Meaning
Capillary migration of fluids along the cut boundaries of a laminated material can compromise the integrity of barrier films and composite packaging. In flexible packaging, edge wicking is the process where liquids or moisture penetrate the unprotected fiber or adhesive layers exposed during the slitting or punching step. This phenomenon exposes the inner adhesive to chemical attack and reduces the bond strength between the functional layers.
The boundary of this risk is defined by the chemical resistance of the adhesive and the density of the substrate fibers.
Capillary Transport
Liquid movement along these narrow channels is driven by the surface energy of the exposed layers. When a low surface tension fluid meets a porous paper or nonwoven layer, it travels rapidly along the interface. This transport is enhanced when the adhesive does not wet the substrate completely, leaving microscopic voids that serve as pathways.
Film Failure
As the liquid advances, it degrades the interlayer adhesion and initiates local separation. This causes the barrier layer to peel away from the structural backing, allowing oxygen to spoil the product. In severe cases, the liquid leaks entirely through the package edge, causing a loss of containment and spoiling neighboring boxes.
Industrial Control
Preventing this infiltration requires either sealing the exposed edges or using hydrophobic barrier adhesives. Moulders and converters can apply a protective lacquer or employ ultrasonic welding to crimp the edges together during the cutting process. This action fuses the layers into a solid boundary that resists fluid ingress.
