Charging roll for electrophotographic apparatus and method for manufacturing charging roll for electrophotographic apparatus

Abstract

To provide a charging roll for an electro-photographic device capable of suppressing a crack on a surface layer due to a surface layer material, and a manufacturing method therefor.SOLUTION: A charging roll 10 for electro-photographic device comprises a shaft body 12, an elastic layer 14 formed on an outer peripheral surface of the shaft body 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The surface layer 16 includes a binder polymer and metal oxide particles. A part or all of the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As a charging roll for electrophotographic equipment, there is known one having an elastic layer with rubber elasticity on the outer peripheral surface of a shaft body such as a core metal, and having a surface layer on the outer peripheral surface of the elastic layer. In the charging roll, for example, depending on charging characteristics and the like, a surface layer binder polymer may be blended with roughness-forming particles, a conductive agent such as metal oxide particles, or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During printing, the charging roll rotates while in contact with the photosensitive drum. The shear stress generated by the roll pressing rotation during printing acts on the interface between the materials constituting the surface layer of the charging roll. Although roughness-forming particles or metal oxide particles may be blended in the surface layer, since the interface between each particle and the surface layer binder polymer is large, a particularly strong shear stress acts on this interface. And stress easily concentrates on the convex shape caused by the aggregation of metal oxide particles, and when the surface layer binder polymer can no longer withstand the shear stress, cracks occur in the surface layer.

[0005] The problem to be solved by the present invention is to provide a charging roll for electrophotographic equipment in which cracks in the surface layer due to the surface layer material are suppressed.

Means for Solving the Problems

[0006] The charging roll for an electrophotographic apparatus according to the present invention includes a shaft body, an elastic body layer formed on the outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic body layer, wherein the surface layer contains a binder polymer and metal oxide particles, and the gist is that part or all of the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier.

[0007] The surface layer preferably further contains roughness-forming particles, and part or all of the surface of the roughness-forming particles is covered with a fluorine-based anionic surface modifier. The fluorine-based anionic surface modifier preferably has a perfluoroalkyl group having 6 or less carbon atoms and a carboxylate group. The metal oxide particles are preferably tin oxide particles.

[0008] And the manufacturing method of the charging roll for an electrophotographic apparatus according to the present invention includes a step of mixing metal oxide particles and a fluorine-based anionic surface modifier to cover part or all of the surface of the metal oxide particles with the fluorine-based anionic surface modifier, and a step of mixing the metal oxide particles whose part or all of the surface is covered with the fluorine-based anionic surface modifier and a binder polymer, and the gist is that it has these steps.

Advantages of the Invention

[0009] According to the charging roll for an electrophotographic apparatus according to the present invention, it includes a shaft body, an elastic body layer formed on the outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic body layer, wherein the surface layer contains a binder polymer and metal oxide particles, and part or all of the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier, so that cracks in the surface layer due to the surface layer material can be suppressed.

[0010] When the surface layer further contains roughness-forming particles, if part or all of the surface of the roughness-forming particles is covered with a fluorine-based anionic surface modifier, the effect of suppressing cracks in the surface layer due to the surface layer material is improved.

[0011] When the fluorine-based anionic surface modifier has a perfluoroalkyl group having 6 or less carbon atoms and a carboxylate group, it easily interacts with the surface functional groups of the metal oxide particles, and the effect of the coating treatment can be easily obtained.

[0012] When the metal oxide particles are tin oxide particles, they exhibit stable interaction in a wide temperature range.

[0013] And according to the method for manufacturing a charging roll for an electrophotographic apparatus according to the present invention, a step of mixing metal oxide particles and a fluorine-based anionic surface modifier to coat a part or all of the surface of the metal oxide particles with the fluorine-based anionic surface modifier, and a step of mixing the metal oxide particles having a part or all of the surface covered with the fluorine-based anionic surface modifier and a binder polymer, are included. Therefore, in the surface layer, a part or all of the surface of the metal oxide particles is covered with the fluorine-based anionic surface modifier, so that cracks in the surface layer due to the surface layer material can be suppressed.

Brief Description of the Drawings

[0014]

Figure 1

Embodiments for Carrying Out the Invention

[0015] The charging roll for an electrophotographic apparatus according to the present invention (hereinafter, may be simply referred to as a charging roll) will be described in detail. FIG. 1 is an external view schematic diagram (a) of a charging roll for an electrophotographic apparatus according to an embodiment of the present invention, and a cross-sectional view taken along line A-A thereof (b).

