JPH09244364A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the elongation at the rear end of an image. SOLUTION: An image forming device has an image carrier 2 provided with an insulating layer 25 formed on a conductive layer 23 and a photosensitive member 9 provided with a photosensitive layer 93 formed on a conductive layer, both being arranged for the insulating layer 25 to be opposed to the photosensitive layer 93. An image is exposed in the state that voltage is applied between both conductive layers and a latent image is formed on the running image carrier 2 by discharge between the photosensitive material 9 and the image carrier 2. The conductive layer 90 of the photosensitive member 9 is linearly formed to be extended perpendicular to the running direction of the image carrier 2.

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. 10, a photosensitive member 101 composed of a small piece 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.
Are sequentially laminated. On the other hand, the charge holding medium 10
2 is an insulating layer support 106, a charge holding medium electrode 107,
And the insulating layer 108 are sequentially stacked. The photoconductor 101 and the charge holding medium 102 are composed of a photoconductive layer 105.
And the insulating layer 108 are arranged so as to 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]

FIG. 11 is a schematic diagram of the device described above.
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. 11B, the image trailing end portion of the electrostatic latent image formed on the charge holding medium 102 is extended 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, and as a result, excess carriers generated in the photoconductor continue discharging even after the exposure is completed, and the exposure is stopped. It was found that the stop of the discharge and the stop of the discharge did not coincide with each other, and the latent image was stretched at the trailing edge of the image. Here, the excess carrier includes a carrier of a component having a very low moving speed among the free carriers, and is a carrier that is not discharged during the exposure among the carriers generated by the exposure.

One of the causes of this excess carrier is that the charged area by the previous main scanning overlaps the charged area by the main scanning exposure this time in the insulating layer of the image carrier, and the potential of this overlapped area rises. As a result, the electric field strength applied to the photosensitive layer is reduced, and it is conceivable that not all of the carriers generated in the exposed region of the photosensitive member are discharged, but some of them are retained in the photosensitive member as excess carriers. In the present invention, the image elongation of the latent image is eliminated by preventing the generation of this excess carrier.

That is, the image forming apparatus of the first invention is
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 so that the insulating layer and the photosensitive layer face each other, and a voltage is applied between the conductive layers. In an image forming apparatus that irradiates light from a light source to perform image exposure and discharges between the photoconductor and the image carrier to form a latent image on the running image carrier, the conductive layer of the photoconductor is used as the image carrier. It is formed in a strip shape extending in a direction orthogonal to the traveling direction.

In the image forming apparatus thus constructed, the conductive layer of the photoconductor is formed in the shape of a strip, so that the electric field formed on the photosensitive layer is not affected by the voltage applied to the conductive layer of the image carrier. The range is limited by the shape of the conductive layer. As a result, carrier pairs are generated in a limited region of the photosensitive layer irradiated with the light from the light source and in which the electric field is applied. Free carriers of the generated carrier pairs 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.

At this time, the region to which the electric field is applied is limited in the photosensitive layer regardless of the irradiation region from the light source, and discharge occurs between the region and the corresponding limited region on the image carrier. Get charged. Therefore, the charged areas do not overlap each other in the traveling direction on the image carrier, and the generation of excess carriers can be prevented. Therefore, all the carriers generated in the photosensitive layer are consumed for discharging, and the expansion of the latent image formed on the insulating layer of the image carrier is eliminated.

It is preferable that the width of the belt-shaped conductive layer is smaller than the diameter of the exposure spot for exposing the photosensitive member. By forming in this way, the amount of charge in the charging area on the image carrier in the running direction of the image carrier becomes rectangular, and the sharpness of the formed image is increased.

In the image forming apparatus of the second invention, the insulating layer and the photosensitive layer face the image carrier having the insulating layer formed on the conductive layer and the photosensitive body having the photosensitive layer formed on the conductive layer. In the image forming apparatus for performing latent image formation on the running image carrier by the discharge between the photoconductor and the image carrier by performing image exposure with the voltage applied between both conductive layers. The conductive layer has a belt-shaped protrusion extending on the photosensitive layer side in a direction orthogonal to the traveling direction of the image carrier.

In the image forming apparatus thus constructed, the conductive layer of the photoconductor has strip-shaped protrusions on the side of the photosensitive layer. Therefore, the voltage is applied between the conductive layer of the image carrier and the conductive layer of the image carrier. The formed electric field concentrates on the strip-shaped protrusions, and the range is limited. As a result, carrier pairs are generated in a limited region of the photosensitive layer which has been image-exposed to light and has an electric field applied thereto. Hereinafter, similarly to the first aspect of the present invention, the charging areas on the image bearing member do not overlap each other in the traveling direction, and the generation of excess carriers can be prevented.

