Material Displacement
Cellulose fibres within a sheet exhibit a time-dependent mechanical response where deformation under constant load gradually increases while stress relaxes over sustained strain. Paperboard viscoelasticity governs this dual nature of solids and fluids within the sheet structure. The property dictates how a package maintains its dimensions when stacked under heavy weight for weeks in a warehouse.
Engineering teams account for this shifting geometry to ensure that the creasing and folding operations do not lose their required stiffness over the shelf life of a carton.
Manufacturing Influence
Fibre orientation during the web formation process determines the directionality of the response. Refining cycles increase the internal bonding and change the rate at which the material yields to permanent creep. High moisture levels in the storage area exacerbate the flow, causing the board to deform far beyond its initial elastic limit.
Performance Expectation
Print registration requires extreme stability that this specific mechanical behavior threatens if the substrate undergoes rapid tension changes on the press. Presses operating at high velocity induce dynamic loads that reveal the creep properties before the ink has a chance to set on the surface. Converting lines mitigate these tendencies by controlling the ambient humidity and limiting the duration of high-tension stress cycles on the web.
Proper board selection relies on minimizing these transient movements to ensure the final package remains square throughout its distribution life.
