JP5282957B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in a development system using a two-component developer, wherein a developer is satisfactorily carried on a developing roller and the developing roller is less deflected in a peripheral direction and a direction of a revolving shaft and toner is hardly stuck to a surface of the developing roller with the passage of time to be able to stably form a good output image regardless of the passage of time, and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: On a surface of a developing roller 13a, a plurality of first grooves 131 formed along the direction of the revolving shaft (and/or so that may incline to the direction of the revolving shaft) are provided at intervals in the peripheral direction, and a plurality of second grooves 132 formed along the peripheral direction are provided at intervals in the direction of the revolving shaft. They are configured to satisfy a relation of Sm&lt;D, wherein Sm is an average interval between adjacent second grooves 132 in the direction of the revolving shaft and D is a weight average particle size of carrier. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, and a developing device and a process cartridge installed therein, and particularly uses a two-component developer. The present invention relates to a developing device, a process cartridge, and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, development using a two-component development method in which a development process is performed using a two-component developer composed of toner and a carrier (including cases where an additive or the like is added). An apparatus is known (see, for example, Patent Document 1 to Patent Document 6).

In such a developing device using a two-component developer, one or a plurality of developing rollers (developer carriers) are installed at positions facing the photosensitive drum (image carrier). The developing roller is mainly composed of a sleeve (cylindrical body) that rotates in a predetermined direction and a magnet installed inside the sleeve.
Then, according to the toner consumption in the developing device, the toner is appropriately replenished in the developing device. The replenished toner is stirred and mixed together with the developer in the developing device by a stirring member such as a transport screw or a transport paddle. Part of the stirred and mixed developer is supplied to the developing roller. After the developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), the toner in the two-component developer is a latent image on the photosensitive drum at a position facing the photosensitive drum. Adhere to.
Here, in Patent Document 1, Patent Document 2, etc., in order to improve the transportability (holding force) of the developer on the developing roller, it is formed on the sleeve surface of the developing roller so as to be along the rotation axis direction. A technique for periodically providing groove portions (V grooves) at intervals in the circumferential direction is disclosed.

On the other hand, in such a developing device using a two-component developer, the toner adheres to the surface of the developing roller (developer carrier) over time, so that the image density on the output image decreases or the output image It is known that background stains may occur and toner scattering may occur (see, for example, Patent Document 3 and Patent Document 4).
In Patent Document 3, Patent Document 4, and the like, for the purpose of preventing toner sticking to the surface of the developing roller, the amount of recesses and the interval between the ridges applied to the sleeve surface of the developing roller by sandblasting, etc. A technique for limiting the above is disclosed.
Patent Documents 3, 5, etc. also disclose techniques for coating the surface of the developing roller with Ni-P or the like.

The developing rollers described in Patent Document 1, Patent Document 2, and the like described above are provided with periodic grooves in the circumferential direction so that the grooves are along the rotation axis direction, and irregular irregularities are formed on the sleeve surface by sandblasting. Compared with developed developing rollers (disclosed in Patent Document 3, Patent Document 4, etc.), (1) The degree of decrease in developer transportability (holding force) over time is small and image deterioration occurs. (2) It has the advantage that the fluctuation in the circumferential direction and the rotation axis direction is small and unevenness of the output image is hardly generated.
However, the developing roller in which periodic grooves are formed in such a circumferential direction has a problem that toner adheres to the surface over time. Such a problem is caused by the pressure and frictional force applied to the developer carried on the developing roller at a position facing the doctor blade and the photosensitive drum when the rotation speed of the developing roller increases as the speed of the image forming apparatus increases. Because of the increase, it was not particularly negligible.

  The present invention has been made to solve the above-described problems. The developer transportability is good on the developing roller, the runout in the circumferential direction and the rotation axis direction of the developing roller is small, and development is performed over time. To provide a developing device, a process cartridge, and an image forming apparatus of a two-component developing system in which toner sticking hardly occurs on the surface of a roller and a good output image can be stably formed over time. .

A developing device according to a first aspect of the present invention is a developing device for developing a latent image formed on an image carrier while containing a developer having a carrier and a toner, One or a plurality of developing rollers that face the body and carry a developer, and the one or a plurality of developing rollers have a surface along the rotation axis direction of the developing roller, and / or the developing roller. A plurality of formed first groove portions are provided at intervals in the circumferential direction of the developing roller so as to be inclined with respect to the rotation axis direction of the roller, and at least one developing roller of the one or plural developing rollers includes: A plurality of second groove portions formed along the circumferential direction of the developing roller on the surface thereof are provided at intervals in the rotation axis direction of the developing roller, and the rotation of the adjacent second groove portions is performed. The average distance between the direction Sm, a weight average particle size of the carrier is D,
Sm <D
The relationship is established.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the at least one developing roller having the second groove portion has a surface hardness higher than that of the carrier. Is formed to be larger.

  According to a third aspect of the present invention, in the developing device according to the second aspect, the at least one developing roller in which the second groove portion is formed is larger in hardness than the carrier on the surface thereof. A film layer having hardness is formed.

  According to a fourth aspect of the present invention, in the developing device according to the third aspect, the coating layer is formed of any one of CrN, ZrN, and TiN.

  According to a fifth aspect of the present invention, in the developing device according to the third or fourth aspect, the coating layer is formed by an ion plating method.

