JPH09230680A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the elongation of the tail of an image. SOLUTION: An image forming device concerned includes an image carrier 2 having an insulative layer 25 formed on a conductive layer 23 and a photo-sensitive element 9 furnished with a photo-sensitive layer 93 on a conductive layer 92, wherein the image carrier 2 and element 9 are arranged so that their insulative layer 25 and photo-sensitive layer 93 are opposing, and image exposure is conducted in the condition that a voltage is impressed between the two conductive layer 23, 92, thereby forming a latent image on the running image carrier 2 through an electric discharge generated between the photo-sensitive element 9 and carrier 2. The arrangement further includes a pattern-form facial electrode layer 94 formed on the surface confronting the insulative layer 25 of the photo- sensitive layer 93 and a bias voltage impressing means 14 to inpress the bias voltage on the facial electrode layer 94.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an electrostatic latent image on an image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, an electrostatic latent image carrier such as a photoconductor is charged by a charging device and then exposed to form an electrostatic latent image. An image forming process is generally known in which a latent image is developed with toner to form a visible image, and the visible image is transferred and fixed on a transfer material.
However, in the conventional imaging method involving corona discharge,
It may lead to environmental damage such as the generation of a large amount of ozone,
In recent years, it has been desired to provide an image forming method that suppresses the generation of ozone because it greatly affects the surface of the photoconductor and shortens the life of the photoconductor.

As a low ozone image forming method, for example, a method described in Japanese Patent Application Laid-Open No. 1-293358 has been proposed. In this image forming method, as shown in FIG. 9, a photoreceptor 101 made of small pieces and a cylindrical charge holding medium 102 are separately provided. The photoconductor 101 includes a photoconductive layer support 103, a photoconductor electrode 104, and a photoconductive layer 105, which are sequentially stacked. On the other hand, the charge holding medium 102
Is an insulating layer support 106, a charge holding medium electrode 107, and an insulating layer 108, which are sequentially stacked. The photoconductor 101 and the charge holding medium 102 are arranged so that the photoconductive layer 105 and the insulating layer 108 face each other with a gap.

Then, a voltage is applied between the photoconductor electrode 104 and the charge holding medium electrode 107, and the photoconductor 101 is placed in a dark place.
When light is incident on the charge carrier 102 to scan it in the axial direction (main scanning direction), the portion of the photoconductive layer 105 on which light is incident exhibits conductivity, and that portion and the insulating layer 108 of the charge carrier medium 102 are A discharge is generated during this period, and charges are accumulated in the insulating layer 108 of the charge holding medium 102 that has been rotated in the direction of arrow b in the figure to form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 109 to become a toner image,
The toner image is transferred by transfer charger 110 to paper or film.

[0005]

With the above-described device, the structure shown in FIG.
As shown in (a), an original consisting of a plurality of long and short lines long in the sub-scanning direction is exposed in the main scanning direction to form an electrostatic latent image. Then, as shown in FIG. 10B, the rear end of the electrostatic latent image formed on the charge holding medium 102 extends by ΔL. This elongation ΔL appears more prominently as the image of the longer line. An object of the present invention is to eliminate such elongation of the trailing edge of the image.

[0006]

As a result, the inventors of the present invention have examined the cause of the extension of the trailing edge of the image. As a result, excess carriers generated in the photoconductor are gradually released even after the exposure is completed, and the discharge continues. As a result, it was found that the stop of the exposure and the stop of the discharge did not coincide with each other, and the latent image had an expansion at the trailing edge of the image. Here, the excess carrier is a trap existing in the photoconductor, in the case of a laminated photoconductor, the carrier is bundled in the trap formed near the interface, or the free carrier has a very high moving speed. It is a carrier of a slow component. In the present invention, the image extension of the latent image is eliminated by eliminating the excess carriers when the exposure is turned off.

