JPH0850392A - Charging device - Google Patents

Abstract

PURPOSE:To prevent the decrease of carrier caused by the carrier comprising a magnetic brush, sticking on the photoreceptor and to ensure the stable electrifying property over a long period. CONSTITUTION:The magnetic brush 2 is composed of the freely rotatable charging sleeve 21, the magnet 22 solidly fixed therein and the carrier (magnetic particle) 23 bound on the surface of the charging sleeve 21 by the magnet 22. The contact nip N is formed by holding the carrier 23 in contact with the photoreceptor 1. The conductive sponge part (elastic body) 24 is disposed in the end part of the magnetic brush 2, namely the part corresponding to the end part of the magnet 22 in the charging sleeve 21. By the sponge part 24, the potential of the photoreceptor 1 surface is equalized to the potential of the magnetic brush 2, and the carrier 23 is prevented from being pushed outside in the length wise direction of the contact nip N. The carrier 23 is prevented form sticking to the photoreceptor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device mounted on an electrophotographic device such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been the mainstream as a charging device mounted on an electrophotographic apparatus such as a copying machine.
In recent years, instead of this, a contact charging device has been put into practical use for the purpose of reducing ozone and reducing power consumption. The contact charging device includes roller charging, blade charging, brush charging, etc. depending on the charging member, but among them, the roller charging type using a conductive roller is excellent in stability of charging.

In roller charging, a conductive elastic roller (hereinafter referred to as "charging roller") is pressed against an object to be charged (for example, an electrophotographic photosensitive member; hereinafter simply referred to as "photosensitive member"), and this is used. A voltage is applied to the photoconductor to charge the photoconductor.

Specifically, since the charging is performed by discharging from the charging roller to the photosensitive member, the charging is started by applying a voltage higher than a certain threshold voltage. As an example, when the charging roller is pressed against the 25 μm-thick OPC photosensitive member, the surface potential of the photosensitive member starts to rise when a voltage of about 640 V or higher is applied, and thereafter, the voltage is applied. The surface potential of the photoconductor increases linearly with a slope of 1 with respect to the voltage.
Hereinafter, this threshold charging is defined as the charging start voltage V _th . That is, in order to obtain the photoreceptor surface potential V _d required for electrophotography, the charging roller needs a DC voltage higher than the required voltage of (V _d + V _th ). In this way D
Charging is a method of charging by applying only the C voltage to the contact charging member.

However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental changes, etc. Further, _Vth fluctuates when the film thickness changes due to abrasion of the photoconductor, so that the potential of the photoconductor is desired. It was difficult to make the value of.

Therefore, as disclosed in Japanese Patent Laid-Open No. 63-149669, in order to further uniformize the charging, the charging start voltage V is changed to the DC voltage corresponding to the desired V _d.
An AC charging method is used in which a superimposed voltage in which an AC component having a peak-to-peak voltage that is at least twice _th is superimposed is applied to the contact charging member. This is for the purpose of leveling the potential by AC, and the potential of the photoconductor converges on V _d which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment. .

However, even in such a contact charging device, the essential charging mechanism uses the discharge phenomenon from the charging roller (charging member) to the photosensitive member (charged member), and therefore, it has been described above. As described above, the voltage applied to the charging member needs to have a value equal to or higher than the surface potential of the photoconductor, and a slight amount of ozone is generated. In addition, when AC charging is performed for uniform charging, further ozone is generated, vibration of the charging member and the photoconductor due to the electric field of AC voltage, noise (hereinafter referred to as “AC charging sound”), and Deterioration of the surface of the photoconductor due to discharge has become remarkable, which has been a new problem.

Therefore, as a new charging method, a charging method by directly injecting an electric charge into a photosensitive member is disclosed in, for example, Japanese Patent Laid-Open No. 06-
It is disclosed in Japanese Patent Publication No. 003921. This charging method is a method in which a voltage is applied to a contact conductive member such as a roller, a brush, or a magnetic brush to inject charges into the conductive particles of the charge injection layer on the surface of the photoconductor to perform contact injection charging. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is only the desired surface potential of the photoconductor and no ozone is generated. Furthermore, since no AC voltage is applied,
It does not generate charging noise and is an ozone-less and low-power charging method superior to the roller charging method.

