Laminate Delamination
Physical separation of the individual layers in a multi-ply board occurs when the out-of-plane shear stress exceeds the strength of the fiber interfaces. Internal ply splitting describes the catastrophic failure of the central layers, typically during a converting operation or a heavy print run. This defect results from weak bonding between the different pulp furnish types used for the top layer, middle layer, bottom layer and back ply.
Adhesion Failure
Surface tension and moisture levels at the wet end of the paper machine determine the quality of the bond between plies. When internal ply splitting occurs during offset printing, the high tack of the ink pulls the surface layer away from the core. This destroys the structural integrity of the sheet and often leads to costly press wash-ups and material rejection.
Conversion Hazard
Creasing and folding rely on a controlled amount of internal movement to prevent the surface of the board from cracking. If the resistance to internal ply splitting is too low, the board will pull apart too easily and lose its ability to hold a shape or protect its contents. If it is too high, the board will be stiff and brittle.
Measuring this property using a Scott Bond tester allows manufacturers to verify that the board will perform as expected on high speed packaging lines. A consistent bond ensures that the final package remains intact during both the filling process and the subsequent handling by consumers.
