New Aspects on the Gloss of Coated Paper, 1991 Coating Conference Proceedings

The ranking of coated papers for gloss by means of TAPPI T480 OM-85 does not always correspond with the visual ranking. To investigate this and other factors relating to the specular reflectance of light from coated papers a simple automated gloss goniophotometer has been constructed using a He-Ne laser and a silicon photodiode detector mounted to have an acceptance angle of 0.5 degrees for light specularly reflected from the coated paper surface. Because of the narrow acceptance angle of the detector, which approaches that of the human eye, the instrument response is related closely to the visual response of observers as tested by a pair comparison method to rank the gloss of coated surfaces. The instrument has also been used to investigate the surface topography of coated paper as it relates to the specular reflection of light. It is found that a simple model of the coated surface, based on mirror-like facets with a distribution of angles about the surface mean plane. can be used to account for the measured effects. The effect of both coat weight applied to a base paper and supercalendering on the intensity of the specular reflection from the coated paper surface is also investigated in the terms of this model.