JPH0728332A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an electrophotographic system image forming device capable of forming an image by using a thin film photoreceptor layer. CONSTITUTION:In the image forming device, an electrifying means 3, an exposing means 4, a developing means 5 having the formation of a conductive magnetic brush and a developing bias voltage applying means 6 are successively disposed on the photosensitive body layer side of an elecrtrophotographic photoreceptor 2 obtained by an a-Si system photosensitive body layer is laminated on an electric conductive substrate, the photosensitive body layer is constituted so that film thickness is 2-24mum and the surface protective layer of an insulator or a semiinsulator is laminated on a layer where a P-type semiconductor layer and an I-type or N-type semiconductor layer or the N-type semiconductor layer and the I-type or P-type semiconductor layer are successively laminated from a substrate side and the potential difference between the exposing/ nonexposing parts of the surface of the photoreceptor on a developing part is set 10-240V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, in particular, a combination of a photoconductor using an amorphous silicon photoconductive layer as a photoconductor layer and a low potential developing method using a conductive magnetic brush. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as the most general electrophotographic recording method, the Carlson method of developing by utilizing high potential contrast on a photoconductor has been widely put into practical use. In the Carlson method, a corona charger, an exposing unit, a developing unit, a transferring unit, a cleaning unit, a discharging unit, and the like are arranged around a drum-shaped or belt-shaped photosensitive member to charge, expose, develop, transfer, and fix. An image is formed on a recording paper through a process. And 5-6 in the corona charger
A high voltage of about kV is applied, the surface potential of the photoconductor immediately after charging (initial charging potential) becomes 500 to 1000 V, and the dark surface potential (dark development potential) of the photoconductor at the developing position.
Is as high as 400-800V. For developing the electrostatic latent image formed on the surface of the photoconductor by the distribution of the surface potential, a two-component developer or an one-component insulating magnetic toner usually composed of an insulating magnetic carrier and an insulating toner is used. An insulating magnetic brush development method is used.

The photoconductor layer required for the photoconductor for the Carlson method is an insulating photoconductor having a small relative permittivity εr of 8 or less and a dark resistivity ρd of 1 × 10 ¹³ Ω · cm or more. Selenium (Se) -based materials and organic photoconductors (OP)
The material C) has been used most often, but the photoreceptor layer has a thick film of 20 to 80 μm.

On the other hand, the amorphous silicon (hereinafter abbreviated as a-Si) type photosensitive material, which has been rapidly expanding in the market in recent years, has a large εr of 11 to 12 and a ρd of 1 × 1.
Since it is a little small, such as about 0 ¹⁰ Ω · cm, it was necessary for the photosensitive layer to be a thick film of at least 30 μm or more.

Further, since the substrate of the photosensitive member used in the usual Carlson method may be a conductive support having no translucency, aluminum (A) which is low in material cost and easy to process.
l) Wood has been commonly used.

By the way, recently, an electrophotographic recording method which does not require corona charging has been proposed in contrast to the above-mentioned Carlson method (Japanese Patent Publication No. 2-4900, Japanese Patent Publication No. 60-59592, and Japanese Patent Laid-Open No. 58-444).
45, JP-A-58-153957, JP-A-61-46961, JP-A-SHO
62-280772, etc.). According to this recording method, a drum-shaped or belt-shaped photoreceptor in which a light-transmissive conductive layer and a photoconductive layer are sequentially laminated on a light-transmissive support is exposed from the light-transmissive support side by an exposure means. At the same time, the surface of the photoconductor is rubbed with a magnetic brush made of conductive magnetic toner on the developing machine to which a bias voltage is applied by the power supply for developing bias, and thereby charging, exposure, and development are performed almost at the same time. Form a toner image. Then, this toner image is transferred onto a recording sheet by using a transfer unit such as a transfer roller or a corona transfer unit, and is fixed by a fixing unit to form a recorded image. On the other hand, the toner remaining on the photoconductor after the transfer is collected by the developing machine and reused. To date, conductive magnetic toner has been used as the developer in this electrophotographic recording method, and there is a problem that it is difficult to transfer the toner image formed on the photoconductor onto plain paper, which is an obstacle to practical use. However, recently, a two-component developer in which a conductive magnetic carrier and an insulating magnetic toner are combined has been proposed, which enables excellent plain paper recording.

In the above recording method, latent image formation and visualization of the latent image by the developer are performed almost at the same time, so that the charging potential or developing potential of the photoconductor is as low as 30 to 100 V, and no corona charger is used. Therefore, ozone is not generated due to corona discharge, the exposure unit is housed inside the photosensitive member, and the cleaning unit for the photosensitive member is not required. Therefore, there are advantages such as downsizing of the image forming apparatus. The film thickness of the photoconductor used for this can be reduced in proportion to the low potential of the photoconductor, and can be improved to about several μm.

[0008]

The above-mentioned Carlson method requires a high voltage power source of 5 to 6 kV for corona charging, and this high voltage is dangerous to the human body, and ozone generated by corona discharge is in the surroundings. There was a problem that it had an adverse effect.

An insulating magnetic brush developing method is generally used for developing the electrostatic latent image, and the developing contrast potential (potential difference between the dark portion and the light portion) on the surface of the photosensitive member at the developing position.
Is required to be 400 to 800 V or higher, and therefore the initial charging potential was as high as 500 to 1000 V.

The photoconductor film thickness required for such high-potential charging is 2 even in the case of Se system or OPC having a small εr and a large ρd.
A thick film having a thickness of 0 to 80 .mu.m and a large .epsilon.r and a relatively small .rho.d require a thick film of at least 30 .mu.m or more.

Deposition of such a thick film requires a long deposition time for a photosensitive material deposited by using an expensive vacuum equipment, for example, an a-Si photosensitive material manufactured by a plasma CVD method. Therefore, the cost is 10 times or more higher than that of the OPC photoconductor, which is a big problem both technically and economically.

Further, the a-Si photosensitive member has the following problems regarding the deposition of a thick film. The decrease in the photoreceptor surface potential in the non-exposed area (dark area) from charging to development is called dark decay. Since the dark decay of the a-Si photoconductor is as large as about 100 V, it is necessary to increase the initial charging potential in anticipation of the dark decay with respect to the required developing potential. When used or in a high temperature and high humidity environment, minute film formation defects existing in the photoconductor layer are gradually destroyed and enlarged, and appear as black spots or white spots in the recorded image, which causes deterioration of image quality. there were.

One of the causes of this dark decay is the generation of thermally excited carriers in the photoconductor layer, and these thermally excited carriers move to the surface of the photoconductor to neutralize the charge and reduce the surface potential. cause. Since the amount of the thermally excited carriers generated increases in proportion to the film thickness of the photoconductor layer, the dark attenuation increases in proportion to the film thickness. Particularly in the a-Si photoconductor, since the band gap of the a-Si material is narrow and the localized level density in the band gap, which is the center of generation of thermally excited carriers, is high, the amount of thermally excited carriers generated is large, and There is a problem that the increase in dark attenuation due to the thicker film is larger than that of the photoconductor material.

When recording a color image by electrophotography, it is desired that the photosensitivity of the photoconductor be panchromatic, that is, the photosensitivity to different exposure wavelengths be substantially uniform. In general, short-wavelength light is easily absorbed by the photoconductor layer and has a low transmittance. Therefore, when the photoconductor layer is thick, it is absorbed by only a part of the photoconductor layer on the exposure side to generate a photocarrier. The photosensitivity of wavelength light tends to be low. On the other hand, long-wavelength light easily transmits through the photoconductor layer, and even when the photoconductor layer is thick, photocarriers are generated in almost the entire region, so that the photosensitivity of long-wavelength light tends to be high. However, when the energy of long-wavelength light becomes smaller than the optical band gap of the photoconductor layer, it is no longer absorbed by the photoconductor layer and the sensitivity sharply decreases. a-Si
In the photoconductor, the photocarrier generation region for exposure to 685 nm is only 2 to 3 μm from the photoconductor layer surface, and most of the other layer regions act as a high resistance carrier transport layer.
There is a problem that the thicker the photoreceptor layer is, the more easily the traveling of the optical carrier is obstructed, which causes a decrease in sensitivity. on the other hand,
For 700 nm exposure, the photocarrier generation region is 30
Since the thickness is about μm and covers almost the entire area of the photoconductor layer, high sensitivity is exhibited. The thicker the film, the greater the difference in the photosensitivity due to such wavelengths, and the panchromaticity deteriorates, making it unsuitable for color image recording.

For the above reasons, the thicker the photoconductor layer in response to the higher potential, the longer the traveling distance of the photocarriers and the poorer the photosensitivity, so that the photosensitivity of the photoconductor becomes insufficient. However, there is a problem that the exposure of the process side becomes insufficient when the recording process is speeded up, a sufficient development contrast potential cannot be formed, and the image density becomes insufficient. Therefore, an LED using an exposure light source that is expected to be low in cost but has a small amount of light, for example, an LED array manufactured by epitaxially growing a III-V group compound semiconductor of gallium-arsenic-phosphorus (GaAsP) system on a Si single crystal substrate
There is also a problem that it is difficult to use a head or an EL head using an EL element array.

