Optimizing Creasing Rule Geometry for Coated Paperboard Packaging
Optimizing creasing rule tip radius and channel geometry enables controlled internal board delamination, eliminating coating cracking and springback jams.
Score Shearing
Creasing Failure
The physical integrity of a folding carton depends on the ability of the scored lines to bend without splitting. An unwanted defect, known as score shearing, occurs when the creasing process applies too much shear stress, causing the internal plies of the board to rupture or tear. This rupture results in a weak fold that has poor appearance and fails to protect the carton contents.
Mechanical Action
Score shearing is caused by a mismatch between the width of the creasing rule, the groove in the counterplate, and the board caliper. If the groove is too narrow, the board is subjected to excessive stretching and pinching, which shear the fibers instead of creating a controlled delamination. This is particularly common in boards with low moisture content or poor fiber flexibility, where the board is naturally more brittle.
Proper adjusting of the crease dimensions is needed to ensure that the fiber layers separate without tearing.
Corrective Action
Printers and converters monitor this defect by testing the folding resistance of the creases. If shearing occurs, the operator must use a wider creasing groove or increase the moisture content of the board by storing it in a humidified area. This ensures that the fibers remain pliable during the converting process.