JP2013109298A - Electrophotographic photoreceptor and image forming apparatus equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor which is excellent in printing durability and can be stably operated at high resolution over a long period of time.SOLUTION: There is provided an electrophotographic photoreceptor in which an undercoat layer, a charge generation layer containing a charge generating material and a charge transport layer containing at least a charge transport material and a filler are sequentially laminated on a conductive support and a refractive index N of the charge transport layer (1) satisfies a relation of the following expression: Na>Nb (wherein, Na represents a refractive index of an area near the surface of the charge transport layer and Nb represents a refractive index of an area the interface between the charge transport layer and the charge generation layer) and (2) gradually decreases from an area near the surface of the charge transport layer towards an area near the interface between the charge transport layer and the charge generation layer.

Description

  The present invention relates to an electrophotographic photosensitive member that is excellent in printing durability, can be stably operated over a long period of time, and an image forming apparatus including the same.

An electrophotographic process using a photoconductive electrophotographic photosensitive member (also referred to as “photosensitive member”) is one of information recording means utilizing a photoconductive phenomenon.
In the electrophotographic process, the surface of the photoconductor is charged uniformly by corona discharge in the dark, and then the image is exposed to selectively discharge the charge on the exposed area to form an electrostatic image on the exposed area. Then, colored charged fine particles (toner) are attached to the latent image by electrostatic attraction or the like to form an image as a visible image.

In this series of processes, the photoreceptor is required to have the following basic characteristics.
1) Able to uniformly charge to an appropriate potential in a dark place 2) High charge retention ability in a dark place and little discharge of charge 3) Excellent photosensitivity and quick discharge of light by light irradiation The photoreceptor is also required to have the following characteristics for stability and durability.
4) The surface of the photoconductor can be easily neutralized, and the residual potential is small. 5) It has mechanical strength and excellent flexibility. 6) Electrical characteristics, especially chargeability and photosensitivity when used repeatedly. 7) Residual potential should not change 7) Resistant to heat, light, temperature, humidity, ozone degradation, etc.

Among these, development of a photoreceptor having high durability and printing durability is desired, and as a means for that, addition of a filler to the charge transport layer or protective layer of the photoreceptor has been studied.
However, the addition of the filler causes problems such as repeated deterioration of electrical characteristics due to carrier trap formation, loss of incident light due to white turbidity, and image blur due to irregular reflection.

In order to solve this problem, for example, JP-A-8-305051 (Patent Document 1), JP-A-11-153877 (Patent Document 2) and JP-A-2006-201744 (Patent Document 3) Techniques for improving the filler content and dispersion state have been proposed.
However, the effects of these techniques are not sufficient, and the development of an electrophotographic photoreceptor that achieves printing durability, repeat stability, and high resolution is desired.

JP-A-8-305051 Japanese Patent Laid-Open No. 11-153877 JP 2006-201744 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member that is excellent in printing durability, can operate stably at a high resolution over a long period of time, and an image forming apparatus including the same.

  As a result of intensive studies to solve the above problems, the present inventor has made the charge transport layer so that the refractive index N gradually decreases from the vicinity of the surface of the charge transport layer toward the vicinity of the interface with the charge generation layer. By adding a filler to the surface of the charge transport layer, the printing durability and scratch resistance are improved near the surface of the charge transport layer, and in the vicinity of the interface of the charge generation layer, the resolution and electrical characteristics during repetition are improved. The present inventors have found that the present invention can be accomplished and have completed the present invention.

Thus, according to the present invention, an undercoat layer, a charge generation layer containing a charge generation material, and a charge transport layer containing at least a charge transport material and a filler are sequentially laminated on the conductive support,
The refractive index N of the charge transport layer is
(1) The following formula:
Na> Nb
(Wherein Na represents the refractive index near the surface of the charge transport layer and Nb represents the refractive index near the interface of the charge transport layer with the charge generation layer) and (2) An electrophotographic photosensitive member is provided that gradually decreases from the vicinity of the surface of the charge transport layer toward the vicinity of the interface between the charge transport layer and the charge generation layer.

  According to the present invention, the electrophotographic photosensitive member described above, a charging unit that charges the electrophotographic photosensitive member, and an exposing unit that exposes the charged electrophotographic photosensitive member 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 material; and transferring the transferred toner image There is provided an image forming apparatus comprising at least fixing means for fixing on the recording material to form an image and cleaning means for removing and collecting toner remaining on the electrophotographic photosensitive member.

  According to the present invention, it is possible to provide an electrophotographic photosensitive member that is excellent in printing durability, can operate stably over a long period of time with high resolution, that is, has little sensitivity change during repeated use, and an image forming apparatus including the same.

In the photoreceptor of the present invention, the refractive index Na in the vicinity of the surface of the charge transport layer is 1.90 to 2.50, and the refractive index Nb in the vicinity of the interface between the charge transport layer and the charge generation layer is 1.10 to 1. By being 40, the above-described excellent effects are exhibited.
In the photoreceptor of the present invention, the charge transport layer has a multilayer structure of at least three layers parallel to the conductive support, and the filler content in the intermediate layer of the multilayer structure is an adjacent layer on the charge generation layer side. More than the number of adjacent layers on the surface side of the charge transport layer, the refractive index N of the charge transport layer can be easily reduced stepwise, and the above-described excellent effects are exhibited.

  Furthermore, the photoreceptor of the present invention exhibits the above-described effects even more excellent when the filler is silica particles and when the charge transport material is an enamine compound represented by the structural formula (I) described later.

FIG. 3 is a schematic cross-sectional view illustrating a configuration of a main part of the photoconductor of the present invention. 1 is a schematic side view illustrating a configuration of an image forming apparatus of the present invention.

In the photoreceptor of the present invention, an undercoat layer, a charge generation layer containing a charge generation material, and a charge transport layer containing at least a charge transport material and a filler are sequentially laminated on a conductive support,
The refractive index N of the charge transport layer is
(1) The following formula:
Na> Nb
(Wherein Na represents the refractive index near the surface of the charge transport layer and Nb represents the refractive index near the interface of the charge transport layer with the charge generation layer) and (2) It is characterized in that it gradually decreases from the vicinity of the surface of the charge transport layer toward the vicinity of the interface between the charge transport layer and the charge generation layer.

In the charge transport layer composed only of the charge transport material and the binder resin, the change in the refractive index N in the film thickness direction is very small, and it is difficult to change the refractive index.
Accordingly, the present inventor has achieved that the refractive index can be arbitrarily changed by blending a filler in the charge transport layer and appropriately controlling the dispersion state and film forming conditions.

  For example, the refractive index of the charge transport layer can be changed by changing the filler content of the charge transport layer. Specifically, the refractive index can be increased by increasing the filler content, and conversely, the refractive index can be decreased by decreasing the filler content. More specifically, it will be described in detail in the section of the charge transport layer.