For the above reason, the thicker the photosensitive layer corresponding to the high potential, the longer the traveling distance of the photocarriers, so that the diffusion of the photocarriers in the film surface direction easily occurs. There is also a problem that the boundary of the electrostatic latent image on the surface of the photoconductor corresponding to the exposure is blurred and the resolution of the image becomes insufficient.

In the a-Si photoconductor, since the photoconductor layer is deposited at a high substrate temperature of about 270 ° C. by the plasma CVD method, the amount of deformation of the Al base drum after film formation is larger than that of other photoconductor materials. large. Therefore, the thickness of the Al substrate is usually required to be 2.5 to 8 mm in order to suppress this deformation, and the material cost of the substrate is higher than that of the OPC photosensitive member of 0.7 to 1.2 mm. there were. Furthermore, A
There is also a problem that only a machining method using a lathe can be used for mirror surface processing of a drum surface, and a mirror surface processing method by extrusion molding, which has a low processing cost, cannot be used.

On the other hand, in the OPC photosensitive member, since the dipping method is used for forming the photosensitive member layer without using a vacuum device, the size of the film thickness is not reflected so much in the cost, and even when the film thickness is increased, the cost is reduced. Can be manufactured. However, since the OPC photoconductor has a low hardness of the photoconductor layer, the OPC photoconductor is liable to be damaged by contact with a recording paper or the like and a cleaning process, and its life is about 1/10 of that of the a-Si photoconductor. Therefore, the frequency of exchanging the photoconductor becomes high when used in an electrophotographic apparatus, which causes a problem that a large amount of industrial waste is generated.

On the other hand, in the case of the Se type photoconductor, the photoconductor layer is formed by the vacuum deposition method, but since the film deposition rate is relatively high, the cost for thickening the film is higher than that of OPC, but it is aS.
It can be lower than i. However, since the Se-based photoconductor contains a toxic element such as As which is harmful to the human body, it is gradually used from the viewpoint of environmental problems and pollution problems.

Therefore, if a photoconductor made of a material having a long life, no pollution, and good for the global environment, such as an a-Si photoconductor, can be manufactured at a low cost, it is most easily accepted in the market. It is desired to reduce the cost.

Further, according to the electrophotographic recording method which does not require the corona charging, the film thickness of the photosensitive member used therefor is about several μm as described above. However, this
When the i-type photosensitive material is used, there are the following problems.

The light-transmissive conductive layer laminated between the light-transmissive support and the photoconductor layer absorbs or reflects a part of the exposure from the light-transmissive support side. The amount of exposure light reached was reduced, which was one of the causes of sensitivity deterioration.

The a-Si photosensitive layer has a structure in which a carrier injection blocking layer and a photoconductive layer are sequentially laminated on a translucent conductive layer. Like the injection blocking layer, a part of the exposure is absorbed. Since the light is reflected or reflected, the amount of exposure light reaching the photoconductive layer that generates photocarriers in the photoconductor layer is reduced, which is one of the causes of sensitivity deterioration.

The decrease in the exposure amount due to the absorption as described above is remarkable especially as the exposure wavelength is short, so that the unevenness of the sensitivity with respect to the exposure wavelength becomes large, and it is applied to a color image recording in which the panchromaticity of the photosensitivity is required. There was a problem in.

In the photoconductor of this recording method, the film thickness of the photoconductor layer may be thin, but the support must be transparent.
A glass tube is generally used for this translucent support because heat resistance is required during a-Si film formation. However, since the dimensional accuracy of the glass tube in the pultrusion molding state is lower than the required accuracy, a desired dimensional accuracy is required. Post-processing is required to obtain. However, since glass is harder than Al and cannot be mirror-finished by cutting with a lathe, it has to rely on polishing, which requires a long processing time and increases costs. Further, since a translucent conductive layer is required between the support and the photoreceptor layer, there is a problem that a separate forming step is required. Therefore, because of these, there is a problem that the cost of the photoconductor of this recording method is higher than that of the photoconductor of the Carlson method.

The present invention has been made as a result of intensive studies conducted by the present inventors in view of the above-mentioned problems.
In an electrophotographic image forming apparatus using a Si photoconductor, it is possible to form an image on a thin photoconductor layer, and increase dark attenuation, decrease photosensitivity, or resolving power caused by thickening the photoconductor layer. It is an object of the present invention to provide an image forming apparatus which makes good use of the excellent electrophotographic characteristics of an a-Si photoconductor without eliminating the deterioration of

Further, according to the present invention, in an electrophotographic image forming apparatus using an a-Si photoconductor, it is possible to form an image on a thin photoconductor layer, thereby reducing the deformation amount of the Al substrate. An object of the present invention is to provide an image forming apparatus in which the thickness of Al is reduced and the cost of materials and processing for the substrate used and the film forming process is reduced.

[0028]

The image forming apparatus of the present invention comprises a charging means, an exposing means, a developing means, and a conductive means for an electrophotographic photoreceptor having an amorphous silicon type photoreceptor layer formed on a conductive substrate. A means for applying a developing bias voltage is provided between the photosensitive substrate and the developing means, and the photosensitive layer is formed from the following (a) to (e) so that the film thickness is within the range of 2 to 24 μm. A laminated structure in which a surface layer of an insulating material or a semi-insulating material is coated on a selected laminated material, and the developing means is electrically conductive by a combination of a conductive magnetic carrier and an insulating toner or a developer composed of a one-component conductive magnetic toner. A magnetic brush is formed, and the potential difference between the exposed area and the non-exposed area on the surface of the photoconductor that contacts the magnetic brush is set to 1
It is characterized in that it is set within the range of 0 to 240V. (A) An I-type semiconductor layer is laminated on the P-type semiconductor layer. (B) An N-type semiconductor layer is laminated on the P-type semiconductor layer. (C) An I-type semiconductor layer and an N-type semiconductor layer are sequentially stacked on the P-type semiconductor layer. (D) An I-type semiconductor layer is laminated on the N-type semiconductor layer. (E) A P-type semiconductor layer is laminated on the N-type semiconductor layer. (F) An I-type semiconductor layer and a P-type semiconductor layer are sequentially stacked on the N-type semiconductor layer.

Further, the image forming apparatus of the present invention comprises an electrophotographic photosensitive member having a photosensitive layer formed on a conductive substrate, a charging unit, an exposing unit and a developing unit, and a space between the conductive substrate and the developing unit. Is provided with a means for applying a developing bias voltage, the relationship between the film thickness d of the photoconductor layer and the relative permittivity εr is set as shown in the following formula, and the developing means is insulated from the conductive magnetic carrier. A conductive magnetic brush is formed from a combination of a conductive toner or a developer composed of a one-component conductive magnetic toner, and the potential difference between the exposed region and the non-exposed region of the surface of the photoconductor contacting the magnetic brush is 10 to 240V. It is characterized by being set within the range. d ≤ 24 μm εr ≥ 2 d / εr ≤ 9

[0030]

The present invention will be described in detail below. FIG. 1 is a schematic configuration diagram of an electrophotographic image forming apparatus 1 using a photoconductor of the present invention as a low potential developing method. In the figure, 2 is a photoconductor, 3 is a corona charger as a charging unit, 4 is an exposing unit, 5 is a developing unit, and 6 is a developing bias voltage applied between the photoconductor 2 and the developing unit 5. A power source, 7 is a corona transfer device as transfer means, and 8 is plain paper or various processed papers or OH.
A recording sheet such as a P sheet, 9 is a cleaner, 10 is an eraser as a charge eliminating unit, and 11 is a heat roller fixing device as a fixing unit. Further, 12 is a toner image formed on the surface of the photoconductor 2, and 13 is residual toner after transfer. In addition to this, a rotating means for the developer and a rotating means for the photoconductor 2 are provided. Here, the charging means 3 is a charging means by a contact charging method,
For example, a charging roller that contacts a conductive rubber roller, a charging brush that contacts a conductive brush, or a particle charger that contacts a conductive magnetic brush formed of conductive magnetic particles may be used. In either case, since low potential charging is sufficient, the voltage of the charging power source can be lowered. Also, when a corona charger is used, the width of the corona house can be narrowed because the charging potential is low, and the size can be reduced. In addition,
From the viewpoint of suppressing ozone generation, it is preferable to use the contact charging method. The charging polarity may be positive or negative,
It is appropriately selected according to the characteristics of the photoconductor. Although the LED head is used here as the exposure means 4, a laser, a liquid crystal shutter array, an EL head, a phosphor dot array head, a plasma image bar, or the like may be used. Further, in the case of a copying machine, the light reflected from the original using a light source such as a halogen lamp is irradiated in a slit shape on the surface of the photoconductor by an optical system in which a lens and a mirror are combined. Although a corona transfer device is used here as the transfer means 7, a transfer conductive rubber roller or the like may be used. The transfer polarity may be either positive or negative, but normally it is opposite to that of charging. A rubber blade is used here as the cleaner 9, but a rubber roller, a brush roller, or the like, or a combination thereof may be used. Here, the eraser 10 as the charge eliminating means has LE
Although light irradiation was performed using the D array, a fluorescent lamp, a halogen lamp, an EL array, or other light source may be used, or an electric charge removal method such as AC corona discharge or AC voltage application may be used. Although the heat roller fixing is used as the fixing unit 11, flash fixing or pressure fixing may be used.

