Static Compression Thresholds for Double Wall Corrugated Boxes under Moisture
Double wall static compression thresholds drop 40 to 60 percent above 80 percent humidity, requiring safety factor adjustments to prevent warehouse collapse.
Starch Adhesive Shear
Bond Resistance
Adhesive performance at the interface between the fluting medium and the linerboard determines the structural integrity of corrugated board under bending stress. In paper converting, starch adhesive shear defines the resistance of the glue lines to sliding forces during the high-speed gluing process. This resistance ensures that the liners do not peel away from the flutes.
It maintains the rigid structure of the board.
Manufacturing Dynamics
Viscosity of the starch mix must be maintained within a tight range to prevent premature shear failure at the corrugator. High shear forces at the application roll can break down the starch polymers, reducing the adhesive strength before it can fully gelatinize. This shear degradation causes weak bonds that fail under subsequent folding or printing.
It results in delamination during die-cutting.
Performance Limit
Bending loads on finished cartons put continuous pressure on the adhesive joints, which can fail if the starch has been weakened by excessive shear during production. When moisture levels rise, the resistance to starch adhesive shear decreases, allowing the fluting and liner to slide against each other. This relative movement ruins the flat crush resistance of the board.
To prevent this, paper converters add cross-linking agents to the starch to improve the wet shear strength.