JP2001066852A - Electrostatic charging device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a charge defect of a body to be charged, as well as preventing an abnormal discharge by preventing a coarse section on a brush from being brought into contact with the body to be charged at the time of charging, in a electrostatic charging device provided with a magnetic brush charging member. SOLUTION: This electrostatic charging device provided with a magnetic particles carrier 2A being a charging member disposed rotationally, and a means 25 applying voltage to the magnetic particles carrier 2A, is composed so as to make the body to be charged 1 charged by letting the magnetic particles 23 stuck/held as the magnetic brush B in binding them with the magnetic force, and moreover the magnetic brush B held in contact with the charged body 1 by applying the voltage on the magnetic particles carrier 2A. In this case, the device is let the magnetic particles carrier 2A rotated before starting the charge on the charged body 1, the magnetic particles carrier 2A fixed during the charge of the charge on the charged body 1, and the position starting charge of the charged body 1 onward the charge nip width is made to be the charge area, and moreover the dense section on the magnetic brush B so as to come into contact with the charged body 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 provided with a contact-type charging member for charging an object to be charged such as an image carrier, and an image forming apparatus provided with the charging device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic or electrostatic recording type image forming apparatus, a non-contact type corona charging is used as a charging means for an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. The vessel was heavily used. This corona charger is
It is disposed in a non-contact manner with a member to be charged such as an image carrier,
When a high voltage (for example, a direct current voltage of 5 to 8 kV) is applied to a discharge wire (metal wire), a strong electric field is generated around the discharge wire to cause gas discharge, and a charge ion generated at that time is generated. By exposing the surface of the object to be charged, the charged ions are adsorbed on the surface of the object to be charged, and the object to be charged is charged.

[0003] The corona charger used in such a conventional image forming apparatus can be charged without mechanically contacting the image carrier, and thus has the advantage of not damaging the image carrier during charging. Have. However, this corona charger has a risk of electric shock or leakage due to the use of high voltage, and ozone generated by gas discharge is harmful to the human body, shortening the life of the image carrier. Had disadvantages. In addition, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity, and furthermore, the corona charger generates noise due to high voltage. This is a major drawback when an electrostatic recording type image forming apparatus is used. Many of the drawbacks of such a corona charger are due to the fact that charging involves gas discharge.

In recent years, as ecology has attracted attention,
Because of its advantages such as low ozone and low power, contact-type contact charging devices have been put into practical use. Examples of the contact charging member used in the contact charging device include a rubber roller, a fixed brush, a roll-shaped fur brush, a magnetic brush, and the like.
There are various members. A roller charging type contact charging device using a roller as a contact charging member is disclosed in, for example,
As disclosed in Japanese Patent Application Laid-Open No. 149669/1992, it has the advantage of good charge stability, but since the roller is pressed against the image carrier and rotated, toner and paper dust remaining on the image carrier are reduced. It has been pointed out that the toner adheres to the roller and deteriorates charging characteristics.

A contact charging device which is less affected by residual toner and paper dust on the image carrier is disclosed in JP-A-6-3927 and JP-A-5-66150. Note that a method has been proposed in which a voltage is applied to a conductive contact charging member to charge a member to be charged such as an image carrier. It is considered that the charging of the member to be charged in this method is due to the discharge in the minute gap between the contact charging member and the member to be charged and the charge injection. As the contact charging member of this type, a magnetic brush charging member or a fur brush charging member is preferably used from the viewpoint of charging of the member to be charged and stability of contact between the contact charging member and the member to be charged.

In this type of contact charging device, it is preferable that the resistance of the contact charging member be lower so as not to hinder the transfer of charge between the contact charging member and the member to be charged. If there is a low-pressure defect such as a scratch or a pinhole on the body, if the resistance of the contact charging member is low, leakage occurs, and the power supply voltage drops, resulting in poor charging. It is necessary to maintain the above resistance. Further, by providing a linear velocity difference between the contact charging member and the image carrier as the member to be charged, residual toner and paper dust on the image carrier are prevented from staying at the same place on the image carrier. , These effects can be minimized.

As described above, the contact charging member used in the contact charging system can be in close contact with the member to be charged.
From the viewpoint that a member capable of having a peripheral speed difference with respect to the member to be charged is preferable, a magnetically constrained charging member (eg, a magnetic brush charging member) such as a ferromagnetic material is suitable. JP-A-59-133569, JP-A-4-21
873 and JP-A-4-116674). Further, in comparison between the magnetic brush charging member and the fur brush charging member, the charging characteristics of the fur brush charging member are deteriorated when the hair falls due to long-term use or long-term storage, whereas the magnetic brush charging member is deteriorated. Such a member does not cause such a phenomenon and can perform stable charging, and a magnetic brush charging member is optimal.

The magnetic brush charging member is a member in which magnetic particles are restrained by a magnetic force on a magnetic particle carrier and adhered and held as a magnetic brush.
A voltage is applied to charge the member to be charged. More specifically, the magnetic brush charging member includes: A magnetic particle carrier has a rotatable sleeve, and a fixed magnet roll (magnet) disposed in the sleeve
A type in which the magnetic particles are constrained on the outer surface of the sleeve by the magnetic force and are attached and held as a magnetic brush (referred to as a sleeve type); There is a type in which the magnetic particle carrier is a rotatable magnet roll, in which magnetic particles are directly restrained on the outer surface of the magnet roll and adhered and held as a magnetic brush (referred to as a magnetic roller type).

