Effects of an external additive on toner adhesion

We have studied the effects of an external additive on the non-electrostati c and electrostatic adhesion of toner. Toner samples with various concentra tions of the additive were prepared. The additive surface coverage on the t oner was evaluated with a scanning electron microscope. The adhesion to a p hotoconductor of non-tribocharged or tribocharged toner was measured by the centrifugal method. It was found that the non-electrostatic adhesion rapid ly decreased with increasing surface coverage, and saturated at a certain c overage. The dependence of the non-electrostatic adhesion on the surface co verage can be explained as a change of the van der Waals force. The electro static adhesion increases in proportion to the square of toner charge to ma ss ratio, and the slope decreases exponentially with increasing surface cov erage. A simple electrostatic image force model cannot explain an enhanced electrostatic adhesion. It is suggested that the enhanced adhesion is cause d by a non-uniform charge distribution in the toner surface. The decrease i n electrostatic adhesion with increasing surface additive is attributed to increasing total charged area on the toner particle.