Optimizing Creasing Rule Geometry for Coated Paperboard Packaging
Optimizing creasing rule tip radius and channel geometry enables controlled internal board delamination, eliminating coating cracking and springback jams.
Scott Bond Value
Bonding Metric
Paper coatings require a quantifiable measure of internal adhesion strength between the fibrous substrate and the applied finish layer to ensure structural integrity during high speed web offset printing. A scott bond value provides this measurement by recording the energy required to rupture the internal structure of paper or paperboard when subjected to a high velocity impact force perpendicular to the surface. Testing laboratories apply a double sided adhesive tape to both sides of the test specimen and then bond it between two metal L shaped brackets.
A pendulum swings downward to strike one bracket with a precise force, causing the material to delaminate internally if the adhesive bond exceeds the internal cohesion of the fibre matrix. Technicians measure the force in joules per square meter, which defines the resistance of the sheet against picking or splitting during the transition through the ink rollers.
Performance Expectation
Mills rely on this data to calibrate the distribution of starch or sizing agents within the wet end of the papermaking machine. When the scott bond value drops below defined production thresholds, operators must adjust the drainage rate or increase the wet strength additives to reinforce the fibre network against mechanical stress. Excessive refining of the cellulose pulp improves initial strength but frequently produces a brittle sheet that fails prematurely during the finishing phase.
Lower values often correlate with high mineral filler content which disrupts the hydrogen bonding between cellulose filaments. Converters verify these figures before committing expensive substrates to heavy ink coverage runs where surface tack poses a risk of sheet delamination. Precise monitoring prevents costly pressroom failures where the coating layer pulls away from the base stock.
Measurement Boundary
Environmental factors such as humidity and temperature alter the moisture content of the sample, which influences the result more than minor variances in machine speed. Samples must remain in a climate controlled room until the material reaches a stable equilibrium before personnel perform the impact test. The test fails to produce accurate data on heavily embossed textures because the geometry of the surface prevents uniform tape contact with the brackets.
Reliable readings assume a homogenous distribution of internal bonding agents across the width of the reel. Constant internal cohesion provides the stability necessary for consistent mechanical performance across varied converting applications.