JP2024047678A - Electrophotographic photoreceptor, process cartridge, and image forming apparatus - Google Patents

Abstract

[Problem] To provide an electrophotographic photoreceptor that suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer. [Solution] An electrophotographic photoreceptor comprising a conductive substrate, an undercoat layer provided on the conductive substrate, a photosensitive layer provided on the undercoat layer, and a surface protective layer provided on the photosensitive layer, in which the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is less than 10 V in a spectrum of period and amplitude obtained by fast Fourier transforming the surface potential when the outer circumferential surface of the electrophotographic photoreceptor is charged and exposed to light. [Selected Figure] None

Description

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

Conventionally, electrophotographic image forming apparatuses are widely known to be equipped with an electrophotographic photoreceptor and sequentially carry out processes such as charging, electrostatic latent image formation, development, transfer, and cleaning.

For example, Patent Document 1 discloses an image forming apparatus including a photoreceptor and a charging means for uniformly charging the surface of the photoreceptor, the photoreceptor having a conductive support and a photosensitive layer and a protective layer provided on the conductive support, the protective layer containing a curable resin cured by electron beam irradiation and conductive particles, the photoreceptor having a Taber abrasion of 0.1 to 1.0 (mg/1000 rotations), the charging means having a charging member arranged in contact with the surface of the photoreceptor, a charging bias application power source that applies a charging bias in which a DC voltage and an AC voltage are superimposed to the charging member to charge the surface of the photoreceptor, and a control means that controls the charging bias with an AC voltage, and the control means determines an AC voltage value when controlling the AC voltage based on the application time of the charging bias.

JP 2004-205581 A

Conventionally, photoreceptors having a conductive substrate, an undercoat layer, a photosensitive layer, and a surface protective layer have tended to have image density unevenness in the circumferential direction of the photoreceptor due to drying unevenness in the photosensitive layer. Therefore, the present disclosure aims to provide a photoreceptor that suppresses image density unevenness in the circumferential direction of the photoreceptor due to drying unevenness in the photosensitive layer, compared to when the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is 10 V or more in a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the photoreceptor is charged and exposed to light.

Means for solving the above problems include the following aspects.
<1> A conductive substrate;
an undercoat layer provided on the conductive substrate;
a photosensitive layer provided on the undercoat layer;
a surface protective layer provided on the photosensitive layer;
Equipped with
An electrophotographic photoreceptor, in which in a spectrum of period and amplitude obtained by fast Fourier transform of a surface potential when an outer peripheral surface of the electrophotographic photoreceptor is charged and exposed to light, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is less than 10 V.
<2> The electrophotographic photoreceptor according to <1>, wherein the photosensitive layer has a thickness of less than 15 μm.
<3> The electrophotographic photoreceptor according to <2>, wherein the photosensitive layer has a thickness of less than 11 μm.
<4> The electrophotographic photoreceptor according to <1>, wherein in the spectrum, the amplitude of a frequency component corresponding to a circumference of the electrophotographic photoreceptor is 7 V or less.
<5> The electrophotographic photoreceptor according to <4>, wherein in the spectrum, the amplitude of a frequency component corresponding to a circumference of the electrophotographic photoreceptor is 5 V or less.
<6> An electrophotographic photoreceptor according to any one of <1> to <5>,
A process cartridge that is detachably attached to an image forming apparatus.
<7> The electrophotographic photoreceptor according to any one of <1> to <5>,
a charging means for charging the surface of the electrophotographic photoreceptor;
an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor;
a developing unit for developing an electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image;
a transfer means for transferring the toner image onto a surface of a recording medium;
An image forming apparatus comprising:

According to the invention related to <1>, there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in a photosensitive layer, as compared with a case in which, in a spectrum of period and amplitude obtained by fast Fourier transform of a surface potential when the outer peripheral surface of the electrophotographic photoreceptor is charged and exposed, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is 10 V or more.
According to the second aspect of the present invention, there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photoreceptor, as compared with a case where the thickness of the photoreceptor layer is 15 μm or more.
According to the third aspect of the present invention, there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photoreceptor, as compared with a case where the thickness of the photoreceptor layer is 11 μm or more.
According to the invention related to <4>, there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to a case in which the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor in the spectrum exceeds 7 V.
According to the invention related to <5>, there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to a case in which the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor in the spectrum exceeds 5 V.
According to the invention related to <6> or <7>, there is provided a process cartridge or image forming apparatus which suppresses image density unevenness in the circumferential direction of the photoconductor caused by uneven drying in the photosensitive layer, compared to a case in which an electrophotographic photoconductor is provided in which, in a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photoconductor is charged and exposed, the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photoconductor is 10 V or more.

FIG. 2 is a schematic cross-sectional view illustrating an example of a layer structure of the electrophotographic photoreceptor according to the present embodiment. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a schematic configuration diagram illustrating another example of an image forming apparatus according to the present embodiment.

Hereinafter, an embodiment of the present invention will be described in detail.
In this specification, in the case of numerical ranges described in stages, the upper limit or lower limit value described in a certain numerical range may be replaced with the upper limit or lower limit value of another numerical range described in stages.
In addition, in a numerical range, the upper limit or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.
When a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.
The term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

In this specification, "electrophotographic photoreceptor" is also referred to as "photoreceptor."

<Electrophotographic Photoreceptor>
The electrophotographic photoreceptor according to the present embodiment comprises a conductive substrate, an undercoat layer provided on the conductive substrate, a photosensitive layer provided on the undercoat layer, and a surface protective layer provided on the photosensitive layer, and in a spectrum of period and amplitude obtained by fast Fourier transform of a surface potential when an outer peripheral surface of the electrophotographic photoreceptor is charged and exposed to light, the amplitude of a frequency component corresponding to a circumferential length of the electrophotographic photoreceptor is less than 10 V.

Conventionally, photoreceptors having a conductive substrate, an undercoat layer, a photosensitive layer, and a surface protective layer have tended to have uneven drying in the photosensitive layer in the circumferential direction of the photoreceptor. This is due to uneven charge mobility caused by uneven heating in the photosensitive layer when drying a coating film obtained by applying a coating liquid for forming the photosensitive layer, which causes unevenness in the distance between the charge transport materials contained in the photosensitive layer. If uneven drying occurs in the photosensitive layer, image density unevenness is likely to occur in the circumferential direction of the photoreceptor when images are repeatedly formed.