According to the image forming apparatus 1 having the above-mentioned structure, the toner image 12 is formed on the surface of the photoconductor through the processes of charging, exposing and developing, and the toner image 12 is transferred onto the transfer material 8 by the transfer means 7. Then, it is fixed by the fixing means 11 to obtain a recorded image. On the other hand, the surface of the photoconductor after transfer is
The residual toner 13 is removed by the cleaner 9, the surface potential is erased by the eraser 10, and the next image forming process is reached again, and the image is repeatedly formed.

Now, the developing section of the image forming apparatus 1 will be described with reference to an enlarged view of the main part of FIG. In FIG. 2, reference numeral 2 is a photoconductor in which the photoconductor layer 15 is laminated on the conductive substrate 14, and 5 is a developing machine. The developing machine 5 includes, for example, a cylindrical magnetic pole roller 16 having eight poles and a conductive sleeve 17 arranged along the outer circumference thereof.
And a two-component developer composed of a one-component conductive magnetic toner or a conductive magnetic carrier and an insulating toner stored in a toner receiver 18 as a developer.
To form the magnetic brush 19. Further, by the power source 6 provided between the sleeve 17 and the base 14,
A voltage of + or −0 to 240 V depending on the potential characteristics of the photoconductor 2 is applied between the both 17 and 14. The arrow in the figure indicates the moving direction of the photoconductor 2 and the magnetic brush 19.

Next, the operation of the low potential developing method performed in the image forming apparatus 1 of the present invention will be described in detail with reference to FIGS. FIG. 3A is a schematic view of a conventional photoconductor and a developing section by a developing method. In the figure, 20 is a conductive substrate 2.
1 is a photoreceptor having a photoreceptor layer 22 laminated thereon, 23 is a conductive sleeve of a developing machine, and 24 is an insulating magnetic brush composed of a two-component developer of an insulating magnetic carrier and an insulating toner. In the figure, d ₁ and d ₂ are the thicknesses of the photoconductor layer and the developer, ε ₁ and ε ₂ are the dielectric constants of the photoconductor layer and the developer, and ρ ₁ and ρ ₂ are the photoconductor layers. and the electrical resistivity of the developer, V _d and V ₁ and V ₂ each represent potential applied to the development potential and the photosensitive layer developer. In the conventional developing method by the Carlson method, an insulating magnetic brush 24 made of a two-component developer composed of an insulating magnetic carrier and an insulating toner or a one-component insulating magnetic toner is provided between the surface of the photoconductor 20 and the conductive sleeve 23. To form. Therefore, the equivalent circuit of the photoconductor and the developer in the developing section can be considered to be a series connection of the capacitance C _{1 of the} photoconductor and the capacitance C ₂ of the developer. This equivalent circuit is shown in FIG. C ₀ shown in FIG.
Is the combined capacitance of C ₁ and C ₂ , + Q _d and −
Q _d is a positive charge and a negative charge induced in C ₀ by the developing bias voltage. This C ₀ is the dielectric constant of the vacuum ε
₀ (= 8.85 × 10 ⁻¹⁴ (F / cm)) is obtained by the following equation. C ₁ = (ε ₁ / d ₁ ) × ε ₀ , C ₂ =
From (ε ₂ / d ₂ ) × ε ₀ C ₀ = 1 / [(1 / C ₁ ) + (1 / C ₂ )] = ε ₀ / [(d ₁ / ε ₁ ) + (d ₂ / ε ₂ )] (1) In the conventional developing method, both the photoreceptor layer and the developer are close to the insulator, and both ρ ₁ and ρ ₂ are large values of 1 × 10 ¹³ Ω · cm or more. This can be ignored in the equivalent circuit of 3 (b). On the other hand, when the electric resistivity of the developer becomes smaller and the electric conductivity of the developer cannot be ignored because it changes from insulating to conductive, the electric resistivity of the developer near the conductive sleeve has a high density of the developer. Therefore, it can be considered that the electric resistance of the developer near the photoconductor becomes high resistance because the density of the developer is small and does not change. The thickness may be regarded as the thickness d ₂ of the insulating developer and may be similarly calculated by the above equation.
Further, when the developer becomes conductive, d ₂ may be regarded as 0.

By the way, since there is no surface charge of the photoconductor in the bright portion of the photoconductor whose surface potential is lowered by the exposure,
Due to the developing bias voltage V _d , a negative charge of −Q _d is generated in the vicinity of the conductive substrate of the photoconductor layer, and a positive charge of + Q _d is added to the toner having a larger electric resistivity than the carrier in the developer. It is induced at the indicated size. In the light area of _{Q d = C 0 × V d} = ε 0 × V d / _{[(d 1 / ε 1) +} (d 2 / ε 2) ] (2) photosensitive member, the photosensitive layer The negative charge −Q _{d in the} vicinity of the conductive substrate and the positive charge + Q _d of the toner in the developer exert an attractive force on each other, and the toner attracts the surface of the photosensitive member to form a toner image on the surface of the photosensitive member. To be done.
At this time, the higher the Q _d in the above formula, the higher the density of the recorded image, but the developing potential V _d required to obtain the Q _d giving the same density is the same as the term d ₁ / ε ₁ of the same photoreceptor layer. On the other hand, the smaller the term d ₂ / ε _{2 of} the developer layer, the lower the requirement. This is considered to be the principle that enables low-potential development when a conductive developer is used.

For example, taking an a-Si photosensitive member as an example, the recording density O. D. = 1.3, the photoreceptor layer has ε ₁ = 1
2, d ₁ = 40 μm, and ε ₂ as an insulating developer layer
= 4 and d ₂ = 40 μm, V _d needs to be 800 V, and Q _{d at} this time is 0.053 μC / cm ² . On the other hand, as a conductive developer layer, ε ₂ = 0, d
_{When 2} = 0 μm, V _d required to obtain the same Q _d is 200 V, and low potential development is possible even with a conventional thick film photoreceptor.

Next, the layer structure of the a-Si photoconductor and the action during charging and development will be described. FIG. 4 is a sectional view showing the layer structure of a conventional positively charged a-Si photoconductor 20. Two
Reference numeral 1 is a conductive substrate made of Al or the like, on which a carrier injection blocking layer 25 made of, for example, P-type heavy-doped a-Si, and an I-type or light-doped N-type.
Type a-Si photoconductive layer 26 and, for example, a-SiC
And a surface layer 27 made of an a-Si based high resistance material such as a-SiN.

When this conventional a-Si photoconductor 20 is positively charged at a high potential in the related art, the P-type heavy-doped carrier injection blocking layer 25 having a film thickness of about 1 to 5 μm forms a photoconductive layer 26. A depletion layer, which is a layer region in which majority carriers are driven out by the electric field applied to the junction, cannot be formed, and all the layers maintain the properties of the semiconductor layer and are not regarded as insulating layers. On the other hand, the depletion layer 28 is formed in the I-type or light-doped N-type photoconductive layer 26 because the carrier density is smaller than that of the injection blocking layer 25. In this case, the photoconductive layer 26 can be considered as being divided into a depletion layer 28 in a layer region having a resistance high enough to be regarded as an insulating layer and a layer region maintaining the properties of the semiconductor layer.

When low-potential development is used for the above-mentioned thick-film photoreceptor, the electric potential applied to the junction between the injection blocking layer 25 and the photoconductive layer 26 is low because the charge potential of the photoreceptor layer is low. Is small and the layer region from which majority carriers are driven out is also small, so that the width of the depletion layer 28 can be ignored. That is, a thin depletion layer 28 is formed in the photoconductive layer 26 having a film thickness of 30 to 80 μm, but the thickness thereof is at most 0.1 to 2 μm.
In the photoconductive layer 26 having the conventional film thickness, the contribution of the high resistance depletion layer 28, which is regarded as an insulating layer, to the withstand voltage and charging is extremely small.

On the other hand, when the total thickness of the photoconductor layer is 2 to 24 μm like the photoconductive layer of the present invention, even if the charging potential is lowered by using low potential development, the photoconductive layer in the photoconductive layer is reduced. Since the ratio of the depletion layer to the whole becomes large and most of the depletion layer becomes the depletion layer, the apparent resistivity of the photoconductor layer increases. as a result,
The charge and withstand voltage per film thickness of the photoconductor layer increase, and a sufficient image density can be obtained.

In order to explain this in more detail, FIG. 5 (a) is a schematic diagram of the photoconductor 2 of the present invention and the developing section of the low potential developing method, and FIG. 5 (b) is its equivalent circuit. Show. In FIG. 5A, reference numeral 2 is a photoconductor in which a photoconductor layer 15 including a carrier injection blocking layer 29, a photoconductive layer 30, and a surface layer 31 is laminated on a conductive substrate 14, and 17 is a conductive sleeve of a developing machine. , 19 represents a magnetic brush formed of a one-component conductive magnetic toner or a two-component developer composed of a conductive magnetic carrier and an insulating toner. Here, the electrical resistivity of the one-component conductive magnetic toner or the two-component developer is 10
^{It is 10} Ω · cm or less, preferably 10 ⁸ Ω · cm or less, and more preferably 10 ² to 10 ⁵ Ω · cm. As the insulating toner, one having an electric resistivity of 10 ¹¹ Ω · cm or more, preferably 10 ¹³ Ω · cm or more is used, and the electric resistivity as a two-component developer is obtained by mixing with the conductive magnetic carrier. To the above value. In FIG. 5B, C ₃ is the electrostatic capacitance C _{1 of the} photosensitive member similar to that in FIG. 3B.
+ Q is the combined electrostatic capacity of the electrostatic capacity C ₂ of the developer and + Q
_D and -Q _D represent the positive and negative charges induced in C ₃ by the developing bias voltage V _D.

