Interlayer Rupture
Internal sheet separation occurs when shear forces parallel to the board surface exceed the z-direction tensile bond strength between individual plies. Converting equipment induces these stress field forces during creasing, folding and rotary die-cutting of multi-ply paperboard grades. The term board delamination describes this structural fracture within the inner fibre network.
This failure boundary excludes superficial surface picking caused by tacky offset printing inks.
Bond Strength
Mechanical refined pulp and starch additions increase internal bond strength between adjacent plies on the paper machine. Wet-end forming of multi-ply boxboard requires precise moisture management to ensure inter-ply hydrogen bonding before the pressing section. Inadequate ply bonding allows board delamination during high-speed scoring, which forms visible blisters along folded package edges.
Laboratory testing measures z-direction tensile strength using double-sided adhesive tape and specialized platen fixtures. Pressing parameters and refining intensity dictate the resistance of the substrate to structural separation under load.
Packaging Strain
Automated packaging equipment subjects carton blanks to multi-directional bending forces during high-speed erection. Unintended board delamination reduces the vertical compression strength of finished packaging, which leads to warehouse pallet collapse. Glue seam integrity decreases when internal plies separate under stress instead of holding the adhesive bond line.
