JP7776298B2 - Electrophotographic photosensitive member, process cartridge equipped with the same, and image forming apparatus - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor that has good electrical properties, as well as good durability and light resistance, and to a process cartridge and image forming apparatus that include the same.

Electrophotographic image forming apparatuses (electrophotographic apparatuses) that form images using electrophotographic technology are widely used in copying machines, printers, facsimile machines, and the like.
The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") used in this electrophotographic process is configured by laminating a photosensitive layer containing a photoconductive material on a substrate, and photoreceptors having a photosensitive layer whose main component is an organic photoconductive material (also referred to as "organic photoreceptor") are widely used.

One drawback of photoconductors is their light resistance. During normal use, photoconductors are not exposed to external light such as fluorescent lights. However, they are exposed to external light when performing maintenance on the photoconductor or peripheral parts, or when removing paper from a machine due to a paper jam. If the photoconductor is exposed to external light, it can be severely damaged, causing problems with the image.
As means for overcoming this drawback, a method of adding an ultraviolet absorber to the photosensitive layer (for example, JP 2016-143024 A: Patent Document 1) and a method of adding a material that absorbs specific wavelengths to the photosensitive layer (for example, JP 10-048856 A: Patent Document 2) have been proposed.

JP 2016-143024 A Japanese Patent Application Publication No. 10-048856

The light from indoor fluorescent lamps to which image forming devices are exposed has a spectral distribution, and the light resistance of the photoreceptor can be improved by incorporating an ultraviolet absorber into the photosensitive layer that has spectral absorption primarily in the wavelength range of 500 to 700 nm. However, if the static elimination light used in an image forming device has a spectral distribution maximum between 550 and 650 nm, and the transmittance of light within this range is suppressed by the ultraviolet absorber, the static elimination light reaching the charge generating layer is suppressed, leading to problems such as reduced static elimination efficiency and increased residual potential.

Furthermore, with the recent increase in contact charging methods using roller charging and the trend toward longer life, smaller size, and higher speeds in electrophotographic devices such as digital copiers and printers, organic photoreceptors are exposed to harsh conditions in which their surfaces are more susceptible to wear. To address this issue, studies have been conducted to improve printing durability by adding fine particles such as silica, alumina, and polyethylene terephthalate (PTFE) as fillers to the outermost surface layer of the photoreceptor.
However, it is known that the addition of fillers tends to reduce the transmittance of the photosensitive layer, and that adding an ultraviolet absorber to a photosensitive layer containing fillers in order to improve lightfastness causes an increase in residual potential, making it difficult to achieve both lightfastness and printing durability.

The present invention aims to provide an electrophotographic photosensitive member that has good electrical characteristics, as well as good durability and light resistance, and a process cartridge and image forming apparatus that include the same.

As a result of extensive research into resolving the above-mentioned issues, the inventors discovered that by incorporating a specific light absorber and silica filler into the outermost layer of a photoreceptor and controlling the dispersion state of the silica filler to optimize the transmittance of the photosensitive layer, they could achieve both durability and prevention of degradation due to external light, thereby resolving the above-mentioned issues and completing the present invention.

Thus, according to the present invention, there is provided an electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive support, or at least the laminated photosensitive layer and a surface protective layer laminated thereon,
the charge transport layer and/or the surface protective layer contains a light absorbing agent;
The electrophotographic photoreceptor is characterized in that the outermost layer of the electrophotographic photoreceptor contains a silica filler, has a transmittance of 50% or more for light having a wavelength of 600 nm, and has a ratio _T600 /T550 of the transmittance T600 for light having a wavelength of 600 nm to the transmittance _T550 for light having a wavelength of 550 nm, that is, _T600 / _T550 , of 1.10 or more and 2.20 or less.

The present invention also provides a process cartridge comprising the above-mentioned electrophotographic photosensitive member and at least one selected from a charging unit that charges the electrophotographic photosensitive member, a developing unit that develops an electrostatic latent image formed by exposure to light to form a toner image, and a cleaning unit that removes toner remaining on the electrophotographic photosensitive member.

Furthermore, according to the present invention, there is provided an image forming apparatus comprising at least the above-mentioned electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, developing means for developing the electrostatic latent image formed by exposure to form a toner image, transfer means for transferring the toner image formed by development onto a recording medium, fixing means for fixing the transferred toner image on the recording medium to form an image, cleaning means for removing and recovering toner remaining on the electrophotographic photosensitive member, and discharging means for discharging surface charges remaining on the electrophotographic photosensitive member.

The present invention provides an electrophotographic photoreceptor that has good electrical properties, as well as good durability and light resistance, and a process cartridge and image forming apparatus equipped with the same.

1 is a schematic cross-sectional view showing the configuration of a main part of a photoreceptor (laminated photoreceptor) 1 of the present invention. 1 is a schematic side view showing the configuration of a main part of an image forming apparatus 100 according to the present invention.

(1) Photoreceptor The photoreceptor of the present invention is an electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive support, or at least the laminated photosensitive layer and a surface protective layer laminated thereon,
the charge transport layer and/or the surface protective layer contains a light absorbing agent;
The outermost surface layer of the electrophotographic photoreceptor contains a silica filler, has a transmittance of 50% or more for light having a wavelength of 600 nm, and is characterized in that the ratio _T600 / _T550 of the transmittance _T600 for light having a wavelength of ₆₀₀ nm to the transmittance T550 for light having a wavelength of 550 nm is 1.10 or more and 2.20 or less.
First, we will explain the characteristics of the present invention, namely, the "light absorber" contained in both or either of the charge transport layer and the surface protective layer, the "silica filler" contained in the outermost layer of the photoreceptor, and the light transmittance of the outermost layer, and then we will explain (1) each configuration of the photoreceptor, (2) a process cartridge equipped with the photoreceptor, and (3) an image forming apparatus.

<Light absorber>
The light absorber has the function of effectively blocking the action of the light wavelength component of external light on the charge generating material.
The reason why external light from fluorescent lamps, LEDs, etc. damages photoreceptors is that the external light passes through the charge transport layer and acts on the charge generating material, generating charge traps.General fluorescent lamps have light wavelength components with wavelengths of 440 nm, 490 nm, 550 nm, 580 nm, and around 620 nm, while white LEDs have light wavelength components with wavelengths of 460 nm and 500 to 700 nm.When these lights pass through the charge transport layer, they act on the charge generating material, generating charge traps.
In the present invention, the light absorbing agent absorbs external light and suppresses the generation of charge traps.
Therefore, the light absorber contained in either or both of the charge transport layer and the surface protective layer is preferably a compound having spectral absorption in the wavelength range of 400 to 700 nm.
More preferably, the light absorber has a spectral absorption in the wavelength range of 450 to 550 nm.