  According to a sixth aspect of the present invention, in the developing device according to the third aspect, the coating layer is formed on the sleeve surface of the developing roller made of aluminum. It is.

  A developing device according to a seventh aspect of the present invention is the developing device according to any one of the first to sixth aspects, wherein the at least one developing roller in which the second groove portion is formed has a surface thereof. It is formed so as to have conductivity.

  The developing device according to an eighth aspect of the present invention is the developing device according to any one of the first to seventh aspects, wherein the at least one developing roller in which the second groove is formed is the developing roller. It faces the developer regulating member that regulates the amount of developer carried thereon.

  According to a ninth aspect of the present invention, there is provided the developing device according to any one of the first to seventh aspects, wherein the at least one developing roller formed with the second groove is disposed on the developing roller. Among the plurality of developing rollers facing the developer regulating member that regulates the amount of the developer carried on the single developing roller, the single developing roller is located on the most downstream side with respect to the traveling direction of the image carrier.

  The developing device according to a tenth aspect of the present invention is the developing device according to any one of the first to ninth aspects, wherein the toner has a weight average particle diameter of 5 to 10 μm and has a weight average. The one having a particle size of 5 μm or less is formed so as to be included in the range of 60 to 80% by number.

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

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

  In the present invention, since the second groove portion is formed on the surface of the developing roller in addition to the first groove portion, and the interval between the second groove portions is optimized, the developer transportability on the developing roller is good. Two-component development system development in which the developing roller has little runout in the circumferential direction and rotation axis direction, and toner sticking hardly occurs on the surface of the developing roller over time, and a good output image is stably formed over time. An apparatus, a process cartridge, and 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. It is the schematic sectional drawing which looked at the circulation path of the developing device in the longitudinal direction. It is a figure which shows the magnitude | size of the magnetic force of the normal line direction by the magnetic pole formed on a developing roller. It is a schematic diagram which shows the developing roller in which the 1st groove part was formed. It is an enlarged view showing a first groove portion of the developing roller. It is a perspective view which shows the surface of the developing roller in which the 1st groove part and the 2nd groove part were formed. It is a schematic diagram which shows the carrier of the vicinity of a 2nd groove part. It is a table | surface figure which shows the conditions and results of experiment. It is a table | surface figure which shows the conditions and result of another experiment. It is a block diagram which shows the principal part of the developing device in Embodiment 2 of this invention. It is a block diagram which shows the principal part of another developing apparatus. It is a block diagram which shows the principal part of another developing apparatus. It is a block diagram which shows the principal part of another developing apparatus.

  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, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original K to an original reading unit 4. 4 is a document reading unit that reads image information of the document K, 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, and 11C. , 11BK is a photosensitive drum as an image carrier on which toner images of each color (yellow, magenta, cyan, black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, 13 Is a developing device for developing an electrostatic latent image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK, and 14 is formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK. A transfer bias roller (primary transfer bias roller) for transferring the toner image superimposed on the recording medium P, and a cleaning unit 15 for collecting untransferred toner on the photosensitive drums 11Y, 11M, 11C, and 11BK. Show.

Reference numeral 16 denotes an intermediate transfer belt cleaning unit that cleans the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred and superimposed, and 18 a color toner image on the intermediate transfer belt 17 on the recording medium P. A secondary transfer bias roller 20 for transferring the toner image onto the recording medium P indicates a fixing device for fixing an unfixed image on the recording medium P.
Although not shown, each color toner (toner particles) that supplies toner (toner particles) of each color (yellow, cyan, magenta, black) to the developing device 13 is disposed above each of the photosensitive drums 11Y, 11C, 11M, and 11BK. Each container is installed.

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 K is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document K placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document K on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected from the original K is imaged on the color sensor via the mirror group and the lens. The color image information of the document K 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, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light L (see FIG. 2) based on the image information of each color 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 (this is a 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 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. 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 in the clockwise direction in FIG. 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 the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, 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 by the transport belt. In the fixing device 20, the color image is fixed on the recording medium P at the nip between the fixing belt 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 paper discharge roller, and a series of image forming processes is completed.

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 and the toner container 28. 3A is a schematic cross-sectional view (horizontal cross-sectional view) of the upper portion of the developing device 13 (the position of the first transport screw 13b1) in the longitudinal direction, and FIG. 3B is a developing device. It is the schematic sectional drawing which looked at the lower part of 13 (it is a position of the 2nd conveyance screw 13b2) in the longitudinal direction. FIG. 4 is a schematic cross-sectional view (vertical cross-sectional view) of the circulation path of the developing device 13 as viewed in the longitudinal direction. FIG. 5 is a diagram showing the magnitude of the magnetic force in the normal direction by the magnetic poles H1 to H4 formed on the developing roller 13a. FIG. 6 is a schematic view showing the developing roller 13a in which the first groove 13a1 is formed, and is a view of the developing roller 13a in the longitudinal direction (the direction perpendicular to the paper surface in FIGS. 2 and 5). . FIG. 7 is an enlarged view showing the first groove 13a1 of the developing roller 13a, and is a cross-sectional view orthogonal to the rotation axis of the developing roller 13a. FIG. 8 is a perspective view showing the surface of the developing roller 13a in which the first groove portion 13a1 and the second groove portion 13a2 are formed. Further, FIG. 9 is a schematic view showing the carrier C in the vicinity of the second groove portion 13a2, and is a view of the surface of the developing roller 13a as viewed in the circumferential direction.
Since each image forming unit has almost the same structure and each toner container has almost the same structure, the image forming unit and the toner container in FIGS. 2 to 9 are denoted by alphabets (Y, C, M, BK) is shown in the figure.

