Developing device

Abstract

To provide a configuration that can achieve both a reduction in attachment of carrier to a developing roller and prevention of deterioration of developer 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, a regulation pole N2 arranged at a position adjacent to the upstream of the holding pole S1, the position facing the regulation blade, and a draw-up pole S2 arranged adjacent to the upstream of the regulation pole N2 for drawing up the developer. 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 holding pole S1>regulation pole N2>draw-up pole S2.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 Art

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

[0003] In such a developing device using the hybrid development method, the developer is carried on a supply roller having a magnet disposed inside, a toner layer is formed on the developing roller from the developer conveyed by the rotation of the supply roller, and an 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, the magnet disposed inside the supply roller has a main pole disposed at a position facing the developing roller, and the magnet disposed inside the developing roller has a receiving pole of a different polarity from the main pole disposed at a position facing the supply roller. Further, on the upstream side of the main pole with respect to the rotation direction of the supply roller, a regulating member for regulating the amount of the developer carried on the supply roller is disposed. The magnet inside the supply roller has a regulating pole of the same polarity as the main pole disposed at a position facing the regulating member on the upstream side of the main pole with respect to the rotation direction of the supply roller, and a holding pole of a different polarity from the main pole is disposed between the regulating pole and the main pole. In Patent Document 1, by providing a holding pole upstream of the main pole, the carrier holding force between the main pole and the holding pole is increased to suppress the adhesion of the carrier to the developing roller.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-233223 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, image forming machines have become faster, resulting in increased rotation speeds for the supply and developing rollers. This makes it easier for carriers in the developer to fly off the supply roller. Therefore, it is desirable to increase the magnetic force of the main and holding poles to suppress carrier adhesion to the developing roller. On the other hand, increasing the magnetic force of the magnetic poles in the supply roller accelerates the deterioration of the developer. When the developer deteriorates, it can lead to a decrease in image quality and abnormal images such as fogging.

[0007] The present invention aims to provide a hybrid development system that can achieve both a reduction in carrier adhesion to the developing rotating body and suppression of developer degradation. [Means for solving the problem]

[0008] One aspect of the present invention is a developing container containing a developer including toner and a carrier; a developing roller for transporting toner to a developing position for developing an electrostatic latent image formed on an image carrier; a supply roller positioned opposite the developing roller, which carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller, wherein, at a position opposite the developing roller, the direction of rotation of the supply roller is opposite to the direction of rotation of the developing roller; a first magnet having a first magnetic pole, which is fixedly positioned in a non-rotating manner inside the developing roller; and a non-rotating fixed object, which is positioned inside the supply roller when the supply roller is facing the developing roller. A second magnetic pole is positioned opposite the image roller and opposite the first magnetic pole, and is of the opposite pole to the first magnetic pole; a third magnetic pole is positioned upstream of the second magnetic pole with respect to the rotation direction of the supply roller and adjacent to the second magnetic pole, and is of the opposite pole to the second magnetic pole; a fourth magnetic pole is positioned upstream of the third magnetic pole with respect to the rotation direction of the supply roller and adjacent to the third magnetic pole, and is of the opposite pole to the third magnetic pole; and a fifth magnetic pole is positioned upstream of the fourth magnetic pole with respect to the rotation direction of the supply roller and adjacent to the fourth magnetic pole, and is of the opposite pole to the fourth magnetic pole. Furthermore, a sixth magnetic pole is positioned upstream of the fifth magnetic pole with respect to the rotational direction of the supply roller, adjacent to the fifth magnetic pole, and is of the opposite pole to the fourth magnetic pole. The system comprises a second magnet having a second magnet, and a regulating member positioned opposite the fourth magnetic pole and regulating the amount of developer carried on the supply roller, wherein the absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller. 5mT or more Larger, the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller is greater than the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the direction normal to the outer circumferential surface of the supply roller. 5mT or more Large, With respect to the rotational direction of the supply roller, the angle between the position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the direction normal to the outer circumferential surface of the supply roller is maximum is 6° or greater than the angle between the position where the magnetic flux density of the third magnetic pole in the direction normal 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 direction normal to the outer circumferential surface of the supply roller is maximum.The developing apparatus is characterized in that, when the positions where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is 50% of the maximum value are defined as the first and second positions, the position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum with respect to the rotational direction of the supply roller is located 3° or more downstream from the position midway between the first and second positions. [Effects of the Invention]

[0009] According to the present invention, in a hybrid development system, it is possible to reduce carrier adhesion to the developing rotating body and suppress developer degradation at the same time. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A control block diagram of an image forming apparatus according to the first embodiment. [Figure 3] A cross-sectional view of a developing apparatus according to the first embodiment. [Figure 4] A graph showing the relationship between the angle of the supply roller in Example 1 and Comparative Examples 1 and 2, the magnetic flux density Br in the normal direction, and the magnetic attractive force Fr in the direction of the center of the supply roller. [Figure 5] A graph showing the relationship between the angle of the supply roller in Examples 1 and 2 and Comparative Example 1, the magnetic flux density Br in the normal direction, and the magnetic attractive force Fr in the direction of the center of the supply roller. [Figure 6] A graph showing the relationship between the angle around the regulating pole N2 of the supply roller in Example 2 and the magnetic flux density Br in the normal direction. [Figure 7] A table showing the experimental results conducted to confirm the effectiveness of the embodiment. [Modes for carrying out the invention]

[0011] <First Embodiment> The first embodiment will be described with reference to Figures 1 to 5. In this embodiment, the developing apparatus is described in the case where it is applied to a tandem-type full-color printer as an example of an image forming apparatus.

