JP2000330381A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the prolongation of a life compatible with the uniformization of a solid image by using specified magnetic carrier and making developer regulating force at a gap (SB part) between a developer carrier and a regulating member stronger than that at an opposed part (SD part) between a latent image forming medium and the developer carrier at the time of applying developing bias. SOLUTION: As for the magnetic carrier to be used, its magnetization amount in magnetic field 1 kOe is within 30 to 200 emu/cm3, its specific resistance is within 1×109 to 1×1014 Ω.cm, and its volume average particle diameter is within 10 to 60 μm. The gap between a photoreceptor drum 3 and a developing sleeve 21 is set to about 500 μm. A blade 18 functioning as a regulating part is arranged to leave a space between the sleeve 21 and the blade 18 below the sleeve 21. The end of the blade 18 proximate to the sleeve 21 is gradually thinned in knife-edge shape, and a distance for securing developer amount on the desired sleeve 21 is set to about 400 μm narrower than the space between the drum 3 and the sleeve 21, Then, the regulating force at the SB part is made stronger than that at the SD part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, and a recorded image display for developing a visible image by developing an electrostatic latent image formed on an image carrier by an electrophotographic method, an electrostatic recording method, or the like. And an image forming apparatus such as a facsimile.

[0002]

2. Description of the Related Art Conventionally, various types of electrophotographic developing devices have been proposed and put into practical use. Broadly speaking,
The developing device is divided into a one-component developing system and a two-component developing system.

In the one-component developing system, most are non-contact systems, but a typical developing method is a one-component jumping developing method using a magnetic toner. This developing method can provide high-quality image with a simple configuration, but has a drawback that a color image cannot be obtained because the toner contains a magnetic substance.

In the one-component developing method using a non-magnetic toner, a color image can be obtained, but it is difficult to apply the toner on a developing sleeve, and at present, coating is performed with an elastic blade. Yes, it lacks stability and durability.

On the other hand, in the two-component developing method, a toner is transported to a developing area by a magnetic carrier to perform development. Usually, a developing step is performed by bringing a developer into contact with a photosensitive drum. Here, the developing step will be described with reference to FIG. In the figure, 30 is a developing sleeve, 35 is a magnet roller fixedly arranged in the developing sleeve, 31 and 32 are stirring screws, 33 is a regulating blade arranged to form a thin layer of developer on the surface of the developing sleeve, and 34 is a regulating blade. It is a developing container.

Here, the developing step of visualizing the electrostatic latent image by a two-component magnetic brush method using the above-described developing device and the developer circulation system will be described. First, with the rotation of the developing sleeve 30, the developer pumped by the N3 pole is regulated by the regulating blade 33 in the process of being transported from the S2 pole to the N1 pole, and a thin layer is formed on the developing sleeve 30.

Here, when the developer formed in a thin layer is conveyed to the developing main pole S1, a spike is formed by magnetic force. The electrostatic latent image is developed with the spike-shaped developer, and the developer on the developing sleeve 30 is returned to the inside of the developing container 34 by the repulsive magnetic field of the N3 pole and the N2 pole. In the two-component development, as described above, a configuration is generally used in which magnetic poles of the same polarity are arranged side by side, and the developer after development is once peeled off from the developing sleeve so as not to leave an image history.

A DC bias and an AC bias are applied to the developing sleeve from a power source (not shown). In general, in the two-component developing method, by applying an AC bias, the developing efficiency is increased, and the image becomes high quality.

As a latent image forming method, an electrophotographic photosensitive member is scanned and exposed by a laser beam modulated in accordance with an image signal to be recorded, and a dot distribution shape, that is, a dot-like latent image is distributed corresponding to an image. A method for forming an electrostatic latent image is known. Among them, the so-called pulse width modulation (PWM) method, which modulates the width (that is, duration) of a laser driving pulse current in accordance with the density of a recorded image, has a high recording density.
(That is, high resolution) and high gradation can be obtained.

