JP4360615B2 - Developing device, image forming apparatus, process cartridge, and apparatus unit - Google Patents

Description

  The present invention relates to a developing device using a two-component developer composed of toner and a carrier, and an image forming apparatus, a process cartridge, and an apparatus unit provided with the developing device.

Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine thereof, a two-component developer (added with an external additive or the like) composed of a non-magnetic toner and a magnetic carrier is added. In many cases, a developing device containing the same is used.
In such a two-component developing type developing device, a technique for supplying the developer to the developing roller while circulating the developer in the longitudinal direction of the developing device by a conveying screw is known for the purpose of downsizing the device. (For example, refer to Patent Document 1).

Specifically, the developing device includes a developing roller (developer carrying member), two transport screws (first transport member and second transport member), and the like.
Then, according to toner consumption in the developing device, toner is appropriately supplied into the device from a toner supply port provided at one end of the developing device. The replenished toner is mixed with the developer in the developing device while being circulated in the device in the longitudinal direction (the same direction as the rotation axis of the developing roller) by two transport screws. A part of the mixed developer is supplied to the developing roller by a conveying screw facing the developing roller. After the developer carried on the developing roller is regulated to an appropriate amount by the doctor blade, the toner in the developer adheres to the latent image on the photosensitive drum at a position facing the photosensitive drum (image carrier). .

  Since the developing device equipped with such a conveying screw positively conveys the developer in the longitudinal direction of the device, the deviation of the developer in the longitudinal direction is unlikely to occur. Thereby, the toner replenishing port can be provided at one end in the longitudinal direction instead of being provided in the entire region in the longitudinal direction. Further, the conveying screw does not require much installation space in the short direction (the direction perpendicular to the longitudinal direction). Therefore, the developing device and the image forming apparatus can be reduced in size.

  On the other hand, since the specific gravity of the toner supplied from the toner supply port is smaller than that of the developer, it floats on the upper surface side of the developer circulating in the apparatus and is dispersed (mixed) in the developer. ) Is known to be difficult (see, for example, Patent Document 1). Thus, if the replenishment toner (fresh toner) is not dispersed in the developer, the replenishment toner is insufficiently charged due to friction with the carrier, and image quality deterioration such as background stain (fogging) occurs.

On the other hand, Patent Document 1 discloses a technique in which magnetic field generating means is installed on the downstream side of the toner replenishing port in the circulation path and on the side or below the second conveying screw.
That is, developer spikes are formed in the circulation path of the developer and the replenishment toner by the magnetic field generating means. Then, the replenishment toner is dispersed in the developer by colliding the replenishment toner with the spikes of the developer.

JP 2000-89550 A

  In the conventional developing device described above, it is difficult to achieve both developer transportability and replenishment toner dispersibility.

Details are as follows.
In the technique of Patent Document 1, since the magnetic field generating means is installed on the side or below the second conveying screw, the strength of the magnetic field generated by the magnetic field generating means is increased when trying to improve the dispersibility of the replenishing toner. There is a need to. In other words, since the replenishment toner recirculates on the upper surface side of the developer that circulates, the replenishment toner does not reach the developer ear unless the developer ear formed by the magnetic field generating means reaches the upper surface side of the developer. It will not collide. In addition, when a repulsive force against the collision of the replenishing toner is required to some extent, the magnetic field strength by the magnetic field generating means installed on the side or the lower side of the second conveying screw must be large to some extent.

  In such a case, the side where the magnetic field generating means is installed or the lower side becomes the maximum position of the magnetic force, so that a strong developer spike is formed and the developer transport is stagnated. When the developer transport is stagnant, the amount of developer supplied from the first transport screw to the developing roller may decrease, resulting in a decrease in density or density deviation of the output image. In particular, when an output image having a high image ratio (the ratio of the image area to the total area of the image area and the background area) is formed, a decrease in image density or the like is likely to occur. Such a problem is a problem that cannot be particularly ignored in a color image forming apparatus in which an image output with a high image ratio is increased.

  On the other hand, if priority is given to developer transportability and the magnetic field strength by the magnetic field generating means installed on the side or lower side of the second transport screw is set to a small value, the replenishment toner dispersibility is lowered and replenishment is performed. Image quality deterioration such as background stains due to toner charging failure occurs.

As a result of repeated researches to solve the above problems, the present inventor has come to know the following matters.
That is, even when the replenishment toner is not sufficiently dispersed in the developer, when an image with a high image ratio is output, the influence on the image quality due to the charging failure of the replenishment toner is small. On the other hand, when an image with a low image ratio is output, the influence on the image quality due to charging failure of the replenishment toner is large, and problems such as background contamination occur.

