JP2000338748A - Electrifying device, electrifying member and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of nondense portion of a magnetic brush and to prevent failure in electrification of a body to be electrified, by rotating magnetic- particle carrier before start of electrification of the body, fixing the nonmagnetic- particle carrier during the electrification of the body, and by using as an electrifying area on and after a width of an electrifying nip from the position where the electrification of the body starts. SOLUTION: In order to form a magnetic brush B with a distance of 200 μm or less between naps onto a sleeve, irregularities are formed on the entire surface of the sleeve, and interspacing between the irregularities is 200 μm or less. Fresh carrier 4 approaches an electrifying nip D by rotating a conductive sleeve before start of electrification of an electrophotographic photoreceptor 6. Further, the electrophotographic photoreceptor 6 is electrified by applying an electrifying bias, in which an AC bias overlaps a DC bias, to a conductive sleeve from a power source without rotating the conductive sleeve during the electrification of the electrophotographic photoreceptor 6, and thereafter an image is formed. In the case, a width of the electrifying nip D is excluded from an electrifying area from the position where the electrification of the electrophotographic photoreceptor 6 starts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charging device, a charging member, and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic system or an electrostatic recording system, a non-contact system is used as a charging means for charging an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. Corona chargers were frequently used. The corona charger is disposed so as to be in non-contact with a member to be charged, and applies a high voltage (for example, 5 to 8 kV of direct current) to a discharge wire (metal wire) to apply a strong electric field around the discharge wire. The gas discharge is generated, and the surface of the charged object is exposed under the charged ions generated at that time, so that the charged ions are adsorbed on the surface of the charged object and the surface of the charged object is charged.

A corona charger used in such a conventional image forming apparatus can charge an object to be charged without mechanically contacting the image carrier, so that the image carrier may be damaged during charging. There is no advantage.
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.
This has the drawback of shortening the life of the image carrier.

Further, the charging potential of an object to be charged by a corona charger is unstable because it is strongly affected by temperature and humidity.
Further, the corona charger generates noise due to a high voltage, which is a major drawback when an image forming apparatus is used as a communication terminal or an information processing apparatus.

[0005] Many disadvantages of such corona dischargers are:
This is because charging of the member to be charged involves gas discharge.

In recent years, as ecology has attracted attention,
A contact-type contact charging device has been put to practical use because it has advantages such as low ozone and low power. As the contact charging member of the contact charging device, there are various members such as a rubber roller, a fixed brush, a roll-shaped fur brush, and an electric brush.

A roller charging type contact charging device using a roller as a contact charging member is disclosed in Japanese Patent Application Laid-Open No. 63-149669.
As described in Japanese Patent Application Laid-Open Publication No. H10-209, there is an advantage that the charging stability is good, but since the roller is pressed against the image carrier and rotated, the toner and paper dust remaining on the image carrier are removed from the roller. It has been pointed out that the charging characteristics are deteriorated by adhering to the surface.

Accordingly, Japanese Patent Application Laid-Open No. 6-392 discloses a contact charging device which is less affected by residual toner and paper dust on an image carrier.
No. 7, JP-A-5-66150, etc., a method of applying a voltage to a conductive contact charging member to charge a member to be charged has been proposed.

It is considered that the charging of the member to be charged in this method is caused by discharge in a minute gap between the contact charging member and the member to be charged and 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. When there is a low-pressure defect such as a scratch or a pinhole, if the resistance of the contact charging member is low, a leak occurs, and the power supply voltage drops to cause charging failure. It is necessary to maintain the resistance of 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 do not stay in the same place of the image carrier, These effects can be minimized.

After all, as a contact charging member of this type,
From the viewpoint that a member capable of being in close contact with the member to be charged and having a peripheral speed difference with respect to the member to be charged is preferable,
A magnetically constrained charging member (magnetic brush charging member) such as a magnetic brush or a ferromagnetic material is suitable (JP-A-59-133).
569, JP-A-4-21873, JP-A-4-21873
-116674).

Further, in comparison between the magnetic brush charging member and the fur brush charging member, the fur brush charging member is deteriorated in chargeability when hair falls due to long-term use or long-term storage. Such a phenomenon does not occur in the magnetic brush charging member, and stable charging can be performed. Therefore, the 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. The magnetic brush is brought into contact with a member to be charged, and a voltage is applied. The object to be charged is charged. More specifically, the magnetic brush charging member comprises: 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 to the outer surface of the sleeve by the magnetic force and adhered and held as a magnetic brush (sleeve type); There is a rotatable magnet roll in which the magnetic particle carrier is rotatable, in which magnetic particles are directly constrained on the outer surface of the magnet roll and adhered and held as a magnetic brush (magnetic roller type).

