JP2016173455A - Developing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a configuration that enables both image unevenness and deterioration of the developer to be restrained.SOLUTION: At least one magnetic pole out of a draw-up pole, a cut pole and a peel-off pole of a magnetic roll arranged in a developing sleeve 44 is subjected to processing in the following way. In a part corresponding to an image formation area of the developing sleeve 44 in the direction of its rotation axis, the magnetic force of the pertinent magnetic pole is increased on the downstream side, relative to the vicinity of the central part of the developing sleeve 44 in the direction of its rotation axis, of the developer conveying direction of a first conveying screw 46a. Further, the average value of the magnetic force in the downstream side of the developer conveying direction, where the magnetic force is increased, is kept at not less than 2.5 mT but not more than 10 mT relative to the average value of the magnetic force corresponding to a one-pitch equivalent of the magnetic force of the first conveying screw 46a in the vicinity of the central part.SELECTED DRAWING: Figure 13

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier such as a photosensitive drum using a developer containing a nonmagnetic toner and a magnetic carrier.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a plurality of functions among these using an electrophotographic system or an electrostatic recording system, an electrostatic formed on an image carrier such as a photosensitive drum. A developer is attached to the latent image to visualize it (develop). 2. Description of the Related Art Conventionally, development apparatuses used for such development use a two-component developer (hereinafter referred to as a developer) composed of non-magnetic particle toner and magnetic particle carrier.

  The developing device includes a developing container having a developing chamber (first chamber) for containing a developer and an agitating chamber (second chamber), the developer in the developing chamber is carried on a developing sleeve, and the developer after development. A configuration is known in which the toner is returned to the developing chamber. Specifically, the developer is circulated between the developing chamber and the stirring chamber, so that the toner and the carrier are conveyed while being mixed and stirred. Then, the developer agitated and conveyed to the developing chamber is pumped up to the developing sleeve, carried and conveyed to a position facing the photosensitive drum, and the electrostatic latent image formed on the photosensitive drum is developed with toner. Thereafter, the developer is peeled off on the developing sleeve and returned to the developing chamber.

  As such a developing device, a configuration is proposed in which the developer is peeled off at the lower side in the vertical direction of the developing device and the developer is pumped up at the upper side in the vertical direction of the developing device (see Patent Document 1). In the configuration described in Patent Document 1, the developer peeled off from the developing sleeve and returned to the developing chamber is stirred by a screw, and the stirred developer is pumped up to the developing sleeve.

JP-A-3-4267

  Here, when an image having a large amount of toner consumption such as a solid image, which is a toner image formed on the entire surface of the image forming area of the photosensitive drum, is output, the developer conveying direction of the developing chamber that supplies the developer to the developing sleeve Image unevenness may occur in a region corresponding to the downstream side. This image unevenness will be described. When an image with a large amount of toner consumption is output as described above, the developer having a low TD ratio (toner concentration) with respect to the carrier of the toner is peeled off from the developing sleeve and returned to the developing chamber. As a result, the developer immediately after being peeled off from the developing sleeve may move on the surface layer of the developer having a relatively high TD ratio in the developing chamber, and a phenomenon that the pump is immediately pumped up to the developing sleeve (accompanying) may occur. At this time, since the developer immediately after being peeled off from the developing sleeve is not sufficiently stirred in the developing chamber, a portion having a high TD ratio and a portion having a low TD ratio are generated in the developing chamber. In this state, when the developer is pumped up to the developing sleeve along the blade of the conveying screw, density unevenness (screw trace) is generated in which an obliquely thin portion along the blade of the conveying screw is generated on the developing sleeve. .

  Such density unevenness is likely to occur in a region corresponding to the downstream side of the developer chamber in the developer conveyance direction. The reason for this is as follows. On the upstream side of the developing chamber, a developer having a relatively high TD ratio after being sufficiently stirred in the agitating chamber is sent, so that the TD ratio tends to be relatively high. On the other hand, on the downstream side of the developing chamber, the developer having a low TD ratio peeled off from the developing sleeve flows, so that the TD ratio tends to be low. As a result, the above-described image unevenness easily occurs in a region corresponding to the downstream side of the developer chamber in the developer transport direction.

  In the case of the configuration described in Patent Document 1, it is considered that such image unevenness can be suppressed to some extent. However, when the developer deteriorates due to long-term use or the like, such image unevenness cannot be sufficiently suppressed. . That is, when the developer deteriorates, the adhesion force to the developing sleeve increases, and the developer immediately after being peeled off from the developing sleeve as described above is easily pumped up to the developing sleeve without being sufficiently stirred.

  Here, in the developing sleeve, a magnet roll as a magnetic field generating means having a plurality of magnetic poles is arranged to pump up or peel off the developer as described above. The magnet roll has, for example, a pumping electrode for pumping up the developer in the developing chamber, a cut electrode (regulatory electrode) disposed to face the developing blade, and a stripping pole for stripping the developer from the developing sleeve.

  In order to suppress the above-described image unevenness, it is conceivable to increase the magnetic force of at least one of the pumping pole, cut pole, and stripping pole. When the magnetic force of the pumping pole is increased, the amount of developer pumped up to the developing sleeve can be increased. For this reason, among the developers pumped up to the developing sleeve, the ratio of the developer at the upper part of the developer surface (developer having a low TD ratio) in which a lot of toner that is relatively insufficiently agitated is relatively reduced. The effect of suppressing the image unevenness can be expected. This is because by increasing the pumping amount, it is possible to pump a large amount of toner below the surface of the developer in the developing chamber (toner that has been agitated so that the toner concentration is close to the target concentration). When the magnetic force of the cut pole is increased, the circulation of the developer is promoted by the agent reservoir on the upstream side of the developing blade, so that the effect of suppressing the above-described image unevenness can be expected. When the magnetic force of the stripping pole is increased, the developer spiked along the magnetic field lines of the stripping pole is stripped while straddling the developer conveyed from the upstream in the developing chamber. For this reason, the developer having a low TD ratio is agitated during one rotation of the conveying screw to reduce the unevenness of the TD ratio, and the effect of suppressing the above-described image unevenness can be expected.

  However, in any of the configurations, simply increasing the magnetic force of the magnetic pole promotes the deterioration of the developer. That is, in any configuration, since the force for attracting the developer increases, the pressure applied to the developer increases, and the deterioration of the developer, particularly the toner, is promoted. When the deterioration of the developer is promoted, the adhesive force of the developer (toner) increases, and an image defect is likely to occur in each of the development, transfer, and fixing processes in the image forming process. Further, when the adhesive force of the developer increases due to the deterioration of the developer, as described above, the developer immediately after being peeled off from the developing sleeve is easily pumped up to the developing sleeve without being sufficiently stirred.

  In view of such circumstances, the present invention has been invented to realize a configuration capable of achieving both suppression of image unevenness and suppression of developer deterioration.

  The developing device of the present invention partitions the first chamber and the second chamber, the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber. A developing container in which a circulation path of the developer is formed between the first chamber and the second chamber, and a developer in the first chamber. A developing sleeve that carries and rotates, a developer regulating member that regulates the amount of the developer carried on the developing sleeve, and a developer that conveys the developer along the rotational axis direction of the developing sleeve in the first chamber. A first conveying screw, a second conveying screw that conveys the developer along the rotation axis direction of the developing sleeve in the second chamber, a non-rotatable arrangement in the developing sleeve, and the developer in the first chamber A pumping pole pumped up to the developing sleeve; A regulating electrode that causes the developer regulating member to regulate the amount of the developer carried on the developing sleeve opposite to the developer regulating member, and the developer carried on the developing sleeve is peeled off to form the first chamber. And a magnetic field generating means having a plurality of magnetic poles including a stripping pole to be returned to.

  Then, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole in the portion corresponding to the image forming area in the rotation axis direction of the developing sleeve. The average value of the magnetic force of the portion where the magnetic force on the downstream side in the developer transport direction is increased from the vicinity of the central portion in the rotation axis direction of the developing sleeve is increased downstream in the developer transport direction. The average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center is in the range of 2.5 mT to 10 mT.

  In addition, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a peak of magnetic force of the magnetic pole in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. The half width, which is an angle between the positions in the rotation direction of the developing sleeve that is halved, is increased on the downstream side of the developer conveying direction of the first conveying screw from the vicinity of the central portion in the rotation axis direction of the developing sleeve. The average half-value width of the portion where the half-value width on the downstream side in the developer conveyance direction is increased is equal to the average value of the region corresponding to one pitch of the first conveyance screw of the half-value width near the center portion. And a range of 1 ° to 4 °.

  Further, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole in a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. The portion where the magnetic force on the downstream side in the developer transport direction is increased with respect to the developer transport direction is increased on the downstream side in the developer transport direction of the first transport screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve. When the two sections having the same length are divided, the average value of the magnetic force of the downstream section of the two sections is larger than the average value of the magnetic force of the upstream section, and the average value of the magnetic force of the downstream section is The average value of the area corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center is in the range of 2.5 mT to 12.5 mT.

  In addition, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a peak of magnetic force of the magnetic pole in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. The half width, which is an angle between the positions in the rotation direction of the developing sleeve that is halved, is increased on the downstream side of the developer conveying direction of the first conveying screw from the vicinity of the central portion in the rotation axis direction of the developing sleeve. When the portion where the half-value width on the downstream side in the developer transport direction is increased is divided into two sections having the same length in the developer transport direction, the average value of the half-widths of the sections on the downstream side of the two sections is upstream. The average value of the half width of the downstream section is larger than the average value of the half width of the section on the side, and the average value of the area corresponding to one pitch of the first conveying screw of the half width near the center portion Against It characterized in that it is in the range of 1 ° to 5 °.

  Further, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole in a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. The portion where the magnetic force on the downstream side in the developer conveyance direction is increased is more downstream than the vicinity of the central portion in the rotation axis direction of the developing sleeve, and the portion where the magnetic force is increased on the downstream side in the developer conveyance direction is the first conveyance screw. The average value of the magnetic force of each region corresponding to one pitch of the screw monotonously increases toward the downstream side, and the average value of the magnetic force of the most downstream region is the magnetic force of the first conveying screw in the vicinity of the central portion. The average value of the area corresponding to one pitch is in the range of 2.5 mT to 15 mT.

  In addition, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a peak of magnetic force of the magnetic pole in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. The half width, which is an angle between the positions in the rotation direction of the developing sleeve that is halved, is increased on the downstream side of the developer conveying direction of the first conveying screw from the vicinity of the central portion in the rotation axis direction of the developing sleeve. The portion where the half-value width on the downstream side in the developer conveying direction is increased is monotonically increased as the average value of the half-value width of each region corresponding to one pitch of the first conveying screw goes to the downstream side. The average value of the half-value width of the downstream region is in the range of 1 ° to 6 ° with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center portion. Features And

  Further, at least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole in a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. The developing sleeve is increased on the downstream side in the developer conveying direction of the first conveying screw from the vicinity of the central portion in the rotation axis direction of the developing sleeve.

  The developing device according to the present invention partitions the first chamber and the second chamber, each of which contains a developer containing toner and a carrier, the first chamber and the second chamber, and the first chamber and the second chamber. A developer container having a partition formed with a communication portion for communicating with the second chamber, wherein a developer circulation path is formed between the first chamber and the second chamber; and development in the first chamber A developing sleeve that carries the developer and rotates; a first conveying screw that conveys the developer along the rotational axis direction of the developing sleeve in the first chamber; and a rotational axis direction of the developing sleeve within the second chamber. A second conveying screw that conveys the developer along the developer sleeve; a pumping pole that is non-rotatably disposed in the developing sleeve and pumps up the developer in the first chamber to the developing sleeve; and a developer carried on the developing sleeve The first chamber Comprising a magnetic field generating means having a plurality of magnetic poles including a stripping pole back, the.

