Developing device

Abstract

The present invention provides a configuration that can prevent developer from clogging the space between the peeling roller 32 and the guide member 45. [Solution] The third magnet 38 of the peeling roller 32 has a receiving pole for receiving developer from the second developing roller 31, a transport pole positioned downstream of the receiving pole, and a peeling pole adjacent to the transport pole and opposite in polarity to the transport pole. Let Br be the normal component of the magnetic flux density at any point on the third sleeve 35 of the peeling roller 32, Bθ be the tangential component, |B| be the absolute value of the combined component of Br and Bθ, d be the distance between the inclined surface 45a of the guide member 45 and any point on the third sleeve 35, and the nearest-nearest position P be the position of the guide member 45 closest to the peeling roller 32. In this case, the position of the maximum value of the index |B| / d is downstream in the rotational direction of the third sleeve 35 from the nearest-nearest position P2.

Description

Technical Field

[0001] The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer.

Background Art

[0002] As a developing device using a two-component developer composed of toner and a magnetic carrier, a configuration is generally adopted in which a magnet composed of a plurality of magnetic poles is provided inside a developing roller, the developer is carried on the developing roller, and an electrostatic latent image formed on an image carrier is developed.

[0003] In addition, as a developing device, a configuration has been proposed in which a developer peeled off from a developing roller by a peeling roller disposed opposite to the side of the developing roller is recovered and delivered to a developer circulation unit that circulates the developer (Patent Document 1). In the developing device described in Patent Document 1, a guide unit is provided below the peeling roller in the vertical direction to guide the developer peeled off from the peeling roller toward a conveying screw for conveying the developer to the developer circulation unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, the peeling roller comprises a rotating peeling sleeve and a peeling magnet positioned inside the peeling sleeve. The developer is carried on the peeling sleeve by the magnetic force of the peeling magnet and, as the peeling sleeve rotates, is transported downstream of the peeling sleeve through the gap between the peeling sleeve and the guide member. Then, at a position close to the transport screw, it is peeled off the peeling sleeve by the magnetic force of the peeling magnet and falls toward the guide by its own weight. The developer that has fallen toward the guide is then guided toward the transport screw by its own weight.

[0006] However, if the developer cannot be sufficiently loaded onto the peeling roller near the area where the peeling sleeve and guide section are in close proximity, and some of the developer falls onto the guide section, there is a risk that the developer will accumulate and clog the space between the peeling sleeve and the guide section.

[0007] The present invention aims to provide a configuration that can suppress the clogging of developer between the peeling roller and the guide section. [Means for solving the problem]

[0008] One aspect of the present invention includes a developing roller having a rotating developing sleeve and a developing magnet non-rotatingly positioned inside the developing sleeve to attract developer to the surface of the developing sleeve by magnetic force, for developing an electrostatic latent image formed on a rotating image carrier with the developer; a peeling sleeve having a portion facing the developing sleeve and rotating in the same direction as the surface of the developing sleeve, and a peeling magnet non-rotatingly positioned inside the peeling sleeve to attract developer to the surface of the peeling sleeve by magnetic force, for peeling off the developer from the developing roller after the electrostatic latent image on the image carrier has been developed by the developing roller; and a guide positioned vertically below the peeling roller to guide the developer peeled off the peeling roller. The peeling magnet comprises a guide portion having a guide surface and a transport member for transporting the developer guided by the guide portion, the peeling magnet having a receiving electrode for receiving the developer from the developing roller, a transport electrode having the opposite polarity to the receiving electrode and positioned downstream of the receiving electrode with respect to the rotational direction of the peeling sleeve, and a peeling electrode for peeling the developer from the peeling sleeve, having the opposite polarity to the transport electrode and positioned adjacent to the transport electrode downstream with respect to the rotational direction of the peeling sleeve, the guide portion being positioned opposite to the peeling electrode via the peeling sleeve, the normal component of the magnetic flux density at any point on the peeling sleeve being Br and the tangential component being Bθ, and the absolute value of the combined component of Br and Bθ derived by the following equation (1) being |B|,

number

[0009] According to the present invention, it is possible to suppress the clogging of developer between the peeling roller and the guide section. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the embodiment. [Figure 3] A diagram showing the magnetic pole arrangement of the first developing roller according to the embodiment. [Figure 4] A diagram showing the magnetic pole arrangement of the second developing roller according to the embodiment. [Figure 5] A diagram showing the magnetic pole arrangement of a peeling roller according to an embodiment. [Figure 6] A diagram showing the arrangement of the second developing roller, peeling roller, and guide member according to the embodiment. [Figure 7] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Comparative Example 1, and (b) A graph showing |B| / d according to Comparative Example 1. [Figure 8] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Example 1, and (b) A graph showing |B| / d according to Comparative Example 1. [Figure 9] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Example 2, and (b) A graph showing |B| / d according to Comparative Example 1. [Figure 10] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Example 3, and (b) A graph showing |B| / d according to Comparative Example 1. [Modes for carrying out the invention]

[0011] Embodiments will be described using Figures 1 to 10(b). First, the schematic configuration of the image forming apparatus of this embodiment will be described using Figure 1.

[0012] [Image forming apparatus] The image forming apparatus 100 is a full-color image forming apparatus, and in the case of this embodiment, for example, it is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in FIG. 1, the image forming apparatus 100 is provided with image forming units PY, PM, PC, and PK for performing image forming processes of yellow, magenta, cyan, and black toner images in parallel.

[0013] Each of the image forming units PY, PM, PC, and PK for each color has a primary charger 21Y, 21M, 21C, 21K, a developing device 1Y, 1M, 1C, 1K, an optical writing unit (exposure device) 22Y, 22M, 22C, 22K, a photosensitive drum 28Y, 28M, 28C, 28K, and a cleaning device 26Y, 26M, 26C, 26K. Further, the image forming apparatus 100 has a transfer device 2 and a fixing device 3. Since the configurations of the image forming units PY, PM, PC, and PK for each color are the same, hereinafter, the image forming unit PY will be described as a representative.

[0014] The photosensitive drum 28Y as an image carrier is a photoreceptor having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. In this embodiment, the linear speed of the surface of the photosensitive drum 28Y is set to 650 mm / s. The primary charger 21Y is composed of a corona discharge electrode disposed around the photosensitive drum 28Y, and the surface of the photosensitive drum 28Y is charged by the generated ions.