FIG. 7 shows a structural model of a contact charging device having the above-mentioned sleeve type magnetic brush charging member. A sleeve type magnetic brush charging member 1 as a magnetic particle carrier has a rotatable non-magnetic conductive sleeve (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) 2 made of aluminum or the like. Is provided with a magnet roll 3 as a magnetic field generating means. This magnet roll 3 has a plurality of magnetic poles alternately N-pole and S-pole in the circumferential direction.
The magnetic particle carrier 1 has a magnetized portion magnetized so as to be a pole, and the sleeve 2 and the magnet roll 3 constitute the magnetic particle carrier 1.

The magnet roll 3 is a non-rotating fixed member, and the sleeve 2 is concentrically rotated around the outer periphery of the magnet roll 3 in a clockwise direction b by a driving mechanism (not shown) at a predetermined peripheral speed. The conductive magnetic particles 4 (hereinafter referred to as carriers) are provided on the outer peripheral surface of the sleeve 2.
The magnetic brush (conductive magnetic brush) B is adhered and held by being restrained by the magnetic force of the magnet roll 2 inside. The carrier 4 forms magnetic ears on the outer peripheral surface of the sleeve 2 due to the restraint by the magnetic force of the magnet roll 3, and these gather to form a brush. The charging bias application power supply 5 applies a charging bias to the sleeve 2.

The member 6 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 1 is in a state where the magnetic brush B is brought into contact with the surface of the charged object 6 to form a nip portion (charging nip) D between the magnetic brush B on the magnetic brush charging member 1 and the charged object 6. Be placed. The magnetic brush B is rotated and conveyed in the same direction as the rotation direction of the sleeve 2 with the rotation of the sleeve 2, rubs the surface of the charged body 6 at the charging nip D, and moves the magnetic brush B from the charging bias applying power source 5 to the sleeve 2. With the applied charging bias, the surface of the charged body 6 is charged by a contact method. In the charging nip D, only the member to be charged 6 is rotated while the sleeve 2 and the magnetic brush B are stationary. The sleeve 2 has a carrying function, a carrying function, and a charging bias applying function of the magnetic brush B.

FIG. 8 shows a structural model of a contact charging device having the above-mentioned magnetic roller type magnetic brush charging member. A magnetic roller type magnetic brush charging member 7 as a magnetic particle carrier is composed of a magnet roll 8 and a conductive layer 9, and the magnet roll 8 is illustrated in a clockwise direction b as indicated by an arrow with a center core 10 serving as both driving and power supply. It is rotationally driven at a predetermined peripheral speed by a drive mechanism that does not.

The outer periphery of the magnet roll 8 is covered with a conductive layer 9 as a charging bias application electrode (power supply surface). The carrier 4 is adhered and held as a magnetic brush B on the outer peripheral surface of the conductive layer 9 by the magnetic force of the magnet roll 8. The magnetic brush B is rotated and conveyed in the same direction as the rotation of the magnet roll 8 with the rotation of the magnet roll 8, rubs the surface of the charged body 6 in the charging nip D, and The surface of the member to be charged 6 is contact-charged by the charging bias applied to the center metal core 10 of the roll 8. The conductive layer 9 provided on the outer peripheral surface of the magnet roll 8 functions to stably supply the charging bias to the magnetic brush B uniformly.

[0019]

In the contact charging device having the above-described magnetic brush charging member, the magnetic brush charging member 1,
The magnetic brushes B are randomly formed on the surface of the magnetic brush B (the surface of the sleeve 2 and the conductive layer 9), and the height of the spikes of the magnetic brushes B and the distance between the spikes are varied. I was Therefore, if there is a sparse portion of the magnetic brush B in the charging nip D where the magnetic brush B and the electrophotographic photosensitive member 6 as a member to be charged are in contact, the carrier 4 does not contact the electrophotographic photosensitive member 6. A portion is formed, and an uncharged area is generated on the electrophotographic photosensitive member 6. Then, in the image forming apparatus, when an image is formed using the electrophotographic photosensitive member 6 in which such an uncharged area is generated, an abnormal image is generated in a final output image.

In addition, abnormal discharge (spark discharge) is generated from the surfaces of the magnetic brush charging members 1 and 7 (the surface of the sleeve 2 and the conductive layer 9), and the image formation is also performed using the electrophotographic photosensitive member 6 in the image forming apparatus. Is performed, an abnormal image is generated in the final output image.

According to the present invention, a charging device, a charging member and a charging member capable of preventing occurrence of sparse portions of a magnetic brush, preventing charging failure of a member to be charged, and preventing abnormal discharge. It is an object to provide an image forming apparatus.

