JPH09329938A - Magnetic brush electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve electrification property by making the relative moving direction of magnetic particle carrying means and an electrified body counter direction in a contact nip of a magnetic brush with the electrified body. SOLUTION: In this device, a photoreceptor drum 1 is rotary driven by a driving mechanism at specified peripheral speed in the clockwise direction as shown the arrow (a), and the rotary direction of a sleeve 21 and the rotary transporting direction of the magnetic brush 24 in accordance with the rotation thereof on a contact nip part D is made so as to be the counter direction corresponding to the rotary direction of the photoreceptor drum 1. As the result of the above movement in the counter direction, the electrification property becomes excellent, by preventing the carrier adhesion on the photoreceptor drum 1, making the peripheral speed difference possible to become large, and making the contact frequency of the carrier with the photoreceptor drum 1 possible to increase. The reason is not yet clear, however it is considered that the effect of peeling off and restoring the carrier on the photoreceptor 1 by a rub of the magnetic brush 24 is working.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging an object to be charged (including a charge removing process), and an image forming apparatus equipped with the charging device.

In particular, the present invention relates to a magnetic brush charging device using a magnetic brush charging member and an image forming apparatus 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, 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 corona discharge. 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 frequently used, a contact-type contact charging device has been put into practical use because of advantages such as low ozone and low electric power in recent years as ecological attention has been paid. There are various types of contact charging members such as a rubber roller type, a fixed brush type, and a roll-shaped fur brush type.

A) Roller charging system In particular, a roller charging system using a conductive roller as a contact charging member is preferably used from the viewpoint 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 photosensitive member of m to perform the charging process, the surface potential of the photosensitive member starts to rise if a voltage of about 640 V or more is applied to the charging roller. After that, the surface potential of the photoconductor increases linearly with an inclination of 1 with respect to the applied voltage. This threshold voltage is defined as charging start voltage Vth.

That is, in order to obtain the photosensitive member surface potential Vd required for electrophotography, the charging roller needs to have Vd + Vth
Therefore, a DC voltage higher than required is required. A method of applying only a DC voltage to the contact charging member to perform charging in this manner is referred to as a “DC charging method”.

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

Therefore, as disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to a desired Vd is provided with a peak-to-peak voltage of 2 × Vth or more in order to further uniformize the charging. An "AC charging method" is used in which a voltage on which a charged AC component is superposed is applied to a contact charging member to charge an object to be charged. This is for the purpose of leveling the potential by the 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 the environment.

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

Further, when AC charging is performed 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 became remarkable, which was a new problem.

Here, in the characteristics required not only for the charging roller but also for the contact charging member, 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. While 1
When the resistance is more than × 10 ⁷ Ω, 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 Ω to 1 × 10 ⁷ Ω.

B) Injection charging method Further, a charging method which is a contact type and which performs charging by directly injecting an electric charge to an object to be charged has been devised (Japanese Patent Application Laid-Open No. 6-3921, Japanese Patent Application No. 5-21). -66150).

In this injection charging method, only a DC voltage corresponding to a desired Vd is applied to a contact conductive member such as a roller type, a brush type, or a magnetic brush type, and charges are injected into a trap level on the surface of the charged body. Alternatively, a desired Vd is obtained by a method of charging the charged body having a protective film in which conductive particles are dispersed with electric charges.

Japanese Unexamined Patent Publication No. 6-3921 discloses a method of injecting electric charges into a float electrode of a charge injection layer of a member to be charged (photoreceptor) having a charge injection layer on the surface to perform contact charging. As a charge injection layer, S made conductive with antimony dope which is a conductive filler in acrylic resin on the surface of the photoreceptor
It is described that a dispersion of nO ₂ (tin oxide) particles can be applied and used.

In this injection charging method, 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.
Further, since the AC voltage is not applied, no charging noise is generated, and the charging method is superior in the low ozone property and the low voltage property as compared with the roller charging method.

In the contact charging method such as the CD charging method and the AC charging method described above, the charging mechanism is based on the discharge, so that 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 the device using the contact charging member, when there is a low withstand voltage defect portion 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 failure occurs. 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 method can be in intimate contact with the member 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 magnetic particle carrying means to be attached and held as a magnetic brush, and the magnetic brush is brought into contact with an object to be charged, A voltage is applied to charge the body to be charged. More specifically, 1) The magnetic particle supporting means is a rotatable sleeve, and a fixed magnet roll (magnet) disposed in the sleeve.
The magnetic particles are bound to the outer surface of the sleeve by the magnetic force of and are attached and held as a magnetic brush (sleeve type), 2) the magnetic particle supporting means is a rotatable magnet roll (magnet), and For example, magnetic particles are directly bound to the outer surface by magnetic force and attached and held as a magnetic brush (magnetic roller type).

FIG. 9A is a schematic view of the sleeve type magnetic brush charging member 2 or the charging device of the above 1).

Reference numeral 21 denotes a non-magnetic conductive sleeve made of aluminum or the like (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) as a magnetic particle supporting means. Two
Reference numeral 2 denotes a magnet roll as a magnetic field generating means inserted and arranged in the sleeve 21. N and S are magnetized portions of the roll. The magnet roll 22 is a non-rotating fixed member, and the sleeve 21 is concentrically driven around the outer circumference of the magnet roll 22 in a clockwise direction b indicated by an arrow by a driving mechanism (not shown) at a predetermined peripheral speed. Reference numeral 23 is a conductive magnetic particle (hereinafter, referred to as a carrier), and the sleeve 2
The magnetic brush (conductive magnetic brush) 24 is constrained by the magnetic force of the magnet roll 22 inside the sleeve on the outer peripheral surface of the magnetic brush 24.
Is retained as attached. 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. E1 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 the clockwise direction a 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 body 1 to be charged 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, rubs the surface of the rotating photoconductor 1 at the contact nip portion D, and is charged by the power source E1 via the sleeve 21 to the magnetic brush 24. By the bias, 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 to the rotating direction of the rotary photosensitive member 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. 9B is a schematic view of the magnetic roller type magnetic brush charging member 2A or the charging device of the above 2).

The magnet roll 22 is rotationally driven at a predetermined peripheral speed by a drive mechanism (not shown) centering on a central core metal 25 that both drives and feeds power. The outer peripheral surface of the magnet roll 22 is covered with a conductive layer 22a as a charging bias applying electrode (power supply surface). The carrier 23 is restrained by the magnetic force of the magnet roll 22 and attached and held as a magnetic brush 24 on the outer peripheral surface of the conductive layer 22a. The magnetic brush 24 is rotatably conveyed in the same direction as the magnet roll 22 rotates, rubs the surface of the rotating photoconductor 1 at the contact nip portion D, and is applied to the central core metal 25 of the magnet roll 22 from the power source E1. By the charging bias, the surface of the rotary photosensitive member 1 as a member to be charged is charged by a contact method. 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.

[0031]

As described above, the charging device using the magnetic brush charging member and the image forming apparatus equipped with the charging device are capable of closely contacting the charging member and the member to be charged. Since it is possible to have a peripheral speed difference with respect to the body, it is possible to increase the chances of contact between the charging member and the body to be charged, which is advantageous in charging property. In the charge injection charging system, the charge injection property is very advantageous.

In comparison between the sleeve type magnetic brush charging member 2 as shown in FIG. 9A and the magnetic roller type magnetic brush charging member 2A as shown in FIG. 9B, the magnetic roller type is the magnet roll 22. Since the spike shape of the magnetic brush 24 in the contact nip portion D changes with the rotation, the charging property is more likely to be nonuniform as compared with the sleeve-type magnetic brush charging member 2, and charging failure may occur. .

The sleeve-type magnetic brush charging member 2 is of a magnetic roller type because the magnetic brush 24 is basically unchanged in the shape of the spikes formed by the rotation of the sleeve 21 and the carrier 23 can be replaced. Charging uniformity is advantageous compared to magnetic brush charging members.

