JP7463128B2 - Conductive member, process cartridge and electrophotographic image forming apparatus - Google Patents

Description

This disclosure is directed to electrophotographic conductive members, process cartridges, and electrophotographic image forming apparatuses.

In an image forming apparatus employing an electrophotographic system (hereinafter referred to as an electrophotographic image forming apparatus), conductive members such as a charging member, a transfer member, a developing member, etc. The conductive member is composed of a conductive layer coated on the outer peripheral surface of a conductive support, and plays a role of transporting electric charge from the conductive support to the conductive member surface and imparting electric charge to a contacting object by discharging or the like.
For example, the charging member is a member that generates a discharge between itself and the photoconductor to charge the surface of the photoconductor, while the transfer member is a member that transfers the developer from the photoconductor to a print medium or an intermediate transfer member, and at the same time generates a discharge to stabilize the developer after transfer.
In response to the recent demand for higher image quality in electrophotographic image forming apparatuses, it has been considered to increase the voltage applied to conductive members in order to achieve high contrast. Under such high voltage application conditions, these conductive members are required to be more uniformly charged with respect to contact objects such as photoconductors, intermediate transfer bodies, and printing media.

Patent Document 1 discloses an electrostatic charging member which is a rubber composition having an islands-in-a-sea structure including a polymer continuous phase made of an ionically conductive rubber material and a polymer particle phase made of an electronically conductive rubber material, the ionically conductive rubber material being mainly composed of raw rubber A having a volume resistivity of 1× ¹⁰ Ω·cm or less, and the electronically conductive rubber material being made conductive by blending conductive particles into raw rubber B.

JP 2002-3651 A

One aspect of the present disclosure is to provide a conductive member for electrophotography that can stably suppress the occurrence of "fogging" on an electrophotographic image even when the charging bias is increased.
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.

According to one aspect of the present disclosure,
a support having an electrically conductive outer surface;
a conductive layer provided on an outer surface of the support,
the conductive layer has a matrix containing a crosslinked product of a first rubber and a plurality of domains dispersed in the matrix,
The domain comprises a crosslinked product of a second rubber and a conductive particle,
At least a portion of the domain is exposed on an outer surface of the conductive member, forming a protrusion on the outer surface of the conductive member;
the outer surface of the conductive member is composed of the matrix and the domain exposed on the outer surface of the conductive member;
a platinum electrode is provided directly on the outer surface of the conductive member, and an AC voltage having an amplitude of 1 V and a frequency of 1.0 Hz is applied between the outer surface of the support and the platinum electrode in an environment of a temperature of 23° C. and a relative humidity of 50%, and the impedance is 1.0×10 ³ Ω or more and 1.0×10 ⁸ Ω or less;
When the length of the conductive layer in the longitudinal direction is L and the thickness of the conductive layer is T, and observation regions of 15 μm square are placed at any three locations in a thickness region from the outer surface of the elastic layer to a depth of 0.1T to 0.9T for each of three locations in a cross section of the conductive layer in the thickness direction, the three locations being the center in the longitudinal direction of the conductive layer and L/4 from both ends of the conductive layer toward the center, 80% or more by number of domains observed in each of all nine observation regions satisfy the following requirement (1) and requirement (2):
(1) The ratio of the cross-sectional area of the conductive particles contained in the domain to the cross-sectional area of the domain is 20% or more;
(2) When the perimeter of a domain is A and the envelope perimeter of the domain is B, A/B is 1.00 or more and 1.10 or less.

According to another aspect of the present disclosure, there is provided a process cartridge that is configured to be detachably mountable to a main body of an electrophotographic image forming apparatus, the process cartridge including the above-mentioned conductive member.
According to yet another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus comprising the above-described conductive member.

According to one embodiment of the present disclosure, it is possible to obtain a conductive member for electrophotography that can be used as a charging member capable of suppressing fogging even when the charging bias is increased.
According to another aspect of the present disclosure, a process cartridge that contributes to the formation of high-quality electrophotographic images can be obtained.
Furthermore, according to another aspect of the present disclosure, it is possible to obtain an electrophotographic image forming apparatus capable of forming high-quality electrophotographic images.

1 is a cross-sectional view of a conductive member according to an embodiment of the present disclosure, taken in a direction perpendicular to the longitudinal direction. 1 is a cross-sectional view of a conductive member according to an embodiment of the present disclosure, taken in a direction perpendicular to the longitudinal direction of a conductive layer. FIG. 4 is an explanatory diagram of impedance measurement of a conductive layer of a conductive member. FIG. 2 is a conceptual diagram illustrating the maximum Feret diameter of a domain according to the present disclosure. FIG. 2 is a conceptual diagram illustrating the envelope perimeter of a domain according to the present disclosure. FIG. 1 is a conceptual diagram of a slice for measuring domain shape according to the present disclosure. FIG. 2 is a cross-sectional view of a process cartridge according to an embodiment of the present disclosure. 1 is a cross-sectional view of an electrophotographic image forming apparatus according to one aspect of the present disclosure.

The present inventors attempted to obtain an electrophotographic image with higher contrast when forming an electrophotographic image using the charging member according to Patent Document 1. Specifically, the charging bias between the charging member and the electrophotographic photosensitive member was increased to a higher voltage (for example, -1500V or higher) than a general charging bias (for example, -1000V). As a result, for example, the reverse toner was developed even in the solid white portion on the photosensitive drum where the toner was not originally developed, and an image with so-called "fog" was formed. In addition, so-called transfer residual toner was adhered to the surface of the charging member, and the charging performance was changed over time.
The present inventors have studied the reason why the charging member according to Patent Document 1 causes fog on an electrophotographic image when the charging bias is increased. In the process, they have focused on the role of the polymer particle phase made of an electronically conductive rubber material in the charging member according to Patent Document 1. That is, it is considered that the polymer particle phase imparts electronic conductivity to the elastic layer by transferring electrons between the polymer continuous phases present in the vicinity in the elastic layer. Then, they have speculated that the occurrence of fog when the charging bias is increased is due to electric field concentration. Electric field concentration is a phenomenon in which current is concentrated at a specific location when electricity is applied.

That is, according to the observations of the present inventors, the polymer particle phase according to Patent Document 1 had an irregular shape and had unevenness on the outer surface. Between such polymer particle phases, the transfer of electrons is concentrated at the convex parts of the polymer particle phase, and the current flow from the vicinity of the conductive support to which the charging bias of the charging member is applied to the outer surface of the charging member becomes uneven. Therefore, the discharge from the outer surface of the charging member to the electrophotographic photosensitive member, which is the member to be charged, becomes uneven, and the surface potential of the electrophotographic photosensitive member also becomes uneven. As a result, it was presumed that fogging occurs in the electrophotographic image.
Therefore, the present inventors have recognized that eliminating the concentration points of electron exchange between polymer particle phases when the charging bias is increased is effective in improving fogging of electrophotographic images.
Based on this recognition, and as a result of further investigation, the present invention has been developed to provide a support having a conductive outer surface,
It has been found that a conductive member having a conductive layer provided on the outer surface of the support and satisfying the following requirements (A) and (B) can effectively suppress fogging of an electrophotographic image even when a high charging bias is applied.
Requirement (A):
The conductive layer has a matrix containing a cross-linked product of the first rubber and a plurality of domains (sea-island structure) dispersed in the matrix, the domains containing a cross-linked product of the second rubber and conductive particles.Furthermore, when a platinum electrode is provided directly on the outer surface of the conductive member and an AC voltage with an amplitude of 1 V and a frequency of 1.0 Hz is applied between the outer surface of the support and the platinum electrode in an environment of a temperature of 23°C and a relative humidity of 50%, the impedance is within the following range.
1.0×10 ³ Ω or more and 1.0×10 ⁸ Ω or less.

Requirement (B):
The length of the conductive layer in the longitudinal direction is L, and the thickness of the conductive layer is T. For each of the cross sections of the conductive layer in the thickness direction at the longitudinal center of the conductive layer and at three locations at L/4 from both ends of the conductive layer toward the center, observation regions of 15 μm square are placed at any three locations in a thickness region from the outer surface of the elastic layer to a depth of 0.1T to 0.9T. At that time, 80% or more by number of the domains observed in each of all nine observation regions satisfy the following requirement (B1) and requirement (B2):
Requirement (B1) The ratio of the cross-sectional area of the conductive particles contained in a domain to the cross-sectional area of the domain is 20% or more;
Requirement (B2): When the perimeter of a domain is A and the envelope perimeter of the domain is B, A/B is 1.00 or more and 1.10 or less.

Each requirement is explained in detail below.
Regarding requirement (A):
Requirement (A) represents the degree of conductivity of the conductive layer. The conductivity of the conductive member is such that the impedance at 1 Hz is in the range of 10 ³ Ω or more and 10 ⁸ Ω or less. By making the impedance 10 ³ Ω or more, an excessive increase in the amount of discharge current is suppressed, and as a result, it is possible to prevent the occurrence of potential unevenness caused by abnormal discharge. Also, by making the impedance 10 ⁸ Ω or less, it is possible to suppress insufficient charging due to an insufficient total amount of discharge charge.

The impedance related to requirement (A) can be measured by the following method.
In order to eliminate the influence of contact resistance between the charged member and the measurement electrode when measuring impedance, it is preferable to form a thin platinum film on the outer surface of the charged member, use the thin film as an electrode, and measure the impedance with two terminals by using the conductive support as a ground electrode.
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 charging member, the method of forming a platinum thin film by deposition is preferred.
When forming a platinum thin film on the surface of a charged member, taking into consideration the simplicity of the process and the uniformity of the thin film, it is preferable to use a vacuum deposition apparatus that is equipped with a mechanism for gripping the charged member and that is further equipped with a rotation mechanism for a charged member having a cylindrical cross section.
For a charged member having a cylindrical cross section, it is preferable to form a platinum electrode with a width of about 10 mm in the longitudinal direction, which is the axial direction of the cylindrical shape, and to connect a metal sheet wrapped around the platinum electrode so as to come into contact with the platinum electrode to a measurement electrode protruding from a measurement device. This makes it possible to perform impedance measurement without being affected by the fluctuation of the outer diameter of the charged member or the surface shape. Aluminum foil, metal tape, etc. can be used as the metal sheet.
The impedance measuring device may be any device capable of measuring impedance, such as an impedance analyzer, a network analyzer, a spectrum analyzer, etc. Among these, it is preferable to measure the impedance using an impedance analyzer because of the electric resistance range of the charging member.
Fig. 3 shows a schematic diagram of a state in which a measurement electrode is formed on a conductive member. In Fig. 3, 31 is a conductive support, 32 is a conductive layer, 33 is a platinum vapor deposition layer which is a measurement electrode, and 34 is an aluminum sheet. Fig. 3(a) shows a perspective view, and Fig. 3(b) shows a cross-sectional view. As shown in the figure, it is important to sandwich the conductive layer 32 between the conductive support 31 and the conductor layer 33 of the measurement electrode.

The aluminum sheet 34 is then connected to the measuring electrode 33 and the conductive support 31 in an impedance measuring device (Solatron 126096W type dielectric impedance measuring system, manufactured by Toyo Corporation, not shown), and impedance measurement is performed.
The impedance is measured in an environment of a temperature of 23° C. and a relative humidity of 50%, with an oscillating voltage of 1 Vpp and a frequency of 1.0 Hz, to obtain the absolute value of the impedance.
The conductive member is divided into five equal regions in the longitudinal direction, and the above measurement is carried out five times in total, once in each region at random, and the average value is regarded as the impedance of the conductive member.

