Conductive member, process cartridge, and electrophotographic image forming apparatus

Abstract

To prevent the occurrence of a white dot image occurring due to a dirt substance attached to an electrifying member in an accelerated and life-extended electrophotographic process.SOLUTION: A conductive member has a support 31 having conductivity and a conductive layer 32 provided on an outer surface of the support. The conductive layer has a matrix including a crosslinked product of first rubber and first conductive particles, and domains including a crosslinked product of second rubber and second conductive particles. The average primary particle diameter d1 of the first conductive particles present in the matrix as primary particles is 200 nm or more. The average primary particle diameter d2 of the second conductive particles in the domain is 50 nm or less, and 80% by number or more of the domains satisfy the requirements: the ratio of the cross-sectional area of a second conductive particle included in the domain to the cross-sectional area of the domain is 20% or more; the equivalent circle diameter of the domain is 4×d2 or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an electroconductive member for electrophotography, a process cartridge, and an electrophotographic image forming apparatus. [Background technology]

[0002] An electrophotographic image forming apparatus has a charging member, a transfer member, and a developing member. The charging member is a member that generates a discharge between itself and an electrophotographic photosensitive member to charge the surface of the electrophotographic photosensitive member. The developing member is a member that controls the charge of the developer coated on its surface by frictional charging to provide a uniform charge distribution, and then uniformly transfers the developer to the surface of the electrophotographic photosensitive member according to an applied electric field. The transfer member is a member that transfers the developer from the electrophotographic photosensitive member to a print medium such as paper or an intermediate transfer member, and at the same time generates a discharge to stabilize the developer after transfer. Conductive members are used as the charging member, transfer member, and developing member. These conductive members must achieve uniform charging of contacting objects, such as electrophotographic photosensitive members, intermediate transfer members, and print media. Known conductive members include a conductive support and a conductive layer disposed on the support. The conductive member transports charge from the conductive support to its surface and imparts charge to contacting objects by discharge or frictional charging.

[0003] Patent Document 1 discloses a charging member for achieving uniform charging. This charging member has an elastic layer in which an electronically conductive polymer particle phase is dispersed in an ionically conductive semiconductive polymer continuous layer. Patent Document 2 discloses a charging member that can stably charge a member to be charged even when applied to a high-speed electrophotographic image forming process. This charging member has a matrix containing a first rubber, a second rubber dispersed in the matrix, and an elastic layer in which a plurality of domains containing an electronically conductive material are dispersed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-3651 [Patent Document 2] Japanese Patent Publication No. 2020-166210 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, electrophotographic image forming processes have become faster and have longer life spans, and in order to reduce the size of the device, electrophotographic image forming devices have been provided that do not have a cleaning member for removing developer (toner) remaining on the photosensitive member (hereinafter also referred to as a "cleanerless configuration"). The present inventors applied the charging members according to Patent Document 1 and Patent Document 2 to the electrophotographic image forming apparatus and attempted to form images over a long period of time. As a result, deposits such as toner that had not been transferred to paper and remained on the photoreceptor accumulated significantly on the surface of the charging member, causing over-discharge at the accumulated locations and resulting in the formation of white speckled images (hereinafter referred to as white spot images).

[0006] One aspect of the present invention is to provide a conductive member that enables high-quality image formation over a long period of time when applied to a high-speed, long-life electrophotographic image forming process, even in a cleaner-less configuration. Another aspect of the present invention is to provide a process cartridge that contributes to high-quality electrophotographic image formation. Still another aspect of the present invention is to provide an electrophotographic image forming apparatus that can form high-quality electrophotographic images. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a conductive member having a conductive support and a conductive layer provided on the outer surface of the support, wherein the conductive layer has a matrix containing a cross-linked product of a first rubber and first conductive particles, and a domain containing a cross-linked product of a second rubber and second conductive particles, and at least a part of the first conductive particles are present as primary particles in the cross-linked product of the first rubber, and the thickness of the conductive layer is determined as follows: A conductive member characterized in that, when 15-μm square observation regions are placed at any three locations in a thickness region from the outer surface of the conductive layer to a depth of 0.1 to 0.9T for each cross section in the direction, the average primary particle diameter d1 of the first conductive particles present as primary particles in the matrix observed in each of the nine observation regions is 200 nm or more, the average primary particle diameter d2 of the second conductive particles in the domains observed in each of the observation regions is 50 nm or less, and 80% or more by number of the domains observed in each of the observation regions satisfy the following requirement (i) and requirement (ii): Requirement(i) a ratio of the cross-sectional area of the second conductive particles contained in the domain to the cross-sectional area of the domain is 20% or more; Requirement (ii) The domain has a circular equivalent diameter of 4×d2 or more. [Effects of the Invention]

[0008] According to the present invention, when applied to a high-speed, long-life electrophotographic image forming process, and even in a cleaner-less configuration, a conductive member usable for a charging member, a developing member, or a transfer member can be obtained, which can maintain high image quality for a long period of time. Also, according to another aspect of the present invention, an electrophotographic image forming apparatus capable of stably outputting high-quality electrophotographic images, and a process cartridge used therein can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 10 is a diagram illustrating a change over time in the amount of discharge current in the electrophotographic process. [Figure 2] 2 is a partial cross-sectional view of a conductive layer of a conductive member according to one embodiment of the present invention. [Figure 3] 1 is a cross-sectional view of a conductive roller according to an embodiment of the present invention. [Figure 4] 10 is a graph showing the change in absolute value of impedance with respect to frequency. [Figure 5] 1 is a cross-sectional view of a process cartridge including a conductive member according to the present invention. [Figure 6] 1 is a schematic diagram illustrating the configuration of an electrophotographic image forming apparatus including a conductive member according to the present invention. [Figure 7] FIG. 10 is a schematic diagram illustrating a state in which a measurement electrode is formed on a charging roller. [Figure 8] FIG. 10 is a cross-sectional view of a charging roller with a measuring electrode formed thereon. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples and are not intended to limit the scope of the present invention. SUMMARY OF THE INVENTION An object of the present invention is to suppress the occurrence of white spots caused by contaminants adhering to a charging member in an electrophotographic image forming process that is being made faster and has a longer life. The term "contaminating substances" as used herein refers to substances that, when toner and external additives on the surface of the photosensitive drum are transferred to paper or an intermediate transfer body during the transfer process, are not transferred in their entirety, but remain partly on the surface of the photosensitive drum, and reach and adhere to the charging member.

[0011] Toner and external additives often have insulating properties because they need to retain a certain charge so that they can be properly transferred to the photosensitive drum during the development process. Therefore, contaminants such as toner and external additives also have insulating properties. In the developer container, the toner and external additives are charged with a polarity that is significantly biased toward either positive or negative. In contrast, the toner and external additive contaminants that remain on the photosensitive drum without being transferred to paper or an intermediate transfer member are subjected to friction and other factors before reaching the charging member, and thus are charged with a certain distribution of positive and negative polarities. On the other hand, the charging member (hereinafter also referred to as "charging roller") is configured to generate a discharge relative to the photosensitive drum. Specifically, a DC voltage is applied to the charging member, generating a potential difference between the charging member and the surface of the photosensitive drum. In this case, it is difficult to prevent components of the potential difference between the charging member and the photosensitive drum, which have a polarity opposite to that of the charging bias, from adhering to the charging member due to electrostatic attraction. Therefore, for charging members intended for long-term use, it is desirable to use a means, as described below, that suppresses abnormal discharge caused by contaminants even if contaminants adhere to the charging roller.

[0012] Next, we will explain white spots caused by abnormal discharge due to contaminants. A discharge phenomenon occurs between the charging roller and the photosensitive drum according to Paschen's law, and the surface of the photosensitive drum is charged with either a negative or positive charge depending on the applied voltage. Because discharge occurs when neutral air is ionized by an electric field, charges of the opposite polarity are simultaneously generated. That is, positive or negative charges of the opposite polarity to the discharge are directed toward the charging roller by the electric field. Because the charging roller is a conductive material, if contaminants do not adhere to the surface of the charging roller, even if the surface of the charging roller is charged with charges of the opposite polarity to the discharge, the charge will escape from the surface to the substrate due to its conductivity. However, if insulating contaminants (toner or external additives) adhere to the surface of the charging roller, the charges of the opposite polarity to the discharge will not escape from the surface to the substrate but will be trapped on the surface. At this time, the contaminants adhered to the surface of the charging roller will carry charges of the opposite polarity to the discharge, i.e., the opposite polarity to the voltage applied to the charging roller. The opposite polarity charges exist in close proximity between the contaminants and the area surrounding the contaminants, creating a very strong electric field that can sometimes cause excessive discharge.