FIG. 6 is a view showing a configuration model of a contact charging device having the above-mentioned sleeve type magnetic brush charging member.
The sleeve type magnetic brush charging member 12A is a rotatable non-magnetic conductive sleeve such as aluminum (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) 21.
In the sleeve 21, a magnet roll 22 as a magnetic field generating means is inserted and arranged. This magnet roll 22 has a plurality of magnetic poles alternately arranged in the circumferential direction.
The sleeve 21 and the magnet roll 22 constitute a sleeve type magnetic brush charging member 12A as a magnetic particle carrier having a magnetized portion magnetized so as to be a pole and an S pole. The magnet roll 22 is a non-rotating fixed member,
The sleeve 21 is concentrically rotated around the outer periphery of the magnet roll 22 at a predetermined peripheral speed by a driving mechanism (not shown) in a clockwise direction b as indicated by an arrow. The conductive magnetic particles 23 (hereinafter, referred to as carriers) are adhered and held as magnetic brushes (conductive magnetic brushes) B on the outer peripheral surface of the sleeve 21 by the magnetic force of the magnet roll 22 in the sleeve 21. That is, the carrier 23 is the magnet roll 22
Magnetic spikes are formed on the outer peripheral surface of the sleeve 21 by the constrained by the magnetic force, and these are gathered to form a brush shape. Further, the charging device is provided with a charging bias application power supply 25, and when the charging target 1 is charged, the sleeve 21 is charged.
Is applied with a charging bias.

The member 1 to be charged is, for example, a drum-type electrophotographic photosensitive member which is rotationally driven by a driving mechanism (not shown) at a predetermined process speed in a clockwise direction a shown by an arrow. The magnetic brush charging member 12A brings the magnetic brush B into contact with the surface of the member 1 to form a contact nip portion (referred to as a charging nip portion) D between the magnetic brush B on the magnetic brush charging member 12A and the member 1 to be charged. It is arranged as it is formed. Magnetic brush B is
As the sleeve 21 rotates, it is rotated and conveyed in the same direction as the rotation direction of the sleeve 21, rubs the surface of the charged body 1 in the charging nip D, and applies the charging bias applied to the sleeve 21 from the charging bias applying power supply 25. Thus, the surface of the member to be charged 1 is charged by a contact method. In the charging nip D, only the member to be charged 1 is rotated while the sleeve 21 and the magnetic brush B are stationary. Further, the sleeve 21 has a carrying function and a carrying function of the magnetic brush B, and a charging bias applying electrode function.

FIG. 7 is a view showing a model of a contact charging device having the above-described magnetic roller type magnetic brush charging member. The magnetic roller type magnetic brush charging member 12B serving as a magnetic particle carrier includes a magnet roll 22 and a conductive layer 26.
And a carrier 23, and the magnet roll 22 is rotationally driven at a predetermined peripheral speed by a driving mechanism (not shown) in a clockwise direction b as indicated by an arrow around a center metal core 24 which also serves as a drive and power supply. The outer periphery of the magnet roll 22 is covered with a conductive layer 26 as a charging bias applying electrode (power supply surface). On the outer peripheral surface of the conductive layer 26, the carrier 23 is restrained by the magnetic force of the magnet roll 22 and the magnetic brush B
Is held as adhered. The magnetic brush B is rotated and conveyed in the same direction as the rotation of the magnet roll 22 with the rotation of the magnet roll 22, rubs the surface of the charged body 1 at the charging nip D, and
The surface of the member to be charged 1 is contact-charged by the charging bias applied from 5 to the central core 24 of the magnet roll 22. The conductive layer 26 provided on the outer peripheral surface of the magnet roll 22 serves to stably supply the charging bias to the magnetic brush B uniformly.

[0012]

In the contact charging device having the magnetic brush charging member 12A (or 12B), the surface of the conductive sleeve 21 of the magnetic brush charging member 12A (or 12B) (or the conductive layer 26 of the magnet roll). The magnetic brush B was randomly formed on the surface of the magnetic brush B, and the height of the spikes and the distance between spikes of the magnetic brush B varied, resulting in a sparse portion of the magnetic brush B. For this reason, in the contact charging system using the magnetic brush B, if there is a sparse portion in the magnetic brush B in the charging nip portion D where the magnetic brush B and the electrophotographic photosensitive member 1 as a member to be charged are in contact. ,
A portion where the carrier 23 does not contact the electrophotographic photosensitive member 1 is formed, and an uncharged area is generated on the electrophotographic photosensitive member 1. In the image forming apparatus, when an image is formed using the electrophotographic photosensitive member 1 in which such an uncharged area is generated, there is a problem that an abnormal image is generated in a final output image. The magnetic brush charging member 12A
An abnormal discharge (spark discharge) is generated from the surface of the conductive sleeve 21 (or the surface of the conductive layer 26 of the magnet roll) of (or 12B), and an image is formed using the electrophotographic photosensitive member 1 in the image forming apparatus. In such a case, there is a problem that an abnormal image is generated in the final output image.

