JPS59143167A - Copying corona discharger - Google Patents

Abstract

PURPOSE:To prevent the intensive peak of copying corona and to transfer the toner pictures with high quality by protruding a shielding member like eaves to the traveling direction of a transfer material from its feeding side so as to cover over the most approximate part between a corona discharge line and an image carrier. CONSTITUTION:A corona discharge lines 72 are strung within a shielding case 71 having a U-shaped cross section which serves as a shielding member. Then an eaves part 73 of the case 71 is protruded from the incoming side to the traveling direction of a transfer material so that it covers over the most approximate part between the lines 72 and a photosensitive drum 1. This part 73 functions to prevent the effect of the corona discharge to the transfer material which is guided by a pair of guide plates 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applied to a transfer type image forming apparatus such as a transfer type electrophotographic device or a recording machine, and is used to discharge a transfer material superimposed on a developed image on an image carrier. The present invention relates to a corona discharge device that transfers the developed image to a transfer material by applying corona discharge from the back side.

FIG. 1 shows a very schematic configuration diagram of a conventional transfer type image forming apparatus equipped with a corona discharger. Reference numeral 1 denotes a photosensitive drum as an image carrier, which is rotatably supported in the direction of the arrow. 2 is an electrostatic latent image forming section that forms an electrostatic latent image on the photosensitive tram 1''; 3 is a developing section that visualizes the electrostatic latent image;
A cleaning section 4 removes toner remaining on the photosensitive drum 2 after transfer from the photosensitive drum.

The transfer material P is aligned in timing with the rotation of the photosensitive drum 1 by a pair of register rotors 5, and guided by a pair of guide plates 6, so that the photosensitive drum 1 and a corona discharge device (hereinafter referred to as a discharge device) 7 face each other. The image is fed to the transfer section A where the image is transferred. Transfer part A
Then, the developed image on the photosensitive drum is transferred onto the transfer material P by the corona discharge of the discharger 7. After the transfer is completed, the transfer material P is
It is separated from the photosensitive tram 1 by a separation roller 8 and sent to a transport system 10 (not shown) via a transport girder (+' 9).

However, in recent years, the transfer type image forming apparatuses are becoming more energy efficient and more compact in order to meet the increasing demand for personal use. In order to achieve this miniaturization, if the entire conventional device shown in Fig. 1 is reduced by -4., the discharger 7 becomes smaller and the gap becomes smaller, causing the corona discharger to become unstable and leakage of the corona discharge t, -4. There will be 4 things. Therefore, even if the diameter of the photosensitive tram l is made smaller, the size of the discharger 7 cannot be made proportionally smaller, and as shown in FIG. 2, the size of the discharger 7 needs to be approximately the same as the conventional one. However, when the diameter of the photosensitive drum 1 is made smaller, the following problems will occur unless the size of the discharger 7 is made smaller in accordance with the diameter of the drum.

(1) Although the contact width between the photosensitive drum 1 and the transfer material P is extremely narrow, the corona discharge width of the discharger 7 is wide (this is due to the fact that the discharger is not miniaturized).
When exposed to corona discharge with a gap between the two before electrodeposition and after peeling off, image blurring (toner scattering around letters, etc.) and hollowing (toner falling out of letters) occur. Produces a shade.

C2) Since the used width between the photosensitive drum 1 and the transfer material P is narrow,
If the rich and young portions of both layers do not match the peak portions of corona discharge, uneven transfer (uneven development density) will occur.

Therefore, in order to narrow the corona discharge width of the discharger 7, the third
As shown in the figure, it is conceivable to bend both ends 71a @ 71b of the shield case 71, which has a U-shaped cross section as a shield plate, to face each other, but in this configuration, the peak of the corona discharge from the corona discharge wire 72 is exposed to light. Acting on the drum 1, the electric field becomes strong at the peak position and weak at other positions. For this reason, if the contact area of the transfer material P with the photosensitive drum 1 is shifted upstream or downstream in the axial direction of the photosensitive drum, or if the width of the used clothing differs in the coaxial direction, the transfer rate will vary depending on the contact width or position. Accordingly, the transfer becomes non-uniform, resulting in uneven transfer.

