Charging roller for electrophotographic equipment and method for manufacturing charging roller for electrophotographic equipment

Abstract

Provided are a charging roller for an electrophotographic device that can suppress charge attenuation from the roller surface due to uneven resistance and can produce a good image, and a method for manufacturing the same. The charging roller 10 for an electrophotographic device comprises a shaft 12, an elastic layer 14 formed on the outer peripheral surface of the shaft 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The elastic layer 14 is made of a material having a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase 14a has a high resistance of Ω·cm or less, and a surface resistance of 1.3×10 2 Ω·cm or more and 4.9×10 3 The second phase 14b is composed of a low resistance of less than Ω·cm, and the second phase 14b contains a DBP absorption of 115cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 110cm 3 / 100g or less of carbon black B and these two types of carbon black.

Description

Technical Field

[0001] The present invention relates to a charging roller for an electrophotographic device that is preferably used in an electrophotographic device such as a copy machine, a printer, or a facsimile machine that adopts an electrophotographic method, and a method for producing the charging roller for an electrophotographic device. Background Art

[0002] In order to improve the charging performance of the charging roller of the electrophotographic apparatus, a method of adding a large amount of conductive agent such as carbon black or an ion conductive agent, a method of mixing a rubber base layer, and the like are adopted.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-166259 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] By adding large amounts of conductive agents such as carbon black and ion conductive agents to the charging roller, the charge content within the roller increases, resulting in an apparent increase in discharge and charge. However, this increased flow of charge to localized areas of uneven resistance within the roller leads to excessive discharge, resulting in black spots on the image. Furthermore, this increased flow of charge to localized areas of uneven resistance within the roller causes uneven discharge and charging, resulting in horizontal streaks and unevenness on the image.

[0008] The problem to be solved by the present invention is to provide a charging roller for an electrophotographic device and a method for manufacturing the same, which can suppress charge attenuation from the roller surface caused by local resistance unevenness and can produce good images.

[0009] Methods used to solve problems

[0010] The charging roller for an electrophotographic device according to the present invention comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein the elastic layer has a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase has a high resistance of less than Ω·cm and a surface resistance of 1.3×10 2 Ω·cm or more and 4.9×10 3 The second phase has a low resistance of Ω·cm or less, and the second phase contains a DBP absorption of 115cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 110cm 3 / 100g or less of carbon black B and these two types of carbon black.

[0011] Alternatively, in the elastomer layer, the first phase constitutes a sea phase and the second phase constitutes an island phase. Alternatively, the content ratio of the carbon black A to the carbon black B in the second phase may be A / B = 3.0 or more and 10.0 or less, in terms of mass ratio. Alternatively, the specific surface area of the carbon black A may be 25 m 2 / g and above 75m 2 / g or less, the specific surface area of the carbon black B is 140m 2 / g and above and 180m 2 / g or less. Alternatively, the average particle size of the carbon black A may be greater than or equal to 35 nm and less than or equal to 75 nm, and the average particle size of the carbon black B may be greater than or equal to 20 nm and less than or equal to 30 nm. Alternatively, with respect to 100 parts by mass of the polymer component contained in the elastomer layer, the content of the carbon black A may be greater than or equal to 5 parts by mass and less than or equal to 75 parts by mass, and the content of the carbon black B may be greater than or equal to 1.5 parts by mass and less than or equal to 20 parts by mass. Alternatively, a non-polar polymer may be contained in the first phase, and a polar polymer may be contained in the second phase. Alternatively, the non-polar polymer may be isoprene rubber or natural rubber, and the polar polymer may be nitrile rubber or epichlorohydrin rubber. Alternatively, in terms of area ratio, the existence ratio of the first phase to the second phase within any 5μm×5μm range of the elastomer layer may be first phase / second phase=greater than or equal to 0.3 and less than or equal to 20. Alternatively, the first phase may be sandwiched between the second phase and the surface layer.

[0012] Moreover, the manufacturing method of the charging roller for electronic photographic equipment involved in the present invention is the above-mentioned manufacturing method of the charging roller for electronic photographic equipment, which is a manufacturing method of mixing the polymer components constituting the first phase after mixing the two carbon blacks, the carbon black A and the carbon black B, with the polymer components constituting the second phase.

[0013] Effects of the Invention

[0014] According to the present invention, the charging roller for an electrophotographic device comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein the elastic layer has a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase has a high resistance of less than Ω·cm, and the surface resistance is 1.3×10 2 Ω·cm or more and 4.9×10 3The second phase has a low resistance of Ω·cm or less, and the second phase contains a DBP absorption of 115cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 110cm 3 Since the carbon black B has an average carbon black content of 1 / 100 g or less, the charge attenuation from the roller surface due to local uneven resistance can be suppressed, and a good image can be obtained.

[0015] When the first phase constitutes a sea phase and the second phase constitutes an island phase in the elastic layer, the first phase enhances the effect of intercepting charges, further absorbing local resistance variations, thereby further suppressing charge attenuation from the roller surface.

[0016] When the mass ratio of carbon black A to carbon black B in the second phase is A / B = 3.0 to 10.0, the balance between capacitance and resistance of carbon black is excellent, thereby improving discharge uniformity and further suppressing image unevenness.

