阅读说明：本技术 导电性构件、处理盒和图像形成设备 (Conductive member, process cartridge, and image forming apparatus ) 是由 菊池裕一 西冈悟 高岛健二 山内一浩 仓地雅大 古川匠 于 2020-03-27 设计创作，主要内容包括：本发明涉及导电性构件、处理盒和图像形成设备。提供了能够防止出现重影图像的可用作充电构件的导电性构件。该构件包括导电性支承体和导电层,导电层具有包含第一交联橡胶的基体和域,域各自包含第二交联橡胶和电子导电剂,域中的至少一部分露出构件的外表面而构成凸部,外表面由基体和露出的域构成,并且在横坐标为频率和纵坐标为阻抗的双对数图中,在频率为1.0×10<Sup>5</Sup>Hz至1.0×10<Sup>6</Sup>Hz时的斜率为-0.8至-0.3,且在频率为1.0×10<Sup>-2</Sup>Hz至1.0×10<Sup>1</Sup>Hz时的阻抗为1.0×10<Sup>3</Sup>至1.0×10<Sup>7</Sup>Ω。(The invention relates to a conductive member, a process cartridge, and an image forming apparatus. Provided is a conductive member that can be used as a charging member and that can prevent the occurrence of ghost images. The member includes a conductive support and a conductive layer having a matrix including a first crosslinked rubber and domains each including a second crosslinked rubber and an electronic conductive agent, at least a part of the domains being exposed to an outer surface of the member to constitute a convex portion, the outer surface being constituted by the matrix and the exposed domains and having a frequency sum on an abscissaOn the ordinate, the logarithmic graph of the impedance at a frequency of 1.0 × 10 5 Hz to 1.0 × 10 6 The slope at Hz is-0.8 to-0.3 and the frequency is 1.0 × 10 ‑2 Hz to 1.0 × 10 1 Impedance at Hz of 1.0 × 10 3 To 1.0 × 10 7 Ω。)

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 first crosslinked rubber and domains dispersed in the matrix,

the domains each comprise a second crosslinked rubber and an electron conductive agent,

at least a part of the domains is exposed to the outer surface of the conductive member to form a convex portion on the outer surface of the conductive member,

the outer surface of the conductive member is constituted by the base and the domain exposing the outer surface of the conductive member, wherein

In a log-log plot with frequency on the abscissa and impedance on the ordinate, 1.0 × 10 at a frequency of 1.0⁵Hz to 1.0 × 10⁶A slope of-0.8 or more and-0.3 or less at a frequency of 1.0 × 10^-2Hz to 1.0 × 10¹Impedance at Hz of 1.0 × 10³To 1.0 × 10⁷Omega, said impedance being measured by applying an alternating voltage of amplitude 1V at a frequency of 1.0 × 10 in an environment comprising a temperature of 23 ℃ and a relative humidity of 50%^-2Hz and 1.0 × 10⁷Hz, between the outer surface of the support and a platinum electrode provided directly on the outer surface of the conductive member.

2. The electroconductive member for electrophotography according to claim 1, wherein the electroconductive layer is disposed directly on an outer surface of the support.

3. The electroconductive member for electrophotography according to claim 1, further comprising an electroconductive resin layer between the electroconductive layer and the outer surface of the support, wherein the frequency is 1.0 × 10^-2Hz to 1.0 × 10¹Impedance at Hz of 1.0 × 10^-5To 1.0 × 10²Omega, said impedance being measured by applying an alternating voltage of amplitude 1V at a frequency of 1.0 × 10 in an environment comprising a temperature of 23 ℃ and a relative humidity of 50%^-2Hz and 1.0 × 10⁷While varying between Hz, between the external surface of the support and a platinum electrode disposed directly on the surface of the resin layer opposite to the surface facing the support.

4. The electroconductive member for electrophotography according to claim 1 or 2, wherein the volume resistivity of the base is more than 1.0 × 10¹²Omega cm and 1.0 × 10¹⁷Omega cm or less.

5. The electroconductive member for electrophotography according to claim 1, wherein an arithmetic average value Dm of the distance between the domain surfaces is 0.2 μm or more and 2.0 μm or less.

6. The electroconductive member for electrophotography according to claim 1, wherein each height of the convex portions is 50nm or more and 200nm or less.

7. The electroconductive member for electrophotography according to claim 1, wherein an arithmetic average Dms of surface-to-surface distances of the domains constituting the convex portions, measured at an outer surface of the electroconductive member, is 2.0 μm or less.

8. The electroconductive member for electrophotography according to claim 1 or 2, wherein the support is a cylindrical support, and the electroconductive layer is disposed on an outer peripheral surface of the cylindrical support.

9. The electroconductive member for electrophotography according to claim 8, wherein

Assuming that three cross sections of the conductive layer in its thickness direction at the center in the length direction of the conductive layer and at L/4 from both ends of the conductive layer toward the center are obtained, where L denotes the length of the conductive layer in the length direction of the cylindrical support, and

assuming that at each cross section, 3 square observation regions of 15 μm on each side are arbitrarily set in a thickness region of 0.1T to 0.9T from the outer surface of the conductive layer, where T denotes the thickness of the conductive layer,

80% or more of the domains observed in each of the nine square observation regions satisfy the following requirements (1) and (2):

requirement (1): the ratio of the sum of the sectional areas of the electronic conductive agents contained in the domain to be measured to the sectional area of the domain 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.

10. The electroconductive member for electrophotography according to claim 1 or 2, wherein the electron conductive agent is electroconductive carbon black.

11. The electroconductive member for electrophotography according to claim 10, wherein the DBP absorption amount of the electroconductive carbon black is 40cm³More than 100g and 170cm³The volume is less than 100 g.

12. The electroconductive member for electrophotography according to claim 1 or 2, wherein when an arithmetic average of the circle-equivalent diameters of the domains is defined as D and a standard deviation of the distribution of D is defined as σ D, a coefficient of variation σ D/D of the circle-equivalent diameters of the domains is 0 or more and 0.4 or less.

13. The electroconductive member for electrophotography according to claim 1, wherein a coefficient of variation σ m/Dm of the inter-domain-surface distance is 0 or more and 0.4 or less when an arithmetic average of the inter-domain-surface distances is defined as Dm and a standard deviation of a distribution of the Dm is defined as σ m.

14. The electroconductive member for electrophotography according to claim 1 or 2, wherein when an average value of ratios of sectional areas of the electroconductive agent portions each contained in the domains to each of sectional areas of the domains appearing in a section in a thickness direction of the electroconductive layer is defined as μ r and a standard deviation of the ratios is defined as σ r, a coefficient of variation σ r/μ r of the ratios of the sectional areas of the electroconductive agent portions is 0 or more and 0.4 or less.

15. The electroconductive member for electrophotography according to claim 1 or 2, wherein the electroconductive member is a charging member.

16. The electroconductive member for electrophotography according to claim 1 or 2, wherein the electroconductive member is a transfer member.

17. A process cartridge configured to be detachably mountable to a main body of an electrophotographic image forming apparatus, characterized in that the process cartridge for electrophotography includes the conductive member according to any one of claims 1 to 16.

18. An electrophotographic image forming apparatus characterized by comprising the conductive member according to any one of claims 1 to 16.

Background

An electroconductive member such as a charging member, a transfer member, or a developing member is used in an electrophotographic image forming apparatus. As the conductive member, a conductive member configured to have a conductive support and a conductive layer disposed on the support is known. Such a conductive member functions in transporting electric charges from the conductive support to the surface of the conductive member and applying the electric charges to a contact object by electric discharge or triboelectric charging.

The charging member is a member that: an electric discharge is caused between the charging member and the electrophotographic photosensitive member, thereby charging the surface of the electrophotographic photosensitive member. The developing member is a member as follows: the charge of the developer coating the surface thereof is controlled by triboelectric charging, thereby imparting a uniform charge amount distribution, and then the developer is uniformly transferred to the surface of the electrophotographic photosensitive member according to the applied electric field. The transfer member is a member as follows: the developer is transferred from the electrophotographic photosensitive member to a printing medium or an intermediate transfer body, while the developer thus transferred is stabilized by electric discharge.

Each of these conductive members is required to achieve uniform charging of an electrophotographic photosensitive member 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 matrix-domain structure comprising a rubber composition mainly comprising a polymer having a volume resistivity of 1 × 10¹²A polymer continuous phase composed of an ionic conductive rubber material of a raw material rubber A of not more than Ω · cm, and a polymer particle phase composed of a conductive rubber material which is made conductive by blending conductive particles with a raw material rubber B, and a charging member having an elastomer layer formed of the rubber composition.

Disclosure of Invention

An aspect of the present disclosure is directed to providing a conductive member that can stably charge a charged body even when applied to a high-speed electrophotographic image forming method, and that can be used as a charging member, a developing member, or a transfer member.

Another aspect of the present disclosure is directed to providing a process cartridge that facilitates formation of high-grade electrophotographic images. A further alternative aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus that can form a high-grade electrophotographic image.

According to an aspect of the present disclosure, there is provided a conductive member for electrophotography including a support having a conductive outer surface and a conductive layer on the outer surface of the support,

the conductive layer has a matrix including a first crosslinked rubber and domains dispersed in the matrix,

the domains each comprise a second crosslinked rubber and an electron conductive agent,

at least a part of the domains is exposed to the outer surface of the conductive member to form a convex portion on the outer surface of the conductive member,

the outer surface of the conductive member is constituted by the base and the domain exposing the outer surface of the conductive member, wherein

In a log-log plot with frequency on the abscissa and impedance on the ordinate, 1.0 × 10 at a frequency of 1.0⁵Hz to 1.0 × 10⁶A slope of-0.8 or more and-0.3 or less at a frequency of 1.0 × 10^-2Hz to 1.0 × 10¹Impedance at Hz of 1.0 × 10³To 1.0 × 10⁷Omega, said impedance being measured by applying an alternating voltage of amplitude 1V at a frequency of 1.0 × 10 in an environment comprising a temperature of 23 ℃ and a relative humidity of 50%^-2Hz and 1.0 × 10⁷Hz, between the outer surface of the support and a platinum electrode provided directly on the outer surface of the conductive member.

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

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

FIG. 1A is a schematic representation of an electrophotographic process.

Fig. 1B is a schematic diagram of the potential distribution before charging.

Fig. 1C is a visual illustration of a potential distribution after charging with a conventional charging member in the absence of a pre-exposure apparatus.

Fig. 1D is a pictorial illustration of the potential distribution after charging with the charging member of the present invention in the absence of a pre-exposure apparatus.