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 driven to rotate 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 15 a 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. 2, toner container 28 contains toner T to be supplied into developing device 13 therein. Specifically, based on information on toner density (which is the ratio of toner in the developer G) detected by a magnetic sensor (not shown) installed in the developing device 13, the shutter driving unit performs shutter. The mechanism 80 is opened and closed, and the toner T is appropriately supplied from the toner container 28 into the developing device 13.
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.
The supply pipe 29 is for reliably guiding the toner T supplied from the toner container 28 into the developing device 13. That is, the toner T discharged from the toner container 28 is supplied into the developing device 13 through the supply pipe 29 from the toner supply port 13e.

  Here, the toner T used in the first embodiment has a weight average particle diameter of 5 to 10 μm, and a toner having a weight average particle diameter of 5 μm or less is included in a range of 60 to 80% by number. It is formed. By using toner with a small particle diameter in this way, the dot reproducibility of the output image can be improved.

Hereinafter, the developing device 13 in the image forming apparatus will be described in detail.
2 to 5, the developing device 13 includes a developing roller 13a (developer carrier), conveying screws 13b1 and 13b2 (auger screws), a doctor blade 13c as a developer regulating member, and the like. Yes.
The developing roller 13a is a developing roller having an outer diameter of about 20 mm, and a sleeve 13a2 formed of a nonmagnetic material such as aluminum, brass, stainless steel, conductive resin or the like in a cylindrical shape is watched by a rotation driving mechanism (not shown). It is configured to be rotated in the direction. 3 and 5, a magnet 13a1 for forming a plurality of magnetic poles H1 to H4 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 H4 formed around the developing roller 13a (sleeve 13a2) by the magnet 13a1. As shown in FIG. 5, the plurality of magnetic poles are formed at positions facing the photosensitive drum 11, positions on the downstream side of the main magnetic pole H <b> 1 and a part of the inner wall surface of the second transport path. The conveying magnetic pole H2 formed on the second conveying path, the agent separating magnetic pole H3 formed above the second conveying path, and the pumping magnetic pole H4 formed from the position facing the first conveying screw 13b1 to the vicinity of the position facing the doctor blade 13c. (Doctor counter magnetic pole), etc.
First, the pumping magnetic pole H4 acts on a carrier as a magnetic body, and the developer G accommodated in the first transport 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 pumping magnetic pole H4 acts is the main magnetic pole H1. It rises at the position and becomes a magnetic brush in the developing region and slides on 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 through the position of the main magnetic pole H1 is transported to the position of the agent separating magnetic pole H3 by the transport magnetic pole H2. The repelling magnetic field acts on the carrier at the position of the agent separating magnetic pole H3, and the developer G after the developing process carried on the developing roller 13a is detached from the developing roller 13a. The detached developer G falls into the second transport path and is transported downstream of the second transport path by the second transport screw 13b2.

Referring to FIG. 2, two conveying screws 13b1 and 13b2 (conveying members) are stirred while circulating the developer G accommodated in the developing device 13 in the longitudinal direction (the direction perpendicular to the paper surface of FIG. 2).・ Mix.
The first transport screw 13b1 (first transport member) is disposed at a position facing the developing roller 13a, and transports the developer G horizontally in the longitudinal direction (rotation axis direction) (see FIG. 3A). In addition, the developer G is supplied onto the developing roller 13a at the position of the pumping magnetic pole H4 (the supply in the direction of the white arrow in FIG. 3A).

The second conveying screw 13b2 (second conveying member) is disposed below 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 H3 after the developing process, and separated in the direction of the white arrow in FIG. 3B. Is transported horizontally in the longitudinal direction (the transport is in the left direction indicated by the broken-line arrow in FIG. 3B). In the first embodiment, the rotation direction of the second conveying screw 13b2 is set to be the same as 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 conveyance shown by the dashed-dotted arrow of FIG. 3 (B)).
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. The two conveying screws 13b1 and 13b2 are formed by spirally winding a screw portion having an outer diameter of 16 mm or less around a shaft portion.

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 isolated from each other by a wall portion.
3 and 4, the downstream side of the transport path (second transport path) by the second transport screw 13b2 and the upstream side of the transport path (first transport path) by the first transport screw 13b1 are 2 It communicates via the relay part 13g. Then, the developer G that has risen and stayed in the vicinity of the second relay portion 13g in the transport path by the second transport screw 13b2 is transported to the upstream side of the transport path by the first transport screw 13b1 via the second relay portion 13g ( Supply).
3 and 4, the downstream side of the conveyance path by the first conveyance screw 13b1 and the upstream side of the conveyance path by the second conveyance screw 13b2 communicate with each other via the first relay unit 13f. Yes. Then, the developer G that has not been supplied onto the developing roller 13a in the first conveying path by the first conveying screw 13b1 falls by its own weight at the first relay portion 13f and reaches the upstream side of the second conveying path. become.

