Patent Grant
9207583
This application is based on Japanese Patent Application No. 2014-165840 filed with the Japan Patent Office on Aug. 18, 2014, the contents of which are hereby incorporated by reference.
The present disclosure relates to a developing device and an image forming apparatus provided with the same.
In an electrophotographic image forming apparatus such as a copier, a printer or a facsimile machine, a toner image is formed on an image carrier (e.g. photoconductive drum or transfer belt) by supplying toner to an electrostatic latent image formed on the image carrier and developing the electrostatic latent image. A touch-down development method using a developer containing nonmagnetic toner and magnetic carrier, a magnetic one-component development method and the like are known as methods for development. In the touch-down development method, a two-component developer layer (so-called magnetic brush layer) is carried on a magnetic roller, toner is moved onto a developing roller from the two-component developer layer and a toner layer is carried on the developing roller. Conventionally, a technology for providing a resin layer on a surface of the developing roller arranged to face a photoconductive drum is known. Further, there is known an immersion method (dip method, dipping method) of manufacturing a developing roller by immersing a stock tube of the developing roller in a resin liquid in which a resin material is dissolved in advance.
A developing device according to one aspect of the present disclosure includes a housing, a developer carrier, a developer container, a conveying member and a surface layer. The developer carrier is formed into a cylindrical shape and supported in the housing rotatably about an axis and carries a developer on a circumferential surface. The developer container is arranged to face the developer carrier. The developer container includes a first conveying portion in which the developer is conveyed in a first conveying direction from one end side toward the other end side in an axial direction of the developer carrier, and a second conveying portion which communicates with the first conveying portion at opposite end parts in the axial direction and in which the developer is conveyed in a second conveying direction opposite to the first conveying direction. The conveying member is rotatably arranged in the first conveying portion and conveys the developer in the first conveying direction and supplies the developer to the developer carrier. The surface layer is arranged on or arranged to face the circumferential surface of the developer carrier and formed on a surface of a predetermined cylindrical base member. The surface layer is formed by an immersion method of immersing the base member in a predetermined immersion tank so that an axial direction of the base member extends along a vertical direction. A lower end side of the base member at the time of the immersion is arranged in an upstream side of the housing in the first conveying direction and an upper end side of the base member at the time of the immersion is arranged in a downstream side of the housing in the first conveying direction.
An image forming apparatus according to another aspect of the present disclosure includes the above developing device and an image carrier. An electrostatic latent image is formed on a surface of the image carrier and the developer is supplied to the image carrier from the developing device.
Hereinafter, an embodiment of the present disclosure is described with reference to the drawings. Note that the present disclosure can be applied to an electrophotographic image forming apparatus such as a copier, a printer, a facsimile machine or a complex machine provided with these functions.
The apparatus main body 11 includes a lower main body 111, an upper main body 112 arranged to face this lower main body 111 from above and a coupling portion 113 interposed between these upper and lower main bodies 112, 111. The coupling portion 113 is a structure for coupling the lower and upper main bodies 111, 112 to each other in a state where the sheet discharging unit 15 is formed between the both, stands from left and rear parts of the lower main body 111 and is L-shaped in a plan view. The upper main body 112 is supported on an upper end part of the coupling portion 113.
The image forming station 12, the fixing device 13 and the sheet feeding unit 14 are housed in the lower main body 111 and the document reading unit 16 is mounted in the upper main body 112.
The image forming station 12 performs an image forming operation of forming a toner image on a sheet P fed from the sheet feeding unit 14. The image forming station 12 includes a yellow unit 12Y, a magenta unit 12M, a cyan unit 12C and a black unit 12Bk respectively using toner of yellow, magenta, cyan and black colors and successively arranged from an upstream side toward a downstream side in a horizontal direction, an intermediate transfer belt 125 stretched on a plurality of rollers such as a drive roller 125A in such a manner as to be able to endlessly travel in a sub scanning direction in image formation, a secondary transfer roller 196 held in contact with the outer peripheral surface of the intermediate transfer belt 125, and a belt cleaning device 198.
