JP7500673B2 - Electrophotographic photoreceptor, process cartridge and electrophotographic device - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor, a process cartridge having the electrophotographic photoreceptor, and an electrophotographic device having the electrophotographic photoreceptor.

Electrophotographic photoreceptors that are widely used in electrophotographic devices contain organic photoconductive substances that act as charge generating substances. In recent years, there has been a demand for improved mechanical durability, i.e., wear resistance, of electrophotographic photoreceptors in order to extend the life of electrophotographic photoreceptors and improve image quality during repeated use.

On the other hand, when the wear resistance of the electrophotographic photoreceptor is improved, discharge products and moisture generated by the discharge that occurs between the photoreceptor and the charging member during the charging process remain on the surface of the electrophotographic photoreceptor. These discharge products and moisture can cause the electrostatic latent image formed on the electrophotographic photoreceptor to collapse, resulting in a phenomenon called image flow, in which the desired electrostatic latent image collapses on the output image on paper, etc.

Discharge on the surface of the electrophotographic photoreceptor generates oxidizing gases such as ozone and nitrogen oxides, which deteriorate the materials used in the surface layer of the electrophotographic photoreceptor and generate discharge products. In addition, the surface of the electrophotographic photoreceptor becomes less resistive due to the adsorption of moisture. These factors are thought to be the cause of image deletion.
As the wear resistance of the surface of the electrophotographic photosensitive member increases, it becomes more difficult to remove substances that cause image deletion, such as the discharge products and moisture, and image deletion becomes more likely to occur.

As a technique for improving image deletion, there is a method in which conductive particles are contained in the surface layer of the electrophotographic photosensitive member to control the volume resistivity of the surface layer of the electrophotographic photosensitive member.
A dark potential is formed on the surface of the electrophotographic photoreceptor by applying a voltage from a charging member in a charging process. It is considered that the charging for forming this dark potential is performed by two types of processes. One is a process in which charging of the surface of the electrophotographic photoreceptor progresses when an air layer between the charging member and the surface of the electrophotographic photoreceptor is broken down according to Paschen's law. In the other process, when the contact potential between the electrophotographic photoreceptor and the charging member is sufficiently small, charging occurs by injection charging in which charges are injected from the charging member into the surface of the electrophotographic photoreceptor without discharging due to the applied voltage.
By controlling the volume resistivity by including conductive particles in the surface layer, the proportion of charging due to the injection charging process from the charging member to the electrophotographic photosensitive member in the charging step can be increased. In other words, the injection charging property of the electrophotographic photosensitive member can be increased, thereby suppressing discharge.

Patent Document 1 discloses a technology in which a component obtained by reacting a curable compound and anatase-type titanium oxide containing niobium atoms are contained in the protective layer (surface layer) of an electrophotographic photoreceptor. Patent Document 1 describes that this technology improves the cleaning performance of an electrophotographic photoreceptor when it is used for a long period of time.

Patent Document 2 also discloses a technology for incorporating N-type semiconductor particles such as tin oxide, titanium oxide, zinc oxide, and indium tin oxide into the surface protection layer (surface layer) of an electrostatic latent image carrier (electrophotographic photoreceptor). Patent Document 2 proposes that this technology can be used to suppress the scavenging phenomenon when a two-component developer is used.

Furthermore, Patent Document 3 discloses a technology in which the protective layer (surface layer) of an electrophotographic photoreceptor contains a metal oxide, a photocurable resin as a binder resin, and a photoreactive graft polymer having a silicone side chain. Patent Document 3 describes that this technology improves the slipperiness of the electrophotographic photoreceptor surface, and that a cleaning method in which a cleaning blade is brought into contact with the surface makes it possible to adequately remove hydrophilic substances that are generated by acidic gas and that adhere to the photoreceptor surface.

JP 2009-229495 A JP 2018-128515 A JP 2015-132639 A

In the techniques disclosed in Patent Documents 1 to 3, the surface layer contains conductive particles, and a configuration is used that makes it possible to control the volume resistivity of the surface layer, but there are cases in which the effect of suppressing image deletion is not sufficient. Also, in the electrophotographic photoreceptor described in Patent Document 1, there is room for improvement in the charging uniformity.

Therefore, the object of the present invention is to provide an electrophotographic photoreceptor that is excellent in suppressing image flow and in charging uniformity. Furthermore, the object of the present invention is to provide a process cartridge equipped with the electrophotographic photoreceptor, and an electrophotographic device equipped with the process cartridge.

The above object is achieved by the present invention described below. An electrophotographic photoreceptor according to one embodiment of the present invention is an electrophotographic photoreceptor having a conductive support, a photosensitive layer, and a protective layer, the protective layer containing conductive particles, the surface of the conductive particles having a metal oxide containing titanium atoms and niobium atoms, the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide being 0.01 or more and 0.20 or less, the conductive particles being surface-treated with a compound having silicon atoms, the content ratio of the conductive particles in the protective layer being 5 volume % or more and less than 40 volume % with respect to the total volume of the protective layer, and the following formulas (1) to (3) are satisfied when the sum of the relative concentration d(C) of carbon atoms, the relative concentration d(O) of oxygen atoms, the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms on the surface of the protective layer determined by X-ray photoelectron spectroscopy is 100.0 atomic %.
0<d(Ti)≦2.0... (1)
0 < d (Si) ≦ 8.0 ... (2)
0.01≦d(Ti)/d(Si)≦1.0 (3)

In addition, a process cartridge according to another aspect of the present invention is characterized in that it integrally supports the electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attached to the main body of an electrophotographic device.

Furthermore, an electrophotographic apparatus according to another aspect of the present invention is characterized by having the above-mentioned electrophotographic photoreceptor, a charging means, an exposure means, a developing means, and a transfer means.

According to the present invention, it is possible to provide an electrophotographic photoreceptor that is excellent in suppressing image flow and in charging uniformity, a process cartridge having such an electrophotographic photoreceptor, and an electrophotographic device having such an electrophotographic photoreceptor.

1 is a schematic diagram illustrating an example of a configuration of an electrophotographic photoreceptor according to the present invention. FIG. 2 is a diagram showing an example of a comb-shaped electrode used for measuring the volume resistivity of an electrophotographic photosensitive member. FIG. 13 is a diagram showing an example of the results of potential measurement in the evaluation of charge retention. FIG. 13 is a diagram for explaining a calculation method in the evaluation of charge retention. 1 is a diagram showing an example of a schematic configuration of a process cartridge in which an electrophotographic photosensitive member according to the present invention is mounted, and an electrophotographic apparatus including the process cartridge; FIG. 2 is a scanning transmission electron microscope (STEM) image of an example of niobium-containing titanium oxide used in an example according to the present invention. FIG. 1 is a schematic diagram of an example of niobium-containing titanium oxide used in an example according to the present invention.

The electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a conductive support, a photosensitive layer, and a protective layer, the protective layer containing conductive particles, the surfaces of the conductive particles having a metal oxide containing titanium atoms and niobium atoms, the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide being 0.01 or more and 0.20 or less, the conductive particles being surface-treated with a compound having silicon atoms, the content of the conductive particles in the protective layer being 5 volume % or more and less than 40 volume % with respect to the total volume of the protective layer,
The protective layer is characterized in that, when the sum of the relative concentration d (C) of carbon atoms, the relative concentration d (O) of oxygen atoms, the relative concentration d (Ti) of titanium atoms, the relative concentration d (Nb) of niobium atoms, and the relative concentration d (Si) of silicon atoms on the surface of the protective layer, which are determined by X-ray photoelectron spectroscopy, is taken as 100.0 atomic %, the following formulas (1) to (3) are satisfied:
0<d(Ti)≦2.0... (1)
0 < d (Si) ≦ 8.0 ... (2)
0.01≦d(Ti)/d(Si)≦1.0 (3)

According to the study by the present inventors, the anatase type titanium oxide containing niobium atoms described in Patent Document 1 has a low content of niobium atoms on the surface. Therefore, the surface resistance of the conductive particles is not optimal, and the injection charging property of the electrophotographic photoreceptor is low. In addition, the anatase type titanium oxide containing niobium atoms used in Patent Document 1 has low hydrophobicity because it is not surface-treated, and there is room for improvement in dispersibility in the protective layer. Therefore, the degree of exposure of the conductive particles on the surface of the protective layer increases, and the resistance of the protective layer decreases due to adsorption of moisture, which may cause image deletion. Furthermore, the conductive particles are unevenly exposed on the surface of the protective layer, which may cause low charging uniformity.
Furthermore, in the technique described in Patent Document 2, the N-type semiconductor particles serving as conductive particles are highly exposed on the surface of the surface protection layer, which can cause image deletion in a high humidity environment.
Furthermore, in the technology described in Patent Document 3, the conductive particles are only exposed to a low degree on the surface of the electrophotographic photoreceptor, so that the injection charging property of the electrophotographic photoreceptor is low, and discharge products accumulate over a long period of use, causing image deletion.

The present inventors speculate that the reason why the electrophotographic photoreceptor according to the present invention is excellent in suppressing image deletion is as follows.
As described above, oxidizing gases such as ozone and nitrogen oxides are generated by discharge on the surface of the electrophotographic photoreceptor, and the oxidizing gases cause deterioration of the materials used in the surface layer of the electrophotographic photoreceptor, generating discharge products. The generation of discharge products on the surface of the electrophotographic photoreceptor and the adsorption of moisture to the surface of the electrophotographic photoreceptor reduce the volume resistivity of the surface of the electrophotographic photoreceptor. It is believed that image deletion occurs due to the reduction in volume resistivity on the surface of the electrophotographic photoreceptor.
By incorporating conductive particles in the surface layer of the electrophotographic photoreceptor, the volume resistivity of the surface layer can be controlled and the injection charging property can be enhanced, thereby suppressing discharge on the surface of the electrophotographic photoreceptor in the charging step, which is believed to suppress the generation of discharge products that cause image deletion.

However, when the conductive particles are exposed to a high degree in the surface layer in order to enhance the injection chargeability, the conductive particles are more likely to adsorb moisture in a high humidity environment, and as a result, image deletion in a high humidity environment may not be sufficiently suppressed.
Therefore, it is considered necessary to suppress moisture adsorption in a high humidity environment while the conductive particles are exposed on the surface to an extent that allows for a sufficiently high injection chargeability.

