Dynamic Crease Stiffness Reduction Ratios under Ultra High Speed Packaging Line Strain Rates
Dynamic crease stiffness reduction ratios must be evaluated under operational strain rates of 1000°/s to 5000°/s to prevent high-speed cartoning line jams.
Inter-Ply Shear Delamination
Layer Separation
Division of multi-ply paperboard into its constituent layers under shear forces is a critical structural failure mode. This phenomenon, known as inter-ply shear delamination, occurs when the internal bond strength of the board is lower than the applied stress. It is a common problem in thick boards subjected to high bending or tension.
Scoring Stress
During the creasing process, the board is subjected to intense localized shear forces that force the plies to separate. This controlled separation is necessary to reduce folding resistance, but uncontrolled splitting weakens the carton walls. If the internal starch or refining levels are inadequate during board manufacturing, the layers will peel apart during folder-gluer operations, which renders the carton unusable for high-speed filling lines.
Therefore, the board mill must balance the use of starch and refining to achieve the exact level of ply bond strength that allows creasing without causing structural collapse.
Material Integrity
The balance between ply adhesion and foldability determines the final performance of the cartonboard. Measuring the internal bond strength using a Scott Bond tester ensures that the board can withstand printing and converting forces without premature splitting. This testing guarantees that the board possesses sufficient structural cohesive strength for its intended application.