JP2024000488A - Electrophotographic photoreceptor, process cartridge, and electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor that can prevent highlight image deletion under high temperature and high humidity, while maintaining high injection electrification characteristics.

SOLUTION: An electrophotographic photoreceptor has a surface layer containing a binder resin and metal oxide particles. The average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less. The content of the metal oxide particles in the surface layer measured from the cross section of the surface layer is 30 volume% or more and 75 volume% or less based on the total volume of the surface layer.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

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

2. Description of the Related Art As electrophotographic photoreceptors mounted in electrophotographic apparatuses, those containing organic photoconductive substances that serve as charge-generating substances are widely used. In recent years, there has been a demand for improved mechanical durability, that is, abrasion resistance, of electrophotographic photoreceptors, with the aim of extending the life of the electrophotographic photoreceptor and improving image quality during repeated use.

On the other hand, in the charging process, oxidizing gases such as ozone and nitrogen oxides are generated due to the discharge that occurs between the electrophotographic photoreceptor and the charging member, and these oxidizing gases cause the surface layer of the electrophotographic photoreceptor to be damaged. The material used in the discharge process deteriorates and discharge products are generated. When this discharge product absorbs moisture in the air, a phenomenon called "image deletion" may occur in which the electrostatic latent image formed on the electrophotographic photoreceptor is destroyed.

The higher the abrasion resistance of the surface of the electrophotographic photoreceptor, the more likely the image deletion will occur because the substances that cause image deletion, such as the discharge products and moisture, will not be removed.

As a technique for improving image blur, there is a method of controlling the volume resistivity of the surface layer of the electrophotographic photoreceptor by incorporating metal oxide particles into the surface layer of the electrophotographic photoreceptor.

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 thought that charging for the formation of this dark potential occurs through two types of processes. One is a process in which the surface of the electrophotographic photoreceptor is charged due to dielectric breakdown of the air layer between the charging member and the surface of the electrophotographic photoreceptor, in accordance with Paschen's law. In another process, when the contact potential difference between the electrophotographic photoreceptor and the charging member is sufficiently small, the charging member directly contacts the electrophotographic photoreceptor at the contact area between the charging member and the electrophotographic photoreceptor without causing discharge. This is a process by injection charging in which charges move.

By controlling the volume resistivity by containing metal oxide particles in the surface layer, it is possible to increase the rate of charging by injection charging from the charging member to the electrophotographic photoreceptor in the charging step. That is, the injection charging properties of the electrophotographic photoreceptor can be improved, thereby suppressing discharge and suppressing the generation of discharge products.

Patent Document 1 discloses that by controlling the particle size of metal oxide particles, which are conductive fine particles contained in the protective layer, with respect to the toner particle size, stable injection charging performance and injection layer stability can be achieved even after repeated use. It describes a technology that makes it possible to prevent scratches and image blur.

Additionally, Patent Document 2 describes a technology that enables conductive particles in the protective layer to protrude by 0.2 μm or more from the surface of the photoreceptor, thereby enabling high-quality image characteristics and stable injection charging even after repeated use. has been done.

Furthermore, Patent Document 3 discloses that a protective layer (surface layer) of an electrophotographic photoreceptor is made to contain a component obtained by reacting a curable compound and anatase-type titanium oxide containing niobium atoms. A technique is described that enables improved cleaning performance when a photographic photoreceptor is used for a long period of time.

Japanese Patent Application Publication No. 2002-214815 Japanese Patent Application Publication No. 2001-305775 Japanese Patent Application Publication No. 2009-229495

According to the studies of the present inventors, in the technologies disclosed in Patent Documents 1 and 2, metal oxide particles are contained in the surface layer and a structure capable of high injection charging property is used, but Under certain circumstances, there was a problem in that the density could not be obtained at low printing rates (highlights) (hereinafter referred to as "highlight image bleeding"). As shown in FIG. 1, highlight image deletion is a phenomenon in which the density decreases when the printing rate is low, that is, in the reversal development method, when the exposed area at the time of the latent image is small.

While the aforementioned image deletion occurs due to discharge products caused by discharge, highlight image deletion is a phenomenon that occurs from the beginning of the developing process, regardless of the presence or absence of discharge products, and is caused by image deletion. It is thought that the mechanism of occurrence is different from that of

Therefore, an object of the present invention is to provide an electrophotographic photoreceptor that maintains high injection chargeability while suppressing highlight image fading even under high temperature and high humidity conditions. Another object of the present invention is to provide a process cartridge equipped with the electrophotographic photoreceptor, and an electrophotographic apparatus equipped with the process cartridge.

The above object is achieved by the present invention as follows. That is, the electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, and wherein the amount of the metal oxide particles measured from a cross section of the surface layer is The average primary particle diameter is 20 nm or more and 70 nm or less, and the content of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30 volume % or more with respect to the total volume of the surface layer. % by volume or less.

Further, a process cartridge according to another aspect of the present invention integrally supports the electrophotographic photoreceptor and at least one means selected from the group consisting of charging means, developing means, and cleaning means, It is characterized by being detachable from 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 electrophotographic photoreceptor, charging means, exposure means, developing means, and transfer means.

According to the present invention, it is possible to provide an electrophotographic photoreceptor that maintains high injection chargeability and can suppress highlight image deletion even under high temperature and high humidity conditions.

FIG. 3 is a diagram showing the relationship between printing rate and density for explaining highlight image deletion. 1 is a schematic diagram showing an example of the configuration of an electrophotographic photoreceptor according to the present invention. It is a STEM image diagram of an example of niobium-containing titanium oxide used in this example. FIG. 2 is a schematic diagram of an example of niobium-containing titanium oxide used in this example. FIG. 3 is a diagram showing an example of a comb-shaped electrode used to measure the volume resistivity of an electrophotographic photoreceptor. 1 is a diagram illustrating an example of a schematic configuration of a process cartridge equipped with an electrophotographic photoreceptor according to the present invention, and an electrophotographic apparatus equipped with the process cartridge. FIG. 3 is a diagram showing a print pattern of an image used when evaluating the precision of an image.

Hereinafter, the present invention will be described in detail by citing preferred embodiments.
The electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, the average primary dimension of the metal oxide particles measured from a cross section of the surface layer. The particle size is 20 nm or more and 70 nm or less, and the content rate of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30 volume % or more and 75 volume % with respect to the total volume of the surface layer. It is necessary that the following is true.

Further, a process cartridge according to another aspect of the present invention integrally supports the electrophotographic photoreceptor and at least one means selected from the group consisting of charging means, developing means, and cleaning means, It can be attached to and detached from the main body of the electrophotographic device.

Furthermore, an electrophotographic apparatus according to yet another aspect of the present invention includes the above electrophotographic photoreceptor, charging means, exposure means, developing means, and transfer means.

High injection charging properties can be achieved by increasing the content of metal oxide particles in the surface layer, but there has been a so-called trade-off relationship in that highlight image blurring deteriorates. Metal oxide particles receive charge by coming into direct contact with a charging member, becoming a so-called charge injection point, so the higher the content of metal oxide particles in the surface layer, the more charges will be received from the charging member. It is thought that it is possible to do so. On the other hand, when the content of metal oxide particles in the surface layer increases, the metal oxide particles become connected to each other, and the charges on the surface of the electrophotographic photoreceptor tend to move along the metal oxide particles. Particularly, in a high temperature, high humidity environment, the surface layer absorbs moisture, the resistance of the surface layer decreases, and charge transfer is accelerated, so it is thought that highlight image deletion becomes noticeable in a high temperature, high humidity environment.

According to the studies of the present inventors, the reason why the electrophotographic photoreceptor according to the present invention, which adopts the above-described unique configuration, suppresses highlight image deletion while maintaining high injection charging property is as follows. That's what I'm guessing.

As mentioned above, in order to maintain high injection chargeability, the content of metal oxide particles in the surface layer needs to be 30% by volume or more and 75% by volume or less with respect to the total volume of the surface layer. . This is because if the content of metal oxide particles is less than 30% by volume, sufficient injection chargeability cannot be maintained, and if it exceeds 75% by volume, the binder resin is insufficient, causing This is because cracks occur, the strength of the film is weak, and metal oxide particles, which serve as charge injection points, are easily detached, resulting in a significant decrease in wear resistance. The content of metal oxide particles in the surface layer is preferably 42% by volume or more and 65% by volume or less based on the total volume of the surface layer.

On the other hand, the results of studies regarding highlight image blurring have revealed that the main cause of highlight image blurring is charge movement in the film thickness direction of the surface layer. In other words, in order to suppress highlight image deletion, it is necessary to suppress charge movement in the surface layer film. By reducing the primary particle diameter of the conductive material, the interfacial area (surface area of the particles) of the metal oxide particles in the surface layer increases. Since the binder resin enters between the metal oxide particles, it is thought that as the interfacial area increases, the interfacial resistance also increases, charge movement in the surface layer is suppressed, and highlight image blurring is suppressed.

If the primary particle diameter of the metal oxide particles exceeds 70 nm, sufficient interfacial resistance cannot be obtained, and suppression of highlight image blur cannot be expected. If the primary particle diameter of the metal oxide particles is smaller than 20 nm, the surface of the surface layer (protective layer) is likely to be covered with the binder resin, resulting in a decrease in injection chargeability. The primary particle diameter of the metal oxide particles is preferably 30 nm or more and 60 nm or less.

Hereinafter, the specific structure of the electrophotographic photoreceptor according to the present invention will be explained.
[Electrophotographic photoreceptor]
The electrophotographic photoreceptor of the present invention is characterized by having a photosensitive layer and a protective layer that is a surface layer.

FIG. 2 is a diagram showing an example of the configuration of an electrophotographic photoreceptor according to the present invention. The electrophotographic photoreceptor shown in FIG. 2 includes a support 21, an undercoat layer 22, a charge generation layer 23, a charge transport layer 24, and a protective layer 25 as a surface layer.

FIG. 2 shows an example in which the photosensitive layer of the electrophotographic photoreceptor is a laminated type photosensitive layer consisting of a charge generation layer 23 and a charge transport layer 24. It may also be a photosensitive layer.

Further, the electrophotographic photoreceptor may have a structure that does not have the undercoat layer 22, or may have a structure that has a conductive layer described below between the support 21 and the undercoat layer 22 or the photosensitive layer. Good too.