As a result of extensive investigations, the present inventors have found that the electrophotographic photoreceptor according to the present invention having the above-mentioned configuration makes it possible to achieve both improved injection charging properties and suppressed moisture adsorption in a high humidity environment.
That is, the conductive particles used in the present invention have a suitable surface resistance, and the electrophotographic photoreceptor according to the present invention contains the conductive particles in an appropriate amount in the protective layer (surface layer). This controls the volume resistivity of the protective layer of the electrophotographic photoreceptor, and can increase the charge injected from the charging member to the electrophotographic photoreceptor in the charging process, thereby suppressing discharge. In addition, in the electrophotographic photoreceptor according to the present invention, the degree of exposure of the conductive particles on the surface of the protective layer is appropriately controlled, and the surfaces of the conductive particles are sufficiently hydrophobized. This allows the electrophotographic photoreceptor to suppress moisture adsorption on the surface of the electrophotographic photoreceptor in a high humidity environment while maintaining uniform chargeability.

In addition, in the charging process of the electrophotographic photoreceptor, the higher the ratio of the dark potential to the applied voltage, the higher the injection chargeability, indicating that discharge in the charging process is suppressed. Therefore, the injection chargeability of the electrophotographic photoreceptor can be evaluated by determining the ratio of the dark potential on the surface of the electrophotographic photoreceptor to the voltage applied to the surface of the electrophotographic photoreceptor.

When the electrophotographic photoreceptor according to the present invention is evaluated for injection chargeability according to the above method, it is preferably 0.75 or more, more preferably 0.85 or more, and even more preferably 0.90 or more.

A specific configuration of the electrophotographic photoreceptor according to the present invention will now be described.
Fig. 1 is a diagram showing an example of the configuration of an electrophotographic photoreceptor according to the present invention, which has a conductive support 21, an undercoat layer 22, a charge generating layer 23, a charge transport layer 24, and a protective layer 25 as a surface layer.
FIG. 1 shows an example in which the photosensitive layer of the electrophotographic photoreceptor is a laminated type photosensitive layer composed of a charge generating layer 23 and a charge transport layer 24, but the photosensitive layer may be a single-layer type photosensitive layer described later.
The electrophotographic photoreceptor may not have an undercoat layer 22, or may have a conductive layer (described later) between the conductive support 21 and the undercoat layer 22 or the photosensitive layer.

<Protective layer (surface layer)>
The protective layer contains conductive particles.
The surfaces of the conductive particles contained in the protective layer have a metal oxide containing titanium atoms and niobium atoms, and the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide is 0.01 or more and 0.20 or less.
The conductive particles contain a metal oxide having titanium atoms and niobium atoms in the above atomic concentration ratio, so that the conductive particles can have a suitable surface resistance, which makes it possible to simultaneously suppress moisture adsorption to an electrophotographic photoreceptor in a high humidity environment and improve the injection charging property of the electrophotographic photoreceptor.
If the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide is 0.01 or more, the contact potential between the protective layer and the charging member is small. This allows the surface of the electrophotographic photoreceptor to be uniformly charged, and improves the injection charging property of the electrophotographic photoreceptor. If the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide is 0.20 or less, the resistivity of the conductive particles does not become too high, and the decrease in the injection charging property of the electrophotographic photoreceptor can be suppressed.
In the metal oxide, the atomic concentration ratio of niobium atoms to titanium atoms is preferably 0.03 or more and 0.18 or less.
The metal oxide is preferably titanium oxide containing niobium atoms.

The atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide that the conductive particles have on their surfaces can be determined as follows.
First, the surface composition of the conductive particles is analyzed by X-ray photoelectron spectroscopy (XPS), and the content of each atom is calculated based on the obtained results. The XPS apparatus and measurement conditions are as follows.
Equipment used: ULVAC-PHI Quantum 2000
Analysis method: narrow analysis X-ray source: Al-Kα
X-ray conditions: 100 μm, 25 W, 15 kV
Photoelectron capture angle: 45°
Pass Energy: 58.70 eV
Measurement range: φ100μm
Measurements are performed under the above conditions, and the peak derived from the C-C bond of the carbon 1s orbital is corrected to 285 eV. The relative sensitivity factor provided by ULVAC-PHI is then applied to the peak area of atoms whose peak tops are detected between 100 eV and 103 eV. The spectral peaks of titanium and niobium atoms are integrated and converted to calculate the titanium and niobium atomic concentrations. The atomic concentration ratio of niobium atoms to titanium atoms is calculated from the obtained atomic concentration values.

Examples of the conductive particles include particles made of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide, which have metal oxides containing titanium atoms and niobium atoms on their surfaces.Specific examples of the conductive particles include particles of metal oxides having titanium atoms doped with niobium atoms or niobium oxide.
Particularly preferred as the conductive particles are titanium oxide particles containing niobium atoms and having a configuration in which the niobium is unevenly distributed near the particle surface. This is because the uneven distribution of niobium atoms near the surface allows efficient transfer of electric charges. More specifically, the titanium oxide particles have a concentration ratio calculated as "niobium atom concentration/titanium atom concentration" at 5% inside the maximum diameter of the particle from the surface of the particle, which is 2.0 times or more, compared to the concentration ratio calculated as "niobium atom concentration/titanium atom concentration" at the center of the particle. The niobium atom concentration and titanium atom concentration are obtained by a scanning transmission electron microscope (STEM) connected to an EDS analyzer (energy dispersive X-ray analyzer). FIG. 6 shows a TEM image of an example (X1) of the titanium oxide particles used in the examples of the present invention. FIG. 7 shows the STEM image of FIG. 6 in schematic form. Details will be described later, but the niobium-containing titanium oxide particles used in the examples of the present invention are produced by coating titanium oxide particles with niobium-containing titanium oxide and then baking them. Therefore, it is considered that the coated niobium-containing titanium oxide grows as a niobium-doped titanium oxide by so-called epitaxial growth along the crystals of the titanium oxide core. The niobium-containing titanium oxide produced in this way has a smaller density near the surface compared to the density at the center of the particle, as shown in Figure 6, and is controlled to have a core-shell like morphology.

The STEM image of FIG. 6 is shown in FIG. 7. In such niobium-containing titanium oxide particles, the niobium/titanium atomic concentration ratio in the vicinity of the surface 32 of the particle is larger than the niobium/titanium atomic concentration ratio in the center 31 of the particle, and niobium atoms are unevenly distributed in the vicinity of the particle surface. Specifically, the niobium/titanium atomic concentration ratio in the center 31 of the particle from the surface of the particle to 5% of the maximum diameter of the particle is 2.0 times or more. By making the niobium/titanium atomic concentration ratio 2.0 times or more, the charge can be easily moved in the protective layer, and the charge injection property can be improved. If the niobium/titanium atomic concentration ratio is less than 2.0 times, it becomes difficult to exchange charges.
In the EDS analysis by STEM, the niobium/titanium atomic concentration ratio is measured by observing with a transmission electron microscope and EDS analysis. The niobium/titanium atomic concentration ratio in the center 31 of the particle can be measured by X-ray 33 that analyzes the center of the particle. In addition, the niobium/titanium atomic concentration ratio in the 5% inner part of the maximum diameter of the particle from the surface of the particle can be measured by X-ray 34 that analyzes the inside of the particle from the surface of the particle to 5% of the primary particle diameter. In addition, the niobium/titanium atomic concentration ratio can be measured directly from the electrophotographic photosensitive member by cutting the electrophotographic photosensitive member into thin slices by means of a microtome, Ar milling, FIB, or the like.

Examples of conductive particles contained in the protective layer include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide, among which titanium oxide is preferred. In particular, anatase-type titanium oxide facilitates charge transfer within the protective layer, resulting in good charge injection. The degree of anatase conversion of anatase-type titanium oxide is preferably 90% or more. The metal oxide particles may be doped with atoms such as niobium, phosphorus, and aluminum, or their oxides, and titanium oxide particles containing niobium and having a configuration in which niobium is unevenly distributed near the particle surface are particularly preferred. The uneven distribution of niobium near the surface allows efficient transfer of charges. By using such conductive particles, charges are easily injected from a charging member in contact with the surface of the conductive particles, and charges are easily transferred within the protective layer, resulting in a high effect of suppressing a decrease in the resistivity of the surface of the electrophotographic photoreceptor.

Conductive particles of various shapes, such as spheres, polyhedrons, ellipsoids, flakes, and needles, can be used. Among these, from the viewpoint of reducing image defects such as black spots, spheres, polyhedrons, and ellipsoids are preferred, and spheres or polyhedrons close to spheres are more preferred.

The conductive particles preferably have a number-average particle size of 60 nm or more and 150 nm or less. When the conductive particles have a number-average particle size of 60 nm or more, the specific surface area of the conductive particles does not become too large, and moisture adsorption to the conductive particles exposed on the surface of the electrophotographic photoreceptor can be suppressed. When the conductive particles have a number-average particle size of 150 nm or less, the dispersibility of the conductive particles in the protective layer can be increased. In addition, since the area of the interface with the binder resin in the protective layer can be increased, the resistance between the conductive particles and the binder resin is reduced, and the charge transfer efficiency is increased, thereby improving the injection charging property of the electrophotographic photoreceptor.

The conductive particles are surface-treated with a compound having silicon atoms, such as a silane coupling agent or a silicone resin. This surface treatment increases the hydrophobicity of the conductive particles. This surface treatment also suppresses uneven dispersion of the conductive particles in the protective layer, thereby suppressing low resistance due to excessive exposure of the conductive particles on the surface of the electrophotographic photoreceptor. This makes it possible to suppress adsorption of moisture to the surface of the electrophotographic photoreceptor in a high humidity environment.
The compound having a silicon atom used for the surface treatment of the conductive particles preferably contains an alkyl group having 12 or less carbon atoms.

式（Ａ）中、Ｒ^１～Ｒ^３は、それぞれ独立に、アルコキシ基またはアルキル基を示す。ただし、Ｒ^１～Ｒ^３の少なくとも２つはアルコキシ基である。Ｒ^４は、炭素数１２以下のアルキル基である。 A silane coupling agent is preferably used for the surface treatment of the conductive particles. As the silane coupling agent, a compound represented by the following formula (A) may be used.

In formula (A), R ¹ to R ³ each independently represent an alkoxy group or an alkyl group, provided that at least two of R ¹ to R ³ are alkoxy groups, and R ⁴ is an alkyl group having 12 or less carbon atoms.

Examples of compounds represented by formula (A) include hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, and dodecyltriethoxysilane.