Fig. 2A is a pictorial illustration of a state in which the total amount of discharge is sufficient in the case of no omission of discharge.

Fig. 2B is a visual illustration of a state in which the total amount of discharge is insufficient due to omission of discharge.

Fig. 3 is an explanatory diagram of a graph of the impedance characteristic.

Fig. 4 is an explanatory diagram of the impedance behavior.

Fig. 5 is a conceptual diagram in the vicinity of a contact portion between the photosensitive drum and the charging member.

Fig. 6 is a sectional view perpendicular to the length direction of the charging roller.

Fig. 7A is a schematic cross-sectional view in the thickness direction of the conductive layer.

Fig. 7B is an enlarged view of the vicinity of the outer surface of the conductive layer in fig. 7A.

Fig. 8 is an explanatory diagram of the envelope circumference.

Fig. 9A is an explanatory view of a cross section cut out from the conductive member in a cross section 92a parallel to the XZ plane 92.

Fig. 9B is an explanatory view of a cross section cut out from the conductive member in the thickness direction of the conductive layer.

Fig. 10 is a schematic view of the process cartridge.

Fig. 11 is a schematic view of an electrophotographic apparatus.

Fig. 12 is a schematic view of a state of the measuring electrode formed in the charging roller.

Fig. 13 is a cross-sectional view of the measuring electrode.

Fig. 14 is a schematic diagram of an impedance measurement system.

Fig. 15 is a schematic diagram of an image used for ghost image evaluation.

Fig. 16 is a diagram showing a log-log graph obtained in example 17.

Fig. 17 is an explanatory view of a method for producing the conductive member.

Detailed Description

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

According to the studies of the present inventors, the charging member as disclosed in japanese patent application laid-open No. 2002-. However, the present inventors recognized that there is still room for improvement of the charging member in recent higher-speed image forming methods. Specifically, according to the charging member of japanese patent application laid-open No.2002-3651, when a high-speed electrophotographic image forming method is performed, it is not possible to sufficiently uniformize very small unevenness in the potential formed on the surface of the charged body before the charging step in some cases. Further, in some cases, an electrophotographic image (hereinafter, also referred to as "ghost image") in which an image that should not be formed appears in an overlapping manner on an original image due to an uneven potential is formed.

The present inventors presume that the following is the reason why the charging member according to japanese patent application laid-open No. 2002-.

A phenomenon in which ghost images occur will be described with reference to fig. 1A to 1D. In fig. 1A, reference numeral 11 denotes a charging member, reference numeral 12 denotes a photosensitive drum, reference numeral 13 denotes a surface potential measuring portion before a charging process, and reference numeral 14 denotes a surface potential measuring portion after the charging process. Generally, a photosensitive drum subjected to a transfer process has a non-uniform surface potential, as shown in fig. 1B. Thus, the uneven surface potential enters the charging process, and the uneven charge potential as shown in fig. 1C is formed according to the uneven surface potential, so that a ghost image appears. In this case, no ghost image occurs as long as the charging member has the ability to impart sufficient charge to uniformize the uneven surface potential.

However, it is considered that the charging member according to japanese patent application laid-open No.2002-3651 cannot sufficiently correspond to the shortening of the discharge interval of the charged object accompanying the high-speed of the electrophotographic image forming method. The mechanism is discussed below.

In the minute gap in the vicinity of the contact portion between the charging member and the photosensitive drum, discharge generally occurs in a region (region) in which the relationship between the strength of the electric field and the minute gap distance satisfies Paschen's law. In an electrophotographic method in which discharge is caused while rotating a photosensitive drum, when one point of the surface of a charging member is monitored over time, it is found that a plurality of discharges occur repeatedly from the start point to the end point of the discharge, rather than occurring in a continuous manner.

The present inventors measured and analyzed the detailed discharge state of the charging member according to japanese patent application laid-open No. 2002-. In the charging member according to japanese patent application laid-open No. 2002-: wherein the charging process portion causes a timing at which a discharge with a high frequency is unlikely to occur, i.e., omission of the discharge. The omission of the discharge presumably reduces the total amount of discharge and does not compensate for the non-uniform surface potential.

Fig. 2A and 2B illustrate visual illustrations of a state in which omission of discharge occurs. Fig. 2A illustrates a state in which the total amount of discharge is sufficient without discharge omission. Fig. 2B illustrates a state in which the total amount of discharge is insufficient due to omission of discharge.

The omission of the discharge occurs presumably because, first, the charge is consumed by the discharge on the surface of the charging member, and then, the charge supply cannot be kept in synchronization with the consumption for the subsequent discharge.

Thus, after the electric charge is consumed by the discharge, in order to quickly supply the subsequent electric charge to the surface of the charging member, omission of the discharge can be suppressed by improving the discharge frequency.

In this case, the present inventors considered that a rapid charging cycle only inside the charging member is insufficient. Specifically, the omission of the discharge can be suppressed by the charge consumption by the discharge and the rapid cycle of the charge supply on the surface of the charging member. However, when the amount of charge that can contribute to the cycle decreases as the time required for the cycle shortens, the amount of single discharge decreases, so that the total amount of discharge cannot reach a level that uniformizes the uneven surface potential. Thus, the present inventors considered that it is necessary not only to suppress the omission of discharge, i.e., to improve the discharge frequency, but also to improve the single discharge amount.

The present inventors have further found that ghost images can be further suppressed by imparting an effect of uniformizing the uneven surface potential of the photosensitive drum not only for the above-described discharge phenomenon but also for the contact portion between the charging member and the photosensitive drum.

Therefore, the present inventors have conducted studies to obtain a conductive member that can accumulate sufficient electric charges in a short time, quickly discharge the electric charges, and further can uniformize the uneven surface potential even in its contact portion with the photosensitive drum. As a result, the present inventors have found that the conductive member configured as described below can satisfactorily satisfy the above requirements.

The conductive member includes a support having a conductive outer surface and a conductive layer disposed on the outer surface of the support. The conductive layer has a matrix including a first crosslinked rubber and a plurality of domains dispersed in the matrix. The domain comprises a second crosslinked rubber and an electron conductive agent.

Platinum electrode was directly established on the outer surface of the conductive member, and an alternating voltage having an amplitude of 1V was applied in an environment including a temperature of 23 ℃ and a humidity of 50% RH at a frequency of 1.0 × 10^-2Hz and 1.0 × 10⁷Hz is applied between the outer surface of the support and the electrode film. Thereby measuring the impedance. Frequency on the abscissa and impedance on the ordinateIn the figure, the following first requirement and second requirement are both satisfied, and the following third requirement for the surface shape is further satisfied as a feature of the surface shape unique to the domain-substrate structure.

< first requirement >

At a frequency of 1.0 × 10⁵Hz to 1.0 × 10⁶The slope at Hz is-0.8 or more and-0.3 or less.

< second requirement >

At a frequency of 1.0 × 10^-2Hz to 1.0 × 10¹Impedance at Hz of 1.0 × 10³To 1.0 × 10⁷Ω。

< third requirement >

At least a portion of the domains is exposed to an outer surface of the conductive member such that the protrusions are disposed on the outer surface of the conductive member, and the outer surface of the conductive member has a matrix and domains that expose the outer surface of the conductive member.

Specifically, the conductive member according to the present aspect can form a uniform potential distribution as shown in fig. 1D without using a pre-exposure apparatus to uniformize the uneven surface potential.

Hereinafter, the conductive member according to the present aspect is described by taking its form as a charging member as an example. The conductive member according to the present aspect is not limited to the charging member as the purpose of use, and may also be applied to, for example, a developing member and a transfer member.

The conductive member according to the present aspect includes a support having a conductive outer surface and a conductive layer provided on the outer surface of the support, the conductive layer having conductivity, and here, the conductivity is defined as less than 1.0 × 10⁸Volume resistivity of Ω · cm. The conductive layer has a matrix including a first crosslinked rubber and a plurality of domains dispersed in the matrix. The domain comprises a second crosslinked rubber and an electron conductive agent. The conductive member satisfies the above<First requirement>、<Second requirement>And<third requirement>。

< first requirement >

The first requirement specifies that stagnation of electric charge within the conductive member is less likely to occur on the high-frequency side.

When the impedance of the conventional conductive member is measured, the slope on the high frequency side is always-1. In this context, the slope refers to a slope with respect to the abscissa in a log-log graph of the impedance characteristic of the conductive member versus frequency, as shown in fig. 3.

The equivalent loop of the conductive member is indicated by the parallel circuit of the resistor R and the capacitor C. The absolute value | Z | of the impedance can be represented by expression (1) given below, where f represents the frequency.

On the high frequency side, the impedance appears as a straight line with a slope of-1, and it is presumed that the movement of electric charges cannot be stopped in accordance with the high frequency voltage, and a resistance value R which is a so-called insulation capacitance is measured as a greatly increased resistance value. The stagnation state of the electric charges can be evaluated as a state in which R in expression (1) approximates infinity. In this aspect, the denominator (R) in the expression (1)^-2+(2πf)²C²) Can be approximated by a factor of R^-2Relative to (2 pi f)²C²Take very small values. Thus, expression (1) can be obtained by eliminating R^-2Morphs to an approximate expression, e.g., expression (2). Finally, expression (2) is transformed into expression (3) in such a manner that logarithms are taken on both sides. Thus, the slope of logf is-1.

log|Z|＝-logf-log(2πC) (3)

The meanings in expressions (1) to (3) will be described with reference to fig. 4. In fig. 4, the ordinate represents the logarithm of the absolute value of the impedance (log | Z |), and the abscissa represents the logarithm of the frequency (logf) of the oscillating voltage for measurement. Fig. 4 illustrates the impedance behavior represented by expression (1). First, as described above, the absolute value of the impedance satisfying the expression (1) increases with frequency, and starts to decrease at a certain frequency. Such a lowered behavior is exhibited as a straight line having a slope of-1 in a log-log graph, as shown in fig. 4, while the slope does not depend on the resistance value, capacitance, and the like of the charging member, as represented by expression (3).

Since the impedance characteristic of the insulating resin layer measured appears as a straight line with a slope of-1, the state where the slope is-1 in the impedance measurement of the conductive layer in the conductive member is presumed to be a characteristic showing a stagnation of movement of electric charges on the high frequency side. When the movement of the electric charge on the high frequency side stagnates, the supply of the electric charge for discharge cannot be kept in synchronization with the discharge frequency. As a result, the timing of discharge is lost, and it is estimated that discharge will be missed.

