JPS60232584A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To enhance image quality, and to prevent light memory action of an electrophotographic sensitive body and deterioration of sensitivity due to light by arranging an electrostatic precharger reverse in polarity to primary charging before or after a preexposure section, and executing primary charging and preexposure at least for one rotation of a photosensitive drum. CONSTITUTION:The photosensitive drum 1 is charged to a constant potential with a primary charger (Figure A), imagewise exposed to form an electrostatic latent image (Figure B), subjected reversal development with a developing device (Figure C), and a toner image is transferred to a plain paper with a transfer charger 5 reverse in polarity to the primary charging to obtain a positive image from a negative image (Figure D). After the drum 1 is cleaned of a residual toner, it is charged to a polarity reverse to that of the primary charging with the precharger 7 provided with grids (Figure E), and at the time of successive copying, it is advanced immediately to the primary charging step. When copying is finished, transfer charging and precharging are turned off, and the primary charging and preexposure are carried out for at least one rotation of the drum 1.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention relates to electrophotography, and particularly to electrophotography using a photosensitive drum type transfer method.

[Conventional technology]

Primary charging on photosensitive drum Image exposure, reversal development, transfer charging -
Electrophotographic processes in which cleaning and pre-exposure are applied sequentially are known.

[Problem that the invention seeks to solve]

In the above conventional electrophotographic process, the transfer charge has a polarity opposite to the primary charge, that is, if the primary charge is negative, the transfer charge is positive. Therefore, unless a photoreceptor sensitive to both positive and negative charges is used, the surface potential of the drum during continuous copying will have a polarity opposite to that of the primary charge due to the transfer charge. Therefore, that potential is erased (hereinafter referred to as erasing)
In order to do this, pre-exposure is performed before the next charging, but this has the disadvantage of increasing the memory rather than achieving the purpose.

This invention aims to solve the above problems.

Structure of the Invention [Means for Solving the Problems] A photosensitive drum is charged to a constant potential with a primary charger (Fig. 2A showing potential fluctuations of the photosensitive layer), and an electrostatic latent image is formed by imagewise exposure. To form a toner image (Fig. 2B), perform reversal development with a developing device (Fig. 2C), - Transfer the toner image onto plain paper using a transfer charger with a polarity opposite to the charging polarity, and convert the negative image into a positive image. obtain(
Figure 2D).

After cleaning the residual toner, a potential with a polarity opposite to that of the primary charging is applied using a pre-charging device having a grid (FIG. 2E), and when continuous copying is performed, the process immediately shifts to the primary charging process.

At the end of copying, transfer charging and pre-charging are turned off, and sub-charging and pre-exposure are performed for at least one revolution of the photosensitive drum.

[Effect]

Due to the transfer charging, the portion of the photosensitive drum that was at the bright area potential becomes the potential of the transfer charging polarity, and a charged portion with opposite polarity is generated on the drum surface (FIG. 2D). Therefore, conventionally, pre-exposure is applied to erase this potential, but
Since it does not become completely zero, the memory of the latent image from the previous process still remains, and erasing is not performed, reducing the image quality in the next cycle.

Therefore, in this invention, pre-exposure is not performed at one time during continuous copying, but instead, the polarity is opposite to that of the primary charge (same polarity as the transfer charge).
Perform pre-charging to make the positive and negative charging potentials on the surface of the photosensitive drum equal to the pre-charging polarity and uniform (Fig. 2E), erase the memory of the previous cycle, that is, perform potential cleaning, and prepare for the next step. Primary charging is performed uniformly over the entire surface.

At the end of the copying operation, only secondary charging and pre-exposure are performed for at least one rotation of the photosensitive drum. Then, the surface of the photoconductor, which has been potential-cleaned by the pre-charging in the previous cycle, is primary charged at a constant potential, and then the pre-exposure is performed. Therefore, the surface potential becomes close to zero.

〔Example〕

FIG. 1 shows a schematic diagram of an apparatus for carrying out the method of the present invention, in which 1 is a photosensitive drum having a photoconductive photoreceptor layer 1b formed on the surface of a grounded conductive support 1a, and 2 is a monolithically charged photosensitive drum. 3 is an image exposure path for a light beam modulated with a document image or an image signal, and 4 is a reversal developing device that attaches 2 toner to the Meito potential area (the toner is charged with the same polarity as the primary charger 2). 5 is a transfer charger with a polarity opposite to that of the primary charger, P is a transfer paper, 6 is a cleaner for removing residual toner, and 7 is a pre-charger with a polarity opposite to that of the primary charger 2, which uniformly charges the surface of the photoreceptor. It has a Glyad 71 for converging the potential. 8 is a pre-exposure path. Note that the same effect can be obtained even if the pre-charger 7 described above is placed after the pre-exposure path 8.

Since the apparatuses for each of the above processes are similar to those known in the art, explanations of their individual configurations will be omitted. As shown in the table below, for example, if the next charge is set to -, then the transfer charge and the pre-charge are set to 10, and the foreshock light 8 is turned off at the time of continuous copying.

When copying is completed, the transfer charger 5 is turned off by the end signal, and then the front charger 7 is also turned off, and only the charging by the negative charger 2 is continued for at least one rotation of the photosensitive drum l. At this time, pre-exposure 8 is performed.

The above sequence control can be performed using a known method.

C. Effects of the Invention In an electrophotographic process using a drum type transfer method, as described in the above section of the operation, - the potential on the photoreceptor is made uniform before charging, and - the potential unevenness on the photoreceptor due to secondary charging is reduced. This improves the image quality since most of the noise can be eliminated. Also, since the entire surface of the photoconductor is not pre-exposed during continuous copying,
This has the effect of suppressing the optical memory and sensitivity deterioration of the electrophotographic photoreceptor due to light to a lower level than usual.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus implementing the present invention, and Fig. 2 is a schematic diagram illustrating potential fluctuations in each process.l is a photosensitive drum, 2 is a monolithic charger, 3 is a fIl exposure optical path, and 4 is a reversal developing device. , 5 is a transfer charger, 6 is a cleaner, 7 is a pre-charger with a grid, and 8 is a pre-exposure optical path. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) In an electrophotographic process in which a photosensitive drum is subjected to primary charging, image exposure, reversal development, transfer charging, cleaning, and pre-exposure in that order, a pre-charger with a polarity opposite to that of the primary charger is placed before or after the pre-exposure section. However, during continuous copying, the pre-exposure described above is turned off. An electrophotographic method characterized in that upon completion of copying, the transfer charging and pre-charging are turned off, and -sub-charging and pre-exposure are performed for at least one rotation of the photosensitive drum.