On the other hand, light wavelength components with wavelengths of 550 to 650 nm must be transmitted because they are used in LEDs and laser beams that expose a photoconductor to form an electrostatic latent image, and in LEDs that remove surface charges remaining on the photoconductor, and therefore the transmittance of the outermost layer of the photoconductor for light with a wavelength of 600 nm and the ratio _T600 / _T550 of the transmittance _T600 for light with a wavelength of 600 nm to the transmittance _T550 for light with a wavelength of 550 nm are set. These transmittances _T600 and the ratio _T600 / _T550 will be explained in the section <Light transmittance of outermost layer>.

The light absorber is not particularly limited as long as it is a compound that has the optical properties described above and does not inhibit the effects of the present invention, and examples thereof include perimidine compounds, azoquinone compounds, and pyrazolone compounds.
Specifically, the light absorber may be a compound represented by the following structural formula (A):

a perimidine compound (perimidine compound (A)) represented by the following structural formula (B):

and an azoquinone compound (azoquinone compound (B)) represented by the following structural formula (C):

These can be suitably used in the present invention.

An example of the perimidine compound (A) is the perimidine compound (A) used in Example 1 (C.I. Solvent Red 179, manufactured by American Dyestuff, product name: Amesolve Red A). An example of the azoquinone compound (B) is the azoquinone compound (B) used in Example 4 (manufactured by Hodogaya Chemical Co., Ltd., product name: EAC-39).
The pyrazolone compound can be synthesized by the method described in Japanese Patent No. 4,041,741, for example.

The content of the light absorber in the charge transport layer is preferably 0.05 to 1.00% by weight based on the total solid content of the charge transport layer.
If the content of the light absorber is less than 0.05% by mass, the effect on light resistance may not be sufficient, whereas if the content of the light absorber is more than 1.00% by mass, the electrical properties of the photoreceptor may deteriorate.
The content of the light absorber is more preferably 0.15 to 0.40% by mass, and particularly preferably 0.20 to 0.35% by mass.

<Silica filler>
The "silica" in silica filler means silicon dioxide (SiO ₂ ).
The silica filler preferably used in the present invention is not limited to those derived from specific manufacturing methods, and examples thereof include dry-process silica such as fumed silica obtained by burning silicon tetrachloride and arc-process silica in which silica is atomized in the gas phase using high energy such as plasma; wet-process silica such as precipitation-process silica synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material, and wet-process silica such as gel-process silica synthesized under acidic conditions; colloidal silica obtained by polymerizing acidic silicic acid in an alkaline state; and sol-gel-process silica obtained by hydrolysis of an organic silane compound.

The silica filler may be surface treated with a surface treatment agent to improve the electrical properties of the photoreceptor.
Examples of the surface treatment agent include hexamethyldisilazane, N-methyl-hexamethyldisilazane, N-ethyl-hexamethyldisilazane, hexamethyl-N-propyldisilazane, dimethyldichlorosilane, and polydimethylsiloxane.
Among these, dimethyldichlorosilane and hexamethyldisilazane are particularly preferred because they have good reactivity with the hydroxyl groups on the surface of silica particles, making it possible to reduce the amount of hydroxyl groups on the surface of the silica filler, thereby suppressing the deterioration of the electrical properties of the photoreceptor due to moisture (humidity).

In the present invention, silica fillers treated with the above-mentioned surface treatment agents can be used, but commercially available silica fine particles treated with a surface treatment agent can also be used. Examples of commercially available silica fine particles include Nippon Aerosil Co., Ltd.'s product names: R972, R972V, R974, R976, RX200, NX130, NX90G, NX90S, NAX50, and RX50; Cabot Japan Co., Ltd.'s product names: TS610, TG709F, and TG6110G; and Admatechs Co., Ltd.'s product name: YA010C.

The silica filler preferably has an average primary particle size of 30 nm or less.
If the average primary particle size of the silica filler exceeds 30 nm, the aggregate structure formed in the photosensitive layer becomes large, which may easily cause problems such as poor cleaning. If the average primary particle size of the silica filler is too small, the silica filler has a strong aggregation force, is difficult to disintegrate, and its dispersibility may decrease, so the lower limit is about 7 nm.
The average primary particle diameter is a measurement value of the average diameter in the Feret direction obtained by observing silica particles under a scanning electron microscope at a magnification of 30,000 to 300,000 times, for example, 10,000 times, randomly selecting 100 particles as primary particles, and analyzing the image.

The silica filler is preferably contained in an amount of 7 to 18% by mass based on the total solid content of the outermost layer of the photoreceptor.
If the silica filler content is less than 7% by weight based on the total solid content of the outermost layer of the photoreceptor, the effect on printing durability may not be sufficient, whereas if the silica filler content exceeds 18% by weight, the electrical properties of the photoreceptor may deteriorate.
The content of the silica filler is more preferably 7 to 15% by mass, and particularly preferably 8 to 13% by mass.

It is preferable that the silica filler is uniformly dispersed and distributed in the charge transport layer and the surface protective layer without agglomeration.
The dispersion state of the silica filler can be controlled by adjusting the shear conditions (dispersion method, dispersion time, media diameter, media amount, media material) of the dispersion treatment in preparing the coating liquid for the charge transport layer or the coating liquid for the surface protective layer. Specific details will be described in the Examples.

<Light transmittance of outermost layer>
The outermost surface layer of the photoreceptor has a transmittance of 50% or more for light with a wavelength of 600 nm, and the ratio T ₆₀₀ /T 550 of the transmittance T ₆₀₀ for light with a wavelength of 600 nm to the transmittance T ₅₅₀ for light with a wavelength of ₅₅₀ nm is 1.10 or more and 2.20 or less.

If the transmittance _T600 for light with a wavelength of 600 nm is less than 50%, the efficiency of static elimination decreases and the residual potential may increase. The upper limit is about 85%.
If the ratio _T600 / _T550 of the transmittance _T600 for light with a wavelength of ₆₀₀ nm to the transmittance T550 for light with a wavelength of 550 nm is less than 1.10, external light may damage the photoreceptor, resulting in image defects. On the other hand, if the ratio _T600 / _T550 exceeds 2.20, an increase in residual potential may occur.
The ratio T ₆₀₀ /T ₅₅₀ is preferably 1.10 or more and 1.50 or less, and more preferably 1.15 or more and 1.30 or less.

<Photoreceptor>
The photoreceptor of the present invention comprises at least a laminated photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive support, or at least the laminated photosensitive layer and a surface protective layer laminated thereon.
The photoreceptor of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.
FIG. 2 is a schematic cross-sectional view showing the configuration of the main part of the photoreceptor (laminated photoreceptor) 1 of the present invention.
The photoreceptor 1 includes a photosensitive layer (laminated photosensitive layer) 14 in which a charge generating layer 15 containing an undercoat layer 18 and a charge generating material 12, and a charge transport layer 16 containing a charge transport material 13, a binder resin 17, a silica filler 19, and a light absorber 20 are laminated in this order on a conductive support 11.
The photoreceptor of the present invention may have a surface protective layer on the photosensitive layer 14. The surface protective layer will be described in the section <Surface protective layer>.

