Electrostatic roller for electrophotographic equipment

Abstract

To provide a charging roll for electro-photographic apparatuses, the roll having an excellent charging property even if the discharge amount is decreased.SOLUTION: A charging roll 10 for electro-photographic apparatuses 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 contains non-polar rubber, polar rubber, and carbon black, a dielectric constant thereof is 7 to 29, and a resistance value thereof is 6.0×104 Ω to 5.0×106 Ω, and the surface layer 16 contains fluororesin and (meth) acrylic resin, a dielectric constant thereof is 10 to 22, and a resistance value thereof is 1.2×104 Ω to 8.8×105 Ω.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 fax machines that employ the electrophotographic method.

Background Art

[0002] The charging roll of electrophotographic equipment is known to have a configuration including a shaft body composed of a core metal or the like, 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. The elastic body layer is composed of a rubber material such as isoprene rubber, and the surface layer is composed of a resin material such as acrylic resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document

Summary of the Invention

Problems to be Solved by the Invention

[0004] The charging roll of electrophotographic equipment often adopts a charging system that charges the photoreceptor by discharging from the charging roll to the photoreceptor. However, in order to sufficiently charge the photoreceptor, when the discharge amount is increased, a large amount of harmful substances such as ozone and NOx are generated, which may cause environmental degradation and image degradation. On the other hand, if the discharge amount is small, the charge amount may be insufficient, which may lead to image degradation.

[0005] The problem to be solved by the present invention is to provide a charging roll for electrophotographic equipment that has excellent charging properties even when the discharge amount is reduced.

Means for Solving the Problems

[0006] The charging roll for an electrophotographic apparatus according to the present invention includes a shaft body, an elastic layer formed on the outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic layer. The elastic layer contains a nonpolar rubber, a polar rubber, and carbon black, has a relative permittivity of 7 or more and 29 or less, and a resistance value of 6.0×10 4 Ω or more and 5.0×10 6 Ω or less. The surface layer contains a fluororesin and a (meth)acrylic resin, has a relative permittivity of 10 or more and 22 or less, and a resistance value of 1.2×10 4 Ω or more and 8.8×10 5 Ω or less.

[0007] The area ratio of the nonpolar rubber to the polar rubber on the surface of the elastic layer is preferably nonpolar rubber:polar rubber = 9:1 to 7:3. The nonpolar rubber is preferably isoprene rubber or natural rubber, and the polar rubber is preferably nitrile rubber or hydrin rubber. The carbon black preferably has an average particle diameter of 36 nm or more and 80 nm or less, and the product of the DBP absorption amount and the specific surface area is 1728 or more and 5445 or less. The content of the carbon black is preferably 15 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass in total of the nonpolar rubber and the polar rubber. The elastic layer is preferably composed of a composition that does not contain an ionic conductive agent. The content ratio of the fluororesin to the (meth)acrylic resin is preferably fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:3 in terms of mass ratio. The fluororesin has a relative permittivity of 8 or more and 10 or less, and a volume resistivity of 1.0×10 13 Ω·cm or more and 1.0×10 14It is preferably below Ω·cm. The fluororesin is preferably polyvinylidene fluoride. The difference in volume resistivity between the fluororesin and the (meth)acrylic resin is preferably 0.2 log Ω or less. The indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less. The indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less. The difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is preferably 0.1 GPa or less, and the difference in elastic recovery rate is preferably 5% or less. The tensile strength of the fluororesin is preferably 28 MPa or more and 40 MPa or less. The difference in relative dielectric constant between the fluororesin and the (meth)acrylic resin is preferably 2 or less. The surface layer preferably further contains particles for forming roughness. The particles for forming roughness are preferably porous particles.

[0008] (1) 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. The elastic body layer contains a nonpolar rubber, a polar rubber, and carbon black, has a relative dielectric constant of 7 or more and 29 or less, and a resistance value of 6.0×10 4 Ω or more and 5.0×10 6 Ω or less. The surface layer contains a fluororesin and a (meth)acrylic resin, has a relative dielectric constant of 10 or more and 22 or less, and a resistance value of 1.2×10 4 Ω or more and 8.8×10 5 Ω or less. [[ID=!4]]

[0009] (2) In the above (1), the area ratio of the nonpolar rubber to the polar rubber on the surface of the elastic body layer is preferably nonpolar rubber:polar rubber = 9:1 to 7:3.

[0010] (3) In the above (1) or the above (2), the nonpolar rubber is preferably isoprene rubber or natural rubber, and the polar rubber is preferably nitrile rubber or hydrin rubber.

[0011] (4) In any one of (1) to (3) above, the carbon black is preferably such that the average particle size is 36 nm or more and 80 nm or less, and the product of the DBP absorption amount and specific surface area is 1728 or more and 5445 or less.

[0012] (5) In any one of (1) to (4) above, the carbon black content is preferably 15 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the total of the non-polar rubber and the polar rubber.

[0013] (6) In any one of (1) to (5) above, the elastic layer may be composed of a composition that does not contain an ionic conductive agent.

[0014] (7) In any one of (1) to (6) above, the content ratio of the fluororesin to the (meth)acrylic resin should be fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:3 by mass.

[0015] (8) In any one of (1) to (7) above, the fluororesin has a relative permittivity of 8 or more and 10 or less, and a volume resistivity of 1.0 × 10 13 Ω cm or more 1.0×10 14 It should be less than or equal to Ω·cm.

[0016] (9) In any one of (1) to (8) above, the fluororesin may be polyvinylidene fluoride.

[0017] (10) In any one of (1) to (9) above, the difference in volume resistivity between the fluororesin and the (meth)acrylic resin is preferably 0.2 log Ω or less.

[0018] (11) In any one of (1) to (10) above, the indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less, and the indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less.

[0019] (12) In any one of (1) to (11) above, it is preferable that the difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is 0.1 GPa or less, and the difference in elastic recovery rate is 5% or less.

