Tone Value Increase Target Derivation for Uncoated Papers
Deriving uncoated paper TVI targets demands separating optical light scattering from capillary ink absorption using M1 spectral data to set inverse RIP curves.
Surface Macro Roughness
Topographic Profile
Physical surface irregularity measurement quantifies large-scale peak-to-valley deviations across paper substrate topographies. Stylus profilometry and air-leak testing methods evaluate surface contours at spatial wavelengths exceeding microscopic pore dimensions. Assessing surface macro roughness predicts ink transfer completeness and contact uniformity during printing cylinder nip compression.
Paper mills use calendering processes to flatten surface peaks and smooth coarse fibre networks.
Contact Friction
Bendtsen and Sheffield air-leak instruments measure airflow rates escaping between a flat test land and paper surface. High air leakage values indicate rough surface profiles, while low values reflect flat calendared paperboard surfaces. Macro roughness causes incomplete ink coverage in gravure print cells, resulting in missing halftone dots and speckled solid areas.
Offset printing blankets deform elastomer surfaces to conform to macro roughness, requiring higher nip pressure on rough stocks. Calendering rolls compress high-density fibre peaks, reducing overall sheet caliper while smoothing macroscopic surface deviations. Surface macro roughness dictates substrate suitability for high-resolution graphics, foil stamping, and barrier coating applications.
Printability Limit
Excessive calendering to eliminate macro roughness crushes internal sheet structure, lowering stiffness and bulk. High surface roughness demands excessive ink film thickness, causing long ink drying times and image blur. Uncoated recycled paperboard exhibits high macro roughness variations, requiring heavy primer coatings prior to printing.