[0022]

In order to achieve the above object, according to the first aspect of the present invention, magnetic particles are restrained by a magnetic force on a rotatable magnetic particle carrier and adhered and held as a magnetic brush. In a charging device for contacting a brush with a member to be charged and applying a voltage to the magnetic particle carrier to charge the member to be charged, the magnetic particle carrier is rotated before charging of the member to be charged is started. During the charging, the magnetic particle carrier is fixed, and a charging area from the charging start position of the charging target to the charging nip width and beyond is defined as a charging area.

According to a second aspect of the present invention, in the charging member of the first aspect, the charging member includes the magnetic particle carrier, and the surface of the magnetic particle carrier supporting the magnetic brush is provided with irregularities. Is not more than 200 μm.

According to a third aspect of the present invention, in the charging device of the first aspect, the charging member includes the magnetic particle carrier, and the surface of the magnetic particle carrier supporting the magnetic brush is provided with irregularities. Are a plurality of grooves extending in the axial direction of the magnetic particle carrier.

According to a fourth aspect of the present invention, in the charging member of the first aspect, the charging member includes the magnetic particle carrier, and the surface of the magnetic particle carrier supporting the magnetic brush is provided with irregularities. Are a plurality of grooves extending in the axial direction and the circumferential direction of the magnetic particle carrier.

According to a fifth aspect of the present invention, in the charging member of the charging device according to the first aspect, the magnetic particle carrier is provided, and a surface of the magnetic particle carrier supporting the magnetic brush is provided with irregularities. Are formed by sandblasting.

According to a sixth aspect of the present invention, there is provided the charging member of the charging device according to any one of the first to fifth aspects, further comprising the magnetic particle carrier, and a volume of the magnetic element held by the magnetic particle carrier. It is characterized in that the resistivity is 10 ³ Ωcm or more.

According to a seventh aspect of the present invention, in the charging member of the charging device according to any one of the first to sixth aspects, the charging member includes the magnetic particle carrier, and the magnetic particle carrier has a rotatable sleeve. The magnetic particles are fixed to the outer surface of the sleeve by the magnetic force of a fixed magnet roll provided in the sleeve, and are adhered and held as a magnetic brush.

According to an eighth aspect of the present invention, there is provided the charging member of the charging device according to any one of the first to sixth aspects, further comprising the magnetic particle carrier, wherein the magnetic particle carrier is rotatable. The magnetic roller is characterized in that magnetic particles are directly restrained on the outer surface of the magnet roll and adhered and held as a magnetic brush.

According to a ninth aspect of the present invention, there is provided an image forming apparatus for forming an image by an image forming process including a step of charging an image carrier by a charging unit, wherein the charging unit is the charging device according to the first aspect. A charging device having any one of the charging members according to items 2 to 8.

[0031]

FIG. 3 shows an embodiment of the present invention. This embodiment is an embodiment of an image forming apparatus including an electrophotographic copying machine. Around the electrophotographic photosensitive member 6 as an image carrier, a contact charging device having a magnetic particle carrier composed of a magnetic brush charging member 1a as a contact charging member, an image exposure system 11, and a developing device 1 having a developing roller
3, a transfer device having a transfer roller 14, a separation charger 15, a pre-cleaning charger 16, a cleaning device 18 having a cleaning roller 17, and a discharging lamp 19 as a discharging unit. The back side of the electrophotographic photosensitive member 6 is grounded.

The electrophotographic photosensitive member 6 has an organic photoconductive layer and has a drum-shaped photosensitive member (O
PC), which is rotationally driven in the direction of the arrow by a drive mechanism (not shown). The magnetic brush charging member 1a is substantially the same as the sleeve type magnetic brush charging member 1 shown in FIG. 7, but the outer peripheral surface of the sleeve 2 has an uneven shape as described later, and the peripheral surface of the electrophotographic photosensitive member 6 The charging process is performed uniformly to a predetermined polarity and potential. The developing roller 12 is composed of a magnet roller, and is rotationally driven by a driving mechanism (not shown). The developing roller 12 is applied with a developing bias from a power supply (not shown), and carries a two-component developer composed of toner and magnetic carrier on the surface thereof to be conveyed.

Next, the image forming operation of this embodiment will be described. Note that a series of image forming processes in this embodiment is performed by a negative / positive process.

A charging bias is applied to the magnetic brush charging member 1a from a charging bias applying power supply 5, and the outer peripheral surface of the electrophotographic photosensitive member 6 is substantially -700 by charge injection and discharge.
V is uniformly charged. The charged surface of the electrophotographic photosensitive member 6
Exposure is performed with light irradiated by the image exposure system 11 to form an electrostatic latent image (the exposed portion potential is -100 V).

