A Laboratory Study into the Effect of Toner Particle Size on Flotation and Agglomeration Kinetics, 1997 Recycling Symposium Proceedings

A laboratory study into the flotation and agglomeration of laser printed office copy paper and the influence of kneading is reported in this paper. The aim was to quantify the kinetics of toner ink flotation, before and after kneading, and the kinetics of microscopic toner ink removal by agglomeration.

Standard laser printed sheets were repulped in a small laboratory blender at 8% consistency and used as the starting material for flotation and agglomeration experiments.

Continuous flotation experiments were performed on kneaded and unkneaded pulp using standard temperature), consistency and chemistry conditions and results of image analysis versus time are presented. Batch agglomeration experiments were also performed on unkneaded pulp under low mixing conditions, at 70°C and 6% consistency, and again image analysis results are presented. Pulp kneading was done in a laboratory disc shearer at 30% consistency and 20°C.

With kneading fused toner specks readily broke down into particles below 100 microns. Particles appeared to fracture in the narrowest dimension producing disc shape fragments with sharp edges. Flotation rates decreased significantly with time and increased as particle size increased from 10 to 100 microns. Where after they decreased as particle size increased beyond about 100 microns. Particle shape also appeared to influence flotation rate as the sharper edged kneaded particles consistently had slightly higher rates of flotation than the unkneaded particles of the same size range. The rate of dice of microscopic particles due to agglomeration was similarly affected by time and particle size.

Disappearance rates similar to flotation were observed initially in the sub 150 micron size classes. In size classes above 350 microns negative disappearance rates occurred signifying an increase of particles in these larger size classes.

With longer agglomeration times both the positive and negative rates decreased in absolute terms towards zero and few particles below 1 mm remained.

Results confirm the role of kneading in enhancing flotation deinking of MOW furnishes and provide useful comparative...