Quantifying Micro Surface Burnishing in Overprint Varnishes under Sled Shear
Surface burnishing under sled shear converts diffuse reflectance to specular gloss through silica displacement, controlled by matrix crosslinking and particle size.
Sled Shear Friction
Board Drag Coefficient
Folding carton lines depend on predictable surface interactions when blanks travel through high speed erecting machinery. Sled shear friction measures the kinetic resistance generated between two overlapping paperboard surfaces during horizontal motion under a constant normal load. Converting plants monitor this specific force value to prevent buckling during automatic feeding and gluing sequences.
High sliding resistance causes blanks to jam inside the magazine hopper while insufficient drag leads to double feeding errors. Laboratory technicians clamp a weighted sled onto a lower specimen sheet and pull the assembly horizontally at a controlled velocity while load cells record the sustained force.
Coating Additive Influence
Aqueous barrier applications and clay pigment layers alter micro surface topography and subsequently modify frictional behavior. Lubricants such as calcium stearate or polyethylene wax emulsions reduce sliding resistance by protruding above the mineral binder matrix to interrupt direct fibre contact. Excessive wax concentration drops the force value below threshold limits, creating unstable carton stacks that slide out of alignment during pallet transport.
Formulators balance these additives against downstream printing ink transfer requirements and hot melt glue adhesion speeds.
Sliding Resistance Boundary
Moisture absorption within corrugated fluting mediums and solid bleached board alters surface energy states and invalidates baseline friction measurements. Ambient relative humidity fluctuations above standard conditioning parameters swell cellulose fibres and increase contact area between sliding planes. Converting machinery operators must compensate for seasonal atmospheric shifts by adjusting blank feeder gate pressures to maintain steady line speeds.
Finished packaging components exposed to deep freeze storage conditions experience thermal contraction that alters the measured drag coefficient before filling operations begin.