Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that can prevent a reduction in the uniformity of image density when image formation is continuously performed and then suspended, and image formation is performed again.SOLUTION: An electrophotographic photoreceptor has a conductive substrate and a photosensitive layer provided on the conductive substrate. An outermost surface includes a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound. The number of carboxyl groups in the fluorine-containing resin particle is 0 or more and 30 or less per 106 carbon atoms. When electrification and exposure are repeated 10000 times in conditions of an electrification potential of -700 V and an exposure intensity of 5 mJ / m2, the absolute value (|RP1-RP10000|) between a residual potential RP1 after the electrification and exposure are performed one time and a residual potential RP10000 after the electrification and exposure are performed 10000 times is 25 V or less.SELECTED DRAWING: Figure 1

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 proposes "an electrophotographic photoreceptor comprising a conductive support provided with a photosensitive layer containing at least a charge generating substance and a charge transporting substance, wherein a protective layer containing at least a filler and a dispersant is formed on the photosensitive layer, and the concentration of the dispersant contained in the protective layer has a concentration change that is lowest in the outermost surface region of the protective layer, and the dispersant contained in the protective layer is an organic compound containing at least one or more carboxyl groups in its structure."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem of the present invention is to provide an electrophotographic photoreceptor having a conductive substrate and a photosensitive layer provided on the conductive substrate, wherein the outermost surface layer contains a binder resin, a charge transport material, and fluorine-containing resin particles, and the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms, and when the absolute value (|RP1 - RP|) exceeds 25 V, or when the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, to suppress a decrease in the uniformity of image density when performing image formation continuously and then pausing and performing image formation again. 6 per carbon atom, in an electrophotographic photoreceptor, when the following absolute value (|RP1 - RP 10000 |) exceeds 25 V, or when the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, as compared with the case where the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, to provide an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density when performing image formation continuously and then pausing and performing image formation again.

Means for Solving the Problems

[0005] The above problems are solved by the following means. That is <1> having a conductive substrate and a photosensitive layer provided on the conductive substrate, wherein the outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound, the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms, 6 and an electrophotographic photoreceptor in which, when charging and exposure are repeated 10,000 times under the conditions of a charging potential of -700 V and an exposure intensity of 5 mJ / m the absolute value (|RP1 - RP 2 |) of the difference between the residual potential RP1 after one charging and exposure and the residual potential RP after 10,000 chargings and exposures is 25 V or less. 10000 10000 <2> The electrophotographic photoreceptor according to <1>, wherein the content of the charge transport material with respect to the binder resin in the outermost surface layer is 59% by mass or more and 72% by mass or less. <3> The electrophotographic photoreceptor according to <2>, wherein the content of the charge transport material with respect to the binder resin in the outermost surface layer is 61% by mass or more and 69% by mass or less. <4> having a conductive substrate and a photosensitive layer provided on the conductive substrate, wherein the outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound, the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms, 6 and an electrophotographic photoreceptor in which the content of the charge transport material with respect to the binder resin in the outermost surface layer is 59% by mass or more and 72% by mass or less. <5> The electrophotographic photoreceptor according to any one of <1> to <4>, wherein the acid dissociation constant (pKa) of the acidic compound is -2.8 or more and 2.5 or less. <6> The electrophotographic photoreceptor according to <5>, wherein the acid dissociation constant (pKa) of the acidic compound is -2 or more and 1.5 or less. ​​​<7> The electrophotographic photoreceptor according to any one of <1> to <6> above, wherein the acidic compound is at least one selected from the group consisting of a sulfonic acid compound, a carboxylic acid compound, a phosphoric acid compound, and a nitric acid compound. <8> The electrophotographic photoreceptor according to any one of <1> to <6> above, wherein the acidic compound is at least one selected from the group consisting of a sulfonic acid compound and a carboxylic acid compound. <9> The sulfonic acid compound is a sulfonic acid compound having a benzene ring, The electrophotographic photoreceptor according to <7> or <8> above, wherein the carboxylic acid compound is a carboxylic acid compound having 2 to 4 carboxyl groups. <10> The electrophotographic photoreceptor according to any one of <1> to <9> above, wherein the content of the acidic compound is 25 ppm or more and 1000 ppm or less with respect to the outermost surface layer. <11> A process cartridge that is detachable from an image forming apparatus and includes the electrophotographic photoreceptor according to any one of <1> to <10>. <12> An image forming apparatus including the electrophotographic photoreceptor according to any one of <1> to <10>, charging means for charging the surface of the electrophotographic photoreceptor, electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, 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, transfer means for transferring the toner image onto the surface of a recording medium, and a cleaning unit. <13> The image forming apparatus according to <12> above, further comprising discharging means for discharging the electrophotographic photoreceptor by irradiating it with a discharging light before charging after the transfer of the toner image.

Advantages of the Invention

[0006] ​According to the invention according to <1>, it has a conductive substrate and a photosensitive layer provided on the conductive substrate, and the outermost surface layer contains a binder resin, a charge transport material, and fluorine-containing resin particles, and the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms 6 In an electrophotographic photoreceptor, when the absolute value (|RP1 - RP 10000 |) exceeds 25 V, an electrophotographic photoreceptor is provided that can suppress a decrease in the uniformity of image density when image formation is continuously performed and then paused and image formation is performed again.

[0007] According to the invention according to <2>, compared with the case where the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, when image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor is provided that can suppress a decrease in the uniformity of image density.

[0008] According to the invention according to <3>, compared with the case where the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 61% by mass or more than 69% by mass, when image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor is provided that can suppress a decrease in the uniformity of image density.

[0009] According to the invention according to <4>, it has a conductive substrate and a photosensitive layer provided on the conductive substrate, and the outermost surface layer contains a binder resin, a charge transport material, and fluorine-containing resin particles, and the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms 6 In an electrophotographic photoreceptor, compared with the case where the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, when image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor is provided that can suppress a decrease in the uniformity of image density.

[0010] According to the invention according to <5>, when the acid dissociation constant (pKa) of the acidic compound is less than -2.8 or more than 2.5, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0011] According to the invention according to <6>, when the acid dissociation constant (pKa) of the acidic compound is less than -2 or more than 1.5, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0012] According to the invention according to <7>, when the acidic compound is hydrogen chloride, which is an acidic compound other than sulfonic acid compounds, carboxylic acid compounds, phosphoric acid compounds, and nitric acid compounds, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0013] According to the invention according to <8>, when the acidic compound is at least one selected from the group consisting of phosphoric acid compounds and nitric acid compounds, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0014] According to the invention according to <9>, when the sulfonic acid compound is a sulfonic acid compound having no benzene ring and the carboxylic acid compound is a carboxylic acid compound having one or more than four carboxyl groups, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0015] According to the invention according to <10>, when the content of the acidic compound is less than 25 ppm or more than 1000 ppm with respect to the outermost surface layer, compared with the case where image formation is continuously performed and then paused and image formation is performed again, an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density is provided.

[0016] <11> to <13>, according to the invention, has a conductive substrate and a photosensitive layer provided on the conductive substrate, and the outermost surface layer contains a binder resin, a charge transport material, and fluorine-containing resin particles, and the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms 6 in an electrophotographic photoreceptor, when the absolute value (|RP1 - RP 10000 |) exceeds 25 V, or when the content of the charge transport material with respect to the binder resin in the outermost surface layer is less than 59% by mass or more than 72% by mass, compared with the case of providing a photoreceptor, a process cartridge or an image forming apparatus including an electrophotographic photoreceptor capable of suppressing a decrease in the uniformity of image density when performing image formation continuously and then pausing and performing image formation again is provided.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments which are an example of the present invention will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0019] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, if there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition. The term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0020] <Electrophotographic photoreceptor> The electrophotographic photoreceptor according to the first embodiment (hereinafter, the "electrophotographic photoreceptor" is also simply referred to as the "photoreceptor") has a conductive substrate and a photosensitive layer provided on the conductive substrate, and the outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound. And the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms. 6 per carbon atom. Furthermore, when charging and exposure are repeated 10,000 times under the conditions of a charging potential of -700 V and an exposure intensity of 5 mJ / m 2 the absolute value of the difference between the residual potential RP1 after one charging and exposure and the residual potential RP 10000 after 10,000 chargings and exposures (|RP1 - RP 10000 ) is 25 V or less.

[0021] The photoreceptor according to the first embodiment, with the above configuration, suppresses a decrease in the uniformity of image density when the photoreceptor pauses after continuously performing image formation and then performs image formation again. The reason is presumably as follows.

[0022] For the purpose of improving the abrasion resistance of the photoreceptor, fluorine-containing resin particles may be included in the outermost surface layer of the photoreceptor. The fluorine-containing resin particles may affect the electrical properties of the photoreceptor. And, in order to ensure the chargeability, which is one of the electrical properties of the photoreceptor, as the fluorine-containing resin particles, the number of carboxyl groups is 10 carbon atoms 6Fluorine-containing resin particles (hereinafter also simply referred to as "specific fluorine-containing resin particles") that are 0 or more and 30 or less per piece may be used.

[0023] However, in the case of a photoreceptor having specific fluorine-containing resin particles in the outermost surface layer, when it pauses after continuous image formation and then performs image formation again, the uniformity of the image density may decrease. When continuous image formation is performed using an image forming apparatus including a photoreceptor having specific fluorine-containing resin particles in the outermost surface layer, the residual potential of the photoreceptor may increase. Then, by pausing the image forming apparatus, the residual potential decreases. However, since various members such as a cleaning member and a charging roller exist around the photoreceptor, the environment around the photoreceptor is not uniform. The rate of decrease of the residual potential may be affected by the environment around the photoreceptor, and the uniformity of the degree of decrease of the residual potential may decrease. Then, when image formation is performed again, the uniformity of the image density is likely to decrease.

[0024] The photoreceptor according to the first embodiment contains an acidic compound in the outermost surface layer of the photoreceptor. The acidic compound increases the probability that carriers (that is, holes or electrons) generated in the photosensitive layer are detrapped even when they are trapped. Therefore, in the photoreceptor according to the first embodiment, the degree of decrease in the residual potential becomes closer to being uniform. Also, the photoreceptor according to the first embodiment has an absolute value (|RP1 - RP 10000 |) of 25 V or less. This indicates that the residual potential of the photoreceptor is less likely to increase. Therefore, by setting the absolute value (|RP1 - RP 10000 |) within the above range, when pausing after continuous image formation, the difference in the degree of decrease in the residual potential is likely to be small.

[0025] From the above, it is presumed that the photoreceptor according to the first embodiment suppresses a decrease in the uniformity of the image density when pausing after continuous image formation and then performing image formation again with the above configuration.

