JPH07219310A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To provide an invention applicable to an electrostatic charging device which makes it possible to assure stable and uniform electrostatic chargeability without generating leakage of electrostatic charge particles, etc., and without deteriorating an electrostatic charging material even in a long-term use. CONSTITUTION:In this electrostatic charging device formed by constituting a photoreceptor 1 in such a manner that the electrostatic charge thereof is made possible via magnetic particle 4 groups carried by two magnet bodies, a main pole A1 and a counter pole B1, a separating pole A4 constituted to separate the magnetic particle 4 groups existing on the upstream side in the rotating direction of the photoreceptor from the main pole A1 separating from an electrostatic charging sleeve 2 and to drop these particle groups onto the photoreceptor 1, is disposed. The average grain size of the magnetic particle 4 groups is set at about 10 to 40mum, the saturation magnetization in a magnetic field of 1KOe of the magnetic particle 4 groups at 50 to 200emu/g and the non-dielectric constant epsilonr at <=40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus based on the so-called Carlson process, such as a copying machine, a printer,
The present invention relates to an invention applied as a charging device incorporated in a facsimile or incorporated in a process cartridge of these devices, and particularly as a charging device in an electrophotographic device for charging a belt-shaped or drum-shaped photosensitive member by particle charging. It relates to the invention to be applied.

[0002]

2. Description of the Related Art Conventionally, process means for exposing, developing, transferring, cleaning (removing residual toner), discharging, and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic devices based on the so-called Carlson process are well known.

The charging means used in this type of apparatus is generally a corotron system in which a high voltage is applied to a thin tungsten wire to perform corona discharge, or a conductive roller is applied with a voltage of several hundreds of volts to contact and charge a photosensitive drum. In addition, there is one in which a voltage is applied to a conductive brush so that the brush is charged while being in contact with the photosensitive drum. However, the corotron method uses a high voltage, and in terms of safety such as generating ozone,
There are many environmental problems. Further, since the charging roller is in line contact with the photosensitive drum, charging is unstable. Further, in the brush charging method, since the drum and the brush contact each other to perform charging, the charging deterioration of the brush is likely to occur.

In order to solve such a drawback, in a state where a charging bias is applied to a charging sleeve having a photosensitive drum and a magnet body inserted therein, a group of magnetic particles is attached to the sleeve to form a brush-shaped magnetic brush on the photosensitive body. A so-called particle charging method has been proposed in which a drum is rubbed and a charging bias is applied to a group of magnetic particles via a sleeve to perform charging. (JP-A-5
9-133569, JP-A-63-187267, etc.)

In such a charging method, when a magnetic brush is formed by a fixed magnet body, the magnetic field is attenuated in proportion to the square of the distance from the magnet body, so that the magnetic particles on the surface of the photosensitive drum are magnetized. The holding power is the weakest. Therefore, when the photosensitive drum is rotated in this state, a centrifugal force acts on the surface of the photosensitive drum, and the magnetic particles electrostatically attached to the photosensitive drum resist the magnetic coercive force (magnetic field) from the fixed magnet assembly. Then, a force acts in the direction in which the magnetic particles separate from the charging area, and the particles attached to the photosensitive drum adversely affect the exposure and development in the next step.

In order to solve such a drawback, as shown in FIG. 3, the fixed magnet body 10 is covered with the electrode 102 to which the charging bias power source 101 is connected without using the charging sleeve.
3 is arranged so as to face the photosensitive drum 104, faces the fixed magnet body 103, and a magnet body 105 of opposite polarity is arranged on the back side of the photosensitive drum 104, and between the magnet body 105 and the fixed magnet body 103. There is disclosed a technique in which the photosensitive member is charged while the magnetic particle group 107 is held in the charging region by the magnetic field formed in the above.

