JPH07181775A - Electrifying system, electrifier and image forming device - Google Patents

Abstract

PURPOSE:To uniformly electrify a wide area in environments from a high temperature and humidity to a low temperature and humidity by providing an electrifying means holding a very small gap while relatively moving to a body to be electrified and facing it, an electric field forming means forming a discharge electric field between the body to be electrified and the electrifying means and an exposing means exposing the surface of the body to be electrified on the upstream side from the proximate position of the body to be electrified to the electrifying means. CONSTITUTION:The discharge electric field is formed in an approaching region (1) and a separating region (2) in the positional relation between an electrifying roller 1 and a photoreceptor drum 2 and a charge emitted from the electrifying roller 1 reaches a photoreceptive layer 2a. However, the photoreceptive layer 2a reaches the proximate position of the middle between the approaching region (1) and the separating region (2), the photosensitive layer 2a is still unelectrified. Then, in the separating region (2), the photosensitive layer 2a is uniformly electrified. After that, the strength of an electric field is rapidly weakened because the spreading of a gap is relative to the electrification of the photosensitive layer 2a and the discharge is completed up to arrival at the gap where an abnormal discharge is generated to complete the uniform electrification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to charging of an image forming apparatus such as a copying machine, a facsimile or a printer, which forms an image by an electrophotographic method. More specifically, the present invention relates to a charging system in which a photoconductive drum or an endless belt, which is a member to be charged, is charged by a contact charging member, a charging device, and an image forming apparatus including the charging device.

[0002]

2. Description of the Related Art Speaking of a charging device in a conventional electrophotographic apparatus, a corotron charger and a scorotron charger, which utilize a corona discharge generated by applying a high voltage to a thin wire such as tungsten, are generally used. However, in recent years, restrictions on ozone, which is harmful to the respiratory system of the human body due to its strong oxidizing action, have become stricter in recent years, and thus electrification (ozone-less electrification), which produces a small amount of ozone, has attracted attention. The concept of ozoneless charging has existed for a long time, and many methods have been proposed in the past.These methods mainly supply the electric charge from the conductive charging member to the photoconductor, which is the member to be charged, to minimize the discharge current. The amount of ozone generated during discharge is reduced.

When the ozoneless charging modes are simply classified, for example, a method using a fur brush as a charging member (Japanese Patent Laid-Open No. 56-147159) and a method using an elastic roller (Japanese Patent Publication No. 62-11343). , A method using a solid-state discharge element (JP-A-60-169863). Regarding the method of forming the discharge electric field, a method of applying a DC voltage to the charging member (Japanese Patent Laid-Open No. 58-1940).
No. 61), and a method of simultaneously applying an AC voltage and a DC voltage (Japanese Patent Laid-Open No. 63-149668). However, the one that has been put into practical use at present is to mainly use an elastic roller as a charging member and to apply the AC voltage and the DC voltage. This is a charging method in which a voltage is applied to the rollers at the same time. This is because when the fur brush is used, there are problems that the contact between the photoconductor and the fur brush is uneven, so that the charging is not stable and that the fur of the fur brush deteriorates with time and falls or falls. .

When the elastic roller is used, the contact state becomes uniform, and the problem of the fur brush can be solved. However, even with elastic rollers, the surface roughness,
Non-uniform charging occurs due to uneven resistance and adhesion of foreign matter.

With respect to the adherence of foreign matter, the developer not transferred to the material to be transferred in the transfer process and the paper dust generated from the paper to be the material to be transferred are removed by the cleaning process, but the developer and the fluidity of fine particles are improved. It is impossible to completely remove silica added for that purpose, paper powder added for improving the smoothness of the transfer target paper, especially filler in the paper powder even in the cleaning process. , The developer that has gone through these cleaning processes,
Silica, paper dust, and the like accumulate on the surface of the elastic roller, deteriorating the contact state and hindering uniform charging. Although attempts have been made to mechanically and electrically remove these adhering foreign substances, complete removal is difficult.

