Charging roll for electrophotographic apparatus

Abstract

Provided is a charging roll for an electrophotographic apparatus, the charging roll being excellent in chargeability and antifouling properties.　A charging roll 10 for an electrophotographic apparatus includes: a shaft body 12; an elastic body layer 14 formed on the outer peripheral surface of the shaft body 12; and a surface layer 16 formed on the outer peripheral surface of the elastic body layer 14. The surface layer 16 contains a binder containing a urethane resin or an acrylic resin, and inorganic fine particles. A microroughness on the surface of the surface layer 16, the microroughness being represented by a maximum height difference within 5 μm, is 10-400 nm, inclusive.

Description

Charging rolls for electrophotographic equipment

[0001] The present invention relates to a charging roll for electrophotographic equipment, which is suitably used in electrophotographic equipment such as copying machines, printers, and facsimiles that employ an electrophotographic system.

[0002] Known charging rolls for electrophotographic devices include those having an elastic layer with rubber elasticity on the outer circumferential surface of a shaft such as a core bar, and a surface layer on the outer circumferential surface of the elastic layer. In charging rolls, the surface layer may be made of a binder polymer containing roughness-imparting particles. Examples of binder polymers for the surface layer include acrylic resins, methacrylic resins, fluororesins, silicone resins, polycarbonate resins, urethane resins, and polyamide resins.

[0003] JP 2018-060162 A

[0004] When urethane resin or acrylic resin is used in the surface layer of a charging roll, its high dielectric properties result in excellent charging properties. However, when urethane resin or acrylic resin is used, the carbonyl group increases the dipole moment, making it more likely to adsorb toner and toner additives. As printing progresses, the roll surface becomes more contaminated, which can lead to image defects such as unevenness and streaks.

[0005] The problem to be solved by the present invention is to provide a charging roll for electrophotographic equipment that is excellent in charging property and antifouling property.

[0006] The electrophotographic device charging roll according to the present invention comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein the surface layer contains a binder containing a urethane resin or an acrylic resin and inorganic fine particles, and the micro-roughness of the surface of the surface layer, which is expressed as the maximum height difference within 5 μm, is 10 nm or more and 400 nm or less.

[0007] The inorganic fine particles may have an average particle diameter of 10 nm or more and 450 nm or less. The content of the inorganic fine particles may be 30 parts by mass or more and 60 parts by mass or less relative to 100 parts by mass of the binder. The inorganic fine particles may have a relative dielectric constant of 13 or less. The inorganic fine particles may be silica fine particles or alumina fine particles. The volume resistivity of the surface layer may be 3.2×10 ４ Ω or more 6.8×10 ９ It is preferable that it is Ω or less.

[0008] The surface layer may further contain roughness-imparting particles, the average particle diameter of the roughness-imparting particles may be 5 μm or more and 30 μm or less, and the content of the roughness-imparting particles may be 15 parts by mass or more and 65 parts by mass or less relative to 100 parts by mass of the binder.

[0009] (1) The conductive roll for electrophotographic equipment according to the present invention comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein the surface layer contains a binder containing a urethane resin or an acrylic resin and inorganic fine particles, and the micro-roughness of the surface of the surface layer, which is expressed as the maximum height difference within 5 μm, is 10 nm or more and 400 nm or less.

[0010] (2) In the above (1), the inorganic fine particles may have an average particle size of 10 nm or more and 450 nm or less.

[0011] (3) In the above (1) or (2), the content of the inorganic fine particles may be 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the binder.

[0012] (4) In any one of (1) to (3) above, the inorganic fine particles may have a relative dielectric constant of 13 or less.

[0013] (5) In any one of the above (1) to (4), the inorganic fine particles may be silica fine particles or alumina fine particles.

[0014] (6) In any one of (1) to (5), the volume resistivity of the surface layer is 3.2 × 10 ４ Ω or more 6.8×10 ９It is preferable that it is Ω or less.

[0015] (7) In any one of the above (1) to (6), the surface layer may further contain particles for providing roughness.

[0016] (8) In the above (7), the average particle diameter of the roughness-imparting particles may be 5 μm or more and 30 μm or less.

[0017] (9) In the above (7) or (8), the content of the roughness-imparting particles may be 15 parts by mass or more and 65 parts by mass or less per 100 parts by mass of the binder.

