JP2019191564A - Charging member, method for manufacturing charging member, electrophotographic device, and process cartridge - Google Patents

Abstract

To provide a charging member that achieves high stability of electric potential even when a difference in peripheral velocity between a body to be charged and the charging member is large.SOLUTION: The charging member comprises a conductive support and a single-layer elastic layer as a surface layer. The elastic layer has domains containing carbon black and rubber, and a matrix having a higher electrical resistance than that of the domains and containing rubber. The surface of the charging member is formed of the surface of the matrix and surfaces of the domains and has a plurality of concave parts. The domains are present at the bottom parts of the concave parts and exposed to the surface of the charging member only at the bottom parts of the concave parts. The volume resistivity of the elastic layer is 1×10or more and 1×10Ω cm or less. When a current value when a DC voltage of 80 V is applied between the conductive support and the surface of the matrix is A1, and a current value when a DC voltage of 80 V is applied between the conductive support and the surfaces of the domains is A2, A2 is 20 times or more of A1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a charging member, a method for manufacturing the charging member, an electrophotographic apparatus, and a process cartridge.

  As a charging member for contact charging, Patent Document 1 includes a matrix containing an ion conductive rubber, a domain made of an electronic conductive rubber material containing a rubber having a butadiene skeleton and carbon black, and the butadiene Disclosed is a charging member having an elastic layer made of a conductive rubber elastic body, in which rubber having a skeleton is terminal-modified with a specific atomic group.

JP 2012-163554 A

The inventors of the present invention have confirmed that the charging member according to Patent Document 1 is effective for further reducing the voltage dependency and ambient environment dependency of the electrical resistance of the charging member.
On the other hand, in recent years, a charging member and an object to be charged such as an electrophotographic photosensitive member arranged in contact with the charging member are independently driven to increase a peripheral speed difference between the charging member and the object to be charged. Thus, an electrophotographic image forming method for further suppressing contamination of the charging member in the electrophotographic image forming process has been proposed.

  However, when the difference in peripheral speed between the charged body and the charging member is increased, the surface potential of the charged body may not converge to a constant value.

One embodiment of the present invention is directed to providing a charging member having high potential stability even when the peripheral speed difference between the charged body and the charging member is large.
Another aspect of the present invention is directed to providing a method for producing a charging member having high potential stability even when the peripheral speed difference between the member to be charged and the charging member is large.
Furthermore, another aspect of the present invention is directed to providing an electrophotographic apparatus capable of forming a high-quality electrophotographic image.
Furthermore, another aspect of the present invention is directed to providing a process cartridge that contributes to the formation of high-quality electrophotographic images.

According to one aspect of the present invention, there is provided a charging member having a conductive support and an elastic layer, the elastic layer being a surface layer of the charging member composed of a single layer, and comprising carbon black and rubber. And a matrix containing rubber having a higher electric resistance than the domain, and the surface of the charging member is composed of the surface of the matrix and the surface of the domain, and has a plurality of recesses. Is present on the surface of the charging member only at the bottom of the recess, and the volume resistivity of the elastic layer is 1 × 10 ⁵ Ωcm or more and 1 × 10 ⁸ Ωcm or less,
A1 is a current value when a DC voltage of 80 V is applied between the conductive support and the cantilever of an atomic force microscope (AFM) in contact with the surface of the matrix constituting the surface of the charging member;
When the current value when a direct current voltage of 80 V is applied between the conductive support and the AFM cantilever in contact with the surface of the domain constituting the surface of the charging member is A2, A2 is A1 A charging member that is 20 times or more is provided.

  According to another aspect of the present invention, there is provided an electrophotographic apparatus comprising: an electrophotographic photosensitive member; and a charging member disposed so as to be capable of charging the electrophotographic photosensitive member. An electrophotographic apparatus as the above-described charging member is provided.

  Furthermore, according to another aspect of the present invention, there is provided a process cartridge that can be attached to and detached from the main body of the electrophotographic apparatus, the electrophotographic photosensitive member, and a charging member that is disposed so that the electrophotographic photosensitive member can be charged. And a process cartridge in which the charging member is the above-described charging member.

Furthermore, according to another aspect of the present invention, there is provided a method for producing a charging member, wherein the charging member has a conductive support and an elastic layer, and the elastic layer is formed of a single layer. A surface layer of the charging member, and including a domain containing carbon black and rubber, and a matrix containing rubber and having a higher electric resistance than the domain, and the surface of the charging member includes a surface of the matrix The surface of the domain, and having a plurality of recesses, the domain is present at the bottom of the recess, and is exposed to the surface of the charging member only at the bottom of the recess,
(A) a step of preparing a carbon masterbatch comprising carbon black and rubber and serving as the domain;
(B) a step of kneading the carbon masterbatch and a rubber composition to be the matrix to prepare a rubber composition having a domain / matrix structure; and (C) a rubber composition having the domain / matrix structure. A step of extruding an object together with a core from a crosshead, and coating the periphery of the core with a rubber composition having the domain matrix structure,
When the die swell value of the carbon master batch is DS (d) and the die swell value of the rubber composition as the matrix is DS (m), the ratio of the die swell values DS (m) / DS (d) There is provided a method of manufacturing a charging member that has a value larger than 1.0.

According to one embodiment of the present invention, a charging member having high potential stability can be obtained even when the peripheral speed difference between the charged body and the charging member is large.
In addition, according to another aspect of the present invention, it is possible to obtain a method for manufacturing a charging member with high potential stability even when the peripheral speed difference between the charged body and the charging member is large. Furthermore, according to another aspect of the present invention, an electrophotographic apparatus capable of forming a high-quality electrophotographic image can be obtained. Furthermore, according to another aspect of the present invention, a process cartridge that contributes to the formation of a high-quality electrophotographic image can be obtained.

It is a schematic diagram which shows the rubber composition of a matrix domain structure. FIG. 3 is a schematic cross-sectional view illustrating a configuration of a charging roller. It is a figure which shows schematic structure of a crosshead extrusion apparatus. It is a figure which shows schematic structure of the apparatus which measures the electric current of a charging roller by AFM. It is a figure which shows schematic structure of the apparatus which measures surface potential. It is a figure which shows an example of the measurement result of the depth of the recessed part by AFM. It is a figure which shows the structure of an electrophotographic apparatus. It is a figure which shows the structure of a process cartridge. It is a schematic diagram which shows the rubber composition (spherical resin particle containing) of a matrix domain structure.