A method for producing the electrophotographic photoreceptor of the present invention includes a method of preparing a coating solution for each layer, which will be described later, and coating the layers on a support in desired order, followed by drying. At this time, examples of methods for applying the coating liquid include dip coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, ring coating, and the like. Among these, dip coating is preferred from the viewpoint of efficiency and productivity.

Each layer will be explained below.
<Protective layer (surface layer)>
The electrophotographic photoreceptor of the present invention has a protective layer containing a binder resin and metal oxide particles as a surface layer. The protective layer contains metal oxide particles in an amount of 30% by volume or more and 75% by volume or less based on the total volume of the protective layer.
The protective layer may contain a charge transport material.

It is preferable that the powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1).
1.0×10 ³ ≦A≦1.0×10 ¹⁰ (1)
When the powder resistivity A of the metal oxide particles is lower than 1.0×10 ³ Ω·cm, it is difficult to suppress charge movement in the protective layer, and highlight image deletion deteriorates. Furthermore, if the powder resistivity A exceeds 1.0×10 10 Ω·cm, the injection charging property will deteriorate. The powder resistivity A is more preferably 1.0×10 ⁵ Ωcm or more and 1.0×10 ⁹ Ωcm or less.

In the present invention, the powder resistivity A of the metal oxide particles is measured under an environment of normal temperature and normal humidity (temperature 23.0° C./relative humidity 55%). In the present invention, a resistivity meter Loresta GP manufactured by Mitsubishi Chemical was used as a measuring device. The metal oxide particles of the present invention to be measured were solidified under a pressure of 500 kg/cm ² to form pellet-shaped measurement samples, and the applied voltage was 100V.

Specific examples of the metal oxide particles include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide. The metal oxide may be doped with an element such as phosphorus or aluminum, or its oxide may be added.

The metal oxide particles may have a laminated structure including core particles and a coating layer covering the particles. Examples of core material particles include metal oxides such as titanium oxide, barium sulfate, and zinc oxide. Examples of the coating layer include metal oxides such as tin oxide.

The metal oxide particles are particularly preferably titanium oxide particles containing niobium.
The titanium oxide particles containing niobium can have various shapes such as spherical, polyhedral, ellipsoidal, flaky, and acicular. Among these, spherical, polyhedral, and ellipsoidal shapes are preferable from the viewpoint of fewer image defects such as black spots. In the present invention, it is more preferable that the niobium-containing titanium oxide particles have a spherical shape or a polyhedral shape close to a spherical shape.

The niobium-containing titanium oxide particles are preferably anatase-type or rutile-type titanium oxide particles, and more preferably anatase-type titanium oxide particles from the viewpoint of improving injection charging properties.

In the present invention, the metal oxide particles are particularly particles having anatase-type titanium oxide particles as a core material and titanium oxide containing niobium that coats the surface of the core material. It is preferable that there be. As for the form in which niobium is contained, it is preferable to contain it in a so-called doped form, which is incorporated into the crystal lattice of titanium oxide, rather than in the form of an oxide. By doping titanium oxide with niobium, the injection charging property becomes higher.

When the metal oxide particles have titanium oxide particles containing niobium, the metal oxide particles preferably contain niobium in an amount of 0.5% by mass or more and 15.0% by mass or less, and preferably 2.6% by mass or more and 10% by mass or less. More preferably, it is .0% by mass or less. If the niobium content in the metal oxide particles is 0.5% by mass or more, the conductivity of titanium oxide can be increased and the injection chargeability can be increased; For example, since the crystal structure of titanium oxide can be maintained, the volume resistivity of the protective layer does not become too large.

Particularly preferred as the metal oxide particles are titanium oxide particles containing niobium and having a structure in which niobium is unevenly distributed near the particle surface. This is because the uneven distribution of niobium near the surface allows for efficient transfer of charges. More specifically, EDS analysis using a scanning transmission electron microscope (STEM) revealed that, with respect to the niobium/titanium atomic ratio at the center of the metal oxide particle, 5% of the primary particle diameter from the surface of the metal oxide particle These are titanium oxide particles in which the niobium/titanium atomic ratio is 2.0 times or more. Figure 3 shows a STEM image of an example of a metal oxide in which a titanium oxide core material is coated with titanium oxide containing niobium, similar to the titanium oxide particles (metal oxide particles 1) used in the examples of the present invention. show. Further, a schematic representation of the STEM image of FIG. 3 is shown in FIG. Although the details will be described later, the titanium oxide particles containing niobium used in this example are produced by coating titanium oxide particles containing niobium on the titanium oxide particles that serve as the core material, and then firing them. . Therefore, it is thought that the coated titanium oxide containing niobium grows as niobium-doped titanium oxide along the crystal of titanium oxide of the core material by so-called epitaxial growth. As shown in FIG. 3, the niobium-containing titanium oxide produced in this manner has a lower density near the surface than the density at the center of the particle, indicating that it has a core-shell-like morphology. In addition, in EDS analysis using STEM, X-rays pass through the entire particle, so as shown in Figure 4, compared to the EDS analysis at the center of the particle as shown in direction 33, the EDS analysis as shown in direction 34 In EDS analysis within 5% of the primary particle diameter from the particle surface, the influence near the surface becomes large. In other words, in the EDS analysis using STEM as described above, the niobium/titanium atomic ratio within 5% of the primary particle diameter from the surface of the particle is 2.0 compared to the niobium/titanium atomic ratio at the center of the particle. The fact that the amount is more than double is considered to be a state in which the niobium element is unevenly distributed near the surface. In FIG. 4, reference numeral 32 is a region of the metal oxide particles within 5% of the primary particle diameter from the surface of the particle, and reference numeral 31 is a region of the metal oxide particles inside the region 32. Further, reference numeral 33 indicates an X-ray for analyzing the center of the metal oxide particle, and reference numeral 34 indicates an X-ray for analyzing the inside of 5% of the particle diameter from the surface of the metal oxide particle.

For EDS analysis using STEM, observation is performed using a transmission electron microscope, and the niobium/titanium ratio is measured by EDS. Further, by cutting the electrophotographic photoreceptor into a thin section using a microtome, Ar milling, FIB, or other means, it is also possible to directly measure the electrophotographic photoreceptor.

Furthermore, the niobium-containing titanium oxide particles contained in the protective layer preferably have oxygen vacancies. Having oxygen vacancies improves injection charging properties. Although the detailed mechanism is not well understood, it is presumed that when titanium oxide particles containing niobium have oxygen vacancies, it becomes easier to receive electric charge, thereby improving injection charging properties. It is preferable that the oxygen vacancy rate of the titanium oxide particles containing niobium is 0.1% or more and 2.0% or less. If the oxygen vacancy rate is less than 0.1%, no improvement in injection chargeability can be expected, and if it exceeds 2.0%, the particles will become dark in color and the transparency of the protective layer will decrease. This causes a decrease in the sensitivity of the electrophotographic photoreceptor. In addition, when the oxygen vacancy rate in the area within 5% of the primary particle diameter from the surface of the titanium oxide particles containing niobium is β, and the oxygen vacancy rate in the other area is γ, the following formula (α) is satisfied. It is preferable to do so.
β > 10×γ (α)
This is because oxygen vacancies, which are more likely to receive electric charge, are unevenly distributed on the surface of the metal oxide particles, thereby allowing effective injection charging.

The oxygen vacancy rate of the metal oxide particles and the ratio of the oxygen vacancy rate in the area within 5% of the primary particle diameter from the surface of the metal oxide particle to the oxygen vacancy rate in the other area are determined by energy dispersive X-ray analysis. (EDS). Furthermore, as mentioned above, in EDS analysis, X-rays pass through the entire particle, so if the above relational expression (α) is satisfied, oxygen vacancies are unevenly distributed near the particle surface. means.

In the present invention, the ratio of the oxygen vacancy rate in the area within 5% of the primary particle diameter from the surface of the metal oxide particle to the oxygen vacancy rate in the other area was measured by STEM-EDS analysis of the metal oxide particle. .

Introduction of oxygen vacancies can be performed by firing in a reducing atmosphere such as ammonia or hydrogen, or by firing together with an organic substance in a nitrogen atmosphere at 600° C. or higher, which is the decomposition temperature of the organic substance.

Although the detailed mechanism is not clear, as mentioned above, the injection charging property increases due to the introduction of niobium doping and oxygen vacancies because conductive particles such as carbon black and graphite commonly used in charging materials It is thought that this is because it becomes easier to transfer charges from the charging member to the electrophotographic photoreceptor, and the transfer of charges from the charging member to the electrophotographic photoreceptor becomes smooth.

Further, the metal oxide particles are surface-treated with a compound containing silicon atoms such as a silane coupling agent or a silicone resin. This surface treatment increases the hydrophobicity of the metal oxide particles. In addition, this surface treatment maintains a high interfacial resistance between metal oxide particles that suppresses uneven dispersion of metal oxide particles in the protective layer, thereby suppressing a decrease in resistance due to poor dispersion of the surface layer. As a result, the surface layer is maintained at high resistance in a high humidity environment, so that highlight image deletion can be suppressed.

The silicon atom-containing compound used for surface treatment of metal oxide 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、アルコキシ基又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 surface treatment of metal oxide 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. However, at least two of R ¹ to R ³ are alkoxy groups. R ⁴ is an alkyl group having 12 or less carbon atoms.

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

In addition, examples of the silane coupling agent include silane coupling agents other than the compound represented by formula (A), such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, Silane, (phenylaminomethyl)methyldimethoxysilane, N-2-(aminoethyl)-3-aminoisobutylmethyldimethoxysilane, N-ethylaminoisobutylmethyldiethoxysilane, N-methylaminopropylmethyldimethoxysilane, vinyltrimethoxy Silane, 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).

A general method is used to surface-treat the metal oxide particles. Examples include a dry method and a wet method.
In the dry method, metal oxide particles are stirred in a high-speed mixer such as a Henschel mixer, and an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added and dispersed uniformly. It is then dried.
In addition, in the wet method, metal oxide particles and a surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads, etc. After dispersion, the solvent is removed by filtration or distillation under reduced pressure. will be held. After removing the solvent, it is preferable to further bake at 100° C. or higher.

Examples of the charge transport substance include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. Among these, triarylamine compounds and benzidine compounds are preferred.

