Developing device

Abstract

To provide a configuration that can prevent the occurrence of an image defect.SOLUTION: A second developing roller 31 has a rotating second developing sleeve 34, and a second developing magnet 37 arranged in a non-rotational manner inside the second developing sleeve 34, and develops an electrostatic latent image formed on a rotating photoconductor drum 28Y with developer. A peeling roller 32 has a rotating peeling sleeve 35, and a peeling magnet 38 arranged in a non-rotational manner inside the peeling sleeve 35, and peels, from the second developing roller 31, the developer after the second developing roller 31 develops the electrostatic latent image on the photoconductor drum 28Y. The second developing sleeve 34 and the peeling sleeve 35 have a surface with a rugged shape.SELECTED DRAWING: Figure 2

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 technology]

[0002] A developing device having a configuration including a peeling roller that peels off and collects developer from a developing roller that develops an electrostatic latent image formed on an image carrier with the developer (Patent Document 1). The developing roller includes a rotating developing sleeve and a non-rotating developing magnet arranged inside the developing sleeve, and the developer is carried on the surface of the developing sleeve by the magnetic force of the developing magnet. Similarly, the peeling roller also includes a rotating peeling sleeve and a non-rotating peeling magnet arranged inside the peeling sleeve, and the developer is carried on the surface of the peeling sleeve by the magnetic force of the peeling magnet. Then, the developer (used developer) that has been carried and transported by the developing sleeve and developed the electrostatic latent image on the image carrier is carried on the surface of the peeling sleeve, and the developer is collected from the developing roller by the peeling roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-124338 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, unless the developer transport force of the peeling sleeve relative to the developing sleeve is at a certain level or more, there is a risk that the peeling roller will not be able to sufficiently collect the used developer transported by the developing sleeve. The used developer that cannot be collected by the peeling roller will be carried along with the developing sleeve or will drop downward and be supplied to the developing sleeve again. As a result, the distribution of the TD ratio (the ratio of the toner weight to the total weight of the carrier and toner) of the developer carried on the developing sleeve will be affected, and image defects such as fluctuations in the color of the toner image after development will occur.

[0005] An object of the present invention is to provide a configuration capable of suppressing the occurrence of image defects. [Means for solving the problem]

[0006] One aspect of the present invention is a developing device comprising: a developing roller having a rotating developing sleeve, a developing magnet that is non-rotatingly arranged inside the developing sleeve and that uses magnetic force to attract developer to the surface of the developing sleeve, and which develops an electrostatic latent image formed on a rotating image carrier with the developer; a rotating peeling sleeve, and a peeling magnet that is non-rotatingly arranged inside the peeling sleeve and that uses magnetic force to attract developer to the surface of the peeling sleeve, and which peels off the developer from the developing roller after the electrostatic latent image on the image carrier has been developed by the developing roller, wherein the surfaces of the developing sleeve and the peeling sleeve each have an uneven shape. Effect of the Invention

[0007] According to the present invention, the occurrence of image defects can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. [Diagram 3] Graph showing surface roughness characteristics. [Figure 4] In the developing device of the first embodiment, (a) a table showing whether or not developer is carried along to the second developing sleeve when driven at a predetermined process speed, and (b) a table showing whether or not developer is carried along to the second developing sleeve when driven at an increased process speed. [Diagram 5] FIG. 11 is a view for explaining a groove ratio according to the second embodiment. [Figure 6] In the developing device of the second embodiment, (a) a table showing whether or not developer is carried along to the second developing sleeve when driven at a predetermined process speed, and (b) a table showing whether or not developer is carried along to the second developing sleeve when driven at an increased process speed. [Figure 7] Graph (a) shows the relationship between the surface roughness Rz of the sleeve and the amount of developer transported, graph (b) shows the relationship between the groove ratio ρ of the sleeve and the amount of developer transported, and graph (c) shows the relationship between the groove ratio ρ and the surface roughness Rz. [Figure 8] In the developing device of the third embodiment, (a) a table showing whether or not developer is carried around to the developing sleeve when driven at a predetermined process speed, and (b) a table showing whether or not developer is carried around to the second developing sleeve when driven at an increased process speed, when the second developing sleeve side is Rz and the stripping sleeve side is a groove ratio ρ. [Figure 9] In the developing device of the third embodiment, (a) a table showing whether or not developer is carried around to the developing sleeve when driven at a predetermined process speed, and (b) a table showing whether or not developer is carried around to the second developing sleeve when driven at an increased process speed, when the second developing sleeve side has a groove ratio ρ and the stripping sleeve side has a groove ratio Rz. [Figure 10] FIG. 11 is a cross-sectional view showing a schematic configuration of a developing device according to a fourth embodiment. [Figure 11](a) A table showing whether or not developer is carried along to the second developing sleeve when the developing device of the first embodiment is driven at an increased process speed, and (b) A table showing whether or not developer is carried along to the second developing sleeve when the developing device of the fourth embodiment is driven at an increased process speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <First embodiment> The first embodiment will be described with reference to Figures 1 to 4. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0010] [Image forming device] The image forming apparatus 100 is a full-color image forming apparatus, and in 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 has image forming units PY, PM, PC, and PK arranged in parallel, which perform image forming processes of four colors of toner images of yellow, magenta, cyan, and black, respectively. In the image forming apparatus 100 of this embodiment, a document reading device connected to the image forming apparatus main body (apparatus main body) or a host device such as a personal computer is connected to the apparatus main body so as to be able to communicate with the image forming apparatus. Therefore, according to image information from the host device, a four-color full-color image of yellow (Y), magenta (M), cyan (C), and black (K) can be formed on a recording material (recording paper, plastic sheet, cloth, etc.) using an electrophotographic method.

[0011] The image forming units PY, PM, PC, and PK of the respective colors include primary chargers 21Y, 21M, 21C, and 21K, developing devices 1Y, 1M, 1C, and 1K, optical writing units (exposure devices) 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning devices 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the image forming units PY, PM, PC, and PK of the respective colors have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0012] The photosensitive drum 28Y as an image carrier is a photosensitive member 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. The primary charger 21Y is made of a corona discharge electrode arranged around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0013] The optical writing unit 22Y incorporates a scanning optical device, and exposes the charged photosensitive drum 28Y based on image data, thereby lowering the potential of the exposed portion and forming a charge pattern (electrostatic latent image) corresponding to the image data. 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 a mixture of carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0014] The transfer device 2 has primary transfer rollers 23Y, 23M, 23C, and 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, and 23K and a plurality of rollers, and is supported so as to be capable of running. The primary transfer rollers 23Y, 23M, 23C, and 23K as primary transfer members correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black) in order from the top in FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24, and is configured so that a recording material can pass between the secondary transfer roller 25 and the intermediate transfer belt 24.

[0015] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred (primary transfer) onto the intermediate transfer belt 24 by the action of a primary transfer bias applied to the primary transfer rollers 23Y, 23M, 23C, and 23K at a primary transfer portion (primary transfer nip) T1 where the intermediate transfer belt 24 and the photosensitive drums 28Y, 28M, 28C, and 28K come into contact with each other. For example, in the case of a four-color full-color image, the toner images are transferred onto the intermediate transfer belt 24 in order from the photosensitive drum 28Y, and a color toner image in which yellow, magenta, cyan, and black layers are superimposed is formed.

[0016] Meanwhile, the recording material S stored in a cassette 110 serving as a recording material storage section is conveyed toward the transfer device 2 via a pickup roller 111 and a registration roller 112. The recording material S is conveyed in synchronization with the toner image on the intermediate transfer belt 24 to a secondary transfer section (nip section) T2 where the intermediate transfer belt 24 and a secondary transfer roller 25 serving as a secondary transfer member come into contact with each other. Then, the toner image formed on the intermediate transfer belt 24 is secondarily transferred onto the recording material S at the secondary transfer section T2 by the action of a secondary transfer bias applied to the secondary transfer roller 25. Pressure and heat are applied to the recording material to which the toner image has been transferred in the fixing device 3. This melts the toner on the recording material, and the color image is fixed onto the recording material. Thereafter, the recording material S is discharged outside the machine.