[0012] [Image forming apparatus] First, the schematic configuration of the image forming apparatus 100 of this embodiment will be described using Figure 1. The image forming apparatus 100 shown in Figure 1 is an electrophotographic full-color printer having four-color (yellow, magenta, cyan, and black) image forming units PY, PM, PC, and PK inside the main body of the apparatus. In this embodiment, an intermediate transfer tandem system is used in which the image forming units PY, PM, PC, and PK are arranged along the rotation direction of the intermediate transfer belt 6, which will be described later. The image forming apparatus 100 forms a toner image (image) on the recording material S in response to an image signal from an unillustrated document reading device connected to the main body of the apparatus or from a host device such as a personal computer that is communicatively connected to the main body of the apparatus. Examples of recording materials include paper, plastic film, and sheet materials such as cloth.

[0013] The toner image formation process will be explained. First, the image forming units PY, PM, PC, and PK will be described. However, the image forming units PY, PM, PC, and PK are almost identical in configuration except for the toner colors (yellow, magenta, cyan, and black). Therefore, the yellow image forming unit PY will be used as an example in the following explanation, and the other image forming units PM, PC, and PK will be omitted.

[0014] The image forming unit PY mainly consists 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 positioned above each image forming unit PY, PM, PC, and PK, and an exposure device 3 is positioned below it. The photosensitive drum 1, which serves as both an image carrier and a photoreceptor, has a photosensitive layer formed on the outer surface of an aluminum cylinder to have either negative or positive charge polarity, and rotates at a predetermined process speed (peripheral speed).

[0015] The charging device 2 charges the surface of the photosensitive drum 1 to a uniform negative or positive dark potential according to, for example, the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a charging roller that contacts and rotates on the surface of the photosensitive drum 1. On the surface of the photosensitive drum 1, after charging, an electrostatic latent image is formed based on image information by an exposure device (laser scanner) 3. The photosensitive drum 1 carries the formed electrostatic latent image, moves in a circular motion, and 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 the carrier from a toner cartridge (not shown).

[0016] The developed toner image is given a predetermined pressing force and a primary transfer bias by a primary transfer roller 61 disposed opposite across the photosensitive drum 1 and the intermediate transfer belt 6, and is primarily transferred onto the intermediate transfer belt 6. The surface of the photosensitive drum 1 after primary transfer is discharged by a pre-exposure unit (not shown). The cleaning device 8 cleans residues such as transfer residual toner remaining on the surface of the photosensitive drum 1 after primary transfer.

[0017] The intermediate transfer belt 6 is stretched by a stretching roller 62 and a secondary transfer inner roller 63. The intermediate transfer belt 6 is driven to move in the direction of arrow R1 in the figure by the secondary transfer inner roller 63 which is also a driving roller. The image formation processes for each color processed by the above-described image forming units PY, PM, PC, and PK are performed at a timing when they are sequentially superimposed on the toner image of the color upstream in the moving direction primarily transferred onto the intermediate transfer belt 6. As a result, finally, a full-color toner image is formed on the intermediate transfer belt 6 and is conveyed to the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip portion formed by a portion of the intermediate transfer belt 6 stretched around the secondary transfer inner roller 63 and a secondary transfer outer roller 64. Note that the transfer 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] For the formation process of the toner image sent to the secondary transfer unit T2, the conveyance process of the recording material S up to the secondary transfer unit T2 is executed at the same timing. In the conveyance process, the recording material S is fed from a sheet cassette or the like (not shown) and sent to the secondary transfer unit T2 in accordance with the image formation timing. In the secondary transfer unit T2, a secondary transfer voltage is applied to the secondary transfer inner roller 63.

[0019] Through the above image formation process and conveyance process, the toner image is secondarily transferred from the intermediate transfer belt 6 to the recording material S in the secondary transfer unit T2. Thereafter, the recording material S is conveyed to the fixing device 7 and heated and pressurized by the fixing device 7, whereby the toner image is melted and fixed on the recording material S. The recording material S on which the toner image is thus fixed is discharged to the discharge tray by the discharge roller.

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

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

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

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

[0024] The temperature and humidity sensor 81 is provided, for example, on a part of the wall of the stirring chamber 43 on the downstream side in the toner transport direction, to detect information regarding the temperature and humidity inside the developing apparatus 4 as an example of a detection means. The control unit 20 calculates the absolute moisture content inside the developing apparatus 4 based on the information regarding the temperature and humidity inside the developing apparatus 4, which is the detection result of the temperature and humidity sensor 81. That is, the temperature and humidity sensor 81 detects information regarding the absolute moisture content inside the developing container 40. In this embodiment, the control unit 20 calculates information regarding volumetric absolute humidity as information regarding absolute moisture content. In this embodiment, the case in which the control unit 20 calculates information regarding volumetric absolute humidity as information regarding absolute moisture content is described, but it is not limited to this, and information regarding gravimetric absolute humidity may be calculated as information regarding absolute moisture content.

[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 mixed coverage rate of toner to a carrier containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) is 8.0% by weight. The toner is a colored resin particle containing a binder resin, a colorant, and other additives as needed, and an external additive such as colloidal silica fine powder is applied to its surface. The toner used in this embodiment is a negatively charged or positively charged polyester resin depending on the charging characteristics of the photosensitive drum 1, and the volume average particle size is approximately 7.0 μm. The carrier used in this embodiment consists of magnetic metal particles such as iron, nickel, and cobalt whose surfaces have been oxidized, and the volume average particle size is approximately 40 μm to 50 μm.

