Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that is excellent in fine line reproducibility and prevents the occurrence of positive ghost.SOLUTION: An electrophotographic photoreceptor comprises: a conductive substrate; an undercoat layer provided on the conductive substrate; and a photosensitive layer provided on the undercoat layer. The amount of change in the mass of the undercoat layer at a temperature of 130°C or more and 155°C or less in differential scanning calorimetry is 0.1 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus.

Background Art

[0002] Patent Document 1 discloses an electrophotographic photoreceptor having "a conductive support, an undercoat layer provided on the conductive support, the undercoat layer being a cured film of a composition containing a binder resin, metal oxide particles, an electron-accepting compound having an anthraquinone structure with a content of 1 part by mass or more and 5 parts by mass or less based on 100 parts by mass of the metal oxide particles, and an isocyanate compound, and the undercoat layer having a weight change amount of 0.05% by mass or more and 0.8% by mass or less from 0 °C to 230 °C in differential thermal / thermogravimetric simultaneous measurement (TG / DTA measurement), and a photosensitive layer provided on the undercoat layer".

[0003] Patent Document 2 discloses an electrophotographic photoreceptor having "a support, an undercoat layer containing at least metal oxide particles and a binder resin and having a mass change amount of 0.65% by mass or less from a temperature of 30 °C to 130 °C in differential thermal / thermogravimetric simultaneous measurement, and a photosensitive layer, in this order".

[0004] Patent Document 3 discloses an electrophotographic photoreceptor having "a support, and an undercoat layer and a photosensitive layer provided on the support in this order, the undercoat layer containing zinc oxide particles, a resin having a urethane bond, and methyl ethyl ketone oxime, and the undercoat layer satisfying the formula: 10 < M / L < 400 (where M represents the ratio (ppm) of the methyl ethyl ketone oxime contained in the undercoat layer, and L represents the average thickness (μm) of the undercoat layer)".

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In a conventional electrophotographic photoreceptor, when attempting to improve the reproducibility of fine lines, when forming repeated images, the surface potential of the photoreceptor in the next cycle at the image exposure part in the previous cycle decreases, the density of that part becomes dark, and the image of the previous cycle appears darkly in the image of the next cycle, resulting in an image quality defect called "positive ghost". In an electrophotographic photoreceptor including a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, compared with the case where the mass change amount at a temperature of 130°C or higher and 155°C or lower by differential scanning calorimetry of the undercoat layer exceeds 0.1% by mass, or the case where the Fermi level of the undercoat layer exceeds 4.48 eV, it is an object to provide an electrophotographic photoreceptor excellent in fine line reproducibility and suppressing positive ghost. [Means for Solving the Problems]

[0007] Specific means for solving the above problems include the following aspects. <1> A conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, and the mass change amount at a temperature of 130°C or higher and 155°C or lower by differential scanning calorimetry of the undercoat layer is 0.1% by mass or less, an electrophotographic photoreceptor. <2> A conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, and the Fermi level of the undercoat layer is 4.48 eV or less, an electrophotographic photoreceptor. <3> The amount of mass change of the lower layer measured by differential scanning calorimetry at temperatures between 30°C and 155°C is 0.3% by mass or less. <1> or <2> The electrophotographic photoreceptor described above. <4> The amount of mass change of the lower layer measured by differential scanning calorimetry at temperatures between 30°C and 155°C is 0.2% by mass or less. <3> The electrophotographic photoreceptor described above. <5> The aforementioned undercoat is a layer composed of a cured film of a composition containing a resin and a blocked isocyanate. <1> ~ <4> An electrophotographic photoreceptor as described in any one of the following. <6> The blocked isocyanate comprises an isocyanate compound blocked by a blocking agent having a boiling point of 130°C or higher and 155°C or lower. <5> The electrophotographic photoreceptor described above. <7> The aforementioned lower layer has an electron-accepting compound content of 0.75% by mass or more and 1.5% by mass or less relative to the total solid content of the lower layer. <1> ~ <6> An electrophotographic photoreceptor as described in any one of the following. <8> The aforementioned underlayer contains inorganic particles, <1> ~ <7> An electrophotographic photoreceptor as described in any one of the following. <9> The aforementioned <1> ~ <8> It comprises an electrophotographic photoreceptor as described in any one of the following: A process cartridge that is attached to and detached from an image forming apparatus. <10> The aforementioned <1> ~ <8> An electrophotographic photoreceptor as described in any one of the following, A charging means for charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing means that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, A transfer means for transferring the toner image onto the surface of a recording medium, An image forming apparatus equipped with the following features. [Effects of the Invention]

[0008] <1> According to the present invention, an electrophotographic photoreceptor is provided that comprises a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, and exhibits superior fine-line reproducibility and suppressed positive ghosting compared to a case where the mass change of the undercoat layer at a temperature of 130°C to 155°C, as measured by differential scanning calorimetry, exceeds 0.1% by mass. <2> According to the present invention, an electrophotographic photoreceptor is provided that comprises a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, and exhibits superior fine-line reproduction and suppressed positive ghosting compared to a case where the Fermi level of the undercoat layer exceeds 4.48 eV. <3> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior fine-line reproducibility and suppressed positive ghosting compared to a case where the mass change of the underlayer, measured by differential scanning calorimetry at temperatures between 30°C and 155°C, exceeds 0.3% by mass. <4> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior fine-line reproducibility and suppressed positive ghosting compared to a case where the mass change of the underlayer, measured by differential scanning calorimetry at temperatures between 30°C and 155°C, exceeds 0.2% by mass. <5> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior fine line reproduction and suppressed positive ghosting compared to a layer composed of a cured film of a composition that does not have blocked isocyanates. <6> According to the invention, compared to a layer composed of a cured film of a composition containing an isocyanate compound blocked by a blocking agent having a boiling point of less than 130°C or more than 155°C, an electrophotographic photoreceptor is provided that exhibits superior fine line reproducibility and suppressed positive ghosting. <7> According to the invention, when the content of the electron-accepting compound in the undercoat is less than 0.75% by mass or more than 1.5% by mass relative to the total solid content of the undercoat, an electrophotographic photoreceptor is provided that exhibits excellent fine-line reproducibility and suppresses positive ghosting. <8> According to the invention, an electrophotographic photoreceptor is provided that exhibits excellent fine line reproduction and suppresses positive ghosting, in the case where the undercoat is an undercoat that does not contain inorganic particles. <9> or <10> According to the present invention, a process cartridge or image forming apparatus is provided that exhibits superior fine line reproduction and suppresses positive ghosting compared to a case in which an electrophotographic photoreceptor is provided in which the mass change amount of the undercoat layer at a temperature of 130°C to 155°C, as determined by differential scanning calorimetry, exceeds 0.1% by mass, or a case in which an electrophotographic photoreceptor is provided in which the Fermi level of the undercoat layer exceeds 4.48 eV. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an example of an image forming apparatus according to this embodiment. [Figure 2] This is a schematic diagram showing another example of the image forming apparatus according to this embodiment. [Figure 3] This is a schematic partial cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor according to this embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present invention are described below. These descriptions and examples are illustrative and do not limit the scope of the embodiments.

[0011] In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit of that range may be replaced by the values ​​shown in the examples.

[0012] In this specification, each component may contain multiple types of the relevant substance. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0013] [Electrophotographic photoconductor] The electrophotographic photoreceptor according to the first embodiment comprises a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, wherein the mass change of the undercoat layer at a temperature of 130°C to 155°C, as determined by differential scanning calorimetry, is 0.1% by mass or less.

[0014] The electrophotographic photoreceptor according to the second embodiment comprises a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer, wherein the Fermi level of the undercoat layer is 4.48 eV or less.

[0015] Hereinafter, embodiments common to the first and second embodiments will also be referred to as "this embodiment," or this description will be omitted.

