Tension Regression
Surface energy loss on polymer-coated paper substrates occurs as the chemically active groups created by electrical discharge rotate back into the bulk material. This reduction in wettability is known as corona treatment decay, a process that limits the storage life of treated rolls before printing or extrusion coating. It reduces the surface tension from high initial values of forty-eight dynes down to inactive levels below thirty-eight dynes.
Testing with dyne pens or contact angle instruments reveals this decay rate, which is steepest during the first forty-eight hours after processing.
Storage Effect
Environmental conditions during storage accelerate the rate at which treated surfaces lose their receptive qualities. High ambient temperature and moisture increase chain mobility in the polymer, allowing the oxidized polar groups to migrate away from the surface. In addition, slip additives and processing waxes present in the polymer formulation migrate to the outer layer, masking the treated areas and preventing proper adhesion of water-based inks.
Print Failure
Improper ink transfer represents the primary consequence of using stock that has experienced extensive decay. When the surface energy falls below the surface tension of the applied coating, the liquid beads up rather than spreading evenly. This lack of wet-out causes poor bond strength, pinholes, and ink flaking on the packaging line.
