JPH10133479A - Dry developing device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the adhesion of carrier in a developer to a latent image carrier by providing a means for preventing a magnetic brush consisting of two-component type developer from coming into contact with a latent image carrier and a gap between a developing sleeve and the contact preventing means so that the magnetic brush may rub the contact preventing means. SOLUTION: An angle formed by a line passing the center of flux density distribution by a main pole M in the periphery direction of the developing sleeve 1 and the center of the sleeve 1 with a line passing the peak of the flux density distribution by a carrying pole in the periphery direction of the sleeve 1 and the center of the sleeve 1, is set to <=25 deg.. Meanwhile, the contact preventing means for preventing the magnetic brush MB2 consisting of the two-component developer formed by the carrying pole from coming into contact with the latent image carrier constituted of a photoreceptor 7 is provided along the peripheral surface of the sleeve 1, and the gap between the sleeve 1 and the contact preventing member 10 is set so that the magnetic brush MB2 consisting of the two-component developer formed by the carrying pole may always rub the member 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing case for containing a two-component developer, a developing sleeve for carrying the two-component developer pumped on the surface thereof while being driven to rotate, and a developing sleeve inside the developing sleeve. A main pole for forming a magnetic brush of a two-component developer on the surface of the developing sleeve, which is provided for visualizing the electrostatic latent image formed on the latent image carrier, and a developing sleeve And transports the two-component developer on the surface of the developing sleeve located downstream of the main pole with respect to the moving direction of the latent image carrier in cooperation with the rotation of the developing sleeve. And a transport pole for returning the two-component developer to the side of the developing case.

[0002]

2. Description of the Related Art A dry developing apparatus of the above-mentioned type used in an image forming apparatus such as an electronic copying machine, a printer or a facsimile has been well known. In this type of developing apparatus using a dry two-component developer having a toner and a carrier, a magnetic brush of the developer is formed by a main pole of a magnet disposed in a developing sleeve, and thereby an electrostatic latent image is formed. Visualized. That is, the toner in the developer is electrostatically transferred to the electrostatic latent image and development is performed. At that time, the carrier in the developer is conveyed while being carried on the developing sleeve without shifting to the electrostatic latent image. Thus, the carrier should not adhere to the latent image carrier.

However, carriers in a developer which should not actually adhere to the latent image carrier sometimes adhere to the surface of the carrier. When such a carrier adhesion phenomenon occurs, white spots occur in the solid image of the developed visible image, and the attached carrier enters another unit in the image forming apparatus and causes an abnormality in the unit. There is a risk of squeezing.

Therefore, various measures have been made to prevent the carrier from adhering to the latent image carrier. For example, a typical method is to provide a carrier removing magnet downstream of the developing device in the moving direction of the latent image carrier, and to attract the carrier adhered to the surface of the latent image carrier by the magnet. However, if such a magnet is provided, the structure becomes complicated and the cost increases.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dry developing apparatus of the type described at the beginning which can eliminate the above-mentioned disadvantages of the prior art and can suppress the adhesion of carriers to a latent image carrier with a simple structure. It is to provide.

[0006]

According to the present invention, there is provided a dry developing apparatus of the type described at the beginning, wherein the center of the magnetic flux density distribution by the main pole in the circumferential direction of the developing sleeve and the center of the developing sleeve are provided. And a straight line passing through the center of the developing sleeve with the peak of the magnetic flux density distribution by the transport pole in the circumferential direction of the developing sleeve is set to 25 degrees or less, and a two-component system formed by the transport pole is formed. Contact prevention means for preventing the magnetic brush of the developer from contacting the latent image carrier is provided outside the developing sleeve and along the peripheral surface of the developing sleeve, and is formed by the transport pole. Dry development of an image forming apparatus, wherein a gap between a developing sleeve and a contact preventing means is set so that a magnetic brush of a two-component developer rubs the contact preventing means. Suggest location (claim 1).