[0017] When the specific surface area of the carbon black A is 25 m 2 / g and above 75m 2 When the specific surface area of carbon black B is 140 m 2 / g and above and 180m 2 When the carbon black B has a low resistance and the resistance is easily maintained in the preferred range, the carbon black B has a low resistance and the resistance is easily maintained in the preferred range.

[0018] When the average particle size of carbon black A is 35 nm to 75 nm, the specific surface area of carbon black A can be easily adjusted to a preferred range, and carbon black A can be easily made high in resistance. Furthermore, when the average particle size of carbon black B is 20 nm to 30 nm, the specific surface area of carbon black B can be easily adjusted to a preferred range, and carbon black B can be easily made low in resistance.

[0019] When the content of the carbon black A is 5 parts by mass or more and 75 parts by mass or less per 100 parts by mass of the polymer component contained in the elastomer layer, the capacitance is easily maintained within the preferred range. Furthermore, when the content of the carbon black B is 1.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polymer component contained in the elastomer layer, the resistance is easily maintained within the preferred range.

[0020] When the first phase contains a nonpolar polymer and the second phase contains a polar polymer, phase separation between the first and second phases is improved, easily suppressing charge decay from the roller surface due to localized resistance variations. Furthermore, when the nonpolar polymer is isoprene rubber or natural rubber and the polar polymer is nitrile rubber or epichlorohydrin rubber, phase separation between the first and second phases is improved, easily suppressing charge decay from the roller surface due to localized resistance variations.

[0021] When the existence ratio of the above-mentioned first phase and the above-mentioned second phase within any 5μm×5μm range of the above-mentioned elastomer layer is first phase / second phase = 0.3 or more and 20 or less in terms of area ratio, the first phase and the second phase are finely dispersed, and the effect of suppressing the charge attenuation from the roller surface caused by the local resistance unevenness is excellent.

[0022] When the first phase is interposed between the second phase and the surface layer, the first phase enhances the effect of intercepting the charge, further absorbing local resistance variations, thereby further suppressing charge attenuation from the roller surface.

[0023] Furthermore, the method for manufacturing a charging roller for an electrophotographic apparatus according to the present invention can provide a charging roller for an electrophotographic apparatus that can suppress charge attenuation from the roller surface due to local resistance unevenness and can produce good images. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 and 1. A schematic diagram (a) showing the appearance of a charging roller for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line AA thereof (b).

[0025] Figure 2 It is a schematic diagram showing the phase structure of an arbitrary 5 μm×5 μm range near the surface layer of the elastomer layer. DETAILED DESCRIPTION

[0026] The charging roller for an electrophotographic apparatus (hereinafter, sometimes simply referred to as a charging roller) according to the present invention will be described in detail. Figure 1 1 and 1. A schematic diagram (a) showing the appearance of a charging roller for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line AA thereof (b). Figure 2 It is a schematic diagram showing the phase structure of an arbitrary 5 μm×5 μm range near the surface layer of the elastomer layer.

[0027] The charging roller 10 includes a shaft 12, an elastic layer 14 formed on the outer peripheral surface of the shaft 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The elastic layer 14 is a layer (base layer) that serves as the base of the charging roller 10. The surface layer 16 is a layer that appears on the surface of the charging roller 10.

[0028] The shaft 12 is not particularly limited as long as it is conductive. Specifically, a core rod made of a solid or hollow metal such as iron, stainless steel, or aluminum can be used. An adhesive, primer, or the like may be applied to the surface of the shaft 12 as needed. In other words, the elastomer layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive, primer, or the like may also be made conductive as needed.

[0029] The elastic layer 14 has a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase 14a has a high resistance of Ω·cm or less, and a surface resistance of 1.3×10 2 Ω·cm or more and 4.9×10 3 The second phase 14b is composed of a low resistance of Ω·cm or less. Figure 2 As shown, the first phase 14a and the second phase 14b exist separately from each other.

[0030] The first phase 14a contains one or more polymers. From the viewpoint of high resistance, the polymer of the first phase 14a is preferably a non-polar polymer. As the polymer of the first phase 14a, 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 terpolymer rubber (EPDM), silicone rubber (Q) and the like can be cited. These can be used alone as the polymer of the first phase 14a, or two or more can be used in combination. From the viewpoints of high resistance and excellent effect as a dielectric phase, isoprene rubber and natural rubber are preferably used among them. From the viewpoint of high resistance, the first phase 14a preferably does not contain a conductive agent such as carbon black, or even if it contains a conductive agent such as carbon black, it is a small amount. The content of the conductive agent of the first phase 14a is at least a small amount compared to the second phase 14b.

[0031] The second phase 14b contains two types of carbon black. The carbon black of the second phase 14b is a carbon black having a DBP absorption of 115 cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 110cm 3Carbon black A, which absorbs a lot of DBP, acts as a dielectric, storing charge. Carbon black B, which absorbs less DBP, rapidly transfers charge. Using two carbon blacks with different DBP absorptions ensures a moderate capacitance while maintaining low resistance. DBP absorption of carbon black is calculated according to JIS K6221 based on the amount of DBP (dibutyl phthalate) absorbed per 100g of carbon black.

