Toner Detachment During Repulping of Laser Printed Office Copy Paper

Specially prepared standard sheets of laser printed office copy paper were repulped in a small laboratory pulper and in a large bench-scale pulper at consistencies between 3 to 9% and 6 to 18%, respectively. Re-sults of both image analysis and visual microscopic examination are presented. In both sets of consistency trials, increasing consistency lead to more small and fewer large toner particles. There was not, however, a corresponding change in the ratio of clean-to-hairy toner particles: these ratios were essentially unchanged for all size classes for the 6 to 18% consistency trials, although there was a significant increase in the 9% laboratory pulper trial. Trials were also conducted at 12% consistency for three sets of conditions and com-pared with the baseline repulping: (1) with (baseline) and without added surfactant; (2) pH = 10 (baseline), pH unadjusted, and pH = 5.5; and (3) T = 40°C (baseline), T = 20°C and T = 60°C. There was no dis-cernible influence of surfactant, and very little, if any, influence of pH. The temperature trials yielded the interesting result that lower temperature facilitated the toner break down into smaller particles, but did not produce better fiber/toner detachment; on the other hand, higher temperature facilitated fiber/toner detach-ment (well beyond any previous result), but did not enhance toner break down. These observations are discussed in terms of the brittleness of the toner at the lower temperature below its softening point, compared to its leathery, tough properties at the higher tempera-ture above its softening point.