Patent Application
20150378277
This application is based on Japanese Patent Application No. 2014-130177 filed with the Japan Patent Office on Jun. 25, 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 developing device supplies toner to an electrostatic latent image formed on a photoconductive drum to develop the electrostatic latent image, whereby a toner image is formed on the photoconductive drum. The developing device includes a developing roller rotatably supported in a housing. The developing roller is arranged with a predetermined gap defined between the developing roller and the photoconductive drum and carries a developer containing at least toner on a circumferential surface. Further, there is known a technology for providing a resin layer on a surface of a developing roller. There is known an immersion method (dip method, dipping method) of manufacturing a developing roller by immersing a raw tube of the developing roller into a resin liquid in which a resin material is dissolved in advance. There is also known a technology for forming a resistance layer on a surface of a photoconductive drum by the immersion method. In such a developing device, an agitating member is arranged to face the developing roller. The agitating member supplies the developer to the developing roller while conveying the developer in a predetermined conveying direction.
A developing device according to one aspect of the present disclosure includes a housing, a developer carrier, a developer storage, 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 storage is arranged in the housing to face the developer carrier. The developer storage 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 on 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 a downstream 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 an upstream 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, one 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 organic photoconductor (OPC) and a charge generation layer, a charge transport layer and the like are formed on a surface by an immersion method similarly to a developing roller 83 to be described later.
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 conveys 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 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.
Next, the developing device 122 is described in detail.
With reference to
In this embodiment, the second communication portion 81d functions as a developer retaining portion. The developer retaining portion is arranged in the downstream side of the first developer storage chamber 81a in the first conveying direction and causes the developer to be partially retained. In a cross-section intersecting with a direction in which the developer is conveyed in the developer storage 81, a cross-sectional area of the second communication portion 81d is set smaller than that of the first developer storage chamber 81a. As a result, a retaining portion K (
A first screw feeder 85 and a second screw feeder 86 for agitating and conveying the developer by rotating about their axes are respectively rotatably housed in the first and second developer storage chambers 81a, 81b. The first and second screw feeders 85, 86 are each provided with a shaft portion and a spiral blade arranged around the shaft portion. Rotating directions of the first and second screw feeders 85, 86 are set to be opposite to each other. This causes the developer to be conveyed in a circulating manner between the first and second developer storage chambers 81a, 81b while being agitated as indicated by arrows D1, D4, D2 and D3 of
The magnetic roller 82 is formed into a cylindrical shape and 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 at a distance from the magnetic roller 82 at a side upstream of the developing roller 83 when viewed in a rotating direction of the magnetic roller 82. The developer regulation blade 84 regulates a layer thickness of the developer supplied from the first screw feeder 85 and 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 by the driving unit 962. As shown in
A clearance S of a predetermined dimension (
The development bias applying unit 88 applies development biases, in which a direct-current voltage and an alternating-current voltage are superimposed, 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.
With reference to
With reference to
With reference to
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, a thin layer part 83C2 (
In
With reference to
Note that the developer having a relatively high toner density is carried on the upstream side of the magnetic roller 82 in the first conveying direction. Thus, the image density tends to be partly higher on the upstream side in the first conveying direction. However, in this embodiment, the coating layer 83C of the developing roller 83 is partly thin on the upstream side in the first conveying direction (thin layer part 83C2). Thus, the gap between the developing roller 83 and the photoconductive drum 121 becomes partly wider and development performance is suppressed on the upstream side in the first conveying direction. Thus, a partial increase in the image density is suppressed.
Further, in this embodiment, the touch-down development method is adopted as described above. In the developing device 122, a magnetic brush composed of the toner and the carrier is formed on the circumferential surface of the magnetic roller 82. The coating layer 83C of the developing roller 83 is abraded by a strong scraping force of the magnetic brush. The scraping force of the magnetic brush varies according to the toner density in the magnetic brush. Particularly, when the toner density is low and the surface of the carrier tends to be exposed, the scraping force of the magnetic brush increases and the abrasion of the coating layer 83C is promoted.
