For the last several years we have prepared you well with the Key Characteristics of Linerboard and Medium and Their Impact on Combined Corrugated Board-Second Edition, how to Get the Best Box, and Understanding Box Performance-Third Edition. Make sure you have these brochures in your library. (available at the AICC Store)
Then at the third Science of Paper School we shifted the focus somewhat from what converters need to know about containerboards in general to combined board characteristics specifically. Recently when compiling a list of sheet feeders for the Associations’ Board of Directors we were reminded to provide members with the key quantitative quality requirements one might want to establish with their internal or external suppliers. Several years ago we publish a series of spreadsheets for singlewall and doublewall combinations listing a few physical properties categories so a converter could establish incoming sheet specifications with their supplies.
Let’s review those and explore a more comprehensive array of properties.
ECT: Yes, it is well know but not completely understood. While the already known losses of box compression will varying with supply chain elements, deterioration rates vary by actual amounts of board crush or flute degradation and the use of semichemical or recycled mediums.
Caliper: spring back or recovered thickness after crushing. While fluting is a resilient material and recovers from much of the sever deformation that occurs during combining and/or converting, its inherent strength contribution to the corrugated may be significantly compromised.
Flat Crush: This measure of actual combined board crush verses the potential resistance to crushing as predicted from the Concora strength of the medium. This, however, is not a good predictor of actual board crush.
Pin Adhesion: Determines the strength of the bonds between the liner(s) and the medium(s).
Four Point Bending Stiffness: Measures the rigidity of the combined board and the sidewall wall robustness of the corrugated box.
Torsional Stiffness: Relatively new to the US, but known elsewhere. This maybe the single best overall determinant of board strength.
Warp: Should have no more than 1/8 deviation from flatness per foot.
Look for more details in an upcoming issue of BoxScore