JP3483397B2 - Charging device and image forming apparatus provided with the charging device - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As is well known, charging means for charging an object to be charged is roughly classified into two systems, a "non-contact system" and a "contact system".

On the other hand, as a typical example of the non-contact system, there is a corona charger. The corona charger is disposed so as to face the member to be charged in a non-contact manner, and a high voltage is applied to generate corona discharge. It is charged by exposing the surface of the body to be charged to corona discharge.

The other contact system is a contact charging device provided with a charging member such as a triboelectric charging member, a roller member or a brush member. In this contact charging device, the charging member is brought into contact with the member to be charged, and a voltage is applied to the charging member to charge the member to be charged.

Conventionally, in an image forming apparatus of, for example, an electrophotographic system or an electrostatic recording system, a non-contact type corona is used as a charging processing means for a charged body such as an electrophotographic photosensitive drum or an electrostatic recording dielectric. Charger was used a lot,
In recent years, as ecological attention has been paid, contact type contact charging devices have been put into practical use because they have advantages such as low ozone and low power consumption. As the contact charging member, rubber roller, fixed brush, roll-shaped fur brush, etc.
There are various members.

A) Roller charging type In particular, a roller charging type contact charging device using a charging roller (conductive elastic roller) as a contact charging member is preferably used from the viewpoint of charging stability.

In this roller charging type contact charging device, a conductive elastic roller as a contact charging member is pressed against and contacted with a member to be charged, and a voltage is applied to the elastic roller to charge the member to be charged. To do. Specifically, since the charging is performed by discharging from the contact charging member to the photoconductor as the member to be charged, the charging is started by applying a voltage equal to or higher than a certain threshold voltage.

As an example, when a charging roller is brought into pressure contact with an OPC photosensitive member having a photosensitive layer having a thickness of 25 μm to perform a charging process, a voltage of about 640 V or more is applied to the charging roller. Then, the surface potential Vd of the photoconductor starts to rise, and thereafter, the surface potential Vd of the photoconductor linearly increases with an inclination 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 required surface potential Vd of the photoconductor in the electrophotographic process, the charging roller needs a DC voltage Vd + Vth, which is higher than that required by the photoconductor. In this way, a method of applying only the DC voltage to the contact charging member to carry out charging is called "DC charging method".

In this DC charging method, however, the resistance value of the contact charging member fluctuates due to environmental changes, etc. Further, the photosensitive layer of the photoconductor is scraped by the contact charging member to change the film thickness and the charging start voltage Vth. Fluctuates, it was difficult to set the charging potential of the photoconductor to a desired value.

Therefore, in order to charge the photoconductor to a desired charging potential and to further homogenize the charging, a desired surface potential Vd is obtained as disclosed in JP-A-63-149669. An “AC charging method” is used in which a voltage obtained by superimposing an AC component having a peak-to-peak voltage Vpp of 2 × Vth or more on a corresponding DC voltage is applied to a contact charging member to charge an object to be charged. This AC charging method is intended for leveling the potential by the AC component, and the potential of the photoconductor converges on the surface potential Vd, which is the center of the peak-to-peak voltage Vpp of the AC voltage, to prevent disturbances such as the environment. Is unaffected.

However, even in such a contact charging member, the essential charging mechanism uses the phenomenon of discharge from the contact charging member to the photosensitive member, so that it is necessary for charging as described above. The voltage is required to have a value equal to or higher than the surface potential of the photoconductor, and a small amount of ozone is generated.

When AC charging is performed in order to make the surface potential of the photoconductor uniform, the generation of more ozone and the vibration noise between the contact charging member and the photoconductor due to the electric field of the AC voltage (AC charging) The generation of noise) and the deterioration of the surface of the photoconductor due to discharge have become remarkable, which has become a new problem.

Here, the characteristics required not only for the charging roller but also for the contact charging member are low withstand voltage defects such as scratches and pinholes on the surface of the photoconductor when a material having a low resistance value is used for the contact charging member. If there is a portion, an excessive leak current flows from the contact charging member to the low withstand voltage defect portion, and charging defects or pinholes may expand around the low withstand voltage defect portion of the photoconductor.
The contact charging member may be damaged by electricity. In order to prevent this, it is necessary to set the resistance value of the contact charging member to about 1 × 10 ⁴ Ω or more. On the other hand, above 1 × 10 ⁷ Ω,
The resistance value is too high to pass the current necessary for charging. Therefore, the resistance value of the contact charging member is 1 × 10 ⁴
It must be in the range of Ω to 1 × 10 ⁷ Ω.

B) Injection charging method Further, an injection charging method, which is a contact system and in which charging is performed by directly injecting an electric charge into a photoconductor, has been devised (Japanese Patent Application Laid-Open No. 6-3921, Japanese Patent Application No. Hei. -66150 gazette etc.).

In this injection charging method, only a DC voltage corresponding to a desired surface potential Vd is applied to a contact conductive member such as a charging roller, a charging brush, a charging magnetic brush, and charges are applied to a trap level on the surface of the photoconductor. And a desired surface potential Vd is obtained by a method such as injecting or charging a photoreceptor having a protective film in which conductive particles are dispersed.
Japanese Unexamined Patent Publication No. 6-13927 discloses a method of injecting electric charges into a float electrode on a photoconductor having a charge injection layer on its surface for contact charging. There is a description that it is possible to coat and use a resin in which SnO ₂ (tin oxide) particles that are made conductive by antimony dope, which is a conductive filler, are dispersed.

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 photoconductor and no ozone is 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 DC charging method or 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 contact charging member and the surface of the photosensitive member. However, in the injection charging method, the contact charging member and the photoconductor directly contact each other to transfer charges, and therefore, it is necessary to take a structure in which both are in close contact with each other and there is no microscopic uneven charging. There is.

Further, the resistance of the charging member is preferably lower so as not to hinder the transfer of charges, but as described above, in the apparatus using the contact charging member, scratches, pinholes, etc. are formed on the photosensitive member. When there is a low withstand voltage defect portion, if the resistance of the contact charging member is low, leakage occurs, the power supply voltage drops and charging failure occurs. Therefore, in practice, the contact charging member holds a certain level of resistance or more. There is a need. When the resistance of the contact charging member is high as described above, the charge injecting property is deteriorated. Therefore, by increasing the rotation speed of the contact charging member, the chance of contact between the contact charging conductive member and the photosensitive member is increased. It is necessary to secure the charge injection capability.

As described above, the contact charging member used in the injection charging method needs to be a member that can be in close contact with the photoconductor and have a peripheral speed difference with respect to the photoconductor. A magnetically constrained charging member (magnetic brush charging member) such as a magnetic brush or magnetic particles is suitable.

C) Magnetic brush charging device The magnetic brush charging device is one in which magnetic particles are restrained by a magnetic force on the magnetic particle holding means and attached and held as a magnetic brush. A voltage is applied to the magnetic particle carrying means to charge the photoconductor. More specifically, 1) The magnetic particle supporting means is a rotatable sleeve, and the magnetic particles are attached to the outer surface of the sleeve by the magnetic force of a fixed magnet roll (magnet) contained in the sleeve to form a magnetic brush. 2) A magnetic roll holding means (sleeve type), in which the magnetic particle carrying means is a rotatable magnet roll (magnet), and the magnetic particles are directly attached to the outer surface of the magnet roll by a magnetic force to form a magnetic brush. For example, it is in a held form (magnetic roller type).

FIG. 12 is a schematic view showing the sleeve type magnetic brush charging device.

Reference numeral 21 denotes a non-magnetic conductive sleeve (hereinafter simply referred to as "sleeve") such as aluminum as a magnetic particle supporting means. Reference numeral 22 denotes a magnet roll that is inserted and arranged in the sleeve 21 and serves as a magnetic field generating means. Reference numerals N and S shown in FIG. 12 denote magnetized portions of the magnet roll 22. The magnet roll 22 is a non-rotating fixed member, and a sleeve 21 is concentrically arranged on the outer circumference of the magnet roll 22. Then, the sleeve 21 is rotationally driven at a predetermined peripheral speed by a drive mechanism (not shown) in the clockwise direction indicated by the arrow b. Reference numeral 23 is a conductive magnetic particle (hereinafter referred to as “carrier”).
A magnetic brush (conductive magnetic brush) 24 by the magnetic force of 2
Is formed. The carrier 23 forms a magnetic spike on the outer surface of the sleeve 21 due to the magnetic force of the magnet roll 22, and these are gathered into a brush shape. S1
Is a power source for applying a charging bias to the sleeve 21.
The magnetic brush charging device 2 is the magnetic roll 2 described above.
2, a sleeve 21, and a carrier 23 are assembled into a magnetic brush 24.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter simply referred to as "photosensitive drum") as a member to be charged,
The photosensitive drum 1 is rotationally driven, for example, in a clockwise direction indicated by an arrow a at a predetermined process speed. The magnetic brush charging device 2 is arranged in a state where the magnetic brush 24 is brought into contact with the surface of the photosensitive drum 1 to form a contact nip portion (charging nip portion) D. The magnetic brush 24 is rotated in the same direction as the sleeve 21 rotates, and rubs the surface of the photosensitive drum 1 at the charging nip portion D, and the magnetic brush 2 from the charging bias applying power source S1 through the sleeve 21.
The surface of the photosensitive drum 1 is charged by a contact method by the charging bias applied to the surface 4. In the contact nip portion D, the rotating direction of the sleeve 21 and the rotating direction of the magnetic brush 24 accompanying it are counter to the rotating direction of the photosensitive drum 1. The sleeve 21 is a magnetic brush 24.
It also has a carrying function, a carrying function, and a charging bias application electrode function.