[0026] [Developing equipment] Next, the developing device 4 will be described in detail with reference to Figure 3. The developing device 4 of this embodiment is a so-called touchdown developing device that uses a magnetic brush made of a two-component developer formed on the supply roller 51 to form a thin layer of toner only on the developing roller 50, and then uses a developing bias, which is a superposition of DC and AC applied to the developing roller 50, to propel the toner towards the electrostatic latent image formed on the photosensitive drum 1, thereby performing development.

[0027] As shown in Figure 3, the developing apparatus 4 comprises a developing container 40, a developing roller 50 as a developing rotating body, and a supply roller 51 as a supply rotating body. The developing container 40 contains a developer containing non-magnetic toner and a magnetic carrier. The developing container 40 has a developing chamber 42 as a first chamber, an agitation chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The agitation chamber 43 is positioned adjacent to the developing chamber 42 such that at least a portion of it overlaps with the developing chamber 42 when viewed from the horizontal direction. The partition wall 41 separates the developing chamber 42 and the agitation chamber 43. The partition wall 41 has openings 41a formed at both ends in the longitudinal direction (direction of the rotation axis of the developing roller 50 and the supply roller 51) as communication parts that connect the developing chamber 42 and the agitation chamber 43. The developing container 40 forms a circulation path for circulating the developer between the developing chamber 42 and the agitation chamber 43 via the openings 41a provided in the partition wall 41.

[0028] In this embodiment, a partition wall 41 is provided approximately in the 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 horizontally. The developing chamber 42 and the stirring chamber 43 are respectively equipped with a rotatable first conveying screw 44 and a second conveying screw 45 for stirring and circulating the developer.

[0029] The first conveying screw 44, as the first conveying member, is positioned at the bottom of the developing chamber 42 (inside the first chamber) along the rotation axis direction (longitudinal direction) of the supply roller 51, and is positioned substantially parallel to and opposite the supply roller 51. The first conveying screw 44 has a rotating shaft 44a and blades 44b arranged spirally around the rotating shaft 44a. The second conveying screw 45, as the second conveying member, is positioned at the bottom of the stirring chamber 43 (inside the second chamber) substantially parallel to the first conveying screw 44. The second conveying screw 45 has a rotating shaft 45a and blades 45b arranged spirally around the rotating shaft 45a.

[0030] The first transport screw 44 and the second transport screw 45 rotate in the directions of arrows R4 and R3, respectively, transporting the developer within the developing chamber 42 and the agitation 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 agitation chamber 43 through the openings 41a at both ends of the partition wall 41. The toner is agitated by the first transport screw 44 and the second transport screw 45, causing it to rub against the carrier and become negatively or positively charged by friction.

[0031] In the stirring chamber 43, a toner concentration sensor 58 (Figure 2) is positioned facing the second transport screw 45. For example, a permeability sensor that detects the permeability of the developer in the developing container 40 is used as the toner concentration sensor 58. Based on the detection result of the toner concentration sensor, the control unit 20 supplies toner from the toner cartridge to the stirring chamber 43 via the toner supply port (not shown).

[0032] As shown in Figure 3, the developing roller 50 and the supply roller 51 are positioned vertically above the developing chamber 42 and the agitation chamber 43. The developing roller 50 is positioned diagonally above the supply roller 51 and between it and the photosensitive drum 1, viewed from the direction of the rotation axis of the supply roller 51. The supply roller 51 and the developing roller 50 are positioned facing each other in the opposing section P1 with their rotation axes approximately parallel. The developing roller 50 faces the photosensitive drum 1 on the opening side of the developing container 40. The developing roller 50 and the supply roller 51 are each provided to be rotatable about their respective rotation axes. The developing roller 50 and the supply roller 51 are rotated counterclockwise (in the direction of arrows R6 and R5) in Figure 3 by a drive unit 9 (Figure 2) provided in the main body of the apparatus. (reverse direction) It rotates, and the rotation speed is made variable by the drive unit 9.

[0033] The supply roller 51 is a non-magnetic cylindrical roller (for example, a cylindrical roller with a diameter of 20 mm or more and 25 mm or less (20 mm in this embodiment)) that rotates counterclockwise in Figure 3, and is provided on the inner circumference side with a magnetic field generating means and second of A non-rotating cylindrical magnet roller 51a, which is a magnet, is rotatably mounted around it. That is, the magnet roller 51a is fixed and non-rotating inside the supply roller 51. The magnet roller 51a has five pieces, each having a pumping pole S2, a regulating pole N2, a holding pole S1, a main pole N1, and a peeling pole S3 on its surface facing the supply roller 51, arranged in order with respect to the rotation direction of the supply roller. Although this embodiment uses a magnet roller with five poles, it may have other poles, for example, a magnet roller with seven poles.