The thickness of the protective layer as a surface layer is preferably 0.1 μm or more and 2.0 μm or less. If the thickness of the protective layer is less than 0.1 μm, it becomes difficult for the surface layer containing metal oxide particles to cover the entire surface of the electrophotographic photoreceptor, resulting in a decrease in injection chargeability. Furthermore, if the thickness of the protective layer exceeds 1.0 μm, the shared voltage will increase, charges will sink into the protective layer, and highlight image deletion will worsen. More preferably, it is 0.1 μm or more and 1.5 μm or less.

The volume resistivity B (Ω cm) of the binder resin used for the protective layer as the surface layer at a temperature of 32.5° C. and a humidity of 80% RH (hereinafter also referred to as "HH environment") is expressed by the following formula (4 ) is preferably satisfied.
1.0×10 ¹² ≦B≦1.0×10 ¹⁵ (4)

Metal oxide particles exist in the surface layer at a high content rate, but there is a high probability that the binder resin will enter between the metal oxide particles, so if the volume resistivity B of the binder resin is high, , the above-mentioned charge movement in the surface layer can be suppressed, and highlight image blurring can be suppressed. If the volume resistivity B of the binder resin is smaller than 1.0×10 ¹² Ω·cm, the above effect cannot be achieved and highlight image deletion cannot be sufficiently suppressed.

Specific examples of the binder resin used in the present invention include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polyarylate resin, polystyrene resin, phenol resin, melamine resin, and epoxy resin. Among these, it is preferable to contain at least one resin selected from the group consisting of polycarbonate resin, polyarylate resin, and acrylic resin.

Further, the protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of reactions at that time include thermal polymerization reactions, photopolymerization reactions, radiation polymerization reactions, and the like. Examples of the polymerizable functional group possessed by the monomer having a polymerizable functional group include an acryloyl group and a methacryloyl group. As the monomer having a polymerizable functional group, a material having charge transport ability may be used.

Further, the protective layer may contain a resin having silicon atoms.
Silicone oil is an example of the silicon-containing resin that may be contained in the protective layer. Examples of the silicone oil include straight silicone oil and modified silicone oil. Examples of the straight silicone oil include dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, and the like. Modified silicone oils include reactive silicone oils such as amino-modified, epoxy-modified, carboxy-modified, carbinol-modified, methacrylic-modified, mercapto-modified, phenol-modified, and non-reactive silicone oils such as polyether-modified, methylstyryl-modified, alkyl-modified. Examples include modification, ester modification, and fluorine modification. Furthermore, as the resin having silicon atoms, a block polymer or a graft polymer in which a polydimethylsiloxane structure is introduced into the side chain or main chain may be used.

The protective layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipperiness agents, and abrasion resistance improvers. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oil, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles. Examples include.

Further, the volume resistivity C (Ω·cm) of the protective layer as a surface layer at a temperature of 32.5° C. and a humidity of 80% RH (HH environment) preferably satisfies the following formula (2).
1.0×10 ¹¹ ≦C≦1.0×10 ¹³ (2)
If the volume resistivity C of the protective layer is less than 1.0×10 ¹¹ Ω·cm, the potential distribution of the latent image cannot be maintained, the latent image is distorted, and highlight image deletion cannot be suppressed. The volume resistivity C is more preferably 7.0×10 ¹¹ Ω·cm or more and 1.0×10 ¹³ Ω·cm or less.

Further, the volume resistivity D (Ω·cm) of the protective layer at a temperature of 23.0° C. and a humidity of 55% RH (hereinafter also referred to as “NN environment”) preferably satisfies the following formula (3).
1.0×10 ¹² ≦D≦1.0×10 ¹⁴ (3)
When the volume resistivity D of the protective layer is less than 1.0×10 ¹² Ω·cm, the risk of leakage increases.

Furthermore, the volume resistivity C (Ω cm) of the protective layer as a surface layer at a temperature of 32.5° C. and humidity of 80% RH, and the volume resistivity of the protective layer as a surface layer at a temperature of 23.0° C. and a humidity of 55% RH. It is preferable that D satisfies the following formula (5).
0.05≦D/C≦1.0 (5)
When the volume resistivities C and D of the protective layer as a surface layer satisfy the relationship of formula (5), charge movement in the surface layer can be suppressed, and highlight image blurring can be suppressed.

The volume resistivity of the protective layer and the binder resin can be measured as follows.
A pA (picoampere) meter is used to measure the volume resistivity. First, a comb-shaped gold electrode shown in FIG. 5 with an inter-electrode distance (D) of 180 μm and a length (L) of 59 mm is fabricated on a PET film by vapor deposition. A protective layer and a binder resin having a thickness (T1) of 2 μm are provided on the produced comb-shaped gold electrode so as to cover the comb-shaped gold electrode. Next, under an environment of temperature 23.0°C/humidity 55% RH (NN) and under an environment of temperature 32.5°C/humidity 80% RH (HH), a 100 V DC voltage was applied between the comb-shaped gold electrodes. (V) is applied, and the DC voltage (I) is measured. Using the obtained measured values, the volume resistivity C (temperature 32.5° C./humidity 80% RH) and volume resistivity D (temperature 23.0° C./humidity 55% RH) are obtained by the following formula (6).
Volume resistivity ρv (Ω cm) = V (V) × T1 (cm) × L (cm) / {I (A) × D (cm)} (6)

If it is difficult to identify the composition of the metal oxide particles, binder resin, etc. of the protective layer, the surface resistivity of the surface of the electrophotographic photoreceptor is measured and converted to volume resistivity. In other words, when measuring the volume resistivity of a protective layer that exists as a surface layer of an electrophotographic photoreceptor rather than the protective layer alone, measure the surface resistivity of the protective layer and convert the obtained value to volume resistivity. do.

Specifically, a comb-shaped gold electrode having an inter-electrode distance (D) of 180 μm and a length (L) of 59 mm as shown in FIG. 5 is formed on the surface of the electrophotographic photoreceptor (the surface of the protective layer) by gold vapor deposition. Next, a 1000V DC voltage (V ) is applied, and the surface resistivity ρs of the protective layer is calculated from the DC voltage (V)/DC voltage (I).
Using the obtained surface resistivity ρs and the film thickness t (cm) of the protective layer, the volume resistivity can be obtained by the following formula (7).
ρv=ρs×t (7)
(ρv: volume resistivity, ρs: surface resistivity, t: thickness of protective layer)

In this measurement, since a minute amount of current is measured, it is preferable to use a device capable of measuring minute currents as the resistance measuring device. For example, a resistance measuring device capable of measuring minute currents includes Picoammeter 4140B manufactured by Hewlett-Packard. The comb-shaped electrodes used and the voltage applied are preferably selected depending on the material and resistance value of the protective layer so that an appropriate SN ratio can be obtained.

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

<Support>
In the present invention, the electrophotographic photoreceptor may have a support. In the present invention, the support is preferably a conductive support having electrical conductivity. Further, the shape of the support includes a cylindrical shape, a belt shape, a sheet shape, and the like. Among these, a cylindrical support is preferred. Further, the surface of the support may be subjected to electrochemical treatment such as anodization, blasting treatment, cutting treatment, or the like.
Preferred materials for the support include metal, resin, and glass.
Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among these, an aluminum support using aluminum is preferable.
Further, conductivity may be imparted to the resin or glass by a process such as mixing or coating with a conductive material.

<Conductive layer>
In the present invention, a conductive layer may be provided on the support. By providing a conductive layer, it is possible to hide scratches and irregularities on the surface of the support, and to control the reflection of light on the surface of the support.The conductive layer may contain conductive particles and a resin. preferable.

Examples of the material for the conductive particles include metal oxides, metals, carbon black, and the like.
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, and the like. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, and silver.
Among these, it is preferable to use metal oxides as the conductive particles, and it is particularly preferable to use titanium oxide, tin oxide, and zinc oxide.
When using a metal oxide 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.
Further, the conductive particles may have a laminated structure including a core particle and a coating layer covering the particle. Examples of the core material particles include titanium oxide, barium sulfate, and zinc oxide. Examples of the coating layer include metal oxides such as tin oxide.
Further, when using a metal oxide as the conductive particles, the volume average particle diameter thereof is preferably 1 nm or more and 500 nm or less, 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.
Further, the conductive layer may further contain a masking agent such as silicone oil, resin particles, and titanium oxide.

The average thickness of the conductive layer is preferably 1 μm or more and 50 μm or less, particularly preferably 3 μm or more and 40 μm or less.

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

<Undercoat layer>
In the present invention, an undercoat layer may be provided on the support or the conductive layer. By providing an undercoat layer, the adhesion function between the layers can be enhanced and an injection charge blocking function can be imparted.

It is preferable that the undercoat layer contains 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 resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinylphenol resin, alkyd resin, polyvinyl alcohol resin, polyethylene oxide resin, polypropylene oxide resin, and polyamide resin. , polyamic acid resin, polyimide resin, polyamideimide resin, cellulose resin and the like.

Examples of the polymerizable functional group of 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, Examples include carboxylic acid anhydride groups and carbon-carbon double bond groups.

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

The metal oxide particles contained in the undercoat layer may be used after surface treatment using a surface treatment agent such as a silane coupling agent. A general method is used to surface treat the metal oxide particles. Examples include a dry method and a wet method.
In the dry method, metal oxide particles are stirred in a high-speed mixer such as a Henschel mixer, and an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added and dispersed uniformly. It is then dried.
In addition, in the wet method, metal oxide particles and a surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads, etc. After dispersion, the solvent is removed by filtration or distillation under reduced pressure. It will be done. After removing the solvent, it is preferable to further bake at 100° C. or higher.

The undercoat layer may further contain additives, such as known materials such as metal powder such as aluminum, conductive substances such as carbon black, charge transport substances, metal chelate compounds, and organometallic compounds. It can be included.

Examples of charge transport substances include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, halogenated aryl compounds, silole compounds, boron-containing compounds, etc. . An undercoat layer may be formed as a cured film by using a charge transporting material having a polymerizable functional group as the charge transporting material and copolymerizing it with the above monomer having a polymerizable functional group.

The undercoat layer can be formed by preparing an undercoat layer coating solution containing each of the above materials and a solvent, forming this coating on a support or conductive layer, and drying and/or curing. can.

Examples of the solvent used in the coating solution for the undercoat layer include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, aliphatic halogenated hydrocarbons, and aromatic compounds. In the present invention, it is preferable to use alcohol-based or ketone-based solvents.

