Thesis (M.Sc.)--Chulalongkorn University, 1997

Toner charging properties are the important factors that control the print quality in electrophotography. A charge control agent, CCA, consisting of two parts, an acceptor site and a donor site, is added to control the magnitude and polarity of toner charge. This thesis investigated the charging properties, q/m, of the different carrier sizes, A-3, F-200, and Iron Shot, and the toner which is different in component, CCA type, CCA wt%, and shape. The toner was charged by three types of charging mechanism: a rotation-charging, a printing-charging, and a hand shaking mechanism. The print qualities, expressed us solid and background densities, and dot gain percentage, were evaluated through printing with an LED printer. It is found that the small sized carrier gives a higher charge than that of large size. The charge of toner with CCA is higher than the one without CCA, because CCA helps increase more effective charging sites on toner to an equilibrium state within a shorter time. The toners without CCA gives more background density, less dot gain, and lower solid density than that with CCA. The increasing CCA amount produces the higher q/m values, solid densities, and the increased dot gain percentages. The affinity for electron exchange of CCA type A is more effective than that of type B, therefore, the q/m value, and the solid density are higher. The increasing CCA amounts of CCA type B is not significantly effective to decrease the background density. In contrast, when increasing the amount of CCA type A, the background density is decreased and disappeared at 0.5 wt%. The spherical-shaped toner gives the higher charge than that of the irregular shape. The spherical-shaped toners give ghost images leading to the increasing background density. The various charging mechanisms give the individual q/m values which cannot be used as a representative value. This thesis postulates a plausible charging mechanism of each charging technique, and studies the effect of relative humidity on toner charge in the presence of CCA and silica.