Effect of Counterion on the Tribocharging of Molecular-Salt Charge Control Agents in Xerographic Toners

Abstract

A series of model toners were prepared by a solution coating technique. The toner series consisted of equivalent amounts (4 μmol/g) of negative charge control agents (CCAs), 3,5-di-t-butylsalicylic acid (HtBSA) and its metal salts (MtBSA, M = Li, Na, K, Rb, Cs), on the surface of 9 μm unpigmented styrene-butadiene toner. The morphological properties of these CCAs in toner were studied by scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and fluorescence spectroscopy. Results revealed that CCAs exist in a variety of physical states on the toner surface: from monomer for HtBSA to dimer or small aggregates for LitBSA to higher aggregates or small microcrystals for NatBSA, KtBSA, RtBSA, and CstBSA. Charging experiments showed that all the toners studied in this work charge negatively against polymer-coated metal beads and that ion-transfer is the major charging mechanism. A counterion effect on toner charging was observed. Specifically, the toner charge becomes less negative as the CCA changes from LitBSA → NatBSA → KtBSA → RbtBSA → CstBSA. The counterion effect was attributable to either a surface area effect or a thermodynamic effect on the ionization process. The HtBSA toner charged not only less negative but also at a slower rate. The anomalously low tribocharge and slow rate were emphasized in terms of a change in charging mechanism.