JP2016090734A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a ghost image.SOLUTION: A developing device 5 according to the present invention includes: a developer carrier 50 that can rotate opposite to an image carrier 1 and carries to supply a two-component developer G to an opposing area 60 formed with the image carrier; and an electrode 59 that is arranged opposite to the developer carrier on the downstream side in the direction of rotation of the developer carrier with respect to the opposing area 60 formed by the image carrier and developer carrier, and when the potential applied to the developer carrier 51 is V1 and the potential on the same polarity side as the charging polarity of the two-component developer G is V2, has the potential V1+V2 applied thereto.SELECTED DRAWING: Figure 8

Description

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

In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is supported by a developer carrier to which a development bias (development potential) in which direct current or direct current is superimposed is applied. Alternatively, development is performed using a two-component developer. As a developing method of the image forming apparatus, a one-component developing method, a two-component developing method, a hybrid developing method, or the like is known. In any method, in order to obtain a uniform and clear full color image with excellent color reproducibility, it is necessary to keep the toner amount on the image carrier faithful to the electrostatic latent image.
For example, in the hybrid development method described in Patent Document 1, the amount of toner on the image carrier changes according to the toner consumption pattern of the immediately preceding image, so that a ghost image is generated when the image density of the next image fluctuates. Also in the two-component development method, it is known that a ghost image is generated depending on development conditions.
Patent Document 2 discloses that a tetrahedral amorphous carbon layer is provided as a low-friction film on the developer carrying member so that the toner hardly remains on the developer carrying member and the ghost image is reduced. ing.
However, in such a ghost image reduction method provided with a low friction film, the cost of a single developer carrier increases, so a new method is being sought.
Although Patent Documents 3 to 6 disclose a configuration in which a voltage is applied to an electrode disposed opposite to a developer carrier, it does not prevent the generation of a ghost image.

  An object of the present invention is to prevent the occurrence of ghost development.

  In order to achieve the above object, a developing device according to the present invention is rotatable so as to face an image carrier and carries a two-component developer in a region facing the image carrier. And the developer carrying member on the downstream side in the rotation direction of the developer carrying member relative to the opposing region between the image carrying member and the developer carrying member, and the potential applied to the developer carrying member is V1, It is characterized by having an electrode to which V1 + V2 is applied when the potential on the same polarity side as the charging polarity of the two-component developer is V2.

  According to the present invention, since the electrostatic force from the electrode acts on the developer on the developer carrier on the downstream side in the developer rotation direction from the opposed region between the image carrier and the developer carrier, the ghost Generation of an image can be prevented.

1 is a schematic diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 3 is an enlarged cross-sectional view illustrating a configuration example of a process cartridge included in the image forming apparatus according to the present invention. FIG. 3 is an enlarged view showing a configuration around a developing device. FIG. 4A is a plan view of the developing device with a part of the casing removed, FIG. 4B is a front view, and FIG. 4C is a view of the screw conveyance unit. A cross-sectional view is shown. FIG. 3 is a diagram schematically illustrating a developer flow in a developing device. The figure explaining the structure which used the casing which is 1st Embodiment of a developing device as an electrode. The figure explaining the structure which provided the electrode in the casing which is a modification of 1st Embodiment of a developing device. The figure explaining the structure which used the doctor blade which is a modification of 2nd Embodiment of a developing device as an electrode. The figure which shows the evaluation method of a ghost image. The block diagram of the control system which controls the electric potential applied to an electrode.

The developing device and the image forming apparatus according to the present invention use a two-component developer composed of toner and a magnetic carrier, and can rotate to face the image carrier, and can be opposed to the image carrier (development). A developer carrier that supports and supplies a two-component developer to a region (also referred to as a development nib portion), and a downstream side in the rotation direction of the developer carrier relative to an opposing region between the image carrier and the developer carrier And an electrode to which V1 + V2 is applied, where V1 is the potential applied to the developer carrier and V2 is the same polarity as the charging polarity of the two-component developer. Characterized by dots.
Embodiments and comparative examples according to the present invention will be described below with reference to the drawings. In the embodiment and the comparative example, components having the same functions and configurations are denoted by the same reference numerals, and redundant description is appropriately omitted. The drawings may be partially omitted to facilitate understanding of the configuration. In the figure, Y, M, C, and K are subscripts attached to components corresponding to yellow, magenta, cyan, and black, and are omitted as appropriate.

