JP3126636B2 - Charging member, charging device, and image forming apparatus - Google Patents

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 performing charging using magnetic particles, and is particularly preferably used for an electrophotographic copying machine and the same printer.

[0002]

2. Description of the Related Art As a charging method in an electrophotographic apparatus, a corona charging method having a wire and a shield has been mainly used. However, recently, from the viewpoint of ecology, a contact charging method with a small amount of ozone products due to discharge has been used. Used. As one of the contact charging methods, there is known a magnetic brush method in which magnetic particles are brought into contact with a photosensitive member as a member 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 over the outside of the magnet roll, and a magnetic force of the magnet roll adsorbing to the surface of the electrode sleeve. A layer of magnetic particles held and held;
Is provided. Here, in order to charge the photoconductor, a layer of magnetic particles is provided so as to be in contact with the photoconductor, and a voltage is applied to the electrode sleeve.

[0003]

In the magnetic brush method, magnetic particles are pushed out to an end region in the longitudinal direction of the charging member (in the direction of the generatrix of the photoconductor). In this end region, the magnetic brush is constantly in contact with the photoconductor. It is difficult to charge uniformly because there is no contact. Therefore, the potential of the photoconductor in the end region is considerably lower than that in the center region. Therefore, in the end region, the potential difference between the electrode sleeve potential and the surface potential of the photoconductor becomes large, and the magnetic particles may move from the charging member to the photoconductor.
If the magnetic particles adhere to the photoreceptor, the magnetic particles of the charging member gradually decrease, so that poor charging gradually occurs.
The magnetic brush method has a problem that it cannot be used for a long time because an image defect occurs due to the charging failure.

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

It is another object of the present invention to provide a charging member, a charging device, and an image forming apparatus that prevent charging failure from occurring over a long period of time.

[0006]

SUMMARY OF THE INVENTION The present invention comprises conductive magnetic particles in contact with a member to be charged, and an electrode member that supports the magnetic particles and to which a voltage is applied. In a charging device for charging by injecting a charge to a member to be charged through, a charging device characterized in that charge is not injected from the electrode member to the magnetic particles at the ends,
And an image forming apparatus using the charging device.

[0007] The present invention also provides a member to be charged comprising a charge holding layer for holding charges and a conductive substrate, and a charging member to which a voltage can be applied to charge the member to be charged. A charging member comprising magnetic particles that can be brought into contact with the member to be charged in a magnetic brush shape, wherein the member to be charged corresponds to an end of the magnetic particles in a longitudinal direction of the charging member. A charging device includes a conductive member that is electrically insulated from the conductive substrate in a region of a member to be charged. The gist of the present invention is an image forming apparatus using the charging device.

[0008]

[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 the present embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (drum) as an image carrier (charged member). The present embodiment is an OPC photosensitive member having a diameter of 30 mm and a negative charge polarity, and is driven to rotate at a process speed (peripheral speed) of 100 mm / sec in a clockwise direction indicated by an arrow.

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. The drum 1 is uniformly charged to a predetermined polarity and potential by the charging device 2 during the rotation process. In this embodiment, a DC charging bias of -700 V is applied to the electrode sleeve 22 of the magnetic brush type charging member 20 from the charging bias application power source S1, and the outer peripheral surface of the rotating drum 1 is made uniform to approximately -700V by charge injection charging. Is charged.

The charged surface of the rotating 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, a polygon mirror, and the like. The scanning exposure L by the laser beam is performed, and an electrostatic latent image corresponding to the target image information is formed on the peripheral surface of the rotating drum 1.

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

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

The transfer material P introduced into the transfer portion T is conveyed by sandwiching the transfer portion T, and the toner image formed and carried on the surface of the rotary drum 1 on the front surface side is sequentially reduced by electrostatic force and pressing force. Is transcribed.

The transfer material P to 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, where the toner image is fixed and the image is formed as an image product (print / copy). It is discharged outside 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 the 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 from the receiving sheet 6.
b prevents splashing out of the device 6.

The printer according to the present embodiment is a process in which four process devices of a drum 1, a contact charging member 20, a developing device 3, and a cleaning device 6 are included in a cartridge 30 and can be detached and replaced in a lump with the printer body. It is a cartridge type device. Reference numeral 31 denotes a detachable guide / support member for the cartridge 30. However, the image forming apparatus is not limited to the detachable type of the process cartridge.