[0015] The optical writing unit 22Y incorporates a scanning optical device, and by exposing the charged photosensitive drum 28Y based on image data, the potential of the exposed portion is reduced, and a charge pattern (electrostatic latent image) corresponding to the image data is formed. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is formed by mixing a carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0016] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, 23K and multiple rollers, and is supported so as to be able to move. The primary transfer rollers 23Y, 23M, 23C, 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black), respectively, from top to bottom in Figure 1. The secondary transfer roller 25 is positioned outside the intermediate transfer belt 24 and is configured so that the recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0017] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are sequentially transferred onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, forming a color toner image with superimposed layers of yellow, magenta, cyan, and black. The formed toner image is then transferred to the recording material being transported from a cassette containing the recording material by the secondary transfer roller 25. The recording material on which the toner image has been transferred is then subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, fixing the color image to the recording material.

[0018] The developer storage units 27Y, 27M, 27C, and 27K are provided in accordance with the developing units 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developer corresponding to the respective colors: yellow, magenta, cyan, and black, from top to bottom. The developer storage units 27Y, 27M, 27C, and 27K are configured to transport (replenish) the developer to the developing unit 1Y, 1M, 1C, and 1K corresponding to the color of the developer stored in them.

[0019] For example, the toner weight ratio of the developer stored in the bottle is 80-95%, while the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is 5-10%. Therefore, when toner is consumed by developing in developing units 1Y, 1M, 1C, and 1K, developer containing an amount of toner corresponding to the consumption is replenished, and the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is maintained at a constant level.

[0020] [Developing equipment] Next, developing units 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 5. Since the configurations of developing units 1Y, 1M, 1C, and 1K are the same, developing unit 1Y will be described as a representative unit below. Figure 2 is a conceptual diagram illustrating developing unit 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams illustrating the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged within developing unit 1Y.

[0021] As shown in Figure 2, the developing apparatus 1Y includes a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these components are housed in a developing container 60.

[0022] The first developing roller 30 is a rotating developer carrier, positioned adjacent to the photosensitive drum 28Y, such that its axis of rotation is approximately parallel to the axis of rotation of the photosensitive drum 28Y. The first developing roller 30 has a first sleeve 33 as a rotating first developing sleeve, and a first magnet (fixed magnet) 36 as a first developing magnet, which is non-rotatingly positioned inside the first sleeve 33 and attracts the developer to the surface of the first sleeve 33 by magnetic force. The first developing roller 30 then attracts (carries) the developer drawn up from the developer supply screw 42 based on magnetic force and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image carrier) with the developer.

[0023] The first sleeve 33 (and the second sleeve 34, described later) of the developing device 1Y is subjected to, for example, a DC developing bias with the same polarity as the charging polarity of the primary charger 21Y, or a developing bias in which an AC voltage is superimposed with a DC voltage of the same polarity as the charging polarity of the primary charger 21Y. As a result, inverse development is performed in which toner charged with the same polarity as the charging polarity of the primary charger 21Y is deposited onto the electrostatic latent image formed by the optical writing unit 22Y. In this embodiment, the charging polarity of the primary charger 21Y and the DC voltage of the developing bias are set to negative, and inverse development is performed in which negatively charged toner is deposited onto the electrostatic latent image.

[0024] The first sleeve 33 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r1 = 12.5 mm) and is rotationally driven around the rotation axis 39. The rotation direction of the first sleeve 33 is clockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions opposite each other. In this embodiment, the linear velocity of the surface of the first sleeve 33 of the first developing roller 30 is set to 1.0 times (= 650 mm / s) the linear velocity of the surface of the photosensitive drum 28Y. Keeping the ratio of the linear velocity of the surface of the first sleeve 33 to the linear velocity of the surface of the photosensitive drum 28Y to approximately 1.0 times or more and 1.2 times or less is advantageous from the viewpoint of toner degradation. On the other hand, there are concerns about the development quality due to the reduced amount of toner supplied to the photosensitive drum 28Y. However, in this embodiment, two developing rollers 30 and 31 are provided, making it possible to maintain the amount of toner supplied to the photosensitive drum 28Y even when the linear velocity ratio is reduced.

[0025] The first magnet 36 is positioned inside the first sleeve 33 and has multiple magnetic poles 101 to 107, as shown in Figure 3. The solid lines of the magnetic poles 101 to 107 in Figure 3 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the first magnet 36, respectively. A space is provided between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36 to allow rotation of the first sleeve 33.

[0026] The developer adsorbed on the first sleeve 33 is transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported toward the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest proximity between the first developing roller 30 and the second developing roller 31, the developer is detached from the first sleeve 33 by the magnetic field generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31, and the developer is transferred toward the second sleeve 34.

[0027] As described below, the second developing roller 31 of the developing apparatus 1Y in this embodiment is positioned vertically above the first developing roller 30. Therefore, the transfer of developer from the first sleeve 33 to the second sleeve 34 must also be performed vertically from downward to upward, against gravity. The first sleeve 33 and the second sleeve 34 are positioned with a 3 mm gap at their nearest contact point.

[0028] The second developing roller 31, acting as a developing roller, is a rotating developer carrier positioned downstream of the first developing roller 30 with respect to the rotation direction of the photosensitive drum 28Y, and with its rotation center O2 positioned above the rotation center O1 of the first developing roller 30 in the vertical direction. Developer is transferred from the first developing roller 30 by magnetic force (Figure 2). In this embodiment, the entire second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30. Similar to the first developing roller 30, the second developing roller 31 is positioned adjacent to the photosensitive drum 28Y, with its rotation axis approximately parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are approximately parallel to each other.

[0029] Such a second developing roller 31 has a second sleeve (second developing sleeve) 34 as a rotating developing sleeve, and a second magnet (second developing magnet, fixed magnet) 37 as a developing magnet that is non-rotatingly positioned inside the second sleeve 34 and attracts the developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) based on magnetic force, attracts (carries) it, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.

[0030] The second sleeve 34 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r2 = 12.5 mm) and is rotationally driven around the rotation axis 40. The rotation direction of the second sleeve 34 is clockwise, as shown by the arrow in Figure 2, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when they are facing each other. Also, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they are facing each other. In this embodiment, the linear velocity on the surface of the second sleeve 34 of the second developing roller 31 is set to be 1.2 times (= 780 mm / s) the linear velocity on the surface of the photosensitive drum 28Y.

[0031] The second magnet 37 is positioned inside the second sleeve 34 and has multiple magnetic poles 201 to 207, as shown in Figure 4. The solid lines on the magnetic poles 201 to 207 in Figure 4 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the second magnet 37, respectively. A space is provided between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37 to allow rotation of the second sleeve 34.