First, an image forming apparatus and a process cartridge will be described, and then an embodiment of a developing device will be described.
The image forming apparatus shown in FIG. 1 is an electrophotographic tandem type color copier 100. On the upper part of the apparatus main body 101 of the color copying machine 100, a document reading unit 32 that conveys and reads a document to the document reading unit is arranged. Under the apparatus main body 101, a paper feed unit 26 that stores a recording medium P such as transfer paper and a paper feed roller 27 that feeds the recording medium P from the paper feed unit 26 are arranged. Below the document reading unit 32, a paper discharge tray 30 on which printed matter on which images are formed is placed. An image provided with photosensitive drums 1Y, 1M, 1C, and 1Bk as image carriers on which toner images of four colors (yellow Y, magenta M, cyan C, and black Bk) are formed inside the apparatus main body 101. Process cartridges 6Y, 6M, 6C, and 6Bk are arranged as forming portions. Around each photosensitive drum, the charging units 4Y, 4M, 4C, and 4Bk that charge each photosensitive drum, and the electrostatic latent image formed on each photosensitive drum are developed with toner constituting the developer. Developing devices 5Y, 5M, 5C, and 5Bk that form toner images of respective colors, an intermediate transfer belt 8 as an intermediate transfer member, and photosensitive member cleaning units 2Y, 2M, 2C, and 2Bk that clean the photosensitive drums, A well-known static eliminating unit (not shown) is arranged.

The endless intermediate transfer belt 8 is wound around a plurality of rollers, and rotates and moves counterclockwise in the drawing. A primary transfer portion for transferring a toner image formed on each photosensitive drum onto the intermediate transfer belt 8 is formed in a portion of the loop-shaped intermediate transfer belt 8 in the loop facing each photosensitive drum. Primary transfer bias rollers 9Y, 9M, 9C, and 9Bk are disposed as primary transfer members. The primary transfer bias rollers 9Y, 9M, 9C, and 9Bk are configured to be applied with a transfer bias having a polarity opposite to the polarity of the toner.
A secondary transfer bias roller 19 as a secondary transfer member is disposed outside the intermediate transfer belt 8 so as to face a secondary transfer backup roller disposed inside the intermediate transfer belt 8. The secondary transfer bias roller 19 forms a secondary transfer portion that collectively transfers the toner image transferred onto the intermediate transfer belt 8 onto the recording medium P.
Between the secondary transfer bias roller 19 and the paper feed roller 27, there is disposed a registration roller 28 that feeds the recording medium P fed from the paper feed unit 26 at a timing that matches the toner image at the secondary transfer unit. Between the secondary transfer bias roller 19 and the paper discharge tray 30, there are a fixing device 20 and a paper discharge roller 29 for fixing the unfixed toner image transferred onto the recording medium P by the secondary transfer portion with heat and pressure. Has been placed. Reference numerals 31Y, 31M, 31C, and 31Bk denote toner containers of respective colors that store toners that are powders of respective colors (yellow, cyan, magenta, and black) and that are replenished to the developing device 5.

Hereinafter, an operation at the time of normal color image formation in the color copying machine 100 will be described. Note that FIG. 2 is also referred to for an explanation of the image forming process performed on the photosensitive drums 1Y, 1M, 1C, and 1Bk.
The document is optically read by the document reading unit 32, imaged on a color sensor (not shown), and read by the color sensor for each RGB (red, green, blue) color separation light. Are converted into electrical image signals, and used as yellow, magenta, cyan, and black color image information.

  Image information of each color of yellow, magenta, cyan, and black is transmitted to a writing unit (not shown). From this writing section, laser light L as exposure light based on the image information of each color is emitted toward the corresponding photosensitive drums 1Y, 1M, 1C, and 1Bk.

