Internal Separation
The physical splitting of multi-ply paperboard along its internal fiber layers happens when the shear or tensile forces exceed the internal bond strength of the material. Converters encounter mechanical delamination during the high-speed creasing and printing of thick boards. This failure ruins the structural integrity of the carton, making it useless for packaging applications.
Shear Stress
During the folding phase of packaging assembly, the outer and inner plies of the paperboard are subjected to intense tensile and compressive stresses. If the internal bond strength between these plies is weak, the shear stress causes the fibers to slide past each other and separate. This weakness is often related to poor fiber refining or insufficient starch spray during the wet-end forming of the board.
The mechanical delamination occurs when the board is forced to bend around a tight radius, creating a visible split on the folded edge.
Performance Assurance
Paperboard manufacturers measure the internal bond strength of their boards using the Scott Bond test to ensure they can withstand converting. Improving the fiber length distribution and increasing the refinement of the pulp helps prevent delamination. These adjustments ensure that the finished carton maintains its protective shape throughout the distribution cycle.
