Charging roller, process cartridge, and electrophotographic image forming apparatus

Abstract

To provide an electrifying roller that quickly eliminates potential unevenness caused by the frictional electrification between the electrifying roller and an electrophotographic photoreceptor.SOLUTION: An electrifying roller has a conductive shaft core body and a conductive layer as a surface layer. The conductive layer has a matrix including a crosslinked product of first rubber and a plurality of dispersed domains. Each of the domains includes a crosslinked product and conductive particles. The volume resistivity of the domains is lower than the volume resistivity of the matrix. The surface resistance value of the electrifying roller is 1.0×10-1 Ω or more and 1.0×103 Ω or less. In 50% by number or more of domains of all the domains, two surfaces of six surfaces of an envelope cuboid of a domain to be determined are surfaces passing through an arbitrary one point in the domain and orthogonal to a line segment L orthogonal to a surface of the shaft core body. When the length in an X-axis direction of the envelope cuboid is x, the length in a Y-axis direction is y, and the length in a Z-axis direction is z, x is longer than y and z. A line segment S orthogonal to the line segment L and parallel to the X-axis can be drawn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure is directed to a charging roller, a process cartridge, and an electrophotographic image forming apparatus. [Background technology]

[0002] In an electrophotographic image forming apparatus employing a contact charging system, a charging roller for charging the surface of an electrophotographic photosensitive member is disposed in contact with the electrophotographic photosensitive member.

[0003] The charging roller has a conductive substrate and a conductive layer on the substrate. In an electrophotographic image forming apparatus, a voltage is applied between the conductive substrate of the charging roller and an electrophotographic photosensitive member, and the surface of the conductive layer of the charging roller facing the electrophotographic photosensitive member (hereinafter also referred to as the "outer surface") is discharged toward the electrophotographic photosensitive member, thereby charging the surface of the electrophotographic photosensitive member facing the charging roller. Patent Document 1 discloses a charging member having an elastic layer containing a polymer continuous phase made of an ionically conductive rubber material and a polymer particle phase made of an electronically conductive rubber material.

[0004] According to the investigations of the present inventors, when the charging roller according to Patent Document 1 was used to form an electrophotographic image in a low-temperature, low-humidity environment, for example, at a temperature of 15°C and a relative humidity of 10%, streaks (hereinafter also referred to as "horizontal streaks") extending in a direction perpendicular to the circumferential direction of the charging roller were sometimes formed on the electrophotographic image. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-3651 Summary of the Invention [Problem to be solved by the invention]

[0006] One aspect of the present disclosure is directed to providing a charging roller that contributes to the stable formation of high-quality electrophotographic images under various environments. Another aspect of the present disclosure is directed to providing a process cartridge that contributes to the stable formation of high-quality electrophotographic images. Still another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, there is provided a charging roller having a conductive mandrel and a conductive layer as a surface layer, The surface resistance measured on the outer surface of the charging roller is 1.0×10 -1 Ω or more, 1.0×10 3 is less than or equal to Ω, The conductive layer has a matrix containing a cross-linked product of a first rubber and a plurality of domains dispersed in the matrix, each of the domains containing a cross-linked product of a second rubber and conductive particles, the volume resistivity of the domains is lower than the volume resistivity of the matrix, and of all the domains contained in a cube with a side length of 20.0 μm sampled from a region from the outer surface of the conductive layer to a depth of 20.0 μm, 50% or more of the domains by number satisfy the following condition: <Condition> Assuming that the domain to be judged is enclosed by an enveloping rectangular parallelepiped, two of the six faces of which pass through any one point in the domain to be judged and are perpendicular to a line segment L perpendicular to the surface of the mandrel, and the length of the enveloping rectangular parallelepiped in the X-axis direction is x, the length of the Y-axis direction is y, and the length of the Z-axis direction is z, x is longer than y and z, and It is possible to draw a line segment S that is perpendicular to the line segment L and parallel to the X axis. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, a charging roller that contributes to the stable formation of high-quality electrophotographic images under various environments can be obtained. According to another aspect of the present disclosure, a process cartridge that contributes to the stable provision of high-quality electrophotographic images can be obtained. Furthermore, according to another aspect of the present disclosure, an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a charging roller according to one embodiment of the present disclosure. [Figure 2] 1A is a schematic diagram of a longitudinal cross section of a conductive layer according to an embodiment of the present disclosure, and FIG. 1B is a schematic diagram showing the state of domains present in a surface region from the outer surface to a depth of 20 μm of a conductive layer according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is an explanatory diagram of one domain in a conductive layer according to one embodiment of the present disclosure. [Figure 4] FIG. 10 is an explanatory diagram of a domain that does not satisfy the conditions according to the present disclosure. [Figure 5] FIG. 1 is an explanatory diagram of angles representing the direction in which domains extend according to the present disclosure. [Figure 6] FIG. 2 is a diagram showing a schematic configuration of a crosshead extrusion device. [Figure 7] This is a histogram summarizing the angular distribution of minor angles. [Figure 8] FIG. 2 is a cross-sectional view of a process cartridge according to an embodiment of the present disclosure. [Figure 9] 1 is a cross-sectional view of an electrophotographic image forming apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] The reason why horizontal streaks occur in an electrophotographic image when the charging member according to Patent Document 1 is used to form the electrophotographic image in a low-temperature, low-humidity environment is presumed to be as follows. Because the charging member rotates while in contact with the electrophotographic photosensitive member, friction with the electrophotographic photosensitive member can generate electric charges on the surface of the contact area (hereinafter also referred to as the "nip area") between the charging member and the electrophotographic photosensitive member. The surface of the charging member is provided with a predetermined conductivity for an ionic or electronic conductive agent to perform the function of discharging electric charges to the electrophotographic photosensitive member. Therefore, although the frictional electric charges generated on the surface of the charging member due to friction with the electrophotographic photosensitive member diffuse, the directionality is not controlled, and therefore, locally high electric charges can exist in the region of the conductive layer from the surface of the nip area to the mandrel. These locally high electric charges then cause uneven discharge from the charging member. It is believed that such uneven discharge causes uneven electric potential on the surface of the electrophotographic photosensitive member.

[0011] Therefore, the present inventors have conducted extensive research into the configuration of a charging member that can control the diffusion direction of frictional charges generated on the surface of a charging roller in order to prevent the generation of localized charge accumulation areas inside the elastic layer, and have found that the diffusion direction of frictional charges generated on the surface can be controlled by the following charging member. That is, a charging member according to one embodiment of the present disclosure includes a conductive mandrel and a conductive surface layer. The conductive layer has a matrix containing a first rubber and a plurality of domains dispersed in the matrix. Each of the domains contains a cross-linked product of a second rubber and conductive particles. The volume resistivity of the domains is lower than that of the matrix. Furthermore, of all domains contained in a cube with a side length of 20.0 μm sampled from a region from the outer surface of the conductive layer to a depth of 20.0 μm, 50% or more by number of the domains satisfy the following condition. <Condition> Assuming that the domain to be judged is enclosed by an enveloping rectangular parallelepiped, two of the six faces of which pass through any one point in the domain to be judged and are perpendicular to a line segment L perpendicular to the surface of the mandrel, and the length of the enveloping rectangular parallelepiped in the X-axis direction is x, the length of the Y-axis direction is y, and the length of the Z-axis direction is z, x is longer than y and z, and It is possible to draw a line segment S that is perpendicular to the line segment L and parallel to the X axis.

[0012] The charging member according to one embodiment of the present disclosure will be described below with reference to the drawings. FIG. 1 is a perspective view of a charge roller 100 according to one embodiment of the present disclosure. The charge roller 100 includes a mandrel 101 having a conductive outer surface and a conductive layer 103 covering the outer peripheral surface of the mandrel 101. FIG. 2 is an explanatory diagram of the configuration of the conductive layer 103 of the charge roller 100, and FIG. 2(a) is a schematic diagram of a cross section of the conductive layer 103 in a direction perpendicular to the circumferential direction of the charge roller 100 (hereinafter also referred to as the "longitudinal direction"). The conductive layer 103 includes a matrix 201 containing a first rubber and domains 203 dispersed in the matrix. FIG. 2(b) is a schematic diagram showing the state of the domains 203 present in a surface region extending from the outer surface of the conductive layer to a depth of 20 μm. In FIG. 2(b), 205A indicates a circumferential cross section of the conductive layer 103 of the charge roller, and 205B indicates a longitudinal cross section of the conductive layer 103. The conductive layer has an outer surface 207, which is the outer surface of the charging roller, i.e., the surface facing the electrophotographic photosensitive member. Each of the domains 203 contains conductive particles such as carbon black (not shown).

