JP2019003171A - Image formation apparatus, electrification member, cartridge and manufacturing method of electrification member - Google Patents

Abstract

To provide an image formation apparatus which can suppress adhesion of a stain to an electrification member while suppressing local image density unevenness and development fogging, and provide an electrification member, a cartridge and a manufacturing method of the electrification member.SOLUTION: The surface roughness (ten-point average roughness Rz) of an electrification member 2 is equal to or greater than 6 μm and equal to or less than 18.8 μm, and the thickness of the surface layer is equal to or greater than 7 μm and equal to or less than 20 μm. When an average particle diameter of the first surface layer particle 21 is defined as D1, and the average particle diameter of the second surface layer particle 22 is defined as D2, 9.8 μm≤D1≤15.8 μm, 2.8 μm≤D2≤5.2 μm and 3≤D1/D2≤5.6 are satisfied. When the mass per the unit area of the first surface layer particle 21 is defined as M1, and the mass per the unit area of the second particle 22 is defined as M2, 0.10≤M1/(M1+M2)≤0.32 is satisfied.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic method or an electrostatic recording method, a charging member, a cartridge used in the image forming device, and a method for manufacturing the charging member. is there.

  2. Description of the Related Art Conventionally, for example, in an image forming apparatus using an electrophotographic system, as a system for charging a photoconductor (electrophotographic photoconductor) as an image carrier, a photoconductor is applied by applying a voltage to a charging member in contact with the photoconductor. There is a contact charging method that charges the battery. A roller-shaped charging roller is often used as the charging member. The charging roller has, for example, a configuration in which a conductive elastic layer is provided on the outer periphery of a conductive support, and the surface of the conductive elastic layer is covered with a conductive surface layer.

  In the contact charging method, the surface of the photoconductor is charged by a discharge (Paschen discharge) generated in a minute gap between the photoconductor and the charging member. The contact charging method includes an “AC charging method” in which a voltage obtained by superimposing a DC voltage and an AC voltage is applied to a charging member, and a “DC charging method” in which only a DC voltage is applied to the charging member. Since the DC charging method does not require an AC power supply, it is advantageous for downsizing, simplification of configuration, and cost reduction. In addition, the DC charging method is advantageous in extending the life of the photoconductor because the amount of discharge is smaller than that in the AC charging method and the surface of the photoconductor is prevented from being scraped. On the other hand, in the DC charging method, the effect of converging the surface potential of the photosensitive member due to the AC voltage obtained in the AC charging method cannot be obtained, so abnormalities in the surface shape of the charging member and adhesion of foreign matters to the surface appear as image defects. There is a tendency to be easy. In the case of the DC charging method, it is required that the abnormality of the surface shape of the charging member is relatively small or small as compared with the AC charging method.

  On the other hand, if the surface of the charging member is too smooth (that is, if the surface roughness is too low), dirt adhering to the photoreceptor (toner that has passed through the cleaning member or external additive that has been detached from the toner) is charged. It becomes easy to adhere to the surface of the member. Then, streaky image density unevenness (image streaks) may occur at a position corresponding to the portion of the charging member where the surface is contaminated, substantially parallel to the moving direction of the surface of the photoreceptor. In order to suppress the adhesion of dirt to the charging member, it is effective to reduce the contact area between the photosensitive member and the charging member by increasing the surface roughness of the charging member.

  Patent Document 1 discloses a charging member having the following configuration for the purpose of suppressing the generation of wrinkles in the outermost layer of the charging member, controlling the surface properties, and ensuring charging uniformity. In other words, the charging member has a surface roughness (Rz) larger than 10 μm and smaller than 25 μm, and the outermost layer is composed of 2 large particles having an average particle diameter A of 15 to 25 μm and small particles having an average particle diameter B of less than 7 μm. Particles of different sizes are dispersed. Further, the ratio (A / B) of the average particle diameter A of the large particles to the average particle diameter B of the small particles is larger than 3 and smaller than 12. The mixing ratio of large particles to small particles (a / (a + b); a is the mixing amount of large particles and b is the mixing amount of small particles) is 0.7 or more and 0.9 or less.

Japanese Patent No. 4047057

  However, as a result of performing an additional test in accordance with Patent Document 1, the present inventors have found that development fogging may occur although image defects such as black spots are suppressed. Note that the black spot is a phenomenon in which black spot-like image density unevenness occurs on an image due to a local insufficient charging potential on the surface of the photoreceptor. Development fogging is a phenomenon in which toner adheres to a relatively wide non-image area due to insufficient charging potential of the photoreceptor.

  The larger the particles dispersed in the surface layer of the charging member (hereinafter also referred to as “surface layer particles”), the more microscopically less potential potential exists on the surface of the photoreceptor. According to the study by the present inventors, it was found that development fogging occurs when the surface layer particles are enlarged, and image defects such as black spots occur when the surface layer particles are further enlarged. . Thus, when the surface layer particles are too large, black spots and development fog are likely to occur. On the other hand, according to the study by the present inventors, if the surface layer particles are too small, it becomes difficult to uniformly disperse the surface layer particles, and the surface layer particles are agglomerated and the development fog and black spots tend to deteriorate. I found out that Further, it has been found that if the surface layer particles are too small, the effect of reducing the contact area between the photoreceptor and the charging member cannot be obtained, and dirt easily adheres to the charging member.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus, a charging member, a cartridge, and a manufacturing method of the charging member that can suppress adhesion of dirt to the charging member while suppressing local image density unevenness and development fog. Is to provide.

  The above object is achieved by the image forming apparatus, the charging member, the cartridge, and the manufacturing method of the charging member according to the present invention. In summary, the present invention provides an image carrier, a charging member that contacts the image carrier and charges the image carrier, a power source that applies a voltage to the charging member, and a developer on the image carrier. Developing means for forming a toner image by supplying the charging member, the charging member comprising a base layer and a surface layer formed on the base layer, wherein the surface layer has a first particle size and a first particle size different from each other. In the image forming apparatus in which 2 surface layer particles are dispersed, the charging member has a surface roughness (ten-point average roughness Rz) of 6 μm or more and 18.8 μm or less, and the surface layer has a thickness of 7 μm or more and 20 μm. 9.8 μm ≦ D1 ≦ 15.8 μm and 2.8 μm ≦ D2 where D1 is the average particle size of the first surface layer particles and D2 is the average particle size of the second surface layer particles. ≦ 5.2 μm and 3 ≦ D1 / D2 ≦ 5.6, the charging unit When the mass of the first surface layer particles per unit area on the surface of the material is M1, and the mass of the second particles is M2, 0.10 ≦ M1 / (M1 + M2) ≦ 0.32 is satisfied. The image forming apparatus is characterized.

  According to another aspect of the present invention, a base layer and a surface layer formed on the base layer are provided, and first and second surface layer particles having different particle diameters are dispersed in the surface layer, and surface roughness (ten The point average roughness (Rz) is 6 μm or more and 18.8 μm or less, the thickness of the surface layer is 7 μm or more and 20 μm or less, and the image carrier is charged by contact with the image carrier and applying a voltage. Wherein the average particle diameter of the first surface layer particles is D1, and the average particle diameter of the second surface layer particles is D2, 9.8 μm ≦ D1 ≦ 15.8 μm, and 2.8 μm ≦ D2 ≦ 5.2 μm and 3 ≦ D1 / D2 ≦ 5.6, and the mass of the first surface layer particle per unit area of the surface of the charging member is M1, the second When the mass of the particles is M2, 0.10 ≦ M1 / (M1 + M2) ≦ A charging member characterized by satisfying 0.32 is provided.

  According to another aspect of the present invention, there is provided a cartridge that is detachable from the apparatus main body of the image forming apparatus and has the charging member of the present invention.

  According to another aspect of the present invention, a base layer and a surface layer formed on the base layer are provided, and first and second surface layer particles having different particle diameters are dispersed in the surface layer, and surface roughness (ten The point average roughness (Rz) is 6 μm or more and 18.8 μm or less, the thickness of the surface layer is 7 μm or more and 20 μm or less, and the image carrier is charged by contact with the image carrier and applying a voltage. A method for producing a charging member for use in the above, comprising the step of preparing a surface layer coating material by blending the first and second surface layer particles in a curable resin solution, and for the surface layer on the base layer A step of forming a coating film of the coating, and a step of curing the coating film to form the surface layer. In the step of preparing the surface layer coating material, the average particle diameter of the first surface layer particles is set to D1, when the average particle diameter of the second surface layer particles is D2, 9.8 μm ≦ D1 ≦ 15.8 μm, 2.8 μm ≦ D2 ≦ 5.2 μm, and the first and second surface layer particles satisfying 3 ≦ D1 / D2 ≦ 5.6, the unit area of the first surface layer particles The surface coating composition is prepared by blending to satisfy 0.10 ≦ M1 / (M1 + M2) ≦ 0.32, where M1 is the weight per unit and M2 is the mass per unit area of the second surface layer particles. A method for manufacturing a charging member is provided.

  According to the present invention, it is possible to suppress adhesion of dirt to the charging member while suppressing local image density unevenness and development fog.

1 is a schematic cross-sectional view of an image forming apparatus. It is a typical sectional view of an image formation part. FIG. 3 is a schematic cross-sectional view of a charging roller and a surface layer of the charging roller. FIG. 2 is a schematic cross-sectional view of a photosensitive drum. It is a graph for demonstrating the measuring method of an elastic deformation power. It is a schematic diagram of the recessed part formed in the surface of a photosensitive drum.

  Hereinafter, the image forming apparatus, the charging member, the cartridge, and the manufacturing method of the charging member according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus of this embodiment. The image forming apparatus 100 according to the present exemplary embodiment has functions of a tandem type (in-line type) copying machine, printer, and facsimile apparatus adopting an intermediate transfer method, which can form a full-color image using an electrophotographic method. It is a multifunction device. The image forming apparatus 100 according to the present exemplary embodiment can form an image on a transfer material P having a maximum A3 size by a DC charging contact charging method.

