JPH08328359A - Electrifying device, process cartridge and image forming device - Google Patents

Abstract

PURPOSE: To prevent magnetic particles from being separated from a contact type magnetic brush electrifying device and the magnetic particles from sticking to a substance to be electrified in the contact type magnetic brush electrifying device and a process cartridge and an image forming device equipped with the electrifying device. CONSTITUTION: This image forming device is equipped with a carrier 21 which carries a magnetic particle layer 24 capable of coming into contact with the object to the electrified 1 and can be impressed with voltage, and provided with an electrifying member electrifying the movable object to be electrified 1. The direction of magnetic force acting on the magnetic particles of the layer 24 at an end position A on a downstream side in the moving direction of the object to be electrified at a contact part D between the object to be electrified 1 and the magnetic particles is reverse to a side where the object to be electrified 1 is set with respect to the tangent of the object to be electrified 1 at the position A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type charging device for charging an object to be charged (including static elimination),
The present invention relates to a process cartridge provided with a charging device and an image forming apparatus.

[0002]

2. Description of the Related Art As a charging device for charging an object to be charged such as a photoconductor, a magnetic brush type charging device having a magnetic particle layer is known from JP-A-6-130777.

The magnetic brush type charging device is one in which magnetic particles are bound to a carrier by magnetic force and attached and held as a magnetic brush. The magnetic brush is brought into contact with an object to be charged and a voltage is applied to the object to be charged. It charges the body.

More specifically, the magnetic brush carrier is a rotatable sleeve, and magnetic particles are bound to the outer surface of the sleeve by the magnetic force of a fixed magnet roll (magnet) arranged in the sleeve. It is of a form (sleeve type) that is adhered and held as.

FIG. 10 is a schematic model view of the above-mentioned sleeve type magnetic brush type charging device.

Reference numeral 21 denotes a non-magnetic conductive sleeve (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) such as aluminum as a magnetic brush carrier.

Reference numeral 22 denotes a magnet roll as a magnetic field generating means inserted and arranged in the sleeve 21. NS
Is the magnetized part of the roll. This magnet roll 22
Is a non-rotating fixing member, and this magnet roll 22
The sleeve 21 is concentrically driven around the outer periphery of the shaft in the clockwise direction b as indicated by an arrow by a drive mechanism (not shown) at a predetermined peripheral speed.

Reference numeral 23 is a conductive magnetic particle (hereinafter referred to as a carrier), which is attached to the outer peripheral surface of the sleeve 21 as a magnetic brush (conductive magnetic brush) 24 by being held by the magnetic force of a magnet roll 22 inside the sleeve. Has been done.

The carrier 23 forms a magnetic spike on the outer surface of the sleeve 21 due to the magnetic restraining force of the magnet roll 22, and these are gathered into a brush shape.

S1 is a power source for applying a charging bias to the sleeve 21.

Reference numeral 1 denotes a member to be charged, which is, for example, a drum type electrophotographic photosensitive member which is rotationally driven in a clockwise direction a as indicated by an arrow at a predetermined process speed.

The magnetic brush charging member 2 is arranged so that the magnetic brush 24 is brought into contact with the surface of the member to be charged 1 to form a contact nip portion (charging nip portion) D.

The magnetic brush 24 is rotatively conveyed in the same direction as the sleeve 21 rotates, and rubs against the surface of the rotating photoconductor 1 at the charging nip portion D, and the sleeve 21 from the power source S1.
By the charging bias applied to the magnetic brush 24 via the magnetic brush 24, the surface of the rotary photosensitive member 1 as the member to be charged is charged by the contact method. In the contact nip portion D, the rotating direction of the sleeve 21 and the accompanying rotating and conveying direction of the magnetic brush 24 are counter directions with respect to the rotating direction of the rotating photoconductor 1 as the charged body.

The sleeve 21 has a carrying function for the magnetic brush 24, a carrying function, and a charging bias application electrode function.

The magnetic brush type charging device described above is particularly preferably applied to the following injection charging method.

In this injection charging system, a DC voltage corresponding to a desired Vd is applied to the contact charging member to inject charges into the trap level on the surface of the charged body, or a protective film having conductive particles dispersed therein is provided. The desired Vd is obtained by charging the electrically conductive particles of the body to be charged.
As a method of injecting electric charge into the float electrode on the charged body (photoreceptor) provided with a charge injection layer on the surface to perform contact charging, as a charge injection layer, an acrylic resin is applied to the surface of the photoreceptor with antimony-doped conductive filler It is possible to coat and use a dispersion of electrically conductive SnO ₂ particles.

In such an injection charging method, since the charging member and the member to be charged are in direct contact with each other to transfer the electric charge,
It is desirable that the two are in intimate contact with each other and that there is no microscopic charge and no residual. Therefore, as the charging device used in the injection charging method, a magnetic brush-like device is suitable from the viewpoint of a member that can be in close contact with the charged body and can have a peripheral speed difference with respect to the charged body. ing.

[0018]

The magnetic brush type charging device has the following problems.

Detachment of the carrier 23 from the magnetic brush 24 and adhesion of the detached carrier 23 to the surface of the member to be charged; that is, the carrier 23 constituting the magnetic brush 24 escapes from the magnetic binding force and is detached to be charged. The carrier 23 of the magnetic brush 24, which contributes to charging by being attached to one surface and carried away, decreases over time, resulting in charging failure.