In addition, as the silane coupling agent, a silane coupling agent other than the compound represented by formula (A), for example, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, (phenylaminomethyl)methyldimethoxysilane, N-2-(aminoethyl)-3-aminoisobutylmethyldimethoxysilane, N-ethylaminoisobutylmethyldiethoxysilane, N-methylaminopropylmethyldimethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, methyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, etc. may be used in combination with the compound represented by formula (A).

The conductive particles can be surface-treated by a common method, such as a dry method or a wet method.
In the dry method, conductive particles are stirred in a mixer capable of high speed stirring, such as a Henschel mixer, while an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added to the conductive particles to disperse them uniformly, and then the particles are dried.
In the wet method, the conductive particles and the surface treatment agent are stirred in a solvent, or dispersed in the solvent using glass beads or the like in a sand mill, and after dispersion, the solvent is removed by filtration or distillation under reduced pressure. After removing the solvent, it is preferable to further perform baking at 100° C. or higher.

The protective layer is characterized in that the atomic concentrations of carbon atoms, oxygen atoms, titanium atoms, niobium atoms, and silicon atoms present on its surface satisfy specific conditions, i.e., when the sum of the relative concentration d(C) of carbon atoms, the relative concentration d(O) of oxygen atoms, the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms on the surface of the protective layer determined by X-ray photoelectron spectroscopy is taken as 100.0 atomic %, the following formulas (1) to (3) are satisfied.
0<d(Ti)≦2.0 (1)
0 < d (Si) ≦ 8.0 ... (2)
0.01≦d(Ti)/d(Si)≦1.0 (3)

If d(Ti) is 2.0 atomic % or less, the degree of exposure of the conductive particles on the surface of the electrophotographic photoreceptor is not too high, and adsorption of moisture to the surface of the electrophotographic photoreceptor in a high humidity environment can be suppressed. If d(Ti) is greater than 0, conductive particles are exposed on the surface of the electrophotographic photoreceptor, and the contact potential between the surface of the electrophotographic photoreceptor and the charging member is reduced, improving the injection charging property of the electrophotographic photoreceptor.

If d(Si) is 8.0 atomic % or less, the conductive particles that have been surface-treated with a compound having silicon atoms are not excessively exposed on the surface of the electrophotographic photoreceptor. In addition, the ratio of hydrophobic resin components having silicon atoms in the protective layer described below is not too high. This makes it possible to suppress a decrease in the injection charging property of the electrophotographic photoreceptor. If d(Si) is greater than 0, the conductive particles that have been hydrophobically treated with a compound having silicon atoms are exposed on the surface of the electrophotographic photoreceptor, or the binder resin contains a hydrophobic resin component having silicon atoms. This makes it possible to suppress the adsorption of moisture to the surface of the electrophotographic photoreceptor in a high humidity environment.

If d(Ti)/d(Si) is 0.01 or more, the surface treatment of the conductive particles with a compound having silicon atoms is not excessive, and the resistivity of the protective layer can be prevented from becoming too high, and the decrease in the injection charging property of the electrophotographic photoreceptor can be suppressed. If d(Ti)/d(Si) is 1.0 or less, the wettability of the binder resin in the protective layer to the surface of the conductive particles can be sufficiently increased, and the dispersibility of the conductive particles in the protective layer is improved. This improves the charging uniformity of the electrophotographic photoreceptor, and by suppressing excessive exposure of the conductive particles on the surface of the electrophotographic photoreceptor, it is possible to suppress the adsorption of moisture to the surface of the electrophotographic photoreceptor in a high humidity environment.

The content of conductive particles in the protective layer is 5% by volume or more and less than 40% by volume of the total volume of the protective layer. If the content of conductive particles in the protective layer is 5% by volume or more, the injection charging property of the electrophotographic photoreceptor can be sufficiently improved. Furthermore, if the content of conductive particles in the protective layer is less than 40% by volume, adsorption of moisture to the surface of the electrophotographic photoreceptor in a high humidity environment can be suppressed.

The protective layer may contain a polymer of a compound having a polymerizable functional group and a resin. Examples of the polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide group, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic anhydride group, a carbon-carbon double bond group, an alkoxysilyl group, and a silanol group. A monomer having a charge transport function may be used as the compound having the polymerizable functional group. The compound having the polymerizable functional group may have a charge transport structure in addition to the chain polymerizable functional group.

Examples of the resin include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polystyrene resin, phenol resin, melamine resin, and epoxy resin. Among them, polycarbonate resin, polyester resin, and acrylic resin are preferable. The protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction include thermal polymerization reaction, photopolymerization reaction, and radiation polymerization reaction. Examples of the polymerizable functional group possessed by the monomer having a polymerizable functional group include an acrylic group and a methacrylic group. A material having a charge transport function may be used as the monomer having a polymerizable functional group.

The protective layer may also contain a resin having a silicon atom.
The resin having silicon atoms that the protective layer may contain may be silicone oil. The silicone oil may be, for example, straight silicone oil or modified silicone oil. The straight silicone oil may be dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, etc. The modified silicone oil may be reactive silicone oil such as amino-modified, epoxy-modified, carboxy-modified, carbinol-modified, methacryl-modified, mercapto-modified, or phenol-modified, and non-reactive silicone oil may be polyether-modified, methylstyryl-modified, alkyl-modified, ester-modified, or fluorine-modified. Furthermore, the resin having silicon atoms may be a block polymer or a graft polymer in which a polydimethylsiloxane structure is introduced into a side chain or a main chain.

The protective layer may contain additives such as antioxidants, UV absorbers, plasticizers, leveling agents, slippage agents, and abrasion resistance improvers. Specific examples of additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

The protective layer can be formed by preparing a coating solution for the protective layer containing the above-mentioned materials and solvent, forming this coating film on the photosensitive layer, and drying and/or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

The thickness of the protective layer is preferably 0.2 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 3 μm or less.

From the viewpoint of charge retention of the electrophotographic photoreceptor, it is preferable that the protective layer satisfies the following condition for volume resistivity: That is, when the volume resistivity of the protective layer in an atmosphere of 23° C. and 50% RH is A [Ω·cm], and the volume resistivity of the protective layer in an atmosphere of 32.5° C. and 80% RH is B [Ω·cm], it is preferable that the protective layer satisfies the following formulas (4) to (6).
11≦logA≦14 (4)
11≦logB≦14 (5)
0<log(A/B)≦2.0... (6)

When log A is 11 or more, it is possible to suppress moisture adsorption onto the surface of the electrophotographic photoreceptor in an atmosphere of 23° C. and 50% RH. When log A is 14 or less, the resistivity of the protective layer is not too high, and it is possible to suppress a decrease in the injection charging property of the electrophotographic photoreceptor.
If log B is 11 or more, moisture adsorption to the surface of the electrophotographic photoreceptor in an atmosphere of 32.5°C and 80% RH can be suppressed. If log B is 14 or less, the resistivity of the protective layer is not too high, and the decrease in the injection charging property of the electrophotographic photoreceptor can be suppressed. In order to reduce the influence of the fluctuation of the volume resistivity due to the change in the temperature and humidity environment, log (A/B) is preferably 2.0 or less. More preferably, log (A/B) is 1.5 or less.

In this measurement, since a minute amount of current is measured, it is preferable to use a resistance measuring device capable of measuring minute currents. For example, an example of a resistance measuring device capable of measuring minute currents is the Picoammeter 4140B manufactured by Hewlett-Packard. It is preferable to select the interdigital electrodes to be used and the voltage to be applied so that an appropriate signal-to-noise ratio is obtained depending on the material and resistance value of the protective layer.

The protective layer preferably has a charge retention of 9.5 or more, and more preferably has a charge retention of 10.0 or more. Here, the charge retention is a value obtained by applying a rectangular wave-shaped charge to the surface of the electrophotographic photoreceptor and measuring the change in the shape over time.

By determining the value of charge retention, it is possible to easily evaluate the stability of charge retention on the surface of the electrophotographic photoreceptor, i.e., the stability of the electrostatic latent image formed on the surface of the electrophotographic photoreceptor. Image deletion occurs when the electrostatic latent image is disturbed, so by evaluating charge retention, it is possible to evaluate the degree to which image deletion is suppressed.

<Support>
The support of the electrophotographic photoreceptor according to the present invention is a conductive support having electrical conductivity. The shape of the support may be cylindrical, belt-like, sheet-like, or the like. Among them, the cylindrical shape is preferable. The surface of the support may be subjected to electrochemical treatment such as anodization, blasting, cutting, or the like.
The material of the support is preferably metal, resin, glass, or the like.
Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, alloys thereof, etc. Among these, an aluminum support using aluminum is preferred.
When resin or glass is used as the material of the support, electrical conductivity is imparted by a treatment such as mixing or coating with an electrically conductive material.

<Conductive Layer>
In the electrophotographic photoreceptor according to the present invention, by providing a conductive layer, scratches and irregularities on the support surface can be concealed and light reflection on the support surface can be controlled. The conductive layer preferably contains conductive particles and a resin.

Examples of materials for the conductive particles include metal oxides, metals, and carbon black.
Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, barium sulfate, etc. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, silver, etc.
Among these, it is preferable to use metal oxides as the conductive particles, and it is particularly preferable to use titanium oxide, tin oxide, or zinc oxide.
When a metal oxide is used as the conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or the like, or the metal oxide may be doped with an element such as phosphorus or aluminum or an oxide thereof.
The conductive particles may have a laminated structure in which particles made of a metal oxide are coated with a metal oxide such as tin oxide or titanium oxide.
When a metal oxide is used as the conductive particles, the number average particle size is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less.

Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, and alkyd resin.
The conductive layer may further contain silicone oil, resin particles, a masking agent such as titanium oxide, and the like.

The conductive layer can be formed by preparing a coating solution for the conductive layer containing the above-mentioned materials and solvent, forming this coating film on a support, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Examples of dispersion methods for dispersing the conductive particles in the coating solution for the conductive layer include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

The thickness of the conductive layer is preferably 1 μm or more and 40 μm or less, and particularly preferably 3 μm or more and 30 μm or less.

<Undercoat layer>
In the present invention, by providing an undercoat layer, the adhesion between layers can be improved and a charge injection blocking function can be imparted.

The undercoat layer preferably contains a resin. Alternatively, the undercoat layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group.
Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl phenol resin, alkyd resin, polyvinyl alcohol resin, polyethylene oxide resin, polypropylene oxide resin, polyamide resin, polyamic acid resin, polyimide resin, polyamideimide resin, and cellulose resin.
Examples of the polymerizable functional group contained in the monomer having a polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide group, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic anhydride group, and a carbon-carbon double bond group.