[0016] The charged roll 10 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 elastic body layer 14 is a layer (base layer) that serves as the base of the charged roll 10. The surface layer 16 is the layer that appears on the surface of the charged roll 10. Although not particularly shown, an intermediate layer such as a resistance adjustment layer may be formed between the elastic body layer 14 and the surface layer 16 as needed.

[0017] The shaft body 12 is not particularly limited as long as it has conductivity. Specifically, examples thereof include a solid body made of metal such as iron, stainless steel, and aluminum, and a core metal made of a hollow body. An adhesive, a primer, etc. may be applied to the surface of the shaft body 12 as needed. That is, the elastic body layer 14 may be adhered to the shaft body 12 via an adhesive layer (primer layer). The adhesive, primer, etc. may be made conductive as needed.

[0018] The elastic body layer 14 contains crosslinked rubber. The elastic body layer 14 is formed of a conductive rubber composition containing uncrosslinked rubber. Crosslinked rubber is obtained by crosslinking uncrosslinked rubber. The uncrosslinked rubber may be a polar rubber or a nonpolar rubber.

[0019] A 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 the polar rubber include hydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of an acrylate 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 preferable from the viewpoint that the volume resistivity is particularly likely to be low.

[0020] Examples of the hydrin rubber include a homopolymer of epichlorohydrin (CO), an epichlorohydrin-ethylene oxide binary copolymer (ECO), an epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), an epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO), and the like.

[0021] Examples of the urethane rubber include a polyether-type urethane rubber having an ether bond in the molecule. The polyether-type urethane rubber can be produced by the reaction of a polyether having hydroxyl groups at both ends with a diisocyanate. The polyether is not particularly limited, and examples thereof include polyethylene glycol and polypropylene glycol. The diisocyanate is not particularly limited, and examples thereof include tolylene diisocyanate and diphenylmethane diisocyanate.

[0022] Examples of the nonpolar rubber include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). Among the nonpolar rubbers, isoprene rubber is more preferable from the viewpoint of excellent tensile physical properties.

[0023] 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.

[0024] 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 polymer polysulfides.

[0025] Examples of the peroxide crosslinking agent include conventionally known peroxide crosslinking agents such as peroxyketal, dialkyl peroxide, peroxyester, ketone peroxide, peroxydicarbonate, diacyl peroxide, and hydroperoxide.

[0026] Examples of the dechlorination crosslinking agent include dithiocarbonate compounds. More specifically, examples include quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, 5,8-dimethylquinoxaline-2,3-dithiocarbonate, and the like.

[0027] From the perspective of being difficult to bleed, etc., the compounding amount of the crosslinking agent is preferably in the range of 0.1 to 2 parts by mass, more preferably in the range of 0.3 to 1.8 parts by mass, and even more preferably in the range of 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the uncrosslinked rubber.

[0028] When using a dechlorination crosslinking agent 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 its weak acid salts. The dechlorination crosslinking accelerator may be used in the form of DBU, but from the perspective of handling, it is preferably used in the form of its weak acid salt. Examples of the weak acid salts of DBU include carbonate, stearate, 2-ethylhexanoate, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, 2-mercaptobenzimidazole salt, and the like.

[0029] From the perspective of being difficult to bleed, etc., the content of the dechlorination crosslinking accelerator is preferably in the range of 0.1 to 2 parts by mass with respect to 100 parts by mass of the uncrosslinked rubber. More preferably, it is in the range of 0.3 to 1.8 parts by mass, and even more preferably in the range of 0.5 to 1.5 parts by mass.

[0030] The elastic layer 14 can be compounded with a conductive agent for imparting conductivity. Examples of the conductive agent include an electron conductive agent and an ion conductive agent. Examples of the electron conductive agent include carbon black, graphite, and a conductive metal oxide. Examples of the conductive metal oxide include a conductive titanium oxide, a conductive zinc oxide, and a conductive tin oxide. Examples of the ion conductive agent include a quaternary ammonium salt, a borate, and a surfactant. Further, various additives may be appropriately added to the elastic layer 14 as needed. Examples of the additives include a lubricant, a vulcanization accelerator, an antioxidant, a light stabilizer, a viscosity modifier, a processing aid, a flame retardant, a plasticizer, a foaming agent, a filler, a dispersant, an antifoaming agent, a pigment, and a mold release agent.

[0031] The elastic layer 14 can be adjusted to a predetermined volume resistivity by factors such as the type of crosslinked rubber, the compounding amount of the ion conductive agent, and the compounding of the electron conductive agent. The volume resistivity of the elastic layer 14 can be appropriately set within a range of 10 2 ~10 10 Ω·cm, 10 3 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm or the like according to the application and the like.

