Paperboard Crease Bending Resistance Evaluation Standard Laboratory Test Protocols
Crease evaluation measures 15-degree sheet stiffness against 90-degree fold resistance, targeting a 30 to 50 percent ratio to prevent cartoning line jams.
Internal Shear
Bonding Property
Inter-layer cohesion describes the strength of the internal bonds between the individual plies of a paperboard sheet. Measuring internal shear allows converters to predict the durability of the material during complex folding and printing operations. This property is determined by the entanglement of fibres at the ply boundaries.
Failure Mode
Rupture usually occurs when the tensile force applied to the surface of the board exceeds the strength of the internal bonds. During a printing run, the tack of the ink can pull the layers apart, leading to a visible bubble or a complete split in the substrate. This type of internal shear failure is common in multi-ply boards where different fibre types are used in the core and the liner.
Such defects render the final product unusable for retail packaging.
Fibre Measurement
Laboratory tests such as the Scott Bond test quantify the energy required to cause this separation. High internal shear values indicate a tightly bonded structure that resists the stresses of creasing and embossing. In contrast, low values might be desirable in specific applications where the material needs to be split or delaminated intentionally.
Refining the pulp and managing the moisture content at the wet end of the paper machine are the primary methods for controlling this strength metric.