(2) Photoreceptor (Drum) 1 The drum 1 as a member to be charged used in the present embodiment is an OPC photoreceptor having a negative charge 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 by the substrate is an undercoat layer, which is provided with a thickness of about 1 mm to smooth out defects and the like of the aluminum drum substrate and to prevent the occurrence of moire due to the reflection of laser exposure. It is a 20 μm conductive layer.

The second layer is a positive charge injecting layer, which serves to prevent positive charges injected from the aluminum drum base from canceling out negative charges charged on the surface of the photoreceptor. A medium resistance layer having a thickness of about 1 μm, the resistance of which is adjusted to about 10 ⁶ Ωcm by nylon.

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

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

The fifth layer is a charge injection layer provided on the surface of the photoreceptor, and is a coating layer of a material in which ultrafine SnO ₂ particles are dispersed in a photocurable acrylic resin. Specifically, antimony-doped, low-resistance particles having a particle size of about 0.03 μm
Is a coating layer of a material in which 70 wt% of SnO ₂ particles are dispersed in a resin. The coating solution 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 of the photoreceptor surface was 1 × 10 ¹⁵ Ωcm compared to 1 × 10 ¹⁵ Ωcm for the charge transport layer alone.
It decreased to 10 ¹² Ωcm. The charge injection layer preferably has a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁵ Ωcm. This volume resistivity is obtained when a voltage of 100 V is applied to the sheet-shaped sample, and is a high resistance of YHP.
RESISTIVI to ANCMETER 4329A
The measurement was performed with a TY CELL 16008A connected.

(3) Charging Device 2 a) Schematic Configuration of the Device In the charging device 2 of this embodiment, the magnetic brush type charging member 20 as shown in FIG. It comprises a non-magnetic electrode sleeve 22 fitted concentrically and rotatably, and a magnetic brush 23 of magnetic particles formed and held on the outer peripheral surface of the electrode sleeve 22 by the magnetic force of an internal magnet roll 21. 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 (photoreceptor) 1 as a member to be charged, and the magnetic brush 23 is brought into contact with the surface of the drum 1 so that the shaft 21a of the magnet roll 21 is rotated.
Are held and arranged in a bearing part (not shown). The magnet roll 21 is fixed and held non-rotatably, and the non-magnetic electrode sleeve 22 is driven to rotate clockwise as indicated by an 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 N while the magnetic brush 23 keeps contact with the surface of the drum 1 in the charging nip N with the drum 1.

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

When the drum 1 and the electrode sleeve 22 are driven to rotate, and a charging bias having a predetermined polarity and potential is applied to the electrode sleeve 22 from the power source S1, the surface of the drum 1 is moved by the magnetic brush 23. 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 an injection charging method.

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

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).

When the peripheral speed ratio is -100%, the magnetic brush 23 is in a stopped state, so that the shape of the magnetic brush 23 stopped on the drum surface becomes a charging failure as it is and appears on an image. In the forward rotation, if the same peripheral speed ratio as that in the counter direction is to be obtained, the rotation speed of the magnetic brush 23 will be high. When the magnetic brush 23 comes into contact with the drum at a low speed in a forward rotation, 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. FIG. 2A is a schematic diagram of a layer structure of a photosensitive member (drum) 1 as a member to be charged in a state where a voltage is applied by bringing a magnetic brush type charging member 20 into contact with the surface, and FIG. 2B is an equivalent circuit thereof. is there.

11 is an aluminum drum substrate of the drum 1, 12 is a charge transport layer (fourth layer), 13 is a charge injection layer (fifth layer) on the outermost surface, 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 as the first to third layers exist between the layer 2 and the layer 2, but they are omitted in the drawing.