[0026] The photoreceptor according to the second embodiment has a conductive substrate and a photosensitive layer provided on the conductive substrate, and the outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound. And the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms. 6 per carbon atom. Furthermore, in the outermost surface layer, the content of the charge transport material with respect to the binder resin is 59% by mass or more and 72% by mass or less.

[0027] The photoreceptor according to the second embodiment, with the above configuration, suppresses a decrease in the uniformity of image density when it pauses after continuous image formation and then performs image formation again. The reason is presumed as follows.

[0028] Since the photoreceptor according to the second embodiment contains an acidic compound in the outermost surface layer of the photoreceptor, for the same reason as above, the degree of decrease in the residual potential becomes closer to being uniform. Also, in the photoreceptor according to the second embodiment, the content of the charge transport material with respect to the binder resin (hereinafter, also simply referred to as "TB ratio") in the outermost surface layer is within the above numerical range. By setting the TB ratio within this range, it becomes difficult to accumulate carriers generated in the photosensitive layer. Also, by setting the TB ratio within this range, the capture cross-sectional area is likely to be reduced. Therefore, the residual potential of the photoreceptor is unlikely to increase. Thus, by setting the TB ratio within the above range, when pausing after continuous image formation, the difference in the degree of decrease in the residual potential is likely to be small.

[0029] From the above, it is presumed that the photoreceptor according to the second embodiment, with the above configuration, suppresses a decrease in the uniformity of image density when it pauses after continuous image formation and then performs image formation again.

[0030] Hereinafter, a photoreceptor that applies to both the photoreceptors according to the first and second embodiments (hereinafter also referred to as "the photoreceptor according to the present embodiment") will be described in detail. However, an example of the photoreceptor of the present invention may be a photoreceptor that applies to either one of the photoreceptors according to the first and second embodiments.

[0031] Hereinafter, the electrophotographic photoreceptor according to the present embodiment will be described with reference to the drawings. The electrophotographic photoreceptor 7 shown in FIG. 1 has, for example, a structure in which an undercoat layer 1, a charge generation layer 2, and a charge transport layer 3 are laminated in this order on a conductive support 4. The charge generation layer 2 and the charge transport layer 3 constitute a photosensitive layer 5.

[0032] Note that the electrophotographic photoreceptor 7 may have a layer structure in which the undercoat layer 1 is not provided. Further, the electrophotographic photoreceptor 7 may be a photoreceptor having a single-layer photosensitive layer in which the functions of the charge generation layer 2 and the charge transport layer 3 are integrated. In the case of a photoreceptor having a single-layer photosensitive layer, the single-layer photosensitive layer constitutes the outermost surface layer.

[0033] Hereinafter, each layer of the electrophotographic photoreceptor according to the present embodiment will be described in detail. Note that the reference numerals are omitted in the description.

[0034] (Outermost surface layer) The outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound. The outermost surface layer contains an additive according to the layer to be applied (the charge transport layer of the multilayer photosensitive layer or the single-layer photosensitive layer). Details of the layer to be applied will be described later.

[0035] -Binder resin- The binder resin is the binder resin contained in the charge transport layer and the single-layer photosensitive layer. Details of the binder resin will be described later. The content of the binder resin is preferably 52% by mass or more and 59% by mass or less, more preferably 53% by mass or more and 57% by mass or less, and still more preferably 54% by mass or more and 56% by mass or less with respect to the total solid content in the outermost surface layer.

[0036] -Charge transport material- Examples of the charge transport material 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 electron transport compounds such as ethylene compounds. Examples of the charge transport material also 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 alone or in combination of two or more, but are not limited thereto.

[0037] From the viewpoint of charge mobility, as the charge transport material, a triarylamine derivative represented by the following structural formula (a-1) and a benzidine derivative represented by the following structural formula (a-2) are preferable.

[0038] [Chemical formula]

[0039] In the structural formula (a-1), Ar T1 , Ar T2 , and Ar T3 each independently represent 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 represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituents for each 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 for each of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0040]

Chemical formula

[0041] In the structural formula (a-2), R T91 and R T92 each independently represent 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 represent 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 T16 each independently represent 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 of 0 or more and 2 or less. Examples of the substituents for each 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 for each of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0042] Here, among the triarylamine derivative represented by the structural formula (a-1) and the benzidine derivative represented by the structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7)(R T8 )-triarylamine derivatives and benzidine derivatives having "-CH=CH-CH=C(R T15 )(R T16 )" are preferred from the viewpoint of charge mobility.

[0043] As the polymer charge transport material, known materials having charge transport properties such as poly-N-vinylcarbazole and polysilane are used. In particular, polyester-based polymer charge transport materials disclosed in JP-A-8-176293, JP-A-8-208820, etc. are particularly preferred. The polymer charge transport material may be used alone or in combination with a binder resin.

[0044] -Fluorine-containing resin particles- The fluorine-containing resin particles have 0 or more and 30 or less carboxyl groups per 10 carbon atoms. 6 per carbon atom. From the viewpoint of improving chargeability, the number of carboxyl groups in the fluorine-containing resin particles is preferably 0 or more and 20.

[0045] Here, the carboxyl group of the fluorine-containing resin particles is, for example, a carboxyl group derived from a terminal carboxylic acid contained in the fluorine-containing resin particles.

[0046] The amount of the carboxyl group in the fluorine-containing resin particles is measured as follows as described in JP-A-4-20507 and the like. The fluorine-containing resin particles were preformed with a press machine to produce a film having a thickness of approximately 0.1 mm. The produced film was measured for infrared absorption spectrum. The infrared absorption spectrum was also measured for the fluorine-containing resin particles in which the carboxylic acid terminals produced by contacting the fluorine-containing resin particles with fluorine gas were completely fluorinated, and the number of terminal carboxyl groups per 10 carbon atoms was determined from the difference spectrum between the two by the following formula: 6 number per carbon atom 10 = (l × K) / t l: absorbance K: correction coefficient t: film thickness (mm) The absorption wave number of the carboxyl group is 3560 cm -1, the correction coefficient shall be 440.

[0047] Examples of the fluorine-containing resin particles include particles of a homopolymer of a fluoroolefin, and particles of a copolymer of two or more kinds, which is a copolymer of one or more kinds of fluoroolefins and a non-fluorine-based monomer (i.e., a monomer having no fluorine atom).

[0048] Examples of the fluoroolefin include perhaloolefins such as tetrafluoroethylene (TFE), perfluorovinyl ether, hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE); and non-perfluoroolefins such as vinylidene fluoride (VdF), trifluoroethylene, and vinyl fluoride. Among these, VdF, TFE, CTFE, HFP, etc. are preferable.

[0049] On the other hand, examples of the non-fluorine-based monomer include hydrocarbon olefins such as ethylene, propylene, and butene; alkyl vinyl ethers such as cyclohexyl vinyl ether (CHVE), ethyl vinyl ether (EVE), butyl vinyl ether, and methyl vinyl ether; alkenyl vinyl ethers such as polyoxyethylene allyl ether (POEAE) and ethyl allyl ether; organosilicon compounds having a reactive α,β-unsaturated group such as vinyltrimethoxysilane (VSi), vinyltriethoxysilane, and vinyltris(methoxyethoxy)silane; acrylic acid esters such as methyl acrylate and ethyl acrylate; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; vinyl esters such as vinyl acetate, vinyl benzoate, and "Veova" (trade name, vinyl ester manufactured by Shell); etc. Among these, alkyl vinyl ether, allyl vinyl ether, vinyl ester, and organosilicon compounds having a reactive α,β-unsaturated group are preferable.

[0050] Among these, as the fluorine-containing resin particles, particles with a high fluorination rate are preferred. Particles such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE) are more preferred, and particles of PTFE, FEP, and PFA are particularly preferred.

[0051] The fluorine-containing resin particles preferably have 0 to 30 carboxyl groups per 10 carbon atoms and the amount of the basic compound is 0 ppm to 3 ppm. 6 and are particles in which the amount of the basic compound is 0 ppm or more and 3 ppm or less. When the number of carboxyl groups and the amount of the basic compound of the fluorine-containing resin particles are within the above ranges, further increase in the residual potential can be suppressed.

[0052] From the viewpoint of suppressing the increase in the residual potential, the amount of the basic compound in the fluorine-containing resin particles is preferably 0 ppm or more and 1.5 ppm or less, and more preferably 0 ppm or more and 1.2 ppm or less. Note that ppm is based on mass.

[0053] The basic compound in the fluorine-containing resin particles is, for example, 1) a basic compound derived from a polymerization initiator used when the fluorine-containing resin particles are granulated together with polymerization, 2) a basic compound used in the step of aggregating after polymerization, and 3) a basic compound used as a dispersion aid for stabilizing the dispersion liquid after polymerization.

[0054] Examples of the basic compound include amine compounds, hydroxides of alkali metals or alkaline earth metals, oxides of alkali metals or alkaline earth metals, acetates, etc. (for example, particularly amine compounds). Examples of the basic compound include basic compounds having a boiling point (boiling point under normal pressure (1 atm)) of 40°C or higher and 130°C or lower (preferably 50°C or higher and 110°C or lower, more preferably 60°C or higher and 90°C or lower).

[0055] Examples of the amine compound include a primary compound, a secondary compound, or a tertiary amine compound. Examples of the primary amine compound include methylamine, ethylamine, propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, hexylamine, 2-ethylhexylamine, secondary butylamine, allylamine, methylhexylamine, and the like.

[0056] Examples of the secondary amine compound include dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, diisobutylamine, di-t-butylamine, dihexylamine, di(2-ethylhexyl)amine, N-isopropyl-N-isobutylamine, di(2-ethylhexyl)amine, disecondary butylamine, diallylamine, N-methylhexylamine, 3-pipecoline, 4-pipecoline, 2,4-lupeptide, 2,6-lupeptide, 3,5-lupeptide, morpholine, N-methylbenzylamine, and the like.

[0057] Examples of the tertiary amine compounds include trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, tri-t-butylamine, trihexylamine, tri(2-ethylhexyl)amine, N-methylmorpholine, N,N-dimethylallylamine, N-methyldiallylamine, triallylamine, N,N-dimethylallylamine, N,N,N’,N’-tetramethyl-1,2-diaminoethane, N,N,N’,N’-tetramethyl-1,3-diaminopropane, N,N,N’,N’-tetraallyl-1,4-diaminobutane, N-methylpiperidine, pyridine, 4-ethylpyridine, N-propyldiallylamine, 3-dimethylaminopropanol, 2-ethylpyrazine, 2,3-dimethylpyrazine, 2,5-dimethylpyrazine, 2,4-lutidine, 2,5-lutidine, 3,4-lutidine, 3,5-lutidine, 2,4,6-collidine, 2-methyl-4-ethylpyridine, 2-methyl-5-ethylpyridine, N,N,N’,N’-tetramethylhexamethylenediamine, N-ethyl-3-hydroxypiperidine, 3-methyl-4-ethylpyridine, 3-ethyl-4-methylpyridine, 4-(5-nonyl)pyridine, imidazole, N-methylpiperazine, and the like.

