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

The compatibility of phosphonium salt charge agents in polyester and styrene/acrylic dry electrophotographic toners was analyzed by surface extraction, differential scanning calorimetry, and solid state NMR techniques. The three techniques detected similar trends in the extent of charge agent phase separation due to charge agent structure, toner binder chemical composition, and toner compounding conditions. The kinetics of charge agent dissolution and the proximity of the toner compounding temperature to the melting point of the charge agent were determined to be the major contributors to the observed differences. The compatibility differences were found to influence profoundly the charging properties of freshly prepared developers. Well-dispersed charge agents gave higher charging toners for the same surface concentration of charge agent than did phase-separated charge agents. Developers made from toners with well-dispersed charge agent also exhibited less aging than those with phase-separated charge agent.