  The image forming apparatus 100 includes first, second, third, and fourth images that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units, respectively. It has image forming units SY, SM, SC, and SK. Note that elements having the same or corresponding functions or configurations in each of the image forming units SY, SM, SC, and SK are Y, M, C, and K at the end of a symbol that represents an element for any color. Omitted, may be explained comprehensively. FIG. 2 is a schematic cross-sectional view showing one image forming unit S as a representative. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6 and the like which will be described later.

  The image forming apparatus 100 includes a photosensitive drum 1 that is a rotatable drum type (cylindrical) photosensitive member as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 in the figure by a drive motor (not shown) as a drive means. In this embodiment, the photosensitive drum 1 is a negatively charged drum-shaped organic photoreceptor, and has a photosensitive layer (OPC layer) on a substrate formed of a conductive material such as aluminum. . The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type charging member as a charging unit. During the charging process, a charging voltage (charging bias) consisting only of a direct voltage (DC voltage, DC component) is applied to the charging roller 2 from a charging power source (high voltage power circuit) E1. The charging process on the surface of the photosensitive drum 1 is performed between at least one of the photosensitive drum 1 and the charging roller 2 upstream or downstream in the rotation direction of the photosensitive drum 1 with respect to the contact portion N between the photosensitive drum 1 and the charging roller 2. This is performed by electric discharge generated in the minute gap. The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device 3 as an exposure means (electrostatic image forming means), and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. In this embodiment, the exposure apparatus 3 is a laser beam scanner using a semiconductor laser.

  The electrostatic image formed on the photosensitive drum 1 is developed (visualized) using a developer by a developing device 4 as a developing unit, and a toner image is formed on the photosensitive drum 1. In this embodiment, the exposure portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged is the same as the charging polarity (negative polarity in this embodiment) of the photosensitive drum 1. Polarized charged toner adheres. That is, in this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner at the time of development, is negative. In the present embodiment, the developing device 4 uses a two-component developer including toner (nonmagnetic toner particles) and a carrier (magnetic carrier particles) as a developer. The developing device 4 is a non-magnetic hollow cylindrical member that is rotatably provided in the developing container 4a so that a part of the developing container 4a that accommodates the developer 4e is exposed to the outside from the opening of the developing container 4a. And a formed developing sleeve 4b. Inside the developing sleeve 4b (hollow part), a magnet roller 4c is arranged fixed to the developing container 4a. The developing container 4a is provided with a regulating blade 4d so as to face the developing sleeve 4b. Further, two stirring members (stirring screws) 4f are provided in the developing container 4a. Toner is appropriately supplied to the developing container 4a from the toner hopper 4g. The amount of the developer 4e carried on the developing sleeve 4b by the magnetic force of the magnet roller 4c is regulated by the regulating blade 4d with the rotation of the developing sleeve 4b, and then is opposed to the photosensitive drum 1 (developing unit). Be transported. The developer 4e on the developing sleeve 4b conveyed to the developing unit is raised by the magnetic force of the magnet roller 4c to form a magnetic brush (magnetic ear), and is brought into contact with or close to the surface of the photosensitive drum 1. Further, during the developing process, the developing sleeve 4b is supplied with a DC voltage (DC voltage, DC component) and an AC voltage (AC voltage, AC component) as a developing voltage (developing bias) from the developing power source (high voltage power circuit) E2. The superimposed vibration voltage is applied. As a result, the toner moves from the magnetic brush on the developing sleeve 4 b to the photosensitive drum 1 according to the electrostatic image on the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1.

In this embodiment, the surface potential (dark portion potential) of the photosensitive drum 1 formed by charging by the charging roller 2 is −800 V, and the surface potential (light portion potential) of the photosensitive drum 1 formed by exposure by the exposure device 3. ) Is adjusted to −300 V, the charge amount and the exposure amount are adjusted. In this embodiment, the DC component of the development voltage is set to -600V. In this embodiment, the process speed is 250 mm / sec, and the width of the image forming area on the photosensitive drum 1 in the rotation axis direction of the photosensitive drum 1 is 360 mm. In this embodiment, the toner charge amount is set to about −40 μC / g, and the toner amount on the photosensitive drum 1 in the solid image portion is set to about 0.4 mg / cm ² .

  An intermediate transfer belt 7 constituted by an endless belt as an intermediate transfer member is disposed so as to face each photosensitive drum 1. The intermediate transfer belt 7 is stretched around a driving roller 71, a tension roller 72, and a secondary transfer counter roller 73 as a plurality of stretching rollers, and is stretched with a predetermined tension. The intermediate transfer belt 7 rotates (circulates) in the direction of the arrow R2 in the drawing at the substantially same peripheral speed as the peripheral speed of the photosensitive drum 1 when the driving roller 71 is driven to rotate. A primary transfer roller 5, which is a roller-type primary transfer member serving as a primary transfer unit, is disposed on the inner peripheral surface side of the intermediate transfer belt 7 corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) T1 where the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other. The toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion T1. During the primary transfer process, a primary transfer voltage (primary transfer bias) that is a DC voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 5 from the primary transfer power supply (high voltage power supply circuit) E3. . For example, when forming a full-color image, yellow, magenta, cyan, and black toner images formed on each photosensitive drum 1 are sequentially transferred so as to be superimposed on the intermediate transfer belt 7.

  On the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 73. The secondary transfer roller 8 is pressed toward the secondary transfer counter roller 73 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact with each other. T2 is formed. As described above, the toner image formed on the intermediate transfer belt 7 is nipped and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 in the secondary transfer portion T2. Secondary transfer onto a transfer material (sheet, recording material) P such as recording paper. During the secondary transfer process, the secondary transfer roller 8 receives a secondary transfer voltage (secondary transfer bias) which is a DC voltage having a polarity opposite to the normal charging polarity of the toner from the secondary transfer power supply (high voltage power supply circuit) E4. ) Is applied.

  The transfer material P is fed one by one by a feeding device (not shown) and conveyed to the registration roller pair 9, and the registration roller pair 9 matches the timing of the toner image on the intermediate transfer belt 7 and the secondary transfer unit. To T2. The transfer material P onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit, and is heated and pressed by the fixing device 10 to fix (melt and fix) the toner image. Thereafter, the transfer material P is discharged (output) to the outside of the apparatus main body 110 of the image forming apparatus 100.

  On the other hand, the toner (primary transfer residual toner) remaining on the photosensitive drum 1 during the primary transfer is removed from the photosensitive drum 1 and collected by the drum cleaning device 6 as a photosensitive member cleaning means. The drum cleaning device 6 includes a cleaning blade 6a as a cleaning member and a cleaning container 6b. The drum cleaning device 6 rubs the surface of the rotating photosensitive drum 1 with a cleaning blade 6 a disposed in contact with the photosensitive drum 1. Thus, the primary transfer residual toner on the photosensitive drum 1 is scraped off from the photosensitive drum 1 and stored in the cleaning container 6b. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a belt cleaning device 74 as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 71. The toner remaining on the intermediate transfer belt 7 during the secondary transfer process (secondary transfer residual toner) is removed from the intermediate transfer belt 7 by the belt cleaning device 74 and collected.

  In this embodiment, in each image forming unit S, the photosensitive drum 1, the charging roller 2, and the drum cleaning device 6 constitute a cartridge (drum cartridge) 11 that is detachably attached to the apparatus main body 110. ing.

2. Summary of Problem and Solution Next, the conventional problem will be further described.

  As described above, in order to suppress the adhesion of dirt to the charging member, it is effective to reduce the contact area between the photosensitive member and the charging member by increasing the surface roughness of the charging member. Generally, the charging member includes a metal core, a base layer formed of an elastic body whose electrical resistance is adjusted by a conductive agent on the outer periphery of the core, a conductive agent and a resin component on the surface of the base layer. And a surface layer formed by coating and drying a liquid dissolved in a solvent. As a method for controlling the surface roughness of the surface layer, there are a method of dispersing micron-sized particles ("surface layer particles"), a method of forming irregularities by polishing, and the like. As described above, Patent Document 1 discloses that surface layer particles are dispersed in the surface layer of a charging member. However, as described above, in the configuration of Patent Document 1, it has been found that although image defects such as black spots are suppressed, development fogging may occur.

  As a result of investigations by the present inventors, it has been found that there are a plurality of causes of image defects such as black spots. One of the causes is the shape of the surface layer of the charging member. In other words, if the gap length between the surface layer and the photoconductor is greatly different from the others, the discharge start voltage is locally different even when the same voltage is applied, so a difference occurs in the surface potential of the photoconductor, This may affect the electrostatic image as an image defect. It has been found that such image defects can be improved by suppressing agglomerates of surface layer particles and uneven drying of the surface layer according to Patent Document 1. One of the other causes lies in the surface layer particles themselves. The surface layer particles dispersed in the surface layer of the charging member are typically elastic particles formed of an elastic body that is not easily worn by friction between the charging member and the photosensitive member. As the material of the surface layer particles, styrene acrylic resin, urethane acrylic resin, urethane resin, nylon resin, and composite materials thereof can be used. Since these resins have high electrical resistance (typically insulating), it is difficult for current to flow through the surface layer particles themselves, and Paschen discharge is generated mainly in the conductive portion of the surface layer without the surface layer particles. That is, the larger the surface layer particles, the more microscopically less potential potential exists on the surface of the photoreceptor. According to the study by the present inventors, it was found that development fogging occurs when the surface layer particles are enlarged, and image defects such as black spots occur when the surface layer particles are further enlarged. .

