JPH06148985A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a chargeless image forming device in which developer is smoothly carried, a distinct toner image is formed without surface staining, and recording is performed by efficiently transferring an image on a transfer material by electric transfer. CONSTITUTION:As to the chargeless image forming device, image light is made incident on the inner surface of a photosensitive drum 1 where an image exposure means 2 is turned, a developing sleeve 7 carries the developer D and brings it into contact with the outer surface of the photosensitive drum 1 at an image light incident position, and an electrode body 9 is provided on the developing sleeve 7 at the image light incident position, and the magnetic pole of a magnet body 8 fixed inside the sleeve 7 is arranged so that repulsive magnetic field is formed at the position of the electrode body 9, then DC voltage having the same polarity as the electrostatic charge of the insulating toner of the developer D is impressed on the electrode 9a of the electrode body 9, and the DC voltage having a reverse polarity to the electrode 9a is impressed on the developing sleeve 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeless image forming apparatus. More specifically, the image exposing means makes image light incident on the inner surface of a rotating photosensitive member, and a developing sleeve holds the image light to convey the image. The developer layer is brought into contact with the outer surface of the photoconductor at the position where the image light is incident to form a toner image on the outer surface of the photoconductor, and the toner image is transferred to the transfer material fed so as to come into contact with the outer surface of the photoconductor. The present invention relates to an image forming apparatus that is fixed and fixed.

[0002]

2. Description of the Related Art Conventionally, as a chargeless image forming apparatus, one using a conductive toner has been known, but this has a problem that electrical transfer is difficult. In order to solve this problem, an image forming apparatus using the developing device shown in FIG. 6 has been proposed. In the figure, 1 is a transparent electrode layer 1a formed on a transparent substrate as shown in FIG. 3, a charge generation layer 1b on the transparent electrode layer 1a side, a hole charge transport layer 1c as an intermediate layer, and a surface charge layer. The photoconductor drum has a structure in which photoconductor layers each including a generation layer 1d are laminated, and rotates in the arrow direction.

Reference numeral 2 is a light emitting element array 2a such as an LED or EL.
And a converging light transmitting body 2b such as a rod lens array, which is provided stationary inside the photosensitive drum 1,
An image exposure unit that repeats the selective lighting of the light emitting elements of the light emitting element array 2a based on the image data to repeat the incidence of the image light on the inner surface of the photosensitive drum 1 along a line substantially perpendicular to the rotation direction, and D is an insulating material. Two-component developer consisting of toner and magnetic carrier or one-component developer of magnetic insulating toner, 71 is a fixed developing sleeve made of non-magnetic conductive material such as aluminum, and 81 is inside the developing sleeve 71. N and S magnetic poles are alternately arranged in the circumferential direction and 50 in the A direction in the figure.
A magnet body that can be rotated at a rotation speed of 0 to 1,000 rpm,
91 is an electrode body made of a conductive metal plate or the like and provided with an insulating layer 91b on the surface facing the developing sleeve 71, and 11 is the developing sleeve 71.
It is a layer thickness regulating blade that regulates the layer thickness of the upper developer D.

By the magnetic force and rotation of the magnet body 81, the developer D on the surface moves in the direction of arrow B while rotating on its axis as shown in the figure, so that the image exposing means 2 enters the developing area A where the image light is incident. It reaches the installed electrode body 91. In the illustrated example, a positive DC voltage of 300 to 1,500 V having the same polarity as that of the toner on the developer layer is applied to the electrode body 91 by the bias power source 15. As a result, the electrode body 91 forms an electrostatic image on the outer surface of the photosensitive drum 1 in combination with the incidence of the image light by the image exposure means 2 described above, and also attaches toner to the electrostatic image and the background portion. To form a toner image.