Requirement (B)
Among the requirements (B), the requirement (B1) specifies the amount of conductive particles contained in each of the domains contained in the conductive layer, and the requirement (B2) specifies that the outer peripheral surface of the domain has little or no irregularities.
When the conductive member described in Patent Document 1 was analyzed, it was confirmed that the domains had irregularities or a shape with a high aspect ratio. As a result of intensive investigation, it was found that the above-mentioned problem of fogging during application of a high voltage can be dramatically suppressed by making the shape of the domain closer to a perfect circle with fewer irregularities.
As described above, in a conductive domain/non-conductive matrix configuration in which only the domains are conductive, multiple domains are conductive inside the conductive member, and charge is exchanged between the domains. If a domain has a convex portion, the electric field is concentrated at the convex portion, making it easier for charge to be exchanged between adjacent domains at the convex portion, and an excessive current flows in the convex portion. In other words, charge is easier to flow from the convex portion of a domain to a domain close to the convex portion. This phenomenon generates strong localized discharges from the surface of the conductive member, causing potential unevenness in the photoconductor when the conductive member is used as a charging member.

In other words, it is effective to make the domain as close to a perfect circle as possible.
Regarding requirement (B1), the present inventors have found that, when focusing on one domain, the amount of conductive particles contained in the domain affects the outer shape of the domain. That is, the inventors have found that as the filling amount of conductive particles in one domain increases, the outer shape of the domain becomes closer to a sphere. The more domains that are closer to a sphere, the fewer the concentration points of electron exchange between domains can be. As a result, the fogging of electrophotographic images observed in the charging member according to Patent Document 1 can be reduced.
According to the study by the present inventors, a domain in which the ratio of the total cross-sectional area of the conductive particles observed in a cross-section to the area of the cross-section of the domain is 20% or more can have an outer shape that can significantly alleviate the concentration of electron exchange between the domains. Specifically, the domain can have a shape closer to a sphere.
The requirement (B2) specifies the degree of the presence of irregularities on the outer peripheral surface of the domain that may become points of concentration for the exchange of electrons.
That is, when the perimeter of a domain is A and the envelope perimeter of the domain is B, when the value (A/B) of the requirement (B2) indicating the degree of unevenness is 1.00, it indicates that there is no unevenness, and the concentration of the electric field can be more reliably suppressed. Also, the larger the value of the requirement (B2), the more uneven the shape is. The larger this value, the more likely the electric field is to concentrate at the convex parts because the domain has an uneven shape. It was found that the electric field concentration caused by the convex parts of the domain shape can be suppressed by setting the value of the requirement (B2) to 1.10 or less. The envelope perimeter is the perimeter (dashed line 52) when the convex parts of the domain 51 observed in the observation area are connected to each other and the perimeter of the concave parts is ignored, as shown in FIG. 5.

From the above results, the inventors have found that when 80% or more of the domains in the cross section of the conductive layer observed in each of the nine observation regions simultaneously satisfy requirements (A) and (B), it is possible to suppress electric field concentration inside the conductive member and achieve uniform discharge. As a result, it is possible to suppress fogging on the photoconductor when a high voltage is applied as a charging member. In requirement (B), the domain observation target is within a depth range of 0.1T to 0.9T from the outer surface of the conductive layer in the cross section in the thickness direction of the conductive layer. This is because it is believed that the movement of electrons in the conductive layer from the conductive support side to the outer surface side of the conductive layer is mainly controlled by the domains present within that range.

The present inventors further investigated the adhesion of toner to the surface, which changes the charging performance of the charging member according to Patent Document 1 over time. The toner remaining on the photoconductor even after the transfer process (hereinafter also referred to as "transfer residual toner") is often charged with the same polarity (positive polarity) as the polarity of the voltage in the transfer process. Therefore, the transfer residual toner that reaches the nip between the photoconductor and the charging member electrostatically adheres to the surface of the charging member. As a result, the surface of the charging member is gradually contaminated with the transfer residual toner, which may inhibit stable discharge from the surface of the charging member. In order to suppress the electrostatic adhesion of the transfer residual toner to the outer surface of the charging member, it is effective to reverse the charge of the transfer residual toner.

Here, the present inventors have investigated reversing the charge of the residual toner using a conductive member that satisfies the above-mentioned requirements (A) and (B), which can effectively suppress fogging of an electrophotographic image even when a high charging bias is applied. As a result, in addition to the above-mentioned requirements (A) and (B), it has been found that exposing at least a part of the domain to the outer surface of the conductive member and generating a convex portion derived from the domain on the outer surface of the conductive member (hereinafter also referred to as requirement (C)) is extremely effective in reversing the charge of the residual toner.

By exposing the domains on the outer surface of the conductive member and forming the convex portions, the transfer residual toner that reaches the nip portion between the charging member and the photosensitive drum is likely to come into physical contact with the convex portions. In addition, the transfer residual toner that is positively charged is electrostatically attracted to the convex portions that have accumulated negative charges. These actions increase the probability of contact between the transfer residual toner and the convex portions derived from the domains. Then, the transfer residual toner that comes into contact with the convex portions is injected with negative charges and becomes negative.
In addition, the domain that has transferred the charge to the residual toner by contacting the residual toner can receive a stable and continuous supply of charge from other domains in the conductive layer, which is believed to make it possible to more reliably convert the residual toner that reaches the nip portion into a negative charge.

Specifically, the height of the convex portions originating from the domains on the outer surface of the conductive member is preferably 50 nm or more and 200 nm or less. By making the convex portions 50 nm or more in height, the contact opportunity between the conductive convex portions and the inverted toner can be increased. Furthermore, by making the height 100 nm or more, the contact opportunity can be further increased and inverted toner fogging can be reduced. On the other hand, since uneven discharge originating from the convex portions is formed in the discharge area, the height of the convex portions is preferably 200 nm or less.

In addition, the arithmetic mean value Dm of the distance between the wall surfaces of the domains on the outer surface of the conductive member (hereinafter, simply referred to as "domain distance Dm") is preferably 2.00 μm or less. By setting the domain distance Dm to 2.00 μm or less, the opportunity for contact between the convex portions resulting from the conductive domains and the inverted toner can be increased.

Therefore, the conductive member makes the domains closer to a perfect circle due to the requirements (A) and (B), suppressing the concentration of the electric field in the conductive layer, and furthermore, due to the requirement (C), suppresses reverse toner adhesion by injection charging due to the convex parts derived from the domains. As a result, it is possible to significantly reduce fogging even when the charging bias is high.

<Conductive member>
As one embodiment of the conductive member for electrophotography according to the present disclosure, a conductive member having a roller shape (hereinafter, also referred to as a "conductive roller") will be described with reference to the drawings.
1 is a cross-sectional view perpendicular to the direction along the axis of the conductive roller (hereinafter also referred to as the "longitudinal direction") The conductive roller 1 has a cylindrical conductive support 2 and a conductive layer formed on the outer periphery of the support 2, i.e., on the outer surface of the support.
2 shows a cross-sectional view of the conductive layer 3 in a direction perpendicular to the longitudinal direction of the conductive roller. The conductive layer 3 has a matrix-domain structure having a matrix 3a and domains 3b. The domains 3b contain conductive particles (not shown). Furthermore, a part of the domains 3b is exposed on the outer surface of the conductive member, that is, the surface facing a member to be charged such as a photoconductor. The domains 3b exposed on the outer surface generate convex portions on the outer surface of the conductive member.

<How to confirm the matrix-domain structure>
The presence of the matrix-domain structure can be confirmed, for example, as follows. Specifically, a thin piece of the conductive layer is prepared from the conductive member and a detailed observation is performed. Examples of a means for forming a thin piece include a sharp razor, a microtome, and an FIB. In addition, in order to favorably perform observation of the matrix-domain structure, a pretreatment such as a dyeing treatment or a deposition treatment may be performed to favorably obtain a contrast between the conductive phase and the insulating phase. The thin piece after the formation of the fracture surface and the pretreatment can be observed with a laser microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM).

The conductivity of the conductive member may be evaluated by impedance measurement at 1 Hz, and specifically, the impedance at 1 Hz is preferably in the range of 10 ³ Ω to 10 ⁸ Ω. By making it ^{10 3} Ω or more, the discharge current amount becomes excessive, and as a result, it is possible to prevent potential unevenness caused by abnormal discharge. By making it ^{10 8} Ω or less, it is possible to suppress insufficient charging due to insufficient total amount of discharge charge.

<Conductive Support>
The material constituting the support can be appropriately selected from materials known in the field of electroconductive members for electrophotography and materials usable as conductive members, and examples thereof 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 treatment with chromium, nickel, etc. As the type of plating, either electric plating or electroless plating can be used. From the viewpoint of dimensional stability, electroless plating is preferred. As the type of electroless plating used here, nickel plating, copper plating, gold plating, and various other alloy platings can be mentioned. 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 may be a solid cylindrical shape or a hollow cylindrical shape (cylindrical shape). In addition, the outer diameter of the support is preferably in the range of 3 mm or more and 10 mm or less.

<Conductive Layer>
<The Matrix>
The matrix contains a first cross-linked rubber. The matrix preferably has a volume resistivity ρm of 1.0×10 ⁸ Ωcm or more and 1.0×10 ¹⁷ Ωcm or less.
When the volume resistivity of the matrix is 1.0×10 ⁸ Ωcm or more, the effect of the conductivity of the matrix on the transfer of charges between conductive domains can be suppressed. In particular, when the conductivity of the matrix is high (volume resistivity is low) and the matrix exhibits ionic conductivity, the matrix excessively promotes the transfer of charges between conductive domains, and when electric field concentration occurs due to a slight change in the domain shape, an excessive current tends to flow. Therefore, in order to suppress the ionic conductivity of the matrix, the volume resistivity ρm is preferably 1.0×10 ⁸ Ωcm or more.
When the volume resistivity ρm is 1.0×10 ¹⁷ Ωcm or less, the necessary conductivity can be obtained for the entire conductive layer without impeding the transfer of charges between conductive domains, and image defects due to insufficient charging can be prevented.
The volume resistivity ρm is more preferably 1.0×10 ¹⁰ Ωcm or more and 1.0×10 ¹⁷ Ωcm or less. Within this range, the influence of the ionic conductivity of the matrix can be suppressed, and the volume resistivity required for the conductive member can be obtained. The most preferable range of the volume resistivity ρm is 1.0×10 ¹² Ωcm or more and 1.0×10 ¹⁷ Ωcm or less. Within this range, even when a high voltage is applied, electric field concentration can be strongly suppressed, and the volume resistivity required for the conductive member can be obtained.