<Conductive support 11>
The conductive support (also referred to as "conductive substrate" or "substrate") 11 functions as an electrode for the photoreceptor and as a support member, and the material constituting the conductive support is not particularly limited as long as it is a material used in the relevant technical field.
Specific examples include metal materials such as aluminum, aluminum alloys, copper, zinc, stainless steel, and titanium, as well as polymer materials such as polyethylene terephthalate, nylon, and polystyrene, whose surfaces are laminated with metal foil, subjected to metal vapor deposition, or vapor-deposited or coated with a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide, hard paper, and glass. Among these, aluminum is preferred from the viewpoint of ease of processing, and aluminum alloys such as JIS 3003, JIS 5000, and JIS 6000 are particularly preferred.
The shape of the conductive support is not limited to the cylindrical (drum) shape shown in FIG. 2, but may be a sheet shape, a columnar shape, an endless belt shape, or the like.
Furthermore, the surface of the conductive support may be subjected to anodizing film treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as needed, to prevent interference fringes caused by laser light, within a range that does not affect image quality.

<Undercoat layer 18>
The photoreceptor of the present invention preferably has an undercoat layer (also called an “intermediate layer”) between the conductive support 11 and the laminated photosensitive layer 14 .
The undercoat layer generally covers and smooths the irregularities on the surface of the substrate, improves the film-forming properties of the laminated photosensitive layer, suppresses peeling of the photosensitive layer from the conductive support, and improves the adhesion between the substrate and the photosensitive layer. Specifically, it prevents charge injection from the substrate into the photosensitive layer, prevents a decrease in the chargeability of the photosensitive layer, and prevents image fogging (so-called black spots).
The undercoat layer can be formed, for example, by preparing a coating liquid for the undercoat layer by dissolving or dispersing a binder resin in a suitable solvent, applying this coating liquid to the surface of the substrate, and then drying to remove the organic solvent.

Examples of binder resins include acetal resins, polyamide resins, polyurethane resins, polyester resins, acrylic resins, epoxy resins, phenolic resins, melamine resins, urethane resins, etc. Binder resins are required to have properties such as not dissolving or swelling in the solvent used when forming the photosensitive layer on the undercoat layer, excellent adhesion to the conductive support, and flexibility. Therefore, among the above binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins and polyamide resins containing piperazine compounds are particularly preferred.
Examples of alcohol-soluble nylon resins include homopolymer or copolymer nylons such as 6-nylon, 66-nylon, 610-nylon, 11-nylon, and 12-nylon, and chemically modified nylons such as N-alkoxymethyl-modified nylons.
A curing agent that crosslinks the binder resin may also be used to form a cured film. Blocked isocyanate is preferred as the curing agent from the viewpoint of storage stability and electrical properties of the coating liquid.

Examples of the solvent include lower alcohols such as water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, and isobutanol, ketones such as acetone, cyclohexanone, and 2-butanone, ethers such as tetrahydrofuran, dioxane, ethylene glycol, and diethyl ether, and halogenated hydrocarbons such as methylene chloride and ethylene chloride.These solvents can be appropriately selected based on the solubility of the binder resin, the surface smoothness of the undercoat layer, and the like, and can be used alone or in combination of two or more.
Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.

The coating solution for the undercoat layer may contain metal oxide particles, which can easily adjust the volume resistivity of the undercoat layer, further suppress charge injection into the charge generating layer, and maintain the electrical properties of the photoreceptor under various environments.
Materials that can be used for the metal oxide particles include, for example, titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide.
The ratio (A/B) of the total mass A of the binder resin and metal oxide particles to the mass B of the solvent in the coating liquid for the undercoat layer is, for example, preferably about 1/99 to 30/70, and particularly preferably about 2/98 to 40/60.
The ratio (C/D) of the mass C of the binder resin to the mass D of the metal oxide particles is preferably, for example, about 90/10 to 1/99, and particularly preferably about 70/30 to 5/95.

The coating method for the undercoat layer coating liquid may be appropriately selected from the most suitable methods taking into consideration the physical properties of the coating liquid, productivity, and the like. Examples of the coating method include spraying, bar coating, roll coating, blade coating, ring coating, and dip coating.
Among these, the dip coating method is a method in which a substrate is immersed in a coating tank filled with a coating liquid and then pulled up at a constant speed or a gradually changing speed to form a layer on the surface of the substrate, and is relatively simple and excellent in terms of productivity and cost, so it can be suitably used for manufacturing photoreceptors. The apparatus used for the dip coating method may be provided with a coating liquid dispersion device, typified by an ultrasonic generator, in order to stabilize the dispersibility of the coating liquid.

The solvent in the coating film may be removed by natural drying, or the solvent in the coating film may be removed forcibly by heating.
The temperature in such a drying step is not particularly limited as long as it is a temperature at which the solvent used can be removed, but a temperature of about 50 to 140°C is appropriate, and a temperature of about 80 to 130°C is particularly preferred.
If the drying temperature is less than 50°C, the drying time may be long and the solvent may not evaporate sufficiently and remain in the photoreceptor layer. If the drying temperature exceeds about 140°C, the electrical characteristics of the photoreceptor may deteriorate during repeated use, resulting in poor quality of the resulting image.
Such temperature conditions are common not only to the formation of the undercoat layer but also to the formation of layers such as the photosensitive layer, which will be described later, and other processes.

The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 to 20 μm, more preferably 0.05 to 10 μm.
If the thickness of the undercoat layer is less than 0.01 μm, sufficient blocking effect against electron injection from the conductive substrate side and sufficient effect against interference fringes due to light scattering may not be obtained. On the other hand, if the thickness of the undercoat layer exceeds 20 μm, the change in sensitivity during continuous printing may become large, which may result in large changes in image density.

<Charge Generation Layer 15>
The charge generation layer 15 has the function of generating charges by absorbing light irradiated by a light emitting device such as a semiconductor laser light beam in an electrophotographic device such as an image forming device, and contains a charge generation substance as its main component and, if necessary, a binder resin and/or additives.

The charge-generating substance may be a compound used in the art, specifically, azo pigments such as monoazo pigments, bisazo pigments, and trisazo pigments; indigo pigments such as indigo and thioindigo; perylene pigments such as peryleneimide and perylene acid anhydride; polycyclic quinone pigments such as anthraquinone and pyrenequinone; phthalocyanine pigments such as metal phthalocyanines and metal-free phthalocyanines, including titanyl phthalocyanine; organic photoconductive materials such as squarylium dyes, pyrylium salts, thiopyrylium salts, and triphenylmethane dyes; and inorganic photoconductive materials such as selenium and amorphous silicon, among others. These charge-generating substances may be used singly or in combination of two or more.
Among these charge generating materials, those represented by the following general formula (A):

(wherein X ¹ , X ² , X ³ and X ⁴ are the same or different and each represents a halogen atom, an alkyl group or an alkoxy group, and r, s, y and z are the same or different and each represents an integer of 0 to 4.)
It is preferable to use titanyl phthalocyanine represented by the following formula:
Titanyl phthalocyanine is a charge-generating material that has high charge generation and charge injection efficiencies in the emission wavelength range (near-infrared light) of currently commonly used laser light and LED light. It generates a large amount of charge by absorbing light and can efficiently inject the generated charge into a charge-transporting material without accumulating it internally.

