JPS5949583B2 - electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new electrophotographic method, in particular an electrophotographic method in which a constant image potential is always obtained by eliminating uneven electrostatic latent image potential during repeated use of a photoreceptor. It is about law.

The present applicant previously proposed an electrophotographic method as described in Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-24748.

In these electrophotographic methods, the surface of the insulating layer of a photoreceptor whose basic components are a conductive support, a photoconductive layer, and an insulating layer is coated with an electrode or corona discharge, etc., so that the photoconductive layer has N-type photoconductivity. In the case of P-type photoconductivity, the charge is positively charged, and in the case of P-type photoconductivity, it is charged negatively to form a charge of opposite polarity to the charge on the surface of the insulating layer near the interface between the photoconductive layer and the insulating layer. At the same time as the original image is irradiated on the surface, alternating current corona discharge or direct current corona discharge with a polarity opposite to the charged polarity is applied to the surface to change the charged state of the photoreceptor according to the light and dark pattern of the original image, and further uniformly cover the entire surface of the insulating layer. By exposing to light, charges near the interface between the photoconductive layer and the insulating layer corresponding to the dark areas of the original image are released, and an electrostatic image of the original image with high contrast is formed on the surface of the photoreceptor. Further, the electrostatic image is developed and visualized with a developer mainly composed of charged colored particles, and then the visible image is transferred to a transfer material such as paper using an internal electric field or an external electric field, and then This is an electrophotographic method in which an electrophotographic copy image is obtained by heating and fixing with an infrared lamp or the like, and after the transfer, the surface of the insulating layer is cleaned to remove remaining charged particles, and the photoreceptor is used repeatedly. . However, in the above electrophotographic method, if the photoreceptor is left in the dark for a long time, free carriers are captured in trap units within the photoconductive layer, resulting in an increase in the dark resistance of the photoreceptor. For this reason, when continuous copying is performed using the electrophotographic method described above, the density of the first copy image is higher than that of the second and subsequent copies, leading to unevenness in the density of the copies that are continuously reproduced. There were flaws. Further, when such a photoreceptor is used repeatedly, the previous electrostatic latent image remains as an optical memory in the photoconductor layer, which has the disadvantage of disturbing the new image that affects the next copying process.

As a method to eliminate the increase in dark resistance due to the electrophotographic photoreceptor being left in the dark for a long time and the drawbacks due to the optical memory of the previous copy, it is proposed to apply alternating current discharge before the electrostatic latent image forming process and simultaneously apply light irradiation. has been done.

However, in the above-mentioned electrophotographic apparatus, when copying is once stopped, the surface of the photoreceptor remains charged by each charging means, i.e., primary charging, secondary charging, etc. .

This has the disadvantage that charge memory is generated on the surface of the photoreceptor, which affects the subsequent copying process and causes image unevenness. A method for removing the image unevenness caused by the charged memory on the photoreceptor is to perform alternating current corona discharge and simultaneous light irradiation on the photoreceptor surface after the copying process is completed and before the equipment is stopped to eliminate static electricity from the photoreceptor surface. Proposed.

However, even if the charge memory removal method described above is carried out, the charge memory is not completely removed. This is considered to be based on the generation of new charge memory due to AC corona discharge and simultaneous light irradiation. SUMMARY OF THE INVENTION An object of the present invention is to provide a method that eliminates the above-mentioned drawbacks and enables good image reproduction from the beginning even after the copying process is stopped and then restarted.

Therefore, the electrophotographic method of the present invention uses a photoreceptor having an insulating layer on the surface of the photoconductive layer, and along the movement path of the photoreceptor,
In an electrophotographic method, the following are arranged and operated in this order: AC discharge/simultaneous exposure means, primary charging means, static elimination means that operates simultaneously with light image exposure, full surface exposure means, developing means, transfer means, and cleaning means. , after the copying process is completed, the AC discharge/simultaneous exposure means, the primary charging means, the static elimination means, and the entire exposure means are operated without applying photoimage exposure to maintain the photoreceptor surface potential at the dark area potential. . The details of the present invention will be explained below using specific examples with reference to the drawings. Figure 1 shows an example of an apparatus in which the electrophotographic method described in the above-mentioned Japanese Patent Publication No. 42-23910 was proposed earlier. The structure is such that the optical memory of the device is removed.

Hereinafter, each of the above-mentioned image unevenness removal methods and the method of the present invention will be explained based on the figures.

In the figure, a photoreceptor drum 1 has a photoconductive layer (which may be either N type or P type, but in this example, N type photoconductive) is provided on a conductive support layer, and an insulating layer is further provided on the surface of the layer. The basic structure is a photoreceptor. Each process means is arranged along the circumference of the photoreceptor drum rotating in the direction of the arrow, and after the memory on the photoreceptor is removed by the AC discharger 2 and the simultaneous exposure means 3,
A primary charger 4 generates a positive uniform charge. At this time, an appropriate primary charging potential is about 1000 to 2000V.
Next, the secondary AC discharger 5 removes the static electricity, and at the same time, the image exposure means 6 performs image exposure. After that, the entire surface exposure means 7
A high-potential electrostatic latent image is formed by rotating the entire surface. This electrostatic latent image is +30 in dark areas.
0 to 800Vs light O to 150V in the bright area. The electrostatic latent image is developed by a developing device 8 in the next step, and the visible image is transferred onto the transfer material P by the action of a transfer corona discharger 9.