The four photosensitive drums 1Y, 1M, 1C, and 1Bk rotate in the clockwise direction in FIG. The surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk are uniformly charged at the facing portions of the charging portions 4Y, 4M, 4C, and 4Bk. Thus, a charging potential is formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk (charging process).
The charged surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk reach the irradiation positions of the respective laser beams L, and receive the laser beams L corresponding to the respective colors emitted from the writing unit. That is, the laser beam L corresponding to the yellow component is irradiated to the surface of the first photosensitive drum 1Y from the left side of the drawing. At this time, the yellow component laser beam L is scanned in the rotational axis direction (main scanning direction) of the photosensitive drum 1Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 1Y after being charged by the charging unit 4Y.
Similarly, the laser beam L corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 1M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser beam L is applied to the surface of the third photosensitive drum 1C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam L is applied to the surface of the fourth photosensitive drum 1Bk from the left side of the paper, and an electrostatic latent image of the black component is formed (exposure step).

Thereafter, the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk on which the electrostatic latent images of the respective colors are formed reach positions facing the developing devices 5Y, 5M, 5C, and 5Bk, respectively. Then, the respective color toners are respectively supplied from the developing devices onto the photosensitive drums 1Y, 1M, 1C, and 1Bk, and the electrostatic latent images on the photosensitive drums 1Y, 1M, 1C, and 1Bk are developed as toner images of the respective colors. (Development process).
The surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk after the development process reach primary transfer portions as opposed portions to the intermediate transfer belt 8, and are formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk. The toner images of the respective colors are sequentially transferred on the intermediate transfer belt 8 (primary transfer process).

  The surfaces of the photoconductor drums 1Y, 1M, 1C, and 1Bk after the transfer process reach positions facing the photoconductor cleaning units 2Y, 2M, 2C, and 2Bk, respectively. Untransferred toner remaining on 1C and 1Bk is collected (cleaning step). Thereafter, the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk pass through a portion facing the neutralization unit, and a series of image forming processes on the photosensitive drums 1Y, 1M, 1C, and 1Bk is completed.

The intermediate transfer belt 8 onto which toner of each color is transferred (carrying) from the photosensitive drums 1Y, 1M, 1C, and 1Bk is rotated and moved counterclockwise in the drawing so as to face the secondary transfer bias roller 19. Reach position. Then, it is carried on the intermediate transfer belt 8 on the recording medium P fed from the paper feed unit 26 at a position (secondary transfer unit) facing the secondary transfer bias roller 19 to which the secondary transfer bias is applied. The color toner images are collectively transferred (secondary transfer step). Thereafter, the surface of the intermediate transfer belt 8 reaches the position of a well-known intermediate transfer belt cleaning unit, and the untransferred toner adhering to the intermediate transfer belt 8 is collected by the intermediate transfer belt cleaning unit, and a series in the intermediate transfer belt 8 is collected. The transfer process ends.
The recording medium P to the secondary transfer unit is fed from the sheet feeding unit 26 by the sheet feeding roller 27, guided to the registration roller 28, and conveyed by the registration roller 28 in time with the image position.

  The recording medium P on which the full color toner image is transferred is guided to the fixing device 20. In the fixing device 20, a full-color toner image is fixed on the recording medium P at a fixing nip between the fixing roller and the pressure roller. The recording medium P after the fixing process is discharged as a printed matter outside the apparatus main body by the paper discharge roller 29 and stacked on the paper discharge tray 30 to complete a series of image forming processes.

  A process cartridge for each color and a developing device for each color in the present embodiment will be described with reference to FIGS. Since the configuration of each process cartridge and each developing device is the same except that the color of the developer used is different, FIGS. 2 and 3 will be described using the configuration of one process cartridge and the developing device. The subscripts Y, M, C, and Bk for identifying the toner color are omitted. In FIG. 1, Y, M, C, and Bk subscripts are attached to the process cartridges and developing devices of the respective colors.

  In FIG. 2, the process cartridge 6 includes a photosensitive member cleaning unit 2, a charging unit 4, and a developing device 5 that are integrally held by a single casing, and is detachable from the apparatus main body 101. The photoconductor cleaning unit 2, the charging unit 4, and the developing device 5 are not unitized as the process cartridge 6, but each has a single configuration and is detachable from the apparatus main body 101. Also good. In this case, the image forming unit indicates a part where the photosensitive member cleaning unit 2, the charging unit 4, the developing device 5 and the like are arranged.