[0020] (13) In any one of (1) to (12) above, the tensile strength of the fluororesin is preferably 28 MPa or more and 40 MPa or less.

[0021] (14) In any one of (1) to (13) above, it is preferable that the difference in the relative permittivity between the fluororesin and the (meth)acrylic resin is 2 or less.

[0022] (15) In any one of (1) to (14) above, the surface layer may further contain roughness-forming particles.

[0023] (16) In the above (15), the roughness-forming particles may be porous particles. [Effects of the Invention]

[0024] According to the electrophotographic equipment charging roll of the present invention, the elastic layer contains non-polar rubber, polar rubber, and carbon black, with a relative permittivity of 7 to 29 and a resistance of 6.0 × 10⁻¹⁴. 4 Ω or more 5.0×10 6 The resistance is less than or equal to Ω, the surface layer contains fluororesin and (meth)acrylic resin, the dielectric constant is between 10 and 22, and the resistance is 1.2 × 10⁻¹⁰. 4 Ω or more 8.8×10 5 Because the impedance is less than Ω, the amount of discharge from the charging roll to the photoreceptor is reduced, suppressing the generation of harmful substances such as ozone and NOx, thereby minimizing environmental degradation and image deterioration. Furthermore, the above configuration facilitates charge transfer at the grounding point between the charging roll and the photoreceptor, allowing the photoreceptor to be charged to the desired level by injecting charge from the charging roll. As a result, excellent charging performance is achieved even with a low discharge amount.

[0025] Here, if the area ratio of the non-polar rubber to the polar rubber on the surface of the elastic layer is non-polar rubber:polar rubber = 9:1 to 7:3, it is easier to keep the relative permittivity of the elastic layer within a specific range.

[0026] Furthermore, if the non-polar rubber is isoprene rubber or natural rubber, and the polar rubber is nitrile rubber or hydrin rubber, it is easier to keep the dielectric constant of the elastic layer within a specific range.

[0027] Furthermore, if the carbon black has an average particle diameter of 36 nm or more and 80 nm or less, and the product of DBP absorption amount and specific surface area is between 1728 and 5445, it is easier to set the dielectric constant of the carbon black to a desired level and bring the relative permittivity of the elastic layer within a specific range.

[0028] Furthermore, if the carbon black content is between 15 and 50 parts by mass per 100 parts by mass of the total of the non-polar rubber and the polar rubber, it is easier to keep the resistance and dielectric constant of the elastic layer within a specific range.

[0029] Furthermore, if the elastic layer is composed of a composition that does not contain an ionic conductive agent, the relative permittivity of the elastic layer does not rise too high, making it easier to keep the relative permittivity of the elastic layer within a specific range.

[0030] Furthermore, if the content ratio of the fluororesin to the (meth)acrylic resin is such that the mass ratio is fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:3, it is easier to keep the dielectric constant of the surface layer within a specific range.

[0031] Furthermore, the fluororesin has a relative permittivity of 8 to 10 and a volume resistivity of 1.0 × 10⁻⁶. 13 Ω cm or more 1.0×10 14 When the dielectric constant is less than Ω·cm, fluororesin has a relatively high dielectric constant and low resistance, making it easy to create a surface layer with a high dielectric constant and low resistance. Furthermore, the electrostatic effect of the fluororesin is also easily maintained in this state.

[0032] Furthermore, if the fluororesin is polyvinylidene fluoride, it has a relatively high dielectric constant and low resistance, making it easy to create a surface layer with a high dielectric constant and low resistance. In addition, the electrostatic effect of the fluororesin is also easily maintained at this time.

[0033] Furthermore, if the difference in volume resistivity between the fluororesin and the (meth)acrylic resin is 0.2 log Ω or less, the unevenness of charge injection from the charging roll to the photoreceptor becomes smaller.

[0034] Furthermore, if the indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less, and the indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less, then the deformation of the charging roll in response to the pressure received from the photoreceptor during rotation becomes uniform, and localized stress concentration is less likely to occur.

[0035] Furthermore, if the difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is 0.1 GPa or less, and the difference in elastic recovery rate is 5% or less, surface cracking due to physical stress from the photoreceptor is easily suppressed. This improves durability.

[0036] Furthermore, if the tensile strength of the fluororesin is between 28 MPa and 40 MPa, the strength of the surface layer improves, and durability is enhanced.

[0037] Furthermore, if the difference in the relative permittivity between the fluororesin and the (meth)acrylic resin is 2 or less, the unevenness of the discharge from the charging roll to the photoreceptor will be reduced.

[0038] Furthermore, if the surface layer contains roughness-forming particles, a suitable discharge space can be formed between the photoreceptor and the charging roll. In this case, if the roughness-forming particles are porous particles, the binder resin of the surface layer and the roughness-forming particles become more integrated, making the surface layer less prone to cracking. In addition, the resistance can be integrated and the injected charge can be made uniform. [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic external view (a) of a charging roll for electrophotographic equipment according to one embodiment of the present invention, and a cross-sectional view of the same along line AA (b). [Modes for carrying out the invention]

[0040] The electrostatic charge roll for electrophotographic equipment (hereinafter sometimes simply referred to as the electrostatic charge roll) according to the present invention will be described in detail. Figure 1 is a schematic external view (a) and a cross-sectional view (b) of the electrostatic charge roll for electrophotographic equipment according to one embodiment of the present invention.

[0041] The electrostatic roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer circumferential surface of the shaft 12, and a surface layer 16 formed on the outer circumferential surface of the elastic layer 14. The elastic layer 14 is the base layer of the electrostatic roll 10. The surface layer 16 is the layer that appears on the surface of the electrostatic roll 10.

[0042] The shaft 12 is not particularly limited as long as it is conductive. Specifically, 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 or primer as needed. In other words, the elastic layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive or primer may be made conductive as needed.

