JPH06186892A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of recovering toner with a simple constitution and attaining an extreme stable uniform electrification without generating ozone. CONSTITUTION:The image forming device is arranged with an electrifier 20 by a magnetic brush served also as a cleaning means, a toner recovering roller 53, a scraper blade 54, an exposing part 15 and a developing unit 30 in the periphery of a photosensitive drum 10. The electrifier 20 served also as the cleaning means is arranged at the upper side of the developing unit 30, and the toner recovered from the photosensitive drum 10 passes an image exposing path and is dropped and recovered in the developing unit 30.

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. In addition, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. Furthermore, the corona charger generates noise due to high voltage, and the electrophotographic image is used as a communication terminal or an information processing device. This is a major drawback when using a forming 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. The charging device can also clean the image forming body by applying a bias voltage having a polarity opposite to that of the charging of the toner of the developer to the magnetic brush.

In the conventional image forming apparatus, the toner of the developer collected at the time of cleaning is processed by first storing the collected toner in a waste toner box and then sending the collected toner to the developer or the toner pool of the developing apparatus or directly in the developing apparatus. Although the toner is sent to the pool of the developer or the toner, it has a complicated structure because a special conveying device is used for this toner recovery cycle.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a toner recovery cycle of a developer, which has a complicated structure in a conventional apparatus, is performed with a simple structure, and there is no dielectric breakdown of an image forming body or generation of ozone. An object of the present invention is to provide an image forming apparatus capable of performing extremely stable and uniform charging.

[0008]

An object of the present invention is to provide an image forming apparatus in which a cleaning means, an exposing means and a developing means are arranged around an image forming body, wherein the cleaning means is arranged above the developing means and the image is formed. This is achieved by an image forming apparatus characterized in that the toner collected from the formed body falls through the image exposure passage and is collected by the developing means.

Further, the spill prevention plate prevents the collected toner from falling during the exposure of the exposing means, while the collected toner is dropped by the operation of the spill prevention plate during the non-exposure of the exposing means, and the cleaning. The above-mentioned image forming apparatus is characterized in that the means also serves as the charging means, and the spill prevention plate opens the image exposure passage in synchronization with the image exposure of the exposing means.

[0010]

In the present invention, the cleaning means is disposed above the developing means, and the toner collected from the image forming body falls through the image exposure passage and is collected by the developing means. Therefore, the toner recovery cycle of the developer can be realized with a simple configuration.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) A first 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 configuration of an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 10 is an image forming member that rotates in the direction of the arrow (clockwise), and the (-) charged O
A charging device 20, which is a photosensitive drum composed of a PC, and which is a charging unit that also serves as a cleaning unit, which will be described later, on the peripheral portion thereof,
A toner collecting roller 53, a scraper blade 54, a spill prevention plate 17, an exposure unit 15 on which the image light L from the exposure device enters, a developing device 30 as a developing unit, a transfer belt 13, and the like are provided.

The photosensitive drum 10, the charging device 20, the toner collecting roller 53, the scraper blade 54, and the spill prevention plate 1
7. The developing device 30 is integrated into the process cartridge 18 as a process member for image formation and is detachably attached to the main body of the apparatus, and the charging device 20 also serving as a cleaning unit is disposed above the developing device 30 and is a photoconductor. Drum 10
The toner thus collected is arranged so as to fall through the image exposure passage and be collected in the developing device 30. The guide member 18A, 18B protruding to the side of the process cartridge 18 is fitted and guided by the guide member 19A, 19B provided on the main body of the apparatus to be attached / detached. When the process cartridge 18 is attached to the apparatus main body, the power transmission system is engaged, the connector is connected to the power supply unit or the control unit, and image formation is enabled.

