JP5349901B2 - Charging member, process cartridge, and electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging member for electrophotographic device, capable of providing superior images by suppressing minute resistance irregularities, images with streaks due to deterioration of charging performance, and ghost images. <P>SOLUTION: A surface layer of the electrifying member contains graphite particles and ferroelectric particles, and the relation between a projecting part derived from the graphite particles (graphite projecting part) and a projecting part derived from the ferroelectric particles (ferroelectric projecting part), both formed on the surface, is controlled, such that the distance L of the apex of the ferroelectric projecting part to a plane formed by three graphite projecting parts adjacent to the ferroelectric projecting part is positive. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a charging member, more specifically, a charging member for charging a surface of an electrophotographic photosensitive member, which is an object to be charged, to a predetermined potential by applying a voltage, and a process cartridge and an electrophotographic image forming apparatus using the charging member. (Hereinafter referred to as “electrophotographic apparatus”).

  An electrophotographic apparatus adopting an electrophotographic system includes an electrophotographic photosensitive member, a charging device, an exposure device, a developing device, a transfer device, and a fixing device.

  As the charging device, a method of charging the surface of the electrophotographic photosensitive member by applying a voltage to a charging member disposed in contact with or close to the surface of the electrophotographic photosensitive member is often employed. As a voltage application method, there are a method in which only a DC voltage is applied (DC charging method) and a method in which an AC voltage is superimposed on a DC voltage (AC charging method).

  From the viewpoint of stable charging and reduction of ozone generation, a contact-type charging method is preferably used. Further, from the viewpoint of low cost and downsizing of the apparatus, the DC charging method is preferably used as the voltage application method to the charging member.

  The DC charging method has an advantage that the cost of the power supply is generally lower than that of the AC charging method. However, the DC charging method does not have a discharge current leveling effect unlike the AC charging method. For this reason, there is a case where a slight unevenness of resistance of the charging member, a decrease in charging performance due to use, or a discharge unevenness due to adhesion of toner or an external additive occurs, resulting in a streak-like image. In addition, there may be a potential difference between the surface potential of the photoreceptor to be charged and the saturation potential (dark part potential VD) after the first charging cycle and second charging cycle. In this case, for example, in the case of the reversal development method, if images are output continuously immediately after forming characters or black graphics, the so-called ghost image in which the immediately preceding characters or black graphics remain on the subsequent images. Sometimes appeared.

  It has been attempted to improve these streaky images by incorporating particles in the surface layer of the charging member used in the DC charging method and forming irregularities on the surface of the charging member (Patent Documents 1, 2, etc.). reference).

  Further, a method for improving ghost images by dispersing ferroelectric fine particles in a surface layer is disclosed (see Patent Document 3).

  As described in Patent Documents 1, 2, and 3, the method of forming irregularities of particles on the surface layer of the charging member or containing specific fine particles can surely improve streak-like images and ghost images. .

However, in recent years, the life of process cartridges has been further demanded, and accordingly, the life of charging members has been further demanded. Even in the above charging member, a streak-like image or a ghost image may be generated in the latter half of the life due to a decrease in charging performance of the charging member due to long-term use and adhesion of toner or external additives on the surface of the charging member. It was.
JP 2007-178599 A JP 09-258523 A Japanese Patent No. 3284626

  An object of the present invention is to provide a charging member and a process capable of providing a good image by suppressing the generation of streak-like images and ghost images caused by minute resistance unevenness and deterioration of charging performance in a charging member for an electrophotographic apparatus. To provide a cartridge and an electrophotographic apparatus.

The present invention is a charging member having a surface layer on a conductive support,
The surface layer includes binder resin, graphite particles, and ferroelectric particles selected from the group consisting of calcium titanate, barium titanate and strontium titanate,
On the surface of the charging member, convex portions derived from graphite particles (graphite convex portions) and convex portions derived from ferroelectric particles (ferroelectric convex portions) are formed on the surface of the charging member,
When a plane including three vertices of the graphite convex portion adjacent to the ferroelectric convex portion is formed, the ferroelectric convex portion lower than the plane is 80% or more of the total ferroelectric convex portion. It is a charging member.

  Since the charging member of the present invention can suppress the generation of streak-like images and ghost images due to minute resistance unevenness and deterioration of charging performance, a good image can be provided when used as a charging member in an electrophotographic apparatus. .

(Charging member)
The charging member of the present invention is a charging member having a surface layer on a conductive support. The surface layer includes a binder resin, graphite particles, and ferroelectric particles selected from the group consisting of calcium titanate, barium titanate, and strontium titanate. Convex portions derived from graphite particles (hereinafter referred to as “graphite convex portions”) and convex portions derived from ferroelectric particles (hereinafter referred to as “ferroelectric convex portions”) are formed on the surface. . When a plane including three vertices of the graphite convex portion adjacent to the ferroelectric convex portion is formed, the ferroelectric convex portion lower than the plane is 80% or more of the total ferroelectric convex portion.

  FIG. 1 is a schematic diagram showing three graphite convex portions adjacent to the ferroelectric convex portion. In the figure, 15 is graphite particles, 16 is ferroelectric particles, and the tops of the graphite convex portions and the vertexes of the ferroelectric convex portions are 15a and 16a, respectively.

  Note that the ferroelectric convex portion is lower than the plane, as shown in FIG. 2, the distance of the vertex 16a of the ferroelectric convex portion to the plane 17 formed by the vertexes 15a of the three graphite convex portions (hereinafter referred to as L ) Is positive.

  First, forming a graphite convex portion on the surface layer has a technical significance of controlling the conductivity of the surface layer. Since the graphite particles have a crystal structure, they exhibit conductivity. The surface layer containing the graphite particles is in a state where current flows preferentially through the graphite particles. By forming such a graphite convex part on the surface of the surface layer, a state advantageous for discharge is formed, and streaky images and ghost images can be suppressed.

  On the other hand, the formation of the ferroelectric protrusions on the surface layer has the technical significance of controlling the dielectric properties of the surface layer. It is known that there is a relationship between the charge accumulated in the electrophotographic photosensitive member and the dielectric property of the charging member (Japanese Patent Laid-Open No. 2005-316263). Therefore, it is possible to increase the discharge capability of the charging member by forming the ferroelectric convex portion on the surface.

  In this case, simply forming the ferroelectric protrusions causes toner and external additives to adhere to the ferroelectric protrusions over a long period of use, and the expected increase in discharge capacity cannot be obtained. Therefore, the relationship between the height of the graphite convex portion and the ferroelectric convex portion is controlled. Specifically, the height relationship is controlled so that the number of the ferroelectric convex portions with L being positive is 80% or more of the total number of the ferroelectric convex portions. This makes it difficult to attach toner and external additives to the ferroelectric protrusions, maintains good discharge performance even during long-term use, and suppresses streak-like images and ghost images. become.

  Examples of the shape of the charging member of the present invention include various shapes such as a roller shape, a flat plate shape, and a belt shape. FIG. 3 shows a roller-shaped charging member (charging roller), FIG. 4 shows a flat plate-shaped charging member, and FIG. 5 shows a schematic sectional view of the belt-shaped charging member.

  The structure of the charging member is basically that the surface layer 3 is provided on the conductive support 1 (1A in FIG. 3, 2A in FIG. 4, 3A in FIG. 5). The conductive elastic layer 2 is often provided between the surface layers 3 (1B in FIG. 3, 2B in FIG. 4, 3B in FIG. 5). The surface is formed with convex portions derived from graphite particles (graphite convex portions) and convex portions derived from ferroelectric particles (ferroelectric convex portions).

  The charging roller will be described in detail with reference to FIG. 3. The structure of the charging roller includes a conductive support 1 and a surface layer 3 (1A), and includes a conductive support, a conductive elastic layer, and a surface layer (1B). Further, some have an intermediate layer. 3C and 1D show examples in which the intermediate layer 21 has one layer and the intermediate layers 21 and 22 have two layers between the elastic layer 2 and the surface layer 3, respectively.

  Hereinafter, a charging roller including a conductive support, a conductive elastic layer, and a surface layer will be described.