In recent years, development of further miniaturization, higher image quality, and longer life using a two-component developing device has been promoted. In order to achieve a long service life, it is necessary to adopt a configuration in which the developer is not compressed and to prevent deterioration of the toner and the carrier. The place where the developer is compressed in the developing container is a developer layer thickness regulating portion. In a normal configuration, the developer layer thickness regulating pole is located on the upstream side in the rotation direction of the developing sleeve with respect to the regulating blade. In the region, the developer attracted to the developer layer thickness regulating electrode is compressed between the sleeve and the container.

In order to weaken the agent compression, it is effective to reduce the force (Fr: magnetic attraction force acting in a direction perpendicular to the developing sleeve) by which the developer layer thickness regulating electrode attracts the developer to the developing sleeve. . As a method for that, it is necessary to reduce the magnetization of the magnetic carrier in the developer (in the direction in which the magnetization of the carrier is reduced, it is said that the force of sliding the toner image developed on the photoreceptor in the developing unit is weakened. And the magnetic field lines from the developer layer thickness regulation pole are hardly wrapped around the adjacent magnetic pole, and a magnetic pattern is formed so as to be as perpendicular to the development sleeve as possible.

As one of the latter methods, a developing method using one of the repulsive magnetic poles of the developing sleeve as a developer layer thickness regulating pole has been proposed. When the maintaining poles of the same polarity are adjacent to each other to form a repulsive magnetic field, the magnetic force lines of the respective magnetic poles are almost perpendicular to the developing sleeve surface. In this case, the rate of change of the magnetic flux density in the direction perpendicular to the developing sleeve surface is small. As a result, the force for attracting the developer to the developing sleeve decreases, and the degree of compression of the developer decreases. As a matter of course, further longer life can be achieved by adopting both of the above methods.

[0013]

However, the above configuration, that is, a configuration in which one pole of the repulsion pole is used as a developer layer thickness regulation pole is adopted, and a magnetic carrier having a low magnetization amount is used as a magnetic carrier. In this case, an image defect occurs in that the black solid image is darkened only for about one round of the developing sleeve from the leading end and the subsequent image is rapidly thinned.

In this development, when a developing bias is applied during image formation, a carrier having a low magnetization amount is pulled toward an opposing portion (hereinafter referred to as an SD portion) between the photosensitive member and the developing sleeve. The amount of developer on the developing sleeve increases, and a dark image is formed first,
It has been found that the developer stays in the portion and scrapes off the developed image, which is caused.

When the compression degree in the gap between the conventional developer regulating electrode and the regulating agent (hereinafter referred to as SB section) is strong, the developing bias is turned on.
Since there is a sufficiently strong compressive force against the change in the developer regulating force of the SD section due to the OFF difference, there is almost no change in the amount of the developer on the developing sleeve. The above-described problem is likely to occur because of a weak regulation force.

Further, since a carrier having a low magnetization amount is used, a desired layer thickness is secured when the same developing device is used, as compared with a case where a carrier having a high magnetization amount such as an iron powder carrier is used. The above-mentioned problem is liable to occur because the SB gap required to perform the above operation must be widened, and as a result, the mechanical restricting force at the SB portion is weakened. This problem becomes more remarkable when a carrier having a small diameter and high resistance is used as the carrier, because the carrier is more easily pulled by the developing bias electric field.

The present invention has been made in view of the above, and an object of the present invention is to use a carrier having a low magnetization amount in order to solve the various problems described above and to extend the life of the developer. When one of the repulsive magnetic poles (of the developing sleeve) is used as the developer layer thickness regulating pole, the black solid image, which is likely to be generated, is darkened only for about one turn of the developing sleeve from almost the leading end of the solid image. An object of the present invention is to provide an image forming apparatus having a configuration capable of eliminating an image defect of thinning and obtaining a uniform black solid image.

[0018]

As a result of intensive studies to solve the above-mentioned problems, it is possible to obtain an image forming apparatus capable of achieving both long life and uniform solid images. The present invention has been completed.

