A process for the manufacture of produced toner - II. Effect of operating conditions

In part 1 of this two part paper, the impact of pH and temperature on structure and rheological properties at the various process steps of the model CPT manufacture were reported. Part 2 uses temperature and pH values established in part I and concentrates on the impact of agitation conditions on the CPT product and their implications for scale-up. It is seen that the main drivers for the process are pH and temperature, but if a product is to be obtained that can meet the typical tight commercial size distribution and morphology specification, then mixing aspects must be understood. The initial stages involving lowering the pH to cause destabilization, flocculation, and gelling required intense micromixing to prevent oversize CPT product. For gel breakage, again intense agitation was necessary to ensure full motion in the gel due to its yield stress. Intense agitation here was also able to reduce the amount of oversize CPT product to meet specification. All these processing aspects are analyzed in detail in this paper in the light of the present knowledge of mixing. The findings also throw some interesting light on the impact of mixing on aggregate structure at scales below the Kolmogoroff microscale of turbulence, appearing to give support to the ideas of Levich.