The present invention has been made in view of the above circumstances, and prevents a sparse portion of a magnetic brush from coming into contact with a member to be charged at the time of charging, preventing charging failure of the member to be charged, and preventing abnormal discharge. An object of the present invention is to provide a charging device including a magnetic brush charging member that can prevent the occurrence of an abnormal image, and an image forming apparatus including the charging device and preventing occurrence of an abnormal image.

[0014]

Means for Solving the Problems As means for solving the above problems, the invention according to claim 1 is a means for rotating a magnetic particle carrier, and means for applying a voltage to the magnetic particle carrier. The magnetic particles are bound to the magnetic particle carrier by a magnetic force and adhered and held as a magnetic brush, the magnetic brush is brought into contact with a member to be charged, and a voltage is applied to the magnetic particle carrier to apply a voltage to the member to be charged. A charging device for charging
Rotate the magnetic particle carrier before the charging of the object to be charged, fix the magnetic particle carrier during the charging of the object to be charged, and charge the nip width after the charging nip width from the charging start position of the object to be charged. In addition to a charging area, a dense portion of the magnetic brush is brought into contact with the member to be charged.

According to a second aspect of the present invention, in the charging device according to the first aspect, the magnetic particle carrier has one or more magnetic poles, and the magnetic particle carrier has a portion facing the object to be charged. Is positioned upstream of the facing portion with respect to the moving direction of the magnetic particles. According to a third aspect of the present invention, in the charging device according to the first or second aspect, the magnetic particles have a volume resistivity of 10 ³ Ωcm or more.

According to a fourth aspect of the present invention, in the charging device according to the first, second or third aspect, the magnetic particle carrier is provided in a rotatable cylindrical sleeve, and is disposed in the sleeve. The magnetic roller has one or more fixed magnetic poles, and magnetic particles are constrained to the outer peripheral surface of the sleeve by the magnetic force of the magnet roll and are attached and held as a magnetic brush. According to a fifth aspect of the present invention, in the charging device according to the first, second, or third aspect, the magnetic particle carrier is a rotatable magnet roll having one or more magnetic poles. The magnetic particles are directly restrained by the magnetic force on the surface and adhered and held as a magnetic brush.

According to a sixth aspect of the present invention, there is provided a method of charging an image carrier as a member to be charged by charging means, a step of forming a latent image on the charged image carrier, and a step of developing the latent image with a developer. 6. The image forming apparatus according to claim 1, wherein the image forming apparatus performs image formation by an image forming process including a visualizing step and a step of transferring the visible image to a transfer material. 7. And a charging device.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the structure, operation and operation of the present invention will be described in detail with reference to the drawings. Here, the present invention will be described with reference to an electrophotographic copying machine (hereinafter, referred to as one of image forming apparatuses).
An embodiment applied to a copier will be described.

FIG. 3 is a view showing one embodiment of the present invention, and is a schematic configuration diagram of an image forming unit which is a main part of a copying machine. First, the schematic configuration and operation of the copying machine according to the present embodiment will be described with reference to FIG. In FIG. 3, an electrophotographic photosensitive member as an image carrier (hereinafter, referred to as a photosensitive member)
1, a contact charging device 2 having a magnetic particle carrier composed of a magnetic brush charging member 2A as a contact charging member, an image exposure system 7, a developing device 3 having a developing roller 3a,
A transfer device having a transfer roller 4, a separation charger 8, a pre-cleaning charger 9, a cleaning device 5 having a cleaning roller 6, and a discharging lamp 10 as a discharging unit are arranged. A fixing device 11 is provided downstream of the separation charger 8 in the transfer material P transport direction. Note that the back surface of the photoreceptor 1 is grounded via a metal core or the like.

The photosensitive member 1 serving as an image carrier is a drum-shaped organic photosensitive member (OPC) having an organic photoconductive layer and having a charge injection function on its surface, and is rotated in the direction of an arrow by a driving mechanism (not shown). Driven. The contact charging device 2 is of a sleeve type in which a sleeve 21 of a magnetic particle carrier 2A as shown in FIG. 1, for example, is rotatable, and the magnetic particle carrier 2A is the same as that shown in FIG. And charges the peripheral surface of the photoreceptor 1 uniformly to a predetermined polarity and potential by contact charging using the magnetic brush B. 1 are the same components as those in FIG. 6, but the outer peripheral surface of the sleeve 21 of the magnetic brush charging member 2A has an uneven shape so as to reduce the sparse portion of the magnetic brush. . Further, a magnet roll 22 disposed and fixed inside the sleeve 21.
A plurality of magnetic poles (N-pole, S-pole) are magnetized on its peripheral surface, and the magnetic poles are arranged on the side of the magnetic brush charging member 2A facing the photoconductor 1 as shown in FIG. The magnetic pole (N pole in the figure) is located upstream of the facing portion with respect to the moving direction of the carrier 23 as the magnetic particles. The reason will be described later.

The developing roller 3a of the developing device 3 is composed of a magnet roller, is rotated by a driving mechanism (not shown), and carries a two-component developer composed of a toner and a magnetic carrier on the surface thereof. Further, a developing bias is applied to the developing roller 3a by a power supply (not shown), and the electrostatic latent image on the photoreceptor 1 is formed by a two-component developer carried and conveyed by the developing roller 3a. Develop and visualize.

