Surface Energy Shift and Gloss Drift under Friction Sled Cycles
Friction sled cycles strip migratory slip agents, elevating polar surface energy while generating micro-roughness that causes severe specular gloss drift.
Surface Energy Shift
Thermodynamic Alteration
Time-dependent changes in total free surface energy alter polar and dispersive forces present on polymer films and coated paperboards. The occurrence of a surface energy shift affects how wet printing inks and liquid adhesives wet out across a substrate face. Storage conditions, chemical degradation and internal additive blooming drive these surface energy modifications.
Inert, untreated glass surfaces and stable metallic foils do not undergo organic surface shifts of this nature.
Surface State
Corona discharge treatment breaks polymer chains and creates polar functional groups such as hydroxyl, carbonyl and carboxyl groups on film surfaces. Over time, polar groups rotate back into the bulk polymer matrix to minimize interfacial energy, reducing active bonding sites. Simultaneously, internal slip additives like erucamide or oleamide diffuse outward and cover polar sites with a non-polar hydrocarbon layer.
Exposure to high ambient humidity and elevated storage temperatures accelerates molecular rotation and additive blooming. The resulting combination lowers surface energy from initial post-treatment levels.
Converting Impact
Press operators measure surface energy in dynes per centimeter to verify that substrate surface tension exceeds ink surface tension by at least ten units. Dropping below required energy thresholds causes ink reticulation, pinholing and catastrophic print adhesion failures during production runs.