As described above, the second communication portion 81d of the developing device 122 functions as the developer retaining portion in this embodiment. The retaining portion K for the developer is formed in the downstream side of the first developer storage chamber 81a in the first conveying direction. Due to the influence of this retaining portion K, the amount of the developer carried on the circumferential surface of the magnetic roller 82 increases on the downstream side of the magnetic roller 82 in the first conveying direction. Particularly, a large amount of the developer is retained on the back of the developer regulation blade 84 and a pressure of the developer increases. As a result, the amount of the developer passing on a downstream side of the developer regulation blade 84 in the first conveying direction also increases as compared with an upstream side. Thus, a region where the scraping force by the magnetic brush on the magnetic roller 82 is strong (region H of
In this embodiment, as described above, the lower end side of the developing roller 83 at the time of immersion having the relatively thick coating layer 83C is arranged in the downstream (front) side of the developing device 122 in the first conveying direction. Accordingly, even if the strong scraping force of the magnetic brush is received, it is suppressed that the coating layer 83C on the downstream side in the first conveying direction becomes drastically thinner than the coating layer 83C on the upstream side in the first conveying direction or is lost. Further, the coating layer 83C is prevented from being peeled by a mechanical force by the magnetic brush.
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 the full-color image forming apparatus 1 as an example, 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) Although the second communication portion 81d functions as the developer retaining portion in the above embodiment, the present disclosure is not limited to this. In a modification, the developer retaining portion may be a paddle member radially projecting from the shaft portion on the downstream side of the first screw feeder 85 in the first conveying direction. The retaining portion K for the developer is formed in the downstream side of the first developer storage chamber 81a in the first conveying direction by the integral rotation of the paddle member with the first screw feeder 85. Further, a region where the pitch of the spiral blade of the first screw feeder 85 is set partly small or a region where the spiral blade is partly arranged in an opposite direction may be the developer retaining portion. As just described, the retaining portion K for the developer can be formed in the downstream side of the first developer storage chamber 81a in the first conveying direction also by the shape of the spiral blade of the first screw feeder 85.
Further, the developer retaining portion may be a region where a cross-sectional area of the downstream end part of the first developer storage chamber 81a in the first conveying direction is set partly small in a cross-section intersecting with the direction in which the developer is conveyed. Specifically, in
(3) Further, although the retaining portion K is formed in the downstream side of the first developer storage chamber 81a to efficiently replenish the toner from the toner replenishing portion 87 in the above embodiment, the present disclosure is not limited to this. An unillustrated developer discharging portion may be arranged instead of the toner replenishing portion 87 in the downstream side of the first developer storage chamber 81a in the first conveying direction. When part of the developer flows into the developer discharging portion from the retaining portion K for the developer, the developer is discharged from an unillustrated discharge port after being conveyed forward by an unillustrated discharge screw. As just described, a trickle technology for discharging part of the developer from the interior of the developing device 122 may be adopted. Further, an unillustrated bearing member for rotatably supporting the first screw feeder 85 may be arranged in the downstream side of the first developer storage chamber 81a in the first conveying direction. In this case, the retaining portion K for the developer may be formed by forming a spiral blade having a reverse pitch on the first screw feeder 85 to prevent the entrance of the developer into the bearing member.
(4) Furthermore, although the above embodiment is described taking the developing device 122 adopting the touch-down development method as an example, the present disclosure is not limited to this.
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 an unillustrated image carrier, on a surface of which an electrostatic latent image is to be formed. The developing roller 931 includes a rotary sleeve 931S and a magnet 931M fixedly arranged in the sleeve 931S. In
In this modification, the sleeve 931S of the developing roller 931 corresponds to a base member of the present disclosure. An unillustrated coating layer is formed on a surface of the sleeve 931S. In other words, the base member is a part of the developing roller 931 and the coating layer is formed on the circumferential surface of the developing roller 931. The coating layer is formed by the immersion method of immersing the sleeve 931S in a predetermined immersion tank so that an axial direction of the sleeve 931S extends along the vertical direction. Further, a lower end side of the sleeve 931 at the time of immersion is arranged in a downstream side of the development housing 930 in the first conveying direction and an upper end side of the sleeve 931S at the time of immersion is arranged in an upstream side of the development housing 930 in the first conveying direction.