As shown in FIG. 5A, the low-potential developer forms the conductive magnetic brush 19 between the surface of the photosensitive member 2 and the conductive sleeve 17 in a spike shape. Here, since the electric resistivity ρ ₁ of the photoconductor of the present invention is about 1 × 10 ¹³ Ω · cm, and the electric resistivity ρ ₂ of the developer is 1 × 10 ⁵ Ω · cm or less, ρ ₂ can be ignored. Therefore, both 2, 1
Since it can be considered that the area between 7 is occupied by a conductive material having a low electrical resistivity ρ ₂ , C ₃ of the equivalent circuit shown in FIG.
The developer capacity C ₂ may be ignored and regarded as only the photoreceptor capacity C ₁ . That is, C ₃ is calculated by the following equation. _{C 3 = C 1 = ε 0} × (ε 1 / d 1) ··· (3) Then, the surface charge in the bright portion of the photoreceptor after exposure does not exist, the developing bias voltage V _D, the photosensitive layer Negative charge of -Q _D is induced in the carrier injection blocking layer 29, and positive charge of + Q _D is induced in the toner having a higher electric resistivity than the carrier in the developer. The potential of both ends at this time becomes V _D ,
Q _D is _calculated by the following equation. Q _D = C ₃ × V _D = ε ₀ × V _D / (d ₁ / ε ₁ ) ... (4) Even in the low potential developing method, this Q
_The larger _D is, the higher the density of the recorded image is. Therefore, in the low-potential developing method, the thinner the thickness d ₁ of the photosensitive member, the larger the relative permittivity ε ₁ of the photosensitive member, and the higher the developing voltage, that is, the applied bias voltage V _D, the higher the recording density.

For example, the recording density O. D. Q _D = 0.053 μC / cm ² is required to obtain = 1.3, but ε ₁ = 12, d ₁ = 10 μm of the photoconductor, and ε ₂ = 0, d of the developer. ₂ = 0 μm, the required V _D
Is as low as 50V.

[0043] Thus in the photoreceptor bright portion, the negative charge on the photosensitive layer with a lower developing bias voltage V _D -Q _D
However, a positive charge + Q _D is induced in the toner in the vicinity of the surface of the photoconductor, and the two exert an electric attractive force to attract the toner to the surface of the photoconductor.

On the other hand, in the dark area of the photoconductor, + Q is applied to the photoconductor.
_Since there is a positive surface charge almost equal to _D and acts as an electrostatic shield, the attraction between + Q _D and -Q _D does not work, so the toner cannot be attracted to the surface of the photoconductor. Therefore, a toner image is formed on the surface of the photoconductor corresponding to the bright and dark parts of the photoconductor.

In the electrophotographic recording method that does not require corona charging, charging, exposure and development are performed at substantially the same position at the same time, so that the toner image is formed only by the relatively simple developing process as described above. It is thought to be due to a complicated process different from the one carried out. For example, it is considered that charging and exposure are related to each other during development, exposure and development are related to each other during charging, and charging and development are related to each other during exposure.
Therefore, it is difficult to adjust the conditions of the image forming process, and it has not yet been put to practical use.

For reference, FIG. 4B shows a typical layer structure of the a-Si photosensitive member 32 used in the electrophotographic recording method which does not require corona charging. 33 in the figure
Is a translucent substrate made of glass or the like, 34 is ITO, SnO
It is a translucent conductive layer composed of ₂ or the like, and a carrier injection blocking layer 25, a photoconductive layer 26, and a surface layer 27 are sequentially laminated thereon. In this recording method, the exposure is performed by the transparent substrate 3 of the photoconductor 32.
The exposure is performed from the so-called back surface on the third side, and the exposure direction is opposite to that of the Carlson method.

Here, reference will also be made to the formation of the contrast potential between the light portion potential and the dark portion potential during development in the low potential developing method of the present invention. In the low-potential developing method of the present invention, since the charging potential of the photoconductor may be low, the charging width in the charging process (the opening width of the corona house or the contact width of the charging roller or charged particles) is narrow, and the charging time is short (0 . 1 second or less), during which the photoreceptor is rapidly charged. At this time, it can be considered that the supply current of the charger is sufficiently large and the charging loss due to the leak current due to the dark resistance of the photoconductor can be ignored. For example, the photoconductor for positive charging has the layer structure of the above (a) to (c), and the electric field at the time of charging is reverse bias, so that the leak current is extremely small. Similarly, the negative charging photoconductor has the layer structure of (d) to (f), and the leak current during charging is extremely small. Therefore, most of the supplied current during charging is consumed for charging, and the leak current of the photoconductor layer is so small that it can be ignored.

Such an equivalent model of the photosensitive member from the initial charging to immediately after charging in the charging process, which can be assumed to have a short charging time and sufficient supply current, considers only the capacitance component C, ignoring the resistance component. Good. At this time, the amount of charge Q ₀ (C / cm ² ) on the surface of the photoconductor is set to V _{0 as the} initial charge potential.
(V), the relative permittivity of the photoconductor layer is ε r, and the permittivity of vacuum is ε
₀ (F / cm) and the film thickness of the photoconductor layer are d (cm). Q ₀ = C × V ₀ = (εr × ε ₀ / d) × V ₀ (5) Here, in order to obtain a sufficient recording density by the low potential developing method,
Q _{0 of} about 1 μC / cm ² and V _{D of} about 50 V are required, and when these are substituted into the above equation, ε r /d=2.26×
It becomes 10 ⁴ . Since εr is about 12 in the a-Si photosensitive layer, d at this time is about 5 × 10 ⁻⁴ cm = 5 μm.

Next, the charge distribution in the photosensitive layer in the process from charging to development in the low potential developing method of the present invention will be described with reference to FIGS. 6 (a) to 6 (c). This figure is a cross-sectional view showing the layer structure of the photoconductor 2 and the charge distribution in each process corresponding thereto. The photoconductor 2 has a carrier injection blocking layer 29, a photoconductive layer 30, and a surface layer 31 on a conductive substrate 14. It has a structure in which layers are sequentially stacked.

In the charging process shown in FIG. 6A, the charging means 3 imparts a charged charge + Q ₀ to the surface of the photoconductor layer to induce a charge of the opposite polarity −Q ₀ in the injection blocking layer 29, and the photoconductor layer. Is charged to the initial charging potential V ₀ . This potential difference V
₀ is actually distributed according to the resistance value of each layer in the photoreceptor.

From this charging, the exposure of FIG.
In the actual process, it takes about 0.1 to 3 seconds to reach the developing process of (c). Therefore, the charged electric charge and the charged potential of the non-exposed portion are due to dark discharge in the photoconductor layer, that is, dark decay. Q ₀ → Q ₀ '→ Q _S and V ₀ → V ₀ ', respectively
→ It decreases to V _S. In this process, a parallel circuit of a capacitor C and a resistor R can be considered as an equivalent circuit of the photoconductor layer as shown in FIG. As a result, the potential V = V ₀ −V _S (V) that decreases due to dark decay after the elapse of t seconds is obtained by the following equation. V = V ₀ × exp (−t / (R × C)) = V ₀ × exp (−t / τ) (6) τ = R × C = R × (ε ₀ × εr / d) = ρ × ε ₀ × εr (7) Here, τ is a time constant, and ρ is a specific resistance of the photoreceptor layer.

In the above equation, assuming that the development potential V _D is half the initial charging potential V ₀ (V _D / V ₀ = 0.5) and the time t from charging to development is 1 second, the a-Si photoconductor In the case of a layer, εr is about 12, so ρ = 1.4 × 10 ¹² (Ω
・ Cm)

The actual measured value is smaller than the calculated value, and ρ of the non-doped hydrogenated a-Si photosensitive layer is 10 ¹⁰ to 10 ¹¹ , but due to impurity doping, alloying or layer constitution of the photosensitive layer described later. , A larger value than 10 ¹¹ -1
It can be 0 ¹³ .

On the other hand, in the photoconductive layer 30 of the exposed portion, as shown in FIG.
As shown in (b), the photocarrier 35 is generated by the exposure E, and the resistance R as an equivalent circuit is reduced by about three digits, so that the charged charges + Q ₀ ′ and −Q ₀ ′ are almost completely discharged in bright light. Then, Q ₀ 'decreases to almost 0 and V ₀ ' decreases to several V or less.

In the photosensitive member 2 which has undergone the developing process of FIG. 6C, the non-exposed portion holds the charged electric charge + Q _S and the charged electric potential V _S because the non-exposed portion has the electric charge holding ability. Has a surface charge distribution, that is, an electrostatic latent image in which the charge is almost 0 and the charge potential is several V or less. This electrostatic latent image is developed by the low potential developing method described above.