Thus, the charge injection charging is from 1 × 10 ⁴ to 1
1 × 10 ⁹ to 10 × 10 ⁷ Ω medium resistance contact charging member 20
The charge injection is performed on the surface of the member to be charged (photosensitive member) having a medium resistance volume resistivity of 1 × 10 ¹⁵ Ωcm. In the present embodiment, the charge is charged in the conductive particles 13 a of the charge injection layer 13. As shown in the equivalent circuit of FIG. 2 (b), the charge transport layer 12 is made of a dielectric material, the aluminum drum base 11 and the conductive particles 13 in the charge injection layer 13 are charged.
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, macroscopically, the photoreceptor surface appears to be charged and charged to a uniform potential, but in reality, SnO ₂ , a myriad of minutely charged conductive particles, covers the photoreceptor surface It is in such a situation. For this reason, even if image exposure is performed by 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 include: kneading resin and magnetic powder such as magnetite to form particles, or conductive carbon or the like for adjusting the resistance value.・ Magnetite, ferrite, or sintered or reduced magnetite or ferrite whose resistance value has been adjusted by reducing or oxidizing them. ・ Coating material with the above magnetic particles whose resistance has been adjusted (such as phenol resin with carbon dispersed). With 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, the charge 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 is a pinhole on the drum surface, current concentrates on the pinhole and the charging voltage drops, making it impossible to charge the drum surface, resulting in charging nip-shaped charging failure. Therefore, the resistance value of the magnetic particles is desirably 1 × 10 ⁴ to 1 × 10 ⁷ Ω. 5. The resistance value of the magnetic particles is determined by placing 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 voltage of 6 kg / cm ² and applying a voltage of 1 to 1000 V.

As for 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 it is desirable that the saturation magnetization is 50 (A · m ² / kg) or more.

Actually, the magnetic particles used in this embodiment are:
The average particle size 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 longitudinal sectional view of one end of the charging member 20. In the present embodiment, the electrode sleeve 22 serving as a power supply portion to the magnetic brush 23 of the charging member 20 has an annular (ring-shaped) thickness on its outer peripheral surface at a longitudinal end (near the end corresponding to the end of the magnet roller 21). The annular insulating portion 24 is provided by attaching a 50 μm polyester tape. The same applies to the other end of the electrode sleeve 22 omitted in FIG.

The width of the insulating portion 24 (the range in the longitudinal direction of the sleeve) is sufficient as long as the magnetic particles are extruded at the charging nip N from the inside with some margins beyond the end of the magnetic brush 23. It is. In this embodiment, the width 2 is 5 mm from the longitudinal end of the charging member.
The range of 0 mm was configured as the insulating part 24.

The margin of the insulating portion 24 in the longitudinal direction of the charging member differs depending on the resistance of the magnetic particles. When the resistance of the magnetic particles is low, a current easily flows through the magnetic particles, so that the potential of the magnetic particles in contact with the photoreceptor is hardly attenuated. Therefore, the potential of the magnetic particles at the end of the magnetic brush does not become sufficiently low, and the electric charges applied to the magnetic particles and the electric field generated by the electric potential 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 potential of the magnetic particles in contact with the photoreceptor is easily attenuated by the resistance of the magnetic particles, 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 to a length corresponding to the resistance of the magnetic particles.

Conventionally, in the charging nip N, the magnetic particles that have been pushed out to the longitudinal outer region D which is a non-charged area where the surface of the drum (photoreceptor) is not at the charged potential are changed by the charge injected into the magnetic particles. Although it adhered to the surface of the drum 1 by an electric force, by adopting this configuration, the conductive path between the magnetic particles and the electrode sleeve 22 was cut off, and electric charge was not injected into the magnetic particles. Since the adhesion electric field does not work on the particles, it was possible to prevent the magnetic particles from adhering to the drum 1 surface.

Although the insulating portion 24 of the present embodiment is formed by sticking a polyester tape, the present invention is not limited to this. The insulating resin such as urethane, acrylic, or phenol is coated on the sleeve. The same effect was obtained.
A similar effect was obtained with a configuration in which an insulating resin cap such as a ring-shaped polycarbonate was put on the sleeve.

<Embodiment 2> (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 end of the magnetic brush of the electrode sleeve 22 is a float electrode portion 223. This eliminates the potential difference between the magnetic particles at the end of the magnetic brush and the surface of the drum, and prevents the magnetic particles pushed out to the longitudinal outer region D at the charging nip N from adhering to the drum.

More specifically, as shown in FIG. 4, the electrode sleeve 22 is provided with a float electrode portion 223 made of aluminum and an insulating portion 2 made of polycarbonate from its longitudinal end.
22, a power supply part 221 made of aluminum as a power supply part to the magnetic brush. The device configuration other than the 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 potential of the electrode portion 223 becomes close to that of the electrode sleeve 22 via the magnetic particles 23, and thus the electrode portion 223 does not sufficiently become a float electrode. In the present embodiment, the width of the insulating portion 222 is set to 5 mm. However, the width may be changed according to the resistance of the magnetic particles. The width is sufficient if the resistance is low and short if the resistance is high.

