JPH08234572A - Image forming device and developing device - Google Patents

Abstract

PURPOSE: To obtain a high performance image forming device capable of stably forming a high quality image excellent in developability, with reduced noise at a low cost. CONSTITUTION: The image forming device is provided with a writing device 22 for irradiating with color resolving light, an image carrier 10 for carrying a latent image corresponding to the color resolving light, developing devices 23 selectively actualizing the latent image in accordance with the color resolving light, to obtain a toner image and a transfer unit 24 transferring the toner image formed superimposing on the image carrier 10 to a transfer material. The developing devices 23 actualize the latent image on a magnet 110 for forming a static magnetic field by anisotropic ferrite sintered magnets 111-114 having >=1200G surface magnetic field, from the closest proximity positions of the developing devices 23 to the image carrier 10 to both sides and a developing sleeve 120 rotating the periphery of the magnet 110, by a magnetic brush consisting of a two-component developer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer material after forming a color-separated electrostatic latent image on an image bearing member by adopting an electrophotographic method and superimposing a multicolor toner image on the image bearing member. The present invention relates to an image forming apparatus that employs an image forming method of transferring images on the surface (hereinafter, this is abbreviated as KNC process) and a developing apparatus that is preferably used for the image forming apparatus.

[0002]

2. Description of the Related Art First, the KNC process will be described.

A uniform charge is previously applied to the peripheral surface of the image carrier by a scorotron charger. When the scanning starts, the laser beam is detected by the index sensor,
The laser beam modulated by the first color signal scans the peripheral surface of the image carrier. The first scanning is performed on the peripheral surface of the image carrier by the main scanning by the laser beam and the sub-scanning by the conveyance of the image carrier.
A latent image corresponding to the color of is formed. This latent image is subjected to reversal development by a developing device loaded with yellow toner that is selectively activated, and a toner image is formed on the surface of the image carrier. The toner image, while being held on the surface of the image carrier, passes under the blade of the cleaning device separated from the peripheral surface of the image carrier, and enters the next image forming cycle.

That is, the image carrier is recharged by the charger, and then the second color signal is input to the writing control section, and the surface of the image carrier is transferred in the same manner as in the case of the first color signal described above. Writing is performed and a latent image is formed. The latent image is reverse-developed by a developing device loaded with magenta toner as the second color which is selectively activated. This magenta toner image is formed in the presence of the already formed yellow toner image. Similarly, a developing device having cyan toner forms a cyan toner image on the surface of the image carrier in the same manner as the first and second colors.

Finally, a developing device having a black toner is used to form a black toner image on the image bearing member in the same manner as in the above-described color. DC and further AC biases are applied to the sleeves of these developing devices, and reversal development is performed on the image carrier without contact. What has been described above is the process of superposing multicolor toner images on the image carrier.

In the multicolor toner image thus formed on the peripheral surface of the image carrier, a high voltage having a polarity opposite to that of the toner is applied to the transfer material fed from the paper feed cassette through the paper feed guide. Is transcribed. That is, the transfer material accommodated in the paper feed cassette is carried out by rotating the paper feed roller so that the uppermost one sheet is carried out and is supplied to the transfer device through the timing roller in time with the image front end on the image carrier. It

The transfer material that has received the image is reliably separated from the rotating image carrier and goes upward, and after the image is fixed by the fixing roller, it is discharged onto the tray through the paper discharging roller. The above is the so-called KNC process.

The reason why the two-component non-contact developing method is adopted in the KNC process is that the toner particles can control triboelectric charging relatively easily and the toner particles do not easily agglomerate. It has good ears and excellent friction with the surface of the image carrier, and also has the characteristics that a sufficient cleaning effect is exhibited even when it is used for cleaning. More importantly, it develops without contacting the surface of the image carrier. It is also suitable for non-contact development.

