Electrophotographic photoreceptor and image forming apparatus equipped with the same

Abstract

To provide an image forming apparatus that can provide an image with a stable quality over a long period.SOLUTION: The above-mentioned problem is solved by providing an electrophotographic photoreceptor that comprises at least a laminated photosensitive layer in which a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material are laminated in this order on a conductive substrate, and the charge transport layer contains inorganic filler, the charge transport material, and a binder resin. The electrophotographic photoreceptor has a surface layer with a surface roundness Rz of 0.05 to 0.60 μm measured in conformity to JIS-0601(1982), and has an AC impedance Z of 1.0 to 6.0×104 Ω in measurement conditions of a temperature of 30°C, a humidity of 85%RH, a DC voltage of 1.0 V, and a frequency of 30 kHz.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") and an image forming apparatus equipped with the same. More specifically, the present invention relates to an electrophotographic image forming apparatus equipped with a photoreceptor and a charging device (charging section) that charges the surface of the rotating photoreceptor while contacting the photoreceptor. [Background technology]

[0002] Electrophotographic image forming apparatuses that form images using electrophotographic technology are widely used in copying machines, printers, facsimile machines, and the like. The charging section of an electrophotographic image forming apparatus commonly uses a corotron charger that uses a wire and a case, or a scorotron charger that uses a wire, a case, and a grid electrode (hereinafter also referred to as a "grid"). In particular, a scorotron charger has the advantage that it can stably control the surface potential of the photosensitive member by using a grid arranged between the wire and the surface of the photosensitive member, and is therefore widely used as a charger.

[0003] However, these chargers require application of a high voltage of 5 to 8 kV, which has the drawback of generating a large amount of ozone. In order to overcome these drawbacks, various types of chargers have been developed, such as contact roller chargers, non-contact roller chargers, brush chargers, and magnetic brush chargers, which bring a charging member into contact with or close to a photosensitive member. These chargers, with the exception of some injection charging type devices, use a charging method that relies on minute gap discharge, and are now the mainstream chargers, as they can reduce power consumption compared to conventional scorotron chargers and solve the drawbacks of the previous devices, such as the need for a high-voltage power supply and ozone generation.

[0004] Although these chargers offer advantages over conventional scorotron chargers, such as lower power costs, they also pose a challenge in achieving uniform charging on the photoconductor surface. Specifically, in image forming apparatuses using a photoconductor and a contact-type charging device, short, streaky charging irregularities can appear on the output image in a direction perpendicular to the output direction. Such image irregularities caused by charging irregularities are particularly likely to occur when the photoconductor is charged using DC charging, in which only a direct current voltage is applied to the charging roller. Therefore, in order to suppress the occurrence of this image unevenness, a contact charging method using an AC charging system has been proposed in which a voltage (pulsating voltage) is applied to a contact charging member, which is a DC voltage corresponding to the desired surface potential of the photosensitive member superimposed with an AC voltage component having a peak-to-peak voltage at least twice the charging start voltage.

[0005] However, in a charger of this type that superimposes an AC voltage, a large amount of AC current is consumed, which causes a large amount of film wear on the photoconductor, and is prone to photoconductor leakage. pp However, if it is made too small, image unevenness due to charging unevenness caused by abnormal discharge, similar to DC charging, is likely to occur. Another method proposed is to suppress streaky charging unevenness by incorporating resin particles into the surface layer of the charging roller and forming irregularities on the surface of the charging roller. This is thought to be because the irregularities on the surface of the charging roller form minute gaps in the nip between the charging roller and the photosensitive member, which is the member to be charged, causing point discharges and suppressing streaky charging unevenness. However, it is known that increasing the irregularities on the surface of the charging roller worsens image fogging.

[0006] It is known that charging unevenness, which causes image abnormalities such as scales and white spots, occurs when the voltage applied to the charging roller exceeds a certain threshold voltage. It is also known that increasing the thickness of the surface layer of the photosensitive member reduces the capacitance of the photosensitive member, worsening charging unevenness (see, for example, Masao Omori and Yutaka Oshima, "Analysis of Discharge Modes in Contact Charging Rollers," Journal of the Imaging Society of Japan, 2017, Vol. 56, No. 1, pp. 98-106 (Non-Patent Document 1)). On the other hand, a photoreceptor used in an electrophotographic process is constructed by laminating a photosensitive layer containing a photoconductive material on a substrate made of a conductive material (also called a "conductive substrate" or "conductive support").

[0007] On the other hand, photoreceptors used in electrophotographic processes are constructed by laminating a photosensitive layer containing a photoconductive material on a conductive substrate made of a conductive material. Photoconductive materials include inorganic photoconductive materials and organic photoconductive materials (organic photoconductors: OPCs). Thanks to recent research and development, photoreceptors with photosensitive layers mainly made of organic photoconductive materials (also called "organic photoreceptors") have become the mainstream of photoreceptors, as they have improved sensitivity and durability.

[0008] Proposed organic photoreceptors include a single-layer photoreceptor structure on a conductive substrate, in which a charge generating substance (also called a "charge generating agent") and a charge transport substance (also called a "charge transfer substance" or "charge transport agent") are dispersed in a binder resin (also called a "binder resin" or "binder resin"), and a negatively charged laminated photoreceptor structure in which a charge transport layer in which a charge transport substance is dispersed in a binder resin is laminated on a charge generating layer in which a charge generating substance is vapor-deposited or dispersed in a binder resin. Of these, the latter function-separated photoreceptor has been widely put to practical use in recent years because it has excellent electrophotographic properties and durability, a high degree of freedom in material selection, and the ability to design various photoreceptor properties.

[0009] From the viewpoint of resource conservation, there is a demand for the development of long-life photoconductors in order to reduce the frequency of photoconductor replacement. One of the factors that determines the lifespan of a photoconductor is the film loss of the outermost surface layer, and as this film loss progresses, image defects such as image fog and black spots due to photoconductor leakage occur. Therefore, attempts are being made to achieve a longer lifespan by increasing the film thickness of the outermost surface layer. As another means for extending the life of a photoreceptor, efforts have been made to improve the mechanical properties (wear resistance, printing durability) of the surface material of the photoreceptor. Specifically, the addition of inorganic fine particles such as silica or alumina (also simply referred to as "inorganic particles") as a filler to the outermost surface layer of the photoreceptor is being considered.

[0010] For example, Japanese Patent Laid-Open Publication No. 2017-049519 (Patent Document 1) discloses a laminated photoreceptor having a photosensitive layer including a charge generation layer containing a charge generation agent and a charge transport layer containing a charge transport agent, a binder resin, a phthalocyanine pigment, and silica particles, wherein the charge transport layer is a single layer and is arranged as the outermost layer, the content of the silica particles is 0.5 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the binder resin, and the average primary particle size of the silica particles is 50 nm or more and 150 nm or less. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2017-049519 A [Non-patent literature]

[0012] [Non-Patent Document 1] Masao Omori and Yutaka Oshima, "Discharge Mode Analysis in Contact Charging Rollers," Journal of the Imaging Society of Japan, 2017, Vol. 56, No. 1, pp. 98-106 Summary of the Invention [Problem to be solved by the invention]

[0013] As described in the above-mentioned prior art, when the thickness of the outermost surface layer of the photosensitive member is increased in order to extend the life of the photosensitive member, there is a problem that charging unevenness occurs in the actual use area of ​​the image forming device, and image abnormalities such as scale-like unevenness and white spots occur. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an electrophotographic photoreceptor capable of providing images of stable quality over a long period of time, and an image forming apparatus equipped with the same. [Means for solving the problem]

[0014] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they unexpectedly found that an image forming apparatus can be provided that can provide images of stable quality over a long period of time, when the photoreceptor comprises at least a laminated photosensitive layer in which a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport material, and a binder resin, and the photoreceptor has a surface layer with a specific surface roughness Rz and a specific AC impedance Z, thereby increasing the film strength of the photoreceptor surface layer and reducing the impedance of the photoreceptor, and thereby completing the present invention.

[0015] The present inventors have focused on not only the physical properties of the photosensitive member but also the physical properties of the charging unit of the image forming apparatus and the combination of these properties, and have investigated the relationship with image characteristics. The inventor then demonstrated through experiments that by incorporating inorganic fine particles (inorganic filler) into the photosensitive surface layer of the photosensitive member provided in the image forming apparatus of the present invention, the surface condition and hygroscopicity of the photosensitive member can be changed, and the impedance of the photosensitive member can be controlled to a predetermined value, thereby easily suppressing charging unevenness in the actual usage range and suppressing the occurrence of image abnormalities such as scales and white spots.He also discovered that it is possible to increase the film thickness of the outermost surface layer of the photosensitive layer, thereby extending the life of the photosensitive member and, as a result, making it possible to form high-quality images over a long period of time, and thereby completed the present invention.

[0016] Thus, according to the present invention, there is provided a photosensitive layer comprising at least a laminated type photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport substance, and a binder resin, The electrophotographic photoreceptor has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982), and has a surface roughness of 1.0 to 6.0 × 10 measured under the measurement conditions of a temperature of 30° C., a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz. 4 It has an AC impedance Z of Ω An electrophotographic photoreceptor characterized by the above-mentioned is provided.