[0007]

According to such a technique,
Since the magnet body for magnetically retaining the magnetic particle group 107 is not arranged only on one side of the charging gap 108 but on both sides thereof, the magnetic field gradient (ΔH / Δt) between the charging gaps 108 is Although it can be set large, the magnetizing force of the magnet body and magnetic particles described above depends on the particle diameter, and as the particle diameter becomes smaller, the magnetic restraining force decreases in a geometrical series, and the centrifugal force and electrostatic force generated on the photosensitive drum are reduced. The particles attached to the surface of the drum due to the static holding force cause particle leakage. If the electric resistivity of the particles is lowered unnecessarily in order to prevent electrostatic adhesion of the particles, dielectric breakdown of the photoconductor or leakage of photoconductor defects occurs, and pinholes or the like on the photoconductor drum side due to the charging bias. Is likely to occur. Therefore, in the above apparatus, the insulating sheet 109 is hung on the side surface of the fixed magnet body 103 toward the photoconductor drum side to mechanically prevent scattering of magnetic particles.

However, in the structure in which the insulating sheet is in contact with the drum as described above, not only can it not withstand long-term use due to abrasion or the like, but unless the magnetic particles are made of a material having good conductivity, the insulating sheet and particles are Particle rubbing and the like may cause particle sticking, which is not preferable.

In view of the above-mentioned drawbacks of the prior art, the present invention is applied as a charging device capable of ensuring a stable and uniform charging ability without causing leakage of the charged particles or deterioration of the charging agent even after long-term use. It is an object of the present invention to provide an invention that is made. Another object of the present invention is to provide an invention applied as a charging device capable of ensuring good circulation of magnetic particles without causing dielectric breakdown. Another object of the present invention is to provide an invention capable of obtaining a charging device having extremely high practicability, which can be sufficiently considered from the viewpoint of manufacturing, the user side, and the environment. To do.

[0010]

According to the present invention, as shown in FIG. 1 (A), a first magnet body (hereinafter referred to as a main pole) fixedly arranged on a charged area of a photoconductor is directed toward the photoconductor. ) Is included, and a second magnet body having a polarity opposite to the main pole (hereinafter referred to as an opposite pole) is arranged on the back side of the photosensitive drum located on the charging area. In a charging device configured to charge a photoconductor through a magnetic particle group carried by a magnet body, the magnetic particle group located upstream of the main pole of the magnetic particle group in the photoconductor rotation direction from a charging sleeve Separation is performed so that a separation pole that can be dropped is disposed on the photoconductor, the average particle size is set to approximately 10 to 40 μm, and the saturation magnetization of the magnetic particle group in a magnetic field of 1 kOe is 50 emu / g to 200 emu / g, relative permittivity εr to 40 or less The feature is that it is set. In the invention according to claim 2, the volume resistivity of the magnetic particle group is 10 or less.
There ⁶ following conductive magnetic particles and a volume resistivity of a mixed particles of ¹⁰⁶ or more high-resistance magnetic particle volume resistivity as a whole in the range of 10 ³ ~10 ⁸ Ω · cm, a high-resistance magnetic particles The average particle size of is larger than the average particle size of the conductive magnetic particles. In this case, it is preferable that the high resistance magnetic particles have a particle distribution of 20 μm or less of 5% or less. In addition, the volume resistivity is 1. Teflon cylinder having an inner diameter of 20 mm and an electrode at the bottom,
It is a value measured by inserting 5 g and inserting an electrode having an outer diameter of 20 mmφ from the upper part, and then applying a load of 1 kg to the upper surface of the electrode.

In this case, the charging sleeve is rotated in the against direction with respect to the rotation direction of the photosensitive drum, and the magnetic flux density on the closest contact point P of the main pole A _{1 is} the closest contact point of the opposite pole B _1. It is preferable that the magnetic flux density on P be higher than the magnetic flux density. Further, the maximum magnetic flux density position Q ₁ is + 5 ° to −30 ° on the upstream side in the rotation direction of the photosensitive drum with the closest contact point P interposed, and the maximum magnetic flux density position Q ₂ is −10 ° to +5 with the closest contact point P interposed. It is better to place it in the range of °. Further, by disposing a second magnet body (hereinafter referred to as shield pole A ₂ ) having the same polarity as the opposing pole B ₁ in the charging sleeve on the downstream side in the moving direction of the photoconductor, magnetic shielding becomes easier.

