Sizing Female Matrix Channels for Uncoated Folding Boxboard Grades
Uncoated folding boxboard requires matrix channel width equal to creasing rule thickness plus 1.8 times caliper to prevent top liner cracking during folding.
Board Factor Multiplier
Thickness Ratio
Mathematical constants derived from the relationship between board thickness and bending resistance define the mechanical potential of a specific grade. The board factor multiplier allows a specifier to estimate the Taber or L and W stiffness of a material when the grammage or calliper changes. It functions as a ratio where the stiffness increases approximately by the cube of the thickness.
Performance Estimation
Calculated values provide a baseline for comparing different mill brands or fiber compositions. Using a board factor multiplier simplifies the selection process during the design phase of a carton. For example, if a 300 micron board has a known stiffness, multiplying the ratio of the new thickness cubed against the original thickness cubed provides the projected resistance.
This method assumes consistent density and fiber orientation within the sheet across the compared grammages. Engineers apply these results to ensure that a lighter material still provides enough strength to protect the contents during stacking.
Structural Limit
Physical testing remains necessary because internal bond strength and ply adhesion vary between manufacturers. While the board factor multiplier offers a reliable theoretical guide, it cannot account for moisture content or coating brittle behavior. Extreme changes in humidity often shift the actual performance away from the predicted value.