FIG. 13 is a schematic view showing the magnetic roller type magnetic brush charging device.

The magnet roll 22 is rotatably driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow b in the drawing around a core metal 25 that also serves as a drive and a power supply.
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 force conductive layer 22a has a carrier 23 adhered to the outer peripheral surface thereof by the magnetic force of the magnet roll 22 and held as a magnetic brush 24. The force conductive layer 22a serves to stably and uniformly supply a charging bias to the magnetic brush 24. Have. The magnetic brush 24 is rotated in the same direction as the magnet roll 22 rotates, rubs the surface of the photosensitive drum 1 at the contact nip portion D, and is applied to the core metal 25 of the magnet roll 22 from the charging bias applying power source S1. By the charging bias, the surface of the photosensitive drum 1 is charged by a contact method.

As described above, in the charging device using the magnetic brush, the contact charging member and the photosensitive drum 1 can be brought into close contact with each other, and a peripheral speed difference with respect to the photosensitive drum 1 can be obtained. This is very advantageous in improving the charge injection performance, such as increasing the chances of contact between the member 2 and the photosensitive drum 1.

In the magnetic roller type magnetic brush charging device, the spike shape of the magnetic brush 24 in the contact nip portion D changes with the rotation of the magnet roll 22, so that the charging property becomes non-uniform as compared with the sleeve type. It was easy to cause charging failure in some cases. The sleeve type magnetic brush charging device causes the magnetic brush 24 to rotate when the sleeve 21 rotates.
Since the shape of the spikes is basically unchanged and the carrier 23 can be exchanged, the charging uniformity is advantageous as compared with the magnetic roller type.

[0029]

However, in the conventional magnetic brush charging device, since the magnetic brush 24 is formed by constraining the carrier 23 by the magnetic force of the magnet roll 22, the magnetic force acting on the carrier 23 is unsatisfactory. If sufficient, there was a problem that the carrier 23 was separated from the magnetic brush 24 and scattered.

That is, if the carrier 23 scatters, the apparatus may be contaminated. For example, if the image exposure optical path is contaminated, there is a drawback that image unevenness occurs. If mixed in a developing device, the developing characteristics change and image unevenness occurs. If it adheres to the surface of the photosensitive drum 1, a problem of so-called carrier adhesion occurs, and 1) the carrier 23 adhered on the photosensitive drum 1 hinders image exposure, and 2) the photosensitive drum 1
Development failure occurs at the position where the upper carrier 23 is attached,
3) When the carrier 23 is mixed in the developing device, the developability is deteriorated, and 4) When the carrier 23 is transferred to a transfer paper as a recording material, the carrier 2 is transferred in the fixing step after the transfer.
3 is not fixed, so that fixing failure occurs, and 5) the carrier 23 that has not been transferred is caught between the cleaning blade and the photosensitive drum 1 at the cleaning position, and the surface of the photosensitive drum 1 is damaged. There was a point.

Further, when the carrier 23 constituting the magnetic brush 24 escapes from the magnetic force and separates, the carrier 23 that contributes to charging decreases over time, which causes a problem of charging failure.

In order to prevent the carrier 23 from being separated from the magnetic brush 24 and scattered, the magnetic flux density and its distribution on the sleeve 21 have been generally devised, but it is not always necessary to devise the magnetic flux density and its distribution. It did not correspond to the removal and scattering prevention of No. 23.

Therefore, the present invention has been made in order to solve the above problems, and substantially eliminates the separation and scattering of the magnetic particles from the magnetic brush so as to prevent charging failure and image failure. An object of the present invention is to provide a charging device and an image forming apparatus including the charging device.

[0034]

In order to achieve the above-mentioned object, a charging device according to a first aspect of the present invention is a magnetic device which includes a fixed magnet and is relatively moved so as to face a member to be charged. The magnetic brush is provided with a particle carrying means and magnetic particles that are attached to the magnetic particle carrying means by the magnetic force of the magnet to form a magnetic brush, and the magnetic brush is moved by the relative movement of the magnetic particle carrying means and the charged body. While being conveyed, the charged body is brought into contact with the charged body, and a voltage is applied to the magnetic particle carrying means to uniformly charge the charged body, and the moving direction of the magnetic particle carrying means is
Wherein a counter direction with respect to the rotation direction before Symbol member to be charged Te contact nip portion odor which is formed between the member to be charged and said magnetic brush, the magnet, the member to be charged and the magnetic particle holding means The charging main pole provided on the downstream side in the moving direction of the magnetic particle supporting means from the closest position of the magnet,
Direction of magnetic force on the magnetic particle supporting means generated by
Among the component Fr, the magnetic particles are supported from the charging main pole.
The first and second peaks on the upstream and downstream sides of the moving direction of the means
Assuming that there are two peaks, the first peak and the second peak
The peak is the rotation direction of the charged body at the contact nip portion.
From the respective positions of the upstream end and the downstream end of
Rotation range of ± 5 ° based on the center of rotation of the magnetic particle carrier
Of the two tangents of the magnetic particle carrying means that are present inside the magnetic particle carrying means, and the direction of the magnetic force acting on the magnetic particles existing at the downstream end is drawn from the downstream end to the magnetic particle carrying means. wherein as is tangential upstream side in the direction of rotation of the magnetic particle carrier than the first tangent toward the center side of the magnetic particle bearing section, and the magnetic force acting on magnetic particles present in the upper stream side end portion of the Of the two tangents of the magnetic particle carrying means which can be drawn from the upstream end to the magnetic particle carrying means, as compared with the second tangent line which is the tangent line on the downstream side in the rotation direction of the magnetic particle carrying body. It is characterized in that the magnet is arranged so as to face the center side of the magnetic particle supporting means.

According to a second aspect of the present invention, a magnetic particle supporting means that relatively moves while facing the body to be charged and includes a fixed magnet, and a magnetic particle supporting means that is attached to the magnetic particle supporting means by the magnetic force of the magnet. A magnetic particle forming a magnetic brush, the magnetic particle carrying means and the charged body are brought into contact with the charged body while being conveyed by the relative movement of the magnetic particle carrying means, and a voltage is applied to the magnetic particle carrying means. By applying the voltage, the charged body is uniformly charged, and the moving direction of the magnetic particle carrying means is the contact nip portion formed between the charged body and the magnetic brush. /> dude a counter direction with respect to the rotation direction before Symbol member to be charged, the magnet is moved downstream side of the magnetic particle bearing section than the closest position between the member to be charged and the magnetic particle bearing section Provided in Includes a charging dominant pole, the magnets generate
Component Fr of the magnetic force on the magnetic particle supporting means
Of the magnetic particle carrying means moving from the charging main pole
Direction upstream and downstream peaks are the first and second peaks
Then, the first peak and the second peak are
The upstream end of the contact nip portion in the rotation direction of the charged body
From the respective positions of the end portion and the downstream end portion,
Exists within a rotation range of ± 5 ° with respect to the center of rotation of the carrier
And is the between the magnetic particle bearing means and the member to be charged, the surface of the magnetic particle bearing section the upstream end of the rotational direction relative to the upstream end of the member to be charged in the contact nip portion An area surrounded by the closest position, the downstream end of the contact nip portion in the rotational direction of the charged body, and the closest position of the surface of the magnetic particle carrying means to the downstream end is defined as a contact nip area. Further, of the two tangents of the magnetic particle carrying means that can be drawn from the downstream side end portion to the magnetic particle carrying means, a tangent located upstream in the rotation direction of the magnetic particle carrying means is a first tangent line, Of the two tangents of the magnetic particle carrying means that can be drawn from the upstream end to the magnetic particle carrying means, the tangent located on the downstream side in the rotation direction of the magnetic particle carrying means is the second tangent, and the contact is made. Magnetic force acting on magnetic particles present in-up area is, the first to the magnetic particle bearing section,
It is characterized in that the magnet is arranged so that, when facing the outside from the second tangential direction, the direction of the magnetic force exists at a position facing the center side of the magnetic particle carrying means in the middle of the trajectory.

