JP2021067743A - Image forming apparatus - Google Patents

Abstract

To provide a technique that can prevent an image defect due to abnormal discharge even in a state where the capacitance is small, the electrification contrast is high, and the amount of discharged electric charge is large, in order to achieve both long life and high image quality.SOLUTION: When the impedance characteristics measured by applying an AC voltage with an amplitude of 1 V to an electrifying member while changing the frequency of the AC voltage is log-log plotted, with the frequency on the horizontal axis and the impedance on the vertical axis, the inclination in a frequency of 1.0×105 Hz to 1.0×106 Hz is -0.8 or more and -0.3 or less. The impedance at a frequency of 1.0×10-2 Hz to 1.0×101 Hz is 1.0×103 Ω to 1.0×107 Ω. An image carrier has a capacitance of 1.56×10-10 F/cm2 or less. The difference between the surface potential of the image carrier formed in an electrifying unit and the surface potential of the image carrier before passage through the electrifying unit is 500 V or more.SELECTED DRAWING: Figure 9

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile apparatus using an electrophotographic method.

The electrophotographic image forming apparatus develops an electrostatic latent image formed on an electrophotographic photosensitive member (photosensitive drum) as an image carrier into a toner image (developer image) by a developing apparatus, and develops this toner image into a sheet or the like. An image is formed on the recording material by transferring and fixing it on the recording material. Prior to the formation of the electrostatic latent image described above, the surface of the photosensitive drum is uniformly charged by the charging device.
As a charging device, an increasing number of image forming devices are equipped with a contact charging method in which a charging member such as a charging roller is brought into contact with the surface of a photosensitive drum and a predetermined charging bias is applied to the charging roller to charge the surface of the photosensitive drum. In recent years, it has become the mainstream of charging devices. Most of the contact charging methods use a conductive roller as a charging roller, and roller charging is used in which the conductive roller is brought into contact with a photosensitive drum to apply a voltage. Then, by applying a bias to the charging roller and repeating the discharge with the photosensitive drum, the surface of the photosensitive drum is uniformly charged, but the discharge damages the photosensitive drum and wears it.
The photosensitive drum generally has a support and a photosensitive layer formed on the support, and the photosensitive layer has a charge generating layer and a charge transporting layer. As the photosensitive layer, a laminated photosensitive layer in which a charge transporting layer containing a charge transporting substance is laminated on a charge generating layer containing a charge generating substance is preferably used.
Further, in order to reduce the running cost, it is required to further extend the life of the image forming apparatus, and as a countermeasure, for example, it may be required to increase the film thickness of the charge transport layer of the photosensitive drum. However, if the thickness of the charge transport layer is large, the exposure light is dispersed before the exposure passes through the charge transport layer and reaches the charge generation layer, and the charge generated in the charge generation layer is transferred to the surface of the photosensitive drum. It may spread due to the long distance before it reaches. As a result, deterioration of image quality due to the inability to form an electrostatic latent image faithful to the exposure pattern may become a problem.
Therefore, in Patent Document 1, by reducing the beam diameter of the exposure means according to the thickness of the charge transport layer of the photosensitive drum, the spread of the electrostatic latent image is suppressed and an electrostatic latent image faithful to the exposure pattern is formed. A method has been proposed.

Japanese Unexamined Patent Publication No. 2005-49397

However, the beam diameter of the exposure apparatus has a diameter that must be technically minimized, and there is a limit to the reduction in diameter. Therefore, in the configuration of Patent Document 1, it may be technically difficult to deal with the case where the film thickness of the charge transport layer is further increased for the purpose of further extending the life. Therefore, as another means for improving the deterioration of image quality due to the spread of the electrostatic latent image, a method of forming the electrostatic latent image deeply and sharply by increasing the amount of exposure light while the surface potential of the photosensitive drum is high is used. Some products are used. However, it is known that when the film thickness of the charge transport layer is increased, the capacitance becomes smaller and abnormal discharge or the like is likely to occur. Further, the higher the charging potential after charging, that is, the larger the charging contrast, which is the charging potential difference before and after charging, the more likely this abnormal discharge is to occur. As the thickness of the charge transport layer increases, the capacitance decreases, so the amount of charge required for the desired charge potential decreases, ionization due to electron collision occurs in an avalanche manner, and dielectric breakdown occurs in the air. , A large current will flow at once. As a result, when the electric charge is accumulated more than the required amount, the electric charge potential of the photosensitive drum becomes overcharged, and abnormal discharge or the like is likely to occur. Further, when the charging contrast is increased, the electric field of the air layer becomes stronger and the amount of discharge current increases, so that the abnormal discharge becomes more severe.

An object of the present invention is to provide a technique capable of suppressing image defects due to abnormal discharge even in a state where the capacitance is small, the charge contrast is high, and the amount of discharge charge is large, for the purpose of achieving both long life and high image quality. That is.

In order to achieve the above object, the image forming apparatus of the present invention
An image forming device that forms an image on a recording material.
At least, an image carrier in which a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance are laminated.
A charging member that charges the surface of the image carrier at the charging portion facing the image carrier,
A charging bias applying means for applying a bias to the charging member, and
With
The charging member has the impedance characteristics measured by applying an AC voltage having an amplitude of 1 V to the charging member while changing the frequency, when the frequency is plotted on the horizontal axis and the impedance is plotted on the vertical axis. The gradient at the frequency of 0 × 10 ⁵ Hz to 1.0 × 10 ⁶ Hz is -0.8 or more and -0.3 or less, and the frequency is 1.0 × 10 ^-2 Hz to 1.0 × 10 ¹ The amplitude at Hz is 1.0 × 10 ³ Ω to ^{1.0 × 10 7 Ω.}
The image carrier has a capacitance of 1.56 × 10 ^-10 F / cm ² or less per unit area of the charge transport layer.
The charging bias applying means has such that the difference between the surface potential formed in the charged portion and the surface potential before passing through the charged portion of the surface potential of the image carrier is 500 V or more. In addition, it is characterized in that the bias applied to the charging member is controlled.

According to the present invention, it is possible to suppress image defects due to abnormal discharge even in a state where the capacitance of the charge transport layer of the photosensitive drum is small, the charge contrast is large, and the amount of discharge charge is large.

Schematic cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. A control block diagram of an image forming apparatus according to an embodiment of the present invention. Explanatory diagram of impedance characteristic graph Explanatory diagram of impedance behavior Schematic cross-sectional view perpendicular to the longitudinal direction of the charging roller Schematic diagram of the state where the measurement electrode is formed on the charging roller Schematic cross-sectional view of the measuring electrode Schematic diagram of impedance measurement system Schematic diagram of sea island structure Explanatory drawing of the envelope circumference Explanatory drawing of cross-section cutting direction The figure which shows an example which measured the frequency characteristic of impedance Image of discharge Schematic cross-sectional view showing a morphological example of the photosensitive drum

In the present invention, unless otherwise specified, the description of "○○ or more and XX or less" and "○○ to XX" indicating a numerical range is a numerical range including the lower limit and the upper limit which are end points (○○ is the lower limit value). , XX is the upper limit).
Hereinafter, embodiments for carrying out the present invention will be described in detail exemplarily with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Embodiment 1]
<Outline configuration of image forming apparatus>
A schematic configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment of the present invention. FIG. 1 shows the configuration of an image forming apparatus in a normal installation state in which the image forming apparatus is placed on a horizontal installation surface, and the horizontal direction of the paper surface corresponds to the horizontal direction and the vertical direction of the paper surface corresponds to the vertical direction of the device. ..

As an example of the image forming apparatus A of the present embodiment, a laser beam printer that forms an image on a recording medium (recording material) 6 such as a recording paper or an OHP sheet by an electrophotographic method according to image information can be mentioned as an example. .. Further, in the image forming apparatus A of the present embodiment, the process cartridge B is detachable from the apparatus main body of the image forming apparatus A, as will be described in detail later. Here, the apparatus main body refers to a component portion of the image forming apparatus A excluding the process cartridge B. In this embodiment, an image forming apparatus having a structure in which a toner image (developer image) formed on a photosensitive drum is directly transferred to a recording material as a transfer target will be described, but the configuration of the image forming apparatus is particularly limited. It's not something. For example, an image forming apparatus (color) in which toner images of different colors formed by a plurality of image forming portions are superimposed and transferred onto an intermediate transfer body as a transfer target to form a color toner image, and this is transferred to a recording material. The present invention can also be applied to (such as a laser printer).

The image forming apparatus A is used by being connected to a host 14 such as a personal computer. The controller unit 31 processes the print request signal and the image data from the host 14 and controls the scanner 3 which is an exposure means to form an electrostatic latent image (electrostatic image) on the photosensitive drum 1. That is, the image forming apparatus A has a cylindrical photosensitive drum 1 that is rotationally driven in the direction of arrow R1 in the drawing as an image carrier (rotating body). In the present embodiment, the photosensitive drum 1 is formed by coating an OPC layer having a film thickness of 24 μm as a photosensitive layer (electrophotographic photosensitive member) around an aluminum cylinder which is a cylindrical substrate. The minimum photoconductor film thickness that can maintain good image quality of the photosensitive drum 1 is 9 μm, and the photoconductor life is reached at that time.

The photosensitive drum 1 is uniformly charged by a roller-shaped charging member that is pressure-contacted with the photosensitive drum 1, that is, a DC contact charging roller (charging roller) 2. In the present embodiment, the charging roller 2 is configured to have a conductive rubber layer provided on the core metal. In the present embodiment, as will be described in detail later, a DC voltage fixed at a predetermined value is applied to the charging roller 2 as a charging bias in the charging portion in contact with the charging roller 2 on the surface of the photosensitive drum 1. The surface of the photosensitive drum 1 is uniformly charged with a negative electrode property. The charging roller 2 is driven (rotated following the rotation of the photosensitive drum 1) in the direction of arrow R4 in the drawing due to the rotation of the photosensitive drum 1. The charging roller 2 is in contact with the photosensitive drum 1 over substantially the entire longitudinal direction (direction orthogonal to the transport direction of the recording medium 6).

The uniformly charged photosensitive drum 1 is exposed by the laser beam L1 from the scanner 3 which is an exposure means, and an electrostatic latent image is formed on the surface thereof. The scanner 3 has a laser light source 3a, a polygon mirror 3b, a lens system 3c, and the like, and can perform scanning exposure on the photosensitive drum 1 under the control of the controller unit 31. The latent image setting of this embodiment was set to Vd = -700V and Vl = -200V regardless of the film thickness of the photosensitive drum 1.

After that, the electrostatic latent image is visualized as a toner image by supplying a developer by the developing device 4. The developing apparatus 4 has a developing container 21 that houses a negatively charged non-magnetic toner (toner) 22 having a normal polarity in this embodiment as a one-component developer. In the present embodiment, as the toner 22, a substantially spherical toner having a weight average particle diameter of about 7 μm was used in order to achieve a small particle size and a low melting point and to improve the transfer efficiency.

A part of the developing container 21 facing the photosensitive drum 1 has an opening over substantially the entire longitudinal direction of the photosensitive drum 1, and a developing roller 23, which is a roller-shaped developer carrier (development means), is formed in the opening. Have been placed. The developing roller 23 is pressed and brought into contact with the photosensitive drum 1 located at the upper left in the drawing of the developing device 4 so as to have a predetermined penetration amount, and is rotationally driven in the direction of arrow R2 in the drawing. Further, the surface thereof has appropriate irregularities in order to increase the probability of rubbing with the toner 22 and to carry out the toner 22 satisfactorily.

At the lower right of the developing roller 23 in the drawing, an elastic roller 24 (developing agent supply member) is brought into contact with the developing roller 23 as a means for supplying the developing agent to the developing roller 23 and stripping the undeveloped toner from the developing roller 23. There is. The elastic roller 24 is rotatably supported by the developing container 21. Further, the elastic roller 24 is a rubber sponge roller from the viewpoint of supplying toner to the developing roller 23 and peeling off undeveloped toner, and is rotationally driven in the direction of arrow R3 in the drawing, which is the same direction as the developing roller 23. Further, the developing apparatus 4 includes a developing blade 25 as a developer layer thickness regulating member that regulates the amount of toner carried on the developing roller 23. The developing blade 25 is made of an elastic thin metal plate made of SUS, and is provided so that the vicinity of the tip on the free end side abuts on the outer peripheral surface of the developing roller 23 by surface contact. The toner carried on the developing roller 23 by rubbing with the elastic roller 24 is charged by triboelectric charging when passing through the contact portion with the developing blade 25, and is restricted to a thin layer.

In the developing apparatus 4 having such a configuration, a DC voltage fixed to a predetermined value is applied to the developing roller 23 from the high-voltage power supply 37 as a developing bias. In this embodiment, the development bias is constant at Vdc = −500V regardless of the film thickness of the photoconductor. As a result, in the present embodiment, the exposed portion of the surface of the uniformly charged photosensitive drum 1 in which the negative charge is attenuated is developed by reverse development.

On the other hand, the recording medium 6 is separated and fed from the recording medium accommodating portion 16 by a supply roller 12a or the like, and temporarily stopped by the resist roller 12b. The resist roller 12b synchronizes the recording position of the recording medium 6 with the timing of forming a toner image on the photosensitive drum 1, and is a portion (transfer portion) facing the transfer roller 5 which is a transfer means (transfer member) and the photosensitive drum 1. ), The recording medium 6 is sent out. Then, the visualized toner image on the photosensitive drum 1 is transferred to the recording medium 6 by the action of the transfer roller 5 (transfer bias applied from the high voltage power source 38 to the transfer roller 5). In the present embodiment, the control unit 35 can set the transfer voltage at the time of image formation based on the detection result of the current detection unit 39 that detects the transfer current. Further, the control unit 35 has a memory 33 as a storage unit for storing information for controlling the image forming operation based on the stored information.