The above object is achieved by an image forming apparatus according to the present invention. In summary, on a rotatable latent image forming medium having been initially charged, an electrostatic latent image is formed by erasing a charge corresponding to an image signal by an image exposing means, and the electrostatic latent image is made visible. A rotatable developer carrier that carries and conveys a two-component developer composed of a non-magnetic toner and a magnetic carrier, facing the image carrier, and fixed inside the developer carrier to develop an image A plurality of magnetic field generating means are provided, and the developing means is provided with a regulating member for regulating the developing layer thickness near one of adjacent magnetic poles of the same polarity among the magnetic field generating means. In the image forming apparatus having the developing device, the developing device is configured such that the two carriers move in opposite directions to each other at a portion where the latent image forming medium and the developer carrier are opposed, and a developing bias is applied at the opposed portion. DC bias with AC bias superimposed A magnetic brush developing apparatus for developing Te, In addition, the magnetic carrier is 1
The magnetization amount in a kOe magnetic field is in the range of ^{30 to} 200 emu / cm ³ , and the specific resistance of the magnetic carrier is 1 ×
10 ⁹ to 1 × 10 ¹⁴ Ω · cm, and the volume average particle diameter of the carrier is within the range of 10 to 60 μm, and the developer regulating force in the gap between the developer carrier and the regulating member is An image forming apparatus is characterized in that the developing force is larger than a developer regulating force at a portion where the latent image forming medium and the developer carrier are opposed when a developing bias is applied.

Further, the image forming apparatus is characterized in that the carrying amount per unit area on the developer carrying member does not change between when the developing bias is applied and when the developing bias is not applied. An image forming apparatus, wherein a gap between members is smaller than a gap between an opposing portion between the latent image forming medium and the developer carrier, and a rotation diameter of the developer carrier is 10 to 20 mm. The image forming apparatus is a feature.

Further, the rotation diameter of the latent image forming medium is 20 to
An image forming apparatus having a size of 60 mm, wherein a pair of sizes G of magnetic poles of the same polarity close to the regulating member is in a range of 500 to 700 gauss. An image forming apparatus, wherein the carrier core of the magnetic carrier is a resin magnetic carrier formed of a binder resin, a magnetic metal oxide and a non-magnetic metal oxide, which is formed by a polymerization method. .

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. In the present invention, in order to develop an electrostatic latent image into a visible image, a rotatable developer carrier that carries and conveys two-component development composed of a non-magnetic toner and a magnetic carrier, facing the image carrier, A plurality of magnetic field generating means fixedly provided inside the developer carrier are provided, and a regulating member for regulating the thickness of the developing layer is provided near one of adjacent magnetic poles of the same polarity among the magnetic field generating means. Having a developing means arranged,
A magnetic brush for developing by applying a DC bias on which an AC bias is superimposed as a developing bias in the facing portion where the latent image forming medium and the developer carrying member move in opposite directions to each other at the facing portion. The magnetic carrier used in the developing device has a magnetization of 30 to 2 in a magnetic field of 1 kOe.
00 emu / cm ³ and a specific resistance of 1 × 10 ⁹ to 1 ×
0 ¹⁴ Ω · cm, and the volume average particle size is 10 to 60.
When it is within the range of μm, the developer regulating force in the gap between the developer carrying member and the regulating member is larger than the developer regulating force in the facing portion between the latent image forming medium and the developer carrying member when the developing bias is applied. The developer carrying member is configured to have a larger carrying amount per unit area on the developer carrying member when the developing bias is applied and when the developing bias is not applied. Is smaller than the gap between the opposed portion of the latent image forming medium and the developer carrier, and the rotational diameter of the developer carrier is 10 to 20.
mm, the rotation diameter of the latent image forming medium is set to 20 to 60 mm, and the size G of one magnetic pole of the same polarity close to the regulating member is set to 500 ≦ G ≦ 700 (gauss). Thus, it is possible to obtain a long-life developing device that can prevent image defects in a solid image.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments and drawings, but the present invention is not limited thereto.

