JPH08254881A - Electrifying device, image forming device and process cartridge - Google Patents

Abstract

PURPOSE: To eliminate a harmful effect due to faulty electrification and the adhesion of magnetic particles to a substance to be electrified by substantially preventing the magnetic particles from being separated from the magnetic brush attributed to a mechanical factor and from adhering to the substance to be electrified in a magnetic roller type magnetic brush electrifying device, and to eliminate trouble such as a faulty image due to the above-mentioned harmful effect in an image forming device. CONSTITUTION: The distribution of the absolute value of flux density in the radial direction of the magnetic roller 22 all over the periphery of the roller 22 has plural maximums. When it is assumed that the average of the maximal value in the distribution of the absolute value of the flux density in the radial direction exerted on the position (c) of the magnetic particles 23 restricted by the roller 22 at the farthest distance is B(T), the number of times that the maximal value of the roller 22 passes through a certain point on the circumference of the roller per hour is N/min, and the moving speed of the substance to be electrified 1 is Vps(cm/h); (-1.58×B+0.098)×10<(-> N</732)> /Vps<8.8×10<-7> holds.

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 carrying out a charging process (including a destaticizing process) on an object to be charged, an image forming apparatus equipped with the charging device and a process cartridge.

In particular, the present invention relates to a charging device using a magnetic brush type contact charging member (magnetic brush charging member), an image forming apparatus and a process cartridge equipped with the charging device.

[0003]

2. Description of the Related Art A means for charging a charged body is "non-contact type".
And "contact system".

A typical non-contact system is a corona charger.
This is because the corona charger is arranged so as to face the body to be charged in a non-contact manner, and a high voltage is applied to generate corona discharge in the corona charger, and the surface of the body to be charged is charged by exposing the surface of the body to be charged to the discharge corona. It is what makes me.

Examples of the contact system include triboelectric charging and a contact charging device that charges a charged member by bringing a charging member such as a roller body or a brush member into contact with the charged member to apply a voltage.

Conventionally, for example, in an electrophotographic or electrostatic recording type image forming apparatus, a corona charging which is a non-contact system is used as a charging processing means for an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. Although a container has been widely used, a contact-type contact charging device has been put into practical use in recent years because of advantages such as low ozone and low power consumption as the ecology has been drawing attention. As the contact charging member, rubber roller, fixed brush, roll-shaped fur brush, magnetic brush, etc.
There are various members.

A) Roller charging system In particular, a roller charging system using a conductive roller as a contact charging member is preferably used in terms of charging stability.

In the roller charging type contact charging device, a conductive elastic roller (charging roller) as a charging member is brought into pressure contact with a member to be charged, and a voltage is applied to the member to charge the member to be charged. . Specifically, since the charging is performed by discharging from the charging member to the body to be charged, the charging is started by applying a voltage equal to or higher than a certain threshold voltage.

As an example, the member to be charged has a thickness of 25 μm.
When the charging roller is pressed against the OPC photoconductor of m to perform the charging process, the charging roller has about 6
When a voltage of 40 V or higher is applied, the surface potential of the photoconductor starts to rise, and thereafter, the surface potential of the photoconductor linearly increases with a slope of 1 with respect to the applied voltage. This threshold voltage is defined as the charging start voltage Vth.

That is, in order to obtain the photosensitive member surface potential Vd required for electrophotography, the charging roller requires a DC voltage higher than the required Vd + Vth. The contact charging method in which only the DC voltage is applied to the contact charging member in this way to charge the body to be charged is called a "DC charging method".

However, in the DC charging method, the resistance value of the contact charging member fluctuates due to environmental fluctuations, and the charging start voltage Vth fluctuates when the film thickness changes due to the abrasion of the photoconductor as the member to be charged. However, it was difficult to set the potential of the photoconductor to a desired value.

Therefore, in order to further homogenize the charging, as disclosed in JP-A-63-149669, etc., the DC voltage corresponding to the desired Vd has a peak-to-peak voltage of 2 × Vth or more. An "AC charging method" is used in which an oscillating voltage on which an AC component is superimposed is applied to a contact charging member to charge a member to be charged. This is for the purpose of leveling the potential by AC, and the potential of the body to be charged converges on Vd which is the center of the peak of the AC voltage, and is not affected by disturbance such as environment.

However, even in such contact charging, since the essential charging mechanism uses the discharge phenomenon from the contact charging member to the member to be charged, the voltage required for charging as described above is used. Is required to have a value higher than the surface potential of the body to be charged, and a small amount of ozone is generated.

