JPH09325564A - Electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent such a developing action that the after image of the toner image of a former process is added to the toner image of a next process and visualized from being executed and to prevent the electrifying voltage of a photoreceptor from being locally electrified high or low. SOLUTION: When toner left after a transfer action is recovered by a magnetic brush 2a arranged on an upstream side, a circulation path for recovering magnetic grains 23 leaked from the brush 2a by a magnetic brush 2b arranged on a downstream side and returning them to the brush 2a on the upstream side from the brush 2b on the downstream side is formed. In such a case, the toner fetched by the brush 2b arranged on the most downstream side in the rotating direction of the photoreceptor is discharged by impressing a DC voltage on the brush 2b on the most downstream side. Besides, the photoreceptor 1 is electrified by impressing a bias obtained by superimposing an AC component on a DC component on at least one brush 2a on the upperstream side than the brush 2b on the most downstream side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device in which a transfer residual toner on a member to be charged is recovered by a developing device at the time of development in the next process.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been used as a charging device in an electrophotographic image forming apparatus. In recent years, a contact charging device has been put into practical use instead of this. This is characterized by low ozone and low power consumption. Among them, the roller charging method using a charging roller as a charging member has the advantage that the charging is stable and the amount of ozone generated is about 1/1000 of that of a corona charger. Therefore, it is suitable for an office environment and has been widely used in recent years.

However, even in such a contact charging device, the essential charging mechanism is a discharge phenomenon from a charging member to a drum type electrophotographic photosensitive member (hereinafter simply referred to as "photosensitive member") as a member to be charged. Therefore, the voltage applied to the charging member needs to have a value obtained by superposing the charging start voltage Vth on the surface potential Vd of the photoconductor, and a slight amount of ozone is generated. In addition, when AC charging is performed for uniform charging, further ozone is generated, and vibration or noise is generated between the contact charging member and the photoconductor due to the electric field of AC voltage (hereinafter referred to as “AC charging sound”). And the deterioration of the surface of the photoconductor due to the discharge became remarkable, which was a new problem.

Therefore, as a new charging method, a charging method by directly injecting an electric charge into a photosensitive member is disclosed in Japanese Patent Laid-Open No. 6-392.
It is disclosed in Japanese Patent Publication No. In this charging method, a voltage is applied to a contact charging member such as a charging roller, a charging brush, and a charging magnetic brush, and charges are injected into the conductive particles of the charge injection layer that is the surface layer of the photoconductor to perform contact injection charging (charge injection). The charging voltage is only the surface potential of the desired photoconductor because the discharge phenomenon is not used, and the amount of ozone generated is less than 1/10 of that of the roller charging method. There is. A fur brush type or a magnetic brush type using magnetic particles is well suited as a charging device used in the contact injection charging method.

By the way, recently, there has been proposed an image forming apparatus utilizing a so-called cleanerless process in which the transfer residual toner on the photoconductor is reused by utilizing this configuration. This cleanerless process is a process in which the transfer residual toner adhering to the photoconductor is collected by the developing device at the time of development in the next process.

As shown in FIG. 3, the image forming apparatus is provided with a contact charging member 2, a reversal developing device 3, and a transfer roller 4 as a transfer member in order along the rotation of the photosensitive member 1 in the direction of the arrow R1. Laser exposure light L for forming an electrostatic latent image on the photoconductor 1 which is primarily charged by the contact charging member 2.
The transfer paper P as a recording material is transferred to the transfer paper P by passing through an exposure unit (not shown) for irradiating the toner and a transfer portion between the photoconductor 1 on which the toner image is formed and the transfer roller 4. Further, the fixing device 5 for thermally fixing the unfixed toner image is provided. In the image forming apparatus shown in FIG. 3, the photosensitive member 1, the contact charging member 2, and the reversal developing device 3 are integrally housed in a cartridge container 6, and the cartridge container 6 is detachably attached to the apparatus main body. It is a cartridge type.

What is important for this cleanerless process is to collect the transfer residual toner in the reversal developing device 3, but for that purpose, it is a major premise that the transfer residual toner has the same charging polarity as that at the time of development. . However, in general, the charge polarity of the transfer residual toner is affected by the transfer charge, and is often the same as the polarity of the transfer charge, that is, the polarity opposite to the charge polarity of the development. When the transfer residual toner enters the developing area with the opposite polarity as described above, it is not collected by the reversal developing device 3 and stains the next process image.