[0016] In recent years, techniques have been developed to further improve image quality by increasing the charging voltage during image formation to increase image density and improve fine line reproduction. However, increasing the charging voltage increases the charging potential (VH) of the photoreceptor, which increases the amount of charge generated, resulting in a larger amount of current flowing through the photoreceptor. Therefore, when the surface of the photoreceptor is charged and exposed under these conditions to form an electrostatic latent image, some of the charge generated during exposure may remain within the layers of the photoreceptor. This phenomenon of charge remaining within the layers of the photoreceptor is particularly pronounced when there is a large amount of residual hardening agent and substances released from the hardening agent contained in the undercoat layer. If residual charge remains within the layers of the photoreceptor, and the surface of the photoreceptor is recharged to form the next electrostatic latent image, the residual charge within the layers moves to the surface, making it easier for the surface potential of that region to decrease. In addition, residual charge within the layers of the photoreceptor easily traps holes generated within the layers, which tends to raise the Fermi level. As a result, in regions where the surface potential has decreased, a phenomenon may occur where the image history from the previous image formation cycle appears superimposed on the image from the next image formation cycle (hereinafter also called "positive ghosting").

[0017] On the other hand, the electrophotographic photoreceptor according to this embodiment, having the above configuration, exhibits excellent fine line reproduction and suppresses positive ghosting. The mechanism of action is not entirely clear, but it is presumed to be as follows.

[0018] In the electrophotographic photoreceptor according to the first embodiment, the mass change in the undercoat layer in the range of 130°C to 155°C is 0.1% by mass or less, indicating that the mass change is kept small. Typically, the curing agent and substances released from the curing agent (e.g., methyl ethyl ketone oxime) that may remain in this undercoat layer often have boiling points in the range of 130°C to 155°C. Therefore, a small mass change in this temperature range indicates that the amount of curing agent and substances released from the curing agent remaining in the undercoat layer is small. As a result, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is thought that charge is less likely to remain in the layers of the photoreceptor, and positive ghosting is suppressed.

[0019] In the electrophotographic photoreceptor according to the second embodiment, the Fermi level of the undercoat layer is 4.48 eV or less. Normally, curing agents that may remain in the undercoat layer and substances released from the curing agent (e.g., methyl ethyl ketone oxime) tend to raise the Fermi level of the undercoat layer in order to capture holes generated within the layers of the photoreceptor. However, in the photoreceptor according to the second embodiment, the Fermi level is kept low, indicating that the amount of curing agent and substances released from the curing agent remaining in the undercoat layer is small. Therefore, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is thought that charge is less likely to remain in the layers of the photoreceptor, and positive ghosting is suppressed.

[0020] The photoreceptor according to this embodiment comprises a conductive substrate, an undercoat layer disposed on the conductive substrate, and a photosensitive layer disposed on the undercoat layer.

[0021] Figure 3 schematically shows an example of the layer configuration of a photoreceptor according to this embodiment. The photoreceptor 7A shown in Figure 3 has a structure in which a base layer 1, a charge generation layer 2, and a charge transport layer 3 are laminated in this order on a conductive substrate 4. The charge generation layer 2 and the charge transport layer 3 constitute the photosensitive layer 5. The photoreceptor 7A may also have a layer configuration in which a protective layer is further provided on the charge transport layer 3.

[0022] In the photoreceptor according to this embodiment, the photosensitive layer may be a functionally separated photoreceptor in which the charge generation layer 2 and the charge transport layer 3 are separated, as shown in the photoreceptor 7A in Figure 3, or it may be a single-layer photoreceptor having charge generation and charge transport capabilities instead of the charge generation layer 2 and the charge transport layer 3.

[0023] The layers of the electrophotographic photoreceptor according to this embodiment will be described in detail below. Reference numerals will be omitted in the description.

[0024] (subbing layer) -Characteristics of the lower layer- • Mass change According to the first embodiment, the undercoat has a mass change of 0.1% by mass or less at a temperature of 130°C to 155°C as determined by differential scanning calorimetry, preferably 0.075% by mass or less, and more preferably 0% by mass or 0.05% by mass or less. According to the second embodiment, the undercoat preferably has a mass change of 0.1% by mass or less at a temperature of 130°C to 155°C as determined by differential scanning calorimetry, more preferably 0.075% by mass or less, and even more preferably 0% by mass or 0.05% by mass or less. If the mass change measured by differential scanning calorimetry at temperatures between 130°C and 155°C falls within the above range, it is believed that the amount of residual hardening agent and substances released from the hardening agent in the undercoat layer is smaller. Therefore, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is less likely for charge to remain in the photoreceptor layer, and positive ghosting is further suppressed.

[0025] According to the first embodiment, the undercoat preferably has a mass change of 0.35 mass% or less at a temperature of 30°C to 155°C as determined by differential scanning calorimetry, more preferably 0.3 mass% or less, and even more preferably 0 mass% or 0.2 mass% or less. According to the second embodiment, the undercoat preferably has a mass change of 0.35 mass% or less at a temperature of 30°C to 230°C as determined by differential scanning calorimetry, more preferably 0.3 mass% or less, and even more preferably 0 mass% or 0.2 mass% or less. If the mass change measured by differential scanning calorimetry at temperatures between 30°C and 230°C falls within the above range, it is thought that the amount of residual solvent, water, etc. in the underlayer is smaller. Therefore, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is thought that charge is less likely to remain in the photoreceptor layer, and positive ghosting is further suppressed.

[0026] The method for keeping the mass change within the above range is not particularly limited, but for example, when forming the undercoat, a coating liquid for forming the undercoat is applied to the conductive substrate, and the coating film is heated and dried under conditions of a temperature of 180°C or higher and a holding time of 20 minutes or more.

[0027] The change in mass of the lower layer in each temperature range is measured as follows: From the electrophotographic photoreceptor, the layer above the undercoat on the outer surface is peeled off using cellophane tape or the like. Then, the undercoat is cut out with a utility knife or the like, and a 10 mg sample is taken and weighed into an aluminum dish for measurement. For measuring the mass change, the "EXSTER TG / DTA 6200" manufactured by SII Nanotechnology is used. Alumina is used as the standard material, and measurements are taken from 30°C to 500°C at a heating rate of 10°C / min, and the mass change between 130°C and 155°C, and the mass change between 30°C and 155°C are determined.

[0028] Fermi level According to the first embodiment, the Fermi level of the lower layer is preferably 4.48 eV or less, more preferably 4.0 eV to 4.48 eV, and even more preferably 4.2 eV to 4.45 eV. According to the second embodiment, the Fermi level of the lower layer is 4.48 eV or less, preferably 4.0 eV to 4.48 eV, and more preferably 4.2 eV to 4.45 eV. When the Fermi level of the undercoat layer is within the above range, the amount of residual hardening agent and substances released from the hardening agent in the undercoat layer is smaller. Therefore, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is thought that charge is less likely to remain in the photoreceptor layer, and positive ghosting is further suppressed.

[0029] The Fermi level of the lower layer is measured as follows. The layers above the undercoat on the outer surface of the electrophotographic photoreceptor are peeled off using cellophane tape (registered trademark) or the like. Then, a piece measuring 2 cm x 2 cm with a thickness of 1.6 mm or less is cut out using a band saw or the like to serve as the test specimen. The Fermi level of the obtained test specimen is determined using an atmospheric photoelectron spectroscopy yield device (RIKEN KEKIN: FAC-2).

[0030] The method for setting the Fermi level of the undercoat to within the above range is not particularly limited, but for example, one method is to apply an undercoat forming solution onto a conductive substrate when forming the undercoat, and then heat-dry the coating film under conditions of a temperature of 180°C or higher and a holding time of 20 minutes or more.

