JP2012133008A - Charging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging roller in which even when torsion is caused in an elastic layer of the charging roller through submissive rotation with a photoreceptor, the torsion may be easily released and the charging roller may minimally slip on the photoreceptor.SOLUTION: A charging roller comprises a conductive base and an elastic layer formed on the conductive base. The elastic layer includes rubber particles dispersed therein, each rubber particle includes a hollow particle having a gas in a shell of a thermoplastic resin, and the thermoplastic resin includes at least one resin selected from the group consisting of acrylonitrile resins, methacrylonitrile resins, vinylidene chloride resins, vinyl chloride resins, styrene resins, polyurethane resins and polyamide resins.

Description

  The present invention relates to a charging member.

  In an electrophotographic apparatus, a roller-shaped charging member (hereinafter referred to as “charging roller”) is used for contact charging of a drum-shaped electrophotographic photosensitive member (hereinafter also referred to as “photosensitive body”). The charging roller is placed in contact with the electrophotographic photosensitive member by a pressing force of a spring or the like and is driven to rotate. By the way, if the charging roller has a high hardness, slippage may occur when the charging roller is driven to rotate by contact with the photosensitive member, and charging unevenness or toner or external additives may adhere to the surface of the charging roller. Therefore, a reduction in the hardness of the charging member has been studied conventionally.

  Patent Document 1 discloses a method in which an elastic layer has a domain structure (sea-island structure). The domain structure refers to a structure having two or more types of phases consisting of a continuous phase (sea phase) and a discontinuous phase (island phase). In this method, among the plurality of blended rubber phases, the conductive agent is unevenly distributed in one rubber phase. Therefore, even if the filling amount of the conductive agent is small, the electric resistance value of the semiconductive region can be obtained, and at the same time, the filling amount can be small, so that a charging member with low hardness can be obtained.

  Patent Document 2 proposes a method of forming a domain structure by pulverizing a previously crosslinked rubber composition and using the rubber particles as a domain phase. Here, since all the conductive agent can be unevenly distributed in either the sea phase or the island phase of the domain structure, a small amount of filler is added to the elastic layer, and a low hardness charging member is obtained. Is disclosed.

JP-A-11-45013 JP 2007-138034 A

  Incidentally, in general, the charging roller is brought into contact with the photosensitive member by applying a load to both end portions of the shaft core. That is, both end portions in the axial direction of the elastic layer of the charging roller are in contact with the photosensitive member with a relatively higher pressure than the central portion. Therefore, when the elastic body layer of the charging roller is flexible, the elastic body layer is twisted between both end portions and the center portion in the direction along the axis of the charging roller. In particular, when the process speed is increased, twist is accumulated in the elastic layer. When the twist is released, slippage may occur between the charging roller and the photosensitive member, and charging failure of the photosensitive member may occur. In particular, due to the improvement in process speed in recent electrophotographic apparatuses, twist accumulated in the elastic layer of the charging roller has increased, and the charging failure due to the release of the twist stabilizes high-quality electrophotographic images. It was recognized that this is a problem that should be solved in order to form a model.

  Accordingly, an object of the present invention is to provide a charging device in which even when the charging roller is driven and rotated by the photosensitive member and the elastic layer of the charging roller is twisted, the twist is easily released and slipping with the photosensitive member is unlikely to occur. To provide a roller.

  According to one aspect of the present invention, there is provided a charging roller having a conductive substrate and an elastic layer formed on the conductive substrate, the elastic layer having rubber particles dispersed therein. The rubber particles contain hollow particles enclosing a gas having a thermoplastic resin shell, and the thermoplastic resin is an acrylonitrile resin, a methacrylonitrile resin, a vinylidene chloride resin, a vinyl chloride resin, a styrene resin, a polyurethane resin, or a polyamide. A charging roller including at least one resin selected from resins is provided.

  According to the charging roller of the present invention, even when the elastic layer is twisted due to the driven rotation with the photoconductor, the twist is easily released and the slip with the photoconductor is not easily generated. For this reason, it is possible to suppress the occurrence of charging unevenness due to the slip between the charging roller and the photosensitive member. Furthermore, it is possible to suppress adhesion of toner or the like to the surface of the charging roller due to the slip. As a result, a high-quality electrophotographic image can be stably formed.

It is sectional drawing of the charging member (roller shape) which concerns on this invention. It is sectional drawing of the charging member (flat plate shape) which concerns on this invention. It is the schematic of the electrical resistance value measuring device of a charging roller. It is a schematic sectional drawing of the single layer crosshead extruder used for manufacture of a charging member and a molded object. 1 is a schematic cross-sectional view of one embodiment of an electrophotographic apparatus according to the present invention. It is a schematic sectional drawing of one Embodiment of the process cartridge which concerns on this invention. FIG. 4 is a schematic diagram illustrating a contact state between a charging roller and an electrophotographic photosensitive member according to the present invention.

<Charging member>
The charging member according to the present invention is an electrophotographic charging member having an elastic layer on a conductive substrate, and is used to charge an object to be charged. This elastic body layer contains rubber particles. The rubber particles contain hollow particles enclosing a gas having a thermoplastic resin as a shell. The thermoplastic resin includes at least one resin selected from acrylonitrile resin, methacrylonitrile resin, vinylidene chloride resin, vinyl chloride resin, styrene resin, polyurethane resin, and polyamide resin.

  The thermoplastic resin is a material having low gas permeability. The hollow particles exhibit high resilience when deformed. This is because the internal pressure of the hollow particles is increased due to the low gas permeability of the shell. The rubber particles are dispersed in the elastic body layer, and form an island phase in the elastic body layer. And since the said island phase contains said hollow particle, it will have high resilience with respect to external force.

  When the island phase is present in the elastic layer, when the elastic layer is twisted, it is considered that stress concentrates on the island phase. And the said island phase shows high resilience by containing a hollow particle as mentioned above. As a result, the twist generated in the elastic layer is easily released and is not easily accumulated. Therefore, the slip between the charging roller and the photosensitive member, which has conventionally occurred when releasing the twist generated in the elastic layer, is less likely to occur, and the occurrence of uneven charging can be suppressed.

  An example of the charging member according to the present invention is shown in FIG. 1 (roller shape) and FIG. 2 (flat plate shape). These drawings show schematic sectional views of the charging member according to the present invention. Hereinafter, the roller shape shown in FIG. 1, that is, the charging roller will be described in detail.

