Conductive roller, image forming apparatus, and detection method for conductive roller

Abstract

A conductive roller includes: a core member including an outer surface extending along and around an axis of the core member; and a surface layer disposed along the outer surface of the core member. The surface layer includes a conductive portion and a surface roughness imparting material in the form of particles dispersed in the conductive portion. The surface roughness imparting material has an average particle size in a range of greater than or equal to 6 microns and less than 10 microns. The number of particles of the surface roughness imparting material per unit area of ​​the surface layer is greater than or equal to 3.5×10 5 Particles / mm 2 and less than or equal to 7.5×10 5 Particles / mm 2 The average thickness of the surface layer is within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.5 micrometers.

Description

Technical Field

[0001] The present invention relates to a conductive roller, an image forming apparatus, and a detection method for the conductive roller. Background Art

[0002] A conductive roller (eg, a charging roller) is generally used in an image forming apparatus (eg, a printer or a copying machine) configured to form an image on a recording medium (eg, paper) using toner by an electrophotographic method.

[0003] For example, the charging roller described in Patent Document 1 includes a core rod and a conductive rubber layer formed on the core rod.

[0004] In order to reduce charging unevenness, Patent Document 1 defines the range of the ten-point height Rz of microscopic roughness of the surface of the charging roller and the range of the average spacing Sm between peaks of the surface of the charging roller.

[0005] Related prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-14141 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] To roughen the surface of a conductive roller, for example, a method is used in which a surface roughness-imparting material in the form of particles is dispersed on the surface of the conductive roller. When this method is applied to a charging roller, discharge occurs between the surface of the photoreceptor and areas of the charging roller surface that are not coated with the surface roughness-imparting material. Image quality depends on the uniformity of charging or discharging across the photoreceptor surface; therefore, it is necessary to define a predetermined range for the discharge gap between the photoreceptor surface and the charging roller, as well as a predetermined range for the distance between discharge points.

[0010] However, the ten-point height Rz of microscopic roughness and the average spacing Sm between peaks defined in Patent Document 1 are each calculated values ​​affected by the unevenness formed, regardless of the presence or absence of a surface roughness-imparting material. Therefore, the ten-point height Rz of microscopic roughness and the average spacing Sm between peaks do not sufficiently correlate with the discharge gap or the distance between discharge points. Therefore, even when a surface roughness-imparting material is applied to the charging roller described in Patent Document 1, it is necessary to output an actual image to determine whether the desired image quality is achieved, which requires a considerable amount of time and effort.

[0011] Means of solving the problem

[0012] In order to solve the above problems, a conductive roller according to one aspect of the present invention includes: a core member, the core member including an outer surface, the outer surface being along and surrounding the axis of the core member; and a surface layer, the surface layer being arranged along the outer surface of the core member, wherein: the surface layer includes: a conductive portion; and a surface roughness imparting material, the surface roughness imparting material being in the form of particles dispersed in the conductive portion, the average particle size of the surface roughness imparting material being in a range of greater than or equal to 6 μm and less than 10 μm, and the number of particles of the surface roughness imparting material per unit area of ​​the surface layer being greater than or equal to 3.5×10 5 Particles / mm 2 and less than or equal to 7.5×10 5 Particles / mm 2 , and the average thickness of the surface layer is in a range of greater than or equal to 0.2 micrometers and less than or equal to 5.5 micrometers.

[0013] According to another aspect of the present invention, a conductive roller includes: a core member including an outer surface, the outer surface being along and around the axis of the core member; and a surface layer arranged along the outer surface of the core member, wherein: the surface layer includes: a conductive portion; and a surface roughness imparting material, the surface roughness imparting material being in the form of particles dispersed in the conductive portion, the average particle size of the surface roughness imparting material being in a range of greater than or equal to 10 μm and less than or equal to 32 μm, and the number of particles of the surface roughness imparting material per unit area of ​​the surface layer being greater than or equal to 1.8×10 3 Particles / mm 2 and less than or equal to 1.7×10 5 Particles / mm 2 , and the average thickness of the surface layer is in a range of greater than or equal to 0.2 micrometers and less than or equal to 5.8 micrometers.

[0014] An image forming apparatus according to an aspect of the present invention includes: the conductive roller described above; and a photoreceptor in contact with or in proximity to the conductive roller.

[0015] According to one aspect of the present invention, a detection method for a conductive roller is a detection method for determining whether the characteristics of the conductive roller are good. The conductive roller includes: a core member, the core member includes an outer surface, the outer surface is along and around the axis of the core member; and a surface layer, the surface layer is arranged along the outer surface of the core member, the surface layer includes: a conductive portion; and a surface roughness imparting material, the surface roughness imparting material is in the form of particles dispersed in the conductive portion, the average particle size of the surface roughness imparting material is within a range of greater than or equal to 6 microns and less than 10 microns, and the average thickness of the surface layer is within a range of greater than or equal to 0.2 microns and less than or equal to 5.5 microns. The detection method includes: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and based on the number of particles being greater than or equal to 3.5×10 5 Particles / mm 2 and less than or equal to 7.5×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

[0016] According to another aspect of the present invention, a detection method for a conductive roller is a detection method for determining whether the characteristics of the conductive roller are good. The conductive roller includes: a core member, the core member includes an outer surface, the outer surface is along and around the axis of the core member; and a surface layer, the surface layer is arranged along the outer surface of the core member, the surface layer includes: a conductive portion; and a surface roughness imparting material, the surface roughness imparting material is in the form of particles dispersed in the conductive portion, the average particle size of the surface roughness imparting material is within a range of greater than or equal to 10 microns and less than or equal to 32 microns, and the average thickness of the surface layer is within a range of greater than or equal to 0.2 microns and less than or equal to 5.8 microns. The detection method includes: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and based on the number of particles being greater than or equal to 1.8×10 3 Particles / mm 2 and less than or equal to 1.7×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

[0017] Effects of the Invention

[0018] According to the present invention, image unevenness can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [ Figure 1 ] is a schematic diagram showing an example of the configuration of an image forming apparatus according to an embodiment.

