JPH1144997A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device of a flat and thin type capable of improving seal property at the device end part, and preventing such as density lowering at the end part. SOLUTION: This device is provided with a developing roll 104 equipping a magnet 104b inside so as to shift a developer to a developing area, and a magnetic blade 115 preventing developer leakage having a developer agitate- transporting means feeding the developer on the developing roll 104, equipping respective gap between the developing roll only on both end of the developing roll along the peripheral direction. The magnetic blade 115, arranged opposite to the magnet 104b, while the magnetic blade in a position opposite to a peeling area where the developer is peeled by the magnetic pole of the magnet 104b on the developing roll 104, is constituted by making the gap G1 between the magnetic blade 115 and the developing roll 104 large. The large gap G1 of the magnetic member (side seal) 115 opposite to the separating part N1 of the developer on the developing roll 104 makes possible to weaken the magnetic field on this section, to improve a separating performance for the developer, to prevent the density lowering on the end part, and thus to obtain the stable image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for preventing a developer from spilling out of the apparatus and reducing the density at the end of an image area.

[0002]

2. Description of the Related Art Conventionally, as a developing device for developing an electrostatic latent image formed on a latent image carrier, various types of devices have been proposed depending on the type of developer used. Particularly in high-speed copying machines, two-component developers are often used. Generally, the developer is made by stirring a developer composed of a carrier composed of an iron powder and a toner mainly composed of a resin in a developing device, and the toner is charged by frictional charging between the two. Then, a magnetic brush is formed on the sleeve of a developing roll in which a permanent magnet is disposed in a cylindrical sleeve made of a non-magnetic material, and only the developing sleeve is driven to rotate so that the two-component developer adheres to the outer periphery of the developing sleeve. Transport. When the developer attached to the developing sleeve comes into contact with the latent image carrier on which the electrostatic latent image is formed, the toner flies and adheres to the electrostatic latent image portion to form a toner image,
Be visualized. On the other hand, the carrier from which the toner has been removed
Due to the magnetic force of the magnet roll, it moves with the rotation of the developing sleeve while being attracted to the surface of the developing sleeve,
The toner collected and consumed in the developing device is supplied and used repeatedly in the above-described developing process.

In recent years, colorization and graphics of printers, copiers, and the like have been advanced, and developers have been miniaturized to meet the demand for improved halftone reproducibility. As a measure for preventing the developer from spilling in the conventional developing device, as shown in FIG. 17, elastic members (side seals) 116 made of Teflon or the like are provided at both ends between the housing 41 and the developing roll 43 of the developing device 4. It was interposed to prevent spills. However, due to the miniaturization of the developer, the developer is easily mixed between the side seal and the developing roll, and the driving load is increased, and the aggregate generated in this portion is mixed into the developing device, and the developing is performed. There has been a case where the agent regulating member (trimmer) is clogged to cause inconvenience such as white spots on an image.

Japanese Patent No. 2505883 discloses a developer carrying member which is provided at an opening of a developing container for accommodating a two-component developer and has a magnet therein so as to carry and transport the developer on the surface. A configuration is disclosed in which a magnetic member is provided along the circumferential direction with a predetermined gap between the magnetic member and the developer carrier at the end. The magnetic member in this developing device includes:
The axial thickness of the developer carrier is 0.2 mm to 1.0 mm
The angle formed by the magnetic member with respect to the normal line of the peripheral surface of the developer carrying member is 45 degrees or less. Prevents leakage to the part.