According to the invention of claim 3, the volume ratio Mc of the magnetic particles in the contact nip portion is expressed by Mc = (M / h) × (1 / ρ) × 100, where M is Magnetic particle amount [g / cm ² ] in a non-earing state per unit area of the magnetic particle supporting means, h is the band
The distance [c] of the closest position between the electric body and the magnetic particle supporting means
m] and ρ are true densities [g / cm ³ ] of the magnetic particles, and the volume ratio of the magnetic particles in the contact nip portion is 30 to 80%.
To

According to a fourth aspect of the present invention, the resistance value of the magnetic particles is 1 × 10 ⁵ to 1 × 10 ⁸ Ωcm.

[0038]

[0039]

According to a fifth aspect of the present invention, there is provided an image forming apparatus according to the first or second aspect of the present invention, in which the charged body is charged, and the charged body charged by the charging apparatus is electrostatically charged. an electrostatic latent image forming means for forming a latent image, said <br/> those having a toner image forming unit that visualizes the electrostatic latent image formed on the member to be charged.

[Operation] Based on the above-described structure, the present invention provides both the upstream and downstream ends of the surface of the charged body in the contact nip region formed between the charged body and the magnetic particle carrying means. The direction of the magnetic force acting on the existing magnetic particles,
The charged particles are directed toward the center of the magnetic particle carrying means from the tangential direction to the surface of the magnetic particle carrying means which is the closest position to the upstream end and the downstream end of the charged body.

According to another aspect of the invention, when the magnetic force acting on the magnetic particles existing in the contact nip region is directed outward from the tangential direction to the magnetic particle carrying means, the magnetic force is magnetized in the course of the direction of the magnetic force. There is a position facing the center side of the particle carrying means, whereby a magnetic force is exerted so as to attract to the magnetic particle carrying means all magnetic particles trying to leave the contact nip area.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. In addition,
In the present embodiment, a laser beam printer using a process cartridge as an image forming apparatus will be described as an example. (1) Image forming apparatus (FIG. 1) The photosensitive drum 1 is an OPC having a diameter of 30 mm in this embodiment.
The photoconductor is 100 mm / clockwise in the clockwise direction of arrow a.
It is driven to rotate at a process speed (peripheral speed) of sec. A magnetic brush charging device (contact charging member) 2 for uniformly charging the peripheral surface of the photosensitive drum 1 to a predetermined polarity and potential is in contact therewith.

The sleeve 21 of the magnetic brush charging device 2
Is applied with a DC charging bias of -700V from the charging bias applying power source S1, and the outer peripheral surface of the photosensitive drum 1 is uniformly charged to approximately -700V by charge injection charging.

The charged surface of the photosensitive drum 1 is irradiated with scanning exposure light L output from a laser beam scanner 7 (not shown) equipped with a laser diode and a polygon mirror. The scanning exposure light L is a laser beam whose intensity is modulated corresponding to the time-series electric digital pixel signal of the target image information, and by irradiating the charged surface of the photosensitive drum 1 with the static image corresponding to the target image information. An electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is
A toner image is developed by the reversal developing device 3 using a magnetic one-component insulating toner (negative toner). The reversal developing device 3 includes a non-magnetic developing sleeve 3a having a diameter of 16 mm and a magnet 3b contained in the non-magnetic developing sleeve 3a.
The non-magnetic developing sleeve 3a is coated with a negative toner, and the non-magnetic developing sleeve 3a and the surface of the photosensitive drum 1 are fixed at a distance of 300 μm and are rotated at the same speed as the photosensitive drum 1. . Further, the non-magnetic developing sleeve 3a has a DC of -500V from the developing bias power source S2.
Voltage and peak voltage 1600V at frequency 1800Hz
A developing bias voltage superposed with the rectangular AC voltage is applied to cause jumping development between the non-magnetic developing sleeve 3a and the photosensitive drum 1. That is, the developing sleeve 3
The negatively charged toner carried by a is attached to the image portion of the electrostatic latent image by an electric field and developed.

On the other hand, the transfer paper P supplied from a paper supply unit (not shown) is between the photosensitive drum 1 and the transfer roller 4 of medium resistance which is in contact with the photosensitive drum 1 with a predetermined pressing force. It is introduced into the pressure contact nip portion (transfer portion) T of at a predetermined timing. A predetermined transfer bias voltage from the transfer bias applying power source S3 is applied to the transfer roller 4. In this embodiment, a roller resistance value of 5 × 10 ⁸ Ω is used and +2
Transfer is performed by applying a DC voltage of 000V.

The transfer sheet P introduced into the transfer section T is nipped and conveyed, and the toner images formed and carried on the surface of the photosensitive drum 1 on the surface side thereof are sequentially transferred by electrostatic force and pressing force. become.

The transfer paper P on which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and then introduced into a fixing device 5 such as a heat fixing system to undergo fixing of the toner image to form an image-formed product (print, It is ejected outside the device as a copy).

Further, the photosensitive drum 1 after the transfer of the toner image
The cleaning device 6 removes and cleans adhered contaminants such as residual toner adhering to the surface thereof, and is repeatedly used for image formation.

In the image forming apparatus of this embodiment, four process devices including a photosensitive drum 1, a contact charging member 2, a reversal developing device 3 and a cleaning device 6 are provided in a cartridge container 9.
The process cartridge 10 is integrally formed by the process cartridge 10 and is attached to the image forming apparatus main body in a detachable and replaceable manner. 8 in the figure
Is a container insertion / removal guide / holding portion provided on the image forming apparatus main body side, and this container insertion / removal guide / holding portion 8 serves as a guide when inserting / removing the process cartridge 10.

By mounting the process cartridge 10 on the main body of the image forming apparatus, the process cartridge 10 and the main body of the image forming apparatus are electrically and mechanically connected to each other. Further, in this state, the lower surface of the photosensitive drum 1 on the process cartridge 10 side abuts on the upper surface of the transfer roller 4 on the image forming apparatus main body side so that an image can be formed.

In the process cartridge 10 of the above-described embodiment, the contact charging member 2 and the contact charging member 2 are provided around the photosensitive drum 1.
Although the example in which the reversal developing device 3 and the cleaning device 6 are provided has been described, at least one of the contact charging member 2, the reversal developing device 3 and the cleaning device 6 is integrally formed into a cartridge around the photosensitive drum 1. May be (2) Regarding charging by injection into the photosensitive drum 1 a) Photosensitive drum 1 (FIG. 2) Next, the photosensitive drum 1 will be described.

FIG. 2 shows the photosensitive drum 1 used in this embodiment.
FIG. 3 is a model diagram showing the layer structure of FIG.

The photosensitive drum 1 used in this embodiment is a negatively charged OPC photosensitive member having a charge injection function on its surface,
The drum base 1a made of aluminum having a diameter of 30 mm is provided with the following first to fifth functional layers in order from the bottom.

The first layer is an undercoat layer 1b, and is provided to smooth the defects on the peripheral surface of the drum substrate 1a and to prevent the occurrence of moire due to the reflection of the laser exposure light L. The conductive layer has a thickness of about 20 μm.

The second layer is the positive charge injection prevention layer 1c,
It plays a role of preventing the positive charge injected from the drum base 1a from canceling out the negative charge charged on the surface of the photosensitive drum 1, and the resistance is adjusted to about 1 × 10 ⁶ Ωcm by the amylan resin and methoxymethylated nylon. Thickness about 1μ
m is a medium resistance layer.

The third layer is a charge generation layer 1d, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and upon receipt of laser exposure light L, positive and negative charge pairs are generated. To do.

The fourth layer is the charge transport layer 1e, which has a thickness of about 20 μm in which hydrazone is dispersed in polycarbonate resin.
m layer, which is a P-type semiconductor. Therefore, the negative charges charged on the surface of the photosensitive drum 1 cannot move in this layer, and only the positive charges generated in the charge generation layer 1d can be transported to the surface of the photosensitive drum 1.

The fifth layer is the charge injection layer 1f, which is a coating layer made of a material in which SnO ₂ is dispersed as ultrafine conductive particles (conductive filler) 1g in a photocurable acrylic resin. Specifically, it is a coating layer made of a material in which antimony-doped SnO ₂ ultrafine particles having a particle size of about 0.03 μm and having a reduced resistance are dispersed in 70% by weight of the resin. The coating liquid thus prepared was applied by dipping to a thickness of about 3 μm to form a charge injection layer.

Charge injection layer 1 which is the surface layer of the photosensitive drum 1.
The volume resistance of f is 10 ⁹ to 1 in order to perform charge injection charging.
It is preferable to have a low resistance layer of 0 ¹⁴ Ωcm. In this embodiment, the volume resistance of the charge injection layer 1f is 1 × 10 ¹³
Ωcm. The volume resistivity of the charge injection layer 1f is about 6 to 7 μm on the conductive sheet (aluminum sheet).
m was applied, and this was measured at a voltage of 100 V by connecting a RESISTIVITY CELL 16008A to a high resistance meter 4329A manufactured by Yokogawa Hewlett-Packard Company.