  FIG. 1A shows a charging roller having a conductive substrate 1 and an elastic layer 2. FIG. 1B shows a charging roller having a conductive substrate 1, an elastic layer 2, and a surface layer 3 on the elastic layer 2. The charging roller according to the present invention has a conductive substrate 1 and an elastic layer 2, the elastic layer 2 contains rubber particles 3, and the rubber particles contain hollow particles 4. The elastic body layer 2 may have a surface layer 5 thereon. The conductive substrate 1 and the elastic body layer 2 or the layers sequentially stacked (for example, the elastic body layer and the surface layer shown in FIG. 1B) may be bonded via an adhesive. In this case, the adhesive is preferably conductive. In order to make it electrically conductive, the adhesive may contain a known conductive agent.

  Examples of the binder of the adhesive include thermosetting resins and thermoplastic resins, and known ones such as urethane, acrylic, polyester, polyether, and epoxy can be used. As a conductive agent for imparting conductivity to the adhesive, it can be appropriately selected from conductive agents described in detail later, and can be used alone or in combination of two or more.

The charging roller according to the present invention usually has an electric resistance value of 1 × 10 ² Ω or more and 1 × 10 ¹⁰ Ω or less in an environment of 23 ° C. and 50% RH in order to improve the charging of the photoreceptor. It is more preferable that As an example, FIG. 3 shows a method for measuring the electrical resistance value of the charging roller 10. Both ends of the conductive substrate 1 are brought into contact with a metal cylinder 6 having the same curvature as that of the electrophotographic photosensitive member by a bearing 7 under load so as to be parallel to each other. In this state, the metal cylinder 6 is rotated by a motor, and a DC voltage of −200 V is applied from the stabilized power supply 8 while the charging roller 10 in contact with the motor is rotated. The current flowing at this time is measured by an ammeter 9 and the electric resistance value of the charging roller 10 is calculated. In the present invention, the load is 4.9 N, the metal cylinder has a diameter of 30 mm, and the rotation of the metal cylinder has a peripheral speed of 45 mm / sec.

[Conductive substrate]
The conductive substrate used in the charging member of the present invention is conductive and has a function of supporting an elastic body layer or the like provided thereon. Examples of the material include metals such as iron, copper, stainless steel, aluminum, nickel, and alloys thereof.

(Elastic body layer)
The elastic layer contains rubber particles, and the rubber particles contain hollow particles enclosing a gas having a thermoplastic resin as a shell, and the thermoplastic resin is an acrylonitrile resin, a methacrylonitrile resin, a vinylidene chloride. It contains at least one resin selected from resin, vinyl chloride resin, styrene resin, polyurethane resin, and polyamide resin.

  As a material used for the elastic layer (excluding rubber particles), a known material can be used. Examples thereof include resins, natural rubber, vulcanized products thereof, and rubbers such as synthetic rubber. As the resin, a resin such as a thermosetting resin or a thermoplastic resin can be used. Of these, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, and the like are more preferable. The following are mentioned as a synthetic rubber. Ethylene propylene diene rubber (EPDM), styrene butadiene rubber (SBR), silicone rubber, urethane rubber, isoprene rubber (IR), butyl rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), acrylic rubber and epichlorohydrin rubber. Alternatively, thermoplastic elastomers such as styrene butadiene styrene block copolymer (SBS) and styrene ethylene butylene styrene block copolymer (SEBS). These may be used alone or in combination of two or more.

  Among these, it is more preferable to use polar rubber because it is easy to adjust the electric resistance value. Among these, epichlorohydrin rubber and NBR can be mentioned. These have the advantage that resistance value control and hardness control of the elastic layer can be performed more easily. In the epichlorohydrin rubber, the polymer itself has conductivity in a medium resistance value region, and can exhibit good conductivity even if the amount of the conductive agent added is small. Moreover, since the variation in the electric resistance value depending on the position can be reduced, it is suitably used as a polymer elastic body. Examples of the epichlorohydrin rubber include the following. Epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-allyl glycidyl ether copolymer and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer. Of these, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is particularly preferably used since it exhibits stable conductivity in a medium resistance value region. The epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer can control conductivity and workability by appropriately adjusting the degree of polymerization and the composition ratio.

  The material used for the elastic layer (excluding rubber particles) may be epichlorohydrin rubber alone, but it may contain epichlorohydrin rubber as a main component and other general rubber as necessary. Other common rubbers include the following. Ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), acrylonitrile butadiene rubber (NBR), chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, urethane rubber, silicone rubber and the like. Moreover, you may contain thermoplastic elastomers, such as a styrene butadiene styrene block copolymer (SBS) and a styrene ethylene butylene styrene block copolymer (SEBS). When said general rubber | gum is contained, it is more preferable that the content is 1-50 mass parts with respect to 100 mass parts of materials of an elastic body layer.

The volume resistivity of the elastic layer is preferably 10 ² Ω · cm or more and 10 ¹⁰ Ω · cm or less as measured in an environment of 23 ° C. and 50% RH. In order to adjust the volume resistivity, a conductive agent such as carbon black, conductive metal oxide, alkali metal salt, or ammonium salt can be appropriately added. When using polar rubber as the material of the elastic layer, it is particularly preferable to use an ammonium salt.

  Moreover, in order to adjust hardness etc., you may add additives, such as softening oil and a plasticizer, to an elastic body layer. The amount of the plasticizer or the like is preferably 1 to 30 parts by mass, more preferably 3 to 20 parts by mass with respect to 100 parts by mass of the material of the elastic layer. It is more preferable to use a polymer type plasticizer. The molecular weight of the polymer plasticizer is preferably 2000 or more, more preferably 4000 or more. Furthermore, the elastic layer may appropriately contain materials that impart various functions. Examples of these include anti-aging agents and fillers.

(Rubber particles)
As a material used for the rubber particles to be contained in the elastic layer, a material having rubber elasticity can be used, and examples of the known rubber exemplified above as a material for the elastic layer (excluding the rubber particles) can be given. In order to suppress the occurrence of uneven resistance values as the charging member, the rubber particles preferably have a volume resistivity equivalent to the material of the elastic layer (excluding the rubber particles). In order to adjust the volume resistivity, a conductive agent such as carbon black, conductive metal oxide, alkali metal salt, or ammonium salt can be appropriately added. When using polar rubber as the material of the rubber particles, it is particularly preferable to use an ammonium salt.

  From the viewpoint of easy resistance adjustment and low compression set like the material of the elastic layer (excluding rubber particles), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), ethylene Rubber particles containing one rubber selected from propylene diene rubber (EPDM) and epichlorohydrin rubber can be suitably used. Furthermore, these have the advantage that resistance value control and hardness control are easier to perform. In addition, as in the case of the elastic layer (excluding rubber particles), additives such as softening oil and plasticizer may be added to the rubber particles in order to adjust the hardness and the like. The compounding amount and molecular weight of the plasticizer and the like are the same as in the case of the elastic layer (excluding rubber particles). Similarly, anti-aging agents, fillers and the like can be used.

