CHARGE AGENT STUDIES .1. CHARGE AGENT SURFACE CONCENTRATION AND CHARGING BEHAVIOR

The compatibility of phosphonium salt charge agents in polyester and s tyrene/acrylic dry electrophotographic toners was analyzed by surface extraction, differential scanning calorimetry, and solid state NMR tec hniques. The three techniques detected similar trends in the extent of charge agent phase separation due to charge agent structure, toner bi nder chemical composition, and toner compounding conditions. The kinet ics of charge agent dissolution and the proximity of the toner compoun ding temperature to the melting point of the charge agent were determi ned to be the major contributors to the observed differences. The comp atibility differences were found to influence profoundly the charging properties of freshly prepared developers. Well-dispersed charge agent s gave higher charging toners for the same surface concentration of ch arge agent than did phase-separated charge agents. Developers made fro m toners with well-dispersed charge agent also exhibited less aging th an those with phase-separated charge agent.