JPH06161207A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device in which ozone is not generated, the electric breakdown of an image forming body is not caused, and extremely stable and uniform electrostatic charging is performed. CONSTITUTION:This image forming device is provided with a non-magnetic conductive electrostatic charging roller 22 rotatably disposed on the outer periphery of a magnetic body 23 fixed in a state where magnetic poles are arranged on its outer periphery, and an electrostatic charging device 20 which electrostatically charges a photosensitive drum 10 by bringing a magnetic brush 21A consisting of the layer of magnetic particles 21 adhering to the outer periphery of the roller 22 into contact with the moving photosensitive drum 10 and forming bias electric field between the roller 22 and the drum 10. Then, a gap DB between a regulation plate 26 and the roller 22 is set to >=0.2mm and <=1.0mm and a gap D1 at a position where the roller 22 and the drum 10 are opposed is regulated to be 0.7 to 1.0 times as large as the DB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrostatic transfer process such as an electrophotographic copying machine and an electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a corona charger has generally been used for charging an image forming body such as a photosensitive drum. This corona charger applies a high voltage to the discharge wire to generate a strong electric field around the discharge wire to perform gas discharge, and the charged ions generated at that time are adsorbed to the image forming body to charge. Done.

Since the corona charger used in such a conventional image forming apparatus can be charged without mechanical contact with the image forming body, it is said that the image forming body is not damaged during charging. Have advantages. However, since this corona charger uses a high voltage, there is a risk of electric shock or leakage, and ozone generated by gas discharge is harmful to humans, which shortens the life of the image forming body. Had. Further, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. Further, the corona charger generates noise due to high voltage, which causes electrophotographic image formation as a communication terminal or an information processing device. This is a major drawback when using the device.

Many drawbacks of such corona chargers are:
The cause is that gas discharge is involved in charging.

Therefore, a magnet body is included as a charging device capable of charging the image forming body without causing high-pressure gas discharge like a corona charger and without mechanically damaging the image forming body. A charging device in which magnetic particles are adsorbed on a cylindrical carrier formed as described above to form a magnetic brush, and the surface of an image forming body is rubbed with the magnetic brush to perform charging is disclosed in Japanese Patent Laid-Open No. 59-133569. Japanese Patent Laid-Open No. 4-21873 and Japanese Patent Laid-Open No. 4-116674.

[0006]

However, even the charging device disclosed in the above publication has a problem that the image forming body cannot be charged completely stably and uniformly. That is, if the amount of magnetic particles on the surface of the cylindrical magnetic particle carrier is not properly maintained in the charging region, uneven charging or local excessive charging may occur, or insulation of the image forming body due to bias voltage may occur. There is a problem that destruction occurs.

An object of the present invention is to solve these problems and to provide an image forming apparatus capable of performing extremely stable and uniform charging without dielectric breakdown of the image forming body or generation of ozone.

[0008]

An object of the present invention is to charge magnetic particles on a carrier to form a magnetic brush, and to place the magnetic brush on the carrier under an oscillating electric field to charge an image forming body. In the forming apparatus, when the gap between the regulation member that regulates the passage amount of the magnetic particles and the transport carrier is DB, and the gap between the image forming body and the transport carrier is DI,
This is achieved by an image forming apparatus characterized in that 0.7DB≤DI≤1.0DB.

Further, the DB is 0.2 ≤ DB ≤ 1.0 (m
The image forming apparatus described above is a preferred embodiment.

[0010]

In the present invention, when the gap between the carrier for the magnetic particles of the charging device of the image forming apparatus and the image forming body is DI and the gap between the regulating member of the charging device and the carrier is DB, 0.7 dB Since it is regulated so that ≦ DI ≦ 1.0 dB, the amount of magnetic particles in the charged region on the carrier is properly maintained, and the charged region is regulated to be constant.

[0011]

EXAMPLES Before describing the examples of the present invention, the particle size of the magnetic particles and the conditions of the carrier will be described.