  Methods for producing rubber particles include a method of pulverizing vulcanized rubber using a freeze pulverization method or a grinding pulverization method, a method of polymerizing from latex, and a method of vulcanizing a composition of rubber particles dispersed in rubber. Etc. Since the rubber particles of the present invention contain hollow particles, a method of pulverizing vulcanized rubber containing hollow particles can be suitably used. Specifically, the rubber, the hollow particles, and the crosslinking agent are mixed and vulcanized. The vulcanized rubber is pulverized by a known pulverization method to obtain the rubber particles of the present invention. In particular, pulverization can be improved by freeze pulverization. By sieving the rubber particles thus produced, the particle size of the rubber particles can be adjusted to a desired size. The average particle size of the rubber particles is preferably 50 μm or more and 300 μm or less, and more preferably 100 μm or more and 200 μm or less. By setting the size of the rubber particles in the elastic body layer, that is, the size of the island phase within this range, the twist applied to the charging member is suppressed to a small extent, and the effect by the island phase of releasing from a minute state is effectively achieved. realizable.

  The average particle diameter of the rubber particles in the charging member is measured by the following method. First, an arbitrary point of the elastic layer is cut out with a focused ion beam (trade name: FB-2000C, manufactured by Hitachi, Ltd.) every 20 nm over 500 μm, and a cross-sectional image is taken. A three-dimensional image is calculated by combining images obtained by photographing the same rubber particles. The projected area of the rubber particle is obtained from the three-dimensional image of the rubber particle, and the diameter of a circle having an area equal to this area is defined as the particle diameter of the rubber particle. Similarly, the particle diameter of the rubber particles is obtained from the cross-sectional projected area of another rubber particle. Such an operation is performed for 10 rubber particles in the field of view. And the same measurement is performed about 10 places of the longitudinal direction of a charging member, and let the arithmetic mean value of the total 100 diameters obtained be an average particle diameter.

  The amount of rubber particles added is preferably 10 parts by weight to 80 parts by weight, more preferably 30 parts by weight to 60 parts by weight with respect to 100 parts by weight of the sea phase rubber component in the domain structure of the elastic layer. . By setting it within this range, the twist of the individual rubber particles is suppressed to a small level, and the island phase characteristics of releasing from a very small state of twist due to high resilience are more effectively realized.

(Hollow particles)
The hollow particles in the rubber particles have a shell structure containing a gas, and the shell is made of a thermoplastic resin. As the material used for the shell of the hollow particles, a material having low gas permeability is selected for the purpose of increasing the resilience of the hollow particles. As a hollow particle shell material suitable for the purpose, a thermoplastic resin containing at least one resin selected from acrylonitrile resin, methacrylonitrile resin, vinylidene chloride resin, vinyl chloride resin, styrene resin, polyurethane resin, polyamide resin is used. Can be mentioned. In particular, a thermoplastic resin including acrylonitrile resin, methacrylonitrile resin, and vinylidene chloride resin having particularly low gas permeability is preferable.

  The average particle size of the hollow particles is preferably 1/2 or less with respect to the average particle size of the rubber particles. Specifically, the average particle diameter of the hollow particles is preferably 10 μm or more and 50 μm or less. Moreover, it is preferable that the porosity in the rubber particles formed by the hollow particles is 30% by volume or more. Here, the porosity means the ratio (%) of the volume of the hollow part contained in the unit volume of the rubber particles. As a result, it is possible to more effectively impart the properties of low hardness and high resilience to the rubber particles. The average particle diameter of the hollow particles can be measured by the same method as that for measuring the average particle diameter of the rubber particles.

  The porosity of the rubber particles derived from the hollow particles is measured by the following method. First, an arbitrary point of the elastic layer is cut out with a focused ion beam (trade name: FB-2000C, manufactured by Hitachi, Ltd.) by 20 nm over 500 μm, and a cross-sectional image is taken. A three-dimensional image is calculated by combining images obtained by photographing the same rubber particles. The volume of the rubber particles including the hollow particles is determined from the three-dimensional image of the rubber particles. Moreover, the sum total of the volume of the hollow part which exists in the same rubber particle as the particle | grains which calculated | required the volume is calculated | required. The porosity of the rubber particles is calculated from the volume of the hollow portion relative to the volume of the rubber particles including the hollow particles. Such an operation is performed for 10 rubber particles in the field of view. And the same measurement is performed about the longitudinal direction 10 places of a charging member, and the average value of a total of 100 obtained is calculated.

  As the hollow particles, particles in which the inside of the particles are bubbles may be used, or the so-called thermal expansibility that includes the inclusion substance inside the particle and expands the inclusion substance by applying heat to become a hollow particle. Microcapsules may be used. When the heat-expandable microcapsule is used in the present invention, the thermoplastic resin that becomes a shell expands due to heat during vulcanization of the unvulcanized rubber composition for rubber particles. By controlling the temperature conditions at the time of molding, the capsule can be molded while maintaining the shell structure without melting or rupturing.

  When using a thermally expandable microcapsule, the substance to be encapsulated expands as a gas at a temperature equal to or lower than the softening point of the hollow particle shell. For example, the following substances are used. Low boiling liquids such as propane, propylene, butene, normal butane, isobutane, normal pentane, and isopentane, and high boiling liquids such as normal hexane, isohexane, normal heptane, normal octane, isooctane, normal decane, and isodecane. These thermally expandable microcapsules can be produced by a known production method such as a suspension polymerization method, an interfacial polymerization method, an interfacial precipitation method, or a submerged drying method.

  In the suspension polymerization method, an oil phase to which raw material monomers are added is added to an aqueous phase containing a dispersion stabilizer, and mixed by stirring to form fine droplets of the raw material monomers, and then heated to react for polymerization. To produce thermally expandable microcapsules. Specifically, an oil phase to which a raw material monomer, the inclusion substance, a polymerization initiator, a crosslinking agent and the like are added is prepared. Next, an aqueous phase to which a dispersion stabilizer, a dispersion stabilization auxiliary agent and the like are added is prepared. These oil phase and aqueous phase are mixed to prepare a dispersion. The dispersion is stirred and mixed, pressurized, and reacted by heating to produce a reaction product. The obtained reaction product is filtered, washed with water, and then dried to obtain a desired thermally expandable microcapsule.

