Conductive member, process cartridge, and electrophotographic image forming apparatus
阅读说明：本技术 导电性构件、处理盒、和电子照相图像形成设备 (Conductive member, process cartridge, and electrophotographic image forming apparatus ) 是由 西冈悟 山内一浩 渡边宏晓 古川匠 伏本康宏 仓地雅大 高岛健二 菊池裕一 佐藤加奈 于 2020-03-27 设计创作，主要内容包括：本发明涉及导电性构件、处理盒和电子照相图像形成设备。提供可以稳定地抑制电子照相图像中起雾的出现的电子照相用导电性构件。所述构件包含具有导电性外表面的支承体,和在支承体的外表面上的导电层,导电层具有包括第一橡胶的交联产物的基体,和分散在基体中的多个域,域各自包括第二橡胶的交联产物和导电性颗粒,域中的至少一部分露出导电性构件的外表面以在构件的外表面上构成凸部,导电性构件的外表面由基体和露出电子照相用导电性构件的外表面的域构成,电子照相用导电性构件的阻抗为1.0×10<Sup>3</Sup>Ω以上且1.0×10<Sup>8</Sup>Ω以下,并且一部分域满足两个特定要求。(The invention relates to a conductive member, a process cartridge, and an electrophotographic image forming apparatus. Provided is a conductive member for electrophotography which can stably suppress the occurrence of fogging in an electrophotographic image. The member includes a support having an electrically conductive outer surface, and an electrically conductive layer on the outer surface of the support, the electrically conductive layer having a matrix including a crosslinked product of a first rubber, and a plurality of domains dispersed in the matrix, the domains each including a crosslinked product of a second rubber and an electrically conductive particleAt least a part of the domains are exposed to the outer surface of the conductive member to form a convex portion on the outer surface of the member, the outer surface of the conductive member is composed of a base and domains exposed to the outer surface of the conductive member for electrophotography, and the impedance of the conductive member for electrophotography is 1.0 × 10 3 Omega is 1.0 × 10 8 Ω or less, and a part of the domain satisfies two specific requirements.)
1. An electroconductive member for electrophotography, characterized by comprising:
a support having an electrically conductive outer surface; and
an electrically conductive layer on the outer surface of the support,
the conductive layer has a matrix including a crosslinked product of a first rubber, and a plurality of domains dispersed in the matrix,
the domains each include a crosslinked product of the second rubber and conductive particles,
at least a part of the domains exposes an outer surface of the electroconductive member for electrophotography to constitute a convex portion on the outer surface of the electroconductive member for electrophotography,
the outer surface of the electroconductive member for electrophotography is composed of the base and the domain exposing the outer surface of the electroconductive member for electrophotography,
wherein the electroconductive member for electrophotography has an impedance of 1.0 × 103Omega is 1.0 × 108Omega or less, the impedance being obtained by applying an alternating voltage having an amplitude of 1V and a frequency of 1.0Hz between the outer surface of the support and a platinum electrode directly provided on the outer surface of the conductive member for electrophotography in an environment of a temperature of 23 ℃ and a relative humidity of 50%, and wherein
When the length of the conductive layer in the length direction is defined as L, and the thickness of the conductive layer is defined as T,
obtaining a cross section of the conductive layer in a thickness direction thereof at three positions including a central position of the conductive layer in a length direction and two positions corresponding to L/4 from both ends of the conductive layer to the center of the conductive layer in the length direction, and
assuming that three observation regions each having a square of 15 μm are arbitrarily provided in a thickness region of each of the cross sections, the thickness region corresponding to a region between a depth of 0.1T and a depth of 0.9T from an outer surface of the conductive layer,
80% by number or more of the domains observed in each of the total nine observation regions satisfy the following requirements (1) and (2):
requirement (1): a ratio of a cross-sectional area of the conductive particles included in a domain to be determined to a cross-sectional area of the domain, among domains included in the observation region, is 20% or more; and
requirement (2): A/B is 1.00 or more and 1.10 or less, where A is a perimeter of the domain, and B is an envelope perimeter of the domain.
2. The electroconductive member for electrophotography according to claim 1, wherein the volume resistivity ρ m of the base is 1.0 × 108Omega cm or more and 1.0 × 1017Omega cm or less.
3. The electroconductive member for electrophotography according to claim 1, wherein an average value of maximum Ferrett diameters Df of the domains satisfying the requirements (1) and (2) is in a range of 0.1 μm or more and 5.0 μm or less.
4. The electroconductive member for electrophotography according to claim 1, wherein the proportion in the claim (1) is 25% or more and 30% or less.
5. The electroconductive member for electrophotography according to claim 1, wherein the electroconductive particles are electroconductive carbon black.
6. The electroconductive structure for electrophotography according to claim 5Wherein the DBP absorption of the conductive carbon black is 40cm3More than 100g and 80cm3The volume is less than 100 g.
7. The electroconductive member for electrophotography according to claim 5, wherein an arithmetic average inter-wall distance C of the electroconductive carbon black included in each of the domains satisfying requirements (1) and (2) is 110nm or more and 130nm or less, and
when the standard deviation of the distance between the walls of the conductive carbon black is defined as sigma m, the sigma m/C is more than 0.0 and less than 0.3.
8. The electroconductive member for electrophotography according to claim 1, wherein the difference between absolute values of solubility parameters of the first rubber and the second rubber is 0.4 (J/cm)3)0.5Above and 4.0 (J/cm)3)0.5The following.
9. The electroconductive member for electrophotography according to claim 1, wherein the height of each of the convex portions is 50nm or more and 200nm or less.
10. The electroconductive member for electrophotography according to claim 1, wherein an arithmetic average inter-wall distance Dm of a domain that exposes an outer surface of the electroconductive member for electrophotography to constitute a convex portion is 2.00 μm or less.
11. The electroconductive member for electrophotography according to claim 1, wherein the volume resistivity ρ m of the base is 1.0 × 1010Omega cm or more and 1.0 × 1017Omega cm or less.
12. The electroconductive member for electrophotography according to claim 1, wherein the volume resistivity ρ m of the base is 1.0 × 1012Omega cm or more and 1.0 × 1017Omega cm or less.
13. An electrophotographic process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, characterized in that the process cartridge comprises the electroconductive member for electrophotography according to any one of claims 1 to 12.
14. A process cartridge according to claim 13, wherein said conductive member for electrophotography is included as a charging member.
15. An electrophotographic image forming apparatus characterized by comprising the electroconductive member for electrophotography according to any one of claims 1 to 12.
16. An electrophotographic image forming apparatus according to claim 15, wherein the electroconductive member for electrophotography is included as a charging member.
Technical Field
The present disclosure relates to an electroconductive member for electrophotography, a process cartridge, and an electrophotographic image forming apparatus.
Background
In an image forming apparatus employing an electrophotographic method (hereinafter, referred to as an electrophotographic image forming apparatus), conductive members such as a charging member, a transfer member, and a developing member are used. The conductive member includes a conductive layer coated on an outer peripheral surface of the conductive support, and is used to transport electric charges from the conductive support to a surface of the conductive member and apply the electric charges to a contact object by discharge or the like.
For example, the charging member is a member that generates electric discharge between the transfer member and the photoreceptor and charges the surface of the photoreceptor. The transfer member transfers the developer from the photoreceptor to a printing medium or an intermediate transfer member, and generates electric discharge to stabilize the transferred developer.
According to the recent demand for improving the image quality of an electrophotographic image forming apparatus, it is considered to raise the voltage applied to the conductive member in order to achieve a high contrast. Under such high voltage application conditions, the conductive member needs to further uniformly charge the photoreceptor or a contact object such as an intermediate transfer body or a printing medium.