The titanyl phthalocyanine represented by the general formula (A) can be produced by a known production method, for example, the method described in Phthalocyanine Compounds by Moser, Frank H. and Arthur L. Thomas, Reinhold Publishing Corp., New York, 1963.
For example, among the titanyl phthalocyanine compounds represented by general formula (A), unsubstituted titanyl phthalocyanine in which r, s, y, and z are 0 can be obtained by synthesizing dichlorotitanyl phthalocyanine by heating and melting phthalonitrile and titanium tetrachloride or by heating and reacting them in a suitable solvent such as α-chloronaphthalene, and then hydrolyzing the resultant with a base or water.
Alternatively, a titanyl phthalocyanine composition can be produced by reacting isoindoline with a titanium tetraalkoxide such as tetrabutoxytitanium under heating in a suitable solvent such as N-methylpyrrolidone.

Methods for forming a charge generation layer include vacuum deposition of a charge generation material onto a conductive support, and coating a coating liquid for a charge generation layer obtained by dispersing a charge generation material in a solvent onto a conductive support. Of these, a preferred method is to disperse a charge generation material in a binder resin solution obtained by mixing a binder resin in a solvent using a conventionally known method, and then coat the coating liquid for a charge generation layer onto a conductive support. This method is described below.

The binder resin is not particularly limited, and any resin known in the art can be used, such as polyester, polystyrene, polyurethane, phenolic resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate, polyarylate, polyphenoxy, polyvinyl butyral, and polyvinyl formal, as well as copolymer resins containing two or more of the repeating units constituting these resins.
Examples of copolymer resins include insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin. These resins can be used alone or in combination of two or more.

Examples of solvents include halogenated hydrocarbons such as dichloromethane and dichloroethane, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran (THF) and dioxane, alkyl ethers of ethylene glycol such as 1,2-dimethoxyethane, aromatic hydrocarbons such as benzene, toluene, and xylene, and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide. These solvents can be used alone or in combination of two or more.

The compounding ratio of the charge generating material to the binder resin is preferably such that the proportion of the charge generating material is in the range of 10 to 99% by mass.
If the proportion of the charge generating substance is less than 10% by mass, the sensitivity may decrease. On the other hand, if the proportion of the charge generating substance exceeds 99% by mass, not only the film strength of the charge generating layer decreases, but also the dispersibility of the charge generating substance decreases, resulting in an increase in coarse particles, which may reduce the surface charge in areas other than those that should be erased by exposure, resulting in image defects, particularly image fogging called black spots, in which toner adheres to a white background and forms tiny black spots.

Before dispersing the charge-generating material in the binder resin solution, the charge-generating material may be pulverized in advance using a pulverizer such as a ball mill, a sand mill, an attritor, a vibration mill, or an ultrasonic disperser.
Examples of dispersing machines used to disperse the charge generating material in the binder resin solution include a paint shaker, a ball mill, a sand mill, etc. Dispersion conditions at this time should be selected appropriately so as to prevent the incorporation of impurities due to wear of the container and components of the dispersing machine.
The coating liquid for the charge generating layer may be applied by the same method as the coating liquid for the undercoat layer, and a dip coating method is particularly preferred.

The thickness of the charge generating layer is not particularly limited, but is preferably 0.05 to 5 μm, and more preferably 0.1 to 1 μm.
If the thickness of the charge generating layer is less than 0.05 μm, the efficiency of light absorption may decrease, and the sensitivity of the photoreceptor may decrease. On the other hand, if the thickness of the charge generating layer is more than 5 μm, the charge transfer within the charge generating layer may become the rate-limiting step in the process of erasing the charge on the surface of the laminated photosensitive layer, and the sensitivity of the photoreceptor may decrease.

<Charge transport layer 16>
The charge transport layer 16 has the function of receiving the charges generated by the charge generating substance and transporting them to the surface of the photoreceptor, and contains a charge transport substance, a binder resin, a light absorber, a silica filler, and additives as required.
In the photoreceptor of the present invention, it is an essential requirement that the light absorber be contained in both or either one of the charge transport layer and the surface protective layer. When the photoreceptor has a surface protective layer that does not contain a light absorber, the light absorber becomes an essential component of the charge transport layer. On the other hand, when the photoreceptor has a surface protective layer that contains a light absorber, the light absorber becomes an optional component of the charge transport layer.
Furthermore, in the photoreceptor of the present invention, it is an essential requirement that the silica filler be contained in the outermost surface layer of the photoreceptor. When the photoreceptor has a surface protective layer containing silica filler, the silica filler becomes an optional component of the charge transport layer. On the other hand, when the photoreceptor does not have a surface protective layer, the silica filler becomes an essential component of the charge transport layer.

As the charge transport material, compounds used in the art can be used.
Specific examples include carbazole derivatives, pyrene derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, polycyclic aromatic compounds, indole derivatives, pyrazoline derivatives, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, triarylmethane derivatives, phenylenediamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, benzidine derivatives, polymers having groups derived from these compounds in the main chain or side chain (such as poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, poly-9-vinylanthracene), and polysilanes. These charge transport materials can be used alone or in combination of two or more.

Among these various charge transport materials, stilbene derivatives, butadiene derivatives, enamine derivatives, and compounds formed by combining multiple types of these compounds are preferred in terms of electrical properties, durability, and chemical stability. Stilbene derivatives are more preferred because they absorb light in the wavelength range of 300 to 480 nm and have a wide absorption range as charge transport materials, and are represented by the following general formula (I):

(In the formula, R ₁ , R ₂ , R ₅ and R ₆ are the same or different and each represents an alkyl group, an alkoxy group, an aryl group or an aralkyl group; m, n, p and q are the same or different and each represents an integer of 0 to 3; and R ₃ and R ₄ are the same or different and each represents a hydrogen atom or an alkyl group.)
The stilbene compounds represented by the following formula are particularly preferred in that they cause little increase in residual potential and little deterioration in sensitivity and can exhibit good electrophotographic properties.

The substituents R ₁ , R ₂ , R ₅ and R ₆ in general formula (I) will be explained below.
Examples of the alkyl group include alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and n-hexyl.
Examples of the alkoxy group include alkoxy groups having 1 to 6 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, tert-butoxy, n-pentyloxy, and n-hexyloxy.
Examples of the aryl group include phenyl, naphthyl, anthryl, phenanthryl, fluorenyl, biphenylyl, and o-terphenyl.
Examples of aralkyl groups include benzyl, phenethyl, benzhydryl, and trityl.
Examples of halogen atoms include fluorine, chlorine, bromine, and iodine.

