual alcohol solvents will consume the polyurethane curing agent, hindering the cross-linking reaction, causing the adhesive layer to become soft and not fully cured. Some pigments and binders are weakly acidic or alkaline, and will react chemically with the polyurethane system, destroying the adhesive layer structure, and causing blistering, fogging, and whitening of the ink layer and the printing plate surface.

In practice, the main cause of incomplete ink drying after printing is the main factor. Residual ink additives and solvents remain inside the ink layer and are sealed by the adhesive layer after compositing, causing slow reactions that lead to subsequent adhesion decline and local delamination. In addition, special high-pigment and high-fillers inks have poor coating density, and the adhesive does not penetrate and infiltrate evenly, which can also cause poor compatibility.

 

The main improvement methods are to match dedicated color printing composite polyurethane adhesives to enhance the adaptability of the inks. At the same time, strictly control the drying effect of printing and the curing time to ensure that the ink is completely dried, and eliminate residual additives. Through raw material matching and process coordination, it is possible to effectively avoid compatibility defects and stabilize the quality of color printing laminated packaging.