[0031] In this embodiment, the undercoat preferably contains less than 220 ppm of methyl ethyl ketone oxime relative to the total solid content of the undercoat, more preferably 0 ppm or 200 ppm or less, and even more preferably 0 ppm or 150 ppm or less. The undercoat preferably contains as close to 0 ppm of methyl ethyl ketone oxime as possible relative to the total solid content of the undercoat.

[0032] When the methyl ethyl ketone oxime content is within the above range, the amount of residual hardener and substances released from the hardener in the undercoat layer is smaller. Therefore, even when the charging voltage is increased during image formation to obtain fine line reproduction and images are repeatedly formed, it is thought that charge is less likely to remain in the photoreceptor layer, and positive ghosting is further suppressed.

[0033] The methyl ethyl ketone oxime content mentioned above is measured as follows. The undercoat layer is peeled off the conductive substrate and its mass is measured. Next, the peeled undercoat layer is sealed in an aluminum cell for TG / DTA measurement using a thermogravimetric analyzer Extra6300 (manufactured by Hitachi High-Tech Science Corporation), and heated from 30°C to 500°C using a TG / DTA heating rate of 10°C / min. The amount of material lost (g) from 30°C to 155°C is considered the amount of blocking agent (g) released from the blocked isocyanate in the undercoat layer. The fact that the component lost from 30°C to 155°C is a blocking agent (e.g., methyl ethyl ketone oxime) is confirmed by GC / MS analysis.

[0034] (composition) The undercoat layer is preferably a layer composed of a cured film of a composition containing a resin and a curing agent, and more preferably a layer composed of a cured film of a composition containing a resin and a blocked isocyanate. The composition may further contain, as needed, a curing catalyst, inorganic particles, electron-accepting compounds, etc.

[0035] -Hardening agent- Examples of curing agents include isocyanate compounds and polyols. The curing agent preferably contains an isocyanate compound, more preferably a blocked isocyanate, and even more preferably an isocyanate compound blocked by a blocking agent having a boiling point of 130°C or higher and 155°C or lower.

[0036] Typically, when the undercoat is a cured film of a composition containing blocked isocyanates (especially blocked isocyanates with a boiling point between 130°C and 155°C), increasing the charging voltage and repeatedly forming images can cause the Fermi level of the undercoat to rise as blocking agents (e.g., methyl ethyl ketone oxime, etc.) released from the remaining blocked isocyanates in the undercoat capture holes generated within the photoreceptor layer. In other words, positive ghosting is more likely to occur when trying to achieve fine line reproduction. In contrast, in the electrophotographic photoreceptor according to this embodiment, the amount of mass change in differential scanning calorimetry of the undercoat layer satisfies the above range, or the Fermi level satisfies the above range. Therefore, even if the layer is composed of a cured film of a composition containing a blocked isocyanate, in which free blocking agents such as methyl ethyl ketone oxime tend to remain, fine line reproducibility is excellent and positive ghosting is suppressed.

[0037] Examples of isocyanate compounds include, Diisocyanates such as methylene diisocyanate, ethylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, 4,4'-biphenylene diisocyanate, dicyclohexylmethane diisocyanate, methylenebis(4-cyclohexyl isocyanate); isocyanurates obtained by trimerizing the above diisocyanates; Blocked isocyanates obtained by blocking the isocyanate group of the aforementioned diisocyanate with a blocking agent such as methyl ethyl ketone oxime, phenol, or alcohol; These are some examples. Among the above, isocyanate compounds are preferably polyfunctional isocyanurates having multiple isocyanate groups, or blocked isocyanates. Blocked isocyanates are particularly preferred from the viewpoint of manufacturability and stability. From the viewpoint of further improving film-forming properties, oligomers or resinous isocyanate compounds are preferred.

[0038] Examples of polyols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 2,2-dimethyl-1,3-propanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 3,3-dimethyl-1,2-butanediol, 2-ethyl-2-methyl-1,3-propanediol, 1,2-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,2-diethyl-1,3-propanediol, and 2,4-dimethyl-2,4-pentanediol. Examples of diols include diols such as 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, hydroquinone, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol, poly(oxytetramethylene) glycol, 4,4'-dihydroxydiphenyl-2,2-propane, and 4,4'-dihydroxyphenylsulfone. Other polyols besides butyral resin include, for example, polyester polyols, polycarbonate polyols, polycaprolactone polyols, polyether polyols, and polyols. One type of polyol may be used, or two or more types may be used in combination.

[0039] -resin- Examples of resins include those having groups that react with a hardening agent. Examples of resins include known polymer compounds such as acetal resins (e.g., polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, cellulose resins, polyurethane resins, polyvinyl acetate resins, phenolic resins, phenol-formaldehyde resins, melamine resins, and urethane resins.

[0040] Among these, the resin used for the undercoat is: A resin insoluble in the upper coating solvent is preferred, and thermosetting resins such as urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin are preferred; more preferably, at least one resin selected from the group consisting of polyamide resin, polyester resin, polyether resin, methacrylic resin, acrylic resin, polyvinyl alcohol resin, and polyvinyl acetal resin. A more preferable option is at least one resin selected from the group consisting of melamine resin, urethane resin, polyvinyl alcohol resin, and polyvinyl acetal resin (preferably polyvinyl butyral, etc.).

[0041] -Curing catalyst- Examples of curing catalysts include amine compounds, organic acid metal salts, and organometallic complexes. Examples of amine compounds include 1,4-diazabicyclo(2,2,2)octane, N,N-dimethylcyclohexylamine, N-methyldicyclohexylamine, N,N,N',N'-tetramethylpropylenediamine, N-ethylmorpholine, N-methylmorpholine, N,N-dimethylethanolamine, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU) and its salts. Examples of organic acid metal salts or organometallic complexes include dibutyltin laurate, stanus octoate, bismuth octoate, bismuth naphthenate, bismuth salicylate, zinc octoate, zinc naphthenate, and zinc salicylate. Examples of commercially available urethane curing catalysts include the K-KAT series from King Industries, Ltd., such as bismuth carboxylate catalysts like K-KAT348, K-KAT XC-C227, K-KAT XK-628, and K-KAT XK-640; aluminum complex catalysts like K-KAT5218; zirconium complex catalysts like K-KAT4205, K-KAT6212, and K-KATA209; and titanium complex catalysts like TA-30 and TC-750 from Matsumoto Fine Chemicals' Orgatics series.

[0042] -Inorganic particles- The lower layer may further contain inorganic particles. The inclusion of inorganic particles in the underlayer makes it easier to adjust the charge and further suppresses positive ghosting.

[0043] As for inorganic particles, for example, powder resistance (volume resistivity) 10 2 Ωcm or more 10 11 Examples include inorganic particles with a size of Ωcm or less. Among these, suitable inorganic particles having the above-mentioned resistance values ​​include, for example, metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, with zinc oxide particles being particularly preferred.

[0044] The specific surface area of ​​inorganic particles using the BET method is, for example, 10 m². 2 A value of 1g or more is preferable. The volume-average particle size of the inorganic particles is preferably between 50 nm and 2000 nm (preferably between 60 nm and 1000 nm).

[0045] The inorganic particle content is preferably 10% by mass or more and 80% by mass or less relative to the binder resin, and more preferably 40% by mass or more and 80% by mass or less.

[0046] The inorganic particles may be surface-treated. Two or more types of inorganic particles with different surface treatments or particle sizes may be mixed and used.

[0047] Examples of surface treatment agents include silane coupling agents, titanate-based coupling agents, aluminum-based coupling agents, and surfactants. Silane coupling agents are particularly preferred, and silane coupling agents having an amino group are more preferred.

[0048] Examples of silane coupling agents having an amino group include, but are not limited to, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane.

