JP2016066057A - Development device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a structure for stabilizing coat property of a developer to a development sleeve 44, and suppressing fall of the developer to an agitation chamber 41b.SOLUTION: A partition wall 41c for partitioning a development chamber 41a and an agitation chamber 41b is extended to a position lower relative to an upper end position of a zero gaussian zone whose apex position 47a is between a magnetic pole N2 and a magnetic pole N3 and magnetic force is almost 0, between a development sleeve 44 and a first transport screw 42. The development sleeve 44 has plural grooves 48 on its surface with intervals. The plural grooves 48 have an opening shape in which, the maximum diameter of an internal contact circle is equal to or more than the diameter of carrier average grain diameter, and the carrier of the average grain diameter can enter the grooves 48 by depth of radius of the carrier or more depth.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier by an electrophotographic system, an electrostatic recording system, or the like to form a visible image.

  Conventionally, in an image forming apparatus using an electrophotographic system, an electrostatic latent image formed on an image carrier such as a photosensitive drum by a developing device is developed with toner. As such a developing device, a vertical stirring function separation type in which a first chamber for supplying a developer to a developing sleeve as a developer carrying member and a second chamber for collecting the developer from the developing sleeve are arranged vertically. The configuration is known. In this configuration, the first chamber and the second chamber are partitioned by a partition wall, and the first chamber and the second chamber are communicated with each other by a pair of communication portions formed in the partition wall. And the second chamber are circulated (see, for example, Patent Document 1).

JP-A-5-333691

  Here, in the vertical agitation function separation type developing device as shown in Patent Document 1, the developer surface of the developer in the first chamber becomes lower toward the communication portion that sends the developer from the first chamber to the second chamber. . Then, the coating property of the developer tends to become unstable, such as unevenness in the developer coated on the developing sleeve. Therefore, it is conceivable that the peak of the partition located between the developing sleeve and the conveying screw is lowered so that the developer can be easily supplied to the developer even at the position where the surface of the developer is lowered.

  However, in the case of the vertical stirring function separation type configuration, the repulsion pole for peeling the developer from the developing sleeve in order to collect the developer from the developing sleeve to the second chamber is easily disposed adjacent to the conveying screw in the substantially horizontal direction. Become. For this reason, when the top of the partition wall is lowered as described above, a region where the magnetic force existing between the repulsive poles is zero is easily located near the position where the developer is supplied from the first chamber to the developing sleeve. Become. In this case, the developer supplied from the first chamber to the developing sleeve is easy to fall without being carried on the developing sleeve. When the developer falls in this way, the developer tends to accumulate in the lower chamber, which is the second chamber. As a result, there is a possibility that the developer in the second chamber is rotated by the developing sleeve and the coating property of the developer on the developing sleeve becomes unstable. Further, there is a possibility that the developer on the developing sleeve cannot be sufficiently taken into the second chamber and the developer overflows.

  In view of such circumstances, the present invention was invented to realize a configuration in which the developer does not easily fall into the second chamber while stabilizing the coatability of the developer on the developer carrying member.

  In the present invention, a developer containing a non-magnetic toner and a carrier having magnetism is carried on a surface and conveyed to develop a latent image, and a developer is accommodated and developed on the developer carrier. A first chamber for supplying a developer; a recovery path that is disposed below the first chamber and collects the developed developer carried on the developer carrier without passing through the first chamber; A second chamber forming a circulation path for circulating the developer between the first chamber, a developing container having a partition partitioning the first chamber and the second chamber, and a center of the first chamber; Is disposed between the upper end and the lower end of the developer carrying member to convey the developer, and the second conveying member is disposed in the second chamber to convey the developer. A regulating member for regulating the amount of the developer carried on the developer carrying body, and a position facing the regulating member. Alternatively, the peak position of the magnetic force is higher than the center of the developer carrier and upstream of the developer carrier in the transport direction of the developer carrier, and the center of the developer carrier and the center of the first transport member. A first magnetic pole disposed downstream of the connecting line in the transport direction; adjacent to the upstream of the first magnetic pole in the transport direction; a peak position of magnetic force is below the center of the developer carrier; and A second magnetic pole having the same polarity as the first magnetic pole and disposed upstream of the line connecting the center of the developer carrier and the center of the second transport member, A multi-pole magnet disposed inside the developer carrier, and the partition wall is located between the developer carrier and the first transport member, and the apex position is between the first magnetic pole and the first carrier member. Than the top position of the zero gauss band where the magnetic force between the second magnetic pole is almost zero The developer carrying member has a plurality of recesses formed on the surface thereof at intervals, and the plurality of recesses have a maximum diameter of an inscribed circle and a diameter of an average particle diameter of the carrier. In the developing device, the carrier having an opening shape as described above is formed so that a carrier having an average particle diameter can enter the concave portion more than its radius.

  According to the present invention, the top of the partition is positioned below the upper end position of the zero gauss band where the magnetic force between the first magnetic pole and the second magnetic pole is substantially zero, so that the developer supplied to the developer carrier Can be increased. Further, since the distance between the first magnetic pole and the second magnetic pole is wide, the region where the magnetic force is almost zero is widened, the developer stripping property is improved, and the developer is brought to the developer carrier. Can be suppressed. As a result, the coatability of the developer on the developer carrying member can be stabilized. Further, the surface of the developer carrying member has an opening shape in which the maximum diameter of the inscribed circle is equal to or larger than the diameter of the average particle diameter of the carrier, and there are a plurality of recesses into which the carrier with the average particle diameter can enter more than the radius. Since it is formed, it is easy to restrain the developer on the developer carrying member. Thus, even if a large amount of developer is supplied from the first chamber to the developer carrier, the developer is unlikely to fall into the second chamber.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic cross-sectional view of a developing device according to a first embodiment. 1 is a schematic longitudinal sectional view of a developing device according to a first embodiment. 2A is a plan view of the developing sleeve according to the first embodiment, FIG. 2B is an enlarged cross-sectional view of a part of the developing sleeve, and FIG. 2C is a schematic diagram illustrating a state where a carrier enters the groove. 2 is a schematic cross-sectional view of a developing device according to Comparative Example 1. FIG. FIG. 6 is a schematic cross-sectional view of a developing device according to Comparative Example 2. The figure which shows the relationship between the surface roughness of a developing sleeve, and the number of image formation. FIG. 5 is a schematic cross-sectional view of a developing device according to a second embodiment of the present invention. FIG. 10 is a schematic cross-sectional view of a developing device according to Comparative Example 3. FIG. 10 is a schematic cross-sectional view of a developing device according to Comparative Example 4; The top view which shows (a) 1st example, (b) 2nd example, (c) 3rd example, (d) 4th example of the developing sleeve which concerns on other embodiment of this invention.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG.

[Image forming apparatus]
The image forming apparatus 100 is an electrophotographic full-color printer including four image forming stations (image forming units) Y, M, C, and K. The image forming apparatus 100 generates a toner image (image) in accordance with an image signal from a document reading device (not shown) connected to the apparatus main body or a host device such as a personal computer connected to the apparatus main body so as to be communicable. It is formed on the recording material P. Examples of the recording material include sheet materials such as paper, plastic film, and cloth. The image forming stations Y, M, C, and K form toner images of yellow, magenta, cyan, and black, respectively.

  The four image forming stations Y, M, C, and K included in the image forming apparatus 100 have substantially the same configuration except that the development colors are different. Therefore, first, the configuration of the yellow image forming station Y will be described as a representative.

  In the image forming station, a cylindrical photosensitive member, that is, a photosensitive drum 1a is provided as an image carrier. The photosensitive drum 1a is rotationally driven in the direction of arrow R1 in the figure. Around the photosensitive drum 1a, a charging device (charging roller) 2a as a charging unit, a developing device 4a, a primary transfer roller 5a as a transfer unit, and a cleaning device 6a as a cleaning unit are arranged. A laser scanner (exposure device) 3a as an exposure unit is disposed above the photosensitive drum 1a in the drawing.