[Embodiment 1] An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an electrophotographic color printer to which the present invention can be applied. This printer includes an electrophotographic photosensitive drum 3 having a diameter of 80 mm and rotating in the direction of an arrow, and a charger 4,
A rotary developing device 1 having developing units 1M, 1C, 1Y, and 1Bk, a transfer discharging unit 10, a cleaning unit 12, and an image forming unit including an LED exposing unit LE disposed above the photosensitive drum 3 in the drawing are arranged. .

Each developing device contains a two-component developer containing toner particles and carrier particles. The developer of the developing device 1M contains magenta toner, the developer of the developing device 1C contains cyan toner, the developer of the developing device 1Y contains yellow toner, and the developer of the developing device 1Bk contains black toner.

The document to be copied is read by a document reading device (not shown). This reading device has a photoelectric conversion element for converting a document image such as a CCD into an electric signal, and outputs image signals corresponding to magenta image information, cyan image information, yellow image information, and monochrome image information of the document, respectively. I do.

The LED exposing means controls the light emission on-off in accordance with these image signals to perform exposure. Although the output signal from the computer can be printed out, the sequence of the entire color printer is
The case of the full color mode will be briefly described as an example.

First, the photosensitive drum 3 is uniformly charged by the charger 4 and then exposed or performed by the LED array L controlled by the magenta image signal.
A dot distribution latent image is formed thereon, and the latent image is reversely developed by a magenta developing device 1M fixed at a developing position in advance.

Paper feed guide 5 taken out of cassette C
a, a transfer material such as paper, which has progressed via a paper feed roller 6 and a paper feed guide 5b, is held by a gripper 7 of a transfer drum 9, and is electrostatically transferred by a contact roller 8 and its opposite pole. 9 wrapped around. The transfer drum 9 rotates in the direction of the arrow in synchronization with the photosensitive drum 3, and the magenta visual image developed by the magenta developing device 1M is transferred to a transfer material by a transfer charger 10 in a transfer section. The transfer drum 9 continues to rotate as it is to move to the next color.
Prepare for the transfer of the image (cyan in FIG. 1).

On the other hand, the photosensitive drum 3 is discharged by the charger 11 and cleaned by the cleaning means 12, charged again by the charger 4, and exposed as described above by the LED array L controlled by the next cyan image signal. As a result, an electrostatic latent image is formed. During this time, the developing device 1 rotates and the cyan developing device 1C is fixed at a predetermined developing position, performs reversal development of the electrostatic latent image corresponding to cyan, and forms a visible image of cyan.

Subsequently, the following steps are performed on the yellow image signal and the black image signal, respectively, and when the transfer of the four-color image (toner image) is completed, the transfer material is transferred to each charging device 13. , 14, the gripper 7 is released, the sheet is separated from the transfer drum 9 by the separation claw 15, and is sent to a fixing device (a heat-pressure roller fixing device) 17 by a transport belt 16. The fixing device 17 fixes the visible images of four colors overlapping on the transfer material. Thus, a series of full-color print sequences is completed, and a desired full-color print image is formed.

This configuration is an example. For example, the charger 4
Is not a corona charger, but a charging roller, an exposure unit is a semiconductor laser, and the transfer charger 10 is also a transfer roller, there are various systems, but basically, as described above, An image is formed through the steps of exposure, development, transfer, and fixing.

Next, one of the developing devices 1M in the image forming system of the present invention will be described with reference to the drawings. FIG. 2 is a configuration diagram showing the developing device 1M used in the embodiment of the present invention. The present developing device includes a developing container 27 as shown in FIG.

The inside of the developing container 27 is divided into a developing chamber (first chamber) R1 and a stirring chamber (second chamber) R2 by a partition wall 29, and the toner is stored above the stirring chamber R2 via the partition wall 29. A chamber R3 is formed, and a replenishment toner (non-magnetic toner) 28 is stored in the toner storage chamber R3. The partition 2
9 is provided with a supply port 26, and an amount of supply toner 28 corresponding to the toner consumed through the supply port 26 is supplied to the stirring chamber R.
It is dropped and replenished into 2.