[0049] Silane coupling agents may be used in combination of two or more types. For example, a silane coupling agent having an amino group may be used in combination with another silane coupling agent. Examples of other silane coupling agents include, but are not limited to, vinyltrimethoxysilane, 3-methacrylateoxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0050] The surface treatment method using the surface treatment agent may be any known method, and may be either a dry or wet method.

[0051] The amount of surface treatment agent applied is preferably, for example, 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0052] -Electron-accepting compounds- The lower layer may contain electron-accepting compounds (acceptor compounds). The inclusion of electron-accepting compounds (more preferably inorganic particles and electron-accepting compounds) tends to improve the long-term stability of electrical properties and carrier blocking properties.

[0053] Examples of electron-accepting compounds include quinone compounds such as chloranil and bromonil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; and diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone; as well as other electron-transporting substances. In particular, compounds having an anthraquinone structure are preferred as electron-accepting compounds. Examples of compounds having an anthraquinone structure include hydroxyanthraquinone compounds, aminoanthraquinone compounds, and aminohydroxyanthraquinone compounds, and specifically, for example, anthraquinone, alizarin, quinizalin, anthralphine, and purpurin are preferred.

[0054] The content of the electron-accepting compound may be 0.75% by mass or more and 1.5% by mass or less, 0.75% by mass or more and 1.25% by mass or less, or 0.75% by mass or more and 1% by mass or less, relative to the total solid content of the lower layer. Normally, residual curing agent in the undercoat and substances released from the curing agent (e.g., methyl ethyl ketone oxime) tend to raise the Fermi level of the undercoat in order to capture holes generated within the photoreceptor layer. On the other hand, conventional electrophotographic photoreceptors contain electron-accepting compounds in the undercoat for cycle stabilization, which also tend to raise the Fermi level of the undercoat in order to capture holes. In contrast, in the electrophotographic photoreceptor according to this embodiment, the amount of mass change in differential scanning calorimetry of the undercoat layer satisfies the above range or the Fermi level satisfies the above range, so the proportion of holes generated within the layers of the photoreceptor tends to be small. Therefore, even if the content of electron-accepting compounds that devolve into the total solid content of the undercoat layer is within the above range, fine line reproducibility is excellent and positive ghosting is suppressed.

[0055] The content of the electron-accepting compound is preferably 0.75% by mass or more and 1.5% by mass or less, more preferably 0.75% by mass or more and 1% by mass or less, relative to the total solid content of the lower layer. When the electron-accepting compound content is 1% by mass or less, the electron-accepting compound accepts electrons even for differences in holes generated within the photoreceptor layer, thereby suppressing the rise in the Fermi level of the underlying layer and further suppressing positive ghosting.

[0056] The content of the electron-accepting compound is preferably, for example, 0.01% by mass or more and 20% by mass or less relative to the inorganic particles, and more preferably 0.01% by mass or more and 10% by mass or less.

[0057] The electron-accepting compound may be dispersed in the underlayer together with inorganic particles, or it may be present attached to the surface of the inorganic particles.

[0058] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry methods or wet methods.

[0059] The dry method involves, for example, adding an electron-accepting compound, either directly or dissolved in an organic solvent, dropwise while stirring inorganic particles with a mixer that has a high shear force, or spraying it with dry air or nitrogen gas, to adhere the electron-accepting compound to the surface of the inorganic particles. When adding or spraying the electron-accepting compound, it is preferable to do so at a temperature below the boiling point of the solvent. After adding or spraying the electron-accepting compound, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained.

[0060] The wet method involves dispersing inorganic particles in a solvent using methods such as stirring, ultrasound, sand milling, attritoring, and ball milling, while adding an electron-accepting compound. After stirring or dispersion, the solvent is removed to adhere the electron-accepting compound to the surface of the inorganic particles. Solvent removal methods include, for example, filtration or distillation. After solvent removal, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained. In the wet method, the water content of the inorganic particles may be removed before adding the electron-accepting compound. Examples of this include removing water while stirring and heating in the solvent, or removing water by azeotrope with the solvent.

[0061] Furthermore, the attachment of the electron-accepting compound may be performed before or after surface treatment with a surface treatment agent on the inorganic particles, or it may be performed simultaneously with the attachment of the electron-accepting compound and surface treatment with the surface treatment agent.

[0062] The undercoat may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of known additives include electron-transporting pigments such as polycyclic condensation and azo pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. As mentioned above, silane coupling agents are used for surface treatment of inorganic particles, but they may also be added to the undercoat as additives.

[0063] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacrylateoxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0064] Examples of zirconium chelate compounds include zirconium butoxide, ethyl zirconium acetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetate zirconium butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, methacrylate zirconium butoxide, stearate zirconium butoxide, and isostearate zirconium butoxide.

[0065] Examples of titanium chelate compounds include tetraisopropyl titanate, tetran-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate ammonium salt, titanium lactate, titanium lactate ethyl ester, titanium triethanolamine, and polyhydroxytitanium stearate.

[0066] Examples of aluminum chelating compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0067] These additives may be used individually or as a mixture or polycondensate of multiple compounds.

[0068] The underlayer should ideally have a Vickers hardness of 35 or higher. The surface roughness (ten-point average roughness) of the undercoat layer should be adjusted to between 1 / (4n) (where n is the refractive index of the upper layer) and 1 / 2 of the exposure laser wavelength λ used, in order to suppress moiré patterns. Resin particles may be added to the undercoat to adjust the surface roughness. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. The surface of the undercoat may also be polished to adjust the surface roughness. Polishing methods include buffing, sandblasting, wet honing, and grinding.

[0069] There are no particular restrictions on the formation of the undercoat, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an undercoat-forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0070] Solvents for preparing the coating solution for forming the undercoat include known organic solvents such as alcohol-based solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone-based solvents, ketone alcohol-based solvents, ether-based solvents, and ester-based solvents. Specific examples of these solvents include common organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellsolve, ethyl cellsolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

[0071] Known methods for dispersing inorganic particles when preparing a coating solution for forming an undercoat include, for example, roll mills, ball mills, vibrating ball mills, attritors, sand mills, colloid mills, and paint shakers.

[0072] Conventional methods for applying the undercoating solution onto a conductive substrate include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0073] The thickness of the undercoat layer is preferably set to a range of 15 μm or more, and more preferably 20 μm to 50 μm.

[0074] (Conductive substrate) Examples of conductive substrates include metal plates, metal drums, and metal belts containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Other examples of conductive substrates include paper, resin films, and belts coated, vapor-deposited, or laminated with conductive compounds (e.g., conductive polymers, indium oxide, etc.), metals (e.g., aluminum, palladium, gold, etc.) or alloys. Here, "conductive" refers to a volume resistivity of 10⁻¹⁰. 13 This refers to a value less than Ωcm.

[0075] When an electrophotographic photoreceptor is used in a laser printer, the surface of the conductive substrate is preferably roughened to a center-line average roughness Ra of 0.04 μm to 0.5 μm in order to suppress interference fringes that occur when irradiated with laser light. While roughening to prevent interference fringes is not particularly necessary when using non-interfering light as the light source, it is beneficial for extending the lifespan by suppressing the occurrence of defects due to surface irregularities of the conductive substrate.

[0076] Methods for roughening a surface include, for example, wet honing, which involves suspending an abrasive in water and spraying it onto a conductive substrate; centerless grinding, which involves pressing a conductive substrate against a rotating grinding wheel and continuously grinding it; and anodizing.

[0077] One method for roughening the surface is to disperse conductive or semiconductive powder in a resin without roughening the surface of the conductive substrate, to form a layer on the surface of the conductive substrate, and then roughen the surface with the particles dispersed in that layer.

