Molecular Attraction
Intermolecular forces arising from temporary dipoles determine how non-polar liquids, including many solvent-based inks and coatings, wet and adhere to a solid substrate. The dispersive surface energy represents the portion of the total surface energy that comes from these London dispersion forces. This value is calculated by measuring the contact angles of various test liquids with known polar and non-polar characteristics.
It governs the adhesion of synthetic films, varnishes and wax coatings on paperboard.
Adhesion Kinetics
Substrates with low surface energy resist wetting, which causes liquid coatings to bead up rather than spread evenly. Treating the substrate with corona discharge or flame exposure increases the polar component but has little impact on the dispersive surface energy, which remains relatively constant. This characteristic is fundamental for formulating adhesives that must bond to polyolefin extrusion coatings.
Inks must be designed so that their surface tension is lower than the surface energy of the board to ensure complete coverage. If the ink tension is too high, it leads to pinholes and uneven solid prints.
Wetting Behavior
Contact angle goniometry is used to determine this property by depositing drops of non-polar liquids onto the paper surface. Analyzing the drop profile yields the contact angle, which is inserted into mathematical models to calculate the dispersive value. For food packaging, a stable dispersive value prevents water from penetrating the cellulose structure.