It is preferable that the width of the protrusion of the conductive layer formed in the band shape is smaller than the diameter of the exposure spot for exposing the photosensitive member. By forming in this way, the amount of charge in the charging area on the image carrier in the running direction of the image carrier becomes rectangular, and the sharpness of the formed image is increased.

[0015]

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 configuration diagram 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 rotated in the direction of arrow a by a driving roller 3 which is rotated by a driving device (not shown) and a heating roller 4 which is provided in parallel with the driving roller 3.

As shown in FIG. 2, the image carrying belt 2 comprises a base 21 made of a dielectric material, a conductive layer 23 formed on the surface thereof, and a dielectric layer 25 serving as an insulating layer formed thereon. 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 fluorocarbon resin having a thickness of 15 μm is further provided thereon. Also, the conductive layer 23
Are grounded by the conductive line 12.

The structure of the image carrier is not limited to such a belt, but 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 carrying belt 2. The optical system 8 includes a housing 81 in which a semiconductor laser generator, a collimating lens, a polygon mirror, an Fθ lens, a reflection mirror, and the like are arranged, and an exposure slit 82 is formed on the 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.

Here, the direction in which the laser beam 83 is scanned and exposed is the width direction of the image carrying belt 2 (front and back directions in FIG. 1).
And this direction is called the 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. Further, in the present embodiment, the diameter R of the exposure spot 19 in the sub-scanning direction is 140.
An optical system 8 that performs scanning exposure with μm is used. The diameter R of the exposure spot 19 is, as shown in FIG. 4, when the maximum light amount at the spot central portion is 1 in the light amount distribution of the light decreasing from the central portion of the exposure spot toward the outside,
The diameter of a range having a light amount of 1 / e ² or more.

As shown in FIG. 2, the photosensitive member 9 has a structure in which a belt-shaped conductive layer 90 and a photosensitive layer 93 are sequentially laminated on a transparent substrate 91. The transparent substrate 91 is a transparent glass plate.
The strip-shaped conductive layer 90 is composed of an ITO film 94 which is a light-transmitting conductive material and a polyamide resin layer 95 which is also a light-transmitting injection preventing layer, and has a width d in the sub-scanning direction as shown in FIG. Is 90 μm and has a strip shape extending in the main scanning direction. The first power supply 13 is connected to the ITO film 94 of the strip-shaped conductive layer 90.

The photosensitive layer 93 is made of semiconductor laser light (wavelength 78
Charge generation layer (CGL) having a carrier pair generation function, which is a function-separated type for negative charging having good sensitivity to long-wavelength light such as 0 nm) and LED light (wavelength 680 nm).
96 and a charge transport layer (CTL) 97 having a free carrier transport function.

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 photoconductor 9 is not in contact with the image bearing belt 2, a stable latent image is formed without contaminating the surface of the photoconductor 9 even if foreign matter is conveyed as the image bearing belt 2 travels. 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 the vicinity of 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 (V _C ) of 1.5 kV is applied to the belt-shaped conductive layer 90 of the photoconductor 9 by the first power supply 13. Therefore, an electric field due to a voltage difference of 1.5 kV is formed between the conductive layer 23 of the image bearing belt 2 and the belt-shaped conductive layer 90 which are grounded.

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 passes through the transparent substrate 91 (support). Then, it further passes through the strip-shaped conductive layer 90 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. Among 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 surface of the dielectric layer 25 of the image bearing belt 2 corresponding to the exposure position of the photoconductor 9 is charged to form an electrostatic latent image. .

At this time, as shown in FIG. 5A, the charged area of the dielectric layer 25 of the image carrying belt 2 by the exposure of this time (second time) partially overlaps with the charged area of the exposure of the previous time (first time). When overlapped (area K), the potential of this overlapped area K rises. The state of the potential distribution at this time is shown in FIG. In this figure, the vertical axis represents the potential, the horizontal axis represents the position (distance), and the slope of the graph represents the strength of the electric field. Dielectric layer 25
The potential distribution is shown by a broken line in the state where the surface of is not charged, and the solid line shows the potential distribution when the surface of the dielectric layer 25 is charged.

