JPH0926682A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent faulty exposure and faulty development from occurring because the conductive magnetic particles of an electrifying magnetic brush adhere to a photoreceptor drum. SOLUTION: The electrifying magnetic brush 2 is constituted by providing a magnetic roller 23 around a core bar 24, providing a conductive layer 22 on the surface of the roller 23 and carrying the conductive magnetic particles 21 on the surface. Voltage is impressed on the brush 2 so as to electrify the photoreceptor drum 1 through the particles 21. The particles 21 are apt to adhere to the drum 1 at the most downstream end (c) on a contact surface between the particles 21 and the drum 1. Then, the interpole space of the roller 23 is set toward the end (c). Thus, napping is not caused at the end (c) and the density of the magnetic particles is high, so that the particles 21 hardly adhere to the drum 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been widely used as an electrophotographic charging device, but in recent years, a contact charging device has been put into practical use in place of this. This is for charging a charged body by applying a voltage to a contact charging member that is in contact with a charged body such as an image carrier, and is intended for low ozone, low power, and the like.

A general characteristic required for the contact charging member (hereinafter simply referred to as "charging member") at this time is to set the resistance value to about 1 × 10 ⁴ to 1 × 10 ⁷ Ω. That is, when a charging member having a low resistance value is used, if there are scratches, pinholes, etc. on the member to be charged, an excessive leakage current flows from the charging member, and charging failure or enlargement of pinholes around the charging member occurs. Energization breakdown occurs. In order to prevent this, the resistance value of the charging member is set to 1 × 10 ⁴
It should be about Ω or more. On the other hand, if it is 1 × 10 ⁷ Ω or more, the resistance value is too high, and the current required for charging cannot be passed. Therefore, the resistance value of the charging member is 1 × 10
It must be in the range of ⁴ to 1 x 10 ⁷ Ω.

Among the above-mentioned charging members, the roller charging method using a conductive roller is preferable from the viewpoint of the stability of charging of the member to be charged.

In the roller charging system, a conductive roller having elasticity (hereinafter referred to as "charging roller") is pressed against and contacted with a member to be charged, and a voltage is applied to the member to charge the member.

In roller charging, charging is mainly performed by discharging from a charging roller to a member to be charged, and therefore charging is started by applying a voltage equal to or higher than a certain threshold (threshold) voltage. For example, when the charging roller is pressed and brought into contact with the OPC photosensitive member having a thickness of 25 μm, about 6
When a voltage of 40 V or higher is applied, the surface potential of the photoconductor starts to rise, and thereafter, the surface potential of the photoconductor linearly increases with a slope of 1 with respect to the applied voltage. Hereinafter, this threshold voltage is referred to as a charging start voltage V _th . That is, in order to obtain the photoreceptor surface potential V _d required for the electrophotographic photoreceptor, it is necessary to apply a DC voltage of (V _d + V _th ) or more to the charging roller. Such a method of applying only the DC voltage to the contact charging member for charging is called DC charging. .

However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, etc. Also, when the film thickness changes due to _abrasion of the photoconductor, _Vth fluctuates. It was difficult to obtain the desired value.

Therefore, as disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to a desired V _d is equal to or more than a peak-to-peak voltage twice V _th , as disclosed in JP-A-63-149669. An AC charging method is used in which a voltage superposed with an AC component having is applied to the contact charging member. This is A
The purpose is to smooth the potential by C, 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, since the essential charging mechanism uses the discharging phenomenon from the charging member to the photosensitive member, the voltage required for charging as described above. Is required to have a value equal to or higher than the surface potential of the photoconductor, and a small amount of ozone is generated. Further, when AC charging is performed to make the charging uniform, a further amount of ozone is generated,
Vibration of the charging member and the photoconductor due to the electric field of the AC voltage, noise (hereinafter referred to as “charging sound”), and deterioration of the photoconductor surface due to discharge have become remarkable, which has become a new problem.