Generally, when the average particle size (weight average) of the magnetic particles is large, (a) since the state of the magnetic brush ears formed on the carrier is rough, even when charged while vibrating by the electric field, The magnetic brush is likely to have unevenness, which causes a problem of uneven charging. To solve this problem, the average particle size of the magnetic particles should be reduced.
It was found that the effect began to appear when the thickness was less than μm, and particularly when the thickness was 100 μm or less, the problem (a) did not substantially occur. However, if the particles are too fine, they tend to adhere to the surface of the image forming body at the time of charging, or easily scatter. These phenomena are related to the strength of the magnetic field acting on the particles and the strength of the magnetization of the particles thereby, but generally, the average particle diameter of the particles becomes prominent at 30 μm or less. In addition,
A magnetized strength of 20 to 200 emu / g is preferably used.

From the above, the average particle diameter (weight average) of the magnetic particles is 150 μm or less, particularly preferably 100 μm or less.
It is preferably 30 μm or more.

Such magnetic particles are the same as the magnetic carrier particles of the conventional two-component developer as a magnetic material,
Ferromagnetism such as metals such as iron, chromium, nickel and cobalt, or their compounds and alloys such as ferric tetroxide, γ-ferric oxide, chromium dioxide, manganese oxide, ferrite and manganese-copper alloys. Body particles or the surface of these magnetic particles is coated with a resin such as styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, or Particles obtained by making a resin containing magnetic fine particles dispersed therein can be obtained by selecting the particle size by a conventionally known average particle size selecting means.

The formation of spherical magnetic particles is
The particle layer formed on the carrier is made uniform, and a high bias voltage can be uniformly applied to the carrier. That is, the fact that the magnetic particles are spherical means that (1) generally, the magnetic particles are easily magnetized and adsorbed in the long-axis direction, but the spherical particles lose their directionality, so that the layers are uniformly formed and local (2) Higher resistance of the magnetic particles is eliminated, and the edge portions seen in conventional particles are eliminated, and electric field concentration on the edge portions is prevented. As a result, even if a high bias voltage is applied to the magnetic particle carrying carrier, uniform discharge is caused on the surface of the image forming body and charging unevenness does not occur.

The spherical particles having the above effects have magnetic particles having a resistivity of 10 ³ Ω · cm or more and 10 ¹² Ω · cm or less, particularly 10 ⁴ Ω.
It is preferable that the conductive magnetic particles are formed so as to be not less than • cm and not more than 10 ⁹ Ω · cm. This resistivity is 0.50 cm for particles
After placing in a container with a cross-sectional area of ² and tapping, applying a load of 1 kg / cm ² on the packed particles and applying a voltage that generates an electric field of 1,000 V / cm between the load and the bottom electrode. Is a value obtained by reading the current value of, and when this resistivity is low, when a bias voltage is applied to the carrier, electric charges are injected into the magnetic particles, and the magnetic particles easily adhere to the surface of the image forming body. Or the dielectric breakdown of the image forming body due to the bias voltage is likely to occur. Also,
If the resistivity is high, charge injection is not performed and charging is not performed.

Further, the magnetic particles used in the present invention are
It is desirable that the magnetic brush constituted by it has a small specific gravity and a suitable maximum magnetization so that the magnetic brush moves lightly due to an oscillating electric field and does not cause external scattering. Specifically, it was found that good results can be obtained by using a material having a true specific gravity of 6 or less and a maximum magnetization of 30 to 100 emu / g.

In summary of the above, the magnetic particles are spherical so that the ratio of the major axis to the minor axis is at most 3 times, there are no protrusions such as needles and edges, and the resistivity is high. The appropriate condition is preferably 10 ⁴ Ω · cm or more and 10 ⁹ Ω · cm or less. Then, such spherical magnetic particles should be selected as spherical as possible for the magnetic particles, and in the particles of the magnetic particle dispersion system, the particles of the magnetic material should be used as much as possible.
After the dispersed resin particles are formed, a spheroidizing treatment is performed, or the dispersed resin particles are formed by a spray drying method.