Further, when the AC charging method is used to make the charging uniform, further generation of ozone amount and vibration noise of the charging member and the charged body due to the electric field of the AC voltage (AC charging sound).
And the deterioration of the surface of the member to be charged due to the discharge becomes remarkable, which is a new problem.

Here, in the characteristics required for the contact charging member as well as the roller charging, when a charging member having a low resistance value is used, there is a low withstand voltage defect portion such as a scratch or a pinhole on the member to be charged. Then, an excessive leak current flows from the charging member to the low withstand voltage defect portion, resulting in defective charging, enlargement of pinholes, and energization breakdown of the charging member in the portion to be charged around the low withstand voltage defect portion. In order to prevent this, the resistance value of the charging member needs to be about 1 × 10 ⁴ Ω or more. on the other hand,
If it is 1 × 10 ⁸ Ω or more, the resistance value is too high, and the current required for charging cannot be passed. Therefore, the resistance value of the contact charging member must be in the range of 1 × 10 ⁴ to 1 × 10 ⁸ Ω.

B) Injection charging method Further, an injection charging method, which is a contact type and performs charging by directly injecting an electric charge to an object to be charged, has been devised (JP-A-6-3927, Japanese Patent Application No. Hei 6-3927). No. 5-66150).

In this injection charging system, only a DC voltage corresponding to a desired Vd is applied to a contact charging member such as a charging roller, a charging fur brush, a charging magnetic brush or the like, and charges are injected into a trap level on the surface of the body to be charged. Alternatively, the desired Vd can be obtained by a method of charging the conductive particles of the charged body having the protective film in which the conductive particles are dispersed. Japanese Unexamined Patent Publication No. 6-3927 discloses a method of injecting electric charges into a float electrode on a charged body (photoreceptor) having a charge injection layer on its surface to perform contact charging. It is described that it is possible to coat the surface of the photoconductor with an acrylic resin in which SnO ₂ particles which are made conductive by antimony dope as a conductive filler are dispersed and used.

In this charging system, since the discharge phenomenon is not used, the voltage required for charging is a DC voltage only for the desired surface potential of the member to be charged, and ozone is not generated. Furthermore, since no AC voltage is applied, no charging noise is generated,
Compared with the roller charging method, this charging method is superior in low ozone property and low voltage property.

In the contact charging method such as the DC charging method and the AC charging method described above, since the charging mechanism is based on the discharge, the charging is performed even if some gap is generated between the charging member and the surface of the member to be charged. However, in the injection charging method, since the charging member and the member to be charged directly contact each other to transfer the electric charge,
It is necessary to adopt a configuration in which the two are in close contact with each other and are not microscopically charged and remain.

Further, it is preferable that the resistance of the charging member is lower so as not to hinder the transfer of charges, but as described above,
In a device using a contact charging member, if there is a low-voltage defect such as a scratch or a pinhole on the member to be charged, if the resistance of the charging member is low, leakage occurs, the power supply voltage drops, and charging becomes defective. Therefore, in practice, the charging member needs to have a certain level of resistance. When the resistance of the charging member is high as described above, the charge injecting property is deteriorated.Therefore, by increasing the contacting speed between the charging member and the member to be charged, a means such as rotating the charging member quickly is used. It is necessary to secure the charge injection capability.

As described above, the charging member used in the injection charging system can be in intimate contact with the body to be charged, and
From the viewpoint of a member capable of having a peripheral speed difference with respect to the body to be charged, a magnetically constrained charging member such as a magnetic brush or a magnetic fluid (magnetic brush charging member) is suitable.

C) Magnetic brush charging member The magnetic brush charging member is one in which magnetic particles are restrained by a magnetic force on a carrier so as to be attached and held as a magnetic brush. It is applied to charge the body to be charged. More specifically: The magnetic brush carrier is a rotatable sleeve, and the magnetic particles are bound to the outer surface of the sleeve by the magnetic force of the magnetic field generating means arranged in the sleeve and adhered and held as a magnetic brush (sleeve type). ,. The magnetic brush carrier is a rotatable magnetic roller,
For example, magnetic particles are directly bound to the outer surface of the magnetic roller by a magnetic force and attached and held as a magnetic brush (magnetic roller type).

FIG. 7 is a structural model view of the sleeve type magnetic brush charging member 2 or charging device.