  Then, at least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve, and the rotation axis of the developing sleeve. The average value of the magnetic force of the portion where the magnetic force on the downstream side in the developer conveyance direction is increased is more in the vicinity of the central portion than the vicinity of the central portion in the direction. It is characterized by being in the range of 2.5 mT or more and 12.5 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw.

  Further, at least one magnetic pole of the pumping pole and the stripping pole has the magnetic force peak of the magnetic pole halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotational direction of the sleeve, is increased more downstream in the developer transport direction of the first transport screw than in the vicinity of the central portion in the rotational axis direction of the developing sleeve. The average half-value width of the portion where the half-value width on the downstream side in the direction is increased is 1 ° or more with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width in the vicinity of the center portion It is the range of 5 degrees or less.

  Further, at least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve, and the rotation axis of the developing sleeve. The portion where the magnetic force is increased on the downstream side in the developer transport direction of the first transport screw relative to the vicinity of the central portion in the direction is equal to the length in the developer transport direction. When divided into sections, the average value of the magnetic force of the downstream section of the two sections is larger than the average value of the magnetic force of the upstream section, and the average value of the magnetic force of the downstream section is near the central portion. It is characterized by being in the range of 2.5 mT or more and 15 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw.

  Further, at least one magnetic pole of the pumping pole and the stripping pole has the magnetic force peak of the magnetic pole halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotational direction of the sleeve, is increased more downstream in the developer transport direction of the first transport screw than in the vicinity of the central portion in the rotational axis direction of the developing sleeve. When the portion where the half-value width on the downstream side in the direction is increased is divided into two sections having the same length in the developer transport direction, the average half-value width of the downstream section of the two sections is half of the upstream section. The average value of the half-value width of the downstream section is larger than the average value of the value width, and the average value of the half-value width in the vicinity of the center portion is 1 with respect to the average value of the region corresponding to one pitch of the first conveying screw. More than 6 degrees It is characterized by the following range.

  Further, at least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve, and the rotation axis of the developing sleeve. The portion increased in the developer conveyance direction downstream side of the first conveyance screw from the vicinity of the central portion in the direction, and the portion where the magnetic force on the downstream side in the developer conveyance direction is increased corresponds to one pitch of the first conveyance screw. The average value of the magnetic force in each region corresponding to the point increases monotonously toward the downstream side, and the average value of the magnetic force in the most downstream region corresponds to one pitch of the first conveying screw of the magnetic force in the vicinity of the central portion. It is the range of 2.5 mT or more and 17.5 mT or less with respect to the average value of the area | region to perform.

  Further, at least one magnetic pole of the pumping pole and the stripping pole has the magnetic force peak of the magnetic pole halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotational direction of the sleeve, is increased more downstream in the developer transport direction of the first transport screw than in the vicinity of the central portion in the rotational axis direction of the developing sleeve. In the portion where the half-value width on the downstream side in the direction is increased, the average value of the half-value width of each region corresponding to one pitch of the first conveying screw monotonously increases toward the downstream side. The average value of the value ranges is in a range of 1 ° to 7 ° with respect to an average value of a region corresponding to one pitch of the first conveying screw having a half-value width near the central portion.

  According to the present invention, both suppression of image unevenness and suppression of developer deterioration can be achieved.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic configuration diagram illustrating a part of the image forming apparatus. 1 is a schematic cross-sectional view of a developing device according to a first embodiment. FIG. 4 is a schematic view illustrating a developing device as viewed from above in FIG. 3 with a part thereof omitted. FIG. 3 is a schematic configuration diagram illustrating a positional relationship between a developing sleeve and a photosensitive drum. (A) The figure which shows magnetic force distribution of the magnet roll which concerns on 1st Embodiment, (b) The schematic diagram which shows magnetic force distribution of the magnet roll in a developing device. FIG. 2 is a schematic diagram showing a developing device of a bottom peeling / up-pump system. FIG. 2 is a schematic diagram showing a developing device of an upper peeling / lower pumping system. The figure which shows the image nonuniformity which is easy to generate | occur | produce when a solid image is output. The figure which shows the relationship between TD ratio and image density. FIG. 3 is a schematic diagram showing a developer flow when the developer deteriorates in the developing device of the bottom peeling / up-pumping system. FIG. 3 is a schematic diagram showing the flow of developer when the developer deteriorates in an upper stripping / lower pumping developing device. FIG. 6 is a schematic diagram showing a distribution of average values of magnetic force or half-value width of magnetic poles in the rotation axis direction of the developing sleeve of the developing device according to the first embodiment. FIG. 9 is a schematic diagram illustrating a distribution of average values of magnetic force or half-value width of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a second embodiment. FIG. 10 is a schematic diagram showing a distribution of average values of magnetic force or full width at half maximum of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a third embodiment. The figure which shows the image nonuniformity which is easy to generate | occur | produce when a halftone image is output continuously after a solid image output. In order to explain the problem according to the fourth embodiment, (a) a schematic diagram of a developing device shown together with a magnetic force distribution of a magnet roll, (b) a part of the developing device viewed from above (a) is omitted. FIG. FIG. 10 is a schematic diagram illustrating a distribution of an average value of magnetic force or full width at half maximum of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a fourth embodiment. FIG. 10 is a schematic diagram showing a distribution of an average value of magnetic force or full width at half maximum of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a fifth embodiment with a part thereof omitted. FIG. 10 is a schematic diagram showing a distribution of an average value of magnetic force or full width at half maximum of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a sixth embodiment with a part thereof omitted. FIG. 10 is a schematic diagram illustrating a distribution of an average value of magnetic force or full width at half maximum of a magnetic pole in a rotation axis direction of a developing sleeve of a developing device according to a seventh embodiment with a part thereof omitted.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, the schematic configuration of the image forming apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2.

[Image forming apparatus]
The image forming apparatus 100 according to the present embodiment receives image information from a document reading apparatus connected to the apparatus main body 101 or a host device such as a personal computer connected to the apparatus main body so as to be communicable. Then, according to the image information, the image forming apparatus 100 uses four-color full-color images of yellow (Y), magenta (M), cyan (C), and black (K) as paper, plastic sheet using an electrophotographic method. The recording material S such as cloth is formed.

  In this embodiment, such an image forming apparatus 100 has a so-called tandem configuration in which four color image forming portions PY, PM, PC, and PK are arranged in the rotation direction of the intermediate transfer belt 51 as an intermediate transfer member. Adopted. The image forming units PY, PM, PC, and PK form yellow, magenta, cyan, and black images, respectively. The intermediate transfer belt 51 provided in the transfer device 5 is formed in each image forming unit on the intermediate transfer belt 51 while moving in the direction indicated by the arrow and passing through each image forming unit PY, PM, PC, PK. The toner image is transferred in a superimposed manner. The multiple toner images superimposed on the intermediate transfer belt 51 are transferred to the recording material S to obtain a recorded image.

  In the present embodiment, the configurations of the image forming units PY, PM, PC, and PK are substantially the same except that the development colors are different. Therefore, the image forming unit PK will be described as a representative with reference to FIG.

  The image forming unit PK has a photosensitive drum 1 made of a drum-shaped photosensitive member as an image carrier. On the outer periphery of the photosensitive drum 1, a charging roller 2, a developing device 4, a transfer device 5, and a cleaning device 7 are disposed. At the time of image formation, first, the surface of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2 as a charging unit. Next, an electrostatic latent image is formed on the photosensitive drum 1 by performing scanning exposure on the surface of the charged photosensitive drum 1 in accordance with an image information signal by an exposure device 3 as an exposure unit. In the present embodiment, the exposure apparatus 3 includes a laser exposure optical system.

  The electrostatic latent image formed on the photosensitive drum 1 is visualized as a toner image with the developer toner using the developing device 4. The toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 51 by the action of the primary transfer bias applied to the primary transfer roller 52 of the transfer device 5 in the primary transfer portion where the intermediate transfer belt 51 and the photosensitive drum 1 abut. 51 is transferred (primary transfer) onto 51. For example, when a four-color full-color image is formed, a toner image is sequentially transferred from the photosensitive drum 1 of each image forming unit onto the intermediate transfer belt 51 from the image forming unit PY, and a four-color toner image is formed on the intermediate transfer belt 51. Is formed to form a multiple toner image.

  Here, the transfer device 5 includes an intermediate transfer belt 51 and a primary transfer roller 52. The intermediate transfer belt 51 is wound around a plurality of rollers and rotates (circulates) in the direction of the arrow in the drawing. The primary transfer roller 52 is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 51 interposed therebetween. Further, a secondary transfer outer roller 53 b is disposed at a position facing the secondary transfer inner roller 53 a that stretches the intermediate transfer belt 51 through the intermediate transfer belt 51.

  Deposits such as toner remaining on the photosensitive drum 1 after the primary transfer step are collected by a cleaning device 7 as a cleaning unit. Thereby, the photosensitive drum 1 is prepared for the next image forming process.

  On the other hand, as shown in FIG. 1, a recording material S is accommodated in a cassette 9 as a recording material accommodation portion. Then, the recording material S in the cassette 9 is conveyed by a recording material conveying member such as a pickup roller, a conveying roller 10 and a registration roller 11. The conveyed recording material S is conveyed by the registration roller 11 to the secondary transfer portion where the intermediate transfer belt 51 and the secondary transfer outer roller 53b are in contact with each other in synchronization with the toner image on the intermediate transfer belt 51. . The multiple toner images on the intermediate transfer belt 51 are transferred onto the recording material S by the action of the secondary transfer bias applied to the secondary transfer outer roller 53b in the secondary transfer portion.

  Deposits such as toner remaining on the intermediate transfer belt 51 after the secondary transfer process are removed by the intermediate transfer belt cleaner 54. The toner removed by the cleaning device 7 and the intermediate transfer belt cleaner 54 is conveyed by a conveyance pipe (not shown) and collected in a collection toner box.

  The recording material S to which the toner image has been transferred at the secondary transfer portion and separated from the intermediate transfer belt 51 is conveyed to the fixing device 6. The toner image transferred onto the recording material S is melted and mixed by being heated and pressurized by the fixing device 6 and is fixed onto the recording material S. Thereafter, the recording material S is discharged to the discharge tray 12.

  Note that the image forming apparatus 100 according to the present embodiment forms a single-color or multi-color image using an image forming unit for a desired single color or some of four colors, such as a black single-color image. Is also possible.

[Developer]
Next, the developing device 4 of this embodiment will be further described with reference to FIGS. The developing device 4 includes a developing container 41 that stores a two-component developer including a nonmagnetic toner and a magnetic carrier. The developing container 41 is provided with a developing sleeve 44 as a developer carrying member, a magnet roll 44a as a magnetic field generating means, a developing blade 42 as a developer regulating member, and the like.

  Specifically, a portion of the developing container 41 facing the photosensitive drum 1 is open, and a part of the developing sleeve 44 is exposed to the developing container as shown in FIG. 41 is supported so as to be rotatable. The developing sleeve 44 and the photosensitive drum 1 are arranged with a predetermined gap. The developing sleeve 44 is formed in a cylindrical shape and can carry a developer on its surface, and is rotationally driven by a driving source such as a motor (not shown). The developing sleeve 44 transports the carried developer to a developing area facing the photosensitive drum 1 so that toner can be supplied to the electrostatic latent image formed on the photosensitive drum 1.