When toner is mixed in the magnetic brush,
Since the toner has a high insulating property, the charging property is lowered and uneven charging occurs. In order to prevent this, it is necessary to lower the charge amount of the toner so that the toner moves to the image forming body at the time of charging. Under the condition that the toner is mixed with magnetic particles and the toner concentration is adjusted to 1%. When the triboelectrification amount of the toner was the same and the charging polarity was 1 to 20 μC / g, the toner could be prevented from accumulating on the magnetic brush. It is considered that this is because even if the toner is mixed, it adheres to the photoconductor during charging. It was confirmed that when the charge amount of the toner is large, it becomes difficult to separate from the magnetic particles, and when it is small, it becomes difficult to electrically move to the image forming body.

The above are the conditions for the magnetic particles. Next, the conditions for the carrier for the magnetic particles for forming the particle layer and charging the image forming body will be described.

A conductive carrier that can apply a bias voltage is used as the carrier for the magnetic particles, and in particular, a magnet having a plurality of magnetic poles inside a conductive charging roller on the surface of which a particle layer is formed. A structure having a body is preferably used. In such a carrier, the relative rotation with the magnet body causes the particle layer formed on the surface of the conductive charging roller to undulate and move, so that new magnetic particles are supplied one after another. Therefore, even if the particle layer on the surface of the carrier has some unevenness in the layer thickness, the effect is sufficiently covered so as not to cause a practical problem due to the corrugation. The transport speed of the magnetic particles by the rotation of the transport carrier may be slower than the moving speed of the image forming body, but is preferably almost the same or higher than that.
In addition, it is preferable that the transporting carrier is rotated in the same direction. Uniformity of charging is better in the same direction than in the opposite direction. However, it is not limited thereto.

The surface of the carrier is preferably 2 to 15 μm in average surface roughness in order to stably and uniformly transfer the magnetic particles. If the surface is smooth, the conveyance cannot be sufficiently performed, and if the surface is too rough, an overcurrent flows from the convex portions on the surface, and in any case, sand blasting which is likely to cause uneven charging is preferably used.

The particle layer formed on the carrier is preferably uniform in thickness. If there are too many magnetic particles on the surface of the carrier in the charging region, the vibration of the magnetic particles will not be sufficiently performed, causing wear and uneven charging of the photoconductor, and overcurrent will easily flow, resulting in a large drive torque of the carrier. There is a drawback that On the other hand, if the amount of the magnetic particles present on the carrier in the charged area is too small, an incomplete portion is formed in contact with the image forming body, resulting in adhesion of the magnetic particles to the image forming body and uneven charging. As a result of repeated experiments, the preferable amount W of magnetic particles in the charged region is 10
A to 300 mg / cm ^2, more preferably found to be 30~150mg / cm ^2. The existing amount is an average value in the contact area of the magnetic brush.

The gap DI between the carrier and the image forming body
Is preferably 0.1 mm to 10 mm, more preferably 0.2 to 5 mm
Is preferred. If the gap DI between the carrier and the image forming body becomes too narrower than 0.2 mm, it will be difficult to form the magnetic brush ears that have a uniform charging action, and sufficient magnetic particles will be supplied to the charging section. I can no longer do it,
If stable charging is not performed and the gap DI exceeds 5 mm, the particle layer is coarsely formed and charging unevenness is likely to occur, and the charge injection effect is deteriorated so that sufficient charging cannot be obtained. become. As described above, when the gap DI between the carrier and the image forming member becomes extreme, the thickness of the particle layer on the carrier cannot be adjusted appropriately, but when the gap DI is in the range of 0.1 to 5 mm, On the other hand, the thickness of the particle layer can be appropriately formed, and it is possible to prevent the occurrence of sweeps due to the rubbing of the magnetic brush. Further, it has been clarified that the most preferable condition exists between the more appropriate transport amount (W) and the gap (DI).