[0043] The elastic layer 14 contains non-polar rubber, polar rubber, and carbon black, with a dielectric constant of 7 to 29 and a resistivity of 6.0 × 10⁻⁶. 4 Ω or more 5.0×10 6 It is less than or equal to Ω.

[0044] Examples of nonpolar rubbers for the elastic layer 14 include isoprene rubber (IR), hydrogenated isoprene rubber, natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), ethylene-propylene rubber (EPM), ethylene-propylene-diene ternary copolymer rubber (EPDM), and silicone rubber (Q). These may be used individually as the nonpolar rubber for the elastic layer 14, or two or more may be used in combination. Among these, isoprene rubber and natural rubber are preferred from the viewpoint of high resistance and excellent dielectric effect.

[0045] Examples of polar rubbers for the elastic layer 14 include nitrile rubber (NBR), hydrin rubber, urethane rubber (U), acrylic rubber (polymer of acrylic acid ester and 2-chloroethyl vinyl ether, ACM), and chloroprene rubber (CR). Examples of hydrin rubbers include epichlorohydrin homopolymer (CO), epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO). These may be used individually as the polar rubber for the elastic layer 14, or two or more may be used in combination. Among these, nitrile rubber (NBR) and hydrin rubber are preferred from the viewpoint of lower resistance and higher dielectric constant.

[0046] As for the combination of non-polar rubber and polar rubber, from the viewpoint of making it easier to keep the relative permittivity of the elastic layer 14 within a specific range, it is preferable that the non-polar rubber is isoprene rubber or natural rubber and the polar rubber is nitrile rubber or hydrin rubber.

[0047] The ratio of non-polar rubber to polar rubber content is preferably such that, although it depends on the mixing method, the area ratio of non-polar rubber to polar rubber on the surface of the elastic layer 14 can be easily set within a specific range, and the mass ratio is preferably non-polar rubber:polar rubber = 8:2 to 6:4. More preferably, the ratio is non-polar rubber:polar rubber = 8:2 to 7:3.

[0048] Preferably, the area ratio of non-polar rubber to polar rubber on the surface of the elastic layer 14 is non-polar rubber:polar rubber = 9:1 to 7:3. This makes it easier to keep the dielectric constant of the elastic layer 14 within a specific range. Furthermore, from this viewpoint, the above area ratio is more preferably non-polar rubber:polar rubber = 9:1 to 8:2.

[0049] The carbon black in the elastic layer 14 contributes to adjusting the resistance and dielectric constant of the elastic layer 14. From the viewpoint of easily bringing the resistance and dielectric constant of the elastic layer 14 within a specific range, it is preferable that the carbon black in the elastic layer 14 has an average particle diameter of 36 nm to 80 nm and a product of DBP absorption (oil absorption) and specific surface area of ​​1728 to 5445. The product of DBP absorption and specific surface area is related to the amount of functional groups such as carbonyl groups and hydroxyl groups in the carbon black, and is related to the resistance and dielectric constant of the carbon black. The average particle size of the carbon black is expressed as the arithmetic mean diameter obtained by observing the carbon black with an electron microscope. The DBP absorption of the carbon black is calculated from the amount of DBP (dibutyl phthalate) absorbed by 100 g of carbon black in accordance with JIS K6221. The specific surface area of ​​the carbon black is a value measured by the BET method.

[0050] Furthermore, the carbon black in elastic layer 14 has a good balance between resistance and dielectric constant, and its DBP absorption is 69 cm². 3 / 100g or more 121cm 3 / 100g or less is preferable. Furthermore, the carbon black in the elastic layer 14 has just the right contact area with the rubber, allowing for a high tolerance for variations in the amount added, and making it easier to control the target resistance value and dielectric constant. From this viewpoint, 45m 2 / g or more 58m 2 Preferably less than / g

[0051] In the elastic layer 14, the carbon black content is preferably 15 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total of the non-polar rubber and polar rubber, from the viewpoint of making it easier to keep the resistance value and relative permittivity of the elastic layer 14 within a specific range. More preferably, it is 20 parts by mass or more and 45 parts by mass or less, and even more preferably 25 parts by mass or more and 40 parts by mass or less.

[0052] The elastic layer 14 is preferably composed of a composition that does not contain an ionic conductive agent. When the elastic layer 14 is composed of a composition that does not contain an ionic conductive agent, the relative permittivity of the elastic layer 14 does not rise too high, making it easier to keep the relative permittivity of the elastic layer 14 within a specific range.

[0053] Various additives may be added to the elastic layer 14 as needed. Examples of additives include lubricants, vulcanization accelerators, anti-aging agents, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoaming agents, pigments, and mold release agents.

[0054] The thickness of the elastic layer 14 is not particularly limited and can be set appropriately within the range of 0.1 to 10 mm depending on the application.

[0055] The surface layer 16 contains fluororesin and (meth)acrylic resin, has a dielectric constant of 10 to 22, and a resistivity of 1.2 × 10⁻⁶. 4 Ω or more 8.8×10 5 It is less than or equal to Ω.

[0056] Fluororesins with relatively high dielectric constant and low resistance are preferred. The relative permittivity of the fluororesin is preferably between 8 and 10. Furthermore, the volume resistivity of the fluororesin is 1.0 × 10⁻⁶. 13 Ω cm or more 1.0×10 14 It is preferable that the dielectric constant is Ω·cm or less. When the relative permittivity and volume resistivity of the fluororesin are within the above range, the fluororesin has a relatively high dielectric constant and low resistance, making it easy to make the surface layer 16 high dielectric constant and low resistance. In addition, the effect of electrostatic properties by the fluororesin is also easily maintained at this time.

[0057] Polyvinylidene fluoride is preferred as the fluororesin. When polyvinylidene fluoride is used as the fluororesin, it has a relatively high dielectric constant and low resistance, making it easy to create a surface layer with a high dielectric constant and low resistance. In addition, the electrostatic effect of the fluororesin is also easily maintained at this time.