[0013] Next, a domain 203 that meets the above conditions will be described with reference to FIG. 3. Note that the mandrel 101 and the domain 203 are not scaled in FIG. 3. A rectangular parallelepiped (hereinafter also referred to as an "enveloping rectangular parallelepiped") 301 that envelops the domain 203 is defined. The enveloping rectangular parallelepiped 301 is defined as a rectangular parallelepiped with all six faces in contact with the domain 203. When a line segment L is drawn that passes through any point within the domain 203 and is perpendicular to the surface of the mandrel 101, two of the six faces that form the enveloping rectangular parallelepiped 301 are perpendicular to the line segment L. Furthermore, when the length of the enveloping rectangular parallelepiped 301 in the X-axis direction is x, the length of the enveloping rectangular parallelepiped 301 in the Y-axis direction is y, and the length of the enveloping rectangular parallelepiped 301 in the Z-axis direction is z, x is longer than y and z. In other words, the longest side of the enveloping rectangular parallelepiped 301 is set to the X-axis. In this case, a line segment S can be drawn for domain 203 according to the present disclosure, which is parallel to the X axis and perpendicular to line segment L. That is, domain 301 satisfying the above-described conditions can be said to exist in the conductive layer in a state where it is elongated in a non-depth direction of the conductive layer, for example, in the longitudinal direction.

[0014] Furthermore, the volume resistivity of the domains 203 is lower than that of the matrix 201. Therefore, it is the domains 203 containing conductive particles that are primarily responsible for the movement of charges within the conductive layer. Therefore, in a conductive layer having a certain number of domains that satisfy the above-described conditions, the volume resistivity of the domains 203 is lower than that of the matrix 201, so that even if frictional charges are generated on the surface of the nip portion, they can be diffused through the domains 203 in the direction of extension of the domains 203. In other words, the movement direction of the frictional charges within the conductive layer can be controlled.

[0015] On the other hand, Figure 4 shows an example of a domain that does not satisfy the above conditions. In Figure 4, when the longest point 405 of the enveloping rectangular parallelepiped 403 of domain 401 is set as the X-axis, the X-axis is perpendicular to the surface of the mandrel 101. Therefore, when a line segment L is drawn that passes through any point within domain 401 and is perpendicular to the surface of the mandrel 101, a line segment S that is perpendicular to line segment L and parallel to the X-axis cannot be drawn. Such a domain 401 extends from the outer surface of the conductive layer toward the mandrel. In this case, frictional charges generated at the surface of the nip portion remain within the region between the surface of the nip portion and the mandrel, which may affect the discharge performance of the charging roller.

[0016] <The minor angle θ formed by line segments P and Q> The enveloping rectangular parallelepiped has a first YZ plane and a second YZ plane that face each other and include the Y axis and the Z axis. Among the line segments connecting the contact points of the domains on the first YZ plane and the contact points of the domains on the second YZ plane, the longest line segment is designated as line segment P. A line segment Q is drawn that has the same starting point as the starting point of line segment P and is perpendicular to the surface of the mandrel, and the minor angle θ formed by line segments P and Q is designated as minor angle θ. When the minor angles θ for all domains in the cube are measured, it is preferable that the most frequent value of the minor angle θ be 60° or more and 90° or less. Since many domains extend in directions other than the depth direction of the conductive layer, the charge generated by frictional charging between the electrophotographic photosensitive member and the charging roller can be quickly moved from the nip position of the charging roller to a non-nip position.

[0017] FIG. 5 is an explanatory diagram of the angle (minor angle) θ representing the extending direction of the domain 203 according to the present disclosure. If the longest side of the enveloping rectangular parallelepiped 301 is the X-axis, the longest line segment 507 connecting the contact point of the first YZ plane 505 with the domain 203 and the contact point of the second YZ plane of the enveloping rectangular parallelepiped with the domain 203 opposite the first YZ plane is line segment P, which represents the maximum length of the domain. When a line segment 501 (line segment Q) is drawn that passes through the contact point of the line segment 507 with the first YZ plane 505 and is perpendicular to the mandrel 101, the minor angle θ formed by the line segment 507 (line segment P) and the line segment 501 (line segment Q) is defined as θ. When the minor angle θ is 90°, it can be said that the domain 203 extends in the tangent direction to the outer surface of the conductive layer 103. As the minor angle θ decreases from 90°, the domain 203 extends in the thickness direction of the conductive layer. Therefore, in order to allow the frictional charges generated on the surface of the charging roller to escape from the nip portion and to prevent uneven discharge from the charging roller, it is preferable that the minor angle θ is set to 60° or more and 90° or less.

[0018] <Length of the enveloping rectangular parallelepiped in the X-axis direction x> The arithmetic mean length x of the enveloping rectangular parallelepiped of the domains satisfying the above conditions in the X-axis direction is preferably in the range of 0.5 μm to 15.0 μm. By setting the average value of x to 0.5 μm or more, charges can be more effectively transferred along the extension direction of the domains. Furthermore, by setting the average value of x to 15.0 μm or less, it is possible to maintain a matrix-domain structure in which each domain exists independently. The method for calculating x will be described in Example 1.

[0019] <Conductive mandrel> The conductive mandrel 101 can be appropriately selected from materials known in the field of electrophotographic conductive materials. Examples of mandrel materials include metals or alloys such as aluminum, stainless steel, conductive synthetic resins, iron, and copper alloys. Furthermore, these may be subjected to oxidation treatment or plating with chromium, nickel, or the like. While both electroplating and electroless plating can be used as the plating method, electroless plating is preferred from the viewpoint of dimensional stability. Examples of electroless plating used here include nickel plating, copper plating, gold plating, and various other alloy platings. The plating thickness is preferably 0.05 μm or more, and considering the balance between work efficiency and anti-corrosion performance, the plating thickness is preferably 0.1 to 30 μm. The conductive mandrel may have a cylindrical or hollow cylindrical shape. The outer diameter φ of this conductive mandrel is preferably in the range of 3 mm to 10 mm.

[0020] <Conductive layer> <Surface resistance> The charge generated by frictional charging between the electrophotographic photosensitive member and the charging roller is generated on the surface of the charging roller. Therefore, it is preferable that the surface shape of the conductive layer has a low resistance so as not to impair the function of the charging roller. Specifically, the surface resistance value measured on the outer surface of the charging roller is 1.0 × 10 -1 Ω or more, 1.0×10 3 It is preferable that the resistance is in the range of Ω or less, which allows the charges generated on the surface to be transferred more quickly. <Matrix> The matrix contains a crosslinked product of the first rubber. The volume resistivity m of the matrix is ​​1.0 × 10 relative to the volume resistivity d of the domain described below. 3 It is preferable that the volume resistivity m of the matrix is ​​1.0×10 times or more the volume resistivity d of the domain. 3 More than twice (m / d≧1.0×10 3 ), charges move to domains in the conductive layer that are regions of low resistance, and then move to adjacent domains along the extension direction of the domains. Therefore, charges generated by frictional charging between the electrophotographic photosensitive member and the charging roller quickly move from the nip position to non-nip positions of the charging roller. This allows the potential difference between the nip position and non-nip position with the electrophotographic photosensitive member at the start of rotation of the charging roller to be equalized. The method for measuring the volume resistivity of the matrix will be described later.

[0021] <First Rubber> The first rubber has the highest compounding ratio in the rubber composition for forming the conductive layer. Since the cross-linked product of the rubber determines the mechanical strength of the conductive layer, it is preferable to use a first rubber that can fully exhibit the strength required for a conductive member for electrophotography after cross-linking in the conductive layer. Examples of the first rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), butyl rubber (IIR), nitrile butadiene rubber (NBR), ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer rubber (EPDM), chloroprene rubber (CR), and silicone rubber.