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

Reference numeral 22 is 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 restrained by the magnetic force of the magnet roll 22 inside the sleeve. Has been done.

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

S1 is a charging bias application power source for 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 in a state where 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 rotatably 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.

FIG. 8 is a schematic model view of the magnetic roller type magnetic brush charging member 2 or charging device.

Magnet roll 22 as a magnetic roller
Is driven to rotate at a predetermined peripheral speed by a drive mechanism (not shown) centering around a central core metal 25 that both drives and supplies power. The carrier 23 is restrained by the magnetic force of the magnet roll 22 on the outer peripheral surface of the magnet roll 22 to be attached and held as a magnetic brush 24.

The magnetic brush 24 is the magnet roll 22.
Is rotated and conveyed in the same direction as the rotation of the contact nip D
At 1, the surface of the rotating photosensitive member is rubbed, and the charging bias applied to the central core metal 25 of the magnet roll 22 from the power source S1 causes the surface of the rotating photosensitive member 1 as a charged body to be contact-charged.

The sleeve type charging device of FIG. 7 is also shown in FIG.
The magnetic roller type charging device of No. 2 also has a contact nip portion (charging nip portion) D between the magnetic brush 24 and the photoconductor 1 that contributes to charging.
In order to secure a sufficient width of the magnetic brush 24, the contact nip portion D between the magnetic brush 24 and the photoconductor 1 is different from the layer thickness of the magnetic brush 24.
The gap (separation distance) α between the charging sleeve 21 and the photosensitive member 1 in the above is set to a predetermined small value, and the contact nip portion D between the charging target 1 and the magnetic brush 24 is located at the downstream end of the charging target surface moving direction. Has a structure in which a reservoir 24a of the magnetic brush carrier is formed.

[0037]

By the way, regarding the charging device using the magnetic brush charging member and the device equipped with the charging device, the carrier 23 is detached from the magnetic brush 24, and the detached carrier 23 is on one surface to be charged. There is a problem of adhesion to.

The magnetic brush carrier reservoir 24a is located farther from the magnet roll 22 than the other magnetic brush portions.
In particular, the carrier 23 at the contact nip end c easily escapes due to escape of the magnetic binding force, and the carrier 23 easily attaches to the surface of the charged body 1.

The detachment of the magnetic brush carrier causes charging failure because the carrier of the magnetic brush 24 that contributes to charging decreases with time. Further, the detachment carrier adheres to the surface of the body to be charged. 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 is caught between the cleaning blade and the photoconductor at the cleaning position, and the photoconductor is damaged.

The detachment / attachment of the magnetic brush carrier with respect to the photoconductor 1 as the member to be charged is classified into an electrostatic factor and a mechanical factor.

The carrier detachment / adhesion due to electrostatic factors causes a potential difference between the magnetic brush 24 and the photoconductor 1 when the photoconductor 1 is not sufficiently charged by the magnetic brush 24. This is a phenomenon in which when the potential difference occurs, electric charges are generated at the tip of the magnetic brush carrier, and the carrier 23 flies and adheres to the photoconductor 1 by electrostatic force. With respect to this, for example, by using the magnetic brush constitution described in the specification of Japanese Patent Application No. 06-208062, good charging characteristics can be obtained and the photoconductor can be sufficiently charged. The potential difference between the two is reduced, and the electrostatic attachment of the carrier can be eliminated. Further, with respect to carrier adhesion at the longitudinal end of the photoconductor that the magnetic brush is not in contact with,
By adopting the configuration of the magnetic brush described in the specification of Japanese Patent Application No. 06-205959, it is possible to suppress the potential difference with the photoconductor to a predetermined value or less and prevent the carrier from electrostatically adhering.

On the other hand, detachment of the carrier due to mechanical factors
Adhesion is a phenomenon in which the carrier 23 of the magnetic brush 24 physically adheres (or scatters) to the photoconductor 1 due to the rubbing of the magnetic brush 24 with the photoconductor 1. In fact, the magnetic brush 2
It can be confirmed that the magnetic brush carrier 23 is attached to the photoconductor even when the bias is not applied to the photosensitive drum 4.

