JP2006251594A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of suppressing the deterioration of a developer with the lapse of time by reducing stress applied to the developer while stabilizing the charged quantity of toner even with the lapse of time, and to provide also a process cartridge and an image forming apparatus. <P>SOLUTION: When it is defined that the quantity of a developer G carried by a developer carrier 23a is M0, the quantity of the developer G in a first developer storing part 23g is M1 and the quantity of the developer G in a second developer storing part 23h is M2, the image forming apparatus is constituted so as to form the relation of M1-M0<M2. <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.
Here, the developing device includes a first developer accommodating portion in which the developing roller and the first conveying screw (first conveying member) are arranged, and a second developer screw in which the second conveying screw (second conveying member) is arranged. 2 developer accommodating portions. The first developer accommodating portion and the second developer accommodating portion communicate with each other at both ends in the longitudinal direction, and a developer circulation path is formed.

  In the developing device configured as described above, toner is appropriately supplied into the device from a toner supply port provided at one end of the developing device in accordance with toner consumption in the 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 the first 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, in a developing device using a two-component developer, the external additive on the toner surface is buried in or detached from the toner, or the carrier surface is exposed to stress while the developer circulates in the device. It is known that a problem that the toner component adheres (spent) to the toner occurs with time. When such a problem occurs, the charging ability of the toner and the carrier is reduced, and background contamination (a phenomenon in which toner adheres to a non-image area on the photosensitive drum or the output image) or toner scattering. Will occur.

On the other hand, in Patent Document 2 and the like, the developer carried on the developing roller is conveyed from the capture region for the purpose of reducing the stress applied when the developer passes through the position of the doctor blade (developer carrying member). A technique for optimizing the magnetic force and the magnetic force distribution from the region to the development region is disclosed.
Patent Document 3 discloses a technique for widening the distance between the doctor blade and the developing roller by optimizing the relationship between the thickness of the doctor blade, the magnetic pole formed in the vicinity thereof, and the diameter of the developing roller. Is disclosed.

  On the other hand, in Patent Document 4 and the like, for the purpose of improving the image quality when spherical toner is used, the degree of sphericity of the toner, the developer transport amount per unit time by the developer stirring and transport member, the toner replenishment amount, A technique for optimizing the number of images formed is disclosed.

Japanese Patent Laid-Open No. 10-69155 JP 2001-109266 A Japanese Patent Laid-Open No. 11-24407 JP 2003-270946 A

The conventional developing device described above cannot reduce the deterioration of the developer over time while stabilizing the charge amount of the toner over time.
In order to stably form a high-quality output image over a long period of time, the charge amount of the toner in the developer needs to be maintained well over time. The charging of the toner is mainly caused by friction with the carrier. In particular, the toner is charged in the vicinity (mainly upstream) of the gap (doctor gap) between the developer regulating member and the developer carrier. The contribution of frictional charging is large.

On the other hand, the techniques described in Patent Document 2 and Patent Document 3 described above reduce the stress applied to the developer in the vicinity of the gap between the developer regulating member and the developer carrier, and are sufficient for the toner. There is a high possibility that charging will not occur. That is, although the effect of reducing the deterioration of the developer over time can be expected to some extent, the charge amount of the toner is likely to become unstable.
Further, the technique disclosed in Patent Document 4 described above improves the rising of charging of the spherical toner, and cannot be expected to suppress the deterioration of the developer with time.

  The present invention has been made to solve the above-described problems, and can suppress the deterioration of the developer over time by reducing the stress applied to the developer while stabilizing the charge amount of the toner over time. Another object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus.

The inventor of the present application has made researches to solve the above-described problems, and as a result, has come to know the following matters.
That is, the stress received by the developer circulating in the developing device is received in the vicinity of the opposed position between the developer carrying body and the developer regulating member, as well as at the opposed position between the developer carrying body and the first conveying member. There is something to receive in the vicinity. The latter stress is also greatly related to the deterioration of the developer over time, as much as the former stress. In the vicinity of the position where the developer carrying member and the first transport member are opposed to each other in the first developer accommodating portion, the developer (developer before the developing process) is pumped up and developed. Since the developer (developer after the developing process) is detached from the developer carrying member, the developer is brought into pressure contact, and the stress on the developer increases.

