Photoreceptor, process cartridge, and method for manufacturing a photoreceptor

Abstract

To provide a photoreceptor that can obtain sufficiently stable electrical characteristics and image quality even through a high temperature and high humidity environment for a long period.SOLUTION: A photoreceptor has an undercoat layer and a photosensitive layer in this order on a conductive support. The undercoat layer contains metal oxide particles. The undercoat layer has an initial resistance of 6.0 GΩ cm or less. After the undercoat layer is energized for 12 sets for five minutes at 1.6 uA / cm2, the ratio (I300 / I10) of a current value I300 after the energization for 300 seconds to a current value I10 after the energization for 10 seconds at 5 V / μm is 10 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a photoreceptor, a process cartridge, an image forming method, and a method for manufacturing a photoreceptor.

Background Art

[0002] In an image forming method using an electrophotographic image forming apparatus, an image is formed by subjecting an electrophotographic photoreceptor to processes such as a charging process, an exposure process, a development process, and a transfer process. In recent years, as a material constituting the electrophotographic photoreceptor, an organic material has been widely used because of advantages in flexibility, thermal stability, film-forming property, etc. In addition, with the rapid progress of full-colorization, high-speedization, and high-definition in image forming apparatuses, further durability and high stability are required for organic photoreceptors using organic materials.

[0003] However, in the current electrophotographic process where the electrophotographic photoreceptor repeats charging and discharging, charge accumulation gradually occurs at the interface of the layers constituting the electrophotographic photoreceptor, and holes are easily injected into the undercoat layer, resulting in a decrease in electrophotographic characteristics.

[0004] As a cause of charge accumulation in the organic photoreceptor, it is considered that the resistance of the undercoat layer is high and charge accumulation easily occurs at the interface. Generally, the undercoat layer is required to achieve and maintain both the "charge injection blocking function" from the conductive support to the photosensitive layer and the "charge transport function" of the charges generated in the photosensitive layer to the conductive support. However, these two functions tend to have an inverse relationship, and charge accumulation gradually occurs at the interface of each layer due to repeated electrostatic charging, and it becomes difficult to achieve and maintain the above two functions over a long period because holes are easily injected into the undercoat layer.

[0005] As a method of imparting a charge injection blocking function or a charge transport function to the undercoat layer, means for improving the charge injection blocking function using a silane coupling agent containing an amino group (for example, see Patent Documents 1 and 2), or a method of incorporating additives such as an electron transporting substance or an acceptor compound into the undercoat layer (for example, see Patent Documents 3 and 4) have been proposed.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] An object of the present invention is to provide a photoreceptor capable of obtaining sufficiently stable electrical characteristics and image quality even after being exposed to a high temperature and high humidity environment for a long time.

MEANS FOR SOLVING THE PROBLEMS

[0007] The photoreceptor of the present invention as a means for solving the above problems is a photoreceptor having an undercoat layer and a photosensitive layer in this order on a conductive support, wherein the undercoat layer contains metal oxide particles, the initial resistance of the undercoat layer is 6.0 GΩ·cm or less, and the undercoat layer is subjected to 1.6 μA / cm 2 for 5 minutes, after 12 sets of energization, the current value I after energization at 5 V / μm for 10 seconds 10 and the current value I after energization for 300 seconds 300 The ratio (I 300 / I 10 ) is 10 or less.

EFFECTS OF THE INVENTION

[0008] According to the present invention, it is possible to provide a photoreceptor capable of obtaining sufficiently stable electrical characteristics and image quality even after being exposed to a high temperature and high humidity environment for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the photoreceptor of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing another example of the photoreceptor of the present invention. [Figure 3]FIG. 3 is a cross-sectional view showing another example of the photoreceptor of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing another example of the photoreceptor of the present invention. [Figure 5] FIG. 5 is a schematic configuration diagram showing an example of the image forming apparatus of the present invention. [Figure 6] FIG. 6 is a schematic configuration diagram showing an example of the process cartridge of the present invention. [Figure 7A] FIG. 7A is a schematic view showing an evaluation image used for the image quality evaluation of the example. [Figure 7B] FIG. 7B is a schematic view showing a case where an afterimage occurs in the evaluation image used for the image quality evaluation of the example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] (Photoreceptor) The photoreceptor of the present invention has an undercoat layer and a photosensitive layer in this order on a conductive support, and further has other layers as necessary. The undercoat layer contains metal oxide particles, the initial resistance of the undercoat layer is 6.0 GΩ·cm or less, and a current value I after energization at 5 V / μm for 10 seconds after energization at 1.6 μA / cm 2 for 5 minutes for 12 sets in the undercoat layer 10 and the current value I after energization for 300 seconds 300 The ratio of (I 300 / I 10 ) is 10 or less. Note that the "photoreceptor" may be referred to as an "electrophotographic photoreceptor", and both are synonymous.

[0011] The photoreceptor of the present invention is an invention based on finding the problems of the prior art, that is, even when using a photoreceptor of the prior art, there are environmental variations such as switching from normal temperature (for example, 23°C and 60% RH) to high temperature and high humidity (for example, 27°C and 80% RH), and it is difficult to maintain the electrical characteristics and image quality of the photoreceptor when it has experienced a long-term high temperature and high humidity environment. As described above, in current electrophotographic processes in which electrophotographic photoreceptors undergo repeated charging and decharging, charge accumulation gradually occurs at the interfaces of the layers constituting the electrophotographic photoreceptor, creating conditions where holes can easily be injected into the underlying layer, resulting in a decrease in electrophotographic properties. In particular, the inventors have found that charge accumulation has a significant impact on the output image when the environment changes, such as from room temperature to high temperature and high humidity, and when it goes through a long period of high temperature and high humidity. Under high temperature and high humidity, the resistance of the underlayer decreases, making it easier for holes to escape, which can cause serious problems such as background staining (also called background staining, fogging, or black spots).

[0012] Therefore, there is a strong need for the development of photoreceptors, image forming apparatuses using such photoreceptors, and process cartridges that can obtain sufficiently stable electrical characteristics and image quality even under environmental fluctuations from room temperature to high temperature and humidity. As a result of their research, the inventors have found that by adding water to the coating liquid of the undercoat layer, an undercoat layer containing metal oxide particles is formed, the initial resistance of the undercoat layer is 6.0 GΩ·cm or less, and the undercoat layer has a current of 1.6 uA / cm². 2 After applying current for 5 minutes for 12 sets, the current value I after applying current at 5V / μm for 10 seconds was measured. 10 and the current value I after 300 seconds of energization 300 The ratio (I 300 / I 10 By satisfying the condition that ) is 10 or less, we have found that it is possible to provide a photoreceptor that can obtain sufficiently stable electrical characteristics and image quality even after being subjected to high temperature and high humidity environments for a long period of time, and thus completed the present invention.

[0013] Hereinafter, embodiments of the photoreceptor of the present invention will be described with reference to the drawings. Figure 1 is a cross-sectional view showing the configuration of one embodiment of the photoreceptor of the present invention, which has a conductive support 31 on which, in this order, an undercoat layer 32 and a photosensitive layer 33 mainly composed of a charge generating material and a charge transporting material are arranged. Figure 2 is a cross-sectional view showing the configuration of another embodiment of the photoreceptor of the present invention, in which a base layer 32 and a charge generating layer 35 mainly composed of a charge generating material and a charge transport layer 37 mainly composed of a charge transport material are laminated on a conductive support 31 as a photosensitive layer. Figure 3 is a cross-sectional view showing the configuration of yet another embodiment of the photoreceptor of the present invention, which has a conductive support 31, an undercoat layer 32, a photosensitive layer 33 mainly composed of a charge generating material and a charge transporting material, and a surface layer 39 on the surface of the photosensitive layer. Figure 4 is a cross-sectional view showing the configuration of yet another embodiment of the photoreceptor of the present invention, in which a base layer 32 and a photosensitive layer consisting of a charge generating layer 35 mainly composed of a charge generating material and a charge transport layer 37 mainly composed of a charge transport material are laminated on a conductive support 31, and a surface layer 39 is further provided on the charge transport layer 37.

