JP2019219498A - Conductive roller - Google Patents

Abstract

To provide a conductive roller capable of suppressing image irregularity.SOLUTION: A conductive roller is provided, comprising a core material, a rubber base material disposed to surround the core material, and a surface layer disposed to surround the rubber base material. The surface layer contains a conductive matrix and a plurality of insulative particles dispersed in the conductive matrix. The particles include large particles, and small particles that are smaller than the large particles.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a conductive roll used for a charging roll of an image forming apparatus.

  The image quality of an image forming apparatus such as an electrophotographic copying machine depends on the uniformity of the charged state of the photoconductor, and the surface roughness of the charging roll affects the uniformity of the charged state. Conventionally, Patent Literatures 1 to 3 are known as techniques that refer to the surface roughness of a charging roll.

Patent Literature 1 discloses a charging member including a conductive support, a conductive elastic layer laminated on the conductive support, and a conductive resin layer laminated as an outermost layer on the conductive elastic layer. (Charging roll) is described. The conductive resin layer contains a matrix material and at least one kind of particles selected from the group consisting of resin particles and inorganic particles, the particles contain the first particles, and the matrix material alone in the conductive resin layer is formed. a [[mu] m] of a layer thickness of a portion that, when the average particle diameter of the particles B1 [[mu] m], and the distance between particles of the particles was _{S m} [μm], a is 10μm~7.0μm, B1 / a is 5.0~30.0, _{S m} is 50μm~400μm.

Patent Document 2 discloses a positively charged single-layer type electrophotographic photoreceptor, a charging device having a contact charging member for charging the surface of the photoreceptor, and exposing the surface of the charged image carrier to form an image bearing member. An exposure device for forming an electrostatic latent image on the surface of a body, a developing device for developing the electrostatic latent image as a toner image, and a transfer device for transferring a toner image from an image carrier to a transfer target There is described a technology relating to an image forming apparatus having the following. The contact charging member is a charging roller made of conductive rubber having a rubber hardness of 62 ° to 81 ° in Asker-C hardness. The roller surface roughness of the charging roller of the contact charging member is such that the average spacing S _{m of the} irregularities is obtained. in a 55Myuemu～130myuemu, and a 9μm~19μm a ten-point average roughness _{R Z.}

  Patent Document 3 discloses a charging roller including a conductive support, a semiconductive elastic layer formed in a roll shape on the conductive support, and a protective layer formed on the surface of the semiconductive elastic layer. Technology is described. The protective layer is formed by applying a coating liquid for forming a protective layer containing fine particles exhibiting a function of preventing external substances from adhering to the protective layer, and the volume average particle diameter of the fine particles is determined by the surface of the protective layer. It is miniaturized so that the roughness is 1 μm or less.

  According to Patent Documents 1 to 3, the surface roughness of the outermost surface of the charging roll is adjusted by the fine particles contained in the surface layer, so that the discharge between the charging roll and the photoconductor is made as uniform as possible, and the image quality is improved. Try to let it.

JP-A-2005-121770 JP 2012-14141 A JP 2005-91414 A

  There is an increasing demand for high image quality for image forming apparatuses.

  An object of the present invention is to provide a conductive roll capable of reducing image unevenness.

  In order to solve the above problem, a conductive roll according to one embodiment of the present invention includes a core material, a rubber substrate disposed around the core material, and a surface layer disposed around the rubber substrate. Comprising, the surface layer comprises a conductive matrix, and a plurality of insulating particles dispersed in the conductive matrix, the particles have a plurality of large particles, a size smaller than the large particles It has a plurality of small particles.

  According to the present invention, since the insulating particles having a plurality of large particles and a plurality of small particles are dispersed in the conductive matrix of the surface layer, the discharge from the surface layer of the conductive roll is uniform, and the image unevenness is reduced. It is thought that it can be done.