  According to the study by the present inventor, it was found that when the particle diameter (diameter) of the surface layer particles is 50 μm or more, it is easily observed as an image defect such as a black spot. Further, it was found that when the particle diameter of the surface layer particles is around 25 μm, it is difficult to observe as an image defect and it is easy to observe as development fog. Further, it was found that when the particle diameter of the surface layer particles is 15 μm or less, it is difficult to observe as development fog. This is considered to be related to the fact that the visibility limit of dots is about 20 to 40 μm because the resolution of the human eye is generally in the range of 600 to 1200 dpi. That is, a dot of 50 μm or more may be recognized as an image defect, but cannot be recognized as a dot in the vicinity of 20 to 40 μm, but is recognized as a development fog since it can be detected as a density. Even smaller dots are less likely to cause toner dots themselves to be fogged because the potential change is small. Thus, when the surface layer particles are too large, black spots and development fog are likely to occur.

  On the other hand, according to the study by the present inventors, if the surface layer particles are too small, it becomes difficult to uniformly disperse the surface layer particles, and the surface layer particles are agglomerated and the development fog and black spots tend to deteriorate. I found out that Further, it has been found that if the surface layer particles are too small, the effect of reducing the contact area between the photoreceptor and the charging member cannot be obtained, and dirt easily adheres to the charging member.

  That is, it is effective to disperse the surface layer particles in the surface layer of the charging member in order to suppress streaky image density unevenness (image streaks) due to adhesion of dirt to the charging member. On the other hand, black spots and development fog increase as the particle diameter of the surface layer particles increases. For this reason, it has been difficult to achieve both suppression of dirt adhesion to the charging member and suppression of black spots and development fog.

  Therefore, in this embodiment, the surface layer of the charging member is dispersed as two or more types of surface layer particles having different particle diameters, the first surface layer particle and the second surface layer particle, thereby causing contamination on the charging member. Both suppression of adhesion and suppression of black spots and development fog are achieved. In other words, the first surface layer particles (“large particles”) having a particle size less than the particle size (average particle size less than 20 μm) that makes the development fog conspicuous on the surface layer of the charging member are dispersed, thereby preventing the contamination of the charging member. Secure. In addition, the gap between the first surface layer particles is filled with second surface layer particles (“small particles”) having a particle size smaller than the particle size of the first surface layer particles, so that the releasability of the charging member against dirt is increased. Secure and maintain contamination resistance. Thereby, since the number of “large particles” can be reduced as compared with the case of using only “large particles” while suppressing the adhesion of dirt to the charging member, black spots and development fog can be suppressed. At this time, local image density unevenness such as black spots and development can be achieved by setting the particle diameter and mass per unit area of the first and second surface layer particles, and the projected area ratio of the surface layer particles within a predetermined range. It is possible to suppress the adhesion of dirt to the charging member while suppressing fogging. This will be described in detail later.

3. Next, the charging roller 2 in this embodiment will be described. FIG. 3A is a schematic cross-sectional view showing the layer configuration of the charging roller 2 in the present embodiment.

  The charging roller 2 includes a support (conductive support, cored bar) 2a, a base layer (conductive elastic layer) 2b formed on the outer periphery of the support 2a, and a surface layer (the outermost layer formed on the base layer 2b). Outer layer) 2c. The charging roller 2 is rotatably supported by bearing members at both ends in the rotational axis direction of the support 2a. Further, the charging roller 2 is such that the bearing members at both ends in the rotation axis direction of the support 2a are urged toward the rotation center of the photosensitive drum 1 by pressing springs as urging means, respectively. Are pressed against each other with a predetermined pressing force. The charging roller 2 is driven to rotate as the photosensitive drum 1 rotates.

  In this embodiment, the support 2a is a shaft made of metal (steel, surface industrial nickel plating) excellent in wear resistance and bending stress.

  The base layer 2b can be formed of rubber, thermoplastic elastomer, or the like conventionally used as a base layer of a charging member. Specifically, a rubber having a base rubber such as polyurethane, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, or epichlorohydrin rubber. The composition or thermoplastic elastomer is not particularly limited, and one or more thermoplastic elastomers selected from general-purpose styrene elastomers and olefin elastomers can be suitably used. Further, solid rubber or foamed rubber may be used according to the required elastic force.

Predetermined conductivity can be imparted to the base layer 2b by adding a conductive agent. The conductive agent is not particularly limited, and lauryltrimethylammonium, stearyltrimethylammonium, octadodecyltrimethylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, dechlorinated fatty acid / dimethylethylammonium perchlorate, chlorate, borofluoride. Cationic surfactants such as quaternary ammonium salts such as hydrohalides, ethosulphate salts, benzyl bromides, benzyl chlorides such as benzyl chloride, aliphatic sulfonates, higher alcohol sulfates , Higher alcohol ethylene oxide addition sulfate ester salt, higher alcohol phosphate ester salt, anionic surfactant such as higher alcohol ethylene oxide addition phosphate ester salt, zwitterionic surfactants such as various betaines Higher alcohol ethylene oxide, polyethylene glycol fatty acid esters, antistatic agents such as nonionic antistatic agents such as polyhydric alcohol fatty acid _{esters, LiCF 3 SO 3, NaClO 4} , LiAsF 6, LiBF 4, NaSCN, KSCN, such as NaCl Group 1 metal salts such as Li ⁺ , Na ⁺ and K ⁺ , electrolytes such as NH ₄ ⁺ salts, and Ca ²⁺ such as Ca (ClO ₄ ) _2, and periodic tables such as Ba ²⁺ . Examples of the group 2 metal salt and those having an antistatic agent having a group having an active hydrogen that reacts with an isocyanate such as at least one hydroxyl group, carboxyl group, or primary or secondary amine group. Furthermore, these and the like, complexes of polyhydric alcohols such as 1,4-butanediol, ethylene glycol, polyethylene glycol, propylene glycol and polyethylene glycol and derivatives thereof, or monools such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether Ionic conductive agents such as complexes with carbon, conductive carbons such as Ketjen Black EC and acetylene black, carbons for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT, and colors subjected to oxidation treatment (Ink) carbon, pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals and metal oxides, polyaniline, poly Pyrrole, a conductive polymer such as polyacetylene. In this case, the blending amount of these conductive agents is appropriately selected according to the type of the composition, and the volume resistivity of the base layer 2b is usually 10 ² to 10 ⁸ Ω · cm, more preferably 10 ³ to 10 ⁶ Ω · cm. It is adjusted to be cm.

  The surface layer 2c can be formed of a resin material suitable as a material for forming the surface of the charging member. Specific examples include polyester resins, acrylic resins, urethane resins, urethane acrylic resins, nylon resins, epoxy resins, polyvinyl acetal resins, vinylidene chloride resins, fluororesins, and silicone resins. Can also be used.

Conductivity can be imparted or adjusted to the surface layer 2c by adding a conductive agent. In this case, the conductive agent is not particularly limited, but conductive carbon such as ketjen black EC and acetylene black, rubber carbon such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT, Oxidized carbon for color (ink), pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals or metal oxides Can be used. Moreover, when using the said electrically conductive agent with an organic solvent, it is preferable to give surface treatments, such as a silane coupling process, to the surface of an electrically conductive agent in consideration of dispersibility. Moreover, the addition amount of the said electrically conductive agent can be suitably adjusted so that the desired electrical resistance may be obtained. When the electric resistance of the surface layer 2c is higher than the electric resistance of the base layer 2b, the charging of the photosensitive drum 1 is stabilized. The volume resistivity of the surface layer 2c is preferably 10 ³ to 10 ¹⁵ Ω · cm, and more preferably 10 ⁵ to 10 ¹⁴ Ω · cm.

FIG. 3B is a schematic enlarged cross-sectional view of the surface layer 2c. The material for forming the surface layer 2 c includes first surface layer particles (“large particles”) 21 and second surface layer particles (“small particles”) having a particle size smaller than the particle size of the first surface layer particles 21. 22 are distributed. The first and second surface layer particles 21 and 22 added (contained) in the conductive resin layer to be the surface layer 2c are organic particles that are insulating particles (10 ¹⁰ Ω · cm or more) other than the conductive agent. Particles or inorganic particles can be used. Examples of the organic particles include urethane resins, urethane acrylic resins, acrylic resins, acrylic / styrene copolymer resins, polyamide resins, silicone rubber particles, and epoxy resin particles. Among these, it is particularly preferable to use urethane resin, urethane acrylic resin, acrylic resin or acrylic / styrene copolymer resin because the rigidity of the material of the surface layer 2c does not change so much. Examples of inorganic particles include calcium carbonate, clay, talc, and silica.

  When inorganic particles are used in a solvent-based paint, it is preferable that a hydrophobic surface treatment is applied so as to be easily dispersed in the paint. Similarly, it is preferable to select organic particles having good compatibility with the resin material of the surface layer 2c because aggregation is less likely to occur.

  Among a plurality of types of surface layer particles having different particle diameters, the average particle diameter (average diameter) of the first surface layer particles (“large particles”) 21 having a relatively large particle diameter is D1, and the first particle having a relatively small particle diameter is D1. The average particle diameter of the surface layer particles 22 (“small particles”) is D2 (FIG. 3B). At this time, 9.8 μm ≦ D1 ≦ 15.8 μm, 2.8 μm ≦ D2 ≦ 5.2 μm, and 3.0 ≦ D1 / D2 ≦ 5.6. Thereby, it is possible to suppress image defects such as black spots and development fog due to the particle size of the surface layer particles (particularly “large particles”) being too large. At the same time, generation of aggregates of surface layer particles due to the particle size of the surface layer particles (particularly “small particles”) being too small can be suppressed, and dispersibility between the particles can be improved.

  The mass per unit area of the first surface layer particles 21 is M1, the mass per unit area of the second surface layer particles 22 is M2, and the mass ratio between the first surface layer particles 21 and the second surface layer particles is M1. / (M1 + M2). At this time, the range is 0.10 ≦ M1 / (M1 + M2) ≦ 0.32. Thereby, about 30 to 100 “small particles” can be arranged for one “large particle”. Therefore, relatively large dirt such as toner adhering to the charging roller 2 is prevented from being crushed and easily attached to the photosensitive drum 1 by “large particles”, while relatively small dirt such as external additives is added. Adhering to the charging roller 2 can be suppressed by “small particles”.