Further, there is an adverse effect due to the detached carrier sticking to the surface of the body to be charged. For example, in the image forming apparatus: Inhibition of image exposure by the carrier attached to the photoconductor as the charged body. Poor development at the carrier attachment position on the photoconductor. Developability is deteriorated when the carrier is mixed in the developing device. When the carrier is transferred to the transfer material, the carrier is not fixed in the fixing process after the transfer. The carrier that has not been transferred may be caught between the cleaning blade and the photosensitive member at the cleaning position, which may cause damages on the photosensitive member.

An object of the present invention is to provide a charging device, a process cartridge, and an image forming apparatus which prevent the magnetic particles from being detached from the magnetic brush-shaped charging device and the magnetic particles from being attached to the member to be charged.

Another object of the present invention is to provide a charging device, a process cartridge, and an image forming apparatus which prevent charging failure due to detachment of magnetic particles from the magnetic brush-shaped charging device.

[0023]

The present invention is a charging device, a process cartridge, and an image forming apparatus characterized by the following configurations.

(1) A charging device having a carrier for carrying a magnetic particle layer capable of contacting a charged body and having a voltage applied thereto, and having a charging member for charging a movable charged body. In the contact portion between the charged body and the magnetic particles, the direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the end position on the downstream side in the moving direction of the charged body is the direction at the end position. A charging device, which is on a side opposite to a side where the charged body is provided with respect to a tangent line of the charged body.

(2) The charging device according to (1), wherein the carrier is a rotatable sleeve, and the charging member includes a non-rotating magnet in the sleeve.

(3) The charging device according to (1) or (2), characterized in that it has a maintaining means for maintaining a constant distance between the carrier and the member to be charged.

(4) The charging device according to (3), characterized in that the maintaining means is a spacer member provided at an end portion in the longitudinal direction of the carrier and in contact with the body to be charged.

(5) The charging device according to (4), wherein the spacer member is pressed toward the body to be charged.

(6) A process cartridge attachable to and detachable from an image forming apparatus, having a movable charged member capable of carrying an image and a charging member charging the charged member, wherein the charging member is In a process cartridge that carries a magnetic particle layer capable of contacting a charged body and is provided with a carrier to which a voltage can be applied, the charged body movement at a contact portion between the charged body and the magnetic particles. The direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the end position on the downstream side in the direction is opposite to the side on which the charged body is provided with respect to the tangent line of the charged body at the end position. Process cartridge characterized by being on the side.

(7) The process cartridge according to (6), wherein the member to be charged has a charge injection layer into which charges are injected from the contact portion.

(8) The volume resistivity of the charge injection layer is 1 ×
The process cartridge according to (7), wherein the process cartridge has a density of 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm.

(9) The process cartridge according to any one of (6) to (8), wherein the member to be charged has an electrophotographic photosensitive layer.

(10) An image forming apparatus having a movable charged body capable of carrying an image and a charging member for charging the charged body, wherein the charging member can contact the charged body. In an image forming apparatus having a carrier capable of carrying a certain magnetic particle layer and capable of being applied with a voltage, an end portion on a downstream side in a moving direction of the charged body at a contact portion between the charged body and the magnetic particles. The direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the position is opposite to the side where the charged body is provided with respect to the tangent line of the charged body at the end position. Image forming apparatus.

(11) The image forming apparatus according to (10), wherein the member to be charged has a charge injection layer into which charges are injected from the contact portion.

(12) The volume resistivity of the charge injection layer is 1
The image forming apparatus according to (11), wherein the image forming apparatus has a density of × 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm.

(13) The image forming apparatus according to any one of (10) to (12), wherein the member to be charged has an electrophotographic photosensitive layer.

<Operation> That is, a magnetic brush type charging device,
Regarding the process cartridge and the image forming apparatus using the charging device, the direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the end position on the downstream side in the moving direction of the charged object at the contact portion between the charged object and the magnetic particles. However, the force of pressing the magnetic particles of the magnetic particle layer against the charged body by configuring the end position at the side opposite to the side on which the charged body is provided with respect to the tangent line of the charged body. Becomes weaker, the magnetic particles do not substantially adhere to the body to be charged, and it is possible to prevent the magnetic particles from separating from the charging device and the magnetic particles from attaching to the body to be charged. It is possible to prevent charge failure due to detachment and adhesion of magnetic particles to the body to be charged, and it is possible to solve problems such as image failure due to the process cartridge and the image forming apparatus.

By having the maintaining means for keeping the distance between the carrier of the charging member and the member to be charged constant, the adhesion of the magnetic particles to the member to be charged can be more stably reduced, and
Since the width of the contact portion of the magnetic particle layer with respect to the member to be charged does not decrease, the contact portion width is always constant, partial charging failure does not occur, and the chargeability is always good, and the image forming apparatus In that case, a uniform image can be obtained.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION

 First Embodiment Example (1) Image Forming Apparatus Example (FIG. 1) FIG. 1 is a schematic view of an image forming apparatus example.

