JPS6039233B2 - electrophotographic method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic method for consistently forming high quality images.

Conventionally, there is a method of forming a static exposure latent image in the following order using a three-layer photoreceptor consisting of an insulating layer, a photoconductive layer, and a conductive substrate.

In other words, by using an N-type or P-type semiconductor material as the photoconductive layer, the surface of the photoreceptor is charged in a reverse manner with the majority carriers in the photoconductive layer (primary charging). }Next, this is a method of obtaining a static exposure latent image by creating a difference in the surface potential of the photoreceptor corresponding to the bright and dark areas of an image that has been subjected to AC charging and image exposure. FIG. 1 shows a schematic diagram of the electrophotographic method.

On the drum-shaped three-layer photoreceptor 1, there are a primary charging station 2, an AC charging/simultaneous exposure station 3-1.
, an electrostatic latent image is formed, and at the development station 4,
Development is performed using fine particles charged with a certain polarity, and the developed particles are transferred onto a transfer paper 6 at a transfer station 5. Fine particles remaining on the photoreceptor 1 are removed at a cleaning station 7, and the photoreceptor reaches the primary charging station 2 again, where the above process is repeated. In the electrophotographic method described above, a widely used device constituting the AC charging/simultaneous exposure station 3-1 is a charger that utilizes corona discharge.

During charging, a voltage V greater than the corona discharge starting voltage Vc is applied to the corona discharge wire to generate a corona discharge current 1, thereby charging the photoreceptor 1 moving relative to the charger. imparts a charge to.
In electrophotography, what is particularly important is to stably obtain the final visible image, in other words, to stabilize the electrostatic latent image, development transfer, etc. Obtaining an electrolatent image is important.

Further, in this case, it is important to make the difference in surface potential of the photoreceptor 1 corresponding to the bright and dark parts of the image as large as possible in order to obtain a clear visible image. - By the way, the AC charging/simultaneous exposure station 3-1 uses a conventional constant voltage AC high voltage power source 8.
It consisted of a charger connected to a For this reason, the temperature
When the corona discharge resistance changes due to atmospheric conditions such as humidity or changes in the distance between the corona discharge wire and the surface of the photoreceptor, the corona discharge current 1 changes, and therefore corresponds to the bright and dark areas of the image on the photoreceptor 1. The value of the surface potential and the difference between the two were fluctuating. Even if corona is discharged by a constant current AC high-voltage power source, this phenomenon may occur due to changes in the corona discharge resistance due to atmospheric conditions such as temperature and humidity or changes in the distance between the corona discharge wire and the surface of the photoreceptor. Since the applied voltage fluctuates, it was not sufficiently compensated for. Although attempts have been made to control the voltage applied to the corona discharge wire by detecting the surface potential of the photoreceptor 1, this method has the disadvantage of complicating the apparatus. Furthermore, in order to maximize the difference in surface potential of the photoreceptor 1 corresponding to the bright and dark areas of an image, the conventional latent image forming method using AC corona discharge in an AC charging/simultaneous exposure station is as follows. I couldn't escape the points of dissatisfaction that I would like to explain.

FIG. 2 shows a pattern of static exposure latent image formation in a conventional secondary charging/simultaneous exposure station 3.

A is a transparent insulating layer, B is a photoconductive layer (here, a case having N-type semiconductor properties is shown), and C is a conductive substrate. 1
, , 12 are the thicknesses of the photoconductive layer B and the transparent insulating layer A, respectively.
, q2 are the conductivities of the photoconductive layer B and the transparent insulating layer A, respectively.
, qo, and q are the amount of charge on the transparent insulating layer A at the end of the AC charging and simultaneous exposure process, and the amount of charge on the transparent insulating layer A and the photoconductive layer B, respectively.
The absolute value of the amount of charge at the boundary between photoconductive layer B and conductive substrate C is the amount of charge at the boundary between photoconductive layer B and conductive substrate C.