[0017] According to the present invention, there is provided a photosensitive drum comprising at least the above-mentioned electrophotographic photosensitive member, a charging unit for charging the surface of the electrophotographic photosensitive member, an exposure unit for irradiating the charged surface of the electrophotographic photosensitive member with light to form an electrostatic latent image, a development unit for developing the electrostatic latent image formed by exposure to form a toner image, a transfer unit for transferring the toner image formed by development onto a recording medium, a fixing unit for fixing the transferred toner image on the recording medium to form an image, and a cleaning unit for removing and recovering residual toner on the surface of the electrophotographic photosensitive member, The charging unit is a charger provided so that its surface is in contact with or in close proximity to the surface of the electrophotographic photosensitive member, and the charger has a surface roughness Rz of 5.0 to 13 μm measured in accordance with JIS-0601 (1994). [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an electrophotographic photoreceptor capable of providing images of stable quality over a long period of time, and an image forming apparatus equipped with the same. [Brief explanation of the drawings]

[0019]

Figure 1

Figure 2

[0020] (1) Electrophotographic photoreceptor The photoreceptor of the present invention comprises at least a laminated photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport substance, and a binder resin; The electrophotographic photoreceptor has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982), and has a surface roughness of 1.0 to 6.0 × 10 measured under the measurement conditions of a temperature of 30° C., a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz. 4 It has an AC impedance Z of Ω It is characterized by:

[0021] FIG. 2 is a schematic cross-sectional view showing the configuration of the main part of the photoreceptor in the image forming apparatus of the present invention. The photoreceptor includes at least a photosensitive layer (laminated photosensitive layer) 4 in which a charge generating layer 8 containing a charge generating substance and a charge transport layer 9 containing a charge transport substance are laminated in this order on a conductive substrate 3. The photosensitive layer 4 may be a single-layer photosensitive layer containing a charge generating substance and a charge transport substance. Hereinafter, the laminated photosensitive layer and the single-layer photosensitive layer will be collectively referred to as the "photosensitive layer." In FIG. 2, reference number 10 denotes an optional undercoat layer, which will be described later, and the "circled +" and "circled -" represent "positive charge" and "negative charge," respectively. The physical properties and components of the photoreceptor will be described below.

[0022] The photoreceptor of the present invention has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982). Surface roughness Rz is an index of the state of aggregation of inorganic filler in the outermost surface layer of a photosensitive member, and the ten-point average roughness Rz defined in JIS-B-0601 (1994) means the difference, expressed in μm, between the average elevation of the fifth highest peak and the average elevation of the fifth deepest valley, measured in a direction perpendicular to the average line from a line that is parallel to the average line and does not intersect the cross-sectional curve, in a section taken over a reference length from the cross-sectional curve of the outermost surface layer of the photosensitive member. If the surface roughness Rz is less than 0.05 μm, the inorganic filler will not aggregate sufficiently, making it difficult to achieve wear resistance, and the inorganic filler's surface area will be large, which will cause it to absorb excessive moisture in the chamber and lower the impedance, but this may worsen the repeated fatigue characteristics (residual potential) of the photoreceptor.On the other hand, if the surface roughness Rz exceeds 0.60 μm, the inorganic filler will aggregate too much, making it easy for part of the edge of the cleaning blade to chip, and the inorganic filler's surface area will be small, making it difficult to sufficiently absorb moisture in the chamber and lowering the impedance. The surface roughness Rz is preferably 0.10 to 0.40 μm, and more preferably 0.15 to 0.30 μm. The measurement method will be explained in the Examples.

[0023] The photoconductor is measured under the following conditions: temperature 30°C, humidity 85% RH, DC voltage 1.0 V, frequency 30 kHz, and the resistivity is 1.0 to 6.0 × 10 4 It has an AC impedance Z of Ω. AC impedance Z is 1.0 x 10 4 Ω or less than 6.0 × 10 4 If it exceeds Ω, scale-like charging unevenness may occur in the image. The preferred AC impedance Z is 2.0 to 5.0 × 10 4 It is Omega. The measurement method will be explained in the Examples.

[0024] In the present invention, it is believed that the impedance of the photoreceptor can be controlled to a predetermined value by incorporating a specific inorganic filler, specifically an inorganic filler of a specific type, manufacturing method, surface treatment, particle size, and dispersion state, into the surface layer of the photoreceptor to change the moisture absorption property inside the surface layer of the photoreceptor. Furthermore, it is believed that the charge injection at the charge generation layer-charge transport layer interface and the dispersion state of the inorganic filler can be controlled by the mass ratio of the charge generation material and charge transport material having a specific ionization potential and the mass ratio of the specific charge transport material and binder resin, and thus the impedance of the photoreceptor can be controlled to a predetermined value.

[0025] (1-1) Conductive substrate: 3 The conductive substrate (also referred to as "substrate" or "conductive support") functions as an electrode for the photoreceptor and as a support member, and its constituent materials are not particularly limited as long as they are materials used in the relevant technical field. Examples of materials constituting the conductive substrate include metal materials such as aluminum, aluminum alloys, copper, zinc, stainless steel, and titanium, as well as polymer materials such as polyethylene terephthalate, polyamide (nylon), polyester, polyoxymethylene, and polystyrene, whose surfaces are laminated with metal foil, subjected to metal vapor deposition, or vapor-deposited or coated with a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide, as well as hard paper and glass. Among these, aluminum and aluminum alloys are preferred from the viewpoint of ease of processing, and aluminum alloys such as JIS3003 series (Al-Mn series), JIS5000 series (Al-Mg series), and JIS6000 series (Ai-Mg-Si series) are particularly preferred.

[0026] The shape of the conductive substrate is not limited to the cylindrical (drum) shape shown in FIG. 2, but may be a sheet shape, a columnar shape, an endless belt shape, or the like. The diameter and length of the conductive substrate are, for example, about 10 to 300 mm and about 200 to 1000 mm, respectively. Furthermore, the surface of the conductive substrate may be subjected to anodizing treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as long as it does not affect the image quality, in order to prevent interference fringes caused by laser light.

[0027] (1-2) Undercoat layer: 10 The photoreceptor 2 preferably has an undercoat layer (also called an “intermediate layer”) between the conductive substrate 3 and the photosensitive layer 4. The undercoat layer generally covers and smooths the irregularities on the surface of the conductive substrate 3, improves the film-forming properties of the photosensitive layer 4, suppresses peeling of the photosensitive layer 4 from the conductive substrate 3, and improves the adhesion between the conductive substrate 3 and the photosensitive layer 4. Specifically, it prevents injection of charges from the conductive substrate 3 into the photosensitive layer 4, prevents a decrease in the chargeability of the laminated photosensitive layer, and prevents the occurrence of image fogging (so-called black spots). The undercoat layer can be formed, for example, by dissolving or dispersing a binder resin in a suitable solvent to prepare a coating liquid for forming the undercoat layer, applying this coating liquid to the surface of the conductive substrate, and then drying to remove the organic solvent.

[0028] Examples of binder resins include acetal resins, polyamide resins, polyurethane resins, polyester resins, acrylic resins, epoxy resins, phenolic resins, melamine resins, urethane resins, casein, gelatin, polyvinyl alcohol, and ethyl cellulose. These can be used alone or in combination of two or more. The binder resin is required to have properties such as not dissolving or swelling in the solvent used when forming the photosensitive layer on the undercoat layer, excellent adhesion to the conductive substrate, and flexibility. Therefore, among the above binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins and polyamide resins containing piperazine-based compounds are particularly preferred. Examples of alcohol-soluble nylon resins include homopolymer or copolymer nylons such as 6-nylon, 66-nylon, 610-nylon, 11-nylon, and 12-nylon, and chemically modified nylons such as N-alkoxymethyl-modified nylons. A curing agent that crosslinks the binder resin may also be used to form a cured film. Blocked isocyanate is preferred as the curing agent from the viewpoint of storage stability and electrical properties of the coating liquid.

[0029] Examples of the solvent include lower alcohols such as water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, and isobutanol, ketones such as acetone, cyclohexanone, and 2-butanone, ethers such as tetrahydrofuran, dioxane, ethylene glycol, and diethyl ether, and halogenated hydrocarbons such as methylene chloride and ethylene chloride. An appropriate solvent is selected from these solvents based on the solubility of the binder resin and the surface smoothness of the undercoat layer, and these solvents can be used alone or in combination of two or more. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0030] The coating liquid for forming the undercoat layer may contain metal oxide particles, which can easily adjust the volume resistivity of the undercoat layer, further suppress charge injection into the charge generating layer and the single-layer photosensitive layer, and maintain the electrical properties of the photoreceptor under various environments. Materials that can be used for the metal oxide particles include, for example, titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide. The ratio (A / B) of the total mass A of the binder resin and metal oxide particles to the mass B of the solvent in the coating liquid for forming the undercoat layer is, for example, preferably about 1 / 99 to 40 / 60, and particularly preferably about 2 / 98 to 30 / 70. The ratio (C / D) of the mass C of the binder resin to the mass D of the metal oxide particles is preferably, for example, about 90 / 10 to 1 / 99, and particularly preferably about 70 / 30 to 5 / 95.