  The magnet roll 44a is made of a magnet having a plurality of magnetic poles, and is disposed in the developing sleeve so as not to rotate. The detailed configuration of the magnet roll 44a will be described later. The developing blade 42 is disposed so as to face the surface of the developing sleeve 44 with a predetermined gap, and regulates the amount (layer thickness) of the developer carried on the developing sleeve 44. The developing sleeve 44 conveys a thin layer of developer regulated by the developing blade 42 to the above-described developing region.

  Further, the developing container 41 includes a developing chamber 41a as a first chamber and a stirring chamber 41b as a second chamber each containing a developer containing toner and a carrier, and a partition wall 45 that partitions the developing chamber 41a and the stirring chamber 41b. And have. A first conveying screw 46a is disposed in the developing chamber 41a, and a second conveying screw 46b is disposed in the stirring chamber 41b. The first conveying screw 46a and the second conveying screw 46b are each provided with a spiral blade on the rotating shaft.

  As shown in FIG. 4, the first conveying screw 46 a conveys the developer in the direction of the arrow D <b> 1 along the rotation axis direction of the developing sleeve 44 in the developing chamber 41 a (first chamber). The second conveying screw 46b agitates the developer in the direction of the arrow D2 which is opposite to the conveying direction of the first conveying screw 46a along the rotation axis direction of the developing sleeve 44 in the agitating chamber 41b (second chamber). While transporting.

  As shown in FIG. 4, the partition wall 45 is formed with a first opening 45 a and a second opening 45 b as communication portions at portions near both ends in the longitudinal direction of the developing device 4 (rotational axis direction of the developing sleeve 44). Yes. The developing chamber 41a and the stirring chamber 41b are communicated with each other by the first opening 45a and the second opening 45b, and a developing agent circulation path is formed by the developing chamber 41a and the stirring chamber 41b.

  Further, as shown in FIG. 3, the developer is replenished to the developing container 41 from a replenishing device 47. The replenishing device 47 is supplied with a developer containing toner and carrier at a predetermined ratio from the toner bottle 8 shown in FIG. The replenishing device 47 replenishes the developer container 41 with the developer according to the amount of toner consumed in image formation or based on other predetermined conditions. As shown in FIG. 4, the developer replenishment position T0 by the replenishing device 47 is located upstream of the second conveying screw 46b in the stirring chamber 41b in the developer conveying direction. The developer is replenished from the replenishing device 47 by dropping the developer into the stirring chamber 41b by gravity. The supplied developer is transported by the second transport screw 46b while being mixed and stirred with the developer in the stirring chamber 41b. Since the developer replenishment position T0 is on the upstream side of the stirring chamber 41b, a sufficient distance for mixing and stirring of the second transport screw 46b can be secured, and the developer that has been replenished and the stirring chamber 41b while transported. Mixing and stirring with the developer inside can be promoted.

  The developer conveyed in the stirring chamber 41b by the second conveying screw 46b is sent to the developing chamber 41a through the first opening 45a. The developer in the developing chamber 41a is transported by the first transport screw 46a. At this time, the developer in the developing chamber 41 a is supplied to the developing sleeve 44. That is, as will be described in detail later, a part of the developer in the developing chamber 41a is pumped up (magnetically attracted) to the developing sleeve 44 by the magnetic force of the magnet roll 44a disposed in the developing sleeve 44. As a result, a developer magnetic brush is formed on the surface of the developing sleeve 44. In the developing area of the developing sleeve 44, toner is selected from the magnetic brush to the electrostatic latent image by an electric field between the photosensitive drum 1 on which the electrostatic latent image is formed and the developing sleeve 44 to which an electrical bias is applied. The electrostatic latent image is developed by supplying and adhering.

  The developer remaining in the developing sleeve 44 after supplying the toner to the electrostatic latent image is peeled off from the developing sleeve 44 and returned to the developing chamber 41a. The developer returned to the developing chamber 41a is conveyed by the first conveying screw 46a while being mixed and stirred with the developer in the developing chamber 41a. The developer transported by the first transport screw 46a is sent to the stirring chamber 41b through the second opening 45b, and is transported while being stirred in the stirring chamber 41b as described above. In this way, the developer circulates between the developing chamber 41a and the stirring chamber 41b.

  As shown in FIG. 4, return screws 48a and 48b for conveying developer in the opposite direction to the respective screws are provided at the downstream end of the first conveying screw 46a and the downstream end of the second conveying screw 46b, respectively. They are arranged together. As a result, the developer conveyed downstream by the first conveying screw 46a is pushed back by the return screw 48a and sent to the stirring chamber 41b through the first opening 45a. Similarly, the developer conveyed downstream by the second conveying screw 46b is pushed back to the return screw 48b and sent to the developing chamber 41a through the second opening 45b.

[Magnet roll]
Next, the magnet roll 44a will be described with reference to FIGS. As described above, the magnet roll 44a is fixed in the developing sleeve 44 so as not to rotate. Then, the developing sleeve 44 rotates with respect to the magnet roll 44a, so that the developer is carried and conveyed to the developing sleeve 44 by the magnetic force of the internal magnet roll 44a and the rotational force of the developing sleeve 44 in the circumferential direction. .

  Here, the magnet roll 44a has a plurality of magnetic poles. FIG. 6A shows a magnetic force distribution in the rotation direction of the developing sleeve 44 of the magnet roll 44a. The magnet roll 44a includes a plurality of magnetic poles such as a development pole Pd, a take-in pole Pe, a stripping pole Pr, a pumping pole Pt, and a cut pole Pk.

  The developing pole Pd is in the vicinity of the position facing the photosensitive drum 1 and is a pole that develops a developer, forms a magnetic brush, puts toner on the electrostatic latent image, and develops it. The take-in pole Pe is a pole that is located downstream of the developing pole Pd in the rotation direction of the developing sleeve 44 and carries the developer and takes the developer into the developing container 41. The stripping pole Pr is located in the developing container 41 downstream of the developing sleeve 44 in the rotation direction of the taking-in pole Pe, and the developer is removed from the developing sleeve so as not to leave a history of toner consumption due to the development in the next development. 44 is a pole once peeled off. That is, it is a pole that peels off the developer carried on the developing sleeve 44 and returns it to the developing chamber 41a. The pumping pole Pt is a pole that pumps the developer in the developing chamber 41 a to the developing sleeve 44. The cut pole (regulatory pole) Pk is a pole that makes the developer coat amount of the developing sleeve constant, that is, the developer blade 42 regulates the amount of developer carried on the developing sleeve 44 facing the developing blade 42. It is.

  Although the above-described magnetic pole arrangement is merely an example, the magnetic pole arrangement of the magnet roll for the two-component developer is generally configured based on the above-described idea. Basically, the S-pole and the N-pole are alternately arranged to promote the conveyance of the developer. On the other hand, the part where the developer is peeled off is made to have the same polarity, so that a part having no magnetic force or extremely weak is made to improve the peelability. When the above configuration is adopted, the number of magnetic poles is generally an odd number.

  Such a plurality of magnetic poles are sequentially arranged in the rotation direction of the developing sleeve 44, and are arranged as shown in FIG. Specifically, the developing sleeve 44 and the magnet roll 44a are arranged so that the central axis is above the central axis of the first conveying screw 46a, and the pumping pole Pt is located below the stripping pole Pr. .

  Next, the configuration of each magnetic pole will be described in more detail. In general, it is preferable that the pole on the side close to the photosensitive drum 1 has a stronger magnetic force than the pole on the side opposite to the photosensitive drum. Among these, it is particularly preferable that the development pole and the pole downstream thereof (in this embodiment, the capture pole) have a pole configuration having a strong magnetic force. The reason is described below.

[Development pole]
The developing pole Pd needs to form a magnetic brush for developing the electrostatic latent image, and needs a strong magnetic force to prevent carrier adhesion. Here, the carrier adhesion means that when the developer carried on the developing sleeve 44 develops the electrostatic latent image on the photosensitive drum 1, the carrier, which should originally remain on the developing sleeve 44, together with the toner is the photosensitive drum. 1 is a phenomenon of adhering to the top. This is due to the balance between the electric force applied to the carrier toward the photosensitive drum 1 and the magnetic force of the magnet roll 44a. If the electric force is greater than the magnetic force, the carrier adheres to the photosensitive drum 1. The adhered carrier is transferred to the recording material and fixed together with the toner, but it affects the transfer device and the fixing device so as to reduce the reliability of the image forming apparatus. In addition, since the unevenness with the carrier attached remains in the output image, the image quality is lowered.

  In order to prevent such carrier adhesion, it is conceivable to reduce the electric force applied to the carrier by adjusting the charging potential of the photosensitive drum 1 and the potential of the developing sleeve 44. However, in this case, image defects such as background contamination in which toner adheres to portions other than the electrostatic latent image are likely to occur. Therefore, in this embodiment, the magnetic force of the developing pole Pd is a relatively strong magnetic force of about 80 mT to 160 mT. In order to reduce carrier adhesion more efficiently, the magnetic force of the developing pole Pd is preferably set to about 100 mT to 140 mT. The lower limit in this case considers carrier adhesion, and the upper limit is a value determined by the volume of the magnet roll 44a and the magnetic force per volume.

[Cut pole]
Since the magnet is a dipole in which the S pole and the N pole are a pair, if the magnetic force of the developing pole Pd is increased, it is necessary to increase the magnetic force of the reverse polarity magnetic pole with a magnetic pole other than the developing pole and balance it. Here, a magnetic pole other than the developing pole and the most suitable magnetic pole having a reverse polarity is a magnetic pole adjacent to the developing pole. Furthermore, the pole upstream of the development pole Pd is generally the cut pole Pk in many cases. When the magnetic force of the cut pole Pk is increased, a large amount of developer gathers in the vicinity of the developing sleeve 44 for making the toner coat amount of the developing sleeve 44 constant, and the pressure of the developer increases, which may cause deterioration of the developer. This is not preferable.

  For this reason, in this embodiment, the magnetic force of the cut pole Pk is a relatively weak magnetic force of about 70 mT to 30 mT. The cut pole Pk has a half width of 40 ° to 20 °, which is the width between two points in the rotation direction of the developing sleeve 44 at which the magnetic force peak of the magnetic pole is halved. In order to further suppress the deterioration of the developer, it is preferable that the magnetic force of the cut pole Pk is about 55 mT to 35 mT and the half width is 35 ° to 20 °. In this case, the lower limit takes into consideration the developer cutting property for forming a thin layer of the developer, and the upper limit is a value determined by the degree of deterioration of the developer, that is, the required life of the developer.

[Capture pole]
On the other hand, the take-in pole Pe, which is the pole downstream of the development electrode Pd, only conveys the developer thin layer, and therefore has little relation to the deterioration of the developer. Therefore, in order to balance with the development pole, it is preferable to increase the magnetic force of the take-in pole Pe, which is the pole downstream of the development pole. The magnetic force of the take-in pole Pe may be designed relatively freely in order to balance the entire magnetic force. However, in the present embodiment, in consideration of the above-described balance, it is set to be equal to or close to the development pole Pd. .

