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.
Stick-Slip Friction
Sliding Instability
Sliding interactions between flexible packaging webs and machine contact surfaces generate dynamic friction force fluctuations during high speed transport. Non-uniform sliding behavior occurs when static friction significantly exceeds kinetic friction along the contact boundary. Stick-slip friction describes the alternating cycles of stopping and sliding that create mechanical vibrations in paperboard converting and web feeding operations.
High static friction holds the moving substrate momentarily until driving force exceeds hold, causing sudden acceleration and tension spikes. Substrate surface roughness and ambient humidity aggravate frictional instability.
Jerk Response
Converting machinery operating with jerky web motion experiences registration errors and variable web tension control. Stiction events stall paperboard sheets in feeding hoppers, causing automatic packaging equipment to jam and shut down. Monitoring stick-slip friction requires friction sled testing with high speed digital load cells capable of capturing rapid force oscillations over short displacement distances.
Applying fatty acid amide slip additives or surface wax coatings smooths the transition between static and kinetic friction regimes. Excess humidity increases hydrogen bonding across cellulose interfaces, promoting stick-slip behavior on uncoated paperboard.
Process Interruption
Erratic sliding forces accelerate mechanical wear on guide rails and pull rollers. Uncontrolled friction oscillations degrade print registration on flexible packaging lines. Stick-slip friction identifies mechanical instability during high speed automated packaging operations.