JPH03209489A - Magnetic brush developing device - Google Patents

Abstract

PURPOSE:To obtain a high-definition image by setting the maximum magnetic flux density of a first magnetic field generating means larger than that of a second magnetic field generating means, and the magnetic flux density distribu tion of the second magnetic field generating means so as to have an inflection point on the upstream side than the position of its maximum magnetic flux density. CONSTITUTION:A magnet 13 has a developing magnetic pole S1 as the first magnetic field generating means, a carrier magnetic pole N1 as the second magnetic field generating means of its downstream side, a second carrying magnetic pole N2 as the three magnetic field generating means of its down- stream side, and magnetic poles S2 and N3 carrying a developer 8. The maxi mum magnetic flux density of the first magnetic field generating means S1 is set larger than that of the second magnetic field generating means N1, and simultaneously the magnetic flux density distribution of the second magnetic field generating means N1 is set so as to have the inflexion point on the up stream side than the position of its maximum magnetic flux density. Thus, the carrying properties of a developer 8 are improved, and a high-definition image is obtained.

Description

[Detailed description of the invention] 11 upright balls! The present invention relates to a developing device applied to an image forming apparatus such as an electrophotographic copying machine, an electrostatic recording machine, a magnetic recording machine, etc., and particularly relates to a magnetic brush developing device.

2. Description of the Related Art Magnetic brush developing devices are widely used as means for developing latent images in image forming apparatuses such as electrophotographic copying machines, electrostatic recording machines, and magnetic recording machines.

Various configurations of magnetic brush developing devices have been proposed;
As a typical example, a non-magnetic cylinder (hereinafter referred to as a "sleeve") serving as a developer support means is rotatably arranged in a developer container containing developer, and inside this sleeve,
There is a developing device having a structure in which a plurality of magnetic field generating means, that is, a magnet roller having magnets arranged thereon is fixedly arranged. Such a developing device transports developer from inside a developing container to a developing position approximately opposite to an image bearing member carrying a latent image by rotation of a sleeve. A magnet (hereinafter referred to as the "developing magnetic pole") is disposed at the developing magnetic pole, and another magnet (hereinafter referred to as the "first conveying magnetic pole") is disposed downstream of the developing magnetic pole in order to convey the developer to the developing position. It is arranged.

Furthermore, if the first transport magnetic pole is disposed in an open position from the developer container, the developer that has stood up on the first transport magnetic pole is likely to scatter. Alternatively, attempts have been made to cover it with a guide member.

Further, in order to improve image quality such as preventing fogging, the magnetic flux density at the development position is increased. In addition, in two-component magnetic brush development using a two-component developer, the magnetic flux density of the developing magnetic pole is increased in order to prevent carrier adhesion.

In addition, in recent years, the demand for high-quality images has increased, and for example, in two-component magnetic brush development, there have been attempts to obtain high-resolution and high-definition images by reducing the toner particle size. Simply making the toner particle size smaller will reduce the toner supply ability, so it is necessary to make the carrier particle size smaller. Therefore, in order to prevent this, the magnetic flux density of the developing magnetic pole is increased, and there are cases where the magnetic flux density on the sleeve is 900 Gauss or more, and even higher than 1000 Gauss. The magnetic flux density of the first transport magnetic pole is (necessarily) smaller than the magnetic flux density of the developing magnetic pole.

Further, the first transporting magnetic pole and another magnet downstream thereof (hereinafter referred to as "second transporting magnetic pole") are of the same polarity and a repulsive magnetic field is formed to peel off and remove the sleeve-shaped developer, A method of stabilizing image quality by constantly supplying fresh developer is known.

However, in the conventional apparatus described above, the maximum magnetic flux density of the first transporting magnetic pole is smaller than the maximum magnetic flux density of the developing magnetic pole, and the first transporting magnetic pole and the second transporting magnetic pole form a repulsive magnetic field. Because of this, the conveyance of the developer at the first conveyance magnetic pole becomes poor, and the developer may stagnate or overflow from the developer container, causing problems such as image defects and scattering. There was a case.

This is particularly likely to occur when a two-component developer consisting of a small particle size carrier and toner is used, and is likely to occur when covered with a guide member that is the first transport magnetic pole.

Therefore, an object of the present invention is to prevent the developer from scattering, improve the developer conveyance by the conveying magnetic pole, especially the second conveying magnetic pole, prevent developer stagnation and developer overflow, and achieve high quality. It is an object of the present invention to provide a developing device, particularly a magnetic brush developing device, capable of obtaining images of 1000 yen.