As is apparent from FIG. 6, the dielectric layer 25
Is charged, the potential difference between the transparent conductive layer 92 of the photoconductor 9 and the surface of the dielectric layer 25 of the image bearing belt 2 becomes small. At that time, the inclination of the graph becomes small, and the photosensitive layer 9
3 and the electric field between the gap between 3 and the dielectric layer 25 and the electric field formed in the photosensitive layer 93 both weaken. Then, the moving speed of the carriers generated in the charge generation layer 96 by the exposure this time in the photosensitive layer 93 becomes slow, and a part of the carrier is not discharged and the photosensitive layer 9 is not discharged.
It stays in 3 as an excess carrier. The excess carriers form space charges in the photosensitive layer 93 and cause elongation of the trailing edge of the image after exposure is completed.

However, the belt-shaped conductive layer 90 of the photoreceptor 9
Is formed in a strip shape that extends narrowly in the main scanning direction, and the region where the electric field is formed in the photosensitive layer 93, that is, the region where the generated carriers move is limited. Carriers are generated in the portion irradiated with the laser beam 83, but in the region where the electric field is not formed, the generated carriers are instantaneously recombined and disappear. On the other hand, in the region where the electric field is formed, the generated carriers move in the photosensitive layer 93 by the electric field and are discharged only in the portion where the electric field is formed. As a result, it is as if the carriers were generated by the laser light irradiation only in the region where the electric field is formed. Then, as shown in FIG.
The charge amount distribution in the sub-scanning direction of the carrier discharged to the dielectric layer 25 of the image bearing belt 2 has a rectangular shape with both ends cut, and the charge becomes uniform. In addition, overlapping of charged areas is eliminated, and generation of excess carriers is prevented. By thus forming the strip-shaped conductive layer 90 in a strip shape that extends thinly in the main scanning direction, it is possible to suppress the generation of excess carriers, the discharge is finished in synchronization with the end of the exposure, and the desired image is almost the same as the exposed image. A latent image can be formed.

Here, the traveling speed (system speed) V _S of the image bearing belt 2 will be described. In the case of this case,
As shown in (b), by using the dielectric layer 25 in a state where the charged areas in the sub-scanning direction do not overlap, the effect is remarkably exhibited. Therefore, it is necessary to appropriately set the traveling speed V _S of the image bearing belt 2. In order to prevent the charged areas from overlapping, a value obtained by dividing the width W of the charged areas in the sub-scanning direction by the exposure interval time, that is, the time from the first exposure to the second exposure, causes the image carrying belt 2 to travel. it is the speed V _S.

Here, the width W in the sub-scanning direction is determined by the strip-shaped conductive layer 9
It is determined by the width d of 0 in the sub-scanning direction and the spot diameter R of the laser light. When the width d of the belt-shaped conductive layer 90 in the sub-scanning direction is equal to or smaller than the spot diameter R of the laser light 83, the width in the sub-scanning direction of the charged region on the dielectric layer 25 that is charged in one main scan is the sub-scanning direction. It is almost equal to the width d in the scanning direction. On the contrary, when the width d of the belt-shaped conductive layer 90 in the sub-scanning direction is larger than the spot diameter R of the laser beam 83, the width in the sub-scanning direction of the charged region on the dielectric layer 25 that is charged in one main scanning is. , The spot diameter R of the laser beam 83 may be considered.

In addition, in an apparatus in which the traveling speed (system speed) V _{S of} the image bearing belt 2 is predetermined, the charging width (charging in one main scan is calculated from the product of the exposure interval time and the traveling speed V _S. The width in the sub-scanning direction) may be calculated and the width d in the sub-scanning direction of the belt-shaped conductive layer 90 may be set to an appropriate value.

Specifically, the exposure interval time of the laser beam 83 is 2.24 ms (a unique value determined by the laser scanning speed), and the width d of the belt-shaped conductive layer 90 in the sub-scanning direction is 90.
Since the spot diameter of the laser beam 83 is 140 μm, the width of the charging region in the sub-scanning direction is 90 μm.
Therefore, the traveling speed (system speed) V _S of the image bearing belt 2 is (90 × 10 ⁻⁶ ) ÷ (2.24 × 10 ⁻³ ).
Therefore, it becomes 40 mm / s.

Next, the process after 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 glass plate having a thickness of 3 mm, on which a strip-shaped conductive layer 90 was formed, was used as a substrate.