In the case where the charging device is the magnetic roller type magnetic brush charging device shown in FIG. 8, the carrier detachment / adhesion due to the mechanical factor is accompanied by the rotation of the magnet roller 22 as a magnetic roller. The magnetic brush carrier pool 24a is swayed by the magnetic poles that repeatedly pass through the position of the magnetic brush carrier pool 24a.
The carrier a is mechanically detached, adheres to the photoconductor, and leaks to the downstream of the photoconductor. From the observation of the magnetic brush 24, it was found that when the magnetic pole of the magnetic roller 22 enters the magnetic brush carrier reservoir 24a, the carrier particles move so as to strip the carrier from the carrier reservoir 24a. Also,
It was also confirmed that the adhesion was concentrated before and after that,
The carrier is attached in a band.

Therefore, in the present invention, in particular, with respect to the above-mentioned magnetic roller type magnetic brush charging device of FIG. 8 and a device equipped with the charging device, the magnetic particles (carriers) 23 are separated from the magnetic brush 24 by a mechanical factor. By substantially eliminating the adherence to the body to be charged 1, the problems such as the above-mentioned charging failure, the adverse effect due to the adhesion of magnetic particles to the body to be charged, and the occurrence of the image failure due to it in the image forming apparatus are solved. The purpose is to

[0045]

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

(1) Magnetic particles are bound to the peripheral surface of the magnetic roller by a magnetic force to be attached and held as a magnetic brush, and the magnetic brush is brought into contact with an object to be charged, and a contact nip portion between the magnetic brush and the object to be charged. In the charging device, the magnetic roller is rotated so that the surface of the magnetic roller moves in a direction opposite to the moving direction of the charged body, the magnetic brush is conveyed, and a voltage is applied to the magnetic brush to charge the charged body. The absolute value distribution of the radial magnetic flux density of the magnetic roller over the entire circumference has a plurality of maxima, and the absolute value of the radial magnetic flux density exerted on the position of the magnetic particles that the magnetic roller constrains at the farthest distance. The average of the maximum values in the distribution is B (T, Tesla), and the number of times the maximum value of the magnetic roller passes a certain point on the circumference of the roller per hour is N (times / min). If the moving speed is Vps (cm / h) The charging device is characterized in that (-1.58 × B + 0.098) × 10 ^{(-N / 732)} / Vps <8.8 × 10 ^-7 .

(2) The radius of the magnetic roller is 0.3 to 2.5.
cm, the absolute value of the radial magnetic flux density on the surface of the magnetic roller over the entire circumference of the magnetic roller, and the average of a plurality of maximum values is 0.05 to 0.3 (T). The charging device according to (1), wherein the number is 4 to 30.

(3) The charging device as described in (1) or (2), wherein the contact angle of the surface of the member to be charged with water is 90 ° or more.

(4) The charging device according to any one of (1) to (3), wherein the charging target is charged by an injection charging method in which charges are directly injected into the surface of the charging target.

(5) An image forming apparatus for forming an image by an image forming process including a step of charging an image carrier, wherein the charging means of the image carrier is described in any one of (1) to (4). An image forming apparatus, which is a charging device.

(6) A process cartridge which includes at least an image carrier and at least a charging member of a charging device for charging the image carrier, and which is attached to and detached from the main body of the image forming apparatus. Is a magnetic brush charging member of the charging device according to any one of (1) to (4).

(7) The process cartridge is characterized in that the charging means, the developing means or the cleaning means, and the image carrier are integrated into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. The process cartridge according to (6).

(8) In the process cartridge, at least one of the charging means, the developing means or the cleaning means and the image carrier are integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. (6) The process cartridge according to (6).

(9) In the process cartridge, at least the developing means and the image carrier are integrated into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. Process cartridge described.

[0055]

It has been confirmed that increasing the number of rotations of the magnetic roller or increasing the number of magnetic poles reduces the amount of magnetic brush magnetic particles attached to the body to be charged. In other words, by increasing the number of poles that pass per hour, it is considered that the unevenness of the magnetic flux density (the magnetic pole position and the position between the poles) that accompanies the rotation of the magnetic roller apparently decreases, and the adhesion amount decreases. Considering the quantitative relationship between the amount of magnetic brush magnetic particles adhered to the body to be charged and its factor, and configuring the device so that the above relational expression holds, the mechanical properties of the magnetic particles from the magnetic brush By eliminating the separation due to the factors and the adhesion to the charged body, the problems such as the charging failure, the harmful effects due to the adhesion of the magnetic particles to the charged body, and the occurrence of the image failure due to it in the image forming apparatus are solved. The present invention has been completed by finding that it is possible. The details are described in Examples below.