For the purpose of improving the printing durability of the photoreceptor, it has heretofore been made to contain a filler in the charge transport layer that is the outermost surface layer of the photoreceptor.
The inclusion of the filler also has an effect of suppressing the appearance of mechanical scratches on the surface of the charge transport layer on the image. In other words, this effect is brought about by increasing the diffraction of the incident light diffracted / diffusely reflected by the surface scratches, that is, suppressing the interference of the incident light affected by the scratches due to the refractive index increased by the inclusion of the filler. Conceivable. This indicates that image blur occurs at the same time.

Therefore, in the present invention, by changing the refractive index N of the charge transport layer so as to decrease stepwise from the vicinity of the surface to the vicinity of the interface with the charge generation layer, it is possible to ignore the influence of the image blur due to the scratch on the surface. Keeping it to a certain extent, it achieves both improved printing durability and high resolution.
In addition, the filler content is reduced in order to reduce the refractive index in the vicinity of the interface of the charge generation layer, but this can suppress the carrier traps derived from the filler and improve the electrical characteristics repeatedly.

The photoconductor of the present invention will be specifically described with reference to the drawings, but the present invention is not limited to the embodiments described below.
FIG. 1 is a schematic cross-sectional view showing the configuration of the main part of the photoreceptor of the present invention.
1 has an undercoat layer 2, a charge generation layer 3 containing a charge generation material, and a charge transport layer 4 containing a charge transport material and a filler in this order on the surface of a conductive support 1. The laminated photosensitive layer 5 is formed in this order.

[Conductive support 1]
The conductive support serves as an electrode for the photoreceptor and also functions as a support member for other layers.

The constituent material of the conductive support is not particularly limited as long as it is a material used in this field.
Specifically, metals and alloy materials such as aluminum, aluminum alloy, copper, brass, zinc, nickel, stainless steel, chromium, molybdenum, vanadium, indium, titanium, gold, platinum: polyethylene terephthalate, polyamide, polyester, polyoxy Polymer material such as methylene, polystyrene, cellulose, polylactic acid, hard paper, glass substrate laminated with metal foil, metal material or alloy material deposited, conductive polymer, tin oxide, oxidation Examples thereof include those obtained by depositing or applying a layer of a conductive compound such as indium or carbon black.

Examples of the shape of the conductive support include a sheet shape, a cylindrical shape, a columnar shape, and an endless belt (seamless belt) shape.
If necessary, the surface of the conductive support is subjected to irregular reflection treatment such as anodic oxide coating treatment, surface treatment with chemicals, hot water, coloring treatment, and surface roughening within a range that does not affect the image quality. May be given.

  The irregular reflection treatment is particularly effective when the photoconductor according to the present invention is used in an electrophotographic process using a laser as an exposure light source. That is, in the electrophotographic process using a laser as an exposure light source, the wavelength of the laser beam is uniform, so the laser beam reflected on the surface of the photoconductor and the laser beam reflected inside the photoconductor cause interference, Interference fringes due to this interference may appear in the image and cause image defects. Therefore, by performing irregular reflection processing on the surface of the conductive support, it is possible to prevent image defects due to interference of laser light having a uniform wavelength.

[Undercoat layer (also referred to as “intermediate layer”) 2]
The undercoat layer has a function of preventing charge injection from the conductive support to the laminated photosensitive layer. That is, a decrease in chargeability of the multilayer photosensitive layer is suppressed, a decrease in surface charge other than a portion to be erased by exposure is suppressed, and occurrence of image defects such as fog is prevented. In particular, during image formation by the reversal development process, it is possible to prevent the occurrence of image fogging called black spots in which minute black dots made of toner are formed on a white background portion.
In addition, the undercoat layer covering the surface of the conductive support reduces the degree of unevenness, which is a defect on the surface of the conductive support, makes the surface uniform, improves the film-forming property of the laminated photosensitive layer, The adhesion (adhesiveness) between the conductive support and the laminated photosensitive layer can be improved.

  The undercoat layer is formed, for example, by dissolving the resin material in an appropriate solvent to prepare a coating solution for the undercoat layer, applying this coating solution to the surface of the conductive support, and removing the solvent by drying. can do. In addition, when the constituent material of the conductive support is aluminum, a layer containing alumite formed by oxidation thereof (alumite layer) may be used as the undercoat layer.

Examples of the resin material include polyethylene resin, polypropylene resin, polystyrene resin, acrylic resin, vinyl chloride resin, vinyl acetate resin, polyurethane resin, epoxy resin, polyester resin, melamine resin, silicone resin, polyvinyl butyral resin, polyvinyl pyrrolidone resin, In addition to resins such as polyacrylamide resins and polyamide resins, and synthetic resins such as copolymer resins containing two or more of the repeating units constituting these resins, casein, gelatin, polyvinyl alcohol, cellulose, nitrocellulose And natural polymers such as ethyl cellulose. One of these may be used alone, or two or more thereof may be used in combination.
Among these resins, it is preferable to use a polyamide resin, and it is particularly preferable to use an alcohol-soluble nylon resin.

  Preferred alcohol-soluble nylon resins include, for example, homopolymerized or copolymerized nylons such as 6-nylon, 6,6-nylon, 6,10-nylon, 11-nylon, 2-nylon and 12-nylon, and N-alkoxy. Examples thereof include resins obtained by chemically modifying nylon, such as methyl-modified nylon and N-alkoxyethyl-modified nylon.

  Examples of the solvent for the coating liquid for the undercoat layer include single solvents such as water and various organic solvents, and mixed solvents thereof. Examples of the organic solvent include alcohols such as methanol, ethanol and butanol, ethers such as tetrahydrofuran and dioxane, and halogen-based organic solvents such as dichloroethane, chloroform and trichloroethane. Among these solvents, non-halogen organic solvents are preferably used in consideration of the global environment.

The undercoat layer may contain metal oxide particles.
The metal oxide particles can easily adjust the volume resistance value of the undercoat layer, can further suppress charge injection into the laminated photosensitive layer, and can maintain the electrical characteristics of the photoreceptor in various environments.
Examples of the metal oxide particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide. The average particle diameter is preferably in the range of 0.02 to 0.5 μm.

When the total blending amount of the resin material and the metal oxide particles in the coating solution for the undercoat layer is A and the blending amount of the solvent is B, the weight ratio (A / B) of both is 1/99 to 40/60. It is preferable that the ratio is 2/98 to 30/70.
Further, when the blending amount of the resin material is C and the blending amount of the metal oxide particles is F, the weight ratio (C / D) of both is preferably 1/99 to 90/10. Particularly preferred is ~ 70/30.

