JPH07140735A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To provide an electrophotographic method by which the residual potential or its accumulation caused in a photoreceptor having a surface protective layer comprising a carbon thin film or a thin film essentially comprising carbon can be efficiently decreased while reduction of the charge potential or reduction of picture quantity due to charge fatigue is hardly caused bus stable electrophotographic characteristics can be maintained. CONSTITUTION:Lots of copies using general paper can be obtd. by repeating steps of main electrification, exposure for an image, development, transfer, separation, discharge, and cleaning for an org. photoreceptor having a carbon thin film or a thin film essentially comprising carbon as a surface protective layer. In this electrophotographic method, a step to give charges in the opposite polarity to the main electrification to the photoreceptor and simultaneously, just before or immediately after this step, another step to expose the photoreceptor are added between the cleaning step and the main electrification step. Further, in the main electrification step, the photoreceptor is electrified under at least two different electrification conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic method for effectively reducing the residual potential of a photosensitive member in an image forming apparatus, reducing charge potential drop and charge fatigue, and having good repetitive stability.

[0002]

2. Description of the Related Art Conventionally, selenium (Se) and amorphous silicon (a-S) have been used as photosensitive materials for electrophotographic photoreceptors.
i) and cadmium sulfide (CdS) have been mainly used, but in recent years, they have been replaced with organic photosensitive materials which are advantageous in terms of price, pollution-free, manufacturing, electrophotographic characteristics and the like. However, the organic photosensitive material has a low Vickers hardness of about ²⁰ to 40 kg / mm ² and thus has low mechanical durability, and when used in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, it has a mechanical strength of 5 to 15 You will be forced to replace it after about 10,000 copies. Therefore, it is necessary to increase the hardness of the outermost surface of the organic photoconductor by some method to improve the abrasion resistance. Then, as one method thereof, a method of forming a protective layer of high hardness on the outermost surface of the photoconductor is known.

The surface protective layer must not impair the electrophotographic properties of the overcoated photoreceptor. Therefore, the surface protective layer must be a thin film that satisfies optical characteristics and electrical characteristics in terms of electrophotographic characteristics, and must be mechanically excellent. Durable and high charge retention,
An example of a thin film suitable as the surface protective layer is carbon or a thin film composed mainly of carbon. As a typical example of this thin film, a diamond-like carbon film (DL) in which each structure of diamond, graphite and polymer is mixed
C film), and the DLC film is a plasma CVD method or a photo CVD method while inflowing a hydrocarbon-based gas such as methane, ethane, butane, propane, and butadiene, and if necessary, hydrogen, fluorine, nitrogen gas, and the like. It is produced by a vacuum film forming method such as a sputtering method. The physical properties of this film change greatly depending on the film forming conditions. Hardness is 10 to 2000 kg / m
m ² , the electric resistance is 10 ⁶ to 10 ¹⁷ Ω · cm, and the light transmittance tends to increase absorption at a short wavelength due to coloring. In a practical film thickness, several nm to 60% at 450 nm, and 780 nm at 780 nm. It is 80 to 100%. When the DLC film is used as the protective layer of the photoconductor, it is necessary to select physical properties such as surface potential and sensitivity that are sufficiently stable to be used even if used for a long period in addition to stability of properties such as mechanical properties. . When overcoating the DLC film on the organic photoreceptor, the substrate temperature condition in the film forming apparatus must be room temperature or lower than room temperature because of the glass transition temperature of the photosensitive layer. By appropriately selecting the film forming conditions such as gas, reaction pressure, RF power, etc., the surface protective layer as an electrophotographic photoreceptor can be prepared.

However, in the case of a photoreceptor having a protective layer overcoated, when the photoreceptor is repeatedly used, residual potential is accumulated, which causes deterioration of image quality such as density decrease, loss of detail, and background stain. There is. It is considered that this is because the injection efficiency of holes or electrons into the DLC film and the mobility in the film are low.