In the first embodiment, the portion on the electrode sleeve 22 corresponding to the end of the magnetic brush 23 is
Therefore, the frictional charging with the magnetic particles causes
In some cases, a potential difference is generated between the insulating part 24 and the surface of the photoconductor, and the magnetic field adheres to the drum 1 in some cases. However, in the present embodiment, by providing the float electrode portion 223 of an electrode different from the power supply portion 221 to the magnetic brush at the end of the electrode sleeve, the local potential due to the triboelectric charging of the magnetic particles is reduced, and the magnetic brush 23 The electric potential of the magnetic particles at the end of was substantially the same as that of the drum 1, no charge was 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 form shown in FIG.
The float electrode portion 223 may be further formed on the surface of the electrode sleeve 22 as a power supply portion for the third electrode 3 with the insulating layer 24 interposed therebetween. 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 make the insulating effect sufficient. The insulating layer 24 is formed as described in Embodiment 1, and the float electrode portion 223 is formed.
Was also effective by dipping a conductive paint such as urethane in which carbon was dispersed on the insulating layer 24 or by attaching a conductive tape.

<Embodiment 3> In the present embodiment, a configuration advantageous for preventing adhesion of magnetic particles to a drum when an AC voltage is applied to 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 C voltage.

This embodiment is particularly effective in a cleanerless process without the cleaning device 6 shown in FIG.

In this process, the transfer residual toner is mixed into the charger because the drum cleaner is omitted. However, since magnetic particles that are very stable in contact are used, it is possible to charge the charged toner. A process capable of repeatedly printing can be configured by collecting the toner in a charger or discharging the toner onto a drum as appropriate. 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 the toner,
This process can be repeated more stably by applying a bias in which the C voltage is superimposed. However, when an AC voltage is superimposed on a DC voltage and applied, a potential difference larger than the DC voltage application is generated 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 shown in FIG. 3 is used in the above-described cleanerless process, an annular insulating layer 24 is provided on the circumference of the sleeve at the end of the magnetic brush, so that the end of the magnetic brush and the drum are electrically cut and the Adhesion of magnetic particles can be reduced. Further, when the charging device shown in FIG. 4 is used in the above-described cleanerless process, the adhesion of the magnetic particles can be further reduced by attaching the electrode portion 223 to the end of the magnetic brush via the insulating portion 222.
However, in these configurations, the potential at the end of the magnetic brush gradually increases as charging is continuously performed, so that when used for a long period of time, some magnetic particles may adhere to the drum. Therefore, this electrode portion 223 is
As shown in (1), it was possible to eliminate the adhesion when it was shared with the drum ground. That is, by setting the electrode portion 223 to ground, the potential of the magnetic brush decreases toward the end, and the potential finally reaches the drum ground, so that the potential of the magnetic brush and the drum (here, the surface of the drum not in contact with the brush) is increased. Since the potential difference substantially disappears, no potential difference occurs and no adhesion occurs even when charging is continued.

The same applies to the configuration of FIG.
By adhering the electrode 223 to the drum ground with the insulating layer 24 interposed therebetween, the adhesion of the magnetic particles could be eliminated.

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

With the above-described configuration, the charging member has a D
Even when the AC voltage is superimposed on the C voltage and applied,
The adhesion of the end of the magnetic brush could be prevented.

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

<Embodiment 4> (FIG. 8) In this embodiment, the outermost surface of the drum 1 at the position corresponding to the end of the magnetic brush at the longitudinal end of the drum 1 as the member to be charged is a conductor (electrode portion) 101. It is characterized by being formed by. Since the electrode portion 101 comes into contact with the end of the magnetic brush 23 and has the same potential as the electrode sleeve 22, even if the magnetic particles are pushed out to the longitudinal outer region D at the charging nip portion N, the electric charge is injected into the magnetic particles. However, since no electric force works, it is possible to prevent the magnetic particles from adhering to the drum.