In addition, in constructing the charging device, when the radius of the magnetic roller is in the range of 0.3 to 2.5 (cm),
Further, the magnetic flux density distribution in the radial direction on the pole surface of the roller 22 has an equal pole arrangement, and the number of poles (maximum number) is 4 to 30 and the strength thereof is 0.05 to 0. Three
When the magnetic roller of (T) is used, the magnetic particle adhesion amount prediction is particularly good when the constituent conditions of the above relational expression are satisfied.

The attachment of the magnetic brush magnetic particles to the body to be charged also depends on the lubricity of the surface of the body to be charged. By giving the surface of the body to be charged the characteristic that the contact angle with water is 90 ° or more, it is possible to accurately predict the magnetic brush magnetic particle adhesion state from the relational expression.

[0058]

【Example】

 (1) Example of image forming apparatus (FIG. 1) FIG. 1 is a schematic diagram of an example of the image forming apparatus.

The image forming apparatus of this embodiment is a laser beam printer (LBP) using a process cartridge attaching / detaching method and a transfer type electrophotographic process.

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

Reference numeral 1 denotes 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 the surface thereof. .4 × 10 ⁴ cm / h (94 mm / se
It is rotationally driven at the process speed (peripheral speed) of c). The layer structure of the photoconductor will be described in detail in item (2).

Reference numeral 2 is 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, it is the magnetic roller type magnetic brush charging member shown in FIG. . The magnetic brush charging member 2 will be described in detail in section (3).

A DC charging bias of -700V is applied from the charging bias applying power source S1 to the magnetic brush charging member 2, and the outer peripheral surface of the rotary photosensitive member 1 is uniformly charged to approximately -700V by charge injection charging. It

A laser whose intensity is modulated corresponding to the time series electric digital pixel signal of the target image information output from the 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 unit (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 the fixing device 5 such as a thermal fixing system to be fixed with the toner image to form an image formed product (print, copy). Is discharged outside the device.

Further, the surface of the photosensitive member after the transfer of the toner image onto the transfer material 30 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, a process in which the four process devices of 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 main body of the image forming device. 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 the charging means, the developing means or the cleaning means, and the 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 schematic diagram of the layer structure of the photoreceptor 1 as the member to be charged used in this embodiment. The photoreceptor 1 used in this example is a negatively charged OPC photoreceptor having a charge injection function on the surface, and φ
The following first to fifth five functional layers 12 to 16 are provided in order from the bottom on a 30 mm aluminum drum substrate 11.

The first layer is an undercoat layer 12 and is provided to smooth out defects and the like on the outer peripheral surface of the aluminum drum substrate 11 and to prevent moire due to reflection of laser exposure from causing a thickness of about 20 μm. 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 photoconductor, 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 generation 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 photo-curable 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 of the surface of the photosensitive member 1 was 1 × 10 ¹⁵ Ωcm in the case of the charge transport layer alone, compared with 1 × 10 ¹⁵ Ωcm.
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 charge flows on the surface. So that the charge injection layer 16 has a resistance of 1 ×
It must be 10 ⁸ Ωcm or more. The resistance value of the charge injection layer 16 is obtained by applying a charge injection layer on an insulating sheet and measuring the surface resistance with a high resistance meter 4329A manufactured by HP at an applied voltage of 100V.

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 a structure having an independent charge injection layer is adopted. It is not limited.

In order to reduce the adhesion of carriers on the magnetic brush charging member side to the surface of the photoconductor, it is preferable that the photoconductor 1 has a property of low surface energy. It has 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 and Charging Device (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, which is the same as that shown in FIG. It is a magnetic roller type magnetic brush charging member. That is, the magnet roll 22 as a magnetic roller is rotationally driven at a predetermined peripheral speed by a drive mechanism (not shown) around the central core metal 25 that also serves as a drive and a power supply, in the clockwise direction b shown by the arrow. The outer peripheral surface of the magnet roll 22 is covered with a conductive layer 22a as a charging bias applying electrode (power feeding surface). The carrier 23 is provided on the outer peripheral surface of the conductive layer 22a.
It is restrained by the magnetic force of 2 and attached and held as a magnetic brush 24.

The magnetic brush 24 is the magnet roll 22.
Is rotated and conveyed in the same direction as the rotation of the contact nip D
At 1, the surface of the rotating photosensitive member is rubbed, and the charging bias applied to the central core metal 25 of the magnet roll 22 from the power source S1 causes the surface of the rotating photosensitive member 1 as a charged body to be contact-charged. The conductive layer 22a provided on the outer peripheral surface of the magnet roll 22 serves to stably and uniformly supply the charging bias to the magnetic brush 24.