Japanese patent application laid-open No.2002-3651 discloses a rubber composition having a sea-island structure and a charging member formed of a rubber composition comprising a polymer continuous phase formed of an ion-conductive rubber material and a polymer particle phase formed of an electron-conductive rubber material, wherein the ion-conductive rubber material mainly contains a polymer having an inherent volume resistivity of 1 × 1012The raw material rubber A having a thickness of not more than Ω · cm and the electronically conductive rubber material have conductivity by containing the raw material rubber B and the conductive particles.
Disclosure of Invention
An object of one aspect of the present disclosure is to provide an electroconductive member for electrophotography that can stably suppress the occurrence of "fogging" in an electrophotographic image even when a charging bias is increased.
It is another object of another aspect of the present disclosure to provide a process cartridge that facilitates stable formation of high-quality electrophotographic images. It is still another object of an aspect of the present disclosure to provide an electrophotographic image forming apparatus that can stably form a high-quality electrophotographic image.
In accordance with one aspect of the present disclosure,
provided is an electroconductive member for electrophotography, which comprises:
a support having an electrically conductive outer surface; and
an electrically conductive layer on the outer surface of the support,
the conductive layer has a matrix (matrix) including a crosslinked product of a first rubber, and a plurality of domains (domains) dispersed in the matrix,
the domains each include a crosslinked product of the second rubber and conductive particles,
at least a part of the domains exposes an outer surface of the electroconductive member for electrophotography to constitute a convex portion on the outer surface of the electroconductive member for electrophotography,
the outer surface of the electroconductive member for electrophotography is composed of the base and the domain exposing the outer surface of the electroconductive member for electrophotography,
wherein the electroconductive member for electrophotography has an impedance of 1.0 × 103Omega is 1.0 × 108Omega or less, the impedance being obtained by applying an alternating voltage having an amplitude of 1V and a frequency of 1.0Hz between the outer surface of the support and a platinum electrode directly provided on the outer surface of the conductive member for electrophotography in an environment of a temperature of 23 ℃ and a relative humidity of 50%, and wherein
When the length of the conductive layer in the length direction is defined as L, and the thickness of the conductive layer is defined as T,
obtaining a cross section of the conductive layer in a thickness direction thereof at three positions including a central position of the conductive layer in a length direction and two positions corresponding to L/4 from both ends of the conductive layer to the center of the conductive layer in the length direction, and
assuming that three observation regions each having a square of 15 μm are arbitrarily set in a thickness region (region) of each of the cross sections, the thickness region corresponding to a region between a depth of 0.1T and a depth of 0.9T from the outer surface of the conductive layer,
80% by number or more of the domains observed in each of the total nine observation regions satisfy the following requirements (1) and (2):
requirement (1): a ratio of a cross-sectional area of the conductive particles included in the region to be determined to a cross-sectional area of the region is 20% or more among the regions included in the observation region; and
requirement (2): A/B is 1.00 or more and 1.10 or less, where A is a perimeter of a domain, and B is an envelope perimeter (envelope perimeter) of the domain.
Further, according to another aspect of the present disclosure, there is provided a process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, wherein the conductive member for electrophotography is included.
Further, according to still another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus including the conductive member for electrophotography.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Drawings
Fig. 1 is a sectional view of an electrophotographic conductive member according to an embodiment of the present disclosure in a direction perpendicular to a longitudinal direction of the electrophotographic conductive member.
Fig. 2 is a sectional view of a conductive layer of a conductive member for electrophotography according to an embodiment of the present disclosure in a direction perpendicular to a length direction of the conductive layer.
Fig. 3A and 3B are explanatory diagrams of impedance measurement of the conductive layer of the conductive member for electrophotography.
Fig. 4 is a schematic diagram illustrating the maximum Feret's diameter of a domain according to the present disclosure.
Fig. 5 is a schematic diagram illustrating an envelope perimeter of a domain according to the present disclosure.
Fig. 6A and 6B are explanatory diagrams for measuring a slice of a domain shape according to the present disclosure.
Fig. 7 is a sectional view of a process cartridge according to an embodiment of the present disclosure.
Fig. 8 is a sectional view of an electrophotographic image forming apparatus according to an embodiment of the present disclosure.
Detailed Description
The inventors have tried to obtain an electrophotographic image with a higher contrast when the electrophotographic image is formed by using the charging member according to japanese patent application laid-open No. 2002-3651. Specifically, the charging bias between the charging member and the electrophotographic photoreceptor is raised to a higher voltage (e.g., -1,500V or more) than a general charging bias (e.g., -1,000V or more). As a result, for example, the reversed toner is also developed on the solid white portion on the photosensitive drum where the toner was not originally developed, thereby forming an image with so-called "fogging". In addition, a so-called transfer residual toner adheres to the surface of the charging member, and charging performance changes with time in some cases.
The inventors have studied the cause of fogging on an electrophotographic image caused when the charging bias is raised according to the charging member of japanese patent application laid-open No. 2002-3651. In the process, the present inventors focused on the action of the polymer particle phase formed of the electron conductive rubber material in the charging member according to japanese patent application laid-open No. 2002-3651. That is, it is considered that electron conductivity is imparted to the elastomer layer by electron exchange between the polymer particle phase and the polymer continuous phase present in the vicinity of the polymer particle phase in the elastomer layer. In addition, it is presumed that the occurrence of fogging is caused by electric field concentration when the charging bias is raised. Electric field concentration is a phenomenon in which current concentrates when a specific portion is energized.
That is, according to the observation of the present inventors, the polymer particle phase according to Japanese patent application laid-open No.2002-3651 has a deformed shape, and there are irregularities on the outer surface of the polymer particle phase. The electron exchange between the polymer particle phases is concentrated on the convex portions of the polymer particle phases, whereby the flow of current becomes uneven 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. Therefore, the discharge from the outer surface of the charging member to the electrophotographic photoreceptor (which is a charged object) becomes uneven, whereby the surface potential of the electrophotographic photoreceptor becomes uneven. As a result, it is presumed that fogging occurs in the electrophotographic image.
Therefore, the present inventors confirmed that fogging in an electrophotographic image is effectively suppressed by eliminating the concentration point of electron exchange between polymer particle phases when the charging bias is raised. Therefore, as a result of intensive studies based on the knowledge, the present inventors found that, by using a conductive member for electrophotography that includes a support whose outer surface is conductive, and a conductive layer on the outer surface of the support, and satisfies the following requirements (a) and (B), fogging in an electrophotographic image can be effectively suppressed even when a high charging bias is applied.
Requirement (A):
the conductive layer has a matrix including a crosslinked product of the first rubber, and a plurality of domains (having a sea-island structure) dispersed in the matrix. The domain includes a crosslinked product of the second rubber and the conductive particles. Further, when a platinum electrode is directly provided on the outer surface of the conductive member for electrophotography, and an Alternating Current (AC) voltage having an amplitude of 1V and a frequency of 1.0Hz is applied between the outer surface of the support and the platinum electrode in an environment of a temperature of 23 ℃ and a relative humidity of 50%, the impedance is in the following range:
1.0×103omega is 1.0 × 108Omega is less than or equal to.
