JP7147036B2 - developing device - Google Patents

Description

The present invention relates to a developing device that develops an electrostatic latent image formed on an image bearing member such as a photosensitive drum using a developer containing toner and carrier.

In image forming apparatuses such as copiers, printers, facsimiles, and multifunctional machines using electrophotography or electrostatic recording, and multifunctional machines among these, electrostatic charges formed on an image carrier such as a photosensitive drum are used. A developer is applied to the latent image to make it visible (develop). As a developing device used for such development, a two-component developer (hereinafter referred to as developer) composed of non-magnetic toner particles and magnetic particle carriers is conventionally known.

In such a developing device, the developer is carried on the surface of the developing sleeve in which the magnet is arranged, and the developer is conveyed by the rotation of the developing sleeve. The amount (layer thickness) of the developer is regulated by a regulating blade as a developer regulating member arranged close to the developing sleeve, and the developer is conveyed to the developing area facing the photosensitive drum. Then, the electrostatic latent image formed on the photosensitive drum is developed with the toner in the developer.

In such a configuration, the amount of developer conveyed to the regulating blade changes due to the positional relationship between the magnetic flux density distribution of the magnet and the regulating blade being shifted. For this reason, the magnetic pole facing the regulating blade has a substantially symmetrical magnetic flux density distribution, and the position of the regulating blade is shifted from the peak position of the magnetic flux density distribution of this magnetic pole and is within the range of the half width of the magnetic flux density. A configuration has been proposed (Patent Document 1).

Note that Patent Document 2 describes a configuration in which a guide member that guides the developer toward the developing sleeve is provided upstream of the regulating blade in the rotation direction of the developing sleeve.

Japanese Patent Application Laid-Open No. 2003-140463 JP 2013-231853 A

By the way, a magnet has a predetermined tolerance with respect to a design reference position. For example, the peak position of the magnetic flux density of the magnetic pole facing the regulating blade deviates within the range of intersection with respect to the designed reference position. If the peak position of the magnetic flux density shifts in this way, the magnetic flux density distribution in the vicinity of the regulating blade also changes, which changes the amount of developer transported, making it difficult for the regulating blade to stably regulate the developer.

Here, when the magnetic flux density distribution is substantially symmetrical as described in the above-mentioned Patent Document 1, it is conceivable to cope with such a tolerance by widening the half width. That is, by widening the half-value width, even if the peak position of the magnetic flux density deviates, it is possible to suppress the change in the distribution of the magnetic flux density in the vicinity of the regulating blade, thereby stabilizing the transport amount of the developer.

However, widening the half-value width of the magnetic flux density distribution widens the width of the magnetic pole. Since the magnet has a plurality of magnetic poles in the circumferential direction, if the width of one magnetic pole is widened in this manner, the degree of freedom in designing the other magnetic poles is reduced. For example, since the radial direction of the magnet is limited in relation to the regulating blade, the circumferential width of the magnet of the other magnetic pole is limited.

On the other hand, it is conceivable to reduce the tolerance of the magnet in order to stabilize the transport amount of the developer, but reducing the tolerance of the magnet increases the manufacturing cost. The problem as described above may also occur in the configuration described in Patent Document 2 above.

The present invention has been made in view of the above problems. SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing device capable of stabilizing the amount of developer carried on a developer carrier.

The developing device of the present invention includes: a developing container containing developer containing toner and carrier; a rotatably provided developer carrier for carrying the developer ; a magnet having a regulating pole arranged fixedly ; In a state in which the amount of developer carried on the body is regulated by the regulating portion, the developer carrying member conveys the developer to the development position, and rotates the developer with respect to the rotation direction of the developer carrying member. The half-value center position located at the center of the half-value width of the magnetic flux density Br of the regulation pole in the normal direction to the outer peripheral surface of the carrier is the magnetic flux density Br of the regulation pole in the normal direction to the outer peripheral surface of the developer carrier. is at least 3° upstream of the maximum position where the maximum and

According to the present invention, the amount of developer carried on the developer carrying member can be stabilized.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention; FIG. 1 is a schematic cross-sectional view of a developing device according to a first embodiment; FIG. 1 is a schematic vertical cross-sectional view of a developing device according to a first embodiment; FIG. FIG. 4 is a schematic diagram showing the directions of magnetic lines of force in the vicinity of the magnetic pole facing the regulation blade according to the first embodiment; FIG. 4 is a schematic diagram showing the distribution of magnetic flux density in the vicinity of the magnetic pole facing the regulating blade according to the first embodiment; 4 is a diagram showing the distribution of the magnetic flux density in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to Example 1. FIG. 8 is a diagram showing the distribution of the magnetic flux density in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to Comparative Example 1. FIG. FIG. 5 is a schematic cross-sectional view of a developing device according to a second embodiment of the present invention; FIG. 10 is a diagram showing the distribution of the magnetic flux density in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to the second embodiment; FIG. 10 is a diagram showing the distribution of the magnetic force in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to the second embodiment; FIG. 9 is a diagram showing the distribution of the magnetic force in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to Comparative Example 2; FIG. 10 is a diagram showing the distribution of the magnetic force in the direction normal to the outer peripheral surface of the developing sleeve of the magnet according to Comparative Example 3;

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG. First, a schematic configuration of an image forming apparatus having the developing device of this embodiment will be described with reference to FIG.

[Image forming apparatus]
The image forming apparatus 100 is an electrophotographic full-color printer having four image forming units Y, M, C, and K corresponding to four colors of yellow, magenta, cyan, and black. The image forming apparatus 100 forms a toner image according to an image signal from a document reading device (not shown) connected to the main body of the image forming apparatus or a host device such as a personal computer communicably connected to the main body of the image forming apparatus. (image) is formed on the recording material P. Examples of the recording material include sheet materials such as paper, plastic film, and cloth. An outline of such an image forming process will be described. Toner images of each color are formed on the . The toner image of each color thus formed is transferred onto the recording material P. As shown in FIG. The recording material onto which the toner image has been transferred is conveyed to a fixing device 25, where the toner image is fixed on the recording material. A detailed description will be given below.

Note that the four image forming units Y, M, C, and K provided in the image forming apparatus 100 have substantially the same configuration except that they have different developed colors. Therefore, hereinafter, the suffixes Y, M, C, and K added to the reference numerals to indicate that the elements belong to any one of the image forming units will be omitted and a general description will be given unless a particular distinction is required. .

In the image forming section, a cylindrical photosensitive member, that is, a photosensitive drum 10 is arranged as an image bearing member. The photosensitive drum 10 is rotationally driven in the direction of the arrow in the figure. Around the photosensitive drum 10 are arranged a charger 21 as charging means, a developing device 1 as developing means, a primary transfer charger 23 as transfer means, and a cleaning device 26 as cleaning means. A laser scanner (exposure device) 22 as exposure means is arranged above the photosensitive drum 10 in the figure.

A recording material conveying belt 24 is arranged to face the photosensitive drum 10 of each image forming section. The recording material conveying belt 24 is stretched by a plurality of rollers and circulates in the direction of the arrow in the figure. A fixing device 25 is arranged downstream of the recording material conveying belt 24 in the recording material conveying direction.

A process for forming, for example, a four-color full-color image using the image forming apparatus 100 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 10 is uniformly charged by the charger 21 . Next, the photosensitive drum 10 is exposed with laser light corresponding to the image signal emitted from the exposure device 22 . As a result, an electrostatic latent image is formed on the photosensitive drum 10 according to the image signal. The electrostatic latent image on the photosensitive drum 10 is visualized by toner accommodated in the developing device 1 and becomes a visible image. The toner in the developer consumed in image formation is replenished from a hopper 20 as a toner replenishing tank.

The toner image formed on the photosensitive drum 10 is conveyed by a recording material conveying belt 24 in a transfer section configured between a primary transfer charger 23 arranged with a recording material conveying belt 24 interposed therebetween. It is transferred to the material P. Toner remaining on the surface of the photosensitive drum 10 after transfer (transfer residual toner) is removed by the cleaning device 26 .