Therefore, as a new charging method, a charging method by directly injecting charges into the photosensitive member is disclosed in Japanese Patent Laid-Open No. 06-003.
Japanese Patent Application No. 05-06.
No. 6150 is being proposed. This charging method is a method of performing contact injection charging by applying a voltage to a contact conductive member such as a charging roller, a charging brush, or a charging magnetic brush, and injecting a charge into a float electrode on a photoconductor having an injection layer on the surface. Is. Specifically, in the above-mentioned Japanese Patent Laid-Open No. 06-003921, as a charge injection layer, SnO is formed on the surface of the photoconductor by making the acrylic resin conductive by antimony doping which is a conductive feeler.
There is a description that it is possible to coat and use a dispersion of _two particles. The charging magnetic brush is a charging member that is formed in a brush shape by magnetically restraining conductive magnetic particles with a magnet roll or the like, and charges the brush by bringing the brush into contact with the photoconductor. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is a DC voltage only for the desired surface potential of the photoconductor, and ozone is not generated. Further, since no AC voltage is applied, no charging noise is generated, and ozone is lower than that of the roller charging method described above.
It is an excellent charging method with low voltage.

FIG. 6 shows an example of the direct charging system. This figure is a schematic view of the entire apparatus when the charging magnetic brush 102 in which the conductive magnetic particles are directly carried on the magnetic roller is used as a charger of an electrophotographic image forming apparatus. Around the photosensitive member 101, a charging magnetic brush 102, an exposure device 10
3, developing device 108, transfer charger 105, cleaner 106
And a fixing device 107 for fixing the toner on the recording paper P.

The charging magnetic brush 102 is constructed by forming a magnetic roller 123 on a core metal 124, covering the surface of the magnetic roller 123 with a conductive layer 122, and further carrying conductive magnetic particles 121 on the surface of the conductive layer 122. Yes, photoconductor 1
01 can be charged to approximately the same potential as the applied bias.

[0013]

However, in the charging magnetic brush 102 described above in which the conductive magnetic particles 121 are carried on the magnetic roller 123, the conductive magnetic particles 121 are released from the magnetic roller 123 and are exposed. Body 10
1. An exposure device 10 that forms an electrostatic latent image when adhered on
There is a problem that the exposure of No. 3 is blocked and an image defect occurs or a development defect occurs.

In the configuration in which the charging magnetic brush 102 is brought into contact with the photoconductor 101 and rotated to charge the photoconductor surface,
The conductive magnetic particles 121 at the most downstream end (M in FIG. 6) of the conductive magnetic particles 121 in contact with the photoconductor 101 adhere to the photoconductor 101. As a result, the attached conductive magnetic particles 121 block the exposure and cause an image defect. Further, even when the electrostatic latent image is developed, the adhered portion of the conductive magnetic particles 121 on the surface of the photoconductor 101 is likely to cause an electric discharge, and a defective development may occur at the place where the electric discharge occurs or the entire longitudinal region.

Therefore, an object of the present invention is to provide an image forming apparatus capable of preventing an image defect caused by adhesion of conductive magnetic particles to an image carrier (photosensitive member in the above case). is there.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, in which the surface of a movable photoconductive image carrier is uniformly charged by a charger, and the light of the exposure device is changed. In an image forming apparatus that forms an electrostatic latent image by irradiation, develops a toner image by adhering toner to the electrostatic latent image, and transfers the toner image to a recording material by a transfer charger, the charger is A magnetic roller having N poles and S poles alternately arranged along the circumferential direction and opposed to the surface of the image carrier with a minute gap therebetween, and magnetically supported on the surface of the magnetic roller. The magnetic roller is provided with conductive magnetic particles that fill the minute gap and contact the surface of the image carrier, and a power source that charges the surface of the image carrier through the conductive particles. Multiple in the radial magnetic flux density distribution It has a peak, 50 of the peak intensity
In a state in which the angular region having a strength of less than 1% is positioned at the first position facing the most downstream end in the moving direction of the image carrier on the contact surface between the surface of the image carrier and the conductive magnetic particles. The surface of the image carrier is charged.

In this case, the magnetic roller may be rotatably supported, the magnetic roller may be rotationally driven during non-image formation, and the magnetic roller may be positioned at the first position during image formation.