[Peeling pole and pumping pole]
Of the plurality of magnetic poles of the magnet roll 44a, the magnetic force of the poles other than the developing pole Pd and the take-in pole Pe may be relatively weak. The reason is as follows. The magnet roll 44a basically has a configuration in which S-poles and N-poles are alternately arranged to facilitate the conveyance of the developer. Therefore, the magnetic pole adjacent to the development pole Pd is a pole having the opposite polarity to the development pole. On the other hand, a stripping portion (in this embodiment, the stripping pole Pr and the pumping pole Pt) that strips the developer from the developing sleeve 44 is adjacent to the developing pole Pd with one magnetic pole. For this reason, the stripping pole Pr and the pumping pole Pt have the same polarity as the development pole Pd, and the two magnetic poles have the same polarity, thereby creating a portion having no magnetic force or extremely weakness. It can improve the peelability.

  Here, these two strips of the developer having the same polarity as the developing pole Pd (the stripping pole Pr and the pumping pole Pt) have a relatively high magnetic force balance in order to increase the magnetic force of the developing pole Pd. A weak magnetic force is preferred. In addition, since this portion is a portion where the developer tends to gather next to the cut pole Pk, the relatively weak magnetic force is less likely to cause the agent deterioration. In order to fulfill the function of the developer peeling portion 2 magnetic poles, in this embodiment, the magnetic force of the peeling pole Pr and the pumping pole Pt is about 10 mT to 50 mT, and the half width is 40 ° to 20 °.

[Arrangement of magnetic poles]
Next, two examples of developing devices having different magnetic pole arrangements of the magnet roll will be described with reference to FIGS. These two examples of the developing device have different magnetic pole arrangements of the magnet roll, and accordingly, the arrangement of the developing blade and the shape of the developing container are different, but the basic configuration of each part is the same. Will be described.

  First, as shown in FIG. 7, the part where the developer t is peeled off from the developing sleeve 44 is located below the developing sleeve 44, and the part where the developer is pumped up to the developing sleeve 44 is located above the developing sleeve 44. A certain configuration will be described. Also in this configuration, the developing sleeve 44 is disposed such that the central axis is above the central axis of the first conveying screw 46a. In addition, the pumping pole of the magnet roll is positioned above the stripping pole so that the stripping site is positioned on the lower side and the pumping site is positioned on the upper side. Hereinafter, such a system is referred to as “under-peeling / up-pumping system”.

  Next, as shown in FIG. 8, the peeling portion for peeling the developer t from the developing sleeve 44 is on the upper side of the developing sleeve 44, and the pumping portion for pumping the developer to the developing sleeve 44 is on the lower side of the developing sleeve 44. The structure in is described. Also in this configuration, the developing sleeve 44 is disposed such that the central axis is above the central axis of the first conveying screw 46a. Further, the pumping pole of the magnet roll is positioned below the stripping pole so that the stripping site is positioned on the upper side and the pumping site is positioned on the lower side. Hereinafter, such a system is referred to as a “top stripping / bottom pumping system”.

[Screw trace]
Next, a detailed description will be given of screw marks, which are image unevenness that occurs in an area corresponding to the downstream side of the developing chamber in the developer transport direction when an image with a large amount of toner consumption such as a solid image is output. First, if the developer carried on the developing sleeve 44 is not peeled off from the developing sleeve 44 once, a portion where the TD ratio is lowered due to toner consumption accompanying the previous image formation remains in the developing sleeve 44. Then, the portion where the TD ratio is low and the developability is lower than the surrounding area reaches the development area again, and is used for development. , “Sleeve ghost”). Therefore, as in the present embodiment, the “sleeve ghost” is suppressed by removing the developer from the developing sleeve 44 once.

  However, when an image with a large amount of toner consumption represented by a solid image is output, the developer having a low TD ratio of the toner to the carrier is peeled off from the developing sleeve and returned to the developing chamber. As a result, the developer immediately after being peeled off from the developing sleeve may move on the surface layer of the developer having a relatively high TD ratio in the developing chamber, and a phenomenon that the pump is immediately pumped up to the developing sleeve (accompanying) may occur. At this time, as shown in FIG. 9, image unevenness in which the image becomes slanted may occur. Since the oblique image unevenness is a trace related to the first conveying screw 46a in the developing chamber 41a, such image unevenness will be referred to as “screw trace” hereinafter.

  As described above, screw traces resulting from toner consumption of a solid image tend to occur at an image position corresponding to the downstream side of the circulation of the agent on the developing chamber side and hardly occur at an image position corresponding to the upstream side. That is, on the upstream side of the developing chamber, the developer that is sufficiently stirred in the stirring chamber and has a relatively high TD ratio is sent, so that the TD ratio tends to be relatively high. On the other hand, on the downstream side of the developing chamber, the developer having a low TD ratio peeled off from the developing sleeve flows, so that the TD ratio tends to be low. As a result, the above-described screw marks are likely to occur in a region corresponding to the downstream side of the developer chamber in the developer conveyance direction.

  More specifically, as shown in FIG. 10, the general relationship between the TD ratio and the image density is that when the TD ratio is high, the image density is in a saturated state. By changing the image density (when the latent image potential is the same). For this reason, if the TD ratio is set to a high value, density unevenness is unlikely to occur, but toner scattering due to the lower charge of the toner becomes a problem. Therefore, the toner ratio (TD ratio) in the developer is usually adjusted to about 5% to 13%. In the conventional developing device, even when the TD ratio is adjusted within this range, as the developer progresses, the screw mark is generated at the image position corresponding to the downstream side of the developer circulation on the developing chamber side as described above. It was easy.

  Here, in any of the configurations of the above-described “under-peeling / uplifting system” and “upper-peeling / underpumping system”, the developer used for development is not immediately drawn up in the developing chamber. After that, the developer is pumped up after the first conveying clew is rotated once. For this reason, the concentration unevenness of the agent can be alleviated while the first conveying screw rotates once.

  However, when the developer has deteriorated due to long-term use, the adhesion of the developer to the developing sleeve increases. In the case of the “under-peeling / up-pumping system”, as shown in FIG. 11, the amount of the developer “together” with the developing sleeve 44 increases. Similarly, in the case of “peeling up / pumping down”, the amount of the developer “together” with the developing sleeve 44 increases as shown in FIG. For this reason, in the conventional developing device, there is a possibility that the above-mentioned screw mark may be generated due to the deterioration of the developer.

[Deterioration of screw marks and developer]
In order to reduce such screw marks, as described above, it is conceivable to increase the magnetic force of at least one of the pumping pole, cut pole, and stripping pole. However, in any of the configurations, simply increasing the magnetic force of the magnetic pole promotes the deterioration of the developer. More specifically, when the magnetic force or full width at half maximum of the cut pole is increased in the entire rotation axis direction of the developing sleeve, pressure is applied to the developer in the agent reservoir where the developer is accumulated on the upstream side of the developing blade. For this reason, embedding of the external additive into the toner base is promoted, and the developer deterioration (toner deterioration) tends to be promoted.

  Further, when the magnetic force or half width of the pumping pole or the stripping pole is increased in the entire rotation axis direction of the developing sleeve, the force for attracting the developer to the developing sleeve increases. For this reason, although it is better than when the magnetic force of the cut pole is increased, the deterioration of the developer (toner deterioration) tends to be promoted.

  Summarizing the above, it becomes as shown in Table 1 below, and in any configuration, the effect of reducing the screw marks can be expected, but the deterioration of the agent tends to be promoted easily. “◯” in Table 1 indicates that screw marks can be reduced, “×” indicates that agent deterioration occurs, and “XX” indicates that agent deterioration occurs particularly.

  From the above, it is desired to achieve both contradictory events of screw mark reduction and developer deterioration suppression. On the other hand, in recent years, the toner base has been shifted to a softer tendency to save energy in the image forming apparatus, so that the external additive is easily embedded in the toner base. In other words, developer deterioration tends to occur easily. Furthermore, since the share of the developer increases as the speed of the image forming apparatus increases, developer deterioration tends to occur.

[Configuration of magnetic pole of this embodiment]
In order to solve the above-described problems, in the present embodiment, attention is paid to how the screw marks are generated during the solid image, and both the screw marks and the deterioration of the developer are suppressed.

  Here, in the developing device 4 of the present embodiment, as shown in FIG. 6, the pumping pole Pr of the magnet roll 44a is positioned below the stripping pole Pt. That is, the “top stripping and bottom pumping system” configuration is adopted. This is due to the following reason. That is, in the case of the “under-peeling / up-pumping system” configuration, if the developer surface in the developing chamber is high to some extent, this becomes a barrier, and the agent with a low TD ratio that is peeled off from the developing sleeve may slide on the developer surface. Hard to occur. For this reason, there is a tendency that the “spinning” of the developer by the above-described developing sleeve hardly occurs. On the other hand, in the case of the “upper stripping / lower pumping system” configuration, even if the developer surface is high, it is difficult to form a barrier that suppresses “catch-up” of the developer. For this reason, when the developer has deteriorated due to long-term use, it is more difficult to suppress “catch-up” of the developer than the “upper stripping / lower pumping system”, and screw marks are likely to occur. Therefore, in the present embodiment, a configuration of “upper peeling / lower pumping system” is adopted.

  In the present embodiment, as described above, the following magnetic poles are used by utilizing the characteristic that a screw mark is likely to be generated in an image at a position corresponding to the downstream side of the first conveying screw 46a of the developing chamber 41a in the developer conveying direction. The configuration is as follows. That is, as shown in FIG. 13, at least one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt increases the magnetic force or the half width at a position corresponding to the downstream side of the developing chamber 41a. I am letting. Specifically, in the portion corresponding to the image forming area of the developing sleeve 44 in the rotation axis direction, the magnetic force or half value width of the magnetic pole of the first conveying screw 46a is set to be larger than that in the vicinity of the central portion of the developing sleeve 44 in the rotation axis direction. It is increased on the downstream side in the developer conveyance direction.

  Here, the image forming region in the rotation axis direction (longitudinal direction) of the developing sleeve 44 is a region facing the maximum size image that can be formed on the photosensitive drum 1 in the region of the developing sleeve 44 in the rotation axis direction. . In the present embodiment, this corresponds to the non-image forming area deviated from the image forming area in the longitudinal direction, even if a screw mark is generated, it does not appear on the image. However, the magnetic force or full width at half maximum may be increased to the non-image forming area.

  The half width is an angle between positions in the rotation direction of the developing sleeve at which the magnetic force peak of the magnetic pole becomes half. In addition, the magnetic force and the half-value width may be increased, or the magnetic force and the half-value width may be increased on the downstream side in the developer transport direction of the first transport screw 46a from the vicinity of the central portion in the rotation axis direction of the developing sleeve 44 of the magnetic pole. Both price ranges may be used.

  This will be described more specifically. In this embodiment, the magnetic force or the full width at half maximum is increased in the entire longitudinal position corresponding to the downstream side from the longitudinal center of the developing sleeve 44. The region where the magnetic force or the half width is increased may be on the downstream side from the vicinity of the central portion of the developing sleeve 44. If the region where the screw mark is likely to be generated in the apparatus is increased, the increased region is the center. It may be from slightly upstream or downstream from the part.

  In this embodiment, the magnetic force and half width of the cut pole Pk, the magnetic force and half width of the pumping pole Pr, and the magnetic force and half width of the stripping pole Pt are all increased on the downstream side of the central portion. Further, the increment Δ is a difference from the average value of the increased portion on the basis of the average value of the region corresponding to one pitch of the first conveying screw 46 in the portion not increasing near the center in the longitudinal direction of the developing sleeve 44. It was. The length of the increased portion naturally has a length of one pitch or more of the first conveying screw 46, and the average value of the magnetic force or the half width within this length range is increased from the above-mentioned reference. ing.