<Volume resistivity ρm of matrix>
The volume resistivity ρm of the matrix can be measured, for example, by cutting a slice of a predetermined thickness (e.g., 1 μm) containing a matrix domain structure from the conductive layer and contacting the matrix in the slice with a microprobe of a scanning probe microscope (SPM) or an atomic force microscope (AFM).
For example, as shown in Fig. 6(a), the slice is cut out from the elastic layer so as to include at least a part of the XZ plane and the flat cross section 62a, where the longitudinal direction of the conductive member is the X axis, the thickness direction of the conductive layer is the Z axis, and the circumferential direction is the Y axis. Alternatively, as shown in Fig. 6(b), the slice is cut out so as to include at least a part of the YZ plane (e.g., 63a, 63b, 63c) perpendicular to the axial direction of the conductive member. For example, a sharp razor, a microtome, a focused ion beam method (FIB), etc. can be used.
To measure the volume resistivity, one side of a flake cut from the conductive layer is grounded. Next, a minute probe of a scanning probe microscope (SPM) or an atomic force microscope (AFM) is brought into contact with the matrix of the surface opposite to the ground surface of the flake, a DC voltage of 50V is applied for 5 seconds, and the arithmetic average value is calculated from the ground current value measured for 5 seconds, and the applied voltage is divided by the calculated value to calculate the electrical resistance value. Finally, the resistance value is converted to volume resistivity using the film thickness of the flake. At this time, the SPM or AFM can measure the film thickness of the flake at the same time as the resistance value.
The volume resistivity value of the matrix in a cylindrical charging member is determined, for example, by cutting out one thin sample from each of the regions obtained by dividing the conductive layer into four in the circumferential direction and five in the longitudinal direction, obtaining the above-mentioned measured values, and then calculating the arithmetic average value of the volume resistivities of a total of 20 samples.

<First Rubber>
The first rubber is the component with the largest compounding ratio in the rubber mixture for forming the conductive layer, and the crosslinked product of the first rubber governs the mechanical strength of the conductive layer. Therefore, the first rubber is used to provide the conductive layer with the strength required for a conductive member for electrophotography after crosslinking, and is capable of phase separation with the second rubber described below to form a matrix-domain structure.

Preferred examples of the first rubber are given below.
Examples of such rubber include 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), and silicone rubber.
<Reinforcing material>
In addition, reinforcing carbon black can be blended as a reinforcing agent in the matrix to the extent that it does not affect the electrical conductivity of the matrix. Examples of the reinforcing carbon black used here include FEF, GPF, SRF, and MT carbon, which have low electrical conductivity.
Furthermore, to the first rubber forming the matrix, 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, may be added as necessary.

<Domain>
The domain is conductive and includes a cross-linked second rubber and conductive particles, where conductive means that the volume resistivity is less than 1.0×10 ⁸ Ωcm.

<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), crumbrene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U).

<Conductive particles>
Examples of conductive particles to be blended in the domain include carbon materials such as conductive carbon black and graphite, oxides such as titanium oxide and tin oxide, metals such as Cu and Ag, and electron conductors such as particles that are surface-coated with an oxide or metal to make them conductive. If necessary, two or more types of these conductive particles may be blended in appropriate amounts and used.
The conductive particles to be mixed 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% to 30%, as specified in requirement (B1). By being in the above range, the conductive particles can be densely packed into the domains. The outer shape of the domain can be made closer to a sphere, and unevenness can be reduced as specified in requirement (B2). Furthermore, a sufficient amount of charge can be supplied even under high-speed processing.
Among the above conductive particles, conductive particles containing conductive carbon black as a main component are preferred because of high conductivity, high affinity with rubber, easy control of the distance between conductive particles, etc. The type of conductive carbon black to be blended into the domain is not particularly limited. Specific examples include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black. Among them, carbon black having a DBP absorption of 40 cm ³ /100 g or more and 80 cm ³ /100 g or less can be particularly preferably used, as described later.

<Shape of conductive domain>
The inventors have discovered that by making the conductive domains closer to a circular shape, electric field concentration caused by the convex shape of the conductive domains is minimized, thereby suppressing excessive charge movement even when a high voltage is applied, enabling the photoconductor to be uniformly charged, and as a result, fogging can be suppressed.
The shape of the domain is defined as three locations, namely, the center of the conductive layer in the longitudinal direction and two locations at L/4 from both ends toward the center, where L is the length of the conductive layer in the longitudinal direction and T is the thickness of the conductive layer. For each of the three locations, a 15 μm square observation region is placed at any three locations in a thickness region from the outer surface of the conductive layer to a depth of 0.1 T or more and 0.9 T or less, for a cross section in the thickness direction of the conductive layer as shown in FIG. 6(b). The shape of the domain is defined as the shape of the domain observed in each of the nine observation regions.
As explained above, the domain shape is preferably close to a circle. Specifically, 80% or more of the domains in a 15 μm square region of a cross section of the conductive layer in the thickness direction must satisfy the following requirements (B1) and (B2).
Requirement (B1): The ratio of the cross-sectional area of the conductive particles contained in a domain to the cross-sectional area of the domain is 20% or more;
Requirement (B2): When the perimeter of a domain is A and the envelope perimeter of the domain is B, A/B is 1.00 or more and 1.10 or less.

The minimum value of the ratio of the domain perimeter to the domain envelope perimeter in requirement (B2) is 1.00, and a state of 1.00 indicates that the domain is a perfect circle or an ellipse. If the ratio exceeds 1.10, the domain will have a large uneven shape, that is, electric field concentration is likely to occur. If requirement (B2) is satisfied, the electric field concentration is suppressed, and it is possible to suppress fogging.
The maximum Feret diameter Df is the value at which the length of the perpendicular line is the longest when the outer periphery of the observed domain 41 is sandwiched between two parallel lines and the two parallel lines are connected by a perpendicular line, as shown in FIG.
The size of the domain is preferably within a certain range, and the maximum Feret diameter, which is an index representing the domain size, is preferably 0.1 μm or more and 5.0 μm or less. If the maximum Feret diameter is within this range, the domain is likely to have a circular shape.
As a result, fogging is reduced. Also, by making the conductive domains finer, the discharge also becomes finer, which enables higher image quality.

<Method of measuring maximum Feret diameter, area, perimeter, envelope perimeter, and number of domains>
The maximum Feret diameter, area, perimeter, envelope perimeter, and number of domains may be measured as follows. First, a slice is prepared in the same manner as in the measurement of the volume resistivity of the matrix described above. Then, a thin piece having a fracture surface can be formed by means of a freeze fracture method, a cross polisher method, a focused ion beam method (FIB), or the like. In consideration of the smoothness of the fracture surface and pretreatment for observation, the FIB method is preferred. In addition, in order to perform an observation of the matrix-domain structure favorably, a pretreatment such as a dyeing treatment or a deposition treatment may be performed to favorably obtain a contrast between the conductive phase and the insulating phase.
The formed and pretreated thin sections can be observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Among these, it is preferable to observe with an SEM at 1,000 to 100,000 magnifications in terms of the accuracy of quantifying the area of the domains.
The maximum Feret diameter, area, perimeter, envelope perimeter, and number of domains of the domains can be measured by quantifying the captured image as described above. That is, the fracture surface image obtained by observation with a SEM is converted to 8-bit grayscale using image processing software (product name: ImageProPlus, manufactured by Media Cybernetics) or the like to obtain a monochrome image with 256 gradations. Next, the black and white of the image are inverted and binarized so that the domains in the fracture surface become white. Next, the maximum Feret diameter, area, perimeter, envelope perimeter, and number of domains can be calculated from each of the domain groups in the image.
For the above measurement, a sample is cut out from three locations, namely, 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. The direction in which the slices are cut out is the direction that forms a cross section perpendicular to the longitudinal direction of the conductive layer.
The reason for evaluating the shape of the domain in a cross section perpendicular to the longitudinal direction of the conductive layer as described above will be described with reference to FIG.
6 shows a diagram illustrating the shape of the conductive member 61 in three dimensions along three axes, specifically, the X, Y, and Z axes. In Fig. 6, the X axis indicates a direction parallel to the longitudinal direction (axial direction) of the conductive member, and the Y and Z axes indicate directions perpendicular to the axial direction of the conductive member.

FIG. 6A shows an image of a conductive member cut out at a cross section 62a parallel to an XZ plane 62. The XZ plane can rotate 360° around the axis of the conductive member. Considering that the conductive member rotates in contact with the photosensitive drum and discharges when passing through a gap between the photosensitive drum, the cross section 62a parallel to the XZ plane 62 indicates a surface on which discharge occurs simultaneously at a certain timing. Therefore, the surface equivalent to a certain amount of the cross section 62a passes, forming the surface potential of the photosensitive drum. Since the locally large discharge caused by the electric field concentration in the conductive member locally increases the surface potential of the photosensitive drum and causes fogging, an evaluation is required that correlates with the surface potential of the photosensitive drum formed by the passage of a set of the cross sections 62a rather than a single cross section 62a of a certain amount. Therefore, rather than analyzing a cross section where discharge occurs simultaneously at a certain moment like the cross section 62a, an evaluation is required on cross sections (63a to 63c) parallel to the YZ plane 63 perpendicular to the axial direction of the conductive member, which allows evaluation of the domain shape including the certain amount of the cross sections 62a. When the longitudinal length of the conductive layer is L, three cross sections 63a to 63c are selected: cross section 63b at the longitudinal center of the conductive layer, and two cross sections (63a and 63c) at L/4 from both ends of the conductive layer toward the center.
The observation positions of each of the cross sections 63a to 63c are as follows: when the thickness of the conductive layer is T, three arbitrary positions are specified in a thickness region from the outer surface of each of the cross sections to a depth of 0.1T to 0.9T. When an observation region of 15 μm square is placed at the three arbitrary positions, a total of nine positions are measured.

<Control of domain shape>
The formation of nearly circular domains in the matrix-domain structure is an important point in realizing the effects of the present disclosure. The formation of nearly circular domains and the reduction of size unevenness in the maximum Feret diameter suppress electric field concentration and domain deformation, thereby reducing resistance fluctuations.
The present inventors have investigated methods for making the cross-sectional shape of the domain circular, that is, for making the domain shape closer to a sphere, and have found that this can be achieved by using the following two methods.
- Reduce the domain size (maximum Feret diameter).
-Increase the amount of carbon gel in the domain.
The reason why the domains become closer to a spherical shape by reducing the domain size (maximum Feret diameter) is speculated to be as follows. Even with the same domain volume fraction, if the domain size is small, the surface area of the domain increases, and as a result, the interface with the matrix increases. Molecules near the interface have more different molecules surrounding them than inside the matrix, and therefore have greater free energy than molecules inside the domain. In order to reduce this interfacial free energy, interfacial tension acts to reduce the interface, and it is thought that the domains become closer to a spherical shape (circular in the cross section in the thickness direction of the conductive layer). As a result, electric field concentration can be suppressed.

・Method to reduce domain size (maximum Feret diameter) Regarding the dispersed particle diameter (domain size) D when two incompatible polymers are melt-kneaded, the Taylor formula, Wu's empirical formula, and Tokita's formula shown in the following formulas (4) to (7) have been proposed (see Sumitomo Chemical Technical Journal 2003-II, 42).
Taylor's formula (4)
D = [C σ / ηm γ] f (ηm / ηd)
Wu's empirical formula (5)
γ D ηm / σ = 4 (ηd / ηm) ^0.84 ηd / ηm > 1
Equation (6)
γ D ηm / σ = 4 (ηd / ηm) ^{- 0.84} ηd / ηm < 1

In formulas (4) to (7),
D: domain size, C: constant, σ: interfacial tension,
ηm: viscosity of the matrix, ηd: viscosity of the domain,
γ: shear rate, η: viscosity of the mixed system, P: probability of collision and coalescence, φ: domain phase volume, and EDK: domain phase cleavage energy.

