INVESTIGATION OF THE CONTACT CHARGING MECHANISM BETWEEN AN ORGANIC SALT DOPED POLYMER SURFACE AND POLYMER-COATED METAL BEADS

The mechanism of contact charging between an organic salt modified pol ymer surface and a dissimilar polymer surface has been studied in the form of a xerographic developer, which consists of toner particles and polymer-coated metal beads. The model toner was prepared by solution coating 0.15 wt % of a negative charge additive, cesium 3,5-di-tert-bu tylsalicylate, on the surface of 9 mu m (diameter) sytrene-butadiene t oner particles. The tribocharge was generated at a relative humidity ( RH) of similar to 20%, by tumbling the model toner with polymer-coated beads (similar to 130 mu m in diameter). It was determined by the sta ndard blow-off procedure inside a Faraday cage. The surfaces of the to ner and the polymer-coated metal beads, before and after the blow-off experiments, were analyzed by time-of-flight secondary ion mass spectr ometry (TOF SIMS) and X-ray photoelectron spectroscopy (XPS). Results show that the cation of the charge additive, Cs+, transfer preferentia lly from the surface of the toner to the surface of the polymer-coated metal beads. The transferred Cs+ distributes uniformly on the bead su rface according to TOF SIMS imaging. The relative Cs- density on the s urface of the beads recovered from experiments where the toner charge varies systematically, either by the length of the contacting time or by the electron affinity of the polymeric surface coating, was determi ned by both TOF SIMS and XPS techniques. Linear relationships with goo d correlation coefficients are consistently obtained between the negat ive toner charge and the relative Cs+ density. The results indicate th at the transfer of Cs+ from the toner to the polymer-coated metal bead s correlates to not only the sign but also the magnitude of the toner charge. This observation, along with the lack of humidity effect on to ner charging, leads us to conclude that the model toner studied in thi s work is charged predominantly by an ion-transfer mechanism.