Predicting Delamination Behaviour in Multi Layer Paperboard Creasing
Predicting paperboard delamination requires balancing Z-direction shear strength to permit core separation while preventing outer liner tensile fracture.
Ply Bond Adhesion
Interfacial Strength
Interfacial strength refers to the force required to separate the individual layers that make up a multi-ply paperboard. In the production of folding cartons, ply bond adhesion ensures that the board remains intact when subjected to the mechanical stresses of printing and converting. The bond is formed at the wet end of the machine when the separate webs are couched together.
It relies on the entanglement of fibers and the formation of hydrogen bonds across the interface.
Mechanical Resistance
During the offset printing process, high tack inks exert a large pulling force on the surface of the board as it exits the nip. If the ply bond adhesion is insufficient, the board will split internally, which leads to equipment downtime and wasted material. Standard tests involve applying a sudden impact or a steady tensile pull to measure the energy absorbed during separation.
Wet end chemistry, such as the addition of starch between plies, is a common method for increasing this internal strength.
Quality Balance
Quality balance must be maintained because a value that is too high can make the board brittle and difficult to crease without cracking. Producers must balance the need for internal integrity with the requirements for flexible scoring and folding.