In the case where particles such as metal oxide particles are contained in the undercoat layer, for example, the metal oxide particles are dispersed in a solution obtained by dissolving or dispersing the resin material in a suitable solvent. What is necessary is just to prepare the application liquid.
In order to disperse the metal oxide particles in the resin solution, a known apparatus such as a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, and a paint shaker may be used. The dispersion conditions may be appropriately selected so that impurities are not mixed due to wear of the container used or the dispersion medium.

The coating method of the coating solution for the undercoat layer may be appropriately selected in consideration of the physical properties and productivity of the coating solution, for example, spray method, bar coating method, roll coating method, blade method, Examples thereof include a ring method and a dip coating method.
Among these coating methods, the dip coating method is a method in which a conductive support is immersed in a coating tank filled with a coating solution and then pulled up at a constant speed or a rate that changes sequentially to form a layer on the surface of the conductive support. It is a method of forming. Since this method is relatively simple and excellent in terms of productivity and cost, it is frequently used in the production of photoreceptors. In order to stabilize the dispersibility of the coating liquid, the apparatus used for the dip coating method may be provided with a coating liquid dispersing apparatus represented by an ultrasonic generator.

Although the solvent in the coating film may be removed by natural drying, the solvent in the coating film may be forcibly removed by heating.
Although the temperature in such a drying process will not be specifically limited if it is the temperature which can remove the used solvent, About 50-140 degreeC is suitable, and about 80-130 degreeC is especially preferable.
When the drying temperature is less than 50 ° C., the drying time may be long, and the solvent may not be sufficiently evaporated and may remain in the charge generation layer. On the other hand, if the drying temperature exceeds about 140 ° C., the electrical characteristics during repeated use of the photoreceptor may deteriorate and the resulting image may deteriorate.
Such temperature conditions are common not only to the undercoat layer but also to the formation of layers such as a photosensitive layer described later and other processes.

The thickness of the undercoat layer is not particularly limited, but is preferably 0.01 to 20 μm, and particularly preferably 0.05 to 10 μm.
If the thickness of the undercoat layer is less than 0.01 μm, the undercoat layer does not substantially function, and there is a possibility that a uniform surface cannot be obtained by covering defects of the conductive support. On the other hand, if the thickness of the undercoat layer exceeds 20 μm, it is difficult to form a uniform undercoat layer, and the sensitivity of the photoreceptor may be lowered.

[Charge generation layer 3]
The charge generation layer formed on the undercoat layer is mainly composed of a charge generation material having a charge generation capability of generating charges by absorbing irradiated light, and optionally containing a binder resin and a known additive. contains.

Examples of the charge generating material (also referred to as “charge generating substance”) include organic and inorganic pigments and photoconductive materials used in this field, and organic materials are preferable in terms of sensitivity and durability.
Examples of organic pigments and photoconductive materials include bisazo pigments such as chlorodian blue, polycyclic quinone pigments such as trisazo pigments, dibromoanthanthrone, perylene pigments, quinacridone pigments, phthalocyanine pigments, Examples thereof include squalium pigments and azulenium salt compounds, and these can be used alone or in combination of two or more.

The charge generation material may be selected in accordance with the wavelength range required for the photoreceptor.
Photoreceptors that perform image formation by a reversal development process using a light source such as a laser beam or an LED are required to have a sensitivity in the long wavelength range of 620 to 800 nm. Conventionally, a phthalocyanine pigment having high sensitivity and excellent durability and Trisazo pigments, particularly phthalocyanine pigments having excellent properties, are being investigated.

Examples of the phthalocyanine pigment include metal-free phthalocyanine, metal phthalocyanine, and mixtures and mixed crystal compounds thereof.
Examples of the crystal type include α-type, β-type, τ-type, Y-type, and amorphous.
Examples of the metal used in the metal phthalocyanine pigment include those having an oxidation state of zero, metal halides such as chlorides and bromides, and oxides thereof. Preferred metals include Cu, Ni, Mg, Pb, V, Pd, Co, Nb, Al, Sn, Zn, Ca, In, Ga, Fe, Ge, Ti, Cr, and the like.
Various methods for producing these phthalocyanine pigments have been proposed, but are not particularly limited, and after being pigmented, various purification processes and dispersion treatments are performed with various organic solvents to convert the crystal form. May be.

The charge generation layer can be formed by a dry method such as vacuum deposition of a charge generation material and a wet method similar to the undercoat layer.
In the wet method, the charge generation layer is prepared by, for example, preparing a charge generation layer coating solution by mixing and dispersing a charge generation material in a solution in which a binder resin is dissolved in an organic solvent, and applying the coating solution to the surface of the undercoat layer. It can be formed by applying to the substrate and removing the solvent by drying.
In preparing the charge generation layer coating solution, a known dispersing device may be used in the same manner as the preparation of the undercoat layer coating solution in order to disperse the charge generation material.
Other processes and conditions are in accordance with the formation of the undercoat layer.

When using a phthalocyanine pigment as the charge generation material, it is preferable to disperse the primary particles and / or their aggregated particle diameters to 3 μm or less.
When the primary particles and / or the aggregated particle diameter thereof exceeds 3 μm, black spots are very likely to occur on a white background in the obtained photosensitive member during reversal development. Therefore, by optimizing the conditions, the primary particles of the phthalocyanine pigment and / or the aggregated particle diameter thereof is dispersed to 3 μm or less, more preferably, the median diameter is 0.5 μm or less, and the mode diameter is 3 μm or less. It is preferable not to contain.

  On the other hand, in order to make a phthalocyanine pigment into fine particles, relatively strong dispersion conditions and a long dispersion time are required due to its chemical structure. Therefore, strong dispersion conditions and long-time dispersion treatment not only reduce the cost efficiency, but also inevitably contain impurities due to wear of the dispersion media, impact due to organic solvents, heat, and dispersion during dispersion. As a result, the crystal form of the phthalocyanine pigment may change, and the sensitivity of the photoreceptor may be greatly reduced. For this reason, it is not preferable to reduce the median diameter to 0.01 μm or less and the mode diameter to 0.1 μm or less.

  Further, when the dispersed coating solution for charge generation layer contains particles of phthalocyanine pigment exceeding 3 μm, it may be filtered to remove coarse particles and aggregates. The material of the filter used for the filtration treatment is not particularly limited as long as it does not swell or dissolve in the organic solvent used for dispersion, and examples thereof include a Teflon (registered trademark) membrane filter having a uniform pore size.