The indices m, n, p and q of the substituents R ₁ , R ₂ , R ₅ and R ₆ are the same or different and are integers of 0 to 3, and when the indices are 2 or more, the respective substituents may be different from each other.
In addition, examples of the alkyl group of the substituents R ₃ and R ₄ in the general formula (I) include alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, and isopropyl.
The stilbene compound represented by the general formula (I) can be synthesized, for example, by the method described in Japanese Patent No. 3272257.

Examples of stilbene compounds represented by general formula (I) include the following compounds (1) to (3), with compound (1) being particularly preferred in terms of printing durability when used in a laminated photosensitive layer.

A preferred method for forming the charge transport layer is to disperse a charge transport material in a binder resin solution obtained by mixing a binder resin in a solvent using a conventionally known method, and then apply the charge transport layer coating liquid onto the charge generation layer. This method is described below.

The binder resin is not particularly limited, and resins having binding properties that are used in the art can be used, and those having excellent compatibility with the charge transport material are preferred.
Specific examples include vinyl polymer resins such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymer resins thereof, as well as resins such as polycarbonate, polyester, polyester carbonate, polysulfone, phenoxy resin, epoxy resin, silicone resin, polyarylate, polyamide, polyether, polyurethane, polyacrylamide, phenolic resin, and polyphenylene oxide, and thermosetting resins obtained by partially crosslinking these resins. These binder resins can be used alone or in combination of two or more.
Among these, polystyrene, polycarbonate, polyarylate and polyphenylene oxide are preferred because they have a volume resistivity of 10 ¹³ Ω or more, are excellent in electrical insulation, and are also excellent in film-forming properties and potential characteristics, with polycarbonate and polyarylate being more preferred, and polycarbonate being particularly preferred.

Examples of solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and monochlorobenzene; halogenated hydrocarbons such as dichloromethane and dichloroethane; ethers such as tetrahydrofuran, dioxane, and dimethoxymethyl ether; and aprotic polar solvents such as N,N-dimethylformamide. Furthermore, if necessary, solvents such as alcohols, acetonitrile, or methyl ethyl ketone can also be added and used. These solvents can be used alone or in combination of two or more.
Among these solvents, for example, non-halogen organic solvents can be preferably used in consideration of the global environment.
The ratio (G/H) of the mass G of the charge transport material to the mass H of the binder resin is preferably, for example, about 10/12 to 10/30.

The thickness of the charge transport layer is not particularly limited, but is preferably about 20 to 40 μm, and more preferably about 25 to 40 μm.
If the thickness of the charge transport layer is less than 20 μm, the effect on light resistance may not be sufficient, whereas if the thickness of the charge transport layer is more than 40 μm, the electrical properties may be deteriorated.

<Surface Protection Layer (not shown in FIG. 1)>
The photoreceptor 1 of the present invention may have a surface protective layer on the photosensitive layer 14 .
The surface protective layer has the function of improving the durability of the photoreceptor, and contains a binder resin, a light absorber, a silica filler, and, if necessary, additives.
In the photoreceptor of the present invention, it is an essential requirement that the light absorber be contained in both or either one of the charge transport layer and the surface protective layer. When the photoreceptor has a charge transport layer that does not contain a light absorber, the light absorber becomes an essential component of the surface protective layer. On the other hand, when the photoreceptor has a charge transport layer that contains a light absorber, the light absorber becomes an optional component of the surface protective layer.
Furthermore, in the photoreceptor of the present invention, it is an essential requirement that the silica filler be contained in the outermost surface layer of the photoreceptor, and when the photoreceptor has a surface protective layer, the silica filler becomes an essential component of the surface protective layer.
The protective layer may contain the same charge transport material or materials as the charge transport layer in order to stabilize the electrical characteristics.
Examples of the binder resin include the binder resins exemplified for the charge transport layer, and among these, polycarbonate and polyarylate are particularly preferred in consideration of wear characteristics and electrical characteristics.
The light absorber and silica filler are the same as those for the charge transport layer.

The thickness of the protective layer is not particularly limited, but is preferably about 3 to 7 μm, and more preferably about 4 to 6 μm.
If the thickness of the protective layer is less than 3 μm, the durability and light resistance may not be sufficiently improved, whereas if the thickness of the protective layer is more than 7 μm, the electrical properties may be deteriorated.

(2) Process Cartridge The process cartridge of the present invention is characterized by comprising the photosensitive member of the present invention, and at least one selected from a charging means for charging the photosensitive member, a developing means for developing an electrostatic latent image formed by exposure to light to form a toner image, and a cleaning means for removing toner remaining on the electrophotographic photosensitive member.

For example, the process cartridge of the present invention is constructed by integrating the photosensitive member, charging device, developing device, and cleaning device of the present invention into a support member. When such a process cartridge is incorporated into the image forming apparatus 100, each of the components of the process cartridge is provided in the image forming apparatus 100.
The process cartridge is detachable from the image forming apparatus 100, which makes it easy to replace it when it is worn out.

(3) Image forming apparatus 100
The image forming apparatus of the present invention is characterized by comprising at least the photosensitive member of the present invention, a charging means for charging the photosensitive member, an exposure means for exposing the charged photosensitive member to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image formed by exposure to form a toner image (visible image), a transfer means for transferring the toner image formed by development onto a recording medium, a fixing means for fixing the transferred toner image on the recording medium to form an image, a cleaning means for removing and recovering toner remaining on the photosensitive member, and a discharging means for discharging surface charges remaining on the photosensitive member.
The image forming apparatus of the present invention and its operation will be described below with reference to the drawings, but the present invention is not limited to the following description.

FIG. 2 is a schematic side view showing the configuration of the main part of the image forming apparatus 100 of the present invention.
The image forming apparatus (laser printer) 100 in Figure 2 is configured to include the photoreceptor 1 of the present invention (corresponding to reference number 1 in Figure 1), exposure means (semiconductor laser) 31, charging means (charger) 32, developing means (developer) 33, transfer means (transfer charger) 34, a conveyor belt (not shown), fixing means (fixer) 35, and cleaning means (cleaner) 36. Reference numeral 51 denotes a recording medium (recording paper or transfer paper).

Photoreceptor 1 is rotatably supported on the main body of image forming apparatus 100 and is driven to rotate around rotation axis 44 in the direction of arrow 41 by a drive means (not shown). The drive means, which may include, for example, an electric motor and a reduction gear, transmits its driving force to the conductive support that forms the core of photoreceptor 1, thereby driving photoreceptor 1 to rotate at a predetermined peripheral speed. Charging means (charger) 32, exposure means 31, developing means (developer) 33, transfer means (transfer charger) 34, and cleaning means (cleaner) 36 are arranged in this order along the outer surface of photoreceptor 1, from upstream to downstream in the direction of rotation of photoreceptor 1, as indicated by arrow 41.