[0032] The developer adsorbed on the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, developing the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer remaining on the second sleeve 34 is transported toward the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near the closest proximity point between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic field generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0033] The peeling roller (recovery roller) 32, which acts as a peeling unit, is positioned on the opposite side of the photosensitive drum 28Y from the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y has been developed by the second developing roller 31. Specifically, the peeling roller 32 is a rotating developer carrier, and is positioned between the second developing roller 31 and the developer recovery screw 44 such that its rotation center R is vertically above the rotation center O2 of the second developing roller 31.

[0034] Furthermore, the peeling roller 32 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second developing roller 31. This peeling roller 32 has a third sleeve 35 as a rotating peeling sleeve and a third magnet (peeling magnet, fixed magnet) 38 which is positioned non-rotating inside the third sleeve 35 and attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to transfer the developer from the second developing roller 31 based on magnetic force.

[0035] The third sleeve 35 is a non-magnetic cylindrical member with an outer diameter of 18 mm (radius of 9 mm) and is rotationally driven around the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is the opposite direction to the rotation direction of the second sleeve 34. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at opposing positions (opposing parts).

[0036] The third magnet 38 is positioned inside the third sleeve 35 and has multiple magnetic poles 301 to 305, as shown in Figure 5. The solid lines of the magnetic poles 301 to 305 in Figure 5 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the third magnet 38, respectively. A space is provided between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38 to allow rotation of the third sleeve 35.

[0037] The developer adsorbed onto the third sleeve 35 (on the peeling sleeve) is transported downstream in the direction of rotation by the rotational movement of the third sleeve 35, and at a position close to the developer recovery screw 44, is peeled off from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32, and falls by its own weight toward the guide member 45 located vertically below. The developer that falls toward the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0038] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47, which is a recovery section for recovering the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is positioned so that its center of rotation is located below the center of rotation of the peeling roller 32 in the vertical direction, and it conveys the developer received (recovered) from the peeling roller 32 while agitating it.

[0039] The guide member 45, acting as a guide, is positioned vertically below the peeling roller 32, and the closest proximity position P2 between the guide member 45 and the peeling roller 32 is vertically above the rotation center O2 of the second developing roller 31 (the rotation center of the second sleeve 34), guiding the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. The guide member 45 is positioned opposite the peeling pole 305 of the third magnet 38 (described later) via the third sleeve 35. The tip position P1 of the guide member 45, which is the end opposite the developer recovery screw 44, is vertically above the rotation center O2 of the second developing roller 31.

[0040] Such a guide member 45 has an inclined surface 45a that serves as a guide surface for guiding the developer peeled off from the peeling roller 32. The inclined surface 45a is tilted so that the developer slides down by its own weight, in order to more reliably guide the peeled developer towards the developer recovery screw 44. That is, the inclined surface 45a is tilted horizontally such that the developer recovery screw 44 side (conveyor member side) is lower than the closest position P2 with respect to the peeling roller 32. In this embodiment, the gap between the peeling roller 32 and the guide member 45 at the closest position P2 is 1.8 mm, and the inclination angle of the inclined surface 45a of the guide member 45 is 8°.

[0041] The developer recovery screw (conveyor screw) 44, acting as a conveying member, conveys the recovered developer to the developer circulation section 46, which will be described below. That is, the developer recovery screw 44 is a screw conveying member used to convey the developer that has slid down the inclined surface 45a of the guide member 45 in one direction while agitating it. Furthermore, the developer recovery screw 44 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second sleeve 34, and the center of rotation of the developer recovery screw 44 is located vertically above the center of rotation O2 of the second developing roller 31.

[0042] The developer circulation unit 46 is a supply unit for supplying developer to the first developing roller 30, and the developer circulation unit 46 has a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation unit 46, the developer is supplied to the first developing roller 30 while being agitated in the developer supply screw 42 and the developer stirring screw 43 and conveyed in a substantially horizontal direction. Also, as described above, the developer recovered by the developer recovery unit 47 falls by its own weight and is introduced into the developer circulation unit 46.

[0043] The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while agitating it. The developer supply screw 42 and developer agitation screw 43 are located below the developer recovery screw 44 in the vertical direction. Furthermore, these developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are arranged so that their rotation axes are approximately parallel to each other. The rotation axis of each of these screws is also approximately parallel to the rotation axis of the first developing roller 30.

[0044] The developer supply screw 42 is located between the first developing roller 30 and the developer agitation screw 43, and a partition wall 48 of the developing container 60 is positioned between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with a communication opening (not shown) that connects a first transport path 61 through which the developer is transported by the developer supply screw 42 and a second transport path 62 through which the developer is transported by the developer agitation screw 43.

[0045] The developer, agitated by the developer recovery screw 44, passes through a communication opening (not shown) formed in the partition wall 63 of the developing container 60 located between the developer recovery screw 44 and the developer supply screw 42, and falls towards the developer supply screw 42 by its own weight. The guide member 45 described above is formed integrally with the partition wall 63, and the developer recovery screw 44 is positioned above the partition wall 63.

[0046] The location of the communication port through which the developer agitated by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulation section 46 is preferably positioned to avoid the area where the developer is supplied toward the first developing roller 30 (the intermediate portion with respect to the rotation axis direction of the developer supply screw 42). In this embodiment, the location of the communication port is set to include the downstream end (terminal end) in the developer transport direction of the first transport path 61 where the developer supply screw 42 is located.

[0047] The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The starting end (upstream end in the developer transport direction) and ending end (downstream end in the developer transport direction) of the first transport path 61 where the developer supply screw 42 is located, and the ending end and starting end of the second transport path 62 where the developer agitation screw 43 is located, are in communication with each other via a communication opening provided in the partition wall 48. Therefore, the developer circulates in the rotational direction of the developer supply screw 42 and the developer agitation screw 43, as indicated by the arrows in Figure 2, and in a substantially horizontal direction within the developing container 60, with a portion of it being supplied toward the first developing roller 30.

[0048] The developer supply port 51 (see Figure 2) is located above the developer agitation screw 43 in the developing container 60 and is connected to the developer storage section 27Y (see Figure 1). The developer supply port 51 is configured to supply the developer stored in the bottle loaded in the developer storage section 27Y to the second transport path 62 where the developer agitation screw 43 is located.

[0049] As described above, the toner weight ratio of the developer stored in the bottles of the developer storage unit 27Y is greater than the toner weight ratio of the developer in the developing device 1Y. Therefore, by adjusting the amount of developer supplied to the developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in the developing device 1.