[0058] Examples of the hydroxides of alkali metals or alkaline earth metals include NaOH, KOH, Ca(OH)2, Mg(OH)2, Ba(OH)2, and the like. Examples of the oxides of alkali metals or alkaline earth metals include CaO, MgO, and the like. Examples of the acetates include zinc acetate, sodium acetate, and the like.

[0059] Examples of the method for reducing the amount of the basic compound in the fluorine-containing resin particles include: 1) a method of washing with water, an organic solvent (such as alcohols like methanol, ethanol, isopropanol, and tetrahydrofuran, etc.) after particle production; 2) a method of heating the particles (for example, heating to 200 °C or higher and 250 °C or lower) after particle production to decompose or vaporize and remove the basic compound.

[0060] The amount of the basic compound in the fluorine-containing resin particles is measured as follows. -Pretreatment- The outermost surface layer containing the fluorine-containing resin particles is immersed in a solvent (e.g., tetrahydrofuran), and substances other than the fluorine-containing resin particles and the insoluble substances in the solvent are dissolved in the solvent (e.g., tetrahydrofuran), then dropped into pure water and the precipitate is filtered off. The solution containing PFOA obtained at this time is collected. Further, the insoluble matter obtained by filtration is dissolved in a solvent, then dropped into pure water and the precipitate is filtered off. This operation is repeated 5 times to obtain fluorine-containing resin particles as a measurement sample. When measuring a composition containing fluorine-containing resin particles, the same treatment as that for the layered product is carried out on the composition to obtain fluorine-containing resin particles as a measurement sample. When measuring the fluorine-containing resin particles themselves, the same treatment as that for measuring from the outermost surface layer is carried out on the fluorine-containing resin particles to obtain fluorine-containing resin particles as a measurement sample.

[0061] -Measurement- On the other hand, a basic compound solution (methanol solvent) with a known concentration is used, and gas chromatography is utilized to obtain a calibration curve (a calibration curve from 0 ppm to 100 ppm) from the values of the basic compound concentration and the peak area of the basic compound solution (methanol solvent) with a known concentration. Then, the measurement sample is measured by gas chromatography, and the amount of the basic compound in the fluorine-containing resin particles is calculated from the obtained peak area and the calibration curve. The measurement conditions are as follows.

[0062] -Measurement Conditions- ·Headspace sampler: (HP7694, manufactured by HP) ·Measuring instrument: Gas chromatograph (HP6890 series, manufactured by HP) ·Detector: Flame ionization detector (FID) ·Column: HP19091S-433 (manufactured by HP) ·Sample heating time: 10 min ·Sprit Ratio: 300:1 ·Flow rate: 1.0 ml / min ·Column temperature rising setting: 60°C (3 min), 60°C / min, 200°C (1 min)

[0063] The average particle size of the fluorine-containing resin particles is not particularly limited, but is preferably 0.2 μm or more and 4.5 μm or less, and more preferably 0.2 μm or more and 4 μm or less.

[0064] The average particle size of the fluorine-containing resin particles is a value measured by the following method. Observe by SEM (scanning electron microscope) at a magnification of 5000 times or more, measure the maximum diameter of the fluorine-containing resin particles (secondary particles in which primary particles are aggregated), and take the average value obtained for 50 particles as the average particle size of the fluorine-containing resin particles. Note that JSM-6700F manufactured by JEOL Ltd. is used as the SEM, and a secondary electron image at an acceleration voltage of 5 kV is observed.

[0065] The specific surface area (BET specific surface area) of the fluorine-containing resin particles is preferably 5 m 2 / g or more and 15 m 2 / g or less from the viewpoint of dispersion stability, and more preferably 7 m 2 / g or more and 13 m 2 / g or less. The specific surface area is a value measured by the nitrogen substitution method using a BET type specific surface area measuring instrument (Flow-Sorb II 2300 manufactured by Shimadzu Corporation).

[0066] The apparent density of the fluorine-containing resin particles is preferably 0.2 g / ml or more and 0.5 g / ml or less, and more preferably 0.3 g / ml or more and 0.45 g / ml or less from the viewpoint of dispersion stability. The apparent density is a value measured in accordance with JIS K6891 (1995).

[0067] The melting temperature of the fluorine-containing resin particles is preferably 300°C or more and 340°C or less, and more preferably 325°C or more and 335°C or less. The melting temperature is the melting point measured in accordance with JIS K6891 (1995).

[0068] The content of the fluorine-containing resin particles is preferably 3% by mass or more and 11% by mass or less, more preferably 5% by mass or more and 10% by mass or less, and still more preferably 7% by mass or more and 9% by mass or less, based on the total solid content in the outermost surface layer.

[0069] The fluorine-containing resin particles include particles obtained by irradiating with radiation (also referred to as "radiation-irradiated fluorine-containing resin particles" in this specification), particles obtained by a polymerization method (also referred to as "polymerization-type fluorine-containing resin particles" in this specification), and the like.

[0070] The radiation-irradiated fluorine-containing resin particles (fluorine-containing resin particles obtained by irradiating with radiation) refer to fluorine-containing resin particles granulated together with radiation polymerization, and fluorine-containing resin particles that are decomposed by radiation irradiation after polymerization to have a lower molecular weight and be micronized. Since a large amount of carboxylic acid is generated by irradiating radiation in the air, the radiation-irradiated fluorine-containing resin particles contain a large amount of carboxyl groups. On the other hand, the polymerization-type fluorine-containing resin particles (fluorine-containing resin particles obtained by a polymerization method) refer to fluorine-containing resin particles granulated together with polymerization by a suspension polymerization method, an emulsion polymerization method, etc. and not irradiated with radiation.

[0071] Examples of the method for making the amount of carboxyl groups of the fluorine-containing resin particles within the above range include 1) a method of not irradiating radiation during the particle manufacturing process, 2) a method of performing the radiation irradiation under conditions where oxygen is absent or the oxygen concentration is reduced, and the like.

[0072] The fluorine-containing resin particles are preferably polymerization-type fluorine-containing resin particles. As described above, the polymerization-type fluorine-containing resin particles are fluorine-containing resin particles granulated together with polymerization by a suspension polymerization method, an emulsion polymerization method, etc. and not irradiated with radiation. Here, the production of fluorine-containing resin particles by the suspension polymerization method is, for example, a method in which additives such as a polymerization initiator and a catalyst are suspended together with a monomer for forming a fluorine-containing resin in a dispersion medium, and then the monomer is polymerized while granulating the polymer. In addition, the production of fluorine-containing resin particles by the emulsion polymerization method is, for example, a method in which additives such as a polymerization initiator and a catalyst are emulsified with a monomer for forming a fluorine-containing resin by a surfactant (i.e., an emulsifier) in a dispersion medium, and then the monomer is polymerized while granulating the polymer. In particular, the fluorine-containing resin particles are preferably particles obtained without performing radiation irradiation in the production process. However, radiation-irradiated fluororesin particles irradiated under conditions where oxygen is absent or the oxygen concentration is reduced may also be applied as the fluororesin particles.

[0073] - Acidic compound - The acidic compound may be either an inorganic acid or an organic acid. The acidic compound may be used alone or in combination of two or more.

[0074] Examples of the inorganic acid include phosphate compounds (PO -3 compounds having a group: for example, phosphoric acid (N3PO4)), nitrate compounds (NO3 - compounds having a group: for example, nitric acid (HNO3)), hydrogen chloride (HCl), etc.

[0075] Examples of the organic acid include sulfonic acid compounds, carboxylic acid compounds, etc.

[0076] The sulfonic acid compound is a compound having a SOH3 - group. Examples of the sulfonic acid compound include sulfonic acid compounds having a benzene ring substituted with an alkyl group having 1 to 20 carbon atoms (preferably 1 to 12 carbon atoms) (toluene sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid, 2,4-dimethyl benzene sulfonic acid, hydroxy benzene sulfonic acid, etc.), alkyl sulfonic acids having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms) (methyl sulfonic acid, ethyl sulfonic acid, propane sulfonic acid, butane sulfonic acid, etc.), and hydrates thereof. A carboxylic acid compound is a compound having a -COOH group. Examples of the carboxylic acid compound include oxalic acid, N,N-dimethylanthranilic acid, maleic acid, pyrrolimet acid, pyruvic acid, tartaric acid, citric acid, trifluoroacetic acid, phthalic acid, and the like.

[0077] That is, as the acidic compound, from the viewpoint of reducing the trap probability of the carrier, suppressing the increase in the residual potential, and making it difficult to generate unevenness in the recovery of the residual potential during the print pause, or making the degree of decrease in the residual potential of the photoreceptor more uniform by increasing the detrapping probability of the carrier, at least one selected from the group consisting of sulfonic acid compounds, carboxylic acid compounds, phosphoric acid compounds, and nitric acid compounds is preferable.

[0078] Among these, from the viewpoint of easily making the acid dissociation constant (pKa) described later fall within a desired range and thereby reducing the resistance of the outermost surface layer, suppressing the degree of increase in the residual potential of the photoreceptor, or making the degree of decrease in the residual potential more uniform, as the acidic compound, at least one selected from the group consisting of sulfonic acid compounds and carboxylic acid compounds is more preferable, and at least one selected from the group consisting of sulfonic acid compounds having a benzene ring and carboxylic acid compounds having 2 to 4 carboxyl groups is even more preferable.

[0079] The acidic compound is preferably an acidic compound having an acid dissociation constant (pKa) of 3 or less in water at 25°C. Here, the acid dissociation constant (pKa) means the first acid dissociation constant (pKa1). By setting the acid dissociation constant (pKa) of the acidic compound within the above range, the outermost surface layer is likely to have a lower resistance. Thereby, it is easy to suppress the degree of increase in the residual potential of the photoreceptor, or the degree of decrease in the residual potential of the photoreceptor is likely to be closer to being more uniform.

[0080] From the viewpoint of reducing the resistance of the outermost surface layer, the acid dissociation constant (pKa) of the acidic compound is preferably -2.8 or more and 2.5 or less, more preferably -2.1 or more and 2.5 or less, even more preferably -2 or more and 2.5 or less, and most preferably 0.5 or more and 2 or less.

[0081] The content of the acidic compound is preferably 25 ppm or more and 1000 ppm with respect to the outermost surface layer, more preferably 30 ppm or more and 700 ppm, and still more preferably 40 ppm or more and 500 ppm. By setting the content of the acidic compound within the above range, the trap probability of the carrier can be reduced, the increase in the residual potential can be suppressed, and unevenness in the recovery of the residual potential during print pauses can be less likely to occur. Or, the detrapping probability of the carrier is more likely to increase, and the degree of decrease in the residual potential of the photoreceptor is more likely to be closer to being uniform.