Such an operation is sequentially performed in each of the yellow, magenta, cyan, and black image forming sections, and four color toner images are superimposed on the recording material P conveyed by the recording material conveying belt 24 . Next, the recording material P is conveyed to a fixing device 25 as fixing means. The toner on the recording material P is melted and mixed by being heated and pressurized by the fixing device 25, and fixed on the recording material P as a full-color image. After that, the recording material P is discharged outside the machine. This completes a series of image forming processes. It should be noted that it is also possible to form a single-color image of a desired color or a multi-color image using only a desired image forming unit.

[Developing device]
Next, the detailed configuration of the developing device 1 will be described with reference to FIGS. 2 to 5. FIG. The developing device 1 includes a developing container 2 containing developer containing toner and carrier, and a developing sleeve 8 as a developer carrier that carries and rotates the developer in the developing container. Conveying screws 5 and 6 are arranged in the developing container 2 as developer conveying members for agitating and conveying the developer in the developing container and for circulating the developer in the developing container. A magnet 8a having a plurality of magnetic poles in the circumferential direction is arranged in the developing sleeve 8 so as not to rotate.

The developer is a two-component developer containing non-magnetic toner and magnetic carrier. The toner has a matrix made of a binder resin containing a colorant and additives added to the matrix. As the toner resin, a negatively chargeable polyester resin is used in this embodiment. The volume average particle diameter is preferably 4 μm or more and 10 μm or less, and in this embodiment, toner with a volume average particle diameter of 7 μm is used. If the particle size of the toner is too small, it becomes difficult to friction with the carrier, making it difficult to control the amount of charge.

The carrier can be surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth metals, alloys thereof, or oxide ferrite. A ferrite carrier with a diameter of 50 μm was used. If the particle size of the carrier is too small, the carrier adheres to the latent image carrier during development, and if it is too large, the carrier disturbs the toner image during development. Further, in this embodiment, 300 g of developer is accommodated in the developing container, and the weight ratio of the toner and the carrier of the developer at the time of installation is set to 1:9.

Such developer is carried on the surface of the developing sleeve 8 by the magnetic force of the magnet 8a included in the developing sleeve 8, and the developer is conveyed in the developer conveying direction b as the developing sleeve 8 rotates. A developer is supplied to the electrostatic latent image formed on the photosensitive drum 10 . The conveying screws 5 and 6 have helical screw blades on their rotating shafts, and convey the developer in the axial direction by rotating.

A more detailed description will be given with reference to FIGS. First, the inside of the developing container 2 is vertically partitioned into a developing chamber 3 and an agitating chamber 4 by a partition wall 7 extending in a direction perpendicular to the plane of the paper at its substantially central portion. It is housed in the stirring chamber 4 .

Conveying screws 5 and 6 are arranged in the developing chamber 3 and the stirring chamber 4, respectively. The conveying screw 5 is arranged along the axial direction of the developing sleeve 8 at the bottom of the developing chamber 3, and is rotated by a motor (not shown) to rotate the developer in the developing chamber 3 along the axial direction c. The developer is supplied to the developing sleeve 8 while being conveyed. The conveying screw 6 is arranged along the axial direction of the developing sleeve 8 at the bottom of the stirring chamber 4 and conveys the developer in the stirring chamber 4 in the axial direction d opposite to the conveying screw 5 . In this embodiment, the rotation shaft rotates at 900 rpm to circulate the developer.

The developing chamber 3 and the stirring chamber 4 are communicated with each other through communicating portions 71 and 72 . In the communication portion 71 , the developer collected from the developing sleeve 8 in the stirring chamber 4 and the developer conveyed from the developing chamber 3 are assembled in the developing chamber 3 . The communication portion 72 conveys the developer that has passed through the developing chamber 3 without being supplied from the developing chamber 3 to the developing sleeve 8 to the stirring chamber 4 . As described above, the developer is circulated between the developing chamber 3 and the stirring chamber 4 through the communicating portions 71 and 72 at both ends of the partition wall 7 by conveying the developer by rotating the conveying screws 5 and 6 . Here, there are the following two paths for stirring and conveying the developer. The first route is a route (a circulation route that contributes to development) that conveys the developer in the order of development chamber 3→development sleeve 8→agitation chamber 4→communication portion 71→development chamber 3. FIG. The second route is a route (a circulation route in the developing container that does not contribute to development) that conveys the developer in the order of development chamber 3→communication portion 72→agitation chamber 4→communication portion 71→development chamber 3. FIG.

Next, the structure for conveying the developer by the developing sleeve 8 will be described in detail with reference to FIG. The developing container 2 has an opening at a position corresponding to the developing area A facing the photosensitive drum 10, and the developing sleeve 8 is rotatably disposed in the opening so as to be partially exposed in the direction of the photosensitive drum 10. there is On the other hand, the magnet 8a contained in the developing sleeve 8 is non-rotatably fixed.

The flow of developer around the developing sleeve 8 will be described. First, as the developer is conveyed by the conveying screw 5 , the developer jumps up and is supplied to the developing sleeve 8 . Since the developer is mixed with a magnetic carrier, it is restrained by the magnetic force generated by the magnet 8a in the developing sleeve 8, and as the developing sleeve 8 rotates, the developer on the developing sleeve 8 is moved by the developer regulating member. passes through the regulating blade 9 and is regulated to a predetermined amount. The developer regulated to a predetermined amount is conveyed to a developing area A facing the photosensitive drum 10, and toner is supplied to the electrostatic latent image. The developer that has passed through the developing area A is collected by the second conveying screw 6 in the developer container.

[Development sleeve]
Such a developing sleeve 8 is rotated by a motor (not shown) to convey the developer to the photosensitive drum 10 . In this embodiment, the developing sleeve 8 is made of aluminum and formed into a cylindrical shape, and has a diameter of 20 mm in cross section at the portion facing the drum. The surface properties of the developing sleeve 8 and the transportability of the developer will be described. First, when the surface of the developing sleeve 8 is smooth like a mirror surface, the developer is hardly transported even if the developing sleeve 8 rotates because the friction between the developer and the surface of the developing sleeve is extremely small. By providing moderate unevenness on the surface of the developing sleeve and creating a frictional force between the surface of the developing sleeve and the developer, the developer follows the rotation of the developing sleeve. In this embodiment, the surface of the developing sleeve 8 is subjected to blasting treatment to provide unevenness with a surface roughness of about 15 μm.

Blasting is a processing method in which particles such as abrasive powder or glass beads having a predetermined particle size distribution are sprayed at high pressure. Hereinafter, the blasted portion will be referred to as the blasted region, and the non-blasted end portion will be referred to as the non-blasted region. Since the developing sleeve transports the developer in the blast area, the blast area must be provided in a range slightly wider than the image formable area.

[magnet]
Inside the developing sleeve 8, a roller-shaped magnet 8a, which is a magnetic field generating means, is fixed to the developing container 2. As shown in FIG. As shown in FIG. 2, the magnet 8a has a total of five magnetic poles N1, N2, N3, S1 and S2 in the circumferential direction. In addition, FIG. 2 shows the maximum value position of the magnetic flux density in the direction normal to the outer peripheral surface of the developing sleeve 8 of each pole. A development magnetic pole N2 is arranged at a position facing the development area A, and the magnetic field of the N2 pole formed in the development area A causes the developer to form a magnetic brush. The magnetic brush contacts the photosensitive drum 10 rotating in the direction of the arrow a in the development area A, and develops the electrostatic latent image into a toner image by electrostatic force of the charged toner.