In the case where the sleeve type magnetic brush charging member 2 is set in the counter direction with respect to the rotating direction of the rotating photoconductor 1 as the member to be charged in the contact nip portion D as in the above example, the rotating direction of the sleeve 21 is set. And there are two types of forward direction.

In the case of the forward direction, in order to increase the relative speed, that is, the peripheral speed difference between the sleeve 21 and the photosensitive member 1 in the contact nip portion D as compared with the counter direction, the sleeve 2 is used.
The number of rotations of 1 must be increased. However, in this case, the carrier 23 forming the magnetic brush 24 is likely to be scattered, the rotating torque is increased, and the apparatus cost is increased.

In the counter direction, the peripheral speed difference can be increased at a low speed, so that the carrier 23 of the magnetic brush 24 can be made.
Since the number of contact between the photosensitive member 1 and the photosensitive member 1 can be increased, there is an advantage that the charging property is improved.

However, when the rotating direction of the sleeve 21 is set to the counter direction, the magnetic brush portion on the upstream side in the sleeve rotating direction of the contact nip portion D is pulled back by the rotation of the photosensitive member 1 as the charged body, and the magnetic brush is applied to this portion. Are likely to stay. When the magnetic brush stays excessively, the smooth movement of the carrier 23 in the contact nip D is hindered, the transportability of the carrier 23 deteriorates, the contact nip D becomes non-uniform, and the contact between the carrier and the photoconductor is made. Occasionally, there were cases where the charging ability deteriorated due to a decrease in opportunities, resulting in poor charging.

Further, smooth movement of the carrier is hindered,
If the movement of the carrier in contact with the surface of the photoconductor becomes poor,
There is also a problem that the carrier itself is charged up, which hinders the injection of charges in the charge injection charging system, resulting in poor charging. Here, the charge-up means a state in which the carrier in contact with the surface of the photoconductor gives an electric charge to the photoconductor to store an opposite charge, and the actual applied voltage decreases.

Although the magnetic pole position on the sleeve, the magnetic flux density, and the distribution thereof have been devised in order to improve the carrier transportability, the carrier transportability has not necessarily corresponded.

In view of this, the present invention is particularly designed to improve the transportability of magnetic particles (carriers) in a magnetic brush charging device using a sleeve type magnetic brush charging member and an image forming apparatus equipped with the charging device. It is an object of the present invention to prevent deterioration of charging ability, prevent charging failure, and solve problems such as occurrence of image failure due to charging failure in an image forming apparatus.

[0041]

The present invention provides a magnetic brush charging device and an image forming apparatus having the following features.

(1) A magnetic brush charging member in which magnetic particles are restrained by a magnetic force and attached and held as a magnetic brush on a rotatable conductive magnetic particle holding means containing a fixed magnet is provided. In a magnetic brush charging device for bringing a magnetic brush of a brush charging member into contact with an object to be charged and transporting the particles by rotation of a magnetic particle carrying means to apply a voltage to charge the object to be charged, a contact nip between the object to be charged and the magnetic brush In the tangential direction on the magnetic particle carrying means acting on the magnetic brush magnetic particles at the closest position of the magnetic particle carrying means to the charged body The magnetic brush charging device is characterized in that the direction of the magnetic force is toward the downstream side in the rotation direction of the magnetic particle carrying means.

(2) In the magnetic brush charging device described in (1) above, the magnetic pole position of the fixed magnet contained in the magnetic particle carrying means at the contact nip between the charged body and the magnetic brush is set as the charged body. A magnetic brush charging device, characterized in that the magnetic brush charging device is located on the downstream side with respect to the rotation direction of the magnetic particle carrying means from the position closest to the magnetic particle carrying means.

(3) In the magnetic brush charging device as described in (1) or (2) above, the charged body and the magnetic body are connected to the charged body from the upstream end portion in the rotation direction of the magnetic particle carrying means of the contact nip between the charged body and the magnetic brush. A magnetic brush charging device characterized in that, in the range up to the position closest to the particle carrying means, the magnetic force in the tangential direction on the magnetic particle carrying means is all directed downstream in the rotational direction of the magnetic particle carrying means.

(4) 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 for the image carrier is one of (1) to (3). An image forming apparatus, which is the magnetic brush charging device described above.

<Operation> 1) That is, as described in (1) above, the rotation direction of the magnetic particle carrying means in the contact nip between the charged body and the magnetic brush is the counter direction with respect to the charged body, and the magnetic particles are The direction of the magnetic force in the tangential direction on the magnetic particle carrying means acting on the magnetic brush magnetic particles (carrier) at the position closest to the charged body of the carrying means is directed to the downstream side in the rotational direction of the magnetic particle carrying means. In the magnetic brush charging device characterized in that the magnetic particle carrying means rotates in the counter direction with respect to the charged body in the contact nip between the charged body and the magnetic brush, thereby carrying the magnetic particle on the charged body. Since it is possible to increase the peripheral speed difference of the means, that is, the magnetic brush, it is possible to increase the chances of contacting the magnetic brush with the body to be charged and improve the charging property. Kill. In the charge injection charging system, the charge injection property is improved and the charge property can be improved.

Further, the direction of the magnetic force in the tangential direction on the magnetic particle carrying means acting on the magnetic brush magnetic particles at the position closest to the charged body of the magnetic particle carrying means is to the downstream side in the rotational direction of the magnetic particle carrying means. By facing, it is possible to set an appropriate magnetic force (magnetic attraction force) that improves the transportability of magnetic particles in the contact nip, and prevent charging failure due to retention of the magnetic brush (or magnetic particles). can do. In the charge injection charging system, it is possible to prevent deterioration of the injection charging ability and prevent charging failure.

2) As described in (2) above, the magnetic pole position of the fixed magnet contained in the magnetic particle carrying means in the contact nip between the charged body and the magnetic brush is determined by the charged body and the magnetic particle carrying means. In the magnetic brush charging device, which is located downstream of the closest position to the magnetic particle carrying means, the magnetic particle carrying means rotates at the contact nip between the charged body and the magnetic brush. Since excessive retention of the magnetic brush on the upstream side in the direction can be prevented, charging failure due to retention of the magnetic brush can be prevented.

3) As described in (3) above, further, the closest contact between the charged body and the magnetic particle carrying means is made from the upstream end in the rotational direction of the magnetic particle carrying means of the contact nip between the charged body and the magnetic brush. In the magnetic brush charging device characterized in that all the tangential magnetic forces on the magnetic particle carrying means are directed downstream in the rotational direction of the magnetic particle carrying means up to the position. Since it can be further improved, it is possible to prevent the charging failure due to the retention of the magnetic brush. In the charge injection charging system, it is possible to prevent deterioration of the injection charging ability and prevent charging failure.

4) In the image forming apparatus using the above-mentioned magnetic brush charging device, the transferability of the magnetic particles, that is, the magnetic brush is improved, so that the charging ability is prevented from being lowered and the charging failure is prevented. Problems such as occurrence of image defects due to defects are eliminated.

[0051]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 7) (1) Example of image forming apparatus (FIG. 1) FIG. 1 is a schematic diagram of a transfer type electrophotographic process according to the present invention.
1 is a schematic configuration diagram of an example of a magnetic brush-contact charging type laser beam printer.

Reference numeral 1 denotes a rotary photosensitive drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum or drum) which is an image bearing member as a member to be charged. In this example, O with a diameter of 30 mm
100 mm in the clockwise direction as shown by the arrow a using a PC photoconductor
It is rotationally driven 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 is a sleeve-type magnetic brush charging member for uniformly charging the peripheral surface of the photosensitive drum 1 to a predetermined polarity and potential. 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 to the charging bias applying power source E1 so that the outer peripheral surface of the rotary photosensitive drum 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 drum 1. Scanning exposure is performed by the beam 7a, and an electrostatic latent image corresponding to desired image information is formed on the peripheral surface of the rotary photosensitive drum 1.