[0050] The toner concentration detection sensor 49 (see Figure 2) is positioned to detect the toner concentration in the developer contained in the developer circulation unit 46. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y and is used to control the replenishment of developer from the developer storage unit 27Y. For example, if it is detected that the toner concentration has fallen below a predetermined value, developer is replenished from the developer storage unit 27Y. Since the magnetic permeability of the developer changes more than the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0051] The regulating member 50 is positioned adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer adsorbed onto the first developing roller 30 based, for example, on the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the regulating member 50.

[0052] The developer in the developing container 60 is transported in a substantially horizontal direction while being agitated in the developer circulation unit 46, and then supplied to the first developing roller 30. From the first developing roller 30, it is transferred to the upper second developing roller 31 based on magnetic force. Next, it is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31, again based on magnetic force. After that, it is peeled off the peeling roller 32 by a third magnet 38 embedded in the peeling roller 32, and then collected in the developer recovery unit 47 and introduced back into the developer circulation unit 46.

[0053] Furthermore, as described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a negatively charged non-magnetic toner and a magnetic carrier. The non-magnetic toner becomes negatively charged through triboelectric charging with the magnetic carrier, and the magnetic carrier becomes positively charged. The non-magnetic toner is made by encapsulating colorants, wax components, etc., in a resin such as polyester or styrene acrylic, and then crushing or polymerizing it into a powder, to which fine powders such as titanium dioxide and silica are added to the surface. The magnetic carrier is made by coating the surface of a core consisting of resin particles mixed with ferrite particles or magnetic powder with resin. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8%.

[0054] Furthermore, the magnetic carriers were 40 Am at an applied magnetic field of 1000 Oersted (79577 A / m). 2 / kg or more, 80Am 2It is preferable to have a magnetization amount per unit weight of 63Am or less. Reducing the magnetization amount of the magnetic carrier has the effect of suppressing scavenging by the magnetic brush, but it becomes difficult for the magnetic carrier to adhere to the non-magnetic sleeve by the magnet inside the developing roller, which may cause image defects such as magnetic carrier adhesion to the photosensitive drum. Scavenging is a phenomenon in which the developed toner is scraped off by the magnetic carrier that has already been developed. Also, if the magnetization amount of the magnetic carrier is greater than the above range, image defects may occur due to the pressure of the magnetic brush as described above. In this embodiment, the magnetization amount per unit weight is 63Am 2 A magnetic carrier of / kg was used.

[0055] The magnetization of the magnetic carrier was measured using a BHV-30 oscillating magnetic field type automatic magnetic property recorder manufactured by RIKEN Electron Systems, Inc. The magnetic property value of the magnetic carrier was determined by creating an external magnetic field of 1000 oorsteds and measuring the magnetization strength at that time. The magnetic carrier was packed tightly into a cylindrical plastic container. The magnetization moment was measured in this state, and the actual weight with the sample inside was measured to determine the magnetization strength (Am). 2 Calculate the value of (kg).

[0056] The true specific gravity of the magnetic carrier is determined using a dry-type automatic density analyzer, AccuPic 1330, manufactured by Shimadzu Corporation. In this embodiment, the true specific gravity (density) is 4.6 g / cm³. 3 A magnetic carrier of the specified type was used. Furthermore, a magnetic carrier with a weight-average diameter of 35 μm (radius b = 17.5 μm) was employed.

[0057] Generally, two-component development systems using toner and carriers have the advantage of less stress on the toner than one-component development systems using a single-component developer, because they charge both the toner and carrier to a predetermined polarity by frictional contact. On the other hand, with prolonged use, the amount of dirt (spent) adhering to the carrier surface increases, and as a result, the ability to charge the toner gradually decreases. This results in problems such as fogging and toner scattering. Increasing the amount of carrier contained in the development unit could be considered to extend the lifespan of the two-component development unit, but this is undesirable because it would lead to a larger development unit.

[0058] To resolve the above-mentioned problems related to two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method that suppresses the increase of degraded carriers by gradually supplying new developer from the developer storage unit 27Y into the developing device 1Y, and gradually discharging the developer with degraded charging performance from the discharge port (not shown) of the developing device 1Y. As a result, the degraded carriers in the developing device 1Y are gradually replaced with new carriers, making it possible to maintain the charging performance of the carriers in the developing device 1Y at a roughly constant level.

[0059] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38, which are contained within the first developing roller 30, second developing roller 31, and peeling roller 32 shown in Figures 3, 4, and 5, will be described.

[0060] As shown in Figure 3, the first magnet 36 enclosed in the first developing roller 30 has a total of seven magnetic poles 101, 102, 103, 104, 105, 106, and 107. Of these, magnetic pole 107 is a transfer pole for transferring developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotational direction of the first sleeve 33. As described above, the solid lines of magnetic poles 101 to 107 shown in Figure 3 represent the position of the peak value (maximum value) of the magnitude of the normal component Br of the magnetic flux density of the first magnet 36 with respect to the surface of the first sleeve 33 (hereinafter sometimes simply referred to as "magnetic flux density Br" or "normal component Br"). The same applies to the magnetic poles 201 to 207 of the second magnet 37 shown in Figure 4, and the magnetic poles 301 to 305 of the third magnet 38 shown in Figure 5.

[0061] The magnetic pole 107, acting as a transfer pole, is used to transfer developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in conjunction with the second magnet 37 of the second developing roller 31. Hereafter, the magnetic pole 107 may be referred to as the transfer pole 107. The magnetic pole 101 is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first sleeve 33. The magnetic poles 102, 103, 104, 105, and 106 are S poles, N poles, S poles, N poles, and S poles, and are used to transport the developer attracted by the magnetic pole 101 upward as the first sleeve 33 rotates. The magnetic pole 107 is an N pole and, as described above, transfers the developer from the first sleeve 33 to the second sleeve 34 facing the first sleeve 33 by a magnetic field generated in conjunction with the magnetic pole 201 in the second magnet 37 enclosed in the second developing roller 31.

[0062] Furthermore, in this embodiment, a low-magnetic-force portion 110 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole 101, which is positioned downstream of the transfer pole 107 with respect to the rotational direction of the first sleeve 33 and is the same pole as the transfer pole 107, and the transfer pole 107. This low-magnetic-force portion 110 facilitates the transfer of developer from the first sleeve 33 to the second sleeve 34. In this embodiment, the low-magnetic-force portion 110 has almost no magnetic force, but it may have a low magnetic force, for example, a magnetic pole with a magnetic force (normal component Br of magnetic flux density) of 5 mT or less. The same applies to the low-magnetic-force portion 210 of the second magnet 37 shown in Figure 4 and the low-magnetic-force portion 310 of the third magnet 38 shown in Figure 5.