  The binder resin can improve the mechanical strength and durability of the charge generation layer, the interlayer binding property, and the like, and a resin having a binding property used in this field can be used. Specifically, homopolymer resins such as melamine resin, epoxy resin, silicon resin, polyurethane resin, acrylic resin, polycarbonate resin, polyarylate resin, phenoxy resin, and butyral resin, and copolymers containing two or more repeating units Examples of the resin include insulating resins such as vinyl chloride-vinyl acetate copolymer resin and acrylonitrile-styrene copolymer resin, and these can be used alone or in combination of two or more.

  Solvents include halogenated hydrocarbons such as methylene chloride and ethane dichloride, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran and dioxane, benzene, toluene and xylene. Aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and the like, and these are used alone or in combination of two or more (as a mixed solvent). be able to.

When the content of the charge generation material containing the phthalocyanine pigment is E and the blending amount of the binder resin is F, the blending ratio (E / F) of both is preferably 10/90 to 99/1. / 60
Particularly preferred is ~ 70/30.
If the amount of the charge generating material is small, the sensitivity of the photoconductor may decrease. If the amount of the charge generating material is large, not only the durability of the photoconductor will be decreased, but also the dispersibility will decrease and the coarse particles will increase. As a result, image defects, particularly black spots, may increase.

  The charge generation layer is a chemical sensitizer, an optical sensitizer, an antioxidant, an ultraviolet absorber, a dispersion stabilizer, a sensitizer, and a leveling agent (surface modifier) as long as the effects of the present invention are not impaired. In addition, an appropriate amount of one or more known additives selected from plasticizers and the like may be contained. These additives may be contained in the charge transport layer described later, or may be contained in both the charge generation layer and the charge transport layer.

The chemical sensitizer and the optical sensitizer improve the sensitivity of the photoreceptor, suppress an increase in residual potential and fatigue due to repeated use, and improve electrical durability.
Examples of chemical sensitizers include acid anhydrides such as succinic anhydride, maleic anhydride, phthalic anhydride, and 4-chloronaphthalic anhydride; cyano compounds such as tetracyanoethylene and terephthalmalondinitrile, 4-nitrobenzaldehyde, and the like. Aldehydes; anthraquinones such as anthraquinone and 1-nitroanthraquinone; polycyclic or heterocyclic nitro compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitrofluorenone; diphenoquinone compounds Examples thereof include electron-withdrawing materials and those obtained by polymerizing these electron-withdrawing materials.

  Examples of the optical sensitizer include xanthene dyes, quinoline pigments, organic photoconductive compounds such as copper phthalocyanine, triphenylmethane dyes represented by methyl violet, crystal violet, knight blue and victoria blue; erythrosin, Acridine dyes typified by rhodamine B, rhodamine 3R, acridine orange and frapeosin; thiazine dyes typified by methylene blue and methylene green; oxazine dyes typified by capri blue and meldra blue; cyanine dyes; styryl dyes; Examples include pyrylium salt dyes and thiopyrylium salt dyes.

Antioxidants can maintain sensitivity stability over a long period of time.
Antioxidants include phenolic antioxidants such as hindered phenols such as 2,6-di-t-butyl-4-methylphenol (2,6-di-t-butyl-p-cresol: BHT). , Amine antioxidants such as hindered amines, vitamin E, hydroquinone, paraphenylenediamine, arylalkanes and derivatives thereof, organic sulfur compounds, organic phosphorus compounds, etc., and these may be used alone or in combination of two or more. Can be used.

The addition amount of the antioxidant is preferably 0.1 to 50 parts by weight, particularly preferably 0.5 to 15 parts by weight with respect to 100 parts by weight of the charge generating material.
When the addition amount of the antioxidant is less than 0.1 parts by weight, a sufficient effect may not be obtained for improving the storage stability of the coating solution and improving the durability of the photoreceptor. Moreover, when the addition amount of antioxidant exceeds 50 weight part, it may have a bad influence on a sensitivity characteristic.

Leveling agents and plasticizers can improve film formability, flexibility and surface smoothness.
Examples of the leveling agent include silicone oil and fluororesin.
Examples of the plasticizer include biphenyl, biphenyl chloride, benzophenone, o-terphenyl, dibasic acid ester, fatty acid ester, phosphoric acid ester, phthalic acid ester, various fluorohydrocarbons, chlorinated paraffin, and epoxy type plasticizer. It is done.

The film thickness of the charge generation layer is not particularly limited, but is preferably 0.05 to 5 μm, particularly preferably 0.08 to 1 μm.
When the thickness of the charge generation layer is less than 0.05 μm, the light absorption efficiency is lowered, and the sensitivity of the photoreceptor may be lowered. In addition, it is necessary to disperse the pigment until it becomes very small, and when a phthalocyanine pigment is used, its crystal form may change. On the other hand, when the film thickness of the charge generation layer exceeds 5 μm, charge transfer inside the charge generation layer becomes a rate-limiting step in the process of erasing the surface charge, and the sensitivity may decrease. Moreover, although a certain sensitivity is shown, it is not preferable in terms of cost, and it becomes difficult to apply uniformly.

[Charge transport layer 4]
The charge transport layer contains as a main component a charge transport material having the ability to accept and transport charges generated in the charge generation material, a filler, and a binder resin that binds them, and optionally contains known additives. .

  As the charge transport material (also referred to as “charge transport material”), hole transport materials and electron transport materials used in the technical field can be used.

  Examples of hole transport materials 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, hydrazones. Compound, polycyclic aromatic compound, indole derivative, pyrazoline derivative, oxazolone derivative, benzimidazole derivative, quinazoline derivative, benzofuran derivative, acridine derivative, phenazine derivative, aminostilbene derivative, triarylamine derivative, triarylmethane derivative, phenylenediamine derivative Stilbene derivatives, enamine derivatives and benzidine derivatives, and groups derived from these compounds. Or a polymer having in the side chain, such as poly -N- vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole - formaldehyde resins, triphenylmethane polymers, such as poly-9-vinyl anthracene, and polysilane, and the like.

Examples of the electron transport material include organic compounds such as benzoquinone derivatives, tetracyanoethylene derivatives, tetracyanoquinodimethane derivatives, fluorenone derivatives, xanthone derivatives, phenanthraquinone derivatives, phthalic anhydride derivatives, and diphenoquinone derivatives.
These charge transport materials can be used singly or in combination of two or more. Among these, the enamine compound represented by the structural formula (I) used in Examples 1 to 3 described later and the enamine compound represented by the structural formula (II) used in Example 4 are preferable. The former is particularly preferable.

As the binder resin, one kind of binder resin similar to that contained in the charge generation layer can be used alone or in combination of two or more kinds.
Among these resins, polystyrene, polycarbonate, polyarylate, and polyphenylene oxide are preferable because they have a volume resistance of 10 ¹³ Ω or more, excellent electrical insulation, and excellent film formability and potential characteristics. Particularly preferred.