The role of each magnetic pole of the magnet 8a and the flow of developer will be described. First, as the developer is conveyed by the conveying screw 5, the developer jumps up and is supplied to the developing sleeve 8. Since the developer is mixed with the magnetic carrier, the magnetism formed by the N1 pole (developer regulation pole) constrained by force. Next, as the developing sleeve 8 rotates, it passes through a position facing the regulating blade 9 and the developer is regulated to a predetermined amount. The regulated developer passes through the S1 pole and is supplied to the N2 pole facing the photosensitive drum 10 . The developer that has passed through the developing area A and has consumed the toner on the electrostatic latent image is taken into the developing container by the S2 pole, and is released from the magnetic restraint force by the magnetic poles between the N3 and N1 poles. , are collected by the conveying screw 6 .

[Regulation blade]
Here, the regulating blade 9 is arranged to face the outer peripheral surface of the developing sleeve 8 with a predetermined gap therebetween, and regulates the layer thickness of the developer carried on the developing sleeve 8 . For this reason, the regulating blade 9 is arranged upstream of the developing area A in the rotational direction of the developing sleeve 8 . In this embodiment, the regulating blade 9 is a plate-like member extending along the rotation axis direction (longitudinal direction) of the developing sleeve 8 . Aluminum was used as the material of the regulation blade 9 . Further, the regulating blade 9 is disposed upstream of the photosensitive drum 10 in the rotation direction of the developing sleeve 8 so that the tip of the blade faces the center of the sleeve. As the developing sleeve 8 rotates, the developer on the developing sleeve 8 passes between the tip of the regulation blade 9 and the developing sleeve 8 and is sent to the developing area A. Therefore, by adjusting the gap between the regulating blade 9 and the surface of the developing sleeve 8, the amount of developer carried on the developing sleeve 8 and transported to the developing area can be adjusted.

If the gap between the regulating blade 9 and the developing sleeve 8 is too narrow, foreign substances in the developer and aggregates of toner tend to be clogged, which is not preferable. Further, if the mass of the developer conveyed on the developing sleeve 8 per unit area is too large, the developer may clog in the vicinity of the position facing the photosensitive drum 10, or the carrier may adhere to the photosensitive drum 10. A problem arises. On the other hand, if the mass of the developer conveyed on the developing sleeve 8 per unit area is too small, a desired toner image cannot be developed, resulting in a problem of lower image density. In this embodiment, the gap between the regulation blade 9 and the developing sleeve 8 is set to 400 μm so that the amount of developer conveyed by the regulation blade 9 is 30 mg/cm ² .

Further, in this embodiment, the diameter of the developing sleeve 8 is set to 20 mm, the diameter of the photosensitive drum 10 is set to 80 mm, and the distance of the closest region between the developing sleeve 8 and the photosensitive drum 10 is set to 400 μm. With this configuration, the developer conveyed to the development area A is set so as to be in contact with the photosensitive drum 10 for development.

With the above configuration, the developing sleeve 8 rotates in the direction of arrow b as shown in FIG. . In the development area, the developer forms a magnetic brush by the magnetic field of the magnet 8a, supplies toner to the electrostatic latent image formed on the photosensitive drum 10, and obtains a toner image. At this time, a developing bias voltage obtained by superimposing a DC voltage and an AC voltage is applied to the developing sleeve 8 from a power source (not shown). In this embodiment, the DC voltage is −500 V, and the AC voltage is a square wave with a peak-to-peak voltage Vpp of 1800 V and a frequency f of 12 kHz. However, the DC voltage value and the AC voltage waveform are not limited to these. In the development area, the non-image area on the photosensitive drum 10 is charged to −600 V, and the image area where the electrostatic latent image is formed is electrostatically charged by the laser so that the potential increases according to the density of the output image. A latent image is formed.

In the developing region A, the developing sleeve 8 moves in the same direction as the moving direction of the photosensitive drum 10. The peripheral speed of the photosensitive drum 10 is 300 mm/s, and the peripheral speed of the developing sleeve 8 is 450 mm/s. The circumferential speed ratio between the developing sleeve 8 and the photosensitive drum 10 is usually set between 1 and 2 times. The larger the peripheral speed ratio, the larger the toner supply amount. Further, the amount of toner consumed at the maximum density is 0.5 mg/cm ² , and 0.31 g is used when the maximum amount of toner is consumed for A4 size.

[Replenishment of developer]
Next, replenishment of the developer to the developer container 2 will be described with reference to FIG. In this embodiment, almost the same amount of toner as the consumed amount is replenished as a replenisher from the hopper 20 (see FIG. 1). FIG. 3 is a cross-sectional view of the developer circulating path in the developing container viewed horizontally in the longitudinal direction. However, the hopper 20 is connected to the developer container 2 so that the route of the replenishment agent S can be known. A hopper 20 containing a replenishment agent S is arranged above the developing device 1 . A hopper 20 constituting a supply means is connected to a supply port 30 of the developing device.

Almost the same amount of toner as that consumed for image formation passes from the hopper 20 through the replenishment port 30 and is replenished into the developer container 2 . The replenisher is conveyed from the replenishment port 30 by the replenishment screw 30a in the direction of the arrow g, and enters the circulation path of the developer. Note that the supply port 30 is provided downstream from the developing chamber 3 . This is to prevent the replenisher that has entered the circulation path from being supplied to the developing sleeve 8 before being agitated. In the vicinity of the communication portion 71 of the developing device 1, a toner concentration sensor (not shown) is provided that detects the magnetic permeability of the developer at a constant volume in the vicinity of the sensor surface and calculates the ratio of toner and carrier. The replenishment amount is adjusted so that the concentration is around 10% by weight.

Here, as the image is formed, the toner in the developing container receives a load, changes its shape and surface properties, and changes its toner characteristics. Such a change in the toner characteristics is caused by the amount of time that the toner is subjected to a load in the developing device. In the case of a color image forming apparatus having a plurality of developing devices, there may be developing devices that do not consume toner. Normally, the minimum amount of toner consumption is determined for each predetermined number of sheets and the number of rotations of the developing sleeve so as to maintain the toner characteristics within a certain range. is developed and replaced with new toner. In this embodiment, the minimum toner consumption amount is set to 1% of the overall consumption when the output of the full-surface maximum density image on the A4 size basis is set to 100%. That is, when the average toner consumption for each predetermined number of sheets is less than 1% of the overall consumption, toner is consumed so that the average toner consumption is 1%. Therefore, the change in the toner characteristics becomes maximum when the image with the toner consumption of 1% is continuously fed. However, about 10,000 sheets must be passed until the average time during which the toner in the developing device receives a load reaches a steady value (hereinafter referred to as image formation with toner consumption of 1%). This can be calculated from the toner consumption amount and the toner amount in the developer.

Next, the transportability of the developer by the developing sleeve 8 will be described. The developing sleeve 8 magnetically restrains the developer containing the carrier that is magnetized by the magnetic flux distribution formed by the magnet 8a contained therein. to convey. The amount of developer transported near the photosensitive drum 10 is determined by the amount of developer that can pass through the gap between the developing sleeve 8 and the regulating blade 9 . The passing angle of the magnetic spikes formed by the developing agent is important. The passage angle of the developer is determined by the magnetic flux distribution of the blade facing portion formed by the magnet. Therefore, it is desirable that the magnetic flux distribution formed in the vicinity of the blade does not change as much as possible, even depending on the process capability of the magnet 8a (tolerance of a single magnet when manufacturing the magnet) and mounting accuracy.

[Magnetic flux distribution formed by magnet and magnetic force related to carrier]
Next, the magnetic flux density and magnetic force produced by the magnet 8a will be described. In describing the present embodiment, Br, Bθ, Fr, and Fθ are defined as follows.
Br: magnetic flux density in the normal direction (perpendicular direction) to the outer peripheral surface (surface) of the developing sleeve 8 at a certain point Bθ: magnetic flux density in the tangential direction to the outer peripheral surface of the developing sleeve 8 at a certain point Fr: developing sleeve 8 at a certain point Magnetic force acting in the normal direction to the outer peripheral surface of
Fθ: Magnetic force acting in a tangential direction to the outer peripheral surface of the developing sleeve 8 at a certain point (however, the direction of rotation of the developing sleeve 8 is assumed to be positive)

Br, B.theta., Fr, and F.theta. refer to the magnetic flux density or magnetic force at a certain point on the developing sleeve 8, unless otherwise specified.