For the purpose of improving electrical properties, the undercoat layer may further contain an electron transporting material, a metal oxide, a metal, a conductive polymer, etc. Among these, it is preferable to use an electron transporting material or a metal oxide.
Examples of the electron transport substance include a quinone compound, an imide compound, a benzimidazole compound, a cyclopentadienylidene compound, a fluorenone compound, a xanthone compound, a benzophenone compound, a cyanovinyl compound, an aryl halide compound, a silole compound, a boron-containing compound, etc. An electron transport substance having a polymerizable functional group may be used as the electron transport substance, and the undercoat layer may be formed as a cured film by copolymerizing the electron transport substance with the monomer having the polymerizable functional group described above.
Examples of metal oxides include indium tin oxide, tin oxide, indium oxide, titanium oxide, zinc oxide, aluminum oxide, silicon dioxide, etc. Examples of metals include gold, silver, aluminum, etc.

The metal oxide particles contained in the undercoat layer may be surface-treated with a surface treatment agent such as a silane coupling agent. The method for surface-treating the metal oxide particles is a general method, such as a dry method or a wet method.
In the dry method, metal oxide particles are stirred in a mixer capable of high-speed stirring, such as a Henschel mixer, while an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added to the metal oxide particles to uniformly disperse them, and then the particles are dried.
In the wet method, the metal oxide particles and the surface treatment agent are stirred in a solvent or dispersed in the solvent using glass beads or the like in a sand mill, and after dispersion, the solvent is removed by filtration or distillation under reduced pressure. After removing the solvent, it is preferable to further perform baking at 100° C. or higher.

The undercoat layer may further contain additives, for example, known materials such as metal powder such as aluminum, conductive materials such as carbon black, charge transport materials, metal chelate compounds, and organometallic compounds.
Examples of the charge transport substance include a quinone compound, an imide compound, a benzimidazole compound, a cyclopentadienylidene compound, a fluorenone compound, a xanthone compound, a benzophenone compound, a cyanovinyl compound, an aryl halide compound, a silole compound, a boron-containing compound, etc. A charge transport substance having a polymerizable functional group may be used as the charge transport substance, and the undercoat layer may be formed as a cured film by copolymerizing the charge transport substance with the monomer having the polymerizable functional group.

The undercoat layer can be formed by preparing a coating solution for the undercoat layer containing the above-mentioned materials and solvent, forming a coating film of this on a support or a conductive layer, and drying and/or curing the coating film.
Examples of the solvent used in the coating solution for the undercoat layer include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, halogenated aliphatic hydrocarbons, aromatic compounds, etc. In the present invention, it is preferable to use alcohol-based and ketone-based solvents.
Examples of a dispersion method for preparing a coating solution for the undercoat layer include methods using a homogenizer, an ultrasonic disperser, a ball mill, a sand mill, a roll mill, a vibration mill, an attritor, and a liquid collision type high-speed disperser.

The thickness of the undercoat layer is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 5 μm or less.

<Photosensitive layer>
The photosensitive layer of an electrophotographic photoreceptor is mainly classified into (1) a laminated type photosensitive layer and (2) a single-layer type photosensitive layer. (1) The laminated type photosensitive layer is a photosensitive layer having a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. (2) The single-layer type photosensitive layer is a photosensitive layer containing both a charge generation material and a charge transport material.

(1) Multi-Layer Photosensitive Layer The multi-layer photosensitive layer has a charge generating layer and a charge transport layer.

(1-1) Charge Generation Layer The charge generation layer preferably contains a charge generation material and a resin.

Examples of the charge generating material include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.
The content of the charge generating material in the charge generating layer is preferably from 40% by weight to 85% by weight, and more preferably from 60% by weight to 80% by weight, based on the total weight of the charge generating layer.

Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, polyvinyl chloride resin, etc. Among these, polyvinyl butyral resin is more preferable.

The charge generating layer may further contain additives such as antioxidants and ultraviolet absorbers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned materials and solvent, forming this coating film on the undercoat layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

The thickness of the charge generating layer is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.15 μm or more and 0.4 μm or less.

(1-2) Charge Transport Layer The charge transport layer preferably contains a charge transport material and a resin.

Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, resins having groups derived from these materials, etc. Among these, triarylamine compounds and benzidine compounds are preferred.
The content of the charge transport material in the charge transport layer is preferably from 25% by weight to 70% by weight, and more preferably from 30% by weight to 55% by weight, based on the total weight of the charge transport layer.

Examples of the resin include polyester resin, polycarbonate resin, acrylic resin, polystyrene resin, etc. Among these, polycarbonate resin and polyester resin are preferable. As the polyester resin, polyarylate resin is particularly preferable.
The content ratio (mass ratio) of the charge transport material to the resin is preferably from 4:10 to 20:10, and more preferably from 5:10 to 12:10.

The charge transport layer may also contain additives such as antioxidants, UV absorbers, plasticizers, leveling agents, slippage agents, and abrasion resistance improvers. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvent, forming this coating film on the charge generation layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents and aromatic hydrocarbon-based solvents are preferred.

The thickness of the charge transport layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

(2) Single-layer type photosensitive layer The single-layer type photosensitive layer can be formed by preparing a coating solution for the photosensitive layer containing a charge generating material, a charge transporting material, a resin and a solvent, forming this coating film on the undercoat layer, and drying it. The charge generating material, the charge transporting material and the resin are the same as the examples of materials in the above "(1) Multi-layer type photosensitive layer".
The thickness of the single-layer photosensitive layer is preferably from 10 μm to 45 μm, and more preferably from 25 μm to 35 μm.

[Process Cartridge, Electrophotographic Apparatus]
The process cartridge according to the present invention is characterized in that it integrally supports the electrophotographic photosensitive member described above and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attachable to the main body of the electrophotographic apparatus.
The electrophotographic apparatus according to the present invention is characterized by comprising the electrophotographic photosensitive member described above, a charging means, an exposing means, a developing means, and a transferring means.

FIG. 5 shows an example of a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photosensitive member.
A cylindrical (drum-shaped) electrophotographic photoreceptor 1 is driven to rotate around an axis 2 in the direction of the arrow at a predetermined peripheral speed (process speed). The surface of the electrophotographic photoreceptor 1 is charged to a predetermined positive or negative potential by a charging means 3 during the rotation process. Although a roller charging method using a roller-type charging member is shown in FIG. 5, a charging method such as a corona charging method, a proximity charging method, or an injection charging method may also be used. Exposure light 4 is irradiated from an exposure means (not shown) onto the charged surface of the electrophotographic photoreceptor 1, and an electrostatic latent image corresponding to the target image information is formed.
The exposure light 4 is light whose intensity is modulated in accordance with a time-series electric digital image signal of the target image information, and is output from an image exposure means such as a slit exposure means or a laser beam scanning exposure means.
The electrostatic latent image formed on the surface of the electrophotographic photoreceptor 1 is developed (normal development or reversal development) with toner contained in the developing means 5 , and a toner image is formed on the surface of the electrophotographic photoreceptor 1 .
The toner image formed on the surface of the electrophotographic photoreceptor 1 is transferred to a transfer material 7 by a transfer means 6. At this time, a bias voltage having a polarity opposite to that of the charge held by the toner is applied to the transfer means 6 from a bias power source (not shown). When the transfer material 7 is paper, the transfer material 7 is taken out from a paper feed section (not shown) and fed between the electrophotographic photoreceptor 1 and the transfer means 6 in synchronization with the rotation of the electrophotographic photoreceptor 1.
The transfer material 7 onto which the toner image has been transferred from the electrophotographic photoreceptor 1 is separated from the surface of the electrophotographic photoreceptor 1 and transported to fixing means 8, where the toner image is subjected to a fixing process, and then printed out outside the electrophotographic device as an image formation (print, copy).

The electrophotographic apparatus may have a cleaning unit 9 for removing deposits such as toner remaining on the surface of the electrophotographic photosensitive member after transfer. Alternatively, a so-called cleanerless system may be used in which the deposits are removed by the developing unit 5 or the like without providing a separate cleaning unit 9.
For example, it may be configured as follows: At least one selected from the charging means 3, the developing means 5, and the cleaning means 9 is integrally supported together with the electrophotographic photosensitive member to form a cartridge, which can be made into a process cartridge 11 that is detachably attached to the main body of the electrophotographic apparatus by using a guide means 12 such as a rail of the main body of the electrophotographic apparatus.
The electrophotographic apparatus may have a charge removing mechanism that removes charge from the surface of the electrophotographic photosensitive member by pre-exposure light 10 from a pre-exposure means (not shown). In addition, a guide means 12 such as a rail may be provided in order to mount and remove the process cartridge 11 to and from the main body of the electrophotographic apparatus.

The electrophotographic photoreceptor according to the present invention can be used in laser beam printers, LED printers, copiers, facsimiles, and combination machines thereof.

The present invention will be described in more detail below using examples and comparative examples. The present invention may be modified in various ways without departing from the gist of the invention, and is not limited by the following examples. In the following examples, "parts" are by mass unless otherwise specified.
Hereinafter, methods for measuring the various physical properties of the electrophotographic photoreceptor and conductive particles according to the present invention will be described.

<Measurement of physical properties of electrophotographic photoreceptor>
<Calculation of primary particle size of conductive particles>
First, the entire electrophotographic photoreceptor was immersed in methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the support of the electrophotographic photoreceptor was taken out. Next, the insoluble matter (photosensitive layer and protective layer containing conductive particles) that does not dissolve in MEK was filtered and dried in a vacuum dryer. Furthermore, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF)/methylal at a volume ratio of 1:1, the insoluble matter was filtered, and the filtered matter was collected and dried in a vacuum dryer. This operation obtained conductive particles and the resin of the protective layer. Furthermore, the filtered matter was heated to 500°C in an electric furnace so that the solid was only the conductive particles, and the conductive particles were collected. In order to ensure the amount of conductive particles required for measurement, the same treatment was performed on multiple electrophotographic photoreceptors.
A part of the collected conductive particles was dispersed in isopropanol (IPA), and the dispersion was dropped onto a grid mesh with a support film (manufactured by JEOL, Cu150J), and the conductive particles were observed in the STEM mode of a scanning transmission electron microscope (JEOL, JEM2800). The observation was performed at a magnification of 500,000 to 1.2 million times to easily calculate the particle diameter of the conductive particles, and STEM images of 100 conductive particles were taken. At this time, the acceleration voltage was set to 200 kV, the probe size was set to 1 nm, and the image size was set to 1024 x 1024 pixels. Using the obtained STEM image, the primary particle diameter was measured using the image processing software "Image-Pro Plus (manufactured by Media Cybernetics)". First, the straight line tool (Straight Line) on the toolbar was used to select the scale bar displayed at the bottom of the STEM image. In this state, when Set Scale is selected from the Analyze menu, a new window opens and the pixel distance of the selected line is entered in the Distance in Pixels field. The value of the scale bar (e.g., 100) is entered in the Known Distance field of the window, the unit of the scale bar (e.g., nm) is entered in the Unit of Measurement field, and the scale setting is completed by clicking OK. Next, a straight line is drawn using a straight line tool so as to be the maximum diameter of the conductive particles, and the particle diameter is calculated. The same operation is performed for 100 conductive particles, and the number average value of the obtained value (maximum diameter) is taken as the primary particle diameter of the conductive particles.