On the other hand, when a non-contact solid-state discharge element is used, a change with time such as adhesion of foreign matter or abrasion of the surface, which is generated due to contact with a photoconductor such as a fur brush or an elastic roller, occurs. do not do. However, since it is difficult to set conditions such as the surface property of the solid-state discharge device and the retention of minute voids, it has been an obstacle to practical use until now.

[0007]

As shown in FIG. 2, a charging device in which a DC voltage is applied from a DC power supply 3 to a charging roller 1 holding a minute gap with respect to a photosensitive drum 2 is incorporated in an electrophotographic apparatus to display an image. The charging uniformity was evaluated by using a brush. The photoconductor drum 2 used in the electrophotographic apparatus (not shown) has an organic photosensitive layer 2a applied to an aluminum tube 2b (drum diameter: φ30, film thickness: 20 μm), and a one-component magnetic developer was used for development. reverse development (developing bias voltage V _B: -350 V) was carried out to use a semi-conductive elastic roller to the transfer. The peripheral speed of the photosensitive drum is 25 mm / s.

To briefly list the specifications of the charging device used at this time, the charging roller 1 comprises a core metal 1b of φ12 and a urethane thin film layer 1a having a thickness of 30 μm and subjected to a semi-conductive treatment. in gold 1b direct current voltage (V _C: -140
0 V) is applied. The charging roller 1 is held by a gap ring (not shown) at both ends with respect to the photosensitive drum 2 with a minute gap of 50 μm, and is configured to be driven by a frictional force between the photosensitive drum and the gap ring.

An image was formed using the electrophotographic apparatus in various environments, and the charging device was evaluated. First, good images were obtained in a normal temperature and normal humidity environment: NN environment (room temperature: 20 ° C., humidity: 50%). Photosensitive layer surface potential V ₀ at this time
Was -550V. Next, high temperature and high humidity environment:
When evaluated in an HH environment (33 ° C., 80%), good images were obtained as in the normal temperature and normal humidity environment. V ₀ at this time
Was -580V. However, when evaluated in a low-temperature and low-humidity environment: LL environment (7 ° C, 20%), small spot-like fog (diameter 50 to 500 μm) on the white background occurs, and spot-like white spots (diameter 50 to 50-diameter) occur on the black background. 500 μm)
There has occurred. At this time, V ₀ was −520V.

V ₀ in these three typical environments
The measured value of is only a measuring device (surface potential measuring device: T
It depends on the resolution of rek model 344), and the value of the average surface potential of an area of about 20 mm square is shown. Therefore, it is impossible to directly measure what the value of the potential unevenness on the photoconductor is due to the background fog and the white spot generated in the LL environment. So V
Indirect evaluation of potential unevenness was performed by shifting _B up and down and by varying the amount of background fog and white spots generated. As a result, if the absolute value of V _B is increased, the background fog and white spots both decrease, and V
_{When B} was lowered, the ground fogging and white spots both increased. From this, it became clear that the potential unevenness was caused by the development of the reversely charged toner in the developer at the portion that was excessively charged than the average V ₀ .

Next, the cause of excessive charging was analyzed. Theoretically, when a discharge phenomenon occurs in a minute void, Townsend discharge occurs according to Paschen's law and the photosensitive layer is charged. When the surface of the photosensitive layer is charged and the potential difference between the charging roller 1 and the surface of the photosensitive member reaches the discharge start voltage, the discharge ends. Therefore, in order to confirm the phenomenon in which excessive charging occurs, an experiment was conducted using the charging roller 1 and the transparent electrode to verify the relationship between the gap distance and the discharge. FIG. 6 is a graph in which the horizontal axis represents the air gap distance and the vertical axis represents the discharge start voltage. The discharge starting voltage was a constant value in the region where the gap was about 8 μm or less, and the discharge starting voltage increased in the region where the void was 8 μm or more.

