Bonding Threshold
Mechanical resistance against internal layer separation governs multi-layer paperboard grades during demanding conversion steps. Inter-ply adhesion dictates how well individual fibrous webs hold together under high speed printing or carton creasing forces. Insufficient internal bonding causes structural delamination when converting machinery exerts sudden tension on the board surface.
Papermakers control this critical property through specific refining parameters and wet end chemical additions during the sheet formation stage on the paper machine.
Rupture Mechanics
Tensile stress applied perpendicularly to the plane of the sheet forces internal fibers apart until failure occurs. Testing equipment measures the specific energy required to split the multi-layer structure under controlled laboratory conditions. Standardized protocols quantify internal bond strength in kilojoules per square meter to verify compliance with folding carton specifications.
High density packaging grades demand higher internal strength values to withstand the physical demands of high speed gluing lines and automatic erecting machinery.
Conversion Limits
Finished packaging materials experience severe internal shear forces during die cutting and aggressive embossing operations. Low internal bond levels lead to board blistering when high viscosity coatings dry too rapidly on the printing press. Converters evaluate incoming board lots carefully before running complex designs that feature heavy crease patterns and tight folds.
Structural integrity relies entirely on maintaining uniform fiber distribution across every individual web layer throughout the entire production run.
