JP5246544B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

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, a developing device containing a two-component developer (including a case where an additive or the like is added) composed of a toner and a carrier is provided. A technique is known in which a plurality of magnetic poles are formed around the substrate and a developing process is performed while the developer is carried on the developer carrying member (see, for example, Patent Document 1, Patent Document 2, 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 the developing roller (developer carrier) at the position of the pumping magnetic pole. The developer carried on the developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), and then the toner in the two-component developer becomes a main region that faces the photosensitive drum (image carrier). It adheres to the latent image on the photosensitive drum at the position of the magnetic pole. The developer that has passed through the region facing the photosensitive drum moves on the developing roller by the conveying magnetic pole, and then is separated from the developing roller at the position of the agent separating magnetic pole and returned to the developing device. A magnet is fixed inside the developing roller, and a plurality of magnetic poles such as a pumping magnetic pole, a main magnetic pole, a transporting magnetic pole, and an agent separating magnetic pole are formed around the developing roller by the magnet.

  In such a developing device, if the developer carried on the developing roller (developer carrying member) at the position of the agent separating magnetic pole is not sufficiently separated toward the developing device, the toner density decreases immediately after the developing process. There is a known problem that density unevenness occurs on the output image when the developed developer is carried on the developing roller by the pumping magnetic pole and used again in the developing process (for example, Patent Document 1, Patent). Reference 2 etc.). Such a problem becomes more prominent as the diameter of the developing roller is reduced as the image forming apparatus is downsized.

  In order to solve such a problem, in Patent Document 1 and the like, a gap (case gap) between the developing roller and the upper case (inner wall) is gradually increased from the upstream side toward the downstream side in the vicinity of the agent separating magnetic pole. A technique for configuring the device to spread is disclosed.

JP 2003-122127 A JP 2005-148366 A

The developing device described in Patent Document 1 and the like described above is configured so that the gap between the developer carrier and the upper case gradually increases from the upstream side toward the downstream side in the vicinity of the agent separation magnetic pole. The effect that the developer carried on the developer carrying member at the position of the separated magnetic pole is sufficiently separated toward the inside of the developing device can be expected to some extent.
However, since the developing device disclosed in Patent Document 1 is configured such that the gap between the developer carrier and the upper case widens from the upstream side toward the downstream side, the gap between the developer carrier and the upper case is large. Therefore, there is a high possibility that the toner is scattered from between the developer carrying member and the upper case without generating a stable suction air flow. Further, the magnetic brush by the developer becomes relatively high at the position of the upstream magnetic pole (agent separating pre-magnetic pole) adjacent to the agent separating magnetic pole, whereas the gap between the developer carrier and the upper case at this position is Since it is relatively narrow, there is a possibility that the developer is packed and a great stress is applied to the developer.
In particular, such a problem cannot be ignored as the speed of rotation of the developer carrier increases with the speed of the image forming apparatus.

  The present invention has been made to solve the above-described problems, and is a developing device in which toner scattering is reduced and the developer after the development process carried on the developer carrying member is reliably separated. Another object of the present invention is to provide a process cartridge and an image forming apparatus.

  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 carrier having a plurality of magnetic poles formed on the periphery thereof and a region facing the image carrier, the developer carrier being disposed on the downstream side in the rotation direction of the developer carrier, A case facing the developer carrier, and the case has a constant region in which a gap with the developer carrier is constant from the upstream side in the rotation direction to the downstream side in the rotation direction of the developer carrier, and Increasing regions where the gap with the developer carrier gradually increases from the upstream side in the rotation direction of the developer carrier to the downstream side in the rotation direction are alternately arranged from the upstream side in the rotation direction of the developer carrier. Formed A.

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the plurality of magnetic poles of the developer carrier release the developer carried on the developer carrier. An agent separating magnetic pole, an agent separating pre-magnetic pole formed on the upstream side in the rotation direction of the developer carrying member with respect to the agent separating magnetic pole, a main magnetic pole formed in a region facing the image carrier, One or a plurality of transport magnetic poles for transporting the developer from the position of the main magnetic pole toward the position of the agent separating pre-magnetic pole, and the case at a position corresponding to a part of the transport magnetic pole The first constant region is disposed on the upstream side in the rotation direction of the developer carrier closest to the main magnetic pole, and is located at a position corresponding to the remaining part of the transport magnetic pole and the first constant region. From the end of the region to the start position of the agent separating pre-pole The first gradually increasing region is disposed, and the second region is located at a position corresponding to a part of the agent separating pre-magnetic pole and beyond a peak position of the agent separating pre-magnetic pole from the end of the first gradually increasing region. The fixed region is disposed, and the second gradually increasing region is disposed from the end of the second constant region.