[0014] <Conductive support> There are no particular restrictions on the shape of the conductive support, and it can be appropriately selected according to the purpose, for example, it can be in the form of a film or a cylinder. Furthermore, there are no particular restrictions on the size of the conductive support, and it can be appropriately selected according to the purpose.

[0015] There are no particular restrictions on the structure and material of the conductive support, and the volume resistivity is 10 10 Materials having conductivity of Ω·cm or less can be appropriately selected depending on the purpose. Examples include materials coated on a substrate by vapor deposition or sputtering of metals, metal oxides, etc., materials coated on a substrate by dispersing conductive powder in a binder resin, and materials in which a conductive layer is provided on a cylindrical substrate using heat-shrinkable tubing containing conductive powder. Examples of metals include aluminum, nickel, chromium, nichrome, copper, gold, silver, and platinum. Examples of metal oxides include tin oxide and indium oxide. Examples of base materials include plastic and paper.

[0016] Examples of conductive powders include carbon black and acetylene black; metal powders such as aluminum, nickel, iron, nichrome, copper, zinc, and silver; and metal oxide powders such as conductive tin oxide and ITO. Examples of binder resins include thermoplastic, thermosetting, or photocurable resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethylcellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyltoluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenolic resin, and alkyd resin. A conductive layer can be provided by dispersing the conductive powder and binder resin in an organic solvent and applying it to a support. Examples of organic solvents include tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.

[0017] Materials for heat-shrinkable tubing include polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, and Teflon (registered trademark).

[0018] Other embodiments of the structure and material of the conductive support include, for example, plates of aluminum, aluminum alloy, nickel, stainless steel, etc., which are prepared as raw tubes by methods such as drawing ironing, impact ironing, extruded ironing, extruded drawing, and cutting, and then surface-treated by cutting, superfinishing, polishing, etc. In addition, endless nickel belts and endless stainless steel belts can also be used as conductive supports.

[0019] <Underlayer> The aforementioned undercoat preferably contains at least metal oxide particles, a binder resin, and a compound having a salicylic acid skeleton, and may further contain other components as needed. The initial resistance of the aforementioned underlayer is 6.0 GΩ·cm or less, and the underlayer has a current of 1.6 uA / cm². 2 After applying current for 5 minutes for 12 sets, the current value I after applying current at 5V / μm for 10 seconds was measured. 10 and the current value I after 300 seconds of energization 300 The ratio (I 300 / I 10 The value is 10 or less.

[0020] Preferably, the undercoat layer has both a function to suppress the injection of unwanted charges (charges with opposite polarity to the charging polarity of the electrophotographic photoreceptor) from the conductive support to the photosensitive layer (charge injection blocking function) and a function to transport charges with the same polarity as the charging polarity of the photoreceptor from among the charges formed in the photosensitive layer (charge transport function). For example, if it is necessary to negatively charge the photoreceptor as part of the image forming process, the undercoat layer must have both a function to prevent hole injection from the support to the photoreceptor layer and a function to transport electrons from the photoreceptor layer to the support. Furthermore, in order to create a photoreceptor that can obtain sufficiently stable electrical characteristics and image quality even after prolonged exposure to high temperature and humidity environments, it is important that the charge injection blocking function and charge transport function remain unchanged even when repeated electrostatic loading and discharge gradually accumulates charge at the layer interface, creating conditions where holes can easily be injected into the underlying layer.

[0021] [Initial resistance of the underlayer] The initial resistance of the underlayer is 6.0 GΩ·cm or less, preferably 5.0 GΩ·cm or less, more preferably 4.0 GΩ·cm or less, even more preferably 3.0 GΩ·cm or less, particularly preferably 2.0 GΩ·cm or less, and most preferably 1.0 GΩ·cm or less. Furthermore, 0.1 GΩ·cm or more is preferred. If the initial resistance is 6.0 GΩ·cm or less, even with environmental fluctuations from room temperature to high temperature and humidity, and even after prolonged exposure to high temperature and humidity, charge accumulation at the interface between the undercoat layer and the charge generation layer can be sufficiently suppressed, thereby suppressing the injection of holes from the support and the undercoat layer. Furthermore, if the initial resistance is 0.1 GΩ·cm or more, the charge injection suppression function of the undercoat layer is activated, providing sufficient leak resistance and offering advantages in that it is less likely to cause abnormalities in image quality such as background contamination.

[0022] [Ratio of current values ​​after fatigue load on the lower layer (I 300 / I 10 )] The ratio of the current values ​​in the lower layer (I 300 / I 10 The value of ) is 10 or less, preferably 7 or less, more preferably 5 or less, even more preferably 4 or less, and particularly preferably 3 or less. The ratio of the current values ​​in the lower layer (I 300 / I 10 ) refers to the lower layer having a "fatigue load" of 1.6 uA / cm². 2 After applying current for 5 minutes for 12 sets, the current value I after applying current at 5V / μm for 10 seconds was measured. 10 and the current value I after 300 seconds of energization 300 The ratio (I 300 / I 10 ) and can be measured and calculated by the following method for measuring the resistance of the underlayer. The ratio of the current values ​​in the lower layer (I 300 / I 10 If the value is 10.0 or less, charge accumulation at the interface between the pre-support layer and the under-drawn layer can be sufficiently suppressed, and hole injection from the support to the under-drawn layer can be suppressed.

[0023] [Method for measuring the resistance of the underlayer] The ratio of the initial resistance of the underlayer to the current value of the underlayer (I 300 / I 10 The measurement and calculation of ) can be performed, for example, by following the procedure below. Specifically, evaluation is performed using a source meter (Source Meter Model 2410, manufactured by Keithley) in the following order: initial resistance measurement of the undercoat layer, fatigue loading, and resistance measurement after fatigue loading. The undercoat layer to be measured is coated onto an Al substrate, and the Al substrate is cut out along with the undercoat layer in a 20 mm circumferential direction and a 40 mm axial direction to obtain a measurement sample. Au is deposited on the surface of the undercoat layer of the measurement sample in a circular pattern with a diameter of 6.5 mm, with an average thickness of approximately 500 nm.

[0024] [Fatigue load conditions] Fatigue load is measured by applying a constant current (1.6 μA / cm²) from the Al substrate side to the measurement sample after Au deposition. 2 This procedure is performed by repeating the following 12 times, with each set consisting of 5 minutes of the process. The "fatigue load" simulation is designed to reproduce the case where charge accumulation occurs at the interface between the conductive support and the undercoat layer, and to evaluate the electrical properties of the undercoat layer when charge accumulation occurs.

[0025] [Resistance measurement conditions (initial)] The initial resistance measurement of the undercoat layer is performed by applying a constant voltage (5.0V / μm) from the Al substrate side to the sample after Au deposition for 5 minutes, followed by a constant voltage (-5.0V / μm) for 5 minutes. This process is repeated three times to complete one set. Then, as the "initial resistance value," the resistance value at the 10-second mark after applying a constant voltage (5.0V / μm) for 5 minutes in the first set is determined.