The image exposure system 11 emits, for example, a laser beam modulated by an image signal from a semiconductor laser, and deflects and scans this laser beam by a hexagonal polygon mirror which rotates at high speed. Is scanned in a direction orthogonal to the rotation direction of the electrophotographic photosensitive member 6. Since the electrophotographic photosensitive member 6 rotates at an extremely low speed as compared with the scanning speed of the laser light from the image exposure system 11, the laser light from the image exposure system 11 can scan the entire surface of the electrophotographic photosensitive member 6.

Next, the developing roller 12 is
The electrostatic latent image on the electrophotographic photosensitive member 6 is developed by the developer carried by the developing roller 12 (the applied voltage of the developing roller 12 is −5).
50V) becomes a toner image. On the other hand, a transfer material (for example, paper) P
Is fed from a paper feeder (not shown) to a pair of upper and lower registration rollers (not shown), which transfer the transfer material P to the electrophotographic photosensitive member 6 in synchronization with the leading end of the toner image on the electrophotographic photosensitive member 6. The toner image is fed to the space between the roller 14 and the toner image on the electrophotographic photosensitive member 6 is transferred to the transfer material P. At this time, +95 from a power source (not shown) is applied to the transfer roller 14.
A transfer bias of 0 V is applied. Then, the transfer material P
Is removed from the electrophotographic photoreceptor 6 by the separation charger 15, and the toner image is fixed by the fixing device 20 and discharged as a copy.

Almost all of the toner adhered to the electrophotographic photosensitive member 6 by the developing roller 12 is negatively charged. However, since the transfer roller 14 supplies a positive charge, the transfer on the electrophotographic photosensitive member 6 is performed. A part of the remaining toner is injected with charge from the transfer roller 14 and becomes a positive polarity toner. The positive polarity toner on the electrophotographic photoreceptor 6 is supplied with a negative corona by the pre-cleaning charger 16 to be negatively charged.

As described above, the charge in the toner needs to be able to quickly change its charging behavior by an external potential difference and charging, and the response speed of the charging behavior to the external electric field of the toner can improve the speed of the entire process and can improve the image quality. Required for stability. An image is formed on the transfer material P by the above operation.

When an image for one sheet is formed, at least one of the rotation direction and the speed of the cleaning roller 17 is switched by control means (not shown), and at the same time, a negative bias is applied from a power supply to the cleaning roller 17. The negative toner collected from the body 6 is discharged to the electrophotographic photosensitive member 6. The toner discharged to the electrophotographic photosensitive member 6 is conveyed to a developing area between the electrophotographic photosensitive member 6 and the developing roller 12 as the electrophotographic photosensitive member 6 rotates.

In the toner collecting mode, a positive bias is applied to the developing roller 12 from a power source (not shown). In the developing area, the magnetic brush of the developing roller 12 gives an impact force to the toner on the electrophotographic photosensitive member 6, and a positive bias is applied to the developing roller 12 from a power source (not shown), so that the toner is Collected by magnetic brush. Through the above operation, the toner can be recycled.

In this image forming apparatus, the developing device 13 and the cleaning device 18 operate in two modes as described above. As a result, there is a great advantage that a complicated mechanism is not required, but 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 electrophotographic photosensitive member 6
Before the area corresponding to the rear end of the toner image formed above passes the cleaning roller 17, the cleaning device 1
8, the mode is switched.

The image area on the electrophotographic photosensitive member 6 and the untransferred toner discharge area pass through each unit. In the contact area between the electrophotographic photosensitive member 6 and the cleaning roller 17, a bias voltage applied to the cleaning roller 17 is used. First, the rotation of the cleaning roller 17 is switched to a condition for collecting the toner from the electrophotographic photosensitive member 6 (toner collecting mode). The remaining portion on the electrophotographic photosensitive member 6 (the electrophotographic photosensitive member 6 and the cleaning roller 17 in the toner discharge mode)
The untransferred toner in the portion passing through the contact area with the cleaning roller 1 is charged to the negative polarity by the pre-cleaning charger 16 and the cleaning roller 1 to which the negative bias is applied.
7 passes through the cleaning roller 17 without being collected. At this time, the toner adhering to the cleaning roller 17 is transferred to the electrophotographic photosensitive member 6.