  According to a third aspect of the present invention, there is provided the developing device according to the second aspect, wherein the plurality of magnetic poles of the developer carrying member are rotated by the developer carrying member with respect to the agent separating magnetic pole. And a pumping magnetic pole that is disposed on the downstream side in the direction and pumps up the developer in the apparatus onto the developer carrying member, and the pumping magnetic pole has the same polarity as the polarity of the agent separating pre-magnetic pole. The agent separation magnetic pole is formed by the pumping magnetic pole and the agent separation pre-magnetic pole.

  According to a fourth aspect of the present invention, there is provided the developing device according to the third aspect, wherein the developer regulating member that regulates the amount of the developer carried on the developer carrying member is the pumping magnetic pole. It is arrange | positioned in position.

  According to a fifth aspect of the present invention, there is provided the developing device according to the third or fourth aspect, wherein the second constant region is the agent separating pre-magnetic pole from the end of the first gradually increasing region. It is arranged up to the half-value position exceeding the peak position.

  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 developer carrier has randomly formed oval dents on the surface thereof. It has been done.

  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 amount of the developer carried on the developer carrying member is regulated. A regulating member is provided below the developer carrying member, and the case is an upper case disposed above the developer carrying member.

  A process cartridge according to an eighth aspect of the present invention is a process cartridge which is detachably installed on the main body of the image forming apparatus, and the development according to any one of the first to seventh aspects. The apparatus 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, “process cartridge” means a charging unit (charging device) for charging an image carrier, a developing unit (developing device) for developing a latent image formed on the image carrier, and an image carrier. It is defined as a unit in which at least one of the cleaning unit (cleaning device) for cleaning the top and the image carrier are integrated and installed detachably with respect to the image forming apparatus main body.

  In the present invention, a constant region where the gap between the case and the developer carrier is constant and a gradually increasing region where the gap between the case and the developer carrier gradually increases from the upstream side to the downstream side are alternately formed. Therefore, it is possible to provide a developing device, a process cartridge, and an image forming apparatus in which toner scattering is reduced and the developer after the developing process carried on the developer carrying member is reliably separated.

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

First, the configuration and operation of the entire image forming apparatus will be described.
As shown in FIG. 1, four toner containers 32Y, 32M, 32C, and 32K corresponding to the respective colors (yellow, magenta, cyan, and black) are attached to and detached from the toner container accommodating portion 31 above the image forming apparatus main body 100. It is installed freely (changeable).
An intermediate transfer unit 15 is disposed below the toner container housing 31. Image forming portions 6Y, 6M, 6C, and 6K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8 of the intermediate transfer unit 15.
Below the toner containers 32Y, 32M, 32C, and 32K, toner replenishing devices 60Y, 60M, 60C, and 60K are disposed, respectively. The toners stored in the toner containers 32Y, 32M, 32C, and 32K are supplied (supplemented) into the developing devices of the image forming units 6Y, 6M, 6C, and 6K by the toner replenishing devices 60Y, 60M, 60C, and 60K, respectively. ) The four toner replenishing devices 60Y, 60M, 60C, and 60K have substantially the same structure except that the colors of toner used in the image forming process are different.

  Referring to FIG. 2, an image forming unit 6Y corresponding to yellow includes a photosensitive drum 1Y as an image carrier, a charging unit 4Y disposed around the photosensitive drum 1Y, and a developing device 5Y (developing unit). , A cleaning unit 2Y, a charge eliminating unit (not shown), and the like. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1Y, and a yellow image is formed on the photosensitive drum 1Y.

  The other three image forming units 6M, 6C, and 6K have substantially the same configuration as that of the image forming unit 6Y corresponding to yellow except that the color of the toner used is different. A corresponding image is formed. Hereinafter, description of the other three image forming units 6M, 6C, and 6K will be omitted as appropriate, and only the image forming unit 6Y corresponding to yellow will be described.

