JPH08106201A - Charging member, charging device, and image forming apparatus - Google Patents

Abstract

(57) Abstract: A charging member (20) having a magnetic brush (23) of magnetic particles and abutting against a charged body (1) having a charge injection layer on its surface to apply a voltage to charge the charged body. In the charging device 2 using the charging member, the image recording device and the process cartridge using the charging member or the charging device, it is possible to prevent the magnetic brush magnetic particles from decreasing due to the transfer to the charged body side.
To improve the uniformity of charging and long-term stability. SOLUTION: A power feeding section 2 to a magnetic brush 23 of a charging member.
The long end of 2 is formed of a member 24 electrically insulated from the power feeding portion, the member is formed of a conductor, and the position of the charged body corresponding to the end of the magnetic brush is the conductive base of the charged body. Is an electrically insulated conductor, the outermost surface of the charged body at that position is formed of a conductor, and the effective width of the magnetic brush is longer than the photosensitive layer coating width of the photosensitive body (charged body). The position of the photosensitive member corresponding to the end portion is formed of a conductor that is electrically insulated from the conductive substrate of the photosensitive member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member, a charging device and an image forming apparatus for charging using magnetic particles, and is particularly preferably used in an electrophotographic copying machine and the same printer.

[0002]

BACKGROUND ART As a charging method in an electrophotographic apparatus, conventionally, a corona charging method including a wire and a shield has been mainly used, but recently, from the viewpoint of ecology, a contact charging method in which ozone products due to discharge are small is often used. It is used. As one of the contact charging methods, a magnetic brush method is known in which magnetic particles are brought into contact with a photoconductor as an object to be charged. This magnetic brush type charging member is, for example, a magnet roll as a magnetic force generating member, a non-magnetic electrode sleeve rotatably provided outside the magnet roll, and attracted to the surface of the electrode sleeve by the magnetic force of the magnet roll. A layer of magnetic particles that are retained by
Is provided. Here, the layer of magnetic particles for charging the photoreceptor is provided so as to contact the photoreceptor, and a voltage is applied to the electrode sleeve.

[0003]

In the magnetic brush method, the magnetic particles are extruded to the end region in the longitudinal direction of the charging member (the generatrix direction of the photoconductor), and in this end region the magnetic brush and the photoconductor are always present. It is difficult to charge uniformly because they are not in contact. Therefore, the potential of the photosensitive member in the end area becomes much lower than that in the central area. Therefore, in the end region, the potential difference between the electrode sleeve potential and the surface potential of the photoconductor becomes large, and magnetic particles may move from the charging member to the photoconductor.
When the magnetic particles adhere to the photoconductor, the magnetic particles in the charging member gradually decrease, so that charging failure gradually occurs.
There is a problem that the magnetic brush method cannot be used for a long period of time because an image defect occurs due to this charging failure.

An object of the present invention is to provide a charging member, a charging device, and an image forming apparatus which prevent magnetic particles from adhering to a member to be charged from the charging member.

Another object of the present invention is to provide a charging member, a charging device and an image forming apparatus which prevent charging failure from occurring for a long period of time.

[0006]

The present invention relates to a charging member that supports magnetic particles and charges a body to be charged, which has a conductive member to which a voltage can be applied. A charging member is characterized in that it has a member electrically insulated from the conductive member at an end of the magnetic particle in the direction. Further, the gist is a charging device and an image forming apparatus using the charging member.

Further, the present invention relates to a charged body provided with a charge holding layer for holding a charge and a conductive substrate, and a charging member to which a voltage can be applied to charge the charged body. A charging device comprising magnetic particles in the form of a magnetic brush, the magnetic particles being capable of contacting the charged body, wherein the charged body corresponds to an end of the magnetic particle in a longitudinal direction of the charging member. The gist of a charging device is characterized in that a conductive member electrically insulated from the conductive substrate is provided in the region of the body to be charged. Further, the gist is an image forming apparatus using the charging device.

The present invention also provides a body to be charged and a charging member to which a voltage can be applied to charge the body to be charged, the magnetic particles being magnetic brush-like and capable of contacting the body to be charged. In a charging device comprising: a charging member provided with the charging member, the force of an electric field that acts on the magnetic particles from the supporting member toward the charged body at the ends of the magnetic particles in the longitudinal direction of the charging member is reduced. Alternatively, the subject is a charging device characterized by having a means for eliminating it. Further, the present invention provides an image forming apparatus using the charging device.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 3) (1) Example of image forming apparatus (FIG. 1) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a laser beam printer using an electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (drum) as an image bearing member (charged member). This embodiment is an OPC photosensitive member having a diameter of 30 mm and having a negative charging polarity, and is rotationally driven in the clockwise direction of the arrow at a process speed (peripheral speed) of 100 mm / sec.

Reference numeral 2 denotes a charging device using a magnetic brush type contact charging member 20, which will be described in detail in the section (3) below. During the rotation process, the drum 1 is uniformly primary-charged by the charging device 2 to a predetermined polarity and potential. In the present embodiment, a DC charging bias of -700V is applied from the charging bias applying power source S1 to the electrode sleeve 22 of the magnetic brush type charging member 20, and the outer peripheral surface of the rotary drum 1 is made uniform to about -700V by the charge injection charging. Be charged to.

The charged surface of the rotary drum 1 is intensity-modulated in accordance with a time-series electric digital pixel signal of target image information output from a laser beam scanner (not shown) including a laser diode and a polygon mirror. Scanning exposure L is performed by the laser beam, and an electrostatic latent image corresponding to desired image information is formed on the peripheral surface of the rotating drum 1.

