JP2017134437A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that allows a simple configuration to suppress occurrence of concentration thinness or solid followability defects even when deterioration or moisture absorption of developer occurs, and further allows even occurrence of ghost image defects.SOLUTION: A developing device comprises: a developer carrier that holds developer and rotates; a development container that rotatably holds the developer carrier to store the developer; a support part that has one end supported by the development container; and a developer regulation member that is anchored to the support part, and regulates the developer to be held by the developer carrier to a prescribed layer thickness. The developer carrier comprises a sea island structure that forms a sea part to be formed by any one of high resistance part and low resistance part on an outer peripheral surface, and an island part to be dispersed from other thereof, and the developer regulation member includes, in order from a downstream side of a rotation direction of the developer carrier: a protrusion part that protrudes toward at least the developer carrier, and is provided with an abutting part which abuts thereon; and an opposing surface that opposes the developer carrier. One end of the opposing surface is configured to connect to the protrusion part, and other end thereof is configured to be a free end.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a developing device in an image forming apparatus such as an electrophotographic printer or an electrophotographic copying machine that forms an image on a recording material.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic image forming process, a developing device having the following is known. That is, a developer carrier that holds and conveys the developer on the surface, a developer reservoir that stores the developer, and a developer that is in contact with the developer carrier and is stored in the developer reservoir. And a developer supply member that supplies the carrier (Patent Document 1).

  On the other hand, in order to further reduce the size of the developing device, a developing device having no developer supply means as shown in Patent Document 1 has been proposed (Patent Document 2). In Patent Document 2, a developer carrying member configured such that a dielectric portion and a grounded conductor portion are distributed regularly or irregularly on the surface is directly or developed by a developer regulating member. By rubbing through the agent, a predetermined charge is applied to the dielectric portion on the developer carrying surface. Then, an electric field is generated on the dielectric part to which electric charge is applied.

  In particular, a minute closed electric field is generated on the adjacent portion between the dielectric portion and the grounded conductor portion, and a large number of the minute closed electric fields are formed on the entire developer carrying member. A developer having an unstable charge amount such as uncharged or low charge in the developer storage means is transported to a large number of areas where electric fields such as minute closed electric fields are generated on the developer carrier. The electrostatic force generated by the electric field, particularly in the case of an uncharged developer, receives a gradient force (Gradient-Force) generated by the minute closed electric field, and is attracted and held on the surface of the developer carrying member.

JP 61-42672 A Japanese Patent Laid-Open No. 6-130792

  However, in the configuration shown in Patent Document 2, when the amount of use of the developing device is increased (for example, at the end of life) or used in a high-temperature and high-humidity environment, due to the deterioration or moisture absorption of the developer, the surface of the developer carrier is changed from the developer. The amount of charge imparted to the dielectric portion is reduced, and the strength of the electric field generated on the surface of the developing carrier is weakened. As a result, the electrostatic force and gradient force for attracting the developer are weakened, and the amount of developer held and transported on the developer carrier is insufficient when forming an image with a high printing rate such as a black solid image. . In some cases, there are problems such as poor solidity and poor solid followability that results in an image fading toward the rear end of a black solid image.

  On the other hand, the developer supply member shown in Patent Document 1 has an action of peeling off the developer remaining on the developer carrying body without being developed at the same time as supplying the developer to the developer carrying body. . Therefore, in a configuration that does not use the developer supply member as shown in Patent Document 2, the developer remaining on the developer carrying member may remain on the developer carrying member without being peeled off. May be likely to occur. This ghost image defect is a phenomenon in which the history of an image developed in the previous round of the developer carrier appears as density unevenness with a phase difference of the developer carrier period in a uniform halftone image after the next round.

  The object of the present invention is to have a simple configuration, and even when the developer is deteriorated or absorbs moisture, it is possible to suppress the occurrence of low density and poor solid followability, and also to suppress the occurrence of ghost image defects. Is to provide a simple developing device.