[0018] The electrophotographic charging roll according to the present invention has a surface layer containing a urethane resin or an acrylic resin, resulting in excellent charging properties. By incorporating inorganic fine particles along with a binder containing a urethane resin or an acrylic resin and setting the micro-roughness of the surface layer within a specific range, the contact area of ​​the toner and external toner additives on the roll surface can be reduced. Furthermore, because the fine particles are composed of inorganic substances with no dipole moment, electrostatic adsorption of the toner and external toner additives caused by the fine particles is suppressed. This prevents contamination of the roll surface. As a result, the charging roll has excellent charging properties and anti-fouling properties.

[0019] When the average particle size of the inorganic fine particles is 10 nm or more and 450 nm or less, the micro-roughness of the surface layer is easily controlled within a specific range, and the effect of preventing the roll surface from being soiled is excellent.

[0020] When the content of the inorganic fine particles is 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the binder, the micro-roughness of the surface layer is easily kept within a specific range, and the effect of preventing contamination of the roll surface is excellent.

[0021] When the inorganic fine particles have a relative dielectric constant of 13 or less, the surface layer does not store too much charge, resulting in excellent discharge properties and good charging properties.

[0022] When the inorganic fine particles are silica fine particles or alumina fine particles, the abrasion resistance is excellent and durability can be improved.

[0023] The volume resistivity of the surface layer is 3.2×10４ Ω or more 6.8×10 ９ When the resistance is Ω or less, the electrostatic charge is excellent.

[0024] Furthermore, when the surface layer further contains roughness-forming particles, suitable surface irregularities are formed on the surface layer, which increases the discharge space between the photoreceptor and the charging roll and promotes discharge, thereby improving charging properties and suppressing image defects such as horizontal streaks and unevenness.

[0025] When the average particle diameter of the roughness-forming particles is 5 μm or more and 30 μm or less, the chargeability is excellent.

[0026] When the content of the roughness-forming particles is 15 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass of the binder, an excellent balance between electrostatic properties and antifouling properties is achieved.

[0027] 1A is a schematic view of the appearance of a charging roll for an electrophotographic apparatus according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA thereof.

[0028] The charging roll for electrophotographic equipment (hereinafter, sometimes simply referred to as the charging roll) according to the present invention will be described in detail. Fig. 1 is a schematic diagram of the appearance of the charging roll for electrophotographic equipment according to one embodiment of the present invention (a) and a cross-sectional view of the same taken along line A-A (b).

[0029] The charge roll 10 includes a shaft 12, an elastic layer 14 formed on the outer peripheral surface of the shaft 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The elastic layer 14 is a layer (base layer) that forms the base of the charge roll 10. The surface layer 16 is a layer that appears on the surface of the charge roll 10. Although not specifically shown, an intermediate layer such as a resistance adjustment layer may be formed between the elastic layer 14 and the surface layer 16, if necessary.

[0030] The shaft 12 is not particularly limited as long as it is electrically conductive. Specific examples include a solid or hollow core made of metal such as iron, stainless steel, or aluminum. The surface of the shaft 12 may be coated with an adhesive, primer, or the like, as needed. That is, the elastic layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive, primer, or the like may be made electrically conductive as needed.

[0031] The elastic layer 14 contains a crosslinked rubber. The elastic layer 14 is formed from a conductive rubber composition containing an uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking the uncrosslinked rubber. The uncrosslinked rubber may be a polar rubber or a non-polar rubber.

[0032] Polar rubber is a rubber having a polar group, and examples of the polar group include a chloro group, a nitrile group, a carboxyl group, and an epoxy group. Specific examples of polar rubber include hydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of acrylic acid ester and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR), and epoxidized natural rubber (ENR). Among the polar rubbers, hydrin rubber and nitrile rubber (NBR) are more preferred from the viewpoint that the volume resistivity tends to be particularly low.

[0033] Examples of the hydrin rubber include an epichlorohydrin homopolymer (CO), an epichlorohydrin-ethylene oxide binary copolymer (ECO), an epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), and an epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO).

[0034] Examples of urethane rubber include polyether-type urethane rubber having an ether bond in the molecule. Polyether-type urethane rubber can be produced by reacting a polyether having hydroxyl groups at both ends with a diisocyanate. Examples of polyethers include, but are not limited to, polyethylene glycol and polypropylene glycol. Examples of diisocyanates include, but are not limited to, tolylene diisocyanate and diphenylmethane diisocyanate.

[0035] Examples of non-polar rubbers include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), etc. Among non-polar rubbers, isoprene rubber is more preferred from the viewpoint of excellent tensile properties.

[0036] Examples of the crosslinking agent include a sulfur crosslinking agent, a peroxide crosslinking agent, and a dechlorination crosslinking agent. These crosslinking agents may be used alone or in combination of two or more.