[0020] [ Figure 2] is a cross-sectional view of a charging roller which is an example of a conductive roller according to the embodiment.

[0021] [ Figure 3 ] is an enlarged cross-sectional view showing the surface layer of the charging roller. DETAILED DESCRIPTION

[0022] The preferred embodiments according to the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the sizes and proportions of the elements may differ from those of the actual product, and some elements may be shown schematically for ease of understanding. The scope of the present invention is not limited to the embodiments described below unless the following description includes a description that specifically limits the scope of the present invention.

[0023] 1. Image Forming Apparatus 100

[0024] Figure 1 1 is a schematic diagram showing an example of the configuration of an image forming apparatus 100 having a conductive roller according to an embodiment. The image forming apparatus 100 is an apparatus, such as a copy machine or a printer, that forms an image on a recording medium M (such as paper for printing) by an electrophotographic method.

[0025] As in Figure 1 , the image forming apparatus 100 includes a photoreceptor 10, a charging device 20, an exposure device 30, a developing device 40, a transfer device 50, a cleaning device 60, and a fixing device (not shown). Among these devices, the charging device 20, the exposure device 30, the developing device 40, the transfer device 50, and the cleaning device 60 are arranged in this order along the outer surface of the photoreceptor 10 in the circumferential direction of the photoreceptor 10.

[0026] The photoreceptor 10 includes a photosensitive layer as the outermost layer, which is formed of a photoconductive insulating material such as an organic photoreceptor (OPC), for example. Figure 1 The photoreceptor 10 in FIG. 1 is a cylindrical member or a columnar member (photosensitive drum) configured to rotate around the axis of the photoreceptor 10 .

[0027] The charging device 20 is a device configured to uniformly charge the outer surface of the photoreceptor 10 by discharge (eg, corona discharge). Figure 1 In the example shown in FIG, the charging device 20 includes a charging roller 21, which is an example of a conductive roller, and is configured to generate discharge, such as corona discharge, between the charging roller 21 and the photoreceptor 10. The charging roller 21 is in contact with the outer surface of the photoreceptor 10, and thus, discharge occurs in a region R1 or R2 near the nip N formed by the contact.

[0028] The exposure device 30 is a device configured to form an electrostatic latent image on the outer surface of the photoreceptor 10 by exposing the charged outer surface of the photoreceptor 10 with light such as laser light according to image information from an external device such as a personal computer.

[0029] The developing device 40 applies toner T to the electrostatic latent image formed on the outer surface of the photoreceptor 10 to visualize the latent image as a toner image, for example, in Figure 1 The developing device 40 includes: a container 41, which is configured to accommodate toner T in the container; a developing roller 42, which is configured to carry the toner T; a toner supply roller 43, which is configured to supply the toner T to the developing roller 42; and an adjusting blade 44, which is configured to adjust the amount of toner T carried by the developing roller 42.

[0030] The transfer device 50 is a device configured to transfer the toner image formed on the photoreceptor 10 to the recording medium M. Figure 1 In the example shown in , the transfer device 50 includes a transfer roller 51 , and a predetermined bias is applied to the transfer roller 51 to transfer the toner image on the photoreceptor 10 to the recording medium M conveyed between the photoreceptor 10 and the transfer roller 51 .

[0031] The recording medium M to which the toner image has been transferred is heated and pressed by a fixing device (not shown). Through the heating and pressing steps, the toner image is fixed to the recording medium M. The fixing device is not particularly limited and may be one of various types of publicly known fixing devices, including those using a roller fixing method, a film fixing method, a flash fixing method, and the like.

[0032] The cleaning device 60 is a device configured to remove the toner T remaining on the outer surface of the photoreceptor 10 after the transfer process. Figure 1 In the example shown in FIG, the cleaning device 60 includes a cleaning blade 61 configured to scrape off toner T from the outer surface of the photoreceptor 10, and a collector 62 configured to collect the toner T scraped off by the cleaning blade 61. The cleaning device 60 may include a cleaning brush instead of the cleaning blade 61, or in addition to the cleaning blade 61.

[0033] 2. Charging roller 21

[0034] Figure 2 2 is a cross-sectional view of a charging roller 21, which is an example of a conductive roller according to an embodiment. Figure 2, the charging roller 21 includes a core member 21a, an elastic layer 21b, and a surface layer 21c. Furthermore, the charging roller 21 has a configuration in which the elastic layer 21b is sandwiched between the core member 21a and the surface layer 21c. Each of the elements of the charging roller 21 will be described in turn.