[0063] As shown in Figure 4, the second magnet 37 enclosed in the second developing roller 31 has a total of seven magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, magnetic pole 201 is the receiving pole for the second developing roller 31 to receive developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotational direction of the second sleeve 34.

[0064] The magnetic pole 201, acting as a receiving pole, is a magnetic pole that receives and adsorbs developer from the first sleeve 33 to the second sleeve 34 through a magnetic field generated in conjunction with the magnetic pole 107 of the first magnet 36 of the first developing roller 30. Hereafter, the magnetic pole 201 may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole that transfers developer from the second sleeve 34 to the third sleeve 35 through a magnetic field generated in conjunction with the third magnet 38 of the peeling roller 32.

[0065] Furthermore, the receiving pole 201 is an S pole, which is the opposite pole to the transfer pole 107, and is used to attract the developer from the first developing roller 30 (first sleeve 33) onto the second sleeve 34, as described above. The magnetic poles 202, 203, 204, 205, and 206 are N pole, S pole, N pole, S pole, and N pole, and are used to transport the developer attracted by the magnetic pole 201 upward as the second sleeve 34 rotates. The magnetic pole 207 is an S pole, and after the developer has passed through the developing area with the photosensitive drum 28Y corresponding to the magnetic pole 203, it is used to transfer the developer from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by the magnetic field generated in conjunction with the magnetic pole 303 in the third magnet 38 enclosed in the peeling roller 32.

[0066] Furthermore, in this embodiment, a low-magnetic-force portion 210 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole 207, which is positioned upstream of the receiving pole 201 with respect to the rotational direction of the second sleeve 34 and has the same pole as the receiving pole 201, and the receiving pole 201. This low-magnetic-force portion 210 facilitates the transfer of developer from the first sleeve 33 to the second sleeve 34. In addition, the low-magnetic-force portion 210 prevents the developer from being attracted to the closest point between the first sleeve 33 and the second sleeve 34, thereby suppressing the pressure on the developer.

[0067] As shown in Figure 5, the third magnet 38 enclosed in the peeling roller 32 has multiple magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotational direction of the third sleeve 35.

[0068] Magnetic pole 303 is an N pole opposite to magnetic pole 207, and as described above, it is a magnetic pole for attracting the developer peeled off from the second sleeve 34 to the third sleeve 35, and hereafter, magnetic pole 303 may be referred to as the receiving pole 303. Magnetic poles 301, 302, and 304 are N pole, S pole, and S pole, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, magnetic pole 304 is a magnetic pole for transporting the developer attracted by magnetic pole 303 downward as the third sleeve 35 rotates, and hereafter, magnetic pole 304 may be referred to as the transport pole 304. Magnetic pole 305 is an N pole, and is a magnetic pole for peeling off the developer attracted to the third sleeve 35 from the third sleeve 35 by the repulsive magnetic field generated in conjunction with magnetic pole 301, which is of the same pole, and hereafter, magnetic pole 305 may be referred to as the peeling pole 305.

[0069] [Planning relationship between peeling roller and guide member] Next, the arrangement of the peeling roller 32 and the guide member 45 in this embodiment will be explained using Figure 6. In this embodiment, as described above, the developer in the developing apparatus 1Y moves from the first sleeve 33 of the first developing roller 30 to the second sleeve 34 of the second developing roller 31, and then moves to the third sleeve 35 of the peeling roller 32. The developer is then carried on the third sleeve 35 by the magnetic force of the third magnet 38, which is fixed in a non-rotating position inside the peeling roller 32, and is transported downstream in the rotational direction by the rotational movement of the third sleeve 35 through the gap between the peeling roller 32 and the guide member 45. The developer is then peeled off the third sleeve 35 by the repulsive magnetic field generated by the cooperation of the like poles 305 and 301 on the third magnet 38, and falls toward the guide member 45 by its own weight. The developer that has fallen toward the guide member 45 is then guided toward the developer recovery screw 44 by its own weight.

[0070] In particular, if the developer falls onto the guide member 45 near the closest proximity point P2 between the peeling roller 32 and the guide member 45, there is a risk that the developer will accumulate and clog the gap between the peeling roller 32 and the guide member 45. On the other hand, if the developer can be peeled off sufficiently downstream of the closest proximity point P2 between the peeling roller 32 and the guide member 45, developer clogging will not occur.

[0071] Therefore, in this embodiment, the developer is carried on the peeling roller 32 (on the peeling roller) at the closest position P2 between the peeling roller 32 and the guide member 45, without falling onto the guide member 45, so that the developer can be peeled off sufficiently downstream of the closest position P2 between the peeling roller 32 and the guide member 45, and can be transported downstream in the rotational direction of the peeling roller 32.

[0072] In this embodiment, the following index |B| / d is located downstream of the nearest-neighbor position P2 in the rotational direction of the third sleeve 35. That is, let Br be the normal component of the magnetic flux density at any point on the third sleeve 35, and Bθ be the tangential component, and |B| be the absolute value of the combined component of Br and Bθ derived by the following equation (1).

number

[0073] Furthermore, as shown in Figure 6, let d be the distance between any point on the third sleeve 35 and the inclined surface 45a of the guide member 45 in the direction perpendicular to the inclined surface 45a of the guide member 45. In other words, distance d is the distance perpendicular to the inclined surface 45a from any point on the outer surface of the peeling roller 32 facing the guide member 45 to the inclined surface 45a of the guide member 45 facing the peeling roller 32. When the position of the guide member 45 closest to the peeling roller 32 is defined as the nearest-nearest position P2, the position of the maximum value of |B| / d, which is an index obtained by dividing the composite component |B| by the distance d, is positioned downstream in the rotational direction of the third sleeve 35 from the nearest-nearest position P2.

[0074] The composite component |B| of the magnetic flux density on the outer surface of the peeling roller 32 described above represents the magnitude of the magnetic field exerted on the magnetic carriers contained in the developer. Furthermore, the distance d has the following relationship in the rotational direction of the third sleeve 35. That is, in the section from the end of the guide member 45 on the second developing roller 31 side (tip position P1) to the nearest-nearest position P2, the distance d gradually decreases, and in the section after reaching the nearest-nearest position P2, the distance d gradually increases.

[0075] In the above explanation, the distance d between the peeling roller 32 and the guide member 45 was taken as the distance perpendicular to the slope 45a. However, even if the distance were taken as the normal direction of the peeling roller 32 or the vertical distance from the slope 45a, the relationship with the rotation direction of the third sleeve 35 would remain the same as described above.