[0034] The main pole (second magnetic pole) N1 is positioned where the supply roller 51 faces the developing roller 50, and has opposite polarity to the receiving pole (first magnetic pole) S4 of the magnet roller 50a inside the developing roller 50, which will be described later. The holding pole (third magnetic pole) S1 is positioned adjacent to the upstream of the main pole N1 with respect to the rotation direction of the supply roller 51, and has opposite polarity to the main pole N1. The regulating pole (fourth magnetic pole) N2 is positioned adjacent to the upstream of the holding pole S1 with respect to the rotation direction of the supply roller 51, and is positioned where the regulating blade 52, which will be described later, faces the supply roller 51, and has the same polarity as the main pole N1. The pumping pole (fifth magnetic pole) S2 is positioned adjacent to the upstream of the regulating pole N2, has opposite polarity to the regulating pole N2, and is a magnetic pole for pumping the developer from the developing container 40 to the supply roller 51. Specifically, the pumping electrode S2 is positioned above the developing chamber 42, facing the first transport screw 44. , the sixth magnetic pole )S3 is positioned adjacent to the upstream of the pumping electrode S2 with respect to the rotational direction of the supply roller 51 and has the same polarity as the pumping electrode S2. The pumping electrode S2, regulating electrode N2, holding electrode S1, main electrode N1, and peeling electrode S3 are positioned adjacent to each other in this order with respect to the rotational direction of the supply roller 51.

[0035] The supply roller 51 carries a developer containing non-magnetic toner and a magnetic carrier, and rotates and conveys it to the portion P1 opposite the developing roller 50. That is, the supply roller 51 is positioned opposite the developing roller 50 and rotates to supply the developer from inside the developing container 40 (inside the developing container) to the developing roller 50. The supply roller 51 is, for example, cylindrical with a diameter of 20 mm and is made of a non-magnetic material such as aluminum or non-magnetic stainless steel, and in this embodiment it is made of aluminum. Furthermore, the outer surface of the supply roller 51 is blast-treated so that the surface roughness is, for example, Rz30 μm.

[0036] The regulating blade 52, acting as a regulating member, is positioned upstream of the position facing the developing roller 50 with respect to the rotational direction of the supply roller 51, and regulates the amount of developer carried on the supply roller 51. Specifically, the regulating blade 52 is a plate-shaped member and is provided in the developing container 40 such that its tip faces the outer circumferential surface of the supply roller 51 where the regulating pole N2 of the magnetic roller 51a is located. 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 particles of the developer carried on the surface of the supply roller 51 are cut by the regulating blade 52, thereby regulating the thickness of the developer layer. Specifically, the regulating blade 52 is made of a metal plate (for example, a stainless steel plate) positioned in the longitudinal direction of the supply roller 51, and the developer is transported in a regulated amount as it passes between the tip of the regulating blade 52 and the supply roller 51. The regulating blade 52 is formed in an L-shape from a magnetic material such as SUS430 with 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 can be made of either a magnetic or non-magnetic material. If a magnetic material is used, the distance between the tip of the regulating blade 52 and the supply roller 51 can be increased, which has the advantage of making it less likely for foreign matter to get stuck. On the other hand, if a magnetic material is used, the developer may be constrained by the magnetic field between the tip of the regulating blade 52 and the supply roller 51, which may make it easier for the developer to deteriorate due to friction. The regulating blade 52 may also be configured by attaching a magnetic material to a part of a non-magnetic material. In this case, some of the advantages of a magnetic material are lost, but it is possible to suppress the deterioration of the developer. In this embodiment, the regulating blade 52 is made of only a magnetic material. Therefore, there is a concern about the deterioration of the developer, but by using the magnetic roller 51a of this embodiment, which will be described later, in combination, it is possible to suppress the deterioration of the developer.

[0038] The developer contained in the developing chamber 42 is adsorbed onto the surface of the supply roller 51 by the pumping electrode S2 facing the developing chamber 42 and transported toward the regulating blade 52. The developer is raised by the regulating electrode N2 facing the regulating blade 52, and the thickness of the layer is regulated by the regulating blade 52. The developer layer is carried and transported via the holding electrode S1 to the portion P1 facing the developing roller 50, and with a magnetic pile formed by the main electrode N1 facing the developing region, toner is supplied to the surface of the developing roller 50. A supply bias consisting of a superimposed DC voltage and AC voltage is applied to the supply roller 51.

[0039] The developing roller 50 is positioned opposite the photosensitive drum 1 and rotates to transport the developer to the developing position where the electrostatic latent image formed on the photosensitive drum 1 is developed. Specifically, the developing roller 50 is a non-magnetic roller that rotates counterclockwise in Figure 3 and has one receiving electrode on its inner circumference. (First magnetic pole) The first non-rotating S4 of The magnet roller 50a, which acts as a magnet, is rotatably mounted around the developing roller 50. The developing roller 50 carries toner and rotates, enabling it to develop the electrostatic latent image on the photosensitive drum 1 in the developing region P2, which is the region facing the photosensitive drum 1. The supply roller 51 and the developing roller 50 face each other with a predetermined gap in their opposing portion P1. The receiving pole S4 of the magnet roller 50a within the developing roller 50 has opposite polarity to the opposing main pole N1.

[0040] A developing bias, consisting of a superimposed DC voltage and AC voltage, is applied to the developing roller 50. The developing bias and supply bias are applied to the developing roller 50 and the supply roller 51 from a bias power supply 82 (Figure 2), which is an example of a voltage application unit, via a bias control circuit. That is, the bias power supply 82 applies a voltage containing DC and AC components between the developing roller 50 and the supply roller 51.