[0005]

However, usually,
In order to peel off the developer after the development process from the developer carrier, the magnets in the developer carrier are provided with the same magnetic poles which are aligned with each other, and the attracting force of the developer is reduced to form a developer peeling portion. However, when a magnetic member is provided with a predetermined gap in the circumferential direction of the developer carrying member as in the disclosed device, a magnetic field is also formed at the separated portion, and as a result, the developer does not peel off, and In some cases, the concentration decreased. In particular, in recent years, the size of the main body of the apparatus has been reduced, and accordingly, the developing apparatus has become thin and flat. In a thin and flat developing device, the developer separated from the developer carrier is collected, and a drop between the new developer and the agitating / conveying member for agitating / conveying is reduced, so that the developer separated from the developer carrier is agitated. Without being able to fall freely onto the conveying member, the toner easily adheres to the developer carrier again, and the density tends to decrease as described above.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages, improves the peelability of the developer, and provides a developing device which can always obtain a stable image quality without a decrease in the density of the edge even in a thin and flat developing device. The purpose is to provide.

[0007]

According to the present invention, there is provided a developing device comprising: a developing roll having a magnet therein; a developer stirring / conveying means for supplying a developer to the developing roll; It consists of a magnetic plate fixed in a non-contact manner along the circumferential direction to prevent developer leakage, and faces the developing roll peripheral surface area (peeling area) where the developer on the developing roll is peeled off by the magnetic pole of the magnet. The magnetic plate to be formed has a wide gap with the developing roll only at that portion, or the magnetic plate is provided with the first magnetic plate provided on the upstream side in the developer moving direction and the magnetic plate provided on the downstream side in the developer moving direction. A second magnetic plate to be provided with a gap in the circumferential direction of the roll,
The circumferential gap between the two magnetic plates is provided at a position opposed to a peeling area where the developer on the developing roll is peeled off by the magnetic pole of the magnet. The developing device having this configuration weakens the magnetic field of the magnetic member (side seal) facing the developer carrier and the peeling portion of the developer, improves the peelability of the developer in this portion, and obtains stable image quality.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a schematic diagram of an image forming apparatus to which the present invention is applied. The image forming apparatus includes an image information writing device 3 that converts an image information signal from an image information output device (not shown) into a light signal on a photosensitive member 1 charged to a predetermined surface potential by a charging device 2. A latent image is formed. The latent image on the photoconductor 1 is visualized as a toner image by the developing device 4. Photoreceptor 1 visualized
Is transferred by the transfer unit 5 to a sheet 14 which is a transfer medium conveyed from the sheet feed trays 12 and 13, and is transferred to the fixing device 10.
Is fixed to the sheet 14 and discharged to the discharge tray 11. Further, the toner image remaining without being transferred onto the paper 14 is
The photosensitive drum 1 is scraped off by the cleaning device 7.

FIG. 1 shows an embodiment of the developing device 4 according to the present invention. The developing device 4 develops a latent image formed on the photoconductor 1 by magnetic brush development. The developing device 4 includes a developer chamber 1 in the housing 101.
02 and the developing roll 104 exposed from the
Agitating and conveying members (augers) 105 and 106 disposed in the housing 101 on the rear side of the developing roller 104;
And a trimmer 111 that regulates the height of the spikes of the developer formed on the developing roll 104. Here, the arrangement of the developing roll 104 and the stirring and conveying member 105 in the housing 101 is such that the rotation center position of the stirring and conveying member 105 is lower than the horizontal line X of the rotation center position of the developing roll 104 and the stirring and conveying member 105
The angle α formed by the line Y connecting the rotation center position of the developing roller 104 and the rotation center position of the developing roll 104 to the horizontal line X of the developing roll 104 is approximately 45 ° or less. By disposing the stirring and conveying member 105 with respect to the developing roll 104 in this manner, the height L of the developing device 4 is reduced.
Can be reduced, and the thickness of the developing device 4 can be reduced.