  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 line arrow in FIGS. 3 and 4. 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), 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 4, the toner replenishing port 13e is located above the upstream side of the transport path by the second transport screw 13b2 and away from the developing area (the range in the longitudinal direction of the developing roller 13a). It is arranged outside.). 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.

Hereinafter, a characteristic configuration and operation of the developing device 13 according to the first embodiment will be described.
In the developing device 13 according to the first embodiment, the first groove 131 and the second groove 132 are formed on the surface of the developing roller 13a (sleeve 13a2) (see FIG. 8).
Referring to FIGS. 6A and 8A, the first groove portion 131 has a circumferential interval along the circumferential direction of the developing roller 13a so as to extend along the rotation axis direction of the developing roller 13a. A plurality are provided. The plurality of first grooves 131 formed on the surface of the developing roller 13a (sleeve 13a2) is for improving the transportability (holding force) of the developer G on the developing roller 13a (sleeve 13a2). The groove shape of the first groove 131 can be set, for example, to any one of FIGS.
Here, in Embodiment 1, the groove shape of the first groove portion 131 is a V-groove shape as shown in FIG. 7A, and the depth is set to 0.2 mm. Then, 60 first groove portions (groove pitch 6 degrees) are formed at equal intervals on the surface of the developing roller 13a having an outer diameter of 20 mm.

In addition, as a form of the 1st groove part 131, as shown to FIG. 6 (A) and FIG. 8 (A), it is not limited to what was formed along the rotating shaft direction of the developing roller 13a.
For example, as the first groove 131, as shown in FIGS. 6B and 8B, a groove formed so as to be inclined with respect to the rotation axis direction of the developing roller 13a can be used. Here, the first groove portions 131 having different inclination directions are formed so as to intersect with each other.
Further, as shown in FIGS. 6C and 8C, the first groove 131 is formed along the rotation axis direction of the developing roller 13a and is inclined with respect to the rotation axis direction. Can be used. Here, in the 1st groove part 131, the center is formed so that a rotating shaft direction may be followed, and both ends are formed so that it may incline with respect to a rotating shaft direction. In addition, as a whole of the developing roller 13a, a plurality of first groove portions 131 are formed in a scale shape.

Further, referring to FIG. 8A, a second groove 132 is formed on the surface of developing roller 13a (sleeve 13a2) according to the first embodiment in a region where first groove 131 is not formed. Yes. The second groove portion 132 is formed along the circumferential direction of the developing roller 13a, and a plurality of second groove portions 132 are provided at intervals (average interval Sm) in the rotation axis direction of the developing roller 13a. The second groove 132 is formed as shown in FIGS. 8B and 8C corresponding to the shape of the first groove 131 shown in FIGS. 6B and 6C. You can also.
Then, as shown in FIG. 9A, when the average interval in the rotation axis direction between the adjacent second groove portions 132 is Sm and the weight average particle diameter of the carrier C is D,
Sm <D
The relationship is established. Specifically, in the first embodiment, the average interval Sm of the second groove portions 132 is set to 30 μm, and the weight average particle diameter D of the carrier C is set to 60 μm. The “average interval Sm” is synonymous with the average length RSm of the contour curve elements in JIS 0601 (2001).
With such a configuration, in the developing roller 13a in which the first groove 131 is periodically formed in the circumferential direction, it is possible to make it difficult for toner to adhere to the surface.

Hereinafter, the relationship between the average interval Sm of the second groove part 132 and the weight average particle diameter D of the carrier C will be described in detail.
FIG. 9B is a diagram illustrating the carrier C on the developing roller 13a when the relationship of Sm> D is established. The carrier C is easily trapped in the second groove portion 132 as compared to the flat portion without the second groove portion 132. Therefore, the carrier C on the surface of the developing roller 13a is trapped in the second groove portion 132 or exists on the surface other than the second groove portion 132 as shown in FIG. 9B. The surface other than the second groove 132 has a weak force for holding the carrier C, but is trapped on the developing roller 13a by being held by the surrounding carrier C. In this state, when the carrier C receives a load at a position facing the doctor blade 13 c or a position facing the photosensitive drum 11, a concentrated load is applied to the end M <b> 1 of the second groove 132. Due to the concentrated load, the toner held on the carrier C and the toner adhering to the surface of the developing roller 13a adhere to and adhere to the end M1 of the second groove 132. On the other hand, the carrier C existing on the surface other than the second groove portion 132 applies a concentrated load to a part M2 of the surface of the developing roller 13a. As a result, the toner adheres to the position M2. Over time, the surface of the surface other than the second groove portion 132 gradually adheres to the toner gradually, so that the image density on the output image decreases, the background stains occur on the output image, the toner The problem that scattering occurs will arise.