At the same time as or immediately after the rear end of the image area on the electrophotographic photosensitive member 6 passes through the cleaning roller 17,
The discharge of the toner from the cleaning roller 17 to the electrophotographic photosensitive member 6 ends. When the next image is formed continuously, the magnetic brush charging member 1a is moved away from the magnetic brush charging member 1a after the rear end of the untransferred toner discharge area on the electrophotographic photosensitive member 6 passes below the magnetic brush charging member 1a. The mechanism contacts the electrophotographic photosensitive member 6 by a mechanism, and image formation is repeatedly performed by the above-described image forming process.

Here, the magnetic brush charging member 1a and the transfer roller 14 are brought into contact with the electrophotographic photosensitive member 6 by the contact / separation mechanism to perform their respective functions, but are contaminated with toner adhered to the electrophotographic photosensitive member 6. There's a problem. As a countermeasure, a process of returning the adhered toner to the electrophotographic photoreceptor 6 by strongly contacting the biased electrophotographic photoreceptor 6 after completion of image formation or after each predetermined number of image formations is completed. It is desirable. The base of the magnetic brush charging member 1a is a solid cylinder or hollow cylinder made of metal such as aluminum or SUS having a circular cross section, and a magnet roll 3 is provided inside.

Next, the magnetic brush charging member 1a as the contact charging member used in this embodiment will be described in detail. The magnetic brush charging member 1a is a sleeve type magnetic brush charging member substantially similar to the sleeve type magnetic brush charging member 1 shown in FIG. That is, the magnetic brush charging member 1a is a non-magnetic conductive sleeve 2A holding the carrier 4 as conductive magnetic particles constituting the magnetic brush B.
Forming irregularities on the entire surface of the sleeve 2A,
The carrier 4 is constrained on the outer peripheral surface of the conductive sleeve 2A by the magnetic force of a magnet roll 3 as a fixed magnetic field generating means disposed in the sleeve 2A and adhered and held as a magnetic brush B.

The magnet roll 3 is a non-rotating fixed member, and has a magnetized portion in which a plurality of magnetic poles are magnetized alternately in the circumferential direction to be N poles and S poles. The sleeve 2A is concentrically rotated around the outer periphery of the magnet roll 3 at a predetermined peripheral speed by a drive mechanism (not shown) in the clockwise direction b as indicated by the arrow. A charging bias is applied to the sleeve 2A from a charging bias applying power source 5.

Next, the carrier 4 will be described.

As the carrier 4 constituting the magnetic brush B, in order to reduce the damage to the electrophotographic photosensitive member 6,
It is preferable to use spherical particles. The average particle size of the carrier 4 is preferably 150 μm or less. However, if the average particle diameter of the carrier 4 is too large, the radius of curvature is large even if the carrier 4 is arranged in the most dense state, and the area not in contact with the electrophotographic photosensitive member 6 increases, causing uneven charging. If the average particle size is too small, the particles tend to move when an AC voltage is applied, and the force exceeds the magnetic force between the particles, causing the particles to scatter and causing carrier adhesion. It is preferable that the diameter is 30 μm or more and 100 μm or less.

Further, if the volume resistivity of the carrier 4 is too low, charge is injected when a charging bias is applied, causing the carrier to adhere to the electrophotographic photosensitive member 6 or causing a dielectric breakdown of the electrophotographic photosensitive member 6 by the charging bias voltage. For example, a material having a volume resistivity of 10 ³ Ωcm or more is used.

Here, in the conventional contact charging device having the magnetic brush charging member 1, the magnetic brush B is randomly formed on the surface (sleeve 2) of the magnetic brush charging member 1,
The height of the ears of the magnetic brush B and the distance between the ears varied, and a sparse portion was generated on the magnetic brush B. For this reason, if there is a sparse portion of the magnetic brush B in the charging nip D where the magnetic brush B and the electrophotographic photosensitive member 6 are in contact, a portion where the carrier 4 does not contact the electrophotographic photosensitive member 6 is formed. An uncharged area is generated on the photoconductor 6. Then, in the image forming apparatus, when an image is formed using the electrophotographic photosensitive member 6 in which such an uncharged area is generated, an abnormal image is generated in a final output image.

Further, when an abnormal discharge (spark discharge) is generated from the surface (sleeve 2) of the magnetic brush charging member 1 and an image is formed using the electrophotographic photosensitive member 6 in the image forming apparatus, a final image is formed. There is a problem that an abnormal image is generated in the output image.

Therefore, the present inventor first observed the magnetic brush B formed on the surface of the conductive sleeve 2 in the conventional contact charging device having the magnetic brush charging member 1 in order to find the cause of the abnormal discharge. However, it has been found that when a portion where the magnetic brush B is sparse is generated, discharge is likely to occur. Further, when the conductive sleeve 2 was rotated, it was observed that the magnetic brush B moved with the change in the magnetic force distribution, and it was found that the magnetic brush B was likely to be sparse. Furthermore, it was found that abnormal discharge easily occurred immediately after the application of the charging bias.