The charging performance itself is also susceptible to transfer, and the presence of transfer residual toner prevents the charge injection layer of the photosensitive member from being efficiently charged by contact injection, resulting in poor charging. Therefore, the finish of the charging process differs depending on whether the toner image was present last time or not. For this reason, when the next development process is started with uneven charging caused by different finishes in the charging process, the residual image of the toner image of the previous process is added to the toner image of the next process and becomes visible (ghost ) Occurs. That is, in order to realize the cleanerless process, is there an ability to charge the surface of the photoconductor directly below the transfer residual toner, that is, the ability to move the transfer residual toner or to charge the transfer residual toner below it? (Charging capacity U
P) and normalizing the charging polarity of the transfer residual toner by the developing process of the next process (normalizing the charging polarity of the toner).

It has been found that the transfer residual toner is collected by the magnetic brush, since the transfer residual toner is achieved by contacting the transfer residual toner with the magnetic particles of the magnetic brush. Further, as a countermeasure for the charging ability UP, AC contact injection charging, which has a capability of actively moving the charging carrier during the charging process to remove residual toner after transfer or a capability of high charging performance, can be considered. Compared to the DC contact injection charging method, the AC contact injection charging method exhibits more stable charging performance even when the contact charging member is deteriorated in durability or the environment changes. Therefore, recently, research on the AC contact injection charging system has been particularly advanced. It is known that the contact injection charging method does not significantly increase the ozone generation amount as compared with DC, unlike the roller charging method, even if an AC bias is applied. The reason is that the roller charging method has a gap between the round solid charging roller and the photosensitive member, in which discharge is likely to occur, whereas the contact charging method using magnetic particles is DC When a bias or an AC bias is applied, the charged fluid magnetic particles forming the magnetic brush are attracted by the opposite charges injected into the photoconductor and move in large amounts, forming a larger contact area than the roller charging method. However, it is considered that the magnetic brush roller and the photoconductor are completely in close contact with each other, and there is no gap in which discharge occurs.

As an AC bias system, Japanese Patent Laid-Open No. 4-21
873 and Japanese Patent Laid-Open No. 4-116674 disclose a magnetic brush charging device for charging an object to be charged by applying an AC bias voltage containing a DC component to the magnetic brush.
The most frequently used type of AC contact injection charging is a DC voltage component near the desired charging potential of several hundreds to several kiloHz.
The AC component having a frequency of 1 and a peak-to-peak voltage Vpp of about the same level is superimposed. For example, a peak voltage Vpp of 1 kV at a frequency of 1 kHz to a DC voltage of 700 V
It is known that the AC effect is higher as the peak-to-peak voltage Vpp is higher.

However, in this AC contact injection charging method, if a voltage Vpp that ensures a desired charging performance is used, the charged surface of the photoconductor is locally charged higher or lower by the voltage Vpp. Therefore, fog (AC fog) may occur. The AC contact injection charging method has a problem that the collected toner is not discharged.

Further, in the AC contact injection charging system, there is a tendency that the transfer residual toner is collected and accumulated in the contact injection charging device without being discharged to the outside, and as a result, the AC contact charging is performed. The electric resistance of the injection charging device is increased and the charging performance is deteriorated, so that problems such as the inability to obtain a desired charging potential and the generation of ghosts will occur even in the AC contact injection charging method.

Therefore, JP-A-4-371975-37
A charging device in which two fur brushes as described in Japanese Patent Publication No. 1977 have been separated into a function for stirring the transfer residual toner and a function for charging the transfer residual toner has been considered. However, there is a problem that the unevenness of the sweep is fatally formed.

There has been considered a charging device as disclosed in Japanese Patent Laid-Open No. 6-348107, in which a charging magnetic brush is arranged on the upstream side and a fur brush for collecting magnetic particles leaked from the upstream magnetic brush is arranged on the downstream side. In such a charging device, since the fur brush having a coarse sweep is arranged on the downstream side, there is a problem that uneven sweep of charging occurs.

For this reason, a charging device has been considered in which two magnetic brushes, as shown in Japanese Patent Application Laid-Open No. 6-161121, in which uneven sweeping is unlikely to occur, are functionally separated for collecting magnetic particles and for charging.

[0016]

However, it has been found that the charging device disclosed in Japanese Unexamined Patent Publication No. 6-161211 has the following problems.