Dispersion methods for preparing the 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 impingement type high-speed disperser.

The average thickness of the undercoat layer is preferably 0.1 μm or more and 50 μm or less, more preferably 0.2 μm or more and 40 μm or less, and particularly preferably 0.3 μm or more and 30 μm or less.

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

(1) Laminated photosensitive layer The laminated photosensitive layer includes a charge generation layer and a charge transport layer.

(1-1) Charge Generating Layer The charge generating layer preferably contains a charge generating substance and a resin.

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

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 preferred.

Further, the charge generation 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 average thickness of the charge generation layer is preferably 0.1 μm or more and 1.0 μm or less, more preferably 0.15 μm or more and 0.4 μm or less.

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

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

Examples of the charge transport substance include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. It will be done. Among these, triarylamine compounds and benzidine compounds are preferred.
The content of the charge transport substance in the charge transport layer is preferably 25% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 55% by mass or less, based on the total mass of the charge transport layer. preferable.

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

Further, the charge transport layer may contain additives such as an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a slipperiness imparting agent, and an abrasion resistance improver. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oil, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles. Examples include.

The average thickness of the charge transport layer is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 40 μm or less, and particularly preferably 9 μm or more and 30 μm or less.

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

(2) Single-layer type photosensitive layer A single-layer type photosensitive layer is formed by preparing a photosensitive layer coating solution containing a charge-generating substance, a charge-transporting substance, a resin, and a solvent, forming this coating film, and drying it. can do. The charge-generating substance, charge-transporting substance, and resin are the same as those exemplified in the above “(1) Laminated photosensitive layer”.

[Process cartridge, electrophotographic device]
The process cartridge of the present invention integrally supports the electrophotographic photoreceptor described above and at least one means selected from the group consisting of charging means, developing means, transfer means, and cleaning means, and It is characterized by being removable from the main body.

Furthermore, the electrophotographic apparatus of the present invention is characterized by having the electrophotographic photoreceptor, charging means, exposure means, developing means, and transfer means described above.

FIG. 6 shows an example of a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photoreceptor.

[Configuration of electrophotographic device]
Note that the electrophotographic apparatus of this example is a so-called tandem type electrophotographic apparatus that is provided with a plurality of image forming sections a to d. The first image forming section a is yellow (Y), the second image forming section b is magenta (M), the third image forming section c is cyan (C), and the fourth image forming section d is black (Bk). ) to form an image using toner of each color. These four image forming sections are arranged in a line at regular intervals, and most of the configurations of each image forming section are substantially the same except for the color of the toner contained therein. Therefore, the electrophotographic apparatus of this embodiment will be described below using the first image forming section a.
The first image forming section a includes a photosensitive drum 1a that is a drum-shaped electrophotographic photosensitive member, a charging roller 2a that is a charging member, a developing device 4a, and a drum cleaning device 5a.
The photosensitive drum 1a is an image carrier that carries a toner image, and is driven to rotate at a predetermined circumferential speed (process speed) in the direction of an arrow R1 in the figure. The developing means 4a stores yellow toner and develops the yellow toner on the photosensitive drum 1a. The drum cleaning means 5a is a means for collecting toner adhering to the photosensitive drum 1a. The drum cleaning unit 5a includes a cleaning blade that contacts the photosensitive drum 1a, and a waste toner box that stores toner and the like removed from the photosensitive drum 1a by the cleaning blade.

An image forming operation is started when a control means (not shown) such as a controller receives an image signal, and the photosensitive drum 1a is rotationally driven. During the rotation process, the photosensitive drum 1a is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this example) by a charging roller 2a, and exposed according to an image signal by an exposing means 3a. . As a result, an electrostatic latent image corresponding to the yellow color component image of the target color image is formed on the photosensitive drum 1a. Next, the electrostatic latent image is developed by the developing means 4a at the developing position and visualized as a yellow toner image on the photosensitive drum 1a. Here, the regular charging polarity of the toner contained in the developing means 4a is negative polarity, and the electrostatic latent image is reversely developed by the toner charged to the same polarity as the charging polarity of the photosensitive drum 1a by the charging roller 2a. . However, the present invention is not limited to this, and the present invention can also be applied to an electrophotographic apparatus that positively develops an electrostatic latent image using toner charged with a polarity opposite to that of the photosensitive drum 1a.
The endless and movable intermediate transfer belt 10 is electrically conductive, contacts the photosensitive drum 1a to form a primary transfer portion N1a, and rotates at substantially the same circumferential speed as the photosensitive drum 1a. Further, the intermediate transfer belt 10 is stretched by a facing roller 13 as a facing member, a drive roller 11 and a tension roller 12 as tension members, and a metal roller 14a, and the tension roller 12 applies a total tension of 60N. It is strung with. The intermediate transfer belt 10 can be moved by rotationally driving the drive roller 11 in the direction of arrow R2 in the figure. Further, each metal roller 14 and the opposing roller 13 are connected to ground via a Zener diode 15 as a constant voltage element.
The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 in the process of passing through the primary transfer portion N1a. The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the drum cleaning means 5a, and then subjected to an image forming process subsequent to charging.
During the primary transfer, a current is supplied to the conductive intermediate transfer belt 10 from a secondary transfer roller 40 as a secondary transfer member that contacts the outer peripheral surface of the intermediate transfer belt 10 . As the current supplied from the secondary transfer roller 40 flows in the circumferential direction of the intermediate transfer belt 10, the toner image is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10. At this time, a voltage of a predetermined polarity (positive polarity in this example) opposite to the normal charging polarity of the toner is applied from the transfer power source 41 to the secondary transfer roller 40 in the J direction.

Thereafter, in the same manner, a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image are formed and transferred onto the intermediate transfer belt 10 in order in an overlapping manner. As a result, toner images of four colors corresponding to the target color image are formed on the intermediate transfer belt 10. Thereafter, the four-color toner image carried on the intermediate transfer belt 10 is transferred to the paper feeder 50 in the process of passing through the secondary transfer portion N2 formed by the contact between the secondary transfer roller 40 and the intermediate transfer belt 10. The image is secondarily transferred all at once onto the surface of the transfer material P such as fed paper or OHP sheet. The transfer material P to which the four-color toner images have been transferred by secondary transfer is then heated and pressed by the fixing means 30, so that the four-color toners are melted and mixed and fixed onto the transfer material P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by a belt cleaning means 16 provided opposite to the opposing roller 13 via the intermediate transfer belt 10 . In addition, a path is provided that does not involve the secondary transfer roller 40 and electrically connects the transfer power source 41 and each metal roller 14 via a constant current diode 42 as a constant current element. Furthermore, when a voltage is applied from the transfer power source 41 to the secondary transfer roller 40, a pinch-off current Id flows through the constant current diode 42 in addition to the current It2 flowing toward the secondary transfer portion N2.

The electrophotographic photoreceptor of the present invention can be used in laser beam printers, LED printers, copying machines, facsimile machines, and multifunctional machines thereof.

Hereinafter, the present invention will be explained in more detail using Examples and Comparative Examples. The present invention is not limited in any way by the following examples unless it exceeds the gist thereof. In the following description of Examples, "parts" are based on mass unless otherwise specified.

(Production method of anatase type titanium oxide particles 1 to 7)
Anatase type titanium oxide particles can be produced by a known sulfuric acid method. In producing titanium oxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce a hydrous titanium dioxide slurry, and the titanium dioxide slurry is dehydrated and fired. As a result, anatase-type titanium oxide particles having an anatase degree of approximately 100% are obtained.
In the above method, anatase type titanium oxide particles 1 to 7 were produced by controlling the solution concentration of titanyl sulfate.

(Method for producing rutile-type titanium oxide particles 1)
200 parts by mass of ultrafine titanium oxide (TTO-55 (A): manufactured by Ishihara Sangyo Co., Ltd.; average primary particle diameter (manufacturer's nominal value): 40 nm) was mixed with 10,000 parts by mass of an aqueous potassium hydroxide solution with a concentration of 17 mol/L, together with Teflon ( (registered trademark) sealed in a tube. This was sealed in a pressure-resistant glass container and held at 110° C. for 20 hours to perform hydrothermal treatment. After the reaction product was neutralized with an aqueous hydrochloric acid solution having a concentration of 1 mol/L, washing with ion-exchanged water and centrifugation were repeated to obtain a white precipitate. Further, the obtained white precipitate was dried and subsequently calcined at 650° C. for 30 minutes to obtain rutile-type titanium oxide particles 1 with a primary particle size of 32 nm.
Regarding the rutile type titanium oxide particles 1, X-ray diffraction spectrum (CuKα) measurement using RINT2000 (manufactured by Rigaku Co., Ltd.) revealed that 27.4°, 36.1°, 41.2° due to rutile titanium oxide, A diffraction peak at 54.3° was confirmed.

Table 1 shows the number average particle diameters of anatase type titanium oxide particles 1 to 7 and rutile type titanium oxide particles 1 produced above.

(Production example of metal oxide particles 1)
Niobium (V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixture of niobium salt and titanium salt (hereinafter referred to as "titanium-niobium mixture").
Anatase type titanium oxide particles 1 were dispersed in water as core particles to form a suspension, and heated to 70° C. with stirring.
While maintaining the pH at 2.5, a titanium-niobium mixture containing 337 g/kg of Ti and 10.3 g/kg of Nb and an aqueous sodium hydroxide solution were simultaneously added to the weight of anatase-type titanium oxide particles 1. . After the addition was completed, the suspension was filtered, washed, and dried at 110° C. for 8 hours. This dried product was fired together with the organic matter at 725° C. for 1 hour in a nitrogen atmosphere to obtain metal oxide particles 1 in which niobium atoms were unevenly distributed near the surface.
When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, the relationship expressed by formula (α) was confirmed as shown in Table 2.

(Production of metal oxide particles 2 to 14)
In the production of metal oxide particles 1, the types of core particles used in the suspension, the weights of niobium atoms and titanium atoms in the titanium-niobium mixed solution during coating, and the firing conditions of the dried product after coating layer formation are shown in Table 2. Modified as shown. Other than that, powders of metal oxide particles 2 to 14 shown in Table 2 were obtained in the same manner as in the production of metal oxide particles 1.
When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, as shown in Table 2, the relationship expressed by formula (α) was confirmed for all particles other than metal oxide particle 13.