On the other hand, the developing chamber R1 and the stirring chamber R2
The inside contains a developer 19. In this embodiment, the developer 19 has an average particle diameter of 8 produced by a pulverization method.
1% by weight of titanium oxide having an average particle diameter of 20 nm externally added to a toner having a particle diameter of 20 μm,
0 emu / cm ³ , average particle size 35 μm, volume resistivity 1 × 10 ¹⁰ Ω
cm of magnetic material dispersed polymer resin magnetic carrier (mixing ratio of non-magnetic toner is about 8% by weight).

The physical properties of the magnetic carrier are limited to the above values. To form a good image, the value of magnetization is ^{30 to} 200 emu / cm ³ and the volume resistivity is 1 × 1.
⁰⁹ to 1 × 10 ¹⁴ Ωcm, volume average particle size of 10 to 60
There is no problem if it is within the range of μm.

An opening is provided in a portion of the developing container 27 close to the photosensitive drum 3, and the opening is formed through the opening.
1 protrudes outside. In this embodiment, the gap between the photosensitive drum and the developing sleeve is set to 500 μm. The developing sleeve 21 is rotatably incorporated in the developing container 27. In the present embodiment, the developing sleeve 21 is
Has a diameter of 24 mm, such as SUS305 AC,
It is made of a non-magnetic material, and has a magnet 23 fixed therein as a magnetic field generating means.

The magnet 23 has a developing magnetic pole N1, a developer layer thickness regulating pole S3 located downstream of the developing magnetic pole N1, and magnetic poles N2, S2 and S1 for transporting the developer 19. The magnet 23 is disposed in the developing sleeve 21 such that the developing magnet N1 faces the photosensitive drum 3. The developing magnetic pole N1 forms a magnetic field near the developing section between the developing sleeve 21 and the photosensitive drum 3, and the magnetic field forms a magnetic brush. At this position, as the developing sleeve rotates, the developer selected in the direction of the arrow contacts the photosensitive drum, and the electrostatic latent image on the photosensitive drum is developed.

At this time, at the proximity position (developing section) between the developing sleeve and the photosensitive drum, the developing sleeve and the photosensitive drum move in opposite directions (counter direction). The developer that has been developed at the N1 pole is peeled off from the developing sleeve by the repulsive magnetic field formed by the S1 and S3 poles, and falls into the developing chamber R1. The developing sleeve 21 is applied with an oscillating bias voltage obtained by superimposing a DC voltage on an AC voltage by a power supply 22. The dark portion potential (non-exposed portion potential) and the light portion potential (exposed portion potential) of the latent image are located between the maximum value and the minimum value of the vibration bias potential.

As a result, an alternating electric field whose direction changes alternately is formed in the developing section. The toner and the carrier vibrate violently in this alternating electric field, and the toner shakes off the electrostatic restraint on the sleeve and the carrier, so that an amount of toner corresponding to the latent image potential adheres to the photosensitive drum. In this embodiment, the dark potential of the photosensitive drum is -550 V, and the bright potential is -1.
00V, and -30 DC as the developing sleeve.
0 V and Vpp 2.0 kV and Frq. 6 kHz are applied as an AC bias.

Below the developing sleeve 21, a blade 18 as a regulating member is arranged at a predetermined distance from the developing sleeve 21. The distance between the developing sleeve 21 and the blade 18 is 400 μm. Blade 18
Is fixed to the developing container 27. The blade 18 is made of a magnetic material such as iron.
In this embodiment, the end portion of the blade close to the developing sleeve is gradually narrowed on the knife edge to secure a desired amount of the developer on the developing sleeve. The SB interval for performing the operation is narrowed. A transport screw 25 is accommodated in the developing chamber R1. The conveying screw 24 used had a diameter of 20 mm and a pitch of 20 mm.

The transport screw 24 is rotated in the direction indicated by the arrow in the figure, and the developer 19 in the developing chamber R1 is transported in the longitudinal direction of the developing sleeve 21 by the rotation of the transport screw 24. In this embodiment, the transport screw 24 is disposed below the developing sleeve 21 in the direction of gravity. The reason for this is that, as will be described later, the uppermost surface of the developer accommodated in the transport screw 24 is set between the developer layer thickness regulating electrode and the stripping electrode.

