JPS6043680A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To erase completely the last electrostatic latent image which is stored and obtain an excellent image by impressing a voltage in contact with a photosensitive body before an electrostatic charge process. CONSTITUTION:When an electrostatic latent image is formed on the photosensitive body 1 which uses amorphous silicon, a conductive rubber roller 7 is provided to impress the voltage in contact with the photosensitive body 1 at least once before the electrostatic charge process for the next electrostatic latent image formation after an electrostatic latent image forming process. Then, the last electrostatic latent image which is stored is erased completely by impressing the voltage from the roller 7 to the photosensitive body 1.

Description

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

Conventionally, as photoconductive material photoreceptors for electrophotography, for example, inorganic Se photoreceptors, CdS binder type photoreceptors, zinc oxide photoreceptors, polyvinyl carbazole organic photoreceptors, etc. are known. Recently, it is written as ra-3iJ. ) is actively being researched into photoreceptors, and attempts are being made to put them into practical use as electrophotographic photoreceptors.

In other words, the a-3i photoconductor has excellent photosensitive properties compared to other photoconductors, particularly sensitivity in the long wavelength range, heat resistance, and high hardness, and is considered promising because it is non-polluting. .

However, the a-3i photoreceptor has the disadvantage of a fast dark decay rate. In order to improve this drawback, there is a method of doping a-3t with a small amount of impurities such as oxygen, nitrogen, boron, carbon, etc. to increase the volume resistance of the photoreceptor (Japanese Patent Laid-Open No. 54-1
No. 45539, JP-A-54-145540, etc.).

Thus, the a-5i photoreceptor doped with impurities has a significantly improved 118 decay rate, reaching a level that poses no problem in practical use.

However, due to doping with impurities, the problem is that the localized levels in a-3i increase. That is, when latent images are repeatedly formed, differences occur in the formation of electrostatic latent space charges. Therefore, in order to prevent the difference in surface potential between the dark and bright areas of the photoreceptor from affecting the next electrostatic latent image, a preliminary exposure (pre-exposure) is performed to remove the static charge before charging to form the latent image. Even if the surface potentials on the photoreceptor are equalized, the previous memory may appear.

On an actual image, cases in which the previous image appears with the previous brightness and darkness (positive image) and cases in which it appears reversed (negative image) are particularly noticeable in halftone areas.

In addition, while the document table or optical system is reversed between document exposures and moved in the opposite direction to that during document exposure, a When exposure is performed, the exposure memory appears on the image and the halftone portion appears white. In some cases, it turns black. A phenomenon occurs.

Additionally, in order to eliminate the influence of localized levels formed by impurities, a charge injection I that prevents charge injection onto the photoreceptor substrate is used.
Even in the case of a photoreceptor made by laminating I:m and laminating an undoped amorphous silicon layer on top of it to achieve high resistance, there are differences in degree due to localized levels existing in the undoped amorphous silicon. There may also be memory.

In order to make these memories practical, the amount of exposure for static elimination exposure performed before charging to form an electrostatic latent image is generally greater than the amount necessary to cancel out the surface charge on the photoreceptor. Then, electron-hole pairs generated by exposure to light are generated excessively in the photoreceptor and captured in empty levels, thereby aligning the space charges within the photoreceptor.

However, these strong exposures performed before charging to form a latent image create a new problem of reducing the dark area potential of the photoreceptor as well as the effect of erasing the memory.

FIG. 1 shows the relationship between the decrease in dark area potential and the amount of pre-exposure (charging for forming an electrostatic latent image is under constant conditions). The vertical axis shows the dark area surface potential (Vo), and the horizontal axis shows the exposure amount, where the exposure amount required to neutralize the surface charge of the photoreceptor is taken as one unit.

For this reason, for the purpose of erasing the memory, if a strong pre-exposure is applied, it is necessary to apply a strong charge in order to obtain an appropriate dark area potential, which adversely affects the durability of the photoreceptor, the withstand voltage of the device, the generation of ozone, etc. give. Furthermore, it may not be possible to completely erase the memory within a range where the dark potential can be maintained appropriately.

The present invention eliminates the above-mentioned conventional drawbacks and makes it possible to obtain uniform and good images over a long period of time.The present invention is an electrophotographic method in which electrostatic latent images are repeatedly formed on a photoreceptor using amorphous silicon. The method includes a means for applying a voltage by contact to the photoreceptor at least once after the electrostatic latent image forming step is completed and before the next charging step for forming the electrostatic latent image; The gist of this paper is an electrophotographic method characterized by erasing the memory of electrostatic latent images by applying voltage.

Below, details of the present invention will be explained by way of specific examples and with reference to the drawings.

Embodiment 1 FIG. 2 is an explanatory diagram of an embodiment of the present invention. In the figure, the photoreceptor 1 is drum-shaped, but in the present invention, C±1! (It is not limited to ram shape).

A photosensitive drum 1 made of amorphous silicon doped with oxygen to increase its resistance rotates in the direction of the arrow.