On the other hand, the developing sleeve 71 has a bias power source 16
Thus, a DC voltage of 50 to 300 V having a polarity opposite to that of the toner of the developer D, that is, a polarity opposite to the voltage applied to the electrode body 91 is applied. As a result, on the downstream side of the electrode body 91, the layer of the developer D reaching the electrode body 91 enters the image light by the image exposure unit 2 of the photosensitive drum 1 and the developer D on the electrode body 91.
The toner adhering to the outer surface of the exposed portion where the charge is injected by the contact with the layer is hardly removed, and all the toner attached to the outer surface of the non-exposed portion where the charge is not injected is removed. First, the developer D on the electrode body 91
The layer makes a toner image made of toner adhering to the electrostatic image formed on the outer surface of the photosensitive drum 1 clear with almost no background stain.

[0006]

However, in the above-described developing device, the developer D moves on the developing sleeve 71 while being attracted toward the developing sleeve 71 by the magnetic force of the magnet body 81, and therefore the electrode body 91. Therefore, there is a problem in that the developer D is not blocked and the developer D is not transported smoothly. This problem cannot be solved even if the developing sleeve 71 is rotated in the direction of arrow B, and the developer D is easily clogged at the electrode body 91, and a clear image cannot be obtained.

The present invention has been made in order to solve the above-mentioned problems, in which the developer is smoothly conveyed, and an insulating toner is used to form a clear toner image without scumming and electrical transfer. It is an object of the present invention to provide a chargeless image forming apparatus capable of efficiently transferring to a transfer material.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which exposes a back surface of a photoconductor and at the same time develops it with a developer carried by a developing sleeve facing the photoconductor. An image forming apparatus is characterized in that it has electrode bodies provided on the developing sleeves facing each other, and a repulsive magnetic field is formed at a position of the electrode body by a magnet body provided in the developing sleeve.

[0009]

In the developing device of the chargeless image forming apparatus of the present invention, since the repulsive magnetic field is formed in the developing area where the electrode body is located by the magnet body in the developing sleeve, the attraction force of the developer toward the developing sleeve is weak. As a result, the developer can smoothly pass over the electrode body.

[0010]

The present invention will be described below with reference to the illustrated examples.

FIG. 1 is a schematic sectional view of an essential part showing an example of the image forming apparatus of the present invention, and FIG. 2 is an enlarged sectional view of the vicinity of the developing area A of the developing device of FIG. 1. In FIGS. The same parts as those in FIG. 6 are represented by the same reference numerals, and detailed description thereof will be omitted. In the figure, 3 is a developing case in which the lower part is a developer reservoir 4, and 5 is a two-component developer of an insulating toner and a magnetic carrier in the developer reservoir 4 or one-component development of a magnetic or non-magnetic insulating toner. This is a stirrer that stirs the developer to charge the insulating toner and supplies the developer D to the surface of the developing sleeve 7.

The developing sleeve 7 is made of a non-magnetic conductive material such as aluminum or stainless steel, and is provided with a magnet body 8 in which N and S magnetic poles are circumferentially arranged, which is fixed by the magnetic force of the magnet body 8. The developer D is adsorbed on and the developing sleeve 7 rotates in the direction of the arrow to convey the developer D in the direction of the arrow. The developer D formed on the surface by it
Of the developing layer A at the position where the image exposing means 2 enters the image light.
Transport to. The electrode body 9 is composed of an electrode 9a formed by adhering nickel or silver or the like on an insulating substrate 9b such as a film or a thin plate by plating or sputtering, and the substrate 9b is the developing sleeve 7 in the developing area A. It is stretched so as to be close to or in contact with the surface.