[Operation] Based on the above construction, the angle region having an intensity of less than 50% of the peak intensity of the magnetic roller is, as described above, the image bearing portion of the contact surface between the image bearing member surface and the conductive magnetic particles. The gap between the magnetic rollers is directed to the state of being positioned at the first position facing the most downstream end in the body movement direction, that is, the most downstream end described above.

When the magnetic roller pole is facing the most downstream end of the conductive magnetic particles, the most downstream conductive magnetic particles stand in a line and the conductive magnetic particles 21 become sparse. When the conductive magnetic particles become sparse, that portion becomes extremely brittle, and is weak against friction with the surface of the image carrier and easily adheres to the surface of the image carrier. At the pole position of the magnetic roller, the magnetic flux density is high and the magnetic binding force is strong, but conversely the magnetic binding force is so strong that the conductive magnetic particles stand up and the surface of the image bearing member moves in that state. At the same time, the spikes of the conductive magnetic particles vibrate. As a result, the adhesion increases. On the other hand, when the gap between the magnetic rollers (between the N pole and the S pole) is directed to the most downstream end, the conductive magnetic particles are very densely present at the most downstream end without standing. At this position, the magnetic binding force is weak, but since the conductive magnetic particles are densely packed, the conductive magnetic particles do not vibrate even when the image carrier slides, and the conductive magnetic particles adhere to the image carrier. There is no.

Further, by rotating the magnetic roller 23 at a certain frequency during non-image formation, and then again positioning so that the distance between the poles faces toward the most downstream end, toner and other toner that slips through the cleaner and enters the charging member. This prevents the charging property of the charging member from being impaired due to the accumulation of contaminants.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a sectional view showing an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 includes a photosensitive drum (image carrier) 1 having a charge injection function on its surface and a charging magnetic brush 2, an exposing unit 3, a developing unit 8, a transfer charging unit 5, and a cleaner 6 arranged around the photosensitive drum 1. The fixing device 7 and the like are configured as main constituent members. The configuration and operation excluding the charging magnetic brush 2 are almost the same as those of the conventional example described with reference to FIG.
The charging magnetic brush 2 which is a feature of the present invention will be mainly described.

As shown in FIG. 2, the charging magnetic brush 2 is
The core metal 24, the magnetic roller 23, the conductive layer 22, and the conductive magnetic particles 21 are main components. After the magnetic roller 23 is formed on the cored bar 24 that also functions as driving and feeding, the conductive layer 22 is formed on the surface of the magnetic roller 23.
The conductive magnetic particles 21 are magnetically bound to the surface of 2 by a magnetic roller 23. As the magnetic roller 23, not only a general permanent magnet such as ferrite but also a powder of this formed with a resin can be used. After that, it is magnetized into a desired magnetic flux pattern at a desired temperature and used. Here, a 4-pole magnetic roller in which N poles and S poles are alternately arranged at equal intervals along the circumferential direction is used. The maximum magnetic flux density on the surface of the magnetic roller 23 was 0.08 (T). In order to supply electric power to the conductive magnetic particles 21 stably and uniformly, the surface of the magnetic roller 23 needs to be made conductive. For example, the conductive layer 22 is provided by covering a tube formed by dispersing conductive powder in a resin, applying a conductive material of the same type, or sticking a conductive tape on one surface. Further, the conductive magnetic particles 21 are carried on the conductive layer 22 to form the magnetic brush 2. Here, as the conductive magnetic particles 21, there were used phyllite particles having an average particle diameter of 15 μm, a volume resistance value of 1 × 10 ⁶ Ω · cm, and a saturation magnetization of 58 (A · m ² / kg). . The resistance of the conductive magnetic particles 21 is measured by the bottom area 28
² g of the conductive magnetic particles 21 was filled in a cylindrical container of 8 mm ² and pressurized, and a voltage of 100 V was applied from the top and bottom to calculate from the current flowing in this system and defined as normalized. As the conductive magnetic particles 21, magnetic metal particles such as ferrite and magnetite, or particles obtained by binding these magnetic metal particles with a resin can be used. Resistance value is 1 × 10 ⁴ to 1 ×
Those having a resistance of 10 ⁷ Ω · cm are advantageous in terms of chargeability and withstand voltage against pinhole leak of the photosensitive drum 1. Further, it is possible to improve the charging property by mixing and using a plurality of conductive magnetic particles 21. The saturation magnetization is 30 (A
m ² / kg) or more is suitable. Particle size is 10
About 50 μm can be used in terms of chargeability and magnetic force retention.

