Inter-Ply Bond Measurement Standards in Recycled Paperboard Production
Inter-ply bond standards mandate TAPPI T 541 or ISO 16260 testing under strict ISO 187 conditioning to prevent converting delamination on recycled paperboard.
Folder-Gluer Shear Stress
Adhesive Resistance
Mechanical forces exerted on a freshly glued carton seam as it passes through the compression section of a folder-gluer test the initial strength of the adhesive. This folder-gluer shear stress occurs when the folded panels try to spring back to their original flat state. If the adhesive cannot withstand this shear force, the joint will open and fail.
This action requires a fast-setting glue with high wet tack.
Dynamic Load
The rate of shear application increases with machine speed, demanding rapid molecular cross-linking from the adhesive formulation. Standard packaging lines run at hundreds of meters per minute, which leaves only fractions of a second for the glue to set. High shear forces can cause the glue line to smear if the tack is too low.
Measuring this dynamic resistance helps mills select the right adhesive chemistry.
Bond Formation
Preventing bond failure under these conditions requires a precise balance between paperboard surface energy and glue viscosity. If the paperboard has a heavy water-based coating, the adhesive may fail to penetrate the fiber, which makes the joint susceptible to shearing. Conversely, a highly porous board might absorb too much glue, leaving a starved joint that cannot handle the spring-back forces.
Operators adjust the compression belt pressure to hold the seam in place until the polymer chains in the adhesive interlock with the fibers. This process ensures that the finished carton maintains its structural integrity throughout the shipping and storage cycle.