[0022] <Reinforcing agent> The matrix may contain a reinforcing agent to the extent that it does not affect the conductivity of the matrix. An example of the reinforcing agent is reinforcing carbon black with low conductivity. Specific examples of reinforcing carbon black include FEF (Fast Extruding Furnace) grade carbon black, GPF (General Purpose Furnace) grade carbon black, SRF (Semi-Reinforcing Furnace) grade carbon black, and MT carbon. Furthermore, if necessary, the first rubber forming the matrix may contain fillers, processing aids, vulcanization aids, vulcanization accelerators, vulcanization acceleration aids, vulcanization retarders, antioxidants, softeners, dispersants, colorants, and the like, which are generally used as compounding agents for rubber.

[0023] <Ionic conductive agent> The matrix is ​​designed to have a resistance of the elastic layer in a medium resistance range (for example, 1.0×10 5 Ω~1.0×10 8 In order to adjust the viscosity to Ω, an ionic conductive agent may be blended to the extent that it does not bleed out. As the ionic conductive agent, the following inorganic ionic substances, cationic surfactants, zwitterionic surfactants, quaternary ammonium salts, and organic acid lithium salts can be used. Inorganic ionic substances include lithium perchlorate, sodium perchlorate, calcium perchlorate, etc. Cationic surfactants include lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, etc. Further cationic surfactants include dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, etc. Further cationic surfactants include trioctyl propyl ammonium bromide, modified aliphatic dimethyl ethyl ammonium ethosulfate, etc. Zwitterionic surfactants include lauryl betaine, stearyl betaine, dimethyl alkyl lauryl betaine, etc. Quaternary ammonium salts include tetraethyl ammonium perchlorate, tetrabutyl ammonium perchlorate, trimethyl octadecyl ammonium perchlorate, etc. Organic acid lithium salts include lithium trifluoromethanesulfonate, etc. The amount of the ionic conductive agent as described above is, for example, 0.5 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the rubber composition.

[0024] <Roughening particles> The rubber composition forming the matrix may contain spherical particles having a particle size in the range of 1 μm to 90 μm, for example, at least one of which may be selected from the following particles: Phenol resin particles, silicone resin particles, polyacrylonitrile resin particles, polystyrene resin particles, polyurethane resin particles, nylon resin particles, polyethylene resin particles, polypropylene resin particles, acrylic resin particles, silica particles, and alumina particles. By using such a rubber composition, convex portions derived from the spherical particles can be formed on the outer surface of the elastic layer.

[0025] <domain> The domain 203 contains a crosslinked product of the second rubber and conductive particles. Here, the conductive property is defined as a volume resistivity of 1.0×10 8 Defined as less than Ω·cm.

[0026] <Second Rubber> Specific examples of rubbers that can be used as the second rubber are listed below. NR, IR, BR, SBR, IIR, NBR, EPM, EPDM, CR, silicone rubber, urethane rubber (UR).

[0027] <Conductive particles> Examples of conductive particles include carbon materials such as conductive carbon black and graphite; conductive oxides such as titanium oxide and tin oxide; metals such as Cu and Ag; and electron conductors such as particles coated with a conductive oxide or metal to make them conductive. Two or more types of these conductive particles may be used in appropriate amounts. It is preferable to use conductive carbon black as the conductive particles. Specific examples of conductive carbon black include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black.

[0028] <Volume resistivity> To better control the flow of charge by the domain containing conductive particles, the relationship between the volume resistivity d of the domain and the volume resistivity m of the matrix should be m / d ≥ 1.0 × 10 3 This makes it easier for charges to move within the domains than within the matrix, so the charges move in the direction of extension of the domains. A specific method for measuring the volume resistivity of the domains is described in Example 1. The thickness of the conductive layer is not particularly limited, but is preferably 0.5 mm (500 μm) to 5 mm.

[0029] <Process cartridge> Fig. 8 is a schematic cross-sectional view of an electrophotographic process cartridge equipped with a charging roller according to an embodiment of the present disclosure. The process cartridge 800 shown in Fig. 8 integrates a developing device and a charging device, and is configured to be detachably attachable to the main body of an electrophotographic image forming apparatus. The developing device is an integrated unit that includes at least a developing roller 803, a toner container 806, and toner 809. The photosensitive drum 801 is an example of an electrophotographic photosensitive member. The charging roller 802 is arranged so as to be able to charge the photosensitive drum 801. The developing device may also include a toner supply roller 804, a developing blade 808, and an agitating blade 810 as necessary. The charging device is an integrated unit that includes at least the photosensitive drum 801 and the charging roller 802. A cleaning blade 805 is arranged in contact with the photosensitive drum 801 to clean residual toner from the photosensitive drum 801. The charging device is also provided with a waste toner container 807 that collects the cleaned residual toner. A voltage is applied to each of the charging roller 802, the developing roller 803, the toner supply roller 804, and the developing blade 808.

[0030] <Electrophotographic image forming apparatus> 9 is a schematic diagram of an electrophotographic image forming apparatus 900 using a charging roller according to an embodiment of the present disclosure. The electrophotographic image forming apparatus 900 shown in FIG. 9 is configured so that four process cartridges 800 can be detachably mounted. Each process cartridge 800 corresponds to one of the colors, black (BK), magenta (M), yellow (Y), and cyan (C), and uses toner of the corresponding color. Each process cartridge 800 has the same configuration, except for the color of toner used. Each process cartridge 800 has basically the same configuration as that shown in Fig. 8. The process cartridge 800 includes a photosensitive drum 801, a charging roller 802, a developing roller 803, a toner supply roller 804, a cleaning blade 805, a toner container 806, a waste toner container 807, a developing blade 808, toner 809, and an agitating blade 810.

[0031] The photosensitive drum 801 rotates in the direction of the arrow and is uniformly charged by a charging roller 802 to which a voltage is applied from a charging bias power supply (not shown). An exposure light 911 is irradiated onto the surface of the photosensitive drum 801, forming an electrostatic latent image on the surface. Meanwhile, toner 809 stored in a toner container 806 is supplied to a toner supply roller 804 by an agitating blade 810. The toner supply roller 804 supplies the toner 809 to a developing roller 803. A developing blade 808, which is disposed in contact with the developing roller 803, uniformly coats the surface of the developing roller 803 with toner 809, and the toner 809 is charged by frictional charging. The electrostatic latent image is developed by the application of toner 809 carried by the developing roller 803, which is disposed in contact with the photosensitive drum 801, and is visualized as a toner image.

[0032] The visualized toner image on the photosensitive drum is transferred onto an intermediate transfer belt 915 by a primary transfer roller 912 to which a voltage is applied from a primary transfer bias power supply. The intermediate transfer belt 915 is supported and driven by a tension roller 913 and an intermediate transfer belt drive roller 914. The toner images of each color are sequentially superimposed to form a color image on the intermediate transfer belt 915. A transfer material 919 is fed into the device by a paper feed roller. The transfer material 919 is transported between an intermediate transfer belt 915 and a secondary transfer roller 916. A voltage is applied to the secondary transfer roller 916 from a secondary transfer bias power supply, and the secondary transfer roller 916 transfers the color image on the intermediate transfer belt 915 onto the transfer material 919. The transfer material 919 onto which the color image has been transferred is fixed by a fixing device 918. The transfer material 919 that has been fixed is discarded outside the device. On the other hand, toner remaining on the photosensitive drum 801 without being transferred is scraped off by a cleaning blade 805 and stored in a waste toner storage container 807. Furthermore, toner remaining on the intermediate transfer belt 915 without being transferred is scraped off by a cleaning device 917 for the intermediate transfer belt.

[0033] <Method of manufacturing the charging roller> As a non-limiting example of a method for producing a charging roller according to one embodiment of the present disclosure, a method including the following steps (A) to (D) will be described. Step (A): preparing a carbon masterbatch (hereinafter also referred to as "CMB") for domain formation, which contains carbon black and rubber; Step (B): preparing a matrix rubber composition (hereinafter also referred to as "MRC"); Step (C): kneading the carbon masterbatch with the rubber composition to prepare a rubber composition having a matrix-domain structure; Step (D): A step of coating the periphery (surface) of the mandrel with the rubber composition having the matrix-domain structure.