The above objects are achieved by the developing device according to the present invention. To summarize, the present invention provides a developer support provided opposite to an image carrier, and a plurality of magnetic field generating means disposed inside the developer support to support the developer on the outer surface of the developer support. In a magnetic brush developing device, the latent image on the image carrier is conveyed and visualized by a developer at a development position opposite to the image carrier, the developer comprising a first magnetic field generating means at the development position and the developer. the second located downstream in the direction of movement of the support;
The magnetic field generating means have different polarities, and the second &tl field generating means and the third ifi field generating means located further downstream have the same polarity, and the maximum magnetic flux density of the first magnetic field generating means is the same as that of the second &tl field generating means. The magnetic flux density is set to be larger than the maximum magnetic flux density of the magnetic field generating means, and the magnetic flux density distribution of the second magnetic field generating means is set to have an inflection point upstream of the position of the maximum magnetic flux density. This is a magnetic brush developing device.

According to a preferred embodiment of the present invention, the magnetic force of the second magnetic field generating means on the developer supporting means has a component in the moving direction of the developer supporting means, and the magnetic force of the second magnetic field generating means has a component in the moving direction of the developer supporting means; The pole position is covered with a developer container, and the magnetic pole position of the second m field generating means is located downstream of the center of the second Mi field generating means section. Furthermore, the developer has a weight average particle size of 2
A two-component developer having magnetic particles of 0 to 65 μm and a non-magnetic toner having a volume average particle diameter of 8 μm or less can be used.

Example 1 Next, an example of the magnetic brush developing device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a first embodiment in which the present invention is applied to a copying machine using a drum type photoreceptor.

In this embodiment, the magnetic brush developing device is used in an electrophotographic copying machine having a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum l, as an image carrier.

Around the photosensitive drum 1, a charging mechanism, an image exposure mechanism, a transfer mechanism, a cleaning mechanism, a static elimination mechanism, etc., which are well-known electrophotographic processes, are arranged, but they are omitted in FIG.

The developing device of this embodiment is for developing a latent image formed on the photosensitive drum l by the above electrophotographic process,
A developing container 2 containing a developer 8, a developing sleeve 3 serving as a developer support, and a blade 4 serving as a developer layer regulating member.
etc.

That is, an opening is formed in the developing container 2 at a position close to the photosensitive drum 1, and the developing sleeve 3 is rotatably provided in this opening. Further, a blade 4 is attached above the developing sleeve 3 with a predetermined gap therebetween.

The developing sleeve 3 is made of a non-magnetic material, rotates in the direction of the arrow shown in the figure during the developing operation, and has a magnet 13 fixed therein as a magnetic field generating means. The magnet 13 is
A developing magnetic pole S as a first magnetic field generating means, a conveying magnetic pole N as a second magnetic field generating means on the downstream side thereof, a second conveying magnetic pole N8 as a third magnetic field generating means on the downstream side, and a developing magnetic pole S as described below. It has magnetic poles S□ and Ns that transport the agent 8.

Further, the blade 4 is made of a non-magnetic material such as aluminum (A2), and as described above, the blade 4 is made of a non-magnetic material such as aluminum (A2).
The surface of the developer sleeve 3 is attached with a predetermined gap between the surface of the developer sleeve 3 and the surface of the developer sleeve 3. to regulate the

Therefore, in this embodiment, since the developer 8 is a two-component developer having a non-magnetic toner 81 and magnetic particles (carrier) 82, there is a gap between the tip of the blade 4 and the surface of the developing sleeve 3. Both non-magnetic toner and magnetic particles pass through and are sent to the developing section.

The non-magnetic toner 81 used had a volume average particle size of 8 μm or less. The volume average particle size was measured using a Coulter Counter TA-■ using an aperture of 100 μm. That is, a Coulter Counter TA-n type (manufactured by Coulter Co., Ltd.) was used as the measuring device, and an interface (manufactured by Nikkakiki Co., Ltd.) for outputting the number average distribution and volume average distribution and a CX-t personal combinator (manufactured by Canon) were used. Connect the electrolyte using 1st grade sodium chloride.
% NaCβ aqueous solution was prepared.

