JP2015187689A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that can suppress patchy unevenness in density when the operation of an image forming apparatus is accelerated, a process cartridge, and an image forming apparatus.SOLUTION: There is provided developing devices 22 that each transfer a developer between a plurality of developer carriers arranged opposite to latent image carriers such as photoreceptor drums 20 to develop latent images on the latent image carriers in multiple stages. In the two developer carriers between which a developer is transferred, the developer conveying force of the developer carrier on the side to receive a developer, such as a second developing roller 62 is made larger than the developer conveying force of the developer carrier on the side to transfer the developer, such as a first developing roller 61.

Description

  The present invention relates to a developing device, a process cartridge, and an image forming apparatus.

  Conventionally, the developer is transported to a developing area, which is an area facing the photosensitive member as a latent image carrier, by a developing roller that is a developer bearing member that carries a two-component developer containing toner and a magnetic carrier, and on the photosensitive member. An image forming apparatus including a developing device that develops the latent image is known.

Patent Document 1 describes a multistage developing device that has a first developing roller and a second developing roller, and develops a latent image on a photoreceptor using these developing rollers. The developer supplied to the first developing roller is scraped off by the amount of the developer being regulated by the doctor blade. The developer that has passed through the doctor blade is transported to the development area and develops the latent image on the photoreceptor. The developer that has passed through the development region is delivered to a second development roller located downstream of the first development roller in the direction of movement of the photoreceptor surface. The developer delivered to the second developing roller is conveyed to the developing area and develops the latent image on the photosensitive drum.
By using the developing device having such a configuration, the latent image on the photoconductor can be developed a plurality of times, and a sufficient image density can be obtained even when the photoconductor is speeded up as the speed of the image forming device is increased. It is stated that you can.

  However, when the speed of the photosensitive member is increased and the rotation speed of each developing roller is increased accordingly in order to increase the speed of the further image forming apparatus, there is a problem that uneven image density unevenness occurs.

  SUMMARY An advantage of some aspects of the invention is that it provides a developing device, a process cartridge, and an image forming apparatus that can suppress uneven density unevenness when the speed of the image forming apparatus is increased. That is.

  In order to achieve the above object, the invention of claim 1 develops the latent image on the latent image carrier in multiple stages while delivering the developer between a plurality of developer carriers each facing the latent image carrier. In the two developer carrying bodies to which the developer is transferred, the developer transport force of the developer carrying body on the developer receiving side is set to be equal to that of the developer carrying body on the developer passing side. It is characterized by being higher than the developer conveying force.

  It is possible to suppress uneven density unevenness when the image forming apparatus is speeded up.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. (A) is a block diagram showing an example of the internal configuration of the developing device, (b) is a side view showing the positional relationship of the developer conveying member in the internal configuration of the developing device as viewed from the X direction of (a), (c) ) Is a schematic view for explaining the state of circulation and conveyance of the developer in the developing device. (A) is a block diagram showing another configuration example of the inside of the developing device, (b) is a cross-sectional view showing the configuration of the front end in the longitudinal direction and the end on the back side in the longitudinal direction of the developing device, (d) FIG. 3B is a side view showing the positional relationship of the developer conveying member in the internal configuration of the developing device as viewed from the direction of arrow X in FIG. The figure which shows magnetic flux density distribution of the normal line direction of the 1st developing roller 61 and the 2nd developing roller. The graph which investigated the developer amount per unit area which passed the doctor gap in each doctor gap using the development sleeve from which surface shape mutually differs. The figure which shows an example of the groove | channel formed in the surface of a developing roller. The figure which shows an example of the cross-sectional shape of a groove | channel. FIG. 3 is a cross-sectional view schematically showing the vicinity of a developing region when a surface-shaped developing sleeve provided with a plurality of parallel grooves is used. FIG. 9 is a cross-sectional view schematically showing the vicinity of a development region in a different state from FIG. 8. FIG. 3 is a cross-sectional view schematically showing the vicinity of a development region when a development sleeve having a surface-scale pattern is used. Explanatory drawing which expand | deploys and shows typically the surface of the developing sleeve of a surface scale pattern. (A) is explanatory drawing which expands and shows typically a part of surface of the image development sleeve shown by FIG. 11, (b) is a cross section in alignment with the VIB-VIB line | wire in FIG. 12 (a). (C) is sectional drawing which follows the VIC-VIC line | wire in Fig.12 (a). Explanatory drawing shown about the other example of an elliptical shaped dent. FIG. 4 is an explanatory diagram illustrating an example in which dents formed in the developing sleeve are regularly arranged. Explanatory drawing which shows the other example by which the dent formed in the image development sleeve is regularly arrange | positioned. Explanatory drawing which expands an outer surface and shows typically the modification which formed the dent so that the magnitude | size of planar view of a dent might become large gradually toward the both ends from the rotation-axis direction center part of a developing sleeve. Explanatory drawing which expand | deploys and shows typically the outer surface of the modification formed so that the number of the dents per unit area might increase toward the both ends from the rotation-axis direction center part of a developing sleeve. Explanatory drawing which shows another example in which the dent formed in the image development sleeve is arrange | positioned irregularly. Explanatory drawing which shows another example in which the dent formed in the developing sleeve is irregularly arranged. FIG. 3 is a schematic configuration diagram illustrating another example of an image forming apparatus. FIG. 21 is a cross-sectional view of the developing device of the image forming apparatus shown in FIG. 20. FIG. 22 is a cross-sectional view of a developing roller of the developing device shown in FIG. 21. The perspective view of a 1st image development sleeve. The perspective view of a 2nd developing sleeve.

  FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 1 denotes a tandem intermediate transfer type image forming apparatus main body as an image forming apparatus, and reference numeral 4 denotes a paper feed table in which a sheet-like transfer paper S is accommodated.

  A tandem intermediate transfer image forming unit (hereinafter referred to as a tandem image forming unit) in which a plurality of image forming units 3Y, 3M, 3C, and 3K as image forming units are arranged in parallel inside the image forming apparatus main body 1. 2) is provided. Note that the subscripts Y, M, C, and K attached to the above symbols indicate yellow, magenta, cyan, and black colors, respectively.

  The image forming apparatus main body 1 is provided with an intermediate transfer belt 30 that is an endless belt-shaped intermediate transfer body near the center. The intermediate transfer belt 30 is looped around a plurality of support rollers and can be rotated and conveyed clockwise in the figure.

  On the intermediate transfer belt 30, four image forming units 3Y, 3M, 3C, and 4K of yellow (Y), magenta (M), cyan (C), and black (K) are arranged horizontally along the conveyance direction. The tandem image forming unit 2 is configured by arranging them side by side. The image forming units 3Y, 3M, 3C, and 3K of the tandem image forming unit 2 are photosensitive drums 20Y, 20M, and 20C as image carriers that carry yellow, magenta, cyan, and black toner images. 20K.

  An exposure apparatus 100 is provided on the tandem image forming unit 2 as shown in FIG. As the exposure apparatus 100 as a latent image forming unit, an optical scanning type exposure apparatus can be used. The optical scanning type exposure apparatus includes, for example, four light source devices (semiconductor laser, semiconductor laser array, or multi-beam light source). An optical scanning type exposure apparatus includes a coupling optical system, a common optical deflector (polygon mirror, etc.), four scanning imaging optical systems, and the like. Then, the exposure device 100 exposes the photosensitive drums 20Y, 20M, 20C, and 20K according to the image information of each color of yellow, magenta, cyan, and black, and forms an electrostatic latent image.

  Further, the following devices are provided around the photosensitive drums 20Y, 20M, 20C, and 20K of the image forming units 3Y, 3M, 3C, and 3K. That is, charging devices 23Y, 23M, 23C, and 23K that uniformly charge the photosensitive drums 20Y, 20M, 20C, and 20K prior to the above exposure are provided. Further, developing devices 22Y, 22M, 22C, and 22K that develop the electrostatic latent image formed by the exposure device 100 with toner of each color are provided. Photoreceptor drum cleaning devices 24Y, 24M, 24C, and 24K are provided for removing transfer residual toner on the photoconductor drum 20. Further, primary transfer rollers 25Y, 25M, 25C, and 25K are provided at primary transfer positions where the toner image is transferred from the photosensitive drums 20Y, 20M, 20C, and 20K to the intermediate transfer belt 30. The primary transfer rollers 25Y, 25M, 25C, and 25K are components of the primary transfer device, and are provided so as to face the photosensitive drums 20Y, 20M, 20C, and 20K with the intermediate transfer belt 30 interposed therebetween.

  Of the plurality of support rollers that support the intermediate transfer belt 30, the support roller 26a is a drive roller that rotationally drives the intermediate transfer belt 30, and is connected to the motor via a drive transmission mechanism (gear, pulley, belt, etc.) not shown. Has been. When a black single color image is formed on the intermediate transfer belt 30, the intermediate transfer belt 30 is separated from the yellow, magenta, and cyan photosensitive drums 20Y, 20M, and 20C as follows. That is, the supporting roller 26b other than the supporting roller 26a, the primary transfer rollers 25Y, 25M, and 25C are moved downward by a moving mechanism (not shown).