[0034] The following Taylor's equation, Wu's empirical formula, and Tokita's formula are known to determine the domain diameter D in the matrix-domain structure formed by melt-kneading two immiscible polymers (see "Structure Control by Kneading," Sumitomo Chemical Technical Journal 2003-II, pp. 44-45). Taylor's formula D=[C·σ / ηm·γ]·f(ηm / ηd) (1) Wu's Empirical Formula γ·D·ηm / σ=4(ηd / ηm)0.84·ηd / ηm>1 (2) γ·D·ηm / σ=4(ηd / ηm)- 1 0.84·ηd / ηm<1 (3) Tokita's Ceremony D=12·P·σ·φ / (π·η·γ)·(1+4·P·φ·EDK / (π·η·γ)) (4)

[0035] In the above equations (1) to (4), D is the domain diameter of the CMB (maximum Feret diameter Df), C is a constant, σ is the interfacial tension, ηm is the viscosity of the matrix, ηd is the viscosity of the domain, γ is the shear rate, η is the viscosity of the mixture, P is the probability of collision and coalescence, φ is the domain phase volume, and EDK is the domain phase cleavage energy. From the above formulas (1) to (4), it is clear that controlling the CMB domain diameter D is effective, for example, by controlling the physical properties of the CMB and MRC and the kneading conditions in step (B). Specifically, it is effective to control the following four items (a) to (d):

[0036] (a) Difference in interfacial tension σ between the CMB and the MRC; (b) The ratio (ηm / ηd) of the viscosity of the CMB (ηd) and the viscosity of the MRC (ηm); (c) Shear rate (γ) and energy content (EDK) during kneading of CMB and MRC in step (B); (d) Volume fraction of CMB relative to MRC in step (B).

[0037] Below, items (a) to (d) will be explained in detail. (a) Interfacial tension difference between the CMB and the MRC; Generally, when two immiscible rubbers are mixed, phase separation occurs. This occurs because the interactions between identical polymers are stronger than those between different polymers, leading to aggregation of identical polymers, reducing free energy and stabilizing the mixture. The interface of a phase-separated structure comes into contact with different polymers, resulting in higher free energy than the interior, which is stabilized by interactions between identical molecules. As a result, interfacial tension is generated, which reduces the contact area with the different polymers to reduce the interfacial free energy. When this interfacial tension is low, the different polymers tend to mix more uniformly in order to increase entropy. A uniform mixture is called a solution, and the SP value, which is an indicator of solubility, tends to correlate with interfacial tension. In other words, the difference in interfacial tension between CMB and MRC is thought to correlate with the difference in SP value between CMB and MRC. Therefore, it is possible to control the interfacial tension by combining MRC and CMB. The difference in absolute value of the solubility parameter between the first rubber in MRC and the second rubber in CMB is 0.4 (J / cm 3 ) 0.5 Above, 4.0(J / cm 3 ) 0.5It is preferable to select a rubber as follows. More preferably, the absolute value of the difference in solubility parameters is 0.4 (J / cm 3 ) 0.5 or more and 2.2 (J / cm 3 ) 0.5 or less. Within such a range, a stable phase-separated structure can be formed.

[0038] <Method for Measuring SP Value> The SP values of MRC and CMB can be accurately calculated by creating a calibration curve using materials with known SP values. This known SP value can also be the catalog value of the material manufacturer. For example, for NBR and SBR, regardless of the molecular weight, the SP value is almost determined by the acrylonitrile and styrene content ratios. Therefore, by analyzing the acrylonitrile or styrene content ratio of the rubbers constituting the matrix and the domain, the SP value can be calculated from the calibration curve obtained from materials with known SP values. Here, for the analysis of the acrylonitrile or styrene content ratio, analytical methods such as pyrolysis gas chromatography (Py-GC) and solid NMR can be used. Also, for isoprene rubber, the SP value is determined by the isomeric structure such as 1,2-polyisoprene, 1,3-polyisoprene, 3,4-polyisoprene, cis-1,4-polyisoprene, and trans-1,4-polyisoprene. Therefore, similar to SBR and NBR, the isomer content ratio can be analyzed by Py-GC and solid NMR, etc., and the SP value can be calculated from materials with known SP values.

[0039] (b) Viscosity ratio of CMB to MRC; The closer the viscosity ratio (ηd / ηm) between CMB and MRC is to 1, the smaller the maximum Feret diameter of the domains. The viscosity ratio between CMB and MRC can be adjusted by selecting the Mooney viscosity of the CMB and MRC and by blending the type and amount of filler. It can also be adjusted by adding a plasticizer such as paraffin oil to the extent that it does not interfere with the formation of a phase-separated structure. Furthermore, the viscosity ratio can be adjusted by adjusting the temperature during kneading. The viscosity of the domain-forming rubber mixture and the matrix-forming rubber mixture can be obtained by measuring the Mooney viscosity ML(1+4) at the rubber temperature during kneading, based on JIS K6300-1:2013.

[0040] (c) Shear rate and energy content during mixing of MRC and CMB; The faster the shear rate during kneading of MRC and CMB, and the greater the amount of energy during shearing, the smaller the maximum Feret diameter Df of the domains. The shear rate can be increased by increasing the inner diameter of the mixing element, such as the blade or screw, reducing the gap between the end face of the mixing element and the inner wall of the mixing element, or by increasing the rotation speed. The energy during shearing can also be increased by increasing the rotation speed of the mixing element or by increasing the viscosity of the first rubber in the CMB and the second rubber in the MRC.

[0041] (d) volume fraction of CMB relative to MRC; The volume fraction of CMB relative to the MRC correlates with the probability of collision and coalescence of the domain-forming rubber mixture with the matrix-forming rubber mixture. Specifically, reducing the volume fraction of the domain-forming rubber mixture relative to the matrix-forming rubber mixture reduces the probability of collision and coalescence between the domain-forming rubber mixture and the matrix-forming rubber mixture. In other words, reducing the volume fraction of the domains in the matrix reduces the domain size, within the range that achieves the required electrical conductivity.

[0042] In the above-mentioned step (C), the CMB that forms the domains and the MRC that forms the matrix are kneaded to prepare an unvulcanized rubber composition having a matrix-domain structure. Examples of the preparation method include the methods described in (C1) and (C2) below. (C1) The CMB that will become the domains and the unvulcanized rubber composition that will become the matrix are mixed using an internal mixer such as a Banbury mixer or a pressure kneader. Then, using an open mixer such as an open roll, the CMB that will become the domains, the unvulcanized rubber composition that will become the matrix, and raw materials such as vulcanizing agents and vulcanization accelerators are kneaded together to form a single product. (C2) The CMB that will become the domains is mixed using an internal mixer such as a Banbury mixer or pressure kneader. Then, the raw materials for the CMB that will become the domains and the unvulcanized rubber composition that will become the matrix are mixed in the internal mixer. Finally, raw materials such as vulcanizing agents and vulcanization accelerators are kneaded and integrated using an open mixer such as an open roll.

[0043] In the above-mentioned step (D), examples of the method for coating the periphery of the mandrel with a rubber composition having a matrix-domain structure include the methods described in the following (D1) and (D2). (D1) extrusion molding in which a rubber composition having a matrix domain structure is extruded together with a mandrel through a crosshead to coat the periphery of the mandrel with the rubber composition having a matrix domain structure; (D2) Molding of a rubber composition having a matrix domain structure by using a molding die to coat the periphery of the mandrel placed in the molding die with the rubber composition having a matrix domain structure.

[0044] 6 is a schematic diagram of an extrusion molding machine 600 equipped with a crosshead used for extrusion molding according to (D1) above. The extrusion molding machine 600 coats the entire circumference of a mandrel 601 with an unvulcanized rubber composition 602 to a uniform thickness, thereby producing an unvulcanized rubber roller 603. The extrusion molding machine 600 is provided with a crosshead 604 into which a mandrel 601 and an unvulcanized rubber composition 602 are fed, a conveying roller 605 that feeds the mandrel 601 into the crosshead 604, and a cylinder 606 that feeds the unvulcanized rubber composition 602 into the crosshead 604. A plurality of mandrels 601 are continuously introduced into a crosshead 604 by a conveying roller 605. A cylinder 606 has a screw 607 therein, and an unvulcanized rubber composition 602 is introduced into the crosshead 604 by rotating the screw 607. The mandrel 601 introduced into the crosshead 604 has its peripheral surface covered with the unvulcanized rubber composition 602 introduced into the crosshead 604 from the cylinder 606. Then, an unvulcanized rubber roller 603, the peripheral surface of which is covered with the unvulcanized rubber composition 602, is fed from a die 608 at the exit of the crosshead 604.

