JPS6043681A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To erase completely the last electrostatic latent image which is stored and obtain an excellent image by exposing and charging electrostatically a photosensitive body at least once before an electrostatic charge process for the formation of an electrostatic latent image. CONSTITUTION:The photosensitive body 1 is precharged electrostatically by an electrifier 7 and preexposed l by an exposure lamp 8 at least once between a cleaning process 6 and the electrostatic charge process 2. At this time, the photosensitive body 1 is preexposed only enough to neutralized the surface charge on the photosensitive body 1, and a -5kV direct current is supplied to the electrifier 7 for the electrostatic precharge. Consequently, the last electrostatic latent image which is stored is erased completely.

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 chloride photoreceptors, and polyvinyl carbazole organic photoreceptors have been known. Recently, research on photoreceptors using amorphous silicon (hereinafter referred to as "r4-3i") has been actively conducted, and attempts have been made to put them into practical use as electrophotographic photoreceptors.

In other words, the a-3i photoconductor is considered to be promising because it has superior photosensitive properties compared to other photoconductors, particularly sensitivity in the long wavelength range, heat resistance, and high hardness, and 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-3i with a small amount of impurities such as fluorine, 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-3i photoreceptor doped with impurities has a significantly improved dark 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, during repeated latent image formation, there is a difference in the formation of space charges in a-3t between exposed light areas and dark areas of the photoreceptor during electrostatic latent image formation. 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, exposure to remove static electricity (pre-exposure) is performed before charging to form a 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, a blackening phenomenon occurs.

In addition, in order to eliminate the influence of localized levels formed by impurities, a charge injection blocking layer is laminated on the photoreceptor substrate to prevent charge injection, and an undoped amorphous silicon layer is laminated on top of this to create a high resistance layer. Even in the case of a photoreceptor that has been doped, memory may exist to varying degrees due to localized levels existing in undoped amorphous silicon.

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 equalizing the space charges within the photoreceptor.

However, these strong exposures performed before charging for forming an AT shadow create a new problem of reducing the dark potential of the photoreceptor as well as the effect of erasing the memory.

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

For this reason, if a strong pre-exposure is applied for the purpose of erasing the memory, it is necessary to apply a strong l/\\ charge in order to obtain an appropriate dark potential. It may have a negative impact on the occurrence of the disease. In some cases, it may not be possible to completely erase the memo 1 as long as the dark potential can be maintained properly.

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 makes it possible to repeatedly form electrostatic latent images on a photoreceptor made of amorphous silicon. In the electrophotographic method, after the electrostatic latent image forming step is completed and before the next charging step for forming the electrostatic latent image, the photoreceptor is exposed to light at least once and charged at least once, and the photoreceptor is The subject matter is an electrophotographic method characterized by erasing the memory of electrostatic latent images.

Hereinafter, details of the present invention will be explained using specific examples 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 l is drum-shaped, but the present invention is not limited to the drum shape).

An amorphous silicon photosensitive drum 1 doped with oxygen to provide high resistance rotates in the direction of the arrow.

During the rotation process, the photosensitive drum 1 is first positively charged in this embodiment by the charger 2, and imagewise exposed in the image exposure section 3 to form an electrostatic latent image. This electrostatic latent image L is developed by a developing device 4 to become a visible image. Next, the transfer material S+, which is sent so as to come into contact with the photosensitive tram, is transferred. At this time, if necessary, the transfer material S is charged from the back side by the transfer charger 51.

After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaner 6 and then used for the next copy.

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 necessary to neutralize the surface charge on the surface of the photoreceptor is set as the pre-exposure amount controller, and the dark area surface potential (VD) is set to 4.
When I set the number and charging conditions so that the number was 00■, the memo IJ car appeared strongly 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 the wood example, between the cleaning step 6 and the charging step 2, the photoreceptor 1 was pre-charged by the charger 7 and subjected to pre-exposure by the exposure lamp 8 in sequence. At this time, the amount of pre-exposure was set to be the amount of exposure necessary to neutralize the surface charge on the photoreceptor, and for pre-charging, a direct current of 15 KV was applied to the charger 7 to perform charging, and the memory was completely erased. 9 is a high voltage transformer for the charger 7.

At this time, the effect was particularly remarkable when a pre-exposure amount containing a large amount of light with a long wavelength of 600 r+m, preferably longer wavelength than 650 nm, or near infrared rays, which is absorbed even inside a-3I, was used.

The dark area surface potential VD of the photoreceptor decreased by 30V because the pre-discharge 7 had the opposite polarity to the charge 2 for forming an electrostatic latent image, but by slightly increasing the current of the charger 2, VD decreased by 400V.
Completely returned to V.

In either case, the pre-charging step 7 and the pre-exposure step 8 are performed at the same time as shown in FIG. 3, or the pre-exposure step 8 is performed before the pre-charging step 7 as shown in FIG. A good memory erasing effect similar to that in the above case was also confirmed.

It has been confirmed that even in the process of transferring an electrostatic latent image onto 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.

When an experiment was conducted to reduce the power removed in the pre-static removing step 7, memory gradually began to appear as the power was reduced.

However, even with a charge of -4 KV, the memory was at a level that would not cause any problems in practical use, and the decrease in VD was even smaller than in the case of -4 KV.

Further, in an experiment in which the number of pre-exposures was reduced, it was confirmed that even if the exposure amount was reduced to one-twentieth of the amount described above, the image quality was still at a level that would not cause any problem in practical use.

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, when the pre-charging 7 was performed with positive DC charging or with AC charging where the DC component was positive, no significant effect of memory erasing could be confirmed.

That is, it is effective for the charging polarity of the pre-charging 7 to be a direct current with a polarity opposite to that of the charging 2 for forming an electrostatic latent image, or an alternating current whose DC component is opposite in polarity to the charging 2.

Example 2 In Example 1, the charge for forming an electrostatic latent image was negative,
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-5i with nitrogen or carbon to increase its resistance. A charge injection blocking layer was provided on the substrate, and an a-5i 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.

[Brief explanation of the drawing]

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 very schematic configuration diagram of an example of an electrophotographic apparatus to which the method of the present invention is applied, and FIGS. 3 and 4 are partial views of modified examples, respectively. 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 pre-charger, and 8 is a pre-exposure lamp. Figure 3 Figure 4 Figure 1 Figure 2 51

Claims (1)

[Claims] (1) In electrophotography in which electrostatic latent images are repeatedly formed on a photoreceptor using amorphous silicon, electrostatic 14!
After the completion of the J image forming process, the photoconductor is exposed to light at least once and charged at least once before the next charging process for forming an electrostatic latent image, thereby preserving the memory of the electrostatic latent image on the photoconductor. An electrophotographic method characterized by erasing.