As the filler, organic and inorganic particles used in the technical field can be used, and those having high hardness as a material and easy to be dispersed in the binder resin are preferable.
Examples of the constituent material of the organic particles include a fluorine resin.
Examples of the constituent material of the inorganic particles include silicon oxide (silica), titanium oxide (titania), zinc oxide (zirconia), calcium oxide (calcia), aluminum oxide (alumina) and other oxides, and silicon nitride and aluminum nitride. And nitrides.
In the present invention, the filler can be used alone or in combination of two or more. Among these, silica particles are particularly preferable from the viewpoint of excellent dispersion stability and printing durability.

  In addition, the filler is a silane coupling agent such as dimethyldichlorosilane, a silylating agent in which atoms such as halogen, nitrogen, and sulfur are bonded to silicon in order to improve dispersibility within a range that does not impair the effects of the present invention. The surface treatment may be performed with an organic compound such as a general coupling agent such as a titanate coupling agent or an aluminum coupling agent.

Although the average particle diameter of a filler is not specifically limited, It is preferable that it is 10-200 nm, and it is especially preferable that it is 20-70 nm.
If the average particle size of the filler is less than 10 nm, the dispersion state may be non-uniform due to aggregation. On the other hand, if the average particle diameter of the filler exceeds 200 nm, light scattering may increase and image loss may occur.

The charge transport layer is prepared by, for example, preparing a charge transport layer coating solution by dissolving and dispersing a charge transport material, a filler, a binder resin and, if necessary, a known additive in an appropriate solvent. It can be formed by applying to the surface of the generating layer and then drying to remove the organic solvent.
In the preparation of the charge transport layer coating solution, a known dispersing device may be used in the same manner as the preparation of the undercoat layer coating solution in order to disperse the charge transport material and the filler.
Other processes and conditions are in accordance with the formation of the undercoat layer.

In the present invention, the refractive index Na in the vicinity of the surface of the charge transport layer and the refractive index Nb in the vicinity of the interface between the charge transport layer and the charge generation layer satisfy the relationship of the formula: Na> Nb, and the charge transport layer. The charge transport layer is formed so that the refractive index N of the charge transport layer gradually decreases from the vicinity of the surface of the charge transport layer to the vicinity of the interface between the charge transport layer and the charge generation layer.
The refractive index Na in the vicinity of the surface of the charge transport layer is preferably 1.90 to 2.50, and the refractive index Nb in the vicinity of the interface between the charge transport layer and the charge generation layer is preferably 1.10 to 1.40. . More preferable Na is 1.90 to 2.25, and more preferable Nb is 1.25 to 1.40.
That is, the refractive index N of the charge transport layer is preferably in the range of 1.10 to 2.50. A more preferred range is 1.25 to 2.25.
It is technically difficult to produce a charge transport layer having a refractive index with Nb, which is the lower limit of the refractive index, of less than 1.10.
On the other hand, if Na, which is the upper limit of the refractive index, exceeds 2.50, the printing durability is improved, but the electrical characteristics may be repeatedly deteriorated and the image may be blurred.

  For this purpose, for example, the charge transport layer has a multilayer structure of at least three layers parallel to the conductive support, and the charge content of the charge transport layer is changed from the layer near the surface of the charge transport layer to the charge generation of the charge transport layer. Stepwise decrease to the layer near the interface with the layer, that is, the filler content in the intermediate layer of the multilayer structure is greater than the adjacent layer on the charge generation layer side and more than the adjacent layer on the surface side of the charge transport layer It is preferable to reduce it.

Specifically, in the preparation of the charge transport layer coating solution, three or more types of charge transport layer primary dispersions containing fillers, binder resins, and solvents having different filler contents are prepared in advance. In addition, a charge transport material, an additional binder resin and a solvent, and, if necessary, known additives are added to prepare three or more types of charge transport layer coating liquids, which are coated with a low filler content. It is sufficient to apply (overcoat) on the surface of the charge generation layer in order.
What is necessary is just to prepare suitably so that content of the charge transport material, the filler, and binder resin in each coating liquid for charge transport layers may become the range mentioned later.

In the overcoating, pre-drying is preferably performed by a known method every time one layer is applied so that the respective coating solutions are not mixed. For example, in the case where a cylindrical conductive support is used as in the embodiment, the conductive support may be rotated for a certain period of time to be naturally dried and dried with hot air after all the coating has been completed.
The application method is not particularly limited, and examples thereof include the same wet method as the undercoat layer. However, since it is necessary to repeat application and drying in overcoating, the spray method using a spray gun is used as in the example. Preferably there is.

When the blending amount of the charge transport material is G and the blending amount of the binder resin is H, the blending ratio (G / H) of both is preferably 10/30 to 10/10. Particularly preferred is / 16.
If the amount of the charge transporting material is small, the carrier mobility in the charge transporting layer may be lowered and the sensitivity of the photoreceptor may be lowered. If the amount of the charge transporting material is large, the printing durability of the photosensitive layer is lowered. As a result, the amount of film loss due to repeated use increases, and the chargeability of the photoreceptor may decrease.

In addition, as described above, the blending amount of the filler needs to be changed step by step for each layer to be laminated. As the range of the upper limit value and the lower limit value, the blending amount of the filler is I, the blending amount of the binder resin. When the amount is H, the weight ratio (I / I) between the two is preferably 2/98 to 20/80, particularly preferably 10/90 to 15/85.
If the blending amount of the filler is small, it is not effective for improving the printing durability. If the blending amount of the filler is large, the printing durability is improved. On the other hand, the electrical characteristics may be repeatedly deteriorated or the image may be blurred.

The thickness of the charge transport layer is not particularly limited, but is preferably 5 to 50 μm, particularly preferably 10 to 40 μm.
When the thickness of the charge transport layer is less than 5 μm, the charge holding ability on the surface of the photoreceptor may be lowered. On the other hand, if the thickness of the charge transport layer exceeds 50 μm, the resolution of the photoreceptor may be lowered.

  The photoreceptor of the present invention can be used in electrophotographic copying machines, various printers using a light source such as a laser or a light emitting diode (LED), and an electrophotographic plate making system.

[Image forming apparatus]
The image forming apparatus of the present invention includes a photosensitive member of the present invention, a charging unit for charging the photosensitive member, an exposure unit for exposing the charged photosensitive member to form an electrostatic latent image, and a static formed by exposure. Developing means for developing an electrostatic latent image to form a toner image, transfer means for transferring the toner image formed by development onto a recording material, and fixing the transferred toner image on the recording material to form an image And a fixing unit that removes and collects toner remaining on the photosensitive member.