[0009]

However, when the magnetic brush is used as the contact charging member in the above-mentioned conventional example, the following problems occur.

As shown in FIG. 8, the magnetic brush 2 includes a rotatable charging sleeve 21, a magnet roller 22 fixedly disposed inside the charging sleeve 21, and the magnet roller 22.
And magnetic particles (hereinafter appropriately referred to as “carrier”) 23 carried on the surface of the charging sleeve 21. The magnetic brush 2 is arranged so that its carrier 23 contacts the surface of the photoconductor 1, and a contact nip N for charging is formed between the two. However, according to this structure, among the carriers 23, the carrier 23 near the end of the magnetic brush 2 in the longitudinal direction, that is, the carrier 23 near the end of the contact nip N, is located outside the contact nip N in the longitudinal direction (region C in the figure). ) Is pushed in the direction of arrow A.
Since the carrier 23 of the magnetic brush 2 is not in constant contact with the C region, the surface of the photoconductor 1 is not uniformly charged, and the surface potential of the photoconductor 1 is considerably lower than the charging potential. However, since a voltage corresponding to the charging potential (for example, −700 V) is applied to the magnetic brush 2,
A potential difference is generated between the magnetic brush 2 and the surface of the photoconductor 1,
The carrier 23 moves from the magnetic brush 2 to the photoconductor 1 by the force (in the direction of arrow B) generated by the charge injected from the charging sleeve 21 into the carrier 23. This phenomenon is a phenomenon peculiar to performing injection charging by the magnetic brush constituted by the medium-resistance carrier 23, and does not occur when a high-resistance magnetic brush or a simple magnetic brush is used for inspection.

In the case of a magnetic brush in two-component development, the development contrast (difference between development potential and photoreceptor surface potential) is usually smaller than the charging contrast (difference between charging potential and photoreceptor surface potential). The carrier adhesion to the photoconductor is not so remarkable as when the magnetic brush is used for charging. Further, when a magnetic brush is used for development, toner is present in the magnetic brush and the toner adheres to the photoconductor before the carrier. This is because the toner is lighter than the carrier and has a higher resistance, so that the held charge is also higher. Therefore, the toner easily adheres to the photoconductor by the electric force.
Therefore, the carrier rarely adheres to the photoconductor.

In the charging by the magnetic brush 2 as shown in FIG. 8, when the carrier 23 adheres to the photoconductor 1, the carrier 23 of the magnetic brush 2 which is a charging member gradually decreases, and gradually the charging failure occurs. As a result, an image defect is caused, so that there is a drawback that it cannot be used for a long period of time.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a charging device which prevents an image defect due to magnetic particles (carriers) of a magnetic brush adhering to a photoconductor.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, in which a contact charging member to which a voltage is applied is brought into contact with a photoreceptor having a charge injection layer on its surface to charge the photoreceptor. In the charging device, the contact charging member is composed of a magnetic brush having a charging base to which a charging voltage is applied, and magnetic particles restrained by a magnetic force on the charging base. It is characterized in that magnetic particles are brought into contact with the photoconductor to form a contact nip, and a conductive elastic member is provided in the vicinity of the end of the magnetic brush.

The elastic body can be rotated integrally with the magnetic brush or can be fixedly arranged. Further, the magnetic brush and the elastic body may be rotatable independently of each other.

Further, the elastic body may be made of elastic foam or conductive fiber.

[0017]

According to the above construction, the elastic body provided at the end of the contact nip can prevent the magnetic particles forming the magnetic brush from moving to the outside in the longitudinal direction of the contact nip. As a result, the potential of the surface of the photoconductor corresponding to the end of the magnetic brush can be made equal to that of the magnetic brush, and the carrier is prevented from adhering to the photoconductor due to the potential difference between the magnetic brush and the photoconductor.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 First, the principle of charge injection charging performed by the charging device according to the present invention will be described.