On the other hand, the photoreceptor according to this embodiment has the above-mentioned configuration, and thus provides a photoreceptor that suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer. The mechanism of this action is not entirely clear, but is presumed to be as follows.

In the photoconductor according to this embodiment, in the spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the photoconductor is charged and exposed, the amplitude of the frequency component corresponding to the circumference of the photoconductor is less than 10 V, and the potential unevenness of the outer peripheral surface of the photoconductor is small. As a result, it is believed that the unevenness of image density in the circumferential direction of the photoconductor caused by uneven drying is suppressed.

(Characteristics of Electrophotographic Photoreceptor)
In a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photosensitive member is charged and exposed, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photosensitive member is less than 10 V, preferably 8 V or less, and more preferably 5 V or less.
When the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photosensitive member in the spectrum is within the above range, unevenness in image density in the circumferential direction of the photosensitive member caused by uneven drying is further suppressed.

The amplitude of the frequency component corresponding to the circumference of the electrophotographic photosensitive member is determined as follows.
The entire outer peripheral surface of the electrophotographic photoreceptor is charged at -400 V using a Trek 344 surface potential meter manufactured by Trek Corporation, exposed to a light amount of 4 mJ/ ^m2 , and then 12 or more sampling points are taken in the circumferential direction over the entire outer peripheral surface to obtain a potential mapping of the surface potential. For the obtained potential mapping, the frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is subjected to Fourier transform analysis for the value of the surface potential in the circumferential direction in any region of the electrophotographic photoreceptor to obtain a spectrum of period and amplitude. The amplitude value in the obtained spectrum is defined as the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photoreceptor.

The specific method for setting the amplitude of the frequency component corresponding to the circumference of the electrophotographic photoreceptor within the above range in the spectrum is not particularly limited, but examples include adjusting the unevenness of the temperature and air volume in the drying furnace; adjusting the thickness of the photosensitive layer to be thin; setting the temperature at which the coating film is dried during the formation of the photosensitive layer to be equal to or higher than the glass transition temperature of the amorphous resin contained in the photosensitive layer; etc.

Hereinafter, the electrophotographic photoreceptor according to the present embodiment will be described in detail with reference to the drawings.
1 is a schematic cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor according to this embodiment. The photoreceptor 107A has a structure in which an undercoat layer 101 is provided on a conductive substrate 104, and a charge generation layer 102, a charge transport layer 103, and a surface protection layer 106 are sequentially formed thereon.
In FIG. 1, the photoreceptor 107A has a laminated type photosensitive layer 105 in which the functions are separated into the charge generating layer 102 and the charge transport layer 103, but the photosensitive layer 105 may be a single-layer type photosensitive layer.
Although not shown, an intermediate layer may further be provided between the conductive substrate 104 and the undercoat layer 101 .

Each layer of the electrophotographic photoreceptor according to this embodiment will be described in detail below. Note that reference numerals will be omitted in the description.

[Photosensitive Layer]
As explained above with reference to FIG. 1, the photosensitive layer may be a laminated type photosensitive layer having separate functions for a charge generating layer and a charge transporting layer, or a single-layer type photosensitive layer.
The photosensitive layer is preferably a laminated type photosensitive layer. With a laminated type photosensitive layer, drying unevenness is more easily suppressed, and charge mobility unevenness is more easily suppressed while ensuring charge generation ability and charge transport ability. As a result, image density unevenness in the circumferential direction of the photoconductor is more easily suppressed.

The following describes the characteristics of the photosensitive layer that are common to both the multi-layer type and single-layer type photosensitive layers.

The thickness of the photosensitive layer (more preferably the thickness of the charge transport layer in a laminated photosensitive layer) is preferably less than 15 μm, more preferably less than 11 μm, and further preferably from 2 μm to 8 μm.
When the thickness of the photosensitive layer (more preferably the thickness of the charge transport layer in the laminated photosensitive layer) is within the above range, the amplitude of the frequency component corresponding to the circumference of the electrophotographic photosensitive member is easily adjusted to the above range, and as a result, the drying unevenness in the photosensitive layer is further suppressed, and the resulting image density unevenness in the circumferential direction of the photosensitive member is also further suppressed.

The photosensitive layer preferably contains a binder resin and a charge transport material.
The types of charge transporting materials are as exemplified in the charge transport layer and the single-layer type photosensitive layer described below.
The types of binder resins are as exemplified in the charge generating layer, charge transport layer and single-layer type photosensitive layer described below.

The binder resin preferably contains an amorphous resin. The amorphous resin may be used alone or in combination of two or more kinds.
When the binder resin contains an amorphous resin, for example, when the photosensitive layer is formed by a coating method, the drying temperature in drying the coating is set to be equal to or higher than the glass transition temperature of the amorphous resin, thereby suppressing the occurrence of unevenness in the distance of the charge transport material in the photosensitive layer. As a result, the drying unevenness is further suppressed, and the amplitude of the frequency component corresponding to the circumference of the electrophotographic photosensitive member is easily adjusted to the above range.

The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in endothermic amount in differential scanning calorimetry (DSC), and specifically refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10 (°C/min).
On the other hand, the term "amorphous" for a resin refers to a half-width exceeding 10° C., a stepwise change in endothermic heat quantity, or no clear endothermic peak being observed.

(Charge Generation Layer)
The charge generating layer is, for example, a layer containing a charge generating material and a binder resin. The charge generating layer may also be a vapor deposition layer of the charge generating material.
This is suitable for use with incoherent light sources such as a 300 MHz IR emitting diode (300 MHz IR emitting diode) or an organic EL (Electro-Luminescence) image array.

Examples of charge generating materials include azo pigments such as bisazo and trisazo; condensed aromatic pigments such as dibromoanthanthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

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

On the other hand, in order to accommodate laser exposure in the near ultraviolet range, preferred charge generating materials are condensed aromatic pigments such as dibromoanthanthrone, thioindigo pigments, porphyrazine compounds, zinc oxide, trigonal selenium, bisazo pigments, etc.