The relationship between the position where the image exposure means 2 makes the image light incident on the photosensitive drum 1, the position where the developing sleeve 7 contacts the layer of the developer D, and the position of the magnetic pole of the magnet body 8 are shown in FIG.
As shown in FIG. 2, which is a partially enlarged view of FIG.
Is closest to the outer surface of the photosensitive drum 1, that is, the center of the developing sleeve 7 and the photosensitive member of the image exposure unit 2 with respect to the center line connecting the center of the photosensitive drum 1 and the center of the developing sleeve 7. In a range in which the angle θi formed by the line connecting the image light incident positions corresponds to the electrode plate, the image light incident position is located upstream of the closest position of the developing sleeve 7 to the photosensitive drum 1. preferable. As a result, the charge transfer time in the photoconductive layer for efficient transfer of charge from the developing sleeve 7 to the photosensitive drum 1 via the layer of the developer D can be secured. When the image light incident position is on the downstream side of the closest position of the developing sleeve 7 to the photosensitive drum 1, the charge transfer time becomes insufficient.

As the magnetic poles of the magnet body 8, N or S poles having the same pole are arranged on both sides of the center line. As a result, a repulsive magnetic field is formed in the developing area A. Angle theta ₁ spanned on the upstream side and downstream side with respect to the center of the developing sleeve 7 from the center line of the magnetic pole position, when theta _2, theta ₁ and theta ₂ are 5 °
It is preferably at least 45 °.

As for the angle formed by the width of the electrode 9a of the electrode body 9 with respect to the center of the developing sleeve 7, the angle upstream of the center line is θ _e1 and the angle downstream of the center line is θ _e2. θ _e1 and θ _e2 are preferably 10 ° or less. Further, the thickness of the electrode body 9 is preferably 50 to 1000 μm, and the gap Dsd between the electrode 9a and the photosensitive drum 1 is preferably 0.3 to 10 mm.

The image light incident position θ ₁ is opposed to the electrode body 9a, preferably upstream of the center line, and θ ₁
≦ θ _e1 .

The developer D attracted to the surface of the developing sleeve 7 by the magnetic force of the magnet body 8 is conveyed to the developing area A by the rotation of the developing sleeve 7, and the repulsive magnetic field is formed in the developing area A. Therefore, the developer D developing sleeve 7
The attracting force to the developer D almost disappears, and the developer D smoothly passes over the electrode body 9 and comes into contact with the outer surface of the photosensitive drum 1. Reference numeral 13 denotes a scraper blade that removes the developer D after passing through the position where it contacts the outer surface of the photosensitive drum 1 from the developing sleeve 7 and drops it into the developer reservoir 4.

A positive DC voltage of 200 to 2,000 V is applied to the electrode 9a of the electrode body 9 through the protective resistance R1 by the bias DC power source 15 in the illustrated example having the same polarity as that of the toner of the developer D. As a result, the electrode 9a forms an electrostatic image on the outer surface of the photosensitive drum 1 in combination with the incidence of image light by the image exposure unit 2 described above, and also attaches toner to the electrostatic image and the background portion. To form a toner layer.

On the other hand, the developing sleeve 7 has a polarity opposite to the charging of the toner of the developer D, that is, the electrode 9a, by the bias DC power source 16 and the bias AC power source 16A via the protection resistor R2.
A bias voltage in which an AC voltage having a frequency of 500 Hz to 10 KHz and an inter-peak value voltage of 300 to 2,000 V is superimposed on a DC voltage of 50 to 300 V having a polarity opposite to that of the voltage applied to is applied. As a result, the toner adhering to the outer surface of the exposed portion, which has been charged by the image light incident by the image exposing means 2 of the photosensitive drum 1 and the contact of the developer D on the developing sleeve 7, is left without being removed. , All the toner adhering to the outer surface of the non-exposed portion where no charge is injected is removed, so that the layer of the developer D of the developing sleeve 7 is first used to form the photosensitive drum 1.
The toner image formed of the toner adhering to the electrostatic image formed on the outer surface of is made clear with almost no background stain.

In the illustrated example, the photoconductor of the photoconductor drum 1 is the OPC photoconductor having the layer structure shown in FIG. 3, but there are the following two types of mechanisms of charge generation and injection in the photoconductor. . In the following description, the charge transfer layer 1c is a hole transfer type.