[0032] From the viewpoint of improving electrostatic capacitance, the DBP absorption of carbon black A is more preferably 120 cm 3 / 100g or more. In addition, from the perspective of improving discharge performance, it is more preferably 150cm 3 / 100g or less, more preferably 140cm 3 On the other hand, from the viewpoint of improving electrostatic capacitance, the DBP absorption of carbon black B is more preferably 80 cm 3 / 100g or more. In addition, from the viewpoint of improving discharge performance, it is more preferably 100cm 3 / 100g or less, more preferably 90cm 3 / 100g or less.

[0033] From the perspective of excellent charge storage function as a dielectric, carbon black A with a large DBP absorption is preferably relatively high in resistance. From this perspective, carbon black A is preferably carbon black with a relatively small specific surface area and a large particle size. Specifically, the specific surface area of carbon black A is preferably 25 m 2 / g and above 75m 2 / g or less. In addition, the average particle size is preferably 35nm or more and 75nm or less. The specific surface area of carbon black A is more preferably 30m 2 / g or above and 70m 2 / g or less, more preferably 30m 2 / g or above and 60m 2 / g or less. The average particle size of Carbon Black A is more preferably 40 nm to 70 nm, and even more preferably 40 nm to 60 nm. When the average particle size of Carbon Black A is 35 nm to 75 nm, it is easy to keep the specific surface area of Carbon Black A within the preferred range and to easily achieve high resistance.

[0034] From the viewpoint of excellent function of rapid charge flow, carbon black B with low DBP absorption is preferably relatively low in resistance. From this viewpoint, carbon black B is preferably carbon black with relatively large specific surface area and small particle size. Specifically, the specific surface area of carbon black B is preferably 140 m 2 / g and above and 180m 2 / g or less. In addition, the average particle size is preferably 20nm or more and 30nm or less. The specific surface area of carbon black B is more preferably 150m 2 / g and above and 180m 2 / g or less, more preferably 150m 2 / g or above and 170m 2 / g or less. The average particle size of carbon black B is more preferably 20 nm or more and 25 nm or less. When the average particle size of carbon black B is 20 nm or more and 30 nm or less, it is easy to adjust the specific surface area of carbon black B to the preferred range and to adjust the resistance of carbon black B to low.

[0035] The specific surface area of carbon black is a value measured by the BET method. The average particle size of carbon black is expressed as the arithmetic mean diameter determined by observing carbon black with an electron microscope.

[0036] The second phase 14b includes one or more polymers. From the viewpoint of low resistance, the polymer of the second phase 14b is preferably a polar polymer. As the polymer of the second phase 14b, nitrile rubber (NBR), epichlorohydrin rubber, polyurethane rubber (U), acrylic rubber (copolymer of acrylate and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR) and the like can be cited. As epichlorohydrin rubber, homopolymer (CO) of epichlorohydrin, epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO) and the like can be cited. These can be used alone as the polymer of the second phase 14b, or two or more can be used in combination. From the viewpoint of further low resistance, among them, nitrile rubber (NBR) and epichlorohydrin rubber are preferred.

[0037] When the first phase 14a contains a nonpolar polymer and the second phase 14b contains a polar polymer, the phase separation between the first phase 14a and the second phase 14b is improved, and the charge attenuation from the roller surface caused by localized resistance variations is easily suppressed. The polymer of the first phase 14a is preferably a polymer with a higher resistance than the polymer of the second phase 14b. Preferred combinations of the polymers of the first phase 14a and the second phase 14b include a combination of isoprene rubber (IR) and nitrile rubber (NBR), and a combination of natural rubber (NR) and nitrile rubber (NBR).

[0038] The surface resistance of the first phase 14a can be adjusted within a desired range by adjusting the polymer type, vulcanization conditions, etc. The surface resistance of the second phase 14b can be adjusted within a desired range by adjusting the polymer type, vulcanization conditions, and the amounts of carbon black A and carbon black B added.

[0039] From the perspective of achieving an excellent balance between the electrostatic capacitance and resistance of carbon black, the content ratio of carbon black A to carbon black B in the second phase 14b is preferably A / B = 3.0 or more and 10.0 or less, in terms of mass ratio. A / B = 3.0 or more and 7.0 or less is more preferred, and A / B = 4.0 or more and 7.0 or less is even more preferred.

[0040] From the viewpoint of easily ensuring electrostatic capacitance, the content of carbon black A is preferably 5 parts by mass or more relative to 100 parts by mass of the polymer component contained in the elastomer layer 14. It is more preferably 10 parts by mass or more, and further preferably 20 parts by mass or more. In addition, from the viewpoint of easily suppressing insufficient discharge, the content of carbon black A is preferably 75 parts by mass or less relative to 100 parts by mass of the polymer component contained in the elastomer layer 14. It is more preferably 70 parts by mass or less, and further preferably 60 parts by mass or less. Moreover, when the content of carbon black A is 5 parts by mass or more and 75 parts by mass or less relative to 100 parts by mass of the polymer component contained in the elastomer layer 14, it is easy to maintain the electrostatic capacitance within the preferred range.