Referring to FIG. 2, a photosensitive drum 1Y as an image carrier is rotationally driven in a clockwise direction in FIG. 2 by a drive motor (not shown). Then, the surface of the photosensitive drum 1Y is uniformly charged at the position of the charging unit 4Y (a charging process).
After that, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure device 7 (see FIG. 1), and the electrostatic latent image corresponding to yellow by exposure scanning at this position. Is formed (this is an exposure step).

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the developing device 5Y, and the electrostatic latent image is developed at this position to form a yellow toner image (developing process).
Specifically, referring to FIGS. 2 and 3, a two-component developer G composed of toner and a carrier (magnetic carrier) is accommodated in the developing device 5Y. The developer G in the developing device 5Y is adjusted so that the toner concentration (the ratio of the toner in the developer G) detected by the magnetic sensor 56Y falls within a predetermined range. That is, according to the toner consumption in the developing device 5Y, the toner is replenished from the toner replenishing device 60Y into the second developer accommodating portion 54Y through the toner replenishing port 64Y. The toner replenishing device 60Y is connected to the toner container 32Y with reference to FIG. Although illustration is omitted, the toner replenishing device 60Y is stored in a drive unit that rotationally drives the toner container 32Y (toner bottle), a toner tank unit that stores toner discharged from the toner container 32Y, and a toner tank unit. A toner conveying section that conveys the toner toward the toner dropping path, a toner dropping path that causes the toner conveyed by the toner conveying section to fall by its own weight toward the developing device 5Y (second developer accommodating section 54Y), and the like. It is configured.

  Referring to FIGS. 2 and 3, the toner replenished in the second developer accommodating portion 54Y is then separated by the partition member while being mixed and stirred together with the developer G by the two transport screws 55Y. It circulates through the first developer accommodating portion 53Y and the second developer accommodating portion 54Y (circulation in the direction of the broken arrow in FIG. 3).

  Specifically, with reference to FIG. 3, the developer G in the first developer accommodating portion 53Y is transported from the right side to the left side by the transport screw 55Y. Thus, a first transport path for transporting the developer G along the longitudinal direction of the developing roller 51Y is formed. On the other hand, the developer G in the second developer accommodating portion 54Y is transported from the left side to the right side of the sheet by the transport screw 55Y. Thus, a second transport path for transporting the developer G in the direction opposite to the first transport path is formed.

  In addition, the first developer accommodating portion 53Y in which the first conveyance path is formed and the second developer accommodating portion 54Y in which the second conveyance path is formed are partitions arranged in regions excluding both longitudinal ends. It is isolated by the member and communicates at both longitudinal ends where no partition member is interposed. That is, the developer G conveyed in the first developer accommodating portion 53Y flows to the second developer accommodating portion 54Y side in the first communication portion A, and then the conveying screw of the second developer accommodating portion 54Y. It is conveyed by 55Y. The developer G conveyed in the second developer accommodating portion 54Y flows to the first developer accommodating portion 53Y side in the second communication portion B, and thereafter, is conveyed by the conveying screw 55Y of the first developer accommodating portion 53Y. Be transported. Thus, a developer G circulation path is formed between the two developer containing portions 53Y and 54Y.

Thus, the toner in the developer G circulating in the circulation path is attracted to the carrier by frictional charging with the carrier and is carried together with the carrier on the developing roller 51Y in which a plurality of magnetic poles are formed.
Here, referring to FIG. 3, the developing roller 51Y includes a magnet 51b that is fixed inside and forms a plurality of magnetic poles on the circumferential surface of the roller, and a sleeve 51a that rotates around the magnet 23a1. . Then, when the sleeve 51a rotates around the magnet 51b on which a plurality of magnetic poles are formed, the developer G moves on the developing roller 51Y (on the sleeve 51a) with the rotation.

  The developer G carried on the developing roller 51Y as the developer carrying member is conveyed with the rotation of the developing roller 51Y in the direction of the arrow, and reaches the position of the doctor blade 52Y as the developer regulating member. Then, after the developer G on the developing roller 51Y is regulated to an appropriate amount at this position, the developer G is conveyed to a position facing the photosensitive drum 1Y (developing area). The toner is attracted to the latent image formed on the photosensitive drum 1Y by the electric field (developing electric field) formed in the developing area.