The spill prevention plate 17 normally closes the exposure window 18C of the process cartridge 18 by an elastic member such as a spiral spring (not shown) as shown by the solid line in FIG. Although it is possible to drop through the developing device 30 through the rotating device, the rotating means (not shown) resists the force of the elastic member at the time of exposure and rotates clockwise about the rotating shaft 17a at the position shown by the broken line in FIG. The exposure window 18C and the image exposure passage are opened by being turned to a tray for receiving falling toner to prevent toner spillage.

The holding roller 13A of the transfer belt 13 is located below the holding roller 13A about the rotation axis of the holding roller 13B by an elastic member (not shown) except when the process cartridge 18 is detached and during transfer. Thus, it is separated from the peripheral surface of the photosensitive drum 10. At the time of transfer, the holding roller 13A is rotated counterclockwise against the force of the elastic member by, for example, a solenoid or a motor that operates under the control of the apparatus body control unit, and the transfer belt 13
Is brought into contact with the photosensitive drum 10 with a predetermined pressure.

It should be noted that the spill prevention plate 17 may be configured to open and close in conjunction with attachment / detachment of the process cartridge.

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. In the exposure unit 15, the image light L of, for example, a laser beam from the image recording unit or the like is formed on the photosensitive drum 10.
The writing of the image is performed by, 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 adheres to the outer circumference of the developing sleeve 31 which is outside the magnet roller 32 and rotates to a magnetic field of the developer. 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 to form a toner image. The developing device 30 is not limited to the two-component developer and may be a one-component developer.

From the paper feed cassette 40, the recording papers P are fed one by one by a 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 belt 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 the fixing device 43 through the carrying means,
It is nipped by a heat fixing roller and a pressure roller, melted and fixed, and then discharged to the outside of the apparatus. The surface of the photosensitive drum 10 which rotates with the toner remaining without being transferred to the recording paper P is cleaned by the magnetic brush 21A of the charging device 20 which is switched to the bias voltage for cleaning and is ready for the next image recording. stand by.

The toner collected by the magnetic brush 21A of the charging device 20 is transferred to the toner collecting roller 53 to which a bias voltage having a polarity opposite to that of the toner is applied, and is scraped by the scraper blade 54, and the spill prevention plate 17 is retracted. And then falls across the open image exposure path into the developer pool of the developing device 30. At the time of the above cleaning, the developing device 30
The developing sleeve 31 is rotating and the collected toner is carried in and mixed in the developer pool.

FIG. 3 is a sectional view showing an embodiment of the charging device 20 used in the image forming apparatus of FIG. In the figure,
Reference numeral 21 is a magnetic particle, 22 is a charging roller that is a carrier for the magnetic particles 21 made of non-magnetic and conductive metal such as aluminum, and the surface thereof has an average surface roughness for stable and uniform transfer of the magnetic particles 21. It is preferable that the thickness is 2 to 15 μm. If it is smooth, the conveyance cannot be sufficiently performed, and if it is too rough, an overcurrent flows from the convex portion of the surface, and uneven charging tends to occur in either case. Sandblasting is preferably used to achieve the above surface roughness. Further, the diameter of the charging roller 22 is preferably 5 to 20 mm. With the above diameter, a 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 is likely to occur. When the diameter is small as described above, the magnetic particles 21 are easily scattered or adhered to the photoconductor drum 10 due to the centrifugal force. Therefore, it is preferable to reduce the linear velocity of the charging roller 22. Reference numeral 23 denotes a columnar magnet body fixedly arranged inside the charging roller 22, and this magnet body 23 has an S pole and an N pole so that the surface of the charging roller 22 has 500 to 1,000 gauss as shown in the figure. It is magnetized with poles arranged. Of these magnetic poles, the magnetic pole 23a of the charging portion closest to the photosensitive drum 10 will be referred to as the main magnetic pole. The charging roller 22 is rotatable with respect to the magnet body 23, and is 0.5 to 1.0 mm at a position facing the photoconductor drum 10.
Is held in the gap of the same direction as the moving direction of the photoconductor drum 10.
It can be rotated at a peripheral speed of 1.2 to 2.0 times.

