Coating improves the brightness stability of wood-free coated papers containing high-yield pulp

High-yield pulp can replace hardwood kraft in wood-free coated papers to increase bulk and reduce costs. This research was undertaken to study the effects of pulp substitution on brightness stability. Light-induced brightness loss was found to occur as a result of both high-yield pulp substitution and the yellowing of the coating color. However, coating improves the brightness stability. The improvement can be significant, depending on the extent of pulp substitution and the coat weight. For a 15% substitution of high-yield pulp, a coat weight of 20 g/m 2 gave the same brightness stability as a 100% kraft sheet coated at 4 g/m 2 . An empirical model was developed to estimate the effect of high-yield pulp and coat weight on the brightness stability of wood-free coated papers. Application: Mills have an opportunity to use more high-yield pulp in wood-free coated papers by adjusting the coat weight to improve the brightness stability.