A transport screw 25 is accommodated in the stirring chamber R2. The transport screw 25 has a diameter of 20 mm, similar to the transport screw 24. The transport screw 25 rotates to transport the toner along the longitudinal direction of the developing sleeve 21, and the toner is supplied to the supply port 2.
6 falls naturally into the stirring chamber R2.

The main configuration of the present embodiment is shown in the following table.

With the above configuration, the amount of the developer on the developing sleeve can be ensured even when the SB gap is narrowed. As a result, even when a carrier having a low magnetization amount is used, the SB gap can be maintained at the SD gap. It became possible to make it narrower than the gap. In addition, by regulating the SB gap to be narrower, the mechanical regulating force is strengthened, and the regulating force in the SB can always be configured to be stronger than the regulating force in the SD section regardless of whether the developing bias is applied or not. This makes it possible to prevent the occurrence of a solid image result as described in the above conventional example.

[Embodiment 2] The main configuration in this embodiment is shown in the following table.

The structure different from that of the first embodiment is that the polarities of the photosensitive drum and the developing sleeve are increased. With this configuration, first, the space between the photosensitive member and the closest portion of the developing sleeve is widened, so that the developer hardly stays in the SD portion, and the attenuation of the developing electric field is increased. The nearby developer is pulled and becomes difficult.

Also in the SB section, the size of the internal magnet is reduced, and as a result, the magnetic concentration on the magnetic blade is reduced, so that the SB gap can be further narrowed. Therefore, it is easier to prevent image defects than in the first embodiment.

[Embodiment 3] The main configuration of this embodiment is shown in the following table.

The feature of this embodiment is that the range of the peak value of the magnetic flux density of the layer thickness regulation pole is defined. Simply SB
In order to reduce the gap, the larger the above G, the better. However, if it is too large, the degree of compression in the SB portion increases and the agent deteriorates. Therefore, the value range of G is as described above, and preferably, 600 ≦ G ≦ 700 (gauss).
The range of s) is desirable. By setting it within this range, it is possible to achieve a longer life without causing image defects of a solid image.

In the present invention, the low-magnetization amount carrier is produced by polymerizing a resin magnetic carrier comprising a binder resin, a magnetic metal oxide and a non-magnetic metal oxide. The amount of magnetization may be controlled by a ferrite carrier or the like.

Hereinafter, a method of measuring the magnetization amount, the particle size, and the volume resistivity will be described. First, for the amount of magnetization, the magnetic properties of the carrier were measured using an oscillating magnetic field type magnetic property automatic recording device manufactured by Riken Denshi Co., Ltd. by measuring the magnetization strength of the carrier packed in a cylindrical shape in an external magnetic field of 1 kOe. Then, the amount of magnetization (emu / cm ³ ) was calculated by multiplying by the true specific gravity of the carrier.

The particle size was determined by taking a photograph of a carrier particle randomly extracted by 300 using a scanning electron microscope, and using the image processing / analyzing device Luzex3 manufactured by Nireco Co., Ltd. to obtain the carrier particle size in terms of the Feret diameter in the horizontal direction. Calculated.

For the volume resistivity, a measuring device shown in FIG. 4 was used. In the cell E, electrodes 40 and 41 are arranged so as to be in contact with the carrier 43, a voltage 42 is applied between the electrodes, and a current flowing at that time is measured to obtain a specific resistance. The specific resistance measurement conditions used in the present invention were as follows: the contact area S between the filled carrier and the electrode was about 2.3 cm 2, the thickness d was about 2 mm, the load on the upper electrode 41 was 180 g, and the measured electric field strength was 5 × 104 V / m. .

[0055]

As described above, according to the present invention, there are provided a developing device and an image forming apparatus in which a solid image is made uniform, an image defect of a solid image can be prevented, and a long life is excellent. A remarkable effect is achieved.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing an outline of a full-color image forming apparatus according to the present invention.