On the other hand, in the conductive member according to the present disclosure, the slope of the impedance of the conductive layer is at 1.0 × 10⁵Hz to 1.0 × 10⁶The frequency of Hz is-0.8 or more and-0.3 or less. Therefore, the supply of electric charge on the high frequency side is less likely to be stagnated. As a result, electric charges can be supplied for discharge in frequencies from a low frequency region where the impedance takes a fixed value to a high frequency region, particularly discharge on the high frequency side where movement of electric charges is apt to stagnate. Since supply of electric charges can be sufficiently realized in a wide frequency region, omission of discharge is suppressed and the total amount of discharge can be improved. The slope of the high frequency region is a discharge region of the maximum frequency among frequencies discharged from the conductive member. Therefore, the omission of discharge seems to easily occur in this region. When the slope shows a value greater than-1 in the above range in such a frequency region, a slope greater than-1 is also obtained in a high frequency region lower than the frequency region. Thus, omission of discharge is suppressed and the total amount of discharge can be improved.

In the case of using a charging roller for electrophotography as a charging member in combination with a photosensitive drum, the present inventors predicted a specific discharge frequency within the following range.

A discharge area in a moving direction on a surface of a charging roller arranged to face an outer surface of the photosensitive drum and moving in synchronization with the photosensitive drum is set to 0.5mm to 1 mm. Since the process speed of the electrophotographic apparatus is 100 to 500mm/sec at the maximum, the surface of the photosensitive drum passesThe time required for the discharge region was 10^-3sec to 10^-2sec in detailed observation of discharge, the length of a discharge area by a single discharge is 0.01mm to 0.1mm, and thus, discharge is presumed to occur at least 5 to 100 times while the same point on the surface of the photosensitive drum passes through the entire discharge area, and thus, the discharge frequency of the charging roller is presumed to fall within a few Hz to 1.0 × 10⁶In the range of Hz, higher process speeds require higher discharge frequencies and require increased discharge times, therefore, it is particularly important to control the discharge rate in the above range from 1.0 × 10⁵Hz to 1.0 × 10⁶Discharge and conduction mechanisms in the high frequency region of Hz.

As described above, the deviation of the slope of the impedance from-1 in the high frequency region is effective for the increase in the number of discharges. This can favorably realize the characteristics of rapid discharge and charge supply for subsequent discharge. The deviation of the slope of the impedance from-1 means that the supply of electric charge within the conductive member does not stagnate. Therefore, such a charging member obtains a characteristic of suppressing discharge omission.

< second requirement >

The impedance on the low frequency side relating to the second requirement represents a characteristic that the electric charge is less likely to stagnate.

This is also apparent from a region where the slope of the impedance on the low frequency side is not-1. The frequency f in expression (1) is approximately zero and thus can be approximated as a resistance value R. Thus, the resistance value R was found to represent the ability of the charge to move in a single direction.

Thus, in the measurement with the applied low-frequency voltage, it can be presumed that the movement amount of the electric charge is simulated in a state in which the movement of the electric charge can be coordinated with the voltage oscillation.

The amount of electric charge that moves at a low frequency is used as an index of the ease with which electric charge moves from the charging member to the measuring electrode, and may also be used as an index of the amount of electric charge that moves from the surface of the charging member to the photosensitive drum by discharging.

The alternating voltage used in the measurement of the impedance related to the first requirement and the second requirement has an amplitude of 1V. The oscillating voltage used for this measurement is considerably low relative to a voltage of several hundred volts to several thousand volts actually applied to the charging member in the electrophotographic image forming apparatus. Thus, it is considered that the measurement of the impedance relating to the first requirement and the second requirement can evaluate the ease of discharge from the surface of the charging member at a higher level.

The ease of discharge can be controlled within a suitable range by meeting the second requirement if the impedance is below 1.0 × 10³Omega, the supply of electric charge for subsequent discharge cannot be kept in synchronization due to too large amount of single discharge, thus resulting in discharge omission⁷Ω, the ease of discharge decreases and the amount of discharge to compensate for the uneven surface potential is not reached.

In the charging member, as shown in fig. 4, the absolute value of the impedance in the low frequency region is a fixed value, for example, an impedance value at a frequency of 1Hz may be used instead of 1.0 × 10^-2Hz to 1.0 × 10¹Impedance in Hz.

The conductive member satisfying both the first requirement and the second requirement is capable of achieving an amount of discharge in a frequency region from a low frequency side to a high frequency side, so that the discharge reaches a level that eliminates uneven surface potential of the photosensitive drum and suppresses ghost images. The omission of the discharge on the high frequency side can be suppressed by satisfying the first requirement. Further, the occurrence of ghost images can be effectively suppressed by satisfying the second requirement and thereby further improving the discharge characteristics.

< method of measuring impedance >

The impedance can be measured by the following method.

Impedance measurement requires elimination of the influence of contact resistance between the conductive member and the measurement electrode. For this purpose, platinum in the low-resistance thin film is accumulated on the surface of the conductive member, and the thin film serves as an electrode. Then, impedance was measured with two terminals by using the conductive support as a ground electrode.

Examples of the forming method of the electrode may include an electrode forming method such as metal deposition, sputtering, coating of a metal paste, and attachment of a metal tape. Among these methods, a method of forming a platinum electrode by depositing a thin film of platinum is preferable from the viewpoint of reducing the contact resistance between the conductive member and the electrode.

In the case of forming a platinum electrode on the surface of a conductive member, a mechanism capable of holding the conductive member is provided to a vacuum deposition apparatus in view of its convenience and uniformity of a thin film. For the conductive member having a cylindrical cross section, it is preferable to use a vacuum deposition apparatus further provided with a rotation mechanism. For example, for a cylindrical conductive member having a curved (e.g., circular) cross section, it is preferable to use the method given below because the platinum electrode as the measurement electrode described above is difficult to connect with the impedance measurement apparatus.

Specifically, a platinum electrode having a width on the order of 10mm to 20mm is formed in the length direction of the conductive member. Then, the metal sheet was wound around the resultant without any gap. The metal sheet may be connected to a measuring electrode from a measuring device and then measured. As a result, an electrical signal from the conductive layer in the conductive member can be appropriately obtained in the measurement apparatus, and impedance measurement can be performed. The metal sheet may be a metal sheet having a resistance value equal to that of a metal portion of a connection cable for a measuring device when measuring impedance. For example, aluminum foil or metal tape may be used.

The impedance measuring device may be a device such as an impedance analyzer, network analyzer or spectrum analyzer, which may be up to 1.0 × 10⁷The frequency region of Hz measures the impedance. Among them, it is preferable to measure the impedance from the resistance region of the conductive member using an impedance analyzer.

Reference will be made to the impedance measurement conditions using an impedance measurement device, at 1.0 × 10^-2Hz to 1.0 × 10⁷The impedance is measured in the frequency region of Hz. The measurements were performed in an environment comprising a temperature of 23 ℃ and a humidity of 50% RH. To reduce the variation of the measurement, it is preferable to establish five or more measurement points at each frequency number (digit). The amplitude of the alternating voltage is 1V.

As for the measurement voltage, measurement may be performed with a direct current voltage applied in consideration of a voltage distribution to be applied to the conductive member in the electrophotographic apparatus. Specifically, such measurement is suitable for quantifying the transfer and accumulation characteristics of electric charges while applying a direct-current voltage of 10V or less and an oscillation voltage in a superimposed manner.

Next, a method for calculating the slope of the impedance will be mentioned.

Based on the measurement results obtained by measurement under the above-described conditions, the absolute value of the impedance is plotted on a log-log graph against the measurement frequency using commercially available spreadsheet software, on the graph obtained by the log-log graph at 1.0 × 10⁵To 1.0 × 10⁶The slope of the absolute value of the impedance in the frequency region of Hz can be determined by using a value at 1.0 × 10⁵To 1.0 × 10⁶The measurement points in the frequency region of Hz. Specifically, for the plot of the graph in this frequency region, an approximate straight line of the linear function is calculated by the least square method, and the slope thereof can be calculated.

Subsequently, the calculation is at 1.0 × 10 in the log-log plot^-2To 1.0 × 10¹The arithmetic mean of the measurement points in the frequency region of Hz, and the obtained value can be regarded as the impedance on the low frequency side.

The measurement of the slope of the impedance of the cylindrical charging member is performed at 5 positions including any position in each region obtained in five equal parts divided in the length direction as the axial direction, and the arithmetic average of the slope measurement values at the 5 positions can be calculated.

< third requirement >

The conductive member including the conductive layer satisfying the specification with respect to the impedance relating to the first requirement and the second requirement can reduce the omission of the discharge. However, in order to obtain a high-grade electrophotographic image, it is considered that a higher speed electrophotographic process needs to further reduce the uneven surface potential of the photosensitive drum.

Therefore, the present inventors have conceived that charge is injected to the photosensitive drum at the contact portion with the photosensitive drum by the convex portion derived from the region where the outer surface of the charging member is exposed, which is related to the third requirement. In this context, injection charging means that charging is caused by injecting electric charge from a conductive portion in the outer surface of the conductive member in contact with the photosensitive drum surface at the contact portion according to a potential difference with respect to the photosensitive drum surface.

Fig. 5 shows a conceptual diagram of the vicinity of a contact portion 53 between the photosensitive drum 51 and the charging member 52 having the conductive support 55 and the conductive layer 56. As shown in fig. 5, the discharge 54 causes a minute gap which applies a potential difference with respect to the contact portion 53 on the upstream side of the process. According to the discharge from the charging member 52, the residual uneven surface potential of the photosensitive drum, which has not been uniformized, can be further uniformized by injection charging from the convex portions.

Since the surface potential of the charging member is a negative value and is constant with respect to the uneven surface potential on the surface of the photosensitive drum, the potential difference at the contact portion and the amount of injected electric charge are larger at a position having a negative small surface potential than at a position having a large surface potential among the uneven surface potential of the photosensitive drum.

In short, injection charging at the contact portion is effective for uniformizing the uneven surface potential.

The conductive member according to the present aspect has a matrix-domain structure that can sufficiently accumulate electric charges and efficiently transfer electric charges within the conductive layer according to the specification of the impedance with respect to the first requirement and the second requirement, and therefore, it is presumed to have not only suppression of omission of electric discharge but also high efficiency of injection charging. Further, the conductive portion has a convex shape and is configured to be separately in contact with the photosensitive drum. This configuration further improves the efficiency of injection charging. In addition, the conductive portion to be contacted is rich in an electron conductive agent having a low resistance with a high charge transfer efficiency. This configuration may also be advantageous for injection charging.