[0035] 2-1. Core member 21a

[0036] The core member 21a is a columnar or cylindrical conductive member including an outer surface along and around the axis AX of the core member 21a. The core member 21a has two ends, each of which can be appropriately provided with a shaft member for a bearing.

[0037] The core member 21a is formed of a material having excellent thermal conductivity and mechanical strength. The material is not particularly limited, and examples of the material include metal materials (e.g., stainless steel materials, nickel (Ni) materials, nickel alloy materials, iron (Fe) materials, magnetic stainless steel materials, cobalt-nickel (Co-Ni) alloy materials, etc.) and resin materials (e.g., polyimide resin (PI) materials, etc.). In addition, one of these materials may be used alone, or alternatively, a combination of two or more of these materials may be used in the form of a mixture, a laminate, or an alloy.

[0038] The core member 21a is manufactured, for example, by a well-known machining technique such as cutting.The surface of the core member 21a may be appropriately subjected to surface treatment such as sandblasting or plating.

[0039] 2-2. Elastic layer 21b

[0040] The elastic layer 21b is disposed over the entire outer surface of the core member 21a. Furthermore, the elastic layer 21b is a conductive and elastic layer. The elastic layer 21b is elastically deformed by the contact between the charging roller 21 and the photoreceptor 10. In regions R1 and R2 close to the nip N formed by the contact between the charging roller 21 and the photoreceptor 10, the elastic deformation causes the distance between the outer surface of the charging roller 21 and the outer surface of the photoreceptor 10 to be equalized along the axis AX.

[0041] exist Figure 3 In the example shown in FIG, the elastic layer 21b is a single layer; however, the elastic layer 21b may be a laminate having two or more layers. Between the core member 21a and the elastic layer 21b, another layer such as an adhesive layer for bonding these layers to each other, a sealing layer for improving the sealing of these layers, or a conditioning layer for conditioning the surface condition of the core member 21a may be appropriately interposed.

[0042] The thickness of the elastic layer 21b is appropriately determined depending on the material of the elastic layer 21b. The thickness of the elastic layer is not particularly limited. To achieve appropriate elasticity of the elastic layer 21b, the thickness of the elastic layer may be, for example, within a range of 0.5 mm or more and 5 mm or less, and preferably within a range of 1 mm or more and 3 mm or less. When a non-contact method is applied to the image forming apparatus 100, in which the charging roller 21 does not contact the photoreceptor 10, the elastic layer 21b may be omitted.

[0043] The elastic layer 21b is formed of, for example, a rubber composition in which a conductivity-imparting agent is added to a rubber material. The elastic layer 21b may be a dense member formed of the rubber composition, or may be a foam member formed of the rubber composition.

[0044] The rubber material is not particularly limited and may be, for example, a synthetic rubber material such as a polyurethane rubber (PUR) material, an epichlorohydrin rubber (ECO) material, a nitrile rubber (NBR) material, a styrene rubber (SBR) material, or a chloroprene rubber (CR) material, and further, one of these materials may be used alone, or alternatively, a combination of two or more of these materials may be used in the form of a copolymer or a blend, etc.

[0045] The rubber material is not limited to a synthetic rubber material, and the rubber material may be a thermoplastic elastomer material. Additives such as a cross-linking agent or a cross-linking aid may be appropriately added to the rubber material. The cross-linking agent is not particularly limited, and examples of the cross-linking agent include sulfur and peroxide vulcanizing agents. Examples of the cross-linking aid include inorganic materials (such as zinc oxide and magnesium oxide) and organic materials (such as stearic acid and amines).

[0046] The conductivity-imparting agent is not particularly limited. Examples of conductivity-imparting agents include electronic conductivity-imparting agents and ionic conductivity-imparting agents. In addition, combinations of two or more of these agents can be used in the form of a mixture. The electronic conductivity-imparting agent is not particularly limited. Examples of electronic conductivity-imparting agents include carbon black and metal powder. In addition, one of the electronic conductivity-imparting agents can be used alone, or a combination of two or more of the electronic conductivity-imparting agents can be used. The ionic conductivity-imparting agent is not particularly limited. Examples of ionic conductivity-imparting agents include organic salts, inorganic salts, metal complexes, and ionic liquids. Examples of organic salts include sodium trifluoride acetate materials, etc. Examples of inorganic salts include lithium perchlorate materials and quaternary ammonium salts, etc. Examples of metal complexes include iron halide-ethylene glycol materials, as shown in Japanese Patent No. 3655364. The ionic liquid is a molten salt that is liquid at room temperature, and the melting point of the ionic liquid is 70 degrees Celsius or lower, preferably 30 degrees Celsius or lower, as shown in Japanese Patent Application Publication No. 2003-202722.

[0047] Because the surface layer 21c, described below, is very thin, the surface shape of the elastic layer 21b tends to take on the shape of the surface of the charging roller 21. Therefore, the surface of the elastic layer 21b is preferably as smooth as possible. Specifically, the surface roughness Rz of the elastic layer 21b is preferably equal to or less than 8.5 microns, and more preferably equal to or less than 6 microns. When the surface roughness Rz is within this range, the effects of the shape of the surface layer 21c, described below, can be appropriately achieved. According to JIS B 0601 (1994), surface roughness Rz represents the ten-point height of microscopic unevenness.

