Pale defect of halftone following solid image in two-component magnetic brush development system in electrophotography

We studied the mechanism of and countermeasures against a pale image defect observed in the halftone area following a solid image in a two-component magnetic brush electrophotographic development system. We manufactured a model apparatus consisting of a pseudo-photoreceptor drum, development sleeve, and stationary magnetic roller. The image was created on an insulated film electrode pasted onto the drum. A parameter experiment confirmed that the image defect was enhanced when the voltage difference applied to the solid area and halftone area was large, ac voltage superposed on the dc development voltage was low, the development gap was large, and the speed ratio (sleeve speed to drum speed) was low. However, the defect was almost entirely independent of the frequency and waveform of the superposed ac voltage. The dynamic behavior of toner particles in the development area was directly observed using a high-speed microscope camera, and the mechanism of this print defect was investigated. The results of this experimental work can be utilized to improve the two-component magnetic brush development electrophotographic system.