As described above, in the dark part, the charging is rapidly performed by the current supplied from the charging device within a short charging time, so that the resistance component of the photoconductor layer can be ignored and can be approximated only by the capacitance component. In the dark decay process from charging to development, a model of a parallel circuit of a resistance component and a capacitance component is approximated. If the resistance component is not large, sufficient surface charge cannot be left during development. The average dark resistivity of the photoconductor layer required for this purpose is 1 × 1 as can be seen from the actually measured value of the a-Si photoconductor.
It becomes more than ⁰⁹ Ω · cm.

On the other hand, in the bright area, the resistance component of the photosensitive layer is sufficiently reduced by the generation of photocarriers by the exposure, and the discharge of the surface charge may be almost completed by the start of the development. Therefore, the average bright resistivity of the photoconductor layer in the bright portion is at least smaller than the average dark resistivity, and is 1 × 10 ⁹ Ω.
・ It must be less than or equal to cm.

The photoreceptor layer applied to the low potential development of the present invention must satisfy these conditions, but in the low potential development, the bright resistivity is 1 × 10 ¹⁰ in the conventional developing method.
It can be applied to materials with a value smaller than about Ω · cm.
Since this is used at a low potential, the charge capacity of the photoconductor layer has a margin and the dark resistance may be small accordingly. Also, since the film thickness is thin, the dark attenuation due to the heat carrier is small, and therefore the dark resistance is small. Is considered to be small, and further, since the film thickness is thin and the sensitivity is good because it is used at a low potential, the allowable range of bright resistance is wide.

[0059]

EXAMPLES The present invention will be specifically described below with reference to examples. The layer structure of the photoreceptor 2 of the present invention is formed by laminating a photoreceptor layer 15 on a conductive substrate 14 as shown in FIG. The conductive substrate 14 is made of a metal such as Al, copper, iron, or SUS, or the surface of an insulating support is subjected to a conductive treatment, for example, a metal film, a conductive film, or a semiconductor film is formed on the surface of glass or resin. The object is used in a drum shape, a belt shape, a sheet shape, or the like. When an Al drum is used as the substrate, the thickness of the a-Si photoconductive layer is smaller and the stress applied to the substrate is smaller than that of the conventional a-Si drum, so the thickness of the Al material can be reduced.

The photoreceptor layer 15 comprises a carrier injection blocking layer 29, a photoconductive layer 30 and a surface layer 31, and the glow discharge decomposition apparatus shown in FIG. 8 was used to manufacture these layers. FIG. 8 is a schematic configuration diagram of the glow discharge decomposition apparatus 36, 37 is a cylindrical metal reaction furnace, 38 is a cylindrical conductive substrate support for mounting the photosensitive drum, 39 is a heater for heating the substrate, and 40 is a heater.
Is a cylindrical glow discharge electrode plate used for a-Si film formation, and a gas ejection port 41 is formed in the electrode plate 40. 42 is a gas inlet for introducing gas into the reaction furnace, 43 is a gas outlet for exhausting residual gas after being exposed to glow discharge, 44 is the substrate support 38 and the electrode plate 4.
It is a high frequency power supply for generating glow discharge between zero. Further, the reaction furnace 37 includes a cylindrical body 37a, a lid body 37b,
A bottom body 37c, and a cylindrical body 37a and a lid body 37.
b and between the cylindrical body 37a and the bottom body 37c, insulating rings 37d are respectively provided, so that the output terminal of the high frequency power supply 44 is electrically connected to the glow discharge electrode plate 40 through the cylindrical body 37a. The ground terminal is the lid 3
The base support 38 is electrically connected to the ground via the base 7b and the bottom 37c. Also, the motor 4 attached on the lid 37b
5, the base support 38 is rotationally driven via the rotary shaft 46, and the base 14 also rotates accordingly.

Using this glow discharge decomposition device 36, a-
To manufacture a Si photosensitive drum, the drum-shaped substrate 14 for a-Si film formation is mounted on the substrate support 38, and a-Si forming gas is introduced into the reaction furnace through the gas introduction port 42. Gas is ejected toward the surface of the substrate through the gas ejection port 41, the substrate is set to a required temperature by the heater 39, and high frequency power is supplied from the high frequency power supply 44 to the substrate support 38 and the electrode plate 40. A glow discharge is generated between the base 14 and the base 14, and the base 14 is rotated.
An a-Si film is formed on the peripheral surface of.

As the material forming the photoconductive layer 30 of the present invention, it is particularly preferable to use an a-Si based photoconductive layer.
In addition to the glow discharge decomposition method (plasma CVD method), the i-based layer is formed by, for example, reactive sputtering method, ECR microwave C
It is formed by a VD method, a photo CVD method, a catalytic CVD method, a reactive vapor deposition method, or the like, and hydrogen (H) or a halogen element is contained at 1 to 40 atomic% for dangling bond termination in forming the same. Further, in order to obtain desired characteristics with respect to electrical characteristics such as dark conductivity and photoconductivity of the layer 30, optical bandgap, etc., a Group IIIa element (hereinafter abbreviated as IIIa element) of the periodic table or A periodic group Va element (hereinafter abbreviated as Va group element) is contained, carbon (C), nitrogen (N),
It is preferable to contain oxygen (O), germanium (Ge), or the like.

In particular, when amorphous silicon carbide (hereinafter abbreviated as a-SiC) is used for the photoconductive layer 30, the x value of Si _1-x C _x is 0 <x ≦ 0.5, preferably. It is preferable to set it in the range of 0.05 ≦ x ≦ 0.45, and this range is desirable in that the resistance becomes higher than that of the a-Si layer and good carrier traveling can be secured. As the group IIIa element and the group Va element, the B element and the P element are desirable because they have excellent covalent bond properties and can sensitively change semiconductor characteristics, and in addition, excellent photosensitivity can be obtained. Non-doped a-Si containing no IIIa group element or Va group element is a weak N-type semiconductor, but if a small amount of IIIa group element is added to make it I-type, or if its amount is increased to be used as P-type. Alternatively, it may be used as an N type by adding a Va group element. Further, this photoconductive layer is not limited to a single layer structure having a single conductivity type, but may be one in which an I-type layer and an N-type layer are sequentially stacked or an I-type layer and a P-type layer depending on the charging polarity of the photoconductor. They may be sequentially laminated, whereby the depletion layer formed between the depletion layer and the injection blocking layer can be expanded and the photoreceptor can be made suitable for low potential development. Then, the a-Si-based photoconductive layer 30 in the present invention
The thickness is preferably 0.5 to 24 μm, preferably 2 to 19 μm, and more preferably 2 to 15 μm.

A carrier injection blocking layer 29 is provided between the conductive substrate 14 and the photoconductive layer 30. The injection blocking layer 29 may be either an a-Si layer or an a-SiC layer, and is O or N in order to improve the adhesion with the conductive substrate 14.
It is advisable to include such elements as. Further, when both the injection blocking layer 29 and the photoconductive layer 30 are formed of an a-SiC layer, the C content may be larger than that of the photoconductive layer 30.

The injection blocking layer 29 is formed of the conductive substrate 14
An impurity element is contained in order to prevent injection of carriers (charges having a polarity opposite to the charge) from the photoconductive layer 30 into the photoconductive layer 30.
That is, in order to prevent the injection of negative charge carriers, the group IIIa element may be contained in an amount of 1 to 10,000 ppm, preferably 50 to 5,000 ppm, while in order to prevent the injection of positive charge carriers, a group Va element may be added. 5,000 ppm or less, preferably 50 to 3,
It is recommended to contain 000 ppm. These elements may be provided with a gradient in the layer thickness direction, in which case the average content of the entire layer should be within the above range. When the injection blocking layer 29 contains a group IIIa element, positive charging and developing bias and negative transfer are used, while when it is non-doped or contains a group Va element, negative charging and developing bias. And positive transfer is used.

As the IIIa group element and the Va group element, the B element and the P element are preferable for the same reason as described above. The thickness of the injection blocking layer 29 is 0.01 to 12 μm.
m, preferably 0.1 to 5 μm, more preferably 0.1 to 2
The range of μm is good, which makes it easy to secure the required injection blocking ability and suppress the rise of the residual potential.

Further, O and / or N is added to the injection blocking layer 29.
And / or C when the total content of each element is contained in the range of 0.01 to 30 atomic%, it is possible to further prevent injection of carriers from the conductive substrate 14, and
The adhesion to the substrate 14 can be further enhanced.

A surface layer 31 made of an insulating or semi-insulating material is laminated on the photoconductive layer 30. Surface layer 3
1 is preferably an insulating layer or a high resistance surface layer so as to trap the charged electric charge and prevent the electric charge from moving in the film surface direction and destroying the electric charge pattern formed by the exposure, and the specific resistance is necessary for holding static electricity. It is preferable to use a material of 1 × 10 ¹² Ω · cm or more.