[0026] [Resistance measurement conditions (after fatigue)] The resistance measurement conditions (post-fatigue) are the same as those for the resistance measurement conditions (initial), except that a measurement sample subjected to fatigue load is used. Specifically, to measure the fatigue resistance of the undercoat layer, the measurement is performed by applying a fatigue load to the sample after Au deposition, then applying a constant voltage (5.0V / μm) from the Al substrate side for 5 minutes, followed by applying a constant voltage (-5.0V / μm) for 5 minutes. This process constitutes one set, and the measurement is repeated three times. And, "Current value (I 10For the first set, determine the current value after 10 seconds when a constant voltage (5.0V / μm) is applied for 5 minutes. Also, "Current value (I 300 For the first set, a constant voltage (5.0V / μm) is applied for 5 minutes, and the current value at the 300-second mark is determined. [Ratio of current values ​​after fatigue load on the tension layer (I 300 / I 10 ) Calculation] Ratio of current values ​​after fatigue load on the tension layer (I 300 / I 10 The current value I obtained as described above is 300 Current value I 10 The ratio (I 300 / I 10 Calculate ).

[0027] <<Metal oxide particles>> There are no particular limitations on the metal oxide particles, and they can be appropriately selected depending on the purpose. Examples include titanium oxide particles, tin oxide particles, zinc oxide particles, indium oxide particles, antimony oxide particles, and ITO (Indium Tin Oxide) particles. These may be used individually or in combination of two or more. Among these, zinc oxide particles are preferred in terms of volume resistivity (powder resistivity) and dispersibility.

[0028] There are no particular restrictions on the particle size of the metal oxide particles, and they can be appropriately selected depending on the purpose, but it is preferable that the average primary particle size is 500 nm or less. The average primary particle diameter of the metal oxide particles can be determined by calculating the average of the long and short axis values ​​of the metal oxide particles observed at 50,000x magnification or higher using a scanning electron microscope (SEM), and then deriving the average of 10 of these average values.

[0029] There are no particular restrictions on the volume resistivity of the metal oxide particles, and they can be appropriately selected depending on the purpose, but 10 2 Ω·cm~10 11 Ω·cm is preferable. The aforementioned volume resistivity is 10 2If the volume resistivity is Ω·cm or higher, the charge injection suppression function of the underlayer will work, sufficient leakage resistance will be obtained, and abnormalities in image quality such as background staining will be less likely to occur. On the other hand, if the volume resistivity is 10 11 If the value is Ω·cm or less, charge transport from the photosensitive layer to the support is sufficient, and the photo-attenuation does not decrease, making it difficult for the residual potential to rise.

[0030] <<Binding resin>> The binder resin is not particularly limited and can be appropriately selected depending on the purpose. Examples include thermoplastic resins and thermosetting resins. These may be used individually or in combination of two or more types. Among these, a binder resin with high solvent resistance to general organic solvents is preferred, considering that the photosensitive layer is applied on top of the undercoat layer. Examples of highly solvent-resistant binder resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate; alcohol-soluble resins such as copolymerized nylon and methoxymethylated nylon; curable resins that form a three-dimensional network structure, such as polyurethane, melamine resin, phenolic resin, alkyd-melamine resin, and epoxy resin; and butyral resins such as polyvinyl butyral.

[0031] There are no particular restrictions on the content of the binder resin, and it can be appropriately selected depending on the purpose, but it is preferably 10 to 200 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of metal oxide particles.

[0032] <<Compounds containing a salicylic acid skeleton>> The underlying layer can be made even more environmentally stable by containing compounds with a salicylic acid skeleton. The compounds having the salicylic acid skeleton are not particularly limited and can be appropriately selected depending on the purpose. For example, acetylsalicylic acid, 5-acetylsalicylic acid, 3-aminosalicylic acid, 5-acetylsalicyamide, 5-aminosalicylic acid, 4-azidosalicylic acid, benzyl salicylate, 4-tert-butylphenyl salicylate, butyl salicylate, 3,5-di-t-butylsalicylic acid, 2-carboxyphenyl salicylate, 3,5-dinitrosalicylic acid, dithiosalicylic acid, ethyl acetylsalicylate, 2-ethylhexyl salicylate, ethyl 6-methylsalicylate, ethyl salicylate, 5-formylsalicylic acid, 4-(2-hydroxyethoxy)salicylic acid, 2-hydroxyethyl salicylate, isoamyl salicylate, isobutyl salicylate, salicylate Examples include isopropyl salicylate, 3-methoxysalicylic acid, 4-methoxysalicylic acid, 6-methoxysalicylic acid, methyl acetylsalicylate, methyl 5-acetylsalicylate, methyl 5-allyl-3-methoxysalicylate, methyl 5-formylsalicylate, methyl 4-(2-hydroxyethoxy)salicylate, methyl 3-methoxysalicylate, methyl 4-methoxysalicylate, methyl 5-methoxysalicylate, methyl 4-methylsalicylate, methyl 5-methylsalicylate, methyl salicylate, methyl 3-methylsalicylic acid, methyl 4-methylsalicylic acid, methyl 5-methylsalicylic acid, methyl thiosalicylate, 4-nitrophenyl salicylate, 5-nitrosalicylic acid, 4-nitrosalicylic acid, 3-nitrosalicylic acid, 4-octylphenyl salicylate, and phenyl salicylate. These may be used individually or in combination of two or more types.

[0033] The content of the compound having a salicylic acid skeleton is preferably 0.3% to 6% by mass relative to the metal oxide particles, more preferably 1.5% to 4.0% by mass, and even more preferably 1% to 3% by mass. By having a salicylic acid skeleton compound content of 0.3% by mass or more, the functions provided by the salicylic acid derivative can be fully exhibited, and good properties can be obtained. Furthermore, by having a salicylic acid derivative content of 6% by mass or less relative to the zinc oxide particles, it does not inhibit the dispersion of the zinc oxide particles, and sufficient properties can be obtained.

[0034] <<Other ingredients>> The aforementioned undercoat layer may contain the other components mentioned above in order to stabilize electrical properties and image quality. The aforementioned other components are not particularly limited and can be appropriately selected depending on the purpose. Examples include electron transport substances; electron transport pigments such as polycyclic condensation systems and azo systems; silane coupling agents; zirconium chelate compounds; titanium chelate compounds; aluminum chelate compounds; fluorenone compounds; titanium alkoxide compounds; organic titanium compounds; antioxidants, plasticizers, lubricants, ultraviolet absorbers, and leveling agents. These may be used individually or in combination of two or more.

[0035] There are no particular restrictions on the average thickness of the undercoat layer, and it can be appropriately selected depending on the electrical characteristics and lifespan of the electrophotographic photoreceptor to be manufactured, but 3 μm to 35 μm is preferred, and 5 μm to 30 μm is more preferred. If the average thickness is 3 μm or more, charges with opposite polarity to the charging polarity of the electrophotographic photoreceptor surface do not flow from the support into the photosensitive layer, making it less likely for image defects resembling background smudges caused by poor charging properties to occur. On the other hand, if the average thickness is 35 μm or less, defects such as decreased photoattenuation due to increased residual potential and decreased repeatability become less likely to occur. Furthermore, as a method for measuring the average thickness, for example, one can select a number of arbitrary points on the undercoat layer and calculate the average thickness of those points. Preferably, the average thickness of 5 points is used, more preferably 10 points, and even more preferably 20 points. The average thickness of other layers can be calculated in the same manner. Examples of instruments for measuring the average thickness include micrometers.

[0036] <Photosensitive layer> There are no particular restrictions on the photosensitive layer; any known photosensitive layer can be appropriately selected depending on the purpose. There are no particular restrictions on the shape, size, and material of the photosensitive layer; they can be appropriately selected according to the purpose. There are no particular restrictions on the structure of the photosensitive layer, and it can be appropriately selected according to the purpose. It may be a single layer (single-layer photosensitive layer, see Figures 1 and 3), or multiple layers (multilayer photosensitive layer, see Figures 2 and 4) in which a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material are sequentially stacked. Among these, the multilayer photosensitive layer is preferred because it is advantageous in that it can achieve a high level of both electrostatic properties and durability.