(Manufacture of metal oxide particles 15)
100 g of 4 anatase-type titanium oxide particles and 1 g of hexametaphosphoric acid were added to 500 cm ³ of water and dispersed using a bead mill. During the dispersion, the pH (pH = 9 to 11) was maintained to avoid the isoelectric point of the titanium oxide used. When the slurry after dispersion was observed using SEM, it was confirmed that the slurry was approximately monodispersed. Further, the median diameter of the slurry after dispersion was measured using a laser diffraction/scattering particle size distribution analyzer (manufactured by Horiba, model number: LA-950), and it was found to be 0.02 μm. This slurry was heated to 95°C. To this dispersion, phosphoric acid was added to the tin chloride aqueous solution so that P was 0.8% by mass based on the tin chloride aqueous solution and the weight of tin oxide, and titanium dioxide was produced by a hydrolysis reaction. Tin hydroxide crystals were deposited on the surface. The wet processed powder was removed, washed and dried. Substantially all of the tin chloride added in the wet treatment was hydrolyzed, and a tin hydroxide compound (stannic hydroxide exhibiting a SnO ₂ pattern in X-ray diffraction) was precipitated on the powder surface. 20g of this dry powder was placed in a quartz tubular furnace, heated at a rate of 10°C/min, and fired in a nitrogen atmosphere for 2 hours while controlling the temperature within the range of 700±50°C. Oxide particles 15 were obtained.
When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, the relationship expressed by formula (α) was confirmed as shown in Table 2.

(Manufacture of metal oxide particles 16)
Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolyzing an aqueous titanyl sulfate solution. Niobium sulfate was added in an amount of 1.8% by mass as niobium ions based on the amount of titanium in the slurry (in terms of titanium dioxide).
Niobium sulfate was added as niobium ions at a ratio of 1.8% by mass to an aqueous titanyl sulfate solution and hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired in the atmosphere at a firing temperature of 1000°C. As a result, metal oxide particles 16, which were anatase-type titanium oxide containing 1.8% by mass of the niobium element, were obtained.
When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, as shown in Table 3, the relationship expressed by formula (α) could not be confirmed.

(Manufacture of metal oxide particles 17)
Metal oxide particles 17 were obtained in the same manner as metal oxide particles 1 except that the concentration of the titanyl sulfate aqueous solution was adjusted.
When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, as shown in Table 3, the relationship expressed by formula (α) could not be confirmed.

(Production of metal oxide particles 18 to 21)
Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolyzing an aqueous titanyl sulfate solution. The amount of niobium sulfate added was 0.2% by mass as niobium ions based on the amount of titanium (in terms of titanium dioxide) in the slurry.
Niobium sulfate was added as niobium ions at a ratio of 0.2% by mass to a titanyl sulfate aqueous solution and hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired in the atmosphere at a firing temperature of 850°C. As a result, metal oxide particles 18, which were anatase-type titanium oxide containing 0.2% by mass of the niobium element, were obtained.
Further, in the above method, anatase type titanium oxide particles 19 to 21 were produced by controlling the solution concentration of titanyl sulfate.

When the distribution of oxygen vacancies in the metal oxide particles was confirmed using the method described above, as shown in Table 3, the relationship expressed by formula (α) could not be confirmed for any of the particles.

Tables 2 and 3 also show the number average particle diameter, powder resistance value, and proportion of niobium element present within 5% of the particle size from the outermost surface of the metal oxide particles 1 to 21 produced above.

<Manufacture of electrophotographic photoreceptor>
(Manufacturing example of electrophotographic photoreceptor 1)
An aluminum cylinder (JIS-A3003, aluminum alloy) with 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 coated with oxygen-deficient tin oxide (SnO ₂ ) (average primary particle diameter 230 nm): 214 parts ・Phenol resin (product name: Pryophen 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, rotation speed: 2000 rpm, and dispersion treatment time. : Dispersion treatment was performed for 4.5 hours at a cooling water set temperature of 18° C. to obtain a dispersion liquid. Glass beads were removed from this dispersion using a mesh (opening: 150 μm). Silicone resin particles (trade name: Tospearl 120, manufactured by Momentive Performance Materials, Inc., average particle size 2 μm) as a surface roughening agent were added to the obtained dispersion. The amount of silicone resin particles added was 10% by mass based on the total mass of metal oxide particles and binding material in the dispersion after removing the glass beads. In addition, silicone oil (trade name: SH28PA, manufactured by Dow Toray Industries, Inc.) as a leveling agent was added so that the amount was 0.01% by mass based on the total mass of metal oxide particles and binding material in the dispersion. was added to the dispersion.
Next, methanol was added so that the total mass of the metal oxide particles, the binding material, and the surface roughening agent in the dispersion (i.e., the mass of the solid content) was 67% by mass based on the mass of the dispersion. and 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion. Thereafter, a coating liquid for a conductive layer was prepared by stirring. This conductive layer coating liquid was dip coated onto a 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 transport substance (compound represented by the following formula (E-1)): 3.0 parts ・Blocked isocyanate (product name: Duranate SBB-70P, manufactured by Asahi Kasei Chemicals Co., Ltd.): 6.5 parts ・Styrene-acrylic Resin (product name: UC-3920, manufactured by Toagosei): 0.4 parts, silica slurry (product name: IPA-ST-UP, manufactured by Nissan Chemical Industries, solid content concentration: 15% by mass, viscosity: 9mPa・s) : 1.8 parts, 1-butanol: 48 parts, and acetone: 24 parts These were mixed and dissolved to prepare a coating solution for an undercoat layer. This undercoat layer coating liquid was applied onto the conductive layer by dip coating and heated at 170° C. for 30 minutes to form an undercoat layer having a thickness of 0.7 μm.

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

Next, the following materials were prepared.
・Charge transport substance (hole transport substance) represented by the following structural formula (C-1): 6.0 parts ・Charge transport substance (hole transport substance) represented by the following structural formula (C-2): 3.0 parts - Charge transport substance (hole transport substance) represented by the following structural formula (C-3): 1.0 parts - Polycarbonate resin (trade name: Iupilon Z400, manufactured by Mitsubishi Engineering Plastics Co., Ltd.) : 10.0 parts Polycarbonate resin having a copolymer 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 = 20,000): 0.02 parts A charge transport layer coating solution was prepared by dissolving these in a mixed solvent of 25 parts of ortho-xylene/25 parts of methyl benzoate/25 parts of dimethoxymethane. . This charge transport layer coating liquid was applied onto the charge generation layer by dip coating 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 22 μm.

・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、平均一次粒子径が６８ｎｍの表面処理金属酸化物粒子１を得た。 Next, the following materials were prepared.
- Metal 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 Department

・Toluene: 200.0 parts These were mixed, stirred for 4 hours using a stirring device, filtered, washed, and then heated at 130°C for 3 hours to obtain a surface-treated metal oxide with an average primary particle size of 68 nm. Particle 1 was obtained.

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０．５μｍの保護層を形成した。このようにして、金属酸化物粒子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。
また、結着樹脂の抵抗率は、上記保護層用塗布液１において、表面処理金属酸化物粒子が入っていない結着樹脂用塗布液１を用いて、保護層用塗布液１と同様の製造方法で膜化し、前述した体積抵抗率の測定で測定した。 Next, the following materials were prepared.
・Surface treated metal oxide particles 1: 197.5 parts ・As a binder resin, it is represented by the following structural formula (O-1), and has a resistivity of 3.5 at a temperature of 32.5° C. and a humidity of 80% RH (HH). 79.0 parts of a compound with a resistance of 6×10 ¹² Ωcm, 100.0 parts of 1-propanol (1-PA), and 100.0 parts of cyclohexane (CH) were mixed and stirred for 6 hours using a stirring device. Thus, protective layer coating liquid 1 was prepared.

This protective layer coating liquid 1 was dip coated onto the charge transport layer to form a coating film, and the resulting coating film was dried at 50° C. for 6 minutes. Thereafter, the coating film was irradiated with an electron beam for 1.6 seconds while rotating the support (irradiated object) at a speed of 300 rpm under conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA in a nitrogen atmosphere. The dose at the protective layer position was 15 kGy. Thereafter, the temperature of the coating film was raised to 117° C. under a nitrogen atmosphere. The oxygen concentration from electron beam irradiation to subsequent heat treatment was 10 ppm.
Next, after naturally cooling the coating film in the atmosphere until the temperature reached 25°C, heat treatment was performed for 1 hour at a temperature of 120°C to form a protective layer with a thickness of 0.5 μm. . In this way, an electrophotographic photoreceptor 1 having a protective layer containing metal oxide particles 1 was manufactured.
In addition, the resistivity of the binder resin was determined in the same way as the coating solution 1 for the protective layer, using the coating solution 1 for the binder resin that does not contain surface-treated metal oxide particles. It was formed into a film by the method and measured by the volume resistivity measurement described above.

(Production example of electrophotographic photoreceptors 2 to 20)
Electrophotographic photoreceptors 2 to 20 were prepared in the same manner as electrophotographic photoreceptor 1, except that the thickness of the protective layer was changed as shown in Table 4 by adjusting the type and number of metal oxides, and the amount of solvent. .

(Manufacturing example of electrophotographic photoreceptor 21)
In the manufacturing example of the electrophotographic photoreceptor 1, a protective layer coating liquid 21 was prepared by changing the types and amounts of the binder resin and mixed solvent used in preparing the protective layer coating liquid as follows.
Binder resin: 33.7 parts of the compound represented by (CTM-1),
3.7 parts of the compound represented by formula (CTM-2) was dissolved in a mixed solution of 59.25 parts of ortho-xylene and 98.75 parts of methyl benzoate.
It has 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, has a weight average molecular weight (Mw) of 100,000, and has a temperature of 32. 41.6 parts of polyester resin having a volume resistivity of 7.8×10 ¹⁴ Ω·cm at 5° C. and 80% RH (HH environment);
Mixed solvent: 948 parts of chlorobenzene/632 parts of dimethoxymethane,
1:112.9 parts of surface-treated metal oxide particles were added to the above mixed solution and stirred for 6 hours using a stirring device to obtain a protective layer coating liquid 21.
The obtained protective layer coating liquid 21 was dip coated onto 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 with a thickness of 0.5 μm. . Electrophotographic photoreceptor 21 was manufactured in the same manner as electrophotographic photoreceptor 1 except for the above.