[0010] As shown in FIG.
A rotatable cylindrical sleeve 104a is provided on the outer periphery of a substantially cylindrical magnet member 104b fixed and supported. The developing roller 104 forms a developer magnetic brush on the sleeve 104a by the magnetic force of the magnet member 104b, and conveys the magnetic brush to a position facing the photoreceptor 1 and a developing area with the rotation of the sleeve 104a. It has a configuration. A plurality of magnetic poles are provided on the magnet member 104b. For example, the peeling pole N1 for peeling the developer, the attracting pole N2 for attracting the developer, the transport pole S2 for transporting the developer, the transport pole N3, and the main developing pole S1 for transferring the developer toward the photoconductor 1 are opposite to each other. They are arranged clockwise in order. These are sequentially magnetized on a magnet roll made of ferrite or plastic.

The developing roll 1 having such a magnetic pole arrangement
In FIG. 4, as shown in FIG. 4, the developer is the sleeve 104a between the attracting pole N2, the transport pole S2, the transport pole N3, the developing pole S1, and the peeling pole N1 in which magnetic poles of different magnets are alternately continuous. Supported by On the other hand, the developer is separated from the sleeve 104a between the separation pole N1 and the adsorption pole N2 where the same magnetic pole (N pole) is adjacent. FIG. 5 shows a specific magnetization pattern. That is, there is a portion where the magnetic force becomes 0 between the peeling pole N1 and the attracting pole N2, and the developer on the sleeve 104a peels off and falls at this portion.

Next, the structure of the conveying and stirring means will be described with reference to FIG. The transport agitating means includes a first transport agitating member (auger) 10 which is disposed so as to be axially aligned with the developing roll 104.
5 and a second transport agitating member (auger) 106 and a partition plate 109 erected on the housing 101 so as to separate these two augers. The rotation direction of each of the first auger 105 and the second auger 106 or the winding direction of the blade is determined so that the transport direction of the developer is opposite to each other. In the conveying and stirring means shown in the drawing, the first auger 105 is moved from the back side to the near side,
Numeral 06 is for transporting and circulating the developer from the near side to the far side. Further, at both ends of the partition plate 109, a region (hereinafter, a first stirring path) 105R in which the first auger 105 is disposed.
And the area where the second auger 106 is provided (hereinafter referred to as the second
A stirring path) 106R is formed, and openings 150 for communicating and connecting the first stirring path 105R and the second stirring path 106R are provided at both ends of the partition plate 109. The opening 150 allows the developer to flow from the first stirring path 105R to the second stirring path 106.
R → the first stirring path 105R and the developer chamber 102 are circulated. Further, a second stirring path 106R of a partition plate 110 for separating the developer chamber 102 and the toner storage chamber 103 is provided.
On the upstream side (front side), a toner supply port 112 </ b> A communicating with the toner storage chamber 103 is provided. This supply port 112A
The toner replenished by the toner supply means 107 flows into the second stirring passage 106R together with the developer conveyed from the first auger 105, and is supplied to the first stirring passage 105R.
The toner is evenly mixed with the developer before circulating to R.

Here, as a toner supply system, in addition to an integral housing type adjacent to the developer chamber 102 as shown in FIG. 6, a toner box (not shown) as shown in FIG. And a configuration in which toner is supplied from a toner supply port 112 </ b> B provided in the second stirring path. The developer sufficiently stirred by the transport stirring means configured as described above is attracted to the developing roll 104 by the magnetic force of the attracting pole N2 to form a magnetic brush, and is formed on the attracting pole N2 and the transport pole S3. While being held by the developing sleeve 104a by the magnetic field, the developer is conveyed along the developer supply path as the sleeve 104a rotates.

A trimmer 111 is provided in the middle of the developer supply path so as to correspond to a gap between the transport pole S2 and the transport pole N3. In the disposition portion of the trimmer 111, the height of the magnetic brush is regulated by the gap between the trimmer 111 and the sleeve 104a, and the transported developer is transported to the developing area with a constant layer thickness. . The trimmer 111 is made of a non-magnetic material such as aluminum or stainless steel. However, even if a magnetic material is used, the height of the spikes can be regulated. Further, as shown in FIG. 2, a configuration may be adopted in which a magnetic plate 111a made of a magnetic material is attached to the tip of the trimmer 111 made of a non-magnetic material to partially magnetize the trimmer 111.