[0078] Anodizing roughening treatment involves forming an oxide film on the surface of a conductive substrate (e.g., aluminum) by anodizing it in an electrolyte solution. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active, easily contaminated, and exhibits large resistance fluctuations depending on the environment. Therefore, it is preferable to perform a sealing treatment on the porous anodic oxide film to block the micropores of the oxide film by volume expansion due to a hydration reaction using pressurized steam or boiling water (metal salts such as nickel may be added), thereby converting it into a more stable hydrated oxide.

[0079] The thickness of the anodic oxide film is preferably, for example, 0.3 μm to 15 μm. When the film thickness is within this range, it tends to exhibit barrier properties against injection and tends to suppress the increase in residual potential due to repeated use.

[0080] The conductive substrate may be treated with an acidic treatment solution or with boehmite. Treatment with an acidic solution is carried out, for example, as follows: First, an acidic solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The mixing ratio of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic solution is, for example, in the range of 10% to 11% by mass for phosphoric acid, 3% to 5% by mass for chromic acid, and 0.5% to 2% by mass for hydrofluoric acid, and the total concentration of these acids is preferably in the range of 13.5% to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness is preferably 0.3 μm to 15 μm.

[0081] The boehmite treatment is carried out, for example, by immersing the material in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting it with heated steam at 90°C to 120°C for 5 to 60 minutes. The film thickness is preferably 0.1 μm to 5 μm. This can be further treated with anodic oxidation using an electrolyte solution with low film solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0082] (Middle class) Although not shown in the diagram, an intermediate layer may be further provided between the undercoat layer and the photosensitive layer. The intermediate layer is, for example, a layer containing a resin. Examples of resins used in the intermediate layer include polymer compounds such as acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, and melamine resin. The intermediate layer may contain an organometallic compound. Examples of organometallic compounds used in the intermediate layer include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used in these intermediate layers may be used individually, as a mixture of multiple compounds, or as polycondensates.

[0083] Among these, the intermediate layer is preferably a layer containing an organometallic compound that contains zirconium atoms or silicon atoms.

[0084] There are no particular restrictions on the formation of the intermediate layer, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an intermediate layer-forming coating solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary. Conventional methods such as immersion coating, push-up coating, wire bar coating, spray coating, blade coating, knife coating, and curtain coating are used to form the intermediate layer.

[0085] The thickness of the intermediate layer is preferably set to a range of 0.1 μm to 3 μm, for example. The intermediate layer may also be used as a base layer.

[0086] (Charge generation layer) The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Alternatively, the charge generation layer may be a vapor-deposited layer of the charge generation material. A vapor-deposited layer of the charge generation material is suitable when using non-coherent light sources such as LEDs (Light Emitting Diodes) or organic EL (Electro-Luminescence) image arrays.

[0087] Examples of charge-generating materials include azo pigments such as bisazo and trisazo; fused aromatic pigments such as dibromoanthonthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0088] Among these, in order to accommodate laser exposure in the near-infrared region, it is preferable to use a metal phthalocyanine pigment or a metal-free phthalocyanine pigment as the charge generating material. Specifically, for example, hydroxygallium phthalocyanine; chlorogallium phthalocyanine; dichlorotin phthalocyanine; and titanyl phthalocyanine are more preferable.

[0089] On the other hand, to accommodate laser exposure in the near-ultraviolet region, preferred charge-generating materials include fused aromatic pigments such as dibromoanthoten; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments.

[0090] Even when using non-coherent light sources such as LEDs and organic EL image arrays with a central emission wavelength between 450 nm and 780 nm, the above charge generating materials may be used. However, from the viewpoint of resolution, when using a thin film of 20 μm or less for the photosensitive layer, the electric field strength in the photosensitive layer becomes high, making it easier for charge reduction due to charge injection from the substrate to occur, resulting in image defects known as black spots. This is particularly noticeable when using charge generating materials that are p-type semiconductors that easily generate dark current, such as trigonal selenium and phthalocyanine pigments.

[0091] In contrast, when n-type semiconductors such as fused aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark currents are less likely to occur, and image defects called black spots can be suppressed even in thin films. Furthermore, the n-type is determined using the commonly used time-of-flight method, based on the polarity of the photocurrent that flows. Those that are more likely to carry electrons as carriers than holes are classified as n-type.

[0092] The binder resin used in the charge generation layer can be selected from a wide range of insulating resins, or it may be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and polysilane. Examples of binder resins include polyvinyl butyral resin, polyarylate resin (polycondensate of bisphenols and aromatic divalent carboxylic acids, etc.), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, and polyvinylpyrrolidone resin. Here, "insulating properties" refers to a volume resistivity of 10 13 This refers to a value of Ωcm or greater. These binder resins can be used individually or in combination of two or more types.

[0093] Furthermore, the mixing ratio of the charge-generating material to the binder resin is preferably within the range of 10:1 to 1:10 by mass ratio.

[0094] The charge generation layer may also contain other well-known additives.

[0095] The formation of the charge generation layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge generation layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it as necessary. The charge generation layer may also be formed by vapor deposition of the charge generation material. Formation of the charge generation layer by vapor deposition is particularly suitable when using fused aromatic pigments or perylene pigments as the charge generation material.

[0096] Solvents for preparing the coating solution for forming the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellsolve, ethyl cellsolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene. These solvents may be used individually or in mixtures of two or more.

[0097] Methods for dispersing particles (e.g., charge-generating materials) in a coating solution for forming a charge-generating layer include, for example, media dispersers such as ball mills, vibrating ball mills, attritors, sand mills, and horizontal sand mills, as well as media-less dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include collision methods, which disperse the dispersion by causing liquid-liquid collisions or liquid-wall collisions under high pressure, and penetration methods, which disperse the dispersion by penetrating fine channels under high pressure. Furthermore, during this dispersion, it is effective to set the average particle size of the charge-generating material in the coating solution for forming the charge-generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0098] Conventional methods for applying the charge-generating layer forming solution onto the undercoat (or intermediate layer) include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0099] The thickness of the charge generation layer is preferably set to a range of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 2.0 μm.

[0100] (charge transport layer) The charge transport layer is, for example, a layer containing a charge transport material and a binder resin. The charge transport layer may also be a layer containing a polymer charge transport material.

[0101] Examples of charge transport materials include quinone compounds such as p-benzoquinone, chloranil, bromanil, and anthraquinone; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone compounds; benzophenone compounds; cyanovinyl compounds; and ethylene compounds, which are electron transport compounds. Other examples of charge transport materials include hole transport compounds such as triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, stilbene compounds, anthracene compounds, and hydrazone compounds. These charge transport materials may be used individually or in combination of two or more, but are not limited to these.

[0102] As charge transport materials, from the viewpoint of charge mobility, the triarylamine derivative shown in the following structural formula (a-1) and the benzidine derivative shown in the following structural formula (a-2) are preferred.

[0103] [ka]

[0104] In structural formula (a-1), Ar T1 ArT2 and Ar T3 each independently represents a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(R T8 ). R T4 , R T5 , R T6 , R T7 , and R T8 each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituents of the above groups include a halogen atom, an alkyl group having 1 to 5 carbon atoms, and an alkoxy group having 1 to 5 carbon atoms. Further, examples of the substituents of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0105]

Chemical formula

[0106] In structural formula (a-2), R T91 and R T92 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms. R T101 , R T102 , R T111 and R T112 each independently represents a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an amino group substituted with an alkyl group having 1 to 2 carbon atoms, a substituted or unsubstituted aryl group, -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ), and R T12 , R T13 , R T14 , R T15 and R T16Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Tm1, Tm2, ​​Tn1, and Tn2 each independently represent an integer between 0 and 2. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0107] Here, among the triarylamine derivative represented by structural formula (a-1) and the benzidine derivative represented by structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7 )(R T8 Triarylamine derivatives having ")" and "-CH=CH-CH=C(R T15 )(R T16 A benzidine derivative having ) is preferred from the viewpoint of charge mobility.