(Conductive support)
The conductive support used for the charging member of the present invention is conductive and has a function of supporting a surface layer, a conductive elastic layer, and the like provided on the support. Examples of the material include metals such as iron, copper, stainless steel, aluminum, nickel, and alloys thereof. In addition, for the purpose of imparting scratch resistance to these surfaces, plating treatment or the like may be performed as long as the conductivity is not impaired. Further, as the conductive support, those made of a resin base material coated with a metal or the like to be surface conductive or those manufactured from a conductive resin composition can be used. The charging roller has a rod-like shape or a cylindrical shape, but a plate-like charging member has a plate shape, and a belt-like charging member has an endless flexible tubular belt. is there.

  The conductive support and the conductive elastic layer, or the sequentially laminated layers (for example, the conductive elastic layer and the surface layer shown in 1B) may be bonded via an adhesive. In this case, the adhesive is preferably conductive. In order to make it conductive, a known conductive agent can be used for the adhesive.

  As the binder of the adhesive, known thermosetting resins and thermoplastic resins such as urethane, acrylic, polyester, polyether, and epoxy can be used.

(Conductive elastic layer)
Since the charging roller of the present invention is used in contact with the electrophotographic photosensitive member, it preferably has elasticity. In the present invention, preferably, the conductive elastic layer 2 is formed on the outer periphery of the conductive support 1. The conductive elastic layer 2 is made of a conductive elastic body.

The conductive elastic body is formed, for example, by dispersing a conductive agent in a polymer elastic body. As the conductive agent, an ionic conductive agent and an electronic conductive agent described in the surface layer can be used. The amount of the conductive agent is preferably such that the electrical resistance of the conductive elastic body is 1 × 10 ³ Ω · cm or more and 1 × 10 ⁹ Ω · cm or less at 23 ° C./50% RH.

  The following can be used as the polymer elastic body. Synthetic rubber such as epichlorohydrin rubber, acrylonitrile-butadiene rubber, chloroprene rubber, urethane rubber, silicone rubber, thermoplastic elastomer such as styrene-butadiene-styrene block copolymer, styrene-ethylene / butylene-styrene block copolymer, and the like. Among these, epichlorohydrin rubber is suitably used as the polymer elastic body. In the epichlorohydrin rubber, the polymer itself has conductivity in the middle resistance region, and good conductivity is exhibited even if the addition amount of the conductive agent is small. Moreover, since the variation in electrical resistance depending on the position can be reduced, it is suitable as a polymer elastic body.

  Examples of epichlorohydrin rubber include the following. Epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-allyl glycidyl ether copolymer, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer. Of these, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is preferred because it exhibits stable conductivity in the medium resistance region. In addition, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer can control conductivity and workability by adjusting the polymerization degree and composition ratio.

  In addition to the above, the conductive elastic body may contain compounding agents such as a plasticizer, a filler, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a scorch preventing agent, a dispersing agent, and a release agent as necessary. It may be added.

  The conductive elastic layer is preferably formed by a known method such as extrusion molding, injection molding, or compression molding after mixing the above-mentioned conductive elastic material with a closed mixer. The conductive elastic layer may be produced by directly forming a conductive elastic body on a conductive support. Alternatively, a conductive elastic body previously formed into a tube shape may be formed on the conductive support. Note that the surface may be polished and the shape may be adjusted after the production of the conductive elastic layer.

  The hardness of the conductive elastic layer is preferably 70 ° or less, and more preferably 60 ° or less in terms of micro hardness (MD-1). When the micro hardness (MD-1) exceeds 70 °, the nip width between the charging member and the photosensitive member becomes small, and the contact force between the charging member and the photosensitive member concentrates in a small area, and the contact pressure. May become larger. In addition, "micro hardness (MD-1)" is the hardness of the charging member measured using Asker micro rubber hardness meter MD-1 type (trade name, manufactured by Kobunshi Keiki Co., Ltd.). Specifically, the hardness meter is a value measured in a peak hold mode of 10 N with respect to a charging member left for 12 hours or more in an environment of normal temperature and normal humidity (23 ° C./50% RH).

(Surface layer)
The surface layer is composed of graphite particles, ferroelectric particles selected from the group consisting of calcium titanate, barium titanate and strontium titanate, a binder resin, and other compounding agents.

[Graphite particles]
The graphite particles used in the present invention are “substances containing carbon atoms having a layer structure by SP ² covalent bond”. Then, as the graphite particle, and the half width .DELTA..nu ₁₅₈₀ of peak intensity at 1580 cm ^-1 in the Raman spectrum is 80 cm ^-1 or less, and it is preferable particle diameter of the particles is 200nm or more. Graphite particles having a peak intensity half width Δν ₁₅₈₀ of 60 cm ⁻¹ or less are more preferable. In the following, the peak width at half maximum Δν ₁₅₈₀ at ₁₅₈₀ cm ⁻¹ in the Raman spectrum is represented as “Δν” unless otherwise specified.

  Examples of such graphite particles include the following. Particles obtained by graphite treatment of artificial graphite, natural graphite, bulk mesophase pitch, particles obtained by graphite treatment of mesocarbon microbeads, particles obtained by coating mesophase on phenol resin and graphite treatment, phenol resin Particles obtained by processing, particles obtained by treating carbon black with graphite, and the like. Hereafter, the manufacturing method of each graphite particle is demonstrated easily.

-Artificial graphite Artificial graphite is obtained by adding a binder such as pitch to a filler such as coke, molding, and then firing. As the filler, residual oil in petroleum distillation or coke obtained by baking raw coke obtained by heating coal tar pitch at about 500 ° C. at 1200 to 1400 ° C. can be used. As the binder, a pitch obtained as a distillation residue of tar can be used.

  As a method of obtaining graphite particles using these raw materials, first, the filler is pulverized and mixed with a binder. Then, it knead | mixes under a heating of about 150 degreeC, and shape | molds using a molding machine. The molded article is heat-treated at 700 ° C. or higher and 1000 ° C. or lower to impart thermal stability. Next, desired graphite particles are obtained by heat treatment at 2600 ° C. or more and 3000 ° C. or less. In the heat treatment, it is preferable to cover the molded product with packing coke in order to prevent oxidation.

・ Natural graphite Natural graphite is produced from the ground with the charcoal layer and the like completely converted to graphite due to geothermal heat and high pressure in the ground. Such natural graphite is a dark gray to black glossy, very soft, slippery crystalline mineral with excellent properties such as heat resistance, chemical stability, lubricity, and fire resistance. It is widely used industrially in the form of powders, solids, and paints for electrical materials. In addition to the hexagonal crystal, some crystal structures belong to other rhombohedral systems and have a complete layered structure. Desired graphite particles can be obtained by pulverizing and classifying natural graphite.

・ Particles obtained by graphite treatment of bulk mesophase pitch Bulk mesophase pitch can be obtained, for example, by extracting β-resin by solvent fractionation from coal tar pitch or the like, followed by hydrogenation and heavy processing. it can. Further, after the heavy treatment, the solvent-soluble component may be removed by pulverization and then benzene, toluene or the like. If this bulk mesophase pitch has a quinoline soluble content of less than 95% by mass, the inside of the particles is difficult to be liquid phase carbonized, and solid phase carbonization causes the particles to remain in a crushed state, making it impossible to obtain a spherical one. Therefore, the quinoline soluble content is preferably 95% by mass or more.

  As a method for obtaining graphite particles using mesophase pitch, first, the bulk mesophase pitch is finely pulverized to 2 μm or more and 25 μm or less, heat-treated in air at 200 ° C. or more and 350 ° C. or less, and lightly oxidized. By this oxidation treatment, only the surface of the bulk mesophase pitch particles is infusible, and melting and fusion are prevented during the graphitizing heat treatment in the next step. The oxidized bulk mesophase pitch particles suitably have an oxygen content of 5% by mass to 15% by mass. In addition, when the oxygen content is less than 5% by mass, fusion between particles during heat treatment may become intense, and when it exceeds 15% by mass, the inside of the particle is oxidized and it is difficult to obtain a spherical product. There may be bugs. Next, desired graphite particles are obtained by heat-treating the oxidized bulk mesophase pitch particles at 1000 ° C. or higher and 3500 ° C. or lower in an inert atmosphere such as nitrogen or argon.

