JPS60256166A - Electrophotographic developing device - Google Patents

Abstract

PURPOSE:To obtain an image of invariably stable density by providing an unexposed part at least one end of the surface of a photosensitive drum which is charged uniformly and electrostatically, and supplying the charging potential of the part to a developing sleeve through a short circuit. CONSTITUTION:A developing measn 4 has a developer storage container 4 made of an insulating material and the developing sleeve 42 which is stored therein and provided closely to the photosensitive drum. The unexposed area 3 is provided at the least one terminal of the drum 1. Further, the short circuit 5 is provided to connect an exposed area 31 to the developing sleeve 42, and this circuit 5 is made of, for example, a conductive metallic brush.

Description

Detailed Description of the Invention (Technical Field) The present invention is an electrophotographic device that utilizes the potential at the time of main charging of the drum photoreceptor as the bias potential without using a dedicated transformer for the bias potential in the developing area. It relates to a developing device.

(Prior Art) In electrophotography, a photoreceptor provided with a photoconductive layer is first charged by means such as corona discharge.

Image exposure is performed to form an electrostatic latent image on the surface of the photoreceptor. Then, a developer is applied to the surface of the photoreceptor to form a toner image corresponding to the electrostatic latent image ~υ, which is electrostatically transferred to copy paper and fixed to obtain a copy. . The toner remaining on the photoreceptor is removed by the next cleaning process and prepared for the subsequent copying cycle.

The latent image type (q is the photoreceptor-1-) used for image formation.

Usually, it ranges from several hundred mV to several hundred thousand mV. The electric field is
It ranges from about 0.01 to 80 μm/μm. However, as mentioned above, photoreceptors are used repeatedly.

The residual potential of the photoreceptor gradually increases, the photodegradation speed slows down, and the electric field strength of the latent image becomes relatively low. Even after the TL of the electrostatic latent image formed on the surface of the photoreceptor has been transferred and cleaned.

It remains on the surface of the photoreceptor and gradually accumulates. This causes fogging during the next copying operation and also causes electrical deterioration of the photoconductive layer.

On the other hand, when the light decay rate is slow, the toner is electrostatically attracted to the photoreceptor surface with a relatively strong attraction even after the transfer process is completed, and as a result, the transfer efficiency of the toner onto the copy paper decreases. becomes lower.

Furthermore, unnecessary removal operations are required to remove the residual toner from the surface of the photoreceptor, which may cause IN scratches on the surface of the photoreceptor.

In order to obtain a stable toner image without being affected by an increase in the residual potential generated on the photoconductor or a decrease in the light attenuation speed, a bias voltage is supplied between the photoconductor and the opposing electrode. . However, the bias potential is constantly supplied from a constant voltage/current source.

Bias control according to the potential of the photoreceptor is not performed.

Alternatively, if you try to control it, other sensors are required.

(Objective of the Invention) An object of the present invention is to provide an electrophotographic developing device that can always maintain stable density and provide images with excellent contrast. Another object of the present invention is to simplify the developing device, thereby reducing costs and reducing the size and size of the device.
The objective is to eliminate the use of electrophotographic developing devices that have become corrupted.

(Structure of the Invention) In the developing device of the present invention, an unexposed portion is provided at at least one end of the uniformly charged surface of the photoreceptor drum.

The above object is achieved by supplying the charging potential of the unexposed portion of the development zone to the development sleeve via a short circuit.

(Example) The present invention will be described below with reference to one embodiment.

As the developing device of the present invention, a commonly used device can be used as is. As shown in the figure, the apparatus of the present invention includes a photosensitive drum 1. Charging means 2 disposed near this drum 1
．． An exposure means 3 and a development means 4 are provided downstream thereof. The developing means 4 includes a developer storage container made of an insulating material and a developing sleeve 42 accommodated therein and provided close to the photosensitive drum 1 .

At least one end of the drum 1 has an unexposed area 31 .

The developing device of the present invention further includes a short circuit 5 that electrically connects the unexposed area 31 of the rollers J and (2) with the developing sleeve 42. This short circuit 5 is composed of, for example, a conductive metal brush.

The photosensitive drum 1 includes, for example, a conductive substrate 11 and a photoconductive photosensitive layer 12 provided thereon. The conductive substrate 11 is.

