Paperboard Wet End Additive Sorption Mechanics and Chemical Retention Verification
Verify paperboard wet end additive retention using dynamic drainage jars and extraction GC-MS to ensure food contact compliance and prevent converting failures.
Z-Direction Ply Splitting
Internal Cohesion
Separation of multi-ply paperboard layers occurs within the sheet thickness when subjected to out-of-plane tensile or shear forces. This specific structural failure, known as z-direction ply splitting, reduces the structural integrity of multi-layer folding cartons during high-speed packaging and filling operations. It occurs when the internal bond strength between individual fiber layers is lower than the mechanical stresses applied by processing machinery.
Adhesive Attachment
During glue application and compression, the adhesive can exert a strong upward force as the carton flaps are opened or folded. If the board’s internal bond strength is insufficient, the paperboard will tear within its own thickness rather than across the glued joint. This results in an unusable package that cannot protect its contents.
Measurement Method
Standardized testing methods such as the Scott internal bond test or z-direction tensile test are used to measure the force required to cause this failure. These laboratory tests evaluate the structural integrity of the sheet by applying a rapid impact or a steady tensile pull perpendicular to the board surface. Papermakers use these measurements to optimize the refining of fiber stock and adjust starch spraying between the plies on the forming section of the board machine.
Maintaining consistent bond strength ensures that the paperboard can withstand the demanding folding and gluing steps on high-speed filling lines.