  Further, the surface roughness (ten-point average roughness Rz) of the surface layer 2c, which is achieved by blending the first and second surface layer particles 21 and 22 as described above, is 6 μm or more and 18.8 μm or less. It is preferable that This suppresses adhesion of dirt to the surface of the charging roller 2 due to the surface of the charging roller 2 being too smooth, and also suppresses image defects such as black spots and developing fog due to the surface shape of the charging roller 2. Can do.

  In order to achieve the surface roughness Rz of the charging roller 2 as described above by blending the first and second surface layer particles 21 and 22 as described above, the thickness d of the surface layer 2c (film) (Thickness) (FIG. 3B) is preferably 7 μm or more and 20 μm or less. The thickness of the surface layer 2c is an average value of the measurement results at a plurality of locations. As a result, it is possible to prevent the surface layer 2c of the charging roller 2 from being too thick and to prevent the surface layer particles from sufficiently protruding onto the surface of the charging roller 2, and to prevent the surface layer particles from being retained by the surface layer 2c being too thin. Can be suppressed.

  The mass of the total solid content of the surface layer 2c excluding the first and second surface layer particles 21 and 22 is M0, and the ratio of the total mass of the first and second surface layer particles 21 and 22 to the mass of the total solid content. (It shall be expressed as a percentage [%]) is the total mass ratio (M1 + M2) / M0. At this time, it is preferable that the range is 14.5% ≦ (M1 + M2) /M0≦38.9%. This suppresses that the desired surface roughness of the charging roller 2 cannot be achieved when the total blending amount is too small, and also causes black spots and development caused by aggregation of the surface layer particles because the total blending amount is too large. Image defects such as fogging can be suppressed.

  A method for forming the surface layer 2c is not particularly limited, but a method of forming a coating film by preparing a paint containing each component and applying the paint by a dipping method or a spray method is preferably used. In the case where the surface layer 2c has a plurality of layers, dipping and spraying may be repeated using the paint forming each layer.

  That is, in this embodiment, the method for producing a charging member includes a step of preparing a surface coating material by blending the first and second surface layer particles in a curable resin solution, and the surface layer coating on the base layer. A step of forming a coating film of the paint, and a step of curing the coating film to form the surface layer. In the step of preparing the coating material for the surface layer, the first condition satisfying 9.8 μm ≦ D1 ≦ 15.8 μm, 2.8 μm ≦ D2 ≦ 5.2 μm, and 3.0 ≦ D1 / D2 ≦ 5.6. The second surface layer particles are blended so as to satisfy 0.10 ≦ M1 / (M1 + M2) ≦ 0.32, thereby preparing a surface layer coating material.

4). Next, an example of a specific method for manufacturing the charging roller 2 will be described. In the following description, “part” means part by mass. Here, an example of a method for manufacturing the charging roller 2 will be described using the prescription for the charging roller 2 of “Comparative Example a” described later. The charging roller 2 of examples other than “Comparative Example a” to be described later also differs from the prescription of the charging roller 2 of “Comparative Example a” in the outer diameter and the number of mass parts of the surface layer particles, but the manufacturing method itself is the same. .

<Preparation of base layer>
Epichlorohydrin rubber (trade name: Epichromer CG102, manufactured by Daiso Co., Ltd.), 100 parts of calcium carbonate as a filler, colored grade carbon as a reinforcing material for improving abrasiveness (trade name: SEAST SO, manufactured by Tokai Carbon Co., Ltd.) ) 2 parts, zinc oxide 5 parts, plasticizer DOP 10 parts, quaternary ammonium perchlorate salt represented by the following formula, 3 parts,

  1 part of an anti-aging agent (2-mercaptobenzimidazole) is kneaded with an open roll for 20 minutes, further 1 part of vulcanization accelerator DM, 0.5 part of vulcanization accelerator TS, and 1 part of sulfur as vulcanizing agent, and further 15 Kneading with an open roll for a minute. This was extruded into a cylindrical shape with a rubber extruder and then cut, and was first vulcanized with a vulcanizing can at 160 ° C. for 40 minutes to obtain a base layer primary vulcanizing tube.

  Next, a thermosetting adhesive (trade name: METALOC U) made of metal and rubber is attached to the center of the cylindrical surface of the cylindrical support (conductive support) 2a (steel, surface industrial nickel plating) in the axial direction. -20) was applied, dried at 80 ° C. for 30 minutes, and further dried at 120 ° C. for 1 hour. The support 2a was inserted into the base layer primary vulcanization tube, and then subjected to secondary vulcanization and adhesive curing by heating at 160 ° C. for 2 hours in an electric oven to obtain an unpolished product. After cutting both ends of this unpolished rubber part, the rubber part was polished with a rotating grindstone to obtain an intermediate product in which a base layer 2b having a ten-point average roughness Rz of 7 μm and a deflection of 25 μm was formed on the support 2a. .

<Preparation of surface layer>
50 parts of conductive tin oxide powder (trade name: SN-100P, manufactured by Ishihara Sangyo Co., Ltd.), 450 parts of 1% isopropyl alcohol solution of trifluoropropyltrimethoxysilane and glass beads having an average particle diameter of 0.8 mm Add 300 parts and disperse in a paint shaker for 48 hours, then filter the dispersion through a 500 mesh screen, then warm this solution in a 100 ° C. water bath while stirring with a Nauter mixer, blow off the alcohol and dry. A silane coupling agent was applied to the surface to obtain surface-treated conductive tin oxide.

  Furthermore, 145 parts of lactone-modified acrylic polyol (trade name: Plaxel DC2009 (hydroxyl value 90 KOHmg / g), manufactured by Daicel Chemical Industries, Ltd.) was dissolved in 455 parts of methyl isobutyl ketone (MIBK) to obtain a solid content of 24.17. A mass% solution was obtained. To 200 parts of this acrylic polyol solution, 50 parts of the above surface-treated conductive tin oxide powder, 0.01 parts of silicone oil (trade name: SH-28PA, manufactured by Toray Dow Corning Silicone Co., Ltd.), fine particle silica ( 1.2 parts of primary particle size 0.02 μm are blended and 4.5 parts of first surface layer particles (“large particles”) (trade name: Chemisnow MX-1000 (average particle size 10 μm), Soken Chemical Co., Ltd. Manufactured), 18 parts of second surface layer particles (“small particles”) (trade name: Chemisnow MX-500 (average particle size 5 μm), manufactured by Soken Chemicals), and glass beads having an average particle size of 0.8 mm 200 parts were added, put into a 450 ml mayonnaise bottle, and dispersed for 12 hours while cooling using a paint shaker.

  Further, 330 parts of this dispersion were mixed with 27 parts of an isophorone diisocyanate block type isocyanurate type trimer (IPDI) (trade name: Bestanat B1370, manufactured by Degussa Huls) and an isocyanurate type trimer of hexamethylene diisocyanate ( HDI) (trade name: Duranate TPA-B80E, manufactured by Asahi Kasei Kogyo Co., Ltd.) 17 parts are mixed, stirred with a ball mill for 1 hour, and finally the solution is filtered through a 200-mesh net. Was 43% by mass to obtain a coating material for the surface layer.

  The surface layer paint was applied to the surface of an intermediate product in which the base layer 2b was formed on the support 2a by dipping. Coating was performed at a lifting speed of 400 mm / min, air-dried for 30 minutes, the axis direction was reversed, coating was performed again at a lifting speed of 400 mm / min, air-dried for 30 minutes, and then dried in an oven at 160 ° C. for 1 hour, and then room temperature 25 It was left for 48 hours in an environment of 50 ° C. and a relative humidity of 50%.

5. Measurement Method and Test Method Next, a measurement method and an evaluation test method for the charging roller 2 will be described.

The average particle diameters D1 and D2 of the first and second surface layer particles 21 and 22 are center particle diameters, respectively, and can be measured by the following method. As a measuring device, a multisizer type II (manufactured by Coulter Co., Ltd.), a Coulter counter, was connected to an interface (manufactured by Nikka) and a CX-1 personal computer (manufactured by Canon) to output the number distribution and volume distribution. Prepare 1% NaCl aqueous solution using special grade or first grade sodium chloride. As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and measured with a 100 μm aperture as an aperture by the multisizer type II of the Coulter counter. The volume and number of particles to be measured are measured, and the volume distribution and number distribution are calculated. Then, 50% of the volume-based particle distribution D ₅₀ can be used as the central particle diameter as the average particle diameter. The average particle diameter ratio D1 / D2 is derived from the average particle diameters D1 and D2 of the first and second surface layer particles 21 and 22.

  Further, from the mass M1 per unit area of the first surface layer particles 21 and the mass M2 per unit area of the second surface layer particles 22, the first surface layer in the total mass of the first and second surface layer particles 21 and 21 is obtained. A mass ratio M1 / (M1 + M2), which is a mass ratio of the particles 21, is derived. Further, from the mass M0 of the total solid content of the surface layer 2c excluding the first and second surface layer particles 21 and 22, the ratio of the total mass of the first and second surface layer particles 21 and 22 to the total solid content [%. ], The total blend amount (M1 + M2) / M0 is derived.

  Further, the surface roughness (ten-point average roughness Rz) of the charging roller 2 was measured in accordance with JIS 1994 as follows. As a measuring device, a surface roughness meter SE-3300H manufactured by Kosaka Laboratory was used. The measurement conditions were a cutoff of 0.8 mm, a measurement distance of 8 mm, and a feed rate of 0.5 mm / sec. Then, the average value of the ten-point average roughness Rz [μm] at three places in the longitudinal direction and three places in the circumferential direction (in increments of 120 ° starting from an arbitrary place) of the charging roller 2 was obtained.