The charge injection charging in the present invention is a contact charging member having a medium resistance, and the charge injection is performed on the surface of the photoreceptor having a medium resistance surface resistance. This charge injection charging is different from the conventional charge injection charging in which charges are injected into the trap potential of the surface material of the photoconductor, and charges the conductive particles in the charge injection layer with charges. .

Specifically, as shown in FIG. 2, a minute capacitor in which the charge transport layer 11 is regarded as a dielectric and the aluminum substrate 14 and the conductive particles 12 in the charge injection layer 13 are regarded as both electrode plates is used. It is based on the theory that the contact charging member 2 charges electric charges. At this time, the conductive particles 12 are electrically independent of each other and form a kind of minute float electrode. Therefore, the surface of the photoconductor 1 seems to be charged and charged to a uniform potential in a macroscopic view, but in reality,
The situation is that countless minute charged SnO ₂ covers the surface of the photoconductor 1. Therefore, even if image exposure is performed with a laser, each SnO ₂ particle is electrically independent, so that an electrostatic latent image can be held.

Next, the outline of the image forming apparatus equipped with the charging device according to the present invention will be described with reference to FIG. The image forming apparatus shown in the figure is a laser beam printer using an electrophotographic method.

The image forming apparatus shown in FIG.
It is provided with a drum type photoconductor 1 which is rotationally driven in the direction of arrow R1. In this embodiment, the photoreceptor 1 is an OP having a diameter of 30 mm.
It is a C photoconductor and is rotationally driven in the direction of arrow R1 at a process speed (peripheral speed) of 100 mm / sec.

A magnetic brush 2 as a contact charging member constituting a charging device is in contact with the photosensitive member 1. The magnetic brush 2 includes a rotatable non-magnetic charging sleeve 21, a magnet 22 arranged inside the charging sleeve 21, and a carrier (magnetic particle) 23 which is restrained on the surface of the charging sleeve 21 by the magnetic force of the magnet 22. There is. The magnetic brush 2 has a voltage of -700V from the charging bias applying power source S1.
The C charging bias is applied, and the surface of the photoconductor 1 is uniformly charged to approximately −700 V by charge injection charging.

A laser beam output from a laser beam scanner (not shown) including a laser diode, a polygon mirror and the like to the charged surface of the photoconductor 1, that is, a time series electric digital pixel signal of the target image information, Scanning exposure L with a laser beam whose intensity is modulated by
An electrostatic latent image corresponding to desired image information is formed on the surface of the photoconductor 1. This electrostatic latent image is developed as a toner image by the reversal developing device 3 using magnetic one-component insulating toner. Reference numeral 3a is a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 3b. The developing sleeve 3a is coated with the above-mentioned negative toner so that the distance from the surface of the photoreceptor 1 is 3
While being fixed at 00 μm, the photosensitive drum 1 is rotated at a constant speed, and a developing bias voltage is applied from the developing bias power source S2 to the developing sleeve 3a. As the voltage, a DC voltage of -500 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superposed, and the developing sleeve 3a is used.
And jumping development is performed between the photoconductor 1 and the photoconductor 1.

On the other hand, a transfer material P as a recording material supplied from a paper feeding unit (not shown) is a photosensitive member 1 and a transfer roller (contact transfer means) of a medium resistance abutted against the photosensitive member 1 with a predetermined pressing force. Four
It is introduced into the pressure contact nip portion (transfer portion) T between and at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 4 from the transfer bias applying power source S3. As the transfer roller 4 of this example, a roller having a roller resistance value of 5 × 10 ⁸ Ω was used, and transfer was performed by applying a DC voltage of + 2000V.

The transfer material P introduced into the transfer section T is nipped and conveyed by the transfer section T, and the toner images on the photosensitive member 1 are sequentially transferred to the surface thereof by electrostatic force and pressing force.

