JP2003173070A - Image forming device - Google Patents

Abstract

(57) [Problem] It has been found that a method of charging twice is effective for uniform charging and high durability of an amorphous silicon photoconductor. In addition, magnetic brush injection charging is effective in terms of ozone-less and charging ability. However, the magnetic brush charger has a problem in durability such as drum scraping, and a system with two magnetic brushes is difficult. Therefore, a charging device configuration that enables reduction of drum scraping and maintenance of charging performance is proposed. [MEANS FOR SOLVING PROBLEMS] A plurality of charges are applied to the amorphous silicon photoconductor by roller charging and magnetic brush injection charging. At this time, in order to prevent contamination of the roller charger, the roller surface is brought into contact with magnetic particles, and the contamination is prevented by rubbing. (Subclaim) The gap between the charger sleeve and the roller charger is smaller than the gap between the charger sleeve and the drum. 3. The roller charger is driven by a drum, and the magnetic brush charger is a drum counter with a peripheral speed ratio of 100% or more. 4. The resistance value of the magnetic particles of the magnetic brush charger is 10

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for developing an electrostatic latent image formed on an image carrier corresponding to an image to be recorded or image data with a developer and recording it on a sheet or the like.

[0002]

2. Description of the Related Art Conventionally, many image forming apparatuses using an electrophotographic system or an electrostatic recording system have been devised, but a schematic configuration and operation will be briefly described with reference to FIG.

In the image forming apparatus shown in FIG. 4, when a copy start signal is input, the photosensitive drum 1 is charged by the corona charger 3 so as to have a predetermined potential. on the other hand,
An original irradiation lamp, a short focus lens array, and a CCD sensor are integrated into a unit 9 for the original G placed on the original table 10 to scan the original while illuminating the original, thereby reflecting the illumination scanning light on the original surface. Light is imaged by the short focus lens array and is incident on the CCD sensor.
The CCD sensor is composed of a light receiving section, a transfer section, and an output section. An optical signal is converted into a charge signal in the CCD light receiving unit, and sequentially transferred to the output unit in synchronization with a clock pulse in the transfer unit, and the charge signal is converted into a voltage signal in the output unit, amplified, reduced in impedance, and output. The obtained analog signal is subjected to known image processing to be converted into a digital signal and sent to the printer section. In the printer unit, an electrostatic latent image corresponding to the original image is formed on the surface of the photosensitive drum 1 by the LED exposure means 2 which emits ON / OFF light upon receiving the image signal.

Next, this electrostatic latent image is developed by a developing device 4 containing toner particles to obtain a toner image on the photosensitive drum 1.

The toner image thus formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material by the transfer device 7. Thereafter, the transfer material is electrostatically separated and conveyed to the fixing device 6, where it is thermally fixed and an image is output.

On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is subjected to the exposure by the pre-exposure means 8 for removing the adhering contaminants such as the transfer residual toner by the cleaner 5 and the optical memory for the image exposure if necessary. Repeatedly used for image formation.

The photoconductor used in the electrophotographic image forming apparatus for forming an image as described above is an organic photoconductor or an amorphous silicon photoconductor (hereinafter referred to as "a-S").
It is referred to as an "i-based photoconductor". ) Etc. are often used,
The a-Si-based photoconductor has a high surface hardness, shows high sensitivity to semiconductor lasers, etc., and hardly deteriorates due to repeated use. Therefore, it can be used in electronic devices such as high-speed copying machines and laser beam printers (LBP). It is used as a photoconductor for photography.

As the method of charging the a-Si type photoreceptor, a corona charging method using corona discharge, a roller charging method of directly discharging by using a conductive roller, and a sufficient contact area with magnetic particles are used. In addition, there is an injection charging method in which charging is performed by directly injecting a charge into the surface of the photoconductor.

Among these, the corona charging method and the roller charging method use electric discharge, so that the discharge product is apt to adhere to the surface, and the a-Si type photoconductor has a very high surface height and is hardly worn, so that the discharge product is generated. Are likely to remain on the surface, and an image deletion phenomenon is likely to occur due to movement of charges on the surface of the photoconductor on which an electrostatic latent image is formed due to adsorption of moisture in a high humidity environment.

On the other hand, the injection charging method is a charging method in which electric charges are directly injected from a portion in contact with the surface of the photoconductor without positively using discharge, and thus the phenomenon of image deletion occurs. Hard to do.

