Stress Release
Gradual reduction of internal mechanical stresses within a polymer or paperboard layer occurs over time after the material has been deformed. This physical phenomenon, known as residual stress relaxation, happens as the polymer chains and cellulose fibers reorganize into a lower-energy state. This relief of internal tension stabilizes the final dimensions of the converted package.
Molecular Reorganization
During the creasing or folding process, the board is subjected to rapid forces that stretch and compress the structure beyond its elastic limit. If these stresses do not relax quickly, the folded carton blank will tend to spring back and resist the adhesive bond. This behavior can cause the carton flaps to open before the glue has had time to cure.
Converting Outcome
The rate at which these stresses dissipate is highly dependent on both the temperature and the moisture content of the paperboard. High temperatures and humidity levels accelerate the relaxation process by increasing the molecular mobility within the fibers and the polymer coating. For this reason, converters often control the environmental conditions in the gluing area or use heated compression belts to assist with stress relief.
This proactive management helps maintain high folding precision and prevents the warping of finished packages during storage.