[0012]

In the present invention, the outflow phenomenon of the magnetic particle group 4 depends on the relationship between the magnetic force and the electrostatic force which the magnetic particle 4 receives at the sleeve closest contact point P of the photoreceptor. That is, the magnetic force Fm acting on the particle at the closest point P is: Fm = k ₁ · d ³ k ₁ : Proportional function d: Particle size That is, the electrostatic force Fc acting on the particle at the closest point P is Fc = k ₂ · (T · d) ² · ΔV ² T: Function dependent on non-dielectric constant ΔV: Potential difference (voltage applied to charging and voltage applied to photosensitive layer) Potential difference ΔV when magnetic particles overcome magnetic force and flow out by electrostatic force is Fc ≧ Fm ΔV ≧ (T) ⁻¹ · (k ₁ · d / k ₂ ) ^1/2 ... 1) Therefore, as is clear from the above formula 1), if the particle size is too small, Fc ≧ Fm and the particles flow out.

On the other hand, if the particle size is too large, the particles do not leak, but as the particle size increases, the packing ratio of the magnetic particles between the sleeve and the drum decreases, and the particles are charged by the same charging bias. As a result, the surface potential of the photosensitive member decreases, and as shown in FIG. 1B, the number of voids 4a between adjacent magnetic particles 4 on the surface of the photosensitive member 1 increases, and uniform uneven charging is likely to occur. Therefore, in the present invention, by setting the average particle size to approximately 10 μm to 40 μm, it is possible to smoothly prevent particle leakage from the charging region.

The magnetic coercive force of the magnetic particle group depends on the saturation magnetization, and the electrostatic force induced in the charging agent increases as the relative dielectric constant of the magnetic particle group increases. Therefore, the saturation magnetization of the magnetic particle group in a magnetic field of 1 kOe is 50 emu /
g to 200 emu / g is preferable, and the relative dielectric constant εr is 40
The following should be set. If the magnetic particle group has a relative permittivity εr of more than 40 at 200 emu / g or more, the magnetic particle group 4 shown in FIG. 2 described later cannot be separated by the separation pole A ₄ and is conveyed to the downstream side in the rotation direction of the charging sleeve. The Rukoto.

The present invention has a volume resistivity of 10 ⁶ Ω · c.
m or less conductive magnetic particles and volume resistivity of 10 ⁶ Ω · c
The magnetic particle group is composed of a mixed particle group of high-resistance magnetic particles of m or more, and the average particle diameter of the high-resistance magnetic particles is larger than the average particle diameter of the conductive magnetic particles, specifically, the high-resistance magnetic particles. By configuring such that the particle distribution of 20 μm or less is 5% or less, leakage that is more likely to occur compared to a single type charging agent is prevented. On the other hand, it is preferable that the average particle diameter of the conductive magnetic particles that contribute to uniform charging be small, for example, 20 μm.
The following are preferred. Further, the mixing ratio of the high resistance magnetic particles and the conductive magnetic particles depends on the volume resistivity of each, but the mixing ratio of the conductive magnetic particles is small, and specifically, it may be set to 5 to 30% by weight.