[0011]

In the above-mentioned a-Si type photosensitive member, the method for producing the a-Si type photosensitive member makes the gas into plasma by high frequency or microwave to solidify it, and deposits it on the aluminum cylinder to form a film. If it is not uniform, film thickness unevenness and composition unevenness occur in the circumferential direction and the longitudinal direction. This allows
Conventionally, potential unevenness of about several tens of volts has occurred in the developing section. This is due to the phenomenon that the difference in electrostatic capacity is caused by the unevenness of the film thickness and the difference in charging ability is caused, and also the potential attenuation in the dark state between the charging and the developing by the pre-exposure used to erase the optical memory in the front cycle ( Hereinafter referred to as dark decay)
However, the difference occurs due to the difference in film thickness and composition, and the potential unevenness in the developing portion is further increased.

When the a-Si type photoconductor is used, the above-mentioned dark decay is very large in the dark state as compared with the organic photoconductor, and further the potential decay due to the optical memory for image exposure is increased.
Pre-exposure means before charging is required to erase the optical memory on the front side. Therefore, the dark decay between charging and development becomes very large, and the potential decay of about 100 to 200 V occurs. At this time, due to the above-mentioned film thickness unevenness and composition unevenness, several 10
V potential unevenness had occurred.

When such potential unevenness occurs, the a-Si type photoconductor having a large electrostatic capacitance has a smaller contrast than the organic photoconductor and is more affected, and the density nonuniformity becomes remarkable.

To solve such a problem, for example, a method of charging a plurality of times is effective. The increase in dark decay due to the optical memory described above is
Since the optical memory can be remarkably reduced by the second charging, the dark decay can be reduced after the second charging. Along with this, the potential ghost and the potential unevenness have been significantly improved.

Here, for example, if charging is performed by a plurality of injection chargers, the potential ghost and the potential unevenness are greatly improved, but many contact points for charge injection are required.
For example, in the case of a magnetic brush charger, the magnetic particle carrier is moved in the counter direction with respect to the photoconductor to cause rubbing with the magnetic particles, so that the surface of the photoconductor is easily worn. Since the surface of the amorphous silicon photoconductor is extremely high in hardness, some durability can be obtained even if a plurality of magnetic brush chargers are used, but the production cost of the photoconductor is high due to the manufacturing method, and therefore it is more durable. desired. On the other hand, if a multiple charging system using a corona charger or roller charger using discharge is performed,
Although it has high durability against abrasion, image deletion easily occurs due to the accumulation of discharge products as described above.

As a method which has a plurality of charging means for reducing the potential ghost and the potential unevenness when the amorphous silicon photoconductor is used, and which can improve the abrasion resistance and prevent the image deletion at the same time, the injection charging method described above is used. It is effective to combine a method with weak rubbing such as a corona charging method or a roller charging method.

As described above, when the injection charging method and the corona charging method or the roller charging method are combined, the discharge products generated by the corona charging or the roller charging can be removed by the rubbing of the injection charging device, and the abrasion can be performed. It is also possible to set the amount to a level close to that when there is only one injection charger.

However, when the wear amount of the amorphous silicon photoconductor is reduced and the photoconductor life is extended, problems such as wire contamination of the corona charger and contamination of the roller surface of the roller charger become a problem. Generally, amorphous silicon photoconductor has 10
In contrast to the life of about 0,000 sheets, the life due to the wire replacement interval of the corona charger and the contamination of the roller charger is about 20 to 40,000 sheets. On the other hand, the injection charger using magnetic particles has a remarkably large surface area due to the use of magnetic particles, and therefore is extremely resistant to contamination and can realize a life of about 100,000 to 300,000 sheets. In order to further extend the life of the magnetic brush charger, the amount of magnetic particles carried must be increased and slowly circulated. By replacing the tens of thousands of sheets with new ones of several grams, the life of the photoconductor can be almost reached. It will be possible.

[0019]

According to the present invention, when a plurality of charging means are provided to reduce potential ghost and potential unevenness when an amorphous silicon photoconductor is used, improvement in abrasion resistance and image deletion are achieved. As a method capable of achieving both preventions, it is an object to prevent contamination of the surface of the roller charger and extend the life of the charger when a magnetic brush charger and a roller charger are used.