Specifically, the height of the convex portion of the conductive portion is preferably 50nm or more and 200nm or less. The height of 50nm or more can realize contact between only the conductive convex portion and the photosensitive drum. On the other hand, the height of the convex portion is preferably 200nm or less because uneven discharge originating from the convex portion occurs in the discharge region.

As described above, according to the configuration according to the present disclosure in which omission of discharge can be suppressed and additionally high-efficiency injection charging can be achieved by the conductive convex portion according to the first requirement and the second requirement, it is presumed that ghost images in high-speed processing can be suppressed.

< conductive Member >

The conductive member according to the present aspect will be described by taking a conductive member having a roller shape (hereinafter, referred to as a conductive roller) as one example with reference to fig. 6. Fig. 6 is a cross-sectional view of the conductive roller in the longitudinal direction perpendicular to the axial direction. The conductive roller 61 includes a columnar conductive support 62 and a conductive layer 63 formed on the outer periphery, i.e., the outer surface, of the support 62.

< conductive support >

A material known in the region of the electroconductive member for electrophotography, or a material that can be used in such an electroconductive member can be appropriately selected and used as a material constituting the electroconductive support. Examples thereof include aluminum, stainless steel, synthetic resins having conductivity, and metals and alloys such as iron and copper alloys. These materials may be further subjected to oxidation treatment or plating treatment with chromium, nickel or the like. Any of electroplating and electroless plating may be used as the type of plating. From the viewpoint of dimensional stability, electroless plating is preferred. In this context, examples of the type of electroless plating used may include nickel plating, copper plating, gold plating, and plating with various alloys. The thickness of the plating layer is preferably 0.05 μm or more. In view of the balance between the working efficiency and the rust inhibitive ability, the plating thickness is preferably 0.1 to 30 μm. The cylindrical shape of the support body may be a solid cylindrical shape or a hollow cylindrical shape. The outer diameter of the support body is preferably in the range of 3mm to 10 mm.

The presence of an intermediate resistive layer or insulating layer between the support and the conductive layer hinders rapid supply of electric charge after the charge is consumed by discharge. Therefore, it is preferable that the conductive layer should be disposed directly on the support, or should be disposed on the outer periphery of the support only via an intermediate layer formed of a film and a conductive resin layer such as a primer or the like.

A known primer may be selected and used depending on the rubber material for forming the conductive layer, the material of the support, and the like. Examples of the material for the primer include thermosetting resins and thermoplastic resins. Specifically, a material such as a phenol resin, a urethane resin, an acrylic resin, a polyester resin, a polyether resin, or an epoxy resin can be used.

The impedance of the resin layer and the support was 1.0 × 10^-2Hz to 1.0 × 10¹At a frequency of Hz preferably at 1.0 × 10^-5To 1.0 × 10²The range of Ω. The support and the resin layer having an impedance in the above range at a low frequency are preferable because sufficient charge supply to the conductive layer can be performed and because the matrix-domain structure that does not obstruct the conductive layer has a function of suppressing discharge omission according to the first requirement and the second requirement.

The impedance of the resin layer can be measured in the same manner as the measurement of the slope of the impedance described above, except that the measurement is performed by peeling off the conductive layer present on the outermost surface. The impedance of the support body can be measured in the same manner as the measurement of the impedance described above in a state before the support body is coated with the resin layer or the conductive layer, or in a state in which the conductive layer or the coating layer formed of the resin layer and the conductive layer is peeled off after the charging roller is formed.

< conductive layer >

The conductive member satisfying the above < first requirement >, < second requirement >, and < third requirement > is preferably, for example, a conductive member having a conductive layer satisfying the following constitutions (i) to (iv).

(ii) the volume resistivity of the matrix is more than 1.0 × 10¹²Omega cm and 1.0 × 10¹⁷Omega cm or less.

(ii) the volume resistivity of the domains is 1.0 × 10¹Omega cm or more and 1.0 × 10⁴Omega cm or less.

(iv) constitutes (iii): the distance between adjacent domains is in the range of 0.2 μm or more and 2.0 μm or less.

Constitution (iv): at least a portion of the domains are exposed to an outer surface of the conductive member such that the protrusions are disposed on the outer surface of the conductive member, and the outer surface of the conductive member has a base and a surface of the domains that exposes the outer surface of the conductive member.

Hereinafter, the factors (i) to (iv) will be described.

Fig. 7A shows a partial sectional view of the conductive layer in a direction perpendicular to the longitudinal direction of the conductive roller. The conductive layer 7 includes a matrix-domain structure having a matrix 7a and domains 7 b. The domain 7b contains conductive particles 7c as an electron conductive agent. Fig. 7B is an enlarged view of the vicinity of a surface of the conductive layer on the opposite side to the conductive support side of the conductive layer (hereinafter, also referred to as "outer surface of the conductive layer").

A voltage is applied between a conductive support and a charged body in a conductive member including a conductive layer in which a domain including an electron conductive agent is dispersed in a matrix. Then, as described below, it is considered that the electric charges in the conductive layer move to the side opposite to the side of the conductive layer facing the conductive support, that is, to the outer surface side of the conductive member. As a result, electric charges are accumulated in the vicinity of the interface between the domain and the matrix. Then, the electric charges are sequentially transferred from the domain located on the conductive support side to the domain located on the opposite side to the conductive support side to reach the surface of the conductive layer on the opposite side to the conductive support side (hereinafter, also referred to as "outer surface of the conductive layer"). In this regard, if the electric charges of all the domains move to the outer surface side of the conductive layer by a single charging step, it takes time to accumulate the electric charges in the conductive layer for the next charging step. In particular, it is difficult to respond to a high-speed electrophotographic image forming method. Therefore, it is preferable to prevent simultaneous charge transfer between domains by applying a bias. Accumulation of a sufficient amount of charge in the domain is also effective for discharge of a sufficient amount by a single discharge in a high-frequency region where the movement of charge is restricted.

As shown in fig. 7B, at least a part of the domain 7B is exposed to the outer surface of the conductive member, so that the convex portion 7B-01 is provided on the outer surface of the conductive member. Such a convex portion constitutes a contact portion with the photosensitive drum. As a result, the electric charges sufficiently accumulated in the domains are efficiently injected into the electrophotographic photosensitive member at the contact portion.

As described above, it is preferable that simultaneous charge transfer between the domains when a bias is applied is prevented, and the configurations (i) to (iv) are satisfied to sufficiently accumulate charges in the domains.

< constitution (i) >

Volume resistivity of the matrix;

when the volume resistivity of the matrix is more than 1.0 × 10¹²Omega cm and 1.0 × 10¹⁷When the value is not more than Ω · cm, the charge can be prevented from moving in the substrate while bypassing the (bypass) domain. Further, it is possible to prevent the electric charges accumulated in the domains from leaking to the base body, and thereby from entering a state where it seems that a connected conductive path is formed within the conductive layer.

With the above-mentioned < first requirement >, it is necessary to move electric charges through the domains in the conductive layer even under application of high frequency bias. The present inventors considered that, for this purpose, a configuration in which conductive regions (domains) in which charges are sufficiently accumulated are separated from each other by electrically insulating regions (substrates) is effective. When the volume resistivity of the base falls within the range of the high-resistance region as described above, electric charges can be sufficiently retained at the interface between each domain and the base, and electric charges of the domains can be prevented from leaking.

The present inventors have also found that a charge movement path limited to a domain-mediated path is effective for a conductive layer satisfying the above < second requirement >. The density of charge present in the domains can be improved by preventing charge leakage from the domains into the matrix, and limiting the charge transport path to a path mediated by multiple domains. Therefore, the amount of charge filled in each domain can be further increased. It is considered that this can improve the total number of charges involved in the discharge of the surface of the domain (which is a conductive phase) as the discharge starting point, and thus can improve the ease of discharge from the surface of the charging member.

As described above, the discharge from the outer surface of the conductive layer draws electric charges from the domain as a conductive phase by an electric field. Meanwhile, positive ions generated by ionization of air by an electric field collide with the surface of the conductive layer having negative charges, thereby generating a gamma effect of releasing charges from the surface of the conductive layer. As described above, a high density of charges may exist in the domain as the conductive phase on the surface of the charging member. Therefore, the discharge efficiency when positive ions collide with the surface of the conductive layer by the electric field can also be improved. In this state, it is presumed that a large amount of charge can be easily generated by discharge as compared with the conventional charging member.

A method for measuring the volume resistivity of the substrate;

the volume resistivity of the matrix can be measured, for example, by cutting out a sheet having a predetermined thickness (e.g., 1 μm) including a matrix-domain structure from the conductive layer, and bringing a microprobe of a Scanning Probe Microscope (SPM) or an Atomic Force Microscope (AFM) into contact with the matrix in the sheet.

For example, the sheet is cut out from the elastic layer as shown in fig. 9A, so that when the length direction of the conductive member is defined as the X axis, the thickness direction of the conductive layer is defined as the Z axis, and the circumferential direction is defined as the Y axis, the sheet includes at least a part of a cross section 92a parallel to the XZ plane. Alternatively, as shown in fig. 9B, the sheet is cut out such that the sheet includes at least a portion of YZ planes (e.g., 93a, 93B, and 93c) perpendicular to the axial direction of the conductive member. Examples of methods of cutting out flakes include sharp razors, microtomes, and Focused Ion Beams (FIBs).

For measuring volume resistivity, one surface of the sheet cut out from the conductive layer is grounded. Subsequently, a microprobe of a Scanning Probe Microscope (SPM) or an Atomic Force Microscope (AFM) is brought into contact with the base portion on the surface on the opposite side to the grounded surface of the wafer. A dc voltage of 50V was applied thereto for 5 seconds, and the ground current value was measured for 5 seconds. An arithmetic average value is calculated from the obtained values, and the applied voltage is divided by the calculated value to calculate a resistance value. Finally, the resistance value is converted into volume resistivity using the film thickness of the sheet. In this regard, the SPM or AFM can measure the film thickness of the flakes simultaneously with the resistance value.

The volume resistivity value of the matrix in the cylindrical charging member is determined, for example, by dividing the conductive layer into 4 parts in the circumferential direction and 5 parts in the longitudinal direction, cutting out one sheet sample per 1 region, obtaining the above-described measurement values, and then calculating the arithmetic average of the volume resistivities of 20 samples in total.

< constitution (ii) >

Volume resistivity of the domain;

the volume resistivity of the domains is preferably 1.0 × 10¹Omega cm or more and 1.0 × 10⁴Omega cm or less. The lower the volume resistivity of the domains, the more effectively the charge transport path can be defined as a path mediated by multiple domains while suppressing undesired movement of charges in the matrix.

