JPS5927908B2 - electrophotographic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electrophotographic apparatus using a three-layered photoreceptor having an insulating layer on the surface that is used repeatedly. It is concerned with effective methods for preventing things that sometimes have negative effects.

The present invention relates to a three-layer photoreceptor basically comprising an insulating layer, a photoconductive layer, and a conductive support, a means for applying primary charging almost uniformly to the photoreceptor, and an alternating current corona at the same time as the original image light is irradiated. Secondary corona discharging means for discharging or corona discharge of opposite polarity to the primary charging. Next, a latent image is formed using a means for applying irradiation light almost uniformly to the surface of the photoreceptor, and then the surface potential of the photoreceptor is increased before developing means. The present invention provides an electrophotographic apparatus having a convergence charge eliminating means.

In conventionally used electrophotographic devices of this type, a plurality of corona discharger chargers are generally provided around a cylindrical or belt-shaped photoreceptor (hereinafter referred to as a photosensitive layer) and are linked to the operation of the device. It is common to perform latent image formation, transfer, etc. by switching between two states, a charging state and a stopped state.

In such devices, the surface potential of the photosensitive layer is often uneven immediately after the charger stops operating, and as is well known, if the photosensitive layer is left in that state for a long time, This may cause adverse effects such as uneven image density when used next time. In order to avoid such adverse effects, in the xerographic method using a photosensitive layer provided with a photoconductive insulating material on the surface of a conductor, as described in U.S. Pat. No. 2,297,691, as is well known, the photosensitive layer All you have to do is irradiate the entire surface with light to discharge the charges. However, in an electrophotographic method using a three-layered photosensitive layer having a support, a photoconductive layer, and an insulating layer, as disclosed in Japanese Patent Publication No. 4223910, the photosensitive layer is irradiated with light. Even though
Since the insulating layer is insulating, the charge is still trapped, so the charge is not lost by itself. FIG. 1 shows an electrophotographic apparatus 1 based on the invention disclosed in Japanese Patent Publication No. 42-23910.

The photosensitive layer 1 provided on the surface of the metal cylinder 11 (hereinafter referred to as photosensitive drum) is uniformly charged by about +13
00V (if the photoconductive layer is a P-type semiconductor (d)), then by applying an alternating current of about 7.6KV to an AC corona discharger 3, which removes the charge and simultaneously irradiates the original image. , an electrostatic latent image is formed on the surface insulating layer of the photosensitive layer 1 due to the difference in surface charge density. Next, by uniformly exposing the entire surface of the photosensitive layer 1 using the entire surface exposure lamp 4,
It creates a difference in surface potential depending on the brightness of the original image, forming a high-contrast electrostatic latent image. At this time, the photosensitive layer has a voltage of +500V in the dark part of the original image and -120V in the bright part. Next, toner was attached to the latent image using the developing device 5 to form a visible image on the photosensitive layer 1, and a voltage of about +6.5 KV was applied to the recording material fed from the paper feed guide 12. Corona transfer is performed by the transfer charger 6. After the transfer, the recording material is separated and sent to the fixing device 7. On the other hand, the toner remaining on the photosensitive layer 1 is removed by a cleaner 8 after the transfer, and the photosensitive layer 1 is reused. In the above-mentioned electrophotographic apparatus, generally, immediately after completing a series of operations,
The photosensitive layer 1 becomes extremely non-uniformly charged, and leaving it in this state will have adverse effects such as uneven image density the next time it is used. Incidentally, in FIG. 1, the potential distribution on the photoreceptor in this state is shown by a broken line. Therefore, conventionally, for example, the operation of the primary charger 2 and the transfer charger 6 is stopped, and while light is applied to the photosensitive layer 1 by the entire surface exposure lamp 4,
A method is known in which the AC corona discharger 3 is operated and the photosensitive drum 11 is rotated separately from the copying process to remove the charge from the photosensitive layer 1. However, when static electricity is removed using an AC corona, the potential of the photosensitive layer generally tends to become negative. Furthermore, as shown in Japanese Patent Publication No. 4,726,911, it is desirable that the corona used for AC charge removal simultaneous exposure emphasize the corona with the opposite polarity to the primary charge.
When the primary charge is positive, the AC corona discharger 3 is desirably designed to emphasize the negative corona. In such a case, if the charge is removed by AC corona without applying a primary charge, the photosensitive layer 1 will be strongly negatively charged. As a result of an experiment using an AC corona that moderately emphasized the negative corona,
It was found that the potential of the photosensitive layer reached -380V in just 2 to 3 rotations. If the potential of the photosensitive layer is set to such a low potential, the potential of the electrostatic latent image will be uniformly lowered the next time it is used, and a good image, such as an image with poor halftone reproduction, will often not be obtained. In addition, when trying to make the charge on the photosensitive layer 1 uniform with a charger other than the AC corona discharger 3, the AC
After stopping the operation of corona discharger 3, primary charger 2 and A
As the photosensitive drum 11 rotates, the uniformly primary charged photosensitive layer located between the C corona dischargers 3 is transferred to the developing device 5.
A large amount of developer adheres to the photosensitive layer 1 through the front surface of the photosensitive layer 1, causing problems such as contaminating the apparatus. The present invention aims to eliminate such drawbacks.