The carrier of the developer used in the present invention has a particle size of 35 to 50 μm and an electric resistance value of 10 ⁸ to 10.
Ferrite particles having a resin resistance of ¹³ Ω · cm are preferably coated with a resin, but are not necessarily limited thereto. Further, the developing device includes a developing sleeve 1
04a at both ends in the axial direction.
A plate-shaped side seal 115 is arranged so as to surround the area a. The side seal 115 is attached to the side wall 101a of the housing 101 (see FIG. 8).

The side seal 115 has a thickness t = 1.0 to
A plate made of a magnetic material of about 2.0 mm, and the trimmer 111
It is arranged until just before. A gap G between the peripheral surface of the developing sleeve 104a and the gap G2, which is a specified gap, is 0.5 mm.
It is set in a range of about 1.0 mm. in this way,
The side seals 115 made of a magnetic material disposed at both ends of the developing sleeve 104a so as to be orthogonal to the rotation axis of the sleeve 104a are magnetized by the magnetic force of the magnet 104b in the developing sleeve 104a. As shown, a magnetic field is generated between the side seal 115 and the developing sleeve 104a, and a magnetic brush T of the developer is formed there. The magnetic brush formed between the developing sleeve 104a and the side seal 115 functions as an end seal between the developing sleeve 104a and the housing 101.

The side seal 115 is a magnet 104
A cutout portion 115c is provided at a portion opposing the same pole portion b (between N1 and N2 poles). The notch 115c provided in the side seal 115 is a portion opposed to the same pole portion (between N1 and N2 poles) of the magnet 104b so that the magnetic field generated between the magnets 104b does not concentrate on the portion where the abrupt interval changes. Then, slowly loose the sleeve 104a
Is changed continuously. That is, the notch 115c forms a chevron-shaped recess having a curved surface, and the gap between the peeling pole N1 corresponding to the end of the side seal 115 and the side seal 115 becomes a gap G2, which is a narrow gap. The gap is increased, and the gap between the separation pole N1 and the adsorption pole N2 is formed as the largest gap G1. Further, the gap is gradually reduced to a gap G2 equal to the gap with the peeling pole N1 at a position facing the adsorption pole N2. Notch 115c provided on side seal 115 and developing sleeve 104a
The largest gap G1 is G1 = 2.0
It is set to about 5.0 mm.

Here, the relationship between the size of the gap G1 of the notch 115c and each characteristic value (developer spill / lower edge density) was examined. The conditions of the experiment at this time were as follows: developing roll: φ18 developer transport amount: 660 g / m ² rotation speed: 450 rpm side seal: t = 1.5 mm distance between magnet and side seal: 0.5 mm developer: carrier 50 μm, The toner was 9 μm. The amount of developer spill was measured without the photoconductor facing the developing roll.

FIG. 9 shows the result. Here, a double circle indicates a state in which the density does not decrease, a triangle to a triangle indicates a state in which the density gradually decreases, and a cross indicates a state in which the density decreases most. As this graph shows,
When the gap G1 is increased, the spill amount of the developer increases.
However, the density at the end does not decrease as the gap G1 becomes larger (wider). Therefore, if the upper limit of the amount of developer spill is 5 mg / min, the gap G1 is set to 5 mm or less, preferably 2 mm or more, so that the amount of spill is within an allowable range and the density decrease is small. Therefore, G1 = G1 of the concave portion 115c of the side seal 115 of the developing device 4
It is set to 2.0 to 5.0 mm.

By configuring the side seal 115 in this way, the distance between the side seal 115 and the surface of the developing sleeve 104a is greatly changed between the N1 and N2 poles to weaken the magnetic field generated between the side seal 115 and the magnet 104b. This prevents the developer separated from the developing sleeve 104a at the separation pole N1 from re-adhering to the sleeve.