The charger 32 is a charging means for uniformly charging the outer peripheral surface of the photoreceptor 1 (corresponding to the photoreceptor F01 in FIG. 2) to a predetermined potential. Examples of the charging means include a non-contact charging method such as a corona charging method using a charger, and a contact charging method using a charging roller or a charging brush.
The exposure unit 31 has a semiconductor laser as a light source, and irradiates the surface of the photoreceptor 1 between the charger 32 and the developer 33 with a laser beam light output from the light source, thereby exposing the charged outer peripheral surface of the photoreceptor 1 in accordance with image information. The light is repeatedly scanned in the main scanning direction, that is, the direction of extension of the rotation axis 44 of the photoreceptor 1, and these are focused to sequentially form electrostatic latent images on the surface of the photoreceptor 1. In other words, the amount of charge on the photoreceptor 1, which has been uniformly charged by the charger 32, differs depending on whether it is irradiated with the laser beam or not, thereby forming an electrostatic latent image.

The developing unit 33 is a developing means that uses developer (toner) to develop the electrostatic latent image formed on the surface of the photoreceptor 1 by exposure. It is provided facing the photoreceptor 1 and includes a developing roller 33a that supplies toner to the outer peripheral surface of the photoreceptor 1, and a casing 33b that rotatably supports the developing roller 33a about an axis of rotation parallel to the axis of rotation 44 of the photoreceptor 1 and contains developer containing toner in its internal space.

Transfer charger 34 is a transfer device that transfers the toner image, which is a visible image formed on the outer surface of photoreceptor 1 by development, onto transfer paper 51, a recording medium that is supplied between photoreceptor 1 and transfer charger 34 from the direction of arrow 42 by a transport device (not shown). Transfer charger 34 is, for example, a contact-type transfer device that includes a charging device and transfers the toner image onto transfer paper 51 by applying a charge of the opposite polarity to the toner to transfer the toner image onto transfer paper 51.

The cleaner 36 is a cleaning device that removes and collects toner remaining on the outer surface of the photoreceptor 1 after the transfer operation by the transfer charger 34. It is equipped with a cleaning blade 36a that removes toner remaining on the outer surface of the photoreceptor 1, and a collection casing 36b that contains the toner removed by the cleaning blade 36a. The cleaner 36 is also provided with a static elimination lamp (not shown).

The image forming apparatus 100 is also provided with a fixing device 35, which is a fixing means for fixing the transferred image, downstream of the transport of the transfer paper 51 that has passed between the photoreceptor 1 and the transfer charger 34. The fixing device 35 is provided with a heating roller 35a having a heating means (not shown), and a pressure roller 35b that is provided opposite the heating roller 35a and is pressed against the heating roller 35a to form a contact portion.
Reference numeral 37 denotes a separating means for separating the transfer paper from the photosensitive member, and reference numeral 38 denotes a housing for accommodating the above-mentioned means of the image forming apparatus.

The image forming operation by this image forming apparatus 100 is performed as follows.
First, when the photosensitive member 1 is driven to rotate in the direction of arrow 41 by the driving means, the surface of the photosensitive member 1 is uniformly charged to a predetermined positive potential by the charger 32, which is located upstream of the image-forming point of the light by the exposure means 31 in the direction of rotation of the photosensitive member 1.

Next, light corresponding to image information is irradiated from the exposure means 32 onto the surface of the photoreceptor 1. This exposure removes surface charge from the areas of the photoreceptor 1 that have been irradiated with light, creating a difference in surface potential between the areas that have been irradiated with light and the areas that have not been irradiated with light, forming an electrostatic latent image.
Toner is supplied from a developing device 33, which is located downstream in the rotational direction of the photosensitive member 1 from the point where light is focused by the exposure means 33, to the surface of the photosensitive member 1 on which the electrostatic latent image is formed, thereby developing the electrostatic latent image and forming a toner image.

In synchronization with the exposure of the photosensitive member 1, a transfer paper 51 is supplied between the photosensitive member 1 and the transfer charger 34. The transfer charger 34 imparts a charge of the opposite polarity to that of the toner to the supplied transfer paper 51, and the toner image formed on the surface of the photosensitive member 1 is transferred onto the transfer paper 51.
The transfer paper 51 onto which the toner image has been transferred is transported by the transport means to the fixing device 35, and is heated and pressed as it passes through the contact area between the heating roller 35a and the pressure roller 35b of the fixing device 35, and the toner image is fixed onto the transfer paper 51 to form a solid image. The transfer paper 51 on which the image has been formed in this way is then ejected to the outside of the image forming apparatus 100 by the transport means.

Meanwhile, any toner remaining on the surface of photoreceptor 1 after the toner image has been transferred by transfer charger 34 is removed from the surface of photoreceptor 1 and collected by cleaner 36. The charge on the surface of photoreceptor 1 from which the toner has been removed in this way is removed by light from the discharging lamp, and the electrostatic latent image on the surface of photoreceptor 1 disappears. Photoreceptor 1 is then rotated again, and the series of operations starting with charging are repeated again, forming images continuously.

The image forming apparatus 100 described above is a monochrome image forming apparatus (printer), but it may also be, for example, an intermediate transfer type color image forming apparatus capable of forming color images. Specifically, it may be a so-called tandem type full-color image forming apparatus configured such that multiple electrophotographic photosensitive elements, on which toner images are respectively formed, are arranged side by side in a predetermined direction (for example, the horizontal direction H or approximately the horizontal direction H). The image forming apparatus 100 may also be another color image forming apparatus, a copier, a multifunction machine, or a facsimile machine.

The present invention will be specifically explained below with reference to the drawings and examples and comparative examples, but the present invention is not limited to these examples.

Example 1
(Formation of Undercoat Layer)
Three parts by mass of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: Tiebaque TTO-D-1) and two parts by mass of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: Amilan (registered trademark), grade: CM8000) were added to 25 parts by mass of methyl alcohol, and the mixture was dispersed for eight hours using a paint shaker to prepare three liters of a coating solution for an undercoat layer.
The obtained coating liquid for the undercoat layer was filled into a coating tank, and an aluminum drum-shaped support having a diameter of 30 mm and a length of 255 mm, serving as the conductive support 11, was immersed therein and then removed. The obtained coating film was allowed to dry naturally, thereby forming an undercoat layer 18 with a thickness of 1 μm on the conductive support 11.

(Formation of Charge Generation Layer)
Titanyl phthalocyanine represented by the following structural formula, which was to be used as a charge generating material, was prepared in advance.

29.2 g of diiminoisoindoline and 200 ml of sulfolane were mixed, and 17.0 g of titanium tetraisopropoxide was added, followed by reaction for 2 hours at 140° C. under a nitrogen atmosphere. The resulting reaction mixture was allowed to cool, and the precipitate was collected by filtration, washed successively with chloroform and a 2% aqueous solution of hydrochloric acid, and then washed successively with water and methanol, and dried to obtain 25.5 g of blue-purple crystals.
Chemical analysis of the resulting compound confirmed that it was titanyl phthalocyanine represented by the above structural formula (yield: 88.5%).