The transfer material P, to which the toner image has been transferred, is separated from the surface of the photosensitive member 1 and introduced into a fixing device 5 such as a heat fixing system, where the transfer of the toner image is performed, and thereafter, an image-formed product ( It is ejected outside the device as a print or copy.

On the other hand, after the toner image is transferred, the photosensitive member 1 after the toner image is transferred is cleaned by the adhering contaminants such as residual toner adhering to the surface thereof removed by the cleaning device 6, and is used for the next image formation.

In the image forming apparatus described above, the photoconductor 1, the contact charging member 2, the developing device 3, and the cleaning device 6 are used.
The process cartridge 20 is configured by integrally assembling the four process devices in the cartridge container 20a, and the process cartridge 20 is detachably attached to the main body of the image forming apparatus. The image forming apparatus to which the apparatus is attached is not limited to the cartridge type.

Next, the photoreceptor 1 will be described.

The photoreceptor 1 is a negatively charged OPC photoreceptor,
The following functional layers from the first layer to the fifth layer are provided in order from the bottom on a φ30 mm aluminum drum substrate.

The first layer is an undercoat layer and is provided to smooth out defects and the like in the aluminum base 14 made of aluminum (see FIG. 2) and to prevent moire due to reflection of laser exposure. The conductive layer has a thickness of about 20 μm.

The second layer is a positive charge injection preventing layer, which plays a role of preventing the positive charges injected from the aluminum substrate 14 from canceling out the negative charges charged on the surface of the photoreceptor 1, and the amylan resin and methoxymethyl. 10 ⁶ Ω by nylon
-It is a medium resistance layer with a thickness of about 1 μm, whose resistance is adjusted to about cm.

The third layer is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs by being exposed to laser.

The fourth layer is a charge transport layer 11, which is a polycarbonate resin in which hydrazone is dispersed, and is a P photoconductor semiconductor. Therefore, the negative charges charged on the surface of the photoreceptor 1 cannot move through this layer, and only the positive charges generated by the charges can be transported to the surface of the photoreceptor 1.

The fifth layer is the charge injection layer 12, which is a coating layer of a material in which ultrafine SnO ₂ is dispersed in a photocurable acrylic resin. Specifically, it is a coating layer made of a material in which antimony-doped SnO ₂ particles having a low resistance and a particle size of about 0.03 μm are dispersed in a resin in an amount of 70% by weight. The coating solution thus prepared was applied by dipping to a thickness of about 2 μm to form the charge injection layer 12.

As a result, the resistance of the surface of the photoreceptor 1 was 1 × 10 ¹⁵ Ω · cm in the case of the charge transport layer alone.
It decreased to 1 × 10 ¹² Ω · cm.

Next, the contact charging member of the charging device, which is a feature of this embodiment, will be described.

As shown in FIG. 1, the magnetic brush 2 as a contact charging member comprises a rotatable non-magnetic charging sleeve 21.
And the magnet 22 arranged inside the charging sleeve 21.
And a carrier 23 constrained by the magnetic force on the surface of the charging sleeve 21 as main constituent elements. The magnetic flux density of the magnet 22 on the charging sleeve 21 is 800 × 10 ⁻⁴ T (Tesla).

The carrier 23 on the charging sleeve 21 is coated with a thickness of 1 mm to form a charging nip (contact nip) N having a width of about 5 mm between the carrier 23 and the photoreceptor 1, and an arrow R2 in FIG.
While contacting the surface of the photoconductor 1 while rotating in the direction (counter direction with respect to the moving direction of the surface of the photoconductor 1 (direction of arrow R1)). In this embodiment, the carrier amount of the magnetic brush 2 is about 10 g, and the gap at the charging nip N between the charging sleeve 21 and the photoconductor 1 is 500 μm. The peripheral speed ratio between the magnetic brush 2 and the photoconductor 1 is defined by the following formula.

Peripheral speed ratio% = {(magnetic brush peripheral speed-photoconductor peripheral speed) / photoconductor peripheral speed} × 100 * The peripheral speed of the magnetic brush is a negative value in the case of counter rotation.

