Measuring Specular Gloss Changes during Standard Paperboard Rub Tests
Measuring specular gloss changes before and after standard rub tests quantifies surface coating durability using exact optical angle decay metrics.
Substrate Delamination
Failure Mode
Interlaminar separation within paper or paperboard structures occurs when internal shear or tensile stresses exceed fiber-to-fiber bond strength. The defect termed substrate delamination splits multi-ply paperboard into distinct layers, compromising structural integrity during converting or product handling. Internal ply separation happens within weaker core layers or along wet-forming ply interfaces.
Standard Z-direction tensile tests measure internal bond strength to predict delamination resistance during high-speed converting operations.
Structural Kinematics
High-tack printing inks exert normal pulling forces on board surfaces during rapid offset press separation. When surface pull forces exceed core ply cohesion, internal fibers tear apart parallel to sheet surfaces. Creasing matrices induce localized internal shear stresses that intentionally initiate controlled delamination along score lines.
Resistance Control
Refining levels during pulp preparation directly govern fiber fibrillation and interply bond area. Inadequate mechanical refining leaves smooth fibers with minimal hydrogen bonding capacity, accelerating delamination under low mechanical stress. Excessive filler content in core plies reduces fiber contact points and degrades internal cohesion.
Starch additions during papermaking strengthen interply bonds and elevate Z-direction tensile strength. Moisture absorption weakens hydrogen bonds between cellulose fibers, reducing resistance to ply separation in humid environments. Die-cutting tools with dull knives tear fiber networks rather than cutting cleanly, inducing peripheral delamination along blank edges that propagates into package side panels.
Testing internal bond strength prevents ply failure during packaging converting operations.