This can be easily explained by using Paschen's law. FIG. 7 shows a graph in which the Paschen's curve is modified and the vertical axis represents the discharge start voltage and the horizontal axis represents the air gap distance. The discharge starting voltage gradually decreases as the gap distance becomes narrower, and a curve is drawn such that the gap has a minimum value at about 8 μm and then rises sharply. Therefore, in the voids of 8 μm or less, discharge is not normally generated. However, even if the minimum gap is 8 μm or less, the charging roller 1 having a curvature always has a region having a gap of 8 μm or more between itself and the transparent electrode. Is a constant value.

When the discharge state is observed, 100 voids are found.
A non-uniform light emission phenomenon was confirmed along with the discharge phenomenon in the region of μm or more. In other words, in the region where the void is 100 μm or more, the electric field may be concentrated due to the uneven surface of the elastic roller and the uneven resistance, and abnormal discharge may occur, causing excessive charge transfer. I guessed.

Therefore, there is a gap between the photosensitive layer and the transparent electrode but no abnormal discharge occurs (1 if the conditions of this experiment are followed).
It was thought that, in principle, if a charging device that discharges in a gap of 00 μm or less) is realized, image defects such as background fog and blank areas in an LL environment can be solved.

However, in the structure of the conventional roller charging device for applying the DC voltage as described above, the charging roller 1
Since the gap between the photosensitive drum 2 and the photosensitive drum 2 gradually approaches and separates from each other, an abnormal discharge is always generated when gradually approaching, and there is a problem that an image defect such as a background fog or a blank image occurs. Was.

In view of the above points, the present invention prevents foreign matters adhering to the photoconductor drum from re-adhering to the surface of the charging member, and causes image defects such as fog and white spots not only in the HH and NN environments but also in the LL environment. An object of the present invention is to provide a uniform charging that does not occur, a charging method, a charging device configured according to this charging method, and an image forming apparatus using the charging device.

[0017]

SUMMARY OF THE INVENTION According to the present invention, there are provided a charged body having photoconductivity, a charging means which is opposed to the charged body while holding a minute gap while moving relative to the charged body, and the charged body and the charging means. A contact characterized in that the surface of the charged body is charged by an electric field forming means for forming a discharge electric field between the charged body and an exposing means for exposing the surface of the charged body upstream of the closest position of the charged body and the charging means. Charging method.

And a charged body having photoconductivity, a charging means which faces the charged body while holding a minute gap while moving relative to the charged body, and an electric field formation for forming a discharge electric field between the charged body and the charging means. And a charging means for charging the surface of the body to be charged by the exposing means for exposing the surface of the body to be charged on the upstream side of the closest position of the body to be charged and the charging means.
And a charged body having photoconductivity, a charging means that holds a minute gap while relatively moving with the charged body and faces each other, and an electric field forming means that forms a discharge electric field between the charged body and the charging means. The image forming apparatus is characterized by comprising a contact charging device that charges the surface of the body to be charged by an exposing unit that exposes the surface of the body to be charged on the upstream side of the closest position of the body to be charged and the charging unit.

[0019]

According to the present invention, the charged body having photoconductivity and the charging means for charging the surface of the charged body while facing the charged body while holding the minute voids perform relative motion with each other. When considering the positional relationship by dividing it into two areas of approaching and spacing, exposure in the approaching area is performed by the exposing means, and the charged electric charge on the surface of the body to be charged due to discharge from the charging means generated by the electric field forming means. The charge is removed by exposure, and finally, the charge is not left on the surface of the body to be charged. After passing through the closest position, in the separated area, charging is performed by holding the charged electric charge on the surface of the member to be charged as it is due to the discharge from the charging means generated by the electric field forming means. Since the discharge in the separated area always has a structure in which the air gap grows from the closest position, the discharge is first generated in a minute air gap in which no abnormal discharge occurs, and the gap increases until it reaches the air gap where the abnormal discharge occurs. The charging of the surface of the charged body is completed. After the charging is completed, the electric charge is accumulated on the surface of the body to be charged, and in addition to the large void, the electric field strength between the charging means and the body to be charged is sufficiently smaller than the discharge electric field, and abnormal discharge does not occur and is uniform. Charge can be achieved. Therefore, the excessive charge on the surface of the member to be charged due to the abnormal discharge does not occur, so that the image abnormality such as the background fog and the white spot does not occur.