A developing device adopting such a non-contact developing method is, for example, a developing sleeve formed in a cylindrical shape from a non-magnetic material such as stainless steel or aluminum, and a plurality of usually 500 to 1,000 gausses on the surface inside the developing sleeve. A magnet body magnetized to a magnetic flux density and having N and S magnetic poles in the circumferential direction is fixed to the casing, and the magnets are closely arranged from the position of the developing sleeve closest to the image carrier to the upstream side and the downstream side in the moving direction of the developing sleeve. By doing so, it is possible to form a uniformly lying magnetic brush, and to keep the gap without contacting the surface of the image bearing member, the gap between the developing sleeve and the regulating blade and the gap between the developing sleeve and the image bearing member. D _sd is adjusted.

[0010]

However, the conventional non-contact developing method has a large variation in the height of the crests of the spikes, and therefore the amount of developer conveyed on the developing sleeve, that is, the density of the developer is rough. As a result, the image carrier does not adhere to the latent image faithfully, and the light and shade depending on the location remarkably appears, causing noise, and the image quality is significantly impaired. Further, if a low-magnetization carrier is used to solve this problem, carrier adhesion may occur on the image carrier, and improvement in image quality cannot be expected.

In order to solve such a problem, the applicant of the present invention fixedly installs highly magnetized magnetic poles of a magnet body on the upstream side and the downstream side in the moving direction of the developing sleeve from the developing sleeve position closest to the image carrier. It is proposed that the developing sleeve is rotated on the magnet body to form a magnetic brush in a uniformly lying state, and such a configuration achieves high image quality. In order to achieve such a purpose, it is possible to adopt a rare earth magnet for high magnetization of 1200 Gauss or more,
There is a problem of high cost.

In view of the above, an object of the present invention is to provide an image forming apparatus and a developing apparatus which can achieve high image quality at low cost.

[0013]

This object is achieved by the following constitution.

(1) An exposure device for irradiating color separation light,
An image carrier that carries a latent image corresponding to the color-separated light, a developing device that selectively visualizes the latent image into a toner image according to the color-separated light, and an overlay on the image carrier. In an image forming apparatus including a transfer device that transfers a toner image formed by transfer to a transfer material, the developing device forms a static magnetic field by a magnet having a surface magnetic field of 1000 G or more on both sides from a position closest to the image carrier. An image forming apparatus, wherein the latent image is visualized by a magnet body, a developing sleeve that rotates on a peripheral surface of the magnet body, and a magnetic brush made of a two-component developer on the developing sleeve.

(2) In the image forming apparatus according to (1), the magnet body is an anisotropic ferrite sintered magnet embedded in the surface of a cylindrical magnet body.

(3) The image forming apparatus according to (2), characterized in that the width in the circumferential direction on the surface of the anisotropic ferrite sintered magnet is set to be smaller than the internal width.

(4) In the image forming apparatus of (1), the magnet body is formed by connecting anisotropic ferrite sintered magnets with a high magnetic permeability material.

(5) A magnet body which forms a static magnetic field by a magnet whose surface magnetic field is 1000 G or more on both sides from the position closest to the image carrier, a developing sleeve which rotates the peripheral surface of the magnet body, and the developing unit. In a developing device for visualizing a latent image formed on the image bearing member by a magnetic brush made of a two-component developer on a sleeve, the magnet is connected by a member made of a high magnetic permeability material. apparatus.

(6) The developing device according to (5), wherein the magnet body is an anisotropic ferrite sintered magnet embedded in a cylindrical magnet body.

(7) The width of the anisotropic ferrite magnetic pole in the circumferential direction at the surface is set to be smaller than the width in the circumferential direction at the inside (6).
Developing device.

(8) The developing device according to any one of (5) to (7), wherein the developer carrier has a small particle size and a low magnetization carrier.

[0022]

In the non-contact type developing device of the present invention, the magnetic field of each permanent magnet of the magnet body in the sleeve of the developing roller is made strong. Especially, the surface magnetic field of the sleeve near the top is 1000
By setting the height to G or more, the height of the peak of the distribution of the spikes is reduced, and by further reducing the thickness of the spikes, the variation in the height in the inter-electrode region is reduced, the developer density is increased, and the image bearing member is increased. It is also possible to narrow the gap with the photoconductor as a result, so that the fidelity of the light and shade in each constituent pixel of the image is less likely to be impaired, and the toner corresponding to each constituent pixel is dispersed to other pixels during flight. The phenomenon in which the image is lost is also avoided, and the sharpness of the image is increased and the image quality is greatly improved.