The image forming apparatus of the present invention will be specifically described with reference to the drawings, but the present invention is not limited to the embodiments described below.
FIG. 2 is a schematic side view showing the configuration of the image forming apparatus of the present invention.
2 includes a photoconductor 21 (for example, the photoconductor of FIG. 1) of the present invention, a charging unit (charging unit) 24, an exposure unit 28, a developing unit (developing unit) 25, and a transfer unit. It includes a means (transfer device) 26, a cleaning means (cleaner) 27, a fixing means (fixing device) 31, and a charge eliminating means (not shown, provided alongside the cleaning means 27). Reference numeral 30 shows a transfer sheet as a recording material.

  The photosensitive member 21 is rotatably supported by the main body of the image forming apparatus 20 (not shown), and is driven to rotate in the direction of the arrow 23 around the rotation axis 22 by a driving unit (not shown). The drive means includes, for example, an electric motor and a reduction gear, and transmits the driving force to a conductive support constituting the core of the photoconductor 21, thereby rotating the photoconductor 21 at a predetermined peripheral speed. . The charger 24, the exposure unit 28, the developing unit 25, the transfer unit 26, and the cleaner 27 are arranged in this order along the outer peripheral surface of the photoconductor 21 from the upstream side in the rotation direction of the photoconductor 21 indicated by the arrow 23. It is provided toward the side.

  The charger 24 is a charging unit that charges the outer peripheral surface of the photoconductor 21 to a predetermined potential. Specifically, for example, the charger 24 is realized by a contact-type charging roller 24a, a charging brush, or a charger wire such as a corotron or a scorotron. Reference numeral 24b shows a bias power source.

  The exposure unit 28 includes, for example, a semiconductor laser as a light source, and is charged by irradiating light 28 a such as a laser beam output from the light source between the charger 24 and the developer 25 of the photosensitive member 21. The outer peripheral surface of the photoconductor 21 is exposed according to image information. The light 28a is repeatedly scanned in the main scanning direction in the direction in which the rotation axis 22 of the photoconductor 21 extends, and accordingly, electrostatic latent images are sequentially formed on the surface of the photoconductor 21.

  The developing unit 25 is a developing unit that develops an electrostatic latent image formed on the surface of the photoreceptor 21 by exposure with a developer. The developing unit 25 is provided facing the photoreceptor 21, and applies toner to the outer peripheral surface of the photoreceptor 21. A developing roller 25a to be supplied and a casing 25b for supporting the developing roller 25a so as to be rotatable around a rotation axis parallel to the rotation axis 22 of the photosensitive member 21 and containing a developer containing toner in the internal space thereof.

  The transfer device 26 supplies a toner image, which is a visible image formed on the outer peripheral surface of the photoconductor 21 by development, between the photoconductor 21 and the transfer device 26 from the direction of the arrow 29 by a conveying unit (not shown). It is a transfer means for transferring onto a transfer sheet 30 that is a recording material (recording medium). The transfer unit 26 is, for example, a non-contact type transfer unit that includes a charging unit and transfers the toner image onto the transfer paper 30 by applying a charge having a polarity opposite to that of the toner to the transfer paper 30.

  The cleaner 27 is a cleaning unit that removes and collects toner remaining on the outer peripheral surface of the photoconductor 21 after the transfer operation by the transfer device 26, and includes a cleaning blade 27 a that peels off toner remaining on the outer peripheral surface of the photoconductor 21, and a cleaning device. A recovery casing 27b for storing the toner separated by the blade 27a. The cleaner 27 is provided together with a charge eliminating lamp (not shown).

  Further, the image forming apparatus 20 is provided with a fixing device 31 as fixing means for fixing the transferred image on the downstream side where the transfer paper 30 that has passed between the photoreceptor 21 and the transfer device 26 is conveyed. . The fixing device 31 includes a heating roller 31a having a heating unit (not shown), and a pressure roller 31b that is provided to face the heating roller 31a and is pressed by the heating roller 31a to form a contact portion.

  The image forming operation by the image forming apparatus 20 is performed as follows. First, when the photosensitive member 21 is rotationally driven in the direction of the arrow 23 by the driving means, the photosensitive member 24 is provided by the charger 24 provided on the upstream side in the rotational direction of the photosensitive member 21 with respect to the imaging point of the light 28a by the exposure means 28. The surface of 21 is uniformly charged to a predetermined positive or negative potential.

  Next, light 28 a corresponding to image information is irradiated from the exposure unit 28 to the surface of the photoconductor 21. With this exposure, the surface charge of the portion irradiated with the light 28a is removed from the photosensitive member 21, and a difference occurs between the surface potential of the portion irradiated with the light 28a and the surface potential of the portion not irradiated with the light 28a. An electrostatic latent image is formed.

  Next, toner is supplied to the surface of the photosensitive member 21 on which the electrostatic latent image is formed from a developing unit 25 provided on the downstream side in the rotation direction of the photosensitive member 21 with respect to the image forming point of the light 28a by the exposure unit 28. The electrostatic latent image is developed to form a toner image.

  In synchronization with the exposure of the photosensitive member 21, the transfer paper 30 is supplied between the photosensitive member 21 and the transfer device 26. The transfer device 26 applies a charge having a polarity opposite to that of the toner to the supplied transfer paper 30, and the toner image formed on the surface of the photoreceptor 21 is transferred onto the transfer paper 30.

  Next, the transfer paper 30 onto which the toner image has been transferred is conveyed to the fixing device 31 by the conveying means, and is heated and pressurized when passing through the contact portion between the heating roller 31a and the pressure roller 31b of the fixing device 31. The toner image is fixed on the transfer paper 30 and becomes a robust image. The transfer paper 30 on which the image is formed in this way is discharged to the outside of the image forming apparatus 20 by the conveying means.

On the other hand, the toner remaining on the surface of the photoconductor 21 even after the transfer of the toner image by the transfer unit 26 is separated from the surface of the photoconductor 21 by the cleaner 27 and collected. The charge on the surface of the photoconductor 21 from which the toner has been removed in this manner is removed by the light from the static elimination lamp, and the electrostatic latent image on the surface of the photoconductor 21 disappears. Thereafter, the photosensitive member 21 is further driven to rotate, and a series of operations starting from charging is repeated to continuously form images.
Further, the image forming apparatus 21 may not be equipped with the cleaning unit 27 and the charge removal unit, depending on the model.

  EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples.

