Wetting Rate
Surface energy characterization of paper and board substrates assesses how rapidly a liquid droplet spreads and penetrates the material. The dynamic contact angle decay measure tracks the reduction in the contact angle of a water or ink droplet over millisecond intervals. This evaluation reveals the surface receptivity of the board to aqueous coatings and adhesives.
Absorption Profile
Droplet volume and shape change continuously as the liquid begins to wet the top sizing layer. Fast decay rates indicate high surface porosity or low levels of internal sizing, which can lead to excessive ink feathering during printing. Conversely, a very slow decay rate suggests heavy sizing or contamination, preventing proper adhesion of water-based adhesives.
Balancing this decay behavior is essential for achieving clean graphics and durable glue seams on folding cartons.
Measurement Technique
Measurement of this phenomenon utilizes a high-speed video camera that captures the profile of the droplet at up to one thousand frames per second. Software analyzes the angle between the droplet edge and the substrate surface, generating a curve that shows wetting speed and penetration rate. Mill technicians use these curves to adjust the application of surface sizing agents and starch in the size press.
This testing ensures that the paperboard performs consistently on high-speed gluing machines where the adhesive must set within a fraction of a second.