[Measuring method of magnetic force or magnetic flux density]
Here, a method for measuring the magnetic force in this embodiment will be described. The magnetic force described in this embodiment can be calculated by the calculation method described below. The magnetic force acting on the carrier is obtained by the following formula (1). Here, _μ0 is the vacuum permeability, μ is the carrier permeability, b is the radius of the carrier, and B is the magnetic flux density.

したがって、

therefore,

From this equation (2), if Br and B.theta. are known, Fr and F.theta. can be obtained. Here, the magnetic flux density Br is measured by F.F. W. Using a magnetic field measuring device “MS-9902” (trade name) manufactured by BELL, the distance between the probe, which is a member of the measuring device, and the surface of the developing sleeve was set to about 100 μm.

Furthermore, Bθ can be obtained as follows. Using the measured magnetic flux density Br, the vector potential A _Z (R, θ) at the measurement position of the magnetic flux density Br is

で求められる。境界条件をＡ_Ｚ（Ｒ，θ）とし、方程式
▽^２Ａ_Ｚ（Ｒ，θ）＝０
を解くことでＡ_Ｚ（ｒ，θ）を求める。そして、

is required. Let the boundary conditions be A _Z (R, θ) and the equation ▽ ² A _Z (R, θ)=0
A _Z (r, θ) is obtained by solving and,

より、Ｂｒ、Ｂθを求めることができる。

Br and Bθ can be obtained from the above.

Fr and Fθ can be derived by applying the measured and calculated Br and Bθ to the equation (1). Further, according to the above formula, the magnetic flux density distribution that forms the Fr distribution required in this embodiment can be obtained.

[Stability of developer transport amount]
Next, the stability of the amount of developer conveyed to the regulation blade 9 by the developing sleeve 8 will be described. In the vicinity of the regulating blade 9 , the developer receives force in a direction opposite to the conveying direction by the developing sleeve 8 . For this reason, when the magnetic brush formed in the blade facing portion of the developing sleeve 8 facing the regulation blade 9 is inclined upstream from the normal direction to the outer peripheral surface of the developing sleeve 8, it is received in the vicinity of the blade facing portion. The force makes it easier for the magnetic spikes to break. Then, the amount of developer passing through the regulating blade 9 becomes unstable, and variations in the transport amount increase.

Therefore, in order to stabilize the amount of developer passing through the regulating blade 9, it is preferable to orient the magnetic brush formed in the vicinity of the blade facing portion toward the downstream. For this purpose, the position near the blade facing portion where the magnetic lines of force extend in the direction normal to the outer peripheral surface of the developing sleeve 8 is defined as the upstream of the blade facing portion. That is, the position on the outer peripheral surface of the developing sleeve 8 at which the magnetic flux density (Bθ) in the tangential direction to the outer peripheral surface of the developing sleeve 8 is 0 is greater than the position on the outer peripheral surface of the developing sleeve 8 at which the regulating blade 9 faces. It is shifted upstream in the rotational direction of the sleeve 8 .

Here, since the N1 pole as the developer regulating pole is arranged to face the regulating blade 9 in order to carry the carrier by magnetic force in the blade facing region, the value of Br in the vicinity of the blade is not reversed. Therefore, the direction of the magnetic lines of force can be determined at the position of Bθ=0 in the vicinity of the blade. As shown in FIG. 4, if the position of Bθ=0 in the vicinity of the blade is upstream of the position facing the regulating blade 9, the magnetic lines of force (broken lines) are directed downstream. As a result of examination by changing the position of the magnetic pole facing the regulation blade 9, when the position of Bθ = 0 in the vicinity of the blade was upstream, the variation in the amount of transport per measurement was 1 mg/cm ² . , 2 mg/cm ² in the downstream case.

As described above, when the magnetic flux density distribution of the developer regulating pole facing the regulating blade is substantially symmetrical, the developer regulating pole It is conceivable to increase the half width of the magnetic flux density distribution. Magnet tolerance includes magnet process capability and magnet mounting accuracy, as described above. The process capability of a magnet is the tolerance at the time of manufacturing the magnet as described above. For example, the magnet manufacturer manufactures the magnet with this tolerance. That is, when the tolerance (process capability) is 2 degrees, the magnet delivered from the magnet manufacturer has a tolerance of 2 degrees. On the other hand, the attachment accuracy is the tolerance when attaching this magnet to the developing device, and although it varies depending on the model, there is, for example, a tolerance of 1 degree. Therefore, according to this example, the tolerance when the magnet is attached to the developing device is 3 degrees. For example, the peak position where the magnetic flux density of the developer regulating pole is maximum is shifted within the range of 3 degrees.

Therefore, when such a tolerance is handled by the half-value width, even if the peak position where the magnetic flux density is maximized deviates from the design position by the intersection amount, the distribution of the magnetic flux density at the blade facing position does not change as much as possible. It is necessary to widen the half-value width as follows. However, if the half-value width of the magnetic pole facing the blade is increased in this way, the design of other magnetic poles is restricted as described above. In particular, in the configuration of the vertical stirring type developing device in which the developing chamber and the stirring chamber are vertically arranged as in this embodiment, the developer surface downstream of the stirring chamber is high. Therefore, if magnetic force is generated in the vicinity of the partition separating the developing chamber and the stirring chamber due to restrictions on the design of the magnetic poles, the following problems arise. That is, the developer with a low toner concentration that has been carried and conveyed by the developing sleeve 8 and has consumed the toner in the development does not collect in the stirring chamber but crosses the partition wall and enters the developer pool where the developer is supplied to the developing sleeve 8 . easier to reach. Then, it is conveyed to the photosensitive drum 10 by the developing sleeve 8 again.

Therefore, in the present embodiment, it is preferable that no magnetic force is generated in the portion facing the partition wall. In addition, since the magnet has other magnetic poles in the circumferential direction, if the width of one magnetic pole is increased, it may be necessary to reduce the width of the other magnetic poles. From the above, it is desirable to make the width of the magnetic pole as small as possible.

[Developer regulation pole]
Therefore, in the present embodiment, the developer regulating pole (N1 pole) of the plurality of magnetic poles of the magnet 8a arranged to face the regulating blade 9 is formed as follows. First, the position on the outer peripheral surface of the developing sleeve 8 where the magnetic flux density in the direction normal to the outer peripheral surface of the developing sleeve 8 is maximum is defined as the maximum value position (peak position). Further, the position on the outer peripheral surface of the developing sleeve 8 corresponding to the center position of the range where the distribution of the magnetic flux density of the developer regulating pole is the half value is defined as the half value center position. In this case, the developer regulating pole is formed such that the maximum value position deviates from the half-value center position by 3 degrees or more in the circumferential direction of the developing sleeve 8 . Further, the developer regulating pole is formed so that the position on the outer peripheral surface of the developing sleeve 8 facing the regulating blade 9 (blade facing position) is located on the side of the half-value center position relative to the maximum value position.

That is, in the magnetic flux density distribution in the normal direction to the outer peripheral surface of the developing sleeve 8, the maximum value position of the developer regulating pole facing the regulating blade 9 is shifted from the half-value center position, and the magnetic flux density of the developer regulating pole is changed. Make the distribution asymmetric. In this embodiment, the tolerance of the magnet 8a is a configuration in which the position of the magnetic pole varies by 3 degrees, that is, the tolerance is 3 degrees. For this reason, the maximum value position of the developer regulation pole is shifted by 3 degrees or more from the half-value center position. As a result, even if the position of the magnetic pole changes by 3 degrees, the change in the magnetic flux density distribution at the position facing the regulation blade 9 can be suppressed.