  The reason for comparing the average values of the lengths of one pitch or more of the first conveying screw 46 is the following two points. The first point is that, in general, the magnetic force and the half-value width in the longitudinal direction of the magnet roll vary somewhat. The second point is a relatively macro unevenness in which the screw mark interval corresponds to one pitch of the first conveying screw 46 (12 mm interval in the present embodiment). For this reason, even if there is a variation in the fine value of the magnetic force of less than 1 pitch, the screw marks are not so much affected.

  The reference in the present embodiment is that the magnetic force of the cut pole Pk is 45 mT and the half width of the cut pole Pk is 30 °. The magnetic force of the pumping pole Pr is 30 mT, and the half width of the pumping pole Pr is 25 °. Further, the magnetic force of the stripping pole Pt was 30 mT, and the half width of the stripping pole Pr was 25 °. Then, the magnetic force or the full width at half maximum is increased with respect to this reference at the longitudinal position corresponding to the downstream side.

  Specifically, the average value of the magnetic force downstream of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 10 mT with respect to the reference. In addition, the average value of the half widths on the downstream side of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in a range of 1 ° to 4 ° with respect to the reference.

  As described above, in this embodiment, the magnetic force or the half-value width is increased on the downstream side where the screw trace of the magnetic pole is likely to be generated, and the magnetic force or half-value width is increased on the upstream side of the central portion and the central portion where the screw trace is not easily generated. I try not to let you. Thereby, it is possible to achieve both suppression of screw marks (image unevenness) and suppression of developer deterioration.

  That is, when the magnetic force or full width at half maximum of the pumping pole Pr is increased, the amount of developer pumped up to the developing sleeve 44 can be increased, so that the ratio of the developer having a low TD ratio of the developer pumped up can be reduced. When the magnetic force or full width at half maximum of the cut pole Pk is increased, the circulation of the developer is promoted in the agent reservoir upstream of the developing blade 42. When the magnetic force or half-value width of the stripping pole Pt is increased, the developer spiked along the magnetic field lines of the stripping pole Pt is stripped while straddling the developer conveyed from upstream in the developing chamber 41a. For this reason, the developer having a low TD ratio is agitated while the first conveying screw 46a makes one rotation, and unevenness of the TD ratio is reduced. Therefore, by increasing the magnetic force or the half-value width of at least one of the magnetic poles in a region corresponding to the downstream side of the central portion of the developing sleeve 44 where the screw trace is likely to occur, the above-described action occurs, and the screw trace is generated. Can be suppressed. On the other hand, by preventing the magnetic force or full width at half maximum from being increased at the central portion of the developing sleeve 44 and the upstream side thereof where screw marks are unlikely to occur, it is possible to suppress an increase in pressure applied by the developer and to suppress deterioration of the developer. .

[Example 1]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or half-value width of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. Also, the value to be increased was changed. In each case, an image was output and evaluated for screw marks and developer deterioration. As for the evaluation method, the screw marks were obtained by evaluating the output images of 20 persons. The evaluation points were 2 points when the screw trace was not visible, 1 point when the screw trace was faint but not worrisome, and 0 when the screw trace was anxious. And the average score of 20 people is calculated, and after rounding off the second decimal place, 1.5 or more and 2 or less is ◯, 0.8 or more, less than 1.5 is △, 0.8 Less than was made x.

  Further, the deterioration level of the developer was evaluated as follows. When the developer is deteriorated, the adherence of the developer to the developing sleeve is increased, so that the developability, transfer property, fixability, and the like are lowered. For this reason, when the deterioration of the developer is progressing, an image in which a solid image has voids is formed. The deterioration of the developer is more likely to proceed at a low image ratio (1%), and in this state, a level at which there is no problem at the time of 10,000 sheets of A4 size paper output was set as the life target. Then, after outputting 10,000 sheets at an image ratio of 1%, a solid image (image ratio 100%) was output, and this was evaluated by 20 people using the same method as described above. The evaluation score was 2 points when the void was not visible, 1 point when the void was faint but not concerned, and 0 when the void was anxious. And the average score of 20 people is calculated, and after rounding off the second decimal place, 1.5 or more and 2 or less is ◯, 0.8 or more, less than 1.5 is △, 0.8 Less than was made x. The evaluation results are shown in Tables 2 to 5. Table 2 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 3 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 4 shows the evaluation results of the screw marks when the half width is changed, and Table 5 shows the evaluation results of the developer deterioration level when the half width is changed.

  As shown in Tables 2 to 5, when the magnetic force or full width at half maximum is increased in the entire longitudinal position corresponding to the downstream side of the central portion in the image forming region of the developing sleeve 44, the following conditions are satisfied. It was found that the deterioration of the screw marks and developer can be suppressed. That is, the average value of the magnetic force of the portion where the magnetic force on the downstream side of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2.5 mT to 10 mT with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 7.5 mT with respect to the reference.

  In addition, the average value of the half-value width of the portion where the half-value width on the downstream side of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 1 ° or more with respect to the reference. It may be within a range of 4 ° or less. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 3 ° with respect to the reference.

  Furthermore, when the pumping pole Pt and the stripping pole Pr are limited to have a small toner share and a large effect of screw mark reduction, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood. That is, the average value of the magnetic force of the portion where the magnetic force on the downstream side of at least one of the pumping pole Pt and the stripping pole Pr is increased is in the range of 2.5 mT to 12.5 mT with respect to the reference. If it is good. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 10 mT with respect to the reference.

  In addition, the average value of the half widths of the portions where the half width on the downstream side of at least one of the pumping pole Pt and the stripping pole Pr is increased is in the range of 1 ° to 5 ° with respect to the reference. If it is good. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 4 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the downstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of screw marks and suppression of developer deterioration.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIG. This embodiment differs from the above-described first embodiment in how to increase the magnetic force or the half width of the magnetic pole. Since other configurations and operations are the same as those of the first embodiment, the following description will be focused on differences from the first embodiment.

  In the case of this embodiment, when the magnetic force or half-value width of the magnetic pole downstream in the developer transport direction is divided into two sections having the same length in the developer transport direction, the downstream section of the two sections The average value of the magnetic force is set larger than the average value of the magnetic force of the upstream section. In other words, the magnetic force or full width at half maximum is monotonously increased in two steps toward the downstream side. In other words, screw marks are more likely to be generated more downstream, so that the magnetic force or half-value width is gradually increased toward the downstream side to suppress screw marks that are likely to be generated downstream. I try to plan. On the other hand, even if it is downstream from the central part, the increase in magnetic force or half-value width in a region where screw marks are relatively difficult to occur is suppressed, and the share given to the developer is lowered to suppress the deterioration of the developer. .

  Specifically, when the portion where the magnetic force on the downstream side of the central portion is increased is divided into two sections A1 and A2 having the same length in the developer transport direction, the magnetic force of the section A2 on the downstream side of the two sections The average value is set larger than the average value of the magnetic force of the upstream section A1. Then, the average value of the magnetic force of the downstream section A2 is in the range of 2.5 mT or more and 12.5 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw 46a of the magnetic force in the vicinity of the center portion. And

  Further, when the portion where the half-value width on the downstream side of the central portion is increased is divided into two sections A1 and A2 having the same length in the developer transport direction, the average of the half-value widths of the section A2 on the downstream side of the two sections The value is made larger than the average value of the half widths of the upstream section A1. And the range of 1 degree or more and 5 degrees or less with respect to the average value of the area | region corresponding to 1 pitch of the 1st conveyance screw 46a of the 1st conveyance screw 46a of the half value width near the center part for the average value of the half value width of the downstream section A2 And

  That is, the average value of the magnetic force of the section A2 on the downstream side of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 12.5 mT with respect to the reference. In addition, the average value of the half widths of the section A2 on the downstream side of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in a range of 1 ° to 5 ° with respect to the reference. The criteria are the same as those in the first embodiment.

[Example 2]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or half-value width of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. The method of increasing is the same as that described above. Also, the value to be increased was changed. In each case, the screw marks and the deterioration level of the developer were evaluated in the same manner as in Example 1 described above. The evaluation results are shown in Tables 6 to 9. Note that the increase in the magnetic force or half-value width of each table is an increase with respect to the standard of the magnetic force or half-value width of the downstream section A2. Table 6 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 7 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 8 shows the evaluation results of the screw marks when the full width at half maximum is changed, and Table 9 shows the evaluation results of the deterioration level of the developer when the full width at half maximum is changed.

  From Tables 6 to 9, when the longitudinal position corresponding to the downstream side of the developing sleeve 44 is divided into two sections having the same length, and the magnetic force or the half-value width is monotonously increased toward the downstream side, the following conditions are satisfied. It was found that when it is satisfied, deterioration of the screw marks and developer can be suppressed. That is, the average value of the magnetic force of the section A2 on the downstream side of the portion where the magnetic force of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2. It may be in the range of 5 mT or more and 12.5 mT or less. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 10 mT with respect to the reference.

  In addition, the average value of the half widths of the section A2 on the downstream side of the portion where the half width of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased It may be in the range of 1 ° to 5 °. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 4 ° with respect to the reference. Thus, in the case of the present embodiment, it was found that the range in which the deterioration of the screw marks and the developer can be suppressed can be widened with respect to the configuration of the first embodiment.

  Furthermore, when the pumping pole Pt and the stripping pole Pr are limited to have a small toner share and a large effect of screw mark reduction, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood. That is, the average value of the magnetic force of the section A2 on the downstream side of the portion where the magnetic force of at least one of the pumping pole Pt and the stripping pole Pr is increased is 2.5 mT or more and 15 mT or less with respect to the reference. Any range is acceptable. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 12.5 mT with respect to the reference.

  In addition, the average value of the half-value width of the section A2 on the downstream side of the portion where the half-value width of at least one of the pumping pole Pt and the stripping pole Pr is increased is 1 ° or more and 6 ° with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 5 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the downstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of screw marks and suppression of developer deterioration.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first and second embodiments described above in how to increase the magnetic force or full width at half maximum of the magnetic pole. Since other configurations and operations are the same as those of the first embodiment, the following description will be focused on differences from the first embodiment.

  In the case of the present embodiment, the average value of the magnetic force of each region corresponding to one pitch of the first conveying screw 46a is on the downstream side of the portion where the magnetic force or the half value width of the magnetic pole on the downstream side in the developer conveying direction is increased. It increases monotonously as it goes. That is, since the screw mark is more likely to be generated more markedly on the downstream side, as in the second embodiment, the magnetic force or the half-value width is increased stepwise toward the downstream side. Suppresses deterioration of traces and developer. In particular, in this embodiment, since the magnetic force or the full width at half maximum is increased step by step for each pitch of the screw, the increase in the magnetic force or the full width at half maximum for suppressing the deterioration of the screw marks and the developer is set in a wider range. it can.

  As described above, the magnetic force in the longitudinal direction and the half-value width of the magnet roll 44a vary somewhat, and the interval between the screw marks corresponds to one pitch of the screw (in this embodiment, an interval of 12 mm). It is. Therefore, in this embodiment, the average value of the magnetic force or full width at half maximum for each pitch of the screw is calculated, which is downstream compared with the average value of the magnetic force or full width at half maximum of the screw 1 pitch portion where the magnetic force in the vicinity of the central portion is not enhanced. It was set as the structure which increases monotonously toward the side.