As shown in the above formula, the formation of nearly spherical domains can be controlled mainly by the following four points.
1. Interfacial tension difference between domain and matrix 2. Viscosity ratio of domain to matrix 3. Shear rate during mixing/amount of energy during shear 4. Volume fraction of domain

1. Difference in interfacial tension between domain and matrix Generally, when two types of polymers are mixed, phase separation occurs. This phenomenon occurs because the interaction between the same polymers is stronger than the interaction between different polymers, so the same polymers aggregate with each other to reduce the free energy and stabilize. Since the interface of the phase-separated structure comes into contact with different polymers, the free energy is higher than the interior, which is stabilized by the interaction between the same molecules. As a result, in order to reduce the free energy of the interface, interfacial tension is generated that tries to reduce the area of contact with the different polymers. When this interfacial tension is small, the different polymers tend to be mixed more uniformly in order to increase the entropy. The state of uniform mixing is dissolution, and the SP value, which is an indicator of solubility, tends to correlate with the interfacial tension. In other words, the interfacial tension difference between the domain and matrix is thought to correlate with the SP value difference of the rubber material that constitutes the domain and matrix, so it is possible to control it by selecting the raw rubber of the matrix and domain. If the difference in absolute value of the solubility parameters of the first rubber and the second rubber is 0.4 (J/ ^cm3 ) ^0.5 or more and 4.0 (J/ ^cm3 ) ^0.5 or less, a stable phase separation structure can be formed. More preferably, it is 0.4 (J/ ^cm3 ) ^0.5 or more and 2.2 (J/ ^cm3 ) ^0.5 or less. If it is within this range, a stable phase separation structure can be formed and the maximum Feret diameter of the domain can also be reduced.

2. Viscosity ratio of domain and matrix The closer the viscosity ratio of domain and matrix (ηd/ηm) is to 1, the smaller the maximum Feret diameter of the domain can be. The viscosity ratio of domain and matrix can be adjusted by selecting the Mooney viscosity of the rubber raw material and by mixing the type and amount of filler. It can also be adjusted by adding a plasticizer such as paraffin oil to an extent that does not interfere with the formation of a phase separation structure. The viscosity ratio can also be adjusted by adjusting the temperature during kneading. The viscosity of the domain and matrix can be obtained by measuring the Mooney viscosity ML (1+4) at the rubber temperature during kneading based on JIS K6300-1:2013. It may also be replaced with the catalog value of the raw rubber.

3. Shear rate during mixing/amount of energy during shear The higher the shear rate during mixing/amount of energy during shear, the smaller the maximum Feret diameter of the domain can be. The shear rate can be increased by increasing the inner diameter of the stirring members such as the blades and screws of the kneader, reducing the gap from the end face of the stirring member to the inner wall of the kneader, or increasing the rotation speed. In addition, the energy during shear can be increased by increasing the rotation speed of the stirring members or increasing the viscosity of the domain raw material rubber and the matrix raw material rubber.

4. Domain volume fraction The domain volume fraction in the conductive layer correlates with the probability of collision and coalescence between the domain and the matrix. Specifically, reducing the volume fraction in the conductive layer reduces the probability of collision and coalescence between the domain and the matrix. In other words, the domain size can be reduced by reducing the domain volume fraction within the range that provides the required conductivity.

<Method of Measuring SP Value>
The SP value of the rubber constituting the matrix and the domain can be calculated with high accuracy by creating a calibration curve using a material with a known SP value. The known SP value can also be a catalog value of the material manufacturer. For example, the SP value of NBR and SBR that can be used in the present disclosure is determined almost entirely by the content ratio of acrylonitrile and styrene, regardless of the molecular weight. Therefore, the content ratio of acrylonitrile or styrene of the rubber constituting the matrix and the domain is analyzed using analytical methods such as pyrolysis gas chromatography (Py-GC) and solid-state NMR. This allows the SP value to be calculated from a calibration curve obtained from a material with a known SP value.
In addition, the SP value of isoprene rubber is determined by the isomer structure of 1,2-polyisoprene, 1,3-polyisoprene, 3,4-polyisoprene, cis-1,4-polyisoprene, trans-1,4-polyisoprene, etc. Therefore, like SBR and NBR, the isomer content ratio is analyzed by Py-GC, solid-state NMR, etc., and the SP value can be calculated from materials whose SP values are known.
The SP values of materials with known SP values were determined by the Hansen sphere method.

Next, we will explain why the domains become closer to a spherical shape by increasing the amount of carbon gel in the domains. Carbon gel is a particulate substance that is in a pseudo-crosslinked state due to rubber molecules being adsorbed onto the carbon black. Carbon gel does not dissolve even in organic solvents that dissolve raw rubber. In other words, it is three-dimensionally crosslinked due to physical and chemical adsorption of rubber molecules onto the carbon black surface, and is thought to behave as rubber particles. As a result, it is speculated that the rubber particles formed by the carbon gel act as nuclei to form domains. By increasing the amount of carbon gel, it is possible to suppress the uneven shape of the domains and electric field concentration, as required by the above-mentioned requirement (B2).

In order to increase the amount of carbon gel, it is preferable to compound a large amount of carbon black with respect to the rubber, and the amount of carbon black that functions as an adsorbent can be increased.
As an index for incorporating a large amount of carbon black into the domain, attention was focused on DBP absorption. DBP absorption ( ^cm3 /100g) is the volume of dibutyl phthalate (DBP) that can be adsorbed by 100g of carbon black, and is measured in accordance with JIS K 6217.
Generally, carbon black has a cluster-like higher-order structure in which primary particles having an average particle size of 10 nm to 50 nm are aggregated. This cluster-like higher-order structure is called structure, and its degree is quantified by DBP absorption ( ^cm3 /100g).
Generally, carbon black with a developed structure has a high reinforcing property for rubber, which makes it difficult to incorporate the carbon black into rubber and also makes the shear torque during kneading very high, making it difficult to fill in large amounts.
The conductive carbon black used in the present disclosure is preferably one having a DBP absorption of 40 ^cm3 /100g or more and 80 ^cm3 /100g or less. By adjusting the DBP absorption to the above range, a large amount of carbon black is blended into the rubber, and the amount of carbon gel increases.
Furthermore, if the DBP absorption is within the above range, the conductive carbon black has a small structure, and therefore the carbon black disperses well in the rubber, so there is little aggregation of the carbon black, and the carbon black alone has little unevenness. Therefore, it is easy to make the domain shape round. When carbon black with a developed structure is used, it is difficult to disperse uniformly in the rubber, and the carbon black tends to disperse in an aggregated state. Originally, carbon black has an uneven shape because it has a tuft-like high-order structure as described above, but when these aggregate, they tend to become a mass with a larger uneven structure. When these carbon black aggregates exist on the outer edge of the domain, they may affect the domain shape and form an uneven structure.

In addition, the amount of conductive carbon black to be mixed into the domain is preferably such that the arithmetic mean of the distance between adjacent carbons, C (hereinafter also referred to as the "arithmetic mean wall distance C"), is 110 nm or more and 130 nm or less. If the arithmetic mean wall distance C is 110 nm or more and 130 nm or less, the transfer of electrons between carbon black particles by the tunnel effect is possible between almost all carbon black particles in the domain. In other words, if the above arithmetic mean wall distance is satisfied, the volume resistivity of the domain becomes almost constant, and electric field concentration is suppressed. In addition, resistance fluctuation due to changes in the carbon black wall distance due to repeated image output is suppressed. Furthermore, the amount of carbon gel that shows crosslinked rubber properties increases in the rubber in which carbon black is dispersed, making it easier to maintain the shape, and making it easier to maintain the domain in a circular shape during molding. As a result, electric field concentration and changes in the domain distance due to deformation of the domain convex parts are suppressed, making it easier to achieve uniform discharge.
Furthermore, it is more preferable that the arithmetic mean wall-to-wall distance C of the conductive carbon black is 110 nm or more and 130 nm or less, and the standard deviation of the distribution of the wall-to-wall distance of the conductive carbon black is σm. At that time, it is more preferable that the coefficient of variation σm/C of the wall-to-wall distance of the conductive carbon black is 0.0 or more and 0.3 or less. The coefficient of variation is a value indicating the variation of the wall-to-wall distance of the conductive carbon black, and is 0.0 when all the wall-to-wall distances of the conductive carbon black are the same.
When the coefficient of variation σm/C is 0.0 or more and 0.3 or less, the variation in the wall distance between the carbon blacks is small, so that electrons can be exchanged between the carbon blacks in the domains by the tunnel effect, and the volume resistivity tends to be almost constant. Furthermore, since the carbon black is uniformly dispersed, uneven distribution of the conductive paths in the domains can be suppressed, and electric field concentration in the domains can be suppressed. As a result, in addition to the domain shape, electric field concentration in the domains can be suppressed, making it easier to achieve more uniform discharge.

The arithmetic mean value C of the distance between the conductive carbon black walls in a domain and the ratio of the carbon black cross section to the domain cross section area may be measured as follows. First, a thin piece of the conductive layer is prepared. In order to favorably observe the matrix-domain structure, a pretreatment such as a dyeing treatment or a deposition treatment may be performed to favorably obtain a contrast between the conductive phase and the insulating phase.
The formed and pretreated thin pieces can be observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Among these, it is preferable to observe with an SEM at 1,000 to 100,000 times magnification in view of the accuracy of quantifying the area of the domains that are the conductive phase. The obtained observation image is binarized and analyzed using an image analyzer or the like to obtain the above arithmetic mean wall-to-wall distance and the above ratio.

<Method of forming convex portions derived from domains>
The convex portions derived from the domains can be formed by grinding the surface of the conductive member. The inventors believe that the convex portions derived from the domains can be suitably formed by a grinding step using a grindstone because the conductive layer has a matrix-domain structure. The convex portions derived from the domains are preferably formed by a method of grinding with a grindstone using a plunge type grinder.
The following is a speculated mechanism by which the domain-derived convex portion can be formed by grinding with a grindstone. First, the domain dispersed in the matrix is filled with conductive particles such as carbon black, and has a higher reinforcing property than the matrix not filled with conductive particles. In other words, when grinding is performed with the same grindstone, the domain is more difficult to grind than the matrix because of its high reinforcing property, and convex portions are more likely to be formed. By utilizing the difference in grinding property caused by this difference in reinforcing property, convex portions derived from the domain can be formed. In particular, since the conductive member according to this embodiment has a configuration in which many conductive particles are filled in the domain, it is possible to preferably form the convex portion.

Here, we will explain the grinding wheel for the plunge grinder used for grinding. The surface roughness of the grinding wheel can be selected appropriately depending on the grinding efficiency and the type of material constituting the conductive layer. The roughness of the grinding wheel surface can be adjusted by the type of abrasive grain, grain size, degree of bonding, binder, structure (abrasive grain ratio), etc.
The above-mentioned "grain size of abrasive grains" indicates the size of the abrasive grains, and is expressed as #80, for example. The number in this case means the number of meshes per inch (25.4 mm) of the mesh used to select the abrasive grains, and the larger the number, the finer the abrasive grains. The above-mentioned "bonding degree of abrasive grains" indicates hardness, and is expressed by the alphabets A to Z. The closer to A, the softer the bond, and the closer to Z, the harder the bond. The more binder is contained in the abrasive grains, the harder the bond of the grindstone will be. The above-mentioned "structure of abrasive grains (abrasive grain ratio)" indicates the volume ratio of abrasive grains to the total volume of the grindstone, and the size of this structure indicates the coarseness or density of the structure. The larger the number indicating the structure, the coarser the structure. A grindstone with a large structure number and large pores is called a porous grindstone, and has the advantage of preventing clogging and grindstone burn.

