Ply Bond: Scott

Definition
Internal bond is a measure of tensile strength of linerboard perpendicular to the sheet plane - i.e., in the z direction.

Influence
The major effects of weak internal bond strength for corrugated products are generally observed at the time the product is used rather than during the combining or converting operations.

Potential Problems
Low internal bond strength contributes to weakness at the manufacturer’s glued joints or at other points where two corrugated board surfaces are glued together. Such joints may fail due to stresses applied during setup, packing, or handling by the product user when one of the facings separates internally at a weak point.

Low internal bond strength may also contribute to peeling or “roll-ups” under friction forces applied to the surface as the board moves through the double-facer on the corrugator, is fed from the bottom of stacks into converting equipment, or is pulled from stack-type compression sections into counter-ejector mechanisms.

Source
McGrattan, W. "Key characteristics of linerboard, corrugating medium, and roll stock mechanical condition and their influence on the manufacture of corrugated products, part 1." Tappi Journal (1990): 99-108.

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