Developing device

Abstract

To provide a configuration that can reduce attachment of carrier to a developing roller in productivity in a hybrid development type developing device.SOLUTION: A developing device has a developing roller that develops an electrostatic latent image formed on a photoconductor drum, a supply roller that supplies developer to the developing roller, and a regulation blade that regulates the amount of developer carried on the supply roller. A magnet roller inside the supply roller has a main pole N1 located at a position facing the developing roller, a holding pole S1 arranged adjacent to the upstream of the main pole N1, and a regulation pole N2 arranged at a position adjacent to the upstream of the holding pole S1, the position facing the regulation blade. The magnitude of the absolute value of the maximum value of the magnetic flux density Br in a normal direction on a surface of the supply roller satisfies main pole N1>holding pole S1>regulation pole N2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of these functions. [Background technology]

[0002] Conventionally, there has been known a developing device that uses a two-component developer (hereinafter referred to as developer) containing non-magnetic toner particles and magnetic carrier particles. As such a developing device, a configuration using a so-called hybrid development method has been proposed, which has a developing roller as a developing rotor disposed opposite a photosensitive drum as an image carrier, and a supply roller as a supply rotor disposed opposite the developing roller (Patent Document 1).

[0003] In a developing device using such a hybrid development method, a supply roller with a magnet inside carries developer, and a toner layer is formed on the developing roller from the developer transported by the rotation of the supply roller, and the electrostatic latent image on the photosensitive drum is developed with toner from the developing roller.

[0004] In the developing device described in Patent Document 1, a magnet disposed inside a supply roller has a main pole positioned opposite the developing roller, and a receiving pole of opposite polarity to the main pole positioned opposite the supply roller. A regulating member that regulates the amount of developer carried by the supply roller is disposed upstream of the main pole in the direction of rotation of the supply roller. The magnet inside the supply roller has a regulating pole of the same polarity as the main pole positioned opposite the regulating member upstream of the main pole in the direction of rotation of the supply roller, and a retaining pole of opposite polarity to the main pole between the regulating pole and the main pole. In Patent Document 1, by providing a retaining pole upstream of the main pole, carrier retention between the main pole and the retaining pole is increased, thereby suppressing carrier adhesion to the developing roller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-3256 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, image forming apparatuses have become faster, and the rotation speeds of the supply roller and the developing roller have become faster. This makes it easier for the carrier in the developer to fly from the supply roller, which in turn makes it easier for the carrier to adhere to the developing roller.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can reduce carrier adhesion to a developing rotor in a developing device using a hybrid development method. [Means for solving the problem]

[0008] One aspect of the present invention is a developer container that contains a developer containing toner and a carrier; a developer roller that carries and transports the toner to a development position where an electrostatic latent image formed on an image carrier is developed; a supply roller that is disposed opposite to the developer roller, carries and transports the developer supplied from the developer container, and supplies only the toner to the developer roller, the supply roller rotating in a direction opposite to the rotation direction of the developer roller at the position opposite to the developer roller; and a first magnetic carrier that is disposed inside the developer roller and fixed so as not to rotate. a first magnet having a pole; a second magnetic pole, which is disposed inside the supply roller in a non-rotatable and fixed manner, the supply roller being disposed at a position where the supply roller faces the developing roller and disposed opposite the first magnetic pole and having a polarity different from that of the first magnetic pole; a third magnetic pole, which is disposed upstream of the second magnetic pole in the rotation direction of the supply roller and disposed adjacent to the second magnetic pole and has a polarity different from that of the second magnetic pole; and a third magnetic pole, which is disposed upstream of the third magnetic pole in the rotation direction of the supply roller and disposed adjacent to the third magnetic pole. a second magnet having a fourth magnetic pole different in polarity from the third magnetic pole, and a regulating member disposed opposite the fourth magnetic pole and regulating an amount of developer carried on the supply roller, wherein an absolute value of a maximum value of a magnetic flux density of the second magnetic pole in a normal direction to the outer circumferential surface of the supply roller is greater than an absolute value of a maximum value of a magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller, and the absolute value of a maximum value of a magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller is greater than an absolute value of a maximum value of a magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller. the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller, and the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum is greater than the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum 15° This is a developing device characterized by its small size. Another aspect of the present invention is a development device including a developer container that contains a developer containing toner and a carrier; a development roller that carries and transports the toner to a development position where an electrostatic latent image formed on an image carrier is developed; a supply roller that is disposed opposite to the development roller, carries and transports the developer supplied from the development container, and supplies only the toner to the development roller, the supply roller rotating in a direction opposite to the rotation direction of the development roller at the position opposite to the development roller; and a supply roller that is disposed inside the development roller so as to be non-rotatable and fixed. The supply roller includes a first magnet having a first magnetic pole, a second magnetic pole that is disposed inside the supply roller in a non-rotating and fixed manner, the second magnetic pole being disposed at a position where the supply roller faces the developing roller and facing the first magnetic pole and having a polarity different from that of the first magnetic pole, a third magnetic pole that is disposed upstream of the second magnetic pole in the rotation direction of the supply roller and adjacent to the second magnetic pole and has a polarity different from that of the second magnetic pole, and a third magnetic pole that is disposed upstream of the third magnetic pole in the rotation direction of the supply roller and adjacent to the third magnetic pole. a second magnet having a fourth magnetic pole, the fourth magnetic pole being disposed adjacent to the third magnetic pole and having a polarity different from that of the third magnetic pole; a fifth magnetic pole, the fifth magnetic pole being disposed downstream of the second magnetic pole in the rotation direction of the supply roller and being disposed adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; and a regulating member, disposed opposite to the fourth magnetic pole, for regulating the amount of developer carried on the supply roller, wherein the absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller, and the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum with respect to the rotation direction of the supply roller isa developing device characterized in that the angle is 10° or more smaller than the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum, and the absolute value of the maximum magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 5 mT or more larger than the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller. Another aspect of the present invention is a development device including a developer container that contains a developer containing toner and a carrier; a development roller that carries and transports the toner to a development position where an electrostatic latent image formed on an image carrier is developed; a supply roller that is disposed opposite to the development roller, carries and transports the developer supplied from the development container, and supplies only the toner to the development roller, the supply roller rotating in a direction opposite to the rotation direction of the development roller at the position opposite to the development roller; and a supply roller that is disposed inside the development roller so as to be non-rotatable and fixed. The supply roller includes a first magnet having a first magnetic pole, a second magnetic pole that is disposed inside the supply roller in a non-rotating and fixed manner, the second magnetic pole being disposed at a position where the supply roller faces the developing roller and facing the first magnetic pole and having a polarity different from that of the first magnetic pole, a third magnetic pole that is disposed upstream of the second magnetic pole in the rotation direction of the supply roller and adjacent to the second magnetic pole and has a polarity different from that of the second magnetic pole, and a third magnetic pole that is disposed upstream of the third magnetic pole in the rotation direction of the supply roller and adjacent to the third magnetic pole. a second magnet having a fourth magnetic pole, the fourth magnetic pole being disposed adjacent to the third magnetic pole and having a polarity different from that of the third magnetic pole; a fifth magnetic pole, the fifth magnetic pole being disposed downstream of the second magnetic pole in the rotation direction of the supply roller and being disposed adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; and a regulating member, disposed opposite to the fourth magnetic pole, for regulating the amount of developer carried on the supply roller, wherein the absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller, and the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum with respect to the rotation direction of the supply roller isThe developing device is characterized in that the angle is smaller than the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum. [Effects of the Invention]

[0009] According to the present invention, in a developing device using a hybrid development method, it is possible to reduce carrier adhesion to a developing rotor. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a control block diagram of the image forming apparatus according to the first embodiment. [Figure 3] FIG. 2 is a cross-sectional view of the developing device according to the first embodiment. [Figure 4] 10 is a graph showing the relationship between the angle of the supply roller, the magnetic flux density Br in the normal direction, and the magnetic attraction force Fr in the center direction of the supply roller according to Example 1 and Comparative Example 1. [Figure 5] 10 is a graph showing the relationship between the angle of the supply roller, the magnetic flux density Br in the normal direction, and the magnetic attraction force Fr in the center direction of the supply roller according to Example 2 and Comparative Example 1. [Figure 6] 10 is a graph showing the relationship between the angle around the holding pole S1 of the supply roller and the magnetic flux density Br in the normal direction according to the second embodiment. [Figure 7] 10 is a graph showing the relationship between the angle of the supply roller, the magnetic flux density Br in the normal direction, and the magnetic attraction force Fr in the center direction of the supply roller according to Example 3 and Comparative Examples 2 and 3. [Figure 8] 10 is a graph showing the relationship between the angle of the supply roller, the magnetic flux density Br in the normal direction, and the magnetic attraction force Fr in the center direction of the supply roller according to Examples 3 and 4 and Comparative Example 2. [Figure 9] 10 is a graph showing the relationship between the angle around the regulating pole N2 of the supply roller and the magnetic flux density Br in the normal direction according to Example 4. [Figure 10]10 is a table showing the results of an experiment conducted to confirm the effects of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment The first embodiment will be described with reference to Figures 1 to 4. In this embodiment, a developing device is applied to a tandem full-color printer as an example of an image forming apparatus.

[0012] [Image forming device] First, the schematic configuration of an image forming apparatus 100 according to this embodiment will be described with reference to FIG. 1. The image forming apparatus 100 shown in FIG. 1 is an electrophotographic full-color printer having four color (yellow, magenta, cyan, and black) image forming units PY, PM, PC, and PK within the main body of the apparatus. In this embodiment, the image forming units PY, PM, PC, and PK are arranged in an intermediate transfer tandem system along the rotation direction of an intermediate transfer belt 6 (described later). The image forming apparatus 100 forms a toner image (image) on a recording material S in response to an image signal from a document reading device (not shown) connected to the main body of the apparatus or a host device such as a personal computer connected to the main body of the apparatus so as to be able to communicate with the main body of the apparatus. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0013] The toner image formation process will be described below. First, the image forming units PY, PM, PC, and PK will be described. However, the image forming units PY, PM, PC, and PK are configured almost identically except for the toner colors they use: yellow, magenta, cyan, and black. Therefore, the following description will be given using the yellow image forming unit PY as a representative example, and descriptions of the other image forming units PM, PC, and PK will be omitted.

[0014] The image forming unit PY is mainly composed of a photosensitive drum 1, a charging device 2, a developing device 4, a cleaning device 8, etc. In this embodiment, an intermediate transfer belt 6 is disposed above each of the image forming units PY, PM, PC, and PK, and an exposure device 3 is disposed below them. The photosensitive drum 1, which serves as an image carrier and photosensitive member, has a photosensitive layer formed on the outer surface of an aluminum cylinder so as to have a negative or positive charging polarity, and rotates at a predetermined process speed (circumferential speed).

