JP2006146013A - Development device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development device for which the load on transport members is relatively small, dispersion of replenished toner is accelerated, without causing faulty transport of developer, and image degradation such as surface stain and lowering of image density and toner flying-off are surely suppressed, and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: Above a circulation path of a developer G formed by a first transport member 23b and a second transport member 23c, a magnetic field generator 43 formed so that the developer G can be attracted by magnetic force is arranged. The developer G, attracted by the magnetic field generator 43, can be constituted detachable. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a developing device and a process cartridge installed therein, and particularly includes a toner and a carrier. The present invention relates to a developing device, a process cartridge, and an image forming apparatus using a two-component developer.

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 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 carrier), two transport screws (a first transport member and a 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) and toner scattering occur. .

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 developing device described in Patent Document 1 and the like described above, there is a possibility that the developer stagnates due to the magnetic field generating means and a conveyance failure occurs, or the load on the conveying member for circulating the developer in the device may increase. It was.

Details are as follows.
In the technique of Patent Document 1, etc., the magnetic field generating means is installed on the side or below the second conveying screw. Therefore, when it is attempted to improve the dispersibility of the replenishment toner, the magnetic field strength by the magnetic field generating means is increased. It needs to be bigger. In other words, since the replenishment toner floats on the upper surface side of the circulating developer, 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.
Further, in order to transport the developer through the transport path in which strong developer spikes are formed by the magnetic field generating means, a large load is applied to the transport member. Therefore, if the output of the drive motor that drives the transport member is not large to some extent, the rotational drive of the transport member may be locked.

  The present invention has been made to solve the above-described problems. When the developer is supplied to the developer carrier while the two-component developer is circulated in the longitudinal direction of the developing device by a plurality of conveying members. The development of the development is such that the load on the conveying member is relatively small, the dispersion of the replenishing toner is promoted without causing a developer conveyance failure, and image quality deterioration and toner scattering such as background contamination and image density reduction are reliably reduced. An apparatus, a process cartridge, and an image forming apparatus are provided.

  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. The second conveying member, a toner replenishing port for replenishing toner into the developer circulating in the circulation path, and the upper side of the circulation path are formed so that the developer can be adsorbed by a magnetic force. Magnetic field generation means The provided, which is constituted detachably the developer adsorbed by the magnetic field generating means.

  According to a second aspect of the present invention, the developing device according to the first aspect of the present invention releases the developer adsorbed by the magnetic field generating means when the toner is not replenished from the toner replenishing port. Is.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the magnetic field generating means is installed above the second transport member.

  According to a fourth aspect of the present invention, there is provided the developing device according to the third aspect, wherein the toner supply port is disposed above the second transport member, and the magnetic field generating means is It is disposed downstream of the circulation path with respect to the toner supply port.

  According to a fifth aspect of the present invention, there is provided the developing device according to the third or fourth aspect, wherein the toner concentration detecting means detects the toner concentration of the developer conveyed by the second conveying member. And the magnetic field generation means is disposed upstream of the circulation path with respect to the toner concentration detection means.

  A 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 generating means is arranged so that the developer is not directly adsorbed to the magnetic field generating means. And the circulation path, and the magnetic field generating means is moved to a position away from the magnetically permeable member, whereby the development attracted to the magnetically permeable member by the magnetic field generating means. The agent is withdrawn.

  A developing device according to a seventh aspect of the invention is the developing device according to the sixth aspect, wherein the magnetic field generating means is a permanent magnet or an electromagnet.

  The developing device according to an eighth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the magnetic field generating means is an electromagnet and stops energizing the electromagnet. As a result, the developer adsorbed by the electromagnet is released.

  According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the developing device is movably disposed between the magnetic field generating means and the circulation path. In addition, a magnetic flux shielding member for shielding the magnetic field is provided, and the developer adsorbed by the magnetic field generating means is released by moving the magnetic flux shielding member between the magnetic field generating means and the circulation path.

  The developing device according to the invention of claim 10 is the developing device according to any one of claims 1 to 9, wherein the carrier has a resin coating layer on a core material surface, The resin coating layer contains conductive particles formed by providing a conductive coating layer composed of a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer on the surface of the substrate particles, The conductive particles are formed so that the oil absorption is 10 to 300 ml / 100 g. The toner includes a binder resin, a release agent, and a colorant. The binder resin includes a vinyl polymer and a polyester. And a hybrid resin having a base polymer, and the hybrid resin content with respect to the release agent content is in the range of 0.5 to 3.

