JPS6141155A - Image forming method - Google Patents

Abstract

PURPOSE:To extend the life of an amorphous silicon photosensitive medium by effecting charging electrostatically 200msec. after light erasing in an image forming on the medium. CONSTITUTION:Around a photosensitive drum 1, which has an amorphous silicon photoconductive layer on a conductive base of aluminum, for instance, there are disposed in the mentioned order a charger 2, an exposure slit 3, a developing unit 4, a transfer separation charger 5, a cleaning unit 6 and an eraser lamp 7. The outputs of the charger 2 and eraser lamp 7 are set to the values such that they have no adverse effects on the photosensitive medium and other elements when they are actually used repeatedly. For example, the output of the charger 2 is set such that the photosensitive medium current is 200muA, and the output of the eraser lamp 7 is set to 48crg/cm<2>. The time from the eraser light illumination till the charging is set to be longer than 200msec. Thus, a satisfactory surface potential can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image forming method using an amorphous silicon photoreceptor.

2. Description of the Related Art The use of amorphous silicon in electrophotographic photoreceptors has been proposed in numerous publications and documents, including Japanese Patent Application Laid-open No. 78135/1983.

This amorphous silicon photoreceptor is made of cadmium, which has traditionally been used as an electrophotographic photoreceptor.

Its surface hardness is significantly higher than that of selenium, arsenic, etc. For this reason, a great deal of research is currently being conducted to put amorphous silicon photoreceptors into practical use.

Problems to be Solved by the Invention When the amorphous silicon photoreceptor described above was installed in a copying machine that uses a conventional photoreceptor and its electrophotographic characteristics were examined, it was found that it was not charged even though its electrical resistance was sufficiently high. However, in order to increase the photoreceptor current, it was necessary to increase the output of the charging device and increase the photoreceptor current. To achieve this, the charging device must be made larger, which not only increases cost but also increases power consumption.Furthermore, increasing the photoconductor current dramatically shortens the life of the photoconductor. also occurs.

The present invention has been made in view of these points, and an object of the present invention is to provide an image forming method that can put an amorphous silicon photoreceptor into practical use without increasing the photoreceptor current.

Explanation of Principle The present inventors have considered the reason why the charging ability of an amorphous silicon photoreceptor is extremely low despite its sufficiently high electrical resistance, and has concluded that the following reason may be one of the reasons.

That is, as shown in FIG. 3, electrons existing in the valence band of amorphous silicon absorb the energy (h
ν), it is excited to an energy level that exists near the bottom of the conduction band. The holes generated in the valence band are not free, but are bound to the electrons excited to this level. As shown in FIG. 4, electrons and holes in such a state attract each other and are in a metastable state, so they do not generate a photocurrent and do not cause a change in the surface potential of the photoreceptor.

However, when a strong electric field is applied in this state to overcome the Coulomb force that binds electrons and holes to each other through the electrophotographic process of charging, the electrons and holes are separated as shown in Figure 5. It will be observed as holes or split currents. As a result, as shown in Figure 6,
A portion of the charge on the surface of the photoreceptor is neutralized, which is observed as a decrease in surface potential or charging ability. This phenomenon is remarkable in amorphous silicon because it has a large localized level density.

The above phenomenon, that is, a decrease in surface potential or chargeability can be prevented by removing the electron-hole pairs existing in the photosensitive layer before charging the photoconductor.

The present inventors focused on the property that excited electrons generally release their energy over time and return to their original stable level, and the electron-hole pairs generated in amorphous silicon also The following experiment was conducted based on the inference that it would disappear with the

Experiment Figure 7 shows the amount of erase light (Er) and photoreceptor current (Ipc) necessary to charge an amorphous silicon photoreceptor to +600V, and the time from irradiation of erase light to charging (
The results of measurement by varying T) are shown.

As is clear from this graph, the charging time (T) from erase light irradiation is from 70m5ec to 110m5ec.
, 220 m5ec, the charging ability of the photoreceptor improves. For example, erase light amount (
When Er) is 3 Q ergB/d, time (T)
or 7QfnBeQ, the photoconductor current (Ipc) is approximately 4
00A.

The time (T) is 1i omse.
When c is about 250JjA, time (T) is 220m8e
When C, it is only necessary to flow about 150 μA, and the time (T) is 220 m5ec compared to when the time (T) is 70 ω.
When this happens, the charging ability is improved by about 3 times.

'From the above results, the charging ability of an amorphous silicon photoreceptor can be improved by making the time from irradiation of erase light to charging longer than the predetermined time during which the electron-hole pairs generated during irradiation of erase light disappear. I came to the conclusion that it can be done.