1. When about 3000 copies are made, the amount of magnetic particles in the magnetic brush is reduced and the charging performance is deteriorated.

2. If the moving direction of the magnetic brush relative to the surface of the photoconductor is even in the same direction, a large amount of magnetic particles will leak from the magnetic brush.

3. Since the magnetic particles flow in opposite directions between the two magnetic brushes, the magnetic particles will stay in contact with each other unless the distance between the magnetic brushes is considerably increased.
Since the magnetic particles do not circulate, the magnetic particles are immediately removed from the sleeve portion where the magnetic particles are not carried, causing charging failure and ghost. For this reason, a compact structure becomes difficult.

4. Accumulation of the transfer residual toner in the charging device is unavoidable, and the resistance value increases and the charging performance deteriorates. There are problems such as the above, and these problems are important matters that must be solved in order to supply a compact and economical cleanerless charging device.

The present invention has been made in order to solve the above problems, and a phenomenon in which a residual image of a toner image of a previous process is superimposed on a toner image of a next process to be visualized and a member to be charged has a problem. An object of the present invention is to provide a charging device capable of eliminating charging unevenness on a charging surface and improving charging performance.

[0022]

In order to achieve the above object, a charging device according to claim 1 of the present invention is designed such that magnetic particles are attached to contact a charged body to directly inject charges. A plurality of rotatable magnetic brushes to which a voltage is applied, wherein opposite magnetic poles are arranged on opposite magnetic poles of adjacent magnetic brushes so as to transfer the magnetic particles between the plurality of magnetic brushes. The moving direction of the side contacting the charged body with the transfer of the magnetic particles is opposite to the moving direction of the surface of the charged body facing the magnetic brush.

According to a second aspect of the present invention, as a power source applied to the plurality of magnetic brushes, a DC bias power source for applying a DC voltage to the magnetic brush located on the most downstream side in the rotation direction of the charged body. A bias power supply to which a voltage in which a direct current component and an alternating current component are superimposed is applied to at least one magnetic brush upstream of the most downstream magnetic brush.

According to a third aspect of the present invention, as a power source applied to the plurality of magnetic brushes, a DC bias power source for applying a DC voltage to the magnetic brush located on the most downstream side in the rotating direction of the charged body. A bias power supply for applying a DC voltage higher than a DC voltage applied to the most downstream magnetic brush to at least one magnetic brush upstream from the most downstream magnetic brush.

According to a fourth aspect of the present invention, the magnetic brush includes a magnet member, a magnetic particle carrier that relatively rotates the outer periphery of the magnet member, and magnetic particles attached to the magnetic particle carrier. It is equipped with and.

According to the fifth aspect of the present invention, the plurality of magnetic brushes contacting each other along the rotation direction of the member to be charged are arranged such that the magnet members adjacent to each other and facing each other are opposite in polarity.

According to a sixth aspect of the present invention, a DC voltage having the same polarity as that when the charged body is charged is applied to the magnetic brush between sheets during image formation.

[Operation] Based on the above configuration, when the transfer residual toner is collected by the upstream magnetic brush, the magnetic particles leaked from the upstream magnetic brush are collected by the downstream magnetic brush, and the magnetic particles are collected. To form a circulation path from the magnetic brush on the downstream side to the magnetic brush on the upstream side.
In this case, a DC voltage is applied to the magnetic brush on the most downstream side in the rotating direction of the body to be charged to eject the toner taken in by the magnetic brush on the most downstream side, and at the same time, upstream from the most downstream magnetic brush. A bias in which an alternating current component is superimposed on a direct current component is applied to at least one magnetic brush on the side to charge the body to be charged.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus to which a charging device according to an embodiment of the present invention is applied.
FIG. 4 is a sectional view illustrating the principle of charge injection charging.

First, the principle of charge injection charging, which is the charging method of the present invention, will be described.

Charge injection is a medium resistance magnetic brush.
Charge injection is performed on the surface of the photoconductor having medium resistance, and in this case, charges are not injected to the trap potential of the surface material of the photoconductor, but are charged to the conductive particles of the charge injection layer. This is a method of charging.