[0017] When forming images on both sides of the recording material, the recording material S that has passed through the fixing device 3 is conveyed to a reversing conveying path 113, and the recording material S that has been turned over is conveyed to registration rollers 112 by conveying rollers 114, and in the secondary transfer portion T2, a toner image is transferred to the back side of the recording material S in the same manner as described above. Then, again in the fixing device 3, the toner image is fixed to the back side of the recording material S.

[0018] The toner and other deposits remaining on the photosensitive drums 28Y, 28M, 28C, and 28K after the primary transfer process are collected by the cleaning devices 26Y, 26M, 26C, and 26K. This prepares the photosensitive drums 28Y, 28M, 28C, and 28K for the next image forming process. In addition, the toner and other deposits remaining on the intermediate transfer belt 24 after the secondary transfer process are removed by the intermediate transfer belt cleaner 29.

[0019] The image forming apparatus 100 of this embodiment can form a single-color or multi-color image, such as a black single-color image, by using image forming units for a desired single color or several colors among four colors. In addition, in FIG. 1, the image forming units PY, PM, PC, and PK for each color are arranged vertically, but they may be arranged horizontally or diagonally. Furthermore, in this embodiment, the outer diameter of the photosensitive drums 28Y, 28M, 28C, and 28K is, for example, 80 [mm], and the image forming operation is performed while rotating at a peripheral speed of 513 mm / sec.

[0020] The developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to the developing devices 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, in order from the top. The developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to the developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0021] For example, the toner weight ratio of the developer stored in the bottle is 80 to 95%, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is 5 to 10%. Therefore, when toner is consumed by development in the developing devices 1Y, 1M, 1C, and 1K, developer containing toner corresponding to the consumed amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0022] [Developing device] Next, the developing devices 1Y, 1M, 1C, and 1K will be described in detail with reference to Fig. 2. Since the developing devices 1Y, 1M, 1C, and 1K have the same configuration, the developing device 1Y will be described below as a representative. As shown in Fig. 2, the developing device 1Y has 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 members are contained in a developing container 60. The developing container 60 contains a two-component developer containing non-magnetic toner and a magnetic carrier.

[0023] The first developing roller 30 is a developer carrier that is driven to rotate, and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 has a rotating first developing sleeve 33 and a first developing magnet (fixed magnet) 36 that is disposed inside the first developing sleeve 33 in a non-rotating manner and that attracts the developer to the surface of the first developing sleeve 33 by magnetic force. The first developing roller 30 attracts (carries) the developer pumped up from a developer supply screw 42 by magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier) with the developer.

[0024] The first developing sleeve 33 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 39. The rotation direction of the first developing sleeve 33 is clockwise as shown by the arrow in FIG. 2, which is opposite to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the first developing sleeve 33 and the photosensitive drum 28Y rotate in the same direction at a position where they face each other (facing portion). That is, the first developing sleeve 33 rotates such that the surface facing the photosensitive drum 28Y moves vertically from below toward above.

[0025] The first developing magnet 36 is disposed inside the first developing sleeve 33, and has, for example, a plurality of sector-shaped magnetic poles and sector-shaped non-magnetic pole portions. Between the inner periphery of the first developing sleeve 33 and the outer periphery of the first developing magnet 36, a space is disposed to allow the first developing sleeve 33 to rotate.

[0026] The developer attracted onto the first developing sleeve 33 is transported toward the photosensitive drum 28Y by the rotational movement of the first developing 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 developing sleeve 33 is transported to the vicinity of the second developing roller 31 by the rotational movement of the first developing sleeve 33. Then, in the vicinity of the closest position between the first developing roller 30 and the second developing roller 31, the developer is peeled off from the first developing sleeve 33 and transferred onto the second developing sleeve 34 by the magnetic field generated by the first developing magnet 36 contained in the first developing roller 30 and the second developing magnet 37 contained in the second developing roller 31.

[0027] The second developing roller 31, which serves as a developing roller, is a developer carrier that is driven to rotate, and is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and above the rotation center of the first developing roller 30 in the vertical direction, and receives the developer from the first developing roller 30 by magnetic force. Similar to the first developing roller 30, the second developing roller 31 is disposed adjacent to the photosensitive drum 28Y such that its rotation axis is substantially 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 substantially parallel to each other.

[0028] The second developing roller 31 has a rotating second developing sleeve 34 and a second developing magnet (fixed magnet) 37 that is non-rotatingly disposed inside the second developing sleeve 34 and attracts the developer to the surface of the second developing sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first developing sleeve 33) based on the magnetic force, attracts (carries) the developer, 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 on the side of the second developing roller 31.

[0029] The second developing sleeve 34 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 40. The rotation direction of the second developing sleeve 34 is clockwise as shown by the arrow in FIG. 2, which is opposite to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the second developing sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other. That is, the second developing sleeve 34 rotates such that the surface facing the photosensitive drum 28Y moves vertically from below toward above. Also, the second developing sleeve 34 and the first developing sleeve 33 rotate in opposite directions at positions facing each other.

[0030] The second developing magnet 37 is disposed inside the second developing sleeve 34 and has, for example, a plurality of sector-shaped magnetic poles and sector-shaped non-magnetic pole portions. Between the inner periphery of the second developing sleeve 34 and the outer periphery of the second developing magnet 37, a space is disposed to allow the second developing sleeve 34 to rotate.

[0031] The developer attracted onto the second developing sleeve 34 is transported toward the photosensitive drum 28Y by the rotational operation of the second developing sleeve 34, and develops the latent image formed on the photosensitive drum 28Y. After the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second developing sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotational operation of the second developing sleeve 34. Then, in the vicinity of the closest position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second developing sleeve 34 to the peeling sleeve 35 of the peeling roller 32 by the magnetic field generated by the second developing magnet 37 contained in the second developing roller 31 and the peeling magnet 38 contained in the peeling roller 32.

[0032] The peeling roller 32 is disposed on the opposite side to the photosensitive drum 28Y with respect to the rotation center R1 of the second developing sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y is developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is disposed between the second developing roller 31 and the developer recovery screw 44 such that its rotation center R2 is above the rotation center R1 of the second developing roller 31.

[0033] The peeling roller 32 is disposed so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 has a rotating peeling sleeve 35 and a peeling magnet (fixed magnet) 38 that is non-rotatingly disposed inside the peeling sleeve 35 and attracts the developer to the surface of the peeling sleeve 35 by magnetic force, and is configured to receive the developer from the second developing roller 31 based on the magnetic force.

[0034] The peeling sleeve 35 is a non-magnetic cylindrical member, and is driven to rotate around a rotation shaft 41. The rotation direction of the peeling sleeve 35 is counterclockwise as indicated by the arrow in Fig. 2, which is the opposite direction to the rotation direction of the second developing sleeve 34 in this embodiment. Therefore, the peeling sleeve 35 and the second developing sleeve 34 rotate in the same direction (forward direction) at positions where they face each other (facing portions).

[0035] The peeling magnet 38 is disposed inside the peeling sleeve 35 and has, for example, a plurality of sector-shaped magnetic poles and sector-shaped non-magnetic pole portions. A space that allows the peeling sleeve 35 to rotate is disposed between the inner periphery of the peeling sleeve 35 and the outer periphery of the peeling magnet 38.