Reasons why the surface potential of the charged body does not converge to a constant value when the charging member according to Patent Document 1 is used in an electrophotographic image forming process having a large peripheral speed difference from the charged body. It was investigated.
As a result, in the electrophotographic image forming process, it is considered that charge injection occurs from the charging member to the charged body at the contact portion between the charging member and the charged body. That is, with the charge injection, the surface potential of the charged body does not converge to a constant value and the surface potential of the charged body increases every time the charged body rotates and rubs against the charging member. It is thought that the surface potential of the body is not stable.

Accordingly, the present inventors have studied a configuration of a charging member that can suppress a phenomenon in which a domain containing carbon black of the charging member contacts the member to be charged and charges are injected into the member to be charged.
As a result, it has been found that a charging member having a structure in which an electronically conductive domain is less likely to come into contact with an object to be charged is effective in achieving the above object.
That is, the charging member according to one embodiment of the present invention includes a conductive support and an elastic layer, and the elastic layer is a surface layer of the charging member formed of a single layer, and carbon black and A domain including rubber and a matrix including rubber and having a higher electric resistance than the domain are included.

The surface of the charging member is composed of the surface of the matrix and the surface of the domain, and has a plurality of recesses, and the domain is present at the bottom of the recess and only at the bottom of the recess. It is exposed on the surface of the charging member.
The volume resistivity of the elastic layer is 1 × 10 ⁵ Ωcm or more and 1 × 10 ⁸ Ωcm or less.
In addition, the current value when a DC voltage of 80 V is applied between the conductive support and the cantilever of the atomic force microscope in contact with the surface of the matrix constituting the surface of the charging member is A1. ,
When the current value when an AC voltage of 80 V is applied between the conductive support and the cantilever of the atomic force microscope brought into contact with the surface of the domain constituting the surface of the charging member is A2. , A2 is 20 times or more of A1.

  In the charging member according to this aspect, the electrical resistance between the domain and the matrix is set to a predetermined ratio, and the domain exposed on the surface is defined as a recess. As a result, since carbon black, which is a conductive particle, exists in the concave portion of the domain, it is possible to prevent charge transfer from the carbon black to the charged body at the contact portion between the charging member and the charged body. Further, in the charging member according to this aspect, the charging uniformity due to the discharge is maintained as compared with the surface where the domain is covered with the matrix. This is because the domain serving as the discharge point constitutes a part of the surface of the charging member.

  Hereinafter, preferred embodiments of the present invention will be described. Hereinafter, a roller-shaped charging member (hereinafter also referred to as a “charging roller”) will be described as an example of the charging member, but the shape of the charging member according to the present invention is not limited to the roller shape. .

  FIG. 2 shows a schematic diagram of the charging roller 2 as an example using the conductive rubber elastic body of this embodiment. The charging roller 2 includes a cored bar 21 and an elastic layer 22 provided on the outer periphery thereof. This elastic layer 22 also serves as a surface layer in contact with the member to be charged.

  As shown in FIG. 1A, the elastic layer has a matrix-domain structure composed of a domain 11 containing carbon black and rubber, and a matrix 12 containing rubber having a higher electrical resistance than the domain. . FIG. 1A is a cross-sectional view taken along a direction parallel to the surface of the charging member that contacts the member to be charged. On the other hand, FIG. 1B is a cross-sectional view cut in a direction perpendicular to the surface of the charging member that contacts the member to be charged. In FIG. 1B, reference numeral 13 denotes the surface side of the charging member in contact with the member to be charged, and reference numeral 14 denotes a domain existing at the bottom of the concave portion existing on the surface of the charging member. FIG. 1C is an overhead view of the vicinity of the surface of the charging member. As shown in FIGS. 1 (a) to 1 (c), the surface of the charging member according to the present invention is composed of a matrix and a domain, and has a plurality of recesses, and the domain is only at the bottom of the recesses. Exposed.

  The domain has a lower resistance than the matrix and contributes to the electrical conductivity in the elastic layer and the discharge with the charged body, while being present in the recess, the injection of charge into the charged body is suppressed. In addition, since the matrix has a higher resistance than the domain, it is in contact with the member to be charged, but there is little injection of charge. The electrical characteristics for obtaining this effect are represented by the ratio of the volume resistance of the elastic layer and the current value of the domain part and the matrix part measured by AFM.

That is, the current value when a direct current voltage of 80 V is applied between the conductive support and the AFM cantilever brought into contact with the surface of the matrix constituting the surface of the charging member is A1, and the conductive support and When the current value when a direct current voltage of 80 V is applied between the AFM cantilever and the surface of the domain constituting the surface of the charging member is A2, A2 is 20 times or more of A1. It is preferable.
As a charging member, on the premise of having an appropriate volume resistance, the current value flowing from the domain portion on the surface of the elastic layer is 20 times or more the current value flowing from the matrix portion, so that Inhibition of the injection of charges from the substrate and charging of the object to be charged by sufficient discharge from the domain part are compatible.

  If the surface potential of the object to be charged does not converge to a certain value, the density of the electrophotographic image changes in the process direction, and the difference in charge injection corresponding to the unevenness of the charging member contamination causes image unevenness. Occurrence of image defects such as becoming is prevented by suppressing charge injection, and a charging member with high potential stability can be obtained.

  The volume fraction of the domain is preferably 5% by volume or more and 25% by volume or less based on the volume of the elastic layer. If the volume is 5% by volume or more, it is possible to obtain a discharge necessary as a charging member without increasing the conductivity of the matrix. On the other hand, if the volume fraction of the domains is 25% by volume or less, it is possible to suppress the injection potential from being increased due to the domains being connected and brought too close together. In addition, it is possible to suppress the occurrence of overdischarge due to low resistance. Further, the volume fraction of the domain is more preferably 10% by volume to 20% by volume.