Requirement (B):
when the length of the conductive layer in the length direction is defined as L, and the thickness of the conductive layer is defined as T,
obtaining a cross section of the conductive layer in a thickness direction thereof at three positions including a central position of the conductive layer in the length direction and two positions corresponding to a center L/4 of the conductive layer in the length direction from both ends of the conductive layer, and assuming that three observation regions each having a 15 μm square are arbitrarily provided in a thickness region of each of the cross sections, the thickness region corresponding to a region between a depth of 0.1T and a depth of 0.9T from an outer surface of the conductive layer, 80% by number or more of domains observed in the total of nine observation regions satisfy the following requirements (B1) and (B2):
requirement (B1): a ratio of a cross-sectional area of the conductive particles included in the region to be determined to a cross-sectional area of the region is 20% or more among the regions included in the observation region;
requirement (B2): A/B is 1.00 or more and 1.10 or less, where A is a perimeter of the domain, and B is an envelope perimeter of the domain.
Hereinafter, each requirement will be described in detail.
In the case of the requirement (A),
requirement (a) indicates the degree of conductivity of the conductive layer. The conductivity of the conductive member for electrophotography is within the following range: impedance of 10 at 1Hz3Omega is 10 or more8Omega is less than or equal to. When the impedance is 103When Ω or more, the amount of discharge current can be suppressed from excessively increasing. As a result, potential unevenness caused by abnormal discharge can be prevented. In addition, when the impedance is 108When Ω or less, insufficient charging due to insufficient total amount of discharge current can be suppressed.
The impedance according to the requirement (a) can be measured by the following method.
When measuring the impedance, in order to clear the influence of the contact resistance between the charging member and the measurement electrode, it is preferable to form a thin film formed of platinum on the outer surface of the charging member, use the thin film as an electrode, use the conductive support as a ground electrode, and measure the impedance at both terminals.
As a method of forming a thin film, a method of forming a metal film by metal vapor deposition, sputtering, coating of a metal paste, and attachment of a metal tape can be used. Among them, a method of forming a thin film formed of platinum by vapor deposition is preferable from the viewpoint of reducing the contact resistance with the charging member.
When forming a platinum thin film on the surface of the charging member, it is preferable to use a mechanism that can hold the charging member to the vacuum vapor deposition apparatus and a vacuum vapor deposition apparatus to which a mechanism that can rotate with respect to the charging member having a cylindrical cross section is imparted, in view of ease of formation and uniformity of the thin film.
It is preferable that a platinum electrode having a width of about 10mm in the length direction (in the axial direction of the cylindrical shape) is formed on the charging member having a cylindrical section, and a metal piece wound around the platinum electrode so as to be in contact with the platinum electrode is connected to a test electrode coming out of the test apparatus to perform the measurement. Therefore, the impedance can be measured without the influence of the vibration of the outer diameter of the charging member or the surface shape. As the metal sheet, aluminum foil, metal tape, or the like can be used.
The device for measuring impedance may be a device that can measure impedance, such as an impedance analyzer, a network analyzer, or a spectrum analyzer. Among them, it is preferable to measure the impedance from the range of the resistance of the charging member with an impedance analyzer.
Fig. 3A and 3B are schematic views showing a state in which a measurement electrode is formed on an electrophotographic conductive member. In fig. 3A and 3B,
In addition, the impedance was measured with an impedance measuring device (Solartron 126096W-type dielectric impedance measuring system, manufactured by TOYO Corporation, not shown) by connecting the measuring electrode 33 from the
The impedance was measured at a vibration voltage of 1Vpp and a frequency of 1.0Hz in an environment of a temperature of 23 c and a relative humidity of 50%, and an absolute value of the impedance was obtained.
The conductive member for electrophotography is divided into five regions in the longitudinal direction, and measurement is arbitrarily performed once from each region, thereby performing five measurements in total. The average value thereof is defined as the resistance of the conductive member for electrophotography.
Requirement (B)
In the requirement (B1) of the requirement (B), the amount of conductive particles included in each domain in the conductive layer is measured. In addition, the requirement (B2) specifies that the domain has small irregularities on its outer peripheral surface or that the domain has no irregularities on its outer peripheral surface.
As a result of analyzing the conductive member for electrophotography disclosed in japanese patent application laid-open No.2002-3651, it was confirmed that the domain has irregularities or has a high aspect ratio. As a result of intensive studies, it was found that the above problem of fogging can be significantly suppressed when a high voltage is applied by making the shape of the domain closer to a true circle having small irregularities.
As described above, in the conductive domain/non-conductive matrix structure in which only the domains have conductivity, inside the conductive member for electrophotography, a plurality of domains provide conductivity, and charge exchange is performed between the domains. In the case where the convex portion exists in the domain, an electric field concentrates on the convex portion, charge exchange between adjacent domains easily proceeds at the convex portion, and a current excessively flows at the convex portion. That is, charges easily flow from the convex portion of the domain to the domain adjacent to the convex portion. By this phenomenon, local strong discharge is generated from the surface of the conductive member for electrophotography, and when the conductive member for electrophotography is used as a charging member, potential unevenness of the photoreceptor is generated.
That is, it is effective to make the domain as close to a true circle shape as possible. In other words, it is preferable that the domains have no irregularities.
Regarding the requirement (B1), the present inventors obtained the following findings: when focusing on a domain, the amount of conductive particles included in the domain affects the shape of the domain. Namely, the present inventors obtained the following findings: as the filling amount of the conductive particles in one domain increases, the shape of the domain becomes closer to a spherical shape. Because the number of domains that are nearly spherical is large, the concentration point of electronic exchange between domains can be reduced. As a result, fogging in the electrophotographic image observed in the charging member according to japanese patent application laid-open No.2002-3651 can be reduced.
Therefore, according to the study of the present inventors, a domain in which the proportion of the total cross-sectional area of the conductive particles observed in the cross-section is 20% or more based on the area of the cross-section of one domain has an outline shape that can significantly alleviate the concentration of electron exchange between domains. In particular, the domains may have a more spherical shape.
The requirement (B2) specifies the existence degree of the unevenness including the convex portion on the outer surface of the domain, which may be a concentration point of the electron exchange between the domains.
That is, when the (a/B) value of the requirement (B2) indicating the degree of unevenness is 1.00 by defining the perimeter of the domain as a and the envelope perimeter of the domain as B, the domain does not have any unevenness on the outer surface thereof, and as a result, the concentration of the electric field can be more firmly suppressed. Further, the larger the increase in the value of the requirement (B2), the more the domain has irregularities on the outer surface thereof, and therefore the domain of the requirement (B2) has a large value, resulting in electric field concentration at the convex portions of the irregularities. It was found that the value of (B2) is required to be 1.10 or less so that the electric field concentration caused by the convex portions of the domains can be suppressed. It should be noted that, as shown in fig. 5, the envelope circumference is a circumference (broken line 52) when the convex portions of the domain 51 observed in the observation region are connected to each other and the circumference of the concave portion is ignored.
From the above results, the present inventors found that, when 80% by number or more of domains in the cross section of the conductive layer observed in each of nine observation regions simultaneously satisfy requirements (a) and (B), electric field concentration inside the conductive member for electrophotography can be suppressed, and uniform discharge can be obtained. As a result, fogging in the photoreceptor when a high voltage is applied by the charging member can be suppressed. It should be noted that, in the requirement (B), the observation target of the domain is in the range from the outer surface of the conductive layer to a depth of 0.1T to 0.9T from the outer surface of the conductive layer in the cross section of the conductive layer in the thickness direction. In this sense, it is considered that the electron transfer from the conductive support to the outer surface of the conductive layer is mainly controlled by the domains existing in this range.