[0048] The durometer hardness of the elastic layer 21b is preferably within a range of 50° or more and 64° or less. The durometer hardness of the elastic layer 21b within this range allows the shape effects of the surface layer 21c described below to be appropriately achieved. The durometer hardness is measured using a "Type A" durometer in accordance with JIS K 6253 or ISO 7619.

[0049] The elastic layer 21b described above is formed, for example, by extrusion molding. This molding may be insert extrusion molding, in which the core member 21a is used as an insert. In this case, the core member 21a and the elastic layer 21b are bonded together simultaneously with the formation of the elastic layer 21b. Alternatively, the elastic layer 21b may be formed by bonding a sheet-like or tubular member formed from the rubber composition described above to the outer surface of the core member 21a. When forming the elastic layer 21b, the thickness and surface roughness of the elastic layer 21b can be appropriately adjusted by grinding the outer surface of the elastic layer 21b using a grinding machine or the like.

[0050] 2-3. Surface layer 21c

[0051] The surface layer 21c, which is arranged on the entire outer surface of the elastic layer 21b, is a conductive layer having a rough surface. The surface layer 21c is arranged as the outermost layer of the charging roller 21 along the outer surface of the core member 21a. Therefore, the surface layer 21c has a rough surface, so that corona charging is uniformly generated between the charging roller 21 and the photoreceptor 10, compared with a configuration in which the surface of the surface layer 21c is a smooth surface. The surface layer is arranged as the outermost layer of the charging roller 21.

[0052] Figure 3 is an enlarged cross-sectional view showing the surface layer 21c of the charging roller 21. Figure 3 As shown in FIG. 1 , the surface layer 21c includes a conductive portion 21c1 and a surface roughness-imparting material 21c2 in the form of particles. The conductive portion 21c1 is used to generate discharge at the region R1 or R2 between the conductive portion 21c1 and the outer surface of the photoreceptor 10, and also serves as an adhesive portion that fixes the dispersed surface roughness-imparting material 21c2 to the elastic layer 21b. Meanwhile, the surface roughness-imparting material 21c2 is used to roughen the surface of the surface layer 21c. The conductive portion 21c1 and the surface roughness-imparting material 21c2 will be described in detail in this order.

[0053] The conductive portion 21c1 is formed of a conductive resin composition in which a conductive agent is added to a resin material as a base material. The resin composition may include another additive such as a modifier or the like.

[0054] The resin material is not particularly limited, and examples of the resin material include urethane resin materials, acrylic resin materials, acrylic urethane resin materials, amino resin materials, silicone resin materials, fluororesin materials, polyamide resin materials, epoxy resin materials, polyester resin materials, polyether resin materials, phenolic resin materials, urea-formaldehyde resin materials, polyvinyl butyral resin materials, melamine resin materials, and nylon resin materials. One of these base materials may be used alone, or alternatively, two or more of these materials may be used in the form of a copolymer or blend, etc.

[0055] The conductive agent is not particularly limited, and examples thereof include carbon black (e.g., acetylene black, Ketjen black, and Tokablack), carbon nanotubes, lithium salts (e.g., lithium perchlorate), ionic liquids (e.g., 1-butyl-3-methylimidazolium hexafluorophosphate), metal oxides (e.g., tin oxide), and conductive polymers. One of these conductive agents may be used alone, or alternatively, a combination of two or more of these conductive agents may be used as a mixture.

[0056] The surface roughness imparting material 21c2 is not particularly limited, and examples of the surface roughness imparting material 21c2 include acrylic particles, urethane particles, polyamide resin particles, silicone resin particles, fluororesin particles, styrene resin particles, phenolic resin particles, polyester resin particles, olefin resin particles, epoxy resin particles, nylon resin particles, carbon particles, graphite particles, carbon spheres, silica particles, aluminum oxide particles, titanium oxide particles, zinc oxide particles, magnesium oxide particles, zirconium oxide particles, calcium sulfate particles, calcium carbonate particles, magnesium carbonate particles, calcium silicate particles, aluminum nitride particles, boron nitride particles, talc particles, kaolin particles, diatomaceous earth particles, glass beads, hollow glass spheres, etc. One of these kinds of particles may be used alone, or alternatively, two or more of these kinds of particles may be used in combination.

[0057] As described above, the charging roller 21 is an example of a conductive roller, and includes a core member 21a having an outer surface along and around the axis AX, and a surface layer 21c arranged along the outer surface of the core member 21a. As described above, the surface layer 21c includes a conductive portion 21c1 having conductivity and a surface roughness-imparting material 21c2 in the form of particles dispersed in the conductive portion 21c1.

[0058] The average particle size of the surface roughness imparting material 21c2 is within a range of greater than or equal to 6 micrometers and less than or equal to 32 micrometers.

[0059] In the case where the average particle size of the surface roughness imparting material 21c2 is within a range of 6 μm or more and less than 10 μm, the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c is within a range of 3.5×10 5 Pieces / mm 2 and less than or equal to 7.5×10 5 Pieces / mm 2 In addition, the average thickness of the surface layer 21c is within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.5 micrometers.

[0060] In the case where the average particle size of the surface roughness imparting material 21c2 is within a range of 10 μm or more and 32 μm or less, the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c is within a range of 1.8×10 3 Particles / mm 2 and less than or equal to 1.7×10 5 Particles / mm 2 In addition, the average thickness of the surface layer 21c is within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.8 micrometers.