To perform charging uniformly and stably at high speed
The condition of 300 ≤ W / DI ≤ 3,000 (mg / cm ³ ) was important. It was confirmed that when W / DI was out of this range, charging became non-uniform.

The diameter of the carrier is preferably 5 to 20 mmφ.
With the above diameter, the contact area necessary for charging is secured. If the contact area is unnecessarily large, the charging current will be excessive, and if it is small, uneven charging will easily occur.

DI is considered to be a factor that determines the chain length of magnetic particles. It is considered that the electric resistance corresponding to the chain length corresponds to the ease of charging and the charging speed. On the other hand, W is considered to be a factor that determines the density of chains of magnetic particles. It is believed that increasing the number of chains improves the charging uniformity.
However, it is considered that when the magnetic particles pass through the narrow gap in the charging region, the compressed state of the chains of the magnetic particles is realized. At this time, the chains of the magnetic particles are in contact with each other, and in a bent state, they are rubbing against the image forming body while being disturbed.

This disturbing condition is considered to be effective for uniform charge by facilitating the transfer of charge without causing charging streaks. That is, when W / DI corresponding to the density of magnetic particles is small, the chains of the magnetic particles become coarse and the ratio of disturbance is small, resulting in non-uniform charging. When W / DI is large, the chains of the magnetic particles are not sufficiently formed due to high packing, and the magnetic particles are less disturbed. It is considered that this hinders the free movement of the charges and prevents uniform charging.

When the transport amount W is less than 10 mg / cm ² , adhesion of magnetic particles and uneven charging appear, and when it is more than 300 mg / cm ² , abrasion of the photosensitive member and uneven charging appear. I couldn't get it. The preferred range in between is
It was 30 to 150 mg / cm ² .

Further, when the distance DI (cm) between the image forming body and the magnetic particle carrier is W under the above-mentioned carrying amount condition, W
It was revealed that by setting / DI to 300 mg / cm ³ <W / DI <3,000 mg / cm ³ , more preferable uniform charging characteristics without adhesion of magnetic particles and charging unevenness can be obtained. Less than 300mg / cm ³ or 3,000mg / cm ³
When it was made larger, phenomena such as adhesion of magnetic particles and uneven charging were observed.

From the above, the preferable condition is to bring a magnetic brush composed of a magnetic particle layer of magnetic particles having a magnetic force adhered onto a carrier to bring it into contact with a moving image forming body so that the space between the carrier and the image forming body is increased. In a charging device for charging the image forming body by forming a bias electric field on the magnetic field, an oscillating electric field is used as the bias electric field, and the abundance W of the magnetic particles in the charging region is 10 to 300 mg / cm ^2. When a magnetic brush is formed on the substrate and the gap between the carrier for carrying the magnetic particles and the image forming body is DI (cm), 300 ≤ W / DI ≤ 3,000 (mg /
The preferred condition is cm ³ ).

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the outline of the construction of an electrostatic recording apparatus which is an image forming apparatus of the present invention. In the figure,
Reference numeral 10 is a photosensitive drum made of (-) charged OPC which is an image forming body rotating in an arrow (clockwise) direction, and image light L from a charging device 20 and an exposure device, which will be described later, is incident on the peripheral portion of the photosensitive drum. An exposure unit, a developing device 30, a transfer roller 13, a cleaning device 50, etc. are provided.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent from an operation unit (not shown) to a control unit (not shown), the control unit controls the photosensitive drum.
10 starts rotating in the direction of the arrow. As the photosensitive drum 10 rotates, the peripheral surface of the photosensitive drum 10 is uniformly charged by a charging device 20 described later and passes through. An image is written on the photoconductor drum 10 by image light L of a laser beam from an image writing device or the like, and an electrostatic latent image corresponding to the image is formed.