[0015] The charging device 2 charges the surface of the photosensitive drum 1 to a uniform negative or positive dark potential depending on the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a charging roller that rotates in contact with the surface of the photosensitive drum 1. After charging, an electrostatic latent image is formed on the surface of the photosensitive drum 1 by an exposure device (laser scanner) 3 based on image information. The photosensitive drum 1 carries the formed electrostatic latent image and moves around, and the formed electrostatic latent image is developed with toner by a developing device 4. The detailed configuration of the developing device 4 will be described later. The toner in the developer consumed in image formation is replenished together with carrier from a toner cartridge (not shown).

[0016] The developed toner image is subjected to a predetermined pressure and a primary transfer bias by a primary transfer roller 61, which is disposed opposite the photosensitive drum 1 with the intermediate transfer belt 6 sandwiched therebetween, and is primarily transferred onto the intermediate transfer belt 6. After the primary transfer, the surface of the photosensitive drum 1 is neutralized by a pre-exposure unit (not shown). A cleaning device 8 cleans off residual matter, such as transfer residual toner, remaining on the surface of the photosensitive drum 1 after the primary transfer.

[0017] The intermediate transfer belt 6 is tensioned by a tension roller 62 and a secondary transfer inner roller 63. The intermediate transfer belt 6 is driven by the secondary transfer inner roller 63, which also serves as a drive roller, to move in the direction of arrow R1 in the figure. The image formation process for each color performed by the image forming units PY, PM, PC, and PK described above is performed at a timing to sequentially superimpose the image onto the toner image of the color upstream in the movement direction that was primarily transferred onto the intermediate transfer belt 6. As a result, a full-color toner image is finally formed on the intermediate transfer belt 6 and transported to the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip formed by the portion of the intermediate transfer belt 6 tensioned by the secondary transfer inner roller 63 and the secondary transfer outer roller 64. Note that residual toner after passing through the secondary transfer unit T2 is removed from the intermediate transfer belt 6 by a belt cleaning device (not shown).

[0018] The recording material S is transported to the secondary transfer portion T2 at the same timing as the toner image formation process for the recording material S sent to the secondary transfer portion T2. ​​In the transport process, the recording material S is fed from a sheet cassette (not shown) or the like, and is sent to the secondary transfer portion T2 in accordance with the image formation timing. At the secondary transfer portion T2, a secondary transfer voltage is applied to the inner secondary transfer roller 63.

[0019] Through the above image forming process and conveying process, the toner image is secondarily transferred from the intermediate transfer belt 6 to the recording material S at the secondary transfer portion T2. ​​Thereafter, the recording material S is conveyed to the fixing device 7, where the toner image is melted and fixed onto the recording material S by applying heat and pressure thereto. The recording material S with the toner image fixed thereon is then discharged onto a discharge tray by a discharge roller.

[0020] [Control Unit] The image forming apparatus 100 is equipped with a control unit 20 for performing various controls such as the image forming operation described above. The operation of each unit of the image forming apparatus 100 is controlled by the control unit 20 provided in the image forming apparatus 100. The series of image forming operations are controlled by the control unit 20 in accordance with each input signal received from an operation unit on the top surface of the apparatus body or via a network.

[0021] 2, the control unit 20 has a CPU (Central Processing Unit) 21 as an arithmetic control means, a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, etc. The CPU 21 controls each part of the image forming apparatus 100 while reading out a program corresponding to a control procedure stored in the ROM 22. The RAM 23 stores working data and input data, and the CPU 21 performs control by referring to the data stored in the RAM 23 based on the above-mentioned program, etc.

[0022] In the control unit 20, an image processing unit 24 processes image information to generate drive signals for each unit, an image formation control unit 25 controls the operation of each unit such as a drive unit 9 that drives the exposure device 3 and the developing device 4, and a replenishment control unit 26 controls toner replenishment to the developing device 4. The drive unit 9 has drive motors that drive a developing roller 50, a supply roller 51, a first transport screw 44, and a second transport screw 45, which will be described later.

[0023] The control unit 20 is connected to a toner concentration sensor 58, an optical sensor 80, a temperature and humidity sensor 81, a bias power supply 82, and the like. The toner concentration sensor 58 will be described later. The optical sensor 80 is disposed opposite the surface of the intermediate transfer belt 6, and detects the density of a patch image, which is a control toner image formed on the intermediate transfer belt 6. Control of the supply of toner to the developing device 4 is performed according to the density of the patch image detected by the optical sensor 80. The bias power supply 82 is a power supply that applies a voltage to the developing roller 50 and the supply roller 51, as will be described later.

[0024] The temperature and humidity sensor 81 is an example of a detection unit and is provided, for example, in a part of the wall of the stirring chamber 43 on the downstream side in the toner transport direction to detect information related to the temperature and humidity inside the developing device 4. The control unit 20 calculates the absolute moisture amount inside the developing device 4 based on the information related to the temperature and humidity inside the developing device 4 detected by the temperature and humidity sensor 81. That is, the temperature and humidity sensor 81 detects information related to the absolute moisture amount inside the developing container 40. In this embodiment, the control unit 20 calculates information related to volumetric absolute humidity as information related to the absolute moisture amount. Furthermore, in this embodiment, the control unit 20 calculates information related to volumetric absolute humidity as information related to the absolute moisture amount, but the present invention is not limited to this and may calculate information related to weight absolute humidity as information related to the absolute moisture amount.

[0025] [Two-component developer] Next, the developer used in this embodiment will be described. In this embodiment, a two-component developer is used, in which the toner mixture coverage ratio with respect to the carrier, which includes non-magnetic toner particles (toner) and magnetic carrier particles (carrier), is 8.0% by weight. The toner is colored resin particles containing a binder resin, a colorant, and, if necessary, other additives, and an external additive such as colloidal silica fine powder is externally added to the surface. The toner used in this embodiment is a negatively or positively charged polyester resin depending on the charging characteristics of the photosensitive drum 1, and has a volume average particle size of approximately 7.0 μm. The carrier used in this embodiment is made of magnetic metal particles, such as iron, nickel, or cobalt, whose surfaces have been oxidized, and has a volume average particle size of approximately 40 μm to 50 μm.

[0026] [Developing device] Next, the developing device 4 will be described in detail with reference to Fig. 3. The developing device 4 of this embodiment is a so-called touch-down development type developing device, which forms a thin layer of only toner on the developing roller 50 using a magnetic brush made of a two-component developer formed on a supply roller 51, and develops the toner by causing it to fly to the electrostatic latent image formed on the photosensitive drum 1 using a developing bias that is a combination of DC and AC applied to the developing roller 50.

[0027] As shown in FIG. 3, the developing device 4 includes a developing container 40, a developing roller 50 as a developing rotator, and a supply roller 51 as a supply rotator. The developing container 40 contains a developer containing non-magnetic toner and a magnetic carrier. The developing container 40 includes a developing chamber 42 as a first chamber, a stirring chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The stirring chamber 43 is disposed adjacent to the developing chamber 42 so as to overlap at least a portion of the developing chamber 42 when viewed horizontally. The partition wall 41 separates the developing chamber 42 from the stirring chamber 43. The partition wall 41 has openings 41a formed on both ends in the longitudinal direction (the direction of the rotational axes of the developing roller 50 and the supply roller 51) as communication portions that connect the developing chamber 42 and the stirring chamber 43. The developing container 40 forms a circulation path that circulates the developer between the developing chamber 42 and the stirring chamber 43 via the openings 41a formed in the partition wall 41.

[0028] In this embodiment, a partition wall 41 is provided in the approximate center of the developing container 40. As a result, the developing container 40 is divided by the partition wall 41 so that the developing chamber 42 and the stirring chamber 43 are adjacent to each other in the horizontal direction. A first transport screw 44 and a second transport screw 45 that can rotate to stir and circulate the developer are disposed in the developing chamber 42 and the stirring chamber 43, respectively.

[0029] The first transport screw 44 as a first transport member is disposed at the bottom of the developing chamber 42 (inside the first chamber) along the rotational axis direction (longitudinal direction) of the supply roller 51, facing and substantially parallel to the supply roller 51. The first transport screw 44 has a rotation shaft 44a and a blade 44b spirally provided around the rotation shaft 44a. The second transport screw 45 as a second transport member is disposed at the bottom of the stirring chamber 43 (inside the second chamber) and substantially parallel to the first transport screw 44. The second transport screw 45 has a rotation shaft 45a and a blade 45b spirally provided around the rotation shaft 45a.

[0030] The first transport screw 44 and the second transport screw 45 rotate in the directions of arrows R4 and R3, respectively, to transport the developer within the developing chamber 42 and the stirring chamber 43. The developer transported by the rotation of the first transport screw 44 and the second transport screw 45 circulates between the developing chamber 42 and the stirring chamber 43 through openings 41a at both ends of the partition wall 41. The toner is stirred by the first transport screw 44 and the second transport screw 45, and rubs against the carrier, becoming frictionally charged to a negative or positive polarity.

[0031] A toner concentration sensor 58 (FIG. 2) is disposed in the stirring chamber 43, facing the second conveying screw 45. As the toner concentration sensor 58, for example, a magnetic permeability sensor that detects the magnetic permeability of the developer in the developing container 40 is used. Based on the detection result of the toner concentration sensor, the control unit 20 replenishes toner from a toner cartridge to the stirring chamber 43 via a toner refill port (not shown).

[0032] As shown in FIG. 3, the developing roller 50 and the supply roller 51 are disposed vertically above the developing chamber 42 and the stirring chamber 43. The developing roller 50 is disposed between the photosensitive drum 1 and obliquely above the supply roller 51 when viewed from the direction of the rotation axis of the supply roller 51. The supply roller 51 and the developing roller 50 are disposed facing each other at the facing portion P1, with their rotation axes being substantially parallel. The developing roller 50 faces the photosensitive drum 1 on the opening side of the developer container 40. The developing roller 50 and the supply roller 51 are disposed so as to be rotatable about their respective rotation axes. The developing roller 50 and the supply roller 51 are driven to rotate counterclockwise in FIG. 3 (in the direction of arrows R6 and R5) by a drive unit 9 (FIG. 2) provided in the main body of the apparatus. That is, the developing roller 50 and the supply roller 51 rotate in opposite directions at the facing portion P1. (reverse direction) The rotation speed is variable by the drive unit 9.