The recording medium 6 on which the toner image is transferred is conveyed to the fixing device 9. Here, the unfixed toner image on the recording medium 6 is permanently fixed on the recording medium 6 by heat and pressure. After that, the recording medium 6 is discharged to the outside of the machine by a discharge roller 12c or the like.

On the other hand, the photosensitive drum 1 after the toner image is transferred to the recording medium 6 is fully exposed (whole surface light irradiation) by the laser beam L2 emitted by the pre-exposure unit 27, which is the pre-exposure means, so that the previously formed image is used. The potential on the surface of the non-uniform photosensitive drum 1 is uniformly leveled. That is, as a static elimination means, the surface of the photosensitive drum 1 is irradiated with light so as to remove the residual charge on the surface of the photosensitive drum 1. The pre-exposure unit 27 (pre-exposure unit) is arranged between the transfer roller 5 on the downstream side in the photosensitive drum 1 rotation direction and between the charging roller 2 on the photosensitive drum 1 rotation direction upstream side. As the light source of the pre-exposure unit 27, an LED, a halogen lamp, or the like can be used. The light source to be used is not particularly limited, but it is preferable to use an LED from the viewpoint of low drive voltage and easy miniaturization of the device. In this embodiment, an LED is used as the pre-exposure light source. Further, the operation of the pre-exposure unit 27 is controlled by the control unit 35.

Further, the transfer residual toner that remains on the photosensitive drum 1 without being transferred is cleaned by the cleaning means (cleaner) 10. That is, the cleaner 10 scrapes the transfer residual toner from the photosensitive drum 1 by the cleaning blade 7 which is a cleaning member, and stores it in the waste toner container 8. The cleaned photosensitive drum 1 is repeatedly subjected to image formation in the same manner as described above.

In the present embodiment, the image forming apparatus A integrally forms a cartridge of an electrophotographic photosensitive member as an image carrier and a process means acting on the image carrier, and the cartridge can be attached to and detached from the apparatus main body. It is said to be a process cartridge method. Here, the process means include a charging means for charging the electrophotographic photosensitive member, a developing means for supplying a developing agent to the electrophotographic photosensitive member, and a cleaning means for cleaning the electrophotographic photosensitive member. That is, the process cartridge has the following configuration. That is, the charging means, the developing means, the cleaning means, and the electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge can be attached to and detached from the apparatus main body. Alternatively, at least one of the charging means, the developing means, and the cleaning means and the electrophotographic photosensitive member may be integrally formed into a cartridge so that the device can be attached to and detached from the main body of the apparatus. Alternatively, at least the developing means and the electrophotographic photosensitive member may be integrally formed into a cartridge so that the cartridge can be attached to and detached from the apparatus main body.

In the present embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaner 10 are integrally formed into a cartridge to form a process cartridge B, which can be attached to and detached from the device main body 13. The process cartridge B is detachably mounted on the device body 13 via the mounting means 15 provided on the device body 13. Further, the recording medium 6 is conveyed to the process cartridge B by the recording medium supply roller 12a, the resist roller 12b, the discharge roller 12c, and the like, and the recording medium 6 after image formation is discharged from the apparatus main body 13. A recording medium transporting means is configured.

In the present embodiment, the process cartridge B is provided with a storage means 26 (storage unit). As the storage means 26, any form can be used, for example, a contact non-volatile memory, a non-contact non-volatile memory, a volatile memory having a power supply, and the like. In the present embodiment, the non-contact non-volatile memory 26 is mounted on the process cartridge B as a storage means. The non-contact non-volatile memory 26 has an antenna (not shown) which is an information transmission means on the memory side, and wirelessly communicates with the control means (CPU) 32 provided in the image forming apparatus main body 13 to obtain information. It can be read and written. In the present embodiment, the CPU 32 has the functions of an information transmission means on the device main body side and an information reading / writing means of the memory 26. The storage means 26 stores information on the film thickness of the photoconductor of the photosensitive drum 1, which will be described later, information on the charging roller 2, and information on the usage environment.

In the above configuration, the power supply 34, which is involved in applying a voltage to the charging roller 2 and the transfer roller 5.
The configuration of 38, the control unit 35, the CPU 32, and the like corresponds to the voltage application unit (charge bias application means, transfer bias application means) of the present invention.

<About abnormal discharge phenomenon>
Abnormal discharge occurs on the surface of the photosensitive drum 1 due to over-discharging that occurs in the long gap on the upstream side of the photosensitive drum 1 rotation direction from the nip formed by the charging roller 2 when a DC voltage is applied to the charging roller 2. Is a phenomenon of overcharging. In the long gap portion, increasing the charging bias on the charging roller 2 (in this embodiment, increasing the charging bias means changing the charging bias to the negative electrode side which is the normal polarity) is weak. The normal discharge that was continuous in time changes to an intermittent discharge that has a large discharge current and is discontinuous in time and space. This abnormal discharge is considered to be in the category of Townsend discharge during normal discharge. This Townsend discharge is a discharge phenomenon that changes depending on the electric field between the electrodes, the type of gas, the pressure of the gas, and the electrode material.

The proximity discharge phenomenon in the atmosphere occurs according to Paschen's law. This abnormal discharge phenomenon is an electron avalanche diffusion phenomenon in which liberated electrons are accelerated by an electric field and collide with molecules and electrodes existing between electrodes to generate electrons, cations, and anions. This electron avalanche diffuses according to the electric field, and the diffusion determines the final amount of discharge charge. If the electric field is excessive than the condition according to Paschen's law, a strong local discharge, that is, an abnormal discharge is likely to occur.
This abnormal discharge phenomenon is likely to occur under the following conditions.

Under low temperature and low humidity, the number of molecules existing between the electrodes is smaller than that under normal temperature and humidity, so the discharge start voltage tends to be higher than the discharge start voltage derived from Paschen's law. As the discharge start voltage becomes higher, the electric field tends to be excessive than the condition according to Paschen's law, and abnormal discharge tends to occur under low temperature and low humidity.

Further, abnormal discharge is likely to occur when the film thickness of the charge transport layer of the photosensitive drum 1 is thick. As the film thickness increases, the capacitance generally decreases, so that the amount of charged charge Q required for the desired charging potential Vd decreases. Ionization due to the collision of electrons occurs in an avalanche manner, and the number of charged particles increases in a murine manner, causing dielectric breakdown in the air. It is estimated that the charging potential of 1 becomes an overcharged state. That is, the contribution of the photosensitive drum 1 of the abnormal discharge is due to the change in capacitance. Therefore, if the photosensitive drum 1 is made of the same material, it depends on the film thickness of the charge transport layer, but even if the film thickness is the same, the capacitance changes due to the change in the material, and the threshold value for the occurrence of abnormal discharge also changes.

Further, when the charging contrast, which is the difference in surface potential of the photosensitive drum 1 before and after charging by the charging roller 2, becomes large, abnormal discharge is likely to occur. Specifically, when the potential difference between the surface potential of the photosensitive drum 1 immediately before charging by the charging roller 2 (hereinafter referred to as the pre-charging potential) and the surface potential of the photosensitive drum 1 immediately after charging is large, the air layer (gap portion) The electric potential becomes stronger, the amount of discharge current increases, and abnormal discharge is likely to occur.

When the charging potential Vd is increased in order to obtain an electrostatic latent image faithful to the exposure pattern, it is attenuated in the exposure process, the transfer process of applying a positive polarity opposite to the charging process, the static electricity elimination process such as preexposure, etc. The charging contrast becomes larger than the pre-charging potential. That is, an important requirement for abnormal discharge is charge contrast, but when the charge potential Vd is increased, the charge contrast naturally increases, and abnormal discharge is likely to occur.

<Photosensitive drum>
Examples of the shape of the electrophotographic photosensitive member include a cylindrical shape, a belt (endless belt) shape, and a sheet shape. In this embodiment, a cylindrical photosensitive drum 1 was used. The cylindrical photosensitive drum 1 has a configuration in which a photosensitive layer is provided on the outer periphery of the support. As the photosensitive layer, a laminated (function-separated) photosensitive layer separated into a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance was used.

As the support, it is preferable that the support exhibits conductivity (conductive support). Examples of the material of the support include metals (alloys) such as iron, copper, gold, silver, aluminum, zinc, titanium, lead, nickel, tin, antimony, indium, chromium, aluminum alloy, and stainless steel. Further, a metal support or a plastic support having a coating film formed by vacuum vapor deposition using aluminum, an aluminum alloy, an indium tin oxide alloy, or the like can also be used. The surface of the support may be subjected to cutting treatment, roughening treatment, alumite treatment or the like for the purpose of suppressing interference fringes due to scattering of laser light. Conduction between the support and the undercoat layer or the photosensitive layer (charge generation layer, charge transport layer) described later for the purpose of suppressing interference fringes due to scattering of laser light and covering scratches on the support. Layers may be provided.
The conductive layer can be formed by applying a coating liquid for a conductive layer obtained by dispersing carbon black, a conductive pigment, a resistance adjusting pigment, etc. together with a binder resin, and drying the obtained coating film. it can.
Further, a compound that cures and polymerizes by heating, ultraviolet irradiation, irradiation, or the like may be added to the coating liquid for the conductive layer. The surface of the conductive layer formed by dispersing a conductive pigment, a resistance adjusting pigment, or the like tends to be roughened. The film thickness of the conductive layer is preferably 0.2 μm or more and 40 μm or less, and more preferably 5 μm or more and 30 μm or less.
Examples of the binder resin used for the conductive layer include polymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, and trifluoroethylene, polyvinyl alcohol, and polyvinyl acetal. , Polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melamine resin, silicon resin, epoxy resin and the like. Examples of the conductive pigment and the resistance adjusting pigment include particles of a metal (alloy) such as aluminum, zinc, copper, chromium, nickel, silver and stainless steel, and those obtained by depositing these on the surface of plastic particles. .. It is also possible to use particles of metal oxides such as zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin-doped indium oxide, and antimony and tantalum-doped tin oxide. it can. These may be used alone or in combination of two or more. When two or more kinds are used in combination, they may be simply mixed, or may be in the form of a solid solution or a fused solution.

Between the support or conductive layer and the photosensitive layer (charge generation layer, charge transport layer), the adhesiveness of the photosensitive layer is improved, the coatability is improved, the charge injection property from the support is improved, and the photosensitive layer is electrically destroyed. An undercoat layer (intermediate layer) having a barrier function and an adhesive function may be provided for the purpose of protecting against the electric charge.
The undercoat layer can be formed by applying a coating liquid for an undercoat layer obtained by dissolving a resin (binding resin) in a solvent and drying the obtained coating film. Examples of the resin used for the undercoat layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, ethylene-acrylic acid copolymer, casein, polyamide, N-methoxymethylated 6 nylon, and copolymerized nylon. , Nylon, gelatin and the like. The film thickness of the undercoat layer is preferably 0.05 μm or more and 7 μm or less, and more preferably 0.1 μm or more and 2 μm or less.

Examples of the charge generating substance used in the photosensitive layer include pyrylium and thiapyrylium dyes, phthalocyanine pigments having various central metals and various crystal forms (α, β, γ, ε, X type, etc.), and anthanthron pigments. Examples thereof include dibenzpyrene quinone pigments, pyranthron pigments, azo pigments such as monoazo, disazo and trisazo, indigo pigments, quinacridone pigments, asymmetric quinosianin pigments and quinosianin pigments. Only one kind of these charge generating substances may be used, or two or more kinds may be used.
Examples of the charge transporting substance used in the photosensitive layer include pyrene compounds, N-alkylcarbazole compounds, hydrazone compounds, N, N-dialkylaniline compounds, diphenylamine compounds, triphenylamine compounds, triphenylmethane compounds, pyrazoline compounds, and styryl. Examples include compounds and stylben compounds.

The charge generation layer can be formed by applying a coating liquid for a charge generation layer obtained by dispersing a charge generation substance together with a binder resin and a solvent, and drying the obtained coating film. Further, the charge generation layer may be a vapor deposition film of a charge generation substance.
The charge transport layer can be formed by applying a coating liquid for a charge transport layer obtained by dissolving a charge transport substance and a binder resin in a solvent, and drying the obtained coating film. Further, when a charge transporting substance having a film forming property is used alone, a charge transporting layer can be formed without using a binder resin.
Examples of the binder resin used for the charge generation layer and the charge transport layer include polymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, and trifluoroethylene. Examples thereof include polyvinyl alcohol, polyvinyl acetal, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, phenol resin, melamine resin, silicon resin, epoxy resin and the like. The film thickness of the charge generation layer is preferably 5 μm or less, more preferably 0.1 to 2 μm.

The film thickness of the charge transport layer is preferably 5 to 50 μm, more preferably 10 to 35 μm.

Further, from the viewpoint of improving the durability of the electrophotographic photosensitive member, the surface layer of the electrophotographic photosensitive member can be made of a crosslinked organic polymer.
For example, the charge transport layer on the charge generation layer can be composed of a crosslinked organic polymer as a surface layer of the electrophotographic photosensitive member. Further, a surface layer made of a crosslinked organic polymer can be formed as a second charge transport layer or a protective layer on the charge transport layer on the charge generation layer. Further, the characteristics required for the surface layer composed of the crosslinked organic polymer are both the strength of the film and the charge transporting ability, and from this viewpoint, the charge transporting substance or the conductive particles and the crosslinkable monomer / It is preferable to form a surface layer with an oligomer.
As the charge transporting substance, the above-mentioned charge transporting substance can be used. Examples of the crosslinkable monomer / oligomer include a compound having a chain polymerizable functional group such as an acryloyloxy group and a styryl group, and a compound having a stepwise polymerizable functional group such as a hydroxyl group, an alkoxysilyl group and an isocyanate group. Can be mentioned.
Further, from the viewpoint of achieving both the strength of the membrane and the charge transporting ability, it is more preferable to use a compound having both a charge transporting structure (preferably a hole transporting structure) and an acryloyloxy group in the same molecule.
Examples of the method of cross-linking and curing include a method using heat, ultraviolet rays, and radiation.
The film thickness of the surface layer composed of the crosslinked organic polymer is preferably 0.1 to 30 μm, and more preferably 1 to 10 μm.