[0082] -Fluorine-based graft polymer- The outermost surface layer may contain a fluorine-based graft polymer as needed. The fluorine-based graft polymer is a dispersant having a fluorine element. Examples of the fluorine-based graft polymer include polymers obtained by homopolymerizing or copolymerizing a polymerizable compound having a fluoroalkyl group (hereinafter also referred to as "fluoroalkyl group-containing polymer").

[0083] Specific examples of the fluorine-based graft polymer include homopolymers of (meth)acrylate having a fluoroalkyl group, random or block copolymers of (meth)acrylate having a fluoroalkyl group and a monomer having no fluorine atom, etc. Here, (meth)acrylate means both acrylate and methacrylate.

[0084] Examples of the (meth)acrylate having a fluoroalkyl group include 2,2,2-trifluoroethyl (meth)acrylate and 2,2,3,3,3-pentafluoropropyl (meth)acrylate.

[0085] Examples of monomers without fluorine atoms include (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, 2-hydroxy (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, hydroxyethyl o-phenylphenol (meth)acrylate, o-phenylphenol glycidyl ether (meth)acrylate.

[0086] Among others, specific examples of fluorine-based graft polymers also include block or branched polymers disclosed in U.S. Patent No. 5,637,142, Japanese Patent No. 4,251,662, etc. Further, specific examples of fluorine-based graft polymers also include fluorine-based surfactants.

[0087] Among these, as the fluorine-based graft polymer, a fluorinated alkyl group-containing polymer having a structural unit represented by the following general formula (FA) is preferable, and a fluorinated alkyl group-containing polymer having a structural unit represented by the following general formula (FA) and a structural unit represented by the following general formula (FB) is more preferable.

[0088] Hereinafter, a fluorinated alkyl group-containing polymer having a structural unit represented by the following general formula (FA) and a structural unit represented by the following general formula (FB) will be described.

[0089] [Chemical formula]

[0090] In general formulas (FA) and (FB), R F1 , R F2 , R F3 and R F4 each independently represents a hydrogen atom or an alkyl group. X F1 represents an alkylene chain, a halogen-substituted alkylene chain, -S-, -O-, -NH-, or a single bond. Y F1 represents an alkylene chain, a halogen-substituted alkylene chain, -(C fx H 2fx-1 (OH))- or a single bond. Q F1 represents -O- or -NH-. fl, fm, and fn each independently represent an integer of 1 or more. fp, fq, fr, and fs each independently represent an integer of 0 or 1 or more. ft represents an integer of 1 or more and 7 or less. fx represents an integer of 1 or more.

[0091] In general formulas (FA) and (FB), R F1 , R F2 , R F3 and R F4 As the groups represented by, a hydrogen atom, a methyl group, an ethyl group, a propyl group, etc. are preferable, a hydrogen atom and a methyl group are more preferable, and a methyl group is even more preferable.

[0092] In general formulas (FA) and (FB), X F1 and Y F1 As the alkylene chain (unsubstituted alkylene chain, halogen-substituted alkylene chain) represented by, a linear or branched alkylene chain having 1 to 10 carbon atoms is preferable. Y F1 The -(C fx H 2fx-1 (OH))- represented by is preferably such that fx represents an integer of 1 to 10. Preferably, fp, fq, fr, and fs each independently represent an integer of 0 or 1 or more and 10 or less. Preferably, fn is, for example, 1 or more and 60 or less.

[0093] Here, in the fluorine-based graft polymer, the ratio of the structural unit represented by the general formula (FA) to the structural unit represented by the general formula (FB), that is, fl:fm, is preferably in the range of 1:9 to 9:1, and more preferably in the range of 3:7 to 7:3.

[0094] In addition to the structural unit represented by the general formula (FA) and the structural unit represented by the general formula (FB), the fluorine-based graft polymer may further have a structural unit represented by the general formula (FC). The content ratio of the structural unit represented by the general formula (FC) is preferably in the range of 10:0 to 7:3, and more preferably in the range of 9:1 to 7:3, as a ratio (fl + fm:fz) to the total of the structural units represented by the general formulas (FA) and (FB), that is, fl + fm.

[0095]

Chemical formula

[0096] In the general formula (FC), R F5 , and R F6 each independently represent a hydrogen atom or an alkyl group. fz represents an integer of 1 or more.

[0097] In the general formula (FC), as the groups represented by R F5 , and R F6 , a hydrogen atom, a methyl group, an ethyl group, a propyl group, etc. are preferable, a hydrogen atom and a methyl group are more preferable, and a methyl group is still more preferable.

[0098] Examples of commercially available products of the fluorine-based graft polymer include GF300, GF400 (manufactured by Toagosei Co., Ltd.), Surflon series (manufactured by AGC Seimi Chemical Co., Ltd.), Fタージェント series (manufactured by Neos Co., Ltd.), PF series (manufactured by Kitamura Chemical Co., Ltd.), Megafac series (manufactured by DIC Corporation), FC series (manufactured by 3M), etc.

[0099] From the viewpoint of improving the dispersibility of the fluorine-containing resin particles, the weight average molecular weight Mw of the fluorine-based graft polymer is preferably 20,000 or more and 200,000 or less, and more preferably 50,000 or more and 200,000 or less.

[0100] The weight average molecular weight of the fluorine-based graft polymer is a value measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is carried out, for example, using GPC·HLC-8120 manufactured by Tosoh as a measurement device, using columns · TSKgel GMHHR-M + TSKgel GMHHR-M (7.8 mm I.D. 30 cm) manufactured by Tosoh, and performing the measurement with a chloroform solvent. The molecular weight calibration curve prepared from the monodisperse polystyrene standard sample is used for calculation from this measurement result.

[0101] The content of the fluorine-based graft polymer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 7% by mass or less, based on the fluorine-containing resin particles, for example. Note that the fluorine-based graft polymer may be used alone or in combination of two or more.

[0102] -TB ratio- The content of the charge transport material (that is, the TB ratio) with respect to the binder resin in the outermost surface layer is 59% by mass or more and 72% by mass or less. From the viewpoint of further suppressing the increase in the residual potential of the photoreceptor, the TB ratio is preferably 60% by mass or more and 71% by mass or less, more preferably 61% or more and 69% or less, and still more preferably 64% or more and 67% or less.

[0103] (Conductive substrate) Examples of the conductive substrate include a metal plate, a metal drum, and a metal belt containing a metal (such as aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or an alloy (such as stainless steel). Further, examples of the conductive substrate include paper, a resin film, a belt, etc. coated, vapor-deposited, or laminated with a conductive compound (such as a conductive polymer, indium oxide, etc.), a metal (such as aluminum, palladium, gold, etc.), or an alloy. Here, "conductive" means that the volume resistivity is less than 10 13 Ω cm.

[0104] When the 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 or more and 0.5 μm or less for the purpose of suppressing interference fringes generated when irradiating laser light. When non-interference light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but it is more suitable for longer life in order to suppress the occurrence of defects due to irregularities on the surface of the conductive substrate.

[0105] Examples of the roughening method include wet honing performed by suspending an abrasive in water and spraying it onto the conductive substrate, centerless grinding performed by pressing the conductive substrate against a rotating grindstone and continuously performing grinding, anodic oxidation treatment, etc.

[0106] Examples of the roughening method also include a method of dispersing conductive or semiconductive powder in a resin without roughening the surface of the conductive substrate, forming a layer on the surface of the conductive substrate, and roughening it with the particles dispersed in the layer.

[0107] The roughening treatment by anodization forms an oxide film on the surface of a conductive substrate made of metal (for example, made of aluminum) as an anode in an electrolyte solution by anodizing. Examples of the electrolyte solution include a sulfuric acid solution and an oxalic acid solution. However, the porous anodic oxide film formed by anodization is chemically active in its original state, is easily contaminated, and has a large resistance variation due to 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 in pressurized steam or boiling water (a metal salt such as nickel may be added) to change it into a more stable hydrated oxide.

[0108] The film thickness of the anodic oxide film is preferably, for example, 0.3 μm or more and 15 μm or less. When the film thickness is within the above range, the barrier property against injection tends to be exhibited, and the increase in the residual potential due to repeated use tends to be suppressed.

[0109] The conductive substrate may be treated with an acidic treatment solution or boehmite-treated. The treatment with the acidic treatment solution is carried out, for example, as follows. First, an acidic treatment solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The mixing ratios of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic treatment solution are, for example, in the range where phosphoric acid is 10% by mass or more and 11% by mass or less, chromic acid is 3% by mass or more and 5% by mass or less, and hydrofluoric acid is 0.5% by mass or more and 2% by mass or less, and the concentration of these acids as a whole is preferably in the range of 13.5% by mass or more and 18% by mass or less. The treatment temperature is preferably, for example, 42°C or more and 48°C or less. The film thickness of the coating is preferably 0.3 μm or more and 15 μm or less.

[0110] The boehmite treatment is carried out, for example, by immersing in pure water at 90°C or more and 100°C or less for 5 to 60 minutes, or by bringing into contact with heated steam at 90°C or more and 120°C or less for 5 to 60 minutes. The film thickness of the coating is preferably 0.1 μm or more and 5 μm or less. This may be further anodized using an electrolyte solution with low film solubility such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, citrate, etc.

[0111] (Underlying layer) The underlying layer is, for example, a layer containing inorganic particles and a binder resin.

[0112] Examples of the inorganic particles include those having a powder resistance (volume resistivity) of 10 2 Ωcm or more and 10 11 Ωcm or less. Among these, examples of the inorganic particles having the above resistance value include metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, and particularly, zinc oxide particles are preferable.

[0113] The specific surface area of the inorganic particles by the BET method is, for example, 10 m 2 / g or more. The volume average particle diameter of the inorganic particles is, for example, 50 nm or more and 2000 nm or less (preferably 60 nm or more and 1000 nm or less).

[0114] The content of the inorganic particles is preferably, for example, 10% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 80% by mass or less, based on the binder resin.

[0115] The inorganic particles may be surface-treated. The inorganic particles may be used by mixing two or more kinds of those having different surface treatments or different particle diameters.

[0116] Examples of the surface treatment agent include silane coupling agents, titanate coupling agents, aluminum coupling agents, surfactants, etc. Particularly, silane coupling agents are preferable, and silane coupling agents having an amino group are more preferable.

[0117] Examples of the silane coupling agent having an amino group include, but are not limited to, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, etc.