The unit of each color of the image forming station 12 integrally includes a photoconductive drum 121 (image carrier), a developing device 122 for supplying the toner (developer) to the photoconductive drum 121, a toner cartridge (not shown) containing the toner, a charging device 123 and a drum cleaning device 127. Further, an exposure device 124 for exposing each photoconductive drum 121 to light is horizontally arranged below the adjacent developing devices 122.
The photoconductive drum 121 is formed into a cylindrical shape and rotated about an axis. The photoconductive drum 121 has an electrostatic latent image formed on the circumferential surface thereof and carries a toner image obtained by developing the electrostatic latent image with the toner. In this embodiment, the photoconductive drum 121 is a known amorphous silicon (a-Si) photoconductor.
The developing device 122 supplies the toner to an electrostatic latent image on the circumferential surface of the photoconductive drum 121 rotating in a direction of an arrow to form a layer of the toner, and forms a toner image corresponding to image data on the circumferential surface of the photoconductive drum 121. The toner is appropriately supplied to each developing device 122 from the toner cartridge.
Each charging device 123 is provided at a position right below the corresponding photoconductive drum 121. The charging device 123 uniformly charges the circumferential surface of each photoconductive drum 121.
The exposure device 124 is provided at a position below the respective charging devices 123. The exposure device 124 irradiates the charged circumferential surface of the photoconductive drum 121 with laser light corresponding to each color based on image data input from a computer or the like or image data obtained by the document reading unit 16, thereby forming an electrostatic latent image on the circumferential surface of each photoconductive drum 121. Note that the exposure device 124 irradiates the laser light according to an exposure light amount set in advance in order to form a predetermined latent image potential on the photoconductive drum 121. The drum cleaning device 127 is provided to the left of each photoconductive drum 121 and cleans the circumferential surface of the photoconductive drum 121 by removing the residual toner.
The intermediate transfer belt 125 is an endless, electrically conductive and soft belt having a laminated structure composed of a base layer, an elastic layer and a coating layer. The intermediate transfer belt 125 is mounted on a plurality of tension rollers arranged substantially in the horizontal direction above the image forming station 12. The tension rollers include the drive roller 125A arranged near the fixing device 13 to rotationally drive the intermediate transfer belt 125 and a driven roller 125E arranged at a predetermined distance from the drive roller 125A in the horizontal direction and configured to rotate, following the rotation of the intermediate transfer belt 125. The intermediate transfer belt 125 is driven to rotate in a clockwise direction in
A secondary transfer bias applying unit (not shown) is electrically connected to the secondary transfer roller 196. A toner image formed on the intermediate transfer belt 125 is transferred to a sheet P conveyed from a pair of conveyor rollers 192 located below by a transfer bias applied between the secondary transfer roller 196 and the drive roller 125A. The belt cleaning device 198 is arranged to face the driven roller 125E via the intermediate transfer belt 125.
The fixing device 13 includes a heating roller 132 internally provided with an electrical heating element such as a halogen lamp as a heat source, and a pressure roller 134 arranged to face the heating roller 132. The fixing device 13 applies a fixing process to a toner image on a sheet P transferred in the image forming station 12 by giving heat from the heating roller 132 while the sheet P is passing through a fixing nip portion between the heating roller 132 and the pressure roller 134. The color-printed sheet P completed with the fixing process is discharged toward a sheet discharge tray 151 provided on the top of the apparatus main body 11 through a sheet discharge conveyance path 194 extending from an upper part of the fixing device 13.
The sheet feeding unit 14 includes a manual feed tray 141 openably and closably provided on a right side wall of the apparatus main body 11 in
The vertically extending sheet conveyance path 190 is formed to the left of the image forming station 12. The pair of conveyor rollers 192 are provided at a suitable position in the sheet conveyance path 190 and convey a sheet P fed from the sheet feeding unit 14 toward a secondary transfer nip portion including the secondary transfer roller 196.
The sheet discharging unit 15 is formed between the lower and upper main bodies 111, 112. The sheet discharging unit 15 includes the sheet discharge tray 151 formed on the upper surface of the lower main body 111. The sheet discharge tray 151 is a tray onto which a sheet P having a toner image formed in the image forming station 12 is discharged after a fixing process is applied thereto in the fixing device 13.