The transferred image on the transfer material P is fixed by the fixing device 10.
On the other hand, the surface of the photosensitive drum is cleaned by a cleaning blade 11 and is reused. FIG. 2 shows the change in surface potential on the photosensitive drum due to the above-described copying process. Next, the method for removing the charge memory on the photoreceptor is to rotate the photoreceptor drum one more time after the copying process is completed in the first illustrated apparatus described above, and activate the AC discharge means 2 and the simultaneous exposure means 3. It is something that makes you

The broken line b in FIG. 3 shows the change in surface potential when the charge memory removal is applied to the copying process described above.
At this time, the surface of the photoreceptor drum becomes slightly negatively charged due to the characteristic of AC corona that tends to generate negative components. For this reason, it is thought that during the copying process in which negative carriers from the photoconductor layer are continuously discharged, injection of charge into the photoconductive layer becomes poor due to primary charging, but the static charge in the next copying process deteriorates. This results in a reduction in the dark potential of the latent image. This has resulted in the inconvenience of a decrease in image density while copying several to several dozen copies. The method of the present invention, which eliminates the above-mentioned drawbacks, will be explained below.

In the device shown in FIG. 1 described above, after performing the step of forming an electrostatic latent image as shown in FIG. The surface of the photoreceptor is positively and uniformly charged by the device 4. Next, static electricity is removed by the secondary AC charger 5. Thereafter, the entire surface is exposed to light 7 to maintain the surface of the photoreceptor at a substantially dark electrostatic potential. When the photoreceptor drum is stopped in this state, in the next copying process, there is less interference with the charge injection into the photoconductive layer due to primary charging, and a continuous, uniform and stable electrostatic latent image is created. can be formed.

The solid line a in FIG. 3 shows the change in surface potential when the charge memory removal method according to the present invention is applied after the copying step showing the second change shown in the figure is performed.

At this time, the surface of the photoreceptor is brought to a substantially dark potential between the end of copying and the stop of the drum, so the potential is +300 to +800V.

Next, in order to facilitate understanding of the present invention, examples of the present invention will be shown together with comparative examples.

First, FIG. 4a shows a case in which a method for removing charge from a charged memory is carried out by simply performing alternating current discharge and simultaneous exposure after the above-mentioned copying process is completed.

After setting the surface potential of the photoreceptor to -60 ■ by this method and leaving it for 24 hours, the dark area potential, intermediate area potential, and light area potential during the copying process were measured for each successive copying process. As can be understood from the figure, in this case, it was necessary to repeat the copying process to make about five copies until the surface potential stabilized, and the potential change during this time was about 50V or more. On the other hand, FIG. 4b shows a case where the method of the present invention is implemented.

According to the method of the present invention, the surface of the photoreceptor drum is set to about 500 V, left for 24 hours, and then the changes in the dark area potential, intermediate area potential, and light area potential in the copying process are repeated continuously according to the number of copies to be made. This is what is shown. As can be understood from the figure, in this case, the surface potential is always constant from the initial state and the potential change is 5V or less, which is 1/1 of the comparative example.
0 or less, very good results were obtained. Further, when carrying out the method of the present invention, the AC static eliminator 2 for optical memory removal, the simultaneous uniform exposure means 3, the secondary AC static eliminator 5, and the simultaneous optical image exposure means 6 shown in FIG. It has been found that preferable results can be obtained if the two are separated by a certain distance.

This is thought to be due to the effect of the exposure means on maintaining the next dark potential. FIG. 5 shows a comparison of the relationship between the exposure amount of the uniform exposure means for memory removal and the dark area potential when the distance a between the two is large and small.
The solid line indicates a case where the interval a is large, and the broken line indicates a case where the interval a is small.

In the first illustrated apparatus, the photoreceptor is approximately 10 (:7!L/se
When moving at c and the distance between the two is 10 mm, approximately 5
5m7! The measurements were taken when t.

As a result, as long as the distance a between the two is sufficiently maintained, even if the light intensity of the uniform exposure means is increased, there will be no hindrance to maintaining a sufficient dark potential. Also, it goes without saying that even if copies were made repeatedly, there was little change in density. Therefore, in this way, the AC static eliminator 2 and the simultaneous uniform exposure means 3, the secondary AC static eliminator 5 and the simultaneous optical image exposure means 6 are kept at appropriate intervals,
Get even better results. As detailed above, the present invention includes:
Since the surface of the photoreceptor is maintained at a uniform dark potential after the copying process is completed, images can be formed under the same conditions at the start of the next copying process, and good continuous copies without density changes can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus for carrying out the electrophotographic method according to the present invention, Fig. 2 is a potential change diagram showing changes in the surface potential of a photoreceptor based on the electrophotographic method, and Fig. 3 is a case where the method of the present invention is carried out. Figure 4 is a graph illustrating changes in surface potential in bright areas, dark areas, etc. during continuous copying, a is a comparative example, and b is a method of the present invention. . FIG. 5 is a potential exposure amount correlation diagram illustrating the influence of static elimination exposure on the dark area electrostatic latent image potential in the pre-copying process. In the figure, 1: photoreceptor, 2: AC discharger for static elimination, 3: simultaneous exposure means.

Claims (1)

[Claims] 1 Using a photoreceptor having an insulating layer on the surface of the photoconductive layer, along the movement path of the photoreceptor, an AC discharge/simultaneous exposure means,
Primary charging means, static eliminating means that acts simultaneously with light image exposure, full-surface exposure means, developing means, transfer means, cleaning means,
In an electrophotographic method in which the following are arranged and operated in this order, after the copying process is completed, the AC discharge/simultaneous exposure means, the primary charging means, the static elimination means, and the entire surface exposure means are operated without applying light image exposure, An electrophotographic method characterized by maintaining the surface potential of the photoreceptor at the dark area potential.