Wetting Behavior
Variance in surface energy between two adjacent materials determines whether a liquid adhesive will spread and form a strong bond or bead up and fail to adhere. A surface energy differential exists when a highly polar substrate like paperboard is paired with a non-polar polymer film like polyethylene or polypropylene. The adhesive cannot wet the low-energy surface unless the energy gap is closed through surface treatment of the plastic film.
This treatment increases the surface energy of the film to match or exceed the surface tension of the adhesive.
Bond Failure
Inadequate wetting caused by a high differential leads to weak adhesion, resulting in delamination along the untreated or poorly treated boundary. As the surface energy differential grows, the adhesive’s contact angle increases, which prevents it from penetrating the microscopic pores of the film. This behavior leads to a dry, non-adhered layer that separates easily under mechanical stress or tension during converting.
Checking surface energy using dyne pens or contact angle measurements is necessary before executing the lamination run.
Modification Processes
Applying corona discharge, plasma, or chemical primers to the non-polar substrate surface lowers the differential and promotes wetting. This step is critical for ensuring that adhesives can flow out and form a continuous, durable laminate structure.