That is, in the image forming apparatus of the present invention, the image carrier having the insulating layer formed on the conductive layer and the photosensitive member having the photosensitive layer formed on the conductive layer are arranged so that the insulating layer and the photosensitive layer face each other. In the image forming apparatus, which is arranged, performs image exposure with a voltage applied between both conductive layers, and forms a latent image on a running image carrier by discharge between the photoconductor and the image carrier, It has a patterned surface electrode layer formed on the surface facing the insulating layer, and a bias voltage application means for applying a bias voltage to the patterned surface electrode layer.

In the image forming apparatus constructed as described above,
A voltage is applied between the conductive layer of the photoconductor and the conductive layer of the image carrier, and a bias voltage is applied to the surface electrode layer of the photoconductor by the bias voltage applying means, and the photoconductor is imagewise exposed in this state. This produces carrier pairs in the photosensitive layer. Free carriers of the generated carrier pairs are
Move to the surface of the photosensitive layer. Due to this phenomenon, the electric field between the photosensitive layer and the image carrier rises to generate discharge, and an electrostatic latent image is formed on the image carrier.

On the other hand, the excess carriers in the generated carrier pairs are not accumulated in the photosensitive layer due to the electric field in the photosensitive layer between the conductive portion of the photosensitive layer and the patterned surface electrode layer, and the excess carrier is promptly transferred. Moving toward the surface electrode layer and discharged or trapped in the electrode layer. Therefore, the excess carriers are continuously discharged even after the exposure is finished, and the continuous discharge prevents the latent image formed on the insulating layer of the image carrier from extending.

The patterned surface electrode layer may be overcoated with an insulating protective film. With such a configuration, it is possible to prevent the oxidation of the electrode exposed to the discharge, and to avoid a local abnormal discharge.

The pattern of the patterned surface electrode layer may be configured to have a slit or a mesh.

The slit width of the patterned surface electrode layer having the slit is 10 μm or more and 150 μm or less,
The width of the conductive portion forming the slit is 2 μm or more and 50 μm
It is preferably formed below.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram of the image forming apparatus 1 according to the first embodiment.
Shows a partially enlarged sectional view of the photoconductor 9 and the image bearing belt 2, which are essential parts. At the center of the image forming apparatus 1, an image bearing belt 2 as an image bearing member is disposed. The image bearing belt 2 is driven in the direction of arrow a by a driving roller 3 rotated by a driving device (not shown) and a heating roller 4 provided in parallel with the driving roller 3.

As shown in FIG. 2, the image bearing belt 2 has a conductive layer 23 formed on the surface of a substrate 21 made of a dielectric material, and a dielectric layer 25 which is an insulating layer formed on the conductive layer 23. Specifically, the conductive layer 2 is formed on the base 21 made of a polyimide film having a thickness of 50 μm, a width of 25 cm and a perimeter of 30 cm.
3 is provided, and a dielectric layer 25 made of a fluororesin having a thickness of several μm is further provided thereon. In addition, the conductive layer 23 is
It is grounded by the conductive wire 12. The structure of the image carrier is not limited to such a belt, and may be drum-shaped. A latent image forming device 5, a developing device 6, and a transfer roller 7 are sequentially arranged around the image carrying belt 2 in the direction of arrow a in the figure.

The latent image forming device 5 comprises an optical system 8 and a photoconductor 9 arranged between the optical system 8 and the image carrier belt 2. The optical system 8 includes a housing 81 in which a semiconductor laser generator, a collimator lens, a polygon mirror, an Fθ lens, a reflection mirror, and the like are arranged, and an exposure slit 82 is formed on a wall surface of the housing 81. The optical system 8 is configured so that a laser beam 83 generated by a semiconductor laser generator is irradiated onto the photoconductor 9 from the exposure slit 82 to perform image exposure. In the present embodiment, an optical system that performs scanning exposure of 300 dpi is used.

Here, the scanning direction of the laser beam 83 is the width direction of the image bearing belt 2 (the front and back direction in FIG. 1).
This direction is hereinafter referred to as a main scanning direction. Further, the traveling direction of the image carrying belt 2 (the vertical direction in FIG. 1) which is orthogonal to the main scanning direction is called the sub-scanning direction.

