A Process for the Manufacture of Chemically Produced Toner (CPT). I. Evolution of Structure and Rheology

A process for the manufacture of chemically produced toner (CPT) has been analyzed using model materials. In part 1 of this two-part paper, the impact of pH and temperature in a Couette-type rheometer and in a combination of two mechanically agitated systems with recirculation between them is reported. The initially stable 100 nm latex suspension at pH ≈ 9 was destabilized by the addition of acid accompanied by vigorous agitation. This destabilization led to the formation of primary aggregates of the original latex suspension of ∼1−2 μm which, at pH < 4, themselves aggregated to give a closely packed paste or gellike structure. This rheologically complex structure had a yield stress and exhibited internal slippage between primary aggregates at certain shearing conditions. The gel was broken by heating to above T g, the glass-transition temperature, leading to the reformation of aggregates of the primary 1−2 μm latex aggregates of ∼6−12 μm, which could be stabilized by raising the pH again to ∼7. The final near-spherical model CPT product was obtained by heating the 6−12 μm aggregates to ≫ T g to cause internal coalescence. These changes of rheological property and structure and the physicochemical reasons for them are reported in detail.