JP2011028216A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device having two conveying members for conveying a developer in a longitudinal direction and forming a circulation path, which are disposed facing a developer carrier, path for supplying and collecting the developer to/from the developer carrier separately, and a developer regulating member disposed below the developer carrier; to prevent screw-pitched density unevenness corresponding to the pitch of the screw part of a first conveying member from being generated on an output image; and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: The first conveying member 13b1 is a screw member constituted by helically winding the screw part around a shaft part. The screw part is formed so that the outer diameter thereof may be continuously or stepwise reduced from the upstream side to the downstream side in a conveying direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a developing device and a process cartridge installed therein, and in particular, a developer in a longitudinal direction. Developer regulation that regulates the amount of developer upstream of the development area, wherein at least two of the plurality of conveyance members that are conveyed to form a circulation path are arranged to face the developer carrier. The present invention relates to a developing device, a process cartridge, and an image forming apparatus in which members are disposed below a developer carrier.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device that contains a two-component developer composed of a toner and a carrier (including a case where an additive or the like is added), and the developer is long. And a developer regulating member for regulating at least two conveying members in a vertical direction among a plurality of conveying members that form a circulation path by conveying in a direction, and for regulating a developer amount upstream of a developing region The technique of arrange | positioning below is known (for example, refer patent documents 1-3 grade | etc.,).

  In a developing device using a two-component developer, toner is appropriately replenished into the developing device from a toner replenishing port provided in a part of the developing device according to toner consumption in the developing device. The replenished toner is agitated and mixed together with the developer in the developing device by a conveying member (agitating and conveying member) such as a conveying screw. Part of the stirred and mixed developer is supplied to a developing roller (developer carrier). After the developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member) installed below the developing roller, the toner in the two-component developer is transferred to the photosensitive drum (image carrier). To the latent image on the photosensitive drum at a position opposite to (). A magnet is fixed inside the developing roller, and a plurality of magnetic poles are formed around the developing roller by the magnet.

  In the developing device in Patent Document 1 or the like, a first conveying member (supply screw) and a second conveying member (collection screw) are installed in the vertical direction, and a developer circulation path is formed by these conveying members. ing. The first conveying member installed below supplies the developer to the developing roller at the position of the pumping magnetic pole while conveying the developer in the longitudinal direction. The second conveying member installed above conveys the developer separated from the developer roller at the position of the agent separating magnetic pole in the longitudinal direction (the direction opposite to the conveying direction by the first conveying member). The downstream side of the conveyance path (first conveyance path) by the first conveyance member and the upstream side of the conveyance path (second conveyance path) by the second conveyance member communicate with each other via the first relay unit. Then, the developer that has reached the downstream side of the first transport path stays at that position and is pushed up to reach the upstream side of the second transport path. Here, a toner supply port is provided on the upstream side of the second conveyance path, and new toner is appropriately supplied. In addition, the upstream side of the first transport path and the downstream side of the second transport path communicate with each other via the second relay unit. Then, the developer that has reached the downstream side of the second conveyance path falls by its own weight on the second relay unit and is moved to the upstream side of the first conveyance path. Note that the first transport member (supply screw) and the second transport member (collection screw) are both disposed so that the shaft portions thereof are parallel to the rotation center axis of the developing roller, and the screw. The outer diameter of the part is formed to be uniform over the longitudinal direction.

  As described above, the developing device in which the plurality of conveying members are arranged in the vertical direction is more developed than the developing device in which the plurality of conveying members are arranged in the horizontal direction (see, for example, FIG. 19 of Patent Document 2). The device can be made compact in the horizontal direction. Therefore, a tandem type color image forming apparatus in which a plurality of developing devices are arranged in parallel in the horizontal direction is often used. In addition, a plurality of transport members are arranged in the vertical direction, and a developer supply path (first transport path) to the developer carrier and a developer recovery path (second transport path) that separates from the developer carrier. ) Is separated from the developing device in which a plurality of conveying members are arranged in parallel in the horizontal direction (see, for example, FIG. 19 of Patent Document 2) and is carried on the developing roller in the developing process. Since the developer to be provided does not easily contain the developer after the development step, the density deviation of the toner image formed on the image carrier can be reduced.

  In addition, the image forming apparatus including the developing device in which the doctor blade (developer regulating member) is disposed below the developing roller as described above has a developing device (for example, a doctor blade disposed above the developing roller (for example, The length of the sheet conveyance path from the sheet feed unit (sheet storage unit) disposed below the image forming apparatus to the sheet discharge tray can be shortened as compared with the apparatus having the image forming apparatus (see FIG. 19 of Patent Document 2). Therefore, the first print time in the tandem type color image forming apparatus can be shortened (see, for example, FIG. 1 of Patent Document 2). Furthermore, since the layout in which the paper discharge tray is arranged above the image forming apparatus can be easily taken even if the paper transport path is relatively short, a tandem color image with a reduced horizontal size is provided. Often used in forming equipment.

  The developing devices described in Patent Documents 1 to 3 and the like described above have a pitch (screw pitch) of the screw portion of the first conveying member at a position on the output image corresponding to the downstream side in the conveying direction of the first conveying path (supply path). Corresponding density unevenness (screw pitch-like density unevenness) may occur.

In the first transport path (supply path), the developer is supplied onto the developing roller (developer carrier) while transporting the developer in the longitudinal direction by the first transport member. This is because the amount of the developer (developer surface) decreases from the upstream side in the transport direction to the downstream side in the transport direction because the amount of developer return to the transport path is small. That is, on the downstream side of the transport of the first transport path, the amount of the developer is reduced, the developer surface is lowered, and the screw portion of the first transport member is exposed without being buried in the developer. In this state, the amount of developer supplied onto the developing roller by the first conveying member (or the amount of developer pumped up on the developing roller) varies. Specifically, if the developer surface becomes low at the position of the screw portion (blade) that is closest to the developing roller, the amount of developer supplied onto the developing roller decreases, and other positions (development) In between the blades closest to the roller), even if the developer surface is low, the amount of developer supplied on the developing roller is not so small. Therefore, at the position corresponding to the downstream side in the transport direction of the first transport path, there is a screw pitch variation in the amount of developer supplied onto the developing roller (or the amount of developer pumped up onto the developing roller). As a result, screw pitch density unevenness also occurs in the toner image formed on the photosensitive drum.
Such a defect is not particularly negligible when the first conveying member is disposed below the developing roller, because the influence of gravity on the developer supply performance to the developing roller by the first conveying member is large. It was a problem.

  The present invention has been made to solve the above-described problems. At least two of the plurality of transport members that transport the developer in the longitudinal direction to form a circulation path are used as the developer carrier. In the case where the developer supply path and the recovery path for the developer carrier are separately provided by installing them so as to face each other, and the developer regulating member is disposed below the developer carrier, and the output It is an object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus in which a problem that density unevenness in a screw pitch shape corresponding to the pitch of a screw portion of a first conveying member occurs on an image is reduced.

  According to a first aspect of the present invention, there is provided a developing device for storing a developer having a carrier and a toner and developing a latent image formed on an image carrier, the image carrier. A developer carrying body that supports the developer and a developer carrier that is disposed below the developer carrying body, and controls the amount of the developer carried on the developer carrying body. And a plurality of conveying members that convey the developer contained in the apparatus in the longitudinal direction to form a circulation path, and the plurality of conveying members face the developer carrier. And a first conveying member that supplies the developer to the developer carrying member while conveying the developer in the longitudinal direction, and is disposed above the first conveying member and faces the developer carrying member. Removed from the developer carrier. A second conveying member that conveys the developer in the longitudinal direction, wherein the first conveying member is a screw member having a screw portion spirally wound around a shaft portion, and at least a part in the longitudinal direction In this range, the outer diameter of the screw portion decreases continuously or stepwise from the upstream side in the transport direction of the developer to the downstream side in the transport direction.

  The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the first conveying member is located on the downstream side in the conveying direction as compared with the shaft portion on the upstream side in the conveying direction of the developer. The shaft portion is arranged to be inclined with respect to the rotation center axis of the developer carrier so that the shaft portion approaches the developer carrier.

  According to a third aspect of the present invention, there is provided the developing device according to the second aspect, wherein the first conveying member is configured so that the outer diameter portion of the screw portion and the outer diameter portion of the screw portion are within a range in the longitudinal direction. The closest distance from the outer peripheral surface of the developer carrying member is the same in the longitudinal direction.