The present inventors further studied that the adhesion of toner to the surface of the charging member changes the charging performance of the charging member according to japanese patent application laid-open No.2002-3651 with time. Even the toner remaining on the photoreceptor after the transfer process (hereinafter, also referred to as "transfer residual toner") is often charged to the same polarity (positive polarity) as that of the voltage in the transfer process. Therefore, the transfer residual toner reaching the nip portion between the photoconductor and the charging member is electrostatically attached to the surface of the charging member. As a result, the surface of the charging member is gradually contaminated with the transfer residual toner, whereby stable discharge from the surface of the charging member may be hindered. Therefore, in order to suppress the transfer residual toner from being electrostatically attached to the outer surface of the charging member, it is effective to reverse the charge of the transfer residual toner.
Here, the inventors studied to reverse the charge of the transfer residual toner using an electroconductive member for electrophotography that can effectively suppress fogging in an electrophotographic image and also satisfies requirements (a) and (B) even when a high charging bias is applied. As a result, it was found that, in addition to the requirements (a) and (B), the charge of the transfer residual toner is extremely efficiently reversed by exposing at least a part of the domain to the outer surface of the electroconductive member for electrophotography to constitute a convex portion on the outer surface of the electroconductive member for electrophotography (hereinafter, also referred to as requirement (C)).
By exposing the domains on the outer surface of the electroconductive member for electrophotography to constitute the convex portions, the transfer residual toner reaching the nip portion between the charging member and the photosensitive drum is likely to physically contact with the convex portions. Further, the transfer residual toner charged positively is electrostatically attached to the convex portions where negative charges are accumulated, and therefore, the contact probability between the transfer residual toner and the convex portions is further increased. As a result of the transfer residual toner coming into contact with the convex portions, negative charges are injected into the transfer residual toner, and the transfer residual toner is made negative.
Further, by contacting a domain that delivers electric charge to the transfer residual toner, electric charge can be stably and continuously received from another domain present in the conductive layer. Therefore, it is considered that the transfer residual toner reaching the nip portion can be made more reliably negative.
Specifically, the height of each convex portion is preferably 50nm or more and 200nm or less. When the height of each convex portion is 50nm or more, the conductive convex portion may be likely to come into contact with the toner being inverted. In addition, when the height of each convex portion is 100nm or more, the conductive convex portion may be more likely to come into contact with the reversed toner, whereby fogging due to the reversed toner may be reduced. Meanwhile, since charge unevenness derived from the convex portions is generated in the discharge region, the height of each convex portion is preferably 200nm or less.
In addition, an arithmetic average value Dm of distances between adjacent walls of the domains of the outer surface of the conductive member for electrophotography (hereinafter, also simply referred to as "inter-domain distance Dm") is preferably 2.00 μm or less. When the inter-domain distance Dm is 2.00 μm or less, the convex portion of the conductive domain is more likely to come into contact with the reversal toner.
Therefore, in the case of the conductive member for electrophotography, electric field concentration in the conductive layer can be suppressed by requiring (a) and (B) to make the domains approach a true circle, and adhesion of reverse toner can be suppressed by requiring (C) charge injection by the convex portions of the domains. As a result, even when the charging bias is raised, fogging can be significantly reduced.
< conductive Member for electrophotography >
A conductive member for electrophotography according to an embodiment of the present disclosure, in particular, a conductive member for electrophotography having a roller shape (hereinafter, also referred to as a "conductive roller") will be described using the drawings.
Fig. 1 is a sectional view perpendicular to a direction along the axis of the conductive roller (hereinafter, also referred to as "longitudinal direction"). The
Fig. 2 is a sectional view of the
< method for confirming matrix-Domain Structure >
For example, the matrix-domain structure can be confirmed as follows. Specifically, a sheet of a conductive layer can be produced from the conductive member for electrophotography for detailed observation. Examples of devices for obtaining flakes may include sharp razors, microtomes, and FIBs. In addition, in order to appropriately perform observation of the matrix-domain structure, pretreatment such as dyeing treatment or vapor deposition treatment that can obtain a preferable contrast between the conductive phase and the insulating phase may be performed. The thin sheet having undergone fracture surface formation and pretreatment may be observed with a laser microscope, a Scanning Electron Microscope (SEM), or a Transmission Electron Microscope (TEM).
The conductivity of the conductive member for electrophotography can be evaluated by measuring the impedance at 1Hz, specifically, the impedance at 1Hz is preferably 103Omega is 10 or more8In the range of not more than Ω. When the impedance at 1Hz is 103When Ω or more, the amount of discharge current can be suppressed from excessively increasing. As a result, potential unevenness caused by abnormal discharge can be prevented. When the impedance at 1Hz is 108When Ω or less, insufficient charging due to insufficient total discharge current can be suppressed.
< conductive support >
As a material constituting the support, a material known in the field of an electrophotographic conductive member, which can be used as a material of an electrophotographic conductive member, can be appropriately selected and used. Examples of the material include aluminum, stainless steel, synthetic rubber having conductivity, metals such as iron and copper alloys, or alloys.
In addition, these materials may be subjected to oxidation treatment or plating treatment with chromium or nickel. As the type of plating, any of electroplating or electroless plating may be used. From the viewpoint of dimensional stability, electroless plating is preferable. Examples of the kind of electroless plating that can be used here include nickel plating, copper plating, gold plating, and plating with other various alloys.
The plating thickness is preferably 0.05 μm or more, and in view of the balance between the work efficiency and the rust inhibitive ability, it is preferable that the plating thickness is 0.10 μm or more and 30.00 μm or less. The cylindrical shape of the support body may be a solid cylindrical shape and may be a hollow cylindrical shape. The outer diameter of the support is preferably in the range of 3mm to 10 mm.
< conductive layer >
< substrate >
The matrix comprises a crosslinked product of a first rubber the matrix preferably has a viscosity of 1.0 × 108Omega cm or more and 1.0 × 1017Volume resistivity ρ m of not more than Ω · cm.
When the volume resistivity of the matrix is 1.0 × 108In particular, in the case where the conductivity of the matrix is high (the volume resistivity of the matrix is low) and ion conductivity is exhibited, the matrix promotes excessive charge exchange between the conductive domains, and in addition, in the case where electric field concentration is generated by a small change in the domain shape, current tends to excessively flow, and therefore, it is preferable that the matrix has 1.0 × 108The volume resistivity ρ m of Ω · cm or more is set so as to suppress the ion conductivity of the substrate.
When the volume resistivity ρ m of the matrix is 1.0 × 1017When Ω · cm or less, the conductivity required for the entire conductive layer can be obtained without hindering the charge exchange between the conductive domains. Therefore, it is possible to suppressImage defects caused by insufficient charge.
More preferably, the substrate has a thickness of 1.0 × 1010Omega cm or more and 1.0 × 1017In this range, the influence of the ion conductivity of the matrix is suppressed, whereby the volume resistivity required for the conductive member for electrophotography can be obtained, the matrix further preferably has a volume resistivity ρ m of 1.0 × 1012Omega cm or more and 1.0 × 1017Volume resistivity ρ m of not more than Ω · cm. In this range, the electric field concentration is strongly suppressed, and the volume resistivity required for the conductive member for electrophotography can be obtained even when a high voltage is applied.
< volume resistivity of matrix ρ m >
For example, by cutting a sheet having a predetermined thickness (for example, 1 μm) included in the matrix-domain structure from the conductive layer and bringing a fine probe of a scanning electron microscope (SPM) or an Atomic Force Microscope (AFM) into contact with a matrix in the sheet, the volume resistivity ρ m of the matrix can be calculated.