[0041] Toner remaining on the developing roller 50 that is not used for developing is transported again to the opposing section P1 between the developing roller 50 and the supply roller 51, where it is rubbed by the magnetic fins on the supply roller 51 and collected by the supply roller 51. The magnetic fins are detached from the supply roller 51 in a detachment region created by the repulsion between the detachment electrode S3 and the pumping electrode S2, which are located downstream of the supply roller 51 in the direction of rotation. The detached developer falls into the developing chamber 42, is mixed and transported with the developer circulating in the developing container 40, is again attracted to the pumping electrode S2 and transported by the supply roller 51.

[0042] [Magnetic roller for supply roller] Next, Example 1 of the magnetic roller 51a of the supply roller 51 of this embodiment, specifically the pumping pole S2, regulating pole N2, and holding pole S1, will be described with reference to Figure 4, in comparison with Comparative Examples 1 and 2. Figure 4 is a schematic diagram showing the distribution of magnetic flux density Br on the supply roller 51 due to the magnetic roller 51a. Note that magnetic flux density Br refers precisely to the component of magnetic flux density B in the normal direction on the surface of the supply roller 51. Hereinafter, "magnetic flux density Br in the normal direction" may be referred to simply as "magnetic flux density" as per convention. When simply referred to as "magnetic flux density," it will refer to "magnetic flux density Br in the normal direction." The magnetic flux density Br (in the normal direction) of each magnetic roller in the example and comparative example was measured using a magnetic field measuring instrument (FWBELL "MS-9902") with a distance of approximately 100 μm between the probe, a component of the magnetic field measuring instrument, and the surface of the supply roller 51.

[0043] Figure 4 also shows a schematic of the magnetic attractive force Fr that pulls the developer (carrier) toward the center of the supply roller 51. The magnetic attractive 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 Equation 1 above, μ is the permeability of the magnetic carrier, μ0 is the permeability of vacuum, and b is the radius of the magnetic carrier. The tangential magnetic flux density Bθ on the surface of the supply roller 51 is calculated from Equation 2 below using the value of Br measured by the method described above.

number

[0045] Figure 4 also shows the magnetic attractive force Fr in the direction of the center of the supply roller 51 acting on the carrier, calculated by equations 1 and 2, simultaneously on the second axis. Hereafter, the "magnetic attractive force Fr in the direction of the center of the supply roller" may be simply referred to as "magnetic attractive force." When simply referred to as "magnetic attractive force," it will refer to the "magnetic attractive force Fr in the direction of the center of the supply roller."

[0046] Here, we will explain the carrier adhesion phenomenon from the supply roller 51 to the developing roller 50 and the contribution of each magnetic roller to the deterioration of the developer in the developing apparatus 4. As mentioned above, the developing roller 50 has a receiving pole S4 that faces the main pole N1 of the supply roller 51. These two magnetic poles form a strong magnetic field at the opposing portion P1 between the developing roller 50 and the supply roller 51, allowing the toner remaining on the developing roller 50 to be recovered and the occurrence of the ghosting phenomenon to be suppressed. The ghosting phenomenon is a phenomenon in which a part of the previously developed image appears as an afterimage (ghost) during the next development, also known as a hysteresis phenomenon.

[0047] On the other hand, because the magnetic restraining force at the opposing portion P1 is strong, there is a risk that carriers may fly off from the developer being transported upstream of the supply roller 51 in the rotational direction, transfer to the developing roller 50, and be transported to the developing area P2. If carriers are transported to the developing area P2, they may adhere to the photosensitive drum 1, making it easier for image defects such as spots to occur in part of the image. Therefore, by providing a holding pole S1 with the same pole as the receiving pole S4 of the developing roller 50 and a high magnetic flux density upstream of the supply roller 51 of the main pole N1 in the rotational direction, the magnetic attractive force Fr is kept strong from the opposing portion P1 to its upstream side, thereby suppressing the transfer of carriers to the developing roller 50. At this time, if the magnetic flux density of the holding pole S1 is smaller than the magnetic flux density of the main pole N1 and larger than the magnetic flux density of the receiving pole S4, carrier adhesion and the occurrence of ghosting can be effectively suppressed.

[0048] In recent years, image forming machines have become faster, and consequently, the rotation speeds of the supply roller 51 and the developing roller 50 have also increased. As a result, the carriers in the developer are more likely to fly off the supply roller 51. For this reason, the magnetic flux density of the holding pole S1 and the main pole N1 is increased. When the magnetic flux density of the holding pole S1 increases, the magnetic attraction force Fr also increases on the upstream side in the rotation direction of the supply roller 51. As mentioned above, if the magnetic attraction force Fr is large in the region where the regulating blade 52 and the supply roller 51 face each other, the developer constrained by the supply roller 51 is more likely to deteriorate due to friction with the regulating blade 52.

[0049] Here, developer degradation refers to the degradation of the developer that occurs as the developing device 4 is driven while rotating the supply roller 51, the first transport screw 44, and the second transport screw 45. In other words, as the supply roller 51, the first transport screw 44, and the second transport screw 45 rotate, the toner is subjected to frictional and contact forces from the carrier, the supply roller 51, and the screws. Due to these frictional and contact forces, the external additives adhering to the toner surface either peel off from the toner itself or become embedded in the toner resin. When toner degradation occurs, changes such as an increase in the adhesion force between toners, a change in bulk density, and a decrease in the fluidity of the developer occur.

[0050] In this embodiment, the following configuration makes it possible to suppress carrier adhesion by increasing the magnetic attraction force Fr from the opposing portion P1 of the developing roller 50 and the supply roller 51 upstream, and to suppress developer deterioration in the opposing region of the regulating blade 52 and the supply roller 51.