Further, by reducing the particle size of the carrier in the developer or lowering the magnetization, the variation in height difference and the noise caused thereby are further reduced, and the image quality is improved.

[0024]

EXAMPLE A main structure of an image forming apparatus adopting the KNC process will be described.

FIG. 9 is a sectional view showing a schematic structure of an image forming apparatus adopting the KNC process of this embodiment, and FIG. 1 is a sectional view showing a schematic structure of a developing device of the first embodiment.

The image carrier 10 is a drum-shaped photosensitive member having a diameter of 180 mm and made of (-) charged coating type OPC in which a photosensitive layer is formed on the surface of a conductive base material made of, for example, aluminum or the like, and has a predetermined linear velocity. Rotate in the direction of the arrow at (mm / sec). The photosensitive layer has a film thickness of 15 to 30 μm, a dielectric constant of 2.0 to 5.0, and the conductive base material is grounded.

The image carrier 10 has a scorotron charger 21, a writing device 22, a plurality of developing devices 23 each containing a developer of a specific color, a transfer device 24, and a cleaning device 25 on the periphery thereof.
Is provided.

The developing device 23 contains, for example, any one of yellow, magenta, cyan, and black developers, and as shown in FIG. 1, is provided with a developing sleeve 120 for keeping a predetermined gap with the image carrier 10. , A latent image on the image carrier 10 is visualized by a non-contact reversal development method, and in particular, from the developing sleeve position closest to the image carrier 10 to the developing sleeve.
By arranging magnetic poles on the upstream side and the downstream side in the moving direction of 120, a magnetic brush in a uniformly lying state is formed. Since the plurality of developing devices have the same configuration, the developing device 100 shown in FIG. Will be described as a representative.

Here, the developing area means the toner of the spiked developer layer on the developing sleeve 120 as described above.
Is a region on the developing sleeve 120 that flies with respect to the developing position. Of the magnets of the magnet body 110 that form the static magnetic field, two magnets that are arranged on both sides of the magnet directly below the developing area and define the developing area are called inter-electrode developing magnets, and the developing area that is located directly below the developing area. The magnet that defines is referred to as the best developing magnet.

As shown in FIG. 1, the developing device 100 includes an image carrier 10 which is grounded to a predetermined reference potential as the developing sleeve 120 rotates during development, a DC power source and an AC power source, and a direct current to an alternating current through a protective resistor. Is applied,
Two inter-electrode developing magnets 111, 112 and their adjacent magnets 113, 11
A developing sleeve 120 made of a non-magnetic material is rotatably provided on the outer peripheral surface of a magnet body 110 in which a plurality of magnets 4 and 115 are arranged on the peripheral surface, an appropriate amount of developer 31 is put therein, and stirring screws 105, 106 are provided. Therefore, the toner and the carrier are evenly mixed and supplied to the peripheral surface of the developing sleeve 120, and the thickness of the spike-up layer of the developer is made substantially uniform by the spike-rising regulating plate blade 102, and the rotation of the developing sleeve 120 causes the spike-like layer to rotate. The developer that has stood up is carried to the development area without coming into contact with the image carrier 10, and the toner in the developer D is separated from the spiked carriers, and the latent image on the image carrier 10 has the magnitude of its charge. The latent image formed on the image carrier 10 is visualized with toner particles while flying a corresponding amount. The developing device adopting this developing method can be called a non-contact developing device in a so-called inter-electrode developing area.

The carrier and the excess toner are returned to the developing tank again, and the toner corresponding to the consumed toner is replenished by the toner replenishing device and the conveying wheel, and the toner and the carrier are charged again by uniform mixing and frictional charging. Is performed by the above-mentioned stirring.

The structure and function of each member will be described below.

