Reasons for Re-Adhesion of Flexible Packaging Polyurethane Laminating Adhesive Composite Film and Comprehensive Rectification Plan

Re-adhesion, also known as re-bonding or post-adhesion, refers to the phenomenon where the film surface becomes sticky, adheres, or gets caked with powder or debris again during storage, cutting, or bag-making processes after the composite film has completed its curing and passed the inspection. This is a typical lagging quality defect. Re-adhesion not only affects subsequent processes but also easily causes the finished products to stick together and be scrapped. It is a hidden and serious technical problem in flexible packaging production.

 

The core root cause of re-adhesion is incomplete cross-linking of the adhesive layer. Insufficient curing agent dosage, uneven mixing of the adhesive, and equipment proportion deviations can lead to a large number of hydroxyl groups not participating in the reaction, causing the adhesive layer to remain in a semi-cured state for a long time and maintaining stickiness on the surface. At the same time, low curing temperature and insufficient curing time result in the surface of the adhesive layer drying while the internal reaction lags behind. As the storage time increases, the unreacted adhesive in the interior slowly seeps out, forming re-adhesion.

Environmental and raw material factors are also crucial. Excessive humidity in the workshop continuously consumes the curing agent, disrupting the cross-linking system. Excessively thick coating will significantly prolong the deep curing cycle, causing internal and external curing to be out of sync. In addition, inferior solvents contain fusel alcohol and have excessive moisture, which will inhibit the polyurethane reaction and continuously cause persistent re-adhesion problems.

 

To solve the problem of re-adhesion, comprehensive rectification is required from the root cause. Regularly calibrate the mixing equipment, strictly control the dosage error, and ensure that the two components fully react. Strictly follow the standard curing process, avoid low-temperature short-curing for shipment, and control the workshop temperature and humidity as well as the purity of the solvent. By improving the cross-linking conditions and standardizing the production process, the potential problems of re-adhesion and re-bonding in the later stage of the composite film can be completely eliminated.