Here, the notch 115c and the sleeve 1
When the gap G between the developing sleeve 104 and the developing sleeve 104 is formed as a concave portion having an abrupt change, the magnetic field concentrates at a step where the distance from the developing sleeve rapidly changes, and a large amount of developer adheres to the developing sleeve 104a.
Since the removability of the developer from above may be hindered, the curved surface is formed to avoid a sudden change in the gap. The magnetic force generated between the N1 and N2 poles is 5 mT on the same polarity side.
(Millitesla) or less, and is set so as not to generate a magnetic force on the opposite polarity side (here, the S pole side). Outside this range, the developer may not reach the developing sleeve 10 at the peeling pole N1.
In many cases, density unevenness or the like occurs at the end without peeling off from the edge 4a.

Further, as shown in FIG. 10, the end 115d of the side seal 115 on the upstream side in the developer moving direction is disposed at a position extending by a dimension n in the direction of the developing pole S1 from the peeling pole N1 of the magnet 104b. ing. By arranging the end portion at this position, the end portion 115 d of the side seal 115 is provided.
A magnetic brush T of the developer is formed between the first and N1 poles by an appropriate magnetic field, and seals the end with the housing 101. On the other hand, as shown in FIG. 11, when the end 115d of the side seal 115 is located closer to N2 than the N1 pole (closer to the peeling region), a strong magnetic field is generated between the end 115d and the upstream side in the developer movement direction. As a result, a large amount of the developer is adsorbed to the tip 115d. And finally the developer T ₀ which the developer flows to the outside beyond the end 115d of the side seal 115 occurs (see Fig. 12).

Next, the other end of the side seal 115, which is the end 115e on the downstream side in the developer movement direction, is
11. The gap G3 between the end 115e on the trimmer 111 side and the trimmer 111 is 0.5
mm or less, desirably zero. If the gap G3 between the trimmer 111 and the end portion 115e of the side seal is large, the sealing property between the end portion of the trimmer 111 and the side seal 115 is reduced, and the developer spills out of this portion.

Next, the side seal 115 and the magnet 1
A description will be given of the setting of the axial positional relationship with FIG.
reference). The side seal 115 is disposed axially outside the end of the magnet 104b. And magnet 1
Assuming that the gap between the end of 04b and the side seal 115 is G5, the gap G5 is set to 0 to 1 mm.

Here, the amount of developer spillage with respect to the gap G5 between the magnet end 104b and the side seal 115 will be examined. The conditions of the developing device in this test are as follows: developing roll: 18 mm developer: carrier: average particle diameter: 50 μm, toner:
··· Average particle diameter 9 µm Amount of developer transported ··· 660 g / m ² Number of rotations: 450 rpm Side seal ··· t = 1.5 mm Magnet length ··· 302 mm G1 gap ··· 3.0 mm

FIG. 14 shows the results. Here, a double circle indicates a state in which the density does not decrease, a triangle to a triangle indicates a state in which the density gradually decreases, and a cross indicates a state in which the density decreases most. According to this graph, the lowering of the density at the end is smaller as the gap G5 is larger, but the spill amount of the developer is sharply increased when the gap G5 is larger than 1 mm. On the other hand, if the allowable amount of the developer spill is 5 mg / 5 min or less, the density is reduced and the amount of the developer spill is within the allowable range by setting the gap G5 to 1 mm or less.

Next, on the side seal 115 side of the tip of the trimmer 111 made of a non-magnetic material according to the present invention,
A case of a developing device to which a magnetic plate 111a made of a magnetic material is attached will be described with reference to FIGS. Trimmer 11
In a configuration in which a part of the magnetic head 1 is magnetized and used, FIG.
As shown in the figure, the gap G4 between the side seal 115 and the end of the magnetic plate 111a is disposed within the range of the thickness t of the side seal 115. This is because, when the end of the magnetic plate 111a is disposed axially inside the end 115b on the inner side in the axial direction of the side seal 115, the developer layer at the end on the developing sleeve 104a rises by this portion. Therefore, the possibility of causing a problem such as spilling of the developer and adhesion of the developer to the photoconductor increases. Conversely, when the end of the magnetic plate 111a is disposed axially outside the end 115f outside the side seal 115, the outside 115 of the side seal 115
This is because the developer easily wraps around from f to the end of the magnetic plate 111a, and the developer may spill if it is forced.