  FIG. 4 shows a magnetic force distribution by a plurality of magnetic poles H1 to H6 formed around the developing roller 51Y (sleeve 51a) by the magnet 51b. As shown in FIG. 4, the plurality of magnetic poles convey the developer G from the position of the main magnetic pole H1 and the main magnetic pole H1 formed in the region facing the photosensitive drum 1Y toward the position of the agent separation pre-magnetic pole H4. Two transport magnetic poles H2 and H3 (a first transport magnetic pole H2 adjacent to the main magnetic pole H1 and a second transport magnetic pole H3 adjacent to the agent separation pre-magnetic pole H4), and the agent separation magnetic pole H5. The developer separation pre-magnetic pole H4 formed on the upstream side in the rotation direction of the developing roller 51Y, the agent separation magnetic pole H5 for releasing the developer G carried on the development roller 51Y, and the rotation of the developing roller 51Y with respect to the agent separation magnetic pole H5 The pumping magnetic pole H6 is disposed on the downstream side in the direction and pumps up the developer G in the developing device 5Y (first developer accommodating portion 53Y) onto the developing roller 51Y. Here, the pumping magnetic pole H6 is disposed at the position of the doctor blade 52Y installed below the developing roller 51Y, and has the same polarity as the agent separation pre-magnetic pole H4 (for example, the S pole). It is formed to become. The agent separation magnetic pole H5 is formed with a magnetic force that eliminates the holding force with respect to the developer G by the pumping magnetic pole H6 and the agent separation pre-magnetic pole H4 formed in the same polarity. Thus, in the present embodiment, only the pumping magnetic pole H6 is formed between the agent separation magnetic pole H5 and the main magnetic pole H1, and the diameter of the developing roller 51Y is reduced.

  First, the pumping magnetic pole H6 acts on a carrier as a magnetic body, and the developer G accommodated in the developer accommodating portion 53Y is carried on the developing roller 51Y. Part of the developer G carried on the developing roller 51Y is scraped off at the position of the doctor blade 52Y (developer regulating member) and returned to the developer containing portion 53Y. On the other hand, the developer G carried on the developing roller 51Y after passing through the doctor gap between the doctor blade 52Y and the developing roller 51Y rises at the position of the main magnetic pole H1 and becomes a magnetic brush in the developing area. Touching the drum 1Y. Thus, the toner in the developer G carried on the developing roller 51Y adheres to the latent image on the photosensitive drum 1Y. Thereafter, the developer G (toner concentration is low) that has passed through the position of the main magnetic pole H1 is transported to the position of the agent separation pre-magnetic pole H4 by the first transport magnetic pole H2 and the second transport magnetic pole H3. Then, the developer G after the development process carried on the developing roller 51Y passes through the position of the agent separating pre-magnetic pole H4 and is detached from the developing roller 51Y at the position of the agent separating magnetic pole H5. The detached developer G is returned again to the developer container 53Y and circulates in the developer containers 53Y and 54Y. Such a flow of the developer G is repeated.

In the present embodiment, although not shown, oval dents are randomly formed on the surface of the developing roller 51Y (sleeve 51a).
Specifically, the random oval shaped dent causes the surface of the sleeve 51a to collide with a medium made of a relatively large cut wire (a metal wire cut into a short length) in the same manner as the sandblasting method. Formed by. As described above, by forming many random elliptical dents on the surface of the developing roller 51Y, irregularities with a rough pitch are formed on the surface of the developing roller 51Y. For this reason, solid developer spikes are formed on the surface of the developing roller 51Y by the dents that are difficult for the developer to slip. Further, these dents are not easily worn, and a stable and good output image without image unevenness can be obtained over a long period of time.

  Note that the toner used in the present embodiment (the toner in the developer or the toner contained in the toner container) is at least a polyester prepolymer having a functional group containing a nitrogen atom, a polyester, a colorant, The toner material liquid in which a release agent is dispersed in an organic solvent is obtained by crosslinking and / or elongation reaction in an aqueous solvent. The pulverized toner has a broad particle size distribution. For this reason, a method for realizing high image quality by increasing the circularity of the toner by a polymerization method or the like and by making the particle size distribution sharp is becoming common. In the toner according to the present embodiment, a toner composition including at least a prepolymer, a colorant, and a release agent is dispersed in an aqueous medium in the presence of resin fine particles, and the toner composition is subjected to a polyaddition reaction. This is a polymerized toner obtained. By using such a toner, there is no pulverization step, resource saving can be achieved, and effects such as a sharp particle size distribution and charge distribution can be obtained.