[0031] The coating method for forming the undercoat layer may be appropriately selected from among methods that are most suitable, taking into consideration the physical properties of the coating solution, productivity, and the like. Examples of such methods include spraying, bar coating, roll coating, blade coating, ring coating, and dip coating. Among these, the dip coating method is a method in which a conductive substrate is immersed in a coating tank filled with a coating liquid and then pulled up at a constant speed or a gradually changing speed to form a layer on the surface of the substrate, and is relatively simple and excellent in terms of productivity and cost, so it can be suitably used for manufacturing photoreceptors. The apparatus used for the dip coating method may be provided with a coating liquid dispersion device, typified by an ultrasonic generator, in order to stabilize the dispersibility of the coating liquid.

[0032] The solvent in the coating film may be removed by natural drying, or the solvent in the coating film may be removed forcibly by heating. The temperature in such a drying step is not particularly limited as long as it is a temperature at which the solvent used can be removed, but a temperature of about 50 to 140°C is appropriate, and a temperature of about 80 to 130°C is particularly preferred. If the drying temperature is below 50°C, the drying time may be long and the solvent may not evaporate sufficiently and remain in the photoreceptor layer.If the drying temperature exceeds approximately 140°C, the electrical characteristics of the photoreceptor may deteriorate during repeated use, resulting in poor quality of the resulting image. Such temperature conditions are common not only to the formation of the undercoat layer but also to the formation of layers such as the photosensitive layer, which will be described later, and other processes.

[0033] The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 to 20 μm, and more preferably 0.05 to 10 μm. If the thickness of the undercoat layer is less than 0.01 μm, it may not be possible to obtain sufficient blocking effect against electron injection from the conductive substrate side and sufficient effect against interference fringes due to light scattering.On the other hand, if the thickness of the undercoat layer is more than 20 μm, the change in sensitivity during continuous printing may become large, which may result in large changes in image density.

[0034] (1-3) Charge generation layer: 8 The charge generation layer 8 has the function of generating charges by absorbing light irradiated by a light emitting device such as a semiconductor laser light beam in an electrophotographic device such as the image forming device 50, and contains a charge generation substance as its main component and, if necessary, a binder resin and / or additives.

[0035] The charge generating layer preferably has an ionization potential of 5.40 to 5.60 eV. If the ionization potential of the charge generating layer is less than 5.40 eV, the occurrence of scaly charging unevenness and white spots may worsen. On the other hand, if the ionization potential of the charge generating layer is more than 5.60 eV, the repeated electrical characteristics (residual potential) of the photoreceptor may deteriorate. The ionization potential of the charge generating layer is more preferably 5.45 to 5.60 eV. The measurement method will be explained in the Examples.

[0036] The charge generating material is not particularly limited as long as it is a material used in the relevant technical field. Examples of charge-generating substances include azo pigments such as monoazo pigments, bisazo pigments, and trisazo pigments; indigo pigments such as indigo and thioindigo; perylene pigments such as perylene imide and perylene anhydride; polycyclic quinone pigments such as anthraquinone and pyrenequinone; phthalocyanine compounds such as metal phthalocyanines such as oxotitanium phthalocyanine and metal-free phthalocyanines; organic photoconductive materials such as squarylium dyes, pyrylium salts, thiopyrylium salts, and triphenylmethane dyes; and inorganic photoconductive materials such as selenium and amorphous silicone. Materials having sensitivity in the exposure wavelength range can be appropriately selected, and these can be used alone or in combination of two or more.

[0037] Among these charge generating materials, phthalocyanine compounds are preferred, oxotitanyl phthalocyanine is more preferred, and crystalline oxotitanyl phthalocyanine (also called "titanyl phthalocyanine") is particularly preferred. Crystalline oxo-titanyl phthalocyanine includes α-type, β-type, Y-type, and other crystal types. Among these, Y-type oxo-titanyl phthalocyanine is preferred in terms of image characteristics that enable the excellent effects of the present invention to be exerted. Particularly preferred is Y-type oxo-titanyl phthalocyanine, which in its X-ray diffraction spectrum using CuKα radiation (wavelength 1.541 Å) has at least diffraction peaks at Bragg angles (2θ±0.2°) of 7.3°, 9.4°, 9.7°, 26.2°, and 27.3°, and in which the overlapping peak bundle at 9.4° and 9.7° is the maximum peak. The oxotitanyl phthalocyanine is represented by the following formula:

[0038] [ka]

[0039] The oxotitanium phthalocyanine represented by the general formula (A) can be produced by known production methods, such as the method described in Phthalocyanine Compounds by Moser, Frank H. and Arthur L. Thomas, Reinhold Publishing Corp., New York, 1963.

[0040] A preferred method for forming the charge generating layer is to disperse a charge generating substance in a binder resin solution obtained by mixing a binder resin in a solvent by a conventionally known method, and then apply a coating liquid for forming the charge generating layer onto a conductive substrate or an undercoat layer. This method is described below.

[0041] The binder resin is not particularly limited, and resins having binding properties used in the art and the binder resins exemplified for the undercoat layer above can be used, and those having excellent compatibility with the charge generating material are preferred. Examples of binder resins include polyester, polystyrene, polyurethane, phenolic resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate, polyarylate, polyphenoxy resin, polyvinyl butyral (PVB), polyvinyl formal, and copolymer resins containing two or more of the repeating units constituting these resins. Examples of copolymer resins include insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin, and these can be used alone or in combination of two or more.

[0042] Examples of the solvent include halogenated hydrocarbons such as dichloromethane and dichloroethane; ketones such as acetone, methyl ethyl ketone and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as tetrahydrofuran (THF) and dioxane; alkyl ethers of ethylene glycol such as 1,2-dimethoxyethane; aromatic hydrocarbons such as benzene, toluene and xylene; and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide. These can be used alone or in combination of two or more. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0043] As with the undercoat layer, a dispersing machine such as a paint shaker, a ball mill, or a sand mill can be used to dissolve or disperse the charge generating material in the binder resin solution. In this case, it is preferable to appropriately set the dispersing conditions so that impurities generated by wear or the like from the components constituting the container and dispersing machine are not mixed into the coating solution. In particular, in the present invention, the average particle size (D50) and CV value of the charge generating material can be adjusted by appropriately setting the dispersion conditions.

[0044] The ratio (E / F) of the mass E of the charge generating substance to the mass F of the binder resin is preferably, for example, about 80 / 20 to 50 / 50.

[0045] The thickness of the charge generating layer is not particularly limited, but is preferably 0.05 to 5 μm, and more preferably 0.1 to 1 μm. If the thickness of the charge generating layer is less than 0.05 μm, the efficiency of light absorption will decrease, which may result in a decrease in the sensitivity of the photoreceptor. On the other hand, if the thickness of the charge generating layer is more than 5 μm, the charge transfer within the charge generating layer will become the rate-limiting step in the process of erasing the charge on the surface of the photoreceptor, which may result in a decrease in the sensitivity of the photoreceptor.

[0046] (1-4) Charge transport layer: 9 The charge transport layer 9 has the function of receiving the charges generated by the charge generating substance and transporting them to the surface of the photoreceptor 2, and contains an inorganic filler, a charge transport substance, a binder resin, and additives as required.

[0047] The photoreceptor of the present invention contains an inorganic filler (fine particles of an inorganic compound) in its outermost layer, for example, in the charge transport layer. Inorganic fillers include silica (silicon dioxide: SiO), alumina (AlO), ceria (CeO), molybdenum oxide (MoO), titania (TiO), zirconia (ZrO), zinc oxide (ZnO), magnetite (FeO), and iron oxides including various forms of FeO, niobium oxide (NbO), vanadium oxide (VO), tungsten oxide (WO), and tin oxide (SnO). These can be used alone or as a mixture or mixed oxide of two or more. Note that the chemical formula in parentheses is a representative oxide form, and different oxide forms may also exist depending on the valence of the metal atoms, and these are included in the present invention.

[0048] Among the above oxides, silica, alumina and titania are preferred in terms of wear resistance, silica and alumina are more preferred, and silica is particularly preferred in terms of electrical properties. The silica filler that can be suitably used in the present invention is not limited to its origin by any manufacturing method. Examples of silica fillers include dry-process silica particles such as fumed silica obtained by burning silicon tetrachloride and arc-process silica, in which silica is atomized in the gas phase using high energy such as plasma; wet-process silica particles such as precipitation-process silica synthesized under alkaline conditions using an aqueous sodium silicate solution as the raw material and gel-process silica synthesized under acidic conditions; colloidal silica particles obtained by polymerizing acidic silicic acid in an alkaline state; and sol-gel-process silica particles obtained by hydrolysis of an organic silane compound.

[0049] The inorganic filler preferably has a primary particle size of 7 to 40 nm. If the primary particle size of the inorganic filler is less than 7 nm, sufficient printing durability may not be obtained, whereas if the primary particle size of the inorganic filler is more than 40 nm, the aggregate structure formed in the photosensitive layer may become large, which may easily cause problems such as poor cleaning.

[0050] The inorganic filler is preferably contained in the charge transport layer at a ratio of 5 to 20% by mass, and is preferably uniformly dispersed. If the inorganic filler content is less than 5% by mass, the effect on abrasion resistance may not be sufficient, whereas if the inorganic filler content exceeds 20% by mass, the dispersibility may be insufficient, resulting in an increase in agglomerates and a deterioration in cleaning properties. The content of the inorganic filler in the outermost layer is more preferably 8 to 15% by mass.