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 4 as an example. The three ears are each formed in a conical shape on the conductive sleeve 2, and the portion indicated by A in FIG. At the tip of the short ear E in the sparse portion A of the magnetic brush B, the electric field intensity becomes very strong, and abnormal discharge occurs.

The inventor calculated the electric field strength at the tip of the short ear E by simulation using the model shown in FIG. 4 with the distance x between ears as a parameter.
The result is shown in FIG. In FIG. 5, the vertical axis indicates the electric field intensity, and the horizontal axis indicates the inter-spike distance x. As shown in FIG. 5, when the electric field strength is 5 × 10 ⁶ V / m or more, that is, the distance
Is larger than 200 μm, it was found that the discharge started. In the simulation, 14
00V was applied, the back surface of the electrophotographic photosensitive member 6 was grounded, the calculation was performed with the average particle size of the carrier 4 being 50 μm and the volume resistivity of the carrier 4 being 10 ⁵ Ωcm.

From the above results, in this embodiment,
In order to form a magnetic brush B having an inter-spike distance x of 200 μm or less on the sleeve 2A, irregularities were formed on the entire surface of the sleeve 2A, and the interval between the irregularities was 200 μm or less. According to this configuration, the magnetic brush B
Since the spikes are formed along the irregularities on the surface of the sleeve 2A, the distance x between spikes can be made 200 μm or less, and occurrence of abnormal discharge can be prevented.

According to this configuration, since irregularities are formed on the entire surface of the sleeve 2A, spikes are not formed at random on the sleeve 2A, and the density of the magnetic brush B can be controlled. Become. Therefore, the problem of poor charging of the electrophotographic photosensitive member 6 due to the occurrence of the sparse portion of the magnetic brush B as described above can be solved.

Hereinafter, a method for forming irregularities on the surface of the conductive sleeve 2A in this embodiment will be described. FIGS. 1 and 2 show examples of irregularities formed on the surface of the conductive sleeve 2A. The example shown in FIG. 1 forms a plurality of grooves 2a extending in the axial direction of the conductive sleeve 2A, and the example shown in FIG. 2 shows a plurality of grooves 2a extending in the axial direction and the circumferential direction of the conductive sleeve 2A. , 2b.

As a method for forming irregularities on the surface of the conductive sleeve 2A, there are a cutting method and a drawing method (Direct).
Ironing, DI) method, sandblasting method and the like. A plurality of grooves 2a extending parallel to the axial direction of the conductive sleeve 2A as shown in FIG.
Since it is formed only by steps, it is advantageous in that irregularities can be formed easily and inexpensively.

The conductive sleeve 2 shown in FIG.
The plurality of grooves 2a and 2b extending in parallel with the axial direction and the circumferential direction of A are formed by combining a drawing method and a cutting method. Such a groove is very advantageous in terms of controlling the formation of the magnetic brush B since the interval between the irregularities can be accurately controlled.

When the surface of the conductive sleeve 2A is roughened by sandblasting to form irregularities on the surface of the conductive sleeve 2A, the controlling factor of the blast surface roughness is the type of abrasive used. -Consider the count, nozzle diameter when ejecting abrasive grains, nozzle-work distance, air pressure, number of works, blast time, etc. In particular, in order to form a fine uneven surface, the influence of the abrasive grain type / count and the air pressure is great. Abrasive grains include amorphous alumina / silicon carbide, spherical glass beads, and the like. Spherical glass beads are particularly effective for forming uniform and fine irregularities. According to such a sand blasting method, there is an advantage that fine irregularities of 100 μm or less can be formed as compared with the above-mentioned drawing method and cutting method. The lower limit of the interval between the irregularities formed on the surface of the conductive sleeve 2A is not particularly set, but may be set to an extent that the carrier 4 can be sufficiently pumped.

According to the above method, the width a of the concave portion (groove 2a) in the unevenness on the conductive sleeve 2A as shown in FIG.
And the width b of the protrusion, the conductive sleeve 2A as shown in FIG.
A plurality of grooves 2 extending in the axial direction and the circumferential direction, respectively.
The widths a and d of a and 2b and the widths b and c of the protrusions are shown in FIG.
Ricoh copier Imagio equipped with a contact charging device having a magnetic brush charging member 1a changed as shown in FIG.
An image forming apparatus (an image forming apparatus similar to the above embodiment as shown in FIG. 3) including the 530 modified machine was prepared as Examples 1 to 6 and Reference Examples 1 and 2, and an image was formed.