  In order to achieve the above object, a developing device according to the present invention holds a developer on an outer peripheral surface, supports a rotating developer carrier, and rotatably supports the developer carrier, and contains the developer. A developer container, a support part supported at one end by the developer container, a developer regulating member fixed to the support part and regulating the developer held on the developer carrier to a predetermined layer thickness The developer carrying member is formed on an outer peripheral surface of an island formed by one of a high resistance portion and a low resistance portion, and an island in which the other of the high resistance portion and the low resistance portion is dispersed. And the developer regulating member includes a contact portion that protrudes and contacts at least the developer carrier in order from the downstream side in the rotation direction of the developer carrier. A projecting portion; and a facing surface facing the developer carrier, wherein the facing surface One end is characterized in that the connection and the other end is a free end in the projecting portion.

  According to the present invention, there is provided a developing device capable of suppressing the occurrence of low density and poor solid followability even when the developer deteriorates or absorbs moisture, and further suppresses the occurrence of ghost image defects. can do.

1 is a diagram illustrating a developing device according to a first embodiment of the present invention. 1 is a diagram illustrating an image forming apparatus equipped with a developing device according to a first embodiment. It is a figure which shows the developer carrier surface which concerns on 1st Embodiment. It is a figure which shows the developer control member which concerns on 1st Embodiment. It is a figure which shows the relationship between Ra and r which concerns on 1st Embodiment. It is a figure which shows the image development apparatus of the comparative example which concerns on 1st Embodiment. It is a figure which shows the developing device which concerns on 2nd Embodiment. It is a figure which shows the surface of the developing agent carrier which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the dimensions, materials, and shapes of the components described in the following embodiments, their relative arrangement, the values of each parameter, and the like are appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. It should be. Therefore, the scope of the present invention is not intended to be limited to the following embodiments.

<< First Embodiment >>
<Overall schematic configuration of image forming apparatus>
First, the overall configuration of an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus) according to the present invention will be described. FIG. 2 is a schematic cross-sectional view of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of this embodiment is a full-color laser printer that employs an inline method and an intermediate transfer method.

  The image forming apparatus 100 can form a full-color image on a recording material (for example, recording paper, plastic sheet, cloth, etc.) according to the image information. The image information is input to the image forming apparatus 100 from an image image reading apparatus or a host device such as a personal computer that is communicably connected to the image forming apparatus 100.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, and third images for forming images of yellow (y), magenta (m), cyan (c), and black (b), respectively. , Fourth process cartridges 10y, 10m, 10c, and 10b. They are arranged in a row in a direction crossing the vertical direction.

  In the present embodiment, the configurations and operations of the first to fourth process cartridges 10y, 10m, 10c, and 10b are substantially the same except that the colors of images to be formed are different. Therefore, in the following, when there is no particular need to distinguish, subscripts y, m, c, and b given symbols to represent elements provided for any color are omitted and are generally described. To do.

  In this embodiment, the image forming apparatus 100 includes four drum-type electrophotographic photosensitive members arranged in parallel in a direction intersecting the vertical direction as a plurality of image carriers, that is, the photosensitive drums 1 (1y, 1m). 1c, 1b). Around the photosensitive drum 1, there are a charging roller 2 (2y, 2m, 2c, 2b), a scanner unit (exposure device) 7, a developing unit (developing device) 3 (3y, 3m, 3c, 3b), and a cleaning member 5. (5y, 5m, 5c, 5b) are arranged.

  The charging roller 2 is a charging unit that uniformly charges the surface of the photosensitive drum 1. The scanner unit 7 forms an electrostatic image (electrostatic latent image) on the photosensitive drum 1 by irradiating a laser based on the output calculated by the CPU 9 from the image information input from the host device such as a personal computer. Exposure means. The developing unit 5 is a developing unit that develops an electrostatic image as a developer (hereinafter, toner) image. The cleaning member 3 is a cleaning unit that removes toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after transfer.