[0037] <<Charge Generation Layer>> The charge generation layer is part of the stacked photosensitive layer and has the function of generating electric charge upon exposure. The charge generation layer mainly contains an electric charge generating substance and may also contain other materials as needed.

[0038] -Charge-generating material- Examples of charge-generating materials include inorganic materials and organic materials. These may be used individually or in combination of two or more.

[0039] Examples of inorganic materials include crystalline selenium, amorphous selenium, selenium-tellurium, selenium-tellurium-halogens, selenium-arsenide compounds, and amorphous silicon. Examples of amorphous silicon include silicon in which dangling bonds are terminated with hydrogen or halogen atoms, and silicon doped with boron or phosphorus atoms.

[0040] As organic materials, known materials can be used, such as metallic phthalocyanines like titanyl phthalocyanine and chlorogallium phthalocyanine, metal-free phthalocyanines, azulenium salt pigments, squareric acid methine pigments, symmetric or asymmetric azo pigments having a carbazole skeleton, symmetric or asymmetric azo pigments having a triphenylamine skeleton, symmetric or asymmetric azo pigments having a fluorenone skeleton, and perylene pigments. Among these, metallic phthalocyanines, symmetric or asymmetric azo pigments having a fluorenone skeleton, symmetric or asymmetric azo pigments having a triphenylamine skeleton, and perylene pigments are preferred because they have relatively high quantum efficiency in charge generation.

[0041] -Other materials- Other materials are not particularly limited and can be selected as appropriate depending on the purpose. Examples include binders, antioxidants, plasticizers, lubricants, low-molecular-weight compounds such as UV absorbers, and leveling agents. These may be used individually or in combination of two or more. However, since the sensitivity may deteriorate when low-molecular-weight compounds and leveling agents are used in combination, the combined content of low-molecular-weight compounds and leveling agents is preferably between 0.1 phr and 20 phr, and more preferably between 0.1 phr and 10 phr. Furthermore, the content of the leveling agent is preferably between 0.001 phr and 0.1 phr.

[0042] There are no particular restrictions on the binder resin, and it can be appropriately selected depending on the purpose. Examples include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, polyarylate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, poly-N-vinylcarbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinylpyridine, cellulose resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone. Among these, polyvinyl butyral is preferred. Furthermore, a polymer charge transport material, as described later, can also be used as the binder resin. These can be used individually or in combination of two or more.

[0043] The binder resin content is preferably 0 to 500 parts by mass, and more preferably 10 to 300 parts by mass, per 100 parts by mass of charge generating material.

[0044] There are no particular restrictions on the method for forming the charge generation layer, and it can be appropriately selected depending on the purpose. Examples include vacuum thin film fabrication methods and casting methods from solution dispersion systems.

[0045] Examples of vacuum thin film fabrication methods include vacuum deposition, glow discharge decomposition, ion plating, sputtering, reactive sputtering, and CVD (chemical vapor deposition), all of which enable the successful formation of charge generation layers containing the aforementioned inorganic and organic materials.

[0046] Casting methods from solution dispersions include, for example, dispersing the aforementioned inorganic or organic materials with a binder resin using a solvent if necessary, and then applying the resulting dispersion after appropriately diluting it to create a charge generation layer. There are no particular restrictions on the solvent, and it can be appropriately selected depending on the purpose. Examples include isopropanol, acetone, methyl ethyl ketone (2-butanone), tetrahydrofuran, cyclohexanone, dioxane, dichloroethane, and butanone. Among these, methyl ethyl ketone, tetrahydrofuran, and cyclohexanone are preferred because they have a low environmental impact. These can be used individually or in combination of two or more.

[0047] There are no particular restrictions on the method of dispersion; it can be appropriately selected depending on the purpose. Examples include using a ball mill, attritor, or sand mill.

[0048] There are no particular restrictions on the method of applying the dispersion, and it can be appropriately selected depending on the purpose. Examples include immersion coating, spray coating, bead coating, nozzle coating, spinner coating, and ring coating.

[0049] There are no particular restrictions on the average thickness of the charge generation layer, and it can be appropriately selected depending on the purpose, but it is preferably 0.01 μm or less and 5 μm or more, and more preferably 0.05 μm or more and 2 μm or less. When the average thickness of the charge generation layer is within the more preferable range, it is advantageous because it provides a good balance between the benefits of thicker films, such as reduced residual potential and increased sensitivity, and the disadvantages of degraded charge retention and space charge formation.

[0050] <<Charge transport layer>> The charge transport layer is a layer that injects and transports the charge generated in the charge generation layer, and is responsible for neutralizing the surface charge of the photoreceptor provided by the charging process. It is part of the multilayer photosensitive layer. The charge transport layer contains a charge transport material, a binder, and, if necessary, other materials.

[0051] There are no particular restrictions on the charge transport material, and it can be appropriately selected depending on the purpose. Examples include low molecular weight electron transport materials, hole transport materials, and high molecular weight charge transport materials. Specifically, examples of electron transport materials include electron-accepting materials such as asymmetric diphenoquinone derivatives, fluorene derivatives, and naphthalimide derivatives. These may be used individually or in combination of two or more.

[0052] There are no particular restrictions on the hole transport substance, and it can be appropriately selected depending on the purpose. Examples include poly(N-vinylcarbazole) and its derivatives, poly(γ-carbazolylethylglutamate) and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, aminobiphenyl derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazoline derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. These may be used individually or in combination of two or more.

[0053] Examples of electron-donating substances include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, butadiene derivatives, 9-(p-diethylaminostyrylanthracene), 1,1-bis-(4-dibenzylaminophenyl)propane, styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives. These may be used individually or in combination of two or more.

[0054] Examples of polymeric charge transport materials include polymers having a carbazole ring, such as poly-N-vinylcarbazole, polymers having a hydrazone structure, polysilylene polymers, and aromatic polycarbonates. These may be used individually or in combination of two or more.

[0055] Compared to low-molecular-weight charge transport materials, polymer charge transport materials have the advantage of suppressing curing defects in the protective layer because, when a protective layer is laminated on top of the charge transport layer, there is less leakage of components constituting the charge transport layer into the protective layer. Furthermore, due to the high molecular weight of the charge transport material, it also has the advantage of having excellent heat resistance, resulting in less degradation due to curing heat when forming the protective layer.

[0056] Examples of binder resins for the charge transport layer include thermoplastic or thermosetting resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethylcellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyltoluene, poly(N-vinylcarbazole), acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenolic resin, and alkyd resin. Among these, polycarbonate and polyarylate are preferred.

[0057] The charge transport substance content is preferably 20 to 300 parts by mass, and more preferably 40 to 150 parts by mass, per 100 parts by mass of the binder resin.

[0058] A charge transport layer can be formed by preparing a coating solution for forming a charge transport layer by dissolving or dispersing a mixture or copolymer mainly composed of a charge transport component and a binder component in a suitable solvent, and then applying and drying this solution. Coating methods include immersion, spray coating, ring coating, roll coating, gravure coating, nozzle coating, and screen printing.

[0059] Examples of dispersion solvents that can be used when preparing coating solutions for charge transport layers include tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, and acetone. These may be used individually or in combination of two or more.

[0060] The average thickness of the charge transport layer is typically 50 μm or less, and is preferably 25 μm or less from the viewpoint of resolution and responsiveness. The lower limit of the average thickness of the charge transport layer depends on the system used (e.g., charging potential), but is preferably 5 μm or more.