  According to a fourth aspect of the present invention, there is provided the developing device according to the first aspect, wherein the first conveying member is on the upstream side in the conveying direction as compared to the shaft portion on the downstream side in the conveying direction of the developer. The shaft portion is arranged to be inclined with respect to the rotation center axis of the developer carrier so that the shaft portion approaches the developer carrier.

  A developing device according to a fifth aspect of the present invention is the developing device according to any one of the first to fourth aspects, wherein an outer diameter portion of the screw portion of the first transport member and the first transport The gap between the member and the inner wall surface of the first transport path is formed so as to widen from the upstream side in the transport direction of the developer to the downstream side in the transport direction within at least a part of the longitudinal direction.

  The developing device according to a sixth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the first conveying member is opposed to the lower side of the developer carrier. It is arranged.

  According to a seventh aspect of the present invention, there is provided the developing device according to any one of the first to sixth aspects, wherein the carrier has a weight average particle diameter of 20 to 60 μm. It is a thing.

  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 unit (developing device) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. At least one of the cleaning units and the image carrier are defined as a unit that is integrated and detachably installed on the image forming apparatus main body.

  The present invention provides a developer for a developer carrying member by installing at least two of the plurality of carrying members that convey the developer in the longitudinal direction to form a circulation path so as to face the developer carrying member. The supply path and the recovery path are separately provided, and the developer restricting member is disposed below the developer carrier, and the screw portion of the first transport member is disposed downstream of the supply path in the transport direction. Since the outer diameter is formed to be small, a developing device and a process cartridge that reduce the occurrence of screw pitch-like density unevenness corresponding to the pitch of the screw portion of the first conveying member on the output image is reduced. An image forming apparatus can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. It is a block diagram which shows an image creation part. (A) The schematic sectional view which looked at the upper part of the developing device in the longitudinal direction, (B) The schematic sectional view which looked at the lower part of the developing device in the longitudinal direction. (A) The schematic sectional drawing which looked at the circulation path of the developing device of Drawing 3 in the longitudinal direction, and (B) The schematic sectional view which looked at the circulation route of the conventional developing device in the longitudinal direction. It is sectional drawing which shows a developing device. In the developing device, (A) a cross-sectional view showing a position corresponding to the upstream side in the transport direction of the first transport path, and (B) a cross-sectional view showing a position corresponding to the downstream side in the transport direction of the first transport path. . It is a schematic diagram which shows the state of the developer of the vicinity of the screw part of a 1st conveying member. It is sectional drawing which shows a part of developing device in Embodiment 2 of this invention. It is sectional drawing which shows a part of developing device in Embodiment 3 of this invention. 9A is a cross-sectional view showing a position corresponding to the upstream side of the first transport path in the transport direction, and FIG. 9B is a cross-sectional view showing a position corresponding to the downstream side of the first transport path in the transport direction. . It is sectional drawing which shows a part of developing device in Embodiment 4 of this invention. It is sectional drawing which shows a part of developing device in Embodiment 5 of this invention. 12A is a cross-sectional view showing a position corresponding to the upstream side of the first transport path in the transport direction, and FIG. 12B is a cross-sectional view showing a position corresponding to the downstream side of the first transport path in the transport direction. . It is a table | surface figure which shows the conditions and results of an Example and a comparative example.

  Hereinafter, embodiments 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 a main body of a tandem type color copier as an image forming apparatus, 3 is a document conveying unit that conveys a document to a document reading unit, 4 is a document reading unit that reads image information of a document, and 5 is an output image. , 7 is a paper feed unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, 11C, and 11BK are each color (yellow). , Magenta, cyan, and black), a photosensitive drum as an image carrier on which a toner image is formed, and a developing device 13 that develops electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. , 14 is a transfer bias roller (primary transfer bias roller) for transferring the toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11BK on the recording medium P in an overlapping manner. It is.
Reference numeral 17 denotes an intermediate transfer belt onto which a plurality of color toner images are transferred, 18 denotes a secondary transfer bias roller for transferring the color toner image on the intermediate transfer belt 17 onto the recording medium P, and 20 denotes a recording medium. A fixing device 28 for fixing an unfixed image on P, and a toner container for each color for supplying toner (toner particles) of each color (yellow, cyan, magenta, black) to the developing device 13.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described. Note that FIG. 2 can also be referred to for the image forming process performed on the photosensitive drums 11Y, 11M, 11C, and 11BK.
First, the document is transported from the document table by the transport rollers of the document transport unit 3 and placed on the contact glass of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document placed on the contact glass.

  Specifically, the document reading unit 4 scans an image of a document on the contact glass while irradiating light emitted from an illumination lamp. Then, the light reflected from the original is imaged on the color sensor via the mirror group and the lens. The color image information of the original is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, image information of each color of yellow, magenta, cyan, and black is transmitted to a writing unit (not shown). Then, a laser beam L (see FIG. 2) based on the image information of each color is emitted from the writing unit toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (see FIG. 2) (charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit, laser beams corresponding to the image signals are emitted from the four light sources corresponding to the respective colors. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y 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 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing device 13, respectively. Then, the respective color toners are supplied from the developing devices 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .)
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at the position of the transfer bias roller 14 (in the primary transfer process). is there.).

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) are run counterclockwise in the drawing, and the secondary transfer bias roller 18 and Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of an intermediate transfer belt cleaning unit (not shown). Then, the untransferred toner attached on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P transported between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is transported from the paper supply unit 7 via the registration roller 9 and the like. It is a thing.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

Then, the recording medium P on which the full color image is transferred is guided to the fixing device 20 thereafter. In the fixing device 20, the color image is fixed on the recording medium P at the nip between the fixing roller and the pressure roller.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a discharge roller and stacked on the discharge tray 5 to complete a series of image forming processes.

Next, the image forming unit in the image forming apparatus will be described in detail with reference to FIGS.
FIG. 2 is a configuration diagram illustrating the image forming unit. 3A is a schematic cross-sectional view (substantially horizontal cross-sectional view) of the upper portion of the developing device 13 (the position of the second transport screw 13b2 as the second transport member) as viewed in the longitudinal direction. 3B is a schematic cross-sectional view of the lower part of the developing device 13 (the position of the first conveying screw 13b1 as the first conveying member) in the longitudinal direction (the rotation center axis of the developing roller and the first conveying screw 13b1). It is sectional drawing which passes a rotation center axis | shaft). 4A is a schematic cross-sectional view (vertical cross-sectional view) of the circulation path of the developing device 13 in the first embodiment in the longitudinal direction, and FIG. 4B is a circulation path of the conventional developing device 13. It is the schematic sectional drawing which looked at the longitudinal direction. FIG. 5 is a cross-sectional view showing the developing device (a cross-sectional view orthogonal to the rotation center axis of the developing roller 13a). Further, FIG. 6 shows, in the developing device, (A) a sectional view showing a position corresponding to the upstream side of the first transport path in the transport direction, and (B) showing a position corresponding to the downstream side of the first transport path in the transport direction. It is sectional drawing. FIG. 7 is a schematic diagram illustrating the state of the developer in the vicinity of the screw portion of the first conveying member.
Since each image forming unit has substantially the same structure, the image forming unit and the developing device are illustrated in FIGS. 2 to 8 without the alphabet (Y, C, M, BK).

As shown in FIG. 2, the image forming unit includes a photosensitive drum 11 as an image carrier, a charging unit 12, a developing device 13 (developing unit), a cleaning unit 15, and the like.
The photoconductor drum 11 as an image carrier is a negatively charged organic photoconductor having an outer diameter of about 30 mm, and is rotated counterclockwise by a rotation drive mechanism (not shown).

The charging unit 12 is a charging roller having elasticity in which a foamed urethane layer having a medium resistance in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape on a core metal. The material of the middle resistance layer of the charging unit 12 is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, etc. It is also possible to use a rubber material in which a conductive material such as the above is dispersed or a foamed material of these materials.
The cleaning unit 15 is provided with a cleaning blade that is in sliding contact with the photosensitive drum 11, and mechanically removes and collects untransferred toner on the photosensitive drum 11.

