CHARGE AGENT STUDIES .2. EFFECTS OF CHARGE AGENT SURFACE CONCENTRATION ON CHARGING AND AGING

The charging, aging, and morphological characteristics of polyester to ners containing methyltriphenylphosphonium p-toluenesulfonate (TPT) as charge agent are compared before and after washing with an aqueous su rfactant solution that removes surface TPT. Charge agent that is not r emoved by the surfactant wash (i.e., ''bulk' TPT) is found to contribu te significantly to the charging properties of the toner. Toners from which the phase-separated charge agent has been removed by washing cau se significantly less developer aging than unwashed, phase-separated t oners. Toners in which the charge agent is well dispersed have much lo wer surface concentrations of charge agent, cause less developer aging , and are not affected by washing. The depth of extraction of TPT from a toner surface by 0.01 M aqueous sodium lauryl sulfate solution is e stimated at about 2.50 nm (25 A) based on ESCA. Solid state P-31 NMR i ndicates that nearly all charge agent present as crystalline TPT in do mains larger than about 100 nm is removed by the surfactant wash. This result is interpreted in terms of a fracture mechanism occurring duri ng grinding of the toner. Preliminary ESCA results indicate that prefe rential segregation of anions to the air/polymer interface may be occu rring in homogeneous toners where charge agent domains are very small. This observation may explain the higher donor/acceptor ratios typical ly encountered with homogeneous toners relative to phase-separated ton ers.