[0061] Furthermore, if necessary, low-molecular-weight compounds such as antioxidants, plasticizers, lubricants, and UV absorbers, as well as leveling agents, may be added to the charge transport layer. These may be used individually or in combination of two or more.

[0062] Next, we will discuss the case where the photosensitive layer is a single-layer photosensitive layer (see Figures 1 and 3). In a single-layer photosensitive layer, the same materials (charge generating material, charge transporting material, binder resin) used in the aforementioned multilayer photosensitive layer (charge generating layer, charge transporting layer) can be used. Furthermore, in the case of a single-layer photosensitive layer, it is preferable to use the following electron transport materials in combination as charge transport materials to increase sensitivity.

[0063] Examples of electron-transporting materials include electron-accepting substances such as chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4-one, 1,3,7-trinitrodibenzothiophene-5,5-dioxide, and benzoquinone derivatives. In a single-layer photosensitive layer, the content of the charge-generating material is preferably 0.1% to 30% by mass, and more preferably 0.5% to 5% by mass, relative to the entire photosensitive layer. A low concentration of the charge-generating material tends to reduce the sensitivity of the photoreceptor, while a high concentration tends to reduce the chargeability and film strength.

[0064] A single-layer photosensitive layer can be formed by dissolving or dispersing a charge-generating material, a charge-transporting material, and a binder resin in a suitable solvent, then coating and drying the mixture. Plasticizers, leveling agents, antioxidants, etc., may also be added as needed.

[0065] The average thickness of the photosensitive layer is preferably 50 μm or less, and more preferably 25 μm or less from the viewpoint of resolution and responsiveness. The lower limit varies depending on the system used (especially the charging potential, etc.), but is preferably 5 μm or more.

[0066] <Other layers> Other layers are not particularly restricted and can be selected as appropriate depending on the purpose, but examples include surface layers. A surface layer may be provided on top of the photosensitive layer for the purpose of protecting the photosensitive layer (see Figures 3 and 4).

[0067] The surface layer is preferably a layer containing a crosslinkable resin, a layer containing a filler, etc., in order to achieve high abrasion resistance. As for the layer containing the crosslinkable resin, it is preferable to cure it using a radical polymerizable monomer and a radical polymerizable compound having a charge transport structure to form a three-dimensional network structure, because this yields a surface layer with a high degree of crosslinking and high hardness.

[0068] Furthermore, the surface layer preferably contains a filler layer to improve the mechanical durability of the surface layer. In particular, when the aforementioned crosslinkable resin is included, the inclusion of a filler is preferable because it increases abrasion resistance and enables longer-term use of the photoreceptor. There are no particular restrictions on the filler, but examples include titanium oxide, tin oxide, zinc oxide, zirconium oxide, indium oxide, antimony oxide, boron nitride, silicon nitride, calcium oxide, barium sulfate, ITO, silicon oxide, colloidal silica, and aluminum oxide. Among these, aluminum oxide, titanium oxide, silicon oxide, and tin oxide are preferred from the viewpoint of the electrical properties of the surface layer. From the viewpoint of light transmittance and abrasion resistance of the surface layer, the average primary particle size of the filler is preferably 0.01 μm to 0.5 μm. If the average primary particle size of the filler is 0.01 μm or larger, sufficient abrasion resistance and dispersibility can be obtained. On the other hand, if the average primary particle size of the filler is 0.5 μm or smaller, the surface roughness of the surface layer does not become too large, and the progression of wear of the blade cleaning member described later can be reduced. Therefore, this is advantageous in that it can prevent adverse effects such as toner cleaning failures and accelerated sedimentation of the filler in the dispersion liquid depending on the specific gravity of the filler particles.

[0069] The filler material content in the surface layer is preferably 50% by mass or less, and more preferably 30% by mass or less, relative to the total solid content. While a higher filler material content in the surface layer improves wear resistance, a content of 50% by mass or less is advantageous because it avoids adverse effects such as an increase in residual potential or scattering of the light written on the surface layer, leading to a decrease in transmittance.

[0070] (Method of manufacturing a photosensitive material) The present invention's method for manufacturing a photoreceptor includes a base layer formation step, and further, if necessary, other steps such as a conductive support formation step, a photoreceptor layer formation step, and a surface layer formation step.

[0071] <Underlayer Formation Process> The aforementioned undercoat formation step is a step of forming an undercoat by applying a coating liquid containing metal oxide particles and water. The coating solution preferably contains at least metal oxide particles and water, a binder resin, a compound having a salicylic acid skeleton, and a solvent, and may further contain other components as needed. In the coating solution, the metal oxide particles, binder resin, compound having a salicylic acid skeleton, and other components can be appropriately selected from those described in the section on each component of the photoreceptor of the present invention. Preferably, the metal oxide particles are zinc oxide particles.

[0072] -water- By including water during the dispersion of the undercoat coating liquid, the resistance of the undercoat can be further reduced. The water content in the undercoat coating liquid is preferably 1.0% to 5.0% by mass, more preferably 2.0% to 5.0% by mass, even more preferably 2.4% to 4.5% by mass, and particularly preferably 2.8% to 4.5% by mass, relative to the metal oxide particles. A water content of 1.0% by mass or more allows the functions of water to be fully utilized, resulting in good properties. Furthermore, a water content of 5.0% by mass or less relative to the metal oxide particles does not hinder the dispersion of the metal oxide particles, thus ensuring sufficient properties.

[0073] There are no particular restrictions on the method for forming the aforementioned undercoat layer, and it can be formed using a suitable solvent and coating method. The timing for adding the binder resin to the undercoat coating liquid used in the coating method may be before the dispersion of the metal oxide particles or after the dispersion of the metal oxide particles.

[0074] The aforementioned solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples include alcohol-based solvents such as methanol, ethanol, propanol, and butanol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as ethyl acetate and butyl acetate; ether-based solvents such as tetrahydrofuran, dioxane, and propyl ether; halogen-based solvents such as dichloromethane, dichloroethane, trichloroethane, and chlorobenzene; aromatic solvents such as benzene, toluene, and xylene; and cellosolve-based solvents such as methyl cellosolve, ethyl cellosolve, and cellosolve acetate. These may be used individually or in combination of two or more.

[0075] There are no particular restrictions on the method for dispersing metal oxide particles in the aforementioned undercoating liquid, and it can be appropriately selected depending on the purpose. Examples include dispersion methods using a ball mill, sand mill, vibration mill, KD mill, three-roll mill, attritor, pressure homogenizer, ultrasonic dispersion, etc.

[0076] There are no particular restrictions on the coating method, and it can be appropriately selected depending on the viscosity of the coating liquid, the average thickness of the desired undercoat layer, etc. Examples include immersion coating, spray coating, bead coating, and ring coating. After coating with the aforementioned undercoating liquid, the material may be heated and dried in an oven or the like as needed. There are no particular restrictions on the drying temperature of the undercoating layer, and it can be appropriately selected depending on the type of solvent contained in the undercoating liquid, but 80°C to 200°C is preferred, and 100°C to 150°C is more preferred.

[0077] <Other processes> The method for manufacturing a photoreceptor according to the present invention may include other steps such as a conductive support formation step, a photosensitive layer formation step, and a surface layer formation step. There are no particular restrictions on the conductive support formation step, the photosensitive layer formation step, and the surface layer formation step; known methods can be appropriately selected depending on the purpose.

[0078] (Image forming apparatus and image forming method) The image forming apparatus of the present invention comprises at least the photoreceptor of the present invention, a charging means, an exposure means, a developing means, and a transfer means, and further comprises other members as necessary. The image forming method of the present invention comprises at least a charging step of charging the surface of the photoreceptor of the present invention, an exposure step, a development step, and a transfer step, and further includes other steps as necessary.