  Further, in order to confirm whether the surface layer particles are actually sufficiently projected (outcrop) on the surface of the charging roller 2, the projections by the first and second surface layer particles 21 and 22 per unit area of the surface of the charging roller 2. The particle projected area ratio was determined as an index indicating the proportion of the projected area occupied by. The protrusions formed by the first and second surface layer particles 21 and 22 may be such that the first and second surface layer particles 21 and 22 are coated with the resin material of the surface layer 2c, or the first and second surface layers. The particles 21 and 22 may be exposed. For convenience, the projected area ratio of the protrusions by the first surface layer particles 21 is “projected area ratio S1 of the first surface layer particles 21”, and the projected area ratio of the protrusions by the second surface layer particles 22 is “second surface layer particles”. Also referred to as a projected area ratio S2 of 22. " The projected area ratios S1 and S2 of the first and second surface layer particles 21 and 22 were measured as follows. Using a laser microscope (VK-8700, manufactured by KEYENCE), observe the surface of the charging roller 2 with a 50 × objective lens (observe substantially parallel to the normal direction of the surface of the charging roller 2), and digitally shoot Went. The obtained image was further enlarged with a digital zoom to obtain a field of view of 100 μm × 100 μm. The number and area of protrusions due to the first and second surface layer particles 21 and 22 in the field of view were determined. The projected area ratio, which is the ratio (expressed as a percentage [%]) of the area (projected area) of each protrusion of the first and second surface layer particles 21 and 22 to the entire area of the visual field, was calculated. In addition, the protrusion by the 1st, 2nd surface layer particle | grains 21 and 22 can be distinguished by the difference in the diameter of a protrusion. In addition, the area of the protrusions formed by the first and second surface layer particles 21 and 22 is determined as the area of a portion that clearly protrudes from a flat portion other than the protrusions in the obtained image. Then, the above measurement is performed at a total of nine points: three in the longitudinal direction of the charging roller 2 and three in the circumferential direction of each of the three points in the longitudinal direction (in increments of 120 ° starting from an arbitrary place). The average values of the projected area ratios S1 and S2 of the second surface layer particles 21 and 22 were obtained.

  Further, when it is necessary to directly measure the diameter of the particles existing on the surface layer 2c of the charging roller, the surface layer 2c of the charging roller is polished and the diameter of the particles existing in the region is measured. Specifically, it measured as follows.

  First, on the surface layer 2c of the charging roller 2 before polishing, the surface of the charging roller 2 is observed with a 50 × objective lens (on the surface of the charging roller 2) using a laser microscope (VK-8700, manufactured by KEYENCE). Observed approximately parallel to the normal direction) and performed digital photography. The obtained image was further magnified with a digital zoom, and the diameter of particles in a 100 μm × 100 μm field of view was measured. Here, the number of particles in the field of view of 100 μm × 100 μm varies depending on the prescription of the charging roller 2, but in most cases, it is in the range of a dozen to a hundred or less. However, if the number of particles that can fit in a 100 μm × 100 μm field of view exceeds 100, the measurement is difficult, so the field size is set to 50 μm × 50 μm, etc. so that the number of particles measured at one time is 100 or less. I made it. On the contrary, when the number of particles that can be accommodated in the field of view of 100 μm × 100 μm is less than 10, there is a possibility that the number of samples is insufficient for calculation of the particle diameter and the error becomes large. In other words, the field size was adjusted to 200 μm × 200 μm or the like so that the number of particles measured at one time was at least 40 or more.

  Next, using a fine sandpaper such as DACS # 1000 manufactured by Sankyo Rikagaku, observe the surface layer 2c of the charging roller 2, and make the surface layer 2c of the charging roller 2 as deep as possible so as to be as average as possible. Polished about 1 μm. Next, the diameter of particles on the surface layer 2c of the charged roller 2 after polishing at the same place as observed before polishing was measured by the same means. Thereafter, the operation of polishing the surface layer 2c of the charging roller 2 to a depth of about 1 μm and measuring the diameter of the particles was repeated until the thickness of the surface layer 2c disappeared. In this way, when the particle diameter is measured after the surface layer 2c of the charging roller 2 is polished, the measured diameter of the particle gradually increases, but as the particle is further polished, the particle becomes smaller. . Then, the value of the diameter of the particle on the charging roller 2 can be obtained by setting the largest value of the diameter of the particle at the same position during polishing as the true diameter of the particle. Moreover, as a method of calculating | requiring the mass M1 or M2 per unit area of the above-mentioned particle | grains, it calculates | requires from the diameter of the particle | grains calculated | required as mentioned above and the number of the particles in a predetermined area. That is, if the particle is assumed to be a true sphere, the volume of the particle can be obtained if the particle diameter is known. If the volume of the particles is known, the weight of each particle can be obtained by multiplying the specific gravity of the particle. Here, as a method of knowing the specific gravity of the particles, it can be known by taking out the particles from the surface layer 2c of the charging roller 2 and conducting elemental analysis by a method such as GS / CM. Thus, if the mass of each particle and the number of particles per predetermined area of the charging roller 2 are known, the mass of the particles in the solid content of the charging roller 2 can be obtained, and there are a plurality of types of particles. The mass ratio can be obtained.

  In this experiment, particles of at least 40 particles and at most 100 particles were measured at one place as described above, and further, three points in the longitudinal direction and three points in the circumferential direction of the charging roller 2 (120 ° starting from any place). Measure at a total of 9 points. Then, the number of particles is calculated between at least 360 and at most 900, and the distribution is taken. Thereby, it is determined whether the particle is a single type of particle or a plurality of types of particles are distributed, and further the values of the center diameters D1 and D2 of the particle and the masses M1 and M2 per unit area of the particle Got.

  Moreover, the evaluation test (endurance test and image evaluation test) of the charging roller 2 was performed as follows. In the test, the image forming apparatus 100 for A3 vertical output according to the present embodiment was used. The process speed (transfer material P output speed) is 250 mm / sec, and the image resolution is 600 dpi. The photosensitive drum 1 is of a reversal development type in which an aluminum cylinder is coated with an OPC layer having a thickness (film thickness) of 20 μm. The toner is obtained by externally adding a pulverized wax-containing toner base material having a volume average particle diameter of 6.5 μm mainly composed of polyester with silica or the like.

  In the durability test, the charging roller 2 to be tested is incorporated in the image forming apparatus 100, and 100,000 images in an image ratio of 5% are continuously obtained in an environment of low temperature and low humidity (L / L: 15 ° C./10% RH). It was done by outputting.

  In the image evaluation test, first, a halftone image is output in the initial state (before the durability test) to evaluate the degree of occurrence of black spots, and then the halftone image is output after the endurance test for 100,000 sheets. The degree of occurrence of streaky image density unevenness (image streaks) due to dirt was evaluated. Separately from these, the fog density on the photosensitive drum 1 was measured as an index of the amount of toner that developed fog (hereinafter also referred to as “fogging toner”) in the initial state and after the durability test. The fog density on the photosensitive drum 1 was measured as follows. First, during the image formation of a predetermined image (solid white or the like), the drive motor of the photosensitive drum 1 is forcibly stopped, and between the development position (development unit) and the primary transfer position (primary transfer unit) on the photosensitive drum 1. A polyester tape was applied to the non-image area at the position, and the toner at the position was collected. The polyester tape was peeled off from the photosensitive drum 1 and attached to white paper, and the reflection density of the polyester tape portion on the paper was measured using a white photometer TC-6DS / A manufactured by Tokyo Denshoku. Separately, the same polyester tape was stuck on a new white paper, and the reflection density of the polyester tape portion was measured with the same measuring device. Then, the density difference (%) between the two measured reflection densities was evaluated as the fog density on the photosensitive drum 1. The reason for evaluating the amount of fog toner by the fog density on the photosensitive drum 1 is as follows. The fog toner on the photosensitive drum 1 often does not have a regular charge, and there is a toner having a charge whose polarity is reversed or a toner whose charge is substantially zero. For this reason, when an attempt is made to evaluate the amount of fog toner on paper, the amount of fog toner may not be correctly evaluated when there is fog toner that is not transferred onto the paper.

  The black spots generated due to the surface shape defect of the charging roller 2 in the initial state were evaluated by visually observing the output halftone image. At this time, ◎ (very good) when black spots do not occur at all, ◯ (good) when it occurs but it is very slight and cannot be understood unless it is closely watched, and it is slight but at a glanceable level Δ (slightly defective), the case of a clearly conspicuous level was evaluated as x (defective). In addition, streaky image density unevenness (image streaks) due to contamination of the charging roller 2 after the durability test is likely to be shifted between the value measured as the density and the visual observation result. Evaluation was made by visual observation. At this time, ◎ (very good) when no image streak occurred, ○ (good) when it was generated but very slight and could not be understood without gazing, and it was slight but at a glanceable level Δ (slightly defective), the case of a clearly conspicuous level was evaluated as x (defective). Further, the fog density on the photosensitive drum 1 is ◎ (very good) when it is 0.5% or less, ◯ (good) when it is more than 0.5%, and ○ (good) when it is 1.0% or less. When it was 2% or less, it was evaluated as Δ (somewhat poor), and when it was larger than 2%, it was evaluated as × (defective).

6). Evaluation Results Table 1 shows the results of the prescription and the evaluation test of the charging roller 2 of “Example A” to “Example D” and “Comparative Example a” to “Comparative Example j”.

<Comparative Example a>
“Comparative example a” is a reproduction test of the charging roller 2 according to Patent Document 1. The average particle diameter D1 of the “large particles” is 19.2 μm, the average particle diameter D2 of the “small particles” is 5.2 μm, and the mass ratio M1 / (M1 + M2) of the “large particles” is 0.90. The total mass ratio (M1 + M2) / M0 is 14.4%, and the thickness of the surface layer 2c is 25 μm. In Comparative Example a, black spots did not occur in the initial state, and the roller stain after durability was evaluated as ◎, but the fog density evaluation in the initial state was Δ.