<Calculation of Niobium Atom/Titanium Atom Concentration Ratio in Conductive Particles Contained in Electrophotographic Photoreceptor>
A sample piece of 5 mm square was cut from the photoreceptor and cut to a thickness of 200 nm at a cutting speed of 0.6 mm/s using an ultrasonic ultramicrotome (Leica, UC7) to prepare a thin sample. This thin sample was observed at magnifications of 500,000 to 1.2 million times using a scanning transmission electron microscope (JEOL, JEM2800) in STEM mode connected to an EDS analyzer (energy dispersive X-ray analyzer).
Among the cross sections of the observed conductive particles, the cross sections of the conductive particles having a maximum diameter of approximately 0.9 to 1.1 times the primary particle diameter calculated above were visually selected. Then, the constituent elements of the cross sections of the selected conductive particles were collected using an EDS analyzer to produce EDS mapping images. The collection and analysis of the spectra were performed using an NSS (Thermo Fisher Scientific). The collection conditions were an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm was appropriately selected so that the dead time was 15 to 30, the mapping resolution was 256 x 256, and the number of frames was 300. The EDS mapping images were obtained for 100 cross sections of the conductive particles.
By analyzing the EDS mapping image thus obtained, the ratio of the niobium atomic concentration (atomic %) to the titanium atomic concentration (atomic %) at the center of the particle and within 5% of the maximum diameter of the measured particle from the particle surface is calculated. Specifically, the "Line Extraction" button of the NSS is pressed first, a straight line is drawn so as to be the maximum diameter of the particle, and information on the atomic concentration (atomic %) on the straight line from one surface through the inside of the particle to the other surface is obtained. If the maximum diameter of the particle obtained at this time is in the range of less than 0.9 times or more than 1.1 times the primary particle diameter calculated above, it is excluded from the subsequent analysis. (The analysis shown below was performed only on particles having a maximum diameter in the range of 0.9 times or more and less than 1.1 times the primary particle diameter.) Next, the niobium atomic concentration (atomic %) is read at the particle surface on both sides within 5% of the maximum diameter of the measured particle from the particle surface. In the same manner, the "titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface" is obtained. Next, using these values, the "concentration ratios of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" on both particle surfaces are calculated according to the following formula.
The concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface =
(Niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface)/(Titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface)

Of the two concentration ratios obtained, the smaller value is adopted as "the concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" in the present invention.
Also, the niobium atom concentration (atomic %) and titanium atom concentration (atomic %) are read at the position on the straight line that is the midpoint of the maximum diameter. Using these values, the "concentration ratio of niobium atoms to titanium atoms at the center of the particle" is calculated using the following formula.
Concentration ratio of niobium atoms to titanium atoms in the particle center =
(Niobium atom concentration (atomic %) at the center of the particle)/(Titanium atom concentration (atomic %) at the center of the particle)

The "concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at a distance 5% from the particle surface to the maximum diameter of the measured particle to the concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at the particle center" is calculated by the following formula.
(concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface)/(concentration ratio of niobium atoms to titanium atoms at the particle center)

<Calculation of Conductive Particle Content>
Next, four sample pieces of 5 mm square were cut out from the photoreceptor, and the protective layer was three-dimensionalized to 2 μm x 2 μm x 2 μm using FIB-SEM Slice & View. The content of the conductive particles in the total volume of the protective layer was calculated from the difference in contrast of FIB-SEM Slice & View. The conditions for Slice & View were as follows:
Analytical sample processing: FIB method Processing and observation equipment: SII/Zeiss NVision 40
Slice interval: 10 nm
Observation conditions:
Acceleration voltage: 1.0 kV
Sample tilt: 54°
WD: 5mm
Detector: BSE detector Aperture: 60 μm, high current
ABC:ON
Image resolution: 1.25 nm/pixel
The analysis area is 2 μm long x 2 μm wide, and the information for each cross section is integrated to obtain the volume V per 2 μm long x 2 μm wide x 2 μm thick (8 μm ³ ). The measurement environment is temperature: 23° C. and pressure: 1×10 ⁻⁴ Pa. As a processing and observation device, a Strata 400S (sample tilt: 52°) manufactured by FEI can also be used. The information for each cross section was obtained by image analysis of the area of the specified conductive particles of the present invention. The image analysis was performed using image processing software: Image-Pro Plus manufactured by Media Cybernetics.
Based on the obtained information, the volume V of the conductive particles of the present invention in a volume of 2 μm × 2 μm × 2 μm (unit volume: 8 μm ³ ) was determined for each of the four sample pieces, and the conductive particle content [volume %] (= V μm ³ / 8 μm ³ × 100) was calculated. The average value of the conductive particle content values in the four sample pieces was taken as the conductive particle content [volume %] of the present invention in the protective layer relative to the total volume of the protective layer.
At this time, for all four sample pieces, processing was performed up to the boundary between the protective layer and the lower layer to measure the film thickness t (cm) of the protective layer, and the value of the film thickness of the protective layer was used to calculate the volume resistivity ρv in the <Method for measuring the volume resistivity of the protective layer> described below.

<Measurement of the relative concentration of each atom on the surface of the protective layer>
Specifically, the X-ray photoelectron spectroscopy analysis of the surface of the protective layer can be carried out as follows.
First, five pieces of 5 mm square are cut out from randomly selected positions on the surface of the electrophotographic photoreceptor to prepare five sample pieces for observation. Next, X-ray photoelectron spectroscopy (XPS) is performed on the protective layer of each sample piece for observation. The XPS device and measurement conditions are as follows.
Equipment used: ULVAC-PHI Quantum 2000
Analysis method: narrow analysis X-ray source: Al-Kα
X-ray conditions: 100 μm, 25 W, 15 kV
Photoelectron capture angle: 45°
Pass Energy: 58.70 eV
Measurement range: φ100μm
Measurements are performed under the above conditions, and the peak derived from the C-C bond of the carbon 1s orbital is corrected to 285 eV. The relative sensitivity factor provided by ULVAC-PHI is then applied to the peak area of atoms whose peak tops are detected between 100 eV and 103 eV. The results obtained from the five observation sample pieces are averaged, and the spectral peaks of carbon atoms, oxygen atoms, titanium atoms, niobium atoms, and silicon atoms are integrated and converted. When the sum of the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms is taken as 100.0 atomic%, the relative concentration d(C) of carbon atoms, the relative concentration d(O) of oxygen atoms, the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms are determined. The atomic concentration ratios d(Nb)/d(Ti), d(Ti), d(Si), and d(Ti)/d(Si) of niobium atoms to titanium atoms in the metal oxide were calculated.

<Measurement of the relative concentration of each atom on the surface of a conductive particle>
Specifically, the X-ray photoelectron spectroscopy of the surface of the conductive particles can be carried out as follows: The conductive particles are subjected to X-ray photoelectron spectroscopy (XPS). The XPS apparatus and measurement conditions are as follows.
Equipment used: ULVAC-PHI Quantum 2000
Analysis method: narrow analysis X-ray source: Al-Kα
X-ray conditions: 100 μm, 25 W, 15 kV
Photoelectron capture angle: 45°
Pass Energy: 58.70 eV
Measurement range: φ100μm
Measurements are performed under the above conditions, and the peak derived from the C-C bond of the carbon 1s orbit is corrected to 285 eV. The relative sensitivity factor provided by ULVAC-PHI is then applied to the peak area of atoms whose peak tops are detected between 100 eV and 103 eV. The obtained results are averaged, and integration and conversion are performed for each of the spectral peaks of carbon atoms, oxygen atoms, titanium atoms, niobium atoms, and silicon atoms. When the sum of the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms is taken as 100.0 atomic%, the relative concentration d(C) of carbon atoms, the relative concentration d(O) of oxygen atoms, the relative concentration d(Ti) of titanium atoms, the relative concentration d(Nb) of niobium atoms, and the relative concentration d(Si) of silicon atoms are determined. The atomic concentration ratio d(Nb)/d(Ti) of niobium atoms to titanium atoms in the metal oxide is calculated.

<Method for measuring volume resistivity of protective layer>
The volume resistivity of the protective layer can be measured as follows.
A pA (picoampere) meter is used to measure the volume resistivity. First, a comb-shaped gold electrode with an interelectrode distance (D) of 180 μm and a length (L) of 59 mm as shown in FIG. 2 is prepared by deposition on a PET film. A protective layer with a thickness (T1) of 2 μm is provided on the prepared comb-shaped gold electrode so as to cover the comb-shaped gold electrode. Next, a direct current (I) is measured when a direct current voltage (V) of 100 V is applied between the comb-shaped electrodes under an environment of temperature 23° C./humidity 50% RH and an environment of temperature 32.5° C./humidity 80% RH. Using the obtained measured value, the volume resistivity A (temperature 23° C./humidity 50% RH) and the volume resistivity B (temperature 32.5° C./humidity 80% RH) are obtained by the following formula (7).
Volume resistivity ρv (Ω cm) = V (V) × T1 (cm) × L (cm) / {I (A) × D (cm)} (7)
When it is difficult to identify the composition of the conductive particles, binder resin, etc. of the protective layer, the surface resistivity of the surface of the electrophotographic photoreceptor is measured and converted into volume resistivity. In other words, when measuring the volume resistivity of the protective layer that exists as the surface layer of the electrophotographic photoreceptor, rather than the protective layer alone, the surface resistivity of the protective layer is measured and the obtained value is converted into volume resistivity.
Specifically, comb-shaped electrodes having an interelectrode distance (D) of 180 μm and a length (L) of 59 mm as shown in Fig. 2 are prepared by gold deposition on the surface of the electrophotographic photoreceptor (surface of the protective layer). Next, a DC voltage (V) of 1000 V is applied between the comb-shaped electrodes in environments of temperature 23°C/humidity 50% RH and temperature 32.5°C/humidity 80% RH, and the DC current (I) is measured, and the surface resistivity ρs of the protective layer is calculated from the DC voltage (V)/DC current (I).
Using the obtained surface resistivity ρs and the film thickness t (cm) of the protective layer, the volume resistivity can be calculated according to the following formula (8).
ρv = ρs × t (8)
(ρv: volume resistivity, ρs: surface resistivity, t: thickness of protective layer) (measurement of volume resistivity of protective layer)
The volume resistivity A (temperature 23° C./humidity 50% RH) and volume resistivity B (temperature 32.5° C./humidity 80% RH) of each electrophotographic photoreceptor were obtained.