Since the magnetic brush 2 is in a stopped state when the peripheral speed ratio is -100%, the stopped shape of the surface of the photoconductor 1 of the magnetic brush 2 remains as a charging failure and appears in the image. Further, in the forward rotation, when the magnetic brush 2 comes into contact with the photoconductor at a slow speed, the carrier 23 of the magnetic brush 2 easily adheres to the photoconductor 1, and when the same peripheral speed ratio as in the counter direction is obtained, The rotation speed of the brush 2 becomes high. Therefore, the peripheral speed ratio is preferably −100% or less, and in this embodiment, it is −150%.

As the carrier 23 of the magnetic brush 2, a resin and a magnetic powder such as magnetite are kneaded and molded into particles, or a conductive carbon for adjusting the resistance value is mixed therewith. Magnetite, ferrite, or those whose resistance value has been adjusted by reduction or oxidation treatment of these, -Coating with the above-mentioned carrier 23 whose resistance has been adjusted (such as those in which carbon is dispersed in phenol resin) or metal such as Ni It is conceivable that the resistance value is set to an appropriate value by plating with. If the resistance value of these carriers 23 is too high, the charge cannot be uniformly injected into the photoconductor 1, resulting in a fog image due to a minute charging failure. If it is too low, when there is a pinhole on the surface of the photoconductor 1, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photoconductor 1 cannot be charged, resulting in a nip-shaped charging failure. Become. Therefore, the resistance value of the carrier 23 is preferably 1 × 10 ⁴ to 1 × 10 ⁷ Ω. The resistance value of the carrier is the metal cell (bottom area 227
mm ² ), after putting 2 g of carrier into it, 6.6 kg / cm ²
The measurement was performed by applying a voltage of 1 to 1000 V.

Regarding the magnetic characteristics of the carrier 23, it is better to increase the magnetic restraining force in order to prevent the carrier from adhering to the photosensitive member 1, and the saturation magnetization is preferably 50 (A · m ² / kg) or more.

In practice, the carrier 23 used in this embodiment
Has an average particle size of 30 μm and a low resistance value of 1 × 10 ⁶ Ω,
The saturation magnetization was 58 (A · m ² / kg).

The end portion of the charging member will be described with reference to FIG. FIG. 1 is a vertical cross-sectional view taken along the longitudinal direction of the magnetic brush 2, showing the longitudinal end portion of the charging sleeve 21 (the magnet 2).
A conductive sponge portion (elastic body) 24 is provided at the end position 2). Although only one end is shown in the figure, the sponge 24 is similarly provided at the other end. The outer diameter of the sponge portion 24 is 16 m in outer diameter of the charging sleeve 21 in order to obtain a sufficient nip for charging.
It is 2 mm thicker than m and has a diameter of 18 mm, but since the pressure is maintained while maintaining the gap with the photoconductor 1 at 500 μm, the diameter is 17 mm. When the sponge portion 24 is not an elastic body such as a sponge but a solid rubber, for example, the contact with the photoconductor 1 is insufficient and uniform charge injection cannot be performed. However, by using the elastic body 24, the elastic body 24 can be brought into uniform contact with the photoconductor 1 and the charge can be uniformly injected. The sponge used here is a foam of EPDM whose resistance value is adjusted to 1 × 10 ⁶ Ω · cm by dispersing carbon, but the sponge is not limited to this, and urethane or carbon or metal oxide dispersed as a conductive material is used. Silicone rubber, NBR, EPM, CR,
A foam such as SBR may be used.

By adopting the above-mentioned structure, the outside of the longitudinal end of the magnetic brush 2 is a conductive sponge portion 2.
Since it is charged by 4, the photoconductor 1 is charged to the same potential as the carrier 23, and the carrier 23 does not adhere to the photoconductor 1. Further, the sponge portion 24 also serves as a seal for the carrier 23, and the carrier 23 is less likely to move to the outside in the longitudinal direction at the charging nip N. Therefore, since the carrier 23 of the magnetic brush 2 does not decrease, stable charging property can be obtained even in continuous use.