  Specifically, the portion where the magnetic force on the downstream side of the central portion is increased is divided into a plurality of stages for each pitch of the screw, and in this embodiment, divided into three stages of regions B1, B2, and B3. Then, the average value of the magnetic force in each region is monotonously increased toward the downstream side. Then, the average value of the magnetic force in the most downstream area B3 is set to a range of 2.5 mT or more and 15 mT or less with respect to the average value of the area corresponding to one pitch of the first conveying screw 46a of the magnetic force in the vicinity of the center. .

  Further, the portion where the half-value width on the downstream side of the central portion is increased is divided into a plurality of stages for each pitch of the screw, and in this embodiment, divided into three stages of regions B1, B2, and B3. And the average value of the half value width of each region is monotonously increased toward the downstream side. And the average value of the half width of the most downstream area B3 is in the range of 1 ° or more and 6 ° or less with respect to the average value of the area corresponding to one pitch of the first conveying screw 46a having the half width near the center. And

  That is, the average value of the magnetic force in the most downstream region B3 of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 15 mT with respect to the reference. In addition, the average value of the half-value width of the most downstream region B3 of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 1 ° to 6 ° with respect to the reference. The criteria are the same as those in the first embodiment.

[Example 3]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or half-value width of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. The method of increasing is the same as that described above. Also, the value to be increased was changed. In each case, the screw marks and the deterioration level of the developer were evaluated in the same manner as in Example 1 described above. The evaluation results are shown in Tables 10 to 13. Note that the increase in the magnetic force or half-value width of each table is an increase with respect to the reference of the magnetic force or half-value width of the most downstream region B3. Table 10 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 11 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 12 shows the evaluation results of the screw marks when the half width is changed, and Table 13 shows the evaluation results of the developer deterioration level when the half width is changed.

  From Table 10 to Table 13, when the magnetic force or the half-value width is monotonously increased toward the downstream side for each pitch of the screw at the longitudinal position corresponding to the downstream side of the developing sleeve 44, It was also found that the deterioration of the developer can be suppressed. That is, the average value of the magnetic force in the most downstream region B3 of the portion where the magnetic force of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2. It may be in the range of 5 mT or more and 15 mT or less. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 12.5 mT with respect to the reference.

  In addition, the average value of the half-value widths of the most downstream region B3 of the portion where the half-value width of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is relative to the reference. It may be in the range of 1 ° to 6 °. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 5 ° with respect to the reference. As described above, in the case of the present embodiment, it was found that the range in which the deterioration of the screw marks and the developer can be suppressed can be widened with respect to the configuration of the second embodiment.

  Furthermore, when the pumping pole Pt and the stripping pole Pr are limited to have a small toner share and a large effect of screw mark reduction, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood. That is, the average value of the magnetic force of the most upstream region B3 of the portion where the magnetic force of at least one of the pumping pole Pt and the stripping pole Pr is increased is 2.5 mT or more and 17.5 mT with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 15 mT with respect to the reference.

  Further, the average value of the half width of the most upstream region B3 of the portion where the half width of at least one of the pumping pole Pt and the stripping pole Pr is increased is 1 ° or more and 7 ° with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 6 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the downstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of screw marks and suppression of developer deterioration.

<Fourth Embodiment>
A fourth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, in addition to the configuration of the third embodiment described above, the magnetic force or the half-value width is increased on the upstream side of the central portion of the magnetic pole in the developer transport direction. Since other configurations and operations are the same as those of the third embodiment, the following description will be focused on differences from the third embodiment.

  First, problems related to this embodiment will be described with reference to FIGS. 16 and 17. First, as described above, the developer is replenished to the developing container 41 from the replenishing device 47 as the image is formed. At this time, the amount of developer replenishment is also controlled by the control unit 49 in accordance with the printing rate of the output image. For example, the developer replenishment amount is controlled based on the video count value. The video count value is an integrated value when the level (0 to 255 level) for each pixel of the input image data is integrated for one image. Therefore, as the printing rate of the output image is higher, more developer is supplied.

  Here, after outputting an image with a large amount of toner consumption represented by a solid image, and outputting a uniform image of the entire surface such as the entire halftone, it is shown in FIG. Such image unevenness may occur. That is, there may be image unevenness in which an image becomes darker at an image position corresponding to the upstream side in the developer conveyance direction of the developing chamber 41a. Since this oblique image unevenness is a trace related to the first conveying screw 46a in the developing chamber 41a, such image unevenness will be referred to as “upstream screw trace” hereinafter.

  The generation mechanism of this “upstream screw trace” will be described with reference to FIGS. In the case of a configuration in which the video replenishment control for controlling the developer replenishment amount according to the output image printing rate is the main control of the developer replenishment control, after outputting an image with a large amount of toner consumption represented by a solid image The developer is supplied into the developing container 41 at the same time. The developer replenished all at once falls first to the replenishment position T0 on the upstream side in the developer transport direction of the second transport screw 46b of the stirring chamber 41b of the developing container 41. The developer that has fallen to T0 is conveyed while being stirred together with the surrounding developer by the rotation of the second conveying screw 46b in the stirring chamber 41b.

  However, when the developer is replenished all at once as described above, there is a possibility that the developer may not be mixed well in the stirring chamber 41b as shown in FIG. That is, a portion having a high TD ratio as indicated by TR in the figure may occur. In this case, due to the specific gravity between the developer (carrier + toner) and the toner, the toner is rich in the upper part of the agent surface or in the immediate vicinity of the upstream with respect to the moving direction of the blades of the second conveying screw 46b. Tends to be high. In this state, when the developer passes through the first opening 45a from the agitating chamber 41b and moves to the developing chamber 41a side, the toner immediately upstream from the upper portion of the agent surface and the moving direction of the blades is not collected. The rich state is also maintained on the developing chamber 41a side. However, since the developer is transported while being stirred by the first transport screw 46a also on the developing chamber 41a side, the unevenness of the TD ratio is remarkable on the upstream side of the developing chamber 41a and is reduced as it goes downstream. Therefore, as shown in FIG. 16, the closer to the image position corresponding to the upstream side in the developer conveyance direction of the developing chamber 41a, the more uneven the image where the oblique image becomes darker, that is, the “upstream screw trace” occurs. Easy to do.

  Therefore, in this embodiment, the magnetic force or half-value width of at least one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pr corresponds to the image forming area in the rotation axis direction of the developing sleeve 44. In the part, it is as follows. That is, as shown in FIG. 18, the magnetic force or half-value width of the magnetic pole is increased on the upstream side in the developer conveying direction of the first conveying screw 46a from the vicinity of the central portion of the developing sleeve 44 in the rotation axis direction.

  Specifically, the average value of the magnetic force of each region corresponding to one pitch of the first conveying screw 46a is directed upstream in the portion where the magnetic force or half width at the upstream side in the developer conveying direction of the magnetic pole is increased. It is trying to increase monotonously. In the case of this embodiment, the magnetic force or the half width at the downstream side of the central portion of the magnetic pole is the same as that of the third embodiment. For this reason, in this embodiment, the average value of the magnetic force or full width at half maximum for each pitch of the screw is calculated, and compared with the average value of the screw 1 pitch portion where the magnetic force in the vicinity of the center is not substantially increased, The structure is monotonically increasing toward the downstream side. The magnetic force and the half-value width may be increased on the upstream side and the downstream side in the developer transport direction of the first transport screw 46a from the vicinity of the central portion in the rotation axis direction of the developing sleeve 44 of the magnetic pole, Both magnetic force and half width may be used.

  As described above, in this embodiment, the magnetic force or the half width is increased on the upstream side where the upstream screw trace of the magnetic pole is likely to be generated, and the magnetic force or half width is not increased in the central portion where the upstream screw trace is difficult to be generated. ing. In addition, the “screw trace” described in the first to third embodiments is also less likely to occur by increasing the magnetic force or the half width at the downstream side. As a result, it is possible to achieve both suppression of any screw marks (image unevenness) and suppression of developer deterioration. In particular, in this embodiment, since the magnetic force or the half-value width is increased stepwise for each pitch of the screw on the upstream side and the downstream side of the central portion, any screw trace can be efficiently suppressed. At the same time, the increase in the magnetic force or the half-value width can be reduced on the central portion side where any screw marks are unlikely to occur, so that the deterioration of the developer can be more preferably suppressed. Note that the configuration of the first or second embodiment may be applied to the configuration of the present embodiment instead of the configuration of the third embodiment described above.

<Fifth Embodiment>
A fifth embodiment of the present invention will be described with reference to FIG. This embodiment differs from the above-described fourth embodiment in how to increase the magnetic force or the half width at the upstream side of the central portion of the magnetic pole. Since other configurations and operations are the same as those of the fourth embodiment, the following description will focus on parts that are different from those of the fourth embodiment.

  Also in this embodiment, at least one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt increases the magnetic force or the half width at positions corresponding to the upstream side and the downstream side of the developing chamber 41a. ing. In FIG. 19, the magnetic force or half width at the downstream side of the magnetic pole is omitted, but this portion may have any configuration in the first to third embodiments described above. However, in order to further suppress the deterioration of the developer, it is preferable to apply the configuration of the third embodiment.

  On the other hand, the upstream side of the magnetic pole will be specifically described. In this embodiment, the magnetic force or half-value width of the magnetic pole in the portion corresponding to the image forming region in the rotation axis direction of the developing sleeve 44 is greater than that in the vicinity of the central portion in the rotation axis direction of the developing sleeve 44. It is increased on the upstream side in the developer conveyance direction. More specifically, the magnetic force or the full width at half maximum was increased in the entire longitudinal position corresponding to the upstream side from the central portion in the longitudinal direction of the developing sleeve 44. The area where the magnetic force or the half width is increased may be upstream from the vicinity of the central portion of the developing sleeve 44. If the area where the screw mark is likely to be generated in the apparatus is increased, the increasing area is the center. It may be from slightly upstream or downstream from the part.

  In the present embodiment, the magnetic force and half-value width of the cut pole Pk, the magnetic force and half-value width of the pumping pole Pr, and the magnetic force and half-value width of the stripping pole Pt are all increased upstream of the central portion. Further, the increment Δ is a difference from the average value of the increased portion on the basis of the average value of the region corresponding to one pitch of the first conveying screw 46 in the portion not increasing near the center in the longitudinal direction of the developing sleeve 44. It was. Specifically, the average value of the magnetic force downstream of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 10 mT with respect to the reference. In addition, the average value of the half widths on the downstream side of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in a range of 1 ° to 4 ° with respect to the reference. The criteria are the same as those in the first embodiment.

[Example 4]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or full width at half maximum of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. The method of increasing is the same as that described above. Also, the value to be increased was changed. The downstream side is not increased. In each case, the screw marks and the deterioration level of the developer were evaluated in the same manner as in Example 1 described above. The evaluation results are shown in Tables 14 to 17. Table 14 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 15 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 16 shows the evaluation results of the screw marks when the half width is changed, and Table 17 shows the evaluation results of the developer deterioration level when the half width is changed.

  From Tables 14 to 17, when the magnetic force or the full width at half maximum is increased in the entire longitudinal position corresponding to the upstream side of the central portion in the image forming region of the developing sleeve 44, when the following conditions are satisfied: It was found that screw marks and developer deterioration can be suppressed. That is, the average value of the magnetic force of the portion where the magnetic force on the upstream side of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2.5 mT or more and 10 mT with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 7.5 mT with respect to the reference.

