Effects of silica concentration and toner surface modification on toner charging, transferring and print quality

Triboelectric property of a two-component developer is an important factor that controls print quality in an electrophotographic system. A surface additive, fumed silica, is added to improve the flow ability and charge stability of the toner in the developer. This thesis investigated the charing properties of the polyester toner, which contains various concentrations of silica from 0 to 1 wt %, and the charges was produced by number of times for attachment forces of the silica particles from 0.5 to 4 times. Other important factors, toner concentration and charging mechanism comprising the vertical rotating, horizontal rotating and hand shaking, were also studied. The print qualities were focused on the solid density, background density, dot gain percentage, and edge sharpness of the characters. When the silica concentration increased, the q/m values and flow ability increased. They produced lower background density, higher solid density and dot gain percentage. The toner without silica gave the lower and inconsistency of q/m values resulting in poor image edge sharpness. The q/m values of the toners containing various silica attachment forces were related with the rubbing forces between the toner and carrier particles in developing step. They inevitably different at the high rubbing force (120-140 rpm) that changed the adherence state and surface area of the silica on the toner surface. However, these silica attachement forces did not impose a significant impact on the flow ability and print quality. When the toner concentration increased, the q/m values decreased. Various charging mechanisms gave different q/m values. Hand shaking charging produced the hishest q/m values, which reached a saturation within a short time, whereas both horizontal and vertical rotating charging gave lower q/m values because of the impaction effect on the glass wall of the vessel.