FIG. 2 is a schematic side view showing an outline of a known developing device for explaining a conventional example.

FIG. 3 is a schematic cross-sectional view illustrating an outline of a developing device according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing an outline of an apparatus for measuring the specific resistance of a carrier according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 rotary developing device (developing device: 1M, 1C, 1Y, 1Bk) 3 photosensitive drum 4 charger 5 paper feed guide (5a, 5b) 6 paper feed roller 7 gripper 8 contact roller 9 transfer drum 10 transfer charger 11 charging Device 12 Cleaning means 13, 14 Charger 15 Separation claw 16 Conveyor belt 17 Fixer 18 Blade 19 Developer 21 Developing sleeve 22 Power supply 23 Magnet 24, 25 Conveyor screw 26 Supply port 27 Developing container 28 Replenished toner 29 Partition wall 30 Developing sleeve 31 , 32 Stirring screw 33 Regulator blade 34 Developing container 35 Magnet roller 40, 41 Electrode 42 Voltage 43 Carry C Cassette E Cell L LED array LE Exposure means N1, N2, N3 Developing magnetic pole R1 Developing chamber (first chamber) R2 Stirring chamber ( (Second chamber) R3 toner storage chamber S1, S2, S3 main developing electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ichiro Ozawa 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H005 AA21 BA03 BA11 CB03 EA01 EA02 EA05 FA01 2H031 AC11 AC14 AC19 AC20 AC33 AC34 AD03 AD09 BA08 BA09 BB01 CA11 CA13 FA01 2H077 AA12 AB02 AB14 AC02 AD06 AD13 AD18 AD36 AE06 BA03 BA07 EA01 FA26 GA13 GA17

Claims (7)

[Claims] An electrostatic latent image is formed on an initially charged rotatable latent image forming medium by erasing a charge corresponding to an image signal by an image exposing means to form the electrostatic latent image. A rotatable developer carrier that carries and conveys a two-component developer composed of a non-magnetic toner and a magnetic carrier, facing the image carrier, and fixed inside the developer carrier to develop a visible image A plurality of magnetic field generating means provided as a plurality of magnetic field generating means, and a regulating member for regulating the thickness of the developing layer is disposed near one of adjacent magnetic poles of the same polarity of the magnetic field generating means. An image forming apparatus comprising a developing device having
In the developing device, the two carriers move in directions opposite to each other at the facing portion of the latent image forming medium and the developer carrier, and apply a DC bias in which an AC bias is superimposed as a developing bias at the facing portion. A magnetic brush developing device for developing the magnetic carrier, wherein the magnetic carrier has a magnetization of 30 to 200 emu / cm ³ in a magnetic field of 1 kOe and a specific resistance of the carrier of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω
cm, and the carrier has a volume average particle size of 10
And the developer regulating force in the gap between the developer carrying member and the regulating member is larger than the developer regulating force in the facing portion between the latent image forming medium and the developer carrying member when the developing bias is applied. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the amount of toner per unit area on the developer carrier does not change between when the developing bias is applied and when the developing bias is not applied. 3. A gap between the developer carrier and the regulating member,
2. The image forming apparatus according to claim 1, wherein the gap is smaller than a gap between the facing portion between the latent image forming medium and the developer carrier. 4. The image forming apparatus according to claim 1, wherein a rotation diameter of the developer carrier is in a range of 10 to 20 mm. 5. The image forming apparatus according to claim 1, wherein a rotation diameter of the latent image forming medium is in a range of 20 to 60 mm. 6. The image forming apparatus according to claim 1, wherein a size G of a pair of magnetic poles having the same polarity close to the regulating member is in a range of 500 to 700 gauss. 7. The magnetic carrier according to claim 1, wherein the carrier core of the magnetic carrier is a resin magnetic carrier formed by a polymerization method and comprising a binder resin, a magnetic metal oxide and a non-magnetic metal oxide. Image forming apparatus.