[0079] The charging means is a means for charging the surface of the photoreceptor. The charging step is a step for charging the surface of the photoreceptor, and can be suitably carried out by the charging means. The exposure means is a means for exposing the surface of the photoreceptor, which has been charged by the charging means, to form an electrostatic latent image. The exposure step is a step for exposing the surface of the photoreceptor, which has been charged by the charging means, to form an electrostatic latent image, and can be suitably carried out by the exposure means. The developing means is a means for developing the electrostatic latent image into a visible image using toner. The developing process is a process for developing the electrostatic latent image into a visible image using toner, and can be suitably carried out by the developing means. The transfer means is a means for transferring the visible image to a recording medium. The transfer step is a step of transferring the visible image to a recording medium, which can be suitably carried out by the transfer means.

[0080] The image forming method described above uses the photoreceptor of the present invention and, for example, after the photoreceptor undergoes at least the processes of charging, image exposure, and development, the toner image is transferred to an image holder (transfer paper), and further fixing and cleaning of the photoreceptor surface are performed as necessary. Furthermore, the image forming apparatus uses the photoreceptor of the present invention and, for example, has means for transferring a toner image to an image holder (transfer paper) after the photoreceptor has undergone at least charging, image exposure, and development, and also has fixing means and cleaning means for the surface of the photoreceptor as needed. The image forming apparatus may have a plurality of image forming elements, each consisting of at least a charging means, an exposure means, a developing means, a transfer means, and an electrophotographic photoreceptor, and the plurality of image forming elements may be arranged in a sequence.

[0081] Figure 5 is a schematic diagram showing an example of the image forming apparatus of the present invention. A charging charger (3) is used as a charging means for charging the photoreceptor (1). Known methods can be used as this charging means, such as a Corotron device, a Scorotron device, a solid discharge element, a needle electrode device, a roller charging device, or a conductive brush device. In particular, this embodiment is especially effective when using a charging means that generates proximity discharge from the charging means, which can cause decomposition of the photoreceptor composition, such as a contact charging method or a non-contact proximity charging method. The aforementioned contact charging method is a charging method in which a charging roller, charging brush, charging blade, etc., directly contacts the photosensitive material. The aforementioned proximity charging method is, for example, a type in which a charging roller is positioned in close proximity to the photoreceptor surface in a non-contact state, such that there is a gap of 200 μm or less between the charging means and the photoreceptor surface. If this gap is too large, the charging tends to become unstable, and if it is too small, the surface of the charging member may become contaminated if there is toner remaining on the photoreceptor. Therefore, the gap is preferably 10 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0082] Next, an image exposure unit (5) is used as an exposure means for forming an electrostatic latent image on a charged photoreceptor (1). Any type of light-emitting material can be used as the light source, including fluorescent lamps, tungsten lamps, halogen lamps, mercury lamps, sodium lamps, light-emitting diodes (LEDs), semiconductor lasers (LDs), and electroluminescent devices (ELs). Furthermore, various filters such as sharp-cut filters, band-pass filters, near-infrared cut filters, dichroic filters, interference filters, and color temperature conversion filters can be used to irradiate only light in the desired wavelength range.

[0083] Next, a developing unit (6) is used as a developing means to visualize the electrostatic latent image formed on the photoreceptor (1). Developing methods include a one-component developing method using dry toner, a two-component developing method, and a wet developing method using wet toner. When a photoreceptor is negatively charged and exposed to light, a positive electrostatic latent image is formed on the surface of the photoreceptor in the case of inversion development. Developing this with a negative polarity toner (electrodetector particles) yields a positive image, while developing it with a positive polarity toner yields a negative image. Furthermore, when a photoreceptor is negatively charged and exposed to light, a negative electrostatic latent image is formed on the surface of the photoreceptor during normal development. Developing this with a positive polarity toner (electrodetector particles) yields a positive image, while developing it with a negative polarity toner yields a negative image.

[0084] Next, a transfer charger (10) is used as a transfer means for transferring the toner image visualized on the photoreceptor onto the transfer body (9). A pre-transfer charger (7) may also be used to improve the transfer process. These transfer means can include mechanical transfer methods such as electrostatic transfer using a transfer charger and bias roller, adhesive transfer, and pressure transfer, as well as magnetic transfer. The aforementioned charging means can be used for electrostatic transfer.

[0085] Next, a separation charger (11) and separation claws (12) are used as means to separate the transfer body (9) from the photoreceptor (1). Other separation means include electrostatic adsorption induction separation, side-end belt separation, tip grip transport, and curvature separation. The separation charger (11) can be the same type as the charging means described above.

[0086] Next, a fur brush (14) and a cleaning blade (15) are used to clean the toner remaining on the photoreceptor after transfer. Furthermore, a pre-cleaning charger (13) may be used to make cleaning more efficient. Other cleaning methods include the web method and the magnetic brush method, and each method may be used individually or in combination.

[0087] Next, a static elimination means is used to remove the latent image on the photoreceptor as needed. A static elimination lamp (2) and a static elimination charger can be used as the static elimination means, and the exposure light source and charging means can be used, respectively. In addition, known processes such as document scanning, paper feeding, fixing, and paper ejection, which are not in close proximity to the photoreceptor, can be used.

[0088] The present invention relates to an image forming method and an image forming apparatus that uses an electrophotographic photoreceptor according to the present invention as such an image forming means. This image forming means may be fixedly incorporated into a copier, facsimile, or printer, or it may be incorporated into such devices in the form of a process cartridge and be detachable.

[0089] (Process cartridge) The process cartridge of the present invention comprises the photoreceptor of the present invention, and at least one means selected from charging means, exposure means, developing means, and transfer means, and further comprises other members as necessary. Preferably, the process cartridge is detachable from the main body of the image forming apparatus. In the process cartridge, the charging means, exposure means, developing means, and transfer means can be appropriately selected from those described in the image forming apparatus of the present invention.

[0090] An example of the process cartridge of the present invention is shown in Figure 6. A process cartridge for an image forming apparatus is a device (component) that incorporates a photoreceptor (101) and also includes at least one of the following: a charging means (102), a developing means (104), a transfer means (106), a cleaning means (107), and a static elimination means (not shown), and is detachable from the main body of the image forming apparatus. The image formation process using the apparatus illustrated in Figure 5 is as follows: The photoreceptor (101) rotates in the direction of the arrow, and is charged by the charging means (102) and exposed by the exposure means (103), forming an electrostatic latent image on its surface corresponding to the exposed image. This electrostatic latent image is developed with toner by the developing means (104), and the developed toner is transferred to a transfer body (105) by the transfer means (106) and printed out. Next, the surface of the photoreceptor after image transfer is cleaned by the cleaning means (107), and then de-staticized by the de-static means (not shown), and the above operations are repeated again. [Examples]

[0091] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples. Note that "parts" all refer to parts by mass.

[0092] (Example 1) <Manufacturing of photoreceptors> <<Formation of the underlayer>> An aluminum conductive support (outer diameter: 60 mm) was coated with the following undercoating solution using an immersion method, so that the average thickness after drying at 150°C for 30 minutes was 4 μm, thereby forming an undercoating layer. The undercoat coating liquid was prepared by mixing the following materials and stirring with 0.5 mm diameter zirconia beads and a vibrating mill at 1,500 rpm for 6 hours.