The above charge generating materials may be used when using incoherent light sources such as LEDs and organic EL image arrays that emit light at a central wavelength between 450 nm and 780 nm. However, from the viewpoint of resolution, when using a thin photosensitive layer of 20 μm or less, the electric field strength in the photosensitive layer becomes high, and a decrease in charge due to charge injection from the substrate, so-called black spots, are likely to occur as image defects. This is particularly noticeable when using charge generating materials that are p-type semiconductors such as trigonal selenium and phthalocyanine pigments and are prone to generating dark current.

In contrast, when an n-type semiconductor such as a fused aromatic pigment, a perylene pigment, or an azo pigment is used as the charge generating material, dark current is unlikely to occur, and image defects called black spots can be suppressed even when the material is made into a thin film.
The n-type is determined by the polarity of the photocurrent that flows using the commonly used time-of-flight method, and those that easily pass electrons as carriers rather than holes are determined to be n-type.

The binder resin used in the charge generating layer may be selected from a wide range of insulating resins, and may also be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, polysilane, and the like.
Examples of binder resins include polyvinyl butyral resins, polyarylate resins (polycondensates of bisphenols and aromatic dicarboxylic acids, etc.), polycarbonate resins, polyester resins, phenoxy resins, vinyl chloride-vinyl acetate copolymers, polyamide resins, acrylic resins, polyacrylamide resins, polyvinylpyridine resins, cellulose resins, urethane resins, epoxy resins, casein, polyvinyl alcohol resins, polyvinylpyrrolidone resins, etc. Here, "insulating" means that the volume resistivity is 10 ¹³ Ωcm or more.
These binder resins may be used alone or in combination of two or more.

It is preferable that the mixing ratio of the charge generating material to the binder resin is within the range of 10:1 to 1:10 by mass.

The charge generating layer may also contain other known additives.

The formation of the charge generation layer is not particularly limited, and a known formation method is used, for example, by forming a coating film of a coating solution for forming a charge generation layer in which the above-mentioned components are added to a solvent, drying the coating film, and heating it as necessary. The formation of the charge generation layer may be performed by vapor deposition of a charge generation material. The formation of the charge generation layer by vapor deposition is particularly suitable when a condensed ring aromatic pigment or a perylene pigment is used as the charge generation material.

Solvents for preparing the coating solution for forming the charge generating 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, etc. These solvents can be used alone or in combination of two or more.

Methods for dispersing particles (e.g., charge generating material) in the coating liquid for forming the charge generating layer include, for example, media dispersers such as ball mills, vibration ball mills, attritors, sand mills, and horizontal sand mills, and medialess dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include a collision type in which the dispersion liquid is dispersed by liquid-liquid collision or liquid-wall collision under high pressure, and a penetration type in which the dispersion liquid is dispersed by penetrating a fine flow path under high pressure.
During this dispersion, it is effective to adjust the average particle size of the charge generating material in the coating liquid for forming the charge generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

Methods for applying the coating liquid for forming the charge generating layer onto the undercoat layer (or onto the intermediate layer) include, for example, conventional methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.

The thickness of the charge generating layer is preferably set within the range of, for example, 0.1 μm to 5.0 μm, and more preferably 0.2 μm to 2.0 μm.

(Charge Transport Layer)
The charge transport layer is, for example, a layer containing a charge transport material and a binder resin, and may be a layer containing a polymer charge transport material.

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

From the viewpoint of charge mobility, the charge transport material is preferably a triarylamine derivative represented by the following structural formula (a-1) or a benzidine derivative represented by the following structural formula (a-2).

In structural formula (a-1), Ar ^T1 , Ar ^T2 , and Ar ^T3 each independently represent a substituted or unsubstituted aryl group, -C ₆ H ₄ -C(R ^T4 )=C(R ^T5 )(R ^T6 ), or -C ₆ H ₄ -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 substituent on each of the above groups include a halogen atom, an alkyl group having from 1 to 5 carbon atoms, and an alkoxy group having from 1 to 5 carbon atoms. Examples of the substituent on each of the above groups also include a substituted amino group substituted with an alkyl group having from 1 to 3 carbon atoms.

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 substituent on each of the above groups include a halogen atom, an alkyl group having from 1 to 5 carbon atoms, and an alkoxy group having from 1 to 5 carbon atoms. Examples of the substituent on each of the above groups also include a substituted amino group substituted with an alkyl group having from 1 to 3 carbon atoms.

Here, among the triarylamine derivatives represented by structural formula (a-1) and the benzidine derivatives represented by structural formula (a-2), the triarylamine derivatives having "-C ₆ H ₄ -CH═CH-CH═C(R ^T7 )(R ^T8 )" and the benzidine derivatives having "-CH═CH-CH═C(R ^T15 )(R ^T16 )" are particularly preferred from the viewpoint of charge mobility.

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 are preferred. The polymer charge transport material may be used alone or in combination with a binder resin.

Examples of binder resins used in 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, polysilanes, 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.

The compounding ratio of the charge transport material to the binder resin is preferably 10:1 to 1:5 by mass.

The charge transport layer may contain other well-known additives.
In particular, the charge transport layer preferably contains a surfactant.
Examples of the surfactant include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

There are no particular limitations on the formation of the charge transport layer, and any known formation method can be used. For example, the charge transport layer can be formed by forming a coating film of a coating solution for forming the charge transport layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary.

The drying temperature of the coating film obtained by applying the coating liquid for forming the charge transport layer is not particularly limited, but it is preferable to heat and dry the coating film at a temperature equal to or higher than the glass transition temperature of the amorphous resin contained in the coating liquid. This makes it easier to suppress uneven drying of the coating film when the coating film is heated and dried, and further suppresses uneven image density in the circumferential direction of the photoreceptor.

Examples of solvents for preparing the coating solution for forming the charge transport layer include ordinary organic solvents such as 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.

Examples of the coating method for applying the coating liquid for forming the charge transport layer onto the charge generating layer include conventional methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.

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

From the viewpoint of further suppressing drying unevenness, the thickness of the charge transport layer is preferably less than 15 μm, more preferably less than 11 μm, and even more preferably 2 μm or more and 8 μm or less.

The single-layer photosensitive layer is explained in detail below.