  The developing device 5 includes a developing roller 50 as a developer carrying member that is disposed to face the photosensitive drum 1 and is rotatable, a doctor blade 52 as a developer regulating unit, a supply screw 53 as a supply unit, and a collection unit as a collection unit. Screws 54 are provided, and these are covered and supported by a casing 58. The casing 58 is filled with a two-component developer (hereinafter referred to as “developer”) G including toner and carrier. In this embodiment, a contact charging method is used in which the surface of the developing roller 50 contacts the surface of the photosensitive drum 1 (hereinafter referred to as “drum surface”) 1a. Good.

,
The developing roller 50 is formed on the surface 1 a of the photosensitive drum 1 by carrying and supplying the developer G to a developing region 60 (also referred to as a developing nip portion) that is a region facing the photosensitive drum 1. The toner in the developer G is supplied to the electrostatic latent image. As shown in FIG. 3, the developing roller 50 includes a developing sleeve 51 as a rotatable cylindrical developer supporting portion, and a magnet as a magnetic field generating portion included in the developing sleeve 51 and supported and fixed to the casing 58. It has the mag roller 55 which has. The developing sleeve 51 is composed of an aluminum cylindrical sleeve. The magnet roller 55 includes a plurality of permanent magnets having different polarities arranged in a fixed portion. In the present embodiment, the surface of the developing roller 50 is the surface 51 a of the developing sleeve 51 (hereinafter referred to as “sleeve surface”). The developing sleeve 51 is configured to rotate on the outer peripheral surface of the mag roller 55 in the counterclockwise direction in the figure. The developing roller 50 is configured to be applied with an applied potential V1 as a developing bias.

The doctor blade 52 regulates the amount of developer carried by regulating the layer thickness of the developer G carried on the developing roller 50 (sleeve surface 51a) to be constant. The supply screw 53 supplies the developer G to the developing roller 50, and the recovery screw 54 recovers and stirs the developer G that has been developed.
The supply screw 53 and the recovery screw 54 are arranged in parallel to each other and are configured to be driven to rotate. In the developing device 5, the toner is stirred and transported after replenishment at the same time by rotating both of them, and the toner and carrier are uniformly mixed and charged. As shown in FIG. 3, the uniformly mixed developer G is conveyed to the sleeve surface 51a by the P5 magnetic force of the mag roller 55 contained in the developing sleeve 51 by the supply screw 53 provided in parallel to the developing sleeve 51. Is done. The conveyed developer G is carried to the developing region 60 formed by the drum surface 1a and the sleeve surface 51a as the developing sleeve 51 rotates in the direction of the arrow in the figure. The applied potential V1 is applied to form a developing electric field, whereby the toner in the developer G develops the latent image on the drum surface 1a. The developed developer G is collected in the developing device 5 as the developing sleeve 51 rotates, and a partition plate (collection guide) 57 formed between the supply screw 53 and the collection screw 54. It is comprised so that it may be collect | recovered by the collection | recovery screw 54 via.

  4A is a plan view of the developing device 5 with part of the casing 58 removed, FIG. 4B is a front view of the developing device 5, and FIG. 4C is a cross-sectional view of the screw conveying unit. . The arrows in the figure indicate the flow of the developer G (flow between the screws and from the developing roller 50 to the collecting screw 54). In the regions a and b at the screw end, the upper recovery screw and the lower supply screw communicate with the agitation / conveying chamber in the vertical direction. In the part a, the developer G is conveyed from the upper part to the lower part and in the part b from the lower part to the upper part. It has come to be. As for the shape of the screw in the communication portion, a paddle or a reverse-wound screw is provided, and the conveying ability in the direction perpendicular to the conveying direction is given.

