Standard Crease Depth and Rule Height Calculation for Multi-Ply Boxboard
Calculate crease rule height by subtracting compressed board caliper from cutting rule baseline, sizing matrix width to rule thickness plus 1.5 to 1.8 times board thickness.
Outer Liner Cracking
Surface Fracture
Splitting of the top layer of paperboard along a folded crease compromises both the appearance and strength of a carton. Occurring when the tensile strain on the surface exceeds the elastic limit of the fibres, outer liner cracking exposes the grey or brown interior of the board. This defect is unacceptable for high-end packaging where a flawless printed surface is required.
Mechanical Stress
Folding the board ninety or one hundred and eighty degrees stretches the outer fibres while compressing the inner layers. If the crease was not formed with sufficient depth and width, the outer liner is forced to stretch beyond its limit, resulting in a clean break or fracture. Low moisture content in the board makes the fibres brittle, which increases the likelihood of cracking during high-speed folding.
This issue often arises during winter months when ambient humidity drops, making the boards drier and less elastic than they would be in controlled summer conditions.
Preventive Measure
Maintaining the correct moisture level in the board and the plant is the most effective way to prevent cracking. Converters use moisturizing systems to add moisture to dry board before it is folded, or adjust the creasing die to create a wider, more protective crease. Selecting board with high-quality, long-grain virgin fibres also improves the elasticity of the outer liner and reduces the risk of failure.