<Powder X-ray diffraction measurement of conductive particles>
It was confirmed by powder X-ray diffraction analysis under the following conditions that the conductive particles contained anatase type titanium oxide, rutile type titanium oxide, or tin oxide. The conductive particles contained in the protective layer of the electrophotographic photoreceptor were recovered according to the method described above (measurement of the atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide contained on the surface of the conductive particles).
From the chart obtained by powder X-ray diffraction analysis using CuKα X-rays, each metal oxide was identified by referring to the inorganic materials database (AtomWork) of the National Institute for Materials Science (NIMS).
<Measurement conditions>
Measuring equipment used: X-ray diffraction device RINT-TTRII (manufactured by Rigaku Corporation)
X-ray tube: Cu
Tube voltage: 50KV
Tube current: 300mA
Scan method: 2θ/θ scan Scan speed: 4.0°/min
Sampling interval: 0.02°
Start angle (2θ): 5.0°
Stop angle (2θ): 40.0°
Attachment: Standard sample holder Filter: Not used Incident monochrome: Used Counter monochromator: Not used Divergence slit: Open Divergence vertical limit slit: 10.00 mm
Scattering slit: open Receiving slit: open Flat plate monochromator: Counter used: Scintillation counter

(Evaluation of Charge Retention)
A photoreceptor tester (product name: CYNTHIA59, manufactured by Gentec Co., Ltd.) is used to measure the charge retention. An electrophotographic photoreceptor is placed in the above-mentioned device under an environment of temperature 23°C/humidity 50% RH and an environment of temperature 32.5°C/humidity 80% RH. A conductive rubber roller with a diameter of 8 mm is used as a charging member, and the charging device is set so that a square wave with a frequency of 1 Hz, Voffset = -450 V, and Vpp = 500 V can be applied to the surface of the electrophotographic photoreceptor.
A surface potential probe (model 6000B-8, manufactured by Trek Japan) is placed at a position 1 mm away from the photoconductor, and the potential is measured using a surface potential meter (model 344, manufactured by Trek Japan).
The electrophotographic photoreceptor is charged while rotating at a rotation speed of 30 rpm, and the surface potential at a position rotated 0.30 seconds from the charging position is obtained at 100 μs intervals to obtain a plot as shown in Fig. 3. Next, as shown in Fig. 4, for each measurement point, the slope of the regression line R obtained from a total of 25 measurement points, including the subsequent 24 measurement points, is determined. Thereafter, the absolute values of the maximum and minimum values of the slope of the regression line R obtained for each measurement point are averaged to calculate the charge retention.

(Production Examples of Anatase-Type Titanium Oxide Particles 1 to 5)
Anatase type titanium oxide particles can be produced by the known sulfuric acid method. In the production of titanium oxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce a hydrous titanium dioxide slurry, which is then dehydrated and fired. This produces an anatase type titanium dioxide with a degree of anatase conversion of almost 100%.
In the above-mentioned method, the concentration of titanyl sulfate in the solution was controlled to prepare anatase type titanium oxide particles 1 to 5.

(Production Example of Anatase-Type Titanium Oxide Particles 6)
Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolysis of an aqueous titanyl sulfate solution in an amount of 1.8 mass % in terms of niobium ions relative to the amount of titanium in the slurry (calculated as titanium dioxide).
Niobium sulfate was added to an aqueous titanyl sulfate solution in a proportion of 1.8% by mass in terms of niobium ions, and the resulting solution was hydrolyzed to obtain a hydrous titanium dioxide slurry. The hydrous titanium dioxide slurry containing niobium ions and the like was then dehydrated and fired at a firing temperature of 1000° C. As a result, anatase-type titanium dioxide particles 6 containing 1.8% by mass of niobium element were obtained.

(Production Example of Anatase-Type Titanium Oxide Particles 7)
Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolysis of an aqueous titanyl sulfate solution in an amount of 0.2 mass% in terms of niobium ions relative to the amount of titanium in the slurry (calculated as titanium dioxide).
Niobium sulfate was added to an aqueous titanyl sulfate solution at a ratio of 0.2% by mass as niobium ions, and the resulting solution was hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired at a firing temperature of 1000° C. In this way, anatase-type titanium dioxide particles 7 containing 0.2% by mass of niobium element were obtained.

(Production Example of Rutile Titanium Oxide Particles 1)
200 parts by mass of titanium oxide nanoparticles (manufactured by Nippon Aerosil Co., Ltd.; average primary particle size (manufacturer's nominal value): 100 nm) were sealed in a Teflon (registered trademark) tube together with 10,000 parts by mass of a 17 mol/L potassium hydroxide aqueous solution. This was sealed in a pressure-resistant glass container and held at 110°C for 20 hours for hydrothermal treatment. The reaction product was neutralized with a 1 mol/L hydrochloric acid aqueous solution, and then repeatedly washed with ion-exchanged water and centrifuged to obtain a white precipitate. The resulting white precipitate was then dried and subsequently baked at 650°C for 30 minutes to obtain rutile-type titanium oxide particles 1 with a primary particle size of 80 nm (longer diameter side).
For the rutile-type titanium oxide particles 1, diffraction peaks at 27.4°, 36.1°, 41.2°, and 54.3° due to rutile-type titanium oxide were confirmed by X-ray diffraction spectrum (CuKα) measurement using RINT2000 (manufactured by Rigaku Corporation).

The number-average particle diameters of the anatase-type titanium oxide particles 1 to 7 and the rutile-type titanium oxide particles 1 prepared as described above are shown in Table 1.

<Production of Conductive Particles>
(Production of Conductive Particles 1)
Niobium (V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixed solution of a niobium salt and a titanium salt (hereinafter referred to as a "titanium-niobium mixed solution").
100 parts of anatase type titanium oxide particles 1 were weighed out and dispersed in water as uncoated particles to prepare a suspension, which was then heated to 670° C. with stirring in a water suspension of 1000 parts.
While maintaining the pH at 2.5, a titanium-niobium mixed liquid containing 337 g/kg of Ti and 10.3 g/kg of Nb relative to the weight of the anatase type titanium oxide particles 1 and an aqueous sodium hydroxide solution were added simultaneously.
In addition, a titanium niobate solution (the weight ratio of niobium atoms to titanium atoms in the solution is 1.0/20.0) was prepared by mixing a niobium solution in which 3 parts of niobium pentachloride (NbCl ₅ ) were dissolved in 100 parts of 11.4 mol/L hydrochloric acid and 200 parts of a titanium sulfate solution containing 12.0 parts of titanium. This titanium niobate solution and a 10.7 mol/L aqueous sodium hydroxide solution were simultaneously dropped (added in parallel) into the aqueous suspension over 3 hours so that the pH of the aqueous suspension was 2 to 3. After the dropwise addition was completed, the suspension was filtered, washed, and dried at 110°C for 8 hours. The dried product was baked together with the organic matter in a nitrogen atmosphere at 725°C (the baking temperature in Table 2) for 1 hour to obtain niobium atom-containing titanium oxide particles 1 in which niobium atoms were unevenly distributed near the surface.

・トルエン：２００．０部
これらを混合し、攪拌装置で４時間攪拌した後、ろ過、洗浄後、さらに１３０℃で３時間加熱処理を行って、導電性粒子１を得た。 Next, the following materials were prepared:
Niobium atom-containing titanium oxide particles 1: 100.0 parts Surface treatment agent 1 (compound represented by the following formula (S-1)) (trade name: trimethoxypropylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.): 6.0 parts

Toluene: 200.0 parts These were mixed and stirred for 4 hours using a stirrer, then filtered, washed, and further heat-treated at 130° C. for 3 hours to obtain conductive particles 1.

(Production of conductive particles 2 to 9, 11 to 15, and 18)
In the production of conductive particle 1, the type of uncoated particles used and the weight ratio of niobium atoms to titanium atoms in the titanium niobate solution during coating were changed as shown in Table 1. Otherwise, the powders of conductive particles 2 to 9, 11 to 15, and 18 shown in Table 2 were obtained in the same manner as in the production of conductive particle 1.

(Conductive Particles 10)
The type and amount of the surface treatment agent used was changed to 4 parts of surface treatment agent 2 (a compound represented by the following formula (S-2)) (product name: decyltrimethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd.). Otherwise, conductive particles 10 were produced in the same manner as in the production of conductive particles 1.

(Production Example of Conductive Particles 16)
The following materials were prepared:
Tin oxide particles (product name: S-2000, manufactured by Mitsubishi Materials Corporation): 100.0 parts Surface treatment agent 1: 20.0 parts Toluene: 200.0 parts These were mixed and stirred for 4 hours using a stirrer, and then filtered and washed. After that, the mixture was further heated at 130° C. for 3 hours for surface treatment to obtain conductive particles 16.

(Production Example of Conductive Particles 17)
100 parts of tin oxide particles (product name: S-2000, manufactured by Mitsubishi Materials Corporation) were dispersed in water to prepare 1000 parts of an aqueous suspension, which was then heated to 60°C.
In addition, a titanium niobate solution (the weight ratio of niobium atoms to titanium atoms in the solution is 1.0/20.0) was prepared by mixing a niobium solution in which 3 parts of niobium pentachloride (NbCl ₅ ) were dissolved in 100 parts of 11.4 mol/L hydrochloric acid and 200 parts of a titanium sulfate solution containing 12.0 parts of titanium. This titanium niobate solution and a 10.7 mol/L sodium hydroxide solution were simultaneously dropped (added in parallel) into the aqueous suspension over 3 hours so that the pH of the aqueous suspension was 2 to 3. After the dropwise addition was completed, the suspension was filtered, washed, and dried at 110°C for 8 hours. This dried product was baked together with the organic matter in a nitrogen atmosphere at 725°C (the temperature at the time of baking in Table 2) for 1 hour, and niobium atom-containing tin oxide particles 1 in which niobium atoms were unevenly distributed near the surface were obtained using tin oxide as pre-coated particles.
Next, the following materials were prepared:
Niobium-containing tin oxide particles 1: 100.0 parts Surface treatment agent 1: 6.0 parts Toluene: 200.0 parts These were mixed and stirred for 4 hours using a stirrer, then filtered and washed, and then further heat-treated at 130°C for 3 hours to obtain conductive particles 17.