[0036] The developer attracted onto the peeling sleeve 35 is transported downstream in the rotation direction by the rotation of the peeling sleeve 35, and is peeled off from the peeling sleeve 35 by a peeling magnet 38 contained in the peeling roller 32 at a position close to the developer recovery screw 44, and falls by its own weight toward a guide member 45 located vertically below. The developer that has fallen onto the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0037] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 as a recovery section that recovers the developer peeled off from the peeling sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is located below the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer delivered (recovered) from the peeling roller 32 while stirring it.

[0038] The guide member 45 as a guide portion is disposed vertically below the center of rotation of the peeling roller 32, and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has a slope 45a along which the developer slides down under its own weight, in order to more reliably guide the peeled off developer toward the developer recovery screw 44. The slope 45a is inclined with respect to the horizontal direction so that the developer recovery screw 44 side is lower than the lower position of the peeling roller 32.

[0039] The developer recovery screw 44, which serves as a recovery member and a transport section, transports the recovered developer to a developer circulating section 46, which will be described next. That is, the developer recovery screw 44 is a screw transport member used to transport the recovered developer in one direction while stirring it as it slides down the inclined surface of the guide member 45.

[0040] The developer circulating section 46 is a supply section for supplying the developer to the first developing roller 30, and includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulating section 46, the developer is stirred in the developer supply screw 42 and the developer stirring screw 43 and transported in a substantially horizontal direction, and is supplied to the first developing roller 30. As described above, the developer collected by the developer collecting section 47 falls by its own weight and is introduced into the developer circulating section 46. That is, the developer circulating section 46 is located lower than the developer collecting section 47 in the vertical direction.

[0041] The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are screw transport members that transport the developer in one direction while stirring it, and the developer supply screw 42 and developer stirring screw 43 are located below the rotation center of the developer recovery screw 44 in the vertical direction. The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are approximately parallel to each other. The rotation axes of these screws are also approximately parallel to the rotation axis of the first developing roller 30.

[0042] The developer supply screw 42 is located between the first developing roller 30 and the developer stirring screw 43, and a partition wall 48 of the developing container 60 is disposed between the developer supply screw 42 and the developer stirring 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 stirring screw 43. The partition wall 48 is provided with a communication port (not shown) that communicates between a first conveying path 61, through which the developer is conveyed by the developer supply screw 42, and a second conveying path 62, through which the developer is conveyed by the developer stirring screw 43.

[0043] The developer stirred by the developer recovery screw 44 passes through a communication port (not shown) formed in a partition wall 63 of the developing container 60 between the developer recovery screw 44 and the developer supply screw 42, and falls by its own weight toward the developer supply screw 42. The above-mentioned guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0044] The position of the communication port through which the developer stirred by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulating section 46 is preferably arranged to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part with respect to the rotational axis direction of the developer supply screw 42). In this embodiment, the communication port is arranged at a position included in the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is arranged.

[0045] The developer transport directions of the developer supply screw 42 and the developer stirring screw 43 are opposite to each other. The start side (upstream end side in the developer transport direction) and the end side (downstream end side in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is arranged communicate with the end side and the start side of the second transport path 62 in which the developer stirring screw 43 is arranged via a communication port provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer stirring screw 43 shown by the arrows in FIG. 2 and in the approximately horizontal direction within the developing container 60, and a part of the developer is supplied toward the first developing roller 30.

[0046] The developer supply port 51 (see FIG. 2) is disposed above the developer stirring screw 43 in the developing container 60, and is connected to the developer storage unit 27Y (see FIG. 1). The developer supply port 51 is configured to be able to supply the developer stored in a bottle loaded in the developer storage unit 27Y to the second conveying path 62 in which the developer stirring screw 43 is disposed.

[0047] As described above, the toner weight ratio of the developer stored in the bottle of developer storage section 27Y is greater than the toner weight ratio of the developer in developing device 1Y, so by adjusting the developer supplied to developer stirring screw 43, it is possible to maintain the toner weight ratio of the developer in developing device 1 constant.

[0048] The toner concentration detection sensor 49 (see FIG. 2) is disposed to detect the toner concentration in the developer contained in the developer circulating section 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 therefore used to control the supply of developer from the developer storage section 27Y. For example, when it is detected that the toner concentration has fallen below a predetermined value, developer is supplied from the developer storage section 27Y. Note that since the magnetic permeability of the developer changes depending on the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0049] The regulating member 50 is disposed adjacent to the first developing roller 30, and is used to regulate the amount of developer supplied from the developer circulating unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer attracted to the first developing roller 30 based on, for example, the gap between the surface of the first developing sleeve 33 of the first developing roller 30 and an end of the regulating member 50.

[0050] The developer circulation path in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulation section 46, and then supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 again by magnetic force, and then peeled off from the peeling roller 32 by a peeling magnet 38 contained in the peeling roller 32, and then collected in the developer collection section 47, and introduced again into the developer circulation section 46.

[0051] 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 non-magnetic toner with a negative charge polarity and a magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic that contains colorants, wax components, etc., and is pulverized or polymerized to form a powder, to which fine powders such as titanium oxide and silica are added on the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, and a resin coating is applied to the surface layer. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of the toner contained in the developer) is 8%.

[0052] In general, the two-component development method using toner and carrier has the characteristic that the toner is subjected to less stress than the one-component development method using a one-component developer, because the toner and carrier are charged to a predetermined polarity by frictional contact between them. On the other hand, with long-term use, the dirt (spent) adhering to the carrier surface increases, and the ability to charge the toner gradually decreases. As a result, problems such as fogging and toner scattering occur. In order to extend the life of the two-component development device, it is possible to increase the amount of carrier contained in the development device, but this is not desirable because it leads to an increase in the size of the development device.

[0053] In order to solve the above problems associated with two-component developer, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method in which new developer is supplied little by little from the developer storage section 27Y to the developing device 1Y, and developer with deteriorated charging performance is discharged little by little from a discharge port (not shown) of the developing device 1Y, thereby suppressing an increase in deteriorated carrier. As a result, deteriorated carrier in the developing device 1Y is gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y approximately constant.

[0054] In the developing device 1Y of the present embodiment thus configured, the developer in the first transport path 61 is supplied to the first developing sleeve 33 by the developer supply screw 42, and a predetermined amount of the developer supplied to the first developing sleeve 33 is carried on the first developing sleeve 33 by the magnetic field generated by the first developing magnet 36 to form a developer pool. As the first developing sleeve 33 rotates, the two-component developer on the first developing sleeve 33 passes through the developer pool and is coated in a thin layer on the surface of the first developing sleeve 33 by the regulating member 50, and is transported to a developing area facing the photosensitive drum 28Y. In the developing area, the developer on the first developing sleeve 33 stands up to form magnetic spikes.

[0055] In the first developing region where the first developing sleeve 33 and the photosensitive drum 28Y face each other, the electrostatic latent image formed on the photosensitive drum 28Y is visualized by the developing bias applied to the first developing sleeve 33. In this embodiment, the developing bias applied to the first developing sleeve 33 has a waveform in which both an AC electric field and a DC electric field are superimposed, but the developing bias may be a DC electric field only.

[0056] After the two-component developer is subjected to the developing process in the first developing region, it is transferred to the second developing sleeve 34 at a position close to the second developing sleeve 34 and transported to the second developing region where the second developing sleeve 34 faces the photosensitive drum 28Y. In the second developing region, the same developing bias as in the first developing region is applied, and the toner image is made uniform by developing and compensating for the lack of toner relative to the potential of the electrostatic latent image on the photosensitive drum 28Y and recovering the toner that has been developed in excess. Here, the developing bias applied to the first developing sleeve 33 and the developing bias applied to the second developing sleeve 34 may have different waveforms.