[0118] Two or more silane coupling agents may be mixed and used. For example, a silane coupling agent having an amino group and another silane coupling agent may be used in combination. Examples of this other silane coupling agent include, but are not limited to, vinyltrimethoxysilane, 3-methacryloxypropyl-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, 3-chloropropyltrimethoxysilane, etc.

[0119] The surface treatment method using the surface treatment agent may be any known method, and either a dry method or a wet method may be used.

[0120] The treatment amount of the surface treatment agent is preferably, for example, 0.5% by mass or more and 10% by mass or less based on the inorganic particles.

[0121] Here, it is preferable that the underlayer contains an electron-accepting compound (acceptor compound) together with the inorganic particles from the viewpoints of enhancing the long-term stability of electrical characteristics and the carrier blocking property.

[0122] Examples of the electron-accepting compound include quinone compounds such as chloranil and bromanil; 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; diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone; and other electron-transporting substances. In particular, as the electron-accepting compound, a compound having an anthraquinone structure is preferable. Examples of the compound having an anthraquinone structure include hydroxyanthraquinone compounds, aminoanthraquinone compounds, amino-hydroxyanthraquinone compounds, etc., and specifically, for example, anthraquinone, alizarin, quinizarin, anthralfin, purpurin, etc. are preferable.

[0123] The electron-accepting compound may be dispersed and contained together with inorganic particles in the undercoat layer, or may be contained in a state of adhering to the surface of the inorganic particles.

[0124] Examples of the method for attaching the electron-accepting compound to the surface of the inorganic particles include a dry method or a wet method.

[0125] The dry method is, for example, a method in which while stirring inorganic particles with a mixer having a large shearing force, an electron-accepting compound dissolved directly or in an organic solvent is dropped and sprayed together with dry air or nitrogen gas to attach the electron-accepting compound to the surface of the inorganic particles. When dropping or spraying the electron-accepting compound, it is preferably carried out at a temperature below the boiling point of the solvent. After dropping or spraying the electron-accepting compound, baking may be further carried out at 100°C or higher. The baking is not particularly limited as long as the electrophotographic characteristics can be obtained at the temperature and time.

[0126] The wet method is, for example, a method in which inorganic particles are dispersed in a solvent by means of stirring, ultrasonic waves, a sand mill, an attritor, a ball mill, etc., an electron-accepting compound is added, and after stirring or dispersing, the solvent is removed to adhere the electron-accepting compound to the surface of the inorganic particles. The solvent removal method is, for example, removed by filtration or distillation. After the solvent is removed, baking may be further performed at 100°C or higher. The baking is not particularly limited as long as the electrophotographic characteristics can be obtained at the temperature and time. In the wet method, the contained moisture of the inorganic particles may be removed before adding the electron-accepting compound, and examples thereof include a method of removing while stirring and heating in a solvent and a method of removing by azeotroping with the solvent.

[0127] Note that the adhesion of the electron-accepting compound may be performed before or after subjecting the inorganic particles to surface treatment with a surface treatment agent, or may be performed simultaneously with the surface treatment with the surface treatment agent.

[0128] The content of the electron-accepting compound is, for example, preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.01% by mass or more and 10% by mass or less, based on the inorganic particles.

[0129] Examples of the binder resin used for the undercoat layer include known polymer compounds such as acetal resins (e.g., polyvinyl butyral, etc.), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, unsaturated polyester resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, urea resins, phenol resins, phenol-formaldehyde resins, melamine resins, urethane resins, alkyd resins, epoxy resins; zirconium chelate compounds; titanium chelate compounds; aluminum chelate compounds; titanium alkoxide compounds; organic titanium compounds; known materials such as silane coupling agents. Examples of the binder resin used for the undercoat layer include a charge transport resin having a charge transport group, a conductive resin (such as polyaniline, etc.).

[0130] Among these, as the binder resin used for the undercoat layer, a resin insoluble in the coating solvent of the upper layer is preferable. In particular, thermosetting resins such as urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin; a resin obtained by the reaction of 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 with a curing agent is preferable. When two or more of these binder resins are used in combination, the mixing ratio is set as required.

[0131] The undercoat layer may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of the additives include known materials such as polycyclic condensed system and azo system electron transport pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. The silane coupling agent is used for the surface treatment of inorganic particles as described above, but may also be further added to the undercoat layer as an additive.

[0132] Examples of the silane coupling agent as an additive include vinyltrimethoxysilane, 3-methacryloxypropyl-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, 3-chloropropyltrimethoxysilane, and the like.

[0133] Examples of the zirconium chelate compound include zirconium butoxide, zirconium ethyl acetoacetate, zirconium triethanolamine, zirconium butoxide acetylacetonate, zirconium butoxide ethyl acetoacetate, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, zirconium butoxide methacrylate, zirconium butoxide stearate, zirconium butoxide isostearate, and the like.

[0134] Examples of the titanium chelate compound include tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, poly titanium acetylacetonate, titanium octylene glycolate, ammonium salt of titanium lactate, titanium lactate, ethyl ester of titanium lactate, titanium triethanolamineate, polyhydroxy titanium stearate, and the like.

[0135] Examples of the aluminum chelate compound include aluminum isopropylate, monobutoxy aluminum diisopropylate, aluminum butyrate, diethyl acetoacetate aluminum diisopropylate, aluminum tris(ethyl acetoacetate), and the like.

[0136] These additives may be used alone or as a mixture or polycondensate of a plurality of compounds.

[0137] The undercoat layer preferably has a Vickers hardness of 35 or more. The surface roughness (ten-point average roughness) of the undercoat layer is preferably adjusted to be from 1 / (4n) (n is the refractive index of the upper layer) to 1 / 2 of the laser wavelength λ used for exposure in order to suppress moiré images. Resin particles or the like may be added to the undercoat layer for adjusting the surface roughness. Examples of the resin particles include silicone resin particles and crosslinked polymethyl methacrylate resin particles. Further, the surface of the undercoat layer may be polished for adjusting the surface roughness. Examples of the polishing method include buff polishing, sandblasting, wet honing, and grinding.

[0138] The formation of the undercoat layer is not particularly limited, and a well-known formation method is used. For example, it is performed by forming a coating film of a coating solution for forming an undercoat layer obtained by adding the above components to a solvent, drying the coating film, and heating it as necessary.

[0139] Examples of the solvent for preparing the coating solution for forming an undercoat layer include known organic solvents such as alcohol solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone solvents, ketone alcohol solvents, ether solvents, and ester solvents. Specific examples of these solvents include ordinary organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, toluene, and the like.

[0140] Examples of the method for dispersing inorganic particles when preparing the coating liquid for forming the undercoat layer include known methods such as roll mills, ball mills, vibration ball mills, attritors, sand mills, colloid mills, paint shakers, and the like.

[0141] Examples of the method for applying the coating liquid for forming the undercoat layer onto the conductive substrate include ordinary methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, curtain coating, and the like.

[0142] The film thickness of the undercoat layer is, for example, preferably set within a range of 15 μm or more, more preferably 20 μm or more and 50 μm or less.

[0143] (Intermediate layer) Although illustration is omitted, 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 the resin used for the intermediate layer include polymer compounds such as acetal resins (e.g., polyvinyl butyral, etc.), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, phenol-formaldehyde resins, melamine resins, and the like. The intermediate layer may be a layer containing an organometallic compound. Examples of the organometallic compound used for the intermediate layer include organometallic compounds containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used for these intermediate layers may be used alone or as a mixture or polycondensate of a plurality of compounds.

[0144] Among these, it is preferable that the intermediate layer is a layer containing an organometallic compound containing a zirconium atom or a silicon atom.

[0145] The formation of the intermediate layer is not particularly limited, and well-known formation methods are used. For example, it is carried out by forming a coating film of a coating solution for forming an intermediate layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary. As the coating method for forming the intermediate layer, ordinary methods such as dip coating method, dip-up coating method, wire bar coating method, spray coating method, blade coating method, knife coating method, and curtain coating method are used.

[0146] The film thickness of the intermediate layer is, for example, preferably set in the range of 0.1 μm or more and 3 μm or less. Note that the intermediate layer may be used as an undercoat layer.

[0147] (Charge generation layer) The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Further, the charge generation layer may be a vapor deposition layer of a charge generation material. The vapor deposition layer of the charge generation material is suitable when using non-interference light sources such as LEDs (Light Emitting Diodes) and organic EL (Electro-Luminescence) image arrays.

[0148] Examples of the charge generation material include azo pigments such as bisazo and trisazo; condensed aromatic pigments such as dibromoanthraquinone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; trigonal selenium, etc.

[0149] Among these, in order to respond to laser exposure in the near-infrared region, as the charge generation material, it is preferable to use a metal phthalocyanine pigment or a metal-free phthalocyanine pigment. Specifically, for example, hydroxygallium phthalocyanine disclosed in JP-A-5-263007, JP-A-5-279591, etc.; chlorogallium phthalocyanine disclosed in JP-A-5-98181, etc.; dichlorotin phthalocyanine disclosed in JP-A-5-140472, JP-A-5-140473, etc.; titanyl phthalocyanine disclosed in JP-A-4-189873, etc. are more preferable.

[0150] On the other hand, in order to respond to laser exposure in the near-ultraviolet region, as the charge generation material, condensed polycyclic aromatic pigments such as dibromoanthraquinone; thioindigo-based pigments; porphyrazine compounds; zinc oxide; trigonal selenium; bisazo pigments disclosed in JP-A-2004-78147, JP-A-2005-181992, etc. are preferable.

[0151] Even when using a non-coherent light source such as an LED or an organic EL image array having a center wavelength of emission in the range of 450 nm or more and 780 nm or less, the above charge generation material may be used. However, from the viewpoint of resolution, when the photosensitive layer is used as a thin film of 20 μm or less, the electric field strength in the photosensitive layer becomes high, and charge injection from the substrate causes charge leakage, so-called image defects called black dots are likely to occur. This becomes prominent when a charge generation material that easily generates dark current, such as trigonal selenium or phthalocyanine pigment, which is a p-type semiconductor, is used.

[0152] On the contrary, when an n-type semiconductor such as a condensed polycyclic aromatic pigment, a perylene pigment, or an azo pigment is used as the charge generation material, it is difficult to generate dark current, and image defects called black dots can be suppressed even in the case of a thin film. Examples of the n-type charge generation material include, but are not limited to, compounds (CG-1) to (CG-27) described in paragraphs

[0288] to

[0291] of JP-A-2012-155282. Note that the n-type determination is made by using the commonly used time-of-flight method and is determined by the polarity of the flowing photocurrent. Those that allow electrons to flow more easily as carriers than holes are defined as n-type.