  A secondary transfer device 31 is provided on the opposite side of the intermediate transfer belt 30 from the tandem image forming unit 2. The secondary transfer device 31 presses the secondary transfer roller 31 a against the secondary transfer counter roller 31 b that is a support roller of the intermediate transfer belt 30 from the front surface side of the intermediate transfer belt 30. A transfer bias is applied between the secondary transfer roller 31a and the secondary transfer counter roller 31b with the intermediate transfer belt 30 interposed therebetween to form a transfer electric field. As a result, the image on the intermediate transfer belt 30 is transferred to a sheet-like transfer sheet S as a transfer medium.

  Also, a fixing device 50 that fixes the image on the transfer paper S to the transfer paper S by pressure or heat on the left side of the secondary transfer device 31 in the drawing and downstream of the secondary transfer device 31 in the transfer paper transport direction. Is provided. The fixing device 50 is configured by pressing a pressure roller 51 against a fixing roller 52. The fixing roller 52 is provided with heating means (not shown) (a heater, a lamp, an electromagnetic induction heating device, or the like).

  The transfer sheet S on which the image is transferred by the secondary transfer device 31 is transported to the fixing device 50 by the transport belt 32 supported by the two rollers 32a and 32b. Of course, the conveyance belt 32 may be a fixed guide member, a conveyance roller, a conveyance roller, or the like.

  When image data is sent to the image forming apparatus main body 1 and an image forming start signal is received, the tandem image forming unit 2 rotates the support roller 26a with a drive motor (not shown) to drive the other plurality of support rollers. Following the rotation, the intermediate transfer belt 30 is rotated in the clockwise direction in the drawing. At the same time, in the image forming units 3Y, 3M, 3C, and 3K, the photosensitive drums 20Y, 20M, 20C, and 20K are rotated counterclockwise by a drive motor (not shown). Then, charging by the charging devices 23Y, 23M, 23C, and 23K and exposure (latent image formation) by the exposure device 100 are performed. Next, a development process using toner of each color of the developing devices 22Y, 22M, 22C, and 22K is performed. As a result, yellow, magenta, cyan, and black monochrome images are formed on the photosensitive drums 20Y, 20M, 20C, and 20K, respectively. Then, along with the conveyance of the intermediate transfer belt 30, the monochrome images are sequentially transferred to the intermediate transfer belt 30 by the primary transfer rollers 25Y, 25M, 26C, and 26K. As a result, a composite color image is formed on the intermediate transfer belt 30.

  On the other hand, in accordance with such an image forming operation, the sheet-like transfer paper S is fed out from the paper feed cassette 4a in the paper feed table 4, guided to the paper feed path 40, and abutted against the registration roller 41 and stopped.

  Then, the registration roller 41 is rotated in accordance with the timing at which the image on the intermediate transfer belt 30 reaches the position of the secondary transfer device 31. As a result, the transfer sheet S is fed between the intermediate transfer belt 30 and the secondary transfer device 31, and the image is transferred from the intermediate transfer belt 30 to the transfer sheet S by the secondary transfer device 31, and the color is transferred onto the transfer sheet S. Record an image.

  After the image is transferred, the transfer sheet S is transported by the transport belt 32 and sent to the fixing device 50. The fixing device 50 applies heat and pressure to fix the image on the transfer sheet S. The transfer sheet S after the image is fixed by the fixing device 50 is discharged out of the device by the discharge roller 42 and stacked on the discharge tray 43.

  On the other hand, on the photosensitive drums 20Y, 20M, 20C, and 20K after image transfer, residual toner remaining on the photosensitive drums 20Y, 20M, 20C, and 20K is removed by the photosensitive drum cleaning devices 24Y, 24M, 24C, and 24K. Is done. Further, after the image is transferred, the residual toner remaining on the intermediate transfer belt 30 is removed by an intermediate transfer belt cleaning device (not shown). After these cleaning steps, the image forming apparatus prepares for another image formation by the tandem type image forming unit 2.

  In addition, toner bottles 10Y, 10M, 10C, and 10K as toner containers that are disposed above the exposure apparatus 100 and filled with toners of yellow, magenta, cyan, and black are disposed. The toner bottles 10Y, 10M, 10C, and 10K are detachably attached to the apparatus main body. The toner of each color of yellow, cyan, magenta, and black in the toner bottles 10Y, 10C, 10M, and 10K is supplied to the developing devices 22Y, Replenished to 22M, 22C, 22K. The toner bottles 10Y, 10M, 10C, and 10K are consumables that are replaced when the toner in the interior runs out, and are removed from the apparatus main body and replaced when the toner runs out.

  In addition, a user operation unit 905 as an operation unit is provided on the upper portion of the image forming apparatus main body 1. The user operation unit 905 is connected to the image forming apparatus main body 1 through an I / F (not shown), and an operation input from the user to the image forming apparatus main body 1 is performed by key input from the user operation unit 905.

  FIG. 2A is a configuration diagram showing an example of the internal configuration of the developing device 22 used in the image forming apparatus according to the present embodiment. 2B is a side view showing the positional relationship of the developer conveying member in the internal configuration of the developing device 22 as viewed from the X direction in FIG. 2A, and FIG. It is a schematic diagram for demonstrating the mode of circulation and conveyance of the developing agent. The configuration and operation of the developing device 22 are the same for the developing devices 22Y, 22M, 22C, and 22K of the respective colors. Therefore, in FIGS. 2A to 2C, the subscripts Y, M, C, and K is abbreviate | omitted and the code | symbol is described (Hereafter, the same also in FIGS. 3-5).

  As shown in FIG. 2A, the developing device 22 includes a case member 67 serving as a developer accommodating member, and includes toner of any one color of black, cyan, yellow, and magenta and a carrier that is magnetic particles. Contains a component developer (hereinafter referred to as a developer). The case member 67 has an opening at a position facing the surface of the photosensitive drum 20 that rotates in the counterclockwise direction in the drawing, and the first development is a developer carrying member that rotates in the clockwise direction in the drawing from the opening. A part of the roller 61 and the second developing roller 62 is exposed. The first developing roller 61 and the second developing roller 62 are accommodated in a case member 67 so as to be rotationally driven so as to be aligned in the vertical direction.

  The first developing roller 61 is a developer carrying member positioned at the most upstream in the surface movement direction of the photosensitive drum 20. Further, the second developing roller 62 is another developer carrying member positioned on the downstream side of the most upstream first developing roller 61. Each of the first developing roller 61 and the second developing roller 62 includes a sleeve that is a non-magnetic cylindrical member that is rotationally driven in a predetermined direction, and a magnet that is fixedly disposed inside the magnet.

  The case member 67 that accommodates the first developing roller 61 and the second developing roller 62 has an opening in the wall on the side facing the photosensitive drum 20, and from each of the peripheral surfaces of the two developing rollers. A part of is exposed.

  A power supply (not shown) for applying a developing bias is connected to the sleeves of the developing rollers 61 and 62. When a developing bias is applied to each of the developing rollers 61 and 62, a developing electric field is formed in a developing region where the surface of the developing roller and the surface of the photosensitive drum 20 face each other. By this developing electric field, the toner in the developer carried on the surface of the developing roller adheres to the electrostatic latent image formed on the photosensitive drum 20 and development is performed.

  The developing device 22 includes a supply screw 63 as a first developer conveying member, a recovery screw 64 as a second developer conveying member, and a stirring as a third developer conveying member in the case member 67. And a screw 65. The supply screw 63, the recovery screw 64, and the stirring screw 65 are disposed in each of a predetermined first space V 1, second space V 2, and third space V 3 provided in the case member 67. The first space V1 in which the supply screw 63 is disposed and the second space V2 in which the recovery screw 64 is disposed serve as a partition member that restricts the flow of the developer between the spaces V1 and V2. The first partition wall 67a is provided. Furthermore, the second space V2 in which the collection screw 64 is disposed and the third space V3 in which the stirring screw 65 is disposed are partitions that restrict the passage of the developer between the spaces V2 and V3. A second partition 67b as a member is provided. Further, the third space V3 in which the stirring screw 65 is disposed and the first space V1 in which the supply screw 63 is disposed are partitions that restrict the passage of the developer between the spaces V3 and V1. A third partition 67c as a member is provided. In the illustrated example, these three partition walls 67 a, 67 b and 67 c are formed integrally with the case member 67.

  These partition walls 67a, 67b, 67c have openings for circulating and conveying the developer among the first space V1, the second space V2, and the third space V3. For example, as illustrated in FIG. 2C, the partition wall 67 a that partitions the first space V <b> 1 and the second space V <b> 2 extends from the first space V <b> 1 to the end on the downstream side in the developer conveyance direction by the supply screw 63. An opening N3 for discharging the developer and transferring it to the second space V2 is provided. Further, the partition wall 67b that divides the second space V2 and the third space V3 discharges the developer from the second space V1 to the downstream end in the developer transport direction by the recovery screw 64, and the third space V3. It has an opening N1 for delivery to the space V3. Further, the partition wall 67c that divides the third space V3 and the first space V1 discharges the developer from the third space V3 to the end on the downstream side in the developer transport direction by the stirring screw 65, and the first space V1. An opening N2 for passing to the space V1 is provided.

  Both ends of the rotation shafts of the screws 63, 64, 65 and the developing rollers 61, 62 are rotatably supported by the case member 67. And it can be rotationally driven in the direction of the arrow in FIG. 2A by a rotational drive means having a drive source and a drive transmission mechanism (not shown). The supply screw 63 stirs and conveys the developer along its own rotation shaft 63 a and supplies the developer to the first developing roller 61. The collection screw 64 agitates and conveys the developer along its own rotation shaft 64 a and collects the developer from the second development roller 62. The agitating screw 65 conveys the developer along its own rotation shaft 65a, and agitates the supplied toner and the existing developer.