-Particles obtained by graphitizing mesocarbon microbeads As a method for obtaining mesocarbon microbeads, coal-based heavy oil or petroleum-based heavy oil is heat-treated at a temperature of 300 ° C to 500 ° C and polycondensed. To produce crude mesocarbon microbeads. Thereafter, the reaction product is subjected to treatment such as filtration, stationary sedimentation, and centrifugal separation to separate mesocarbon microbeads, followed by washing with a solvent such as benzene, toluene, xylene, and the like, followed by drying.

  In order to obtain graphite particles using these mesocarbon microbeads, first, in order to prevent coalescence of the particles after the graphite treatment and to obtain a uniform particle size, the mesocarbon microbeads that have been dried are not damaged. First, mechanically disperse. The mesocarbon microbeads that have finished the primary dispersion are subjected to primary heat treatment at 200 ° C. or higher and 1500 ° C. or lower in an inert atmosphere to be carbonized. After the primary heat treatment, it is preferable to mechanically disperse the carbide with a force that does not destroy the carbide in order to prevent coalescence of the particles after the graphite treatment and to obtain a uniform particle size. The carbide that has undergone the secondary dispersion treatment is subjected to a secondary heat treatment at 1000 ° C. or more and 3500 ° C. or less in an inert atmosphere to obtain desired graphite particles.

-Particles obtained by coating mesophase on phenol resin and performing graphite treatment As the phenol resin, for example, a resol type phenol resin which is a condensate of phenol and aldehydes can be used. The resol-type phenol resin is a resin obtained by reacting an aromatic compound having a phenolic hydroxyl group and an aldehyde in the presence of a catalyst, followed by heat curing. As a method of obtaining graphite particles using this phenol resin, bulk mesophase pitch is coated on the surface of the phenol resin spherical particles by, for example, a mechanochemical method. And desired graphite particle | grains are obtained by baking after heat processing by oxidizing atmosphere formation.

-Particles obtained by graphite treatment of phenol resin As the phenol resin that is a precursor, for example, a resol type phenol resin that is a condensate of phenol and aldehydes is used. This phenol resin is fired at 1000 ° C. or higher and 1500 ° C. or lower in an inert gas atmosphere to obtain graphite particles. At this time, the flow rate of the inert gas is preferably 0.1 ml / min or more per 1 g of phenol resin. By doing in this way, a volatile matter can be efficiently removed from a phenol resin. Alternatively, the firing pressure may be a low pressure of 50 kPa or less. By baking at a pressure of 50 kPa or less, volatile components from the phenol resin can be efficiently removed from the reaction system.

-Particles obtained by graphite-treating carbon black The particles obtained by graphite-treating carbon black are obtained by heat-treating raw carbon black in a non-oxidizing atmosphere and graphitizing. This particle has no functional group on the surface, has good conductivity, has a very low content of impurities (for example, S, Cl, etc.), and has a low moisture adsorptivity. There are few features. The graphite treatment is performed by filling the raw material carbon black in a graphite crucible, placing it in a normal heating furnace such as an Atchison furnace or a high-frequency furnace, and heating at 1700 ° C. to 3200 ° C. in a non-oxidizing atmosphere. The crystallinity of the carbon black can be adjusted by changing the firing temperature during the firing.

(Measurement of half-value width Δν ₁₅₈₀ (Δν) of Raman spectrum of graphite particles)
The graphite particles contained in the surface layer are measured under the following conditions using the graphite particles cut out from the surface layer as a measurement sample.
Measuring instrument: Laser Raman spectrometer “LabRAM HR” (trade name, manufactured by Horiba Joban Yvon)
Laser: He-Ne laser (peak wavelength: 632 nm)
Filter: D0.3
Hall: 1000μm
Slit: 100 μm
Center spectrum: 1500cm ^-1
Measurement time: 1 second x 16 times Grating: 1800
Objective lens: × 50

In the above measurement, a band width at a height corresponding to ½ of a peak existing in a region from 1570 cm ⁻¹ to 1630 cm ⁻¹ derived from graphite is defined as “Δν”.

[Ferroelectric particles]
The ferroelectric particles in the present invention refer to ferroelectric particles selected from the group consisting of calcium titanate, barium titanate and strontium titanate. Here, the ferroelectric is a substance that causes spontaneous polarization. Since the above titanate has a crystal structure called a perovskite structure, it can exhibit a very strong dielectric property at room temperature.

(Measurement of relative permittivity)
The relative dielectric constant of the ferroelectric particles in the present invention is measured as follows. First, a powder sample is put in a cylinder having a bottom area of 2.26 cm ² , and 15 kg of pressure is applied to the upper and lower electrodes. At the same time, an alternating voltage of 1 Vpp and 1 MHz is applied, the current at that time is measured, and then normalized to calculate the relative dielectric constant.

[Surface shape of surface layer and L]
The shape of the surface layer of the charging member of the present invention is controlled to a specific state by the graphite convex portion and the ferroelectric convex portion. The state is a state in which the ferroelectric convex portions with L being positive are 80% or more of the total number of the ferroelectric convex portions.

  First, in the present invention, the ferroelectric convex portion refers to particles that are present on the side closest to the surface of the charging member when the convex portion on the surface of the charging member is observed using a laser microscope to be described later. It is defined as a convex part that is a characteristic particle. The graphite convex portion is defined as a convex portion in which particles existing on the side closest to the surface of the charging member are graphite particles.

  The distance L is measured as follows.

  The surface of the charging member is observed with a laser microscope “LSM5 PASCAL” (trade name, manufactured by Carl Zeiss) at a visual field of 0.5 mm × 0.5 mm.

  By changing the wavelength of the laser to be excited and examining the spectrum of the excitation light, it is identified whether the convex portion in the field of view is derived from ferroelectric particles or graphite particles. Then, two-dimensional image data is obtained by scanning the laser in the XY plane within the field of view. Further, the focal point is moved in the Z direction, and the above scanning is repeated to obtain three-dimensional image data.

  Next, paying attention to an arbitrary ferroelectric protrusion in the field of view, three graphite protrusions adjacent to the ferroelectric protrusion are determined. Here, “adjacent” refers to a state in which the sum of the distances between the vertexes of the ferroelectric convex portions and the vertexes of the respective graphite convex portions is minimized. The distance between the plane including three vertices of the graphite convex portion thus determined and the focused ferroelectric convex portion is calculated from the above-described three-dimensional image data (FIG. 2). Such an operation is performed on ten ferroelectric particles in the field of view. Then, the same measurement is performed for 10 points in the longitudinal direction of the charging member, and the distribution of distances between a total of 100 obtained vertices of ferroelectric convex portions and planes including three vertices of graphite convex portions is examined.

  Then, when the vertex of the ferroelectric convex portion is below the plane including three vertexes of the graphite convex portion, L is “positive”, and when it is above, L is “negative”. . Here, L of the ferroelectric convex portion occupying 80% or more of the total number of the ferroelectric convex portions is more preferably in the range of +2 μm to +15 μm, and more preferably +2 μm to +10 μm. This is because the ferroelectric convex portion can be sufficiently protected from adhesion of toner and external additives, and a sufficient discharge can be generated between the photosensitive member surface. Further, by setting the ratio of the ferroelectric convex portions having a positive L to the total number of ferroelectric convex portions to 80% or more, the generation of streak-like images and ghost images is suppressed in almost all practical areas of the charging member. Has the technical significance of being able to.

  The average particle diameter of these graphite particles and ferroelectric particles is preferably 1 μm or more and 30 μm or less. More preferably, they are 1 micrometer or more and 20 micrometers or less. By making the average particle diameter within this range, the effects of the present invention can be further exhibited.