  The photosensitive drum 1 and the charging roller 2, the developing unit 3, and the cleaning member 5 as process means acting on the photosensitive drum 1 are integrated to form a process cartridge 10. The process cartridge 10 can be attached to and detached from the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the image forming apparatus 100.

  Further, an intermediate transfer belt 61 as an intermediate transfer body for transferring the toner image on the photosensitive drum 1 to the recording material P is disposed facing the four photosensitive drums 1. The intermediate transfer belt 61 formed of an endless belt contacts the intended photosensitive drum 1 and circulates (rotates) in the direction of the arrow R2 (clockwise) in the figure. The intermediate transfer belt 61 is stretched around a secondary transfer counter roller 62, a driving roller 63, and a driven roller 64 as a plurality of support members.

  Four primary transfer rollers 4 (4y, 4m, 4c, 4b) as primary transfer means are arranged in parallel on the inner peripheral surface side of the intermediate transfer belt 5 so as to face the respective photosensitive drums 1. Yes. The primary transfer roller 4 presses the intermediate transfer belt 61 toward the photosensitive drum 1 to form a primary transfer portion where the intermediate transfer belt 61 and the photosensitive drum 1 are in contact with each other.

  A secondary transfer roller 65 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 62 on the outer peripheral surface side of the intermediate transfer belt 61. The secondary transfer roller 65 is in pressure contact with the secondary transfer counter roller 62 via the intermediate transfer belt 65 to form a secondary transfer portion where the intermediate transfer belt 61 and the secondary transfer roller 65 are in contact with each other. The recording material P onto which the toner image has been transferred is conveyed to a fixing device 8 as a fixing unit. The toner image is fixed to the recording material P by applying heat and pressure to the recording material P in the fixing device 8.

  The image forming apparatus 100 may form a single-color or multi-color image using only one desired image forming unit or using only some (not all) image forming units. It can be done.

<Image formation process>
At the time of image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the surface of the photosensitive drum 1 charged with a laser beam emitted from the scanner unit 7 is scanned and exposed on the photosensitive drum 1 based on the output calculated by the CPU 9 from the image information input from the host device. An electrostatic image according to the image information is formed. Next, the electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the developing unit 3.

  A voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 4 from a primary transfer voltage power source (high voltage power source) as a primary transfer voltage application unit. As a result, the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 61. At the time of forming a full-color image, the above-described process is sequentially performed in the first to fourth process cartridges 10y, 10m, 10c, and 10b, and the toner images of the respective colors are next superimposed on the intermediate transfer belt 61 to perform primary transfer. Is done.

  Thereafter, the recording material P is conveyed to the secondary transfer city in synchronization with the movement of the intermediate transfer belt 61. Then, a voltage having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 65 from a secondary transfer voltage power source (high voltage power source) as a secondary transfer voltage applying unit (not shown). As a result, the four-color toner images on the intermediate transfer belt 61 are collectively conveyed by the feeding means by the action of the secondary transfer roller 65 in contact with the intermediate transfer belt 61 via the recording material P. Secondary transfer is performed on the material P.

  The recording material P onto which the toner image has been transferred is conveyed to a fixing device 8 as a fixing unit. In the fixing device 8, the recording material P is applied with heat and pressure, whereby the transferred toner image is fixed and discharged from the image forming apparatus 100.

  The primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer process is removed and collected by the cleaning member 51.

  The developing unit 3 performs reverse development by bringing a developing roller (described later) as a developer carrying member into contact with the photosensitive drum 1. That is, the toner charged to the same polarity as the charged polarity of the photosensitive drum 1 (negative polarity in this embodiment) is attached to the portion of the photosensitive drum 1 where the charge is attenuated by exposure (image portion, exposed portion). The developing unit 4 for developing the electrostatic image was used.

