Interfacial Shear Strain and Delamination Dynamics in Thermal Plastic Board Lamination
Interfacial shear strain from thermal mismatch drives delamination; controlling cooling gradients and dyne levels prevents bond failure at crease lines.
Interfacial Shear Strain
Layer Stress
Deformation of the adhesive or fibrous boundary between adjacent plies of a multi-layer board under bending loads dictates the internal stability of the structure. This deformation, known as interfacial shear strain, occurs when the individual layers attempt to slide past each other during flexing. If the plies are bound too rigidly, the board suffers from elevated internal stresses that can cause surface cracking or premature failure.
Delamination Resistance
Internal ply bond strength must be balanced to resist separation while allowing enough flexibility to prevent splitting during converting. High interfacial shear strain can lead to localized delamination when the cartonboard passes through tight nip rollers or undergoes scoring. Starch application between plies is adjusted to optimize this boundary region, ensuring that the sheet maintains structural integrity under shear load.
Multi-ply boards must withstand these forces during both offset printing, which pulls on the surface, and automated folding, which compresses the inner plies.
Deformation Control
Bending stiffness and crease formation are directly influenced by the distribution of shear stresses across the sheet profile. When interfacial shear strain is too high, the board is prone to flaking or ply separation during die-cutting. Proper fibre selection in the inner plies helps distribute this stress evenly.