Surface Defect
Microscopic voids appearing in a dry ink or coating film expose the underlying substrate and compromise the protective properties of the finish. Often found in high-speed coating applications, pinhole cavitation results from air bubbles or solvent vapours trapped during the transition from liquid to solid state. The resulting holes are typically invisible to the naked eye but allow moisture or oxygen to bypass the barrier.
This failure is a common cause of rejected batches in flexible packaging and metalized papers.
Coating Interaction
Surface tension imbalances between the liquid coating and the paperboard frequently trigger the formation of these tiny craters. If the substrate is contaminated with oils or waxes, pinhole cavitation will occur as the coating pulls away from the low-energy areas. High viscosity can also contribute by preventing the liquid from flowing back together after a bubble bursts.
Correcting the problem usually involves adding wetting agents or adjusting the drying profile.
Quality Threshold
Barrier performance drops sharply when the density of these defects exceeds the limit specified for sensitive products like pharmaceuticals. Testing involves dye penetration or electrolytic porosity checks to identify the presence of holes. Once the coating thickness falls below a certain level, the risk of structural failure increases.