Additives can be added to each layer of the electrophotographic photosensitive member. Examples of the additive include deterioration inhibitors such as antioxidants and ultraviolet absorbers, organic resin particles such as fluorine atom-containing resin particles and acrylic resin particles, and inorganic particles such as silica, titanium oxide and alumina. Be done.

FIG. 14 is a schematic cross-sectional view showing a embodiment of the photosensitive drum 1 in this embodiment. Figure 1
As shown in 4, the photosensitive drum 1 includes a cylindrical and conductive support 1d, a conductive layer 1e as an undercoat layer of the support 1d, and a photosensitive layer (charge) formed on the undercoat layer 1e. It is composed of a generation layer 1f1, a charge transport layer 1f2) 1f, and a protective layer 1g formed on the photosensitive layer 1f.
<Measuring method of capacitance of photosensitive drum>
The capacitance C of the photosensitive drum 1 is represented by the following formula (X).
C = ε0 × S / d equation (X)
ε0: Permittivity of free space, ε: Relative permittivity, S: Unit area, d: Distance between electrodes S unit area is ^{assumed to be 1 cm 2} and can be treated as a constant, and ε0 is a constant. is there. Therefore, the capacitance of the photosensitive drum 1 is a value determined by the relative permittivity and the film thickness.
The sample for measuring the capacitance is cut into a size that can be installed in a measuring instrument, and a gold electrode is sputtered on the charge transport layer 1f2, which is the surface of the photosensitive drum 1, so as to have a size ^{of 1 cm 2.} It was formed and used as a measurement sample.
Regarding the electrode material, if it is conductive and used as an electrode, the material and the electrode forming method are not limited to these, and even if the electrode area is not 1 cm ^2, it is converted per 1 cm ^{2 by calculation.} It is not limited to this because it can be done.
Using such a sample, measurement was performed using an impedance measuring device (YHP 4192A), and a value of 1 kHz was used as the measured value.
The capacitance of the photosensitive drum 1 is the sum of the capacitances of the respective layers, but it is considered to be the same as when capacitors are connected in series. When considering a laminated photoconductor, the capacitance of the charge injection blocking layer and the charge generating layer is considerably smaller than the capacitance of the charge transport layer 1f2, and the capacitance of the photosensitive drum 1 is usually charged. It depends mostly on the capacitance of the transport layer 1f2.
Therefore, in this embodiment, the same material is used so that the relative permittivity is uniform, and the film thickness of the charge transport layer is changed to match the capacitance of the photosensitive drum 1, that is, the capacitance of the charge transport layer 1f2. Verification was performed.

<Details of charging roller>
Normally, an electric discharge occurs in a region where the relationship between the strength of the electric field and the distance between the minute voids satisfies Paschen's law in the minute voids near the charged portion, which is the contact portion between the charging roller and the photosensitive drum.
In the charging process in which an electrophotographic photosensitive member is rotated to generate a discharge, when one point on the surface of the charging roller is traced over time, the discharge is not continuously generated from the start point to the end point of the discharge. , It is known that multiple discharges occur repeatedly.
In the conventional charging roller, it is considered that a conductive path capable of transporting electric charges is formed from the outer surface of the support to the outer surface of the conductive layer 53 covering the outer periphery thereof. Therefore, most of the electric charges accumulated in the conductive layer are discharged toward the charged body such as a photoconductor and toner in one discharge. Here, as an example of the conventional charging roller, the present inventors have measured and analyzed the discharge state of the charging roller according to Comparative Example 1 described below in detail with an oscilloscope. As a result, it was confirmed that in the charging roller according to Comparative Example 1, as the process speed increased, so-called discharge discharge, which was not discharged at the timing when discharge should originally occur, occurred.

FIG. 13 shows an image diagram of a state in which a discharge is generated. FIG. 13 (a) shows a state in which there is no discharge and the total amount of discharge is satisfied, and FIG. 13 (b) shows a state in which discharge occurs and the total amount of discharge is insufficient.
The reason why the discharge is discharged is that after the electric charge from the conductive layer 53 covering the support 52 of the charging roller 2 is consumed by the electric charge accumulated in the conductive layer 53, the conductive layer for the next discharge is performed. It is considered that this is because the charge accumulation in 53 is not in time. Here, the present inventors can eliminate the discharge from the discharge if a large amount of electric charge can be accumulated in the conductive layer 53 and the accumulated electric charge is not consumed at one time even by one discharge. I considered it as a thing. As a result of further studies based on such considerations, it has been found that the charging roller provided with the configuration according to the present disclosure can well meet the above requirements.

<Slope of impedance>
The charging roller 2 according to the embodiment of the present invention is characterized by having a predetermined impedance characteristic. Impedance is measured by applying an AC voltage having an amplitude of 1 V to the charging roller 2 ^{while changing the frequency between 1.0 × 10 -2} Hz to 1.0 × 10 ^{6 Hz.} The measurement result, and the horizontal axis the frequency of the AC voltage, the slope at the time of log-log plot of impedance acquired vertical axis, in the frequency range ^{1.0 × 10 5 Hz~1.0 × 10 6} Hz, It is -0.8 or more and -0.3 or less.
When conventional charging roller to the impedance measurement, between ^{1.0 × 10 5 Hz~1.0 × 10 6} Hz, always slope is -1.
Here, as shown in FIG. 3, the inclination is an inclination with respect to the horizontal axis when the impedance characteristics of the conductive member (charging roller) are log-log plotted with respect to the frequency. Conventionally, the slope is -1 as shown by the solid line, whereas in the present embodiment, the slope is between 1.0 × 10 ⁵ Hz and 1.0 × 10 ^{6 Hz as shown by the broken line.} It is 0.8 or more and -0.3 or less.

The equivalent circuit of the conductive member (charging roller) is represented by a parallel circuit of the electric resistance R and the capacitance C, and the absolute value | Z | of the impedance can be expressed by the following equation (1). At this time, f in the equation (1) indicates the frequency of the applied AC voltage.

On the high frequency side, the straight line with the slope of impedance -1 is that the movement of the electric charge cannot follow the high frequency voltage and stagnates, so the electric resistance value R greatly increases, so to speak, the capacitance of insulation. It can be inferred that the state is being measured. Assuming a state in which the electric charge is stagnant, in the equation (1), R can be approximated to infinity by the equation (1). At this time, in the equation (2) in which the element of the denominator is extracted, it ^{is possible to approximate that R-2} takes a very small value with respect to (2πfC) ^2. Therefore, the equation (1) can be transformed into the equation (3) by removing ^R-2. Finally, when the equation (3) is modified to take the logarithm of both sides, the equation (4) is obtained, and the slope of logf becomes -1.
R- ² + (2πfC) ² equations (2)

The meanings of the above equations (1) to (4) will be described with reference to FIG. In FIG. 4, the vertical axis represents the logarithm of the absolute value of impedance, and the horizontal axis represents the logarithm of the frequency of the measured vibration voltage. FIG. 4 shows the behavior of the impedance expressed by the equation (1). First, as described above, the absolute value of the impedance satisfying the equation (1) decreases at a certain frequency as the frequency increases. Then, in the log-log plot as shown in FIG. 4, the decreasing behavior is such that the inclination does not depend on the electric resistance value or the capacitance of the charging roller, as shown by the equation (4), and the inclination is -1. It becomes a straight line of.

When the impedance characteristics of the insulating conductive member are measured, the slope becomes a straight line of -1, so in the impedance measurement of the conductive member, when the slope is -1, the movement of electric charge is stagnant on the high frequency side. It is presumed that the characteristic that is being used appears. When the movement of electric charge on the high frequency side is stagnant, the supply of electric charge for discharge cannot keep up with the frequency of discharge. As a result, it is presumed that there is a timing at which discharge cannot be performed, and that discharge is lost.

On the other hand, the conductive member (charging roller 2) having an impedance gradient of −0.8 or more and −0.3 or less in a high frequency region of ^{1.0 × 10 5 Hz to 1.0 × 10 6 Hz} , The charge supply is unlikely to stagnate on the high frequency side. As a result, it is possible to supply electric charge to the discharge of the frequency from the low frequency region to the high frequency region where the impedance takes a constant value, particularly to the discharge on the high frequency side where the charge stagnation is likely to occur. Since the electric charge can be supplied abundantly, it is possible to suppress the discharge from the discharge and improve the total amount of the discharge. Since the range of the high frequency region is the region having the highest frequency among the frequencies of the discharge generated from the conductive member (charging roller 2), it is considered that the discharge is likely to occur. .. By showing a value in the above range in which the slope is larger than -1 in such a frequency region, a slope larger than -1 is obtained even in a high frequency region lower than the frequency region, and the occurrence of discharge omission is suppressed. , The total amount of discharge can be improved.

The inventors think that when the discharge frequency is specifically predicted by using the case where the charging roller 2 and the photosensitive drum 1 are combined, the range is as follows.
The discharge region where the discharge to the photosensitive drum 1 is performed depends on the diameter of the photosensitive drum 1 and the charging roller 2 and the like. For example, the width of the discharge region in the moving direction of the surface of the charging roller 2 which is provided so as to face the outer surface of the photosensitive drum 1 and rotates in synchronization with the photosensitive drum 1 (on the peripheral surface of the charging roller in the rotation direction of the charging roller). The width measured along the peripheral surface of the photosensitive drum 1) or the circumferential width of the peripheral surface of the photosensitive drum 1 (the width measured along the peripheral surface of the photosensitive drum 1 in the rotation direction of the photosensitive drum 1) is set to 0.5 mm to 1 mm. .. Assuming that the maximum process speed of the electrophotographic apparatus is 100 to 500 mm / sec (surface speed of the photosensitive drum), the time required for the surface of the photosensitive drum to pass through the discharge region is 10 ^{-3 sec to 10 -2} sec or more. Further, when the discharge is observed in detail, the length of the discharge region (region of the peripheral surface of the photosensitive drum) due to the single discharge is 0.01 mm to 0.1 mm, so that the same point on the surface of the charging roller passes through the discharge region. It is estimated that at least 5 to 100 discharges have occurred during this period. Therefore, the frequency of the discharge charging roller is generated, it is in the range of several Hz~1.0 × ¹⁰ 6 Hz is estimated. According to a more becomes fast process, since the frequency of the discharge higher to it is necessary to increase the number of discharge, among the above range, such as ^{1.0 × 10 5 Hz~1.0 × 10 6} Hz Control of discharge and conduction mechanisms in the high frequency range is important.
As described above, in order to increase the number of discharges, it is effective to deviate the slope of the impedance in the high frequency region from -1. Thereby, the property of rapidly supplying the electric charge for the discharge and the subsequent discharge can be well achieved. When the slope of the impedance deviates from -1, it means that the supply of electric charge in the conductive member (charging roller 2) is not stagnant. Can be obtained.

<Impedance on the low frequency side>
The impedance on the low frequency side expresses the characteristic that charge stagnation is unlikely to occur.
This can be seen from the fact that the slope of the impedance on the low frequency side is not -1. Then, in the equation (1), when the frequency is approximated to zero, it can be approximated to the electric resistance value R. Therefore, it can be seen that the electric resistance value R represents the ability of the electric charge to move in one direction.
Therefore, in the measurement while applying a low frequency voltage, it can be assumed that the amount of electric charge movement in a state where the electric charge movement can follow the vibration of the voltage is simulated.
The amount of charge transfer at a low frequency is an index of the ease of charge transfer from the charging roller to the measurement electrode, and further, the charge can be transferred from the surface of the charging roller to the photosensitive drum by electric discharge. It can be used as an index of the amount of electric charge.
Further, the AC voltage used for measuring the impedance has an amplitude of 1 V. The vibration voltage for this measurement is significantly lower than the voltage actually applied to the charging roller in the electrophotographic image forming apparatus of several 100V to several 1000V. Therefore, it is considered that the ease of discharging from the surface of the charging roller can be evaluated at a higher level.
In addition, the ease of discharge can be controlled within an appropriate range. When the impedance ^{becomes lower than 1.0 × 10 3} Ω, the amount of one discharge becomes too large, the supply of electric charge for the next discharge cannot follow, and the discharge works in the direction of discharge. On the other hand, when the impedance exceeds 1.0 × 10 ⁷ Ω, out easiness of discharge is reduced.
That is, the impedance at a frequency of 1.0 × 10 ^{-2 Hz to 1.0 × 10 1} Hz is preferably 1.0 × 10 ³ Ω to 1.0 × 10 ^{7 Ω.}
As described with reference to FIG. 4, in the low frequency region, the absolute value of the impedance takes a constant value, and the impedance at 1.0 × 10 ⁻² Hz to 1.0 × 10 ¹ Hz is, for example, 1 Hz. The value of impedance at frequency can be substituted.

<Measurement method of impedance>
In measuring impedance, in order to eliminate the influence of contact resistance between the conductive member (charging roller 2) and the measuring electrode, a low-resistance thin film is deposited on the surface of the conductive member (charging roller 2). A thin film is used as an electrode, while the conductive support 52 is used as a ground electrode to measure impedance at two terminals.

Examples of the method for forming the thin film include a method for forming a metal film such as metal vapor deposition, sputtering, application of a metal paste, and application of a metal tape. Among these, a method of forming a metal thin film such as platinum or palladium as an electrode by vapor deposition is preferable from the viewpoint of reducing the contact resistance with the conductive member.