  The average particle diameter of these graphite particles and ferroelectric particles is calculated as follows. An arbitrary point on the surface layer is cut out with a focused ion beam “FB-2000C” (trade name, manufactured by Hitachi, Ltd.) every 20 nm over 500 μm, and a cross-sectional image thereof is taken. And the image which image | photographed the same particle | grains is combined by 20 nm space | interval, and a three-dimensional particle shape is created. This operation is performed at an arbitrary 100 points. For the average particle diameter of the particles, the projected area is calculated from the three-dimensional particle shape obtained above, and the equivalent circle diameter of the obtained area is calculated. The volume average particle diameter is obtained from the equivalent circle diameter, and the value is defined as the average particle diameter. In addition, the said measuring method is applicable also to the measurement of the particle diameter of a electrically conductive agent and other particle | grains.

Further, the volume resistivity of the graphite particles is preferably 1 × 10 ⁻⁵ Ωcm or more and 1 × 10 ⁵ Ωcm or less. More preferably, it is 1 × 10 ⁻⁵ Ωcm or more and 1 × 10 ⁴ Ωcm or less. By making the volume resistivity of the graphite particles in the above range, the effect of the present invention is further exhibited.

In the present invention, the volume resistivity of the graphite particles is determined by applying a voltage of 10 V to the sample using a resistance measuring device “Loresta-GP” (trade name, manufactured by Mitsubishi Chemical Corporation) in a 23 ° C./50% RH environment. When measured. As a sample to be measured, a sample compressed by applying a pressure of 9.8 MPa (10 ² kgf / cm ² ) is used.

  In addition, the measuring method of said volume resistivity is applicable also to a electrically conductive agent and other particle | grains in this invention.

  The content of the graphite particles and the ferroelectric particles in the surface layer is preferably 2 parts by mass or more and 120 parts by mass or less, more preferably 5 parts by mass or more and 100 parts by mass or less, with respect to 100 parts by mass of the binder resin. More preferably, it is at least 50 parts by mass. By setting it as this range, the effect of this invention is exhibited more.

[Binder resin]
As a binder resin used for the surface layer of the present invention, a known binder resin can be appropriately selected and used. Specifically, a resin such as a thermosetting resin or a thermoplastic resin can be used as the resin. Of these, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, and the like are preferable. As synthetic rubber, EPDM, SBR, silicone rubber, urethane rubber, IR, butyl rubber, NBR, chloroprene rubber (CR), acrylic rubber, epichlorohydrin rubber, and the like can be used. These may be used alone or in combination of two or more, or may be a copolymer.

[Other ingredients]
The surface layer can contain other materials as long as the effects of the present invention are not impaired. Examples of other materials include a conductive agent, insulating particles made of a polymer compound, and a release agent.

-Conductive agent As a conductive agent, conductive agents, such as an ionic conductive agent and an electronic conductive agent, can be used.

  The following can be mentioned as an ionic conductive agent. Inorganic ionic substances such as lithium perchlorate, sodium perchlorate, calcium perchlorate, lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, trioctylpropylammonium Cationic surfactants such as bromide, modified aliphatic dimethylethylammonium ethosulphate, zwitterionic surfactants such as lauryl betaine, stearyl betaine, dimethylalkyl lauryl betaine, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, Quaternary ammonium salts such as trimethyloctadecyl ammonium perchlorate, trifluoro Organic acid lithium salts such as lithium methanesulfonate or the like. These can be used singly or in combination of two or more.

  Examples of the electron conductive agent include metal fine particles, metal oxide fine particles, and carbon black. Examples of the metal fine particles include aluminum, palladium, iron, copper, silver and the like. Examples of the metal oxide fine particles include titanium oxide, tin oxide, and zinc oxide. Examples of carbon black include furnace black, thermal black, acetylene black, and PAN (polyacrylonitrile) carbon. As furnace black, the following can be mentioned, for example. SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, I-ISAF-HS, HAF-HS, HAF, HAF-LS, T-HS, T-NS, MAF, FEF, GPF, SRF-HS- HM, SRF-LM, ECF, FEF-HS. Moreover, FT, MT, etc. are mentioned as thermal black.

  Moreover, these electrically conductive agents can be used individually or in combination of 2 or more types.

  The conductive agent preferably has an average particle size of 0.01 μm to 0.9 μm, and more preferably 0.01 μm to 0.5 μm. Within this range, the volume resistivity of the surface layer can be easily controlled.

The amount of these conductive agents added to the surface layer is suitably in the range of 2 to 80 parts by weight, preferably 20 to 60 parts by weight with respect to 100 parts by weight of the binder.
The surface of the conductive agent may be treated. As the surface treating agent, organosilicon compounds such as alkoxysilanes, fluoroalkylsilanes, polysiloxanes, titanate-based, aluminate-based and zirconate-based coupling agents, oligomers or polymer compounds can be used. These may be used alone or in combination of two or more. Preferred are organosilicon compounds such as alkoxysilane and polysiloxane, and various coupling agents of titanate, aluminate or zirconate.

  When carbon black is used as a conductive agent, it is preferably used as composite conductive fine particles in which metal oxide fine particles are coated with carbon black. Since carbon black forms a structure, it tends to be difficult for the carbon black to exist uniformly with respect to the binder. When carbon black is used as composite conductive fine particles coated with a metal oxide, the conductive agent can be uniformly present in the binder, and the volume resistivity can be controlled more easily.

  Specifically, the metal oxide fine particles used for this purpose include zinc oxide, tin oxide, indium oxide, titanium oxide (titanium dioxide, titanium monoxide, etc.), iron oxide, silica, alumina, magnesium oxide, zirconium oxide. Etc.

  The metal oxide fine particles are preferably surface-treated. As the surface treatment, organosilicon compounds such as alkoxysilane, fluoroalkylsilane and polysiloxane, titanate-based, aluminate-based and zirconate-based coupling agents, oligomers or polymer compounds can be used. These may use 1 type or may use 2 or more types together.

Insulating particles made of a polymer compound Examples of insulating particles made of a polymer compound include the following insulating particles made of a polymer compound. Polyamide resin, silicone resin, fluororesin, (meth) acrylic resin, styrene resin, phenol resin, polyester resin, melamine resin, urethane resin, olefin resin, epoxy resin, resins such as copolymers, modified products, and derivatives, Ethylene-propylene-diene copolymer (EPDM), styrene-butadiene copolymer rubber (SBR), silicone rubber, urethane rubber, isoprene rubber (IR), butyl rubber, acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR ) Rubber, polyolefin-based thermoplastic elastomer, urethane-based thermoplastic elastomer, polystyrene-based thermoplastic elastomer, fluororubber-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, Li butadiene thermoplastic elastomer, ethylene vinyl acetate type thermoplastic elastomers, polyvinyl chloride thermoplastic elastomer, and thermoplastic elastomers such as chlorinated polyethylene based thermoplastic elastomer. In particular, fine particles made of (meth) acrylic resin, styrene resin, urethane resin, fluororesin, and silicone resin are preferable.

-Release agent As the release agent, those having low surface energy and those having slidability can be used. By including a release agent in the surface layer, the relative movement of the charging member with respect to the photosensitive member becomes smooth, and the occurrence of an irregular movement state such as stick-slip is reduced. As a result, the occurrence of irregular wear on the surface of the charging member, the generation of abnormal noise, and the like are suppressed. Moreover, when a mold release agent is a liquid, it acts also as a leveling agent when forming a surface layer. As the release agent,
Specifically, metal oxides such as molybdenum disulfide, tungsten disulfide, boron nitride, and lead monoxide can be used. In addition, oil- or solid-state (release resin or powder thereof, a part of the polymer into which a part having release property is introduced) silicon or fluorine-containing compound, wax, higher fatty acid, salt thereof , Esters and other derivatives can also be used.

  The surface layer of the present invention preferably has a thickness of 0.1 μm or more and 100 μm or less. More preferably, they are 1 micrometer or more and 50 micrometers or less.

  As shown in FIGS. 7 (a) and 7 (b), the thickness of the surface layer is obtained by cutting the roller cross section with a sharp blade at nine positions, three in the longitudinal direction and three in the circumferential direction. The average value is observed with an optical microscope or an electron microscope.

  The surface layer may be further subjected to a surface treatment. Examples of the surface treatment include a surface processing treatment using UV or electron beam, and a surface modification treatment for adhering and / or impregnating a compound or the like on the surface.