The volume resistivity of the domain is more preferably 1.0 × 10²When the volume resistivity of the domain is reduced to the above range, the amount of charge moved in the domain can be greatly improved, and therefore, the conductive layer can be formed at a frequency of 1.0 × 10^-2Hz to 1.0 × 10¹Impedance at Hz is adjusted to 1.0 × 10 or less⁵The lower range of Ω, and the charge transfer path can be further effectively defined as a path mediated by the domain.

The volume resistivity of the domains is adjusted by using an electron conductive agent for the rubber component of the domains, thereby setting the conductivity thereof to a predetermined value.

The rubber composition including the rubber component for the matrix may be used as the domain rubber material. The difference between the solubility parameter (SP value) of the rubber composition and the solubility parameter (SP value) of the rubber material constituting the matrix is preferably in the following range to form a matrix-domain structure: the difference in SP values was 0.4 (J/cm)³)^0.5Above and 5.0 (J/cm)³)^0.5Hereinafter, particularly, 0.4 (J/cm) is more preferable³)^0.52.2 (J/cm) or more³)^0.5The following.

The volume resistivity of the domains can be adjusted by appropriately selecting the type of the electron conductive agent and the addition amount of the electron conductive agent for adjusting the volume resistivity of the domains to 1.0 × 10¹Omega cm or more and 1.0 × 10⁴The electron conductive agent having Ω · cm or less is preferably an electron conductive agent whose volume resistivity can be greatly changed from high resistance to low resistance depending on the dispersion amount of the electron conductive agent.

Examples of the electron conductive agent blended into the domain include: carbon materials such as carbon black and graphite; conductive oxides such as titanium oxide and tin oxide; metals such as Cu and Ag; and particles that are conductive by coating their surfaces with a conductive oxide or metal.

Two or more of these electron conductive agents may be blended in an appropriate amount for use, if necessary.

Among the electron conductive agents as described above, conductive carbon black is preferably used because conductive carbon black has a large affinity for rubber, and because the distance between the particles of the electron conductive agent is easily controlled. The type of carbon black blended into the domains is not particularly limited. Specific examples thereof include gas furnace carbon black, oil furnace carbon black, pyrolysis carbon black, lamp black, acetylene black, and ketjen black (Ketjenblack).

Among them, DBP absorption of 40cm can be suitably used³More than 100g and 170cm³A conductive carbon black in an amount of 100g or less and capable of imparting high conductivity to these domains.

It is preferable to blend an electronic conductive agent such as conductive carbon black into the domains at 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the rubber component contained in the domains.the blending ratio is particularly preferably 50 parts by mass or more and 100 parts by mass or less¹Omega cm or more and 1.0 × 10⁴Omega cm or less. If necessary, an additive that is generally used as a blending agent for rubber may be added to the domain rubber composition without inhibiting the advantageous effects according to the present disclosure.

Examples of such additives include fillers, processing aids, crosslinking agents, crosslinking aids, crosslinking accelerators, antioxidants, crosslinking acceleration aids, crosslinking retarders, softeners, dispersants, and colorants.

A method of measuring volume resistivity of the domain;

the measurement of the volume resistivity of the domain can be performed in the same manner as the above < measurement method of volume resistivity of substrate > except that: changing the measurement location to a location corresponding to the domain; and the voltage applied at the time of measuring the current value was changed to 1V.

In this context, the domains preferably have a uniform volume resistivity. In order to improve the uniformity of the volume resistivity of the domains, it is preferable to uniformize the amount of the electron conductive agent in the domains. This can further stabilize the discharge from the outer surface of the conductive member to the charged body.

Specifically, the ratio of the sectional area of the portion of the electron conductive agent contained in each of the domains appearing in the section in the thickness direction of the conductive layer to the sectional area of each of the domains is preferably, for example, in the following range: when the standard deviation of the ratio of the total cross-sectional area of the conductive particles to the cross-sectional area of the domains is defined as σ r and the average value of the ratio is defined as μ r, the coefficient of variation σ r/μ r is preferably 0 or more and 0.4 or less.

A method of reducing the variation in the number or amount of the conductive agents contained in each domain may be used in σ r/μ r of 0 or more and 0.4 or less. When uniformity of volume resistivity based on such an index is given to the domain, electric field concentration in the conductive layer can be suppressed, and the presence of a matrix to which an electric field is locally applied can be reduced. This can minimize the conductivity of the matrix.

σ r/μ r is more preferably 0 or more and 0.25 or less, this can further effectively suppress electric field concentration in the conductive layer, and can further be at 1.0 × 10^-2Hz to 1.0 × 10¹The impedance at Hz is reduced to 1.0 × 10⁵Omega is less than or equal to.

In order to improve the uniformity of the volume resistivity of the domains, it is preferable to increase the amount of the electron conductive agent such as carbon black blended with the second crosslinked rubber in the step of preparing the rubber composition for domain formation (CMB) described below.

A method for measuring a homogeneity indicator of the volume resistivity of the domain;

the uniformity of the volume resistivity of the domains is determined by the amount of the conductive agent in the domains, and thus can be evaluated by measuring the change in the amount of the electron conductive agent in the domains.

First, a cut piece was prepared in the same manner as the method used in the measurement of the volume resistivity of the substrate described above. Subsequently, a fracture surface is formed by means such as a freeze-cleaving method, a cross-mill, or a Focused Ion Beam (FIB). FIB is preferred in view of smoothness of the fracture surface and pretreatment for observation. In addition, in order to appropriately perform observation of the matrix-domain structure, a pretreatment for appropriately generating contrast between the domain as the conductive phase and the matrix as the insulating phase, such as a dyeing treatment or a deposition treatment, may be performed.

The sections after fracture surface formation and pretreatment were observed under a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM) to confirm the presence of the matrix-domain structure. Among these methods, observation under SEM 1000 times to 100000 times is preferable because of accurate quantification of the area of the domain. Specific procedures will be mentioned later.

< constitution (iii) >

Arithmetic mean value Dm of distances between surfaces of adjacent domains (hereinafter, also referred to as "inter-domain-surface distance")

The arithmetic mean value Dm of the distances between the domain surfaces is preferably 0.2 μm or more and 2.0 μm or less.

Dm is preferably 2.0 μm or less, particularly preferably 1.0 μm or less, because the conductive layer in which the domain having the volume resistivity related to the constitution (ii) is dispersed in the matrix having the volume resistivity related to the constitution (i) satisfies the above < second requirement >.

On the other hand, Dm is preferably 0.2 μm or more, and particularly preferably 0.3 μm or more, in order to reliably separate the domains from each other by using as a base of the insulating region and thereby sufficiently accumulate electric charges in the domains.

A method of measuring the distance between the domain surfaces;

the method of measuring the distance between the domain surfaces may be performed as follows.

First, a cut piece was prepared in the same manner as the method used in the measurement of the volume resistivity of the substrate described above. In addition, in order to appropriately perform observation of the matrix-domain structure, a pretreatment for appropriately generating contrast between the conductive phase and the insulating phase, such as a dyeing treatment or a deposition treatment, may be performed.

The sections after fracture surface formation and platinum deposition were observed under a Scanning Electron Microscope (SEM) to confirm the presence of matrix-domain structures. Among these methods, observation under an SEM of 1000 times to 100000 times is preferable because the area of the domain is accurately quantified. Specific procedures will be mentioned later.

Uniformity of inter-domain surface distance Dm;

with respect to the constitution (iii), a uniform distribution of the distance between the domain surfaces is more preferable. When the supply of electric charges is caused to stagnate compared with the surroundings by locally generating some positions where the inter-domain surface distance is long within the conductive layer, the uniform distribution of the inter-domain surface distance can reduce the phenomenon of suppressing easy discharge.

In the cross section of the charge transport, that is, the cross section in the thickness direction of the conductive layer as shown in fig. 9B, observation regions of 50 μm square were obtained at arbitrary 3 positions in the thickness region of a depth of 0.1T to 0.9T in the support direction from the outer surface of the conductive layer. In this regard, the variation coefficient σ m/Dm calculated using the average value Dm of the inter-domain-surface distances in the observation area and the variation σ m of the inter-domain-surface distances is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.30 or less.

A method of measuring the uniformity of the inter-domain-surface distance Dm;

the uniformity of the inter-domain surface distance can be measured by quantifying an image obtained by directly observing the fracture surface in the same manner as in the measurement of the inter-domain surface distance. Specific procedures will be mentioned later.

The conductive member according to the present aspect may be formed by, for example, a method including the following steps (i) to (iv):

(i) preparing a rubber composition for domain formation (hereinafter, also referred to as "CMB") containing carbon black and a second rubber;

(ii) preparing a rubber composition for matrix formation (hereinafter, also referred to as "MRC") containing a first rubber;

(iii) kneading the CMB and the MRC to prepare a rubber composition having a matrix-domain structure; and

(iv) (iv) forming a layer of the rubber composition prepared in step (iii) on the conductive support directly or via an additional layer, and curing (crosslinking) the layer of the rubber composition to form the conductive layer according to the present aspect.

For example, the constitutions (i) to (iii) may be controlled by selecting the material used in each step and adjusting the production conditions. Hereinafter, the method thereof will be described.

First, with regard to the composition (i), the volume resistivity of the matrix depends on the composition of the MRC.

At least one low-conductivity rubber, such as natural rubber, butadiene rubber, butyl rubber, acrylonitrile-butadiene rubber, urethane rubber, silicone rubber, fluorine rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber or polynorbornene rubber, may be used as the first rubber used in the MRC. If necessary, fillers, processing aids, crosslinking agents, crosslinking aids, crosslinking accelerators, crosslinking accelerating aids, crosslinking retarders, antioxidants, softeners, dispersants and/or colorants may be added to the MRC on the premise that the volume resistivity of the matrix may fall within the above-mentioned range. On the other hand, it is preferable that the MRC should not contain an electron conductive agent such as carbon black in order to adjust the volume resistivity of the matrix to the above range.

The composition (ii) can be adjusted by the amount of the electron conductive agent in the CMB. Examples of methods for this include using DBP absorption at 40cm³More than 100g and 170cm³A method of using conductive carbon black having a weight of 100g or less as an electron conductive agent. Specifically, the configuration (ii) can be realized by preparing CMB so as to contain 40 mass% or more and 200 mass% or less of the conductive carbon black with respect to the total mass of the CMB.