The first is the case where the charge generation layer 1b on the transparent electrode layer 1a side is used as shown in the schematic sectional view of the image forming portion in FIG. In this case, a negative bias voltage is applied to the electrode 9a of the electrode body 9, and the holes generated in the portion of the charge generation layer 1b where the image light is incident are attracted to the surface of the photoreceptor to be trapped. Then, a negatively charged toner is used as the insulating toner and adheres to the surface of the photoconductor.

The reason for providing the charge generating layer 1d on the surface of the photoconductor is that the positive charge remaining on the surface after the toner image is transferred and the surface is cleaned is erased by uniform exposure. When the charge generation layer 1d is uniformly exposed from the inner surface side or the outer surface side of the photoconductor, charges are generated and the positive charges trapped are released. The uniform exposure means for removing the electric charge may be provided on the inner surface side or the outer surface side of the photoreceptor.

The second mechanism is the case of using the surface charge generation layer 1d as shown in the schematic sectional view of the image forming portion of FIG. In this case, a positive bias voltage is applied to the electrode 9a of the electrode body 9 so that the holes generated in the portion of the charge generation layer 1d where the image light is incident are released to the transparent electrode layer 1a side and the surface of the photoreceptor To trap negative charges. Then, positively charged toner is used as the insulating toner and adheres to the surface of the photoconductor.

The reason why the charge generation layer 1b on the transparent electrode layer 1a side is provided is that the negative charges remaining on the surface after transfer and cleaning are erased by uniform exposure. When the charge generation layer 1b is uniformly exposed from the inner surface side or the outer surface side of the photoreceptor, the positive charges generated in the charge generation layer 1b move to the surface and neutralize the trapped negative charges.

Unlike the example shown in FIG. 3, when the photoconductor layer of the photoconductor has a single-layer structure and has bipolar charge transferability, the bias voltage of the electrode 9a of the electrode body 9 is positive and negative. Either voltage can be used, but since image light is largely absorbed on the side of the photoconductor substrate, the bias voltage is set in consideration of the mobility of holes or electrons in the photoconductor layer, as in the first mechanism described above. It is preferable to apply.

Further, the photoconductor layer of the photoreceptor is the conventional OPC.
As described above, a charge transfer layer provided with a charge generation layer on one side can also be used, but the charge tends to be less likely to disappear even if the charge is removed by uniform exposure.

The bias voltage applied to the electrode 9a of the electrode body 9 is preferably a DC voltage as shown in the drawing, and an AC component in a range in which the polarity is not reversed is preferably superimposed. That is, a high bias voltage may be applied to quickly move the charges in the photoconductor layer, but if a high DC voltage is simply applied, a breakdown occurs between the electrode body 9 and the photoconductor to form a charge image. It will be destroyed. On the other hand, when a bias voltage having an AC component in the range that does not reverse the polarity is applied, the moving speed of the charge can be increased with a low voltage that does not destroy the charge image, and the AC component causes vibration to the developer layer. Thus, a uniform toner image can be attached to the photoconductor. If the polarity is reversed due to the superposition of AC components, the charge transfer efficiency decreases, so
It is preferable to set the bias voltage under the condition that the polarity is not inverted.

Further, it is preferable that an AC component is superimposed on the developing sleeve 7 in addition to the DC voltage as shown in the drawing. That is, the AC component vibrates the layer of the developer D to effectively remove the toner adhering to the non-image portion of the photoconductor, and a clear toner image with less background stain is obtained. Like The AC component in the bias voltage of the developing sleeve 7 may cause polarity reversal, but the electric charge has already been trapped, so it does not matter.

As the developer D, it is preferable that it is a two-component developer and that the magnetic carrier is also insulative, from the viewpoints of the toner charge control and the stripping effect by the developing sleeve 7, and the magnetic carrier is spherical. It is preferable that the agglomeration is improved from the viewpoints of improving the stirring property of the toner and the carrier and the transporting property of the developer, and making the aggregation of the toner and the carrier less likely to occur. The spherical magnetic carrier preferably has an average particle size of 30 to 80 μm. By doing so, the bias voltage of the electrode 9a can be applied uniformly.