Further, in this embodiment, in addition to making the magnetic flux density distribution of the developer regulating pole asymmetrical as described above, the regulating blade 9 is arranged to face the side where the magnetic flux density distribution becomes gradual. That is, by shifting the maximum value position of the developer regulating pole from the half-value center position, the distribution of the magnetic flux density has a portion with a gentle slope and a portion with a steep slope, as shown in FIG. . As is clear from FIG. 5, the slope of the magnetic flux density distribution becomes gentler on the side where the half-value center position exists than the maximum value position, and becomes steeper on the opposite side. In the present embodiment, the regulating blade 9 is arranged to face the direction of the gentle slope, so that even if the position of the magnetic pole shifts due to tolerance, the regulating blade 9 faces the region where the distribution of the magnetic flux density has a gentle slope. do. Therefore, even if the position of the magnetic pole shifts, the change in magnetic flux density is moderate, and the change in the transport amount of the developer can be suppressed.

However, the half-value width, which is the width of the half-value range of the magnetic flux density distribution of the developer regulating pole, is set to 70 degrees or less, preferably 60 degrees or less, and more preferably 50 degrees or less. This is because if the half width is larger than 70 degrees, the width of the developer regulating pole becomes too large, which affects the degree of freedom in designing other magnetic poles.

In order to make the regulating blade 9 more reliably face the region where the gradient of the magnetic flux density distribution is gentle, it is preferable to shift the maximum value position of the developer regulating pole by 4 degrees or more with respect to the half-value center position. It is preferable to shift by 5 degrees or more. Further, when the tolerance is larger than 4 degrees or 5 degrees, it is preferable to increase the amount of deviation of the maximum value position from the half-value center position, for example, 8 degrees or more. However, the deviation of the maximum value position from the half-value center position is preferably 20 degrees or less.

Further, the developer regulating pole is formed so that the maximum value position is shifted downstream in the rotation direction of the developing sleeve 8 from the blade facing position and the half-value center position on the outer peripheral surface of the developing sleeve 8 facing the regulating blade 9 . preferably. This is because deterioration of the developer can be suppressed when there is a region where the distribution of the magnetic flux density is gentle upstream of the position facing the blade. That is, before the developer is regulated by the regulating blade 9 upstream of the blade facing position, a large amount of developer is carried on the developing sleeve 8 . At this time, if there is a region where the magnetic flux density abruptly changes upstream of the blade facing position, the magnetic force applied to the developer carried on the developing sleeve 8 increases. As a result, the load on the developer increases, and the developer tends to deteriorate. However, in order to stabilize the transportability of the developer passing through the regulating blade 9, it is sufficient that the change in the magnetic flux density at the position facing the regulating blade 9 is gentle. It's good to be.

Further, magnetic poles having an asymmetric distribution of magnetic flux density as in the present embodiment are affected by the asymmetry of adjacent magnetic poles. That is, when the adjacent magnetic poles are distant and the magnetic poles are small, the change in magnetic flux density becomes gradual, and when the adjacent poles are close and the magnetic force is large, this change becomes steep. Therefore, in the present embodiment, a magnetic pole with a small magnetic force is arranged separately upstream of the developer regulating pole, and a magnetic pole with a larger magnetic force than the upstream magnetic pole is arranged closer to the upstream magnetic pole than the upstream magnetic pole. is preferred. The positional relationship of the magnetic poles is set at the position of the maximum value of the magnetic flux density.

In the case of the present embodiment, as described above, the maximum value position deviates from the half-value center position by 3 degrees or more, and the position on the outer peripheral surface of the developing sleeve facing the regulating blade 9 is the half-value center relative to the maximum value position. The side on which the position exists. Therefore, it is possible to suppress the change in the distribution of the magnetic flux density near the regulating blade 9 at low cost while suppressing the influence on the degree of freedom in designing other magnetic poles.

That is, the distribution of the magnetic flux density of the developer regulating pole becomes asymmetric because the maximum value position is shifted from the half-value center position by 3 degrees or more. For this reason, the distribution of the magnetic flux density of the developer regulating pole changes more slowly on the side where the half-value center position exists than the maximum value position. Since the regulating blade 9 faces the side where this change is gradual, even if the positional relationship between the maximum value position of the developer regulating pole and the regulating blade 9 deviates due to tolerances, etc., the magnetic flux near the material of the regulating blade 9 Changes in density distribution can be suppressed. As a result, even if the magnetic flux density distribution deviates from the regulating blade 9 due to tolerance, the amount of developer conveyed by the developing sleeve 8 can be suppressed from changing. In addition, it is possible to suppress image defects caused by changes in the amount of developer to be transported.

In addition, by making the distribution of the magnetic flux density asymmetric in order to cope with deviations such as tolerances, the width of the developer regulating pole can be suppressed, and the influence on the degree of freedom in designing other magnetic poles can be suppressed. In addition, since the maximum value position is 3 degrees or more with respect to the half-value center position, the tolerance does not need to be reduced more than necessary, and cost reduction can be achieved.

<Example 1>
As described above, in the present embodiment, the magnet 8a is made asymmetrical such that it changes gently upstream of the maximum value position of the magnetic flux density of the developer regulating pole and sharply changes downstream. The regulation blade 9 is arranged upstream of the maximum value position (Br peak position). As a result, the distribution of the magnetic flux density is gently changed upstream of the regulating blade 9 to reduce the change in the distribution of the magnetic flux density at the position facing the blade, thereby suppressing the change in transportability due to the process capability and mounting accuracy of the magnet. while suppressing the increase in the pole width. In order to confirm such an effect, an experiment was conducted under the following conditions.

In the magnet used in Example 1, the tolerance of the process capability and mounting accuracy of the developer regulating pole (blade opposing pole) was 3 degrees in total. For this reason, the maximum value of the blade opposing pole is shifted up to 3 degrees upstream and downstream with respect to the designed reference position. Therefore, in Example 1, the position of the maximum value of the magnetic flux density of the blade facing pole near the outer peripheral surface of the developing sleeve 8 is set 8 degrees downstream of the half-value center position. Further, the blade facing position where the regulating blade 9 faces the developing sleeve 8 is arranged 4 degrees upstream of the maximum value position of the magnetic flux density.

FIG. 6 shows the distribution of Br on the outer peripheral surface (sleeve surface) of the developing sleeve 8 of the magnet 8a (mag 1) of Example 1 having such a configuration. As for the reference of the angle, the horizontal position on the drum side is 0 degree, and the rotation direction is the opposite direction to the rotation direction of the sleeve. The vertical dashed line in FIG. 6 indicates the position (blade facing position) where the regulating blade 9 faces the outer peripheral surface of the developing sleeve 8, which is 86 degrees. Dotted lines on both sides of this dashed line indicate a range in which the blade facing position is 3 degrees upstream and downstream. The maximum value of the magnetic flux density of the blade facing pole (N1 pole) was set to 40 mT, and the half width of the magnetic flux density distribution was set to 60 degrees. Further, the deviation between the maximum value position and the half-value center position was set to 8 degrees as described above. In Example 1, the change in the amount of developer conveyed due to the tolerance of the magnet was 3 mg/cm ² .

On the other hand, as Comparative Example 1, a symmetrical magnet (Mag 2) was prepared in which the maximum value position and the half-value center position of the magnetic flux density distribution were aligned. FIG. 7 shows the distribution of Br on the outer peripheral surface (sleeve surface) of the developing sleeve 8 of the magnet of Comparative Example 1, similarly to FIG. In Comparative Example 1, as in Example 1, the blade facing position where the regulating blade 9 faces the developing sleeve 8 was arranged 4 degrees upstream of the maximum value position of the magnetic flux density. In Comparative Example 1, the half-value width of the magnetic flux density distribution was set to 76 degrees, and the change in the amount of developer transported due to the tolerance of the magnet was set to 3 mg/cm ² as in Example 1. Other conditions are the same as in Example 1. Table 1 shows the results of comparison between Example 1 and Comparative Example 1.

As is clear from Table 1, in Example 1, the variation in the amount of developer transported due to the tolerance of the magnet was suppressed to 3 mg/cm ² , which is the same as in Comparative Example 1, and the half-value width was 16 degrees compared to Comparative Example 1. I was able to narrow it down.