  The interfacial polymerization method is a method in which an emulsified dispersion prepared by mixing an aqueous phase to which an emulsifying dispersant and a hydrophilic raw material monomer are added and an oil phase to which a hydrophobic raw material monomer is added is heated to react with water. This is a method for producing a thermally expandable microcapsule by performing polymerization at the interface between the phase and the oil phase. Specifically, an aqueous phase to which a hydrophilic raw material monomer and an emulsifying dispersant are added is prepared. Next, an oil phase in which the hydrophobic raw material monomer, the inclusion substance, and the crosslinking agent are dissolved is prepared. These aqueous phase and oil phase are mixed and mixed by stirring to prepare an emulsified dispersion in which the oil phase is dispersed in the aqueous phase. By stirring and mixing the dispersion, pressurizing and heating, the polymerization proceeds at the interface between the aqueous phase and the oil phase, and a reaction product is produced. The obtained reaction product is filtered, washed with water, and then dried to obtain a desired thermally expandable microcapsule.

  The interfacial precipitation method is a production method in which a thermoplastic resin is precipitated and encapsulated using a difference in solubility between a solvent and a thermoplastic resin according to temperature, pH, solubility parameters, and the like. Specifically, first, a thermoplastic resin prepared in advance by a polymerization reaction is dissolved in a solvent containing the inclusion substance. By adding a solvent (poor solvent) having low solubility to the thermoplastic resin to the solution, particles of the thermoplastic resin are precipitated. At this time, the inclusion substance may be added in advance to the poor solvent. Alternatively, the thermoplastic resin may be dissolved in a solvent containing an inclusion substance, and then a poor solvent containing the inclusion substance may be added. Alternatively, the thermoplastic resin particles may be precipitated by heating and dissolving the thermoplastic resin in a solvent containing the inclusion substance, and then cooling. In any method, a desired thermally expandable microcapsule can be obtained by filtering, washing and drying.

  The in-liquid drying method is a production method in which a polymer is dissolved in a solvent and added to a medium containing a dispersant to prepare a dispersion, and then the solvent is removed and encapsulated. Specifically, first, a resin solution is prepared by dissolving a thermoplastic resin prepared in advance by a polymerization reaction in a solvent containing the inclusion substance. Next, the resin solution is dispersed in an aqueous medium to which a dispersant is added, and the solvent is removed by heating and decompression. Thereafter, the desired thermally expandable microcapsules can be obtained by filtration, washing and drying.

(Formation of elastic layer)
There is no restriction | limiting in particular as a formation method of an elastic body layer, What is necessary is just to use a well-known method suitably. For example, as this forming method, a known method such as mixing the above-mentioned various rubber components and other components with a ribbon blender, nauter mixer, Henschel mixer, super mixer, Banbury mixer, pressure kneader or the like is used. An unvulcanized rubber composition for the elastic layer is obtained. Furthermore, the above-mentioned rubber particles are mixed with the obtained unvulcanized rubber composition using a two-roll machine or the like.

  The preformed body can be prepared by integrally extruding the conductive substrate and the unvulcanized rubber composition using an extruder equipped with a crosshead, and the unvulcanized rubber composition containing the obtained rubber particles. it can. A crosshead is an extrusion die that is used at the tip of a cylinder of an extruder, which is used to form a coating layer for electric wires and wires. Furthermore, the obtained preform is heated and crosslinked in a high temperature atmosphere such as a hot stove to obtain a charging member.

  Alternatively, after forming an unvulcanized rubber composition containing rubber particles into a sheet shape or a tube shape formed in advance to a predetermined film thickness, it is bonded or covered to a conductive substrate to produce a charging member preform. . Next, there is a method in which the preform is placed in a cylindrical mold or split mold having a cylindrical cavity and heated to obtain a charging member having a predetermined dimension. Further, a method in which an unvulcanized rubber composition and a conductive substrate are placed in the cylindrical mold and then heat-crosslinked is also used.

  The surface of the charging member may be polished at an appropriate time. Examples of the cylindrical polishing machine that performs the polishing process include a traverse type NC cylindrical polishing machine and a plunge cut type NC cylindrical polishing machine.

(Surface layer)
The charging member of the present invention may have a configuration in which a surface layer is formed on an elastic layer. By forming the surface layer, the releasability of the charging member can be improved. As the binder used for the surface layer, a known binder resin can be employed. For example, a resin such as a thermosetting resin or a thermoplastic resin can be used. Among these, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, acrylic urethane resin, silicone resin, butyral resin, and the like are more preferable. These may be used alone or in combination of two or more. Moreover, you may use the copolymer which copolymerized the monomer which is the raw material of these resin. Among these, as the binder used for the surface layer, it is preferable to use a resin from the viewpoint that the electrophotographic photosensitive member and other members are not contaminated and the releasability is high.

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 an environment of 23 ° C. and 50% RH. If the volume resistivity of the surface layer is smaller than this, if a pinhole occurs in the electrophotographic photosensitive member, an excessive current flows through the pinhole and the applied voltage drops, and the entire length of the pinhole portion is reduced. Band-shaped image unevenness may occur. On the other hand, if the volume resistivity is too large, it is difficult for current to flow through the charging roller, and the electrophotographic photosensitive member cannot be charged to a predetermined potential, and the image may not have a desired density.

  The volume resistivity of the surface layer is determined as follows. First, the surface layer is peeled off from the roller state and cut into strips having a length of about 5 mm and a width of about 5 mm. Metal is vapor-deposited on both surfaces to produce an electrode and a guard electrode, and a measurement sample is obtained. Alternatively, it is applied on an aluminum sheet to form a surface layer coating film, and a metal for vapor deposition is deposited on the coating surface to obtain a measurement sample. A voltage of 200 V is applied to the obtained measurement sample using a microammeter (trade name: ADVANTEST R8340A ULTRA HIGH RESISTANCE METER, manufactured by Advantest). Then, the current after 30 seconds is measured and calculated from the film thickness and the electrode area.

  The volume resistivity of the surface layer can be adjusted by the conductive agent described above. The addition amount of the conductive agent added to the surface layer is 2 to 80 parts by mass, preferably 20 to 60 parts by mass with respect to 100 parts by mass of the binder.

  The surface layer can contain other particles as long as the effects of the present invention are not impaired. Examples of other particles include insulating particles. The insulating particles may be used singly or in combination of two or more, and may be those subjected to surface treatment, modification, introduction of functional groups or molecular chains, coating, and the like. In order to improve the dispersibility of the particles, the particles are more preferably subjected to a surface treatment.

  The surface layer may further contain a release agent in order to improve the releasability. By including a release agent in the surface layer, it is possible to prevent dirt from adhering to the surface of the charging member and improve the durability of the charging member. When the release agent is a liquid, it also acts as a leveling agent when forming the surface layer.