Although a sponge is used as the elastic body in the present embodiment, a similar effect can be obtained with a medium resistance felt or the like. <Embodiment 2> This embodiment is characterized in that the end portion of the magnetic brush, that is, the end portion of the charging sleeve is formed by a fur brush.

Specifically, as shown in FIG. 4, a fur brush 25 made of fiber in which carbon is dispersed in rayon is provided at the end of the charging sleeve 21. The fur brush 25 has a resistance value of 5 × 10 ⁶ Ω · cm, a density of 300 denier / 50 filaments, and a density of 155 filaments per square millimeter.

Fur fur brush materials are REC-B, REC-C and REC-M manufactured by Unitika Ltd.
1, REC-M10, SA-7 manufactured by Toray Industries, Inc.,
Thunderon manufactured by Japan Silkworm Co., Ltd., Bertron manufactured by Kanebo, Cracabo manufactured by Kuraray Co., Ltd., carbon dispersed in rayon, and lobal manufactured by Mitsubishi Rayon Co., Ltd. REC-B, REC-C, REC-M1, REC-M1 manufactured by Unitika Ltd.
0 is desirable.

By adopting such a configuration, the outside of the end portion in the longitudinal direction of the magnetic brush 2 is charged by the fur brush 25, so that the photoconductor 1 is charged to the same potential as the carrier 23, and the carrier 23 does not adhere to the photoconductor 1. Therefore, since the carrier 23 of the magnetic brush 2 does not decrease, stable charging property can be obtained even in continuous use.

Further, the use of the fur brush 25 makes the contact with the photosensitive member 1 flexible, which has the advantage of reducing the contact torque. <Embodiment 3> This embodiment is characterized in that the image area of the charging member is a magnetic brush and a fixed conductive sponge is provided at the end.

FIG. 5 shows a specific structure. The conductive sponge 26 is fixed to the support member 27, and the charging sleeve 2
1 has the same potential as the magnetic brush 2 that supplies power to the photosensitive member 1 and charges the photosensitive member 1. Conductive sponge 26 used in this embodiment
Is an EPD with the same carbon dispersion as that used in Example 1.
It is a foam of M. In addition, the conductive sponge 26 is used in the second embodiment.
The fur brush 25 described above may be used.

With this structure, as in the above-described embodiment, the outside of the end portion in the longitudinal direction of the magnetic brush 2 is charged by the conductive sponge 26, so that the potential on the photoconductor is the same as that of the carrier 23. Since it is charged, the carrier 23 does not adhere to the photoconductor 1. Further, in the above-described first and second embodiments, since the elastic body such as the sponge portion 24 at the end portion and the fur brush 25 rotates together with the magnetic brush 2, the carrier 23 is separated from the charging nip. The carrier 23 may adhere to the surface of the elastic body, and the next time the photosensitive body 1 and the elastic body come into contact with each other, the carrier 23 may enter between the photosensitive body 1 and the elastic body and damage the surface of the photosensitive body 1. With the configuration of the embodiment, the surface of the same elastic body is always in contact with the photoconductor, so that the carrier 23 does not enter,
Damage to the photoreceptor 1 is reduced.

Therefore, since the carrier 23 of the magnetic brush 2 is not reduced, a stable charging property can be obtained even in continuous use, and an image defect due to a scratch on the photoconductor 1 is improved. <Embodiment 4> This embodiment is characterized in that the image area of the charging member corresponds to the magnetic brush, and the end portion is provided with a conductive sponge which rotates independently of the magnetic brush.

FIG. 6 shows a specific structure. The conductive sponge 28 is attached to the small-diameter portion 21a of the charging sleeve 21 and is supplied with electric power in contact with the magnetic brush 2. Therefore, the conductive sponge 28 has the same potential as the magnetic brush 2 and charges the photoconductor 1. Here, the conductive sponge 28 and the charging sleeve 21 rotate independently of each other as shown in FIG. Specifically, in the magnetic brush 2, the charging sleeve 21 is driven and rotated in the arrow R2 direction, the photoconductor 1 is driven and rotated in the arrow R1 direction, and the conductive sponge 28 is driven and rotated in the arrow R3 direction. . The conductive sponge 28 used in this example is the same carbon-dispersed EPDM foam as that used in Example 1. Instead of the conductive sponge 28, it is possible to use the fur brush as described in the second embodiment.

