Optical Scattering
Optical measurement standards for high-gloss coated papers quantify the stray light scattered at narrow angles adjacent to the specular reflection peak. On premium cast-coated paperboard and gloss-varnished packaging, surface gloss haze produces a milky appearance or shallow image depth that reduces visual clarity. Small-scale surface roughness and micro-scratches scatter reflected light away from the specular angle.
Standard goniophotometers measure haze by comparing light intensity at two degrees off the specular angle to total specular reflectance. High haze values indicate compromised image sharpness despite high total specular gloss readings.
Coating Microstructure
Formulation and calendering conditions dictate micro-topography on coated board surfaces. When surface gloss haze develops in overprint varnishes, incomplete leveling or phase separation of wax additives scatters light at the coating-air interface. Fine pigment particles in coating formulations must remain fully dispersed to prevent micro-agglomeration during drying.
Excessive calender roll temperature or uneven nip pressure creates localized surface damage that increases light scattering. Optimizing coating rheology and drying speed promotes a smooth, continuous surface film that minimizes wide-angle light dispersion.
Measurement Limit
Haze quantification loses accuracy on low-gloss or matte substrates where diffuse scattering dominates specular reflection. Standardized haze formulas apply exclusively to high-gloss surfaces exhibiting specular gloss values above seventy units. Below this reflection threshold, diffuse reflection obscures narrow-angle scattering signals.