  The number of domains in the elastic layer is preferably 1 or more and 500 or less in a 10 μm cube. Incidentally, in the above-mentioned number of domains and volume fraction, the approximate domain diameter is about 0.5 μm to 5 μm. When the number of domains is 500 or less, it is possible to suppress an increase in injection potential due to the domains being connected and approached too much. In addition, it is possible to suppress the occurrence of overdischarge due to low resistance. On the other hand, when the number of domains is one or more, it is necessary to increase the conductivity of the matrix due to the small number of domains, and it is possible to suppress an increase in injection potential. Moreover, it can suppress that resistance becomes high and discharge shortage occurs.

  The depth of the concave portion where the domain is exposed at the bottom is preferably 1.0 μm or more and 4.0 μm or less. It is preferable that the thickness is 1.0 μm or more because the contact between the domain and the member to be charged is suppressed while the charging member is in contact with the member to be charged. On the other hand, when the thickness is 4.0 μm or less, even when dirt is attached to the concave portion, the dirt can be electrostatically returned to the charged body side.

(Material of elastic layer)
The domain is made of an electronically conductive rubber material. The electronically conductive rubber material includes, for example, a material in which carbon black is dispersed in a binder polymer that does not exhibit electrical conductivity to adjust electric resistance.

  As the binder polymer, butadiene rubber, acrylonitrile butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene, which are conventionally used for conductive elastic layers of charging members, for example, conductive elastic layers of charging rollers for electrophotographic apparatuses, are used. A rubber composition containing rubber, ethylene-propylene rubber, polynorbornene rubber, epichlorohydrin rubber or the like is preferably used.

  The type of carbon black blended in the domain is not particularly limited as long as it is a conductive carbon black that can impart conductivity to the domain. Specific examples include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black.

  Further, in the rubber composition forming the domain, if necessary, a filler, a processing aid, a crosslinking aid, a crosslinking accelerator, a crosslinking accelerator, a crosslinking retarder generally used as a rubber compounding agent , Softeners, dispersants, colorants and the like may be added.

  The matrix does not contain conductive particles such as carbon black and has a higher electrical resistance than the domain. Examples of the binder polymer contained in the matrix include butadiene rubber, isoprene rubber, chloroprene rubber, and styrene-butadiene, which are conventionally used for conductive elastic layers of charging members, for example, conductive elastic layers of charging rollers for electrophotographic apparatuses. A rubber composition containing rubber, ethylene-propylene rubber, polynorbornene rubber, epichlorohydrin rubber or the like is preferably used.

The rubber composition constituting the above matrix has a bleed in order to adjust the resistance of the elastic layer to a middle resistance range suitable for a charging member (for example, 1.0 × 10 ⁵ Ω to 1.0 × 10 ⁸ Ω). You may mix | blend an ion conductive agent to such an extent that it does not out. However, it is preferable to minimize the matrix containing the ionic conductive agent because charge injection tends to increase.

  Examples of the ionic conductive agent include inorganic ionic substances such as lithium perchlorate, sodium perchlorate, and calcium perchlorate; lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl. Cationic surfactants such as ammonium chloride, trioctylpropylammonium bromide, modified aliphatic dimethylethylammonium ethosulphate; amphoteric surfactants such as lauryl betaine, stearyl betaine, dimethylalkyl lauryl betaine; tetraethylammonium perchlorate, Quaternary ammonia such as tetrabutylammonium perchlorate and trimethyloctadecylammonium perchlorate Umushio; it can be exemplified organic acid lithium salts of lithium trifluoromethanesulfonate and the like.

The amount of the ion conductive agent as described above is, for example, 0.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the rubber composition.
Further, for example, spherical particles having a particle diameter in the range of 1 μm to 90 μm may be added to the rubber composition forming the matrix. Specifically, for example, from phenol resin particles, silicone resin particles, polyacrylonitrile resin particles, polystyrene resin particles, polyurethane resin particles, nylon resin particles, polyethylene resin particles, polypropylene resin particles, acrylic resin particles, silica particles, and alumina particles There may be mentioned at least one spherical particle selected. By using such a rubber composition, it is possible to provide a charging member in which the outer surface of the elastic layer has convex portions derived from spherical particles.

  FIG. 9 illustrates a charging member according to one embodiment of the present invention, in which the elastic layer 22 includes spherical particles 15 and the outer surface of the elastic layer 22 includes convex portions derived from the spherical particles 15. FIG. Specifically, FIG. 9 is a cross-sectional view of the elastic layer 22 where the convex portions 901 derived from the spherical particles 15 are formed in the thickness direction of the elastic layer and the outer surface of the convex portions 901. It is a partial enlarged view. As shown in FIG. 9, the outer surface of the convex part 901 derived from the spherical particles 15 has a plurality of concave parts, and the domain 11 is exposed only at the bottom part of the concave part. Therefore, even if the convex portion 901 derived from the spherical particles 15 is present on the outer surface, the conductive domain is difficult to directly contact with an object to be charged (not shown). Therefore, charge injection from the charging member to the member to be charged is significantly suppressed, and as a result, the charged potential of the member to be charged is further stabilized.

  In general, when an incompatible polymer blend is used as the material of the elastic layer, the matrix domain structure depends on the polymer viscosity and blending conditions, but the rubber composition with a large composition ratio and the rubber with a low viscosity are used. The composition tends to be a matrix. Therefore, the volume fraction of the domain requires 5% by volume or more and 25% by volume or less. As a result, a stable domain can be formed, and the matrix domain structure of the entire conductive rubber composition is stabilized.

  Furthermore, in order to make a stable matrix-domain structure appear, in the value of ML1 + 4 at 100 ° C. using a Mooney viscometer, the viscosity of the domain is higher than the viscosity of the matrix, and the viscosity difference is 5 points or more and 60 points. More preferably, it is as follows.

(Conductive support)
The conductive support is not particularly limited as long as it has conductivity, can support the surface layer, etc., and can maintain strength as a charging member, typically as a charging roller.

<Method for manufacturing charging member>
As an example of a method for manufacturing a charging member according to an aspect of the present invention, a method that is effective from the viewpoint that the manufacturing process is simple will be described. The manufacturing method includes the following steps (A) to (D).
(A) a step of preparing a carbon masterbatch (CMB) for domain formation containing carbon black and rubber;
(B) a step of preparing a rubber composition to be a matrix;
(C) a step of kneading the carbon master batch and the rubber composition to prepare a rubber composition having a domain / matrix structure;
(D) A step of extruding the rubber composition having a matrix domain structure together with a core metal from a crosshead, and coating the periphery of the core metal with the rubber composition having the matrix domain structure.

