Structural Separation
The failure of the internal bond between the various layers of a paperboard sheet causes the material to split into its constituent plies. This multi-ply delamination occurs when the shear or tensile forces exceed the strength of the starch or fiber entanglement holding the layers together. It is a critical defect that renders packaging unusable for structural applications.
Failure Cause
High tension during the printing process or the use of heavy, tacky inks can pull the surface ply away from the core. Multi-ply delamination is also triggered by the mechanical stresses of the creasing and folding stages in a folder gluer.
Quality Control
Board manufacturers monitor the ply bond strength to ensure that the material can withstand the demands of the converting line. If the moisture content of the board is too high or too low, the risk of multi-ply delamination increases due to the change in the flexibility of the internal bonds. This property is vital for items like cereal boxes and high end cosmetics packaging where a clean, sharp fold is required.
Testing involves measuring the energy required to separate the plies in a controlled laboratory environment. Maintaining the correct starch application rate at the wet end of the board machine is essential for preventing this defect.