The electrostatic latent image is developed as a toner image by the reversal developing device 3 using magnetic one-component insulating toner (negative toner). 3a is a diameter 1 including the magnet 3b
It is a non-magnetic developing sleeve of 6 mm. The developing sleeve 3a is coated with the above-mentioned negative toner and is rotated at a constant speed with the drum 1 while the distance from the surface of the drum 1 is fixed at 300 μm. A developing bias voltage is applied from S2. The voltage is DC of -500V
Voltage, frequency 1800Hz, peak-to-peak voltage 1600V
Using a rectangular AC voltage superimposed on the sleeve 3a
And jumping development is performed between the photosensitive member 1 and the photosensitive member 1.

On the other hand, a transfer material P as a recording material is supplied from a paper feeding unit (not shown), and the rotary drum 1 and 10 ⁶ to 10 10 as a contact transfer means abutted against the rotary drum 1 with a predetermined pressing force.
It is introduced into the pressure contact nip portion (transfer portion) T with the transfer roller 4 having a medium resistance of ⁹ Ω at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roll 4 from the transfer bias applying power source S3. In this embodiment, the roll resistance value is 5
Transfer was performed by using a DC voltage of +2000 V using a film of × 10 ⁸ Ω.

The transfer material P introduced into the transfer portion T is nipped and conveyed by the transfer portion T, and the toner images formed and carried on the surface of the rotary drum 1 on this surface side are sequentially subjected to electrostatic force and pressing force. Will be transcribed.

The transfer material P on which the toner image has been transferred is separated from the surface of the drum 1 and introduced into a fixing device 5 such as a heat fixing system to receive the toner image fixing, and as an image formed product (print / copy). It is discharged to the outside of the device.

The drum surface after the transfer of the toner image onto the transfer material P is cleaned by the cleaning device 6 to remove adhered contaminants such as residual toner, and is repeatedly used for image formation. The toner is removed by the cleaning blade 6a, and the toner in the cleaning device 6 is removed by the receiving sheet 6
By b, it is prevented from scattering outside the device 6.

In the printer of this embodiment, the process in which the four process devices of the drum 1, the contact charging member 20, the developing device 3, and the cleaning device 6 are included in the cartridge 30 and which can be attached to and detached from the main body of the printer in a batch can be replaced. It is a cartridge type device. Reference numeral 31 is an attachment / detachment guide / support member for the cartridge 30. However, the image forming apparatus is not limited to the process cartridge detachable type.

(2) Photoreceptor (Drum) 1 The drum 1 as the member to be charged used in this embodiment is an OPC photoreceptor having a negative charging polarity, and is mounted on a grounded aluminum drum base 1a having a diameter of 30 mm. The following first to fifth functional layers are sequentially provided.

The first layer supported on the substrate is an undercoat layer, and has a thickness of about 1 nm to smooth out defects and the like of the aluminum drum substrate and to prevent moire due to reflection of laser exposure. It is a conductive layer of 20 μm.

The second layer is a positive charge injection layer, which plays a role of preventing the positive charges injected from the aluminum drum substrate from canceling out the negative charges charged on the surface of the photosensitive member, and the amylan resin and methoxymethylation. It is a medium resistance layer having a thickness of about 1 μm whose resistance is adjusted to about 10 ⁶ Ωcm by nylon.

The third layer is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.
Positive and negative charge pairs are generated by receiving the laser exposure.

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

The fifth layer is a charge injection layer provided on the surface of the photoconductor, and is a coating layer of a material in which SnO ₂ ultrafine particles are dispersed in a photocurable acrylic resin. Specifically, antimony is doped to reduce the resistance, and the particle size is about 0.03 μm.
Is a coating layer of a material in which 70 wt% of SnO ₂ particles is dispersed in a resin. The coating liquid thus prepared was applied by dipping to a thickness of about 2 μm to form a charge injection layer. As a result, the volume resistance value on the surface of the photosensitive member was 1 × 10 ¹⁵ Ωcm in the case of the charge transport layer alone, compared to 1 × 10 ¹⁵ Ωcm
It decreased to 10 ¹² Ωcm. The volume resistivity of the charge injection layer is preferably 1 × 10 ⁹ to 1 × 10 ¹⁵ Ωcm. This volume resistivity is obtained when a voltage of 100 V is applied to a sheet-shaped sample, and is a YHP HIGH RESIST.
ANSIMETER 4329A with RESISTIVI
TY CELL 16008A was connected and measured.

(3) Charging device 2 a) Schematic configuration of the device In the charging device 2 of this example, a magnetic brush type charging member 20 as shown in FIG. 2 (a) is composed of a magnet roll 21 and the roll outside thereof. It is composed of a non-magnetic electrode sleeve 22 concentrically rotatably fitted to the outside, and a magnetic brush 23 made of magnetic particles which is formed and held by the magnetic force of an internal magnet roll 21 on the outer peripheral surface of the electrode sleeve 22. The magnetic flux density by the magnet roll 21 on the electrode sleeve 22 is 800 × 10 ⁻⁴ T (Tesla).

The charging member 20 is arranged substantially in parallel with the drum (photosensitive member) 1 as the member to be charged, and the magnetic brush 23 is brought into contact with the surface of the drum 1 to make the shaft 21a of the magnet roll 21.
Is held by a bearing portion (not shown). The magnet roll 21 is non-rotatably fixed and held, and the non-magnetic electrode sleeve 22 is rotationally driven in the clockwise direction indicated by the arrow at a predetermined peripheral speed by a driving means (not shown). That is, the electrode sleeve 22 rotates in the counter direction with respect to the rotation direction of the drum 1 in the nip portion N while the magnetic brush 23 keeps contact with the surface of the drum 1 in the charging nip portion N with the drum 1.