  FIG. 3 is a schematic configuration diagram of the crosshead extrusion molding machine 3. The crosshead extrusion molding machine 3 is an apparatus for producing an unvulcanized rubber roller 33 in which the core metal 31 is placed in the center by uniformly coating the unvulcanized rubber composition 32 over the entire circumference of the core metal 31. .

  The cross head extrusion molding machine 3 includes a cross head 34 to which the core metal 31 and the unvulcanized rubber composition 32 are fed, a conveying roller 35 for feeding the core metal 31 to the cross head 34, and an unvulcanized rubber to the cross head 34. And a cylinder 36 for feeding the composition 32.

  The transport roller 35 continuously feeds a plurality of core bars 31 to the cross head 34 in the axial direction. The cylinder 36 includes a screw 37 inside, and the unvulcanized rubber composition 32 is fed into the cross head 34 by the rotation of the screw 37.

  When the metal core 31 is fed into the cross head 34, the entire circumference is covered with the unvulcanized rubber composition 32 fed into the cross head from the cylinder 36. The cored bar 31 is fed out from a die 38 at the outlet of the crosshead 34 as an unvulcanized rubber roller 33 whose surface is coated with an unvulcanized rubber composition 32.

Here, when the die swell value of the carbon master batch prepared in the step (A) is DS (d) and the die swell value of the rubber composition prepared in the step (B) is DS (m), the die swell The value ratio DS (m) / DS (d) is greater than 1.0. Thus, the charging member according to this aspect can be formed.
The die swell value will be described. When the rubber is extruded using a die extruder, the rubber that has been compressed due to pressure being applied is released from the extrusion port, and the extruded rubber expands within the extruder. The thickness becomes larger than the size of the gap between the extrusion ports of the die. The die swell value is an index representing the degree of rubber expansion when extruded from the extrusion port.

  In the method for producing a charging member according to this aspect, a carbon masterbatch for domain formation that satisfies the relationship DS (m) / DS (d)> 1.0 and a rubber composition for matrix formation are mixed, A rubber composition having a matrix domain structure is prepared. Next, the rubber composition having the matrix domain structure is extruded from the crosshead extrusion port while swelling. Then, since the expansion coefficient of the matrix is larger than the expansion coefficient of the domain, the matrix around the domain existing on the surface of the extruded rubber layer is raised, and as a result, the surface has a recess, and A layer of an unvulcanized rubber composition in which a domain is present at the bottom of the recess is formed. The DS (m) / DS (d) is preferably 1.1 or more in order to more easily form the structure of the surface layer according to this aspect.

  The die swell value of the carbon masterbatch for domain formation and the rubber composition for matrix formation can be adjusted by, for example, the filler type and amount to be added. Specifically, the die swell value decreases as the amount of filler added increases. In addition, when a filler having a high reinforcing effect of rubber such as carbon black or silica, or a flaky filler such as bentonite or graphite is used as the filler, the die swell value is smaller than that when calcium carbonate is used. .

In the step (C), as a method of kneading the CMB as a domain and the unvulcanized rubber composition as a matrix to obtain an unvulcanized rubber composition having a matrix / domain structure, for example, The method described in (i) and (ii) can be mentioned.
(I) After each of CMB as a domain and an unvulcanized rubber composition as a matrix are mixed using a closed mixer such as a Banbury mixer or a pressure kneader, an open type such as an open roll is mixed. A method in which a CMB as a domain, an unvulcanized rubber composition as a matrix, and raw materials such as a vulcanizing agent and a vulcanization accelerator are kneaded and integrated using a mixer.
(Ii) After the CMB as the domain is mixed using a closed mixer such as a Banbury mixer or a pressure kneader, the raw material of the uncured rubber composition as the matrix and the CMB as the matrix is mixed into the closed mixer. After mixing, the raw materials such as a vulcanizing agent and a vulcanization accelerator are kneaded and integrated using an open type mixer such as an open roll.

  The layer of the unvulcanized rubber composition having a concave portion on the surface of the step (D) and having a domain at the bottom of the concave portion is then subjected to a vulcanization step as the step (E), and this aspect It can be a surface layer. Specific examples of the heating method include hot blast furnace heating with a gear oven, heating vulcanization with far infrared rays, and steam heating with a vulcanizing can. Of these, hot stove heating and far infrared heating are preferable because they are suitable for continuous production.

  In order to better maintain the surface shape formed by the above method and having a domain at the bottom of the recess, it is preferable not to polish the surface of the obtained charging roller. Therefore, when the outer shape of the elastic layer of the charging roller according to the present embodiment is made to be a crown shape, by controlling the extrusion speed of the core metal from the cross head and the extrusion speed of the unvulcanized rubber composition, It is preferable to shape the outer diameter shape of the vulcanized rubber layer into a crown shape. The crown shape refers to a shape in which the outer diameter of the central portion of the elastic layer in the longitudinal direction is larger than the outer diameter of the end portion.

  Specifically, the relative ratio between the core metal feed speed of the core metal 31 by the conveying roller 35 and the unvulcanized rubber composition feed speed from the cylinder 36 is changed. At this time, the feed rate of the unvulcanized rubber composition 32 from the cylinder 36 to the cross head 34 is constant. The thickness of the unvulcanized rubber composition 32 is determined by the ratio between the feed speed of the core metal 31 and the feed speed of the unvulcanized rubber composition 32. Thereby, an elastic layer can be made into a crown shape, without grind | polishing.

The vulcanized rubber composition at both ends of the vulcanized rubber roller is removed in a separate process later to complete the vulcanized rubber roller. Therefore, both ends of the core metal are exposed in the completed vulcanized rubber roller.
The surface layer may be subjected to a surface treatment by irradiation with ultraviolet rays or electron beams.

(Electrophotographic equipment)
The charging member according to one embodiment of the present invention can be used for an electrophotographic apparatus such as a laser printer and a process cartridge that can be attached to and detached from the electrophotographic apparatus.

  FIG. 7 is a schematic cross-sectional view of an electrophotographic apparatus according to one embodiment of the present invention. An electrophotographic photosensitive member (hereinafter abbreviated as “photosensitive member”) 71 as a member to be charged includes a conductive support 71b and a photosensitive layer 71a formed on the conductive support 71b, and has a cylindrical shape. Then, it is driven with a predetermined peripheral speed in the clockwise direction in the figure around the shaft 71c.

