Laboratory high-consistency dispersion studies of laser-printed office copy paper. Part II

This paper presents the second part of a laboratory study of high-consistency dispersion using a bench-scale hand-fed refiner. The influence of dispersion consistency, temperature, and specific energy input is investigated. Dispersion trials were conducted at three consistencies (21, 28, and 36%) and at two plate gap widths (0.040 and 0.060 in.). Dispersion consistency has a very strong influence on toner particle breakdown and size reduction, especially at 36% consistency. Microscopic visual examination of the toner particles reveals, however that very litte change in the ratio of clean (no fiber retained on particle after repulping) to hairy (undetached fiber retained on particle) particles takes place as a result of dispersion. High-temperature trials were conducted at 58, 69, and 75°C. Higher temperatures lead to less particle size reduction with the production of fewer small particles compared to trials at 25°C. There is some evidence, however, that high-temperature dispersion somewhat enhances fiber detachment from toner although considerable deformation of toner particles occurs. The temperature studies are interpreted in terms of the physical state of the thermoplastic toner above or below its softening point. Specific energy input was investigated over a wide range, centering on that of practical interest. Increased specific energy input leads to greater particle breakdown and size reduction, as expected. However for a given specific energy input increased dispersion consistency greatly enhanced particle breakdown. Application : this paper discusses the influences of important operating parameters on toner particle breakdown and fiber detachment from toner.