[0045] When the charging roller according to the present disclosure is produced by the method according to (D1) above, the elongation state of the domains can be controlled by, for example, the materials, kneading conditions, and extrusion conditions. First, as mentioned above, the maximum Feret diameter Df of the domains in the matrix domain structure can be controlled by the materials of the MRC and CMB and their mixing conditions. The larger the maximum Feret diameter Df of the domains, the larger the length x of the enveloping rectangular parallelepiped in the X-axis direction of the elongated domains formed by the extrusion process of a rubber composition with a matrix domain structure. Therefore, to achieve the target length x of the enveloping rectangular parallelepiped in the X-axis direction of the elongated domains, it is sufficient to appropriately adjust the viscosity ratio of the CMB and MRC and the shear rate during mixing depending on the polymer used.

[0046] Next, the extrusion conditions will be described. The minor angle θ between line segments P and Q shown in Figure 5 can be adjusted by adjusting the flow rate of the rubber composition, the inner diameter of the extruder die, and the thickness of the rubber composition layer during the extrusion process, in which a rubber composition having a matrix domain structure is co-extruded with a mandrel through a crosshead to form a layer of the rubber composition on the outer circumferential surface of the mandrel. For example, the minor angle θ can be brought closer to 90° by applying a larger shear stress (shear) to the rubber composition during the process of forming a layer of the rubber composition on the outer circumferential surface of the mandrel. In the crosshead extrusion process, the shear stress applied to the rubber composition can be increased, for example, by reducing the inner diameter of the die or increasing the flow rate of the rubber composition. By reducing the inner diameter of the die, the rubber composition extruded onto the outer circumferential surface of the mandrel is stretched with greater force. At this time, a larger shear force can be applied to a thickness region of the rubber composition layer extending to a depth of 20.0 μm from the surface opposite the side that contacts the outer circumferential surface of the mandrel. Therefore, many of the domains present in the region can be elongated in the direction along the movement direction of the mandrel, and as a result, it becomes possible for 50% or more of all domains contained in a cube with a side length of 20.0 μm sampled from the region to satisfy the above condition.

[0047] Next, the unvulcanized rubber composition layer containing domains elongated in the direction along the mandrel movement direction obtained in the above-mentioned step (D) is then subjected to a vulcanization step as step (E) to form a conductive layer. In this way, the charging roller according to this embodiment can be obtained. Specific examples of methods for heating the rubber composition layer include hot air oven heating using a gear oven, heat vulcanization using far infrared rays, and steam heating using a vulcanizer. Among these, hot air oven heating and far infrared heating are preferred because they are suitable for continuous production.

[0048] In the conductive layer according to the present disclosure formed by the above method, which contains domains elongated in a predetermined direction, it is preferable not to polish the outer surface of the conductive layer so as not to lose the domains elongated so that the minor angle θ is 90° or less, which are more prevalent on the side closer to the outer surface of the conductive layer. Alternatively, even if polishing is performed, it is preferable to polish the conductive layer so as not to lose as much of the domains elongated so that the minor angle θ is 90° or less, which are more prevalent on the side closer to the outer surface of the conductive layer. Therefore, if the outer shape of the elastic layer of the charging roller according to this embodiment is to be crowned, extrusion molding is performed taking such polishing into consideration. For example, during extrusion molding, it is preferable to form the outer diameter shape of the unvulcanized rubber layer into a crowned shape by controlling the extrusion speed of the mandrel and the extrusion speed of the unvulcanized rubber composition from the crosshead. Specifically, it is preferable to change the relative ratio between the mandrel feed speed of the mandrel 601 by the conveying roller 605 and the unvulcanized rubber composition feed speed from the cylinder 606. At this time, the feed speed of the unvulcanized rubber composition 602 from the cylinder 606 to the crosshead 604 is constant. The thickness of the layer of the unvulcanized rubber composition 602 formed on the circumferential surface of the mandrel 601 is determined by the ratio of the feed speed of the mandrel 601 to the feed speed of the unvulcanized rubber composition 602. This allows the elastic layer to be formed into a crown shape without polishing. In addition, in molding, it is preferable to use a crown-shaped mold and perform light polishing to form the outer diameter shape of the unvulcanized rubber layer into a crown shape. Note that the crown shape refers to a shape in which the outer diameter of the elastic layer at the center in the longitudinal direction of the mandrel is larger than the outer diameter at the ends. The vulcanized rubber composition at both ends of the vulcanized rubber roller is removed in a separate process later, completing the vulcanized rubber roller. Therefore, both ends of the mandrel of the completed vulcanized rubber roller are exposed. The surface layer may be subjected to a surface treatment by irradiating it with ultraviolet light or electron beams, as long as this does not affect the matrix-domain structure or the domain shape. [Example]

[0049] The following materials were prepared as materials used in manufacturing the charging rollers according to the examples and comparative examples. <nbr> ·N230SV (Product name: JSR NBR N230SV, manufactured by JSR Corporation) DN401LL (product name: Nipol DN401LL, manufactured by Zeon Corporation) <sbr> T2003 (product name: Tufuden 2003, manufactured by Asahi Kasei Corporation) A303 (product name: Asaprene 303, manufactured by Asahi Kasei Corporation) <Chloroprene rubber (CR)> B31 (product name: SKYPRENE B31, manufactured by Tosoh Corporation)

[0050] <epdm> E505A (product name: Esprene505A, manufactured by Sumitomo Chemical Co., Ltd.) <Butadiene rubber (BR)> BR150B (product name: UBEPOL BR150B, manufactured by Ube Industries, Ltd.) <Isoprene rubber (IR)> IR2200L (product name: Nipol IR2200L, manufactured by Zeon Corporation) <Conductive particles> #7270 (product name: TOKABLACK #7270SB, manufactured by Tokai Carbon Co., Ltd.) #44 (product name: #44, manufactured by Mitsubishi Chemical Corporation) #7360 (product name: TOKABLACK #7360SB, manufactured by Tokai Carbon Co., Ltd.) #5500 (product name: TOKABLACK #5500SB, manufactured by Tokai Carbon Co., Ltd.)

[0051] <Vulcanizing agent> Sulfur (product name: SULFAX PMC, manufactured by Tsurumi Chemical Industry Co., Ltd.) <Vulcanization accelerator> TBzTD (product name: Suncerer TBZTD, manufactured by Sanshin Chemical Industry Co., Ltd.) TBSI (product name: SANTOCURE-TBSI, manufactured by FLEXSYS) TS (product name: Suncellar TS, manufactured by Sanshin Chemical Industry Co., Ltd.) CZ (product name: Noccela CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) TOT (product name: Noccela TOT-N, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) <Vulcanization accelerator> ZnO (product name: zinc oxide type 2, manufactured by Sakai Chemical Industry Co., Ltd.) <Roughening particles> PMMA particles (product name: SE-010T, manufactured by Negami Chemical Industries, Ltd., average particle size: 10 μm) Polyethylene particles (product name: Mipelon XM-221U, manufactured by Mitsui Chemicals, average particle size: 25 μm) Polyurethane particles (product name: Grandpearl GU-2000P, manufactured by Aica Kogyo Co., Ltd., average particle size 20 μm) <Reinforcing material> MT carbon (product name: Thermax Flowform N990, manufactured by CanCarb)

[0052] Example 1 <Preparation of Carbon Masterbatch (CMB) 1> Table 1 shows the carbon masterbatch (CMB) raw material composition. The blending amounts shown in Table 1 indicate the blending amounts when the SBR used is 100 parts by mass. CMB1 was prepared by mixing the carbon masterbatch (CMB) raw materials shown in Table 1 in the blending amounts shown in Table 1. A 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used as the mixer. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

[0053] [Table 1]

[0054] <Preparation of Unvulcanized Rubber Composition 1> Table 2 shows the MRC raw material blending table used to prepare kneaded rubber composition A. The blending amounts shown in Table 2 indicate the blending amounts when the NBR used is 100 parts by mass. The raw materials (MRC) shown in Table 2 were added to the above CMB1 and kneaded to obtain kneaded rubber composition A. The mixing ratio of CMB1 and MRC was 75 parts by mass of NBR used in MRC and 25 parts by mass of SBR used in CMB1. A 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used as the mixer. The mixing conditions were a filling rate of 70 vol% and a blade rotation speed of 30 rpm. 2 , 16 minutes.

