White spots, white fog, and mottling that occur during the lamination printing of films are common high-frequency appearance defects in color-printed flexible packaging, mainly concentrated in light-colored and solid-printed areas, which seriously affect the aesthetic appearance of the finished products. This problem is mostly related to the compatibility of the polyurethane laminating adhesive, the state of the printing ink, and the lamination processing environment, and is not merely a problem of the glue quality. It requires targeted investigation and control.
The main reason is poor compatibility between the ink and the glue. Some alcohol-soluble inks and residual diluents can react adversely with the
Polyurethane Glue, destroying the uniformity of the glue layer and forming fine white spots after curing. At the same time, the printing film retains trace solvents and water vapor, which hinders the wetting and spreading of the glue after coating, causing local shrinkage cavities and point-like blank areas, resulting in visible white spot defects.
Improper process operation can also trigger white spots. Inconsistent glue mixing, high viscosity, poor leveling, and uneven microscopic thickness of coating. Insufficient composite pressure, dirty rollers, and inability to discharge micro air between the films, resulting in dense white spots. In a high-humidity production environment, water vapor mixed into the glue layer can cause white spot-like defects in the glue layer.
To solve this problem, it is necessary to select a dedicated
Polyurethane Adhesive for printing and lamination with excellent compatibility with the ink, ensuring good glue leveling. At the same time, strictly control the residual solvents of the printing film, maintain a low-humidity production environment, optimize the coating viscosity and lamination pressure, and clean the surface of the rollers. Multiple process controls can completely eliminate the white spot problem, ensuring the transparent and uniform appearance of the color-printed lamination film and stable product quality.