  Below each image forming station in FIG. 1, an endless intermediate transfer belt 7 is provided as an intermediate transfer member. The intermediate transfer belt 7 is pressed from the back side thereof by primary transfer rollers 5a, 5b, 5c, and 5d, and the surface thereof is brought into contact with the photosensitive drums 1a, 1b, 1c, and 1d. The intermediate transfer belt 7 rotates in the direction of arrow R7 as the secondary transfer counter roller 8 also serving as a driving roller rotates in the direction of arrow R8. The rotation speed of the intermediate transfer belt 7 is set to be approximately the same as the rotation speed (process speed) of each of the photosensitive drums 1a, 1b, 1c, and 1d.

  A secondary transfer roller (secondary transfer means) 9 is disposed at a position corresponding to the secondary transfer counter roller 8 on the surface of the intermediate transfer belt 7. The secondary transfer roller 9 holds an intermediate transfer belt 7 between the secondary transfer counter roller 8 and a secondary transfer nip (secondary transfer) between the secondary transfer roller 9 and the intermediate transfer belt 7. A transfer portion) is formed.

  The recording material P to be used for image formation is stored in a state of being loaded on the cassette 10. The recording material P is supplied to the above-described secondary transfer nip portion by a feeding / conveying device (all not shown) having a paper feeding roller, a conveying roller, a registration roller, and the like. On the downstream side of the secondary transfer nip portion along the conveyance direction of the recording material P, a fixing device 11 having a fixing roller 12 and a pressure roller 13 pressed against the fixing roller 12 is disposed. A discharge tray (not shown) is disposed on the downstream side of the apparatus 11.

  A process for forming, for example, a four-color full-color image by the image forming apparatus 100 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 1a is uniformly charged by the charging device 2a. Next, the photosensitive drum 1a is exposed with a laser beam corresponding to an image signal emitted from the exposure device 3a. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1a (on the image carrier). The electrostatic latent image on the photosensitive drum 1a is visualized by toner stored in the developing device 4a to become a visible image. In this embodiment, a reversal development method is used in which toner is attached to the bright portion potential exposed by laser light.

  The toner image formed on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 7 at a primary transfer portion formed between the toner image and the primary transfer roller 5a disposed with the intermediate transfer belt 7 interposed therebetween. At this time, a primary transfer bias is applied to the primary transfer roller 5a. Toner remaining on the surface of the photosensitive drum 1a after the primary transfer (transfer residual toner) is removed by the cleaning device 6a. The photosensitive drum 1a from which the transfer residual toner has been removed is used for the next image formation.

  Such an operation is sequentially performed at each of the yellow, magenta, cyan, and black image forming stations, and the four color toner images are superimposed on the intermediate transfer belt 7. That is, similarly to the image forming station Y described above, toner images of respective colors are formed on the respective photosensitive drums 1b, 1c, and 1d. Then, the toner images of the respective colors are sequentially transferred on the intermediate transfer belt 7. Note that the subscripts a, b, c, and d indicating the configuration of each image forming station indicate the configurations of the image forming stations of yellow, magenta, cyan, and black, respectively.

  Thereafter, the recording material P accommodated in the cassette 10 is conveyed by the secondary transfer unit in accordance with the toner image formation timing. Then, by applying a secondary transfer bias to the secondary transfer roller 9, the four color toner images on the intermediate transfer belt 7 are secondarily transferred onto the recording material P all at once. The toner remaining on the intermediate transfer belt 7 without being completely transferred at the secondary transfer portion is removed by the intermediate transfer belt cleaner 14.

  Next, the recording material P is conveyed to a fixing device 11 as a fixing unit. Then, the recording material P on which the toner image has been transferred is passed through the fixing nip formed by the fixing roller 12 and the pressure roller 13, whereby the recording material P is heated and pressurized. The toner on the recording material P is melted and mixed to be fixed on the recording material P as a full-color image. Thereafter, the recording material P is discharged to a discharge tray. This completes a series of image forming processes. Note that it is also possible to form a single color or a plurality of colors of a desired color using only a desired image forming unit.

[Developer]
Next, the developing device 4a will be described with reference to FIGS. Since the developing devices of the image forming stations of the present embodiment have the same configuration, the following description is the same for the developing devices 4b, 4c, and 4d. 2 is a schematic cross-sectional view of the developing device 4a cut in a direction perpendicular to the rotation axis direction of the developing sleeve 44, which will be described later, and FIG. 3 is a schematic vertical cross-sectional view cut along the rotation axis direction of the developing sleeve 44. FIG.

  The developing device 4a includes a developing container 41, and a two-component developer containing a nonmagnetic toner and a magnetic carrier as a developer is accommodated in the developing container 41. Here, the developer will be described. In this embodiment, a two-component developing method is used as a developing method, and a nonmagnetic toner and a magnetic carrier are mixed and used as a developer. The non-magnetic toner is obtained by encapsulating a colorant, a wax component and the like in a resin such as polyester or styrene acryl, and pulverizing or polymerizing the powder. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder.

  Further, the developing container 41 has a developing sleeve 44 as a developer carrying member and a regulating blade 46 as a regulating member that regulates the ears of the developer carried on the developing sleeve 44. The developing sleeve 44 is made of a nonmagnetic material such as aluminum or stainless steel, is rotatably supported with respect to the developing container 41, and is driven to rotate in the direction of the arrow in FIG. Inside the developing sleeve 44, a magnet roller 45 as a multipolar magnet is installed in a non-rotating state.

  In this embodiment, the inside of the developing container 41 is divided into a developing chamber 41a as a first chamber and an agitating chamber 41b as a second chamber by a partition wall 41c whose substantially central portion extends in a direction perpendicular to the paper surface of FIG. It is partitioned. That is, the developing chamber 41a and the stirring chamber 41b are partitioned by the partition wall 41c. In the developing device 4a of the present embodiment, the stirring chamber 41b has a vertical stirring type structure arranged below the developing chamber 41a, and the developer is accommodated in the developing chamber 41a and the stirring chamber 41b, respectively. As shown in FIG. 3, openings 41d and 41e are provided at both ends in the axial direction of the developing sleeve 44 of the partition wall 41c so as to communicate the developing chamber 41a and the stirring chamber 41b. Further, a rising portion 47 that rises upward is formed on the side of the developing sleeve 44 of the partition wall 41c. The rising portion 47 is positioned between the developing sleeve 44 and the first conveying screw 42 described below. doing.

  A first conveying screw 42 as a first conveying member that conveys the developer while stirring the developer chamber 41a, and a second conveying member as a second conveying member that conveys the developer while stirring the developer chamber 41b. Screws 43 are respectively arranged. The first conveying screw 42 is disposed substantially in parallel along the axial direction of the developing sleeve 44 at the bottom of the developing chamber 41a, and rotates in the direction of the arrow (clockwise direction) in FIG. 2 to develop the developing chamber 41a. The agent is conveyed in one direction along the axial direction. The reason for the clockwise rotation is that it is advantageous from the viewpoint of supplying the developer to the developing sleeve 44. Further, the first conveying screw 42 is disposed so that the center thereof is located between the upper end and the lower end of the developing sleeve 44. In the present embodiment, the first conveying screw 42 is disposed adjacent to the developing sleeve 44 in a substantially horizontal direction. In addition, the second conveying screw 43 is disposed substantially in parallel with the first conveying screw 42 at the bottom of the stirring chamber 41b, and rotates in the opposite direction (counterclockwise) to the first conveying screw 42 to move into the stirring chamber 41b. The developer is transported in the direction opposite to the first transport screw 42.

  As described above, the developer is conveyed between the developing chamber 41a and the agitating chamber 41b through the openings (communication portions) 41d and 41e at both ends of the partition wall 41c by being conveyed by the rotation of the first conveying screw 42 and the second conveying screw 43. It is circulated in. That is, the developing chamber 41a and the stirring chamber 41b form a developer circulation path. The toner is charged by agitating and conveying the developer through this circulation path. The developer conveyed to the developing chamber 41 a is supplied to the developing sleeve 44 and is adsorbed and supported on the surface of the developing sleeve 44 by a magnetic field formed by the magnet roller 45 disposed in the developing sleeve 44. Specifically, the toners adhere to the surface of the carrier having a particle size sufficiently larger than that of the toner by charging with opposite polarities. Then, the magnetic carrier having the toner attached to the surface is attracted and supported on the surface of the developing sleeve 44 by the magnetic field formed by the magnet roller 45. The developing sleeve 44 is driven to rotate in the direction of the arrow to convey the carried developer to a portion (developing portion) facing the photosensitive drum 1a.