Specifically, by arranging the magnetic brush charger and the roller charger in close proximity to each other so that the magnetic particles rub against the surface of the roller charger, the adhered matter on the surface of the roller charger is caused by the magnetic particles. By scraping off, contamination of the roller charger can be prevented.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 5 is a schematic sectional view showing the structure of a positively charging a-Si photosensitive member used in the present embodiment.

The a-Si type photosensitive member shown in FIG. 5 has a conductive support 201 made of Al or the like, and a photosensitive layer 205 (a charge injection blocking layer 202 and an optical layer 205) sequentially deposited on the surface of the conductive support 201. It is composed of a photoconductive layer 203) having conductivity and a surface layer 204. Here, the charge injection blocking layer 202 is for blocking the injection of charges from the conductive support 201 to the photoconductive layer 203, and is provided as necessary. The photoconductive layer 203 is made of an amorphous material containing at least silicon atoms and exhibits photoconductivity. Further, the surface layer 204 contains silicon atoms and carbon atoms (and, if necessary, hydrogen atoms and / or halogen atoms), and has the ability to hold a latent image in an electrophotographic apparatus.

The a-Si type photoconductor is manufactured by a method in which a gas is turned into plasma by high frequency or microwave to be solidified and deposited on an aluminum cylinder to form a film. It causes unevenness. As a result, a potential unevenness of about several tens of volts has conventionally been generated in the developing section. This is because the difference in electrostatic capacity due to unevenness in film thickness causes a difference in charging ability, and the potential attenuation between charging and development due to pre-exposure used to erase the optical memory in the front cycle is caused by the film thickness and It is caused by a difference depending on the composition and further increasing the potential unevenness in the developing portion.

The above optical memory will be described below.
When the Si-based photoconductor is charged and imagewise exposed, photocarriers are generated and the potential is attenuated. However, at this time, the a-Si-based photoreceptor has many tangling bonds (unbonded hands), which serve as a localized level to trap a part of the photocarriers and reduce its traveling property. Alternatively, it reduces the recombination probability of photogenerated carriers. Therefore, in the image forming process, a part of the photo carriers generated by exposure is released from the localized level at the same time when an electric field is applied to the a-Si-based photoconductor at the time of charging in the next step, and the exposed and unexposed parts are exposed. Then, a difference occurs in the surface potential of the a-Si photosensitive member, and this finally becomes an optical memory.

Therefore, it is common to erase the optical memory by performing uniform exposure in the pre-exposure step so that the number of optical carriers latent in the a-Si photosensitive member becomes excessive and uniform over the entire surface. . At this time, the pre-exposure source 8
From the spectral sensitivity peak of the a-Si photosensitive member 8 (about 680 to 70).
It is possible to erase the optical memory (ghost) more effectively by bringing the optical memory (ghost) closer to 0 nm).

However, if the a-Si-based photoconductor has uneven film thickness as described above, the electric field applied between the photoconductive layers is different, so that there is a difference in the release of photocarriers from the localized level. The smaller the film thickness is, the larger the potential decay is, and even if the charging section can uniformly charge, the potential unevenness occurs in the developing section. Further, with respect to the charging ability, the smaller the film thickness is, the larger the electrostatic capacity is, which is disadvantageous, and when the charging ability is lowered, the charging unevenness in the developing portion becomes more remarkable. This potential unevenness remains even after image exposure, and appears as a remarkable density unevenness in a low density region which is particularly easily recognized by the eyes when a developing process is performed.

Further, in the a-Si type photoreceptor, even when the film thickness is constant, composition unevenness is liable to occur in the circumferential direction and the longitudinal direction due to the manufacturing method, and the generation amount of photocarriers varies within the plane. In many cases, potential unevenness occurred due to the dark attenuation not being constant in the surface direction.

There is a method of charging a plurality of times as a method of reducing such dark attenuation and potential unevenness caused by the photocarrier. By significantly reducing the photocarriers in the first charging, it is possible to significantly reduce the dark decay after the second charging, so that the potential unevenness and the potential ghost can be significantly improved.

Here, as a charging member for the a-Si type photoreceptor described above, a device using corona charging has been put into practical use. However, a-Si has a relative dielectric constant of 11 to 12
Since the size is larger than that of the organic photoconductor, the electrostatic capacity is increased, and accordingly, the chargeability is lowered, and the flow of an image due to the flow of a latent image due to discharge is likely to occur.

