Effect of using a high high-yield pulp (HYP) substitution (40%) on printability and print quality of coated wood free papers—A comparison of commercial prints and lab printed samples

The paper industry in China is motivated to increase the high-yield pulp (HYP) content to a very high level (40–50%) from the traditional level (10–20%) for the functionality (e.g. bulk, opacity) and cost advantage of the HYP. In this paper, two coated paper samples were obtained from a modern Chinese paper mill that were produced in mill trials with HYP contents of 17% (normal level) and 40% (a very high level), respectively. The commercial prints of these two paper samples were also received and evaluated. The print quality characterizations showed that these two sheets had similar printability except a significantly higher dot again for the 40% HYP sample. To find out what caused this difference (paper-caused reasons or press room-related reasons), we carried out print evaluation to quantify the differences in printing quality attributes and microscopic analysis to compare coating layer structure and ink layer thickness. In addition, lab printing on two commercial coated paper samples was carried out. It was concluded that there is no direct correlation between the HYP substitution level and the print quality. The difference of the print quality was attributed to the higher ink load for the 40% HYP sample, which in turn, leads to a higher half-tone dot gain. This finding indicates that if press room conditions are appropriately adjusted, coated wood-free paper containing a very high amount of HYP (e.g. 40%) can have print quality similar to that with low HYP level.