Further, as shown in FIG. 1, the magnetic particles 4 guided to the charging gap 5 of the sleeve closest contact point P of the photosensitive drum 1 have the gap 5 as a bottleneck, but the closest contact point P at the main pole A ₁ . and the magnetic flux density B _A1, when the magnetic flux density of the closest point P of the counter electrode B ₁ was B _B1 "B _A1> B
_Since it is set to " _B1 ", it is sucked from the photosensitive drum 1 side to the charging sleeve 2 side. Further, according to the present invention, since the charging sleeve 2 is rotated with respect to the photosensitive drum 1 toward the opposite direction, that is, toward the upstream side of the charging area, the magnetic particles 4 attached to the charging sleeve 2 are moved from the charging gap 5 position. The separation electrode A ₄ flowing toward the upstream side of the charging area allows the magnetic particles 4 to be separated from the charging sleeve 2 and circulate in the charging area, so that the particles do not deteriorate even after long-term use.

The magnetic flux density on the closest contact point P is set to "B _A1 > B _B1 " in order to achieve the effect that the particles can move to the charging sleeve 2 side at the charging gap 5 position.

In order to achieve the condition "B _A1 > B _B1 " most effectively, the maximum magnetic flux density position Q _{1 of the} opposing pole B ₁ determines the closest contact point P, although it depends on the half width of each magnet. It is preferable to set it in the range of + 5 ° to −30 ° on the upstream side with respect to the rotation direction of the photosensitive drum 1 while sandwiching it, and further, the maximum magnetic flux density position Q ₂
Is preferably set in the range of -20 ° to + 5 ° with the contact point P placed in between. The angle photosensitive drum axis O ₁ and the charging sleeve O ₂ of the line connecting the recently axis from the contact P O ₂
The side direction is set to 0 °, the upstream side of the photosensitive drum is set to a minus angle, and the downstream side is set to a plus angle.

[0019]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 2
The configuration of the charging device according to the embodiment of the present invention will be described based on FIG. As described above, the charging device is in the opposite direction to the photosensitive drum 1 at the charging area position via the charging gap 5 (closest spacing) of about 0.5 mm with respect to the photosensitive drum 1 rotating to the right in the figure. That is, the non-magnetic charging sleeve 2 is disposed so as to be rotatable in the against direction (the left direction in the drawing, and the same rotating direction when viewed from the rotation axis), and the rear side of the sleeve 2 is provided. A magnet assembly 3 is fixedly arranged on the downstream side of the charging area. still,
A bias power source 7 applies a developing bias to the conductive magnetic particle group 4 via a conductive blade or a non-magnetic sleeve 2 (not shown).

Next, the arrangement of the magnetic poles of the charging sleeve 2 and the photosensitive drum 1 which is the subject matter of the present invention will be described. First, in the magnet assembly 3, the magnetic particles 4 are mainly formed on the charging gap 5 or slightly upstream of the charging gap 5 in the rotation direction of the charging sleeve 2 and between the opposing magnetic pole B ₁ on the back side of the photosensitive drum 1. the main pole a ₁ N pole for magnetic seal for preventing leakage, further charging sleeve 2 rotating direction upstream side of the main poles a _1, the magnet body S pole for magnetic seal for performing the magnetic seal assisted by repulsive magnetic field (Hereinafter shield auxiliary pole A
₂ ), and a separation pole A ₄ which is a non-magnetic band having a small magnetic force of about 50 gauss or less is formed on the sleeve 2 downstream of the main pole A _{1 in} the rotation direction of the charging sleeve 2. The magnetic particles 4 are transported by the magnet body A ₃ of the S pole that is transported while being carried on the surface of the sleeve 2 by the strike rotation, and the magnetic particles 4 are dropped to the photosensitive drum 1 side on the upstream side of the charging area.

Further, a group of conductive magnetic particles 4 is provided on the charging area sandwiched between the charging sleeve 2 and the photosensitive drum 1. Although the details of the magnetic particles 4 will be described later, the volume resistivity is arbitrarily set in the range of 10 ³ to 10 ⁸ Ω · cm, and the particle size is arbitrarily set in the range of 10 to 30 μm in average particle size.

