Substitution of hardwood bleached kraft pulp with aspen high-yield pulp in LWC wood-free papers, part 2: Impact on coated paper quality

The effect of high-yield pulp (HYP) substitution on the properties of basestock, coated, and calendered sheets are examined, specifically in lightweight coated (LWC) wood-free papers. Part 1 (TAPPI JOURNAL, March 2006, p. 21) focused on the impact on basestock properties. Part 2 presents results on coated paper properties including surface quality, coating coverage, and printability. The increased bulk created by HYP substitution is partially preserved after coating and softnip calendering. There is no significant effect on roughness and gloss at a HYP substitution of below 20%. Above 20%, a higher roughness and lower gloss are observed, but the effect can be minimized with a higher calendering load. Coated sheets containing HYP hava slightly poorer coating coverage, which can be attributed to the slight increase in roughness. Coating coverage is unaffected at HYP substitution ranging from 10%-30%. There is no significant effect on printability at low HYP substitution levels (e.g., 10%). A higher ink demand found at a high HYP substitution level (e.g., 30%) is attributed to the higher surface roughness. Application: Substitution of hardwood kraft pulp with aspen HYP up to 20% in LWC wood-free papers can increase the bulk without any negative effect on the final coated paper quality.