If the average particle size of the magnetic carrier is too small, the magnetic carrier is likely to adhere to the surface of the photoconductor, and the stripping effect of the developing sleeve 7 deteriorates. If it is too large, the state of the ears of the magnetic brush of the layer of the developer D becomes rough, the toner concentration of the ears becomes low, and the formation of the toner layer on the electrode body 9 becomes insufficient or becomes asymmetric. As a result, the applied state of the bias voltage becomes non-uniform, and the stripping of the developing sleeve 7 becomes rough.

The preferable magnetic carrier as described above is iron, which is the same as a conventional magnetic carrier as a magnetic material.
Metals such as chromium, nickel and cobalt, or their compounds and alloys such as ferric tetroxide, γ-ferric oxide,
The ferromagnetic particles such as chromium dioxide, manganese oxide and ferrite are made spherical, or the surface of these magnetic particles is styrene resin, silicon resin, fluorine resin, vinyl resin, ethylene resin, rosin modified resin, acrylic Particles obtained by spherical coating with a resin such as a base resin, a polyamide resin, an epoxy resin, or a polyester resin, or by making spherical particles of a resin containing magnetic fine particles dispersed therein are obtained by a conventionally known method. It is obtained by selecting the particle size by means of particle size classification.

In addition to the above-mentioned effect, forming the carrier into a spherical shape by using a resin or the like as described above may also be performed when the toner is attached by being magnetized and adsorbed in the long axis direction of the non-spherical carrier. There is a drawback that it causes directionality when peeling off, and since there is an edge part, the electric field is concentrated at the edge part and the dielectric layer of the photoconductor layer is apt to cause dielectric breakdown, which disturbs the image formed on the photoconductor. By eliminating the drawbacks described above, the toner can be adhered and peeled off without directivity, and a high bias voltage can be applied to form a clear toner image without disturbance. It also gives the effect of saying.

The spheroidized carrier having the above-mentioned effects further has a carrier resistivity of 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm.
It is preferable that the insulating magnetic particles are formed so as to have an Ωcm or more. The resistivity after tapping putting particles in a container having a sectional area of 0.50 cm ^2, a load of 1 kg / cm ² on packed particles, 1 between the load and a bottom electrode,
It is a value obtained by reading the current value when a voltage that generates an electric field of 000 V / cm is applied. If this resistivity is low, when a bias voltage is applied to the electrode body 9 and the developing sleeve 7, it becomes a carrier. Charges are injected and carriers are easily attached to the surface of the photoconductor, or dielectric breakdown of the photoconductor layer due to bias voltage is likely to occur.

In summary, the magnetic carrier is spherical so that the ratio of the major axis to the minor axis is at least 3 times or less, and there are no protrusions such as needles and edges, and the resistivity is high. Is 10 ⁸
It is a proper condition that it is Ωcm or more, preferably 10 ¹³ Ωcm or more. Such a magnetic carrier is a spherical magnetic particle having a high resistance or a resin-coated carrier. For the magnetic particle, a spherical magnetic particle is selected as much as possible, and a resin coating treatment is applied to the magnetic particle. In career,
It is produced by using magnetic fine particles as much as possible and then subjecting the dispersed resin particles to a spheroidizing treatment, or obtaining dispersed resin particles by a spray drying method.

Next, the toner will be described. Generally, when the average particle size of the toner particles becomes small, the charge amount qualitatively decreases in proportion to the square of the particle size, and the adhesion force such as the van der Waals force is relatively increased. Becomes large, the toner becomes difficult to separate from the carrier, the toner layer formed on the photoconductor surface by the electrode body 9 becomes insufficient, and the toner adhered to the non-image portion on the photoconductor surface by the developing sleeve 7 is removed. If the developing sleeve 7 is rubbed by the layer of the developer D, it is not easily removed, and fogging, that is, scumming is likely to occur. When the bias voltage of the electrode 9a and the developing sleeve 7 is a DC voltage,
If the average particle diameter of the toner particles is 10 μm or less, the above-mentioned problems will appear.