The electrostatic latent image is developed as a toner image by the reversal developing device 3 using magnetic one-component insulating toner. Reference numeral 3a designates a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 3b. The developing sleeve is coated with the above-mentioned negative toner so that the distance from the surface of the photosensitive drum is 300.
While being fixed to μm, the photosensitive drum 1 is rotated at a constant speed and a developing bias voltage is applied to the sleeve 3a from the developing bias applying power source E2. In this example, -500V DC
Voltage, frequency 1800Hz, peak-to-peak voltage 1600V
Using a rectangular AC voltage superimposed on the sleeve 3a
And jumping development is performed between the photosensitive drum 1 and the photosensitive drum 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 a transfer of medium resistance as a contact transfer means is brought into contact with the photosensitive drum 1 with a predetermined pressing force. It is introduced into the pressure contact nip portion (transfer portion) T with the roller 4 at a predetermined timing.

A transfer bias application power source E is applied to the transfer roller 4.
From 3 a predetermined transfer bias voltage is applied. In this example, a transfer roller 4 having a roller resistance value of 5 × 10 ⁸ Ω was used, and a DC voltage of +2000 V was applied to transfer.

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 photosensitive drum 1 are sequentially charged 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 photosensitive drum 1 and 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.

Further, the surface of the photosensitive drum 1 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.

The image forming apparatus of this embodiment includes a photosensitive drum 1, a magnetic brush charging member 2, a developing device 3 and a cleaning device 6.
The four process devices are collectively referred to as a process cartridge 10 which can be attached to and detached from the image forming apparatus main body. Reference numeral 9 is a cartridge housing in which the above-mentioned four process devices 1, 2, 3, and 6 are incorporated in a predetermined manner. 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 coupling state is electrically established, and the lower surface of the photosensitive drum 1 on the side of the process cartridge 10 is brought into a predetermined contact with the transfer roller 4 on the side of the main body of the image forming apparatus, whereby the image forming can be executed.

The process cartridge 10 is one in which a charging unit, a developing unit or a cleaning unit, and an electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. . In addition, at least one electrophotographic photosensitive member including a charging unit, a developing unit, and a cleaning unit is integrally formed into a cartridge, which is attachable to and detachable from the main body of the image forming apparatus.
Further, at least the developing means and the electrophotographic photosensitive member are integrally formed into a cartridge so as to be detachable from the image forming 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 example.

The photoreceptor 1 used in this example is a negatively charged OPC photoreceptor having a charge injection function on its surface. The following 1st to 5th are placed on a drum base 11 made of aluminum having a diameter of 30 mm.
5 functional layers 12 to 16 are sequentially provided from the bottom.

The first layer is an undercoat layer 12 and is provided to smooth out defects on the outer peripheral surface of the aluminum drum substrate 11 and to prevent moire due to reflection of laser exposure, and has 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 substrate 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 in which a disazo pigment is dispersed in a resin and has a thickness of about 0.3 μm, and which generates positive and negative charge pairs when exposed to laser.

The fourth layer is the charge transport layer 15, which is a layer of hydrazone dispersed in polycarbonate resin and has a thickness of about 20 μm, and is a P-type semiconductor. Therefore, the negative charges charged on the photoreceptor surface cannot move through this layer, and only the positive charges generated in the charge generation layer can be transported to the photoreceptor surface.

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 weight percent is dispersed. The coating liquid thus prepared was applied by dipping to a thickness of about 3 μm to form a charge injection layer.

The volume resistance of the charge injection layer 16 which is the surface layer of the photosensitive member is 10 ⁹ to 10 ^{14 in} order to perform charge injection charging.
It is preferable to have a low resistance layer of Ω · cm, and in this example, the volume resistance of the charge injection layer 16 is 1 × 10 ¹³ Ω · cm.
And

The volume resistivity of the charge injection layer 16 is about 6 to 7 when the charge injection layer is formed on a conductive sheet (aluminum sheet).
It was applied at a voltage of 100 V by applying RESISTIVITY CELL 16008A to a high resistance meter 4329A manufactured by Yokogawa Hewlett-Packard Company.

The charge injection layer 16 intentionally creates injection sites for uniformly charging the surface by directly injecting charges from the magnetic brush charging device 2, but the latent image charges flow on the surface. The surface resistance of the charge injection layer 16 needs to be 1 × 10 ⁸ Ω or more so as not to exist.

The surface resistance of the charge injection layer 16 is obtained by coating the charge injection layer on an insulating sheet and applying the charge injection layer to Yokogawa Hewlett
It is measured with a high resistance meter 4329A manufactured by Packard at an applied voltage of 100V.

B) Injection charging (FIG. 3) The principle of charging by using the above-mentioned photoreceptor 1 and the contact charging member will be described.

The charge injection charging in this example is a contact charging member having a medium resistance (magnetic brush charging member) for injecting charges on the surface of the photoconductor having a medium resistance surface resistance. Instead of injecting charges into the trap potential, this is a method of charging the conductive particles 16a of the charge injection layer 16 with charges.

By applying a desired voltage to the magnetic brush charging member 2 at the time of charging, charges are injected into the charge injection layer 16 so that the surface of the photosensitive member as the charged body is finally the magnetic brush 24.
Is charged (charged) to the same potential as.

Specifically, as shown in the model diagrams and equivalent circuit diagrams 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. It is based on the theory of charging a minute capacitor with a contact charging member.

At this time, 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 looks macroscopically charged and charged to a uniform potential, but in reality, a large number of minute charged conductive particles 16a cover the photoconductor surface. Has become. Therefore, even if image exposure is performed with a laser, each conductive particle 16a is electrically independent, so that it is possible to hold an electrostatic latent image.

(3) Magnetic Brush Charging Device (FIG. 4) a) Magnetic Brush Charging Member 2 FIG. 4 (a) is a structural model diagram of the magnetic brush charging member 2 or the magnetic brush charging device of the present embodiment, and the above-mentioned diagram. It is of a sleeve type similar to that of 9 (a).

That is, 21 is a means for supporting magnetic particles,
It is a non-magnetic conductive sleeve (charging sleeve) made of aluminum or the like.

Reference numeral 22 denotes a magnet roll as a magnetic field generating means inserted and arranged in the sleeve 21. N1
S1, N2 and S2 are magnetized portions of the roll. The magnet roll 22 is a non-rotating fixed member, and the outer circumference of the magnet roll 22 is concentrically driven by the sleeve 21 to rotate clockwise at a predetermined peripheral speed by a drive mechanism (not shown) in the clockwise direction shown by the arrow b. .

Reference numeral 23 is a conductive magnetic particle (carrier), which is bound and held as a magnetic brush (conductive magnetic brush) 24 on the outer peripheral surface of the sleeve 21 by the magnetic force of the magnet roll 22 inside the sleeve. . Carrier 2
Reference numeral 3 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 gather to form a brush shape.

A charging bias applying power source E1 is applied to the sleeve 21.
A charging bias is applied from (FIGS. 1 and 3). If the charging bias is too high, leakage occurs between the magnetic brush 24 and the photosensitive drum 1, and if it is too low, the charging potential becomes low and the developing contrast becomes small, so that the image becomes poor. Therefore, the charging voltage is preferably 100V to 1500V.

Reference numeral 26 is a magnetic brush layer thickness regulating blade (regulating blade) facing the sleeve 21 with a small gap,
The sleeve 21 regulates the thickness of the magnetic brush layer that is supported and conveyed to the charging area.

D is a contact nip portion (charging nip portion) formed by bringing the magnetic brush 24 into contact with the surface of the photosensitive drum 1.