[0013] In addition, we conducted a detailed analysis of the discharge state during high-speed processing using an oscilloscope. Specifically, we tracked a single point on the surface of a photosensitive drum over time during an electrophotographic process in which discharge occurs while the photosensitive drum is rotating. Figure 1 illustrates the change in discharge current over time. In the electrophotographic process, discharge does not occur continuously from the start to the end of the discharge, but rather multiple discharges occur repeatedly, as shown in Figure 1(a). At times when high-frequency discharges are unlikely to occur, a discharge gap occurs, as shown in Figure 1(b). In some cases, as shown in Figure 1(c), excessive charge may be supplied in the discharge following the discharge gap, resulting in a large discharge, i.e., an overdischarge.

[0014] From the above, the inventors have discovered that in order to suppress the occurrence of white spot images in an electrophotographic image forming process that is fast and has a long life, it is necessary to satisfy the following conditions (a) and (b). (a) Suppressing the charge buildup of contaminants and avoiding the application of a very strong electric field to areas where contaminants are attached; (b) Suppressing discharge leakage even in the high frequency range where discharge is difficult, and preventing excessive charge from being supplied to the surface immediately after discharge leakage.

[0015] Furthermore, as a result of extensive research, the present inventors have found that a charging roller that satisfies the following requirements (A) and (B) can suppress the occurrence of white dot images even in processes that are faster and have a longer life, by satisfying the above conditions (a) and (b).

[0016] Requirement(A): The conductive layer has a matrix containing a cross-linked product of a first rubber and first conductive particles, and domains containing a cross-linked product of a second rubber and second conductive particles. At least a portion of the first conductive particles are present as primary particles in the cross-linked product of the first rubber. The longitudinal length of the conductive layer is defined as L, and the thickness of the conductive layer is defined as T. Three 15-μm square observation regions are placed at any three locations in a thickness direction cross section of the conductive layer, at the longitudinal center of the conductive layer and at three locations spaced at L / 4 from both ends of the conductive layer toward the center, within a thickness region extending from the outer surface of the conductive layer to a depth of 0.1 to 0.9T. The average primary particle diameter d1 of the first conductive particles present as primary particles in the matrix observed in each of the nine observation regions is 200 nm or greater.

[0017] Requirement (B): The average primary particle diameter d2 of the second conductive particles in the domains observed in each of the above observation regions is 50 nm or less, and 80% or more by number of the domains observed in each of the observation regions satisfy the following requirements (B1) and (B2). Requirement (B1): The ratio of the cross-sectional area of the second conductive particles contained in the domain to the cross-sectional area of the domain is 20% or more. Requirements (B2): The domain has an equivalent circle diameter of 4×d2 or more.

[0018] The above requirement (A) indicates that the first conductive particles exist in the form of primary particles without forming a structure in the matrix of the matrix-domain structure, and are not conductive. Here, "conductive" means that the electronic conductive agent forms a structure, allowing charge to move through the structure and significantly reducing electrical resistance. In this invention, the state of primary particles is defined as a state in which there is no interface within the particle. The above requirement (B) indicates that the second conductive particles dispersed in the domains in a matrix-domain structure in which the domains are dispersed in the matrix but not connected to each other have a small average primary particle size and are highly packed. In other words, requirement (B) indicates that the interfacial area between the second rubber and the second conductive particles in the domains is very large, and that the second conductive particles form a structure that exhibits high conductivity.

[0019] Figure 2 shows a partial cross-sectional view of a conductive layer perpendicular to the longitudinal direction of a roller-shaped conductive member (hereinafter also referred to as a "conductive roller") according to one embodiment of the present invention. As shown in Figure 2, the conductive layer has a matrix-domain structure having a matrix 21 and domains 23. The matrix 21 contains a cross-linked first rubber and first conductive particles 22. The domains 23 contain a cross-linked second rubber and second conductive particles 24.

[0020] In the above matrix-domain structure, requirement (A) prevents the matrix 21 from being conductive. Requirement (B) ensures that the primary particle size of the second conductive particles 24 is small and highly packed. This significantly increases the interfacial area between the second rubber and the second conductive particles 24, allowing the domains 23 to accumulate a large amount of charge near the interface with the matrix 21 within the domain. When the charge accumulated in the domain is consumed by discharge on the surface of the charging member, the charge is quickly supplied to the surface of the charging member by the shared voltage applied to the domain, the first rubber in the matrix, and the domain, as described below. This characteristic of quickly supplying charge immediately after discharge prevents the occurrence of discharge loss, as shown in Figure 1(b). As a result, it is possible to prevent the phenomenon of excessive charge being supplied at the next discharge timing, which could lead to overdischarge, as shown in Figure 1(c).

[0021] When a voltage is applied from the conductive support side, the voltage is applied to the first rubber in the matrix, the first conductive particles, and the domains in a shared manner (hereinafter, also referred to as "shared voltage"). However, because the first conductive particles in the matrix are conductors and exist independently, the interfacial area between the first conductive particles and the first rubber is small. Therefore, the shared voltage applied to the first conductive particles is significantly small, and most of the voltage applied to the conductive layer is applied to the first rubber in the matrix and the domains. As a result, the presence of the first conductive particles in the matrix in the form of primary particles increases the shared voltage applied to the first rubber in the matrix and the domains. The increased shared voltage applied to the domains facilitates the release of charge accumulated in the domains when they are supplied to the surface. In addition, the increased shared voltage applied to the first rubber in the matrix speeds up the supply of charge between domains or between domains and the first conductive particles. This allows the charge consumed during discharge to be more quickly supplied by using the charge accumulated in the domains before the next discharge timing.

[0022] Furthermore, the first conductive particles present in the matrix as specified in requirement (A) are themselves conductors as described above, and because they exist independently, they have a small interface area with the first rubber. Therefore, unlike domains, they have almost no charge storage capacity, and therefore can more quickly discharge the charge that has built up to the opposite polarity when contaminants deposited on the surface of the charging member are discharged to the conductive support side than domains. Furthermore, since the charged-up electric charge has the opposite polarity to the voltage applied from the conductive support side, it is attracted by the electric field and escapes to the conductive support side. However, as described above, the presence of the first conductive particles as primary particles in the matrix increases the shared voltage applied to the matrix and domains. Therefore, the charged-up electric charge that escapes via the matrix and domains can also be more quickly escaped to the conductive support side. From the above, a charging member that satisfies requirements (A) and (B) can suppress the occurrence of white spots and provide high-quality, stable images in a high-speed, long-life electrophotographic image forming process by satisfying the above-mentioned conditions (a) and (b).

[0023] The conductive member according to the present invention will be described with reference to Fig. 3, taking a conductive roller as an example. Fig. 3 is a cross-sectional view showing the configuration of a cross section perpendicular to the longitudinal direction, which is the axial direction, of the conductive roller. The conductive roller has a cylindrical conductive support 31 and a conductive layer 32 formed on the outer peripheral surface, i.e., the outer surface, of the support 31.

[0024] <Conductive support> The material for the support 31 can be appropriately selected from materials known in the field of electrophotographic conductive materials and materials usable as conductive materials, and can be used. Examples include metals and alloys such as aluminum, stainless steel, conductive synthetic resins, iron, and copper alloys. Furthermore, these may be subjected to oxidation treatment or plating treatment with chromium, nickel, etc. As the type of plating, either electroplating or electroless plating can be used. From the viewpoint of dimensional stability, electroless plating is preferred. Examples of the types 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 rust prevention ability, the plating thickness is preferably 0.10 μm or more and 30.00 μm or less. The cylindrical shape of the support 31 may be a solid cylindrical shape or a hollow cylindrical shape. The outer diameter of the support is preferably in the range of 3 mm or more and 10 mm or less.

[0025] <Conductive layer> To prevent white spots from occurring even in electrophotographic processes with increased speed and longer life, the device satisfies the requirements (A) and (B) described above. Specifically, it prevents excessive charge from being supplied to the surface of the charging member by suppressing the charge buildup of contaminants and suppressing discharge loss in the high-frequency range. Requirement (A) indicates that the first conductive particles exist in the form of primary particles without forming a structure in the matrix in the matrix-domain structure, and that because they exist in the form of primary particles, the matrix portion is not conductive. Requirement (B) indicates that the second conductive particles dispersed in the domain have a small average primary particle diameter and are highly packed, resulting in a very large interfacial area between the second rubber and the second conductive particles and in the domain exhibiting high conductivity.