In the strip-shaped conductive layer 90 as shown in FIG. 3, a mask sheet having a strip-shaped slit portion is brought into close contact with the surface of the glass plate, and an ITO film 94 is formed to a thickness of about 0.2 μm by a known ion plating method (ITO). The sheet resistance of the film is about 100 Ω / □), and a polyamide resin layer 95 of about 0.5 μm as an injection preventing layer is further applied thereon by a dipping method, and then the mask sheet is removed to form.

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, the photosensitive paint is applied to the strip-shaped conductive layer 9 of the substrate.
No. 0 surface and a glass plate were coated 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.

[0039]

Embedded image

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. In addition, the transparent substrate 9
1 is not particularly limited as long as it is a substrate that is transparent to the light to be exposed and serves as a support.

The conductive portion of the strip-shaped conductive layer 90 (the ITO film 9
4) is not particularly limited to ITO as long as it is a transparent conductive material that can be patterned on a substrate such as glass or a transparent resin. However, in order to avoid a voltage drop, it is preferable to use a material having a sheet resistance of 1000 Ω / □ or less. Conductive portion of the strip-shaped conductive layer 90 (ITO film 9
The formation method of 4) is not limited to the above-mentioned method, and the conductive material layer may be formed by a method such as vapor deposition or sputtering instead of the ion plating method. Alternatively, the pattern may be formed by photolithography after the conductive material layer is formed by the above method without using a mask sheet. Further, printing may be performed using transparent conductive ink. Also,
The injection prevention layer is not limited to the polyamide resin, and a known material having a light transmitting property may be used.

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, the image forming apparatus 1 of the above-described embodiment
A concrete experiment conducted for confirming the effect of the above, that is, the effect of eliminating the elongation at the trailing edge of the image will be described. This experiment was carried out under various conditions by using the photoreceptor 9 having the belt-shaped conductive layer 90 extending in the main scanning direction shown in FIGS. 2 and 3 and the image bearing belt 2. As conditions common to all the experimental examples, the voltage V _C applied to the belt-shaped conductive layer 90 of the photoconductor 9 is 1.5 kV, the film thickness d _p of the photosensitive layer 93 is 21 μm, and the air layer thickness d _a (photosensitive layer 93 The distance from the surface to the surface of the dielectric layer 25) 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 exposure light amount for exposing the photoconductor 9 was set to 0.35 mW / dot. Other configurations, materials and the like are the same as those in the above-described embodiment.

Table 1 shows the conditions of the experimental examples and comparative examples and the experimental results thereof. In Experimental Examples 1 to 5, the exposure spot diameter R of the laser beam was set to 140 μm, and the width d of the belt-shaped conductive layer 90 in the sub-scanning direction was changed. Next, in Experimental Examples 6 to 10,
The exposure spot diameter R of the laser beam was set to 200 μm, and the width d of the belt-shaped conductive layer 90 in the sub-scanning direction was changed as in Experimental Examples 1 to 5. Further, as a comparative example, a flat conductive layer is used on the entire surface, and the exposure spot diameter R of the laser beam is set to 140.
μm and 200 μm are shown and the system speed V _S is changed.

In each of the experimental examples and the comparative examples, as shown in FIG. 11A, the length is 10 mm to 40 mm and the width is 4 mm.
A test pattern composed of dot vertical lines (lines in the sub-scanning direction) is exposed by laser light, and the line length extension ΔL (see FIG. 11B) 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, regarding those that have practical problems such as breaks and blurring in the line image itself, *
Was added.

[0048]

[Table 1]

According to the results of Experimental Examples 1 to 10 and Comparative Examples 1 to 8, as compared with the case where the conductive layer is provided on the entire surface of the light-transmissive substrate 91 of the photoconductor 9, the band-shaped strip-shaped conductive layer extending in the main scanning direction. 9
It is clear that when 0 is provided, the elongation at the trailing edge of the image is significantly improved. Further, it is clear that it is effective to set the width d of the belt-shaped conductive layer 90 in the sub-scanning direction to be smaller than the spot diameter R of the laser light.

FIG. 7 shows a partially enlarged structural view of the photosensitive member 9 and the image carrying belt 2 which are the essential parts of the second embodiment. still,
Except for the photoconductor 9, the configuration of the entire apparatus and other parts have substantially the same configuration as in the first embodiment.
The same parts are designated by the same reference numerals and the description thereof will be omitted.