The carrier in the developer G used in the present embodiment is formed so that the weight average particle diameter is 20 to 65 μm. When the weight average particle diameter of the carrier is less than 20 μm, the uniformity of the toner particles adhering to the carrier is lowered and carrier adhesion is likely to occur. On the other hand, if the weight average particle diameter of the carrier exceeds 65 μm, the reproducibility of the image details is lowered and it becomes difficult to obtain a fine image. The weight average particle diameter of the carrier can be measured using a “Microtrac particle size analyzer (SRA type)” (manufactured by Nikkiso Co., Ltd.) with a range setting of 0.7 to 125 μm. At this time, methanol is used as a solvent for the dispersion liquid, and the refractive index is set to 1.33, and the refractive indexes of the carrier and the core material are set to 2.42.
The carrier in the present embodiment has a resin coat film on the magnetic core material, and the resin coat film is a resin component obtained by crosslinking a thermoplastic resin such as acrylic and a melamine resin. In which a charge adjusting agent is contained. By using a magnetic carrier, the impact can be absorbed to prevent film scraping, and large toner particles can be held with a strong adhesive force. Furthermore, it is possible to achieve both balance between preventing the impact on the coating film and cleaning the spent object. That is, the carrier film is prevented from being scraped and spent, thereby extending the life of the carrier.

Referring to FIG. 2, after the development process described above, the surface of photoreceptor drum 1Y reaches a position facing intermediate transfer belt 8 and first transfer bias roller 9Y, and on this surface of photoreceptor drum 1Y. The toner image is transferred onto the intermediate transfer belt 8 (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.
Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the cleaning unit 2Y, and untransferred toner remaining on the photosensitive drum 1Y at this position is mechanically collected by the cleaning blade 2a (in the cleaning process). is there.).
Finally, the surface of the photosensitive drum 1Y reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1Y is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

The image forming process described above is performed in the other image forming units 6M, 6C, and 6K in the same manner as the yellow image forming unit 6Y. That is, the laser beam L based on the image information is emitted from the exposure unit 7 disposed below the image forming unit onto the photosensitive drums of the image forming units 6M, 6C, and 6K. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven.
Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 1, the intermediate transfer unit 15 includes an intermediate transfer belt 8, four primary transfer bias rollers 9Y, 9M, 9C, 9K, a secondary transfer backup roller 12, a plurality of tension rollers, and an intermediate transfer. It consists of a cleaning unit, etc. The intermediate transfer belt 8 is stretched and supported by a plurality of roller members, and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 8.

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 8 are transferred onto a recording medium P such as transfer paper conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of an intermediate transfer cleaning unit (not shown). At this position, the untransferred toner on the intermediate transfer belt 8 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from a paper feeding unit 26 disposed below the apparatus main body 100 via a paper feeding roller 27, a registration roller pair 28, and the like. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the rollers of the registration roller pair 28.

  The recording medium P transported to the registration roller pair 28 temporarily stops at the position of the roller nip of the registration roller pair 28 whose rotation drive has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred to the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt and the pressure roller.
Thereafter, the recording medium P is discharged to the outside of the apparatus through the rollers of the discharge roller pair 29. The recording media P discharged to the outside of the apparatus by the discharge roller pair 29 are sequentially stacked on the stack unit 30 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Hereinafter, the configuration and operation of the developing device 5Y, which are characteristic in the present embodiment, will be described in detail with reference to FIGS.
Referring to FIG. 4, the developing roller 51Y is located above the developing roller 51Y (developer carrying member) and downstream of the developing roller 51Y in the rotation direction with respect to the area facing the photosensitive drum 1Y (image carrying member). An upper case 57Y is installed as a case facing the roller 51Y.
Here, the upper case 57Y (case) in the present embodiment has a gap N with the developing roller 51Y (hereinafter referred to as “case gap” as appropriate) from the upstream side in the rotational direction of the developing roller 51Y to the downstream side in the rotational direction. The constant regions M1 and M3 that are constant over time, and the gradually increasing regions M2 and M4 in which the case gap N gradually increases from the upstream side in the rotational direction of the developing roller 51Y to the downstream side in the rotational direction, alternately from the upstream side in the rotational direction of the developing roller 51Y It is formed to be disposed. That is, from the upstream side, the constant region and the gradually increasing region are alternately formed in the order of the first constant region M1, the first gradually increasing region M2, the second constant region M3, and the second gradually increasing region M4. .