[0041] From the viewpoint of easily ensuring low resistance, the content of carbon black B is preferably 1.5 parts by mass or more relative to 100 parts by mass of the polymer component included in the elastomer layer 14. It is more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. In addition, from the viewpoint of easily suppressing excessive discharge, the content of carbon black B is preferably 20 parts by mass or less relative to 100 parts by mass of the polymer component included in the elastomer layer 14. It is more preferably 15 parts by mass or less. Moreover, when the content of carbon black B is 1.5 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the polymer component included in the elastomer layer 14, it is easy to maintain the resistance within the preferred range.

[0042] like Figure 2 As shown, it is preferred that in the elastomer layer 14, the first phase 14a constitutes a sea phase and the second phase 14b constitutes an island phase. As a result, the effect of intercepting the charge based on the first phase 14a is improved, the local resistance unevenness can be further absorbed, and the charge attenuation from the roller surface can be further suppressed. The above-mentioned sea island structure of the elastomer layer 14 can be formed by adjusting the existence ratio of the first phase 14a and the second phase 14b, adjusting the content ratio of carbon black A and carbon black B, and adjusting the mixing method of the first phase 14a and the second phase 14b. The above-mentioned sea phase can be called a matrix phase, a continuous phase, etc. The above-mentioned island phase can be called a regional phase, a dispersed phase, etc. The second phase 14b is represented as a phase dispersed in the form of islands in the sea of the first phase 14a.

[0043] When the first phase 14a constitutes a sea phase and the second phase 14b constitutes an island phase in the elastic layer 14, the second phase 14b is basically a phase that does not appear at the interface between the elastic layer 14 and the surface layer 16. As such, the second phase 14b is preferably a phase that does not contact the surface layer 16. In other words, Figure 2 As shown, it is preferable to sandwich the first phase 14a between the second phase 14b and the surface layer 16. When the first phase 14a is sandwiched between the second phase 14b and the surface layer 16, the charge interception effect of the first phase 14a is enhanced, further absorbing local resistance variations. This further suppresses charge attenuation from the roller surface. To ensure excellent charge interception effect by the first phase 14a, the thickness t of the first phase 14a sandwiched between the second phase 14b and the surface layer 16 is preferably 10 nm or greater. It is more preferably 50 nm or greater, and even more preferably 100 nm or greater. Furthermore, to facilitate discharge, the thickness t of the first phase 14a sandwiched between the second phase 14b and the surface layer 16 is preferably 2.0 μm or less. It is more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. The thickness t of the first phase 14a sandwiched between the second phase 14b and the surface layer 16 can be determined by electron microscopic observation.

[0044] From the perspective of achieving the effect of intercepting the charge by the first phase 14a, the first phase 14a preferably has a higher resistance than the surface layer 16. In other words, the first phase 14a preferably has a higher resistance than the second phase 14b and a higher resistance than the surface layer 16. Furthermore, from the perspective of facilitating discharge, the second phase 14b preferably has a lower resistance than the surface layer 16, or has the same resistance as the surface layer 16. The resistance in this case is the surface resistance.

[0045] In the elastomer layer 14, the first phase 14a and the second phase 14b are preferably microdispersed with each other. Specifically, in terms of area ratio, the existence ratio of the first phase 14a and the second phase 14b in any 5μm×5μm range of the elastomer layer 14 is preferably first phase 14a / second phase 14b=0.3 or more and 20 or less. The above-mentioned area ratio is more preferably 0.5 or more and 10 or less, and further preferably 1.0 or more and 5.0 or less. When the first phase 14a and the second phase 14b are microdispersed with each other, the effect of suppressing the charge attenuation from the roller surface caused by the local resistance unevenness is excellent. The above-mentioned dispersed structure of the elastomer layer 14 can be formed by adjusting the existence ratio of the first phase 14a and the second phase 14b, adjusting the content ratio of carbon black A and carbon black B, and adjusting the kneading method of the first phase 14a and the second phase 14b. The above-mentioned dispersed structure of the elastomer layer 14 can be obtained by observation using an electron microscope.

[0046] Various additives may be added as needed to the elastomer layer 14. Examples of additives include lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoamers, pigments, and release agents.

[0047] The thickness of the elastic layer 14 is not particularly limited and may be appropriately set within a range of 0.1 to 10 mm depending on the intended use.

[0048] The main material forming the surface layer 16 is not particularly limited, and examples thereof include polyamide (nylon), acrylic, polyurethane, silicone, and fluorine-based polymers. These polymers may also be modified polymers. Examples of the modifying group include N-methoxymethyl, silicone, and fluorine groups.

[0049] The surface layer 16 may also contain roughness-forming particles. These particles are used to impart roughness to the surface of the surface layer 16. In other words, they are used to impart surface irregularities to the surface of the surface layer 16. The surface irregularities of the surface layer 16 increase the discharge space between the photoreceptor and the charging roller 10, promoting discharge. This improves charging performance and prevents image defects such as horizontal streaks and unevenness.