The present invention will be described in detail below with reference to Examples. In Figure 2, 2 is a primary charger, 3 is an AC corona discharger, and 10
1 is an AC static eliminator for converging the surface potential of a photosensitive drum according to the present invention, and is provided within the beam of uniform light irradiation over the entire surface. Further, a high voltage is applied to the primary charger 2, AC corona discharger 3, and corona charger 6 from a first high voltage transformer, and a high voltage is applied to the AC static eliminator 10 from a second high voltage transformer. When the original image is not irradiated onto the photosensitive drum 11, the AC static eliminator 10 operates to converge the photosensitive drum surface potential to zero volts. This is because positive and negative ions are mutually generated from the charged wire of the AC static eliminator 10 and attempt to reduce the potential on the surface of the insulating layer to zero. In the case of this embodiment, it is sufficient to select the AC applied voltage in the range of 5 to 7 KV. Further, the higher the frequency, the higher the surface potential convergence efficiency due to AC static elimination, but this comes with drawbacks such as an increase in leakage current from the high voltage cable, so for practical purposes, about 400 Hz is good. Also, instead of AC applied voltage, DC
A voltage may be applied to the static eliminator 10. However, since it is necessary to have a convergence effect, it is better to use a grid as an example. Next, FIG. 3 shows a sequence diagram of an electrophotographic apparatus to which the present invention is applied. The operations at the operation switching points a to g may overlap to the extent that they do not cause any adverse effects on the device configuration. Next, the uniformization of the photosensitive drum surface potential at the end of copying when the present invention is applied will be described.

Here, the signal point e is defined as the position where the scanning of the original image for the final copy ends and the inversion signal of the optical system is input. Further, the signal point f indicates the position where the recording material has completed transferring the toner image on the photosensitive drum and has completely passed through the transfer charger 6. In other words, the time between e and f is approximately equal to the rotation time of the photosensitive drum 11 from the AC corona discharger 3 to the transfer charger 6. The first transformer stops operating at approximately the same time that the recording material comes out of the transfer charger 6, and from then on until the photosensitive drum 11 stops, the AC static eliminator 10 and the entire surface are Only the exposure lamp 4 acts, and the photosensitive drum 1
1. Eliminate static electricity from the insulating layer on the surface. Then, the AC static eliminator 10 full-surface exposure lamp 4 operates for more than one rotation of the photosensitive drum to equalize the potential over the entire surface of the photosensitive drum. Therefore, charging memory, optical memory, etc. that tend to occur when the photosensitive drum is stopped can be completely prevented, making it possible to obtain extremely high-quality images. As is clear from the above explanation, AC
The position where the static eliminator 10 is set must be between the AC corona discharger 3 and the developing means 5. In other words, the first
At the end of the operation of the transformer, the surface of the photosensitive drum 11 facing the primary charger 2 is approximately 13 mm thick, as shown in FIG.
When this part is charged to 00V and passes through the developing means 5 without surface charge removal by the AC static eliminator 10, not only toner but also a large amount of carrier is transferred to the photosensitive drum 11.
This is because the adsorbed carrier contaminates the inside of the machine, such as the transfer charger 6 and the cleaner 8, and this contamination causes problems such as machine failure. FIG. 4 shows an example of the timing control.