<Comparative Example b to Comparative Example d>
Next, in order to examine the effect of only “large particles”, the following three types of charging rollers 2 were evaluated. That is, only “large particles” are included as surface layer particles, “Comparative Example b” having an average particle diameter D1 of 19.2 μm, “Comparative Example c” having an average particle diameter D1 of 15.8 μm, and an average particle diameter D1 of 9 These are three types of charging rollers 2 of “Comparative Example d” of 8 μm. As a result, the evaluation of the black spot in the initial state was Δ for all of “Comparative Example b”, “Comparative Example c”, and “Comparative Example d”. When the surfaces of these charging rollers 2 were observed with an optical microscope, there were minute undulations and wrinkles on the surface, and there were portions where surface layer particles were aggregated in some places. This is considered to be caused by the deterioration of the evaluation of the black spot in the initial state. That is, it was reconfirmed that in order to maintain the dispersibility of the particles and prevent the formation of aggregates, at least a plurality of types of surface layer particles having different particle sizes are necessary.

  However, in “Comparative Example c” and “Comparative Example d” in which the average particle diameter D1 is smaller than “Comparative Example b”, the fog density is improved. It was found that it is possible to improve. On the other hand, the image lines after the durability test in “Comparative Example c” and “Comparative Example d” are worse than those in “Comparative Example a”, and the contamination of the charging roller 2 deteriorates when the particle size is reduced with a single particle. I found out that That is, it was found that the single particles cannot sufficiently suppress all of black spots, developing fog, and contamination of the charging roller 2.

<Comparative Example e>
Next, with respect to “Comparative Example a”, the amount of “large particles” is reduced to about ¼, the amount of “small particles” is increased about 10 times, and the mass ratio M1 / (M1 + M2) of “large particles” is increased. ) Was reduced to 0.20, and the charging roller 2 of “Comparative Example e” was evaluated. As a result, compared with “Comparative Example a”, there was a tendency that the fog density slightly improved.

<Comparative Example f>
Next, with respect to “Comparative Example e”, the charging roller 2 of “Comparative Example f” in which the average particle diameter D1 of “large particles” was lowered from 19.2 μm to 15.8 μm was evaluated. As a result, the fog density was further improved from Δ to ○ in “Comparative Example e”. However, since the average particle diameter D1 of the “large particles” is lowered to 15.8 μm while the thickness of the surface layer 2c is 25 μm, the surface roughness Rz is lowered to 4.2 μm, and the image streak is from It got worse until.

<Example A>
Next, the charging roller 2 of “Example A” was evaluated. In “Example A”, the average particle diameter D1 of “large particles” is 15.8 μm, and the average particle diameter D2 of “small particles” is 5.2 μm. In addition, “Example A” is lower than “Comparative Example f” by reducing M1 / (M1 + M2), which is a mass ratio of “large particles”, to 0.10, and further reducing the thickness of the surface layer 2c to 20 μm. The thickness Rz was increased to 6.0 μm. As a result, black spots do not occur in the initial state, the evaluation is ◎, the fog density in the initial state is also 0.5% or less, and the evaluation is ◎. The evaluation of the fog density after the durability test is ○, after the durability test The image streak was also slight and the evaluation was good.

  From the results so far, it has been found that the average particle diameter of the surface layer particles needs to be at least 15.8 μm or less in order to improve black spots and development fog. Further, it was found that the surface roughness Rz is preferably 6.0 μm or more in order to improve the contamination of the charging roller 2 while improving black spots and development fog. Further, it was found that it is preferable to set M1 / (M1 + M2), which is the mass ratio of “large particles”, to a lower value rather than the range of 0.70 to 0.90.

<Example B>
Next, with respect to “Example A”, the thickness of the surface layer 2c is reduced to 15 μm, and the mass ratio M1 / (M1 + M2) of the “large particles” is increased to 0.32, so that the surface roughness Rz is 18. The charging roller 2 of “Example B” raised to 8 μm was evaluated. As a result, all evaluations of black spots, fog density, and image streaks were evaluated as ◎.

<Comparative Example g>
Next, with respect to “Example B”, the charging of “Comparative Example g” in which the mass ratio M1 / (M1 + M2) of “large particles” was further increased to 0.35 and the surface roughness Rz was increased to 19.2 μm. Evaluation of roller 2 was performed. As a result, both black spots and fog density in the initial state were Δ. When the surface of the charging roller 2 was observed with an optical microscope, aggregates of “large particles” and “small particles” appeared. From this, it is considered that the amount of the surface layer particles is excessively increased, the dispersibility is deteriorated, and black spots and development fog are generated.

<Comparative Example h>
Next, with respect to “Example B”, the charging roller 2 of “Comparative Example h” in which the mass ratio M1 / (M1 + M2) of “large particles” was reduced to 0.08 was evaluated. As a result, the image stripe has deteriorated. Although the surface roughness Rz of the charging roller 2 of “Comparative Example h” is 6.0 μm or more, the image streak is deteriorated. The reason for this is that the contact area between the photosensitive drum 1 and the charging roller 2 increases because the number of “large particles” is excessively reduced, and the “large particles” are scraped off due to durability. This is thought to be due to the fact that the toner easily adheres to the charging roller 2.

  From the results so far, in order to improve black spots and development fog and improve roller dirt (image streaks), the mass ratio M1 / (M1 + M2) of “large particles” is 0.10 or more, and A range of 0.32 or less is preferred. The surface roughness Rz is preferably in the range of 6.0 μm or more and 18.8 μm or less. However, even if the surface roughness Rz is within this range, in the case of a single particle, the roller dirt may be poor, so at least two types of surface layer particles having different center diameters are required.

  Next, in order to examine the lower limits of the average particle diameters D1 and D2 of “large particles” and “small particles”, the following “Comparative Example i”, “Example C”, “Comparative Example j”, “Example D” The four types of charging rollers 2 were evaluated.

<Comparative Example i>
First, the charging roller 2 of “Comparative Example i” was evaluated. In “Comparative Example i”, the average particle diameter D1 of “large particles” is 9.8 μm while maintaining the mass ratio M1 / (M1 + M2) of “large particles” between 0.10 and 0.32. The average particle diameter D2 of “small particles” was set to 5.2 μm. That is, D1 / D2, which is the ratio of the diameters of “large particles” and “small particles”, was 1.9. In “Comparative Example i”, the thickness of the surface layer 2c was 10 μm, and the surface roughness Rz was 10.6 μm. As a result, the ranks of black spots and development fog were Δ. This is because, when the average particle diameter D2 of the “small particles” is too close to the average particle diameter D1 of the “large particles”, the effect of improving the dispersibility between the particles by using plural kinds of surface layer particles having different particle diameters. This seems to be due to the decline.

<Example C>
Next, the charging roller 2 of “Example C” was evaluated. In “Example C”, the average particle diameter D1 of “large particles” is 9.8 μm while maintaining the mass ratio M1 / (M1 + M2) of “large particles” between 0.10 and 0.32. The average particle diameter D2 of the “small particles” was 2.8 μm. That is, D1 / D2, which is the ratio of the diameters of “large particles” and “small particles”, was set to 3.5. Furthermore, in “Example C”, the surface roughness Rz was set to 8.1 μm by reducing the film thickness of the surface layer 2c to 7 μm. As a result, even though the surface layer particles were small, all of black spots, development fog, and roller stains gave a result of 0 or more.

<Comparative Example j>
Next, the charging roller 2 of “Comparative Example j” was evaluated. In “Comparative Example j”, the average particle diameter D1 of “large particles” is 4.9 μm while maintaining the mass ratio M1 / (M1 + M2) of “large particles” between 0.10 and 0.32. The average particle diameter D2 of “small particles” was 1.8 μm. That is, D1 / D2, which is the ratio of the diameters of “large particles” and “small particles”, was 2.7. In “Comparative Example j”, the surface roughness Rz was set to 5.2 μm. As a result, the evaluation of the black spot in the initial state and the image streak after the durability test was x. In the state where the average particle diameter D2 of “small particles” is 1.8 μm, even if the amount of “small particles” is increased, the surface roughness Rz does not exceed 6.0 μm, and agglomerates are generated and black spots are generated. The result was worse.

<Example D>
Next, the charging roller 2 of “Example D” was evaluated. In “Example D”, the average particle diameter D1 of “large particles” is 15.8 μm while maintaining the mass ratio M1 / (M1 + M2) of “large particles” between 0.10 and 0.32. The average particle diameter D2 of the “small particles” was 2.8 μm. That is, D1 / D2, which is the ratio of the diameters of “large particles” and “small particles”, was 5.6. Furthermore, in “Example D”, the film thickness of the surface layer 2 c was 11 μm, and the surface roughness Rz was 14.2 μm. As a result, a result of ◯ or more was obtained in all of black spots, development fog, and roller stains.

  From the results so far, the average particle diameter D1 of the “large particles” is preferably 9.8 μm or more and 15.8 μm or less. In addition, the average particle diameter D2 of the “small particles” is preferably in a range of 2.8 μm or more and 5.2 μm or less. If the average particle diameter D2 of the “small particles” is too close to the average particle diameter D1 of the “large particles”, the effect of using a plurality of types of surface layer particles having different particle diameters cannot be obtained sufficiently. For this reason, the ratio D1 / D2 of the diameters of “large particles” and “small particles” is preferably 3.0 or more and 5.6 or less.

  Further, regarding the mass ratio M1 of the “large particles” and the mass ratio M2 of the “small particles”, the mass ratio M1 / (M1 + M2) of the “large particles” is preferably 0.10 or more and 0.32 or less. .

  Further, the film thickness of the surface layer 2c is preferably in the range of 7.0 μm or more and 20 μm or less.

  In addition, the “large particle” projected area ratio S1 and the “small particle” projected area ratio S2 on the charging roller 2 of “Example A” to “Example D” and “Comparative Example a” to “Comparative Example j” Correlation with black potty and fog density was investigated. As a result, it was found that the projected area ratio S1 of “large particles” is preferably 1.0% or more and 3.9% or less. Further, it was found that the projected area ratio S2 of “small particles” is preferably 13.5% or more and 25.5% or less. That is, it is preferable to set the ranges of 1.0% ≦ S1 ≦ 3.9% and 13.5% ≦ S2 ≦ 25.5%.

