CHARACTERIZATION OF CALENDER BLACKENING B Y IMAGE-ANALYSIS

When SC papers are being supercalendered, fibre crossings tend to beco me transparent. The areas which appear dark to reflected light are the areas of highest translucence. Furthermore, the printing process enha nces this effect oi calender blackening as the sheets tend to look ,,g reyish'' and might cause complaints by printers or their clients. Base d on visual assessment from printers and test panels at two research i nstitutes a task was made to correlate these evaluations against a tes t method based on image analysis. It became evident that some SC paper s are two-sided concerning calender blackening with an intensified eff ect on the wire (bottom) side. The best correlation with other paper p roperties is against paper density. There is a lower relationship with KL smoothness and gloss. The introduced calender blackening index doe s not correlate with the print quality (in terms of missing dots and p rint density) of the different SC papers that were tested.