  The charging roller 72 is placed in contact with the photoconductor 71 to charge the photoconductor 71 to a predetermined potential. The charging roller 72 includes a cored bar 72a and an elastic layer 72b formed on the cored bar 72a. Both ends of the cored bar 72a are pressed against the photoconductor 71 by a pressing unit (not shown). Followed by driving. The photoconductor 71 is charged to a predetermined potential by applying a predetermined DC voltage of the cored bar 72a by the rubbing electrode 73a by the power source 73.

  The charged photoreceptor 71 then forms an electrostatic latent image corresponding to target image information on its peripheral surface by the exposure means 74. The electrostatic latent image is then sequentially visualized as a toner image by the developing member 75. The toner images are sequentially transferred to the transfer material 77. The transfer material 77 is conveyed from a sheet feeding unit (not shown) to the transfer unit between the photoconductor 71 and the transfer unit 76 at an appropriate timing in synchronization with the rotation of the photoconductor 71. The transfer unit 76 is a transfer roller, and the toner image on the photoconductor 71 side is transferred to the transfer material 77 by charging from the back of the transfer material 77 with a polarity opposite to that of the toner. The transfer material 77 that has received the transfer of the toner image on the surface is separated from the photoreceptor 71 and conveyed to a fixing means (not shown) to fix the toner, and is output as an image formed product. The toner remaining on the surface of the photoreceptor 71 is removed from the peripheral surface of the photoreceptor 71 after the image transfer by a cleaning member 78 represented by an elastic blade. The cleaned peripheral surface of the photoreceptor 71 moves to the electrophotographic image forming process of the next cycle.

  The charging member (charging roller) according to one embodiment of the present invention is used when the difference in outer diameter between the center and the end of the crown shape increases due to an increase in the deflection of the charging roller as the diameter decreases, or when the charging roller and the object to be charged Can be suitably used even when there is a large difference in peripheral speed between the charged object and the charging member, such as when the charging roller is prevented from being soiled by rubbing to provide a peripheral speed difference.

<Process cartridge>
FIG. 8 shows a process cartridge according to one embodiment of the present invention. The process cartridge is detachable from the electrophotographic apparatus. The process cartridge includes an electrophotographic photosensitive member 81, a charging roller 80 arranged to be able to charge the electrophotographic photosensitive member 81, a developing roller 82, and a cleaning member 83. As the charging roller 80, the charging member according to one embodiment of the present invention is used.

[Example 1]
<Preparation of carbon masterbatch (CMB) 1>
CMB1 was prepared by mixing the carbon masterbatch (CMB) raw materials shown in Table 1 below in the blending amounts shown in Table 1. As the mixer, a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

<Calculation of CMB die swell>
For the CMB1 prepared above, the die swell value (DS (d)) was calculated by the following method.
That is, the die swell is measured using a capillary rheometer (trade name: Capillograph 1D type, manufactured by Toyo Seiki Co., Ltd.) in accordance with JIS K 7199: 1999.
Capillary length: 10 mm, capillary diameter D: 2 mm, furnace body diameter: 9.55 mm, load cell type: 20 kN, measurement temperature = 80 ° C. As the die swell, the diameter R [mm] of the extruded strand was measured at a piston speed of 100 mm / min (shear rate: 1.52 × 10 ² ), and calculated as die swell DS = R / D.

<Calculation of die swell value of raw material 1 for kneaded rubber composition formation>
The materials listed in Table 2 were prepared as raw materials for the kneaded rubber composition.
These materials were mixed in the amounts shown in Table 2. As the mixer, a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes. With respect to the obtained mixture, the die swell value (DS (m)) of the mixture was calculated in the same manner as the CMB die swell calculation method.

<Preparation of unvulcanized rubber composition 1>
A kneaded rubber composition was obtained by adding the raw materials shown in Table 2 to the CMB1 and kneading them. As the mixer, a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.
The raw material shown in Table 3 was added to the obtained A kneaded rubber composition and further kneaded to obtain an unvulcanized rubber composition 1 as a B kneaded rubber composition. As the mixer, an open roll having a roll diameter of 12 inches (0.30 m) was used. The mixing conditions were a front roll rotation speed of 10 rpm and a rear roll rotation speed of 8 rpm, and after turning left and right a total of 20 times with a roll gap of 2 mm, thinning was performed 10 times with a roll gap of 0.5 mm.

(Calculation of volume fraction of CMB1)
The measurement of the volume fraction of CMB1 was calculated according to the following calculation formula (1) from the specific gravity and blending part of CMB1 and the specific gravity and blending part of unvulcanized rubber composition 1.
Formula (1)
CMB1 volume fraction (%) = ((CMB1 blending mass part) / (CMB1 specific gravity)) / ((unvulcanized rubber composition 1 mass part) / (unvulcanized rubber composition 1 specific gravity) ) × 100

  The specific gravity was measured using an electronic hydrometer (trade name: EW-300SG; manufactured by Alpha Mirage). The specific gravity was measured by preparing three test specimens (1 cm long, 1 cm wide, 2 mm thick) from CMB1 and unvulcanized rubber composition 1 and measuring the specific gravity using each test specimen. The average value of the obtained results was used as the specific gravity of CMB1 and unvulcanized rubber composition 1 in the above calculation.

(Molding of vulcanized rubber layer)
First, in order to obtain a metal core having an adhesive layer for adhering the vulcanized rubber layer, the following operation was performed. In other words, a conductive vulcanizing adhesive (trade name: METALOC U-20; Toyo Chemical Co., Ltd.) is attached to the central portion 222 mm in the axial direction of a cylindrical conductive core bar (made of steel, surface is nickel-plated) having a diameter of 6 mm and a length of 252 mm. (Manufactured by Laboratory) and dried at 80 ° C. for 30 minutes.

  The unvulcanized rubber composition 1 prepared above was coated on the metal core having the adhesive layer with a crosshead extrusion molding machine to obtain a crown-shaped unvulcanized rubber roller. The molding temperature was 100 ° C., the screw rotation speed was 10 rpm, and molding was performed while changing the feed rate of the cored bar. The die inside diameter of the crosshead extrusion molding machine is 8.4mm, and the unvulcanized rubber roller is molded thicker. The outer diameter of the unvulcanized rubber roller in the axial direction is 8.6mm, and the outer diameter of the end is It was 8.5 mm.