For example, as shown in fig. 6A, when the length direction of the conductive member for electrophotography is the X-axis, the thickness direction of the conductive layer is the Z-axis, and the circumferential direction of the conductive layer is the Y-axis, the sheet is cut out from the conductive layer so that the sheet includes at least a part of a cross section 62a parallel to the XZ plane. In addition, as illustrated in fig. 6B, the sheet is cut out so that at least a part of the YZ plane (e.g., 63a, 63B, and 63c) is perpendicular to the axial direction of the conductive member for electrophotography. Examples of the apparatus for obtaining a thin slice may include a sharp razor, a microtome, and a Focused Ion Beam (FIB) method.
For the measurement of volume resistivity, one surface of a sheet cut out from a conductive layer is grounded. Next, a fine probe of a scanning electron microscope (SPM) or an Atomic Force Microscope (AFM) was brought into contact with the base portion of the surface opposite to the ground surface of the chip, a Direct Current (DC) voltage of 50V was applied thereto for 5 seconds, and the resistance value was calculated by calculating an arithmetic average of values obtained by measuring the ground current value for 5 seconds and dividing the applied voltage by the calculated value. Finally, the resistance value is converted into volume resistivity by using the thickness of the sheet. In this case, the resistance value and the thickness of the sheet may be measured simultaneously by SPM or AFM.
One sheet sample was cut out from each of the regions obtained by dividing the conductive layer into four in the circumferential direction and five in the longitudinal direction, measurement values were obtained, and then the arithmetic average of the volume resistivities of 20 samples in total was calculated, thereby obtaining the value of the volume resistivity of the matrix in the cylindrical charging member.
< first rubber >
The first rubber is a component mixed at the maximum mixing ratio in the rubber mixture for forming the conductive layer, and the mechanical strength of the conductive layer depends on the first rubber crosslinked product. Therefore, the first rubber exhibits the strength of the conductive layer required for the conductive member for electrophotography after crosslinking, and a rubber that can be separated from a second rubber described later and can form a matrix-domain structure is used as the first rubber.
Preferred examples of the first rubber may include the following.
Examples of the first rubber may 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 (EPEM), Chloroprene Rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated NBR (H-NBR), and silicone rubber.
< reinforcing Material >
In addition, as the reinforcing material, reinforcing carbon black may be contained in the matrix to the extent that the conductivity of the matrix is not affected. Examples of reinforcing carbon black used herein may include FEF, GPF, SRF, and MT carbon, which have low conductivity.
In addition, if necessary, fillers, processing aids, vulcanization accelerators, vulcanization acceleration aids, vulcanization retarders, antioxidants, softeners, dispersants, colorants, and the like, which are generally used as rubber compounding agents, may be added to the first rubber constituting the matrix.
< Domain >
The domains are electrically conductive and include a second rubber crosslinkHere, conductive means a volume resistivity of less than 1.0 × 108Ω·cm。
< second rubber >
As a specific example, the second rubber is preferably 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 terpolymer rubber (EPEM), Chloroprene Rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U).
< conductive particles >
Examples of the material of the conductive particles included in the domains may include carbon materials such as conductive carbon black or graphite; oxides such as titanium oxide or tin oxide; a metal such as Cu or Ag; and electron conductive agents such as conductive particles having a surface coated with an oxide or a metal. In addition, two or more of these conductive particles may be used in combination in a suitable amount, if necessary.
Further, it is preferable that the proportion in (B1) is required to be at least 20% or more, and preferably 25% or more and 30% or less. Within the above range, the conductive particles may be filled in the domains at a high density. Therefore, the outer shape of the domain can be made close to a sphere, and small irregularities as specified in requirement (B2) can be realized. Further, even in a high-speed process, the electric charge can be supplied in a sufficient amount.
Among various conductive particles, conductive particles containing conductive carbon black as a main component are preferable because the conductive particles have high affinity with rubber and the distance between the conductive particles is easily controlled. The type of the conductive carbon black included in the domain may not be particularly limited. Specific examples of the conductive carbon black may include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black. Among them, as described below, in particular, a DBP absorption of 40cm can be suitably used3More than 100g and 80cm3Carbon black of 100g or less.
< shape of conductive Domain >
The present inventors found that by bringing the conductive domain further close to a circular shape, the electric field concentration due to the convex shape of the conductive domain can be minimized, and thus excessive charge transfer can be suppressed, and the photoreceptor can be uniformly charged when a high voltage is applied. As a result, fogging can be suppressed.
The shape of each domain is determined as follows. Here, the length of the conductive layer in the length direction is defined as L and the thickness of the conductive layer is defined as T. The cross section of the conductive layer in the thickness direction thereof is obtained at three positions including a central position of the conductive layer in the length direction and two positions corresponding to L/4 from both ends of the conductive layer to the center of the conductive layer in the length direction, respectively. Then, three observation regions each having a square of 15 μm are provided at arbitrary three positions in the thickness region of each cross section. The thickness region corresponds to a region between a depth of 0.1T and a depth of 0.9T from the outer surface of the conductive layer, as shown in fig. 6B. In this case, the shape observed in each of all nine observation regions is defined as the shape of the domain.
Preferably, the shape of the domains is more rounded as described above. Specifically, it is necessary that 80% or more of domains in a region 15 μm square in the cross section in the thickness direction of the conductive layer satisfy the following requirements (B1) and (B2).
Requirement (B1): a ratio of a cross-sectional area of the conductive particles included in the region to be determined to a cross-sectional area of the region is 20% or more among the regions included in the observation region; and
requirement (B2): A/B is 1.00 or more and 1.10 or less, where A is a perimeter of the domain, and B is an envelope perimeter of the domain.
In requirement (B2), the minimum value of the ratio of the perimeter of the domain to the envelope perimeter of the domain is 1.00. A state with a ratio of 1.00 indicates that the domain has a true circle or ellipse. When the ratio exceeds 1.10, a large uneven shape exists in the domain, that is, electric field concentration is easily generated. When the requirement (B2) is satisfied, electric field concentration is suppressed, whereby fogging can be suppressed.
As shown in fig. 4, the maximum feret diameter Df is a value when the length of the perpendicular line obtained by sandwiching the outer periphery of the
The size of the domains is preferably within a certain range. The maximum Ferrett diameter, which is an index indicating the size of the domain, is preferably 0.1 μm or more and 5.0 μm or less. When the maximum feret diameter is within the above range, the domains are likely to have a circular shape.
As a result, fogging is reduced. Further, by making the size of the conductive domain fine, the discharge is made fine, whereby the image quality can be improved.
< method for measuring maximum Ferrett diameter, area, perimeter, envelope perimeter, and number of domains >
The method of measuring the maximum feret diameter, area, circumference, envelope circumference, and number of domains of a domain can be performed as follows. First, a cut piece was prepared in the same manner as in the method in the measurement of the volume resistivity of the substrate described above. Next, a sheet having a fracture surface may be formed by a method such as a freeze fracture method, a cross-grinding method, or a focused ion beam method (FIB). The FIB method is preferable in view of smoothness of the fracture surface and pretreatment for observation. In addition, in order to preferably perform observation of the matrix-domain structure, pretreatment such as dyeing treatment or vapor deposition treatment that can obtain contrast between the conductive phase and the insulating phase may be performed.
The sheet subjected to fracture surface formation and pretreatment can be observed with a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM). Among these, from the viewpoint of the accuracy of quantification of the area of the domain, it is preferable to perform observation with an SEM at a magnification of 1,000 to 100,000.