The charge injection layer 1f intentionally creates injection sites for uniformly charging the surface by directly injecting charges from the magnetic brush charging device 2, but the charges of the electrostatic latent image are on the surface. The surface resistance of the charge injection layer 1f is required to be 1 × 10 ⁸ Ω or more so as not to flow in the electric field. The surface resistance of the charge injection layer 1f is measured by coating a charge injection layer on an insulating sheet and using a high resistance meter 4329A manufactured by Yokogawa Hewlett-Packard Company at an applied voltage of 100V.

B) Injection charging (FIG. 3) The principle of injection charging the photosensitive drum 1 using the contact charging member 2 will be described.

In the charge injection charging in this embodiment, the contact charging member 2 having a medium resistance is used to inject charge into the surface of the photosensitive drum 1 having a medium resistance surface resistance. Instead of injecting electric charges into the trapping potential, it is a method in which the conductive particles 1g of the electric charge injection layer 1f are charged with electric charges for charging.

At the time of charging, by applying a desired voltage to the contact charging member 2, charges are injected into the charge injection layer 1f, and the surface of the photosensitive drum 1 is finally charged (charged) to the same potential as the magnetic brush 24. It

Specifically, the model diagram of FIG. 3 (a) and (b)
As shown in the equivalent circuit diagram of FIG. 1, the photosensitive drum 1 is a microcapacitor in which the charge transport layer 1e is a dielectric and the drum substrate 1a and the conductive particles (SnO ₂ ) 1g in the charge injection layer 1f are both electrode plates. It can be regarded as a parallel assembly, and the injection charging is based on the theory of charging the individual minute capacitors with the contact charging member 2.

At this time, the conductive particles 1g are electrically independent from each other and form a kind of minute float electrode.
Therefore, the surface of the photosensitive drum 1 seems to be charged and charged to a uniform potential macroscopically, but in reality, a myriad of minute electrically conductive particles 1g that are charged cover the surface of the photosensitive drum 1. The situation is as follows. Therefore, even if image exposure is performed with a laser beam, the respective conductive particles 1g are electrically independent, so that an electrostatic latent image can be held. (3) Magnetic Brush Charging Device (FIG. 4) Next, a magnetic brush charging device as a contact charging member, which is a feature of this embodiment, will be described.

FIG. 4 is a model diagram showing the structure of the magnetic brush charging device of this embodiment, which is a sleeve type magnetic brush charging device similar to that shown in FIG.

Reference numeral 21 is a non-magnetic conductive sleeve (hereinafter referred to as "sleeve") such as aluminum as a magnetic particle supporting means. Reference numeral 22 is a magnet roll as a magnetic field generating means included in the sleeve 21.
N and S in the figure are magnetized portions of the magnet roll 22.
The magnet roll 22 is a non-rotating fixed member, and a sleeve 21 concentrically arranged on the outer circumference is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow b in the drawing by a drive mechanism (not shown). Reference numeral 23 denotes a conductive carrier, and a magnetic brush (conductive magnetic brush) 24 is formed on the outer peripheral surface of the sleeve 21 by being restrained by the magnetic force of the magnet roll 22. That is, the carrier 23 forms magnetic ears on the outer peripheral surface of the sleeve 21 due to the magnetic force of the magnet roll 22, and these are gathered into a brush shape to form the magnetic brush 24. If the charging bias application voltage from the charging bias applying power source S1 to the sleeve 21 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. Therefore, the toner image becomes poor. Therefore, the charging bias voltage is preferably DC 100V to 1500V. 25
Is a magnetic brush layer thickness regulating blade (regulating blade) arranged so that a small gap is formed with respect to the sleeve 21.
Thus, the layer thickness of the magnetic brush 24 held by the sleeve 21 is regulated.

D is a magnetic brush 2 on the surface of the photosensitive drum 1.
4 is a contact nip portion (charging nip portion) with which 4 comes into contact. The photosensitive drum 1 is rotationally driven in the clockwise direction indicated by the arrow a at a predetermined peripheral speed by a drive mechanism (not shown).
In the contact nip portion D, the rotation direction of the sleeve 21 and
What is the moving direction of the magnetic brush 24 that accompanies it?
The counter direction is the rotation direction of.

When the moving direction of the magnetic brush 24 is set to the forward direction, the carrier 23 forming the magnetic brush 24 tends to adhere to the photosensitive drum 1 more easily than in the reverse direction (counter direction). 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 easily scattered, the rotation torque is increased, and the cost of the device is increased.

On the other hand, when the moving direction of the magnetic brush 24 is counter to the rotating direction of the photosensitive drum 1, the adhesion of the carrier 23 to the photosensitive drum 1 can be suppressed,
The peripheral speed difference can be increased at low speeds. Therefore,
Since the number of contacts between the carrier 23 and the photosensitive drum 1 can be increased, the chargeability is improved. Although the clear reason why the carrier 23 is less attached to the photosensitive drum 1 when the moving direction of the magnetic brush 24 is counter to the rotating direction of the photosensitive drum 1 has not been clarified yet, It is considered that the action of peeling and pulling back the carrier 23 on the photosensitive drum 1 works by rubbing. If the photosensitive drum 1 is charged while the rotation of the sleeve 21 is stopped, the shape of the magnetic brush 24 becomes defective as it is and the toner image appears. For this reason, the rotating and conveying direction of the magnetic brush 24 is preferably the counter direction.

Next, the positions of the contact nip portion and the magnetic pole structure will be described with reference to FIG.

In the figure, L is a line indicated by a one-dot chain line connecting the rotation center of the sleeve 21 and the rotation center of the photosensitive drum 1, and this line L indicates the center of opposition between the sleeve 21 and the photosensitive drum 1. Is. The line L is the closest position between the sleeve 21 and the photosensitive drum 1. h is an interval showing the distance at the closest position between the sleeve 21 and the photosensitive drum 1, and this interval h is preferably 0.15 to 2.0 mm, more preferably 0.3 to 1.0 mm. If the interval h is too small, leakage tends to occur, it becomes difficult to regulate the layer thickness of the magnetic brush 24 uniformly by the regulation blade 25, and uneven charging is likely to occur. Further, if the interval h is too small, a sufficient amount of carrier cannot be supplied to the contact nip portion D, and charging failure tends to occur. On the contrary, if the interval h becomes too large, the layer thickness of the magnetic brush 24 must be increased, and the magnetic force of the surface layer portion of the magnetic brush 24 becomes weak. The unevenness is likely to occur, the charge injection property is also deteriorated, and the charging failure is likely to occur.

In the injection charging, the charging between the magnetic brush 2 is performed.
Since charging is carried out by contact between the carrier 23 forming 4 and the photosensitive drum 1, it is necessary to smoothly move the carrier 23 in the contact nip portion D and sufficiently bring the carrier 23 and the photosensitive drum 1 into contact with each other. is there. In order to improve the charge injection property, the volume ratio Mc of the carrier 23 in the contact nip portion D, that is, the volume ratio of the carrier 23 in the contact nip space is preferably 30 to 80%.

Here, it is assumed that the volume ratio Mc is in accordance with Equation 1.

[0076]

## EQU1 ## Mc = (M / h) × (1 × ρ) × 100 where M is the carrier amount per unit area of the sleeve 21 in a non-peaking state [g / cm ² ] and h is the charging area space Is the true density [g / cm ³ ] of the carrier 23.

If the volume ratio Mc becomes too small,
The contact between the carrier 23 and the photosensitive drum 1 tends to be insufficient, the contact nip portion D becomes uneven, and the carrier 2
There is less chance of contact between 3 and photosensitive drum 1,
The injection charging ability is lowered and charging failure is likely to occur. on the other hand,
If the volume ratio Mc becomes too large, the carrier 23 tends to stay in the contact nip portion D, which hinders smooth movement of the carrier 23 in the contact nip portion D, resulting in uneven contact nip portion D. Or the chances of contact between the carrier 23 and the photosensitive drum 1 are reduced, the injection charging capability is reduced, and charging failure is likely to occur. In addition, the carrier 23
When the smooth movement of the carrier 23 is hindered and the movement of the carrier 23 in contact with the surface of the photosensitive drum 1 is deteriorated, the carrier 23 itself is charged up, which hinders the injection of the charge and easily causes the charging failure. Here, the charge-up means the carrier 23 in contact with the surface of the photosensitive drum 1.
However, it is said that a reverse charge is stored by giving a charge to the photosensitive drum 1 and the actual applied voltage is reduced.