[0057] The developer that has passed through the second developing region is peeled off in a peeling magnetic field region formed by a second developing magnet 37 contained in the second developing sleeve 34. The developer peeled off from the second developing sleeve 34 is attracted to the surface of the peeling sleeve 35 by a magnetic field formed by a peeling magnet 38 contained in the peeling sleeve 35 of the peeling roller 32, and is transported along the rotation direction of the peeling sleeve 35. The developer is then detached from the surface of the peeling sleeve 35 by the peeling magnetic field formed by the peeling magnet 38, and is collected in a developer collecting section 47.

[0058] Here, in order to form a high-quality image using the developing device 1Y having the above-mentioned configuration, it is required that there is no leakage during the transfer of the developer from the second developing sleeve 34 to the peeling sleeve 35. If leakage occurs during the transfer, the developer will spill downward in the vertical direction from between the second developing sleeve 34 and the developing container 60. If this occurs, the developer will fall onto the first developing sleeve 33 and be immediately supplied to the first developing sleeve 33 from the first conveying path 61 without being agitated in the developer circulation path. In addition, the developer will fall between the first developing sleeve 33 and the second developing sleeve 34, be conveyed to the second developing sleeve 34, and be immediately supplied to the second developing area. As a result, developer with an uneven amount of toner is provided to the developing process, causing fluctuations in density.

[0059] This phenomenon is more likely to occur when the image formation speed (process speed) is high, that is, when the rotation speeds of the first developing sleeve 33, the second developing sleeve 34, and the peeling sleeve 35 are high. For this reason, the second developing sleeve 34 and the peeling sleeve 35 are each required to have an appropriate developer transport capacity.

[0060] If the transport capacity of the second developing sleeve 34 increases and the transport capacity of the peeling sleeve 35 is insufficient to accommodate it, a portion of the developer transported by the second developing sleeve 34 will be released from magnetic restraint by the peeling magnetic field area of ​​the second developing magnet 37 and then fall vertically downward without being restrained by the peeling magnet 38 of the peeling sleeve 35.

[0061] In this embodiment, the first developing sleeve 33 operates at a peripheral speed of 513 mm / sec, the same as the photosensitive drum 28Y, the second developing sleeve 34 operates at a peripheral speed of 616 mm / sec, and the peeling sleeve 35 operates at a peripheral speed of 740 mm / sec.

[0062] [Surface structure of the second developing sleeve and peeling sleeve] Therefore, in this embodiment, the co-rotation of the developer is suppressed by optimizing the surface shapes of the second developing sleeve 34 and the stripping sleeve 35. First, the surface shapes of the second developing sleeve 34 and the stripping sleeve 35 will be described.

[0063] In recent years, two types of surface processing methods for improving the developer transport capacity of a developer carrier such as the second developing sleeve 34 have become known: a method of roughening the surface mainly by blasting, and a method of forming groove shapes by cutting or etching. The former, blasting, is a processing method in which fine abrasive particles such as alundum are uniformly blown onto an aluminum or other raw tube together with air compressed by a compressor to create fine irregularities on the surface. The surface shape of the second developing sleeve 34 created by blasting is managed mainly using roughness indices such as Rz (ten-point average roughness), Ra (arithmetic mean roughness), and Sm (average spacing of irregularities).

[0064] In this embodiment, a surface roughness measuring instrument SE600 manufactured by Kosaka Laboratory Co., Ltd. was used to measure Rz and Ra based on the JIS94 standard. As a result of measuring Rz and Ra using this surface roughness measuring instrument, Rz and Ra have an approximately linear correlation relationship as shown in Figure 3, and it is considered that there is a similar relationship regardless of which roughness index is used. For this reason, although only Rz is handled in this embodiment, the same can be said when it is converted to Ra as a ratio.

[0065] The developer transport capacity of the second developing sleeve 34 is affected by the surface roughness of the second developing sleeve 34 as well as the rotation speed of the second developing sleeve 34. The amount of developer transferred from the first developing sleeve 33 to the second developing sleeve 34 is determined by the developer transport capacity of the first developing sleeve 33. The developer transport capacity of the first developing sleeve 33 is affected by the rotation speed of the first developing sleeve 33 and the surface roughness of the first developing sleeve 33, just like the second developing sleeve 34, but by adjusting the width of the gap between the first developing sleeve 33 and the regulating member 50, the amount of developer optimal for the development process is set to be supplied to the first developing region and the second developing region.

[0066] Here, when the developer is transferred from the second developing sleeve 34 to the peeling sleeve 35, if the peeling sleeve 35 does not have a sufficient developer transport capacity, the developer that could not be received passes through the gap between the second developing sleeve 34 and the peeling sleeve 35, and is separated from the second developing sleeve 34 by the developer peeling region of the second developing magnet 37 and falls vertically downward. A part of the developer that has been separated from the second developing sleeve 34 may fly in the direction of the gap between the second developing sleeve 34 and the first developing sleeve 33 due to the tangential transport force of the second developing sleeve 34. For this reason, the developer transport capacity of the peeling sleeve 35 is required to have a certain level of transport capacity relative to the developer transport capacity of the second developing sleeve 34.

[0067] In this embodiment, the surfaces of the second developing sleeve 34 and the stripping sleeve 35 each have an uneven shape, and this uneven shape is formed by applying a blasting process. If the ten-point mean roughness of the surface of the second developing sleeve 34 is Rz1 and the ten-point mean roughness of the surface of the stripping sleeve 35 is Rz2, then 0.35×Rz1≦Rz2 (Formula 1) and 7μm≦Rz1≦15μm (Formula 2) We strive to satisfy the following criteria.

[0068] 4(a) and (b) show the results of an experiment to investigate the relationship between the occurrence of the above-mentioned developer dragging phenomenon when the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the peeling sleeve 35 are varied. In the experiment, the dragging phenomenon was evaluated when the above-mentioned process speed was set to a predetermined process speed (the peripheral speed of the photosensitive drum 28Y was 513 [mm / sec]), and when the peripheral speed of the photosensitive drum 28Y was set to 564.3 [mm / sec], which is 10% higher than the predetermined process speed.

[0069] The operating speed of the entire developing device 1Y, including the first developing sleeve 33 and the second developing sleeve 34, when the peripheral speed of the photosensitive drum 28Y is increased is also set to be 10% higher than the operating speed of the entire developing device 1Y when the photosensitive drum 28Y is set to a specified process speed. In addition, the symbol "◯" in the tables of Figures 4(a) and (b) indicates that there was no occurrence of the dragging phenomenon, "△" indicates that there were signs of dragging phenomenon behavior but they were not visible in the image, and "×" indicates that the dragging phenomenon occurred.

[0070] 4A shows the presence or absence of co-rotation when multiple combinations of the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the stripping sleeve 35 are used at a given process speed. It was confirmed that no co-rotation occurs at any of the combinations at the given process speed.

[0071] Fig. 4(b) shows whether or not the toner rotation occurs when the process speed is increased by 10% from a given process speed and when multiple conditions of the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the peeling sleeve 35 are combined. Here, the symbol "◆" in the table of Fig. 4(b) indicates that the toner fusion phenomenon to the surface of the second developing sleeve 34 has occurred.

[0072] Generally, in an image forming apparatus using an electrophotographic method, the developing sleeve has a surface roughness Rz of about 7 μm to 15 μm. For this reason, in the experiment, the second developing sleeve 34 was prepared with a surface roughness of about 7, 9, 11, and 15 μm. On the other hand, the peeling sleeve 35 was prepared with a surface roughness Rz1 of 16.5 μm, which is 10% larger than the surface roughness Rz1 of the second developing sleeve 34, and the surface roughness Rz2 was changed while gradually smoothing it using an abrasive sheet. Then, in the evaluation of Figures 4(a) and (b), the occurrence of the drag phenomenon was confirmed by changing each combination.