<Configuration of process cartridge>
Next, the overall configuration of the process cartridge 10 mounted on the image forming apparatus 100 of the present embodiment will be described. The process cartridges 10 for each color have the same shape except for an identification unit (not shown), and yellow (y), magenta (m), and cyan (c) are included in the development unit 4 of the process cartridge 10 for each color. , Black (b) toners are accommodated.

  The developing unit 3 used a non-magnetic one-component toner as a developer. Hereinafter, description will be made with reference to FIG. 2 showing a cross section intersecting with the longitudinal direction (rotation axis direction) of the photosensitive drum 1. The process cartridge 10 is configured by integrating a photosensitive unit including the photosensitive drum 1 and a developing unit (developing device) 3 including a developing roller 22 that can be rotated.

  In addition to the photosensitive drum 1, the photosensitive unit includes a cleaning unit (cleaning device) 5 in which a cleaning blade 51 and a charging roller 2 are arranged on a cleaning frame so as to come into contact with the peripheral surface of the photosensitive drum 1. doing.

  The photosensitive drum 1 is supported rotatably with respect to the cleaning unit 5 via a bearing (not shown). The photosensitive drum 1 is configured to be driven to rotate in a direction indicated by an arrow R1 (counterclockwise) in accordance with an image forming operation when a driving force of a driving unit (a driving source) (not shown) is transmitted to the photosensitive unit. In the cleaning unit 5, the transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 51 is dropped and stored in the cleaning frame, and the conductive rubber roller portion of the charging roller 2 is the photosensitive drum 1. It is set as the structure which press-contacts to and rotates following.

  On the other hand, as shown in FIG. 1, the developing unit 3 includes a developing roller 22 as a developer carrying member that carries toner T, a developing blade (regulating member) 11 as a developer regulating member, and development for fixing them. And a developing device frame 20 as a container. The developing frame 20 as a developing container supports the developing roller 22 rotatably and accommodates the developer. The developing frame 20 includes a developing chamber 20a in which the developing roller 22 is disposed, and a blowout prevention sheet 20b that seals a developing opening (opening) connected from the developing chamber 20a to the outside.

  In the present embodiment, the developing roller 22 and the photosensitive drum 1 are rotated so that the surfaces of the developing roller 22 and the photosensitive drum 1 move in the same direction (in this embodiment, the direction from the upper side to the lower side in the gravitational direction). Then, a predetermined DC voltage is applied to the developing roller 22, and the electrostatic latent image is visualized in the developing unit that contacts the photosensitive drum 1 with toner negatively charged by frictional charging to form a toner image. Yes. In the present embodiment, the developing roller 22 is disposed in contact with the photosensitive drum 1, but the developing roller 22 is disposed adjacent to the photosensitive drum 1 at a predetermined interval. May be.

  Hereinafter, the developing device in the present embodiment will be described in detail.

<Detailed Configuration of Developing Device in this Embodiment>
1) Detailed Configuration of Developing Roller The configuration of the developing roller 22 in this embodiment will be described in detail with reference to FIG. The developing roller 22 has a diameter of 11.5 mm including a urethane surface layer 22-1 having a thickness of about 0.1 mm, a silicon base layer 22-2 having a thickness of about 2.7 mm, and a metal core 22-3 having a radius of 3 mm. These rollers are arranged so as to be rotationally driven in the direction of the arrow in the figure. As shown in FIG. 3, the surface of the developing roller 22 has a structure in which a dielectric portion 22-1a exemplified by an island is scattered on a urethane surface layer 22-1 exemplified by the sea in a very small area to form a sea island structure. Yes. Further, for the purpose of adjusting the surface roughness and adjusting the developer transport amount to an appropriate amount, the roughened particles 22-1b are scattered.