[0037] Examples of the sulfur crosslinking agent include conventionally known sulfur crosslinking agents such as powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, thiuram vulcanization accelerators, and polymeric polysulfides.

[0038] Examples of the peroxide crosslinking agent include conventionally known peroxide crosslinking agents such as peroxyketals, dialkyl peroxides, peroxyesters, ketone peroxides, peroxydicarbonates, diacyl peroxides, and hydroperoxides.

[0039] Examples of the dechlorinating crosslinking agent include dithiocarbonate compounds, more specifically, quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, and 5,8-dimethylquinoxaline-2,3-dithiocarbonate.

[0040] The amount of the crosslinking agent to be added is preferably within a range of 0.1 to 2 parts by mass, more preferably within a range of 0.3 to 1.8 parts by mass, and even more preferably within a range of 0.5 to 1.5 parts by mass, per 100 parts by mass of the uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0041] When a dechlorination crosslinking agent is used as the crosslinking agent, a dechlorination crosslinking accelerator may be used in combination. Examples of the dechlorination crosslinking accelerator include 1,8-diazabicyclo(5,4,0)undecene-7 (hereinafter abbreviated as DBU) or a weak acid salt thereof. The dechlorination crosslinking accelerator may be used in the form of DBU, but from the viewpoint of handling, it is preferable to use it in the form of a weak acid salt. Examples of weak acid salts of DBU include carbonate, stearate, 2-ethylhexyl salt, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, and 2-mercaptobenzimidazole salt.

[0042] The content of the dechlorination crosslinking accelerator is preferably within a range of 0.1 to 2 parts by mass, more preferably 0.3 to 1.8 parts by mass, and even more preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0043] A conductive agent can be blended into the elastic layer 14 to impart conductivity. Examples of conductive agents include electronic conductive agents and ionic conductive agents. Examples of electronic conductive agents include carbon black, graphite, and conductive metal oxides. Examples of conductive metal oxides include conductive titanium oxide, conductive zinc oxide, and conductive tin oxide. Examples of ionic conductive agents include quaternary ammonium salts, borates, and surfactants. Various additives may also be added to the elastic layer 14 as needed. Examples of additives include lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, antifoaming agents, pigments, and mold release agents.

[0044] The elastic layer 14 can be adjusted to a predetermined volume resistivity by adjusting the type of crosslinked rubber, the amount of ionic conductive agent, the amount of electronic conductive agent, etc. ２ ~10 １０ Ω cm, 10 ３ ~10 ９ Ω cm, 10 ４ ~10 ８ The range may be appropriately set to Ω·cm.

[0045] The thickness of the elastic layer 14 is not particularly limited, and may be set appropriately within the range of 0.1 to 10 mm depending on the application.

[0046] The surface layer 16 contains a binder and inorganic fine particles. The surface layer 16 may further contain particles for providing roughness.

[0047] The binder is the base material constituting the surface layer 16. Examples of binders include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, butyral resin (PVB), alkyd resin, polyester resin, fluororubber, fluororesin, a mixture of fluororubber and fluororesin, silicone resin, silicone-grafted acrylic polymer, acrylic-grafted silicone polymer, nitrile rubber, and urethane rubber. In the present invention, the binder contains a urethane resin or an acrylic resin. Urethane resin and acrylic resin have high dielectric properties due to carbonyl groups, so by including a urethane resin or an acrylic resin in the binder, excellent electrostatic chargeability can be achieved. The binder of the surface layer 16 may contain other materials as long as the main component is a urethane resin or an acrylic resin. The main component refers to 50% by mass or more of the binder. The main component is more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0048] By blending inorganic fine particles in the surface layer 16, it is possible to form minute irregularities with nano-order micro-roughness on the surface of the surface layer 16. The minute irregularities with micro-roughness reduce the area of ​​contact between the toner and external toner additives and the surface of the surface layer 16, making it difficult for the toner and external toner additives to adhere to the surface of the surface layer 16. Furthermore, since the inorganic fine particles are made of an inorganic substance that does not have a dipole moment, it makes it difficult for the toner and external toner additives to electrostatically adsorb to the surface of the surface layer 16. These make it possible to prevent contamination of the roll surface.