At this time, on the surface of the developing sleeve, the intensity of the magnetic field in the normal direction of the developing sleeve due to the main pole is approximately half of the maximum value of the magnetic flux density distribution shown outside the normal direction of the developing sleeve. Among the intersections of the arc with the center of the developing sleeve and the lines on both sides of the magnetic flux density distribution, a straight line connecting one intersection and the center of the developing sleeve, and the other intersection and the center of the developing sleeve. It is particularly advantageous to configure the main pole so that the angle between the main pole and the straight line connecting is not more than 30 degrees (claim 2).

[0008]

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

FIG. 1 shows a dry developing device in an electronic copying machine. Reference numeral 1 denotes a developing sleeve made of a non-magnetic material which is driven to rotate clockwise. A plurality of magnets 2 and 3 are provided inside the developing sleeve 1. , 4 and 5 are fixedly arranged in the circumferential direction of the developing sleeve 1. The magnetic poles S and N of each magnet facing the inner peripheral surface of the developing sleeve 1 are set as illustrated in FIG. Of these, the magnetic pole of the magnet 4 substantially facing the photoreceptor 7 described later is the main pole M, and the magnetic pole of the adjacent magnet 5 is the transport pole T.

The developing case 6 contains a dry two-component developer having a toner and a magnetic carrier, and the two-component developer is pumped up to the vicinity of the developing sleeve 1 by a pumping means (not shown). Next, the two-component developer is attracted to the peripheral surface of the developing sleeve 1 by the magnetic force of the magnets 2 and 3 serving as the pumping magnets. At this time, since the developing sleeve 1 is rotating clockwise, the two-component developer adsorbed on the developing sleeve 1 is conveyed in the rotating direction of the sleeve 1 and is scraped by the doctor blade 8. The two-component developer whose transport amount is regulated by the doctor blade 8 is continuously transported while being carried on the developing sleeve 1. When the two-component developer is transported close to the main pole M, the two-component developer is brushed by the magnetic force of the main pole M. become. That is, the magnetic brush MB1 of the two-component developer
Is formed.

On the other hand, a belt-shaped photoreceptor 7, which is an example of a latent image carrier, is transported in the direction of arrow A, and an electrostatic latent image is formed on the surface of the photoreceptor 7 by a latent image forming means (not shown). Are formed. The photoreceptor 7 passes through the magnetic brush MB1 formed by the main pole M as described above. At this time, the magnetic brush MB1 is rubbed against the electrostatic latent image on the photoreceptor 7 to form the magnetic brush MB1. The toner in the component developer electrostatically transfers to the latent image, and the latent image is visualized.

As described above, the main pole M disposed in the developing sleeve develops the magnetic brush MB1 of the two-component developer used for visualizing the electrostatic latent image formed on the photosensitive member 7. For forming on the sleeve 1.

The two-component developer that has passed through the main pole M is disposed in the developing sleeve, and is transferred to the transport pole T located downstream of the main pole M with respect to the moving direction of the photoconductor 7. Due to the magnetic force, the toner is conveyed while being carried on the developing sleeve 1, and then separated from the developing sleeve 1 and returned to the bottom of the developing case 6. Thus, the transport pole T cooperates with the rotating developing sleeve 1 to transport the two-component developer on the developing sleeve 1 back to the developing case 6. 9
Reference numeral denotes a scraper for removing the two-component developer from the developing sleeve 1.

As described above, the dry developing device of the illustrated image forming apparatus has a developing case 6 containing a two-component developer.
And a developing sleeve 1 that carries the two-component developer pumped on its surface while being driven to rotate, and a static image formed on the latent image carrier formed of the photoconductor 7 and disposed in the developing sleeve. A main pole M for forming a magnetic brush MB1 of a two-component developer on the surface of the developing sleeve, which is used for visualizing the electrostatic latent image, and a movement of the latent image carrier, which is also arranged in the developing sleeve. The two-component developer on the surface of the developing sleeve located downstream of the main pole M with respect to the direction is transported in cooperation with the rotation of the developing sleeve 1, and the two-component developer is transferred to the developing case 6. And a transport pole T that returns to the side of.