[0033] The supply roller 51 is a non-magnetic cylindrical roller that rotates counterclockwise in FIG. 3, and is provided with a magnetic field generating means and a second ofThe magnetic roller 51a is rotatably mounted around a cylindrical, non-rotating magnet roller 51a. That is, the magnet roller 51a is fixedly mounted inside the supply roller 51 without rotating. The magnet roller 51a has five pieces, each of which has a surface facing the supply roller 51 and a draw-up pole S2, a regulating pole N2, a holding pole S1, a main pole N1, and a stripping pole S3, arranged in order in the direction of rotation of the supply roller. While this embodiment uses a five-pole magnet roller, other poles are acceptable, such as a seven-pole magnet roller. However, the wider the angle between the regulating pole and the main pole, the weaker the magnetic force acting between the main pole and the holding pole, making carrier adhesion more likely to occur. Therefore, a five-pole configuration for the magnet roller 51a, as in this embodiment, is preferable for suppressing carrier adhesion.

[0034] main pole (Second magnetic pole) N1 is a position where the supply roller 51 is disposed opposite the developing roller 50, and the supply roller 51 is located at a position where the supply roller 51 faces the developing roller 50. (first magnetic pole) It has the opposite polarity to S4. (Third magnetic pole) S1 is disposed adjacent to and upstream of the main pole N1 in the rotation direction of the supply roller 51, and has a polarity opposite to that of the main pole N1. (Fourth magnetic pole) N2 is located adjacent to the upstream of the holding pole S1 in the rotation direction of the supply roller 51, and is positioned so that the regulating blade 52 (described later) faces the supply roller 51, and has the same polarity as the main pole N1. (5th magnetic pole)S2 is a magnetic pole arranged adjacent to and upstream of the regulating pole N2, has a polarity opposite to that of the regulating pole N2, and draws up the developer from the developing container 40 to the supply roller 51. Specifically, the drawing-up pole S2 is arranged above the developing chamber 42 facing the first transport screw 44. The peeling pole (strip-off pole) S3 is arranged adjacent to and upstream of the drawing-up pole S2 in the rotational direction of the supply roller 51, and has the same polarity as the drawing-up pole S2. The peeling pole S3 is also arranged adjacent to and downstream of the main pole N1 in the rotational direction of the supply roller 51, and corresponds to a downstream pole having a polarity opposite to that of the main pole N1. The drawing-up pole S2, regulating pole N2, holding pole S1, main pole N1, and peeling pole S3 are arranged adjacent to each other in this order in the rotational direction of the supply roller 51.

[0035] The supply roller 51 carries a developer having non-magnetic toner and a magnetic carrier, and rotates to transport the developer to the opposing portion P1 of the developing roller 50. That is, the supply roller 51 is disposed opposite the developing roller 50, and rotates to supply the developer in the developing container 40 (inside the developing container) to the developing roller 50. The supply roller 51 is cylindrical, for example, with a diameter of 20 mm to 25 mm (20 mm in this embodiment), and is made of a non-magnetic material such as aluminum or non-magnetic stainless steel, and is made of aluminum in this embodiment. The outer circumferential surface of the supply roller 51 is also blasted to have a surface roughness of, for example, Rz 30 μm.

[0036] The regulating blade 52, which serves as a regulating member, is disposed upstream of the position facing the developing roller 50 in the rotational direction of the supply roller 51 and regulates the amount of developer carried by the supply roller 51. Specifically, the regulating blade 52 is a plate-shaped member and is provided in the developer container 40 so that its tip faces the outer circumferential surface of the supply roller 51, on which the regulating pole N2 of the magnetic roller 51a is disposed. A predetermined gap is provided between the tip of the regulating blade 52 and the outer circumferential surface of the supply roller 51. The magnetic chains of the developer carried on the surface of the supply roller 51 are cut off by the regulating blade 52, thereby regulating the thickness of the developer layer. Specifically, the regulating blade 52 is made of a metal plate (e.g., a stainless steel plate) disposed in the longitudinal direction of the supply roller 51. When the developer passes between the tip of the regulating blade 52 and the supply roller 51, the developer is conveyed in a regulated state at a constant amount. The regulating blade 52 is formed in an L-shape from a magnetic member such as SUS430 having a thickness of about 1.5 mm, and is fixed to the developing container 40 so as to extend in the direction of the rotation axis of the supply roller 51.

[0037] The regulating blade 52 may be made of either a magnetic or non-magnetic material. If the regulating blade 52 is made of a magnetic material, a magnetic field is formed between the tip of the regulating blade 52 and the supply roller 51, and a magnetic attraction force acts on the surface of the regulating blade 52. As a result, the developer is more easily scraped off. Another advantage is that the gap between the tip of the regulating blade 52 and the supply roller 51 can be increased, making it less likely for foreign matter to clog. On the other hand, if the regulating blade 52 is made of a magnetic material, the developer is constrained by the magnetic field between the tip of the regulating blade 52 and the supply roller 51, which may cause developer deterioration due to friction. The regulating blade 52 may also be made of a non-magnetic material with a magnetic material attached to a portion thereof. This somewhat reduces the benefits of a magnetic material, but makes it possible to suppress developer deterioration.

[0038] The developer contained in the developing chamber 42 is attracted to the surface of the supply roller 51 by the drawing-up pole S2 facing the developing chamber 42, and is transported toward the regulating blade 52. The developer is made into chains by the regulating pole N2 facing the regulating blade 52, and the layer thickness is regulated by the regulating blade 52. The developer layer is carried and transported via the retaining pole S1 to the portion P1 facing the developing roller 50, and in a state where magnetic chains are formed by the main pole N1 facing the development area, toner is supplied to the surface of the developing roller 50. A supply bias, which is a superimposed DC voltage and AC voltage, is applied to the supply roller 51.

[0039] The developing roller 50 is disposed opposite the photosensitive drum 1, and by rotating, conveys developer to a developing position where the electrostatic latent image formed on the photosensitive drum 1 is developed. That is, the developing roller 50 is a non-magnetic roller that rotates counterclockwise in FIG. 3, and has one receiving pole provided on the inner circumferential side. (first magnetic pole) Non-rotating first with S4 of The supply roller 51 is provided rotatably around the magnet roller 50a, which serves as a magnet. The developing roller 50 carries toner and rotates to develop the electrostatic latent image on the photosensitive drum 1 in a developing area P2, which is an opposing area facing the photosensitive drum 1. The supply roller 51 and the developing roller 50 face each other at an opposing portion P1 with a predetermined gap between them. The receiving pole S4 of the magnet roller 50a in the developing roller 50 has a polarity opposite to that of the opposing main pole N1.

[0040] A developing bias, which is a superposition of a DC voltage and an AC voltage, is applied to the developing roller 50. The developing bias and supply bias are applied to the developing roller 50 and supply roller 51 from a bias power supply 82 (FIG. 2), which is an example of a voltage application unit, via a bias control circuit. In other words, the bias power supply 82 applies a voltage including a DC component and an AC component between the developing roller 50 and supply roller 51.

[0041] The toner remaining on the developing roller 50 without being used for development is transported again to the opposing portion P1 of the developing roller 50 and the supply roller 51, where it is rubbed by the magnetic brush on the supply roller 51 and collected by the supply roller 51. The magnetic brush is peeled off from the supply roller 51 in a peeling region created by the repulsion of the peeling pole S3 and the pumping pole S2 located downstream in the rotation direction of the supply roller 51. The peeled developer falls into the developing chamber 42, where it is agitated and transported with the developer circulating in the developer container 40, attracted to the pumping pole S2 again, and transported by the supply roller 51.

[0042] [Magnetic roller for supply roller] Next, Example 1 of the main pole N1, holding pole S1, regulating pole N2, and peeling pole S3 of the magnet roller 51a of the supply roller 51 of this embodiment will be described with reference to FIG. 4, while comparing it with Comparative Example 1. FIG. 4 is a diagram schematically illustrating the distribution of magnetic flux density Br on the supply roller 51 by the magnet roller 51a. More precisely, magnetic flux density Br refers to the normal component of magnetic flux density B on the surface of the supply roller 51. Hereinafter, "normal magnetic flux density Br" may be referred to simply as "magnetic flux density" according to convention. When simply referring to "magnetic flux density," it refers to "normal magnetic flux density Br." The (normal) magnetic flux density Br of each magnet roller of the Example and Comparative Example was measured using a magnetic field measuring device (FWBELL MS-9902) with the distance between the probe of the magnetic field measuring device and the surface of the supply roller 51 being approximately 100 μm.

[0043] 4 also shows an outline of the magnetic attraction force Fr that attracts the developer (carrier) toward the center of the supply roller 51. The magnetic attraction force Fr of the supply roller 51 can be derived from the magnetic flux density Br in the normal direction, and is expressed by the following equation 1.

number

[0044] In the above formula 1, μ is the magnetic permeability of the magnetic carrier, μ0 is the magnetic permeability of a vacuum, and b is the radius of the magnetic carrier. The magnetic flux density Bθ in the tangential direction on the surface of the supply roller 51 is calculated from the following formula 2 using the value of Br measured by the above method.

number

[0045] In Figure 4, the magnetic attraction force Fr acting on the carrier in the direction of the center of the supply roller 51, calculated using equations 1 and 2, is also shown on the second axis. Hereinafter, the "magnetic attraction force Fr in the direction of the center of the supply roller" may be simply referred to as the "magnetic attraction force." When simply referred to as the "magnetic attraction force," it refers to the "magnetic attraction force Fr in the direction of the center of the supply roller."

[0046] Here, we will explain the contribution of each magnet roller to the carrier adhesion phenomenon from the supply roller 51 to the developing roller 50. As mentioned above, the developing roller 50 has a receiving pole S4 facing the main pole N1 of the supply roller 51. These two magnetic poles form a magnetic chain with strong binding force at the opposing portion P1 of the developing roller 50 and supply roller 51, making it possible to collect toner remaining on the developing roller 50 and suppress the occurrence of the ghost phenomenon. The ghost phenomenon is a phenomenon in which part of the developed image from the previous stage appears as an afterimage (ghost) during the next development, a so-called hysteresis phenomenon.

[0047] On the other hand, because the magnetic binding force at the opposing portion P1 is strong, developer stagnation occurs, and the carrier and toner move together to the developing roller 50 and are transported to the developing region P2, which makes it easy for the carrier to adhere to the photosensitive drum 1 and cause spotted image defects in parts of the image. Therefore, the receiving pole S4 on the developing roller 50 side has its magnetic flux density peak positioned upstream of the line connecting the centers of rotation of the developing roller 50 and the supply roller 51 in the direction of rotation of the developing roller 50.

[0048] That is, the position of the maximum value of the magnetic flux density Br in the normal direction on the surface of the developing roller 50 (the peak position where the magnetic flux density Br in the normal direction on the surface of the developing roller 50 is maximum) of the receiving pole S4 is located upstream in the rotation direction of the developing roller 50 from the straight line connecting the rotation center position of the developing roller 50 and the rotation center position of the supply roller 51. As a result, the magnetic brush is formed tilted upstream in the rotation direction of the developing roller 50. In this embodiment, the receiving pole S4 is positioned upstream in the rotation direction of the developing roller 50 from the straight line connecting the rotation centers by an angle of about 1° to 10°, preferably about 3° to 7°, and more preferably about 5°.