The above-mentioned volume ratios are the gap between the sleeve 21 and the regulating blade 25, the sleeve 21 and the photosensitive drum 1.
The required value can be set by correlating the gap between the carrier and the carrier, the true density of the carrier 23, and the like.

In order to improve the charge injection property, the contact nip portion D is preferably 2 mm or more, more preferably 4 mm or more. If the contact nip portion D becomes too small, the chances of contact between the carrier 23 and the photosensitive drum 1 are reduced, the charging becomes uneven, and the injection charging capability is deteriorated, so that charging failure is likely to occur.

In the present embodiment, the contact nip D is located downstream of the interval h which is the closest position in the rotational direction of the sleeve 23 so that the charging is uniform, the injection charging ability is sufficient, and the charging property is improved. The width is about 2 mm, the reverse width is about 3 mm on the upstream side, and the total width is about 5 mm.

Next, the carrier 23 according to the present embodiment.
Will be described.

Carrier 23 constituting magnetic brush 24
As for (1) resin and magnetic powder such as magnetite were kneaded and molded into particles, or conductive carbon was mixed with this to adjust the resistance value, (2) sintered magnetite, ferrite, or these Those whose resistance value has been adjusted by reduction or oxidation, (3) The particles formed in (1) or (2) above are coated with a resistance-adjusted coating material (such as phenol resin with carbon dispersed). Or N
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 the damage to the photosensitive drum 1, it is desirable that the carrier 23 be spheroidized.

If the carrier 23 has an excessively high resistance value, charges are not uniformly injected into the photosensitive drum 1 and a fog image due to a minute charging failure occurs. Further, if the resistance value is too low, when there is a pinhole on the surface of the photosensitive drum 1, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photosensitive drum 1 cannot be charged. Nip-shaped charging failure will occur. Therefore, the resistance value of the carrier 23 is preferably 1 × 10 ⁵ to 1 × 10 ⁸ Ωcm. The carrier 23 was prepared by placing 2 g of the carrier 23 in a metal cell (bottom area 228 mm ² ) to which voltage can be applied, and then 6.
The resistance value is measured by applying a load of 6 kg / cm ² and applying a voltage of 1 to 1000 V. For example, a voltage of 100 V was applied, the resistance value was calculated from the measured current flowing in this system, and the resistance value was defined as normalized.

It is also possible to improve the chargeability by mixing and using a plurality of types of carriers 23.

If the particle size of the carrier 23 is too small, the magnetic force becomes small and the carrier adheres to the surface of the photosensitive drum 1. On the other hand, if it is too large, the contact area with the photosensitive drum 1 is reduced and the charging failure increases. Therefore, the average particle size of the carrier 23 is preferably about 5 to 50 μm from the viewpoint of chargeability and magnetic retention. The average particle size of the carrier 23 was determined by randomly extracting 100 or more particles with an optical microscope or a scanning electrophotographic microscope, calculating the volume particle size distribution with the maximum chord length in the horizontal direction, and determining 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 1, and the saturation magnetization is 30 (A / m ² / kg) or more, more preferably 50. (A / m ² / kg) or more is desirable.

Actually, the carrier 2 used in this embodiment
No. 3 has an average particle size of 30 μm, a spherical shape, and a resistance value of 1 ×
It was 10 ⁶ Ωcm and the 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.

The saturation magnetization and magnetic permeability were measured by using a vibrating sample magnetometer (trade name: VSM-P-1 type manufactured by Toei Industry Co., Ltd.) to measure the magnetization of carriers placed in a magnetic field of maximum 10,000 Oersted. Then, it was determined based on the hysteresis curve drawn on the recording paper.

Magnet roll 2 used in the present embodiment
2 will be described with reference to FIGS.

FIG. 5 is a diagram for explaining the positions of the contact nip portion and the magnetic pole structure. In the figure, P is the closest position on the sleeve 21 with respect to the photosensitive drum 1,
Q is the closest position on the photosensitive drum 1 with respect to the sleeve 21. S is the position of the main charging pole S1, and the main charging pole S1
Is located downstream of the closest position P to the photosensitive drum 1 in the rotational direction of the sleeve 21. θ is an angle formed by the charging main pole S1 and the line L with respect to the rotation center of the sleeve 21. A1 is the end position of the contact nip portion on the downstream side in the rotation direction on the photosensitive drum 1, and A2 is the end position on the upstream side in the rotation direction on the photosensitive drum 1. L1 and L2 are photosensitive drums 1
A straight line drawn from the end positions A1 and A2 of the respective contact nips above to the surface of the sleeve 21 closest to the end positions A1 and A2 (first contact point).
Line, second tangent line) . C1 and C2 are straight lines L1 and L2
Is a position in contact with the surface of the sleeve 21. L11, L
12 is the end position A1 of the contact nip portion on the photosensitive drum 1.
It is a straight line connecting A2 and the rotation center of the sleeve 21.
B1 and B2 are positions closest to the end positions A1 and A2 of the contact nip portion with respect to the sleeve 21, and are straight lines L11 and L1.
This is the position where 2 and the surface of the sleeve 21 intersect. Here, the arc from the end position A1 to A2 and the closest position B
The contact nip region Vn (see FIG. 5) is surrounded by an arc extending from 1 to B2, a line segment from the end position A1 to the closest position B1, and a line segment from the end position A2 to the closest position B2.
(Shaded part).

When the position of the main charging pole S1 is set to the upstream side of the closest position P to the photosensitive drum 1 with respect to the rotating direction of the sleeve 21, the magnetic brush is brushed by the main charging pole S1 on the upstream side of the contact nip portion. The carrier conveyed by the rotation of the sleeve 21 standing up is the closest positions P and Q of the contact nip portion.
Works to stop the passage between
Carriers easily accumulate on the upstream side of the contact nip portion.
When the carrier stays on the upstream side of the contact nip portion, the width of the contact nip portion D fluctuates, or the chance of contact between the carrier and the photosensitive drum 1 decreases, so that the injection charging ability is deteriorated and charging failure is likely to occur. . In addition, the carrier itself is likely to be charged up, which hinders the injection of electric charges, and the charging failure is likely to occur.

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 with respect to the sleeve rotation direction, the distance between the sleeve 21 and the photosensitive drum 1 is the narrowest, and the carrier is conveyed. Is the closest position P and Q
Since the magnetic brush does not stand up to the interval between and, the carrier is smoothly transported. And the carrier is the closest position P
Since the magnetic brush stands up after the space is expanded by passing between Q and Q, the carrier of the magnetic brush is not hindered by the rise of the magnetic brush. Therefore, the carrier does not stay and the carrier can move smoothly in the contact nip portion, the number of contact between the photosensitive drum 1 and the carrier not charged up increases, and charging failure occurs. Disappear. If the position of the main charging pole S1 is too far from the closest position P, the magnetic force for attracting the carrier from the intermediate portion in the contact nip portion toward the outlet becomes weak, and the carrier transportability may be weakened. Therefore, the position of the main charging pole S1 is preferably θ = 0 ° to 30 ° on the downstream side of the closest position P to the photosensitive drum 1 with respect to the rotation direction of the sleeve 21, and more preferably θ = 0.
° to 15 ° is good.

FIG. 6 is a diagram for explaining the magnetic force F on the sleeve 21, where F is the magnetic force on the sleeve 21, Fr.
Is the magnetic force in the direction normal to the surface of the sleeve 21, Fθ
Indicates the magnetic force in the tangential direction on the surface of the sleeve 21.

Since the carrier is not saturated due to magnetism in the usual magnetic brush charging device, and the carrier is not saturated even in the configuration of this embodiment, the magnetic force F acting on the carrier in the magnetic field is expressed by the following formula 2. Represented.

[0095]

## EQU2 ## F = [(μ−μ ₀ ) / {μ ₀ (μ + 2μ
₀ )}] · 2πb ³ · ∇B ² where μ ₀ is the magnetic permeability of vacuum (= 4π · 10 ⁻⁷ ) [H / m] μ is the relative permeability of the carrier B is the magnetic flux density [T = wb · m ² ] b is the radius [m] of the carrier, and the radius b of the carrier is one half of the weight average particle.

The magnetic force F can be calculated using the equation 2, and the magnetic force F has a value proportional to the square of the magnetic flux density B.

FIG. 7 is a diagram for explaining the magnetic force Fr at the end positions A1 and A2 of the contact nip portion on the photosensitive drum 1, and F is the magnetic force at the end positions A1 and A2 on the photosensitive drum 1. , Fr is a magnetic force in the normal direction to the surface of the sleeve 21 at the end positions A1 and A2, and Fθ is a magnetic force in the tangential direction to the surface of the sleeve 21 at the end positions A1 and A2.