The document reading unit 16 includes a contact glass 161 which is mounted in an upper surface opening of the upper main body 112 and on which a document is to be placed, a document pressing cover 162 which is free to open and close and presses a document placed on this contact glass 161 and a scanning mechanism 163 which scans and reads an image of a document placed on the contact glass 161. The scanning mechanism 163 optically reads an image of a document using an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) and generates image data. Further, the apparatus main body 11 includes an image processing unit (not shown) for generating an image from this image data.
<Configuration of the Developing Device>
Next, the developing device 122 is described in detail.
With reference to
The magnetic roller 82 is rotatably supported in the development housing 80 to face the developing roller 83 along the longitudinal direction of the developing device 122. The magnetic roller 82 is driven to rotate in a clockwise direction in
The magnetic roller 82 magnetically draws up (receives) the developer onto a circumferential surface 82A thereof from the developer storage 81 by a magnetic force of the draw-up pole 821. The magnetic roller 82 magnetically carries the drawn-up developer as a developer layer (magnetic brush layer) on the circumferential surface 82A. Then, the magnetic roller 82 supplies the toner to the developing roller 83. With the rotation of the magnetic roller 82, the developer is conveyed toward the developer regulation blade 84.
The developer regulation blade 84 is arranged to face the magnetic roller 82 on a side upstream of a region, where the developing roller 83 and the magnetic roller 82 face each other, in a rotating direction of the magnetic roller 82. The developer regulation blade 84 regulates a layer thickness of the developer magnetically adhering to the circumferential surface 82A of the magnetic roller 82. A regulation gap G of a predetermined dimension is formed between the developer regulation blade 84 and the circumferential surface 82A of the magnetic roller 82. This causes a developer layer having a uniform predetermined thickness to be formed on the circumferential surface 82A.
The developing roller 83 is arranged to extend along the longitudinal direction of the developing device 122 and in parallel to the magnetic roller 82 and rotationally driven in a clockwise direction in
The developing roller 83, the magnetic roller 82 and the first and second screw feeders 85, 86 are rotationally driven in synchronization by the driving unit 962. A clearance S of a predetermined dimension (
The development bias applying unit 88 applies development biases, in which an alternating-current voltage is superimposed on a direct-current voltage, to the magnetic roller 82 and the developing roller 83. A high alternating-current voltage is applied between the photoconductive drum 121 and the developing roller 83 and between the developing roller 83 and the magnetic roller 82. Particularly, since the toner is supplied from the magnetic roller 82 to the developing roller 83 and further supplied from the developing roller 83 to the photoconductive drum 121, a higher alternating-current voltage is applied to the developing roller 83 for the movement of the toner as compared with known one-component and two-component developing devices.
With reference to
The developer discharging portion 87 communicates with the second developer storage 81b on a side before the reverse conveying portion 86A. The developer discharging portion 87 includes a hollow cylindrical wall portion internally including a space part and a discharge screw 87A configured to rotate in the space part. The discharge screw 87A is a screw blade coaxially fixed to the second screw feeder 86. The discharge screw 87A is arranged in the same direction as the screw blade of the second screw feeder 86. If part of the developer flows into the developer discharging portion 87 beyond the reverse conveying portion 86A from a developer retaining portion formed by the reverse conveying portion 86A, the developer is discharged from an unillustrated discharge port after being conveyed backward by the discharge screw 87A of the developer discharging portion 87 (arrow D5 of
With reference to
With reference to
A process of forming the coating layer 83C on the alumite layer is performed after the heating process. Specifically, a mixture liquid is prepared by mixing 100 weight parts of alcohol-soluble nylon resin as binder resin, pigments, 50 to 125 weight parts of titanium oxide as a conductive agent and 800 weight parts of methanol as a dispersion medium together with zirconia beads having a diameter of 1.0 mm in a ball mill for 48 hrs. The alumite-processed sleeve 830 having a diameter of 12 to 20 mm is pulled up after being immersed in that mixture liquid for a predetermined time, and dried for 10 mins. under a high-temperature environment of 130° C. Note that the sleeve 830 is so immersed into the mixture liquid that an axial direction of the cylindrical shape extends along a vertical direction, and then pulled up. Further, when the sleeve 830 is pulled up, the mixture liquid adhering to the surface is scraped off by a hollow cylindrical blade made of polytetrafluoroethylene. As a result, the sleeve 830 coated with the coating layer 83C having a thickness of 2 to 11 μm is manufactured. As just described, cracks are formed on the alumite layer by the heating process in advance before the coating layer 83C is coated. This prevents the conductive agent contained in the coating layer 83C from being unevenly distributed due to the influence of a convection generated in the coating layer 83C during the drying of the coating layer 83C. As a result, it is possible to form the coating layer 83C in which the conductive agent is evenly dispersed. Further, since only titanium oxide is dispersed as the conductive agent in the coating layer 83C, the coating layer 83C is formed to be harder and the abrasion of the coating layer 83C is reduced.