On the other hand, on the rear surface side of the photosensitive drum 1, an S-pole magnet body (hereinafter referred to as the opposing pole B) is provided at a downstream portion of the charging area slightly upstream of the main pole A _{1 in} the rotational direction of the photosensitive drum 1.
₁ ) and an N-pole magnet body (hereinafter referred to as “adjacent”) for forming a magnetic field (hereinafter referred to as “horizontal magnetic field”) horizontal to the surface of the photoconductor drum 1 adjacent to the opposite pole B ₁ on the upstream side of the charging area. pole B ₂ hereinafter) and an adjacent arrangement, a magnetic field perpendicular to the photosensitive drum surface (hereinafter referred to as "vertical field") between the main pole a ₁ and the counter electrode B _1, also adjacent to the opposite pole B ₁ A horizontal magnetic field is formed on the photosensitive drum 1 with the pole B ₂ .

That is, the main pole A ₁ and the counter pole B ₁ which are opposed to each other are arranged on the downstream side of the charging area in the rotation direction of the photosensitive drum ₁ , and the vertical magnetic field formed between the magnets A ₁ and B ₁ is formed. be magnetically holding said magnetic particles 4 due, also adjacent poles B ₂
Is arranged adjacent to the counter electrode B ₁ on the upstream side of the charging area,
The magnetic particle group 4 is brought into close contact with the photoconductor drum 1 by a horizontal magnetic field on the photoconductor drum 1 mainly formed between the two magnet bodies B ₂ and B ₁ .

More specifically, the magnetic pole arrangement of each of the magnetic poles will be described in detail with reference to FIG. The shield auxiliary pole A ₂ is located upstream of the main pole A _{1 in the} rotation direction of the charging sleeve, and the maximum magnetic flux density position Q _{3 of the} shield auxiliary pole A _{2 on} the charging sleeve is set in the range of 45 ° to 90 °. ing. The angle is 0 ° when the direction of the line connecting the axis O ₂ to the closest contact point P with the charging sleeve O ₂ as the center is 0 °.
This is a value in which the deflection angle toward the downstream side in the moving direction of the photoconductor is set to be positive. The main pole A ₁ has a maximum magnetic flux density position Q ₂ on the charging sleeve of the main pole A _{1 and} a downstream side of the maximum magnetic flux density position Q ₁ on the photosensitive drum of the opposing pole B _{1 in} the photosensitive drum rotation direction. It is configured to be positioned, and more specifically, Q ₂ has a closest contact point P between −20 ° and
It is preferable to set in the range of + 5 °, and more preferably in the range of −10 ° to + 5 °. Further, the opposing pole B ₁ has a maximum magnetic flux density position Q _{1 in} the range of + 5 ° to −30 ° on the upstream side in the rotation direction of the photoconductor drum with the closest contact point P in between, and the magnetic flux on the closest contact point P of the main pole A ₁ is. The density is set to be higher than the magnetic flux density on the closest contact P of the counter pole B ₁ . The angle in this case is the value shown in the column of action. The relationship between the main pole A ₁ and the opposing pole B ₁ is that the line connecting the charging sleeve axis O ₂ and the maximum magnetic flux density position Q ₂ of the main pole A ₁ and the photosensitive drum axis O ₁ face each other. The narrow angle of the line connecting the maximum magnetic flux density position Q ₁ of the pole B ₁ is set to 0 to 50 °.