[0026] In addition to the requirements (A) and (B), it is more preferable to satisfy the following features (i) to (v). (i) The volume resistivity of the matrix is 1.0 × 10 8 Ω·cm or greater than 1.0×10 17 Must be Ω·cm or less. (ii) The volume resistivity of the domain is 1.0 × 10 1 Ω cm or more, 1.0×10 4Must be Ω·cm or less. (iii) The distance between adjacent wall surfaces of the domains is within the range of 0.2 μm to 2.0 μm. (iv) 90% or more of the first conductive particles in the matrix are primary particles, and the distance between the first conductive particles and the nearest domain in the matrix is 0.1 μm or more. (v) When the number of first conductive particles in the matrix is N(A) and the number of domains is N(B), N(A) / N(B) is 0.2 to 3.0.

[0027] <Configuration (i)> In this configuration, as described above, the first conductive particles exist as primary particles in the matrix, and the voltage applied to the domain increases, promoting charge transfer through the domain. Therefore, when the volume resistivity of the matrix is 1.0 × 10 8 Ω·cm or greater than 1.0×10 17 If the resistivity is in the range of Ω·cm or less, the charge bypasses the domains and leaks into the matrix, which makes it possible to prevent a situation in which a conductive path that connects the conductive layer 32 is formed. Furthermore, the volume resistivity of the matrix is 1.0 × 10 12 Ω·cm or greater than 1.0×10 17 It is more preferable that the resistivity is Ω·cm or less.

[0028] <Method for measuring volume resistivity of matrix> The volume resistivity of the matrix can be measured using a microprobe by cutting a thin section of the conductive layer 32. Examples of the means for cutting a thin section include a sharp razor, a microtome, and a focused ion beam (FIB) method. When preparing thin sections, it is necessary to eliminate the influence of domains and measure the volume resistivity of only the matrix. For this reason, it is preferable to prepare thin sections with a thickness smaller than the interdomain distance measured in advance using a scanning electron microscope (SEM) or transmission electron microscope (TEM). Therefore, the preferred method for thinning is to use a means that can prepare very thin samples, such as a microtome.

[0029] To measure volume resistivity, first, one side of the flake is grounded, and then the locations of the matrix and domains within the flake are identified. These locations can be identified using a means capable of measuring the volume resistivity or hardness distribution of the matrix and domain, such as a scanning probe microscope (SPM) or atomic force microscope (AFM). Next, a probe is contacted with the matrix, and a DC voltage of 50 V is applied for 5 seconds. The arithmetic mean of the ground current value over the 5 seconds is measured, and the measured value is divided by the voltage to calculate the electrical resistance. The electrical resistance value is then converted to volume resistivity using the film thickness of the flake. In this case, a means capable of measuring the shape of the flake, such as an SPM or AFM, is preferred, as it can measure the film thickness of the flake and therefore the volume resistivity. To measure the volume resistivity of the matrix in a cylindrical conductive member, the conductive layer is divided into four regions in the circumferential direction, and then further divided into five regions in the longitudinal direction, from each of which a thin slice sample is cut. After obtaining the above measurements for each thin slice sample, the arithmetic mean value of the volume resistivity of a total of 20 samples is calculated.

[0030] <Configuration (ii)> The volume resistivity of the domain is 1.0×10 1 Ω cm or more, 1.0×10 4 If the resistivity is Ω·cm or less, the volume resistivity of the domains can be kept sufficiently low, which in turn limits the charge transport pathway to a more effective pathway through multiple domains while suppressing unwanted charge migration in the matrix. Furthermore, the volume resistivity of the domain is 1.0 × 10 2 It is more preferable that the resistivity is Ω·cm or less. The volume resistivity of the domain is adjusted by using a conductive agent in the rubber component of the domain to adjust the conductivity to a predetermined value. A rubber composition containing a rubber component for the matrix can be used as the rubber material for the domain. However, in this case, in order to form a matrix-domain structure, it is preferable that the difference in solubility parameter (SP value) between the rubber material forming the matrix and the domain be within the following range. That is, the difference in SP value should be 0.4 (J / cm 3 ) 0.5 or more, 5.0(J / cm 3 ) 0.5 Below 0.4 (J / cm 3 ) 0.5 Above, 2.2(J / cm 3 ) 0.5 It is more preferable to do the following:

[0031] The volume resistivity of the domain can be adjusted by appropriately selecting the type and amount of the electronic conductive agent. 1 Ω cm or more, 1.0×10 4 The conductive agent used to control the resistivity to Ω·cm or less is preferably an electronic conductive agent that can greatly change the volume resistivity from high to low depending on the amount dispersed. Examples of the electronic conductive agent to be blended into the domain include oxides such as carbon black, graphite, titanium oxide, and tin oxide; metals such as Cu and Ag; and particles coated with an oxide or metal to make them conductive. If necessary, two or more of these conductive agents may be blended in appropriate amounts.

[0032] Among the above-mentioned electronic conductive agents, it is preferable to use conductive carbon black, which has a high affinity with rubber and allows easy control of the distance between the electronic conductive agents. The type of carbon black to be compounded in the domain is not particularly limited, but sufficient conductivity can be obtained by using an electronic conductive agent with an average primary particle size of 50 nm or less. More preferably, the average primary particle size is 30 nm or less. The conductive agent such as conductive carbon black is preferably blended into the domain in an amount of 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the rubber component contained in the domain. A particularly preferred blending ratio is 50 parts by mass or more and 100 parts by mass or less. Blending the conductive agent at these ratios preferably results in a larger amount of conductive agent blended compared to general conductive members for electrophotography. This allows the volume resistivity of the domain to be increased to 1.0×10 1 Ω cm or more, 1.0×10 4 It can be easily controlled to a range of Ω·cm or less. If necessary, fillers, processing aids, crosslinking aids, crosslinking accelerators, antioxidants, crosslinking accelerator aids, crosslinking retarders, softeners, dispersants, colorants, and the like, which are generally used as compounding agents for rubber, may be added to the rubber composition for the domains within a range that does not impair the effects of the present invention.

[0033] <Method for measuring volume resistivity of domain> The volume resistivity of the domain can be measured in the same manner as the above-described method for measuring the volume resistivity of the matrix, except that the measurement location is changed to a location corresponding to the domain and the applied voltage when measuring the current value is changed to 1 V.

[0034] <Configuration (iii)> When the distance between adjacent wall surfaces between domains (hereinafter also referred to as "domain distance") is 0.2 μm or more and 2.0 μm or less, there is no leakage of charge from the domain to the matrix, and the charge accumulated in the domain can be effectively supplied from domain to domain. Furthermore, from the viewpoint of efficiently supplying charges from one domain to another, the inter-domain distance is preferably 2.0 μm or less, and from the viewpoint of suppressing charge leakage to the matrix, the inter-domain distance is more preferably 0.3 μm or more.

[0035] <Method for measuring interdomain distance> The interdomain distance may be measured as follows. First, a section is prepared using the same method as in the measurement of the volume resistivity of the matrix described above. Then, a fracture surface is formed by freeze fracturing, cross polishing, focused ion beam (FIB), or other methods. Considering the smoothness of the fracture surface and pretreatment for observation, the FIB method is preferred. Furthermore, to obtain a contrast between the domains and the matrix and first conductive particles, it is preferable to stain the domains using a staining process. The fracture surface and pretreated sections are observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to confirm the presence of matrix domain structures. Among these, observations using an SEM at magnifications of 1,000x to 100,000x are preferred for accurate quantification of domain area.

[0036] The interdomain distance is preferably measured by quantifying the image of the fracture surface where the matrix-domain structure is apparent. The fracture surface image obtained by SEM observation is converted to an 8-bit grayscale image using image processing software (e.g., "Luzex" (trade name, manufactured by Nireco Corporation)) to obtain a monochrome image with 256 gradations. The image is then binarized by inverting the black and white of the image so that the domains within the fracture surface appear white. The interwall distance of the domain size group in the image is then calculated. The interwall distance is the shortest distance between adjacent domains. In the case of a cylindrical charging member, where the longitudinal length of the conductive layer is L and the thickness of the conductive layer is T, cross sections of the conductive layer in the thickness direction are obtained at three locations: the longitudinal center of the conductive layer, and three locations at L / 4 from both ends of the conductive layer toward the center. For each of the obtained cross sections, 50 μm square observation areas are placed at three arbitrary locations in the thickness region from the outer surface of the conductive layer to a depth of 0.1T to 0.9T toward the support, and the interdomain distances observed in each of these nine observation areas are measured. Since it is necessary to observe the surface including the outer surface of the conductive layer from the support, which is the direction of charge movement, the slices are cut in a direction that allows observation of a cross section including a normal originating from the central axis of the support.

[0037] <Configuration (iv)> 90% or more of the first conductive particles in the matrix are primary particles, and the distance between the first conductive particles in the matrix and the nearest domain is 0.1 μm or more. This indicates that the first conductive particles in the matrix do not form a structure, and the first conductive particles in the matrix are not connected to the domains, for example, so that excessive charge transfer does not occur due to connection between the first conductive particles and the domains. This allows charge to accumulate in the domains. In addition, it is also possible to determine whether the first conductive particles form a structure in the matrix and whether the first conductive particles are connected to domains and significant charge transfer is not occurring by measuring the impedance characteristics described below.