As a measure to be taken when a residual potential is generated or the stability of the uniform charging potential is insufficient, it is necessary to consider the conditions around the photoconductor from the copying process, and (i) a cleaning step and a uniform charging step. The conductive flexible member, to which an AC bias voltage is applied, is brought into contact with the a-Si photosensitive member to release the trapping (JP-A-60-1).
No. 42355), (ii) a conductive flexible member to which an AC or DC bias voltage is applied and heated between the cleaning step and the uniform charging step is brought into contact with the a-Si-based photosensitive member to perform trapping. Release (Japanese Patent Laid-Open No. 60-1)
(56068 gazette), (iii) By applying an alternating electric field to the surface of the photoconductor before performing uniform charging, the surface of the photoconductor is charged before and after the waveform peak of one polarity applied, and the trapping is released by the generated electric field. (Iv) prior to uniform charging and / or static elimination, pre-charging of the same polarity as uniform charging (Japanese Patent Laid-Open No. 61-165664), (v) Static neutralization is performed by direct current corona charging having a polarity opposite to that of uniform charging (Japanese Patent Laid-Open No. Sho-6)
0-10266) and the like.

Of these, (i), (ii), (iii) and (iv) are all a-Si type photoconductors having no protective layer, which are used for trapping holes and / or electrons trapped in the photoconductor. Prior to the charging step, an AC bias (and photo-erasing, heating) is applied to open the battery, and the electric resistance and electrostatic capacity are restored to repeatedly reduce the charging potential and improve the memory phenomenon. Further, in the method (v), 40 to 90% of the current required for reverse polarity charging is flowed to correct the decrease in charging potential.

[0007]

[Problems to be Solved by the Invention]
In the cases of (i), (ii), (iii) and (iv), since there is no surface protection layer, the bias voltage due to AC acts relatively easily and the expected effect can be obtained, but D is almost close to the insulating layer.
In the case of the surface protection layer made of LC film, it is difficult to work, so
Little effect can be expected. On the other hand, in the case of (v), although it is effective for the purpose of preventing the image density reduction, if the reverse charge is applied before the cleaning step,
This is affected in the case of a photoreceptor having no protective layer, and sometimes, in the case of a photoreceptor having a protective layer, fogging development may occur due to defective cleaning of toner, resulting in remarkable deterioration of image quality.

The present invention has been made in view of the above-mentioned state of the art, and efficiently reduces the residual potential and its accumulation that occur in a photoconductor having a DLC film as a protective layer, while charging due to charge fatigue. It is an object of the present invention to provide an electrophotographic method which is capable of maintaining stable electrophotographic characteristics without causing a decrease in potential and a decrease in image quality.

[0009]

As a measure for preventing the problem in the case of the above (v), it is conceivable to dispose a DC corona discharge device and a discharge lamp of opposite polarity between the cleaning device and the charging device. This is expected to suppress the accumulation of residual potential and improve the SN ratio of the image. However, in this case, when the residual potential becomes higher than usual,
If excessive charges of opposite polarity are applied to set the residual potential to a prescribed potential, the charge potential will drop significantly due to repeated copying, and the potential required to form an image will decrease, resulting in good image quality. There is a problem that the potential margin for guarantee becomes narrow.

In the case of an organic photoreceptor, a charge injection blocking layer (undercoat layer) is provided between the support and the photosensitive layer in order to prevent deterioration of charging characteristics due to charge injection from the support during charging. However, this undercoat layer is sometimes a factor that influences the characteristics of the photoreceptor. For example,
In the undercoat layer or the like in which the fine powder of the metal oxide is dispersed, the charge is easily trapped at the interface between the fine powder and the resin, which hinders the canceling of the charge. Therefore, deterioration of photosensitivity and residual potential occur. It is possible to suppress the problem due to the undercoat layer to a level that does not pose a practical problem by giving an electric charge of opposite polarity prior to charging and exposing it to long-wavelength light.

As described above, in order to reduce the residual potential, the intended purpose can be achieved by the method of applying the reverse charge and the exposure prior to the main charging, but the photoreceptor is charged with the reverse charge of several hundred volts. When the electric charge due to the main charging is charged with, a large electric field is momentarily applied to the photoconductor at the time of switching. For this reason, when it is continuously used in this state for a long time, the charge potential of the photoconductor is gradually lowered due to charge fatigue, and the charging characteristics are deteriorated, or in some cases, the discharge-destructive symptom locally occurs. It also causes a deterioration in image quality. For this reason, it is necessary to set the charging conditions by the soft charge method so that the load on the photoconductor is minimized.