[0061] The range of the average particle size of the surface roughness imparting material 21c2, the range of the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c, and the range of the average thickness of the surface layer 21c are defined as described above, so that by using the charging roller 21, electric charge can be uniformly charged or discharged to the outer surface of the photoreceptor 10.

[0062] In particular, the average distance S between the peaks m Compared to the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c, the distance between the protrusions due to the surface roughness imparting material 21c2 has a higher correlation. m Compared with the conventional technique for performing definition, the variation in the distance L between the discharge points is reduced regardless of the shape of the conductive portion 21c1.

[0063] Compared with the micro roughness ten-point height RZ, the average particle size of the surface roughness imparting material 21c2 has a higher correlation with the height of the protrusions caused by the surface roughness imparting material 21c2. ZCompared to conventional techniques for defining the discharge gap G, regardless of the shape of the conductive portion 21c1, the variation in the discharge gap G is reduced. In order to reduce the variation in the discharge gap G, it is preferred that the standard deviation (variation) of the particle size of the surface roughness imparting material 21c2 is as small as possible; specifically, the standard deviation of the particle size is preferably equal to or less than 1.5 microns, more preferably equal to or less than 1 micron.

[0064] Furthermore, since the relationship between the average thickness of the surface layer 21c and the average particle size of the surface roughness imparting material 21c2 is defined, it is possible to obtain protrusions each having a desired height due to the surface roughness imparting material 21c2. Therefore, it is possible to obtain a discharge gap G having a desired length.

[0065] As described above, the range of the average particle size of the surface roughness imparting material 21c2, the range of the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c, and the range of the average thickness of the surface layer 21c are defined, and therefore, a desired discharge gap G and a desired distance L between discharge points can be obtained. As a result, by using the charging roller 21, electricity can be uniformly charged or discharged to the outer surface of the photoreceptor 10.

[0066] By measuring the average particle size of the surface roughness-imparting material 21c2, the average thickness of the surface layer 21c, and the number of particles of the surface roughness-imparting material 21c2 per unit area of ​​the surface layer 21c, it is possible to determine whether the characteristics of the charging roller 21 are good based on the measurement results. In other words, it is determined that the characteristics of the charging roller 21 are good based on the measurement results being within the range described above. As described above, it is possible to provide a detection method that can determine whether the charging roller 21 is good without evaluating the quality of an image output from the image forming apparatus 100 to which the charging roller 21 is actually mounted.

[0067] As described above, the charging roller 21 according to this embodiment includes the conductive elastic layer 21b disposed between the core member 21a and the surface layer 21c. With this configuration, the distance between the outer surface of the photoreceptor 10 and the outer surface of the charging roller 21 can be uniform along the axis AX, based on the contact between the charging roller 21 and the outer surface of the photoreceptor 10.

[0068] Preferably, the surface roughness imparting material 21c2 is formed of insulating particles. In this case, discharge to the protrusion due to the surface roughness imparting material 21c2 can be reduced. Figure 3In the example shown in , the surface roughness-imparting material 21c2 is partially exposed to the outside from the conductive portion 21c1; however, the surface roughness-imparting material 21c2 may be completely embedded in the conductive portion 21c1.

[0069] As described above, the conductive portion 21c1 is formed of a resin composition including a resin material and a conductive agent, and therefore, the conductive portion 21c1 is appropriately used to generate discharge at the region R1 or R2 between the conductive portion 21c1 and the outer surface of the photoreceptor 10, and to fix the surface roughness imparting material 21c2 in a dispersed state to the elastic layer 21b.

[0070] As described above, in the image forming apparatus 100 including the charging roller 21 and the photoreceptor 10, the charging roller 21 charges the outer surface of the photoreceptor 10 by applying a voltage between the charging roller 21 and the outer surface of the photoreceptor 10. The voltage (in other words, the charging voltage) may be a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage. In the case where the charging voltage is a voltage obtained by superimposing an AC voltage on a DC voltage, the charging voltage has the advantage that charging unevenness is less likely to occur than in the case where the charging voltage is a DC voltage.

[0071] The surface layer 21c described above is formed by a coating liquid in which the resin composition described above is dissolved in a solvent and the surface roughness imparting material described above is dispersed in the coating liquid. Specifically, the coating liquid is applied to the outer surface of the elastic layer 21b and then hardened or cured to form the surface layer 21c.

[0072] The method of applying the coating liquid is not particularly limited, and examples of the method include dip coating, roller coating, spray coating, etc. In order to cure or harden the coating liquid, heat treatment, ultraviolet irradiation treatment, etc. may be appropriately performed.

[0073] The solvent used for the coating liquid is not particularly limited, and examples of the solvent include water-based solvents (e.g., water, etc.), ester-based solvents (e.g., methyl acetate, ethyl acetate, or butyl acetate, etc.), ketone-based solvents (e.g., methyl ethyl ketone (MEK) or methyl isobutyl ketone (MIBK), etc.), alcohol-based solvents (e.g., methanol, ethanol, butanol, or 2-propanol (IPA), etc.), hydrocarbon-based solvents (e.g., acetone, toluene, xylene, hexane, or heptane, etc.), and halogenated solvents (e.g., chloroform, etc.). One of these solvents may be used alone, or alternatively, a combination of two or more of these solvents may be used in the form of a mixture, etc.