  On the other hand, FIG. 9A is a diagram showing the carrier C on the developing roller 13a when the relationship of Sm <D is established, and shows the configuration in the first embodiment. Even in such a case, the carrier C on the surface of the developing roller 13 a is trapped in the second groove portion 132. However, since the space entering the surface other than the second groove 132 is small, the carrier C is unlikely to exist. Further, even if the carrier C exists on the surface other than the second groove portion 132, the carrier C is trapped in one of the second groove portions 132 because the holding force is weak. Since the relationship of Sm <D is established, there are more second grooves 132 than the number of carriers C on the surface of the developing roller 13a. In this state, when the carrier C receives a load at a position facing the doctor blade 13c or a position facing the photosensitive drum 11, the carrier C trapped in the second groove 132 concentrates only on the end M1 of the second groove 132. A load is applied. On the other hand, since the carrier C does not exist on the surface other than the second groove 132, no concentrated load is applied. Therefore, over time, toner sticking does not occur on the surface other than the second groove 132 (toner sticking occurs only at the end M1 of the second groove 132). As a result, it is possible to reduce the occurrence of toner sticking on the surface of the developing roller 13a, and to reduce problems such as a decrease in image density on the output image, background stains on the output image, and toner scattering. Become.

  Further, the carrier C trapped in the second groove 132 moves along the second groove 132 along with the rotation of the developing roller 13a, and does not easily exist on the surface other than the second groove 132. That is, when the carrier C moves on the surface of the developing roller 13a by the magnetic force of the magnet 13a1, the minute second groove 132 formed regularly along the circumferential direction plays the role of a rail, and moves in the circumferential direction. The movement of the carrier C is promoted. As a result, even if the carrier C receives a load in the compression direction at a position facing the doctor blade 13c or a position facing the photosensitive drum 11, the carrier C is upstream or downstream of the second groove 132 formed in the circumferential direction. Since it is guided to the side, it is possible to suppress a problem of being pressed at one place. Therefore, occurrence of toner sticking to the surface of the developing roller 13a with time is reduced.

FIG. 10 shows the result of examining the margin of occurrence of abnormal images due to toner fixation when the average interval Sm of the second groove 132 is changed using the carrier C having a weight average particle diameter D of 60 μm. is there.
Here, “the margin for occurrence of an abnormal image due to toner fixation” means that the larger the margin is, the less the occurrence of an abnormal image and the better the image quality. The margin increases in the order of x, Δ, ○, ◎, and Δ is the boundary of the allowable level.
From the result of FIG. 10, when the average interval Sm of the second groove 132 is larger than the weight average particle size D of the carrier C, the margin for toner fixation is low, and the average interval Sm of the second groove 132 is the weight average particle of the carrier C. It can be seen that the smaller the diameter D, the higher the margin for toner fixation. As described above with reference to FIG. 9, the number of the second groove portions 132 increases as the average interval Sm of the second groove portions 132 is smaller than the weight average particle diameter D of the carrier C. This is because the carrier C is easily trapped. As described above, from the experimental results, it was proved that the developing roller 13a according to the first embodiment has a configuration advantageous for toner fixation.

Here, in the first embodiment, the surface of the developing roller 13a (sleeve 13a2) on which the second groove 132 is formed is formed so that the hardness of the surface is larger than the hardness of the carrier C.
Specifically, a coating layer having a hardness larger than the hardness of the carrier C is formed on the sleeve surface of the developing roller 13a made of aluminum. That is, a coating layer having a hardness larger than that of the carrier C is formed on the sleeve 13a2 made of aluminum. As a result, even if the carrier C is pressed against the second groove 132 formed on the developing roller 13a, the problem that the second groove 132 wears out and spreads is reduced. The effect of suppressing sticking is stably maintained over time.
The carrier C used in the first embodiment is a magnetite core material having a Vickers hardness Hv (which can be measured by a method according to JIS Z 2244) coated with a silicone resin.

In particular, the coating layer formed on the sleeve surface of the developing roller 13a is preferably formed of CrN, ZrN, or TiN.
FIG. 11 shows the result of examining the margin of occurrence of abnormal images due to toner adhesion when the sleeve surface of the developing roller 13a is formed of aluminum and a coating layer of various materials is formed on the surface. is there. The “abnormal image due to toner fixation” in FIG. 11 has the same meaning as that in FIG. Further, “None” of the material of the coating layer in FIG. 11 indicates that the coating layer is not provided on the sleeve surface of the developing roller 13a, and the surface material of the developing roller 13a is the material (aluminum) of the sleeve surface. ing.
From the results of FIG. 11, it can be seen that when the material of the coating layer is Ni or Cr, the margin for toner fixation is equivalent to the case where the material of the roller surface is aluminum. On the other hand, when the material of the coating layer is CrN, ZrN, or TiN, it can be seen that the margin for toner fixation is greatly improved. Such a result may be due to a difference in the coefficient of friction of the coating layer, but is largely due to a difference in hardness of the coating layer. As shown in FIG. 11, even when compared with Vickers hardness, CrN, ZrN, and TiN have twice or more hardness as compared with Ni and Cr.