'' indicates the arrangement of charges at the end of primary charging, (A' indicates the progress of AC charging and simultaneous exposure, and [U' indicates the arrangement of charges at the end of AC charging and simultaneous exposure. [A] The right half of } and [u} corresponds to the bright part of the image, and the left half corresponds to the dark part of the image.
The potential inside the photoreceptor at the end of simultaneous exposure is shown in line with the photoreceptor. The solid line L is the potential curve corresponding to the bright part of the image, and the broken line D is the potential curve corresponding to the bright part of the image.
is the potential curve corresponding to the dark part of the image. Although FIG. 2 shows an ideal case assuming that there are no charges trapped in the photoconductive layer B, most of the actual trends can be explained by this. Now, of the electrostatic tank image finally obtained in 'u),
The surface potential VL corresponding to the bright part of the image and the surface potential Vo corresponding to the dark part of the image are expressed using the symbols shown in FIG.

From this, the difference Vc between the two (hereinafter referred to as contrast potential Vc) is given by:

However, q3, qe', q, q2 corresponding to the bright part of the image
, q also mean q, , q2 corresponding to the dark part of the q-color image. Here, when the AC charging and simultaneous exposure process is performed using a charger using the secondary AC high-voltage power supply 8, as shown in A, the corona discharge resistance corresponding to the dark part of the image is It was inevitable that the AC charge amount would be smaller in the dark areas of the image than in the bright areas. This is the formula '3', which reduces the first term and increases the second term (q color > q three)
This was one of the causes of the decrease in the contrast potential Vc. Therefore, it is an object of the present invention to deal with fluctuations in atmospheric conditions such as temperature and humidity,
It is possible to stably obtain a visible image by performing corona charging that is substantially unaffected by changes in corona discharge resistance due to changes in the distance between essentially increasing the difference in surface potential of the body 1.

The present invention achieves the above objects by using AC corona discharge with a constant current difference instead of conventional AC corona discharge.

In AC corona discharge, the current difference between the positive component current 1 of the corona discharge current 1 and the negative component current le is △1 = 1 reason - le
(hereinafter referred to as current difference Δ1) focuses on the point that determines the surface potential due to charging. That is, in AC charging, regardless of the magnitude of the total current amount of corona discharge, when Δ1=0, the surface potential of the photoreceptor 1 does not change due to AC charging (zero charging tendency). , △1>
When the voltage is 0, the surface potential of the photoreceptor 1 becomes △ due to AC charging.
1 (positive charging tendency), △1<
When the value is 0, the surface potential of the photoreceptor 1 becomes △1 due to AC charging.
changes in the negative direction depending on the size of (negative charging tendency)
. In the present invention, charging is performed by alternating current corona discharge with this current difference Δ1 kept constant to form a static latent image.

FIG. 3 shows a schematic diagram of an electrophotographic method using an AC charging process according to the present invention.

9 is an AC transformer, 1 river inverter, 11 is a DC current detector, 12 is an amplifier, 13 is a DC controller, and 14 is a DC generator.

The current difference Δ1 of the high voltage output is detected by the DC current detector 11 and input to the DC controller 13 through the amplifier 12-1. The DC controller 13 provides feedback to the DC generator 14 to maintain the current difference at a predetermined value. Further, the shield of the charger forming the AC charging/simultaneous exposure station is composed of an insulating shield that is transparent at least in the optical path portion. That is, when three sides other than the closed part are constructed with insulating shields, corona discharge is extremely insufficient in DC charging and is not practical, but sufficient corona discharge can be obtained in AC charging.
Moreover, since the difference in current flowing outside through the shield can be made substantially zero, the difference in output current becomes the current difference Δ1 in corona discharge. In this way, if the DC controller 13 is set so that the current difference becomes zero, AC charging will occur with zero charging tendency, and D
If the C controller 13 is set, AC charging has a positive charging tendency, and if the DC controller 13 is set so that the current difference is negative, AC charging has a negative charging tendency. The primary charging can be stabilized by supplying a high voltage output having any of these charging tendencies to the corona charger of the primary charging station. FIG. 4 shows the arrangement of charges inside the photoreceptor 1 at the AC charging/simultaneous exposure station when an electrostatic latent image is formed by the method shown in FIG.

The meanings of the symbols are the same as in Figure 2. The difference from FIG. 2 is that when AC charging and simultaneous exposure proceed, equal amounts of charging are applied to areas corresponding to bright areas and areas corresponding to dark areas of the image.