  The respective rotation shafts 63 a, 64 a, 65 a of the three screws 63, 64, 65 are provided in parallel to each other with respect to the rotation axis of the photosensitive drum 20. The three screws 63, 64, 65 are, in a vertical relationship, the supply screw 63 on the upper side, the recovery screw 64 on the lower side, and the stirring screw 65 at a position approximately halfway between the screw 63 and the screw 64. Is arranged. Further, these three screws 63, 64, 65 are rotated by a driving force from a driving source (not shown) to stir and convey the developer in the case member 67. As a result, the developer in the case member 67 is circulated and conveyed as indicated by arrows S1, S2, S3, S4, S5, and S6 in the figure.

  As shown in FIG. 2A, the supply screw 63 supplies the developer to the first developing roller 61 while stirring and conveying the developer. The first developing roller 61 that rotates clockwise in the drawing forms a magnetic brush by holding the developer supplied from the supply screw 63 by a magnetic force. The doctor blade 66 regulates the height of the magnetic brush formed on the first developing roller 61 and returns the regulated developer to the supply screw 63. As shown in FIG. 2 (c), the developer stirred and conveyed to the downstream position (left side in the figure) of the supply screw 63 without being supplied to the first developing roller 61 is the developer. It is discharged from the opening N3 as a delivery part and falls around the end of the recovery screw 64.

  As the first developing roller 61 rotates, the developer that has been transported to the first developing area where the first developing roller 61 and the photosensitive drum 20 face each other and contributed to the development is disposed below the first developing roller 61. It is delivered to a second developing roller 62 as a receiving side developer carrier. Thereafter, with the rotation of the second developing roller 62, the second developing roller 62 and the photosensitive drum 20 are sent to the second developing region facing each other, and contribute to the development again here. The developer that has completed the second development step is recovered from the second developing roller 62 by stirring and transporting the recovery screw 64, and the downstream position of the recovery screw 64 in the developer transport direction (left side in FIG. 2C). It is conveyed to. The developer transported to a position downstream of the recovery screw 64 in the developer transport direction moves to the stirring screw 65 obliquely upward through the opening N1 due to a certain amount of stay. The moved developer is conveyed to the downstream position in the conveyance direction (the right side in FIG. 2C) by the agitating and conveying of the agitating screw 65 together with the toner replenished from the replenishing port N4. The developer agitating and conveying by the agitating screw 65 is performed by partition walls 67b and 67c provided in the width of the image area where the photosensitive drum 20 forms a latent image so as not to be mixed with the developer agitating and conveying other screws. This is done in a blocked state.

  FIG. 3A is a configuration diagram showing another configuration example of the inside of the developing device 22 used in the image forming apparatus according to the present embodiment. FIG. 3B is a cross-sectional view illustrating the configuration of the front end portion in the longitudinal direction and the rear end portion in the longitudinal direction of the developing device 22. FIG. 3D is a side view showing the positional relationship of the developer conveying member in the internal configuration of the developing device 22 as viewed from the direction of the arrow X in FIG. 3 (a) to 3 (d), parts similar to those in FIG.

  In the developing device 22 shown in FIG. 3, at least one of the plurality of screws (stirring screw) 68 has an end on the downstream side of the upstream end of the rotating shaft 68a in the developer transport direction. It is installed at a high position. Further, the developer is stirred and conveyed by being blocked by the partition wall 69 so that the developer stirred and conveyed by the other supply screw 63 and the recovery screw 64 is not mixed.

  The developer having a reduced toner concentration used for development in the first and second development areas is collected by agitating and conveying the collecting screw 64 and conveyed downstream of the collecting screw 64 in the developer conveying direction. The developer conveyed to the downstream side in the developer conveying direction of the collection screw 64 is retained at the downstream position, and thus the upstream end of the stirring screw 68 in the developer conveying direction on the side passing through the opening N1 ( Move to the left side in FIG. The developer that has moved to the upstream end of the agitating screw 68 in the developer conveying direction is agitated and conveyed by the agitating screw 68 together with the toner replenished from the replenishing port N4, and the downstream end of the developer conveying direction (FIG. 3D). ) Is transported around the right side). The developer transported to the downstream end portion of the stirring screw 68 in the developer transport direction moves to the upstream side in the developer transport direction of the supply screw 63 located on the side through the opening N2 by staying at that position. The developer moved to the supply screw 63 is supplied to the first developing roller 61.

  The developing device 22 described above employs a system in which the supply screw 63 and the collection screw 64 are arranged one above the other, and the developer is circulated and conveyed in one direction so as to separately supply and collect the developer. Such a one-way circulation type developing device 22 tends to have a uniform toner density along the longitudinal direction of the first developing roller 61, and is useful for realizing high image quality.

FIG. 4 is a diagram showing the magnetic flux density distribution in the normal direction of the first developing roller 61 and the second developing roller.
As shown in FIG. 4, five magnetic poles N1, S1, N2, S2, and S3 are arranged in the sleeve of the first developing roller 61 along the surface movement direction of the first developing roller. The magnetic pole N1 is a development magnetic pole that generates a development magnetic force for causing the developer carried on the surface of the first development roller 61 to rise in the first development region. The magnetic pole S <b> 2 is a pumping magnetic pole that generates a magnetic force for pumping up the developer in the first space V <b> 1 in which the supply screw 63 is disposed on the surface of the first developing roller 61. The magnetic pole N2 is a restriction that generates a restriction magnetic force for causing the developer to rise when passing through a restriction gap formed between the surface of the first developing roller 61 and a doctor blade 66 as a developer restriction member. It is a magnetic pole. The magnetic pole S3 is a transport magnetic pole that generates a magnetic force for transporting the developer carried on the surface of the first developing roller 61 to the developing region. The magnetic pole S <b> 1 is a delivery magnetic pole that forms a repulsive magnetic field in cooperation with the magnetic pole S <b> 2 and generates a magnetic force for peeling the developer from the surface of the first developing roller 61 and passing it to the second developing roller 62. .

  Also in the sleeve of the second developing roller 62, five magnetic poles S1, N1, S2, S3, N2 are arranged along the surface moving direction of the second developing roller 62. The magnetic pole S1 is a development magnetic pole that generates a development magnetic force for causing the developer carried on the surface of the second development roller 62 to rise in the second development region. The magnetic pole N1 is a transport magnetic pole that generates a magnetic force for transporting the developer carried on the surface of the second developing roller 62 to the second space V2 in which the recovery screw 64 is disposed. The magnetic poles S2 and S3 cooperate with each other to form a repulsive magnetic field so that the developer is peeled off from the surface of the second developing roller 62 and collected in the second space V2 in which the collecting screw 64 is disposed. It is a recovery magnetic pole. The magnetic pole N <b> 2 is a receiving magnetic pole that generates a magnetic force for receiving the developer from the first developing roller 61.

  In the present embodiment, as shown in FIG. 4, the polarity of the transfer magnetic pole S <b> 1 that transfers the developer of the first developing roller 61 to the second developing roller, and the developer of the first developing roller 61 of the second developing roller 62. The receiving magnetic poles N2 receiving the magnetic poles have different polarities. With this configuration, the developer delivered from the first developing roller 61 to the second developing roller 62 is held by the magnetic force between the delivery magnetic pole S1 and the reception magnetic pole N1. As a result, even if the rotation speed of each of the developing rollers 61 and 62 is increased along with the increase in the speed of the image forming apparatus, the developer carried on the first developing roller 61 is on the downstream side of the transfer unit U due to the momentum of conveyance. It can suppress moving to. As a result, the developer can be successfully delivered at the delivery unit U.

  However, if the rotation speed of the developing rollers 61 and 62 is further increased to further increase the speed of the image forming apparatus, the magnetic force cannot be fully constrained, and a part of the developer on the first developing roller 61 can be obtained. Moves to the downstream side of the transfer section U with the momentum of conveyance. Then, it is separated from the first developing roller 61 on the downstream side of the transfer unit U and is transferred to the second developing roller 62. As described above, the developer delivered downstream of the delivery unit U is conveyed to the delivery unit U by the second developing roller 62. As a result, in the delivery unit U, since the developer delivered downstream of the delivery unit U is added to the developer delivered in the delivery unit U, the developer in the delivery unit becomes excessive, and the delivery is performed. The developer stays in the portion U. Then, a part of the staying developer is influenced by the developing magnetic pole N1 of the first developing roller 61, and is separated from the second developing roller 62 toward the first developing roller 61 as indicated by an arrow X in the figure. A flow like this occurs. As a result, the developer amount of the second developing roller 62 in the portion where such a flow occurs is reduced, the developing ability of the portion is lowered, and the image density is lowered. The flow in which the developer moves away from the second developing roller 62 toward the first developing roller 61 at the transfer unit U is randomly generated in the axial direction of the second developing roller 62 and disappears after a predetermined time has elapsed. As a result, there was a problem that spotted density unevenness occurred in the image. Such a problem did not occur at the rotational speed of each developing roller corresponding to the linear speed of 440 mm / s of the photosensitive drum 20, but the rotational speed of each developing roller corresponding to the linear speed of 630 mm / s of the photosensitive drum 20 ( (Linear speed: 915 mm / s).

