Fiber/Toner Detachment Studies: Repulping and Flotation of Laser Printed Paper, Part I, 1994 Pulping Conference Proceedings

D. A. Johnson, E. V. Thompson

The presence of toner particles (fragments) which contain undetached fibers after the repulping of laser printed paper is illustrated and discussed. These toner particles are denoted “hairy” particles, and two experimental studies are presented which illustrate the influence of hairy particles in flotation operations. In the first study two samples with different flotation efficiency vs. time (rate) responses are described, and a microscopic examination of the percentages of clean and hairy particles is presented. It is shown that the slower response of one sample can be attributed to the hairy particles presented. In the second study a technique for fractionating toner particles using a Bauer-McNett fiber classifier is described. Data is presented for two flotation rejects samples which were fractionated into four fractions or size classes, 100-200, 200-300, 300-420, and >420 µm. Image analysis results of the four fractions of each sample indicate many smaller particles present in the fractions than would be predicted form the Bauer-McNett screen cut-offs of 100, 200, 300, and 420 µm. Microscopic examination of the fractions indicate that these smaller particles are almost invariably hairy particles. Since image analysis and visual size classification measure only the size of the black toner particle, and not the fibers attached to it, it is hypothesized that hairy particles possess a larger, “hydrodynamic” size or volume, and this is what determines in which fraction the toner particle/fiber agglomerate will appear. It is further hypothesized that this hydrodynamic size is a better indicator of floatability or flotation efficiency than size as determined by image analysis.