  As described above, in this embodiment, in the configuration employing the DC charging method, the particle size and the mass per unit area of the two types of surface layer particles 21 and 22 having different particle sizes dispersed in the surface layer 2c of the charging roller 2 are used. The surface property of the charging roller 2 is controlled by setting the ratio within a predetermined range. As a result, it is possible to improve the charging uniformity and suppress the adhesion of dirt to the charging roller 2, thereby suppressing the occurrence of image defects. That is, according to this embodiment, in the configuration employing the DC charging method, it is possible to suppress the adhesion of dirt to the charging member while suppressing local image density unevenness such as black spots and development fog.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus according to the present exemplary embodiment are the same as those of the image forming apparatus according to the first exemplary embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In recent years, in order to extend the life of the photosensitive drum 1, the surface layer of the photosensitive drum 1 (the layer located on the outermost surface of the photosensitive drum 1 (outermost layer)) has been reduced in wear. For example, a protective layer formed using a curable resin as a binder resin may be provided as a surface layer of the photosensitive drum 1 (Japanese Patent No. 394472).

  FIG. 4 is a schematic cross-sectional view showing the layer structure of the photosensitive drum 1 of this embodiment. In this embodiment, the photosensitive drum 1 is a negatively charged drum-shaped organic photoreceptor (OPC) using an organic material as a photoconductive substance (a charge generating substance or a charge transporting substance) as in the first embodiment. is there. The photosensitive drum 1 has a laminated structure in which a charge generation layer 1b, a charge transport layer 1c, and a protective layer 1d are provided in this order on a base (conductive base) 1a. Further, an intermediate layer (undercoat layer) having a barrier function or an adhesive function, and a conductive layer for preventing interference fringes may be provided between the base 1a and the charge generation layer 1b. In this embodiment, the protective layer 1d is formed using a curable phenol resin as a binder resin. Note that the binder resin of the surface layer of the photosensitive drum 1 is not limited to that of the present embodiment, and any available curable resin can be used. For example, a technique is known in which a surface of the photosensitive drum 1 is a cured film obtained by curing a monomer having a carbon-carbon double bond using heat or light energy. In this embodiment, the surface layer of the photosensitive drum 1 is a protective layer, but the protective layer may contain conductive particles. In addition to the function as a protective layer, the surface layer of the photosensitive drum 1 is substantially a single layer including a charge transport layer containing a charge transport material (even if it is a charge transport layer different from the lower charge transport layer). It may be a single charge transport layer).

  In this embodiment, the elastic deformation power of the surface of the photosensitive drum 1 is 47% or more (especially 48% in this embodiment). As a result, the abrasion of the surface of the photosensitive drum 1 due to the friction between the surface of the photosensitive drum 1 and the cleaning blade 6a is suppressed, and the life of the photosensitive drum 1 is extended.

  The elastic deformation power of the surface of the photosensitive drum 1 is a value measured using a microhardness measuring apparatus Fischerscope H100V (Fischer) in an environment of 25 ° C./50% RH (relative humidity). This Fischer scope H100V has a continuous hardness by making an indenter contact the object to be measured (the surface of the photosensitive drum 1), continuously applying a load to the indenter, and directly reading the indentation depth under the load. It is a device that can be obtained. As the indenter, a Vickers square pyramid diamond indenter with a facing angle of 136 ° is used. The final load applied to the indenter (final load) is 6 mN, and the time for holding the final load of 6 mN on the indenter (holding time) Was 0.1 seconds. The measurement points were 273 points.

  FIG. 5 is a graph for explaining a method for measuring the elastic deformation power of the surface of the photosensitive drum 1. In FIG. 5, the vertical axis represents the load F (mN) applied to the indenter, and the horizontal axis represents the indentation depth h (μm). FIG. 5 shows the results when the load applied to the indenter is increased stepwise to finally maximize the load (here 6 mN) (A → B), and then the load is decreased stepwise (B → C). Is shown. The elastic deformation power is determined by the amount of work (energy) performed by the indenter on the measurement target (the surface of the photosensitive drum 1), that is, the change in energy due to the increase or decrease of the load on the measurement target (the surface of the photosensitive drum 1). Can be sought. Specifically, a value (We / Wt) obtained by dividing the elastic deformation work We by the total work Wt is the elastic deformation power (represented as a percentage [%]). Note that the total work amount Wt is the area of the region surrounded by A-B-D-A in FIG. 5, and the elastic deformation work amount We is the area of the region surrounded by C-B-D-C in FIG. It is.

  If the elastic deformation power of the surface of the photosensitive drum 1 is too small, the elastic force of the surface of the photosensitive drum 1 is insufficient, and the photosensitive drum 1 at the contact portion between the photosensitive drum 1 and the contact member such as the cleaning blade 6a. Wear on the surface of the steel tends to occur. By setting the elastic deformation power of the surface of the photosensitive drum 1 to 47% or more, wear of the surface of the photosensitive drum 1 is remarkably suppressed as compared with the case where the elastic deformation power is less than 47%, and the length of the photosensitive drum 1 is increased. It is known that the life can be extended. On the other hand, if the elastic deformation power of the surface of the photosensitive drum 1 is too large, the amount of plastic deformation of the surface of the photosensitive drum 1 also increases, and the photosensitive drum is in contact with the contact member such as the photosensitive drum 1 and the cleaning blade 6a. Fine scratches are likely to occur on the surface of 1. For this reason, it has been found that the elastic deformation power of the surface of the photosensitive drum 1 is preferably 60% or less. The elastic deformation power of the surface of the photosensitive drum 1 can be adjusted by a combination of materials and manufacturing conditions.

  As described above, in this embodiment, the surface layer of the photosensitive drum 1 is reduced in wear so that the life of the photosensitive drum 1 is extended. However, in such a configuration, the surface of the photosensitive drum 1 tends to be depressed due to, for example, rubbing against the developer carrier, and holes are likely to be formed. For this reason, in such a configuration, due to the gap between the cleaning blade 6a and the hole, toner and external additives are likely to slip through the cleaning blade 6a, and the charging roller 2 is likely to be contaminated.

  As another problem, when the surface layer of the photosensitive drum 1 is reduced in wear, there is a tendency that slip between the charging roller 2 and the photosensitive drum 1 is likely to occur. When this slip occurs, the charging roller 2 does not follow the rotation of the photosensitive drum 1 properly, so that the charging uniformity of the photosensitive drum 1 is reduced or the wear of the surface of the photosensitive drum 1 is promoted. The slip tends to occur more easily as the surface roughness of the charging roller 2 is larger and the contact ratio between the charging roller 2 and the photosensitive drum 1 is decreased.

  On the other hand, in the present embodiment, as in the first embodiment, the particle size and mass ratio of the two types of surface layer particles 21 and 22 having different particle sizes dispersed in the surface layer 2c of the charging roller 2 are set within a predetermined range. Thus, the surface property of the charging roller 2 is controlled. As a result, it was found that even in the configuration in which the surface layer of the photosensitive drum 1 is reduced in wear, the charging uniformity can be improved and the adhesion of dirt to the charging roller 2 can be suppressed. Further, since the number of “large particles” can be reduced as compared with the case where only “large particles” are used, the surface roughness of the charging roller 2 is suppressed from being increased more than necessary. It has been found that the effect of reducing slip with the drum 1 can also be obtained.

[Example 3]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus according to the present exemplary embodiment are the same as those of the image forming apparatus according to the first exemplary embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  When the surface layer of the photosensitive drum 1 is reduced in wear, the frictional force between the photosensitive drum 1 and the cleaning blade 6a increases, and chattering (abnormal vibration) and bending (free end of the cleaning blade 6a in the rotation direction of the photosensitive drum). A phenomenon of dripping), and further, chipping and wear are likely to occur. Therefore, a plurality of independent recesses may be formed on the surface of the photosensitive drum 1 in order to control the frictional force between the photosensitive drum 1 and the cleaning blade 6a to suppress the above problems (Japanese Patent No. 4101278). Publication).

  In the present embodiment, a plurality of independent recesses as described above are formed on the surface of the photosensitive drum 1 (more specifically, the surface of the protective layer 1d similar to that of the second embodiment). FIG. 6 is a schematic view of a part of the surface of the photosensitive drum 1 of this embodiment as viewed from the normal direction of the surface of the photosensitive drum 1. In the drawing, a circular portion (the shape of a cross section substantially parallel to the circumferential direction of the photosensitive drum 1 is a downward dome shape) is a specific concave portion described later, and the other portion is a flat portion described later.

  Typically, this concave portion satisfies a predetermined condition in the region when a 500 μm square region with one side parallel to the rotation direction of the photosensitive drum 1 is arranged at an arbitrary position on the surface of the photosensitive drum 1. It is provided so that the area ratio of the specific recess becomes a predetermined value.

  Here, the definition of the specific concave portion and the flat portion in a square region having a side of 500 μm will be described. The specific concave portion or flat portion on the surface of the photosensitive drum 1 can be observed using a microscope such as a laser microscope, an optical microscope, an electron microscope, or an atomic force microscope. First, the surface of the photosensitive drum 1 is enlarged and observed with a microscope or the like. When the surface of the photosensitive drum 1 is a curved surface curved along the rotation direction, a cross-sectional profile of the curved surface is extracted and the curve is fitted. The cross-sectional profile is corrected so that the curve becomes a straight line, and a surface obtained by extending the obtained straight line in the longitudinal direction of the photosensitive drum 1 is used as a reference surface. A region where the height difference from the obtained reference plane is within a predetermined range (for example, within ± 0.2 μm) is defined as a flat portion in the square region having a side of 500 μm. A part located below the flat part is defined as a concave part. Regarding the depth and the longest diameter of the opening, the maximum distance from the flat portion to the bottom surface of the recess is the depth of the recess, and the cross section of the recess by the flat portion is the opening of the recess. The length of the longest line segment is the longest diameter of the opening of the recess.