More specifically, as shown in FIG.
Is formed at the end of the electrode portion 101 made of a conductor. The position of the electrode portion 101 may be from the end of the magnetic brush 23 to a position where the magnetic particles may spread to the longitudinal outer region D of the charging nip portion N. Slightly from the end of the charging nip N
The electrode portion 101 was formed from the inside of the longitudinal direction of the sample and had a width of 15 mm. However, an insulating layer such as a charge transport layer exists below the electrode section 101, and the electrode section 101 is electrically insulated from the drum base 11. Further, by newly providing an insulating layer of polycarbonate or the like, it is more effective as a lower layer of the electrode portion 101.

In this embodiment, the electrode portion 101 is dipped with a coating material in which carbon graphite is dispersed in an acrylic resin, and then dried at normal temperature to have a thickness of about 20 μm.
m. The configuration of the electrode portion 101 is not limited to this, and the coating has conductivity, has good slipperiness of magnetic particles, has good adhesion to the outermost layer of the drum, and is hardly shaved. It is preferably a solvent that can be dried at room temperature, or a solvent that does not contaminate the drum surface. In addition to an acrylic resin, a urethane resin, a phenol resin, or the like can be used. Instead of carbon graphite, metal oxides such as carbon black and tin oxide can be used. As for the coating method, roll coating, spray coating and the like are possible in addition to dipping.

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

With the above-described structure, the upper end of the drum contacted by the magnetic particles pushed out from the charging nip N becomes a conductive portion and has the same potential as the magnetic particles. No more sticking on top. In the first, second, and third embodiments, the electrical configuration of the longitudinal end is determined on the electrode sleeve 22 side.
When the magnetic particles spread at least slightly outward in the longitudinal direction at the charging nip portion N, the magnetic particles that spread as compared with the present embodiment slightly adhered to the drum, but in this embodiment, the end on the drum 1 side is a magnetic brush. Since the potential of the magnetic particles is the same as that of the magnetic particles 23, the spread magnetic particles do not adhere to the drum even if the spread of the magnetic particles has the same potential as the magnetic particles.
Therefore, even when this apparatus is used for a long period of time, the magnetic particles do not decrease, so that an image having good chargeability can be obtained stably.

Reference numeral 11 denotes an aluminum drum base of the drum 1, reference numeral 12 denotes a charge transport layer (fourth layer), and reference numeral 13 denotes a topmost 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 exist between the drum substrate 11 and the charge transport layer 12, but are not shown in the drawing. The photoconductor of the present embodiment and the first embodiment
It may be used in combination with the charging members of (1) to (3).

<Embodiment 5> (FIG. 9) In this embodiment, the drum 1 serving as a member to be charged is electrically insulated from the drum base 11 at a position corresponding to the end of the magnetic brush at the longitudinal end. A conductive portion (electrode portion) 102 is formed. That is, the effective width of the magnetic brush is longer than the application width of the photosensitive layer. Thereby, this electrode part 1
Since 02 has the same potential as the magnetic brush 23, the magnetic particles can be prevented from being electrically attached to the drum.

Specifically, as shown in FIG. 9, the drum 1 is moved from its longitudinal end to an aluminum electrode 102,
Drum section 1 composed of insulating section 103 made of polycarbonate, charge transport layer 102, charge injection layer 13 and the like
04 (the undercoat layer, the positive charge injection layer, and the charge generation layer are omitted in the figure). The drum base 11 was partially configured as shown in the drawing to take the ground.

In the 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 this embodiment, and the magnetic particles may adhere to the drum to some extent. However, by configuring as in the present embodiment, the electrode portion 102 is not lost even if it is slightly scraped off, and the magnetic particles are not reduced even if this device is used for a long time, so that the magnetic particles are reduced. Without this, an image having good chargeability can be obtained stably. The photoreceptor of the present embodiment and the charging members of the first to third embodiments can be used in combination.

<Embodiment 6> (FIG. 10) In this embodiment, as a configuration of the charging member 20, as shown in FIG. 10A, magnetic particles are directly adhered to a multi-pole magnet roll 21A, and a magnetic brush 23 is formed. To 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 easily reduced by the distance between the magnet roll 21 and the surface of the sleeve 22 as compared with the present embodiment. By forming the magnetic brush 23 by attaching and holding the magnetic particles directly on the surface of the roll 21A, the adhesion of the magnetic particles to the drum can be greatly improved.

The magnet roll 21A used had a diameter of 1
With a magnetic flux pattern of 5 mm and 8 poles, the maximum magnetic flux density on the roll surface is 1500 Gauss. The height of the ears of the 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 a roller.