Therefore, as a result of further intensive studies, the present inventors have completed the present invention. That is, according to the present invention, the main charging of the organic photoreceptor having a surface protective layer of carbon or a thin film composed mainly of carbon,
In an electrophotographic method for obtaining a large number of copies on plain paper by repeating the steps of image exposure, development, transfer, separation, charge removal and cleaning, a polarity opposite to the main charging is provided between the cleaning step and the main charging step. An electrophotographic method, characterized in that a reverse charge application / exposure step is carried out at the same time as or immediately before or immediately after the charge is applied to the photoconductor, and the main charging step is performed under at least two different charging conditions. Will be provided. Further, according to the present invention, in the above structure, after the charging potential of the photoconductor is set to +200 to +700 V by the reverse charge application / exposure process, the photoconductor is charged under the first charging condition in the main charging process. After setting the potential to +300 to -500 volts,
An electrophotographic method is provided in which the charging potential of the photoconductor is set to a predetermined potential for latent image formation under the second charging condition. Furthermore, according to the present invention, as the photoreceptor,
An organic photoreceptor having a surface protective layer made of carbon or a thin film composed mainly of carbon having a Knoop hardness of 350 kg / mm ² or more on the order of specific resistance of 10 ¹³ to 10 ¹⁵ Ω · cm is used. There is provided an electrophotographic method characterized in that the difference in charging potential on the surface of the photoconductor under the first charging condition and the second charging condition in the main charging step is 400 to 1200 volts.

The present invention will be described in more detail below with reference to the accompanying drawings. FIG. 1 shows an example of the constitution of the organic photoconductor used in the present invention. In the photoreceptor of FIG. 1A, an undercoat layer (UL) 2 made of a resin in which a metal oxide such as SnO ₂ or TiO ₂ is dispersed or Al ₂ O ₃ is formed on a conductive support 1. , A photosensitive layer 3 formed thereon by a dipping method, a spray method, an evaporation method, or the like, the photosensitive layer 3 being a charge generation layer (CGL) from below.
4 is a laminated (function separation type) photoconductor composed of a charge transport layer (CTL) 5. However, the photosensitive layer 3 is shown in FIG.
The CGL4 and the CTL5 may have the opposite configurations as shown in FIG. 1, or the photosensitive layer 3 may have the CGL4 and the CTL5 as shown in FIG.
It may have a single layer structure having both the functions of TL5. When the UL2 is charged, charges are injected from the conductive support 1 to deteriorate the surface potential, and the image quality S is reduced.
It is formed to prevent the N ratio from decreasing. A protective layer 6 is formed on the photosensitive layer 3 to further improve mechanical durability. The protective layer 6 is formed on the conductive support 1 by U
The above-mentioned plasma C obtained by forming L2 and the photosensitive layer 3 is formed.
Set it in a vacuum film forming apparatus such as the VD method, and use methane, ethane,
Hydrocarbon-based gas such as ethylene, butane, butadiene,
If necessary, hydrogen, oxygen, fluorine, nitrogen gas, etc. are introduced, while the film forming conditions such as reaction pressure, RF power, bias voltage, etc. are set, and the film is formed as a DLC film of about 1 to 5 μm. . The specific resistance of the protective layer 6 is 10 ¹³ to 10 ¹⁵ Ω · cm
The optimum range is on the order of 10 ¹³ Ω · cm, and if it is lower than 10 ¹³ Ω · cm, the sharpness becomes insufficient. On the other hand, the specific resistance is 10
If it is larger than ¹⁵ Ω · cm, the residual potential becomes high, and even if the residual potential is temporarily lowered, the process may not be able to be completely compensated for due to the large charge accumulation. The accumulation of residual potential is liable to cause deterioration of image quality characteristics and malfunction of the apparatus, and therefore it should be kept as low as possible. The Knoop strength of the protective layer 6 is preferably 350 kg / mm ² or more from the viewpoint of mechanical durability and wear resistance.

