Photon Diffusion
Light redirection caused by non-uniformities within a paper matrix determines how brightness and opacity register on the converting line. Optical scattering occurs when incident photons encounter refractive index boundaries between cellulose fibres and air voids inside a sheet. Titanium dioxide fillers or clay coatings amplify this internal deflection by presenting microscopic obstacles that prevent unhindered transmission.
Converting machinery relies on this photon dispersion to prevent print show-through on lightweight packaging stocks.
Scatter Coefficient
Wavelength-dependent photon deviation is quantified by specific scattering coefficients derived through the Kubelka-Munk turbid media theory during laboratory pulps evaluation. Mill laboratories measure reflectance values on opaque backing pads to calculate the exact scattering power per gram of dry fibre network. Coated paper grades demand precise control over this metric to guarantee that high-speed flexographic inks maintain high contrast against unprinted background areas.
Low scattering values produce translucent packaging substrates that fail barrier opacity thresholds demanded by pharmaceutical carton manufacturers.
Anisotropic Dispersion
Fibre orientation alignment dictates directional variance in photon paths across machine and cross directions on fourdrinier paper machines. Refined chemical pulps with high fibrillation levels increase internal surface area, which subsequently raises total photon deviation angles within corrugated linerboard layers. Calendering pressure flattens the sheet structure, reducing internal air void volume and diminishing scattering efficiency to enhance surface gloss at the expense of opacity.
Final opacity performance depends directly on maintaining optimal void fractions throughout the wet pressing stages of paper production.