As shown in FIG. 2, the photoreceptor 9 has a transparent conductive layer 92, a photosensitive layer 93, and a surface electrode layer 9 on a transparent substrate 91.
4 and the surface protection layer 95 are laminated in this order. The transparent substrate 91 is a transparent glass plate, and the transparent conductive layer 92 is made of an ITO film. The first power supply 13 is connected to the translucent conductive layer 92. The photosensitive layer 93 is made of semiconductor laser light (wavelength 780 nm) or LED light (wavelength 680 n).
m) and the like, which is a function-separated type for negative charging having good sensitivity to long-wavelength light and has a charge generation layer (CGL) 96 having a carrier pair generating function, and a charge transporting function having a free carrier transporting function. Layer (CTL) 97.

As shown in FIG. 3, the surface electrode layer 94 has a shape having four slit-like conductive portions 98 provided in parallel with each other in the main scanning direction so that three slits 99 are formed between them. The second power supply 14 is connected to the surface electrode layer 94. The surface protection layer 95 is an amorphous carbon film obtained by plasma-polymerizing 1,3-C ₄ H ₆ .
It is formed with a thickness of 0.15 μm. The surface protection layer 95 is not always necessary. However, it is preferable to provide an insulative surface protective layer 95 on the surface electrode layer 94 in order to prevent oxidation of the surface electrode layer 94 exposed to discharge and to avoid local abnormal discharge.

As shown in FIG. 1, a spacer 10 made of fluororesin is provided between the photoconductor 9 and the image bearing belt 2.
Thus, an air gap is provided, and the photosensitive layer 93 of the photoconductor 9 and the dielectric layer 25 of the image bearing belt 2 are arranged to face each other via the air gap. Since the photosensitive member 9 is not in contact with the image bearing belt 2, the surface of the photosensitive member 9 is not contaminated even if foreign matters are conveyed as the image bearing belt 2 travels, and a stable latent image is formed. Can be done easily. Further, the member to be the spacer 10 is not particularly limited to the fluororesin, but may be any member as long as it has a small coefficient of friction with the image carrying belt 2 and is hard to be scratched.

The developing device 6 includes a toner containing portion 61 containing a one-component developer (hereinafter referred to as toner) and a developing sleeve 62 arranged in proximity to the image carrying belt 2.
The supply roller 63 supplies toner to the developing sleeve 62 by stirring the toner stored in the toner storage portion 61. The toner used in the developing device 6 is of a negative charging type and has a mean particle size of 10 μm obtained by kneading, pulverizing and classifying a mixture containing a bisphenol A type polyester resin and carbon black as main components by a known method. is there. An appropriate developing bias voltage is applied to the developing sleeve 62 in order to prevent background fogging.

The transfer roller 7 faces the heating roller 4 with the image bearing belt 2 interposed therebetween, and
It is arranged in pressure contact with. The recording paper S is passed between the transfer roller 7 and the image carrying belt 2.

In the image forming apparatus 1 configured as described above, the process of latent image formation will be described first.
A voltage of 1.5 kV (V _C ) is applied to the translucent conductive layer 92 of the photoconductor 9 by the first power supply 13, and a voltage of 50 V (V _P ) is applied to the surface electrode layer 94 by the second power supply 14. Is being applied. Therefore, between the conductive layer 23 and the translucent conductive layer 92 of the image carrying belt 2 which are grounded, 1.
An electric field due to a voltage difference of 5 kV and an electric field due to a voltage difference of 1.45 kV are formed between the surface electrode layer 94 and the translucent conductive layer 92.

