Influence of mechanical treatment of DIP on the printability of recycled fibre based SC paper

The traditional SC furnish includes groundwood, chemical pulp and fillers. The strategy adopted by the German paper industry and which aims at a further increase of the utilization rate of recovered paper calls for recycled fibre to be used in uncoated mechanical paper grades. The preferred recovered paper grade (D39) used for newsprint production comes from household collections. Approx 40 % of the recovered paper for deinking consists of old newspapers. Mechanical pulps used in newsprint manufacture - mostly TMP - exhibit a coarser structure. These coarser pulp fibers tend to deteriorate the surface properties of SC papers after supercalendering and may ultimately lead to an unsatisfactory printability in rotogravure process. For enhanced printability and print image quality, the deinked pulp has to be post-treated mechanically with a view to modifying the fibre morphology such as obtain fibre fractions and fibre length distributions resembling a virgin SC groundwood. Deinked pulp was refined in lab, pilot and industrial scales to explore the influences of different refining techniques on the development of rotogravure printability on SC paper. It has been found that during the refining process, most printability parameters develop positively. Nevertheless, a compromise has to be found in refining process conditions and optimized calandering conditions to improve all printability parameters by varying the calendering conditions.