Specifically, the magnetic brush 23 on the electrode sleeve 21 is formed by coating magnetic particles with a thickness of 1 mm, and a charging nip portion N having a width of about 5 mm is formed between the magnetic brush 23 and the drum 1. . In this embodiment, the amount of magnetic particles of the magnetic brush 23 is about 10 g, and the gap at the charging nip portion N between the electrode sleeve 22 and the drum 1 is 500 μm. A charging bias is applied from the charging bias applying power source S1 to the electrode sleeve 22 as a power feeding portion to the magnetic brush 23.

Thus, the drum 1 and the electrode sleeve 22 are rotationally driven, and a charging bias of a predetermined polarity and potential is applied to the electrode sleeve 22 from the power source S1, so that the surface of the drum 1 is driven by the magnetic brush 23. The charge is injected into the conductive particles of the charge injection layer, and the surface of the drum 1 is charged to a predetermined polarity and potential by the injection charging method.

The peripheral speed ratio between the magnetic brush 23 and the drum 1 is
It is defined by the following formula.

Peripheral speed ratio% = {(magnetic brush peripheral speed-drum peripheral speed) / drum peripheral speed} × 100 (the peripheral speed of the magnetic brush 23 is a negative value in the case of counter rotation).

Since the magnetic brush 23 is in a stopped state when the peripheral speed ratio is -100%, the stopped shape of the magnetic brush 23 on the surface of the drum directly causes defective charging and appears in the image. Further, in the forward rotation, if an attempt is made to obtain the same peripheral speed ratio as in the counter direction, the rotational speed of the magnetic brush 23 will increase. When the magnetic brush 23 comes into contact with the drum in a normal rotation at a low speed, the magnetic particles of the magnetic brush easily adhere to the drum. Therefore, the peripheral speed ratio is preferably −100% or less, and in this embodiment, it is −150%.

B) Principle of charging (FIG. 2) The principle of charge injection charging will be described with reference to FIG. 2A is a layer configuration model diagram of the photoconductor (drum) 1 as a member to be charged in a state where the magnetic brush type charging member 20 is brought into contact with the surface and a voltage is applied, and FIG. 2B is an equivalent circuit thereof. is there.

Reference numeral 11 is an aluminum drum base of the drum 1, 12 is a charge transport layer (fourth layer), 13 is an outermost charge injection layer (fifth layer), and 13a is conductive particles (SnO) in the charge injection layer. ₂ ) Drum substrate 11 and charge transport layer 1
As described above, the undercoat layer, the positive charge injection layer, and the charge generation layer, which are the first to third layers, exist between the first and second layers, but they are omitted in the drawing.

Therefore, the charge injection charging is 1 × 10 ⁴ to 1
× 10 ⁷ Ω 1 × 10 ⁹ with a medium resistance contact charging member 20
Charge injection is performed on the surface of a charged body (photoreceptor) having a volume resistivity of 1 × 10 ¹⁵ Ωcm, and in the present embodiment, the conductive particles 13a of the charge injection layer 13 are charged with electric charges. 2B, the charge transport layer 12 is a dielectric, the aluminum drum base 11 and the conductive particles 13 in the charge injection layer 13 are used.
This is based on the theory that the contact charging member 20 charges a minute capacitor having a as both electrode plates. At this time, the conductive particles 13a are electrically independent of each other and form a kind of minute float electrode. For this reason, the surface of the photoconductor looks macroscopically charged and charged to a uniform potential, but in reality SnO ₂ which is a myriad of charged conductive particles covers the surface of the photoconductor. The situation is as follows. Therefore, even if image exposure is performed with a laser, each SnO ₂ particle is electrically independent, so that an electrostatic latent image can be held.

C) Magnetic Particles The magnetic particles constituting the magnetic brush 23 are as follows: resin and magnetic powder such as magnetite are kneaded and molded into particles, or conductive carbon or the like for adjusting the resistance value. Mixed materials: -Sintered magnetite, ferrite, or those whose resistance value has been adjusted by reducing or oxidizing them-Coated material in which the resistance of the above magnetic particles has been adjusted (such as carbon dispersed in phenol resin) Coat or N
It is conceivable that the resistance value is adjusted to an appropriate value by plating with a metal such as i.

If the resistance value of these magnetic particles is too high, electric charges cannot be uniformly injected into the drum as the member to be charged, resulting in a fog image. If it is too low, when there are pinholes on the drum surface, current concentrates on the pinholes, the charging voltage drops, and the drum surface cannot be charged, resulting in a charging nip-shaped charging failure. Therefore, the resistance value of the magnetic particles is preferably 1 × 10 ⁴ to 1 × 10 ⁷ Ω. The resistance value of the magnetic particles was determined after putting 2 g of the magnetic particles in a metal cell (bottom area 227 mm ² ) to which a voltage can be applied.
The measurement was performed by applying a load of 6 kg / cm ² and applying a voltage of 1 to 1000 V.

Regarding the magnetic characteristics of the magnetic particles, it is better to increase the magnetic restraining force for preventing the magnetic particles from adhering to the drum, and the saturation magnetization is preferably 50 (A.m ² / kg) or more.

Actually, the magnetic particles used in this embodiment are
The average particle diameter was 30 μm, the resistance value was 1 × 10 ⁶ Ω, and the saturation magnetization was 58 (A · m ² / kg).