When the photoconductor 9 is irradiated with the laser beam 83 emitted by the optical system 8 in the state where the electric field is formed as described above, the laser beam 83 is exposed to the transparent substrate 91 (support). The light is transmitted through the transparent conductive layer 92 and reaches the charge generation layer 96. The charge generation layer 96 generates a carrier pair when absorbing light in the presence of an electric field. Of the generated carrier pairs,
The freed carriers move toward opposite electrodes having opposite polarities. At this time, the freed positive carriers move to the surface of the photosensitive layer 93 through the charge transport layer 97. As a result, the electric field between the gaps on the surface of the photosensitive layer 93 and the surface of the image bearing belt 2 rises. When this electric field exceeds a threshold value determined by the passion law, discharge is generated, and the dielectric layer 25 of the image bearing belt 2 corresponding to the exposure position of the photoconductor 9 is generated.
The surface is charged and an electrostatic latent image is formed.

At this time, in the photosensitive layer 93 and the charge generation layer 9
Carriers trapped in the trap formed near the interface between the charge transport layer 6 and the charge transport layer 97 and free carriers having a very slow moving speed in the photosensitive layer 93 are generated as excess carriers.
These excess carriers are weak in the exposure light amount, and the photosensitive layer 93
When the internal electric field is small, space charges are formed in the photosensitive layer 93, and after the exposure is completed, the latent image is adversely affected and the trailing edge of the image is elongated.

However, since the surface electrode layer 94 is provided on the surface of the photosensitive layer 93 on the photosensitive member 9 and the bias voltage is applied from the second power source 14, the electric field in the photosensitive layer 93 is always maintained at a high electric field. ing. Therefore, the excess carriers reach the surface of the photosensitive layer 93 without delay and are discharged, or are captured by the surface electrode layer 94, so that the excess carriers are not accumulated in the photosensitive layer 93. Therefore, even after the end of the exposure, the discharge is continued and the trailing edge of the latent image is stretched. By providing the surface electrode layer 94 in this manner, the discharge ends immediately in synchronization with the end of exposure, and a desired latent image that is substantially the same as the exposed image can be formed.

Next, the process after the formation of the latent image will be described. The electrostatic latent image formed on the image bearing belt 2 is conveyed to the developing section by the rotation of the driving roller 3 and the heating roller 4,
The toner is developed by the developing device 6. After that, the toner image formed on the image carrying belt 2 is further transferred to the driving roller 3
Also, it is conveyed by the rotation of the heating roller 4, is heated by the heating element 11 provided inside the heating roller 4, and is simultaneously transferred onto the recording sheet S by the transfer roller 7. At this time, the toner image is melted and transferred, so that the toner does not remain on the image bearing belt 2 and is almost completely transferred to the recording paper S and is fixed at the same time.

As the photoconductor 9 of the above-mentioned embodiment,
The one manufactured by the following method is used. First, a translucent substrate 91 having a substantially plate shape that is long in the main scanning direction, specifically, a width in the main scanning direction of 250 mm, a width in the sub scanning direction of 30 mm,
A transparent conductive layer 92 is formed on the surface of a transparent glass plate having a thickness of 3 mm.
The base material was formed. The transparent conductive layer 92 is I
The TO film was made to have a thickness of about 0.2 by a known ion plating method.
.mu.m (the area resistance of the ITO film is about 100 .OMEGA ./. quadrature.), and about 0.5 .mu.m as an injection preventing layer thereon.
Was coated by the dipping method.

Subsequently, 1 part by weight of τ (tau) type metal-free phthalocyanine, 2 parts by weight of polyvinyl butyral resin, and 100 parts by weight of tetrahydrofuran were placed in a ball mill pot and dispersed for 24 hours to obtain a photosensitive coating. The viscosity of the photosensitive paint at this time is 15 cp at 20 ° C. As the polyvinyl butyral resin, a resin having an acetylation degree of 3 mol% or less, a butylation degree of 70 mol% and a polymerization degree of 1000 was used. Then, this photosensitive coating was applied to the surface of the transparent conductive layer 92 of the substrate by a dipping method to form a charge generation layer 96 having a thickness of 0.4 μm after drying.

