Mechanisms of Charge-Exchange in Xerographic Toner Powders

Abstract

The mechanism of charge-exchange between a fresh uncharged toner and a charged toner in a xerographic developer has been studied using model toners in a cross-over experiment. The two model toners studied were prepared by solution-coating charge control additives cesium 3,5-di-t-butylsalicylate (CstBSA) and rubidium 3,5-di-t-butylsalicylate (RbtBSA) onto the surface of 9-μm unpigmented stryene—butadiene toner particles at a concentration of 4 μmole/g. We previously showed that these toners acquire negative charges when they are rubbed against the surface of polymer-coated metal beads. We further showed that the transfer of the cation from the surface of the toner to the surface of the metal beads is the major charging mechanism. In this work, we studied the mechanism of charge-exchange in these toners. The charge-exchange is monitored by the so-called “admix time,” the time required for the uncharged and charged toners to become equilibrated chargewise after mixing together. The mechanism was studied by adding 1% fresh uncharged RbtBSA toner to a charged developer consisting of 2% CstBSA toner and 98% of the polymer-coated metal beads. The surfaces of the toner particles and the polymer-coated metal beads, before and after toner admix, were examined by the time-of-flight secondary ion mass spectrometry technique. Results show that (1) both Cs+ and Rb+ are randomly distributed on the surfaces of toner particles after admix and (2) the surface of the metal beads consists of both cations. The mechanism of charge-exchange is discussed in terms of a dual mechanism involving an ion-exchange process between the charged and uncharged toners and a contact charging (ion-transfer) process between the fresh toner and the polymer-coated metal beads.