The developing roller 931 receives the one-component developer from the first screw feeder 932 and supplies the developer to the unillustrated image carrier. When the developer on the developing roller 931 is consumed by the image carrier, the amount of the developer on a downstream side of the developing roller 931 in the first conveying direction tends to be smaller than that of the developer on an upstream side in the first conveying direction. According to the above configuration, a surface layer of the developing roller 931 is partly thick on the downstream side in the first conveying direction. Thus, a gap between the developing roller 931 and the image carrier becomes smaller and development performance is enhanced on the downstream side in the first conveying direction. Thus, the developer is stably supplied from the developing roller 931 to the image carrier also on the downstream side in the first conveying direction having a relatively small amount of the developer. As a result, the occurrence of an image density variation along the first conveying direction is suppressed.
Further, if an unillustrated developer retaining portion is arranged in a downstream side of the first conveying portion 930A in the first conveying direction as in the above embodiment, a larger amount of the developer is retained on the back (region TA of
Next, preferred modes of the developing roller 83 in the developing device 122 according to the embodiment are described by way of a plurality of examples.
This evaluation experiment was conducted under the following experimental conditions.
The lower end side of the developing roller 83 at the time of immersion is arranged in the downstream side of the development housing 80 in the first conveying direction in Example 1 of
On the other hand, in Example 1, the gap between the developing roller 83 and the photoconductive drum 121 is narrow although the amount of the toner carried on the downstream side of the developing roller 83 in the first conveying direction is relatively small. Thus, the image density is maintained higher than in Comparative Example 1. Further, since the gap between the developing roller 83 and the photoconductive drum 121 is wide although the amount of the toner carried on the upstream side of the developing roller 83 in the first conveying direction is large, the image density is suppressed. As a result, the image density is stably maintained along the axial direction of the developing roller 83 (magnetic roller 82).
This evaluation experiment was conducted under the following experimental conditions.
Note that, in Evaluation 2, the retaining portion K for the developer is formed by the second communication portion 81d as in the above embodiment. In Evaluation 2, different developing rollers are used as Example 2 and Comparative Example 2. In the developing roller used in Comparative Example 2, the alumite processing is applied to an aluminum sleeve having a diameter of 20 mm and a spray coating layer having a thickness of about 6 μm is formed on an alumite layer. In the coating layer, 100 weight parts of titanium oxide and 5 weight parts of carbon black are added to urethane. On the other hand, in the developing roller used in Example 2, the alumite processing is applied to an aluminum sleeve having a diameter of 20 mm and a dipping film (coating layer 83C) is formed on an alumite layer by the immersion method as in the above embodiment. A film thickness on a lower end side of the dipping film at the time of immersion is 10 μm and 100 weight parts of titanium oxide is added to nylon in the dipping film. In each of Example 2 and Comparative Example 2, 100 K (100×1000) pages of images having an image density of 50% are printed. Further, in Example 2, the lower end side of the developing roller 83 at the time of immersion is arranged in the downstream side of the development housing 80 in the first conveying direction as in the above embodiment. Tables 1 show a transition of the film thickness of the coating layer of each developing roller.
As shown in Tables 1, in Comparative Example 2, a downstream side of the coating layer formed by spray coating in the first conveying direction became drastically thin and the alumite layer of the developing roller was, as a result, exposed after printing 80 k pages. This is because the amount of the developer on the magnetic roller 82 is increased by the retaining portion K and the coating layer of the developing roller tends to be ground. If the alumite layer is exposed in this way, an adhesive force between the toner and the developing roller increases and a density reduction is brought about by the deterioration of development performance.
On the other hand, in Example 2, the pool part 83C1 of the developing roller 83 is arranged in the downstream side of the development housing 80 in the first conveying direction. Thus, even if the coating layer was ground by the developer on the magnetic roller 82, the thickness thereof did not fall below 3 μm after the printing of 100 k pages was finished and stable images were maintained.
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 |
|---|---|---|---|
| 2014-130177 | Jun 2014 | JP | national |