The maximum feret diameter, area, circumference, envelope circumference, and number of domains of the domain can be measured by quantifying the images taken above. That is, a 256-gray-scale monochrome Image of a fracture surface obtained by observation with an SEM was obtained by 8-bit graying using Image processing software (trade name: Image-ProPlus, manufactured by MediaCybernetics, Inc.). Next, black-and-white image inversion processing is performed to whiten the domain in the fracture surface, and the image is binarized. Subsequently, the maximum Ferrett diameter, area, perimeter, envelope perimeter, and number of domains for each domain in the set of domains in the image may be calculated.
When the length of the conductive layer of the conductive member for electrophotography in the longitudinal direction is defined as L, samples for the above measurement are obtained from slices of three sites located at the center of the conductive layer in the longitudinal direction and two sites corresponding to L/4 from both ends of the conductive layer to the center of the conductive layer.
The reason for evaluating the shape of the domains in the cross section perpendicular to the length direction of the conductive layer as described above will be described with reference to fig. 6A and 6B.
Fig. 6A and 6B illustrate the shape of the
Fig. 6A shows a view of a domain of the electroconductive member for electrophotography, which is cut out from a cross section 62a parallel to the XZ plane 62. The XZ plane can be rotated 360 ° around the axis of the electroconductive member for electrophotography. A cross section 62a parallel to the XZ plane 62 shows a surface where discharge is generated simultaneously at a certain timing, considering that the conductive member for electrophotography rotates while being in contact with the photosensitive drum, and the conductive member for electrophotography discharges while passing through a gap between the conductive member for electrophotography and the photosensitive drum. Therefore, the surface potential of the photosensitive drum is formed by passing the surface corresponding to a certain amount of the cross section 62 a. Since the large discharge on the surface of the photosensitive drum is locally increased by the local large discharge due to the electric field concentration in the electroconductive member for electrophotography, and thus the fogging is generated, it is necessary to perform evaluation relating to the surface potential of the photosensitive drum formed by passing a certain portion of a group of cross sections 62a, not a single cross section 62 a. Therefore, it is necessary to perform evaluation in a cross section (63a to 63c) parallel to the
The observation positions of the cross sections of the
< control of Domain shape >
The shape of the nearly circular domains in the matrix-domain is the focus of the effect of the present disclosure. Since the electric field concentration and the deformation of the domains are suppressed by the formation of the domains close to a circular shape or the reduction of the dimensional fluctuation of the maximum feret diameter, the fluctuation of the resistance is reduced.
The present inventors studied a method of making the sectional shape of the domain circular, that is, making the shape of the domain close to spherical. As a result, it was determined that the shape of the domain can be achieved by using the following two methods.
Reduce the size of the domain (maximum feret diameter).
Increase the amount of carbon gel in the domains.
The reason why the domain is made close to spherical by reducing its size (maximum feret diameter) is presumed as follows. The surface area of the domains increases even in the case where the size of the domains is small at the same volume fraction. As a result, the interface of the matrix and the domain increases. Since the number of molecules around the interface is larger than the number of molecules inside the matrix, the free energy of the molecules near the interface is larger than the free energy of the molecules inside the domain. In order to lower the free energy at the interface, it is considered that the interfacial tension acts to reduce the interface so that the domains approach a sphere (a circle in a cross section of the conductive layer in the thickness direction). As a result, electric field concentration can be prevented.
Method of reducing the size of the domains (maximum Ferrett diameter)
For the dispersed particle diameter (domain size) D when two types of incompatible polymers are melt-kneaded, formulas of Taylor, an empirical formula of Wu (Wu), and a formula of Tokita, represented by the following formulas (4) to (7), are proposed (see technical magazines 2003-II, 42, published by Sumitomo Chemical co.
Taylor's formula
Formula (4)
D＝[C·σ/ηm·γ]·f(ηm/ηd)
Empirical formula of Wu
Formula (5)
γ·D·ηm/σ＝4(ηd/ηm)0.84·ηd/ηm>1
Formula (6)
γ·D·ηm/σ＝4(ηd/ηm)-0.84·ηd/ηm<1
Tokita's formula
Formula (7)
In the formulae (4) to (7), D represents the domain size, C represents a constant, σ represents the interfacial tension, η m represents the viscosity of the matrix, η D represents the viscosity of the domain, γ represents the shear velocity, η represents the viscosity of the mixed system, P represents the collision coalescence probability,represents the volume of the domain phase, and EDK represents the domain phase cleavage energy.
As shown in the above equation, the shape of the domain close to a sphere can be formed mainly by controlling the following four points.
1. Difference in interfacial tension between domain and substrate
2. Ratio of viscosity of domains to viscosity of matrix
3. Shear rate at mixing/energy at shear
4. Volume fraction of domain
1. Difference in interfacial tension between domain and substrate
Generally, in the case of mixing two types of polymers, the phases thereof are separated. This phenomenon occurs because the same polymers are aggregated and the free energy is reduced to stabilize because the interaction between the same polymers is stronger than the interaction between different polymers. Since different macromolecules contact each other at an interface having a phase-separation structure, the free energy at the interface is higher than the free energy inside the phase-separation structure in which the interaction between the same macromolecules is stabilized. As a result, the free energy at the interface is reduced, thereby generating an interfacial tension that reduces the area in contact with the different polymer. In the case of small interfacial tensions, different polymers tend to be homogeneously mixed so as to increase entropy. The state where the high molecules are uniformly mixed indicates dissolution, and the SP value and the interfacial tension, which are the solubility criteria, tend to be correlated with each other. That is, since it is considered that the difference in interfacial tension between the domains and the matrix is related to the difference in SP value of the rubber materials constituting the domains and the matrix, the tension difference can be controlled by selecting the raw material rubber of the matrix, the domains, and the like. When the difference between the absolute values of the solubility parameters of the first rubber and the second rubber is 0.4 (J/cm)3)0.5Above and 4.0 (J/cm)3)0.5In the following, a stable phase-separated structure can be formed. The difference is more preferably 0.4 (J/cm)3)0.52.2 (J/cm) or more3)0.5The following. Within this range, a stable phase-separated structure can be formed, and the maximum Ferrett diameter of the domain can also be reduced.
2. Ratio of viscosity of domains to viscosity of matrix
Since the ratio of the viscosity of the domains to the viscosity of the matrix (η d/η m) is close to 1, the maximum Feret diameter of the domains can be reduced. The ratio of the viscosity of the domains to the viscosity of the matrix can be adjusted by selecting the mooney viscosity of the raw rubber, or the kind or amount of filler to be added. In addition, a plasticizer such as paraffin oil may also be added to the extent that the formation of a phase-separated structure is not hindered. The viscosity ratio can be adjusted by adjusting the temperature during kneading. It should be noted that the respective viscosities of the domains and the matrix can be obtained by measuring the mooney viscosity ML (1+4) at the rubber temperature at the time of kneading based on JIS K6300-1: 2013. In addition, the viscosity may be replaced with the index value of the raw rubber.
3. Shear rate at mixing/energy at shear
Since the shear rate at the time of mixing/the energy at the time of shearing are large, the maximum feret diameter of the domain can be reduced. The shear rate can be increased by increasing the inner diameter of the stirring member of the mixer such as a blade or a screw, decreasing the gap from the end face of the stirring member to the inner wall of the mixer, or increasing the rotational speed of the stirring member. In addition, the energy at the time of shearing can be increased by increasing the rotation speed of the stirring member, or increasing the viscosity of the raw material rubber for the domains and the viscosity of the raw material rubber for the matrix.