[0051] In view of the above, it is preferable that the inorganic filler is fumed silica having a primary particle size of 12 to 40 nm, and is contained in the charge transport layer in an amount of 5 to 20% by mass.

[0052] The inorganic filler is preferably surface-treated with a surface treatment agent in order to improve the electrical properties of the photoreceptor. When the inorganic filler is silica particles, examples of the surface treatment agent include hexamethyldisilazane, N-methyl-hexamethyldisilazane, N-ethyl-hexamethyldisilazane, hexamethyl-N-propyldisilazane, dimethyldichlorosilane, and polydimethylsiloxane. Among these surface treatment agents, dimethyldichlorosilane and hexamethyldisilazane are particularly preferred because they have good reactivity with the hydroxyl groups on the silica particle surface, reducing the number of hydroxyl groups on the silica particle surface, and as a result, can suppress the deterioration of the electrical properties of the photoreceptor due to moisture (humidity). In the present invention, silica particles obtained by treating with the above-mentioned surface treatment agent can be used, but commercially available silica fine particles treated with a surface treatment agent can also be used. Examples of commercially available silica fine particles include R972, R976, RX50, and VPRX40S, both manufactured by Nippon Aerosil Co., Ltd., and TG-C390, both manufactured by Cabot Japan Co., Ltd.

[0053] The charge transport material is not particularly limited, and any compound used in the art can be used. Examples of the charge transport material include carbazole derivatives, pyrene derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, amine derivatives, and the like. Examples of such compounds include stilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene derivatives, enamine derivatives, benzidine derivatives, polymers having groups derived from these compounds in the main chain or side chain (poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, poly-9-vinylanthracene, etc.), polysilanes, and the like. These can be used alone or in combination of two or more.

[0054] The charge transport material preferably has an ionization potential of 5.40 to 5.60 eV. The ionization potential of the charge transport material affects charge injection at the charge generation layer-charge transport layer interface, and the smaller the charge injection barrier, the more the impedance can be reduced. If the ionization potential of the charge transport material is less than 5.40 eV, the repeated electrical characteristics (residual potential) of the photoreceptor may deteriorate, while if the ionization potential of the charge transport material is more than 5.60 eV, the occurrence of scale-like charging irregularities and white spots may worsen. The ionization potential of the charge transport material is more preferably 5.45 to 5.55 eV. The measurement method will be explained in the Examples.

[0055] A preferred method for forming the charge transport layer is to disperse a charge transport material in a binder resin solution obtained by mixing a binder resin in a solvent by a conventionally known method, and then apply a coating liquid for forming the charge transport layer onto the charge generating layer. This method is described below.

[0056] The binder resin is not particularly limited, and any resin having binding properties that is used in the art can be used, and it is preferable that the resin has excellent compatibility with the charge transport material. Examples of binder resins include vinyl polymer resins such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymer resins thereof, as well as resins such as polycarbonate, polyester, polyester carbonate, polysulfone, polyphenoxy resin, epoxy resin, silicone resin, polyarylate, polyamide, polyether, polyurethane, polyacrylamide, phenol resin, and polyphenylene oxide, and thermosetting resins obtained by partially crosslinking these resins, and these can be used alone or in combination of two or more. Among these, polystyrene, polycarbonate, polyarylate and polyphenylene oxide have a volume resistivity of 10 13 It is preferable because it has a hardness of Ω or more, is excellent in electrical insulation, and is also excellent in film-forming properties and potential characteristics, and polycarbonate is particularly preferable.

[0057] Examples of the solvent include aromatic hydrocarbons such as benzene, toluene, xylene, and monochlorobenzene; halogenated hydrocarbons such as dichloromethane and dichloroethane; ethers such as tetrahydrofuran, dioxane, and dimethoxymethyl ether; and aprotic polar solvents such as N,N-dimethylformamide. If necessary, a solvent such as an alcohol, acetonitrile, or methyl ethyl ketone can also be added and used. These solvents can be used alone or in combination of two or more. Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

[0058] The charge transport layer preferably contains a charge transport material and a binder resin in a mass ratio of 10 / 12 to 10 / 24. If the resin ratio is low, such as 10 / 12 or even 10 / 8, the inorganic filler may aggregate and the desired dispersion state may not be maintained. On the other hand, if the resin ratio is high, such as 10 / 24 or even 10 / 30, the inorganic filler aggregation can be suppressed, but the repeated electrical characteristics (residual potential) of the photoreceptor may deteriorate. A more preferable mass ratio of the charge transport material to the binder resin is 10 / 14 to 10 / 20.

[0059] The thickness of the charge transport layer is not particularly limited, but is preferably about 13 to 46 μm, and more preferably about 20 to 40 μm. If the thickness of the charge transport layer is less than 13 μm, the charge retention ability of the photoreceptor surface may decrease, whereas if the thickness of the charge transport layer is more than 46 μm, the resolution of the photoreceptor may decrease. The laminated photosensitive layer of the charge generating layer and the charge transport layer preferably has a film thickness of 34 to 46 μm. This improves the lifespan of the photoreceptor and enables the formation of high-quality images. In addition, in experiments conducted by the inventors, good print quality was achieved when the thickness of the charge transport layer was set to 34 μm, 40 μm, and 46 μm. If the thickness of the laminated photosensitive layer is less than 34 μm, the life of the photosensitive member may not be extended, whereas if the thickness of the laminated photosensitive layer is more than 46 μm, the resolution of the photosensitive member may be reduced. The thickness of the multilayer photosensitive layer is more preferably 34 to 40 μm.

[0060] (2) Image forming device The image forming apparatus of the present invention comprises at least the photoreceptor of the present invention, a charging unit that charges the surface of the electrophotographic photoreceptor, an exposure unit that irradiates the charged surface of the electrophotographic photoreceptor with light to form an electrostatic latent image, a development unit that develops the electrostatic latent image formed by exposure to form a toner image, a transfer unit that transfers the toner image formed by development onto a recording medium, a fixing unit that fixes the transferred toner image on the recording medium to form an image, and a cleaning unit that removes and collects residual toner on the surface of the electrophotographic photoreceptor, The charging unit is a charger provided so that its surface is in contact with or in close proximity to the surface of the electrophotographic photosensitive member, and is characterized in that the charger has a surface roughness Rz of 5.0 to 13 μm measured in accordance with JIS-0601 (1994). The configuration and operation of the main parts of the image forming apparatus will be described below with reference to the drawings, but the present invention is not limited to these drawings and the following description.

[0061] FIG. 1 is a schematic side view showing the configuration of the main part of an image forming apparatus according to one embodiment of the present invention. The image forming device 50 includes at least a photosensitive member 2, a charging unit (charger) 7 that charges the surface of the photosensitive member, an exposure unit 11 that irradiates the surface of the charged photosensitive member with light to form an electrostatic latent image, a development unit 12 that develops the electrostatic latent image formed by exposure to form a toner image, a transfer unit 13 that transfers the toner image formed by development onto a recording medium 26, a fixing unit 19 that fixes the transferred toner image on the recording medium to form an image, and a cleaning unit 14 that removes and collects residual toner from the surface of the photosensitive member.

[0062] The image forming apparatus 50 is an electrophotographic image forming apparatus that forms images using electrophotographic technology. The image forming apparatus 50 may be a monochrome image forming apparatus capable of forming monochrome images as shown in FIG. 1, or may be an intermediate transfer color image forming apparatus capable of forming color images. The color image forming apparatus is, for example, a so-called tandem full-color image forming apparatus having a configuration in which multiple photoconductors, on which toner images are respectively formed, are arranged side by side in a predetermined direction (for example, horizontally or vertically). The image forming apparatus 50 may also be another color image forming apparatus, a copier, a multifunction machine, or a facsimile machine.

[0063] (2-1) Photoreceptor: 2 The photoreceptor 2 is a member on whose surface an electrostatic latent image and a toner image are formed, and images are continuously formed as the photoreceptor 2 rotates. The photoreceptor 2 is, for example, a photoreceptor drum. The photoreceptor 2 is rotatably supported on the main body (not shown) of the image forming apparatus 50 and is driven to rotate in the direction of the arrow by a driving means (not shown). The driving means includes, for example, an electric motor and a reduction gear, and transmits its driving force to the conductive substrate 3 that forms the core of the photoreceptor 2, thereby driving the photoreceptor 2 to rotate at a predetermined peripheral speed. The charging unit 7, exposure unit 11, development unit 12, transfer unit 13, and cleaning unit 14 are provided in this order along the outer circumferential surface of the photoreceptor 2 from upstream to downstream in the direction of rotation of the photoreceptor 2. These components that make up the image forming apparatus 50 are housed in a housing 23.

[0064] (2-2) Charging section: 7 The charging section (charger) 7 is a device that charges the outer peripheral surface of the photoreceptor 2 uniformly to a predetermined potential. As the charger 7, for example, a contact charger in the shape of a roller, a belt, or a blade can be used. It is best to apply only DC voltage to charging members such as charging rollers, from the viewpoints of the cost of the power supply (high voltage application device) 18a and the lifespan of the photosensitive member 2 and charging members. In other words, it is preferable for the charger to output DC voltage.

[0065] Here, an example in which a roller-type contact charger is used as the charger 7 will be described. The charger 7 can have a conductive substrate 28 as a base, and an elastic layer 29 and a resistance layer 30 as coating layers on the outer circumferential surface of the conductive substrate 28 in this order. The method for forming the charging portion will be described in detail in the examples.