  The present invention has been made to solve the above-described problems, and a developing device that supplies a developer to a developer carrier while circulating a two-component developer in the longitudinal direction of the developing device by a plurality of conveying members. Is used to provide a developing device, an image forming apparatus, a process cartridge, and an apparatus unit that do not cause deterioration in image quality such as a decrease in image density or background contamination regardless of the image ratio of the image.

A developing device according to a first aspect of the present invention is a developing device that contains a developer having toner and a carrier and that develops a latent image formed on the image carrier, and the image carrier. A developer carrying body that carries the developer, a first carrying member that faces the developer carrying body and carries the developer in the longitudinal direction of the developer carrying body, and a partition The developer is opposed to the first conveying member via a member, and the developer is conveyed in a direction opposite to the conveying direction of the first conveying member to form the developer circulation path together with the first conveying member. A second conveying member; a toner replenishing port for replenishing toner into the developer circulating in the circulation path; and the developer that is installed above the second conveying member and recirculates below the second conveying member. To attract Comprising a magnetic field generator for a magnetic flux density of the magnetic field is configured to be variable to be generated, said magnetic field generator, so that the magnetic flux density is small when the image ratio of the image formed on the image bearing member is larger When the image ratio is small, the magnetic flux density is controlled to be large .

The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the magnetic field generator is controlled so that the magnetic flux density is increased when a large amount of toner is replenished from the toner replenishing port. When the toner amount is small, the magnetic flux density is controlled to be small.

According to a third aspect of the present invention, in the developing device according to the second aspect, the control of the magnetic field generator according to the toner amount is performed when image output is not performed.

According to a fourth aspect of the present invention, there is provided the developing device according to any one of the first to third aspects, wherein the magnetic field generator has the magnetic flux density in a range of 0 to 0.3 Tesla. It is configured to be variable.

According to a fifth aspect of the present invention, there is provided the developing device according to any one of the first to fourth aspects, wherein the image ratio is written when a latent image is formed on the image carrier. This is determined by the number of written images of the copy.

The developing device according to a sixth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the magnetic field generator is in the circulation path and from the toner supply port. It is disposed between the first conveying member and the first conveying member.

The developing device according to a seventh aspect of the present invention is the developing device according to any one of the first to sixth aspects, wherein the toner has a shape factor SF-1 and / or a shape factor SF-2 of 100. It is formed so that it may become -180.

According to an eighth aspect of the present invention, in the developing device according to any of the first to seventh aspects, the toner replenished from the toner replenishing port is replenished together with the carrier. .

An image forming apparatus according to a ninth aspect of the invention includes the developing device according to any one of the first to eighth aspects.

According to a tenth aspect of the present invention, there is provided a process cartridge according to any one of the first to eighth aspects, wherein the developing device according to any one of the first to eighth aspects and the image carrier are integrated to form a main body of the image forming apparatus. It is configured to be detachable.

A process cartridge according to an eleventh aspect of the present invention is the process cartridge according to the tenth aspect of the present invention, comprising: a charging unit that charges the image carrier; and a cleaning unit that cleans the image carrier. At least one is further integrated.

An apparatus unit according to a twelfth aspect of the invention is an apparatus unit that includes the developing device according to any one of the first to eighth aspects and is configured to be detachable from the image forming apparatus main body. The image carrier, a charging unit that charges the image carrier, a transfer unit that transfers an image formed on the image carrier onto a transfer material, and a cleaning unit that cleans the image carrier. And a toner replenishing unit that replenishes toner to the developing device are integrated with the developing device.

  According to the present invention, in the developing device that supplies the developer to the developer carrying member while circulating the two-component developer in the longitudinal direction of the developing device by a plurality of conveying members, the dispersion force for the replenishing toner is variably formed. Therefore, it is possible to provide a developing device, an image forming apparatus, a process cartridge, and an apparatus unit that do not cause deterioration in image quality such as a decrease in image density or background stain regardless of the size of the image.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a color copying machine as an image forming apparatus, 2 is a writing unit that emits laser light based on image information, and 20Y, 20M, 20C, and 20BK are each color (yellow, magenta, cyan, black). , A photosensitive drum as an image carrier housed in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, and 23 is a photosensitive drum. A developing unit (developing device) that develops the electrostatic latent image formed on 21, 24 is a transfer bias roller that transfers the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27, and 25 is a photosensitive drum. 21 is a cleaning unit for collecting untransferred toner, and 27 is an intermediate transfer as an image carrier on which toner images of respective colors are transferred in an overlapping manner. 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the transfer material P, and 30 is a transfer for transferring the transfer material P onto which the four color toner images are transferred. The belts 32Y, 32M, 32C, and 32BK are toner replenishing units that replenish toners of the respective colors to the developing units 23 of the process cartridges 20Y, 20M, 20C, and 20BK. A paper section 66 is a fixing section that fixes an unfixed image on the transfer material P, and 120 is a scanner that optically reads a placed document.