  The surface layer can be formed by a coating method such as electrostatic spray coating or dipping coating. It can also be formed by adhering or covering a sheet-shaped or tube-shaped layer previously formed to a predetermined film thickness. Alternatively, a method of curing and molding the material into a predetermined shape in the mold can also be used. Among these, it is preferable to apply the surface layer coating solution by a coating method to form a coating film to form the surface layer.

  When the surface layer is formed by a coating method, the solvent used in the coating solution may be any solvent that can dissolve the binder resin. Specifically, the following solvents can be used. Alcohols such as methanol, ethanol, isopropanol, ketones such as acetone, methyl ethyl ketone, cyclohexanone, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, tetrahydrofuran, dioxane, ethylene Ethers such as glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aromatic compounds such as xylene, ligroin, chlorobenzene and dichlorobenzene. These solvents are appropriately selected according to the binder resin used.

  As a method for dispersing the binder, particles and the like in the coating solution, known solution dispersing means such as a ball mill, a sand mill, a paint shaker, a dyno mill, and a pearl mill can be used.

In the present invention, the volume resistivity of the surface layer is preferably 1 × 10 ³ Ω · cm or more and 1 × 10 ¹⁵ Ω · cm or less in a 23 ° C./50% RH environment. If the volume resistivity of the surface layer is smaller than this range, if a pinhole occurs in the photoreceptor, an excessive current flows through the pinhole and the applied voltage drops, and the entire longitudinal direction of the pinhole part is strip-shaped. May appear in the image as a charging failure. On the other hand, if it is larger than this range, it may be difficult for the current to flow through the charging roller, and the photosensitive member may not be charged to a predetermined potential, resulting in an adverse effect that the image does not have the desired density.

  The volume resistivity of the surface layer can be measured, for example, by the following method. First, the surface layer is peeled off from the roller state and cut into a rectangle of about 5 mm × 5 mm. Metal is vapor-deposited on both surfaces to produce an electrode and a guard electrode, and a measurement sample is obtained. Alternatively, the surface layer coating solution is formed on an aluminum sheet to form a surface layer coating film, and a metal is deposited on the coating surface to obtain a measurement sample. About the obtained measurement sample, a voltage of 200 V was applied using a microammeter “ADVANTEST R8340A ULTRA HIGH RESISTANCE METER (trade name, manufactured by Advantest Co., Ltd.). The current after 30 seconds was measured, Calculated from thickness and electrode area.

  In addition, the said measuring method is applicable also to the measurement of the volume resistivity of a conductive elastic layer.

  The charging member according to the present invention has a relationship between the height of the convex portion derived from graphite particles (graphite convex portion) existing on the surface of the surface layer and the convex portion derived from ferroelectric particles (ferroelectric convex portion). One feature is that it is controlled and protected from the adhesion of toner and external additives associated with long-term use. A method for obtaining a surface layer having such a surface shape will be described below.

  First, as the graphite particles, those larger than the average particle size of the ferroelectric particles are preferably used. The difference in average particle diameter is preferably 2 μm or more.

  The method for preparing graphite particles and ferroelectric particles having a predetermined average particle diameter is not particularly limited, and a known method can be used. For example, the size of the average particle diameter can be controlled by classifying the powder of particles and selectively collecting coarse powder or fine powder.

  The amount of the ferroelectric particles to be contained in the binder resin is preferably larger than the amount of the carbon particles, specifically 1.5 times or more, more preferably 2.0 times or more.

  A known method can be used for dispersing the graphite particles and the ferroelectric particles in the binder resin. However, in order to obtain the charging member according to the present invention, after the dispersion of the graphite particles and the ferroelectric particles in the binder resin, the relationship between the average particle size of the graphite particles and the ferroelectric particles before the dispersion is also determined. It is important to ensure that it is maintained. That is, under the general dispersion conditions of the filler in the binder for the purpose of uniform dispersion, the graphite particles and the ferroelectric particles are pulverized in the dispersion step, which is different from the initial average particle size. There is a case. In this case, it becomes difficult to control the surface shape of the finally formed charging member. Therefore, in the present invention, when dispersing the graphite particles and the ferroelectric particles in the binder, the dispersion time is made shorter than usual to avoid pulverization of the graphite particles and the ferroelectric particles as much as possible, It is preferable to make it more gradual than usual.

  In the following, the preparation of the surface layer coating solution using glass beads and the coating method will be described as an example.

  First, a component to be dispersed excluding graphite particles and ferroelectric particles, for example, conductive fine particles, is mixed with a glass bead having a diameter of 0.8 mm in a binder, and a paint shaker disperser is used for 24 to 36 hours. scatter. Next, graphite particles and ferroelectric particles are added for further dispersion, and the dispersion time is 5 minutes to 30 minutes, preferably 5 minutes to 10 minutes. Thereby, the pulverization of the graphite particles and the ferroelectric particles being dispersed is suppressed, and the relationship between the average particle diameters of the graphite particles and the ferroelectric particles is substantially maintained throughout the dispersion. Thereafter, the viscosity is adjusted to 5 mPa · s to 30 mPa · s, particularly 8 mPa · s to 20 mPa · s to obtain a surface layer coating solution. And the electroconductive base | substrate which formed the elastic layer in the surrounding surface is immersed in the said surface layer coating liquid, and the said coating liquid is applied. Thereafter, the coating film on the elastic layer surface is dried to form a surface layer. According to such a method, the difference in the average particle diameter between the initial graphite particles and the ferroelectric particles is reflected, and as a result, the surface-state charging member according to the present invention can be obtained. Here, the viscosity of the surface layer coating solution is a single cylinder type rotational viscometer “Bismetron VS-A1” (trade name, manufactured by Shibaura System Co., Ltd.), using a No. 1 rotor at 23 ° C. The measured value.

The charging roller of the present invention usually has an electrical resistance of 1 × 10 ⁴ Ω · cm or more and 1 × 10 ¹⁰ Ω · cm in a 23 ° C./50% RH environment in order to improve the charging of the photoreceptor. The following is preferable.

  FIG. 6 shows an example of a method for measuring the electrical resistance of the charging roller. Both ends of the conductive support 1 are brought into contact with a cylindrical metal 32 having the same curvature as that of the photosensitive member by a bearing 33 under load so as to be parallel to each other. In this state, the cylindrical metal 32 is rotated by a motor (not shown), and the charging roller 5 abutted thereby is driven to rotate. Then, a DC voltage of −200 V is applied from the stabilized power supply 34. The current flowing at this time is measured by an ammeter 35, and the resistance of the charging roller is calculated. Here, the load is 4.9 N, the metal cylinder is φ30 mm, and the rotation of the metal cylinder is a peripheral speed of 45 mm / sec.

  The charging roller of the present invention preferably has a so-called crown shape in which the central portion in the longitudinal direction is the thickest and becomes thinner toward both ends in the longitudinal direction from the viewpoint of making the longitudinal nip width uniform with respect to the photoreceptor. As the crown amount, it is preferable that the difference between the outer diameter of the central portion and the outer diameter at a position 90 mm away from the central portion is 30 μm or more and 200 μm or less.

  In the charging roller of the present invention, the surface ten-point average roughness Rzjis is preferably 2 μm or more and 20 μm or less, and the surface irregularity average interval Rsm is preferably 15 μm or more and 150 μm or less. By setting the surface roughness Rzjis and the average unevenness interval Rsm of the charging roller within this range, the contact state between the charging roller and the electrophotographic photosensitive member can be made more stable. Thereby, the photoreceptor can be easily and uniformly charged.

  The ten-point average roughness Rzjis of the charging roller surface and the average unevenness interval Rsm of the surface are measured in accordance with the standard of JIS B0601-2001 surface roughness, and a surface roughness measuring instrument “SE-3400” (trade name) , Manufactured by Kosaka Laboratory Ltd.). For Rzjis, the charging member is randomly measured at six locations, and the average value of the values obtained at each location is defined as Rzjis of the charging member. Similarly, Rsm is measured at six locations on the charging member at random, and the average value of the values obtained at each location is taken as Rsm of the charging member.