The present invention is based on the matters described above. That is, the developing device according to the first aspect of the present invention accommodates the developer having the toner and the carrier and is formed on the image carrier. A developing device for developing a latent image, the developer carrying member facing the image carrier, the developer carrying member carrying the developer, and the first conveyance facing the developer carrier and the developer carrier A first developer accommodating portion in which the developer is conveyed along the longitudinal direction of the developer carrier by the first conveying member, and the first conveying through the partition member. A second conveying member facing the member is disposed, and the developer is conveyed in a direction opposite to a conveying direction of the first developer accommodating portion, together with the first developer accommodating portion. Second developer collection forming a circulation path An amount of the developer carried on the developer carrying member is M0, and the amount of the developer in the first developer containing portion is M1, and the amount in the second developer containing portion is When the amount of developer is M2,
M1-M0 <M2
The relationship is established.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the developer transport amount per unit time by the first transport member is the developer by the second transport member. This is configured to be larger than the transport amount per unit time.

  According to a third aspect of the present invention, there is provided the developing device according to the second aspect, wherein the developer transport speed by the first transport member is greater than the developer transport speed by the second transport member. In this configuration, a difference in transport amount between the first transport member and the second transport member is provided.

  According to a fourth aspect of the present invention, there is provided the developing device according to the third aspect, wherein the first conveying member is rotated at a rotational speed greater than that of the second conveying member. A difference in transport speed between the first transport member and the second transport member is provided.

  A developing device according to a fifth aspect of the present invention is the developing device according to any one of the second to fourth aspects, wherein the screw diameter of the first conveying member is larger than the screw diameter of the second conveying member. By being configured to be large, a difference in the transport amount between the first transport member and the second transport member is provided.

  A developing device according to a sixth aspect of the present invention is the developing device according to any one of the second to fifth aspects, wherein the screw pitch of the first conveying member is larger than the screw pitch of the second conveying member. By being configured to be large, a difference in the transport amount between the first transport member and the second transport member is provided.

  A 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 discharging unit discharges a part of the developer accommodated in the device. And a replenishing unit for newly replenishing the carrier or the developer in the apparatus.

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

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

  The present invention optimizes the amount of developer in the first developer accommodating portion and the second developer accommodating portion, and reduces stress on the developer in the vicinity of the opposing position between the developer carrying member and the first conveying member. ing. As a result, it is possible to provide a developing device, a process cartridge, and an image forming apparatus in which the toner charge amount is stabilized over time and the deterioration of the developer over time is suppressed.

  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.
The 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, FIG. 3 is a cross-sectional view in the longitudinal direction (the direction perpendicular to the paper in FIG. 2) showing the developing device, and FIG. 4 is a cross-sectional view showing only the developing device. It is.
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 photosensitive drum 21 has an outer diameter of 30 mm, and the outer peripheral linear velocity is set to 240 mm / sec.

  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.

  Further, the developing device 23 is provided with a first developer containing portion 23g and a second developer containing portion 23h separated by a partition member 23e. Referring to FIG. 3, the first developer accommodating portion 23g and the second developer accommodating portion 23h communicate with each other at both ends in the longitudinal direction (the range in which the partition member 23e is not interposed), and the developer circulation path. Is forming. A developing roller 23a, a first conveying screw 23b, and a doctor blade 23d are disposed in the first developer accommodating portion 23g. A second transport screw 23c and a magnetic sensor 40 are disposed in the second developer accommodating portion 23h.

  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. A plurality of magnetic poles (main pole, transport pole, pumping pole, agent cutting pole, etc.) are formed on the developing roller 23a (sleeve 23a2) by the magnet 23a1. The developing roller 23a has an outer diameter of 18 mm and an outer peripheral linear velocity of 408 mm / sec.

  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 ± 0.05 mm. The gap (doctor gap) between the developing roller 23a and the doctor blade 23d is set to be 0.5 ± 0.04 mm. The doctor blade 23d is made of a SUS material. The first conveying screw 23b is formed by forming a blade having an outer diameter of 14 mm in a spiral shape at a pitch of 16 mm on a shaft portion having a diameter of 6 mm. The second transport screw 23c is formed substantially the same as the first transport screw 23b.

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 5.5 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.

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 density (TC) is controlled so as to fall within the range of 4 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 reduce the decrease in toner charge amount. Further, by controlling the toner concentration to be 4% by weight or more, it is possible to prevent the output image from decreasing in image density.

In the developing device 23 of the first embodiment, the developer amount in the first developer accommodating portion 23g and the developer amount in the second developer accommodating portion 23h are controlled as follows.
The amount of developer G carried on the developing roller 21a is M0, the amount of developer G in the first developer container 23g is M1, and the amount of developer G in the second developer container 23h is M2. And when
M1-M0 <M2
It is controlled so that the following relationship is established.