  Here, the photosensitive drum 21, the charging unit 22, the developing unit 23, and the cleaning unit 25 are integrated with each of the process cartridges 20Y, 20M, 20C, and 20BK. Then, image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
Each of the four photosensitive drums 21 rotates in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.

  On the other hand, when a color original is placed on the original placement portion of the scanner 120, image information of the original is optically read by a reading portion (not shown). That is, the original is scanned with an illumination light source, and an original image is formed on a color CCD (not shown). Then, an original image, that is, reflected light of light irradiation on the original is photoelectrically converted by a color CCD to generate R, G, and B image signals. These image signals are transmitted to the writing unit 2. Thereafter, in the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each color component of yellow, magenta, cyan, and black (this is an exposure process).

The yellow component laser light is reflected by the mirrors 6 to 8 and then irradiated to the surface of the photosensitive drum 21 of the first process cartridge 20Y from the right side of the drawing. At this time, the yellow component laser light is scanned in the rotational axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image of a yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.
Similarly, the magenta component laser light is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the right side of the paper, thereby forming an electrostatic latent image of the magenta component. The The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the right side of the paper, thereby forming an electrostatic latent image of the cyan component. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the right side of the drawing to form a black component electrostatic latent image.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed further rotates and reaches a position facing the developing unit 23. Then, the toner of each color is supplied from the developing unit 23 onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, the image of each color formed on the photosensitive drum 21 is sequentially transferred onto the intermediate transfer belt 27 at the position of the transfer bias roller 24 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full color image on the intermediate transfer belt 27 is secondarily transferred onto the transfer material P at the position of the second transfer bias roller 28 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of an intermediate transfer belt cleaning unit (not shown). At this time, the intermediate transfer belt cleaning unit has moved to a position where it contacts the intermediate transfer belt 27. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the transfer material P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the transfer material P is guided to the registration roller 64 after passing through the conveyance guide 63. The material P to be transferred that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the transfer material P onto which the full-color image has been transferred is guided to the fixing unit 66 by the transfer belt 30. In the fixing unit 66, the color image is fixed on the transfer material P at the nip between the heating roller 67 and the pressure roller 68.
Then, the transfer material P after the fixing process is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 69, and a series of image forming processes is completed.

Next, the process cartridge installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the process cartridge, and FIG. 3 is a cross-sectional view taken along line AA showing the developing portion (developing device) 23 thereof.
The four process cartridges and the toner replenishing unit 32 installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T to be stored is different. Therefore, the alphabets (Y, M, C, BK) The figure is removed.

As shown in FIG. 2, the process cartridge 20 mainly includes a photosensitive drum 21 as an image carrier, a charging unit 22, a developing unit 23, and a cleaning unit 25, which are integrally stored in a case 26. Has been.
The developing unit 23 mainly includes a developing roller 23a as a developer carrying member facing the photosensitive drum 21, a first conveying screw 23b as a first conveying member facing the developing roller 23a, and a partition member 23d. A second conveying screw 23c as a second conveying member facing the first conveying screw 23b, a doctor blade 23d facing the developing roller 23a, a magnetic field generator 46 as a dispersing means facing the second conveying screw 23c, Consists of. In the developing unit 23, a two-component developer composed of a magnetic carrier C and a nonmagnetic toner T is accommodated. The developing roller 23a includes a magnet that is fixed inside and forms a magnetic field on the roller peripheral surface, and a sleeve that is made of a nonmagnetic material and rotates around the magnet.

The development process in the image forming process described above will be described in more detail.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developers T and C in the developing unit 23 are driven by the rotational drive of the first transport screw 23b and the second transport screw 23c disposed so as to interpose the partition member 23e therebetween. The toner T is circulated in the longitudinal direction while being agitated and mixed with the toner T replenished through the toner replenishing port 26a from the replenishing portion 32 (circulation in the direction of the arrow in FIG. 3). The toner T that is frictionally charged and adsorbed on the carrier C is supplied to the developing roller 23a together with the carrier C by the first conveying screw 23b, and the developers T and C are carried on the developing roller 23a.