  The surface layer 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. The film thickness of the surface layer can be measured by cutting the charging member cross section with a sharp blade and observing with an optical microscope or an electron microscope.

  The surface layer may be 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.

(Formation of surface layer)
The surface layer can be formed by a coating method such as electrostatic spray coating, dipping coating or ring coating. Or it can also form by adhere | attaching or coat | covering the sheet-shaped or tube-shaped layer beforehand formed into 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 a paint by a coating method to form a coating film.

  When the layer is formed by a coating method, the solvent used in the coating solution may be any solvent that can dissolve the binder. Specific examples include the following. 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.

  As a method for dispersing the binder, the conductive agent, the insulating 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.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. Production Examples 1 to 7 are production examples of thermally expandable microcapsules 1 to 7 used as hollow particles. Production Examples 8 to 11 are production examples of rubber particles 1 to 4. Production Examples 12 to 15 are production examples of the unvulcanized rubber compositions 1 to 4. Production Examples 16 to 18 are production examples of the surface layer coating solutions 1 to 3. Production Examples 19 to 24 are production examples of thermally expandable microcapsules 8 to 13 used as hollow particles. Production Examples 25 to 80 are production examples of rubber particles 5 to 60.

[Production Example 1] Preparation of thermally expandable microcapsule 1 To a reaction vessel, 8000 parts by mass of ion-exchanged water, 9 parts by mass of colloidal silica and 0.3 parts by mass of polyvinylpyrrolidone as a dispersion stabilizer were added, and an aqueous dispersion medium was prepared. Prepared. Next, an oily material comprising 200 parts by mass of acrylonitrile as a raw material monomer, 25 parts by mass of normal hexane as an inclusion substance, 1.5 parts by mass of dicumyl peroxide as a polymerization initiator, and 1.0 part by mass of methyl methacrylate as a crosslinking substance. A mixture was prepared. This liquid was added to the water-soluble dispersion medium, and 0.8 parts by mass of sodium hydroxide was further added to obtain a dispersion.

  The resulting dispersion was stirred and mixed using a homogenizer, charged into a nitrogen-substituted reaction vessel, pressurized, and reacted at 60 ° C. for 20 hours to obtain a reaction product. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules. This was classified into a thermally expandable microcapsule 1 having a volume average particle diameter of 12 μm.

[Production Example 2] Production of thermally expandable microcapsules 2 Thermally expandable microcapsules 2 having a volume average particle diameter of 12 µm were obtained in the same manner as in Production Example 1 except that the raw material monomer was methacrylonitrile.

[Production Example 3] Production of thermally expandable microcapsules 3 Thermally expandable microcapsules 3 having a volume average particle diameter of 12 μm were obtained in the same manner as in Production Example 1, except that the raw material monomer was vinylidene chloride.

[Production Example 4] Production of thermally expandable microcapsules 4 Thermally expandable microcapsules 4 having a volume average particle size of 12 µm were obtained in the same manner as in Production Example 1 except that the raw material monomer was styrene.

[Production Example 5] Production of thermally expandable microcapsule 5 In a reaction vessel, 10 parts by mass of an emulsifier was dissolved in 800 parts by mass of ion-exchanged water to prepare an aqueous dispersion medium. Subsequently, an oily mixed solution composed of 80 parts by mass of hexamethylenediamine, 15 parts by mass of diethylenetriamine, 100 parts by mass of isobutane, 100 parts by mass of isophthalic acid chloride, and 120 parts by mass of methyl ethyl ketone (MEK) was prepared. This liquid was added to the water-soluble dispersion medium to prepare a dispersion. The obtained dispersion was stirred and mixed using a homogenizer and reacted at 60 ° C. for 10 hours to obtain a reaction product. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules. This was classified to obtain thermally expandable microcapsules 5 having a volume average particle diameter of 12 μm.

[Production Example 6] Production of thermally expandable microcapsule 6 In a reaction vessel, 2 parts of sodium dodecylbenzenesulfonate was added to 400 parts by mass of ion-exchanged water to prepare a water-soluble dispersion medium. Next, an oily mixed liquid comprising 100 parts by mass of vinyl chloride, 200 parts by mass of isopentane, 100 parts by mass of n-butyl acrylate, 2 parts by mass of trimethylolpropane triacrylate, and 2 parts by mass of 2,2-azobisisobutyronitrile is prepared. did. This liquid was added to the water-soluble dispersion medium to prepare a dispersion. The obtained dispersion was stirred and mixed using a homogenizer, charged into a reaction vessel purged with nitrogen, and reacted at 80 ° C. for 30 minutes to obtain a reactive organism. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules. This was classified to obtain thermally expandable microcapsules 6 having a volume average particle diameter of 12 μm.

[Production Example 7] Production of thermally expandable microcapsule 7 To 325 parts by mass of polyethylene terephthalate, 500 parts by mass of toluene was added, and further 70 parts by mass of isophorone diisocyanate (IPDI) was added, and the mixture was refluxed at 120 ° C for 5 hours. After performing the reaction, it was cooled to room temperature. Next, 13 parts by mass of hexamethylene diamine and 10 parts by mass of diethylenetriamine were added and reacted at 60 ° C. for 5 hours, and then toluene was distilled off under reduced pressure. A polyurethane having hydroxyl groups at both ends and urethane and urea bonds. A resin was obtained. 200 parts by mass of the obtained resin, 6 parts by mass of yellow iron oxide, 30 parts by mass of normal hexane, and 185 parts by mass of ethyl acetate were mixed, and 1000 parts by mass of a 0.5% aqueous polyvinyl alcohol solution prepared in advance at room temperature for 5 hours. The mixture was stirred and dispersed while dropping to obtain an aqueous dispersion of thermally expandable microcapsules. The obtained aqueous dispersion of thermally expandable microcapsules was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules. This was classified to obtain thermally expandable microcapsules 7 having a volume average particle diameter of 12 μm.

[Production Example 8] Production of rubber particles 1 The following four components were added to 100 parts by mass of acrylonitrile butadiene rubber (NBR) (trade name: N230SV, manufactured by JSR), and the mixture was adjusted to 50 ° C with a sealed mixer 15 Kneaded for a minute.
Carbon black (trade name: Toka Black # 7360SB, manufactured by Tokai Carbon Co., Ltd.): 48 parts by mass
-Zinc stearate (trade name: SZ-2000, manufactured by Sakai Chemical Industry Co., Ltd.): 1 part by mass,
-Zinc oxide (trade name: Zinc Hana 2 types, manufactured by Sakai Chemical Industry Co., Ltd.): 5 parts by mass
Calcium carbonate (trade name: Silver W, manufactured by Shiroishi Kogyo Co.): 20 parts by mass.