Table 2 shows the surface properties and particle diameters (number average particle diameter) of the conductive particles 1 to 18 obtained above.

<Production of Electrophotographic Photoreceptor>
(Production Example of Electrophotographic Photoreceptor 1)
An aluminum cylinder (JIS-A3003, aluminum alloy) having a diameter of 24 mm and a length of 257.5 mm was used as a support (conductive support).

Next, the following materials were prepared:
Titanium oxide (TiO ₂ ) particles (average primary particle size 230 nm) coated with oxygen-deficient tin oxide (SnO ₂ ): 214 parts Phenol resin (product name: Plyofen J-325, manufactured by DIC Corporation, resin solid content: 60% by mass): 132 parts 1-methoxy-2-propanol: 98 parts These were placed in a sand mill using 450 parts of glass beads with a diameter of 0.8 mm, and dispersion treatment was carried out under the conditions of rotation speed: 2000 rpm, dispersion treatment time: 4.5 hours, and cooling water temperature setting: 18°C, to obtain a dispersion. The glass beads were removed from this dispersion using a mesh (mesh size: 150 μm). Silicone resin particles (product name: Tospearl 120, manufactured by Momentive Performance Materials Co., Ltd., average particle size 2 μm) were added to the obtained dispersion as a surface roughening agent. The amount of silicone resin particles added was 10% by mass based on the total mass of the metal oxide particles and the binder material in the dispersion after removing the glass beads. Silicone oil (product name: SH28PA, manufactured by Dow Toray Co., Ltd.) was added as a leveling agent to the dispersion to be 0.01% by mass based on the total mass of the metal oxide particles and the binder material in the dispersion.
Next, a mixed solvent of methanol and 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion so that the total mass of the metal oxide particles, the binder material, and the surface roughening agent in the dispersion (i.e., the mass of the solid content) was 67 mass% relative to the mass of the dispersion. The mixture was then stirred to prepare a conductive layer coating liquid. The conductive layer coating liquid was dip-coated on the support and heated at 140°C for 1 hour to form a conductive layer with a thickness of 30 μm.

Next, the following materials were prepared:
Electron transporting material (compound represented by the following formula (E-1)): 3.0 parts Blocked isocyanate (trade name: Duranate SBB-70P, manufactured by Asahi Kasei Chemicals Corporation): 6.5 parts Styrene-acrylic resin (trade name: UC-3920, manufactured by Toagosei Co., Ltd.): 0.4 parts Silica slurry (product name: IPA-ST-UP, manufactured by Nissan Chemical Industries, Ltd., solid content concentration: 15% by mass, viscosity: 9 mPa·s): 1.8 parts 1-butanol: 48 parts Acetone: 24 parts These were mixed and dissolved to prepare an undercoat layer coating liquid. This undercoat layer coating liquid was dip-coated on the conductive layer and heated at 170° C. for 30 minutes to form an undercoat layer having a film thickness of 0.7 μm.

Next, the following materials were prepared:
10 parts of hydroxygallium phthalocyanine in a crystalline form having peaks at 7.5° and 28.4° in a chart obtained by CuKα characteristic X-ray diffraction 5 parts of polyvinyl butyral resin (product name: S-LEC BX-1, manufactured by Sekisui Chemical Co., Ltd.) These were added to 200 parts of cyclohexanone and dispersed for 6 hours in a sand mill device using glass beads with a diameter of 0.9 mm.
This was further diluted with 150 parts of cyclohexanone and 350 parts of ethyl acetate to obtain a coating solution for a charge generating layer. The obtained coating solution was dip-coated on the undercoat layer and dried at 95° C. for 10 minutes to form a charge generating layer having a thickness of 0.20 μm.

Next, the following materials were prepared:
Charge transport material (hole transport material) represented by the following structural formula (C-1): 6.0 parts Charge transport material (hole transport material) represented by the following structural formula (C-2): 3.0 parts Charge transport material (hole transport material) represented by the following structural formula (C-3): 1.0 part Polycarbonate resin (product name: Iupilon Z400, manufactured by Mitsubishi Engineering Plastics Corporation): 10.0 parts Polycarbonate resin having a copolymerization unit having a structure represented by the following structural formula (C-4) and a structure represented by the following structural formula (C-5) (x/y=0.95/0.05: viscosity average molecular weight=20000): 0.02 parts These were dissolved in a mixed solvent of 25 parts orthoxylene/25 parts methyl benzoate/25 parts dimethoxymethane to prepare a coating solution for the charge transport layer. This charge transport layer coating liquid was dip coated onto the charge generating layer to form a coating film, and the coating film was dried at 120° C. for 30 minutes to form a charge transport layer having a thickness of 12 μm.

この保護層用塗布液１を電荷輸送層上に浸漬塗布して塗膜を形成し、得られた塗膜を６分間５０℃で乾燥させた。その後、窒素雰囲気下にて、加速電圧７０ｋＶ、ビーム電流５．０ｍＡの条件で支持体（被照射体）を３００ｒｐｍの速度で回転させながら、１．６秒間電子線を塗膜に照射した。保護層位置の線量は１５ｋＧｙであった。その後、窒素雰囲気下にて、塗膜の温度を１１７℃に昇温させた。電子線照射から、その後の加熱処理までの酸素濃度は１０ｐｐｍであった。
次に、大気中において塗膜の温度が２５℃になるまで自然冷却した後、塗膜の温度が１２０℃になる条件で１時間加熱処理を行い、膜厚２μｍの保護層を形成した。このようにして、導電性粒子１を含有する保護層を有する電子写真感光体１を製造した。電子写真感光体１の物性を表４に示す。 Next, the following materials were prepared:
Conductive particles 1: 76.0 parts; Binder resin: 79.0 parts of a compound represented by the following structural formula (O-1); 1-propanol (1-PA): 100.0 parts; Cyclohexane (CH): 100.0 parts. These materials were mixed and stirred for 6 hours with a stirrer to prepare a coating solution for the protective layer.

This protective layer coating solution 1 was applied by dip coating on the charge transport layer to form a coating film, and the obtained coating film was dried at 50°C for 6 minutes. Then, under a nitrogen atmosphere, the coating film was irradiated with an electron beam for 1.6 seconds while rotating the support (irradiated body) at a speed of 300 rpm under the conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA. The dose at the protective layer position was 15 kGy. Then, under a nitrogen atmosphere, the temperature of the coating film was raised to 117°C. The oxygen concentration from the electron beam irradiation to the subsequent heat treatment was 10 ppm.
Next, the coating film was naturally cooled in the atmosphere until the temperature reached 25° C., and then heat treatment was performed for 1 hour under conditions such that the temperature of the coating film reached 120° C., forming a protective layer with a thickness of 2 μm. In this manner, electrophotographic photoreceptor 1 having a protective layer containing conductive particles 1 was produced. The physical properties of electrophotographic photoreceptor 1 are shown in Table 4.

(Production Examples of Electrophotographic Photoreceptors 2 to 25, 27 to 38)
In the production example of the electrophotographic photoreceptor 1, protective layer coating liquids 2 to 25 and 27 to 38 were prepared by changing the type and amount of conductive particles used in preparing the protective layer coating liquid as shown in Table 3. Electrophotographic photoreceptors 2 to 25 and 27 to 38 were produced in the same manner as the electrophotographic photoreceptor 1, except that the obtained protective layer coating liquids 2 to 25 and 27 to 38 were used instead of the protective layer coating liquid 1.
The silicone resin used in the preparation of the protective layer coating liquid was a silicone resin having a weight average molecular weight of about 4000 (SR-213 (manufactured by Dow Corning Toray Co., Ltd.)).

(Production Example of Electrophotographic Photoreceptor 26)
In the manufacturing example of the electrophotographic photoreceptor 1, the types and amounts of the binder resin and mixed solvent used in preparing the protective layer coating liquid were changed as follows to prepare a protective layer coating liquid 26.
Binder resin: 1 part of polyester resin having a weight average molecular weight (Mw) of 100,000, containing a structural unit represented by the following formula (O-2) and a structural unit represented by the following formula (O-3) in a ratio of 5/5. Mixed solvent: 12 parts of chlorobenzene/8 parts of dimethoxymethane. The obtained protective layer coating liquid 26 was dip-coated on the charge transport layer to form a coating film, and the coating film was dried at 120° C. for 30 minutes to form a protective layer having a film thickness of 2 μm. Except for this, electrophotographic photoreceptor 26 was produced in the same manner as electrophotographic photoreceptor 1. The physical properties of electrophotographic photoreceptor 26 are shown in Table 4.

表中、Ｃは、「粒子表面から測定粒子の最大径の５％内部におけるニオブ原子とチタン原子との濃度比率」であり、Ｄは、「粒子中心部におけるニオブ原子とチタン原子との濃度比率」である。粉末Ｘ線回折分析の列における、Ａは、アナターゼ型酸化チタンの含有、Ｒはルチル型酸化チタンの含有、Ｓは酸化スズの含有がそれぞれ確認されたことを示す。

In the table, C is the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface," and D is the "concentration ratio of niobium atoms to titanium atoms in the particle center." In the column for powder X-ray diffraction analysis, A indicates that the inclusion of anatase-type titanium oxide, R indicates that the inclusion of rutile-type titanium oxide, and S indicates that the inclusion of tin oxide were confirmed.

<Evaluation of Electrophotographic Photoreceptor>
(Evaluation of Injection Charging Properties)
For the measurement of injection charging properties, a modified laser beam printer (electrophotographic device) (product name: HP LaserJet Enterprise Color M553dn, manufactured by Hewlett-Packard Co.) was used. The modified device used for the evaluation was modified so that the image exposure amount, the amount of current flowing from the charging roller to the support of the electrophotographic photosensitive member (hereinafter also referred to as the total current), and the voltage applied to the charging roller could be adjusted and measured.
In addition, the process cartridge for cyan color of the above modified machine was modified to mount a potential probe (model 6000B-8: manufactured by Trek Japan Co., Ltd.) at the development position. Next, the surface potential of the central part of the electrophotographic photosensitive member was measured using a surface potential meter (model 344: manufactured by Trek Japan Co., Ltd.).
An electrophotographic photoreceptor was attached to the modified machine in an environment of 32.5° C. temperature and 80% RH humidity, and a direct current of 1000 V was applied to the charging roller to charge the photoreceptor while rotating it at 60 rpm. The potential of the photoreceptor surface at this time was taken as A, and the injection chargeability was evaluated according to the following evaluation criteria, with injection chargeability = A/1000. The evaluation results are shown in Table 5.
A: The injection chargeability is 0.90 or more.
B: The injection charge property is 0.85 or more and less than 0.90.
C: The injection charge property is 0.75 or more and less than 0.85.
D: The injection chargeability is less than 0.75.