However, when an AC component is applied to the bias voltage, in the developing area A where the electrode body 9 is located, the toner adhering to the developer layer is separated from the developer D by the vibration applied electrically, and the toner surface It becomes easy to transfer to the image area and the non-image area, and a sufficient toner layer is formed on the surface of the photoconductor to prevent the transfer of the carrier. Further, here, as described above, it is preferable to set the bias voltage so that there is no bias component of the opposite polarity that hinders the movement of charges. Further, in the developing sleeve 7, the toner adhered to the non-image portion on the surface of the photoconductor is effectively removed by the vibration to which the developer D is electrically applied, and a clear toner image without fog is formed on the surface of the photoconductor. Therefore, a toner having an average particle diameter of several μm can be used without any problem.

Even when a magnetic one-component insulating developer is used, the effect of adding an AC component to the Baice voltage is almost the same. That is, by vibrating the toner, a sufficient toner layer is uniformly formed on the photosensitive surface, the toner in the non-image area is effectively stripped, and a clear toner image without fog can be formed.

As the two-component developer, a developer in which the spherical carrier and the toner as described above are mixed in the same proportion as in the conventional two-component developer is preferably used.
Further, if necessary, a fluidizing agent for improving flow slip of particles, a cleaning agent useful for cleaning the surface of the photoreceptor, and the like are mixed. As the fluidizing agent, colloidal silica, titanium oxide or a nonionic surface active agent can be used, and as the cleaning agent, a fatty acid metal salt, an organic group-substituted silicon or a surface active agent such as fluorine can be used.

The thickness of the layer of the developer D formed on the developing sleeve 7 is preferably such that the adhered developer D is sufficiently scraped off by the layer thickness regulating blade 11 to form a uniform layer. , And the gap between the electrode body 9 and the photoconductor surface is
100 to 10,000 μm is preferable. If this gap becomes too narrower than 100 μm, it becomes difficult to form a uniform toner layer or a developer layer that effectively acts to remove toner, or the developer D is clogged in the gap. As a result, the toner image may not be formed. Also, the gap
If it exceeds 10,000 μm, the counter electrode effect is deteriorated, the electrostatic image and the toner layer are not sufficiently formed, and the toner in the non-image area is not sufficiently peeled off, so that the toner image does not have a fog. Will not be formed.

As described above, when the gap between the electrode body 9 and the photoconductor becomes extremely large, the thickness of the layer of the developer D on the electrode body 9 cannot be made appropriate, but the gap becomes 100.
In the range of μm to 10,000 μm, the thickness of the layer of the developer D can be appropriately formed. Therefore, it is preferable to set the thickness of the layer of the developer D to the condition that the layer of the developer D contacts the outer surface of the photosensitive member at the position where the image light is incident in the absence of the oscillating electric field. This prevents the toner image from being swept or fogged.

The specific bias voltage is as follows:
In the electrode 9a, the voltage of 200 to 2,000V, which has the same polarity as the toner charge
When superimposing an AC component on the DC voltage of
0 Hz to 10 KHz, preferably 5 to 10 KHz, which is a voltage in which a peak-to-peak voltage V _PP that does not invert the polarity is superimposed with an AC voltage of 200 to 2,000 V is preferable. Frequency is 1 to 10 for DC voltage
A voltage obtained by superimposing an AC voltage whose peak-to-peak voltage is higher than the AC component of the bias voltage of the electrode 9a at KHz is preferable.