(Single-layer type photosensitive layer)
The single-layer type photosensitive layer (charge generation/charge transport layer) is, for example, a layer containing a binder resin, a charge generation material, a charge transport material, and, if necessary, other well-known additives. Note that these materials are the same as those described for the charge generation layer and the charge transport layer.
The content of the charge generating material in the single-layer photosensitive layer is preferably 0.1% by mass to 10% by mass, more preferably 0.8% by mass to 5% by mass, based on the total solid content, and the content of the charge transport material in the single-layer photosensitive layer is preferably 5% by mass to 50% by mass, based on the total solid content.
The method for forming the single-layer type photosensitive layer is similar to the method for forming the charge generating layer and the charge transport layer.
The thickness of the single-layer photosensitive layer is, for example, from 5 μm to 50 μm, and preferably from 10 μm to 40 μm.

From the viewpoint of further suppressing drying unevenness in the single-layer photosensitive layer, the film thickness of the single-layer photosensitive layer is preferably less than 15 μm, more preferably less than 11 μm, and even more preferably 2 μm or more and 8 μm or less.

[Conductive Substrate]
The conductive substrate may be, for example, a metal drum containing a metal (such as aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, or platinum) or an alloy (such as stainless steel). Here, "conductive" means that the volume resistivity is less than ¹⁰ Ω cm.
The conductive substrate is preferably in the form of a metal drum, i.e., a cylinder. Even if a cylindrical conductive substrate is used, air bubbles and color spots can be suppressed.

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 to 0.5 μm inclusive in order to suppress interference fringes that occur when irradiating the substrate with laser light. When non-interfering light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but it is suitable for a longer life because it suppresses the occurrence of defects due to unevenness on the surface of the conductive substrate.

Methods for roughening the surface include, for example, wet honing, in which an abrasive is suspended in water and sprayed onto the conductive substrate; centerless grinding, in which the conductive substrate is pressed against a rotating grindstone and continuously ground; and anodizing.

As a method of roughening, there is also a method in which, without roughening the surface of the conductive substrate, conductive or semiconductive powder is dispersed in a resin to form a layer on the surface of the conductive substrate, and the surface is roughened by the particles dispersed in the layer.

In the roughening treatment by anodization, an oxide film is formed on the surface of a conductive substrate made of metal (e.g., aluminum) by anodizing the substrate in an electrolyte solution using the substrate as the anode. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodization is chemically active in its original state, easily contaminated, and has a large resistance fluctuation due to the environment. Therefore, it is preferable to perform a sealing treatment on the porous anodic oxide film, in which the micropores of the oxide film are filled by volume expansion caused by a hydration reaction in pressurized steam or boiling water (metal salts such as nickel may be added), and the porous anodic oxide film is converted into a more stable hydrated oxide.

The thickness of the anodic oxide film is preferably, for example, 0.3 μm or more and 15 μm or less. If the thickness is within the above range, the film tends to exhibit barrier properties against injection and also tends to suppress the increase in residual potential due to repeated use.

The conductive substrate may be subjected to a treatment with an acidic treatment solution or a boehmite treatment.
Treatment with an 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, phosphoric acid in the range of 10 mass% to 11 mass%, chromic acid in the range of 3 mass% to 5 mass%, and hydrofluoric acid in the range of 0.5 mass% to 2 mass%, and the total concentration of these acids is preferably in the range of 13.5 mass% to 18 mass%. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness of the coating is preferably 0.3 μm to 15 μm.

The boehmite treatment is carried out, for example, by immersing the material in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting the material with heated steam at 90°C to 120°C for 5 to 60 minutes. The thickness of the coating is preferably 0.1 μm to 5 μm. This may be further anodized using an electrolyte solution with low coating solubility, such as adipic acid, boric acid, borates, phosphates, phthalates, maleates, benzoates, tartrates, or citrates.

The thickness of the conductive substrate is preferably 1 mm or more, and more preferably 2 mm or more.
When the conductive substrate is thick, air bubbles tend to diffuse into the coating liquid during the formation of the charge transport layer, and color spots tend to occur. Even if the conductive substrate has a thickness of 1 mm or more, air bubbles can be suppressed and color spots can be suppressed.
The upper limit of the thickness of the conductive substrate is, for example, 2.5 mm or less.

[Undercoat layer]
The undercoat layer is, for example, a layer containing inorganic particles and a binder resin.

The inorganic particles may, for example, have a powder resistivity (volume resistivity) of 10 ² Ωcm or more and 10 ¹¹ Ωcm or less.
Among these, examples of inorganic particles having the above-mentioned resistance value include metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, and zinc oxide particles are particularly preferred.

The specific surface area of the inorganic particles as measured by the BET method is preferably, for example, 10 m ² /g or more.
The volume average particle size of the inorganic particles is, for example, from 50 nm to 2000 nm (preferably from 60 nm to 1000 nm).

The content of inorganic particles is, for example, preferably 10% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 80% by mass or less, relative to the binder resin.

The inorganic particles may be surface-treated. Two or more types of inorganic particles with different surface treatments or different particle sizes may be used in combination.

Examples of surface treatment agents include silane coupling agents, titanate coupling agents, aluminum coupling agents, surfactants, etc. In particular, silane coupling agents are preferred, and silane coupling agents having an amino group are more preferred.

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

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

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

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

Here, it is preferable for the undercoat layer to contain an electron-accepting compound (acceptor compound) together with the inorganic particles, from the viewpoint of improving the long-term stability of the electrical properties and the carrier blocking properties.

Examples of the electron-accepting compound include electron-transporting substances such as quinone compounds such as chloranil and bromoanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; and diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone.
In particular, the electron-accepting compound is preferably a compound having an anthraquinone structure, such as a hydroxyanthraquinone compound, an aminoanthraquinone compound, or an aminohydroxyanthraquinone compound, and more specifically, such as anthraquinone, 1-hydroxyanthraquinone, alizarin, quinizarin, anthraphin, or purpurin.

The electron accepting compound may be dispersed together with the inorganic particles in the undercoat layer, or may be attached to the surface of the inorganic particles.

Methods for attaching an electron-accepting compound to the surface of inorganic particles include, for example, a dry method or a wet method.