In the measurement, 0.1 to 5 rnj2 of a surfactant, preferably an alkylbenzene sulfonate, as a dispersant was added to the electrolytic aqueous solution of 100 to 150 mρ, and 0.5 to 50 mg of the measurement sample was added. The electrolytic solution in which the sample was suspended was dispersed for about 1 to 3 minutes using an ultrasonic disperser, and then dispersed for 2 to 3 minutes using a 100 gm aperture using the Coulter Counter TA-II.
The particle size distribution of 40 μm particles was measured to determine the volume average distribution.

From these determined volume average distributions, the volume average particle diameter can be obtained.

When using the above-mentioned toner 81, the magnetic particles 82 preferably have a weight average particle size of 20 to 65 μm, but in this example, particles with a weight average particle size of about 50 μm were used.

The weight average particle size was measured by mesh and was 300/400.
80% passed the mesh, and 75% passed the 300/350 mesh. The magnetic particles used were ferrite particles coated with a resin, and the relative magnetic permeability was 5.0.

The developer 8 is carried by the developing sleeve 3 and conveyed to the developing section, that is, the developing magnetic pole Sl, and further conveyed to the conveying magnetic pole N while being held by the developing sleeve 3.

The developing device is further provided with a guide member 14,
In this embodiment, the guide member 14 extends upstream of the transport magnetic pole N1 with a predetermined gap from the developing sleeve 3, and the length ε from the upstream end of the transport magnetic pole N1 to the portion facing the transport magnetic pole N is It is said to be 7mm.

The developer 8 sent to the developing section is transported to the transport magnetic pole N while being held by the developing sleeve 3.
Since the developer that has stood up in spikes is sufficiently covered by the guide member 14, the developer is prevented from scattering out of the developer container.

Incidentally, the inside of the developing container 2 is divided into a developing chamber (first chamber) S-1 and a stirring chamber (second chamber) S-8 by a partition wall 5 extending perpendicular to the plane of the paper in FIG. A toner storage chamber S-1 is formed above the chamber S-□ with a partition wall 6 in between.
Replenishment toner (non-magnetic toner) 81 is stored in the toner storage chamber s-1. In addition, the bulkhead 6 has a supply port 6a.
is open, and an amount of replenishment toner 81 commensurate with the amount of consumed toner is dropped and replenished into the stirring chamber s1 through the replenishment port 6a. Moreover, the above-mentioned developing chamber s-1 and stirring chamber S-2
A developer 8 is housed inside. Note that the partition wall 5 is located at the front and back ends of the developer container 2 in FIG.
is not formed, and the developing chamber S- is not formed at both ends.
An opening (not shown) is formed to allow communication between the stirring chamber S-1 and the stirring chamber S-z.

The developer chamber S-1 is located at the inner bottom of the developer container 2 near the developer sleeve 3 and rotates in the direction of the arrow shown in the figure (counterclockwise) to move the developer 8 from the back side to the front side in FIG. 1, and a first conveying means 9, which is located above the first conveying means 9 and rotates in the direction of the arrow shown (counterclockwise), and conveys the developer 8 from the front side to the back side in FIG. 2 conveying means 10 are provided. Further, the first conveying means 9 is provided in the stirring chamber S-2.
A third conveying means 11 is provided which is located at approximately the same horizontal position as the third conveying means 11 and rotates in the direction of the arrow shown in the figure (clockwise) to convey the developer 8 from the front side to the rear side in FIG.

Above 1. The second and third conveying means 9.10.11 are specifically constituted by screws having a spiral shape.

FIG. 2 is a diagram for explaining the form of magnetic flux density distribution, where the vertical direction shows the magnitude of the magnetic flux density [Gauss J] on the developing sleeve 3, and the horizontal direction shows the circumferential position of the developing sleeve in angles. It shows.

Next, the meaning of "magnetic pole part" used in this specification will be explained.

In the example of a developing magnetic pole in which adjacent magnetic poles have different polarities, the developing magnetic pole section is defined as the position where the magnetic flux density on the upstream side of the developing magnetic pole is zero Gauss, and the magnetic flux density on the downstream side of the developing magnetic pole is zero Gauss, as shown in the figure. In this example, one of the adjacent magnetic poles (downstream side) is the same polarity as the first transport magnetic pole.
The transport magnetic pole portion is defined as a region from a position where the magnetic flux density is zero Gauss on the upstream side of the first transport magnetic pole to a position where the magnetic flux density shows a minimum value on the downstream side of the first transport magnetic pole.