[0032] The thickness of the elastic layer 14 is not particularly limited and can be appropriately set within a range of 0.1 to 10 mm according to the application and the like.

[0033] The surface layer 16 includes a binder polymer and metal oxide particles. The surface layer 16 may further include roughness-forming particles.

[0034] The binder polymer is a base polymer constituting the surface layer 16. Examples of the binder polymer include a urethane resin, a polyamide resin, an acrylic resin, an acrylic silicone resin, a butyral resin (PVB), an alkyd resin, a polyester resin, a fluororubber, a fluororesin, a mixture of a fluororubber and a fluororesin, a silicone resin, a silicone graft acrylic polymer, an acrylic graft silicone polymer, a nitrile rubber, and a urethane rubber.

[0035] As the binder polymer, a polymer having a carbonyl group is preferable. This is because a polymer having a carbonyl group is a material with a relatively high relative dielectric constant, and it is easy to ensure excellent charging properties for the charging roll 10. Examples of the polymer having a carbonyl group include urethane resins, polyamide resins, acrylic resins, acrylic silicone resins, silicone graft acrylic polymers, acrylic graft silicone polymers, and urethane rubbers. Among these, from the viewpoint of excellent abrasion resistance and the like, polyamide resins, acrylic resins, acrylic silicone resins, silicone graft acrylic polymers, and acrylic graft silicone polymers are particularly preferable. The polyamide resin may be a modified one. Examples of the modified polyamide include alkoxylated polyamides such as N-methoxymethylated nylon.

[0036] The metal oxide particles function as a conductive agent for the surface layer 16. The metal oxide particles are conductive metal oxide particles. In the surface layer 16, part or all of the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier. Part of the surface of the metal oxide particles may be covered with the fluorine-based anionic surface modifier, or all of the surface may be covered with the fluorine-based anionic surface modifier. Part of the surface preferably has an area of 30% or more of the surface of the metal oxide particles. More preferably, it is 50% or more, and even more preferably, it is 70% or more. When part of the surface is covered, the portion covered with the fluorine-based anionic surface modifier needs to be dispersed over the entire surface of the metal oxide particles.

[0037] On the surface of metal oxide particles, polar functional groups such as hydroxyl groups and carboxyl groups are present. A fluorine-based anionic surface modifier can cover the surface of metal oxide particles by the electrostatic interaction between its own anionic group and the functional groups on the surface of the metal oxide particles. Thereby, the aggregation of the metal oxide particles is suppressed. At this time, its own fluorine-containing group is oriented so as to face the outside of the metal oxide particles. The fluorine-containing group oriented so as to face the outside of the metal oxide particles on the surface of the metal oxide particles can reduce the friction at the interface between the metal oxide particles and the binder polymer and relieve the shear stress applied to the binder polymer. By these, cracks in the surface layer 16 due to the surface layer material can be suppressed. If the surface modifier is not anionic but cationic or nonionic, the surface modifier cannot interact with the functional groups on the surface of the metal oxide particles and cannot cover the surface of the metal oxide particles. Further, if the surface modifier is not fluorine-based but silicone-based or the like, the effect of reducing the friction at the interface between the metal oxide particles and the binder polymer is not sufficient. Further, if it is carbon black instead of metal oxide particles, the surface functional groups of carbon black hardly interact with the fluorine-based anionic surface modifier, so that the fluorine-based anionic surface modifier cannot well cover the surface of carbon black.

[0038] The metal oxide particles are not particularly limited as long as they have excellent conductivity. Examples of the metal oxide particles include tin oxide particles, zinc oxide particles, indium oxide particles, and titanium oxide particles. Among these, tin oxide particles are particularly preferable from the viewpoint of exhibiting stable interaction in a wide temperature range.

[0039] The particle diameter (primary particle diameter) of the metal oxide particles is not particularly limited, but from the viewpoint of image uniformity and the like, it is preferably 0.001 μm or more and 0.5 μm or less. More preferably, it is 0.005 μm or more and 0.1 μm or less. Further, the diameter of the aggregate (secondary particle diameter) in which the metal oxide particles aggregate is preferably 0.002 μm or more and 0.7 μm or less from the viewpoint of dispersibility. More preferably, it is 0.6 μm or less. The diameter of the aggregate of the metal oxide particles can be kept small by covering the surface of the metal oxide particles with a fluorine-based anionic surface modifier.