  Here, a toner replenishing unit 32 provided in the apparatus main body is configured to be replaceable with a toner bottle 33 and a bottle holding unit that holds and rotates the toner bottle 33 and replenishes the developing unit 23 with fresh toner T. Part 34. The toner bottle 33 stores toner T (which is one of yellow, magenta, cyan, and black).

The toner T in the toner bottle 33 is appropriately supplied into the developing unit 23 from the toner supply port 26a as the toner T in the developing unit 23 is consumed. Consumption of the toner T in the developing unit 23 is indirectly detected by a toner density sensor 28 (reflection type optical sensor) facing the photosensitive drum 21.
The toner replenishing port 26a of the case 26 is provided at one end in the longitudinal direction (the vertical direction in FIG. 3) of the second transport screw 23c and above the second transport screw 23c.

Thereafter, the developers T and C carried on the developing roller 23a are adjusted to an appropriate amount at the position of the doctor blade 23d, and then reach a position facing the photosensitive drum 21 (developing area). At the opposite position, the toner T in the developer adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T adheres to the latent image by an electric field formed by a potential difference between the latent image potential of the image portion irradiated with the laser beam L and the developing bias applied to the developing roller 23a.
Thereafter, most of the toner T adhering to the photosensitive drum 21 is transferred onto the transfer material P. Then, the toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b that are in contact with the photosensitive drum 21.

  Here, referring to FIG. 2, a magnetic field generator 46 as a dispersing unit is installed inside the developing unit 23 above the second transport screw 23 c. Referring to FIG. 3, the magnetic field generator 46 is in the circulation path of the developers T and C, and is between the toner supply port 26a and the first transport screw 23b (downstream of the toner supply port 26a). .).

  The magnetic field generator 46 is an electromagnet. And the magnetic flux density of the magnetic field which generate | occur | produces from the magnetic field generator 46 can be changed in the range of 0-0.3 Tesla (3000 gauss) by adjusting the electric current which flows into the magnetic field generator 46 by the control part 70. it can.

Referring to FIG. 4, when a predetermined magnetic field is formed by magnetic field generator 46, developers T and C that circulate thereunder are attracted to magnetic field generator 46, and developer spike F is formed. .
On the other hand, the toner T1 replenished from the toner replenishing port 26a recirculates on the upper surface side of the recirculating developers T and C. Thereafter, the replenishing toner T1 moving on the upper surface side collides with the developer spike F formed there at the position of the magnetic field generator 46. At this time, the developer spike F collapses while taking in the replenishment toner T1, and the replenishment toner T1 is dispersed and mixed in the developers T and C.

Here, the magnitude of the magnetic flux density by the magnetic field generator 46 correlates with the dispersion force for dispersing the replenished toner T1 in the developers T and C.
That is, when the magnetic flux density by the magnetic field generator 46 is large, a large developer spike F is formed, and the dispersion force for dispersing the supplied toner T1 in the developers T and C is also increased. At this time, the transportability of the developers T and C passing through the position of the magnetic field generator 46 is lowered by the large developer spike F formed in the circulation path.
On the other hand, when the magnetic flux density by the magnetic field generator 46 is small, a small developer spike F is formed, and the dispersion force for dispersing the replenished toner T1 in the developers T and C becomes small. At this time, the transportability of the developers T and C passing through the position of the magnetic field generator 46 is hardly deteriorated by the small developer spikes F formed in the circulation path.

Specifically, the magnetic flux density by the magnetic field generator 46 is adjusted according to the image ratio of the image formed on the photosensitive drum 21.
That is, when outputting an image with a high image ratio such as a solid image or a photographic image, the background portion of the image is small, so that the influence of background contamination due to charging failure of the replenishing toner is difficult to be manifested. On the other hand, since the toner consumption in the developing unit 23 is large, it is necessary to quickly transport the replenishment toner T1 and the developers T and C to the position of the first transport screw 23b facing the developing roller 23a. Therefore, when outputting an image with a high image ratio, the control unit 70 performs control to reduce the magnetic flux density by the magnetic field generator 46 or control not to form a magnetic field. As a result, even when an image with a high image ratio is output, it is possible to output a good image with reduced image density and image density deviation.