A frictional force is applied to the surface of the developing roller 13a because the carrier C made of a magnetic material such as magnetite or ferrite rubs strongly at a position facing the doctor blade 13c or a position facing the photosensitive drum 11. When such contact with the developer G (carrier C) is repeated, the surface of the developing roller 13a is eventually scraped, and minute irregularities are formed there. The toner T is trapped in a minute recess on the surface of the developing roller 13a, and is fused to the surface of the developing roller 13a by receiving pressure and friction, leading to toner fixation.
In the developing device 13 in which the two-component developer G composed of the toner T and the carrier C is accommodated, a static electricity formed on the photosensitive drum 11 using an electrostatic field between the developing roller 13 a and the photosensitive drum 11. The electrostatic latent image is visualized as a toner image. The toner is charged by frictional charging with the carrier (mainly at the position of the doctor blade 13c), and moves in the above-described electrostatic field. For this reason, a desired charging ability is exhibited by giving the toner a certain amount of resistance. When the toner adheres to the surface of the developing roller 13a, an electric charge is applied to the adhering portion, and the surface potential of the developing roller 13a partially changes. As a result, the electrostatic field between the developing roller 13a and the photosensitive drum 11 is partially changed, and an abnormal image such as background contamination or density reduction occurs and image quality deteriorates.
On the other hand, by forming a hard coating layer made of any of CrN, ZrN, and TiN on the surface of the developing roller 13a, the surface of the developing roller 13a can be scraped even when subjected to pressure or friction due to contact with the carrier. The trouble is reduced. Accordingly, it becomes difficult to form minute irregularities for trapping the toner on the surface of the developing roller 13a, and toner adhesion to the surface of the developing roller 13a is reliably reduced. As a result, it is possible to suppress the occurrence of an abnormal image due to toner fixing to the developing roller 13a. In addition, even if the layer thickness of the coating layer is set to about 2 to 10 μm, it has sufficient durability.

The coating layer made of any one of CrN, ZrN, and TiN formed on the surface of the developing roller 13a is preferably formed by an ion plating method.
The ion plating method is a kind of PVD method (physical vapor deposition method) and is a vapor deposition method capable of coating a substrate without heating it to a high temperature. Specifically, when forming a coating layer using an ion plating method, the deposition temperature is 150 to 200 ° C. for CrN, the deposition temperature is 180 to 220 ° C. for ZrN, and the deposition temperature is TiN. A deposition temperature of 200 to 250 ° C. is required.
If the vapor deposition temperature during the coating process is high, the developing roller 13a is thermally deformed, causing vibrations in the circumferential direction or warping in the direction of the rotation axis. By forming the coating layer by an ion plating method having a relatively low vapor deposition temperature, such a problem is less likely to occur.

  Here, in Embodiment 1, the hardness of the surface of the developing roller 13a is set larger than the hardness of the carrier C by forming a hard coating layer on the sleeve surface of the developing roller 13a made of aluminum. On the other hand, the sleeve 13a2 itself of the developing roller 13a can be formed of a material having a hardness larger than the hardness of the carrier C without forming a coating layer on the sleeve surface of the developing roller 13a. However, in that case, it becomes difficult to form the second groove 132 and the like by cutting the sleeve surface. On the other hand, according to the configuration of the first embodiment, after the surface of the sleeve made of aluminum having a Vickers hardness Hv of about 100 is cut to form the second groove 132 and the like, the hard coating layer is provided on the surface. Therefore, the processability of the developing roller can be improved.

In the first embodiment, the surface of the developing roller 13a is preferably formed to have conductivity. For example, when a coating layer is formed on the sleeve surface of the developing roller 13a, a coating layer having conductivity is formed.
Here, consider the case where an insulator is used as the material of the surface of the developing roller 13a. Such a state can be replaced with the case where the toner adheres to the entire surface of the developing roller 13a. When charges are applied to the roller surface made of an insulator in this way, the charges accumulate on the roller surface without moving. As a result, the electrostatic field between the developing roller 13a and the photosensitive drum 11 changes, and background stains and density reduction occur in the image formed on the photosensitive drum 11.
On the other hand, by imparting conductivity to the surface of the developing roller 13a, even if a charge is applied to the roller surface, the charge does not move immediately and accumulate on the roller surface. Therefore, problems that background stains and density reduction occur in the image formed on the photosensitive drum 11 are suppressed.

  As described above, in the first embodiment, the second groove 132 is formed on the surface of the developing roller 13a in addition to the first groove 131, and the interval Sm between the second grooves 132 is optimized. The developer G on the developing roller 13a has good transportability, and the developing roller 13a has a small runout in the circumferential direction and the rotational axis direction. An image can be stably formed over time.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 12 is a configuration diagram illustrating a main part of the developing device 13 according to the second embodiment. 13 to 15 are configuration diagrams showing the main part of another developing device 13, respectively.
The developing device 13 in the second embodiment is different from that in the first embodiment in which a plurality of developing rollers 13aA to 13aC are installed, and a single developing roller 13a is installed.

Although a part of the illustration is omitted, the developing device 13 in the second embodiment is also composed of a developing roller, a conveying screw, a doctor blade as a developer regulating member, etc., as in the first embodiment. Yes.
Here, in the developing device 13 shown in FIG. 12, the three developing rollers 13 a </ b> A to 13 a </ b> C are installed at positions facing the photosensitive drum 11 along the rotation direction of the photosensitive drum 11. All of the three developing rollers 13aA to 13aC rotate clockwise with respect to the photosensitive drum 11 rotating counterclockwise. The three developing rollers 13aA to 13aC have the first groove 131 formed on any surface. In addition, the first developing roller 13aA that is in the uppermost stream with respect to the rotation direction (traveling direction) of the photosensitive drum 11 is disposed so as to face the doctor blade 13c.
When the developer is pumped from the developing device 13 onto the first developing roller 13aA, the amount of the developer carried on the first developing roller 13aA is regulated at a position facing the doctor blade 13c thereafter. . The developer carried on the first developing roller 13aA is subjected to the first developing process at a position facing the photosensitive drum 11 (first developing region), and then the second developing roller 13aB. Passed over. The developer carried on the second developing roller 13aB is subjected to the second developing step at a position facing the photosensitive drum 11 (second developing region), and then the third developing roller 13aC. Passed over. The developer carried on the third developing roller 13aC is directed into the developing device 13 after the third developing process is performed at a position facing the photosensitive drum 11 (third developing region). And is withdrawn.