[0066] (2-2-1) Conductive support: 28 There are no particular limitations on the conductive support 28 as long as it has conductivity and can maintain the strength required for a charging member, and examples thereof include a round bar made of at least one metal material selected from iron, copper, stainless steel, aluminum, and nickel. Furthermore, the surface of the conductive support 28 may be plated to provide rust prevention and scratch resistance, as long as the conductivity is not impaired.

[0067] (2-2-2) Elastic layer: 29 The elastic layer 29 has appropriate conductivity and elasticity to supply power to the photosensitive member as the member to be charged and to ensure good uniform adhesion of the charging roller to the photosensitive member F. In order to ensure uniform adhesion between the charging roller and the photosensitive member, it is preferable that the elastic layer 29 is polished so that it is thickest at the center and becomes thinner from the center to both ends (so-called crown shape). Typically, the charging roller contacts the photoreceptor 2 by applying a predetermined pressure to both ends of the conductive support. Therefore, the pressure is weaker in the center and stronger toward the ends. While this is not a problem if the charging roller is sufficiently straight, if it is not, uneven density can occur in the image corresponding to the center and both ends. Furthermore, as the charging area expands with the increase in A3+ compatible models and color machines, the charging device 7 itself is prone to bending due to the pressure only on the both ends of the conductive support 28, creating a gap in the center. For these reasons, it is preferable to form the elastic layer 29 in a crown shape.

[0068] The elastic layer 29 can be formed by a known method by adding an appropriate amount of a conductive agent having an electron conduction mechanism, such as carbon black, graphite, or conductive metal oxide, and an appropriate amount of a conductive agent having an ion conduction mechanism, such as alkali metal salt or quaternary ammonium salt, to an elastic material such as rubber. The volume resistivity of the elastic layer 29 is 1×10 10 It is preferably tailored to exhibit a conductivity of less than Ωcm. Examples of elastic materials include synthetic rubbers such as natural rubber, ethylene propylene rubber (EPDM), styrene butadiene rubber (SBR), silicone rubber, urethane rubber, epichlorohydrin rubber, isoprene rubber (IR), butadiene rubber (BR), nitrile butadiene rubber (NBR), and chloroprene rubber (CR), as well as polyamide resin, polyurethane resin, and silicone resin.

[0069] The thickness of the elastic layer is not particularly limited, but is preferably 1 to 3 mm, and more preferably 1.5 to 2 mm.

[0070] (2-2-3) Resistance layer: 30 The resistance layer 30 is formed in contact with the elastic layer 29 and is provided to prevent the softening oil, plasticizer, etc. contained in the elastic layer 29 from bleeding out onto the surface of the charger, and to adjust the electrical resistance of the entire charger. Examples of materials that can be used to form the resistance layer include epichlorohydrin rubber, nitrile butadiene rubber (NBR), polyolefin-based thermoplastic elastomers, urethane-based thermoplastic elastomers, polystyrene-based thermoplastic elastomers, fluororubber-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, polybutadiene-based thermoplastic elastomers, ethylene vinyl acetate-based thermoplastic elastomers, polyvinyl chloride-based thermoplastic elastomers, and chlorinated polyethylene-based thermoplastic elastomers. These can be used alone or in combination of two or more types as a mixture or copolymer.

[0071] The resistive layer 30 is conductive or semiconductive, and is formed by appropriately adding a conductive agent having an electron conduction mechanism (e.g., conductive carbon, graphite, conductive metal oxide, copper, aluminum, nickel, iron powder, etc.) or a conductive agent having an ion conduction mechanism (e.g., alkali metal salt, ammonium salt, etc.) to the above-mentioned material. In this case, two or more kinds of conductive agents may be used in combination to obtain the desired electrical resistance. However, in consideration of environmental changes and contamination of the photoreceptor, it is preferable to use a conductive agent having an electron conduction mechanism.

[0072] The charging unit of the image forming apparatus of the present invention is a charger provided so that its surface is in contact with or in close proximity to the surface of the photoreceptor, and the charger preferably has a surface roughness Rz of 5.0 to 13 μm measured in accordance with JIS-0601 (1994). This can improve the image quality of the image forming apparatus. Furthermore, in experiments conducted by the present inventors, good print quality was achieved when the surface roughness Rz of the charging roller was set to 5.0 μm, 8.2 μm, or 13.0 μm. If the surface roughness Rz is less than 5.0 μm, scale-like charging unevenness and white spots may worsen, while if the surface roughness Rz exceeds 13 μm, image fogging may worsen. The surface roughness Rz is more preferably 7.0 to 13 μm. Indices that indicate surface roughness include, for example, ten-point average surface roughness (Rz), arithmetic mean roughness (Ra), maximum roughness (Ry), and mean spacing between irregularities (Sm). In the present invention, however, unless otherwise specified, "surface roughness" means ten-point average surface roughness (Rz). The measurement method will be explained in the Examples.

[0073] The surface of the charger 7 is usually uneven, but by keeping the surface roughness of the charger within the above range, a stable charging potential can be ensured at all times, and a problem-free level of toner cleaning performance can be ensured, thereby always producing good images. In particular, when only a DC voltage is applied to the charger 7, the convex portions (protrusions) on the surface of the charging roller become appropriate discharge points, ensuring a stable charging potential at all times. In other words, by forming convex portions and concave portions on the surface of the charging roller, the convex portions charge the photosensitive element F. If the surface roughness of the charging portion 7 is less than 5.0 μm, scaly charging unevenness and white spots may worsen. On the other hand, if the surface roughness of the charging portion 7 is more than 13 μm, streaky charging unevenness on halftone images can be suppressed, but image fog may worsen. The preferred surface roughness of the charging portion is 7.0 to 13 μm.

[0074] The surface roughness can be adjusted by changing the polishing conditions for the surface layer (resistive layer) of the charging roller. Furthermore, to further stabilize charging, the surface layer (resistive layer) of the charging roller may contain a filler. In this case, it is desirable to improve the dispersion of the protrusions on the charging roller surface by changing the type and particle size of the filler.

[0075] The filler is not particularly limited as long as it does not significantly impair the effects of the invention. Examples of fillers include calcium carbonate, talc, mica, silica, alumina, aluminum hydroxide, magnesium hydroxide, barium sulfate, zinc oxide, zeolite, wollastonite, diatomaceous earth, glass beads, bentonite, montmorillonite, asbestos, hollow glass spheres, graphite, molybdenum disulfide, titanium oxide, aluminum fibers, stainless steel fibers, brass fibers, aluminum powder, wood flour, rice husks, graphite, metal powder, conductive metal oxides, organometallic compounds, and organometallic salts, and these can be used alone or in combination of two or more. The thickness of the resistance layer is not particularly limited, but is preferably 5 to 100 μm, and more preferably 5 to 20 μm.

[0076] (2-4) Exposure section: 11 The exposure unit 11 is a device that emits light modulated based on image information. The exposure unit 11 can be equipped with a semiconductor laser or a light-emitting diode as a light source, and irradiates the surface (outer peripheral surface) of the photoconductor 2 between the charger 7 and the developer 12 with a laser beam light output from the light source, thereby exposing the charged surface of the photoconductor 2 according to the image information. The light is repeatedly scanned in the main scanning direction, which is the direction of extension of the rotation axis of the photoconductor 2, and these are focused to sequentially form electrostatic latent images on the surface of the photoconductor 2. In other words, the amount of charge on the photoconductor 2, which is uniformly charged by the charger 7, differs depending on whether or not it is irradiated with the laser beam, thereby forming an electrostatic latent image.

[0077] (2-5) Development unit: 12 The developing section (developing device) 12 is a device that develops an electrostatic latent image formed on the surface of the photosensitive member 2 by exposure using a developer (toner) 25, and is provided with a developing roller 31 that is disposed opposite the photosensitive member 2 and supplies toner to the surface of the photosensitive member 2, and a casing 32 that supports the developing roller 31 rotatably around a rotation axis that is parallel or approximately parallel to the rotation axis of the photosensitive member 2 and contains a developer containing toner in its internal space.

[0078] (2-6) Transcription section: 13 The transfer unit (transfer charger) 13 is a device that transfers a toner image, which is a visible image formed on the surface of the photoreceptor 2 by development, onto transfer paper, which is a recording medium 26, that is supplied between the photoreceptor 2 and the transfer charger 13 from a predetermined transport direction (the direction of the arrow) by a transport means (not shown). The transfer unit applies a predetermined high voltage to a transfer nip formed between the photoreceptor 2 and the transfer charger 13 by a power supply unit (high voltage application device) 18b. The transfer unit 13 can be configured in the same manner as the charging unit 7 described above, and is, for example, a contact-type transfer unit that transfers the toner image onto the recording medium P by applying a charge of the opposite polarity to that of the toner 25 to the recording medium 26.

[0079] (2-7) Fixing section: 19 The fixing section (fixing device) 19 is a device that fixes the toner image transferred to the recording medium 26 by the transfer section 13 to the recording medium 26. The fixing section 19 is provided downstream of the transfer nip between the photoreceptor 2 and the transfer section 13 in the conveyance direction of the recording medium 26, and includes, for example, a heating roller and a pressure roller provided opposite thereto, and the pressure roller is pressed against the heating roller to form the fixing nip.