1 is a schematic diagram illustrating an example of an image forming apparatus using a charging roll according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view illustrating an example of a charging roll according to the embodiment of the present invention. It is sectional drawing of the rubber base material and the surface layer cut | disconnected along the axial direction of the charging roll which concerns on embodiment. It is sectional drawing of the rubber base material and the surface layer cut | disconnected along the axial direction of the charging roll which concerns on a comparative example.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Hereinafter, a charging roll will be described as an example of the conductive roll. In the drawings, the scale does not necessarily accurately represent the product or the sample of the embodiment, and some dimensions may be exaggerated.

  As shown in FIG. 1, the image forming apparatus according to the embodiment of the present invention includes a photoconductor 1. Around the photoconductor 1, a developing unit 2, an exposing unit 3, a charging unit 4, a transfer unit 6, and a cleaning unit 5 are arranged. The developing unit 2 is provided with a developing roll 20, a regulating blade 21, and a supply roll 22, and is filled with toner 23. The charging unit 4 is provided with a charging roll 40. The transfer unit 6 transfers the toner image to a paper sheet 60 as a recording medium. The toner image transferred by the transfer unit 6 is fixed by a fixing unit (not shown).

  The cylindrical and rotating photoreceptor 1 is in contact with the cylindrical and rotating charging roll 40 at the nip 50. In the gap region 51 before the nip 50 in the rotation direction of the photoconductor 1 and the charging roll 40 (in some cases, the gap region 52 after the nip 50 in addition to the front gap region 51), the photoconductor 1 and the charging roll 40 A discharge occurs between the two, and the surface of the photoconductor 1 is charged. It is preferable that the charged state of the surface of the photoconductor 1 is uniform in the circumferential direction and the axial direction of the photoconductor 1.

FIG. 2 is a cross-sectional view illustrating an example of the charging roll according to the embodiment of the present invention.
As shown in FIG. 2, the charging roll 40 has a core material 401, a rubber base 402 formed on the outer peripheral surface of the core 401, and a surface layer 403 coated on the outer peripheral surface of the rubber base 402. A surface layer 403 made of a coating component is formed on the outer peripheral surface of the rubber base material 402, and the surface roughness of the surface layer 403 and the components of the surface layer 403 are appropriately adjusted, so that the discharge unevenness between the photoconductor 1 and the charging roll 40 is eliminated. As a result, it is possible to uniformly discharge the photoconductor 1, and the developing unit 2 can adhere the amount of toner that exactly corresponds to the latent image formed by the exposure unit 3 to the surface of the photoconductor 1.

<Core material>
The core material 401 can be formed of, but not limited to, a metal or a resin material having excellent thermal conductivity and mechanical strength, such as a SUS alloy, nickel (Ni), a nickel alloy, and iron (Fe). ), Magnetic stainless steel, metal materials such as cobalt-nickel (Co-Ni) alloys, and resin materials such as PI (polyimide resin). The structure of the core material 401 is not particularly limited, and may be hollow or not hollow.

<Rubber substrate>
The rubber base 402 is disposed on the outer peripheral surface of the core 401 and is made of conductive rubber having conductivity. The rubber base 402 may have one layer or two or more layers. Further, an adhesive layer, an adjustment layer, and the like may be provided between the core material 401 and the rubber substrate 402 as necessary.

  The rubber substrate 402 can be formed by molding a rubber composition obtained by adding a conductivity-imparting material, a crosslinking agent, and the like to a conductive rubber, around the core material 401. Examples of the conductive rubber include polyurethane rubber (PUR), epichlorohydrin rubber (ECO), nitrile rubber (NBR), styrene rubber (SBR), and chloroprene rubber (CR).

As the conductivity imparting material, an electronic conductivity imparting material such as carbon black and metal powder, an ionic conductivity imparting material, or a mixture thereof can be used.
Examples of the ionic conductivity-imparting material include organic salts, inorganic salts, metal complexes, and ionic liquids. Examples of the organic salts include sodium trifluoride acetate, and examples of the inorganic salts include lithium perchlorate and quaternary ammonium salts. Examples of the metal complex include ferric halide-ethylene glycol and the like, and specific examples include those described in Japanese Patent No. 36555364. The ionic liquid is a molten salt that is liquid at room temperature and is also called a room temperature molten salt, and particularly has a melting point of 70 ° C. or less, preferably 30 ° C. or less. Specifically, there can be mentioned those described in JP-A-2003-202722.