[0038] Frequency measured by superimposing DC voltage on AC voltage: 1.0 x 10 -1 In impedance measurements at 100 Hz, the impedance at a DC voltage of 0 V is defined as impedance A, and the impedance at a DC voltage of 10 V is defined as impedance B. The above judgment is based on the fact that impedance A / impedance B is 60 or less. If the first conductive particles do not form a structure in the matrix, or if the first conductive particles and domains are connected and significant charge transfer occurs, it becomes difficult to accumulate charge in the domains as the DC voltage is increased. For this reason, impedance B when a DC voltage of 10 V is applied becomes significantly smaller than impedance A when no DC voltage is applied. As a result, impedance A / impedance B becomes larger. The inventors have determined that if impedance B / impedance A≦60, sufficient charge can be accumulated in the domains. Here, impedance A is 1.0×10 3 Ω~1.0×10 8 It is preferably Ω.

[0039] <Impedance measurement method> When measuring impedance, in order to eliminate the influence of contact resistance between the conductive member and the measurement electrode, a low-resistance thin film is deposited on the surface of the conductive member, and the thin film is used as an electrode, while the conductive support is used as a ground electrode to measure the impedance using two terminals. Examples of the method for forming the thin film include metal deposition, sputtering, application of a metal paste, application of a metal tape, etc. Among these, from the viewpoint of reducing the contact resistance with the conductive member, a method for forming a metal thin film such as platinum or palladium as an electrode by deposition is preferred. When forming a metal thin film on the surface of a conductive member, it is preferable to provide a vacuum deposition apparatus with a mechanism for gripping the charged member, taking into consideration the ease of the process and the uniformity of the thin film. Furthermore, for conductive members with a cylindrical cross section, it is preferable to use a vacuum deposition apparatus further equipped with a rotation mechanism.

[0040] For conductive members with a curved cross section, such as a circular cross section, connecting the above-mentioned metal thin film as the measurement electrode to an impedance measurement device is difficult, so the following method is preferably used. Specifically, a metal thin film electrode with a width of approximately 10 mm to 20 mm is formed in the longitudinal direction of the conductive member, and then a metal sheet is tightly wrapped around the conductive member. The metal sheet is then connected to the measurement electrode extending from the measurement device for measurement. This allows the measurement device to efficiently acquire electrical signals from the conductive layer of the conductive member, enabling impedance measurement. The metal sheet may be any metal sheet that has an electrical resistance equivalent to that of the metal part of the connection cable of the measurement device when measuring impedance; for example, aluminum foil or metal tape can be used. The impedance measurement equipment is an impedance analyzer, a network analyzer, a spectrum analyzer, etc., and is 1.0 x 10 7 Any device capable of measuring impedance in a frequency range up to 100 Hz may be used. Among these, it is preferable to measure impedance using an impedance analyzer, since it is in the range of electrical resistance of conductive members.

[0041] The impedance measurement conditions are as follows: An impedance measurement device was used, and the impedance was measured at 1.0 x 10 -1 Impedance is measured in the Hz frequency range. Measurements are performed in an environment with a temperature of 23°C and a humidity of 50% RH. To reduce measurement variability, it is preferable to set five or more measurement points per frequency digit. The amplitude of the AC voltage is 1V. Regarding the measurement voltage, first, measurement is performed using only AC voltage without applying DC voltage, and then measurement is performed while applying DC voltage superimposed on the AC voltage. The superimposed DC voltage is preferably 10 V. This is because the voltage applied to the charging roller in a typical electrophotographic image forming apparatus is about 10 V.

[0042] <Configuration (v)> In the present invention, domains densely filled with second conductive particles accumulate charge at the interface between the domain and the matrix, but as mentioned above, the first conductive particles present in the matrix as primary particles hardly accumulate charge. Therefore, the voltage shared between the first rubber and the domain in the matrix increases, allowing the charge accumulated in the domain to be quickly supplied after the charge on the surface of the charging member is consumed by discharge. This prevents excessive charge transfer due to discharge loss in the high-frequency range. In addition, the charge built up on the contaminants can be quickly discharged to the conductive substrate, preventing the occurrence of white spots. When the number of first conductive particles in the matrix is N(A) and the number of domains is N(B), it is preferable that N(A) / N(B) is 0.2 to 3.0. If N(A) / N(B) is less than 0.2, the number of first conductive particles is insufficient, and the above-mentioned effect is not fully achieved. If N(A) / N(B) is more than 3.0, the number of first conductive particles is so large that the proportion of first conductive particles present as primary particles, as explained in configuration (iv), decreases, and regions where domains and first conductive particles are connected to each other are more likely to occur. More preferably, N(A) / N(B) is 0.35 to 0.70.

[0043] In the present invention, it is more desirable that the following impedance characteristics be satisfied. <First requirement> Frequency 1.0 x 10 5 Hz~1.0×10 6 The slope of the impedance at Hz (hereinafter referred to as "high frequency impedance slope") is -0.8 or more. <Second requirement> Frequency 1.0 x 10 -2 Hz~1.0×10 1 Hz impedance (hereinafter referred to as "low frequency impedance") is 1.0 x 10 3 Ω or more, 1.0×10 8 Being Omega. The equivalent circuit of a conductive member is expressed as a parallel circuit of electrical resistance R and capacitance C, and the absolute value Z of the impedance can be expressed by the following equation (1).

[0044] TIFF0007721392000001.tif13155

[0045] The first requirement indicates that charge stagnation is unlikely to occur within conductive materials at high frequencies. When charge movement cannot keep up with high-frequency voltage and stagnates, it can be assumed that the electrical resistance value R has increased significantly, in other words, that the capacitance of the insulation is being measured. The state in which charge stagnates can be considered as a state in which R in formula (1) is approximated to infinity, and in the following formula (2) with the denominator element removed, R -2 is (2πf) 2 C 2 Therefore, equation (1) can be approximated as R -2 Finally, by taking the logarithm of both sides of equation (3), we obtain equation (4) below, where the slope of logf becomes -1.

[0046] TIFF0007721392000002.tif27155

[0047] In other words, when the slope of the high-frequency impedance is -1, it means that the movement of the charge cannot keep up with the high-frequency voltage, and the supply of charge for discharge cannot keep up with the discharge frequency, resulting in a time when discharge is not possible. The occurrence of a time when discharge is not possible means that the accumulated charge may move all at once at the immediately following discharge time, and if a large amount of charge moves at once, it may induce excessive discharge.

[0048] On the other hand, conductive materials with a high-frequency impedance gradient of -0.8 or greater are less likely to experience charge stagnation on the high-frequency side. As a result, they enable charge supply for discharges from the low-frequency range where impedance remains constant to the high-frequency range, particularly for discharges on the high-frequency side where charge stagnation is likely to occur. Because charge can be supplied abundantly, no discharge loss occurs. It is possible to prevent charge from moving all at once, thereby suppressing excessive discharge. This high-frequency range is considered to be a region where discharge loss is likely to occur because it is the region with the highest frequency among the frequencies of discharges generated from conductive members. In other words, this is a region where discharge loss is likely to occur and excessive discharge is likely to be induced at the timing of the discharge immediately thereafter. By indicating a value in the above range where the slope is greater than -1 in this frequency region, it is possible to suppress the occurrence of excessive discharge due to discharge loss. The inventors believe that the measurement frequency range of high frequency impedance will be as follows, assuming a typical discharge frequency when a charging roller for electrophotography as a charging member is combined with a photosensitive drum:

[0049] The discharge area in the moving direction of the surface of the charging roller, which is provided opposite the outer surface of the photosensitive drum and rotates and moves in synchronization with the photosensitive drum, is set to 0.5 mm to 1 mm. If the process speed of the electrophotographic image forming apparatus is set to a maximum of 100 to 500 mm / sec, the time it takes for the surface of the photosensitive drum to pass through the discharge area is 1.0 × 10 -3 sec~1.0×10 -2sec or more. Furthermore, when observing the discharge in detail, the length of the discharge area due to a single discharge is 0.01 mm to 0.1 mm, so it is estimated that at least 5 to 100 discharges occur while the same point on the surface of the charging roller passes through the discharge area. Therefore, the frequency of the discharge generated by the charging roller is several Hz to 1.0 x 10 6 Hz range. As the process speed increases, it is necessary to increase the discharge frequency and the number of discharges. 5 Hz~1.0×10 6 It is considered important to control the discharge and conduction mechanism in the high frequency range such as Hz. The second requirement, low-frequency impedance, represents the property that electric charges do not easily stagnate. When the frequency is approximated to 0, it can be approximated to the electrical resistance value R, which shows that the electrical resistance value R represents the ability of electric charges to move in a single direction. Therefore, it can be assumed that measurements made while applying a low-frequency voltage simulate the amount of charge movement in a state where the charge movement can follow the voltage oscillation.