[0049] The microroughness is expressed as the maximum height difference within a 5 μm range on the surface of the surface layer 16. The microroughness of the surface layer 16 is 10 nm or more and 400 nm or less. If the microroughness of the surface layer 16 is less than 10 nm, the microroughness is too small, resulting in a low effect of reducing the contact area with toner and toner external additives, and a low effect of reducing contamination during endurance testing. From this perspective, the microroughness of the surface layer 16 is preferably 15 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. On the other hand, if the microroughness of the surface layer 16 exceeds 400 nm, the microroughness is too large, making it easy for toner and toner external additives to penetrate into the recesses of the irregularities created by the inorganic fine particles, which can easily cause localized contamination during endurance testing. From this perspective, the microroughness of the surface layer 16 is preferably 350 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less.

[0050] The micro-roughness of the surface layer 16 can be determined from an image taken using a scanning probe microscope. For example, in a measurement image of a 20 μm × 20 μm measurement area, the maximum height difference within any 5 μm is measured at 100 points, and the average value can be calculated. The micro-roughness of the surface layer 16 can be adjusted by the particle size, amount, and type (material) of the inorganic microparticles.

[0051] The average particle diameter of the inorganic microparticles is preferably 10 nm or more and 450 nm or less. When the average particle diameter of the inorganic microparticles is within the above range, the microroughness of the surface layer 16 is easily controlled within a specific range, resulting in an excellent effect of preventing contamination of the roll surface. From the viewpoint of increasing the microroughness of the surface layer 16 and reducing the contact area of ​​the toner and toner external additives with the roll surface, the average particle diameter of the inorganic microparticles is more preferably 15 nm or more, even more preferably 20 nm or more, and particularly preferably 30 nm or more. Furthermore, from the viewpoint of reducing the contact area of ​​the toner and toner external additives with the roll surface, the average particle diameter of the inorganic microparticles is more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less. The average particle diameter of the inorganic microparticles is measured by laser diffraction and expressed as the average of 20 arbitrary points.

[0052] The content of inorganic fine particles is preferably 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of binder. When the content is 30 parts by mass or more, the inorganic fine particles are sufficiently filled in the surface layer 16, thereby suppressing the occurrence of localized contamination. From this viewpoint, the content is more preferably 35 parts by mass or more. Furthermore, when the content is 60 parts by mass or less, aggregation of the inorganic fine particles is suppressed, making it easier to ensure uniformity of discharge. From this viewpoint, the content is more preferably 55 parts by mass or less, and even more preferably 50 parts by mass or less.

[0053] The dielectric constant of the inorganic fine particles is preferably 13 or less. When the dielectric constant of the inorganic fine particles is 13 or less, the surface layer 16 does not accumulate too much charge due to the influence of the inorganic fine particles, resulting in excellent discharge properties and good charging properties. From this viewpoint, the dielectric constant of the inorganic fine particles is more preferably 10 or less, even more preferably 7 or less, and particularly preferably 5 or less. On the other hand, the lower limit of the dielectric constant of the inorganic fine particles is not particularly limited, but is preferably 2 or more.

[0054] The material of the inorganic fine particles is not particularly limited. Since the inorganic fine particles are not used as a conductive agent, they may have low conductivity. As the inorganic fine particles, silica fine particles, alumina fine particles, etc. are preferred from the viewpoints of low conductivity, excellent abrasion resistance, and improved durability.

[0055] The roughness-forming particles are particles for imparting micron-order roughness to the surface of the surface layer 16. In other words, they are particles for imparting micron-order irregularities to the surface of the surface layer 16. The micron-order surface irregularities of the surface layer 16 caused by the roughness-forming particles increase the discharge space between the photoreceptor and the charging roll 10, promoting discharge. This improves charging properties and can suppress image defects such as horizontal streaks and unevenness.

[0056] The roughness-forming particles may be resin particles or inorganic particles. The material of the roughness-forming particles is not particularly limited. The roughness-forming particles are preferably composed of a polymer having a carbonyl group. This is because a polymer having a carbonyl group is a material with a relatively high dielectric constant, and it is easy to ensure excellent charging properties for the charging roll 10. Examples of polymers having a carbonyl group include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, silicone-grafted acrylic polymer, acrylic-grafted silicone polymer, and urethane rubber. Of these, urethane resin, urethane rubber, and acrylic resin are preferred from the viewpoints of relative dielectric constant and charging properties.

[0057] The size of the roughness-forming particles is not particularly limited, but from the viewpoint of easily ensuring uniform charging properties, an average particle diameter of 3.0 μm or more and 50 μm or less is preferable. An average particle diameter of 5.0 μm or more and 30 μm or less is more preferable. The average particle diameter of the roughness-forming particles is expressed as the average of 20 arbitrary points when the surface of the surface layer 16 is observed with a laser microscope, and the diameter of the roughness-forming particles visible during surface observation is taken as the particle size.