There is a two-component developer in the developing device 30, which is agitated by the agitating screws 33A and 33B, and then adhered to the outer periphery of the developing sleeve 31 which is outside the magnet roller 32 and rotates, so that the magnetic force of the developer is increased. A brush is formed, a predetermined bias voltage is applied to the developing sleeve 31, and reversal development is performed in the developing area facing the photoconductor drum 10.

From the paper feed cassette 40, the recording papers P are fed one by one by the first paper feed roller 41. The fed recording paper P is sent onto the photosensitive drum 10 by the second paper feed roller 42 which operates in synchronization with the toner image on the photosensitive drum 10. Then, by the action of the transfer roller 13, the toner image on the photoconductor drum 10 is transferred onto the recording paper P and separated from the photoconductor drum 10. The recording paper P on which the toner image has been transferred is sent to a fixing device (not shown) via the conveying means 80, is sandwiched by a heat fixing roller and a pressure bonding roller, is fused and fixed, and is then discharged to the outside of the apparatus. Recording paper P
The surface of the photosensitive drum 10 which has toner remaining without being transferred to and is rotated is scraped off and cleaned by a cleaning device 50 having a blade 51 and the like, and waits for the next copying.

FIG. 2 is a sectional view showing an embodiment of the charging device 20 used in the image forming apparatus of FIG. In the figure,
21 is a magnetic particle, 22 is a charging roller that is a carrier for the magnetic particles 21 formed of a non-magnetic and conductive metal such as aluminum having a surface roughness of 7 μm that has been sandblasted, and 23 is fixed inside the charging roller 22. The magnet body 23 is magnetized by arranging the S and N poles on the periphery of the charging roller 22 so as to be 500 to 1,000 gausses as shown in the figure. There is. Of these magnetic poles, the magnetic pole of the charging portion closest to the photoconductor drum 10 is referred to as a main magnetic pole. The position of the main magnetic pole is the closest position between the charging roller 22 and the photosensitive drum 10, that is, near the center line connecting the center of the photosensitive drum 10 and the center of the charging roller 22, and the center of the charging roller 22. As a result of experiments, it has been found that the angle θ formed by the straight line connecting the magnetic poles and the center line is preferably in the range of −15 ° ≦ θ 2 ≦ 15 °.

Reference numeral 25 denotes a casing forming a storage portion for the magnetic particles 21, in which the charging roller 22 and the magnet body 23 are arranged, and at the outlet of the casing 25, the passage amount of the magnetic particles 21. A non-magnetic restricting plate 26, which is a restricting member for restricting the temperature, is provided to restrict the thickness of the layer of magnetic particles 21 attached to the charging roller 22 and carried out. The gap DB between the regulation plate 26 and the charging roller 22 is 0.2 mm or more 1.
The charging roller 22 is set to be 0 mm or less and the magnet body 23
The gap DI at the position facing the photosensitive drum 10 is 0.7 to 1.0 times DB, that is, 0.7DB≤D.
The speed may be lower than that of the image forming body in the same direction as the movement direction of the photosensitive drum 10 while being held within the range of I ≤ 1.0 dB, but it is preferably rotated at a peripheral speed of 1.2 to 2.0 times.

As a result, the carrying amount of the magnetic particles 21, that is, the existing amount of the magnetic particles 21 on the charging roller 22 in the charging area is 10 to 10.
Adjusted to 300 mg / cm ² . The gap DI between the photosensitive drum 10 and the charging roller 22 is a magnetic particle 21 whose thickness is regulated.
It is connected by the magnetic brush 21A. The stirring plate 27 is made of magnetic particles 21.
It is a rotating body having a plate-shaped member for correcting the deviation of No.

The photosensitive drum 10 comprises a conductive base material 10b and a photosensitive body layer 10a covering the surface thereof, and the conductive base material 10b is grounded.