Next, on the charge generation layer 96, a solvent comprising 8 parts by weight of a hydrazone compound represented by the following structural formula (Formula 1), 0.1 part by weight of an orange dye, 10 parts by weight of a polycarbonate resin and 180 parts by weight of tetrahydrofuran. The coating solution dissolved therein was applied by a depping method and dried to form a charge transport layer 97 having a film thickness of 21 μm.

[0030]

Embedded image

Next, a surface electrode layer 94 having a slit pattern as shown in FIG. 3 is provided on the surface of the photosensitive layer 93, more specifically, the surface of the charge transport layer 97, and a surface protective layer 95 is further provided thereon. . The surface electrode layer 94 of this slit pattern
Was formed by depositing aluminum with the mask sheet in close contact with the surface of the photosensitive layer 93, and then removing the mask.

The thickness of the strip-shaped conductive portion 98 forming the slit 99 of the surface electrode layer 94 is 0.1 μm. still,
If the adhesiveness with the photosensitive layer 93 can be secured and the strength has a substantially constant thickness within a range not causing a problem in practical handling and durability, there is no particular problem, and 0.03 μm or more 5
It is considered appropriate that the thickness is less than μm. As will be described later, the slit width L is preferably 10 μm or more and 150 μm or less, and the width W of the strip-shaped conductive portion is preferably 2 μm or more and 50 μm or less.

As described above, the transparent conductive layer 92 is formed on the transparent substrate 91 (support) to serve as a substrate, and the charge generating layer (function separation type photosensitive layer 93) is formed thereon. CG
L) 96 and the charge transport layer (CTL) 97 were laminated, and the surface electrode layer 94 and the surface protective layer 95 were further formed thereon to obtain a photoreceptor 9.

With respect to the structure of the photosensitive layer 93, in addition to the function separation type described above, it may be an inverse laminated type or a so-called single layer type. Further, as the charge generating material, the charge transporting material, the binder resin, the additive, etc., known materials may be appropriately selected according to the purpose. In addition, the photosensitive material is not limited to the organic material, and an inorganic material such as zinc oxide, cadmium sulfide, selenium alloy, amorphous silicon alloy, amorphous germanium alloy may be used. Further, a publicly known undercoat layer may be provided for the purpose of improving charging performance, image quality, adhesion to a substrate and the like. The substrate is not particularly limited as long as it has a conductive surface and is a substrate that is transparent to the light to be exposed and serves as a support.

The surface electrode layer 94 is made of aluminum, a metal material such as chromium, titanium, magnesium, gold, or platinum,
Alternatively, a conductive oxide film such as tin oxide, indium oxide, or ITO, or a material such as a conductive paste or a conductive ink can be used. The surface electrode layer 94 is not particularly limited as long as it is electrically conductive.
In the structure in which 5 is not provided, the surface electrode layer 94 is directly exposed to discharge, and therefore it is preferable to use a material in which oxidation is difficult to proceed.

The method of forming the surface electrode layer 94 is not limited to this, and the electrode may be formed by a method such as ion plating or sputtering instead of vapor deposition. Alternatively, the pattern may be formed by photolithography after forming the electrodes by the above method without using the mask sheet. Further, printing may be performed using a conductive paste or conductive ink.

The surface protective layer 95 should be made of an insulating organic film such as polyester or polyamide, an organic plasma polymerized film such as amorphous carbon, or a metal oxide film such as alumina, titanium oxide or silicon oxide. You can The thickness of the surface protective layer 95 is preferably as thin as possible so as not to affect the voltage drop and the movement of carriers, and is generally 0.0
It is considered appropriate to be 5 μm or more and 2 μm or less.

The material of the dielectric material that can be used for the substrate 21 and the dielectric layer 25 of the image bearing belt 2 of the above-described embodiment is not limited to the above-mentioned polyimide or fluororesin, but may be polyethylene, polypropylene, ionomer. , Polyvinyl alcohol, polyvinyl acetate, ethylene vinyl acetate copolymer, poly-4-methylpentene-
1, polymethyl methacrylate, polycarbonate polystyrene, acrylonitrile methyl acrylate copolymer,
Acrylonitrile butadiene styrene copolymer, polyterephthalate ethylene, polyuretanelastomer, cellulose acetate, cellulose triacetate, cellulose nitrate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, regenerated cellulose, nylon 6, nylon 66, nylon 11, nylon 12 , Polysulfone, polyether sulfone, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, polyvinylidene chloride, vinylidene chloride, vinyl chloride copolymer, vinyl nitrile rubber alloy, polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluoride Materials such as vinyl, polyvinylidene fluoride, and polyethylene tetrafluoroethylene copolymer may be used.