On the other hand, a contact charging member using a conductive roller, a fur brush roller, a magnetic roller carrying magnetic particles, etc. as a charging member is used under the condition of keeping a sufficient contact state with a photoreceptor. When the a-Si based photoreceptor is charged, the surface of the a-Si based photoreceptor is 10 ⁹ to 10 10.
By being formed of a layer made of a material of ¹⁴ Ω · cm, it is possible to obtain a charging potential on the surface of the image carrier that is almost the same as the DC component of the bias applied to the contact charging member. Such a charging method is called injection charging because charges are directly injected into the photoconductor without using discharge and charging is performed. The use of this injection charging has attracted attention because it enables complete ozone-less and low power consumption type charging because it does not utilize the discharge phenomenon that occurs when the image carrier is charged using a corona charger. In addition, it is possible to prevent deterioration of charging ability and image deletion, and it is easy to control the potential because the charging is performed in the vicinity of the applied voltage.

However, in order to carry out the injection charging, a sufficient contact state with the photoconductor is required, so that the charging device is usually moved with a peripheral speed difference with respect to the photoconductor, so that a rubbing force is generated. The amount of abrasion of the photoconductor becomes larger than that of a corona charger or a roller charger. Since the surface layer of the a-Si photosensitive member is extremely hard, sufficient durability can be obtained even by using the injection charging method, but the manufacturing cost is high in the current manufacturing method, and therefore higher durability is required.

On the other hand, in the roller charging system in which the conductive roller is driven by the photosensitive member to rotate at a constant speed and the voltage is applied to charge the photosensitive member, the amount of wear of the photosensitive member is smaller than that of the injection charging system, and ozone is generated. The amount is much smaller than that of the corona charger, but since the charging method uses direct discharge, phenomena such as image deletion in high humidity due to the adhesion of discharge products to the surface of the photoconductor are likely to occur.

Utilizing the characteristics of each charging method as described above,
In this embodiment, as shown in FIG. 2, the roller charger 31 is used as the first charger and the magnetic brush type injection charger 30 is used as the second charger.

By performing the charging twice in this way, the dark decay can be reduced as described above, and the potential unevenness and the potential ghost can be improved. Further, the discharge product generated by the roller charging is scraped by the rubbing by the magnetic brush charger, so that it is possible to prevent image deletion, and the charging is performed by the magnetic brush type injection charger after the roller charging. As a result, it became possible to perform uniform charging. Also regarding wear of a-Si type photoconductors
By using the roller charger as the charger, the wear could be reduced and the durability could be maintained at high performance.

Reference numeral 30 in FIG. 2 denotes a magnetic brush type injection charger used in this embodiment. The magnetic brush type injection charger magnetically restrains conductive magnetic particles directly on the magnet or on the sleeve containing the magnet and stops or rotates it to bring it into contact with the image carrier, and apply a voltage to it. Charging is started by applying the voltage. The magnetic brush charger 30 used in the present embodiment is provided with a fixed magnet 302 inside, and a magnetic particle 304 for charging, which is regulated by the magnetic particle regulating means 301, is placed on a rotatable non-magnetic charging sleeve 303. The magnetic particles 304 for charging are formed in a brush shape by the rotation of the non-magnetic sleeve 303. The charging sleeve 34 rotates in the counter direction with respect to the photosensitive drum 1, and the rotation speed of the photosensitive drum 1 is 200 mm.
/ Sec, the magnetic brush charger 30 is 300 mm / s
It is rotating in ec. By applying a charging voltage to the charging sleeve 303, charges are given from the charging magnetic particles 304 onto the photosensitive drum 1 and charged to a value close to a potential corresponding to the charging voltage.

In the magnetic brush charger 30, the contact nip width of the charging magnetic particles 304 formed on the photosensitive drum 1 is adjusted to be 6 mm. The magnetic particles for charging have an average particle size of 10 to 100 μm.
m, saturation magnetization 20 to 250 emu / cm ³ , resistance 1
It is preferably from 0 ² to 10 ¹⁰ Ω · cm, and preferably from 10 ⁶ Ω · cm or more in view of the presence of insulation defects such as pinholes on the photosensitive drum. Since it is better to use a small as possible resistance to improve the charging performance, in the present embodiment, the average particle diameter of 25 [mu] m, saturation magnetization 200 emu / cm ^3, charging magnetic resistors 5 × 10 ⁶ Ω · cm Particles were used. In addition, the charging magnetic particles used in the present embodiment are obtained by subjecting the surface of ferrite to oxidation and reduction treatment to adjust the resistance.