  To this, 13 parts by mass of the thermally expandable microcapsule 1, 1.2 parts by mass of sulfur as a vulcanizing agent, and tetrabenzyl thiuram disulfide (TBzTD) (trade name: Parkasit TBzTD, manufactured by Flexis) as a vulcanization accelerator. 5 parts by mass was added and kneaded for 10 minutes in a two-roll machine cooled to 25 ° C. to obtain an unvulcanized rubber composition. This unvulcanized rubber composition was vulcanized in a 160 ° C. mold and then vulcanized in an oven at 160 ° C. The vulcanized rubber was cut into 2 mm squares, frozen, pulverized with a mill, and classified to obtain rubber particles 1 having an average particle diameter of 150 μm. In the vulcanization stage, the thermally expandable microcapsule expanded to form hollow particles, which were present in the rubber particles 1.

[Production Example 9] Production of rubber particles 2 Epichlorohydrin rubber (EO-EP-AGE ternary co-compound) (trade name: Epion ON301, manufactured by Daiso Corporation) The mixture was kneaded for 10 minutes with a controlled closed mixer.
Calcium carbonate (trade name: Nanox # 30, manufactured by Maruo Calcium Co.): 60 parts by mass
Aliphatic polyester plasticizer (trade name: Polycizer P-202, manufactured by Dainippon Ink & Chemicals, Inc.): 10 parts by mass
-Zinc stearate (similar to Production Example 8): 1 part by mass,
2-mercaptobenzimidazole (trade name: NOCRACK NS-5, manufactured by Ouchi Shinsei Chemical Co., Ltd.): 0.5 parts by mass,
-Zinc oxide (similar to Production Example 8): 2 parts by mass,
-Quaternary ammonium salt (trade name: Adeka Sizer LV70, manufactured by Asahi Denka Kogyo Co., Ltd.): 2 parts by mass,
Carbon black (trade name: Seast GSO, manufactured by Tokai Carbon Co., Ltd.): 5 parts by mass.

  To this, 1 part by mass of thermally expandable microcapsule 3, 0.8 parts by mass of sulfur as a vulcanizing agent, dibenzothiazyl sulfide (DM) as a vulcanization accelerator (trade name: Noxeller DM, Ouchi Shinsei Chemical Industry Co., Ltd.) 1 part by mass, tetramethylthiuram monosulfide (TS) (trade name: Noxeller TS, manufactured by Ouchi Shinsei Chemical Co., Ltd.) 0.5 part by mass, and 10 rolls at 25 ° C. Kneading for a minute gave an unvulcanized rubber composition. Using this unvulcanized rubber composition, rubber particles 2 having an average particle diameter of 50 μm were produced in the same manner as in Production Example 8.

[Production Example 10] Production of rubber particles 3 The following 6 components were added to 100 parts by mass of styrene butadiene rubber (SBR) (trade name: SBR1500, manufactured by JSR), and the mixture was adjusted to 80 ° C with a sealed mixer 15 Kneaded for a minute.
-Zinc oxide (similar to Production Example 8): 5 parts by mass,
・ Stearic acid sub-oxide (as in Production Example 8): 2 parts by mass,
Carbon black (trade name: Ketjen Black EC600JD, manufactured by Lion): 8 parts by mass
Carbon black (trade name: Seast S, manufactured by Tokai Carbon Co.): 40 parts by mass
Calcium carbonate (similar to Production Example 8): 15 parts by mass
Paraffin oil (trade name: PW380, manufactured by Idemitsu Kosan Co., Ltd.): 20 parts by mass.

  To this, 5 parts by mass of thermally expandable microcapsules 1, 1 part by mass of sulfur as a vulcanizing agent, 1 part by mass of dibenzothiazyl sulfide (DM) (as in Production Example 9), tetramethylthiuram mono 1 part by mass of sulfide (TS) (similar to Production Example 9) was added and kneaded for 10 minutes in a two-roll mill cooled to 25 ° C. to obtain an unvulcanized rubber composition. Using this unvulcanized rubber composition, rubber particles 3 having an average particle diameter of 150 μm were produced in the same manner as in Production Example 8.

[Production Example 11] Preparation of rubber particles 4 Sealed type in which ethylene propylene diene rubber (EPDM) (trade name: Esprene EPDM505A, manufactured by Sumitomo Chemical Co., Ltd.) was added to the following 6 components and adjusted to 80 ° C. It knead | mixed for 15 minutes with the mixer.
Zinc oxide (similar to Production Example 8): 5 parts by mass Zinc stearate (similar to Production Example 8): 2 parts by mass
Carbon black (trade name: Ketjen Black EC600JD, manufactured by Lion): 8 parts by mass
Carbon black (trade name: Seast S, manufactured by Tokai Carbon Co.): 30 parts by mass
Calcium carbonate (similar to Production Example 8): 15 parts by mass
Paraffin oil (same as Production Example 10): 20 parts by mass.

  To this, 1 part by mass of the thermally expandable microcapsule 3, 1 part by mass of sulfur as a vulcanizing agent, 1 part by mass of dibenzothiazyl sulfide (DM) (as in Production Example 9), tetramethylthiuram mono 1 part by mass of sulfide (TS) (similar to Production Example 9) was added and kneaded for 10 minutes in a two-roll mill cooled to 25 ° C. to obtain an unvulcanized rubber composition. Using this unvulcanized rubber composition, rubber particles 4 having an average particle size of 100 μm were produced in the same manner as in Production Example 8.

[Production Example 12] Preparation of unvulcanized rubber composition 1 using NBR In Production Example 8, instead of thermally expandable microcapsules, 50 parts by weight of rubber particles 1 were added to 100 parts by weight of NBR. Except for this, an unvulcanized rubber composition 1 was produced in the same manner as in Production Example 8.

[Production Example 13] Production of unvulcanized rubber composition 2 using epichlorohydrin rubber In Production Example 9, 50 parts by mass of rubber particles 1 were added to 100 parts by mass of epichlorohydrin rubber instead of the thermally expandable microcapsules. An unvulcanized rubber composition 2 was produced in the same manner as in Production Example 9 except that the product was used.

[Production Example 14] Production of unvulcanized rubber composition 3 using SBR In Production Example 10, instead of thermally expandable microcapsules, 50 parts by mass of rubber particles 1 were added to 100 parts by mass of SBR Except that, an unvulcanized rubber composition was prepared in the same manner as in Production Example 10.

[Production Example 15] Production of unvulcanized rubber composition 4 using EPDM In Production Example 11, instead of thermally expandable microcapsules, 50 parts by weight of rubber particles 1 were added to 100 parts by weight of EPDM. Except that, an unvulcanized rubber composition 4 was produced in the same manner as in Production Example 11.