  The urethane surface layer 22-1 has a resistance value of about 10 ^ 5 Ω · cm, a dielectric portion 22-1a of about 10 ^ 11 to 10 ^ 14 Ω · cm, and a rough particle 22-1b of about 10 ^ 8 Ω · cm. A relatively high resistance portion and a low resistance portion are formed. Thus, the developing roller 22 has, on the outer peripheral surface, a sea portion formed by one of the high resistance portion and the low resistance portion, an island portion in which the other of the high resistance portion and the low resistance portion is dispersed, It has a sea-island structure that forms

2) Detailed Configuration of Developing Blade Next, the configuration of the developing blade 11 that regulates the developer on the developing roller 22 to a predetermined layer thickness in the present embodiment will be described in detail with reference to FIG. The developing blade 11 is in contact with the developing roller 22 so as to face the counter direction, and regulates the toner coating amount and applies a charge. In the present embodiment, a plate spring-like SUS plate support portion 11a having a thickness of 50 to 120 μm is used as the developing blade 11, and the surface of the blade portion 11 is developed on the developing roller 22 by utilizing the spring elasticity of the support portion 11a. It is made to contact. The blade portion 11 a is configured such that, in the short direction, the blade portion 11 b is formed at one end, and the other end is connected to and supported by a support member S fixed to the developing device frame 20.

  The developing blade 11 is not limited to the above embodiment, and a SUS plate may be used as the support portion 11a, or a metal thin plate such as phosphor bronze or aluminum may be used. On the other hand, the blade portion 11b is formed by covering the surface of the support portion 11a with a thin film made of a conductive resin such as polyamide elastomer, urethane rubber or urethane resin.

  The blade portion 11b according to the present embodiment includes, in order from the downstream side in the rotation direction of the developing roller 22, a protruding portion 11b2 that protrudes and contacts the developing roller 22, one end connected to the protruding portion 11b2, and the other end is a free end. And an opposing surface 11b1 facing the roller 22.

  In the present embodiment, the distance of the straight line connecting both ends of the continuous surface constituting the opposing surface 11b1, that is, the length of the opposing surface 11b1 up to the step constituting the protruding portion 11b2 protruding from the free end (tip) on the blade portion 1lb side. The thickness L (mm) was set to 0.85 mm. Further, H is the maximum height of the protrusion 11b2 from the connecting portion of the facing surface 11b1 and the protrusion 11b2 in the direction orthogonal to the surface extending in the short direction of the support 11a, that is, the protrusion size of the protrusion 11b2. H = 0.3 mm.

  Further, as a result of the study by the present inventor, when the opposing surface 11b1, the protruding portion 11b2, and the developing roller 22 of the developing blade 11 are in contact with each other to form a wedge space, toner accumulates in the wedge space, so that the toner powder pressure As a result, it was found that a force to push up the developing blade 11 was generated. Therefore, it has been found that the regulation pressure of the developing blade 11 against the developing roller 22 is likely to decrease. When the regulation pressure is lowered, a regulation failure that the density becomes high at the leading edge of the image occurs.

  In order to prevent poor regulation, it is necessary to optimize the relationship between the arithmetic average roughness Ra of the developing roller 22 and the curvature radius r of the regulating edge of the developing blade 11 shown in FIG. FIG. 5 shows the relationship between Ra and r.

  In FIG. 5, in the image forming apparatus of the present embodiment, a developing device in which the surface roughness of the developing roller 22 and the radius of curvature r of the regulating edge of the developing blade 11 are changed is used. Then, a black image having the highest density level was printed on the entire surface of the image forming area of the transfer material P, and the optical reflection density was measured by a densitometer RD-1255 manufactured by Macbeth. Specifically, the density of the first rotation of the developing roller 22 from the front end of the image is measured at five points in the longitudinal direction, the average is calculated, and the density of the second rotation of the developing roller 22 is measured at five points in the longitudinal direction. After calculating the average, the concentration difference Δ between the two was determined.

  The density difference Δ is preferably 0.3 or less. That is, it was found that Ra <2.7 μm (Ra is less than 2.7 μm) and r <250 μm are preferable. In this embodiment, the surface roughness of the developing roller 22 is 2.0 μm, and the radius of curvature r of the regulating edge of the developing blade 11 is 200 μm.