[0037] Here, the resistance value of the charging magnetic particles, after which the bottom area is placed 2g of magnetic particles for charging to metal cell of 228 mm ^2, weighted by 6.6 kg / cm ^2, applying a voltage of 100V Next, reference numeral 31 in FIG. 2 denotes a roller charger used in this embodiment.

Charging roller 31 used in this embodiment
Is a conductive core metal 314, an elastic layer 313, and a surface layer 312.
Is equipped with. The core metal 314 is made of iron, aluminum, stainless steel.
And so on. The elastic layer 313 is made of urethane or silicone.
Recon rubber, EPDM (3 of ethylene propylene diene
Solid copolymer or foamed solid elastic body such as
And carbon and metal oxides such as TiO2 and ZnO
In addition, volume resistivity 10 ^Four-10^ThirteenIn Ωcm
is there. The surface layer 312 is a resin such as resin (trade name).
Iron-based resin, polyethylene, polyester, fiber
Synthetic resin skin made conductive with fluorine resin, polypropylene, etc.
It is a film. The resistance value is larger than the resistance of the inner elastic body.
Is desirable. As a result, the surface of the electrophotographic photoreceptor is
Even if there are pinholes on the surface, the current should not concentrate and flow in.
Yes. In this embodiment, carbon is dispersed in urethane.
Nylon resin is made conductive to the elastic layer whose resistance is adjusted.
A charging roller provided with a surface layer of a synthetic resin film was used.

In this embodiment, as described above, the magnetic brush charger 30 and the roller charger 31 are as shown in FIG. 2, and the charging magnetic particles 304 of the magnetic brush charger 30 are the surface layers of the roller charger 31. They are continuously arranged so as to come into contact with 312.

When performing the charging step, for example, a DC voltage of 900 V is applied to the conductive core metal 314 of the roller charger 31 and a voltage of 500 V is applied to the charging sleeve 303 of the magnetic brush charger 30. The surface potential at the developing position at this time was 450 V (in a state where the pre-exposure lamp 8 having a wavelength of 660 nm was irradiated).

As a comparative example, 900 V is applied only to the conductive core metal 314 of the roller charger 31, and the magnetic brush charger 30 is used.
The surface potential at the developing position is 300V when the charging sleeve 303 of No. 3 is floated, and the conductive core metal 314 of the roller charger 31 is floated and 500V is applied to the charging sleeve 303 of the magnetic brush charger 30. The surface potential at the developing position was 300 V (in the state where the pre-exposure lamp 8 having a wavelength of 660 nm was irradiated).

As described above, by performing the charging a plurality of times, the dark decay is reduced and the charging potential at the developing position is increased, and in addition, the potential unevenness and ghost of the photosensitive drum are also improved, and the charging potential is improved. Uniformity was also improved.

The above-mentioned effect is naturally seen even when the roller charger and the magnetic brush charger are not in contact with each other, and is due to charging a plurality of times. The effect of the contact between the roller charger and the magnetic brush charger of the present invention is to prevent contamination of the roller charger.

When the cleaning means is provided as in the present embodiment, most of the untransferred toner is removed by the cleaning means, but some of the toner and external additives externally added to the toner may slip off. is there. If these adhere to the roller charger and the contamination progresses, the charging performance is deteriorated. Although the progress of this contamination is not a problem in many cases when the life of thousands to tens of thousands of sheets is sufficient, a-Si
When the system type photoconductor is used, the life of the photoconductor is one million or more. Therefore, it is desired that the life of the charger is also hundreds of thousands or more. Therefore, it is required to prevent the adherence of contaminants to the roller surface.

To prevent contamination on the roller surface, for example, a scraper or the like may be contacted and scraped, but in consideration of durability of several hundred thousand sheets or more, a space for accommodating scraped contaminants, a screw for conveying, etc. are required It becomes a cause of the enlargement of the device.

Therefore, in the present invention, by disposing the roller surface of the roller charger so as to contact the magnetic particles of the magnetic brush charger, it is possible to prevent contamination of the roller surface without any special contaminant removing means. is doing.

Specifically, the distance between the charging sleeve of the magnetic brush charger and the photosensitive member is set to 500 μm at the closest portion,
The distance between the charging sleeve and charging roller is 400μ at the closest point.
It is set to m. At this time, the gap between the charging sleeve and the charging roller is set to be narrower than the gap between the charging sleeve and the photoconductor, so that the surface of the charging roller and the magnetic particles can be in contact with each other. However, if the charging sleeve and the charging roller are too close to each other or come into contact with each other, a leak phenomenon or a defective conveyance of magnetic particles may occur. It is desirable to provide an interval of 200 μm or more.