The developing sleeve 120 has a thickness of 10 to 2 as described above.
It is formed into a cylindrical shape from a non-magnetic material such as stainless steel or aluminum having a diameter of 5 mm, and is rotatable with respect to the included magnet body 110. The magnet body 110 is a highly magnetized magnet 111 to 1 in which the orientation of the ferrite particles is aligned in a specific direction on the surface and sintered.
It has 15 in the circumferential direction and is fixed to the casing 101. The developing sleeve 120 rotates in the leftward direction shown by the arrow.

Further, the strength of the magnetic field on the surface of the developing sleeve 120 of the inter-electrode developing magnets 111, 112 of the magnet body 110 in the developing area is 1000 G or more, preferably 1300 G or more. The magnetic force forms a layer of the developer D composed of toner particles and carrier particles, that is, a magnetic brush on the surface of the developing sleeve 120. The magnetic brush is a developing sleeve 120.
Is moved in the same direction as the rotation of the developing sleeve 120 and is conveyed to the developing area. The magnetic brush formed on the developing sleeve 120 is in a state of a nap at the closest contact point of the image carrier due to the inter-electrode developing magnets 111 and 112 arranged in the vicinity of the developing region, and does not come into contact with the surface of the image carrier 10 to form a gap. The gap between the developing sleeve 120 and the regulating blade 102 and the gap D _sd between the developing sleeve 120 and the image carrier 10 (hereinafter, also abbreviated as D _sd ) are adjusted so as to maintain the above condition. In this embodiment, D _sd is preferably 500 μm or less.

Here, θ ₁ and θ ₂ are angles between magnetic poles which are arranged close to the upstream and downstream sides in the moving direction of the developing sleeve 120 from the developing sleeve position closest to the image carrier 10.
It is desirable that θ ₁ and θ ₂ are each 5 to 45 °. By doing so, it is possible to form the magnetic brush in a uniformly lying state.

The stirring screws 105 and 106 circulate and stir the developer D before and after in the figure to make the components uniform.

The regulation blade 102 is molded from a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush. The cleaning blade 103 removes the magnetic brush passing through the developing area A from the developing sleeve 120.

The bias power source E is a power source for outputting the DC power source and the AC power source through the protective resistance as described above.
When the photosensitive layer surface of the image carrier 10 is charged to -850 (V), the DC power supply outputs a voltage of -750 V to prevent fogging during reversal development, and the AC power supply has a frequency of 500 Hz to 20 KHz. Is an AC power source that outputs an AC voltage of 200 to 4000 V _pp , and these voltages are arranged in series and applied to the developing sleeve 120.

The AC component supplied from the AC power supply is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or the like. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer is vibrated, which facilitates the separation and flight of the toner particles from the carrier particles, but on the other hand, the phenomenon of fog or lightning strike occurs. Dielectric breakdown easily occurs. The generation of fogging is prevented by a DC component, and the insulation breakdown is caused by coating the surface of the developing sleeve 120 with a resin, an oxide film, or the like so as to be insulating or semi-insulating, or the carrier particles of the developer with spherical insulating carrier particles. It can be prevented by using it.

The reason why the two-component non-contact developing method is adopted in the KNC process is that the toner particles can control triboelectric charging relatively easily as described above and the frictional property with the surface of the image carrier is improved. It is excellent and has a feature that a sufficient cleaning effect is exhibited even when it is used also for cleaning. More importantly, it is suitable for non-contact development which develops in non-contact with the surface of the image carrier.

The developer D generally has an average particle size of 15 to 60 μm.
The magnetic carrier particles and the non-magnetic toner particles having an average particle size of about 3 to 10 μm are used. Since the toner particles and carrier particles are fine, there is an advantage that delicate lines, dots, or density differences can be reproduced with high image quality.

