The causes of failure in corona treatment of flexible packaging films and its impact on composite bonding

Corona treatment is a crucial process before printing and compounding of flexible packaging films. It involves high-voltage discharge to break through the surface of the films, enhancing the surface tension of the substrate, and enabling the polyurethane laminating adhesive and ink to have good wetting and anchoring capabilities. Failure of corona treatment can lead to a sudden drop in adhesion on the film surface, which is one of the core hidden causes of composite delamination, ink loss during printing, and glue shrinkage cavities. Many batch quality accidents are caused by substandard corona treatment.

 

Corona treatment failure can be classified into two types: insufficient treatment and aging attenuation. Improper equipment parameters, excessive machine speed, electrode dust accumulation, and uneven discharge can result in lower local corona values on the film, leading to initial treatment failure. Moreover, PE and PP polyolefin films have extremely unstable surface activity, and their corona treatment will gradually recede and attenuate over time. The longer the storage period, the more significant the decrease in surface tension. Overnight films and inventory films are prone to failure.

In addition, excessive addition of film raw material lubricants and release agents will form a migrating and precipitated layer on the film surface, covering the corona activation interface and directly blocking the glue infiltration for bonding, resulting in false corona compliance and actual bonding failure. High temperatures and high humidity in the workshop will accelerate the attenuation of film surface activity, intensifying the risk of corona failure.

 

Production control requires regular detection of surface tension, cleaning of corona electrodes, matching reasonable machine speed and voltage, and preventing over-speed production. Adhere to treating first and then using, strictly control the storage period of films, and avoid using expired inventory films directly on the machine. At the same time, select low-extraction auxiliary film materials to ensure the stability of polyurethane laminating adhesive bonding and avoid adhesive failure defects.