Such a surface layer includes, in particular, a-SiC or a
It is preferable to use an a-Si high resistance surface layer such as -SiN, a-SiO, a-SiCO, and a-SiNO, and these are formed by the same thin film forming means as the a-Si photoconductive layer. When a-SiC is used for both the surface layer 31 and the photoconductive layer 30, the C content of the surface layer is higher than the C content of the photoconductive layer.
Is included in the surface layer 31, and the amount of C in the surface layer 31 is Si _1-x C
_x value of x is 0.3 ≦ x ≦ 1.0, preferably 0.5 ≦ x ≦
A range of 0.95 is good. These a-Si based high resistance surface layers also contain H or a halogen element for dangling bond termination. Further, a group IIIa element or a group Va element may be contained for adjusting electric characteristics.

In addition to the above, aC, aB, a-
Inorganic insulating materials such as BN, a-BC and Al ₂ O ₃ , silicone resin, polycarbonate, polystyrene, polyester, polybutylene, polyethylene, fluororesin,
A resin-based insulating material such as polysilane, polyimide resin, polyurethane or acrylic resin can also be used.

The surface layer 31 has a thickness of 0.05 to 10 μm,
The thickness is preferably 0.1 to 5 μm, and when it is less than 0.05 μm, this layer contributes to the improvement of sufficient withstand voltage and the effective trapping of electrostatic charge to retain an electrostatic latent image. Cannot be used, and when it is used repeatedly, it has a short life due to wear. When the thickness exceeds 10 μm, an electric field spreads in the film surface direction in this layer in forming a fine charge pattern, thereby lowering the resolution and failing to obtain sufficient resolution. Further, since the electric charges remaining on the surface increase and the residual potential increases, problems such as a decrease in image density, back fog, and a change in image density during repeated use occur.

A change layer may be provided between the surface layer 31 and the photoconductive layer 30. It is preferable that the change layer has an elemental composition intermediate between the surface layer and the photoconductive layer and has a composition gradient in the layer thickness direction. By providing such a change layer, the travel of the photocarriers generated in the photoconductive layer 30 to the surface of the surface layer 31 becomes smooth. The thickness of this change layer is 0.01 to 1 μm, preferably 0.05 to 0.5 μm.
m is good.

The film thickness of the entire photoconductor layer formed by the above structure is 2 to 24 μm, preferably 2 to 19 μm.
Within the range of.

Since the photosensitive layer of the a-Si photosensitive member of the present invention is basically composed of three layers, the film thickness d of the entire photosensitive layer is
The ratio of the relative permittivity εr and the relative permittivity εr is a combination of the ratio of the film thickness of each layer and the relative permittivity. The thicknesses of the photoconductor layer, surface layer, photoconductive layer and injection blocking layer are d _T , d _a , d _b and d _c , and the relative permittivity is ε.
_T , ε _a , ε _b , and ε _c are obtained by the following equation. (D _T / ε _T ) = (d _a / ε _a ) + (d _b / ε _b ) + (d _c / ε _c ) ... (8) In the a-Si photoconductor of the present invention, the relative dielectric constant of the surface layer is The relative permittivity is slightly different from the other layers, but because the total film thickness is relatively thin and the relative permittivities of the photoconductive layer and injection blocking layer are almost the same, the overall relative permittivity ε _T (= ε r) Is the relative permittivity of the photoconductive layer ε _b
The film thickness d may be represented by the total film thickness d _T of each layer. That is, the relative permittivity is ε _a = 4 , ε _b = ε _c = 1
2. The film thickness is d _a = 0.5 μm, d _b = 8.0 μm, d _c
= 0.5 μm, ε _T = ε _b = 12, d _T =
It may be approximated to 9.0 (μm), and d _T / ε _T (= d / ε
r) = 0.8.

This d / εr is preferably 9 or less, preferably 0.05 to 8, and more preferably 0.05 to 7.
Is good. When d / εr exceeds 9, the charge + Q _D induced in the toner becomes small according to the formula (4) of the low potential developing method, and a sufficient recording density cannot be obtained. This means that the film thickness d
It can also be seen from the fact that the value becomes large and the attractive force to the toner becomes small. When d / εr is less than 0.05, for example, the film thickness of the photoconductor layer is as thin as 0.6 μm or less for a-Si having a relatively large relative permittivity εr of 12, which makes the photoconductor layer resistant to charging. Is not preferable because it becomes insufficient.

When this d / εr is in the range of 0.05 to 9, various conventionally known photoconductive materials can be used as the constituent material of the photosensitive layer. Taking the case where the total thickness of the photoconductor layer is 9 μm as an example, d / εr is about 1.3 for the Se type photoconductor (εr is about 7) and about d for the OPC photoconductor (εr is about 3 to 4). Two
.About.3, and a sufficient recording density is obtained in each case.

In the low potential developing method of the present invention, as can be seen from equation (4), the larger the relative permittivity εr, the larger the induced charge to the toner and the higher the recording density can be obtained. Conversely, εr
If the value becomes smaller, it is difficult to obtain a high recording density, and the developing bias voltage V _D must be increased accordingly.
Since the present invention is characterized by a low surface potential of the photoconductor and a low developing bias voltage, it is considered that εr also has a lower limit value. According to the inventor's confirmation, the existing dielectric material having the smallest relative dielectric constant (tetrafluoroethylene: εr =
Since low potential development was possible even in 2), the relative permittivity εr is preferably in the range of εr ≧ 2.

Also, with the OPC photosensitive member having a total film thickness of 24 μm, the recording density was slightly reduced to about 1.2, but a sufficient value was obtained, which was at a practical level. However, when the film thickness becomes thicker than this, a decrease in recording density and a decrease in resolution are observed in the low potential developing method of the present invention, and no improvement in electrophotographic characteristics is observed.

This can be explained from the equation (4). That is, when the total film thickness is more than 24 μm, the induced charge Q _D to the toner becomes small, so that the recording density decreases, and the recording density O.I. D. Cannot be secured to 1.3 or higher. Further, the developing electric field is also reduced and the electric attraction acting on the toner is weakened, so that the image is blurred in the boundary region between the bright portion and the dark portion, and it is difficult to obtain the resolving power required for high quality recording.

On the other hand, if the total film thickness is 2 μm or less, it becomes difficult to form a photoconductor having a structure in which a plurality of layers as described above are laminated, and the thickness of the depletion layer formed in the photoconductor layer becomes insufficient. Further, most of the exposure with long-wavelength light having a wavelength of 685 nm or more is transmitted through the photoconductor layer, the long-wavelength sensitivity is drastically lowered, and panchromaticity is also impaired.

In the laser beam printer, the wavelength is 780n
Semiconductor lasers of around m are often used, especially a-Si
In the photoconductor, such sensitivity to long-wavelength light is almost proportional to the film thickness, so that if the total film thickness is 2 μm or less, an electrostatic latent image can no longer be formed on the photoconductor surface.

As the photoconductive material of the photoreceptor layer of the present invention,
In addition to the a-Si-based material, various chalcogenide-based materials such as various OPC-based and a-Se-based materials and inorganic crystal / resin-dispersed materials may be used.

Such OPC materials include dye-sensitized photoconductors, charge transfer sensitized photoconductors, and function-separated photoconductors. As the dye-sensitized photoconductor, there is one in which a sensitizing dye such as penzopyrylium dye is dispersed in a photoconductive material such as polyvinylcarbazole (PVCz).
Examples of the charge transfer sensitized photoconductor include PVCz to which acids, acid anhydrides, quinone polycyan compounds, and Lewis acids such as 2,4,7-trinitro-9-fluorenone (TNF) are added.

The function-separated photoconductor includes a single-layer photoconductor and a laminated photoconductor, and the single-layer photoconductor includes Cu--
There are PC-hydrazone photoconductors and eutectic complex photoconductors. The laminated photoconductor comprises a combination of a carrier generator (CGM) and a carrier transport agent (CTM). For CGM, a perylene-based or eutectic complex, an azo-based or a phthalocyanine-based photoconductive material, or an a-Se-based or a-Si-based photoconductive material is used. CTM has a hole transfer agent and an electron transfer agent, and one of them is used depending on the charging polarity and the layer structure.
There are VCz-based, pyrazoline-based, hydrazone-based, amine-based, phenylmethane-based, oxadiazole-based photoconductive materials and the like.

For the amorphous chalcogenide system, a-
Se and a-SeTe, a-SeAs, a-Se 2 As 3
And the like, and the inorganic crystal / resin dispersion system includes ZnO-resin system and CdS-resin system. In recent years, photoconductive materials such as polysilane-based photoconductive materials such as polymethylphenylsilane and tetra (m-tolyl) -m-diaminobenzene have been actively developed. Since these materials show high hole mobility, they are used as CTM. It has been used.

[Example 1] Glow discharge decomposition apparatus 3 shown in FIG.
6, the conductive base 14 has a diameter of 30 mm and a length of 260
mm, thickness 1.5 mm, mirror-finished Al drum was set, and under the conditions shown in Table 1, an injection blocking layer 29, a photoconductive layer 30, and a surface layer 31 were sequentially laminated as shown in FIG. Then, a positively charged P ⁺ N type a-Si photoconductor A was produced. Since the injection blocking layer 29 of the photoconductor A is heavily doped, a depletion layer cannot be formed by charging, but a depletion layer region 47 is formed in the photoconductive layer 30 by charging.