[0050] Resin particles, etc., are used as the roughness-forming particles. The material of the roughness-forming particles is not particularly limited. The roughness-forming particles are preferably composed of a polymer having a carbonyl group. This is because polymers having a carbonyl group have a relatively high dielectric constant and can easily ensure excellent charging properties for the charging roller 10. Examples of polymers having a carbonyl group include polyurethane resins, polyamide resins, acrylic resins, acrylic silicone resins, silicone-grafted acrylic polymers, acrylic-grafted silicone polymers, and polyurethane rubber.

[0051] The size of the roughness-forming particles is not particularly limited, but from the perspective of ensuring uniform charging properties, particles having an average particle size of 3.0 μm to 50 μm are preferred. More preferably, the particles have an average particle size of 5.0 μm to 30 μm. The surface of the surface layer 16 is observed under a laser microscope, and the diameter of the roughness-forming particles observed during the observation is used as the particle size. The average particle size of the roughness-forming particles is expressed as the average of twenty arbitrary points.

[0052] The content of the roughness-forming particles in the surface layer 16 is not particularly limited, but is preferably 3 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the binder polymer in the surface layer 16, and more preferably 5 parts by mass or more and 30 parts by mass or less, from the perspective of easily ensuring uniform charging properties.

[0053] To impart conductivity, conventionally known conductive agents such as carbon black, graphite, conductive titanium oxide, conductive zinc oxide, conductive tin oxide, and ion conductive agents (quaternary ammonium salts, borates, surfactants, etc.) may be appropriately added to the surface layer 16. Furthermore, various additives may be appropriately added as needed.

[0054] From the viewpoint of chargeability, the volume resistivity of the surface layer 16 can be set in the semi-conductive region. Specifically, for example, it can be set at 1.0×10 7 ~1.0×10 10 The volume resistivity can be measured in accordance with JIS K6911. The thickness of the surface layer 16 is not particularly limited and can be set in the 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 (such as "VK-9510" manufactured by Keyence). For example, the distance from the surface of the elastomer layer 14 to the surface of the surface layer 16 can be measured at five arbitrary positions, and the average thereof can be expressed.

[0055] The charging roller 10 can be manufactured by forming the elastic layer 14 on the outer peripheral surface of the shaft and forming the surface layer 16 on the outer peripheral surface of the elastic layer 14 .

[0056] The elastomer layer 14 can be formed, for example, as follows: First, a shaft is coaxially placed in the hollow portion of a roll forming mold, an uncrosslinked elastomer layer-forming composition is injected, heated, cured (crosslinked), and then demolded, or the uncrosslinked elastomer layer-forming composition is extruded onto the surface of the shaft, thereby forming the elastomer layer 14 on the outer periphery of the shaft.

[0057] The elastomer layer-forming composition can be formed by kneading two types of carbon black, carbon black A and carbon black B, with the polymer component constituting the second phase 14 b and then kneading the polymer component constituting the first phase 14 a .

[0058] A surface layer forming composition is used to form the surface layer 16. The surface layer forming composition is composed of the above-mentioned main material, a conductive agent, and other additives as needed.

[0059] From the viewpoint of adjusting viscosity, the surface layer forming composition may appropriately contain solvents such as organic solvents such as methyl ethyl ketone, toluene, acetone, ethyl acetate, butyl acetate, methyl isobutyl ketone (MIBK), THF, and DMF, and water-soluble solvents such as methanol and ethanol.

[0060] The surface layer 16 can be formed by applying a surface layer-forming composition to the outer peripheral surface of the elastomer layer 14. Various coating methods can be used, such as roll coating, dip coating, and spray coating. The applied surface layer 16 may be subjected to ultraviolet irradiation or heat treatment as needed.

[0061] The charging roller 10 constructed as described above achieves rapid charge flow and low resistance by including carbon black B, which has low DBP absorption, in the low-resistance second phase 14b of the elastomer layer 14. Furthermore, carbon black A, which has high DBP absorption and is present in the low-resistance second phase 14b along with carbon black B, functions as a dielectric to store charge. Furthermore, the high-resistance first phase 14a, separated from the low-resistance second phase 14b, acts as a dielectric phase, intercepting and equalizing charge, thereby absorbing localized resistance variations. This suppresses charge attenuation from the roller surface caused by localized resistance variations, enabling the production of excellent images.

[0062] Example

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

[0064] (Example 1)

[0065] <Preparation of Elastomer Layer-Forming Composition>

[0066] 50 parts by mass of carbon black A-1 and 10 parts by mass of carbon black B-1 were added to 40 parts by mass of NBR, and these were stirred and mixed in a stirrer to prepare a second-phase-forming composition. Next, 60 parts by mass of isoprene rubber, 5 parts by mass of a peroxide crosslinking agent, 3 parts by mass of a vulcanization accelerator, and 3 parts by mass of a catalyst were added to the second-phase-forming composition, and these were stirred and mixed in a stirrer to prepare an elastomer layer-forming composition.

[0067] <Production of the Elastomer Layer>

[0068] A core rod (8 mm in diameter) was mounted in a tubular mold, and the elastomer layer-forming composition was injected. The mixture was heated at 180°C for 30 minutes, cooled, and demolded to form an elastomer layer with a thickness of 1.9 mm on the outer periphery of the core rod.