Reference numeral 24 denotes a bias power source for applying a bias voltage between the charging roller 22 and the conductive base material 10b, and the charging roller 22 is grounded via the bias power source 24.

The bias power supply 24 is a power supply for supplying an AC bias voltage in which an AC component is superimposed on a DC component set to the same value as the voltage to be charged, and a gap DI between the charging roller 22 and the photosensitive drum 10. DI is 0.2 to 1.0 mm, although it varies depending on the size of, the charging voltage for charging the photosensitive drum 10, etc.
It is held between and is almost the same as the voltage to be charged -500V ~
By supplying an AC bias voltage in which a DC component of −1,000 V is superimposed with an AC component of 200 to 3,500 V and 0.3 to 10 KHz as a peak-to-peak voltage (V _PP ) through a protective resistor 28, a preferable charging condition can be obtained. I was able to get it. The bias power source 24 performs constant voltage control for the DC component and constant current control for the AC component.

Next, the operation of the charging device 20 described above will be described.

When the charging roller 22 is rotated in the same direction as the arrow at a peripheral speed of 1.2 to 2.0 times the peripheral speed of the photosensitive drum 10 while rotating the photosensitive drum 10 in the direction indicated by the arrow, the charge roller 22 adheres to the charging roller 22. The layer of the magnetic particles 21 conveyed is magnetically connected by a magnetic force line of the magnet body 23 at a position facing the photoconductor drum 10 on the charging roller 22 to form a kind of brush shape, which is a so-called magnetic brush 21A. It is formed. And this magnetic brush 21
A is a photosensitive drum that is conveyed in the rotation direction of the charging roller 22.
10 photoconductor layers 10a are contacted and rubbed. Since the AC bias voltage is applied between the charging roller 22 and the photoconductor drum 10, the photoconductor layer 10a passes through the conductive magnetic particles 21.
The electric charge is injected on the upper surface to perform charging. Especially in this case,
An oscillating electric field was formed by applying an AC bias, and the gap DB between the regulation plate 26 and the charging roller 22 was 0.2.
The photosensitive drum 10 is set to be 1.0 mm or more and 1.0 mm or less.
Since the gap DI at the position opposed to is regulated to 0.7 to 1.0 times that of DB, the amount of the magnetic particles 21 in the charging region is properly maintained and the efficiency of charge injection from the magnetic brush 21A is improved, and charging is performed. It is possible to make the area proper and perform extremely stable high speed and uniform charging without unevenness.

In the above embodiments, the charging roller
The results of changing the frequency and voltage of the AC voltage component applied to 22 are shown in FIG.

In FIG. 3, the range shaded by vertical lines is the range where dielectric breakdown is likely to occur, the range shaded by diagonal lines is the range where uneven charging is likely to occur, and the range not shaded is stable. This is a preferable range in which electrostatic charging is obtained. As is clear from the figure, the preferable range changes slightly depending on the change of the AC voltage component. The waveform of the AC voltage component is not limited to a sine wave, and may be a rectangular wave or a triangular wave. Further, in FIG. 3, the low frequency region shaded with dots is a range where uneven charging occurs due to the low frequency.

As the magnetic particles 21 in the above-mentioned embodiment, spherical ferrite particles coated so as to have conductivity are used. In addition, conductive magnetic resin particles obtained by pulverizing the magnetic particles and a resin as main components after thermal smelting can also be used. In order to perform good charging, the outer shape is spherical and the particle size is adjusted to 50 μm, the specific resistance is 10 ³ Ω · cm, and the frictional charge amount with the toner is −5 μC / g under the condition that the toner concentration is 1%. .