The AC component frequency of the bias voltage applied to the electrode 9a must be sufficiently higher than the reciprocal of the moving time of the charges moving in the photoconductor layer. If it is not set in this way, it affects the moving charges and causes unevenness in the movement of the charges. Therefore, the AC component frequency of the bias voltage applied to the electrode 9a is set higher.

In FIG. 1, reference numeral 17 denotes a transfer material P fed by a timing roller 18 in synchronism with the toner image on the photoconductor drum 1 and brought into pressure contact with the outer surface of the photoconductor drum 1 to transfer a transfer bias having a polarity opposite to that of the toner charge. A transfer roller that applies a voltage to transfer a toner image onto the transfer material P. Since the toner is an insulating toner in the chargeless image forming apparatus of the present invention, the transfer material is applied by the bias voltage applied to the transfer roller 17. The transfer efficiency of the toner image onto P can be significantly increased.

Reference numeral 19 denotes a scraper blade for scraping off paper dust, toner and the like adhering to the transfer roller 17 into the toner reservoir 20. The transfer material P on which the toner image is transferred has the toner image fixed by a fixing unit such as a heat roller fixing device (not shown), and is discharged to the outside of the apparatus.

Reference numeral 21 denotes the photosensitive drum 1 downstream of the transfer position.
Is a static elimination exposure unit composed of an LED array, an EL or the like for uniformly exposing the inner surface of the photosensitive drum 1 to erase the electrostatic charge on the photosensitive drum 1 and moving the residual toner easily. It is a scraper blade that is removed from the body drum 1 and reduced to the developer pool 4. As a result, it is possible to form and record a clear toner image with further less background stain.

The present invention is not limited to the above-mentioned example, and the scraper blade 22 and the charge eliminating exposure means 21 may be omitted. This is because the transfer efficiency of the transfer roller 17 onto the transfer material P is high, and the layer of the developer D of the developing sleeve 7 also serves as a scraper blade. It should be noted that if the charge eliminating exposure means 21 is omitted, a part of the charges may remain on the photoconductor to adversely affect the image.

Of course, a corona discharge electrode may be used as the transfer means, and the image forming body may be a photosensitive belt. When a photoconductor belt is used, a laser beam scanner that causes the image exposure unit 2 to scan a laser beam modulated based on image data by a deflecting unit such as a rotary polygon mirror to make image light incident on the inner surface of the photoconductor belt. Can be easily used. Alternatively, the rod lens array may be omitted, and the LED or EL array may be directly brought into close contact with the inner surface of the photoconductor to allow the image light to enter.

[0048]

As described above, according to the present invention, since the repulsive magnetic field is formed at the position of the electrode body, the developer smoothly passes over the electrode body in the developing region, the developer is not clogged, and there is almost no background stain. It is possible to provide a chargeless image forming apparatus capable of forming a clear toner image and efficiently transferring it to a transfer material by electric transfer for recording.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing an example of an image forming apparatus of the present invention.

FIG. 2 is an enlarged cross-sectional view of the vicinity of the developing area A of the image forming apparatus of FIG.

FIG. 3 is a partial schematic cross-sectional view of a photoconductor.

FIG. 4 is a schematic sectional view of an image forming unit.

FIG. 5 is a schematic sectional view of an image forming unit.

FIG. 6 is a sectional view showing a developing device used in a conventional chargeless image forming apparatus.

[Explanation of symbols]

 1 Photosensitive drum 2 Image exposure means 7,71 Development sleeve 8,81 Magnet body 9,91 Electrode body 9a Electrode 15,16 Bias DC power supply 16A Bias AC power supply 17 Transfer roller A Development area D Developer

Claims (1)

[Claims] 1. An image forming apparatus which exposes a back surface of a photoconductor and at the same time develops with a developer conveyed by a development sleeve facing the photoconductor, the image forming apparatus being provided on the development sleeve facing an exposure position. An image forming apparatus having an electrode body, wherein a repulsive magnetic field is formed at a position of the electrode body by a magnet body provided in the developing sleeve.