FIG. 5 is a diagram illustrating how the developer G is deposited in the developing device 5. In the case of the configuration shown in FIG. 5, the developer G is supplied to the developing roller 50 (developing sleeve 51) while being agitated and conveyed by the supply screw 53, and all is recovered to the recovery screw 54. For this reason, the accumulation state of the developer G becomes oblique in the screw axis direction (the amount of developer in the supply screw 53 decreases in the downstream direction). When the relationship between developer conveyance capacity: Wm and developer conveyance amount: Ws on the developing sleeve 51 determined from the diameter, pitch, and rotation speed of the supply screw 53 is Wm> Ws, the developer G is uniformly developed. 51 is transported on the top. If this condition is not satisfied, the developer G becomes insufficient on the downstream side of the supply screw 53, and the developer G cannot be supplied to the developing sleeve 51.
As shown in FIG. 3, in the developing device 5, the recovery screw 54 is disposed on the upper side, the supply screw 53 is disposed on the lower side, and the doctor blade 52 is provided below the developing roller 50. For this reason, in the embodiment in which the transfer member (intermediate transfer belt 8) is provided at the upper part of the developing device 5, the developer G used for the development is unidirectionally circulated without returning to the supply path, and the photosensitive drum 1 is provided. On the other hand, a developing system (with development) in which the developing sleeve 51 rotates in the forward direction at a mutually opposing portion (developing region 60) can be established.

  The magnetic pattern of the developing roller 50 will be described. In FIG. 3, the developing sleeve 51 rotates counterclockwise in the figure, and the developer G is conveyed by this rotation. Note that the radial line segments attached to the developing roller 50 in FIG. 3 indicate positions where the respective magnetic forces of the P1 pole to the P5 pole reach a peak.

  The developer G is, for example, a toner (5.8 μm) mainly composed of a polyester resin and a carrier (35 μm) that is magnetic fine particles uniformly mixed to 7 wt%. The developing device 5 is filled with a certain amount of such developer G in the casing 58, and rotates the supply screw 53 and the collection screw 54 arranged in parallel at 600 to 800 rpm. As a result, the toner is stirred and conveyed after replenishment at the same time, and the toner and carrier are uniformly mixed and charged. The uniformly mixed developer G is transported by a supply screw 53 provided in parallel near the developing sleeve 51 and supplied to the developing sleeve 51. Then, the P5 magnetic force of the mag roller 55 included in the developing sleeve 51 is carried on the sleeve surface 51 a by the magnetic force of the mag roller 55 as a developer spike made of toner and carrier (magnetic particles) on the developing sleeve 51. The toner in the developer brush (magnetic brush) is mixed with a carrier to obtain a specified charge amount. The frictional charging between the toner and the carrier is caused by the frictional force generated when the toner is made uniform by rotating / conveying the recovery screw 54 and the supply screw 53, and the toner is conveyed while the gap between the developing sleeve 51 and the doctor blade 52 is held in a magnetic field. Thus, the toner is charged.

Next, a mechanism for generating a ghost image will be described.
In the case of the hybrid development system, the ghost image is a phenomenon in which the image density of the next image fluctuates because the amount of toner on the developing roller, which is a developer carrier, changes according to the toner consumption pattern of the immediately preceding image. This is because, in the hybrid development method, a constant amount of toner is always supplied to the developing roller, so that the toner amount on the developing roller varies depending on the number of times the toner is supplied. That is, when the previous image prints an image with low toner consumption, the amount of residual toner on the developing roller is large, and after toner supply, the amount of toner on the developing roller further increases and the image density becomes high. On the other hand, after printing an image with high toner consumption, the amount of residual toner on the developing roller is small, and after toner supply, the amount of toner on the toner carrier is reduced and the image density is reduced.

  On the other hand, in the case of the two-component development method using the developer G that is a two-component developer, the toner adheres on the developing roller 50 that is the developer carrying member according to the immediately preceding image history, and adheres on the developing roller 50. The toner development amount of the next image varies in accordance with the electric potential of the charged toner. That is, the toner development amount of the next image varies depending on the previous image history. Specifically, first, toner is applied to the developing sleeve 51 because the toner receives an electrostatic force on the developing sleeve 51 side of the developing roller 50 in the non-image portion. Since the toner adhering to the developing sleeve 51 has an electric charge, the developing potential is raised by the amount of electric charge of the toner on the developing sleeve 51 during printing, and the toner development amount increases.