[0076] The index |B| / d, obtained by dividing the combined component |B| of the magnetic flux density on the outer surface of the peeling roller 32 by the distance d between the peeling roller 32 and the guide member 45, represents the magnitude of the magnetic field exerted on carriers at any position on the surface of the guide member 45 facing the peeling roller 32. The larger the magnitude of the index |B| / d, the greater the effect of attracting carriers on the surface of the guide member 45 facing the peeling roller 32 to the outer surface of the peeling roller 32 with the magnetic field.

[0077] As described above, the developer in this embodiment uses a mixture of a negatively charged, non-magnetic toner and a positively charged, magnetic carrier, and the two attract each other through electrostatic attraction and non-electrostatic adhesion. Therefore, it can be said that the larger the magnitude of the index |B| / d, the greater the effect of attracting the developer on the surface of the guide member 45 facing the peeling roller 32 to the outer surface of the peeling roller.

[0078] As described above, the index |B| / d indicates the effect of attracting the developer on the surface of the guide member 45 facing the peeling roller 32 onto the outer surface of the peeling roller 32. Therefore, in order to carry the developer on the peeling roller 32 without letting it fall onto the guide member 45 in the gap between the peeling roller 32 and the guide member 45, and to transport it downstream in the rotational direction of the peeling roller 32, the position of the maximum value of the index |B| / d is configured to be downstream in the rotational direction of the third sleeve 35 from the closest position P2 between the peeling roller 32 and the guide member 45, where developer is most likely to clog. This allows the developer to be sufficiently attracted onto the peeling roller 32 downstream in the rotational direction of the third sleeve 35, and further downstream the developer can be peeled off from the peeling roller 32. As a result, it is possible to suppress the clogging of developer between the peeling roller 32 and the guide member 45.

[0079] On the other hand, if the gap between the peeling roller 32 and the guide member 45 at their closest proximity position P2 is too wide, the developer peeled off from the peeling roller 32 may fall directly from the gap between the tip position P1 of the guide member 45 and the second developing roller 31, or accumulate on the guide member 45 and fall off. The developer on the peeling roller 32 is in a state where the proportion of toner is low because the electrostatic latent image on the photosensitive drum 28Y has been developed by the toner in the developing section of the first developing roller 30 and the second developing roller 31. Therefore, if the developer with a low proportion of toner mixes with the developer on the first developing roller 30 or the second developing roller 31, or with the developer in the developer circulation section 46, the amount of toner that moves to the photosensitive drum 28 when developing the toner image on the photosensitive drum 28 will be uneven, resulting in unevenness in density in the final output image.

[0080] Therefore, the gap between the peeling roller 32 and the guide member 45 at their closest proximity position P2 is preferably 15 mm or less, more preferably 10 mm or less, and even more preferably 5 mm or less. However, if the gap is too narrow, the developer carried on the peeling roller 32 will approach the guide member 45, and the developer will easily clog this gap, which is undesirable. Therefore, the gap between the peeling roller 32 and the guide member 45 at their closest proximity position P2 is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more.

[0081] In the gap between the peeling roller 32 and the guide member 45 described above, the narrower the gap, the greater the attractive force due to the combined component |B| of the magnetic flux density on the outer surface of the peeling roller 32 acts on the developer on the guide member 45, resulting in a higher effect. Also, as mentioned above, the inclined surface 45a of the guide member 45 is inclined with respect to the horizontal direction such that the developer recovery screw 44 side is lower than the lower position of the peeling roller 32. A shallower angle is preferable because it allows the gap between the peeling roller 32 and the guide member 45 to be narrower downstream of the third sleeve 35 in the rotational direction than the closest proximity position P2 between the peeling roller 32 and the guide member 45. Therefore, the angle of the inclined surface 45a with respect to the horizontal direction is preferably 15° or less, more preferably 10° or less, and even more preferably 8° or less.

[0082] [Magnetic flux density distribution of the peeling roller] Next, using Comparative Example 1 and Examples 1 to 3 that satisfy the requirements of this embodiment, we will specifically describe the magnetic flux density distribution of the third magnet 38 for positioning the maximum value of the index |B| / d downstream of the nearest-neighbor position P2 in the rotational direction of the third sleeve 35, as described above. Note that the comparative example has the same configuration as the example except for the items described below.

[0083] Figures 7(a) and 7(b) show the magnetic flux density distribution and |B| / d of the third magnet 38 for Comparative Example 1, and Figures 8(a) to 10(b) show the magnetic flux density distribution and |B| / d for Examples 1 to 3, respectively. Figures 7(a), 8(a), 9(a), and 10(a) also schematically show the distribution of the normal component Br of the magnetic flux density on the third sleeve 35 due to the third magnet 38 with a solid line, and the distribution of the tangential component Bθ of the magnetic flux density with a dashed line. Figures 7(b), 8(b), 9(b), and 10(b) also schematically show the index |B| / d on the third sleeve 35 due to the third magnet 38. In Figures 7(a) to 10(b), the horizontal line H (Figure 6) passing through the rotation center R of the peeling roller 32 intersects the surface of the third sleeve 35, with the point on the second developing roller 31 side (developing roller side) set as 0°, and the angles are indicated in a clockwise direction in Figure 6 (opposite to the direction of arrow U in Figure 6 (the rotation direction of the third sleeve 35)).

[0084] The normal component Br of the magnetic flux density more precisely refers to the component of magnetic flux density B normal to the third sleeve 35. The normal component Br of the magnetic flux density of each magnet 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 third sleeve 35. The tangential component Bθ of the magnetic flux density more precisely refers to the component of magnetic flux density B tangential to the third sleeve 35. The tangential component Bθ of the magnetic flux density can be calculated using the value of the normal component Br of the magnetic flux density from the following equation (2).

number

[0085] Table 1 also shows the absolute value of |Br|, the full width at half maximum, the peak angle of |Br|, and the inter-pole angle between the carrier pole 304 and the separation pole 305 of the third magnet 38. [Table 1]

[0086] Here, the full width at half maximum (FWHM) is the angle representing the width of the portion where the normal component Br of the magnetic flux density of each magnetic pole is half of its peak value. It is sometimes called the full width at half maximum to distinguish it from the half width at half maximum, but in this specification, the term "full width at half maximum" refers to the full width at half maximum. Furthermore, the peak angle of |Br| of the magnetic pole (the angle of the position where |Br| is at its maximum value (peak position)) is also expressed in a clockwise direction as shown in Figure 6, with the point on the second developing roller 31 side of the point where the horizontal line H passing through the rotation center R of the peeling roller 32 intersects the surface of the third sleeve 35 set to 0°.