When forming a metal thin film on the surface of the charging roller 2, in consideration of its simplicity and uniformity of the thin film, a mechanism capable of gripping the charging roller is provided to the vacuum vapor deposition apparatus, and the charging roller 2 having a columnar cross section is provided. On the other hand, it is preferable to use a vacuum vapor deposition apparatus further provided with a rotation mechanism. For a cylindrical charging roller 2 having a curved cross section such as a circular shape, it is difficult to connect the metal thin film as the measurement electrode and the impedance measuring device as follows. It is preferable to use the above method. Specifically, after forming a metal thin film electrode having a width of about 10 mm to 20 mm in the longitudinal direction of the charging roller 2, the metal sheet is wound tightly and connected to the metal sheet and the measuring electrode coming out of the measuring device. And measure it. As a result, the electric signal from the conductive layer of the charging roller 2 can be suitably acquired by the measuring device, and the impedance measurement can be performed. The metal sheet may be any metal sheet having an electric resistance value equivalent to that of the metal portion of the connection cable of the measuring device when measuring the impedance, and for example, aluminum foil or metal tape can be used.

Impedance measuring devices, impedance analyzer, network analyzer, spectrum analyzer or the like, may be any device that impedance can be measured in the frequency range of up to 1.0 × 10 6 ^Hz. Among these, it is preferable to measure from the electric resistance range of the charging roller with an impedance analyzer.
The impedance measurement conditions will be described. An impedance measuring device is used to measure the impedance in the frequency range of ^{1.0 × 10 -2} Hz to 1.0 × 10 ^{6 Hz.} The measurement is performed in an environment of a temperature of 23 ° C. and a humidity of 50% RH. In order to reduce measurement variation, it is preferable to provide 5 or more measurement points per digit of frequency. The amplitude of the AC voltage is 1V.
The measured voltage may be measured while applying a DC voltage in consideration of the shared voltage applied to the charging roller in the electrophotographic image forming apparatus. Specifically, it is suitable for quantifying the characteristics of charge transport and accumulation by measurement while superimposing a DC voltage of 10 V or less on the vibration voltage.

FIG. 12 shows an example of the impedance measurement result. The solid line shows the impedance measurement result of the charging roller 2 of the present embodiment, and the broken line shows the impedance measurement result of the conventional charging roller 2. In the graph obtained by this log-log plot, ^{the slope of the absolute value of the impedance in the frequency domain of 1.0 × 10 5 to} 1.0 × 10 ⁶ Hz is -1 in the conventional charging roller, whereas the charging of the present invention It can be read that the roller 2 has a value of about −0.5.

<Calculation method of impedance slope>
For the measurement results measured under the above conditions, plot the absolute value of impedance with a log-log graph against the measurement frequency using spreadsheet software (for example, "Windows Excel" (trade name, manufactured by Microsoft)). to. graph obtained in this log-log plot, the slope of 1.0 × ¹⁰ 5 Hz~1.0 × ¹⁰ 6 absolute value of the impedance in the frequency region of Hz, 1.0 × ¹⁰ 5 Hz~1. It may be obtained by using the measurement points in the frequency region of 0 × 10 ⁶ Hz. Specifically, the approximate straight line of the linear function is calculated by the minimum square method for the plot of the graph in the frequency range, and the gradient is calculated. It may be calculated.
^{Next, the arithmetic mean value of the measurement points in the frequency domain of 1.0 × 10 -2 Hz to 1.0 × 10 1} Hz in the log-log graph is calculated, and the obtained value is used as the impeen on the low frequency side. It can be a dance. In the measurement of the slope of the impedance in the cylindrical charging roller, the measurement is performed at 5 places in each region when the longitudinal direction as the axial direction is divided into 5 equal parts, and the measured values of the slopes at 5 places. The arithmetic mean of

With reference to FIG. 5, the charging roller 2 according to the present embodiment will be described by taking the charging roller 2 having a roller shape as an example. FIG. 5 is a schematic cross-sectional view perpendicular to the longitudinal direction, which is the axial direction of the charging roller 2. The charging roller 2 has a columnar conductive support 52 and a conductive layer 53 formed on the outer periphery of the support 52, that is, on the outer surface.
Further, in the measurement in the present embodiment, as a pretreatment, a measurement electrode was prepared by vacuum platinum vapor deposition on the charging roller 2 while rotating. At this time, a masking tape was used to prepare a strip-shaped electrode having a width of 1.5 cm in the longitudinal direction and a uniform electrode in the circumferential direction. By forming the electrode, the influence of the contact resistance between the measurement electrode and the charging roller can be eliminated as much as possible due to the surface roughness of the charging roller. Next, an aluminum sheet was wound around the electrode without a gap to form a measurement electrode on the charging roller side.

FIG. 6 shows a schematic view of a state in which a measurement electrode is formed on a charging roller. In FIG. 6, 52 is a conductive support, 53 is a conductive layer having a matrix domain structure described later, 60 is a platinum-deposited layer which is a measurement electrode, and 61 is an aluminum sheet.
FIG. 7 shows a schematic cross-sectional view of a state in which a measurement electrode is formed on a charging roller. As shown in FIG. 7, it is important that the conductive layer 53 having a matrix domain structure is sandwiched between the conductive support 52 and the platinum-deposited layer 60 which is a measurement electrode.
Then, the aluminum sheet 61 was connected to the measurement electrode on the impedance measuring device 70 (Solartron 1260 and Solartron 1296, manufactured by Solartron Co., Ltd.).
FIG. 8 shows a schematic diagram of this measurement system. Impedance measurement was performed by using the conductive support 52 and the aluminum sheet 61 as two electrodes for measurement.
When measuring the impedance, the charging roller 2 described later was left in an environment of a temperature of 23 ° C. and a humidity of 50% RH for 48 hours to saturate the amount of water in the conductive member.

Measurements of impedance, temperature 23 ° C., a humidity of 50% RH environment, when an AC voltage of amplitude 1Vpp, the measurement (frequency at a frequency ^{1.0 × 10 -2 Hz~1.0 × 10 6} Hz changes an order of magnitude The absolute value of the impedance was obtained by measuring 5 points at a time. Next, the measurement results were log-log plotted with the absolute value of the impedance and the frequency using spreadsheet software such as Excel (registered trademark). From the graph obtained by the log-log plot, (a) 1.0 × 1
The arithmetic averages of the slopes from 0 ⁵ Hz to 1.0 × 10 ⁶ Hz and (b) absolute values of impedance from ^{1.0 × 10 -2} Hz to 1.0 × 10 ^{1 Hz were calculated.} Regarding the measurement position, the conductive layer of the charging roller 2 (length in the longitudinal direction: 230 mm), which will be described later, is divided into five equal regions in the longitudinal direction, and one point is arbitrarily divided from each region, for a total of five points. A measurement electrode was formed, and the above measurement and arithmetic mean value were calculated.

<Method of forming matrix domain structure>
As a uniform state of the charging roller 2 of the present embodiment, a charging roller 2 having a conductive layer having a domain matrix structure (sea island structure) is exemplified. The domain matrix structure is a structure having a matrix 54 (forming a sea phase) and a plurality of domains 55 (forming an island phase) dispersed and scattered in the matrix 54.
Specific means for achieving the matrix domain structure that plays an important role in exhibiting the effects of the present invention will be described.

The configuration of the domain 55 as the conductive phase and the matrix 54 as the insulating phase according to the present embodiment is obtained by a method of phase-separating or dispersing the conductive material and the insulating material as long as the effects of the present invention are not impaired. be able to. Among them, as the conductive layer 53, in order to bring the conductive layer 53 into contact with other members and stably exhibit its function, a matrix 54 containing a first rubber having an insulating property and a second matrix 54 having a conductive property. It is essential to have a matrix domain type phase separation structure due to the phase separation of the rubber.
Here, in the present specification, the "conductive phase" and the "conductive layer" are different from each other. The conductive "phase" refers to the "phase" forming the domain 55 of the phase-separated domain matrix structure, while the conductive "layer" is made of a material having a domain matrix structure including the domain 55 and the matrix 54. Indicates a "layer".

As a method for forming such a matrix domain type phase-separated structure, a phase-separated structure can be formed by kneading two types of incompatible rubber materials.
There is an SP value as a parameter expressing compatible / incompatible. The SP value is the square root of the agglutination energy density of molecules, and represents the magnitude of the agglutination force (intermolecular force) between molecules. Therefore, by optimizing the SP value difference between the two, the miscibility (compatibility) state can be controlled and the phase separation structure can be controlled. The SP value of rubber can be controlled by adjusting it by selecting a material or a copolymerization ratio of a segment containing a polar group.

In the present embodiment, in order to form the domain matrix structure, it is preferable that the SP value difference between the two types of rubber materials is 5.0 or less. It is more preferable that the SP value is 2.0 or less, and a domain matrix structure having a domain of a smaller size can be formed.

In order to increase the amount of charge in a single discharge, the present inventors limit the path of the charge moving through the conductive layer 53 and transport the charge only to the domain having a low volume fraction, as described above. We have found that impedance characteristics can be realized.
In order to control the impedance when the frequency is 1.0 × 10 ^{-2 Hz to 1.0 × 10 1} Hz, the following control is required.
First, in order to transport the charge only to the domain 55, not to the matrix 54, and further to suppress the electric field concentration between the domains 55, to suppress the local charge flow to the matrix 54. 54 volume resistance, domain 55 volume resistance, distance between domains 55, domain 55 placement uniformity, and domain 55 shape control In addition, domain 55 volume resistance uniformity, electron conductive Controlling quantity uniformity, domain 55 size uniformity, domain 55 size uniformity, domain 55 body integration, and the like are control factors for limiting charge transport to domain 55.

<Conductive layer>
As the charging roller 2 (charging member) in the embodiment of the present invention, for example, it is preferable that the conductive layer 53 satisfies the following component (i) to component (iii). Hereinafter, the conductive member of the present invention will be described using the charging roller as an example, but the conductive member is not limited to the charging roller 2. That is, the present invention can be suitably applied to a member capable of generating an electric discharge with the surface of the photosensitive drum 1. For example, a conductive roller different from the charging roller 2 may be provided, and the configuration thereof may be the same as that of the charging roller 2 of the present embodiment. Alternatively, the present invention may be applied to the transfer roller 5 so as to generate a discharge with a small amount of uneven discharge from the photosensitive drum 1. When the present invention is applied as the transfer roller 5, a discharge with a small amount of uneven discharge (uniformization of the discharge amount) may be performed on the surface of the photosensitive drum 4 at the same time as the transfer during image formation. Further, the discharge with less unevenness of the discharge amount (uniformization of the discharge amount) may be performed by using both the transfer roller 5 and the charging roller 2, or may be performed by using either one.
Component (i): The volume resistivity of the matrix is greater ^{than 1.0 × 10 12} Ω · cm and not more than 1.0 × 10 ¹⁷ Ω · cm.
Component (ii): The volume resistivity of the domain is 1.0 × 10 ¹ Ω · cm or more and 1.0 × 10 ⁴ Ω · cm or less.
Component (iii): The distance between adjacent wall surfaces of the domain is within the range of 0.2 μm or more and 2.0 μm or less.

FIG. 9 shows a partial cross-sectional view of the conductive layer 53 in a direction perpendicular to the longitudinal direction of the charging roller. The conductive layer 53 has a matrix domain structure having a matrix 54 and a domain 55. Then, the domain 55 contains the conductive particles 56 as the electron conductive agent.
The charging roller 2 provided with the conductive layer 53 satisfying the components (i) to (iii) can accumulate a sufficient charge in each domain 55 when a bias is applied between the charging roller 2 and the photosensitive drum 1. Simultaneous charge transfer between 55 can be suppressed. As a result, it is possible to prevent most of the electric charges accumulated in the conductive layer 53 from being released by one discharge. As a result, the electric charge for the next discharge can still be accumulated in the conductive layer 53, so that the discharge can be stably generated in a short cycle. Such a discharge state achieved by the charging roller according to the present disclosure is hereinafter also referred to as "fine discharge".

In the case of the charging roller 2 of the present embodiment capable of generating a fine electric discharge, the dark part potential (VD) obtained by uniformly charging the photosensitive drum 1 by the electric discharge is equivalent to that of the conventional charging roller. However, as described above, since the VD is formed by reducing the amount of each discharge and increasing the amount of each discharge, the micro-uniformity of the VD is dramatically improved as compared with the conventional charging roller. Therefore, when the charging roller 2 according to the embodiment of the present invention is used, the discharge uniformity is dramatically improved with respect to the abnormal discharge, and the excessive discharge generated locally is suppressed, so that the abnormal discharge is effective. Can be resolved.
Hereinafter, the components (i) to (iii) above will be described.

<Component (i)>
・ Volume resistivity of matrix;
By making the volume resistivity of the matrix 54 ^{larger than 1.0 × 10 12} Ω · cm, it is possible to prevent the charge from moving in the matrix 54 by bypassing the domain 55. In addition, it is possible to suppress the consumption of most of the electric charges accumulated in one discharge. Further, it is possible to prevent the electric charge accumulated in the domain 55 from leaking to the matrix 54, resulting in a state as if a conductive path communicating in the conductive layer is formed.
The upper limit of the volume resistivity of the matrix 54 is not particularly limited, but as a guide, ^{it is preferably 1.0 × 10 17} Ω · cm or less. In order to transfer the charge through the domain 55 in the conductive layer in order to achieve the above-mentioned fine discharge mode, the region (domain 55) in which the charge is sufficiently accumulated is electrically insulating. The present inventors consider that a configuration divided by a region (matrix 54) is effective. By setting the volume resistivity of the matrix 54 to the range of the high resistance region as described above, sufficient charges can be retained at the interface with each domain 55, and charge leakage from the domains 55 can be suppressed. ..
Further, in order to achieve a fine discharge and a necessary and sufficient discharge amount, that is, in order to obtain the conductive layer 53 satisfying the condition that the slope of the impedance on the low frequency side is not -1, the transfer of electric charge It is extremely effective to limit the route to a route mediated by the domain 55. By suppressing the leakage of charge from the domain 55 to the matrix 54 and limiting the charge transport path to the path via the plurality of domains 55, the density of the charge existing in the domain 55 can be improved. The charge charge in each domain 55 can be further increased. As a result, the total number of charges that can participate in the discharge can be improved on the surface of the domain 55 as the conductive phase that is the starting point of the discharge, and as a result, the ease of discharging from the surface of the charging roller 2 can be improved. Is thought to be possible.