Whether or not the carrier leaves the magnetic brush, that is, whether or not the carrier scatters, is not directly related to the magnetic flux density on the sleeve 21, but is related to the magnitude of the magnetic force that attracts the carrier to the sleeve 21. . The detachment of the carrier from the magnetic brush is determined by a balance between a magnetic force as a force for restraining the carrier to the sleeve 21 and a Coulomb force, a mirroring force, a centrifugal force, etc. as a force for peeling the carrier from the sleeve 21. Further, the magnetic flux density exponentially decreases with the distance from the sleeve 21, and the magnetic force further decreases with the square of the magnetic force. Therefore, the photosensitive drum 1 and the sleeve 21
When the distance between the photosensitive drum 1 and the sleeve 21 is short, it is possible to magnetically restrain the carrier on the photosensitive drum 1 to the sleeve 21 relatively easily. It becomes difficult to magnetically constrain the carrier on 1 to the sleeve 21.

Further, the carrier is easily detached or scattered at the contact nip portion. In the contact nip portion, the photosensitive drum 1
The upper end positions A1 and A2 are farthest from the sleeve 21, and the magnetic force acting as a force for restraining the carrier to the sleeve 21 has the smallest effect in this portion. Therefore,
The carriers are most likely to be detached and scattered at the end positions A1 and A2, and suppressing the detachment and scattering of the carriers in this part is the most effective against the detachment and scattering. That is, by arranging the magnetic force acting on the end positions A1 and A2 on the photosensitive drum 1 toward the sleeve 21 side (inner side) from the tangential direction to the surface of the sleeve 21, the carrier is generated by the magnetic force. Since the carrier can be attracted to the sleeve 21, it is possible to effectively prevent the carrier from coming off the contact nip portion and scattering.

In the present embodiment, as shown in FIG. 7, the direction of the resultant force F of the magnetic force acting on the end positions A1 and A2 of the contact nip portion on the photosensitive drum 1 is set inward from the tangential direction to the surface of the sleeve 21. Since it is configured to face the carrier, it is possible to effectively prevent the carrier from coming off the contact nip portion and scattering.

Further, with respect to all the carriers existing on the photosensitive drum 1 in the contact nip region Vn, (1) the direction of the magnetic force acting on the carriers is directed inward from the tangential direction of the surface of the sleeve 21, or ( 2) When the direction of the magnetic force acting on the carrier is outward from the tangential direction of the surface of the sleeve 21, be sure to position it inward of the tangential direction of the surface of the sleeve 21 in the course of the trajectory of the magnetic force. By making it exist, since a magnetic force that attracts all the carriers trying to separate from the photosensitive drum 1 to the sleeve 21 acts, it is possible to more effectively suppress the carrier from separating from the contact nip portion and scattering. You can

FIG. 8 is a diagram for explaining the magnetic force F in the contact nip area Vn. X0 is the contact nip area V
n is an arbitrary position on the photosensitive drum 1, LX0 is an arbitrary position X
The tangent line F0 drawn from 0 to the surface of the sleeve 21 is the magnetic force at the arbitrary position X0, and in this example, the direction of the magnetic force F0 is outward from the tangent line LX0. L1 is a tangent line drawn from the end position A1 on the photosensitive drum 1 to the surface of the sleeve 21, X is a straight line drawn from the arbitrary position X0 in the direction of the magnetic force F0, and X1 is a position where the straight line X and the tangent line L1 intersect. is there.
X2 is a specific position on a line segment from the arbitrary position X0 to the position X1, LX2 is a tangent line drawn from the specific position X2 to the surface of the sleeve 21, F2 is the magnetic force at the specific position X2, and the direction of the magnetic force F2 is the tangent line. It faces inward from LX2. The carrier existing at the arbitrary position X0 on the photosensitive drum 1 in the contact nip region Vn is once moved to the straight line X by the action of the magnetic force F0.
However, since it is pulled in the direction of LX0 by the action of the magnetic force F2 at a specific position X2 in the middle of the trajectory,
The sleeve 21 is eventually attached to the carrier existing at the arbitrary position X0.
A magnetic force that attracts to will act. In this way, when the direction of the magnetic force in the contact nip region Vn is outward of the tangential direction of the surface of the sleeve 21, the magnetic force is always inward of the tangential direction of the surface of the sleeve 21 in the course of the direction of the magnetic force. Since the magnetic force attracting the sleeve 21 can be applied to all the carriers that are going to leave the contact nip region Vn, the contact nip portion of the carrier can be more effectively provided. It is possible to suppress the separation and scattering from.

Further, with respect to all carriers existing in the contact nip area Vn, (1) the direction of the magnetic force acting on the carriers is from the tangential direction with the surface of the sleeve 21 to the sleeve 2
1), or (2) When the direction of the magnetic force acting on the carrier is outside the tangential direction with the surface of the sleeve 21, be sure to make contact with the tangent line of the surface of the sleeve 21 in the course of the direction of the magnetic force. With the configuration in which the position facing the sleeve 21 side from the direction exists, the contact nip region Vn
Since the magnetic force that attracts all the carriers that try to separate from the sleeve 21 acts on the sleeve 21, it is possible to more effectively suppress the carrier from separating from the contact nip portion and scattering.

The way of applying the magnetic force in this case is similar to that of FIG. 8, and if the arbitrary position X0 on the photosensitive drum 1 in the contact nip area Vn is replaced with an arbitrary position in the contact nip area Vn, Similarly, a magnetic force acts, and the description thereof will be omitted.

FIG. 9 is a view for explaining the distribution form of the magnetic flux density Br and the distribution form of the magnetic force Fr of the charging main pole S1, and the lateral direction indicates the circumferential position of the sleeve by an angle, The vertical direction indicates the magnitude of the magnetic force Fr on the sleeve or the magnitude of the magnetic flux density Br on the sleeve. In this example, the magnetic force Fr is applied to the position S of the charging main pole S1.
There are two peaks, but the peak on the upstream side in the rotation direction of the sleeve is F1 and the peak on the downstream side is F2. α1
Is the angle between the position S of the charging main pole S1 and the peak F1 of the magnetic force Fr, and α2 is the position S of the charging main pole S1 and the magnetic force Fr.
Is an angle with respect to the peak F2.

For example, the outer diameter of the sleeve is 16 mm, the outer diameter of the photosensitive drum is 30 mm, the distance h between the photosensitive drum and the sleeve is 0.5 mm, and the width of the contact nip portion D is 2 mm upstream of the photosensitive drum and downstream. 3 mm, the angles formed by the closest position Q (see FIG. 5) on the photosensitive drum and the end positions A1 and A2 are about 21.5 ° and 14.3 °, respectively, and the closest position P on the sleeve is P. And the closest positions B1 and B2 form angles of about 18.7 ° and 13.0 °, respectively. Then, the angles α1 and α2 between the position S of the main charging pole S1 and the peaks F1 and F2 of the magnetic force Fr are set to 25 ° and 7 °, respectively, and the main charging pole S is set.
If the position S of 1 is arranged 6 ° downstream of the closest position P to the photosensitive drum 1 with respect to the rotation direction of the sleeve, the closest position P on the sleeve and the peak position F1 of the magnetic force Fr,
The angles with F2 are (25-6 = 19 °) and (13-
6 = 7 °), which is almost the same as the closest position B1 to the downstream end position A1 of the contact nip portion on the photosensitive drum 1 and the closest position B2 to the upstream end position A2 of the contact nip portion. Be in position.

The peak positions F1 and F2 of the magnetic force Fr are preferably near the closest positions B1 and B2 on the sleeve. Specifically, it is preferably within ± 5 °, more preferably within ± 3 °.

In particular, in order to reduce the size and cost of the magnetic brush charging device, in order to reduce the diameter of the sleeve and to improve the charge injection property, the contact nip portion D is enlarged and the downstream side of the photosensitive drum. When the width is increased, intentionally making the position of the charging main pole and the peak position of the magnetic force Fr considerably large has a great effect as described above in order to prevent the carrier from adhering. Since no device was devised, there was a limit to miniaturization and cost reduction of the magnetic brush charging device. As will be described later, according to the present embodiment,
It is possible to reduce the size and cost of the magnetic brush charging device while preventing the carrier from adhering.

Next, the method for measuring the magnetic flux density in the present invention will be described.

FIG. 10 is a diagram for explaining a method for measuring the magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction on the charging sleeve 21 or at a position of 0.5 mm on the sleeve, which is a Gauss meter model of Bell Co. It measured using 9903. In the figure, the sleeve 21 is fixed horizontally, and the magnet roll 22 in the sleeve 21 is rotatably attached. 42 is a biaxial probe (YOA99- manufactured by Bell Co.)
1802), which is fixed so that the center of the sleeve 21 and the center of the probe 42 are substantially in the same horizontal plane with a slight distance from the sleeve 21, and is connected to the Gauss meter 41. 0.5 mm
The magnetic flux densities in the normal direction and the tangential direction at the position of are measured. It can be considered that the rotation center of the sleeve 21 and the rotation center of the magnet roll 22 are concentric circles, and the distance between the sleeve 21 and the magnet roll 22 is equal everywhere. Therefore, by rotating the magnet roll 22, the magnetic flux densities in the normal direction and the tangential direction at the position of 0.5 mm above the sleeve 21 can be measured in all circumferential directions.