On the other hand, in the case of forming the coating layer 83C by the immersion method as described above, the mixture liquid adhering to the surface of the sleeve 830 tends to drip downward due to gravity when the sleeve 830 is pulled up. Thus, the coating layer 83C relatively thicker than in an axial central part is formed on the surface of a part of the sleeve 830 located on a lower end side at the time of immersion. Particularly, a pool part 83C1 where the thickness of the coating layer 83C is large tends to be formed on a lower end part of the sleeve 830. Further, the coating layer 83C (thin layer part 83C2) thinner than in the axial central part is formed on the surface of a part of the sleeve 830 located on an upper end side at the time of immersion.
In
The second screw feeder 86 adjacent to the magnetic roller 82 supplies the developer to the magnetic roller 82 while conveying the developer in the conveying direction (first conveying direction) from one axial end side toward the other axial end side in the second developer storage 81b. At this time, a developer agitating time by the second screw feeder 86 becomes longer toward the downstream side in the first conveying direction. Thus, a charge amount of the developer on the upstream side in the first conveying direction tends to be lower than that of the developer on the downstream side. If the charge amount of the toner on the magnetic roller 82 on the upstream side in the first conveying direction is low, a charge amount of the toner on the developing roller 83 is also low. Since the responsiveness of the toner to a development electric field formed by a development bias is low if the charge amount of the toner is low, development performance is reduced. On the other hand, since the charge amount of the toner is relatively high on the downstream side in the first conveying direction, development performance is partially increased. As a result, an image density tends to vary along the first conveying direction. Even in such a case, in this embodiment, the lower end side of the sleeve 830 at the time of immersion is arranged in the upstream side of the development housing 80 in the first conveying direction and the upper end side of the sleeve 830 at the time of immersion is arranged in the downstream side of the development housing 80 in the first conveying direction. Thus, on the upstream side in the first conveying direction, the gap between the developing roller 83 and the photoconductive drum 121 becomes narrower and development performance is adjusted to be partially high. Thus, also on the upstream side in the first conveying direction where the charge amount of the toner is relatively low, the toner is stably supplied from the developing roller 83 to the photoconductive drum 121. On the other hand, on the downstream side in the first conveying direction, the gap between the developing roller 83 and the photoconductive drum 121 becomes wider and development performance is adjusted to be partially low. As a result, a variation of the image density in the axial direction of the developing roller 83 is suppressed even if the charge amount of the toner is distributed to be higher along the first conveying direction.
Further, in this embodiment, the developer is partly retained by the reverse conveying portion 86A (region K of
In this embodiment, the upper end side of the developing roller 83 at the time of immersion is arranged on the downstream side in the conveying direction of the second screw feeder 86. Specifically, with reference to
On the other hand, the developer is transferred from the first developer storage 81a to the second developer storage 81b via the first communication portion 81c on the upstream side in the conveying direction of the second screw feeder 86. The transferred developer is conveyed in the direction of the arrow D2 of
In this embodiment, the lower end side of the developing roller 83 at the time of immersion is arranged on the upstream side in the first conveying direction of the second screw feeder 86 to solve a problem occurring on the upstream side of the magnetic roller 82 in the first conveying direction as described above. Specifically, with reference to
Further, the developing device 122 includes the developer discharging portion 87 in this embodiment. A life of the developer is maintained long by gradually exchanging the developer, particularly the carrier, in the developer storage 81. As a result, stable images are formed over a long period of time. Even if the developer is retained by the reverse conveying portion 86A on the downstream end part of the second screw feeder 86, the clogging and spill-out of the developer, and further drastic thinning of the coating layer 83C are suppressed since the upper end side of the developing roller 83 at the time of immersion is arranged on the downstream side in the first conveying direction.