  In the developing area 60, when a solid image is developed, an electrostatic force is applied in the direction in which the toner moves toward the latent image carrier (photosensitive drum 1 side). Since the toner having the electric charge is reattached in the developer G during development, the developing sleeve 51 is not contaminated with toner. If the solid image is continuously developed in this state, when the developing sleeve 51 is rotated and developed, the development bias of the toner contamination is not increased and the toner development amount becomes normal (development from the non-image portion). The amount decreases). Since the above process occurs for solid black after solid white and solid just after paper, it is estimated that the image density increases by a distance corresponding to the circumference of the developing sleeve, leading to the generation of ghost images. Is done.

(First embodiment)
Therefore, in the present embodiment, as shown in FIG. 6, the developing three portion 51 of the developing roller 50 is located downstream of the developing region 60 in the rotation direction of the developing roller 50 (developing three portion 51) (after passing the developing nip portion). The electrode 59 is provided so as to face the electrode 59, and when the potential V1 applied to the developing roller 50 is set to the potential V2 on the same polarity side as the charging polarity of the developer G, V1 + V2 is applied to the electrode 59. did.
In the case of the configuration shown in FIG. 6, the electrode 59 is on the downstream side in the rotation direction of the developing sleeve 51 with respect to the developing region 60 (developing nip portion), and before the developer G is separated from the developing sleeve 51 (developing roller 50). It is provided in the region D to be a position. Specifically, the electrode 59 is disposed at a portion of the developing roller 50 facing the normal direction magnetic patterns P2 and P3. As the electrode 59, as shown in FIG. 6, a portion of the casing 58 of the developing device 5 facing the normal direction magnetic patterns P <b> 2 and P <b> 3 is made of metal and connected by a power source 200 and wiring 201 to form an electrode 59. In FIG. 7, a film-like electrode member 590 is disposed on the inner surface 58 a of the casing 58 of the developing device 5 facing the normal magnetic patterns P <b> 2 and P <b> 3, and is connected to the power source 200 by the wiring 201 to form the electrode 59.

(Second Embodiment)
In the present embodiment, as shown in FIG. 8, the developing roller 50 (developing three portion 51) faces the developing three portion 51 of the developing roller 50 on the downstream side of the developing roller 50 (developing three portion 51) in the rotation direction (after passing the developing nip portion). In this way, the metal doctor blade 52 is connected to the power source 200 by the wiring 201, and the electrode 59 is formed by applying V1 + V2.

Next, a method for evaluating a ghost image will be described.
The ghost in the image plane was evaluated by combining the imagio MP c5000 remodeled machine and the developing devices 1 to 4 shown below.
<Ghost image evaluation method>
For ghost images, a commercially available digital full-color copier (image MP MP5000 manufactured by Ricoh Co., Ltd.) is modified, developer G is set in developing devices A1 to A4 described below, and a 20K chart with an image area of 5% is output. After that, a ghost confirmation image is printed, and the density difference between the developing sleeve 51 (a) and after (c) (b) is shown in FIG. 9 as an X-Rite 939 (X-Rite 939). The average density difference (b1-a1, b2-a2, b3-a3) at three locations was ΔID, and the following ranking was performed.
A: 0.01 ≦ ΔID
○: 0.01 <ΔID ≦ 0.03
Δ: 0.03 <ΔID ≦ 0.06
×: 0.06 <ΔID
◎: Very good, ○: Good, Δ: Acceptable, ×: Unusable level for practical use, ◎, ○, △ were accepted and x was rejected.

Next, the configuration of the developing devices 1 to 4 used for evaluation will be described.
(Developing device 1)
This developing device 1 is a comparative example, and is a developing device having a conventional configuration in which the electrode 59 is removed from the developing device 5 shown in FIG. 6, as shown in FIG.
·conditions
Developer Cyan developer Developing roller Aluminum development bias DC
(Developing device 2)
This developing device 2 is a comparative example, and is a developing device having a configuration of Patent Document 2 in which a tetrahedral amorphous carbon layer is provided as a low friction film on a developing sleeve.
·conditions
Developer Cyan developer Developer roller Aluminum developer roller with ta-C coating (deviation 0.3 μm at 0.6 μm center)
Development bias DC
(Developing device 3)
The developing device 3 is the developing device having the configuration described in the first embodiment in which the electrode 59 is formed on the casing 58 shown in FIG.
・ Conditions Image forming device
Developer Cyan developer
Developing roller Aluminum
Development bias DC
Applied potential to electrode Applied potential to developing roller -100V
(Developing device 4)
The developing device 4 is a developing device having the configuration described in the second embodiment in which the doctor blade 52 shown in FIG.
·conditions
Developer Cyan developer Developing roller Aluminum development bias DC
Applied potential to electrode Applied potential to developing roller -200V
Table 1 shows the evaluation results of the ghost images of the developing devices 1 to 4.