As described above, the rotation speed of the charging sleeve is 150 in the counter direction with respect to the rotation direction of the photosensitive drum.
% (Photosensitive drum 200 mm / sec, charging sleeve 30
The peripheral speed is 0 mm / sec), and the charging roller is driven to rotate with respect to the photosensitive drum, so that the charging roller and the magnetic particles are rubbed with a speed difference of 100 mm / sec. By providing the speed difference in this way, the removal of contamination is promoted.

In the case of roller charging, the applied voltage also has a discharge threshold because it is a charging method accompanying discharge, and when charging is performed by a DC voltage, the same potential applied to the roller charger is charged. The voltage is set higher than the DC component of the voltage applied to the magnetic brush charger. Therefore, in the case of an image forming apparatus of an image exposure system in which the photosensitive drum and the toner have the same charge polarity, the electric field formed is also promoted so that the toner particles are transferred from the roller charger to the magnetic brush charger side. Become. On the other hand, in the case of background exposure in which the charge polarities of the photosensitive drum and the toner are opposite, it is necessary to set the applied bias of the roller charger lower than the applied bias of the magnetic brush charger. By doing so, it becomes possible to transfer the toner particles on the roller to the magnetic brush charger even when the charge polarity of the toner is opposite.

The present invention is applicable to both image exposure and background exposure as described above.
In the case of the image charging, charging higher than the second charging is more effective in terms of charging ability and reduction of dark attenuation. Therefore, image exposure in which the charging polarity of the photoconductor and the charging polarity of the toner are the same is preferable. In the case of, it is a particularly effective method.

As described above, in the image forming apparatus using the amorphous silicon photoconductor as in the present embodiment, the magnetic brush charger and the roller charger are arranged in close proximity to each other and the magnetic particles slide on the surface of the roller charger. By charging with a rubbing structure, it is possible to scrape off the deposits on the surface of the roller charger with magnetic particles and prevent contamination of the roller charger, which makes it possible to reduce high charging ability and dark decay for a long period of time. It is possible to obtain a uniform and good image.

(Embodiment 2) In Embodiment 1, the roller surface of the roller charger is in contact with the magnetic particles of the magnetic brush charger as shown in FIG. As in No. 3, a belt type charger was used.

The belt-type charger used in this embodiment includes a conductive core metal 324, an elastic layer 323, and a surface belt layer 322. In the present embodiment, a belt layer 322 is formed by molding a synthetic resin film in which a nylon resin is made conductive into a belt shape on an elastic layer whose resistance is adjusted by dispersing carbon in urethane similar to that of the first embodiment. The provided one was used as a belt charger.

The installed structure is such that the electroconductive belt is laid between an elastic roller having an elastic layer on a conductive cored bar and a conductive roller 321 arranged close to the charging sleeve of the magnetic brush charger. is doing.

At this time, the conductive roller 321 and the charging sleeve 303 are arranged so that the surface of the belt comes into contact with the magnetic particles.
Is controlling the interval. Specifically, as in the first embodiment, the distance between the charging sleeve 303 of the magnetic brush charger and the photoconductor is set to 500 μm at the closest portion, and the charging sleeve 303 is set.
The distance between the surface of the belt 322 and the surface of the belt 322 mounted on the conductive roller 321 is set to 400 μm at the closest portion. With this setting, the area where the belt 322 and the magnetic particles 304 come into contact with each other as shown in FIG. 3 can be made wider than in the case of the roller of the first embodiment. Therefore, the performance of removing contaminants is improved.

Further, since the bias applied to the core metal 324 of the belt charger and the bias applied to the conductive roller 321 do not necessarily have to be the same, contaminants due to the electric field between the conductive roller 321 and the charging sleeve 303 can be removed. As for transfer, contaminants on the belt surface can be removed while the charging performance is optimized. For example, in the case of an image forming apparatus of a background exposure system in which the charging polarity of the photosensitive drum and the charging polarity of the toner are different, in the first embodiment, the bias applied to the first roller charger is set to the second magnetic brush charger. It was necessary to set it lower than the applied bias,
It is desirable to set the first charging bias high in order to improve charging ability and dark decay. On the other hand, the second embodiment
In such a case, a voltage higher than that of the charging sleeve 303 is applied to the conductive core metal 324, and the conductive roller 32
By applying a voltage lower than that of the charging sleeve 303 to No. 1, it is possible to sufficiently improve the charging ability and the dark decay and also to remove the contaminants on the surface of the charging belt 322.

