Reflectance Geometry
Optical surface properties that measure the proportion of light reflected at an angle equal to the angle of incidence determine the shininess of printed and unprinted paperboard. Standard measurement of specular gloss utilizes specific angles of twenty, sixty, or eighty-five degrees to capture the behavior of reflected light from a surface. This property is determined by comparing the light reflected from the sample surface against a polished black glass reference standard.
It is critical for defining the visual quality of gloss coatings, varnishes, and calendared papers in the packaging industry.
Process Variables
The level of gloss achieved on paperboard is directly influenced by the coating formulation, the fiber structure of the base board, and the pressure applied during the calendering process. Printers of premium cartonboard monitor specular gloss during production to ensure that different sheets look identical when arranged on a retail shelf. Adjusting the ratio of clay to latex in the coating formulation allows the board manufacturer to target specific gloss levels for different print technologies.
Aesthetic Standards
Brand owners demand precise gloss values to maintain a premium look for their products. The specular gloss value helps converters select the correct varnish to match the expectations of the package design. Inconsistent gloss readings can signal underlying issues with ink curing or varnish absorption into the porous paperboard.