The charging system of the present invention requires a high voltage power supply and a large number of parts, and has a DC voltage of a lower voltage than that of a scorotron charger having a complicated structure or a contact roller charging device which requires an expensive AC power supply. Since it is composed of only a power source, a solid-state discharge element having a simple structure, and a light source for removing light, it can be implemented at low cost. Further, since there is no change with time such as adhesion of foreign matter, abrasion, damage, etc., it is possible to provide a charging device having a long life and high reliability.

Further, the exposure means provided in the approaching area has conventionally been affected by the exposure pattern of the pre-rotation of the photoconductor during the next rotation, and in particular, it is used as an optical filter for preventing an optical memory for generating a ghost image on a halftone image. Since it can be shared with electric appliances, there is no need to add new parts, so the cost does not rise.

[0022]

【Example】

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a charging device used in an electrophotographic apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a metal charging roller. The charging roller 1 has a photosensitive drum 2 having an organic photosensitive material applied on the surface thereof and a gap ring (not shown) at both ends, which is 50 μm.
It is held in a minute gap of the photosensitive drum 2 and is rotated by the frictional force between the photosensitive drum 2 and the gap ring.

To the core metal 1a of the charging roller, a negative DC voltage is applied by the DC power source 3 for forming a discharge electric field in the minute gap between the charging roller 1 and the photosensitive layer 2a. If the positional relationship between the charging roller 1 and the photosensitive drum 2 is divided into two areas, (1) an approach area where the charging roller 1 and the photosensitive drum 2 gradually approach each other. (2) Separation area where the charging roller 1 and the photosensitive drum 2 are gradually separated.

Of these, a discharge electric field is formed in (1) the approaching area and (2) the spacing area, and the charges discharged from the charging roller 1 reach the photosensitive layer 2a. However, at this time, (1) the photosensitive layer 2a is exposed by the LED 4 in the approaching area, so that the photosensitive layer 2a is apparently made conductive, and the electric charge reaching the photosensitive layer 2a is not retained on the surface of the photosensitive drum. It will leak to the earth side of 2. Therefore, the photosensitive layer 2
The photosensitive layer 2a remains uncharged when a reaches the closest position between the (1) approaching area and the (2) spacing area. Next, in (2) the separated area, discharge continues from (1) the approach area. In the minute gap, only Townsend discharge is generated and no abnormal discharge is generated.
a is uniformly charged. After that, the gap is expanded and the photosensitive layer 2a is charged, and the electric field is abruptly weakened, and the discharge is completed and the uniform charging is completed by the time the gap reaches where the abnormal discharge occurs.

At this time, the charging roller 1 covers the outer circumference of the core metal 1b with the semiconductive layer 1a to control the movement of excessive electric charges.
The volume resistance value of the semiconductive layer is preferably about 10 ⁶ to 10 ¹² Ω · cm. When the resistance value is 10 ⁶ Ω · cm or less, the charge supply capacity during discharging is too high. Therefore, when there are pinholes, dent scratches or abrasion scratches on the photosensitive layer 2a, the photosensitive layer 2a
As a result, the withstand voltage of the photosensitive layer 2a is reduced, and when the photosensitive layer 2a is dielectrically destroyed, excess charges flow into the ground side through pinholes or the like and destroy the photosensitive layer 2a. When the resistance value is 10 ¹² Ω · cm or more, the applied voltage needs to be increased because the charge supply capacity during discharge is too low. If the applied voltage is increased, not only the efficiency is lowered, but also the discharge is generated at the contact between the core metal 1a and the electrode (not shown), and the applied voltage value to the charging roller 1 is changed to make the charging unstable. The charge supply capability at this time is a general term that defines the mobility of electrons inside the semiconductive layer 1a and the ease of electron emission on the surface of the semiconductive layer 1a. Since there are materials that are easily affected by the temperature and humidity environment, the range of this resistance value is a value that includes the change.