[0050] The amount of charge transfer at low frequencies is an indicator of the ease of charge transfer between the charging member and the measurement electrode, and can also be used as an indicator of the amount of charge that can be transferred by discharge from the surface of the charging member to the photosensitive drum. The amplitude of the AC voltage used in measuring the impedance is 1 V. This oscillating voltage for measurement is significantly lower than the voltage of several hundred volts to several thousand volts that is actually applied to a charging member in an electrophotographic image forming apparatus. Therefore, it is believed that measuring the impedance according to the first and second requirements makes it possible to evaluate at a higher level the ease with which discharge occurs from the surface of the charging member. Low frequency impedance is 1.0 x 10 3 If the resistance is lower than Ω, the amount of one discharge becomes too large, which may induce over-discharge when contaminants are charged up. On the other hand, the low frequency impedance is 1.0×10 8If the resistance exceeds Ω, the discharge performance will be reduced, and if contaminants are present on the surface of the charging member, sufficient charge will not be applied to the photosensitive member, resulting in a difference in the amount of discharge depending on the amount of contaminants. As a result, unevenness in the amount of accumulated contaminants may occur as uneven potential on the photosensitive member.

[0051] Figure 4 shows the change in the absolute value of impedance Z (Ω) versus frequency f (Hz). As shown in Figure 4, in the charging member, the absolute value of impedance is constant in the low frequency range. 1.0 × 10 -2 Hz~1.0×10 1 The impedance in Hz can be substituted with the value of the impedance at a frequency of, for example, 0.1 Hz.

[0052] The conductive member according to the present invention can be formed, for example, by a method including the following steps (a) to (d). Step (a): preparing a domain-forming rubber mixture (hereinafter also referred to as "CMB") containing second conductive particles and a second rubber; Step (b): preparing a matrix-forming rubber mixture (hereinafter also referred to as "MRC") containing first conductive particles and a first rubber; Step (c): kneading the CMB and MRC to prepare a rubber mixture having a matrix-domain structure; Step (d): A step of forming the rubber composition prepared in step (c) directly or via another layer on a conductive support, and curing the layer of the rubber composition to form the conductive layer according to the present invention. The MRC includes a first rubber and first conductive particles as described above.

[0053] <First Rubber> The first rubber is the component with the largest compounding ratio in the rubber mixture for forming the conductive layer, and the cross-linked product of the first rubber determines the mechanical strength of the conductive layer. Therefore, the first rubber used is one that, after cross-linking, provides the conductive layer with the strength required for a conductive member for electrophotography. Preferred examples of the first rubber are listed below. Natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated NBR (H-NBR), epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer, and silicone rubber. If necessary, fillers, processing aids, crosslinking agents, crosslinking accelerators, antioxidants, etc. may also be added.

[0054] <First conductive particles> Examples of the first conductive particles include carbon black and conductive metal oxides such as titanium oxide, but as mentioned above, in order to accumulate sufficient charge in the domain, the conductive particles must exist in the form of primary particles without forming a structure. For example, in the case of carbon black, it is preferable to select carbon black with a large primary particle diameter and a small DBP absorption amount. Carbon black that meets the above characteristics must have a primary particle diameter of 200 nm or more and a DBP absorption of 40 cm 3 It is preferable that the carbon content is less than 100g / 100g. Specifically, MT carbon is exemplified. The DBP absorption is the volume of dibutyl phthalate (DBP) that can be adsorbed by 100 g of carbon black, and is measured in accordance with JIS K 6217. Carbon black has a cluster-like higher-order structure (hereinafter referred to as "structure") in which primary particles aggregate, and the degree of structure is expressed as the DBP absorption (cm 3 It is quantified in units of 100g / 100g. The conductive metal oxide preferably has a primary particle size of 200 nm or more.

[0055] <Method for measuring primary particle diameter of first conductive particles> The primary particle diameter of the first conductive particles can be observed using the method described in the first conductive particle confirmation method. The particle diameter is calculated using image processing software after adjusting the first conductive particles to appear white and the matrix polymer portion to appear black using binarization or other processing. The slices are sampled at three locations: the center of the conductive layer in the longitudinal direction, and two locations at L / 4 from both ends of the conductive layer toward the center, where L is the longitudinal length of the conductive layer of the conductive member. Slices are cut from these three locations. The measurement locations are three locations in the matrix portion of each slice, ranging from the outer surface to a depth of 0.1T to 0.9T, for a total of nine locations, where T is the thickness of the conductive layer. The particle diameters of the first conductive particles are calculated for all nine locations, and the arithmetic mean value is taken as the average particle diameter of the first conductive particles.

[0056] The domains include the second rubber and the second conductive particles as described above. <Second Rubber> Specific examples of the second rubber include at least one selected from the group consisting of natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), butyl rubber (IIR), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), chlorprene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U).

[0057] <Second conductive particles> Examples of the second conductive particles include carbon materials such as conductive carbon black and graphite, and metal oxides such as titanium oxide and tin oxide. Two or more types of these conductive particles may be blended together as appropriate. The second conductive particles to be blended into the domains are preferably added in an amount such that the ratio of the cross-sectional area of the conductive particles to the cross-sectional area of the domain is at least 20%, preferably 25% or more. There is no particular upper limit to the ratio of the cross-sectional area of the conductive particles to the cross-sectional area of the domain, but it is preferably 30% or less. As the second conductive particles to be compounded in the domains, conductive carbon black is preferably used because it has high conductivity, high affinity with rubber, and the distance between conductive particles can be easily controlled. The type of conductive carbon black to be compounded in the domain is not particularly limited. Specific examples include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black. However, from the viewpoint of the charge supply mentioned above, the primary particle diameter should be 50 nm or less, and the DBP oil supply amount should be 40 cm. 3 / 100g or more, 170cm 3 It is preferable that the amount is 100g or less. It is also preferable that the primary particle size of conductive metal oxides such as titanium oxide and tin oxide is 50 nm or less.

[0058] <Process cartridge> FIG. 5 is a schematic cross-sectional view of an electrophotographic process cartridge equipped with the conductive member according to the present invention as a charging roller. This process cartridge integrates a developing device and a charging device and is detachably mounted in the main body of an electrophotographic image forming apparatus. The developing device integrates at least a developing roller 53 and a toner container 56, and may optionally include a toner supply roller 54, toner 59, a developing blade 58, and an agitating blade 510. The charging device integrates at least a photosensitive drum 51 and a charging roller 52, and may also include a cleaning blade 55 and a waste toner container 57. Note that a cleanerless configuration does not include the cleaning blade 55 and the waste toner container 57. Voltages are applied to the charging roller 52, developing roller 53, toner supply roller 54, and developing blade 58, respectively. The charging roller 52, which is a charging member, is positioned so as to charge the photosensitive drum 51, which is an electrophotographic photosensitive member.

[0059] <Electrophotographic image forming apparatus> FIG. 6 is a schematic diagram of an electrophotographic image forming apparatus using the conductive member according to the present invention as a charging roller. This electrophotographic image forming apparatus is composed of an electrophotographic photosensitive member, a charging device, a latent image forming device, a developing device, a transfer device, a cleaning device, a fixing device, etc. The charging device charges the electrophotographic photosensitive member. The latent image forming device exposes the electrophotographic photosensitive member to light to form an electrostatic latent image. The developing device develops the electrostatic latent image into a toner image. The transfer device transfers the toner image to a transfer material. The cleaning device collects residual toner from the electrophotographic photosensitive member. The fixing device fixes the toner image to the transfer material. In the case of a cleaner-less configuration, there is no cleaning device for collecting residual toner. The electrophotographic roller according to the present invention can be used as the electrophotographic roller provided in the charging device of this electrophotographic image forming apparatus. The electrophotographic roller, which is a charging member, is arranged so as to be able to charge the electrophotographic photosensitive member.

[0060] The electrophotographic photoreceptor 62 is a rotating drum having a photosensitive layer on a conductive substrate. The electrophotographic photoreceptor 62 is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow. The charging device has a contact-type charging roller 61 that is placed in contact with the electrophotographic photoreceptor 62 by abutting against it with a predetermined pressing force. The charging roller 61 is configured to rotate in accordance with the rotation of the electrophotographic photoreceptor 62. A predetermined DC voltage is applied to the charging roller 61 from a charging power source 69, causing the charging roller 61 to charge the electrophotographic photoreceptor 62 to a predetermined potential. An exposure device such as a laser beam scanner is used as a latent image forming device (not shown) that forms an electrostatic latent image on the electrophotographic photoreceptor 62. An electrostatic latent image is formed by irradiating the uniformly charged electrophotographic photoreceptor 62 with exposure light 67 corresponding to image information.