The charging magnetic brush 2 has a longitudinal direction (core 24
Spacers (not shown) are provided at both ends in the axial direction of FIG. By bringing these spacers into contact with the surface of the photosensitive drum 1, the closest distance between the surface of the photosensitive drum 1 and the surface of the magnetic roller 23 is set to 0.5 mm. As a result, the conductive magnetic particles 21 come into contact with the surface of the photosensitive drum 1 with an appropriate width. The photosensitive drum 1 and the charging magnetic brush 2 are rotationally driven in the same direction (clockwise direction in the figure). Therefore, the surface of the photosensitive drum 1 and the surface of the conductive magnetic brush 2 in the contact portion of the conductive magnetic particles 21 move in opposite directions. Then, at the time of charging, charges are injected into the charge injection layer 16 (see FIG. 3) on the surface of the photosensitive drum 1 by applying a desired voltage to the conductive layer 22, and the surface of the photosensitive drum 1 finally becomes the charged magnetic brush 2. It is charged (charged) to the same potential.

As shown in the sectional view of FIG. 3, the photosensitive drum 1 has an undercoat layer 1 on an aluminum base 11.
2. A structure in which a charge injection layer 16 is further applied onto a general OPC drum in which the positive charge injection prevention layer 13, the charge generation layer 14, and the charge transport layer 15 are applied in this order. The charge injection layer 16 used in the present embodiment is made by dispersing SnO ₂ ultrafine particles (having a diameter of about 0.03 μm) in a photo-curing acrylic resin. The charge injection layer 16 intentionally creates injection sites for uniformly charging the surface by directly injecting the charges from the charging magnetic brush 2. However, in order to prevent the latent image charge from flowing on the surface, Charge injection layer 1
The resistance value of 6 must be 1 × 10 ⁸ Ω · cm or more. The resistance value of the charge injection layer 16 is obtained by, for example, applying a charge injection layer on an insulating sheet and measuring the surface resistance with a measuring instrument (high resistance meter 4329A manufactured by HP) at an applied voltage of 100V. . Further, although the charge injection layer 16 is formed as an independent layer in the present embodiment, it is important that the surface layer of the photosensitive drum has an electron level capable of donating electrons, and in particular, the charge injection layer 16 has an independent charge injection layer 16. It is not limited to the configuration. Further, in order to reduce the adhesion of the conductive magnetic particles 21 to the surface of the photosensitive drum, the surface of the photosensitive drum 1 preferably has a low surface energy characteristic, and a desired lubricant is added to the outermost surface of the photosensitive drum to obtain a certain smoothness. .

Next, the operation of the image forming apparatus will be described. A voltage of -700 V is applied to the charging magnetic brush 2 described above, and the photosensitive drum 1 is charged to the same potential as this. After that, the image portion is scanned by the exposure device 3 such as a laser scanner according to the print pattern to form an electrostatic latent image on the photosensitive drum 1. Then, the developing sleeve 8a (see FIG. 3) fixed with a distance of 0.3 mm from the surface of the photosensitive drum has a voltage of -500V.
DC voltage, frequency 1.8 kHz, peak-to-peak voltage 1.
By applying a voltage in which a rectangular wave AC voltage of 6 kV is superimposed, the negatively frictionally charged toner carried on the developing sleeve 8a is adhered to the image portion of the latent image by the transfer electric field and developed. The developed toner image on the photosensitive drum 1 is transferred by the transfer charger 5 to the recording material P whose back surface is charged,
It is fixed on the surface of the recording material P by the fixing device 7. Transfer charger 5
A transfer roller is used as the transfer roller, and the transfer roller has a cored bar with a medium resistance foam layer. Its resistance is 5 × 10
Transfer of ⁸ Ω was used and a voltage of +2.0 kV was applied to the core metal. Photosensitive drum 1 after transfer of toner image
, The toner remaining on the surface is scraped off by the cleaner 6,
The charging magnetic brush 2 supplies the next image forming apparatus starting from charging. By repeating the above, the recording materials P are sequentially
An image can be formed on it. The outline of the configurations and operations of the image forming apparatus, the charging magnetic brush 2 and the photosensitive drum 1 has been described above.

