Mathematical Modeling of Mechanical Tone Value Increase across Recycled Testliner
Dynamic impression squeeze on porous recycled testliner forces lateral ink spread, requiring prepress Yule-Nielsen n-factor recalibration to prevent gain.
Secondary Fiber Compressibility
Recycled Compliance
Z-directional deformation under load defines the mechanical thickness reduction experienced by paper or paperboard produced from recovered paper stock during nip transit. Secondary fiber compressibility measures how recycled pulp structures compact and recover when subjected to normal pressures in calender stacks, printing nips, and corrugating rolls. Repeated drying and re-wetting cycles induce hornification in chemical wood fibers, stiffening the cell walls and reducing their internal swelling capacity.
Recycled furnishes containing high proportions of old corrugated containers or deinked pulp exhibit different compaction characteristics than virgin pulp networks. The property stops at the destructive crushing threshold where internal fiber bonds fail permanently under excessive static or dynamic pressure.
Morphological Behavior
Hornified secondary fibers possess flattened cross-sections, low conformability, and reduced cell wall flexibility relative to flexible virgin fibers. When a recycled web enters a compression nip, the stiff fiber network resists initial deformation, yielding lower initial strain at low compressive loads. Higher loads cause abrupt rearrangement and mechanical collapse of brittle fiber fragments, fines, and mineral debris packing the sheet voids.
Elastic recovery after exiting the nip decompression zone is typically lower in secondary fiber sheets because damaged fibrils lack the elastic spring-back of intact virgin fibers. Calendering operations on recycled testliner therefore require higher line pressures to achieve equivalent surface smoothness, which permanently crushes sheet caliper and degrades bending stiffness. In corrugating medium, reduced secondary fiber compressibility impairs fluting moldability, causing flute fracture or uneven medium thickness during high-speed single-facing operations.
Converting Impact
Corrugated box plants adjust printing impression pressures and die-cutting clearances to prevent crush damage on secondary fiber linerboards. Sheet caliper retention directly preserves box compression strength during converting and multi-tier pallet storage.