That is, when the adjacent magnetic poles are different, the boundary is the position where the magnetic flux density is zero Gauss, and when the adjacent magnetic poles are the same, the boundary is the position where the magnetic flux density is minimum.

In FIG. 2, KA indicates the range of the first carrier magnetic pole section in terms of angle, and KP indicates the angle from the upstream boundary of the first carrier magnetic pole section to the first carrier magnetic pole.

Next, to explain the form of the magnetic flux density distribution in the first transport magnetic pole part, the solid line in FIG. 2 is an example where there is an inflection point upstream of the first transport magnetic pole, and the broken line is an example where there is no inflection point. . The fact that there is an inflection point means that the magnetic flux density B is divided into two machines (δ
This means that there are times when ``B, )/(δ3θ)20.

The inventor confirmed through experiments that the first transport magnetic pole N
It has been confirmed that when the inflection point is set upstream of , the developer transportability in the first transport magnetic pole portion is improved. The present inventor believes that the reason for this is that the magnetic force in the horizontal direction on the developing sleeve 3 in the first transport magnetic pole portion is related. That is, it is believed that this is because the magnetic force of the first transport magnetic pole portion was displaced in the direction of transporting the developer.

Next, the magnetic force of the developing sleeve, which is the developer supporting means, will be explained with reference to FIG.

In FIG. 3, the symbol F represents the magnetic force on the developing sleeve 3;
F is the magnetic force in the vertical direction, and Fe is the magnetic force [Newton] in the horizontal direction. Now, if we assume that the moving direction of the developing sleeve 3 is negative and the opposite direction is positive, the magnetic force Fe [
Newton] is calculated using the following formula.

B ” = B r ” + B eIn the formula,
Since Δθ is calculated for every 3° angle and is in radian, Δθ=3π/180.

Here, μ. ;Magnetic permeability in vacuum, 4π·lOq[)1/set] μ, ;Relative magnetic permeability b of magnetic particles;Radius of magnetic particles [μl Br;Vertical magnetic flux density on developing sleeve [Gauss] Bθ; This is the horizontal magnetic flux density (Gauss) on the developing sleeve.

Fe was calculated using the above formula for cases in which there is and is not an inflection point of the magnetic flux density upstream of the first transport magnetic pole shown in FIG. The minimum value of F, (Fe 2 )□, tended to be smaller than in the case without, and in some cases, (Fe) MIN was negative. That is, in the example without an inflection point, (Fe) + * + w was positive, but this means that a magnetic force is acting in the direction of pulling the developer back, so it is necessary to provide an inflection point. The fact that (Fe)v+s has become smaller means that the force in the direction of pulling back the developer has been reduced, which means that the transportability has been relatively improved. Also, (Fe
) The fact that 111N is negative means that there is a magnetic force in the direction of transporting the developer, and this is understood to be the reason why the transportability of the developer is improved.

In this embodiment, since the first transporting magnetic pole immediately downstream of the developing magnetic pole is covered with the guide member 14 for the purpose of preventing scattering, the transportability of the developer is disadvantageous. Furthermore, in order to prevent fogging and carrier adhesion, the magnetic flux density of the developing magnetic pole is increased, so the magnetic flux density of the first transporting magnetic pole N1 is considerably smaller than that of the developing magnetic pole. The structure of the developer is quite difficult to transport.

In such a configuration, the form of the magnetic flux density of the first transport magnetic pole is particularly important, and although the details will be described later, it is desirable to have an inflection point of the magnetic flux density upstream of the first transport magnetic pole of the first transport magnetic pole. By providing this, the developer transportability of the first transport magnetic pole portion can be improved.

Furthermore, by giving the magnetic force Fe of the first transporting magnetic pole a negative component, that is, giving it a component in the direction of movement of the developing sleeve, the developer transportability of the first transporting magnetic pole can be made extremely good. can do.

Next, a method for actually determining the magnetic force Fθ will be exemplified below. Note that the vertical magnetic flux density Br and the horizontal magnetic flux density Be on the developing sleeve 3 are measured using a Gaussmeter manufactured by Bell, which will be described later. Here, θ is the reference position θ
. It is assumed that the angle [radians] is larger on the downstream side with respect to the moving direction of the developing sleeve 3.

Now, to further explain (aB,'')/(clθ), when θ is differentiated from the + side, and when θ is differentiated from one side.