[0058] The content of the roughness-forming particles in the surface layer 16 is not particularly limited, but from the viewpoints of achieving an excellent balance between chargeability and antifouling properties and easily ensuring uniform chargeability, the content is preferably 15 parts by mass or more and 65 parts by mass or less, and more preferably 20 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the binder in the surface layer 16.

[0059] If necessary, various additives may be added appropriately to the surface layer 16. Examples of the additives include a plasticizer, a leveling agent, a filler, a vulcanization accelerator, a processing aid, and a mold release agent.

[0060] The volume resistivity of the surface layer 16 is preferably set to a semiconductive region from the viewpoint of electrostatic chargeability. ４ Ω or more 6.8×10 ９ The thickness of the surface layer 16 is preferably set in the range of Ω or less. The thickness of the surface layer 16 is not particularly limited, and may be set in the range of 0.1 to 30 μm. The thickness of the surface layer 16 can be measured by observing the cross section using a laser microscope (such as Keyence's "VK-9510"). For example, the distance from the surface of the elastic layer 14 to the surface of the surface layer 16 can be measured at five arbitrary positions, and the thickness can be expressed as the average of the measured distances.

[0061] The elastic layer 14 can be formed, for example, as follows: First, the shaft 12 is placed coaxially in the hollow portion of a roll molding die, and an uncrosslinked conductive rubber composition is injected and heated and cured (crosslinked), and then the composition is demolded, or the uncrosslinked conductive rubber composition is extruded onto the surface of the shaft 12, thereby forming the elastic layer 14 on the outer periphery of the shaft 12.

[0062] The surface layer 16 can be formed by using a material for forming the surface layer 16, applying the material to the outer peripheral surface of the elastic layer 14, and then appropriately performing a drying process, etc. The material for forming the surface layer 16 may contain a diluent solvent. Examples of the diluent solvent include ketone solvents such as methyl ethyl ketone (MEK) and methyl isobutyl ketone, alcohol solvents such as isopropyl alcohol (IPA), methanol, and ethanol, hydrocarbon solvents such as hexane and toluene, acetic acid solvents such as ethyl acetate and butyl acetate, ether solvents such as diethyl ether and tetrahydrofuran, and water.

[0063] The charging roll 10 configured as described above has excellent charging properties because the surface layer 16 contains a urethane resin or an acrylic resin. By incorporating inorganic fine particles along with a binder containing a urethane resin or an acrylic resin and setting the micro-roughness of the surface layer 16 within a specific range, the area of ​​contact between the toner and external toner additives and the roll surface can be reduced. Furthermore, because the fine particles are composed of inorganic matter with no dipole moment, electrostatic adsorption of the toner and external toner additives caused by the fine particles is suppressed. This prevents contamination of the roll surface. As a result, the charging roll 10 has excellent charging properties and anti-fouling properties.

[0064] The present invention will be described in detail below using examples and comparative examples.

[0065] (Example 1) <Preparation of conductive rubber composition> 30 parts by mass of carbon black, 6 parts by mass of zinc oxide, 2 parts by mass of stearic acid, 1 part by mass of sulfur, 0.5 parts by mass of a thiazole-based vulcanization accelerator, 0.5 parts by mass of a thiuram-based vulcanization accelerator, and 50 parts by mass of heavy calcium carbonate were blended with 100 parts by mass of isoprene rubber, and the mixture was kneaded for 10 minutes using an internal mixer whose temperature was adjusted to 50°C to prepare a conductive rubber composition.

[0066] The following materials were prepared as materials for the conductive rubber composition. Isoprene rubber (IR): "JSR IR2200" manufactured by JSR Carbon black: "Showblack N762" manufactured by Cabot Japan Zinc oxide: "Zinc oxide type 2" manufactured by Sakai Chemical Industry Co., Ltd. Stearic acid: "Sakura stearate" manufactured by Nippon Oil & Fats Co., Ltd. Sulfur: "Powdered sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. Thiazole vulcanization accelerator: "Noccela DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Thiram vulcanization accelerator: "Noccela TRA" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Heavy calcium carbonate: "Whiten B" manufactured by Shiraishi Calcium Co., Ltd., average particle size 3.6 μm

[0067] <Preparation of Elastic Layer> A core metal (diameter 8 mm) was set in a molding die (pipe-shaped), the above composition was injected, and the mixture was heated at 180°C for 30 minutes, cooled, and demolded to form an elastic layer made of a conductive rubber elastic body having a thickness of 1.9 mm around the outer periphery of the core metal.