However, when the toner particles and the carrier particles are made into fine particles, a clear image cannot be obtained due to the conspicuous side effects such as the aggregation phenomenon of the toner particles and the adhesion of the carrier particles. Therefore, the toner particles and the carrier particles are made into fine particles. Things are really difficult. Specifically, if the toner particles have an average particle size of 20 μm or less, especially 10 μm or less, the influence of the Van der Waals force appears relatively to the Coulomb force during development, and the background portion of the image background appears. In other words, so-called fogging in which toner particles adhere is generated, and it becomes difficult to prevent fogging even by applying a DC bias voltage to the developing sleeve 120. Further, it becomes difficult to control the triboelectric charging of the toner particles, and aggregation easily occurs. On the other hand, when the carrier particles are made finer, the carrier particles also adhere to the electrostatic image portion of the image carrier 10. or,
As the bias voltage increases, carrier particles also adhere to the background of the image background. It is considered that this is because the magnetic force decreases and the carrier particles adhere to the image carrier 10 side together with the toner particles. In this embodiment, the carrier preferably has an insulating property, specifically a specific resistance of 10 ⁸ Ωcm or more. Furthermore, it is preferable that the particle diameter of the toner and carrier is within the range of 0.1 to 100 μm.

The developing mechanism in the above-mentioned magnetic brush developing method, that is, the electric field condition at the time of development and the behavior of the magnetic brush under the electric field condition are shown in FIGS. It will be described with reference to the drawings.

2 and 3 are enlarged sectional views of the developing region in the developing device of this embodiment, and FIG. 4 is an enlarged sectional view of the developing region in the conventional developing device.

First, the carrying state of the developer D in the developing area will be described.

The behavior of the spike of the developer in the developing area is as shown in the partial side sectional views of FIGS. In contrast to the gap D _sd between the developing sleeve 120 and the image carrier 10 in the developing area, there is still a gap C between the developer layer and the developer layer, and the gap D _sd can be made smaller. Further, the height of the spiked developer layer until the peak position of the developer layer of the inter-electrode developing magnets 111 and 112 following the developing area is also kept low.

On the other hand, in the conventional example shown in FIG. 4, the height of the spike developing agent layer in the developing area is also the height of the spike developing agent layer in the area until it reaches the magnets 111, 112 for the following gap developing and the gap developing. The height of the spiked developer layer at the peaks of the magnets 111 and 112 was much larger, and it was impossible to reduce the gap D _sd . The developer density on the developing sleeve 120 is much higher in this embodiment than in the conventional one,
The difference between the peaks and valleys, that is, the variation in the height of the spikes is smaller in this embodiment.

Therefore, the image carrier 10 has a surface potential V of the photosensitive layer.
_s is charged to, for example, -850 (V), and the developing sleeve 12
Assuming that a DC component of −750 (V) and an AC component of 200 to 4000 V _{pp at} a frequency of 50 Hz to 20 KHz, preferably 500 Hz to 20 KHz are applied to 0, the image bearing between the image bearing member 10 and the developing sleeve 120 is performed. By forming an oscillating electric field in the body 10, the toner particles formed by the magnetic brush move alternately between the image carrier 10 and the developing sleeve 120 by the oscillating electric field to form a latent image on the image carrier 10. A flying toner is assisted to visualize a uniform toner image. The DC voltage applied to the developing sleeve 120 prevents fogging as described above. In this way, a high quality image can be obtained.

On the other hand, at the time of non-development, the image carrier 10 is charged to the surface potential V _s of the photosensitive layer at -850 (V), and the developing sleeve 120 has a DC component of -750 (V) and a frequency of 50 Hz to 20 KH.
z, since preferably is in a state in which the AC component of 200～4000V _pp was applied in 50～15KHz, the developing sleeve 12 and the image carrier 10
An oscillating electric field still exists between 0 and. However, by stopping the rotation of the developing sleeve 120, the developer conveyed to the developing area does not exist, so the developing action by the oscillating electric field is not performed, and the toner image is first formed on the image carrier 10. It does not cause color mixing or destruction.

In the present embodiment, the developing device 100 has been described as developing a latent image, but the present invention is not limited to this, and it is obvious that a magnetic latent image can also be visualized. Is.

FIG. 5 is a curve graph showing the relationship between the height of the scatter of the developer layer in the gap between the poles and the magnetic flux density on the sleeve surface at the pole upper portion.