4. Volume fraction of domain
The volume fraction of domains in the conductive layer is related to the probability of collisional coalescence between the domains and the matrix. Specifically, as the volume fraction in the conductive layer decreases, the probability of collisional coalescence between the domains and the matrix decreases. That is, the size of the domains can be reduced by reducing the volume fraction of the domains within a range in which desired conductivity is obtained.
< method for measuring SP value >
By making a calibration curve using a material whose SP value is known, the SP value of the rubber constituting the matrix and the domain can be accurately calculated. As the known SP value, a catalog value of a raw material manufacturer can be used. For example, the NBR and SBR used in the present disclosure do not depend on molecular weight, and the SP value of the NBR and SBR is almost determined by the content ratio of acrylonitrile and styrene. Therefore, the content ratio of acrylonitrile and styrene in the rubber constituting the matrix and the domains was analyzed by pyrolysis gas chromatography (Py-GC) and solid-state NMR analysis methods. Thus, the SP value can be calculated from an analysis method of a calibration curve obtained from a material whose SP value is known.
In addition, the SP value of the isoprene rubber is determined in the structure of 1, 2-polyisoprene, 1, 3-polyisoprene, 3, 4-polyisoprene, cis-1, 4-polyisoprene, or trans-1, 4-polyisoprene isomer. Therefore, similarly to SBR and NBR, the SP value can be calculated from a material whose SP value is known by analyzing the content ratio of isomers by Py-GC and solid-state NMR.
The SP value of the material with known SP value was obtained by Hansen ball method.
Next, the reason why the domains are made close to spherical by increasing the amount of carbon gel in the domains will be described. Carbon gel is a particulate matter in a pseudo-crosslinked state due to adsorption of rubber molecules on carbon black. The carbon gel is not dissolved even in an organic solvent in which the raw material rubber is dissolved. That is, it is considered that three-dimensional crosslinks are formed by physical adsorption or chemical adsorption of rubber molecules on the surface of carbon black, and the carbon gel functions as rubber particles. As a result, it is presumed that the rubber particles formed in the carbon gel become nuclei and form domains. By increasing the amount of the carbon gel, the uneven shape of the domains can be suppressed and the electric field concentration can be suppressed as required (B2).
In order to increase the amount of the carbon gel, it is preferable to add carbon black in a large amount relative to the rubber, and the amount of carbon black functioning as a conductive adsorbent can be increased.
The DBP absorption is noted as an index for adding a large amount of carbon black to the domains. DBP absorption (cm)3Per 100g) is the volume of dibutyl phthalate (DBP) which can be adsorbed by 100g of carbon black and is measured according to JIS K6217.
Generally, carbon black has a clustered high order (tufted high order) structure in which primary particles having an average particle diameter of 10nm or more and 50nm or less are aggregated. The clustered high-order structures are called structures, the extent of which is absorbed by the DBP (cm)3100g) was used.
Generally, since carbon black having a developed structure has high reinforcing properties with respect to rubber, introduction of carbon black into rubber is deteriorated, and shear torque at the time of kneading is very high, and high filling is difficult.
As the conductive carbon black used in the present disclosure, it is preferable to use one having a DBP absorption of 40cm3More than 100g and 80cm3Carbon black of 100g or less. When the DBP absorption amount is within the above range, carbon black is added in a large amount relative to the rubber, so that the amount of carbon gel is increased.
In addition, when the DBP absorption amount is within the above range, the dispersibility of carbon black to rubber is good due to the small structure of conductive carbon black so that carbon black is less aggregated and the shape of unevenness is small even in a carbon black unit. Therefore, the shape of the domain is easily rounded. In the case of using carbon black having a developed structure, uniform dispersion with respect to rubber is difficult, and there is a possibility that carbon black is dispersed in an aggregated state. Initially, as described above, carbon black has a concave-convex shape because it has a cluster-like high-order structure, and a block having a large concave-convex structure is easily formed by aggregating the carbon black. When the aggregate of carbon black exists at the outer edge of the domain, the uneven structure can be formed by affecting the shape of the domain.
Further, it is preferable to add the conductive carbon black included in the domains so that C (also referred to as "arithmetic average inter-wall distance C") which is an arithmetic average of distances between adjacent carbons is 110nm or more and 130nm or less. When the arithmetic mean wall-to-wall distance C is 110nm or more and 130nm or less, electron exchange between carbon black particles by the tunnel effect is possible between almost all carbon blacks in the domain. That is, this is because, when the arithmetic mean inter-wall distance is satisfied, the volume resistivity of the domain becomes almost constant, and the electric field concentration is suppressed. In addition, this is because the resistance fluctuation is suppressed by the change in the distance between the carbon black walls caused by the repetition of the image output. Further, the amount of carbon gel exhibiting a crosslinked rubber property in the rubber in which carbon black is dispersed makes it easy to maintain the shape of the domains, and the molding domain is easily maintained in a circular shape. As a result, electric field concentration or variation in inter-domain distance due to deformation of the convex portions of the domains is suppressed, and uniform discharge is easily achieved.
The arithmetic mean wall-to-wall distance C of the conductive carbon black is 110nm or more and 130nm or less, and the standard deviation of the distribution of the wall-to-wall distances of the conductive carbon black is defined as σ · m. In this case, the coefficient of variation σ · m/C of the distance between the conductive carbon black walls is more preferably 0.0 or more and 0.3 or less. The coefficient of variation is a value representing variation (dispersion) in the distance between the walls of the conductive carbon black. When the distances between the conductive carbon black walls were all the same, the coefficient of variation was 0.0.
When the coefficient of variation σ · m/C is 0.0 or more and 0.3 or less, electron exchange by the tunnel effect between carbon blacks in the domains is possible due to a small deviation in the distance between the carbon black walls, whereby the volume resistivity is likely to be almost constant. In addition, since the carbon black is uniformly dispersed, uneven distribution of the conductive paths in the domains can be suppressed, whereby electric field concentration in the domains can be suppressed. As a result, since the shape of the domains and the electric field concentration in the domains can be suppressed, more uniform discharge is easily achieved.
The arithmetic mean C of the distances between the conductive carbon black walls in the domains and the ratio of the carbon black cross section to the cross-sectional area of the domains can be measured as follows. First, a sheet of a conductive layer is prepared. In order to preferably perform observation of the matrix-domain structure, a pretreatment such as a dyeing treatment or a vapor deposition treatment that can obtain a preferable contrast between the conductive phase and the insulating phase may be performed.
The sheet subjected to fracture surface formation and pretreatment can be observed with a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM). Among them, from the viewpoint of the accuracy of quantification of the area of the domain as the conductive phase, it is preferable to perform observation with an SEM at a magnification of 1,000 to 100,000. The arithmetic mean inter-wall distance and the above-mentioned ratio are obtained by binarizing the obtained observation image with an image analyzer or the like and analyzing the obtained observation image.
< method for Forming convex portions of domains >
The convex portion of the domain can be formed by grinding the surface of the conductive member for electrophotography. Further, the present inventors considered that since the conductive layer has a matrix-domain structure, the convex portions of the domains can be preferably formed by a grinding process using a grindstone. The convex portion of the domain is preferably formed by a grinding method using a grinding stone with a plunge grinder.
A mechanism of presumption that the convex portion of the domain can be formed by grinding the grindstone will be described. First, the domains are filled with conductive particles such as carbon black and dispersed in a matrix, whereby the matrix has higher reinforcing properties than a matrix not filled with conductive particles. That is, when grinding is performed using the same grindstone, since the region has high reinforcement, it is difficult to grind the region compared to the base, and the convex portion is easily formed. The convex portion of the domain may be formed by using a difference in grindability caused by a difference in reinforcement. In particular, the conductive member for electrophotography according to the present embodiment is constituted by filling a domain with many conductive particles, whereby it is possible to preferably form a convex portion.