D) Electrode sleeve 22 (FIG. 3) FIG. 3 is a schematic vertical sectional view of one end of the charging member 20. In the present embodiment, the electrode sleeve 22 as a power feeding portion to the magnetic brush 23 of the charging member 20 has a ring-shaped (ring-shaped) thickness on the outer peripheral surface of its longitudinal end (near the end corresponding to the end of the magnet roller 21). A 50 μm polyester tape is attached to provide the annular insulating portion 24. The same applies to the other end side of the electrode sleeve 22 omitted in FIG.

The insulating portion 24 has a width range (longitudinal direction of the sleeve) as long as the magnetic particles are extruded at the charging nip portion N from the inner side of the magnetic brush 23 with a margin to some extent. Is. In this embodiment, the width of the charging member is 2 mm from the inner side 5 mm from the longitudinal end.
The range of 0 mm was configured as the insulating portion 24.

The margin of the insulating portion 24 to the inside of the lengthwise direction of the charging member depends on the resistance of the magnetic particles. When the resistance of the magnetic particles is low, an electric current easily flows through the magnetic particles, so that the potential of the magnetic particles in contact with the photoconductor is less likely to be attenuated. Therefore, the electric potential of the magnetic particles at the end of the magnetic brush does not become sufficiently low, and the electric charges injected into the magnetic particles and the electric field acting by the electric potential cause the electric particles to adhere to the photoconductor. Therefore, it is preferable to increase the length of the insulating portion in the magnetic brush. on the other hand,
When the resistance of the magnetic particles is high, the resistance of the magnetic particles easily attenuates the potential of the magnetic particles in contact with the photoconductor, so that the length of the insulating portion in the magnetic brush can be shortened.
That is, the length of the insulating portion in the magnetic brush is preferably set according to the resistance of the magnetic particles.

Conventionally, at the charging nip portion N, the magnetic particles extruded to the longitudinal outer region D, which is a non-charged region where the surface of the drum (photoreceptor) is not at the charging potential, are caused by the charges injected into the magnetic particles. Although it was attached to the surface of the drum 1 by an electric force, this configuration prevents the electric conduction path between the magnetic particles and the electrode sleeve 22 from being cut off, so that electric charges are not injected into the magnetic particles, and the magnetic particles are prevented from being injected. Since the adhesion electric field does not act on the particles, it was possible to prevent the magnetic particles from adhering to the surface of the drum 1.

The insulating portion 24 of this embodiment is formed by sticking a polyester tape, but the structure is not limited to this, and the sleeve is coated with an insulating resin such as urethane, acrylic, or phenol. Even if it had the same effect.
Further, the same effect can be obtained by covering the sleeve with an insulating resin cap such as a ring-shaped polycarbonate.

<Second Embodiment> (FIGS. 4 and 5) Next, another embodiment of the charging member will be described.

The present embodiment is characterized in that the portion corresponding to the magnetic brush end portion of the electrode sleeve 22 is the float electrode portion 223. As a result, the potential difference between the magnetic particles at the end of the magnetic brush and the drum surface is eliminated, and the magnetic particles extruded to the outer longitudinal region D at the charging nip portion N can be prevented from adhering to the drum.

More specifically, as shown in FIG. 4, the electrode sleeve 22 is arranged from its longitudinal end portion to a float electrode portion 223 made of aluminum and an insulating portion 2 made of polycarbonate.
22 and a power feeding portion 221 made of aluminum as a power feeding portion to the magnetic brush. The device configuration other than such an end shape of the electrode sleeve 22 is the same as that of the first embodiment. Here, if the width of the insulating portion 222 is too short, the electrode portion 223 has a potential close to that of the electrode sleeve 22 via the magnetic particles 23, and thus the float electrode is not sufficiently formed. In the present embodiment, the width of the insulating portion 222 is set to 5 mm, but this width may be changed according to the resistance of the magnetic particles. If the resistance is low, it may be long, and if it is high, it may be short.

In the above-described first embodiment, the insulating portion 24 is provided on the portion on the electrode sleeve 22 corresponding to the end portion of the magnetic brush 23.
Therefore, the insulating portion 24 is formed by frictional charging with the magnetic particles.
May have a potential locally, and a potential difference may be generated between the insulating portion 24 and the surface of the photoconductor, and the electric field may cause magnetic particles to adhere to the drum 1. However, in the present embodiment, by providing the float electrode portion 223, which is an electrode different from the feeding portion 221 for the magnetic brush, at the end portion of the electrode sleeve, the local potential due to frictional charging of the magnetic particles is also reduced, and the magnetic brush 23 The electric potential of the magnetic particles at the end of was equal to the electric potential of the drum 1, and the electric charges were not injected into the magnetic particles, and the magnetic particles did not adhere to the drum.

The structure of the float electrode portion 223 is not limited to the configuration shown in FIG.
It is also possible to form a float electrode portion 223 on the surface by interposing a single insulating layer 24 on the surface of the electrode sleeve 22 as a power feeding portion to the electrode 3. At this time, the insulating portion 24 is set to be longer than the electrode portion 223 by about 5 mm toward the center in the longitudinal direction in order to sufficiently achieve the insulating effect. The insulating layer 24 is formed as described in the first embodiment, and the float electrode portion 223 is formed.
It was also effective to use a method in which a conductive paint such as urethane in which carbon is dispersed is dipped on the insulating layer 24 or a conductive tape is attached.

<Embodiment 3> In the present embodiment, a configuration advantageous in preventing magnetic particles from adhering to the drum when an AC voltage is applied in a charger using a magnetic brush will be described.