[0108] As polymer charge transport materials, known charge transport materials such as poly-N-vinylcarbazole and polysilane can be used. Polyester-based polymer charge transport materials are particularly preferred. Polymer charge transport materials may be used alone or in combination with a binder resin.

[0109] Examples of binder resins used in the charge transport layer include polycarbonate resin, polyester resin, polyarylate resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinylcarbazole, and polysilane. Among these, polycarbonate resin or polyarylate resin is preferred as the binder resin. These binder resins can be used individually or in combination of two or more. The preferred mixing ratio of the charge transport material to the binder resin is between 10:1 and 1:5 by mass.

[0110] The charge transport layer may also contain other well-known additives.

[0111] The formation of the charge transport layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge transport layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0112] Suitable solvents for preparing the coating solution for forming the charge transport layer include common organic solvents such as aromatic hydrocarbons like benzene, toluene, xylene, and chlorobenzene; ketones like acetone and 2-butanone; halogenated aliphatic hydrocarbons like methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers like tetrahydrofuran and ethyl ether. These solvents can be used individually or in mixtures of two or more.

[0113] Conventional methods for applying a charge transport layer forming coating solution onto a charge generation layer include blade coating, wire bar coating, spray coating, immersion coating, bead coating, air knife coating, and curtain coating.

[0114] The thickness of the charge transport layer is set, for example, preferably within the range of 5 μm to 50 μm, and more preferably within the range of 10 μm to 30 μm.

[0115] (protective layer) A protective layer is provided on the photosensitive layer as needed. The protective layer is provided, for example, to prevent chemical changes in the photosensitive layer when charged, or to further improve the mechanical strength of the photosensitive layer. Therefore, it is preferable to apply a protective layer composed of a cured film (crosslinked film). Examples of such layers include those shown in 1) or 2) below.

[0116] 1) A layer composed of a cured film of a composition containing a reactive group-containing charge transport material having a reactive group and a charge transport skeleton within the same molecule (i.e., a layer containing a polymer or crosslinked form of the reactive group-containing charge transport material). 2) A layer composed of a cured film of a composition comprising a non-reactive charge transport material and a non-charge transport material containing reactive groups that does not have a charge transport skeleton but has reactive groups (i.e., a layer comprising a non-reactive charge transport material and a polymer or crosslinked form of the non-charge transport material containing reactive groups).

[0117] The reactive groups in the reactive group-containing charge transport material include chain polymerizable groups, epoxy groups, -OH, -OR [where R represents an alkyl group], -NH2, -SH, -COOH, and -SiR. Q1 3-Qn (OR Q2 ) Qn [However, R Q1 R represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Q2 Examples of well-known reactive groups include hydrogen atoms, alkyl groups, and trialkylsilyl groups. Qn represents an integer from 1 to 3.

[0118] The chain polymerizable group is not particularly limited as long as it is a functional group capable of radical polymerization, for example, a functional group having at least one carbon double bond. Specifically, examples include groups containing at least one selected from vinyl groups, vinyl ether groups, vinyl thioether groups, styryl groups (vinyl phenyl groups), acryloyl groups, methacryloyl groups, and their derivatives. Among these, the chain polymerizable group is preferably a group containing at least one selected from vinyl groups, styryl groups (vinyl phenyl groups), acryloyl groups, methacryloyl groups, and their derivatives, due to its excellent reactivity.

[0119] The charge-transporting skeleton of the reactive group-containing charge-transporting material is not particularly limited as long as it is a known structure in electrophotographic photoreceptors. Examples include skeletons derived from nitrogen-containing hole-transporting compounds such as triarylamine compounds, benzidine compounds, and hydrazone compounds, in which the nitrogen atom is conjugated. Among these, the triarylamine skeleton is preferred.

[0120] These reactive groups and charge-transporting skeletons, including reactive group-containing charge transport materials, non-reactive charge transport materials, and reactive group-containing non-charge transport materials, can be selected from well-known materials.

[0121] The protective layer may also contain other well-known additives.

[0122] There are no particular restrictions on the formation of the protective layer, and well-known formation methods can be used. For example, it can be formed by adding the above components to a solvent to create a protective layer coating solution, drying the coating, and then performing a curing treatment such as heating as necessary.

[0123] Solvents for preparing coating solutions for forming a protective layer include aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; cellosolve solvents such as ethylene glycol monomethyl ether; and alcohol solvents such as isopropyl alcohol and butanol. These solvents can be used individually or in combination of two or more. Furthermore, the coating solution for forming the protective layer may be a solvent-free coating solution.

[0124] Conventional methods for applying a protective layer-forming coating solution onto a photosensitive layer (e.g., a charge transport layer) include immersion coating, push-up coating, wire bar coating, spray coating, blade coating, knife coating, and curtain coating.

[0125] The thickness of the protective layer is set, for example, preferably within the range of 1 μm to 20 μm, and more preferably within the range of 2 μm to 10 μm.

[0126] (Single-layer photosensitive layer) A single-layer photosensitive layer (charge generation / charge transport layer) is, for example, a layer comprising a charge generation material, a charge transport material, and, if necessary, a binder resin and other well-known additives. These materials are the same as those described for the charge generation layer and the charge transport layer. Furthermore, the content of the charge-generating material in the single-layer photosensitive layer is preferably 0.1% to 10% by mass, and more preferably 0.8% to 5% by mass, relative to the total solid content. In addition, the content of the charge-transporting material in the single-layer photosensitive layer is preferably 5% to 50% by mass, relative to the total solid content. The method for forming a single-layer photosensitive layer is the same as the method for forming a charge generation layer or a charge transport layer. The thickness of the single-layer photosensitive layer is, for example, preferably 5 μm to 50 μm, and more preferably 10 μm to 40 μm.

[0127] [Image forming apparatus (and process cartridge)] The image forming apparatus according to this embodiment comprises an electrophotographic photoreceptor, a charging means for charging the surface of the electrophotographic photoreceptor, an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor, a developing means for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, and a transfer means for transferring the toner image to the surface of a recording medium. The electrophotographic photoreceptor according to this embodiment is used as the electrophotographic photoreceptor.

[0128] The image forming apparatus according to this embodiment includes a fixing means for fixing a toner image transferred to the surface of a recording medium; a direct transfer method apparatus for directly transferring a toner image formed on the surface of an electrophotographic photoreceptor to a recording medium; an intermediate transfer method apparatus for first transferring a toner image formed on the surface of an electrophotographic photoreceptor to the surface of an intermediate transfer body, and secondarily transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; a cleaning means for cleaning the surface of the electrophotographic photoreceptor after the transfer of the toner image and before it is charged; a static elimination means for irradiating the surface of the electrophotographic photoreceptor with static elimination light to eliminate static charge after the transfer of the toner image and before it is charged; and a well-known image forming apparatus such as an electrophotographic photoreceptor heating member for raising the temperature of the electrophotographic photoreceptor and reducing the relative temperature.

[0129] In the case of an intermediate transfer method apparatus, the transfer means may include, for example, an intermediate transfer body on which a toner image is transferred; a primary transfer means for primaryly transferring the toner image formed on the surface of an electrophotographic photoreceptor to the surface of the intermediate transfer body; and a secondary transfer means for secondary transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium.

[0130] The image forming apparatus according to this embodiment may be either a dry developing type image forming apparatus or a wet developing type image forming apparatus (a developing method using a liquid developer).

[0131] In the image forming apparatus according to this embodiment, for example, the portion comprising the electrophotographic photoreceptor may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge comprising the electrophotographic photoreceptor according to this embodiment is preferably used. In addition to the electrophotographic photoreceptor, the process cartridge may also include at least one selected from the group consisting of, for example, a charging means, an electrostatic latent image forming means, a developing means, and a transfer means.