  In the present embodiment, there is an opening at a position corresponding to the developing area of the developing container 41 facing the photosensitive drum 1a, and the developing sleeve 44 can be rotated so that a part of the developing sleeve 44 is exposed in the direction of the photosensitive drum 1a. It is arranged. Here, the diameter of the developing sleeve 44 is 20 mm, the diameter of the photosensitive drum 1 a is 80 mm, and the closest region between the developing sleeve 44 and the photosensitive drum 1 a is about 300 μm. As a result, the developer conveyed to the developing section by the developing sleeve 44 is set so that development can be performed in a state where the developer is in contact with the photosensitive drum 1a. That is, the developer carried on the developing sleeve 44 is brought into contact with the photosensitive drum 1a and a predetermined developing bias of the developing sleeve 44 is applied, whereby the electrostatic latent image formed on the photosensitive drum 1a is converted into toner. Develop with The developer remaining on the developing sleeve 44 after development is collected in the stirring chamber 41b without passing through the developing chamber 41a. That is, the developing device 4a of the present embodiment includes a developing chamber 41a that supplies a developer to the developing sleeve 44, and a stirring chamber that is disposed below the developing chamber 41a and forms a collection path for collecting the developer from the developing sleeve 44. 41b, a so-called vertical stirring function separation type configuration.

  A part of the agitation chamber 41b is provided with a toner supply port for supplying toner. A developer replenishing device (not shown) is connected to the toner replenishing port so as to replenish the toner consumed by the development into the developing container 41. In order to stir the toner and the carrier as much as possible until the developer is supplied from the developing chamber 41a to the developing sleeve 44 and stabilize the toner charge amount, the toner supply port is generally provided in the stirring chamber 41b. is there.

  Next, the configuration of the developing sleeve 44 and the magnet roller 45 of this embodiment will be described in detail. First, the magnetic pole arrangement of the magnet roller 45 will be described.

[Magnetic pole arrangement]
As shown in FIG. 2, the magnet roller 45 has a plurality of magnetic poles S1, S2, N1, N2, and N3. The positions where the reference numerals of the magnetic poles in FIG. 2 are indicated generally indicate positions where the magnetic force of the magnetic poles reaches a peak. The magnetic pole S1 is a developing pole disposed in the developing unit facing the photosensitive drum 1a. The magnetic pole N2 as the first magnetic pole is disposed at a position substantially facing the regulating blade 46 on the upstream side in the rotation direction (conveying direction) of the developing sleeve 44 of the regulating blade 46. The magnetic pole N2 is disposed such that the peak position of the magnetic force is above the center of the developing sleeve 44 and downstream of the line α1 connecting the center of the developing sleeve 44 and the center of the first conveying screw 42. Yes. Magnetic poles S2 and N1 are disposed between the magnetic pole S1 and the magnetic pole N2. The magnetic pole N3 as the second magnetic pole is disposed on the downstream side in the rotation direction of the developing sleeve 44 of the magnetic pole S1. The magnetic pole N3 is arranged so that the peak position of the magnetic force is below the center of the developing sleeve 44 and upstream of the line α2 connecting the center of the developing sleeve 44 and the center of the second conveying screw 43. ing. In other words, the peak positions of the magnetic forces of the magnetic poles N2 and N3 serving as repulsive poles are located outside the region sandwiched between the lines α1 and α2. Thereby, the space | interval of the magnetic pole N2 and the magnetic pole N3 can be widened.

  In the case of the present embodiment, the magnetic poles N2 and N3 are arranged so that the center of the first conveying screw 42 is positioned between the magnetic pole N2 and the magnetic pole N3 that are repulsive poles in the vertical direction. In other words, the first conveying screw 42 is arranged so that the center thereof is below the magnetic force peak position of the magnetic pole N2 and above the magnetic force peak position of the magnetic pole N3. The magnetic pole arrangement of the magnet roller 45 of the present embodiment is characterized by a magnetic pole N2 arranged substantially opposite to the developing sleeve 44 of the regulating blade 46, and a magnetic pole that is one pole upstream (upstream in the transport direction) of the magnetic pole N2. N3 is the same polarity. The developer carried on the developing sleeve 44 is peeled off from the surface of the developing sleeve 44 between the magnetic pole N2 and the magnetic pole N3 and collected in the stirring chamber 41b.

  In this way, by arranging the same poles adjacent to each other, the magnetic flux lines hardly exist between the magnetic poles N2 and N3, and have a zero gauss band that can be regarded as almost zero gauss. Here, in the case of the present embodiment, the zero gauss band is an area that is 50 gauss or less. For this reason, there is a position (zero Gaussian band) where the magnetic force is almost zero between the magnetic pole N2 as the first magnetic pole and the magnetic pole N3 as the second magnetic pole. Thereby, it is possible to prevent a large amount of developer from being present in the vicinity of the regulating blade 46, and to reduce the stress applied to the developer. In the case of this embodiment, the minimum position where the magnetic force is the smallest among the positions where the magnetic force is almost zero (zero gauss band) is on a substantially horizontal line passing through the center of the developing sleeve 44 in FIG. When replaced with a watch, the position is approximately 3 o'clock). The minimum position moves depending on the arrangement of the magnetic poles. However, when the cross-section of the developing sleeve 44 is replaced with a clock, it is preferably located approximately in the range from 1 o'clock to 5 o'clock. It is more preferable to set any position in the 4 o'clock range. In other words, the minimum position is preferably located in any of the range of 30 ° to 150 ° clockwise from the upper end position (0 o'clock position) of the developing sleeve 44, and any of the range of 60 ° to 120 °. It is more preferable to set the position.

[Vertical position of partition wall]
Here, as described above, the developing device 4a of the present embodiment has a vertical stirring function separation type configuration, and the developer passes between the openings 41d and 41e at both ends of the partition wall 41c, and the developing chamber 41a and the stirring chamber 41b. Circulated between. Therefore, as shown in FIG. 3, the amount of developer T present in the developing chamber 41a decreases as the developer T moves from the developing chamber 41a toward the opening 41d that is sent to the stirring chamber 41b. That is, the surface of the developer T is lowered. This is because the developer is transported downstream in the transport direction while supplying the developer to the developing sleeve 44 by the first transport screw 42, so that the developer becomes more downstream in the developer transport direction of the first transport screw 42. It means that the amount is decreasing. As a result, the developer surface height of the developer T is lowered in the vicinity of the opening 41d of the first conveying screw 42, the developer is hardly supplied to the developing sleeve 44, and the developer coating on the developing sleeve 44 is not applied. Sometimes it became stable.

  Therefore, in the present embodiment, as shown in FIG. 2, the partition wall 41c has a magnetic force between the developing sleeve 44 and the first conveying screw 42, the apex 47a being substantially magnetic between the magnetic pole N2 and the magnetic pole N3. It extends to a position below the position where it becomes zero. That is, the position of the apex 47a of the rising portion 47 of the partition wall 41c is set below the position where the magnetic force is almost zero. In other words, the height of the apex 47a of the partition wall 41c between the first conveying screw 42 and the developing sleeve 44 is set so that the region formed by the magnet roller 45 where the magnetic force is almost zero is in the upper position. Yes. That is, the vertex 47a of the partition wall 41c is below the upper end position of the zero gauss band. Furthermore, in the present embodiment, the position of the vertex 47a is below the minimum position of the magnetic force in the zero gauss band. The height of the apex 47a is the same over the axial direction of the developing sleeve 44. The partition wall 41c is formed so that the position of the vertex 47a is below the line α1 connecting the center of the developing sleeve 44 and the center of the first conveying screw 42. The position of the vertex 47a is the line α1. It may be higher than. In short, the position of the vertex 47a may be lower than the position where the magnetic force is almost zero. However, it is preferable that the position of the apex 47a is lower than the line α1 in that the amount of development supplied from the developing chamber 41a to the developing sleeve 44 increases. However, since the developer supplied from the developing chamber 41a to the developing sleeve 44 is likely to fall, the problem of developer dropping described later becomes significant.

  It should be noted that the height of the apex 47a of the rising portion 47 of the partition wall 41c is ensured to be high enough to hold the developer in the developing chamber 41a. That is, the developer chamber 41 a formed between the partition wall 41 c including the rising portion 47 and the developing container 41 is held in a developing chamber 41 a while being agitated and conveyed by the first conveying screw 42, and holds a sufficient amount of developer that can be supplied to the developing sleeve 44 The height of the rising portion 47 is set so that it can be done.