The end of the magnet roll 21A is sealed by a seal member 26 so that the magnetic particles do not spread 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.
6 and the magnet roll 21A, but there is actually no magnetic particles where the seal member 26 is. When the seal member 26 is installed with a slant from the outside to the inside in the rotation direction of the magnet roll as shown in FIG. (In the direction of arrow E), it is more effective. The magnetic particles are the same as the magnetic particles described in the first embodiment.
5 g were used. The device has the configuration shown in the first embodiment except for the charging member 20.

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

Surface Conduction 27 of Magnet Roll 21A
As a specific method, only the end of the roll was masked, and a conductive paint was applied by dipping. The conductive paint used here is obtained by dispersing carbon graphite in urethane and performing a resistance lowering treatment.

In the present embodiment, the end portion of the magnetic brush 23 is regulated by the seal member 26, and the magnetic binding force acts on the outside of the magnetic brush 23. At the portion N, the magnetic particles of the magnetic brush 23 tend to spread in the longitudinal direction. However, by adopting the above-described configuration, the magnetic particles of the magnetic brush 23 are extremely unlikely to adhere to the drum. Further, the conductive member 1 is provided on the surface of the end of the drum described in Embodiments 4 and 5 in the configuration of the charging member of this embodiment.
By adding a configuration in which the magnetic particles 01 and 102 are provided, it is possible to further prevent the magnetic particles from adhering to the drum. Accordingly, it has become possible to maintain good charging properties in long-term use of the charging device.

The magnet roll 21 used in this embodiment
Since A was an insulator, this configuration was adopted,
When a magnet made of a conductor is used, the longitudinal end of the magnet is connected to the electrode sleeve 2 shown in the first embodiment.
The same effect as in the present embodiment was obtained even when the insulator 24 was used as in the end of No. 2.

It is to be noted that all the magnetic brush type contact charging members described above may be of a configuration using a rotating endless belt member. Further, it may be in the form of a non-rotating rod, square bar, horizontally long plate, or the like.

In the case of a magnetic brush such as a magnetic brush two-component developing device, the developing contrast (difference between the developing potential and the drum surface potential) is usually smaller than the charging contrast (the difference between the charging potential and the drum surface potential). The carrier of the magnetic brush on the drum is not so noticeable as when the magnetic brush is used for the charging device. Furthermore, when a magnetic brush is used for development, toner is present in the magnetic brush,
The 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 retained charge is higher. Therefore, the toner easily adheres to the drum by an electric force.
Therefore, the carrier of the magnetic brush rarely adheres to the drum.

In all of the above embodiments, the adhesion of the magnetic particles to the photoconductor is reduced by reducing or eliminating the potential difference between the potential of the magnetic particles in contact with the photoconductor at the end of the charging member and the potential of the photoconductor. Could be prevented.

[0077]

As described above, according to the present invention, there is no 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 have the same potential as the charged object or the image bearing member, it is possible to prevent the magnetic particles from adhering to the charged member or the image bearing member.

Therefore, the magnetic particles are used as a member to be charged (image carrier).
It is possible to improve the uniformity and long-term stability of the charge on the surface of the member to be charged without being reduced due to the transfer to the side. 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 the drawings]

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

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

FIG. 3 is a schematic longitudinal sectional view of one end side of the magnetic brush type charging member of the first embodiment.

FIG. 4 is a schematic longitudinal sectional view of one end of a magnetic brush type charging member according to a second embodiment.

FIG. 5 is a schematic longitudinal sectional view of one end of a charging member according to a modification of the second embodiment.

FIG. 6 is a schematic longitudinal sectional view of one end of a magnetic brush type charging member according to a third embodiment.

FIG. 7 is a view showing a modification of the third embodiment.

FIG. 8 is a schematic longitudinal cross-sectional view of one end side of a drum and a magnetic brush type charging member of the device of Embodiment 4.

FIG. 9 is a schematic longitudinal sectional view of one end side of a drum and a magnetic brush type charging member of the device of Embodiment 5.