However, the electric resistivity of the material of the dielectric layer 25 is preferably 10 ¹¹ Ωcm or more in order to prevent the charging potential from decreasing with time. Also, the dielectric layer 25
The thickness is not particularly limited as long as the strength is within a range that does not cause a problem in practical handling and durability.
Generally, it is considered that about 2 to 100 μm is appropriate.

Next, a concrete experiment conducted for confirming the effect of the image forming apparatus of the above-described embodiment, that is, the effect of eliminating the elongation at the trailing edge of the image will be described. This experiment is
Structures of the photoconductor 9 and the image bearing belt 2 shown in FIG. 2, and FIG.
The conditions are changed for the surface electrode layer 94 having the slit pattern having the configuration shown in FIG. As a condition common to all the experimental examples, the film thickness d _p of the photosensitive layer 93 is 21 μm.
m, air layer thickness d _a (from the surface of the photosensitive layer 93 to the dielectric layer 25
The distance to the surface) was 30 μm, and the film thickness d _i of the dielectric layer 25 of the image bearing belt 2 was 15 μm. Further, the system speed (moving speed of the image bearing belt 2) was 38 mm / sec, the exposure light amount for exposing the photoconductor 9 was 0.35 mW / dot, and the diameter of the exposure spot 19 at the time of exposure was 140 μm. Other configurations, materials, etc. are as described above.

Table 1 shows the conditions of the experimental examples and comparative examples and the experimental results thereof. In Experimental Examples 1 to 9, the voltage of the translucent conductive layer 92 of the photoconductor is set to 1.5 kV and the voltage of the surface electrode layer 94 is set to 50 V, and the width W of the belt-shaped conductive portion 98 and the width of the slit 99 (band-shaped) are set. The distance between conductive parts) L was changed. next,
In Experimental Examples 10 to 16, the width W of the strip-shaped conductive portion 98 was 30 μm.
The width of the slit 99 (distance between the strip-shaped conductive portions) L is 90 μm
The voltage applied to the translucent conductive layer 92 of the photoconductor 9 and the voltage applied to the surface electrode layer 94 having a slit pattern were changed by using the surface electrode layer 94 having a slit pattern of m.
Further, as a comparative example, one having no surface electrode layer 94 was used.

As shown in FIG. 10 (a), each of the experimental examples and the comparative examples has a length of 10 mm to 40 mm and a width of 4 mm.
A test pattern consisting of dot vertical lines (lines in the sub-scanning direction) is exposed by laser light, and the line length extension ΔL (see FIG. 10B) of the toner image actually reproduced on the recording paper S is measured. did.

A very good condition in which the measured value of ΔL is in the range of ± 30 μm ◎ A good condition in the range of ± 50 μm ○ A less disturbing condition in the range of ± 100 μm ◇ Within the range of ± 200 μm A somewhat anxious state was evaluated as Δ, and a practically problematic state with a fluctuation range of more than that was evaluated as ×. In addition, when evaluation was not possible due to a problem on the image, "-" was added.

[0044]

[Table 1]

According to Experimental Examples 1 to 9, the width L of the slit 99 (distance between the strip-shaped conductive portions 98) L is 10 μm to 150 μm.
The range of μm is considered suitable. This is because if the width L of the slit 99 is less than 10 μm, the image density may decrease, and if the width L of the slit 99 exceeds 150 μm, the effect of stretching the image is expected. This is because it cannot be done. Practically, it is desirable that the slit width L be in the range of 35 μm to 130 μm.