Magnet roll 22 as a magnetic roller
In addition to a general permanent magnet such as ferrite, these powders can be molded together with a resin and magnetized to a desired magnetic flux pattern at a desired temperature for use.

In this embodiment, magnet rolls 22 having NSNS with four poles arranged at equal intervals were used. The surface of the magnet roll 22 is preferably made conductive so as to stably and uniformly supply power to the magnetic brush 24.
Is provided. The conductive layer 22a can be formed by covering the magnet roll 22 with a tube formed by dispersing conductive powder in a resin, applying a conductive material of the same kind, or sticking a conductive tape on one surface.

The charging sleeve 21 and the photoreceptor 1 at the contact nip portion (charging nip portion) D between the magnetic brush 24 and the photoreceptor 1
The gap (separation distance) α between and was set to 500 μm by the spacer members arranged at both longitudinal ends of the magnet roll 22.

The magnet roll 22 is rotated in the counter direction with respect to the surface of the rotary photosensitive member 1. Magnetic brush 24
The magnet roll 22 rotates in the same direction as the magnet roll 22 rotates, and the carrier 23 constituting the magnetic brush is conveyed, and the carrier passes through the contact nip portion D while successively contacting the surface of the photoconductor 1.

A) Carrier 23 Carrier 2 which is magnetic particles constituting 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.

The carrier 23 used in this example has an average particle size of 15 μm, a resistance value of 1 × 10 ⁶ Ω, and a saturation magnetization of 58.
It is ferrite particles of A · m ² / kg.

If the resistance value of the carrier 23 is too high, charges cannot be uniformly injected into the photosensitive member 1 and a fog image is formed due to 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 carrier 2
The resistance value of 3 is preferably 1 × 10 ⁴ to 1 × 10 ⁸ Ω. The resistance value of the carrier 23 is set such that 2 g of the carrier is put into a metal cell (bottom area 228 mm ² ) to which a voltage can be applied and then weighted, and the voltage is 1 to 1000 V, for example 100
V was applied, and it was defined as a value calculated from the measured current flowing in this system and normalized.

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 restraining force becomes small and the carrier adheres to the surface of the photoreceptor 1. On the other hand, if it is too large, the contact area with the photoconductor 1 is reduced and charging failure increases. Therefore, the average particle size of the carrier is preferably about 5 to 500 μm from the viewpoints of chargeability and magnetic retention.

[0097] 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.

B) Detachment of Magnetic Brush Carrier and Prevention of Adhesion to Charged Member As described above, with respect to detachment of the magnetic brush carrier due to mechanical factors and adhesion to the photosensitive member, a magnetic roller type magnetic brush charging device is used. In this case, the magnetic brush carrier pool 24a is shaken by the magnetic poles that repeatedly pass through the position of the magnetic brush carrier pool 24a as the magnet roller 22 as a magnetic roller rotates, and the carrier in the pool 24a is mechanically moved. And then adheres to the photoconductor and leaks to the downstream of the photoconductor. From the observation of the magnetic brush 24, it was found that when the magnetic poles of the magnetic roller enter the magnetic brush carrier reservoir 24a, the carrier particles move so as to strip the carrier from the carrier reservoir 24a. It was also confirmed that the adhesion was concentrated before and after that, and the adhesion was formed in a band shape.

Therefore, when the number of rotations of the magnet roll 22 as a magnetic roller is increased or the number of magnetic poles per roller is increased, the photosensitive member 1 as a charged body is obtained.
It was confirmed that the amount of carrier adhering to
That is, it is considered that the increase in the number of poles passing per hour apparently reduces the unevenness of the magnetic flux density (the magnetic pole position and the position between the poles) due to the rotation of the magnet roll 22, and thus the adhesion amount is reduced.

Further, the amount of adhesion is reduced by increasing the magnetic flux density. This is because the magnetic restraining force of the magnetic brush carrier on the magnet roll 22 as a magnetic roller increases. In particular, the magnetic brush 24 and the photoconductor 1
Nip end e on the downstream side of the contact nip portion D in the photosensitive member moving direction
Is related to the magnetic flux density at.

As described above, the detachment of the carrier from the magnetic brush carrier reservoir 24a, particularly the nip end e of the contact nip D, and the adhesion to the photosensitive member 1 pass through the magnet roll 22 as a rotating magnetic roller per unit time. It was clarified that it depends greatly on the number of poles and magnetic flux density.