Specifically, as shown in FIG. 2, a minute capacitor having the charge transport layer 1a as a dielectric and the aluminum substrate 1d and the conductive particles (SnO ₂ ) 1b in the charge injection layer 1c as both electrode plates. In addition, it is based on the theory that the electric charge is charged by the magnetic brush 2. At this time, the conductive particles 1b are electrically independent from each other and form a kind of minute float electrode. For this reason, the surface of the photoconductor 1 seems to be charged and charged to a uniform potential on a macroscopic scale, but in reality, countless minute SnO ₂ particles that have been charged seem to cover the surface of the photoconductor 1. It is a situation. Therefore, even if image exposure is performed by the laser exposure light L, each SnO
_{Since the two} particles are electrically independent, they can hold an electrostatic latent image.

Next, the image forming apparatus of this embodiment will be described.

The image forming apparatus of this embodiment shown in FIG. 1 is a laser beam printer utilizing an electrophotographic process.
In FIG. 3, the same components as those in FIG. 3 are designated by the same reference numerals to omit redundant description. In the figure, the photosensitive member 1 of the present embodiment is an OPC photosensitive member having a diameter of 30 mm, and is rotationally driven in the clockwise direction indicated by an arrow R1 at a process speed (peripheral speed) of 150 mm / sec. The two magnetic brushes 2a and 2b are in contact with the photoconductor 1.

The magnetic brushes 2a and 2b are electrode sleeves 21a and 21 as rotatable non-magnetic magnetic particle carriers.
The magnets 22a and 22b as magnet members are included in b and arranged, and the magnetic particles 23 are attached by the magnetic force of the magnets 22a and 22b. The one magnet 22a is divided into, for example, two pieces in the longitudinal direction, and the magnetic poles are in contact with each other such that the magnetic poles are N poles and N poles, while the other magnet 22b is divided into two pieces, for example, in the longitudinal direction. The magnetic poles have a repulsive structure in which the same poles are in contact with each other such as S pole and S pole, and the magnetic pole of the magnet 22a of one magnetic brush 2a and the magnetic pole of the magnet 22b of the other adjacent magnetic brush 2b are arranged. The opposite poles are arranged so as to face each other in the relationship of N pole and S pole.

By constructing the magnets 22a and 22b in this manner, the magnetic particles 23 are arranged between the electrode sleeves 21a and 21b in a belt shape as shown in FIG. As a result, the magnetic particles 23
It smoothly circulates between the two electrode sleeves 2a and 2b,
The density of the transfer residual toner contained in the magnetic particles 23 is almost equal in any of the two magnetic brushes 2a and 2b. The necessary condition for circulating the magnetic particles 23 is that the magnetic particles 2 are between the two electrode sleeves 21a and 21b.
3 is to be given and received, and the magnetic particles 2 having a completely equal amount
3 is not exchanged between the electrode sleeve 21a and the electrode sleeve 21b. That is, it need not be a perfect belt.

The magnetic brush 2a has a DC voltage of -700V from the charging bias applying power source S1a at 1000 Hz,
A bias in which an AC voltage of 1000 Vpp between peaks is superimposed is applied to perform highly efficient charging. It is easy to collect the residual toner after transfer under high-efficiency charging conditions, and the magnetic particles 2
3 is easy to leak. A bias of DC voltage of -700V is applied to the magnetic brush 2b from the charging bias applying power source S1b to uniformly charge the outer peripheral surface of the photoconductor 1 to approximately -700V by charge injection charging. At the time of DC charging, the transfer residual toner has returned to the same polarity as that at the time of development due to friction with the magnetic particles 23, so that the toner is easily discharged and the magnetic particles 23 are easily collected (actually, the tip of the magnetic brush 2b). It is necessary to optimize the condition of the difference between the partial potential and the surface potential of the photosensitive member 1). With the above configuration,
Ozone-less and cleaner-less processes could be realized without producing the above-mentioned ghost. Other processes and materials are described in detail below.

On the charged surface of the photosensitive member 1, laser exposure is performed in which the intensity is modulated corresponding to the time series electric digital pixel signal of the image information from a laser beam scanner (not shown) including a laser diode and a polygon mirror. Light L
Is output, and an electrostatic latent image corresponding to target image information is formed on the peripheral surface of the photoconductor 1. This electrostatic latent image is developed as a toner image by the reversal developing device 3 using magnetic one-component insulating toner (negative toner). The reversal developing device 3 includes a non-magnetic developing sleeve 3 having a diameter of 16 mm and containing a magnet 3b.
a. The developing sleeve 3a is coated with the negative toner, and the distance from the surface of the photoconductor 1 is set to 30.
While being fixed at 0 μm, the photoconductor 1 rotates at the same speed as the peripheral speed. The developing sleeve 3a receives a DC voltage of -500V from the developing bias power source S2 and a frequency of 18
A developing bias voltage on which a rectangular AC voltage of 00 Hz and a peak-to-peak voltage of 1600 Vpp is superimposed is applied, and jumping development is performed with the photoconductor 1.