[0040] In the surface layer 16, the content of the metal oxide particles is preferably 30 parts by mass or more with respect to 100 parts by mass of the binder polymer from the viewpoint of conductivity and the like. More preferably, it is 50 parts by mass or more, and still more preferably, it is 70 parts by mass or more. Further, in the surface layer 16, the content of the metal oxide particles is preferably 200 parts by mass or less with respect to 100 parts by mass of the binder polymer from the viewpoint of stress dispersibility and the like. More preferably, it is 150 parts by mass or less.

[0041] The fluorine-based anionic surface modifier is used for the purpose of covering the surface of the metal oxide particles to suppress the aggregation of the metal oxide particles or modifying the surface of the metal oxide particles. Further, when the surface layer 16 contains roughness-forming particles, it is used for the purpose of covering the surface of the roughness-forming particles to suppress the aggregation of the roughness-forming particles, suppressing the interaction between the roughness-forming particles and the metal oxide particles, or modifying the surface of the roughness-forming particles.

[0042] The fluorine-based anionic surface modifier has an anionic group. Examples of the anionic group include a carboxylate group (-COO - ), a sulfonate group (-SO4 2- ), and a phosphate group. Among these, the carboxylate group is particularly preferable from the viewpoint of excellent balance of the interaction with the functional groups on the surface of the metal oxide.

[0043] The fluorine-based anionic surface modifier is composed of a compound having an organic group containing fluorine (a compound having a fluorine-containing group). Examples of the fluorine-containing group include fluoroalkyl groups having 1 to 20 carbon atoms. The fluoroalkyl group may be a perfluoroalkyl group in which all hydrogen atoms of the alkyl group are substituted with fluorine atoms, or a fluoroalkyl group in which some hydrogen atoms of the alkyl group are substituted with fluorine atoms. Among these, from the viewpoint of excellent surface modification effect of metal oxide particles by the fluorine-containing group, etc., a perfluoroalkyl group is more preferable. Also, the fluorine-containing group preferably has 6 or less carbon atoms. More preferably, it has 1 to 6 carbon atoms, and even more preferably, it has 2 to 6 carbon atoms. Since there are strong concerns about environmental regulations when the carbon number of the fluorine-containing group is 8 or more, the carbon number of the fluorine-containing group is preferably 6 or less. Also, when the carbon number of the fluorine-containing group is 2 or more, it is preferable in terms of excellent surface tension reducing effect.

[0044] The fluorine-based anionic surface modifier preferably has one or more fluorine-containing groups in the molecule. However, from the viewpoints of small steric hindrance and excellent coating efficiency when the surface modifier is oriented on the surface of metal oxide particles by the coating treatment, etc., those having one fluorine-containing group in the molecule are particularly preferable. Also, the fluorine-based anionic surface modifier preferably has one or more anionic groups in the molecule. However, from the viewpoints of excellent uniformity of interaction with metal oxide particles, etc., those having one anionic group in the molecule are particularly preferable.

[0045] The fluorine-based anionic surface modifier may be a monomer or a polymer. From the perspective that the obstacle is small when the surface modifier is oriented on the surface of the metal oxide particles during the coating treatment, the monomer is more preferable than the polymer. From the perspective of the stability of the interaction state, the molecular weight (number average molecular weight) of the fluorine-based anionic surface modifier is preferably 400 or more. More preferably 500 or more, and even more preferably 1000 or more. Also, from the perspective of the number of reactive groups, the molecular weight (number average molecular weight) of the fluorine-based anionic surface modifier is preferably less than 3000. More preferably 2500 or less, and even more preferably 2000 or less.

[0046] The amount of the fluorine-based anionic surface modifier is preferably 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the metal oxide particles. More preferably, it is 0.3 part by mass or more and 3.0 parts by mass or less, and even more preferably 0.5 part by mass or more and 3.0 parts by mass or less. Also, when the surface layer 16 further contains particles for forming roughness, the amount of the fluorine-based anionic surface modifier is preferably 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the metal oxide particles. More preferably, it is 0.3 part by mass or more and 3.0 parts by mass or less, and even more preferably 0.5 part by mass or more and 3.0 parts by mass or less. Also, when the surface layer 16 further contains particles for forming roughness, the total amount of the fluorine-based anionic surface modifier is preferably 5.0 parts by mass or less with respect to 100 parts by mass of the metal oxide particles.