[0069] <Preparation of Surface Layer Forming Composition>

[0070] The roughness-forming particles and the binder polymer were mixed, 200 parts by mass of methyl ethyl ketone (MEK) was added, and the mixture was mixed and stirred at a predetermined stirring speed to prepare a surface layer-forming composition.

[0071] Adhesive polymer (PU): Negami Industries' "ART Resin UN-333"

[0072] Roughness-forming particles (PU): Negami Industry's "Art Pearl C-600 Transparent," with an average particle size of 10 μm.

[0073] <Surface layer production>

[0074] While continuing to stir the surface layer forming composition, the outer peripheral surface of the elastomer layer was roll-coated and heat-treated to form a surface layer having a thickness of 1.0 μm on the outer periphery of the elastomer layer.

[0075] (Example 2)

[0076] In the preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the blending amounts of carbon black A and carbon black B were changed.

[0077] (Example 3)

[0078] In preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the mixing ratio of IR and NBR and the type of carbon black A were changed.

[0079] (Example 4 to Example 5)

[0080] In the preparation of the elastic layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the type of carbon black A was changed.

[0081] (Example 6)

[0082] In preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the type of carbon black B and the blending amounts of carbon black A and carbon black B were changed.

[0083] (Example 7)

[0084] In the preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the blending ratio of IR and NBR and the blending amount of carbon black B were changed.

[0085] (Example 8 to Example 11)

[0086] In the preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the blending amounts of carbon black A and carbon black B were changed.

[0087] (Example 12 to Example 13)

[0088] In preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the mixing ratio of IR and NBR was changed.

[0089] (Comparative Examples 1 to 5)

[0090] In the preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the type of carbon black was changed.

[0091] (Comparative Examples 6 to 7)

[0092] In the preparation of the elastomer layer-forming composition, a charging roller was produced in the same manner as in Example 1, except that the vulcanization conditions for IR and NBR were changed. In Comparative Example 6, the vulcanization temperature was increased and the vulcanization time was shortened compared to Example 1. Furthermore, in Comparative Example 7, the vulcanization temperature was decreased and the vulcanization time was prolonged compared to Example 1.

[0093] (Comparative Examples 8 to 9)

[0094] In the preparation of the elastic layer-forming composition, a charging roller was produced in the same manner as in Example 1 except that the blending amount of carbon black B was changed.

[0095] (Comparative Example 10)

[0096] In preparing the composition for forming the elastomer layer, a charging roller was produced in the same manner as in Example 1, except that 50 parts by mass of carbon black A-1, 10 parts by mass of carbon black B-1, 5 parts by mass of an oxide crosslinking agent, 3 parts by mass of a vulcanizing aid, and 3 parts by mass of a catalyst were added to 100 parts by mass of the isoprene rubber, and the mixture was stirred and mixed using a stirrer. Thus, the elastomer layer consisted of only a single phase comprising isoprene rubber.

[0097] (Comparative Example 11)

[0098] In preparing the composition for forming the elastomer layer, a charging roller was produced in the same manner as in Example 1, except that 50 parts by mass of carbon black A-1, 10 parts by mass of carbon black B-1, 5 parts by mass of an oxide crosslinking agent, 3 parts by mass of a vulcanization accelerator, and 3 parts by mass of a catalyst were added to 100 parts by mass of NBR, and these were stirred and mixed using a stirrer. Thus, the elastomer layer consisted of only one phase containing NBR.

[0099] The following materials were prepared as materials for the elastic layer-forming composition.

[0100] (Base polymer)

[0101] Isoprene rubber (IR): Nipol IR2200 manufactured by Zeon, Japan

[0102] Nitrile rubber (NBR): "Nipol 1041" manufactured by Zeon, Japan

[0103] (Carbon Black A)

[0104] A-1 (DBP absorption is 124ml / 100g, BET specific surface area is 43m 2 / g, average particle size 41nm): Asahi Carbon Manufacturing "Asahi #60H (N-568)"

[0105] A-2 (DBP absorption is 160ml / 100g, BET specific surface area is 75m 2 / g, average particle size 35nm): Denka "Denka Black"

[0106] A-3 (DBP absorption is 115ml / 100g, BET specific surface area is 42m 2 / g, average particle size 44nm): "Seast SO" manufactured by Tokai Carbon

[0107] A-4 (DBP absorption is 155ml / 100g, BET specific surface area is 25m 2 / g, average particle size 75nm): "Seast GFY" manufactured by Tokai Carbon

[0108] A-5 (DBP absorption is 125ml / 100g, BET specific surface area is 126m 2 / g, average particle size 20nm): "Seast 7HM" manufactured by Tokai Carbon

[0109] (Carbon Black B)

[0110] B-1 (DBP absorption is 70ml / 100g, BET specific surface area is 180m 2 / g, average particle size 25nm): Orion Engineered Carbons "Special Black 4"

[0111] B-2 (DBP absorption is 110ml / 100g, BET specific surface area is 140m 2 / g, average particle size 20nm): Showa Cabot "SHOWBLACK IP1500"

[0112] B-3 (DBP absorption is 110ml / 100g, BET specific surface area is 20m 2 / g, average particle size 85nm): Asahi Carbon Manufacturing "Asahi #50H"

[0113] (Other carbon black)

[0114] X-1 (DBP absorption is 175ml / 100g, BET specific surface area is 165m 2 / g, average particle size 21nm): Mitsubishi Chemical "#3400B"

[0115] X-2 (DBP absorption is 58ml / 100g, BET specific surface area is 180m 2 / g, average particle size 18nm): Mitsubishi Chemical "#1000"

[0116] X-3 (DBP absorption is 360ml / 100g, BET specific surface area is 800m 2 / g, average particle size 32nm): "Ketjen EC300J" manufactured by Ketjenblack International

[0117] The surface resistance values of the first and second phases of the produced charging rollers were measured. The area ratio of the first and second phases was also measured. Furthermore, the following image evaluation was performed.

