JPS5944064A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To prevent variation in picture density due to the repetition of a continuous picture forming process by bringing the surface potential of a photoreceptor after a picture forming process approximate to a mean surface potential in the picture forming process, and setting a development bias after the picture forming process to a bias value which disallows transfer of a developer from a developing means to the photoreceptor. CONSTITUTION:The difference in photoreceptor surface potential between the 50th picture in 50-sheet continuous copying operation and the 1st picture is almost eliminated as much as possible by holding the surface potential of the photoreceptor after the picture forming process at a potential closest to the mean surface potential in the picture forming process (750V in this case), and even when numbers of copies are taken continuously, the difference in picture density is prevented from appearing according to the number of copies. At this time, a development bias voltage applied to a developing sleeve after the picture forming process is raised to about or above the 750V bias voltage during the picture forming process before the electrified photoreceptor surface faces the sleeve, and consequently almost no toner electrified negatively is transferred from the sleeve to the photoreceptor.

Description

[Detailed description of the invention] This invention relates to an electrophotographic method using a photoreceptor.

An electrophotographic method using a photoreceptor of many types is well known, but when the image forming process is continuously repeated using this method, the image density decreases as the number of sheets increases. The reason for this is that the surface position of the photoreceptor changes with the number of repetitions, and it becomes more noticeable as the speed of the image carrier forming process becomes faster. At the same time, the objective is to obtain high-quality and stable images.

In general, an electrophotographic method using the above-mentioned photoreceptor (i. unevenness in surface potential of the photoreceptor at the end of the image forming process)
In order to remove the memory, a charging process is provided to uniformize the level of frost on the surface of the photoreceptor. (The surface potential of the photoreceptor obtained in this charging step is hereinafter referred to as the surface of the photoreceptor after the completion of the III image forming process.) In this step. 11:
'), the surface potential of the photoreceptor is usually from o■ to -400
set to V.

In the present invention, the average surface potential of the photoreceptor (
time average) as close as possible to the
This is a method of preventing changes in the image limit even in the repetition of the conventional continuous image forming process.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows 2j4. 41j, a drum-shaped three-layer structure with a photoconductive layer in which CdS particles are dispersed with a binder on the second side of the aluminum substrate, and a transparent insulating layer on top of the photoconductive layer. With an electrophotographic copying film using photoreceptor 1)). Photoreceptor 1 rotates in the direction of the arrow.

- Before performing banding t, as step I, the pre-exposure lamp 2 is
At the same time, the surface of the photoreceptor 10 is irradiated, and at the same time, the charge is eliminated by the negative corona of the pre-discharge charger O, and the optical memory and charge memory are erased. Next, in step (2), the surface of the photoreceptor 1 is uniformly charged positively by the positive corona discharge of the primary charger 4, and a negative potential is secured. Next, in step 111, the optical image 6 of the original is projected onto the drum surface simultaneously with the negative or AC corona discharge of the secondary charger 5. Next, in step (2), the drum surface is uniformly irradiated with the entire surface exposure lamp 7 to form a static latent image. 8 is a developing sleeve, and photoreceptor 1
The photoreceptor 1 vc is rotated in the direction of the arrow with a layer of negatively charged toner 10 supplied from the dry toner supply box 9 on its surface.
, this toner is applied, and the latent image is developed and visualized in steps 1 and 17.

During the image forming process, a bias potential having a value between the bright area potential and the dark area potential of the latent image is applied to the sleeve 8, thereby making it possible to perform development while preventing edge phenomena and fogging. The transfer paper is sent by the conveyance roller 11, and in step (2), the photoreceptor 1 is charged by positive corona discharge of the transfer charger 12.
0 Transfer the toner image on the surface to transfer paper. The transfer paper is separated from the photoreceptor 1 by the separation roller 13 and sent to the fixing device, and in step Vll, the toner left on the photoreceptor 1 after the transfer is collected by the cleaner blade 14. One image forming process P is completed by steps I to (2) above. This process may be repeated continuously depending on the number of copies required, or it may be completed once and enter a rest period.

FIG. 2 shows the surface potential of the photoreceptor measured in the copying apparatus shown in FIG. In the figure, dark areas indicate the surface potential curves in the dark areas of the image, and bright areas indicate the surface potential curves in the bright areas of the image. From FIG. 2, the average surface potential (time average potential) of the photoreceptor during the image forming process in this example is approximately +
It is 750V.