  Thereafter, the unvulcanized rubber composition 1 layer was vulcanized by heating in an electric furnace at a temperature of 160 ° C. for 40 minutes to obtain a vulcanized rubber layer. Both ends of the vulcanized rubber layer were cut, and the length in the axial direction was set to 232 mm to obtain a vulcanized rubber roller.

(Electron beam irradiation of the vulcanized rubber layer after extrusion)
The surface of the obtained vulcanized rubber roller was irradiated with an electron beam to obtain a charging roller 1 having a cured region on the surface of the elastic layer (surface layer). For the electron beam irradiation, an electron beam irradiation apparatus (manufactured by Iwasaki Electric Co., Ltd.) having a maximum acceleration voltage of 150 kV and a maximum electron current of 40 mA was used, and nitrogen was filled during irradiation. The electron beam irradiation conditions were acceleration voltage: 150 kV, electron current: 35 mA, dose: 1323 kGy, processing speed: 1 m / min, and oxygen concentration: 100 ppm.

(Confirmation of domain existence and measurement of the number of domains)
A slice of the elastic layer having a thickness of 1 mm was cut out from the charging roller. This section was immersed in a 5% aqueous solution of phosphotungstic acid for 15 minutes, and then the section was taken out, washed with pure water, and further dried at room temperature (25 ° C.). The stained sections thus obtained were observed for matrix domain structure using FIB-SEM. Specifically, FIB-SEM (trade name: Dual Beam SEM Helios 600, manufactured by FEI) was used. A specific measurement method is shown below.

  Cut the blade of the cutter perpendicularly to the surface of the charging roller and cut out 1 mm square sections in the x-axis direction (roller longitudinal direction) and the y-axis direction (tangential direction of the circular cross section of the cross section of the roller perpendicular to the x axis) It was. The cut sections were observed from the z direction (normal direction with respect to the roller surface perpendicular to the xy plane) at an acceleration voltage of 10 kV and a magnification of 1000 using a FIB-SEM apparatus. Next, a total of 100 cross-sectional images were taken from the surface to a depth of 10 μm from the surface at an interval of 100 nm in the z direction using a gallium ion beam with an ion beam current amount of 20 nA. The presence / absence of a domain / matrix structure and the number of domains were counted from a three-dimensional image obtained by three-dimensional reconstruction from the cross-sectional image. When counting the number of domains, the domain having a part at the boundary of the image was excluded, and the number of domains having a true sphere diameter of 200 μm or more corresponding to the volume of the domain was counted.

(Volume resistivity)
The elastic layer of the charging roller was cut out with a razor to obtain a semi-cylindrical piece of rubber. The volume resistivity of the cut surface of this rubber was measured by a 4-terminal 4-probe method. The measurement conditions were a resistivity meter (trade name: Loresta GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) in an environment of 23 ° C / 50% RH (relative humidity), applied voltage 90V, load 10N, distance between pins. 1.0 mm, pin tip 0.04R, and spring pressure 250 g. The volume resistivity was 4.7 × 10 ⁵ Ωcm.

(Measurement of recess depth and current value by AFM)
The surface shape of the charging member, the confirmation of the presence of the domain at the bottom of the concave portion, and the current value of the domain and the matrix were measured using an atomic force microscope (AFM) (Easy Scan2, Nanosurf) Measurement values measured in the spreading resistance mode can be adopted. FIG. 4 shows a configuration diagram of the conductivity measuring apparatus. A DC power supply (PL-650-0.1, Matsusada Precision Co., Ltd.) 44 is connected to the conductive base of the charging roller 41, and 80V is applied. The free end of the cantilever 42 is brought into contact with the surface layer, and the AFM main body A current image is obtained through 43. Measurement conditions are: cantilever: ANSCM-PC, operation mode: spreading resistance, measurement environment: in the atmosphere, set point: 20 nN, P-gain: 3000, I-gain: 600, D-gain: 0, tip voltage: 3V Image width: 100 μm, number of lines: 256.

  The composition image of the domain matrix structure, the shape image of the AFM measurement, and the position of the current image obtained by observing the surface of the charging member with a scanning electron microscope (SEM) (trade name: S-3700N, manufactured by Hitachi High-Technologies Corporation) in advance While matching, the depth of the concave portions of the domain and the matrix and the current value are measured. The measurement conditions of the composition image by SEM are not particularly limited as long as it is adjusted so that a clear image can be obtained, but the measurement is performed at a vacuum degree: high vacuum, signal: BSE (COMPO), acceleration voltage: 15 kV, WD: 5 mm. can do.

  A shape image and a current image are simultaneously acquired during the AFM measurement. Of the composition image obtained by SEM of the shape image, a domain portion is extracted from the AFM shape image. FIG. 6 is a line profile of an AFM shape image, and 61 indicates an extracted domain part. The value obtained by subtracting the average value in the height direction Z of the domain part from the average value of the part other than the domain part was defined as the depth of the recess. The depth of the recess was 2.0 μm.

  In addition, the average value of the current values of the domains extracted when calculating the depth of the recesses was A2. On the other hand, a portion other than the domain portion was used as a matrix, and the average value of the current values was A1. It shows that the electrical resistance of a domain is low compared with a matrix, so that A2 / A1 is large. A2 / A1 was 97.

(Evaluation of charge injection properties)
The charging roller thus produced is brought into contact with an object to be charged (OPC drum) of an electrophotographic apparatus (trade name: LBP7200C manufactured by Canon Inc., for A4 paper vertical output), and the charging roller and the object to be charged can be driven independently. It was incorporated into a jig (FIG. 5) and the charge injection property was evaluated. In an environment of 30 ° C./80% RH (relative humidity), −500 V is applied to the charging roller 51, the rotation speed of the charged body 52 is 180 mm / sec, and the rotation speed of the charging roller is 200 mm / sec. model 370, Trek Japan Co., Ltd.). Then, a voltage was applied, and the average value of the surface potential on the first rotation of the charged body was taken as the potential due to charge injection. The reason why the applied voltage was set to -500 V is to measure the change in the potential due to the injection with almost no charging due to the discharge.