[0051] Specifically, in this embodiment, the absolute value |Br| of the maximum value of the magnetic flux density normal to the surface of the supply roller 51 (the maximum value of the magnetic flux density normal to the surface of the supply roller 51) is set such that the regulating pole N2 is larger than the pumping pole S2, and the holding pole S1 is larger than the regulating pole N2. That is, the magnitude of the absolute value |Br| of the magnetic flux density is set such that holding pole S1 > regulating pole N2 > pumping pole S2. Table 1 shows the results of measuring the absolute value |Br| of the maximum value (maximum value) of the magnetic flux density normal to each magnetic pole in Example 1, which satisfies this embodiment having such a relationship of magnetic flux density, and in Comparative Examples 1 and 2, which do not satisfy this embodiment. [Table 1]

[0052] The absolute value |Br| of the magnetic flux density of the receiving pole S4 of the magnet roller 50a of the developing roller 50 was set to 40mT in all of Example 1 and Comparative Examples 1 and 2. The relationship of the magnitude of the absolute value |Br| of the magnetic flux density of the magnet roller 51a of the supply roller 51 was such that in Example 1, holding pole S1 > restricting pole N2 > pumping pole S2, in Comparative Example 1, restricting pole N2 > holding pole S1, and in Comparative Example 2, pumping pole S2 > restricting pole N2.

[0053] Figure 4 shows the magnetic flux density Br of Example 1 (solid line), the magnetic flux density Br of Comparative Example 1 (dashed line), and the magnetic flux density Br of Comparative Example 2 (dotted line). The magnetic attractive force Fr for each is also shown simultaneously with a thick line. In Figure 4, as indicated by the arrows, the direction from right to left on the horizontal axis is the rotation direction of the supply roller 51, and in the following explanation, when we simply refer to "upstream" and "downstream," we are referring to the "upstream" and "downstream" in relation to the rotation direction of the supply roller 51.

[0054] In all of Examples 1 and Comparative Examples 1 and 2, the magnetic attraction force is maintained at a high level in the region from the main electrode N1 to the holding electrode S1, thereby reducing carrier adhesion from the supply roller 51 to the developing roller 50. On the other hand, focusing on the regulating electrode N2, Example 1 reduces the magnetic flux density of the regulating electrode N2 compared to Comparative Example 1, resulting in a lower magnetic attraction force around the regulating electrode N2 and suppressing developer degradation. Also, as in Comparative Example 2, when the pumping electrode S2 is larger than the regulating electrode N2, the magnetic attraction force upstream of the regulating electrode N2 increases. Upstream of the regulating electrode N2, the amount of developer transported is restricted by the regulating blade 52, causing the developer to stagnate and resulting in high pressure and easy developer degradation. Therefore, in order to suppress developer degradation, it is necessary to reduce the magnetic attraction force upstream of the regulating electrode N2 as much as possible.

[0055] As described above, by setting the magnitude of the absolute value of the magnetic flux density |Br| to hold pole S1 > restricting pole N2 > pumping pole S2, as in this embodiment, it is possible to achieve both a reduction in carrier adhesion to the developing roller 50 and suppression of development deterioration.

[0056] Here, it is desirable that the magnitude of the magnetic flux density Br of each pole differs by 5 mT or more, and more preferably by 10 mT or more. That is, the absolute value |Br| of the maximum value (maximum) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is preferably 5 mT or more greater for the holding pole S1 than for the regulating pole N2, and more preferably 10 mT or more greater. Furthermore, the absolute value |Br| of the maximum value (maximum) of the magnetic flux density in the normal direction on the surface of the supply roller 51 is preferably 5 mT or more greater for the regulating pole N2 than for the pumping pole S2, and more preferably 10 mT or more greater. This is to prevent the relative magnitudes of the absolute values ​​|Br| of each magnetic flux density from being reversed depending on the component tolerances of the magnet roller 51a.

[0057] Furthermore, it is preferable that, in addition to the relative sizes of the pumping pole S2, regulating pole N2, and holding pole S1, the main pole N1 also be in the same order as in Example 1, where main pole N1 > holding pole S1 > regulating pole N2 > pumping pole S2. 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 greater for the main pole N11 than for the holding pole S1. This is because a stronger magnetic field is formed in the opposing portion P1 of the supply roller 51 and the developing roller 50, thereby effectively recovering toner from the developing roller 50 and suppressing the occurrence of ghosting.

[0058] <Second Embodiment> The second embodiment will be described with reference to Figure 3 and Figures 5 to 7. This embodiment modifies the distribution of the magnetic flux density of the regulating pole N2 compared to the first embodiment. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are used for similar components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0059] In this embodiment as well, the magnitude of the absolute value |Br| of the maximum value of the magnetic flux density is the same as in the first embodiment, with holding pole S1 > restricting pole N2 > pumping pole S2. On the other hand, in this embodiment, unlike in the first embodiment, the distribution of magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the restricting pole N2 is such that the position where the magnetic flux density is maximum is maximum value The position is determined by finding the position that is 50% of the local maximum (maximum value). 1 Location and 2 When considering the position, maximum value The position is, 1 Position and 2 It has a shape that is located downstream in the rotational direction of the supply roller 51, rather than at an intermediate position between the two positions.