[0073] The results of this experiment in FIG. 4(b) show that when the process speed is fast relative to a specified process speed, the drag phenomenon begins to occur when the surface roughness Rz2 of the peeling sleeve 35 becomes 30% or less of the surface roughness Rz1 of the second developing sleeve 34, and tends to become minor at 35%.

[0074] On the other hand, when the surface roughness of the second developing sleeve 34 and the peeling sleeve 35 is increased, the conveying performance of the magnetic brush is too high, so that the frictional force at the opposing portion between the second developing sleeve 34 and the peeling sleeve 35 increases, and the toner fusion phenomenon was confirmed on the surface of each sleeve. The location where the fusion phenomenon occurred is where the developer on the opposing surface between the second developing sleeve 34 and the peeling sleeve 35 accumulates and starts to clog. When fusion occurs on the surface of the second developing sleeve 34, the surface roughness Rz of the fused portion tends to become even larger, so that the amount of developer conveyed to the second development area increases and the density becomes high only in the fused portion, resulting in an image defect in which the toner is developed on the photosensitive drum 28Y while crushing the electrostatic latent image.

[0075] For this reason, in this embodiment, the surface roughness Rz2 of the peeling sleeve 35 is set to the above-mentioned 0.35×Rz1≦Rz2 (Formula 1) However, it is preferable that the maximum value of Rz1 is 15 [μm]. Also, it is preferable that the minimum value of Rz1 is 7 [μm]. 7μm≦Rz1≦15μm (Formula 2) It is desirable to also satisfy the above.

[0076] 4(b), it is preferable to satisfy 0.40×Rz1≦Rz2, more preferably Rz2≦1.20×Rz1, and further preferably Rz2≦1.00×Rz1.

[0077] In this embodiment, the surfaces of the second developing sleeve 34 and the peeling sleeve 35 are each made uneven. This can improve the developer transporting power of each sleeve. As a result, the occurrence of the developer dragging phenomenon on the second developing sleeve 34 can be suppressed, and the occurrence of image defects can be suppressed. Furthermore, in this embodiment, by setting the relationship between the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the peeling sleeve 35 as described above, the occurrence of the developer dragging phenomenon can be further suppressed. In particular, since the occurrence of the developer dragging phenomenon can be suppressed even when the process speed is increased, an image forming apparatus with high quality and high image quality can be provided.

[0078] In this embodiment, the second developing sleeve 34 has a peripheral speed of 616 mm / sec, and the peeling sleeve 35 has a peripheral speed of 740 mm / sec, making the peripheral speed of the peeling sleeve 35 faster than the peripheral speed of the second developing sleeve 34. This increases the developer transport capacity of the peeling sleeve 35, improves the developer recovery capacity of the peeling sleeve 35, and prevents the developer peeled off from the second developing sleeve 34 from falling downward.

[0079] <Second embodiment> The second embodiment will be described with reference to FIG. 2 and FIG. 5 to FIG. 6(b). In the above-mentioned first embodiment, the uneven shape of the surface of the second developing sleeve 34 and the peeling sleeve 35 is formed by blasting. In contrast, in this embodiment, the uneven shape of the surface of the second developing sleeve 34 and the peeling sleeve 35 is formed so that a plurality of grooves are aligned in the circumferential direction. Since the other configurations and functions are the same as those of the above-mentioned first embodiment, the following description will focus on the differences from the first embodiment and will omit or simplify illustrations and descriptions of the same configurations as those of the first embodiment.

[0080] In recent years, in electrophotographic image forming apparatuses, the surface of the developing sleeve provided in the developing device has a groove-shaped surface with multiple cut sections in the circumferential direction that are uniform in the longitudinal direction. Generally, the method of processing such grooves includes a method of applying a resist to the non-grooved part of a blank tube and spraying an etching solution to corrode and melt the metal in the groove part to create the groove shape, and a method of attaching the blank tube to a die having a blade in the groove part and performing an extrusion or drawing process to create the groove shape. The grooves formed on the sleeve surface in this way are managed using indicators such as the groove width, the number of grooves, and the groove ratio calculated from the sleeve circumference.

[0081] In this embodiment, sleeves having grooves formed therein by the latter extrusion process are used as the first developing sleeve 33, the second developing sleeve 34, and the peeling sleeve 35. Even if the method for forming the grooves is different, basically the same results as those in the examples described below can be obtained.

[0082] In this embodiment, the uneven shape of the surface of the second developing sleeve 34 and the stripping sleeve 35 is a shape formed by arranging a plurality of grooves in the circumferential direction (hereinafter, also referred to as a "groove shape"). As shown in FIG. 5, the width of the groove 121 of a certain sleeve 120 is d, the number of grooves per revolution is N, the circumferential length is L, and the groove ratio ρ is ρ=(d×N) / L (Formula 3) It is defined as:

[0083] In addition, when the groove ratio on the surface of the second developing sleeve 34 is ρ1 and the groove ratio on the surface of the stripping sleeve 35 is ρ2, 0.40×ρ1≦ρ2 (Formula 4) and 0.07≦ρ1≦0.23 (Formula 5) That is, in this embodiment, an index called a groove ratio ρ is used as an index representing the relationship between the surface shape of the groove-shaped sleeve and the conveying capacity.

[0084] In this configuration having a groove shape on the surface, the developer transport capacity changes depending on the size of the groove ratio ρ, similar to the surface roughness Rz in the first embodiment. When the groove ratio ρ is large, the transport force is high, and when the groove ratio ρ is small, the transport force is low. In this embodiment, a groove-shaped sleeve with a V-shaped cross section perpendicular to the rotation axis direction is used as shown in FIG. 5, but the transport force can be expressed in terms of the groove ratio in the same way even if the bottom is rounded or trapezoidal. If the shape of the groove is constant, the groove depth is uniquely determined when the groove width is determined because the shapes are similar. Even if the groove shape is not constant, it is possible to calculate the groove ratio according to the cross-sectional position of the cylinder of the sleeve.

[0085] 6(a) and (b) show the results of an experiment to investigate the relationship between the occurrence of the above-mentioned developer dragging phenomenon and the groove ratio ρ, as in the case of the surface roughness Rz of the first embodiment. In this experiment, the dragging phenomenon was evaluated when the above-mentioned process speed was set to a predetermined process speed (the peripheral speed of the photosensitive drum 28Y was 513 [mm / sec]), and when the peripheral speed of the photosensitive drum 28Y was set to 564.3 [mm / sec], which is 10% higher than the predetermined process speed.

[0086] The operating speed of the entire developing device 1Y, including the first developing sleeve 33 and the second developing sleeve 34, when the peripheral speed of the photosensitive drum 28Y is increased is also set to be 10% higher than the operating speed of the entire developing device 1Y when the photosensitive drum 28Y is set to a specified process speed. In addition, the symbol "◯" in the tables of Figures 6(a) and (b) indicates that there was no occurrence of the dragging phenomenon, "△" indicates that there were signs of dragging phenomenon behavior but they were not visible in the image, and "×" indicates that the dragging phenomenon occurred.

[0087] Fig. 6(a) shows whether or not co-rotation occurs when multiple conditions of the groove ratio ρ1 of the second developing sleeve 34 and the groove ratio ρ2 of the stripping sleeve 35 are combined for a predetermined process speed. Fig. 6(b) shows whether or not co-rotation occurs when multiple conditions of the groove ratio ρ1 of the second developing sleeve 34 and the groove ratio ρ2 of the stripping sleeve 35 are combined for a case where the process speed is increased by 10% from a predetermined process speed. The horizontal axis of the tables in Fig. 6(a) and Fig. 6(b) shows the groove ratio ρ1 of the second developing sleeve 34, and the vertical axis shows the ratio of the groove ratio ρ2 of the stripping sleeve 35 to the groove ratio ρ1 of the second developing sleeve 34.