FIG. 2 is a schematic diagram of an apparatus suitable for carrying out the method of the present invention. According to the method of the present invention, first, the photosensitive member 10 having the above-described structure is uniformly charged by the main charging device 11 including the shield case 11a, the charge wire 11b, and the grid electrode 11c under at least two different charging conditions. give. The first charging condition is +30
The charging is performed to 0 to -500 V, and the second charging is performed after the charging is performed. The second charging condition is that the charging potential required for forming a predetermined latent image is increased. Although it is electrification, it is generally 400 to 1200 V, preferably 600 to 800 V with respect to the electrification potential due to the first electrification, although it depends on specific characteristics such as withstand voltage and electric resistance of the photoconductor.
This causes a potential difference of volt. Potential difference is 40
If the voltage is less than 0 volt or more than 1200 volt, charge fatigue is likely to occur, and it becomes difficult to maintain a practical charging potential when used for a long period of time.
In the illustrated example, the main charging device 11 has two charge wires (double charge wire type) 11b stretched thereon, and the grid electrode 11c installed between the charge wire 11b and the photoconductor 10 is The distance between the metal wires constituting the main charging device 11 is narrowed on the inlet side of the main charging device 11 and widened on the outlet side of the main charging device 11 to make a difference in the amount of charges flowing to the photoconductor 10. As a result, charging is performed under the two types of charging conditions described above, and the reverse charge applying device 17
The rapid charging of charges into the photoconductor 10 by the main charging device 11 at the time of shifting to the main charging is suppressed by
It is possible to reduce the charge fatigue and prevent the charging potential from falling below the practicability, and at the same time maintain the repeated stability. It is desirable to separate the charge wires 11b from each other within a range in which the influences of the charge wires 11b are not exerted, or to install a shield plate between the charge wires 11b. Grid electrode 1
1c is a control grid, which is a grid electrode 11
A voltage is applied to c in order to control the current flowing into the photoconductor 10. A voltage of 0 to ± 1000 volts is applied to the grid electrode 11c by, for example, a high voltage power source, or
The voltage can be applied by using a constant voltage passive element such as a varistor capable of applying the voltage in the above range.

FIG. 3 and FIG. 4 each show an example of the structure of another main charging device that performs the same operation as the main charging device in FIG.
In the main charger of FIG. 3, for example, a fixed resistor R is connected between the two charge wires 11b, and the photosensitive member 1 on the photosensitive member inlet side is connected.
The current flowing into 0 is suppressed. A shield plate may be installed between the two charge wires 11b. In the case of this method, the metal wire intervals of the grid electrode may be the same. Figure 4 shows two charge wires 11b
This is an example in which there is a height difference. Although not shown, a method of dividing the grid electrode and providing a difference in applied voltage between the front part and the rear part can be used.

An image exposure device 12 forms a latent image according to an input signal (original) on the photoconductor 10 to which an electric charge is applied, and a developing device 13 develops the latent image so that the photoconductor 10 is visualized. The visible image on the photoconductor 10 is transferred to the supplied copy paper 19 by the transfer / separation device 14 and separated from the photoconductor. The transferred copy paper 19 is conveyed to a fixing device (not shown) and made into a hard copy. On the other hand, the surface of the photoconductor 10 after the transfer is discharged by the discharging device 15 so that the charge becomes 50 to 100 V or less in order to facilitate the cleaning, and then cleaned by the cleaning device 16.

After that, a process for further reducing the residual potential is performed. In this process, basically, between the cleaning device 16 and the main charging device 11, a reverse charge applying device 17 and an exposure device 18 that apply a charge having a polarity opposite to that of the charge to the photoconductor 10 are arranged. Prior to charging, the photoconductor 10 is provided with a charge and an exposure opposite to the main charge. There are the following three methods for applying the opposite charge and the exposure to the photoconductor 10. (1) A method of exposing after applying a charge opposite to the main charge (2) A method of exposing at the same time as applying a reverse charge (3) A method of performing reverse charging after applying an exposure Reverse charge alone or exposure alone Has almost no effect, and applying only the reverse charge only lowers the charging potential. Therefore, the actions of both devices 17 and 18 are necessary.
As the light source for the exposure device 18, a semiconductor element such as an LED or a miniature lamp coated with a filter can be used. The wavelength of the light source is not particularly limited as long as it is a wavelength range in which the photoconductor 10 does not fatigue.