  Table 1 shows the result of performing the ghost image evaluation environment for the developing devices 1 to 4 in a standard environment at a temperature of 23 ° and a humidity of 50%. From the results shown in Table 1, in the developing devices 2 to 4, the generation of ghost images did not occur or were acceptable. Among these acceptable levels, the developing device 3 (first embodiment) in which the casing 58 was formed as the electrode 59 was the best result.

  Table 2 shows the evaluation results when the ghost images for the developing devices 1 to 4 are evaluated in an environment on the low temperature and low humidity side (temperature 10 ° humidity 11%) with respect to the evaluation environment of Table 1. In general, the toner charge amount tends to increase toward the low-temperature and low-humidity environment, so that toner contamination on the developing roller 50 (developing sleeve 51) is less likely to occur. It is assumed that it was higher than that.

  Therefore, the potential difference between the developing roller 50 (developing sleeve 51) and the electrode 59 is increased to -200V and -400V in the developing device 3 and the developing device 4 to -200V and -400V, which are twice as large as those in the evaluation test of Table 1. The results are shown in Table 3.

  As described above, even in the low temperature and low humidity environment, when the potential V2 is increased, the ghost can be reduced to the same extent as in the standard environment.

  That is, as in the configuration of the present embodiment, the two-component developer (in the developing region 60 that is rotatable facing the photosensitive drum 1 that is an image carrier and is opposed to the photosensitive drum 1). The developing roller 50, which is a developer carrying member for carrying and supplying the developer G), and the downstream side in the rotation direction of the developing roller 50 from the facing region 60 between the photosensitive drum 1 and the developing roller 50. If the electrode 59 to which V1 + V2 is applied is provided when the potential V1 applied to the developing roller 50 and the potential on the same polarity side as the charging polarity of the developer G is V2, The toner contamination on the (surface 51a of the developing sleeve 51) can be kept at an appropriate amount, and as a result, the generation of a ghost image can be prevented without variation depending on the environment.

  The potential V2 applied to the electrode 59 is set to be different depending on at least the environmental conditions of temperature and humidity. That is, the charge amount of the toner changes according to temperature and humidity, which are examples of the environment. By setting the potential V2 to be added to the low temperature and low humidity environment side where the toner charge amount is large, the potential V2 to be added is set to be small. The toner contamination on the developing sleeve 51) of the developing roller 50 can be kept at an appropriate amount, and as a result, the occurrence of ghost can be prevented without variation depending on the environment. In this embodiment, as an example of the low-temperature and low-humidity environment side, the temperature is 10 ° C. and the humidity is 11%, and the higher temperature and humidity environment side is 23 ° C. and the humidity is 50%. Normally, a temperature of 23 ° C. and a humidity of 50% is a standard environment, but when viewed from a low temperature and low humidity environment, it is on the high temperature and high humidity environment side. As the change and setting of the potential V2, for example, as shown in FIG. 10, the temperature and humidity of the installation environment of the image forming apparatus 100, the temperature and humidity in the apparatus main body 101, and the temperature sensor 301 and the humidity sensor serving as environmental condition detection means. 302 detects and inputs the detected value to the control unit 300. The control unit 300 is configured by a computer, and a potential V <b> 2 corresponding to detection values from the temperature sensor 301 and the humidity sensor 302 is set. The control unit 300 may set the value of the potential V2 from the detection values of the temperature sensor 301 and the humidity sensor 302 and control the power source 200 so that the potential V2 can be changed according to the environmental condition of the potential V1 + V2 applied to the electrode 59. .