[0088] First, when the groove ratio ρ1 of the second developing sleeve 34 is 0.06 or less, almost no transport capacity for transporting two-component developer is obtained, and the developer transport capacity is almost the same as that of a mirror cylinder without grooves. Also, when the groove ratio ρ1 is greater than 0.23, the developer retention force of the grooves increases, and co-rotation is likely to occur regardless of the rotation speed of the developing sleeve. Therefore, regardless of the relationship between the second developing sleeve 34 and the peeling sleeve 35, the groove ratio ρ1 of the second developing sleeve 34 is 0.07≦ρ1≦0.23 It is desirable to satisfy the following.

[0089] In this embodiment, from the above-mentioned optimum range of the groove ratio, the groove ratio ρ2 of the second developing sleeve 34 is set to 0.15. Also, in this embodiment, the surface shape of the first developing sleeve 33 is made the same as the surface shape of the second developing sleeve 34 so that the developer supply amounts in the first developing region and the second developing region are equal. In reality, a combination of different shapes may be used depending on the development characteristics in the developing region.

[0090] Also, from FIG. 6B, even when the surface shapes of the second developing sleeve 34 and the peeling sleeve 35 are both grooved, the groove ratio ρ2 of the peeling sleeve 35 is 0.40×ρ1≦ρ2 It is preferable that the above formula is satisfied, and further, ρ2≦1.67×ρ1 It is preferable that the following is satisfied.

[0091] That is, the groove ratio ρ1 of the second developing sleeve 34 and the groove ratio ρ2 of the stripping sleeve 35 are 0.40×ρ1≦ρ2≦1.67×ρ1 and 0.07≦ρ1≦0.23 It is preferable that the following is satisfied.

[0092] 6(b), it is preferable that 0.53×ρ1≦ρ2 is satisfied, more preferably that 1.00×ρ1≦ρ2 is satisfied, and further preferably that ρ2≦1.60×ρ1 is satisfied.

[0093] In the case of a grooved sleeve, the uneven shape is larger than that of a sleeve with a blasted surface, and the unevenness of a size that the toner can be caught is small, so toner fusion is less likely to occur. Therefore, the upper and lower limits of the groove ratio are both determined depending on whether or not the developer is carried along. In this embodiment, by setting the relationship between the groove ratio ρ1 of the second developing sleeve 34 and the groove ratio ρ2 of the peeling sleeve 35 as described above, the occurrence of the developer is suppressed even when the process speed is increased, and an image forming apparatus with high quality and high image quality can be provided.

[0094] <Third embodiment> The third embodiment will be described with reference to FIG. 2 and with reference to FIG. 7(a) to FIG. 9(b). In the first embodiment, the uneven surface shape of the second developing sleeve 34 and the peeling sleeve 35 is formed by blasting, and in the second embodiment, the uneven surface shape of each sleeve is a groove shape. In contrast, in this embodiment, the uneven surface shape of the second developing sleeve 34 and the peeling sleeve 35 is a combination of a blasted surface shape and a groove shape. Since the other configurations and functions are the same as those of the first and second embodiments, the following description will focus on the differences from the first and second embodiments, and illustrations and descriptions of the same configurations as those of the first and second embodiments will be omitted or simplified.

[0095] In this embodiment, a combination will be described in which the uneven surface shape of the second developing sleeve 34 is formed by blasting and the uneven surface shape of the peeling sleeve 35 is groove-shaped, and conversely, a combination will be described in which the uneven surface shape of the second developing sleeve 34 is groove-shaped and the uneven surface shape of the peeling sleeve 35 is formed by blasting.

[0096] Fig. 7(a) shows the relationship between the surface roughness Rz of a sleeve with a blasted surface and the amount of developer transported, and Fig. 7(b) shows the relationship between the groove ratio ρ of a grooved sleeve and the amount of developer transported. Figs. 7(a) and (b) are graphs plotting combinations that can transport the same amount of developer in each case. These graphs are data obtained from the amount of developer transported when only the surface shape of the sleeve is changed when the closest distance between the surface of the first developing sleeve 33 and the regulating member 50 and the rotation speed of the first developing sleeve 33 are fixed, as in the case of the first developing sleeve 33, and show the relationship between the surface shape and the transport force.

[0097] According to Fig. 7(a) and (b), the surface roughness Rz of the sleeve with blasted surface and the groove ratio ρ of the sleeve with grooved surface show an approximately linear relationship. From the graph shown in Fig. 7(c), the relationship between the surface roughness Rz and the groove ratio ρ is as follows: Rz = α × ρ + β (Equation 6) The following relational expression is obtained.

[0098] This relationship makes it possible to present an optimal configuration of the second developing sleeve 34 and the stripping sleeve 35, which is a combination of a sleeve with a blasted surface and a sleeve with a grooved surface. α=67.2703, β=1.4186 was used to apply it to Equation 6, which is the relationship between Rz and groove ratio ρ.

[0099] That is, by substituting the above values ​​into Equation 6, Rz=67.2703×ρ+1.4186 (Formula 7) was used as the conversion formula from the groove ratio ρ to the ten-point average roughness Rz.

[0100] In this embodiment, the level of developer entrainment on the second developing sleeve 34 was confirmed for each of the following combinations: a combination in which the uneven surface shape of the second developing sleeve 34 was formed by blasting and the uneven surface shape of the peeling sleeve 35 was a groove shape (see Figures 8(a) and (b) described below), and a combination in which the uneven surface shape of the second developing sleeve 34 was a groove shape and the uneven surface shape of the peeling sleeve 35 was formed by blasting (see Figures 9(a) and (b) described below).

[0101] As shown in the first embodiment, the upper limit of Rz of the transport capacity of the second developing sleeve 34 having a blasted surface is limited by the adhesion to the surface. On the other hand, as shown in the second embodiment, the lower limit of the groove ratio ρ of the second developing sleeve having a grooved surface is limited by the transport capacity, and the upper limit of the groove ratio ρ is limited by the dragging performance.

[0102] 8(a), 8(b), 9(a), and 9(b) show the results of an experiment investigating the relationship between the occurrence of the above-mentioned developer dragging phenomenon and the change in surface roughness Rz or groove ratio ρ, as in the first and second embodiments. In the experiment, the dragging phenomenon was evaluated when the above-mentioned process speed was set to a predetermined process speed (the peripheral speed of the photosensitive drum 28Y was 513 [mm / sec]), and when the peripheral speed of the photosensitive drum 28Y was set to 564.3 [mm / sec], which is 10% higher than the predetermined process speed.

[0103] The operating speed of the entire developing device 1Y, including the first developing sleeve 33 and the second developing sleeve 34, when the peripheral speed of the photosensitive drum 28Y is increased is also set to be 10% higher than the operating speed of the entire developing device 1Y when the photosensitive drum 28Y is set to a specified process speed. In addition, the symbol "◯" in the tables of Figures 8(a), (b) and Figures 9(a), (b) indicates that there was no occurrence of the dragging phenomenon, "△" indicates that there were signs of dragging phenomenon behavior but they were not visible in the image, and "×" indicates that the dragging phenomenon occurred. In addition, the symbol "◆" indicates that the toner melting phenomenon occurred on the surface of the second developing sleeve 34.

[0104] Fig. 8(a) shows the presence or absence of a dragged image when the surface roughness Rz1 of the second developing sleeve 34 and the groove ratio ρ2 of the stripping sleeve 35 are combined for a predetermined process speed. Fig. 9(a) shows the presence or absence of a dragged image when the groove ratio ρ1 of the second developing sleeve 34 and the surface roughness Rz2 of the stripping sleeve 35 are combined for a predetermined process speed.