The position of the main magnetic pole 23a of the magnet body 23 closest to the photosensitive drum 10 is the charging roller 22 and the photosensitive drum.
The position closest to the center of the photosensitive drum 10, that is, on both sides of the center line connecting the center of the photosensitive drum 10 and the center of the charging roller 22, the angle formed by the center line of the straight line connecting the center of the charging roller 22 and the main magnetic pole 23a. As a result of experiments, it was found that θ is preferably in the range of −15 ° ≦ θ ≦ 15 °.

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

Reference numeral 24 is 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 source 24 switches and supplies an AC bias voltage for charging and an AC bias voltage for cleaning in which an AC component is superposed on a DC component set to the same value as the voltage to be charged, under the control of a CPU (not shown). For charging with the power supply, the charging roller 22 and the photosensitive drum 10
Although it depends on the size of the gap between the photoconductor drum 10 and the charging voltage for charging the photosensitive drum 10, etc., when the gap is held between 0.1 and 5 mm, it is almost the same as the voltage to be charged, -500 V to -1.0.
Voltage between peak values (V _PP ) 200 to 3,50 for DC component of 00V
By supplying an AC bias voltage on which an AC component of 0 V (frequency 0.3 to 10 KHz) is superimposed via a protection resistor R,
It is possible to obtain preferable charging conditions. Further, for cleaning, preferable cleaning can be performed by supplying an AC bias in which the above-mentioned AC voltage component is superimposed on the toner of the developer and a voltage opposite to the charging polarity via the protective resistor R. The bias power source 24 performs constant voltage control for the DC component and constant current control for the AC component.

Reference numeral 25 denotes a casing forming a storage portion for the magnetic particles 21. The charging roller 22 and the magnet body 23 are arranged in the casing 25, and the casing 25 has an outlet for regulating the magnetic brush 21A. The regulation plate 26 is provided to regulate the thickness of the layer of the magnetic particles 21 attached to and discharged from the charging roller 22. The gap between the regulation plate 26 and the charging roller 22 is such that the transport amount of the magnetic particles 21, that is, the existing amount of the magnetic particles 21 on the charging roller 22 in the charging region is 10 to 300 mg /
cm ² Particularly preferably adjusted to be 30 to 150 mg / cm ² . The gap between the photosensitive drum 10 and the charging roller 22 is connected by a magnetic brush of magnetic particles 21 whose thickness is regulated. 27 is a stirring plate composed of a rotating body having a plate-like member for correcting the bias of the magnetic particles 21 around the axis.

The particle size of the magnetic particles 21 and the conditions of the carrier (charging roller 22) used in the charging device 20 of the above embodiment will be described.

Generally, when the average particle size (average weight) of magnetic particles is large, (a) since the state of the magnetic brush ears formed on the carrier is rough, even if 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 magnetic particles should be reduced.
It has been found that the effect starts to appear when the thickness is m or less, and particularly when the thickness is 100 μm or less, the problem (a) does 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 size 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 (average weight) of the magnetic particles is 150 μm or less, particularly preferably 100 μm or less and 30 μm or more.

Such magnetic particles are the same as those used in 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.

In the spherical particles having the above effects, the magnetic particles have a resistivity of 10 ³ Ω · cm or more and 10 ¹² Ω · cm or less, particularly 10 ⁴ Ω · cm or less.
It is preferable that the conductive magnetic particles are formed so as to be Ω · cm or more and 10 ⁹ Ω · cm or less. This resistivity is 0.50 for particles
After tapping in a container with a cross-sectional area of cm ² ,
A value obtained by applying a load of 1 kg / cm ² on the packed particles and reading the current value when a voltage that generates an electric field of 1,000 V / cm is applied between the load and the bottom electrode. When the 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 occurs. It can happen easily. 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, the magnetic particles are spherical so that at least the ratio of the major axis to the minor axis is 3 times or less, there is no protrusion such as a needle-shaped portion or an edge portion, 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 is the conditions for the magnetic particles, and 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. Then, it is preferable that the transport speed of the magnetic particles due to the rotation of the transport carrier is substantially the same as or faster than the moving speed of the image forming body. 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 carrier for carrying magnetic particles is not limited to the one composed of a charging roller having a magnet body that is fixed or rotated inside, and the carrier does not have a charging roller and the magnet body rotates, and N and S alternate. It may be composed only of the magnet body magnetized in the above.