[0068] <Preparation of Surface Layer Material> 50 parts by mass of carbon black, 30 parts by mass of particles for forming roughness (urethane particles 5 μm), and 35 parts by mass of inorganic fine particles (silica 300 nm) were blended with 100 parts by mass of urethane resin, and 200 parts by mass of methyl ethyl ketone (MEK) was added. The mixture was mixed and stirred at a predetermined stirring speed to prepare a composition for forming a surface layer.

[0069] The surface layer-forming composition was roll-coated onto the outer peripheral surface of the elastic layer, and the resulting mixture was heat-treated to form a surface layer having a thickness of 1.0 μm on the outer periphery of the elastic layer. This produced the charging roll of Example 1.

[0070] Examples 2, 4-5, 10-12 Charging rolls were produced in the same manner as in Example 1, except that the surface layer material was prepared using the formulations shown in the table.

[0071] (Example 3) <Preparation of conductive rubber composition> 5 parts by mass of a vulcanization aid, 10 parts by mass of carbon, 0.5 parts by mass of a vulcanization accelerator, 2 parts by mass of sulfur, and 50 parts by mass of a filler were added to 100 parts by mass of hydrin rubber, and these were stirred and mixed using a stirrer to prepare a conductive rubber composition.

[0072] The following materials were prepared as materials for the conductive rubber composition: Hydrin rubber (ECO, "Hydrin H1100" manufactured by Nippon Zeon Co., Ltd.) Vulcanization aid (zinc oxide, "Zinc Oxide Type 2" manufactured by Mitsui Metals Co., Ltd.) Carbon ("Ketjenblack EC300J" manufactured by Ketjenblack International Co., Ltd.) Vulcanization accelerator (2-mercaptobenzothiazole, "Noccela MP" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Sulfur ("Sulfax PTC" manufactured by Tsurumi Chemical Industry Co., Ltd.) Filler (calcium carbonate, "Shiraenka CC" manufactured by Shiraishi Kogyo Co., Ltd.)

[0073] <Preparation of Elastic Layer> In the same manner as in Example 1, an elastic layer made of a conductive rubber elastic material was molded.

[0074] <Preparation of Surface Layer> A charging roll was prepared in the same manner as in Example 1, except that the formulation of the surface layer material was changed to that shown in the table.

[0075] Examples 6 to 9 and 13 Charging rolls were produced in the same manner as in Example 3, except that the surface layer material was prepared using the formulations shown in the table.

[0076] Example 14 A charging roll was produced in the same manner as in Example 1, except that the formulation of the surface layer material was changed as shown in the table. In Example 14, no roughness-imparting particles were added.

[0077] Comparative Example 1 A charging roll was produced in the same manner as in Example 1, except that the surface layer material was prepared using the formulation shown in the table. In Comparative Example 1, the binder for the surface layer was changed to a silicone resin.

[0078] Comparative Example 2 A charging roll was produced in the same manner as in Example 3, except that the surface layer material was prepared using the formulation shown in the table. In Comparative Example 2, the inorganic fine particles in the surface layer were changed to organic fine particles.

[0079] Comparative Example 3 A charging roll was produced in the same manner as in Example 3, except that the surface layer material was prepared using the formulation shown in the table. In Comparative Example 3, the inorganic fine particles in the surface layer were changed to 9 nm silica.

[0080] Comparative Example 4 A charging roll was produced in the same manner as in Example 3, except that the surface layer material was prepared using the formulation shown in the table. In Comparative Example 4, the inorganic fine particles in the surface layer were changed to 500 nm silica.

[0081] Comparative Example 5 A charging roll was produced in the same manner as in Example 1, except that the formulation of the surface layer material was changed as shown in the table. In Comparative Example 5, the amount of inorganic fine particles in the surface layer was reduced.

[0082] Comparative Example 6 A charging roll was produced in the same manner as in Example 1, except that the formulation of the surface layer material was changed as shown in the table. In Comparative Example 6, the amount of inorganic fine particles in the surface layer was increased.