  In order to suppress such problems, the magnetic force of the transfer magnetic pole S1 of the first developing roller 61 and the receiving magnetic pole N2 of the second developing roller 62 is increased, and the magnetic force acting on the developer at the transfer unit U is increased to increase the magnetic force. It is conceivable to increase the binding force. However, when the magnetic force of the receiving magnetic pole N2 of the second developing roller 62 is increased, the magnetic force of the receiving magnetic pole N2 affects the repulsive magnetic field formed to the opposite side and the magnetic poles S2 and S3. As a result, a problem occurs when the developer does not leave the developer from the second developing roller 62 well.

  Therefore, in the present embodiment, the developer conveying force of the second developing roller 62 is set higher than the developer conveying force of the first developing roller 61. Here, the developer conveying force is a developer conveying amount per unit area, and can be measured by measuring the amount of developer passing through the doctor blade 66. In the measurement, the same magnet, doctor blade, developer, etc. are used in the developing roller, and only the sleeve on the developing roller surface is replaced. By making the surface shape of the second developing roller 62 and the surface shape of the first developing roller 61 different from each other, the developer conveying force (the developer conveying amount per unit surface area) of the second developing roller 62 is changed to the first. The conveying force of the developing roller 61 can be made higher.

FIG. 5 is a graph showing the amount of developer per unit area passing through the doctor gap in each doctor gap using the developing sleeve A and the developing sleeve B having different surface shapes. In the graph, the measurement result of the developing sleeve A is indicated by a one-dot chain line, and the measurement result example of the developing sleeve B is indicated by a dotted line. As shown in the figure, the developing sleeve A has a larger amount of developer passing than the developing sleeve B. Therefore, in this case, it can be determined that the developing sleeve A has a higher developer conveying force. Note that the developer conveying force need not be measured at each doctor gap, but may be measured at the target doctor gap. In this way, by making the surface shape of the first developing roller 61 and the surface shape of the second developing roller 62 different from each other, the developer conveying force of the second developing roller 62 is made larger than the conveying force of the first developing roller 61. It can be seen that it can be higher. In the present embodiment, the first developing roller 61 has a developer passing amount per unit area of about 30 mg / cm ² when the doctor gap is 0.5 mm, and the developer passing amount per unit area of the second developing roller 62. About 38 mg / cm ² .

The developer conveying force due to the surface shape of the second developing roller 62 can be increased as compared with the first developing roller 61 as follows.
(1) Periodic grooves are provided by machining or extrusion, and the number of grooves of the second developing roller 62 is increased or the groove depth is made deeper than that of the first developing roller 61.
(2) A periodic groove is provided only on the second developing roller 62, and no groove is provided on the surface of the first developing roller 61.
(3) The surface of the second developing roller 62 is sandblasted to make the surface rougher than the first developing roller 61.
(4) The number of grooves of the second developing roller 62 is increased or the groove depth is increased as compared with the first developing roller 61, and the surface roughness of the second developing roller 62 is set to be higher than that of the first developing roller 61. Make it rough.
The above-described (1) to (4) are examples, and the configuration in which the developer conveying force of the second developing roller 62 is higher than that of the first developing roller 61 is limited to the above (1) to (4). I can't.

  As shown in (1) above, by increasing the number of grooves or increasing the depth of the groove, the developer can be easily caught on the surface of the developing roller, and the developer conveying force can be increased. Further, as shown in the above (3), when the surface is rough, the developer is easily caught on the irregularities on the surface of the developing roller 61, and the developer conveying force can be increased.

  As the surface shape of each developing roller, a shape in which a plurality of parallel grooves parallel to the rotation axis direction are provided as shown in FIG. 6A, or a groove as shown in FIG. 6B is inclined in the rotation axis direction. They may be crossed to create a pattern on the surface. Moreover, as shown in FIG.6 (c), many ellipse-shaped dents may be provided and the surface may be made into a scale pattern. Further, as the cross-sectional shape of the groove, for example, a V shape as shown in FIG. 7A, a square shape as shown in FIG. 7B, an arc shape as shown in FIG. be able to.

  Thus, by making the developer conveying force of the second developing roller 62 higher than the conveying force of the first developing roller 61, the conveying force of the second developing roller 62 becomes dominant in the transfer unit U. As a result, the developer conveying force on the first developing roller 61 that has been conveyed to the delivery unit U can be weakened by the developer conveying force of the second developing roller 62. Thereby, it is possible to suppress the developer on the first developing roller 61 from moving to the downstream side of the delivery unit U. As a result, it is possible to suppress the developer from staying in the transfer unit U, and it is possible to suppress the flow that returns to the first developing roller 61 from the transfer unit U. As a result, it is possible to suppress the occurrence of a portion where the developer amount is less than the specified amount on the second developing roller 62, and the latent image on the photosensitive drum can be developed uniformly in the axial direction. Therefore, it is possible to suppress the occurrence of patchy density unevenness in the image.

  Even when the transfer paper S is a thick paper, if image formation is performed at high speed, the fixing property is deteriorated and a good image cannot be formed. For this reason, in this embodiment, when image formation is performed on thick paper, the image formation speed is reduced. By reducing the image forming speed, it is possible to slow the transport speed of cardboard and to weaken the impact when entering the secondary transfer nip. Thereby, it is possible to suppress sudden speed fluctuations in the intermediate transfer belt, and to suppress shock jitter. In addition, a sufficient amount of heat can be applied to the image on the cardboard, and the image can be satisfactorily fixed on the cardboard. In the present embodiment, the linear velocity of the photosensitive drum during thick paper is 380 mm / s. On the other hand, the linear velocity of the photosensitive member other than thick paper is 630 mm / s.

  In the case of thick paper, the linear velocity of the photosensitive drum 20 is decreased to decrease the linear velocity of the developing rollers 61 and 62 accordingly. The developer separated from the second developing roller 62 is pushed by the subsequent developer, and flows into the second space V2 in which the recovery screw 64 is disposed. However, when the paper is thick, if the linear velocity of the second developing roller 62 is decreased, this pushing becomes weaker. As a result, the developer separated from the second developing roller may remain in the vicinity of the gap Y between the second developing roller 62 and the case member 67 (the circled portion in FIG. 4). As a result, the developer remaining in the vicinity of the gap Y may be scattered due to an increase in internal pressure in the developing device. However, in the present embodiment, since the developer conveying force of the second developing roller 62 is increased, the developer separated from the second developing roller 62 even if the linear speed of the second developing roller 62 is low, It can be pushed in well. as a result. The developer separated from the second developing roller 62 can be satisfactorily poured into the second space V2 in which the recovery screw 64 is disposed, and the developer is placed near the gap Y shown in FIG. It can suppress staying. Thereby, toner scattering at a low speed can be suppressed.

  Table 1 shows various conditions of the developing rollers 61 and 62 of the present embodiment.

  By setting as shown in Table 1, the latent image can be developed satisfactorily and a good image can be obtained both when the low-speed image is formed on thick paper and when the other high-speed image is formed. The surface shape of each developing roller is a shape in which a plurality of parallel grooves parallel to the rotation axis direction shown in FIG.

Next, a verification test conducted by the applicant will be described.
The present applicant performed image evaluation by using four developing sleeves having different groove depths as developing sleeves of the second developing roller 62. The test was performed under the same conditions as in Table 1 except for the groove depth. The test was performed during high-speed image formation (photosensitive drum linear velocity: 630 mm / s, developing roller 61, 62 linear velocity: 915 mm / s). The results are shown in Table 2.

The developer transport amount shown in Table 2 is the developer transport amount that has passed through the doctor blade when the doctor gap is 0.5 mm.
As shown in Table 2, in Comparative Examples 1 and 2 in which the developer conveying force of the second developing roller 62 is equal to or less than that of the first developing roller 61, patchy image density unevenness (moya image) occurred. On the other hand, in Example 1 and Example 2 in which the developer conveying force of the second developing roller 62 is higher than that of the first developing roller 61, the uneven image density unevenness (moya image) could be suppressed to an allowable level. . In particular, in Example 2 in which the developer conveyance amount was 8 mg / cm ² or more larger than that of the first developing roller, generation of a haze image could not be confirmed, and a good image could be obtained.

In the above description, the embodiment has been described in which the developer conveying force of the second developing roller is higher than the developer conveying force of the first developing roller depending on the depth of the groove. An example is as follows.
・ Diameter of each developing roller: φ20mm
・ Surface shape of each developing roller: parallel groove (FIG. 6A)
・ Cross sectional shape of each developing roller: V shape (Fig. 7)
-Groove depth of each developing roller: 0.1 mm,
・ V-shaped angle of each developing roller: 90 °
Under the above conditions, by setting the number of grooves of the first developing roller 61 to 60 and the number of grooves of the second developing roller 62 to 90, uneven image density unevenness (money image) or the like is formed during high-speed image formation. A good image without image abnormality can be obtained.

  An example of a configuration that suppresses the occurrence of spotted image density unevenness (smooth image) by the surface roughness of each developing roller is as follows. When the diameter of each developing roller 61, 62 is φ25 mm, the surface of the first developing roller 61 Roughness: 1.4 μm, surface roughness of the second developing roller: 3.7 μm. By obtaining the relationship between the surface roughness of the first and second developing rollers as described above, a good image free from image abnormalities such as spotted image density unevenness (moya image) can be obtained during high-speed image formation. Can do. Note that the surface roughness can be controlled by sand type and spraying conditions to be sprayed on the surface of the developing roller when performing sandblasting. The surface roughness is a roughness evaluation based on JIS B0601 and JIS B0031.