  Thus, by reducing the height of the partition wall 41c between the developing chamber 41a and the developing sleeve 44, the amount of developer supplied from the developing chamber 41a to the developing sleeve 44 can be increased. As a result, sufficient developer can be supplied to the developing sleeve 44 even on the downstream side in the developer conveying direction by the first conveying screw 42 of the developing chamber 41a in which the developer surface height decreases, and the developer coating on the developing sleeve 44 can be performed. Sex can be stabilized.

  In the present embodiment, the vertical position of the rotation center of the first conveying screw 42 is lower than the vertical position of the rotation center of the developing sleeve 44. In other words, the developing sleeve 44 is disposed such that its center position is higher than the center position of the first conveying screw 42. Thereby, the height of the position where the magnetic force of the magnet roller 45 arranged inside the developing sleeve 44 becomes almost zero can be made as high as possible with respect to the first conveying screw 42. As a result, the height of the position where the magnetic force of the magnet roller 45 becomes almost zero can be easily made higher than the position of the vertex 47a of the partition wall 41c.

  Further, in the case of the present embodiment, since the interval between the magnetic pole N2 and the magnetic pole N3 that are repulsive poles is widened as described above, the zero gauss band can be widened. That is, when the interval between the repulsion poles is narrow, the zero gauss band is also narrowed, so that the developer is easily removed without being peeled off from the developing sleeve, and the coatability of the developer on the developing sleeve may become unstable. . On the other hand, in the case of this embodiment, the zero gauss band is widened by widening the interval between the repulsive poles. For this reason, the peelability of the developer is improved, the developer can be prevented from being carried around the developer carrier, and the coatability of the developer on the developing sleeve 44 can be stabilized.

[Surface shape of developing sleeve]
On the other hand, when a large amount of developer is supplied to the developing sleeve 44 in this way, the developer supplied to the developing sleeve 44 falls down unless the restraining force of the developer by the developing sleeve 44 is secured. . That is, when the developer is supplied to a position where the magnetic flux density formed by the magnetic poles N2 and N3 is near zero, the developer is not sufficiently restrained by the developing sleeve 44 and may drop downward. In particular, in the case where the zero gauss band is wide as in the present embodiment, the developer is less likely to be restrained by the developing sleeve 44, so that the developer is more likely to fall. If the developer falls into the stirring chamber 41b as it is, the developer is likely to be accumulated in the stirring chamber 41b. As a result, the developer in the stirring chamber 41b is rotated by the developing sleeve 44, and the coatability of the developer on the developing sleeve 44 may become unstable. Further, there is a possibility that the developer on the developing sleeve 44 cannot be sufficiently taken into the stirring chamber 41b and the developer overflows.

  As the shape of the surface of the developing sleeve, a configuration in which the surface roughness is roughened by performing random unevenness processing by blasting or the like is conventionally known. However, in the case of a developing sleeve in which such minute irregularities are formed on the surface, if the usage period is long, the surface is scraped and the binding force of the developer is reduced. For this reason, in such a configuration, the risk of the developer dropping increases as the usage period becomes longer.

  Therefore, in the case of the present embodiment, as shown in FIGS. 2 and 4, the developing sleeve 44 has a plurality of groove portions 48 as a plurality of concave portions formed on the surface at intervals. That is, as shown in FIG. 4A, a plurality of groove portions 48 are formed on the surface of the developing sleeve 44 along a direction (axial direction) that intersects the rotation direction (conveying direction) of the developing sleeve 44. Yes. The plurality of grooves 48 are formed in parallel to each other at intervals in the rotation direction. Further, the plurality of groove portions 48 have an opening shape in which the maximum diameter of the inscribed circle is equal to or larger than the diameter of the average particle diameter of the carrier, and carriers having an average particle diameter can enter the groove portion 48 (inside the recesses) beyond the radius. Is formed.

  The shape of the plurality of grooves 48 is V-shaped as shown in FIG. That is, the shape is such that the distance between the side walls 48a increases toward the opening of the groove 48. Then, by appropriately regulating the interval and the inclination angle of the side wall 48a, the carrier having an average particle diameter can enter the groove 48 more than its radius. This is because, if the groove portion 48 is not shaped so that more than half of the carrier having an average particle diameter can enter, the carrier becomes difficult to be restrained by the surface of the developing sleeve 44, and the developer conveying ability is lowered by the developing sleeve 44. Because.

  Specifically, as shown in FIG. 4C, when the interval between the openings of the groove 48 is L, the maximum diameter of the inscribed circle of the groove 48 is L. Therefore, when the diameter of the carrier 50 having an average particle diameter is R, the groove portion 48 is formed so as to satisfy L> R. Further, as shown in FIG. 4C, a state in which the carrier 50 having an average particle diameter has entered most into the groove portion 48, here, a state in which the surface of the spherical carrier 50 is in contact with a pair of opposing side walls 48a. think of. In this state, the groove portion 48 is formed such that the position of the center Q of the carrier 50 having an average particle diameter is located on the deeper side of the groove portion 48 than the virtual surface M connecting the opening edge portions of the groove portion 48. The virtual surface M is also a surface in which convex portions 49 between adjacent groove portions 48 are continuous.

  In this embodiment, the diameter of the developing sleeve 44 is 20 mm, the number of the groove portions 48 is 80, the depth of the groove portions 48 is 60 μm, and the groove angle θ is 100 °. Further, the plurality of groove portions 48 described above are formed at least in the region of the image forming width in the image forming apparatus 100. In the present embodiment, the image formation width is 330 mm, and the formation width of the grooves 48 is 330 mm, which is the same as the image formation width. Moreover, the average particle diameter of a carrier is 20-100 micrometers, and the carrier with an average particle diameter of 40 micrometers was used in this embodiment. The average particle diameter of the carrier is measured using a laser diffraction particle size distribution analyzer SALD-3000 (manufactured by Shimadzu Corporation) according to the operation manual of this measuring apparatus. Specifically, 0.1 g of the magnetic carrier is introduced into the apparatus for measurement, the number of samples is measured for each channel, the median diameter d50 is calculated, and the number average particle size of the samples is obtained. The shape of the groove 48 is measured by a conventionally known measuring method using a probe or a laser.

  In this way, by forming the plurality of grooves 48 having the above-described shape on the surface of the developing sleeve 44, the surface of the developing sleeve 44 is formed with minute concavities and convexities by blasting or the like. Can be higher than the configuration. Further, since the plurality of groove portions 48 are formed at intervals, even if the usage period is long, the convex portions 49 between the plurality of groove portions 48 are not easily scraped by the developer, and the developer is restrained over a long period of time. High power can be maintained.

  In the case of the present embodiment, the interval between the plurality of groove portions 48 (concave portions), that is, the length of the convex portion 49 in the rotation direction of the developing sleeve 44 is equal to or greater than the maximum diameter of the inscribed circle of the opening shape of the groove portion 48. In other words, the interval L is greater than or equal to the interval L between the openings. For this reason, the convex part 49 is hardly scraped off, and the binding force of the developer can be stably maintained over a longer period.

[Counter member]
In the present embodiment, the partition wall 41 c includes a facing member 47 b provided so as to face the developing sleeve 44 in close proximity. The facing member 47 b is formed so as to protrude from the rising portion 47 toward the developing sleeve 44, and a surface facing the surface of the developing sleeve 44 is curved along the peripheral surface of the developing sleeve 44. Further, the position where the facing member 47b faces is between the magnetic pole N2 and the magnetic pole N3 where the same pole is adjacent. Thereby, the interval between the developing sleeve 44 and the partition wall 41c is narrowed, and the developer supplied from the developing chamber 41a to the developing sleeve 44 can be made difficult to fall by the stirring chamber 41b. In this embodiment, the distance between the developing sleeve 44 and the facing member 47b is set between 0.35 mm and 2.5 mm. Thus, even if the carrier carried on the surface of the developing sleeve 44 is about to fall between the developing sleeve 44 and the opposing member 47b, it is held therebetween.