[0080] (2-8) Cleaning section: 14 The cleaning unit (cleaner) 14 is a cleaning device that removes and collects the toner 25 remaining on the surface of the photoreceptor 2 after the transfer operation by the transfer unit 13. The cleaner 14 includes a cleaning blade 34 that separates the toner 25 remaining on the surface of the photoreceptor 2, and a collection casing 35 that contains the toner 25 separated thereby.

[0081] (2-9) Static elimination unit: not shown The image forming apparatus 50 preferably further includes a charge eliminating unit that eliminates surface charges remaining on the photoreceptor 2, and is preferably provided together with the cleaning unit . As the static eliminator, a device known in the art can be used.

[0082] Moreover, it is preferable that the image forming apparatus of the present invention further comprises a separation section (separation claw) 20 that separates the recording medium 26 from the photoreceptor 2.

[0083] (2-10) Control unit: 15 The control unit 15 is a part that controls the image forming apparatus 50, and includes, for example, a microcontroller having a CPU, memory, timer, input / output ports, etc. The memory of the control unit 15 stores control software for controlling the image forming apparatus 50. The image forming apparatus 50 may also include a temperature and humidity sensor that is provided to detect the environment in which the image forming apparatus 50 is used.

[0084] (2-11) Operation of image forming device The operation of the image forming apparatus of the present invention will be explained using the image forming apparatus 50 described above. First, when the photosensitive element 2 is rotated in a predetermined rotation direction (arrow direction) by the drive unit, a negative charge is supplied to the surface of the photosensitive element 2 from the charger 7, which is located upstream of the light imaging point by the exposure unit 11 in the rotation direction of the photosensitive element 2, and the surface of the photosensitive element 2 is uniformly charged to a predetermined potential. For example, as shown in Figure 2, negative charges accumulate on the surface of the photoreceptor 2, charging the surface of the photoreceptor 2, while positive charges are generated on the surface of the conductive substrate 3 facing the charged surface of the photoreceptor 2 due to the Coulomb force of the negative charges on the surface of the photoreceptor 2. This stabilizes the negative charges on the surface of the photoreceptor 2, and the surface of the photoreceptor 2 is uniformly charged. Therefore, in order to prevent uneven charging, it is important to quickly generate positive charges on the surface of the conductive substrate 3 due to the Coulomb force of the negative charges on the surface of the photoreceptor 2.

[0085] Next, light corresponding to image information is irradiated from the exposure unit 11 onto the uniformly charged surface of the photoreceptor F. This exposure removes the surface charge from the areas of the photoreceptor 2 that are irradiated with light, creating a difference in surface potential between the areas irradiated with light and the areas not irradiated with light, forming an electrostatic latent image. Toner 25 is supplied from the developing unit 12, which is located downstream in the rotation direction of the photosensitive member 2 from the point where light is focused by the exposure unit 11, to the surface of the photosensitive member 2 on which the electrostatic latent image is formed, thereby developing the electrostatic latent image and forming a toner image.

[0086] In synchronization with the exposure of the photoreceptor 2, a recording medium 26 is supplied from the transfer paper transport direction (the direction of the arrow) to the transfer nip between the photoreceptor 2 and the transfer unit 13. The transfer unit 13 imparts a charge of the opposite polarity to that of the toner 25 to the supplied recording medium 26, and the toner image formed on the surface of the photoreceptor 2 is transferred onto the recording medium 26. The recording medium 26 onto which the toner image has been transferred is conveyed by the conveying unit to the fixing unit 19, and the toner image is heated and pressurized as it passes through the fixing nip, the contact area between the heating roller and pressure roller of the fixing unit 19, and is fixed to the recording medium 26 to form a robust image. The recording medium 26 on which the image has been formed in this way is ejected to the outside of the image forming apparatus 50 by the conveying unit.

[0087] On the other hand, the toner 25 remaining on the surface of the photoreceptor 2 after the toner image is transferred by the transfer unit 13 is peeled off from the surface of the photoreceptor 2 by the cleaning blade 34 of the cleaning unit 14 and collected in a collection casing 35. In this way, the charge on the surface of the photoreceptor 2 from which the toner 25 has been removed is removed, and the electrostatic latent image on the surface disappears. After that, the photoreceptor 2 is rotated again, and the series of operations starting with charging are repeated again, forming images continuously. If the image forming device 50 is equipped with a discharge unit downstream of the cleaning unit 14 and before the charging unit 7, the light from the discharge lamp of the discharge unit efficiently and reliably removes the charge on the surface of the photosensitive member 2, thereby eliminating the electrostatic latent image on the surface of the photosensitive member 2. [Example]

[0088] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples and comparative examples, photoreceptors and charging rollers were fabricated, and they were incorporated into image forming apparatuses and evaluated. Further, the physical properties of the photoreceptor were measured by the following methods.

[0089] <AC impedance Z of photoconductor> Using a precision LCR meter (Agilent Technologies, model: 4284A), the conductive substrate side of the photoreceptor is earthed in an environment of 30°C / 85% humidity, a voltage of 1.0 V is applied to the surface layer side of the photoreceptor, and the impedance (Ω) is measured at a measurement frequency of 30 kHz.

[0090] <Surface roughness Rz of photoconductor and charging roller> Using a surface roughness measuring instrument (Tokyo Seimitsu Co., Ltd., model: Surfcom1400D), the surface roughness Rz (μm) of the center part is measured with the horizontal direction of the outermost surface layer of the photosensitive member as the measurement position, using a method with a reference length of 0.8 mm, a cutoff wavelength of 0.8 mm, a measurement speed of 0.1 mm / sec, and a Gaussian cutoff type.

[0091] <Ionization potential of charge transport material and charge generation layer> The ionization potential (eV) is measured using an atmospheric photoelectron spectrometer (manufactured by Riken Keiki Co., Ltd., model AC-2) under the condition of an output power of 10 nW to 100 nW.

[0092] Example 1 (Production of photoreceptor) (Formation of undercoat layer) 3 parts by weight of titanium oxide (manufactured by Showa Denko K.K., product name: TS-043) and 2 parts by weight of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: CM8000) were added to 25 parts by weight of methyl alcohol, and the mixture was dispersed for 8 hours using a paint shaker (disperser) to prepare 3 kg of a coating solution for forming an undercoat layer. Next, by a dip coating method, specifically, the obtained coating solution was filled into a coating tank, and an aluminum drum-shaped substrate having a diameter of 30 mm and a length of 357 mm was immersed in the coating solution, then pulled out and dried to form an undercoat layer with a thickness of 1.0 μm.

[0093] (Formation of Charge Generation Layer) The charge generating material may be a compound of the following formula: [ka] One part by mass of a Y-type oxo-titanyl phthalocyanine represented by the formula (manufactured by Nippon Shizai Co., Ltd., product name: TPL-530 / CG1) and 1 part by mass of a polyvinyl butyral (PVB) resin (manufactured by Sekisui Chemical Co., Ltd., product name: BX-1) as a binder resin were added to 98 parts by mass of methyl ethyl ketone, and the mixture was dispersed for 2 hours using glass beads (manufactured by AS ONE Corporation, product name: BZ-1, bead diameter: 1 mm) as a medium in a paint shaker to prepare 3 kg of a coating solution for forming a charge generating layer. Next, the charge generation layer-forming coating liquid was applied to the surface of the undercoat layer by a dip coating method, similar to the formation of the undercoat layer. Specifically, the obtained charge generation layer-forming coating liquid was filled into a coating tank, and the drum-shaped substrate on which the undercoat layer had been formed was immersed in the coating liquid, then pulled out and air-dried to form a charge generation layer with a thickness of 0.2 μm.

[0094] (Formation of charge transport layer) Next, 10 parts by mass of silica particles (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) as an inorganic filler and 10 parts by mass of a compound represented by the following formula: [ka] To 30 parts by mass of a triphenylamine compound (TPD) represented by the formula (TPD) (manufactured by Tokyo Chemical Industry Co., Ltd., product name: D2448 / CT1) and 60 parts by mass of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050) as a binder resin, 400 parts by mass of tetrahydrofuran was added, stirred and mixed, and then stirred in a ball mill for 30 hours.

[0095] The resulting mixture was subjected to 10-pass dispersion treatment using a particle dispersing device (Microfluidics, model: Microfluidizer M110P) to prepare 3 kg of a coating solution for forming a charge transport layer. The resulting coating solution for forming a charge transport layer was transferred to a glass container and subjected to roll stirring in a ball mill for 12 hours. After stirring was completed, the container was left to stand at 20°C for 3 days to prepare 3 kg of a coating solution for forming a charge transport layer. The obtained coating solution for forming the charge transport layer was applied onto the charge generation layer 15 by the same immersion method as in the case of forming the undercoat layer, and the resulting coating film was dried at 120°C for 1.5 hours to form a charge transport layer with a film thickness of 40 μm, thereby producing the photoreceptor shown in Figure 2.

[0096] (Production of charging member (charging roller)) (Formation of elastic layer) Rubber for forming the elastic layer was obtained by kneading 100 parts by mass of ethylene-propylene-diene terpolymer (ethylene propylene rubber, EPDM) as the elastic material, 10 parts by mass of carbon black as the conductive agent, and 10 parts by mass of foamed urethane as the foaming agent. The obtained rubber was poured into a mold in which a conductive support made of SUM23 (free-cutting steel) with a diameter of 9 mm and a length of 355 mm had been set, and heated in an electric furnace at an internal temperature of 160°C for 30 minutes to vulcanize and foam the rubber, forming an elastic layer with a thickness of 2 mm.

