Stacking pressure must be calculated in advance. If twenty layers are stacked on a single pallet, the bottom box bears the weight of the nineteen layers above it. Just because the outer shipping carton has sufficient compressive strength, it does not mean the inner retail boxes do as well. Placing a corrugated divider between the retail boxes helps distribute the pressure.
Internal inserts are also helpful. A custom-fitted insert that sits against the box walls acts as a support for the corners. In an empty box without an insert, the corners are the most vulnerable points—especially in “lid-and-base” (two-piece) style boxes, where both the lid and the base corners require reinforcement.
Clients might not specifically inspect the corners, but if a box collapses, that is the first thing they will notice.
Humid environments weaken structural integrity. As the moisture content of the paperboard rises, its compressive strength drops—a critical factor to consider for ocean freight or storage in southern regions. At the very least, implement one of the following: moisture-proof inner liners, desiccant packets, or warehouse dehumidification.
The glued joints are another critical area. If there is insufficient adhesive, the corners may pop open under the pressure of stacking; conversely, too much glue can squeeze out and ruin the box’s appearance. Settings for the folder-gluer—such as pressure, temperature, and adhesive volume—must be adjusted based on the grammage (basis weight) of the paperboard. Thicker paper requires more adhesive, while thinner paper requires less; a “one-size-fits-all” set of parameters will not work.
A box may look crisp and sturdy coming off the production line, but after the rigors of loading, ocean transit, and warehousing, the four corners are the most likely points to collapse. Corner strength is not determined solely by the thickness of the paperboard.
The quality of die-cut corners sets the foundation. If the corner radius on the cutting die is too small, the paper fibers will be overstretched during the creasing process; the box might look fine when folded, but it will crack as soon as it is subjected to pressure. Standard practice involves incorporating a slight radius at the corners and ensuring consistent depth for all crease lines, which prevents the folded edges from becoming uneven or misaligned.