[0060] In other words, in this embodiment, the distribution shape of the magnetic flux density Br is made asymmetrical so that the absolute value of the change in Br per 1 degree of angle |ΔBr| at the regulating pole N2 is larger downstream than upstream in the rotational direction of the supply roller 51. Specifically, the |ΔBr| at the points where the magnetic flux density Br is 0 on the upstream and downstream sides of the regulating pole N2 is 2.0 mT / deg upstream and 3.0 mT / deg downstream, respectively.

[0061] Figure 5 shows the magnetic flux density Br (dotted line) of Example 2 satisfying this embodiment, the magnetic flux density Br (solid line) of Example 1 described in the first embodiment, and the magnetic flux density Br (dotted line) of Comparative Example 1. The magnetic attractive force Fr for each is also shown simultaneously with a thick line. In Figure 5, as indicated by the arrows, 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 we simply refer to "upstream" and "downstream," we are referring to "upstream" and "downstream" with respect to the rotation direction of the supply roller 51.

[0062] In Example 2, compared to Example 1, the absolute value of |ΔBr| of the change in Br on the upstream side of the rotational direction of the supply roller 51 of the regulating electrode N2 is reduced, thereby lowering the absolute value of the magnetic attractive force Fr upstream of the opposing position between the supply roller 51 and the regulating blade 52 compared to Example 1. Therefore, Example 2 can suppress developer degradation more effectively than Example 1.

[0063] Here, the asymmetric shape of the distribution of magnetic flux density Br at the restricting pole N2 in this embodiment will be explained using Figure 6. Figure 6 is an enlarged view of the area around the restricting pole N2 of Br in Embodiment 2 described in Figure 5. Point A is the position where the magnitude of the magnetic flux density Br at the restricting pole N2 is maximum. maximum value Point B is the point where the magnetic flux density is 50% of that of point A (point C1). 1 position), point C2 (position 2 It is an intermediate position between the positions of (position). In this embodiment, since the position of point A is located downstream of the rotation direction of the supply roller 51 relative to point B, the distribution of the magnetic flux density Br of the regulating pole N2 is asymmetrical.

[0064] The angular difference between the positions of point A and point B is preferably 3° or more, and more preferably 4° or more. That is, in the regulating pole N2, the first position (point A) where the magnetic flux density is maximum is preferably located 3° or more downstream of the intermediate position (point B) with respect to the rotational direction of the supply roller 51, and more preferably 4° or more downstream.

[0065] Furthermore, it is desirable, and more preferably, 8° or more, that the difference in pole position between point A of the regulating pole N2 and the position where the magnetic flux density of the pumping pole S2 is maximum is 6° or more greater than the difference in pole position between point A of the regulating pole N2 and the position where the magnetic flux density of the holding pole S1 is maximum. That is, when the position where the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the pumping pole S2 is maximum is designated as the fourth position, and the position where the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the holding pole S1 is maximum is designated as the fifth position, it is desirable, and more preferably, 8° or more greater, than the angle between the first position (point A) and the fourth position with respect to the rotational direction of the supply roller 51. This is to make the magnetic flux density Br of the regulating pole N2 asymmetric even within the component tolerance range of the magnet roller 51a.

[0066] The table in Figure 7 shows the results of experiments conducted to confirm the effects of Examples 1 and 2. Example 3, in which the magnitude of the absolute value of magnetic flux density |Br| is S1 > main pole N1 > restricting pole N2 > pumping pole S2, was also verified. In Example 3, the magnitude of the absolute value of magnetic flux density |Br| satisfies the relationship S1 > restricting pole N2 > pumping pole S2. However, the absolute value of the maximum value of the magnetic flux density Br in the normal direction on the surface of the supply roller 51 is greater for the main pole N1 than for the restricting pole N2, and greater for the holding pole S1 than for the main pole N1. In other words, the relationship of the absolute values ​​of magnetic flux density |Br| of the main pole N1 and the holding pole S1 is reversed compared to the relationship of "main pole N1 > holding pole S1 > restricting pole N2 > pumping pole S2" in Example 1.

[0067] The effectiveness was confirmed by visually observing the presence or absence of carrier adhesion and ghosting (history development) in the test images formed with each configuration. In Figure 7, images with ghosting (images where ghosting occurred) and images with carrier adhesion are marked with ×, while images without these phenomena are marked with ○.

[0068] The degree of developer degradation was measured by placing 300g of developer into each configuration of the 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 degree of toner coagulation 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 degree of toner coagulation was measured using a powder tester (Hosokawa Micron Corporation). Three layers of sieves were set up in the powder tester in the order of 60 mesh, 100 mesh, and 200 mesh from top to bottom. A 5g sample was then gently placed on top of the sieves, and vibration was applied at a voltage of 17V for 15 seconds. The weight of the toner remaining on each sieve was measured, and the degree of toner coagulation was calculated according to the following formula.

[0069] Here, let T be the amount of toner on the upper mesh, C be the amount of toner on the middle mesh, and B be the amount of toner on the lower mesh. 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 represented as follows.

[0070] The degree of toner aggregation increases as the developer deteriorates. The toner aggregation degree of a new developer is 20%. In addition, the above-mentioned degraded agents were used to check for fouling in the images, and cases where fouling occurred were marked with ×, and cases where it did not occur were marked with ○.

[0071] The pumping performance was confirmed by varying the amount of developer placed in the developing device 4 and determining the minimum amount of developer that could be carried and transported across the entire rotation axis direction of the supply roller 51. If the developer cannot be carried across the entire rotation axis direction of the supply roller 51, there will be areas where toner cannot be supplied to the developing roller 50, resulting in image defects when creating a full-screen image with an electrostatic latent image formed across the entire surface of the photosensitive drum 1. The amount of developer at which image defects no longer occurred when outputting a full-screen image while increasing the amount of developer is shown as the result of the pumping performance.