The photosensitive drum 1 is rotationally driven in the clockwise direction indicated by the arrow a by a driving mechanism (not shown) at a predetermined peripheral speed, and in the contact nip portion D, the rotational direction of the sleeve 21 and the magnetic brush 24 associated therewith. The rotational conveyance direction of is a counter direction with respect to the rotation direction of the photosensitive drum 1.

When the rotating and conveying direction of the magnetic brush 24 in the contact nip portion D is in the forward direction with respect to the rotating direction of the photosensitive drum 1, the carrier 23 forming the magnetic brush 24 is compared with the counter direction in comparison with the counter direction. 1 tends to adhere. Further, in order to increase the relative speed between the sleeve 21 and the photosensitive drum 1, that is, the peripheral speed difference, the rotation speed of the sleeve 21 becomes high. Therefore, the carrier 23 is likely to be scattered and the rotation torque is increased,
The equipment cost is also high.

In the counter direction, the carrier adhesion to the photosensitive drum 1 can be suppressed and the peripheral speed difference can be increased at a low speed. Therefore, the number of contact between the carrier and the photosensitive drum can be increased, so that the charging property becomes good.

The reason why the counter direction is better for the carrier adhesion to the photosensitive drum has not been clarified yet, but the action of peeling the carrier on the photosensitive drum and pulling it back by the rubbing of the magnetic brush 24 works. I believe.

When the rotation of the sleeve 21 is stopped, the shape of the magnetic brush 24 remains uncharged and appears in the image.

For this reason, the rotating and conveying direction of the magnetic brush 24 is preferably the counter direction.

However, when the rotation direction of the sleeve 21 is set to the counter direction, the magnetic brush portion on the upstream side of the contact nip portion D in the sleeve rotation direction is the photosensitive drum 1 as the charged body.
The magnetic brush tends to stay in this part because the magnetic brush is pulled back by the rotation of the magnetic disk. When the magnetic brush stays excessively, the smooth movement of the carrier in the contact nip portion D is hindered, the transportability of the carrier deteriorates, the contact nip portion D becomes uneven, and the carrier and the photoconductor contact each other. In some cases, the injection charging ability is deteriorated due to a decrease in charge, and charging failure may occur. However, as described later, by setting an appropriate magnetic force, carrier transportability can be improved.

Further, in order to improve the charge injection property, it is preferable to make the contact nip D large, but the sleeve 21
Using the fact that the magnetic brush easily stays in the counter direction, the swelling layer of the magnetic brush is positively created in the upstream part of the contact nip, that is, a suitable collecting part of the magnetic brush. By positively creating the (bank), increasing the contact nip portion D, and further improving the carrier transportability, the charge injection property is improved, and good chargeability can be obtained. . Here, the term “appropriate accumulation of magnetic brushes” refers to a state in which carriers are accumulated to some extent but are smoothly transported without being stagnant.

In order to improve the charge injection property, the width of the contact nip portion D is preferably 2 mm or more, more preferably 4 mm or more. If the contact nip portion D is too small, the chances of contact between the carrier and the photosensitive member are reduced, the charging becomes uneven, and the injection charging ability is deteriorated, so that charging failure is likely to occur.

In this embodiment, the contact nip portion D has a width of about 2 mm upstream from the closest contact nip position downstream in the sleeve rotation direction so that the charging is uniform, the injection charging ability is sufficient, and the charging property is improved. The width was set to about 3 mm on the side, and the total width was set to about 5 mm. When the photosensitive drum 1 and the sleeve 21 have a small diameter as in this example, it is difficult to increase the contact nip portion D, but the rotation direction of the sleeve 21 is set to the counter direction,
By increasing the size of the nip portion on the upstream side in the sleeve rotation direction, it is possible to increase the overall nip.

L is a virtual straight line connecting the center of rotation of the sleeve 21 and the center of rotation of the photosensitive drum 1, and indicates the opposing center of the sleeve 21 and the photosensitive drum 1. At this portion, the sleeve 21 and the photosensitive drum 1 are It is the closest position.

H is the distance at the closest position between the sleeve 21 and the photosensitive drum 1. The minimum distance h between the sleeve 21 and the photosensitive drum 1 is preferably 0.15 to 2.0 mm,
3 to 1.0 mm is more preferable. If the interval h is too small, leakage easily occurs, it becomes difficult to uniformly regulate the thickness of the magnetic brush layer by the regulation blade 26, uneven charging is likely to occur, and a sufficient carrier amount is applied to the contact nip. It becomes impossible to supply it to the portion D, so that charging failure is likely to occur. On the other hand, if the interval h is too large, the thickness of the magnetic brush layer must be increased, and the magnetic binding force of the surface layer portion of the magnetic brush 24 becomes weak, so that the magnetic brush layer becomes rough and uneven charging occurs. Prone to occur,
In addition, the charge injection property is also lowered, and charging failure is likely to occur.

In the injection charging, since the photosensitive member is charged by the charge injection by the contact between the carrier 23 forming the magnetic brush 24 and the photosensitive member, the carrier 23 is smoothly moved in the contact nip portion D, It is necessary to sufficiently contact the carrier and the photoconductor.

In order to improve the charge injection property, the volume ratio Mc of the carrier in the contact nip portion D, that is, the volume ratio of the carrier in the contact nip portion space is preferably 30 to 80%.

Here, the volume ratio Mc is in accordance with the following formula.

Mc = (M / h) × (1 / ρ) × 100 However, M is the carrier amount per unit area of the sleeve (in the non-brushing state) [g / cm ² ], and h is the charged area space. Is the true density [g / cm ³ ] of the carrier.

If the volume ratio Mc becomes too small,
The contact between the carrier and the photoconductor is likely to be insufficient, the contact nip portion D becomes non-uniform, and the chance of contact between the carrier and the photoconductor is reduced, so that the injection charging capability is lowered and the charging failure is likely to occur.

On the other hand, if the volume ratio Mc becomes too large, the carrier tends to stay in the contact nip portion D, hindering the smooth movement of the carrier in the contact nip portion D, and the contact nip portion becomes unsatisfactory. The chargeability becomes low due to the uniformity and the chance of contact between the carrier and the photoreceptor is reduced, and charging failure is likely to occur. Further, when the smooth movement of the carrier is obstructed and the movement of the carrier in contact with the surface of the photoconductor is impaired, the carrier itself is charged up, which hinders the injection of electric charges and easily causes charging failure.

The above-mentioned volume ratio Mc is the gap between the sleeve 21 and the regulating blade 26, the sleeve 21 and the photosensitive drum 1.
It can be set to a required value by correlatively setting the gap h, the true density of carriers, and the like.

B) Carrier 23 Carrier 2 which is magnetic particles constituting the magnetic brush 24
3 includes: -a resin and a magnetic powder such as magnetite are kneaded and molded into particles, or a mixture of this with conductive carbon or the like to adjust the resistance value-sintered magnetite, ferrite, or these Those whose resistance value has been adjusted by reduction or oxidation, ・ Coating or N with the above-mentioned magnetic particles whose resistance has been adjusted (such as those in which carbon is dispersed in phenol resin)
It is conceivable that the resistance value is set to an appropriate value by plating with a metal such as i. In order to reduce damage to the photosensitive drum 1, it is desirable that the carrier 23 be spherically processed.

If the resistance value of these carriers 23 is too high, charges cannot be uniformly injected into the photosensitive drum, resulting in a fog image due to minute charging failure. If it is too low, when there are pinholes on the surface of the photosensitive drum, current concentrates on the pinholes, the charging voltage drops, and the surface of the photosensitive drum cannot be charged, resulting in a charging nip-shaped charging failure.

Therefore, as the resistance value of the carrier 23,
It is preferably 1 × 10 ⁵ to 1 × 10 ⁸ Ω · cm. The resistance value of the carrier is the metal cell (bottom area 228
mm ² ), after putting 2 g of the carrier 23 into it, 6.6 kg / c
The measurement was performed by applying a weight of m ² and applying a voltage of 1 to 1000 V. For example, 100 V was applied, and it was defined by being normalized from the measured current flowing in this system.

