Surface Property
Intermolecular forces at the boundary of a solid polymer or paperboard substrate determine how readily liquids wet the material. Solid materials possess a baseline surface energy that dictates the initial receptivity to inks and adhesives before any chemical or physical treatment is applied. This characteristic is measured in millinewtons per meter and determines whether a coating will spread evenly or bead up.
Adhesion Behavior
Ink droplets applied to a low energy surface fail to coalesce into a continuous film causing pinholes and poor dry rub resistance. When the baseline surface energy of the paperboard is lower than the surface tension of the applied fluid wetting does not occur. Mechanical converting steps such as corona discharge treatment must raise this value to ensure proper ink laydown on high speed press runs.
For water based inks a surface must typically reach at least forty dynes per centimeter before printing. Lower speeds or solvent formulations can sometimes accommodate less active surfaces but still require consistent monitoring.
Process Verification
Routine testing with calibrated fluids provides the necessary feedback for the converting line operator. If the baseline surface energy falls below the run limit the board is rejected to prevent ink flaking during folding and gluing processes.
