Application of yellowing inhibitors to improve the brightness stability of coated mechanical papers

We used laboratory and pilot film coaters to evaluate the effect of yellowing inhibitors on the brightness stability, physical properties, and printability of a coated high-brightness paper made from 100% bleached thermomechanical pulp (BTMP). The yellowing inhibitors consisted of a hydroxyphenylbenzotriazole ultraviolet absorber (UVA) and a hindered hydroxylamine radical scavenger (RS). After 250 days of ambient light exposure a sheet with a 4 g/m 2 /side coating lost 27 points ISO brightness. A sheet with 1.0% RS and 0.11% UVA added to the coating color lost only 11 points brightness. The inhibitors were compatible with the coating formulation and caused no runnability problems. The yellowing inhibitors had a negligible effect on the physical properties and printability of the treated paper.