<Description of effects>
Next, in order to explain the effects of reducing the density, poor solid followability, and ghost suppression when the developer is deteriorated or absorbs moisture, which is the object of this embodiment, a comparison is made with this embodiment. A comparative example will be described.

(Comparative Example 1)
Developing blade: no projecting portion, no facing surface, edge contact Developing roller: with dielectric portion FIG. 6A shows an enlarged cross-sectional view of a regulating portion of the developing device of Comparative Example 1. FIG. In addition, the structure shown in patent document 2 is disclosed as a structure similar to this comparative example. The same developing roller 22 is used in Comparative Example 1 and this embodiment. The developing blade 11 is not configured to have a protruding portion or an opposing surface as in the present embodiment, but is brought into edge contact with a metal flat developing blade.

(Comparative Example 2)
Developing blade: no projecting portion, facing surface, belly pad Developing roller: with dielectric portion FIG. 6C is an enlarged cross-sectional view of the restricting portion of the developing device of Comparative Example 2. The difference from Comparative Example 1 is that the developing blade 11 is set to be a belly pad and has a facing surface.

(Comparative Example 3)
Developing blade: with protrusion, facing surface, edge contact Developing roller: without dielectric part FIG. 6E shows an enlarged cross-sectional view of the restricting portion of the developing device of Comparative Example 3. In Comparative Example 3 and this embodiment, the same developing blade 11 is used. The developing roller 23 of Comparative Example 3 has a surface layer configuration different from that of the developing roller 22 of this embodiment. FIG. 6 (f) shows the surface layer of the developing roller 23, in which there is no dielectric portion and the rough particles 23-1 are scattered.

<Comparison result>
An image evaluation test was performed on the developing devices of this embodiment, Comparative Example 1, Comparative Example 2, and Comparative Example 3 using the image forming apparatus 100 of FIG. 2, specifically, MF726Cdw (Canon brand name). Specifically, an image evaluation test was performed when the developing device was new in a high-temperature and high-humidity environment (temperature of 30 ° C. and humidity of 80%) and when durability was passed through 2000 sheets. For the image evaluation, a solid black image and a ghost image were used, and the density thinness, the solid followability and the ghost were evaluated.

  The solid black image is a black image having the highest density level printed on the entire surface of the image forming area of the transfer material. A ghost image is obtained by printing a vertical band of halftone density after printing a 1 cm square solid black patch with a length of one round of the developing roller. The image evaluation test results are shown in Table 1.

(Thin density evaluation standard)
The evaluation was performed by outputting a solid black image and measuring the optical reflection density with a densitometer RD-1255 manufactured by Macbeth. More specifically, the density at the leading edge of the image (the first rotation of the developing rollers 22 and 23) is measured at five points in the longitudinal direction, and the average is calculated. An average was calculated by measuring 5 points at a time in the circumferential direction of the developing roller. Thereafter, the density difference Δ between the two was determined and determined according to the following criteria.
○: Density difference Δ is less than 0.3,
Δ: Density difference Δ is 0.3 or more and less than 0.5 ×: Density difference Δ is 0.5 or more

(Evaluation criteria for solid trackability)
In the solid followability evaluation, a solid black image was output and visually determined according to the following criteria.
○: No white spot occurs ×: White spot occurs

(Ghost evaluation criteria)
The ghost was evaluated by outputting a ghost image and visually judging according to the following criteria.
◯: The shadow of the patch is slightly visible on the second rotation of the developing roller. Δ: The shadow of the patch is clearly visible on the second rotation of the developing roller.

(Effect of the present embodiment on low density and solid followability)
In Comparative Examples 1 and 2, it was observed that durability was low, and in Comparative Example 3, generation of low density and poor solid followability was observed from the time of new products. In this embodiment, the occurrence of low density and solid followability was not confirmed under any conditions. This is because toner accumulates in the wedge space formed by the developing blade 11 and the developing roller 22 and the powder pressure increases, so that the movement of the toner in the wedge space becomes active.

  When the movement of the toner becomes active, the contact opportunity between the surface of the developing roller 22 and the toner increases, and the amount of charge applied from the toner to the dielectric portion on the surface of the developing roller 22 increases. As a result, the strength of the minute closed electric field generated on the dielectric portion and the adjacent portion of the dielectric portion and the grounded conductor portion is increased, and the electrostatic force and the gradient force are increased.

  On the other hand, Comparative Example 1 and Comparative Example 2 have the above-described electrostatic force and gradient force since the fluidity of the toner is high when new and there are many opportunities to contact the dielectric portion on the surface of the developing roller 22. And no solid follow-up failure occurs. However, since the developing blade 11 does not have the facing surface 11b1 shown in FIG. 4 as in this embodiment, the electrostatic force and the gradient force cannot be sufficiently generated, and the density is low.

  Further, during the durability, the fluidity of the toner is lowered, the chance of contact with the dielectric portion on the surface of the developing roller 22 is reduced, and the electrostatic force and the gradient force are reduced as compared with a new product. As a result, low density and poor solid followability occur. In Comparative Example 3, since the developing roller 23 does not have a dielectric portion on the surface, the electrostatic force and the gradient force are not generated, and the toner cannot be attracted. As a result, both low density and poor solid followability occur from the time of the new article.

  In any of the comparative examples shown in FIG. 6, the residual toner has a large charge under the condition that the charging property of the toner is high, that is, when the developing device is new, and in a normal temperature and normal humidity environment or a low temperature and low humidity environment. For this reason, other toners can be attracted by the electrostatic force, and there was no occurrence of low density and poor solid followability.

(Effect of this embodiment on development ghost)
In Comparative Example 1 and Comparative Example 2, ghosts were observed during durability, and in Comparative Example 3, ghosts were observed after the third rotation of the developing roller from the new product. In this embodiment, generation of ghost was not confirmed under any conditions. The reason why a ghost does not occur in this embodiment is considered as follows. That is, toner accumulates in the wedge space formed by the developing blade 11 and the developing roller 22, and the powder pressure increases, so that the toner remaining on the developing roller 22 without development (development residual toner) and the powder pressure from the wedge space. This is because the toner that moves to escape runs backward and rubs.

  By rubbing each other, there is a charge averaging effect in which the charge is equalized between the development residual toner having a large charge amount and the toner having a small charge amount in the wedge space. As a result, the electrostatic adhesion force between the development residual toner and the development roller is reduced, and it becomes easy to peel off by the regulation pressure of the development blade 11, and the history of the image developed in the previous round is reset. As described above, in order to suppress the ghost image defect, it is necessary to remove the charge by the charge averaging effect and the regulation pressure.

  In Comparative Example 2, there is a space in which toner accumulates between the free end of the developing blade 11 and the contact portion between the developing blade 11 and the developing roller 22, and the charge averaging effect can be obtained. It is insufficient. For this reason, a ghost image defect occurs. Hereinafter, the reason why the stripping is insufficient will be described.

  FIG. 6B shows the measured contact pressure distribution of the developing blade 11 of Comparative Example 1, and FIG. 6D shows the measured result of Comparative Example 2. The measurement was performed using a Nittah tuck tile sensor. The peak pressure (maximum value of pressure in the pressure distribution) is smaller in FIG. 6D where the developing blade 11 hits the edge against the developing roller 22 than in FIG. In FIG. 6C, if the developing blade 11 is further set to enter the developing roller 22, the peak pressure similar to that in FIG. 6B can be obtained. However, since the total pressure applied from the developing blade 11 to the developing roller 22 becomes very high, the stress received by the toner increases and the toner deterioration is promoted.