Control of the following 4 factors (a) to (d) is effective for the constitution (iii):

(a) the difference in interfacial tension σ between CMB and MRC;

(b) a ratio (η m/η d) of the viscosity (η m) of the MRC to the viscosity (η d) of the CMB;

(c) in step (iii), shear rate (γ) at the time of kneading CMB and MRC and Energy (EDK) at the time of shearing; and

(d) (iv) volume fraction of CMB relative to MRC in step (iii).

(a) The difference in interfacial tension between CMB and MRC;

in the case of mixing two immiscible rubbers, phase separation generally occurs. This is because, since the interaction between the same polymers is stronger than that between different polymers, the same polymers are aggregated with each other to reduce free energy for stabilization. The interface of the phase separation structure is in contact with different polymers and thus has a higher free energy than the internal free energy stabilized by the interaction between the same polymers. As a result, interfacial tension intended to reduce the contact area with different polymers is generated so as to reduce the free energy of the interface. When the interfacial tension is small, even different polymers are more uniformly mixed so as to increase entropy. The homogeneously mixed state is dissolution. Therefore, the interfacial tension tends to be correlated with the SP value (solubility parameter) as an index of solubility.

In short, it is considered that the difference in interfacial tension between CMB and MRC is correlated with the difference in SP value between rubbers respectively contained therein. For selecting the rubber, the first rubber in the MRC and the second rubber in the CMB are preferably rubber raw materials having a difference in absolute values of solubility parameters within the following range: the difference in the absolute values of SP values is preferably 0.4 (J/cm)³)^0.5Above and 5.0 (J/cm)³)^0.5Below, 0.4 (J/cm) is particularly preferable³)^0.52.2 (J/cm) or more³)^0.5The following. Within this range, a stable phase separation structure can be formed, and the domain diameter D of CMB can be reduced. In this context, specific examples of the second rubber that can be used for CMB include Natural Rubber (NR), Isoprene Rubber (IR), Butadiene Rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), ethylene-propylene rubber (EPM and EPDM), Chloroprene Rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U), at least one of which may be used.

The thickness of the conductive layer is not particularly limited as long as the desired function and effect of the conductive member are obtained. The thickness of the conductive layer is preferably 1.0mm or more and 4.5mm or less.

The mass ratio between the domain and the matrix (domain: matrix) is preferably 5:95 to 40:60, more preferably 10:90 to 30:70, and further preferably 13:87 to 25: 75.

< method for measuring SP value >

The SP value can be accurately calculated by using a material having a known SP value and making a calibration curve. A catalog value provided by the material manufacturer may be used as the known SP value. For example, the SP values of NBR and SBR are essentially determined by the acrylonitrile and styrene content percentages, and do not depend on their molecular weights. The rubbers constituting the matrix and domains were analyzed for their acrylonitrile or styrene content percentage using analytical methods such as pyrolysis gas chromatography (Py-GC) or solid NMR. Thus, their SP values can be calculated from calibration curves obtained from materials with known SP values. The SP value of isoprene rubber is determined by the isomer structure such as 1, 2-polyisoprene, 1, 3-polyisoprene, 3, 4-polyisoprene, cis-1, 4-polyisoprene and trans-1, 4-polyisoprene. Therefore, as in SBR and NBR, the content percentage of the isomer is analyzed by a method such as Py-GC or solid NMR, and the SP value of the isoprene rubber can be calculated from a material having a known SP value. The SP value of a material with a known SP value was determined by the Hansen solubility sphere method.

(b) Viscosity ratio between CMB and MRC

As the viscosity ratio (η d/η m) between CMB and MRC approaches 1, the maximum Ferrett diameter of the domains can be reduced. Specifically, the viscosity ratio is preferably 1.0 or more and 2.0 or less. The viscosity ratio between CMB and MRC can be adjusted by selecting the mooney viscosity of the raw rubber used in CMB and MRC or adjusting the type or amount of filler to be blended therewith. A plasticizer such as paraffin oil may be added thereto without interfering with the formation of a phase separated structure. In addition, the viscosity ratio can be adjusted by adjusting the kneading temperature. The viscosities of CMB and MRC were obtained by measuring the Mooney viscosity ML (1+4) at the rubber temperature at the kneading based on JIS K6300-1: 2013.

(c) Shear rate (. gamma.) and energy at shear when kneading MRC and CMB

The inter-domain-surface distances Dm and Dms (to be mentioned later) may be decreased as the shearing speed at the time of kneading the MRC and CMB is faster or as the energy at the time of shearing is larger.

The gap from the end face of the stirring member to the inner wall of the kneader can be reduced by increasing the inner diameter of the stirring member such as a blade or a screw in the kneader; or by increasing the number of revolutions. By increasing the number of revolutions of the stirring member; or increasing the viscosity of the first rubber in the CMB and the second rubber in the MRC, an increase in energy at shear can be achieved.

(d) Volume fraction of CMB relative to MRC

The volume fraction of CMB relative to MRC is related to the probability of coalescence of the domain-forming rubber compound and matrix-forming rubber compound collisions. Specifically, the coalescence probability of the collision of the domain-forming rubber compound with the matrix-forming rubber compound decreases as the volume fraction of the domain-forming rubber compound relative to the matrix-forming rubber compound decreases. In short, the domain-surface distances Dm and Dms (to be mentioned later) can be reduced by reducing the volume fraction of the domains in the matrix in a range that produces the necessary conductivity.

The volume fraction of CMB to MRC (i.e., the volume fraction of domains to the matrix) is preferably 15% or more and 40% or less.

In the conductive member, when the length in the length direction of the conductive layer is defined as L and the thickness of the conductive layer is defined as T, a cross section in the thickness direction of the conductive layer as shown in fig. 9B is obtained at 3 positions, i.e., at the center in the length direction of the conductive layer and L/4 from both ends of the conductive layer toward the center. Each cross section in the thickness direction of the conductive layer preferably satisfies the following.

For each cross section, 15 μm square observation regions were provided at arbitrary 3 positions in a thickness region having a depth of 0.1T to 0.9T from the outer surface of the conductive layer. In this regard, 80% by number or more of domains observed in each of the total 9 observation regions preferably satisfy the following constitutions (v) and (vi).

Constitution (v)

The ratio [ mu ] r of the cross-sectional area of the electron conductive agent contained in the domain to the cross-sectional area of the domain is 20% or more.

Constitution (vi)

When the perimeter of the domain is defined as A and the envelope perimeter of the domain is defined as B, A/B is 1.00 or more and 1.10 or less.

The configuration (v) and the configuration (vi) may define a domain shape. The "domain shape" is defined as a cross-sectional shape of a domain appearing in a cross section in the thickness direction of the conductive layer.

The shape of the domain is preferably a shape having no irregularities on the peripheral surface thereof, that is, a shape approximating a sphere. The nonuniformity of the electric field between the domains can be reduced by reducing the number of the shape-dependent concave-convex structures. In short, the number of locations where electric field concentration occurs can be reduced, thereby reducing the phenomenon of charge transport in excess of necessity in the matrix.

The present inventors have obtained the following findings: the amount of the electron conductive agent (conductive particles) contained in one domain influences the outer shape of the domain.

Specifically, the present inventors have obtained the following findings: as the amount of conductive particles filled in one domain increases, the profile of the domain more approaches a spherical shape. As the number of domains increases, the number of concentration points of electron transfer between domains decreases.

According to the study of the present inventors, a domain in which the ratio of the total sectional area of the conductive particles observed at the section of one domain to the sectional area of the domain is 20% or more can assume a shape closer to a sphere, although the reason thereof is not clear. As a result, such domains may exhibit a profile that enables the concentration of electron transfer between domains to be significantly relaxed, and thus are preferable. Specifically, the ratio of the cross-sectional area of the conductive particles contained in the domains to the cross-sectional area of the domains is preferably 20% or more, more preferably 25% or more and 30% or less.

The present inventors have found that a domain shape having no concavity and convexity on the outer periphery should preferably satisfy the following expression (5):

1.00≤A/B≤1.10...(5)

(A: perimeter of domain, B: perimeter of envelope of domain)

Expression (5) represents the ratio of the perimeter a of the domain to the envelope perimeter B of the domain. In this context, the envelope circumference refers to a circumference obtained by connecting convex portions of the domain 81 observed in the observation area as shown in fig. 8.

The ratio of the perimeter of the domain to the envelope perimeter of the domain is 1 as a minimum. The ratio of 1 means that the domain has a shape without a recess in the sectional shape, such as a true circle or an ellipse. A ratio of 1.1 or less means that the domains do not have a large uneven shape. Therefore, anisotropy of the electric field is unlikely to be exhibited.

< method for measuring shape parameter of field >

An ultra-thin cut piece having a thickness of 1 μm was cut out from the conductive layer of the conductive member (conductive roller) at a cutting temperature of-100 ℃ using a microtome (trade name: Leica EMFCS, manufactured by Leica Microsystems GmbH). However, as described below, it is necessary to prepare a slice at a cross section perpendicular to the longitudinal direction of the conductive member and evaluate the shape of the domain on the fracture surface of the slice. The reason for this will be mentioned below.

Fig. 9A and 9B are diagrams showing the shape of the conductive member 91 three-dimensionally on 3 axes, specifically on X, Y and the Z axis. In fig. 9A and 9B, the X axis depicts a direction parallel to the longitudinal direction (axial direction) of the conductive member, and the Y axis and the Z axis each depict a direction perpendicular to the axial direction of the conductive member.

Fig. 9A shows a pictorial representation of a cut out from the conductive member at a section 92a parallel to the XZ plane 92. The XZ plane may be rotated 360 ° about the axis of the conductive member. The conductive member rotates in contact with the photosensitive drum and discharges electricity when passing through a gap with the photosensitive drum. In view of this, a cross section 92a parallel to the XZ plane 92 depicts the surface where simultaneous discharges occur at a certain time. The surface potential of the photosensitive drum is formed by passing a certain amount of the surface corresponding to the cross section 92 a.

Therefore, analysis of a cross section where simultaneous discharge occurs at a certain time, such as the cross section 92a, is not sufficient to evaluate the shape of the domain, which is associated with electric field concentration within the conductive member. Since the domain shape including a given amount of the cross section 92a can be evaluated, it is necessary to perform the evaluation on a cross section parallel to the YZ plane 93 perpendicular to the axial direction of the conductive member.

When the length in the length direction of the conductive layer is defined as L, a total of 3 positions, that is, a cross section 93b at the center in the length direction of the conductive layer, and cross sections (93a and 93c) at two positions of L/4 from both ends of the conductive layer to the center are selected for this evaluation.

The following measurements were made at the observation positions of the cross sections 93a to 93 c: when the thickness of the conductive layer is defined as T, observation regions 15 μm square are provided at arbitrary 3 positions in the thickness region having a depth of 0.1T or more and 0.9T or less from the outer surface in each slice. Measurements can be made in a total of 9 positions of the field of view.