  The developing device 13 is disposed such that a developing roller 13a as a developer carrying member is close to the photosensitive drum 11, and a developing region (developing) where the photosensitive drum 11 and the magnetic brush are in contact with each other. Nip) is formed. A developer G (two-component developer) composed of toner T and carrier C is accommodated in the developing device 13. The developing device 13 develops the electrostatic latent image formed on the photosensitive drum 11 (forms a toner image). The configuration and operation of the developing device 13 will be described in detail later.

Referring to FIG. 1, toner container 28 contains toner T to be supplied into developing device 13 therein. Specifically, toner conveyance (not shown) is performed based on information on the toner density (the ratio of toner in the developer G) detected by a magnetic sensor (not shown) installed in the developing device 13. The toner T is appropriately supplied from the toner supply port 13e from the toner container 28 into the developing device 13 through the tube.
The supply of the toner T is not limited to the toner density information, but may be performed based on the image density information detected from the reflectance of the toner image formed on the photosensitive belt or the intermediate transfer belt. Good. Further, the implementation of the supply of the toner T may be determined by combining these different pieces of information.

Hereinafter, the developing device 13 in the image forming apparatus will be described in detail.
2 to 7, a developing device 13 includes a developing roller 13a as a developer carrier, conveying screws 13b1 and 13b2 (auger screws) as conveying members, a doctor blade 13c as a developer regulating member, and a partition. It is comprised by the member 13d.
A developing roller 13a as a developer carrying member is a developing roller having a small outer diameter of about 18 mm, and includes a sleeve 13a2 formed by forming a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin into a cylindrical shape. It is configured to be rotated counterclockwise at about 150 to 600 rpm by a rotation driving mechanism (not shown). 3 and 5, a magnet 13a1 for forming a plurality of magnetic poles H1 to H6 is fixed on the peripheral surface of the sleeve 13a2 in the sleeve 13a2 of the developing roller 13a. The developer G carried on the developing roller 13a is conveyed as the developing roller 13a rotates in the direction of the arrow, and reaches the position of the doctor blade 13c. The developer G on the developing roller 13a is regulated to an appropriate amount at this position, and then conveyed to a position facing the photosensitive drum 11 (which is a developing region). The toner is attracted to the latent image formed on the photosensitive drum 11 by the electric field (developing electric field) formed in the developing area.

FIG. 5 shows a plurality of magnetic poles H1 to H6 formed around the developing roller 13a (sleeve 13a2) by the magnet 13a1. As shown in FIG. 5, the plurality of magnetic poles are a first magnetic pole H <b> 1 (main magnetic pole) formed at a position facing the photosensitive drum 11, a position on the downstream side of the first magnetic pole H <b> 1 and on the top of the developing case. The second magnetic pole H2 (conveying magnetic pole) formed on the second magnetic pole H3, the third magnetic pole H3 (agent separating pre-magnetic pole) formed downstream of the second magnetic pole H1 and above the developing roller 13a, the third magnetic pole H3 and the fifth magnetic pole H3 A fourth magnetic pole H4 (agent separating magnetic pole) formed between the magnetic pole H5 and above the tip of the partition member 13d, and a fifth magnetic pole H5 formed above the first transport path (after agent separation). Magnetic pole), a sixth magnetic pole H6 (pumping magnetic pole) formed from the position facing the first conveying screw 13b1 to the vicinity of the position facing the doctor blade 13c, and the like.
First, the sixth magnetic pole H6 (pumping magnetic pole) acts on the carrier as a magnetic body, and the developer G accommodated in the first transport path (supply path) is pumped onto the developing roller 13a. Part of the developer G carried on the developing roller 13a is scraped off at the position of the doctor blade 13c and returned to the first transport path. On the other hand, the developer G carried on the developing roller 13a through the doctor gap between the doctor blade 13c and the developing roller 13a at the position of the doctor blade 13c where the magnetic force by the sixth magnetic pole H6 acts is the first magnetic pole H1. It rises at the position of the (main magnetic pole) and becomes a magnetic brush in the developing region, and comes into sliding contact with the photosensitive drum 11. Thus, the toner T in the developer G carried on the developing roller 13 a adheres to the latent image on the photosensitive drum 11. Thereafter, the developer G that has passed the position of the first magnetic pole H1 is conveyed to the position of the fourth magnetic pole H4 (agent separating magnetic pole) by the second magnetic pole H2 and the third magnetic pole H3. The repelling magnetic field acts on the carrier at the position of the agent separating magnetic pole H4, and the developer G after the development process carried on the developing roller 13a is detached from the developing roller 13a. The detached developer G falls into the second transport path (collection path) and is transported downstream of the second transport path by the second transport screw 13b2.

  Here, the six magnetic poles H1 to H6 described above are formed by five poles magnetized on the magnet 13a1 of the developing roller 13a. That is, out of the six magnetic poles H1 to H6, only the fourth magnetic pole H4 (agent separating magnetic pole) is not directly formed by the pole magnetized on the magnet 13a1, but the same pole (the first embodiment). Then, it is formed between two magnetic poles (the third magnetic pole H3 and the fifth magnetic pole H5).

Referring to FIG. 2 and the like, the doctor blade 13c as a developer regulating member is a non-magnetic plate-like member disposed below the developing roller 13a (a part of which can be formed of a magnetic material). It is. The developing roller 13a rotates counterclockwise in FIG. 2, and the photosensitive drum 11 rotates clockwise in FIG.
With such a configuration, the photosensitive drum 11 is disposed below the intermediate transfer belt 17 for the purpose of shortening the conveyance path of the recording medium P and reducing the horizontal size of the image forming apparatus main body 1. Even so, since the rotation direction of the developing roller 13a can be the forward direction with respect to the photosensitive drum 11 in the developing gap, the doctor blade 13c is provided above the developing roller 13a and the photosensitive drum 11 is disposed. As compared with the case where the rotation direction of the developing roller 13a is opposite, the developing time in the developing gap can be sufficiently secured and the developing ability can be enhanced.

The two conveying screws 13b1 and 13b2 (conveying members) stir and mix the developer G accommodated in the developing device 13 while circulating in the longitudinal direction (the direction perpendicular to the paper surface of FIG. 2).
The first conveying screw 13b1 (screw member) as the first conveying member is disposed at a position facing the lower side of the developing roller 13a, and horizontally conveys the developer G in the longitudinal direction (rotating axis direction) ( In addition, the developer G is supplied onto the developing roller 13a at the position of the pumping magnetic pole H6 (sixth magnetic pole) (the white conveyance in FIG. 3B). Supply in the direction of the arrow). The first transport screw 13b1 rotates counterclockwise in FIG.

The second conveying screw 13b2 as the second conveying member is disposed above the first conveying screw 13b1 and at a position facing the developing roller 13a. Then, the developer G separated from the developing roller 13a (the developer G forcibly separated from the developing roller 13a by the agent separating magnetic pole H4 after the developing process, and is separated in the direction of the white arrow in FIG. 3A. Is transported horizontally in the longitudinal direction (the transport in the right direction indicated by the broken-line arrow in FIG. 3A). In the first embodiment, the rotation direction of the second conveying screw 13b2 is set to be opposite to the rotation direction of the developing roller 13a (the clockwise direction in FIG. 2).
Then, the second transport screw 13b2 has a second developer G circulated from the downstream side of the transport path by the first transport screw 13b1 via the first relay portion 13f to the upstream side of the transport path by the first transport member 13b1. It conveys via the relay part 13g (it is the conveyance shown by the dashed-dotted arrow of FIG. 3).
The two conveying screws 13b1 and 13b2 are arranged so that the rotation shaft is substantially horizontal, like the developing roller 13a and the photosensitive drum 11. Moreover, as for the two conveyance screws 13b1 and 13b2, the screw part (screw pitch: about 40 mm, the number of threads: 1 or 2) is spirally wound around the shaft part having a shaft diameter of about 6 to 10 mm. Screw member. Moreover, the rotation speed of the two conveyance screws 13b1 and 13b2 is set to about 600 to 900 rpm.
In addition, both of the two conveying screws 13b1 and 13b2 can be integrally formed with a shaft portion and a screw portion by injection molding with a resin material, and the shaft portion and the screw portion are each made of a metal material. After being formed separately, the screw part can be joined to the shaft part by brazing or the like. Regardless of such a manufacturing method, these conveying screws 13b1 and 13b2 are defined as “screw members each having a screw portion wound around a shaft portion”.