Although the residual potential shows a decrease depending on the amount of the reverse charge, the film thickness of the undercoat layer, the photosensitive layer and the protective layer constituting the photoconductor 10, the electric resistance, the electrostatic capacity, the electrons and the holes. Limited by physical properties such as mobility. The residual potential decreases as the amount of reverse charge increases, but the amount of decrease in the charging potential tends to increase, so the reverse charging potential is preferably in the range of 200 to 700 volts. If it is less than 200 V, the effect will be insufficient, and if it exceeds 700 V, the charge potential will be greatly lowered during repeated use over a long period of time, and the image quality will be impaired.

FIG. 5 shows a configuration example of a conventional main charging device 11 '(generally adopted in a process that does not give a reverse charge) to one charge wire (single charge wire type) 11b' and a grid electrode 11c. 'Is installed. If the photoconductor 10 is previously charged with a charge having a polarity opposite to that of the main charge, current flows into the photoconductor 10 when the main charge is applied. However, in the single charge wire system, the desired surface potential is suddenly set. Therefore, the larger the opposite polarity charging potential is, the more current flows into the photoconductor 10. Therefore, when the photoconductor 10 is repeatedly used for a long period of time, there is a risk that this effect may appear as a phenomenon such as charge fatigue of the photoconductor 10 or local discharge breakdown.

FIG. 6 schematically shows a charged state when an organic photoconductor overcoated with a protective layer is given a reverse charge (+) and an exposure, and then a charge (-) is given by a main charging device. Is. In the figure, a indicates a charging state when the conventional main charging device shown in FIG. 5 is used, and b indicates a charging state by the double charge wire type main charging device shown in FIG. a is, for example, approximately +700 V to −8
In the case of being charged to 00 volts, b is +70, for example.
The figure shows the charging state when the battery is charged to 0 volt, then to about -200 volt, and then to -800 volt.

In the present invention, when the main charging is performed under at least two charging conditions, the burden on the photoconductor due to excessive charges is reduced, so that charge fatigue and discharge breakdown are reduced, and the photoconductor is prolonged. Can be used. That is, it is possible to minimize the influence on the photoconductor by balancing the reverse charging potential, the surface potential on the inlet side of the main charging device, and the surface potential of the photoconductor on the inlet side and the outlet side of the main charging device. This contributes to the long-term stability of the photoconductor.

[0022]

EXAMPLES The present invention will now be described in more detail with reference to examples.

Example 1 A polyamide resin having ultrafine particles of TiO ₂ (manufactured by Ishihara Sangyo Co., Ltd.) dispersed on an aluminum cylinder having a diameter of 80 mm and a length of 340 mm by about 2 μm to form an undercoat layer (UL). A 0.15 μm charge generation layer (CGL) in which a trisazo pigment is dispersed in a polyester resin, and a stilbene compound as a polycarbonate resin (Panlite C
-1400: Teijin Chemical Co., Ltd.) and a charge-transporting layer (CTL) of about 28 μm dispersed in each layer is laminated to form a functional separation type OP.
A C photoreceptor was produced. This OPC photoconductor is plasma CV
Set it in the D device and use C ₂ H ₄ (100 sc
cm), NF ₃ and H ₂ gas, and RF power (1
3.56 MHz) 120 W, self-bias 5 W, reaction pressure 0.02 Torr, film thickness 2.0 to 2.2 μm, Knoop hardness 500 to 530 kg / mm ² , specific resistance 3 to 6 × 1.
A DLC film of 0 ¹⁴ Ω · cm was formed into a photoconductor sample.