[0055] [Table 2]

[0056] Table 3 shows the raw material blending table used to prepare kneaded rubber composition B. The raw materials shown in Table 3 were added to 100 parts by mass of kneaded rubber composition A obtained above, and further kneaded to obtain unvulcanized rubber composition 1 as kneaded rubber composition B. An open roll with a roll diameter of 12 inches (0.30 m) was used as the mixer. The mixing conditions were as follows: the front roll rotation speed was 10 rpm, the rear roll rotation speed was 8 rpm, and the roll gap was 2 mm, and the mixer was turned left and right a total of 20 times, and then the roll gap was set to 0.5 mm and the mixer was thin-passed 10 times.

[0057] [Table 3]

[0058] <Forming of vulcanized rubber layer> First, a mandrel with an adhesive layer for bonding the vulcanized rubber layer was obtained. Specifically, a cylindrical conductive mandrel with a diameter of 6 mm and a length of 252 mm was used. The mandrel was made of steel and its surface was nickel-plated. A conductive vulcanizing adhesive (product name: Metalock U-20; manufactured by Toyo Kagaku Kenkyusho) was applied to the axial center of the mandrel and dried at 80°C for 30 minutes. The width of the central part where the vulcanizing adhesive was applied was 222 mm. Using an extruder equipped with a crosshead at its tip, the unvulcanized rubber composition 1 prepared above was co-extruded with the mandrel having the adhesive layer, forming a layer of unvulcanized rubber composition 1 on the outer peripheral surface of the mandrel, thereby obtaining a crown-shaped unvulcanized rubber roller. The molding temperature was 100°C, the inner diameter of the cylinder 606 was 70 mm, the extrusion screw rotation speed was 20 rpm, and the flow rate of the rubber composition 1 introduced from the cylinder to the crosshead was 53 m / sec (the flow rate was calculated from the weight of the rubber portion of the molded unvulcanized rubber roller). The inner diameter of the die of the crosshead was 8.0 mm. The mandrel feed speed was changed during molding to control the central and end outer diameters of the unvulcanized rubber roller along its axis, so that the outer diameter of the unvulcanized rubber roller was larger than the inner diameter of the die. Specifically, the outer diameter of the unvulcanized rubber roller at the center along the axis was 8.6 mm, and the outer diameter of the end was 8.5 mm. Then, it was heated in a hot air oven at a temperature of 190°C for 60 minutes to vulcanize the layer of unvulcanized rubber composition 1 to form a vulcanized rubber layer. Both ends of the vulcanized rubber layer were cut to give a length in the axial direction of 232 mm, thereby obtaining a vulcanized rubber roller.

[0059] <UV irradiation of vulcanized rubber layer after extrusion> The surface of the obtained vulcanized rubber roller was irradiated with ultraviolet light to obtain a charging roller 1 having a UV-treated area on the surface of the elastic layer (surface layer). A low-pressure mercury lamp (product name: GLQ500US / 11, manufactured by Toshiba Lighting & Technology Corporation) was used to irradiate ultraviolet light uniformly while rotating the charging roller. The amount of ultraviolet light was 9000 mJ / cm2 at a sensitivity of a 254 nm sensor. 2 I made it so that it would be like this.

[0060] <Measurement of charging roller surface resistance> The prepared charging roller was left standing for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%. Then, under the same environment, the following meter and probe were used: the probe pressure was set to 10 μN, a DC voltage of 100 V was applied, and the current was measured for 2 seconds at a sampling frequency of 100 Hz, one second after the voltage was applied. This measurement was performed at three points: the center position in the longitudinal direction of the conductive layer, and positions +90 mm and -90 mm from the center position in the longitudinal direction. Furthermore, measurements at these points were performed every 90° in the circumferential direction. The arithmetic average of the measurements obtained at 12 points was taken as the surface resistance value of the charging roller. High resistance meter (product name: Model 6517B Electrometer, Keithley Corporation) Probe (200 μm pitch, 2 probes) The surface resistance values ​​obtained by the above measurements are shown in Table 5 (Table 5 is described at the end of the following description).

[0061] <Checking for the presence or absence of domains and measuring the domain shape> A FIB-SEM equipped with a cryostat was used to perform 3D reconstruction of the rubber piece cut from the charging roller. The cryostat-equipped FIB-SEM can be a "Helios G4 UC" (trade name: Thermo Fisher Scientific) or a "Cryo Transfer System PP3010T" (trade name: Quorum). The obtained 3D reconstruction data was analyzed using image analysis software (trade name: Amira-Avizo; Thermo Fisher Scientific) to confirm the presence or absence of domains and measure their shapes. The specific processing steps are described below. The longitudinal direction of the charging roller is the a-axis, and the tangent direction of the arc drawn by the roller surface in a cross section of the roller perpendicular to the longitudinal direction a is the b-axis. A razor blade was placed perpendicular to the roller surface to cut it so that a rectangle with a width of 5 mm in the b-axis direction and a length of 5 mm in the a-axis direction was created, centered on the point of contact between the arc and the tangent. Finally, the portion in contact with the mandrel was cut out along the mandrel to produce a rubber piece 5 mm in the a-axis direction, 5 mm in the b-axis direction, and the thickness of the vulcanized rubber layer. These rubber pieces were taken from a total of 12 locations, four locations spaced 90° apart around the circumference of the charging roller: the center position in the longitudinal direction of the conductive layer, and three locations at +90 mm and -90 mm from the center position in the longitudinal direction.

[0062] Each rubber piece was attached to a 10 mm diameter cylindrical copper stub using silver paste so that the part that had been the roller surface was facing up, and then dried at room temperature (25°C) for 1 hour to obtain a sample for observation. This observation sample was subjected to three-dimensional reconstruction using a cryo-equipped FIB-SEM (device name: Helios G4 UC, manufactured by ThermoFisher Scientific, and Cryo Transfer System PP3010T, manufactured by Quorum). Specifically, the observation sample was cooled to -140°C using a cryo system and frozen. The frozen observation sample was processed using an FIB to expose a square cross section measuring 20.0 μm in the depth direction (hereinafter also referred to as the "c direction") and 20.0 μm in the b-axis direction from the surface that was the surface of the charging roller of the observation sample. This cross section is also referred to as the first bc-plane. The FIB processing conditions were an acceleration voltage of 30 kV and a current of 1.6 nA. Next, an SEM image of this first bc plane was obtained. The SEM observation was performed using a secondary electron image at an accelerating voltage of 350 V and a current of 13 pA. Next, the first bc plane was cut 100 nm in the a-axis direction to expose the second bc plane. An SEM image of this second bc plane was then acquired. Subsequently, similarly, the observed bc plane was cut 100 nm in the a-axis direction, and SEM images of the new bc plane exposed by this cutting were acquired repeatedly. This operation was terminated when the cutting depth in the a-axis direction reached 20.0 μm. In this way, 200 SEM images of the bc plane were obtained. These were then used for 3D reconstruction of a cubic-shaped portion 20.0 μm in the depth direction, 20.0 μm in the a-axis direction, and 20.0 μm in the b-axis direction from the surface of the conductive layer using image analysis software (trade name: Amira-Avizo; Thermo Fisher Scientific).