The operation of this embodiment will be briefly described below with reference to FIG. 1. The magnetic particle group 4 located in the charging area is described below.
Is adhered to the photoconductor drum 1 in close contact with it on the horizontal magnetic field 4A between the opposite pole B ₁ and the adjacent pole B ₂ , and when the photoconductor drum 1 rotates clockwise in this state, it is exposed on the horizontal magnetic field 4A. While the body drum 1 is being charged, it moves to the charging gap 5 side, and at the position of the charging gap 5, the magnetic particle group 4 generates a repulsive magnetic field between the magnetic auxiliary particles A ₂ and the opposing pole B ₁ and the main pole. The magnetic shield created by the A ₁ opposite pole B ₁ is assisted, and the direction of the force is tilted to the upstream side of the photosensitive drum by the upward force of A ₁ and B ₁ and moved to the upper left sleeve 2 side in the figure. The separation pole A ₄ prevents the magnetic particles from being conveyed to the downstream side of the sleeve 2 without magnetic force on the sleeve 2. In this case, the saturation magnetization of the magnetic particle group 4 in the magnetic field of 1 KOe is set to 50 emu / g to 200 emu / g, but when it exceeds 200 emu / g, the magnetic particles easily pass through the separation pole A ₄ and are conveyed to the downstream side of the charging sleeve 2. The Rukoto. On the other hand, when it is 50 emu / g or less, the magnetic particle group 4 is hard to adhere to the main pole A ₁ side, and as a result, circulation becomes difficult.

In this case, although the composite vector of the magnetic forces on the closest point P formed by the shield pole A ₂ and the counter pole B ₁ is not shown, it is set by the direction toward the charging gap 5 entrance side, The pushback direction by the magnetic field works together with the repulsive magnetic field, which is more preferable. Further, the combined vector of magnetic forces formed by the main pole A ₁ , the counter pole B ₁ and the shield pole A ₂ in the normal direction of the sleeve closest contact point P of the photosensitive drum is set to face the charging sleeve 2. . As a result, the magnetic particles on the charging gap move to the charging sleeve 2 side and are attracted thereto.

The magnetic particles 4B adsorbed on the charging sleeve 2 side are returned to the upstream side of the charging area as the sleeve 2 rotates, and then the separation pole A ₄ provided downstream of the magnet body A _3.
Are laid out on the upstream side of the charging area, so that the magnetic particle group 4 conveyed to the upstream side of the charging area.
C is magnetically released, falls on the side of the photosensitive drum 1, and the magnetic particles 4 are circulated.

Next, the leakage of the magnetic particles 4 from the charging gap 5 using such a device is confirmed by an experiment. First, the experimental conditions will be described. The photoconductor drum 1 is an OPC drum, the diameter is 30 mmφ, and the linear velocity is 25 m /
Set to sec. The charging sleeve 2 uses an aluminum tube,
The diameter is set to 12 mmφ and the linear velocity is set to 8 m / sec.

The magnetic flux density of each magnetic pole is the opposite pole B.
₁ and the adjacent pole B ₂ of each of the photosensitive drum 1 on the maximum magnetic flux density, respectively S630G of, N730G, further the maximum magnetic flux density on the main poles A ₁ and the shield auxiliary pole A ₂ of each of the charging sleeve 2 respectively Set to N900G and S770G respectively.
And the main pole A ₁ is 0 ° (the maximum magnetic flux density is N900
G), when the counter pole B _{1 is set} to −15 ° and the shield auxiliary pole A ₂ is set to 60 °, respectively, the main pole A ₁ , the counter pole B ₁ and the shield auxiliary pole A ₂ on the closest contact P are formed. It was confirmed by simulation that the combined vector of the magnetic force generated by the magnetic force was generated toward the gap entrance of the charging sleeve.

In this state, it is incorporated into an LED printer manufactured by our company and 400 V is applied to the charging bias power source 7 to rotate the charging sleeve in the against direction with respect to the moving direction of the photosensitive drum to circulate the magnetic particles. The state of leakage to the photosensitive drum was confirmed visually and by image formation. The magnetic particles have an average particle size of 15 μm and a volume resistivity of 10 μm.
Saturation magnetization is 70 emu / in a magnetic field of ⁵ Ω · cm and 1 KOe
g of ferrite carrier was used (Sample 1). Further, as a comparative example, the magnetic particles have an average particle size of 30 μm, a volume resistivity of 10 ⁵ Ω · cm, and a saturation magnetization of 210 in a magnetic field of 1 KOe.
An iron powder carrier of emu / g was used (Sample 2). In addition,
The non-dielectric constant of each carrier was 40 or less. As a result of this experiment, in the sample 1, magnetic particles are circulated well,
A good image was obtained. On the other hand, the sample 2 has the separation electrode A.
_The magnetic particles cannot be separated by ₄ and the charging sleeve 2
Magnetic particles were surrounded, and it was not circulated smoothly, and uneven charging appeared in the image.