More specifically, a first constant region M1 is disposed at a position corresponding to a part of the transport magnetic poles H2 and H3 and upstream in the rotation direction of the developing roller 51Y closest to the main magnetic pole H1, and the transport magnetic poles H2 and H3. The first gradually increasing region M2 is disposed from the end of the first constant region M1 to the starting end position of the agent separation pre-magnetic pole H4, and corresponds to a part of the agent separation pre-magnetic pole H4. The second constant region M3 is disposed from the end of the first gradually increasing region M2 to the position beyond the peak position H4a of the agent separation pre-magnetic pole H4, and the end of the second constant region M3. The upper case 57Y is formed so that the second gradually increasing region M4 is disposed.
In other words, a first constant region M1 in which the case gap N is constant is formed from the entrance (uppermost stream side) of the upper case 57Y to a predetermined position (near the upstream of the second transport magnetic pole H3). . A first gradually increasing region M2 in which the case gap N gradually increases from the upstream side to the downstream side is formed from the upstream vicinity of the second transport magnetic pole H3 to the terminal position (starting position of the agent separation pre-magnetic pole H4). A second constant region M3 in which the case gap N is constant is formed from the starting end position of the agent separation pre-magnetic pole H4 to a position beyond the peak position H4a. Finally, a second gradually increasing region M4 is formed in which the case gap N gradually increases from the upstream side to the downstream side from the position beyond the peak position H4a of the agent separation pre-magnetic pole H4.

FIG. 5 is a graph showing the relationship between the case gap N (or the constant regions M1 and M3 and the gradually increasing regions M2 and M4) and the magnetic poles H2 to H5.
In FIG. 5, the horizontal axis indicates the positions of the first transport magnetic pole H2, the second transport magnetic pole H3, the agent separation pre-magnetic pole H4, and the agent separation magnetic pole H5, the left vertical axis indicates the case gap N, and the right vertical axis indicates the magnetic pole. Showing magnetic force. In FIG. 5, the solid curve indicates the magnetic force distribution (corresponding to the right vertical axis) of each of the magnetic poles H2 to H5 described above, and the broken line S corresponds to the case gap N (left vertical axis) in the present embodiment. ) Fluctuations. A two-dot chain line Q0 indicates a variation of the case gap N in a conventional developing device (the case gap N is constant and can be referred to FIG. 7), and a one-dot chain line Q1 is a developing device disclosed in Patent Document 1 or the like. The variation of the case gap N in (the case gap N gradually increases after passing through a certain region and can be referred to FIG. 8) is shown.
Specifically, in the present embodiment, the case gap N in the first constant region M1 is set to 1.5 mm, and the case gap N in the first gradually increasing region M2 is 3 mm from 1.5 mm (upstream side). It is set to gradually increase (downstream), the case gap N in the second constant region M3 is set to 3 mm, and the case gap N in the second gradually increasing region M4 is 5 mm from 3 mm (upstream side). It is set to gradually increase (downstream).

With such a configuration, first, a suction air flow is generated between the upper case 57Y and the developing roller 51Y at the position of the first constant region M1. That is, the first constant region M1 is a suction region that sucks air into the developing device 5Y.
Then, at the position of the first gradually increasing region M2, the case gap N gradually increases so as to match the developer (magnetic brush) whose height gradually increases toward the position of the agent separation pre-magnetic pole H4. A problem that a large stress is applied to the developer in a state where the developer is packed is prevented.
Further, since the case gap N becomes constant again at the position of the second constant region M3, the suction air flow generated at the position of the first constant region M1 can be drawn into the developing device 5Y. That is, the suction airflow generated between the upper case 57Y and the developing roller 51Y is maintained, and the toner is less likely to be scattered from between the upper case 57Y and the developing roller 51Y toward the outside of the developing device 5Y.
At the position of the second gradually increasing region M4, the case gap N gradually increases so as to match the behavior of the developer that gradually starts to be separated from the developing roller 51Y toward the agent separating magnetic pole H5. The developer that has separated from the developing roller 51Y is likely to drop toward the partition member side (the left side in FIG. 4) of the developer containing portion 53Y, and the developer immediately after having separated from the developing roller 51Y is pumped up by the magnetic pole H6. This prevents the problem of being carried again on the developing roller 51Y. That is, the developer detachability from the developing roller 51Y is improved.
In summary, by using the upper case 57Y in the present embodiment, toner scattering from between the upper case 57Y and the developing roller 51Y is reduced, and the developer after the developing process carried on the developing roller 51Y. The problem that G is surely separated and density unevenness occurs on the output image is suppressed. Furthermore, a problem that a large stress is applied to the developer between the upper case 57Y and the developing roller 51Y and the deterioration of the developer is accelerated is suppressed.