In the charging by the magnetic brush, the potential applied to the charging member can be applied to the drum as it is.
It can be charged by applying a C voltage.

This embodiment is particularly effective in a cleanerless process in which the cleaning device 6 shown in FIG. 1 is eliminated.

In this process, since the drum cleaner is omitted, the transfer residual toner is mixed in the charging device. However, since the magnetic particles that are very stable in contact are used, the transfer residual toner can be charged, and the mixed toner is removed. It is possible to construct a process in which printing can be repeated by collecting in a charger or appropriately discharging on a drum. It is preferable that the residual toner is finally cleaned at the same time as the developing operation is performed by the developing device 3. However,
At this time, in order to eliminate the influence of toner, the magnetic brush A
By applying a bias with the C voltage superimposed, this process can be repeated more stably. However, when the AC voltage is superimposed on the DC voltage and applied, a potential difference larger than that applied by the DC voltage occurs between the charging member (sleeve) and the drum, which is disadvantageous in terms of adhesion of magnetic particles.

It is desirable to eliminate the potential difference between the end of the magnetic brush and the drum to reduce the adhesion of magnetic particles from the magnetic brush to the drum. When the charging device of FIG. 3 described above is used in the above cleanerless process, the annular insulating layer 24 is provided on the sleeve periphery of the magnetic brush end, so that the magnetic brush end and the drum are electrically cut to form the drum. Adhesion of magnetic particles can be reduced. Further, when the charging device of FIG. 4 is used in the above-mentioned cleanerless process, the attachment of the magnetic particles can be further reduced by attaching the electrode portion 223 to the end portion of the magnetic brush via the insulating portion 222.
However, in these configurations, the potential of the end portion of the magnetic brush gradually increases as the charging is continuously performed, so that some magnetic particles may adhere to the drum when used for a long period of time. Therefore, this electrode portion 223 is shown in FIG.
As shown in (3), when it was used in common with the drum ground, adhesion could be eliminated. That is, when the electrode portion 223 is grounded, the potential of the magnetic brush decreases toward the end, and the potential eventually goes to the drum ground, so that the magnetic brush and the drum (here, the drum surface where the brush is not in contact) are separated. Since the potential difference is substantially eliminated, the potential difference does not occur and the adhesion does not occur even if the charging is continued.

The same applies to the configuration of FIG.
By sandwiching the insulating layer 24 between the electrodes 2 and the electrode 223 in common with the drum ground, the adhesion of magnetic particles could be eliminated.

The positional relationship between the brush end and the electrode in the configuration shown in FIGS. 6 and 7 will be described in detail. In this embodiment, when the drum diameter is 30 mm, the sleeve diameter is 16 mm, and the distance between the drum and the sleeve is 0.5 mm, the brush end portion 3 is
At least 5 mm from the end of the magnetic brush because the magnetic particles are sparse in the region of ~ 5 mm and are weak against the electric field.
It is important to set the end electrode boundary (F in FIGS. 6 and 7) apart from each other.

By configuring as described above, the charging member is
Even when the AC voltage is superimposed on the C voltage and applied,
It was possible to prevent the end of the magnetic brush from adhering.

The charging device shown in FIGS. 6 and 7 can also be used when a DC voltage is applied to the charging member without applying an AC voltage.

<Embodiment 4> (FIG. 8) In this embodiment, a conductor (electrode portion) 101 is provided on the outermost surface of the drum 1 at the position corresponding to the end of the magnetic brush of the longitudinal end of the drum 1 as the member to be charged. It is characterized in that it is formed by. Since the electrode portion 101 comes into contact with the end portion of the magnetic brush 23 and has the same potential as the electrode sleeve 22, even if the magnetic particles are extruded to the longitudinal outer region D at the charging nip portion N, electric charges are injected into the magnetic particles. Since no electric force is exerted, magnetic particles can be prevented from adhering to the drum.

Specifically, as shown in FIG. 8, the drum 1
An electrode portion 101 made of a conductor is formed at the end portion of. The position of the electrode portion 101 may be from the end portion of the magnetic brush 23 to a position where magnetic particles may spread to the outer longitudinal region D of the charging nip portion N, but in the present embodiment, the magnetic brush 23 is provided for safety. Slightly from the end of the charging nip N
The electrode portion 101 was formed from the inner side of the longitudinal direction of the to have a width of 15 mm. However, an insulating layer such as a charge transport layer exists under the electrode portion 101, and the electrode portion 101 is electrically insulated from the drum base 11. Also, by newly providing an insulating layer such as polycarbonate, it is more effective as a lower layer of the electrode portion 101.

In this embodiment, the electrode portion 101 is dip-coated with a coating material in which carbon graphite is dispersed in acrylic resin, and then dried at room temperature to a thickness of about 20 μm.
m. The structure of the electrode part 101 is not limited to this, and it has conductivity as a paint, good slipperiness of magnetic particles, good adhesiveness to the outermost layer of the drum, and is not easily scraped. A material that can be dried at room temperature, a solvent that does not contaminate the drum surface, and the like are preferable, and urethane resin, phenol resin, and the like can be used in addition to the acrylic resin. Further, instead of carbon graphite, carbon black or a metal oxide such as tin oxide can be used. In addition to dipping, the coating method may be roll coating, spray coating, or the like.