The image forming apparatus of this embodiment is a laser beam printer using a process cartridge attachment / detachment type transfer type electrophotographic process.

Further, the image carrier is an OPC photosensitive member having a charge injection function on its surface, and the magnetic brush charging member is used as the contact charging member, and the image carrier is subjected to the primary charging process by the injection charging method. .

Reference numeral 1 is a rotary drum type electrophotographic photosensitive member as an image bearing member, and in the present embodiment, it is an OPC photosensitive member having a diameter of 30 mm and having a charge injection function on its surface, and is 100 mm in the clockwise direction a shown by the arrow. It is driven to rotate at a process speed (peripheral speed) of / sec. The layer structure of the photoconductor will be described in detail in item (2).

Reference numeral 2 denotes a contact charging member for uniformly charging the peripheral surface of the photosensitive member 1 to a predetermined polarity and potential, and in this embodiment, the sleeve type magnetic brush charging member shown in FIG. The magnetic brush charging member 2 will be described in detail in section (3).

The sleeve 21 of the magnetic brush charging member 2
A -700V DC charging bias is applied from the charging bias applying power source S1 to the charging roller, so that the outer peripheral surface of the rotating photoconductor 1 is uniformly charged to about -700V by charge injection charging.

A laser whose intensity is modulated corresponding to a time-series electric digital pixel signal of target image information output from a laser beam scanner 7 including a laser diode, a polygon mirror, etc. on the charged surface of the rotating photosensitive member 1. Scanning exposure L is performed by the beam, and an electrostatic latent image corresponding to target image information is formed on the peripheral surface of the rotating photoconductor 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
A non-magnetic developing sleeve of 6 mm, the developing sleeve 3a is coated with the above negative toner, and the gap (separation distance) from the surface of the photoconductor 1 is fixed to 300 μm,
The photoconductor 1 is rotated at the same speed and a developing bias voltage is applied to the developing sleeve 3a from the developing bias power source S2. As the voltage, a DC voltage of -500 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superposed, and jumping development is performed between the sleeve 3 a and the photoconductor 1. That is, the negatively charged toner carried by the developing sleeve 3a is attached to the image portion of the latent image by an electric field to develop the latent image.

On the other hand, a transfer material 30 as a recording material is supplied from a paper feeding portion (not shown), and the rotary photosensitive member 1 and a contact transfer means abutting against the rotary photosensitive member 1 with a predetermined pressing force have a medium resistance. It is introduced into the pressure contact nip portion (transfer portion) T with the transfer roller 4 at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 4 from the transfer bias applying power source S3. In this embodiment, as the transfer roller 4, a roller having a resistance value of 5 × 10 ⁸ Ω having a core metal formed with a medium resistance foam layer is used, and a DC voltage of +2000 V is applied to the core to charge the back surface of the transfer material. Transferred.

The transfer material 30 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 photoconductor 1 are sequentially held on the surface side thereof by electrostatic force and pressing force. Will be transcribed.

The transfer material 30 to which the toner image has been transferred is separated from the surface of the photoconductor 1 and is introduced into a fixing device 5 such as a heat fixing system to receive the toner image fixing, and an image-formed product (print, copy). Is discharged outside the device.

The surface of the photoconductor after the transfer of the toner image to 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.

In the image forming apparatus of this embodiment, four process devices including the photoconductor 1, the magnetic brush charging member 2, the developing device 3 and the cleaning device 6 are collectively attached to and detachable from the image forming apparatus main body. The cartridge 10 is provided. 9 is the above four process devices 1, 2, 3, 6
Is a cartridge housing in which is mounted in a predetermined arrangement. Reference numeral 8 denotes a process cartridge insertion / removal guide / holding portion on the image forming apparatus main body side.

In a state where the process cartridge 10 is mounted in the image forming apparatus main body in a predetermined manner, the process cartridge 10 side and the image forming apparatus main body side are mechanically
The mutual mutual coupling is established electrically, and the lower surface of the photosensitive member 1 on the process cartridge 10 side is brought into contact with the transfer roller 4 on the image forming apparatus main body side in a predetermined manner, so that the image formation can be executed.

The process cartridge is a cartridge in which a charging unit, a developing unit or a cleaning unit, and an electrophotographic photosensitive member are integrally formed, and the cartridge can be attached to and detached from the main body of the image forming apparatus.
Further, at least one of the charging means, the developing means, and the cleaning means and the electrophotographic photosensitive member are integrally made into a cartridge so that it can be attached to and detached from the main body of the image forming apparatus. Further, it means that at least the developing means and the electrophotographic photosensitive member are integrally made into a cartridge so as to be attachable to and detachable from the apparatus main body.

(2) Photoreceptor 1, Injection Charging a) Regarding Photoreceptor 1 (FIG. 2) FIG. 2 is a model diagram of the layer structure of the photoreceptor 1 as the member to be charged used in this embodiment. The photoconductor 1 used in this example is a negatively charged OPC photoconductor having a charge injection function on the surface, and the following first to fifth functional layers on a drum base 11 made of aluminum having a diameter of 30 mm. 12 to 16 are provided in order from the bottom.