Next, the quantitative relationship between the carrier adhesion amount and its factor will be found from the detailed measurement, which will be described.

The factors of carrier adhesion are the magnetic restraining force of the carrier at the nip end e which is restrained at the farthest distance from the magnet roll 22 as a magnetic roller, that is, the magnetic flux density at the nip end e and the number of times the magnetic pole passes through the nip. Is as described above.

FIG. 5 shows the result of measuring the magnetic flux density at the nip end e with respect to the angle in the circumferential direction and showing the absolute value thereof.

Here, the magnet rolls 22 as magnetic rollers are evenly arranged, and there are four maximum values of ABCD in the figure. Let B (T) be the average of the maximum values.

On the other hand, the number of poles of the magnetic roller 22 (the maximum number)
Is n and the number of revolutions is f (rpm), the number of passing poles per unit time is given by N = n × f (poles / min).

For the magnetic flux density B at the nip end e and the number of passing poles N per unit time, 1 per 1 cm of the magnetic brush length.
FIG. 6 shows a result obtained by converting the adhesion amount m (g / h) of the carrier onto the photoreceptor 1 with respect to time and converting it into a mathematical expression. The formula is as follows:

M = (− 1.58 × B + 0.098) × 10 ^{(−N / 732)} (g / h) (1) The adhered amount m decreases in the first order due to the increase of the magnetic flux density B, while passing With respect to the number of poles N, the characteristic that the number of poles decreases exponentially with increasing N is shown.

From this characteristic, the magnetic flux density B is 0.06.
When it exceeds 2 (T), the calculation formula becomes zero. Actually B> 0.
In 062, the adhesion was very small and a good image was obtained.

On the other hand, from the viewpoint of image deterioration, it is necessary to consider to what extent the carrier attachment to the photoconductor 1 can be allowed. Therefore, the allowable amount was calculated next.

Regarding the relationship between the amount of adhering carrier to the photosensitive member and the image deterioration, naturally, the larger the amount of adhering carrier, the more the adhered carrier obstructs the image exposure, so that the image deteriorates. In the case of an image defect, in the image formation of the reversal development system, the light-shielded portion is unexposed, and therefore, a white void portion appears finely in the black portion. In fact, when the image was subjectively evaluated, it was found that if the adhesion amount m was 8.8 × 10 ⁻⁷ (g / cm ² ) or less, there was no problem with the image defect.

Further, the carrier adhesion amount per unit area of the photoconductor 1 is calculated by m / Vps (g / cm ² ) ... (2) when the photoconductor moving speed is Vps (cm / h).

Therefore, the conditions for the magnetic brush structure that does not cause image defects are: m / Vps <8.8 × 10 ⁻⁷ (g / cm ² ) ... (3) The above (1), (2), ( From the equation (3), (-1.58 × B + 0.098) × 10 ^{(-N / 732) /} Vps <8.8 × 10 ⁻⁷ (g / cm ² ) ... (4) is obtained.

Therefore, in order to prevent the image defect due to the adhesion of the magnetic brush carrier, it is effective to set the magnetic brush configuration to the condition satisfying the expression (4).

Further, in constructing the charging device, when the radius of the magnetic roller 22 is in the range of 0.3 to 2.5 (cm), the magnetic flux density distribution in the radial direction on the pole surface of the roller 22 is further increased. Is a homopolar arrangement, and when using a magnetic roller in which the number of poles (maximum number) in the absolute value of the magnetic flux density is 4 to 30 and the strength thereof is 0.05 to 0.3 (T), especially (4 ) Good prediction of the amount of carrier adhesion when the constitutional conditions of equation (4) are satisfied.

The adhesion of the carrier to the photosensitive member also depends on the lubricity of the surface of the photosensitive member as the member to be charged. According to the measurement by the present inventors, by giving the characteristic that the contact angle to water is 90 ° or more on the surface of the photoconductor, it is possible to accurately predict the carrier adhesion state and prevent image defects from the equation (4). You can

Next, Table 1 shows the constitution of the magnetic brush of the example together with the comparative example.

[0118]

[Table 1] As other conditions, the moving speed of the photoconductor 1 is Vps.
= 3.4 × 10 ⁴ cm / h.

When the eight-pole magnetic roller of the comparative example shown in Table 1 was used, the carrier adhesion amount to the photosensitive member was 1.
It was 2 × 10 ⁻⁶ (g / cm ² ), and since it exceeded 8.8 × 10 ⁻⁷ , image defects due to carrier adhesion occurred.