As the surface shape of the developing roller, a scale pattern provided with a large number of oval-shaped recesses as shown in FIG.
8 and 9 are cross-sectional views schematically showing the vicinity of the developing region D when the surface-shaped developing sleeve 200a provided with a plurality of parallel grooves 202a parallel to the rotation axis direction shown in FIG. 6A is used. FIG. FIG. 10 is a cross-sectional view schematically showing the vicinity of the development region D when using a development sleeve 200b having a surface scale pattern having a plurality of elliptical recesses 202b.
Usually, the developing sleeve is driven to rotate at a surface speed 1.1 to 2.5 times that of the photosensitive drum 20. When the developer 203 passes through the development area D at high speed, friction with the relatively low-speed photosensitive drum 20 becomes load resistance. When a portion of the developing sleeve 200a where the parallel groove 202a is not provided reaches the developing region D, the developer 203 carried on the portion where the parallel groove 202a is not provided is caused to develop the developer sleeve 200a by the load resistance. Slip against the surface of the. For this reason, as shown in FIG. 8, in the developing region D, the amount of developer on the downstream side is smaller than that on the upstream side in the photosensitive drum surface movement direction. As a result, the developing ability is lowered, and the image density may be reduced.

  On the other hand, when the portion where the parallel groove 202a is formed reaches the developing region D, the developer 203 is caught by the parallel groove 202a and does not slip with respect to the developing sleeve 200a in the developing region D. As a result, as shown in FIG. 9, the developer 203 comes into contact with the photoconductor 20 in the entire development region D, and good development can be performed.

  Since the phenomenon shown in FIGS. 8 and 9 occurs alternately due to the surface movement of the developing sleeve 202a, when the developing sleeve 200a having a plurality of parallel grooves 202a is used, image density unevenness corresponding to the pitch of the parallel grooves 202a is used. May occur.

  On the other hand, in the development sleeve 200b having the surface-scale pattern, the oval recesses 202b are formed at very short intervals in the surface movement direction (circumferential direction) of the development sleeve. Therefore, even if a frictional resistance with the photosensitive drum 20 is generated, the developer 203 is restrained from being caught and slipped by the elliptical recess 202b. As a result, as shown in FIG. 10, deviation in the developer amount is suppressed in the development region D, and the developer 203 can be brought into contact with the photosensitive drum 20 in the entire development region D, which is favorable. Development can be performed.

  In addition, in the case of the developing sleeve 200a provided with a plurality of parallel grooves 202a, the developer conveyance amount at a place where there is no groove between the parallel grooves is lower than at a place where the parallel groove 202a is provided. As a result, a deviation in the developer conveyance amount occurs in the circumferential direction of the developing sleeve 200a. On the other hand, in the development sleeve 200b having the surface scale pattern, since the oval dents are formed at very short intervals in the circumferential direction of the development sleeve, there is a merit that a deviation in the developer conveyance amount is less likely to occur in the circumferential direction. There is also.

FIG. 11 is an explanatory view schematically showing a developed surface of the development sleeve 200b having a surface scale pattern. FIG. 12A is an explanatory diagram schematically showing a part of the surface of the developing sleeve 200b shown in FIG. 11, and FIG. 12B is a diagram illustrating VIB- in FIG. It is sectional drawing which follows a VIB line, (c) is sectional drawing which follows the VIC-VIC line in Fig.12 (a). 11 and 12A, the left-right direction in the figure is the rotation axis direction of the developing sleeve, and the up-down direction in the figure is the circumferential direction.
As shown in FIG. 11, a plurality of elliptical recesses 202b formed on the surface of the developing sleeve are arranged side by side along the rotation axis direction of the developing sleeve 200b. Further, the developing sleeves adjacent to each other in the circumferential direction are arranged so as to be displaced in the rotation axis direction by about half of the length of the recess 202b.

  The recess 202b is arranged in a state where the longitudinal direction thereof is slightly inclined (hereinafter referred to as substantially parallel) with respect to the rotation axis direction of the developing sleeve. The recess 202b may be arranged in parallel to the rotation axis direction of the developing sleeve.

  In addition, as shown in FIG. 11 (b), the recess 202b has a V-shaped cross section in the short direction, and a curved surface having a circular cross section in the long direction as shown in FIG. 11 (c). Is formed. Depending on the method of manufacturing the recess 202b, as shown in FIG. 13, the longitudinal direction may be slightly curved in a bow shape, but the length is longer than the width and the outer edge is curved. Thus, even if the longitudinal direction is a straight line or slightly curved, it is generally an elliptical shape.

The length (major axis) in the longitudinal direction of the recess 202b is preferably 1.0 mm or more and 2.3 mm or less, and the lateral direction (minor axis) is preferably 0.3 mm or more and 0.7 mm or less. Further, the depth of the recess 202b is preferably 0.05 mm or more and 0.15 mm or less. Furthermore, it is preferable to provide about 50 to 250 recesses 202b per 100 mm ² of the outer surface of the developing sleeve 202b. That is, the total capacity of the plurality (large number) of recesses 202b is preferably 0.5 mm ³ or more and 7.0 mm ³ or less per 100 mm ² of the outer surface of the developing sleeve 202b. Furthermore, it is preferable to provide 1.0 or more and 3.0 or less recesses 202b per mm in the circumferential direction of the photosensitive drum 20 that rotates together with the developing sleeve 200b.

Generally, the developer conveyance performance improves as the depth of the recess 202b increases, but periodic pitch unevenness is likely to occur as in the case of the developing sleeve provided with a plurality of parallel grooves. On the other hand, as the depth of the dent 202b is shallower, pitch unevenness is less likely to occur, but the developer transport performance decreases. Particularly in recent years, the image reproducibility has been improved due to the progress of image forming technology for small particle size toner and magnetic carrier and the image forming technology for proximity development. For this reason, as described above, the depth of the dent 202b is set as shallow as 0.05 mm or more and 0.15 mm or less, and about 50 to 250 dents 202b are provided per 100 mm ² of the outer surface of the developing sleeve 202b. It is preferable to increase the distribution density of the recesses 202b. Thereby, it is possible to achieve both of the developer conveyance performance and the prevention of pitch unevenness.

  Further, as shown in FIG. 11 above, as an aspect in which the recesses are regularly arranged so that the interval between the recesses 202b adjacent to each other in the circumferential direction and the rotation axis direction of the developing sleeve 202b is constant, The following aspects can be mentioned. For example, as shown in FIG. 14, the recesses 202b are arranged in two rows in a spiral shape in the circumferential direction, and the first row and the second row have the same pitch in the circumferential direction. A mode in which 202b is arranged in the direction of the rotation axis is mentioned. Further, as shown in FIG. 15, the recesses 202b are arranged in two rows in a spiral shape in the circumferential direction, and the first row and the second row have the same pitch in the circumferential direction, and the recesses 202b in each row are arranged. There can be mentioned a mode in which they are shifted in the circumferential direction so as not to be aligned in the rotation axis direction. Further, the arrangement of the recesses 202b may be three rows or more in a spiral shape.

  Further, the interval between the recesses 202b adjacent to each other in the circumferential direction and the rotation axis direction is not constant and may be irregularly arranged. Examples of the irregular arrangement of the recesses 202b include the following modes. For example, as shown in FIG. 16 and FIG. 17, the aspect which makes the space | interval of the circumferential direction of the dent 202b narrow from the center of a rotating shaft direction toward an edge part can be mentioned. In FIG. 16, the length in the short direction of the recess 202b is increased from the center of the developing sleeve 202b toward the end, and the circumferential interval of the recess 202b is changed from the center to the end of the rotation axis. It is the aspect narrowed toward. In FIG. 17, the size of each recess 202b is the same, the number of recesses 202b per unit area is increased from the central portion in the direction of the rotation axis toward both ends, and from the center to the end in the direction of the rotation axis. This is a mode in which the circumferential interval between the recesses 202b is narrowed.

  In addition, as shown in FIG. 18, the recesses 202b are arranged in two rows of spirals in the circumferential direction, and the pitches in the circumferential direction of the first row and the second row are made different (for example, the pitch in the first row). P1> second row pitch P2). And the aspect which aligned the dent 202b to the rotating shaft direction at a certain position of the circumferential direction can also be mentioned. Further, as shown in FIG. 19, the recesses 202b are arranged in two rows of spirals in the circumferential direction, and the pitches in the circumferential direction of the first row and the second row are made different (for example, the pitch in the first row). P1> second row pitch P2). And the aspect arrange | positioned so that the dent 202b may not align with the rotating shaft direction can be mentioned at any position in the circumferential direction.

Next, another example of the image forming apparatus to which the present invention is applied will be described.
FIG. 20 is a schematic configuration diagram illustrating another example of the image forming apparatus.
As shown in FIG. 20, an image forming apparatus 101 of another example includes an apparatus main body 102 (only part of which is shown in FIG. 20), a registration roller 103, a transfer member 104, a fixing device 105, and laser writing (not shown). An apparatus and at least a process cartridge 106 are provided.