CP is a copy start signal from the copy button, DHP is a drum home position signal indicating that the photosensitive drum has come to a specific position, and is detected by a cam installed on the drum.
is a home position signal indicating that the document glass is in the normal position, BP is a back position signal that indicates that the document glass is at the position to move backward, and CUP is a signal for feeding the last sheet of the preset number of copies. The count-up signals shown are both generated by a cam installed on the document table and a micro switch on the machine body.
FF1 to FF3 are set by a pulse signal to terminal S, a step signal is output from terminal Q, a signal zero is output from terminal Q,
This is a flip-flop circuit that resets a pulse signal to terminal R and inverts its output. BC is a well-known binary counter that counts the DHP signal, and a decoder generates a 1 count signal and 1 and 2 count signals. This counter is set by the CP signal when it is I, by the output of G2 when it is set, and by the output of FF1 in both cases. T1 is a timer that delays the input signal by 900 rotation angles. STAT is a document platen forward movement start signal obtained from the drum image, and is generated slightly later than DHP. This is to remove the DHP from the image area. As described above in detail, the present invention provides a uniform charge-eliminating and uniform light irradiation means between a series of latent image forming means and a developing means, so that the surface of the photosensitive drum other than the original picture iron is removed by the operation of the charge remover. Since the potential is kept below the developable potential, excess toner consumption is prevented, and a large amount of developer is prevented from adhering to the photosensitive layer and contaminating the device. At the same time, extremely high-quality reproduced images with no image unevenness can be obtained. This makes it possible to provide an electrophotographic apparatus that obtains the following.

[Brief explanation of the drawing]

1 is a sectional view of an electrophotographic apparatus, FIG. 2 is a sectional view of an electrophotographic apparatus to which the present invention is applied, FIG. 3 is a sequence diagram, and FIG. 4 is a control circuit diagram. 1...Photosensitive layer, 2...Primary charger, 3
...AC corona discharger, 4...Exposure lamp, 5...1 developer, 6...Transfer charger, 10...AC Static eliminator, 11...
metal cylinder.

Claims (1)

[Scope of Claims] 1. The surface of the insulating layer of a rotating three-layer photoreceptor, which is basically composed of a conductive support, a photoconductive layer, and an insulating layer, is almost uniformly discharged by a first corona discharge means as it rotates. charged to,
Next, at the same time as the original image is irradiated, the surface of the insulating layer is exposed to alternating current or corona discharge of opposite polarity to the first corona discharge means by a second corona discharge means, and then the entire surface of the insulating layer is uniformly exposed by an entire surface exposure means. An electrophotographic apparatus that executes an image forming process by sequentially performing the steps of forming a latent image, then developing the latent image on a photoreceptor with a developing means, and then transferring the developed image to a recording material using a transfer means. In the above second
A third corona discharge means for neutralizing the photoreceptor is provided at a position between the corona discharge means and the latent image developing means and within the light flux of the entire surface exposure means.
An electrophotographic apparatus characterized in that the operation of the corona discharge means is stopped, and the operation of the third corona discharge means and the entire surface exposure means is continued while the photoreceptor rotates at least one more time after the image forming process is completed. . 2. The electrophotographic apparatus according to claim 1, wherein the third corona discharge means is an AC corona discharge means. 3. The electrophotographic apparatus according to claim 1 or 2, wherein the transformer of the third corona discharge means is different from the transformers of the first and second corona discharge means.