As a conductive member of the electrode portion 101, a method of attaching a metal foil such as aluminum or copper, EPDM
It was also effective to cover with a thin layer tube of conductive rubber in which carbon was dispersed. If the thickness of the electrode portion 101 is too thick, magnetic particles will adhere to the steps of the electrode portion 101, so it is preferable that the thickness of the electrode portion 101 be as thin as possible. From that viewpoint, forming the electrode portion 101 by the vapor deposition method was most effective. Specifically, the charging area in the longitudinal direction of the drum was masked, and the electrode portion 101 was formed into a film of copper with a thickness of 0.5 μm by rotating the drum by a vacuum evaporation method. It is also possible to form a conductive electrode on the surface of the silicon drum by the vapor deposition method, and this configuration can be applied to the silicon drum.

With the configuration as described above, the upper end of the drum in contact with the magnetic particles extruded from the charging nip portion N becomes a conductive portion and has the same electric potential as the magnetic particles. No more sticking on top. In the first, second, and third embodiments described above, the electrical configuration of the longitudinal end portion is determined on the side of the electrode sleeve 22.
When the magnetic particles spread to the outside in the longitudinal direction at the charging nip portion N even slightly, the spread magnetic particles slightly adhered to the drum as compared with the present embodiment. However, in the present embodiment, the end portion on the drum 1 side is the magnetic brush. Since the potential is the same as 23, even if the magnetic particles are spread, the spread portion has the same potential as the magnetic particles, so that the spread magnetic particles do not adhere to the drum.
Therefore, even if this apparatus is used for a long period of time, magnetic particles do not decrease, and stable images with good charging properties can be obtained.

Reference numeral 11 is an aluminum drum base of the drum 1, 12 is a charge transport layer (fourth layer), and 13 is an outermost charge injection layer (fifth layer). As described above, the undercoat layer, the positive charge injection layer, and the charge generation layer as the first to third layers are present between the drum substrate 11 and the charge transport layer 12, but they are omitted in the drawing. The photoconductor of the present embodiment and the first embodiment
You may use it combining with the charging member of--3.

<Embodiment 5> (FIG. 9) In this embodiment, the drum base 11 is electrically insulated from the drum base 11 at a position corresponding to the magnetic brush end of the longitudinal end of the drum 1 as the member to be charged. It is characterized in that the conductive portion (electrode portion) 102 is formed. That is, the effective width of the magnetic brush is longer than the coating width of the photosensitive layer. As a result, this electrode unit 1
Since 02 has the same potential as the magnetic brush 23, it is possible to prevent magnetic particles from electrically attaching to the drum.

Specifically, as shown in FIG. 9, the drum 1 is attached to the aluminum electrode portion 102 from its longitudinal end portion.
A drum unit 1 including an insulating unit 103 made of polycarbonate, a charge transport layer 102, a charge injection layer 13 and the like.
04 (undercoat layer, positive charge injection layer, charge generation layer are omitted in the figure). The drum base 11 has a structure as shown in a partial view in order to establish a ground.

In the above-described fourth embodiment, when the apparatus is used for a long period of time, the electrode portion 101 is more likely to be scraped than in the present embodiment, and magnetic particles may attach to the drum to some extent. However, with the configuration of the present embodiment, the electrode portion 102 is not lost even if it is scraped to some extent, and magnetic particles do not adhere even if this device is used for a long period of time, so that the magnetic particles are also reduced. It is possible to stably obtain an image with good chargeability. The photoreceptor of this embodiment and the charging member of Embodiments 1 to 3 can be used in combination.

<Embodiment 6> (FIG. 10) In this embodiment, as a structure of the charging member 20, as shown in FIG. 10A, magnetic particles are directly attached to a multi-pole magnet roll 21A to form a magnetic brush 23. Form and hold,
The magnet roll 21A is driven to rotate. In the combination of the fixed magnet roll 21 and the rotating electrode sleeve 22 as in the above-described embodiment, the magnetic flux density is likely to decrease depending on the distance between the magnet roll 21 and the surface of the sleeve 22 as compared with the present embodiment. By directly attaching and holding the magnetic particles to the surface of the roll 21A to form the magnetic brush 23, the attachment of the magnetic particles to the drum can be greatly improved.

The magnet roll 21A used has a diameter of 1
The maximum magnetic flux density on the roll surface is 1500 gauss with a magnetic flux pattern of 5 mm and 8 poles. The height of spikes of magnetic particles was regulated to 1.5 mm by a magnetic blade, and the gap between the magnet roll 21A and the drum 1 was set to 500 μm by means of rollers.

The end of the magnet roll 21A is sealed by a seal member 26 so that magnetic particles do not spread to the outside in the longitudinal direction. In (a), the magnetic particles of the magnetic brush 23 are spread over the entire circumference of the magnet roll 21A to form the seal member 2.
6 and the magnet roll 21A, the magnetic particles do not actually exist where the seal member 26 exists. In order to prevent the magnetic particles from spreading to the outside in the longitudinal direction, the sealing member 26 is installed so as to be inclined from the outside in the longitudinal direction to the inside in the rotating direction of the magnet roll as shown in (b). Since it is returned to (the direction of arrow E), it is more effective. The magnetic particles are the same as the magnetic particles shown in the first embodiment.
5 g was used. The apparatus has the configuration shown in Embodiment 1 except for the charging member 20.

Magnet roll 2 used in this embodiment
1A itself is an insulator, and the surface of the roll 21A is subjected to a conductive treatment 27 in order to apply a voltage to the magnetic brush 23. In this electroconductivity treatment, the inside of the roll longitudinal direction from the end of the magnetic brush 23 regulated by the seal member 26 was electroconducted as shown in (c). As a result, since the end of the magnet roll 21A is insulative, even if the magnetic brush 23 spreads to the outside of the length of the roll at the charging nip portion N, the conductive path of the electric charge is cut and the electric charge is not injected into the magnetic particles.
Magnetic particles do not stick to the drum.