The dry method is, for example, a method in which an electron-accepting compound is attached to the surface of inorganic particles by dropping an electron-accepting compound directly or dissolved in an organic solvent, or spraying the electron-accepting compound together with dry air or nitrogen gas, while stirring inorganic particles with a mixer or the like that exerts a large shearing force. When dropping or spraying the electron-accepting compound, it is preferable to do so at a temperature below the boiling point of the solvent. After dropping or spraying the electron-accepting compound, baking may be performed at 100° C. or higher. The temperature and time of baking are not particularly limited as long as electrophotographic properties can be obtained.

The wet method is a method in which inorganic particles are dispersed in a solvent, for example, by stirring, ultrasonic waves, a sand mill, an attritor, a ball mill, etc., while an electron-accepting compound is added, and after stirring or dispersing, the solvent is removed to attach the electron-accepting compound to the surface of the inorganic particles. The solvent is removed, for example, by filtration or distillation. After the solvent is removed, baking may be performed at 100°C or higher. There are no particular limitations on the temperature and time for baking, so long as electrophotographic properties are obtained. In the wet method, moisture contained in the inorganic particles may be removed before the electron-accepting compound is added. Examples of such methods include a method in which the moisture is removed while stirring and heating in a solvent, and a method in which the moisture is removed by azeotropy with the solvent.

The attachment of the electron-accepting compound may be carried out before or after the inorganic particles are surface-treated with a surface treatment agent, or the attachment of the electron-accepting compound and the surface treatment with the surface treatment agent may be carried out simultaneously.

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

Examples of the binder resin used in the undercoat layer include known materials 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, and epoxy resins; zirconium chelate compounds; titanium chelate compounds; aluminum chelate compounds; titanium alkoxide compounds; organic titanium compounds; and silane coupling agents.
Examples of the binder resin used in the undercoat layer include charge transporting resins having charge transporting groups, conductive resins (such as polyaniline), and the like.

Among these, as the binder resin used in the undercoat layer, a resin insoluble in the coating solvent of the upper layer is preferred, and in particular, a resin obtained by reacting at least one resin selected from the group consisting of a thermosetting resin such as a urea resin, a phenol resin, a phenol-formaldehyde resin, a melamine resin, a urethane resin, an unsaturated polyester resin, an alkyd resin, and an epoxy resin with a curing agent is preferred.
When two or more of these binder resins are used in combination, the mixing ratio thereof is set as required.

The undercoat layer may contain various additives for improving electrical properties, environmental stability, and image quality.
Examples of the additives include known materials such as polycyclic condensation and azo-based electron transport pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, silane coupling agents, etc. As described above, silane coupling agents are used for surface treatment of inorganic particles, and may also be added to the undercoat layer as an additive.

Examples of the silane coupling agent as an additive include vinyltrimethoxysilane, 3-methacryloxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4
N-(2-(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.

Examples of zirconium chelate compounds include zirconium butoxide, zirconium ethyl acetoacetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetoacetate zirconium butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, methacrylate zirconium butoxide, stearate zirconium butoxide, isostearate zirconium butoxide, etc.

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

Examples of aluminum chelate compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

These additives may be used alone or as a mixture or polycondensation of multiple compounds.

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 between 1/(4n) (n is the refractive index of the upper layer) and 1/2 of the wavelength λ of the exposure laser used in order to suppress moire images.
Resin particles or the like may be added to the undercoat layer to adjust the surface roughness. Examples of the resin particles include silicone resin particles and crosslinked polymethyl methacrylate resin particles. The surface of the undercoat layer may be polished to adjust the surface roughness. Examples of the polishing method include buffing, sandblasting, wet honing, grinding, and the like.

There are no particular limitations on the formation of the undercoat layer, and any known formation method can be used. For example, the undercoat layer can be formed by forming a coating film of a coating solution for forming the undercoat layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary.

Examples of the solvent for preparing the coating liquid for forming the undercoat layer include known organic solvents, such as alcohol-based solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone-based solvents, ketone alcohol-based solvents, ether-based solvents, and ester-based solvents.
Specific examples of these solvents include 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, and toluene.

Methods for dispersing inorganic particles when preparing the coating solution for forming the undercoat layer include known methods such as using a roll mill, ball mill, vibrating ball mill, attritor, sand mill, colloid mill, paint shaker, etc.

Methods for applying the coating liquid for forming the undercoat layer onto the conductive substrate include, for example, conventional methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.

The average thickness of the undercoat layer is preferably from 15 μm to 70 μm, and more preferably from 20 μm to 50 μm.
If the average thickness of the undercoat layer is large, when the edge of the undercoat layer on the immersion side becomes rough during dip coating, deep recesses are likely to occur and air bubbles are likely to be mixed into the coating liquid for forming the charge transport layer.
However, even if the average thickness of the coating layer is within the above range, air bubbles and color spots can be suppressed.
The average thickness of the undercoat layer is determined by measuring the thickness of the undercoat layer at three locations in the axial center of the conductive substrate with an eddy current thickness meter, and averaging the measured values.

[Middle class]
Although not shown, 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 in 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, and melamine resins.
The intermediate layer may be a layer containing an organometallic compound. Examples of the organometallic compound used in the intermediate layer include organometallic compounds containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon.
The compounds used in the intermediate layer may be used alone or as a mixture or polycondensation product of a plurality of compounds.

Among these, it is preferable that the intermediate layer is a layer containing an organometallic compound containing zirconium atoms or silicon atoms.

The formation of the intermediate layer is not particularly limited, and a well-known formation method can be used. For example, the intermediate layer can be formed 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 if necessary.
The intermediate layer can be formed by any of the usual coating methods, such as dip coating, push-up coating, wire bar coating, spray coating, blade coating, knife coating and curtain coating.

The thickness of the intermediate layer is preferably set in the range of 0.1 μm to 3 μm. The intermediate layer may also be used as an undercoat layer.

[Surface protective layer]
In this embodiment, a surface protective layer (hereinafter also referred to as a "protective layer") is provided on the photosensitive layer.
The protective layer serves, for example, to prevent chemical changes in the photosensitive layer when the photosensitive layer is charged and to further improve the mechanical strength of the photosensitive layer.
The protective layer is preferably a layer made of a cured film (crosslinked film). Examples of such a layer include the following layers 1) and 2).