10A is a cross-sectional model diagram of a magnetic brush type charging member of the device of Embodiment 6, FIG. 10B is a plan model diagram, and FIG. 10C is a longitudinal cross-sectional model diagram of one end side.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Mashimo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Non-corporation (72) Inventor Yasushi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-6-11951 (JP, A) JP-A-6-27805 ( JP, A) JP-A-6-3928 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 G03G 15/09 G03G 21/00 350

Claims (22)

(57) [Claims] 1. An image forming apparatus comprising: conductive magnetic particles in contact with a member to be charged; and an electrode member that supports the magnetic particles and to which a voltage is applied. The electrode member charges the member to be charged via the magnetic particles. A charging device for charging by injecting an electric charge, wherein a charge is not injected from the electrode member into the magnetic particles at the end portions. 2. The resistance of the magnetic particles is 1 × 10 ⁴ to 1
The charging device according to claim 1, wherein the charging device has a resistance of 10 ⁷ Ω. 3. An insulating member is provided at a position corresponding to a magnetic particle end on the surface of said electrode member.
Or the charging device according to 2. 4. The charging device according to claim 1, wherein an end of the electrode member to which the voltage is applied is located inside magnetic particles. 5. An image carrier, comprising: conductive magnetic particles that come into contact with the image carrier; and an electrode member that supports the magnetic particles and to which a voltage is applied. An image forming apparatus in which charge is injected by injecting an electric charge into an image carrier, wherein an electric charge is not injected from an electrode member into magnetic particles at an end portion. 6. The magnetic particles have a resistance of 1 × 10 ⁴ to 1 ×.
6. The image forming apparatus according to claim 5, wherein the resistance is 10 ⁷ Ω. 7. An insulating member is provided at a position corresponding to an end of a magnetic particle on the surface of the electrode member.
Or, the image forming apparatus according to 6. 8. The image forming apparatus according to claim 5, wherein an end of the electrode member to which the voltage is applied is located inside magnetic particles. 9. The image forming apparatus according to claim 5, wherein the image carrier has a charge injection layer into which charges are injected from magnetic particles. 10. The volume resistivity of the charge injection layer is 1 ×
The image forming apparatus according to claim 9, wherein the value is 10 ⁹ to 1 × 10 ¹⁵ Ωcm. 11. A charging member, comprising a charge holding layer for holding charges and a conductive substrate, to which a voltage can be applied to charge an object to be charged. A charging member including magnetic particles that can be contacted, wherein the charged body is provided with the conductive substrate in a region of the charged body corresponding to an end of the magnetic particle in a longitudinal direction of the charging member. And a conductive member electrically insulated from the charging member. 12. The charging device according to claim 11, wherein the conductive member is provided on a surface of the member to be charged. 13. The charging device according to claim 12, wherein the conductive member is capable of contacting the magnetic particles. 14. The magnetic particles have a resistance of 1 × 10 ⁴ or more.
The charging device according to claim 11, wherein the charging device has a resistance of 1 × 10 ⁷ Ω. 15. The image forming apparatus according to claim 11, wherein the object to be charged is an image carrier, and the image carrier and the charging device are provided in a process cartridge that is detachable from an image forming apparatus. The charging device according to any one of the above. 16. An image carrier having a charge retention layer for retaining a charge and a conductive substrate, and a charging member to which a voltage can be applied to charge the image carrier, wherein the charging member is a magnetic brush. A charging member including magnetic particles that can be brought into contact with the image carrier, wherein the image carrier is an image carrier corresponding to an end of the magnetic particles in a longitudinal direction of the charging member. An image forming apparatus comprising: a conductive member that is electrically insulated from the conductive base in a region. 17. The image forming apparatus according to claim 16, wherein the charge holding layer is a charge injection layer, and charges are injected into the charge injection layer by contact with the magnetic particles. 18. The volume resistivity of the charge injection layer is 1 ×
The image forming apparatus according to claim 17, wherein the value is 10 ⁹ to 1 × 10 ¹⁵ Ωcm. 19. The image forming apparatus according to claim 16, wherein the conductive member is provided on a surface of the image carrier. 20. The image forming apparatus according to claim 19, wherein the conductive member is capable of contacting the magnetic particles. 21. The resistance of the magnetic particles is 1 × 10 ⁴
The image forming apparatus according to any one of claims 16 to 20, wherein the image forming apparatus has a resistance of from about 1 to 10 ⁷ Ω. 22. The charge holding layer has a photosensitive layer, and an effective width of the magnetic brush is longer than a coating width of the photosensitive layer in a longitudinal direction of the charging member. 22. The image forming apparatus according to any one of claims 21 to 21.