[Examples 2 to 13]
<Preparation of CMB2 to CMB13>
CMB2 to CMB13 were prepared in the same manner as CMB1 except that the materials shown in Table 4 were used in the blending amounts shown in Table 4. The die swell value was calculated in the same manner as CMB1.

<Calculation of die swell values of raw materials 2 to 13 for forming the kneaded rubber composition>
The die swell value of the raw material for forming the kneaded rubber composition A was calculated in the same manner as in Example 1 except that the materials shown in Table 5 were used in the amounts shown in Table 5.

<Preparation of Unvulcanized Rubber Compositions 2-13 and Production of Charging Rollers 2-13>
The unvulcanized rubber compositions 2 to 13 were prepared in the same manner as the unvulcanized rubber composition 1 according to Example 1, except that the CMB2 to CMB13 and the raw material 2 to 13 for kneading the rubber composition were used. did.
And the charging rollers 2-13 were produced and evaluated similarly to Example 1 except having used the unvulcanized rubber compositions 2-13.

[Comparative Examples 1-2]
<Calculation of die swell value of raw materials 14 to 15 for kneaded rubber composition formation>
Except having used the material of Table 6 by the compounding quantity of Table 6, it carried out similarly to Example 1, and calculated the die swell value of raw materials 14-15 for A kneaded rubber composition formation.

<Preparation of Unvulcanized Rubber Compositions 14-15 and Production of Charging Rollers 14-15>
Unvulcanized rubber compositions 14 to 15 were prepared in the same manner as the unvulcanized rubber composition 5 according to Example 5 except that the raw materials 14 to 15 for forming the A kneaded rubber composition were used. Except for using unvulcanized rubber compositions 14-15, charging rollers 14-15 were prepared and evaluated in the same manner as in Example 1.

[Comparative Example 3]
In the process of Example 1, the surface of the vulcanized rubber layer of the vulcanized rubber roller before (molding of the vulcanized rubber layer) (before irradiation of the vulcanized rubber layer after extrusion) is polished with a plunge cut. And a crown shape having an end diameter of 8.3 mm and a center diameter of 8.5 mm was obtained. A charging roller 16 was prepared in the same manner as in Example 1 except that the step of Example 1 (electron beam irradiation of the vulcanized rubber layer after extrusion) of Example 1 was performed after the polishing step, and evaluation was performed in the same manner.

[Comparative Example 4]
In the process of Example 1, (molding of the vulcanized rubber layer) was molded by a mold instead of extrusion, and was the same as in Example 1 except that the crown shape had an end diameter of 8.5 mm and a center diameter of 8.6 mm. The charging roller 17 was produced by the method described above and evaluated in the same manner.
The molding conditions of the mold were a split mold and a press machine, pressurization: 10 MPa, temperature: 160 ° C., and time: 40 minutes.

[Comparative Example 5]
Example 1 except that (preparation of carbon masterbatch) in the step of Example 1 was not carried out, but (preparation of unvulcanized rubber composition), and kneaded material containing NBR, SBR, and carbon black was kneaded at the same time. The charging roller 18 was produced by the same method as in No. 1 and evaluated in the same manner.

The evaluation results of Examples 1 to 13 and Comparative Examples 1 to 5 are shown in Table 7 and Table 8.

Example 14
In <Preparation of Unvulcanized Rubber Composition 1> in Example 1, CMB1 and the raw materials shown in Table 2 and spherical acrylic resin particles (trade name: Techpolymer MBX-20, particle diameter 20 μm, Sekisui Plastics Co., Ltd.) 10 mass) was added as a blending amount. Other than that, the charging roller 19 was prepared and evaluated in the same manner as in Example 1.
Since the spherical acrylic resin particles are crosslinked, they are not compatible with NBR constituting the matrix.
Since the spherical acrylic resin particles are electrically insulative, they are treated as part of a matrix containing rubber and having a higher electrical resistance than the domain, and the volume fraction of the domain is calculated as DS (m) / DS (d) The number of domains and A2 / A1 were measured.

Example 15
In <Preparation of unvulcanized rubber composition 1> in Example 1, in addition to the raw materials shown in CMB1 and Table 2, spherical urethane resin particles (trade name: Art Pearl C-400, transparent, particle diameter 20 μm, Negami Chemical Industry Co., Ltd.) Product) was added in an amount of 10 parts by mass. Other than that, the charging roller 21 was prepared and evaluated in the same manner as in Example 1.
Since the spherical urethane resin particles are crosslinked, they are not compatible with NBR constituting the matrix.
Since the spherical urethane resin particles are electrically insulating, as in Example 14, it is treated as part of a matrix containing rubber and having a higher electrical resistance than the domain, and the volume fraction of the domain is calculated, DS ( m) / DS (d), number of domains, and A2 / A1 were measured.

Example 16
In Example 14, as in Example 1, the electron beam was irradiated. Instead of this electron beam irradiation, a charging roller 21 was prepared and evaluated in the same manner as in Example 14 except that the process was changed so that ultraviolet irradiation was performed under the following conditions.
Ultraviolet irradiation was performed uniformly using a low-pressure mercury lamp (trade name: GLQ500US / 11, manufactured by Toshiba Lighting & Technology Co., Ltd.) while rotating the charging roller. The amount of ultraviolet light was set to 8000 mJ / cm ² with a sensitivity of a sensor of 254 nm.

Example 17
In Example 15, as in Example 1, the electron beam was irradiated. Instead of electron beam irradiation, a charging roller 22 was prepared and evaluated in the same manner as in Example 15 except that the process was changed so that ultraviolet irradiation was performed under the following conditions.
Ultraviolet irradiation was performed uniformly using a low-pressure mercury lamp (trade name: GLQ500US / 11, manufactured by Toshiba Lighting & Technology Co., Ltd.) while rotating the charging roller. The amount of ultraviolet light was set to 8000 mJ / cm ² with a sensitivity of a sensor of 254 nm.

Example 18
A spherical polyethylene resin particle master batch PE-MB1 was prepared as follows.
The materials listed in Table 9 were prepared as raw materials. These materials were mixed in the blending amounts shown in Table 9 to obtain spherical polyethylene resin particle master batch PE-MB1.
As the mixer, a 6 liter pressure kneader (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were filling rate: 50 vol%, blade rotation speed 10 rpm, and 5 minutes. The maximum temperature reached during mixing was 80 ° C., which was a value sufficiently lower than 120 ° C., which is the melting point of polyethylene.