[0087] Furthermore, the inter-pole angle is the angle between the peak positions of adjacent magnetic poles, and in Table 1, it is the angle between the peak position of the transport pole 304 and the peak position of the peeling pole 305. That is, the inter-pole angle is the angle between the line connecting the position on the third sleeve 35 where the absolute value |Br| of the normal component of the magnetic flux density of the transport pole 304 is maximum and the rotation center R of the third sleeve 35, and the line connecting the position on the third sleeve 35 where the absolute value |Br| of the normal component of the magnetic flux density of the peeling pole 305 is maximum and the rotation center R of the third sleeve 35. Note that the third magnet 38 of each peeling roller 32 in Comparative Example 1 and Examples 1 to 3 has the same configuration other than the distribution of magnetic flux density (for example, the number of magnetic poles and the order of their arrangement).

[0088] [Comparative Example 1] In the magnetic flux density distribution of the peeling roller 32 of Comparative Example 1 shown in Figure 7(a), as shown in Figure 7(b), the index |B| / d at the closest proximity position P2 between the peeling roller 32 and the guide member 45 has decreased to 75% of the maximum value of index |B| / d. As a result, there is a risk that the developer may not be sufficiently supported near the closest proximity position P2, causing peeling to begin and the developer to accumulate and clog.

[0089] [Example 1] On the other hand, in the magnetic flux density distribution of the peeling roller 32 in Example 1 shown in Figure 8(a), the peak position of the normal component Br of the magnetic flux density of the peeling pole 305 is located well downstream of the nearest-neighbor position P2 with respect to the rotational direction of the third sleeve 35. As a result, the transport force of the developer downstream in the rotational direction of the third sleeve 35 in the gap between the peeling roller 32 and the guide member 45 is increased.

[0090] In Example 1 shown in Figure 8(b), the maximum value of the index |B| / d is located downstream of the nearest-closest position P2 in the rotational direction of the third sleeve 35. Therefore, the developer can be carried on the peeling roller 32 without falling onto the guide member 45 and transported downstream of the nearest-closest position P2 in the rotational direction of the third sleeve 35. This prevents the developer from getting stuck between the peeling roller 32 and the guide member 45.

[0091] If the peak position of the peeling electrode 305 is moved too far downstream in the rotational direction of the third sleeve 35 compared to the nearest contact position P2, it will result in poor peeling of the developer from the peeling roller 32, causing the developer to remain supported on the peeling roller 32 and rotate together with the peeling roller 32 without being peeled off, a phenomenon known as "co-rotation." Therefore, it is preferable to set the relationship between the peak position of the peeling electrode 305 and the nearest contact position P2 as follows.

[0092] When the horizontal line H passing through the rotation center R of the peeling roller 32 intersects the surface of the third sleeve 35, with the point on the second developing roller 31 side being 0°, and the angle is expressed in the direction of rotation of the third sleeve 35 (in the direction of arrow U in Figure 6 (counterclockwise in Figure 6)), the position on the peeling roller 32 that is the nearest contact position P2 is in the range of 80° to 100°. In this case, the position on the third sleeve 35 where the absolute value of the normal component of the magnetic flux density of the peeling pole 305 is maximum (peak position) is downstream from the position on the peeling roller 32 that is the nearest contact position P2, and is preferably in the range of 180° or less, more preferably in the range of 175° or less, and even more preferably in the range of 150° or less.

[0093] Furthermore, if the inter-pole angle between the transport pole 304 and the peeling pole 305 is made too large, the developer retention force will decrease and there is a risk of the developer scattering. Therefore, the inter-pole angle is preferably 90° or less, more preferably 75° or less, and even more preferably 60° or less.

[0094] [Example 2] In the magnetic flux density distribution of the peeling roller 32 in Example 2 shown in Figure 9(a), the following requirement is added to the requirement of Example 1, which is that the peak position of the normal component Br of the magnetic flux density of the peeling pole 305 is positioned sufficiently downstream of the nearest-neighbor position P2 with respect to the rotational direction of the third sleeve 35: That is, the transport pole 304 is positioned sufficiently close to the peeling pole 305 so that the inter-pole angle between the transport pole 304 and the peeling pole 305 is not too far apart. The inter-pole angle between the transport pole 304 and the peeling pole 305 is, for example, 40° or less. In Example 2, it is set to 37°.

[0095] By reducing the inter-pole angle between the transport pole 304 and the peeling pole 305 in this way, the transport force of the developer downstream in the rotational direction of the third sleeve 35 in the gap between the peeling roller 32 and the guide member 45 is increased. In the embodiment 2 shown in Figure 9(b), the maximum value of the index |B| / d is located downstream in the rotational direction of the third sleeve 35 from the nearest point P2. Therefore, the developer can be carried on the peeling roller 32 without falling onto the guide member 45 and transported downstream in the rotational direction of the third sleeve 35 from the nearest point P2. As a result, it is possible to suppress the accumulation of developer between the peeling roller 32 and the guide member 45.

[0096] [Example 3] In the magnetic flux density distribution of the peeling roller 32 in Example 3 shown in Figure 10(a), in addition to the requirements of Example 1, the absolute value of the normal component of the magnetic flux density of the peeling pole 305, |Br1|, is also made to be sufficiently large. As a result, the effect of attracting the developer to the downstream side in the rotational direction of the third sleeve 35 is enhanced, and the transport force of the developer to the downstream side in the rotational direction of the third sleeve 35 in the gap between the peeling roller 32 and the guide member 45 is increased.

[0097] In Example 3 shown in Figure 10(b), the maximum value of the index |B| / d is located downstream of the nearest-closest position P2 in the rotational direction of the third sleeve 35. Therefore, the developer can be carried on the peeling roller 32 without falling onto the guide member 45 and transported downstream of the nearest-closest position P2 in the rotational direction of the third sleeve 35. This prevents the developer from getting stuck between the peeling roller 32 and the guide member 45.

[0098] [Other embodiments] The present invention is not limited to the configuration of the embodiments described above. For example, the image forming apparatus 100 is not limited to an MFP, but may be a copier, printer, or facsimile machine. Furthermore, the configuration of the developer supply screw 42, the developer agitation screw 43, and the developer recovery screw 44 is not particularly limited as long as they can transport the developer, and for example, spiral blades or paddle-shaped blades can be applied.

[0099] Furthermore, although the above embodiment described the case where the first developing roller 30 is positioned upstream and the second developing roller 31 is positioned downstream with respect to the rotation direction of the photosensitive drum 28Y, the same effect can be obtained even when the second developing roller 31 is positioned upstream and the first developing roller 30 is positioned downstream.