Surface conductivity of magnet roll 21A 27
As a specific method of (3), only the end portion of the roll was masked and the conductive paint was applied by dipping. The conductive paint used here is urethane having carbon graphite dispersed therein and subjected to a resistance lowering treatment.

In the present embodiment, the end of the magnetic brush 23 is regulated by the seal member 26, and the magnetic restraining force also acts on the outside of the magnetic brush 23. Therefore, the charging nip is different from that in the first embodiment. At the portion N, the magnetic particles of the magnetic brush 23 easily spread in the longitudinal direction. However, with the above-described configuration, the magnetic particles of the magnetic brush 23 are much less likely to adhere to the drum. Further, in the structure of the charging member of the present embodiment, the conductive portion 1 is formed on the surface of the end portion of the drum described in the fourth and fifth embodiments.
By adding the constitution in which 01 and 102 are provided, it is possible to further prevent the magnetic particles from adhering to the drum. Therefore, it becomes possible to maintain a good charging property when the charging device is used for a long period of time.

The magnet roll 21 used in this embodiment
Since A is an insulator, it has such a structure.
When a magnet made of a conductor is used, the electrode sleeve 2 whose longitudinal end is shown in the first embodiment is used.
The same effect as that of the present embodiment was obtained even when the insulator 24 was used as in the case of the second end.

It should be noted that all the magnetic brush type contact charging members shown above may be constructed using a rotating endless belt member. Further, it may have a non-rotating rod shape, a rectangular bar shape, a horizontally long plate shape, or the like.

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

In all of the above embodiments, the magnetic particles are prevented from adhering to the photoconductor by reducing or eliminating the potential difference between the potential of the magnetic particles contacting the photoconductor at the end of the charging member and the potential of the photoconductor. I was able to prevent it.

[0077]

As described above, the present invention eliminates the potential difference between the charging member and the member to be charged or the image carrier even at the longitudinal end of the magnetic brush of the charging member.
Since the magnetic particles extruded to the non-charged area at the charging nip portion have the same potential as the charged body or the image bearing body, it is possible to prevent the magnetic particles from adhering to the charged body or the image bearing body.

Therefore, the magnetic particles are charged bodies (image bearing bodies).
It is possible to improve the uniformity and long-term stability of charging on the surface of the member to be charged without being transferred to the side and decreasing, and in the image recording device, the uniformity and long-term stability of charging Even in long-term use, it is possible to stably output a high-quality image with no charging failure or the like.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.

2A and 2B are explanatory views of the principle of injection charging.

FIG. 3 is a vertical cross-sectional schematic view of one end side of the magnetic brush type charging member according to the first embodiment.

FIG. 4 is a vertical cross-sectional schematic view of one end side of the magnetic brush type charging member according to the second embodiment.

FIG. 5 is a vertical cross-sectional model view of one end side of a charging member according to a modified example of the second embodiment.

FIG. 6 is a vertical cross-sectional model view of one end side of the magnetic brush type charging member according to the third embodiment.

FIG. 7 is a diagram of a modified example of the third embodiment.

FIG. 8 is a vertical cross-sectional schematic diagram of one end side of the drum and the magnetic brush type charging member of the apparatus according to the fourth embodiment.

FIG. 9 is a schematic vertical cross-sectional view of one end of a drum and a magnetic brush type charging member of the apparatus according to the fifth embodiment.

10A is a cross-sectional model view of a magnetic brush type charging member of an apparatus of Embodiment 6, FIG. 10B is a plan model view, and FIG. 10C is a vertical cross-sectional model view of one end side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive member (drum) as charged body 11 Drum substrate 12 Charge transport layer 13 Charge injection layer 13a Conductive particle 2 Magnetic brush type charging device 20 Magnetic brush type charging member 21 / 21A Magnet roll 22 Electrode sleeve 23 Magnetic of magnetic particles Brush 24 Insulating part 26 Sealing member 101/102 Electrode part 103 Insulating part 222 Insulating part 223 Float electrode part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Mashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canono (72) Inventor Yasushi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (39)