In the embodiment, the bias applied to the magnetic brush charger and the roller charger is described only for the case of the DC component, but the present invention is not limited to this, and for example, the case where an alternating voltage is superposed is sufficient. The effect is obtained.

Regarding the magnetic brush charger, in the embodiment, the magnetic particles 304 carried on the charging sleeve 303 by the magnetic force of the fixed magnet 302 are charged to the charging sleeve 30.
However, the present invention is not limited to this, and, for example, a method of directly carrying magnetic particles on a magnet roller whose surface is treated to be conductive and carrying the magnetic particles by rotation of the magnet roller. You can take it.

Regarding the a-Si type photoconductor, a positively charged photoconductor was taken as an example in the embodiment, but it has been confirmed that the same effect can be obtained even when the negatively charged photoconductor is used. .

[0060]

As described above, the present invention has a plurality of charging means for reducing potential ghost and potential unevenness when an amorphous silicon photoconductor is used. At this time, as a method capable of achieving both improvement of abrasion resistance and prevention of image deletion, there is a case where a magnetic brush charger, a roller charger or a belt charger is used. It is an object of the present invention to prevent surface contamination of a roller charger or a belt charger and extend the life of the charger.

Specifically, by arranging the magnetic brush charger and the roller charger or the belt charger in close proximity to each other so that the magnetic particles rub the surface of the roller charger or the belt, It is possible to prevent the roller charger from being contaminated by scraping off the deposits on the surface with the magnetic particles.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus used in an embodiment of the present invention.

FIG. 2 is a schematic diagram of a charging device used in the first embodiment of the present invention.

FIG. 3 is a schematic diagram of a charging device used in a second embodiment of the present invention.

FIG. 4 is a schematic diagram of an image forming apparatus used in a conventional example.

FIG. 5 is a diagram showing an example of a layer structure of an a-Si based photosensitive member used in an embodiment of the present invention.

[Explanation of symbols]

1 photosensitive drum 2 LED exposure means 3 Corona charger 4 Developing device 5 cleaner 6 fixing device 7 Transfer device 8 Pre-exposure lamp 9 Scanner unit 10 Platen 30 Magnetic brush charger 31 Roller charger 32 Belt charger

Claims (6)

[Claims] 1. A latent image is formed by a developer carrying member carrying a developer by charging a photosensitive member containing at least amorphous silicon with a charging member, forming an electrostatic latent image on the photosensitive member by image exposing means. In an image forming apparatus that includes a developing unit that develops a toner image to form a toner image, and transfers the toner image to a transfer material to form an image, the charging member includes a plurality of contact charging members, and the first charging member is a roller. A contact charger having a belt shape or a belt shape, the second charging member is a magnetic brush charger using magnetic particles, and
The contact charger of 1 is in contact with the magnetic particles of the second magnetic brush charger. 2. The distance between the surface of the magnetic particle carrier and the surface of the first contact charging member is more than the distance between the surface of the magnetic particle carrier of the magnetic brush charger that is the second charging member and the amorphous silicon photoconductor. The image forming apparatus according to claim 1, wherein the interval is narrower. 3. The image forming apparatus according to claim 1, wherein the volume resistance of the magnetic particles used in the magnetic brush charger satisfies a condition of 10 ⁶ to 10 ¹⁰ Ω · cm ³ . 4. The moving direction of the first charging member follows the moving direction of the amorphous silicon photosensitive member, and the moving of the magnetic particle carrier of the magnetic brush charger, which is the second charging member. 2. The image according to claim 1, wherein the directions are the moving direction of the amorphous silicon photoconductor and the counter direction, and the moving speed of the magnetic particle carrier has a speed difference with respect to the moving speed of the amorphous silicon photoconductor. Forming equipment. 5. The absolute value of the DC component of the voltage applied to the first charging member is higher than the absolute value of the DC component of the voltage applied to the second charging member. The image forming apparatus according to item 1. 6. The triboelectrification polarity of the toner particles used in the image forming apparatus according to claim 5 is the same as the electrification polarity of the amorphous silicon photoconductor.