Since the magnet roll 22 is rotated in the direction of the arrow R22 in the figure, the charging main pole S
The angle of the regulation pole N1 becomes larger than 1. That is, the measurement is performed in the direction in which the angle increases on the upstream side with respect to the rotation direction of the sleeve 21 in FIG.

Next, a numerical example will be described.

In this embodiment, the photosensitive drum 1 has a peripheral speed of 100 mm / sec, an outer diameter of 30 mm, and a sleeve 21.
Has a peripheral speed of 150 mm / sec and an outer diameter of 16 mm. The rotating direction of the sleeve 21 is counter to the rotating direction of the photosensitive drum 1. Surface of photosensitive drum 1 and sleeve 2
The distance h from the surface of No. 1 was 0.5 mm. The position of the charging main pole S1 is closer to the sleeve 2 than the closest position P to the photosensitive drum 1.
It was set to 6 ° (−6 °) on the downstream side with respect to the rotation direction of 1. At this time, the peak value of the magnetic flux density on the sleeve surface of the charging main pole S1 which is the magnet fixed in the sleeve 21 was 950 × 10 ⁻⁴ T (Tesla) in the direction normal to the sleeve surface. The amount of carrier of the magnetic brush 24 is about 15g
The length of the magnetic brush 24 in the longitudinal direction is 210 mm, the layer thickness of the magnetic brush 24 on the sleeve 21 is about 1 mm, and the contact nip width D is about 2 mm on the upstream side and about 3 m on the downstream side.
m, width was about 5 mm overall.

When an image was formed by using the image forming apparatus of this embodiment, a good image without charge failure or image failure was obtained without causing the problem of separation and scattering of the carrier 23.

In particular, in order to reduce the size and cost of the magnetic brush charging device as in this embodiment, the diameter of the sleeve 21 is reduced and the contact nip portion D is formed in order to improve the charge injection property. If the width of the photosensitive drum 1 on the downstream side is increased, the charging main pole S is
Intentionally increasing the position of 1 and the peak position of the magnetic force Fr considerably has the great effect as described above, but since such a device has not been conventionally devised, the magnetic brush charging device can be downsized, There was a limit to cost reduction. According to the present embodiment, it is possible to reduce the size and cost of the magnetic brush charging device while preventing separation and scattering.

As described above, according to this embodiment, it is possible to substantially eliminate the separation and scattering of the carrier from the magnetic brush, and solve the problems such as the charging failure and the image failure.

Further, in the magnetic brush charging device of the above-described embodiment, various magnet rolls are used to change the position of the charging main pole S1 in various ways and to change the direction of the magnetic force in the contact nip area Vn in various ways. When an image is formed, in the case where the magnetic forces acting on the end positions A1 and A2 of the contact nip portion on the photosensitive drum 1 are arranged to be outward from the tangential direction to the surface of the sleeve 21, respectively. , The carrier is detached or scattered, and a charging failure occurs, resulting in an image failure. The direction of the magnetic force acting on the end positions A1 and A2 of the contact nip portion on the photosensitive drum 1 is tangential to the surface of the sleeve 21. In the case of being configured so as to face inward from the direction, there was no problem of carrier separation or scattering, and there were no charging defects and no image defects, and good images were obtained. <Second Embodiment> Next, a second embodiment of the present invention will be described.

FIG. 11 is a schematic configuration diagram of a main part showing a digital electrophotographic copying machine as an image forming apparatus equipped with a charging device according to the second embodiment of the present invention. The configuration of the present embodiment is one in which the present invention is applied to an image forming apparatus using a developing device that also serves as cleaning, and does not use a process cartridge and uses a two-component magnetic brush developing device and a dedicated cleaning device. It differs from the first embodiment in that the device is omitted and the setting of the magnetic brush charging device is slightly different accordingly. 11, those parts that are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted.

Reference numeral 30 is a developing device as a toner image forming means using a two-component magnetic brush contact developing method which has been widely used. The developer used was a two-component developer consisting of a non-magnetic toner and a magnetic carrier. As toner particles, 1% by weight of titanium oxide having an average particle size of 20 mm was used with respect to negative toner having an average particle size of 6 μm produced by a polymerization method. An externally added carrier was used, and a carrier having a saturation magnetization of 66 (A · m ² / kg) and an average particle size of 35 μm was used. Further, a developer in which a negative toner and a carrier were mixed at a weight ratio of 6:94 was used. 31 is a diameter of 16 mm which encloses the magnet roll 32 fixedly arranged inside
Non-magnetic developing sleeve (hereinafter referred to as "developing sleeve")
Is driven to rotate in the forward direction at the same speed as the photosensitive drum 1 by a drive mechanism (not shown), that is, in the counterclockwise direction indicated by the arrow c in the figure. The developing sleeve 31 is coated with the above-mentioned developer, and 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. -500V from the developing bias power source S2 on the developing sleeve 31.
DC voltage, frequency 2000Hz, peak-to-peak voltage 15
A developing bias voltage is applied by superimposing it with a rectangular AC voltage of 00V.

Next, the magnetic brush charging device 2 will be described. The magnetic brush charging device 2 used in this embodiment is
The rest of the configuration is the same as that of the first embodiment except that the charging bias application conditions are different.

As the charging bias, a DC voltage superimposed with an AC voltage is used. When only DC voltage is used as the charging bias, good charging property is initially obtained,
Since there is no dedicated cleaning device in this embodiment,
When the image formation is repeated (during durability), the transfer residual toner cannot be sufficiently collected in the magnetic brush charging device, which may cause charging failure or image failure.

On the other hand, when a charging voltage in which an AC voltage is superimposed on a DC voltage is used as the charging bias, the transfer residual toner can be sufficiently collected in the magnetic brush charging device, and the charging property can be improved and It is possible to improve the property. The reason why the transfer residual toner can be sufficiently collected by the AC voltage is that positive and negative voltages are applied to the transfer residual toner, so that both positively charged toner and negatively charged toner are charged. It is thought that this can be recovered. 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 device. It is considered that this is because the carrier vibrates and actively moves due to the action of the AC voltage, so that the chances of contact with the photosensitive drum 1 increase.

If the frequency of the AC voltage is too low, frequency irregularity appears and charging irregularity occurs. If the frequency of the AC voltage is too high, it approaches the DC voltage, and the effect is weakened.
Therefore, the frequency is preferably 400 Hz to 4000 Hz. If the peak-to-peak voltage Vpp of the AC voltage is too low, it approaches the DC voltage, and the effect is weakened. If the peak-to-peak voltage Vpp is too high, a leak may occur between the photosensitive drum and the photosensitive drum, or carrier may be attached. Therefore, the peak-to-peak voltage V
pp is preferably in the range of 50 to 5000V. In this embodiment, a DC voltage of −700 V and a rectangular AC voltage having a frequency of 1000 Hz and a peak-to-peak voltage of 800 V are superimposed on each other and applied to the charging sleeve 21.

As described above, in the present embodiment, since the AC bias is superimposed on the DC voltage is used as the charging bias of the magnetic brush charging device 2, the carrier vibrates and actively moves due to the action of the AC voltage. As a result, the chances of contact with the photosensitive drum 1 are increased, and the chargeability can be improved even if the transfer residual toner is mixed in the magnetic brush charging device. Further, since positive and negative voltages are applied to the transfer residual toner, it is possible to collect the respective toners charged with positive and negative polarities. Therefore, when an image is formed using the image forming apparatus according to the present embodiment, the separation and scattering of the carrier from the magnetic brush is substantially eliminated, and a good image without charging failure or image failure is obtained. To be

Further, in order to reduce the size and cost of the magnetic brush charging device as in this embodiment, the charging sleeve 2 is used.
When the contact nip D is increased and the width of the photosensitive drum 1 on the downstream side is increased in order to reduce the diameter of 1 and to improve the charge injection property, in order to prevent the carrier from separating or scattering,
Intentionally increasing the position of the main charging pole and the peak position of the magnetic force Fr intentionally has a great effect as described above, but since such a device has not been conventionally devised, the magnetic brush charging device can be miniaturized. However, there was a limit to cost reduction. According to the present embodiment, it is possible to reduce the size and cost of the magnetic brush charging device while preventing the carrier from separating and scattering.