-Measurement method of matrix volume resistivity;
The volume resistivity of the matrix 54 can be measured by thinning the conductive layer 53 and using a micro probe. Examples of the means for thinning include a sharp razor, a microtome, and a focused ion beam method (FIB).
Regarding the preparation of flakes, it is necessary to eliminate the influence of the domain 55 and measure the volume resistance of only the matrix 54. Therefore, the domain measured in advance with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It is necessary to prepare flakes with a thickness smaller than the distance between 55. Therefore, as a means for flaking, a means capable of producing a very thin sample such as a microtome is preferable.

In the measurement of volume resistivity, first, one side of the flakes is grounded, and then the locations of the matrix 54 and the domain 55 in the flakes are identified. These locations can be identified by a scanning probe microscope (SPM), an atomic force microscope (AFM), or the like, which can measure the volume resistivity or hardness distribution of the matrix 54 and the domain 55. Next, the probe is brought into contact with the matrix 54, a DC voltage of 50 V is applied for 5 seconds, the arithmetic mean value of the ground current value for 5 seconds is measured, and the electric resistance value is calculated by dividing by the voltage. Then, the film thickness of the flakes may be used to convert into volume resistivity. At this time, any means capable of measuring the shape of the flakes, such as SPM or AFM, is suitable because the film thickness of the flakes can be measured and the volume resistivity can be measured.
To measure the volume resistivity of the matrix 54 in the conductive layer 53 of the columnar charging roller 2, one thin sample is cut out from each of the regions in which the conductive layer 53 is divided into four in the circumferential direction and five in the longitudinal direction. After obtaining the above measured values, it can be performed by calculating the arithmetic mean value of the volume resistivity of a total of 20 samples. FIG. 11A shows a state in which a flaky sample is cut out in one of the five divided regions.

<Component (ii)>
・ Volume resistivity of the domain;
The volume resistivity of the individual domains 55 is smaller than the volume resistivity of the matrix 54. This is preferable because it becomes easy to limit the charge transport path to the path via the plurality of domains 55 while suppressing the movement of unintended charges in the matrix 54.
Further, the volume resistivity of the domain 55 is preferably 5 orders of magnitude or more larger than the volume resistivity of the matrix 54.
More specifically, the volume resistivity of the domain 55 is preferably 1.0 × 10 ¹ Ωcm or more and 1.0 × 10 ⁴ Ωcm or less. By lowering the volume resistivity of the domain 55, the charge transport path is more effectively limited to the path via the plurality of domains 55 while suppressing the unintended charge transfer in the matrix 54. Can be done.

Further, the volume resistivity of the domain 55 ^{is more preferably 1.0 × 10 2} Ωcm or less. By lowering the volume resistivity of the domain 55 to this range, the amount of electric charge transferred within the domain 55 can be dramatically improved. Therefore, the charge transport path can be effectively limited to the domain 55.

The volume resistivity of the domain 55 is adjusted by using a conductive agent with respect to the rubber component of the domain 55 to bring the conductivity to a predetermined value.
As the rubber material for the domain 55, a rubber composition containing a rubber component for the matrix 54 can be used, but the solubility parameter (SP value) with the rubber material forming the matrix 54 to form the matrix domain structure can be used. ) Is 0.4 (J / cm ³ ) ^0.5 or more, 5.0 (J / cm ³ ) ^0.5 or less, especially 0.4 (J / cm ³ ) ^0.5 or more 2 .2 (J / cm ³ ) ^0.5 or less is more preferable.

The volume resistivity of the domain 55 can be adjusted by appropriately selecting the type of the electron conductive agent and the amount of the electron conductive agent added thereto. As a conductive agent used to control the volume resistivity of the domain 55 to 1.0 × 10 ¹ Ωcm or more and 1.0 × 10 ⁴ Ωcm or less, the volume resistivity increases from high resistance to low resistance depending on the amount of dispersion. An electronically conductive agent that can be changed is preferable.
Regarding the electronic conductive agent blended in the domain 55, oxides such as carbon black, graphite, titanium oxide and tin oxide; metals such as Cu and Ag; particles whose surface is coated with oxides or metals and made conductive, etc. Take as an example. Further, if necessary, two or more kinds of these conductive agents may be blended in appropriate amounts and used.
Among the above-mentioned electronic conductive agents, it is preferable to use conductive carbon black, which has a high affinity with rubber and can easily control the distance between the electronic conductive agents. The type of carbon black blended in the domain 55 is not particularly limited. Specific examples thereof include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and Ketjen black.
Among them, high conductivity can be imparted to a domain 55, DBP oil absorption of 40 cm ^3/100 g or more 170cm ^3/100 g can be preferably used in which conductive carbon black below.
It is preferable that the conductive electronic conductive agent such as carbon black is blended in the domain 55 in an amount of 20 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the rubber component contained in the domain 55. A particularly preferable blending ratio is 50 parts by mass or more and 100 parts by mass or less. It is preferable that the conductive agent is blended in these proportions in a large amount as compared with a general charging roller for electrophotographic. Thereby, the volume resistivity of the domain can be easily controlled in the range of ^{1.0 × 10 1} Ωcm or more and 1.0 × 10 ^{4 Ω · cm or less.}
In addition, if necessary, fillers, processing aids, cross-linking aids, cross-linking accelerators, anti-aging agents, cross-linking accelerators, cross-linking retarders, softeners, and dispersants commonly used as rubber compounding agents. , Colorants and the like may be added to the rubber composition for the domain as long as the effects according to the present invention are not impaired.

-Measurement method of domain volume resistivity;
For the measurement of the volume resistivity of the domain 55, the measurement location is changed to a location corresponding to the domain 55, and the applied voltage at the time of measuring the current value is set to 1 V, as compared with the method for measuring the volume resistivity of the matrix 54 described above. It may be carried out in the same manner except for the change.
Here, the volume resistivity of the domain 55 is preferably uniform. In order to improve the uniformity of the volume resistivity of the domains 55, it is preferable to make the amount of the electron conductive agent in each domain 55 uniform. As a result, the discharge from the outer surface of the charging roller 2 to the charged body can be further stabilized.
Specifically, for each cross-sectional area of the domain 55 appearing in the cross section of the conductive layer 53 in the thickness direction, the total cross-sectional area of the portion made of the electronic conductive agent contained in each of the domains 55, for example, the conductive particles When the standard deviation of the ratio of the ratio of the domain 55 to the cross-sectional area is σr and the average value is μr, the coefficient of variation σr / μr is preferably 0 or more and 0.4 or less.
Since σr / μr is 0 or more and 0.4 or less, it is possible to reduce variations in the number or amount of conductive agents contained in each domain 55. By imparting the uniformity of the volume resistivity of the domain 55 based on such an index, the electric field concentration in the conductive layer 53 can be suppressed, and the presence of the matrix 54 to which the electric field is locally applied can be reduced. As a result, the conductivity of the matrix 54 can be reduced as much as possible.
A more preferable σr / μr is 0 or more and 0.25 or less, and the electric field concentration in the conductive layer 53 can be suppressed more effectively, and 1.0 × 10 ^-2 Hz to 1.0 × 10 ^{1 Hz.} impedance it is possible to further reduced to less than 1.0 × 10 ⁵ Ω and in.
In order to improve the uniformity of the volume resistivity of the domain 55, it is preferable to increase the blending amount of carbon black with respect to the second rubber in the step of preparing the domain-forming rubber mixture (CMB) described later.

-Measuring method of domain volume resistivity uniformity;
Since the uniformity of the volume resistivity of the domain 55 is governed by the amount of the electron conductive agent in the domain 55, it can be evaluated by measuring the variation in the amount of the electron conductive agent in each domain 55.
First, a section is prepared by the same method as the method for measuring the volume resistivity of the matrix 54 described above. Next, a fracture surface is formed by means such as a freeze-cutting method, a cross polisher method, and a focused ion beam method (FIB). The FIB method is preferable in consideration of the smoothness of the fracture surface and the pretreatment for observation. Further, in order to preferably observe the matrix domain structure, a pretreatment such as a dyeing treatment or a thin-film deposition treatment may be performed so as to preferably obtain a contrast between the domain 55 as the conductive phase and the matrix 54 as the insulating phase. ..
The presence of the matrix domain structure is confirmed by observing the fractured surface formed and pretreated sections with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Among these, from the viewpoint of the accuracy of quantification of the area of the domain 55, it is preferable to perform the observation by SEM at 1000 to 100,000 times.

The measurement of the uniformity of the volume resistivity of the domain 55 is preferably performed by quantifying the photographed image of the fracture surface in which the matrix-domain structure appears. An 8-bit grayscale image is obtained by using image processing software (for example, "ImageProPlus", manufactured by Media Cybernetics) on the fracture surface image obtained by observation with SEM to obtain a 256-tone monochrome image. .. Next, the black and white of the image is inverted and binarized so that the domain 55 in the fracture surface becomes white. Next, for the binarized image, the cross-sectional area S of the domain 55 and the cross-sectional area Sc of the portion made of the conductive agent in each domain 55 are calculated by the counting function in the image processing software. Then, the standard deviation σr and the average value μr of the area ratio Sc / S in the domain 55 of the electron conductive agent may be calculated, and σr / μr may be calculated as an index of the uniformity of the volume resistivity of the domain 55.

In the case of the cylindrical charging roller 2, when the length of the conductive layer 53 in the longitudinal direction is L and the thickness of the conductive layer 53 is T, the center of the conductive layer 53 in the longitudinal direction and both ends of the conductive layer 53. The cross sections of the conductive layer 53 in the thickness direction as shown in FIG. 11B are acquired at three locations of L / 4 toward the center. For each of the obtained cross sections, 15 μm square observation regions are acquired at any three locations in the thickness region from the outer surface of the conductive layer 53 to the depth of 0.1 T to 0.9 T in the support 52 direction. .. By binarizing and quantifying the observation region by the above method, σr / μr as an index of the uniformity of the volume resistivity of the domain 55 is calculated, and the arithmetic mean of the measured values from a total of 9 observation regions. Can be quantified as an index of domain size uniformity.

<Component (iii)>
-Distance between adjacent walls between domains (hereinafter also referred to as "distance between domains")
The distance between the domains 55 is preferably 0.2 μm or more and 2.0 μm or less.
The distance between the domains 55 in the conductive layer 53 is preferably 2.0 μm or less, particularly 1.0 μm or less, in order to transfer charges between the domains 55. Further, since the domains 55 are electrically separated from each other in the insulating region (matrix) and the electric charge is easily accumulated in the domains, the distance between the domains 55 is set to 0.2 μm or more, particularly 0.3 μm or more. Is preferable.

・ Measurement method of inter-domain distance;
The method for measuring the distance between the domains 55 may be carried out as follows.
First, a section is prepared by the same method as the method for measuring the volume resistivity of the matrix 54 described above. Next, a fracture surface is formed by means such as a freeze-cutting method, a cross polisher method, and a focused ion beam method (FIB). The FIB method is preferable in consideration of the smoothness of the fracture surface and the pretreatment for observation. Further, in order to preferably observe the matrix domain structure, a pretreatment such as a dyeing treatment or a vapor deposition treatment may be performed to obtain a suitable contrast between the conductive phase and the insulating phase.
The presence of the matrix domain structure is confirmed by observing the fractured surface formed and pretreated sections with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Among these, from the viewpoint of the accuracy of quantification of the domain area, it is preferable to perform the observation by SEM at 1000 to 100,000 times.

The measurement of the distance between the domains 55 is preferably performed by quantifying the photographed image of the fracture surface in which the matrix-domain structure appears. The fracture surface image obtained by observation with SEM is grayscaled to 8 bits using image processing software (for example, "Luzex" (trade name, manufactured by Nireco)), and 256-tone monochrome. Get an image. Next, the black and white of the image is inverted and binarized so that the domain 55 in the fracture surface becomes white. Next, the distance between the walls of the domain size group in the image is calculated. The distance between the wall surfaces at this time is the shortest distance between adjacent domains 55.

In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, observation regions of 50 μm square were placed at arbitrary three locations in the thickness region from the outer surface of the conductive layer 53 in the direction of the support 52 to a depth of 0.1 T to 0.9 T. The distance between each domain 55 observed in each of the nine observation regions may be measured. Since it is necessary to observe the surface including the outer surface of the conductive layer 53 from the support 52, which is the direction of charge transfer, the section includes a cross section including a normal starting from the central axis of the support 52. Cut out in the direction that can be done.

・ Uniform distance between domains;
It is more preferable that the distribution of the distance between the domains 55 is uniform with respect to the above component (iii). For example, a phenomenon in which the ease of discharge is suppressed when a part of the conductive layer 53 where the distance between domains 55 is long is locally formed so that the supply of electric charge is stagnant compared to the surroundings. May occur. The uniform distribution of distances between the domains 55 can reduce the occurrence of such a phenomenon.

In the cross section in which the electric charge is transported, that is, in the cross section in the thickness direction of the conductive layer 53 as shown in FIG. 11B, the depth from the outer surface of the conductive layer 53 toward the support 52 is 0.1 T to 0. .9T
When an observation region of 50 μm square is acquired at any three locations in the thickness region up to, the coefficient of variation is used by using the arithmetic mean value Dm of the distance between domains 55 in the observation region and the variation σm of the distance between domains 55. It is preferable that σm / Dm is 0 or more and 0.4 or less.

・ Measurement method of inter-domain distance uniformity;
The measurement of the uniformity of the distance between the domains 55 can be performed by quantifying the image obtained by the direct observation of the fracture surface, as in the measurement of the distance between the domains 55 described above.
For the binarized image of the fracture surface obtained by measuring the distance between domains 55, use image processing software such as LUZEX (manufactured by Nireco Co., Ltd.) to determine the distance between domains of the domain size group in the image. The average value Dm and the standard deviation σm of Dm may be calculated, and σm / Dm may be calculated as an index of the uniformity of the interdomain distance.