Platinum was deposited in the obtained slices to obtain deposited slices. Subsequently, the surface of the deposited section was photographed at 1000 times or 5000 times under a Scanning Electron Microscope (SEM) (trade name: S-4800, manufactured by Hitachi High-Technologies Corp.) to obtain an observation image.

Next, in order to quantify the domain shape in the analyzed Image, 8-bit grayscale processing (gradycaled) was performed on the Image using Image processing software Image-ProPlus (product name, manufactured by Media Cybernetics inc.) to obtain a black-and-white Image having 256 gradations. Subsequently, the image is processed by monochrome inversion to whiten the domain within the fracture plane to obtain a binarized image.

< method for measuring the ratio of the cross-sectional area of conductive particles in the Domain >

The sectional area ratio of the electron conductive agent in the domain can be measured by quantifying a binarized image of the observation image photographed at 5000 times.

The Image is subjected to 8-bit grayscale processing using Image processing software (trade name: Image-Pro Plus; manufactured by Media Cybernetics inc.) to obtain a black-and-white Image having 256 gradations. Binarization of the observed image is performed in a manner that allows identification of the carbon black particles to obtain a binarized image. The obtained image is applied to a counting function to calculate a sectional area S of a domain in the analysis image and a total sectional area Sc of carbon black particles contained in each domain as an electron conductive agent.

Then, the arithmetic mean value μ r of Sc/S at 9 positions was calculated as the cross-sectional area ratio of the electron conductive agent in each domain.

The sectional area ratio μ r of the electron conductive agent affects the uniformity of the volume resistivity of the domains. In addition to the measurement of the cross-sectional area ratio μ r, the uniformity of the volume resistivity of the domain can be measured as follows.

From the standard deviation σ r of μ r and μ r by the above measurement method, σ r/μ r is calculated as an index of uniformity of volume resistivity of the domain.

< method for measuring perimeter A and envelope perimeter B of field >)

With the counting function of the image processing software, for a domain group present in a binarized image of an observation image photographed at 1000 times, the following items are calculated:

the circumference A (. mu.m) and

enveloping perimeter B (μm).

These values are substituted into the following expression (5), and the arithmetic average of the evaluation images from 9 positions is taken:

1.00≤A/B≤1.10...(5)

(A: perimeter of domain; B: perimeter of envelope of domain)

< method for measuring shape index of field >)

The shape index of the domains can be calculated as the percentage of the number of domains in which μ r (area%) is 20% or more and the circumferential ratio a/B satisfies expression (5) with respect to the total number of domains. The shape index of the domain is preferably 80% by number or more and 100% by number or less.

The binarized images were applied to a counting function of Image processing software Image-Pro Plus (manufactured by Media Cybernetics inc.) to calculate the number of domains in each binarized Image. The percentage of the number of domains satisfying μ r ≧ 20 and expression (5) can be further determined.

The high density of the conductive particles filled in the domains as specified in the configuration (v) makes the outer shape of the domains close to a spherical shape, and can reduce the irregularities as specified in the configuration (vi).

In order to obtain domains filled with the electron conductive agent at a high density as defined in constitution (v), the electron conductive agent preferably has a DBP absorption at 40cm³More than 100g and 170cm³Carbon black of 100g or less.

DBP absorption (cm)³Per 100g) means the volume of dibutyl phthalate (DBP) that can be absorbed by 100g of carbon black, and is measured according to Japanese Industrial Standard (JIS) K6217-4: 2017 (carbon black for rubber industry-basic characteristics-part 4: determination of oil uptake (OAN) and oil uptake (COAN) of compressed samples (Determination of oil uptake number (OAN) and oil uptake number of compressed sample (COAN))).

Generally, carbon black has a grape-like structure (botryoid transformation) having aggregated primary particles with an average particle diameter of 10nm or more and 50nm or less. The grape-like structure is called structure, the extent of which is determined by the absorption capacity (cm) of DBP³100g) quantification.

The conductive carbon black having a DBP absorption amount within the above range has a structure that is not sufficiently developed, and thus exhibits less aggregation of carbon black particles and good dispersibility in rubber. Therefore, such conductive carbon black can be filled in a large amount in the domains. As a result, a domain having a more spherical outer shape can be easily obtained.

The conductive carbon black having the DBP absorption amount within the above range is less likely to form aggregates, and thus contributes to the formation of the domain associated with the requirement (vi).

< constitution (iv) >

With regard to the outer surface of the conductive member according to the present disclosure, as described in the < third requirement > section, at least a part of the domain serving as the conductive portion is exposed as a convex portion to the outer surface of the conductive member, so that highly efficient injection charging is achieved.

The convex portion is configured to have high conductive responsiveness as obtained by a conductive mechanism derived from the matrix-domain structure of the present disclosure, and is rich in an electron conductive agent such as carbon black. In such a configuration, contact of only the convex portion with the photosensitive drum can be further achieved.

Thus, the conductive member according to the present disclosure can exhibit injection charging with high efficiency from the convex portion derived from the domain existing on the outer surface, and therefore, the uneven surface potential can be uniformized even at the contact portion with the photosensitive drum.

Specifically, the height of the domain-derived convex portion is preferably 50nm or more and 200nm or less. The height of 50nm or more can realize the contact between the convex part derived from the domain and the photosensitive drum. The height is more preferably 150nm or more. On the other hand, the height of the projection is preferably 200nm or less because uneven discharge from the projection occurs in the discharge region.

The domains in which the convex portions are provided on the outer surface of the conductive member are present such that the arithmetic mean Dms (arithmetic mean inter-surface distance) of the distances between the convex portions of adjacent domains is preferably 2.0 μm or less, particularly preferably 0.2 μm or more and 2.0 μm or less. When the distance between the convex portions falls within the above range, electric charges can be injected to the photosensitive drum surface at many points. Therefore, the injection charging property of the projections derived from the domains can be improved.

< method for Forming convex portions derived from domains >

The convex portions originating from the domains may be formed by polishing the surface of the conductive member. The present inventors also considered that, since the conductive layer has a matrix-domain structure, the convex portions derived from the domains can be appropriately formed by a polishing step using a grindstone. The domain-derived projections are preferably formed by a grinding method using a plunge-cut grinding machine and a grinding stone.

A mechanism of supposition that the domain-derived convex portion can be formed by grinding with a grindstone will be given. First, the domains dispersed in the matrix are filled with an electron conductive agent such as carbon black, and thus are reinforced more highly than the matrix not filled with the electron conductive agent. Specifically, in the case where the polishing process is performed using the same grindstone, the highly reinforced domain is more resistant to polishing than the base body, and therefore, the convex portion is easily formed. The convex portions derived from the domains can be formed by utilizing the difference in grindability caused by such a difference in reinforcement. In particular, the conductive member according to the present embodiment is configured such that the domains are filled with a large amount of carbon black. Therefore, the convex portion can be formed appropriately.

Here, a grinding whetstone of a plunge grinder for grinding will be described. The surface roughness of the abrasive grindstone may be appropriately selected depending on the grinding efficiency and the type of material constituting the conductive layer. This surface roughness of the grindstone can be adjusted by the type of abrasive grains, grain size, degree of bonding, binder, texture (abrasive grain percentage), and the like.

"grain size of abrasive grains" refers to the size of abrasive grains and is represented by #80, for example. In this case, the number refers to the minimum number of openings per inch (25.4mm) in the screen through which the abrasive particles are screened. A larger number indicates finer abrasive particles. "grade of abrasive grain" refers to hardness and is represented by the letters A through Z. A closer to a for this grade means softer, while a closer to Z for the grade means harder. The binder rich abrasive particles form a harder grade of the stone. "texture of abrasive grain (percent abrasive grain)" refers to the volume ratio of abrasive grain to the total volume of the grindstone. The coarseness and fineness of the texture are indicated by the magnitude or size of the texture. A larger number representing texture means a coarser. A grinding stone having a large amount of such texture and having large pores is called a porous grinding stone, and has advantages such as prevention of clogging and grinding burn caused by the grinding stone.

Generally, the abrasive grindstone can be produced by mixing raw materials (abrasives, binders, pore-forming agents, etc.), followed by press forming, drying, firing, and finishing. As the abrasive grains, green silicon carbide (GC), black silicon carbide (C), white corundum (WA), brown alumina (a), zirconia alumina (Z), or the like can be used. These materials may be used alone or as a mixture of two or more thereof. Depending on the purpose, vitrified (V), resin (B), resin reinforcement (BF), rubber (R), silicate (S), magnesium oxide (Mg), shellac (E), or the like can be used as a binder as appropriate.

In this context, the outer diameter shape in the length direction of the grinding whetstone is preferably 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 into a crown shape. 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 more in the longitudinal direction.

Further, the outer diameter shape of the grinding stone may be a shape represented by any of various mathematical expressions such as a quartic curve (quaternary curve) and a sine function. For the outer shape of the grinding stone, it is preferable that the outer diameter should be smoothly changed. Alternatively, the outer shape may be a shape in which a circular arc curve or the like is approximated as a polygon having straight lines. The width in the direction corresponding to the axial direction of the grinding stone is preferably equal to or greater than the width in the axial direction of the conductive roller.

The convex portions derived from the domains can be formed by appropriately selecting a grindstone in consideration of the above-mentioned factors, and performing the grinding step under conditions that promote the difference in grindability between the domains and the base.

In particular, the conditions preferably relate to controlled abrasion or the use of dull abrasive particles. The convex portions derived from the domains can be appropriately formed, for example, by employing means such as grinding using a treated grindstone to shorten the time of the precision grinding step after rough grinding. Examples of the treated grindstone include grindstones treated with a rubber member, specifically, for example, grindstones treated by abrading abrasive grains by grinding the surface of the grindstone finished with a rubber member blended with the abrasive grains.

< method for confirming projections originated from domains >

A thin slice comprising the surface is taken out of the conductive layer. The confirmation of the convex portions originating from the domains and the measurement of the heights of the convex portions can be performed using a microprobe.

Examples of means of making thin sections include sharp razors, microtomes, and FIBs. Among these means, FIBs that can form a very smooth cross section are preferable. When the length of the conductive layer in the length direction is defined as L, the cut-out position of the conductive layer is 3 positions, i.e., at the center in the length direction and L/4 from both ends of the conductive layer toward the center.

The thin section for observation may be subjected to a pretreatment for suitably producing a contrast between the domain as the conductive phase and the matrix as the insulating phase, such as a dyeing treatment or a deposition treatment, in order to perform more accurate observation of the matrix-domain structure.