Next, the magnetic roller 23 which is a feature of the present invention.
The configuration and operation of the conductive magnetic particles 21 will be described.

The conductive magnetic particles 21 are directly applied to the magnetic roller 23.
The charging magnetic brush 2 configured to carry the toner has a big problem that the conductive magnetic particles 21 adhere to the photosensitive drum 1. The adhered conductive magnetic particles 21 may block latent image exposure and cause an image defect. Therefore, in the present embodiment, when the latent image is formed on the photosensitive drum 1, the conductive magnetic particles 21
It is configured to be carried out under a pole position condition (described later) with less adherence of. However, when the charging magnetic brush 2 is used in a state where it is always stopped, the charging property of the charging magnetic brush 2 may be impaired due to the retention of toner and other contaminants that pass through the cleaner 6 and enter the charging magnetic brush 2. is there.

In order to prevent such deterioration of the charging magnetic brush 2, the charging magnetic brush 2 is rotated at the time of non-image formation to prevent contaminants from staying on the contact surface with the surface of the photosensitive drum 1, and at the time of image formation. By re-fixing in a pole position that is advantageous for adhesion, a good brush contact surface can always be maintained.

Next, the setting of the pole position of the magnetic roller 23 will be described. FIG. 2 is a diagram showing details of the charging magnetic brush 2. In the present embodiment, the charging magnetic brush 2 is rotated in the same rotation direction as the photosensitive drum 1, and the surface of the photosensitive drum 1 and the surface of the magnetic roller 23 move in opposite directions at the contact surface of the conductive magnetic particles 21. Therefore, a pooled portion of the conductive magnetic particles 21 is formed on the downstream side in the moving direction of the surface of the photosensitive drum 1. When the pole of the magnetic roller 23 is facing the most downstream end of the conductive magnetic particles 21 (point c in the figure), the conductive magnetic particles 21 in the pooling portion stand in a linear shape and the conductive magnetic particles 21 are sparse. become. When the conductive magnetic particles 21 become sparse, the pooled portion becomes extremely brittle and weak against friction with the surface of the photosensitive drum 1 and easily adheres to the surface of the photosensitive drum 1. Further, at the pole position of the magnetic roller 23, the magnetic flux density is high and the magnetic binding force is strong, but conversely, the magnetic binding force is strong, so that the conductive magnetic particles 21 stand up and the photosensitive drum 1 rotates in that state. With 1, the spikes of the conductive magnetic particles 21 vibrate. As a result, the adhesion increases. On the other hand, when the gap is facing the most downstream end of the pooled portion, the conductive magnetic particles 21 are very densely present in the pooled portion without forming spikes.
At this position, the magnetic restraining force toward the magnetic roller 23 is weak, but since the conductive magnetic particles 21 are densely packed, the conductive magnetic particles 21 do not vibrate even when the photosensitive drum 1 slides, and the photosensitive drum 1 does not vibrate. There is no attachment of the conductive magnetic particles 21 to 1. Therefore, as described above, the gap between the magnetic rollers 23 is positioned (fixed) at the first position facing the most downstream end of the pooled portion of the conductive magnetic particles 21 during image formation, and further during non-image formation. Magnetic roller 2 at a certain frequency
By rotating 3 and fixing it again so that the gap is directed toward the most downstream end of the pooled portion, it is possible to prevent image deterioration due to the adhesion of the conductive magnetic particles 21 and perform good image formation.