In addition, the resistivity of the binder resin was determined by using the coating liquid 21 for a binder resin which does not contain the surface-treated metal oxide particles 1 in the coating liquid 21 for a protective layer. It was formed into a film using the manufacturing method and measured using the volume resistivity measurement method described above.

(Production example of electrophotographic photoreceptors 22 to 68 and 70)
The electrophotographic photoreceptors 22 to 68 were the same as the electrophotographic photoreceptor 21, except that the type of metal oxide particles, the presence or absence of surface treatment of the metal oxide particles, and the number of copies were changed as shown in Tables 4 and 5. , and 70 were prepared.

(Manufacturing example of electrophotographic photoreceptor 69)
The metal oxide particles to be added to the protective layer and the number of parts to be added are tin oxide particles without surface treatment (product name: SP-2, powder resistance 1 x 10 ³ Ω・cm, average primary particle diameter 20 nm, Mitsubishi Materials). Electrophotographic photoreceptor 69 was prepared in the same manner as electrophotographic photoreceptor 23, except that 196.1 parts of electrophotographic photoreceptor (manufactured by Denshi Kasei Co., Ltd.) were used.

(Manufacturing example of electrophotographic photoreceptor 71)
Instead of polyester resin, it has a structure represented by the formula (PC-I), has a viscosity average molecular weight of 40,000, and has a volume resistivity of 2.5 Electrophotographic photoreceptor 71 was produced in the same manner as electrophotographic photoreceptor 23 except that polycarbonate resin (1) having a resistance of 10 ¹³ Ω·cm was used.

(Production example of electrophotographic photoreceptors 72 and 73)
Electrophotographic photoreceptors 72 and 73 were produced in the same manner as electrophotographic photoreceptor 71, except that the type of metal oxide, the number of parts, and the thickness of the protective layer are shown in Table 5.

(Manufacturing example of electrophotographic photoreceptor 74)
In the manufacturing example of the electrophotographic photoreceptor 1, a protective layer coating liquid 74 was prepared by changing the types and amounts of the binder resin and mixed solvent used in preparing the protective layer coating liquid as follows.
263.3 parts of surface-treated metal oxide particles 1, 59.25 parts of N-methoxymethylated nylon 6 (methoxymethylation rate: 28 to 33%), and copolymerized nylon resin (product name: Amilan CM8000, manufactured by Toray Industries) 19.75 parts were mixed with a mixed solvent of 1185 parts of methanol and 790 parts of 1-butanol, and the mixture was stirred for 6 hours using a stirring device to prepare a protective layer coating liquid 74.
The obtained protective layer coating liquid 74 was dip coated onto the charge transport layer to form a coating film, and the coating film was dried at 100° C. for 30 minutes to form a protective layer with a thickness of 0.5 μm. . Electrophotographic photoreceptor 74 was manufactured in the same manner as electrophotographic photoreceptor 1 except for the above.

Further, the resistivity of the binder resin was determined by using the coating liquid 74 for a binder resin which does not contain the surface-treated metal oxide particles 1 in the coating liquid 74 for a protective layer. A film was formed using the manufacturing method, and the volume resistivity was measured as described above. The volume resistivity of the binder resin under an environment of temperature 32.5° C. and humidity 80% RH (HH) was 6.1×10 ¹¹ Ω·cm.

(Method for manufacturing electrophotographic photoreceptor 75)
Electrophotographic photoreceptor 75 was manufactured in the same manner as electrophotographic photoreceptor 1 except that the protective layer was formed using the following method.
Titanium oxide (M-1; primary particle size 350 nm, manufactured by Ishihara Sangyo) 18.2 parts Polyvinyl butyral resin 7.8 parts (XYHL; manufactured by UCC)
A mixture consisting of 122.2 parts of cyclohexanone (manufactured by Kanto Kagaku) was placed in a ball mill pot, and after ball milling for 48 hours using a φ10 mm SUS ball, the milling liquid was taken out and a 10% cyclohexanone solution of toluene-2,4-diisocyanate was added. 2 parts of cyclohexanone (manufactured by Kanto Kagaku), and 114.1 parts of methyl ethyl ketone (manufactured by Kanto Kagaku) were added and mixed and stirred to prepare a coating solution for a protective layer. This coating solution was spray-coated onto the charge transport layer, and then dried at 130° C. for 15 minutes to form a protective layer with a thickness of 2.5 μm.

(Method for manufacturing electrophotographic photoreceptor 76)
Electrophotographic photoreceptor 76 was manufactured in the same manner as electrophotographic photoreceptor 75 except that the material of the protective layer coating liquid was changed as shown below and the film thickness was 0.2 μm. The average particle size of the coating solution for the protective layer was measured using a centrifugal automatic particle size distribution analyzer CAPA-700 (Horiba, Ltd.) and found to be 0.4 μm.
Metal oxide particles 22: 18 parts Alcohol-soluble nylon: 8 parts (product name: Amilan CM8000, manufactured by Toray) Methanol: 50 parts Butanol: 20 parts

(Method for manufacturing electrophotographic photoreceptor 77)
Titanium oxide (ET-500W; primary particle size 250 nm, manufactured by Ishihara Sangyo) 18.2 parts Naphthalene carboxylic acid derivative represented by formula (CTM-3) as a charge transport material (manufactured by Ricoh) 3 parts,
A mixture consisting of 7.8 parts of polyvinyl butyral resin (XYHL; manufactured by UCC) and 122.2 parts of cyclohexanone (manufactured by Kanto Kagaku) was placed in a ball mill pot and subjected to ball milling for 48 hours using a Φ10 mm SUS ball, and then the milling liquid was taken out and toluene-2 , 10.2 g of a 10% cyclohexanone solution of 4-diisocyanate, 171.1 g of cyclohexanone (manufactured by Kanto Kagaku), and 114.1 g of methyl ethyl ketone (manufactured by Kanto Kagaku) were added and mixed and stirred to prepare a coating solution for a protective layer. Electrophotographic photoreceptor 77 was prepared in the same manner as electrophotographic photoreceptor 1 except that this protective layer coating solution was spray applied onto the charge transport layer and dried at 130° C. for 15 minutes to form a protective layer with a thickness of 2 μm. was created.

(Method for manufacturing electrophotographic photoreceptor 78)
The metal oxide particles to be added to the protective layer and the number of additives are tin oxide particles without surface treatment (product name: S-2000, powder resistance 3 x 10 Ω・cm, average primary particle diameter 20 nm, Mitsubishi Materials Electronic Chemicals Co., Ltd.) Electrophotographic photoreceptor 78 was prepared in the same manner as electrophotographic photoreceptor 68, except that the amount was changed to 196.1 parts (manufactured by Co., Ltd.).

これらを、平均粒径１．０ｍｍのガラスビーズ２００部を用いた縦型サンドミルに入れ、分散液温度２３±３℃、回転数１５００ｒｐｍ（周速５．５ｍ／ｓ）の条件で２時間分散処理を行い、分散液を得た。
この分散液からメッシュでガラスビーズを取り除いた後の分散液を、ＰＴＦＥ濾紙（商品名：ＰＦ０６０、アドバンテック東洋製）を用いて加圧ろ過し、保護層用塗布液を調製した。
次に、この保護層用塗布液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２．０ｍＡ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。電子線照射における酸素濃度は８１０ｐｐｍ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３．０μｍの保護層を形成した。このようにして、保護層を有する円筒状（ドラム状）の電子写真感光体７９を作製した。 (Method for manufacturing electrophotographic photoreceptor 79)
Electrophotographic photoreceptor 79 was manufactured in the same manner as electrophotographic photoreceptor 1, except that the material for the coating liquid for the protective layer and the method for forming the protective layer were as shown below, and the film thickness was 3.0 μm.
20 parts of the compound represented by the above structural formula (O-1) is mixed with a mixed solvent of 130 parts of 2-propanol and 14 parts of tetrahydrofuran, and this solution is mixed with anatase titanium oxide (AMT600, manufactured by Teika Co., Ltd. (particle size 30 nm). )) and 2.00 parts of an organic salt represented by the following structural formula (A-1) were added and stirred.

These were placed in a vertical sand mill using 200 parts of glass beads with an average particle size of 1.0 mm, and dispersed for 2 hours at a dispersion temperature of 23±3°C and a rotation speed of 1500 rpm (peripheral speed 5.5 m/s). A dispersion liquid was obtained.
Glass beads were removed from this dispersion using a mesh, and the dispersion was filtered under pressure using PTFE filter paper (trade name: PF060, manufactured by Advantech Toyo) to prepare a coating solution for a protective layer.
Next, this protective layer coating solution was applied onto the charge transport layer by dip coating to form a coating film, and the resulting coating film was dried at 50° C. for 6 minutes. Thereafter, the coating film was irradiated with an electron beam for 1.6 seconds under the conditions of an acceleration voltage of 70 kV and a beam current of 2.0 mA in a nitrogen atmosphere while rotating the support (irradiated object) at a speed of 300 rpm. The oxygen concentration during electron beam irradiation was 810 ppm. Next, the coating film was naturally cooled in the air until the temperature reached 25°C, and then heat-treated for 1 hour at a temperature of 120°C to form a protective layer with a thickness of 3.0 μm. did. In this way, a cylindrical (drum-shaped) electrophotographic photoreceptor 79 having a protective layer was produced.

(Method for manufacturing electrophotographic photoreceptor 80)
In the method for manufacturing electrophotographic photoreceptor 79, the type of metal oxide particles is rutile-type titanium oxide (SC150, manufactured by Teika Co., Ltd. (particle size 50 nm), powder resistance 1.3 × 10 ¹⁰ Ω・cm), and organic Electrophotographic photoreceptor 80 was produced in the same manner as electrophotographic photoreceptor 79 except that the type of salt was changed to an organic salt represented by the following structural formula (A-2).

(Examples 1 to 73 and Comparative Examples 1 to 8)
The physical properties of the electrophotographic photoreceptor produced above were measured, the fineness of the output image was evaluated, and the injectability was evaluated.
Examples 1 to 73 are cases in which electrophotographic photoreceptors 1 to 59, 61 to 63, 68 to 74, and 78 to 80 are used, and cases in which electrophotographic photoreceptors 60, 64 to 67, and 75 to 77 are used. are Comparative Examples 1 to 8.