That is, in Example 1, the maximum value position of the magnetic flux density of the blade facing pole was set 8 degrees downstream of the half-value center position, and the blade facing position was arranged 4 degrees upstream of the maximum value position of the magnetic flux density. Therefore, even when the maximum value position of the blade-opposing pole swung upstream and downstream by 4 degrees, the change in the magnetic flux distribution in the vicinity of the regulating blade 9 was moderate. As a result, even when the distribution of the magnetic flux density changed due to the tolerance, the change in the transport amount of the developer could be suppressed. Specifically, due to the tolerance of the magnet, the magnetic poles may shift 3 degrees upstream and downstream, but within the range of 3 degrees upstream and downstream of the blade facing position (vertical dotted line), the change in magnetic flux distribution becomes gradual. Therefore, it was possible to suppress the change in the transport amount of the developer. At this time, the half width of the blade-opposing electrode of Example 1 was 60 degrees.

On the other hand, in Comparative Example 1, it was necessary to set the half-value width to 76 degrees in order to make the change in the conveying amount of the developer similar to that in Example 1. As described above, in Example 1, which is a specific example of the present embodiment, the half-value width could be reduced by 16 degrees compared to Comparative Example 1 in which the distribution of the magnetic flux density of the blade opposing pole is symmetrical. As a result, the width of the blade-opposing pole can be narrowed while the transportability of the developer near the regulating blade 9 is stabilized, and the degree of freedom in designing the other magnetic poles is increased.

<Second embodiment>
A second embodiment of the present invention will be described with reference to FIGS. 8 to 12. FIG. This embodiment is an example in which the present invention is applied to a developing device 1A provided with a guide member 11 that guides the developer in the developing container toward the developing sleeve 8, unlike the developing device 1 of the above-described first embodiment. is. Since other configurations are the same as those of the first embodiment described above, descriptions and illustrations that overlap with those of the first embodiment are omitted or simplified, and configurations similar to those of the first embodiment are given the same reference numerals. However, the following description will focus on the portions that differ from the first embodiment.

First, in a developing device using a two-component developer containing toner and carrier, the following problems may occur. That is, upstream of the regulating blade in the rotation direction of the developing sleeve, there is a boundary portion between a portion (non-moving layer) where the flow of the developer is dammed by the regulating blade and a portion where the developer is transported following the rotation of the developing sleeve. A sheared surface is generated. Then, the toner is separated from the carrier by rubbing the developer with this sheared surface, and the separated toner may adhere to each other to form a toner layer. When such a toner layer occurs, the developer conveyed by the developing sleeve to the portion facing the photosensitive drum is partially reduced due to the influence of the toner layer, and a sufficient amount of toner for development cannot be supplied, resulting in output. Image density decreases.

In order to address such a problem, the above-mentioned Patent Document 2 proposes to increase the total magnetic attraction force applied to the developer near the regulating blade while reducing the total developer conveying force along the developing sleeve. there is As a result, the developer in the vicinity of the regulating blade moves toward the center of the developing sleeve, thereby suppressing the formation of a toner layer.

In the present embodiment, as in the configuration described in Japanese Patent Laid-Open No. 2002-200002, while suppressing the developer transport failure due to the toner layer, as in the first embodiment, the change in the transport amount due to the magnet tolerance is suppressed. . A specific description will be given below.

As shown in FIG. 8, a partition wall 7A that separates the developing chamber 3 and the agitating chamber 4 has a shape extending to the vicinity of the regulating blade 9, and develops the developer contained in the developing chamber 3 from above in the direction of gravity. It has a guide member 11 that guides the sleeve 8 . The guide member 11 is provided to face the upstream side of the developing sleeve 8 in the rotational direction of the regulating blade 9 . A surface (guide surface) of the guide member 11 facing the regulating blade 9 also functions as a guide for properly supplying the developer from the gap between the regulating blade 9 and the guide member 11 when the conveying screw 5 is driven.

Further, the guide member 11 is arranged to face the developing sleeve 8 in the circumferential direction, thereby functioning as a regulating portion that regulates the supply start position P1 of the developer from the developing chamber 3 to the developing sleeve 8 . The angle of the guide surface of the guide member 11 is set in the direction normal to the surface of the developing sleeve 8 . The closest distance of the guide member 11 to the developing sleeve 8 is set to 1 mm. The supply start position P1 of the guide member 11 is set at a position 115 degrees from the horizontal position between the developing sleeve 8 and the photosensitive drum 10 in the direction opposite to the rotating direction of the developing sleeve 8 . In this embodiment, the position P3 of the partition wall 7A, which is closest to the developing sleeve 8 and upstream in the rotating direction of the developing sleeve 8, is 180 degrees from the horizontal position in the direction opposite to the rotating direction of the developing sleeve 8. position.

Next, the flow of developer in this embodiment will be described with reference to FIG. First, the closest position P3 of the guide member 11 to the developing sleeve 8 is downstream of the repulsive force area formed by the same poles (N1 pole, N3 pole, see FIG. 2), and the developer is released from the developing sleeve 8 by the repulsive force. It is stripped in the repulsive area to receive the force in the direction of separation. Therefore, the developer does not pass through the gap between the developing sleeve 8 and the partition wall 7A. In other words, the developer is supplied to the regulating blade 9 through the passage from the conveying screw 5 over the guide member 11 , and the overriding developer is stored between the regulating blade 9 and the guide member 11 . be.

In the present embodiment, the vertex position P4 of the guide member 11 and the lower point position P2 of the regulating blade 9 (the closest position to the developing sleeve 8) are such that the line connecting the positions thereof is at an elevation angle of 30° with respect to the horizontal direction. is set to be That is, the vertex position P4 of the guide member 11 is positioned above the closest position between the regulating blade 9 and the developing sleeve 8 in the horizontal direction. The reason for this is that the developer is stored in the space between the regulation blade 9 and the guide member 11 in such an amount that the developing sleeve 8 can be stably coated with the developer. In addition, the length of the guide member 11 is 11 mm. Further, in this embodiment, the guide member 11 is formed integrally with the partition wall 7A and is made of the same material as the developer container 2 .

Further, the desirable range of the distance from the regulating blade 9 to the developer supply start position P1 of the guide member 11 (the circumferential distance of the developing sleeve 8) is 2 mm or more and 8 mm or less, and is set to about 5 mm in this embodiment. ing. This is because if the distance from the regulating blade 9 to the guide member 11 is 2 mm or less, the conveying path through which the developer is conveyed becomes narrow, and there is a risk of clogging. On the other hand, if the gap is too large, the contact distance between the developing sleeve 8 and the developer becomes long, and the magnetic force rubs the developer for a long time, which is not preferable because the developer may deteriorate.

When the conveying screw 5 is positioned substantially laterally with respect to the position of the regulating blade 9 as in this embodiment, the guide member 11 has a function of guiding the developer and a function of storing the developer. Along with this, it also has the effect of shielding the developer from being pressed when the conveying screw 5 is driven. As the conveying screw 5 is driven, the developer is conveyed while being pressed in the axial direction of the screw, and is also pressed in the radial direction of the screw. When the positional relationship between the regulating blade 9 and the conveying screw 5 is substantially horizontal, pressing in the radial direction applies a developer conveying force in a substantially vertical direction to the surface of the regulating blade 9, resulting in uneven conveyance. and undesirable. Therefore, it is preferable to dispose the guide member 11 particularly at the vertex position P4 (shown in FIG. 8) high in order to shield the influence of the pressing force of the conveying screw 5 as well. It is preferable to position the apex position P4 of the guide member 11 at least above the line connecting the lower point position P2 of the regulating blade and the axial center of the conveying screw 5 .