1) A layer composed of a cured film of a composition containing a reactive group-containing charge transport material having a reactive group and a charge transport skeleton in the same molecule (i.e., a layer containing a polymer or crosslinked product of the reactive group-containing charge transport material).
2) A layer constituted of a cured film of a composition containing a non-reactive charge transport material and a reactive group-containing non-charge transport material that does not have a charge transport skeleton and has a reactive group (i.e., a layer containing a non-reactive charge transport material and a polymer or crosslinked product of the reactive group-containing non-charge transport material).

Examples of the reactive group of the reactive group-containing charge transport material include well-known reactive groups such as a chain polymerizable group, an epoxy group, -OH, -OR [wherein R represents an alkyl group], -NH ₂ , -SH, -COOH, -SiR ^Q1 _3-Qn (OR ^Q2 ) _Qn [wherein R ^Q1 represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group, R ^Q2 represents a hydrogen atom, an alkyl group, or a trialkylsilyl group, and Qn represents an integer of 1 to 3].

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

The charge transport skeleton of the reactive group-containing charge transport material is not particularly limited as long as it is a known structure in electrophotographic photoreceptors, and examples thereof include a skeleton derived from a nitrogen-containing hole transport compound such as a triarylamine compound, a benzidine compound, or a hydrazone compound, and a structure conjugated with a nitrogen atom. Among these, a triarylamine skeleton is preferred.

The reactive group-containing charge transport material having a reactive group and a charge transport skeleton, the non-reactive charge transport material, and the reactive group-containing non-charge transport material may be selected from well-known materials.

The protective layer may also contain other known additives.

There are no particular limitations on the formation of the protective layer, and well-known formation methods can be used. For example, the protective layer can be formed by forming a coating film of a coating solution for forming the protective layer in which the above components are added to a solvent, drying the coating film, and, if necessary, subjecting it to a curing treatment such as heating.

Examples of solvents for preparing a coating liquid for forming a protective layer include aromatic solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as tetrahydrofuran and dioxane, cellosolve solvents such as ethylene glycol monomethyl ether, and alcohol solvents such as isopropyl alcohol and butanol. These solvents may be used alone or in combination of two or more.
The protective layer-forming coating liquid may be a solvent-free coating liquid.

Methods for applying the protective layer-forming coating solution onto the photosensitive layer (e.g., charge transport layer) include conventional methods such as dip coating, push-up coating, wire bar coating, spray coating, blade coating, knife coating, and curtain coating.

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

<Image forming apparatus (and process cartridge)>
The image forming apparatus according to the present embodiment includes an electrophotographic photoreceptor, a charging unit for charging the surface of the electrophotographic photoreceptor, an electrostatic latent image forming unit for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, a developing unit for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, and a transfer unit for transferring the toner image to the surface of a recording medium. The electrophotographic photoreceptor according to the present embodiment is applied as the electrophotographic photoreceptor.

The image forming apparatus according to this embodiment may be any of known image forming apparatuses, such as an apparatus equipped with a fixing unit that fixes a toner image transferred to the surface of a recording medium; an apparatus using a direct transfer method that directly transfers a toner image formed on the surface of an electrophotographic photoreceptor to a recording medium; an apparatus using an intermediate transfer method that performs a primary transfer of a toner image formed on the surface of an electrophotographic photoreceptor to the surface of an intermediate transfer body, and a secondary transfer of the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; an apparatus equipped with a cleaning unit that cleans the surface of an electrophotographic photoreceptor before charging after the transfer of a toner image; an apparatus equipped with a discharging unit that irradiates a discharging light onto the surface of an electrophotographic photoreceptor before charging after the transfer of a toner image to discharging the surface; and an apparatus equipped with an electrophotographic photoreceptor heating member for increasing the temperature of the electrophotographic photoreceptor and reducing the relative temperature.

In the case of an intermediate transfer type device, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the electrophotographic photoreceptor onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

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

In the image forming apparatus according to the present embodiment, for example, the portion including the electrophotographic photoreceptor may be a cartridge structure (process cartridge) that is detachably attached to 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. In addition to the electrophotographic photoreceptor, the process cartridge may include at least one selected from the group consisting of a charging means, an electrostatic latent image forming means, a developing means, and a transfer means.

Below, an example of an image forming device according to this embodiment is shown, but the present invention is not limited to this. Note that only the main parts shown in the figure will be explained, and explanations of other parts will be omitted.

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

The process cartridge 300 in FIG. 2 supports the electrophotographic photoreceptor 7, the charging device 8 (an example of a charging means), the developing device 11 (an example of a developing means), and the cleaning device 13 (an example of a cleaning means) in a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is arranged so as to contact the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member instead of the cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

In addition, FIG. 2 shows an example of an image forming device equipped with a fibrous member 132 (roll-shaped) that supplies lubricant 14 to the surface of electrophotographic photoreceptor 7, and a fibrous member 133 (flat brush-shaped) that assists in cleaning, but these are arranged as necessary.

The following describes each component of the image forming device according to this embodiment.

-Charging device-
As the charging device 8, for example, a contact type charger using a conductive or semiconductive charging roller, charging brush, charging film, charging rubber blade, charging tube, etc. Also, a non-contact type roller charger, a scorotron charger or corotron charger that utilizes corona discharge, or other chargers known per se, can be used.

--Exposure equipment--
The exposure device 9 may be, for example, an optical device that exposes the surface of the electrophotographic photoreceptor 7 with light such as semiconductor laser light, LED light, or liquid crystal shutter light in a predetermined image. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photoreceptor. The wavelength of the semiconductor laser is mainly near infrared light having an oscillation wavelength of about 780 nm. However, it is not limited to this wavelength, and a laser having an oscillation wavelength of 600 nm or more or a blue laser having an oscillation wavelength of 400 nm or more and 450 nm or less may also be used. In addition, a surface-emitting type laser light source capable of outputting multiple beams is also effective for forming a color image.

-Developing device-
The developing device 11 may be, for example, a general developing device that develops by contacting or non-contacting a developer. The developing device 11 is not particularly limited as long as it has the above-mentioned functions, and may be selected according to the purpose. For example, a known developing device that has a function of attaching a one-component developer or a two-component developer to the electrophotographic photoreceptor 7 using a brush, roller, or the like may be used. Among them, a developing roller that holds a developer on its surface is preferred.