In general, this grinding wheel can be manufactured by mixing raw materials (abrasive, binder, pore agent, etc.), pressing, drying, sintering, and finishing. As the abrasive grains, green silicon carbide (GC), black silicon carbide (C), white alumina (WA), brown alumina (A), zirconia alumina (Z), etc. can be used. These materials can be used alone or in combination. As the binder, vitrified (V), resinoid (B), resinoid reinforced (BF), rubber (R), silicate (S), magnesia (Mg), shellac (E), etc. can be used as appropriate depending on the application.
Here, the outer diameter shape of the grinding wheel in the longitudinal direction is preferably an inverted crown shape in which the outer diameter gradually decreases from the end to the center so that the conductive roller can be polished into a crown shape. The outer diameter shape of the grinding wheel is preferably an arc curve or a higher order curve of second degree or higher in the longitudinal direction. In addition, the outer diameter shape of the grinding wheel may be a shape expressed by various mathematical formulas such as a quartic curve or a sine function. The outer diameter shape of the grinding wheel is preferably one in which the change in the outer diameter changes smoothly, but it may also be a shape in which the arc curve or the like is approximated to a polygonal shape by straight lines. The width of the grinding wheel in the axial direction is preferably equal to or greater than the axial width of the conductive roller.
By appropriately selecting a grindstone in consideration of the factors listed above and carrying out the grinding step under conditions that promote the difference in grindability between the domain and the matrix, it is possible to form convex portions derived from the domain.

Specifically, conditions under which polishing is suppressed and conditions using abrasive grains with a dull cutting edge are preferred. For example, by shortening the time of the precision polishing step after rough cutting and polishing with a treated grindstone, protrusions derived from the domains can be suitably formed.
The treated grindstone may be, for example, a grindstone that has been treated with a rubber member, specifically, a grindstone that has been dressed with a rubber member containing abrasive grains and then the surface of the grindstone is polished to wear down the abrasive grains.

<Method for measuring protrusions derived from domains>
A flake including the surface is taken out from the conductive layer, and a microprobe is used to confirm and measure the convex shape due to the domain. The surface profile and electrical resistance profile are measured with an SPM for the flake sampled from the conductive member. This makes it possible to confirm that the convex portion is a convex portion derived from the domain. At the same time, the height of the convex portion can be quantified and evaluated from the shape profile. The specific procedure will be described later.

<Method of measuring inter-domain distance Dm on outer surface of conductive member>
When the length of the conductive layer in the longitudinal direction is L and the thickness of the conductive layer is T, a sample is cut out using a razor from three locations, the center of the longitudinal direction of the conductive layer and L/4 from both ends of the conductive layer toward the center, so as to include the outer surface of the charging member. The size of the sample is 2 mm in the circumferential direction and the longitudinal direction of the charging member, and the thickness is the thickness T of the conductive layer. For each of the three samples obtained, an analysis area of 50 μm square is placed at any three locations on the surface corresponding to the outer surface of the charging member, and the three analysis areas are photographed at a magnification of 5000 times using a scanning electron microscope (product name: S-4800, manufactured by Hitachi High-Technologies Corporation). Each of the nine photographed images obtained is binarized using image processing software (product name: LUZEX; manufactured by Nireco Corporation).
The binarization procedure is as follows: the captured image is converted to 8-bit grayscale to obtain a monochrome image with 256 gradations. Then, the captured image is binarized so that the domains in the captured image become black, to obtain a binarized image of the captured image. Next, for each of the nine binarized images, the distance between the walls of the domains is calculated, and their arithmetic mean value is calculated. This value is called Dm. The distance between the walls is the distance between the walls of the closest domains, and can be obtained by setting the measurement parameter to the distance between adjacent walls in the image processing software.

<Method of manufacturing conductive member>
An example of a method for producing a conductive member according to the present disclosure is shown below. In this example, the production method is characterized by including the following steps (A) to (C), but is not particularly limited as long as the configuration of the present disclosure can be achieved.

Step (A): preparing a carbon master batch (hereinafter also referred to as "CMB") for domain formation, comprising carbon black and rubber;
Step (B): preparing a matrix-forming rubber composition (hereinafter also referred to as "MRC");
Step (C): A step of kneading the CMB and the MRC to prepare a rubber composition having a matrix-domain structure.
Step (D): A step of forming a conductive layer on a conductive support by a known method such as extrusion molding, injection molding, or compression molding using the rubber composition prepared in steps (A) to (C).
The conductive layer may be attached to the conductive support via an adhesive as required. The conductive layer formed on the conductive support may be vulcanized as required, polished, and then subjected to a surface treatment such as ultraviolet light treatment.

<Process cartridge>
7 is a schematic cross-sectional view of an electrophotographic process cartridge 100 having a conductive member according to an embodiment of the present disclosure as a charging member (charging roller). This process cartridge is configured to integrate a developing device and a charging device and be detachable from the main body of an electrophotographic device. The developing device is configured to integrate at least a developing roller 103, a toner container 106, and a toner 109, and may include a toner supply roller 104, a developing blade 108, and an agitating blade 110 as necessary. The charging device is configured to integrate at least a photosensitive drum 1-1 and a charging roller 102, and may include a cleaning blade 105 and a waste toner container 107. The charging roller 102, the developing roller 103, the toner supply roller 104, and the developing blade 108 are each configured to be applied with a voltage.

<Electrophotographic Image Forming Apparatus>
FIG. 8 is a schematic diagram of an electrophotographic image forming apparatus 200 using the conductive member according to an embodiment of the present disclosure as a charging member (charging roller). This apparatus is a color electrophotographic apparatus in which the four process cartridges 100 are detachably mounted. Each process cartridge uses toner of each color, black, magenta, yellow, and cyan. The photosensitive drum 201 rotates in the direction of the arrow, is uniformly charged by the charging roller 202 to which a voltage is applied from a charging bias power supply, and an electrostatic latent image is formed on the surface by exposure light 211. Meanwhile, the toner 209 stored in the toner container 206 is supplied to the toner supply roller 204 by the stirring blade 210 and transported onto the developing roller 203. Then, the toner 209 is uniformly coated on the surface of the developing roller 203 by the developing blade 208 arranged in contact with the developing roller 203, and the toner 209 is charged by frictional charging. The electrostatic latent image is developed by the toner 209 transported by the developing roller 203 arranged in contact with the photosensitive drum 101, and is visualized as a toner image.

The visualized toner image on the photosensitive drum is transferred by a primary transfer roller 212 to which a voltage is applied by a primary transfer bias power supply, onto an intermediate transfer belt 215 supported and driven by a tension roller 213 and an intermediate transfer belt drive roller 214. The toner images of each color are superimposed in order to form a color image on the intermediate transfer belt.
A transfer material 219 is fed into the apparatus by a paper feed roller, and is transported between an intermediate transfer belt 215 and a secondary transfer roller 216. A voltage is applied to the secondary transfer roller 216 from a secondary transfer bias power supply, and the secondary transfer roller 216 transfers the color image on the intermediate transfer belt 215 onto the transfer material 219. The transfer material 219 onto which the color image has been transferred is fixed by a fixing device 218, and is then discarded outside the apparatus, completing the printing operation.
Meanwhile, the toner remaining on the photosensitive drum without being transferred is scraped off by a cleaning blade 205 and stored in a waste toner storage container 207, and the above-mentioned process is repeated for the cleaned photosensitive drum 201. In addition, the toner remaining on the primary transfer belt without being transferred is also scraped off by a cleaning device 217.
Although a color electrophotographic device is shown as an example, in a monochrome electrophotographic device (not shown), the process cartridge uses only black toner. A monochrome image is formed directly on the transfer material by the process cartridge and the primary transfer roller (without a secondary transfer roller) without the intermediate transfer belt. The image is then fixed by the fixing device and the paper is discharged outside the device, completing the printing operation.

Next, the conductive members in the examples and comparative examples of this disclosure were made using the materials shown below.

<NBR>
NBR (1) (product name: JSR NBR N230SV, acrylonitrile content: 35%, Mooney viscosity ML (1+4) 100°C: 32, SP value: 20.0 (J/ ^cm3 ) ^0.5 , manufactured by JSR Corporation, abbreviation: N230SV)
NBR (2) (product name: JSR NBR N215SL, acrylonitrile content: 48%, Mooney viscosity ML (1+4) 100°C: 45, SP value: 21.7 (J/ ^cm3 ) ^0.5 , manufactured by JSR Corporation, abbreviation: N215SL)
NBR (3) (product name: Nipol DN401LL, acrylonitrile content: 18.0%, Mooney viscosity ML (1+4) 100°C: 32, SP value: 17.4 (J/ ^cm3 ) ^0.5 , manufactured by Zeon Corporation, abbreviation: DN401LL)
<Isoprene rubber IR>
Isoprene rubber (product name: Nipol IR2200L, Mooney viscosity ML (1+4) 100°C: 70, SP value: 16.5 (J/ ^cm3 ) ^0.5 , manufactured by Zeon Corporation, abbreviation: IR2200L)
<Butadiene rubber BR>
Butadiene rubber (1) (product name: UBEPOL BR130B, Mooney viscosity ML (1+4) 100°C: 29, SP value: 16.8 (J/ ^cm3 ) ^0.5 , manufactured by Ube Industries, Ltd., abbreviation: BR130B)
Butadiene rubber (2) (product name: UBEPOL BR150B, Mooney viscosity ML (1+4) 100°C: 40, SP value: 16.8 (J/ ^cm3 ) ^0.5 , manufactured by Ube Industries, abbreviation: BR150B)
<SBR>
SBR (1) (product name: Asaprene 303, styrene content: 46%, Mooney viscosity ML (1+4) 100° C.: 45, SP value: 17.4 (J/cm ³ ) ^0.5 , manufactured by Asahi Kasei Corporation, abbreviation: A303)
SBR (2) (product name: Tufden 2003, styrene content: 25%, Mooney viscosity ML (1+4) 100° C.: 33, SP value: 17.0 (J/cm ³ ) ^0.5 , manufactured by Asahi Kasei Corporation, abbreviation: T2003)
SBR (3) (product name: Tufden 2100R, styrene content: 25%, Mooney viscosity ML (1+4) 100° C.: 78, SP value: 17.0 (J/cm ³ ) ^0.5 , manufactured by Asahi Kasei Corporation, abbreviation: T2100R)
SBR (4) (product name: Tufden 2000R, styrene content: 25%, Mooney viscosity ML (1+4) 100° C.: 45, SP value: 17.0 (J/cm ³ ) ^0.5 , manufactured by Asahi Kasei Corporation, abbreviation: T2000R)
SBR (5) (product name: Tufden 1000, styrene content: 18%, Mooney viscosity ML (1+4) 100° C.: 45, SP value: 16.8 (J/cm ³ ) ^0.5 , manufactured by Asahi Kasei Corporation, abbreviation: T1000)
<Chloroprene rubber (CR)>
Chloroprene rubber (product name: SKYPRENE B31, Mooney viscosity ML (1+4) 100°C: 40, SP value: 17.4 (J/ ^cm3 ) ^0.5 , manufactured by Tosoh Corporation, abbreviation: B31)
<EPDM>
EPDM (product name: Esprene 505A, Mooney viscosity ML (1+4) 100°C: 47, SP value: 16.0 (J/ ^cm3 ) ^0.5 , manufactured by Sumitomo Chemical Co., Ltd., abbreviation: E505A)