[0074] As described above, the surface layer 21c is formed by solidifying or hardening the coating agent including the surface roughness imparting material 21c2. Based on the area of ​​the surface layer 21c, the inclusion rate of the surface roughness imparting material 21c2 in the coating agent, the mass of the coating agent used to form the surface layer 21c, and the average mass of each particle of the surface roughness imparting material 21c2, the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the surface layer 21c can be calculated. Therefore, even without using a device such as a microscope, the number of particles of the surface roughness imparting material 21c2 per unit area of ​​the obtained surface layer 21c can be determined. Therefore, when the thickness of the surface layer 21c and the average particle size of the surface roughness imparting material 21c2 are known, it is possible to determine whether the characteristics of the charging roller 21 are good by using the detection method described above.

[0075] For example, the average mass of each particle of the surface roughness imparting material 21c2 is calculated based on the density of the material constituting the surface roughness imparting material 21c2 and the volume of each particle of the surface roughness imparting material 21c2. For example, the volume of each particle of the surface roughness imparting material 21c2 is calculated based on the average particle size of the surface roughness imparting material 21c2.

[0076] 3. Variant

[0077] Various modifications can be made to the above-described embodiment. Specific modifications that can be applied to the above-described embodiment are described below. Two or more modifications freely selected from the following modifications can be combined as long as this combination does not conflict.

[0078] 3-1. First variant

[0079] In the embodiments described above, the conductive roller according to the present invention is used as a charging roller; however, the present invention is not limited to this example. In addition to being suitable for use as a charging roller in image forming equipment (e.g., electrophotographic copiers or printers), the conductive roller according to the present invention is also suitable for use in developing rollers, transfer rollers, static charge eliminating rollers, toner supply rollers, and the like.

[0080] 3-2. Second variant

[0081] In the embodiment described above, a configuration in which the charging roller contacts the outer surface of the photoreceptor has been described; however, the present invention is not limited to this configuration, and a configuration in which the conductive roller is close to the outer surface of the photoreceptor may be used. For example, if the conductive roller is a developing roller, the developing method may be either a contact method or a non-contact method.

[0082] 3-3. Third variant

[0083] In the embodiment described above, an example in which the image forming apparatus according to the present invention is a monochrome image forming apparatus is shown; however, the image forming apparatus is not limited to this example. For example, the image forming apparatus according to the present invention is applicable to a color image forming apparatus in addition to a monochrome image forming apparatus. A color image forming apparatus may use a rotary developing method or a tandem developing method. In the case where the image forming apparatus includes an intermediate transfer element, a conductive roller may be applied to the primary transfer roller or the secondary transfer roller. In addition, the image forming apparatus may use wet toner or dry toner, and the toner may be a magnetic or non-magnetic single-component developer or a two-component developer.

[0084] Example

[0085] Specific examples of the present invention will be described below. The present invention is not limited to the following examples.

[0086] A. Manufacturing of Conductive Rollers

[0087] A-1. First Example

[0088] Fabrication of elastic layer

[0089] First, a roll mixer is used to knead the rubber composition. The rubber composition includes the following components.

[0090] Epichlorohydrin rubber ("Epichlomer-CG-102" manufactured by Osaka Soda Co., Ltd.) used as a rubber material: 100 parts by mass

[0091] Sodium trifluoroacetate used as a conductivity-imparting agent: 0.5 parts by mass

[0092] Zinc oxide used as a crosslinking aid: 3 parts by mass

[0093] Stearic acid used as a crosslinking aid: 2 parts by mass

[0094] Cross-linking reagent: 1.5 parts by mass

[0095] The kneaded rubber composition is formed into a sheet-like material and then wound around the surface of a stainless steel core member having a diameter of 8 mm. The kneaded rubber composition is then compression-molded to form a layer made of cross-linked epichlorohydrin rubber. The surface of this layer is then ground using a grinding machine to form an elastic layer having a thickness of 2.0 mm. During the grinding process, after the thickness of the elastic layer reaches a predetermined thickness, the rotational speed of the grinding wheel of the grinding machine is sequentially increased from 1000 rpm to 2000 rpm and then to 3000 rpm to grind the surface of the elastic layer through dry grinding, thereby minimizing the surface roughness of the elastic layer.

[0096] The hardness of the obtained elastic layer was measured using a "Type A" durometer in accordance with JIS K 6253 or ISO 7619; as a result, the measured hardness was within a range of 50° to 64°.

[0097] Manufacturing of surface layer

[0098] First, a coating liquid for forming a surface layer is prepared. The coating liquid includes the following components.

[0099] Ethyl acetate used as diluent

[0100] Urethane resin (polyol ("T5650E" manufactured by Asahi Kasei Chemicals Corporation) and isocyanurate ("TPA-100" manufactured by Asahi Kasei Chemicals Corporation) used as resin materials

[0101] Carbon dispersion liquid used as a conductive material ("MHI-BK" manufactured by Mikoku Pigments Co., Ltd. (carbon content 20% to 30% by mass))

[0102] Acrylic silicone polymer used as an additive ("Modifier FS700" manufactured by NOF Corporation)

[0103] Urethane beads ("C-200" manufactured by Negami Chemical Industry Co., Ltd.) used as a surface roughness imparting agent had an average particle size of 32 μm and a density of 1160 kg / m 3

[0104] The coating liquid having the above-described components in an appropriate combination ratio was stirred for 3 hours using a ball mill.