<Measurement of physical properties of electrophotographic photoreceptor>
Hereinafter, a method for measuring each physical property of the electrophotographic photoreceptor according to the present invention will be explained.

<Calculation of primary particle diameter of metal oxide particles>
First, the entire electrophotographic photoreceptor was attached to methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the base of the electrophotographic photoreceptor was taken out. Next, insoluble components that do not dissolve in MEK (photosensitive layer and protective layer containing metal oxide particles) were filtered off and dried in a vacuum dryer. Further, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF)/methylal in a volume ratio of 1:1, and after filtering out insoluble matter, the filtered material was collected and dried in a vacuum drier. Through this operation, metal oxide particles and a protective layer resin were obtained. Furthermore, the filter material was heated to 500° C. in an electric furnace so that only the metal oxide particles were solid, and the metal oxide particles were recovered. In order to secure the necessary amount of metal oxide particles for measurement, a plurality of electrophotographic photoreceptors were subjected to similar treatment.
A part of the recovered metal oxide particles was dispersed in isopropanol (IPA), and the dispersion liquid was dropped onto a grid mesh with a support film (manufactured by JEOL Ltd., Cu150J) and subjected to a scanning transmission electron microscope (JEOL, JEM2800). ) Metal oxide particles were observed in STEM mode. The observation was performed at a magnification of 500,000 times to 1,200,000 times to easily calculate the particle diameter of the metal oxide particles, and STEM images of 100 metal oxide 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 image processing software "Image-Pro Plus (manufactured by Media Cybernetics)". First, use the Straight Line tool on the toolbar to select the scale bar displayed at the bottom of the STEM image. When Set Scale is selected from the Analyze menu in this state, a new window opens and the pixel distance of the selected straight line is entered in the Distance in Pixels field. Enter the value of the scale bar (for example, 100) in the Known Distance column of the window, enter the unit of the scale bar (for example, nm) in the Unit of Measurement column, and click OK to complete the scale setting. Next, using a straight line tool, a straight line was drawn so as to correspond to the maximum diameter of the metal oxide particles, and the particle diameter was calculated. The same operation was performed for 100 metal oxide particles, and the number average value of the obtained values (maximum diameter) was taken as the primary particle diameter of the metal oxide particles.

<Calculation of niobium atom/titanium atom concentration ratio>
One 5 mm square sample piece was cut out from the photoreceptor and cut into a 200 nm thick sample using an ultrasonic ultramicrotome (Leica, UC7) at a cutting speed of 0.6 mm/s to produce a flaky sample. This thin sample was examined at a magnification of 500,000 times to 1.2 million times in the STEM mode of a scanning transmission electron microscope (JEM2800, manufactured by JEOL) connected to an EDS analyzer (energy dispersive X-ray analyzer). I made an observation.
Among the observed metal oxide particles, metal oxide particles having a maximum diameter approximately 0.9 times or more the primary particle diameter calculated above were visually selected. Subsequently, spectra of the constituent elements of the selected metal oxide particles were collected using an EDS analyzer, and an EDS mapping image was created. Spectra were collected and analyzed using NSS (Thermo Fisher Scientific). The acquisition conditions were an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm so that the dead time was 15 to 30, a mapping resolution of 256 x 256, and a frame number of 300. EDS mapping images were obtained for 100 metal oxide particles.
By analyzing the EDS mapping images obtained in this way, it was possible to determine the niobium atomic concentration (atomic %) and the titanium atomic concentration (atomic %) in the center of the particle and within 5% of the maximum diameter of the measured particle from the particle surface. Calculate the ratio. Specifically, first press the NSS "Line Extraction" button, draw a straight line to the maximum diameter of the particle, and calculate the atomic concentration on the straight line from one surface through the inside of the particle to the other surface. Obtain information on (atomic %). If the maximum diameter of the particles obtained at this time was less than 0.9 of the primary particle diameter of the particles calculated above, they were excluded from further analysis. That is, the analysis shown below was performed only on particles having a maximum diameter of 0.9 times or more the primary particle diameter. Next, on both particle surfaces, read the niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface, and calculate the Soka average value of the two values obtained. From this, the niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle is obtained. Similarly, 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 ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" is obtained from the following formula.
Concentration ratio of niobium atoms and 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) / (from the particle surface Titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured atom
Also, read the niobium atomic concentration (atomic %) and titanium atomic concentration (atomic %) at a position on the above straight line and at the midpoint of the maximum diameter. Using these values, the "concentration ratio of niobium atoms and titanium atoms in the center of the particle" is obtained from the formula below.
Concentration ratio of niobium atoms and titanium atoms in the center of the particle =
(Niobium atomic concentration at the center of the particle (atomic %)) / (Titanium atomic concentration at the center of the particle (atomic %))
Furthermore, "concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at the center of the particle and concentration ratio calculated as niobium atomic concentration/titanium atomic concentration within 5% of the maximum diameter of the measured particle from the particle surface" ” is calculated using the following formula.
(The concentration ratio calculated as niobium atomic concentration/titanium atomic concentration at the particle center and the concentration ratio calculated as niobium atomic concentration/titanium atomic concentration within 5% of the maximum diameter of the measured particle from the particle surface) =
(Concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface) / (concentration ratio of niobium atoms and titanium atoms in the center of the particle)

<Calculation of content of metal oxide particles>
Next, four 5 mm square sample pieces were cut out from the electrophotographic photoreceptor, and the protective layer was three-dimensionally sized to 2 μm x 2 μm x 2 μm using FIB-SEM Slice & View. The content of metal oxide particles in the total volume of the protective layer was calculated from the difference in contrast between slices and views of FIB-SEM. The conditions for Slice & View were as follows.
Sample processing for analysis: FIB method processing and observation device: NVision 40 manufactured by SII/Zeiss
Slice interval: 5nm
Observation conditions:
Acceleration voltage: 1.0kV
Sample tilt: 54°
WD: 5mm
Detector: BSE detector aperture: 60μm, high current
ABC:ON
Image resolution: 1.25nm/pixel
The analysis area was 2 μm long x 2 μm wide, and the information for each cross section was integrated to determine the volume V per 2 μm long x 2 μm wide x 2 μm thick (8 μm ³ ). The measurement environment was a temperature of 23° C. and a pressure of 1×10 −4 Pa. Note that as a processing and observation device, Strata 400S manufactured by FEI (sample inclination: 52°) can also be used. Information on each cross section was obtained by image analysis of the area of metal oxide particles. Image analysis was performed using image processing software: Image-Pro Plus, manufactured by Media Cybernetics.

Based on the obtained information, the volume V of metal oxide particles in a volume of 2 μm×2 μm×2 μm (unit volume: 8 μm ³ ) was determined for each of the four sample pieces. Then, (Vμm ³ /8μm ³ ×100) was calculated. The average value of the values of (Vμm ³ /8μm ³ ×100) in the four sample pieces was taken as the content ratio [volume %] of the metal oxide particles in the protective layer with respect to the total volume of the protective layer.

Furthermore, by processing all four sample pieces up to the boundary between the protective layer and the layer immediately below it, the film thickness t (μm) of the protective layer was measured, and the volume resistivity of the protective layer of the photoreceptor was determined as follows. It was used as the value of the film thickness of the protective layer when calculating the volume resistivity ρ _v in the measurement method of .
The obtained results are shown in Tables 6 and 7.

<Quantification of niobium atoms contained in metal oxide particles>
The niobium atoms contained in the metal oxide particles are determined as follows.
The metal oxide particles recovered from the electrophotographic photoreceptor in the above <Calculation of primary particle diameter of metal oxide particles> are pelletized by the press molding described below to prepare a sample. Using the prepared sample, measurement is performed using an X-ray fluorescence analyzer (XRF), and the niobium atom content of the entire metal oxide particle is determined by the FP method.
Specifically, the amount of niobium pentoxide is determined and converted into the content of niobium atoms contained.
(i) Example of equipment used Fluorescent X-ray analyzer 3080 (Rigaku Denki Co., Ltd.)
(ii) Sample Preparation For sample preparation, a sample press molding machine MAEKAWA Testing Machine (manufactured by MFG Co, Ltd.) is used. 0.5 g of metal oxide particles are placed in an aluminum ring (model number: 3481E1) and pressed at a load of 5.0 tons for 1 minute to pelletize.
(iii) Measurement conditions Measurement diameter: 10φ
Measurement potential, voltage 50kV, 50-70mA
2θ angle 25.12°
Crystal plate LiF
Measurement time 60 seconds

<Method for measuring volume resistivity of protective layer>
A pA (picoampere) meter was used to measure the volume resistivity of the present invention.
First, a comb-shaped gold electrode shown in FIG. 5 with an inter-electrode distance (D) of 180 μm and a length (L) of 59 mm was fabricated on a PET film by vapor deposition, and a protective layer with a thickness (T1) of 2 μm was provided thereon. . Next, the DC voltage (I) when 100V DC voltage (V) was applied between the comb-shaped electrodes in an environment of temperature 23°C/humidity 50%RH and temperature 32.5°C/humidity 80%RH was measured, and the volume resistivity ρ _v (Ω·cm) was obtained using the following formula (6).
Volume resistivity ρ _v (Ω・cm) = V (V) × T1 (cm) × L (cm) / {I (A) × D (cm)} (6)

If it is difficult to identify the composition of the metal oxide particles, binder resin, etc. of the protective layer, the surface resistivity is measured on the surface of the electrophotographic photoreceptor and converted into volume resistivity. When measuring the volume resistivity of a protective layer coated on the surface of a photoreceptor rather than just the protective layer, it is best to measure the surface resistivity of the protective layer and convert it to volume resistivity. desirable.
In the present invention, a comb-shaped electrode having an inter-electrode distance (D) of 180 μm and a length (L) of 59 mm as shown in FIG. 5 is formed by gold vapor deposition on the surface of the protective layer of an electrophotographic photoreceptor. Next, in an environment of temperature 23°C/humidity 50% RH, we measured the DC voltage (I) when 1000V DC voltage (V) was applied between the comb-shaped electrodes, and measured the DC voltage (V)/ The surface resistivity ρ _s of the protective layer was calculated from the DC voltage (I).
Furthermore, using the film thickness t (cm) of the protective layer measured in the above-mentioned <Analysis of the cross section of the protective layer of the electrophotographic photoreceptor>, the volume resistivity ρ _v (Ω cm) is calculated by the following formula (7). did.
ρ _v = ρ _s ×t (7)
(ρ _v : volume resistivity, ρ _s : surface resistivity, t : thickness of protective layer)
In this measurement, since a minute amount of current is measured, it is preferable to use a device capable of measuring minute currents as the resistance measuring device. For example, Picoammeter 4140B manufactured by Hewlett-Packard may be used. The comb-shaped electrodes used and the voltage applied are preferably selected depending on the material and resistance value of the charge injection layer so that an appropriate S/N ratio can be obtained.