Specifically, in order to satisfy the above equation, the developing device 23 of the first embodiment has a developer transport amount per unit time of the developer G by the first transport screw 23b of the developer G by the second transport screw 23c. It is set to be larger than the transport amount per unit time.
Specifically, the rotational speed of the first transport screw 23b is set to be larger than the rotational speed of the second transport screw 23c. Thereby, the conveyance speed of the developer G by the 1st conveyance screw 23b becomes larger than the conveyance speed of the developer G by the 2nd conveyance screw 23c. As described above, each of the first transport screw 23b and the second transport screw 23c is formed by forming a blade having an outer diameter of 14 mm in a spiral shape at a pitch of 16 mm on a shaft portion having a diameter of 6 mm. The conveyance force (the amount of developer that can be conveyed per unit distance) is also equivalent.

With such a configuration, in the developing device 23 in operation, the developer amount in the first developer accommodating portion 23g is smaller than the developer amount in the second developer accommodating portion 23h. It should be noted that the following model formula is established in each developer accommodating portion 23g, 23h.
(Developer transport amount per unit time) [g / sec]
= (Developer transport speed) [mm / sec] x (Developer transport force) [g / mm]

Therefore, in the first embodiment, the conveying force of the first conveying screw 23b and the second conveying screw 23c is made constant, and the rotational speed (developer conveying speed) of the first conveying screw 23b and the second conveying screw 23c is different. By providing the difference in developer transport amount per unit time of both, the above formula (M1-M0 <M2) was satisfied.
On the other hand, by providing a difference in the transport force between the first transport screw 23b and the second transport screw 23c, it is also possible to provide a difference in the developer transport amount per unit time. Specifically, by providing differences in the screw diameter, screw pitch, cross-sectional shape, and the like of the first conveyance screw 23b and the second conveyance screw 23c, it is possible to provide a difference in both developer conveyance forces.

  In the developing device 23 configured and operated in this manner, the developer amount at the position where the developing roller 23a and the first conveying screw 23b are opposed to each other is moderately smaller than that of the conventional one with reference to FIG. As a result, the stress applied to the developer G is reduced at the position where the developing roller 23a and the first transport screw 23b face each other. That is, the spent of the carrier C and the burying and detachment of the external additive from the toner T are reduced, and the life of the developer G is improved.

  Although there is a stress that the developer G receives in the vicinity of the position where the doctor blade 23d and the developing roller 23a face each other, the stress that is received at this position is necessary for the toner T just before the developing process to be charged well. . Therefore, in the first embodiment, only the stress that has little influence on the charging property of the toner T is actively reduced.

However, if the amount of developer in the first developer accommodating portion 23g is too small, an image (for example, a black solid image) that consumes a large amount of toner is continuously formed on the developing roller 23a. The developer supply will not be in time. For this reason, the inventor of the present application has obtained the above formula (M1-M0 <M2) as a result of repeated experiments.
M2 × 0.4 ≦ M1-M0 ≦ M2 × 0.8
It came to know that it is preferable.

Further, in the vicinity of the position where the first conveying screw 23b and the developing roller 23a face each other, the developer G on the developing roller 23a that has completed the developing process (the developer that has consumed the toner) is developed by the developer cutting pole. 23a is a position to be removed from above. Therefore, if the vicinity of the position where the first conveying screw 23b and the developing roller 23a are opposed to each other is pressed with the developer, the developer G on the developing roller 23a is not separated from the developing roller 23a without being separated by the agent cutting pole. (This phenomenon is called “accompaniment”) occurs. In such a case, the accompanying developer (of insufficient toner concentration) is mixed with the developer G (of sufficient toner concentration) newly pumped onto the developing roller 23a. As a result, the image density of the image formed thereafter becomes non-uniform.
In the first embodiment, since the developer amount in the vicinity of the position where the first conveyance screw 23b and the developing roller 23a are opposed to each other is controlled to be relatively small, the pressure contact of the developer G at that position is reduced. Thus, the accompanying rotation of the developer G is suppressed.

  In the first embodiment, the amount of developer in the second developer accommodating portion 23h increases as the amount of developer in the first developer accommodating portion 23g is smaller than that of the conventional one. Accordingly, the fresh toner replenished from above in the second developer accommodating portion 23h is easily dispersed and mixed in the developer G. Therefore, the detection accuracy of the toner concentration by the magnetic sensor 40 is increased, the toner concentration is prevented from being excessive, and the chargeability of the toner is improved.