Next, the intermittent rotation of the charging magnetic brush 2 will be described. As described above, the charging magnetic brush 2 is intermittently rotated during non-image formation. The rotation timing is as follows: when the photosensitive drum is stopped, after the photosensitive drum is started, before image formation,
It is possible to perform either one of the recording materials P during continuous image formation and before the photosensitive drum is stopped or an appropriate combination thereof. However, adverse effects on the incorporation of the conductive magnetic particles 21 into the developing device, transfer or cleaning. In consideration of the above, it is preferable to stop the photosensitive drum. For example, the charging current flowing from the charging magnetic brush 2 to the ground of the photosensitive drum 1 at the time of charging is monitored to detect a charging failure due to dirt on the charging magnetic brush 2, and the charging magnetic brush 2 is intermittently rotated at a desired timing. Is also effective. Further, if the charging and rotating operation of the charging magnetic brush 2 is made to have a desired slope, it is possible to reduce the adhered amount at the time of rotation, so that a better device configuration can be taken.

Next, the definitions of the poles and the poles in the magnetic roller 23 will be described. FIG. 4 shows the result of measuring the magnetic flux density distribution in the radial direction of the magnetic roller 23 of this embodiment. In the present embodiment, the angular range indicating the pole is in the magnetic flux density distribution, and the peak intensity is 50 at the maximum.
A range of angles having a strength of not less than% (range of X in FIG. 4). On the other hand, the angle range indicating the gap means a range of angles having an intensity of less than 50% (Y range in FIG. 4).

Next, the structure of the charging magnetic brush 2 of the present embodiment is shown in FIG. 7 together with a comparative example.

In the structure of the comparative example, when the charging magnetic brush 2 is constantly rotated, the image exposure is blocked from the beginning of printing to the end of its durability, so that white spots are present in the solid black portions, and it is not possible to develop due to discharge during development. There was a white spot in the area. Further, under the condition 2 of the first embodiment, when the charging magnetic brush 2 was fixed to a gap advantageous for adhesion and charging was performed, a good image could be obtained at the initial stage, As a result, the charging magnetic brush 2 is contaminated and the charging performance is significantly deteriorated, so that the charging property is significantly decreased, and the decrease in the charging property increases the potential difference between the charging magnetic brush 2 and the photosensitive drum 1. The adhesion phenomenon of the conductive magnetic particles 21 was observed as a physical factor. On the other hand, under the condition 1 of the first embodiment, a gap that is advantageous for adhesion is used during image formation, and is rotated appropriately during non-image formation to prevent the accumulation of deposits, thus ensuring a good contact surface. By making the above, it became possible to perform good image formation at the initial stage and after the endurance. <Second Embodiment> FIG. 5 is a schematic diagram of an image forming apparatus according to a second embodiment.

The structure is the same as that of the first embodiment, and the description thereof will be omitted.

Regarding the operation, the rotating direction of the charging magnetic brush 2 is opposite to that of the photosensitive drum 1, and the mutual surfaces of the contact portions of the conductive magnetic particles 21 move in the same direction. That is, the rotating direction of the charging magnetic brush 2 is opposite to that in the first embodiment. Therefore, the accumulated portion of the conductive magnetic particles 21 is formed on the upstream side in the moving direction of the surface of the photosensitive drum 1. Even in this case, the adhesion is still performed by the conductive magnetic particles 21 existing at the most downstream end (in this case, meaning downstream of the drum) adhering to the drum. Also in this case, as in the first embodiment, at the point d in FIG.
When the pole of (1) is directed, the conductive magnetic particles 21 stand and the magnetic flux density becomes sparse. As a result, the ears of the conductive magnetic particles 21 vibrate as the photosensitive drum 1 moves, and the conductive magnetic particles 21 easily adhere. On the other hand, when the gap is toward the point d, the conductive magnetic particles 21 are densely present, and therefore the magnetic force toward the magnetic roller 23 is low, but densely present, and therefore against the friction with the photosensitive drum 1. Stronger and therefore less adherent. Further, in the case of the second embodiment, since the accumulated portion of the conductive magnetic particles 21 is formed on the upstream side in the moving direction of the photosensitive drum 1, there are few spikes on the downstream side of the photosensitive drum. Therefore, it is more advantageous for adhesion than the configuration of the first embodiment, and is an excellent configuration in terms of maintaining chargeability.