<Conductive particles>
Carbon black (1) (product name: TOKABLACK #5500, DBP absorption: 155 cm ³ /100 g, manufactured by Tokai Carbon Co., Ltd., abbreviation: #5500)
Carbon black (2) (product name: TOKABLACK #7360SB, DBP absorption capacity: 87 cm ³ /100 g, manufactured by Tokai Carbon Co., Ltd., abbreviation: #7360)
Carbon black (3) (product name: TOKABLACK #7270SB, DBP absorption capacity: 62 cm ³ /100 g, manufactured by Tokai Carbon Co., Ltd., abbreviation: #7270)
Carbon black (4) (product name: #44, DBP absorption: 78 cm ³ /100 g, manufactured by Mitsubishi Chemical Corporation, abbreviation: #44)
Carbon black (5) (product name: Asahi #35, DBP absorption: 50 cm ³ /100 g, manufactured by Asahi Carbon Co., Ltd., abbreviation: #35)
Carbon black (6) (product name: #45L, DBP absorption capacity: 45 cm ³ /100 g, manufactured by Mitsubishi Chemical Corporation, abbreviation: #45L)
Tin oxide (product name: S-2000, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd., abbreviation: tin oxide)
<Vulcanizing agent>
Vulcanizing agent (1) (product name: SULFAX PMC, sulfur content 97.5%, manufactured by Tsurumi Chemical Industry Co., Ltd., abbreviation: sulfur)
<Vulcanization accelerator>
Vulcanization accelerator (1) (product name: Sancerer TBZTD, tetrabenzyl thiuram disulfide, manufactured by Sanshin Chemical Industry Co., Ltd., abbreviation: TBZTD)
Vulcanization accelerator (2) (product name: Noccela TBT, tetrabutylthiuram disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., abbreviation: TBT)
Vulcanization accelerator (3) (product name: Noccela EP-60, vulcanization accelerator mixture, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., abbreviation: EP-60)
Vulcanization accelerator (4) (product name: SANTOCURE-TBSI, N-t-butyl-2-benzothiazole sulfenimide, manufactured by FLEXSYS, abbreviation: TBSI)
<Filler>
Filler (1) (product name: Nanox #30, calcium carbonate, manufactured by Maruo Calcium Co., Ltd., abbreviation: #30)
Filler (2) (product name: Nipsil AQ, silica, manufactured by Tosoh Corporation, abbreviation: AQ)

The conductive member, process cartridge, and electrophotographic image forming apparatus of the present disclosure will be specifically described below in detail, but the technical scope of the present disclosure is not limited thereto. First, a method for producing the conductive member in the examples and comparative examples of the present disclosure will be specifically described.
Example 1
[1-1. Preparation of carbon master batch (CMB) for domain formation]
The materials shown in Table 1 in their types and amounts were mixed in a 6 L 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.

[1-2. Preparation of rubber composition for forming matrix]
The materials shown in Table 2 in their types and amounts were mixed in a 6 L pressure kneader (product name: TD6-15MDX, manufactured by Toshin Corporation) to obtain a rubber composition for forming a matrix. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 18 minutes.

The materials shown in Table 3 were mixed in the amounts and types in 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.

2. Forming of conductive member
A round bar with a total length of 252 mm and an outer diameter of 6 mm was prepared, the surface of which was made of free-cutting steel and electroless nickel plating was applied. Next, an adhesive (product name: Metalock U-20, manufactured by Toyo Kagaku Kenkyusho Co., Ltd.) was applied using a roll coater over the entire circumference of the round bar, a range of 230 mm, excluding 11 mm at each end. In this example, the round 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 temperature of the extruder and the crosshead was 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 the conductive resin layer was fed from the extruder, and the outer periphery of the conductive support was coated with the rubber composition for forming the conductive resin layer in the crosshead, to obtain 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, thereby obtaining a conductive roller having a conductive resin layer formed on the outer periphery of the conductive support. Then, 10 mm of each of both ends of the conductive resin layer was cut off, so that the length of the conductive resin layer in the longitudinal direction was 232 mm.

[2-1. Polishing of Conductive Layer]
Next, the surface of the conductive layer was polished under the polishing conditions described below in Polishing Condition 1 to obtain a crown-shaped conductive member 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.
(Polishing Condition 1)
A cylindrical grinding wheel (manufactured by Teiken Co., Ltd.) having a diameter of 305 mm and a length of 235 mm was prepared as the grinding wheel. The type, grain size, degree of bonding, bonding agent, and structure (abrasive grain ratio) of the abrasive grains are 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 rotation speed of the grindstone of 2100 rpm and a rotation speed of the conductive member of 250 rpm, and in the rough cutting process, the grindstone was inserted into the conductive member at a penetration speed of 20 mm/sec, and penetrated 0.24 mm after contacting the outer peripheral surface of the conductive member.
As a precision polishing step, the penetration speed is changed to 0.5 mm/sec., and after penetration of 0.01 mm, the grindstone is removed from the conductive member to complete the polishing.
The polishing method used is the upper cut method in which the grindstone and the conductive member rotate in the same direction.

Conductive members 2 to 45 were produced in the same manner as conductive member 1, except that the starting materials shown in Tables 4-1, 4-2, and 4-3 were used, and the polishing conditions were changed as shown below. The parts by mass and physical properties of the starting materials used to produce each conductive member are shown in Tables 4-1, 4-2, and 4-3.

Polishing conditions 2 to 5 are shown in detail below.
(Polishing Condition 2)
The polishing conditions were the same as those in the polishing conditions 1, except that the penetration speed in the precision polishing step was set to 2.0 mm/sec.
(Polishing Condition 3)
The polishing conditions were the same as those in the polishing conditions 1, except that the penetration speed in the precision polishing step was 1.0 mm/sec.
(Polishing Condition 4)
The polishing conditions were the same as those in the polishing conditions 1, except that the penetration speed in the precision polishing step was set to 0.2 mm/sec.
(Polishing Condition 5)
The polishing conditions were the same as those in the polishing conditions 1, except that the penetration speed in the precision polishing step was changed to 0.1 mm/sec, and polishing was continued for 4 seconds after penetration of 0.01 mm.
The results obtained are shown in Tables 5-1 and 5-2.

3. Characterization
Next, the characteristic evaluations for the following items in the examples and comparative examples of the present disclosure will be described below.
<Confirmation of matrix-domain structure>
The presence or absence of the formation of a matrix-domain structure in the conductive layer is confirmed by the following method.
A slice (500 μm thick) is cut out using a razor so that a cross section perpendicular to the longitudinal direction of the conductive layer of the conductive member can be observed. Next, platinum is evaporated and the cross-sectional image is taken at 1000 times magnification using a scanning electron microscope (SEM) (product name: S-4800, manufactured by Hitachi High-Technologies Corporation).
Furthermore, in order to quantify the captured images, the fracture surface images obtained by SEM observation are converted to 8-bit grayscale using image processing software (product name: ImageProPlus, manufactured by Media Cybernetics, Inc.) to obtain a monochrome image with 256 gradations. Next, the black and white of the image are inverted so that the domains in the fracture surface become white, and then a binarization threshold is set for the brightness distribution of the image based on the algorithm of Otsu's discriminant analysis method to obtain a binarized image.
A counting function is used on the binary image to calculate the number (percentage K) of domains that are isolated and not connected to each other, as described above, out of the total number of domains that exist within a 50 μm square area and have no contact with the border of the binary image.
Specifically, the counting function of the image processing software is set so that domains that have contact points with the frame lines at the four ends of the binary image are not counted.
The conductive layer of the conductive member is divided equally into 5 equal parts in the longitudinal direction and into 4 equal parts in the circumferential direction, and slices are prepared at random points from each of the obtained regions, for a total of 20 points, and the arithmetic average value of K (number %) when the above measurement is performed is calculated.
When the arithmetic mean value of K (number %) is 80 or more, the matrix domain structure is evaluated as "present," and when the arithmetic mean value of K (number %) is below 80, the matrix domain structure is evaluated as "absent."

<Method of measuring maximum Feret diameter, perimeter, and envelope perimeter of a domain>
The maximum Feret diameter, perimeter, and envelope perimeter of the domain according to the present disclosure may be measured as follows.
First, a thin piece having a thickness of 1 μm is cut out from the conductive layer of the conductive member at a cutting temperature of −100° C. using a microtome (product name: Leica EM FCS, manufactured by Leica Microsystems).
The cutting positions from the conductive layer are the center in the longitudinal direction and L/4 from both ends toward the center, where L is the longitudinal length of the conductive layer and T is the thickness of the conductive layer.
Platinum was vapor-deposited on the slice obtained by the above method to obtain a vapor-deposited slice. The surface of the vapor-deposited slice was then photographed at 5,000 times magnification using a scanning electron microscope (SEM) (product name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain a surface image.
The maximum Feret diameter, perimeter, and envelope perimeter of the domain according to the present disclosure can be obtained by quantifying the image captured above. The obtained fracture surface image is converted to 8-bit grayscale using image software (product name: ImageProPlus, manufactured by Media Cybernetics) to obtain a monochrome image with 256 gradations. Next, the black and white of the image are inverted and binarized so that the domains in the fracture surface become white. Next, the maximum Feret diameter, perimeter A, and envelope perimeter B were calculated from each of the domains in the image.
The above measurements were performed on observation areas of 15 μm square at three arbitrary locations in the thickness region from the outer surface to a depth of 0.1T to 0.9T on each of the three slices, for a total of nine locations, where T is the thickness of the conductive layer.
The value of A/B is calculated using the perimeter and envelope perimeter measured for each of the domains observed in each observation region. The percentage of the number of domains that satisfy requirement (B2) among all the observed domains was calculated.
For the domains satisfying the requirements (B1) and (B2), the arithmetic mean value of A/B, which is an index of the irregular shape of the domain, and the arithmetic mean value of the maximum Feret's diameter were calculated. The evaluation results are shown in Table 5-2.

<Method of measuring volume resistivity of matrix>
The volume resistivity of the matrix is measured using a scanning probe microscope (SPM) (trade name: Q-Scope 250, manufactured by Quesant Instrument Corporation) operated in contact mode.
First, a section was cut out at the same position and in the same manner as in the measurement of the maximum Feret diameter, perimeter, envelope perimeter, and number of domains. Next, in an environment of 23° C. and 50% RH, the section was placed on a metal plate, and a part directly in contact with the metal plate was selected, and the part corresponding to the matrix was brought into contact with the cantilever of the SPM. Then, a voltage of 50 V was applied to the cantilever, and the current value was measured.
The surface shape of the measurement piece was observed with the SPM, and the thickness of the measurement point was calculated from the obtained height profile. The volume resistivity was calculated from the thickness and the current value, and was regarded as the volume resistivity of the matrix.
The measurement positions were three arbitrary positions in the matrix portion of each slice in a thickness region from the outer surface to a depth of 0.1T to 0.9T, totaling nine positions, where T is the thickness of the conductive layer. The average value was regarded as the volume resistivity of the matrix. The evaluation results are shown in Table 5-1.