When the carrier in the two-component developer carried on the developing sleeve 1 adheres to the photoreceptor 7 during the above-described developing operation, as described above, the visible image after development becomes white. Problems such as dropouts occur. Conventionally, to remove this defect, the carrier attached to the photoreceptor surface was removed by a carrier removing magnet. However, the addition of such a magnet did not avoid problems such as a complicated structure. .

On the other hand, the dry developing apparatus of this embodiment can reduce the adhesion of the carrier to the photosensitive member only by disposing the magnet in the developing sleeve without complicating the structure and increasing the cost. It is configured as follows. That is, according to an experiment performed by the inventor, the relative position between the transport pole T and the main pole M has a significant effect on carrier adhesion, and the closer the transport pole T is to the main pole M, the more the carrier adhesion can be reduced. It turned out. This will be described in detail with reference to FIG.

FIG. 2 is an explanatory diagram showing the magnetic flux density distribution in the sleeve circumferential direction by the magnets 2, 3, 4, and 5 in the developing sleeve 1. In other words, the distribution is obtained by measuring the strength of the magnetic field in the normal direction of the developing sleeve 1 on the peripheral surface of the developing sleeve 1 and showing the measured value outside the normal direction of the developing sleeve 1. X in FIG. 2 is a magnetic flux density distribution due to the main pole M, and Y is a magnetic flux density distribution due to the transport pole T.

Here, in the circumferential direction of the developing sleeve 1,
Let B be a straight line passing through the center of the magnetic flux density distribution X by the main pole M and the center O of the developing sleeve 1, and pass through the peak of the magnetic flux density distribution Y by the transport pole T in the circumferential direction of the developing sleeve 1 and the center O of the developing sleeve 1. Assuming that the straight line is C, the smaller the angle θ between B and C of the two straight lines is compared with that of a conventional developing device of this type, the more the carrier adheres to the photoconductor 7 can be reduced.

The adhesion of the carrier to the photoreceptor 7 is affected by the characteristics of the two-component developer, the linear velocity of the developing sleeve 1, the strength of the magnetic force of the main pole M, and the like. As a result, by setting θ ≦ 25 degrees, it was possible to more effectively reduce carrier adhesion to the photoconductor 7 than in the related art. In the drawings, the angle θ is set to 2 in order to make the figures easy to understand.
The figure is shown with the angle greater than 5 degrees.

As described above, the dry developing device of the present embodiment has a straight line B passing through the center of the magnetic flux density distribution X by the main pole M in the circumferential direction of the developing sleeve 1 and the center O of the developing sleeve 1.
And the angle θ formed by the straight line C passing through the peak of the magnetic flux density distribution Y due to the transport pole T in the circumferential direction of the developing sleeve 1 and the center O of the developing sleeve 1 is set to 25 degrees or less. Carrier adhesion to the carrier can be reduced.

When the transport poles T are arranged as described above, the following inconvenience may occur. That is, the magnetic brush MB2 (FIG. 1) of the two-component developer formed by the transport pole T sometimes comes into contact with or rubs against the surface of the photoconductor 7 due to fluttering of the belt-shaped photoconductor 7, and the like. The visible image after the development may be abnormal or the carrier may scatter from the magnetic brush MB2 of the transport pole T.

Therefore, in the dry developing apparatus of this embodiment, the magnetic brush M of the two-component developer formed by the transport pole T is used.
Contact prevention means for preventing B2 from contacting the latent image carrier made of the photoconductor 7 is provided outside the developing sleeve 1 and along the peripheral surface of the developing sleeve 1. In the embodiment shown in FIG. 1, the contact preventing means comprises a non-magnetic member preventing member 10 formed integrally with the developing case 6, which comprises a magnetic brush MB2 and a photosensitive member 7.
The magnetic brush MB
2 and the photoconductor 7 are prevented from contacting with each other. As a result, the above-described problem can be prevented from occurring. Further, even if such a prevention member 10 is provided, the effect relating to the carrier adhesion to the photoconductor is not lost.