On the other hand, the transfer paper P supplied from a paper supply unit (not shown) is brought into pressure contact with the photoconductor 1 and a medium resistance transfer roller 4 which is in contact with the photoconductor 1 with a predetermined pressing force. It is introduced into the nip portion (transfer portion) T at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 4 from a transfer bias application power source S3. In this embodiment, the transfer roller 4 having a resistance value of 5 × 10 ⁸ Ω is used.
Transfer is performed by applying a DC voltage of 1000V.

After the transfer paper P is introduced, the transfer section T transfers the toner images carried on the surface of the photoconductor 1 by sandwiching and conveying the transfer paper P to the surface of the transfer paper P sequentially by electrostatic force and pressing force. The force acting on the toner on the photoconductor 1 during the transfer of the toner image is not only the transfer electric field due to the transfer bias but also the photoconductor 1.
Adhesive to the surface of. Therefore, the toner is 100%
It is not transferred and remains as untransferred toner on the photoconductor 1 without being transferred, and is conveyed as the photoconductor 1 rotates.

The transfer paper P on which the toner image has been transferred is separated from the surface of the photosensitive member 1 and fixed by a fixing device 5 such as a heat fixing system.
The unfixed toner image is fixed and printed,
It is discharged outside the apparatus as an image-formed product such as a copy.

In the image forming apparatus according to the present embodiment, the cartridge container 6 includes the three process devices of the photoconductor 1, the magnetic brushes 2a and 2b, and the developing device 3, and is collectively attached to and detached from the main body of the image forming device. Although it has been described that the process cartridge system is replaceable, the invention is not limited to this.

Next, the photoconductor 1 used in this embodiment will be described.

The photoreceptor 1 is a negatively charged OPC photoreceptor,
The following first to fifth functional layers are formed in order from the bottom on a drum base made of aluminum having a diameter of 30 mm.

The first layer is an undercoating layer and has a thickness of about 20 μm and is provided to smooth defects such as the drum substrate and prevent moire due to reflection of the laser exposure light L. It is a conductive layer.

The second layer is a positive charge injection preventing layer, which plays a role of preventing the positive charges injected from the drum substrate from canceling out the negative charges charged on the surface of the photoconductor 1, and the amylan resin and methoxymethyl. 1 x 10 depending on nylon
It is a medium resistance layer with a thickness of about 1 μm adjusted to about ⁶ Ωcm.

The third layer is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.
By receiving the laser exposure light L, positive and negative charge pairs are generated.

The fourth layer is a charge transport layer, which is a polycarbonate resin in which hydrazone is dispersed, and is a P-type semiconductor. Therefore, negative charges charged on the surface of the photoconductor 1 cannot move through this layer, and only positive charges generated in the charge generation layer can be transported to the surface of the photoconductor 1.

The fifth layer is a charge injection layer, which is a coating layer of a material in which ultrafine particles of SnO ₂ are dispersed in a photocurable acrylic resin. Specifically, doping with antimony,
This is a coating layer of a material in which 70% by weight of SnO ₂ particles 1b having a reduced resistance and a particle size of about 0.03 μm are dispersed in a resin. The coating solution thus prepared was applied to a thickness of about 2 μm by a dipping coating method to form a charge injection layer.

Next, the magnetic brush used in this embodiment will be described.

The magnetic brushes 2a, 2b include a rotatable non-magnetic electrode sleeve 21a, 21b and a magnet 22a,
The magnetic particles 23 are attached by the magnetic force of 22b. The magnetic flux density by the magnets 22a and 22b on the electrode sleeves 21a and 21b is 800 × 10.
^-4 T (Tesla).