[0047] The particles for forming roughness are particles for imparting roughness to the surface of the surface layer 16. That is, they are particles for imparting unevenness to the surface of the surface layer 16. The surface unevenness of the surface layer 16 increases the discharge space between the photoreceptor and the charging roll 10 and promotes discharge. Thereby, the chargeability can be improved, and image defects such as horizontal streaks and unevenness can be suppressed.

[0048] Particles for forming roughness are made of resin particles, inorganic particles, etc. The material of the particles for forming roughness is not particularly limited. The particles for forming roughness 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 relative permittivity, and it is easy to ensure excellent chargeability of the charging roll 10. Examples of the polymer having a carbonyl group include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, silicone graft acrylic polymer, acrylic graft silicone polymer, urethane rubber, etc. Among these, polyamide resin, acrylic resin, acrylic silicone resin, silicone graft acrylic polymer, and acrylic graft silicone polymer are particularly preferable from the viewpoints such as excellent wear resistance.

[0049] Part of or all of the surface of the particles for forming roughness may be covered with a fluorine-based anionic surface modifier. When the surface of the particles for forming roughness is covered with a fluorine-based anionic surface modifier, the interaction between the polar functional groups present on the surface of the particles for forming roughness and the functional groups on the surface of the metal oxide particles becomes small, and it becomes difficult for the metal oxide particles to gather on the surface of the particles for forming roughness. As a result, stress concentration due to aggregation of the metal oxide particles on the surface of the particles for forming roughness is suppressed, and the generation of cracks due to the shear stress of the binder polymer in the surface layer 16 is easily suppressed. In addition, since the friction on the surface of the particles for forming roughness is reduced, the generation of cracks due to shear stress at the interface between the particles for forming roughness and the binder polymer is also suppressed. Part of the surface preferably has an area of 30% or more of the surface of the particles for forming roughness. More preferably, it is 50% or more, and still more preferably, it is 70% or more. When part of the surface is covered, the portion covered with the fluorine-based anionic surface modifier needs to be dispersed throughout the surface of the particles for forming roughness.

[0050] The fluorine-based anionic surface modifier that covers the surface of the roughness-forming particles is the same as those used to cover the surface of the metal oxides described above. The fluorine-based anionic surface modifier that covers the surface of the roughness-forming particles may be the same as or different from the fluorine-based anionic surface modifier that covers the surface of the metal oxides.

[0051] The size of the roughness-forming particles is not particularly limited, but from the viewpoint of easily ensuring uniform chargeability, etc., those with an average particle diameter of 3.0 μm or more and 50 μm or less are preferred. More preferably, those with an average particle diameter of 5.0 μm or more and 30 μm or less are preferred. The average particle diameter of the roughness-forming particles is observed with a laser microscope on the surface of the surface layer 16, and the diameter of the roughness-forming particles 16 visible during surface observation is taken as the particle diameter and represented by the average of any 20 points.

[0052] The content in the surface layer 16 of the roughness-forming particles is not particularly limited, but from the viewpoint of easily ensuring uniform chargeability, etc., it is preferably 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the binder polymer in the surface layer 16. More preferably, it is 5 parts by mass or more and 30 parts by mass or less.

[0053] Various additives may be appropriately added to the surface layer 16 as needed. Examples of the additives include plasticizers, leveling agents, fillers, vulcanization accelerators, processing aids, mold release agents, etc.

[0054] The volume resistivity of the surface layer 16 may be set in the semiconductive region from the viewpoint of chargeability, etc. Specifically, for example, 1.0×10 7 ~1.0×10 10It is preferably set within the range of Ω·cm. The volume resistivity can be measured in accordance with JIS K6911. The thickness of the surface layer 16 is not particularly limited and may be set, for example, within 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 "VK-9510" manufactured by Keyence). For example, at five locations at arbitrary positions, the distance from the surface of the elastic body layer 14 to the surface of the surface layer 16 can be measured respectively, and it can be represented by the average value.

[0055] The elastic body layer 14 can be formed, for example, as follows. First, the shaft body 12 is coaxially installed in the hollow part of a roll forming die, an uncrosslinked conductive rubber composition is injected, heated and cured (crosslinked), and then demolded, or the elastic body layer 14 is formed on the outer periphery of the shaft body 12 by extruding the uncrosslinked conductive rubber composition onto the surface of the shaft body 12.

[0056] The surface layer 16 can be formed by using the forming material of the surface layer 16, applying this to the outer peripheral surface of the elastic body layer 14, and appropriately performing drying treatment, etc. The forming material of the surface layer 16 may contain a diluting solvent. Examples of the diluting 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, acetate solvents such as ethyl acetate and butyl acetate, ether solvents such as diethyl ether and tetrahydrofuran, and water.