The magnet body contained in the developing sleeve is formed by embedding an inexpensive anisotropic ferrite sintered magnet on the surface of a cylindrical isotropic ferrite sintered magnet and in the circumferential direction on the surface of the anisotropic ferrite sintered magnet. By setting the width of the developer to be smaller than the width in the circumferential direction inside, the height difference of the developer becomes smaller as the magnetic flux density increases, and the developer approaches a smooth surface. Along with this, the density of the bristling developer layer becomes much larger than that of the conventional example, and the gap D _sd between the image carrier 10 and the developing sleeve 120 can be made small, so that the unevenness of the image density is eliminated and the noise is also reduced. Is improved. Further, since the conventional developing device cannot increase the carry amount Dws so much, high-speed development is impossible. However, even if the carry amount Dws is increased by using a highly magnetized magnet as in the present embodiment, the maximum and minimum heights can be increased. It is shown that stable high speed development is possible because the difference in depth does not increase and the image density does not decrease.

Next, FIG. 5 also shows that the particle size of the carrier is changed from the usual 50 μm to a small particle size of 30 μm. By decreasing the particle size, the height of the developer layer is further reduced. It is possible to keep the difference low. Next, Table 1 shows the results of experiments conducted by changing the carrier particle size from 50 μm to 30 μm and using carriers of each particle size with low magnetization.

Here, the low magnetization carrier is the saturation magnetization amount б.
_s is 50 emu / g or less, preferably 40 emu / g or less.

[0055]

[Table 1]

No. 1 is the inter-electrode developing magnets 111, 11 of the magnet body 110.
The surface magnetic field in the developing sleeve 120 of 2 is 700G,
The carrier has a particle size of 50 μm, and the difference between the maximum and minimum heights of the spiked developer layer (variation) is 300 μm, which causes noise and the image quality is not good.

In No. 2, the magnet body 110 has a structure in which anisotropic ferrite is embedded in the surface of cylindrical isotropic ferrite, and the surface magnetic field in the developing sleeve 120 of the inter-electrode developing magnets 111 and 112 is 1100G. , Carrier particle size is normal 50μ
Further, at m, the carrier is magnetized in a normal state, and the difference between the maximum height and the minimum height of the spiked developer layer (variation)
Is considerably reduced to 200 μm, noise is reduced, and image quality is improved, but some drawbacks still remain. However, it can be said that there is no problem in practical use.

No. 3 has the same structure as No. 2, but the surface magnetic field in the developing sleeve 120 of the inter-electrode developing magnets 111 and 112 is 1300 G, and the difference between the maximum and minimum heights of the spiked developer layers ( (Variation) is further reduced to 180 μm, and noise and image quality are further improved.

No. 4 has the same structure as No. 2, but the surface magnetic field in the developing sleeve 120 of the inter-electrode developing magnets 111, 112 is 1300 G, and the difference between the maximum and minimum heights of the spiked developer layers ( (Variation) is further reduced to 130 μm, and noise and image quality are good.

No. 5 is one in which anisotropic ferrite is embedded in the surface of a cylindrical isotropic ferrite, and the circumferential width of the anisotropic ferrite surface is made smaller than the internal circumferential width. By setting the surface magnetic field to be 1500 G, the difference (variation) in maximum and minimum heights of the spiked developer layer is further reduced to 60 μm, and the noise is good.

No. 6 has the same structure as No. 5, but the surface magnetic field in the developing sleeve 120 of the inter-electrode developing magnets 111, 112 is
It is 2000 G, the variation in the maximum and minimum heights of the spiked developer layer is 100 μm, and the noise becomes even better.

In No. 7, the structure of the magnet body is the same as that of No. 6, but by using a developer with a low magnetization carrier, the variation becomes 70 μm, the noise is further reduced, and the image quality is greatly improved.

In No. 8, anisotropic magnets were used for the inter-electrode developing magnets 111 and 112, and these two magnets were connected by a Fe-Si material, and the surface magnetic field was 1300G. The variation in height difference of the spiked developer layer at this time is 130 μm,
The noise image quality is good.

In No. 9, anisotropic ferrite was used for the inter-electrode developing magnets 111 and 112, and these two magnets were connected by a Fe-Si material, and the surface magnetic field was 1500G. The variation in height difference of the spiked developer layer at this time is 130 μm,
The noise image quality is good.