<Method for measuring DBP absorption of carbon black>
The DBP absorption amount of carbon black was measured in accordance with JIS K 6217. Values in the manufacturer's catalog may also be used.
<Method of measuring arithmetic mean C, standard deviation σm, coefficient of variation σm/C of distance between conductive carbon black walls in a domain, and ratio of cross-sectional area of carbon black in a domain to domain area>
The arithmetic mean C of the distance between the conductive carbon black wall surfaces in a domain, the standard deviation σm, the coefficient of variation σm/C, and the ratio of the cross-sectional area of the carbon black contained in the domain to the domain area may be measured as follows.
First, slices are prepared in the same manner as in the method for measuring the maximum Feret diameter, area, perimeter, and envelope perimeter of the domain described above.
Platinum was vapor-deposited on the slice obtained by the above-mentioned method to obtain a vapor-deposited slice. The surface of the vapor-deposited slice was then photographed at 20,000 times magnification using a scanning electron microscope (SEM) (product name: S-4800, manufactured by Hitachi High-Technologies Corporation) to obtain a surface image.
The arithmetic mean wall distance and area of the carbon black in the domain can be obtained by quantifying the photographed image as described above. The fracture surface image obtained by observation with the SEM is converted to 8-bit grayscale using an image analyzer (product name: LUZEX-AP, manufactured by Nireco Corporation) to obtain a monochrome image with 256 gradations. Next, the black and white of the image are inverted and binarized so that the domains in the fracture surface become white.
Next, an observation area large enough to accommodate at least one domain is extracted from the SEM image. Then, the wall-to-wall distance Ci of the carbon black in the domain is calculated. Then, the arithmetic mean of the wall-to-wall distances is calculated to calculate the arithmetic mean wall-to-wall distance C.
The cross-sectional area of the domain and the cross-sectional area of the carbon black within the domain are also calculated from the above SEM image.
The domain cross-sectional area and the arithmetic mean wall-to-wall distance and cross-sectional area of the carbon black in the domain can be obtained as follows: That is, when the thickness of the conductive layer is T, measurements are taken at three arbitrary locations in the domain part in the thickness region from the outer surface of each of the three slices to a depth of 0.1T to 0.9T, for a total of nine locations, and the arithmetic mean of the measured values is calculated.
The standard deviation σm is calculated from the distance between the conductive carbon black walls in the obtained domain and its arithmetic mean C. The standard deviation σm is then divided by the arithmetic mean C to obtain the coefficient of variation σm/C. The percentage of the number of domains that satisfy requirement (B1) among all observed domains was calculated.
For domains satisfying requirements (1) and (2), the arithmetic mean wall distance C of the carbon black, the coefficient of variation σm/C, and the arithmetic mean value of the ratio of the cross-sectional area of the carbon black to the cross-sectional area of the domain were calculated.
The results are shown in Table 5-2.

<SP Values of Rubber Constituting the Matrix and Domain>
The SP value can be measured using a conventional swelling method. The rubber constituting the matrix and the domain is separated using a manipulator or the like, immersed in solvents with different SP values, and the degree of swelling is measured from the change in mass of the rubber. The Hansen solubility parameter (HSP) can be calculated by analyzing using the value of the degree of swelling for each solvent. In addition, it is possible to calculate with high accuracy by creating a calibration curve using a material with a known SP value. The known SP value can also be the catalog value of the material manufacturer. The evaluation results are shown in Table 5-1.

<Analysis of Chemical Composition of First Rubber and Second Rubber>
Identification of the materials, the first rubber and the second rubber, the styrene content in the SBR, and the acrylonitrile content in the NBR can be performed using conventional analytical equipment such as FT-IR and 1H-NMR. The evaluation results are shown in Table 5-1.
<Method of measuring impedance of conductive member>
The impedance of the conductive member was measured by the following method.
First, as a pretreatment, a measurement electrode was prepared by vacuum-depositing platinum on a rotating conductive member. At this time, a masking tape was used to prepare an electrode having a width of 1.5 cm 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 conductive member can be reduced as much as possible. Next, an aluminum sheet was wrapped around the electrode so as to contact the platinum deposition film, and a measurement sample shown in FIG. 3 was formed.
An impedance measuring device (Solatron 126096W, manufactured by Toyo Corporation) was then connected from the aluminum sheet to the measuring electrodes, and to the conductive support.
The impedance was measured in an environment of a temperature of 23° C. and a relative humidity of 50%, with an oscillating voltage of 1 Vpp and a frequency of 1.0 Hz, to obtain the absolute value of the impedance.
The conductive member (length in the longitudinal direction: 232 mm) was divided into five equal regions in the longitudinal direction, and measurement electrodes were formed at one arbitrary point in each region, for a total of five points, and the above measurement was performed. The average value was taken as the impedance of the conductive member. The evaluation results are shown in Table 5-1.

<Measurement of protrusions derived from domains>
A thin slice having a thickness of 1 μm is cut out from the conductive layer of the conductive member using a microtome (product name: Leica EM FCS, manufactured by Leica Microsystems) at a cutting temperature of −100° C. At this time, the thin slice is cut in a plane perpendicular to the axis of the conductive support.
The cutting positions from the conductive layer are set at three locations: the center in the longitudinal direction, and L/4 from both ends of the conductive layer toward the center, where L is the longitudinal length of the conductive layer.
At this time, in order to confirm the convex shape derived from the domain, care should be taken not to apply any processing to the surface of the conductive member. Next, the surface of the conductive member was measured under the following conditions using an SPM (MFP-3D-Origin, manufactured by Oxford Instruments Co., Ltd.) for the slice containing the conductive member surface obtained as described above. The electrical resistance profile and shape profile were measured by this measurement.
・MFP-3D-Origin manufactured by Oxford Instruments Ltd.
Measurement mode: AM-FM mode Probe: Olympus OMCL-AC160TS
・Resonant frequency: 251.825 to 261.08 kHz
Spring constant: 23.59 to 25.18 N/m
・Scan speed: 0.8 to 1.5 Hz
Scan size: 10 μm, 5 μm, 3 μm
Target Amplitude: 3V and 4V
Set Point: All 2V
Next, it is confirmed that the convex portions in the profile of the surface shape obtained by the above measurement are derived from domains that have higher conductivity than the surrounding area in the electrical resistance profile.
Furthermore, the height of the convex shape is calculated from the profile.
The calculation method is to obtain the difference between the arithmetic mean value of the domain-derived shape profile and the arithmetic mean value of the adjacent matrix shape profile, which is calculated from the values measured for 20 randomly selected convex portions in each of the slices cut from the above three locations.
The values are shown in Table 5-2.

<Measurement of Interdomain Distance Dm on the Outer Surface of a Conductive Member>
The domain distance Dm on the outer surface of the conductive member is measured as follows.
When observing the outer surface of the conductive member and measuring Dm, a measurement sample is cut out with a razor from the surface of the conductive member, with a length of about 2 mm in each of the circumferential and longitudinal directions of the conductive layer of the conductive member, and a depth of about 500 μm including the surface of the conductive member in the depth direction. The cutting positions from the conductive layer are the center in the longitudinal direction and three positions at L/4 from both ends of the conductive layer toward the center, where L is the longitudinal length of the conductive layer.
Platinum is vapor-deposited on the surface of the obtained slice corresponding to the outer surface of the conductive member to obtain a vapor-deposited slice. Next, an observation image of the surface of the vapor-deposited slice is obtained at 5000 times magnification using a scanning electron microscope (product name: S-4800, manufactured by Hitachi High-Technologies Corporation). A binary image is obtained from the obtained observation image using image processing software LUZEX (manufactured by Nireco Corporation).
The binarization procedure is as follows: the observed image is converted to 8-bit grayscale to obtain a monochrome image with 256 gradations. Then, the image is inverted to black and white so that the domains in the fracture surface become white, and binarization is performed. Next, the distribution of the distance between the walls of the domains is calculated for the binarized image, and the arithmetic mean value Dm of the distribution is calculated. The distance between the walls is the shortest distance between adjacent domains.
Specifically, in the image processing software, the measurement parameter is set as the distance between adjacent wall surfaces.
The arithmetic mean value of 10 observation images randomly selected on the outer surface of the conductive member is used.
The values are shown in Table 5-2.

4. Image evaluation
[4-1] Fog Evaluation Using the obtained conductive member, an image was formed as follows, and a fog evaluation was performed to check for uneven discharge of the conductive member. As an electrophotographic image forming apparatus, a Laserjet M608dn (product name) manufactured by HP was prepared, which was modified so that a high voltage could be applied to the charging member and the developing member from an external power source (product name: Model 615; manufactured by Trek Japan).
Next, the conductive member, the modified electrophotographic image forming apparatus, and the process cartridge were left in an environment of 30° C. and 80% RH for 48 hours. Then, the conductive member was incorporated as a charging member of the process cartridge. Then, a DC voltage of −1700 V was applied to the conductive support of the conductive member, and a voltage was applied to the developing member so that Vback (a voltage obtained by subtracting the voltage applied to the developing member from the surface potential of the photoconductor) was −350 V, and an all-white image was output.
The developer of this electrophotographic image forming apparatus is negatively charged, so that normally when an all-white image is output, the developer does not transfer to the photoconductor or paper. However, when a positively charged developer is present in the developer, the positively charged developer transfers to the overcharged portion of the photoconductor surface due to a strong localized discharge from the charging member, resulting in so-called inversion fogging. As a result, this becomes evident as fogging on the paper. This phenomenon is more likely to occur when Vback is large, such as -350V.
Using the electrophotographic image forming apparatus thus set, an all-white image was output in an environment of 30° C./80% RH, and the amount of fog on the paper was measured. The amount of fog was measured by the following method. (Measurement of the amount of fog on paper)
A white image was printed on the entire surface, and 9 random points on the paper after the image formation were observed with an optical microscope at 500x magnification, and the number of developer particles present in an observation area of 400 μm square was counted and taken as the amount of fog on the paper. If the amount of fog on the paper is 60 particles or less, a good image with little fog can be obtained. More preferably, it is 50 particles or less. The evaluation results are shown in Table 5.

<Examples 2 to 5>
Conductive members 2 to 5 were produced in the same manner as in Example 1, except that the polishing conditions in Example 1 were changed to polishing conditions 2 to 5, and evaluations were performed in the same manner as in Example 1. The results of each evaluation in Examples 2 to 5 are shown in Tables 5-1 and 5-2.

<Examples 6 to 45>
Similarly to the conductive member 1 in Example 1, conductive members 6 to 45 were used as charging rollers, and evaluations were performed in the same manner as in Example 1. The results of the evaluations in Examples 6 to 45 are shown in Tables 5-1 and 5-2.

<Example 46>
Conductive member 1 of Example 1 was subjected to ultraviolet treatment as a surface treatment to prepare conductive member 46. Except for this, evaluations were performed in the same manner as in Example 1. The evaluation results are shown in Tables 5-1 and 5-2.
(surface UV treatment)
While rotating the conductive member, the surface of the conductive member was irradiated with ultraviolet light for 5 minutes using a low-pressure mercury lamp (Harrison Toshiba Lighting Co., Ltd.). The low-pressure mercury lamp emitted ultraviolet light with a wavelength of 254 nm, and the cumulative amount of ultraviolet light was about 10,000 mJ/ ^cm2 (ultraviolet light intensity was 35 mW/ ^cm2 ).