[0049] Furthermore, the main pole N1 on the supply roller 51 side has a magnetic flux density peak located downstream in the rotation direction of the supply roller 51 from a line connecting the centers of rotation of the developing roller 50 and the supply roller 51. That is, the position of the maximum value of the magnetic flux density Br in the normal direction to the surface of the supply roller 51 (the peak position where the magnetic flux density Br in the normal direction to the surface of the supply roller 51 is maximum) of the main pole N1 is located downstream in the rotation direction of the supply roller 51 from a line connecting the rotation centers of the developing roller 50 and the supply roller 51. As a result, the magnetic brush is formed inclined downstream in the rotation direction of the supply roller 51. In this embodiment, the main pole N1 is located downstream in the rotation direction of the supply roller 51 from the line connecting the rotation centers by an angle of approximately 6° to 22°, preferably approximately 10° to 18°, and more preferably approximately 14°.

[0050] In this way, by tilting either or both of the receiving pole S4 of the developing roller 50 and the main pole N1 of the supply roller 51, the magnetic chain formed between the developing roller 50 and the supply roller 51 is tilted downstream in the rotation direction of the supply roller 51. This makes it easier for the developer transported from the upstream side in the rotation direction of the supply roller 51 to be introduced into the opposing portion P1 between the developing roller 50 and the supply roller 51. Therefore, by eliminating the accumulation of developer in the opposing portion P1, the transport of developer containing carrier to the developing roller 50 is suppressed, and a decrease in the quality of the formed image can be suppressed.

[0051] In recent years, image forming devices have become faster, and the rotational speeds of the supply roller 51 and the developing roller 50 have also increased accordingly. This has led to a risk that carrier particles are more likely to fly from the developer transported upstream in the rotation direction of the supply roller 51, transfer to the developing roller 50, and be transported to the development region P2, which may result in spotted image defects. In this embodiment, the following configuration is used to strengthen the magnetic attraction force Fr from the opposing portion P1 between the developing roller 50 and the supply roller 51 to the upstream portion thereof, thereby suppressing carrier adhesion.

[0052] Specifically, in this embodiment, the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is set to be larger for the holding pole S1 than for the regulating pole N2, and larger for the main pole N1 than for the holding pole S1. That is, the magnitude of the absolute value |Br| of the magnetic flux density is set to be main pole N1>holding pole S1>regulating pole N2.

[0053] The results of measuring the absolute values ​​|Br| of the maximum values ​​(maximum values) of the magnetic flux density in the normal direction of each magnetic pole for Examples 1-1 to 1-5, which have such a magnetic flux density relationship as defined in this embodiment, and Comparative Example 1, which does not, are shown in Table 1, and the inter-pole angles of each magnetic pole are shown in Table 2. The inter-pole angles are the angles in the rotation direction of supply roller 51 between the positions (peak positions) of the maximum values ​​(maximum values) of the magnetic flux density in the normal direction of adjacent magnetic poles. [Table 1] [Table 2]

[0054] As shown in Tables 1 and 2, Examples 1-1 and 1-2 are configured so that the magnitude of the absolute value |Br| of the magnetic flux density in the normal direction satisfies the relationship of main pole N1 > holding pole S1 > regulating pole N2 and holding pole S1 > separating pole S3. That is, the absolute value of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is larger for holding pole S1 than for regulating pole N2, and larger for main pole N1 than for holding pole S1. Furthermore, the holding pole S1 upstream of the main pole N1 is larger than the separating pole S3, which is the pole downstream of the main pole N1.

[0055] Moreover, Example 1-3 is configured so that the inter-pole angle between the main pole N1 and the holding pole S1 is smaller than that of Comparative Example 1. Moreover, Example 1-4 is configured so that the inter-pole angle between the main pole N1 and the holding pole S1 is smaller than the inter-pole angle between the main pole N1 and the peeling pole S3. That is, the position (peak position) of the maximum value (maximum value) of the magnetic flux density Br of the main pole N1 in the normal direction to the surface of the supply roller 51 is defined as the first position, the position (peak position) of the maximum value (maximum value) of the magnetic flux density Br of the holding pole S1 in the normal direction to the surface of the supply roller 51 is defined as the second position, and the position (peak position) of the maximum value (maximum value) of the magnetic flux density Br of the regulating pole N2 in the normal direction to the surface of the supply roller 51 is defined as the third position. In this case, with respect to the rotation direction of the supply roller 51, the angle between the second position (peak position of the holding pole S1) and the first position (peak position of the main pole N1) is smaller than the angle between the second position (peak position of the holding pole S1) and the third position (peak position of the regulating pole N2).

[0056] In addition, Examples 1-5 are configured so that the magnitude of the absolute value |Br| of the magnetic flux density in the normal direction is main pole N1 > holding pole S1 > regulating pole N2, and holding pole S1 > peeling pole S3. Furthermore, the inter-pole angle between the main pole N1 and holding pole S1 is smaller than the inter-pole angle between the holding pole S1 and regulating pole N2 and the inter-pole angle between the main pole N1 and peeling pole S3. That is, the position (peak position) of the maximum value (maximum value) of the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the peeling pole S3 is defined as the fourth position. In this case, with respect to the rotation direction of the supply roller 51, the angle between the second position (peak position of the holding pole S1) and the first position (peak position of the main pole N1) is smaller than the angle between the second position (peak position of the holding pole S1) and the third position (peak position of the regulating pole N2), and is also smaller than the angle between the first position (peak position of the main pole N1) and the fourth position (peak position of the peeling pole S3).

[0057] 4 shows, as examples, the magnetic flux density Br (solid line) of Examples 1-5, which have the highest effect of suppressing carrier adhesion, and the magnetic flux density Br (dashed line) of Comparative Example 1. The respective magnetic attraction forces Fr are also shown with thick lines. The dashed frame indicates the position of the opposing portion P1. Furthermore, as shown by the arrow in FIG. 4, the direction from right to left on the horizontal axis is the rotation direction of the supply roller 51, and in the following description, when simply referring to "upstream" and "downstream," it is assumed that these refer to "upstream" and "downstream" with respect to the rotation direction of the supply roller 51.

[0058] Furthermore, developing devices having the configurations of the respective Examples and Comparative Examples were incorporated into an image forming apparatus as shown in Fig. 1, and test images were actually output to evaluate image formation performance, and the presence or absence of carrier adhesion in the test images was visually observed. The test results are shown in Table 1. In Table 1, a case where no carrier adhesion occurred on the image was marked with an ⊚, a case where almost no carrier adhesion occurred on the image (i.e., where carrier adhesion occurred to an extent that did not affect quality) was marked with an O, and a case where carrier adhesion occurred on the image was marked with an X.

[0059] The development conditions were a peripheral speed of the photosensitive drum 1 of 450 mm / sec, and a dark potential of the surface potential of the photosensitive drum of 350 V. The AC bias Vpp of the developing roller 50 was 1.6 kV, a frequency of 4 kHz, a duty ratio of 30%, and a DC bias Vdc of 30 V. The AC bias Vpp of the supply roller 51 was 0.4 kV, a frequency of 4 kHz, a duty ratio of 70%, and a DC bias Vdc of 300 V.

[0060] Other conditions were that the gap between the developing roller 50 and the supply roller 51 was 300 μm, the peripheral speed ratio of the supply roller 51 to the developing roller 50 was 1.5 times, and the peripheral speed ratio of the developing roller 50 to the photosensitive drum 1 was 1.5 times.

[0061] As shown in Tables 1 and 2, the relationship in magnitude of the absolute value |Br| of the magnetic flux density of the magnet roller 51a of the supply roller 51 of Comparative Example 1 is configured so that the main pole N1 > the holding pole S1 and the regulating pole N2 > the holding pole S1. The relationship in the peak positions of the magnetic flux density is configured so that the difference in the inter-pole angle between the main pole N1 and the holding pole S1, the inter-pole angle between the holding pole S1 and the regulating pole N2, and the inter-pole angle between the main pole N1 and the peeling pole S3 is 5° or less. The peak position of the magnetic flux density of the main pole N1 was set 16° downstream in the direction of rotation of the supply roller 51, and the peak position of the magnetic flux density of the receiving pole S4 of the magnet roller 60b of the development roller 50 was set 5° upstream in the direction of rotation of the development roller 50, relative to the closest position between the development roller 50 and the supply roller 51.

[0062] As shown in FIG. 4, the magnetic attraction force Fr of the carrier in Comparative Example 1 is generally smaller upstream of the opposing portion P1 in the direction of rotation of the supply roller 51 than in Examples 1-5. If the magnetic attraction force Fr is small in this region, the centrifugal force caused by the rotation of the supply roller 51 overcomes the magnetic attraction force Fr, and the carrier is more likely to fly from the developer conveyed upstream of the rotation direction of the supply roller 51. This may increase the risk of image defects due to carrier adhesion. As is clear from Table 1, in Comparative Example 1, in which the magnetic attraction force Fr of the carrier is small upstream of the opposing portion P1 in the direction of rotation of the supply roller 51, carrier adhesion occurred on the image.

[0063] In contrast, in Examples 1-1 to 1-5, no or almost no carrier adhesion occurred on the image. The reason for the improvement in carrier adhesion is believed to be as follows: The magnetic attraction force Fr that attracts the carrier toward the center of the supply roller 51 is the product of the magnitude of the magnetic flux density Br and its change (partial derivative) in the r direction (normal direction) (see Equation 1 above).

[0064] As can be seen from Tables 1 and 2, by making the magnitude of the absolute values ​​|Br| of magnetic flux density in the normal direction in Examples 1-1 and 1-2 such that main pole N1 > holding pole S1 > regulating pole N2, the magnetic flux lines of holding pole S1 tend to extend toward main pole N1, which has a larger absolute value |Br| of magnetic flux density. Furthermore, by making the relationship of holding pole S1 > release pole S3, the magnetic flux lines of main pole N1 tend to extend toward holding pole S1, which has a larger absolute value |Br| of magnetic flux density. As a result, in Examples 1-1 and 1-2, magnetic flux lines tend to concentrate between main pole N1 and holding pole S1 more easily than in Comparative Example 1, making the magnetic flux density Br larger, and the magnetic attraction force Fr, which is the product of these, tends to be larger.