[0153] The binder resin used in the charge generation layer is selected from a wide range of insulating resins. As the binder resin, an organic photoconductive polymer such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, or polysilane may also be selected. Examples of the binder resin include polyvinyl butyral resin, polyarylate resin (such as a polycondensate of bisphenols and aromatic dicarboxylic acids), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinyl pyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, polyvinyl pyrrolidone resin, and the like. Here, "insulating" means that the volume resistivity is 10 13 Ω·cm or more. These binder resins may be used alone or in combination of two or more.

[0154] Note that the mixing ratio of the charge generation material and the binder resin is preferably in the range of 10:1 to 1:10 by mass ratio.

[0155] The charge generation layer may also contain other well-known additives.

[0156] The formation of the charge generation layer is not particularly limited, and well-known formation methods are used. For example, it is carried out by forming a coating film of a coating solution for forming a charge generation layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary. Note that the charge generation layer may be formed by vapor deposition of the charge generation material. The formation of the charge generation layer by vapor deposition is particularly suitable when a condensed aromatic pigment or a perylene pigment is used as the charge generation material.

[0157] Examples of solvents for preparing the coating liquid for forming the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, toluene, and the like. These solvents may be used alone or in combination of two or more.

[0158] Examples of methods for dispersing particles (e.g., charge generation materials) in the coating liquid for forming the charge generation layer include media dispersers such as ball mills, vibration ball mills, attritors, sand mills, horizontal sand mills, etc., and media-less dispersers such as stirring, ultrasonic dispersers, roll mills, high-pressure homogenizers, etc. Examples of high-pressure homogenizers include a collision method in which a dispersion liquid is dispersed by liquid-liquid collision or liquid-wall collision in a high-pressure state, and a penetration method in which the dispersion liquid is dispersed by passing through a fine flow path in a high-pressure state. In addition, during this dispersion, it is effective to make the average particle size of the charge generation material in the coating liquid for forming the charge generation layer 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0159] Examples of methods for applying the coating liquid for forming the charge generation layer onto the undercoat layer (or intermediate layer) include ordinary methods such as blade coating method, wire bar coating method, spray coating method, dip coating method, bead coating method, air knife coating method, curtain coating method, etc.

[0160] The film thickness of the charge generation layer is set, for example, preferably in the range of 0.1 μm or more and 5.0 μm or less, more preferably 0.2 μm or more and 2.0 μm or less.

[0161] (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 be a layer containing a polymer charge transport material.

[0162] Examples of the charge transport material 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 electron transport compounds such as ethylene compounds. Examples of the charge transport material also 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 alone or in combination of two or more, but are not limited thereto.

[0163] From the viewpoint of charge mobility, as the charge transport material, a triarylamine derivative represented by the following structural formula (a-1) and a benzidine derivative represented by the following structural formula (a-2) are preferable.

[0164]

Chemical formula

[0165] In the structural formula (a-1), Ar T1 , Ar T2 , and Ar T3 each independently represent 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 represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituents of each 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 each of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0166]

Chemical formula

[0167] In structural formula (a-2), R T91 and R T92 each independently represent 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 represent 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 T16 each independently represent 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 of 0 or more and 2 or less. Examples of the substituents of each 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 each of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0168] Here, among the triarylamine derivative represented by structural formula (a-1) and the benzidine derivative represented by the above structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7)(R T8 )-containing triarylamine derivatives and benzidine derivatives having "-CH=CH-CH=C(R T15 )(R T16 )" are preferred from the viewpoint of charge mobility.

[0169] As the polymer charge transport material, known materials having charge transport properties such as poly-N-vinylcarbazole and polysilane are used. In particular, polyester-based polymer charge transport materials disclosed in JP-A-8-176293, JP-A-8-208820, etc. are particularly preferred. The polymer charge transport material may be used alone or in combination with a binder resin.

[0170] Binder resins used for the charge transport layer include polycarbonate resins, polyester resins, polyarylate resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl acetate resins, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, silicone resins, silicone alkyd resins, phenol-formaldehyde resins, styrene-alkyd resins, poly-N-vinylcarbazole, polysilane, and the like. Among these, polycarbonate resins or polyarylate resins are preferred as the binder resin. These binder resins may be used alone or in combination of two or more.

[0171] The mixing ratio of the charge transport material and the binder resin is preferably from 10:1 to 1:5 by mass ratio.

[0172] The charge transport layer may also contain other well-known additives.

[0173] The formation of the charge transport layer is not particularly limited, and well-known formation methods are used. For example, it is carried out by forming a coating film of a coating solution for forming a charge transport layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary.

[0174] As the drying conditions of the coating film, it is preferable to perform heating at 100 °C or higher and 150 °C or higher for 15 minutes or more and 60 minutes or less. For a photoreceptor in which a charge transport layer is formed by setting the drying conditions of the coating film within the above range, after continuously performing image formation and then pausing, when image formation is performed again, a decrease in the uniformity of image density is more suppressed. The reason is presumed as follows. By setting the drying conditions of the coating film within the above range, the amount of residual solvent in the charge transport layer is likely to be reduced, and thermal decomposition of the charge transport material is likely to be suppressed. By reducing the residual solvent in the charge transport layer or suppressing the thermal decomposition of the charge transport material, the hole transport property is likely to exhibit its original performance, and thereby the residual potential of the photoreceptor is less likely to increase. From the above, it is presumed that when image formation is continuously performed and then paused, and image formation is performed again, a decrease in the uniformity of image density is more suppressed.

[0175] Examples of the solvent for preparing the coating liquid for forming the charge transport layer include aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; ketones such as acetone and 2-butanone; halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers such as tetrahydrofuran and ethyl ether. These solvents can be used alone or in combination of two or more.

[0176] Examples of the coating method when applying the coating liquid for forming the charge transport layer onto the charge generation layer include ordinary methods such as blade coating method, wire bar coating method, spray coating method, dipping coating method, bead coating method, air knife coating method, and curtain coating method.

[0177] The film thickness of the charge transport layer is set, for example, preferably in the range of 5 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less.

[0178] (Single-layer type photosensitive layer) The single-layer photosensitive layer (charge generation / charge transport layer) is a layer containing, for example, 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. In the single-layer photosensitive layer, the content of the charge generation material is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.8% by mass or more and 5% by mass or less, based on the total solid content. Also, in the single-layer photosensitive layer, the content of the charge transport material is preferably 5% by mass or more and 50% by mass or less, based on the total solid content. The method for forming the single-layer photosensitive layer is the same as the method for forming the charge generation layer and the charge transport layer. The film thickness of the single-layer photosensitive layer is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 40 μm or less.

[0179] (Absolute value of the difference in residual potential |RP1 - RP 10000 |) When charging and exposure are repeated 10,000 times in accordance with the following procedure for the photoreceptor according to the present embodiment, the absolute value of the difference (|RP1 - RP 10000 ) between the residual potential RP1 after one charging and exposure and the residual potential RP after 10,000 chargings and exposures 10000 is 25 V or less.

[0180] In the measurement of the residual potentials RP1 and RP 10000 , charging and exposure of the photoreceptor are performed according to the following procedure. The photoreceptor is charged in an environment of 30°C and 85% RH using a scorotron charger with a grid application voltage of -700 V so that the potential on the surface of the photoreceptor (i.e., the charging potential) becomes -700 V. Then, 0.1 second after charging, the photoreceptor is flash-exposed using a semiconductor laser with a wavelength of 780 nm at a light amount of 10 mJ / m 2 . The potential (V) on the surface of the photoreceptor 0.05 second after exposure is measured, and this measured value is taken as the residual potential RP1. The charging and exposure operations of the photoreceptor are repeated in the same procedure (at this time, the potential (V) on the surface of the photoreceptor is not measured). After 10,000 charging and exposure operations, the potential (V) on the surface of the photoreceptor 0.1 second after exposure is measured, and this measured value is taken as the residual potential RP10000 shall be used.

[0181] From the viewpoint of making the difference in the degree of decrease in the residual potential smaller when the image formation is continuously performed and then paused, the absolute value (|RP1 - RP 10000 |) is preferably 25 V or less, more preferably 20 V or less, and even more preferably 10 V or less. From the viewpoint of making the difference in the degree of decrease in the residual potential smaller when the image formation is continuously performed and then paused, the absolute value (|RP1 - RP 10000 |) is preferably 0 V, but may be 1 V or more, or may be 3 V or more.

[0182] Here, as a method of setting the absolute value (|RP1 - RP 10000 |) within the above numerical range, for example, it is preferable that the outermost layer contains an acidic compound and the TB ratio is 54% or more and 75% or less.

[0183] Residual potential RP 10000 The absolute value (|RP 10000 |) is preferably 100 V or less, more preferably 70 V or less, and even more preferably 40 V or less from the viewpoint of suppressing a decrease in the uniformity of the image density when the image formation is continuously performed and then paused and the image formation is performed again. Residual potential RP 10000の The absolute value (|RP 10000 |) is preferably 0 V, but may be 3 V or more from the viewpoint of suppressing a decrease in the uniformity of the image density when the image formation is continuously performed and then paused and the image formation is performed again.

[0184] <Image forming apparatus (and process cartridge)> The image forming apparatus according to this embodiment includes an electrophotographic photosensitive member, a charging unit that charges the surface of the electrophotographic photosensitive member, an electrostatic latent image forming unit that forms an electrostatic latent image on the charged surface of the electrophotographic photosensitive member, a developing unit that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image, and a transfer unit that transfers the toner image onto the surface of a recording medium. And, as the electrophotographic photosensitive member, the electrophotographic photosensitive member according to this embodiment is applied.

[0185] The image forming apparatus according to this embodiment is an apparatus including a fixing unit that fixes the toner image transferred onto the surface of a recording medium; a direct transfer type apparatus that directly transfers the toner image formed on the surface of the electrophotographic photosensitive member onto a recording medium; an intermediate transfer type apparatus that first transfers the toner image formed on the surface of the electrophotographic photosensitive member onto the surface of an intermediate transfer member and then secondarily transfers the toner image transferred onto the surface of the intermediate transfer member onto the surface of a recording medium; an apparatus including a cleaning unit that cleans the surface of the electrophotographic photosensitive member after transfer of the toner image and before charging; an apparatus including a discharging unit that discharges the surface of the electrophotographic photosensitive member by irradiating it with discharging light after transfer of the toner image and before charging; a well-known image forming apparatus such as an apparatus including an electrophotographic photosensitive member heating member for raising the temperature of the electrophotographic photosensitive member and reducing the relative humidity is applicable.

[0186] In the case of an intermediate transfer type apparatus, the transfer unit has, for example, a configuration including an intermediate transfer member onto which the toner image is transferred, a primary transfer unit that first transfers the toner image formed on the surface of the electrophotographic photosensitive member onto the surface of the intermediate transfer member, and a secondary transfer unit that secondarily transfers the toner image transferred onto the surface of the intermediate transfer member onto the surface of a recording medium.