Here, a grinding whetstone for a plunge grinder used in grinding will be described. The surface roughness of the grinding whetstone may be appropriately selected depending on the grinding efficiency or the type of the constituent material of the conductive layer. The surface roughness of the grindstone can be adjusted by the type, grain size, degree of bonding, binder, and structure (abrasive grain rate) of the abrasive grains.
Note that "the particle size of the abrasive particles" indicates the size of the abrasive particles, and is represented by #80, for example. The number in this case refers to the mesh number per 1 inch (25.4mm) of the net used to select the abrasive grains, and indicates that the larger the number, the finer the abrasive grains. "degree of bonding of abrasive grains" means hardness, and is represented by letters a to Z. It means that as the degree of bonding approaches a, the abrasive particles are soft; and as the degree of bonding approaches Z, the abrasive particles are hard. Since the abrasive grains contain a large amount of binder, the grindstone has a high degree of binding. "structure of abrasive grains (abrasive grain rate)" means a volume ratio of abrasive grains to a total volume ratio of the grindstone, and the density of the structure is represented by the size of the structure. The abrasive particles are coarser as the number representing the structure is larger. A grindstone having a large number of structures and large pores is called a porous grindstone, and has advantages such as prevention of clogging and burning of the grindstone.
In general, an abrasive grindstone can be produced by mixing raw materials (abrasives, binders, pore-forming agents, etc.) and performing press forming, drying, firing, and finishing. As the material of the abrasive grains, green silicon carbide (GC), black silicon carbide (C), White Alumina (WA), brown alumina (a), zirconia alumina (Z), or the like can be used. These materials may be used alone or in a mixture of two or more thereof. Further, vitrified (V), resin (B), resin reinforcement (BF), rubber (R), silicate (S), magnesium oxide (Mg), shellac (E), and the like can be used as appropriate as a binder according to the application.
Here, it is preferable that the shape of the outer diameter of the grinding stone in the longitudinal direction is formed in an inverted crown shape in which the outer diameter is gradually reduced from the end portion toward the central portion, so that the conductive roller can be ground in the crown shape. The shape of the outer diameter of the grinding stone is preferably a shape having a circular arc curve or a high-order curve of a quadratic or higher order with respect to the longitudinal direction. Further alternatively, the shape of the outer diameter of the grindstone may be a shape represented by a plurality of numerical expressions, such as a quartic curve or a sinusoidal function. It is preferable that the outer diameter shape of the grindstone is smoothly changed, but may be a shape obtained by approximating a circular arc curve to a polygon by a straight line. It is preferable that the width in the direction equivalent to the axial direction of the grinding stone is equal to or larger than the width in the axial direction of the conductive roller.
In view of the above, the grinding stone is appropriately selected, and the grinding process is performed under conditions that promote a difference in grindability between the domains and the base, whereby the convex portions of the domains can be formed.
Specifically, a condition in which abrasion is suppressed, and a condition in which the abrasive grains have low sharpness are preferable. For example, it may be preferable to form the convex portions of the domains by a method in which the time of the precision polishing process after the rough grinding is shortened, and the polishing is performed using a treated grindstone.
Examples of the treated grindstone may include a grindstone treated with a rubber member. Specific examples of the treated grindstone may include grindstones treated as follows: such as by abrading the abrasive particles by grinding the surface of a grinding stone dressed with a rubber member including the abrasive particles.
< method for measuring convex part of domain >
The sheet with the surface is removed from the conductive layer and the convex shape of the field can be confirmed and measured with a tiny probe. The surface profile and the resistance profile of the sheet sampled from the conductive member for electrophotography were measured by SPM. By doing so, it can be confirmed that the convex portion is a convex portion of the domain. At the same time, the height of the projections can be quantified and evaluated from the shape profile. The specific steps will be described later.
< method for measuring inter-domain distance Dm on outer surface of electroconductive member for electrophotography >
When the length of the conductive layer in the length direction is defined as L and the thickness of the conductive layer is defined as T, samples are cut out using a blade from three locations, which are located at the center of the conductive layer in the length direction and correspond to two locations from both ends of the conductive layer to the center L/4 of the conductive layer, respectively, so that the samples include the outer surface of the charging member. The size of the sample was 2mm each in the circumferential direction and the length direction of the charging member, and the thickness of the sample was the thickness T of the conductive layer. In each of the three samples obtained, analysis regions each having a square of 50 μm were provided at any three locations of the surface corresponding to the outer surface of the charging member, and images of the three analysis regions were taken at a magnification of 5,000 with a scanning electron microscope (trade name: S-4800, manufactured by Hitachi High-Technologies Corporation). The obtained nine captured images in total were binarized using image processing software (trade name: LUZEX, manufactured by nireo CORPORATION).
The binarization process is performed as follows. A 256-gray-scale monochrome image of the captured image is obtained by performing 8-bit graying. Then, binarization is performed, and a binarized image of the captured image is obtained to blacken the field in the captured image. Next, for each of the nine binarized images, the inter-wall distance of the domain is calculated, and the arithmetic average thereof is calculated. This value is defined as Dm. It should be noted that the inter-wall distance is the distance between the walls closest to the domain, and can be obtained by setting the measurement parameter to the distance between adjacent walls using image processing software.
< method for producing conductive Member for electrophotography >
An example of a method for producing the electroconductive member for electrophotography according to the present disclosure will be described below. In this example, the production method includes the following steps (a) to (C), but the present disclosure is not particularly limited as long as it is within a range capable of achieving the constitution of the present disclosure.
Step (A): a step of preparing a carbon masterbatch for domain formation (hereinafter, also referred to as "CMB") containing carbon black and rubber;
step (B): a step of preparing a rubber composition for matrix formation (hereinafter, also referred to as "MRC");
step (C): a step of preparing a rubber composition having a matrix-domain structure by kneading the CMB and the MRC; and
step (D): a step of forming a conductive layer on the conductive support by a known method such as extrusion molding, injection molding, or compression molding by using the rubber composition prepared in steps (a) to (C).
It should be noted that the conductive layer may be adhered to the conductive support by an adhesive, if necessary. If necessary, the conductive layer formed on the conductive support may be subjected to a vulcanization treatment and a surface treatment with ultraviolet rays after the polishing treatment.
< Process Cartridge >
Fig. 7 is a schematic sectional view of an
< electrophotographic image forming apparatus >
Fig. 8 is a schematic sectional view of an electrophotographic
The visualized toner image on the photosensitive drum is transferred to an
The
On the other hand, the toner remaining on the photosensitive drum without being transferred is wiped off by the
Although a color electrophotographic apparatus is used as an example, only a black toner product is used as a process cartridge in a monochrome electrophotographic apparatus (not shown). The monochrome image is directly formed on the transfer material by the process cartridge and the primary transfer roller (without the secondary transfer roller) without using the intermediate transfer belt. Thereafter, the transfer material is fixed by a fixing device, and the resultant is discharged to the outside of the apparatus, thereby completing the printing operation.
According to one aspect of the present disclosure, it is possible to obtain an electroconductive member for electrophotography that can be used as a charging member capable of suppressing fogging even when a charging bias is raised. Further, according to another aspect of the present disclosure, a process cartridge that contributes to stable formation of a high-quality electrophotographic image can be obtained.
Further, according to still another aspect of the present disclosure, an electrophotographic image forming apparatus that can form a high-quality electrophotographic image can be obtained.