In this embodiment, the Fr between the position of the guide member 11 and the regulating blade 9 is always in the direction of the attractive force, and Fr increases sharply and monotonically as the regulating blade 9 is approached. That is, the plurality of magnetic poles of the magnet 8b of the present embodiment are such that the absolute value of the magnetic force Fr in the normal direction of the developing sleeve 8 is positioned from the rear end of the guide member 11 to the regulating blade 9 with respect to the rotational direction of the developing sleeve 8. is formed to monotonically increase toward Here, "monotonically increasing" means that when Fr is measured in the circumferential direction of the developing sleeve 8, Fr monotonically increases when sampled in the range of an angle of 2 degrees or more and 10 degrees or less with respect to the circumferential direction of the sleeve. Point.

Further, the upstream side of the guide member 11 (the upstream side of the position P3) is configured such that Fr is approximately 0 or a positive region (repulsive force region). In the repulsive force region, Fr may be a negative value as long as the absolute value is small enough to separate the developer from the surface of the developing sleeve 8 due to the centrifugal force generated by the rotation of the developing sleeve 8 . In the present embodiment, the repulsive force region is located at a position of about 180° to 200°, and Fr increases from the repulsive force region toward the downstream side in the rotation direction of the developing sleeve 8 .

Fr is a magnetic attraction force in the sleeve direction. Therefore, the Fr distribution between the guide member 11 and the regulating blade 9 tends to monotonically increase as the regulating blade 9 is approached. By doing so, the developer near the regulating blade 9 shown in FIG. Since the developer near the regulating blade 9 is desired to flow in the vertical direction (parallel to the regulating blade, substantially parallel to the normal direction of the outer peripheral surface of the developing sleeve 8), Fr near the regulating blade is preferably large. In this embodiment, the maximum value of Fr between the guide member 11 and the regulating blade 9 is the portion facing the regulating blade 9 . That is, the plurality of magnetic poles of the magnet 8b face the regulating blade 9 at the position where the absolute value of the magnetic force Fr is maximum in the region from the rear end of the guide member 11 to the position of the regulating blade 9 in the rotational direction of the developing sleeve. It is formed so as to be in a position where

On the other hand, Fr is preferably as small as possible. Since the developer transport accompanying the rotation of the developing sleeve 8 is effected by the frictional force between the developer and the developing sleeve 8, the normal force=magnetic attraction force Fr and the developer transport force are in a proportional relationship. Therefore, in order to weaken the developer conveying force parallel to the developing sleeve 8 which collides with the regulating blade 9 and causes the non-moving layer, it is desirable that the total Fr between the regulating blade 9 and the guide member 11 is small. become.

The flow of the developer in the vicinity of the regulating blade 9 is due to the force of the developer in the vicinity of the regulating blade in the vertical direction and the force in the lateral direction (the direction perpendicular to the regulating blade and substantially parallel to the tangential direction of the outer peripheral surface of the developing sleeve 8). Determined by size relationship. Therefore, in order to make the developer flow in the vertical direction in the vicinity of the regulation blade, the Fr in the vicinity of the regulation blade is strengthened to increase the force in the vertical direction, and the total Fr between the regulation blade and the conveying guide is reduced. Therefore, weakening the lateral force becomes a necessary and sufficient condition. In order to satisfy both of the above two phenomena, it is preferable that the Fr distribution between the regulating blade 9 and the guide member 11 is such that the Fr is large only in the vicinity of the regulating blade. In other words, it is qualitatively desirable that the Fr distribution between the regulating blade 9 and the guide member 11 has a tendency to increase sharply and monotonically as the regulating blade 9 is approached.

Here, a value obtained by integrating Fr from the regulating blade 9 to a position 2 mm upstream of the regulating blade 9 in the rotation direction of the developing sleeve 8 is defined as FrNear. Further, the total sum of Fr obtained by integrating Fr from the rear end of the guide member 11 to the regulation blade 9 with respect to the rotation direction of the developing sleeve 8 is defined as FrAll. At this time, as described in Patent Document 2, quantitatively, coating defects do not occur when the ratio of FrNear to the integrated value FrAll is 60% or more. Therefore, in this embodiment, the plurality of magnetic poles of the magnet 8b are formed such that FrNear to FrAll is at least 60% or more.

The area 2 mm upstream from the regulating blade is an area where the developer is compressed and a non-moving layer is likely to be formed.

Here, in order to increase the ratio of FrNear to FrAll, Fr in the vicinity of the regulating blade 9 needs to be larger than other regions between the guide member 11 and the guide member 11 . For that purpose, it is necessary to increase the change in the magnetic distribution near the regulation blade 9, as can be seen from the above formula (1). If an attempt is made to increase the ratio of FrNear to FrAll by using a magnet having a substantially symmetrical distribution of magnetic flux density in the developer regulation pole (blade-opposed pole) facing the regulation blade 9, the half width will be narrowed. When the half-value width is narrowed, the change in the magnetic flux density distribution in the vicinity of the regulating blade becomes large, and the change in the amount of developer conveyed due to the tolerance of the magnet becomes large.

Therefore, in this embodiment, the distribution of the magnetic flux density of the developer regulating pole of the magnet 8b is made asymmetric as in the first embodiment. That is, in this embodiment, the distribution of the magnetic flux density of the developer regulating pole changes gently upstream in the rotational direction of the developing sleeve 8 at the maximum value position and sharply changes downstream. Then, the regulating blade 9 is arranged upstream in the rotational direction of the developing sleeve at the maximum value position. As described above, the maximum value position is the position on the outer peripheral surface of the developing sleeve 8 where the magnetic flux density (Br) in the normal direction to the outer peripheral surface of the developing sleeve 8 is maximized. Further, the blade facing position is a position on the outer peripheral surface of the developing sleeve 8 that the regulating blade 9 faces, and the half-value center position is the outer circumference of the developing sleeve 8 corresponding to the center position of the range where the distribution of the magnetic flux density is half the value. position on the surface.

In this way, by steeply dropping the peak of Br downstream of the regulating blade 9, Fr in the vicinity of the regulating blade can be steeply raised. Then, while increasing the ratio of FrNear to FrAll, changes in the distribution of the magnetic flux density upstream of the regulating blade 9 are reduced to suppress changes in transportability due to the process capability and mounting accuracy of the magnets.

<Example 2>
In order to confirm such effects of this embodiment, the following experiments were conducted. In the magnet used in Example 2, the tolerance of the process capability and mounting accuracy of the developer regulating pole (blade opposing pole) was 3 degrees in total. For this reason, the maximum value of the blade opposing pole is shifted up to 3 degrees upstream and downstream with respect to the designed reference position. Therefore, in Example 2, the position of the maximum value of the magnetic flux density of the blade facing pole near the outer peripheral surface of the developing sleeve 8 is set 20 degrees downstream of the half-value center position. Further, the blade facing position where the regulating blade 9 faces the developing sleeve 8 is arranged 3 degrees upstream of the maximum value position of the magnetic flux density.

FIG. 9 shows the distribution of Br on the outer peripheral surface (sleeve surface) of the developing sleeve 8 of the magnet 8b (mag 3) of Example 2 having such a configuration. As for the reference of the angle, the horizontal position on the drum side is 0 degree, and the rotation direction is the opposite direction to the rotation direction of the sleeve. The vertical dashed line in FIG. 9 indicates the position (blade facing position) where the regulating blade 9 faces the outer peripheral surface of the developing sleeve 8, which is 86°. Dotted lines on both sides of this dashed line indicate a range in which the blade facing position is 3 degrees upstream and downstream. A long dashed line indicates the position where the guide member 11 faces the outer peripheral surface of the developing sleeve 8 . The maximum value of the magnetic flux density of the blade facing pole (developer regulating pole) was set to 40 mT, and the half width of the magnetic flux density distribution was set to 45 degrees. Further, the deviation between the maximum value position and the half-value center position was set to 20 degrees as described above. In Example 2, the change in the amount of developer conveyed due to the tolerance of the magnet was 3 mg/cm ² .