  The developing device according to an eleventh aspect of the present invention is the developing device according to any one of the first to tenth aspects, wherein the carrier is formed such that a weight average particle diameter is in a range of 20 to 65 μm. It has been done.

  The developing device according to a twelfth aspect of the present invention is the developing device according to any one of the first to eleventh aspects, wherein the toner has an average particle size in the range of 3.5 to 7.5 μm. It is formed as follows.

  A developing device according to a thirteenth aspect of the present invention is the developing device according to any one of the first to twelfth aspects, wherein the toner concentration in the developer is within a range of 6 to 12% by weight. It is to be controlled.

  A process cartridge according to a fourteenth aspect of the present invention is a process cartridge which is detachably installed on the main body of the image forming apparatus, and is according to any one of the first to thirteenth aspects. The developing device and the image carrier are integrated.

  An image forming apparatus according to a fifteenth aspect of the present invention includes the developing device according to any one of the first to thirteenth aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing device (developing unit) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. It is defined as a unit in which at least one of the cleaning units and the image carrier are integrated and configured to be detachable from the image forming apparatus main body.

  In the present invention, when a developer is supplied to a developer carrying member while circulating a two-component developer in the longitudinal direction of the developing device by a plurality of conveying members, a magnetic field is generated that attracts the developer circulating in the circulation path with a magnetic force. The means is installed above the circulation path, and the developer adsorbed by the magnetic field generating means can be removed. As a result, the load on the conveying member is relatively small, and the dispersion of the replenishing toner is promoted without causing a developer conveyance failure, and image quality deterioration such as background contamination and image density reduction and toner scattering are reliably reduced. , A developing device, a process cartridge, and an image forming apparatus can be provided.

  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.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a color copying machine as an image forming apparatus, 2 is a writing section (exposure section) that emits laser light based on input image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta). , Cyan, and black), 21 is a photosensitive drum as an image carrier accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, Reference numerals 23Y, 23M, 23C, and 23BK denote developing devices (developing units) that develop the electrostatic latent image formed on the photosensitive drum 21, and 24 denotes a toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27. A transfer bias roller 25 for transferring represents a cleaning unit for collecting untransferred toner on the photosensitive drum 21.

  In addition, 27 is an intermediate transfer belt on which toner images of a plurality of 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 recording medium P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a conveyance belt that conveys a recording medium P on which a four-color toner image is transferred, and 32Y, 32M, 32C, and 32BK are developing devices 23Y and 23M. , 23C and 23BK, a toner replenishing unit for replenishing each color toner, 51 a document conveying unit for conveying the document D to the document reading unit 55, 55 for a document reading unit (scanner) for reading image information of the document D, and 61 for transferring A paper feed unit 66 for storing a recording medium P such as paper, and a fixing unit 66 for fixing an unfixed image on the recording medium P are shown.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. The process cartridges 20Y, 20M, 20C, and 20BK are exchanged with respect to the apparatus main body 1 in a predetermined exchange cycle. Similarly, the developing devices 23Y, 23M, 23C, and 23BK are also replaced with a predetermined replacement cycle with respect to the apparatus main body 1 based on the lifetime of the developer.
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.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, an image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like on the basis of RGB color separation image signals, so that yellow, magenta, cyan, and black are processed. Get color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the photosensitive drums 21 of the corresponding process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, the four photosensitive drums 21 rotate 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). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
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 of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation 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 corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component 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 left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. 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 left side of the drawing to form a cyan component electrostatic latent image. 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 left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK 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 the position facing the intermediate transfer belt 27 after passing the position facing the photosensor 41 (see FIG. 2). 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, at the position of the transfer bias roller 24, the images of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the intermediate transfer belt 27 (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 recording medium P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the recording medium 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 recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P 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 recording medium P on which the full-color image is transferred is guided to the fixing unit 66 by the conveyance belt 30. In the fixing unit 66, the color image is fixed on the recording medium P at the nip between the heating roller 67 and the pressure roller 68.
Then, the recording medium P after the fixing process is discharged as an output image by the paper discharge roller 69 to the outside of the apparatus main body 1, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the image forming unit, and FIG. 3 is a cross-sectional view in the longitudinal direction (vertical direction in FIG. 2) showing the developing device.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. (Y, M, C, BK) is omitted for illustration.

  As shown in FIG. 2, the process cartridge 20 mainly contains a photosensitive drum 21 as an image carrier, a charging unit 22, and a cleaning unit 25 integrally in a case 26. The cleaning unit 25 is provided with a cleaning blade 25 a and a cleaning roller 25 b that are in contact with the photosensitive drum 21.