  The apparatus main body 102 is formed in a box shape, for example, and is installed on a floor or the like. The apparatus main body 102 accommodates a registration roller 103, a transfer member 104, a fixing device 105, a laser writing device, and a process cartridge 106. The registration roller 103 feeds the recording paper 107 between the transfer member 104 and a photosensitive drum 108 described later. The transfer member 104 presses the recording paper 107 as a transfer material against the outer peripheral surface of the photosensitive drum 108 and sends the recording paper 107 toward the fixing device 105. The fixing device 105 fixes the toner image formed on the photosensitive drum 108 or the like to the recording paper 107. The laser writing device irradiates the outer peripheral surface of the photosensitive drum 108 uniformly charged by a charging roller 109 described later with a laser beam 110 to form an electrostatic latent image.

  The process cartridge 106 is detachable from the apparatus main body 102. The process cartridge 106 includes a cartridge case 111, a charging roller 109 as a charging device, a photosensitive drum 108 as an image carrier, a cleaning blade 112 as a cleaning device, and a developing device 113. Therefore, the image forming apparatus 101 includes at least a charging roller 109, a photosensitive drum 108, a cleaning blade 112, and a developing device 113.

  The cartridge case 111 is detachable from the apparatus main body 102 and accommodates a charging roller 109, a photosensitive drum 108 as a photosensitive member, a cleaning blade 112, and a developing device 113. The charging roller 109 uniformly charges the outer peripheral surface of the photosensitive drum 108. The photosensitive drum 108 is formed in a columnar shape or a cylindrical shape that is rotatable around an axis. The photosensitive drum 108 transfers a toner image obtained by developing the electrostatic latent image formed and carried by the laser writing apparatus and developing the toner onto a recording paper 107 positioned between the transfer member 104. . The cleaning blade 112 removes the transfer residual toner remaining on the outer peripheral surface of the photosensitive drum 108 after the toner image is transferred to the recording paper 107.

  As shown in FIGS. 20 and 21, the developing device 113 includes a developer supply unit 114, a case 119, a doctor blade 116 as a regulating member, a plurality of developing rollers 115, and an interlocking rotating unit as an interlocking rotating unit. 120 (shown in FIG. 21). The developer supply unit 114 includes a storage tank 117 and a stirring screw 118 as a stirring member. The storage tank 117 is formed in a box shape having a length substantially equal to that of the photosensitive drum 108.

  The storage tank 117 stores the developer. The developer contains toner and a magnetic carrier. The toner is appropriately supplied into the storage tank 117 described above. The toner is spherical fine particles produced by an emulsion polymerization method or a suspension polymerization method. The toner may be obtained by pulverizing a lump composed of a synthetic resin in which various dyes or pigments are mixed and dispersed. The average particle diameter of the toner is 3 μm or more and 7 μm or less. The toner may be formed by pulverization or the like.

  The magnetic carrier 135 is accommodated in the storage tank 117. The average particle diameter of the magnetic carrier 135 is 20 μm or more and 50 μm or less. The magnetic carrier 135 includes a core material 136, a resin coat film 137 covering the outer surface of the core material 136, and alumina particles 138 dispersed in the resin coat film 137.

  The core 136 is made of ferrite as a magnetic material and is formed in a spherical shape. The resin coat film 137 covers the entire outer surface of the core material 136. The resin coat film 137 contains a resin component obtained by crosslinking a thermoplastic resin such as acrylic and a melamine resin, and a charge adjusting agent. This resin coat film 137 has elasticity and strong adhesive force. The alumina particles 138 are formed in a spherical shape whose outer diameter is larger than the thickness of the resin coat film 137. The alumina particles 138 are held with a strong adhesive force of the resin coat film 137. The alumina particles 138 protrude from the resin coat film 137 to the outer peripheral side of the magnetic carrier 135.

  The stirring screw 118 is housed in the housing tank 117. The longitudinal direction of the stirring screw 118 is parallel to the longitudinal directions of the storage tank 117, the developing roller 115, and the photosensitive drum 108. The agitating screw 118 is provided so as to be rotatable around an axis, and rotates around the axis to agitate the toner and the magnetic carrier 135 and convey the developer along the axis.

  According to the configuration described above, the developer supply unit 114 conveys the toner supplied into the storage tank 117 in the axial direction while stirring with the magnetic carrier 135. The developer supply unit 114 agitates the toner and the magnetic carrier 135 in the storage tank 117 and supplies the toner and the magnetic carrier 135 to the outer surface of a first developing roller 115a described later while being conveyed in the axial direction.

  The case 119 is formed in a box shape, is attached to the storage tank 117 of the developer supply unit 114 described above, and covers the plurality of development rollers 115 and the like together with the storage tank 117. In addition, an opening is provided in a portion of the case 119 facing the photosensitive drum 108.

  The doctor blade 116 is attached in the vicinity of the opening of the case 119 near the photosensitive drum 108. The doctor blade 116 is attached to the case 119 described above with a space from the outer surface of the developing sleeve 132 of the first developing roller 115a. The doctor blade 116 scrapes the developer on the outer surface of the developing sleeve 132 of the first developing roller 115a, which exceeds the desired thickness, into the storage tank 117 and transports the developing sleeve 132a to the developing region 131. The developer on the outer surface is made to the desired thickness.

  The first developing roller 115a and the second developing roller 115b are disposed with a space from the photosensitive drum 108, respectively. The developing rollers 115a and 115b are arranged in parallel to each other. The axis of each of the developing rollers 115a and 115b is parallel to the axis of the photosensitive drum 108 and the longitudinal direction of the storage tank 117 described above. These two developing rollers 115a and 115b are juxtaposed in the vertical direction in the illustrated example.

  The space between each of the developing rollers 115a and 115b and the photosensitive drum 108 is a developing area in which the toner of the developer adheres to the outer peripheral surface of the photosensitive drum 108 and the electrostatic latent image is developed to obtain a toner image. 131. In the developing area 131, the developing rollers 115a and 115b and the photosensitive drum 108 face each other.

  As shown in FIGS. 21 and 22, each of the developing rollers 115a and 115b includes a cored bar 134, a cylindrical magnet roller (also referred to as a magnet body) 133, and the above-described cylindrical developing sleeve 132. . The cored bar 134 is arranged in parallel with the longitudinal direction of the photosensitive drum 108 and is fixed to the case 119 without rotating.

  The magnet roller 133 is made of a magnetic material, is formed in a cylindrical shape, and is attached with a plurality of fixed magnetic poles (not shown). The magnet roller 133 is fixed to the outer periphery of the core bar 134 without rotating around the axis.

  The fixed magnetic pole is a long and rod-shaped magnet, and is attached to the magnet roller 133. The fixed magnetic pole extends along the longitudinal direction of the magnet roller 133, that is, the developing roller 115, and is provided over the entire length of the magnet roller 133. The magnet roller 133 having the above-described configuration is accommodated (enclosed) in the developing sleeve 132.

  One fixed magnetic pole attached to the magnet roller 133 of the first developing roller 115a positioned above in FIG. 21 is opposed to the agitating screw 118 described above. This one fixed magnetic pole serves as a pumping magnetic pole, and generates a magnetic force on the outer surface of the first developing sleeve 132a, that is, the first developing roller 115a, so that the developer in the storage tank 117 is transferred to the first developing roller 115a. Adsorb to the outer surface of the first developing sleeve 132a.

  Another fixed magnetic pole attached to the magnet roller 133 of the first developing roller 115a is opposed to the above-described photosensitive drum 108. The fixed magnetic pole forms a developing magnetic pole, and generates a magnetic force on the outer surface of the first developing sleeve 132a, that is, the first developing roller 115a, so that a magnetic field is generated between the first developing sleeve 132a and the photosensitive drum 108. Form. The fixed magnetic pole forms a magnetic brush by a magnetic field, so that the developer toner adsorbed on the outer surface of the first developing sleeve 132a is delivered to the photosensitive drum 108.

  One fixed magnetic pole attached to the magnet roller 133 of the second developing roller 115b located at the lower side in FIG. 21 is opposed to the above-described photosensitive drum 108. The fixed magnetic pole forms a developing magnetic pole, and generates a magnetic force on the second developing sleeve 132b of the second developing roller 115b, that is, the outer surface of the second developing roller 115b, so that the second developing sleeve 132b and the photosensitive drum 108 are generated. A magnetic field is formed between The fixed magnetic pole forms a magnetic brush by a magnetic field, so that the toner of the developer adsorbed on the outer surface of the second developing sleeve 132b after the toner is once supplied to the photosensitive drum 108 by the first developing roller 115a. Is transferred to the photosensitive drum 108.

  The magnet roller 133 of each of the developing rollers 115a and 115b is provided with at least one fixed magnetic pole in addition to the above-described pumping magnetic pole and developing magnetic pole. The at least one fixed magnetic pole is provided for transporting the developer.

  When the developer is adsorbed to the outer surface of each of the developing sleeves 132a and 132b, a plurality of the magnetic carriers 135 of the developer are overlapped along the magnetic force lines generated by the fixed magnetic pole, and the above-described fixed magnetic poles of the developing sleeves 132a and 132b. Stand on the outer surface. As described above, the magnetic carrier 135 stands up on the outer surface of the developing sleeves 132a and 132b in a state where the magnetic carrier 135 overlaps along the magnetic field lines and stands on the outer surface of the developing sleeves 132a and 132b. . Then, the above-described toner is adsorbed to the magnetic carrier 135 that is raised. In other words, the developing sleeves 132 a and 132 b attract the developer to the outer surface by the magnetic force of the magnet roller 133.