  As described above, according to the first embodiment, the amount of the developer G in the first developer accommodating portion 23g and the second developer accommodating portion 23h is optimized, and the developing roller 23a and the first conveying screw 23b are optimized. The stress with respect to the developer G in the vicinity of the position opposite to is reduced. As a result, it is possible to reduce the deterioration of the developer G over time while stabilizing the charge amount of the toner T over time.

  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.

Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a cross-sectional view showing the developing device in the second embodiment, and corresponds to FIG. 4 in the first embodiment. In the second embodiment, the first transport screw 23b and the second transport screw 23c have different cross-sectional shapes, a discharge unit that discharges the developer, and a supply unit that supplies the developer. This is different from that of the first embodiment.

  Referring to FIG. 5, in the second embodiment, similarly to the first embodiment, the amount of developer G transported per unit time by the first transport screw 23b is equal to the developer G by the second transport screw 23c. It is set to be larger than the transport amount per unit time. In the second embodiment, unlike the first embodiment, the rotational speed of the first transport screw 23b is set to be equal to the rotational speed of the second transport screw 23c. The shaft diameter of the first transport screw 23b is configured to be smaller than the shaft diameter of the second transport screw 23c. That is, the screw diameter of the first conveying screw 23b is configured to be larger than the screw diameter of the second conveying screw 23c.

  In other words, the developer transport amount per unit time between the first transport screw 23b and the second transport screw 23c is changed so as to satisfy the formula (M1-M0 <M2) described in the first embodiment. Provided. As a result, similarly to the first embodiment, the amount of developer at the position where the developing roller 23a and the first conveying screw 23b face each other is reduced to such an extent that the stress of the developer G can be reduced without accompanying rotation.

Further, in the second embodiment, discharging means 23j, 45, and 46 for discharging a part of the developer G stored in the developing device 23 to the outside of the device, and replenishment for supplying the developing device 23 with the fresh developer G. Means 23k.
Specifically, a developer discharge port 23j is provided above the second developer accommodating portion 23h. When the amount of developer in the second developer accommodating portion 23h increases and the upper surface reaches the position of the developer discharge port 23j, the developer is discharged from the developer discharge port 23j. The developer discharged from the developer discharge port 23j is transferred to the waste bottle through the discharge path 45 by the transfer oven 46.

  On the other hand, a developer supply port 23k is provided above the second developer accommodating portion 23h, in addition to the toner supply port 23f. A fresh developer conveyed from a developer bottle (not shown) is appropriately supplied from the developer supply port 23k toward the inside of the developing device 23.

Thus, the ratio of the deteriorated developer in the developing device 23 is reduced by discharging the developer by the discharging means 23j, 45 and 46 and supplying fresh developer by the supplying means 23k. Therefore, the life of the developer accommodated in the developing device 23 is further increased.
In the second embodiment, the fresh developer G is supplied from the developer supply port 23k. However, a fresh carrier C may be supplied from the developer supply port 23k. In this case, the same effect as described above can be obtained.

  As described above, according to the second embodiment, as in the first embodiment, the amount of the developer G in the first developer container 23g and the second developer container 23h is optimized, The stress on the developer G in the vicinity of the position where the developing roller 23a and the first conveying screw 23b face each other is reduced. As a result, it is possible to reduce the deterioration of the developer G over time while stabilizing the charge amount of the toner T over time.

Hereinafter, examples and comparative examples for confirming the effects in the above-described embodiments will be described with reference to FIG.
In Examples 1 to 4 and Comparative Examples 1 and 2, as shown in FIG. 6, the shaft diameters, screw pitches, and rotational speed levels of the first transport screw 23 b and the second transport screw 23 c are varied, and the first developer. The level of the developer amount (M1-M0) in the storage portion 23g and the developer amount (M2) in the second developer storage portion 23h is varied to evaluate the occurrence of toner scattering and background contamination. Note that the total developer amount in the figure is the sum of M0, M1, and M2 described above.

  Specifically, 100,000 images having an image area ratio of 5% were continuously output using the image forming apparatus of the first embodiment under the conditions shown in FIG. Subsequently, the toner contamination in the apparatus main body 1 and the image quality of the output image were checked to evaluate the degree of toner scattering and background contamination. The evaluations of toner scattering and background stain were both visually, and were ranked in three stages based on limit samples. In FIG. 6, “◯” is a good level, “Δ” is an acceptable level, and “X” is an unacceptable level.

