Surface Fracture
The formation of minute fractures in the mineral coating or polymer barrier layer of paperboard during scoring or folding represents a structural failure that compromises package integrity. This mechanical micro cracking occurs when the tensile forces generated during bending exceed the elasticity of the coating. It exposes the underlying fibers, reducing the protection of the barrier.
Bending Stress
Applying excessive pressure or using incorrect crease geometry on the converting line is the primary driver of this failure. Coating formulations with high pigment-to-binder ratios are particularly susceptible because they lack the flexibility to stretch around tight fold radii. This localized tearing of the coating layer can be detected under magnification as a series of fine lines along the crease.
Adjusting the crease depth and using elastic binders in the coating can help mitigate this defect.
Coating Protection
Compromising the barrier layer can lead to the failure of the entire package by allowing moisture, oxygen or oils to penetrate the substrate. For liquids or greasy foods, these microscopic openings become pathways for product leakage or paperboard softening. Printers and convertors must test the foldability of the board using standard creasing testers to ensure that the coating does not rupture during high-speed carton erecting.
Selecting board grades with high-quality long fibers provides better support for the coating layer, reducing the risk of cracks during transport.