  The crosslinking agent is not particularly limited, and includes, for example, sulfur and a peroxide vulcanizing agent.

  Furthermore, a crosslinking aid or the like that promotes the function of the crosslinking agent may be added to the rubber composition as needed. Examples of the crosslinking aid include inorganic zinc oxide and magnesium oxide, and organic stearic acid and amines. For the purpose of shortening the crosslinking time, a thiazole-based or other crosslinking accelerator may be used. Other additives may be added to the rubber composition as needed.

In the present embodiment, the surface of the rubber substrate 402 formed on the outer peripheral surface of the core material 401 is polished by a grinder, adjusted to a predetermined thickness, and then subjected to dry polishing with a polishing grindstone. A surface layer 403 is formed on the outer peripheral surface of the layer 402. The polishing is performed in this way to appropriately adjust the surface roughness of the rubber base material 402 and to adjust the surface roughness of the outer surface layer 403 outside the rubber base material 402.
When reducing the surface roughness of the rubber substrate 402 as much as possible, the surface roughness of the rubber substrate 402 (JIS B 0601: ten-point average roughness conforming to 1994) R _Z is preferably less 8.5μm . In this case, the surface roughness _RZ is a value measured by a contact type surface roughness meter.
The dry polishing is performed by, for example, moving the rotary grindstone in the axial direction while contacting the rubber base 402 with the rubber base 402 being rotated (traverse polishing). When the surface roughness of the rubber substrate 402 is to be minimized, the rotation speed of the grindstone of the polishing machine may be sequentially increased, for example, to 1000 rpm, 2000 rpm, or 3000 rpm during rotation. Alternatively, the type of the grinding wheel may be changed. For example, the grinding may be performed by sequentially increasing the number of a GC (green carborundum) grinding wheel like GC60, GC120, and GC220.
In addition, after the surface of the rubber substrate 402 is dry-polished, the surface may be further polished by wet-polishing with a wet-polishing machine using a water-resistant polishing paper or the like. Here, in the wet polishing, polishing is performed by using a water-resistant polishing paper, for example, a water-resistant sandpaper, and bringing the rubber substrate 402 into contact with the rubber substrate 402 while supplying a polishing liquid thereto.

<Rubber hardness of rubber substrate>
The hardness of the rubber substrate 402 measured using a durometer (“Type A” based on “JIS K 6253”) is preferably in the range of 50 ° to 64 °.
Since the surface layer 403 outside the rubber base 402 is thin, the hardness of the surface of the charging roll 40 is affected by the rubber base 402. If the hardness of the rubber substrate 402 is less than 50 °, the convex portions on the surface of the charging roll 40 will be crushed, and the photoreceptor 1 will be easily stained, and image defects will occur. On the other hand, if the hardness of the rubber base 402 is greater than 64 °, the projections on the surface of the charging roll 40 may be reflected on the image.

<Surface>
In the present embodiment, the surface layer 403 can be formed by applying a coating liquid to the outer peripheral surface of the rubber base 402 and drying and curing the coating liquid. As a method of applying the coating liquid, a dip coating method, a roll coating method, a spray coating method, or the like can be used. For example, the coating solution is agitated, the coating solution is spray-coated on the surface of the rubber substrate 402, dried in an electric furnace at 80 ° C. to 160 ° C. for 20 to 60 minutes, and the outer layer 403 is formed on the outer peripheral surface of the rubber substrate 402. To form a charging roll.

  As shown in FIG. 3, the cured surface layer 403 has a conductive matrix 404 and a plurality of particles 405, 406 dispersed in the conductive matrix 404. Particles 405 and 406 are insulating, and particles 405 have a larger diameter than particles 406. Hereinafter, the particles 405 will be referred to as large particles, and the particles 406 will be referred to as small particles.

