Adaptation Issues and Rectification Solutions of Polyurethane Laminating Adhesive and Ink

In the dry lamination production of flexible packaging, the poor compatibility between ink and polyurethane laminating adhesive is a hidden core problem that leads to ink leakage, color fading, printing plate smudging, and re-adhesion after curing. Many batch failures are not due to the quality of the adhesive, but rather conflicts between the ink system, solvent system and the adhesive layer reaction. After printing and composite, ink layer migration, background color smearing, printing plate smudging, local adhesion points, and even complete batch printing and composite failure may occur.

 

The conflict of solvent systems is the main cause of ink leakage. Some surface printing and inner printing inks have poor solvent resistance. The ethyl acetate used to dilute the polyurethane laminating adhesive has strong penetration and will slightly dissolve and swell the partially un-solidified ink layer after coating, causing pigment diffusion and ink layer smearing, resulting in ink leakage, color fading, printing plate blurring. High solid content and strong penetration adhesives will have more obvious damage to low solvent resistance inks.

Inadequate ink curing is prone to cause composite re-adhesion and color fading. After printing, if the ink does not dry thoroughly and residual binders and additives remain, it will react with the polyurethane laminating adhesive layer after composite, hindering the cross-linking and curing of the PU adhesive, causing the adhesive to remain soft and sticky after curing, and the ink layer to fall off. At the same time, excessive waxes and smoothers in the ink will form a separation layer on the film surface, causing poor adhesion of the adhesive, local delamination, and a sharp drop in adhesion strength.

 

On-site rectification requires matching compatible ink and adhesive systems. Ensure full drying during printing and eliminate residual wet ink layers. Appropriately adjust the purity of the diluent to avoid excessive strong corrosive solvents. Reserve a printing curing and static setting time before composite. For inks with excessive smoothers, the coating amount can be adjusted to improve the adhesion of the ink layer. In necessary cases, replace with compatible laminating adhesives to completely solve the problems of ink-adhesive incompatibility, such as ink leakage, re-adhesion, and color fading.