[0065] Furthermore, the magnetic flux density distribution of the main pole N1 in Example 1-3 has a shape in which the peak position of the magnetic flux density of the holding pole S1 is closer to the peak position of the magnetic flux density of the main pole N1, and the magnetic flux density increases more rapidly (has a steeper slope) from the holding pole S1 to the main pole N1 than in Comparative Example 1. In the region where the magnetic flux density changes rapidly, the change in the r direction (partial derivative) also tends to be large. As a result, although the absolute value of the magnetic flux density in Example 1-3 is the same as in Comparative Example 1, the inter-pole angle between the main pole N1 and the holding pole S1 in Example 1-3 is smaller than in Comparative Example 1, so the change in the r direction (partial derivative) tends to be large, and the magnetic attraction force Fr, which is the product of these, tends to be large.

[0066] Furthermore, in the magnetic flux density distribution of the main pole N1 in Example 1-4, the peak position of the magnetic flux density of the holding pole S1 is closer to the peak of the magnetic flux density of the main pole N1 than the peak position of the magnetic flux density of the separation pole S3, and the magnetic flux lines of the main pole N1 are more likely to extend toward the holding pole S1 than in Comparative Example 1. As a result, in Example 1-4, the magnetic flux lines are more likely to concentrate between the main pole N1 and the holding pole S1 than in Comparative Example 1, making the magnetic flux density larger, and the magnetic attractive force Fr, which is the product of these, is more likely to be larger.

[0067] In particular, in Example 1-5, in which no carrier adhesion occurred on the image, the magnitude of the absolute value |Br| of the magnetic flux density of the magnet roller 51a was such that the main pole N1 > the holding pole S1 > the regulating pole N2, and the holding pole S1 > the peeling pole S3. Furthermore, by making the inter-pole angle between the main pole N1 and the holding pole S1 smaller than the inter-pole angle between the main pole N1 and the peeling pole S3, magnetic flux lines were concentrated between the main pole N1 and the holding pole S1, which tended to increase the magnetic flux density. Furthermore, by making the inter-pole angle between the main pole N1 and the holding pole S1 smaller than the inter-pole angle between the holding pole S1 and the regulating pole N2, the magnetic flux density changed more rapidly than in Comparative Example 1, and the change in the r direction (partial differential) was likely to be large. As a result, the magnetic attraction force Fr, which is the product of the magnitude of the magnetic flux density and its change in the r direction (partial differential), was likely to be large.

[0068] In fact, looking at Figure 4, it can be seen that in the area where the change (slope) in the θ direction (circumferential direction) of the magnetic flux density Br is large from the opposing portion P1 between the developing roller 50 and the supply roller 51 upstream of the rotation direction of the supply roller 51, the magnetic attraction force Fr is also larger in Example 1-5 compared to Comparative Example 1.

[0069] As described above, by setting the magnitude of the absolute value |Br| of the magnetic flux density of the magnet roller 51a of the supply roller 51 to be main pole N1 > holding pole S1 > regulating pole N2 and holding pole S1 > peeling pole S3, the magnetic flux density Br between the main pole N1 and holding pole S1 is increased. Furthermore, by making the inter-pole angle between the main pole N1 and holding pole S1 smaller than the inter-pole angle between the holding pole S1 and regulating pole N2 and the inter-pole angle between the main pole N1 and peeling pole S3, the change (gradient) in the θ direction of the magnetic flux density Br is increased. This increases the magnetic attraction force Fr from the opposing portion P1 upstream in the rotation direction of the supply roller 51, thereby suppressing carrier adhesion to the developing roller 50.

[0070] Here, it is desirable that the difference between the magnitudes of the magnetic flux densities Br be 5 mT or more, preferably 10 mT or more, and more preferably 15 mT or more. In particular, it is desirable that the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 be 5 mT or more, preferably 10 mT or more, and more preferably 15 mT or more, larger for the main pole N1 than for the holding pole S1. It is also desirable that the holding pole S1 be 5 mT or more, preferably 10 mT or more, and more preferably 15 mT or more larger for the regulating pole N2. It is also desirable that the holding pole S1 be 5 mT or more, preferably 10 mT or more, and more preferably 15 mT or more larger for the separating pole S3. This is to prevent the magnitude relationship of the absolute values ​​|Br| of the magnetic flux densities from being reversed due to component tolerances of the magnet roller 51a.

[0071] Furthermore, it is desirable that the difference between the inter-pole angle between the main pole N1 and the holding pole S1 and the inter-pole angle between the holding pole S1 and the regulating pole N2 be 10° or more, preferably 15° or more, and more preferably 20° or more. That is, it is desirable that the angle between the second position (peak position of the holding pole S1) and the first position (peak position of the main pole N1) be smaller by 10° or more, preferably 15° or more, and more preferably 20° or more than the angle between the second position (peak position of the holding pole S1) and the third position (peak position of the regulating pole N2). This allows a sufficient magnetic attraction force Fr to be obtained.

[0072] Furthermore, it is desirable that the difference between the inter-pole angle between the main pole N1 and the holding pole S1 and the inter-pole angle between the main pole N1 and the stripping pole S3 be 10° or more, preferably 15° or more, and more preferably 20° or more. That is, it is desirable that the angle between the first position (peak position of the main pole N1) and the second position (peak position of the holding pole S1) be smaller than the angle between the first position (peak position of the main pole N1) and the fourth position (peak position of the stripping pole S3) by 10° or more, preferably 15° or more, and more preferably 20° or more. This allows a sufficient magnetic attraction force Fr to be obtained.

[0073] The magnetic flux density and arrangement angle of the magnet roller 51a on the supply roller 51 side, including the main pole N1, the holding pole S1, and the regulating pole N2, can be set appropriately according to the specifications of the developing device. That is, it is sufficient to strengthen the magnetic attraction force Fr from the opposing portion P1 between the developing roller 50 and the supply roller 51 to its upstream portion, and in order to strengthen the magnetic attraction force Fr, the magnetic flux density Br may be increased, or the change in the r direction of the magnetic flux density Br (partial differential) may be increased.

[0074] <Second embodiment> The second embodiment will be described using Figures 5 and 6 with reference to Figure 3. In this embodiment, the distribution of magnetic flux density of the holding pole S1 is changed compared to the first embodiment. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used to designate the same configurations, and explanations and illustrations will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0075] In this embodiment, the magnitude of the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density is set to be the main pole N1>holding pole S1>regulating pole N2, as in the first embodiment. Meanwhile, in this embodiment, unlike the first embodiment, the distribution of the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the holding pole S1 is such that the position where the magnetic flux density is maximum (maximum) is called the first holding pole position, and the position where it is 50% of the maximum value (maximum value) is called the second holding pole position. (1st position) and the third holding pole position (2nd position), the first holding pole position is located downstream in the rotation direction of the supply roller 51 from the intermediate position between the second holding pole position and the third holding pole position.

[0076] In other words, in this embodiment, the shape of the magnetic flux density Br distribution is made asymmetric so that the absolute value |ΔBr| of the amount of change in Br per angle of 1 degree at the holding pole S1 is larger downstream than upstream in the rotation direction of the supply roller 51. Examples 2-1 to 2-2 that satisfy this embodiment and have such a relationship in magnetic flux density will be specifically described below. In the following description, when simply referring to "upstream" and "downstream," it is assumed that they refer to "upstream" and "downstream" with respect to the rotation direction of the supply roller 51.

[0077] First, in Example 2-1, the |ΔBr| at the point where the magnetic flux density Br becomes 0 on the upstream and downstream sides of the holding pole S1 was 1.5 mT / deg on the upstream side and 2.6 mT / deg on the downstream side. The magnitude of the absolute value of the magnetic flux density |Br| was 90 mT for the main pole N1, 43 mT for the holding pole S1, 40 mT for the regulating pole N2, 42 mT for the pumping pole S2, and 41 mT for the separating pole S3. The relationship between the peak positions of the magnetic flux density was as follows: the inter-pole angle between the main pole N1 and the holding pole S1 was 42°, the inter-pole angle between the holding pole S1 and the regulating pole N2 was 61°, the inter-pole angle between the regulating pole N2 and the pumping pole S2 was 48°, the inter-pole angle between the pumping pole S2 and the separating pole S3 was 126°, and the inter-pole angle between the main pole N1 and the separating pole S3 was 83°.

[0078] Next, in Example 2-2, the magnitude of the absolute value of the magnetic flux density in the normal direction, |Br|, is configured so that the retaining pole S1 is greater than the separating pole S3, as in Example 1-5 described in the first embodiment. Furthermore, the |ΔBr| at the point where the magnetic flux density Br becomes 0 on the upstream and downstream sides of the retaining pole S1 is 2.1 mT / deg on the upstream side and 4.0 mT / deg on the downstream side. The relationship between the peak positions of the magnetic flux density was as follows: the inter-pole angle between the main pole N1 and the retaining pole S1 was 39°, the inter-pole angle between the retaining pole S1 and the regulating pole N2 was 64°, the inter-pole angle between the regulating pole N2 and the pumping pole S2 was 48°, the inter-pole angle between the pumping pole S2 and the separating pole S3 was 126°, and the inter-pole angle between the main pole N1 and the separating pole S3 was 83°.

[0079] In addition, in Examples 2-1 and 2-2, the peak position of the magnetic flux density of the main pole N1 was set at 16° downstream of the rotation direction of the supply roller 51 relative to the closest position between the developing roller 50 and the supply roller 51, and the peak position of the magnetic flux density of the receiving pole S4 of the magnet roller 60b of the developing roller 50 was set at 5° upstream of the rotation direction of the developing roller 50.

[0080] 5 shows the magnetic flux density Br (solid line) of Example 2-1, the magnetic flux density Br (two-dot chain line) of Example 2-2, and the magnetic flux density Br (dotted line) of Comparative Example 1. The magnetic attraction force Fr of each is also shown by a thick line. In FIG. 5, the direction from right to left on the horizontal axis is the rotation direction of supply roller 51, as indicated by the arrow.

[0081] In Example 2-1, the absolute value |ΔBr| of the amount of change in Br on the downstream side of the retaining pole S1 in the rotation direction of the supply roller 51 is made larger than in Comparative Example 1, and therefore the magnetic flux density between the main pole N1 and the retaining pole S1 changes more rapidly than in Comparative Example 1, and the change in the r direction (partial differential) is likely to be larger. As a result, the magnetic attractive force Fr formed by the product of the change in the r direction (partial differential) is likely to be larger, and the magnetic attractive force Fr from the opposing portion P1 to the upstream side in the rotation direction of the supply roller 51 is larger, making it possible to suppress carrier adhesion to the developing roller 50.