Since these are continuous, it can be assumed that they are equal no matter which way they are differentiated. Therefore, from formula ■+formula ■, we get:

Here, if Δθ is calculated every 3 degrees, the unit is radian, so Δθ=3 x / 180.

Therefore However, Δθ=3π/180.

Then, an actual calculation example of the magnetic force Fe [Newton J is shown below. Here, the radius of the magnetic particle b = 25 μm,
The magnetic permeability μ of the magnetic particles is 5.0, and the magnetic flux density BzBe on the developing sleeve is at an angle θ (degrees) from the reference position.
Suppose that it is as shown in the table below.

(1) To find Fθ at position A, (aB,”)/(a
B) must be found.

However, B ” = B r ” + BeΔθ=3π/
l 80 Δθ is calculated every 3° and the unit is radian, so △
θ: 3π/180.

B and Bθ at the 13° position of position A are each 118G,
852G, and B at position A +3°.

0 are 62G each, It is 95G.

Substituting these into the formula below, we get (however, Bt = B, * Bem ) becomes.

Here the formula, (a B r”) mentioned above. / (δθ) and b=25, μr = 5゜ 0, μ. =4π×1 Substituting O-7 =7.71XlO-' [two ton l becomes.

Similarly, Fe at position B is F, = 6.78X10-' [Newton], The FO at position C is FO=4.97X10-' [Newton].

In FIG. 1, a first transport magnetic pole N1, a second transport magnetic pole N,
are of the same polarity, and a repulsive magnetic field is generated between them.

Therefore, while being held in the sleeve 3, the first transport magnetic pole N
The developer conveyed to the sleeve 1 is removed from the sleeve 3 by the action of this repulsive magnetic field, stirred and mixed by the first conveyance means 9, and a new developer is supplied near the magnetic pole N2. That is, the developer that has undergone the development history on the sleeve 3 is peeled off and new developer that has been sufficiently mixed is constantly supplied to the sleeve 3, so that stable and good images can be obtained.

Next, a method for measuring magnetic flux density in the present invention will be explained. A Bell Gaussmeter model 640 was used as the device.
The magnetic flux density B and Bθ were measured using Bell's axial probe model 5AB4-1802.

FIG. 4 is a diagram for explaining a method of measuring the vertical magnetic flux density BT on the sleeve 3.

In FIG. 4, the sleeve 3 is fixed horizontally, and the sleeve 3
The inner magnet roller 13 is rotatably attached.

The axial probe 17 is mounted with a slight distance from the sleeve 3 so that the center of the sleeve 3 and the center of the probe 17 are approximately on the same horizontal plane. Measure the magnetic flux density in the vertical direction above. Sleeve 3 and magnetic roller 1
3 are approximately concentric circles, and the spacing between the sleeve 3 and the magnet roller 13 can be considered to be equal everywhere. Therefore, by rotating the magnet roller 13, the vertical magnetic flux density B on the sleeve 3 can be changed in the entire circumferential direction. can be measured against

Since the magnet roller is rotated in the direction of the arrow, the angle of the transport magnetic pole N1 is larger than that of the developing magnetic pole Sl, for example. That is, with respect to the moving direction of the sleeve 3 in FIG. 1, the measurement is made in a direction in which the angle increases on the downstream side.

FIG. 5 is a diagram for explaining a method of measuring the horizontal magnetic flux density Bθ on the sleeve 3.

In this measurement, the axial probe 17 is fixed vertically with a slight distance from the sleeve 3 so that the center of the sleeve 3 and the center of the measurement part of the probe 17 are approximately horizontal, and is connected to the Gauss meter 16. Thereby, the horizontal magnetic flux density Bθ on the sleeve is measured.

In this measurement as well, as explained in FIG. 4, by rotating the magnet roller 13 in the direction of the arrow, the horizontal magnetic flux density Bθ on the sleeve 3 can be measured in the entire circumferential direction.

Here, the sleeve 3 containing the magnet 13 shown in FIG.
The member consisting of the above will be referred to as a "developing roller".

Based on the specifications shown in Table 1, Table 2 shows experimental data obtained regarding the developer transportability of the first transport magnetic pole portion on the sleeve 3 and the developer scattering state using various developing rollers.

In Example 4 shown in Table 2, a scattering prevention member was provided in the developing device shown in FIG. 1, and the details will be described later.