[0105] The conductive roller was formed by forming a surface layer on the outer surface of the elastic layer described above using a coating liquid. Specifically, the stirred coating liquid was applied to the outer surface of the elastic layer by spraying, and then the stirred coating liquid was dried in an electric furnace at 120°C for 60 minutes to form a surface layer with an average thickness of 2.4 microns.

[0106] The amount of coating liquid used for each conductive roller was 2.1 g. Therefore, based on the amount of coating liquid used and the combination ratio of the surface roughness imparting material in the coating liquid described above, the number of particles of the surface roughness imparting material included in the surface layer of a single conductive roller was calculated; as a result, the calculated value was 7.7×10 7 particles.

[0107] The outer diameter of the elastic layer is 12 mm, and the coating liquid is applied to an area of ​​the elastic layer having a length of 340 mm in the axial direction of the elastic layer. Therefore, based on the area to which the coating liquid is applied (in other words, the area of ​​the surface layer becomes 12×π×340 [mm 2 ]) to calculate the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; the calculated value is 6.0×10 3 [particles / mm 2 ].

[0108] The average thickness of the surface layer was measured by first observing a cross section of the elastic layer and a cross section of the surface layer with a laser microscope (“VK-X200” manufactured by KEYENCE Corporation) (the cross section of the elastic layer and the cross section of the surface layer were taken along a line in the thickness direction of the elastic layer and the surface layer), then measuring the distance from the surface of the conductive roller to the boundary between the surface layer and the elastic layer at 20 different points in the circumferential direction of the conductive roller, and then calculating the average value of the measured distances.

[0109] A-2. Second to twentieth examples, and first and second comparative examples

[0110] The conductive rollers according to the second to twentieth examples and the conductive rollers according to the first and second comparative examples were manufactured in substantially the same manner as in the first example, except that the combination ratio of the components of the coating agent was changed so that the average particle size of the surface roughness-imparting material in the surface layer, the number of particles of the surface roughness-imparting material, and the average thickness of the surface layer were the values ​​listed in Table 1. The combination ratio of the components of the coating agent was adjusted so that the amount of the coating liquid used per conductive roller was 2.1 g.

[0111] [Table 1]

[0112] Table 1

[0113]

[0114] Table 1 lists the average particle size of the surface roughness imparting material in the surface layer, the number of particles of the surface roughness imparting material, and the average thickness of the surface layer for each of the Examples and each of the Comparative Examples, and the results of the evaluation described below.

[0115] In the fourth to eighth examples, urethane beads ("C-300" manufactured by Negami Chemical Industry Co., Ltd.) were used as a surface roughness imparting material having an average particle size of 22 micrometers. In the ninth to thirteenth examples, urethane beads ("C-400" manufactured by Negami Chemical Industry Co., Ltd.) were used as a surface roughness imparting material having an average particle size of 15 micrometers. In the fourteenth to eighteenth examples, urethane beads ("C-600" manufactured by Negami Chemical Industry Co., Ltd.) were used as a surface roughness imparting material having an average particle size of 10 micrometers. In the nineteenth and twentieth examples, as well as the first and second comparative examples, urethane beads ("C-800" manufactured by Negami Chemical Industry Co., Ltd.) were used as a surface roughness imparting material having an average particle size of 6 micrometers.

[0116] B. Evaluation of Conductive Roller

[0117] Image unevenness of images printed by a copier ("MP C5503" manufactured by Ricoh Co., Ltd.) using a conductive roller according to each of the Examples or each of the Comparative Examples as a charging roller was evaluated. The copier was a color multifunctional printer (MFP) configured to use a voltage obtained by superimposing an AC voltage on a DC voltage as a charging voltage.

[0118] In the evaluation described below, a charging current was used in which the charging current was set to an AC current (1.45 mA) lower than the normal current (1.56 mA). Printing was performed at a printing rate of 30 sheets per minute at an ambient temperature of 23° C. and a humidity of 55%.

[0119] B-1. Is there image unevenness caused by partial discharge?

[0120] A halftone image was printed, and then an evaluation was performed by visually determining the presence or absence of white dots, black dots, white streaks, or black streaks, which appear as image unevenness caused by partial discharge, on the printed image based on the following criteria. A summary of the evaluation results is shown in Table 1 described above.

[0121] <Standard>

[0122] P: No image unevenness caused by partial discharge

[0123] F: There is image unevenness caused by partial discharge

[0124] B-2. Is there image unevenness caused by dirt buildup?

[0125] A solid white image was printed, and then evaluation was performed by visually determining whether or not there was image unevenness caused by dirt buildup based on the following criteria: A summary of the evaluation results is shown in Table 1 described above.

[0126] <Standard>

[0127] P: No fouling

[0128] F: There is fouling

[0129] "Fog" is also known as "fog" and means printing on non-printed areas. When fouling occurs on a printed pure white image, the brightness of the printed image is reduced.

[0130] B-3. ​​Overall Assessment

[0131] In the case where the evaluation in B-1 described above and the evaluation in B-2 described above are both P, the overall evaluation is defined as P, and in cases other than the above-described cases, the overall evaluation is defined as F. The summary of the evaluation results is shown in Table 1 described above.