In Table 1, the symbols of superiority and inferiority in image quality are ranked according to the following symbols in the order of superiority.

⊚: Very good ○: Good Δ: Difficult but good ×: Bad As mentioned above, it is conceivable to use a rare earth magnet to obtain a high magnetic force of 1000 G or more. However, if the Nd-Fe-B rare earth material or the Sm-Co rare earth material is used as the magnetic core material, there is a problem that the cost becomes high. A developing device that solves such a problem and achieves high image quality is proposed below.

FIG. 6 is a cross-sectional view of essential parts in the developing devices of the second to fourth embodiments.

Since the developing device 100 shown in FIG. 6 has substantially the same structure as that shown in FIG. 1, the members having the same structure and the same function are designated by the same reference numerals and the description thereof will be omitted. To do.

The developing sleeve 120 is formed in a cylindrical shape from a non-magnetic material such as stainless steel or aluminum having a diameter of 10 to 25 mm as in the above-described embodiment, and is rotatable with respect to the magnet body 110 contained therein.

The magnet body 110 is a columnar magnet made of an isotropic magnetic material (hereinafter referred to as a columnar magnet 117).
And the highly magnetized magnets 111B to 112B (hereinafter,
This is sometimes referred to as inter-pole developing magnets 111B and 112B. ) In the circumferential direction, a strong magnetic field generated especially between the inter-electrode developing magnets 111B and 112B is circulated through the columnar magnet 117, so that the inter-electrode developing of the magnet body 110 in the developing area is performed. The strength of the magnetic field on the surface of the developing sleeve 120 of the magnets 111B and 112B can be set to 1000 G or more, preferably 1300 G or more. According to such a configuration, since the rare earth material is not used for the magnetic core, the cost can be reduced.

FIG. 7 is a cross-sectional view of essential parts in the developing devices of the fifth to seventh embodiments.

Since the developing device 100 shown in FIG. 7 has a structure substantially similar to that of the third embodiment, the members having the same structure and the same function are designated by the same reference numerals and the description thereof will be omitted. .

The magnet body 110 is a columnar magnet made of an isotropic magnetic material (hereinafter referred to as a columnar magnet 117).
In addition, the highly magnetized magnets 111C to 114C in which the orientations of the ferrite particles are aligned in a specific direction on the surface thereof and sintered (hereinafter, of these, the highly magnetized magnets 111C and 112C are referred to as the inter-pole developing magnet 111).
It may be C or 112C. ) Are arranged in the circumferential direction, the magnetic flux generated particularly between the inter-electrode developing magnets 111C and 112C passes through the columnar magnet 117, and the developing sleeve 120 surface of the inter-electrode developing magnets 111C and 112C of the magnet body 110 in the developing area. Strength of the magnetic field at 1000G or more, preferably 1300G
The above can be done. According to such a configuration, since the rare earth material is not used for the magnetic core, the cost can be reduced.

Furthermore, the highly magnetized magnet 111C to
114C concentrates the magnetic flux on the surface by setting the width of the columnar magnet 117 in the surface direction to be smaller than the internal width, and particularly in the developing area.
The strength of the magnetic field on the surface of the developing sleeve 120 of the zero gap developing magnets 111C and 112C is increased.

FIG. 8 is a sectional view of the essential parts of the developing devices of the eighth and ninth embodiments.

Since the developing device 100 shown in FIG. 8 has substantially the same structure as that shown in FIG. 1, the members having the same structure and the same function are designated by the same reference numerals and their description is omitted. To do.

The developing sleeve 120 has a thickness of 10 to 2 as described above.
It is similar to that shown in FIG. 1 that it is formed in a cylindrical shape from a non-magnetic material such as stainless steel or aluminum having a diameter of 5 mm and is rotatable with respect to the magnet body 110 contained therein.