The first layer is the undercoat layer 12, which is provided for smoothing out defects on the outer peripheral surface of the aluminum drum substrate 11 and for preventing moire due to reflection of laser exposure from being about 20 μm thick. Of the conductive layer.

The second layer is a positive charge injection preventing layer 13, which plays a role of preventing the positive charges injected from the aluminum base 11 from canceling out the negative charges charged on the surface of the photoreceptor, and the amylan resin and methoxymethyl. It is a medium resistance layer having a thickness of about 1 μm whose resistance is adjusted to about 10 ⁶ Ωcm by means of nylon.

The third layer is the charge generating layer 14, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs by being exposed to laser.

The fourth layer is the charge transport layer 15, 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 13 can be transported to the surface of the photoconductor.

The fifth layer is the charge injection layer 16, which is made of a photocurable acrylic resin and ultrafine conductive particles (conductive filler).
16a is a coating layer of a material in which SnO ₂ is dispersed.
Specifically, antimony-doped SnO ₂ particles with a low resistance of about 0.03 μm are added to the resin in an amount of 70%.
It is a coating layer of a material in which overlapping percentages are dispersed. 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 resistance on the surface of the photosensitive member 1 was 1 × 10 ¹⁵ Ωcm in the case of the charge transport layer alone, compared with 1
It decreased to × 10 ¹³ Ωcm.

The charge injection layer 16 intentionally creates injection sites for uniformly charging the surface by directly injecting charges from the magnetic brush charging member 2, but the latent image charges flow on the surface. So that the charge injection layer 16 has a resistance of 1 ×
It is good that it is 10 ⁸ Ωcm or more. The resistance value of the charge injection layer 16 is obtained by coating a charge injection layer on aluminum and applying Y
High resistance meter 4 made by HP (Yokogawa Hewlett-Packard)
The volume resistivity was measured at an applied voltage of 100 V at 329 A. The volume resistivity of the injection layer is preferably 1 × 1
0 ¹⁰ to 10 ¹⁴ Ωcm is preferable.

In this embodiment, the charge injection layer 16 is formed as an independent layer. However, it is important that the surface layer of the photoconductor has an electron level capable of donating electrons, and the charge injection layer 16 is independently provided. It is not limited.

In order to reduce the adhesion of the carrier on the magnetic brush charging member side to the surface of the photoconductor, it is preferable that the photoconductor 1 has a characteristic of low surface energy, and a desired lubricant is added to the outermost surface of the photoconductor to make it uniform. Good to get smoothness.

B) Regarding Injection Charging (FIG. 3) The charge injection charging of the photoconductor in this embodiment is a contact charging member having a medium resistance, and the charge injection is performed on the surface of the photoconductor having a medium resistance surface resistance. The charge injection layer 16 does not inject charges into the trap potential of the surface material of the photoconductor.
This is a method of charging the conductive particles 16a by charging. When a desired voltage is applied to the magnetic brush charging member 2 at the time of charging, charges are injected into the charge injection layer 16 and the surface of the photoreceptor 1 as a charged body is finally charged (charged) to the same potential as the magnetic brush 24. To be done.

Specifically, as shown in the model diagram / equivalent circuit diagram of FIGS. 3A and 3B, the photoconductor 1 is composed of the charge transport layer 1
5 can be regarded as a dielectric, and the aluminum drum substrate 11 and the conductive particles 16a (SnO ₂ ) in the charge injection layer 16 can be regarded as a parallel assembly of minute capacitors. This is based on the theory that the contact charging member 2 charges a minute capacitor.

The conductive particles 16a are electrically independent of each other and form a kind of minute float electrode. For this reason, the surface of the photoconductor 1 seems to be charged and charged to a uniform potential on a macroscopic scale, but in reality, a myriad of charged electrically conductive particles 16a cover the photoconductor surface. Has become. Therefore, even if the image exposure L is performed by the laser, the conductive particles 16a are electrically independent, so that the electrostatic latent image can be held.

(3) Magnetic Brush Charging Member 2 (FIG. 4) FIG. 4 is a structural model view of the magnetic brush charging member 2 as the contact charging member used in this embodiment. belongs to.

That is, the carrier holding the carrier 23 constituting the magnetic brush 24 is a rotatable non-magnetic conductive sleeve 21 (hereinafter referred to as sleeve or charging sleeve).
The carrier 23 is constrained to the outer surface of the sleeve 21 by the magnetic force of the fixed magnet roll 22 as the magnetic field generating means disposed in the sleeve 21, and is attached and held as the magnetic brush 24.

In this embodiment, the outer diameter of the sleeve 21 is 16 m.
m. The amount of carrier of the magnetic brush 24 is about 10 g,
The gap α between the charging sleeve 21 and the photoconductor 1 at the contact nip portion (charging nip portion) D between the magnetic brush 24 and the photoconductor 1 is 500 μm. Also, the longitudinal width of the magnetic brush is 2
30 mm.

The carrier 23 on the sleeve 21 has a thickness of 1 m.
The magnetic brush 24 is formed and held by forming a contact nip portion D having a width of about 5 mm between the magnetic brush 24 and the photoconductor 1, and the sleeve 21 is brought into contact with the surface of the rotary photoconductor 1. To rotate in the counter direction (the photosensitive member moving direction and the sleeve moving direction are opposite to each other at the nip portion D).
The magnetic brush 24 rotates in the same direction as the sleeve 21 by the rotation of the sleeve 21, and the carrier 23 constituting the magnetic brush is conveyed. The carrier passes through the contact nip portion D while successively contacting the surface of the photoconductor 1. To go.

