JPS62116987A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To eliminate a decrease in image density due to a transfer process by providing a mechanism which gives a charge having the same polarity as the polarity of electrostatic charging to the surface of a photosensitive body between the transfer mechanism and optical discharging mechanism of a reversal development type electrophotographic device. CONSTITUTION:A photosensitive body 1 rotates as shown by an arrow X and is charged electrostatically and uniformly by an electrostatic charging electrode 2 to about 900V, and then a character and graphic form equivalent area is irradiated by laser exposure 3, so that the potential falls to about 100V. A developing device 4 is applied with about 700V as a bias voltage and toner leaves carriers and sticks on an exposed part to from a visible image. This visible image is transferred to a transfer material 6 with a voltage of -5.5kV applied to a transfer electrode 5. A history erasing electrode 8 is provided between the transfer electrode 5 and a discharging mechanism 9 and +5.5kV is applied thereto to hold the entire area of the photosensitive body surface at a plus potential. Then, optical discharging is performed by the discharging mechanism 9, charges in the whole area are removed by this exposure and a history based upon negative charges disappears.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic apparatus, and more particularly to an electrophotographic apparatus such as an output terminal device of an information processing apparatus or a digital copying machine having intelligent functions.

[Prior art and its problems]

In the electrophotographic image forming method, the development method differs depending on the method of image exposure to the charged surface of an electrophotographic photoreceptor (hereinafter also simply referred to as photoreceptor). In other words, a method is adopted in which only the area corresponding to the characters or figures on the surface of the photoreceptor, which is uniformly charged by corona charging, is exposed, and all other areas are exposed.
The charges in the exposed area disappear, and charges remain on the surface of the photoreceptor only in areas corresponding to letters and figures, forming a static image of wrinkles. Such an electrostatic latent image is developed by adhering charged colored particles of opposite polarity to the monostatic charge by electrical attraction and becomes visible (visualized).On the other hand, areas corresponding to letters and figures on the surface of the photoreceptor In the case of a method that only captures light, the charge disappears only in the area corresponding to the text or figure, while the charge in other areas remains, leaving a negative electrostatic latent image of the letter or figure on the surface of the photoreceptor. Such an electrostatic latent image is visualized by the so-called reversal development method, in which charged colored particles of the same polarity as the charged polarity are attached by electrical repulsion and a negative image is developed as a positive image. Ru.

The four light sources for the output terminal device/equipment of an information processing device or an electrophotographic device such as a digital copying machine include a semiconductor laser diode (LD), a light emitting element (LED), a general light source such as a halogen lamp, and a liquid crystal shutter (LC8).
A combination of these light sources is used, and the charged surface of one photoreceptor is exposed to light controlled according to output signals from these light sources. At this time, in order to reduce the brightness and extend the life of the light source, areas corresponding to letters and figures are usually exposed to form a negative electromagnetic image. Therefore,
In such an apparatus, the above-mentioned reversal development method is adopted.

In the image formation method using the reversal development method, since the charge of the charged colored particles used is the same polarity as the charged polarity, transfer for transferring the image of the developed charged t/iI color particles onto the transfer material is necessary. The polarity of the electrode is necessarily opposite to the charged polarity.

In addition, when forming a painter, whether the charged polarity of the surface of the photoreceptor, that is, the surface of the photosensitive layer should be positive or negative, depends on which part of the photosensitive layer receives light and generates hole-electron carrier pairs during exposure. It depends on whether the polarity of the transport charge of the photoconductive material used in the photosensitive material is positive or negative. When the carrier generation region is near the surface of the photosensitive layer, the carriers of one polarity of the generated carrier pair pass through the photosensitive layer and reach the conductive substrate, and the carriers of the other polarity pass through the photosensitive layer and reach the conductive substrate. By immediately combining with the charge, the surface charge on the exposed portion of the surface of the photosensitive layer disappears. Therefore, the charge polarity of the surface of the photosensitive layer should be the same as the polarity of the transport charges of the photosensitive layer. For example, in the case of a photoreceptor with a photosensitive layer made of a selenium-based photoconductive material, the carrier generation region is near the surface of the photosensitive layer, and the transport charge is a hole, so the charged polarity of the photoreceptor is positive. Ru.