Referring to FIG. 6, in Comparative Example 1, the developer conveyance amounts of the two conveyance screws 23b and 23c are the same, and the developer amount (M1-M0) of the first developer accommodating portion 23g and the second development are the same. The developer amount (M2) in the agent container 23h was the same. In addition, an unacceptable level of toner scattering and background contamination occurred.
In the first embodiment, the developer amount in the first developer accommodating portion 23g is changed to the developer amount in the second developer accommodating portion 23h by increasing the developer conveying amount by increasing the screw pitch of the first conveying screw 23b. Was less than. Further, the generation level of toner scattering and background contamination has been improved to an acceptable level.

In the second embodiment, the developer pitch of the first developer accommodating portion 23g is increased by further increasing the screw pitch of the first conveying screw 23b to increase the developer conveying amount, thereby developing the developer in the second developer accommodating portion 23h. It was even less than the amount. In the third embodiment, the developer amount in the first developer accommodating portion 23g is changed to the developer amount in the second developer accommodating portion 23h by increasing the rotation speed of the first conveying screw 23b to increase the developer conveying amount. It was even less than. In the fourth embodiment, the developer amount in the first developer accommodating portion 23g is increased by reducing the shaft diameter of the first conveying screw 23b (increasing the screw diameter) to increase the developer conveying amount. The amount of developer was further smaller than that of the portion 23h. In all of the examples, the toner level was improved to a good level without causing toner scattering and background stains.
On the other hand, in Comparative Example 2, when the amount of developer accommodated in the developing device 23 was reduced as a whole, unacceptable levels of toner scattering and background contamination occurred.

Further, a developing device (provided above) that includes a developer replenishing means (supplementing 1 g of carrier for 1000 image output sheets) and a discharging means under the same conditions as in the first to fourth embodiments. When the image output of 300,000 sheets was carried out using the development device of Form 2, the toner was scattered at a satisfactory level and the background stain was not generated under any conditions.
As described above, the effects in the above-described embodiments were confirmed.

  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. It is sectional drawing which shows the developing device in Embodiment 2 of this invention. It is a graph which shows the conditions and result of the Example and comparative example which were performed in order to confirm an effect.

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),
23d doctor blade (developer regulating member),
23e partition member, 23f toner supply port,
23g first developer accommodating portion, 23h second developer accommodating portion,
23k developer supply port (supply means), 23j developer discharge port (discharge means),
32, 32Y, 32M, 32C, 32BK toner supply unit,
45 discharge path, 46 transport auger,
G Two-component developer (developer), C carrier, T toner.

Claims (9)

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;
The developer carrier and a first transport member facing the developer carrier are disposed, and the developer is transported along the longitudinal direction of the developer carrier by the first transport member. A first developer container;
A second conveying member is disposed opposite the first conveying member via a partition member, and the developer is conveyed in a direction opposite to the conveying direction of the first developer accommodating portion. A second developer accommodating portion that forms a circulation path of the developer together with the developer accommodating portion,
The amount of the developer carried on the developer carrying member is M0, the amount of the developer in the first developer containing portion is M1, and the amount of the developer in the second developer containing portion is M2. And when
M1-M0 <M2
A developing device characterized in that the following relationship is established. 2. The apparatus according to claim 1, wherein a transport amount per unit time of the developer by the first transport member is larger than a transport amount of the developer by the second transport member per unit time. The developing device described. By transporting the developer by the first transport member so as to be larger than the transport speed of the developer by the second transport member, transport between the first transport member and the second transport member is performed. The developing device according to claim 2, wherein a difference in amount is provided. The rotational speed of the first transport member is made larger than the rotational speed of the second transport member, thereby providing a difference in transport speed between the first transport member and the second transport member. Item 4. The developing device according to Item 3. By configuring the screw diameter of the first conveying member to be larger than the screw diameter of the second conveying member, a difference in conveying amount between the first conveying member and the second conveying member is provided. The developing device according to claim 2, wherein the developing device is characterized in that: By configuring the screw pitch of the first conveying member to be larger than the screw pitch of the second conveying member, a difference in conveying amount between the first conveying member and the second conveying member is provided. The developing device according to claim 2, wherein the developing device is characterized in that: Discharging means for discharging a part of the developer contained in the apparatus;
The developing device according to claim 1, further comprising a replenishing unit that replenishes the carrier or the developer into the device. A process cartridge that is detachably installed on the main body of the image forming apparatus,
8. 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.

Images