A magnetic plate 111 is provided inside the trimmer 111.
An actual running test was carried out on the developing device provided with a. The conditions of the developing device are as follows. Photoreceptor: φ84 mm OPC-ST Process speed: 280 mm / sec Developer: Carrier, average particle diameter 50 μm Ferrite Resistance value 10 ⁹ Ω · cm Toner: average particle diameter 9 μm Polyester resin Developing device: development roll: φ18 mm Surface processing: 50 V-grooves (aluminum) Number of rotations: 410 rpm Developing magnetic pole force: 120 mT Amount of developer transport: 600 g / m ² Side seal t = 1.5 mm Gap (gap) G1: 3 mm Gap G2: 0. 5 mm Gap G3: 0.3 mm Gap G4: 0.5 mm Gap G5: 0.5 mm Distance between photoconductor and developing sleeve 0.5 mm About 100,000 copies (A4 horizontal feed) were run.
It was confirmed that the developer did not spill out from the side seal 115 and the developer did not enter the bearings and the like.

Another embodiment according to the present invention will be described with reference to FIG. Side seal 1150
Is a first side seal 115 provided on the peeling pole N1 side.
0a and a second side seal 1150b disposed on the trimmer 111 side. The first side seal 1150a and the second side seal 1150b are arranged with a predetermined interval h, and the separation pole N1 and the adsorption pole N
2, there is no side seal 1150 at a position corresponding to the developing roll 104, and an interval h is located. The first side seal 1150a has a leading end extending toward the developing region from a position corresponding to the peeling pole N1, and a leading end 1151a having a constant gap G with the developing roll 104;
There is another end 1153a that gradually increases the gap G with the other end. The second side seal 1150b is almost
2 is disposed at a position corresponding to the magnetic plate 111a disposed on the trimmer 111 from the position corresponding to the position No. 2 and the end 1151b corresponding to the adsorption pole N2 is an end surface having a curvature. The other end 1153b is a magnetic plate 1 disposed on the trimmer 111.
11a is arranged at 0.5 mm or less.

Also in the developing device of this embodiment, the side seal 1150 is provided with a portion where the side seal does not exist corresponding to the developing roll between the peeling pole N1 and the attracting pole N2.
The magnetic field generated between the side seal 115 and the magnet 104b is weakened to prevent the developer separated from the developing roll 104 from re-adhering to the developing roll at the separating pole N1.
As a result, there is no lowering of the density at the end, and a reliable function of sealing the end of the apparatus is achieved. Further, in this embodiment, the rotation center of the stirring / conveying member is disposed within a lower portion of 45 ° from the horizontal line of the rotation center position of the developing roll. From the viewpoint of properties, even if the rotation center of the stirring / conveying member is disposed at a position lower than or equal to 45 ° from the rotation center of the developing roll, the effect can be sufficiently obtained.

[0031]

According to the present invention, in a developing apparatus using a side seal made of a magnetic material as an end seal, a magnetic member (side seal) opposed to a developer peeling portion of a developer carrier. It is possible to provide a developing device in which the magnetic field is weakened by widening a part of the gap, the releasability of the developer is improved, and a stable image quality is obtained without causing a density reduction at the end. In addition, since the disposition position of the developer conveying device is not immediately below the developing roll, the size of the device in the height direction can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a cross section of a developing device according to the present embodiment.

FIG. 2 is an explanatory diagram illustrating an axial section of the developing device.

