JPS6144213Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus that prevents developer from adhering to areas other than predetermined positions on a photoreceptor when performing reversal development in an electrophotographic apparatus.

Conventionally, in electrophotographic reversal development in an electrophotographic device, a method has been used in which the toner of the developer is not applied to the charged parts of the electrostatic latent image, but the toner is applied to the uncharged parts. There is. For example, the surface of a photosensitive drum made of selenium, zinc oxide, or the like is uniformly charged by corona discharge in a dark place. Next, a light image is exposed to a charged portion of the photoreceptor drum by an exposure section to form an electrostatic latent image.

Therefore, if a toner with the same polarity as the charge is used and a bias voltage of the same polarity is applied for development, the toner will adhere only to the areas where the electric charge has disappeared due to the incidence of light, and the toner will not adhere to the areas where the electric charge remains.
So-called reversal development is obtained.

However, when developing with this method, if there is an uncharged portion on the surface of the photoreceptor drum, the toner adheres thereto, apparently in the same state as the exposed portion where the charge has disappeared. That is, since the toner is deposited on unnecessary locations, there are problems in that not only is the toner wasted, but the inside of the device is also stained by the toner.

The present invention has been developed in view of the above circumstances, and its purpose is to provide an electrophotographic apparatus that can perform development without toner adhering to unnecessary portions that are not previously charged.

An embodiment of the present invention will be described below based on the drawings. In the figure, 1 is a photoreceptor drum that rotates in the counterclockwise direction of the arrow, 2 is a charger that charges the surface of the photoreceptor drum 1 by uniformly corona discharge, and 3
4 is an exposure unit for obtaining an electrostatic latent image by performing imagewise exposure on the surface of the photosensitive drum 1 to attenuate the charged charges, such as an optical fiber cathode ray tube (hereinafter referred to as OFT); 4 is a magnetic This is a developing device that develops an electrostatic latent image while applying a bias voltage to the external conductive surface of the roll 5. Development is performed by applying the OFT 3 to a charged portion of the photoreceptor drum 1.
This light causes the toner to be electrostatically attracted to the areas that are no longer charged.

Further, reference numeral 6 denotes transfer paper to be placed in a stacked state, and the transfer paper 6 is taken out one by one by take-out rollers 7, 7 and is superimposed on the toner image formed on the photosensitive drum 1.

Reference numeral 8 denotes a transfer device that performs corona discharge from the back side of the transfer paper 6, and the transfer device 8 transfers the toner image onto the transfer paper 6. A fixing device 9 fixes the toner image attached to the transfer paper 6 by heating.

Furthermore, 10 is a cleaning device for removing toner remaining on the photosensitive drum 1 after transfer, and the photosensitive drum 1 cleaned by the cleaning device 10 is transferred to the next process. Note that 11 is a bias power source.

In such a transfer device, in order to form a toner image on the transfer paper 6 up to both ends of the optical image (in the drawing, both ends in the direction perpendicular to the paper surface), the effective width of the charger 2 (in the drawing, in the direction perpendicular to the paper surface) is required. Although it would be ideal to make the effective width of the OFT 3 and the effective width of the developing device 4 the same, the reality is that it is difficult to make them match in practice. Therefore, the effective width of charger 2 and developer 4 is set to OFT3.
It is conceivable to make the width wider than the effective width of . However, since the toner adheres to the spare area, the toner is wasted, and the toner also scatters inside the machine, causing dirt.

Therefore, the present invention focuses on the fact that in the case of reversal development, toner does not adhere to areas where charges remain. That is, in one embodiment of the present invention, the effective width of the charger 2 is made wider than the effective width of the developing device 4 in order to reliably apply charges to the above-mentioned extra portion.

Therefore, the toner adheres only to the portion where the charge due to the optical image projection of the OFT 3 is attenuated, and good transfer can be obtained.

Although one embodiment of the present invention has been described using OFT for optical image exposure, the invention is not limited to this; for example, optical exposure using a lens or exposure by scanning a laser beam may be used. . Further, the developing method is not limited to the dry method, and it goes without saying that the same objective can be achieved even in the case of a wet method.

As explained above, the present invention has practical effects in electrophotographic devices, such as making the effective width of the charging device wider than the effective width of the developing device, thereby preventing toner from adhering to unnecessary areas. .

[Brief explanation of the drawing]

The drawing is a schematic front view of an electrophotographic apparatus showing an embodiment of the present invention. 2... Charger, 3... Exposure section (optical fiber cathode ray tube), 1... Photoreceptor drum, 4...
Developing device.

Claims (1)

[Scope of utility model registration request] In a device that visualizes an electrostatic latent image formed on the surface of a photoconductor by a charger and an exposure section with a toner of the same polarity as the charger, the effective width of the developer is An electrophotographic apparatus characterized in that the effective width of the charger is wider than that of the charger.