The developing device 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 23e. The second conveying screw 23c as a second conveying member facing the first conveying screw 23b and a doctor blade 23d facing the developing roller 23a are configured. Referring to FIG. 3, the developing roller 23a includes a magnet 23a1 that is fixed inside and forms a magnetic pole on the peripheral surface of the roller, and a sleeve 23a2 that rotates around the magnet 23a1. The sleeve 23a2 has an outer diameter of 25 mm and a width of 328 mm, and V-shaped grooves are formed on the outer peripheral surface at equal pitch intervals in the circumferential direction. Seven magnetic poles are formed on the developing roller 23a by the magnet 23a1. Of the seven magnetic poles, the main pole formed in the development region is formed so that the main pole angle is 3 degrees, the peak magnetic force is 120 mT, and the half width is 23 degrees. Of the seven magnetic poles, the pumping magnetic pole for pumping the developer G onto the developing roller 23a is formed so that the pumping amount is 35 ± 7.5 mg / cm ² .

  The gap (development gap) between the developing roller 23a and the photosensitive drum 21 in the developing region (opposing position) is set to be 0.3 ± 0.1 mm. The gap (doctor gap) between the developing roller 23a and the doctor blade 23d is set to be 0.3 ± 0.04 mm. The doctor blade 23d is made of a magnetic material, and is disposed on a magnetic pole (P6 magnetic pole) having a peak magnetic force of 60 mT formed on the developing roller 23a. The 1st conveyance screw 23b and the 2nd conveyance screw 23c are what formed the screw whose outer diameter is 18 mm on a core axis with a diameter of 8 mm at a pitch of 25 mm.

In the developing device 23, a two-component developer G composed of carrier C and toner T is accommodated.
The carrier C in the developer G has a resin coating layer on the surface of the core material. The resin coating layer of the carrier contains conductive particles in which a conductive coating layer comprising a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer is provided on the surface of the substrate particles. ing. The conductive particles contained in the resin coating layer are formed so that the oil absorption is 10 to 300 ml / 100 g.
The oil absorption amount of the conductive particles can be measured according to “21 oil absorption amount” in JIS-K5101 “Pigment test method”.

  As the base particles of the conductive particles, at least one of aluminum oxide, titanium dioxide, zinc oxide, silicon dioxide, barium sulfide, and zirconium oxide can be used. The powder specific resistance of the conductive particles is formed to be 200 Ω · cm or less. The layer of the resin coating layer contains non-conductive particles in addition to the conductive particles. The volume resistivity of the carrier C is formed to be in the range of 10 to 16 Log (Ω · cm).

As described above, since the carrier C of the first embodiment has the tin dioxide layer and the indium oxide layer containing tin dioxide sequentially formed on the surface of the base particle, the conductive layer is uniform on the particle surface. It is firmly fixed.
The conductive particles contained in the resin coating layer are formed so that the oil absorption is 10 to 300 ml / 100 g. Here, when the oil absorption is less than 10 ml / 100 g, the compatibility with the coating resin becomes insufficient, the adhesiveness is lowered, and the dispersibility is also lowered. Can not be. When the oil absorption exceeds 300 ml / 100 g, the adhesion with the binder resin becomes too strong and covers the surface of the conductive particles, so that the resistance cannot be adjusted sufficiently.
The carrier configured as described above can stably adjust the resistance over time without containing carbon black as a resistance adjusting agent, and can prevent carrier adhesion and the like and can stabilize the toner charge amount over time. .

In the first embodiment, the carrier C in the developer G is formed so that its weight average particle diameter is 35 μm. The weight average particle diameter of the carrier C is preferably in the range of 20 to 65 μm.
When the weight average particle size of the carrier is smaller than 20 μm, the magnetic force acting on each carrier is small, and thus carrier adhesion occurs. On the other hand, when the particle size of the carrier is larger than 65 μm, it becomes difficult for the toner to adhere faithfully to the latent image to which the toner should adhere, so that the granularity of the output image is lowered.

In addition, the toner T in the first exemplary embodiment is formed so that the average particle diameter is 6.8 μm.
The average particle size of the toner T is preferably formed to be in the range of 3.5 to 7.5 μm. When the average particle diameter of the toner is smaller than 3.5 μm, the toner adhesion amount in the toner image is small, and therefore, the trailing edge white spot and the halo image are likely to occur. On the other hand, when the average particle diameter of the toner is larger than 7.5 μm, it becomes difficult for the toner to adhere faithfully to the latent image to which the toner should adhere, so that the granularity of the output image decreases. .