In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, 50 μm square observation regions are acquired at any three locations in the thickness region from the outer surface of the conductive layer 53 to the depth of 0.1 T to 0.9 T in the support 52 direction. .. The observation region is binarized and quantified by the above method to calculate σm / Dm of the distance between domains 55, and the arithmetic mean of the measured values from a total of 9 observation regions is the uniformity of the distance between domains 55. It may be quantified as an index of.

The charging roller 2 used in this embodiment can be formed, for example, by a method including the following steps (i) to (iv).
Step (i): Preparing a domain-forming rubber mixture (hereinafter, also referred to as “CMB”) containing carbon black and a second rubber;
Step (ii): A step of preparing a matrix-forming rubber mixture (hereinafter, also referred to as “MRC”) containing the first rubber;
Step (iii): A step of kneading CMB and MRC to prepare a rubber mixture having a matrix-domain structure;
Step (iv): A layer of the rubber mixture prepared in step (iii) is formed on the conductive support directly or via another layer, and the layer of the rubber composition is cured to obtain the present embodiment. A step of forming the conductive layer.

Then, the component (i) to the component (iii) can be controlled, for example, by selecting the material used in each of the above steps and adjusting the manufacturing conditions. This will be described below.

First, with respect to component (i), the volume resistivity of the matrix 54 is determined by the composition of the MRC.
The first rubber used for MRC is natural rubber, butadiene rubber, butyl rubber, acrylonitrile butadiene rubber, urethane rubber, silicone rubber, fluororubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene, which have low conductivity. At least one kind of rubber such as rubber and polynorbornene rubber is used. Further, on the premise that the volume resistivity of the matrix can be within the above range for MRC, if necessary, a filler, a processing aid, a cross-linking agent, a cross-linking aid, a cross-linking accelerator, and a cross-linking accelerator Agents, cross-linking retarders, anti-aging agents, softeners, dispersants, colorants may be added. On the other hand, it is preferable that the MRC does not contain an electron conductive agent such as carbon black in order to keep the volume resistivity of the matrix within the above range.

Further, the component (ii) can be adjusted by the amount of the electron conductive agent in the CMB. For example, as an electron conductive agent, DBP oil absorption ^amount, 40 cm 3/100 g or ^more, taking as an example the case of using a conductive carbon black is not more than 170cm 3/100 g, based on the total weight of the CMB, 40 wt% or more The component (ii) can be achieved by preparing the CMB to contain less than 200% by weight of conductive carbon black.

Further, regarding the component (iii), it is effective to control the following four (a) to (d).
(A) Difference in interfacial tension σ between CMB and MRC;
(B) The ratio of the viscosity of CMB (ηd) to the viscosity of MRC (ηm) (ηm / ηd);
(C) Shear velocity (γ) during kneading of CMB and MRC and energy amount (EDK) during shearing in step (iii);
(D) Volume fraction of CMB with respect to MRC in step (iii).

(A) Difference in interfacial tension between CMB and MRC Generally, when two kinds of incompatible rubbers are mixed, they are phase-separated. This is because the interaction between the same polymers is stronger than the interaction between different polymers, so that the same polymers aggregate to reduce the free energy and stabilize it. Since the interface of the phase-separated structure comes into contact with different macromolecules, the free energy is higher than that of the inside stabilized by the interaction between the same molecules. As a result, in order to reduce the free energy of the interface, an interfacial tension is generated to reduce the area of contact with the dissimilar polymer. When this interfacial tension is small, even dissimilar polymers tend to be mixed more uniformly in order to increase entropy. The uniformly mixed state is dissolution, and the SP value (solubility parameter), which is a measure of solubility, tends to correlate with the interfacial tension.

That is, it is considered that the difference in interfacial tension between CMB and MRC correlates with the difference in SP value of the rubber contained therein. For the first rubber in MRC and the second rubber in CMB, the difference between the absolute values of the solubility parameters is 0.4 (J / cm ³ ) ^0.5 or more, 5.0 (J / cm ^3). ) It is preferable to select a rubber having a value of ^0.5 or less, particularly 0.4 (J / cm ³ ) ^0.5 or more and 2.2 (J / cm ³ ) ^{0.5 or less.} Within this range, a stable phase-separated structure can be formed, and the domain diameter D of the CMB can be reduced. Here, specific examples of the second rubber that can be used for CMB include, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), and the like. Examples thereof include ethylene-propylene rubber (EPM, EPDM), kururuprene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U). At least one of these can be used.
The thickness of the conductive layer 53 is not particularly limited as long as the function and effect of the target conductive member (charging roller) can be obtained. The thickness of the conductive layer 53 is preferably 1.0 mm or more and 4.5 mm or less.

<Measurement method of SP value>
The SP value can be calculated accurately by creating a calibration curve using a material having a known SP value. As this known SP value, the catalog value of the material manufacturer can also be used. For example, for NBR and SBR, the SP value is almost determined by the content ratio of acrylonitrile and styrene regardless of the molecular weight. Therefore, a material whose SP value is known by analyzing the content ratio of acrylonitrile or styrene in the rubber constituting the matrix and domain by using an analysis method such as pyrolysis gas chromatography (Py-GC) and solid-state NMR. The SP value can be calculated from the calibration curve obtained from. The isoprene rubber is an isomer such as 1,2-polyisoprene, 1,3-polyisoprene, 3,4-polyisoprene, and cis-1,4-polyisoprene, trans-1,4-polyisoprene. The structure determines the SP value. Therefore, the isomer content ratio can be analyzed by Py-GC, solid-state NMR, or the like in the same manner as SBR and NBR, and the SP value can be calculated from a material having a known SP value.

(B) Viscosity ratio between CMB and MRC The closer the viscosity ratio between CMB and MRC (ηd / ηm) is, the smaller the maximum ferret diameter Dmax of the domain 55 can be. Specifically, the viscosity ratio is preferably 1.0 or more and 2.0 or less. The viscosity ratio of CMB and MRC can be adjusted by selecting the Mooney viscosity of the raw rubber used for CMB and MRC, and by blending the type and amount of the filler. It is also possible to add a plasticizer such as paraffin oil to the extent that it does not interfere with the formation of the phase-separated structure. Further, the viscosity ratio can be adjusted by adjusting the temperature at the time of kneading. The viscosity of the domain-forming rubber mixture or the matrix-forming rubber mixture can be obtained by measuring the Mooney viscosity ML (1 + 4) at the rubber temperature at the time of kneading based on JIS K6300-1: 2013.

(C) Shear velocity during kneading between MRC and CMB and amount of energy during shearing The faster the shear rate during kneading between MRC and CMB, and the greater the amount of energy during shearing, the smaller the distance between domains. can do.
The shear rate can be increased by increasing the inner diameter of the stirring member such as the blade or screw of the kneader, reducing the gap from the end face of the stirring member to the inner wall of the kneader, or increasing the rotation speed. Further, the energy at the time of shearing can be increased by increasing the rotation speed of the stirring member or increasing the viscosities of the first rubber in the CMB and the second rubber in the MRC.

(D) Volume Fraction of CMB with respect to MRC The volume fraction of CMB with respect to MRC correlates with the collision coalescence probability of the domain-forming rubber mixture with respect to the matrix-forming rubber mixture. Specifically, reducing the volume fraction of the domain-forming rubber mixture with respect to the matrix-forming rubber mixture reduces the collision-coalescence probability of the domain-forming rubber mixture and the matrix-forming rubber mixture. That is, the interdomain distance can be reduced by reducing the volume fraction of the domains in the matrix within the range in which the required conductivity can be obtained. The volume fraction of CMB with respect to MRC is preferably 15% or more and 40% or less.

Further, it is preferable that the conductive member (charging roller 2) according to the present embodiment satisfies the following component (iv) and component (v). Specifically, first, when the length of the conductive layer 53 in the longitudinal direction is L, there are three locations, the center of the conductive layer 53 in the longitudinal direction and L / 4 from both ends of the conductive layer 53 toward the center. , Take a cross section of the conductive layer 53 in the thickness direction. Then, for each of the cross sections, when 15 μm square observation regions are placed at arbitrary three locations in the thickness region from the outer surface of the conductive layer 53 to a depth of 0.1 T to 0.9 T, a total of nine observation regions are formed. Domain 55 is observed in each of the observation regions. It is preferable that 80% or more of the observed domains 55 satisfy the following component (iv) and component (v).

<Component (iv)>
The ratio of the cross-sectional area of the conductive particles contained in the domain 55 to the cross-sectional area of the domain 55 is 20% or more.
<Component (v)>
When the perimeter of the domain 55 is A and the perimeter of the domain 55 is B, the A / B is 1.00 or more and 1.10 or less.

The above-mentioned component (iv) and the component (v) can be said to be related to the shape of the domain 55. The "domain shape" is defined as the cross-sectional shape of the domain 55 that appears in the cross-sectional shape of the conductive layer 53 in the thickness direction. In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, observation regions of 15 μm square are placed at any three locations in the thickness region from the outer surface of the conductive layer 53 toward the support 52 in the depth region of 0.1 T to 0.9 T. The domain shape is defined by the shape of each domain 55 observed in each of the nine observation regions.

The shape of the domain 55 is preferably a shape having no unevenness on its peripheral surface. By reducing the number of concavo-convex structures related to the shape, the non-uniformity of the electric field between the domains 55 can be reduced, that is, the number of places where the electric field is concentrated is reduced, and the phenomenon that more charge transport occurs in the matrix 54 is reduced. it can.

The present inventor has obtained the finding that the amount of conductive particles contained in one domain 55 affects the outer shape of the domain 55. That is, it was found that as the filling amount of the conductive particles of one domain 55 increases, the outer shape of the domain 55 becomes closer to a sphere. As the number of domains 55 closer to the sphere increases, the concentration point of electron transfer between the domains 55 can be reduced.

According to the study by the present inventors, the reason is not clear, but the ratio of the total cross-sectional area of the conductive particles observed in the cross section is 20% based on the area of the cross section of one domain 55. The above domain 55 can take a shape closer to a sphere. As a result, it is possible to obtain an outer shape that can significantly alleviate the concentration of electron transfer between the domains 55, which is preferable. Specifically, the ratio of the cross-sectional area of the conductive particles contained in the domain 55 to the cross-sectional area of the domain 55 is preferably 20% or more.

The present inventors have found that it is preferable to satisfy the following formula (5) with respect to the shape of the peripheral surface of the domain 55 having no unevenness.
1.00 ≤ A / B ≤ 1.10 (5)
(A: Perimeter of domain 55, B: Perimeter of enveloping domain 55)

Equation (5) shows the ratio of the perimeter A of the domain 55 to the perimeter B of the envelope 55 of the domain 55. Here, the envelope perimeter is, as shown in FIG. 10, the perimeter when the convex portions of the domain 55 observed in the observation region are connected.
The ratio of the peripheral length of the domain 55 to the envelope peripheral length of the domain 55 is the minimum value of 1, and the state of 1 means that the domain 55 has a cross-sectional shape such as a perfect circle or an ellipse without any recess. Shown. When these ratios exceed 1.1, a large uneven shape is present in the domain 55, that is, anisotropy of the electric field is exhibited.

<Measurement method of each parameter related to domain shape>
First, a section is prepared by the same method as the method for measuring the volume resistivity of the matrix 54 described above. However, as described below, it is necessary to prepare a section with a cross section perpendicular to the longitudinal direction of the charging roller 2 and evaluate the shape of the domain 55 in the fracture surface of the section. The reason for this will be described below.

FIG. 11 shows a diagram showing the shape of the charging roller 2 as three dimensions, specifically, three dimensions of the X, Y, and Z axes. In FIG. 11, the X-axis shows a direction parallel to the longitudinal direction (axial direction) of the charging roller 2, and the Y-axis and the Z-axis show a direction perpendicular to the axial direction of the charging roller 2.

FIG. 11A shows an image diagram in which a part of the conductive layer 53 is cut out from the conductive layer 53 of the charging roller 2 with a cross section 82a parallel to the XZ plane 82. The XZ plane can rotate 360 ° about the axis of the charging roller 2. Considering that the charging roller 2 is brought into contact with the photosensitive drum 1 to rotate and discharge when passing through the gap with the photosensitive drum 1, the cross section 82a parallel to the XZ plane 82 is simultaneously formed at a certain timing. It shows the surface where the discharge occurs. The surface potential of the photosensitive drum 1 is formed by passing a surface corresponding to a certain amount of the cross section 82a.

Therefore, in order to evaluate the shape of the domain 55, which correlates with the electric field concentration in the charging roller 2, a fixed amount of the cross section 82a is included instead of the analysis of the cross section in which the discharge occurs at the same time in a certain moment as in the cross section 82a. It is necessary to evaluate the domain shape in a cross section parallel to the YZ plane 83 perpendicular to the axial direction of the charging roller 2. For this evaluation, a total of three cross sections (83a and 83c) of a cross section 83b at the center of the conductive layer 53 in the longitudinal direction and two cross sections (83a and 83c) of L / 4 from both ends of the conductive layer 53 toward the center were used. select.
Regarding the observation positions of the cross sections 83a to 83c, when the observation regions of 15 μm square are placed at any three positions in the thickness region from the outer surface of each section to a depth of 0.1 T or more and 0.9 T or less. The measurement may be performed in a total of 9 observation areas.

The fracture surface can be formed by means such as a freeze fracture method, a cross polisher method, and a focused ion beam method (FIB). The FIB method is preferable in consideration of the smoothness of the fracture surface and the pretreatment for observation. Further, in order to preferably observe the matrix domain structure, a pretreatment such as a dyeing treatment or a thin-film deposition treatment may be performed to obtain a suitable contrast between the conductive phase and the insulating phase.

The matrix domain structure can be observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) on the sections to which the fracture surface has been formed and pretreated. Among these, from the viewpoint of the accuracy of quantification of the area of the domain 55, it is preferable to perform the observation by SEM at 1000 to 100,000 times.