The gap between the developing sleeve 1 and the contact preventing member 10 is set so that the magnetic brush MB2 of the two-component developer formed by the transport pole T always rubs the preventing member 10 which is an example of the contact preventing means. Have been. As a result, the magnetic brush MB2 closes the gap formed by the contact preventing member 10 and the developing sleeve 1, that is, the opening toward the outside, so that the toner is prevented from blowing out from inside the developing case 6 through this opening. And scattering of the toner can be prevented.

It is obvious that the above-described configurations can be widely applied to an image forming apparatus using a drum-shaped latent image carrier and a developing device of an image forming apparatus using a latent image carrier other than a photosensitive member. Shows an example of an image forming apparatus in which the latent image carrier is configured as a drum-shaped photoconductor.

In FIG. 3, the developing sleeve 11 is driven to rotate counterclockwise, and five magnets P1 to P5 are developed in the circumferential direction inside the developing sleeve so as to face the inner peripheral surface. The magnetic poles S and N of each magnet are fixedly arranged in the circumferential direction of the sleeve 11, and are set as illustrated in the figure. Of these, the magnetic pole of the magnet P1 substantially facing the photoconductor 12 is the main pole.

The two-component developer contained in the developing case 13 is pumped up while being transported by the developer agitating transporting pumping member 14, and then this developer is urged by the magnetic force of the magnets P3 and P4 to form a peripheral surface of the developing sleeve 11. Is adsorbed.

At this time, since the developing sleeve 11 is rotating in the counterclockwise direction, the two-component developer adsorbed on the developing sleeve 11 is conveyed in the rotating direction of the developing sleeve 11 and is scraped off by the doctor blade 15. Receive. The two-component developer whose transport amount is regulated by the doctor blade 15 is continuously transported while being carried on the developing sleeve 11, and when this is transported near the main pole of the magnet P1, the brush is brushed by the magnetic force of the main pole. To form a two-component developer magnetic brush.

On the other hand, a drum-shaped photosensitive member 12, which is an example of a latent image carrier, is rotated in the direction of the arrow, and an electrostatic latent image is formed on the surface of the photosensitive member 12 by a latent image forming means (not shown). Have been.

The photoreceptor 12 passes through the magnetic brush formed by the main pole as described above. At this time, the magnetic brush is rubbed against the electrostatic latent image on the photoreceptor 12 to constitute the magnetic brush. The toner in the two-component developer electrostatically transfers to the electrostatic latent image, and the electrostatic latent image is visualized.

As described above, also in the embodiment shown in FIG. 3, the main pole, which is the magnetic pole of the magnet P1 disposed in the developing sleeve 11 that is driven to rotate, is the electrostatic pole formed on the photosensitive member 12. A magnetic brush of a two-component developer used for visualizing a latent image is formed on a developing sleeve. Further, the magnetic pole of the magnet P2 is disposed in the developing sleeve 11, and the two-component developer on the surface of the developing sleeve located downstream of the main pole with respect to the moving direction of the photoconductor 12 is rotated by the rotation of the developing sleeve 11. Cooperates with the developing member 13 to return the two-component developer to the developing case 13 side.

By the way, the carrier in the developer adheres to the surface of the latent image carrier, causing white spots in the solid image of the developed visible image, which is one factor that deteriorates the image quality. Other factors that degrade the image quality include the fact that the value of the ratio of the thick line between the vertical and horizontal lines of the visible image to the original image (vertical / horizontal line image ratio) deviates from a desirable value, and the leading edge of a solid image or the like. A jagged white spot is formed on the side and the rear end side. Hereinafter, this point will be clarified more specifically.

The carrier and the toner particles of the two-component developer used in this type of developing device are frictionally charged to different polarities. At the time of the frictional charging, the toner particles and the substances contained therein are charged to the carrier. The so-called spent phenomenon may be caused to remain, and the triboelectric charging property may be reduced. Conventionally, a developer containing a carrier coated with a substance having a low surface energy (high-resistance substance) such as polyfluoroethylene, silicone resin, or styrene-methalkylacryl has been used as a developer. It is difficult.