Here, the definitions of the poles and the poles are in accordance with the first embodiment. The intermittent rotation of the charging magnetic brush 2 is also the same as in the first embodiment.

As described above, even in the configuration in which the magnetic roller 23 rotates in the opposite direction to the photosensitive drum 1, that is, in the configuration in which the pooled portion of the conductive magnetic particles 21 is provided on the upstream side in the photosensitive drum moving direction, the conductive magnetic particles 21 are formed. By fixing the magnetic roller 23 to the most downstream end point d of the magnetic roller 23, the image deterioration due to the adhesion of the conductive magnetic particles 21 is prevented, and at the same time, the magnetic roller 23 is rotated to rotate the charging magnetic brush during non-image formation. (2) It is possible to prevent retention of contaminants on the surface, prevent the conductive magnetic particles 21 from adhering to the photosensitive drum 1, eliminate image defects, and maintain good chargeability.

[0038]

As described above, according to the present invention,
At the time of image recording, magnetic flux distribution is arranged so that the conductive magnetic particles carried on the surface of the magnetic roller do not adhere to the image carrier, that is, the magnetic roller is positioned so that the gap between the magnetic rollers faces the most downstream end of the conductive magnetic particles. By disposing and charging, the conductive magnetic particles can be prevented from adhering to the image carrier, and image defects due to the adherence can be prevented to realize good image formation. Further, by appropriately rotating the charging member during non-image recording to diffuse the contaminants entering the conductive magnetic particles, image defects due to adhesion of the conductive magnetic particles to the image carrier can be prevented, and good charging property can be obtained. It will be possible to maintain.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a detailed configuration diagram of the charger according to the first embodiment.

FIG. 3 is a schematic configuration diagram of a photosensitive drum (charged body) according to the first embodiment.

FIG. 4 is a diagram showing a magnetic flux density distribution of a magnetic roller.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 7 is a diagram showing comparison and evaluation of configurations of magnetic brushes.

[Explanation of symbols]

 1 Image Carrier (Photosensitive Drum) 2 Charging Member (Charging Magnetic Brush) 3 Exposure Device 5 Transfer Charger 6 Cleaner 7 Fixer 8 Developer 11 Aluminum Substrate 12 Undercoat Layer 13 Positive Charge Injection Prevention Layer 14 Charge Generation Layer 15 Charge Transport layer 16 Charge injection layer 21 Conductive magnetic particles 22 Conductive layer 23 Magnetic roller 24 Core bar c Downstream end

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Seiji Mashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A surface of a movable photoconductive image carrier is uniformly charged by a charging device, an electrostatic latent image is formed by light irradiation of an exposing device, and toner is attached to the electrostatic latent image. In the image forming apparatus, in which the toner image is developed as a toner image, and the toner image is transferred to a recording material by a transfer charger, the charger has N poles and S poles arranged in a circumferential direction alternately. A magnetic roller disposed opposite to the surface of the image carrier through a minute gap; conductive magnetic particles magnetically carried on the surface of the magnetic roller and filling the minute gap to contact the surface of the image carrier; A power source for charging the surface of the image bearing member through conductive particles, wherein the magnetic roller has a plurality of peaks in a magnetic flux density distribution in a radial direction on the surface of the magnetic roller, and 50% of the peak intensity. Angular region with intensity less than Charges the surface of the image carrier while being positioned at a first position facing the most downstream end in the moving direction of the image carrier on the contact surface between the surface of the image carrier and the conductive magnetic particles. An image forming apparatus characterized by the above. 2. The magnetic roller is rotatably supported, the magnetic roller is rotationally driven during non-image formation, and the magnetic roller is positioned at the first position during image formation. The image forming apparatus according to item 1.