  As described above, in the case of the present embodiment, the position of the apex 47a of the partition wall 41c is set lower than the upper end position of the zero gauss band where the magnetic force is almost zero between the magnetic pole N2 and the magnetic pole N3. For this reason, the developer supplied to the developing sleeve 44 can be increased, and the coatability of the developer on the developing sleeve 44 can be stabilized. Further, since the gap between the magnetic poles N2 and N3, which are repulsive poles, is widened and the zero gauss band is widened, the developer stripping property is improved, and the developer is brought to the developer carrier. Can be suppressed. Therefore, also from this point, the coatability of the developer on the developing sleeve 44 can be stabilized. Further, the surface of the developing sleeve 44 has an opening shape in which the maximum diameter of the inscribed circle is equal to or larger than the diameter of the average particle diameter of the carrier, and a plurality of groove portions 48 into which the carrier with the average particle diameter can enter more than the radius thereof. Is formed. For this reason, it is easy to restrain the developer on the developing sleeve 44. As a result, even if a large amount of developer is supplied from the developing chamber 41a to the developing sleeve 44, or even if the developer is not easily restrained by the developing sleeve 44 by widening the zero gauss band, the developing chamber 41b is not filled with the developer. Is hard to fall. As a result, it is possible to provide the developing device 4a in which density unevenness and developer overflow are unlikely to occur while ensuring the coatability of the developer on the developing sleeve 44.

[Example 1]
Next, an experiment conducted for confirming the effect of the above-described embodiment will be described. In the experiment, Example 1 which is the configuration of the present embodiment described in FIG. 2 and the like was compared with the configurations of Comparative Examples 1 and 2 shown in FIGS. First, the structure of the comparative example 1 is demonstrated using FIG. In the case of the developing device 400 of Comparative Example 1, the developing sleeve 440 ensures the transportability of the surface of the developing sleeve 440 by performing random unevenness processing on the surface by blasting and roughening the surface roughness. Further, the height of the apex 470a of the partition wall 410c between the first conveying screw 42 and the developing sleeve 440 is set to a position above the zero gauss band where the magnetic force formed by the magnet roller 45 is almost zero. That is, the height of the rising portion 470 is made higher than that in the present embodiment so that the position where the magnetic force becomes almost zero is lower than the vertex 470a.

  This is due to the following reason. That is, also in the comparative example 1, the magnet roller 45 disposed inside the developing sleeve 440 has the same magnetic pole arrangement as that of the present embodiment. For this reason, at the position where the magnetic flux density formed by the magnetic poles N2 and N3 is close to zero, it is difficult to restrain the developer in the developing sleeve 44, and the developer easily falls into the stirring chamber 41b as it is. In particular, as in Comparative Example 1, the developing sleeve 440 using a process for roughening the surface roughness by performing a random unevenness process tends to change the surface roughness and the like depending on the number of image formations. Therefore, if the use period becomes longer, the developer conveying force of the developing sleeve 44 may be reduced. Therefore, in Comparative Example 1, the height of the vertex 470a of the partition wall 410c is set to a position above the zero gauss band where the magnetic force formed by the magnet roller 45 is almost zero, so that the developer does not easily fall into the stirring chamber 41b. Yes. Also, in the case of Comparative Example 1, as in the present embodiment, the facing member 470b is provided on the partition wall 410c. Other configurations are the same as those of the present embodiment.

  Next, the configuration of Comparative Example 2 will be described with reference to FIG. In the case of the developing device 401 of Comparative Example 2, as in Comparative Example 1, the developing sleeve 440 is subjected to random unevenness processing on the surface by blasting to roughen the surface roughness. On the other hand, the height of the apex 47a of the partition wall 41c between the first conveying screw 42 and the developing sleeve 440 is similar to the height of the zero gauss band where the magnetic force formed by the magnet roller 45 is almost zero. Is also in the lower position. Other configurations are the same as those of the present embodiment.

  The developing device 4a of Example 1 as shown in FIG. 2, the developing device 400 of Comparative Example 1 shown in FIG. 5, and the developing device 401 of Comparative Example 2 shown in FIG. The following comparative experiment was conducted by incorporating the image forming apparatus 100 as shown in FIG. The experimental conditions were such that the weight ratio (T / D) of the toner and carrier in the developer at the start was 8%, and image formation was repeated on A4 paper after matching the conditions such as the image ratio and environment. Thereafter, the images and phenomena in the developing devices 4a, 400, and 401 were compared. First, as a result of repeating 200,000 sheets in an environment of 25 ° C. and 50%, no problem occurred in all the developing devices.

  Subsequently, as a result of repeating 200,000 image formation on A4 paper in an environment of 30 ° C. and 85%, in the developing device 400 of Comparative Example 1 in the middle of image formation, it corresponds to the downstream portion in the transport direction of the first transport screw 42. Density unevenness occurred at the position where When the developing device 400 of Comparative Example 1 is observed in this situation, the flowability of the developer present in the developing device 400 is reduced, and the developer surface height at the downstream portion in the transport direction of the first transport screw 42 is the image. It can be seen that it is lower than before the formation. As a result, it was found that the developer could not be supplied to the developing sleeve 440, and density unevenness was caused by the instability of the developer coating. Further, the inventors have further studied that the change in fluidity tends to decrease more in a high temperature and high humidity environment. For the developing devices of Comparative Example 2 and Example 1, no particular problem occurred.

  Furthermore, as a result of repeating 200,000 image formation on A4 paper in an environment of 20 ° C. and 10%, density unevenness began to occur in the developing device 401 of Comparative Example 2 during the image formation. Then, before reaching 200,000 sheets, a carrier adhesion image was generated at a position corresponding to the upstream side of the first conveying screw 42 in the conveying direction. In this situation, when the developing device 401 of Comparative Example 2 was observed, a large amount of developer was present on the stirring chamber 41b side. Then, after the developing process is completed at the position where the developer coated on the developing sleeve 440 faces the photosensitive drum 1a, the developer enters the stirring chamber 41b when the developer is collected in the stirring chamber 41b. It was found that there was so much developer. When observed more closely, it can be seen that the coating amount of the developer on the developing sleeve 440 is reduced, and when the surface of the developing sleeve 440 is observed, the surface roughness is reduced and the gloss is increased.

  Accordingly, the surface roughness of the developing sleeve 440 is determined using a contact type roughness measuring device Surfcoder SE3-300 (Kosaka Laboratory Co., Ltd.) capable of calculating a ten-point average roughness Rz (JIS B 0601: 1994). It was measured. The measurement conditions were cut-off value = 0.8 mm, measurement length = 2.5 mm, feed speed = 0.1 mm / sec, and vertical magnification = 5000 times. As a result, Rz before image formation was 15 μm, whereas Rz was 5 μm when the carrier adhesion image was generated. The developer coating amount when the developing sleeve 440 having Rz of 5 μm and 15 μm is used is measured by using the developer before image formation. As a result, the developing sleeve having Rz of 5 μm decreases by about 40%. It was found that the transportability was reduced by about 40%. FIG. 7 shows the relationship between the number of formed images and the surface roughness of the developing sleeve 440. It can be seen that as the number of images formed increases, Rz decreases, and about 550000 sheets, Rz is about 5 μm.

  As a result of the experiment of Comparative Example 2, the developer sleeve 440 has deteriorated in transportability, so that the developer cannot be transported by the developing sleeve 440 and the developer falls to the stirring chamber 41b side, and the developer falls to the stirring chamber 41b side. I knew that it would accumulate a lot. It was found that the developer could not be taken into the stirring chamber 41b and the developer overflowed, resulting in a carrier adhesion image. In this regard, the inventors have also clarified that there is almost no environmental difference.

  On the other hand, in the developing device 4a of Example 1, the developer coating amount of the developing sleeve 44 before the image formation and after the image formation of 600000 sheets was almost the same. Further, it has been found that the developing device 4a of Example 1 has no particular problem and can provide a developing device that is less likely to cause density unevenness and developer overflow.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIGS. The developing device 40a of the present embodiment relates to a configuration that employs a multistage developing system that can increase development opportunities. Specifically, a predetermined density is secured by using a plurality of developing sleeves. More specifically, in this embodiment, two developing sleeves are used. Such a configuration is suitably used for further speeding up of the image forming apparatus. Other configurations and operations are the same as those of the first embodiment described above, and therefore, the same configurations are omitted or denoted by the same reference numerals, the description thereof is omitted or simplified, and hereinafter the first embodiment. The description will focus on the parts different from the form. In this embodiment as well, the developing device 40a of the yellow image forming station Y (see FIG. 1) will be described, but the configuration is the same for the developing devices of other image forming stations.