(Image deletion evaluation)
First, the modified machine and the electrophotographic photoreceptor were left for 24 hours or more in a normal humidity environment of 23.0° C. temperature and 50% RH humidity, and in a high humidity environment of 32.5° C. temperature and 80% RH humidity, respectively. After that, the electrophotographic photoreceptor left in each environment was mounted in a cyan cartridge of the modified machine.
Next, the applied voltage was increased stepwise from -400 V to -2000 V in 100 V intervals, and the total current was measured at each applied voltage. A graph was then created with the applied voltage on the horizontal axis and the total current on the vertical axis, and the applied voltage at which the current value deviated from the linear approximation curve for applied voltages of -400 V to -800 V was 100 μA was determined, and the applied voltage was set to the determined value.
Next, a solid image was output in monochromatic cyan using plain paper (product name: CS-680 (68 g/m ² ), manufactured by Canon Marketing Japan Inc.). When this solid image was measured using a spectrodensitometer (product name: X-Rite 504, manufactured by X-Rite Corporation), the image exposure light amount was set so that the density on the paper was 1.45. Next, 10 sheets of A4 size square grid images with a line width of 0.1 mm and line spacing of 10 mm were output in succession in monochromatic cyan. The obtained images were evaluated for image flow using the following evaluation criteria. The evaluation results are shown in Table 5.
A: No abnormality was observed in the grid image.
B: The horizontal lines of the grid image are broken, but no abnormalities are observed in the vertical lines.
C: The horizontal lines of the grid image are missing and the vertical lines are broken.
D: The horizontal lines of the grid image have disappeared, and the vertical lines have also disappeared.
In this case, the horizontal lines in the grid image refer to lines parallel to the cylindrical axial direction of the electrophotographic photosensitive member, and the vertical lines refer to lines perpendicular to the cylindrical axial direction of the photosensitive member.

Next, the following test was performed using the electrophotographic photoreceptor that had been left in a high humidity environment of 32.5° C./80% RH for 24 hours or more. First, a square grid image with a line width of 0.1 mm and a line spacing of 10 mm was output in a single color of cyan for 20,000 sheets in succession, with two sheets intermittently, for an intermittent time of 2 seconds, using plain paper (product name: CS-680 (68 g/m ² ), Canon Marketing Japan Inc.). After the image output, the main power supply of the electrophotographic device was turned off and the device was left in a high humidity environment of 32.5° C./80% RH for 3 days. After the image was left, the main power supply of the electrophotographic device was turned on, and the above square grid image was output in the same manner, and the image flow of the output image was visually observed, and the image flow was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5.
A: No abnormality was observed in the grid image.
B: The horizontal lines of the grid image are broken, but no abnormalities are observed in the vertical lines.
C: The horizontal lines of the grid image are missing and the vertical lines are broken.
D: The horizontal lines of the grid image have disappeared, and the vertical lines have also disappeared.
In this case, the horizontal lines in the grid image refer to lines parallel to the cylindrical axial direction of the photoconductor, and the vertical lines refer to lines perpendicular to the cylindrical axial direction of the photoconductor.

(Evaluation of charging uniformity)
The modified machine was placed in a high humidity environment of 32.5°C and 80% RH to output 10,000 sheets of text images with a printing ratio of 1%, and then a halftone (20H) image was formed. The resulting images were evaluated for roughness (uniformity of density) to evaluate the charging uniformity of the electrophotographic photoreceptor. Plain paper (product name: CS-680 (68 g/m ² ), Canon Marketing Japan Inc.) was used. The 20H image is a halftone image in which 256 gradations are expressed in hexadecimal, with 00H being solid white (non-image) and FFH being solid black (full image).
The roughness of the image was evaluated according to the following criteria. Density measurements were performed at 20 randomly selected points, and the difference between the maximum and minimum density values was taken as density uniformity and judged according to the following criteria. The density was measured using an X-Rite color reflection densitometer (product name: X-Rite 500 Series, manufactured by X-Rite Corporation). The evaluation results are shown in Table 5.
A: Density uniformity is less than 0.04 B: Density uniformity is 0.04 or more and less than 0.06 C: Density uniformity is 0.06 or more and less than 0.08 D: Density uniformity is 0.08 or more

The disclosure according to an embodiment of the present invention includes the following configuration.
(Configuration 1)
An electrophotographic photoreceptor having a conductive support, a photosensitive layer, and a protective layer,
The protective layer contains conductive particles,
the surface of the conductive particle has a metal oxide containing titanium atoms and niobium atoms;
In the metal oxide, the atomic concentration ratio of niobium atoms to titanium atoms is 0.01 or more and 0.20 or less;
the conductive particles are surface-treated with a compound having a silicon atom;
a content ratio of the conductive particles in the protective layer is 5 volume % or more and less than 40 volume % with respect to a total volume of the protective layer,
the relative concentration of carbon atoms d(C) and oxygen atoms d(O) at the surface of the protective layer as determined by X-ray photoelectron spectroscopy;
When the sum of the relative concentration d (Ti) of titanium atoms, the relative concentration d (Nb) of niobium atoms, and the relative concentration d (Si) of silicon atoms is 100.0 atomic%, the following formulas (1) to (3) are satisfied:
1. An electrophotographic photoreceptor comprising:
0<d(Ti)≦2.0 (1)
0 < d (Si) ≦ 8.0 ... (2)
0.01≦d(Ti)/d(Si)≦1.0 (3)
(Configuration 2)
The electrophotographic photoreceptor according to Configuration 1, wherein when the volume resistivity of the protective layer in an atmosphere of 23° C. and 50% RH is A [Ω cm] and the volume resistivity of the protective layer in an atmosphere of 32.5° C. and 80% RH is B [Ω cm], the following formulas (4) to (6) are satisfied:
11≦logA≦14 (4)
11≦logB≦14 (5)
0≦log(A/B)≦2.0 (6)
(Configuration 3)
3. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide is titanium oxide containing niobium atoms.
(Configuration 4)
The electrophotographic photoreceptor according to Configuration 3, wherein the conductive particles have a niobium atom/titanium atom concentration ratio of 2.0 times or more within 5% of the maximum diameter of the particle from the surface of the particle compared to the niobium atom/titanium atom concentration ratio at the center of the particle, as determined by energy dispersive X-ray analysis (EDS analysis) connected to a scanning transmission electron microscope (STEM).
(Configuration 5)
5. The electrophotographic photoreceptor according to claim 4, wherein the conductive particles have a number-average particle size of 60 nm or more and 150 nm or less.
(Configuration 6)
A process cartridge which integrally supports the electrophotographic photosensitive member according to any one of Configurations 1 to 5 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably mountable to a main body of an electrophotographic apparatus.
(Configuration 7)
6. An electrophotographic apparatus comprising the electrophotographic photoreceptor according to any one of Configurations 1 to 5, a charging unit, an exposing unit, a developing unit, and a transferring unit.

21 Conductive support 22 Undercoat layer 23 Charge generating layer 24 Charge transport layer 25 Protective layer 1 Electrophotographic photoreceptor 2 Shaft 3 Charging means 4 Exposure light 5 Developing means 6 Transfer means 7 Transfer material 8 Fixing means 9 Cleaning means 10 Pre-exposure light 11 Process cartridge 12 Guide means 31 Center of particle 32 Near the surface of particle 33 X-ray for analyzing center of particle 34 X-ray for analyzing inside 5% of primary particle diameter from the surface of particle

Claims (7)

An electrophotographic photoreceptor having a conductive support, a photosensitive layer, and a protective layer,
The protective layer contains conductive particles,
the surface of the conductive particle has a metal oxide containing titanium atoms and niobium atoms;
In the metal oxide, the atomic concentration ratio of niobium atoms to titanium atoms is 0.01 or more and 0.20 or less;
the conductive particles are surface-treated with a compound having a silicon atom;
a content ratio of the conductive particles in the protective layer is 5 volume % or more and less than 40 volume % with respect to a total volume of the protective layer,
the relative concentration of carbon atoms d(C) and oxygen atoms d(O) at the surface of the protective layer as determined by X-ray photoelectron spectroscopy;
When the sum of the relative concentration d (Ti) of titanium atoms, the relative concentration d (Nb) of niobium atoms, and the relative concentration d (Si) of silicon atoms is 100.0 atomic%, the following formulas (1) to (3) are satisfied:
1. An electrophotographic photoreceptor comprising:
0<d(Ti)≦2.0 (1)
0 < d (Si) ≦ 8.0 ... (2)
0.01≦d(Ti)/d(Si)≦1.0 (3) 2. The electrophotographic photoreceptor according to claim 1, wherein when the volume resistivity of the protective layer in an atmosphere of 23° C. and 50% RH is A [Ω cm] and the volume resistivity of the protective layer in an atmosphere of 32.5° C. and 80% RH is B [Ω cm], the following formulas (4) to (6) are satisfied:
11≦logA≦14 (4)
11≦logB≦14 (5)
0≦log(A/B)≦2.0 (6) The electrophotographic photoreceptor according to claim 1, wherein the metal oxide is titanium oxide containing niobium atoms. The electrophotographic photoreceptor according to claim 3, wherein the conductive particles have a niobium atom/titanium atom concentration ratio of 2.0 times or more at a depth of 5% from the surface of the particle to the maximum diameter of the particle compared to the niobium atom/titanium atom concentration ratio at the center of the particle, as determined by energy dispersive X-ray analysis (EDS analysis) connected to a scanning transmission electron microscope (STEM). The electrophotographic photoreceptor according to claim 4, wherein the conductive particles have a number-average particle size of 60 nm or more and 150 nm or less. A process cartridge that integrally supports the electrophotographic photosensitive member according to any one of claims 1 to 5 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably mountable to the main body of an electrophotographic device. An electrophotographic apparatus comprising the electrophotographic photoreceptor according to any one of claims 1 to 5, a charging means, an exposure means, a developing means, and a transfer means.

Images