Testing Mechanism
Measured compression strength under applied load evaluates the Scott Bond Test performance of multilayer cartonboards by determining the internal bond energy per unit area. Converters specify this property to ensure that folding boxboard resists delamination during high speed gluing and creasing operations. Testing machines apply a rapid pendulum impact perpendicular to the plane of the substrate, measuring the total energy required to split the interior z-direction fibre matrix.
High grammage packaging grades demand higher internal strength values to prevent ply separation when subjected to the severe mechanical stresses imposed by die cutting machinery. Lower energy thresholds indicate inadequate wet end refining or insufficient starch pickup during the size press application, which leads directly to structural failure on automated filling lines.
Tensile Vector
Fiber orientation within the papermaking machine direction dictates the specific plane where internal rupture occurs during the impact sequence. Suppliers optimize refining intensity and headbox jet to wire ratios to balance cross direction and machine direction forces, preventing directional weakness in the finished container. Paperboard manufacturers monitor these values continuously to maintain compliance with strict pharmaceutical packaging specifications where carton integrity governs barrier protection.
Low internal bond values cause blisters and surface lifting during high speed offset printing, particularly when high tack inks pull against the topliner.
Conversion Tolerance
Finished packaging components require predictable z-direction strength to withstand the vacuum suction pads and high speed mechanical feeding mechanisms operating on modern cartoning equipment. Converters adjust creasing matrix widths based on internal bond results, ensuring that the board deforms cleanly without internal cracking or core fracture. Specifications derived from this evaluation method establish the acceptable performance limits for recycled greyback and white lined chipboards utilized in heavy duty consumer goods packaging.
Substrate failure occurs when the applied converting stress exceeds the internal bonding energy established during the initial pressing and drying stages at the paper mill.