[0105] 8(b) shows whether or not a dragged image occurs when the surface roughness Rz1l of the second developing sleeve 34 and the groove ratio ρ2 of the stripping sleeve 35 are combined when the process speed is increased by 10% from a predetermined process speed. Also, FIG. 9(b) shows whether or not a dragged image occurs when the groove ratio ρ1 of the second developing sleeve 34 and the surface roughness Rz2 of the stripping sleeve 35 are combined when the process speed is increased by 10% from a predetermined process speed.

[0106] 8(a) and (b) also show the value of the groove ratio ρ2 of the stripping sleeve 35 converted to Rz using equation 7. Also, in Fig. 9(a) and (b) also show the value of the surface roughness Rz2 of the stripping sleeve 35 converted to ρ. Equation 7 is an equation for converting ρ to Rz, but an equation for converting Rz to ρ can be found by modifying this equation 7.

[0107] As in the first embodiment, even if the drag does not occur when the process speed of the image forming apparatus is a predetermined speed, the drag will occur when the process speed is increased in a configuration with a small surface roughness. On the other hand, by using the conversion formula of Equation 7 to configure the configuration to satisfy the conditions of Equations 1 and 2, the drag phenomenon can be suppressed when the process speed is increased even in the combination of a blasted sleeve and a grooved sleeve. Also, as in the second embodiment, by using the conversion formula of Equation 7 to configure the configuration to satisfy the conditions of Equations 4 and 5, the drag phenomenon can be suppressed when the process speed is increased even in the combination of a blasted sleeve and a grooved sleeve.

[0108] In this manner, in the present embodiment, even if the surface shape of the second developing sleeve 34 and the surface shape of the peeling sleeve 35 are different, the relationship between the values ​​converted using the conversion formula of Equation 7 satisfies the conditions of the first and second embodiments, so that the occurrence of the drag phenomenon can be suppressed even when the process speed is increased, and a high-quality, high-image-quality image forming apparatus can be provided.

[0109] <Fourth embodiment> The fourth embodiment will be described with reference to Figures 10 to 11(b). In the above-described embodiments, the rotation center R2 of the peeling roller 32 is located vertically above the rotation center R1 of the second developing roller 31. In contrast, in this embodiment, the rotation center R2 of the peeling roller 32 is located vertically below the rotation center R1 of the second developing roller 31. Since the other configurations and functions are the same as those of the first embodiment, the following description will focus on the differences from the first embodiment and will omit or simplify illustrations and descriptions of the configurations similar to those of the first embodiment.

[0110] In the developing device 1A of this embodiment, when the developer carried by the second developing sleeve 34 is peeled off by the peeling magnetic field area formed by the second developing magnet 37, the peeling roller 32 receives the developer with almost no leakage, and the developer can be recovered in the developer recovery section 47.

[0111] 10, in this embodiment, the positional relationship between the second developing roller 31 and the peeling roller 32 is optimized. That is, in this embodiment, a horizontal line B passing through the rotation center R2 of the peeling roller 32 is positioned vertically lower than a horizontal line A passing through the rotation center R1 of the second developing roller 31.

[0112] As a result, the influence of the magnetic force of the second developing magnet 37 on the developer peeled off from the surface of the second developing sleeve 34 is reduced, and the developer peeled off from the surface of the second developing sleeve 34 is carried on the surface of the peeling sleeve 35 by the magnetic field formed by the peeling magnet 38, and is transported to the developer recovery section 47.

[0113] Here, it is desirable that the rotation direction of the peeling sleeve 35 is such that the circumferential speed direction of the surface of the peeling sleeve 35 is opposite to the circumferential speed direction of the surface of the second developing sleeve 34 at the portion facing the second developing sleeve 34. This is the most effective way to prevent the developer from dropping vertically downward.

[0114] At this time, if the conveying capacity of the peeling sleeve 35 is low, the peeling sleeve 35 cannot sufficiently receive the developer from the second developing sleeve 34, and the developer that is not received falls vertically downward within the peeling magnetic field region of the second developing magnet 37 and is carried around. On the other hand, if the peripheral speed of the second developing sleeve 34 and the peripheral speed of the peeling roller are set to be in the forward direction on the opposing surface, the peeling sleeve 35 conveys the developer received from the second developing sleeve 34 toward the developer recovery section 47 while carrying it vertically downward. At this time, when the rotating direction of the peeling sleeve 35 is compared between the reverse direction and the forward direction, the conveying capacity required for the surface of the peeling sleeve 35 is higher in the forward direction.

[0115] In this embodiment, similarly to the first embodiment, the surfaces of the second developing sleeve 34 and the peeling sleeve 35 are subjected to blast processing.

[0116] 11(a) and (b) show the results of an experiment to investigate the relationship between the occurrence of the above-mentioned developer entrainment phenomenon when the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the peeling sleeve 35 are varied. In the experiment, the above-mentioned process speed was set to a predetermined process speed (the peripheral speed of the photosensitive drum 28Y is 513 [mm / sec]) and the peripheral speed of the photosensitive drum 28Y was set to 615.6 [mm / sec], and the entrainment phenomenon was evaluated when the process speed was increased by 20% from the predetermined process speed.

[0117] The operating speed of the entire developing device 1A, including the first developing sleeve 33 and the second developing sleeve 34, when the peripheral speed of the photosensitive drum 28Y is increased is also set to be 20% higher than the operating speed of the entire developing device 1A when the photosensitive drum 28Y is set to a specified process speed. In addition, the symbol "◯" in the tables of Figures 11(a) and (b) indicates that there was no occurrence of the dragging phenomenon, "△" indicates that there were signs of dragging behavior but not visible in the image, and "×" indicates that the dragging phenomenon occurred. In addition, the symbol "◆" indicates that the toner melting phenomenon occurred on the surface of the second developing sleeve 34.

[0118] 11(a) shows the presence or absence of co-rotation when multiple combinations of surface roughness Rz1 of the second developing sleeve 34 and surface roughness Rz2 of the stripping sleeve 35 are used in the configuration of the first embodiment, where the process speed is increased by 20% from a given process speed. The combinations are sleeves whose surfaces have been blasted, with the horizontal axis representing the surface roughness Rz1 of the second developing sleeve 34 and the vertical axis representing the surface roughness Rz2 of the stripping sleeve 35 expressed as a roughness ratio to the surface roughness Rz1 of the second developing sleeve 34. When the stripping sleeve 35 rotates in the forward direction relative to the second developing sleeve 34, the performance of co-rotation is improved when the conveying capacity is increased by the surface shape.

[0119] FIG. 11(b) shows whether or not co-rotation occurs when multiple combinations of conditions for the surface roughness Rz1 of the second developing sleeve 34 and the surface roughness Rz2 of the peeling sleeve 35 are used when the process speed is increased by 20% from a specified process speed in the configuration of this embodiment.

[0120] As shown in FIG. 11(a), when the process speed was increased by 20%, minor dragging occurred when the peeling sleeve 35 rotated in the forward direction under conditions of low conveying capacity. On the other hand, as shown in FIG. 11(b), when the process speed was increased by 20%, dragging was unlikely to occur even under conditions of low conveying capacity surface shape when the peeling sleeve 35 rotated in the reverse direction relative to the second developing sleeve 34. Also, in areas with high conveying capacity, the closest position between the peeling sleeve 35 and the second developing sleeve 34 was more likely to be in the peeling magnetic field area of ​​the second developing magnet 37. Therefore, friction between the developer and the blasted surface was reduced, making it difficult for the fusion phenomenon to occur, and reducing image defects.

[0121] In this manner, in the present embodiment, the arrangement of the peeling roller 32 relative to the second developing roller 31 is optimized, and at the opposing portion where the second developing sleeve 34 and the peeling sleeve 35 face each other, the surface of the peeling sleeve 35 rotates in the opposite direction to the surface of the second developing sleeve 34. This makes it possible to prevent the drag phenomenon from occurring even when the process speed is increased, and a high-quality, high-image-quality image forming device can be provided.

