Parameters that influence toner charging characteristics and electrophotographic print quality

Abstract

The triboelectric properties, q/m, of a two-component developer are important factors in an electrophotographic system. The toner charge is an important parameter that controls the developer mass and the print quality. This thesis investigated the charging properties of differently shaped toners, spherical-shaped and irregular-shaped toners, and carrier particles which are different in components and currents, i.e., a ferrite carrier and steel carriers roduced with different currents (17, 31, 76, and 182 muA). The important parameters of toner charging are the mixing force, the toner concentration, the shape of toner, the carrier type, and the current of the carrier surface. The study of the print quality focused on the solid density, densities at 60 an 40% halftones, background density, and edge sharpness of the characters. The charge-to-mass ratio increased with increasing mixing force. At high speeds of mixing, the deformation of toner particles occurred. The q/m value increased to a maximum and then immediately decreased. This was confirmed by SEM photographs. When the toner concentration increased, the coverage of toner particles on the carrier surface increased to more than one layer. The outer toners could not be charged with the carrier, so the q/m value decreased. The spherically shaped toner was more efficiently tribocharged than the irregularly shaped toner. Therefore, the spherically shaped toner gave higher q/m values, which produced higher densities at 60 and 40% halftones. The edge sharpness of the characters from the spherically shaped toner was higher than those from the others. The solid densities of the different toners were close to each other. The carrier particles containing only Fe gave stronger contact with the toner than the carriers with Cu, Zn, and Fe. The current on the carrier surface influenced the q/m value; the higher the current, the greater the friction force between two surfaces leading to the high value of q/m. This thesis explains key parameters that affect the toner charging characteristics and their print qualities.