[0100] Furthermore, although the above-described embodiment described a case where two developing rollers, a first developing roller 30 and a second developing roller 31, are arranged to develop the electrostatic latent image on the photosensitive drum, the present invention can also be applied to a configuration with only one developing roller. Also, although the above-described embodiment described a case where the third magnet 38 enclosed in the peeling roller 32 has five poles, the present invention can also be applied to a configuration where, for example, two poles are added between the receiving pole 303 and the transporting pole 304, resulting in a total of seven poles. In other words, the receiving pole 303 and the transporting pole 304 do not have to be adjacent to each other. [Explanation of symbols]

[0101] 1Y, 1M, 1C, 1K... Developing equipment 28Y, 28M, 28C, 28K... Photosensitive drum (image carrier) 30...First developing roller 31...Second developing roller (developing roller) 32... Stripping roller 33...First sleeve (first developing sleeve) 34...Second sleeve (developing sleeve, second developing sleeve) 35...Third sleeve (peel-off sleeve) 36. First magnet (first developing magnet) 37. Second magnet (developing magnet, second developing magnet) 38. Third magnet (detachable magnet) 44. Developer recovery screw (conveyor component, conveyor screw) 45. Guide component (guide part) 45a...Slope (guide surface) 303... Receiving address 304... Transport pole 305... Stripping electrode

Claims

1. A developing roller having a rotating developing sleeve, a developing magnet positioned non-rotating inside the developing sleeve and attracting developer to the surface of the developing sleeve by magnetic force, and developing an electrostatic latent image formed on a rotating image carrier with developer, In the opposing portion facing the developing sleeve, there is a peeling sleeve that rotates in the same direction as the surface of the developing sleeve, and a peeling magnet that is non-rotatingly positioned inside the peeling sleeve and attracts developer to the surface of the peeling sleeve by magnetic force, and a peeling roller that peels off the developer from the developing roller after the electrostatic latent image on the image carrier has been developed by the developing roller, A guide portion is positioned vertically below the peeling roller and has a guide surface that guides the developer peeled off from the peeling roller, A transport member for transporting the developer guided by the guide portion, Equipped with, The aforementioned peeling magnet is A receiving electrode for receiving developer from the developing roller, A transport electrode of the opposite polarity to the receiving electrode, positioned downstream of the receiving electrode with respect to the rotational direction of the peeling sleeve, A peeling electrode for peeling developer from the peeling sleeve, comprising a peeling electrode of opposite polarity to the transport electrode, which is positioned adjacent to the transport electrode on the downstream side with respect to the rotational direction of the peeling sleeve, It has, The guide portion is positioned opposite the peeling electrode via the peeling sleeve, Let Br be the normal component and Bθ be the tangential component of the magnetic flux density at any point on the peeling sleeve. Let |B| be the absolute value of the combined component of Br and Bθ derived by the following equation (1). [Math 1] With respect to the direction perpendicular to the guide surface, let d be the distance between any point on the peeling sleeve and the guide surface. When the position of the guide portion closest to the peeling roller is defined as the nearest-closest position, The position of the maximum value of |B| / d, which is the index obtained by dividing |B| by d, is located downstream of the nearest contact position in the rotational direction of the peeling sleeve. A developing apparatus characterized by the following features.

2. The guide surface is inclined with respect to the horizontal direction such that the side facing the conveying member is lower than the nearest contact point. The developing apparatus according to feature 1.

3. The transport member is a transport screw whose axis of rotation is arranged to be substantially parallel to the axis of rotation of the developing sleeve. The rotation center of the transport screw is located vertically above the rotation center of the developing sleeve. The developing apparatus according to feature 1.

4. The rotation center of the peeling sleeve is located vertically above the rotation center of the developing sleeve. The developing apparatus according to feature 1.

5. The gap between the guide portion and the peeling roller at the nearest contact position is 15 mm or less. The developing apparatus according to feature 1.

6. The gap between the guide portion and the peeling roller at the nearest contact position is 10 mm or less. The developing apparatus according to feature 5.

7. The gap between the guide portion and the peeling roller at the nearest contact position is 5 mm or less. The developing apparatus according to feature 5.

8. The gap between the guide portion and the peeling roller at the nearest contact position is 0.8 mm or more. The developing apparatus according to feature 1.

9. The gap between the guide portion and the peeling roller at the nearest contact position is 1.0 mm or more. The developing apparatus according to feature 8.

10. The gap between the guide portion and the peeling roller at the nearest contact position is 1.2 mm or more. The developing apparatus according to feature 8.

11. When a horizontal line passing through the rotation center of the peeling roller intersects the surface of the peeling sleeve, with the point on the developing roller side being defined as 0°, and the angle is expressed in the direction of rotation of the peeling sleeve, The position on the peeling roller that constitutes the nearest contact position is in the range of 80° to 100°. The position on the peeling sleeve where the absolute value of the normal component of the magnetic flux density of the peeling pole is maximum is downstream of the nearest-neighbor position on the peeling roller and within a range of 180° or less. The developing apparatus according to feature 1.

12. The position on the separation sleeve where the absolute value of the normal component of the magnetic flux density of the separation pole is maximum is within the range of 175° or less. The developing apparatus according to feature 11.

13. The position on the separation sleeve where the absolute value of the normal component of the magnetic flux density of the separation pole is maximum is within the range of 150° or less. The developing apparatus according to feature 11.

14. The inter-pole angle, which is the angle between the line connecting the position on the peeling sleeve where the absolute value of the normal component of the magnetic flux density of the transport pole is maximum and the rotation center of the peeling sleeve, and the line connecting the position on the peeling sleeve where the absolute value of the normal component of the magnetic flux density of the peeling pole is maximum and the rotation center of the peeling sleeve, is 90° or less. The developing apparatus according to feature 1.

15. The aforementioned pole-to-pole angle is 75° or less. The developing apparatus according to feature 14.

16. The aforementioned pole-to-pole angle is 60° or less. The developing apparatus according to feature 14.

17. A first developing roller having a rotating first developing sleeve and a first developing magnet which is non-rotatingly positioned inside the first developing sleeve and attracts developer to the surface of the first developing sleeve by magnetic force, and which develops an electrostatic latent image formed on the rotating image carrier with developer, The system further comprises a supply unit for supplying developer to the first developing roller, The developing sleeve is a second developing sleeve, the developing magnet is a second developing magnet, and the developing roller is a second developing roller. The second developing roller is positioned downstream of the first developing roller with respect to the rotation direction of the image carrier, and above the center of rotation of the first developing roller with respect to the vertical direction, and the developer is transferred from the first developing roller by magnetic force. The developing apparatus according to feature 1.

Images