With this structure, as in the above-described embodiment, the outer side of the end of the magnetic brush 2 in the longitudinal direction is charged by the conductive sponge 28. Is charged to the carrier 23
Does not adhere to the photoconductor 1. Further, in this embodiment, since the conductive sponge (elastic body) 28 at the end portion is driven and rotated by the photoconductor 1, the carrier 23 is elastic conductive sponge 2.
Even if the carrier 23 enters between the photoconductor 1 and the photoconductor 1, the photoconductor 1 is not damaged because the carrier 23 passes through the nip while being sandwiched at the same position.

Therefore, since the carrier 23 of the magnetic brush 2 does not decrease, a stable charging property can be obtained even in continuous use, and the photoconductor 1 is not scratched, so that a defective image due to scratches is eliminated.

[0059]

As described above, according to the present invention,
By providing a conductive elastic body at the end of the magnetic brush, the potential of the surface of the photoconductor that contacts this elastic body can be made equal to the potential of the magnetic brush. Since the magnetic particles can be prevented from being pushed out to the outside, the carrier does not adhere to the photoconductor from the magnetic brush, and the magnetic particles of the magnetic brush do not decrease even when used for a long period of time. Therefore, stable chargeability can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view for wetting a shape of an end portion in a longitudinal direction of a charging member according to a first exemplary embodiment.

FIG. 2 is a conceptual diagram illustrating the principle of injection charging.

FIG. 3 is a schematic diagram showing a configuration of an image forming apparatus to which the present invention has been applied.

FIG. 4 is a vertical cross-sectional view showing the shape of the end portion in the longitudinal direction of the charging member of Example 2.

FIG. 5 is a vertical cross-sectional view showing the shape of the end portion in the longitudinal direction of the charging member of Example 3.

FIG. 6 is a vertical cross-sectional view showing the shape of an end portion in the longitudinal direction of a charging member of Example 4.

FIG. 7 is a perspective view illustrating a configuration of a charging member according to a fourth exemplary embodiment.

FIG. 8 is a diagram illustrating a problem in the configuration of the conventional charging member.

[Explanation of symbols]

 1 Photoconductor 2 Charging Member (Magnetic Brush) 3 Developing Device 4 Charging Roller 5 Transfer Device 6 Cleaning Device 11 Charge Transport Layer 12 Conductive Particles 13 Charge Injection Layer 14 Aluminum Base 21 Charging Base (Charging Sleeve) 22 Magnet 23 Magnetic Particles (Carrier) ) 24 elastic body (conductive sponge) 25 elastic body (fur brush) 26 elastic body (conductive sponge) 28 conductive sponge N contact nip (charging nip) P transfer material

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tadashi Furuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (6)

[Claims] 1. A charging device for charging by charging a contact charging member to which a voltage is applied to a photoreceptor having a charge injection layer on its surface, wherein the contact charging member is a charging substrate to which a charging voltage is applied. A magnetic brush having magnetic particles restrained by a magnetic force on the charging substrate, the magnetic brush contacting the magnetic particles with the photosensitive member to form a contact nip, and the magnetic brush A charging device, characterized in that a conductive elastic member is provided in the vicinity of the end of the brush. 2. The charging device according to claim 1, wherein the elastic body rotates integrally with the magnetic brush. 3. The charging device according to claim 1, wherein the elastic body is fixedly arranged. 4. The charging device according to claim 1, wherein the magnetic brush and the elastic body are rotatable independently of each other. 5. The charging device according to claim 1, wherein the elastic body is made of an elastic foam. 6. The charging device according to claim 1, wherein the elastic body is made of a conductive fiber.