Photoreceptor 1 and magnetic brush 2 as members to be charged
A carrier reservoir 24a is formed at an end of the contact nip portion D of FIG.

A) Peripheral speed ratio between the magnetic brush 24 and the photoconductor 1 The peripheral speed ratio between the magnetic brush 24 and the photoconductor 1 is defined by the following formula.

Peripheral speed ratio% = (magnetic brush peripheral speed-photoconductor peripheral speed) / photoconductor peripheral speed x 100 * The peripheral speed of the magnetic brush is a negative value in the case of counter rotation. The peripheral speed ratio of -100% is the magnetic brush. Since 24 is in a stopped state, the stopped shape of the magnetic brush 24 on the surface of the photoconductor is likely to cause a charging failure. Also, the forward rotation is
When the magnetic brush 24 comes into contact with the photoconductor 1 at a slow speed, the carrier 23 of the magnetic brush 24 easily adheres to the photoconductor 1, and when the same peripheral speed ratio as the counter direction is obtained,
The rotation speed of the magnetic brush 24 will increase. Therefore,
The peripheral speed ratio is preferably -100% or less, and in the present embodiment, -1.
It was set to 50%.

B) Carrier 23 Carrier 2 which is magnetic particles constituting the magnetic brush 24
3, the resin and magnetic powder such as magnetite are kneaded and molded into particles, or conductive carbon or the like is mixed to adjust the resistance value, sintered magnetite, ferrite, or these Whose resistance value has been adjusted by reduction or oxidation treatment of the above carrier, or the above carrier coated with a resistance-adjusted coating material (such as phenol resin with carbon dispersed) or N
It is considered that the resistance value is set to an appropriate value by plating with a metal such as i. In order to reduce the damage to the photoconductor 1, the carrier 23 is preferably spheroidized.

If the resistance value of these carriers 23 is too high, the charge cannot be uniformly injected into the photosensitive member 1 and a fog image is formed due to a minute charging failure. If it is too low, when there are pinholes on the surface of the photoconductor, current concentrates on the pinholes, the charging voltage drops, and the surface of the photoconductor cannot be charged, resulting in charging nip-shaped charging failure. Therefore, as the resistance value of the carrier 23, 1 × 10 ⁴ to 1 × 10 ⁷ Ω
Is desirable. With respect to the resistance value of the carrier 23, 2 g of the carrier was put in a metal cell (bottom area 228 mm ² ) to which a voltage can be applied, and then the carrier was weighted at 6.6 kg / cm ² , and the voltage was 1
It is defined as a value obtained by applying a voltage of up to 1000 V, for example 100 V, and calculating from the measured current flowing in this system and normalizing it.

It is also possible to improve the chargeability by mixing and using a plurality of types of carriers.

If the particle size of the carrier 23 is too small, the magnetic binding force becomes small, and the carrier tends to adhere to the surface of the photosensitive member 1. On the other hand, if it is too large, the contact area with the photosensitive member 1 is reduced, and the charging failure tends to increase.
Therefore, the average particle size of the carrier is preferably about 5 to 500 μm from the viewpoints of chargeability and magnetic retention.

[0078] The magnetic properties of the carrier, it is better to increase the magnetic binding force in order to prevent the carrier adhesion to the photosensitive member, the saturation magnetization 30A · m ² / kg or more, more preferably 50A · m ² / More than kg is desirable.

The saturation magnetization of the particles is measured using an oscillating magnetic field type automatic recording apparatus for magnetic characteristics BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic characteristic value of the carrier powder is an external magnetic field of ± 1 kilo-Oersted, and the strength of magnetization when the magnetic field is 1 kilo-Oersted is obtained from the Hysteris curve at that time.

The carrier 23 actually used in this embodiment is
The average particle size is 30 μm, the shape is spherical, and the resistance value is 1 × 10 ^6.
Ω, the saturation magnetization was 58 A · m ² / kg.

(C) Magnetic Force The fixed magnet roll 22 as the magnetic field generating means used in this embodiment is a S ₁ · N ₁ · S ₂ · N ₂ quadrupole magnetizing roll, and the surface of the charging sleeve 21 is FIG. 5 shows the magnetic flux density distribution of the magnet roll 22 in the normal direction. The negative value on the vertical axis indicates the S pole, the positive value indicates the N pole, and the direction in which the angle on the horizontal axis decreases is the charging sleeve rotation direction.

The main magnetic pole S ₁ of the fixed magnet roll 22 is near the closest position (point P in FIG. 4) between the charging sleeve 21 and the photoconductor 1 so that the carrier 23 of the magnetic brush 24 does not adhere to the photoconductor 1. Is desirable. In this embodiment, the magnetic flux density of the main magnetic pole S ₁ and the carrier 23 of the magnetic brush 24 is retained in the gap α of the contact nip D so as not to inhibit the charging property, the closest position of the main magnetic pole S ₁ P
It is set at a position (point S in FIG. 4) further displaced by 6 ° (−6 °) toward the rotation direction of the charging sleeve. As a result, the force with which the carrier of the magnetic brush 24 is pulled out from the closest position P acts, and the movement (conveyance) of the magnetic brush carrier in the gap α of the contact nip portion D becomes smooth.

