JPS59119365A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To prevent slipping of an image and to obtain a high-quality image by charging the surface of a photosensitive body using AC and giving photosensitivity. CONSTITUTION:In a state (A) just at the end of the first image formation, positive charge is brought into the adsorption layer 2a of a photosensitive body 10, and a negative charge corresponding thereto is induced. When the body 10 in this state is charged with unbalanced AC, negative charge due to negative ions emitted from a charger reaches the surface of the body 10 and begins to enter the adsorption layer 2a (B). It is attracted with positive charge present in the layer 2a and neutralises it. As a result, the charge in the layer 2a disappears and the surface of the body 10 is positively charged (C). Then, it undergoes imagewise exposure (D), development (E), and image transfer (F). Since the charge caught in the layer 2a is erased and resistance of the layer 2a does not lower, slipping of an image is avoided and a high-quality image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electrophotography using amorphous silicon photoreceptors.

When an image carrier is repeatedly used to form an image in an electrophotographic apparatus, a phenomenon called image deletion may occur. As a result, the charge of the electrostatic latent image is diffused on the surface of the photoreceptor, causing the boundaries of bright areas of the image to flow, degrading the quality of the formed image. The photoreceptor that is the image carrier is S+e
- In the case of CdS・0PC (organic photoconductor), or in the case of a photoreceptor whose surface is covered with a polymeric material such as polyester, the image blurring phenomenon occurs when the humidity is high. It doesn't happen when the humidity is low.

This is thought to be caused by moisture adsorbed on the surface of the photoreceptor.

However, when an amorphous silicon (hereinafter referred to as RA-3I) photoreceptor is used and the photoreceptor is used several thousand times, image deletion occurs even when the humidity is low. The characteristic of image blurring that occurs at such low humidity is that the degree of blurring becomes more significant in proportion to the number of times that images are continuously formed.

Figure 1 shows the occurrence of image deletion caused by low humidity in an a-Si photoreceptor, and the vertical axis represents the degree of image deletion;
The horizontal axis indicates the number of consecutive uses of the photoreceptor. There is almost no flow during the first use, but the flow becomes worse with each use. When the flow reaches about 100 times, the flow does not get any worse and becomes stable. If you stop using the photoconductor for 1 hour, leave it for about 1 to 2 minutes, and then start using it again, there will be almost no flow the first time after restarting, and after that, it will flow every time, just like the previous continuous use. The severity of this condition becomes severe and remains stable.

When the photoreceptor is left for 5 seconds, the flow after restarting is as shown by the dotted line, which causes a considerable flow even the first time, and becomes worse with each subsequent time, until it reaches a level that is approximately the same as the stable state described above. stable in the state.

This image blurring that occurs at low humidity is thought to be caused by the following mechanism.

Figure 2 (1) is a cross section of an amorphous silicon photoreceptor.
■ is a conductive substrate such as aluminum or nickel (in the following example, the substrate is electrically grounded), 2 is a-
It is a photoconductor of St. When this photoconductor 2 is used a considerable number of times, toner, paper components, components in the outside air, etc. are adsorbed to the surface and a very thin layer is deposited on the surface of the A-5I layer 2 (see Figure 2).
An adsorption layer 2a as shown in ) is formed. This adsorption layer 2
When the surface of a is charged with corona, the charge on the surface is slowly taken into the adsorption layer 2a with a time constant of several seconds. Since the charge taken into the adsorption layer 2a lowers the electrical resistance of the adsorption layer 2a, the latent image charge moves in the lateral direction of the adsorption layer 2a, causing layer flow. When the binding force is removed, the charges taken into the adsorption layer 2a are released from the adsorption layer with a time constant of several tens of seconds. Therefore, if the photoreceptor is used carefully for about 1 to 2 minutes as described above, image deletion will not occur immediately after restarting.

Figure 3 shows the changes in charging state and charge during this period.
(a) shows the first image forming process, (b') shows the second and subsequent steps, and the image forming process uses the Carlson process.
It is followed. As is well known, the Carlson process uses a photoreceptor that does not have a transparent insulation W on its surface.
Immediately before image exposure, the surface of the photoreceptor is uniformly charged (for convenience, this is referred to as photosensitive charging), and the charges resulting from this charging are discharged in correspondence to the exposed image pattern. This is a process in which a charged pattern is used as an electrostatic latent image and developed. In the first step (a), (a) shows the case where the photosensitizing charge is uniformly applied, and the positive charges have started to move into the adsorption layer 2a, but have not yet been incorporated. In (b), image exposure 4 is performed to form an electrostatic latent image, during which time the charge is gradually taken in. Next, in (c), development is performed with the toner T having a negative charge, but since not much charge is taken in, no image flow occurs. (d) is a step in which the transfer material 5 is positively charged from the back side and the developed toner is transferred. After this, the remaining toner is cleaned and the image forming process is started again.