[0187] The image forming apparatus according to this embodiment may be either a dry developing type image forming apparatus or a wet developing type (developing method using a liquid developer) image forming apparatus.

[0188] In the image forming apparatus according to the present embodiment, for example, a portion including the electrophotographic photoreceptor may have a cartridge structure (process cartridge) that is detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge including the electrophotographic photoreceptor according to the present embodiment is preferably used. Note that the process cartridge may include at least one selected from the group consisting of charging means, electrostatic latent image forming means, developing means, and transferring means, in addition to the electrophotographic photoreceptor.

[0189] Here, the image forming apparatus preferably has a discharging means for irradiating the surface of the electrophotographic photoreceptor with discharging light for discharging before charging after the transfer of the toner image. In the image forming apparatus having such a configuration, since the amount of light irradiation received by the electrophotographic photoreceptor during image formation is large, the increase amount of the residual potential when continuously performing image formation is large. Therefore, when the image formation is stopped after continuously performing image formation and then the image formation is performed again, the uniformity of the image density may be easily reduced. Therefore, by applying the photoreceptor according to the present embodiment, the increase in the residual potential of the photoreceptor can be suppressed. Thus, even in the image forming apparatus having the above configuration, the reduction in the uniformity of the image density when the image formation is stopped after continuously performing image formation and then the image formation is performed again can be suppressed.

[0190] Hereinafter, an example of the image forming apparatus according to the present embodiment will be shown, but the present invention is not limited thereto. Note that the main parts shown in the drawings will be described, and the description of the others will be omitted.

[0191] FIG. 2 is a schematic configuration diagram showing an example of the image forming apparatus according to the present embodiment. As shown in FIG. 2, the image forming apparatus 100 according to the present embodiment includes a process cartridge 300 including an electrophotographic photosensitive member 7, an exposure device 9 (an example of an electrostatic latent image forming unit), a transfer device 40 (a primary transfer device), and an intermediate transfer member 50. In the image forming apparatus 100, the exposure device 9 is disposed at a position where it can expose the electrophotographic photosensitive member 7 from an opening of the process cartridge 300, the transfer device 40 is disposed at a position facing the electrophotographic photosensitive member 7 via the intermediate transfer member 50, and a part of the intermediate transfer member 50 is disposed in contact with the electrophotographic photosensitive member 7. Although not shown, the image forming apparatus also has a secondary transfer device that transfers the toner image transferred to the intermediate transfer member 50 to a recording medium (e.g., paper). The intermediate transfer member 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) correspond to an example of transfer means.

[0192] In FIG. 2, the process cartridge 300 integrally supports an electrophotographic photosensitive member 7, a charging device 8 (an example of charging means), a developing device 11 (an example of developing means), and a cleaning device 13 (an example of cleaning means) in a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, and the cleaning blade 131 is disposed so as to contact the surface of the electrophotographic photosensitive member 7. Note that the cleaning member may be a conductive or insulating fibrous member instead of the form of the cleaning blade 131, and this may be used alone or in combination with the cleaning blade 131.

[0193] Note that FIG. 2 shows an example of an image forming apparatus including a fibrous member 132 (in a roll shape) that supplies a lubricant 14 to the surface of the electrophotographic photosensitive member 7 and a fibrous member 133 (in a flat brush shape) that assists cleaning, but these are disposed as needed.

[0194] Hereinafter, each component of the image forming apparatus according to the present embodiment will be described.

[0195] - Charging Device - As the charging device 8, for example, a contact charging device using a conductive or semiconductive charging roller, charging brush, charging film, charging rubber blade, charging tube, etc. is used. Also, a non-contact type roller charger, a charger such as a scorotron charger or a corotron charger using corona discharge, which is a charger known per se, is also used.

[0196] -Exposure device- As the exposure device 9, for example, an optical system device that exposes light such as semiconductor laser light, LED light, liquid crystal shutter light, etc. to the surface of the electrophotographic photoreceptor 7 in a defined image pattern is mentioned. The wavelength of the light source is within the spectral sensitivity region of the electrophotographic photoreceptor. As the wavelength of the semiconductor laser, near-infrared having an oscillation wavelength in the vicinity of 780 nm is the mainstream. However, it is not limited to this wavelength, and lasers having an oscillation wavelength in the 600 nm range or lasers having an oscillation wavelength of 400 nm or more and 450 nm or less as blue lasers may also be used. Also, for color image formation, a surface-emitting type laser light source of a type that can output multi-beams is also effective.

[0197] -Developing device- As the developing device 11, for example, a general developing device that develops by bringing the developer into contact or non-contact is mentioned. The developing device 11 is not particularly limited as long as it has the above-mentioned functions, and is selected according to the purpose. For example, a known developer having a function of attaching a one-component developer or a two-component developer to the electrophotographic photoreceptor 7 using a brush, roller, etc. is mentioned. Among them, those using a developing roller that holds the developer on its surface are preferred.

[0198] The developer used in the developing device 11 may be a one-component developer of toner alone, or a two-component developer containing toner and carrier. Also, the developer may be magnetic or non-magnetic. Well-known ones are applicable to these developers.

[0199] -Cleaning device- As the cleaning device 13, a cleaning blade method device including a cleaning blade 131 is used. In addition to the cleaning blade method, a fur brush cleaning method or a simultaneous development and cleaning method may also be adopted.

[0200] -Transfer device- As the transfer device 40, for example, known transfer chargers such as a contact type transfer charger using a belt, roller, film, rubber blade, etc., a scorotron transfer charger using corona discharge, or a corotron transfer charger can be mentioned.

[0201] -Intermediate transfer member- As the intermediate transfer member 50, a belt-shaped one (intermediate transfer belt) containing a polyimide, polyamideimide, polycarbonate, polyarylate, polyester, rubber, etc. having semiconductive properties is used. Also, as the form of the intermediate transfer member, a drum-shaped one may be used in addition to the belt-shaped one.

[0202] FIG. 3 is a schematic configuration diagram showing another example of the image forming apparatus according to the present embodiment. The image forming apparatus 120 shown in FIG. 3 is a tandem type full-color image forming apparatus equipped with four process cartridges 300. In the image forming apparatus 120, four process cartridges 300 are arranged in parallel on the intermediate transfer member 50, and one electrophotographic photoreceptor is used for each color. Note that the image forming apparatus 120 has the same configuration as the image forming apparatus 100 except that it is of the tandem type.

Examples

[0203] Examples will be described below, but the present invention is not limited to these examples in any way. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0204] <Production of fluorine-containing resin particles> -Production of fluorine-containing resin particles (1)- Fluorine-containing resin particles (1) were produced as follows. 100 parts by mass of commercially available homopolymer polytetrafluoroethylene fine powder (standard specific gravity 2.175 measured in accordance with ASTM D 4895 (2004)) and 2.4 parts by mass of ethanol as an additive were collected in a bag made of barrier nylon, and the entire bag was purged with nitrogen. Then, it was irradiated with cobalt-60 γ-rays at room temperature at 150 kGy to obtain low-molecular-weight polytetrafluoroethylene powder. The obtained powder was pulverized to obtain fluorine-containing resin particles (1).

[0205] -Production of fluorine-containing resin particles (2)- Fluorine-containing resin particles (2) were produced in the same manner as the production of fluorine-containing resin particles (1), except that the entire bag was purged with nitrogen so that the oxygen concentration became 8%.

[0206] -Production of fluorine-containing resin particles (3)- 3 liters of deionized water, 3.0 g of ammonium perfluorooctanoate, and 110 g of paraffin wax (manufactured by Nippon Oil Corporation) as an emulsion stabilizer were charged into an autoclave. The system was purged with nitrogen three times and then with TFE (tetrafluoroethylene) twice to remove oxygen. Then, the internal pressure was set to 1.0 MPa with TFE, and while stirring at 250 rpm, the internal temperature was maintained at 70°C. Next, 150 cc / min of ethane at normal pressure as a chain transfer agent and a 20 ml aqueous solution in which 300 mg of ammonium persulfate as a polymerization initiator was dissolved were charged into the system to start the reaction. During the reaction, the temperature inside the system was maintained at 70°C, and TFE was continuously supplied so that the internal pressure of the autoclave was always maintained at 1.0 ± 0.05 MPa. When the amount of TFE consumed in the reaction reached 1000 g after the addition of the initiator, the supply of TFE and stirring were stopped, and the reaction was terminated. Then, the particles were separated by centrifugation, and further 400 parts by mass of methanol was collected and washed with stirring at 250 rpm for 10 minutes while irradiating with ultrasonic waves, and the supernatant was filtered. After repeating this operation three times, the filtrate was dried under reduced pressure at 60°C for 17 hours. Through the above steps, fluorine-containing resin particles (3) were produced.

[0207] -Production of fluorine-containing resin particles (C1)- In the production of the fluorine-containing resin particles (1), the fluorine-containing resin particles (C1) were produced in the same manner as in the production of the fluorine-containing resin particles (1), except that the radiation irradiation was carried out in air.

[0208] <Example 1> -Production of Photoconductor- Using the obtained fluorine-containing resin particles, a photoconductor was produced as follows.

[0209] Zinc oxide: (average particle size 70 nm: manufactured by Tayca Corporation: specific surface area value 15 m 2 / g) 100 parts were stirred and mixed with 500 parts of tetrahydrofuran, 1.4 parts of a silane coupling agent (KBE503: manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the mixture was stirred for 2 hours. Then, toluene was distilled off under reduced pressure, and baking was carried out at 120 °C for 3 hours to obtain zinc oxide surface-treated with a silane coupling agent. 110 parts of the surface-treated zinc oxide were stirred and mixed with 500 parts of tetrahydrofuran, and a solution prepared by dissolving 0.6 part of alizarin in 50 parts of tetrahydrofuran was added, and the mixture was stirred at 50 °C for 5 hours. Then, zinc oxide to which alizarin was imparted was filtered off by vacuum filtration, and further dried under reduced pressure at 60 °C to obtain alizarin-imparted zinc oxide. 60 parts of this alizarin-imparted zinc oxide, 13.5 parts of a curing agent (blocked isocyanate Sumidur 3175, manufactured by Sumitomo Bayer Urethane Co., Ltd.), 15 parts of a butyral resin (Esrec BM-1, manufactured by Sekisui Chemical Co., Ltd.), and 85 parts of methyl ethyl ketone were mixed to obtain a mixed solution. 38 parts of this mixed solution and 25 parts of methyl ethyl ketone were mixed, and dispersion was carried out using 1 mmφ glass beads in a sand mill for 2 hours to obtain a dispersion. 0.005 part of dioctyltin dilaurate as a catalyst and 30 parts of silicone resin particles (Tospearl 145, Momentive Performance Materials Japan Co., Ltd.) were added to the obtained dispersion to obtain a coating solution for an undercoat layer. This coating solution was applied onto a cylindrical aluminum substrate by dip coating method, and dried and cured at 170 °C for 30 minutes to obtain an undercoat layer with a thickness of 24 μm.