[evaluation]
(Evaluation of definition of output image)
As an electrophotographic apparatus for evaluation, a modified Hewlett-Packard laser beam printer Color LaseJet Enterprise M552 was used. As a modification, the charging conditions and laser exposure amount were made variable. Each of the electrophotographic photoreceptors manufactured above is attached to a process cartridge for black color, and attached to the station of the process cartridge for black color, and the process cartridges for other colors (cyan, magenta, yellow) are attached to the laser beam. It is now possible to operate without having to attach it to the printer itself. When outputting an image, only the process cartridge for black color was attached to the laser beam printer main body, and a monochrome image using only black toner was output. Further, the laser intensity was adjusted so that the dark potential Vd was -600V and the bright potential Vl was -250V, and the developing bias Vdc applied to the charging member was adjusted to be -450V.

The fineness of the output image is determined by outputting an image pattern (isolated dot pattern) that is exposed with a 3-dot interval for each exposed dot as shown in Figure 7 in an environment with a temperature of 32.5°C and relative humidity of 80%. The evaluation was based on the density of the output image. If the latent image of the isolated dot pattern is clearly formed on the electrophotographic photoreceptor, the image of the isolated dot pattern is clearly output on paper, and as a result, an output product with high image density can be obtained. Furthermore, if the latent image of the isolated dot pattern is not clearly formed on the electrophotographic photoreceptor, the image of the isolated dot pattern will not be clearly output on paper, resulting in an output product with low image density. Therefore, the fineness of the output image can be evaluated based on the density of the obtained output image.

The density of the output image was calculated from the difference between the whiteness of the portion where the exposed image pattern was formed and the whiteness of the portion (white background portion) where the exposed image pattern was not formed in the output image. The density of the output image was measured using a white photometer TC-6DS/A manufactured by Tokyo Denshoku Co., Ltd. using an amber filter. In the present invention, when the density of the obtained output image is 8.0% or more, it is determined that the output image has high definition. The results are shown in Tables 6 and 7.

(Evaluation of injectability)
For the evaluation of injection properties, a modified electrophotographic device (laser beam printer) (trade name: HP LaserJet Enterprise Color M553dn, manufactured by Hewlett-Packard) was used. The electrophotographic device used in the evaluation was modified so that the voltage applied to the charging roller could be adjusted and measured.
In addition, the cyan process cartridge of the electrophotographic apparatus was modified, and a potential probe (model 6000B-8, manufactured by Trek Japan Co., Ltd.) was attached to the development position. Next, the surface potential of the central portion of the electrophotographic photoreceptor was made to be able to be measured using a surface electrometer (model 344, manufactured by Trek Japan Co., Ltd.).
The electrophotographic photoreceptor according to each example and comparative example was mounted in an environment with a temperature of 23.0° C. and a humidity of 55% RH, and a DC current of -500 V was applied to the charging roller to remove the electrophotographic photoreceptor. was charged while rotating at 60 rpm. At this time, the potential A on the surface of the electrophotographic photoreceptor was measured, and injection property = A/-500 was determined. The results are shown in Tables 6 and 7.

The disclosure of this embodiment includes the following configurations.
(Configuration 1)
An electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles,
The average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less,
The content of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30% by volume or more and 75% by volume or less with respect to the total volume of the surface layer.
An electrophotographic photoreceptor characterized by:
(Configuration 2)
The electrophotographic photoreceptor according to configuration 1, wherein the surface layer has a thickness of 0.1 μm or more and 1.5 μm or less.
(Configuration 3)
The electrophotographic photoreceptor according to configuration 1 or 2, wherein the content of the metal oxide particles in the surface layer is 42% by volume or more and 65% by volume or less with respect to the total volume of the surface layer.
(Configuration 4)
The electrophotographic photoreceptor according to any one of configurations 1 to 3, wherein a powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1).
1.0×10 ³ ≦A≦1.0×10 ¹⁰ (1)
(Configuration 5)
The electrophotographic photoreceptor according to any one of configurations 1 to 4, wherein a volume resistivity C (Ω·cm) of the surface layer at 32.5° C. and humidity and 80% RH satisfies the following formula (2).
1.0×10 ¹¹ ≦C≦1.0×10 ¹³ (2)
(Configuration 6)
The electrophotographic photoreceptor according to any one of configurations 1 to 5, wherein a volume resistivity D (Ω·cm) of the surface layer at 23.0° C. and humidity 55% RH satisfies the following formula (3).
1.0×10 ¹² ≦D≦1.0×10 ¹⁴ (3)
(Configuration 7)
The electrophotograph according to any one of configurations 1 to 6, wherein the volume resistivity B (Ω cm) of the binder resin at a temperature of 32.5° C. and a humidity of 80% RH satisfies the following formula (4). Photoreceptor.
1.0×10 ¹² ≦B≦1.0×10 ¹⁵ (4)
(Configuration 8)
8. The electrophotographic photoreceptor according to any one of configurations 1 to 7, wherein the metal oxide particles are titanium oxide particles containing niobium.
(Configuration 9)
In the EDS analysis of the metal oxide particles using a scanning transmission electron microscope (STEM), the niobium/titanium atomic ratio at the center of the metal oxide particles is compared to 5% of the primary particle diameter from the surface of the metal oxide particles. 9. The electrophotographic photoreceptor according to configuration 8, wherein the niobium/titanium atomic ratio in % is 2.0 times or more.
(Configuration 10)
The volume resistivity C (Ω cm) of the surface layer at a temperature of 32.5° C. and a humidity of 80% RH and the volume resistivity D of the surface layer at a temperature of 23.0° C. and a humidity of 55% RH are expressed by the following formula (5). The electrophotographic photoreceptor according to any one of configurations 1 to 9, which satisfies the following.
0.05≦D/C≦1.0 (5)
(Configuration 11)
The electrophotographic photoreceptor according to any one of configurations 1 to 10, wherein the metal oxide particles are surface-treated with a compound having a silicon atom.
(Configuration 12)
The electronic device according to any one of configurations 1 to 12, wherein the surface layer contains, as the binder resin, at least one resin selected from the group consisting of polyarylate resin, polycarbonate resin, and acrylic resin. Photographic photoreceptor.
(Configuration 13)
The electrophotographic photoreceptor according to any one of configurations 1 to 12 and at least one means selected from the group consisting of charging means, developing means, transfer means, and cleaning means are integrally supported, A process cartridge characterized by being removably attached to the main body of a device.
(Configuration 14)
An electrophotographic apparatus comprising the electrophotographic photoreceptor according to any one of Structures 1 to 12, as well as charging means, exposure means, developing means, and transfer means.

1a, 1b, 1c, 1d Electrophotographic photoreceptor 2a, 2b, 2c, 2d Charging means 3a, 3b, 3c, 3d Exposure light 4a, 4b, 4c, 4d Developing means 5a, 5b, 5c, 5d Cleaning means N1a, N1b , N1c, N1d Primary transfer means 10 Intermediate transfer belt P Transfer material N2 Secondary transfer means 30 Fixing means 10 Pre-exposure light

Claims (14)

An electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles,
The average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less,
The content of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30% by volume or more and 75% by volume or less with respect to the total volume of the surface layer.
An electrophotographic photoreceptor characterized by: The electrophotographic photoreceptor according to claim 1, wherein the surface layer has a thickness of 0.1 μm or more and 1.5 μm or less. The electrophotographic photoreceptor according to claim 1, wherein the content of the metal oxide particles in the surface layer is 42% by volume or more and 65% by volume or less with respect to the total volume of the surface layer. The electrophotographic photoreceptor according to claim 1, wherein a powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1).
1.0×10 ³ ≦A≦1.0×10 ¹⁰ (1) The electrophotographic photoreceptor according to claim 1, wherein the volume resistivity C (Ω·cm) of the surface layer at 32.5° C. and humidity 80% RH satisfies the following formula (2).
1.0×10 ¹¹ ≦C≦1.0×10 ¹³ (2) The electrophotographic photoreceptor according to claim 1, wherein a volume resistivity D (Ω·cm) of the surface layer at 23.0° C. and humidity 55% RH satisfies the following formula (3).
1.0×10 ¹² ≦D≦1.0×10 ¹⁴ (3) The electrophotographic photoreceptor according to claim 1, wherein a volume resistivity B (Ω·cm) of the binder resin at a temperature of 32.5° C. and a humidity of 80% RH satisfies the following formula (4).
1.0×10 ¹² ≦B≦1.0×10 ¹⁵ (4) The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles are titanium oxide particles containing niobium. In the EDS analysis of the metal oxide particles using a scanning transmission electron microscope (STEM), the niobium/titanium atomic ratio at the center of the metal oxide particles is compared to 5% of the primary particle diameter from the surface of the metal oxide particles. 9. The electrophotographic photoreceptor according to claim 8, wherein the niobium/titanium atomic ratio in % is 2.0 times or more. The volume resistivity C (Ω cm) of the surface layer at a temperature of 32.5° C. and a humidity of 80% RH and the volume resistivity D of the surface layer at a temperature of 23.0° C. and a humidity of 55% RH are expressed by the following formula (5). The electrophotographic photoreceptor according to claim 1, which satisfies the following.
0.05≦D/C≦1.0 (5) The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles are surface-treated with a compound having a silicon atom. The electrophotographic photoreceptor according to claim 1, wherein the surface layer contains, as the binder resin, at least one resin selected from the group consisting of polyarylate resin, polycarbonate resin, and acrylic resin. The electrophotographic photoreceptor according to any one of claims 1 to 12 and at least one means selected from the group consisting of charging means, developing means, transfer means, and cleaning means are integrally supported, A process cartridge characterized in that it can be freely attached to and detached from the main body of a photographic device. An electrophotographic apparatus comprising the electrophotographic photoreceptor according to any one of claims 1 to 12, charging means, exposure means, developing means, and transfer means.

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