  Here, the outer diameter of the screw portion of the second transport screw 13b2 is set to about 20 mm (the outer diameter is uniform over the longitudinal direction). On the other hand, the screw portion of the first transport screw 13b1 extends from the upstream side in the transport direction (the right side in FIG. 3B) to the downstream side in the transport direction (the left side in FIG. 3B). The outer diameter is formed so as to be continuously reduced. Specifically, the outer diameter of the screw portion of the first conveying screw 13b1 is set to about 20 mm at the most upstream portion in the conveying direction and about 15 mm at the most downstream portion in the conveying direction. The first transport screw 13b1 will be described in more detail later.

Further, the conveyance path (first conveyance path) by the first conveyance screw 13b1 and the conveyance path (second conveyance path) by the second conveyance screw 13b2 are separated from each other by a wall portion.
Referring to FIGS. 3 and 4A, the downstream side of the conveyance path (second conveyance path) by the second conveyance screw 13b2 and the upstream side of the conveyance path (first conveyance path) by the first conveyance screw 13b1 Are communicated via the second relay part 13g. The developer G that has reached the downstream side of the second conveyance path by the second conveyance screw 13b2 falls by its own weight at the second relay portion 13g and reaches the upstream side of the first conveyance path.
3 and 4A, the downstream side of the transport path by the first transport screw 13b1 and the upstream side of the transport path by the second transport screw 13b2 are connected via the first relay portion 13f. Communicate. Then, the developer G that has not been supplied onto the developing roller 13a in the first conveyance path by the first conveyance screw 13b1 stays in the vicinity of the first relay portion 13f and rises up, and then passes through the first relay portion 13f. It is transported (supplied) to the upstream side of the second transport path by the two transport screws 13b2.
In addition, in order to improve the transportability of the developer (transfer of the developer against the direction of gravity from the first transport path to the second transport path) in the first relay portion 13f, the first transport screw 13b1 A paddle-shaped portion or a screw portion in which the winding direction of the screw is formed in the reverse direction can be provided at a downstream position (a position corresponding to the first relay portion 13f).

  With such a configuration, a circulation path for circulating the developer G in the longitudinal direction in the developing device 13 is formed by the two conveying screws 13b1 and 13b2. That is, when the developing device 13 is operated, the developer G accommodated in the device flows in the direction of the broken arrow in FIGS. 3 and 4A. Thus, the developer G supply path (the first transport path by the first transport screw 13a1) to the developing roller 13a and the developer G recovery path (second transport screw) separated from the developing roller 13a. 13a2) is separated (separately provided), the density deviation of the toner image formed on the photosensitive drum 11 can be reduced.

Although illustration is omitted, a magnetic sensor for detecting the toner concentration of the developer circulating in the apparatus is installed in the conveyance path by the second conveyance screw 13b2. Then, based on the toner density information detected by the magnetic sensor, the toner container 28 is directed into the developing device 13 through the toner supply port 13e (located in the vicinity of the first relay portion 13f). New toner T is supplied.
3 and 4A, the toner replenishing port 13e is located on the upstream side of the transport path by the second transport screw 13b2 and away from the developing region (the longitudinal direction of the developing roller 13a). Outside the range of directions.). By installing the toner replenishing port 13e in the vicinity of the first relay portion 13f in this way, the developer detached from the developing roller 13a falls from above the replenishment toner having a small specific gravity in the second transport path, and the second transport path. The replenishment toner can be sufficiently dispersed and mixed with respect to the developer over a relatively long time toward the downstream side.
In the first embodiment, the toner replenishment port 13e is disposed in the conveyance path by the second conveyance screw 13a2, but the position of the toner replenishment port 13e is not limited to this, and for example, the first conveyance path It can also be arranged above the upstream side.

Referring to FIG. 4A, in the first transport path, in order to supply the developer to the developing roller 13a while transporting the developer in the longitudinal direction, the vicinity of the first relay portion 13f is excluded. The level of the developer G becomes lower from the upstream side toward the downstream side. On the other hand, in the second transport path, the developer surface of the developer G is directed from the upstream side toward the downstream side in order to collect the developer separated from the developing roller 13a while transporting the developer in the longitudinal direction. Is getting higher.
FIG. 4B is a view showing the developer surface of the developer in the conventional developing device 130 (the outer diameter of the screw portion of the first conveying screw 130b1 is uniformly formed in the longitudinal direction). is there. Comparing FIG. 4A and FIG. 4B, in the developing device 13 in the first embodiment, the developer surface on the downstream side of the first transport path is higher than the conventional one. I can see that This is because the developing device 13 according to the first embodiment is formed so that the outer diameter of the screw portion of the first conveying screw 13b1 on the downstream side in the conveying direction is smaller than that on the upstream side in the conveying direction. This is because the transport force in the longitudinal direction of the first transport screw 13b1 on the downstream side in the transport direction of the first transport path is reduced. As described above, the increase in the developer level on the downstream side in the transport direction leads to an improvement in the supply of the developer to the developing roller 13a1 by the first transport screw 13b1 on the downstream side in the transport direction. In such a case, the amount of the developer staying in the vicinity of the first relay portion 13f increases, but it hardly affects the delivery of the developer from the first transport path to the second transport path in the first relay portion 13f. do not do.

Referring to FIG. 5, the developing device 13 in Embodiment 1 includes a partition member 13 d (separating plate) that partitions the first transport path and the second transport path at a position facing the developing roller 13 a. Is provided. In other words, the developer G released from the developing roller 13a is reduced from being carried on the developing roller 13a again between the first conveying path and the second conveying path at a position facing the developing roller 13a. A partition member 13d is provided.
Specifically, the partition member 13d functions as a wall portion that separates the first conveyance path and the second conveyance path, and is formed to protrude toward the developing roller 13a. Further, the partition member 13d is formed integrally with a developing case (a case member indicated by hatching in FIG. 2). The partition member 13d is formed so that the gap between the facing surface facing the developing roller 13a and the developing roller 13a is 2 mm or less (preferably 0.1 to 0.5 mm).
In the boundary area between the second transport path and the first transport path, a magnetic field is formed from the inside of the second transport path toward the developing roller 13a (on the first transport path side) due to the influence of the fifth magnetic pole H5. The By providing the partition member 13d at a position that blocks this magnetic field, it is possible to prevent a problem that the developer immediately after being collected in the second transport path is re-supported by the developing roller 13a. Further, since the partition member 13d is disposed so as to face the developing roller 13a in a non-contact manner, it is possible to reduce a problem that damages the surface of the developing roller 13a.
Since the partition member 13d is formed of a nonmagnetic material, the carrier, which is a magnetic body, is magnetically attracted to the partition member 13d to obstruct the flow of the developer in the second transport path. Problems such as promoting the movement of the developer to the transport path are reduced.

With reference to FIG. 5, in the first embodiment, the second transport screw 13b2 (second transport member) is viewed in a cross section (FIG. 5) perpendicular to the rotation center axis of the developing roller 13a. In addition, the position of the rotation center axis of the second transport screw 13b2 is disposed below the virtual horizontal line passing through the upper end of the developing roller 13a and above the virtual horizontal line passing through the lower end of the developing roller 13a. . That is, the position of the rotation center axis of the second transport screw 13b2 is disposed in the range indicated by the double arrow M1.
Further, the position on the developing roller 13a that equally divides the two magnetic poles H3 and H5 forming the agent separating magnetic pole H4 when viewed in a cross section (FIG. 5) orthogonal to the rotation center axis of the developing roller 13a. K is formed so as to be above the virtual horizontal line S1 passing through the rotation center axis of the developing roller 13a. The position K described above passes through the straight line A3 passing through the peak magnetic force position of the third magnetic pole H3 and the center position of the developing roller 13a, and the peak magnetic force position of the fifth magnetic pole H5 and the center position of the developing roller 13a. The straight line drawn at an equal angle with the straight line A5 intersects the surface of the developing roller 13a (of the two points where the straight line and the surface of the developing roller 13a intersect, the one closer to the second conveying screw 13b2. ). In the first embodiment, the distance between the axes of the developing roller 13a and the second conveying screw 13b2 is set to about 26 mm.
With this configuration, the developer G after the development process carried on the developing roller 13a has a magnetic force acting in a direction in which the developer G is positively separated from the developing roller 13a at the position of the agent separating magnetic pole H4. In addition to the force, a centrifugal force caused by the rotation of the developing roller 13a, a pressure pushed by the developer on the downstream side, and a resultant force such as gravity act. As a result, the developer G after the development process carried on the developing roller 13a is efficiently separated from the developing roller 13a without causing a failure to separate from the developing roller 13a in the second quadrant of FIG. The separated developer G is smoothly collected in the second transport path. Therefore, the developer G after the developing process separated from the developing roller 13a in the second transport path is hardly re-supported by the developing roller 13a immediately thereafter, and image density unevenness (density deviation) occurs on the output image. Defects are reliably reduced.