(Electrophotographic equipment)
FIG. 8 is a schematic configuration diagram of an electrophotographic apparatus according to the present invention. The electrophotographic apparatus includes a photosensitive member 4, a charging device 5 that charges the photosensitive member 4, a latent image forming device 11 that performs exposure, a developing device 6 that develops a toner image, and a transfer device 8 that transfers to a transfer material 7. It has been. Further, a cleaning device 10 for collecting the transfer toner on the photoconductor and a fixing device 9 for fixing the toner image on the transfer material are provided.

  The photoreceptor 4 is a rotary drum type having a photosensitive layer on a conductive substrate. The photoreceptor is driven to rotate in the direction of the arrow at a predetermined peripheral speed (process speed).

  The charging device 5 includes a contact-type charging roller that is placed in contact with the photosensitive member by being pressed with a predetermined force. The charging roller is driven rotation that rotates in accordance with the rotation of the photosensitive member, and charges the photosensitive member to a predetermined potential by applying a predetermined DC voltage from a charging power source.

  For example, an exposure apparatus such as a laser beam scanner is used as the latent image forming apparatus 11 that forms an electrostatic latent image on the photosensitive member. An electrostatic latent image is formed by performing exposure corresponding to image information on a uniformly charged photoconductor.

  The developing device 6 has a contact-type developing roller disposed close to or in contact with the photoreceptor. The toner electrostatically processed to the same polarity as the photosensitive member charge polarity is developed by reversal development to visualize and develop the electrostatic latent image into a toner image.

  The transfer device 8 has a contact-type transfer roller. The toner image is transferred from the photoreceptor to a transfer material 7 such as plain paper (the transfer material is conveyed by a paper feed system having a conveyance member).

  The cleaning device 10 has a blade-type cleaning member and a collection container, and after transferring, mechanically scrapes and collects transfer residual toner remaining on the photosensitive member. Here, by adopting a development simultaneous cleaning system in which the transfer residual toner is collected by the developing device, the cleaning device can be omitted.

  The fixing device 9 is constituted by a heated roll or the like, and fixes the transferred toner image on a transfer material and discharges it outside the apparatus.

  It is also possible to use a process cartridge as shown in FIG. 9 in which the photoreceptor 4, the charging device 5, the developing device 6, the cleaning device 10, etc. are integrated and designed to be detachable from the image forming apparatus.

  That is, in the process cartridge of the present invention, the charging member is at least integrated with the member to be charged (photosensitive member) and is configured to be detachable from the main body of the electrophotographic apparatus, and the charging member is the charging member. It is.

  Furthermore, at least the electrophotographic apparatus of the present invention is an electrophotographic apparatus having a process cartridge, an exposure device, and a developing device, and the process cartridge is the process cartridge. In the electrophotographic apparatus, it is preferable to charge only the direct current voltage to the charging member to charge the member to be charged.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the technical scope of the present invention is not limited thereto.

Production Example 1 (Preparation of graphite particles 1)
Β-resin was extracted from coal tar pitch by solvent fractionation, and this was subjected to heavy treatment by hydrogenation. Subsequently, the solvent-soluble component was removed with toluene to obtain a bulk mesophase pitch. After this bulk mesophase pitch was mechanically pulverized, the temperature was increased to 270 ° C. in air at a temperature increase rate of 300 ° C./h, and an oxidation treatment was performed. During the pulverization, the average particle size was adjusted to about 7 μm. Subsequently, in a nitrogen atmosphere, the temperature was increased to 3000 ° C. at a temperature increase rate of 1500 ° C./h, and heat treatment was performed at 3000 ° C. for 15 minutes. Thereafter, classification was performed to obtain graphite particles 1 having an average particle diameter of 8.8 μm.

Production Example 2 (Production of graphite particles 2)
Graphite particles 2 having an average particle size of 4.3 μm were obtained in the same manner as in Production Example 1 except that the mechanical pulverization of the bulk mesophase pitch was performed so that the average particle size was about 4 μm.

Production Example 3 (Preparation of graphite particles 3)
Graphite particles 2 having an average particle diameter of 15 μm were obtained in the same manner as in Production Example 1 except that the mechanical pulverization of the bulk mesophase pitch was performed so that the average particle diameter was about 14 μm.

Production Example 4 (Production of graphite particles 4)
The flaky graphite “CNP35” (trade name, manufactured by Ito Graphite Industries Co., Ltd.) was pulverized so as to have an average particle size of 9.0 μm. Thereafter, classified graphite particles 4 having an average particle diameter of 8.5 μm were obtained.

Production Example 5 (Preparation of graphite particles 5)
Graphite particles 5 having an average particle size of 3.8 μm were obtained in the same manner as in Production Example 4 except that the pulverization treatment was performed so that the average particle size was about 3.0 μm.

Production Example 6 (Production of graphite particles 6)
Graphite particles 6 having an average particle diameter of 15 μm were obtained in the same manner as in Production Example 4 except that the pulverization treatment was performed so that the average particle diameter was about 14 μm.

Production Example 7 (Preparation of graphite particles 7)
The phenol resin particles having an average particle diameter of 10.0 μm were air-classified to obtain particles having a sharp distribution having an average particle diameter of 10.0 μm. The obtained particles were heat-stabilized at 300 ° C. for 1 hour in an oxidizing atmosphere, and then fired at 2200 ° C. The fired particles were further classified by wind to obtain graphite particles 3 having an average particle size of 9.0 μm.

Production Example 8 (Preparation of graphite particles 8)
Graphite particles 8 having an average particle diameter of 5.0 μm are obtained in the same manner as in Production Example 7 except that phenol resin particles having an average particle diameter of 3.0 μm are used and the air classification is performed so that the average particle diameter is about 3 μm. It was.

Production Example 9 (Preparation of graphite particles 9)
Graphite particles 9 having an average particle diameter of 5 μm were obtained in the same manner as in Production Example 7 except that phenol resin particles having an average particle diameter of 3.0 μm were used and the air classification was performed so that the average particle diameter was about 14 μm. .

Production Examples 10 to 12 (Production of Ferroelectric Particles 1 to 3)
After strontium titanate was fired at 1300 ° C., mechanical pulverization was performed. By adjusting the pulverization time, ferroelectric particles 1 (average particle size 4.5 μm), ferroelectric particles 2 (average particle size 1.5 μm), or ferroelectric particles 3 (average particle size 10. 0 μm) was obtained.

Production Examples 13 to 15 (Production of Ferroelectric Particles 4 to 6)
After calcining barium titanate at 1300 ° C., mechanical grinding was performed. By adjusting the grinding time, ferroelectric particles 4 (average particle size 4.1 μm), ferroelectric particles 5 (average particle size 2.2 μm) or ferroelectric particles 6 (average particle size 10 μm) Got.

Production Examples 16 to 18 (Production of Ferroelectric Particles 7 to 9)
After calcining calcium titanate at 1300 ° C., mechanical grinding was performed. By adjusting the grinding time, ferroelectric particles 7 (average particle size 4.3 μm), ferroelectric particles 8 (average particle size 1.9 μm) or ferroelectric particles 9 (average particle size 11 μm) Got.

Production Example 19 (Production of composite conductive fine particles)
To 7.0 kg of silica particles (average particle diameter 15 nm, volume resistivity 1.8 × 10 ¹² Ω · cm), 140 g of methyl hydrogen polysiloxane was added while operating the edge runner, and 588 N / cm (60 kg / cm ) Was mixed and stirred for 30 minutes. The stirring speed at this time was 22 rpm. Into this, 7.0 kg of carbon black particles (particle diameter 20 nm, volume resistivity 1.0 × 10 ² Ω · cm, pH 6.0) was added over 10 minutes while operating the edge runner, and further 588 N / The mixture was stirred for 60 minutes with a linear load of cm (60 kg / cm). In this way, carbon black was adhered to the surface of the methylhydrogenpolysiloxane-coated silica particles. Thereafter, drying was performed at 80 ° C. for 60 minutes using a dryer to obtain composite conductive fine particles. The stirring speed at this time was 22 rpm. The obtained composite conductive fine particles had an average particle diameter of 60 nm and a volume resistivity of 1.1 × 10 ² Ω · cm.