In the photoconductor 9 shown in FIG. 7, a light-transmissive conductive layer 92 is provided on the entire surface of a light-transmissive substrate 91 having a strip-shaped protruding portion 91a elongated in the main scanning direction, and a photosensitive layer 93 is further laminated. It is a composition. The strip-shaped protruding portion 91a provided on the transparent substrate 91 has a width in the sub-scanning direction of 90 μm and a height of 5 μm.
It is a μm protrusion. An ITO film 94 is formed on the entire surface of the translucent substrate 91 having the protrusions by about 0.2 μm by a known ion plating method (the area resistance of the ITO film is about 100Ω / □), and further thereon. Then, a polyamide resin layer 95 having a thickness of about 0.5 μm was formed as an injection preventing layer by a dipping method to form a translucent conductive layer 92, and a single-layer type photosensitive layer 93 was formed thereon. Due to the presence of the protruding portion 91 a on the transparent substrate 91, the protrusion 98 is formed on the surface of the transparent conductive layer 92.

In the image forming apparatus of the second embodiment configured as described above, the transparent conductive layer 92 has the projection 9
8, the electric field is concentrated on the protrusion 98 closest to the conductive layer 23 of the image bearing belt 2. For this reason, similarly to the first embodiment, the charge amount distribution in the sub-scanning direction has a rectangular shape with both ends cut, and as a result of no overlap of the charge regions, generation of excess carriers is prevented. By forming the strip-shaped projections 98 thinly extending in the main scanning direction on the translucent conductive layer 92 in this manner, generation of excess carriers can be suppressed, and discharge ends in synchronism with the end of exposure, and the exposed image It is possible to form a desired latent image almost the same as

Next, a concrete experiment conducted for confirming the effect of the image forming apparatus of the second embodiment described above, that is, the effect of eliminating the elongation at the trailing edge of the image will be described. In this experiment, the image forming apparatus shown in FIG. 1 was used and Experimental Examples 11 to 19 were performed using the constitution of the photoconductor 9 and the image carrying belt 2 shown in FIG.
The experiment was done. With respect to these experimental examples, the same test patterns were exposed under the same conditions as those of the experimental examples and comparative examples shown in Table 1 except for the conditions shown in Table 2, and the experiment was conducted.

The conditions of the experimental examples and the experimental results thereof are shown in Table 2.
Shown in In Experimental Examples 11 to 15, the exposure spot diameter R of the laser beam was 140 μm, the width d of the protrusion 98 of the transparent conductive layer 92 in the sub-scanning direction was 90 μm, and the height h of the protrusion 98 was changed. Next, in Experimental Examples 16 to 19, the exposure spot diameter R of the laser beam was 140 μm, and the projection 9 of the translucent conductive layer 92 was formed.
8 has a height h of 5 μm, and the protrusion 98 has a width d in the sub-scanning direction.
Is changed, and further, the system speed V _S is changed according to the charging width (width d of the protrusion or exposure spot diameter R) on the dielectric 25 in the sub-scanning direction. The evaluation is also as described above.

[0055]

[Table 2]

According to the results of Experimental Examples 11 to 19, by providing the translucent substrate 91 of the photosensitive member 9 with the strip-shaped projection 91a in the main scanning direction and the translucent conductive layer 92 with the projection 98, the image It is clear from the comparison with the comparative example of Table 1 (where the planar transparent conductive layer is provided on the entire surface) that the elongation is remarkably improved. Further, from Experimental Examples 11 to 15, it is preferable that the height h of the strip-shaped protrusion 98 is 3 μm or more. Furthermore, from Experimental Examples 15 to 19
It is clear that it is effective to set the width d of the sub-scanning direction 8 in the sub-scanning direction smaller than the spot diameter R of the laser light.

FIGS. 8 and 9 show an image forming apparatus according to the third embodiment in which exposure is performed from the photosensitive layer side of the photosensitive member. 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. 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.

On the other hand, on the contrary, the support and the conductive layer for holding the photosensitive layer 93 of the photosensitive member 9 may not have a light transmitting property. Therefore, in this embodiment, the conductive support 99 of the substrate made of aluminum which is a conductor as shown in FIG. 9 is used as the support / conductive layer of the photoconductor 9. Then, with respect to the other portions in which the conductive support 99 is provided with the strip-shaped projections 98a extending in the main scanning direction,
The structure is almost the same as that of the above-mentioned embodiment, and the same reference numerals are given and the description thereof is omitted.