In the developing device 13 in which the plurality of developing rollers 13aA to 13aC are installed as described above, the first embodiment is applied to all of the plurality of developing rollers 13aA to 13aC in order to suppress the occurrence of abnormal images due to toner fixation. Similarly, the second groove 132 can be provided, or a coating layer can be formed on the roller surface. However, in this case, the cost of the developing device 13 is increased.
Therefore, in the second embodiment, the second groove portion 132 is formed only on the developing roller facing the doctor blade 13c, or a hard coating layer is formed on the roller surface. Specifically, in the developing device 13 of FIG. 12, the second groove 132 is formed only on the first developing roller 13aA facing the doctor blade 13c among the three developing rollers 13aA to 13aC, and CrN is formed on the roller surface. Etc. are formed.

Here, as shown in FIG. 12, toner sticking that occurs in the developing device 13 in which the three developing rollers 13aA to 13aC are installed will be described.
In such a developing device 13, the first developing roller 13aA facing the doctor blade 13c is most likely to cause toner sticking compared to the other developing rollers 13aB and 13aC. When the developer rubs strongly on the first developing roller 13aA at the position facing the doctor blade 13c and the toner adheres to the roller surface, the toner charging ability (has negative charging characteristics) is assumed. ), The roller surface is charged up to the same polarity as the toner. As a result, a potential difference is generated between the first developing roller 13aA and the second developing roller 13aB (the surface potential of the first developing roller 13aA becomes negative compared to the surface potential of the second developing roller 13aB). .) The negatively charged toner moves (develops) from the first developing roller 13aA to the second developing roller 13aB according to the potential difference. The toner developed on the second developing roller 13aB is fused to the surface of the second developing roller 13aB by being rubbed by the developer. This is because the toner is easily developed and attached to the roller surface of the second developing roller 13aB, so that the toner is easily trapped in minute irregularities on the roller surface. As a result, toner sticking occurs on the surface of the second developing roller 13aB. By the same mechanism, toner sticking also occurs on the surface of the third developing roller 13aC. As described above, when toner fixation occurs on the first developing roller 13aA, the toner fixation is also accelerated on the other developing rollers 13aB and 13aC using this as a trigger. As a result, background dirt or density reduction occurs on the output image.

On the other hand, only the first developing roller 13aA (the developing roller facing the doctor blade 13c) that is most likely to cause toner sticking and is a source of toner sticking to other developing rollers. By forming the second groove 132 and forming a coating layer such as CrN on the roller surface, it is possible to reliably reduce the occurrence of abnormal images due to toner fixation while suppressing an increase in the cost of the developing device 13.
Note that friction is applied to the surfaces of the other developing rollers 13aB and 13aC that do not face the doctor blade 13c only at a position facing the photosensitive drum 11, and therefore, compared to the first developing roller 13aA that faces the doctor blade 13c. The degree of toner sticking is very low. However, when a potential difference due to toner fixation occurs between adjacent developing rollers as described above, toner fixation tends to occur on the surface of the developing roller. Therefore, as described above, by restricting the toner fixing of only the first developing roller 13aA, the toner fixing of the other developing rollers 13aB and 13aC can be significantly suppressed.

Here, as shown in FIG. 13, the second groove portion is also provided for all of the developing rollers 13aA and 13aC opposed to the doctor blades 13cA and 13cC in the developing device 13 provided with the plurality of doctor blades 13cA and 13cC. 132 can be formed, or a hard coating layer can be formed on the roller surface.
13, the first doctor blade 13cA faces the first developing roller 13aA, and the second doctor blade 13cC faces the third developing roller 13aC (rotates counterclockwise). Is configured to do. Even in such a case, the first developing roller 13aA (the developing roller facing the doctor blade 13cA) that is the most likely to cause toner sticking and is a source of toner sticking to other developing rollers. With respect to the third developing roller 13aC (developing roller facing the doctor blade 13cC), the second groove portion 132 is formed, and a coating layer such as CrN is formed on the roller surface, whereby the developing device Thus, the generation of abnormal images due to toner fixation can be reliably reduced while suppressing the cost increase of 13.