Referring to FIG. 5, in the first embodiment, when viewed in a cross section orthogonal to the rotation center axis of the developing roller 13a, the tip of the partition member 13d is assumed to pass through the rotation center axis of the developing roller 13a. It is formed so as to be above the horizontal line S1 and below the position K. Accordingly, the developer G detached from the developing roller 13a is smoothly guided to the second transport path along the inclined surface of the partition member 13d at the position K or a position in the vicinity thereof.
Further, with reference to FIG. 5, in the first embodiment, when viewed in a cross section orthogonal to the rotation center axis of the developing roller 13a, the tip of the partition member 13d has the rotation center axis of the second transport screw 13b2. It is formed so as to be above the virtual horizontal line S2 that passes therethrough. As a result, it is possible to reduce a problem that the developer G collected in the second transport path flows over the partition member 13d and flows into the first transport path.

Here, referring to FIG. 5, in the first embodiment, the position of the rotation center axis of the first conveyance screw 13b1 is the second conveyance screw when viewed in a cross section orthogonal to the rotation axis of the developing roller 13a. The first conveying screw 13b1 is between the virtual vertical line passing through the rotation center axis of 13b2 and the virtual vertical line passing through the rotation center axis of the developing roller 13a (between the range M2 in FIG. 5). Is arranged.
Thus, the first conveying screw 13b1 can be brought close to the pumping magnetic pole H6 of the developing roller 13a, and the supply capability of the developer G to the developing roller 13a by the first conveying screw 13b1 can be improved.

Hereinafter, the developer G used in Embodiment 1 will be briefly described.
The toner T (the toner in the developer G and the toner in the toner container 28) used in the first embodiment is a polymerized toner, and a styrene-acrylonitrile-acrylic acid ester copolymer is used as a binder resin. Styrenic resins (monopolymer or copolymer containing styrene or styrene-substituted product), polyester resins, epoxy resins, or composites thereof can be used. In addition, as a production method (polymerization method) of these polymerized toners, bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, and the like can be used.
Further, as the external additive of the toner T, it is preferable to use inorganic fine particles (for example, those having 1.0% by weight of silica and 0.5% by weight of titanium oxide). Furthermore, oxidized rice wax, low molecular weight polypropylene wax, carnauba wax and the like can be used as a release agent. Moreover, a charge control agent can be contained as required.
Further, the toner T used in the first embodiment has a volume average particle diameter of 5.8 μm, and is formed so that a toner having a particle diameter of 5 μm or less is 60 to 80% by number.
In the first embodiment, polymerized toner is used, but pulverized toner can also be used.

The carrier C in the developer G used in Embodiment 1 is formed so that the weight average particle diameter is 20 to 60 μm. In the first embodiment, carrier C having a weight average particle diameter of 35 μm is used.
Specifically, the carrier C is formed by coating the ferrite particles serving as the core material with a methyl methacrylate resin (MMA) having a film thickness of 0.5 μm so as to have the above-described particle size. As the carrier C, a coating carrier having magnetite as a core material can also be used.
By using the carrier C having such a small particle diameter, the solid uniformity of the output image and the halftone image quality can be improved.
In the first embodiment, the developing device 13 is filled with 225 g of developer G that is uniformly mixed with a toner concentration of 7% by weight.

Hereinafter, a characteristic configuration and operation of the developing device 13 according to the first embodiment will be described.
Referring to FIGS. 3 and 6, first transport screw 13b1 in the first embodiment is transported upstream (in the right side of FIG. 3B) to downstream in the transport direction (FIG. 3B). The outer diameter of the screw part is continuously reduced. Specifically, the outer diameter of the screw portion of the first transport screw 13b1 on the upstream side (the most upstream portion) in the transport direction shown in FIG. 6A is set to about 20 mm, and FIG. The outer diameter of the screw portion of the first conveying screw 13b1 on the downstream side in the conveying direction (the most downstream portion) is set to about 15 mm.

With such a configuration, the transport force of the developer G by the first transport screw 13b1 (if this is large, the amount of developer transported in the longitudinal direction increases) becomes closer to the downstream side in the transport direction. Become. Therefore, as described above with reference to FIG. 4A, the surface of the developer G on the downstream side in the transport direction in the first transport path (the left side of FIG. 4A) is maintained in a relatively high state. can do. That is, most of the screw portions of the first transport screw 13b1 are buried in the developer G on the transport downstream side of the first transport path. As a result, the supply amount of the developer G supplied onto the developing roller 13a by the first conveying screw 13b1 (or the pumping amount of the developer G pumped up on the developing roller 13a) is less likely to vary (development in the longitudinal direction). The supply amount of the agent is made uniform.)
Specifically, if the surface of the developer G is lowered at the position of the screw portion (blade) that is closest to the developing roller 13a, the amount of the developer G supplied onto the developing roller 13a is reduced. At other positions (between the blades closest to the developing roller), the amount of developer G supplied onto the developing roller 13a is not so reduced even if the surface of the developer G is low. The developer pitch supplied to the developing roller 13a (or the developer G pumped up on the developing roller 13a) varies in a screw pitch shape and is formed on the photosensitive drum 11. The toner pitch also has screw pitch density unevenness.
On the other hand, in the first embodiment, the level of the developer G is raised to some extent even at the position of the screw portion (blade) closest to the developing roller 13a. Screw pitch variation is less likely to occur in the supply amount (or the amount of developer G pumped up on the developing roller 13a). Therefore, screw pitch density unevenness is less likely to occur in the toner image formed on the photosensitive drum 11. Particularly, in the developing device 13 according to the first embodiment, the first conveying screw 13b1 is disposed below the developing roller 13a, and the influence of gravity on the developer supply performance to the developing roller 13a by the first conveying screw 13b1. However, since the outer diameter of the screw portion of the first conveying screw 13b1 is gradually decreased from the upstream side in the conveying direction toward the downstream side in the conveying direction, there is a problem in that screw pitch-like density unevenness occurs on the output image. It can be certainly reduced.

If the outer diameter of the screw portion on the upstream side in the transport direction of the first transport screw 13b1 is reduced in the same manner as that on the downstream side in the transport direction, the developer transport force on the upstream side in the transport direction is reduced. In addition, the overall circulation of the developer in the developing device 13 is affected, and the same effect as in the first embodiment cannot be obtained. In the first embodiment, even if the developer conveyance force decreases, the first conveyance is downstream in the conveyance direction of the first conveyance path, which hardly affects the overall developer circulation in the developing device 13. The outer diameter of the screw portion of the screw 13b1 can be reduced.
In addition, when the screw pitch of the screw portion on the downstream side in the transport direction of the first transport screw 13b1 is set longer than that on the upstream side in the transport direction, the outer diameter of the screw portion on the downstream side in the transport direction of the first transport screw 13b1 is set. Similar to the case where the size is smaller than the upstream side in the transport direction, the developer amount on the downstream side in the transport direction can be increased. However, in that case, since the casing gap CG on the downstream side in the transport direction is not widened, the same effect as in the first embodiment cannot be sufficiently obtained.

Here, with reference to FIG. 6, in the first embodiment, the shaft portion (rotation center axis) of the first conveying screw 13b1 and the rotation center axis of the developing roller 13a are arranged substantially in parallel. Has been. Therefore, the gap CG (casing gap) between the outer diameter portion of the screw portion of the first conveyance screw 13b1 and the inner wall surface of the wall portion 13m of the first conveyance path by the first conveyance screw 13b1 is the conveyance direction of the developer G. It is formed so as to become wider from the upstream side toward the downstream side in the transport direction. That is, the casing gap CG shown in FIG. 6 (B) is wider than the casing gap CG shown in FIG. 6 (A).
With such a configuration, referring to FIG. 7A, on the downstream side in the transport direction of the first transport path, on the back side of the screw portion of the first transport screw 13b1 (on the back side with respect to the developer transport direction indicated by the white arrow). The developer G easily enters the space (the developer moves in the direction of the arrow). Therefore, screw pitch variations are less likely to occur in the amount of developer G supplied onto the developing roller 13a (or the amount of developer G pumped up onto the developing roller 13a).

