Liquid Pressure
Outward force exerted by a liquid product against the internal surfaces of a paperboard or composite container during and immediately after the dispensing process determines the required wet-strength of the packaging material. This hydrostatic filling load increases linearly with the depth of the liquid and the density of the product. Designing against this pressure prevents the container from bulging or leaking before the seal is completed and cooled.
Structural Deflection
Resistance to bulging under liquid weight depends on the stiffness of the barrier-coated board and the geometry of the container corners. If the hydrostatic filling load exceeds the flexural rigidity of the paperboard panels, the carton walls will bow outward, which can compromise the secondary packaging fit and the seal integrity. This deflection is particularly critical in liquid packaging board grades used for milk and juice cartons.
Applying a polymer coating or a plastic lining helps the paperboard resist moisture absorption that would otherwise weaken the fiber network and accelerate bowing.
Stress Distribution
Concentration of force at the bottom seams of the container requires reinforced adhesive bonds or heat seals to prevent failure. Corner geometries can be rounded or creased to distribute the hydrostatic force more evenly across the lower panels of the pack.
