Motohiro asks,
The JAPAN PALLET ASSOCIATION (JPA), has told us that the “swelling of the cardboard box” is at the rate of 4% in the length direction, when a cardboard box was piled up.
JPA also said that 4% is based on the information of NWPCA or AICC.
Can you explain in detailed reason of this 4% growth?
I do not have any personal knowledge from my thirty years in the paper and corrugated industry of this exact percent change in the one specific dimension of a corrugated box. Corrugated fiberboard products do expand and contact in all three dimensions with changes in relative humidity and exposure to liquid water. Corrugated sheets and boxes produced in Japan from a variety of different recovered fibres and manufactured with a variety of process are likely to expand and contact at different rates. This is especially true compared to boxes manufactured in this country with new stronger fibres. Research does show that corrugated at 95% relative humidity can increase in moisture content to 25% versus its stable conditions at 7%.
I think a 4% growth simply from increased moisture content is a bit extreme. However, in your question you mention a 4% growth when “piled up”. It would make more sense that this is possibly a combination of the weight of the pile and perhaps extra moisture therefore weakening the structural integrity of the box resulting in the 4% expansion.
I could not find any technical data in the literature that references what you have described. I would add that any laminated high graphics top sheet would change in dimension at a different rate than the corrugated itself.
— Ralph
askralph 