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

If the particle size of the carrier is too small, the magnetic binding force becomes small, and the carrier adheres to the surface of the photosensitive drum. On the other hand, if it is too large, the contact area with the photosensitive drum is reduced and charging failure increases. Therefore, the average particle size of the carrier is preferably about 5 to 50 μm from the viewpoint of chargeability and magnetic retention. The average particle size of the carrier was determined by randomly extracting 100 or more particles with an optical microscope or a scanning electron microscope, calculating the volume particle size distribution with the maximum chord length in the horizontal direction, and calculating the 50% average particle size.

Regarding the magnetic characteristics of the carrier 23, it is better to increase the magnetic force in order to prevent the carrier from adhering to the photosensitive drum, and the saturation magnetization is 30 (A · m ² / kg) or more,
More preferably, it is 50 (A · m ² / kg) or more.

In practice, the carrier 23 used in this example has an average particle size of 30 μm, a spherical shape, and a resistance value of 1 × 10 ^6.
Ω · cm, saturation magnetization was 64 (A · m ² / kg). The true density of the carrier 23 is about 5.8 g / cm ^3.
The magnetic permeability was about 5.0.

Saturation magnetization and magnetic permeability were measured by a vibrating sample magnetometer (trade name: VSM-P-1-type manufactured by Toei Industry Co., Ltd.) to magnetize magnetic particles placed in a maximum magnetic field of 10,000 Oersted. Was measured and determined based on the hysteresis curve drawn on the recording paper.

C) Magnet roll 22 (FIGS. 4 to 6) Regarding the magnet roll 22 used in this example, FIGS.
Will be described in detail. FIG. 4B is a diagram for explaining the positions of the contact nip portion D and the magnetic pole configuration.

L is a sleeve 2 as a magnetic particle supporting means.
1 is a virtual straight line connecting the center of rotation of the photosensitive drum 1 as a member to be charged and shows the opposing center of the sleeve 21 and the photosensitive drum 1. In this portion, the sleeve 2
1 and the photosensitive drum 1 are the closest positions.

H is the distance at the closest position between the sleeve 21 and the photosensitive drum 1.

P is the closest position on the sleeve 21 to the photosensitive drum 1, and Q is the closest position on the photosensitive drum 1.

S is a sleeve 21 corresponding to the charging main pole S1.
In the upper position, θ is an angle formed between the virtual straight line F connecting the rotation center of the sleeve 21 and the charging main pole S1 and the virtual straight line F. That is, the main charging pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the rotation direction of the sleeve 21.

A is the position of the contact nip portion D between the photosensitive drum 1 and the magnetic brush 24 on the photosensitive drum 1 on the downstream side in the photosensitive drum rotation direction.

L1 is an imaginary straight line connecting the downstream end position A of the nip portion on the photosensitive drum 1 and the rotation center of the sleeve 21.

B is the closest position on the sleeve 21 to the downstream end position A of the nip portion on the photosensitive drum 1, and is the position where the virtual straight line L1 and the surface of the sleeve 21 intersect.

When the position of the main charging pole S1 is located upstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the magnetic brush stands on the upstream side of the nip portion and is conveyed by the rotation of the sleeve. The function of stopping the carried carrier from trying to pass through the closest nip part works,
The carrier easily stays in the nip portion. When the carrier stays in the nip portion, the nip portion D becomes non-uniform, and the chances of contact between the carrier and the photosensitive member are reduced, so that the injection charging ability is deteriorated and charging failure is likely to occur. Also,
The carrier itself is likely to be charged up, which hinders the injection of electric charges and easily causes charging failure.

On the other hand, when the position of the main charging pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the distance between the sleeve 21 and the photosensitive drum 1 is the smallest, and the carrier can be conveyed. Since the magnetic brush is not erected up to the most severe position P / Q, the carrier is conveyed smoothly, and the magnetic brush erears after the space passes through the position N / P closest to the nip portion to expand the space. The carrier of the magnetic brush is not hindered by the rising of the magnetic brush.

Therefore, the carrier does not stay,
The carrier in the nip portion D can move smoothly, the number of contact between the photoconductor and the carrier not charged up increases, and the charging failure does not occur.

The position of the main charging pole S1 is the photosensitive drum 1.
If the distance is too far from the closest position P to the carrier, the magnetic force for attracting the carrier in the nip portion toward the outlet of the nip portion becomes weak, so that the carrier transportability may be slightly inferior.

The position of the main charging pole S1 is 0 ° downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction.
-30 ° (θ) is preferable, and 0 ° -15 ° is more preferable.

FIG. 5 is a diagram for explaining the magnetic force on the sleeve 21 as the magnetic particle supporting means, where F is the magnetic force on the sleeve 21 and Fr is the magnetic force in the direction normal to the sleeve surface on the sleeve 21. The force, Fθ, indicates the magnetic force in the tangential direction of the sleeve surface on the sleeve 21.

Here, the magnetic force Fθ is the following proportional expression Fr∝∂B ² / ∂θ∝ {B ² (θ + Δθ) −B ² (θ−Δθ)} / 2Δθ, where B ² (θ + Δθ) = B ² r (Θ + Δθ) + B ² θ (θ + Δθ) B ² (θ−Δθ) = B ² r (θ−Δθ) + B ² θ (θ−Δθ)

Therefore, by obtaining {B ² (θ + Δθ) -B ² (θ-Δθ)} / 2Δθ, the relative magnitude of the magnetic force Fθ can be known, and the distribution form of the magnetic force Fθ and the magnetic force Fθ can be obtained. You can know the direction of the.

The magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction on the magnetic particle supporting means (sleeve) are measured using a Gauss meter manufactured by Bell Co. as described later. Br
(Θ) is the magnetic flux density [Gauss] in the normal direction on the magnetic particle supporting means, and Bθ (θ) is the magnetic flux density [Gauss] in the tangential direction on the magnetic particle supporting means.

Here, θ is an angle [radian] from the reference position θ0, and the angle becomes larger toward the upstream side with respect to the sleeve rotation direction.

∂B ² / ∂θ will be further explained.
When is differentiated from the + side,

[0134]

[Equation 1] When θ is differentiated from the + side,

[0135]

[Equation 2] Since these are continuous, it can be assumed that they are equal no matter which derivative is performed.

[0136]

(Equation 3) Becomes Therefore, ∂B ² / ∂θ = {B ² (θ + Δθ) −B ² (θ−Δθ)} / 2Δθ.

For example, when Δθ is calculated every 3 °, the unit is radian, and therefore Δθ = 3π / 180 [radian].

Whether or not the carrier can smoothly move in the contact nip portion D, that is, whether or not the carrier can be easily conveyed is not directly related to the magnetic flux density on the sleeve 21, but the carrier on the sleeve 21 is It is related to the magnitude of the magnetic force moving in the tangential direction. This will be described with reference to FIG.

The carrying property of the carrier on the sleeve 21 is such that the carrier is held on the sleeve and the held carrier is carried by the rotation of the sleeve as it is, and the photosensitive drum 1 rotates in the counter direction. Therefore, it is determined by the balance with the conveyance suppressing action such as pulling back the carrier in the contact nip portion D in the upstream direction of the sleeve. In addition, the ease of transportation is determined by the distance between the contact nip portions and the amount of carrier. The transport promoting action and the transport suppressing action are not only the dynamic action due to the rotation of the sleeve and the photosensitive drum,
The action by magnetic force is involved. That is, if the magnetic force acting on the carrier in the contact nip portion is oriented in the transport direction, the transportability is promoted, and if it is oriented in the opposite direction, the transportability is suppressed. That is, the direction of the magnetic force Fθ in the tangential direction on the sleeve determines whether the transportability by the magnetic force is promoted or suppressed.