At this time, before the electrification of the electrophotographic photosensitive member 6 is started, the conductive sleeve 2A is rotated so that the new carrier 4 comes to the charging nip portion D. -90 without rotating 2A
A charging bias in which an AC bias having a peak-to-peak voltage of 1000 V and a frequency of 5 kHz is superimposed on a DC bias of 0 V and applied to the conductive sleeve 2A from a power supply to the electrophotographic photosensitive member 6
After the charging, the electrostatic latent image on the electrophotographic photosensitive member 6 was developed with a toner having a positive polarity in the developing device 13 without exposing the electrophotographic photosensitive member 6 to form an image. The width of the charging nip D from the charging start position on the electrophotographic photosensitive member 6 was excluded from the charging area. FIG. 6 shows an evaluation result of the formed image (output image).

From FIG. 6, the distances a, b, c, d between the grooves 2a, 2b on the conductive sleeve 2A as shown in FIGS.
Is 200 μm or less, it can be seen that a good image can be obtained without generating a blank portion in the output image. In Reference Example 3, the electrophotographic photoreceptor 6 was charged while rotating the conductive sleeve 2A in Example 5 described above.
An image was formed. At this time, white spots occurred in the output image, and more white spots were observed particularly at the leading end of the image.

That is, according to the first to third embodiments having the conductive sleeve 2A as shown in FIG. 1, the spike is formed along the groove 2a extending in the axial direction of the conductive sleeve 2A. The distance x between the spikes in the circumferential direction of the conductive sleeve 2A is 200 μm or less, and occurrence of abnormal discharge can be prevented. In addition, since the density of the magnetic brush B in the circumferential direction of the conductive sleeve 2A is controlled, poor charging of the electrophotographic photosensitive member 6 can be prevented.

The conductive sleeve 2 shown in FIG.
According to the fourth to sixth embodiments having the groove A, the grooves 2 extending in the axial direction and the circumferential direction of the conductive sleeve 2A, respectively.
Since the spikes are formed along a and b, the distance x between the spikes in the axial direction and the circumferential direction of the conductive sleeve 2A is 20
0 μm or less, which is more effective in preventing occurrence of abnormal discharge. In addition, since the density of the magnetic brush B in the axial direction and the circumferential direction of the conductive sleeve 2A is controlled, defective charging of the electrophotographic photosensitive member 6 can be more effectively prevented.

In the above embodiment and Examples 1 to 6, the sleeve type magnetic brush charging member having the rotatable conductive sleeve 2A is used as the magnetic brush charging member. A magnetic roller type magnetic brush charging member having a carrier attached may be used. In this case, a coat layer is applied and dried on the outer peripheral surface of a magnet roll as a magnetic particle carrier for holding a carrier constituting the magnetic brush B, and irregularities are formed on the surface of the coat layer in the same manner as described above. can do. Further, irregularities may be formed on the magnet roll when the magnet roll is formed.

The present invention is not limited to the above-described embodiments and examples. For example, the unevenness provided on the surface of the magnetic particle carrier holding the magnetic brush may be any uneven shape having the above-described effect. In this case, the average interval between the irregularities (the average interval between the projections) provided on the surface of the magnetic particle carrier holding the magnetic brush may be 200 μm or less. The member to be charged may be a belt-shaped electrophotographic photosensitive member or the like.

[0068]

As described above, according to the first aspect of the present invention, abnormal discharge can be prevented by the above configuration. According to the second aspect of the present invention, the electric field intensity at the tip can be prevented from becoming too high due to the average interval of the unevenness being 200 μm or less, and the occurrence of abnormal discharge of the magnetic brush is prevented. be able to. Also,
Since spikes are not formed randomly on the magnetic particle carrier and the movement of the magnetic brush can be suppressed as much as possible during charging, the density of the magnetic brush can be controlled. Therefore, the problem of poor charging of the member to be charged due to the generation of the sparse portion of the magnetic brush can be solved at the same time.

According to the third aspect of the present invention, with the above structure, the interval between the unevenness in the axial direction of the magnetic particle carrier can be accurately controlled, so that the magnetic brush in the circumferential direction of the magnetic particle carrier can be controlled. It can be done reliably. Further, the unevenness can be formed by only one step of the drawing method, which is advantageous in that the unevenness can be formed easily and inexpensively.

According to the fourth aspect of the present invention, with the above configuration, the distance between the unevenness in the axial direction and the circumferential direction of the magnetic particle carrier can be accurately controlled. An excellent effect that the control of the magnetic brush in the circumferential direction can be surely performed is achieved. According to the invention according to claim 5, with the above configuration, 100 μm
This is advantageous in that the following fine irregularities can be formed.