[0087]

[Table 1]

Further, the film forming conditions of the photoconductor A were changed to those shown in Table 2, and the other conditions were the same as shown in FIG. 9B, and the light-doped P-type injection blocking layer 29 and the light-doped N-type photoconductive layer were used. Layer 3
0 and the surface layer 31 were sequentially laminated to produce a positively charged PN type a-Si photoconductor B. Since the injection blocking layer 29 of the photoconductor B is lightly doped, a depletion layer region 48 is formed by charging, and a depletion layer region 47 is formed in the photoconductive layer 30 by charging similarly to the photoconductor A.

[0089]

[Table 2]

Furthermore, the film forming conditions of the photoconductor A were changed to those shown in Table 3, and the other conditions were similarly changed to the N type injection blocking layer 29, the P type photoconductive layer 30, the surface as shown in FIG. 9B. The layers 31 were sequentially laminated to prepare a negatively charged NP type a-Si photoconductor C. The photoconductor C has a charging polarity opposite to that of the photoconductors A and B, but has the same operation effect and characteristics as the photoconductor. Like the photoconductor B, the photoconductor C also has the injection blocking layer 2
Since 9 is lightly doped, a depletion layer region 48 is formed by charging, and a depletion layer region 47 is formed in the photoconductive layer 30 by charging, like the photoconductor A.

[0091]

[Table 3]

Next, the glow discharge decomposition device 36 shown in FIG.
In addition, the conductive substrate 21 has a diameter of 30 mm and a length of 260 m.
m, and an Al drum having a wall thickness of 2.5 mm and having a mirror finish is set, and an injection blocking layer 25, a photoconductive layer 26, and a surface layer 27 are sequentially laminated under the conditions of Table 4 as shown in FIG. Then, a conventional positively charged a-Si photoconductor D was produced.

[0093]

[Table 4]

Similarly, the translucent substrate 33 has a diameter of 3
A glass drum having a thickness of 0 mm, a length of 260 mm, and a wall thickness of 1.8 mm was formed with a thickness of 0.1 μm by an active reaction vapor deposition method.
After setting the TO transparent conductive layer 34 formed, the injection blocking layer 25, the photoconductive layer 26, and the surface layer 27 are sequentially laminated under the conditions of Table 5 as shown in FIG. An a-Si photoconductor E for electrophotographic recording method, which does not require conventional corona charging, was produced.

[0095]

[Table 5]

The photoconductor characteristics of the photoconductors A to E thus produced were measured by the following methods. As the initial charging potential, the dark part surface potential when the surface charge amount of the drum was 0.2 μC / cm ² was measured, and the charging rate was calculated by dividing this initial charging potential by the total film thickness. The dark decay is% of the surface potential after 0.5 seconds in the dark divided by the initial charging potential.
Displayed and asked. As for the withstand voltage, the V-I characteristic (V: charging potential, I: current flowing into the drum) is measured, and the V when the correspondence between V and I begins to deviate from the linear relationship (becomes no longer proportional).
Was divided by the total film thickness. Next, the exposure energy required to reduce the surface potential to one half of that before exposure was measured as _half- sensitivity, and was expressed as sensitivity E _1/2 . Further, as the exposure sensitivity, the exposure energy required for the surface potential to be _{1/15 of} that before the exposure was measured and expressed as the sensitivity E _1/15 . Then, the sensitivity ratio E _1/15 / E _1/2 was obtained, and the goodness of the tail of the curve in the EV characteristic (E: exposure energy, V: surface potential) was shown. Further, the residual potential was measured as the surface potential when an exposure energy 10 times the exposure energy required for the sensitivity E _1/15 was applied. The image density is the optical density of the image part,
The fog is the optical density of the background (white background), and the resolution is 600.
The resolution of dpi (dot / inch) is evaluated,
The pass level is shown as ◯, the slightly inferior level is shown as Δ, and the fail level is shown as x.

Table 6 shows the constitution of each of the above photoconductors and the measurement results of each characteristic. As can be seen from Table 6, according to the photoconductors A, B and C of the present invention thus obtained, in their electrophotographic characteristics, the charging rate per unit film thickness, dark decay rate, withstand voltage, sensitivity, residual All of the potentials showed better characteristics than the conventional photoconductors D and E. Particularly, in the photoconductors A, B and C of the present invention, the photoconductive layer is a thin film,
Since the photoconductor is used at a low electric potential, the exposure energy required for lowering the electric potential by a certain amount is 1/2 or less as compared with the conventional photoconductor.

Table 6 also shows the types of developers, the exposure directions, and the development potentials as the conditions when the image evaluation was performed on each photosensitive member. All of these had almost the same image density and resolution, and good images were obtained.
In combination with the low-potential developing method, the photoreceptors A, B, and C of the present invention have a much lower developing potential than the conventional photoreceptor D, and a simpler process than the developing method of the photoreceptor E to obtain a good image. Thus, an image forming apparatus having excellent image quality with a thinned photoreceptor layer can be provided.

[0099]

[Table 6]

The graph shown in FIG. 10 shows a comparison of the wavelength sensitivity characteristics of the photoconductor A and the photoconductor D. In this graph, the horizontal axis is the exposure wavelength and the vertical axis is the reciprocal of the sensitivity E _1/15 (1 /
E _1/15 ). 1 / E _1/15 indicates that the higher the value, the higher the photosensitivity. From the figure, it can be seen that the photosensitivity characteristic of the photoconductor of the present invention is flatter with respect to the exposure wavelength. As described above, since the sensitivity to the exposure wavelength is more uniform than that of the conventional photoconductor, when a color image was formed using the photoconductor A, a color image recording property excellent in color reproducibility was obtained. .

In the photoreceptor of the present invention, the injection blocking layer 29 of the photoreceptor A is composed of a heavy-doped P ⁺ type semiconductor,
It has almost no photoconductivity. A depletion layer is hardly formed during charging in a layer formed of such a snake-doped P ⁺ type semiconductor and having a film thickness of about 1 to 5 μm, and all layers are semiconductor layers and have an insulating layer property. Absent. On the other hand, the photoconductive layer 30 is made of, for example, a light-doped N-type or I-type semiconductor, and this layer 30 is in a reverse bias state at the time of charging, and is a carrier payout region generated at the junction with the injection blocking layer 29. Considering the depletion layer region 47 and the remaining semiconductor layer region separately, the depletion layer region 47 of 1 to 5 μm is formed in the photoconductive layer 30 of 1 to 20 μm in thickness. Since the depletion layer region 47 serves as a carrier payout region, the depletion layer region 47 has a high resistance and a property close to that of an insulator. Since the proportion of the film thickness exhibiting a property close to that of an insulator in the photoconductive layer 30 is large, the existence of the depletion layer region 47 contributes significantly to the withstand voltage and charging.

On the other hand, in the case of the N ⁺ P type photoconductor opposite to the photoconductor A, it is used by negative charging and is in the reverse bias state, and the photoconductivity of the P type or I type semiconductor at the junction with the injection blocking layer 29 is obtained. In the layer 30, a depletion layer region 4 which is a carrier payout region
Yields 7.

The thickness of these depletion layer regions 47 varies depending on the charging potential, but in the region where the potential is lowered by exposure, the thickness becomes thin and the film resistance of the photoconductive layer 30 becomes small, so that the sensitivity characteristics are improved. Has the effect of

The thickness of these depletion layer regions 47 also changes depending on the doping concentration of the valence electron controlling impurities into the photoconductive layer 30. In the case of a-Si, it is 5μ when non-doped
m, which is almost 0μ with doping of 200 ppm or more.
It becomes m. Further, this thickness is determined by other sub constituent elements such as C,
It also changes with the addition of N, O and the like, and the addition of these usually weakens the effect of impurity doping for valence electron control. In that case, the same result can be obtained by increasing the impurity doping amount.

The photoconductor layer of the photoconductor A has a three-layer structure, and the film thickness of the entire photoconductor layer and the relative dielectric constant are the same as those of the photoconductor layer, the surface layer, the photoconductive layer, and the carrier injection blocking layer. The thickness is d _T , d _a , d _b , d _c , and the relative permittivity is ε _T , ε _a ,
If ε _b and ε _c , the relative permittivity of the surface layer is slightly different from the other layers, but since the film thickness is relatively thin and the relative permittivity of the photoconductive layer and the injection blocking layer are almost the same, The relative dielectric constant of the whole may be represented by the relative dielectric constant of the photoconductive layer, and the film thickness may be represented by the total of the film thicknesses of the layers. That is, ε _T = ε _b = 12, d _T
= 9.0 (μm), d _T / ε _T = 0.8
Becomes

According to the photoconductor A having d _T / ε _T = 0.8, all of the charging rate, the dark decay rate, the withstand voltage, the sensitivity, and the residual potential are superior to those of the conventional photoconductor D. It was Such high sensitivity is because the photoconductor layer is a thin film and can be used at a low potential, so that the exposure energy required for lowering the potential by a certain amount is half or less than that of the conventional photoconductor. It is believed that

In the photoconductor B, since the injection blocking layer 29 is composed of a light-doped P-type semiconductor, the depletion layer region 48 can be formed in this layer 29 as shown in FIG. 9B. . The depletion layer region 48 has a property as an insulating layer in the injection blocking layer 29. Similarly, a photoconductive layer 3 made of a light-doped N-type semiconductor and having a film thickness of 1 to 20 μm.
At 0, a depletion layer region 47 of 1 to 5 μm is formed. Therefore, in the photoconductor B, the charge ratio, the dark decay rate, and the withstand voltage were improved by the amount of the depletion layer region increased compared to the photoconductor A.