  As shown in FIG. 8, the developing device 40 a of this embodiment includes a developing container 41, and a two-component developer containing toner and a carrier as a developer is accommodated in the developing container 41. Further, in the developing container 41, a developing sleeve 44a as a first developer carrying member, a developing sleeve 44b as a second developer carrying member, and a regulating blade for regulating the spikes of the developer carried on the developing sleeve 44a 46. The developing sleeve 44a carries the developer supplied from the developing chamber 41a on its surface and conveys it. The developing sleeve 44b is provided below the developing sleeve 44a, and carries the developer transferred from the developing sleeve 44a on the surface thereof and transports it. The developing sleeve 44 a is arranged so that the center position thereof is higher than the center position of the first conveying screw 42. The first conveying screw 42 is disposed so that the center thereof is located between the upper end and the lower end of the developing sleeve 44a. In the present embodiment, the first conveying screw 42 is disposed adjacent to the developing sleeve 44a in a substantially horizontal direction.

  The developing sleeve 44a rotates in the direction indicated by the arrow (counterclockwise) during development. Then, a developer is supplied from the developing chamber 41a as the first chamber, and the two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the regulating blade 46 is carried. Then, this is conveyed to a developing area A1 facing the photosensitive drum 1a, and a developer is supplied to the electrostatic latent image formed on the photosensitive drum 1 to develop the latent image. On the other hand, the developing sleeve 44b rotates in the direction indicated by the arrow (counterclockwise) during development. Then, the toner is delivered from the surface of the developing sleeve 44a that has passed through the developing region A1. The developer delivered to the developing sleeve 44b is transported to the developing area A2 downstream of the developing area A1 in the rotation direction of the photosensitive drum 1, and the developer is again applied to the electrostatic latent image formed on the photosensitive drum 1. Supply and develop the latent image. Thereafter, the developer contributing to the development is collected from the developing sleeve 44b in the stirring chamber 41b as the second chamber without passing through the developing chamber 41a. That is, the stirring chamber 41b forms a recovery path for recovering the developed developer carried on the developing sleeve 44b without passing through the developing chamber 41a.

  Also in this embodiment, like the developing sleeve 44 of the first embodiment, a plurality of parallel grooves 48 are formed along the axial direction on the surface of the developing sleeve 44a. Similarly, a plurality of parallel grooves 48 are formed along the axial direction on the surface of the developing sleeve 44b. The developing sleeve 44b may be blasted like the developing sleeve 440 shown in FIG.

  Inside the developing sleeve 44a, a magnet roller 45a similar to the magnet roller 45 of the first embodiment is disposed. The positions where the reference numerals of the magnetic poles in FIG. 8 are indicated generally indicate positions where the magnetic force of the magnetic poles reaches a peak. Similar to the first embodiment, the magnetic pole N2 as the first magnetic pole is disposed so as to be substantially opposed to the regulating blade 46 and the peak position of the magnetic force is above the center of the developing sleeve 44a. In addition, the magnetic pole N2 is disposed downstream of the line β1 connecting the center of the developing sleeve 44a and the center of the first transport screw 42 in the transport direction. Further, the magnetic pole N3 as the second magnetic pole is disposed adjacent to the upstream side of the magnetic pole N2, and the peak position of the magnetic force is located below the center of the developing sleeve 44a. In addition, the magnetic pole N3 is disposed upstream of the line β2 connecting the center of the developing sleeve 44a and the center of the second transport screw 43 in the transport direction. The magnetic pole N3 is disposed at a position closest to the developing sleeve 44b among the plurality of magnetic poles of the magnet roller 45a. For this reason, the magnetic pole N3 also functions as a delivery pole for delivering the developer from the developing sleeve 44a to the developing sleeve 44b.

  In the case of the present embodiment, the magnetic poles N2 and N3 are arranged so that the center of the first conveying screw 42 is positioned between the magnetic pole N2 and the magnetic pole N3 that are repulsive poles in the vertical direction. In other words, the first conveying screw 42 is arranged so that the center thereof is below the magnetic force peak position of the magnetic pole N2 and above the magnetic force peak position of the magnetic pole N3. Similarly to the first embodiment, the partition wall 41c also has a magnetic force of almost zero between the developing sleeve 44a and the first conveying screw 42, the apex 47a between the magnetic pole N2 and the magnetic pole N3. It extends to a position below the upper end of the position zero Gauss band. Also in the present embodiment, the position of the apex 47a is below the minimum position of the magnetic force in the zero gauss band. The definition of such a zero gauss band and the minimum position is the same as in the first embodiment.

  The partition wall 41c is formed so that the position of the apex 47a is below the line β1 connecting the center of the developing sleeve 44a and the center of the first conveying screw 42. In particular, in the case of a configuration having two developing sleeves as in the present embodiment, in consideration of the recoverability of the developer from the lower developing sleeve 44b to the stirring chamber 41b, the position of the developing sleeve 44b is set to the stirring chamber 41b. On the other hand, it is preferable to dispose as high as possible. For example, the developing sleeve 44 b is preferably arranged so that the center position thereof is higher than the center position of the second conveying screw 43. If it does so, the position of the developing sleeve 44a arrange | positioned above the developing sleeve 44b will also become high, As a result, the position of the vertex 47a will tend to be below the line β1. In this case, the developer supplied from the developing chamber 41a to the developing sleeve 44a is likely to drop. Therefore, in the configuration using two developing sleeves as in the present embodiment, there is a problem of the developer dropping into the stirring chamber 41b. Becomes more prominent.

  On the other hand, a magnet roller 45b is disposed inside the developing sleeve 44b. The magnet roller 45b has a plurality of magnetic poles S3, S4, S5, N4, and N5. The magnetic pole N4 is a developing pole disposed in the developing portion that faces the photosensitive drum 1a. The magnetic pole S3 is disposed at a position substantially opposite to the magnetic pole N3 of the magnet roller 45a in the developing sleeve 44a, and the developer is transferred from the developing sleeve 44a at this position. The magnetic pole S5 is disposed adjacent to the upstream side in the rotation direction of the developing sleeve 44b of the magnetic pole S3. Therefore, the developer carried on the developing sleeve 44b is peeled off from the surface of the developing sleeve 44b between the magnetic pole S5 and the magnetic pole S3 and collected in the stirring chamber 41b. Magnetic poles S4 and N5 are disposed between the magnetic pole S5 and the magnetic pole N4.

  The partition wall 41c includes a developing sleeve 44a and a facing member 47c provided so as to face and face the developing sleeve 44b. The facing member 47c is formed so as to protrude from the middle part to the rising part 47 of the partition wall 41c toward the developing sleeve 44a and the developing sleeve 44b. Further, in the facing member 47c, the surface facing the surface of the developing sleeve 44a is curved along the peripheral surface of the developing sleeve 44a, and the surface facing the surface of the developing sleeve 44b is curved along the surface of the developing sleeve 44b. doing. Further, the positions at which the facing member 47c faces are between the magnetic poles N2 and N3 adjacent to each other, and between the magnetic poles S5 and S3. Thereby, the intervals between the developing sleeve 44a and the developing sleeve 44b and the partition wall 41c are narrowed, and the developer supplied from the developing chamber 41a to the developing sleeve 44a can be made difficult to fall into the stirring chamber 41b. In this embodiment, the distance between the developing sleeve 44a and the facing member 47c is set between 0.35 mm and 2.5 mm. Thus, even if the carrier carried on the surface of the developing sleeve 44 is about to fall between the developing sleeve 44 and the opposing member 47b, it is held therebetween.