Next, an image forming operation by the copying machine having the configuration shown in FIG. 3 will be described. In the present embodiment, a series of image forming processes is performed by a negative / positive process. As shown in FIG. 1, a charging bias is applied to the magnetic brush charging member 2A of the charging device 2 from a charging bias application power supply 25, and the outer peripheral surface of the photoconductor 1 is reduced to approximately -700 V by charge injection charging and discharging. Likewise charged. The charged surface of the uniformly charged photoreceptor 1 is exposed to light irradiated by the image exposure system 7 to form an electrostatic latent image (the exposed portion potential is -10).
0V) is formed. The image exposure system 7 includes, for example, a laser optical system using a semiconductor laser, emits a laser beam modulated by an image signal from the semiconductor laser, and rotates the laser beam at high speed. Deflected by a mirror (polygon mirror), the deflected light beam is condensed on the surface of the photoconductor 1 by a scanning image forming lens or the like, and the surface of the photoconductor 1 is scanned in a direction orthogonal to the rotation direction of the photoconductor 1. An electrostatic latent image is formed by optical writing. At this time, since the photoconductor 1 rotates at an extremely low speed as compared with the scanning speed of the laser beam from the image exposure system 7, the laser beam from the image exposure system 7 can scan the entire surface of the photoconductor 1.

Next, the electrostatic latent image on the photosensitive member 1 is developed with the toner of the two-component developer carried by the developing roller 3a of the developing device 3 (the voltage applied to the developing roller 3a is, for example, -550 V). An image is formed. On the other hand, a transfer material (for example, recording paper) P is fed from a paper supply device (not shown) to a pair of upper and lower registration rollers (not shown). Is fed between the photoreceptor 1 and the transfer roller 4,
The toner image on the photoconductor 1 is transferred to the transfer material P. At this time, for example, +95
A transfer bias of 0 V is applied. Then, the transfer material P
Is removed from the photoreceptor 1 by the separation charger 8, the toner image is fixed by the fixing device 11, and is discharged as a copy to a discharge tray (not shown).

In the above developing step, the developing roller 3a
Almost all of the toner adhered to the photoreceptor 1 is negatively charged. However, since a positive charge is supplied by the transfer roller 4 in the next transfer step, one of the remaining toner on the photoreceptor 1 remains untransferred. The portion is charged with charge from the transfer roller 4 and becomes a toner of positive polarity. The positive polarity toner on the photoconductor 1 is supplied with a negative corona by the pre-cleaning charger 9, is recharged to a negative polarity, and is removed by the cleaning roller 6 of the cleaning device 5. As described above, the charge in the toner needs to be able to quickly change its charging behavior by an external potential difference and a charger.The response speed of the charging behavior to the external electric field of the toner is required to improve the speed of the entire process and the stability of an image. is necessary.

An image is formed on the transfer material P by the above-described image forming operation. In the copying machine having the configuration shown in FIG. 1, when one sheet of image is formed, the cleaning device 5 discharges toner. Mode and the cleaning roller 6
At least one of the rotation direction and the speed is switched by a control unit (not shown), and at the same time, a negative bias is applied from a power supply (not shown) to discharge the negative toner collected from the photoconductor 1 to the photoconductor 1. The toner discharged to the photoconductor 1 is conveyed to a developing area between the photoconductor 1 and the developing roller 3a as the photoconductor 1 rotates. A positive bias is applied to the developing roller 3a from a power source (not shown) when the toner on the photoconductor 1 is collected. In the developing area, the magnetic brush of the developing roller 3a applies an impact force to the toner on the photoconductor 1, and the developing roller 3a
When a positive bias is applied to the toner, the toner is electrostatically attracted to the magnetic brush of the developing roller 3a and collected. Through the above operation, the toner can be recycled.

This image forming apparatus is characterized in that the developing device 3 and the cleaning device 5 operate in two modes, respectively, as described above, which has a great advantage that a complicated mechanism is not required. In addition, there is a problem that the interval between image formations becomes longer by completely separating the operations of image formation and toner collection. Therefore, the mode of the cleaning roller 6 is switched before the area corresponding to the rear end of the toner image formed on the photoconductor 1 passes through the cleaning roller 6.

In this image forming apparatus, the image area on the photosensitive member 1 and the untransferred toner discharge area pass through each unit. In the contact area between the photosensitive member 1 and the cleaning roller 6, the cleaning roller 6 The bias voltage to be applied and the rotation of the cleaning roller 6 are set so that the toner is initially removed from the photoconductor 1 and collected by the cleaning roller 6, but the toner is discharged while passing through the image area on the photoconductor 1. It switches to the condition to do. The remaining transfer toner on the remaining portion of the photoreceptor 1 is charged to the negative polarity by the pre-cleaning charger 9, but passes through the cleaning roller 6 to which the negative bias is applied without being collected. At this time, the cleaning roller 6
Is transferred to the photoconductor 1.

At the same time as or immediately after the rear end of the image area on the photosensitive member 1 passes through the cleaning roller 6, the discharge of the toner from the cleaning roller 6 to the photosensitive member 1 ends.
When the next image is continuously formed, the magnetic brush charging member 2A is moved by a contact / separation mechanism (not shown) after the rear end of the transfer residual toner discharge area on the photoreceptor 1 passes below the magnetic brush charging member 2A. Image formation is repeatedly performed by the above-described image forming process in contact with the photoconductor 1.