Although the developing device 122 and the image forming apparatus 1 according to the embodiment of the present disclosure are described above, the present disclosure is not limited to these. For example, the following modifications can be adopted.
(1) Although the above embodiment is described taking a full-color image forming apparatus as the image forming apparatus 1, the present disclosure is not limited to this. The image forming apparatus 1 may be a monochromatic image forming apparatus for printing a black-and-white image.
(2) In the above embodiment, the reverse conveying portion 86A (developer retaining portion) is described to partially retain the developer to discharge the developer from the developer discharging portion 87. The present disclosure is not limited to this. An unillustrated bearing portion for rotatably supporting the second screw feeder 86 may be mounted on the downstream end part of the second screw feeder 96 in the conveying direction in the development housing 80. The reverse conveying portion 86A may cause the developer to be partially retained to suppress the entrance of the developer into the above bearing portion.
(3) Although the above embodiment is described using the developing device 122 adopting the touch-down development method, the present disclosure is not limited to this.
The developing device 9 includes a development housing 930 (housing), the developing roller 931 (developer carrier), a first screw feeder 932 (conveying member), a second screw feeder 933 and a regulation blade 60 (layer thickness regulating member). A magnetic one-component development method is adopted for the developing device 9.
A developer storage 930H is provided in the development housing 930. A magnetic one-component developer is stored in the developer storage 930H. Further, the developer storage 930H includes a first conveying portion 930A in which the developer is conveyed in a first conveying direction (direction perpendicular to the plane of
The developing roller 931 is arranged at a distance from a photoconductive drum 921 (
Further, the developing roller 931 is rotated in a direction of an arrow D61 of
In this modification, the sleeve 931S of the developing roller 931 corresponds to a base member of the present disclosure. A coating layer 931C (
With reference to
The developing roller 931 receives the one-component developer from the first screw feeder 932 and supplies the developer to the photoconductive drum 921. In the first conveying portion 930A, a developer agitating time by the first screw feeder 932 becomes longer toward the downstream side in the first conveying direction. As a result, a charge amount of the developer on the developing roller 931 on the upstream side in the first conveying direction becomes relatively lower and an image density on the photoconductive drum 921 on the upstream side in the first conveying direction tends to be reduced. Further, in such a region where the charge amount is low, the developer easily scatters around and developer fogging easily occurs. A number of revolutions of the first screw feeder 932 of less than 100 rpm, particularly 10 to 60 rpm can be cited as a condition on which the charge amount of the developer easily varies along the first conveying direction in this way. In this modification, out of the coating layer 931C of the developing roller 931, a film thickness on the upstream side in the first conveying direction is set to be partly large (roller thick layer part 931C1,
Further, in this modification, different magnetic poles are alternately arranged along the circumferential direction in the magnet 931M as described above. Thus, as compared with the case where a strong peeling magnetic pole is formed, the developer is less likely to be peeled from the sleeve 931S of the developing roller 931 and the developer tends to continue to turn around on the sleeve 931S while moving in the first conveying direction. Since such a developer passes through the regulation blade 60 a plurality of number of times as it moves toward the downstream side in the first conveying direction, the charge amount is increased by frictional charging. Thus, the image density tends to vary along the first conveying direction. Even in such a case, the lower end side of the sleeve 931S at the time of immersion is arranged in the upstream side of the housing in the first conveying direction and the upper end side of the sleeve 931S at the time of immersion is arranged in the downstream side of the housing in the first conveying direction. As a result, the gap between the developing roller 931 and the photoconductive drum 921 is partly adjusted to suppress a variation of the image density along the first conveying direction.
Note that, with reference to
Next, a preferred mode of the developing device 122 according to the previous embodiment is described by way of examples. Each of the following experiments were conducted under the following experimental conditions.