In the conventional developing device, as shown in FIG. 7B, the outer diameter of the first conveying screw 130b1 is formed on the downstream side in the conveying direction of the first conveying path, and the developer amount at that position is small. Become. Therefore, it becomes difficult for the developer G to enter the space on the back side of the screw portion of the first transport screw 130b1 (the back side with respect to the developer transport direction indicated by the white arrow) (the developer moves in the arrow direction). .
On the other hand, in the first embodiment, as shown in FIG. 7A, the outer diameter of the first transport screw 13b1 is formed small on the downstream side in the transport direction of the first transport path, and the position thereof The amount of developer increases. Therefore, the developer G easily enters the space on the back side of the screw portion of the first conveying screw 13b1, and screw pitch-like density unevenness hardly occurs on the output image.

  As described above, in the first embodiment, the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer G in the longitudinal direction to form a circulation path are used as the developing roller 13a (developer carrier). The developer blade 13c (developer regulating member) is provided separately by providing a developer G supply path (first transport path) and a recovery path (second transport path) to the developing roller 13a by installing them so as to face each other. This is a case where the screw roller is disposed below the developing roller 13a, and is formed so that the outer diameter of the screw portion of the first conveying screw 13b1 (first conveying member) is reduced downstream in the conveying direction of the supply path. In addition, it is possible to reduce a problem that density unevenness in a screw pitch shape corresponding to the pitch of the screw portion of the first conveying screw 13b1 occurs on the output image.

  In the first embodiment, the range in which the outer diameter of the screw portion of the first transport screw 13b1 gradually decreases from the upstream side in the transport direction to the downstream side in the transport direction is set to almost the entire area in the longitudinal direction of the first transport path. On the other hand, the range in which the outer diameter of the screw portion of the first transport screw 13b1 gradually decreases from the upstream side in the transport direction to the downstream side in the transport direction can be set as a partial range in the longitudinal direction of the first transport path. . For example, the outer diameter of the screw portion of the first transport screw 13b1 is upstream in the transport direction only in the range from the center in the transport direction of the first transport path to the most downstream portion in the transport direction (a range approximately half the longitudinal direction). It can also be formed so as to gradually decrease from the downstream side in the transport direction. The range in which the outer diameter of the screw portion is gradually reduced depends on the optimum conditions depending on the circulation of the developer in the entire developing device 13 and the supply of the developer to the developing roller 13a by the first conveying screw 13b1. It is preferable to vary so that

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is a cross-sectional view showing a part of the developing device 13 in the second embodiment, and corresponds to FIG. 3B in the first embodiment. The developing device according to the second embodiment is such that the outer diameter of the screw portion of the first transport member 13b1 is formed so as to decrease stepwise from the upstream side in the transport direction to the downstream side in the transport direction. The outer diameter of the screw portion 13b1 is different from that of the first embodiment in which the outer diameter is continuously reduced from the upstream side in the transport direction to the downstream side in the transport direction.

  Similarly to the first embodiment, the developing device 13 in the second embodiment also has a developing roller 13a (developer carrier), two transport screws 13b1 and 13b2 (screw members), a doctor blade 13c (developer). A restricting member), a partition member 13d, and the like. The first conveying screw 13b1 in the second embodiment is also formed so that the outer diameter of the screw portion becomes smaller from the upstream side in the conveying direction to the downstream side in the conveying direction, as in the first embodiment. Yes.

  Here, referring to FIG. 8, the first conveying screw 13b1 in the second embodiment is different from that in the first embodiment, and the outer diameter of the screw portion is from the upstream side in the conveying direction to the downstream side in the conveying direction. It is formed so as to become smaller step by step. Specifically, the outer diameter of the screw portion is set to 20 mm in the most upstream range W1 in the first transport path, and the outer diameter of the screw portion is set to 19 mm in the second upstream range W2 adjacent to the range. In the third upstream range W3 adjacent to the range, the outer diameter of the screw portion is set to 18 mm, and in the fourth upstream range W4 adjacent to the range, the outer diameter of the screw portion is set to 17 mm. In the fifth upstream range W5 adjacent to the range, the outer diameter of the screw portion is set to 16 mm, and in the most downstream range W6, the outer diameter of the screw portion is set to 15 mm.

Even with such a configuration, as in the first embodiment, the level of the developer surface of the developer G on the downstream side in the transport direction of the first transport path can be reduced, and the transport direction Since the downstream casing gap CG can be widened, the developer G easily enters the space behind the screw portion of the first conveying screw 13b1, and the screw pitch density unevenness is unlikely to occur on the output image. Become.
And since the 1st conveyance screw 13b1 in this Embodiment 2 changes the outer diameter of a screw part in steps, what changed the outer diameter of a screw part continuously (the said implementation) Compared with Embodiment 1), the processing restrictions are reduced. That is, the first conveying screw 13b1 according to the second embodiment is easier to manufacture and has a lower component cost than that according to the first embodiment. In particular, when the first conveying screw 13b1 is injection-molded with a resin material, the mold can be easily processed. Furthermore, since the relationship between the position in the longitudinal direction and the outer diameter dimension of the screw portion is clarified, the first conveying screw 13b1 in the second embodiment can easily perform component inspection.

  As described above, also in the second embodiment, as in the first embodiment, the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer G in the longitudinal direction to form a circulation path are developed. The developer G supply path (first transport path) and the recovery path (second transport path) are separately provided for the developing roller 13a by installing the roller 13a so as to face the developer carrier. In the case where the blade 13c (developer regulating member) is disposed below the developing roller 13a, the outer diameter of the screw portion of the first transport screw 13b1 (first transport member) is downstream of the supply path in the transport direction. Since it is formed so as to be small, it is possible to reduce a problem that density unevenness in the screw pitch shape corresponding to the pitch of the screw portion of the first conveying screw 13b1 occurs on the output image. That.

Embodiment 3 FIG.
9 and 10, the third embodiment of the present invention will be described in detail.
FIG. 9 is a cross-sectional view showing a part of the developing device 13 in the third embodiment, and corresponds to FIG. 3B in the first embodiment. FIG. 10A is a cross-sectional view showing the developing device 13 at a position corresponding to the upstream side of the first transport path in the transport direction, and corresponds to FIG. 6A in the first embodiment. FIG. 10B is a cross-sectional view showing the developing device 13 at a position corresponding to the downstream side in the transport direction of the first transport path, and corresponds to FIG. 6B in the first embodiment.
In the developing device according to the third embodiment, the shaft of the first transport member 13b1 is arranged such that the shaft portion of the first transport member 13b1 is inclined with respect to the rotation center axis of the developer carrier 13a. This is different from that of the first embodiment in which the portion is arranged so as to be parallel to the rotation center axis of the developer carrier 13a.

  The developing device 13 according to the third embodiment also has a developing roller 13a (developer carrying member), two conveying screws 13b1 and 13b2 (screw members), a doctor blade 13c (developer) as in the above embodiments. A restricting member), a partition member 13d, and the like. Further, the first conveying screw 13b1 in the third embodiment is also configured so that the outer diameter of the screw portion continuously decreases from the upstream side in the conveying direction to the downstream side in the conveying direction, as in the first embodiment. Is formed.

Here, referring to FIG. 9 and FIG. 10, the first transport screw 13b1 in the third embodiment is different from that in the first embodiment in the upstream in the transport direction (the right side in FIG. The shaft portion on the downstream side in the transport direction (the left side in FIG. 9 and the position corresponding to FIG. 10B) compared to the shaft portion in FIG. The shaft portion is disposed so as to be inclined by an angle θ with respect to the rotation center axis of the developing roller 13a so as to approach the roller 13a.
9 and 10, the closest distance SG between the outer diameter portion of the screw portion of the first conveying screw 13b1 and the outer peripheral surface of the developing roller 13a is the same in the longitudinal direction. ing. Here, as shown in FIGS. 9 and 10, the above-mentioned “closest distance SG” is the screw closest to the outer peripheral surface of the developing roller 13a in the range of one pitch of the screw portion of the first conveying screw 13b1. Distance between the outer diameter portion of the portion and the outer peripheral surface of the developing roller 13a (a distance on a straight line passing through the axial centers of both the members 13a and 13b1 when viewed in a cross section perpendicular to the axial center of the developing roller 13a). It is.