As a device for confirming the effect, a modified Ricoh digital copying machine Imagio 420 was prepared. The contents of the remodeling are as follows: a reverse charge applying device and an exposure device (exposure amount of 17 to 20 μW / cm ² ) using a 660 nm LED as a light source are installed between the cleaning device and the main charging device, and nickel plating of 40 mm width is used as the main charging device. A shield case made of iron plate is prepared, and a charge wire with a double wire structure is provided by stretching a 0.06 mm loop-shaped tungsten wire, and a tungsten wire of 0.06 mm is used as a grid electrode at the entrance side of the photoconductor of 20 mm. At a width of 2 mm, and at the exit side of 20 mm, a tungsten wire of 0.1 mm is stretched at a width of 3.5 mm at a distance of 12 mm from the charge wire so that a voltage can be applied to each grid electrode by an external power source. did.

A high positive voltage was applied to the reverse charge applying device, and the drum current was set so that the surface potential of the photoconductor was approximately +600 volts. Next, in common for both grid electrodes, -3
When a high voltage was applied to the main charging device with 50 V applied, the output of the high voltage power supply was adjusted so that the surface potential of the photoconductor at the position of the developing device was approximately -750 V. At this time, the surface potential after application of the reverse charge at the time of passing 20 mm on the photoreceptor entrance side of the main charging device is approximately -150 to.
It was equivalent to 180 volts.

As an evaluation method, 200,000 sheets were repeatedly run for 8 hours a day with no paper passing with the developing device and the cleaning device removed, and during that period, the surface potential of the photoreceptor was periodically measured by gray scale. The characteristics of the photoconductor were evaluated by measuring, forming a blank sheet, and forming an image on a designated test chart. FIG. 7 shows the transition result of the in-machine surface potential. As is apparent from FIG. 7, the method according to the present invention shows a stable transition of the potential of the charging portion and has no practical problem.
On the other hand, the potential of the image area temporarily drops and then starts to rise, but the rise is small and there is no practical problem at all. In terms of image quality, no abnormal image such as white / black spots was generated even after 200,000 sheets and there was no problem.

Comparative Example 1 The same photoconductor as in Example 1 was used, only the main charging device of the experimental machine was changed to a standard product of Ricoh Copier Imagio 420 machine, and other experimental conditions were the same as those of Example 1. Characteristic evaluation was carried out. Fig. 7 shows the transition result of the in-flight surface potential in this case.
Are also shown. In the case of the method of this comparative example, the potential of the image portion did not cause any particular problem, but the potential of the charging portion decreased by about 85 to 90 volts compared to the start value after 200,000 sheets. This amount of reduction does not cause any problems in practical use, but it is a level at which the problems become apparent when continued. On the other hand, in terms of image quality, after 200,000 sheets, several black spots having a diameter of 0.1 to 0.5 μm were confirmed on a blank copy, and it was found that there was a problem in practical use with further continuation.

Examples 2 to 7 The same experimental machine and photoconductor sample as in Example 1 were used. The surface potential of the photoconductor was set by changing the voltage applied to the reverse charge applying device, and by connecting different external power supplies to the grid electrode of the main charging device and changing the input voltage to the charge wire. Table 1 shows the conditions of the reverse charging position and the potential on the inlet side of the main charging device.

[0029]

[Table 1]

The evaluation of the photoconductors in Examples 2 to 7 was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0031]

[Table 2]

As shown in the above results, according to the method of the present invention, the potential difference between the surface potential of the photoconductor by the reverse charging device and the main charging device is small, and the amount of change in the potential can be changed by setting the balance well. It was relatively small, and the influence on the image quality was suppressed.

Comparative Examples 2 to 4 The same experimental machine and photoreceptor sample as those used in Comparative Example 1 were used, and the evaluation was carried out under the conditions shown in Table 3. The evaluation results are shown in Table 4.