For the unvulcanized rubber composition 1 prepared in Example 1, 14.3 parts by mass of the spherical polyethylene resin particle master batch PE-MB1 prepared above was added in an amount, and kneaded with an open roll. Unvulcanized rubber composition 16 was prepared.
The maximum reached temperature of the unvulcanized rubber composition 16 during open roll kneading was 92 ° C.
Since the spherical polyethylene resin particles are kneaded at a melting temperature or lower, they are not compatible with the matrix NBR.
Since the spherical polyethylene resin particles are electrically insulative, they are treated as part of a matrix containing rubber and having a higher electrical resistance than the domain, and the volume fraction of the domain is calculated as DS (m) / DS (d) The number of domains, A2 / A1, was measured.
A charging roller 23 was prepared and evaluated in the same manner as in Example 1 except that the unvulcanized rubber composition 16 was used instead of the unvulcanized rubber composition 1.

Table 10 shows the evaluation results of Examples 14 to 18.

  Among Examples 1 to 18, in the charging member satisfying a certain volume resistivity, A2 / A1 is large, the number of domains is small, the volume fraction of domains is small, and the deeper the concave portion, the lower the injection potential. It was. In Example 10, ion conductive hydrin rubber was used, charge transfer due to contact was more likely to occur than NBR, and the injection potential was 5V. In Example 11, since the volume fraction of domains was small, the conductivity of the matrix had to be high, and as a result, charge transfer due to contact was likely to occur, and the injection potential was 9V. In Example 12, since the volume fraction of the domains was large, electric field concentration occurred due to the distance between the domains approaching, and charge transfer was likely to occur, so the injection potential was 6V. In Example 13, since the number of domains was large, electric field concentration occurred due to the domains being connected to each other, and charge transfer was likely to occur, so the injection potential was 7V.

  In Comparative Examples 1 and 2, in the charging member satisfying a certain volume resistivity, A2 / A1 was small, and the injection potentials were 22 V and 25 V, respectively. In Comparative Example 3, the surface shape was not such that the domain was present only in the recess due to polishing molding, and the injection potential was 27V. Similarly, Comparative Example 4 did not have a surface shape in which the domain was present only in the recess because of molding, and the injection potential was 32V. Comparative Example 5 did not have a domain matrix structure, and carbon black was uniformly present in the elastic layer. Therefore, the injection potential was 38V.

11 Domain including carbon black and rubber 12 Matrix having higher electric resistance than domain 13 Surface of elastic layer 14 Domain exposed in recess of surface of elastic layer

Claims (8)

A charging member having a conductive support and an elastic layer,
The elastic layer is a surface layer of the charging member composed of a single layer,
And a domain containing carbon black and rubber, and a matrix containing rubber and having a higher electrical resistance than the domain,
The surface of the charging member is composed of the surface of the matrix and the surface of the domain, and has a plurality of recesses,
The domain is present at the bottom of the recess, and is exposed on the surface of the charging member only at the bottom of the recess,
The elastic layer has a volume resistivity of 1 × 10 ⁵ Ωcm to 1 × 10 ⁸ Ωcm,
A1 is a current value when a DC voltage of 80 V is applied between the conductive support and the cantilever of the atomic force microscope brought into contact with the surface of the matrix constituting the surface of the charging member;
When the current value when an AC voltage of 80 V is applied between the conductive support and the cantilever of the atomic force microscope brought into contact with the surface of the domain constituting the surface of the charging member is A2. , A2 is 20 times or more of A1.   The charging member according to claim 1, wherein the volume fraction of the domain is 5% by volume or more and 25% by volume or less based on the volume of the elastic layer.   The charging member according to claim 1, wherein the number of the domains existing in a 10 μm cube in the elastic layer is 1 or more and 500 or less.   An electrophotographic apparatus comprising: an electrophotographic photosensitive member; and a charging member arranged to be able to charge the electrophotographic photosensitive member, wherein the charging member is according to any one of claims 1 to 3. An electrophotographic apparatus comprising the charging member described above. A process cartridge that is removable from the main body of the electrophotographic apparatus,
It comprises an electrophotographic photosensitive member and a charging member arranged to be able to charge the electrophotographic photosensitive member, and the charging member is the charging member according to any one of claims 1 to 3. Process cartridge characterized by. A method for manufacturing a charging member, comprising:
The charging member has a conductive support and an elastic layer,
The elastic layer is a surface layer of the charging member composed of a single layer,
And a domain containing carbon black and rubber, and a matrix containing rubber and having a higher electrical resistance than the domain,
The surface of the charging member is composed of the surface of the matrix and the surface of the domain, and has a plurality of recesses,
The domain is present at the bottom of the recess, and is exposed on the surface of the charging member only at the bottom of the recess,
The production method includes the following steps (A) to (C):
(A) a step of preparing a carbon masterbatch comprising carbon black and rubber and serving as the domain;
(B) a step of kneading the carbon masterbatch and a rubber composition to be the matrix to prepare a rubber composition having a domain / matrix structure; and (C) a rubber composition having the domain / matrix structure. A step of extruding an object together with a core bar from a cross head, and coating the periphery of the core bar with a rubber composition having the domain matrix structure;
When the die swell value of the carbon master batch is DS (d) and the die swell value of the rubber composition as the matrix is DS (m), the ratio of the die swell values DS (m) / DS (d) Is larger than 1.0, The manufacturing method of the charging member characterized by the above-mentioned.   The method for manufacturing a charging member according to claim 6, wherein the DS (m) / DS (d) is 1.1 or more. The volume resistivity of the elastic layer is 1 × 10 ⁵ Ωcm or more and 1 × 10 ⁸ Ωcm or less,
A1 is a current value when a DC voltage of 80 V is applied between the conductive support and the cantilever of the atomic force microscope brought into contact with the surface of the matrix constituting the surface of the charging member;
When the current value when applying a direct current voltage of 80 V between the conductive support and the cantilever of the atomic force microscope brought into contact with the surface of the domain constituting the surface of the charging member is A2, The method for manufacturing a charging member according to claim 6, wherein A2 is 20 times or more of A1.

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