[Production Example 16] Preparation of surface layer coating solution 1 Methyl isobutyl ketone (MIBK) was added to a caprolactone-modified acrylic polyol solution (trade name: Plaxel DC2016, manufactured by Daicel Chemical Industries) so that the solid content was 17% by mass. It was adjusted. The following three components were added to 588.24 parts by mass of this solution (100 parts by mass of acrylic polyol solid content) to prepare a mixed solution.
Carbon black (trade name: # 52, manufactured by Mitsubishi Chemical Corporation): 45 parts by mass
Modified dimethyl silicone oil (trade name: SH28PA, manufactured by Toray Dow Corning Silicone): 0.08 parts by mass,
Block isocyanate mixture (7: 3 mixture of each butanone oxime block body of HDI (trade name: Duranate TPA-B80E, manufactured by Asahi Kasei Kogyo) and IPDI (trade name: Bestanat B1370, manufactured by Degussa Huls)): 80. 14 parts by weight.
At this time, the blocked isocyanate mixture was such that the amount of isocyanate was “NCO / OH = 1.0”.

  200 g of the above mixed solution is put 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 28 hours using a paint shaker disperser to remove the glass beads and apply for the surface layer. Liquid 1 was obtained.

[Production Example 17] Preparation of surface layer coating solution 2
The following 4 components were added to 100 parts by mass of N-methoxymethylated nylon to prepare a mixed solution.
Carbon black (trade name: # 52, manufactured by Mitsubishi Chemical Corporation): 45 parts by mass
-Methanol: 256 parts by mass,
-Toluene: 135 parts by mass
Citric acid: 2 parts by mass
The mixed solution was dispersed in the same manner as in Production Example 16 for 24 hours using a paint shaker disperser. Thereafter, the glass beads were removed to obtain a surface layer coating solution 2.

[Production Example 18] Preparation of surface layer coating solution 3 Surface layer coating solution 3 was obtained by mixing the following four components.
Trifunctional acrylate monomer (trade name: SR-454, manufactured by Nippon Kayaku Co., Ltd.): 90 parts by mass
Silane coupling agent (trade name: KBM-5103, manufactured by Shin-Etsu Chemical Co., Ltd.): 10 parts by mass
Carbon black (trade name: # 52, manufactured by Mitsubishi Chemical Corporation): 50 parts by mass
MIBK: 488 parts by mass.

[Production Examples 19 to 24] Production of thermally expandable microcapsules 8 to 13 By classifying the thermally expandable microcapsules produced in each of Production Examples 1 to 6, thermally expandable microcapsules 8 having an average particle size of 8 μm are classified. ~ 13 were made.

[Production Examples 25-80] Production of rubber particles 5-60 The type (number) and amount of thermally expandable microcapsules are as shown in Table 1, and other production conditions are any of Production Examples 8-11. As a condition, rubber particles 5 to 60 were prepared. After each rubber particle was prepared, it was pulverized and classified to obtain rubber particles having an average particle size shown in Table 1.

[Example 1]
A thermosetting adhesive (trade name: METALOC U-20, manufactured by Toyo Chemical Laboratory Co., Ltd.) is applied to a stainless steel rod having a diameter of 6 mm and a length of 258 mm, and left in a hot air oven at 180 ° C. for 30 minutes. Thus, a conductive substrate was obtained. Subsequently, the unvulcanized rubber composition 1 obtained in Production Example 12 was coated coaxially and cylindrically with the conductive substrate as the central axis using an extrusion molding apparatus having a crosshead shown in FIG. Thus, a charging member preform was obtained in which the outer diameter of the layer of the unvulcanized rubber composition was 12.5 mm. This molded body was heated and vulcanized at 160 ° C. for 1 hour in a hot air furnace to form an elastic layer on the outer periphery of the conductive substrate. The end of this elastic layer was removed to obtain a charging roller having an elastic layer with a length of 224.2 mm. Next, the outer peripheral surface of the elastic body layer is polished using a plunge cut type cylindrical polishing machine to adjust the outer diameter of the elastic body layer to 12 mm, and the elastic body layer has an outer diameter of 12 mm and a length of 224.2 mm. A charging roller 1 having the following characteristics was obtained.

  The type of rubber component of the elastic layer (rubber removal particles), the number of the thermally expandable microcapsule, the material of the shell, the production conditions of the unvulcanized rubber composition, the type of rubber particles ( No.) and the amount of rubber particles used in the production of the unvulcanized rubber composition are shown in Table 2. With respect to the charging roller 1, the average particle diameter of rubber particles, the average particle diameter of hollow particles, and the porosity of rubber particles were measured by the methods described above. The results are shown in Table 2.

[Evaluation of durability]
A color laser printer (trade name: HP Color LaserJet 4700dn, manufactured by Hewlett-Packard Company), which is an electrophotographic apparatus having the configuration shown in FIG. 5, is modified and used to output a recording medium at 220 mm / sec (A4 vertical output). did. The primary charging output is a DC voltage (Vdc) of −1100V. The resolution of the image is 600 dpi. The charging roller was removed from the process cartridge of the electrophotographic apparatus, and the charging roller 1 was set. Further, as shown in FIG. 7, the charging roller 1 was brought into contact with the photosensitive member by a pressing force of a spring of 4.9 N at one end and a total of 9.8 N at both ends.

The process cartridge on which the charging roller 1 was set was left in a 15 ° C., 0% RH environment (environment 1), 23 ° C., 50% RH environment (environment 2), and 30 ° C., 80% RH environment (environment 3) for 24 hours. Later, durability performance was evaluated in each environment. Specifically, a two-sheet intermittent endurance performance test of a 1% print density image at a process speed of 220 mm / sec (endurance performance evaluation by stopping the rotation of the printer for 3 seconds for every two sheets) was performed. A halftone image (an image that draws a horizontal line with a width of 1 dot and an interval of 2 dots in the direction perpendicular to the rotation direction of the photoconductor) is output in the middle (at the end of 12,000 sheets, at the end of 24000 sheets, and at the end of 36000 sheets). ,evaluated. In the evaluation, the obtained halftone image was visually observed, and the fine streak-like image, the point-like image and the rust-like image generated due to the above-described contamination on the surface of the charging roller were determined according to the following criteria.
Rank 1: No streak-like image, potty-like image, or rough image is generated.
Rank 2: Only a slight streak-like image, a point-like image, or a rough image is recognized.
Rank 3: A streak-like image, a point-like image, and a rough image can be confirmed in part with the pitch of the charging roller, but there is no practical problem.
Rank 4: streak-like images, potty-like images, and fuzzy images are conspicuous, and deterioration in image quality is observed.

