Dynamic Z Direction Tensile Stress Propagation in Recycled Fibers during High Speed Creasing
High speed creasing generates Z-direction tensile stress waves that fracture short recycled fibers unless matrix clearance absorbs elastic strain energy.
Acrylic Dispersion Barrier
Surface Chemistry
Polymer emulsions applied to paperboard form an acrylic dispersion barrier by coalescing into a continuous film during the drying phase of converting. Waterborne chemistry relies on surfactant packages and stabilizing colloids to maintain particle suspension before thermal energy drives the coalescence process. Coated folding boxboards achieve grease resistance and moisture vapour retardation through this deposited polymer matrix without requiring petroleum-derived laminates.
Coaters govern film weight application through metered rod systems or air knife assemblies to ensure the functional layer remains continuous across porous cellulose substrates. Converting speeds and web tension determine whether micro-cracks develop in the dry polymer layer during subsequent crewing and folding operations. Drying tunnels must supply adequate latent heat capacity to evaporate continuous water phases before the web reaches high-temperature cylinder groups.
Coating Weight
Grammage targets for the laid polymer film typically range from five to twelve grams per square metre depending on end-use migration limits and barrier demands. Thicker applications reduce oxygen transmission rates through dense molecular packing but increase the risk of curl distortion during offset lithographic printing. Converters balance functional performance against bending stiffness degradation because rigid polymer films alter the scoring characteristics of folding carton blanks.
Laboratory testing measures grease penetration resistance through turpentine test durations or Cobb sizing values to verify that emulsion coverage is free from pinholes.
Film Integrity
Substrate smoothness dictates the minimum wet pick-up required because rough fibre topologies leave microscopic valleys unfilled beneath thin dispersion layers. Calendered baseboards reduce binder demand by presenting a uniform planar surface for the incoming aqueous suspension. Thermal crosslinking agents added to the liquid formulation improve blocking resistance when stacked reels experience sustained pressure during high-humidity storage intervals.
Complete film coalescence depends strictly on drying temperatures exceeding the minimum film formation temperature of the specific polymer grade selected for the run. Barrier failure occurs when residual moisture or inadequate drying energy prevents polymer chains from entangling fully across the interstitial voids of the paperboard matrix.