Here, the magnetic flux density in the normal direction of the main magnetic pole S ₁ (point S in FIG. 4) is about 840 × 10 ⁻⁴ T (Tesla) at the 270 ° position on the horizontal axis of the graph of FIG. , Magnetic brush 2
The magnetic flux density at the closest position (point P in FIG. 4) between the charging sleeve 21 of No. 4 and the photoconductor 1 is 276 ° on the horizontal axis of the graph of FIG.
It is about 816 × 10 ⁻⁴ T at the position.

The magnetic force F acting on the carrier within the magnetic flux density is F = (μ-μo) / {μo (μ + 2μo)} 2πb ³ gr
It is represented by adiantB ² .

Μ o: Permeability of vacuum μ: Permeability of magnetic particles (carrier) b: Radius of magnetic particles B: Magnetic flux density The magnetic force can be calculated using this formula, and the magnetic force F
Is a value proportional to the square of the magnetic flux density B.

Therefore, the photoconductor 1 and the magnetic brush 24 are at positions where it is determined whether the carrier 23 of the magnetic brush 24 adheres to the surface of the photoconductor 1 as the charged body or not.
Let Fr be the component in the normal direction of the magnetic force at the downstream end position A of the photosensitive member in the contact nip portion D and the component in the tangential direction be Fθ, the resultant force vector F of these forces at position A The magnetic force acts on the magnetic brush carrier.
Note that Fr is a component in the normal direction of the magnet roll 22, and Fθ is a component in the tangential direction of the magnet roll 22.

As shown in FIG. 6, when the resultant force vector F is directed toward the inside of the photoconductor from the tangential direction C of the photoconductor, the magnetic force is a force for pressing the magnetic brush carrier at the position A against the surface of the photoconductor. Will end up.

Therefore, in the present embodiment, as shown in FIG. 7, the fixed magnetic roll is such that the resultant force F of the magnetic force is directed to the side opposite to the side where the photoconductor is provided with respect to the tangent line C of the photoconductor at the position A. 22 of the magnetic flux density distribution. As a result, the magnetic brush carrier at the position A is no longer pressed against the photoconductor 1 by the magnetic force, so that the adhesion of the magnetic brush carrier 23 to the photoconductor 1 can be significantly reduced. Therefore, the image defect due to the magnetic brush carrier 23 adhering to the photoconductor 1 can be improved.

This relationship will be described with reference to FIG.
The outside of the photoconductor of Fθ is taken as a reference line, which is set to 0 ° (180 ° toward the photoconductor), the angle between the direction C of the tangential direction of the photoconductor surface and the reference line is taken as θC, and the angle between the vector F and the reference line is taken. Is θF, θF is ARCTAN (Fθ / F
It can be calculated by r), and when θF <θC, the magnetic force acting on the magnetic brush carrier at the position A is not directed to the photoconductor 1.

The nip width at which the magnetic brush and the photosensitive member come into contact with each other in the moving direction of the photosensitive member is preferably 2 to 10 mm in order to perform sufficient charging, and more preferably 3 to.
It is good to set it to 7 mm. Also, the closest position P and the end position A
The length of and is 0.5 to 9 mm for sufficient charging.
It is preferable that the thickness is 2 mm, more preferably 2 to 6 mm.

The magnet roll 22 used in this embodiment
Then, by changing the magnetic pole arrangement variously, the magnetic brush carrier 2
3 was measured on the surface of the photoconductor 1, and when the main magnetic pole S ₁ moved more than 30 ° from the closest position P in the direction opposite to the sleeve rotation direction (+ 30 °), the resultant force vector F was The amount of adhesion was very large because the surface of the photoconductor was oriented in the tangential direction C. Further, when the position was ± 20 ° with respect to the main magnetic pole S ₁ , the adhesion amount became the minimum. Therefore, the main magnetic pole S ₁ is + 30 ° from the closest position P.
Since the magnetic poles are located at the following positions, and more preferably, the main magnetic pole S ₁ is located at ± 20 ° with respect to the closest position P, the magnetic flux density arrangement is good for preventing carrier adhesion.

In this embodiment, the fixed magnet roll 22 is used.
The magnetic force acting on the magnetic brush carrier at the position A was controlled by changing the magnetic flux density distribution of the magnetic brush 2.
By arranging a magnetic material or magnet outside 4,
It is also possible to obtain the desired direction of magnetic force. In this case, the magnetic force in the vicinity of the contact nip portion D between the magnetic brush 24 and the photosensitive member 1 can be designed in detail, and an effective structure can be easily obtained by preventing the magnetic brush carrier from adhering. .

As is clear from the above description, the direction of the resultant force F of the magnetic force depends on the magnitudes of Fr and Fθ and the end position A.
It is decided by and.