  The large particles 405 are a surface roughness imparting material (also referred to as a roughness imparting material), and give the surface layer 403 an appropriate surface roughness. The small particles 406 are arranged between the large particles 405. When the small particles 406 are also exposed from the conductive matrix 404, they function as a roughness imparting material. The conductive matrix 404 has a role of holding the large particles 405 and the small particles 406 at fixed positions and a role of discharging the photoconductor 1. As described above, discharge occurs between the charging roll 40 and the photoconductor 1 in the gap region 51 (and in some cases, the gap region 52).

  In the example shown in FIG. 3, the large particles 405 and the small particles 406 are not completely buried in the conductive matrix 404, but may be completely buried. When the thickness of the conductive matrix 404 is small, the conductive matrix 404 has an appropriate thickness for the diameters of the large particles 405 and the small particles 406 because the ability to hold the large particles 405 and the small particles 406 is low. It is preferred to have When the thickness of the conductive matrix 404 is large and the electric resistance of the conductive matrix 404 is large, discharge tends to be difficult to occur, but by increasing the proportion of the conductive agent contained in the conductive matrix 404, In addition, the electric resistance of the conductive matrix 404 can be reduced, and discharge can be easily generated.

In this embodiment, the large particles 405 (and small particles 406 as the case may be) are dispersed in the surface layer 403 formed on the rubber base material 402 having the adjusted surface roughness. The surface roughness of the surface layer 403 is adjusted. In the present embodiment, the thickness of the conductive matrix 404 of the surface layer 403 is preferably 2 μm or more and 15 μm or less, more preferably 3 μm to 14 μm. If the thickness exceeds 15 μm, the surface roughness of the surface layer 403 becomes too small, causing image unevenness. Preferred surface roughness of the surface layer 403 (JIS B 0601: ten-point average roughness conforming to 1994) _{R Z} is more 1,7Myuemu.

  The diameter of the large particles 405 and the small particles 406 is 0.5 μm or more and 60 μm or less.

  The diameter of the large particles 405 is preferably 1.5 to 15 times the diameter of the small particles 406.

  It is considered that the discharge of the charging roll 40 to the photoconductor 1 in the gap region 51 (and in some cases, the gap region 52) easily occurs in a portion of the surface layer 403 where the large particles 405 and the small particles 406, which are insulators, do not exist. . The dotted line shown in FIG. 3 schematically shows an assumed discharge in the gap region 51. According to this embodiment, insulating particles 405 and 406 having a plurality of large particles 405 and a plurality of small particles 406 are dispersed in the conductive matrix 404 of the surface layer 403, and the small particles 406 are located between the large particles 405. Because of the arrangement, it is considered that the discharge locations from the surface layer 403 of the charging roll 40 are dispersed. As a result, it is considered that the discharge is made uniform and image unevenness can be reduced.

  FIG. 4 shows a charging roll 40 according to a comparative example. In this comparative example, the surface layer 403 has the conductive matrix 404 and the large particles 405 dispersed in the conductive matrix 404, and does not include the small particles 406. In the comparative example, since the small particles 406 do not exist in the gaps between the large particles 405 in the surface layer 403, the discharge locations are not dispersed, and the discharge is not uniform as indicated by the dotted line.

  3 and 4 are cross-sectional views along the axial direction of the charging roll 40. In the present embodiment, small particles 406 are also arranged between the large particles 405 in the circumferential direction of the charging roll 40.

In the present embodiment, the total content of the large particles 405 and the small particles 406 in the surface layer 403 is preferably 0.5% by weight to 70% by weight. Often particle content, since the overlap between the particles, unevenness of the pitch of the surface layer 403 (the average length of the average irregularity distance S _m and the roughness profile elements RSm) is large, and the cause of image unevenness. Average irregularity interval S _m is, JIS B 0601: 1994 conforms to, for example, is measured by a laser microscope contactless. The average length RSm of the roughness curve element conforms to JIS B 0601: 2001, and is measured by, for example, a non-contact laser microscope. Preferred average irregularity distance _{S m} of the surface layer 403 is, for example, 200μm or less.

