Delamination Resistance
Multi-layered paperboard relies on inter ply bonding to withstand the mechanical stresses encountered during folding carton conversion and high speed offset printing. Shear forces generated by blanket cylinders pull the individual fibrous webs apart if internal adhesion fails to match the stiffness of the outer layers. Chemical additives introduced at the wet end of the paper machine create hydrogen bonds between refined cellulose microfibrils to establish this required internal strength.
Starch solutions applied at the size press further penetrate the sheet structure, reinforcing the internal Z direction tensile strength across the cross direction of the web.
Adhesion Limits
Cylinder nip pressures and dryer temperatures dictate the maximum mechanical interlocking achieved before the sheet enters the converting facility. Excessive drying rates drive moisture outward too rapidly, generating steam pockets that delaminate the central plies before final consolidation occurs on the machine calendar. Converters measure this internal resistance using Scott internal bond testers that quantify the energy absorbed during rapid out of plane impact.
Low internal strength causes board lifting during high speed flexographic printing where tacky inks exert severe perpendicular pulling forces on the top liner.
Performance Thresholds
Packaging specifications demand precise control over internal adhesion to prevent structural failure during corrugated medium combining and box erection sequences. Laminated substrates subjected to creasing and die cutting operations develop internal fractures along the fold line if the Z direction tensile strength falls below the minimum threshold required for the specific grammage. Board manufacturers adjust refining intensity and binder ratios to maintain this critical balance between stiffness and internal cohesion across every production batch.
Proper internal adhesion ensures that heavy liquid packaging cartons maintain structural integrity under compressive loads without suffering catastrophic layer separation during pallet stacking.