<Second Embodiment> (FIG. 9) In this embodiment, the contact nip between the photoconductor 1 as the member to be charged and the magnetic brush 24 of the magnetic brush charging member 2 is further added to the first embodiment. The magnetic brush charging member 2 is supported so that the gap α between the surface of the photoconductor 1 in the portion D and the surface of the charging sleeve 22 as a magnetic brush carrier is constant. Since the structure other than the structure of the supporting means is the same as that of the first embodiment, the repetitive description will be omitted.

FIG. 9 shows the supporting structure on the one end side of the magnetic brush charging member 2 in the longitudinal direction, and the other end side has the same structure.

Charging sleeve 21 of magnetic brush charging member 2
Both ends of each of the bearings are rotatably supported by bearings 26. The bearing 26 is held by a holding member (not shown) having a degree of freedom of movement in the contacting / separating direction with respect to the photoconductor 1.

A spacer ring (gap roller) 27 for restricting the gap α between the sleeve 21 and the photosensitive member 1 to 500 μm is rotatably fitted on both ends of the charging sleeve 21.

Magnet roll 2 as magnetic field generating means
Reference numeral 2 denotes a non-rotatably fixed, internally-arranged sleeve 21, and the sleeve 21 is rotationally driven concentrically with the fixed magnet roll 22 at a predetermined peripheral speed by a drive system (not shown). A carrier 23 is provided on the outer peripheral surface of the sleeve 21.
Are bound by magnetic force and attached and held as a magnetic brush 24.

Then, the bearings 26 at both ends of the sleeve 21 are pressed and urged toward the photoconductor 1 by the coil springs 29 that are compressed between the bearings 26 at both ends, respectively, and the spacer rings 27 at the both ends of the sleeve 21 are moved. On the surface of both ends of
One side of 500 g and the total of 1000 g are constantly in pressure contact. As a result, the gap α between the charging sleeve 21 and the photoconductor 1 is always maintained at the prescribed 500 μm by the spacer ring 27. The spacer ring 27 rotates following the rotation of the photoconductor 1.

The width of the magnetic brush 24 on the charging sleeve 21 is regulated by the end regulating member 31 so that the magnetic brush 24 does not spread outside the prescribed regulation width in the sleeve longitudinal direction.
The magnetic brush regulation width needs to be longer than the image forming width, and in this embodiment, the regulation width is 230 mm.

As in this embodiment, the surface of the charging sleeve 21 as the magnetic brush carrier and the photoreceptor 1 as the member to be charged.
A spacer member 27 which is driven and rotated by the surface of the photosensitive member 1 is interposed between the surfaces, and the charging sleeve 21 is pressed by the pressing means 29 toward the photosensitive member so that the spacer member 27 is always kept in contact with the surface of the photosensitive member 1. By urging the pressure, the gap α between the surface of the photoconductor 1 and the surface of the charging sleeve at the contact nip portion D between the photoconductor 1 and the magnetic brush 24 is reduced.
If the spacer is eccentric, the spacer member 2
It is possible to always maintain a predetermined constant distance defined by 7.

Therefore, the width of the contact nip portion D between the magnetic brush 24 and the photosensitive member 1 as the member to be charged is always constant,
It is possible to prevent the occurrence of charging failure due to the variation of the width, and it is possible to solve the problem of image failure due to charging failure in the image forming apparatus.

When the photoconductor 1 and the charging sleeve 21 are individually fixed, the surface of the photoconductor 1 and the charging sleeve 2 are fixed.
The distance of the gap α of 1 is not always constant, and the magnetic brush carrier portion at the downstream end position A in the photoconductor rotating direction in the contact nip portion D between the photoconductor 1 and the magnetic brush 24 described in the first embodiment is provided. The magnetic force that works changes. Therefore, the direction of the magnetic force at the position A may be more toward the inside of the photoconductor than the tangent to the surface of the photoconductor, in which case the magnetic brush carrier is attached to the photoconductor 1.

In the case of the present embodiment, when an image was actually output and evaluated using the image forming apparatus described above, there was no charging unevenness and there was no image defect due to the adhesion of the magnetic brush carrier. It was possible to obtain a good image that does not exist. The structure of this embodiment is an effective means for further stabilizing the structure of the first embodiment.

In each of the above embodiments, the magnetic brush is used as the contact charging member of the injection charging method, but the magnetic brush charging member of the present invention is used as the charging member in the contact charging method other than the injection charging method. You can also

The image forming apparatus is not limited to the process cartridge attaching / detaching method of the embodiment. It is not limited to laser beam printers.

[0107]

As described above, according to the present invention, in the magnetic brush type charging device, the process cartridge and the image forming apparatus using the charging device, the charged body moves at the contact portion between the charged body and the magnetic particles. The direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the end position on the downstream side in the direction is opposite to the side where the charged body is provided with respect to the tangent line of the charged body at the end position. With such a configuration, the force of pressing the magnetic particles of the magnetic particle layer against the charged body becomes weak, the magnetic particles do not substantially adhere to the charged body, and the magnetic particles are separated from the charging device. It is possible to prevent magnetic particles from adhering to the member to be charged, prevent magnetic particles from being separated from the charging device, and prevent charging failure due to adhesion of magnetic particles to the member to be charged. Is It is possible to solve the problems such as generation of image defects caused by Les.