Example 1
The following ingredients:
Metal oxide fine particles: Silica-coated titanium oxide fine particles 1 part by weight (manufactured by Showa Denko KK, product name: Maxlite (registered trademark) TS-043)
Binder resin: Polyamide resin 9 parts by weight (Product name: Amilan (registered trademark) CM8000, manufactured by Toray Industries, Inc.)
Solvent: 50 parts by weight of ethanol Solvent: 50 parts by weight of tetrahydrofuran was put into a stirring tank having a capacity of 20,000 ml. Next, the components in the agitation tank were flowed through a diaphragm pump into a dispersing machine in which 0.5 mm diameter silicon nitride beads were introduced as a dispersion medium into a horizontal bead mill with a capacity of 16,500 ml, and the flow rate was 3,000 ml / min. The resulting solution was fed at a rate of about 15 hours, and circulated and dispersed for 15 hours to prepare an undercoat layer coating solution of 3,000 g.
The obtained coating solution is filled in a coating tank having a capacity of 2,500 ml, and an aluminum cylindrical support having a diameter of 30 mm and a total length of 340 mm as the conductive support 1 is immersed, pulled up, and then naturally dried to obtain a film thickness. An undercoat layer 2 of 0.15 μm was formed on the conductive support 1.

Then the following ingredients:
Charge generation material: τ-type metal-free phthalocyanine 2 parts by weight (manufactured by Toyo Ink Co., Ltd., product name: Liophoton TPA-891)
Binder resin: Polyvinyl butyral resin 2 parts by weight (manufactured by Sekisui Chemical Co., Ltd., product name: ESREC BM-S)
Solvent: 100 parts by weight of methyl ethyl ketone was mixed, and dispersion treatment was performed for 12 hours in a ball mill with a capacity of 4,000 ml filled with 30% by volume of ZrO ₂ beads (φ3 mm) as a dispersion medium. Prepared.
The obtained coating solution is applied onto the previously provided undercoat layer 2 by the same dip coating method as in the case of forming the undercoat layer, and dried with hot air at 120 ° C. for 10 minutes to generate a charge with a thickness of 0.8 μm. Layer 3 was formed.

Then the following ingredients:
Filler: 1 part by weight of dimethyldichlorosilane surface-treated silica particles (average particle diameter 17 nm) (manufactured by Cabot Specialty Chemicals Inc., product name: TS-610)
Binder resin: 1 part by weight of polycarbonate resin (Mitsubishi Engineering Plastics Co., Ltd., product name: Z200)
Solvent: Cyclohexanone 80 parts by weight is mixed, and further dispersed in a 5,000 ml ball mill filled with 50% by volume of ZrO ₂ beads (φ3 mm) as a dispersion medium for 5 hours to form a charge transport layer primary dispersion (A) 500 ml was prepared.
Further, two kinds of primary charge transport layer dispersions (B) and (C) were prepared in the same manner as described above except that the amount of silica particles as the filler was 7 parts by weight and 14 parts by weight, respectively. .

Then the following ingredients:
Charge transport material: Enamine compound represented by the following structural formula (I) 18 parts by weight Binder resin: 20 parts by weight of polycarbonate resin (Mitsubishi Engineering Plastics Co., Ltd., product name: Z200)
Leveling agent: 0.02 part by weight of methylphenyl silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF50)
Solvent: 120 parts by weight of tetrahydrofuran mixed with primary dispersions (A), (B) and (C) for charge transport layer, respectively, and further filled with 50% by volume of ZrO ₂ beads (φ3 mm) as a dispersion medium 900 g of three kinds of coating liquids (A), (B) and (C) for the charge transport layer were prepared by dispersion treatment for 15 hours in a 1,000 ml ball mill.

  The spray gun is filled with the obtained three kinds of coating liquids for charge transport layer, and the coating liquid for filler transport layer (A), (B) and (C) is ordered in order from the coating liquid having the lowest filler concentration. It apply | coated on the electric charge generation layer 3 provided previously. In addition, after apply | coating 1 type of coating liquid, before the coating film dried, the aluminum cylindrical support body of the electroconductive support body 1 was rotated at 60 rpm for 10 minutes, and was pre-dried. After applying the three types of coating solutions, they were dried with hot air at 120 ° C. for 60 minutes to form a charge transport layer 4 having a thickness of 30 μm consisting of three layers, and a photoreceptor having the structure shown in FIG. 1 was obtained.

A photoconductor sample for refractive index measurement was prepared in the same manner as described above.
The obtained photoconductor sample was cut in the film surface direction using a microtome (manufactured by Reichert-Nissei, model: ULTRACUT N) to prepare a sample for measurement, and an ellipsometer (manufactured by JA Woollam, model: M -2000 U), the refractive index in the film thickness direction of the charge transport layer was calculated.
The refractive index Na in the vicinity of the surface of the charge transport layer is 2.12, the refractive index Nb in the vicinity of the interface between the charge transport layer and the charge generation layer is 1.23, and the refractive index of the charge transport layer is determined from the charge generation layer side. It was found that the direction changed gradually from 1.23 to 2.12.

(Example 2)
Except that the amount of the silica particles in the charge transport layer coating solutions (A), (B) and (C) was 0.5 parts by weight, 5 parts by weight and 10 parts by weight, respectively, the same as in Example 1. To obtain a photoreceptor.
When the refractive index of the charge transport layer was measured in the same manner as in Example 1, it was found that the charge transport layer changed in steps from 1.15 to 1.94 in the film thickness direction from the charge generation layer side.

(Example 3)
Photosensitivity is the same as in Example 1 except that the amount of the silica particles in the charge transport layer coating solutions (A), (B) and (C) is 1 part by weight, 14 parts by weight and 21 parts by weight, respectively. Got the body.
When the refractive index of the charge transport layer was measured in the same manner as in Example 1, it was found that the charge transport layer changed in steps from 1.25 to 2.43 in the film thickness direction from the charge generation layer side.

Example 4
Photosensitization was carried out in the same manner as in Example 1 except that 10 parts by weight of the enamine compound represented by the following structural formula (II) was used instead of 18 parts by weight of the enamine compound represented by the structural formula (I) as the charge transport material. Got the body.
The enamine compound represented by the structural formula (II) was produced by the method described in Japanese Patent No. 4101668.
The refractive index of the charge transport layer was measured in the same manner as in Example 1. As a result, it was found that the charge transport layer changed stepwise from 1.30 to 2.24 in the film thickness direction from the charge generation layer side.

(Comparative Example 1)
A charge transport layer coating liquid is prepared without using a charge transport layer primary dispersion containing a filler, and the resulting charge transport layer coating liquid is used to form an undercoat layer and a charge generation layer. A photoconductor was obtained in the same manner as in Example 1 except that the charge transport layer was formed by the same dip coating method.
The refractive index of the charge transport layer was measured in the same manner as in Example 1, and it was 1.28.

(Comparative Example 2)
One kind of charge transport layer primary dispersion with 8 parts by weight of silica particles as a filler is prepared, and one kind of charge transport layer coating solution is prepared by mixing this, and the resulting charge transport is obtained. A photoconductor was obtained in the same manner as in Example 1 except that the charge transport layer was formed by the same dip coating method as that used for forming the undercoat layer and the charge generation layer.
When the refractive index of the charge transport layer was measured in the same manner as in Example 1, it was 1.75.