In addition, the toner T in the first embodiment is mainly composed of a binder resin, a release agent, and a colorant. The binder resin of the toner T contains a hybrid resin having a vinyl polymer and a polyester polymer. Further, the content of the hybrid resin with respect to the content of the release agent is formed to be in the range of 0.5 to 3.
A hybrid resin can be obtained by performing a condensation polymerization reaction and an addition polymerization reaction simultaneously or independently in the same reaction vessel using a mixture containing a condensation polymerization resin raw material monomer and an addition polymerization resin raw material monomer. . As the release agent, carnauba wax, montan wax, oxidized rice wax or the like can be used, and the content thereof is preferably 3.5 to 10% by weight.

  The toner T configured as described above provides an output image with high durability, high image quality without uneven gloss, and less defects such as toner aggregation and fixing offset. On the other hand, since the specific gravity of the toner T configured as described above is smaller than that of the developer G (having the carrier C described above), the fresh toner T is supplied to the developer G. In addition, the toner T floats on the upper surface side of the developer G and is difficult to be dispersed (mixed) in the developer G. Therefore, when the toner T and the carrier C of the first embodiment are used, the effect of dispersing the replenishment toner (fresh toner) by the permanent magnet 43 (magnetic field generating means) described later becomes particularly large.

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developer G in the developing device 23 is generated by the rotation of the first conveying screw 23 b and the second conveying screw 23 c arranged so as to interpose the partition member 23 e therebetween in the arrow direction. It circulates in the longitudinal direction while being agitated and mixed with the toner T replenished from the replenishing section 32 through the toner replenishing port 23f (circulation in the direction of the broken arrow in FIG. 3). The first conveying screw 23b as the first conveying member conveys the developer G to the left side in FIG. 3, and the second conveying screw 23c as the second conveying member conveys the developer G to the left side in FIG. It is conveyed in the direction opposite to the conveying direction of the conveying screw 23b.

  Then, the toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23 a together with the carrier C. The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d. The developer G on the developing roller 23a is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area).

  Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently exposed by the electric field formed by the potential difference (development potential) between the latent image potential (exposure potential) of the image area irradiated with the laser light L and the development bias applied to the development roller 23a. Adhere to the image.

  Thereafter, most of the toner T adhering to the photosensitive drum 21 in the developing process is transferred onto the intermediate transfer belt 27. The untransferred 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.

  In the first embodiment, as the developing bias applied to the developing roller 23a, the AC component developing bias is not applied, and only the DC component developing bias is applied. This relatively simplifies the configuration and control of the power supply unit that supplies the developing bias. Further, by applying only the DC component developing bias to the developing roller 23a, it is possible to reduce the occurrence of a blurred image with respect to a carrier having a low resistance.

  Here, a toner replenishing unit 32 provided in the apparatus main body 1 includes a toner bottle 33 configured to be replaceable, and a toner hopper unit 34 that holds and rotates the toner bottle 33 and replenishes the developing device 23 with fresh toner T. And is composed of. The toner bottle 33 contains toner T (any one of yellow, magenta, cyan, and black). In addition, a spiral protrusion is formed on the inner peripheral surface of the toner bottle 33.

  The toner T in the toner bottle 33 is appropriately supplied into the developing device 23 from the toner supply port 23f as the toner T in the developing device 23 is consumed. The toner T in the developing device 23 is consumed by a reflection type photo sensor 41 facing the photosensitive drum 21 and a magnetic sensor 40 (toner density detecting means) installed below the second conveying screw 23c of the developing device 23. , Indirectly or directly. Further, the toner replenishing port 23f is provided at one end in the longitudinal direction of the second transport screw 23c (the left-right direction in FIG. 3) and above the second transport screw 23c.

Here, in the first embodiment, the toner concentration (TC) is controlled to be in the range of 6 to 12% by weight. Specifically, toner replenishment is performed so that the detection results of the magnetic sensor 40 and the reflection type photosensor 41 have an output value corresponding to the above-described toner density range (the ratio of the toner T in the developer G). The toner is supplied from the unit 32 to the developing device 23 through the toner supply port 23f.
By controlling the toner concentration to be equal to or less than 12% by weight, it is possible to reduce the progress of toner spent and to reduce the decrease in the toner charge amount. Further, by controlling the toner density to be 6% by weight or more, it is possible to prevent the image density of the output image from being lowered.