  Further, the average value of the half widths of the portions where the half width on the upstream side of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 1 ° or more with respect to the reference. It may be within a range of 4 ° or less. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 3 ° with respect to the reference.

  Furthermore, if the pumping pole Pt and the stripping pole Pr are limited so that the toner share is small and the effect of reducing the upstream screw mark is large, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood that. That is, the average value of the magnetic force of the portion where the magnetic force on the upstream side of at least one of the pumping pole Pt and the stripping pole Pr is increased is in the range of 2.5 mT to 12.5 mT with respect to the reference. If it is good. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 10 mT with respect to the reference.

  In addition, the average value of the half-value width of the portion where the half-value width on the upstream side of at least one of the pumping pole Pt and the stripping pole Pr is increased is in the range of 1 ° to 5 ° with respect to the reference. If it is good. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 4 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the upstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of upstream screw marks and suppression of developer deterioration.

<Sixth Embodiment>
A sixth embodiment of the present invention will be described with reference to FIG. This embodiment differs from the above-described fifth embodiment in how to increase the magnetic force or full width at half maximum of the magnetic pole. Since other configurations and operations are the same as those of the fifth embodiment, the following description will be focused on differences from the fifth embodiment.

  In the case of the present embodiment, when the magnetic force or the half-value width of the magnetic pole upstream in the developer transport direction is divided into two sections having the same length in the developer transport direction, the upstream section of the two sections The average value of the magnetic force is made larger than the average value of the magnetic force of the downstream section. In other words, the magnetic force or the full width at half maximum is monotonously increased in two steps toward the upstream side. In other words, the upstream screw traces are more likely to be generated more prominently on the upstream side. Therefore, the screw traces that are likely to be generated on the upstream side are increased by increasing the magnetic force or the half-value width stepwise toward the upstream side. I try to suppress this. On the other hand, even if it is upstream from the center, it suppresses the increase in magnetic force or full width at half maximum in areas where it is relatively difficult for the upstream screw marks to occur, thereby reducing the share given to the developer and suppressing the deterioration of the developer. ing.

  Specifically, when the portion where the magnetic force on the upstream side of the central portion is increased is divided into two sections A3 and A4 having the same length in the developer transport direction, the magnetic force of the section A4 on the upstream side of the two sections is divided. The average value is set larger than the average value of the magnetic force of the downstream section A3. Then, the average value of the magnetic force of the upstream section A4 is in the range of 2.5 mT or more and 12.5 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw 46a of the magnetic force in the vicinity of the center portion. And

  Further, when the portion where the half width on the upstream side of the central portion is increased is divided into two sections A3 and A4 having the same length in the developer transport direction, the average of the half width of the upstream section A4 of the two sections The value is set to be larger than the average value of the half-value width of the downstream section A3. And the range of 1 degree or more and 5 degrees or less with respect to the average value of the area | region corresponding to 1 pitch of the 1st conveyance screw 46a of the 1st conveyance screw 46a of the half width near the center part for the average value of the half value width of upstream A4 And

  That is, the average value of the magnetic force of the section A4 on the upstream side of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 12.5 mT with respect to the reference. In addition, the average value of the half width of the section A4 on the upstream side of the pumping pole Pr, the cutting pole Pk, and the stripping pole Pt is increased in the range of 1 ° to 5 ° with respect to the reference. The criteria are the same as those in the first embodiment.

[Example 5]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or full width at half maximum of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. The method of increasing is the same as that described above. Also, the value to be increased was changed. The downstream side is not increased. In each case, the screw marks and the deterioration level of the developer were evaluated in the same manner as in Example 1 described above. The evaluation results are shown in Table 18 to Table 21. It should be noted that the increase in the magnetic force or half-value width of each table is an increase with respect to the reference of the magnetic force or half-value width of the upstream section A4. Table 18 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 19 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 20 shows the evaluation results of the screw marks when the half width is changed, and Table 21 shows the evaluation results of the developer deterioration level when the half width is changed.

  From Tables 18 to 21, when the longitudinal position corresponding to the upstream side of the developing sleeve 44 is divided into two sections having the same length, and the magnetic force or the half-value width is monotonously increased toward the upstream side, the following conditions are satisfied. It was found that the screw marks and the deterioration of the developer can be suppressed when it is satisfied. That is, the average value of the magnetic force of the section A4 on the upstream side of the portion where the magnetic force of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2. It may be in the range of 5 mT or more and 12.5 mT or less. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 10 mT with respect to the reference.

  In addition, the average value of the half widths of the section A4 on the upstream side of the portion where the half width of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased It may be in the range of 1 ° to 5 °. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 4 ° with respect to the reference. Thus, in the case of the present embodiment, it was found that the range in which the upstream screw mark and the deterioration of the developer can be suppressed can be widened with respect to the configuration of the fifth embodiment.

  Furthermore, if the pumping pole Pt and the stripping pole Pr are limited so that the toner share is small and the effect of reducing the upstream screw mark is large, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood that. That is, the average value of the magnetic force of the section A4 on the upstream side of the portion where the magnetic force of at least one of the pumping pole Pt and the stripping pole Pr is increased is 2.5 mT or more and 15 mT or less with respect to the reference. Any range is acceptable. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 12.5 mT with respect to the reference.

  Further, the average half-value width of the upstream section A4 of the portion where the half-value width of at least one of the pumping pole Pt and the stripping pole Pr is increased is 1 ° or more and 6 ° with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 5 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the upstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of upstream screw marks and suppression of developer deterioration.

<Seventh Embodiment>
A seventh embodiment of the present invention will be described with reference to FIG. This embodiment is different from the above-described fifth and sixth embodiments in how to increase the magnetic force or full width at half maximum of the magnetic pole. Since other configurations and operations are the same as those of the fifth embodiment, the following description will be focused on differences from the fifth embodiment.

  In the case of the present embodiment, each of the areas corresponding to one pitch of the first conveying screw 46a is the portion where the magnetic force or half width at the upstream side of the developer conveying direction of the magnetic pole is increased, as in the fourth embodiment. The average value of the magnetic force increases monotonously as it goes upstream. That is, since the upstream screw mark is more likely to be generated more prominently on the upstream side, as in the sixth embodiment, the magnetic force or the full width at half maximum is increased in steps toward the upstream side. The upstream screw mark and the deterioration of the developer are suppressed. In particular, in this embodiment, since the magnetic force or the half-value width is increased step by step for each pitch of the screw, the increase in the magnetic force or the half-value width for suppressing deterioration of the upstream screw mark and the developer is wider. Can range.

  As described above, the magnetic force in the longitudinal direction and the full width at half maximum of the magnet roll 44a vary somewhat, and the distance between the upstream screw traces corresponds to one pitch of the screw (12 mm interval in this embodiment). It is an unevenness. Therefore, in this embodiment, the average value of the magnetic force or full width at half maximum for each pitch of the screw is calculated, and it is upstream of the average value of the magnetic force or full width at half maximum of the screw 1 pitch portion where the magnetic force in the vicinity of the center is not enhanced. It was set as the structure which increases monotonously toward the side.

  Specifically, the portion where the magnetic force on the upstream side of the central portion is increased is divided into a plurality of stages for each pitch of the screw, and in this embodiment, divided into three stages of regions B4, B5, and B6. Then, the average value of the magnetic force in each region is monotonously increased toward the upstream side. The average value of the magnetic force in the most upstream area B6 is set to a range of 2.5 mT or more and 15 mT or less with respect to the average value of the area corresponding to one pitch of the first conveying screw 46a of the magnetic force in the vicinity of the center. .

  Further, the portion where the half width on the upstream side of the central portion is increased is divided into a plurality of stages for each pitch of the screw, and in this embodiment, divided into three stages of regions B4, B5, and B6. Then, the average value of the half widths of the respective regions is monotonously increased toward the upstream side. And the average value of the half width of the most upstream area B6 is a range of 1 ° or more and 6 ° or less with respect to the average value of the area corresponding to one pitch of the first conveying screw 46a having the half width near the center. And

  That is, the average value of the magnetic force in the most upstream region B6 of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 2.5 mT to 15 mT with respect to the reference. Further, the average value of the full width at half maximum of the most upstream region B6 of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt is increased in the range of 1 ° to 6 ° with respect to the reference. The criteria are the same as those in the first embodiment.

[Example 6]
Next, an experiment conducted by the inventor to confirm the effect of the present embodiment will be described. In the experiment, using the developing device as described above, the magnetic force or full width at half maximum of any one of the pumping pole Pr, the cut pole Pk, and the stripping pole Pt was increased with respect to the above-described reference. The method of increasing is the same as that described above. Also, the value to be increased was changed. The downstream side is not increased. In each case, the screw marks and the deterioration level of the developer were evaluated in the same manner as in Example 1 described above. The evaluation results are shown in Tables 22 to 25. Note that the increase in the magnetic force or half-value width of each table is an increase with respect to the reference of the magnetic force or half-value width of the most upstream region B6. Table 22 shows the evaluation results of the screw marks when the magnetic force is changed, and Table 23 shows the evaluation results of the developer deterioration level when the magnetic force is changed. Table 24 shows the evaluation results of the screw marks when the half-value width is changed, and Table 25 shows the evaluation results of the developer deterioration level when the half-value width is changed.

From Tables 22 to 25, when the magnetic force or half-value width is monotonously increased toward the upstream side for each screw pitch at the longitudinal position corresponding to the upstream side of the developing sleeve 44, It was also found that the deterioration of the developer can be suppressed. That is, the average value of the magnetic force in the most upstream region B6 of the portion where the magnetic force of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is 2. It may be in the range of 5 mT or more and 15 mT or less. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 12.5 mT with respect to the reference.

  In addition, the average value of the half width of the most upstream region B6 in the portion where the half width of at least one of the pumping pole Pt, the cut pole Pk, and the stripping pole Pr is increased is compared to the reference. It may be in the range of 1 ° to 6 °. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 5 ° with respect to the reference. Thus, in the case of this embodiment, it was found that the range in which the deterioration of the screw marks and the developer can be suppressed can be widened with respect to the configuration of the sixth embodiment.

  Furthermore, when the pumping pole Pt and the stripping pole Pr are limited to have a small toner share and a large effect of screw mark reduction, the deterioration of the screw mark and the developer can be suppressed when the following conditions are satisfied. I understood. That is, the average value of the magnetic force in the most upstream region B6 of the portion where the magnetic force of at least one of the pumping pole Pt and the stripping pole Pr is increased is 2.5 mT or more and 17.5 mT with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the magnetic force is in the range of 5 mT to 15 mT with respect to the reference.

  Further, the average value of the half widths of the most upstream region B6 in the portion where the half width of at least one of the pumping pole Pt and the stripping pole Pr is increased is 1 ° or more and 7 ° with respect to the reference. The following range may be sufficient. Moreover, it is more preferable if the average value of the full width at half maximum is in the range of 2 ° to 6 ° with respect to the reference. As described above, when the magnetic pole for increasing the magnetic force or the half width at the upstream side is limited to at least one of the pumping pole Pt and the stripping pole Pr, compared to the case including the cut pole, in a wider range. It is possible to achieve both suppression of screw marks and suppression of developer deterioration.

<Other embodiments>
The image forming apparatus in which the developing device of the present invention is incorporated includes a copying machine, a printer, a facsimile machine, and a multifunction machine having a plurality of these functions.

  Further, in each of the above-described embodiments, the case where the present invention is applied to the configuration of the “lower peeling / uplifting system” as the developing device has been described. However, the present invention is applied to the “upper peeling / lower lifting system”. Is also applicable.