[0058] Here, if the relative permittivity of the fluororesin is set to be greater than the above range, the relative permittivity of the surface layer 16 can be set to the desired value even when using fluororesin alone. However, in order to set the relative permittivity of the fluororesin to be greater than the above range, it is necessary to modify the fluororesin. Modification reduces the effectiveness of using fluororesin, so it is difficult to set the relative permittivity of the surface layer 16 to the desired value using fluororesin alone. Therefore, in the surface layer 16, (meth)acrylic resin is used together with fluororesin in order to set the relative permittivity of the surface layer 16 to the desired value. Note that if the resin component of the surface layer 16 is (meth)acrylic resin alone, the relative permittivity is too high, making it difficult to set the relative permittivity of the surface layer 16 to the desired value.

[0059] (Meth)acrylic resin is a resin selected from acrylic resin and methacrylic resin. Examples of (meth)acrylic resin include polymers (homopolymers or copolymers) of (meth)acrylate. (Meth)acrylate may be monofunctional or polyfunctional.

[0060] Monofunctional (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate. Examples include (meth)acrylates having hydroxyl groups such as t, alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and butoxyethyl (meth)acrylate, phenoxyalkyl (meth)acrylates such as phenoxyethyl acrylate and nonylphenoxyethyl (meth)acrylate, and alkoxyalkylene glycol (meth)acrylates such as ethoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate.

[0061] Examples of polyfunctional (meth)acrylates include alkyldiol di(meth)acrylates such as 1,9-nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylates such as diethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylates such as dipropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol tri(meth)acrylate, polyvalent (meth)acrylates obtained by the addition reaction of ethylene glycol diglycidyl ether with compounds having an ethylenically unsaturated bond and active hydrogen, such as unsaturated carboxylic acids and unsaturated alcohols, polyvalent (meth)acrylates obtained by the addition reaction of unsaturated epoxy compounds such as glycidyl(meth)acrylate with compounds having active hydrogen, such as carboxylic acids and amines, polyvalent (meth)acrylamides such as methylenebis(meth)acrylamide, and polyvalent vinyl compounds such as divinylbenzene.

[0062] From the viewpoint of dielectric constant, volume resistivity, indentation Young's modulus, and elastic recovery rate, methacrylic resin is more preferred. Furthermore, from the viewpoint of dielectric constant, volume resistivity, indentation Young's modulus, and elastic recovery rate, alkyl (meth)acrylate and cycloalkyl (meth)acrylate are more preferred as (meth)acrylic resins.

[0063] The content ratio of fluororesin to (meth)acrylic resin is preferably such that the mass ratio is fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:3. This makes it easier to keep the dielectric constant of the surface layer 16 within a specific range. The above content ratio is more preferably fluororesin:(meth)acrylic resin = 9:1 to 7:3, and even more preferably fluororesin:(meth)acrylic resin = 8:2 to 7:3.

[0064] Furthermore, it is preferable that the difference in relative permittivity between the fluororesin and the (meth)acrylic resin be 2 or less. This reduces uneven discharge from the charging roll 10 to the photoreceptor. Also, it is preferable that the difference in volume resistivity between the fluororesin and the (meth)acrylic resin be 0.2 log Ω or less. This reduces uneven charge injection from the charging roll 10 to the photoreceptor.

[0065] Here, it is preferable that the indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less, and the indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less. This ensures that the deformation of the charging roll 10 in response to the pressure received from the photoreceptor during rotation is uniform, and localized stress concentration is less likely to occur. Furthermore, it is preferable that the difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is 0.1 GPa or less, and the difference in elastic recovery rate is 5% or less. This makes it easier to suppress cracking of the surface layer 16 due to physical stress received from the photoreceptor, improving durability. The indentation Young's modulus can be measured from a sheet-like sample using a micro-indentation hardness tester. The elastic recovery rate can be measured from a sheet-like sample using a tensile tester.

[0066] Furthermore, the fluororesin should have a tensile strength of 28 MPa to 40 MPa. This improves the strength of the surface layer 16 and enhances its durability. The tensile strength of the fluororesin can be measured by the elongation at break of a sheet-like sample using a tensile testing machine.

[0067] The surface layer 16 may contain roughness-forming particles. These roughness-forming particles are particles that impart roughness to the surface of the surface layer 16. In other words, they are particles that create irregularities on the surface of the surface layer 16. The surface irregularities of the surface layer 16 form a discharge space between the photoreceptor and the charging roll 10.

[0068] The roughness-forming particles can be made of resin, inorganic particles, etc. The roughness-forming particles may be solid particles or porous particles. If the roughness-forming particles are porous particles, the roughness-forming particles become more integrated with the binder resin of the surface layer 16, such as fluororesin or (meth)acrylic resin, making the surface layer 16 less prone to cracking. In addition, the resistance can be integrated and the injected charge can be made uniform.

[0069] Examples of materials for roughness-forming particles include urethane resin, polyamide resin, (meth)acrylic resin, (meth)acrylic silicone resin, silicone grafted (meth)acrylic polymer, (meth)acrylic grafted silicone polymer, urethane rubber, and silica. Of these, (meth)acrylic resin is more preferred from the viewpoint of affinity and integration with the binder resin of the surface layer 16.

[0070] The size of the roughness-forming particles is not particularly limited, but from the viewpoint of ensuring uniform charging properties, an average particle diameter of 3.0 μm to 50 μm is preferred. More preferably, an average particle diameter of 5.0 μm to 30 μm is preferred. The average particle diameter of the roughness-forming particles is determined by observing the surface of the surface layer 16 with a laser microscope, and the diameter of the roughness-forming particles visible during surface observation is defined as the particle size, expressed as the average of 20 arbitrary points.

[0071] The content of roughness-forming particles in the surface layer 16 is not particularly limited, but from the viewpoint of ensuring uniform electrostatic properties, it is preferably 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of binder resin in the surface layer 16. More preferably it is 5 parts by mass or more and 30 parts by mass or less.

