Application of calcium carbonate for uncoated digital printing paper from 100% eucalyptus pulp

Increasing the filler content in paper to reduce the cost of materials is an ongoing effort among papermakers. Selecting the proper calcium carbonate additive for each type of paper is the key to achieving this goal. Calcium carbonate is the most widely used filler material in the paper industry. On average, it is applied at levels of 18% to 30%. Quality requirements of each type of paper vary widely, according to use; understanding the effect that different types of calcium carbonate have on paper properties allows producers to choose the best filler for each use. Given that the market for uncoated digital printing paper is expected to grow, this study focused on selecting the optimal calcium carbonate for the production of uncoated digital printing paper made from 100% eucalyptus pulp. In this study, 13 varieties of calcium carbonates were used to prepare handsheets for the detailed analyses of structural, optical, and strength properties. The samples included nine varieties of precipitated calcium carbonate (PCC) (two rhombic and seven scalenohedral, covering a particle size range from 1.2 μm to 2.9 μm) and four varieties of ground calcium carbonate (GCC) (three anionic and one cationic, with a particle size range of 0.7 μm to 1.5 μm). From the results of this study, we determined that the optimal calcium carbonate for uncoated digital printing paper made from eucalyptus pulp is scalenohedral PCC with a particle size of 1.9 μm, because of its positive effects on caliper, stiffness, brightness, and opacity.