[0057] The forming material of the surface layer 16 contains a binder polymer and metal oxide particles. The forming material of the surface layer 16 may further contain roughness-forming particles as required. As described above, a part or all of the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier. Also, as described above, a part or all of the surface of the roughness-forming particles is covered with a fluorine-based anionic surface modifier.

[0058] The forming material of the surface layer 16 may be prepared as follows. First, metal oxide particles and a fluorine-based anionic surface modifier are mixed to cover part or all of the surface of the metal oxide particles with the fluorine-based anionic surface modifier. Next, the metal oxide particles whose part or all of the surface is covered with the fluorine-based anionic surface modifier and a binder polymer are mixed. In this way, by mixing the metal oxide particles and the fluorine-based anionic surface modifier first before mixing the metal oxide particles with the binder polymer, part or all of the surface of the metal oxide particles can be covered with the fluorine-based anionic surface modifier.

[0059] When the forming material of the surface layer 16 contains roughness-forming particles, the roughness-forming particles may also be mixed with a fluorine-based anionic surface modifier before being mixed with the binder polymer. Thereby, part or all of the surface of the roughness-forming particles can be covered with the fluorine-based anionic surface modifier. When the surface of the roughness-forming particles is also covered with the fluorine-based anionic surface modifier, before mixing with the binder polymer, the metal oxide particles and the roughness-forming particles may be mixed together with the fluorine-based anionic surface modifier, or may be mixed separately with the fluorine-based anionic surface modifier. Mixing separately enhances the effect of coating the surface of each particle and the effect of suppressing the aggregation of metal oxide particles on the surface of the roughness-forming particles.

[0060] According to the charging roll 10 having the above configuration, since part or all of the surface of the metal oxide particles contained in the surface layer 16 is covered with the fluorine-based anionic surface modifier, the aggregation of the metal oxide particles is suppressed. Further, the friction at the interface between the metal oxide particles and the binder polymer is reduced by the fluorine-containing groups oriented so as to face the outside of the metal oxide particles, and the shear stress applied to the binder polymer can be relaxed. Thereby, cracks in the surface layer 16 due to the surface layer material are suppressed.

[0061] When the aggregation of metal oxide particles is suppressed, the resistance unevenness of the surface layer 16 becomes small. The resistance unevenness of the surface layer 16 can be represented by measuring the resistance of 100 points on the surface of the surface layer 16 randomly by AFM and calculating the ratio of the difference between the maximum value and the minimum value of the resistance to the average value of the resistance of the 100 points ((resistance maximum value - resistance minimum value) / resistance average value). When a part or all of the surface of the metal oxide particles contained in the surface layer 16 is covered with a fluorine-based anionic surface modifier, the above ratio becomes as small as about 15%. When a part or all of the surface of the metal oxide particles contained in the surface layer 16 is not covered with a fluorine-based anionic surface modifier (when the resistance unevenness is large), the ratio becomes as large as about 30%.

[0062] Furthermore, when a part or all of the surface of the roughness-forming particles contained in the surface layer 16 is covered with a fluorine-based anionic surface modifier, it becomes difficult for metal oxide particles to gather on the surface of the roughness-forming particles, stress concentration due to the aggregation of metal oxide particles on the surface of the roughness-forming particles is suppressed, and cracks are less likely to occur due to the shear stress of the binder polymer in the surface layer 16. Also, since the friction on the surface of the roughness-forming particles is reduced, cracks are less likely to occur due to the shear stress at the interface between the roughness-forming particles and the binder polymer.

Examples

[0063] Hereinafter, the present invention will be described in detail using examples and comparative examples.

[0064] (Example 1) (Preparation of the composition for the elastic body layer) To 100 parts by mass of hydrin rubber (ECO, "Epicroma CG102" manufactured by Daiso), 5 parts by mass of vulcanization aid (zinc oxide, "Zinc Oxide No. 2" manufactured by Mitsui Mining & Smelting Co., Ltd.), 10 parts by mass of carbon ("Ketjenblack EC300J" manufactured by Ketjenblack International), 0.5 parts by mass of vulcanization accelerator (2-mercaptobenzothiazole, "Nocceler M-P" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 2 parts by mass of sulfur ("Sulfax PTC" manufactured by Tsurumi Chemical Industry Co., Ltd.), and 50 parts by mass of filler (calcium carbonate, "Hakuenka CC" manufactured by Shiraishi Kogyo) were added, and these were stirred and mixed by a stirrer to prepare a conductive rubber composition.

