Cohesion Resistance
Layer separation occurs inside multi-ply packaging boards when internal z-directional forces exceed the limits of the substrate matrix. Interfacial bond strength defines the threshold where fibrous layers pull apart under perpendicular tensile loading during high-speed printing or converting operations. Paper mills regulate this internal property through strict control of refining levels and wet-end chemical retention programs during the papermaking stage.
Low values cause delamination during rapid ink tack release on offset presses or heavy vacuum lifting on carton-forming machinery.
Ply Delamination
Structural failure happens across the median plane of folding boxboard when converting machinery applies severe mechanical stress to the substrate. Interfacial bond strength dictates whether carton blanks survive crease scoring and die cutting without internal splitting along the edges. Converting plants measure this performance metric using Scott internal bond testers that drop a pendulum to record the energy required to rupture the sheet in the z-axis.
Board converters reject incoming paper reels failing to meet minimum kilo-joule thresholds because internal fracture ruins subsequent gluing and packaging integrity.
Fibre Matrix
Refining intensity establishes the density of hydrogen bonds holding adjacent cellulose layers together throughout the papermaking process. Interfacial bond strength depends directly on the degree of interweaving achieved during headbox deposition and subsequent press section consolidation. Papermakers balance refining energy against bulk reduction to ensure adequate internal cohesion without sacrificing stiffness or folding endurance in finished cartons.
Optimizing z-directional tensile properties prevents spontaneous layer separation inside corrugated containers exposed to sustained compressive loads during warehouse storage.