[0132] The following is an example of an image forming apparatus according to this embodiment, but it is not limited to this example. The main parts shown in the figure will be described, and other parts will be omitted from the explanation.

[0133] Figure 1 is a schematic diagram showing an example of an image forming apparatus according to this embodiment. As shown in Figure 1, the image forming apparatus 100 according to this embodiment includes a process cartridge 300 equipped with an electrophotographic photoreceptor 7, an exposure device 9 (an example of an electrostatic latent image forming means), a transfer device 40 (a primary transfer device), and an intermediate transfer body 50. In the image forming apparatus 100, the exposure device 9 is positioned to expose the electrophotographic photoreceptor 7 from the opening of the process cartridge 300, and the transfer device 40 is positioned facing the electrophotographic photoreceptor 7 via the intermediate transfer body 50, with a portion of the intermediate transfer body 50 in contact with the electrophotographic photoreceptor 7. Although not shown, the apparatus also includes a secondary transfer device that transfers the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). The intermediate transfer body 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) are examples of transfer means.

[0134] In Figure 1, the process cartridge 300 integrally supports an electrophotographic photoreceptor 7, a charging device 8 (an example of a charging means), a developing device 11 (an example of a developing means), and a cleaning device 13 (an example of a cleaning means) within a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is positioned to contact the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member, rather than a cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

[0135] Figure 1 shows an example of an image forming apparatus equipped with a fibrous member 132 (roll-shaped) that supplies lubricant 14 to the surface of the electrophotographic photoreceptor 7, and a fibrous member 133 (flat brush-shaped) that assists in cleaning. These can be arranged as needed.

[0136] The following describes the various components of the image forming apparatus according to this embodiment.

[0137] -Charging device- As the charging device 8, for example, a contact-type charger using conductive or semiconductive charging rollers, charging brushes, charging films, charging rubber blades, charging tubes, etc. may be used. Non-contact roller chargers, known chargers such as scorotron chargers and corotron chargers that utilize corona discharge may also be used.

[0138] -Exposure equipment- Examples of exposure devices 9 include optical equipment that exposes the surface of an electrophotographic photoreceptor 7 to a predetermined image using light such as semiconductor laser light, LED light, or liquid crystal shutter light. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photoreceptor. As for the wavelength of the semiconductor laser, near-infrared lasers with an oscillation wavelength of around 780 nm are the mainstream. However, the wavelength is not limited to this, and lasers with oscillation wavelengths in the 600 nm range or blue lasers with oscillation wavelengths between 400 nm and 450 nm may also be used. Furthermore, for color image formation, surface-emitting laser light sources capable of outputting multiple beams are also effective.

[0139] -Developing equipment- Examples of developing devices 11 include general developing devices that develop by contacting or not contacting the developing agent. There are no particular restrictions on the developing device 11 as long as it has the above-described functions, and it can be selected according to the purpose. For example, known developing devices that have the function of applying a one-component or two-component developing agent to the electrophotographic photoreceptor 7 using a brush, roller, etc. Among these, those that use a developing roller that holds the developing agent on its surface are preferred.

[0140] The developer used in the developing device 11 may be a one-component developer consisting of toner alone, or a two-component developer containing toner and a carrier. Furthermore, the developer may be magnetic or non-magnetic. Well-known developers are applicable.

[0141] -Cleaning device- The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131. In addition to the cleaning blade method, a fur brush cleaning method or a developing-simultaneous cleaning method may also be used.

[0142] -Transfer device- Examples of the transfer device 40 include contact-type transfer chargers using belts, rollers, films, rubber blades, etc., and transfer chargers that are known themselves, such as scorotron transfer chargers and corotron transfer chargers that utilize corona discharge.

[0143] -Intermediate Transcript- As the intermediate transfer body 50, a belt-shaped material (intermediate transfer belt) containing semiconducting polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc. is used. In addition to the belt shape, the intermediate transfer body may also be in the form of a drum.

[0144] Figure 2 is a schematic diagram showing another example of the image forming apparatus according to this embodiment. The image forming apparatus 120 shown in Figure 2 is a tandem-type multi-color image forming apparatus equipped with four process cartridges 300. In the image forming apparatus 120, the four process cartridges 300 are arranged in parallel on the intermediate transfer body 50, and one electrophotographic photoreceptor is used for each color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem-type apparatus. [Examples]

[0145] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" is based on mass.

[0146] [Fabrication of electrophotographic photoreceptors] <Example 1> -Formation of the lower layer- Zinc oxide particles (manufactured by Teika Corporation, volume-average particle size: 70 nm, specific surface area: 15 m²) 260 parts by mass of zinc oxide ( / g) was mixed with 500 parts by mass of tetrahydrofuran by stirring. As a silane coupling agent (surface treatment agent), 1.25 parts by mass of KBM603 (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) was added per 100 parts by mass of zinc oxide particles, and the mixture was stirred for 2 hours. After that, the tetrahydrofuran was removed by vacuum distillation, and the mixture was baked at 120°C for 3 hours to obtain zinc oxide particles surface-treated with the silane coupling agent.

[0147] 100 parts by mass of zinc oxide particles surface-treated with the above-mentioned silane coupling agent, 22.5 parts by mass of curing agent 1: blocked isocyanate (Sumijule 3173, manufactured by Sumitomo Bayern Urethanes), and 25 parts by mass of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.) were dissolved in 142 parts by mass of methyl ethyl ketone. 38 parts by mass of this solution was mixed with 25 parts by mass of methyl ethyl ketone, and the mixture was dispersed for 4 hours using 1 mm diameter glass beads in a sand mill to obtain a dispersion. To the obtained dispersion, 0.008 parts by mass of dioctyl tin dilaurate as a catalyst and 6.5 parts by mass of silicone resin particles (Tospar 145, manufactured by GE Toshiba Silicone Co., Ltd.) were added to obtain a coating solution for forming the undercoat layer. This coating solution was applied to a 30 mm diameter aluminum substrate by immersion coating, and heated and dried at a heating temperature of 190°C for 45 minutes to obtain an undercoat layer, which was a cured film with a thickness of 23.5 μm.

[0148] -Formation of a charge generation layer- Next, as a charge generating material, a mixture consisting of 15 parts by mass of chlorogallium phthalocyanine crystal having strong diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.4°, 16.6°, 25.5°, and 28.3° for CuKα characteristic X-rays, 10 parts by mass of vinyl chloride-vinyl acetate copolymer resin (VMCH, manufactured by Union Carbide Japan Co., Ltd.), and 300 parts by mass of n-butyl alcohol was dispersed for 4 hours using glass beads with a diameter of 1 mm in a sand mill to obtain a coating solution for forming a charge generating layer. This coating solution for forming a charge generating layer was immersed and coated onto the undercoat, and dried to obtain a charge generating layer with a thickness of 0.2 μm.

[0149] -Formation of a charge transport layer- Next, 8 parts by mass of tetrafluoroethylene resin particles (average particle size: 0.2 μm), 0.015 parts by mass of alkyl fluoride-containing methacrylic copolymer (weight-average molecular weight: 30000), 4 parts by mass of tetrahydrofuran, and 1 part by mass of toluene were stirred and mixed at a liquid temperature of 20°C for 48 hours to obtain tetrafluoroethylene resin particle suspension A.

[0150] Next, 4 parts by mass of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1']biphenyl-4,4'-diamine was mixed with 6 parts by mass of bisphenol Z-type polycarbonate resin (viscosity-average molecular weight: 40,000) and 0.1 parts by mass of 2,6-di-t-butyl-4-methylphenol as an antioxidant. 24 parts by mass of tetrahydrofuran and 11 parts by mass of toluene were then mixed and dissolved to obtain mixed solution B.