  Also in this embodiment, the position of the apex 47a of the partition wall 41c is set below the position where the magnetic force between the magnetic pole N2 and the magnetic pole N3 becomes almost zero. For this reason, the developer supplied to the developing sleeve 44a can be increased, and the coatability of the developer on the developing sleeve 44a can be stabilized. Further, since the gap between the magnetic poles N2 and N3, which are repulsive poles, is widened and the zero gauss band is widened, the developer stripping property is improved, and the developer is brought to the developer carrier. Can be suppressed. Therefore, also from this point, the coatability of the developer on the developing sleeve 44a can be stabilized. Further, the surface of the developing sleeve 44a has an opening shape in which the maximum diameter of the inscribed circle is equal to or larger than the diameter of the average particle diameter of the carrier, and a plurality of grooves 48 into which the carrier having the average particle diameter can enter more than the radius. Is formed. For this reason, it is easy to restrain the developer on the developing sleeve 44a. As a result, even if a large amount of developer is supplied from the developing chamber 41a to the developing sleeve 44a, and even if it is difficult for the developer to be restrained by the developing sleeve 44a by widening the zero gauss band, the developer is put into the stirring chamber 41b. Is hard to fall. In particular, the developer is prevented from dropping even when the two developing sleeves are provided as in this embodiment, the upper developing sleeve 44a is high, and the vertex 47a is below the line β. it can. As a result, it is possible to provide the developing device 4a that is free from density unevenness and developer overflow while ensuring the coatability of the developer on the developing sleeve 44a.

[Example 2]
Next, an experiment conducted for confirming the effect of the above-described embodiment will be described. In the experiment, Example 2 which is the configuration of the present embodiment described with reference to FIG. 8 was compared with the configurations of Comparative Examples 3 and 4 shown in FIGS. 9 and 10. First, the structure of the comparative example 3 is demonstrated using FIG. In the case of the developing device 402 of Comparative Example 3, the developing sleeves 440a and 440b are subjected to random unevenness processing on the surface by blasting to increase the surface roughness, thereby ensuring the transportability of the surface of the developing sleeves 440a and 440b. Is. Further, the height of the apex 470a of the partition wall 410c between the first conveying screw 42 and the developing sleeve 440a is set to a position above the zero gauss band where the magnetic force formed by the magnet roller 45a is almost zero. That is, the height of the rising portion 470 is made higher than that in the present embodiment so that the position where the magnetic force becomes almost zero is lower than the vertex 470a. Also, in the case of Comparative Example 3, as in the present embodiment, the opposing member 470c is provided on the partition wall 410c. Other configurations are the same as those of the present embodiment.

  Next, the structure of the comparative example 4 is demonstrated using FIG. In the case of the developing device 403 of Comparative Example 4, as in Comparative Example 3, the developing sleeves 440a and 440b are subjected to random unevenness processing on the surface by blasting to roughen the surface roughness. On the other hand, the height of the apex 47a of the partition wall 41c between the first conveying screw 42 and the developing sleeve 440a is similar to the height of the zero gauss band where the magnetic force formed by the magnet roller 45 is almost zero, as in this embodiment. Is also in the lower position. Other configurations are the same as those of the present embodiment.

  The developing device 40a of Example 2 as shown in FIG. 8, the developing device 402 of Comparative Example 3 shown in FIG. 9, and the developing device 403 of Comparative Example 4 shown in FIG. The following comparative experiment was conducted by incorporating the image forming apparatus 100 as shown in FIG. The experimental conditions were such that the weight ratio (T / D) of the toner and carrier in the developer at the start was 8%, and image formation was repeated on A4 paper after matching the conditions such as the image ratio and environment. Thereafter, the images and phenomena in the developing devices 40a, 402, and 403 were compared.

  First, in the developing device 402 of Comparative Example 3 (FIG. 9), density unevenness occurred in a high temperature and high humidity environment. In the developing device 403 of Comparative Example 4 (FIG. 10), when the number of formed images is increased, the image first becomes rough and then the carrier adheres to a position corresponding to the upstream side of the first conveying screw 42 in the conveying direction. An image has occurred. When the developing device 403 of Comparative Example 4 was observed in this situation, the amount of the developer coated on the developing sleeve 440b was about three times that of the state before image formation. Then, it was found that the developer stays in the area A2 which is the closest part between the photosensitive drum 1a and the developing sleeve 440b, and the developer overflows. It was also found that the surface roughness of the developing sleeve 44a was reduced to about 5 μm.

  This is because the developer that has dropped between the developing sleeve 440a and the opposing member 470c provided in the vicinity of Zero Gauss has passed between the developing sleeve 440a and the developing sleeve 440b and is supplied to the developing sleeve 440b. . That is, the developer supplied to the developing sleeve 440b in this way merges with the developer delivered from the developing sleeve 440a to the developing sleeve 440b through a normal route, and the developer coating amount of the developing sleeve 440b increases. It was. As a result, the coating amount becomes about three times, and it becomes impossible to pass through the closest portion between the photosensitive drum 1 and the developing sleeve 440b, and a carrier adhesion image is generated.

  On the other hand, it has been found that there is no particular problem with the developing device 40a of Example 1 (FIG. 8), and it is possible to provide the developing device 4 that is less likely to cause density unevenness and developer overflow.

<Other embodiments>
In each of the embodiments described above, a plurality of grooves 48 are formed as a plurality of recesses on the surface of the developing sleeves 44 and 44a. However, the plurality of concave portions are not limited to the groove portions, and the surface shape is hardly changed even when the number of image formations is increased, and other shapes may be used as long as the change in developer transportability is small. It may be a thing. For example, as shown in FIG. 11A, a plurality of groove portions 48A may be formed on the surface of the developing sleeve 44A so as to intersect at two different angles. Further, as shown in FIG. 11B, a plurality of concave portions 48B having circular openings may be formed on the surface of the developing sleeve 44B. Further, as shown in FIG. 11C, a plurality of concave portions 48C having an elliptical opening may be formed on the surface of the developing sleeve 44C. Furthermore, as shown in FIG. 11 (d), a plurality of concave portions 48D having a polygonal opening may be formed on the surface of the developing sleeve 44D. The groove 48A and the recesses 48B, 48C, and 48D have an opening shape in which the maximum diameter of the inscribed circle is equal to or larger than the diameter of the average particle diameter of the carrier, and the carrier having the average particle diameter enters the groove or the recess more than its radius. It is made possible.

  In addition, the specific cross-sectional shapes of the groove portion 48 of each of the above-described embodiments and the groove portion 48A, the concave portions 48B, 48C, and 48D shown in FIG. 11 may be V-shaped as shown in FIG. However, other shapes may be used. For example, the cross-sectional shape may be a curved shape, or a concave shape having a bottom surface and a side wall surrounding the bottom surface. In any case, if the inscribed circle has an opening shape in which the maximum diameter is equal to or larger than the average particle diameter of the carrier, and the carrier having the average particle diameter is formed so as to be able to enter into the recess more than its radius, the recess The opening shape and the cross-sectional shape may be any shape.

  In each of the above-described embodiments, the configuration in which the regulating blade 46 as the regulating member is disposed at a position facing the magnetic pole N2 as the first magnetic pole has been described. This is because, as described above, a large amount of developer is prevented from being present in the vicinity of the regulating blade 46, and stress applied to the developer is reduced. However, the developing device of the present invention is not limited to such a configuration, and can also be applied to a configuration in which the regulating blade 46 faces, for example, the magnetic pole S2 in FIG. That is, the first magnetic pole is arranged at a position facing the regulating blade 46 or upstream of the position in the rotation direction of the developing sleeve, and a second magnetic pole of the same polarity as the first magnetic pole is arranged adjacent to the upstream. If so, the present invention is applicable.

  Further, the material of the photosensitive drum, the developer, the configuration of the image forming apparatus, and the like used in the image forming apparatus of each embodiment described above are not limited to these, and the present invention is applied to various developers and image forming apparatuses. It goes without saying that it is possible. Specifically, the toner color, the number of colors, the presence / absence of wax, the order in which each color toner is developed, the number of first and second conveying screws, and the like are not limited to the above description. For example, the present invention can be applied to other types of developing devices such as a function separation type in which the first and second conveying screws are arranged at a certain angle with respect to the top and bottom.

  Further, an image forming apparatus using the developing device of the present invention is an image forming apparatus that forms an image using an electrophotographic system, and in particular, a copier, a printer, a FAX, or a multifunction machine having a plurality of these functions. Etc. are applicable.