[0061] The developing device has a developing sleeve or developing roller 63 arranged in close proximity to or in contact with the electrophotographic photosensitive member 62. The developing device develops the electrostatic latent image by reversal development using toner that has been electrostatically treated to have the same polarity as the charge polarity of the electrophotographic photosensitive member 62, thereby forming a toner image. The transfer device has a contact-type transfer roller 64. The toner image is transferred from the electrophotographic photosensitive member 62 to a transfer material such as plain paper. The transfer material is transported by a paper feed system having a transport member. The cleaning device has a blade-type cleaning member 66 and a collection container 68. The cleaning device mechanically scrapes off and collects the residual toner remaining on the electrophotographic photosensitive member 62 after the developed toner image has been transferred to the transfer material. It is possible to omit the cleaning device if a simultaneous development and cleaning method is adopted in which the residual toner is collected by the developing device. The toner image transferred to the transfer material is fixed to the transfer material by passing between a fixing belt 65 heated by a heating device (not shown) and a roller arranged opposite the fixing belt 65. [Example]

[0062] Specific examples and comparative examples according to the present invention are shown below. Conductive members in the examples and comparative examples of the present invention were produced using the materials shown in Table 1.

[0063] [Table 1]

[0064] In the tables shown below, "phr" stands for "per hundred rubber" and represents the amount compounded relative to 100 parts by mass of rubber. In the following Examples 1 to 30 and Comparative Examples 1 to 4, the charge rollers of Examples 1 to 30 are referred to as "charge roller 1" to "charge roller 10," respectively, and the charge rollers of Comparative Examples 1 to 4 are referred to as "charge roller 31" to "charge roller 34," respectively.

[0065] Example 1 1. Preparation of unvulcanized rubber composition for forming conductive layer used to form conductive layers in Examples and Comparative Examples [1-1. Preparation of carbon masterbatch (CMB) for domain formation] The materials shown in Table 2 were mixed in a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Corporation) to obtain CMB for domain formation. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

[0066] [Table 2]

[0067] [1-2. Preparation of matrix-forming rubber composition (MRC)] A rubber composition for forming a matrix was obtained by mixing the materials of the types and amounts shown in Table 3 in a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Corporation). The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

[0068] [Table 3]

[0069] [1-3. Preparation of Unvulcanized Rubber Composition for Forming Conductive Layer] The materials of the types and amounts shown in Table 4 were mixed using an open roll to prepare a rubber composition for forming a conductive resin layer. An open roll with a roll diameter of 12 inches was used as the mixer. The mixing conditions were a front roll rotation speed of 10 rpm, a rear roll rotation speed of 8 rpm, a roll gap of 2 mm, and a total of 20 left and right turns, followed by 10 thin passes with a roll gap of 1.0 mm.

[0070] [Table 4]

[0071] 2. Fabrication of conductive materials [2-1. Formation of conductive layer] As a support, a core bar with a total length of 252 mm and an outer diameter of 6 mm, made of free-cutting steel with an electroless nickel-plated surface, was prepared. This core bar was used as a support, which is a conductive mandrel. Using a roll coater, an adhesive (product name: Metalock U-20, manufactured by Toyo Kagaku Kenkyusho Co., Ltd.) was applied over the entire circumference of the core bar, within a range of 230 mm, excluding 11 mm at each end. In this example, the core bar coated with the adhesive was used as a conductive support. Next, a die with an inner diameter of 10.0 mm was attached to the tip of a crosshead extruder having a mechanism for feeding the conductive support and a mechanism for discharging the unvulcanized rubber roller, and the temperatures of the extruder and crosshead were adjusted to 100° C., and the conveying speed of the conductive support was adjusted to 60 mm / sec. Under these conditions, the rubber composition for forming a conductive resin layer was fed from the extruder, and the outer periphery of the conductive support was coated with the rubber composition for forming a conductive resin layer in the crosshead, thereby obtaining an unvulcanized rubber roller. Next, the unvulcanized rubber roller was placed in a hot-air vulcanizing furnace at 170°C and heated for 60 minutes to vulcanize the unvulcanized rubber composition, resulting in a conductive roller with a conductive resin layer formed on the outer periphery of the conductive support. Then, 10 mm of each end of the conductive resin layer was cut off, leaving a longitudinal length of 232 mm for the conductive resin layer.

[0072] [2-2. Conductive layer polishing] Next, the surface of the conductive layer was polished under the polishing conditions described in the following polishing condition 1 to obtain a crown-shaped charging roller 1 having a diameter of 8.5 mm at the center and a diameter of 8.44 mm at each position 90 mm from the center to both ends.

[0073] (Polishing condition 1) A cylindrical grinding wheel (manufactured by Teiken Co., Ltd.) with a diameter of 305 mm and a length of 235 mm was prepared. The type of abrasive grain, grain size, degree of bonding, bonding agent, and structure (abrasive grain ratio) were as follows: Abrasive material: GC (green silicon carbide), (JIS R6111-2002) Abrasive grain size: #80 (average grain size 177 μm JIS B4130) Abrasive grain bond: HH (JIS R6210) Binder: V4PO (vitrified) Abrasive grain structure (abrasive grain ratio): 23 (abrasive grain content 16% JIS R6242) The polishing conditions were a grinding wheel rotation speed of 2100 rpm and a conductive member rotation speed of 250 rpm. In the rough cutting process, the grinding wheel penetrated the conductive member at a speed of 20 mm / sec, penetrating 0.24 mm after contacting the outer surface of the conductive member. In the fine polishing process, the penetration speed was changed to 0.5 mm / sec, penetrating 0.01 mm. The grinding wheel was then removed from the conductive member to complete the polishing. The polishing method used was the upper cut method, in which the grindstone and the conductive member rotate in the same direction.

[0074] 3. Characterization [3-1. Confirmation of the presence or absence of matrix domain structure] The presence of a matrix-domain structure in the conductive layer was confirmed by the following method. A section (500 μm thick) was cut using a razor so that a cross section perpendicular to the longitudinal direction of the conductive layer of the conductive member could be observed. Platinum was then vapor-deposited on the surface of the section corresponding to the cross section of the conductive layer. The platinum-deposited surface of the section was photographed at 5000x magnification using a scanning electron microscope (SEM) (product name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain an SEM image. When the SEM image confirmed that multiple domains were dispersed in a matrix and the matrix was interconnected, the matrix-domain structure was determined to be "present."

[0075] [3-2. Measurement of matrix volume resistivity] The volume resistivity of the matrix was measured in contact mode using a scanning probe microscope (SPM) (product name: Q-Scope250, manufactured by Quesant Instrument Corporation) as follows: The measurement environment was a temperature of 23°C and a relative humidity of 50%. First, a section approximately 2 μm thick was cut from the conductive layer of the charging roller 1 using a microtome (trade name: Leica EM FCS, manufactured by Leica Microsystems) at a cutting temperature of −100° C. Next, the section was placed on a metal plate so that one side of the section corresponding to the cross section of the conductive layer was in contact with the surface of the metal plate. Then, on the side of the section opposite the side in contact with the surface of the metal plate, a cantilever of an SPM was brought into contact with a portion corresponding to the matrix. Next, a voltage of 50 V was applied to the cantilever, and the current value was measured. The surface shape of the slice was observed with an SPM, and the thickness of the measurement point was calculated from the obtained height profile. Furthermore, the area of the recess at the contact point of the cantilever was calculated from the surface shape observation results. The volume resistivity was calculated from the thickness and the recess area, and was taken as the volume resistivity of the matrix.

[0076] [3-3. Measurement of domain volume resistivity] The volume resistivity of the domain was measured in the same manner as in 3-2 above, except that the contact position of the cantilever was set to the point corresponding to the domain and the voltage applied to the cantilever was set to 1 V. The average value of the values at each measurement point was calculated.

[0077] [3-4. Measuring the inter-domain distance] The section prepared for measuring the volume resistivity of the matrix in 3-2 above was stained with phosphotungstic acid, with only the second rubber in the domain. Platinum was then vapor-deposited on the surface corresponding to the cross section of the conductive layer. The platinum-deposited surface was then photographed at 10,000x magnification using an SEM (product name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain an SEM image. Next, the SEM image was converted to an 8-bit grayscale using an image processing analyzer (product name: LUZEX-AP, manufactured by Nireco Corporation) to obtain a monochrome image with 256 gradations. The binarized image was then inverted so that the stained domains in the monochrome image appeared white, and a binarization threshold was set for the image brightness distribution based on the Otsu discriminant analysis algorithm to obtain a binarized image. For the binarized image, 15 μm square observation regions were placed in three arbitrary locations within the thickness region corresponding to a depth of 0.1T to 0.9T from the outer surface of each of the three sections, where T is the thickness of the conductive layer, for a total of nine locations. The interdomain distance was calculated for each observation region, and the average of the measured interdomain distances for all nine observation regions was calculated.