(Comparative Example 3)
One kind of primary dispersion for charge transport layer with 20 parts by weight of silica particles as a filler is prepared, and one kind of charge transport layer coating liquid is prepared by mixing the primary dispersion. A photoconductor was obtained in the same manner as in Example 1 except that the charge transport layer was formed by the same dip coating method as that used for forming the undercoat layer and the charge generation layer.
When the refractive index of the charge transport layer was measured in the same manner as in Example 1, it was 2.32.

  The obtained photoreceptors of Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to (a) accelerated fatigue test and (b) actual machine printing test.

(A) Accelerated fatigue test Digital copying machine modified for accelerated fatigue test and provided with a surface potential meter (Model: MODEL344 manufactured by Trek Japan Co., Ltd.) so that the surface potential of the photoreceptor in the image forming process can be measured. (Sharp Co., Ltd., model: MX-M450N) mounted with a photoconductor, under high temperature / high humidity (H / H, 35 ° C./85%) environment with an exposure amount of 0.6 μJ / cm ² The surface potential VL (V) on the photosensitive member at the time of irradiation was measured (initial charging voltage -600 V, exposure development time 70 msec), and VL (V) at the time of exposure after repeating charge-exposure-static discharge 30,000 times The electrical characteristics were compared repeatedly with ΔVL (V) as the difference from VL (V) at the first (initial) exposure.

(B) Actual machine durability test In order to evaluate the durability of each characteristic by mounting a photoconductor on a digital copying machine (manufactured by Sharp Corporation, model: MX-M450N), sensitivity characteristics at the end of 300K sheets of actual shooting aging, Image characteristics and printing durability were evaluated.
Sensitivity characteristics (electrical characteristics) were evaluated based on the surface potential upon irradiation with an exposure amount of 0.6 μJ / cm ² .

Image characteristics were evaluated by microscopic observation of dot (DOT) reproducibility when printed at 1200 dpi.
(Evaluation criteria)
G (GOOD): DOT can be reproduced. NG (NOT GOOD): Some DOT blur is observed, but there is no problem in actual use. B (BAD): DOT blur is large and can be visually confirmed on the image.

The scratch level was evaluated on the basis of the surface roughness on the surface of the photosensitive drum after 300K sheets were actually aged. Using a surface roughness measuring machine (Surfcom 1400D, manufactured by Tokyo Seimitsu), Rz (10-point average roughness) and Pc (peak count) were used as indices.
(Evaluation criteria)
Scratch level 1: Rz: 0.6 or less and Pc: 10 or less
2: Rz: 0.8 or less and Pc: 20 or less
3: Rz: 1.0 or less and Pc: 20 or less
4: Rz: 1.5 or less and Pc: 30 or less
5: Rz: 1.5 or more or Pc: 30 or more The printing durability (durability) was evaluated on the basis of the amount of film reduction (μm / 100 K rotation) after 100 K rotation of the photoreceptor.
The obtained results are shown in Table 1 together with the refractive index of the charge transport layer.

From the results shown in Table 1, the photoreceptor of the present invention in which the charge transport layer having a refractive index N that gradually decreases from the vicinity of the surface of the charge transport layer to the vicinity of the interface with the charge generation layer (Examples 1 to 4). ) Is excellent in printing durability and can be stably operated over a long period of time with high resolution.
On the other hand, conventional photoreceptors (Comparative Examples 1 to 3) in which a charge transport layer having no refractive index N that gradually decreases from the vicinity of the surface of the charge transport layer toward the vicinity of the interface with the charge generation layer are laminated. It can be seen that the printing durability, resolution and long-term stable operation are inferior to the photoreceptor of the present invention. Specifically, when the refractive index of the charge transport layer is low, that is, when the filler content is low, the effect of improving the original printing durability of the filler is not exhibited, and the surface of the photoreceptor is likely to be scratched. Yes (see Comparative Example 1). On the other hand, when the refractive index of the charge transport layer is high, that is, when the filler content is large, the surface of the photoreceptor is hardly scratched, but the electrical characteristics (sensitivity characteristics) are reduced (Comparative Example 2 and 2). 3).

DESCRIPTION OF SYMBOLS 1 Conductive support body 2 Undercoat layer 3 Charge generation layer 4 Charge transport layer 5 Laminated type photosensitive layer

20 Image forming apparatus 21 Electrophotographic photosensitive member 22 Rotating axis (photosensitive member rotating shaft)
23, 29 Arrow 24 Charging means (charger)
24a Charging roller 24b Bias power supply 25 Developing means (developer)
25a Developing roller 25b Casing 26 Transfer means (transfer device)
27 Cleaning means (cleaner)
27a Cleaning blade 27b Recovery casing 28 Exposure means 28a Light 30 Recording material (transfer paper)
31 Fixing means (fixing device)
31a Heating roller 31b Pressure roller

Claims (6)

On the conductive support, an undercoat layer, a charge generation layer containing a charge generation material, and a charge transport layer containing at least a charge transport material and a filler are sequentially laminated,
The refractive index N of the charge transport layer is
(1) The following formula:
Na> Nb
(Wherein Na represents the refractive index near the surface of the charge transport layer and Nb represents the refractive index near the interface of the charge transport layer with the charge generation layer) and (2) An electrophotographic photosensitive member characterized by a stepwise decrease from the vicinity of the surface of the charge transport layer toward the vicinity of the interface between the charge transport layer and the charge generation layer.   The refractive index Na in the vicinity of the surface of the charge transport layer is 1.90 to 2.50, and the refractive index Nb in the vicinity of the interface between the charge transport layer and the charge generation layer is 1.10 to 1.40. The electrophotographic photosensitive member according to claim 1.   The charge transport layer has a multilayer structure of at least three layers parallel to the conductive support, and the filler content in the intermediate layer of the multilayer structure is larger than that of the adjacent layer on the charge generation layer side. The electrophotographic photosensitive member according to claim 1, wherein the electrophotographic photosensitive member is less than an adjacent layer on the surface side of the charge transport layer.   The electrophotographic photosensitive member according to claim 1, wherein the filler is silica particles. The charge transport material has the following structural formula (I):
The electrophotographic photosensitive member according to any one of claims 1 to 4, which is an enamine compound represented by the formula:   An electrophotographic photosensitive member according to claim 1, a charging means for charging the electrophotographic photosensitive member, and exposing the charged electrophotographic photosensitive member to form an electrostatic latent image. Exposure means; development 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 material; An image forming apparatus comprising: a fixing unit that fixes a toner image on the recording material to form an image; and a cleaning unit that removes and collects toner remaining on the electrophotographic photosensitive member.