If the magnetic force Fθ can be directed to the sleeve rotation downstream side at all positions on the sleeve 21, the magnetic force F will act in a direction that facilitates transportability at all positions on the sleeve. However, even if the magnetic flux density distribution is devised, such a configuration is impossible.

Therefore, it is important to make the magnetic force Fθ act on the sleeve in the direction of promoting the transportability at a portion (contact nip portion) of high importance for the transportability.

At which position in the contact nip D the direction of the magnetic force Fθ is effective is the position at which carrier conveyance is most severe, that is, the closest position P where the distance between the sleeve 21 and the photosensitive drum 1 is small. It is thought that the magnetic force of is closely related. That is, it is effective to direct the magnetic force Fθ at the closest position P to the transport direction, that is, to the downstream side of the sleeve rotation. In addition, if the transportability of the carrier on the upstream side of the sleeve rotation at the closest position P is insufficient, the action of pushing the carrier toward the closest position P and packing is performed, so that the carrier easily accumulates. Therefore, it is more preferable that the direction of the magnetic force in the area from the upstream end position B of the contact nip portion to the closest position P is in the transport direction.

On the other hand, for the carrier on the downstream side of the rotation of the sleeve at the closest position P, since the distance between the sleeve and the drum is widened, even if the carrier acts due to the magnetic force, the normal magnetic force is applied. If so, it is possible to obtain sufficient transportability as a total balance.

As described above, in order to improve the transportability of the carrier on the sleeve, the direction of the magnetic force Fθ at the position P closest to the photosensitive drum on the sleeve is directed to the downstream side of the sleeve rotation. effective. Further, it is more preferable to direct all the magnetic force from the upstream end position B of the contact nip portion on the sleeve to the closest position P to the downstream side of the sleeve rotation.

FIG. 6A shows the distribution form of the magnetic flux density Br and the magnetic force F of the charging main pole S1 of the "magnet roll A".
FIG. 4 is a diagram for explaining a distribution form of θ, in which the horizontal direction indicates the position in the sleeve circumferential direction (in angle), the vertical direction indicates the position in the charging sleeve circumferential direction (in angle), and the sleeve 21 The magnitude of the upper magnetic force Fθ or the sleeve 2
1 shows the magnitude of the magnetic flux density Br above 1.

When the magnetic force Fθ is positive, it indicates that the direction of the magnetic force Fθ is toward the sleeve rotation upstream side (right direction in the figure), and when the magnetic force Fθ is negative, the direction of the magnetic force Fθ is the sleeve. It shows that it is facing the downstream side of the rotation (left direction in the figure). S is the position of the main charging pole S1, P is the closest position to the photosensitive drum 1 on the sleeve 21, and B is the upstream end position of the nip portion on the sleeve 21. In this example, the magnetic force F is generated in the entire area from the position B to the position P and further to the position S.
θ is negative, which means that the magnetic force Fθ is all directed toward the downstream side of the sleeve rotation in this portion.

For example, the outer diameter of the sleeve 21 is 16 mm,
If the outer diameter of the photosensitive drum 1 is 30 mm, the distance h between the photosensitive drum 1 and the sleeve 21 is 0.5 mm, and the width of the contact nip portion D is 2 mm on the upstream side of the photosensitive drum 1 and 3 mm on the downstream side, the position on the photosensitive drum The angle between Q and position A is about 21.5
The angle between the position P on the sleeve and the position B is about 18.7 °.

When the position S of the main charging pole S1 is located 6 ° downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the angle between the sleeve upper position S and the position B is [18]. .7 − (− 6) = 24.7 °].

6 (b), (c), and (d) are distribution patterns and magnetic fields of the magnetic flux density Br of the charging main pole S1 of the "magnet roll B", "magnet roll C", and "magnet roll D". It is a figure of the distribution form of force F (theta). Symbol is Fig. 6
(A).

A method of measuring the magnetic flux density will be described with reference to FIG. This figure is a diagram for explaining a method of measuring the magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction on the sleeve 21,
The measurement was performed using a Gauss meter model 9903 manufactured by Bell Corporation.
The sleeve 21 is fixed horizontally, and the magnet roll 22 in the sleeve 21 is rotatably attached. 42
Is a biaxial probe (YOA99-1802 manufactured by Bell Co.), and the sleeve 2 is slightly spaced from the sleeve 21.
The center of 1 and the center of the probe 42 are fixed so as to be substantially in the same horizontal plane and are connected to the Gauss meter 41, and the magnetic flux densities on the sleeve 21 in the normal direction and the tangential direction are measured. The sleeve 21 and the magnet roll 22 are substantially concentric, and the sleeve 21 and the magnet roll 22 are
You can think that the intervals of are equal everywhere. Therefore, by rotating the magnet roll 22, the magnetic flux densities in the normal direction and the tangential direction on the sleeve 21 can be measured in all circumferential directions.

Since the magnet roll 22 is rotated in the direction of the arrow, for example, the regulation pole N1 rather than the charging main pole S1 is used.
The angle of becomes a large value. That is, the measurement is performed in the direction in which the angle increases on the upstream side with respect to the moving direction b of the sleeve in FIGS. 1 and 4.

(4) Experimental Example In this example, the peripheral speed of the photosensitive drum 1 is 100 mm / sec, the outer diameter is 30 mm, and the peripheral speed of the charging sleeve 21 is 150 mm /.
sec, the outer diameter of the sleeve 21 was 16 mm. The rotating direction of the sleeve 21 was counter to the photosensitive drum 1. The distance h between the photosensitive drum 1 and the sleeve 21 was 0.5 mm. The position of the main charging pole S1 is the photosensitive drum 1.
And 6 ° (−6 °) on the downstream side with respect to the sleeve rotation direction with respect to the closest position P. At this time, the peak value of the magnetic flux density in the direction normal to the sleeve surface of the charging main pole S1, which is a magnet fixed in the sleeve 21, was 940 × 10 ⁻⁴ T (Tesla). Magnetic brush 24
Carrier amount is about 15 g, the longitudinal width of the magnetic brush 24 is 210 mm, the thickness of the coat layer of the magnetic brush 24 on the charging sleeve is about 1 mm, and the width of the contact nip portion D is about 2 mm on the upstream side. Width about 3mm on the downstream side, total width about 5mm
And Table 1 shows the results obtained regarding the carrier transportability and the charging property at this time.

Further, as the magnet roll 22, the magnetic flux density of the charging main pole S1 shown in FIG.
10 ^-4 T of (Tesla) and "Role A", "Role B" of the magnetic flux density of the charged main pole S1 is 950 × 10 ^-4 T (tesla)
Table 1 shows the results obtained with respect to the carrier transportability and the chargeability when various positions of the charging main pole were changed using.

[0154]

[Table 1] In Table 1, the meanings of the symbols are as follows.

Regarding Evaluation of "Conveyability" O: Very Good Conveyance X: Poor Conveyability O: Evaluation of "Chargeability" O: Very Good Charging Poor: Poor Charging Table 1 As can be seen, Experimental Examples 1-1 to 1-3, 1
As shown in -6, the magnetic force F?
When all the magnetic forces Fθ of S are negative, the transportability was very good and the chargeability was very good.
4, 1-5, 1-7, the magnetic force Fθ at the position S
Is positive and the magnetic forces Fθ at the positions B to S are positive / negative, the transportability is poor and the charging property is poor.

When the magnetic force Fθ at the position S is negative and the position of the charging main pole is downstream of the position P closest to the photosensitive drum 1 in the sleeve rotation direction, the carrier is not retained. , It has very good transportability, good chargeability,
The images were also good.

