Strength Assessment
Resistance of a overlapping bonded joint to parallel pulling forces determines the structural integrity of paperboard boxes and shipping cartons under mechanical strain. Lap shear adhesion measures the maximum force per unit area required to slide or shear a test joint apart along its bonding plane. This metric is evaluated by gluing two strips of substrate together with a defined overlap, then tensioning them in opposite directions until failure occurs.
It is an essential specification for corrugated box joint-sealing and high-speed folder-gluer operations.
Mechanical Variables
Value measurements generated by this test depend on adhesive film thickness, curing duration, and substrate stiffness. High-rigidity paperboards tend to concentrate stress at the edges of the lap joint, whereas more flexible boards distribute the load more evenly across the bond area. This stress concentration can lead to premature failure if the adhesive does not possess sufficient elasticity to deform under shear.
Matching the shear profile of the glue to the stiffness of the packaging board prevents failure during shipping.
Quality Standard
Achieving consistent high shear performance requires tight control over coating application and drying speeds. If the adhesive is under-cured or applied too thickly, it will fail cohesively at low shear forces.