The perimeter of the domain 55, the perimeter of the envelope, and the number of domains 55 can be measured by quantifying the captured image as described above. For the fracture surface image obtained by observation with SEM, using image processing such as ImageProPlus (manufactured by Media Cybernetics), analysis area of 15 μm square from 9 images obtained at each observation position. It is extracted and grayscaled to 8 bits to obtain a 256-tone monochrome image. Next, the black and white of the image is inverted so that the domain 55 in the fracture surface becomes white, and the image is binarized to obtain a binarized image for analysis.

<< Method for measuring the cross-sectional area ratio μr of conductive particles in the domain >>
The cross-sectional area ratio of the conductive particles in the domain 55 can be measured by quantifying the above binarized image. For the binarized image, the cross-sectional area S of the domain 55 and the total cross-sectional area Sc of the portion made of the conductive agent in each domain 55 are calculated by the counting function in the image processing software ImageProPlus (manufactured by Media Cybernetics). To do. Then, the arithmetic mean value μr (%) of Sc / S may be calculated.

In the case of the cylindrical charging roller 2, the conductivity as shown in FIG. 11 (b) at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of the layer 53 in the thickness direction. For each of the obtained cross sections, the above measurement was performed in any three 15 μm square regions in a thickness region from the outer surface of the conductive layer 53 toward the support 52 in a depth region of 0.1 T to 0.9 T. , And calculate from the arithmetic mean of the measured values from a total of 9 points.

<< Measurement method of domain perimeter A and envelope perimeter B >>
The perimeter of the domain 55, the perimeter of the envelope, and the number of domains 55 can be measured by quantifying the above binarized image. For the binarized image, use the counting function of the image processing software ImageProPlus (manufactured by Media Cybernetics).
The peripheral length A of each domain of the domain size group in the image and the envelope peripheral length B of the domain may be calculated, and the arithmetic mean value of the domain peripheral length ratio A / B may be calculated.

In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, the above measurement was performed in any three 15 μm square regions of the thickness region from the outer surface of the conductive layer 53 toward the support to a depth of 0.1 T to 0.9 T. Then, it may be calculated from the arithmetic mean of the measured values from a total of 9 points.

<< Measurement method of domain shape index >>
For the shape index of the domain 55, the number percentage of the total number of domains 55 of the domain group in which μr (%) is 20% or more and the peripheral length ratio A / B of the domain 55 satisfies the above formula (5) is calculated. do it. For the above binarized image, the count function of the image processing software ImageProPlus (manufactured by Media Cybernetics) is used to calculate the number of domain groups in the binarized image, and μr ≧ 20 and the above formula (5). ) Satisfy the number of domains.

In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, the above measurement was performed in any three 15 μm square regions of the thickness region from the outer surface of the conductive layer 53 toward the support to a depth of 0.1 T to 0.9 T. Then, it may be calculated from the arithmetic mean of the measured values from a total of 9 points.

As specified in the component (iv), by filling the domain 55 with conductive particles at a high density, the outer shape of the domain 55 can be made closer to a sphere, and as specified in the component (v). The unevenness can be small.

As defined in component (iv), since the conductive particles to obtain a domain 55 that are densely packed, as the conductive particles, DBP oil absorption amount is less than 40 cm ^3/100 g or more 80 cm ^3/100 g carbon Black can be used particularly preferably. DBP oil absorption ^(cm 3 / 100g) and is the volume of dibutyl phthalate carbon black 100g can adsorb (DBP), Japanese Industrial Standards (JIS) K 6217-4: 2017 (the carbon black for rubber - basic characteristics -Part 4: Measured according to how to determine the amount of oil absorbed (including compressed samples)). In general, carbon black has a tufted higher-order structure in which primary particles having an average particle size of 10 nm or more and 50 nm or less are aggregated. The tufted conformation called structure, the degree is quantified by the DBP oil absorption ^(cm 3 / 100g).

In general, carbon black with a well-developed structure has a high reinforcing property against rubber, the uptake of carbon black into rubber is poor, and the share torque at the time of kneading becomes very high. Therefore, it is difficult to increase the filling amount in the domain.
On the other hand, the conductive carbon black having the DBP oil absorption amount within the above range has an undeveloped structure structure, so that the carbon black is less agglomerated and has good dispersibility in rubber. Therefore, the filling amount in the domain 55 can be increased, and as a result, the outer shape of the domain can be easily obtained to be closer to a sphere.

Further, in the carbon black having a developed structure, the carbon blacks are likely to aggregate with each other, and the aggregates are likely to be a mass having a large uneven structure. When such an aggregate is contained in the domain 55, it is difficult to obtain the domain 55 related to the component (v). The formation of agglomerates may affect the shape of the domain 55 to form an uneven structure. On the other hand, the conductive carbon black having the DBP oil absorption amount within the above range is difficult to form an agglomerate, and is therefore effective in creating the domain 55 related to the component (v).

<Domain size>
The domain 55 according to the present embodiment has a maximum ferret diameter of the domain 55 included in each of the above-mentioned component (iv) and the domain 55 satisfying the component (v) (hereinafter, also simply referred to as “domain diameter”). The average D of Dmax is preferably 0.1 μm or more and 5.0 μm or less.
By setting the average value D of the domain diameter Dmax to 0.1 μm or more, it is possible to effectively limit the path of charge transfer in the conductive layer 53. Further, by setting the average value D of the domain diameter Dmax to 5.0 μm or less, the ratio of the surface area to the total volume of the domain 55, that is, the specific surface area can be exponentially increased, and the charge from the domain 55 can be increased. The release efficiency can be dramatically improved. For the above reasons, the average value D of the domain diameter Dmax is preferably 2.0 μm or less, more preferably 1.0 μm or less.

In order to reduce the electric field concentration between the domains 55, it is preferable to make the outer shape of the domain 55 closer to a sphere. For that purpose, it is preferable to make the domain diameter Dmax smaller within the above range. As a method thereof, for example, in the step (iv), MRC and CMB are kneaded, MRC and CMB are phase-separated, and a rubber mixture in which the domain 55 of CMB is formed in the matrix 54 of MRC is prepared. In the step of performing the process, a method of controlling the domain diameter Dmax of the CMB to be reduced can be mentioned. By reducing the domain diameter Dmax of the CMB, the specific surface area of the CMB increases and the interface with the matrix 54 increases. Therefore, a tension for reducing the tension acts on the interface of the domain 55 of the CMB. As a result, the domain 55 of the CMB has an outer shape closer to a sphere.

Here, with respect to the factors that determine the domain diameter Dmax in the matrix-domain structure formed when two incompatible polymers are melt-kneaded, Taylor's formula (formula (6)) and Wu's empirical formula (formula). (7), (8)), and Tokita's formula (formula (9)) are known.
・ Taylor's formula Dmax = [C ・ σ / ηm ・ γ] ・ f (ηm / ηd) (6)
・ Wu's empirical formula γ ・ Dmax ・ ηm / σ = 4 (ηd / ηm) 0.84 ・ ηd / ηm> 1 (7)
γ ・ Dmax ・ ηm / σ = 4 (ηd / ηm) −0.84 ・ ηd / ηm <1 (8)
・ Tokita's formula Dmax = 12 ・ P ・ σ ・ φ / (π ・ η ・ γ) ・ (1 + 4 ・ P ・ φ ・ EDK / (π ・ η ・ γ)) (9)

In formulas (6) to (9), Dmax is the maximum shear diameter of the domain 55 of the CMB, C is a constant, σ is the interfacial tension, ηm is the viscosity of the matrix 54, and ηd is the viscosity of the domain 55, γ. Is the shear rate, η is the viscosity of the mixed system, P is the collision coalescence probability, φ is the domain volume, and EDK is the domain breaking energy.

In order to make the inter-domain distance uniform in relation to the above component (iii), it is effective to reduce the domain size according to the above equations (6) to (9). Further, the matrix domain structure is dominated by where the kneading step is stopped in the process in which the raw rubber of the domain 55 is split in the kneading step and the grain system gradually becomes smaller. Therefore, the uniformity of the inter-domain distance can be controlled by the kneading time in the kneading process and the kneading speed which is an index of the strength of the kneading, and the longer the kneading time, the higher the kneading speed. The larger the value, the more uniform the distance between domains can be improved.

・ Domain size uniformity;
It is preferable that the domain size is uniform, that is, the particle size distribution is narrow. By making the size distribution of the domain 55 through which the electric charge passes in the conductive layer 53 uniform, the concentration of the electric charge in the matrix domain structure is suppressed, and the ease of discharging is effectively increased over the entire surface of the charging roller 2. can do. In the cross section in which the electric charge is transported, that is, in the cross section in the thickness direction of the conductive layer 53 as shown in FIG. 5, the depth from the outer surface of the conductive layer 53 toward the support 52 is 0.1 T to 0.9 T. The ratio σd / D (coefficient of variation σd / D) of the standard deviation σd of the domain size and the average value D of the domain size is 0 or more when the observation area of 50 μm square is acquired at any three locations of the thickness region of. It is preferably 0.4 or less.

In order to improve the uniformity of the domain size, it is the same as the above-mentioned method of improving the uniformity of the distance between domains, and if the domain size is reduced according to the equations (6) to (9), the uniformity of the domain size is also improved. To do. Further, the matrix domain structure is dominated by where the kneading process is stopped in the process in which the raw rubber of the domain 55 is split and the grain system gradually becomes smaller in the kneading process. Therefore, the uniformity of the domain size can be controlled by the kneading time in the kneading process and the kneading rotation speed which is an index of the kneading strength, and the longer the kneading time, the larger the kneading rotation speed. The more uniform the domain size can be, the better.

・ Measurement method of domain size uniformity;
The measurement of domain uniformity can be performed by quantifying the image obtained by direct observation of the fracture surface, which is obtained by the same method as the measurement of the uniformity of the inter-domain distance described above.
Specifically, for the binarized image having the domain 55 and the matrix 54 obtained by the measurement of the distance between the domains 55 described above, the domain is used by the counting function in the image processing software ImageProPlus (manufactured by Media Cybernetics). The ratio σd / D of the standard deviation σd of the size group and the average value D may be calculated.

In the case of the cylindrical charging roller 2, the index of domain size uniformity can be quantified by calculating the σd / D of the inter-domain distance on the normal line starting from the central axis of the support 52.
In the case of a cylindrical charging roller, the conductive layer as shown in FIG. 11B is located at the center of the conductive layer 53 in the longitudinal direction and at three locations L / 4 from both ends of the conductive layer 53 toward the center. Obtain a cross section of 53 in the thickness direction. For each of the obtained cross sections, observation regions of 50 μm square are acquired at any three locations in the thickness region from the outer surface of the conductive layer 53 toward the support to a depth of 0.1 T to 0.9 T. The observation region is binarized and quantified by the above method to calculate the σd / D of the interdomain distance, and the arithmetic mean of the measured values from a total of 9 observation regions is used as an index of domain size uniformity. It may be quantified.

<How to check the matrix domain structure>
The presence of the matrix domain structure in the conductive layer 53 can be confirmed by making a slice from the conductive layer 53 and observing the fracture surface formed in the slice in detail.
Examples of the means for thinning include a sharp razor, a microtome, and a FIB. Further, in order to carry out a more accurate observation of the matrix domain structure, a pretreatment such as a dyeing treatment or a vapor deposition treatment in which the contrast between the domain 55 as the conductive phase and the matrix 54 as the insulating phase is preferably obtained is used for observation. It may be applied to flakes.
Existence of matrix domain structure by observing the fracture surface with a laser microscope, scanning electron microscope (SEM) or transmission electron microscope (TEM) on the slices that have been formed and pretreated as necessary. Can be confirmed. As a method for confirming the sea-island structure easily and accurately, it is preferable to observe with a scanning electron microscope (SEM).

A thin piece of the conductive layer 53 is obtained by the above method, and an image obtained by observing the surface of the thin piece at 1000 to 10000 times is obtained, and then image processing such as ImageProPlus (manufactured by Media Cybernetics) is performed. It is used to grayscale 8-bit to obtain a 256-tone monochrome image. Next, the black and white of the image is inverted and binarized so that the domain 55 in the fracture surface becomes white, and an analysis image is acquired. The presence or absence of the matrix domain structure may be determined from the analysis image obtained by image processing the domain 55 and the matrix 54 so as to be distinguished by binarization.

When the analysis image contains a structure in which a plurality of domains 55 exist in an isolated state in the matrix 54 as shown in FIG. 9, the presence of the matrix domain structure in the conductive layer 53 is confirmed. Can be done. The isolated state of the domain 55 is a state in which each domain 55 is not connected to another domain 55, the matrix 54 is communicated in the image, and the domain 55 is divided by the matrix 54. Good. Specifically, when the analysis region is 50 μm square in the analysis image, the domain 55 existing in an isolated state as described above with respect to the total number of domains having no contact with the border of the analysis region. A state in which the number of the above is 80% or more is defined as a state having a sea-island structure.
For the above confirmation, the conductive layer 53 is evenly divided into 5 equal parts in the longitudinal direction and 4 equal parts in the circumferential direction, and the section is prepared from a total of 20 points, one point arbitrarily from each region. The above measurement may be performed.

<Example / Comparative example>
The manufacturing method of the charging roller used in this embodiment will be described.
(1. Production of unvulcanized rubber mixture (CMB) for domain formation)
[1-1. Preparation of unvulcanized rubber mixture]
Each material shown in Table 1 was mixed with a 6-liter pressurized kneader (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) in the blending amount shown in Table 1 to obtain CMB. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 20 minutes.

(Table 1)

[1-2. Preparation of rubber mixture for matrix formation (MRC)]
Each material shown in Table 2 was mixed with a 6-liter pressurized kneader (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) at the blending amount shown in Table 2 to obtain MRC. The rate was 70 vol%, the blade rotation speed was 30 rpm, and the blade rotation speed was 16 minutes.

(Table 2)

[1-3. Preparation of unvulcanized rubber mixture for forming conductive layer]
The CMB and MRC obtained above were mixed in the blending amounts shown in Table 3 using a 6-liter pressurized kneader (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.). The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and 16 minutes.