On the other hand, when outputting an image with a low image ratio such as a character image, since the background portion of the image is large, the influence of background stains due to charging failure of the replenishment toner tends to become obvious. On the other hand, since the toner consumption in the developing section 23 is small, it is not necessary to quickly transport the replenishment toner T1 and the developers T and C to the position of the first transport screw 23b facing the developing roller 23a. Therefore, when outputting an image with a low image ratio, the control unit 70 performs control to increase the magnetic flux density by the magnetic field generator 46. As a result, even when an image with a low image ratio is output, background stains are reduced, the charge distribution of the toner T in the developer becomes sharp, and a good image with no transfer omission can be output.
The image ratio of the image formed on the photosensitive drum 21 can be determined based on the number of pixels written by the writing unit 2 at the time of image formation, the emission time of the laser light L, and the like.

In the present embodiment, the toner T and the replenishment toner T1 in the developer are polymerized toners produced by an emulsion polymerization method, and the shape factor SF-1 and the shape factor SF-2 are 100 to 180, respectively. A substantially spherical toner formed as described above is used.
Here, the shape factor SF-1 indicates the sphericity of the toner particles, and is obtained by the following equation.
SF-1 = (M ² / S) × (100π / 4)
In the above equation, M is the maximum particle size (the largest particle size among sparse particle sizes) on the toner particle projection surface, and S is the area of the toner particle projection surface. Therefore, toner particles having a shape factor SF-1 of 100 are true spheres, and the sphericity decreases as the value increases from 100.

The shape factor SF-2 indicates the degree of unevenness of the toner particles, and is obtained by the following equation.
SF-2 = (N ² / S) × (100 / 4π)
In the above equation, N is the circumference of the toner particle projection surface, and S is the area of the toner particle projection surface. Therefore, the toner particles having the shape factor SF-2 of 100 have no irregularities, and the irregularities increase as the value increases from 100.
The shape factor SF-1 and the shape factor SF-2 are obtained by analyzing a toner particle photograph taken with a scanning electron microscope “S-800” (manufactured by Hitachi, Ltd.) and an image analyzer “LUSEX3” (manufactured by Nireco). )

  By using the toner T with no irregularities and high sphericity, the fluidity of the toner is enhanced, and the dispersibility in which the replenishment toner T1 is dispersed in the developers T and C is also enhanced. Thereby, the effect of this Embodiment mentioned above is further heightened.

  As described above, in the present embodiment, the developer T is supplied to the developing roller 23 a while circulating the two-component developers T and C in the longitudinal direction of the developing unit 23 by the first conveying screw 23 b and the second conveying screw 23 c. , C in the developing device adjusts the dispersion force with respect to the replenishment toner T1 by the magnetic field generator 46 in accordance with the image ratio of the image. Thereby, regardless of the size of the image ratio of the image, it is possible to suppress image quality deterioration such as a decrease in image density and background stains.

  In the present embodiment, the dispersion force by the magnetic field generator 46 is adjusted according to the image ratio of the output image. On the other hand, the dispersion force by the magnetic field generator 46 can also be adjusted according to the supply amount of the toner T1 supplied from the toner supply unit 32. Specifically, when a large amount of toner is replenished from the toner replenishing port 26a, the dispersibility by the magnetic field generator 46 is improved, and when a small amount of toner is replenished from the toner replenishing port 26a, the magnetic field generator 46 is used. By reducing the dispersibility of the toner, the degree of mixing of the replenished toner and the developer that is refluxed can always be kept constant. In this case, in order to make the control according to the present embodiment (the control to obtain a low dispersion force at a high image ratio and a high dispersion force at a low image ratio) effective, the dispersion force according to the toner replenishment amount. The adjustment is preferably performed when image output is not performed (for example, during process control adjustment).

  In the present embodiment, the present invention is applied to the developing device 23 in which the toner T is supplied from the toner supply port 26a. In contrast, the present invention can also be applied to the developing device 23 that replenishes the two-component developer (toner T and carrier C) from the toner replenishing port 26a. In such a developing device, the toner concentration of the supplied developer is larger than the toner concentration of the developer that recirculates in the device, and its specific gravity is small. Therefore, the supplied developer recirculates. The upper surface side of the developer is moved. Therefore, similar to the present embodiment, the same effect can be obtained by variably configuring the magnetic field strength of the magnetic field generator 46 installed above.

