JPS60168164A - Electrophotographic apparatus - Google Patents

Abstract

PURPOSE:To prevent deterioration of image quality due to a toner attached to optional parts by exposing a prescribed part of a photosensitive drum and executing tertiary electrostatic charging between secondary charging and simultaneous imagewise exposure and uniform exposure. CONSTITUTION:An electrostatic latent image is formed on a photosensitive drum 4 comprising, from the surface, an insulating layer 1, a photosensitive layer 2, and a conductive layer 3 with a primary charger 5, a secondary charger and simultaneous imagewise exposing device 6 and a uniform exposing lamp 9. Then, it is developed with a toner in a developing device 10, the obtained toner image is transferred to a transfer paper 13 fed from a paper feed roller 12 with a transfer charger 11, the transferred toner image is fixed to the transfer paper 13 with a fixing device 14 composed of heating and pressing rollers, and the image fixed paper 13 is ejected. The drum 4 having the toner not transferred and remaining on the surface is cleaned of the residual toner with a cleaning device 15. In said process, a black-erasing exposing device 7 for irradiating unnecessary parts and a tertiary charger 8 are installed between the device 6 and the lamp 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic apparatus that basically forms an electrostatic latent image on a photoreceptor through simultaneous image exposure of primary charging and secondary charging and full-surface exposure.

Conventionally, in this type of electrophotographic device, when a photoreceptor is used partially due to differences in copy size or copy magnification, unnecessary parts such as areas outside the image area or areas before and after image exposure are used. Since secondary charging and simultaneous exposure are not performed, the surface potential is high and toner adheres to the surface, which causes more toner to be consumed than necessary, and unnecessary parts are transferred onto the transfer paper, reducing image quality. Ta.

The present invention aims to eliminate the above-mentioned drawbacks, and in the known image forming process, after the secondary charging and simultaneous image exposure, the above-mentioned unnecessary portions are exposed to light, and then the secondary charging is performed. A characteristic effect is that by performing tertiary charging with the same polarity as the secondary charging, the surface potential of that portion is lowered to prevent toner from adhering.

FIG. 1 shows an embodiment of the present invention. From the surface as shown in FIG. Simultaneous image radiator 6
・An electrostatic latent image is formed by the full-surface exposure lamp 9, and the developing device 1
0, the toner image is transferred to the transfer paper l\3 fed by the paper feed roller 12 by the transfer charger 11, and the toner image is transferred to the transfer paper 13 by the fixing device 14 consisting of a heating and pressure roller. The image is fixed and the paper is ejected. Further, the cleaning device 15 cleans the remaining toner from the photosensitive drum having toner on its surface that has not been completely transferred.

The present invention is a process according to item 2, in which a black-erasing exposure device 7 and a tertiary charger 8 are provided between the charging simultaneous image exposure device 6 and the entire surface exposure lamp 9 for irradiating the unnecessary portions. It is.

FIG. 3 shows an embodiment of the black eraser exposure device 7, in which the LED element 1
7 are lined up in a row, and the LED elements corresponding to the blacked-out portions are lit.

The operation will be explained below with reference to FIGS. 2(a) to 2(e).

(a) If the photosensitive layer 2 is an n-type semiconductor, the surface of the insulating layer is positively charged by first being positively charged by the negative charger 5, and the gap between the photosensitive layer 2 and the conductive layer is correspondingly charged. The induced negative charge moves the photosensitive layer to the boundary with the insulating layer. Next, (b) Image exposure 16 is performed while performing negative charging or AC static elimination using the secondary charging simultaneous image exposure device 6, but in the bright part of the image exposure 16, the resistance of the photosensitive layer 2 decreases and the surface of the insulating layer 1 decreases. At the same time as the positive charge is removed, the negative charge existing between the photosensitive layer 2 and the insulating layer 1 moves to the conductive layer 3 and disappears, and there is no change in subsequent processes.

In the dark and blackened areas of the image exposure 16, the positive charge on the surface of the insulating layer 1 is removed to some extent, and a corresponding amount of positive charge is induced between the photosensitive layer 2 and the conductive layer 3.

(C) Next, the black-erasing exposure device 7 exposes the black-erased portions to lower the resistance of the photosensitive layer 2, so that the positive charge existing between the photosensitive layer 2 and the conductive layer 3 and the corresponding amount of the photosensitive layer 2 are removed. The negative charge existing between the insulating layer 1 and the insulating layer l disappears. Since the image area is not exposed to blackout, there is no change in the dark area.

(d) Next, by charging with the tertiary charger 8 having the same polarity as the secondary charging, the positive charge on the surface of the insulating layer 1 is removed to some extent in the blackened area, and the photosensitive layer 2 and conductive layer 3 are charged by a corresponding amount. A positive charge is induced between them. The condition of the image exposure area is almost the same as in the case of secondary charging and simultaneous image exposure. Next, (e) uniform exposure is performed using the entire surface exposure lamp 9. There is no change in the bright areas of image exposure because the charges have already disappeared, but in the dark areas and blackened areas of image exposure, the photosensitive layer 2 As the resistance decreases, the positive charge existing between the photosensitive layer 2 and the conductive layer 3 and the corresponding negative charge existing between the photosensitive layer 2 and the insulating layer 1 disappear, and the positive charge existing on the surface of the insulating Nl disappears. The amount of charge is expressed as surface potential.

(f) Next, by performing development under development conditions such that the blackened areas are not developed and the dark areas of the image exposure are developed, the image exposure is made visible and copying is performed without the blacked out areas being developed.

Example: Using the black-erasing exposure unit 7 shown in FIG. 3 and lighting the LED elements 17 in the portions corresponding to the black-erasing areas, image exposure was performed at 400 V for the dark areas, 0V for the bright areas, and 100 V for the black-era areas. The surface potential was , and a clear, high-quality copy image was obtained without background fog in the erased areas.

As explained above, by adding the step of exposing an arbitrary part to light and then performing tertiary charging with the same polarity as the secondary charging, between the simultaneous image exposure with secondary charging and the entire surface exposure, the arbitrary part can be This solves the problem of toner adhering to the surface and deteriorating image quality, and also prevents wasted toner consumption.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of an electrophotographic apparatus to which the present invention is applied;
FIG. 2 is an explanatory diagram of the latent image forming process of the present invention, and FIG. 3 is a schematic diagram of an embodiment of a black erasure exposure device. 4 is a photosensitive drum, 5 is a primary charger, 6 is a secondary charger and simultaneous image exposure, 7 is a black erasure exposure device, 8 is a tertiary charger, 9 is a full-surface exposure lamp, and 17 is an LED element. Figure 3 Figure 2 Light section ===: 11e Figure 1 (d) (e)

Claims (1)

[Claims] (1) In an electrophotographic device that basically forms an electrostatic latent image on a photoconductor by primary charging φ secondary charging simultaneous image exposure and full surface exposure, there is a gap between the secondary charging simultaneous image exposure and the full surface exposure. , means for exposing an arbitrary portion on the photoreceptor;
An electrophotographic apparatus comprising means for performing secondary charging and charging with the same polarity.