  The layer thickness is adjusted by the doctor blade 52 by providing the electrode 59 on the downstream side of the developing region 60 in the rotation direction of the developing roller 50 and before the developer G leaves the magnetic force from the developing roller 50. Since the potential can be applied from the electrode 59 to the developer G in the state in which the toner G is formed, the amount of toner stains can be stabilized on the developing roller 50 regardless of the change in the fluidity of the developer G over time, resulting in a ghost image. Can be more stably prevented.

The electrode 59 is formed as a casing 58 that covers the developing roller, that is, the electrode 59 needs to be newly provided by wiring to the existing casing 58 of the developing device 5 and causing a part of the electrode 59 to function as the electrode 59. In addition, since the installation space of the electrode 59 can be taken into consideration and the increase in the number of parts can be suppressed, the generation of a ghost image can be prevented with an inexpensive configuration.
The electrode 59 is formed as the doctor blade 52, that is, by wiring to the existing doctor blade 52 and functioning as the electrode 59, there is no need to newly provide the configuration of the electrode 59, and the installation space of the electrode 59 is considered. In addition, since an increase in the number of parts can be suppressed, the generation of ghost images can be prevented with an inexpensive configuration.

  A color copying machine 100 as an image forming apparatus according to the present invention includes four process cartridge units 6Y, 6M, 6C, and 6Bk corresponding to four colors of yellow, cyan, magenta, and black, and has electrodes. As the developing device, at least one of the developing devices 5Y, 5M, 5C, and 5Bk of at least four colors, preferably a developing device provided in a process cartridge unit that generates a ghost image or a color that makes a ghost image stand out. Use it. With such a configuration, it is only necessary to change the existing developing device to a developing device having the electrode 59 as much as necessary, so that the generation of a ghost image can be prevented with an inexpensive configuration.

  When the four process cartridge units 6Y, 6M, 6C, and 6Bk serving as a plurality of image forming units are provided as in the present embodiment, the developing devices provided in all the process cartridges are all the developing devices including the electrodes 59. By doing so, it is possible to more reliably prevent the generation of a ghost image regardless of the color.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.
For example, the image forming apparatus is not limited to a color copying machine, but may be a printer, a facsimile machine, a plotter printer, or a multifunction machine that combines at least one of a scanner and a printer, a facsimile machine, a plotter printer, or a copying machine. Also good.
The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 (Y, M, C, Bk) Image carrier 5 (Y, M, C, Bk) Developing device 6 (Y, M, C, Bk) Image forming unit 50 (Y, M, C, Bk) Developer Carrier 52 (Y, M, C, Bk) Restriction part 58 (Y, M, C, Bk) Casing 60 (Y, M, C, Bk) Opposite area (development nip)
100 Image forming apparatus A Rotating direction of developer carrier D Position before developer leaves G Two-component developer V1 Potential applied to developer carrier V2 Potential of same polarity as charging polarity of two-component developer V1 + V2 On electrode Applied potential

Japanese Patent No. 3356948 JP2012-168225A JP-A-11-265118 JP 2007-086447 A JP 2013-225097 A JP 2013-231914 A

Claims (7)

A developer carrier that is rotatable opposite to the image carrier and carries and supplies a two-component developer to a region facing the image carrier;
An electric potential applied to the developer carrying member is arranged opposite to the developer carrying member on the downstream side in the rotation direction of the developer carrying member from a facing region between the image carrying member and the developer carrying member. Is a developing device having an electrode to which V1 + V2 is applied, where V1 is a charge polarity of the two-component developer and a potential on the same polarity side as V2. The developing device according to claim 1,
The developing device in which the potential V2 is set to be different depending on at least the environmental conditions of temperature and humidity. In the developing device according to claim 1 or 2,
The developing device is provided at a position downstream of the developer carrying member in the rotation direction with respect to a region facing the image carrying member and before the developer is separated from the developer carrying member. The developing device according to claim 3.
The developing device, wherein the electrode is formed as a casing covering the developer carrying member. The developing device according to claim 1 or 2,
The developing device in which the electrode forms a developer regulating portion that regulates the amount of the developer carried on the surface of the developer carrying body.   An image forming apparatus comprising an image forming unit comprising at least one developing device according to claim 1.   An image forming apparatus including a plurality of image forming units, each image forming unit including the developing device according to claim 1.

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