As described above, by directing the direction of the magnetic force Fθ at the position P closest to the photosensitive drum 1 on the sleeve 21 toward the downstream side of the sleeve rotation, it is possible to improve the carrier transportability. Further, it is more preferable to direct all the magnetic forces in the region from the end position B on the upstream side of the contact nip portion on the sleeve to the closest position P to the downstream side of the sleeve rotation.

Particularly, in order to reduce the size and cost of the magnetic brush charging device as in this example, the charge injection property tends to be insufficient when the charging sleeve 21 has a small diameter. In the counter direction and positively create a bulging layer of the magnetic brush in the upstream part of the contact nip,
By enlarging the contact nip portion, charge injection property is improved, and good chargeability can be obtained. When the sleeve is rotated in the counter direction, the magnetic brush is likely to stay, so that the transportability is likely to be insufficient. However, setting the magnetic force Fθ on the sleeve appropriately has a great effect as described above. There is.

<Embodiment 2> (FIG. 8) This embodiment is an application example of a so-called cleanerless system to an image forming apparatus. FIG. 8 is a schematic configuration diagram of an example of the image forming apparatus.

This image forming apparatus is different from the image forming apparatus shown in FIG. 1 in that the cleaning device 6 is omitted, the two-component magnetic brush developing device 3A is used as the developing device, and the magnetic brush charging device is set. The laser beam printer uses the transfer type electrophotographic process and has the same configuration as that of the image forming apparatus in FIG. 1 except that it is slightly different and not the process cartridge system, and thus the repetitive description will be omitted. .

In the case of such an image forming apparatus of the cleanerless system, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the toner image is transferred from the rotary photosensitive drum 1 to the transfer material 30 reaches the developing device 3A, so-called simultaneous development. By the cleaning action, the toner is collected in the developing device (developing device that also serves as cleaning). The image forming apparatus of the cleanerless system can be downsized and reduced in cost by omitting a dedicated cleaning device.

A) Developing Device 3A The developing device 3A in this image forming apparatus is a developing device using a two-component magnetic brush contact developing method which has been widely used in the past. The developer used is a two-component developer consisting of a non-magnetic toner and a magnetic carrier, and the toner particles have a weight ratio of titanium oxide having an average particle size of 20 nm to negatively charged toner having an average particle size of 6 μm produced by a polymerization method. A magnetic carrier having a saturation magnetization of 66 (A · m ² / kg) and an average particle size of 35 μm was used as the carrier. A mixture of this toner and a carrier in a weight ratio of 6:94 was used as a developer.

Reference numeral 31 is a non-magnetic developing sleeve having a diameter of 16 mm, which encloses a magnet roll 32 fixedly arranged therein, and is driven by a drive mechanism (not shown) at the same speed as the photosensitive drum 1 in the forward direction, that is, as indicated by arrow c. It is rotated counterclockwise as shown.

The developing sleeve 31 is coated with the above-mentioned developer so that the closest distance to the surface of the photosensitive drum 1 is 0.5 mm.
And is set so that development can be performed in a state where the developer is in contact with the photosensitive drum 1.

A developing bias applying power source E is applied to the sleeve 31.
A developing bias voltage is applied from 2. In this example, -50
A direct current voltage of 0 V and a rectangular alternating voltage having a frequency of 2000 Hz and a peak-to-peak voltage of 1500 V were superimposed and applied.

B) Magnetic Brush Charging Device 2 The magnetic brush charging device 2 used in this example is different from the one in the first embodiment only in the condition for applying the charging bias to the magnetic brush charging member, but is different in configuration. Is the same as that of the first embodiment, and thus the repetitive description will be omitted.

That is, in the present example, a charging bias for the magnetic brush charging member is obtained by superimposing an AC voltage on a DC voltage.

When only the DC voltage is used as the charging bias, a good charging property is initially obtained, but the image forming apparatus of the cleanerless system does not have a dedicated cleaning device like the image forming apparatus of this embodiment. In the case of, when the image formation is repeatedly performed (during durability), the transfer residual toner cannot be sufficiently collected in the magnetic brush charging member,
In some cases, charging failure may occur or image failure may occur.

However, when the charging bias in which the AC voltage is superimposed on the DC voltage is used, the transfer residual toner can be sufficiently collected in the magnetic brush charging member,
It is possible to improve the charging property and the image property.

The reason why the transfer residual toner can be sufficiently collected by the AC voltage is that positive and negative voltages are applied. Therefore, both the positively charged toner and the negatively charged toner are collected. It is considered possible. Further, when the AC voltage is superposed, the charging property can be improved even if the transfer residual toner is mixed in the magnetic brush charging member. The reason for this is considered to be that the carrier vibrates and actively moves due to the action of the AC voltage, so that the chances of contact with the photoconductor increase.

If the frequency of the AC voltage is too low,
Frequency unevenness appears and charging unevenness occurs. Too high,
The effect is diminished because it approaches the DC voltage. Therefore, the frequency is preferably 400 peak Hz to 4000 Hz. If the peak-to-peak voltage (Vpp, amplitude) of the AC voltage is too low, it approaches the DC voltage, and the effect is weakened. If it is too high, a leak may occur between the photosensitive drum and the carrier and the carrier may be attached. Therefore, the peak-to-peak voltage is 50-
5000V is preferable.

In this example, the charging sleeve 21 has -700V.
DC voltage, frequency 1000Hz, peak-to-peak voltage 80
A rectangular alternating voltage of 0 V was applied.

In this example, as the magnet roll 22, the "roll A" and "roll B" used in the first embodiment and the magnetic flux density of the charging main pole S1 are 910 × 10 ^-4 T.
(Tesla) “Roll C” and “Roll D” whose main magnetic pole S1 has a magnetic flux density of 890 × 10 ⁻⁴ T (Tesla) are used.
Table 2 shows the results obtained with respect to carrier transportability and chargeability when the position of the charging main pole was changed variously.

[0174]

[Table 2] In Table 2, the meanings of the symbols are as follows. Regarding evaluation of “transportability” ○: Very good transportability Δ: Good transportability ×: Poor transportability ○: Evaluation of “chargeability” ○: Very good chargeability Δ: Good chargeability ×: Regarding the evaluation of "ghost" with poor chargeability ○: Very good with no ghost △: Slightly with ghost, but practically unproblematic ×: With ghost, defective Note: "Ghost" has a certain history It is a phenomenon that causes image unevenness with a different pattern.

As shown in Table 2, Experimental Examples 2-1 to 2
As shown in -6, 2-8, and 2-10, when the magnetic force Fθ at the position S is negative, the transportability and the charging property are good and the ghost is very good. Experimental Examples 2-1 to 3, 2-6, and 2-8 in which all the magnetic forces Fθ were negative were very good in transportability and very good in chargeability. However, as shown in Experimental Examples 2-4, 2-5, and 2-7, when the magnetic force Fθ at the position S is positive and the magnetic forces Fθ at the positions B to S are positive / negative, the conveyance is performed. The chargeability was poor, and the ghost was slightly generated.

As described above, by directing the direction of the magnetic force Fθ at the position P closest to the photosensitive drum 1 on the sleeve 21 to the downstream side of the sleeve rotation, it is possible to improve the carrier transportability. Further, it is more preferable to direct all the magnetic forces in the region from the end position B on the upstream side of the contact nip portion on the sleeve to the closest position P to the downstream side of the sleeve rotation.

Particularly, in order to reduce the size and cost of the magnetic brush charging device as in this example, the charge injection property tends to be insufficient when the diameter of the charging sleeve is reduced, but the rotation direction of the sleeve is changed. By positively forming the swelling layer of the magnetic brush on the upstream side of the contact nip portion in the counter direction and enlarging the contact nip portion, the charge injection property is improved, and good chargeability can be obtained. When the sleeve is rotated in the counter direction, the magnetic brush is likely to stay, so that the transportability is likely to be insufficient. However, setting the magnetic force Fθ on the sleeve appropriately has a great effect as described above. There is.