[0034]

[Table 3]

[0035]

[Table 4]

Examples 8 to 13 The specific resistance and hardness of the DLC film, which is the protective layer of the photoconductor, were set under the manufacturing conditions (mainly the reaction pressure was 0.01 to 0.05 Torr,
The bias power was varied between 3 and 15 W). Further, the main charging device is the same as the charging device of the first embodiment, and a power source is connected to each of the grid electrodes to control the surface potential of the photoconductor in accordance with the voltage applied to the charge wire. The effect on image quality was observed by the same confirmation method as in Example 1 by changing the current flowing into the photoconductors on the side of the outlet and the side of the outlet and changing the potential difference. The surface potential of the photoconductor by the reverse charge applying device at this time was +600 to 660 volts. DLC
The physical properties of the film and the conditions of the surface potential difference are shown in Table 5, and the evaluation results are shown in Table 6.

[0037]

[Table 5]

[0038]

[Table 6]

When the specific resistance is less than 10 ¹³ Ω · cm, the image deletion occurs, and when the specific resistance is more than 10 ¹⁵ Ω · cm, the potential of the image area increases and the image quality deteriorates. The hardness of the DLC film is 3
The limit is 50 kg / mm ² , and hardness higher than that is required. Further, it was found that the potential difference between the inlet side and the outlet side of the main charger is small or large, and the electric field to the photoconductor is greatly damaged.

[0040]

According to the present invention, because of the above-mentioned structure,
It is possible to efficiently reduce the residual potential and its accumulation that occur in the photoconductor having the DLC film as the protective layer, and prevent the reduction of the charging potential and the deterioration of the image quality due to the charge fatigue, and the stable electrophotographic characteristics for a long time. It is possible to maintain.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a constitutional example of an organic photoreceptor used in the method of the present invention.

FIG. 2 is a schematic diagram of an apparatus suitable for carrying out the method of the present invention.

FIG. 3 is a diagram showing a main charging device in which a resistor is installed between two charge wires to make a difference in discharge current.

FIG. 4 is a diagram showing a main charging device in which two charge wires are provided with a height difference and a discharge current is made different.

FIG. 5 is a diagram showing a conventional single charge wire type main charging device.

FIG. 6 is a diagram showing a charging state in a reverse charging step and a main charging step.

FIG. 7 is a diagram showing a comparison of changes in the in-machine potential at the time of repeating 200,000 sheets in the method of the present invention and the conventional method.

[Explanation of symbols]

1 Conductive Support 2 Undercoat Layer (UL) 3 Photosensitive Layer 4 Charge Generation Layer (CGL) 5 Charge Transport Layer (CTL) 6 Protective Layer 10 Photoconductor 11 Main Charging Device 11a Shield Case 11b Charge Wire 11c Grid Electrode 12 Image Exposure device 13 Developing device 14 Transfer / separation device 15 Static eliminator 16 Cleaning device 17 Reverse charge applying device 18 Exposure device 19 Copy paper

Claims (3)

[Claims] 1. A plain paper obtained by repeating steps of main charging, image exposure, development, transfer, separation, charge removal and cleaning of an organic photoreceptor having a surface protective layer of carbon or a thin film composed mainly of carbon. In the electrophotographic method for obtaining a large number of copies, during the cleaning step and the main charging step, a charge having a polarity opposite to that of the main charging is applied to the photoreceptor at the same time, or immediately before or immediately after the exposure, a reverse charge application is performed. An electrophotographic method characterized in that an exposure step is provided and charging is performed under at least two different charging conditions in the main charging step. 2. The charging potential of the photoconductor is set to +200 to +700 volts by the reverse charge application / exposure step, and then the charging potential of the photoconductor is set to +300 to −500 volts under the first charging condition in the main charging step. 2. The electrophotographic method according to claim 1, wherein the charging potential of the photoconductor is set to a predetermined potential for latent image formation under the second charging condition. 3. The photosensitive member has a specific resistance of 10 ¹³ to 1 1.
Knoop hardness of 350 kg / m on the order of 0 ¹⁵ Ω · cm
An organic photoconductor having a surface protective layer made of m ² or more carbon or a thin film mainly composed of carbon is used, and the photoconductor surface is subjected to the first charging condition and the second charging condition in the main charging step. The difference in the charging potential of 400 to 120
The electrophotographic method according to claim 1, wherein the electrophotographic method is 0 volt.