  The concave portion on the surface of the photosensitive drum 1 can be formed by a method (imprint) in which a mold having a predetermined shape is pressed against the surface of the photosensitive drum 1 and shape transfer is performed. For example, it can be formed by continuously pressing and pressing the mold on the surface (circumferential surface) of the photosensitive drum 1 while rotating the photosensitive drum 1 by a press-fitting shape transfer processing apparatus having a mold. In addition, a method of forming a concave portion having a predetermined shape on the surface of the photosensitive drum 1 by laser irradiation is also known.

  The plurality of specific recesses provided on the peripheral surface of the photosensitive drum 1 may all have the same shape, the longest diameter of the opening, and the depth, or may have different shapes, the longest diameter of the opening, and the depth. It may be mixed. Further, the shape of the specific recess (both the surface shape viewed from the normal direction of the surface of the photosensitive drum 1 and the cross-sectional shape substantially parallel to the circumferential direction of the photosensitive drum 1) is limited to that of this embodiment. Instead, it may have any shape as required. Examples of the shape include a circle, an ellipse, or a polygon such as a square, a rectangle, a triangle, a quadrangle, a pentagon, and a hexagon. Moreover, the specific recessed part may be arrange | positioned and may be arrange | positioned at random.

  In this embodiment, a recess is formed on the surface of the photosensitive drum 1 by imprinting. In this embodiment, the specific recess is a circle having a longest opening diameter (diameter) of 30 μm when viewed from the normal direction of the surface of the photosensitive drum 1, and the depth of the specific recess is 0.7 μm. The rate is 56%. The area ratio of the specific recesses is expressed as a ratio (percentage [%]) of the total opening area of the specific recesses to the sum of the total opening area of the specific recesses and the total area of the parts other than the specific recesses in the predetermined region. It shall be.)

  As described above, in the present embodiment, a plurality of independent recesses are formed on the surface of the photosensitive drum 1, and chattering, turning, chipping, and wear of the cleaning blade 6a are suppressed, and the life of the cleaning blade 6a is extended. It is illustrated. However, in such a configuration, due to the gap between the cleaning blade 6a and the concave portion on the surface of the photosensitive drum 1, the toner and the external additive are likely to pass through the cleaning blade 6a, and the charging roller 2 is easily contaminated. Tend to be. Further, the contact ratio between the charging roller 2 and the photosensitive drum 1 decreases due to the concave portion on the surface of the photosensitive drum 1, and the slip between the charging roller 2 and the photosensitive drum 1 tends to occur easily.

  On the other hand, in the present embodiment, as in the first embodiment, the particle size and mass ratio of the two types of surface layer particles 21 and 22 having different particle sizes dispersed in the surface layer 2c of the charging roller 2 are set within a predetermined range. Thus, the surface property of the charging roller 2 is controlled. As a result, it was found that even in a configuration in which a plurality of independent recesses are formed on the surface of the photosensitive drum 1, the charging uniformity can be improved and the adhesion of dirt to the charging roller 2 can be suppressed. Further, since the number of “large particles” can be reduced as compared with the case where only “large particles” are used, the surface roughness of the charging roller 2 is suppressed from being increased more than necessary. It has been found that the effect of reducing slip with the drum 1 can also be obtained.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  Although the charging system of the image forming apparatus of the above-described embodiment is the DC charging system, the present invention can also be applied to an AC charging system image forming apparatus.

  In the above-described embodiment, two types of surface layer particles are dispersed on the surface layer of the charging roller. However, three or more types of surface layer particles may be dispersed as long as the surface property of the charging roller described above is satisfied. For example, the surface layer of the charging roller 2 may include third surface layer particles having an average particle diameter smaller than that of the second surface layer particles in the above-described embodiment.

  In the above-described embodiments, the image forming apparatus is a color image forming apparatus having a plurality of image forming units, but the present invention can also be applied to a monochrome image forming apparatus having only one image forming unit.

  The charging member is not limited to a roller-like member, and may be an endless belt or a blade-like member that is stretched around a plurality of stretch rollers. Further, the image carrier is not limited to a drum-shaped photoreceptor (photosensitive drum), but may be an endless belt-shaped photoreceptor (photosensitive belt). In the case of an electrostatic recording type image forming apparatus, the image carrier may be a drum-like or endless belt-like electrostatic recording dielectric.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 2c Surface layer 3 Exposure apparatus 4 Developing apparatus 21 1st surface layer particle (large particle)
22 Second surface layer particles (small particles)

Claims (16)

An image carrier, a charging member that contacts the image carrier and charges the image carrier, a power source that applies a voltage to the charging member, and a developer that is supplied to the image carrier to form a toner image Developing means, and the charging member includes a base layer and a surface layer formed on the base layer, wherein first and second surface layer particles having different particle diameters are dispersed in the surface layer. In the image forming apparatus
The charging member has a surface roughness (ten-point average roughness Rz) of 6 μm or more and 18.8 μm or less, and the thickness of the surface layer is 7 μm or more and 20 μm or less,
When the average particle diameter of the first surface layer particles is D1 and the average particle diameter of the second surface layer particles is D2, 9.8 μm ≦ D1 ≦ 15.8 μm and 2.8 μm ≦ D2 ≦ 5.2 μm And 3 ≦ D1 / D2 ≦ 5.6 is satisfied,
When the mass of the first surface layer particles per unit area of the surface of the charging member is M1, and the mass of the second particles is M2, 0.10 ≦ M1 / (M1 + M2) ≦ 0.32 is satisfied. An image forming apparatus.   When the projected area ratio of protrusions by the first surface layer particles per unit area of the surface of the charging member is S1, and the projected area ratio of protrusions by the second surface layer particles is S2, 1.0% ≦ S1 2. The image forming apparatus according to claim 1, wherein ≦ 3.9% and 13.5% ≦ S2 ≦ 25.5% are satisfied.   The image forming apparatus according to claim 1, wherein the first and second surface layer particles are particles formed of urethane, urethane acrylic, acrylic, or acrylic / styrene copolymer.   The image forming apparatus according to claim 1, wherein the image bearing member is a photoconductor, and an elastic deformation power of a surface of the photoconductor is 47% or more.   The image forming apparatus according to claim 1, wherein the image bearing member is a photoconductor, and a plurality of independent recesses are formed on a surface of the photoconductor.   The image forming apparatus according to claim 1, wherein only a direct current voltage is applied to the charging member when the image carrier is charged. A base layer and a surface layer formed on the base layer, wherein first and second surface layer particles having different particle sizes are dispersed in the surface layer, and a surface roughness (ten-point average roughness Rz) is 6 μm or more. And 18.8 μm or less, and the thickness of the surface layer is 7 μm or more and 20 μm or less, and is a charging member used for charging the image carrier by contacting the image carrier and applying a voltage.
When the average particle diameter of the first surface layer particles is D1 and the average particle diameter of the second surface layer particles is D2, 9.8 μm ≦ D1 ≦ 15.8 μm and 2.8 μm ≦ D2 ≦ 5.2 μm And 3 ≦ D1 / D2 ≦ 5.6 is satisfied,
When the mass of the first surface layer particles per unit area of the surface of the charging member is M1, and the mass of the second particles is M2, 0.10 ≦ M1 / (M1 + M2) ≦ 0.32 is satisfied. A charging member.   When the projected area ratio of protrusions by the first surface layer particles per unit area of the surface of the charging member is S1, and the projected area ratio of protrusions by the second surface layer particles is S2, 1.0% ≦ S1 The charging member according to claim 7, wherein ≦ 3.9% and 13.5% ≦ S2 ≦ 25.5% are satisfied.   The charging member according to claim 7 or 8, wherein the first and second surface layer particles are particles formed of urethane, urethane acrylic, acrylic, or acrylic / styrene copolymer.   10. The charging member according to claim 7, wherein only a DC voltage is applied when the image carrier is charged. 11.   A cartridge which is detachable from an apparatus main body of an image forming apparatus and has the charging member according to any one of claims 7 to 10.   The cartridge according to claim 11, further comprising a photoconductor as the image carrier to be charged by the charging member. A base layer and a surface layer formed on the base layer, wherein first and second surface layer particles having different particle sizes are dispersed in the surface layer, and a surface roughness (ten-point average roughness Rz) is 6 μm or more. And 18.8 μm or less, the thickness of the surface layer is 7 μm or more and 20 μm or less, and a method of manufacturing a charging member used for charging the image carrier by applying a voltage to the image carrier and applying a voltage. There,
In the curable resin solution, a step of preparing the surface layer paint by blending the first and second surface layer particles;
Forming a coating film of the surface layer paint on the base layer;
Curing the coating film to form the surface layer;
Have
In the step of preparing the surface layer coating material, when the average particle diameter of the first surface layer particles is D1 and the average particle diameter of the second surface layer particles is D2, 9.8 μm ≦ D1 ≦ 15.8 μm, and 2.8 μm ≦ D2 ≦ 5.2 μm and the first and second surface layer particles satisfying 3 ≦ D1 / D2 ≦ 5.6, and the mass per unit area of the first surface layer particles is M1, When the mass per unit area of the second surface layer particles is M2, the surface layer coating material is prepared by blending so as to satisfy 0.10 ≦ M1 / (M1 + M2) ≦ 0.32. Manufacturing method of charging member.   In the charging member, when the projected area ratio of the projections by the first surface layer particles per unit area of the surface of the charging member is S1, and the projected area ratio of the projections by the second surface layer particles is S2, 1 The charging member manufacturing method according to claim 13, wherein 0.0% ≦ S1 ≦ 3.9% and 13.5% ≦ S2 ≦ 25.5% are satisfied.   The method for producing a charging member according to claim 13 or 14, wherein the first and second surface layer particles are particles formed of urethane, urethane acrylic, acrylic, or acrylic / styrene copolymer.   16. The image forming apparatus according to claim 13, wherein the charging member is a member to which only a DC voltage is applied when the image carrier is charged.

Images