[0097] (Creating the resistance layer (surface layer)) 100 parts by mass of a polyamide thermoplastic elastomer as an elastic material and 20 parts by mass of carbon black as a conductive agent were kneaded together to obtain a rubber for forming a resistance layer. The resulting rubber was melt-extruded using a circular die to produce a seamless tube that would serve as the resistance layer. Air was blown into one end of the resulting seamless tube to expand it, and a conductive support (roller) with an elastic layer formed on it was inserted into the tube to form a resistance layer. The surface of the resulting charging roller was then processed to produce a 12 mm diameter charging roller with a surface roughness Rz of 8.4 μm, as shown in Figure 3.

[0098] (surface roughness measurement) The surface roughness R of the obtained charging roller was measured as the ten-point average surface roughness (Rz) using a surface roughness measuring device (manufactured by Kosaka Laboratory Co., Ltd., model: SE-30H). As a result, the surface roughness R of the charging roller Z was 8.2 μm. In the following examples and comparative examples, the surface roughness Rz of the charging roller was measured in the same manner.

[0099] Example 2 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the inorganic filler silica particles were changed from 10 parts by weight to 5 parts by weight, the charge transport material triphenylamine compound was changed from 30 parts by weight to 32 parts by weight, and the binder resin polycarbonate was changed from 60 parts by weight to 63 parts by weight.

[0100] Example 3 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the inorganic filler silica particles were changed from 10 parts by weight to 20 parts by weight, the charge transport material triphenylamine compound was changed from 30 parts by weight to 27 parts by weight, and the binder resin polycarbonate was changed from 60 parts by weight to 53 parts by weight.

[0101] Example 4 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) of the inorganic filler were replaced with silica particles (fumed silica, primary particle diameter: 12 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R974).

[0102] Example 5 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles (fumed silica, primary particle diameter: 40 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) RX50) were used instead of the silica particles of the inorganic filler (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972).

[0103] Example 6 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles (fumed silica, primary particle diameter: 80 to 100 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) VPRX40S) were used instead of the silica particles of the inorganic filler (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972).

[0104] Example 7 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles (colloidal silica, primary particle diameter: 62 nm, manufactured by Cabot Corporation, product name: TG-C390) were used instead of silica particles (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) of the inorganic filler.

[0105] Example 8 Instead of the triphenylamine-based compound as the charge transport material, a compound of the following formula: [ka] The photoreceptor shown in FIG. 2 and the charging roller shown in FIG. 3 were produced in the same manner as in Example 1, except that a stilbene compound (CT2) represented by the following formula was used:

[0106] Example 9 Instead of the triphenylamine-based compound as the charge transport material, a compound of the following formula: [ka] The photoreceptor shown in FIG. 2 and the charging roller shown in FIG. 3 were produced in the same manner as in Example 1, except that an enamine compound (CT3) represented by the following formula was used:

[0107] Example 10 Instead of the triphenylamine-based compound of the charge transport material, a compound of the following formula: [ka] The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that a butadiene-based compound represented by the following formula (trade name: T405 / CT4, manufactured by Takasago International Corporation) was used.

[0108] Example 11 Instead of the triphenylamine-based compound of the charge transport material, a compound of the following formula: [ka] The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that a triphenylamine compound represented by the following formula (4-(2,2-diphenylethyl)-4′,4″-dimethyl-triphenylamine / CT5, manufactured by Takasago International Corporation) was used.

[0109] Example 12 charge Generation The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that 1 part by mass of the Y-type oxo-titanyl phthalocyanine was replaced with 2 parts by mass of α-type oxo-titanyl phthalocyanine (having the same chemical structure as CG1, manufactured by Nippon Shizai Co., Ltd., product name TPL-364 / CG2).

[0110] Example 13 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the coating liquid for forming a charge generating layer was prepared and then stored at a temperature of 35° C. for 3 days, thereby converting the crystal type of the charge generating substance from Y type to β type (chemical structural formula is the same as CG1, CG3).

[0111] Example 14 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the triphenylamine-based compound charge transport material was changed from 30 parts by weight to 41 parts by weight, and the polycarbonate binder resin was changed from 60 parts by weight to 49 parts by weight.

[0112] Example 15 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the triphenylamine compound charge transport material was changed from 30 parts by weight to 27 parts by weight, and the polycarbonate binder resin was changed from 60 parts by weight to 64 parts by weight.

[0113] Example 16 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the triphenylamine-based compound charge transport material was changed from 30 parts by weight to 45 parts by weight, and the polycarbonate binder resin was changed from 60 parts by weight to 45 parts by weight.

[0114] Example 17 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the triphenylamine compound charge transport material was changed from 30 parts by weight to 25 parts by weight, and the polycarbonate binder resin was changed from 60 parts by weight to 65 parts by weight.

[0115] Example 18 By adjusting the conditions of the dip coating method, charge transport Layer Film thickness of 40 μm 34 μm The photosensitive member shown in FIG. 2 and the charging roller shown in FIG. 3 were produced in the same manner as in Example 1, except that the above-mentioned conditions were met.

[0116] Example 19 By adjusting the conditions of the dip coating method, charge transport Layer Film thickness of 40 μm 46 μm The photosensitive member shown in FIG. 2 and the charging roller shown in FIG. 3 were produced in the same manner as in Example 1, except that the above-mentioned conditions were met.

[0117] Example 20 By adjusting the conditions of the dip coating method, charge transport Layer Film thickness of 40 μm 48 μm The photoreceptor shown in FIG. 2 was produced in the same manner as in Example 1, except that:

[0118] (Examples 21 to 25) The photoreceptor shown in FIG. Furthermore, by adjusting the surface processing conditions, charging rollers of FIG. 3 were produced for Examples 21 to 25, each having a surface roughness Rz of 3.1 μm, 5.0 μm, 13.0 μm, 15.3 μm, and 8.2 μm.

[0119] Example 26 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that aluminum oxide nanoparticles (primary particle diameter: 20 nm, manufactured by EM Japan Co., Ltd., product name: NP-ALO-10-100) were used instead of silica particles (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) as an inorganic filler.

[0120] Example 27 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles (fumed silica, primary particle diameter: 7 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R976) were used instead of the silica particles (fumed silica, primary particle diameter: 16 nm, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) of the inorganic filler.

[0121] Example 28 By adjusting the conditions of the dip coating method, charge transport Layer Film thickness of 40 μm 30 μm The photoreceptor shown in FIG. 2 was produced in the same manner as in Example 1, except that:

[0122] (Comparative Example 1) The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that silica particles were not used as the inorganic filler in the preparation of the coating liquid for forming the charge transport layer.

[0123] (Comparative Example 2) The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the inorganic filler silica particles were changed from 10 parts by weight to 3 parts by weight, the charge transport material triphenylamine compound was changed from 30 parts by weight to 32 parts by weight, and the binder resin polycarbonate was changed from 60 parts by weight to 65 parts by weight.

[0124] (Comparative Example 3) The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the inorganic filler silica particles were changed from 10 parts by weight to 25 parts by weight, the charge transport material triphenylamine compound was changed from 30 parts by weight to 25 parts by weight, and the binder resin polycarbonate was changed from 60 parts by weight to 50 parts by weight.

[0125] Comparative Example 4 The photoreceptor of FIG. 2 and the charging roller of FIG. 3 were produced in the same manner as in Example 1, except that the inorganic filler silica particles were changed from 10 parts by weight to 30 parts by weight, the charge transport material triphenylamine compound was changed from 30 parts by weight to 23 parts by weight, and the binder resin polycarbonate was changed from 60 parts by weight to 47 parts by weight.

[0126] [evaluation] The photoreceptors and charging rollers prepared in Examples 1 to 28 and Comparative Examples 1 to 4 were installed in a test copier modified from a digital copier (manufactured by Sharp Corporation, product name: MX-B455W), and each image forming apparatus was evaluated.

[0127] [Printed image evaluation experiment] The image forming device was evaluated for scaly charging unevenness, white spots, and fogging under constant environments of temperature 30°C / relative humidity 85% (high temperature / high humidity) and temperature 5°C / relative humidity 10% (low temperature / low humidity). Here, the high voltage output of the charging roller in Examples 1 to 24 and 26 to 28 and Comparative Examples 1 to 4 was a direct current voltage DC plus AC output, with Vpp = 1.3 kV and frequency f = 2.0 kHz at high temperature / high humidity and Vpp = 1.5 kV and frequency f = 2.0 kHz at low temperature / low humidity, while Example 25 used only a direct current voltage DC.

