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 (mu)m 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 Tg, the glass-transition temperature, leading to the reformation of aggregates of the primary 1-2 (mu)m latex aggregates of ~6-12 (mu)m, 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 (mu)m aggregates to >Tg to cause internal coalescence. These changes of rheological property and structure and the physicochemical reasons for them are reported in detail.