Interfacial Property
Liquid spreading on solid substrates is governed by the thermodynamic interaction between the surface tension of the liquid and the surface energy of the solid. This interaction, surface energy wetting, determines how effectively printing inks or adhesives adhere to a paperboard surface. The phenomenon is analyzed during the formulation of water-based inks and during surface treatment processes like corona discharge.
Adhesion Mechanism
High surface energy of the paperboard substrate allows water-based coatings to wet the surface and spread evenly rather than bead up. When the surface energy is too low, the liquid ink cannot penetrate the capillary pores, resulting in poor adhesion and pinholes in the printed film. Optimizing surface energy wetting ensures that adhesives can form strong mechanical anchors with the paper fibers.
Converters measure this property using dyne test pens or contact angle goniometers to verify that the board is ready for the gluing section.
Treatment Method
Corona or flame treatment is frequently applied to plastic-coated boards to increase their surface energy prior to printing. This process introduces polar groups to the surface, which enhances the receptivity of water-based inks. Monitoring the decay of this treatment over time is necessary to ensure consistent surface energy wetting during production runs.