In this embodiment, the photosensitive layer 93 is provided on the surface of the conductive support 99 having the protrusion 98a, and the electric field formed on the photosensitive layer 93 is concentrated on the protrusion 98a. Therefore, as in the above-described embodiment, the laser light 83
Among them, only a part of the laser light incident on the part where the electric field is formed reacts to generate a carrier pair, and the dielectric layer 25 of the image carrier 2 is discharged. I won't. Therefore, the stretch of the image (stretching of the trailing edge of the latent image)
Can be effectively dealt with. In addition, also in this embodiment, the single-layer type photosensitive layer 93 is used.

Since the conductive support 99 does not need to have a light-transmitting property, any metal material having conductivity may be used. However, in order to avoid a voltage drop, a volume resistance of 10 ⁷ Ω · cm or less is preferable.
Further, the protrusion 98a does not have to be integrally configured, and the strip-shaped protrusion 9 extending in the main scanning direction is formed on the surface of the flat metal substrate by an electro-forcing method or a known method.
8a may be formed or added.

Further, the projections 98 and 98a of the conductive layer of the photoconductor 9 shown in the second and third embodiments do not necessarily need to be continuous in the main scanning direction, and are in a range that does not affect the image. The protrusions may be intermittent. In any of the above embodiments, the semiconductor laser is used as the light source for exposing the photoconductor 9, but the present invention is not limited to this, and any LED can be used as long as the photoconductor 9 can be irradiated and appropriately exposed.
A known exposure method such as a method, a liquid crystal shutter method, a PLZT method can be used. Needless to say, the non-exposed area can be developed without developing the exposed area by changing the characteristics of the developer.

As in the present case, the photosensitive member 9 has a shape in which the electric field formed on the photosensitive layer 93 is concentrated in a strip shape extending in the main scanning direction.
Even if the exposure optical system is not made finer by forming the conductive layer of No. 2, the pixel density in the sub-scanning direction can be increased by narrowing the width of the electric field forming region and appropriately setting the system speed V _S. , Enables the creation of high-definition images.
Therefore, high definition can be achieved at low cost. Further, since the electric field is concentratedly formed in a specific region, the amount of electric charges charged by the discharge is increased, and an image with high contrast can be formed.

[0063]

As is apparent from the above description, according to the present invention, a belt-shaped conductive layer extending in the main scanning direction is used for the photoconductor, or a similar protrusion is formed on the conductive layer.
By concentrating the electric field formed on the photosensitive layer, it is possible to eliminate the overlap of charged areas on the image carrier. 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 conceptual 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 diagram showing a shape of a belt-shaped conductive layer of a photoconductor.

FIG. 4 is a diagram showing a light amount distribution of laser light.

5A is a diagram showing a charging area and a charging amount on an image carrying belt when a light shielding layer is not provided, and FIG.
It is a figure which shows a charging area and a charging amount when a light shielding layer is provided and charging areas do not overlap.

FIG. 6 is a diagram showing a potential distribution when a voltage is applied to the conductive layer.

FIG. 7 is an enlarged view of a main part of the second embodiment.

FIG. 8 is a diagram showing a conceptual diagram of an image forming apparatus according to a third embodiment of the present invention.

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

FIG. 10 is a diagram showing a conventional image forming apparatus.

FIG. 11A is a diagram showing a test pattern of a document image, and FIG. 11B 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, 23 ... conductive layer, 25 ... dielectric layer (insulating layer), 90 ... belt-shaped conductive layer, 92
... translucent conductive layer, 93 ... photosensitive layer, 98, 98a ... protrusions,
99 ... Conductive support.

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. In an image forming apparatus for performing latent image formation on a traveling image carrier by performing image exposure with a voltage applied, a conductive layer of the photoreceptor is arranged in a traveling direction of the image carrier. An image forming apparatus, which is formed in a strip shape extending in a direction orthogonal to the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the width of the conductive layer formed in the band shape is smaller than the diameter of the exposure spot for exposing the photosensitive member. 3. 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 so that the insulating layer and the photosensitive layer face each other, and a voltage is applied between the conductive layers. In an image forming apparatus in which a latent image is formed on a traveling image carrier by performing image exposure while applying a voltage, a conductive layer of the photoconductor is provided on the photosensitive layer side. An image forming apparatus having a strip-shaped projection extending in a direction orthogonal to a running direction of a body. 4. The image forming apparatus according to claim 3, wherein the width of the projection of the conductive layer formed in the band shape is smaller than the diameter of the exposure spot for exposing the photosensitive member.