JPH065401B2 - Multicolor image forming device - Google Patents

Description

The present invention relates to the arrangement and operating conditions of developing devices in a multicolor image forming apparatus.

(Prior Art) Conventionally, a plurality of developing devices such as a black developing device and a red developing device are arranged around the image carrier, and the developing device is appropriately selected to form an image on the image carrier in black or red. An image is formed in a plurality of colors.

Normally, a magnetic toner is used as the black toner, but a non-magnetic toner is used as the red toner in order to obtain the proper tint, and it is configured to form a good red image without turbidity.

(Problems to be Solved by the Invention) In this conventional multicolor image forming apparatus, when non-magnetic toner having a weak adhesion to the sleeve is used, the non-magnetic toner scatters from the developing unit, and a scattering measure is taken in the configuration. Or, a means for electrically collecting was needed and a considerable space had to be secured.

(Object of the Invention) The present invention enables efficient removal of color toner scattering, which is a drawback of the above-mentioned conventional example, without taking up space.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a movable image bearing member and a rotatable developer bearing member carrying a black toner at a position facing the image bearing member. A black developing device for developing a latent image on the image bearing member and a rotatable developer bearing member for bearing a non-magnetic colored toner other than black are provided at positions facing the image bearing member. A color developing device for developing an image, and the black developing device is arranged downstream of the color developing device with respect to the moving direction of the image carrier, and both the black developing device and the color developing device are AC. In a multicolor image forming apparatus capable of applying a developing bias in which a DC component is superposed on a component, a bias in which a DC component is superposed on an AC component is applied to the color developing device at the time of development by the color developing device, and the black developing is performed. AC component into the vessel It is characterized in that a bias composed of a DC component having a polarity opposite to the charging polarity of the FF color toner is applied and the developer carrier of the black developing device is rotated.

(Embodiment) FIG. 1 is a schematic view of a copying machine used in the present invention. Reference numeral 1 is a photosensitive drum using OPC. The photosensitive drum uniformly charged by the charger 2 receives the optical image 5 corresponding to the original and forms an electrostatic latent image. Reference numeral 3 is a red toner developing device and 4 is a black toner developing device.

This device is configured to develop one color with one light image. When you want to make a two-color copy, you develop two light images with each developing device, so as to obtain two colors. The copy method is used. The image visualized by the developing device is a paper (not shown) by the transfer charger 7.
And is separated from the drum 1 by the separation charger 8 and sent to a fixing device (not shown). The toner slightly left at the transfer portion is cleaned by the cleaning device 9, and the surface potential is adjusted by the pre-exposure device 10, and then the next cycle is started.

In the present embodiment, the OPC used was one having a surface potential of 700 V charged, and the toner polarity was positive in both red and black. For the development, jumping development was used for both colors. Magnetic toner for black toner, Japanese Patent Application No. 58-15102 for red toner
The non-magnetic toner shown in 8 was used. When developing with black toner for the first time, 1200 Vp-p 150
A bias condition in which a DC component of −200 V was superimposed on an AC of 0 Hz was applied. At this time, the AC bias was OFF and the DC bias was -400 V to the red toner developing device 3 under the condition that the red toner was not developed. At this time, the sleeve of the developing device 3 for red toner was not rotated.

Under this condition, the red toner was hardly developed. If the bias value is set to a value higher than this, the reverse toner on the sleeve on the drum facing surface tends to be slightly developed. On the contrary, when the bias value is set to a low value on the minus side, the sleeve is stopped, so that only the drum-opposing surface is developed, but it is not further developed. Further, the toner developed on the portion corresponding to the drum-opposing surface could be cleaned by the cleaning device 9 by developing the toner on the non-image portion, and did not appear on the image.

Next, when developing with red toner, a bias condition for normally developing red toner was applied to the developing device 3 for red toner, but 1200 Vp-p, 1500 Hz as in the case of black development.
The DC of -200V was superposed on the AC of.
At this time, AC is applied to the developing device for black toner as a bias.
Was OFF, and DC voltage of -600V was applied. At this time, the sleeve of the black developing device was rotated.

The red non-magnetic toner scatters slightly downward, but was captured by the black sleeve under this bias condition and did not scatter below. The background fog on the image was also improved. The amount of red toner captured by the black sleeve was very small and did not appear as a color mixture at the time of the next development of black toner.
Actually, even if about 20% of red toner was mixed in the developing device, it did not appear on the image.

In the above-described embodiment, two colors of red and black have been described, but the same applies to the case where there are two or more color toner developing devices.

(Effects of the Invention) As described above, according to the present invention, since the toner scattering from the color developing device is captured by the black developing device, it is not necessary to provide any additional means for capturing and the device configuration is simplified. Can be converted.

[Brief description of drawings]

FIG. 1 shows a schematic view of a copying machine. In the figure, 1 is a photosensitive drum, 3 is a developing device for red toner, and 4 is a developing device for black toner.

Claims (1)

[Claims] 1. A movable image bearing member, and a black developing device for developing a latent image on the image bearing member by providing a rotatable developer bearing member bearing a black toner at a position facing the image bearing member. ,
A rotatable developing agent carrying member carrying a non-magnetic colored toner other than black is provided at a position facing the image carrying member to develop a latent image on the image carrying member; The black developing device is arranged on the downstream side of the color developing device with respect to the moving direction of the carrier, and both of the black developing device and the color developing device can apply a developing bias in which a DC component is superimposed on an AC component and a multicolor developing bias can be applied. In the image forming apparatus, at the time of development by the color developing device, a bias in which the DC component is superimposed on the AC component is applied to the color developing device, and the polarity opposite to the charge polarity of the color toner in which the AC component is turned off is applied to the black developing device. Is applied and a developer carrier of the black developing device is rotated, the multicolor image forming apparatus.