[0082] In Example 2-2, compared to Comparative Example 1, the magnitude of the absolute value of the magnetic flux density |Br| is set to main pole N1 > holding pole S1 > regulating pole N2 and holding pole S1 > release pole S3, which makes it easier for magnetic flux lines to concentrate between the main pole N1 and holding pole S1, increasing the magnetic flux density Br. Also, by increasing the absolute value of the change in Br on the downstream side of holding pole S1 in the rotation direction of supply roller 51, |ΔBr|, the magnetic flux density between the main pole N1 and holding pole S1 changes more rapidly than in Comparative Example 1, making the change in the r direction (partial differential) easier to increase. As a result, the magnetic attraction force Fr, which is the product of the magnitude of the magnetic flux density Br and its change in the r direction (partial differential), is easier to increase.

[0083] 5, in the region where the change (gradient) in the θ direction of the magnetic flux density Br is large upstream of the opposing portion P1 of the developing roller 50 and the supply roller 51 in the direction of rotation of the supply roller 51, the magnetic attractive force Fr is also larger in Examples 2-1 and 2-2 compared to Comparative Example 1. Furthermore, in Example 2-2, where the magnitude of the absolute value of the magnetic flux density |Br| is such that main pole N1 > holding pole S1 > regulating pole N2 and holding pole S1 > release pole S3, the magnetic flux density Br between the main pole N1 and holding pole S1 is larger than in Example 2-1, and the magnetic attractive force Fr, which is the product of these values, is also larger. Therefore, carrier adhesion to the developing roller 50 can be suppressed more effectively than in Example 2-1.

[0084] The asymmetric shape of the magnetic flux density Br of the holding pole S1 of this embodiment will now be described with reference to FIG. 6. FIG. 6 is an enlarged view of the periphery of the holding pole S1 of Br in Example 2-2 shown in FIG. 5. Point A is the position (first holding pole position) where the magnitude of the magnetic flux density Br in the holding pole S1 is maximized (maximum). Point B is an intermediate position between points C1 (second holding pole position) and C2 (third holding pole position), where the magnetic flux density is 50% of that at point A. In this embodiment, point A is located downstream of point B in the rotation direction of the supply roller 51, resulting in an asymmetric distribution of the magnetic flux density Br of the holding pole S1.

[0085] The angular difference between the positions of points A and B is desirably 3° or more, preferably 4° or more, and more preferably 5° or more. In other words, it is desirably that the first hold pole position (point A) is located downstream of the intermediate position (point B) in the rotation direction of the supply roller 51 by 3° or more, preferably 4° or more, and more preferably 5° or more.

[0086] Furthermore, it is desirable that the pole position difference between point A of the holding pole S1 and the position (peak position) where the magnetic flux density of the regulating pole N2 is maximized (maximum) is greater than the pole position difference between point A of the holding pole S1 and the position (peak position) where the magnetic flux density of the main pole N1 is maximized (maximum) by 10° or more, preferably 15° or more, and more preferably 20° or more. This is to make the magnetic flux density Br of the holding pole S1 asymmetric even within the component tolerance range of the magnet roller.

[0087] Table 3 shows the results of measuring the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction of each magnetic pole, as well as the inter-pole angle of the magnetic poles, for Examples 2-1 to 2-2 and Comparative Example 1. Furthermore, developing devices having the configurations of each Example and Comparative Example were incorporated into an image forming apparatus such as that shown in FIG. 1, test images were actually output, and image formation performance was evaluated. The test results, in which the presence or absence of carrier adhesion in the test images was visually observed, are also shown in Table 2. The evaluation conditions were the same as those described in Table 1. In Table 2, a ◎ indicates that no carrier adhesion occurred on the image, a ○ indicates that almost no carrier adhesion occurred on the image (i.e., that carrier adhesion occurred to an extent that did not affect quality), and an × indicates that carrier adhesion occurred on the image. [Table 3]

[0088] From Table 3, it was confirmed that in Examples 2-1 and 2-2, by making the shape of the magnetic flux density Br distribution asymmetric so that the absolute value |ΔBr| of the amount of change in Br per angle of 1 degree was larger on the downstream side of the holding pole S1 in the direction of rotation of the supply roller 51 than on the upstream side, carrier adhesion was reduced more than in Comparative Example 1. Furthermore, in Example 2-2, by making the magnitude of the absolute value |Br| of the magnetic flux density such that main pole N1 > holding pole S1 > regulating pole N2 and holding pole S1 > peeling pole S3, the magnetic attractive force Fr on the upstream side of the rotation direction of the supply roller 51 from the opposing portion P1 was larger than in Example 2-1, and carrier adhesion was further reduced.

[0089] The magnetic flux density and arrangement angle of the magnet roller 51a on the supply roller 51 side, including the main pole N1, the retaining pole S1, and the regulating pole N2, and the magnetic flux density of the magnet roller 60b on the developing roller 50 side can be set appropriately according to the specifications of the developing device.

[0090] <Third embodiment> The third embodiment will be described using Fig. 7 with reference to Fig. 3. In this embodiment, the magnitude of the absolute value of the magnetic flux density |Br| is set to be the following: holding pole S1 > regulating pole N2 > pumping pole S2. Since the other configurations and functions are the same as those of the first embodiment described above, the same components are denoted by the same reference numerals, and their explanation and illustration will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0091] In this embodiment, the regulating blade 52 is made of only a magnetic material. Therefore, developer deterioration is a concern, but by using the magnet roller 51a of this embodiment in combination, it is possible to suppress developer deterioration. However, as in the first embodiment, the regulating blade 52 may be made of either a magnetic material or a non-magnetic material.

[0092] Example 3 of the pumping pole S2, regulating pole N2, and holding pole S1 of the magnet roller 51a of the supply roller 51 of this embodiment will be described with reference to FIG. 7, while comparing them with Comparative Examples 2 and 3. FIG. 7 is a diagram schematically illustrating the distribution of magnetic flux density Br on the supply roller 51 by the magnet roller 51a. More precisely, magnetic flux density Br refers to the normal component of magnetic flux density B on the surface of the supply roller 51. Hereinafter, "normal magnetic flux density Br" may be referred to simply as "magnetic flux density" according to convention. When simply referring to "magnetic flux density," it refers to "normal magnetic flux density Br." The (normal) magnetic flux density Br of each magnet roller of the example and comparative example was measured using a magnetic field measuring device (FWBELL MS-9902) with the distance between the probe of the magnetic field measuring device and the surface of the supply roller 51 set to approximately 100 μm. FIG. 7 also shows an outline of the magnetic attraction force Fr that attracts the developer (carrier) toward the center of the supply roller 51.

[0093] Here, we will explain the carrier adhesion phenomenon from the supply roller 51 to the developing roller 50 and the contribution of each magnet roller to developer deterioration in the developing device 4. As mentioned above, the developing roller 50 has a receiving pole S4 facing the main pole N1 of the supply roller 51. These two magnetic poles form a magnetic chain with strong binding force at the opposing portion P1 of the developing roller 50 and supply roller 51, which makes it possible to collect toner remaining on the developing roller 50 and suppress the occurrence of ghosting. The ghosting phenomenon is a phenomenon in which part of the developed image from the previous stage appears as an afterimage (ghost) during the next development, a so-called hysteresis phenomenon.

[0094] On the other hand, because the magnetic binding force at the opposing portion P1 is strong, there is a risk that carrier particles will fly from the developer transported upstream in the rotation direction of the supply roller 51, migrate to the developing roller 50, and be transported to the development area P2. If the carrier particles are transported to the development area P2, they will adhere to the photosensitive drum 1, easily causing image defects such as spots on part of the image. Therefore, by providing a retaining pole S1 with the same polarity as the receiving pole S4 of the developing roller 50 and a high magnetic flux density upstream of the main pole N1 in the rotation direction of the supply roller 51, a strong magnetic attraction force Fr is maintained from the opposing portion P1 upstream, thereby suppressing carrier migration to the developing roller 50. In this case, if the magnetic flux density of the retaining pole S1 is smaller than that of the main pole N1 and larger than that of the receiving pole S4, carrier adhesion and the occurrence of ghosting can be effectively suppressed.

[0095] In recent years, image forming devices have become faster, and the rotation speeds of the supply roller 51 and the developing roller 50 have also increased. This makes it easier for carrier in the developer to fly from the supply roller 51. For this reason, the magnetic flux density of the retaining pole S1 and the main pole N1 is increased. When the magnetic flux density of the retaining pole S1 increases, the magnetic attraction force Fr also increases upstream of the rotation direction of the supply roller 51. As described above, if the magnetic attraction force Fr is large in the opposing region between the regulating blade 52 and the supply roller 51, the developer confined by the supply roller 51 is more likely to deteriorate due to friction with the regulating blade 52.

[0096] Here, developer deterioration refers to deterioration of the developer caused by driving the developing device 4 while rotating the supply roller 51, the first transport screw 44, and the second transport screw 45. That is, as the supply roller 51, the first transport screw 44, and the second transport screw 45 rotate, the toner is subjected to frictional force and contact force from the carrier, the supply roller 51, and the screws. Due to the frictional force and contact force, external additives that adhere to the toner surface are peeled off from the toner itself or are embedded in the toner resin. Toner deterioration causes changes such as an increase in the adhesive force between toner particles, a change in bulk density, and a decrease in fluidity as a developer.

[0097] In this embodiment, the following configuration makes it possible to suppress carrier adhesion by strengthening the magnetic attraction force Fr from the opposing portion P1 between the developing roller 50 and the supply roller 51 to its upstream portion, and to suppress developer deterioration in the opposing area between the regulating blade 52 and the supply roller 51.

[0098] Specifically, in this embodiment, the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is set to be larger for the regulating pole N2 than for the drawing-up pole S2, and larger for the holding pole S1 than for the regulating pole N2. That is, the magnitude of the absolute value |Br| of the magnetic flux density is set to be holding pole S1 > regulating pole N2 > drawing pole S2. Table 4 shows the results of measuring the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction for each magnetic pole of Example 3, which satisfies this embodiment and has such a magnetic flux density relationship, and Comparative Examples 2 and 3, which do not satisfy this embodiment. [Table 4]

[0099] The absolute value |Br| of the magnetic flux density of the receiving pole S4 of the magnetic roller 50a of the developing roller 50 was set to 40 mT in all of Example 3 and Comparative Examples 2 and 3. The relationship in magnitude of the absolute value |Br| of the magnetic flux density of the magnetic roller 51a of the supply roller 51 was such that in Example 3, the relationship was such that the holding pole S1 > the regulating pole N2 > the drawing-up pole S2, in Comparative Example 2, the relationship was such that ...

[0100] 7 shows the magnetic flux density Br (solid line) of Example 3, the magnetic flux density Br (dashed line) of Comparative Example 2, and the magnetic flux density Br (dotted line) of Comparative Example 3. The respective magnetic attractive forces Fr are also shown by thick lines. In FIG. 7, the direction from right to left on the horizontal axis, as indicated by the arrow, is the rotation direction of supply roller 51, and in the following description, when terms such as "upstream" and "downstream" are used, they refer to "upstream" and "downstream" relative to the rotation direction of supply roller 51.