Regarding the surface roughness of the charging roller 1,
(2) Surface performance is required so that abnormal discharge does not occur in the minute voids in the separated region. It has been confirmed by experiments by the inventor of the present patent that abnormal discharge does not occur if the maximum surface roughness of the charging roller 1 is 20 μm (Rmax) or less.

Next, an experiment in which the inventor of the present patent has confirmed the principle of the charging method and the charging device will be described with reference to specific numerical values.

The charging roller 1 is applied to the photosensitive drum 2 rotating at a peripheral speed of 25 mm / s by 100 g at both ends, and the gap rings at both ends are pressed against the photosensitive drum 2. At this time, the charging roller 1 is driven to rotate at a peripheral speed substantially equal to that of the photosensitive drum 2 by frictional force. The charging roller 1 is made of an aluminum cored bar 1b having a shaft diameter of 12 mm and a semiconductive urethane thin film layer 1a having a thickness of 30 μm formed on the outer peripheral surface thereof, and has a volume resistance value of 10 ⁸ Ω · cm. . A DC voltage of -1400 V is applied to the core metal to charge it. The LED 4 is adjusted to 7 according to the wavelength sensitivity of the photosensitive layer 2a
An LED having a peak wavelength at 80 nm was used.

In this charging device, when the photosensitive layer 2a is made of an organic photosensitive material and the film thickness is about 20 μm, the current value flowing through the charging roller 1 is about 20 μA, which is one of the current consumption of the conventional scorotron charger. It was / 10 or less, and the ozone generation amount was 1/100 or less.

When an image is actually printed in a low-temperature and low-humidity environment, if the LED 4 is not turned on, abnormal discharge occurs and horizontal streaky fog occurs at both ends of the paper.
When the approaching area was irradiated with the static elimination light from the LED, the entire surface was uniformly charged, and a uniform image without fog in the white background portion and white spots in the black solid portion was obtained.

In this embodiment, the core metal 1b is made of aluminum, but other metals can be used without any change in effect. The material of the thin film layer of the semi-conductive layer 1a is not limited to urethane, and the effect is the same as long as it is a resin material capable of forming a thin film of uniform thickness such as polyamide or acrylic. It is also possible to omit the semiconductive urethane thin film layer 1a by forming the semiconductive resin into a roller shape.

(Embodiment 2) As a second embodiment, a schematic configuration diagram of a charging device using a fixed charging member is shown in FIG.

In the charging block 9 of this embodiment, a member in which the surface of a block 9b made of aluminum is coated with a semiconductive urethane thin film layer 9a is used. Both the upstream side and the downstream side of the surface facing the photosensitive layer 2a are cut into C planes to sufficiently secure (1) the approaching area and (2) the spacing area. The flat portion facing the photosensitive drum 2 has a width (1) such that the static elimination light of the LED 4 irradiating the approaching area does not reach (2) the separating area. It is possible to prevent the static elimination light from being reflected between the photosensitive layer 2a and the flat portion.

The holding of a minute gap with the photosensitive drum 2 is performed by gap spacers (not shown) at both ends.

Also in this embodiment, as in the first embodiment, the material of the charging block 9 is aluminum aluminum,
The effect is not limited to urethane, and other metals and resin materials may be used.