FIG. 3 is a schematic diagram of an image forming apparatus according to the embodiment.

FIG. 4 is an explanatory diagram of the vicinity of a developing roll of the developing device.

FIG. 5 is an explanatory view showing an example of a magnetized pattern of a magnet.

FIG. 6 is an explanatory top view of the developing device.

FIG. 7 is a partially cutaway top view showing another embodiment of the developer transfer device.

FIG. 8 is an explanatory view of disposing a side seal according to the embodiment.

FIG. 9 is a graph showing a relationship between a gap (G1) between a cutout portion of a side seal and a developing roll and each characteristic value.

FIG. 10 is an explanatory diagram of an operation of a side seal.

FIG. 11 is an explanatory view of the operation of another side seal.

FIG. 12 is an explanatory diagram of an operation of another side seal.

FIG. 13 is an explanatory diagram illustrating a positional relationship between a side seal and a magnet according to the present embodiment.

FIG. 14 is a graph showing a relationship between a gap (G5) between a magnet end portion and a side seal and each characteristic value.

FIG. 15 is an explanatory diagram showing a positional relationship between a magnetic plate of the trimmer and a side seal.

FIG. 16 is an explanatory sectional view showing another embodiment of the side seal.

FIG. 17 is an explanatory view of an axial section showing a conventional side seal.

[Explanation of symbols]

1 photoconductor, 4 developing device, 101 housing,
102 developer chamber, 103 toner storage chamber, 104
Developing roll, 105, 106 developer transport stirring member, 111 trimmer, 115 side seal,
1150a first side seal, 1150b second
Side seal.

Claims (6)

[Claims] 1. A developing roll in which a magnet is arranged so as to move a developer to a developing area; a developer stirring and conveying means for supplying a developer to the developing roll; A developing device having a magnetic plate for preventing developer leakage, which is disposed along the circumferential direction with a gap between the developing roll and the developing roller, wherein the magnetic plate is disposed to face the magnet And a magnetic plate disposed at a position facing a peeling region where the developer on the developing roll is peeled off by the magnetic pole of the magnet, and a gap between the magnetic plate and the developing roll is configured to be large. 2. A developing roller in which a magnet is provided so as to move the developer to a developing area, a developer agitating / conveying means for supplying a developer to the developing roller, A magnetic plate for preventing developer leakage, which is provided with a gap between the developing roll and the developing roll along the circumferential direction, wherein the magnetic plate is disposed to face the magnet. And a first magnetic plate disposed on the upstream side in the developer movement direction, and a second magnetic plate disposed on the downstream side in the developer movement direction. The magnetic plate of No. 2 is disposed with a gap in the circumferential direction of the developing roll, and the circumferential gap faces a peeling area where the developer on the developing roll is peeled by the magnetic pole of the magnet. A developing device arranged at a position. 3. The magnetic plate according to claim 1, wherein the gap between the magnetic plate and the developing roll is gradually increased continuously in a peripheral region of the developing roll where the developer on the developing roll is peeled. Developing device. 4. The first magnetic plate and the second magnetic plate are formed so that the gap-side end surface in the circumferential direction of the developing roll gradually increases the distance from the developing roll. 3. The developing device according to 2. 5. The developer stirring and conveying means is disposed below a horizontal line at the rotation center of the developing roll, and a line connecting the rotation center of the developer stirring and conveying means to the rotation center of the developing roll. 3. The developing device according to claim 1, wherein an angle between the rotation center of the developing roller and a horizontal line is within a range of 45 [deg.]. 6. The magnetic plate according to claim 1, wherein an end of the magnetic plate on an upstream side in a developer moving direction is a developer of an adjacent one of the same magnetic poles provided on the magnet for separating the developer from the developing roll. 3. The developing device according to claim 1, wherein the developing device is disposed closer to the developing region than the magnetic pole arrangement position that is upstream in the moving direction.