Next, it is considered that the width W of the strip-shaped conductive portion 98 in the sub-scanning direction (electrode width between the slits 99) W is preferably in the range of 2 μm to 50 μm. Width W of the band-shaped conductive portion 98
However, if it is less than 2 μm, unevenness may occur in the image due to voltage drop, and the width W of the belt-shaped conductive portion 98 is
If it exceeds 50 μm, the image density may decrease, or the formed image may become a discontinuous dot image. Practically, the width W of the belt-shaped conductive portion 98 is 10
It is desirable to set it in the range of μm to 30 μm.

In addition, in a preferable range of the width L of the slit 99 and the width W of the strip-shaped conductive portion 98, the aperture ratio L / (L
It is considered that + W) is preferably 0.7 or more. This is because if the aperture ratio is less than 0.7, carriers generated by exposure that contribute to discharge are reduced, and the image density may be reduced, or the formed image may be a discontinuous dot image. Because.

Next, from the results of Experimental Examples 10 to 16, the voltage V _C applied to the translucent conductive layer 92 of the photoconductor 9 is ± (8
It is considered suitable to apply in the range of 00 to 2000) V. This is because if a voltage higher than 2000 V is applied, noise may occur due to abnormal discharge, and if the voltage is less than 800 V, the image density may decrease. In addition, the applied voltage V to the surface electrode layer 94
_P is (-400 to +1) when the voltage V _C has a positive polarity.
000) V and the voltage V _C have a negative polarity (-100
It is considered suitable to apply in the range of 0 to +400) V. Since the influence of excess carriers in the photosensitive layer 93 has a great influence on the elongation of the image, in practice, the photosensitive layer 93
It is considered to be related to the electric field applied inside. Therefore,
To be effective against _{elongation, │ (V C -V P)} / d
_It is considered necessary to determine the voltage V _P applied to the surface electrode layer 94 in correspondence with the voltage V _C applied to the translucent conductive layer 92 of the photoconductor 9 so that _p | becomes 40 V / μm or more. To be

4 to 7 show another embodiment of the surface electrode layer 94. The one shown in FIG. 4 has four strip-shaped conductive portions 98a parallel to each other arranged in the main scanning direction.
A large number of strip-shaped conductive portions 98b parallel to each other are arranged in the sub-scanning direction to form a mesh shape. In the structure shown in FIG. 5, two strip-shaped conductive portions 98 parallel to each other are arranged in the main scanning direction, and only one slit 99 is formed between them. As described above, it is not always necessary to provide a plurality of slits, and at least one slit may be provided at the position in the main scanning direction at which the exposure spot 19 is irradiated. In addition, as shown in FIG.
The slits are slanted by arranging the strip-shaped conductive portions 98a in the main scanning direction and arranging a large number of parallel strip-shaped conductive portions 98b that are inclined in both the main scanning direction and the sub-scanning direction. It was formed in. Further, in the structure shown in FIG. 7, one strip-shaped conductive portion 98a is arranged in the main scanning direction, and a large number of parallel strip-shaped conductive portions 98b are arranged in a comb shape so as to be orthogonal to the main scanning direction. By doing so, a slit is formed.

In addition, the surface electrode layer 94 may have any shape as long as it has an aperture ratio of 70% or more in the exposed region of the photosensitive layer 93 and does not affect the image. good. Further, the surface electrode layer 94 is
It does not necessarily have to be on the surface of the photosensitive layer 93.
It suffices if it is located near the surface of No. 3 where the discharge after exposure due to excess carriers can be removed.

FIG. 8 shows an image forming apparatus of another embodiment which performs exposure from the surface side of the photosensitive layer 93. In this image forming apparatus 40, the optical system 8 is arranged inside the image carrying belt 41 so that the irradiation direction of the laser beam is from the surface side of the photosensitive layer 93 (the surface side facing the image carrying belt 41). is there. Therefore, it is necessary to form the image carrying belt 41 so as to have a light transmitting property.