With such a configuration, it is possible to reduce the level of the developer surface of the developer G on the downstream side in the transport direction of the first transport path and to further increase the casing gap CG on the downstream side in the transport direction. In addition, the developer G easily enters the space behind the screw portion of the first conveying screw 13b1, and the screw pitch density unevenness is further less likely to occur on the output image.
Furthermore, according to the third embodiment, the closest distance SG between the first transport screw 13b1 and the developing roller 13a on the downstream side in the transport direction of the first transport path is formed in the same manner as that on the upstream side in the transport direction. The Thereby, the supply property of the developer G from the first transport screw 13b1 to the developing roller 13a (or the pumping property of the developer G onto the developing roller 13a) is the same as the upstream side in the transport direction. It will not change so much. This is because the distance SG until the developer G, which is splashed up against the direction of gravity by the rotation of the first conveying screw 13b1, reaches the developing roller 13a, is made uniform in the longitudinal direction. That is, on the downstream side in the transport direction, the amount of developer G returned to the first transport path without reaching the developing roller 13a after being flipped up against the direction of gravity by the rotation of the first transport screw 13b1 is reduced. It depends.

  As described above, also in the third embodiment, as in the above-described embodiments, the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer G in the longitudinal direction to form a circulation path are developed. The developer G supply path (first transport path) and the recovery path (second transport path) are separately provided for the developing roller 13a by installing the roller 13a so as to face the developer carrier. In the case where the blade 13c (developer regulating member) is disposed below the developing roller 13a, the outer diameter of the screw portion of the first transport screw 13b1 (first transport member) is downstream of the supply path in the transport direction. Since it is formed so as to be small, it is possible to reduce a problem that density unevenness in the screw pitch shape corresponding to the pitch of the screw portion of the first conveying screw 13b1 occurs on the output image. That.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 11A is a cross-sectional view showing a part of the developing device 13 in the fourth embodiment, and corresponds to FIG. 3B in the first embodiment. FIG. 11B is a cross-sectional view showing a part of another embodiment of the developing device 13 and corresponds to FIG. 3B in the first embodiment.
In the developing device according to the fourth embodiment, the wall portion of the first transport path is arranged such that the wall portion 13m of the first transport path is inclined with respect to the rotation center axis of the developer carrier 13a. This is different from that of the first embodiment in which 13m is arranged so as to be parallel to the rotation center axis of the developer carrier 13a.

  The developing device 13 according to the fourth embodiment also has a developing roller 13a (developer carrier), two conveying screws 13b1 and 13b2 (screw members), a doctor blade 13c (developer), as in the above embodiments. A restricting member), a partition member 13d, and the like. Further, the first conveying screw 13b1 in the fourth embodiment is also configured so that the outer diameter of the screw portion continuously decreases from the upstream side in the conveying direction to the downstream side in the conveying direction, as in the first embodiment. Is formed. Further, in the developing device 13 in the fourth embodiment, the outer diameter portion of the screw portion of the first conveying screw 13b1 and the wall of the first conveying path by the first conveying screw 13b1 as in the first embodiment. A gap CG (casing gap) with the inner wall surface of the portion 13m is formed so as to increase from the upstream side in the transport direction to the downstream side in the transport direction (CG1 <CG2).

Here, with reference to FIG. 11A, the developing device 13 in the fourth embodiment differs from that in the first embodiment in that the wall portion 13m of the first transport path is angled with respect to the horizontal direction. It is inclined by α1. Specifically, the wall portion 13m of the first transport path is formed to be inclined so that the upstream side in the transport direction is closer to the developing roller 13a than the downstream side in the transport direction. The casing gap CG2 on the downstream side in the transport direction in the first transport path is formed to be wider than the casing gap CG1 on the upstream side in the transport direction.
Even with such a configuration, as in the first embodiment, the level of the developer surface of the developer G on the downstream side in the transport direction of the first transport path can be reduced, and the transport direction Since the downstream casing gap CG can be widened, the developer G easily enters the space behind the screw portion of the first conveying screw 13b1, and the screw pitch density unevenness is unlikely to occur on the output image. Become.

Note that the developing device 13 in FIG. 11A is formed by inclining the wall portion 13m of the first transport path so that the upstream side in the transport direction is closer to the developing roller 13a than the downstream side in the transport direction.
On the other hand, as shown in FIG. 11B, the wall portion 13m of the first transport path may be inclined and formed so that the upstream side in the transport direction is farther from the developing roller 13a than the downstream side in the transport direction. it can. Even in such a case, by forming the casing gap CG2 on the downstream side in the transport direction in the first transport path so as to be wider than the casing gap CG1 on the upstream side in the transport direction, the same effect as described above is obtained. Can be obtained.
Note that the magnitude of the difference between the casing gap CG2 on the downstream side in the transport direction in the first transport path and the casing gap CG1 on the upstream side in the transport direction depends on the height of the developer surface on the downstream side in the transport direction and the output image. It is preferable to determine the density according to the degree of unevenness of the screw pitch shape generated above.

  As described above, also in the fourth embodiment, as in each of the above embodiments, the developer G is transported in the longitudinal direction to develop the two transport screws 13b1 and 13b2 (transport members) that form a circulation path. The developer G supply path (first transport path) and the recovery path (second transport path) are separately provided for the developing roller 13a by installing the roller 13a so as to face the developer carrier. In the case where the blade 13c (developer regulating member) is disposed below the developing roller 13a, the outer diameter of the screw portion of the first transport screw 13b1 (first transport member) is downstream of the supply path in the transport direction. Since it is formed so as to be small, it is possible to reduce a problem that density unevenness in the screw pitch shape corresponding to the pitch of the screw portion of the first conveying screw 13b1 occurs on the output image. That.

Embodiment 5 FIG.
A fifth embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 12 is a cross-sectional view showing a part of the developing device 13 according to the fifth embodiment, and corresponds to FIG. 3B in the first embodiment. FIG. 13A is a cross-sectional view showing the developing device 13 at a position corresponding to the upstream side in the transport direction of the first transport path, and corresponds to FIG. 6A in the first embodiment. FIG. 13B is a cross-sectional view showing the developing device 13 at a position corresponding to the downstream side in the transport direction of the first transport path, and corresponds to FIG. 6B in the first embodiment.
In the developing device according to the fifth embodiment, the first transport member 13b1 is inclined so that the shaft portion on the downstream side in the transport direction of the first transport member 13b1 is farther from the developer carrier 13a than the shaft portion on the upstream side in the transport direction. The first conveying member 13b1 is inclined so that the shaft portion on the upstream side in the conveying direction of the first conveying member 13b1 is further away from the developer carrier 13a than the shaft portion on the downstream side in the conveying direction. This is different from that of the third embodiment.

  The developing device 13 according to the fifth embodiment also has a developing roller 13a (developer carrier), two transport screws 13b1 and 13b2 (screw members), a doctor blade 13c (developer), as in the above embodiments. A restricting member), a partition member 13d, and the like. Also, the first conveying screw 13b1 in the fifth embodiment is also configured so that the outer diameter of the screw portion continuously decreases from the upstream side in the conveying direction to the downstream side in the conveying direction, as in the first embodiment. Is formed.

Here, referring to FIGS. 12 and 13, the first transport screw 13b1 in the fifth embodiment is different from that in the third embodiment in the upstream in the transport direction (on the right side in FIG. The shaft portion on the downstream side in the transport direction (the left side in FIG. 12 and the position corresponding to FIG. 13B) compared to the shaft portion in FIG. The shaft portion is disposed so as to be inclined by an angle β with respect to the rotation center axis of the developing roller 13a so as to be away from the roller 13a.
With such a configuration, the closest distance SG (the outer diameter of the screw portion of the first conveying screw 13b1) is set without reducing the screw diameter (the outer diameter of the screw portion) on the downstream side in the conveying direction of the first conveying screw 13b1. And the casing gap CG can be easily set so that the developer conveyance state in the first conveyance path is optimized. Therefore, the degree of freedom in design for achieving both optimization of developer transportability in the first transport path and suppression of screw pitch-shaped density unevenness is improved.