[0083] The materials used for the surface layer are as follows: The particle diameters of the roughness-imparting particles and fine particles are average particle diameters. (Binder) ・Urethane resin: ADEKA "ADEKA BONTITOR HUX380" ・Acrylic resin: TOAGOSEI "ARON A-104" ・Silicone resin: Shin-Etsu Silicones "KW-255" (Roughness-forming particles) ・Urethane resin 5μm: Negami Chemical Industries "Art Pearl C-800 Transparent" ・Urethane resin 30μm: Negami Chemical Industries "Art Pearl C-200 Transparent" ・Acrylic resin 5μm: Sekisui Plastics "Techpolymer MBX-5" ・Acrylic resin 30μm: Sekisui Plastics "Techpolymer MBX-30" (Inorganic fine particles) ・Silica 9nm: Nissan Chemical Industries "Snowtex ST-S" ・Silica 12nm: Nissan Chemical Industries "Snowtex ST-30" ・Silica 300nm: Nippon Shokubai "Seahoster KE-S30"・Silica 450nm: Nissan Chemical "Snowtex MP-4540M" ・Silica 500nm: Nippon Shokubai "Seahoster KE-S50" ・Silica 300nm: micromod "43-02-302", high dielectric silica (relative dielectric constant 12.9), carboxyl group modified ・Alumina 170nm: Sumitomo Chemical "AKP-53" ・Alumina 200nm: Sumitomo Chemical "AKP-50" ・Alumina 420nm: Sumitomo Chemical "AKP-20" ・Calcium carbonate 40nm: SkySpring Nanomaterials "1957RH" (organic fine particles) ・PMMA 150nm: Nippon Shokubai "Eposter MX100W" (conductive agent) ・Carbon black: Tokushiki "8653BLACK"

[0084] The produced charging roll was used to evaluate the image, and the micro-roughness, relative dielectric constant, and volume resistivity were also measured.

[0085] (Micro-roughness) Using a scanning probe microscope (Hitachi "AFM5000II"), an image of a 20 μm × 20 μm area of ​​the surface of the surface layer was taken. After the taken image was subjected to three-dimensional tilt correction processing, the maximum height difference (Rp-v) within any 5 μm area in the image was measured at 100 points, and the average value was calculated to be the micro-roughness.

[0086] (Dielectric constant) A solution of fine particles dispersed in pure water or acetone was dropped onto a PET sheet on which an aluminum electrode had been previously vapor-deposited, and the sheet was dried. An aluminum electrode was vapor-deposited on the surface of the resulting sheet, and the dielectric constant was measured using an LCR meter ZM2353 manufactured by NF Corporation. Measurement conditions: voltage 1V / frequency 1MHz Measurement environment: 25°C x 50%RH

[0087] (Method of Measuring Volume Resistivity) The volume resistivity was measured by contacting an electrode probe ("Surface Resistivity Measuring Electrode SME-8302" manufactured by Hioki E.E.) with the charging roll and using a "Super Insulation Meter SM7110" manufactured by Hioki E.E.

[0088] (Uneven image: durable stain) The produced charging roll was attached to a unit (black) of an actual machine ("bizhub C650i" manufactured by Konica Minolta), and images were output at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was performed after 1.5 million sheets were printed. Images that were free of unevenness caused by toner or toner external additives were rated as very good "◎", images that had slight unevenness but within an acceptable range were rated as good "◯", and images that had unevenness outside the acceptable range were rated as poor "×".

[0089] (Streaky image: durable staining) The produced charging roll was attached to a unit (black) of an actual machine ("bizhub C650i" manufactured by Konica Minolta), and images were output at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was performed after 1.5 million sheets were printed. Images that were free of streaks caused by toner or toner external additives were rated as very good "◎", images that had slight streaks but were within an acceptable range were rated as good "◯", and images that had streaks outside the acceptable range were rated as poor "×".

[0090] (Black Spot Image: Charging Property) The produced charging roll was attached to a unit (black) of an actual machine ("bizhub C650 i" manufactured by Konica Minolta), and images were output at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was performed after 1.5 million sheets were printed. Images with no black spots were evaluated as good "◎", images with slight black spots occurring but within an acceptable range were evaluated as good "◯", and images with black spots occurring outside the acceptable range were evaluated as poor "×".

[0091]

[0092]

[0093]

[0094] The surface layer of the example contains a urethane resin or acrylic resin binder, which provides excellent electrostatic charging and reduces black spot images. Furthermore, the surface layer contains inorganic fine particles along with the urethane resin or acrylic resin binder, and the micro-roughness of the surface layer is within a specific range, reducing the area of ​​contact between the toner and external toner additives on the roll surface. Furthermore, the fine particles are composed of inorganic substances with no dipole moment, which reduces electrostatic adsorption of the toner and external toner additives caused by the fine particles. These features prevent contamination of the roll surface and reduce uneven and streaky images during durability testing.