In the process of rotation, the photosensitive drum 1 is first positively charged by the charger 2 & in this embodiment, and imagewise exposed by the image exposure section 3 to form an electrostatic latent image. This electrostatic latent image I± is developed by the developer 4 to become a visible image. The next number is transferred to the transfer material St that is sent so as to come into contact with the photosensitive drum. At this time, if necessary, the transfer material S is charged from the back side by the transfer charger 5.

After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaner 6 in preparation for the next copying.

First, as an experiment prior to the embodiment of the present invention, the above process was carried out using only the amount of pre-exposure from the exposure lamp 8 without performing pre-static discharge. At this time, the amount of front light is the amount necessary to neutralize the surface charge on the surface of the photoreceptor, and the dark area surface potential (Vo) is set to 40
When the charging conditions were set so that the voltage was 0V, memory was clearly visible on the image.

Therefore, when we increased the pre-exposure amount to erase the memory, we found that in order to bring the memory to a level that would not cause any problems in practical use, we needed a pre-exposure amount that was 10 times the amount of exposure necessary to neutralize the surface charge. Ta.

At this time, the dark surface potential VD of the photoreceptor is half of the initial value (20
0V). However, the memory is not completely erased yet.

On the other hand, in this embodiment, between the cleaning step 6 and the charging step 2, a voltage was applied to the surface of the photoreceptor by bringing the conductive rubber roller 7 into contact with the surface of the photoreceptor.

9 is a voltage applying power source.

When a DC voltage of 150 V was applied, the memory was completely erased.

Further, when the voltage was applied by the conductive rubber rollerf and the exposure amount was performed by the pre-exposure lamp 8, the effect was even more remarkable.

At this time, the dark surface potential VD of the photoreceptor decreased by a maximum of 40 V compared to when only the pre-exposure amount was applied, but by slightly increasing the current of the charger 2, Vo was completely restored to 400 V.

A similar memory erasing effect was confirmed in experiments in which pre-exposure was performed before voltage application as shown in FIG. 3, or before and after voltage application as shown in FIG.

Furthermore, it has been confirmed that even in a process of transferring an electrostatic latent image to a transfer material or the like without forming a visible image, the photoreceptor memory after the latent image has been transferred can be erased by the method described above.

In addition, the voltage application for memory erasing was performed not with direct current but with alternating current whose direct current component was negative. In this case as well, the same effect of memory erasing as above was confirmed.

However, no significant memory erasing effect could be confirmed when applying a positive DC voltage or applying an AC voltage with a positive DC component.

That is, in the present invention, the voltage applied to the photoreceptor by contact with the voltage applying means 7 is effective to be a direct current with a polarity opposite to that of charging for forming an electrostatic latent image, or an alternating current whose direct current has a polarity opposite to that of charging. It is.

Example 2 In Example 1, a negative charge for forming an electrostatic latent image was used,
When an experiment was conducted in the same manner as in Example 1 except that the voltage application for erasing the memory was positive, the same effect as in Example 1 was confirmed.

Example 3 Photoreceptor 1 was made by doping a-3i with nitrogen or carbon to increase its resistance. A charge injection blocking layer was provided on the substrate, and an a-S+ photosensitive layer was laminated thereon to increase its resistance. When experiments similar to those in Example 1.2 were conducted on photoreceptors such as objects, similar effects were confirmed in both cases.

Example 4 In Examples 1 to 3, by using the roller 7 on which a thin film of insulator, for example, 9 gm Mylar film (trade name) was spread on the surface of conductive rubber, and bringing it into contact with the photoreceptor. The same experiment as in Examples 1 to 3 was conducted except that a voltage was applied to the photoreceptor.

However, the voltage applied to the roller at this time was higher than that in the case without Mylar.

In this case as well, the same effects as in Examples 1 to 3 were confirmed regarding memory erasure.

? The fi pressure applying means 7 may be supported so that it can freely approach and separate from the photoreceptor 1, and may be brought into contact with the surface of the photoreceptor 1 when necessary.

[Brief explanation of drawings]

Figure 1 is a graph of the relationship between the pre-exposure amount and the surface potential of the dark area on the photoreceptor when the charging for the electrostatic latent image is kept constant;
The figure is a schematic configuration diagram of an example of an electrophotographic apparatus to which the method of the present invention is applied, and FIG. 3 and FIG. 4 are partial views of modified examples. 1 is a photoreceptor, 2 is a charger, 3 is an image exposure section, 4 is a developer,
5 is a transfer charger, 6 is a cleaner, 7 is a voltage application member, 8
is the pre-exposure lamp. Figure 3 2 Figure 4 Figure 1 Figure 2

Claims (1)

[Claims] (1) In an electrophotographic method in which electrostatic latent images are repeatedly formed on a photoreceptor using amorphous silicon, at least once after the electrostatic latent image forming process is completed and before the final charging process for forming the next electrostatic latent image. 1. An electrophotographic method comprising means for applying a voltage to a photoconductor by contact with the photoconductor, and erasing a memory of an electrostatic latent image by applying a voltage to the photoconductor by means of the means.