  In the charging roller 1 of the present embodiment, rank 1 was obtained, and no streak-like image, potty-like image, or rough image was generated, and a good image was obtained. The evaluation results are shown in Tables 2 and 4.

Examples 2 to 65, 69 and 70
The types (numbers) of the rubber particles, the production conditions of the unvulcanized rubber composition, and the number of added rubber particles at that time were the conditions shown in Table 2 or Table 3. The charging rollers 2 to 65, 69, and 70 were produced in the same manner as in Example 1 except for these conditions. About each obtained charging roller, the average particle diameter of rubber particles and hollow particles and the porosity of rubber particles were measured by the same method as in Example 1, and the durability performance was evaluated by the same method as in Example 1. . The evaluation results are shown in Tables 2 to 5.

Example 66
The surface layer coating solution 1 produced in Production Example 16 was dipped on the charging roller produced in the same manner as in Example 65. After coating, the film was air-dried at room temperature for 30 minutes or more, and then dried with a hot air circulating dryer at 80 ° C. for 1 hour and further at 160 ° C. for 1 hour to obtain a charging roller 66 having a surface layer formed on the elastic layer. The dipping coating conditions are as follows. The dipping time was 9 seconds, the pulling speed was an initial speed of 20 mm / s, a final speed of 2 mm / s, and the speed was changed linearly with respect to the time. The evaluation results are shown in Tables 3 and 5.

Example 67
A charging roller 67 was obtained in the same manner as in Example 66 except that the surface layer coating solution 2 produced in Production Example 17 was used. It shows in Table 3 and Table 5.

Example 68
The surface layer coating solution 3 produced in Production Example 18 was ring-coated on the charging roller produced in the same manner as in Example 65. 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 the 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 68 having a surface layer was obtained. The evaluation results are shown in Tables 3 and 5.

[Comparative Example 1]
In Example 1, NBR was isoprene rubber (IR) (trade name: IR2200L, manufactured by Nippon Zeon Co., Ltd.) as the raw rubber in Production Example 8, and rubber particles 61 were prepared without adding thermally expandable microcapsules. A charging roller 71 was produced in the same manner as in Example 1 except that rubber particles 61 were used, NBR was IR as the raw rubber in Production Example 12, and an unvulcanized rubber composition was produced. The evaluation results are shown in Tables 3 and 5.

[Comparative Example 2]
A charging roller 72 was produced in the same manner as in Comparative Example 1 except that rubber particles 62 prepared by adding silicone rubber hollow particles having an average particle diameter of 20 μm were used instead of the thermally expandable microcapsules in Production Example 8. . The evaluation results are shown in Tables 3 and 5.

[Comparative Example 3]
Fluororubber (trade name: Daiel G-755L, polyol vulcanized binary system, manufactured by Daikin Industries, Ltd.) is added to the following three components, and kneaded for 15 minutes in a two-roll mill cooled to 30 ° C. Thus, an unvulcanized rubber composition was obtained.
MT carbon black (trade name: Thermax N-990, manufactured by CANCARB Ltd): 10 parts by mass,
Magnesium oxide (trade name: Kyowa Mag MA-150, manufactured by Kyowa Chemical Industry Co., Ltd.): 3 parts by mass
Calcium hydroxide (trade name: CALDIC-2000, manufactured by Omi Chemical Co., Ltd.): 6 parts by mass.

  This unvulcanized rubber composition was vulcanized in a mold at 160 ° C. and then vulcanized in an oven at 170 ° C. This vulcanized rubber was cut into 2 mm squares, frozen, pulverized with a mill, and classified to obtain fluororubber rubber particles 63 having an average particle diameter of 150 μm. Except for adding 50 parts by mass of the rubber particles 63 to 100 parts by mass of the fluororubber, an unvulcanized rubber composition of fluororubber was obtained in the same manner as the rubber particle preparation method using the fluororubber.

  A primer (trade name: FC5150, manufactured by Sumitomo 3M) was applied to a stainless steel rod having a diameter of 6 mm and a length of 252.5 mm, and the dried product was used as a conductive substrate. Together with this conductive substrate, the unvulcanized rubber composition was extruded with an extruder with a crosshead and molded into a roller shape with an outer diameter of about 12.5 mm to prepare a charging roller preform. This molded body was heated in a hot air oven at 160 ° C. for 1 hour and vulcanized to form an elastic layer on the outer periphery of the conductive substrate. The end of the elastic layer was removed to obtain a charging roller having an elastic layer having a length of 224.2 mm. Next, the outer peripheral surface of the elastic layer was polished in the same manner as in Example 1 to obtain a charging roller 73 having an elastic layer with an outer diameter of 12 mm and a length of 224.2 mm. The evaluation results are shown in Tables 3 and 5.

[Comparative Example 4]
In Comparative Example 3, when producing an unvulcanized rubber composition used for producing rubber particles, rubber particles 64 produced by adding 13 parts by mass of silicone rubber hollow particles having an average particle diameter of 20 μm to 100 parts by mass of fluororubber. A charging roller 74 was produced in the same manner as in Comparative Example 3 except that was used. The evaluation results are shown in Tables 3 and 5.

DESCRIPTION OF SYMBOLS 1 ... Conductive base | substrate 2 ... Elastic body layer 3 ... Rubber particle 4 ... Hollow particle 5 ... Surface layer 6 ... Metal cylinder 7 ... Bearing 8, 25, 26, 27 ... Power supply 9 ... Ammeter 10 ... charging roller 11 ... extruder 12 ... charging member preform 13 ... crosshead 14 ... feed roll 15 ... electrophotographic photosensitive member 16 ... developing roller 17 ... printing media 18 ... Transfer roller 19 Fixing unit 20 Cleaning blade 21 Latent image forming device (exposure device)
22... Pre-charge exposure device 23... Elastic regulation blade 24 .. Toner supply roller 28.

Claims (2)

  A charging roller having a conductive substrate and an elastic layer formed on the conductive substrate, wherein the elastic layer has rubber particles dispersed therein, and the rubber particles are made of thermoplastic resin. It contains hollow particles enclosing a shell gas, and the thermoplastic resin is at least one resin selected from acrylonitrile resin, methacrylonitrile resin, vinylidene chloride resin, vinyl chloride resin, styrene resin, polyurethane resin and polyamide resin. A charging roller comprising:   The charging roller according to claim 1, wherein the rubber particles include one rubber selected from acrylonitrile butadiene rubber, styrene butadiene rubber, ethylene propylene diene rubber, and epichlorohydrin rubber.

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