Hereinafter, the permanent magnet 43 as the magnetic field generating means, which is characteristic in the first embodiment, will be described in detail with reference to FIGS. 4 and 5.
FIG. 4 is a cross-sectional view of the developing device 23 in the vicinity of the position where the permanent magnet 43 is installed. FIG. 5 is a schematic view showing the circulation path of the second conveying screw 23c in the width direction. In addition, in FIG. 5, illustration of the 2nd conveyance screw 23c is abbreviate | omitted.

As shown in FIGS. 4 and 5, a permanent magnet 43 is installed above the circulation path of the developer G through a case 23 g as a magnetically permeable member. Specifically, referring to FIGS. 3 to 5, the permanent magnet 43 is located above the second conveying screw 23 c and from the toner supply port 23 f in the circulation path of the developer G (T, C) to the magnetic sensor 40 ( Until the toner density detecting means). In other words, the permanent magnet 43 is disposed downstream of the toner supply port 23 f in the developer G circulation path and upstream of the magnetic sensor 40.
Further, the permanent magnet 43 is configured to be movable in the vertical direction (moving in the direction of arrow A in FIG. 4) by a drive unit (not shown).

The permanent magnet 43 configured as described above operates as follows.
Referring to FIG. 5A, when the replenishing toner T1 is replenished from the toner replenishing port 26f, the permanent magnet 43 moves to the case 23g (second transport screw 23c) side. Thereby, the magnetic field by the permanent magnet 43 is formed in the circulation path of the 2nd conveyance screw. Then, due to the magnetic force of the permanent magnet 43, a part of the developers T and C refluxed below is adsorbed by the permanent magnet 43 through the case 23g, and the developer spike F is formed.

  On the other hand, the replenishing toner T1 replenished from the toner replenishing port 23f floats on the upper surface side of the recirculating developers T and C. After that, the replenishing toner T1 moving on the upper surface side collides with the developer spike F formed there at the position of the permanent magnet 43, and its path is directed downward. Thus, the replenishment toner T1 that moves on the upper surfaces of the developers T and C is dispersed and mixed in the developers T and C, and sufficient frictional charging with the carrier C is performed. As a result, it is possible to reduce image quality deterioration such as background stains and toner scattering.

In the first embodiment, since the permanent magnet 43 is disposed above the circulation path (second transport screw 23c), the replenishment toner T1 that moves on the upper surface of the developer is efficiently supplied to the developer. Can be dispersed in. That is, the developer spike F can be formed above the developer that is refluxed with a relatively small magnetic force. Thereby, the load for rotationally driving the second conveying screw 23c can also be made relatively small.
Further, since the permanent magnet 43 is disposed on the downstream side of the circulation path close to the toner supply port 23f, the toner T1 immediately after supply is quickly dispersed in the developer G. Thereby, it is possible to secure a sufficient time for performing frictional charging with the carrier C.
Further, since the permanent magnet 43 is disposed on the upstream side of the circulation path with respect to the magnetic sensor 40, the toner density after the replenishment toner T1 is sufficiently dispersed in the developer G can be detected. Thereby, the detection accuracy with respect to the toner concentration of the magnetic sensor 40 is increased, and it is possible to suppress the occurrence of problems such as background contamination and toner scattering due to excessive toner replenishment.

  On the other hand, referring to FIG. 5B, after the dispersion of the replenishment toner T1 is completed (after a predetermined time from when the toner replenishment is stopped), the permanent magnet 43 is moved to the case 23g (second transport screw). 23c) is moved away from the position. Thereby, the magnetic field by the permanent magnet 43 is lost in the circulation path of the second conveying screw. Then, the developers T and C adsorbed to the permanent magnet 43 through the case 23g are detached (dropped) from the case 23g (permanent magnet 43), and move along the circulation path together with the circulating developers T and C. It will be.

As described above, in the first embodiment, when the replenishment toner T1 is not replenished (when the replenishment toner T1 is not dispersed), the second magnet screw 23c is not attracted by the permanent magnet 43. It is possible to keep the load applied to the minimum. In other words, only when the replenishment toner T1 is dispersed, the developer spike F is formed in the circulation path, and the load on the second transport screw 23c slightly increases.
In the first embodiment, the developer ear F is formed above the circulation path with a relatively small adsorption force, and the developer ear F is appropriately detached. Stagnation (conveyance failure) is also suppressed. As a result, it is possible to prevent a decrease in density of the output image and a density deviation due to an insufficient supply amount of the developer to the developing roller 23a.

