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.
Spectral Light Scattering
Diffuse Reflection
Optical phenomenon describes multidirectional light reflection caused by refractive index variations inside paper matrices. Pigment particles, mineral fillers, and cellulose fibres bounce incoming light rays in random directions within substrate surfaces. Measuring spectral light scattering quantifies paper brightness, opacity, and visual appearance under illuminated viewing conditions.
Kubelka-Munk theoretical equations model light scattering coefficients using measured spectral reflectance data.
Refractive Index
Titanium dioxide and calcium carbonate fillers increase light scattering due to high refractive index differentials relative to cellulose. Small filler particles dispersed between wood fibres maximize scattering surface areas, raising sheet opacity significantly. High scattering coefficients reduce light transmission through thin paper sheets, preventing ink print-through on reverse sides.
Coated paper coatings optimize pigment particle size distribution to maximize light scattering efficiency in visible spectrum wavelengths. Spectral light scattering dictates how bright and opaque a paperboard sheet appears under standard D65 illuminant conditions. Paper mills refine raw material formulations to balance optical scattering performance against mechanical sheet strength requirements.
Particle Limit
Over-loading paper furnish with mineral filler pigments reduces inter-fibre bonding, drastically lowering tensile strength. High filler content increases surface dusting during printing press runs, contaminating dampening systems and printing blankets. Wet end retention aids must be carefully managed to prevent uneven pigment distribution across paper webs.