By having the maintaining means for keeping the distance between the carrier of the charging member and the member to be charged constant, the adhesion of magnetic particles to the member to be charged can be more stably reduced, and
Since the width of the contact portion of the magnetic particle layer with respect to the member to be charged does not decrease, the contact portion width is always constant, partial charging failure does not occur, and the chargeability is always good, and the image forming apparatus In that case, a uniform image can be obtained.

[Brief description of drawings]

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

FIG. 2 is a model diagram of the layer structure of a photoconductor.

FIG. 3 is an explanatory diagram of the principle of injection charging.

FIG. 4 is a structural model diagram of a magnetic brush charging member as a contact charging member used in this embodiment.

FIG. 5: Magnetic flux density distribution graph of magnet roll

FIG. 6 is an explanatory diagram of the magnetic force acting on the magnetic brush carrier at the end portion of the contact nip portion between the photoconductor and the magnetic brush on the downstream side in the photoconductor rotation direction (Part 1).

FIG. 7 is an explanatory diagram of the magnetic force acting on the magnetic brush carrier at the end position on the downstream side in the photoconductor rotation direction in the contact nip portion between the photoconductor and the magnetic brush (No. 2).

FIG. 8 is an explanatory diagram of the magnetic force acting on the magnetic brush carrier at the end portion of the contact nip portion between the photoconductor and the magnetic brush on the downstream side in the photoconductor rotation direction (Part 3).

FIG. 9 is a schematic view of a support structure on the longitudinal one end side of the magnetic brush type charging device.

FIG. 10 is a schematic configuration model diagram of a sleeve type magnetic brush type charging device.

[Explanation of symbols]

 1 Charged Member (Electrophotographic Photosensitive Member) 2 Magnetic Brush Charging Member 21 Sleeve 22 Magnet Roll 23 Magnetic Particles (Carrier) 24 Magnetic Brush 25 Core Metal 26 Bearings 27 Spacer Member (Gap Roll) 28 Spring Bearing 29 Pressing Means (Coil Spring) 31 magnetic brush end regulating member S1 charging bias applying power source 3 developing device 4 transfer roller 5 fixing device 6 cleaning device 10 process cartridge 30 recording material (transfer material)

Front page continuation (72) Inventor Yasunori Kono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeo Yamamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Within

Claims (13)

[Claims] 1. A carrier, which carries a magnetic particle layer that is capable of contacting a body to be charged and to which a voltage can be applied,
In a charging device having a charging member for charging a movable charged body, magnetic particles of the magnetic particle layer at an end position on the downstream side in the moving direction of the charged body at a contact portion between the charged body and the magnetic particles. The charging device is characterized in that the direction of the magnetic force acting on is opposite to the side where the charged body is provided with respect to the tangent line of the charged body at the end position. 2. The charging device according to claim 1, wherein the carrier is a rotatable sleeve, and the charging member includes a non-rotating magnet in the sleeve. 3. The charging device according to claim 1, further comprising a maintaining unit that maintains a constant distance between the carrier and the body to be charged. 4. The charging device according to claim 3, wherein the maintaining unit is a spacer member that is provided at an end portion in the longitudinal direction of the carrier and contacts the member to be charged. 5. The charging device according to claim 4, wherein the spacer member is pressed toward the body to be charged. 6. A process cartridge attachable to and detachable from an image forming apparatus, comprising a movable charged member capable of carrying an image, and a charging member charging the charged member, wherein the charging member is the charged member. In a process cartridge that carries a magnetic particle layer capable of contacting a charged body and is provided with a carrier to which a voltage can be applied, the moving direction of the charged body at a contact portion between the charged body and the magnetic particles. The direction of the magnetic force acting on the magnetic particles of the magnetic particle layer at the downstream end position is opposite to the side on which the charged body is provided with respect to the tangent line of the charged body at the end position. Process cartridge characterized by being. 7. The charged body comprises a charge injection layer into which charges are injected from the contact portion.
The process cartridge described in 1. 8. The volume resistivity of the charge injection layer is 1 × 10.
8. The resistance is ¹⁰ to 1 × 10 ¹⁴ Ωcm.
The process cartridge described in 1. 9. The process cartridge according to claim 6, wherein the member to be charged has an electrophotographic photosensitive layer. 10. An image forming apparatus, comprising: a movable charged member capable of carrying an image and movable; and a charging member for charging the charged member, wherein the charging member is capable of contacting the charged member. In an image forming apparatus that carries a magnetic particle layer and is provided with a carrier to which a voltage can be applied, an end position on the downstream side in the moving direction of the charged body at a contact portion between the charged body and the magnetic particles. The direction of the magnetic force acting on the magnetic particles of the magnetic particle layer in is the side opposite to the side where the charged body is provided with respect to the tangent line of the charged body at the end position. Image forming apparatus. 11. The image forming apparatus according to claim 10, wherein the charged body includes a charge injection layer into which charges are injected from the contact portion. 12. The volume resistivity of the charge injection layer is 1 × 1.
The image forming apparatus according to claim 11, wherein the image forming apparatus has a resistance of 0 ¹⁰ to 1 × 10 ¹⁴ Ωcm. 13. The image forming apparatus according to claim 10, wherein the member to be charged has an electrophotographic photosensitive layer.