[0210] Next, one part of hydroxygallium phthalocyanine having strong diffraction peaks at Bragg angles (2θ ± 0.2°) of 7.5°, 9.9°, 12.5°, 16.3°, 18.6°, 25.1°, and 28.3° in the X-ray diffraction spectrum was mixed with one part of polyvinyl butyral (Esrec BM-5, manufactured by Sekisui Chemical Co., Ltd.) and 80 parts of n-butyl acetate, and this was dispersed with glass beads using a paint shaker for 1 hour to prepare a coating solution for the charge generation layer. The obtained coating solution was dip-coated onto a conductive support on which an undercoat layer was formed, and heated and dried at 130°C for 10 minutes to form a charge generation layer with a film thickness of 0.15 μm.

[0211] As a charge transport material, 39 parts of a benzidine compound represented by the following formula (CTM1) (TB ratio: 43%), as a binder resin, 52 parts of a polymer compound having a repeating unit represented by the following formula (PCZ1) (viscosity average molecular weight: 40,000), and as an acidic compound, malonic acid in the amount (parts by mass) shown in Table 1 (hereinafter, the acidic compound is blended so as to be in the amount shown in Table 1 (the amount (ppm) with respect to the solid content of the outermost layer)) were dissolved in 350 parts of toluene and 150 parts of tetrahydrofuran, 9.8 parts of fluorine-containing resin particles (1) and 1 part of a fluorine-containing dispersant GF400 (manufactured by Toagosei Co., Ltd.) were added, and the mixture was treated 5 times with a high-pressure homogenizer to prepare a coating solution for the charge generation layer. The obtained coating solution was coated onto the above charge generation layer by a dip coating method, and heated at 140°C for 45 minutes to form a charge transport layer with a film thickness of 31 μm.

[0212]

Chemical formula

[0213]

Chemical formula

[0214] Through the above steps, each photoreceptor was fabricated.

[0215] <Examples 2 to 43, Comparative Examples 1 to 9, and Reference Examples 1 and 2> A photoreceptor was produced in the same manner as in Example 1, except that the type and amount of the acidic compound, the type of the fluorine-containing resin particles, the drying temperature during the formation of the charge transport layer, and the addition amounts of the binder resin and the charge transport material were changed to the TB ratios shown in Tables 1 to 3. The total addition amount of the binder resin and the charge transport material was the same as in Example 1.

[0216] <Evaluation> (Various Measurements) Regarding the fluorine-containing resin particles, the following characteristics were measured according to the method described above. · Number of carboxyl groups (denoted as "COOH" in the table) per 10 carbon atoms 6 (number per unit) Regarding the photoreceptors obtained in each example, the following characteristics were measured according to the method described above. · Absolute value (|RP1 - RP 10000 |) (denoted as "ΔRP" in the table)

[0217] - Measurement of Charging Potential - The photoreceptor was charged with a scorotron charger at a grid applied voltage of -700 V in an environment of 30°C and 85% RH. Then, 0.1 second after charging, the potential (V) on the surface of the photoreceptor was measured, and this measured value was defined as the charging potential VH1. Thereafter, using a semiconductor laser with a wavelength of 780 nm, the photoreceptor was flash-exposed with a light amount of 10 mJ / m 2 to discharge the photoreceptor. The charging and exposure operations of the photoreceptor were repeated in the same procedure (at this time, the potential (V) on the surface of the photoreceptor was not measured). 0.1 second after the 10,000th charging, the potential (V) on the surface of the photoreceptor was measured, and this measured value was defined as the charging potential VH 10000 . Then, the absolute value of the difference between VH1 and VH 10000 (|VH1 - VH 10000 |) (denoted as "ΔVH" in the table) was calculated.

[0218] - Evaluation of Image Density Non-uniformity - The obtained photoreceptor was installed in the copier "Versant 180i Press" manufactured by Fuji Xerox Co., Ltd., and 10,000 consecutive images with an image density of 30% were output under the conditions of 30°C / 85%RH. Then, the copier was stopped for 12 hours. After that, one image with an image density of 30% was output again, and the density change of the image was visually inspected. The evaluation criteria are as follows. The acceptable range is A to C. A: No density change B: Almost no density change C: Slight density change, and problems may occur in actual use D: Density change, unable to withstand actual use

[0219]

Table 1

[0220]

Table 2

[0221]

Table 3

[0222] The abbreviations in the table are shown below. ·DBSA: Dodecylbenzenesulfonic acid

[0223] (Actual machine evaluation) -Image forming apparatus for evaluation- The photoreceptors obtained in Example 2 and Comparative Example 2 were installed in the Versant 180i Press manufactured by Fuji Xerox Co., Ltd., which is provided with a charge elimination means for irradiating the surface of the electrophotographic photoreceptor with charge elimination light before charging after the transfer of the toner image. This apparatus was used as an image forming apparatus for evaluation.

[0224] -Evaluation of image density unevenness- Using the evaluation image forming apparatus, images with an image density of 30% were continuously output 10,000 sheets under the conditions of 30°C / 85%RH. Then, the copying machine was paused for 12 hours. After that, an image with an image density of 30% was output again, and the density change of the image was visually inspected. As a result, when using the evaluation image forming apparatus equipped with the photoreceptor obtained in Example 2, there was no density change in the obtained image. On the other hand, when using the evaluation image forming apparatus equipped with the photoreceptor obtained in Comparative Example 2, there was a density change in the obtained image and it could not withstand actual use.

[0225] From the above results, it can be seen that the photoreceptor of this example can suppress a decrease in the uniformity of the image density when pausing after continuous image formation and then performing image formation again. Note that Reference Example 1 is a photoreceptor containing fluorine-containing resin particles with more than 30 carboxyl groups per 10 carbon atoms in the outermost surface layer, and it can be seen that there is no decrease in the uniformity of the image density. 6 It can be seen that there is no decrease in the uniformity of the image density.

Explanation of Signs

[0226] 1 Undercoat layer, 2 Charge generation layer, 3 Charge transport layer, 4 Conductive substrate, 7A, 7 Electrophotographic photoreceptor, 8 Charging device, 9 Exposure device, 11 Developing device, 13 Cleaning device, 14 Lubricant, 40 Transfer device, 50 Intermediate transfer body, 100 Image forming device, 120 Image forming device, 131 Cleaning blade, 132 Fibrous member (roll shape), 133 Fibrous member (flat brush shape), 300 Process cartridge

Claims

1. It has a conductive substrate and a photosensitive layer provided on the conductive substrate, The outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound, The number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms ６ and is, The acid dissociation constant (pKa) of the acidic compound is 0.5 or more and 3.0 or less, In the outermost surface layer, the content of the charge transport material with respect to the binder resin is 59% by mass or more and 72% by mass or less, When charging and exposure are repeated 10,000 times under the conditions of a charging potential of -700 V and an exposure intensity of 10 mJ / m ２ of the absolute value of the difference between the residual potential RP １ after one charging and exposure and the residual potential RP １００００ after 10,000 chargings and exposures (|RP １ - RP １００００ |) is 25 V or less, an electrophotographic photoreceptor.

2. It has a conductive substrate and a photosensitive layer provided on the conductive substrate, The photosensitive layer is a laminated photosensitive layer composed of a charge generation layer and a charge transport layer, and the outermost surface layer is a charge transport layer, The outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound, The number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 carbon atoms ６ and is, The acid dissociation constant (pKa) of the acidic compound is 0.5 or more and 3.0 or less, When charging and exposure are repeated 10,000 times under the conditions of a charging potential of -700 V and an exposure intensity of 10 mJ / m ２ of the absolute value of the difference between the residual potential RP １ after one charging and exposure and the residual potential RP １００００ after 10,000 chargings and exposures (|RP １ - RP １００００An electrophotographic photoreceptor having a surface potential (V) of 25 V or less.

3. The electrophotographic photoreceptor according to claim 1 or claim 2, wherein the content of the charge transport material with respect to the binder resin in the outermost surface layer is 61% by mass or more and 69% by mass or less.

4. comprising a conductive substrate and a photosensitive layer provided on the conductive substrate, wherein the outermost surface layer contains a binder resin, a charge transport material, fluorine-containing resin particles, and an acidic compound, the number of carboxyl groups of the fluorine-containing resin particles is 0 or more and 30 or less per 10 ６ carbon atoms, the acid dissociation constant (pKa) of the acidic compound is 0.5 or more and 3.0 or less, The electrophotographic photoreceptor, wherein the content of the charge transport material with respect to the binder resin in the outermost surface layer is 59% by mass or more and 72% by mass or less.

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the acid dissociation constant (pKa) of the acidic compound is 0.5 or more and 2.5 or less.

6. The electrophotographic photoreceptor according to claim 5, wherein the acid dissociation constant (pKa) of the acidic compound is 0.5 or more and 1.5 or less.

7. The electrophotographic photoreceptor according to any one of claims 1 to 6, wherein the acidic compound is at least one selected from the group consisting of a sulfonic acid compound, a carboxylic acid compound, and a phosphoric acid compound.

8. The electrophotographic photoreceptor according to claim 7, wherein the acidic compound is at least one selected from the group consisting of a sulfonic acid compound and a carboxylic acid compound.

9. The sulfonic acid compound is a sulfonic acid compound having a benzene ring, The electrophotographic photoreceptor according to claim 7 or claim 8, wherein the carboxylic acid compound is a carboxylic acid compound having 2 or more and 4 or less carboxyl groups.

10. The electrophotographic photoreceptor according to any one of Claims 1 to 9, wherein the content of the acidic compound is 25 ppm or more and 1000 ppm or less with respect to the outermost surface layer.

11. The electrophotographic photoreceptor according to any one of Claims 1, 3 to 10, wherein the photosensitive layer is a laminated photosensitive layer composed of a charge generation layer and a charge transport layer, and the outermost surface layer is a charge transport layer.

12. An electrophotographic photoreceptor according to any one of Claims 1 to 11, A process cartridge that is detachable from an image forming apparatus.

13. An electrophotographic photoreceptor according to any one of Claims 1 to 11, and Charging means for charging the surface of the electrophotographic photoreceptor, Electrostatic latent image forming means for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, 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, Transfer means for transferring the toner image onto the surface of a recording medium, An image forming apparatus comprising the same.

14. The image forming apparatus according to Claim 13, further comprising discharging means for irradiating the surface of the electrophotographic photoreceptor with a discharging light to discharge the charge after the transfer of the toner image and before charging.

Images