  As described above, according to the first embodiment, the permanent magnet 43 that attracts the developer G that circulates in the circulation path by magnetic force is installed above the circulation path, and the developer G that is attracted by the permanent magnet 43. It is configured to be able to leave. As a result, the load on the conveying member 23c is relatively small, and the dispersion of the replenishing toner T1 is promoted without causing the conveyance failure of the developer G, and image quality deterioration such as background contamination and image density reduction and toner scattering are ensured. It is reduced.

  In the first embodiment, the process cartridges 20Y, 20M, 20C, and 20BK are configured by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. Further, each developing device 23Y, 23M, 23C, 23BK is configured as a single unit. On the other hand, the developing devices 23Y, 23M, 23C, and 23BK can be integrated with the process cartridges 20Y, 20M, 20C, and 20BK. In other words, the process cartridge 20 can be configured by the photosensitive drum 21, the charging unit 22, the developing device 23, and the cleaning unit 25. Also in this case, the same effect as in the first embodiment is obtained. Furthermore, the maintainability of the image forming unit is improved.

  In the first embodiment, the case 23g of the developing device 23 is used as the magnetically permeable member so that the developer is not directly attracted to the permanent magnet 43. On the other hand, apart from the case 23g of the developing device 23, a magnetically permeable member for preventing the developer from being directly adsorbed to the permanent magnet 43 can be provided as a separate member.

Embodiment 2. FIG.
6 and 7, the second embodiment of the present invention will be described in detail.
FIG. 6 is a cross-sectional view illustrating the developing device according to the second embodiment, and corresponds to FIG. 4 according to the first embodiment. FIG. 7 is a schematic diagram illustrating a state where the developer is adsorbed and separated in the circulation path, and corresponds to FIG. 5 in the first embodiment. The second embodiment is different from that of the first embodiment in which the permanent magnet 43 as a magnetic field generating means is rotated and moved.

As shown in FIGS. 6 and 7, a permanent magnet 43 is installed above the circulation path of the developer G through a case 23 g as a magnetically permeable member. The permanent magnet 43 is disposed above the second conveying screw 23 c and between the toner supply port 23 f and the magnetic sensor 40 in the developer G circulation path.
Further, the permanent magnet 43 is configured to be rotationally moved (moving in the direction of arrow B in FIG. 6) about the rotation shaft 44 by a drive unit (not shown).

The permanent magnet 43 configured as described above operates as follows.
Referring to FIG. 7A, when the replenishing toner T1 is replenished from the toner replenishing port 23f, the permanent magnet 43 rotates and moves closer to the case 23g (second transport screw 23c) side. Thereby, the magnetic field by the permanent magnet 43 is formed in the circulation path of the 2nd conveyance screw. Then, the developer spike F is formed above the circulation path, and the replenishment toner T1 is efficiently dispersed.

  On the other hand, referring to FIG. 7B, after the replenishment of the replenishment toner T1 is completed, the permanent magnet 43 is rotationally moved to a position away from the case 23g (second transport screw 23c). Thereby, the magnetic field by the permanent magnet 43 is lost in the circulation path of the second conveying screw. The developer spike F is detached from the case 23g (permanent magnet 43) and moves along the circulating path with the circulating developers T and C.

  As described above, also in the second embodiment, as in the first embodiment, the permanent magnet 43 that adsorbs the developer G circulating in the circulation path with a magnetic force is installed above the circulation path and is permanently The developer G adsorbed by the magnet 43 can be removed. As a result, the load on the conveying member 23c is relatively small, and the dispersion of the replenishing toner T1 is promoted without causing the conveyance failure of the developer G, and image quality deterioration such as background contamination and image density reduction and toner scattering are ensured. It is reduced.

Embodiment 3 FIG.
8 and 9, the third embodiment of the present invention will be described in detail.
FIG. 8 is a cross-sectional view showing the developing device in the third embodiment, and corresponds to FIG. 4 in the first embodiment. FIG. 9 is a schematic diagram illustrating a state where the developer is adsorbed and separated in the circulation path, and corresponds to FIG. 5 in the first embodiment. The third embodiment is different from the first embodiment in which the electromagnet 46 is used as the magnetic field generating means, and the permanent magnet 43 is used as the magnetic field generating means.

