Surface Wetting
Optical droplet measurement quantifies liquid surface interaction by evaluating the tangent angle formed where a liquid interface meets a solid substrate. Laboratory technicians utilize contact angle goniometry to assess the wettability and surface energy of paperboard, polymer coatings, and treated barrier films. A precise volume of test liquid drops onto the substrate surface while digital cameras record the droplet profile over time.
Droplet profile changes reveal liquid absorption rates and dynamic surface wetting behavior.
Surface Energy
Mathematical calculation converts static droplet angles into polar and dispersive components of solid surface energy using polar and non-polar probe liquids. High initial contact angles with water indicate hydrophobic surface properties, whereas low angles demonstrate hydrophilic behavior. Corona or plasma surface treatments increase surface energy on polyolefin coatings, lowering water contact angles and improving water-based ink adhesion.
Paper mills monitor dynamic contact angle changes to verify sizing efficiency and barrier coating consistency.
Coating Adhesion
Surface tension measurements provide essential data for controlling flexographic printing and adhesive bonding operations. Drops of distilled water or diiodomethane placed on treated paperboard indicate whether surface energy meets minimum requirements for liquid spreading. Rapid spreading and low contact angles confirm adequate surface activation, preventing ink flaking or foil delamination during converting.
When contact angles exceed target thresholds, surface coatings fail to wet out, resulting in pinholes and poor bond strength. Contact angle goniometry detects hydrophobic surface contamination and surface sizing defects before printing runs commence.