Further, by using the magnet 8b (mag 3) of Example 2 described above, the ratio of FrNear to FrAll was increased to sharply change the distribution of magnetic flux density downstream of the regulating blade. FIG. 10 shows the distribution of the magnetic force (Fr) applied to the carrier on the surface of the sleeve in the direction of the center of the sleeve when the magnet 3 is used. In Example 2, the Fr near the regulation blade was relatively large, and the ratio of FrNear to FrAll was 65%.

On the other hand, as Comparative Example 2, MAG 1 having an asymmetric distribution of the magnetic flux density of the developer regulating pole used in Example 1 was used. A symmetrical mug 2 was prepared. These magnets 2 and 3 were incorporated into a developing device as shown in FIG. At this time, the change in the amount of developer conveyed due to the tolerance of the magnet was 3 mg/cm ² as in the second embodiment.

11 shows the distribution of the magnetic force (Fr) applied to the carrier on the surface of the sleeve in the case of using the MAG 1 and the case of using the MAG 2 in FIG. 12, respectively. In Comparative Example 2, the ratio of FrNear to FrAll was 55%, and in Comparative Example 3, the ratio of FrNear to FrAll was 50%. Other conditions are the same as in Example 2. Table 2 shows the results of comparison between Example 2 and Comparative Examples 2 and 3.

As is clear from Table 2, in Example 2, the change in the amount of developer conveyed due to the tolerance of the magnet was suppressed to 3 mg/cm ² , which is the same as in Comparative Examples 2 and 3, and half that in Comparative Examples 2 and 3. I was able to narrow the price range. That is, in Example 2, the maximum value position of the magnetic flux density of the blade facing pole was set 20 degrees downstream of the half-value center position, and the blade facing position was arranged 3 degrees upstream of the maximum value position of the magnetic flux density. For this reason, even when the maximum value of the blade-opposing pole swung upstream by 3 degrees, the change in the magnetic flux distribution in the vicinity of the regulating blade was gradual. As a result, even when the distribution of the magnetic flux density changed due to the tolerance, the change in the transport amount of the developer could be suppressed. Further, in Example 2, since the ratio of FrNear to FrAll was 65%, the formation of the above-described toner layer upstream of the regulating blade was suppressed, and developer transport failure did not occur. That is, since the magnetic flux density distribution changes sharply downstream of the regulating blade, the magnetic force in the vicinity of the regulating blade becomes greater than that in the other region between the guide member 11, resulting in a large FrNear/FrAll. . As a result, it was possible to prevent the developer from being transported poorly.

On the other hand, in Comparative Examples 2 and 3, since FrNear/FrAll was small at less than 60%, the formation of a toner layer could not be sufficiently suppressed, and the amount of developer was reduced during running or when continuously forming images with a low printing ratio. There was a case where transportation failure occurred. As described above, in Example 2, which is a specific example of the present embodiment, the half width can be reduced, the width of the blade opposing pole can be narrowed while the developer transportability in the vicinity of the regulation blade 9 is stabilized, and the width of the blade opposing pole can be reduced. increased the degree of freedom in design. In addition, since the FrNear/FrAll ratio was set to 65%, it was possible to prevent the transport failure of the developer. However, in the configuration of Comparative Example 2, since the distribution of the magnetic flux density of the developer regulating pole is asymmetrical, the effects of the present invention can be obtained. In this example, in addition to the effect of Example 1, by setting FrNear/FrAll to 60% or more, it is possible to impart an effect of suppressing the generation of a non-moving layer with a simple configuration. As for the non-moving layer, it is possible to cope with the problem by discharging the developer in the developing device onto the photosensitive drum when the image is not formed at a predetermined timing.

<Other embodiments>
In each of the above-described embodiments, as shown in FIG. 1, the image forming apparatus employs a configuration in which the image is directly transferred from the photosensitive drums 10Y, 10M, 10C, and 10K onto the recording material P conveyed by the recording material conveying belt 24 . However, the present invention is also applicable to configurations other than this. For example, instead of the recording material conveying belt 24, a configuration in which an intermediate transfer member such as an intermediate transfer belt is provided is also applicable. That is, even in an image forming apparatus having a configuration in which a toner image of each color is primarily transferred from the photosensitive drums 10Y, 10M, 10C, and 10K to an intermediate transfer member, and then a composite toner image of each color is secondarily transferred onto the recording material P collectively. The present invention is applicable. Also, the charging method, transfer method, cleaning method, and fixing method are not limited to the above methods.

In each of the above-described embodiments, an example in which the present invention is applied to a vertical stirring type developing device in which the developing chamber is arranged on the upper side of the developing container and the stirring chamber is arranged on the lower side has been described. However, the present invention can be applied to other configurations as long as a magnet is arranged in the developing sleeve to carry and convey the developer, and the thickness of the layer of the developer carried by the regulating blade is regulated. . For example, it can be applied to a configuration in which the developing chamber and the stirring chamber are arranged horizontally. Further, the present invention can be applied to configurations other than the configuration in which the developing chamber for supplying the developer to the developing sleeve and the stirring chamber for collecting the developer from the developing sleeve are separately provided as in the above-described embodiment. For example, it is possible to adopt a configuration in which the developing chamber supplies and collects the developer to and from the developing sleeve, and the agitating chamber circulates the developer with the developing chamber.

DESCRIPTION OF SYMBOLS 1, 1A...Development apparatus/2...Development container/8...Development sleeve/8a, 8b...Magnet/9...Regulation blade (developer regulation member)/11...Guide member

Claims (12)

a developer container containing developer containing toner and carrier;
a developer carrier provided rotatably and carrying the developer;
a magnet having a regulating pole, fixed and non-rotatably arranged inside the developer carrier;
a regulating portion that regulates the amount of the developer carried on the developer carrying member by the magnetic force formed by the regulating pole;
with
The developer carrier conveys the developer to a development position in a state where the amount of the developer carried on the developer carrier is regulated by the regulation unit,
Regarding the rotation direction of the developer carrier,
The half-value center position located at the center of the half-value width of the magnetic flux density Br of the regulation pole in the normal direction to the outer peripheral surface of the developer carrier is the position of the regulation pole in the normal direction to the outer peripheral surface of the developer carrier. Located 3° or more upstream from the maximum position where the magnetic flux density Br is maximum,
and,
A developing device, wherein a position where the restricting portion faces the outer peripheral surface of the developer carrier is upstream of the maximum position. Regarding the rotation direction of the developer carrier,
2. The developing device according to claim 1, wherein the facing position is downstream of a position where the magnetic flux density B[theta] of the regulation pole in the tangential direction to the outer peripheral surface of the developer carrier is zero. Regarding the rotation direction of the developer carrier,
3. The developing device according to claim 1, wherein the half-value center position is upstream of the maximum position by 4 degrees or more. Regarding the rotation direction of the developer carrier,
3. The developing device according to claim 1, wherein the half-value center position is upstream of the maximum position by 5[deg.] or more. Regarding the rotation direction of the developer carrier,
3. The developing device according to claim 1, wherein the half-value center position is upstream of the maximum position by 3 degrees or more and 20 degrees or less. Regarding the rotation direction of the developer carrier,
3. The developing device according to claim 1, wherein the half-value center position is upstream of the maximum position by 4° or more and 20° or less. Regarding the rotation direction of the developer carrier,
3. The developing device according to claim 1, wherein the half-value center position is upstream of the maximum position by 5 degrees or more and 20 degrees or less. The developing device according to any one of claims 1 to 7, wherein the half width is 70° or less. The developing device according to any one of claims 1 to 7, wherein the half width is 60° or less. The developing device according to any one of claims 1 to 7, wherein the half width is 50° or less. The magnet further has a magnetic pole having the same polarity as the regulating pole, the magnet being arranged upstream of the regulating pole with respect to the rotating direction of the developer carrying member and arranged adjacent to the regulating pole. The developing device according to any one of claims 1 to 10. The magnet has a plurality of magnetic poles including the regulation pole,
The developing device according to any one of claims 1 to 11, wherein the number of the plurality of magnetic poles is five.

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