Further, in the magnetic brush charging device of the above-described embodiment, various magnet rolls are used to change the position of the main charging pole S1 in various ways, and the contact nip region Vn is changed.
When the image formation is performed by changing the direction of the magnetic force inside, the direction of the magnetic force acting on the end positions A1 and A2 of the contact nip portion on the photosensitive drum 1 is changed from the tangential direction of the surface of the sleeve 21 to the outside. In the case of the configuration in which the toner is directed, the carrier comes off or scatters, resulting in charging failure and image failure, but the end positions A1, A of the contact nip portion on the photosensitive drum 1 are generated.
When the direction of the magnetic force acting on 2 is directed inward from the tangential direction of the surface of the sleeve 21, there is no problem of carrier separation or scattering, there is no charging failure, and there is no image failure. was gotten.

[0127]

As described above, according to the first aspect of the present invention, both ends of the contact nip region between the charged body and the magnetic particle carrying means on the upstream side and the downstream side of the surface of the charged body. Direction of the magnetic force acting on the magnetic particles existing in the magnetic particles is determined from the tangential direction with respect to the surface of the magnetic particles which is the closest position to the upstream end and the downstream end of the charged body. Since the magnet is arranged so as to face the center side of
A magnetic force that attracts the magnetic particles to the magnetic particle supporting means acts, and the magnetic particles are substantially prevented from separating and scattering from the contact nip region, and it is possible to prevent defective charging and defective images.

According to the invention of claim 2,
The magnetic force acting on the magnetic particles existing in the contact nip area is
When facing outward from the tangential direction to the magnetic particle supporting means, in the middle of the trajectory of the direction of the magnetic force, the position facing the center side of the magnetic particle supporting means from the tangential direction to the surface of the magnetic particle supporting means from the middle Since it is made to exist, the magnetic force that attracts all the magnetic particles that try to separate from the contact nip area to the magnetic particle supporting means acts, and the magnetic particles do not substantially separate or fly out from the contact nip, resulting in poor charging or It is possible to prevent image defects from occurring.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a model diagram showing a layer structure of a photosensitive drum as a member to be charged.

FIG. 3 illustrates the principle of injection charging using a contact charging member, (a) is a model diagram illustrating the principle of injection charging,
(B) is the equivalent circuit diagram.

FIG. 4 is a structural model view of a magnetic brush charging device.

FIG. 5 is a diagram for explaining positions of a contact nip portion and a magnetic pole configuration.

FIG. 6 is a diagram for explaining a magnetic force Fr on a charging sleeve.

FIG. 7 is a diagram for explaining a magnetic force F at both ends of the contact nip on the photosensitive drum.

FIG. 8 is a diagram for explaining a magnetic force F in a contact nip area Vn.

FIG. 9 is a diagram for explaining a distribution form of a magnetic flux density Br and a distribution form of a magnetic force Fr of a main charging pole S1.

FIG. 10 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 charging sleeve.

FIG. 11 is a schematic configuration diagram of main parts showing a digital electrophotographic copying machine according to a second embodiment of the present invention.

FIG. 12 is a schematic configuration diagram showing a sleeve type magnetic brush charging device.

FIG. 13 is a schematic configuration diagram showing a magnetic roller type magnetic brush charging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Charged object (electrophotographic photosensitive member, photosensitive drum) 2 Magnetic brush charging device 21 Charging sleeve (sleeve) 22 Magnet roll 23 Magnetic particles (carrier) 24 Magnetic brush F Magnetic force A1 End of contact nip part on photosensitive drum A2 End L1 of the contact nip on the photosensitive drum Tangent line L2 drawn from the position A1 to the closest position of the sleeve L2 Tangent line drawn from the position A2 to the closest position of the sleeve P Closest position to the photosensitive drum on the sleeve S Charging main Position of pole S1 on sleeve Vn Contact nip area

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 15/02

Claims (5)

(57) [Claims] 1. A magnetic particle carrying means that moves relative to a member to be charged and that contains a fixed magnet, and a magnetic brush formed by being attached to the magnetic particle carrying means by the magnetic force of the magnet. Magnetic particles to be, contact with the charged body while carrying the magnetic brush by the relative movement of the magnetic particle carrying means and the charged body,
In a charging device for uniformly charging the charged body by applying a voltage to the magnetic particle carrying means, the moving direction of the magnetic particle carrying means is in front of the charged body.
Te contact nip portion odor which is formed between the serial magnetic brush
A counter direction with respect to the rotation direction before Symbol member to be charged,
The magnet has a charging main pole provided on the downstream side in the moving direction of the magnetic particle carrying means with respect to the closest position between the charged body and the magnetic particle carrying means, and the magnetic particle carrying means generated by the magnet. Magnetic force on
Of the normal direction component Fr of
The peaks on the upstream side and the downstream side in the moving direction of the particle carrying means are
When the first peak and the second peak are defined as the first peak and the second peak,
Upstream side end and downstream side in the rotation direction of the charged body
Rotation of the magnetic particle carrier from each position of the end
Center is present within the rotation range of ± 5 ° relative to the orientation of the magnetic force acting on magnetic particles present in the downstream end, the magnetism can be subtracted to the magnetic particle bearing section from the downstream end Of the two tangent lines of the particle carrying means, the first tangent line which is the tangent line on the upstream side in the rotation direction of the magnetic particle carrying body is directed toward the center side of the magnetic particle carrying means, and in front of the first tangent line.
Magnetic force in a direction acting on the magnetic particles present in serial on the upstream side end, the magnetic particle carrier of the two tangent lines of the magnetic particle bearing means can be subtracted to the magnetic particle bearing section from the upstream end The charging device is characterized in that the magnet is arranged so as to face the center side of the magnetic particle supporting means with respect to the second tangent line which is the tangent line on the downstream side in the rotation direction of. 2. A magnetic particle carrying means that moves relative to the member to be charged and that contains a fixed magnet, and a magnetic brush formed by being attached to the magnetic particle carrying means by the magnetic force of the magnet. Magnetic particles to be, contact with the charged body while carrying the magnetic brush by the relative movement of the magnetic particle carrying means and the charged body,
In a charging device for uniformly charging the charged body by applying a voltage to the magnetic particle carrying means, the moving direction of the magnetic particle carrying means is in front of the charged body.
Te contact nip portion odor which is formed between the serial magnetic brush
A counter direction with respect to the rotation direction before Symbol member to be charged,
The magnet has a charging main pole provided on the downstream side in the moving direction of the magnetic particle carrying means with respect to the closest position between the charged body and the magnetic particle carrying means, and the magnetic particle carrying means generated by the magnet. Magnetic force on
Of the normal direction component Fr of
The peaks on the upstream side and the downstream side in the moving direction of the particle carrying means are
When the first peak and the second peak are defined as the first peak and the second peak,
Upstream side end and downstream side in the rotation direction of the charged body
Rotation of the magnetic particle carrier from each position of the end
It exists within a rotation range of ± 5 ° with respect to the center, and between the charged body and the magnetic particle carrying means, an upstream side end portion of the charged body in the rotation direction of the contact nip portion. The closest position of the surface of the magnetic particle carrying means to the upstream end, the downstream end of the contact nip portion in the rotation direction of the charged body, and the surface of the magnetic particle carrying means to the downstream end. Is a contact nip region, and the rotation of the magnetic particle carrying means of the two tangent lines of the magnetic particle carrying means that can be drawn from the downstream end to the magnetic particle carrying means. The tangent line located on the upstream side in the direction is defined as a first tangent line, and of the two tangent lines of the magnetic particle carrying means that can be drawn from the upstream end to the magnetic particle carrying means, the downstream side in the rotation direction of the magnetic particle carrying means. Located in When the tangent line is a second tangent line, when the magnetic force acting on the magnetic particles existing in the contact nip region is outward from the first and second tangential directions with respect to the magnetic particle carrying means, The charging device, wherein the magnet is arranged so that the direction of the force is located in the middle of the trajectory so as to be located at a position facing the center of the magnetic particle supporting means. 3. The volume ratio Mc of the magnetic particles in the contact nip portion is expressed by Mc = (M / h) × (1 / ρ) × 100, where M is per unit area of the magnetic particle supporting means. Amount of magnetic particles [g / cm ² ] in a non-brushing state, and h is the distance [c] between the charged body and the magnetic particle supporting means.
m] and ρ are true densities [g / cm ³ ] of the magnetic particles, and the volume ratio of the magnetic particles in the contact nip portion is 30.
The charging device according to claim 1 or 2, wherein the charging device is set to -80%. 4. The resistance value of the magnetic particles is from 1 × 10 ⁵ to
The charging device according to claim 1 or 2, wherein the charging device has a density of 1 × 10 ⁸ Ωcm. 5. The charging device according to claim 1, which charges the charged body, and an electrostatic latent image forming means for forming an electrostatic latent image on the charged body charged by the charging device. An image forming apparatus comprising: a toner image forming unit that visualizes the electrostatic latent image formed on the member to be charged.