However, in the first and second embodiments, by increasing the rotation speed of the magnetic roller 22 or using the magnetic roller 22 having a large magnetic flux density, it is possible to reduce the amount of carrier adhered to the photosensitive member. It was possible to improve the image defect.

As described above, by adopting the configuration of the magnetic brush charging device satisfying the expression (4), the image defect due to the adhesion of the magnetic brush carrier to the photoconductor 1 as the charged body is eliminated, and a good image is obtained. Recording is possible.

In the above embodiment, a magnetic brush is used as the contact charging member of the injection charging system, but the magnetic brush charging device of the present invention can be used for contact charging other than the injection charging system.

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.

[0124]

INDUSTRIAL APPLICABILITY As described above, the present invention particularly relates to a charging device using a magnetic roller type magnetic brush charging member and a device equipped with the charging device, in which magnetic particles are separated from the magnetic brush by a mechanical factor. By substantially eliminating the adherence to the charged body, it is possible to solve problems such as poor charging, harmful effects due to adhesion of magnetic particles to the charged body, and occurrence of image failure caused by the image forming apparatus. .

[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 schematic diagram of the configuration of the magnetic roller type charging member or charging device used.

FIG. 5 is a graph showing a magnetic flux density distribution of a magnetic roller.

FIG. 6 is a graph showing equation (4).

FIG. 7 is a schematic diagram of a sleeve type magnetic brush charging member or charging device.

FIG. 8 is a schematic configuration model diagram of a magnetic roller type magnetic brush charging member or 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 S1 Charging Bias Applying Power Supply 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 Seiji Mashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeo Yamamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Within

Claims (9)

[Claims] 1. A magnetic roller restrains magnetic particles on a peripheral surface of the magnetic roller by a magnetic force to adhere and hold the magnetic roller as a magnetic brush, and the magnetic brush is brought into contact with an object to be charged, and at a contact nip portion between the magnetic brush and the object to be charged. A charging device that rotates a magnetic roller so that the surface of the magnetic roller moves in a direction opposite to the moving direction of the charged body, conveys the magnetic brush, and applies a voltage to the magnetic brush to charge the charged body. The absolute value distribution of the magnetic flux density in the radial direction of the roller over the entire circumference has a plurality of maxima, and the absolute value distribution of the magnetic flux density in the radial direction exerts on the position of the magnetic particles that the magnetic roller constrains at the farthest distance. Let B (T) be the average of the maximum values at, and the number of times the maximum value of the magnetic roller passes a certain point on the roller circumference per hour is N (times / time).
min), and when the moving speed of the charged body is Vps (cm / h), (-1.58 × B + 0.098) × 10 ^{(-N / 732)} / Vps <8.8 × 10 ^-7 And charging device. 2. The radius of the magnetic roller is 0.3 to 2.5 cm.
And the absolute value of the magnetic flux density in the radial direction on the surface of the magnetic roller over the entire circumference of the magnetic roller is taken, and the average of a plurality of maximum values is 0.05 to 0.3 (T), and the maximum number is Is 4
The charging device according to claim 1, wherein the charging device is from 30 to 30. 3. The contact angle of water on the surface of the body to be charged is 9
The charging device according to claim 1 or 2, wherein the charging device is at least 0 °. 4. The charging device according to claim 1, wherein the charging target is charged by an injection charging method in which charges are directly injected into the surface of the charging target. 5. An image forming apparatus for performing image formation by an image forming process including a step of charging an image carrier, wherein the charging means of the image carrier is the charging device according to any one of claims 1 to 4. An image forming apparatus characterized by being an apparatus. 6. A process cartridge that includes at least an image carrier and at least a charging member of a charging device for charging the image carrier, and is a process cartridge that is attached to and detached from an image forming apparatus main body. A process cartridge comprising the magnetic brush charging member of the charging device according to any one of claims 1 to 4. 7. The process cartridge is characterized in that a charging unit, a developing unit or a cleaning unit, and an image carrier are integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. The process cartridge according to claim 6. 8. The process cartridge comprises at least one of a charging means, a developing means or a cleaning means, and an image carrier which are integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. 7. The process cartridge according to claim 6, which is characterized in that. 9. The process cartridge comprises at least:
7. The process cartridge according to claim 6, wherein the developing means and the image carrier are integrally made into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus.