JP2020067578A - Developer carrier, developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

Kind Code: A1 To suppress the occurrence of low density and solid black follow-up failure, and to suppress the occurrence of fogging and density unevenness in a halftone region, even when deterioration or moisture absorption of a developer occurs, with a simple configuration. To provide a developing device capable of A developer carrier is a rotatable developer carrier that carries a developer. A conductive portion having a first surface roughness and a first electrical resistance and a second surface roughness smaller than the first surface roughness and the first electrical resistance are formed on the surface of the developer carrier. A dielectric portion is provided having a second electrical resistance greater than. The average width of the dielectric portion in the axial direction of the rotating shaft of the developer carrying member is larger than the average width of the dielectric portion in the rotating direction of the developer carrying member orthogonal to the axial direction. [Selection drawing] Fig. 1

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile apparatus, etc., which utilizes an electrophotographic method or an electrostatic recording method, a developing device used in the image forming apparatus, a developer carrier and a process cartridge.

  Conventionally, a developing device of an image forming apparatus using an electrophotographic image forming process has a developer carrier that carries a developer on its surface and conveys it, and a developer storing means for storing the developer. Further, the developing device has a developer supply member that comes into contact with the developer carrying member and supplies the developer stored in the developer storing means to the developer carrying member (Patent Document 1). However, when the developing device is at the end of its life or when the developing device is used in an environment of high temperature and high humidity, there is a possibility that the charge amount of the developer may decrease due to deterioration of the developer or moisture absorption. At this time, even if the developer is physically supplied by the developer supply member, the charge amount of the developer is low, the image force with the developer carrier becomes insufficient, and the developer cannot be conveyed by the developer carrier. The phenomenon occurs. As a result, a phenomenon in which the density is insufficient in a high print image such as a solid black image (so-called solid black following defect) occurs.

  In order to solve such a problem, in the developing device disclosed in Patent Document 2, the potential of the developer supply member is set to an intermediate potential between the developer on the charge series and the developer carrying member. Further, the developer carrying member has a surface layer in which a dielectric portion that forms a minute closed electric field by dispersing insulating particles in a conductive material in a substrate made of a conductor is regularly or irregularly exposed. . When the surface layer is rubbed by the developer supply member or the developer, the dielectric portion is charged to a polarity opposite to the charging polarity of the developer. The dielectric part of the developer carrying member is triboelectrically charged with the developer supplying member, so that a predetermined charge is applied to the dielectric part and an electric field is generated on the applied dielectric part. In particular, a minute closed electric field is generated on the adjacent portion between the dielectric portion and the conductive portion, and a large number of minute closed electric fields are formed on the entire developer carrier. This electric field causes the developer to adhere to the surface layer. The developer whose charge amount is unstable, such as uncharged or low-charged, in the developer container is transported to a large number of electric field generation areas such as minute closed electric fields on the developer carrier. The conveyed developer receives a force (gradient force) generated by the minute closed electric field, and is adsorbed and carried by a dielectric portion having a polarity opposite to that of the developer in particular. As a result, even when the charge amount of the developer is extremely low, the developer transport amount can be secured, and it is possible to output an image with a uniform density even for a high print image such as a solid black image.

JP 61-42672 A JP-A-4-156569

  In the developing device having the configuration disclosed in Patent Document 2, it is possible to convey a developer having no charge or a low charge amount, and the solid black following defect is improved, but the charge amount of the developer is insufficient at the developing position. Therefore, a bad image such as fogging may occur. Fogging is a phenomenon in which a developer that cannot be charged to a predetermined charge amount is developed even when it is an electric field in a non-developing portion when it is conveyed to a developing position. This phenomenon is because the developer adhered to the developing carrier due to the influence of the above-mentioned minute closed electric field cannot sufficiently obtain the frictional electrification opportunity due to the rolling in the charge imparting means such as the developing blade, resulting in a predetermined charge amount. It occurs because it cannot be charged.

  Further, in the developing device disclosed in Patent Document 2, there is a possibility that a difference in shade occurs in the solid black image that is output, and the uniformity of the density deteriorates. This is because when the fluidity of the toner decreases as the toner in the developing device deteriorates, a difference in toner supply amount occurs between the region having a small dielectric portion and the region having a large dielectric portion of the developer carrier.

  Therefore, an object of the present invention is a simple structure, even when the deterioration or moisture absorption of the developer occurs, while suppressing the occurrence of solid black followability defects, image formation such as fog and deterioration of the uniformity of solid black images. It is to provide a technique capable of suppressing the problem.

In order to achieve the above object, the developer carrying member of the present invention is
A developer carrying member that carries a developer and is rotatable,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characterize.
In order to achieve the above object, the developing device of the present invention is
A developer carrying member carrying a developer,
A developing device having a regulating member for regulating the developer carried on the surface of the developer carrying body,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characterize.
Further, in order to achieve the above object, the process cartridge of the present invention is
A developer carrying member carrying a developer,
A regulating member for regulating the developer carried on the surface of the developer carrying body,
A process cartridge having an image carrier that carries a developer image,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characterize.
Further, in order to achieve the above object, the image forming apparatus of the present invention,
A developer carrying member carrying a developer,
A regulating member for regulating the developer carried on the surface of the developer carrying body,
An image bearing member carrying a developer image,
An image forming apparatus having a transfer member,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characterize.

  According to the present invention, it is possible to suppress image problems such as fog and a decrease in uniformity of a solid black image while suppressing the occurrence of a solid black following defect even when the developer is deteriorated or moisture is absorbed. it can.

FIG. 3 is an explanatory diagram of a developing roller described in Embodiment 1. 3 is a schematic cross-sectional view of the image forming apparatus described in Embodiment 1. FIG. FIG. 5 is an explanatory diagram of the developing unit described in the first embodiment. 6A and 6B are explanatory diagrams of a minute closed electric field that acts on the developing roller according to the first exemplary embodiment. Explanatory drawing of the gradient force described in Example 1. 6A and 6B are explanatory views of the toner charge imparting action described in the first exemplary embodiment. 7A and 7B are explanatory views of the arrangement action of the dielectric portion and the conductive portion described in the first embodiment. 6A and 6B are explanatory diagrams of the relationship between the size of Sy and the toner particle size described in Embodiment 1. FIG. FIG. 6 is an explanatory diagram of a developing roller described in Comparative Example 1. FIG. 9 is an explanatory diagram of a developing roller described in Comparative Example 2. FIG. 6 is an explanatory diagram of a developing roller described in Embodiment 2. FIG. 10 is a diagram illustrating a method of calculating a tilt section width described in the third embodiment.

  Embodiments of the present invention will be exemplified below with reference to the drawings. However, the dimensions, materials and shapes of the components described in the embodiments, their relative arrangements, etc. should be appropriately changed depending on the configuration of the device to which the invention is applied, various conditions, etc. The scope is not limited to the following embodiments.

(Example 1)
Hereinafter, Example 1 of the present invention will be described. First, the overall configuration of the electrophotographic image forming apparatus (hereinafter, image forming apparatus) according to the present embodiment will be described. FIG. 2 is a schematic sectional view of the image forming apparatus 100 of this embodiment.

  The image forming apparatus 100 of this embodiment is a full-color laser printer that employs a so-called in-line method or an intermediate transfer method.

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

  The image forming apparatus 100 includes first, second, and third image forming units for forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. , And fourth process cartridges Sa, Sb, Sc, Sd. In the present embodiment, the first to fourth process cartridges Sa, Sb, Sc, Sd are arranged in a line in a direction intersecting the vertical direction (upward on the paper surface). In addition, in the present embodiment, the configurations and operations of the first to fourth process cartridges Sa, Sb, Sc, and Sd are substantially the same except that the colors of the images to be formed are different. Therefore, in the following description, the subscripts a, b, c, and d given to the reference numerals to represent the elements provided for any of the colors will be omitted unless a particular distinction is required. explain.

In this embodiment, the image forming apparatus 100 includes four drum-type electrophotographic photoconductors, that is, the photoconductor drums 1 (1a, 1b), arranged as a plurality of image carriers in a direction intersecting the vertical direction.
1c, 1d). The photosensitive drum 1 is rotationally driven by a driving unit (driving source) not shown. Around the photosensitive drum 1, a charging roller 2 (2a, 2b, 2c, 2d), a scanner unit (exposure device) 3 (3a, 3b, 3c, 3d), a developing unit (developing device) 4 (4a, 4b, 4c, 4d) are arranged. The charging roller 2 is a charging unit that uniformly charges the surface of the photosensitive drum 1. Further, the scanner unit 3 irradiates a laser on the photosensitive drum 1 based on an output calculated by a CPU (not shown) from image information input from a host device such as a personal computer, so that an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. ) Is an exposure means. The developing unit 4 is a developing unit that develops the electrostatic image as a developer (hereinafter, toner) image. The photosensitive drum 1, the charging roller 2 as a process unit that acts on the photosensitive drum 1, and the developing unit 4 are integrated to form a process cartridge S. The process cartridge S is detachably provided in the image forming apparatus 100 by a mounting guide such as a mounting guide or a positioning member in the image forming apparatus 100.

  Further, an intermediate transfer belt 10 as an intermediate transfer member for transferring the toner image on the photosensitive drum 1 to the recording material P is arranged at a position facing each photosensitive drum 1. The intermediate transfer belt 10 is formed of an endless belt, contacts the photosensitive drums 1, and circulates (rotates) in the direction of arrow R3 in the figure. The intermediate transfer belt 10 is stretched around a secondary transfer counter roller 13, a drive roller 11, and a tension roller 12 as a plurality of supporting members.

  On the inner peripheral surface side of the intermediate transfer belt 5, four primary transfer rollers 14 (14a, 14b, 14c, 14d) as transfer members are arranged so as to face the respective photosensitive drums 1. The primary transfer roller 14 presses the intermediate transfer belt 10 toward the photosensitive drum 1, and forms a primary transfer portion where the intermediate transfer belt 10 and the photosensitive drum 1 contact each other.

  A secondary transfer roller 20 as a secondary transfer unit is arranged at a position facing the secondary transfer counter roller 13 on the outer peripheral surface side of the intermediate transfer belt 10. The secondary transfer roller 20 is in pressure contact with the secondary transfer counter roller 13 via the intermediate transfer belt 10 and forms a secondary transfer portion in which the intermediate transfer belt 10 and the secondary transfer counter roller 13 contact each other.

  The recording material P to which the toner image is transferred is conveyed to the fixing device 30 as a fixing unit. The toner image is fixed on the recording material P by applying heat and pressure to the recording material P in the fixing device 30. Note that the image forming apparatus 100 can also form a single-color or multi-color image by using any one image forming unit or a plurality (not all) of the image forming units. The image forming apparatus 100 in this embodiment is, for example, a printer compatible with A4 size paper with a process speed of 148.2 mm / sec.

<Image forming process>
Next, an image forming process in the image forming apparatus 100 will be described. When forming an image, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the image information input from the host device outside the image forming apparatus 100 is processed by the CPU to form an electrostatic image. Then, based on the calculation result, the surface of the photosensitive drum 1 charged with the laser light emitted from the scanner unit 3 is scanned and exposed, and an electrostatic image according to the calculation result is formed on the photosensitive drum 1. The electrostatic image formed on the photosensitive drum 1 is developed as a toner image (developer image) by the developing unit 4. Then, a voltage having a polarity opposite to the regular charging polarity of the toner is applied to the primary transfer roller 14 from a primary transfer voltage power supply 15 (high voltage power supply) as a primary transfer voltage applying unit. As a result, the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 10. At the time of forming a full-color image, the above-described process is sequentially performed in the first to fourth process cartridges Sa, Sb, Sc, and Sd, and the toner images of the respective colors are superposed on the intermediate transfer belt 10 and then primary-transferred. To be done.

  Then, the recording material P is conveyed to the secondary transfer portion in synchronization with the movement of the intermediate transfer belt 10. Then, a voltage having a polarity opposite to the regular charging polarity of the toner is applied to the secondary transfer roller 20 from a secondary transfer voltage power source 21 (high voltage power source) as a secondary transfer voltage applying unit. As a result, the four color toner images on the intermediate transfer belt 10 are conveyed by the feeding means by the action of the secondary transfer roller 20 that is in contact with the intermediate transfer belt 10 via the recording material P. It is secondarily transcribed on the above. The recording material P to which the toner image is transferred is conveyed to the fixing device 30 as a fixing unit. In the fixing device 30, heat and pressure are applied to the recording material P, so that the transferred toner image is fixed and is discharged from the image forming apparatus 100.

  In order to control the developing amount of toner, the developing unit 4 sets the rotational speed of the developing roller 22 as a developer bearing member to be different from the rotational speed of the photosensitive drum 1, and the developing roller 22 and the photosensitive drum. 1 and 1 are brought into contact with each other to perform reversal development. In other words, the toner charged to the same polarity as the charging 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 the exposure (image portion, exposed portion), so that the toner remains static. The image is developed. In the present embodiment, as an example, the developing roller 22 is driven so that the ratio of the rotational speed of the developing roller 22 to the rotational speed of the photosensitive drum 1 is 1.4 times.

  Further, the toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 in the primary transfer step is collected by the developing roller 22 described later and reused. The transfer residual toner on the surface of the photosensitive drum 1 is charged to a regular charging polarity (negative polarity) when passing through the charging roller 2. Thereafter, an electric field generated due to a difference between the electric potential of the photosensitive drum 1 formed by the charging roller 2 and the electric potential of the developing roller 22 formed by applying a DC voltage to the developing roller 22 causes the transfer residual toner to be transferred to the developing roller. 22 collected and reused.

<Structure of process cartridge>
Next, the overall configuration of the process cartridge S mounted in the image forming apparatus 100 of this embodiment will be described. The process cartridges S for each color have the same shape except for an identification portion (not shown) and the like, and in the developing unit 4 of the process cartridge S for each color, yellow (Y), magenta (M), and cyan (C), respectively. ) And black (K) toners are stored. A non-magnetic one-component developer is used as the toner of the developing unit 4.

  The process cartridge S is configured by integrating a photosensitive unit including the photosensitive drum 1 and the charging roller 2 and a developing unit (developing device) 4 including the developing roller 22 and the like. Further, the charging roller 2 and the developing roller 22 are configured to be rotatable around bearings (not shown) that are rotating shafts.

  The photosensitive drum 1 is rotatably supported via bearings. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the drawing in accordance with an image forming operation by transmitting the driving force of a driving unit (driving source) (not shown) to the photosensitive member unit. The charging roller 2 is driven to rotate by the roller portion made of conductive rubber coming into pressure contact with the photosensitive drum 1.

On the other hand, in the developing unit 4, as shown in FIG. 3, a developing roller 22 carrying toner, a developing blade 23 (regulating member), a supply member 26 provided in contact with the developing roller 22, and fixing these members. And a developing frame body 24 for The developing device frame 24 includes a developing chamber 24a in which the developing roller 22 is arranged, and a blowout preventing sheet 24b that seals a developing opening (opening) that connects the developing chamber 24a and the outside of the developing device frame 24. One end of the developing blade 23 is fixed to a fixing member 25 fixed to the developing device frame 24, and the other end of the developing blade 23 contacts the developing roller 22. The developing blade 23 is configured so that the amount of toner coating on the developing roller 22 can be regulated and charges can be applied. The developing roller 22 is disposed in the developing opening and is provided so as to be able to contact the photosensitive drum 1. Details of the developing roller 22 will be described later. Developing roller 2
2 is arranged to be rotationally driven in the direction of arrow R4 in the figure.

  In the present embodiment, the developing roller 22 and the photosensitive drum 1 are arranged such that the respective surfaces of the developing roller 22 and the photosensitive drum 1 facing each other move in the same direction (in the present embodiment, the direction from the upper side to the lower side in the gravity direction). Is rotated. Then, a predetermined DC voltage is applied to the developing roller 22, and the electrostatic latent image is visualized and a toner image is formed in the developing section where the toner negatively charged by frictional charging contacts the photosensitive drum 1.

  As shown in FIG. 3, the developing blade 23 comes into contact with the surface of the developing roller 22 in a state where its tip end faces the counter direction located upstream of the rotating direction of the developing roller 22 in the rotating direction of the developing roller 22. Regulates the amount of toner coat and imparts electric charge. In this embodiment, the developing blade 23 uses the spring elasticity of a supporting member (not shown) of a leaf spring-shaped SUS plate having a thickness of 50 to 120 μm so that the surface of the developing blade 23 contacts the developing roller 22. The developing blade 23 has a blade portion formed at one end in the lateral direction, and the other end is fixed to and supported by the developing device frame 24. The supporting member for the developing blade 23 may be configured by using a thin metal plate such as phosphor bronze or aluminum in addition to the SUS plate. On the other hand, as the developing blade 23, a blade formed by coating the surface of a supporting member with a thin film made of a conductive resin such as polyamide elastomer, urethane rubber or urethane resin is used. Alternatively, the supporting member itself may be brought into contact with the developing roller 22 as the developing blade 23. Further, a predetermined DC voltage is applied as a blade bias to the developing blade 23, and the potential difference from the voltage applied to the developing roller 22 is controlled, so that the toner conveyance amount on the developing roller 22 described later is controlled.

  The supply member 26 is composed of a conductive core of φ4 (mm) and a urethane sponge layer formed around the conductive core and made of flexible open cells. The outer diameter of the supply member 26 is φ11 (mm). By using an open-cell urethane sponge for the supply member 26, toner can be stored inside the sponge. During the development processing by the image forming apparatus 100, the supply member 26 is in contact with the development roller 22 and is supported by the development frame 24 so as to be rotationally driven in the direction of arrow R5 in the drawing.

<Explanation of the developing roller 22>
The configuration of the developing roller 22 in this embodiment will be described in detail with reference to FIGS. 1A and 1B. FIG. 1A is a diagram schematically showing a cross section of a plane perpendicular to the rotation axis of the developing roller 22. In the developing roller 22, a base layer 22b made of a silicone rubber composition shown in Table 1 below and a surface layer 22c made of urethane shown in Table 2 below are sequentially laminated on a metal core 22a, and further the surface layer 22c shown in Table 3 below. It has a configuration in which an insulating coating material made of the described material is applied. A development bias is applied to the surface layer 22c and the base layer 22b via the metal cored bar 22a.

  The manufacturing method, materials, dimensions and the like of the developing roller 22 in this embodiment will be described below.

1. Formation of Metal Core Bar 22a As an example of the metal core bar 22a, a primer (trade name: DY35-051, manufactured by Toray Dow Corning Co., Ltd.) is applied to a core bar made of SUS304 having an outer diameter of 6 mm and a length of 259.9 mm. Then, it is formed by heating at a temperature of 150 ° C. for 20 minutes.

2. Formation of Conductive Elastic Layer In the developing roller 22, the conductive elastic layer has a one-layer structure or a laminated structure of two or more layers. The conductive elastic layer preferably has a laminated structure of two or more layers. Particularly in the non-magnetic one-component contact developing system process, a developing roller having a conductive elastic layer having a two-layer laminated structure is suitably used as the developing roller 22. In this embodiment, the base layer 22b and the surface layer 22c are 2
The conductive elastic layer having a layered structure will be described. Further, the conductive elastic layer preferably contains a conductive agent in order to obtain conductivity. Examples of the conductive agent include ion conductive agents and electronic conductive agents such as carbon black. Carbon black is preferable as the conductive agent in that the conductivity of the conductive elastic layer and the charging performance of the conductive elastic layer with respect to the toner can be controlled. The volume resistivity (first electrical resistance) of the conductive elastic layer is preferably in the range of 1 × 10̂3Ω · cm or more and 1 × 10̂11Ω · cm or less.

2-1. Formation of Base Layer 22b In forming the base layer 22b, the metal cored bar 22a is placed in a cylindrical mold having an inner diameter of 10.0 mm so as to be concentric with the cylinder of the mold. Then, as an example of the material of the base layer 22b, an addition type silicone rubber composition obtained by mixing the materials shown in Table 1 below with a mixer (trade name: Trimix TX-15 Inoue Seisakusho) was heated to a temperature of 120 ° C. Inject into mold. After injecting the material, it is heat-molded at a temperature of 120 ° C. for 10 minutes, cooled to room temperature, and then released from the mold to obtain a base layer roller having a base layer 22b having a thickness of 2.00 mm formed on the outer periphery of the mandrel.

2-2. Formation of Surface Layer 22c In forming the surface layer 22c, the materials shown in Table 2 below are weighed and mixed with stirring. Then, the obtained mixture is added to and mixed with methyl ethyl ketone (manufactured by Aldrich) so that the solid content concentration is 28% by mass, and uniformly dispersed by a bead mill (manufactured by Ashizawa Finetech) to obtain a coating material. Further, the base layer roller is dipped in this coating material by an overflow type circulation coating machine to apply the coating, so that the surface layer has a thickness of 15 μm. Then, it is heated at a temperature of 130 ° C. for 90 minutes to dry and cure the coating film to obtain an elastic layer roller having the surface layer 22c formed on the base layer roller. In addition, the conductive portion roughening described below refers to a region in which the surface roughness of the conductive portion 22e is controlled by controlling the addition of the resin particles described in Table 2 below.

3. Formation of Dielectric Portion 22d In a partial area on the surface of the developing roller 22, a plurality of dielectric portions 22d are present. More specifically, the surface of the developing roller 22 is configured to include at least the surfaces of the plurality of dielectric portions 22d and the exposed portion of the conductive elastic layer that is not covered with the dielectric portions 22d. As a result, the dielectric portion 22d is formed on the surface of the developing roller 22 by covering a part of the surface of the conductive portion 22e. The dielectric portion 22d is provided so as to be scattered in the region of the conductive portion 22e. Further, on the surface of the developing roller 22, the area occupied by the dielectric portion 22d is smaller than the area occupied by the conductive portion 22e. The volume resistivity (second electrical resistance) of the dielectric portion 22d of the developing roller 22 is preferably 1 × 10̂13Ω · cm or more and 1 × 10̂18Ω · cm or less. That is, in this embodiment, the electric resistance of the dielectric portion 22d is higher than the electric resistance of the conductive portion 22e.

  In forming the dielectric portion 22d, the materials shown in Table 3 below are weighed and mixed by stirring. Then, the obtained mixture is dissolved and mixed in methyl ethyl ketone (manufactured by Aldrich) so that the solid content concentration becomes 3% by mass to obtain a coating material for forming a dielectric part.

As a method of forming the dielectric portion 22d on the conductive elastic layer, various printing methods can be mentioned. In order to make the plurality of dielectric portions 22d exist in a partial region on the surface of the conductive elastic layer, a jet method is used. The dispenser method and the inkjet method are preferred. At this time, the surface of the surface layer 22c on which the dielectric portion 22d is not formed and which is exposed is referred to as a conductive portion 22e. In this embodiment, the dielectric portion 22d is formed by the jet dispenser method. Further, in this embodiment, the charge polarity of the dielectric portion 22d is the same as the charge polarity of the developer when the developer carried on the developing roller 22 is charged by friction with the developing blade 23 (this embodiment). Then the negative polarity).

<Roughness of conductive elastic layer and dielectric part>
The surface roughness of the dielectric part 22d and the surface roughness of the conductive part 22e are different. More specifically, the surface roughness Ray of the dielectric portion 22d is lower than the surface roughness Rad of the conductive portion 22e, that is, smoother. As a result of examination by the present inventors, the surface roughness (first surface roughness) of the conductive portion 22e is 0.8 μm <Rad <2.7 μm, and the surface roughness of the dielectric portion 22d (second surface roughness). Is preferably Ray <0.8 μm. In this embodiment, the dielectric portion 22d does not contain resin particles, whereas the conductive portion 22e contains resin particles. This makes it possible to obtain a difference in surface roughness between the dielectric portion 22d and the conductive portion 22e.

  A toner charge imparting action, which will be described later, is performed by the regulating portion, and the toner is imparted by rolling the toner between the conductive portion 22e and the developing blade 23. That is, the toner on the dielectric portion 22d is quickly conveyed to the conductive portion 22e existing on the downstream side in the rotation direction of the developing roller 22, so that the toner charge is applied on the conductive portion 22e. When the surface roughness of the dielectric portion 22d is 0.8 μm or more, the amount of toner carried on the developing roller 22 increases, and toner that does not have a chance to give an electric charge to the conductive portion 22e is generated. As a result, the toner charge imparting action is reduced. Further, even if the surface roughness of the conductive portion 22e is 2.7 μm or more, the amount of toner carried on the developing roller 22 increases and the toner charge imparting action is reduced, which is not preferable.

<Measurement method of surface roughness of dielectric part and conductive part>
In this embodiment, the surface roughness Ray of the dielectric portion 22d and the surface roughness Rad of the conductive portion 22e are measured as follows.

  A laser microscope VK-X100 (trade name, manufactured by Keyence Corporation) is equipped with an objective lens having a magnification of 20 times. Then, the image and height information of the surface of the developing roller 22 are obtained by two-dimensionally scanning the surface of the developing roller 22 in the area of 1.5 mm × 1 mm by the laser confocal optical system using the image connecting function of the microscope. Can be obtained. Among these, a square area (referred to as an evaluation area) having a side of 900 μm is an evaluation target.

  After the inclination is corrected in the quadric surface correction mode based on this height information, the dielectric part 22d is extracted. Here, of the dielectric part 22d, the dielectric part 22d whose whole is included in the evaluation region is the measurement target, and the dielectric part 22d whose part is not included in the evaluation region is not the measurement target. Then, the analysis software attached to the measuring device is used to perform the evaluation in the mode for measuring the surface roughness, and the surface roughness Ray in the evaluation region is calculated. As for the surface roughness of the conductive portion 22e, a region excluding the dielectric portion 22d from the evaluation region is extracted, and the surface roughness Rad is calculated for the extracted region in the same manner as the calculation of the surface roughness of the dielectric portion 22d.

<Measurement method of average dielectric part width>
In the present invention, the average dielectric portion width Sy in the rotation direction of the developing roller 22 is measured as follows. A laser microscope VK-X100 (trade name, manufactured by Keyence Corporation) is equipped with an objective lens having a magnification of 10 times, and the surface of the developing roller 22 in a region of 1.5 mm × 1 mm is two-dimensionally scanned by a laser confocal optical system. I do. As a result, a high-contrast image on the surface of the developing roller 22 can be acquired. Then, in the acquired image, a square area (referred to as an evaluation area) having a side of 900 μm is set as an evaluation target.

  Then, the dielectric part 22d is extracted from the image of the evaluation area, and the image is binarized. Then, the obtained binarized image is analyzed, and the number of pixels of the dielectric portion 22d that is continuous in the rotation direction of the developing roller 22 is calculated. Then, the average value of the calculated number of pixels is calculated, and further, the average dielectric portion width Sy is calculated based on the resolution.

  Further, the average dielectric portion width Sx in the direction orthogonal to the rotation direction of the developing roller 22, that is, the rotation axis direction of the developing roller 22 is calculated. The binarized image obtained above is analyzed, and the number of pixels of the dielectric portion 22d that is continuous in the rotation axis direction of the developing roller 22 is calculated. Then, the average value of the calculated number of pixels is calculated, and further, the average dielectric portion width Sy is calculated based on the resolution. In this embodiment, the average dielectric portion width Sy in the rotation direction of the developing roller 22 is 100 μm, and the average dielectric portion width Sx in the rotation axis direction of the developing roller 22 is 140 μm. That is, Sx / Sy = 1.4 holds.

<Action of gradient force>
As shown in FIG. 1B, the developing roller 22 has a dielectric portion 22d and a conductive portion 22e (where the base layer 22b and the metal cored bar 22a are conducted) mixedly distributed on the surface. The surface of the developing roller 22 is rubbed with the developing blade 23, which is a regulating member, directly or via toner, so that electric charges are applied to the dielectric portion 22d of the developing roller 22. Then, an electric field is generated in the dielectric portion 22d to which the electric charge is applied. A minute closed electric field E is generated in a portion where the dielectric portion 22d and the conductive portion 22e are adjacent to each other, and a large number of minute closed electric fields E are formed in the developing roller 22 as a whole.

For example, when a charge is applied to the dielectric portion 22d by rubbing the developing blade 23 with the developing roller 22 via toner, a minute closed electric field extending in an arc shape from the dielectric portion 22d to the conductive portion 22e as shown in FIG. E is formed. As a result, on the developing roller 22, toner having an unstable charge amount such as no charge or low charge in the developing chamber 24 a is conveyed into the minute closed electric field E on the developing roller 22. The toner carried in the minute closed electric field E receives an electrostatic force generated by the electric field and, in the case of an uncharged developer, a gradient force (Gradient Force) described later generated by the minute closed electric field E, and the developing roller receives the toner. It is attracted to and carried on the surface of 22.

  Here, the gradient force will be described with reference to FIG. 5A and 5B schematically show the movement of dielectric particles (developer particles) in an electric field. As shown in FIG. 5A, when the charged dielectric particles (toner particles) 71 are in the electric field applied from the outside, the charged dielectric particles 71 are in the same direction as or opposite to the direction of the electric field depending on the polarity of the charge. It receives an electrostatic force in the direction. Further, as shown in FIG. 5B, when a so-called unequal electric field having different sizes depending on positions is formed, the uncharged dielectric particles (toner particles) 72 in the unequal electric field have no electric charge. Both receive a force toward a region where the electric field is strong (rightward on the paper surface in FIG. 5B). This force is called the gradient force (Ueda et al., "Basics of Electrostatics", p. 15, published by Asakura Shoten in 1969).

<Toner charge imparting action>
The toner carried on the developing roller 22 by the gradient force is regulated to a predetermined thickness by the developing blade 23. Further, since the developing blade 23 rubs the surface of the developing roller 22 via the toner, the toner has a polarity corresponding to the position of the materials of the developing roller 22 and the developing blade 23 on the triboelectric charging series, and is necessary for the development. Is charged to a predetermined charge amount.

  As shown in FIG. 6, the developing roller 22 is configured so that the surface roughness of the dielectric portion 22d and the surface roughness of the conductive portion 22e are different on the surface. When the developing roller 22 rubs against the developing blade 23 via the toner, the toner attached to the dielectric portion 22d is scraped off by the regulating force of the developing blade 23, or a conductive portion on the downstream side in the rotation direction of the developing roller 22. It is moved to 22e. The toner attached to the conductive portion 22e receives a force that is conveyed in the moving direction of the developing roller 22 from the surface of the conductive portion 22e. Further, the toner receives a force in a direction opposite to the rotation direction of the developing roller 22 due to the sliding friction with the developing blade 23. As a result, the toner rolls, and frictional charging is promoted by the sliding friction caused by the rolling, so that the toner is charged. As described above, the multi-layered toner having the adhering amount and the charging amount required for the development is stably carried on the developing roller 22.

  That is, in order to stably supply the toner and impart the charge, it is preferable that the dielectric portions 22d and the conductive portions 22e are alternately present in the rotation direction of the developing roller 22, as shown in FIG. Further, for the purpose of stably supplying and charging the toner in the rotation axis direction of the developing roller 22, the average dielectric portion width Sx of the developing roller 22 in the rotation axis direction is the average dielectric portion width of the developing roller 22 in the rotation direction. It is configured to be larger than Sy.

  As a result, a region where the dielectric portions 22d and the conductive portions 22e are alternately present in the rotation direction of the developing roller 22 can be stably formed in the rotation axis direction of the developing roller 22. As a result, a stable toner coat layer can be formed in the rotation axis direction of the developing roller 22.

  Next, the relationship between the average dielectric width of the developing roller 22 and the stability of the toner coat layer will be described with reference to FIG. FIG. 7A shows a schematic arrangement of the dielectric portion 22d and the conductive portion 22e where Sx / Sy = 1.0. The area indicated by "area Z" in the drawing is an area that does not have a portion where the dielectric portion 22d overlaps on the downstream side in the rotation direction of the developing roller 22. In such an area, the toner supply amount may be insufficient. On the other hand, FIG. 7B shows a schematic arrangement of the dielectric portion 22d and the conductive portion 22e where Sx / Sy = 1.4. As shown in FIG. 7B, it can be seen that the number of regions Z decreases when Sx becomes larger than Sy.

  As a result of intensive studies, the inventors have found that the uniformity of a solid black image can be effectively obtained when Sx / Sy is 1.4 or more. Therefore, in the present invention, Sx / Sy is preferably 1.4 or more.

Further, the average dielectric portion width Sy in the rotation direction of the developing roller 22 is preferably larger than the average particle diameter D of the toner. The average particle diameter of the toner in this embodiment is 6.5 μm, for example. If the average particle size of the toner is 6.5 μm, Sy / D = 2.0
= 13 μm. The method for measuring the average particle size of the toner in this example is as follows: A liquid module is attached to a LS-230 type laser diffraction particle size distribution measuring device manufactured by Beckman Coulter Inc., and a particle size of 0.04 to 2000 μm is set as a measuring range, It was calculated from the obtained volume-based particle size distribution.

  FIG. 8A schematically shows the relationship between the dielectric portion 22d and the toner particles T when Sy / D = 2.0, Sy / D = 1.0, and Sy / D = 0.6. When the average particle diameter of the toner is 6.5 μm, Sy = 13 μm when Sy / D = 2.0. Further, FIG. 8A shows the arrangement of charges on the dielectric portion 22d when the surface charge densities are equal. FIG. 8B shows a potential distribution formed when the dielectric portion 22d, the toner particles T, and the charges are arranged as shown in FIG. 8A. When Sy / D = 2.0 and 1.0, the potential change (gradient force) generated in the region where the toner particles T are present is large. On the other hand, when Sy / D = 0.6, the potential change occurring in the area where the toner particles T are present is small, and the toner supply amount is insufficient. Therefore, in order to form a stable potential and stably carry the toner, it is preferable that Sy is equal to or more than the average particle diameter of the toner, that is, Sy / D is 1.0 or more.

<Explanation of effects>
Next, in the present embodiment, the effects of solid black followability, fog and uniformity of a solid black image when the developer is deteriorated or moisture is absorbed will be described with reference to comparative examples. The outline of the comparative example is as follows.

(Comparative Example 1)
Surface roughening treatment of conductive portion of developing roller: Yes Dielectric portion of developing roller: No FIGS. 9A and 9B are schematic diagrams illustrating the developing roller 22 in Comparative Example 1. 9A and 9B are diagrams corresponding to FIGS. 1A and 1B, respectively. The difference from the present embodiment is that the dielectric portion 22d is not provided.

(Comparative example 2)
Surface Roughening Treatment of Conductive Portion of Developing Roller: None Dielectric Portion of Developing Roller: Present FIGS. 10A and 10B are schematic diagrams illustrating the developing roller 22 in Comparative Example 2. 10A and 10B are diagrams corresponding to FIGS. 1A and 1B, respectively. The difference from the present embodiment is that the surface layer of the conductive portion 22e does not contain resin particles. That is, the surface roughness of the dielectric part 22d and the surface roughness of the conductive part 22e are configured to be equal.

  Here, in addition to the above Example 1, the following Examples 2 and 3 according to the present invention are added for comparison.

(Example 2)
Dielectric Portion of Developing Roller: Stretching in the Rotational Axis Direction of Developing Roller 22 FIG. 11 is a schematic diagram illustrating the developing roller 22 in the second embodiment. The difference from the first embodiment is that the dielectric portion 22d is formed as a region extending in the rotation axis direction of the developing roller 22.

(Example 3)
Example 3 will be described below. The basic configuration and operation of the image forming apparatus 100 according to the third embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus 100 according to the third embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 according to the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

  In the third embodiment, there are many sections (peripheral sections) in which the tangent of the boundary line between the conductive section 22e and the dielectric section 22d is continuous for a predetermined width or more in a state of being inclined with respect to the rotation axis direction of the developing roller 22. To do. A specific example of the predetermined width will be described below.

  That is, in the third embodiment, the angle (hereinafter, also referred to as a crossing angle) formed by the tangent of the boundary line between the dielectric portion 22d and the conductive portion 22e to the straight line parallel to the rotation axis of the developing roller 22 is θ. At this time, in one dielectric part 22d, the section where the intersection angle θ is an acute angle is continuous for a predetermined width or more. Note that the intersection angle θ being an acute angle means that 0 (deg) <θ <90 (deg) or 0 (deg)> θ> −90 (deg) holds.

  Further, for the dielectric portion 22d in a square area having one side of the surface of the developing roller 22 of 900 μm, a section in which the intersection angle θ is an acute angle is a width in the rotation axis direction of the developing roller 22 (hereinafter, referred to as a tilt section width). ). In the third embodiment, when the average particle diameter of the toner is D, the dielectric portion 22d having a section whose inclination section width is larger than 2πD exists in the square area. Further, when the number of sections having a slope section width of 50 μm or more is W1 and the number of sections having a slope section width of less than 50 μm is W2, W1 is W2 or more, for a section having a slope section width of more than 2πD. Here, it is assumed that the crossing angle θ has a positive angle from the rotational axis direction of the developing roller 22 to the rotational direction of the developing roller 22 and a negative angle to the opposite direction to the rotational direction of the developing roller 22.

  A method of calculating the slope section width in the third embodiment will be described with reference to FIG. However, the method of calculating the inclination section width is not limited to the method described below, and may be one using another measuring device or image processing method.

  First, a laser microscope VK-X100 (trade name, manufactured by Keyence Corporation) is equipped with an objective lens having a magnification of 10 times. Then, with the microscope, a 1.5 mm × 1.0 mm area on the surface of the developing roller 22 is two-dimensionally scanned by a laser confocal optical system to obtain a high-contrast image on the surface of the developing roller 22. A square area having a side of 900 μm as shown in FIG. 12A is set in the obtained image, and this area is set as an evaluation target. Then, in the square area, the boundary line between the dielectric portion 22d and the conductive portion 22e is detected, and the intersection angle θ is calculated based on the detected boundary line.

  Next, as shown in FIG. 12B, evaluation points are set at a predetermined pitch I in the rotation direction of the developing roller 22 on the boundary line between the dielectric section 22d and the conductive section 22e, and the tangent line at each evaluation point (an example in the figure is shown. Tangent lines L1 to L4 are shown as). Then, for each obtained tangent line, an intersection angle θ formed by the tangent line and a straight line (indicated by straight lines H1 to H6 in the figure as an example) which is parallel to the rotation axis of the developing roller 22 passing through the evaluation point where the tangent line is obtained is calculated. . In the third embodiment, as an example, the above-mentioned predetermined pitch I is set to 0.01 mm pitch, and the crossing angle θ is calculated.

Next, based on the intersection angle θ calculated for each evaluation point, a section in which the intersection angle θ is an acute angle and a width (inclination section width) of the section in the rotation axis direction of the developing roller 22 are calculated. For example, in the example shown in FIG. 12C, the sections where the intersection angle θ is an acute angle are Section A and Section B. In Example 3, the inclination section width of the section where the intersection angle θ is an acute angle is larger than 2πD, which means that there is a section in which one toner particle can roll for one rotation or more. Further, regarding a section having a tilt section width of more than 2πD, W1 is more preferably W2 or more, where W1 is the number of sections having a tilt section width of 50 μm or more and W2 is the number of sections having a tilt section width of less than 50 μm.

  In addition, the calculation of the inclination section width is performed by setting the square area to 1 in each of the 10 areas obtained by dividing the developing roller 22 into 10 equal parts in the longitudinal direction of the developing roller 22, that is, the rotation axis direction. And set it. In Example 3, since the toner having the average particle diameter of 6.5 μm is used, the inclination section width of larger than 2πD means that the inclination section width is larger than 20 μm. Also, as an example, it was found that the number W1 of the sections having the inclination section width of 50 μm or more was 22, and the number W2 of the sections having the inclination section width of less than 50 μm was 12, and W1 was larger than W2.

  Therefore, the toner carried and carried on the surface of the developing roller 22 is rubbed at the regulating portion where the developing roller 22 and the developing blade 23 contact each other. As a result, the toner moves in the rotation axis direction (longitudinal direction) of the developing roller 22 when rolling on the surface of the developing roller 22. Specifically, at the boundary between the dielectric portion 22d and the conductive portion 22e, there is a section having an inclination with respect to the rotation axis direction of the developing roller 22, so that the toner in the rotation axis direction (longitudinal direction) of the developing roller 22 is formed. Movement is promoted.

  The reason why it is preferable that there are many sections having a slope section width of 50 μm or more in the evaluation area is presumed as follows. It is said that the visual spatial resolution is about 100 μm (about 50 μm for point discrimination). Therefore, in the section where the inclination section width is less than 50 μm, it is considered that the toner movement in the rotation axis direction of the developing roller 22 is small and it is difficult to visually recognize the above effect, and when the inclination section width is 50 μm or more, This is because it is considered that the effect of will be visible.

  The dielectric portion 22d in the third embodiment is formed by spray coating the surface of the surface layer 22c of the developing roller 22 with the coating material that forms the dielectric portion 22d. Specifically, a paint is produced and applied by spray coating on the surface of the roller on which the surface layer 22c is formed so that the applied amount of the paint is 0.040 g. Furthermore, the coating film is dried and cured by heating at a temperature of 140 ° C. for 80 minutes. Although the dielectric portion 22d is formed by the spray method in the third embodiment, the invention is not limited to this, and a dispenser method or an inkjet method may be used. In this case, conditions such as the type of material and the discharge amount may be adjusted appropriately. In Example 3, the average dielectric portion width Sx in the direction orthogonal to the rotation direction of the developing roller 22 was 64 μm, the average dielectric portion width Sy in the rotation direction of the developing roller 22 was 45 μm, and Sx / Sy = 1. .42.

<Comparison result>
An image evaluation test was performed using the developing devices in Examples 1 to 3 and Comparative Examples 1 and 2 using the image forming apparatus 100 of FIG. 2, specifically, MF726Cdw (trade name, manufactured by Canon Inc.). Specifically, in a high temperature and high humidity environment (temperature of 30 ° C. and humidity of 80%), “when new” before passing (0 sheet) of the developing device and “when durable” after 5000 sheets have been passed. The image evaluation test was performed. In the image evaluation, a so-called solid black image was used for solid black followability, and a so-called solid white image was used for fogging. The image evaluation test results are shown in Table 4.

  The evaluation results regarding solid black followability, fog, and solid black image uniformity in "new" and "durable" using the developing devices of Examples and Comparative Examples will be described below.

(Evaluation criteria for solid black followability)
In the evaluation of the solid black followability, the solid black image is output by the image forming apparatus 100, and visually determined by the following criteria.
A: White spots (solid black followability are not generated) B: White spots (solid black followability is not generated)

(Cover evaluation criteria)
In the evaluation of fog, the paper on which a solid white image is output by the image forming apparatus 100 and the paper (reference paper) on which the fog toner is output without adhering to the transfer material by masking the transfer material at the same time are used. . Then, the reflectance of the paper on which the solid white image is output and the reflectance of the reference paper are measured using a reflectance meter, and the difference between the reflectances is used as an index value indicating fog.
A: Difference value is less than 3.0 B: Difference value is 3.0 or more

(Evaluation criteria for solid black image uniformity)
In the evaluation of the uniformity of the solid black image, the solid black image is output by the image forming apparatus 100 and visually determined by the following criteria.
AA: No vertical streak-like density unevenness occurred A: Vertical streak-like density unevenness occurred several (for example, 2 or 3) B: Many vertical streak-like density unevenness occurred (for example, 4 or more)

(Effects of Examples 1 to 3 on solid black followability)
In Comparative Example 1, the occurrence of solid black followability was observed during durability. On the other hand, in Examples 1 to 3, the occurrence of solid black followability was not confirmed at the time of new article and durability. The reason why the solid black followability defect occurred in Comparative Example 1 is considered as follows. Since the developing roller 22 in Comparative Example 1 is configured not to have the dielectric portion 22d, the above gradient force does not act on the toner. Therefore, when the product is new, the amount of toner charge required for development is sufficient, so that the toner is carried on the developing roller 22 by the image force and solid black followability does not occur. On the other hand, in a situation where the toner is deteriorated as in the case of durability and the charge amount of the toner is insufficient such as in a high humidity environment, a low-charged toner and an uncharged toner are required unless the gradient force acts on the toner. Is not carried by the developing roller 22, resulting in poor solid black followability.

(Effects of Examples 1 to 3 on fogging)
In Comparative Example 2, occurrence of fogging was observed during durability. On the other hand, in Examples 1 to 3, the occurrence of fogging was not confirmed at the time of new article and at the time of durability. The reason why fogging occurred in Comparative Example 2 is considered as follows. The developing roller 22 in Comparative Example 2 is configured such that the surface layer of the conductive portion 22e does not contain resin particles. Therefore, when the toner on the developing roller 22 conveyed by the gradient force is rubbed by the regulating portion, the toner is conveyed in the rotating direction of the developing roller 22 by the surface of the conductive portion 22e having the surface roughening treatment. Cannot receive the power to As a result, the charge imparting action due to the rolling of the toner cannot be sufficiently obtained, and the fog appears more conspicuously. On the other hand, in the developing roller 22 in Comparative Example 1, the toner conveyed to the regulation portion and passed through the regulation portion was sufficiently charged in the conductive portion 22e, and therefore the occurrence of fogging was not confirmed.

(Effects of Examples 1 to 3 on solid black image uniformity)
In both Comparative Example 1 and Comparative Example 2, the solid black image uniformity deteriorated. In Comparative Example 1, it is considered that the solid black image uniformity deteriorated as the solid black followability deteriorated. Further, in Comparative Example 2, it is considered that the solid black image uniformity was deteriorated due to toner supply failure in the area where the dielectric portion 22d is small at the time of endurance with advanced toner deterioration. On the other hand, in Examples 1 to 3, the possibility that a region having a small dielectric portion 22d is generated in the direction orthogonal to the rotation direction of the developing roller 22 as in Comparative Example 2 is suppressed, so that stable toner supply provides high uniformity. It can be said that a solid black image can be obtained. Furthermore, in Examples 2 and 3, the uniformity of the solid black image was better than that in Example 1.

  Here, in Example 2, since the dielectric portion 22d is continuously formed in the direction orthogonal to the rotation direction of the developing roller 22, it is considered that the toner supply failure does not occur. However, in Example 2, a slight horizontal line-shaped gradation difference was visually recognized.

  On the other hand, in the third embodiment, as described above, a large number of sections (tilt sections) having an inclination with respect to the rotation axis direction of the developing roller 22 are provided at the boundary between the dielectric section 22d and the conductive section 22e. As a result, when the toner rolls, the toner moves in the rotation axis direction (longitudinal direction) of the developing roller 22 in the regulating portion where the developing roller 22 and the developing blade 23 contact each other. As a result, it is considered that the influence of the unevenness of the toner supply amount is further reduced and the uniformity of the solid black image is further improved.

  As described above, according to the above-described embodiment, even when the developer is deteriorated or moisture is absorbed, the problem of the image such as the fog is suppressed while suppressing the occurrence of the solid black followability defect, which is more preferable. A uniform solid black image can be realized.

100 ... Image forming apparatus, 22 ... Developing roller, 22d ... Dielectric part, 22e ... Conductive part, T ... Toner

Claims (13)

A developer carrying member that carries a developer and is rotatable,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characteristic developer carrier.   The charge polarity of the dielectric portion is the same as the charge polarity of the developer when the developer is charged by friction with a regulation member that regulates the developer carried by the developer carrier. The developer carrying member according to claim 1, wherein: In the dielectric portion, an intersection angle θ formed by a tangent line on the outer periphery of the dielectric portion and a straight line parallel to the rotation axis is 0 (deg) <θ <90 (deg) or 0 (deg)>θ> −. Has at least one outer peripheral section of 90 (deg),
When the average particle diameter of the developer is D, the dielectric portion has an outer peripheral section in which the width in the axial direction of the rotation shaft is larger than 2πD in the at least one outer peripheral section. Alternatively, the developer carrying member according to the item 2.   In the area including at least a part of the dielectric portion on the surface of the developer carrier, the width of the at least one outer peripheral section in which the width in the axial direction of the rotation shaft is larger than 2πD. 4. The developer carrying member according to claim 3, wherein W1 is W2 or more, where W1 is the number of outer circumferential sections having a width of 50 μm or more and W2 is the number of outer circumferential sections having a width of less than 50 μm. .   5. The ratio of the average value of the widths of the plurality of dielectric portions in the rotation direction of the developer carrier to the average particle diameter of the developer is 1.0 or more. The developer carrying member according to 1.   The ratio of the average value of the widths of the plurality of dielectric portions in the axial direction of the rotation axis of the developer carrier to the average value of the width of the dielectric portion in the rotation direction of the developer carrier is 1. It is 4 or more, The developer carrying body according to any one of claims 1 to 5 characterized by things.   7. The dielectric part is formed on the surface of the developer carrier by covering a part of the surface of the conductive part formed on the surface of the developer carrier. The developer carrier according to the item 1.   The developer carrier according to claim 1, wherein on the surface of the developer carrier, the dielectric portions are arranged so as to be scattered in the region of the conductive portion.   The developer carrier according to claim 8, wherein an area occupied by the dielectric part is smaller than an area occupied by the conductive part on the surface of the developer carrier.   The developer carrier according to claim 1, wherein the developer is a non-magnetic one-component developer. A developer carrying member carrying a developer,
A developing device having a regulating member for regulating the developer carried on the surface of the developer carrying body,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characteristic developing device. A developer carrying member carrying a developer,
A regulating member for regulating the developer carried on the surface of the developer carrying body,
A process cartridge having an image carrier that carries a developer image,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. Characteristic process cartridge. A developer carrying member carrying a developer,
A regulating member for regulating the developer carried on the surface of the developer carrying body,
An image bearing member carrying a developer image,
An image forming apparatus having a transfer member,
On the surface of the developer carrying member, a conductive portion having a first surface roughness and a first electric resistance, a second surface roughness smaller than the first surface roughness and the first electric resistance. A dielectric portion having a second electrical resistance greater than
The average value of the width of the dielectric portion in the axial direction of the rotation axis of the developer carrier is larger than the average value of the width of the dielectric portion in the rotation direction of the developer carrier orthogonal to the axial direction. A characteristic image forming apparatus.

Images