The developer used in the developing device 11 may be a one-component developer containing only toner, or a two-component developer containing toner and a carrier. The developer may be magnetic or non-magnetic. Well-known developers are used.

-Cleaning device-
The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131 .
In addition to the cleaning blade system, a fur brush cleaning system or a simultaneous development and cleaning system may also be used.

-Transfer device-
Examples of the transfer device 40 include a contact type transfer charger using a belt, roller, film, rubber blade, etc., and a known transfer charger such as a scorotron transfer charger or corotron transfer charger that utilizes corona discharge.

- Intermediate transfer body -
A belt-like intermediate transfer belt containing semiconductive polyimide, polyamideimide, polycarbonate, polyarylate, polyester, rubber, or the like is used as the intermediate transfer body 50. The intermediate transfer body may be in the form of a drum other than a belt.

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

The following describes examples of the present invention, but the present invention is not limited to the following examples. Note that "parts" and "%" are by weight unless otherwise specified.

Example 1
- Preparation of undercoat layer -
100 parts by mass of zinc oxide (average particle size 70 nm: manufactured by Teica Corporation; specific surface area value 15 ^m2 /g) was mixed with 500 parts by mass of tetrahydrofuran and stirred, and 1.3 parts by mass of a silane coupling agent (KBM503: manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred for 2 hours. Thereafter, the tetrahydrofuran was distilled off under reduced pressure, and the mixture was baked at 120°C for 3 hours to obtain zinc oxide surface-treated with a silane coupling agent.

44.6 parts by mass of the zinc oxide particles surface-treated with the silane coupling agent, 0.45 parts by mass of 1-hydroxyanthraquinone as an electron-accepting compound, 10.2 parts by mass of blocked isocyanate (Sumidur 3173, manufactured by Sumitomo Bayern Urethane Co., Ltd.) as a curing agent, 3.5 parts by mass of butyral resin (product name: S-LEC BM-1, manufactured by Sekisui Chemical Co., Ltd.), 0.005 parts by mass of dioctyltin dilaurate as a catalyst, and 41.3 parts by mass of methyl ethyl ketone were mixed and dispersed for 2 hours in a sand mill using glass beads with a diameter of 1 mm to obtain a dispersion liquid.

3.6 parts by mass of silicone resin particles (Tospearl 145, Momentive Performance Materials, Inc.) were added to the resulting dispersion to obtain a coating solution for forming an undercoat layer. The viscosity of the coating solution for forming an undercoat layer at a coating temperature of 24°C was 235 mPa·s. The above coating solution for forming an undercoat layer was applied to a conductive substrate (aluminum substrate, diameter 30 mm, length 365 mm, thickness 1.0 mm) by dip coating at a coating speed of 220 mm/min, and dried and cured at 190°C for 24 minutes to obtain a 19 μm thick undercoat layer.

- Preparation of photosensitive layer -
Preparation of a charge generating layer Hydroxygallium phthalocyanine pigment as a charge generating material: 15 parts by mass of hydroxygallium phthalocyanine having diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.3°, 16.0°, 24.9°, and 28.0° in the X-ray diffraction spectrum using Cukα characteristic X-rays, 10 parts by mass of vinyl chloride-vinyl acetate copolymer (VMCH, manufactured by Nippon Unicar Co., Ltd.) as a binder resin, and 200 parts by mass of n-butyl acetate were dispersed in a sand mill using glass beads with a diameter of 1 mmφ for 4 hours. 175 parts by mass of n-butyl acetate and 180 parts by mass of methyl ethyl ketone were added to the obtained dispersion and stirred to obtain a coating liquid for forming a charge generating layer. This coating liquid for forming a charge generating layer was applied by dip coating on the undercoat layer and dried at room temperature (25° C.) to form a charge generating layer having a film thickness of 0.2 μm.

Preparation of Charge Transport Layer Next, 12 parts by weight of the charge transport material represented by the following structural formula (CT1A), 28 parts by weight of the charge transport material represented by the following structural formula (CT2A), 0.01 parts by weight of a surfactant (KP340 manufactured by Shin-Etsu Chemical Co., Ltd.), and 60 parts by weight of bisphenol Z-type polycarbonate resin (molecular weight 50,000) were added to 340 parts by weight of tetrahydrofuran and dissolved to obtain a coating liquid for forming a charge transport layer. The obtained coating liquid for forming a charge transport layer was applied by dip coating on the charge generating layer, and the coating speed was adjusted to form a charge transport layer having a thickness shown in Table 1. In addition, the coating was dried by heating at a temperature of 135° C. for 35 minutes.

- Preparation of surface protective layer -
A surface protective layer made of a thermosetting film of a composition containing a reactive group-containing charge transport material having a reactive group and a charge transport skeleton in the same molecule was formed as follows.
70 parts by mass of compound (2) represented by the structural formula shown below, which is a reactive group-containing charge transport material, 15 parts by mass of compound (3) represented by the structural formula shown below, which is a reactive group-containing charge transport material, and 4.4 parts by mass of a curable resin: benzoguanamine resin (Nikarak BL-60 manufactured by Sanwa Chemical Co., Ltd.; (H)-17 described above), which is a reactive group-containing non-charge transport material, were added to 220 parts by mass of 2-propanol, mixed and dissolved, and then 0.1 parts by mass of NACURE 5225 (manufactured by King Industry Co., Ltd.) was added as a curing catalyst to obtain a coating liquid for forming a surface protective layer.
This surface protective layer forming coating liquid was dip-coated on the charge transport layer, air-dried at room temperature (25°C) for 30 minutes, and then heated from room temperature to 155°C under a nitrogen stream with an oxygen concentration of 110 ppm, and held for 35 minutes (holding time) for heat treatment and curing. Thus, a surface protective layer with a thickness of 7 μm was formed.

Through the above steps, an electrophotographic photoreceptor of Example 1 was produced.
For the electrophotographic photoreceptor of Example 1, the amplitude of the frequency component corresponding to the circumference of the electrophotographic photoreceptor was obtained in the spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photoreceptor was charged and exposed by the above-mentioned method. The results are shown in Table 1.