  4 ... developing device / 41 ... developing container / 41a ... developing chamber (first chamber) / 41b ... stirring chamber (second chamber) / 42 ... developing blade (developer regulating member) /44...developing sleeve / 44a ... magnet roll (magnetic field generating means) / 45 ... partition wall / 45a ... first opening (communication part) / 45b ... second opening (communication part) ) / 46a ... first conveying screw / 46b ... second conveying screw / Pd ... developing electrode / Pe ... take-in electrode / Pr ... peeling electrode / Pt ... pumping electrode / Pk ... Cut poles (regulatory poles)

Claims (30)

A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. Increased in the developer conveying direction downstream of the first conveying screw from the vicinity of the central portion in the rotation axis direction of
The average value of the magnetic force at the portion where the magnetic force on the downstream side in the developer conveying direction is increased is 2. 2. The average value of the magnetic field near the center portion corresponding to one pitch of the first conveying screw. The range is 5 mT or more and 10 mT or less.
A developing device. The average value of the magnetic force at the portion where the magnetic force on the downstream side in the developer transport direction is increased is 5 mT or more with respect to the average value of the magnetic field near the center portion corresponding to one pitch of the first transport screw. A range of 7.5 mT or less,
The developing device according to claim 1, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulation pole, and the stripping pole has a half of the magnetic force peak of the magnetic pole in a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve. A half width that is an angle between positions in the rotation direction of the developing sleeve is increased on the downstream side in the developer conveying direction of the first conveying screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve,
The average half-value width of the portion where the half-value width on the downstream side in the developer conveyance direction is increased is compared to the average value of the region corresponding to one pitch of the first conveyance screw of the half-value width near the center portion. 1 ° or more and 4 ° or less.
A developing device. The average half-value width of the portion where the half-value width on the downstream side in the developer conveyance direction is increased is compared to the average value of the region corresponding to one pitch of the first conveyance screw of the half-value width near the center portion. 2 ° or more and 3 ° or less.
The developing device according to claim 3, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole in a direction corresponding to the image forming region in the rotation axis direction of the developing sleeve. The developer is increased on the downstream side in the developer conveying direction of the first conveying screw from near the center,
The average value of the magnetic force at the portion where the magnetic force on the downstream side in the developer conveying direction is increased is 2. 2. The average value of the magnetic field near the center portion corresponding to one pitch of the first conveying screw. The range is 5 mT or more and 12.5 mT or less.
A developing device. The average value of the magnetic force at the portion where the magnetic force on the downstream side in the developer transport direction is increased is 5 mT or more with respect to the average value of the magnetic field near the center portion corresponding to one pitch of the first transport screw. A range of 10 mT or less,
The developing device according to claim 5, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force peak of the magnetic pole of the developing sleeve that is halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotation direction, is increased on the downstream side in the developer conveyance direction of the first conveyance screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve;
The average half-value width of the portion where the half-value width on the downstream side in the developer conveyance direction is increased is compared to the average value of the region corresponding to one pitch of the first conveyance screw of the half-value width near the center portion. 1 ° or more and 5 ° or less.
A developing device. The average half-value width of the portion where the half-value width on the downstream side in the developer conveyance direction is increased is compared to the average value of the region corresponding to one pitch of the first conveyance screw of the half-value width near the center portion. 2 ° or more and 4 ° or less.
The developing device according to claim 7, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. Increased in the developer conveying direction downstream of the first conveying screw from the vicinity of the central portion in the rotation axis direction of
When the portion where the magnetic force on the downstream side in the developer transport direction is increased is divided into two sections having the same length in the developer transport direction, the average value of the magnetic force in the downstream section of the two sections is the upstream section. The average value of the magnetic force of the downstream section is larger than the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the central portion. The range is 5 mT or more and 12.5 mT or less.
A developing device. The average value of the magnetic force of the downstream section is in the range of 5 mT or more and 10 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center portion.
The developing device according to claim 9, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulation pole, and the stripping pole has a half of the magnetic force peak of the magnetic pole in a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve. A half width that is an angle between positions in the rotation direction of the developing sleeve is increased on the downstream side in the developer conveying direction of the first conveying screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve,
When the portion where the half width at the downstream side in the developer transport direction is increased is divided into two sections having the same length in the developer transport direction, the average value of the half width at the downstream section of the two sections is the upstream side. Is larger than the average value of the half-value widths of the sections, and the average value of the half-value widths of the downstream sections is the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center. On the other hand, the range is 1 ° or more and 5 ° or less.
A developing device. The average value of the half-value width of the downstream section is in the range of 2 ° or more and 4 ° or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the central portion. is there,
The developing device according to claim 11, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole in a direction corresponding to the image forming region in the rotation axis direction of the developing sleeve. The developer is increased on the downstream side in the developer conveying direction of the first conveying screw from near the center,
When the portion where the magnetic force on the downstream side in the developer transport direction is increased is divided into two sections having the same length in the developer transport direction, the average value of the magnetic force in the downstream section of the two sections is the upstream section. The average value of the magnetic force of the downstream section is larger than the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the central portion. A range of 5 mT to 15 mT,
A developing device. The average value of the magnetic force of the downstream section is in the range of 5 mT or more and 12.5 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center portion.
The developing device according to claim 13, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force peak of the magnetic pole of the developing sleeve that is halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotation direction, is increased on the downstream side in the developer conveyance direction of the first conveyance screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve;
When the portion where the half width at the downstream side in the developer transport direction is increased is divided into two sections having the same length in the developer transport direction, the average value of the half width at the downstream section of the two sections is the upstream side. Is larger than the average value of the half-value widths of the sections, and the average value of the half-value widths of the downstream sections is the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center. On the other hand, the range is 1 ° or more and 6 ° or less.
A developing device. The average value of the half-value width of the downstream section is in the range of 2 ° to 5 ° with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center portion. is there,
The developing device according to claim 15, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. Increased in the developer conveying direction downstream of the first conveying screw from the vicinity of the central portion in the rotation axis direction of
In the portion where the magnetic force on the downstream side in the developer transport direction is increased, the average value of the magnetic force of each region corresponding to one pitch of the first transport screw monotonously increases toward the downstream side, and the most downstream region The average value of the magnetic force is a range of 2.5 mT or more and 15 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center portion.
A developing device. The average value of the magnetic force in the most downstream region is in the range of 5 mT to 12.5 mT with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center portion.
The developing device according to claim 17, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulation pole, and the stripping pole has a half of the magnetic force peak of the magnetic pole in a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve. A half width that is an angle between positions in the rotation direction of the developing sleeve is increased on the downstream side in the developer conveying direction of the first conveying screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve,
In the portion where the half width on the downstream side in the developer transport direction is increased, the average value of the half width in each region corresponding to one pitch of the first transport screw monotonously increases toward the downstream side. The average value of the half-value width of the region is a range of 1 ° or more and 6 ° or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center portion.
A developing device. The average value of the full width at half maximum of the most downstream region is within a range of 2 ° or more and 5 ° or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half width near the center portion. is there,
The developing device according to claim 19, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole in a direction corresponding to the image forming region in the rotation axis direction of the developing sleeve. The developer is increased on the downstream side in the developer conveying direction of the first conveying screw from near the center,
In the portion where the magnetic force on the downstream side in the developer transport direction is increased, the average value of the magnetic force of each region corresponding to one pitch of the first transport screw monotonously increases toward the downstream side, and the most downstream region The average value of the magnetic force is a range of 2.5 mT or more and 17.5 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the central portion.
A developing device. The average value of the magnetic force in the most downstream region is a range of 5 mT or more and 15 mT or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the magnetic force in the vicinity of the center portion.
The developing device according to claim 21, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement within the developing sleeve, a pumping electrode for pumping up developer in the first chamber to the developing sleeve, and a stripping electrode for stripping off the developer carried on the developing sleeve and returning it to the first chamber A magnetic field generating means having a plurality of magnetic poles including:
At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force peak of the magnetic pole of the developing sleeve that is halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotation direction, is increased on the downstream side in the developer conveyance direction of the first conveyance screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve;
In the portion where the half width on the downstream side in the developer transport direction is increased, the average value of the half width in each region corresponding to one pitch of the first transport screw monotonously increases toward the downstream side. The average value of the half-value width of the region is a range of 1 ° or more and 7 ° or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half-value width near the center portion.
A developing device. The average value of the full width at half maximum of the most downstream region is within a range of 2 ° or more and 6 ° or less with respect to the average value of the region corresponding to one pitch of the first conveying screw of the half width near the center portion. is there,
24. The developing device according to claim 23, wherein: At least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. Is increased on the upstream side in the developer conveying direction of the first conveying screw than the vicinity of the center in the rotational axis direction of
The developing device according to any one of claims 1, 2, 9, 10, 17, and 18. At least one magnetic pole of the pumping pole, the regulation pole, and the stripping pole has a half of the magnetic force peak of the magnetic pole in a portion corresponding to the image forming area in the rotation axis direction of the developing sleeve. A half-value width, which is an angle between positions in the rotation direction of the developing sleeve, is increased on the upstream side in the developer conveying direction of the first conveying screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve.
21. The developing device according to claim 3, wherein the developing device is any one of claims 3, 4, 11, 12, 19, and 20. At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force of the magnetic pole in a direction corresponding to the image forming region in the rotation axis direction of the developing sleeve. The developer is increased on the downstream side in the developer conveying direction of the first conveying screw than in the vicinity of the center.
The developing device according to any one of claims 5, 6, 13, 14, 21, and 22. At least one magnetic pole of the pumping pole and the stripping pole has a magnetic force peak of the magnetic pole of the developing sleeve that is halved in a portion corresponding to the image forming region in the rotation axis direction of the developing sleeve. A half-value width that is an angle between positions in the rotation direction is increased on the upstream side in the developer conveyance direction of the first conveyance screw with respect to the vicinity of the central portion in the rotation axis direction of the developing sleeve;
The developing device according to any one of claims 7, 8, 15, 16, 23, and 24. The developing sleeve is arranged such that a central axis is above the central axis of the first conveying screw,
The pumping pole is located below the stripping pole;
The developing device according to any one of claims 1 to 28, wherein: A communication portion that partitions the first chamber and the second chamber, each containing a developer containing toner and a carrier, and the first chamber and the second chamber, and communicates the first chamber and the second chamber. A developing vessel in which a developer circulation path is formed between the first chamber and the second chamber;
A developing sleeve that carries the developer in the first chamber and rotates;
A developer regulating member for regulating the amount of developer carried on the developing sleeve;
A first conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the first chamber;
A second conveying screw for conveying the developer along the rotation axis direction of the developing sleeve in the second chamber;
A non-rotatable arrangement in the developing sleeve, and a pumping electrode for pumping the developer in the first chamber to the developing sleeve, and an amount of the developer carried on the developing sleeve facing the developer regulating member A magnetic pole generating means having a plurality of magnetic poles including a regulating pole to be regulated by the developer regulating member and a peeling pole that peels off the developer carried on the developing sleeve and returns the developer to the first chamber;
At least one magnetic pole of the pumping pole, the regulating pole, and the stripping pole has a magnetic force of the magnetic pole at a portion corresponding to an image forming region in the rotation axis direction of the developing sleeve. Is increased on the downstream side in the developer conveying direction of the first conveying screw than the vicinity of the central portion in the rotation axis direction of
A developing device.