The magnetic particles 23 on the electrode sleeves 21a and 21b are coated with a thickness of 1 mm to form a charging nip with a width of about 5 mm between the magnetic particles 23 and the photosensitive member 1, and the direction of the arrow R2 shown in FIG. It contacts the surface of the photoconductor 1 while rotating in the counter direction with respect to the surface of 1. The amount of the magnetic particles 23 of the magnetic brushes 2a and 2b in this embodiment is about 10
g, the nip N between the electrode sleeve 21b and the photoconductor 1
The gap at p is 500 μm. Here, the peripheral speed ratio between the magnetic brushes 2a and 2b and the photoconductor 1 is defined by Equation 1.

[0053]

## EQU1 ## Peripheral speed ratio (%) = {(magnetic brush peripheral speed−photoconductor peripheral speed) / photoconductor peripheral speed} × 100 However, the peripheral speed of the magnetic brushes 2a and 2b is a negative value in the case of counter rotation. .

When the peripheral speed ratio is -100%, the magnetic brushes 2a and 2b are in a stopped state. Therefore, the shapes of the stopped magnetic brushes 2a and 2b on the surface of the photoconductor 1 are not charged properly. And appear in the toner image.
When the magnetic brushes 2a and 2b rotate in the forward direction, the rotational speed of the magnetic brushes 2a and 2b must be increased to obtain the same peripheral speed ratio as in the counter direction. When the magnetic brushes 2a and 2b rotate in contact with the photoconductor 1 in a forward rotation at a low peripheral speed, the magnetic particles 23 of the magnetic brushes 2a and 2b easily adhere to the photoconductor 1. Therefore, the peripheral speed ratio is preferably −100% or less, and is set to −150% in the present embodiment.

As the magnetic particles 23 of the magnetic brushes 2a and 2b, * the ones obtained by kneading resin and a magnetic fluid such as magnetite to form particles, or the ones in which conductive carbon or the like is mixed to adjust the resistance value. , * Sintered magnetite, ferrite, or those whose resistance value is adjusted by reducing or oxidizing them, * Coating material whose resistance is adjusted to the above-mentioned magnetic particles 23 (such as one in which carbon is dispersed in phenol resin) For example, a coat or a metal such as Ni is plated to adjust the resistance value to an appropriate value. If the resistance value of these magnetic particles 23 is too high, electric charges cannot be uniformly injected into the photoconductor 1 and a fog image is formed due to minute charging failure. If the resistance value is too low, the surface of the photoconductor 1 is pinched. When there is a hole, current concentrates on the pinhole, the charging voltage drops, and the surface of the photoconductor 1 cannot be charged, resulting in charging nip-shaped charging failure. Therefore, the resistance value of the magnetic particles 23 is preferably 1 × 10 ⁴ to 1 × 10 ⁷ Ω. The resistance value of the magnetic particles 23 is determined by placing 2 g of the magnetic particles 23 in a metal cell (bottom area 228 mm ² ) to which a voltage can be applied and then applying a weight.
The voltage was measured by applying 1 to 1000 V.

Regarding the magnetic characteristics of the magnetic particles 23, in order to prevent the magnetic particles 23 from adhering to the photoreceptor 1, it is better to increase the magnetic binding force, and the saturation magnetization is 50 (A · m ² / k).
g) or more is desirable.

Actually, the magnetic particles 2 used in the present embodiment
No. 3 has an average particle size of 30 μm and a resistance value of 1 × 10 ⁶ Ω,
The saturation magnetization was 58 (A · m ² / kg). <Second Embodiment> In FIG. 1, an image forming apparatus according to the second embodiment is different from the image forming apparatus shown in FIG. ) Is applied, and other components are the same as those in the first embodiment.

By applying a high DC bias from the power source S1a, the toner polarity after transfer is opposite to the charging polarity of the magnetic brush 2a, so the magnetic brush 2a is applied with a high DC bias and adheres to the photoconductor 1. It is considered that the transfer residual toner that has been transferred is sucked up by the magnetic brush 2a and the surface of the photoconductor 1 can be uniformly charged. At this time, it was confirmed by measurement that the charging potential of the photoconductor 1 was about -630V. The absorbed transfer residual toner is normally charged by friction with the magnetic particles 23, and is conveyed to the magnetic belt and guided to the magnetic brush 2b. When the applied bias of the magnetic brush 2b is set to -700V or the like, the toner negatively charged by the potential difference between the potential of about -700V at the tip of the magnetic brush 2b and the charging potential of -630V of the photoconductor 1 is transferred to the photoconductor 1. Will be exhaled.
After passing through the magnetic brush 2b, the surface of the photoconductor 1 is a target −
It will be charged to about 700V. <Third Embodiment> In the third embodiment, a DC bias having the same polarity as the discharging polarity for discharging is applied to the magnetic brush 2a between papers where no transfer residual toner is present. That is, the transfer residual toner collected by the magnetic brush 2a is not immediately discharged from the downstream magnetic brush 2b, but is discharged after circulating the belt-shaped magnetic particles 23, which takes time, It may be necessary to effectively eject the collected toner. As a supplementary means, it has been found that it is preferable to apply a DC bias having the same polarity as that at the time of charging for discharging to the magnetic brush 2a between the papers where no transfer residual toner is left.