Table 1 It can be seen that, as in Examples 1 to 3, by providing the inflection point of the magnetic flux density upstream of the first transport magnetic pole, the developer transportability is improved. Furthermore, as in Examples 1 and 3, the minimum value (
It can be seen that when Fe)min is negative, a magnetic force acts in the developer transport direction, and the developer transportability becomes extremely good.

In addition, as in Examples 1 and 2, the pole position (Kp) of the first transport magnetic pole N is set downstream (KP>IKA) of the center (for repair) of the first transport magnetic pole, and the developing magnetic pole It can be seen that there is extremely little developer scattering when the position is far away from the .

In Example 4, the developing roller of Example 3 was used, the developing device shown in FIG. 6 was used, and a scattering prevention member 12 was further provided. The scattering prevention member 12 has one end connected to the guide member 1.
4, the other end is a free end, and a part of it is in contact with the developer upstream of the transport magnetic pole N. According to this embodiment, development can be performed even without this scattering prevention member 12. The scattering of the agent was at a sufficiently tolerable level, but by providing a scattering prevention member, the scattering was further reduced, resulting in an extremely good condition. Incidentally, the developer transportability was also extremely good as in Example 3.

In the above embodiment, the non-magnetic toner 8 is used as the developer.
Although a two-component developer having a magnetic particle carrier 82 and a carrier 82 of magnetic particles was used, an l-component developer may also be used.

Further, in the above embodiment, at the development position, the development magnetic pole S
Although the method of pole position development in which the developer is developed with the developer standing up is adopted, the present invention can also be suitably adopted in a developing device that adopts the method of pole-to-pole development in which the developer is developed in a state where it is laid down. obtain. In this case, the relationship between the downstream side developing magnetic pole of the current magnetic pole group and the downstream first and second conveying magnetic poles may be configured as described in the above embodiment.

11 Zako 1 As described in detail above, the present invention provides that even if the maximum magnetic flux density of the second m-field generating means (transporting magnetic pole) is smaller than the maximum magnetic flux density of the first magnetic field generating means (developing magnetic pole), Since the magnetic flux density distribution of the second magnetic field generating means is set to have an inflection point upstream from the position of the maximum magnetic flux density, it is possible to prevent the developer from scattering and to improve the conveyance of the developer by the second magnetic field generating means. It has the advantage of being able to improve the image quality, prevent developer stagnation and overflow, and obtain high quality images.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view showing an embodiment of a magnetic brush developing device according to the present invention. FIG. 2 is a chart showing the magnetic flux density distribution in the developing sleeve. FIG. 3 is a diagram for explaining the magnetic force F. Figures 4 and 5 show the vertical magnetic pole density B, respectively.
FIG. 4 is a diagram for explaining a method of measuring magnetic pole density B in the horizontal direction. FIG. 6 is a longitudinal sectional side view showing another embodiment of the magnetic brush developing device according to the present invention. l: Image carrier 3: Developing sleeve (developer support) Sl: Developing magnetic pole (first m field generating means) Nl: Transport magnetic pole (second magnetic field generating means) N,: Transport magnetic pole (third ffl field generating means) r Figure 6

Claims (1)

[Scope of Claims] 1) A developer support is provided opposite to the image carrier, and the developer is supported on the outer surface of the developer support by a plurality of magnetic field generating means arranged inside the developer support. , a magnetic brush developing device configured to convey a latent image on the image carrier with a developer at a development position opposite to the image carrier, the magnetic brush developing device comprising: a first magnetic field generating means at the development position; The second magnetic field generating means located downstream in the direction of movement of the agent support have different polarities, and the second magnetic field generating means and the third magnetic field generating means located further downstream have the same polarity. , the maximum magnetic flux density of the first magnetic field generating means is set larger than the maximum magnetic flux density of the second magnetic field generating means, and the second
A magnetic brush developing device characterized in that the magnetic flux density distribution of the magnetic field generating means is set to have an inflection point upstream of the position of maximum magnetic flux density. 2) The magnetic brush developing device according to claim 1, wherein the magnetic force on the developer supporting means of the second magnetic field generating means has a component in the moving direction of the developer supporting means. 3) At least a pole position of the second magnetic field generating means is covered with a developer container, and the magnetic pole position of the second magnetic field generating means is located downstream of the center of the second magnetic field generating means section. A magnetic brush developing device according to claim 1. 4) The magnetic brush development according to claim 1, wherein the developer is a two-component developer having magnetic particles having a weight average particle size of 20 to 65 μm and a non-magnetic toner having a volume average particle size of 8 μm or less. Device.