The magnet body 110 is composed of highly magnetized magnets 111A to 114A in which ferrite particles are aligned in a specific direction and sintered, and are arranged in the circumferential direction, and the magnetized material 111 corresponds to the inter-electrode developing magnet.
A, 112A (hereinafter also referred to as inter-pole developing magnets 111A, 112A) is made of high permeability magnetic material such as permalloy (21.5% Fe-Ni alloy), Mn-Zn ferrite, pure iron, mild steel. Since the magnetic flux generated in the inter-electrode developing magnets 111A and 112A is circulated through the connecting member 116 having a high magnetic permeability by connecting with the connecting member 116 consisting of The strength of the magnetic field on the surface of the developing sleeve 120 of the developing magnets 111A and 112A can be 1000 G or more, and preferably 1300 G or more. According to such a configuration, since the rare earth material is not used for the magnetic core, the cost can be reduced.

[0079]

According to the inventions of claims 1 to 4, the image forming apparatus having the above-mentioned constitution can stably obtain high-quality image formation with good developability and reduced noise at low cost. Could be provided.

According to the fifth to eighth aspects of the present invention, by providing the above-mentioned structure, it is possible to stably obtain high-quality image formation with good developability and reduced noise at low cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a developing device according to a first embodiment.

FIG. 2 is an enlarged cross-sectional view of a developing area in the developing device of this embodiment.

FIG. 3 is an enlarged cross-sectional view of a developing area in the developing device of this embodiment.

FIG. 4 is an enlarged cross-sectional view of a developing area in a conventional developing device.

FIG. 5 is a curve graph showing the relationship between the height of scatter of the developer layer in the gap between the poles and the magnetic flux density on the sleeve surface at the pole upper portion.

FIG. 6 is a cross-sectional view of essential parts in a developing device according to second to fourth embodiments.

FIG. 7 is a cross-sectional view of essential parts in a developing device according to fifth to seventh embodiments.

FIG. 8 is a cross-sectional view of essential parts in a developing device according to eighth and ninth embodiments.

FIG. 9 is a cross-sectional view showing a schematic configuration of an image forming apparatus adopting the KNC process of this embodiment.

[Explanation of symbols]

 10 image carrier 22 writing device (exposure device) 23,100 developing device 110 magnet body 111,112 inter-electrode developing magnet 113,114,115 adjacent magnet 120 developing sleeve D developer

Front page continuation (72) Inventor Shoichi Kawabata Konica Stock Association, Sakura-cho, Hino City, Tokyo

Claims (8)

[Claims] 1. An exposure device for irradiating color-separated light, an image carrier for carrying a latent image according to the color-separated light, and a latent image selectively developed on the toner image according to the color-separated light. In an image forming apparatus including a developing device for forming an image and a transfer device for transferring a toner image formed by superimposing on the image carrier onto a transfer material, the developing device is provided on both sides from a position closest to the image carrier. The latent image is formed by a magnet body that forms a static magnetic field by a magnet having a surface magnetic field of 1000 G or more, a developing sleeve that rotates the circumferential surface of the magnet body, and a magnetic brush composed of a two-component developer on the developing sleeve. An image forming apparatus characterized by making it visible. 2. The image forming apparatus according to claim 1, wherein the magnet body is an anisotropic ferrite sintered magnet embedded in the surface of a cylindrical magnet body. 3. The image forming apparatus according to claim 2, wherein the circumferential width of the surface of the anisotropic ferrite sintered magnet is set to be smaller than the internal width. 4. The image forming apparatus according to claim 1, wherein the magnet body is formed by connecting anisotropic ferrite sintered magnets with a high magnetic permeability material. 5. A magnet body that forms a static magnetic field by a magnet having a surface magnetic field of 1000 G or more on both sides from a position closest to the image carrier, a developing sleeve that rotates the peripheral surface of the magnet body, and the developing sleeve. In a developing device for visualizing a latent image formed on the image carrier by a magnetic brush made of a two-component developer, the magnet is connected by a member made of a high magnetic permeability material. . 6. The developing device according to claim 5, wherein the magnet body is an anisotropic ferrite sintered magnet embedded in a cylindrical magnet body. 7. The developing device according to claim 6, wherein the circumferential width of the surface of the anisotropic ferrite magnetic pole is set to be smaller than the inner circumferential width of the magnetic pole. 8. The developing device according to claim 5, wherein the carrier of the developer is a carrier having a small particle size and low magnetization.