[0128] [Rating 1: Scaly charging unevenness] Under each environment, the photoreceptor surface potential V0 / development bias DVB was set to -750V / -600V, -600V / -450V, -450V / -300V, and -300V / -150V, and the scale-like charging unevenness was evaluated using halftone images printed out. From the obtained results, the image output at the worst photoreceptor surface potential V0 / developing bias DVB was judged according to the following criteria. ◎: No unevenness is observed, very good 〇: Almost no unevenness is observed, good △: Some unevenness is observed in places, but it is still usable ×: Clear unevenness is observed, not good

[0129] [Rating 2: White point] Under each environment, the photoreceptor surface potential V0 / development bias DVB was set to -750V / -600V, -600V / -450V, -450V / -300V, and -300V / -150V, respectively, and white spots were evaluated on halftone images output. From the obtained results, the image output at the worst photoreceptor surface potential V0 / developing bias DVB was judged according to the following criteria. ◎: No white spots were observed, very good ◯: Almost no white spots are visible, good △: White spots are visible in some places, but still usable ×: Clear white spots are observed, not good

[0130] [Rating 3: Overlapping] In a high temperature and high humidity environment, the photoreceptor surface potential V0 / developing bias DVB was set to -750V / -600V, and 200,000 sheets of actual white solid images were printed for aging. The whiteness at the initial stage and after aging was measured using a spectrophotometer (colorimetric colorimeter, manufactured by Nippon Denshoku Industries Co., Ltd., Model: SZ90) to measure the difference in image fog (ΔB.G.) between the initial stage and after aging, and the image fog was evaluated. The results obtained were judged according to the following criteria. ◎: Very good (ΔB.G.<0.40) 〇: Good (0.40≦ΔB.G.<0.70) △: Fairly good (0.70≦ΔB.G.<1.00) ×: Not good (1.00≦ΔB.G.)

[0131] [Photoreceptor printing durability evaluation experiment] [Rating 4: Printing durability] Under a high temperature and humidity environment, the photoconductor surface potential V0 / development bias DVB is set to -750V / -600V, and the film thickness of the photoconductor is measured initially and after 500K rotation fatigue, and the amount of film reduction Δd of the photoconductor is calculated. The remaining film thickness of the photoconductor at 3000K rotation calculated from this amount of film reduction is d. end (μm) and the photosensitive printing durability was evaluated. The results obtained were judged according to the following criteria. ◎: Very good (Δd<1.5 μm, d end >30μm) ◯: Good (1.5≦Δd<2.5, 30≧d end >25) △: Fairly good (2.5≦Δd<3.5, 25≧d end >19) ×: Not good (3.5≦Δd, d end ≦19)

[0132] [Photoreceptor repeated fatigue evaluation test] [Rating 5: Residual potential increase] In a high temperature and high humidity environment, the photoconductor surface potential V0 / development bias DVB is set to -750V / -600V, and the initial residual potential Vr ini After subjecting the photoconductor to 500K rotation fatigue, the residual potential Vr end The difference between these values, the residual potential increase width ΔVr, was evaluated. The results obtained were judged according to the following criteria. ◎: Very good (ΔVr<20V) 〇: Good (20≦ΔVr<40) △: Fairly good (40≦ΔVr<60) ×: Not good (60≦ΔVr)

[0133] [comprehensive evaluation] Based on the evaluation results of 1 to 5, an overall evaluation was made according to the following criteria. ◎: For each item, there are 5 or more ◎ ratings, and no △ or × ratings. 〇: No △ rating in each item △: There are 2 or less △ ratings ×: 3 or more △ ratings or 1 or more × ratings The results obtained are shown in Table 1. The configurations and physical properties of the photoreceptor and charging roller are shown in Tables 1 and 2, and the evaluation results obtained are shown in Tables 3 and 4. The "Materials" in Tables 1 and 2 each represent the abbreviation or product name described in the specification, and the inorganic filler symbols "FS" represent fumed silica, "CS" represent colloidal silica, and "AL" represent alumina.

[0134] [Table 1]

[0135] [Table 2]

[0136] [Table 3]

[0137] [Table 4]

[0138] The following can be seen from Tables 1 to 4. A laminated photosensitive layer is provided, in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport substance, and a binder resin, and has a surface layer with a surface roughness Rz of 0.05 to 0.40 μm measured in accordance with JIS-0601 (1982), and a surface roughness of 1.0 to 4.0 × 10 measured under the conditions of a temperature of 30°C, a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz.4 An image forming apparatus can be provided in which a photoreceptor having an AC impedance Z of Ω has excellent image quality and printing durability (Examples 1 to 28). When the fumed silica has a primary particle diameter of 12 to 40 nm and is contained in the charge transport layer at a ratio of 5 to 20% by mass, an image forming apparatus with better image quality and printing durability can be provided (Examples 1 to 7 and 26). When the charge transport material has an ionization potential of 5.40 to 5.60 eV, an image forming apparatus with better image quality and printing durability can be provided (Examples 1, 8 to 11). When the charge generating layer has an ionization potential of 5.40 to 5.60 eV, an image forming apparatus with better image quality and printing durability can be provided (Examples 1, 12, and 13). When the charge transport layer contains a charge transport material and a binder resin in a mass ratio of 10 / 12 to 10 / 24, an image forming apparatus with better image quality and printing durability can be provided (Examples 1, 14 to 17). When the laminated photosensitive layer has a thickness of 34 to 46 μm, an image forming apparatus with better image quality and printing durability can be provided (Examples 1, 18 to 20). The charging unit is a charger provided so that its surface is in contact with or in close proximity to the surface of the photoreceptor, and when the charger has a surface with a surface roughness Rz of 5.0 to 13 μm measured in accordance with JIS-0601 (1994), an image forming apparatus with better image quality and printing durability can be provided (Examples 1, 21 to 24). Even if the charger outputs a direct current (DC) voltage, an image forming apparatus with excellent image quality and printing durability can be provided (Example 25).

[0139] The present invention is not limited to the above-described embodiments, but can be embodied in various other forms. Therefore, these embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited in any way by the text of the specification. Furthermore, all modifications and variations that fall within the equivalent scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0140] 2. Electrophotographic photoreceptor 3. Conductive substrate 4 Photosensitive layer (laminated photosensitive layer) 8. Charge generation layer 9 Charge transport layer 10 Undercoat layer

[0141] 50 Image forming device 23 Housing Arrow: Rotation direction of electrophotographic photosensitive member 7 Charging unit (charger) 28 Conductive support 29 Elastic layer 30 resistance layer 18a Power supply unit (high voltage application device) 11 Exposure section 12 Development unit (developer) 31 Developing roller 32 Casing 25 Developer (including toner) 13 Transfer unit (transfer charger) 18b Power supply unit (high voltage application device) 14 Cleaning section (cleaner) 34 Cleaning blade 35 Recovery casing 15 Control Unit 19 Fixing unit (fixing device) 26 Recording media (recording paper or transfer paper) 20 Separation part (separation claw)

Claims

1. a laminated photosensitive layer including a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance laminated in this order on a conductive substrate, the charge transport layer containing an inorganic filler, a charge transport substance, and a binder resin; The electrophotographic photoreceptor has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982), and has a surface roughness of 1.0 to 6.0×10 measured under the measurement conditions of a temperature of 30° C., a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz. 4 has an AC impedance Z of Ω, The inorganic filler is fumed silica having a primary particle diameter of 12 to 40 nm, and is contained in the charge transport layer in an amount of 5 to 20% by mass. An electrophotographic photoreceptor characterized by:

2. A photosensitive layer comprising at least a laminated layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport substance, and a binder resin; the electrophotographic photoreceptor has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982), and an AC impedance Z of 1.0 to 6.0×10 4 Ω measured under the conditions of a temperature of 30° C., a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz; The charge transport material has an ionization potential of 5.40 to 5.60 eV. An electrophotographic photoreceptor characterized by:

3. A photosensitive layer comprising at least a laminated layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive substrate, and the charge transport layer contains an inorganic filler, a charge transport substance, and a binder resin; the electrophotographic photoreceptor has a surface layer with a surface roughness Rz of 0.05 to 0.60 μm measured in accordance with JIS-0601 (1982), and an AC impedance Z of 1.0 to 6.0×10 4 Ω measured under the conditions of a temperature of 30° C., a humidity of 85% RH, a DC voltage of 1.0 V, and a frequency of 30 kHz; The laminated photosensitive layer has a film thickness of 34 to 46 μm. An electrophotographic photoreceptor characterized by:

4. 2. The electrophotographic photoreceptor according to claim 1, wherein the charge generating layer has an ionization potential of 5.40 to 5.60 eV.

5. 5. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer contains a charge transport material and a binder resin in a mass ratio of 10 / 12 to 10 / 24.

6. 6. The electrophotographic photoreceptor according to claim 1, wherein the laminated photosensitive layer has a film thickness of 34 to 46 μm.

7. an electrophotographic photosensitive member according to any one of claims 1 to 6; a charging unit that charges the surface of the electrophotographic photosensitive member; an exposure unit that irradiates the charged surface of the electrophotographic photosensitive member with light to form an electrostatic latent image; a development unit that develops the electrostatic latent image formed by exposure to form a toner image; a transfer unit that transfers the toner image formed by development onto a recording medium; a fixing unit that fixes the transferred toner image on the recording medium to form an image; and a cleaning unit that removes and collects residual toner on the surface of the electrophotographic photosensitive member, The image forming apparatus is characterized in that the charging unit is a charger provided so that its surface is in contact with or in close proximity to the surface of the electrophotographic photosensitive member, and the charger has a surface with a surface roughness Rz of 5.0 to 13 μm measured in accordance with JIS-0601 (1994).

8. 8. The image forming apparatus according to claim 7, wherein the charger outputs a direct current (DC) voltage.

Images