Here, the magnetic brush charging member 2A and the transfer roller 4 come into contact with the photosensitive member 1 by a contact / separation mechanism (not shown) to perform their respective functions. However, there is a problem that the toner adheres to the photosensitive member 1 and becomes dirty. is there. As a countermeasure,
It is desirable to execute a process of returning the adhered toner to the photoconductor 1 by strongly contacting the photoconductor 1 to which a bias has been applied after the completion of image formation or after each predetermined number of image formations. The base of the sleeve 21 of the magnetic brush charging member 2A is a metal hollow cylinder having a circular cross section, such as aluminum or stainless steel (SUS).
Is provided.

Next, the contact charging device 2 used in this embodiment
The magnetic brush charging member 2A as the charging member will be described in detail. FIG. 1 shows an example of the magnetic brush charging member 2A of the present embodiment. The basic configuration of the magnetic brush charging member 2A is substantially the same as that of the magnetic brush charging member 12A shown in FIG. The same components are denoted by the same reference numerals. That is, the magnetic brush charging member 2A is a nonmagnetic conductive sleeve 21 having a carrier holding the carrier 23 as conductive magnetic particles constituting the magnetic brush B, and is disposed and fixed inside the sleeve 21. The carrier 23 is transferred to the conductive sleeve 2 by the magnetic force of the magnet roll 22 as the magnetic field generating means.
The magnetic brush B is attached to and held on the outer peripheral surface of the magnetic brush B. The magnet roll 22 is a non-rotating fixed member, and has a magnetized portion in which a plurality of magnetic poles are alternately arranged in the circumferential direction so as to be N poles and S poles. The magnet roll 22 is fixed to a non-rotating shaft 24, but the sleeve 21 is rotatably provided with respect to the shaft 24 via a bearing.
2 is concentrically driven to rotate in the direction of arrow b. A charging bias is applied to the sleeve 21 by a charging bias application power supply 25.

Next, the carrier (magnetic particles) 23 will be described. As the carrier 23 constituting the magnetic brush B, it is preferable to use spherical particles in order to reduce damage to the surface of the photoreceptor 1 which is a member to be charged.
The average particle size of No. 3 is preferably 150 μm or less. However, if the average particle size of the carrier 23 is too large, the radius of curvature is large even if the carrier 23 is arranged in the closest density, and the area not in contact with the photoreceptor 1 increases, causing uneven charging.
Conversely, if the average particle size is too small, the particles tend to move when an AC voltage is applied, exceeding the magnetic force between the particles, causing the particles to scatter and causing the carrier to adhere to the photoreceptor 1. Therefore, the average particle size of the carrier 23 is 30 μm
As described above, the thickness is preferably 100 μm or less. further,
Regarding the volume resistivity of the carrier 23, if the volume resistivity is too low, charge is injected into the carrier 23 when a charging bias is applied, causing the carrier to adhere to the surface of the photoconductor 1 or insulating the photoconductor 1 by the charging bias voltage. In order to cause destruction, the carrier 23 has a volume resistivity of 10 ³ Ωcm
Use the above.

In the contact charging device having the conventional magnetic brush charging member 12A shown in FIG. 6, the magnetic brush B is formed at random on the surface of the conductive sleeve 21 of the magnetic brush charging member 12A. The height of the ears and the distance between the ears varied, resulting in a sparse portion of the magnetic brush B. For this reason, in the contact charging method using the magnetic brush B, if there is a sparse part of the magnetic brush B in the charging nip portion D where the magnetic brush B and the photoreceptor 1 as a member to be charged are in contact, Carrier 23 on body 1
However, a non-contact portion is formed, and an uncharged area is generated on the photoconductor 1. Then, in the image forming apparatus, when an image is formed using the photoconductor 1 having such an uncharged area, an abnormal image is generated in a final output image. Further, when an abnormal discharge (spark discharge) is generated from the surface of the conductive sleeve 21 of the magnetic brush charging member 12A and an image is formed using the photoconductor 1 in the image forming apparatus, a final output image is formed. There is a problem that an abnormal image is generated.

In order to find out the cause of the abnormal discharge, the inventors of the present invention used a magnetic brush B formed on the surface of the conductive sleeve 21 in the conventional charging device having the magnetic brush charging member 12A shown in FIG. It was found that when a portion where the magnetic brush B became sparse was generated, discharge was likely to occur. In addition, when the conductive sleeve 21 was rotated, it was observed that the magnetic brush B moved with a change in the magnetic force distribution, and it was found that the magnetic brush B was likely to be sparse. Further, it was found that abnormal discharge easily occurred immediately after the application of the charging bias.

Here, the cause of the abnormal discharge will be described with reference to the model of the magnetic brush B shown in FIG. FIG. 4 shows three ears of the carrier 23 as an example. In FIG. 4, the upper boundary is the surface of the conductive sleeve 21, and the lower boundary is the surface of the photoconductor 1. Carrier 23
The three ears are each formed in a conical shape, and the portion indicated by A in the figure is a sparse portion of the magnetic brush B. At the tip of the short ear E in the sparse portion A, the electric field intensity becomes very strong, and abnormal discharge occurs.