On the other hand, the carrier generation region is exposed to light tI! If it is on the side that is in contact with the conductive substrate, the carriers that have passed through the photosensitive layer 4 out of the carrier pairs born at dawn will combine with the surface charge, so the charge polarity of the surface at 1° of exposure will be - The polarity should be opposite to that of the transport charge of the layer. For example, in the case of organic photoconductive materials, materials currently in practical use generally have a photosensitive structure like this, and the polarity of the transport charge is positive, so the photosensitive material is negatively charged. In both cases where the carrier generation layer is near the photosensitive layer surface and near the conductive substrate, if the photosensitive layer surface is charged to a polarity opposite to that described above, some of the carriers generated during exposure will be removed. Since the carriers that should pass through the photosensitive layer and contribute to the disappearance of the surface charges cannot pass through the photosensitive layer, the surface charges do not disappear.

This means that if a charge with a polarity opposite to the normal charge polarity of the photosensitive layer is applied to the surface of the photosensitive layer, that charge cannot be eliminated even by photostatic charge removal. .

In the image forming method that adopts the reversal development method, ・Transfer [I
The polarity of E is opposite to the charging polarity, and when a large amount of charge is applied to the surface of the photosensitive layer during transfer and the charging polarity is reversed, it remains as aIflE, and when image formation is repeated, the charging potential becomes lower. This causes a decrease in the image aIf. In particular, the part of the photosensitive layer where no transfer material exists, in the case of fIJ, the transfer material is supplied at certain intervals, but the part corresponding to the supply gap receives a large bite, and the subsequent #J1 quadratic acid However, there is a drawback in that the image density of the area concerned is significantly reduced.

[Purpose of the invention]

The present invention is an electrophotography using a reversal development method that eliminates the above-mentioned drawbacks and eliminates the decrease in image density caused by the transfer process! ! The purpose is to provide

[Key points of the invention]

The object of the present invention is achieved by providing a mechanism for applying a charge having the same polarity as the charge polarity to the surface of the photoreceptor between the transfer mechanism and the optical charge removal mechanism of an electrophotographic IC device of a reversal development type.

[Embodiments of the invention]

FIG. 1 is a principle sectional view showing one embodiment of the present invention.

The photoreceptor 1 has a photosensitive layer made of a selenium-tellurium alloy and has sufficient sensitivity to semiconductor laser light with a wavelength of 780 nm. The photoreceptor 1 is exposed in the direction of the arrow X, and the surface of the photoreceptor layer is irradiated with about 900VK average-Kfr (by the fog light 3 of the laser beam) by the band or tunic pole 2, and only the area corresponding to the character 1 figure is irradiated with electric charge. disappears, and the potential of the exposed area becomes about 100 V. 4 is a magnetic brush development 4;
It has an agent consisting of iron powder called a carrier and colored particles called a toner, and the toner has a -! It is positively charged by J-friction electrification, and is attached by electrical attraction to the surface of the carrier, which is attached to the surface of the magnet roll in a cylindrical manner by magnetic force. Approximately 700 V is applied as a bias voltage to the developing device 4, and when the tip of the carrier of the developing device comes into contact with the surface of the photoreceptor, the unexposed area on the surface of the photoreceptor becomes 9.
Since it is charged to 00 V, the electrical repulsion force causes the carrier to stick to the carrier.
Since the charged potential in the exposed area is reduced to 100V, the toner leaves the carrier and adheres to the exposed area, and the exposed area, that is, the electrostatic latent image is developed and becomes a visible image. This visible image is the transfer electrode 5
The image is transferred onto the transfer material 6 by a voltage of -5.5 kV applied to the transfer material 6. The next visible image is formed on the rotating photoreceptor at a certain interval, and in synchronization with this, the transfer material moves in the direction of arrow Y.
However, the transfer electrode is applied continuously, so that the charge from the transfer electrode is applied directly to the surface of the photoreceptor in the supply gap of the transfer material 6.7.