  In the present embodiment, the components of the coating liquid as the material of the surface layer 403 include at least a base material, a conductive agent, large particles 405, and small particles 406. After the curing of the coating liquid, the base material and the conductive material become components of the conductive matrix 404.

The coating liquid is obtained, for example, by dissolving the following components in a diluting solvent (coating liquid composition).
-Base material: 10 to 80 parts by weight-Conductive agent: 1 to 50 parts by weight

  By appropriately adjusting the particle size and the added amount of the large particles 405 and the particle size and the added amount of the small particles 406, the surface roughness and the pitch of the unevenness of the surface layer 403 can be appropriately adjusted. It is believed that the state of discharge from 403 can be improved. Therefore, it is considered that the discharge between the charging roll 40 and the photoconductor 1 is substantially uniform, an image having a desired density is formed, and the image quality is improved.

<Base material>
The base material contained in the coating liquid is an insulator. As a base material, urethane resin, acrylic resin, acrylic urethane resin, amino resin, silicone resin, fluorine resin, polyamide resin, epoxy resin, polyester resin, polyether resin, phenol resin, urea resin, polyvinyl butyral resin, melamine resin, Nylon resin and the like can be mentioned. These base materials can be used alone or in any combination.

<Conductive agent>
Examples of the conductive agent contained in the coating solution include carbon black such as acetylene black, Ketjen black, and talka black, carbon nanotubes, ions such as lithium perchlorate, and ions such as 1-butyl-3-methylimidazolium hexafluorophosphate. Ionic liquids, metal oxides such as tin oxide, and conductive polymers. These conductive agents can be used alone or in any combination.

<Particles 405, 406>
The large particles 405 and the small particles 406 contained in the coating liquid include acrylic particles, urethane particles, polyamide resin particles, silicone resin particles, fluororesin particles, styrene resin particles, phenol resin particles, polyester resin particles, olefin resin particles, epoxy Resin particles, nylon resin particles, carbon, graphite, balun, silica, alumina, titanium oxide, magnesium oxide, zirconium oxide, calcium sulfate, calcium carbonate, magnesium carbonate, calcium silicate, aluminum nitride, boron nitride, talc, kaolin clay Diatomaceous earth, glass beads, hollow glass spheres and the like. These particles can be used alone or in any combination.

Urethane beads manufactured by Negami Industry Co., Ltd. can be used as the urethane particles. The relationship between the average particle size of the urethane beads and the product name is as follows. However, in practice, one product contains particles having a particle size different from the average particle size. The following is an example for an average particle size of 6 μm to 30 μm.
φ 6 μm: Urethane beads “C-800”
φ10μm: Urethane beads “C-600”
φ15 μm: Urethane beads “C-400”
φ22μm: Urethane beads “C-300”
φ30 μm: Urethane beads “C-200”

<Diluent solvent>
The diluting solvent contained in the coating liquid is not particularly limited, but may be aqueous or methyl acetate, ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methanol, ethanol, butanol, 2-propanol ( Solvent systems such as IPA), acetone, toluene, xylene, hexane, heptane, chloroform and the like.

  As described above, the charging roll has been described as an embodiment, but the conductive roll according to the present invention is, in addition to a charging roll of an image forming apparatus such as an electrophotographic copying machine or a printer, a developing roll, a transfer roll, a charge removing roll, The present invention is also applicable to a toner supply roll and the like.

1: Photoconductor 4: Charger 40: Charging roll 401: Core material 402: Rubber substrate 403: Surface layer 404: Conductive matrix 405: Large particles 406: Small particles 50: Nip 51: Gap region 52: Gap region

Claims (2)

Core material, comprising a rubber substrate disposed around the core material, and a surface layer disposed around the rubber substrate,
The surface layer includes a conductive matrix, and a plurality of insulating particles dispersed in the conductive matrix,
The conductive roll, wherein the particles include a plurality of large particles and a plurality of small particles having a size smaller than the large particles. The conductive roll according to claim 1, wherein the small particles are arranged between the large particles.

Images