<Examples 2 to 5, Comparative Examples 1 and 2>
In preparing the charge transport layer, the specifications were the same as in Example 1, except that "the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photosensitive member in the spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photosensitive member is charged and exposed to light" and the film thickness were set to the specifications shown in Table 1, and electrophotographic photosensitive members of each example were obtained.

In Table 1, "amplitude of frequency component" refers to the amplitude of the frequency component corresponding to the circumference of the electrophotographic photosensitive member in a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photosensitive member is charged and exposed to light.
In Table 1, "film thickness" refers to the film thickness of the charge transport layer.

<Evaluation of Image Density Unevenness>
The electrophotographic photoreceptor of each example was mounted on an "Apeos C6570" manufactured by FUJIFILM Business Innovation Co., Ltd., and used as an image forming apparatus for evaluation. Using the image forming apparatus for evaluation of each example, five halftone images with an image density of 60% were output on A3 size paper. The obtained halftone images were visually observed, and the image density unevenness was evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: Image density unevenness cannot be visually confirmed.
B: Image density unevenness is visible, but acceptable.
C: Image density unevenness is visually confirmed and is unacceptable.

The above results show that the electrophotographic photoreceptor of the embodiment suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to the electrophotographic photoreceptor of the comparative example.

(((1))) A conductive substrate;
an undercoat layer provided on the conductive substrate;
a photosensitive layer provided on the undercoat layer;
a surface protective layer provided on the photosensitive layer;
Equipped with
An electrophotographic photoreceptor, in which in a spectrum of period and amplitude obtained by fast Fourier transform of a surface potential when an outer peripheral surface of the electrophotographic photoreceptor is charged and exposed to light, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is less than 10 V.
(((2))) The electrophotographic photoreceptor according to (((1))) above, wherein the photosensitive layer has a thickness of less than 15 μm.
(((3))) The electrophotographic photoreceptor according to (((2))) above, wherein the photosensitive layer has a thickness of less than 11 μm.
(((4))) The electrophotographic photoreceptor described in any one of (((1))) to (((3))), wherein in the spectrum, the amplitude of a frequency component corresponding to the circumference of the electrophotographic photoreceptor is 7 V or less.
(((5))) The electrophotographic photoreceptor according to (((4))), wherein in the spectrum, the amplitude of a frequency component corresponding to the circumference of the electrophotographic photoreceptor is 5 V or less.
(((6))) An electrophotographic photoreceptor according to any one of (((1))) to (((5))),
A process cartridge that is detachably attached to an image forming apparatus.
(((7))) The electrophotographic photoreceptor according to any one of (((1))) to (((5))) above;
a charging means for charging the surface of the electrophotographic photoreceptor;
an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor;
a developing unit for developing an electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image;
a transfer means for transferring the toner image onto a surface of a recording medium;
An image forming apparatus comprising:

According to the invention related to (((1))), there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, as compared with a case in which, in a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photoreceptor is charged and exposed to light, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is 10 V or more.
According to the invention related to (((2))), an electrophotographic photoreceptor is provided which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to when the thickness of the photosensitive layer is 15 μm or more.
According to the invention related to ((3)), an electrophotographic photoreceptor is provided which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to when the thickness of the photosensitive layer is 11 μm or more.
According to the invention related to (((4))), there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, compared to a case in which the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor in the spectrum exceeds 7 V.
According to the invention related to ((5))), there is provided an electrophotographic photoreceptor which suppresses image density unevenness in the circumferential direction of the photoreceptor caused by drying unevenness in the photosensitive layer, as compared with a case in which the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor in the spectrum exceeds 5 V.
According to the invention related to ((6)) or ((7)), there is provided a process cartridge or image forming apparatus which suppresses image density unevenness in the circumferential direction of the photoconductor caused by uneven drying in the photosensitive layer, compared to a case in which an electrophotographic photoconductor is provided in which, in a spectrum of period and amplitude obtained by fast Fourier transform of the surface potential when the outer peripheral surface of the electrophotographic photoconductor is charged and exposed, the amplitude of the frequency component corresponding to the circumferential length of the electrophotographic photoconductor is 10 V or more.

101 undercoat layer, 102 charge generation layer, 103 charge transport layer, 104 conductive substrate, 105 organic photosensitive layer, 106 inorganic protective layer, 107A electrophotographic photosensitive member, 7 electrophotographic photosensitive member, 8 charging device, 9 exposure device, 11 developing device, 13 cleaning device, 14 lubricant, 40 transfer device, 50 intermediate transfer member, 100 image forming apparatus, 120 image forming apparatus, 131 cleaning blade, 132 fibrous member (roll-shaped), 133 fibrous member (flat brush-shaped), 300 process cartridge

Claims (7)

A conductive substrate;
an undercoat layer provided on the conductive substrate;
a photosensitive layer provided on the undercoat layer;
a surface protective layer provided on the photosensitive layer;
Equipped with
An electrophotographic photoreceptor, in which in a spectrum of period and amplitude obtained by fast Fourier transform of a surface potential when an outer peripheral surface of the electrophotographic photoreceptor is charged and exposed to light, the amplitude of a frequency component corresponding to the circumferential length of the electrophotographic photoreceptor is less than 10 V. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer has a thickness of less than 15 μm. The electrophotographic photoreceptor according to claim 2, wherein the thickness of the photosensitive layer is less than 11 μm. The electrophotographic photoreceptor according to claim 1, wherein in the spectrum, the amplitude of the frequency component corresponding to the circumference of the electrophotographic photoreceptor is 7 V or less. The electrophotographic photoreceptor according to claim 4, wherein the amplitude of the frequency component corresponding to the circumference of the electrophotographic photoreceptor in the spectrum is 5 V or less. The electrophotographic photoreceptor according to any one of claims 1 to 5 is provided,
A process cartridge that is detachably attached to an image forming apparatus. The electrophotographic photoreceptor according to any one of claims 1 to 5,
a charging means for charging the surface of the electrophotographic photoreceptor;
an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor;
a developing unit for developing an electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image;
a transfer means for transferring the toner image onto a surface of a recording medium;
An image forming apparatus comprising:

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