One part by weight of the obtained titanyl phthalocyanine and one part by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: S-LEC BM-2) were added to 98 parts by weight of methyl ethyl ketone, and the mixture was dispersed for two hours using a paint shaker to prepare 3 liters of a coating liquid for the charge generating layer.
The obtained coating liquid for the charge generating layer was applied onto the undercoat layer 18 by the same immersion method as in the case of forming the undercoat layer, and the obtained coating film was allowed to dry naturally to form a charge generating layer 15 with a film thickness of 0.3 μm.

(Formation of Charge Transport Layer)
Next, 70.0 g of silica particles (number average primary particle size 16 nm, surface treated with dimethyldichlorosilane, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972) were added to 390 g of tetrahydrofuran and suspended, and then glass beads (162 g, approximately 20% by volume of the mixed solution) with a diameter of 2 mm were added and stirred for 15 hours in a ball mill, after which the glass beads were removed. The obtained silica filler suspension was degassed for 10 minutes using a rotation-revolution mixer (Thinky Corporation, Awatori Rentaro atmospheric pressure type, model: ARE-310).

Next, 250 g of stilbene compound (1) as a charge transport material, 375 g of polycarbonate (manufactured by Teijin Chemical Co., Ltd., product name: TS2050), 1.75 g of perimidine compound (A) (C.I. Solvent Red 179, manufactured by American Dyestuff, product name: Amesolve Red A) as a light absorber, and 2400 g of tetrahydrofuran were added to the obtained silica filler suspension and stirred for 30 hours in a ball mill. The obtained mixture was subjected to 6-pass dispersion treatment using a particle dispersion device (manufactured by Microfluidics, model: Microfluidizer M110P). The obtained mixture was left to stand for 1 week at a temperature of 20 ° C. to prepare 3207 g of a coating solution for a charge transport layer.
The obtained coating liquid for the charge transport layer was applied onto the charge generation layer 15 by the same immersion method as in the case of forming the undercoat layer, and the obtained coating film was dried at a temperature of 120° C. for 1 hour to form a charge transport layer with a film thickness of 30 μm, thereby obtaining the photoreceptor 1 shown in FIG. 1.
As the charge transport material, a stilbene compound (1) prepared in advance based on the method described in Japanese Patent No. 3272257 was used.

Example 2
Photoreceptor 1 of Example 2 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge transport layer, silica particles (number average primary particle size 16 nm, surface treated with dimethyldichlorosilane, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) ADMAFINE NX-130) were used instead of silica particles (number average primary particle size 16 nm, surface treated with dimethyldichlorosilane, manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972).

Example 3
Photoreceptor 1 of Example 3 was prepared in the same manner as in Example 1, except that in forming the charge transport layer, the coating time was adjusted to change the thickness of the charge transport layer from 30 μm to 28 μm.

Example 4
Photoreceptor 1 of Example 4 was produced in the same manner as in Example 1, except that in preparing the coating solution for the charge transport layer, an azoquinone compound (B) (manufactured by Hodogaya Chemical Co., Ltd., product name: EAC-39) was used as the light absorber instead of the perimidine compound (A).

Example 5
Photoreceptor 1 of Example 5 was produced in the same manner as in Example 1, except that in preparing the coating liquid for the charge transport layer, silica particles (number average primary particle size 40 nm, hexamethyldisilazane surface treatment, Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) RX50) were used instead of silica particles (number average primary particle size 16 nm, dimethyldichlorosilane surface treatment, Nippon Aerosil Co., Ltd., product name: AEROSIL (registered trademark) R972).

Example 6
Photoreceptor 1 of Example 6 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 40.0 g and 220 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 1.70 g and 2,450 g, respectively.

Example 7
Photoreceptor 1 of Example 7 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 47.0 g and 260 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 1.70 g and 2,435 g, respectively.

(Example 8)
Photoreceptor 1 of Example 8 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 138 g and 765 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 1.90 g and 2,295 g, respectively.

Example 9
Photoreceptor 1 of Example 9 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 147 g and 815 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 1.90 g and 2,280 g, respectively.

(Examples 10 to 13)
Photoreceptors 1 of Examples 10 to 13 were prepared in the same manner as in Example 1, except that in forming the charge transport layer, the coating time was adjusted to change the thickness of the charge transport layer from 30 μm to 18 μm, 20 μm, 40 μm, and 42 μm, respectively.

(Comparative Example 1)
Photoreceptor 1 of Comparative Example 1 was prepared in the same manner as in Example 1, except that the perimidine compound (A) was not used as the light absorber in the preparation of the coating liquid for the charge transport layer.

(Comparative Example 2)
Photoreceptor 1 of Comparative Example 2 was prepared in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, the light absorbers were changed from 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran to 1.55 g and 2,500 g, respectively.

(Comparative Example 3)
Photoreceptor 1 of Comparative Example 3 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 111 g and 615 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 3.70 g and 2,350 g, respectively.

(Comparative Example 4)
Photoreceptor 1 of Comparative Example 4 was prepared in the same manner as in Example 1, except that in the preparation of the silica filler suspension for the charge transport layer coating liquid, 70.0 g of silica particles and 390 g of tetrahydrofuran were changed to 157 g and 875 g, respectively, and in the preparation of the charge transport layer coating liquid, 1.75 g of perimidine compound (A) and 2,400 g of tetrahydrofuran were changed to 4.35 g and 2,270 g, respectively.
For the photoreceptors 1 of Examples 1 to 13 and Comparative Examples 1 to 4, the main constituent materials of the charge transport layer, their contents, and film thicknesses are shown in Table 1.

[evaluation]
The photoreceptors 1 produced in Examples 1 to 13 and Comparative Examples 1 to 4 were evaluated for the following items.
In evaluations 2 and 3, each photoreceptor 1 was attached to a unit of a digital copying machine (manufactured by Sharp Corporation, model: MX-B455W) that had been modified for the test, and the evaluation was carried out.

[Evaluation 1: Transmittance]
Using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, model: UV-2450), the transmittances T 550 (%) and T ₆₀₀ (%) of the charge transport layer, which is the outermost layer of each photoreceptor 1, for light with wavelengths of 550 nm and 600 nm were measured in an environment of a temperature of 20°C and a relative humidity of ₅₀ %, and the ratio T ₆₀₀ /T ₅₅₀ was calculated.