[0072] Various additives may be added to the surface layer 16 as needed.

[0073] The thickness of the surface layer 16 is not particularly limited and can be set to a range of 0.1 to 3.0 μm. The thickness of the surface layer 16 can be measured by observing the cross-section using a laser microscope (for example, 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 locations, and the thickness can be expressed by the average of these measurements.

[0074] The electrostatic roll 10 can be manufactured by forming an elastic layer 14 on the outer circumferential surface of the shaft and forming a surface layer 16 on the outer circumferential surface of the elastic layer 14.

[0075] The elastic layer 14 can be formed, for example, as follows: First, the shaft 12 is coaxially placed in the hollow part of a roll molding die, an uncrosslinked elastic layer forming composition is injected, heated and cured (crosslinked), and then the mold is removed, or the uncrosslinked elastic layer forming composition is extruded onto the surface of the shaft 12 to form the elastic layer 14 on the outer circumference of the shaft.

[0076] To form the surface layer 16, a surface layer forming composition is used. The surface layer forming composition consists of the above-mentioned main material and other additives as needed.

[0077] The surface-forming composition may appropriately contain organic solvents such as methyl ethyl ketone, toluene, acetone, ethyl acetate, butyl acetate, methyl isobutyl ketone (MIBK), THF, and DMF, or water-soluble solvents such as methanol and ethanol, from the viewpoint of adjusting viscosity.

[0078] The surface layer 16 can be formed by methods such as coating the outer surface of the elastic layer 14 with a surface layer forming composition. Various coating methods such as roll coating, dipping, and spray coating can be applied. The coated surface layer 16 may be subjected to ultraviolet irradiation or heat treatment as needed.

[0079] The electrostatic roll 10 having the above configuration has an elastic layer 14 containing non-polar rubber, polar rubber, and carbon black, with a relative permittivity of 7 to 29 and a resistance of 6.0 × 10⁻¹⁴. 4 Ω or more 5.0×10 6 The resistance is less than or equal to Ω, the surface layer 16 contains fluororesin and (meth)acrylic resin, the relative permittivity is between 10 and 22, and the resistance is 1.2 × 10⁻¹⁰. 4 Ω or more 8.8×10 5 The resistance is less than Ω. As a result, the amount of discharge from the charging roll 10 to the photoreceptor is reduced, suppressing the generation of harmful substances such as ozone and NOx, thereby reducing environmental degradation and image deterioration. Furthermore, the above configuration facilitates charge transfer at the grounding point between the charging roll 10 and the photoreceptor, and by injecting charge from the charging roll 10 to the photoreceptor, the photoreceptor can be charged to the desired level. This results in excellent charging performance even with a low discharge amount.

[0080] If the relative permittivity of the surface layer 16 or the elastic layer 14 is too high, too much charge will accumulate, making it difficult for charge to transfer at the contact point from the charged roll 10 to the photoreceptor. On the other hand, if this relative permittivity is too low, there will be more discharge from the charged roll 10 to the photoreceptor, resulting in increased generation of harmful substances such as ozone and NOx. Similarly, if the resistance of the surface layer 16 or the elastic layer 14 is too high, there will be less for charge to transfer at the contact point from the charged roll 10 to the photoreceptor. On the other hand, if this resistance is too low, there will be more discharge from the charged roll 10 to the photoreceptor, resulting in increased generation of harmful substances such as ozone and NOx.

[0081] Furthermore, from the above viewpoint, the relative permittivity of the elastic layer 14 is more preferably 10 or more, and 15 or more. Also, it is 25 or less, and 20 or less. And the resistance value of the elastic layer 14 is more preferably 8.0 × 10⁻⁶. 4 Ω or more, 1.0×10 5 It is greater than or equal to Ω. Also, 1.0 × 10 6 Ω or less, 5.0×10 5It is less than or equal to Ω. Similarly, the relative permittivity of the surface layer 16 is more preferably 12 or more, and 14 or more. Also, it is less than or equal to 20 and 18 or less. And the resistance value of the surface layer 16 is more preferably 2.0 × 10 4 Ω or more, 5.0×10 4 It is greater than or equal to Ω. Also, 8.0 × 10 5 Ω or less, 5.0×10 5 It is less than or equal to Ω.

[0082] To bring the dielectric constant and resistivity of the elastic layer 14 within the above range, it is advisable to use a small amount of polar rubber with a non-polar rubber base, and to select the appropriate carbon black. A suitable combination of non-polar and polar rubber can be selected from those listed above. Since non-polar and polar rubbers have low compatibility, the surface area ratio is important in terms of their content ratio. By setting the area ratio within the above-mentioned specific range, it is easier to bring the dielectric constant of the elastic layer 14 within the specified range. For carbon black, the average particle size and the product of DBP absorption and specific surface area are important factors, and it is advisable to select a suitable product for the product of DBP absorption and specific surface area, which is an indicator of the dielectric constant of carbon black.

[0083] To bring the dielectric constant and resistivity of the surface layer 16 within the above range, it is preferable to select a fluororesin with a relatively high dielectric constant and lower resistivity as the base material, while using a small amount of (meth)acrylic resin, which has a higher dielectric constant than the fluororesin. The fluororesin is preferably one having the above-mentioned specific dielectric constant and volume resistivity. By setting the content ratio of the fluororesin and (meth)acrylic resin within the above-mentioned specific range, it is easier to bring the dielectric constant of the surface layer 16 within the specified range. By selecting a fluororesin and (meth)acrylic resin with similar indentation Young's modulus and elastic recovery rate, cracking of the surface layer 16 due to physical stress from the photoreceptor is suppressed, improving durability. [Examples]

[0084] The present invention will be described in detail below using examples and comparative examples.

[0085] (Examples 1-7, Comparative Examples 1-10) <Preparation of compositions for forming elastic layers> A composition for forming an elastic layer was prepared by blending polar rubber, non-polar rubber, and carbon black in the proportions (parts by mass) shown in the table, along with a peroxide crosslinking agent, a vulcanization aid, and a catalyst. These were then stirred and mixed using a stirrer.