[0093] [Undercoat coating liquid] • Metal oxide particles: Zinc oxide particles (MZ-200, manufactured by Teika Co., Ltd.); 350 units • Compounds containing a salicylic acid skeleton: 3,5-di-t-butylsalicylic acid (TCI-D1947, manufactured by Tokyo Chemical Industry Co., Ltd.); 1.5 parts • Binding resin: Blocked isocyanate (Sumijule® 3175, solid content concentration 75% by mass, manufactured by Sumika Bayer Urethane Co., Ltd.); 60 parts 225 parts of a 20% solids solution obtained by dissolving butyral resin (BM-1, manufactured by Sekisui Chemical Co., Ltd.) in 2-butanone; • Solvent: 2-butanone; 365 parts ·Wed; 4.97 copies

[0094] <<Formation of charge generation layer>> The formed undercoat was immersed in the following charge-generating layer coating solution and heated and dried at 90°C for 20 minutes to form a charge-generating layer with an average thickness of 0.2 μm. The charge-generating layer coating solution was prepared by mixing the following materials and stirring for 8 hours using 1 mm diameter glass beads and a bead mill.

[0095] [Charge-generating layer coating liquid] • Titanylphthalocyanine; 8 parts • Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., BX-1); 5 parts 2-Butanone; 400 copies

[0096] <<Formation of a charge transport layer>> The resulting charge generation layer was immersion coated with the charge transport layer coating solution described below, and then heated and dried at 120°C for 20 minutes to form a charge transport layer with an average thickness of 25 μm. The charge transport layer coating solution was prepared by mixing the following materials and stirring with a stirrer for 3 hours until all materials were dissolved.

[0097] [Charge transport layer coating liquid] Z-type polycarbonate (manufactured by Teijin Chemicals Ltd., TS-2050); 10 parts Charge transport material shown in the following structural formula (1); 10 parts, Terorahydrofuran; 100 copies, [ka]

[0098] <<Formation of the surface layer and fabrication of the photoreceptor>> The resulting charge transport layer was spray-coated using the surface layer coating liquid described below, and then illuminated with a metal halide lamp (irradiation intensity: 500 mW / cm²). 2 Light irradiation was performed under the condition of irradiation time: 160 seconds. Furthermore, the photoreceptor of Example 1 was obtained by drying at 130°C for 30 minutes to form a 4.0 μm surface layer. The surface coating solution was prepared by mixing the following materials and stirring with a stirrer for 3 hours until all materials were dissolved.

[0099] [Surface coating liquid] • Radical polymerizable monomer (trimethylolpropaneacrylate) (manufactured by Nippon Kayaku Co., Ltd., KAYARAD TMPTA); 10 parts • Compound with the following structural formula (2); 10 parts • Photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals Co., Ltd.); 1 part Tetrahydrofuran; 100 copies, [ka]

[0100] (Example 2) The photoreceptor of Example 2 was obtained by the same method as in Example 1, except that the amount of water in the undercoat coating liquid was changed from 4.97 parts to 6.97 parts (the ratio of parts by mass of water to parts by mass of metal oxide particles was changed from 1.42% by mass to 1.99% by mass).

[0101] (Example 3) The photoreceptor of Example 3 was obtained by the same method as in Example 1, except that the amount of water in the undercoat coating solution was changed to 8.44 parts (the ratio of parts by mass of water to parts by mass of metal oxide particles was changed to 2.41% by mass).

[0102] (Example 4) The photoreceptor of Example 4 was obtained by the same method as in Example 1, except that the amount of water in the undercoat coating solution was changed to 9.94 parts (the ratio of parts by mass of water to parts by mass of metal oxide particles was changed to 2.84% by mass).

[0103] (Example 5) The photoreceptor of Example 5 was obtained by the same method as in Example 1, except that the amount of water in the undercoat coating solution was changed to 14.91 parts (the ratio of parts by mass of water to parts by mass of metal oxide particles was changed to 4.26% by mass).

[0104] (Comparative Example 1) A photoreceptor for Comparative Example 1 was obtained using the same method as in Example 1, except that water was not added to the undercoat coating solution.

[0105] (Comparative Example 2) In Comparative Example 2, a photoreceptor was obtained using the same method as in Example 1, except that water was not added to the undercoat coating solution and the dispersion time of the undercoat coating solution was changed from 6 hours to 5 hours.

[0106] (Comparative Example 3) In Comparative Example 3, a photoreceptor was obtained using the same method as in Example 1, except that water was not added to the undercoat coating solution and the dispersion time of the undercoat coating solution was changed from 6 hours to 7 hours.

[0107] (Comparative Example 4) In Comparative Example 4, a photoreceptor was obtained using the same method as in Example 1, except that water was not added to the undercoat coating solution and the dispersion time of the undercoat coating solution was changed from 6 hours to 8 hours.

[0108] <Rating> The electrical characteristics and image quality of the photoreceptors obtained in Examples 1-5 and Comparative Examples 1-4 were evaluated according to the following procedure. The results are shown in Table 1.

[0109] <<Electrical Characteristics: Measurement of Initial Resistance of the Underlay Layer>> The initial resistance of the underlayer was measured using a source meter (Source Meter Model 2410, manufactured by Keithley). An undercoat layer to be measured was coated onto an Al substrate as a conductive support. The Al substrate was then cut out along with the undercoat layer in a circumferential direction of 20 mm and in the axial direction of 40 mm to obtain a measurement sample. Au was deposited on the surface of the undercoat layer of the measurement sample in a circular pattern with a diameter of 6.5 mm, with an average thickness of approximately 500 nm. Measurements were performed by applying a constant voltage (5.0V / μm) from the Al substrate side to the sample after Au deposition for 5 minutes, followed by a constant voltage (-5.0V / μm) for 5 minutes. This process was repeated three times, with each set being considered one measurement. The resistance value at the 10-second mark after applying the constant voltage (5.0V / μm) for 5 minutes in the first set was determined as the "initial resistance value".

[0110] <<Electrical characteristics: Ratio of current values ​​after fatigue load on the lower layer (I 300 / I 10 ) Measurement >> [Fatigue load conditions] Fatigue load is applied to the measurement sample after Au deposition by applying a constant current (1.6 μA / cm²) from the Al substrate side. 2 The procedure was performed by repeating the following 12 times, with each set consisting of 5 minutes of the action. [Resistance measurement conditions (after fatigue)] The resistance measurement conditions (after fatigue) were the same as those for the initial resistance measurement conditions, except that the measurement sample subjected to fatigue load was used. Specifically, for measuring the fatigue resistance of the underlayer, the measurement was performed by applying a fatigue load to the measurement sample after Au deposition, then applying a constant voltage (5.0V / μm) from the Al substrate side for 5 minutes, followed by applying a constant voltage (-5.0V / μm) for 5 minutes. This process constituted one set, and the measurement was repeated three times. Then, the current value at the 10-second mark when a constant voltage (5.0V / μm) is applied for 5 minutes in the first set is called the "current value (I 10 ) was requested as such. Furthermore, the current value at the 300-second mark when a constant voltage (5.0V / μm) is applied for 5 minutes in the first set is called the "current value (I 300 ) was requested as such. [Ratio of current values ​​(I 300 / I 10 ) Calculation] Ratio of current values ​​after fatigue load on the tension layer (I 300 / I 10 The current value I obtained as described above is 300 Current value I 10 The ratio (I 300 / I 10 ) was calculated.

[0111] <<Image Quality: Photoreceptor degradation test and background contamination evaluation>> -Evaluation device- A modified digital copier (ProC900, manufactured by Ricoh Co., Ltd.) was used, and a scorotron-type charging element (discharge wire was a tungsten-molybdenum alloy with gold plating and a diameter of 50 μm) was used as the charging element. In addition, a 780 nm laser diode light (LD light) was used as the image exposure light source (image writing by polygon mirror, resolution 1,200 dpi). Development was performed using two-component development with black toner, a transfer belt was used as the transfer element, and an anti-static lamp was used for static elimination.