Referring to FIG. 13, in the fifth embodiment, the outer diameter portion of the screw portion of the first transfer screw 13b1 and the inner wall surface of the wall portion 13m of the first transfer path by the first transfer screw 13b1 The gap CG (casing gap) is formed so as to increase from the upstream side in the transport direction of the developer G toward the downstream side in the transport direction. That is, the casing gap CG shown in FIG. 13 (B) is wider than the casing gap CG shown in FIG. 13 (A).
With such a configuration, as described above with reference to FIG. 7A, on the downstream side in the transport direction of the first transport path, the back side of the screw portion of the first transport screw 13b1 (the developer indicated by the white arrow) The developer G can easily enter the space (the back side in the transport direction) (the developer moves in the direction of the arrow). Therefore, screw pitch variations are less likely to occur in the amount of developer G supplied onto the developing roller 13a (or the amount of developer G pumped up onto the developing roller 13a).

  As described above, also in the fifth embodiment, as in each of the above embodiments, the two conveying screws 13b1 and 13b2 (conveying members) that convey the developer G in the longitudinal direction to form a circulation path are developed. The developer G supply path (first transport path) and the recovery path (second transport path) are separately provided for the developing roller 13a by installing the roller 13a so as to face the developer carrier. In the case where the blade 13c (developer regulating member) is disposed below the developing roller 13a, the outer diameter of the screw portion of the first transport screw 13b1 (first transport member) is downstream of the supply path in the transport direction. Since it is formed so as to be small, it is possible to reduce a problem that density unevenness in the screw pitch shape corresponding to the pitch of the screw portion of the first conveying screw 13b1 occurs on the output image. That.

Example.
FIG. 14 is a table showing conditions and results of experiments conducted by the inventors of the present application in order to confirm the effects described in the above embodiments.
In the experiment, three types of developing devices (Comparative Example, Example 1 and Example 2) were prepared, and each was installed in the image forming apparatus 1 to form a solid image on a recording medium P of A3 vertical size. Are output, and the presence or absence of screw pitch-like density unevenness on the output image and its degree are visually confirmed. Further, the level of the amount of the developer G to be filled in the developing device is varied by several levels.
14, in the comparative example, a conventional developing device (the outer diameter of the screw portion of the first conveying screw 130b1 is uniform in the longitudinal direction and is shown in FIG. 4B) is used. In Example 1, the developing device 13 in Embodiment 1 (the outer diameter of the screw portion of the first conveying screw 130b1 is continuously reduced toward the downstream side, and the shaft portion is disposed in parallel to the developing roller 13a. In Example 2, the developing device 13 in Embodiment 3 (the outer diameter of the screw portion of the first conveying screw 130b1 is continuously reduced toward the downstream side, and the shaft portion is reduced. Is disposed to be inclined with respect to the developing roller 13a). In FIG. 14, “◯” indicates a state in which no screw pitch-shaped density unevenness occurs on the output image, and “Δ” indicates a slight level of screw pitch-shaped density unevenness acceptable on the output image. “X” is a state where screw pitch-shaped density unevenness of an unacceptable level occurs on the output image. Further, no experiment was conducted with “-” in FIG.

From the experimental results shown in FIG. 14, it can be seen that, in the comparative example, if the total developer amount reaches 215 g, screw pitch-like density unevenness occurs on the output image.
On the other hand, in the first embodiment, since the outer diameter of the screw portion of the first transport screw 13b1 gradually decreases toward the downstream side in the transport direction of the first transport path, the total amount of developer is reduced. It can be seen that no screw pitch-like density unevenness occurs on the output image even at 210 g.
In the second embodiment, the closest distance SG between the first transport screw 13b1 and the developing roller 13a on the downstream side in the transport direction of the first transport path is formed in the same manner as that on the upstream side in the transport direction. It can be seen that no screw pitch density unevenness occurs on the output image even when the total developer amount is 180 g.

  In each of the above embodiments, the toner T is supplied from the toner container 28 toward the developing device 13. However, the developer G (toner T and carrier C) is directed toward the developing device 13 from the toner container (developer container). Can also be supplied. In that case, a means for appropriately discharging excess developer from the developing device 13 is provided. Even in such a case, it is possible to obtain the same effects as those of the above embodiments.

  In each of the above embodiments, the present invention is applied to an image forming apparatus in which the developing device 13 is configured as a unit that is detachably attached to the main body of the image forming apparatus. However, the application of the present invention is not limited to this, and the present invention can naturally be applied to an image forming apparatus in which a part or all of the image forming unit is formed as a process cartridge. In that case, the workability of maintenance of the image forming unit is improved.

Further, in each of the above embodiments, the present invention is applied to the developing device 13 in which two conveying screws as conveying members are installed. However, three or more conveying screws are installed, and at least two conveying screws are included. The present invention can also be applied to a developing device installed so as to face the developing roller 13a. In each of the above embodiments, the number of magnetic poles H1 to H6 formed around the developing roller 13a is six. However, the number of magnetic poles formed around the developing roller 13a is five or less, or seven or more. It can also be.
In these cases, the same effects as those of the above-described embodiments can be obtained by gradually decreasing the outer diameter of the screw portion of the conveying screw installed in the supply path toward the downstream side in the conveying direction.

  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 image forming apparatus body (apparatus body),
11, 11Y, 11C, 11M, 11BK Photosensitive drum (image carrier),
13 Developing device (developing part),
13a Development roller (developer carrier),
13b1 first conveying screw (first conveying member, screw member),
13b2 second conveying screw (second conveying member),
13c Doctor blade (developer regulating member),
13d partition member,
13e Toner supply port,
13f 1st relay part, 13g 2nd relay part,
G developer (two-component developer), T toner, C carrier.

Japanese Patent Laid-Open No. 11-174810 JP 2008-26408 A Japanese Patent No. 3950735

Claims (9)

A developing device that contains a developer having a carrier and toner and that develops a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer;
A developer regulating member that is disposed so as to face the lower side of the developer carrying member and regulates the amount of the developer carried on the developer carrying member;
A plurality of transport members that transport the developer contained in the apparatus in the longitudinal direction to form a circulation path;
With
The plurality of conveying members are:
A first conveying member facing the developer carrying member and supplying the developer to the developer carrying member while conveying the developer in the longitudinal direction;
A second conveying member disposed above the first conveying member to face the developer carrying member and convey the developer detached from the developer carrying member in the longitudinal direction;
Comprising
The first conveying member is a screw member in which a screw portion is spirally wound around a shaft portion, and the screw is at least partly in the longitudinal direction from the upstream side in the developer conveying direction to the downstream side in the conveying direction. A developing device characterized in that the outer diameter of the portion is formed so as to decrease continuously or stepwise.   The first conveying member has the shaft portion of the developer carrying body such that the shaft portion on the downstream side in the carrying direction is closer to the developer carrying body than the shaft portion on the upstream side in the developer carrying direction. The developing device according to claim 1, wherein the developing device is disposed to be inclined with respect to the rotation center axis.   The first conveying member is disposed so that the closest distance between the outer diameter portion of the screw portion and the outer peripheral surface of the developer carrying member is the same in the longitudinal direction in the range of at least a part in the longitudinal direction. The developing device according to claim 2.   The first transport member has the shaft portion of the developer carrier so that the shaft portion on the upstream side in the transport direction is closer to the developer carrier than the shaft portion on the downstream side in the developer transport direction. The developing device according to claim 1, wherein the developing device is disposed to be inclined with respect to the rotation center axis.   The gap between the outer diameter portion of the screw portion of the first conveying member and the inner wall surface of the first conveying path by the first conveying member is upstream of the developer conveying direction within a range of at least a part in the longitudinal direction. The developing device according to claim 1, wherein the developing device is formed so as to widen from the side toward the downstream side in the transport direction.   The developing device according to claim 1, wherein the first conveying member is disposed to face a lower side of the developer carrying member.   The developing device according to claim 1, wherein the carrier has a weight average particle diameter of 20 to 60 μm. 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