While repeating the above steps several times, the amount of charge taken into the adsorption layer 2a gradually increases. Then, the same figure (b
In the charged state shown in (a) when the a-3i layer 2 is charged to impart photosensitivity, not only the surface of the a-3i layer 2 has a charge, but also the charge is taken into the adsorption layer 2a. (B)
When image exposure 4 is performed at , the surface charge in the bright area disappears, but
Since the charges taken into the adsorption layer 2a are located inside, they hardly disappear. In the bright area, the potential becomes low because the asserted charge has disappeared, so in the adsorption layer 2a, which has absorbed the charge and has a low resistance, the charge moves toward the bright area (indicated by a dotted line). At the time of development, as shown in (c), the M-absorbing layer 2a
Since the charges have moved, the electrostatic latent image is developed in a diffused and flowing state. It is transferred onto the transfer material 5 as shown in (d). This state becomes an image of low humidity flow.

As the amount of charge taken into the adsorption layer 2a increases, the degree of image blurring becomes more severe, and when the amount of charge taken in reaches a saturated state, the degree of layer flow becomes constant.

The above is the mechanism by which image blurring occurs, but the present invention is an electrophotographic method that prevents such image blurring and makes it possible to obtain high-humidity images even with worn-out photoreceptors. .

That is, it is charged by alternating current to eliminate the charges taken into the adsorption layer 2a, and is also charged to impart photosensitivity to prevent image deletion.

FIG. 4 shows a wiring diagram of the corona charger 6 and the power supplies 8 and 9 for charging by alternating current. An 8t DC power supply and 9 an AC power supply are connected in series.

Therefore, a biased alternating current as shown in FIG. 5 is applied to the charging wire 7 of the charger 6.

In the section indicated by A in the figure, a positive voltage is applied, so corona ions of positive polarity are generated, and in the section B, a negative voltage is applied, so corona ions of negative polarity are generated. If we compare the amount of generated ions integrally, we can see that the amount of positive corona discharge is greater than the amount of negative corona discharge because the alternating current is biased toward the positive side, and the surface of the photoreceptor is positively charged to impart photosensitivity. Ru.

FIG. 6 shows the change in charge when an image is formed by charging by alternating current. Figure (A) shows the state of charge when the first image forming process is completed.
This corresponds to (a) in FIG. 3(b). A positive charge is taken into the adsorption layer 2a, and a corresponding charge is transferred to the conductive substrate 1.
is induced by. When the photoreceptor in this state is charged with biased alternating current, the negative charge caused by the negative ions emitted from the charger reaches the surface of the photoreceptor and begins to penetrate into the adsorption layer, as shown in (b). . At this time, the infiltration speed is attracted by the positive charges in the adsorption layer, so the positive charges are neutralized during the charging process much faster than when the adsorption layer has no charge or has charges of the same polarity. As a result, the charge in the adsorption layer disappears, and the surface of the photoreceptor is charged to impart photosensitivity to pressure, as shown in (c). That is, the state is the same as (a) in FIG. 3(b).

The subsequent steps are image exposure (d), development (e), and transfer (f).
is carried out, and the process from charging by alternating current is repeated again.

In this way, in the process of photosensitizing charging, the charges taken into the adsorption layer 2a disappear, so that the resistance of the adsorption layer 2a does not decrease. As a result, latent image charges are not diffused, image deletion can be prevented, and an extremely high quality image can be obtained.

The above description has been made regarding the case where the photoreceptor is positively charged to impart photosensitivity, but the a-3i photoreceptor can form an image even if it is charged to either the positive or negative polarity. In the case of negative photosensitization charging, the same effect can be obtained by charging with alternating current in which the amount of negative corona discharge is greater than the amount of positive corona discharge. In this case, as for the voltage applied to the charger 6, if a negative voltage is applied by the DC power source 8 and an alternating current from the AC power source 9 is added thereto, the amount of negative discharge will increase. Further, even if alternating current is applied only by the alternating current power source 9 without the direct current power source 8, the same effect can be obtained because more negative corona ions are generated in the air.

FIG. 7 shows an example of an electronic copying machine that implements the electrophotographic method of the present invention. The drum 10 of the a-5i photoreceptor rotates in the direction of the arrow and is charged by the corona charger 6 to impart photosensitivity. An electrostatic latent image is formed thereon by image exposure by the optical system 13. The electrostatic latent image is visualized by toner supplied from the developing device 14, and the image toner is transferred onto the transfer material 5 by the transfer charger 15. The image toner on the transfer material is fixed, while the remaining toner on the drum 10 is cleaned by a cleaner 16. Furthermore, the surface of the drum is illuminated by a uniform exposure lamp 11 to remove surface charges. Next, photoactivation is applied once again by alternating current, and at this time, the charge taken into the adsorption layer disappears.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the extent of image blurring, Figure 2 is a cross-sectional view of the photoreceptor, Figure 3 is a diagram explaining changes in charge, Figure 4 is a wiring diagram of the charger and power supply, and Figure 5 6 is a diagram illustrating the change in alternating current voltage, FIG. 6 is a diagram illustrating the change in electric charge when charging is performed according to the present invention, and FIG. 7 is a schematic diagram illustrating an example of an electronic copying machine implementing the present invention. . 6 is a charger, 8 is a DC power source, 9 is an AC power source, and 10 is a photoreceptor 6

Claims (1)

[Claims] (1) Carlson with amorphous silicon photoconductor
An electrophotographic method in which an image is formed by a process, which is characterized in that the surface of a photoreceptor is charged with photosensitivity by alternating current.