It is also possible to use the charging device 20 of this embodiment to eliminate the charge on the photosensitive drum 10. The static elimination can be performed by setting only the DC component of the bias voltage to zero. After the image formation, only the AC component is applied to rotate the image forming body to eliminate the charge on the photosensitive drum 10. When the charge removal of the photoconductor drum 10 is completed, the application of the AC component is stopped, and the magnetic pole of the magnet body 23 is rotated so as to be parallel to the tangent line of the facing portion of the photoconductor drum 10. Is parallel to the tangential direction of the portion facing the photoconductor drum 10 due to the horizontal magnetic field, and the magnetic particles 21 are transferred to the photoconductor drum.
The tip of the magnetic brush 21A can be separated from the photoconductor drum 10 without adhering to the ten circumferential surfaces.

Further, in the image forming method in which the above charging device is used as a cleaning device, reversal development is preferable to regular development in developing. This is because the toner is easily discharged from the charging device during charging, the discharged toner has the same polarity during reversal development, and is collected by the developing bias in the developing section, so that image fogging can be prevented.

The magnetic particles 21 of the toner remaining on the surface of the photoconductor drum 10 without being cleaned due to long-term use.
In many cases, the magnetic brush 21A is highly mixed with the layer and the resistance of the magnetic brush 21A is increased, so that the charging efficiency is deteriorated. This includes the charging roller when the photosensitive drum 10 rotates before or after image formation.
If the polarity of the DC bias voltage applied to 22 is set high or the AC voltage is set high, the toner is
It is possible to prevent the toner from being mixed by setting conditions in which the toner easily adheres. In particular, when the photosensitive drum 10 has the same polarity as the toner, such as in an image forming apparatus that performs reversal development, the toner polarity in the developing device 30 is the same as that of the toner. It does not appear as a fog in the image and is a very suitable combination.

Further, the carrier for the magnetic brush 21A is not limited to the structure of the charging roller 22 having the magnet body 23 therein, but the magnet body 23 is rotated and the charging roller 22 is not provided. It may be composed of only the magnetized magnet body 23.

[0052]

According to the present invention, since the image forming body is charged by directly injecting the electric charge through the magnetic brush formed on the carrier, the bias voltage can be lowered and the generation of ozone can be prevented. Further, the gap DB between the restriction member and the carrier is set to be 0.2 mm or more and 1.0 mm or less,
The gap DI at the position where the carrier and the image forming body face each other is DB.
Since the oscillating electric field is formed between the magnetic brush and the image forming body as a bias electric field, the amount of the magnetic particles forming the magnetic brush in the charging area is properly maintained. The magnetic particles are not clogged to prevent the charging area from unnecessarily expanding and overcurrent from occurring, preventing the dielectric breakdown of the image forming body and the adhesion of the magnetic particles to the image forming body. It is possible to provide an image forming apparatus capable of performing extremely stable and uniform charging without unevenness.

[Brief description of drawings]

FIG. 1 is a sectional view showing the outline of the configuration of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the charging device of FIG.

FIG. 3 is a charging characteristic diagram when a frequency and a voltage of an AC voltage component are changed.

[Explanation of symbols]

 10 Photosensitive drum (image forming body) 20 Charging device 21 Magnetic particles 21A Magnetic brush 22 Charging roller (conveying carrier) 23 Magnet body 24 Bias power supply 26 Regulation plate (regulation member) 28 Protection resistance

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masakazu Fukuchi 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Shizuo Morita 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Invention Noriyuki Hiroshi Nomori 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (3)

[Claims] 1. An image forming apparatus for charging an image forming body by supplying magnetic particles onto a carrier to form a magnetic brush, and placing the magnetic brush on the carrier under an oscillating electric field. When the gap between the regulation member that regulates the passage amount of the image carrier and the transport carrier is DB and the gap between the image forming body and the transport carrier is DI, 0.7DB≤DI≤1.0DB Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the DB is 0.2 ≦ DB ≦ 1.0 (mm). 3. An image forming apparatus for charging an image forming body by supplying magnetic particles onto a carrier to form a magnetic brush, and placing the magnetic brush on the carrier under an oscillating electric field. The surface roughness of the carrier for carrying
An image forming apparatus having a size of 15 μm.