[0095] The surface layer of Comparative Example 1 is composed of a silicone resin binder. As a result, it has poor charging properties and black dot images occur. The surface layer of Comparative Example 2 contains organic fine particles, rather than inorganic fine particles, together with a urethane resin. The organic fine particles are composed of PMMA. PMMA has a carbonyl group, which gives it a large dipole moment and makes it prone to electrostatic adsorption of toner and toner external additives. Furthermore, in Comparative Example 2, contamination of the roll surface during endurance testing is not suppressed, and uneven images during endurance testing are not suppressed.

[0096] The surface layer of Comparative Example 3 contains a urethane resin as a binder and inorganic fine particles together with the urethane resin, but the average particle diameter of the inorganic fine particles is too small, resulting in too little micro-roughness of the surface layer. Furthermore, Comparative Example 3 is only weakly effective in reducing the contact area of ​​the toner and toner external additives with the roll surface, so contamination of the roll surface during endurance testing is not suppressed, and uneven images during endurance testing are not suppressed. The surface layer of Comparative Example 4 contains a urethane resin as a binder and inorganic fine particles together with the urethane resin, but the average particle diameter of the inorganic fine particles is too large, resulting in too much micro-roughness of the surface layer. Furthermore, Comparative Example 4 allows the toner and toner external additives to penetrate into the recesses of the unevenness created by the inorganic fine particles, so localized contamination during endurance testing is not suppressed, and streak images during endurance testing are not suppressed.

[0097] The surface layer of Comparative Example 5 contains an acrylic resin as a binder and inorganic fine particles together with the acrylic resin, but the amount of inorganic fine particles is too small, resulting in too little micro-roughness of the surface layer. Furthermore, Comparative Example 5 is not effective in reducing the contact area of ​​the toner and toner external additives with the roll surface, so contamination of the roll surface during endurance testing is not suppressed, and uneven images during endurance testing are not suppressed. The surface layer of Comparative Example 6 contains an acrylic resin as a binder and inorganic fine particles together with the acrylic resin, but the amount of inorganic fine particles is too high, resulting in too much micro-roughness of the surface layer. Furthermore, Comparative Example 6 allows the toner and toner external additives to penetrate into the recesses of the unevenness created by the inorganic fine particles, so localized contamination during endurance testing is not suppressed, and streak images during endurance testing are not suppressed.

[0098] From the above examples and comparative examples, it can be seen that when the surface layer contains a binder containing a urethane resin or an acrylic resin and inorganic fine particles, and the micro-roughness, which is expressed as the maximum height difference within 5 μm of the surface of the surface layer, is 10 nm or more and 400 nm or less, excellent electrostatic properties and anti-fouling properties are achieved.

[0099] Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications are possible within the scope of the invention.

[0100] 10 charging roll 12 shaft body 14 elastic layer 16 surface layer

Claims

1. A charging roll for electrophotographic equipment, comprising a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein the surface layer contains a binder containing a urethane resin or an acrylic resin and inorganic fine particles, and wherein the micro-roughness of the surface of the surface layer, represented by the maximum height difference within 5 μm, is 10 nm or more and 400 nm or less.

2. The charging roll for electrophotographic equipment according to claim 1, wherein the inorganic fine particles have an average particle size of 10 nm or more and 450 nm or less.

3. The charging roll for electrophotographic equipment according to claim 1 or 2, wherein the content of the inorganic fine particles is 30 parts by weight or more and 60 parts by weight or less per 100 parts by weight of the binder.

4. The charging roll for electrophotographic equipment according to any one of claims 1 to 3, wherein the inorganic fine particles have a relative dielectric constant of 13 or less.

5. The charging roll for electrophotographic equipment according to any one of claims 1 to 4, wherein the inorganic fine particles are silica fine particles or alumina fine particles.

6. The volume resistivity of the surface layer is 3.2 x 10 ４ Ω or more 6.8×10 ９ The charging roll for an electrophotographic apparatus according to any one of claims 1 to 5, wherein the surface roughness is Ω or less.

7. The charging roll for an electrophotographic device according to any one of claims 1 to 6, wherein the surface layer further contains particles for providing roughness.

8. The charging roll for electrophotographic equipment according to claim 7, wherein the roughness-imparting particles have an average particle size of 5 μm or more and 30 μm or less.

9. A charging roll for an electrophotographic device according to claim 7 or 8, wherein the content of the roughness-forming particles is 15 parts by mass or more and 65 parts by mass or less per 100 parts by mass of the binder.

Images