[Claims] 1. A charging member that supports magnetic particles and charges a body to be charged, the charging member having a conductive member to which a voltage can be applied, wherein an end portion of the magnetic particles in a longitudinal direction of the charging member. In the charging member, the charging member has a member electrically insulated from the conductive member. 2. The charging member according to claim 1, wherein the member electrically insulated from the conductive member is a second conductive member. 3. The charging member according to claim 2, wherein the second conductive member is grounded. 4. The charging member according to claim 1, wherein the conductive member supports the magnetic particles. 5. The charging member according to claim 1, wherein the member electrically insulated from the conductive member can come into contact with the magnetic particles. 6. A charging member for charging an object to be charged, the magnetic particles being in the shape of a magnetic brush and capable of contacting the gas to be charged,
In a charging device having a charging member including a conductive member to which a voltage can be applied, the charging member is electrically insulated from the conductive member at an end of the magnetic particle in a longitudinal direction of the charging member. A charging device comprising a member. 7. The charging device according to claim 6, wherein the member electrically insulated from the conductive member is a second conductive member. 8. The charging device according to claim 7, wherein the second conductive member is grounded. 9. The charging device according to claim 6, wherein the conductive member supports the magnetic particles. 10. The charging device according to claim 6, wherein the member electrically insulated from the conductive member is contactable with the magnetic particles. 11. The resistance of the magnetic particles is from 1 × 10 ⁴ to
11. 6 to 10 characterized in that it is 1 × 10 ⁷ Ω.
Charging device. 12. The image carrier according to claim 6, wherein the member to be charged is an image carrier, and the image carrier and the charging device are provided in a process cartridge detachable from an image forming apparatus. Charging device. 13. An image carrier and a charging member for charging the image carrier, wherein the charging member is magnetic brush-like magnetic particles capable of contacting with the image carrier, and conductive material capable of applying a voltage. And a charging member including a charging member, the charging member including a member electrically insulated from the conductive member at an end of the magnetic particle in a longitudinal direction of the charging member. An image forming apparatus characterized by the above. 14. The image carrier has a charge injection layer,
The image forming apparatus according to claim 13, wherein charges are injected into the charge injection layer by contact with the magnetic particles. 15. The volume resistivity of the charge injection layer is 1 ×
The image forming apparatus according to claim 14, wherein the image forming apparatus has a resistance of 10 ⁹ to 1 × 10 ¹⁵ Ωcm. 16. The image forming apparatus according to claim 13, wherein the member electrically insulated from the conductive member is a second conductive member. 17. The image forming apparatus according to claim 16, wherein the second conductive member is grounded. 18. The image forming apparatus according to claim 13, wherein the conductive member supports the magnetic particles. 19. The image forming apparatus according to claim 13, wherein the member electrically insulated from the conductive member can come into contact with the magnetic particles. 20. The resistance of the magnetic particles is 1 × 10 ⁴ to
14. The method according to claim 13, wherein the resistance is 1 × 10 ⁷ Ω.
9. Image forming apparatus. 21. A charged body comprising a charge holding layer for holding a charge and a conductive substrate, and a charging member to which a voltage can be applied to charge the charged body, which is a magnetic brush. In a charging device having a charging member provided with magnetic particles capable of contacting the charged body, the charged body is a member of the charged body corresponding to an end of the magnetic particle in a longitudinal direction of the charging member. A charging device comprising a conductive member electrically insulated from the conductive substrate in a region. 22. The charging device according to claim 21, wherein the conductive member is provided on a surface of the body to be charged. 23. The charging device according to claim 22, wherein the conductive member can contact the magnetic particles. 24. The resistance of the magnetic particles is 1 × 10 ⁴ to 1
24 × 23 ⁷ Ω.
Charging device. 25. The object to be charged is an image carrier, and the image carrier and the charging device are provided in a process cartridge detachable from an image forming apparatus. Charging device. 26. An image carrier comprising a charge retention layer for retaining charges and a conductive substrate; a charging member to which a voltage can be applied to charge the image carrier, which is in the form of a magnetic brush. In an image forming apparatus having a charging member provided with magnetic particles capable of contacting with the image carrier, the image carrier is the image carrier corresponding to an end of the magnetic particle in a longitudinal direction of the charging member. An image forming apparatus comprising: a conductive member electrically insulated from the conductive substrate in a region. 27. The image forming apparatus according to claim 26, wherein the charge retention layer is a charge injection layer, and charges are injected into the charge injection layer by contact with the magnetic particles. 28. The volume resistivity of the charge injection layer is 1 ×
28. The image forming apparatus according to claim 27, wherein the image forming apparatus has a resistance of 10 ⁹ to 1 × 10 ¹⁵ Ωcm. 29. The image forming apparatus according to claim 26, wherein the conductive member is provided on the surface of the image carrier. 30. The image forming apparatus according to claim 29, wherein the conductive member is capable of contacting the magnetic particles. 31. The resistance of the magnetic particles is from 1 × 10 ⁴ to
26. The method according to claim 26, wherein the resistance is 1 × 10 ⁷ Ω.
0 image forming apparatus. 32. The charge holding layer has a photosensitive layer, and the effective width of the magnetic brush is longer than the coating width of the photosensitive layer in the longitudinal direction of the charging member. 31 through 31. 33. An object to be charged, and a charging member to which a voltage can be applied to charge the object to be charged, the charging member including magnetic particles in the form of a magnetic brush that can contact the object to be charged. , A means for reducing or eliminating the force of the electric field acting on the magnetic particles from the support member toward the charged body at the end of the magnetic particles in the longitudinal direction of the charging member. A charging device characterized by having. 34. The resistance of the magnetic particles is from 1 × 10 ⁴ to
The charging device according to claim 33, wherein the charging device has a resistance of 1 × 10 ⁷ Ω. 35. The charging device according to claim 33, wherein the member to be charged is an image bearing member, and the charging device is provided in a process cartridge detachable from the image forming apparatus. 36. An image carrier, and a charging member to which a voltage can be applied to charge the image carrier, the charging member having magnetic particles in the form of a magnetic brush and capable of contacting with the image carrier. An image forming apparatus having a means for reducing or eliminating the force of an electric field acting on the magnetic particles from the supporting member toward the image carrier at the end portion of the magnetic particles in the longitudinal direction of the charging member. An image forming apparatus comprising: 37. The image carrier has a charge injection layer,
The image forming apparatus according to claim 36, wherein charges are injected into the charge injection layer by contact with the magnetic particles. 38. The volume resistivity of the charge injection layer is 1 ×.
It is 10 ⁹ to 1 × 10 ¹⁵ Ω, and
7 image forming apparatus. 39. The resistance of the magnetic particles is 1 × 10 ⁴ to 1
39. 38 to 38, wherein x10 ⁷ Ω.
Image forming apparatus.