  As shown in FIG. 21, the interlocking rotating unit 120 includes a motor 143 as a drive source, a pinion 144, a rotating gear 145, and a first chain 146. Further, a gear (not shown) fixed to the developing sleeves 132 a and 132 b of the developing rollers 115 a and 115 b and a second chain 148 are provided. The motor 143 is fixed to the cartridge case 111, the storage tank 117, the case 119, and the like.

  The pinion 144 is attached to the output shaft of the motor 143. The rotating gear 145 is rotatably supported by the cartridge case 111, the storage tank 117, the case 119, and the like. The first chain 146 is formed in an endless annular shape (ring shape), and is stretched over the pinion 144 and the rotating gear 145 so as to mesh with them. The first chain 146 circulates around the outer periphery of the pinion 144 and the rotating gear 145 by the driving force of the motor 143 to rotate the rotating gear 145.

  The gears are arranged coaxially with the developing sleeves 132a and 132b, respectively, and are fixed to the end portions of the developing sleeves 132a and 132b. The outer diameters of the gears are equal to each other. The second chain 148 is formed in an endless annular shape (ring shape), is spanned between the rotating gear 145 and the gear, and meshes with these. The second chain 148 circulates around the rotation gear 145 and the outer periphery of the gear by rotation of the rotation gear 145 by the driving force of the motor 143, and rotates the gears, that is, the developing sleeves 132a and 132b in the same direction. Rotate by number.

  Each developing sleeve 132a, 132b is formed in a cylindrical shape as shown in FIG. Each of the developing sleeves 132a and 132b includes a magnet roller 133 (contains), and is provided so as to be rotatable around the axis. Each of the developing sleeves 132a and 132b is rotated so that the inner peripheral surface thereof is sequentially opposed to the fixed magnetic pole.

FIG. 23 is a perspective view of the first developing sleeve 132a.
The first developing sleeve 132a is made of stainless steel (SUS), and a stainless steel wire is thermally sprayed on the outer surface of the first developing sleeve 132a by metal spraying means to form irregularities on the surface of the sleeve. As stainless steel, a hollow tube (outer diameter 30 mm, wall thickness 1 mm, length 490 mm) made of SUS304 is prepared, and the outer surface of this hollow tube is subjected to blasting to a surface roughness of 6 μm (Rz). Thereafter, a SUS304 wire was arc sprayed to form irregularities 139a on the sleeve surface (Rz 20-50 μm, average thickness 30-80 μm). Furthermore, in order to improve the wear resistance, a TiN coating layer (average thickness of 1 to 4 μm) is formed on the surface of the coating layer.

  By spraying a high-hardness stainless steel on the surface of the first developing sleeve 132a to form irregularities, it is possible to prevent the irregularities 139a on the sleeve surface from being worn due to aging. As a result, the first developing roller 151a can stably draw up the developer over a long period of time (a decrease in the amount of the developer drawn up due to secular change can be prevented). Further, by using a stainless steel material for the first developing sleeve 132a, the fusion property with the stainless steel spray material is high, the spray material is hardly peeled off, and the durability can be further enhanced. In addition, since the thermal expansion coefficient is smaller than that of aluminum during thermal spraying of stainless steel, thermal deformation due to temperature rise of the sleeve is small, and since mechanical strength is stronger than that of aluminum, deformation due to impact force during thermal spraying of stainless steel is not possible. Few. Therefore, as compared with the case of aluminum, it is possible to suppress deterioration of the outer diameter fluctuation accuracy of the developing sleeve and to suppress periodic fluctuations in image density.

FIG. 24 is a perspective view of the second developing sleeve 132b.
The second developing sleeve 132b is made of an aluminum alloy, and a large number of elliptical recesses 139b are provided on the surface, and the surface is processed into a scale pattern. Aluminum alloys are excellent in terms of workability and lightness. When an aluminum alloy is used, it is preferable to use A6063, A5056, and A3003. Further, in order to improve the wear resistance, a TaC coating layer (average thickness of 0.1 to 1.5 μm) is formed on the surface of the coating layer.

  Since the second developing sleeve 132b is made of an aluminum alloy that is easy to extrude, the cost can be reduced and the outer diameter can be shaken more accurately, and the gap fluctuation between the photosensitive drum 108 and the second developing sleeve 132b can be reduced. In addition, aluminum alloy has better workability than stainless steel, and the recess 139b can be easily processed. As a result, the machining time of the recess 139b can be shortened, the replacement cycle of the cutting tool can be lengthened, and the manufacturing cost can be suppressed.

  Further, by making the surface of the second developing roller 151b a scale pattern, periodic image density unevenness occurs as compared with the configuration in which a plurality of parallel grooves are provided on the surface of the second developing roller 151b as described above. Can be suppressed. Further, the developer conveying force of the second developing roller 115b can be made higher than the developer conveying force of the first developing roller 115a. Thereby, even if the image forming speed is increased, the developer does not stay in the region where the developer is transferred from the first developing roller 115a to the second developing roller 115b, and the latent image can be developed satisfactorily.

  Furthermore, the oval-shaped dent 139b formed on the surface is less likely to be worn than a convex portion formed on the surface by sandblasting or electromagnetic blasting. Thereby, compared with the case where unevenness | corrugation is formed in the surface by sandblasting or electromagnetic blasting, a developer conveyance force can be maintained over time. The configuration in which the recess 139b is provided on the outer surface of the developing sleeve 132b is inferior in durability to the configuration in which the stainless steel material is sprayed to form irregularities on the outer surface of the developing sleeve. However, when the stainless steel material is sprayed to form irregularities on the outer surface of the developing sleeve, the unevenness of the spraying thickness deteriorates the runout accuracy of the developing sleeve, or heat deformation occurs due to the temperature rise of the developing sleeve, and the outer surface of the developing sleeve Radial runout accuracy deteriorates. Further, the wear on the sleeve surface is caused by the rubbing of the developer by the developer, particularly in a portion where the sleeve and the doctor blade 116 are close to each other. On the other hand, since the doctor blade does not face the second developing roller 151b, the force with which the developer slides on the sleeve is small, and the developing sleeve is less worn. Therefore, the durability of the developing device is not affected even if the developing sleeve 132b of the second developing roller 151b is not formed by spraying a stainless material and forming irregularities on the outer surface of the developing sleeve. Rather, by using a surface-scaled developing sleeve as the developing sleeve of the second developing roller 151b, the runout accuracy can be increased as compared with the configuration in which the stainless steel material is sprayed to form irregularities on the outer surface of the developing sleeve. Therefore, the gap fluctuation between the photosensitive drum 108 and the second developing sleeve 132b can be reduced, and the periodic fluctuation of the image density can be prevented.

On the other hand, as described above, the first developing sleeve 132a of the first developing roller 115a is formed by spraying a stainless material to form the unevenness 139a on the outer surface of the developing sleeve, and the flare accuracy is deteriorated. However, in the multi-stage roll development method, the final image quality is determined in the development process with the second development roller on the downstream side in the direction of movement of the photoreceptor surface. That is, the developing ability depends on the developing efficiency of the first developing roller 115a, and the image quality such as dot reproducibility, white spot and image density fluctuation strongly depends on the developing process in the second developing roller 115b. For this reason, even if the outer diameter fluctuation accuracy of the first developing sleeve 132b is somewhat poor and the image density of the image developed by the first developing roller fluctuates in the rotation cycle of the developing sleeve, the development by the second developing roller 115b is not possible. What is necessary is just to improve the image density fluctuation. As described above, since the developing sleeve having a surface scale pattern with good outer diameter deflection accuracy is used as the developing sleeve of the second developing roller 115b, the image density of the image developed by the first developing roller varies. However, it can be improved by the developing process of the second developing roller 115b. In particular, since the second developing sleeve 132b is made of an aluminum alloy that is easy to extrude, the cost is low and the deflection accuracy of the outer diameter can be improved. Therefore, even if the first developing sleeve 132a of the first developing roller 115a is formed by spraying a stainless material to form irregularities on the outer surface of the developing sleeve, the image is not affected. In addition, the fluctuation cycle of the image density fluctuation due to the deterioration of the outer diameter shake accuracy is one rotation period of the developing sleeve, and the image density fluctuation period is longer than that of the developing sleeve provided with the parallel grooves on the surface of the parallel groove pitch period. . Therefore, even if the image quality improvement by the second developing roller is not sufficient, there is an advantage that the developing sleeve is less perceptible than the developing sleeve provided with the parallel grooves on the surface of the developing sleeve.
Further, the developing sleeve 132a of the first developing roller faces the doctor blade 116, and as described above, the developer rubs the sleeve and easily wears at the portion where the sleeve and the doctor blade 116 are close to each other. For this reason, as the developing sleeve 132a of the first developing roller, the durability of the first developing sleeve can be improved by using a material in which a stainless steel material is sprayed to form irregularities on the outer surface of the developing sleeve. The lifetime of the device can be increased.

  Further, it is preferable to form a coating layer having a hardness larger than the hardness of the carrier on the surface of each developing sleeve 132a, 132b. Thereby, the surface of each developing sleeve can be prevented from being scraped by the carrier, and the durability of each developing roller can be further improved. As the coating layer, CrN, ZrN, TiN, TaC, etc. that are used for general purposes can be used. By covering the surfaces of the developing sleeves 132a and 132b with these commonly used materials, the durability of the developing roller can be improved at low cost.