[0063] For each of all domains observed in the three-dimensional images created from the 12 measurement samples, an enveloping rectangular parallelepiped was created, two of whose six faces pass through any one point in the domain to be evaluated and are perpendicular to a line segment L perpendicular to the surface of the mandrel. Here, of the three sides constituting the three axes of the enveloping rectangular parallelepiped, the axis to which the longest side belongs is designated the X-axis, and the axes to which the remaining two sides belong are designated the Y-axis and Z-axis, or the Z-axis and Y-axis. Then, the following three items were calculated. The domains for which the enveloping cuboid was created were limited to those whose entire area was included in the 3D image. In other words, domains that were only partially included in the 3D image were not included in the creation of the enveloping cuboid.

[0064] Number of elongated domains (%) Of all the enveloping rectangular parallelepipeds, the number of enveloping rectangular parallelepipeds on which a line segment S that is perpendicular to the line segment L and parallel to the X axis can be drawn was counted. This was divided by the total number of enveloping rectangular parallelepipeds to determine the number % of domains extending in the longitudinal direction of the charging roller (extended domains) of the charging roller to be measured. · The minor angle θ between line segments P and Q For each enveloping rectangular parallelepiped, the longest line segment connecting the contact point of the domain on the first YZ surface of the enveloping rectangular parallelepiped with the contact point of the domain on the second YZ surface was designated as line segment P. Line segment Q, which had the same starting point as line segment P and was perpendicular to the surface of the mandrel, was then drawn, and the minor angle θ, defined as the minor angle formed by line segments P and Q, was calculated. Next, a histogram of the calculated minor angles θ and the number of enveloping rectangular parallelepipeds was created in a range of 0° to 90° with a class width of 10° (see FIG. 7). In the histogram, the class with the largest number of angles (the mode) was designated the minor angle θ of the charging roller related to the measurement target. Length of the enveloping rectangular parallelepiped in the X-axis direction x For each of the enveloping rectangular parallelepipeds onto which the line segment S could be drawn, the length x in the X-axis direction was measured and the arithmetic mean value was calculated. This value serves as an index of the degree of elongation of the elongated domain in the charging roller being measured in the longitudinal direction of the charging roller. These results are shown in Table 5.

[0065] <Measurement of the volume resistivity ratio m / d between the matrix and domain> To evaluate the volume resistivity of the matrix contained in the conductive layer, the following measurements were carried out using a scanning probe microscope (SPM) (trade name: Q-Scope 250, manufactured by Quesant Instrument Corporation) operated in contact mode. First, ultrathin sections with a thickness of 1 μm were cut from the conductive layer of the conductive member A1 using a microtome (trade name: Leica EM FCS, manufactured by Leica Microsystems) at a cutting temperature of -100°C. When cutting the ultrathin sections, the cross-sectional direction was perpendicular to the longitudinal direction of the conductive member, taking into account the direction of charge transport due to discharge. Next, the ultrathin sections were placed on a metal plate in an environment with a temperature of 23°C and a relative humidity of 50%. Then, a portion of the section that was in direct contact with the metal plate was selected, and the SPM cantilever was brought into contact with the portion corresponding to the matrix. In this state, a voltage of 50 V was applied to the cantilever for 5 seconds, the current value was measured, and the arithmetic average value for the 5 seconds was calculated.

[0066] The surface shape of the measurement section was observed with the SPM, and the thickness of the measurement point was calculated from the obtained height profile. Furthermore, the area of ​​the matrix was calculated from the surface shape observation results. The volume resistivity was calculated from the thickness and the area of ​​the matrix, and was taken as the volume resistivity m of the matrix. The conductive layer of the conductive member A1 (longitudinal length: 232 mm) was divided into 5 equal parts in the longitudinal direction and further divided into 4 equal parts in the circumferential direction, and the above measurement was performed on the slices prepared at random points from each region, for a total of 20 points. The average value of the slices was taken as the volume resistivity m of the matrix. In order to evaluate the volume resistivity d of the domains contained in the conductive layer, the volume resistivity d of the domains was measured in the same manner as in the measurement of the volume resistivity m of the matrix, except that the measurement was carried out at a location corresponding to the domain of the ultrathin section and the measurement voltage was set to 1 V. Table 5 shows the matrix-domain volume resistivity ratio m / d calculated from the obtained matrix volume resistivity m and domain volume resistivity d.

[0067] <Evaluation of horizontal streak images> An electrophotographic image forming apparatus (product name: Laserjet M608dn, manufactured by Hewlett-Packard Company) was prepared. In order to perform an evaluation in a high-speed process, the electrophotographic image forming apparatus was modified so that the number of sheets output per unit time was 80 sheets / minute using A4 size paper, which was higher than the original number of sheets output. First, the charging roller, the electrophotographic image forming apparatus, and the process cartridge were left in an environment of a temperature of 15° C. and a relative humidity of 10% for 48 hours in order to acclimate them to the measurement environment. Next, the charging roller was incorporated as a charging roller in a process cartridge. Using this, a halftone image was output, and the output image was evaluated. When the electrophotographic photosensitive member starts to rotate, charge is generated by frictional charging at the nip position between the electrophotographic photosensitive member and the charging roller. The charge moves from the surface of the charging roller to a domain with low resistance within the charging roller. If the charge present in the domain remains during the charging process, a low-density horizontal streak image is generated due to excessive discharge. The horizontal streak image was evaluated as follows. The evaluation results are shown in Table 5.

[0068] The horizontal streak image was scanned using a scanner (product name: Image RUNNER ADVANCE C5240F, manufactured by HP) to obtain a JPEG data image so that the horizontal streaks were aligned horizontally. The scan resolution was set to 400 × 400 dpi. The resulting JPEG data image of the horizontal streaks was subjected to bitmap analysis using image analysis software (product name: Image-Pro, manufactured by Hakuto Co., Ltd.). Bitmap analysis makes it possible to compare the image density numerically. In other words, the degree of horizontal streak occurrence can be quantitatively evaluated by calculating the bit value difference, which is the difference in bit values ​​between horizontal streak areas where horizontal streaks occur and non-horizontal streak areas where horizontal streaks do not occur. Specifically, the calculation method was to calculate the arithmetic mean of the bit values ​​in the horizontal direction (the lengthwise direction of the charging roller) of the area where the halftone image was printed, for each pixel in the vertical direction, and then calculate the horizontal average bit value for each pixel in the vertical direction. The difference between the highest horizontal average bit value at the horizontal streak position and the horizontal average bit value at the non-horizontal streak position was defined as the bit value difference. The bit value difference was evaluated according to the following criteria. Rank A: Bit value difference is 0.00 or more and 0.46 or less (Horizontal streaks cannot be seen with a magnifying glass) Rank B: Bit value difference is 0.47 or more and 0.83 or less (Horizontal streaks can be seen with a magnifying glass, but not with the naked eye) Rank C: Bit value difference is 0.84 or more and 1.91 or less (It can be seen with the naked eye that the horizontal lines are extremely thin and discontinuous along the length.) Rank D: Bit value difference is 1.92 or more (It can be seen with the naked eye that the horizontal lines are extremely thin and continuous along the length.)

[0069] Examples 2 to 42 The formulations of the unvulcanized rubber compositions according to Examples 1 to 42 and the rotation speeds of the pressure kneader blades during kneading A of the unvulcanized rubber compositions are shown in Table 4-1. The extrusion conditions for the unvulcanized rubber compositions of Examples 1 to 37 and 39 to 42 are shown in Table 4-2. Furthermore, the vulcanization conditions, the surface treatment UV integrated light amount or electron beam (EB) treatment amount, and whether or not the outer surface of the conductive layer after vulcanization was polished for the unvulcanized rollers according to Examples 1 to 42 are shown in Table 4-3.