The thickness of the particle layer formed on the carrier is preferably such that it is sufficiently scraped off by the regulation plate to form a uniform layer. 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 the magnetic particles in the charging region is 10 to 30.
A 0 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 D between the carrier and the image forming body is
0.1 mm ≤ D ≤ 10 mm is preferable, more preferably 0.2 mm ≤
D ≦ 5 mm is preferable. The surface gap between the carrier and the image forming body
If it is too narrower than 100 μm, it becomes difficult to form the ears of a magnetic brush that uniformly acts on it, and it becomes impossible to supply sufficient magnetic particles to the charging section, and stable charging is achieved. If it is not performed and the gap exceeds 5,000 μm, the particle layer is coarsely formed and charging unevenness is likely to occur, and the charge injection effect is deteriorated and sufficient charging cannot be obtained. As described above, when the gap between the carrier and the image forming member becomes extremely large, the thickness of the particle layer on the carrier cannot be adjusted appropriately. However, when the gap is in the range of 100 to 5,000 μm, 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 (D).

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

D 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 magnetic particles contact each other,
In the bent state, the image forming body is rubbed while being disturbed.

It is considered that this disturbing condition is effective for uniform charge by facilitating the movement of charge without causing charge stripes. That is, when the W / D corresponding to the magnetic particle density is small, the chains of the magnetic particles become coarse and the ratio of disturbance is small, resulting in non-uniform charging. When W / D becomes large,
The chains of the magnetic particles are not well formed due to the 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 , magnetic particles adhere and uneven charging appears, and when it is more than 300 mg / cm ² , the photoconductor wears and uneven charging appears. I couldn't get it. The preferred range in between is 30
It was ~ 150 mg / cm ² .

Further, when the distance between the image forming body and the magnetic particle carrying carrier is D (cm) under the above carrying amount condition, W
By setting / D to be 300 mg / cm ³ <W / D <3,000 mg / cm ³ , it has been clarified that more preferable uniform charging characteristics without adhesion of magnetic particles or uneven charging can be obtained. When the amount was less than 300 mg / cm ^{3 or} more than 3,000 mg / cm ³ , there was a phenomenon that magnetic particles adhered and uneven charging occurred.

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 on 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 the charging device for charging the image forming body by forming the 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 magnetic recording medium and the gap between the carrier for carrying the magnetic particles and the image forming body is D (cm), it is preferable that 300 ≦ W / D ≦ 3,000 (mg / cm ³ ). .

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

When the charging roller 22 is rotated in the same direction as the arrow at a peripheral speed of 0.2 to 2.0 times the peripheral speed of the photosensitive drum 10 while rotating the photosensitive drum 10 in the direction shown 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 for charging is applied between the charging roller 22 and the photoconductor drum 10, charges are injected onto the photoconductor layer 10a via the conductive magnetic particles 21 to perform charging. .

When the bias voltage is switched for cleaning, the toner remaining on the photosensitive drum 10 is sucked and collected by the magnetic brush 21A to which a DC component having a polarity opposite to that of the toner is applied.

In the above charging and cleaning, especially,
An AC bias was applied to form an oscillating electric field, and the main magnetic pole 23a was set in a range of ± 15 °, preferably on the upstream side θ> 0, and the ears of the magnetic brush 21A connected in a chain of magnetic particles 21 were laid down. As a result, the efficiency of charge injection from the magnetic brush 21A can be improved, the charging area can be expanded, and extremely stable high-speed uniform charging and cleaning can be performed.