The charging block 9 is not limited to the shape shown in FIG. 3, and the photosensitive drum 2 is finally charged. (2) Even the shape on the separation area side does not form a non-uniform electric field. If the shape is obtained, uniform charging can be performed, so that the effect is the same even if the shape is as shown in FIG.

(Embodiment 3) As a third embodiment, FIG. 5 shows a schematic configuration diagram of an electrophotographic apparatus equipped with the charging device described in the first embodiment.

The photosensitive drum 2 which has been discharged and charged by the LED 4 and the charging roller 1 rotates in the direction of the arrow. At this time, in the case of a disposable cartridge in which the LED 4 and the charging roller 1 are integrally configured with the developing device 11 related to the developing process, the photosensitive drum 2, the cleaner 25, etc., they may be disposable as constituent elements of the cartridge, but electrophotographic It can also be used up to the machine life as a component of the device. The LED 4 has a life of several thousand hours, which is a sufficient life. The life of the charging roller 1 is not in contact with the photoconductor drum 2, and therefore wear and foreign matters do not occur in both cases of stop, independent drive or driven through a gap ring, which is sufficient. Have a lifespan.

First, when a print signal is input to the electrophotographic apparatus 10 from a controller (not shown), charging,
Each process of development, transfer, cleaning, and fixing starts an initial running-in operation called initialization, and when the reception of the image and character data sent from the controller is finished next, the image formation on the photosensitive drum 2 is started. It In the image forming area of the photosensitive drum 2, a voltage is applied to the charging roller 1 and the LED 4 by a power source (not shown), and the charging and the exposure are simultaneously performed. The details are the same as in Example 1.

The photosensitive drum 2 is formed by coating the surface of the aluminum tube 2b with an organic photosensitive layer, and has a negative charging polarity. Therefore, a DC voltage of -1400 V is applied to the core metal 1b of the charging roller 1 by a DC power source (not shown) with respect to the aluminum tube 2b that is grounded. The LEDs 4 are formed in an array so as to have an exposure range equal to or longer than the effective length of the photosensitive drum 2. LED
The emission wavelength of is 780 nm according to the sensitivity wavelength of the photoconductor.

Next, a laser scanner unit (hereinafter referred to as LS
By being exposed to the laser beam 13a based on the image and character data emitted from U, the charge on the surface of the photosensitive layer 2a is selectively removed, and an image pattern (hereinafter abbreviated as an electrostatic latent image) based on the potential is generated. ) Is formed on the photosensitive drum 2.

An image pattern (hereinafter abbreviated as "visual image") is exposed by adhering the developer to the electrostatic latent image by an electric field force by a developing device 11 which holds a negatively charged developer (not shown) in its container. It is formed on the body drum 2.

On the other hand, the cut sheets 24 stored in the paper cassette 20 are fed one by one to the registration rollers 17 by the pickup roller 19. When the visible image formed on the photoconductor drum 2 arrives at the position of the transfer roller 14, the registration roller 17 and the backup roller 18 use the cut paper to cut the cut paper.
To the nip position of.

In the nip between the photoconductor drum 2 and the transfer roller 14, the visible image on the photoconductor drum 2 is transferred to the cut paper 24. The transfer roller 14 has a power source (not shown) of +20.
A DC voltage of 00V is applied. The transfer voltage forms a transfer electric field from the photosensitive drum 2 toward the transfer roller, and the negatively charged developer is transferred from the photosensitive drum 2 to the cut paper. In addition, the cut paper 24
The developer is held on the cut sheet 24 even after the positive charge is injected into the back surface of the sheet and the cut sheet 24 is separated from the photosensitive drum 2.

The cut sheet 24 to which the developer is transferred is conveyed to the fixing device 12, and is heat-fixed on the cut sheet 24 by heat and pressure by the heat roller 15 and the backup roller 16.

The cut sheet 24 after fixing is discharged to the sheet discharge tray 26, and a series of image forming processes is completed.