This is a constant current difference (△
In some cases, this becomes possible only by applying and producing AC charging (1<0). If we pay attention to the contrast potential Vc at the end of secondary charging and simultaneous exposure, we can make the first term large (q also → large) and make the second term zero ( qe=q colors), the contrast potential Vc increases. This is an important improvement in making the visible image clearer. Next, FIG. 5 shows the temporal characteristics of the surface potential of the photoreceptor 1 during electrostatic latent image formation by the conventional method and the method of the present invention. (1) is by the conventional method, and (b) is by the method of the present invention. It can be seen that the contrast potential Vc increases because the surface potential D corresponding to the dark part of the image can be moved significantly in the negative direction compared to the conventional method. FIG. 6 shows another embodiment.

15 is an AC current detector, 16 is a DC current detector, 17 is an AC controller, and 12-2 and 12-3 are amplifiers.

The output current difference Δ1 of the AC transformer is kept constant in the same manner as shown in FIG. 1 2 through the AC controller 17 respectively.
is input to the DC controller 13, and in response to this, the DC-AC
Feedback is provided to the inverter 0 and the DC generator 14, respectively, and control is performed to keep the output power constant. By supplying the AC output controlled in this way to the corona discharge wire, the corona discharge current difference △1 can be kept constant, and the voltage applied to the corona discharge wire can be kept constant, so temperature, humidity, etc. Even if a change in the corona discharge resistance occurs due to a change in the atmospheric condition or a change in the distance between the corona discharge wire and the photoreceptor 1, the surface potential of the photoreceptor 1 does not substantially change. Therefore, conventional AC corona discharge and D
Instead of constant voltage and constant current control, which is theoretically impossible to achieve with C corona discharge, AC corona discharge can control constant voltage and constant current differences. A coexisting effect can be obtained, and a stable electrostatic latent image can be obtained.

Note that the same effect can be obtained by using a conductive shield instead of the insulating shield. Incidentally, if the photoreceptor has a high memory capacity, it is possible to sequentially perform primary corona charging, exposure, and secondary corona charging, which is particularly effective when the influence of corona discharge resistance due to brightness and darkness of exposure remains.

It is also possible to sequentially perform primary charging, secondary charging, and exposure. The present invention is not limited to the so-called copying process in which an original image is exposed to light to form a latent image.

It can also be applied to processes that form latent images using light beams. It can also be applied to processes without a primary charging step. As described above, in the present invention, the charging process is carried out by AC corona discharge in which the current difference between the positive component and the negative component is kept constant. Electrophotography that forms a static latent image that is stable against changes in corona discharge resistance due to changes in the state of the image, and that can maintain good contrast by increasing the difference in surface potential of the photoreceptor corresponding to bright and dark areas of the image. The law is fulfilled.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an electrophotographic method using secondary AC charging;
Figure 2 is a schematic diagram showing the charge distribution within the photoreceptor and the finally obtained potential characteristics when forming an electrostatic latent image by secondary AC charging and simultaneous exposure, and Figure 3 is a diagram showing the constant current difference of the present invention. A schematic diagram of the electrophotographic method using charging, FIG. 4 shows the AC charging and
A schematic diagram showing the charge amount arrangement within the photoconductor and the finally obtained potential characteristics when a static latent image is formed by simultaneous exposure, FIG. FIG. 6 is a schematic diagram of an electrophotographic method with another embodiment of AC charging according to the present invention. 1...Photoreceptor, 2...Primary charging station, 3-1,
3-2: Secondary charging/simultaneous exposure station, 4: Developing station, 5: Transfer station, 6: Transfer paper, 7: Cleaning station, 81: DC high voltage power supply, 9: AC transformer, 10 ...Inverter, 11
・・DC current detector, 12-1, 12-2, 12-3・
- Amplifier, 13...DC controller, 14...DC generator. Figure 1: Figure 3: Purple Z Figure: Leopard 4: Tsutomuyo Figure: Figure 5

Claims (1)

[Claims] 1 In electrophotography, in which charging by alternating current corona discharge and image exposure are performed simultaneously on a photoreceptor to form an electrostatic latent image,
Performing the AC corona discharge by supplying power from a DC power source and an AC power source, and detecting a difference between a positive component current and a negative component current of the AC corona discharge current by detecting the DC component of the AC corona discharge, An electrophotographic method characterized in that the DC power source is controlled according to the detected value so as to keep the difference constant.