[0072] As shown in Figure 7, in Examples 1, 2, and 3, by satisfying the condition that the absolute value of magnetic flux density |Br| is S1 > regulating electrode N2 > pumping electrode S2, carrier adhesion was suppressed, and the toner coagulation was lower than in Comparative Examples 1 and 2, resulting in reduced developer degradation. In Example 2, by making the distribution of magnetic flux density Br of the regulating electrode N2 asymmetric, developer degradation was further reduced than in Example 1, but the pumping performance was slightly reduced. In Example 3, setting S1 > N1 resulted in the occurrence of ghost images.

[0073] <Other Embodiments> In the embodiments described above, the present invention was explained in the case where it is applied to a developing apparatus used in a tandem-type image forming apparatus. However, the present invention is also applicable to developing apparatuses used in other types of image forming apparatuses. Furthermore, the image forming apparatus is not limited to full color; it may be monochrome or monocolor. Alternatively, by adding necessary equipment, fixtures, and housing structures, it can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices.

[0074] Furthermore, regarding the configuration of the developing apparatus, as mentioned above, it is not limited to a configuration where the developing chamber and agitation chamber are arranged horizontally, but may also be arranged in a direction inclined to the horizontal. In short, it is sufficient if the developing chamber (as the first chamber) and the agitation chamber (as the second chamber) are arranged adjacent to each other so that at least a portion of them overlap when viewed from the horizontal. [Explanation of Symbols]

[0075] 1. Photosensitive drum (image carrier) 4. Developing equipment 40... Developing container 41. Partition wall 41a...Opening (communication part) 42...Development chamber (1st chamber) 43. Stirring chamber (second chamber) 44. First conveying screw (first conveying component) 45...Second conveying screw (second conveying component) 50. Developing roller (developing rotating body) 50a...Magnetic roller (first magnet) 51. Supply roller (supply rotating body) 51a...Magnetic roller (second magnet) 52. Regulatory blade (regulatory component)

Claims

1. A developing container containing a developer including toner and carrier, A developing roller that transports toner to a developing position for developing the electrostatic latent image formed on the image carrier, A supply roller positioned opposite the developing roller, which carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller, wherein, at a position opposite the developing roller, the direction of rotation of the supply roller is opposite to the direction of rotation of the developing roller, A first magnet having a first magnetic pole is fixedly positioned inside the developing roller in a non-rotating manner, A second magnet is fixedly positioned inside the supply roller in a non-rotating manner, having a second magnetic pole positioned opposite the first magnetic pole and opposite to the first magnetic pole, a third magnetic pole positioned upstream of the second magnetic pole and adjacent to the second magnetic pole with respect to the rotational direction of the supply roller and opposite to the second magnetic pole, a fourth magnetic pole positioned upstream of the third magnetic pole and adjacent to the third magnetic pole with respect to the rotational direction of the supply roller and opposite to the third magnetic pole, a fifth magnetic pole positioned upstream of the fourth magnetic pole and adjacent to the fourth magnetic pole with respect to the rotational direction of the supply roller and opposite to the fourth magnetic pole, and a sixth magnetic pole positioned upstream of the fifth magnetic pole and adjacent to the fifth magnetic pole with respect to the rotational direction of the supply roller and opposite to the fourth magnetic pole. The system comprises a regulating member positioned opposite the fourth magnetic pole and for regulating the amount of developer carried on the supply roller, The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer circumferential surface of the supply roller is 5 mT or more greater than the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller. The absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller is 5 mT or greater than the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the direction normal to the outer circumferential 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 fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the direction normal to the outer 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 direction normal to the outer surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum is 6° or more. When the positions where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer circumferential surface of the supply roller is 50% of the maximum value are defined as the first and second positions, With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum is located at least 3° downstream from the position midway between the first and second positions. A developing apparatus characterized by the following features.

2. With respect to the rotation direction of the supply roller, The position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum is located at a position at least 4° downstream from the midpoint between the first and second positions. The developing apparatus according to feature 1.

3. 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 direction normal to the outer surface of the supply roller is maximum and the position where the magnetic flux density of the fifth magnetic pole in the direction normal to the outer 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 direction normal to the outer surface of the supply roller is maximum and the position where the magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is maximum is 8° or more. The developing apparatus according to claim 1 or 2.

4. The absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the supply roller is 10 mT or more greater than the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller. A developing apparatus according to any one of claims 1 to 3.

5. The absolute value of the maximum magnetic flux density of the fourth magnetic pole in the direction normal to the outer surface of the supply roller is 10 mT or more greater than the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the direction normal to the outer surface of the supply roller. A developing apparatus according to any one of claims 1 to 4.

6. The absolute value of the maximum magnetic flux density of the second magnetic pole in the direction normal to the outer surface of the supply roller is greater than the absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the supply roller. A developing apparatus according to any one of claims 1 to 5, characterized by the features described herein.

7. The absolute value of the maximum magnetic flux density of the second magnetic pole in the direction normal to the outer surface of the supply roller is smaller than the absolute value of the maximum magnetic flux density of the third magnetic pole in the direction normal to the outer surface of the supply roller. A developing apparatus according to any one of claims 1 to 5, characterized by the features described herein.

Images