However, in this type of developing device,
The line latent image parallel to the moving direction of the photoreceptor surface and the line latent image in the direction orthogonal thereto have different developing capabilities,
The ratio of the vertical line width to the original image obtained by visualizing a parallel line latent image and the similar horizontal line thickness obtained by visualizing a line latent image in the direction perpendicular to the original image (vertical and horizontal). (Line drawing ratio) greatly deviates from 1 and image quality may be degraded. As the value of this ratio is closer to 1, the thickness of the vertical and horizontal lines is more balanced, and a visible image faithful to the original image is obtained.

On the other hand, when developing at the “solid portion”, the linear velocity when the developer on the developing sleeve moves is
As shown in FIG. 9, in the case of the so-called “wiz mode” in which the moving direction of the photosensitive member is faster than that of the photosensitive member and the moving direction of the both members, as shown in FIG. The rear end portion is in a jagged white state,
As shown in (1), the edge of the blank image (negative image) is jagged. Hereinafter, such a thing is referred to as “radiid”.

On the other hand, in a so-called counter mode in which the moving direction of the photosensitive member and the moving direction of the developer on the developing sleeve are opposite to each other, the leading end side of the image is radiated. Eventually, the occurrence of such a radix significantly reduces the image quality.

The embodiment shown in FIG. 3 is configured as follows in order to eliminate the above-mentioned disadvantage.

FIG. 4 shows the magnets P1 and P1 shown in FIG.
9 shows a magnetic flux density distribution of P2, P3, P4, and P5. That is, the strength (Oersted) of the magnetic field in the normal direction of the developing sleeve 11 made of a non-magnetic material is measured on the surface (peripheral surface) of the developing sleeve 11, and the value is taken outside in the normal direction of the developing sleeve 11. It shows the distribution shown. At this time, in this example, the magnetic flux density distribution by the main pole (hereinafter, the main pole is denoted by reference numeral P1) is set as follows.

Now, assuming that the line L is the center of the main pole P1 in the circumferential direction of the developing sleeve 11, the magnetic flux density distribution shows that the strength of the magnetic field rises at a stroke toward the main pole center L, and the main pole center L Has the maximum value at.

Here, the rotation center of the developing sleeve 11 is O
₁ , the main pole P1
The intensity of the magnetic field in the normal direction of the developing sleeve is approximately half of the maximum value of the magnetic flux density distribution indicated outside the normal direction of the developing sleeve, and the lines E and F on both sides of the magnetic flux density distribution , A line on the circumferential direction of the developing sleeve (that is, passing through E and F, the center of the developing sleeve O)
A straight line L ₁ connecting _one intersection H and the center O _{1 of the} developing sleeve 11 among two intersections H and I of an arc (centered at ₁ ) G and lines E and F on both sides of the magnetic flux density distribution, and A straight line L ₂ connecting the other intersection point I and the center O ₁ of the developing sleeve 11
The main pole is configured so that the angle α formed by the main pole is 30 degrees or less.

When the angle α increases, the width of the magnetic flux density distribution increases, and when the angle α decreases, the width of the magnetic flux density distribution narrows. The length between the points I and H in the circumferential direction of the developing sleeve in the magnetic flux density distribution is referred to as a half-width for convenience and the angle α is referred to as a half-value angle. α is about 39 degrees, and the half width is wide.

On the other hand, in this example, the half-value angle α is set to 30 degrees or less, for example, 27 degrees, and the half-value width is narrower than the conventional case.

If the half-width of the magnetic flux density distribution is wide, the tendency to produce the radix (FIGS. 9 and 10) as described above becomes strong. However, according to an experiment conducted by the present inventors, the half-width has a large value. Has a significant effect on the occurrence, and the half-value angle α is 3
It has been found that if the angle is set to 0 degrees or less, the occurrence of radid can be suppressed as much as possible.

