| 摘要 |
PROBLEM TO BE SOLVED: To obtain a good multicolor image without color mixture by applying an amount of electric charge equal to or greater than a specified level to the toner of the toner image of first color on an image carrier so that the toner of the toner image of the first color is prevented from being mixed in a developing device with the toner of second and succeeding colors caused when the toner of first color is peeled in the case of the development of the toner of the second and the succeeding colors. SOLUTION: In order to apply a charge amount capable of preventing the toner of first color on a photoreceptor drum from being mixed, in a second developing device, into the toner of first color on the photoreceptor, a duty bias in which the ratio of the time T2 of a potential Vmin energizing the toner in a direction from the photoreceptor drum toward the developing sleeve of a first developing device to the time T1 of a potential Vmax energizing the toner in a direction from a developing sleeve toward the photoreceptor drum is different in the one cycle of an AC component is used as a developing bias in the case of the development of the toner of the first color. The toner charge amount needed for preventing toner mixing is -45 μC/g and the duty ratio of T1/(T1+T2) is 20% to 40%, so that the charge amount equal to or more than -45 μC/g is applied to the toner of the first color. |