Next, the surface potential of the photoreceptor after the completion of the image forming process is measured using the lamp 2. After erasing the original charge memory using the charger B, by operating the charger 4 and/or the secondary charger 5 while rotating the photoreceptor 1, the voltage is changed from -400 volts to +150 volts.
It changed and transformed down to 0 volts.

After resting for 30 minutes, potential changes on the surface of the photoreceptor during continuous copying of 50 sheets were measured, and the results shown in FIG. 6 were obtained. The original used had an optical reflection density of 0.6. In FIG. 6, the horizontal axis is the surface potential of the photoreceptor charged by the primary and/or secondary charger as described above after the image forming process is completed, and the vertical axis is the photoreceptor surface potential of the 50th image in 50 sheets of continuous copying. This is the difference between the body surface potential and the photoreceptor surface potential of the first image.

As is clear from the figure, by keeping the surface potential of the photoreceptor as close as possible to the average surface potential during the image forming process (75 ov in this example) after the image forming process, the difference in surface potential can be reduced to It will be as close to 0 as possible. In other words, even if a large number of copies are made in succession, it is possible to prevent differences in image sharpness from occurring depending on the number of copies. Furthermore, the body! #:, time is 1 hour.

Even when the time was set to 6 hours and 20 hours, similar results to those shown in FIG. 6 were obtained.

According to the present invention, as shown in step vllll in FIG. 2, after the image forming process is completed, while rotating the photoreceptor 1, the original memory and charged memory are first removed by removing the original memory and the charged memory, and then step). The primary charger 4 is activated by a gourd to bring the surface potential of the photoreceptor 10 over its entire width and circumference to 750 cm during the image forming process.
Make it as close to 0v as possible. At this time, the positive voltage applied to the negative charger 4 is made weaker than the positive voltage applied during the program ψ forming process, that is, the amount of corona discharge of the primary charger 4 is made smaller than that during the jLii image forming process. Alternatively, in step Vl, the secondary chargers 4, 50
Both may be used. In this case, if the voltage applied to the negative charger 4 is the same as that in the 1lIII image forming process, the negative voltage applied to the secondary band 't4 unit 517 is made weaker in step vm than in the image forming process.

In other words, if the positive corona discharge 11 of the primary electric appliance 4 is the same as that during the image forming process, then the negative corona discharge of the secondary electric appliance 5 should be smaller than that during the image forming process.
Converge the photoreceptor surface to the above 750V or 750V
It should be converged in the vicinity. In addition, in step Vl (charging process after the image forming process), secondary chargers 4 and 50 are used.
When both are operated, it is preferable that lamp 7 is also operated. This is because the amount of charge held in the photoconductive layer near the interface between the insulating layer and the photoconductive layer is balanced by the amount of surface charge on the insulating layer after partial static charge removal by the secondary charger 5 and the irradiation from the lamp 7. In addition, this is to prevent excessive electrical load from being applied to the photoconductive layer.

As explained above, the final charging step is carried out after the image forming step in which the surface potential of the photoreceptor C after the image forming step is set to a value close to the surface potential (time average value) of the photoreceptor during the image forming step. By implementing ii! in continuous image formation! ii) A stable image with no change in image density was obtained even during the high-speed image formation process.

However, if the surface potential of the photoreceptor is maintained at the average surface potential of the photoreceptor during the image forming process as described above during the rest period, toner from the developing sleeve 8 will be transferred and adhered to the surface of the photoreceptor. As a result, not only is toner wasted, but the development marks at this time appear on the image to be formed next time, resulting in an unsightly appearance.

Therefore, after the image forming process is completed, the developing bias voltage applied to the developing sleeve 8 is changed to the bias voltage during the image forming process, before the surface of the photoreceptor charged in step (2) reaches the position facing the sleeve 8. The voltage is set to be around 750 V or higher than 750 V. In this way, an electric field is created between the sleeve and the photoreceptor that hardly or not at all transfers even the negatively charged toner from the sleeve to the photoreceptor. In this way, the waste of developer and the appearance of development marks can be prevented.

[Brief explanation of the drawing]

1, 2, and 6 are diagrams for explaining the present invention in detail, 1 is a photoreceptor, 4 is a primary charger, 5 is a secondary charger, and 7 is a light rung on the entire surface. , 8 is a developing sleeve.

Claims (1)

[Claims] In an electrophotographic method using a photoreceptor having nine conductive layers and two conductive layers and an insulating layer on the surface, the surface potential of the photoreceptor after the completion of the image forming process is defined as the average surface potential of the photoreceptor during the image forming process. 17, and the developing bias after the image forming process is set to a bias value that prevents the transfer of developer from the developing means to the photoreceptor. Photography method. △