Subsequently, the surface profile and the resistance distribution of the thin slice sampled from the conductive member were measured under SPM. This confirmed that the projections were domain-originated projections. At the same time, the height of the projections can be quantitatively evaluated from the shape profile. For example, a device such as an SPM (MFP-3D-Origin, manufactured by Oxford Instruments K.K.) can be used.

The resistance value distribution and the shape profile are measured by measuring the surface of the conductive member using the apparatus.

Subsequently, it was confirmed that the convex portion in the surface shape profile obtained by the above measurement originated from a domain having higher conductivity than the periphery of the resistance value distribution. The height of the protrusion is further calculated from the profile.

The calculation method includes determining the height by obtaining a difference between an arithmetic mean of the shape profile from the domain and an arithmetic mean of the shape profile from the substrate adjacent thereto.

Randomly selected 20 convex portions were measured in each slice cut out from three positions, and an arithmetic average of values of 60 convex portions in total may be calculated.

< method for measuring distance Dms between surfaces of projections derived from field >

The method of measuring the inter-surface distance Dms of the projections originating from the domain can be performed as follows.

When the length in the length direction of the conductive layer is defined as L and the thickness of the conductive layer is defined as T, a sample including the outer surface of the charging member was cut out from 3 positions, i.e., at the center in the length direction of the conductive layer and L/4 from both ends of the conductive layer toward the center, using a razor. The size of the sample was 2mm in both the circumferential direction and the length direction of the charging member, and its thickness was set to the thickness T of the conductive layer. For each of the obtained 3 samples, 50 μm square analysis regions were provided at arbitrary 3 positions in the surface corresponding to the outer surface of the charging member. 3 analysis fields were photographed at 5000-fold under a scanning electron microscope (trade name: S-4800, manufactured by Hitachi High-Technologies Corp.). Each of the thus obtained total 9 captured images was binarized using image processing software (trade name: LUZEX; manufactured by Nireco corp.).

The procedure for binarization proceeds as follows: the photographed image is subjected to 8-bit gray scale processing to obtain a black-and-white image having 256 gray scales. Then, the photographed image is binarized to blacken the domains in the image, thereby obtaining a binarized image of the photographed image. Subsequently, the inter-domain-surface distance was calculated for each of the 9 binarized images, and the arithmetic average thereof was further calculated. This value is considered to be Dms. The inter-surface distance refers to the distance between the walls of the domain located closest and can be determined by setting the measurement parameters to the distance between adjacent walls in the image processing software.

< Domain diameter D >

The arithmetic mean of the circle-equivalent diameters D of the domains (hereinafter, also simply referred to as "domain diameter D") is preferably 0.1 μm or more and 5.0 μm or less.

The average domain diameter D of 0.10 μm or more can more effectively restrict the charge movement path in the conductive layer. The average domain diameter D is more preferably 0.15 μm or more, and still more preferably 0.20 μm or more.

The average domain diameter D of 5.0 μm or less can exponentially increase the ratio of the surface area to the total volume of the domain, i.e., the specific surface area of the domain, and can dramatically improve the efficiency of charge release from the domain. For the above reasons, the average domain diameter D is more preferably 2.0 μm or less, and still more preferably 1.0 μm or less.

To further reduce the electric field concentration between the domains, it is preferable that the domains should have a more crystalline spherical shape. For this purpose, it is preferable that the domain diameter should be small within the above range. Examples of the method thereof include the following methods, which involve: the MRC and CMB are kneaded in step (iii) to phase separate the MRC and CMB, and then the domain diameter attributable to CMB is controlled to be smaller in the step of preparing the rubber composition including the domains derived from CMB formed in the matrix derived from MRC. The reduced domain diameter increases the specific surface area of the domain and increases the interface between the domain and the matrix. Therefore, the tension acts at the interface of the domains, so that the tension is reduced. As a result, the domains have a more spherical shape.

In this context, the following expression is known as to the determinant of the domain diameter (maximum feret diameter D) in the matrix-domain structure formed by melt kneading two immiscible polymers.

-Taylor's formula

D＝[C·σ/ηm·γ]·f(ηm/ηd)...(6)

Empirical equation for Wu (Wu)

γ·D·ηm/σ＝4(ηd/ηm)0.84·ηd/ηm>1...(7)

γ·D·ηm/σ＝4(ηd/ηm)-0.84·ηd/ηm<1...(8)

-Tokita equation

In the expressions (6) to (9), D represents the maximum feret diameter of the domain from CMB, C represents a constant, σ represents interfacial tension, η m represents viscosity of the matrix, η D represents viscosity of the domain, γ represents shear velocity, η represents viscosity of the mixed system, P represents coalescence probability of collision, Φ represents volume of the domain phase, and EDK represents fracture energy of the domain phase.

Regarding the constitution (iii), reducing the domain size according to the expressions (6) to (9) is effective for the uniformity of the distance between the domain surfaces. The matrix-domain structure is further governed by when the kneading step is stopped during the process of splitting the domain raw material rubber in the kneading step to gradually reduce its particle diameter. Therefore, the uniformity of the distance between the domain surfaces can be controlled by the kneading time in the kneading process and the number of kneading revolutions which is an index of the kneading intensity. Longer kneading time or larger number of kneading revolutions can improve the uniformity of the distance between the domain surfaces.

Uniformity of domain size;

the more uniform the domain size, i.e., the narrower the particle size distribution, the more preferred. The uniform domain size distribution through which charges pass in the conductive layer can suppress charge concentration in the matrix-domain structure and effectively improve the ease of discharge over the entire surface of the conductive member.

In the cross section of the charge transport, that is, the cross section in the thickness direction of the conductive layer as shown in fig. 6, observation regions in the 50 μm square direction were obtained at any 3 positions in the thickness region having a depth of 0.1T to 0.9T from the outer surface of the conductive layer in the support direction. In this regard, the ratio σ D/D (coefficient of variation σ D/D) of the standard deviation σ D of the domain size to the average value D of the domain size is preferably 0 or more and 0.4 or less, and more preferably 0.10 or more and 0.30 or less.

In order to improve the uniformity of the domain diameters, the reduction of the domain diameters according to expressions (6) to (9) improves the uniformity of the domain diameters, as in the above-mentioned method of improving the uniformity of the distance between the domain surfaces. The uniformity of the domain diameter varies further depending on when the kneading step is stopped in the course of splitting the raw material rubber for the domains to gradually reduce the particle diameter thereof in the step of kneading the MRC and the CMB. Therefore, the uniformity of the domain size can be controlled by the kneading time in the kneading process and the number of kneading revolutions which is an index of the kneading intensity. Longer kneading time or larger number of kneading revolutions can improve the uniformity of domain size.

A method of measuring uniformity of domain size;

the uniformity of the domain diameter can be measured by quantifying an image obtained by directly observing the fracture surface in the same manner as the above-described measurement of the uniformity of the distance between the domain surfaces. Specific means will be mentioned below.

< method for confirming matrix-Domain Structure >

The presence of the matrix-domain structure in the conductive layer can be confirmed by detailed observation of the fracture surface formed in the thin section made of the conductive layer. Specific procedures will be mentioned later.

< Process Cartridge >

Fig. 10 is a schematic sectional view of a process cartridge for electrophotography including a conductive member according to the present disclosure as a charging roller. The process cartridge includes a developing device and a charging device integrated with each other, and is configured to be detachably mounted to a main body of an electrophotographic device. The developing apparatus includes at least a developing roller 103 and a toner container 106 integrated with each other, and may optionally include a toner supply roller 104, a toner 109, a developing blade 108, and an agitating blade 1010. The charging apparatus includes at least the photosensitive drum 101, the cleaning blade 105, and the charging roller 102, which are integrated with each other, and may include a waste toner container 107. A voltage is applied to each of the charging roller 102, the developing roller 103, the toner supply roller 104, and the developing blade 108.

< electrophotographic apparatus >

Fig. 11 is a schematic view of an electrophotographic apparatus employing a conductive member according to the present disclosure as a charging roller. This electrophotographic apparatus is a color electrophotographic apparatus to which the above-described 4 process cartridges are detachably mounted. Each process cartridge uses toner of each color (black, magenta, yellow, or cyan). The photosensitive drum 111 rotates in a direction indicated by an arrow, and is uniformly charged by the charging roller 112 to which a voltage has been applied from a charging bias power supply. An electrostatic latent image is formed on the surface of the photosensitive drum by the exposure light 1111.

At the same time, the toner 119 stored in the toner container 116 is supplied to the toner supply roller 114 by the stirring blade 1110, and conveyed onto the developing roller 113. Then, the surface of the developing roller 113 is uniformly coated with the toner 119 by a developing blade 118 disposed in contact with the developing roller 113, while electric charge is applied to the toner 119 by frictional charging. The electrostatic latent image is developed by applying toner 119 conveyed by a developing roller 113 disposed in contact with the photosensitive drum 111, and visualized as a toner image.

The visualized toner image on the photosensitive drum is transferred to an intermediate transfer belt 1115 supported and driven by a tension roller 1113 and an intermediate transfer belt driving roller 1114 by a primary transfer roller 1112 to which a voltage is applied from a primary transfer bias power source. The toner images of the respective colors are sequentially superposed to form a color image on the intermediate transfer belt.

The transfer material 1119 is fed into the apparatus by a feed roller, and is conveyed between the intermediate transfer belt 1115 and the secondary transfer roller 1116. A voltage is applied from the secondary transfer bias power source to the secondary transfer roller 1116, and the color image on the intermediate transfer belt 1115 is transferred to the transfer material 1119 by the secondary transfer roller. The transfer material 1119 on which the color image is transferred is subjected to a fixing process by a fixer 1118, and is discharged from the apparatus to terminate the printing operation.

Meanwhile, the toner remaining on the photosensitive drum without being transferred is scraped off by the cleaning blade 115 and stored in the waste toner container 117. The cleaned photosensitive drum 111 repeats the above steps. The toner remaining on the primary transfer belt without being transferred is also scraped off by the cleaning device 1117.

According to an aspect of the present disclosure, the following conductive member can be obtained: the charging object can be stably charged even when it is applied to a high-speed electrophotographic image forming method, and can be used as a charging member, a developing member, or a transfer member. According to another aspect of the present disclosure, a process cartridge that facilitates formation of a high-grade electrophotographic image can be obtained. According to a further alternative aspect of the present disclosure, an electrophotographic image forming apparatus capable of forming an electrophotographic image of a high grade can be obtained.