Effect of poorly deinkable paper on deinked pulp quality

Abstract

Laboratory tests were performed to assess the influence of various digital prints and packaging paper products on the quality of deinked pulp. Boards and digital prints were dosed to a certain percentage in basic mixtures of offset printed newspapers and offset and rotogravure printed magazines. After pulping, the fiber suspensions were treated in a single step flotation process and the deinked pulp was characterized by optical properties. Effects on optical properties of deinked pulp are presented. Each proportion of 4% corrugated board in a basic mixture of recovered paper results in a 1 point loss in luminosity of the deinked pulp. The luminosity decrease corresponds with increasing degree of printing ink on the board. With increasing proportions of corrugated board, a shift in the color locus and increased filtrate darkening were observed, simultaneously. All effects were smaller for boxboard than for corrugated board. The negative impact of digital prints in a basic recovered paper mixture in terms of luminosity of deinked pulp was greatest with inkjet printed newspapers. A proportion of 30% inkjet printed newsprint results in a luminosity drop of almost 7 points, combined with a shift of the color locus into the green area. Regarding liquid toner prints in the basic mixture of recovered paper, a significant increase of the total dirt speck area from 200 mm²/m² to 1100 mm²/m² was observed after a single laboratory flotation process.