Standard Laboratory Rub Testing for Matte Overprint Varnishes
Laboratory rub testing evaluates matte overprint varnish durability by measuring specular gloss shifts and receptor color transfer under standardized shear loads.
Kinetic Friction Threshold
Friction Criterion
Surface slip prevention relies on the kinetic friction threshold to govern how corrugated board stacks behave under dynamic line acceleration during high speed palletizing. Sliding resistance drops below static holding capability once motion begins on automated conveying paths. Converting plants measure this dynamic boundary force to stop stacked cartons from drifting during rapid deceleration phases.
Coated folding boxboard requires specific surface treatments to maintain sufficient drag between adjacent sheets. Low friction values cause pallet loads to destabilize when automated guided vehicles corner sharply on factory floors.
Slip Boundary
Coaster production and carton erection machines generate high lateral forces that test sliding resistance limits continuously. Wax emulsions and aqueous varnishes alter the sliding coefficient of the top sheet significantly during finishing operations. Converting engineers calculate the dynamic drag limit by dragging a sled across a stationary board sample at constant velocity.
Pressure rollers in printing presses exert vertical loads that change the effective sliding resistance between paper webs. Laboratory technicians record the horizontal force required to maintain motion and divide that reading by the normal sled weight.
Load Stability
Stacked corrugated containers experience severe horizontal shaking during transit inside commercial delivery trucks over rough roads. Warehouses stack pallets several meters high, placing immense weight on the bottom boxes of every column. Corrugated medium fluting profiles and linerboard finish types dictate how well individual boxes resist lateral sliding forces.
High humidity softens paper fibers, reducing the sliding resistance between stacked units and increasing cargo shift risks. Packaging designers specify anti slip coatings to raise the dynamic drag limit whenever heavy contents threaten to slide off pallets.