To explain this in detail, as an example, the case where the surface of the developing sleeve 11 moves in the same direction as the surface of the photoreceptor 12 in the developing section and the developer on the developing sleeve moves. Consider a developing condition in which the developing sleeve rotates under the condition that the linear velocity is higher than that of the photoconductor. Here, in order to suppress scattering of the toner from the developing sleeve 11 as much as possible and to prevent background contamination, the main pole P1 (see FIG. 3) is conventionally connected between the developing sleeve and the photoconductor. From the closest part,
For example, when the diameter of the developing sleeve is 40 mm, it is shifted by about 1 to 4 mm to the upstream side in the rotation direction of the developing sleeve 11. This shift amount has to be set larger as the former half width becomes wider.

By the way, the development electric field becomes the strongest
As is already known, this is a portion on the main pole where the carrier chain stands, and development is almost completed at this portion. In the remaining developing area of the width in the circumferential direction of the developing sleeve (so-called developing nip portion) where the developer comes in contact with the photoreceptor 12 except for the part where the carrier chain stands, the toner adhering to the photoreceptor is rather scraped off. This is considered to be where the so-called scavenging action is performed.

The fact that the half width is large means that the area where such scavenging which does not substantially contribute to the development is carried out is widened. The longer the distance (the point at which the developer on the developing sleeve separates from the photoreceptor), the more radiated the rear end of the image formed on the photoreceptor, for example, just before the rear end of the image passes through the development nip. Tends to occur.

On the main pole P1, the carrier on the sleeve facing the background of the photoreceptor loses part of the toner and has a high potential. That is, the charging potential is higher than before. When the carrier overtakes the surface of the photoconductor that advances slowly and faces the rear end of the image (the rear end of the latent image on the photoconductor), the carrier acts to attract and collect toner from the photoconductor, This is one of the factors that cause radii at the end of the image and that the visible image of the horizontal line in the direction perpendicular to the direction of movement of the photoreceptor surface does not appear as a good copy, and that the vertical / horizontal line ratio greatly deviates from 1 as described above. It becomes one.

From such a point, the half width of the magnetic flux density distribution of the main pole may be narrowed. For this purpose, for example, the width of the main pole P1, that is, the width in the sleeve circumferential direction is used. May be determined so that the half-value angle of the magnetic flux density distribution is 30 degrees or less, whereby the distance from the point where the developing electric field becomes strongest to the end point of the developing nip portion can be shortened. In addition, the above scavenging action can be suppressed as much as possible, and radid can be hardly generated.

FIG. 5 shows the magnetic flux density distribution of each magnet when the half angle α is 24 degrees. FIG. 6 shows another example of the dry developing device, and FIG. 7 shows the magnetic flux density distribution of each magnet in the developing device. The half-value angle α of the magnetic flux density distribution by the main pole P1 is set to 22 degrees in this example. .

Table 1 shows the evaluation results (experimental results) of the images when the half-value angle is changed.

[0050]

[Table 1]

As shown in Table 1, the half value angle is 27 degrees,
If the angle is made as small as 24 degrees, the evaluation rank for radis rises, radis are less likely to occur, and the image quality is improved.

The "double" in the table indicates the magnification of the thickness of the visible image of the horizontal line and the vertical line with respect to the original image, for example, the line image of the original to be copied, and the horizontal line (horizontal line drawing)
When the half-value angle is reduced, the image becomes slightly fat and slightly sharper as a line image, so that the image quality is improved. As for the vertical line (vertical line drawing), when the half value angle is reduced, the vertical line becomes slightly thinner, and the value of the vertical / horizontal line drawing ratio becomes closer to 1 than before. The value of this ratio is preferably closer to 1 as described above.

It goes without saying that the above-described configuration can also be widely applied to an image forming apparatus using a belt-like latent image carrier or an image forming apparatus using a latent image carrier other than a photoreceptor.