As shown in FIGS. 8 and 9, an electromagnet 46 is installed above the circulation path of the developer G through a case 23 g as a magnetically permeable member. The electromagnet 46 is disposed above the second conveying screw 23 c and between the toner supply port 23 f and the magnetic sensor 40 in the developer G circulation path.
The electromagnet 46 includes an iron core, a coil wound around the outer peripheral surface of the iron core, a power source for supplying a DC current (or AC current) to the coil, a switch for turning on / off the coil, and the like.

The electromagnet 46 configured as described above operates as follows.
Referring to FIG. 9A, when the replenishment toner T1 is replenished from the toner replenishing port 23f, energization to the electromagnet 46 is started. Thereby, the magnetic field by the electromagnet 46 is formed in the circulation path of the second conveying screw. Then, the developer spike F is formed above the circulation path, and the replenishment toner T1 is efficiently dispersed.

  On the other hand, referring to FIG. 9B, after the dispersion of the replenishment toner T1 is completed, the energization to the electromagnet 46 is stopped. Thereby, the magnetic field by the electromagnet 46 disappears in the circulation path of the second transport screw. Then, the developer F leaves the case 23g (electromagnet 46) and moves along the circulating path with the circulating developers T and C.

  As described above, in the third embodiment, the electromagnet 46 that adsorbs the developer G circulating in the circulation path by the magnetic force is installed above the circulation path, and the developer G adsorbed by the electromagnet 46 can be detached. Thus, the energization to the electromagnet 46 is controlled to stop. As a result, the load on the conveying member 23c is relatively small, and the dispersion of the replenishment toner T1 is promoted without causing the conveyance failure of the developer G, and image quality deterioration such as background contamination and image density reduction and toner scattering are ensured. It is reduced.

  In the third embodiment, the electromagnet 46 is disposed above the circulation path via the case 23g. However, the electromagnet 46 is directly above the circulation path (inside the developing device 5) without the case 23g. It can also be arranged. That is, since the magnetic field generated by the electromagnet 46 can be arbitrarily formed / disappeared by turning on / off the energization, there is no problem due to the developer G adsorbing directly on the electromagnet 46.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 10 is a cross-sectional view showing the developing device in the fourth embodiment, and corresponds to FIG. 4 in the first embodiment. FIG. 11 is a schematic diagram illustrating a state where the developer is adsorbed and separated in the circulation path, and corresponds to FIG. 5 in the first embodiment. The fourth embodiment is different from the first embodiment in which the developer is removed by the movement of the permanent magnet 43 in that the developer is removed by using the magnetic flux shielding member 47. .

As shown in FIGS. 10 and 11, a permanent magnet 43 is fixed above the circulation path of the developer G through a case 23g. The permanent magnet 43 is disposed above the second conveying screw 23 c and between the toner supply port 23 f and the magnetic sensor 40 in the developer G circulation path.
In the fourth embodiment, a magnetic flux shielding member 47 that shields the magnetic field from the permanent magnet 43 is provided. The magnetic flux shielding member 47 can be formed of, for example, an iron plate. The magnetic flux shielding member 47 is configured to be moved between the permanent magnet 43 and the case 23g (moving in the direction of arrow D in FIG. 10) by a drive unit (not shown).

The magnetic flux shielding member 47 configured in this manner operates as follows.
Referring to FIG. 11A, when replenishing toner T1 is replenished from toner replenishing port 23f, magnetic flux shielding member 47 moves to a position away from case 23g. Thereby, the magnetic field by the permanent magnet 43 is formed in the circulation path of the 2nd conveyance screw. Then, the developer spike F is formed above the circulation path, and the replenishment toner T1 is efficiently dispersed.

  On the other hand, referring to FIG. 11B, after the dispersion of the replenishing toner T1 is completed, the magnetic flux shielding member 47 moves between the case 23g (second transport screw 23c) and the permanent magnet 43. Thereby, the magnetic field by the permanent magnet 43 formed in the circulation path of the second conveying screw is shielded by the magnetic flux shielding member 47. The developer spike F is detached from the case 23g (permanent magnet 43) and moves along the circulating path with the circulating developers T and C.