[0078] [3-5. Measurement of the primary particle abundance ratio of the first conductive particle] Using the SEM image obtained in the measurement of the interdomain distance in 3-4 above, the number N of first conductive particles dispersed in the matrix and the number N(C) of particles among the first conductive particles that did not have an interface within the particle were counted. The primary particle abundance ratio of the first conductive particles was calculated by (N(C) / N)×100.

[0079] [3-6. Measurement of the average primary particle size of the first conductive particles] In the SEM image analyzed in the measurement of the primary particle abundance ratio of the first conductive particles in 3-5 above, the average diameter of the primary particles present was calculated. Using the image processing software "Image-pro plus" (product name, manufactured by Media Cybernetics), the observed image was converted to 8-bit grayscale, obtaining a monochrome image with 256 gradations. Next, the image was inverted to make the domains in the monochrome image white, and a binarization threshold was set for the brightness distribution of the image based on the algorithm of Otsu's discriminant analysis method, obtaining a binary image. Next, an observation area large enough to accommodate one first conductive particle in the matrix was extracted from the obtained binary image. Then, using the counting function, the cross-sectional area S1 of the first conductive particles was calculated, and the average primary particle diameter d1 was calculated as d1 = (S1 / 2π) 0.5 It was calculated by:

[0080] [3-7. Measurement of the average distance between the first conductive particle and the nearest domain] In the same manner as in the measurement of the matrix volume resistivity in 3-2 above, a section having a thickness of about 2 μm was cut from the conductive layer of the charging roller 1 using a microtome (trade name: Leica EM FCS, manufactured by Leica Microsystems) at a cutting temperature of −100° C. Platinum was then vapor-deposited onto the surface corresponding to the cross section of the conductive layer. Next, the platinum-deposited surface was photographed at 10,000x magnification using an SEM (trade name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain an SEM image. Next, the SEM image was converted to an 8-bit grayscale image using an image processing analyzer (product name: LUZEX-AP, manufactured by Nireco Corporation) to obtain a monochrome image with 256 gradations. The binarized image was then inverted so that the domains and first conductive particles in the monochrome image appeared white, and a binarization threshold was set for the brightness distribution of the image based on the algorithm of Otsu's discriminant analysis method to obtain a binarized image. For the binarized image, 15 μm square observation areas were placed in three arbitrary locations within the thickness region corresponding to a depth of 0.1T to 0.9T from the outer surface of each of the three sections, where T is the thickness of the conductive layer, for a total of nine locations. In each observation area, the position of the first conductive particle was identified from the observation image before binarization, and only the distance to the domain adjacent to the first conductive particle was calculated. The distances to multiple adjacent domains were calculated for each first conductive particle, and the shortest distance among them was taken as the distance to the nearest domain of that first conductive particle. The same measurement was performed on all of the first conductive particles in the observation region, and then the average value was calculated to calculate the average distance between the first conductive particle and the nearest domain.

[0081] [3-8. Measurement of the ratio of first conductive particles to domain] Using the SEM image obtained in the measurement of the volume resistivity of the matrix in 3-2 above, the number of domains N(B) and the number of first conductive particles N(A) present in the observed image area were counted, and N(A) / N(B) was calculated as the ratio of the first conductive particles to the domains.

[0082] [3-9. Measurement of the cross-sectional area ratio of the second conductive particle in the domain] A section having a thickness of about 100 nm was cut from the conductive layer of the charging roller 1 using a microtome (trade name: Leica EM FCS, manufactured by Leica Microsystems) at a cutting temperature of -100°C, and platinum was vapor-deposited on the surface corresponding to the cross section of the conductive layer. Next, the platinum-deposited surface was photographed at 20,000x magnification using an SEM (trade name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain an SEM image. Next, the image was binarized using image processing software "Image-pro plus" (product name, manufactured by Media Cybernetics) so that the carbon black in the domains could be distinguished. Next, an observation area large enough to fit one domain was extracted from the obtained binarized image. Furthermore, the counting function was used to calculate the cross-sectional area S of the domain and the cross-sectional area Sc of the carbon black contained in the domain as the second conductive particle, and the cross-sectional area ratio of the second conductive particle in the domain was calculated using Sc / S.

[0083] [3-10. Measurement of the circle equivalent diameter of the second conductive particle in the domain] Using the cross-sectional area S of the domain measured in 3-9 above, the circular equivalent diameter D of the domain is calculated as D = (S / 2π) 0.5 It was calculated by:

[0084] [3-11. Measurement of primary particle size of second conductive particles] The slices used in measuring the cross-sectional area ratio of the second conductive particles in the domains in 3-9 above were photographed at 50,000x magnification using a TEM (product name: JEM-2800, manufactured by JEOL Ltd.) to obtain TEM images. The observation area was set to include the domains. Next, using image processing software "Image-pro plus" (product name, manufactured by Media Cybernetics), binarization was performed so that the carbon black serving as the second conductive particles in the domains could be distinguished. Then, the primary particle diameter of the second conductive particles was calculated using a counting function, and the average value was taken as the primary particle diameter of the second conductive particles.

[0085] [3-12. Measurement of charge decay rate on the surface of the charging roller] Using a charge amount measuring device (trade name: DRA-2000L, manufactured by QEA Corporation), the surface potential of the charging roller due to corona discharge was measured. Specifically, the corona discharger of the charge amount measuring device was positioned so that the gap between its grid and the surface of the charging roller was 1 mm. Next, a voltage of 8 kV was applied to the corona discharger to generate a discharge, charging the surface of the charging roller, and the surface potential of the charging roller was measured immediately after the end of the discharge and 10 seconds after the end of charging. The surface potential immediately after the end of the discharge (or immediately after charging) was defined as E0, and the surface potential 10 seconds after the end of the discharge (or charging) was defined as E 10 The charge decay rate Q was calculated using the following formula (5): The charge decay rate Q is preferably 83% or more.

[0086] TIFF0007721392000007.tif11170

[0087] [3-13. Impedance measurement] As a pretreatment, platinum was vapor-deposited onto the outer surface of the rotating charging roller to create a measurement electrode. At this time, masking tape was used to create an electrode 1.5 cm wide and uniform in the circumferential direction. By forming this electrode, the contribution of the contact area between the measurement electrode and the conductive member due to the surface roughness of the charging roller can be minimized. Next, an aluminum sheet was tightly wrapped around the electrode, and the aluminum sheet was connected to the measurement electrode of an impedance measuring device (trade names: Solartron 1260 and Solartron 1296; manufactured by Solartron Corporation).

[0088] A schematic diagram of the state in which the measurement electrodes are formed on the charging roller is shown in Figure 7. In Figure 7, 71 is the conductive support, 72 is the conductive layer with a matrix-domain structure, 73 is the platinum vapor deposition layer, and 74 is the aluminum sheet. Figure 8 shows a cross-sectional view of a charging roller with a measurement electrode formed on it. 81 is the conductive support, 82 is the conductive layer with a matrix-domain structure, 83 is the platinum vapor-deposited layer, and 84 is the aluminum sheet. As shown in Figure 8, it is important to sandwich the conductive layer with a matrix-domain structure between the conductive support 81 and the measurement electrode. The aluminum sheet was then connected to a measurement electrode on the side of an impedance measurement device (Solatron 1260 and Solartron 1296, manufactured by Solartron Corporation). Impedance measurement was performed using the conductive support and the aluminum sheet as two electrodes for measurement.

[0089] Impedance measurements were performed in an environment with a temperature of 23°C and a relative humidity of 50%, with an AC voltage of 1 Vpp and a frequency of 1.0 x 10 -2 Hz~1.0×10 7 The measurement was performed at 1.0 × 10 Hz (measurements were taken at five points when the frequency changed by one digit), and the absolute value of the impedance was obtained. Next, using the measurement results, a graph was created in which the absolute value of the impedance and the frequency were plotted logarithmically. From this graph, it was found that the frequency was 1.0 × 10 -2 Hz~1.0×10 1 Impedance Z0 in Hz and 1.0 x 10 5 Hz~1.0×10 6 The slope of the impedance in Hz was calculated. Next, a similar measurement was performed with a DC voltage of 10 V superimposed on an AC voltage of 1 V, and the impedance Z 10 Calculate Z0 / Z, which represents the influence of DC voltage. 10 was calculated.