  1a, 1b, 1c, 1d ... photosensitive drums / 4a, 4b, 4c, 4d, 40a ... developing device / 41 ... developing container / 41a ... developing chamber (first chamber) / 41b ... Stirring chamber (second chamber) / 41c ... partition wall / 41d, 41e ... opening / 42 ... first conveying screw (first conveying member) / 43 ... second conveying screw (second (Conveying member) / 44, 44A, 44B, 44C, 44D ... developing sleeve (developer carrier) / 44a ... developing sleeve (first developer carrier) / 44b ... developing sleeve (second development) Agent carrier) / 45, 45a ... magnet roller (multipolar magnet) / 46 ... regulating blade (regulating member) / 47 ... rising part / 47a ... apex / 47b, 47c ... opposite Member / 48, 48A ... Groove (recess) / 48B, 4 C, 48D ... recess / 100 ... image forming apparatus / N2 ... pole (first magnetic pole) / N3 ... pole (second pole)

Claims (17)

A developer carrying member for carrying a developer containing a non-magnetic toner and a carrier having magnetism on a surface and transporting the developer, and developing a latent image;
A first chamber that contains a developer and supplies the developer to the developer carrier, and a developer after development that is disposed below the first chamber and is carried on the developer carrier. A partition that separates the first chamber from the second chamber; a second chamber that forms a recovery path for collecting without passing through the chamber; a circulation path for circulating the developer between the first chamber; A developing container having
A first conveying member arranged in the first chamber so that its center is positioned between an upper end and a lower end of the developer carrying member, and conveys the developer;
A second conveying member disposed in the second chamber for conveying the developer;
A regulating member for regulating the amount of developer carried on the developer carrying body;
The position of the magnetic force at a position facing the regulating member or upstream of the developer carrier in the transport direction from the position above the center of the developer carrier and the center of the developer carrier and the first position. A first magnetic pole disposed so as to be downstream in the transport direction with respect to a line connecting the center of one transport member, and adjacent to the upstream in the transport direction of the first magnetic pole, and the peak position of the magnetic force is the developer carrier. A second pole having the same polarity as the first magnetic pole, which is arranged below the center of the first carrier and upstream of the line connecting the center of the developer carrier and the center of the second transport member. A magnetic pole, and a multipolar magnet disposed inside the developer carrier,
The partition wall is between the developer carrier and the first transport member, and the top position of the partition wall is from the upper end position of the zero gauss band where the magnetic force is substantially zero between the first magnetic pole and the second magnetic pole. Is also located at the lower position,
The developer carrying member has a plurality of recesses formed on the surface at intervals,
The plurality of recesses have an opening shape in which the maximum diameter of the inscribed circle is equal to or greater than the diameter of the average particle diameter of the carrier, and the carrier having an average particle diameter is formed so as to be able to enter the recess more than its radius.
A developing device. The position of the apex of the partition wall is below the minimum position where the magnetic force is the smallest in the zero gauss band,
The developing device according to claim 1, wherein: The multipolar magnet is disposed at a position where the first magnetic pole faces the regulating member.
The developing device according to claim 1, wherein The first conveying member is disposed so that the center thereof is below the peak position of the magnetic force of the first magnetic pole and above the peak position of the magnetic force of the second magnetic pole.
The developing device according to any one of claims 1 to 3, wherein the developing device is characterized in that: The partition is formed such that the position of the apex is below a line connecting the center of the developer carrier and the center of the first transport member,
The developing device according to claim 1, wherein the developing device is any one of the above. The partition wall has a facing member provided so as to face and face the developer carrier.
The developing device according to claim 1, wherein the developing device is any one of the above. The developer carrier is disposed such that the center position thereof is higher than the center position of the first transport member.
The developing device according to any one of claims 1 to 6, wherein the developing device is characterized in that: The interval between the plurality of recesses is not less than the maximum diameter of the inscribed circle of the opening shape of the recess,
The developing device according to any one of claims 1 to 7, wherein the developing device is characterized in that: The plurality of recesses are a plurality of grooves formed along a direction intersecting the transport direction of the developer carrier.
The plurality of grooves are formed at intervals in the transport direction.
The developing device according to any one of claims 1 to 8, wherein the developing device is characterized in that: The recess is formed by at least one of a circle, an ellipse, and a polygon.
The developing device according to any one of claims 1 to 8, wherein the developing device is characterized in that: The second chamber collects the developer from the developer carrier.
The developing device according to any one of claims 1 to 10, wherein the developing device is characterized in that: A first developer carrier as the developer carrier;
A second developer carrier provided below the first developer carrier and carrying the developer transferred from the first developer carrier on the surface thereof;
The second chamber collects the developer from the second developer carrier;
The developing device according to any one of claims 1 to 10, wherein the developing device is characterized in that: A developer carrier for carrying a developer containing non-magnetic toner and magnetic carrier on the surface;
A first chamber that contains a developer and supplies the developer to the developer carrier, and a developed developer that is disposed below the first chamber and carried on the developer carrier is the first chamber. A partition that separates the first chamber from the second chamber; a second chamber that forms a recovery path for collecting without passing through the chamber; a circulation path for circulating the developer between the first chamber; A developing container having
A first conveying member arranged in the first chamber so that its center is positioned between an upper end and a lower end of the developer carrying member, and conveys the developer;
A second conveying member disposed in the second chamber for conveying the developer;
A regulating member for regulating the amount of developer carried on the developer carrying body;
A first magnetic pole disposed so that a peak position of the magnetic force is positioned above the center of the developer carrying body at a position facing the regulating member or upstream of the position in the transport direction of the developer carrying body from the position; A second magnetic pole adjacent to the upstream of the first magnetic pole in the transport direction and having the same magnetic pole as the first magnetic pole, the magnetic pole being positioned below the center of the developer carrier. A multi-pole magnet disposed inside the developer carrier,
The partition wall is between the developer carrier and the first transport member, and the top position of the partition wall is from the upper end position of the zero gauss band where the magnetic force is substantially zero between the first magnetic pole and the second magnetic pole. Is also extended to a lower position,
The developer carrying member has a plurality of recesses formed on the surface at intervals,
The plurality of recesses have an opening shape in which the maximum diameter of the inscribed circle is equal to or greater than the diameter of the average particle diameter of the carrier, and the carrier having an average particle diameter is formed so as to be able to enter the recess more than its radius.
A developing device. The position of the apex of the partition wall is below the minimum position where the magnetic force is the smallest in the zero gauss band,
The developing device according to claim 13, wherein: A first developer carrying member for carrying and carrying a developer containing non-magnetic toner and a carrier having magnetism on the surface;
A second developer carrier provided below the first developer carrier and carrying the developer delivered from the first developer carrier on the surface;
A first chamber that contains a developer and supplies the developer to the first developer carrier, and a developed developer that is disposed below the first chamber and carried on the second developer carrier. A second passage that forms a collection path for collecting the developer without passing through the first chamber, a circulation path for circulating the developer between the first chamber, the first chamber, and the second chamber; A developing container having a partition wall for partitioning;
A first conveying member arranged in the first chamber so that the center thereof is positioned between an upper end and a lower end of the first developer carrier, and conveys the developer;
A second conveying member disposed in the second chamber for conveying the developer;
A regulating member for regulating the amount of developer carried on the first developer carrying body;
The first position is such that the peak position of the magnetic force is above the center of the first developer carrier upstream of the position facing the regulating member or upstream of the position in the transport direction of the first developer carrier. A second magnetic pole that is adjacent to the magnetic pole and upstream of the first magnetic pole in the conveying direction and has the same magnetic pole as the first magnetic pole, and is disposed so that the peak position of the magnetic force is below the center of the first developer carrier. A multipolar magnet having a magnetic pole and disposed inside the first developer carrier,
The partition wall is between the first developer carrier and the first transport member, and the top of the zero gauss band where the apex position is substantially zero between the first magnetic pole and the second magnetic pole. Extending to a position below the position,
The first developer carrier has a plurality of recesses formed on the surface at intervals,
The plurality of recesses have an opening shape in which the maximum diameter of the inscribed circle is equal to or greater than the diameter of the average particle diameter of the carrier, and the carrier having an average particle diameter is formed so as to be able to enter the recess more than its radius.
A developing device. The position of the apex of the partition wall is below the minimum position where the magnetic force is the smallest in the zero gauss band,
The developing device according to claim 15, wherein: The second magnetic pole is disposed at a position closest to the second developer carrier among the plurality of magnetic poles of the multipolar magnet.
The developing device according to claim 15 or 16, wherein the developing device is characterized in that:

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