Production Example 20 (Production of surface-treated titanium oxide particles)
1000 g of acicular rutile-type titanium oxide particles (average particle size 15 nm, length: width = 3: 1, volume resistivity 2.3 × 10 ¹⁰ Ω · cm), surface treatment agent isobutyltrimethoxysilane 110 g, and toluene 3000 g A slurry was prepared by blending. This slurry was mixed with a stirrer for 30 minutes, and then supplied to Viscomill in which 80% of the effective internal volume was filled with glass beads having an average particle diameter of 0.8 mm, and wet crushing was performed at a temperature of 35 ± 5 ° C. Toluene was removed from the resulting slurry by distillation under reduced pressure (bath temperature: 110 ° C., product temperature: 30-60 ° C., degree of vacuum: about 100 Torr) using a kneader, and the surface treatment agent was baked at 120 ° C. for 2 hours. Went. The baked particles were cooled to room temperature and then pulverized using a pin mill to obtain surface-treated titanium oxide particles.

Production Example 21 (Production of a roller having an elastic layer)
A stainless steel rod having a diameter of 6 mm and a length of 252.5 mm was coated with a thermosetting adhesive containing 4% by mass of carbon black based on the resin content, and dried to prepare a conductive support.

On the other hand, the following components were added to 100 parts by mass of epichlorohydrin rubber (EO / EP / AGE = 73 mol% / 23 mol% / 4 mol%), and kneaded for 10 minutes in a closed mixer adjusted to 50 ° C. Was prepared.
Calcium carbonate 80 parts by weight Aliphatic polyester plasticizer 10 parts by weight Zinc stearate 1 part by weight 2-mercaptobenzimidazole (MB) (anti-aging agent) 0.5 part by weight Zinc oxide 2 parts by weight Quaternary ammonium salt 2 parts by weight Carbon black (average particle size 100 nm, volume resistivity 0.1 Ω · cm) 5 parts by mass

  To this, 0.8 parts by mass of sulfur as a vulcanizing agent, 1 part by mass of dibenzothiazyl sulfide (DM) and 0.5 parts by mass of tetramethylthiuram monosulfide (TS) as vulcanization accelerators were added, and the mixture was heated to 20 ° C. The mixture was kneaded for 10 minutes with a cooled two-roll mill to obtain an elastic layer compound.

  Along with the conductive support, the elastic layer compound was extruded by an extrusion molding machine with a crosshead and molded into a roller shape having an outer diameter of about 9 mm. Then, it baked at 160 degreeC in the electric oven for 1 hour. Cut off both ends of the rubber to make the rubber length 228 mm, then polish the surface so that it has a roller shape with an outer diameter of 8.5 mm, and form an elastic layer on the conductive support. A roller having was obtained. The crown amount of this roller (the difference between the outer diameter at the center and the outer diameter at a position 90 mm away from the center) was 120 μm.

Example 1
(Preparation of coating solution for surface layer)
Methyl isobutyl ketone was added to the caprolactone-modified acrylic polyol solution, and the following components were added to 714.3 parts by mass (100 parts by mass of acrylic polyol solids) adjusted to a solid content of 14% by mass, and urethane resin The mixed solution was prepared.
Composite conductive fine particles (produced in Production Example 19) 45 parts by mass Surface-treated titanium oxide particles (produced in Production Example 20) 20 parts by mass Modified dimethyl silicone oil (* 1) 0.08 parts by mass Blocked isocyanate mixture (* 2) 80 .14 parts by mass At this time, the blocked isocyanate mixture was such that the amount of isocyanate was “NCO / OH = 1.0”.
(* 1) Modified dimethyl silicone oil “SH28PA” (trade name, manufactured by Toray Dow Corning Silicone Co., Ltd.).
(* 2) 7: 3 mixture of each butanone oxime block of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).

  200 g of the above mixed solution was placed in a glass bottle with an internal volume of 450 mL together with 200 g of glass beads having an average particle diameter of 0.8 mm as a medium, and dispersed for 24 hours using a paint shaker disperser. Into this, 10 parts by mass of graphite particles 1 (created in Production Example 1) and 5 parts by mass of ferroelectric particles (created in Production Example 10) were added and dispersed for 5 minutes. Thereafter, the glass beads were removed by filtration to obtain a surface layer coating solution.

(Production of charging roller)
Using the surface layer coating solution, dipping coating was performed once on the elastic roller manufactured in Production Example 21. After coating, the film was air-dried at room temperature for 30 minutes or more, dried with a hot air circulating dryer at 80 ° C. for 1 hour, and further at 160 ° C. for 1 hour to form a surface layer on the elastic layer.

  The dipping application was performed with a dipping time of 9 seconds, and thereafter, the pulling was performed with an initial speed of 20 mm / s and a final speed of 2 mm / s, with the speed changing linearly with respect to time.

(Measurement of half-value width Δν ₁₅₈₀ of Raman spectrum)
With respect to the graphite particles contained in the surface layer of the obtained charging member 1, Δν was measured by the method described above. The measurement results are shown in Table 1.

(Measurement of surface roughness)
The surface roughness (Rzjis, Rsm) of the surface layer of the obtained charging member 1 was measured by the method described above. The measurement results are shown in Table 1.

(Measurement of distance L between the vertex of the ferroelectric convex portion and a plane including three vertexes of the graphite convex portion adjacent to the ferroelectric convex portion)

  According to said method, L of the produced charging member 1 was measured and the ratio (frequency) that the distance was positive was computed. The measurement results are shown in Table 1.

(Evaluation of streaky images and ghost images)
As an electrophotographic apparatus having the configuration shown in FIG. 6, a color laser jet printer “LBP5400” (trade name) manufactured by Canon Inc. was modified to a recording medium output speed of 200 mm / sec (A4 vertical output). The resolution of the image is 600 dpi, and the primary charging output is a DC voltage of −1100V. The process cartridge for the printer was used as a process cartridge having the configuration shown in FIG. 7 (for black).

  The process cartridge incorporating the charging roller 1 produced as a charging roller is mounted on the electrophotographic apparatus, and 50 single-color solid images are continuously output in a normal temperature and humidity environment (23 ° C./50% RH). One solid white image was passed. This operation was repeated 10 times to output a total of 500 single-color solid images. Through this operation, toner and external additives were forcibly adhered to the surface of the charging roller 1. Thereafter, this charging roller 1 was used for evaluation as shown below.

The primary charging was evaluated using the above charging roller 1 in a normal temperature and normal humidity environment (23 ° C./50% RH). Specifically, an endurance test was performed in which a 4% print density image (an image in which a horizontal line with a width of 2 dots and an interval of 50 dots is drawn in the direction perpendicular to the rotation direction of the photosensitive member) is printed at a process speed of 200 mm / sec. went. Then, a halftone image (an image in which a horizontal line having a width of 1 dot and an interval of 2 dots is drawn in the direction perpendicular to the rotation direction of the photosensitive member) was output for image checking after 6000 images were output. About the obtained image, the streak-like image and the ghost image were observed visually, and the following reference | standard evaluated.
A: Neither streak-like images nor ghost images were generated.
B: Although a streak-like image or a ghost image is slightly generated, there is no practical problem.
C: A streak-like image or a ghost image is clearly seen, and the image quality is deteriorated.

  As for the charging roller 1, neither a streak-shaped image nor a ghost image was generated, and a good image was obtained. The results are shown in Table 1.

Examples 2 and 3
The charging roller is the same as in Example 1 except that ferroelectric particles 4 (produced in Production Example 13) or ferroelectric particles 7 (produced in Production Example 16) are used as the ferroelectric particles. 2 or 3 was produced. The manufactured charging rollers 2 and 3 were measured for Δν, surface roughness and frequency, and streak-like images and ghost images were evaluated in the same manner as in Example 1. The results are shown in Table 1. For the charging rollers 2 and 3, neither streak-like images nor ghost images were generated, and good images were obtained.