[0031]

As described above, according to the present invention, stable charging ability can be secured for a long period of time without causing leakage of magnetic particles during particle charging and without deterioration of the charging agent even after long-term use. . Further, according to the present invention, it is applied as a charging device capable of ensuring good circulation of magnetic particles. Further, according to the present invention, it is possible to obtain a charging device having extremely high practicality, because it is possible to sufficiently consider the environment from the viewpoint of manufacturing, the user side, and the like. It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is an overall view showing a charging device according to an exemplary embodiment of the present invention.

FIG. 3 is a table showing a charging device according to a conventional technique.

[Explanation of symbols]

1 Photoconductor drum 2 Charging sleeve 3 Magnet assembly 4 Magnetic particles 5 Charging gap P Closest contact A ₁ Main pole B ₁ Counter pole A ₂ Shield auxiliary pole A ₄ Separation pole

Claims (6)

[Claims] 1. A non-magnetic charging sleeve which encloses a first magnet body (hereinafter referred to as a main pole) fixedly arranged on the charging area of the photoconductor, and which is located on the charging area. A second magnet body having a polarity opposite to that of the main pole (hereinafter referred to as an opposite pole) is arranged on the back side of the photoconductor, and while rotating the charging sleeve, the magnetic particle groups carried by the both magnet bodies are arranged. In a charging device configured to be capable of charging a photoconductor via a magnetic particle group, the magnetic particle group located upstream of the main pole of the magnetic particle group in the photoconductor rotating direction is separated from the charging sleeve and dropped onto the photoconductor. It is characterized in that a separation pole configured as possible is arranged, an average particle size is approximately 10 to 40 μm, a saturation magnetization in a magnetic field of 1 kOe is set to 50 emu / g to 200 emu / g, and a relative permittivity εr is set to 40 or less. Charging device 2. A magnetic particle group, a mixed group of particles volume resistivity of 10 ⁶ or less electrically conductive magnetic particles and a volume resistivity of 10 ⁶ or more high-resistance magnetic particles, the volume resistivity of the entire 10 ^2. The charging device according to claim 1, wherein the average particle size of the high resistance magnetic particles is in the range of ³ to 10 < ⁸ > [Omega] .cm and is larger than the average particle size of the conductive magnetic particles. 3. The charging device according to claim 2, wherein the high resistance magnetic particles have a particle distribution of 5 μm or less of 20 μm or less. 4. The charging sleeve is rotated in the against direction with respect to the moving direction of the photoconductor, and the magnetic flux density on the sleeve closest contact point P of the photoconductor of the main pole is the closest contact point P of the opposite pole. The magnetic flux density is set to be higher than the above magnetic flux density.
Charging device described 5. The maximum magnetic flux density position Q ₂ on the charging sleeve of the main pole is located downstream of the maximum magnetic flux density position Q ₁ on the photosensitive drum of the opposite pole in the photosensitive drum rotation direction. In addition, the maximum magnetic flux density position Q ₁ is + 5 ° to −30 ° on the upstream side in the rotation direction of the photoconductor drum with the closest contact point P interposed, and the maximum magnetic flux density position Q ₂ is −10 with the closest contact point P interposed. ° ~ +
The charging device according to claim 1, wherein the charging device is arranged in a range of 5 °. 6. A third magnet body (hereinafter referred to as a shield auxiliary pole) having the same polarity as the counter pole is arranged in the charging sleeve on the downstream side in the moving direction of the photosensitive body.
Charging device described