Interlayer Adhesion
Mechanical testing of multi-ply paperboard measures internal cohesion between individual fiber layers formed during web consolidation on wet end paper machines. Evaluation of ply bond strength determines the force required to separate internal plies when subjected to Z-direction tensile stress or Scott Bond impact force. Fiber refining and wet-end starch addition establish hydrogen bonding density between adjacent plies.
This structural property applies to multi-ply recycled boards and solid bleached sulphate substrates, but does not apply to single-ply paper grades.
Delamination Resistance
Insufficient interlayer bonding allows plies to split apart during high-stress converting operations such as scoring and folding. Low ply bond strength causes scorelines to rupture or bulge when folding cartons are formed on high-speed gluing equipment. In offset lithographic printing, high-tack inks exert surface pulling forces that cause internal ply separation, resulting in blister defects.
Board mills adjust cationic starch dosing and press section dewatering to maintain internal bond integrity across paperboard plies.
Converting Integrity
High internal bond strength enables paperboard to endure mechanical deformation without structural failure. In blister packaging applications, paperboard must maintain ply bond strength to prevent backing cards from peeling apart under heavy product loads. Testing devices apply sudden impact forces to double-sided tape samples, measuring energy absorption in joules per square metre.
Board grades with consistent bond strength exhibit clean creasing and reliable performance on automated packaging lines. Measuring internal adhesion ensures paperboard meets strict customer specifications for demanding structural applications.