The photosensitive drum 2 which is not transferred and remains
The upper developer is cleaned by the cleaner 25, and the surface of the photoconductor drum 2 becomes clean.

After the cleaning is completed and the photosensitive drum 2 has returned to the charging step again, almost no developer remains on the surface, but the photosensitive layer 2 is formed by the optical memory by the exposure of the LSU 13 and the transfer memory by the transfer electric field of the transfer roller 14.
Potential unevenness occurs in a. In the normal optical memory, the surface of the photoconductor drum 2 is entirely exposed by a charge eliminating lamp after cleaning, so that the charge of the photosensitive layer 2a is uniformly eliminated. On the other hand, since the transfer memory is charged to the opposite polarity (plus in this embodiment) to the charge polarity of the photosensitive layer 2a, it is impossible to remove the charge with the conventional charge removing lamp. However, according to the charging method of the present invention, (1) the transfer memory can be erased because the charging and the discharging are simultaneously performed in the approaching area.

As described above, according to the present embodiment, not only the problems of the background fog in the white background area and the blank areas in the black solid area in the LL environment but also the optical memory and the transfer memory of the photosensitive drum 2 are solved.

In any of the examples, (1) the member for exposing the approaching area and performing the light elimination is not limited to the LED 4, but the sensitivity of the photosensitive layer 2a such as a cold cathode tube, a glow lamp, a halogen lamp, a semiconductor laser. It goes without saying that the light source that emits the wavelength of the above can be freely selected according to the cost, the configuration, the speed, and the like.

The photosensitive layer 2a is not limited to the organic photosensitive material, and the effect of the present invention does not change even if any photosensitive material such as Se or α-Si is used.

When the charging device of the present invention is used, the charging roller 1 and the photosensitive drum 2 do not contact each other, so the cleaner 2
It is also possible to easily realize a cleanerless process in which 5 is omitted.

[0053]

As described above, according to the present invention,
To provide a charging method, a charging device, or an image forming apparatus which has long life, high reliability, small size, low price, less ozone generation, and uniform charging in a wide range from high temperature and high humidity environment to low temperature and low humidity environment. It is possible and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a charging device according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional charging device.

FIG. 3 is a schematic configuration diagram of a charging device according to a second embodiment of the present invention.

FIG. 4 is another schematic configuration diagram of the charging device according to the second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an electrophotographic apparatus according to a third embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the gap distance between the transparent electrode and the charging roller and the discharge start voltage formed therebetween.

FIG. 7 is a graph showing a Paschen curve.

[Explanation of symbols]

 1 Charging Roller 2 Photoreceptor Drum 3 DC Power Supply 4 LED 9 Charging Block 11 Developing Device 12 Fixing Device 13 LSU 13a Laser Light 14 Transfer Roller 20 Paper Feed Cassette 24 Cut Paper 25 Cleaner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichi Suzuki, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A charged body having photoconductivity, a charging means that faces the charged body while holding a minute gap while moving relative to the charged body, and a discharge electric field between the charged body and the charging means. Contact charging, characterized in that the surface of the charged body is charged by an electric field forming means to be formed and an exposing means for exposing the surface of the charged body upstream of the closest position of the charged body and the charging means. method. 2. A charged body having photoconductivity, a charging unit that faces the charged body while holding a minute gap while moving relative to the charged body, and a discharge electric field between the charged body and the charging unit. Contact charging, characterized in that the surface of the charged body is charged by an electric field forming means to be formed and an exposing means for exposing the surface of the charged body upstream of the closest position of the charged body and the charging means. apparatus. 3. A charged body having photoconductivity, a charging means that faces the charged body while holding a minute gap while moving relative to the charged body, and a discharge electric field between the charged body and the charging means. An electric field forming means to be formed; and a contact charging device for charging the surface of the charged body by an exposing means for exposing the surface of the charged body upstream of the closest position of the charged body and the charging means. A characteristic image forming apparatus.