Example 4
(Preparation of coating solution for surface layer)
The following materials were mixed to prepare a nylon resin surface layer coating solution.
N-methoxymethylated nylon 100 parts by mass Composite conductive fine particles (produced in Production Example 7) 45 parts by mass Surface-treated titanium oxide particles (produced in Production Example 8) 20 parts by mass Methanol 256 parts by mass Toluene 135 parts by mass Citric acid 2 parts by mass Part

  The above material was dispersed for 24 hours using a paint shaker disperser in the same manner as in Example 1, and 10 parts by mass of graphite particles 1 and 5 parts by mass of ferroelectric particles 1 were added thereto and dispersed for 5 minutes. . Thereafter, the glass beads were removed by filtration to obtain a surface layer coating solution.

(Production of charging roller)
Using this surface layer coating solution, the elastic roller produced in Production Example 21 was dipped once. After air-drying at room temperature for 30 minutes or more, it was dried at 150 ° C. for 1 hour with a hot-air circulating dryer to obtain a charging roller 4 having a surface layer formed on the elastic layer.

  For the obtained charging roller 4, Δν, surface roughness and frequency were measured and streak-like images and ghost images were evaluated in the same manner as in Example 1. The results are shown in Table 1.

  As for the charging roller 4 as in Example 1, neither a streak-shaped image nor a ghost image was generated, and a good image was obtained.

Examples 5 and 6
A charging roller 5 or 6 was produced in the same manner as in Example 4 except that the ferroelectric particles 4 or the ferroelectric particles 7 were used as the ferroelectric particles. The manufactured charging rollers 5 and 6 were measured for Δν, surface roughness and frequency, and streak-like images and ghost images were evaluated. The results are shown in Table 1.

  As for the charging rollers 5 and 6, neither streak-like images nor ghost images were generated, and good images were obtained.

Example 7
(Preparation of coating solution for surface layer)
An acrylic resin surface layer coating solution was prepared using the following materials.
Trifunctional acrylate monomer “SR-454” (trade name, manufactured by Nippon Kayaku Co., Ltd.)
90 parts by mass Silane coupling agent “KBM-5103” (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.)
10 parts by mass Composite conductive fine particles (produced in Production Example 19) 50 parts by mass Surface-treated titanium oxide particles (produced in Production Example 20) 30 parts by mass MIBK 488 parts by mass

  The above materials were mixed to obtain a mixed solution. This was put into a glass bottle together with glass beads having an average particle diameter of 0.8 mm as a medium, and dispersed for 60 hours using a paint shaker disperser. Into this, 10 parts by mass of graphite particles 1 and 5 parts by mass of ferroelectric particles 1 were added and dispersed for 5 minutes. Thereafter, the glass beads were removed by filtration to obtain a surface layer coating solution.

(Production of charging roller)
Using this surface layer coating solution, the elastic roller produced in Production Example 21 was applied by ring coating. After coating, air-dry at room temperature for 30 minutes or more, and then use an electron beam irradiation device (Iwasaki Electric Co., Ltd.) to irradiate an electron beam under conditions of an acceleration voltage of 150 kV, a dose of 1200 kGy and an oxygen concentration of 300 ppm or less, A charging roller 7 having a surface layer was obtained.

  For the obtained charging roller 7, Δν, surface roughness and frequency were measured and streak-like images and ghost images were evaluated in the same manner as in Example 1. The results are shown in Table 1.

  As for the charging roller 7 as in Example 1, neither streak-like images nor ghost images were generated, and a good image was obtained.

Examples 8 and 9
A charging roller 8 or 9 was produced in the same manner as in Example 7 except that the ferroelectric particles 4 or the ferroelectric particles 7 were used as the ferroelectric particles 1. The charging rollers 8 and 9 thus manufactured were measured for Δν, surface roughness and frequency, and streak-like images and ghost images were evaluated. The results are shown in Table 1.
As for the charging rollers 8 and 9, neither streak-like image nor ghost image was generated, and a good image was obtained.

Example 10
A charging roller 10 was prepared in the same manner as in Example 1 except that graphite particles 4 (prepared in Production Example 4) were used as the graphite particles, and Δν, surface roughness, and frequency were measured in the same manner as in Example 1. Measurement and evaluation of streak-like images and ghost images were performed. The results are shown in Table 1.

  As for the charging roller 10, as in Example 1, neither streak-like images nor ghost images were generated, and good images were obtained.

Examples 11-87, Comparative Example 1
Charging rollers 11 to 88 were produced in the same manner as in Example 1 except that the binder resin, graphite particles, and ferroelectric particles used for the preparation of the surface layer coating solution were changed as shown in Table 1. About the produced charging rollers 11 to 88, in the same manner as in Example 1, Δν, surface roughness and frequency were measured, and a streak-like image and a ghost image were evaluated. The results are shown in Table 1.

  As for the charging rollers 11 to 54, neither streak-like images nor ghost images were generated, and good images were obtained.

  For the charging rollers 55 to 81, no streak-like image was generated, but a little ghost image was generated. However, it was a level with no problem in practical use.

  As for the charging rollers 82 to 85, a streak-like image was slightly generated, but the level was not problematic in practical use. A ghost image was not generated and was good.

  As for the charging rollers 86 and 87, both streak-like images and ghost images are slightly generated, but they are at a level that causes no problem in practical use.

  With respect to the charging roller 88 produced in Comparative Example 1, streaky images and ghost images were conspicuous, and deterioration in image quality was recognized.

  As described above, the charging roller (charging member) of the present invention is capable of suppressing fine streak unevenness and streak-like images due to deterioration of charging performance and providing a good image. It is preferable to be incorporated in a cartridge.

It is a schematic diagram showing the state of the graphite convex part and the ferroelectric convex part of the surface layer surface of a charging member. It is a schematic diagram showing the distance of the top part of a ferroelectric convex part, and the plane containing three graphite convex parts. It is sectional drawing of the charging member (roller shape) of this invention. It is sectional drawing of the charging member (plate shape) of this invention. It is sectional drawing of the charging member (belt shape) of this invention. It is the schematic of the electrical resistance value measurement of the charging roller of this invention. It is the schematic showing the measurement location of the film thickness of a surface layer. 1 is a schematic cross-sectional view of an example of an electrophotographic apparatus of the present invention. It is a cross-sectional schematic diagram of an example of the process cartridge of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Conductive elastic layer 3 Surface layer 4 Electrophotographic photoreceptor 5 Charging device (charging roller)
6 Developing device (Developing roller)
7 Transfer material (print media, paper)
8 Transfer device (transfer roller)
9 Fixing device 10 Cleaning device (blade-type cleaning member)
11 Latent image forming device (exposure)
12 Pre-charging exposure device 13 Elastic regulation blade 14 Toner supply roller 15 Graphite particle 15a Graphite convex portion vertex 16 Ferroelectric particle 16a Ferroelectric convex portion vertex 17 Plane 18 formed by three graphite convex portions 19, 20 Power source 21 Intermediate layer 22 Second intermediate layer 30 Toner seal 32 Cylindrical metal 33 Bearing 34 Stabilizing power source 35 Ammeter L The plane formed by the apexes of the three graphite convex portions and the apex of the ferroelectric convex portions distance

Claims (5)

A charging member having a surface layer on a conductive support,
The surface layer includes binder resin, graphite particles, and ferroelectric particles selected from the group consisting of calcium titanate, barium titanate and strontium titanate,
On the surface of the charging member, convex portions derived from graphite particles (graphite convex portions) and convex portions derived from ferroelectric particles (ferroelectric convex portions) are formed.
When a plane including three vertices of the graphite convex portion adjacent to the ferroelectric convex portion is formed, the ferroelectric convex portion lower than the plane is 80% or more of the total ferroelectric convex portion. Charging member.   2. The charging member according to claim 1, wherein the surface roughness of the charging member is a ten-point average roughness Rzjis of 2 μm or more and 20 μm or less and an average interval Rsm of irregularities of 15 μm or more and 150 μm or less.   3. A process cartridge in which a charging member is at least integrated with a member to be charged and is configured to be detachable from the main body of the electrophotographic apparatus, wherein the charging member is the charging member according to claim 1 or 2. Process cartridge.   An electrophotographic apparatus comprising at least a process cartridge, an exposure apparatus, and a developing apparatus, wherein the process cartridge is the process cartridge according to claim 3.   5. The electrophotographic apparatus according to claim 4, wherein only the DC voltage is applied to the charging member to charge the member to be charged.