(Table 3)

Next, the vulcanizing agent and the vulcanization accelerator shown in Table 4 were added to 100 parts by mass of the mixture of CMB and MRC in the blending amounts shown in Table 4, and an open roll having a roll diameter of 12 inches (0.30 m) was used. To prepare a rubber mixture for forming a conductive layer. The mixing conditions were a front roll rotation speed of 10 rpm and a rear roll rotation speed of 8 rpm, and after turning left and right 20 times in total with a roll gap of 2 mm, thinning was performed 10 times with a roll gap of 0.5 mm.

(Table 4)

(2. Fabrication of Conductive Member (Charging Roller 2))
[2-1. Preparation of a support with a conductive outer surface]
As the support 52 having a conductive outer surface, a round bar having a total length of 252 mm and an outer diameter of 6 mm was prepared by subjecting the surface of stainless steel (SUS) to electroless nickel plating.

[2-2. Molding of conductive layer]
A die with an inner diameter of 9.5 mm is attached to the tip of a crosshead extruder having a supply mechanism for the support 52 and a discharge mechanism for unvulcanized rubber rollers, and the temperature of the extruder and the crosshead is raised to 80 ° C. to convey the support. The speed was adjusted to 60 mm / sec. Under these conditions, a rubber mixture for forming a conductive layer was supplied from the extruder, and the outer peripheral portion of the support 52 was covered with the rubber mixture for forming a conductive layer in the crosshead to obtain an unvulcanized rubber roller. ..
Next, the unvulcanized rubber roller is put into a hot air vulcanizer at 160 ° C. and heated for 60 minutes to vulcanize the rubber mixture for forming the conductive layer, and the conductive layer 53 is formed on the outer peripheral portion of the support 52. I got a roller that was vulcanized. After that, both ends of the conductive layer 53 were cut off by 10 mm each to make the length of the conductive layer 53 in the longitudinal direction 232 mm.
Finally, the surface of the conductive layer 53 was polished with a rotary grindstone. As a result, a crown-shaped charging roller 2 having a diameter of 8.44 mm and a diameter of 8.5 mm at the center was obtained at a position of 90 mm from the center to both ends.
The domain matrix structure of the charging roller 2 used in the present embodiment thus obtained has the structure as shown in FIG.

The charging rollers used in Examples 1 to 3 which are specific examples of the charging rollers 2 of the present embodiment are charging rollers having a domain matrix structure (Table 5: charging rollers a, charging rollers b, charging rollers c).
As the charging roller c used as Example 2, Toughden 2100R (SBR) was used as the rubber composition of the matrix 54, and 230SL (NBR) was used as the rubber composition of the domain 55. The volume resistivity of the domain 55 is 69.9 Ω · cm, the average domain size is 4.4 ^{μm, the volume resistivity of the matrix is 5.9 × 10 12} Ω · cm, the average inter-domain distance is 0.3 μm, and the distribution of the inter-domain distance σm / The Dm was 0.22 and the domain shape was circular. A rubber having this matrix domain structure was formed so as to cover the conductive roller to form a rubber roller. The resistance of the rubber roller was 8.8 × 10 ⁴ Ω, and the impedance gradient at frequencies of 1.0 × 10 ⁵ Hz to 1.0 × 10 ⁶ Hz was −0.63 (Table 5: Charging roller c).

Unlike the examples, the charging roller d and the charging roller e used as comparative examples have no domain matrix structure, and the conductive layer is a rubber composition in which carbon black, which is a conductive agent, is dispersed, and as a conductive member. It has a single conductive path.
NBR was used as the rubber composition, the resistance of the rubber roller was 6.2 × 10 ⁷ Ω, and the impedance gradient at frequencies of 1.0 × 10 ⁵ Hz to 1.0 × 10 ⁶ Hz was -1.00 (Table). 5: Charging roller d).

(Table 5)

(Experiment)
From Table 5, using the charging roller c as an example and the charging roller d as a comparative example, 50,000 images were formed. The confirmation was performed in a low temperature and low humidity environment (temperature 15 ° C., humidity 10%) where abnormal discharge is likely to occur.

Table 6 shows the image evaluation results.
For image evaluation, photosensitive drums 1 having different capacitances were prepared, and imaging was performed by changing the charging contrast, which is the difference between the pre-charging potential and the post-charging potential. The charge contrast was adjusted by arranging the pre-exposure unit 27 as a static elimination step upstream of the photosensitive drum 1 in the rotation direction and varying the charging potential Vd while constantly eliminating the pre-charging potential.
The one in which image defects due to abnormal discharge occurred even a little was marked with "x", and the one in which no image defect occurred was marked with "○". It is the result of the examination when using.

(Table 6)

As shown in Table 6, the charging roller d having no domain matrix configuration used as a comparative example charges a photosensitive drum ^{having a capacitance of 1.56 × 10 -10} F / cm ^{2 or less per unit area.} Image defects occurred due to abnormal discharge when the contrast was 500 V or higher. Further, in a photosensitive drum having a capacitance of 1.32 × 10 ^-10 F / cm ² or less, image defects due to abnormal discharge occurred even when the charging contrast was 400 V. In the charging roller c having the domain matrix configuration of this embodiment, even if ^{the photosensitive drum has a capacitance of 1.56 × 10-10} F / cm ² or less and the charging contrast is 500 V or more, abnormal discharge does not occur at all. I didn't.

The reason why the abnormal discharge could be suppressed by using the charging roller c of this embodiment was that the supply of electric charge that could cause an abnormal discharge in the long gap portion could be controlled by the impedance characteristic of the charging roller 2. It is due to the fact.
By having a domain matrix structure, a large amount of electric charge stays in the conductive phase, which is the domain 55 dispersed and arranged in an island shape in the matrix 54 of the insulating phase, and reaches the member surface. That is, when the charge is transferred, the insulating matrix 54 phase is always present between the domains, and a sufficient charge is always present in the conductive phase of the domain 55. As a result, it is possible to control the local excessive discharge and suppress the continuation of the abnormal discharge. That is, the change in impedance on the high frequency side is small with respect to the impedance in the low frequency region, and the absolute value of the slope is small, so that abnormal discharge due to local overdischarge in the long gap can be suppressed. It was.

Here, as will be described again, abnormal discharge is likely to occur when the charge transport layer 1f2 has a large film thickness, that is, a small capacitance, as the photosensitive drum 1. Also, the charging potential is likely to occur at a higher charging contrast.
Since abnormal discharge is a phenomenon that occurs when the discharge current flows excessively, it is known that the charging roller 2 tends to improve by making the resistance high so that the current does not flow easily. Has been done. However, if the resistance is set too high, the charging performance will be insufficient, so there is a limit to the direction in which the resistance of the charging roller 2 is increased.
Therefore, as another example, a charging roller a and a charging roller b having a matrix domain configuration and different domain sizes and domain resistances have an impedance larger than that of the charging roller d as a comparative example having different impedances in the range of maintaining the charging performance. The charging roller e of the above was similarly image-evaluated.
As a result, the charging roller a and the charging roller b did not undergo abnormal discharge like the charging roller c.
Then, the charging roller e, which has an impedance more than double that of the charging roller d, has an image defect due to an abnormal discharge in the same region as the charging roller d.
That is, the range of occurrence of abnormal discharge of the charging rollers d and e having impedances that differ by more than twice was the same.

^{On the other hand, the charge transport layer 1f2 of 1.56 × 10 -10} [F / cm ² ] and 1.32 × 10 ^-10 [F / cm ^ 2] in which the capacitance of the photosensitive drum 1 differs depending on whether or not it is generated. The difference in film thickness is 3 μm. The photosensitive drum 1 in a general image forming apparatus can be scraped by 10 μm or more from the time of new product after use, that is, the film thickness of the charge transport layer 1f2 can generally change.
That is, the occurrence of abnormal discharge is greatly affected by the capacitance of the photosensitive drum 1 on the sensitivity due to the impedance of the charging roller 2.
Therefore, it can be seen that in the conventional charging roller having no matrix domain configuration, the capacitance of the photosensitive drum 1 is 1.56 × 10 ^-10 [F / cm ² ] or less, and the risk of abnormal discharge is high.

^{From the above results, the capacitance of the photosensitive drum 1 is 1.56 × 10 -10} [F / cm ² ], which is a condition in which the possibility of abnormal discharge is high in the conventional charging roller having no matrix domain structure. Below, even if the charging contrast is 500V or more, the charging roller 2 has a matrix domain structure and has the above-mentioned predetermined impedance characteristics, so that the occurrence of abnormal discharge can be improved.

A ... Image forming device, 1 ... Photosensitive drum, 2 ... Charging roller, 3 ... Scanner, 4 ... Developing device, 35 ... Control unit, 52 ... Support, 53 ... Conductive layer, 54 ... Matrix, 55 ... Domain

Claims (16)

An image forming device that forms an image on a recording material.
At least, an image carrier in which a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance are laminated.
A charging member that charges the surface of the image carrier at the charging portion facing the image carrier,
A charging bias applying means for applying a bias to the charging member, and
With
The charging member has the impedance characteristics measured by applying an AC voltage having an amplitude of 1 V to the charging member while changing the frequency, when the frequency is plotted on the horizontal axis and the impedance is plotted on the vertical axis. The gradient at the frequency of 0 × 10 ⁵ Hz to 1.0 × 10 ⁶ Hz is -0.8 or more and -0.3 or less, and the frequency is 1.0 × 10 ^-2 Hz to 1.0 × 10 ¹ The amplitude at Hz is 1.0 × 10 ³ Ω to ^{1.0 × 10 7 Ω.}
The image carrier has a capacitance of 1.56 × 10 ^-10 F / cm ² or less per unit area of the charge transport layer.
The charging bias applying means has such that the difference between the surface potential formed in the charged portion and the surface potential before passing through the charged portion of the surface potential of the image carrier is 500 V or more. An image forming apparatus characterized in that the bias applied to the charging member is controlled. The charged member has a conductive support and a conductive layer provided on the outer surface of the support.
The impedance characteristic is that a metal film is provided on the outer surface of the conductive layer, and the amplitude is 1 V between the outer surface of the support and the metal film in an environment of a temperature of 23 ° C. and a humidity of 50% RH. the image forming apparatus according to claim 1, an alternating voltage, characterized in that it is measured by applying while changing between the frequency ^{1.0 × 10 -2 Hz~1.0 × 10 6} Hz. The charged member has a conductive support and a conductive layer provided on the outer surface of the support.
The image forming apparatus according to claim 1 or 2, wherein the conductive layer has a sea-island structure in which a plurality of domains forming an island phase are scattered in a matrix forming the sea phase. The image forming apparatus according to claim 3, wherein in the sea-island structure, the matrix forms an insulating phase and the domain forms a conductive phase. The image forming apparatus according to claim 3 or 4, wherein the domain is filled with conductive particles. The invention according to any one of claims 3 to 5, wherein the volume resistivity of the matrix ^{is larger than 1.0 × 10 12} Ω · cm and not more than 1.0 × 10 ^{17 Ω · cm.} Image forming device. The image according to any one of claims 3 to 6, wherein the volume resistivity of the domain is 1.0 × 10 ¹ Ω · cm or more and 1.0 × 10 ^{4 Ω · cm or less.} Forming device. The image forming apparatus according to any one of claims 3 to 7, wherein the arithmetic mean value Dm of the inter-domain distances of the plurality of domains is 0.2 μm or more and 2.0 μm or less. When the arithmetic mean value of the inter-domain distances of the plurality of domains is Dm and the standard deviation of the distribution of the Dm is σm, the coefficient of variation σm / Dm of the inter-domain distance is 0 or more and 0.4 or less. The image forming apparatus according to any one of claims 3 to 8, wherein the image forming apparatus is characterized. The image forming apparatus according to any one of claims 3 to 9, wherein the average maximum ferret diameter in each of the plurality of domains is 0.1 μm or more and 5.0 μm or less. When the arithmetic mean value of the maximum ferret diameter in each of the plurality of domains is D and the standard deviation of the distribution of the D is σd, the coefficient of variation σd / D of the maximum ferret diameter is 0 or more and 0.4 or less. The image forming apparatus according to any one of claims 3 to 10. When the length of the conductive layer in the longitudinal direction of the columnar support is L and the thickness of the conductive layer is T, the center of the conductive layer in the longitudinal direction and from both ends of the conductive layer to the center. For each of the cross sections of the conductive layer in the thickness direction at three locations of L / 4, any three locations in the thickness region from the outer surface of the conductive layer to a depth of 0.1 T to 0.9 T. When an observation area of 15 μm square is placed in, 80% or more of the domains observed in each of the nine observation areas satisfy the following requirements (1) and (2). The image forming apparatus according to any one of claims 3 to 11.
Requirement (1): The ratio of the cross-sectional area of the conductive particles contained in the domain to the cross-sectional area of the domain is 20% or more.
Requirement (2): When the perimeter of the domain is A and the perimeter of the domain is B, the A / B is 1.00 or more and 1.10 or less. When the average value of the ratio of the cross-sectional area of the conductive particles contained in each of the domains to the cross-sectional area of each of the domains appearing in the cross-sectional area in the thickness direction of the conductive layer is μr, and the standard deviation of the ratio is σr. The image forming apparatus according to any one of claims 3 to 12, wherein the coefficient of variation σr / μr of the ratio is 0 or more and 0.4 or less. The charging member according to any one of claims 3 to 13, wherein the support is a columnar support and the conductive layer is provided on an outer peripheral surface of the columnar support. Image forming device. Any one of claims 1 to 14, wherein the charging member is provided so as to be in contact with the image carrier and is configured to rotate following the rotating image carrier. The image forming apparatus according to the section. Any one of claims 1 to 15, further comprising a static elimination means for statically eliminating the surface of the image carrier upstream of the charged portion of the image carrier in the rotation direction of the image carrier. The image forming apparatus according to.

Images