When the surface of the photoconductor is positively charged when the conductive substrate of the photoconductor is set to the reference potential, for example, the ground potential,
The developing bias voltage also has the same positive polarity and the transfer polarity is the opposite negative polarity, so that the toner is efficiently transferred to the recording paper. Conversely, when the surface of the photoconductor is negatively charged, the developing bias voltage also has a good negative polarity, and by setting the transfer polarity to the negative polarity, the toner is efficiently transferred to the recording paper.

Therefore, the photosensitive member is required to have a small leakage current and a high charging ability at the time of charging, and on the other hand, a large inflow current and a property of not being charged at the time of transfer. Especially during transfer, changes in paper quality (thickness, paper width, resistance, environmental changes, etc.)
Since the load such as voltage and current to the photoconductor tends to fluctuate, it is desirable that the impedance of the photoconductor is sufficiently low. Otherwise, the dielectric breakdown of the photoconductor will occur during the transfer process, and the film will interfere with charging. Defects will occur.

As the layer constitution satisfying the above requirements, the constitutions (a) to (c) described above are used when the charge has a positive polarity, and the constitutions (d) to (f) described above when the charge has a negative polarity. Is good.
Here, by inserting the I-type semiconductor layer as in (c) or (f), a smaller leakage current and a higher charging ability in the charging process can be obtained in proportion to the film thickness.

Example 2 A glow discharge decomposition apparatus 3 shown in FIG.
6, the conductive base 14 has a diameter of 30 mm and a length of 260
9mm, thickness 1.5mm and 4.0mm mirror-finished Al drum was set, the film formation time of each layer was changed according to the conditions of Table 1, and the film thickness was changed. In this manner, the injection blocking layer 29, the photoconductive layer 30, and the surface layer 31 were sequentially laminated to produce positively charged P ⁺ N type a-Si photoconductors F, G and H. The thicknesses of the photoconductors F, G and H are set so that d / εr is 0.05, 0.75 and 9.2, respectively, and the values are shown in Table 7 together with the thickness of Al. It was
Further, in the same table, as in Table 6, the evaluation results of the characteristics of the photoconductor are also shown.

[0112]

[Table 7]

As can be seen from Table 7, with the photoconductor F having d / εr of 0.05, the required initial charging potential was not obtained, and the fog was so bad that a recorded image could not be obtained. Further, with the photoconductor G having d / εr of 0.75, a good recorded image was obtained as with the photoconductor A. Further, in the photosensitive member H having d / εr of 9.2, although the initial charging potential has a margin, the resolution of the image was poor under the low potential developing conditions.

Example 3 When the surface potential of the photosensitive member, which is an image evaluation condition, was set to +10 V using the photosensitive member G, as shown in Table 8, when the developing bias voltage was set to +90 V, the surface of the dark portion of the photosensitive member was measured. Since the amount of electric charge is small, the shielding effect in the dark part becomes insufficient, and the toner is attracted to the photoconductor, so that the image is badly fogged and the resolution cannot be evaluated.

Similarly, when the surface potential of the photosensitive member was set to +270 V using the photosensitive member G, the surface potential was not lowered due to insufficient photosensitivity. As shown in Table 8, when the developing bias voltage was set to +90 V, the photosensitive Since the surface charge of the light portion of the body remains, the shielding action in the light portion remains and the toner is not sufficiently attracted to the photoconductor, and the image density becomes insufficient, and the resolution cannot be evaluated. In addition, the pressure resistance is insufficient,
Dielectric breakdown of the photoreceptor layer occurred during continuous use, and an increase in black dots was observed in the image.

[0116]

[Table 8]

From the above results, the potential difference between the exposed area and the non-exposed area on the surface of the photoreceptor in the present invention is 10 to 240 V.
It was confirmed that the above range was suitable.

[0118]

As described in detail above, according to the present invention, an image forming apparatus capable of forming an image using a photoconductor provided with a thin photoconductor layer having good electrophotographic and image properties. Was able to provide. According to the photoconductor of the present invention, the film thickness of the photoconductor layer is made smaller than that of the conventional photoconductor, and the amount of deformation of Al used as the substrate is reduced, whereby the material and processing of the photoconductor layer and the substrate are performed. Since both costs can be reduced, an image forming apparatus having a low cost photoconductor and excellent cost performance can be provided.

Further, according to the image forming apparatus of the present invention, the dark attenuation characteristic, the photosensitivity characteristic and the deterioration of the resolution due to the increase in the film thickness of the photoconductor are eliminated, and the excellent charging characteristic, the photosensitivity characteristic and the resolution are obtained. A photoconductor can be provided, and thereby a photoconductor and an image forming apparatus suitable for color image recording can be provided.

Further, according to the image forming apparatus of the present invention, the excellent photosensitivity characteristic of the photoconductor layer can be fully utilized, so that the range of selection of the exposure light source can be widened. Thereby, for example, a GaAsP-based III-
It has become possible to use LED heads and EL heads manufactured by epitaxially growing a group V compound, and it has become possible to reduce the cost of the exposure light source.

Furthermore, by using an a-Si-based material for the photoreceptor layer, it is possible to provide a photoreceptor having excellent durability, long life, harmless to the human body and pollution-free at a low cost, and a large amount of industrial waste. An image forming apparatus that does not generate matter and is excellent in environmental problems can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic image forming apparatus of the present invention.

FIG. 2 is an enlarged view of a main part of a developing unit of the image forming apparatus of the present invention.

3 (a) and 3 (b) are a schematic view of a conventional photosensitive member and a developing portion by a developing method, and an equivalent circuit thereof.

4A and 4B are cross-sectional views showing a layer structure of a conventional a-Si photoconductor.

5 (a) and 5 (b) are a schematic view of a photosensitive member of the present invention and a developing portion by a developing method, and an equivalent circuit thereof.

6A to 6C are cross-sectional views showing the layer structure of the photoconductor of the present invention and the charge distribution in the image forming process thereof.

FIG. 7 is an equivalent circuit of a photoconductor layer of the photoconductor of the present invention.

FIG. 8 is a schematic configuration diagram of a glow discharge decomposition apparatus.

9A and 9B are cross-sectional views showing a layer structure in an example of the photoconductor of the present invention.

FIG. 10 is a graph showing wavelength sensitivity characteristics of a photoconductor.

[Explanation of symbols]

 1 ... Image forming device 2 Photoreceptor 3 Charging means 4 Exposure device 5 Developing device 6 ... Bias power supply 14, 21 ... Conductive substrate 15, 22 ... Photoconductor layer 16 ... Magnetic pole roller 17 ... Conductive sleeve 19 ... Magnetic brush 27, 31 ...・ Surface layer

Claims (2)

[Claims] 1. A charging means, an exposing means and a developing means, and a developing bias voltage between the conductive base and the developing means, on an electrophotographic photoreceptor having an amorphous silicon type photoreceptor layer formed on a conductive substrate. An applying means is provided, and a surface layer of an insulator or a semi-insulator is formed on the laminate selected from the following (a) to (f) so that the photosensitive layer has a film thickness in the range of 2 to 24 μm. In a laminated structure of coating, a conductive magnetic brush is formed on the developing means by a combination of a conductive magnetic carrier and an insulating toner or a developer composed of a one-component conductive magnetic toner, and the conductive magnetic brush is brought into contact with the magnetic brush. An image forming apparatus characterized in that a potential difference between an exposed area and a non-exposed area on a surface of a photoconductor is set within a range of 10 to 240V. (A) An I-type semiconductor layer is laminated on the P-type semiconductor layer. (B) An N-type semiconductor layer is laminated on the P-type semiconductor layer. (C) An I-type semiconductor layer and an N-type semiconductor layer are sequentially stacked on the P-type semiconductor layer. (D) An I-type semiconductor layer is laminated on the N-type semiconductor layer. (E) A P-type semiconductor layer is laminated on the N-type semiconductor layer. (F) An I-type semiconductor layer and a P-type semiconductor layer are sequentially stacked on the N-type semiconductor layer. 2. An electrophotographic photoconductor having a photoconductor layer formed on a conductive substrate, a charging unit, an exposing unit, a developing unit, and a developing bias voltage applying unit between the conductive substrate and the developing unit. Along with the arrangement, the relationship between the film thickness d of the photoconductor layer and the relative permittivity εr is set according to the following equation, and the developing means is a combination of a conductive magnetic carrier and an insulating toner or a one-component conductive material. A conductive magnetic brush is formed from a developer composed of a magnetic toner, and the potential difference between the exposed region and the non-exposed region of the surface of the photoconductor contacting the magnetic brush is set to 1
An image forming apparatus characterized by being set within a range of 0 to 240V. d ≤ 24 μm εr ≥ 2 d / εr ≤ 9