[0086] <Fabrication of elastic layers> A mandrel (8 mm in diameter) was set in a molding die (pipe-shaped), an elastic layer-forming composition was injected, and after heating at 180°C for 30 minutes, it was cooled and demolded to form an elastic layer with a thickness of 1.9 mm on the outer circumference of the mandrel.

[0087] <Preparation of surface-forming composition> A surface-forming composition was prepared by blending fluororesin, (meth)acrylic resin, carbon black, and roughness-forming particles in the proportions (parts by mass) shown in the table, diluting with methyl ethyl ketone (MEK), and mixing and stirring at a predetermined stirring speed.

[0088] <Preparation of the surface layer> A surface layer with a thickness of 1.0 μm was formed on the outer surface of the elastic layer by roll coating the surface layer with the surface layer forming composition while continuously stirring the surface layer forming composition, followed by heat treatment. This resulted in the fabrication of an electrostatically charged roll.

[0089] The following materials were prepared as materials for the composition for forming the elastic layer. (Polar rubber) • Polar rubber <1> (NBR): Nippon Zeon "Nipol 1041" • Polar rubber <2> (ECO): Nippon Zeon "Hydrin H1100" • Polar rubber <3> (CR): Denka Chloroprene DCR-107 manufactured by Denka (Non-polar rubber) Non-polar rubber <1> (IR): Nippon Zeon "Nipol IR2200" Non-polar rubber <2> (NR): Maxell Kureha "GW540N" Non-polar rubber <3> (BR): UBE elastomer "UBEPOL BR130B" (Carbon Black) • Carbon Black <1> Mitsubishi Chemical's "Mitsubishi Carbon Black #25," average particle size 47nm, oil absorption capacity (DBP absorption capacity) 69cm³ 3 / 100g, specific surface area 55m 2 / g • Carbon Black <2> Mitsubishi Chemical's "Mitsubishi Carbon Black #20," average particle size 50nm, oil absorption capacity (DBP absorption capacity) 121cm³ 3 / 100g, specific surface area 45m 2 / g • Carbon Black <3> Tokai Carbon's "TOKABLACK #7270SB", average particle size 36nm, oil absorption capacity (DBP absorption capacity) 62cm 3 / 100g, specific surface area 58m 2 / g • Carbon Black <4> Mitsubishi Chemical's "Diablack G," average particle size 80nm, oil absorption capacity (DBP absorption capacity) 84cm³ 3 / 100g, specific surface area 28m 2 / g • Carbon Black <5> Nippon Steel Carbon's "HTC#SSRF," average particle size 68nm, oil absorption capacity (DBP absorption capacity) 72cm³ 3 / 100g, specific surface area 24m 2 / g • Carbon Black <6> : Asahi Carbon "Asahi #70L", average particle size 25nm, oil absorption (DBP absorption) 85cm 3 / 100g, specific surface area 75m 2 / g

[0090] The following materials were prepared as components for the surface-forming composition. (Fluororesin) Fluororesin <1> (PVDF): Arkema "Kynar 711", volume resistivity 1.0 × 10⁻⁶ 14 Ω·cm, relative permittivity 8, indentation Young's modulus 0.65 GPa, elastic recovery rate 40% Fluororesin <2> (PVDF): Arkema "Kynar HSV900", volume resistivity 1.0 × 10⁻⁶ 13 Ω·cm, relative permittivity 10, indentation Young's modulus 0.75 GPa, elastic recovery rate 50% Fluororesin <3> (PTFE+PFA): Daikin Industries' "Neoflon PFA AP-230AS", volume resistivity 1.4 × 10⁻⁶ 13 Ω·cm, relative permittivity 8.2, indentation Young's modulus 0.71 GPa, elastic recovery rate 48% Fluororesin <4> (PVDF): Kureha Corporation "KF Polymer #1000", volume resistivity 2.1 × 10⁻⁶ 14 Ω·cm, relative permittivity 7.6, indentation Young's modulus 0.72 GPa, elastic recovery rate 40% ((meth)acrylic resin) (Meth)acrylic resin <1> (PMMA): Mitsubishi Chemical's "Dianal BR107", relative permittivity 10, indentation Young's modulus 0.65 GPa, elastic recovery rate 50% (Meth)acrylic resin <2> (PMMA): Mitsubishi Chemical's "Acrypet IRH50001", relative permittivity 11, indentation Young's modulus 0.75 GPa, elastic recovery rate 40% (Carbon Black) • Carbon Black: Tokushiki "9027BLACK" (Particles for creating roughness) • Particles for roughness formation <1> (PMMA): "Techpolymer MBP-8" manufactured by Sekisui Kasei, average particle size 8 μm, porous particles • Particles for roughness formation <2> (PMMA): "Chemisnow MZ-8HN" manufactured by Soken Chemical, average particle size 8 μm, solid particles

[0091] (Method for preparing the sample) A resin (fluororesin or acrylic resin) was added to a mixed solvent of acetone and water (9:1) to a concentration of 5 wt%, dissolved by stirring with a blade for 24 hours, cast at 28°C and 60% RH, and then fired at 100°C for 30 minutes to prepare measurement samples (sheet form) composed of each resin.

[0092] (Method for measuring the physical properties of a sample) (Volume resistivity) The volume resistivity of the obtained sheet-like samples was measured in accordance with JIS K7194, using a HIOKI RM3545 resistance meter and a HIOKI RM9010-01 four-probe probe.

[0093] (dielectric constant) The obtained sheet-like samples were measured using a precision LCR meter E4980A (manufactured by Agilent Technologies) with a 10kHz frequency applied, in accordance with JIS C2138.

[0094] (Indented Young's modulus) The obtained sheet-like samples were subjected to nanoindentation testing, and the indentation Young's modulus was measured using an ultra-micro indentation hardness tester (nanomindentation tester: ENT-1100a, manufactured by Elionik).