[0122] <Other embodiments> The above-mentioned fourth embodiment is applicable not only to the configuration of the first embodiment but also to the configurations of the second and third embodiments. That is, even if the surfaces of the second developing sleeve 34 and the peeling sleeve 35 are grooved, or even if the surface of one of these sleeves is unevenly shaped by blasting and the surface of the other sleeve is grooved, as in the fourth embodiment, the arrangement of the peeling roller 32 relative to the second developing roller 31 may be optimized and the surface of the peeling sleeve 35 may be configured to rotate in the opposite direction to the surface of the second developing sleeve 34 at the opposing portion where the second developing sleeve 34 and the peeling sleeve 35 face each other.

[0123] In addition, in each of the above-described embodiments, the developing device has been described as having two developing rollers, but the present invention can also be applied to a configuration having only one developing roller. That is, the present invention can also be applied to a configuration having one developing roller for developing an electrostatic latent image on an image carrier such as a photosensitive drum, and a peeling roller for peeling the developed image from the developing roller.

[0124] The present invention is not limited to the configurations of the above-mentioned embodiments. For example, the image forming apparatus 100 is not limited to an MFP, and may be a copier, a printer, or a facsimile machine. In addition, the configurations of the developer supply screw 42, the developer stirring screw 43, and the developer recovery screw 44 are not particularly limited as long as they can transport the developer, and for example, a spiral blade or a paddle-shaped blade can be applied. [Explanation of symbols]

[0125] 1Y, 1M, 1C, 1K... Developing device 28Y, 28M, 28C, 28K...Photosensitive drum (image carrier) 30...First developing roller 31 Second developing roller 32 Peeling roller 33 First developing sleeve 34 Second developing sleeve 35...Peel-off sleeve 36...First developing magnet 37 Second developing magnet 38. Peeling magnet 46 Developer circulation section (supply section) 47 Developer recovery section (recovery section) 100 Image forming apparatus

Claims

1. A first chamber containing the developer, including toner and carrier, A second room separated from the first room by a partition wall, A first roller to which a developer is supplied, the first roller which carries and transports the developer to develop an electrostatic latent image, A first magnet placed inside the first roller, A second roller to which the developer is transferred, the second roller being positioned opposite the first roller, and which collects the developer into the second chamber after the electrostatic latent image has been developed, The device comprises a second magnet disposed within the second roller, Multiple first grooves are formed on the outer circumferential surface of the first roller so as to be aligned in the circumferential direction of the first roller. Multiple second grooves are formed on the outer circumferential surface of the second roller so as to be aligned in the circumferential direction of the second roller. Let d1 be the width of the first groove, N1 be the number of first grooves per circumference of the first roller, L1 be the circumference of the first roller, and ρ1 be the groove ratio of the first grooves, ρ1 = (d1 × N1) / L1. When the width of the second groove is d2, the number of the second grooves per circumference of the second roller is N2, the circumference of the second roller is L2, and the groove ratio ρ2 of the second groove is ρ2 = (d2 × N2) / L2, 0.40 × ρ1 ≤ ρ2 and 0.07 ≤ ρ1 ≤ 0.23 A developing apparatus characterized by satisfying the following conditions.

2. 0.53 × ρ1 ≤ ρ2 The developing apparatus according to claim 1, characterized in that it satisfies the following conditions.

3. 1.00 × ρ1 ≤ ρ2 The developing apparatus according to claim 1, characterized in that it satisfies the following conditions.

4. ρ² ≤ 1.67 × ρ¹ The developing apparatus according to claim 1, characterized in that it satisfies the following conditions.

5. ρ² ≤ 1.60 × ρ¹ The developing apparatus according to claim 1, characterized in that it satisfies the following conditions.

6. The second roller rotates at a faster peripheral speed than the first roller. The developing apparatus according to feature 1.

7. The direction of rotation of the second roller at the position where it faces the first roller is the same as the direction of rotation of the first roller at the position where it faces the second roller. The developing apparatus according to feature 1.

8. The center of rotation of the second roller is located above the center of rotation of the first roller. The developing apparatus according to feature 1.

9. A first transport screw is located in the first chamber and transports the developer contained in the first chamber, The system further comprises a second transport screw located in the second chamber for transporting the developer collected in the second chamber, The rotation center of the second conveyor screw is located above the rotation center of the first conveyor screw. The developing apparatus according to feature 1.

10. A third roller is supplied with the developer contained in the first chamber, and at least a portion of it is positioned opposite the first roller, and the third roller carries and transports the developer to develop the electrostatic latent image, The present invention further comprises a third magnet disposed within the third roller, The direction of rotation of the first roller at the position where the first roller faces the third roller is opposite to the direction of rotation of the third roller at the position where the third roller faces the first roller. The developer is transferred from the third roller to the first roller via the magnetic field generated by the third magnet. The developing apparatus according to feature 1.

11. A first chamber containing the developer, including toner and carrier, A second room separated from the first room by a partition wall, A first roller to which a developer is supplied, the first roller which carries and transports the developer to develop an electrostatic latent image, A first magnet placed inside the first roller, A second roller to which the developer is transferred, the second roller being positioned opposite the first roller, and which collects the developer into the second chamber after the electrostatic latent image has been developed, The device comprises a second magnet disposed within the second roller, Multiple grooves are formed on the outer surface of the first roller so as to be arranged in the circumferential direction of the first roller. The outer surface of the second roller is subjected to a blasting process. Let d be the width of the groove, N be the number of grooves per circumference of the first roller, L be the circumference of the first roller, and ρ be the groove ratio ρ = (d × N) / L. When the average roughness of the outer surface of the second roller is Rz, 0.35 × (67.2703 × ρ + 1.4186) ≤ Rz and 7 μm ≤ (67.2703 × ρ + 1.4186) ≤ 15 μm A developing apparatus characterized by satisfying the following conditions.

12. 0.40 × (67.2703 × ρ + 1.4186) ≤ Rz The developing apparatus according to claim 11, characterized in that it satisfies the following conditions.

13. Rz ≤ 1.20 × (67.2703 × ρ + 1.4186) The developing apparatus according to claim 11, characterized in that it satisfies the following conditions.

14. Rz ≤ 1.00 × (67.2703 × ρ + 1.4186) The developing apparatus according to claim 11, characterized in that it satisfies the following conditions.

15. 0.07 ≤ ρ ≤ 0.23 The developing apparatus according to claim 11, characterized in that it satisfies the following conditions.

16. The second roller rotates at a faster peripheral speed than the first roller. The developing apparatus according to feature 11.

17. The direction of rotation of the second roller at the position where it faces the first roller is the same as the direction of rotation of the first roller at the position where it faces the second roller. The developing apparatus according to feature 11.

18. The center of rotation of the second roller is located above the center of rotation of the first roller. The developing apparatus according to feature 11.

19. A first transport screw is located in the first chamber and transports the developer contained in the first chamber, The system further comprises a second transport screw located in the second chamber for transporting the developer collected in the second chamber, The rotation center of the second conveyor screw is located above the rotation center of the first conveyor screw. The developing apparatus according to feature 11.

20. A third roller is supplied with the developer contained in the first chamber, and at least a portion of it is positioned opposite the first roller, and the third roller carries and transports the developer to develop the electrostatic latent image, The present invention further comprises a third magnet disposed within the third roller, The direction of rotation of the first roller at the position where the first roller faces the third roller is opposite to the direction of rotation of the third roller at the position where the third roller faces the first roller. The developer is transferred from the third roller to the first roller via the magnetic field generated by the third magnet. The developing apparatus according to feature 11.

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