[0132] It can be understood from the above evaluation results that image unevenness can be reduced in each of the examples shown in Table 1. In contrast to this result, image unevenness occurs in each of the comparative examples.

[0133] Description of Reference Signs

[0134] 10…photoreceptor, 20…charging device, 21…charging roller, 21a…core member, 21b…elastic layer, 21c…surface layer, 21c1…conductive portion, 21c2…surface roughness imparting material, 30…exposure device, 40…developing device, 41…container, 42…developing roller, 43…toner supply roller, 44…regulating blade, 50…transfer device, 51…transfer roller, 60…cleaning device, 61…cleaning blade, 62…collector, 100…image forming apparatus, AX…axis line, G…discharge gap, L…distance between discharge points, M…recording medium, N…imprint portion, R1…area, Sm…average spacing between peaks, T…toner.

Claims

1. A detection method for a conductive roller, the detection method being a detection method for determining whether the characteristics of the conductive roller are good, the conductive roller comprising: a core member including an outer surface along and surrounding an axis of the core member; and a surface layer arranged along an outer surface of the core member, the surface layer comprising: a conductive portion; and a surface roughness imparting material in the form of particles dispersed in the conductive portion, the surface roughness imparting material having an average particle size within a range of greater than or equal to 6 micrometers and less than 10 micrometers, and the surface layer having an average thickness within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.5 micrometers, the detection method comprising: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and Based on the number of particles greater than or equal to 3.5×10 5 Particles / mm 2 and less than or equal to 7.5×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

2. A detection method for a conductive roller, the detection method being a detection method for determining whether the characteristics of the conductive roller are good, the conductive roller comprising: a core member including an outer surface along and surrounding an axis of the core member; and a surface layer arranged along an outer surface of the core member, the surface layer comprising: a conductive portion; and a surface roughness imparting material in the form of particles dispersed in the conductive portion, the surface roughness imparting material having an average particle size within a range of greater than or equal to 10 micrometers and less than or equal to 32 micrometers, and an average thickness of the surface layer within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.8 micrometers, the detection method comprising: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and Based on the number of particles greater than or equal to 1.8×10 3 Particles / mm 2 and less than or equal to 1.7×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

3. The detection method for a conductive roller according to claim 1 or 2, wherein: the surface layer is formed by curing or hardening a coating agent including the surface roughness imparting material, Calculating the number of particles includes calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer based on: the area of ​​the surface layer; The inclusion rate of the surface roughness imparting material in the coating reagent; the mass of the coating agent used to form the surface layer; and The surface roughness imparts an average mass per particle of the material.

4. A method for manufacturing a conductive roller, the conductive roller comprising: a core member including an outer surface along and surrounding an axis of the core member; and a surface layer arranged along an outer surface of the core member, the surface layer comprising: a conductive portion; and a surface roughness imparting material in the form of particles dispersed in the conductive portion, the manufacturing method comprising: forming the surface layer; and Determine whether the characteristics of the conductive roller are good, wherein the average particle size of the surface roughness imparting material is within a range of greater than or equal to 6 micrometers and less than 10 micrometers, and the average thickness of the surface layer is within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.5 micrometers, Wherein, determining whether the characteristics of the conductive roller are good includes: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and The number of particles of the surface roughness imparting material per unit area of ​​the surface layer is greater than or equal to 3.5×10 5 Particles / mm 2 and less than or equal to 7.5×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

5. A method for manufacturing a conductive roller, the conductive roller comprising: a core member including an outer surface along and surrounding an axis of the core member; and a surface layer arranged along an outer surface of the core member, the surface layer comprising: a conductive portion; and a surface roughness imparting material in the form of particles dispersed in the conductive portion, the manufacturing method comprising: forming the surface layer; and Determine whether the characteristics of the conductive roller are good, wherein the average particle size of the surface roughness imparting material is within a range of greater than or equal to 10 micrometers and less than or equal to 32 micrometers, and the average thickness of the surface layer is within a range of greater than or equal to 0.2 micrometers and less than or equal to 5.8 micrometers, Wherein, determining whether the characteristics of the conductive roller are good includes: calculating the number of particles of the surface roughness imparting material per unit area of ​​the surface layer; and The number of particles of the surface roughness imparting material per unit area of ​​the surface layer is greater than or equal to 1.8×10 3 Particles / mm 2 and less than or equal to 1.7×10 5 Particles / mm 2 Within the range, it is determined that the characteristics of the conductive roller are good.

6. The method for manufacturing a conductive roller according to claim 4 or 5, further comprising: forming the surface layer by curing or hardening a coating agent including the surface roughness imparting material; as well as The number of particles of the surface roughness imparting material per unit area of ​​the surface layer is calculated based on: the area of ​​the surface layer; The inclusion rate of the surface roughness imparting material in the coating reagent; the mass of the coating agent used to form the surface layer; and The surface roughness imparts an average mass per particle of the material.

7. The method for manufacturing a conductive roller according to claim 4 or 5, wherein: The conductive roller further includes a conductive elastic layer disposed between the core member and the surface layer.

8. The method for manufacturing a conductive roller according to claim 4 or 5, wherein: The surface roughness imparting material is formed of an insulating material.

9. The method for manufacturing a conductive roller according to claim 4 or 5, wherein: The conductive portion is formed of a resin composition including a resin material and a conductive agent.

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