[0059]

As described above, according to the charging device of the present invention, when the transfer residual toner is collected by the upstream magnetic brush, the magnetic particles leaked from the upstream magnetic brush are collected in the downstream magnetic brush. Since the circulation path for returning the magnetic particles from the magnetic brush on the downstream side to the magnetic brush on the upstream side is formed, the following effects can be obtained.

1. It is possible to prevent the retention of magnetic particles between the magnetic brushes.

2. The distance between the magnetic brushes can be reduced and a compact structure can be achieved.

3. The transfer residual toner collected by the upstream magnetic brush can be returned to the downstream magnetic brush.

4. Since the magnetic particles leaking from the upstream magnetic brush are collected by the most downstream magnetic brush,
It is possible to sufficiently apply a bias that improves the charging performance to the upstream magnetic brush.

There are advantages such as

Further, a DC voltage is applied to the magnetic brush on the most downstream side in the rotating direction of the body to be charged to eject the toner taken in by the magnetic brush on the most downstream side, and the magnetic brush on the most downstream side is discharged. Since the charged object is charged by applying a bias in which an alternating current component is superimposed on a direct current component to at least one magnetic brush on the upstream side, the charged object can be uniformly charged without ozone, and a ghost image can be obtained. And the charging performance without AC fog or uneven sweep can be obtained.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view illustrating the principle of charge injection charging according to the present invention.

FIG. 3 is a schematic configuration diagram showing an image forming apparatus of a conventional typical injection charging cleanerless process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charged object (photoreceptor) 2a Magnetic brush 2b Magnetic brush 21a Magnetic particle carrier (electrode sleeve) 21b Magnetic particle carrier (electrode sleeve) 22a Magnet member (magnet) 22b Magnet member (magnet) 23 Magnetic particle

Claims (6)

[Claims] 1. A charging device having a plurality of rotatable magnetic brushes to which magnetic particles are attached and to which a voltage is applied so as to directly inject charges by contacting a body to be charged, wherein a plurality of magnetic brushes are provided between the plurality of magnetic brushes. The opposite magnetic poles are arranged on the opposite magnetic poles of the adjacent magnetic brushes so as to transfer the magnetic particles, and the moving direction of the side in contact with the charged body due to the transfer of the magnetic particles faces the magnetic brush. The charging device is characterized in that the charging direction is opposite to the moving direction of the surface of the charged body. 2. A DC bias power source for applying a DC voltage to the magnetic brush located on the most downstream side in the rotating direction of the charged body, as a power source applied to the plurality of magnetic brushes, and a DC bias power source for the most downstream side. The charging device according to claim 1, further comprising: a bias power supply to which a voltage obtained by superimposing an alternating current component on a direct current component is applied to at least one magnetic brush upstream of the magnetic brush. 3. A DC bias power source for applying a DC voltage to the magnetic brush located on the most downstream side in the rotation direction of the body to be charged, as a power source applied to the plurality of magnetic brushes, and a DC bias power source for the most downstream side. 2. A bias power supply for applying a DC voltage higher than a DC voltage applied to the most downstream magnetic brush to at least one magnetic brush upstream of the magnetic brush. Charging device. 4. The magnetic brush includes a magnet member, a magnetic particle carrier that relatively rotates the outer periphery of the magnet member, and magnetic particles attached to the magnetic particle carrier. The charging device according to claim 1. 5. The charging according to claim 1, wherein a plurality of magnetic brushes contacting each other along the rotation direction of the body to be charged are arranged such that the magnet members adjacent to and facing each other are opposite in polarity. apparatus. 6. The charging device according to claim 1, wherein a DC voltage having the same polarity as that when the charged body is charged is applied to the magnetic brush between sheets during image formation.