  As a result, the fluidity of the toner is lowered, which may lead to poor fogging due to the deterioration of density thinness / solid followability and the toner charging property. Moreover, although the control pressure is sufficient as shown in FIG. 6B, Comparative Example 1 has a configuration that does not have the facing surface 11b1 shown in FIG. 4 as in this embodiment. For this reason, the charge averaging effect cannot be obtained, and the ghost is not good.

  Comparative Example 3 has a facing surface 11b1 shown in FIG. 4, and the developing blade 11 is an edge contact. Therefore, a sufficient peak pressure can be obtained. However, since there is no dielectric portion on the surface layer of the developing roller 23, a sufficient amount of toner cannot be conveyed into the wedge space. Therefore, the charge averaging effect cannot be obtained. Therefore, the electrostatic adhesion force between the development residual toner and the development roller 23 cannot be reduced, and ghost generation cannot be suppressed.

  As described above, according to this embodiment, even when developer deterioration or moisture absorption occurs, the occurrence of low density, poor solid followability, and ghost image failure is effectively suppressed with a simple configuration. Thus, a high quality image can be output.

<< Second Embodiment >>
When the life of the developing device is extended with the configuration of the first embodiment, there are cases in which poor regulation or toner leakage occurs. The reason will be described below. In the present embodiment, as in the first embodiment, as shown in FIG. 4, in the image area, the opposing surface 11b1 and the protruding surface 11b2 of the developing blade are uniformly present in the longitudinal direction. However, if a large amount of toner is conveyed outside the image area in the longitudinal direction, a large amount of undeveloped toner is generated without being developed.

  When a large amount of undeveloped toner is generated, the powder pressure of the toner accumulated in the wedge space between the developing roller 22 and the developing blade 11 becomes higher outside the image area than the image area, the developing blade 11 is pushed up, and the contact pressure is increased. Becomes weaker. Particularly, when the toner is used for a longer period due to the longer life, the toner deteriorates and the degree of aggregation of the toner increases. The toner having a high degree of aggregation stays in the wedge space, and the developing blade 11 is more easily pushed up. As a result, poor regulation and toner leakage occur.

  In the present embodiment, as a more preferable form, as shown in FIG. 7A inside the image area and as shown in FIG. 7B outside the image area, the facing surface 11b1 does not exist only outside the image area of the developing blade 22. ,. Alternatively, as a more preferable form, as shown in FIG. 8A within the image area and as shown in FIG. 8B outside the image area, it is preferable that the dielectric portion 22-1a does not exist only outside the image area. . By adopting such a configuration, it is possible to prevent the development blade 11 from being pushed up by toner powder pressure outside the image area while suppressing the occurrence of low density, poor solid followability, and ghost image defect in the image area. it can.

11.Development blade, 11b1, ... opposite surface, 11b2, ... protruding part, 20 .... developing frame, 22 .... developing roller, 22-1 ... urethane surface layer, 22-1a ... dielectric part, S ..Supporting part

Claims (2)

A developer carrier that holds the developer on the outer peripheral surface and rotates;
A developer container that rotatably supports the developer carrier and contains the developer;
A support portion supported at one end by the developer container;
A developer regulating member which is fixed to the support and regulates the developer held on the developer carrying member to a predetermined layer thickness;
Have
The developer carrying member forms, on an outer peripheral surface, a sea portion formed by one of a high resistance portion and a low resistance portion, and an island portion in which the other of the high resistance portion and the low resistance portion is dispersed. With a sea-island structure
The developer regulating member includes, in order from the downstream side in the rotation direction of the developer carrier, at least a projecting portion provided with a contact portion that projects and abuts toward the developer carrier, and faces the developer carrier. A developing device, wherein one end of the facing surface is connected to the protruding portion and the other end is a free end.   The surface roughness Ra of the developer carrying member is less than 2.7 μm, and the curvature radius of the contact portion of the developer regulating member with the developer carrying member is 250 μm. The developing device described.