Means to Solve the Problems Based on the above experimental results, as an image forming method that increases the surface potential of an amorphous silicon photoreceptor without increasing the photoreceptor current flowing through it, we have developed an image forming method that increases the time from irradiation of erase light to charging. It is set to a predetermined time or longer for the electron/hole pairs generated during the erasing light irradiation to disappear.

The electron-hole pairs generated in the photosensitive layer during irradiation with the action erase light disappear before a strong electric field is formed due to charging, so the charge imparted to the photoreceptor surface is Neutralization by holes is prevented, and the surface potential does not decrease.

Embodiment FIG. 2 is a diagram for explaining the image forming method according to the present invention, and (1) is a photosensitive drum formed by forming an amorphous silicon photoconductive layer on a conductive substrate (for example, aluminum). , around it are a charger (2) and an exposure screen! J) (3), a developing device 1 (41), a transfer separation charger (5), a cleaning device [+61] and an eraser lamp (7) are arranged in this order. is set to a value that will not adversely affect the photoreceptor and other elements when actually used repeatedly.For example, the output of the charger (2) is set to a value that makes the photoreceptor current 200 μA. and the output of the eraser lamp (7) is 48 er
g8/cd j is set.

In order to determine the optimum value of the time required for the photoreceptor drum (1) to reach the charger (2) from the eraser lamp (force) in the apparatus described in Section 1, the following experiment was conducted.

In other words, we placed three types of amorphous silicon photoreceptors (LA) + (1B) + (IC) with different charging capacities, and varied the time from irradiation with erase light to charging, and observed changes in their surface potentials. As a result of the investigation, the graph shown in Figure 1 was obtained. As is clear from this result, when the time from erase light irradiation to charging is longer than 200m5eC, the surface potential increases uniformly depending on the time, whereas when it is shorter than 200m8eQ, the surface potential decreases rapidly. are doing. From this, it can be seen that the time from the erasing light agent to charging is 2000
It can be seen that a good surface potential can be obtained if it is m5eC or higher.

Based on this result, the time from when the photosensitive drum (1) is irradiated with the erase light until it is charged is set to 200 m5 ec or more. For example, when the circumferential speed of the photoreceptor drum fil is 26 an/sec, the eraser lamp (
The arrangement angle (θ) between the force and the charger (2) is 74.
Set to 5 degrees or higher.

In the above configuration, the photoreceptor drum (1) rotating counterclockwise is uniformly charged by the charger, imagewise exposed through the exposure slit (3), and an electrostatic latent image is formed. (4). The developed copy image is transferred onto a copy paper (not shown) by a transfer/separation charger (5), and the copy paper after transfer is peeled off from the surface of the photoreceptor drum (1). After transfer and separation, residual toner is removed from the photoreceptor drum +11 by a cleaning device (6), and residual charges are removed by an erase light emitted by an eraser lamp (force). After 200 m5 ec from 200 m5, uniform charging is performed by the charger (2), and the next copying process is executed.

Effects of the Invention As is clear from the above explanation, according to the present invention, it is possible to charge an amorphous silicon photoreceptor to a sufficient potential without increasing the photoreceptor current, thereby shortening the life of the photoreceptor. (Amorphous silicon photoreceptors can be put into practical use without the need to increase the size of the charging device.)

[Brief explanation of the drawing]

Figure 1 is a graph showing how the charging potential of amorphous silicon changes depending on the time from irradiation with erase light to charging. Figure 2 is a diagram showing an embodiment of the present invention. Figure 3 is a graph showing how the charging potential of amorphous silicon changes depending on the time from irradiation with erase light to charging. Figure 4 shows how electrons in silicon atoms are excited; Figure 4 schematically shows how electron-hole pairs are formed in the photosensitive layer immediately after irradiation with erase light; Figure 5. Figure 6 schematically shows the behavior of electron-hole pairs when a charge is applied to the surface of the photoreceptor in the state shown in Figure 4. Fig. 7 is a graph showing how the correlation between the photoconductor current and the amount of erase light when charging an amorphous silicon photoconductor to +600 cm changes depending on the time from irradiation of the erase light to charging. be. 1... Amorphous silicon photoreceptor, 2... Charger, 7... Eraser lamp. Applicant Minolta Camera Co., Ltd. Figure 1 Ey-CHG Tiwe (711sec”) Figure 2 Figure 3 Figure 4 Figure 5 Figure 4

Claims (1)

[Claims] 1. An image forming method in which an amorphous silicon photoreceptor is repeatedly subjected to photo-erasing, charging, and image exposure, characterized in that charging is performed 200 msec after photo-erasing.