[0118] (Measurement of surface resistance)

[0119] The cross section of the produced charging roller was scanned 1 μm using a scanning probe microscope "AFM5100N" manufactured by Hitachi Science using a cantilever "SI-DF3" in DFM mode, and the surface resistance (Ω·cm) of each of the first phase and the second phase was derived.

[0120] (Measurement of Area Ratio)

[0121] The cross section of the produced charging roller was observed at 1,000,000 magnification in an area of 5 μm×5 μm using a scanning electron microscope “JSM-7200F” manufactured by JEOL Ltd., and the area ratio of the first phase to the second phase was calculated.

[0122] (Uneven image)

[0123] The produced conductive roller was incorporated into a Konica Minolta bizhub C658 multifunction printer. After printing 550,000 sheets in a 1% print density, halftone images were printed at a 25% print density using a ruled line pattern at 10°C and 10% RH. No image unevenness was observed, and the result was rated "good" (good), while any unevenness was rated "poor" (bad).

[0124] (Horizontal stripe image)

[0125] The resulting conductive roller was incorporated into a Konica Minolta bizhub C658 multifunction printer. After printing 550,000 sheets in a 1% ruled-line pattern at a 1% print density, a halftone image at a 25% print density was printed under a 10°C, 10% RH environment. Images with no horizontal streaks were rated "good" (○), while images with horizontal streaks were rated "poor" (×).

[0126] (Black dot image)

[0127] The resulting conductive roller was incorporated into a Konica Minolta bizhub C658 multifunction printer. After printing 550,000 sheets in a 1% print density, a ruled line pattern was used under a 10°C, 10% RH environment. A halftone image with a print density of 25% was then printed. Images with no black spots were rated "good" (○), while images with black spots were rated "poor" (×).

[0128]

[0129]

[0130] The elastomer layer of Comparative Example 1 is composed of two phases: a first phase containing IR and a second phase containing NBR. However, the second phase does not contain DBP. The absorption amount is 115 cm 3 / 100g or more and 160cm 3 Carbon black A below 100g contains only carbon black with a DBP absorption of 70cm 3 / 100g or more and 110cm 3 / 100g or less of carbon black B. As a result, the electrostatic capacity is insufficient, resulting in insufficient charging, and horizontal streaks are generated in image evaluation. The elastomer layer of Comparative Example 2 is composed of two phases: a first phase containing IR and a second phase containing NBR. However, the second phase does not contain carbon black A, but contains carbon black B and has a DBP absorption exceeding 160cm 3 Therefore, the electrostatic capacity becomes too large, resulting in insufficient discharge and insufficient charging, which causes horizontal streaks in image evaluation.

[0131] The elastomer layer of Comparative Example 3 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, the second phase did not contain carbon black B, but only carbon black A. Consequently, dielectric properties were overly prioritized, resulting in insufficient discharge and insufficient charging, which caused horizontal streaks in image evaluation. The elastomer layer of Comparative Example 4 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, the second phase did not contain carbon black B, but contained carbon black A, and had a DBP absorption of less than 70 cm 3Therefore, the electrostatic capacity is insufficient and the charge becomes insufficient, resulting in horizontal streaks in image evaluation.

[0132] The elastomer layer of Comparative Example 5 is composed of two phases: a first phase containing IR and a second phase containing NBR. However, the second phase does not contain carbon black B, but contains carbon black A and a DBP absorption exceeding 160 cm 3 / 100g of carbon black. The DBP absorption exceeds 160cm 3 The specific surface area of carbon black per 100g is as high as 800m 2 / g, so that charges flow excessively and discharge becomes excessive (abnormal discharge), resulting in black spots in image evaluation.

[0133] The elastomer layer of Comparative Example 6 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, due to the excessively high surface resistance of the first phase, dielectric properties took precedence, resulting in insufficient discharge and insufficient charging, which caused horizontal streaks in image evaluation. The elastomer layer of Comparative Example 7 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, due to the excessively low surface resistance of the first phase, excessive charge flowed, resulting in excessive discharge (abnormal discharge), which caused black spots in image evaluation.

[0134] The elastomer layer of Comparative Example 8 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, due to the excessively low surface resistance of the second phase, excessive charge flow resulted in excessive discharge (abnormal discharge), resulting in black spots in image evaluation. The elastomer layer of Comparative Example 9 consisted of two phases: a first phase containing IR and a second phase containing NBR. However, due to the excessively high surface resistance of the second phase, insufficient resistance resulted in insufficient charging, resulting in horizontal streaks in image evaluation.