What has been described above is an example, and the present invention has a specific effect for each of the following aspects.
(Aspect 1)
A developing device 22 that develops a latent image on a latent image carrier in multiple stages while delivering the developer between a plurality of developer carriers opposite to the latent image carrier such as the photosensitive drum 20. In the two developer carriers to which the developer is transferred, the developer conveying force of the developer carrier on the side receiving the developer such as the second developing roller 62 is set to be on the side where the developer such as the first developer roller 61 is transferred. The developer carrying power of the developer carrier was set higher.

  As described above, as a result of intensive studies on the cause of the occurrence of the uneven density of spots, the present applicant has found the following. That is, when the rotational speed of each developer carrier such as the developing roller is increased as the moving speed of the surface of the latent image carrier such as the photosensitive drum 20 increases, the transfer unit U such as the first developing roller 61 The moving speed of the developer carried on the developer carrying member on the developer delivery side is also increased. As a result, a part of the developer on the delivery developer carrying member moves to the downstream side in the moving direction of the developer carrying member on the delivery side from the delivery unit U, and moves there in the second developing roller 62 and the like. Is transferred to the developer carrier on the side receiving the developer. As a result, since the developer delivered downstream of the delivery unit U is added to the developer delivered by the delivery unit U, the developer in the delivery unit U becomes excessive, and development is performed in the delivery unit U. The stagnation of the agent occurs. Then, a part of the staying developer is attracted to the magnetic pole on the upstream side from the agent separation portion of the developer carrier on the delivery side, and separated from the developer carrier on the side where the developer is received at the delivery portion U and delivered. The flow toward the developer carrier on the side is generated. As a result, the developer amount on the developer carrier on the receiving side of the portion where such a flow occurs is reduced, the developing ability of that portion is lowered, and the image density is lowered. The flow away from the developer carrier on the developer receiving side in the delivery unit U and toward the developer carrier on the delivery side is randomly generated in the axial direction of the developer carrier and disappears after a predetermined time. . As a result, it has been found that uneven density unevenness occurs in the image.

  (Aspect 1) is made on the basis of such a background. The developer carrying force of the developer carrier on the side receiving the developer such as the second developing roller 62 is set to be equal to that of the first developing roller 61 or the like. The developer conveyance force of the developer carrying side of the developer delivery side was set higher. By increasing the developer conveying force of the receiving developer carrier, the developer is received at the transfer unit U where the developer is transferred from the receiving developer carrier to the receiving developer carrier. The developer carrying force of the developer carrier on the side becomes dominant. Thus, when the developer is transferred from the developer carrier on the delivery side to the developer carrier on the receiving side, the developer on the receiving side receives the momentum in the moving direction of the developer carrier on the developer passing side. It can be suppressed by the carrying force of the carrier. Thereby, it is possible to suppress the developer carried on the developer carrier on the delivery side from moving downstream from the delivery unit U in the direction of movement of the developer carrier on the delivery side. Thereby, it is possible to suppress the developer from staying in the transfer unit U, and it is possible to suppress the flow toward the developer carrier on the side where the developer is transferred in the transfer unit U. As a result, it is possible to suppress the occurrence of a portion where the developer amount of the developer carrier on the receiving side is reduced in the developing region, to perform uniform development in the axial direction, and to suppress uneven density unevenness. Can be obtained.

(Aspect 2)
In (Aspect 1), the developer conveying force due to the surface shape of the developer carrier on the developer receiving side is made higher than the developer conveying force due to the surface shape on the developer passing side.
According to (Aspect 2), with a simple configuration, the developer transport force of the developer carrier on the developer receiving side can be made higher than the developer transport force on the developer passing side.

(Aspect 3)
In (Aspect 2), the surface of the developer carrier on the side receiving the developer such as the second developing roller 62 and the surface of the developer carrier on the side of passing the developer such as the first developer roller 61 are periodically arranged. The number of grooves on the developer carrier on the developer receiving side is larger than the number of grooves on the developer carrier on the developer passing side.
According to (Aspect 3), as described in the embodiment, the developer is easily caught on the surface of the developer carrying member by increasing the number of grooves. Thereby, the developer carrying force of the developer carrier on the receiving side such as the second developing roller 62 can be increased more than the developer carrier on the passing side such as the first developing roller 61.

(Aspect 4)
In (Aspect 2) or (Aspect 3), the developer carrier on the side that receives the developer such as the second developing roller 62 and the surface of the developer carrier on the side that passes the developer such as the first development roller 61 A plurality of periodic grooves are formed, and the groove depth of the developer carrier on the developer receiving side is made deeper than the groove depth of the developer carrier on the developer passing side.
As described in the embodiment, the developer can be easily caught on the surface of the developer carrier by increasing the depth of the groove. Thereby, the developer carrying force of the developer carrier on the receiving side such as the second developing roller 62 can be increased more than the developer carrier on the passing side such as the first developing roller 61.

(Aspect 5)
In any one of (Aspect 2) to (Aspect 4), the surface roughness of the developer carrier on the side receiving the developer such as the second developing roller 62 is set to the development on the side receiving the developer such as the first developing roller 61. It was rougher than the surface roughness of the agent carrier.
As described in the embodiment, the developer can be easily caught on the surface of the developer carrier by increasing the surface roughness. Thereby, the developer carrying force of the developer carrier on the receiving side such as the second developing roller 62 can be increased more than the developer carrier on the passing side such as the first developing roller 61.

(Aspect 6)
In any one of (Aspect 1) to (Aspect 5), the magnetic pole (delivery magnetic pole S1) of the developer carrier on the developer delivery side, such as the first developing roller 61, at the location where the developer is delivered, and the second The magnetic poles (receiving magnetic pole N2) of the developer bearing member on the developer receiving side such as the developing roller 62 are made different from each other.
According to (Aspect 6), as described in the embodiment, the receiving unit U can generate a magnetic force that restrains the developer. As a result, the momentum of the developer transport on the developer carrier on the passing side such as the first developing roller 61 can be weakened by the magnetic force. As a result, it is possible to prevent the developer on the developer carrier on the delivery side from moving downstream from the delivery unit U in the direction of movement of the developer carrier surface on the delivery side.

(Aspect 7)
An image forming apparatus including a latent image carrier such as a photosensitive drum 20 that carries a latent image, and a developing unit such as a developing device 22 that develops the latent image on the latent image carrier. The developing device according to any one of (Aspect 1) to (Aspect 6) was used.
According to (Aspect 7), even if the image forming speed is increased, a good image with suppressed uneven density can be obtained.

(Aspect 8)
At least the latent image carrier and the development in an image forming apparatus comprising a latent image carrier such as a photosensitive drum 20 that carries a latent image, and a developing unit such as a developing device 22 that develops the latent image on the latent image carrier. In the process cartridge such as the image forming unit 3 that is held on a common holding body as a unit and can be attached to and detached from the image forming apparatus main body, any of (Aspect 1) to (Aspect 6) is used as the developing means. The developing device was used.
According to (Aspect 8), it is possible to provide a process cartridge capable of obtaining a good image in which uneven density unevenness is suppressed even when the image forming speed is increased.

3: image forming unit 20: photosensitive drum 22: developing device 61: first developing roller 62: second developing roller 66: doctor blade 108: photosensitive drum 113: developing device 115a: first developing roller 115b: second developing Roller 116: Doctor blade

JP 2011-197141 A

Claims (8)

A developing device that develops the latent image on the latent image carrier in multiple stages while delivering the developer between a plurality of developer carriers each facing the latent image carrier,
In the two developer carriers to which the developer is transferred, the developer carrying force of the developer carrier on the developer receiving side is higher than the developer carrying force of the developer carrier on the developer passing side. A developing device characterized by that. The developing device according to claim 1,
A developing device characterized in that a developer conveying force due to the surface shape of the developer carrying member on the developer receiving side is higher than a developer conveying force due to the surface shape on the developer passing side. The developing device according to claim 2,
A plurality of periodic grooves are formed on the surface of the developer carrier on the side receiving the developer and the developer carrier on the side passing the developer,
A developing device characterized in that the number of grooves on the developer carrier on the developer receiving side is greater than the number of grooves on the developer carrier on the developer passing side. The developing device according to claim 2, wherein
A plurality of periodic grooves are formed on the surface of the developer carrier on the side receiving the developer and the developer carrier on the side passing the developer,
2. A developing device according to claim 1, wherein a groove depth of the developer carrier on the developer receiving side is made deeper than a groove depth of the developer carrier on the developer passing side. The developing device according to claim 2, wherein
A developing device characterized in that the surface roughness of the developer carrier on the side receiving the developer is made rougher than the surface roughness of the developer carrier on the side receiving the developer. The developing device according to any one of claims 1 to 5,
A developing device characterized in that a magnetic pole of a developer carrying body on the developer delivery side and a magnetic pole of a developer carrying body on the side receiving the developer are made different from each other in a place where the developer is delivered . An image forming apparatus comprising: a latent image carrier that carries a latent image; and a developing unit that develops the latent image on the latent image carrier.
An image forming apparatus using the developing device according to claim 1 as the developing means. In an image forming apparatus comprising a latent image carrier that carries a latent image and a developing unit that develops the latent image on the latent image carrier, at least the latent image carrier and the developing unit are shared as one unit. In the process cartridge that is held by the holding body and is detachable from the image forming apparatus main body,
A process cartridge using the developing device according to claim 1 as the developing means.

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