Structural Separation
Interfacial failure modes in multi-ply paperboard describe how individual layers separate under mechanical load. The operation of delamination mechanisms occurs when tensile or shear forces exceed the internal bond strength of the fibrous plies. This failure is common in offset printing where high-tack inks pull at the surface layer.
Stress Distribution
Internal adhesive forces between fiber plies are influenced by pulp refining, wet-end starches and coating binder migration. When printing forces apply out-of-plane tension, the delamination mechanisms can cause the sheet to split internally rather than tearing on the surface. Minimizing this effect requires controlled wet-end chemistry and balanced pressure in the press section of the paper machine.
Proper fiber preparation ensures that the middle plies can absorb energy without failing.
Packaging Performance
Converting operations like creasing and folding depend on localized ply separation to form clean corners. If the delamination mechanisms are restricted by excess starch or binders, the board will crack on the outer fold instead of shearing internally. Conversely, too little internal bond strength leads to bulging or edge splitting during the carton filling and stacking stages.
Testing the z-directional tensile strength ensures that the paperboard provides the required performance on the packaging line.