[0065] <Fabrication of the elastomeric layer> A shaft body (diameter 8 mm) with nickel plating on an iron core was set in a molding die (pipe-shaped), the above composition for the elastomeric layer was injected, heated at 180 °C for 30 minutes, then cooled and demolded to form an elastomeric layer made of a conductive rubber elastomer with a thickness of 1.9 mm on the outer periphery of the core.

[0066] <Coating treatment of the particles> To 100 parts by mass of metal oxide, 0.7 parts by mass of a fluorine-based anionic surface modifier was blended, 100 parts by mass of MEK was added, and the mixture was stirred at 40 °C or lower for 30 minutes. Thus, a metal oxide coated with a fluorine-based anionic surface modifier was obtained. Also, to 50 parts by mass of roughness-forming particles ("Orgasol 2001UDNAT1" manufactured by Arkema), 0.3 parts by mass of a fluorine-based anionic surface modifier was blended, 50 parts by mass of MEK was added, and the mixture was stirred at 40 °C or lower for 30 minutes. Thus, roughness-forming particles coated with a fluorine-based anionic surface modifier were obtained.

[0067] <Fabrication of the surface layer> To 100 parts by mass of a polyamide resin (binder polymer), 50 parts by mass of a melamine resin, 100 parts by mass of metal oxide particles coated with a fluorine-based anionic surface modifier, and 50 parts by mass of roughness-forming particles coated with a fluorine-based anionic surface modifier were added, and the mixture was mixed with 100 parts by mass of MEK to prepare a surface layer-forming composition. Next, the surface layer-forming composition was roll-coated on the outer peripheral surface of the elastomer layer and heat-treated to form a surface layer with a thickness of 10 μm on the outer periphery of the elastomer layer. Thereby, a charged roll was produced.

[0068] (Examples 2-8, 10) The surface layer material was constituted with the blending composition described in Table 1.

[0069] (Example 9) In the composition for the elastomer layer, the base polymer was changed from hydrin rubber to isoprene rubber (IR, "JSR IR2200" manufactured by JSR).

[0070] (Comparative Example 1) A charged roll was produced in the same manner as in Example 1, except that the metal oxide particles were not coated in the surface layer material.

[0071] (Comparative Example 2) A charged roll was produced in the same manner as in Example 1, except that carbon black was used instead of metal oxide particles as the conductive agent in the surface layer material.

[0072] (Comparative Example 3) A charged roll was produced in the same manner as in Comparative Example 2, except that the carbon black used as the conductive agent was not coated.

[0073] (Comparative Examples 4-7) A charged roll was produced in the same manner as in Example 10, except that the surface modifier was changed in the surface layer material.

[0074] The materials used for the surface layer material are as follows. · Metal oxide particle <1>: Conductive tin oxide, (manufactured by Ishihara Sangyo Co., Ltd., "SN-100P"), average particle diameter 0.01 - 0.03 μm · Metal oxide particle <2>: Conductive zinc oxide, (manufactured by Hakusuitec Co., Ltd., "Pazet GK-40"), average particle diameter 0.02 - 0.04 μm · Carbon black: (manufactured by Cabot Japan Ltd., "Shoublack N762") · Surface modifier <1>: Fluorine-based, anionic (containing carboxylate group), (manufactured by DIC Corporation, "Megafac F-410") · Surface modifier <2>: Fluorine-based, anionic (containing sulfonate group), (manufactured by Neos Co., Ltd., "Fujagent 110") · Surface modifier <3>: Fluorine-based, cationic (containing quaternary ammonium group), (manufactured by Neos Co., Ltd., "Fujagent 300") · Surface modifier <4>: Fluorine-based, nonionic, (manufactured by DIC Corporation, "Megafac F-554") · Surface modifier <5>: A carboxyl group-containing silicone-based surface modifier (manufactured by Shin-Etsu Silicone Co., Ltd., "X-22-3710") saponified with sodium hydroxide to have an anionic group (carboxylate group) · Roughness-forming particle <1>: Made of polyurethane, (manufactured by Negami Kogyo Co., Ltd., "Art Pearl C-800T"), average particle diameter 6 μm · Roughness-forming particle <2>: Made of polyamide, (manufactured by Arkema Co., Ltd., "Orgasol 2001UDNAT1"), average particle diameter 5 μm · Binder polymer <1>: Polyamide, (manufactured by Echi City Co., Ltd., "Fine Resin FR-101") · Binder polymer <2>: Polyurethane, (urethane resin, manufactured by Tosoh Corporation, "Nipolan 5196")

[0075] Using the manufactured charging roll, the occurrence of cracks on the surface layer was examined.