[0151] After adding the tetrafluoroethylene resin particle suspension A to this mixed solution B and stirring, the mixture is heated to 4900 N / cm using a high-pressure homogenizer (manufactured by Yoshida Machinery & Engineering Co., Ltd.) equipped with a through-chamber with fine channels. 2 (500 kgf / cm 2 The dispersion treatment was repeated six times after increasing the pressure to ). Fluorine-modified silicone oil (product name: FL-100, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to this mixture at a concentration of 5 ppm, and the mixture was stirred to obtain a coating solution for forming the charge transport layer.

[0152] This coating solution was applied onto the charge generation layer and dried at 140°C for 25 minutes to form a charge transport layer, obtaining an electrophotographic photoreceptor 1 with a thickness of 32.0 μm.

[0153] <Examples 2-8, Reference Example 1, Comparative Examples 1-4> In preparing the undercoat, each example of electrophotographic photoreceptor was obtained using the same method as in Example 1, except that the temperature and holding time when applying the coating solution to the conductive substrate and heating and drying, the type of curing agent, the boiling point of the blocking agent in the blocked isocyanate, the content of the electron-accepting compound relative to the total solid content of the undercoat, the content of inorganic particles relative to the total solid content of the undercoat, and the type of inorganic particles were as shown in Table 1. Note that "-" in each item in the table indicates that the material of that item is not included in the composition.

[0154] The following types of hardeners were prepared. • Hardener 1: Blocked isocyanate (Sumijule 3175 (indicated as "3175" in the table), manufactured by Sumitomo Bayern Urethanes Co., Ltd.), in which the isocyanate group is blocked with a blocking agent containing methyl ethyl ketone oxime; boiling point of the blocking agent: 152°C • Hardener 2: Blocked isocyanate (Coronate BI301 (indicated as "BI301" in the table), manufactured by Tosoh Corporation), in which the isocyanate group is blocked with a blocking agent containing methyl ethyl ketone oxime; boiling point of the blocking agent: 152°C • Hardener 3: Blocked isocyanate (Coronate 2554 (indicated as "2554" in the table), manufactured by Tosoh Corporation), in which the isocyanate group is blocked with a blocking agent that does not contain methyl ethyl ketone oxime; boiling point of the blocking agent: 136°C

[0155] The following types of electron-accepting compounds were prepared. • Electron-accepting compound 1: The following anthraquinone derivatives • Electron-accepting compound 2: Alizarin

[0156] [ka]

[0157] Table 1 shows the results for the obtained undercoat film thickness, the methyl ethyl ketone oxime content relative to the total solid content of the undercoat (indicated as "MEKO residual amount" in the table), the mass change of the undercoat at temperatures between 130°C and 155°C as measured by differential scanning calorimetry (indicated as "between 130°C and 155°C" in the table), the mass change of the undercoat at temperatures between 30°C and 155°C as measured by differential scanning calorimetry (indicated as "between 30°C and 155°C" in the table), and the Fermi level value of the undercoat (indicated as "Fermi level" in the table). Note that the photoreceptor in Example 7 used a curing agent that does not release methyl ethyl ketone oxime, and no methyl ethyl ketone oxime content relative to the total solid content of the undercoat was detected.

[0158] -Evaluation of fine line reproducibility- The electrophotographic photoreceptors obtained in each example were mounted in an electrophotographic image forming apparatus (Fujifilm Business Innovation Co., Ltd.: Versant 2100 Press), and 100,000 1% print charts were formed on A4 paper under conditions of 25°C and 20% RH. For the initial (10th sheet), 1,000th, 10,000th, 50,000th, and 100,000th prints, as well as after 72 hours of standing after 100,000 prints, 1on1off images (images where 1-dot lines are arranged parallel to each other with 1-dot spacing) at a resolution of 2,400 dpi (dots per inch) were formed as 5cm x 5cm charts perpendicular to the development direction on the upper left, center, and lower right of the A4 paper. The line spacing of each chart printed on the obtained samples was observed using a magnifying glass with a 100x scale to check for areas where the spacing was narrowed due to toner splatter, or areas where the spacing was wider due to the thinning of fine lines. Based on the observation results and the line spacing of the observed areas, a grade evaluation was performed according to the following criteria. The results are shown in Table 1.

[0159] -Evaluation Criteria- G1: In all charts, there is no decrease in line spacing due to scattering or an increase in line spacing due to thinning lines. G2: When a decrease or increase in line spacing is observed, but at least one chart shows thin lines. G3: If there are two or more charts where the spacing between thin lines is indistinguishable or where thin lines are missing.

[0160] -Posighost evaluation- The electrophotographic photoreceptors obtained in each example were mounted in an electrophotographic image forming apparatus (Fujifilm Business Innovation Co., Ltd.: Versant 2100 Press). A 1cm square 100% black image was printed on A3 size paper in the area corresponding to the first cycle (147mm from the leading edge of the paper). Then, a full-screen halftone image with an image density of 20% (a full-screen halftone image in cyan) was printed in the area corresponding to the second cycle, starting from 147mm from the leading edge of the paper. The printed full-screen halftone image was then observed, and the density difference (positive ghosting) between the 1cm square and its surroundings was graded from G0 to G5 in 1G increments. In the grading, a smaller G number indicates a smaller density difference and less positive ghosting. All image output was performed under conditions of 10°C and 15% RH. The results are shown in Table 1.

[0161] [Table 1]

[0162] As shown in the table, the electrophotographic photoreceptor of the example was found to have superior fine line reproduction and reduced positive ghosting compared to the electrophotographic photoreceptor of the comparative example. [Explanation of symbols]

[0163] 10 Image holder, 12 Charging device, 14 Exposure device, 16 Developing device, 18 Transfer device, 20 Cleaning device, 22 Fixing device, 24 Housing, 24A Opening, 24B Opening, 24C Mounting rail, 30 Substrate, 31 Conductive elastic layer, 32 Conductive surface layer, 101 Image forming apparatus, 102 Process cartridge, 121 Charging member, 122 Cleaning member, 123 Conductive bearing, 122A Substrate, 122B Elastic layer, 124 Power supply

Claims

1. A conductive substrate, A base layer provided on the conductive substrate, A photosensitive layer provided on the aforementioned undercoat layer, The change in mass of the aforementioned lower layer, measured by differential scanning calorimetry, at temperatures between 130°C and 155°C is 0.03% by mass or less. The Fermi level of the aforementioned lower layer is 4.2 eV or higher and 4.45 eV or lower. The aforementioned underlayer contains zinc oxide particles and an electron-accepting compound. The aforementioned underlayer has an electron-accepting compound content of 0.75% by mass or more and 1% by mass or less relative to the total solid content of the underlayer. Electrophotographic photoreceptor.

2. The electrophotographic photoreceptor according to claim 1, wherein the amount of mass change of the lower layer at a temperature of 30°C to 155°C, as determined by differential scanning calorimetry, is 0.3% by mass or less.

3. The electrophotographic photoreceptor according to claim 2, wherein the amount of mass change of the lower layer at a temperature of 30°C to 155°C, as determined by differential scanning calorimetry, is 0.2% by mass or less.

4. The electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the undercoat layer is a layer composed of a cured film of a composition containing a resin and a blocked isocyanate.

5. The electrophotographic photoreceptor according to claim 4, wherein the blocked isocyanate comprises an isocyanate compound blocked with a blocking agent having a boiling point of 130°C or higher and 155°C or lower.

6. The electrophotographic photoreceptor is provided according to any one of claims 1 to 5, A process cartridge that is attached to and detached from an image forming apparatus.

7. An electrophotographic photoreceptor according to any one of claims 1 to 5, A charging means for charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing means that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, A transfer means for transferring the toner image onto the surface of a recording medium, An image forming apparatus equipped with the following features.

Images