[0054]

According to the first aspect of the present invention, the adhesion of the carrier to the latent image carrier can be prevented or reduced by a very simple configuration for determining the position of the transport pole with respect to the main pole. In addition, it is possible to prevent a problem that the magnetic brush formed by the transport pole contacts the latent image carrier. Further, the blowing of the toner can be prevented by using the contact preventing means.

According to the second aspect of the present invention, a jagged white image is formed at the leading end or the trailing end of the image by a very simple structure that only reduces the half width of the magnetic flux density distribution of the main pole. It is possible to suppress the occurrence of a defect that causes a dropout as much as possible, a horizontal line drawing can be made sharper, and the vertical and horizontal line drawing ratio can be made closer to 1.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a developing device according to the present invention.

FIG. 2 is an explanatory diagram showing a magnetic flux density distribution formed by a magnet in a developing sleeve.

FIG. 3 is a cross-sectional view illustrating a developing device according to another embodiment.

FIG. 4 is an explanatory diagram showing a magnetic flux density distribution formed by a magnet in a developing sleeve.

FIG. 5 is an explanatory diagram showing a magnetic flux density distribution formed by a magnet in a developing sleeve.

FIG. 6 is a cross-sectional view illustrating a developing device according to still another embodiment.

FIG. 7 is an explanatory diagram showing a magnetic flux density distribution formed by a magnet in a developing sleeve in the embodiment of the embodiment.

FIG. 8 is an explanatory diagram showing a magnetic flux density distribution formed by a magnet in a developing sleeve in a conventional developing device.

FIG. 9 is a diagram for explaining that radii occur in a solid image.

FIG. 10 is a diagram illustrating that a radiid occurs in a negative image.

[Explanation of symbols]

1 developing sleeve 6 development case 11 developing sleeve 13 a developing case B linear C linear line E F line H intersecting point I intersection L ₁ linearly L ₂ straight M dominant pole MB1 magnetic brush MB2 magnetic brush O center O ₁ center P1 dominant pole of the developing sleeve T Carrier pole X Magnetic flux density distribution Y Magnetic flux density distribution α angle θ angle

Continued on the front page (72) Inventor Akio Kutta 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Junji Kurokawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Masaru Tanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (2)

[Claims] A developing case for containing a two-component developer, a developing sleeve for carrying the two-component developer pumped on the surface thereof while being driven to rotate, and a developing sleeve disposed in the developing sleeve; A main pole for forming a magnetic brush of a two-component developer on the surface of the developing sleeve, which is used for visualizing the electrostatic latent image formed on the latent image carrier, and is also disposed in the developing sleeve. Transporting the two-component developer on the surface of the developing sleeve located downstream of the main pole with respect to the moving direction of the latent image carrier in cooperation with the rotation of the developing sleeve; In the dry developing device of the image forming apparatus having a transport pole for returning the developer to the side of the developing case, a straight line passing through the center of the magnetic flux density distribution by the main pole in the circumferential direction of the developing sleeve and the center of the developing sleeve, and In the circumferential direction Angle of straight line 25 passing through the peak of the magnetic flux density distribution due Okukyoku the center of the developing sleeve
Degree or less, contact prevention means for preventing the magnetic brush of the two-component developer formed by the transport pole from contacting the latent image carrier, outside the developing sleeve,
The gap between the developing sleeve and the contact preventing means is provided along the peripheral surface of the developing sleeve, and the magnetic brush of the two-component developer formed by the transport pole rubs the contact preventing means. A dry developing device for an image forming apparatus. 2. On the surface of the developing sleeve, the intensity of the magnetic field in the normal direction of the developing sleeve due to the main pole is substantially half of the maximum value of the magnetic flux density distribution shown outward in the normal direction of the developing sleeve. A straight line connecting one intersection and the center of the developing sleeve, and the other intersection and the center of the developing sleeve, of the two arcs passing through the arc having the center of the developing sleeve as the center and the lines on both sides of the magnetic flux density distribution. 2. The dry developing device for an image forming apparatus according to claim 1, wherein the main pole is formed so that an angle between the straight line and the connecting straight line is 30 degrees or less.