Then, the present inventors calculated the electric field strength at the tip of the short ear E by simulation using the model shown in FIG. The results are shown in the graph of FIG. In FIG. 5, the vertical axis indicates the electric field intensity, and the horizontal axis indicates the inter-spike distance x. According to the graph of FIG. 5, the electric field strength of the electric discharge starting electric field is 5 × 10 ⁶ V / m.
At this time, it was found that the discharge was started when the inter-spike distance x exceeded 200 μm. In this simulation, 1400 V was applied to the sleeve 21, the back surface of the photoconductor 1 was grounded, and the average particle size of the carrier 23 was 50 μm.
m, and the volume resistivity was calculated as 10 ⁵ Ωcm.

The magnetic brush B on the sleeve 21
Observation of the formation process revealed that the magnetic brush B was formed along the lines of magnetic force. That is, since the magnetic field lines are directed to the normal direction right above the magnetic poles, the magnetic brush B stands in the normal direction directly above the magnetic poles, but the magnetic field lines are directed between the magnetic poles along the circumferential surface of the sleeve. Also, the magnetic brush B also lies down along the line of magnetic force (along the peripheral surface of the sleeve). Further, it was also found that the magnetic brush lines are likely to be sparse just above the magnetic poles because the magnetic lines of force directly above the magnetic poles are directed in the normal direction, but the magnetic lines of force on both sides are directed in opposite directions. Therefore, as shown in FIG. 6, the magnetic poles of the magnet roll 22 of the magnetic brush charging member 12A (N in the figure)
When the pole is located directly above the opposing portion (charging nip portion D) of the photoconductor 1, the sparse portion of the magnetic brush B is located at the charging nip portion D, and the above-described abnormal discharge may occur. There is.

From the above results, in this embodiment,
As shown in FIG. 1, carriers 23 which are magnetic particles are provided on the outer peripheral surface of the rotatable sleeve 21 of the magnetic brush charging member 2A.
Is constrained by the magnetic force of the magnet roll 22 and is adhered and held as a magnetic brush B. The magnetic brush B is brought into contact with the photoreceptor 1 which is a member to be charged, and a voltage is applied to the sleeve 21 to charge the photoreceptor 1. In the charging device 2, the sleeve 21 is rotated before the charging of the photoconductor 1 is started, and the sleeve 21 is fixed while the photoconductor 1 is being charged. At the same time, the position of the magnetic pole is slightly shifted from the opposing portion of the photoconductor and the sleeve, and the dense portion of the magnetic brush B is brought into contact with the photoconductor 1. More specifically, of the plurality of magnetic poles of the magnet roll 22 in the sleeve 21, the magnetic pole (N pole in the figure) located on the side (charging nip portion D) of the magnetic brush charging member 2A facing the photoconductor 1 However, the magnetic brush B is fixed to the photosensitive member 1 so as to be shifted with respect to the moving direction of the carrier 23 (the direction of the arrow b in the drawing) so as to be located upstream of the opposing portion (charging nip portion D). On the other hand, it is configured to make contact in a relatively dense part in the state of lying. With such a configuration, occurrence of abnormal discharge can be prevented, and the problem of poor charging of the photoconductor 1 due to occurrence of a sparse portion of the magnetic brush B as described above can be solved.

Although FIG. 1 shows an example of the magnetic brush charging member 2A having a configuration using a rotatable conductive sleeve 21, the carrier is directly mounted on a rotatable magnet roll 22 as shown in FIG. In the case of the magnetic brush charging member 2B having the configuration in which the magnetic brush B is formed by adhering and holding the magnetic roller 23, the magnet roll 22 is rotated before the charging of the photoconductor 1 is started, and the magnetic roll 22 is rotated while the photoconductor 1 is being charged. Is fixed, and the charging area from the charging start position of the photoconductor 1 to the charging nip width is defined as the charging area. At this time, of the plurality of magnetic poles of the magnet roll 22, the side facing the photoconductor 1 (charging nip D) The magnetic pole (N pole in the figure) located at
The magnetic brush B is fixed to the photosensitive member 1 by displacing and fixing it so as to be located on the upstream side of the opposing portion (charging nip portion D) with respect to the moving direction (the direction of the arrow b in the drawing).
, It can be configured to make contact with a relatively dense part in a lying state, it is possible to prevent the occurrence of abnormal discharge in the same manner as described above, 1 can be solved.

(Examples) Next, the present invention will be described specifically with reference to examples, but the present invention is not limited to the following examples. The charging device 2 has a configuration using a sleeve type magnetic brush charging member 2A using the conductive sleeve shown in FIG.
2, the magnetic pole (N pole in the figure) located on the side of the magnetic brush charging member 2A facing the photosensitive member 1 (charging nip D) is in the moving direction of the carrier 23 (arrow in the figure). (direction b) with respect to the magnetic pole (N pole) of the magnet roll 22 and the normal direction of the photoreceptor 1. Is set to θ = + 15 ° (+ 10 ° in the moving direction of the carrier 23 with respect to the facing portion (charging nip portion D)).
And). A Ricoh copier Imagio5 equipped with an image forming unit having the configuration shown in FIG.
An image was formed using a 30-model modified machine and evaluated. At this time, the conductive sleeve 21 is rotated before the charging of the photoconductor 1 so that a new carrier 23 comes to the charging nip D,
Further, during charging of the photoreceptor 1, the conductive sleeve 21 is fixed without rotating, and the charging bias applying power supply 25 controls the conductive sleeve 21 to -9.
After applying a charging bias in which a DC voltage of 00 V is superimposed with an AC voltage having a peak-to-peak voltage of 1000 V and a frequency of 5 kHz, charging is performed, development is performed with a toner having a positive polarity without performing exposure, and image formation is performed. went. As a result, a good image was obtained except for the width of the charging nip D from the charging start position.