[0101] In Example 3 and Comparative Examples 2 and 3, a strong magnetic attraction force is maintained in the region from the main pole N1 to the retaining pole S1, thereby reducing carrier adhesion from the supply roller 51 to the developing roller 50. Meanwhile, focusing on the regulating pole N2, Example 3 reduces the magnetic flux density of the regulating pole N2 compared to Comparative Example 2, thereby reducing the magnetic attraction force around the regulating pole N2 and suppressing developer deterioration. Furthermore, when the drawing-up pole S2 is large relative to the regulating pole N2, as in Comparative Example 3, the magnetic attraction force increases upstream of the regulating pole N2. Because the regulating blade 52 restricts the amount of developer transport upstream of the regulating pole N2, the developer accumulates and exerts a large developer pressure, easily causing developer deterioration. Therefore, to suppress developer deterioration, it is necessary to reduce the magnetic attraction force upstream of the regulating pole N2 even slightly.

[0102] From the above, by setting the magnitude of the absolute value of the magnetic flux density |Br| to be such that the holding pole S1 > the regulating pole N2 > the pumping pole S2, as in this embodiment, it is possible to reduce carrier adhesion to the developing roller 50 and suppress development deterioration at the same time.

[0103] Here, the difference in magnitude of each magnetic flux density Br is preferably 5 mT or more, and more preferably 10 mT or more. That is, the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is preferably 5 mT or more larger for the holding pole S1 than for the regulating pole N2, and more preferably 10 mT or more larger. Furthermore, the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is preferably 5 mT or more larger for the regulating pole N2 than for the drawing pole S2, and more preferably 10 mT or more larger. This is to prevent the magnitude relationship of the absolute values ​​|Br| of the magnetic flux densities from being reversed due to component tolerances of the magnet roller 51a.

[0104] In addition to the size relationship between the pumping pole S2, regulating pole N2, and holding pole S1, it is also preferable for the main pole N1 to be in the order of main pole N1 > holding pole S1 > regulating pole N2 > pumping pole S2, as in Example 3. That is, it is preferable that the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is larger for the main pole N11 than for the holding pole S1. This is because a stronger magnetic chain is formed at the opposing portion P1 of the supply roller 51 and the developing roller 50, which effectively collects toner from the developing roller 50 and suppresses the occurrence of ghosting.

[0105] <Fourth embodiment> The fourth embodiment will be described with reference to Fig. 3 and Fig. 8 to Fig. 10. In this embodiment, the distribution of magnetic flux density of the regulating pole N2 is changed from that of the third embodiment. Since the other configurations and functions are the same as those of the third embodiment, the same configurations are denoted by the same reference numerals, and the description and illustrations thereof will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0106] In the present embodiment, the magnitude of the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density is set to be as follows: holding pole S1 > regulating pole N2 > pumping pole S2, as in the third embodiment. Meanwhile, in the present embodiment, unlike the third embodiment, the distribution of the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the regulating pole N2 has a shape such that, when the position where the magnetic flux density is maximum (maximum) is defined as the first regulating pole position and the positions where the magnetic flux density is 50% of the maximum value (maximum value) are defined as the second regulating pole position and the third regulating pole position, the first regulating pole position is located downstream in the rotation direction of the supply roller 51 from the intermediate position between the second regulating pole position and the third regulating pole position.

[0107] In other words, in this embodiment, the distribution shape of the magnetic flux density Br is made asymmetric so that the absolute value |ΔBr| of the amount of change in Br per angle of 1 degree at the regulating pole N2 is larger downstream than upstream in the rotation direction of the supply roller 51. Specifically, |ΔBr| at the point where the magnetic flux density Br becomes 0 on the upstream and downstream sides of the regulating pole N2 is 2.0 mT / deg on the upstream side and 3.0 mT / deg on the downstream side.

[0108] 8 shows the magnetic flux density Br (two-dot chain line) of Example 4 that satisfies the requirements of this embodiment, the magnetic flux density Br (solid line) of Example 3 described in the third embodiment, and the magnetic flux density Br (dotted line) of Comparative Example 2. The respective magnetic attractive forces Fr are also shown by thick lines. In FIG. 8, the direction from right to left on the horizontal axis, as indicated by the arrow, is the rotation direction of supply roller 51, and in the following description, when terms such as "upstream" and "downstream" are used, they refer to "upstream" and "downstream" relative to the rotation direction of supply roller 51.

[0109] In Example 4, the absolute value |ΔBr| of the change in Br on the upstream side of the regulating pole N2 in the rotation direction of the supply roller 51 is made smaller than in Example 3, so that the absolute value of the magnetic attractive force Fr upstream of the opposing position between the supply roller 51 and the regulating blade 52 is lower than in Example 3. Therefore, Example 4 can suppress developer deterioration more effectively than Example 3.

[0110] Here, the asymmetric shape of the distribution of the magnetic flux density Br of the regulating pole N2 of this embodiment will be described with reference to FIG. 9. FIG. 9 is an enlarged view of the regulating pole N2 periphery of Br of Example 4 shown in FIG. 8. Point D is the position (first regulating pole position) where the magnitude of the magnetic flux density Br at the regulating pole N2 is maximized (maximum). Point E is an intermediate position between points F1 (second regulating pole position) and F2 (third regulating pole position) where the magnetic flux density is 50% of that at point A. In this embodiment, point D is located downstream of point E in the rotation direction of the supply roller 51, so that the distribution of the magnetic flux density Br of the regulating pole N2 is asymmetric.

[0111] The angular difference between the positions of points D and E is preferably 3° or more, and more preferably 4° or more. That is, in the regulating pole N2, the first regulating pole position (point D) where the magnetic flux density is maximized (maximum) is preferably located downstream of the intermediate position (point E) by 3° or more in the rotation direction of the supply roller 51, and more preferably by 4° or more.

[0112] Furthermore, the pole position difference between point D of the regulating pole N2 and the position where the magnetic flux density of the pumping pole S2 is maximized is preferably 6° or more, more preferably 8° or more, larger than the pole position difference between point D of the regulating pole N2 and the position where the magnetic flux density of the holding pole S1 is maximized. That is, if the position where the magnetic flux density Br of the pumping pole S2 in the normal direction to the surface of the supply roller 51 is maximized is defined as the fourth position, and the position where the magnetic flux density Br of the holding pole S1 in the normal direction to the surface of the supply roller 51 is maximized is defined as the fifth position, the angle between the first regulating pole position (point D) and the fourth position with respect to the rotation direction of the supply roller 51 is preferably 6° or more larger, more preferably 8° or more larger than the angle between the first regulating pole position (point D) and the fifth position. This is to ensure that the magnetic flux density Br of the regulating pole N2 is asymmetric even within the component tolerance range of the magnet roller 51a.

[0113] The table in FIG. 10 shows the results of an experiment conducted to confirm the effects of Examples 3 and 4. Example 5, in which the magnitude of the absolute value of the magnetic flux density |Br| is as follows: holding pole S1 > main pole N1 > regulating pole N2 > pumping pole S2, was also examined. Example 5 also satisfies the magnitude of the absolute value of the magnetic flux density |Br|: holding pole S1 > regulating pole N2 > pumping pole S2. However, the absolute value of the maximum value (maximum value) of the magnetic flux density Br in the normal direction to the surface of the supply roller 51 is larger for the main pole N1 than for the regulating pole N2, and larger for the holding pole S1 than for the main pole N1. In other words, the magnitude relationship of the absolute value of the magnetic flux density |Br| between the main pole N1 and the holding pole S1 is reversed, compared to the relationship of "main pole N1 > holding pole S1 > regulating pole N2 > pumping pole S2" in Example 3.

[0114] To confirm the effectiveness, the test images formed with each configuration were visually inspected for the presence or absence of carrier adhesion and ghost (history development). In Figure 10, ghost images (images in which the ghost phenomenon occurred) and carrier adhesion on the image were marked with an "x", and no occurrence was marked with an "o".

[0115] The developer degradation was measured by placing 300 g of developer in each developing device 4, driving the supply roller 51, developing roller 50, first transport screw 44, and second transport screw 45, and circulating the developer within the developing device 4 for 3 hours. The toner cohesion in the developer was measured. At this time, the photosensitive drum 1 was not placed opposite the developing roller 50, so no toner was consumed. The toner cohesion was measured using a powder tester (Hosokawa Micron Corporation). Three sieves were placed on top of each other in the order of 60 mesh, 100 mesh, and 200 mesh from top to bottom. A weighed 5 g sample was gently placed on the sieve and subjected to vibration at 17 V for 15 seconds. The weight of the toner remaining on each sieve was measured, and the toner cohesion was calculated using the following formula:

[0116] Here, the amount of toner on the upper mesh is T, the amount of toner on the middle mesh is C, and the amount of toner on the lower mesh is B. In this case, if X=T / 5×100, Y=C / 5×100×0.6, and Z=B / 5×100×0.2, then Cohesion degree (%)=X+Y+Z It is expressed as:

[0117] The more the developer deteriorates, the greater the toner cohesion. The toner cohesion of a new developer is 20%. Furthermore, fog images were checked using the above deteriorated developer, and if a fog image occurred, it was marked with an "X," and if it did not occur, it was marked with an "O."

[0118] The pumping performance was confirmed by changing the amount of developer put into the developing device 4 and checking the minimum amount of developer that can carry and transport developer over the entire area in the rotational axis direction of the supply roller 51. If the developer cannot be carried over the entire area in the rotational axis direction of the supply roller 51, there will be areas where toner cannot be supplied to the developing roller 50, and image voids will occur when creating a full-area image in which an electrostatic latent image is formed over the entire area of ​​the photosensitive drum 1. The amount of developer was increased while outputting a full-area image, and the amount of developer at which no image voids occurred was shown as the result of pumping performance.

[0119] 10, in Examples 3, 4, and 5, the magnitude of the absolute value of the magnetic flux density |Br| satisfies the relation of retaining pole S1 > regulating pole N2 > pumping pole S2, thereby suppressing carrier adhesion and lowering the degree of toner cohesion compared to Comparative Examples 2 and 3, thereby confirming that developer deterioration is reduced. In Example 4, by making the distribution of the magnetic flux density Br of the regulating pole N2 asymmetric, developer deterioration is further reduced compared to Example 3, but the pumping performance is slightly reduced. In Example 5, by making the retaining pole S1 > main pole N1, ghost images are generated.

[0120] <Other embodiments> The third and fourth embodiments described above can be implemented in combination with the first and second embodiments as appropriate. For example, in the third or fourth embodiment, the magnetic flux density distribution of the holding pole S1 may satisfy the requirements for the magnetic flux density distribution of the holding pole S1 in the second embodiment.