[0112] <<<Photoreceptor degradation test>>> A degradation test of the photoreceptor was conducted by printing a total of 500,000 sheets using a chart with a 5% writing rate (where, on average, 5% of the image area of ​​an A4 sheet is covered by text). Under high temperature and high humidity conditions (HH) at 27°C and 80% RH, image evaluation (ground staining) after the degradation test was performed using the evaluation image shown in Figure 7A. Figure 7A shows the evaluation image (a) used for evaluating the image quality of the example, and Figure 7B shows the evaluation image used for evaluating the image quality of the example when afterimage occurs (b). In Figure 7A, p indicates the photoreceptor period. In Figure 7A, the solid area in the first photoreceptor cycle p does not appear as an afterimage in the next photoreceptor cycle, but in Figure 7B, the solid area exists as an afterimage in the next photoreceptor cycle and is printed in the gray area.

[0113] <<<Image evaluation (ground stains)>>> Five consecutive prints of a completely white background image were produced using gloss-coated paper. The number of visible background stains was counted at 10 arbitrary 8mm x 11mm viewing points on the printed gloss-coated paper, and the average was calculated. A rating of "△" indicates that the stain is within a usable range. [Evaluation Results] ◎: The average number of stains on the ground is between 0 and 10. ○: The average number of stains on the ground is between 10 and 100. △: The average number of stains on the surface is between 100 and 200. ×: The average number of stains on the ground is 200 or more.

[0114] [Table 1]

[0115] The results from the examples showed that the photoreceptors of Examples 1-5 could obtain sufficiently stable electrical characteristics and image quality even after environmental fluctuations from room temperature to high temperature and high humidity, and after rigorous degradation testing under long-term high temperature and high humidity conditions. In particular, it was found that even better electrical characteristics and image quality could be obtained when the initial resistance of the undercoat layer was 5.0 GΩ·cm or less, as in Examples 3-5. On the other hand, in cases where the undercoat coating liquid does not contain water, as in conventional methods (Comparative Examples 1-4), it was found that both the electrical properties and image quality were inferior due to the effects of environmental fluctuations and charge accumulation caused by fatigue load on the undercoat.

[0116] Examples of the present invention are as follows: <1> A photoreceptor having an undercoat layer and a photosensitive layer in that order on a conductive support, The aforementioned undercoat contains metal oxide particles, The initial resistance of the aforementioned underlayer is 6.0 GΩ·cm or less. In the aforementioned lower layer, 1.6 uA / cm 2 After applying current for 5 minutes for 12 sets, the current value I after applying current at 5V / μm for 10 seconds was measured. 10 and the current value I after 300 seconds of energization 300 The ratio (I 300 / I 10 This photoreceptor is characterized by having a value of 10 or less. <2> The initial resistance of the aforementioned underlayer is 5.0 GΩ·cm or less. <1> This is the photosensitive material described in [reference]. <3> The metal oxide particles are zinc oxide particles. <1> from <2> It is a photoreceptor as described in any of the following. <4> The aforementioned undercoat further contains a compound having a salicylic acid skeleton. <1> from <3> It is a photoreceptor as described in any of the following. <5> The aforementioned <1> from <4> A photoreceptor as described in any of the following, A charging means for charging the surface of the photoreceptor, An exposure means for exposing the surface of the photoreceptor, which has been charged by the charging means, to form an electrostatic latent image, A developing means for developing the electrostatic latent image into a visible image using toner, The image forming apparatus is characterized by having at least a transfer means for transferring the visible image onto a recording medium. <5> The aforementioned <1> from <4> A photoreceptor as described in any of the following, The process cartridge is characterized by having at least one means selected from charging means for charging the surface of the photoreceptor, exposure means for exposing the surface of the photoreceptor charged by the charging means to form an electrostatic latent image, developing means for developing the electrostatic latent image into a visible image with toner, and transfer means for transferring the visible image to a recording medium. <7> A method for manufacturing a photoreceptor having an undercoat layer and a photosensitive layer on a conductive support, The method for manufacturing a photoreceptor is characterized by including a step of forming an undercoat layer by applying a coating liquid containing metal oxide particles and water to form an undercoat layer. <8> The water content is 2.0% by mass or more and 5.0% by mass or less relative to the metal oxide particles. <7> This is a method for manufacturing a photoreceptor as described above. <9> The metal oxide particles are zinc oxide particles. <7> from <8> This is a method for manufacturing a photoreceptor as described in any of the above. <10> The coating solution further contains a compound having a salicylic acid skeleton. <7> from <9> This is a method for manufacturing a photoreceptor as described in any of the above.

[0117] The aforementioned <1> from <4> A photoreceptor as described in any of the above <5> The image forming apparatus described above, <6> The process cartridge described above, and the <7> from <10> A method for manufacturing a photoreceptor described in any of the above can solve the aforementioned problems of the conventional method and achieve the objective of the present invention. [Prior art documents] [Patent Documents]

[0118] [Patent Document 1] Japanese Patent Application Publication No. 08-166679 [Patent Document 2] Japanese Patent Application Publication No. 11-133649 [Patent Document 3] Japanese Patent Publication No. 2012-058597 [Patent Document 4] Japanese Patent Publication No. 2006-030700 [Explanation of Symbols]

[0119] 1 photoreceptor 2 Static elimination means 3. Charging means 5. Exposure means 6. Developing means 7. Pre-transfer charger 9. Recording media 10 Transfer means 11 Separation Charger 12 Separation claw 13. Charger before cleaning 14. Fur Brush 15 Cleaning Blades 31 Support 32 Lower layer 33 Single-layer photosensitive layer 35 Charge generation layer 37 Charge transport layer 39 Surface layer 101 Photoreceptor 102 Charging means 104 Developing means 105 Recording media 106 Transfer means 107 Cleaning methods

Claims

1. A photoreceptor having an undercoat layer and a photosensitive layer in that order on a conductive support, The aforementioned undercoat contains zinc oxide particles, The average thickness of the aforementioned undercoat layer is 3 μm or more and 5 μm or less. The initial resistance of the aforementioned underlayer is 0.1 GΩ·cm or more and 5.0 GΩ·cm or less. In the aforementioned lower layer, 1.6 uA / cm ２ After applying current for 5 minutes for 12 sets, the current value I after applying current at 5V / μm for 10 seconds was measured. １０ and the current value I after 300 seconds of energization ３００ The ratio (I ３００ / I １０ A photoreceptor characterized in that the ratio of ) is 5 or less.

2. The photoreceptor according to claim 1, wherein the undercoat further contains a compound having a salicylic acid skeleton.

3. A photoreceptor according to claim 1 or 2, A charging means for charging the surface of the photoreceptor, An exposure means for exposing the surface of the photoreceptor, which has been charged by the charging means, to form an electrostatic latent image, A developing means for developing the electrostatic latent image into a visible image using toner, An image forming apparatus characterized by having at least a transfer means for transferring the visible image onto a recording medium.

4. A photoreceptor according to claim 1 or 2, A process cartridge characterized by having at least one means selected from charging means for charging the surface of the photoreceptor, exposure means for exposing the surface of the photoreceptor charged by the charging means to form an electrostatic latent image, developing means for developing the electrostatic latent image into a visible image with toner, and transfer means for transferring the visible image to a recording medium.

5. A method for manufacturing a photoreceptor according to claim 1 or 2, A method for manufacturing a photoreceptor, characterized by including a step of forming an undercoat layer by applying a coating solution containing zinc oxide particles and water to form the undercoat layer having an average thickness of 3 μm or more and 5 μm or less.

6. The method for producing a photoreceptor according to claim 5, wherein the water content is 2.0% by mass or more and 5.0% by mass or less with respect to the zinc oxide particles.

7. The method for producing a photoreceptor according to claim 5, wherein the coating solution further contains a compound having a salicylic acid skeleton.

Images