[0095] (Elastic recovery rate) The elastic recovery rate of the obtained sheet-like samples was measured using a tensile testing machine (AE-F Strograph, manufactured by Toyo Seiki Seisakusho) in accordance with JIS K6251.

[0096] (Tensile strength) The obtained sheet-like samples were subjected to a tensile testing machine (AE-F Strograph, manufactured by Toyo Seiki Seisakusho) to measure the elongation at break, in accordance with JIS K6251.

[0097] (relative permittivity of the elastic layer) The elastic layer before the surface layer was formed was cut out as a 1cm × 1cm × 0.3cm sample piece, and the resulting sheet-like sample was measured using a precision LCR meter E4980A (manufactured by Agilent Technologies) with a 10kHz frequency applied, in accordance with JIS C2138.

[0098] (Relative permittivity of the surface layer) The surface-forming composition was cast in a 28°C × 60%RH environment, and then fired at 100°C for 30 minutes to prepare a measurement sample (sheet-like) composed of the surface-forming composition. The obtained sheet-like sample was measured using a precision LCR meter E4980A (manufactured by Agilent Technologies) with a 10kHz frequency applied, in accordance with JIS C2138.

[0099] (Resistance value of the elastic layer) The elastic layer before the surface layer was formed was cut out as a 1cm × 1cm × 0.3cm sample piece. The resistance of the resulting sheet-like sample was measured in accordance with JIS K7194 using a HIOKI RM3545 resistance meter and a HIOKI RM9010-01 four-probe probe.

[0100] (Surface resistance value) A surface-forming composition was cast in a 28°C × 60%RH environment, and then fired at 100°C for 30 minutes to prepare a measurement sample (sheet-like) composed of the surface-forming composition. The resistance of the obtained sheet-like sample was measured in accordance with JIS K7194 using a HIOKI RM3545 resistance meter and a HIOKI RM9010-01 four-probe probe.

[0101] (Ratio of surface area of ​​rubber) The elastic layer before the surface layer was formed was cut out as an 11cm × 1cm × 0.3cm sample piece, stained with Os staining, and then observed at 2000x magnification using a scanning electron microscope. Since the darker and lighter areas of Os staining indicate the presence of rubber, their occupied areas were measured.

[0102] (Evaluation / Determination Method) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10%RH environment. The evaluation was then conducted after 1 million prints of durability.

[0103] (Black and white dots): Chargeability (discharge amount) Images with no white or black spots were rated as "Excellent" (◎), those with a few spots but low density and within an acceptable range were rated as "Good" (○), and those with many spots and high density were rated as "Unacceptable" (×).

[0104] (Flurry): Chargeability (amount of charge) Images with no haze were rated as "Excellent" (◎), those with a few hazes but low density and within an acceptable range were rated as "Good" (○), and those with many hazes and high density were rated as "Unacceptable" (×).

[0105] (Unevenness): Stain-resistant Images with no unevenness were rated as "Excellent" (◎), those with slight unevenness but within an acceptable range were rated as "Good" (○), and those with significant unevenness were rated as "Unacceptable" (×).

[0106] (Cracks): Durability Rolls with no cracks on the surface were rated "Excellent" (◎), while those with a few cracks that did not affect the image were rated "Good" (○).

[0107] [Table 1]

[0108] [Table 2]

[0109] In Comparative Example 1, the area ratio of polar rubber on the surface of the elastic layer is too small, resulting in a low relative permittivity of the elastic layer. This leads to excessive discharge and image degradation of the black and white dots. In Comparative Example 3, the area ratio of polar rubber on the surface of the elastic layer is too large, resulting in a high relative permittivity of the elastic layer. This leads to insufficient charging and image degradation due to fogging. In Comparative Example 2, the carbon black content of the elastic layer is too low, resulting in a high resistance value of the elastic layer. This leads to insufficient charging and image degradation due to fogging. In Comparative Example 4, the carbon black content of the elastic layer is too high, resulting in a low resistance value of the elastic layer. This leads to excessive discharge and image degradation of the black and white dots.

[0110] Comparative Example 5 has too much fluororesin in the surface layer, resulting in a low dielectric constant of the surface layer. This leads to excessive discharge and deterioration of the black and white dot image. Comparative Example 7 has too little fluororesin in the surface layer, resulting in a high dielectric constant of the surface layer. This leads to insufficient charging and deterioration of the fogging image. Comparative Example 6 has too little carbon black in the surface layer, resulting in a high resistance of the surface layer. This leads to insufficient charging and deterioration of the fogging image. Comparative Example 8 has too much carbon black in the surface layer, resulting in a low resistance of the surface layer. This leads to excessive discharge and deterioration of the black and white dot image.

[0111] In Comparative Example 9, the product of the oil absorption amount and specific surface area of ​​the carbon black in the elastic layer is large, and the relative permittivity of the elastic layer is too high. As a result, insufficient charging causes image degradation due to fogging. Also, the resistance value of the elastic layer is too low. As a result, the discharge amount is too high, causing image degradation of black and white dots. In Comparative Example 10, the relative permittivity of the fluororesin in the surface layer is low at 7.6, and the relative permittivity of the surface layer is too low. As a result, the discharge amount is too high, causing image degradation of black and white dots. Also, the volume resistivity is 2.1 × 10⁻⁶. 14 The resistance is large (Ω·cm), indicating a high surface resistance. This results in insufficient charging, causing image degradation due to fogging.

[0112] In contrast, the example describes an elastic layer containing non-polar rubber, polar rubber, and carbon black, with a dielectric constant of 7 to 29 and a resistivity of 6.0 × 10⁻⁶. 4 Ω or more 5.0×10 6 The resistance is less than or equal to Ω, the surface layer contains fluororesin and (meth)acrylic resin, the dielectric constant is between 10 and 22, and the resistance is 1.2 × 10⁻¹⁰. 4 Ω or more 8.8×10 5 The resistance is less than Ω. As a result, the discharge amount is reduced, and image degradation of black and white dots is suppressed. In addition, the above configuration facilitates charge transfer, resulting in excellent charging performance even with a low discharge amount. Therefore, image degradation due to fogging caused by insufficient charging is also suppressed.