  As described above, in the fourth embodiment, the permanent magnet 43 that attracts the developer G circulating in the circulation path with a magnetic force is installed above the circulation path, and the developer G adsorbed by the permanent magnet 43 is removed. The magnetic flux shielding member 47 is used for separation. As a result, the load on the conveying member 23c is relatively small, and the dispersion of the replenishing toner T1 is promoted without causing the conveyance failure of the developer G, and image quality deterioration such as background contamination and image density reduction and toner scattering are ensured. It is reduced.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. It is sectional drawing which looked at the developing device to the longitudinal direction. It is sectional drawing which shows a developing device. (A) The schematic which shows the state which adsorb | sucked the developer with the permanent magnet, (B) The schematic which shows the state which moved the permanent magnet upwards and isolate | separated the developer. It is sectional drawing which shows the developing device in Embodiment 2 of this invention. (A) The schematic which shows the state which adsorb | sucked the developer with the permanent magnet, (B) The schematic which shows the state which rotationally moved the permanent magnet and isolate | separated the developer. It is sectional drawing which shows the developing device in Embodiment 3 of this invention. (A) Schematic diagram showing a state in which developer is adsorbed by an electromagnet, and (B) Schematic diagram showing a state in which energization to the electromagnet is stopped and the developer is detached. It is sectional drawing which shows the developing device in Embodiment 4 of this invention. (A) The schematic which shows the state which adsorb | sucked the developer with the permanent magnet, (B) The schematic which shows the state which moved the magnetic flux shielding member and detach | leaved the developer.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20M, 20C, 20BK Process cartridge,
21 photosensitive drum (image carrier), 22 charging unit,
23, 23Y, 23M, 23C, 23BK Developing device (developing unit),
23a Development roller (developer carrier),
23b 1st conveyance screw (1st conveyance member),
23c 2nd conveyance screw (2nd conveyance member), 23e Partition member,
23f toner supply port, 23g case (magnetically permeable member),
25 Cleaning section,
32, 32Y, 32M, 32C, 32BK toner supply unit,
40 Magnetic sensor (toner concentration detection means)
43 Permanent magnet (magnetic field generating means), 44 Rotating shaft,
46 electromagnet (magnetic field generating means), 47 magnetic flux shielding member,
G Two-component developer (developer), T toner, C carrier.

Claims (15)

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 generating means installed above the circulation path and formed so that the developer can be attracted by a magnetic force;
A developing device characterized in that the developer adsorbed by the magnetic field generating means can be detached. The developing device according to claim 1, wherein when the toner is not replenished from the toner replenishing port, the developer adsorbed by the magnetic field generating unit is released. The developing device according to claim 1, wherein the magnetic field generation unit is installed above the second transport member. The toner supply port is disposed above the second conveying member,
The developing device according to claim 3, wherein the magnetic field generation unit is disposed downstream of the circulation path with respect to the toner supply port. A toner concentration detecting means for detecting a toner concentration of the developer conveyed by the second conveying member;
The developing device according to claim 3, wherein the magnetic field generation unit is disposed upstream of the circulation path with respect to the toner concentration detection unit. A magnetically permeable member disposed between the magnetic field generating means and the circulation path so that the developer is not directly adsorbed to the magnetic field generating means;
6. The developer adsorbed to the magnetically permeable member by the magnetic field generating means is released by moving the magnetic field generating means to a position away from the magnetically permeable member. The developing device according to any one of the above. The developing device according to claim 6, wherein the magnetic field generating unit is a permanent magnet or an electromagnet. The magnetic field generating means is an electromagnet,
The developing device according to claim 1, wherein the developer adsorbed by the electromagnet is released by stopping energization of the electromagnet. A magnetic flux shielding member that is movably disposed between the magnetic field generating means and the circulation path and shields the magnetic field;
9. The developer adsorbed by the magnetic field generation unit is released by moving the magnetic flux shielding member between the magnetic field generation unit and the circulation path. The developing device according to 1. The carrier has a resin coating layer on the core surface,
The resin coating layer contains conductive particles formed by providing a conductive coating layer composed of a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer on the surface of the substrate particles,
The conductive particles are formed so that the oil absorption is 10 to 300 ml / 100 g,
The toner includes a binder resin, a release agent, and a colorant,
The binder resin contains a hybrid resin having a vinyl polymer and a polyester polymer so that the content of the hybrid resin is in the range of 0.5 to 3 with respect to the content of the release agent. The developing device according to claim 1, wherein the developing device is formed as described above. 11. The developing device according to claim 1, wherein the carrier is formed so that a weight average particle diameter is in a range of 20 to 65 [mu] m. The developing device according to claim 1, wherein the toner is formed so that an average particle diameter is in a range of 3.5 to 7.5 μm. 13. The developing device according to claim 1, wherein a toner concentration in the developer is controlled to be in a range of 6 to 12% by weight. A process cartridge that is detachably installed on the main body of the image forming apparatus,
14. A process cartridge, wherein the developing device according to claim 1 and the image carrier are integrated. An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

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