Furthermore, as shown in FIGS. 14 and 15, in the case of the developing device 13 having a plurality of developing rollers facing the doctor blade, among the plurality of developing rollers, the rotation direction (traveling direction) of the photosensitive drum 11. Thus, the second groove 132 can be formed only on the most downstream side of the developing roller, or a hard coating layer can be formed on the roller surface.
The developing device 13 of FIG. 14 is configured such that all of the three developing rollers 13aA to 13aC face the doctor blades 13cA, 13cB, and 13cC, respectively. For such a developing device 13, the second groove 132 is formed only in the third developing roller 13 a C that is the most downstream of the three developing rollers 13 a A to 13 a C, or a film such as CrN is formed on the roller surface. Or forming a layer. With such a configuration, toner sticking occurs on the surfaces of the two upstream development rollers 13aA and 13aB, and the photosensitive drum 11 is placed on the development areas (first development area and second development area). Therefore, background stains and density reduction occur in an image that is developed in a short time. However, toner adhesion is unlikely to occur on the surface of the most downstream third developing roller 13aC, and a good developing process is performed in the developing area (third developing area). And can compensate for the decrease in concentration. Therefore, as a result, it is possible to reduce the occurrence of background contamination and density reduction in the output image. As described above, compared to the case where the second groove portion 132 and the coating layer are provided on all of the three developing rollers 13aA to 13aC, it is possible to reduce the occurrence of an abnormal image due to toner fixation while suppressing the cost increase of the developing device 13. it can.

  Further, as shown in FIG. 15, the doctor blade is also provided for the developing device 13 configured such that two of the three developing rollers 13 aA to 13 aC are opposed to the doctor blades 13 cA and 13 cB. The second groove 132 can be formed only on the second developing roller 13aB which is the most downstream of the developing rollers 13aA and 13aB opposed to each other, or a hard coating layer can be formed on the roller surface. As a result, it is possible to reduce the occurrence of abnormal images due to toner fixation while suppressing an increase in the cost of the developing device 13.

  As described above, in the second embodiment, the second groove 132 is formed in addition to the first groove 131 on the surface of at least one of the plurality of developing rollers 13aA to 13aC, and the second groove Since the interval Sm 132 is optimized, the developer G can be transported well on the developing rollers 13aA to 13aC, and the developing rollers 13aA to 13aC have small fluctuations in the circumferential direction and the rotation axis direction. Toner sticking hardly occurs on the surfaces of the rollers 13aA to 13aC, and a good output image can be stably formed over time.

  In the second embodiment, the present invention is applied to the developing device 13 in which the three developing rollers 13aA to 13aC are installed. However, in the developing device in which two or four or more developing rollers are installed. Of course, the present invention is naturally applicable. And even if it is such a case, the effect similar to the effect in this Embodiment 2 mentioned above can be acquired.

  Furthermore, in each of the above embodiments, the present invention is applied to the developing device 13 in which the conveyance screw for conveying the developer in the longitudinal direction is installed. However, a conveyance paddle or the like for conveying the developer in the short direction is installed. Naturally, the present invention can also be applied to a developed developing device (for example, the developing device described in Patent Document 6). Even in such a case, the same effects as those of the above embodiments can be obtained.

  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.

  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, 13aA, 13aB, 13aC developing roller,
13c, 13cA, 13cB, 13cC Doctor blade (developer regulating member),
131 first groove,
132 second groove,
G developer (two-component developer), T toner, C carrier.

JP 2000-321864 A JP 2003-270923 A JP 2002-62725 A JP 2004-163906 A JP 2004-85630 A JP 2002-268382 A

Claims (12)

A developing device for containing a developer having a carrier and toner and developing a latent image formed on an image carrier,
A single or a plurality of developing rollers facing the image carrier and carrying a developer;
The first or the plurality of developing rollers are formed on the surface thereof so as to be along the rotation axis direction of the developing roller or / and to be inclined with respect to the rotation axis direction of the developing roller. Are provided at intervals in the circumferential direction of the developing roller,
At least one developing roller of the one or a plurality of developing rollers has a plurality of second grooves formed on the surface thereof along the circumferential direction of the developing roller at intervals in the rotation axis direction of the developing roller. Provided,
When the average interval in the rotation axis direction between the adjacent second groove portions is Sm, and the weight average particle diameter of the carrier is D,
Sm <D
A developing device characterized in that the following relationship is established.   2. The developing device according to claim 1, wherein the at least one developing roller in which the second groove portion is formed is formed such that a surface hardness thereof is larger than a hardness of the carrier.   3. The developing device according to claim 2, wherein the at least one developing roller in which the second groove portion is formed has a coating layer having a hardness larger than a hardness of the carrier on a surface thereof.   The developing device according to claim 3, wherein the coating layer is formed of any one of CrN, ZrN, and TiN.   The developing device according to claim 3, wherein the coating layer is formed by an ion plating method.   The developing device according to claim 3, wherein the coating layer is formed on a sleeve surface of the developing roller made of aluminum.   The developing device according to claim 1, wherein the at least one developing roller in which the second groove portion is formed is formed so that a surface thereof has conductivity.   The at least one developing roller in which the second groove is formed faces a developer regulating member that regulates the amount of developer carried on the developing roller. The developing device according to any one of the above.   The at least one developing roller in which the second groove portion is formed is configured to run the image carrier among a plurality of developing rollers facing a developer regulating member that regulates the amount of developer carried on the developing roller. The developing device according to claim 1, wherein the developing device is a single developing roller located on the most downstream side with respect to the direction.   2. The toner according to claim 1, wherein the toner has a weight average particle diameter of 5 to 10 [mu] m and a toner having a weight average particle diameter of 5 [mu] m or less in a range of 60 to 80% by number. The developing device according to claim 9. A process cartridge that is detachably installed on the main body of the image forming apparatus,
11. A process cartridge in which 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