[0070] [Table 4-1] [Table 4-2] [Table 4-3]

[0071] In the polishing of Examples 13 to 18, a rotating grindstone was brought into contact with the outer surface of the conductive layer to remove a thickness of 10 μm. Thus, a crown-shaped charging roller was obtained, with a diameter of 8.5 mm at both longitudinal ends and a diameter of 8.6 mm at the center. Note that, before polishing, a large number of domains in which the minor angle θ was elongated to 90° or less were present in a region from the outer surface of the conductive layer to a depth of 20 μm. Therefore, by setting the polishing amount to 10 μm, it was possible to leave domains in the conductive layer after polishing with a minor angle θ of 90° or less. The electron beam irradiation in Example 37 was performed using an electron beam irradiation device (manufactured by Iwasaki Electric Co., Ltd.) with a maximum acceleration voltage of 150 kV and a maximum electron current of 40 mA, and nitrogen was filled during irradiation. The electron beam irradiation conditions are shown below. Accelerating voltage: 150 kV Electron current: 35 mA Dose: 1323 kGy Processing speed: 1 m / min Oxygen concentration: 100 ppm

[0072] Furthermore, in Example 38, press molding was performed using unvulcanized rubber composition 1 prepared in the same manner as in Example 1. A split mold and a press were used for press molding. A mandrel, which had been heated in the same manner, was placed in the split mold heated to 160°C, and an amount of unvulcanized rubber composition exceeding the volume of the split mold was placed along the mandrel. The weight of the placed unvulcanized rubber composition was 10 g. Press molding was performed while heating the split mold containing the mandrel and unvulcanized rubber composition. After that, flash generated during molding and both ends of the vulcanized rubber layer were removed, and UV treatment was performed in the same manner as in Example 1 to obtain a charging roller with an axial length of 232 mm, a central outer diameter of 8.6 mm, and an end outer diameter of 8.5 mm. The molding conditions are shown below. Pressure: 10 MPa Temperature: 160℃ Time: 40 min

[0073] Table 5 shows the surface resistance values ​​of the charging rollers produced in Examples 1 to 42, the minor angle between line segment P and line segment Q in the elongated domain, the length x, the volume resistivity ratio m / d between the matrix and the domain, the number % of the elongated domains, the image rank, and the bit value difference.

[0074] Comparative Example 1 50 parts by weight of conductive tin oxide powder was mixed with 500 parts by weight of a 1% isopropyl alcohol solution of trifluoropropyltrimethoxysilane and 300 parts by weight of glass beads with an average particle size of 0.8 mm, and dispersed for 70 hours using a paint shaker. SN-100P (manufactured by Ishihara Sangyo Kaisha, Ltd.) was used as the conductive tin oxide powder. The dispersion was then filtered through a 500-mesh screen. Next, the solution was heated in a 100°C water bath while stirring with a Nauta mixer to evaporate the alcohol and dry. After drying, a silane coupling agent was applied to the surface to obtain surface-treated conductive tin oxide.

[0075] 137 parts by weight of polyester polyol (trade name: Kyowapol 1000PA, hydroxyl value 112 mgKOH / g, manufactured by Kyowa Hakko Co., Ltd.) was dissolved in 463 parts by weight of MIBK (methyl isobutyl ketone) to prepare a solution with a solids content of 16.0% by weight. To 200 parts by weight of this polyester polyol solution, 41.6 parts by weight of the surface-treated conductive tin oxide powder and 200 parts by weight of 0.8 mm diameter glass beads were added. The mixture was placed in a 450 ml mayonnaise bottle and dispersed for 6 hours using a paint shaker. Furthermore, 29.1 parts by weight of a blocked isocyanurate trimer of isophorone diisocyanate (IPDI) and 13.3 parts by weight of an isocyanurate trimer of hexamethylene diisocyanate (HDI) were mixed with 330 parts by weight of this dispersion. The mixture was then stirred for 1 hour using a ball mill. Bestanate B1370 (manufactured by Degussa-Hüls AG) was used as the IPDI, and Duranate TPA-B80E (manufactured by Asahi Chemical Industry Co., Ltd.) was used as the HDI. Finally, the solution was filtered through a 200-mesh screen to adjust the solid content to 39.6% by mass, and a surface layer coating material was obtained. The surface of the vulcanized rubber roller obtained in Example 1 was coated with the above coating material by dipping. Specifically, the film was coated at a lifting speed of 400 mm / min and air-dried for 30 minutes. The axial direction was then reversed, and the film was coated again at a lifting speed of 400 mm / min and air-dried for 30 minutes. Finally, the film was dried in an oven at 160°C for 1 hour. The film thickness was 25 μm.

[0076] Comparative Example 2 A charging roller was obtained by coating in the same manner as in Comparative Example 1, except that no surface-treated conductive tin oxide was added. The coating thickness was 26 μm.

[0077] Comparative Example 3 The same procedures as in Example 21 were carried out except that a crown-shaped unvulcanized rubber roller with an end diameter of 8.6 mm and a center diameter of 8.7 mm was obtained by crosshead extrusion molding, and the surface of the obtained vulcanized rubber roller was ground to a depth of 50 μm with a rotary grindstone, thereby obtaining a crown-shaped charging roller with an end diameter of 8.5 mm and a center diameter of 8.6 mm.

[0078] Comparative Example 4 A charging roller having a crown shape with an end diameter of 8.5 mm and a central diameter of 8.6 mm was produced in the same manner as in Example 1, except that the die inner diameter in the extrusion molding of the crosshead was changed to 8.6 mm and molding was performed while changing the mandrel feed speed.

[0079] Table 6 shows the surface resistance values, the minor angle θ between line segment P and line segment Q, the length of x, the volume resistance ratio m / d between the matrix and domain, the number % of elongated domains, the image rank, and the bit value difference for the above-mentioned Comparative Examples 1 to 4.

[0080] [Table 5]

[0081] [Table 6] [Explanation of symbols]

[0082] 100 charging roller 101 Mandrel 103 Conductive layer 201 Matrix 203 Domain 207 Outer surface of conductive layer 301 Enveloped Rectangular Parallelepiped 303 The longest side of the enclosing rectangular parallelepiped 301 505 First YZ plane 507 A line segment representing the maximum length of the domain< / epdm> < / sbr> < / nbr>

Claims

1. A charging roller having a conductive mandrel and a conductive layer as a surface layer, the surface resistance value measured on the outer surface of the charging roller is 1.0×10 −1 Ω or more and 1.0×10 3 Ω or less; the conductive layer has a matrix containing a cross-linked product of a first rubber and a plurality of domains dispersed in the matrix, Each of the domains includes a crosslinked product of a second rubber and conductive particles, the volume resistivity of the domain is lower than the volume resistivity of the matrix; A charging roller characterized in that, of all domains contained in a cube with a side length of 20.0 μm sampled from a region from the outer surface of the conductive layer to a depth of 20.0 μm, 50% or more of the domains satisfy the following condition: conditions Assuming that the domain to be determined is enclosed by an enveloping rectangular parallelepiped, two of the six faces of which pass through any one point in the domain to be determined and are perpendicular to a line segment L perpendicular to the surface of the mandrel, and the length of the enveloping rectangular parallelepiped in the X-axis direction is x, the length of the enveloping rectangular parallelepiped in the Y-axis direction is y, and the length of the enveloping rectangular parallelepiped in the Z-axis direction is z, x is longer than y and z, and It is possible to draw a line segment S that is perpendicular to the line segment L and parallel to the X axis.

2. Among the line segments connecting the contact portion of the domain on the first YZ plane of the enveloping rectangular parallelepiped and the contact portion of the domain on the second YZ plane, the longest line segment is designated as line segment P, and a line segment Q is drawn that has the same starting point as the starting point of line segment P and is perpendicular to the surface of the mandrel; 2. The charging roller according to claim 1, wherein when the minor angle formed by the line segments P and Q is defined as the minor angle θ, the most frequent value of the minor angle θ in all domains in the cube is in the range of 60° or more and 90° or less.

3. 3. The charging roller according to claim 1, wherein the average length x in the X-axis direction of an enveloping rectangular parallelepiped enclosing the domains satisfying the above conditions is in the range of 0.5 [mu]m or more and 15.0 [mu]m or less.

4. The volume resistivity d of the domain and the volume resistivity m of the matrix are m / d ≧ 1.0×10 ３ 4. The charging roller according to claim 1, wherein the following relationship is satisfied:

5. A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, comprising: an electrophotographic photosensitive member; and a charging roller arranged so as to be able to charge the electrophotographic photosensitive member, wherein the charging roller is the charging roller according to any one of claims 1 to 4.

6. An electrophotographic image forming apparatus comprising an electrophotographic photosensitive member and a charging roller arranged so as to be able to charge the electrophotographic photosensitive member, wherein the charging roller is the charging roller according to any one of claims 1 to 4.

Images