Here, referring to FIG. 4, the second constant region M3 is disposed from the end of the first gradually increasing region M2 to the half-value position H4b beyond the peak position H4a of the agent separation pre-magnetic pole H4. That is, the terminal position of the second constant region M3 is disposed between the peak position H4a of the agent separation pre-magnetic pole H4 and the half-value position H4b on the downstream side of the agent separation pre-magnetic pole H4. Here, the “peak position H4a of the agent separation pre-magnetic pole H4” is a position where the magnetic force in the normal direction of the agent separation pre-magnetic pole H4 is maximum, and the “half-value position H4b of the agent separation pre-magnetic pole H4” This is the position at which the magnetic force in the normal direction of the separated pre-magnetic pole H4 becomes half of the maximum value.
The developer carried on the developing roller 51Y starts to be actively separated from the developing roller 51Y from the time when it passes through the half-value position H4b on the downstream side of the agent separating pre-magnetic pole H4. By gradually increasing the case gap N from the front position, the developer can be efficiently separated from the developing roller 51Y.

In order to confirm the above-described effect, the inventor of the present application prepares three developing devices having different case gaps N and performs a running test for a predetermined time for each of them, (1) density unevenness of the output image, (2) An experiment was conducted to confirm the degree of toner scattering from the upper case and (3) the ability of the developer to be pumped onto the developing roller 51Y. FIG. 6 is a table showing the experimental conditions and experimental results.
Referring to FIG. 6, in the example, developing device 5Y in the present embodiment is used. In the embodiment, the case gap N in the first constant region M1 is 1.5 mm, and the case gap N in the first gradually increasing region M2 is gradually increased from 1.5 mm (upstream side) to 3 mm (downstream side). The case gap N in the second constant region M3 was set to 3 mm, and the case gap N in the second gradually increasing region M4 was set to gradually increase from 3 mm (upstream side) to 5 mm (downstream side).
In Comparative Example 1, the developing device 500Y shown in FIG. 7 was used. In Comparative Example 1, the case gap N between the developing roller 51Y and the upper case 570Y was set to be constant (1.5 mm).
In Comparative Example 2, the developing device 501Y shown in FIG. 8 was used. In Comparative Example 1, the case gap N between the developing roller 51Y and the upper case 571Y is constant (1.5 mm) on the upstream side, and then gradually increases from 1.5 mm (upstream side) to 5 mm (downstream side). Set to do.
As a result, in Comparative Example 1, density unevenness due to defective agent separation occurred on the output image and toner scattering occurred, and in Comparative Example 2, the generation of suction airflow was insufficient and a large amount of toner scattering occurred. On the other hand, in the example, the separation of the agent from the developing roller 51Y was good, there was no density unevenness on the output image, and there was almost no toner scattering. In addition, the pumping property of the developer onto the developing roller 51Y was good in all of Example, Comparative Example 1, and Comparative Example 2.

  As described above, in the present embodiment, the constant regions M1 and M3 in which the gap N between the upper case 57Y (case) and the developing roller 51Y (developer carrier) is constant, the upper case 57Y and the developing roller 51Y. The gap N is gradually increased from the upstream side to the downstream side, so that the toner scattering is reduced and the development after the development process carried on the development roller 51Y is reduced. The agent G can be reliably released.

  In the present embodiment, some or all of the image forming units 6Y, 6M, 6C, and 6K may be a process cartridge. Even in that case, the same effects as those of the present embodiment described above can be obtained.

In the present embodiment, the upper case 57Y is formed of one member and the case gap N is formed between the upper case 57Y and the developing roller 51Y. However, the upper case 57Y is formed of a plurality of members and the developing roller 51Y is formed. A case gap N can be formed between the two. For example, the fixed areas M1 and M3 and the gradually increasing areas M2 and M4 can be formed by appropriately depositing the inner wall surface of the upper case with another member. The upper case formed of a plurality of members is also one upper case, and the “case (upper case)” in the present application refers to all the gaps N that can form the gap N as described above facing the developing roller. It shall mean a member.
In the present embodiment, two transport magnetic poles H2 and H3 for transporting the developer from the position of the main magnetic pole H1 to the position of the agent separation pre-magnetic pole H4 are provided. However, the number of transport magnetic poles may be one. There may be three or more.