On the other hand, on the contrary, the support 43 which holds the photosensitive layer 93 of the photosensitive member 9 and the conductive layer 92 of the photosensitive member 9 do not need to have a light-transmitting property. In addition, since the optical system 8 is installed inside the image carrying belt 41, it is necessary to make the inside of the belt large, and the auxiliary roller 44 is provided. The other parts have almost the same configuration as the above-mentioned embodiment, and are denoted by the same reference numerals, and the description thereof will be omitted.
Even with this structure, the photosensitive layer 9 is the same as in the above embodiment.
By providing a surface electrode layer 94 on the surface of No. 3 and applying a voltage, it is possible to effectively deal with the expansion of the image (expansion of the trailing edge of the latent image).

Although the semiconductor laser is used as the light source for exposing the photosensitive member 9 in any of the above-described embodiments, the present invention is not limited to this, and the photosensitive member 9 can be appropriately exposed as long as it can be exposed. A known exposure method such as an LED method, an LED method, a liquid crystal shutter method, and a PLZT method can be used. Also, by changing the characteristics of the developer,
It goes without saying that it is possible to develop the unexposed area without developing the exposed area.

[0054]

As is apparent from the above description, according to the present invention, excess carriers can be removed by forming the surface electrode layer on the surface of the photosensitive layer of the photoreceptor. Therefore, the discharge is promptly performed at a point corresponding to the exposure position of the photoconductor, and the discharge is promptly stopped when the exposure is completed, so that the image is faithfully generated without causing the image to extend particularly in the traveling direction of the image carrier. The image can be reproduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic sectional view of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a main part of the image forming apparatus shown in FIG.

FIG. 3 is a view showing the shape of a surface electrode layer of a photoconductor.

FIG. 4 is a diagram showing a pattern shape of a surface electrode layer according to another embodiment.

FIG. 5 is a diagram showing a pattern shape of a surface electrode layer according to still another embodiment.

FIG. 6 is a diagram showing a pattern shape of a surface electrode layer according to still another embodiment.

FIG. 7 is a diagram showing a pattern shape of a surface electrode layer according to still another embodiment.

FIG. 8 is a schematic sectional view of an image forming apparatus according to another embodiment of the invention.

FIG. 9 is a view showing a conventional image forming apparatus.

FIG. 10A is a diagram showing a test pattern of an original image, and FIG. 10B is a diagram showing a conventional example of a toner image of the test pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image carrying belt (image carrying body), 3
... drive roller, 4 ... heating roller, 5 ... latent image forming device, 6
... developing device, 9 ... photoconductor, 13 ... first power source, 14 ... second
Power source (bias voltage applying means), 23 ... Conductive layer, 25 ...
Dielectric layer (insulating layer), 92 ... Translucent conductive layer, 93 ... Photosensitive layer, 94 ... Surface electrode layer, 95 ... Surface protective layer.

Claims (4)

[Claims] 1. An image carrier having an insulating layer formed on a conductive layer and a photosensitive member having a photosensitive layer formed on the conductive layer are arranged such that the insulating layer and the photosensitive layer face each other, and a voltage is applied between the conductive layers. An image forming apparatus that forms a latent image on a traveling image carrier by performing image exposure under the condition that a voltage is applied, and forming a latent image on a traveling image carrier by a discharge between the photoreceptor and the image carrier. An image forming apparatus comprising: the patterned surface electrode layer, and a bias voltage applying unit that applies a bias voltage to the patterned surface electrode layer. 2. The image forming apparatus according to claim 1, wherein the patterned surface electrode layer is overcoated with an insulating protective film. 3. The image forming apparatus according to claim 1, wherein the pattern of the patterned surface electrode layer has a shape having a slit or a mesh shape. 4. The pattern-shaped surface electrode layer having the slits has a slit width of 10 μm or more and 150 μm or less, and a conductive portion forming the slits has a width of 2 μm or more 50
The image forming apparatus according to claim 3, wherein the image forming apparatus has a thickness of not more than μm.