Comparative Example 1
A conductive layer was produced in the same manner as in Example 1, except that a round bar similar to that in Example 1 was used as the conductive support, the domain-forming carbon master batch (CMB), the matrix-forming rubber composition (MRC), and the conductive layer-forming rubber composition were changed to those shown in Table 6, and the matrix-forming MRC was not used. A surface layer was then formed on the conductive layer as described below, to produce a conductive roller.

The raw materials in Table 6 above are as follows:
CG102: epichlorohydrin rubber (EO-EP-AGE ternary compound) (product name: Epichromer CG102, SP value: 18.5 (J/cm ³ ) 0.5, manufactured by Osaka Soda Co., Ltd.)
LV: Quaternary ammonium salt (product name: Adeka Cizer LV70, manufactured by ADEKA Corporation)
P202: Aliphatic polyester plasticizer (product name: Polycizer P-202, manufactured by DIC Corporation)
MB: 2-mercaptobenzimidazole (product name: Nocrac MB, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
TS: Tetramethylthiuram monosulfide (product name: Noccela TS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
DM: Di-2-benzothiazolyl disulfide (DM) (product name: Noccela DM-P (DM), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
EC600JD: Ketjen Black (product name: Ketjen Black EC600JD, manufactured by Lion Specialty Chemicals Co., Ltd.)
PW380: Paraffin oil (product name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.)
25-B-40: 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne (product name: Perhexa 25B-40, manufactured by Nippon Oil Corporation)
TAIC-M60: Triallyl isocyanurate (product name: TAIC-M60, manufactured by Mitsubishi Chemical Corporation)
Next, a surface layer was further provided on the conductive layer of the conductive layer roller obtained above according to the following method to produce a two-layer conductive member C1, which was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 8.
First, methyl isobutyl ketone was added to the caprolactone-modified acrylic polyol solution to adjust the solid content to 10% by mass. A mixed solution was prepared using the materials shown in Table 7 below for 1000 parts by mass of this acrylic polyol solution (100 parts by mass of solid content). At this time, the mixture of block HDI and block IPDI had an "NCO/OH = 1.0".

Next, 210 g of the mixed solution and 200 g of glass beads having an average particle size of 0.8 mm as media were mixed in a 450 mL glass bottle, and pre-dispersed for 24 hours using a paint shaker disperser to obtain a coating material for forming a surface layer.
The conductive roller obtained above was immersed in the coating material for forming the surface layer by a dipping method with its longitudinal direction being vertical. The immersion time for the dip coating was 9 seconds, and the lifting speed was an initial speed of 20 mm/sec and a final speed of 2 mm/sec, during which the speed was changed linearly with respect to time. The obtained coating material was air-dried at room temperature for 30 minutes, then dried in a hot air circulation dryer set at 90°C for 1 hour, and further dried in a hot air circulation dryer set at 160°C for 1 hour.

In this comparative example, the conductive member C1 has a two-layer structure of an ion-conductive conductive layer and an electron-conductive surface layer, but the surface layer does not have a matrix-domain structure. This reduces the uniformity of dispersion of the conductive particles, causing electric field concentration and making it easy for excess charge to flow through the conductive path. As a result, the number of fogs on the paper was 95.
<Comparative Example 2>
A conductive member C2 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB was changed to one shown in Table 6 and no matrix-forming MRC was used. The evaluation results are shown in Table 8.
In this comparative example, the conductive layer of the conductive member C2 does not have a matrix-domain structure and is composed only of domain materials, so that electric field concentration occurs in the conductive layer and excess charge tends to flow in the conductive path. Therefore, the fog on the paper was 121, and a significant fog image was confirmed.

<Comparative Example 3>
A conductive member C3 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C3 has a domain and a matrix, but the number of domains that satisfy the requirements (B1) and (B2) is small, and the domain shape is irregular, so that excessive charge migration occurs due to electric field concentration resulting from the domain shape. Therefore, the number of fogs on paper was 103.

<Comparative Example 4>
A conductive member C4 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, conductive particles are added to the matrix of the conductive member C4, so the volume resistivity is low, and the conductive member has a single conductive path, so that electric field concentration occurs in the conductive layer and excess charge tends to flow in the conductive path. Therefore, the number of fogs on the paper was 110.

<Comparative Example 5>
A conductive member C5 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C5 has a matrix-domain structure, but since no conductive agent is added to the domain, the volume resistivity is high, and since conductive particles are added to the matrix, the volume resistivity is low. In other words, since the conductive member has a single conductive path, electric field concentration occurs in the conductive layer, and excess charge is likely to flow in the conductive path. Therefore, the number of fogs on the paper was 105.

<Comparative Example 6>
A conductive member C6 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C6 does not have a matrix-domain structure, but has a structure in which the conductive phase and the insulating phase are co-continuous. In other words, since the conductive member has a single conductive path, electric field concentration occurs in the conductive layer, and excess charge is likely to flow in the conductive path. Therefore, the number of paper fogs was 107.

<Comparative Example 7>
A conductive member C7 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C7 has a matrix-domain structure, but the number of domains satisfying the requirements (B1) and (B2) was 80% or less. The reason for this is thought to be that the amount of carbon black added to the domains was small, and the amount of carbon gel was not sufficient to form, so the domain shape was not circular, and the unevenness and aspect ratio became large. As a result, electric field concentration occurred in the conductive layer, and the structure was such that excess charge was likely to flow in the conductive path. Therefore, the number of fogs on the paper was 97.

<Comparative Example 8>
A conductive member C8 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB and the matrix-forming MRC were changed to those shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C8 has a matrix-domain structure, but the number of domains satisfying the requirements (B1) and (B2) was 0%. This is believed to be due to the following two reasons.
(1) Since reinforcing silica is added, the carbon master batch which forms the domains has a high viscosity, and the viscosity difference between the carbon master batch and the rubber composition for forming the matrix is large.
(2) The difference in SP value between the first rubber and the second rubber is large.
Therefore, it is considered that the domain shape was not circular, and the unevenness and aspect ratio became large. As a result, the electric field concentration occurred in the conductive layer, and the configuration was such that excess charge was likely to flow in the conductive path. Therefore, the number of fogs on the paper was 132, and significant fog was confirmed.

<Comparative Example 9>
A conductive member C9 was produced and evaluated in the same manner as in Example 1, except that the domain-forming CMB was changed to rubber particles obtained by heat-vulcanizing the conductive layer-forming rubber of Comparative Example 2 alone and then freezing and pulverizing it, and the matrix-forming MRC was changed to that shown in Table 6. The evaluation results are shown in Table 8.
In this comparative example, the conductive member C9 has a matrix-domain structure, but the domains that satisfy the requirements (B1) and (B2) were 0% by number. The reason for this is that large, anisotropic conductive rubber particles formed by freeze-pulverization are dispersed. As a result, electric field concentration occurs in the conductive layer, and excessive charges tend to flow in the conductive path. Therefore, the number of fogs on the paper was 126, and significant fog was confirmed.

1 Conductive member 2 Conductive support 3 Conductive layer 3a Matrix 3b Domain 3c Conductive particles

Claims (16)

a support having an electrically conductive outer surface;
a conductive layer provided on an outer surface of the support,
the conductive layer has a matrix containing a crosslinked product of a first rubber and a plurality of domains dispersed in the matrix,
The domain comprises a crosslinked product of a second rubber and a conductive particle,
At least a portion of the domain is exposed on an outer surface of the conductive member, forming a protrusion on the outer surface of the conductive member;
the outer surface of the conductive member is composed of the matrix and the domain exposed on the outer surface of the conductive member;
a platinum electrode is provided directly on the outer surface of the conductive member, and an AC voltage having an amplitude of 1 V and a frequency of 1.0 Hz is applied between the outer surface of the support and the platinum electrode in an environment of a temperature of 23° C. and a relative humidity of 50%, and the impedance is 1.0×10 ³ Ω or more and 1.0×10 ⁸ Ω or less;
A conductive member characterized in that, when a length in the longitudinal direction of the conductive layer is L and a thickness of the conductive layer is T, and observation regions of 15 μm square are placed at any three locations in a thickness region from an outer surface of the conductive layer to a depth of 0.1T to 0.9T for each of three locations in a cross section of the conductive layer in the thickness direction, the three locations being the center in the longitudinal direction of the conductive layer and L/4 from both ends of the conductive layer toward the center, 80% or more by number of domains observed in each of all nine observation regions satisfy the following requirement (1) and requirement (2):
Requirement (1) The ratio of the cross-sectional area of the conductive particles contained in a domain to the cross-sectional area of the domain is 20% or more;
Requirement (2) When the perimeter of a domain is A and the envelope perimeter of the domain is B, A/B is 1.00 or more and 1.10 or less. The conductive member according to claim 1, wherein the volume resistivity ρm of the matrix is 1.0×10 ⁸ Ωcm or more and 1.0×10 ¹⁷ Ωcm or less. The conductive member according to claim 1 or 2, wherein the average maximum Feret diameter Df of the domains that satisfy requirements (1) and (2) is in the range of 0.1 μm to 5.0 μm. The conductive member according to any one of claims 1 to 3, wherein the ratio of the cross-sectional area of the conductive particles to the cross-sectional area of the domain in requirement (1) is 25% or more and 30% or less. The conductive member according to any one of claims 1 to 4, wherein the conductive particles are conductive carbon black. 6. The conductive member according to claim 5, wherein the conductive carbon black has a DBP absorption of 40 cm ³ /100 g or more and 80 cm ³ /100 g or less. The conductive member according to claim 5 or 6, wherein the arithmetic mean wall-to-wall distance C of the conductive carbon black contained in each of the domains satisfying requirements (1) and (2) is 110 nm or more and 130 nm or less, and σm/C is 0.0 or more and 0.3 or less, where σm is the standard deviation of the wall-to-wall distance of the conductive carbon black. The conductive member according to any one of claims 1 to 7, wherein a difference in absolute value of solubility parameter between the first rubber and the second rubber is 0.4 (J/cm ³ ) ^0.5 or more and 4.0 (J/cm ³ ) ^0.5 or less. The conductive member according to any one of claims 1 to 8, wherein the height of the protrusions is 50 nm or more and 200 nm or less. The conductive member according to any one of claims 1 to 9, wherein the arithmetic mean value Dm of the distance between the wall surfaces of the domains that generate the convex portions is 2.00 μm or less. The conductive member according to any one of claims 1 to 10, wherein the volume resistivity ρm of the matrix is 1.0 x 10 ¹⁰ Ωcm or more and 1.0 x 10 ¹⁷ Ωcm or less. The conductive member according to any one of claims 1 to 11, wherein the volume resistivity ρm of the matrix is 1.0 x 10 ¹² Ωcm or more and 1.0 x 10 ¹⁷ Ωcm or less. 13. A process cartridge for electrophotography which is detachably mountable to a main body of an electrophotographic image forming apparatus, comprising the conductive member according to claim 1. The process cartridge according to claim 13, wherein the conductive member is provided as a charging member. An electrophotographic image forming apparatus comprising the conductive member according to any one of claims 1 to 12. The electrophotographic image forming apparatus according to claim 15, wherein the conductive member is provided as a charging member.

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