<Concerning Experimental Conditions>
In Example 1 (Table 1), the developing roller 83 was so mounted in the development housing 80 that the lower end side of the developing roller 83 at the time of immersion was arranged on the upstream side in the first conveying direction of the second screw feeder 86 and the upper end side of the developing roller 83 at the time of immersion was arranged on the downstream side in the first conveying direction. On the other hand, in Comparative Example 1 (Table 2), the developing roller 83 was so mounted in the development housing 80 that the upper end side of the developing roller 83 at the time of immersion was arranged on the upstream side in the first conveying direction of the second screw feeder 86 and the lower end side of the developing roller 83 at the time of immersion was arranged on the downstream side in the first conveying direction. In each of Example and Comparative Example, 500 K (500×1000) images having an image density of 3.8% were successively printed. A change of the film thickness of each coating layer and an image evaluation of leading end high density are shown in Tables 1 and 2. Note that the leading end high density is such an image defect that the image density is partly higher on a leading end of a sheet in a conveying direction in the case of printing a whole surface solid image (image density of 100%). Particularly, when toner recovery from the developing roller 83 to the magnetic roller 82 is poor on the upstream side of the magnetic roller 82 in the conveying direction of the second screw feeder 86, the amount of the toner carried on the developing roller 83 temporarily increases and the image density becomes higher. In Tables 1 and 2, ◯ denotes a case where the leading end high density did not occur and x denotes a case where the leading end high density occurred.
As shown in Table 1, the developer easily passed through between the developing roller 83 and the magnetic roller 82 by arranging the upper end side (having an initial film thickness of 4 μm) of the developing roller 83 at the time of immersion on the downstream side in the first conveying direction of the second screw feeder 86 in Example 1. Thus, the film thickness of the coating layer 83C was not below 3 μm when the printing of 500 K images was finished. Further, throughout the experiment, the leading end high density did not occur and stable images were maintained. On the other hand, in Comparative Example 1, the coating layer 83C was thinned by arranging the lower end side (having an initial film thickness of 10 μm) of the developing roller 83 at the time of immersion on the downstream side in the first conveying direction of the second screw feeder 86 and the film thickness of the coating layer 83C was below 3 μm when the printing of 500 K images was finished. Furthermore, toner recovery from the developing roller 83 was poor from the initial stage to the end of the experiment, resulting in the occurrence of the leading end high density.
Next, a preferred mode of the developing device 9 is described by way of examples. Each of the following experiments was conducted under the following experimental conditions.
<Concerning Experimental Conditions>
In Example 2, the coating layer 931C was formed on the sleeve 931S of the developing roller 931 by the immersion method (dipping method) as shown in the previous modification. The thickness of the coating layer 931C was set at 8 μm in a longitudinal (axial) central part. The upper end side of the developing roller 931 at the time of immersion was arranged on the downstream side in the first conveying direction of the first screw feeder 932 and the lower end side of the developing roller 931 at the time of immersion was arranged on the upstream side in the first conveying direction. On the other hand, in Comparative Example 2, the coating layer 931C was not formed on the sleeve 931C of the developing roller 931, i.e. a non-coated sleeve was used. In both Example 2 and Comparative Example 2, 3000 images having an image density of 0.2% were printed in a single intermittent mode. Each evaluation result after printing is shown in Table 3.
In Table 3, a Model 210HS-2Aq/m Meter produced by Trek was used to measure the toner charge amount. Further, a Densit Meter TC-6DS produced by Tokyo Denshoku Co., Ltd. was used to measure the image density (I.D.) after printing. Further, in the evaluation of toner fogging, ◯ denotes a level having no visual problem and x denotes a level in which fogging was visually confirmed.
In both Example 2 and Comparative Example 2, the toner charge amount on the downstream side in the first conveying direction of the first conveying portion 930A (
On the other hand, in Example 2, a result was obtained in which development performance was adjusted by compensating for a difference in the toner charge amount by the gap between the photoconductive drum 921 and the developing roller 931 and a difference in the image density was reduced. Further, on the upstream side in the first conveying direction, the roller thick layer part 931C1 (
Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-165840 | Aug 2014 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20090311012 | Mabuchi et al. | Dec 2009 | A1 |
| 20100080611 | Kurachi | Apr 2010 | A1 |
| 20120213549 | Mori | Aug 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 2009-300677 | Dec 2009 | JP |