[Evaluation 2: Electrical characteristics (sensitivity)]
The developing unit was removed from the digital copier, and a surface potential meter (manufactured by Trek Japan, model 344) was attached to the developing portion instead. 5,000 sheets of paper were passed through and aged in an environment of a temperature of 25°C and a relative humidity of 50%, and the residual potential Vr (-V) on the photoreceptor surface after static elimination immediately after aging was measured.
The results obtained were evaluated according to the following criteria.
<Evaluation criteria>
VG: Vr<40
Can be used without problems in high-speed multifunction devices or printers that require high sensitivity. G: 40≦Vr<60
Can be used without problems with medium to low speed multifunction devices or printers. NB: 60≦Vr<100
If you are using a slow, inexpensive multifunction device or printer, the density may be a little low, but it can be used without any problems. B: 100≦Vr
Poor sensitivity results in low concentration, which is problematic for practical use

[Evaluation 3: Light exposure]
All but a portion of the surface of the photoreceptor was masked with black paper, and the unmasked portion was irradiated with light from a white fluorescent lamp adjusted to an illuminance of 400 Lux for 5 minutes, and then left for 5 minutes.A halftone image was printed on one A4 sheet of paper, and the resulting image was visually observed.
The results obtained were evaluated according to the following criteria.
<Evaluation criteria>
VG: No difference between irradiated and non-irradiated areas G: A slight difference is observed between irradiated and non-irradiated areas, but not a large difference NB: A slight difference is observed between irradiated and non-irradiated areas (no problem in actual use)
B: A large difference is observed between the irradiated and non-irradiated areas (problems in practical use)

[comprehensive evaluation]
Based on the results of evaluations 2 and 3, an overall evaluation was made according to the following criteria.
In the overall evaluation, for VG, G, and NB, it is an essential requirement that the transmittance _T600 (%) for light with a wavelength of 600 nm (Evaluation 1) is 50% or more, and that the ratio _T600 / _T550 to the transmittance _T550 (%) for light with a wavelength of 550 nm is 1.10 or more and 2.20 or less.
VG: VG rating in all categories (very good)
G: Some items may be rated G, but all items are rated G or better (can be used without problems except for high-resolution multifunction devices or printers)
NB: Some items may be NB, but all items may be NB or better. (Inexpensive multifunction devices or printers can be used without any problems.)
B: Any item was rated B, and the product cannot be used in practice. The evaluation results are shown in Table 2.

The following can be seen from Tables 1 and 2.
(1) The photoreceptors (Examples 1 to 13) containing both a light absorber and a silica filler in the charge transport layer have better electrical properties and superior resistance to external light exposure compared to the photoreceptor (Comparative Example 1) not containing a light absorber in the charge transport layer and the photoreceptor (Comparative Example 2) not containing a silica filler in the charge transport layer.

(2) In the charge transport layer, photoreceptors (Examples 1 to 13) having a transmittance of 50% or more for light with a wavelength of ₆₀₀ nm and a ratio _T600 / _T550 of the transmittance _T600 for light with a wavelength of 600 nm to the transmittance _T550 for light with a wavelength of 550 nm of 1.10 or more and 2.20 or less have better electrical properties and superior resistance to exposure to external light than photoreceptors having a _T600 of less than 50% or a ratio T600/ _T550 of less than 2.20.

(3) The transmittance T ₆₀₀ for light with a wavelength of 600 nm is preferably 60% or more based on the results of Examples 2 and 3, and is preferably 70% or more based on the result of Example 1.

(4) Based on the results of Example 5, the average primary particle diameter of the silica filler contained in the outermost layer (charge transport layer) is preferably 30 nm or less. If the particle diameter is 30 nm or more, the residual potential tends to increase and the electrical properties deteriorate.

(5) Based on the results of Examples 6 to 9, the silica filler content in the outermost layer (charge transport layer) is preferably 7 to 18% by weight. If it is less than 7% by weight, the effect on light resistance is insufficient, and if it exceeds 18% by weight, the electrical properties deteriorate.

(6) Based on the results of Examples 10 to 13, the thickness of the outermost layer (charge transport layer) is preferably 20 μm to 40 μm. A thickness less than 20 μm does not sufficiently improve light resistance, and a thickness greater than 40 μm results in deterioration of electrical properties.

1. Electrophotographic photoreceptor (laminated electrophotographic photoreceptor)
11: Conductive support; 12: Charge generating material; 13: Charge transport material; 14: Photosensitive layer (laminated photosensitive layer);
15 Charge generation layer 16 Charge transport layer 17 Binder resin 18 Undercoat layer 19 Silica filler 20 Light absorber

31 Exposure means (semiconductor laser)
32 Charging means (charger)
33 Developing means (developer)
33a Developing roller 33b Casing 34 Transfer means (transfer charger)
35 Fixing means (fixing device)
35a Heating roller 35b Pressure roller 36 Cleaning means (cleaner)
36a Cleaning blade 36b Collection casing 37 Separation means 38 Housing 41, 42 Arrows 44 Rotation axis 51 Recording medium (recording paper or transfer paper)
100 Image forming device (laser printer)

Claims (8)

An electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance are laminated in this order on a conductive support, or at least the laminated photosensitive layer and a surface protective layer laminated thereon ,
the outermost surface layer of the electrophotographic photoreceptor contains a light absorber and a silica filler dispersed with glass beads , has a transmittance of 50% or more for light having a wavelength of 600 nm, and has a ratio _T600 /T550 of the transmittance T600 for light having a wavelength of 600 nm to the transmittance _T550 for light having a wavelength of 550 nm, that is, _T600 / _T550 , of 1.10 or more and 2.20 or less ;
the silica filler has an average primary particle diameter of 30 nm or less and is contained in an amount of 7 to 18% by mass relative to the total solid content of the outermost layer of the electrophotographic photoreceptor;
An electrophotographic photoreceptor characterized by the above-mentioned. 2. The electrophotographic photoreceptor according to claim 1, wherein the ratio T ₆₀₀ /T ₅₅₀ is 1.10 or more and 1.50 or less. The electrophotographic photoreceptor according to claim 1 or 2, wherein the light absorber is a compound that has spectral absorption in the wavelength range of 400 to 700 nm. The light absorber has the following structural formula (A):
a perimidine compound represented by the following structural formula (B):
and an azoquinone compound represented by the following structural formula (C):
4. The electrophotographic photoreceptor according to claim 1, wherein the compound is selected from pyrazolone compounds represented by the following formula: 5. The electrophotographic photoreceptor according to claim 1, wherein the light absorber is contained in an amount of 0.20 to 0.35% by mass based on the total solid content of the charge transport layer. 6. The electrophotographic photoreceptor according to claim 1 , wherein the charge transport layer has a thickness of 20 μm or more and 40 μm or less. 7. A process cartridge comprising: the electrophotographic photosensitive member according to claim 1; and at least one selected from a charging unit that charges the electrophotographic photosensitive member; a developing unit that develops an electrostatic latent image formed by exposure to light to form a toner image; and a cleaning unit that removes toner remaining on the electrophotographic photosensitive member. an electrophotographic photosensitive member according to any one of claims 1 to 6 ; a charging unit that charges the electrophotographic photosensitive member; an exposure unit that exposes the charged electrophotographic photosensitive member to light to form an electrostatic latent image; a developing unit that develops the electrostatic latent image formed by exposure to form a toner image; a transfer unit that transfers the toner image formed by development onto a recording medium; a fixing unit that fixes the transferred toner image on the recording medium to form an image; a cleaning unit that removes and collects toner remaining on the electrophotographic photosensitive member; and a discharging unit that discharging surface charges remaining on the electrophotographic photosensitive member.