The present invention has been proposed in view of the above, and an object of the present invention is to obtain a transfer corona discharger suitable for an image forming apparatus having a smaller overall configuration.

The present invention, which achieves the above object, is characterized in that a shield member is provided in an eaves-like manner from the transfer material entrance side in a direction in which the transfer material advances so as to cover the closest portion between the corona discharge wire and the image carrier. do.

The embodiments shown in the drawings will be described below. FIG. 4 is a schematic diagram showing an embodiment of the corona discharger for transfer according to the present invention, in which a corona discharge wire 72 is stretched in a shield case 71 having a U-shaped cross section as a shield member. An eaves portion 73 is provided so as to protrude from the transfer material entry side of the shield case 71 in the transfer material advancing direction so as to cover the closest portion of the shield case 71 and the photosensitive drum l.

With the above configuration, the eaves section 73 has a function of preventing corona discharge from acting on the transfer material P. (1) The transfer material P travels along the eaves section 73 and completely adheres to the photosensitive tram 1. Since the image is then subjected to a corona discharge effect, image blurring and hollow spots do not occur.

+2) Since the eaves portion 73 covers the line A-1-2 connecting the corona discharge line 72 and the center of the photosensitive drum l, that is, the closest portion between the two, the transfer material P is not subjected to the peak of corona discharge. As a result, the transfer material P receives a uniform corona discharge of approximately - from the corona discharge amount L1 of the shield case 71, and even if the contact width with the photosensitive drum 1 deviates slightly, the transfer rate etc. do not change. Good transfer can be performed without causing uneven transfer.

Effects such as this can be obtained.

FIG. 5 shows another embodiment of the corona discharger for transfer according to the present invention, in which a metal shield case 71 is grounded, and an insulator 74 is provided on the inner surface of the shield case on the transfer material discharge side and on the inner surface of the eaves part.
In this example, the spread of the corona is suppressed by the electric charges on the surface of the insulator 74, and the above-mentioned effects can be more prominently obtained while improving the discharge efficiency.

FIG. 6 shows still another embodiment, in which the eaves part 73 forms a part of the transfer material guide 6, and since the transfer material guide can be shortened, the image forming apparatus can be made smaller. It is effective for

As described above, according to the transfer corona discharger configured according to the present invention, it is possible to apply a bias electric field for transfer without generating a strong transfer corona peak. Therefore, even when the transfer material is not in contact with the toner image carrier with a sufficient nip width or the contact portion is offset from the rotational axis direction of the drum, the toner image is not disturbed, and the transfer is possible. The toner image can be transferred satisfactorily without causing non-uniformity of the image.

Note that the corona discharger of the present invention can be applied not only to a developed image on a photosensitive drum but also to an insulating drum or a belt-shaped toner carrier that draws an arc in a transfer section.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an image forming apparatus equipped with a conventional corona transfer device, Figure 2 is a smaller version of the image forming apparatus.
FIG. 3 is a schematic diagram showing a modification of the transfer device in which the corona discharge opening is narrowed. 71 is a shield case, 72 is a corona discharge wire, 73 is an eaves portion, and 74 is an insulator. Figure 3 Figure 5 "V 7Z a: Mi,: l j-Ding Xiao-2'L,'

Claims (1)

[Claims] (1) In a corona discharger used to transfer the developed image to the transfer material by applying corona discharge from the back side of the transfer material superimposed on the developed image on the image carrier, the corona discharge wire and the image carrier A corona discharge device characterized in that a shield member of the corona discharge device is provided in an eave-like manner from the transfer material entry side in a direction in which the transfer material advances so as to cover the closest portion of the corona discharge device.