<Others> 1) The magnetic brush charging device according to the present invention is not limited to the charging process of the image carrier in the image forming apparatus of the embodiment,
It is needless to say that it is widely effective as a contact charging treatment means for a body to be charged.

2) The body to be charged may be one in which charging by discharge is dominant. As a contact charging system by means of discharge, as a contact charging means of AC charging method, as disclosed in Japanese Patent Publication No. 52058/1990 proposed by the present applicant, a predetermined direct current voltage component is applied to a contact charging member. A method of applying an oscillating voltage having a predetermined alternating voltage component (an alternating voltage having a peak-to-peak voltage that is more than twice the charging start voltage value of the charged body when a direct current voltage is applied to the contact charging member) is applied to uniform charging. Excellent in. As the alternating voltage component (AC bias component), a sine wave, a square wave (rectangular wave), a triangular wave, a sawtooth wave or the like having an appropriate waveform can be used. It also includes a rectangular wave formed by periodically turning on and off a DC power supply. The present invention can also be applied to such contact charging means.

3) Regarding the image forming apparatus, the image forming process is optional. The transfer system may be a direct system in which an image is formed directly on photosensitive paper (electrofax paper) or electrostatic recording paper without an image transfer process.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the primary surface of the dielectric surface is uniformly charged to a predetermined polarity and potential, the target electrostatic latent image is written and formed by selectively neutralizing with a neutralizing means such as a neutralizing needle head or an electron gun.

The electrostatic latent image developing system and means are arbitrary,
A reversal development system or a regular development system may be used.

As the transfer method, not only the roller transfer shown in the embodiment but also the blade transfer and other contact charging methods, and further the transfer drum, the transfer belt, the intermediate transfer member and the like are used, and not only the single color image formation It goes without saying that it can be applied to an image forming apparatus that forms a multicolor or full-color image by multiple transfer or the like.

Further, an electrophotographic photosensitive member or an electrostatic recording dielectric as an image bearing member is formed into a rotating belt type, and a toner image corresponding to required image information is formed on the rotating belt type by means of process steps of charging, latent image formation and development. There is also an image display device in which the toner image forming section is formed, the image is displayed by positioning the toner image forming section on the reading display section, and the image carrier is repeatedly used for forming the display image. The image forming apparatus of the present invention includes such an image display apparatus.

[0185]

As described above, according to the present invention, the relative movement direction between the magnetic particle carrying means and the charged body in the contact nip between the charged body and the magnetic brush is set to the counter direction so that the charged body can be charged. On the other hand, since it is possible to increase the peripheral speed difference of the magnetic particle supporting means, that is, the magnetic brush, it is possible to increase the number of opportunities for contacting the magnetic brush with the body to be charged and improve the charging property. In the charge injection charging system, the charge injection property is improved and the charge property can be improved. Further, the direction of the magnetic force in the tangential direction on the magnetic particle carrying means acting on the magnetic brush magnetic particles at the position closest to the charged body of the magnetic particle carrying means is toward the downstream side in the rotation direction of the magnetic particle carrying means. By that,
It is possible to set an appropriate magnetic force (magnetic attraction force) that improves the transportability of magnetic particles in the contact nip, and it is possible to prevent charging failure due to retention of the magnetic brush. In the charge injection charging system, it is possible to prevent deterioration of the injection charging ability and prevent charging failure.

In addition to this, the magnetic pole position of the fixed magnet contained in the magnetic particle supporting means at the contact nip between the charged body and the magnetic brush is determined from the closest position between the charged body and the magnetic particle supporting means. By arranging it on the downstream side with respect to the rotation direction of the magnetic particle carrying means, it is possible to prevent excessive retention of the magnetic brush at the contact nip between the charged body and the magnetic brush on the upstream side in the rotational movement direction of the magnetic particle carrying means. Therefore, it is possible to prevent the charging failure due to the retention of the magnetic brush.

Furthermore, in the range from the upstream end of the magnetic particle carrying means in the contact nip between the charged body and the magnetic brush to the closest position between the charged body and the magnetic particle carrying means, the magnetic particle carrying means is held. Since the direction of the magnetic force in the tangential direction on the device is all directed downstream in the rotational direction of the magnetic particle supporting device, the transportability of the magnetic particles can be further improved, and thus charging failure due to retention of the magnetic brush can be prevented. can do. In the charge injection charging system, it is possible to prevent deterioration of the injection charging ability and prevent charging failure.

In the image forming apparatus using the above-mentioned magnetic brush charging device, since the transportability of the magnetic particles, that is, the magnetic brush is improved, the charging ability is prevented from being lowered and the charging failure is prevented. Problems such as occurrence of image defects due to the problems are solved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic diagram of a layer structure of a photoconductor as a member to be charged;

FIG. 3 is a diagram for explaining the principle of injection charging.

FIG. 4A is a structural model diagram of a magnetic brush charging device,
(B) is a figure for demonstrating the position of a contact nip part and a magnetic pole structure.

FIG. 5 is a diagram for explaining a magnetic force Fθ on the charging sleeve 21.

FIG. 6 is a diagram for explaining a distribution form of a magnetic flux density Br of a charging main pole S1 and a distribution form of a magnetic force Fθ.

FIG. 7: Magnetic flux density Br in the normal direction on the charging sleeve 21
And a diagram for explaining a method of measuring the magnetic flux density Bθ in the tangential direction

FIG. 8 is a schematic configuration diagram of an image forming apparatus example of a cleanerless system according to the second embodiment.

9A is a schematic configuration model diagram of a sleeve type magnetic brush charging device, and FIG. 9B is a schematic configuration model diagram of a magnetic roller type magnetic brush charging device.

[Explanation of symbols]

 1 Charged Member (Electrophotographic Photosensitive Member, Photosensitive Drum) 2 Magnetic Brush Charging Member 21 Charging Sleeve (Magnetic Particle Carrier) 22 Magnet Roll 23 Magnetic Particle (Carrier) 24 Magnetic Brush 25 Control Blade 3 Developing Device 4 Transfer Roller 5 Fixing Device 6 Cleaning device 10 Process cartridge 30 Recording material (transfer material) E1 Charging bias application power source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Kono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A magnetic brush charging member in which magnetic particles are restrained by a magnetic force and attached and held as a magnetic brush on a rotatable conductive magnetic particle supporting means containing a fixed magnet. In a magnetic brush charging device in which a magnetic brush of a charging member is brought into contact with a body to be charged and conveyed by rotation of a magnetic particle carrying means, and a voltage is applied to charge the body to be charged, in a contact nip between the body to be charged and the magnetic brush. The rotating direction of the magnetic particle carrying means is the counter direction with respect to the charged body, and the magnetic brush acting on the magnetic brush magnetic particles at the position of the magnetic particle carrying means closest to the charged body is the tangential magnetic force on the magnetic particle carrying means. The magnetic brush charging device is characterized in that the direction of force is toward the downstream side in the rotation direction of the magnetic particle carrying means. 2. The magnetic brush charging device according to claim 1, further comprising: a fixed magnet included in the magnetic particle supporting means.
Magnetic brush charging characterized in that the magnetic pole position in the contact nip between the charged body and the magnetic brush is located downstream of the closest position between the charged body and the magnetic particle carrying means in the rotation direction of the magnetic particle carrying means. apparatus. 3. The magnetic brush charging device according to claim 1 or 2, wherein the charged body and the magnetic particle carrying means are provided from an end of the contact nip between the charged body and the magnetic brush in the rotational direction upstream side of the magnetic particle carrying means. The magnetic brush charging device is characterized in that the magnetic force in the tangential direction on the magnetic particle carrying means is all directed downstream in the rotational direction of the magnetic particle carrying means in the range up to the closest position. 4. An image forming apparatus for executing 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 magnetic device according to claim 1. An image forming apparatus, which is a brush charging device.