| 摘要 |
<p>PURPOSE: To make it possible to maintain the high image quality of a first toner image on a photosensitive drum, to separate and recover first toners without accumulating these toners in a second developing device in case the first toners intrude into this second developing device and to easily obtain two-color images having high quality without affecting the second toner image by the first toners. CONSTITUTION: A method for developing magnetic one-component toner with alternate electric fields without contact by using magnetic toners (second toners 19) is adopted for second development. The positions on a triboelectrification series are made more reverse polar backward in order of the second toners 19 > an elastic blade 12 > the first toners 18 by adjusting the kinds of the binders of the first toners 18 and the second toners 19, the kinds of external additives and the material of the elastic blade 12 of the second developing device 6, by which the average electrostatic charge quantity of the first toners 18 after the intrusion into the second developing device 6 is made smaller than that of the second toners 19. As a result, the mirroring power of the first toners 18 intruded therein to the developing sleeve 7 of the second developing device 6 is weakened and, therefore, the first toners 18 are suspended by the developing bias in the developing region thereof and are separated and discharged outside the second developing device 6.</p> |