It does not need to be anything special; for example, it may be a conductive metal such as aluminum or a resin film treated to be conductive. The photosensitive layer 12 also does not need to be special; usually, an inorganic photosensitive layer such as selenium or zinc oxide, or an organic photosensitive layer such as polyvinylcarbazole, which has desired charging characteristics, is used as appropriate. For example, the charging means 2 may be one.

The corona charger charges the photosensitive layer 12 to, for example, a positive charge depending on the charging characteristics of the photosensitive layer.

Charging is usually carried out so that the surface voltage is within the range of 5500 to 100 OV. The exposure means 3 forms an electrostatic latent image corresponding to the original image on the surface of the photoreceptor.

The exposure means 3 comprises a light source and an optical system for forming a light beam image of the original image on the photosensitive layer 12. At this time.

An unexposed area 31 at at least one end of the drum l is configured not to be exposed.

The surface of the developing sleeve 42 is made of a non-magnetic and conductive material, and a magnet, for example, is provided behind it. The developing sleeve 42 is housed in the developer storage container 41 together with the developer 44 . The storage container 41 is made of an insulating resin material such as polyethylene terephthalate. The developer 44 is a two-component developer composed of a toner made of various pigments and a resin binder, and a magnetic carrier that gives charge to the toner, or a one-component magnetic developer using only toner. A developer is used as appropriate. Is the toner polarity static? it'f;1
The toner has a polarity opposite to that of the fourth image, and is charged to a negative polarity for a positive latent image. The developer 44 is.

For example, a magnetic brush is formed on the developing sleeve.

The electrostatic latent image is developed with toner by bringing this magnetic brush into contact with the photosensitive layer 12. At this time, since the unexposed area 31 of the drum 1 and the developing sleeve 42 are electrically connected through the short circuit 5, the surface potential of the unexposed area 31 is constantly supplied to the developing sleeve 42. This potential is.

It has the same function as a commonly used bias potential. Moreover, there is no need to control the bias potential as in the case of conventional bias potentials, and the bias potential of the developing area is determined according to the amount of charge of the latent image on the photoreceptor 12 in the developing area, so correction control is automatically performed. It will be the same thing.

As a result, a stable toner image free from fog can be obtained at all times, regardless of an increase in the residual potential generated on the photoreceptor drum 1 or a decrease in the light attenuation rate. When this toner image is electrostatically transferred to transfer paper, a visible image with excellent contrast is obtained. Further, since there is no need to provide a bias transformer for supplying a bias potential as in the prior art, the developing device can be simplified, lighter, and smaller.

The short circuit 5 is not limited to a conductive member such as the conductive metal brush described above, and the conductivity of the developer may be used. In this case, it is necessary to extend the magnetic brush of the developing sleeve to the unexposed area. Further, in order to always maintain the bias potential supplied to the developing sleeve 42 through the short circuit 5 at a predetermined level, 9, for example, Tr! , a pressure regulating diode, etc. may be employed.

(Effects of the Invention) As described above, the developing device of the present invention can determine the bias potential of the developing area according to the amount of charge on the surface of the photoreceptor in the developing area, without providing a dedicated transformer. , it is possible to always supply images with stable density and excellent contrast.

Since there is no dedicated transformer, the developing device can be simplified.
As a result, costs can be reduced and the device can be made smaller and lighter.

[Brief explanation of drawings]

The figure is a perspective view of essential parts showing an embodiment of the developing device of the present invention. ■...Photosensitive drum, 2...Charging means, 3...1 stage of exposure 54...Developing means, 5...Short circuit, 11.
...Conductive substrate, 12... Photoconductive photosensitive layer 531...
- Unexposed area, 41...Developer storage container, 42...
Developing sleeve, 44...developer. Applicant: Sanda Kogyo Co., Ltd. Attorney, Shusaku Yamamoto, Patent Attorney

Claims (1)

[Claims] 1. An unexposed area is provided on at least one end of the uniformly charged surface of the photosensitive drum, and the charged potential of the unexposed area in the developing area is supplied to the developing sleeve via a short circuit. An electrophotographic developing device comprising: 2. The electrophotographic developing device according to claim 1, wherein the short circuit is a conductive metal brush. 3. The electrophotographic developing device according to claim 1, wherein the short circuit is a carrier in the developer.