[0113] Although embodiments and examples of the present invention have been described above, the present invention is not limited in any way to the above embodiments and examples, and various modifications are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0114] 10 Electrostatic Rolls 12 Axis Body 14 Elastic layer 16 Surface layer

Claims

1. It comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, The elastic layer contains non-polar rubber, polar rubber, and carbon black, has a dielectric constant of 7 to 29, and a resistivity of 6.0 × 10⁻⁶. ４ Ω or more 5.0×10 ６ It is less than or equal to Ω, The surface layer contains fluororesin, (meth)acrylic resin, and carbon black, with the carbon black content of the surface layer being 20 to 60 parts by mass per 100 parts by mass of the total of the fluororesin and (meth)acrylic resin, the dielectric constant being 10 to 22, and the resistivity being 1.2 × 10⁻¹⁰. ４ Ω or more 8.8×10 ５ A charging roll for electrophotographic equipment with a resistance of Ω or less.

2. The electrophotographic roller for electrophotographic equipment according to claim 1, wherein the area ratio of the non-polar rubber to the polar rubber on the surface of the elastic layer is non-polar rubber:polar rubber = 9:1 to 7:

3.

3. The electrophotographic roller for electrophotographic equipment according to claim 1 or 2, wherein the non-polar rubber is isoprene rubber or natural rubber, and the polar rubber is nitrile rubber or hydrin rubber.

4. The electrophotographic roll for electrophotographic equipment according to claim 1 or claim 2, wherein the carbon black of the elastic layer has an average particle diameter of 36 nm or more and 80 nm or less, and the product of DBP absorption amount and specific surface area is 1728 or more and 5445 or less.

5. The electrophotographic roller according to claim 1 or claim 2, wherein the carbon black content of the elastic layer is 15 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the total of the non-polar rubber and the polar rubber.

6. The electrophotographic roller according to claim 1 or 2, wherein the elastic layer is composed of a composition that does not contain an ion conductive agent.

7. The electrophotographic roller for electrophotographic equipment according to claim 1 or claim 2, wherein the content ratio of the fluororesin to the (meth)acrylic resin is, by mass ratio, fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:

3.

8. The aforementioned fluororesin has a relative permittivity of 8 or more and 10 or less, and a volume resistivity of 1.0 × 10 １３ Ω・cm or more 1.0×10 １４ A charging roll for electrophotographic equipment according to claim 1 or claim 2, wherein the value is Ω·cm or less.

9. The electrophotographic roller according to claim 1 or claim 2, wherein the fluororesin is polyvinylidene fluoride.

10. The electrophotographic roller for electrophotographic equipment according to claim 1 or claim 2, wherein the difference in volume resistivity between the fluororesin and the (meth)acrylic resin is 0.2 log Ω or less.

11. The electrophotographic roller for electrophotographic equipment according to claim 1 or claim 2, wherein the indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less, and the indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less.

12. The electrophotographic roller for electrophotographic equipment according to claim 1 or 2, wherein the difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is 0.1 GPa or less, and the difference in elastic recovery rate is 5% or less.

13. The electrophotographic roller for electrophotographic equipment according to claim 1 or claim 2, wherein the tensile strength of the fluororesin is 28 MPa or more and 40 MPa or less.

14. The electrophotographic roller according to claim 1 or claim 2, wherein the difference in relative dielectric constant between the fluororesin and the (meth)acrylic resin is 2 or less.

15. The electrophotographic roller for electrophotographic equipment according to claim 1 or claim 2, wherein the surface layer further contains roughness-forming particles.

16. The electrophotographic roller according to claim 15, wherein the roughness-forming particles are porous particles.

17. The area ratio of the non-polar rubber to the polar rubber on the surface of the elastic layer is non-polar rubber:polar rubber = 9:1 to 7:

3. The non-polar rubber is isoprene rubber or natural rubber, and the polar rubber is nitrile rubber or hydrin rubber. The carbon black in the elastic layer has an average particle diameter of 36 nm or more and 80 nm or less, and the product of DBP absorption amount and specific surface area is 1728 or more and 5445 or less. The carbon black content of the elastic layer is 15 parts by mass or more and 50 parts by mass or less, based on 100 parts by mass of the total of the non-polar rubber and the polar rubber. The elastic layer is composed of a composition that does not contain an ionic conductive agent. The content ratio of the fluororesin to the (meth)acrylic resin is such that, by mass ratio, fluororesin:(meth)acrylic resin = 9.5:0.5 to 7:

3. The aforementioned fluororesin has a relative permittivity of 8 or more and 10 or less, and a volume resistivity of 1.0 × 10 １３ Ω・cm or more 1.0×10 １４ It is less than or equal to Ω·cm, The aforementioned fluororesin is polyvinylidene fluoride. The difference in volume resistivity between the fluororesin and the (meth)acrylic resin is 0.2 log Ω or less. The indentation Young's modulus of the fluororesin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 40% or more and 50% or less, and the indentation Young's modulus of the (meth)acrylic resin is 0.65 GPa or more and 0.75 GPa or less, and the elastic recovery rate is 45% or more and 50% or less, The difference in indentation Young's modulus between the fluororesin and the (meth)acrylic resin is 0.1 GPa or less, and the difference in elastic recovery rate is 5% or less. The tensile strength of the aforementioned fluororesin is 28 MPa or more and 40 MPa or less. The difference in relative permittivity between the fluororesin and the (meth)acrylic resin is 2 or less. The aforementioned surface layer further contains roughness-forming particles, The electrophotographic roller according to claim 1, wherein the roughness-forming particles are porous particles.

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