Reference Example 1 Next, as Reference Example 1, in the above embodiment, the angle θ between the magnetic pole (N pole) of the magnet roll 22 and the normal direction of the photoconductor 1 is θ = 0 ° (the magnetic pole is When an image was formed with the same configuration as that of the example except that the position was opposite to the photoconductor 1 (the configuration in FIG. 6), white spots occurred in the output image at this time.

Reference Example 2 Next, as Reference Example 2, in the above embodiment, the angle θ between the magnetic pole (N pole) of the magnet roll 22 and the normal direction of the photoconductor 1 is θ = −15 ° (magnetic pole). Was formed downstream of the opposing portion with respect to the moving direction of the carrier), and an image was formed in the same configuration as in the example. However, carrier adhesion was confirmed.

Reference Example 3 Next, as Reference Example 3, an image was formed in the same manner as in the above embodiment except that the photosensitive member 1 was charged while the conductive sleeve 21 was rotated. However, white spots have occurred in the output image at this time, and in particular, many white spots were observed at the leading end of the image.

As is clear from the results of the above embodiment and Reference Examples 1 to 3, according to the configuration shown in the embodiment, the magnetic brush B contacts the photosensitive member 1 while lying down, and the magnetic brush B Since an area where B does not become sparse (a relatively dense area) is charged by being brought into contact with the photoreceptor 1, occurrence of abnormal discharge and poor charging can be prevented. Further, the position (magnetic pole) where the magnetic force is strong is upstream of the opposing portion (charging nip portion D) with respect to the moving direction of the carrier (magnetic particles) 23 (photosensitive member 1).
(The downstream side with respect to the rotation direction of the photoconductor), the carrier adhering to the photoreceptor can be collected by the magnetic force, and the carrier adhesion can be prevented.

In the above embodiment, the sleeve type magnetic brush charging member 2A using the rotatable conductive sleeve 21 having the structure shown in FIG. 1 as the magnetic brush charging member.
However, even when a magnetic roller type magnetic brush charging member 2B having a configuration in which a carrier is directly adhered to and held by the rotatable magnet roll 22 having the configuration shown in FIG. Among the plurality of magnetic poles 22, the magnetic pole (N pole in the figure) located on the side facing the photosensitive member 1 (charging nip part D) is positioned with respect to the moving direction of the carrier 23 (the direction of the arrow b in the figure). By displacing and fixing it so as to be located on the upstream side of the opposing portion (charging nip portion D), the same result as in the above example was obtained.
FIG. 3 shows an example of the image forming apparatus according to the present invention.
In the image forming unit having the above structure, the magnetic brush charging device having the structure shown in FIG. 1 or FIG. 2 is used as the charging device 2. However, the photoreceptor 1 to be charged is not limited to a drum shape but a belt shape. The transfer device is not limited to the transfer roller, and may be a transfer belt or a transfer charger. Further, the configuration of the other developing device 3 and cleaning device 5 is not limited to the illustrated one, and various configurations can be applied.

[0045]

As described above, according to the first aspect of the present invention, there is provided a magnetic particle carrier rotatably provided, and means for applying a voltage to the magnetic particle carrier. In a charging device, the magnetic particles are fixed to the body by magnetic force and adhered and held as a magnetic brush, the magnetic brush is brought into contact with a member to be charged, and a voltage is applied to the magnetic particle carrier to charge the member to be charged. Rotate the magnetic particle carrier before the charging of the object to be charged, fix the magnetic particle carrier during the charging of the object to be charged, and charge the nip width after the charging nip width from the charging start position of the object to be charged. The structure is such that a dense portion of the magnetic brush is brought into contact with the object to be charged, and abnormal discharge can be prevented. Charging problem It can be solved.

According to a second aspect of the present invention, in the charging device according to the first aspect, the magnetic particle carrier has one or more magnetic poles, and a portion of the magnetic particle carrier facing the charged object. The magnetic pole located on the side is configured to be located on the upstream side of the opposing portion with respect to the moving direction of the magnetic particles, so that the magnetic brush contacts the member to be charged while lying down,
And the area where the magnetic brush does not become sparse (relatively dense area)
Can be brought into contact with the member to be charged, and the occurrence of abnormal discharge and poor charging can be prevented. In addition, since the position (magnetic pole) where the magnetic force is strong is located on the upstream side of the opposing portion with respect to the moving direction of the magnetic particles, it is possible to collect the magnetic particles adhering to the member to be charged, Adhesion can be prevented. According to the third aspect of the present invention, in the charging device according to the first or second aspect, the volume resistivity of the magnetic particles is not less than 10 ³ Ωcm. Of the magnetic particles attached to the member to be charged due to the injection of the electric charge into the member, and dielectric breakdown of the member to be charged due to the charging bias voltage can be prevented.