FIG. 2 shows the surface potential of the photoreceptor immediately after the transfer with respect to the circumference of the photoreceptor. A in FIG. 2 shows the area where the transfer material was present, and B shows the area where the transfer material did not exist.

Region B is given a large amount of negative charge and has a negative potential. Reference numeral 8 denotes a history erasing electrode for applying a charge of the same polarity as the at-polarity to the surface of the photoreceptor according to the present invention, and a corotron discharge electrode similar to that used as a charging or transfer electrode. +5.5 kV is applied to this electrode 8 to give a positive charge to the surface of the photoreceptor so that the surface potential of the photoreceptor becomes positive over the entire area as shown in FIG. The surface of the photoconductor is then photostatically neutralized by a static elimination mechanism 9 that includes a halogen lamp with a blue filter, but since the entire area of the photoconductor surface is positively charged, the charge on the entire area disappears due to detachment, causing a negative charge. The history caused by this phenomenon disappears, and in the subsequent charging process, the entire surface of the photoreceptor is charged uniformly, and the resulting image has a uniform density over the entire area.

In the case where there is no history erasing electrode 8 according to the present invention, the negative charges are not eliminated even by photostatic discharge, so the surface potential of the photoreceptor after photostatic discharge becomes as shown in FIG. 4, and the subsequent charging step The subsequent surface potential of the photoreceptor is not uniform as shown in Figure 5 (there is a potential difference of Vc). The potentials are shown in Figure 6. C indicates the exposed area.

The potential difference va between the exposed part and the unexposed part in the B area is smaller than the potential difference VA in the A area by about vO.
The image density of the electrostatic latent image formed in the region after development is lower than the density of the image formed in the A region by an amount corresponding to Va.

〔Effect of the invention〕

In the present invention, a mechanism is provided between the transfer mechanism and the optical charge removal mechanism of a reversal development type electrophotographic device to apply charges of the same polarity as the charging polarity to the surface of the photoreceptor. This mechanism eliminates the charges of the opposite polarity to the charged polarity applied to the surface of the photoreceptor during tape transfer, and makes the charges in the entire area the same polarity as the charged polarity. Since such (abundant charges) can be erased by a light shadow, the surface of the photoconductor can be uniformly photostatically removed, and in the subsequent charging process, the entire area of the photoconductor surface can be uniformly charged. Even if the grooves are formed repeatedly, the image @ image quality decreases due to the transfer process, and the qln reversal image 1
This makes it possible to obtain an electrophotographic device based on the image method.

[Brief explanation of drawings]

Fig. 1 is a principle cross-sectional view showing an embodiment of the present invention, Fig. 2 is a diagram showing the circumference of the photoreceptor at position 4 on the photoreceptor surface after the transfer process, and Fig. 3 is a Wjt history of the present invention. A diagram showing the circumference of the photoreceptor surface potential after being charged by the erasing electrode, and FIG. Figure 5 is a diagram showing the circumferential portion of the photoreceptor surface potential when the photoreceptor surface potential is charged by photoreceptor immersion in a conventional device. FIG. 3 is a diagram showing the photoconductor surface potential divided by the circumference of the photoconductor when performing the following steps. 1... Photoreceptor, 2... Charged electrode, 3... Exposure light, 4
...One patent attorney Yamaguchi breath ゛ξ゛;

Claims (1)

[Claims] 1) Equipped with charging, exposure, development, transfer, and optical static elimination mechanisms,
In an electrophotographic apparatus of a reversal development type that uses charged colored particles having the same polarity as the charge polarity of the electrophotographic photoreceptor, charges having the same polarity as the charge polarity are transferred between the transfer mechanism and the optical charge removal mechanism to the electrophotographic photoreceptor. An electrophotographic device comprising a history erasing mechanism applied to the surface.