  In the present embodiment, the magnetic field generator 46 is used as the dispersing means. However, the application of the present invention is not limited to this, and for example, a flexible member capable of variably moving the vertical position can be used as the dispersing means. In this case, when the image ratio of the output image is high, the flexible member is moved downward, and the replenishment toner and the developer are damped to increase the dispersibility. On the other hand, when the image ratio of the output image is low, the flexible member is moved upward to weaken the dispersibility without increasing the replenishing toner and developer, thereby increasing the transportability. Even in such a case, the same effect as the present embodiment can be obtained.

  In the present embodiment, the developing unit (developing device) 23 on which the magnetic field generator 46 is mounted is integrated in the process cartridge 20. On the other hand, the developing device 23 can be detachably attached to the image forming apparatus main body 1 as a single unit. Further, the developing device 23 may be an apparatus unit integrated with at least one of the photosensitive drum 21, the charging unit 22, the transfer unit 24, the cleaning unit 25, and the toner replenishing unit 32. it can.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is obvious that the embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the embodiment. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a suitable number, position, shape, and the like in practicing the present invention.

1 is a configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a side sectional view showing a process cartridge in the image forming apparatus of FIG. 1. FIG. 3 is a cross-sectional view showing an AA cross section of a developing unit in the process cartridge of FIG. 2. FIG. 6 is a schematic diagram illustrating a state where replenishment toner is dispersed in a developer by a dispersion unit.

Explanation of symbols

1 image forming apparatus body (apparatus body), 2 writing unit,
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23 developing section (developing device), 23a developing roller,
23b 1st conveyance screw (1st conveyance member),
23c 2nd conveyance screw (2nd conveyance member), 23e Partition member,
24 transfer bias roller, 25 cleaning unit, 26a toner supply port,
27 intermediate transfer belt, 28 second transfer bias roller, 30 transfer belt,
32, 32Y, 32M, 32C, 32BK toner supply unit,
33 toner bottle, 46 magnetic field generator (dispersing means),
61 paper feeding unit, 66 fixing unit, 70 control unit.

Claims (12)

A developing device for containing a developer having toner and a carrier and developing a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying the developer;
A first conveying member facing the developer carrying member and carrying the developer in a longitudinal direction of the developer carrying member;
Opposite the first conveying member via a partition member, convey the developer in a direction opposite to the conveying direction of the first conveying member, and form a circulation path for the developer together with the first conveying member A second conveying member that
A toner replenishing port for replenishing toner into the developer circulating in the circulation path;
A magnetic field generator configured to be able to vary a magnetic flux density of a magnetic field that is installed above the second conveying member and is generated to attract the developer that circulates below the second conveying member;
With
The magnetic field generator is controlled so that the magnetic flux density is reduced when an image ratio of an image formed on the image carrier is large, and is controlled so that the magnetic flux density is increased when the image ratio is small. A developing device. The magnetic field generator is controlled so that the magnetic flux density is increased when the amount of toner supplied from the toner supply port is large, and is controlled so that the magnetic flux density is decreased when the amount of toner is small. The developing device according to claim 1. The developing device according to claim 2, wherein the control of the magnetic field generator according to the toner amount is performed when image output is not performed . The developing device according to claim 1 , wherein the magnetic field generator is configured to be able to vary the magnetic flux density in a range of 0 to 0.3 Tesla . 5. The developing device according to claim 1, wherein the image ratio is determined by the number of written images of a writing unit when a latent image is formed on the image carrier . 6. The development according to claim 1, wherein the magnetic field generator is disposed in the circulation path and between the toner supply port and the first transport member. apparatus. 7. The developing device according to claim 1 , wherein the toner is formed so that a shape factor SF- 1 and / or a shape factor SF- 2 is 100 to 180. 8 . The developing device according to claim 1, wherein the toner supplied from the toner supply port is supplied together with a carrier . An image forming apparatus comprising the developing device according to claim 1. The developing device according to any one of claims 1 to 8 and the image carrier are integrated,
A process cartridge configured to be detachable from a main body of an image forming apparatus. The process cartridge according to claim 10, wherein at least one of a charging unit that charges the image carrier and a cleaning unit that cleans the image carrier is further integrated. An apparatus unit comprising the developing device according to claim 1 and configured to be detachable from the image forming apparatus main body.
The image carrier, a charging unit that charges the image carrier, a transfer unit that transfers an image formed on the image carrier onto a transfer material, and a cleaning unit that cleans the image carrier. And a toner replenishing section for replenishing toner to the developing device, wherein at least one of the developing device and the developing device is integrated.

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