In the above embodiment, the result of changing the frequency and voltage of the AC voltage component applied to the charging roller 22 in the case of charging is shown in FIG.

In FIG. 4, 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. 4, the low frequency region shaded with dots is a range in which uneven charging occurs due to the low frequency.

In the image forming apparatus using the charging device 20 that also serves as cleaning, 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.

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 remove the charge from the photoconductor drum 10 by using the charging device 20 of this embodiment. 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.

The magnetic particles 21 of the toner remaining on the surface of the photosensitive drum 10 without being cleaned due to long-term use.
There is a case where the amount of the particles mixed in the layer is increased, the resistance of the magnetic brush is increased, and the charging efficiency is deteriorated. To this end, the polarity of the DC bias voltage applied to the charging roller 22 at the time of rotation of the photosensitive drum 10 before or after image formation is set to be high, or the AC voltage is set to be high so that toner adheres to the photosensitive drum 10. Toner mixing can be prevented by setting easy conditions. Especially when the charging polarity of the photoconductor drum 10 is the same as that of the toner, as in the image forming apparatus that performs reversal development, a developing device.
Since it has the same polarity as that of the toner in 30, the contamination by the toner is less likely to occur, and it does not appear as a fog in the image at the time of development, resulting in an extremely suitable combination.

(Embodiment 2) FIG. 2 is a sectional view showing the outline of the configuration of another embodiment of the image forming apparatus of the present invention. In FIG. 2, 20 is a charging device dedicated to charging, and 51 is a cleaning blade as a cleaning means. Figure 1 in other parts
The same parts as those of the first embodiment shown in are shown by the same reference numerals, and detailed description thereof will be omitted. The charging device 20 is the charging device shown in FIG.
Same as 20, but the bias power supply 24 only supplies AC bias voltage for charging. As shown in FIG. 2, the charging device 20, the spill prevention plate 17, and the developing device 30 are arranged below the cleaning blade 51, and the toner collected from the photosensitive drum 10 by the cleaning blade 51 is charged by the charging device 20.
It crosses the back surface and the image exposure path and falls into the developer reservoir of the developing device 30. At the time of this cleaning, the developing sleeve 31 of the developing device 30 is rotating and the collected toner is carried in and mixed in the developer reservoir.

[0059]

According to the present invention, the cleaning means or the charging means also functioning as the cleaning means is arranged above the developing means, and the toner collected from the image forming body falls through the image exposure passage to develop the toner. Since the toner is collected by the means, the toner collecting cycle is performed with an extremely simple structure, and the image forming body is charged by directly injecting the electric charge through the magnetic brush formed on the carrier of the charging means.
It is possible to provide an image forming apparatus capable of lowering the bias voltage and preventing the generation of ozone.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing the outline of the configuration of another embodiment of the image forming apparatus of the invention.

FIG. 3 is a cross-sectional view showing an embodiment of the charging device of FIGS. 1 and 2.

FIG. 4 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) 17 Spill prevention plate 18 Cartridge 20 Charging device 21 Magnetic particles 22 Charging roller (conveying carrier) 23 Magnet body 24 Bias power supply 25 Casing 26 Regulation plate 51 Cleaning blade 53 Toner collecting roller 54 Scraper blade R 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 (4)

[Claims] 1. An image forming apparatus comprising a cleaning means, an exposing means and a developing means arranged around an image forming body, wherein the cleaning means is arranged above the developing means and the toner collected from the image forming body is An image forming apparatus, wherein the image forming apparatus is dropped through an image exposure passage and collected by the developing means. 2. The spill prevention plate prevents the collected toner from falling during the exposure of the exposure means, and the collected toner falls by the operation of the spill prevention plate during the non-exposure of the exposure means. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein the cleaning unit also serves as a charging unit. 4. The image forming apparatus according to claim 1, wherein the spill prevention plate opens the image exposure passage in synchronization with the image exposure of the exposure unit.