[0076] (Image evaluation) The manufactured charging roll was attached to the unit (black) of an actual machine (RICOH's "MP C6004"), and evaluation (streak evaluation) was performed after printing 500,000 sheets at a 25% density halftone in an environment of 10°C × 10% RH. Those without the occurrence of streak images due to cracks on the surface layer were marked as "〇", and those with the occurrence of streak images due to cracks on the surface layer were marked as "×".

[0077]

Table 1

[0078] In Comparative Example 1, the surface of the metal oxide particles is not coated with a surface modifier. Therefore, the aggregation of the metal oxide particles cannot be suppressed, and the cracks on the surface layer caused by the surface material cannot be suppressed. In Comparative Examples 2 and 3, the conductive agent is carbon black. In Comparative Example 2, although the surface of the carbon black is treated with a surface modifier, since the surface functional groups of the carbon black interact difficultly with the surface modifier, the effect of the coating treatment cannot be exerted, and the aggregation cannot be suppressed. Therefore, in Comparative Example 2, the cracks on the surface layer caused by the surface material cannot be suppressed. In Comparative Example 3, the surface of the carbon black is not coated with a surface modifier. Therefore, the aggregation of the carbon black cannot be suppressed, and the cracks on the surface layer caused by the surface material cannot be suppressed.

[0079] In Comparative Examples 4 and 5, the surface modifier is a fluorine-based cationic surface modifier. In Comparative Example 6, the surface modifier is a fluorine-based nonionic surface modifier. In Comparative Examples 4 to 6, since the surface modifier does not interact with the surface functional groups of the metal oxide particles, the metal oxide particles are not coated with the surface modifier, and the aggregation of the metal oxide particles is not suppressed. Therefore, in Comparative Examples 4 to 6, the cracks on the surface layer by the surface layer material are not suppressed. In Comparative Example 7, the surface modifier is a silicone-based anionic surface modifier. In Comparative Example 7, although the metal oxide particles are coated with the surface modifier, since there is no fluorine-containing group oriented so as to face the outside of the metal oxide particles, the effect of reducing the friction at the interface between the metal oxide particles and the binder polymer is insufficient, and the cracks on the surface layer by the surface layer material are not suppressed.

[0080] On the other hand, in the Examples, metal oxide particles are used as the conductive agent, and the surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier. Therefore, the aggregation of the metal oxide particles is suppressed. Further, the friction at the interface between the metal oxide particles and the binder polymer is reduced by the fluorine-containing groups oriented so as to face the outside of the metal oxide particles, and the shear stress applied to the binder polymer is relaxed. As a result, the cracks on the surface layer by the surface layer material are suppressed.

[0081] As described above, the embodiments and examples of the present invention have been explained. However, the present invention is not limited to the above embodiments and examples at all, and various modifications are possible without departing from the spirit of the present invention.

Explanation of Reference Numerals

[0082] 10 Charging roll 12 Shaft body 14 Elastomer layer 16 Surface layer

Claims

1. A charging roll for an electrophotographic apparatus, comprising: a shaft body; an elastic body layer formed on an outer peripheral surface of the shaft body; and a surface layer formed on an outer peripheral surface of the elastic body layer, wherein the surface layer contains a binder polymer and metal oxide particles, and a part or all of a surface of the metal oxide particles is covered with a fluorine-based anionic surface modifier.

2. The charging roll for an electrophotographic apparatus according to claim 1, wherein the surface layer further contains roughness-forming particles, and a part or all of a surface of the roughness-forming particles is covered with a fluorine-based anionic surface modifier.

3. The charging roll for an electrophotographic apparatus according to claim 1 or 2, wherein the fluorine-based anionic surface modifier has a perfluoroalkyl group having 6 or less carbon atoms and a carboxylate group.

4. The charging roll for an electrophotographic apparatus according to any one of claims 1 to 3, wherein the metal oxide particles are tin oxide particles.

5. A method for manufacturing a charging roll for an electrophotographic apparatus according to any one of claims 1 to 4, comprising: mixing metal oxide particles and a fluorine-based anionic surface modifier to cover a part or all of a surface of the metal oxide particles with the fluorine-based anionic surface modifier; and mixing the metal oxide particles having a part or all of a surface covered with the fluorine-based anionic surface modifier and a binder polymer.

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