[0135] The elastomer layer of Comparative Example 10 was not composed of two phases, a first phase containing IR and a second phase containing NBR, but was composed only of a single phase containing IR, and the phase containing IR contained two types of carbon black A and carbon black B. Furthermore, the elastomer layer of Comparative Example 11 was not composed of two phases, a first phase containing IR and a second phase containing NBR, but was composed only of a single phase containing NBR, and the phase containing NBR contained two types of carbon black A and carbon black B. Consequently, in Comparative Examples 10 and 11, there was no phase that could serve as a dielectric phase, resulting in insufficient electrostatic capacitance and insufficient charging, which caused horizontal streaks in image evaluation.

[0136] In contrast, the elastic layer of the embodiment has a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase has a high resistance of less than Ω·cm, and the surface resistance is 1.3×10 2 Ω·cm or more and 4.9×103 The second phase has a low resistance of less than Ω·cm, and the second phase contains a DBP absorption of 115cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 110cm 3 / 100g or less of the two carbon blacks, carbon black B. Therefore, the charge attenuation from the roller surface caused by the local uneven resistance portion can be suppressed, and a good image can be obtained. As shown in Comparative Example 1, even if the elastomer layer contains a first phase with high resistance, but only contains carbon black B with a small DBP absorption, the electrostatic capacity is insufficient, and the charging becomes insufficient and insufficient. In addition, as shown in Comparative Example 3, even if the elastomer layer contains a second phase with low resistance, but only contains carbon black A with a large DBP absorption, the dielectric property is overly prioritized, resulting in insufficient discharge, and insufficient charging. In addition, as shown in Comparative Examples 10 and 11, even if the elastomer layer contains two types of carbon black A and carbon black B, when the phase containing the two types of carbon black A and carbon black B is only one phase, the electrostatic capacity is insufficient, and the charging becomes insufficient and insufficient. As shown in the embodiment, by including a high-resistance first phase and a low-resistance second phase in the elastomer layer, and including both carbon black A with a large DBP absorption amount and carbon black B with a small DBP absorption amount in the second phase, the charge attenuation from the roller surface caused by local resistance unevenness can be suppressed, and a good image can be obtained.

[0137] While the embodiments and examples of the present invention have been described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

[0138] Description of Reference Numerals

[0139] 10: Charging roller;

[0140] 12: shaft;

[0141] 14: Elastomer layer;

[0142] 16: surface;

[0143] 14a: first phase;

[0144] 14b: Second phase.

Claims

1. A charging roller for an electrophotographic device, wherein: The charging roller for an electrophotographic device includes a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer. The elastomer layer has a surface resistance of 1.6×10 14 Ω·cm or more and 8.8×10 15 The first phase has a high resistance of less than Ω·cm and a surface resistance of 1.3×10 2 Ω·cm or more and 4.9×10 3 The second phase has a low resistance of less than Ω·cm. The second phase contains a DBP absorption of 120 cm 3 / 100g or more and 160cm 3 / 100g or less of carbon black A, and DBP absorption of 70cm 3 / 100g or more and 90cm 3 / 100g or less of carbon black B and these two types of carbon black.

2. The charging roller for an electrophotographic apparatus according to claim 1, wherein In the elastomer layer, the first phase constitutes a sea phase, and the second phase constitutes an island phase.

3. The charging roller for an electrophotographic apparatus according to claim 1 or 2, wherein The content ratio of the carbon black A to the carbon black B in the second phase is A / B = 3.0 or more and 10.0 or less in terms of mass ratio.

4. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 3, wherein The specific surface area of the carbon black A is 25 m 2 / g and above 75m 2 / g or less, the specific surface area of the carbon black B is 140m 2 / g and above and 180m 2 / g or less.

5. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 4, wherein The average particle size of the carbon black A is 35 nm or more and 75 nm or less, and the average particle size of the carbon black B is 20 nm or more and 30 nm or less.

6. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 5, wherein The content of the carbon black A is 5 parts by mass to 75 parts by mass, and the content of the carbon black B is 1.5 parts by mass to 20 parts by mass, relative to 100 parts by mass of the polymer component contained in the elastomer layer.

7. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 6, wherein The first phase contains a non-polar polymer, and the second phase contains a polar polymer.

8. The charging roller for an electrophotographic apparatus according to claim 7, wherein The non-polar polymer is isoprene rubber or natural rubber, and the polar polymer is nitrile rubber or epichlorohydrin rubber.

9. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 8, wherein In terms of area ratio, the abundance ratio of the first phase to the second phase in an arbitrary area of 5 μm×5 μm of the elastomer layer is first phase / second phase=0.3 or more and 20 or less.

10. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 9, wherein The first phase is sandwiched between the second phase and the surface layer.

11. A method for manufacturing a charging roller for an electrophotographic device, which is the method for manufacturing a charging roller for an electrophotographic device according to any one of claims 1 to 10, wherein: After the two carbon blacks, carbon black A and carbon black B, are kneaded with the polymer component constituting the second phase, the polymer component constituting the first phase is kneaded.

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