The causes and improvement solutions for the low bonding strength of inert films with flexible packaging polyurethane laminating adhesives

In the flexible packaging production process, PE, PP and other polyolefin films belong to low surface energy inert materials. When using ordinary polyurethane laminating adhesives for bonding, problems such as weak initial adhesion, low peel strength after curing, and false adhesion occur easily. Even if the glue and process parameters are normal, there are still problems of weak bonding, and the film can peel off with slight external force, which is a frequent difficult issue in the composite of inert substrates in the flexible packaging industry.

 

The surface characteristics of the inert film are the core reason for the failure of bonding. The molecular structure of PE and PP films is stable, and they have no polar groups, with extremely low surface tension. Flexible packaging polyurethane adhesives have difficulty achieving full wetting, spreading and anchoring on the film surface. If the electrostatic treatment of the film does not meet the standards or the surface tension decays too quickly, the interface between the glue and the substrate cannot form effective molecular bonding, and it is only a simple physical adhesion. Eventually, this manifests as insufficient bonding strength and peeling off.

Improper production processes will further weaken the bonding effect. Residual lubricants, opening agents, oil stains and dust on the substrate surface will form a barrier layer at the interface, blocking the bonding reaction between the Polyurethane Glue and the film. Low coating dryness and too thin glue layer cannot compensate for the microscopic unevenness of the film surface. Inadequate curing and solidification also significantly reduce the interfacial adhesion and overall bonding strength.

 

On-site, standardized processes can be used to completely improve the situation. Strictly control the electrostatic value of the inert film to ensure that the surface tension meets the standards and does not decay, thoroughly clean the film surface of additives and impurities. Select dedicated low surface energy base material polyurethane laminating adhesives to enhance the adhesion ability of the glue. Reasonably control the coating dryness and strictly implement the curing process to ensure that the glue layer is fully cross-linked, solving the problems of low bonding strength and poor peeling off of the inert film from two dimensions of interface bonding and adhesive performance.