[0121] In the above-described embodiments, the present invention has been described as being applied to a developing device used in a tandem-type image forming apparatus. However, the present invention can also be applied to developing devices used in other types of image forming apparatuses. Furthermore, the image forming apparatus is not limited to being full-color, but may be monochrome or mono-color. Alternatively, by adding necessary devices, equipment, and housing structures, the present invention can be implemented for a variety of uses, such as printers, various printing machines, copiers, fax machines, and multifunction machines.

[0122] Furthermore, the configuration of the developing device is not limited to the above-mentioned configuration in which the developing chamber and the stirring chamber are arranged horizontally, but may be configured so that they are arranged in a direction inclined relative to the horizontal direction. In short, it is sufficient that the developing chamber as the first chamber and the stirring chamber as the second chamber are arranged adjacent to each other so that they at least partially overlap when viewed horizontally. [Explanation of symbols]

[0123] 1. Photosensitive drum (image carrier) 4. Developing device 40 Developer container 41. Partition wall (divider wall) 41a...Opening (communication part) 42...Development chamber (1st chamber) 43. Mixing chamber (chamber 2) 44... First conveying screw (first conveying member) 45... Second conveying screw (second conveying member) 50...Developing roller (developing rotating body) 50a···Magnet roller (first magnet) 51 Supply roller (supply rotating body) 51a···Magnet roller (second magnet) 52 Regulating blade (regulating member)

Claims

1. a developer container containing a developer containing toner and a carrier; a developing roller that carries and transports the toner to a developing position where the electrostatic latent image formed on the image carrier is developed; a supply roller disposed opposite to the developing roller, which carries and transports the developer supplied from the developer container and supplies only the toner to the developing roller, and which rotates in a direction opposite to the rotation direction of the developing roller at a position opposite to the developing roller; a first magnet having a first magnetic pole and fixedly disposed inside the developing roller in a non-rotatable manner; a second magnet disposed inside the supply roller in a non-rotatable fixed state, the second magnet having a second magnetic pole disposed at a position where the supply roller faces the developing roller and facing the first magnetic pole, the second magnetic pole having a polarity different from that of the first magnetic pole; a third magnetic pole disposed upstream of the second magnetic pole in the rotational direction of the supply roller and adjacent to the second magnetic pole, the third magnetic pole having a polarity different from that of the second magnetic pole; and a fourth magnetic pole disposed upstream of the third magnetic pole in the rotational direction of the supply roller and adjacent to the third magnetic pole, the fourth magnetic pole having a polarity different from that of the third magnetic pole; a regulating member disposed opposite the fourth magnetic pole and regulating the amount of developer carried by the supply roller, an absolute value of a maximum value of the magnetic flux density of the second magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller; an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the fourth magnetic pole in a normal direction to the outer peripheral surface of the supply roller; With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 15° or more; A developing device characterized by:

2. The absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

2. The developing device according to claim 1.

3. The absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

2. The developing device according to claim 1.

4. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

4. The developing device according to claim 1, wherein the developing device is a developing unit.

5. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

4. The developing device according to claim 1, wherein the developing device is a developing unit.

6. the second magnet further includes a fifth magnetic pole that is disposed downstream of the second magnetic pole in the rotation direction of the supply roller and adjacent to the second magnetic pole, the fifth magnetic pole being a polarity different from that of the second magnetic pole; The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

6. The developing device according to claim 1, wherein the developing device is a developing unit.

7. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

7. The developing device according to claim 6.

8. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

7. The developing device according to claim 6.

9. the second magnet further includes a fifth magnetic pole that is disposed downstream of the second magnetic pole in the rotation direction of the supply roller and adjacent to the second magnetic pole, the fifth magnetic pole being a polarity different from that of the second magnetic pole; With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum; 6. The developing device according to claim 1, wherein the developing device is a developing unit.

10. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 10° or more; 10. The developing device according to claim 9.

11. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 15° or more; 10. The developing device according to claim 9.

12. When the positions where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 50% of the maximum value are defined as the first position and the second position, With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum is located downstream of an intermediate position between the first position and the second position by 3° or more.

12. The developing device according to claim 1, wherein the developing device is a developing unit.

13. When the positions where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 50% of the maximum value are defined as the first position and the second position, With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum is located downstream of the intermediate position between the first position and the second position by 4° or more.

12. The developing device according to claim 1, wherein the developing device is a developing unit.

14. the second magnet further includes a fifth magnetic pole that is disposed upstream of the fourth magnetic pole in the rotation direction of the supply roller and adjacent to the fourth magnetic pole, the fifth magnetic pole being a polarity different from that of the fourth magnetic pole; The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

6. The developing device according to claim 1, wherein the developing device is a developing unit.

15. The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

15. The developing device according to claim 14.

16. The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

15. The developing device according to claim 14.

17. the second magnet further includes a fifth magnetic pole that is disposed upstream of the fourth magnetic pole in the rotation direction of the supply roller and adjacent to the fourth magnetic pole, the fifth magnetic pole being a polarity different from that of the fourth magnetic pole; With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum; 6. The developing device according to claim 1, wherein the developing device is a developing unit.

18. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 6° or more; 18. The developing device according to claim 17.

19. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 8° or more; 18. The developing device according to claim 17.

20. A developing container containing a developer containing toner and a carrier; a developing roller that carries and transports the toner to a developing position where the electrostatic latent image formed on the image carrier is developed; a supply roller disposed opposite to the developing roller, which carries and transports the developer supplied from the developer container and supplies only the toner to the developing roller, and which rotates in a direction opposite to the rotation direction of the developing roller at a position opposite to the developing roller; a first magnet having a first magnetic pole and fixedly disposed inside the developing roller in a non-rotatable manner; a second magnet disposed inside the supply roller in a non-rotatable fixed state, the second magnet being disposed at a position where the supply roller faces the developing roller, facing the first magnetic pole and having a polarity different from that of the first magnetic pole; a third magnetic pole being disposed upstream of the second magnetic pole in the rotational direction of the supply roller and adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; a fourth magnetic pole being disposed upstream of the third magnetic pole in the rotational direction of the supply roller and adjacent to the third magnetic pole and having a polarity different from that of the third magnetic pole; and a fifth magnetic pole being disposed downstream of the second magnetic pole in the rotational direction of the supply roller and adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; a regulating member disposed opposite the fourth magnetic pole and regulating the amount of developer carried by the supply roller, an absolute value of a maximum value of the magnetic flux density of the second magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller; an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the fourth magnetic pole in a normal direction to the outer peripheral surface of the supply roller; With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle is 10° or more smaller than the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum, The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller. A developing device characterized by:

21. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 10 mT or more greater than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller.

21. The developing device according to claim 20.

22. a developer container containing a developer containing toner and a carrier; a developing roller that carries and transports the toner to a developing position where the electrostatic latent image formed on the image carrier is developed; a supply roller disposed opposite to the developing roller, which carries and transports the developer supplied from the developer container and supplies only the toner to the developing roller, and which rotates in a direction opposite to the rotation direction of the developing roller at a position opposite to the developing roller; a first magnet having a first magnetic pole and fixedly disposed inside the developing roller in a non-rotatable manner; a second magnet disposed inside the supply roller in a non-rotatable fixed state, the second magnet being disposed at a position where the supply roller faces the developing roller, facing the first magnetic pole and having a polarity different from that of the first magnetic pole; a third magnetic pole being disposed upstream of the second magnetic pole in the rotational direction of the supply roller and adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; a fourth magnetic pole being disposed upstream of the third magnetic pole in the rotational direction of the supply roller and adjacent to the third magnetic pole and having a polarity different from that of the third magnetic pole; and a fifth magnetic pole being disposed downstream of the second magnetic pole in the rotational direction of the supply roller and adjacent to the second magnetic pole and having a polarity different from that of the second magnetic pole; a regulating member disposed opposite the fourth magnetic pole and regulating the amount of developer carried by the supply roller, an absolute value of a maximum value of the magnetic flux density of the second magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller; an absolute value of a maximum value of the magnetic flux density of the third magnetic pole in a normal direction to the outer peripheral surface of the supply roller is greater than an absolute value of a maximum value of the magnetic flux density of the fourth magnetic pole in a normal direction to the outer peripheral surface of the supply roller; With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum; A developing device characterized by:

23. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 15° or more; 23. The developing device according to claim 22.

24. The absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

24. The developing device according to claim 22 or 23.

25. The absolute value of the maximum value of the magnetic flux density of the second magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

24. The developing device according to claim 22 or 23.

26. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

26. The developing device according to claim 22, wherein the developing device is a developing unit.

27. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

26. The developing device according to claim 22, wherein the developing device is a developing unit.

28. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

28. The developing device according to claim 22, wherein the developing device is a developing unit.

29. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

29. The developing device according to claim 28.

30. The absolute value of the maximum value of the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the fifth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

29. The developing device according to claim 28.

31. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 10° or more; 31. The developing device according to claim 22, wherein the developing device is a developing unit.

32. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the second magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 15° or more; 31. The developing device according to claim 22, wherein the developing device is a developing unit.

33. When the positions where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 50% of the maximum value are defined as the first position and the second position, With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum is located downstream of an intermediate position between the first position and the second position by 3° or more.

33. The developing device according to claim 22, wherein the developing device is a developing unit.

34. When the positions where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is 50% of the maximum value are defined as the first position and the second position, With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the third magnetic pole in the normal direction to the outer circumferential surface of the supply roller is maximum is located downstream of the intermediate position between the first position and the second position by 4° or more.

33. The developing device according to claim 22, wherein the developing device is a developing unit.

35. The second magnet further has a sixth magnetic pole that is arranged upstream of the fourth magnetic pole in the rotation direction of the supply roller and adjacent to the fourth magnetic pole, and is of a polarity opposite to that of the fourth magnetic pole; The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum value of the magnetic flux density of the sixth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

35. The developing device according to claim 22, wherein the developing device is a developing unit.

36. The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 5 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the sixth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

36. The developing device according to claim 35.

37. The absolute value of the maximum value of the magnetic flux density of the fourth magnetic pole in the normal direction to the outer circumferential surface of the supply roller is 10 mT or more larger than the absolute value of the maximum value of the magnetic flux density of the sixth magnetic pole in the normal direction to the outer circumferential surface of the supply roller.

36. The developing device according to claim 35.

38. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the sixth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum; 38. The developing device according to claim 35, wherein the developing device is a developing unit.

39. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the sixth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 6° or more; 39. The developing device of claim 38.

40. With respect to the rotation direction of the supply roller, The angle between the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the sixth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum is the angle between the position where the magnetic flux density of the third magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the normal direction to the outer peripheral surface of the supply roller is maximum by 8° or more; 39. The developing device of claim 38.

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