According to the sixth aspect of the present invention, when the charging bias is applied, the electric charge is injected into the magnetic particles and the magnetic particles adhere to the charged object, or the dielectric breakdown of the charged object is caused by the charging bias voltage. Can be prevented. According to the seventh aspect of the present invention, since the magnetic particles are restrained on the outer surface of the sleeve by the magnetic force of the fixed magnet roll disposed in the sleeve and adhered and held as the magnetic brush, the magnetic brush is charged. The member to be charged can be charged by bringing the member into contact with the body and applying a voltage to the magnetic brush charging member.

According to the eighth aspect of the present invention, with the above-described structure, the magnetic particles are directly constrained on the outer surface of the magnet roll and adhered and held as a magnetic brush. An object to be charged can be charged by applying a voltage to the charging member. According to the ninth aspect of the present invention, with the above configuration, it is possible to obtain a good image without an abnormal image such as white spots as an output image.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view showing a part of an example of a conductive sleeve according to an embodiment of the present invention.

FIG. 2 is a plan view and a side view showing a part of another example of the conductive sleeve according to the embodiment of the present invention.

FIG. 3 is a sectional view schematically showing an embodiment of the present invention.

FIG. 4 is a diagram showing a model of a magnetic brush on a magnetic brush charging member.

FIG. 5 is a diagram showing a result of calculating the electric field intensity at the tip of a short spike on the magnetic brush charging member by simulation.

FIG. 6 is a diagram illustrating evaluation results of output images of each embodiment and the reference example of the present invention.

FIG. 7 is a diagram showing a configuration model of a contact charging device having a sleeve type magnetic brush charging member.

FIG. 8 is a view showing a configuration model of a contact charging device having a magnetic roller type magnetic brush charging member.

[Explanation of symbols]

 1a Magnetic brush charging member 2A Conductive sleeve 2a, 2b Groove 6 Electrophotographic photosensitive member 13 Developing device 14 Transfer roller 18 Cleaning device

Claims (9)

[Claims] The present invention relates to a rotatable magnetic particle carrier, wherein magnetic particles are restrained 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. In the charging device for charging the object to be charged, the magnetic particle carrier is rotated before the charging of the object to be charged, and the magnetic particle carrier is fixed during the charging of the object to be charged. A charging device characterized in that a charging area is from a start position to a charging nip width and thereafter. 2. The charging member of a charging device according to claim 1, further comprising: the magnetic particle carrier, wherein a surface of the magnetic particle carrier supporting a magnetic brush is provided with irregularities, and an average distance between the irregularities is 200 μm or less. A charging member, characterized in that: 3. The charging member of a charging device according to claim 1, further comprising: the magnetic particle carrier, and a surface of the magnetic particle carrier for holding a magnetic brush having irregularities, the irregularities being the magnetic particle carrier. A plurality of grooves extending in the axial direction of the charging member. 4. The charging member of a charging device according to claim 1, further comprising: the magnetic particle carrier, and a surface of the magnetic particle carrier supporting a magnetic brush, the surface of which is provided with a magnetic brush. A plurality of grooves extending in the axial direction and the circumferential direction of the charging member. 5. The charging member for a charging device according to claim 1, further comprising: the magnetic particle carrier, wherein a surface of the magnetic particle carrier supporting a magnetic brush is provided with irregularities, and the irregularities are formed by sandblasting. A charging member characterized in that it is a charging member. 6. A charging member according to claim 1, further comprising the magnetic particle carrier, wherein a magnetic element held by the magnetic particle carrier has a volume resistivity of 1%.
A charging member having a resistivity of at least 0 ³ Ωcm. 7. The charging member of the charging device according to claim 1, further comprising the magnetic particle carrier, wherein the magnetic particle carrier has a rotatable sleeve, and is disposed in the sleeve. A charging member characterized in that magnetic particles are restrained on the outer surface of the sleeve by the magnetic force of a fixed magnet roll provided and adhered and held as a magnetic brush. 8. The charging member of the charging device according to claim 1, further comprising the magnetic particle carrier, wherein the magnetic particle carrier is a rotatable magnet roll,
A charging member characterized in that magnetic particles are directly confined to the outer surface of the magnet roll and adhered and held as a magnetic brush. 9. An image forming apparatus for forming an image by an image forming process including a step of charging an image carrier by a charging unit, wherein the charging unit is the charging device according to claim 1 or the charging device according to claim 2. An image forming apparatus comprising: a charging device having any one of charging members.