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

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. FIG. 4 is a cross-sectional view of the developing device and the photosensitive drum as viewed from above. It is the elements on larger scale which show the neighborhood of a development roller and an upper case. It is a graph which shows the relationship between a case gap and a magnetic pole. It is a table | surface figure which shows an experimental condition and an experimental result. FIG. 4 is a diagram illustrating a part of a developing device of Comparative Example 1; FIG. 10 is a diagram illustrating a part of a developing device of Comparative Example 2.

Explanation of symbols

1Y photosensitive drum (image carrier),
5Y developing device,
51Y developing roller (developer carrier),
52Y Doctor blade (developer regulating member),
57Y Upper case (case),
100 Image forming apparatus body (apparatus body),
H1 main magnetic pole, H2 first transport magnetic pole, H3 second transport magnetic pole,
H4 agent separation pre-magnetic pole, H5 agent separation magnetic pole, H6 pumping magnetic pole,
M1 first constant region, M2 first incremental region,
M3 second constant region, M4 second incremental region,
N gap (case gap).

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 having a plurality of magnetic poles formed around it;
A case disposed on the downstream side in the rotation direction of the developer carrier relative to a region facing the image carrier, and facing the developer carrier;
With
In the case, the gap between the developer carrier and a constant region where the gap with the developer carrier is constant from the upstream side in the rotation direction to the downstream side in the rotation direction of the developer carrier and the gap between the developer carrier and the developer carrier. And a gradually increasing region that gradually increases from the upstream side in the rotational direction to the downstream side in the rotational direction. The developing device is formed so as to be alternately arranged from the upstream side in the rotational direction of the developer carrier. The plurality of magnetic poles of the developer carrier are:
An agent separating magnetic pole for separating the developer carried on the developer carrying member;
An agent separation pre-magnetic pole formed on the upstream side in the rotation direction of the developer carrier relative to the agent separation magnetic pole;
A main magnetic pole formed in a region facing the image carrier;
One or a plurality of transport magnetic poles for transporting the developer from the position of the main magnetic pole toward the position of the agent separation pre-magnetic pole;
Comprising
In the case, the first constant region is disposed at a position corresponding to a part of the transport magnetic pole and upstream in the rotation direction of the developer carrier closest to the main magnetic pole, and the remaining of the transport magnetic pole The first gradually increasing region is disposed from a terminal end of the first constant region to a starting end position of the agent separation pre-magnetic pole, and corresponds to a part of the agent separation pre-magnetic pole. The second constant region is disposed from the end of the first gradually increasing region to a position beyond the peak position of the pre-agent separating magnetic pole, and from the end of the second constant region to the second The developing device according to claim 1, wherein the gradually increasing area is disposed. The plurality of magnetic poles of the developer carrier are disposed on the downstream side in the rotation direction of the developer carrier with respect to the agent separation magnetic pole, and the developer in the apparatus is pumped onto the developer carrier. It further has a pumping magnetic pole,
The pumping magnetic pole is formed to have the same polarity as the polarity of the agent separating pre-magnetic pole,
The developing device according to claim 2, wherein the agent separation magnetic pole is formed by the pumping magnetic pole and the agent separation pre-magnetic pole.   4. The developing device according to claim 3, wherein a developer regulating member that regulates the amount of the developer carried on the developer carrying member is disposed at the position of the pumping magnetic pole.   The said 2nd fixed area | region was arrange | positioned from the terminal of the said 1st gradually increasing area | region to the half value position beyond the peak position of the said agent separation pre magnetic pole, The Claim 3 or Claim 4 characterized by the above-mentioned. Development device.   The developing device according to claim 1, wherein the developer carrying member has randomly formed oval dents on the surface thereof. A developer regulating member for regulating the amount of developer carried on the developer carrying body is provided below the developer carrying body,
The developing device according to claim 1, wherein the case is an upper case disposed above the developer carrying member. A process cartridge that is detachably attached to the image forming apparatus main body,
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.

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