[0090] 4. Image Evaluation In order to confirm the stain resistance performance of the charging roller 1 under long life conditions, the following evaluation was carried out. First, an electrophotographic laser printer (product name: Laser Jet Pro M203dw, manufactured by HP) was prepared as an electrophotographic image forming apparatus. To evaluate the high-speed process, the laser printer was modified so that the number of sheets per minute was 75 sheets per minute for A4 size paper, which was higher than the original output number. The output speed of the recording media was set to 370 mm / sec. Next, the charging roller 1, the electrophotographic image forming apparatus, and the process cartridge were left in an environment of 15° C. / 30% RH for 48 hours in order to acclimate them to the evaluation environment. The charging roller 1 that had been left in the above environment was set as a charging roller for a process cartridge and incorporated into a laser printer, after which images were output continuously on a total of 50,000 sheets under the same environment. The image output was a 4-point alphabet letter "E" printed on an A4 size sheet of paper with a print rate of 1.0%. Thereafter, a halftone image (an image in which horizontal lines with a width of 1 dot and an interval of 2 dots are drawn in the direction perpendicular to the rotation direction of the photosensitive drum) was output. This halftone image was visually observed, and the white dot image was evaluated according to the following criteria.

[0091] [Evaluation of white spots on halftone images] Rank A: No white spots are visible on the halftone image even when observed under a microscope. Rank B: No white dots are visible on the halftone image when observed with the naked eye, but they are visible when observed under a microscope. Rank C: White spots are visible on some parts of the halftone image. Rank D: White dots are visible all over the halftone image.

[0092] (Examples 2 to 28) Charge rollers 2 to 28 were produced in the same manner as charge roller 1 of Example 1, except that the starting materials were changed as shown in Table 5. The parts by mass and physical properties of the starting materials used to produce each conductive member are shown in Tables 5 and 6. The property evaluation and image evaluation results of the completed charge rollers 2 to 28 are shown in Tables 7 and 8.

[0093] Example 29 The charging roller 29 was produced in the same manner as in Example 4, except that the starting materials shown in Table 5 were used, the conductive layer was formed by the following method, and no polishing step was performed. A core metal coated with adhesive was used as the conductive support. A die with an inner diameter of 8.4 mm was attached to the tip of a crosshead extruder equipped with a mechanism for feeding the conductive support and a mechanism for discharging the unvulcanized rubber roller. The temperature of the extruder and crosshead was set to 100°C, and extrusion was performed while varying the conveying speed of the conductive support. The outer diameter of the unvulcanized rubber roller was molded to be larger than the die diameter, resulting in a crown-shaped unvulcanized rubber roller with an outer diameter of 8.5 mm at the center and diameters of 8.44 mm at positions 90 mm from the center to both ends. Next, the unvulcanized rubber roller was placed in a hot air vulcanizing furnace at 170°C and heated for 60 minutes to vulcanize the unvulcanized rubber composition, thereby obtaining a conductive roller having a conductive resin layer formed on the outer periphery of the conductive support. After that, 10 mm was cut off from each end of the conductive resin layer to make the longitudinal length of the conductive resin layer portion 232 mm, thereby producing charging roller 29.

[0094] Example 30 The charging roller 30 was produced in the same manner as in Example 29, except that the starting materials shown in Table 5 were used.

[0095] [Table 5] [Table 6] [Table 7] [Table 8] Comparative Example

[0096] (Comparative Example 1) A charging roller 31 of Comparative Example 1 was produced in the same manner as in Example 1, except that the material used in Example 1 was changed to the material shown in E-31 in Tables 9 and 10. The results of the characteristic evaluation and image evaluation of the completed charging roller 31 are shown in Tables 11 and 12.

[0097] (Comparative Example 2) A charging roller 32 of Comparative Example 2 was produced in the same manner as in Example 1, except that the material used in Example 1 was changed to the material shown in E-32 in Tables 9 and 10. The results of the characteristic evaluation and image evaluation of the completed charging roller 32 are shown in Tables 11 and 12.

[0098] (Comparative Example 3) A charging roller 33 of Comparative Example 3 was produced in the same manner as in Example 1, except that the material used in Example 1 was changed to the material shown in E-33 in Tables 9 and 10. The results of the characteristic evaluation and image evaluation of the completed charging roller 33 are shown in Tables 11 and 12.

[0099] Comparative Example 4 The charging roller 34 of Comparative Example 4 was produced in the same manner as in Example 1, except that the material used in Example 1 was changed to the material shown in E-34 in Tables 9 and 10. The results of the characteristic evaluation and image evaluation of the completed charging roller 34 are shown in Tables 11 and 12.

[0100] [Table 9] [Table 10] [Table 11] [Table 12] [Explanation of symbols]

[0101] 21. Matrix 22 First conductive particles 23 Domains 24 Second conductive particles 31 Support 32 Conductive layer

Claims

1. A conductive member having a conductive support and a conductive layer provided on an outer surface of the support, the conductive layer has a matrix containing a cross-linked product of a first rubber and first conductive particles, and a domain containing a cross-linked product of a second rubber and second conductive particles, at least a portion of the first conductive particles are present as primary particles in the cross-linked product of the first rubber, When the length of the conductive layer in the longitudinal direction is L and the thickness of the conductive layer is T, 15 μm square observation regions are placed at any three locations in a thickness region from the outer surface of the conductive layer to a depth of 0.1 to 0.9T on each of a cross section of the conductive layer in the thickness direction, that is, at the center of the conductive layer in the longitudinal direction and at three locations spaced at L / 4 from both ends of the conductive layer toward the center, and the average primary particle diameter d1 of the first conductive particles present as primary particles in a matrix observed in each of the nine observation regions is 200 nm or more, a conductive member characterized in that the average primary particle diameter d2 of the second conductive particles in the domains observed in each of the observation regions is 50 nm or less, and 80% or more by number of the domains observed in each of the observation regions satisfy the following requirements (i) and (ii): Requirement (i) a ratio of the cross-sectional area of the second conductive particles contained in the domain to the cross-sectional area of the domain is 20% or more; Requirement (ii) The domain has a circular equivalent diameter of 4×d2 or more.

2. 2. The conductive member according to claim 1, wherein 90% or more of the first conductive particles are present as primary particles in the matrix.

3. The conductive member has a metal film as an outer surface thereof, and in an environment of a temperature of 23° C. and a humidity of 50% RH, an amplitude of 1 V and a frequency of 1.0×10 －１ The impedance when an AC voltage of 1.0 × 10 Hz is applied is defined as impedance A, and the amplitude is 1 V and the frequency is 1.0 × 10 －１ When an AC voltage of 10 Hz and a DC voltage of 10 V are applied, the impedance B is 1.0 × 10 ３ Ω ~ 1.0 x 10 ８ Ω, Impedance B / impedance A≦60 The conductive member according to claim 1 or 2, wherein

4. When the length of the conductive layer in the longitudinal direction is L and the thickness of the conductive layer is T, 15 μm square observation regions are placed at any three locations in a thickness region from the outer surface of the conductive layer to a depth of 0.1 to 0.9T on each of a cross section of the conductive layer in the thickness direction, at the center of the longitudinal direction of the conductive layer and at three locations at L / 4 from both ends of the conductive layer toward the center, and when the number of first conductive particles observed in each of the nine observation regions is N(A) and the number of domains is N(B), 0.35≦N(A) / N(B)≦0.70 The conductive member according to any one of claims 1 to 3, wherein

5. 5. The conductive member according to claim 1, wherein the arithmetic mean value of the distance between the first conductive particle and the nearest domain is 0.1 μm or more.

6. The conductive member according to any one of claims 1 to 5, wherein the arithmetic mean value of the interdomain distance is 0.2 µm or more and 2.0 µm or less.

7. The volume resistivity of the matrix is 1.0×10 ８ Ω cm or more, 1.0 × 10 １７ The conductive member according to any one of claims 1 to 6, having a resistivity of Ω·cm or less.

8. When the distance between the grid portion of the corona discharger and the surface of the conductive member is 1.0 mm and a voltage of 8 kV is applied to the grid portion to charge the surface of the conductive member with the corona discharger, the surface potential of the surface of the conductive member immediately after charging is E0, and the surface potential of the surface of the conductive member 10 seconds after charging is completed is E10, The conductive member according to any one of claims 1 to 7, wherein the charge decay rate Q expressed by the following formula is 83% or more.

9. A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, comprising: an electrophotographic photosensitive member; and a charging member arranged so as to be able to charge the electrophotographic photosensitive member, wherein the charging member is the conductive member according to any one of claims 1 to 8.

10. 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 conductive member according to any one of claims 1 to 8.

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