According to a fourth aspect of the present invention, in the charging device according to the first, second, or third aspect, the magnetic particle carrier is provided with a rotatable cylindrical sleeve, and is disposed in the sleeve. A magnetic roller having one or more magnetic poles fixed and fixed, wherein the magnetic force of the magnet roll restrains the magnetic particles on the outer peripheral surface of the sleeve and holds the magnetic particles as a magnetic brush. The magnetic particles are constrained to the outer peripheral surface of the sleeve by the magnetic force of the fixed magnet roll disposed on the sleeve and adhered and held as a magnetic brush.The dense portion of the magnetic brush is brought into contact with the member to be charged, and a voltage is applied to the sleeve. Therefore, it is possible to prevent the occurrence of abnormal discharge and poor charging.

According to a fifth aspect of the present invention, in the charging device according to the first, second or third aspect, the magnetic particle carrier is a rotatable magnet roll having one or more magnetic poles. Magnetic particles are directly confined to the outer peripheral surface of the magnet roll by magnetic force and adhered and held as a magnetic brush. Magnetic particles are directly constrained on the outer peripheral surface of the magnet roll and adhered and held as a magnetic brush. Since the dense portion of the magnetic brush is brought into contact with the member to be charged and a voltage is applied to the magnet roll to charge the member, the occurrence of abnormal discharge and poor charging can be prevented.

According to the sixth aspect of the present invention, the step of charging the image carrier as a member to be charged by the charging means, the step of forming a latent image on the charged image carrier, and the step of developing the latent image 6. An image forming apparatus which performs image formation by an image forming process including a step of visualizing with an agent and a step of transferring the visible image to a transfer material, wherein the charging means is any one of claims 1 to 5. With the configuration including the described charging device, it is possible to prevent the occurrence of abnormal discharge and charging failure during the charging process, and to provide an output image after development and transfer without any abnormal image such as white spots. Image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention, and is a diagram illustrating a configuration model of a charging device having a sleeve-type magnetic brush charging member.

FIG. 2 is a view showing another embodiment of the present invention, and is a view showing a configuration model of a charging device having a magnetic roller type magnetic brush charging member.

FIG. 3 is a view showing an embodiment of the present invention, and is a schematic configuration diagram of an image forming unit which is a main part of a copying machine.

FIG. 4 is a view showing a model of a magnetic brush (spike) formed on the surface of a conductive sleeve of a conventional magnetic brush charging member.

FIG. 5 is a diagram illustrating a result of calculating, by simulation, a relationship between a distance between spikes of the magnetic brush illustrated in FIG. 4 and an electric field intensity of a spike.

FIG. 6 is a view showing a configuration model of a charging device having a conventional sleeve-type magnetic brush charging member.

FIG. 7 is a view showing a configuration model of a charging device having a conventional magnetic roller type magnetic brush charging member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor (charged body) 2 Charging device 2A Sleeve type magnetic brush charging member 2B Magnetic roller type magnetic brush charging member 3 Developing device 3a Developing roller 4 Transfer roller 5 Cleaning device 6 Cleaning roller 7 Image exposure system 8 Separation charger 9 Cleaning Front charger 10 Static elimination lamp 11 Fixing device 21 Conductive sleeve 22 Magnet roll 23 Carrier (magnetic particles) 25 Charging bias application power supply 26 Conductive layer B Magnetic brush P Transfer material

Claims (6)

[Claims] 1. A magnetic particle carrier rotatably provided,
A means for applying a voltage to the magnetic particle carrier, wherein the magnetic particles are bound to the magnetic particle carrier by a magnetic force and adhered and held as a magnetic brush, and the magnetic brush is brought into contact with a member to be charged; In a charging device for applying a voltage to the carrier to charge the member to be charged, the magnetic particle carrier is rotated before the charging of the member to be charged is started, and the magnetic particle carrier is charged during charging of the member to be charged. A charging device, wherein a charging area from a charging start position of the charging target to a charging nip width and beyond is set as a charging area, and a dense portion of the magnetic brush is brought into contact with the charging target. 2. The charging device according to claim 1, wherein the magnetic particle carrier has one or more magnetic poles, and a magnetic pole located on a side of the magnetic particle carrier opposite to the member to be charged is: A charging device, wherein the charging device is located upstream of the facing portion with respect to a moving direction of the magnetic particles. 3. The charging device according to claim 1, wherein the magnetic particles have a volume resistivity of 10 ³ Ωcm or more. 4. The charging device according to claim 1, wherein the magnetic particle carrier comprises a rotatable cylindrical sleeve and one or more magnetic poles disposed and fixed in the sleeve. A charging device, comprising: a magnetic roll having magnetic particles constrained on the outer peripheral surface of the sleeve by a magnetic force of the magnet roll and adhered and held as a magnetic brush. 5. The charging device according to claim 1, wherein said magnetic particle carrier is a rotatable magnet roll having one or more magnetic poles, and said magnetic particle carrier is directly magnetized on an outer peripheral surface of said magnet roll. A charging device, wherein the particles are bound by a magnetic force and adhered and held as a magnetic brush. 6. A step of charging an image carrier, which is a member to be charged, by a charging means; a step of forming a latent image on the charged image carrier; a step of visualizing the latent image with a developer; An image forming apparatus for forming an image by an image forming process including a step of transferring a visible image to a transfer material, comprising the charging device according to any one of claims 1 to 5 as the charging unit. An image forming apparatus comprising: