JP4778914B2 - Electrophotographic photosensitive member and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an electrophotographic photosensitive member and an image forming apparatus using the same. More particularly, the present invention relates to an electrophotographic photosensitive member used for electrophotographic image formation and an image forming apparatus using the same.

  In an electrophotographic image forming apparatus (hereinafter also referred to as an electrophotographic apparatus) that is frequently used as a copying machine, a printer, a facsimile machine, or the like, an image is formed as follows. That is, the surface of an electrophotographic photoreceptor (hereinafter also simply referred to as a photoreceptor) is uniformly charged by a charging means such as a charging roller. Next, the surface is exposed to form an electrostatic latent image corresponding to the image information. Next, the electrostatic latent image is developed with fine particles called toner to form a visible toner image. Further, the formed toner image is transferred and fixed on a transfer material such as transfer paper, whereby an image is formed on the transfer material. The photoconductor after the toner image is transferred is cleaned by a cleaning blade or the like, so that toner remaining on the surface of the photoconductor without being transferred onto the transfer material during the transfer operation is removed.

  An electrophotographic photoreceptor is formed by laminating a photosensitive layer containing a photoconductive material on a conductive support. Conventionally, inorganic photoconductive materials such as selenium have been used as photoconductive materials. However, in recent years, organic photoreceptors are widely used because of environmental considerations, manufacturing costs, and freedom of materials. Advantages of the organic photoreceptor are that materials corresponding to various exposure light sources from visible light to infrared light can be selected, materials free from environmental pollution can be selected, and manufacturing costs are low. On the other hand, the disadvantages are that the mechanical strength is weak and foreign substances are likely to adhere, the chemical durability is weak, the electrostatic characteristics of the photoreceptor are deteriorated when a large number of sheets are printed, and the surface is scratched. Further, as the organic photoreceptor, a function-separated type photoreceptor in which a charge generation function and a charge transport function are respectively assigned to different substances is used. The functional separation type photoreceptor is a single-layer type photosensitive member provided with a photosensitive layer in which a charge generation material having a charge generation function and a charge transport material having a charge transport function are co-dispersed in a binder resin called a binder resin. And a multi-layer type photoreceptor having a photosensitive layer in which a charge generation layer in which a charge generation material is dispersed and a charge transport layer in which a charge transport material is dispersed are laminated.

  Multilayer photoreceptors dominate organic photoreceptors because they have the advantage that the photosensitive layer can be easily designed and an electrophotographic photoreceptor excellent in sensitivity and stability can be produced relatively easily. On the other hand, a single-layer type photoreceptor has a single photosensitive layer, so it has higher productivity than a laminated photoreceptor, can be manufactured at a low manufacturing cost, and ozone, which is a harmful substance, is generated during charging. Since it can be used in a difficult positive charging process, it has begun to be put into practical use.

  The performance required for the electrophotographic photosensitive member in the image forming process is excellent in electrical characteristics such as chargeability, charge retention ability, photosensitivity and responsiveness, and small fluctuations in characteristics due to environmental changes such as temperature and humidity. It is excellent in environmental stability. In the electrophotographic apparatus, the above-described image forming process is repeated many times. Therefore, the photoreceptor is required to have excellent wear resistance, that is, mechanical durability in repeated use, and to have the above-described electrical characteristics stable even in repeated use, and excellent in electrical durability. When the photosensitive layer is formed by coating, the coating solution is required to be physically and chemically stable in order to improve production efficiency.

Further, as described above, since the electrophotographic apparatus is required to have high durability, the photoreceptor is also required to have improved electrical durability and mechanical durability. The electrical durability and mechanical durability of the photosensitive member are affected by the film strength, that is, the printing durability of the photosensitive layer serving as the surface layer of the photosensitive member. If the film strength of the photosensitive layer is low and the printing durability is not sufficient, the surface of the photosensitive layer is scraped off by repeated use, and the film thickness of the photosensitive layer decreases. As a result, the photoreceptor tends to cause characteristic changes such as a decrease in charging potential and an increase in residual potential.

  As prior art for improving the printing durability of the photosensitive layer, there is a technique for providing a protective layer on the outermost surface layer of the photoreceptor (Patent Document 1), a technique for imparting lubricity to the protective layer (Patent Document 2), and protection. A technique for curing a layer (Patent Document 3) and a technique for containing filler particles in a protective layer (Patent Document 4) are known. These protective layers are basically desired to be as thin as possible from the viewpoint of not inhibiting the basic function of the photosensitive layer. In addition, the provision of the protective layer causes various harmful effects. For example, when the photoreceptor and the protective layer have a discontinuous layer structure, the protective layer may be peeled off due to long-term use. In addition, the exposed portion potential increases due to repeated use over a long period of time. On the contrary, when the protective layer and the photosensitive layer are dissolved in a continuous layer structure, that is, when the photosensitive layer is dissolved by the protective layer coating solution to be subsequently applied, the image characteristics of the photosensitive layer are deteriorated depending on the dissolution state.

  Among them, the technology for incorporating filler particles gives a new influencing factor on the characteristics of the photoreceptor, that is, control of the dispersibility of the filler particles. That is, the characteristics cannot be defined only by the amount of filler particles added. Patent Document 5 discloses that the printing durability is improved by adding up to about 0.1 to 10% by weight with respect to the total solid content of the protective layer. However, for example, it can be easily estimated that protective layers having completely different dispersion states give different image characteristics / electrical characteristics / printing durability to the photoreceptor even when the addition amount is the same. In addition, when the dielectric constant of the protective layer is nonuniform, image thickening and toner scattering may occur at the edge when black solid images are output, and the dispersion state of the filler particles inside the protective layer is thus considered to be a photoconductor. It can be seen that this greatly affects the properties of From this, if the dispersibility of the filler particles in the coating liquid is improved, the dispersion of the filler particles in the protective layer can be made uniform, and at the same time, a surface layer having a uniform surface energy can be formed. Therefore, if an appropriate dispersion state can be created in the coating solution, the above-described adverse effects are suppressed.

When printing durability is improved, as an adverse effect, image blur and image flow due to the influence of a charged product or the like adhering to the surface of the photoreceptor (drum) occur particularly under high temperature and high humidity. In order to eliminate these adverse effects, a technique for providing a uniform and inactive drum surface by a method of designing a photoconductor that “shaves” to some extent or a method of devising a cleaning means is disclosed (Patent Document 6).
In the function-separated type photoconductor, if a wear-resistant effect can be imparted to the outermost surface, an extra step is not included in the production process, so that there is a great cost advantage compared to the case where a protective layer is imparted. Further, it is possible to avoid the above-described adverse effects caused by providing the photosensitive layer and the protective layer in a stacked manner. However, on the other hand, it is necessary to consider new issues on the system. For example, when filler particles are added to improve the printing durability, traps over the entire charge transport layer of several tens of μm occur between the filler particles and the polymer bulk (binder resin) contained in the photosensitive layer. As a result, the risk of increasing the residual potential of the exposed portion becomes extremely large as compared with the case where it is added to the protective layer. In addition, in the case of a multilayer photoreceptor, image defects may occur due to non-uniformity of the layer in the vicinity of the interface between the charge generation layer and the charge transport layer, which may be due to the interaction between the filler particles and the charge generation layer. is there.

In addition, an image forming apparatus using an organic photoreceptor has been increasingly demanded for a printer or the like as an image output terminal in recent years. There is also a need for an image forming apparatus that can output a high-definition digital image. With such digitization, as a light source corresponding to the recording method, for example, a small and inexpensive semiconductor laser or light emitting diode with high reliability is often used. The light emission wavelength of the semiconductor laser that is most frequently used at present is in the near-infrared light region near 780 to 800 nm. The emission wavelength of a typical light emitting diode is 740 nm.

  On the other hand, recently, purple to blue short-wavelength lasers or light-emitting diodes having a transmission wavelength of 400 to 500 nm have been developed and marketed as exposure light sources corresponding to this digital recording system.

For example, when a short wavelength laser whose transmission wavelength is about half that of a conventional near infrared laser is used as an exposure light source, the following formula (2)
D = 1.22λ / NA (2)
(D: Spot diameter on photoconductor, λ: Laser wavelength, NA: Lens numerical aperture)
As shown in the figure, it is possible to theoretically make the spot diameter of the laser beam on the photoreceptor considerably small. Therefore, these lasers are very useful for increasing the writing density of the latent image, that is, the resolution.

  Such a short wavelength laser is greatly expected to improve the recording density of the optical disk. However, it was hardly expected as an exposure light source for electrophotography.

  This is because conventional electrophotographic photoreceptors do not exhibit sensitivity in this wavelength range for the following reasons. Conventional laminated type photoreceptors are generally put into practical use in which a charge generation layer and a charge transport layer are laminated in this order on a conductive substrate. Therefore, if a charge generating material that absorbs at a wavelength of 500 nm or less is used, the exposure should generally be sensitive to exposure of a short wavelength laser of 500 nm or less. However, since the charge transport layer actually absorbs light having a wavelength of 500 nm or less, the exposure light of the short wavelength laser used as the exposure light source is absorbed before reaching the charge generation layer. Therefore, the laminated photoreceptor does not show sensitivity in this wavelength range. Furthermore, short wavelength lasers emit high-intensity light with uniform wavelength components, so that the exposed charge transporting material and charge generating material are likely to be altered, and the sensitivity of the photoreceptor is reduced by long-term use, and high image quality cannot be maintained. There is also a problem.

  An organic photoreceptor having a surface layer containing filler particles is likely to cause laser light scattering. A photoconductor using a short wavelength laser using an organic fine particle filler as an organic photoconductor has been proposed (Patent Document 7). However, although there is an effect of improving sharpness, a surface layer containing filler particles is formed. In this case, the dispersion stability of the filler particles in the coating liquid is low, and the particles are aggregated to easily form coarse aggregated particles. These agglomerated particles increase the scattering of laser light and prevent the formation of a surface layer having uniform characteristics. As a result, an abnormal image such as a black spot occurs in the electrophotographic image, which causes a problem that the image quality is remarkably deteriorated. In addition, this is a tandem method used in color image formation (a development method that uses a plurality of photoconductors to superimpose images), which further promotes laser light scattering, resulting in image blurring and reduced sharpness. Cause it.

Japanese Unexamined Patent Publication No. 57-30846 JP-A-1-23259 JP 61-72256 A JP-A-1-172970 JP-A-1-205171 JP 2004-61560 A JP 2005-221720 A

The object of the present invention is to provide a high-quality image output that is excellent in abrasion resistance / cleaning property / electric durability and is free of abnormal images even when used for a long period of time under exposure to light having a short wavelength. It is an object to provide a possible electrophotographic photosensitive member and an image forming apparatus using the same.

Thus, according to the present invention, an electrophotographic photosensitive member having at least a charge generation layer and a charge transport layer in this order on a conductive substrate,
The charge transport layer that is the outermost surface layer of the electrophotographic photoreceptor contains filler particles,
Filler particles in the outermost surface layer are represented by the following formula (1).
1.0 × 10 ⁻³ ≦ (df × b ³ ) / (dm × a ³ ) ≦ 2.5 × 10 ^-2 (1)
(In the formula, a means the average distance between filler particles (nm), b means the average filler particle diameter (nm), df means the density of filler particles (g / cm ³ ), and dm is the maximum. It is a uniform dispersion state satisfying the average density (g / cm ³ ) of the solid content of the surface layer,
An electrophotographic photosensitive member is provided in which the charge generation layer includes a material capable of generating charge by exposure light having an oscillation wavelength of 350 to 500 nm.

  Furthermore, according to the present invention, there is provided an image forming apparatus comprising a photoconductor, a charging unit, an exposure unit, a developing unit, and a transfer unit, wherein the photoconductor includes the electrophotographic photoconductor.

  According to the present invention, there is provided an electrophotographic photosensitive member that has excellent printing durability, retains electrical stability over a long period of use, can form an image with good sharpness, and has no defects such as abnormal images. The used image forming apparatus can be provided.

Hereinafter, the present invention will be described in detail.
FIG. 1 is a partial cross-sectional view showing a simplified configuration of an electrophotographic photosensitive member 1 according to a first embodiment of the present invention. The electrophotographic photoreceptor 1 (hereinafter abbreviated as “photoreceptor”) of this embodiment is a cylindrical conductive substrate 11 made of a conductive material and a layer laminated on the outer peripheral surface of the conductive substrate 11. A charge generation layer 12 containing a charge generation material, and a charge transport layer 13 which is further laminated on the charge generation layer 12 and contains a charge transport material. The charge generation layer 12 and the charge transport layer 13 constitute a photosensitive layer 14. That is, the photoreceptor 1 is a multilayer photoreceptor.

(Conductive substrate)
The conductive substrate 11 serves as an electrode of the photoreceptor 1 and also functions as a support member for the other layers 12 and 13. In addition, although the shape of the electroconductive base | substrate 11 is cylindrical shape in FIG. 1, it is not limited to this, A column shape, a sheet form, an endless belt shape, etc. may be sufficient.

  As the conductive material constituting the conductive substrate 11, for example, a single metal such as aluminum, copper, zinc, nickel, or titanium, or an alloy such as an aluminum alloy or stainless steel can be used. Also, without being limited to these metal materials, metal (aluminum, gold, silver, copper, zinc, nickel, titanium) foil on the surface of polymer materials such as polyethylene terephthalate, nylon or polystyrene, hard paper or glass Laminated, metal (aluminum, gold, silver, copper, zinc, nickel, titanium) vapor deposited material, or conductive polymer, tin oxide, indium oxide or other conductive compound layer deposited or applied A thing etc. can also be used. These conductive materials are used after being processed into a predetermined shape.

If necessary, the surface of the conductive substrate 11 is irregularly reflected within a range that does not affect the image quality, such as anodic oxide film treatment, surface treatment with chemicals or hot water, coloring treatment, or roughening the surface. Processing may be performed. In an electrophotographic process using a laser as an exposure light source, the wavelengths of the laser light are uniform. For this reason, the laser beam reflected on the surface of the photoconductor and the laser beam reflected inside the photoconductor cause interference, and interference fringes due to this interference may appear on the image, resulting in an image defect. By performing the above-described treatment on the surface of the conductive substrate 11, image defects due to interference of laser light having the same wavelength can be prevented.

(Charge generation layer)
The charge generation layer 12 contains, as a main component, a charge generation material that generates charges by absorbing light. The main component means that the component contains an amount capable of expressing its main function. Substances effective as a charge generation substance include monoazo pigments, bisazo pigments, azo pigments such as trisazo pigments, indigo pigments such as indigo or thioindigo, perylene pigments such as peryleneimide or perylene anhydride, anthraquinone or Polycyclic quinone pigments such as pyrenequinone, phthalocyanine pigments such as metal phthalocyanine or metal-free phthalocyanine, triphenylmethane dyes represented by methyl violet, crystal violet, knight blue, victoria blue, erythrosine, rhodamine B, rhodamine 3R Acridine dyes such as acridine orange and frappeosin, thiazine dyes such as methylene blue and methylene green, oxazine dyes such as capri blue and meldra blue, Qualylium dyes, pyrylium salts and thiopyrylium salts, thioindigo dyes, bisbenzimidazole dyes, quinacridone dyes, quinoline dyes, lake dyes, azo lake dyes, dioxazine dyes, azurenium dyes, triallylmethane dyes, xanthenes Examples thereof include organic photoconductive materials such as cyano dyes, cyanine dyes, and triphenylmethane dyes, and inorganic photoconductive materials such as selenium and amorphous silicon.

Among the charge generation materials described above, it is preferable to use an azo pigment, a perylene pigment, a multi-sensitive quinone pigment, or the like having high sensitivity characteristics in the wavelength region of 350 to 500 nm as the charge generation material.
One of these charge generation materials may be used alone, or two or more of these charge generation materials may be used in combination.
Examples of optional components other than the charge generation material contained as the main component include sensitizing dyes, binder resins, antioxidants, leveling agents, and plasticizers.

  Examples of sensitizing dyes include triphenylmethane dyes such as methyl violet, crystal violet, knight blue and victoria blue, erythrosine, rhodamine B, rhodamine 3R, acridine dyes such as acridine orange and frapeosin, methylene blue and Examples include thiazine dyes typified by methylene green, oxazine dyes typified by capri blue and meldra blue, cyanine dyes, styryl dyes, pyrylium salt dyes, and thiopyrylium salt dyes. The sensitizing dye is preferably used in a proportion of 10 parts by weight or less, more preferably in a proportion of 0.5 to 2.0 parts by weight with respect to 100 parts by weight of the charge generating substance.

  As a method for forming the charge generation layer 12, the above-described charge generation material is vacuum-deposited on the surface of the conductive substrate 11, or the charge generation layer coating obtained by dispersing the above-described charge generation material in a suitable solvent. The method etc. which apply | coat a liquid to the surface of the electroconductive base | substrate 11 are mentioned. Among these, in a binder resin solution obtained by mixing a binder resin as a binder in a solvent, a charge generating material is dispersed by a conventionally known method to prepare a coating solution for a charge generating layer, A method of applying the obtained coating solution to the surface of the conductive substrate 11 is preferably used. Hereinafter, this method will be described.

Examples of the binder resin used for the charge generation layer 12 include polyester resin, polystyrene resin, polyurethane resin, phenol resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate resin, and polyarylate resin. , Phenoxy resins, polyvinyl butyral resins and polyvinyl formal resins, and copolymer resins containing two or more of the repeating units constituting these resins. Specific examples of the copolymer resin include insulating resins such as vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, and acrylonitrile-styrene copolymer resin. Can do. The binder resin is not limited to these, and a commonly used resin can be used as the binder resin. One kind of these resins may be used alone, or two or more kinds thereof may be mixed and used.

  Examples of the solvent for the charge generation layer coating solution include halogenated hydrocarbons such as tetrachloropropane and dichloroethane, ketones such as acetone, isophorone, methyl ethyl ketone, acetophenone, and cyclohexanone, and esters such as ethyl acetate, methyl benzoate, and butyl acetate. , Tetrahydrofuran (THF), dioxane, dibenzyl ether, ethers such as 1,2-dimethoxyethane or dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, tetralin, diphenylmethane, dimethoxybenzene, dichlorobenzene , Sulfur-containing solvents such as diphenyl sulfide, fluorine-based solvents such as hexafluoroisopropanol, and aprotic polar solvents such as N, N-dimethylformamide or N, N-dimethylacetamide are used. . Moreover, the solvent which mixed 2 or more types of these solvents can also be used. Among these solvents, non-halogen organic solvents are preferably used in consideration of the global environment.

  In the charge generation layer 12 including the charge generation material and the binder resin, the ratio W1 / W2 between the weight W1 of the charge generation material and the weight W2 of the binder resin is 10/100 (10/100). It is preferable that it is 100 or less (100/10) or less. If the ratio W1 / W2 is less than 10/100, the sensitivity of the photoreceptor 1 may be lowered, which is not preferable. When the ratio W1 / W2 exceeds 100/10, not only the film strength of the charge generation layer 12 is decreased, but also the dispersibility of the charge generation material is decreased and coarse particles may be increased. For this reason, surface charges other than those that should be erased by exposure are reduced, and image fogging, particularly fogging of an image called black spots where toner adheres to a white background and minute black spots are formed may increase. The ratio W1 / W2 is more preferably 10/40 or more and 100/40 or less.

  The charge generation material may be previously pulverized by a pulverizer before being dispersed in the binder resin solution. Examples of the pulverizer used for the pulverization treatment include a ball mill, a sand mill, an attritor, a vibration mill, and an ultrasonic disperser.

  Examples of the disperser used when dispersing the charge generating substance in the binder resin solution include a paint shaker, a ball mill, and a sand mill. As a dispersion condition at this time, it is preferable to select an appropriate condition so that impurities are not mixed due to wear of members constituting the container and the disperser.

  Examples of the coating method for the charge generation layer coating liquid include a spray method, a bar coating method, a roll coating method, a blade method, a ring method, and a dip coating method. Among these coating methods, an optimum method can be selected in consideration of the physical properties and productivity of coating. Among these coating methods, the dip coating method is a method in which a substrate is immersed in a coating tank filled with a coating solution, and then a layer is formed on the surface of the substrate by pulling it up at a constant speed or a sequentially changing speed. It is. As described above, the dip coating method is relatively simple and excellent in terms of productivity and cost. Therefore, it is frequently used for producing an electrophotographic photosensitive member. In addition, in order to stabilize the dispersibility of a coating liquid, the apparatus used for the dip coating method may be provided with a coating liquid dispersing apparatus represented by an ultrasonic generator.

The film thickness of the charge generation layer 12 is preferably 0.05 μm or more and 5 μm or less, and more preferably 0.1 μm or more and 1 μm or less. If the film thickness of the charge generation layer 12 is less than 0.05 μm, the light absorption efficiency is lowered, and the sensitivity of the photoreceptor 1 may be lowered, which is not preferable. If the thickness of the charge generation layer 12 exceeds 5 μm, the charge transfer within the charge generation layer 12 becomes the rate-determining step in the process of erasing the surface charge of the photosensitive layer 14, and the sensitivity of the photoreceptor 1 may decrease. It is not preferable.

(Charge transport layer)
A charge transport layer 13 is provided on the charge generation layer 12. The charge transport layer 13 is mainly composed of a charge transport material having the ability to accept and transport the charge generated by the charge generation material contained in the charge generation layer 12, and filler particles that improve the durability of the photoreceptor. In addition, it can optionally comprise a charge transport material and a binder resin that binds the filler particles. The binder resin is preferably in the range of 30-80% by weight. In addition to the binder resin, an antioxidant, an ultraviolet absorber, a leveling agent, a plasticizer, and the like can be given. As the charge transport material, a hole transport material and an electron transport material 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, 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, enamine derivatives, benzidine derivatives and the like. Examples of the polymer having a group derived from these compounds in the main chain or side chain include poly-N-vinylcarbazole, poly-1-vinylpyrene, ethylcarbazole-formaldehyde resin, triphenylmethane polymer, and poly-9-vinyl. Anthracene etc. or polysilane etc. are mentioned.

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.
The charge transport materials are not limited to those listed here, and can be used alone or in admixture of two or more.

However, in the laminated photoconductor, it is desirable to appropriately select a charge transport material or a binder resin that is transparent to the emission wavelength of the semiconductor laser used as described above. Specifically, among the above-described charge transport materials, arylamine-based and benzidine-based compounds that do not absorb in the wavelength region of 350 to 500 nm are preferable.
The binder resin constituting the charge transport layer 13 is not particularly limited, and any resin known in the art can be used. In particular, a resin containing polycarbonate as a main component is preferable from the viewpoint of film strength.

Examples of resins other than polycarbonate include vinyl polymer resins such as polymethyl methacrylate resin, polystyrene resin, polyvinyl chloride resin, and the like, copolymer resins containing two or more of repeating units constituting these, and polyester resins, Polyester carbonate resin, polysulfone resin, phenoxy resin, epoxy resin, silicone resin, polyarylate resin, polyamide resin, methacrylic resin, acrylic resin, polyether resin, polyurethane resin, polyacrylamide resin, phenol resin, polyphenylene oxide resin, etc. . Moreover, the thermosetting resin which partially bridge | crosslinked these resin is also mentioned. These resins may be used alone or in a mixture of two or more.

  Furthermore, the filler particles constituting the charge transport layer 13 are roughly classified into organic fillers and inorganic fillers centered on metal oxides. In general, organic fillers, mainly fluorine-based materials, are used for the purpose of controlling the wettability of the photoreceptor surface and suppressing adhesion of foreign substances, etc., and inorganic fillers are mainly used for the purpose of improving printing durability. Used for. In the present invention, it is preferable to use an inorganic filler. As the inorganic filler, a material having high hardness as a material and easily dispersible in the binder resin is preferable. Examples thereof include oxides such as silicon oxide (silica), titanium oxide, zinc oxide, calcium oxide, and aluminum oxide (alumina), and nitride compounds such as silicon nitride and aluminum nitride. In particular, silicon oxide (silica) having a small difference from the refractive index of components other than the filler particles is suitable as a result of considering light scattering in the charge transport layer.

The filler particles are added in an amount within the range defined by the following formula (1), taking into account the dispersion state, because the dispersion state greatly affects the wear resistance and electrical stability. . When the amount is within this range, a photoreceptor showing good printing durability can be obtained.
1.0 × 10 ⁻³ ≦ (df × b ³ ) / (dm × a ³ ) ≦ 2.5 × 10 ^-2 (1)
In the above formula, a is the average distance between filler particles (nm), b is the average filler particle diameter (nm), df is the density of filler particles (g / cm ³ ), and dm is the average density of solid content in the outermost surface layer ( g / cm ³ ). In addition, a, b, df, and dm can be measured by the following method.

In addition, it is preferable to accurately measure a by TEM cross-sectional observation, but if a uniform dispersion state can be confirmed, a may be obtained as a calculated value from the amount of filler particles added and the volume of the coating film as a medium. .
Although b can be calculated | required correctly by SEM observation, if it is a commercially available filler particle, you may quote from a catalog value.
df may be calculated by measuring the volume and weight of the filler particles before production, or may be a catalog value for a commercial product.
The dm is obtained by measuring and calculating the volume and weight of the coating film.
Here, the solid content of the outermost surface layer is a coating film of the charge transport layer obtained by applying a coating liquid and drying the solvent to solidify.

  The uniform dispersion state means that the state close to the primary particle diameter in FIG. 2 in the coating solution is fixed after solidifying as a coating film, and the average particle diameter of the fine particles in the coating film is the same as before the preparation. This refers to the state that is almost equal to the primary particle size of the raw material fine particles. That is, in this equation, filler particles having a true sphere and no particle size distribution are assumed in a homogeneous solid medium, and these particles are uniformly dispersed in the medium. That is, if the addition amount / particle diameter / density of the filler and the density of the medium (more precisely, the density of the entire solid content including the filler) are determined, a: the average distance between the filler particles is determined. By substituting the obtained value a into the formula (1), it can be determined whether or not the filler particles satisfy the formula (1).

  In other words, equation (1) assumes that the filler particles are uniformly “distributed”. Therefore, in this invention, the addition density | concentration of a filler particle is prescribed | regulated so that dispersion | distribution of the filler particle in a coating liquid / coating film may be uniform, and the said Formula (1) may be satisfy | filled.

  Here, a is preferably small in order to minimize the adverse effects on light scattering and electrical carriers (electrons and / or holes) in the system. Specifically, 400 nm or less (primary particle diameter) is preferable. More preferably, the range of a is 20 to 200 nm.

The range of b is preferably 5 to 100 nm, and more preferably 5 to 20 nm. Preferably the range of df is 1.5~7g / cm ^3, more preferably 1.5~3g / cm ^3. Preferably the range of dm is 1 to 2 g / cm ^3, more preferably 1-1.5 g / cm ^3.

  In adding the filler particles, various dispersion methods such as a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, or a paint shaker can be used to form a uniform particle dispersion state. In order to draw out the excellent characteristics of the electrophotographic photosensitive member, it is desired to grasp the dispersion state in the dispersion liquid for forming the coating film on the outermost surface of the electrophotographic photosensitive member or after the formation of the coating film. In FIG. 2, 3.1 parts by weight of the same coating liquid formulation (polycarbonate resin (Z400: manufactured by Teijin Chemicals) and 3.1 parts by weight of silica (TS-610: manufactured by Cabot Specialty Chemicals: primary particle diameter: 17 μm) were added to 55 parts of tetrahydrofuran. In the case where two types of dispersions were carried out in (. 8 parts by weight), the difference in the particle size distribution state in the coating liquid after the dispersion treatment was compared. In FIG. 2, ◆ indicates the particle size distribution of the silica particles in the primary dispersion coating solution for charge transport layer obtained by dispersing for 5 hours with a ball mill, and □ indicates the coating obtained by dispersing for 5 hours with a paint shaker. The particle size distribution of the silica particle in a liquid is shown. It can be seen that ♦ is stably dispersed to a state close to the primary particle diameter, while □ indicates that micron-order aggregates are formed. Although it is certain that □ indicates that an aggregate is formed by reaggregation, the detailed cause for obtaining this state has not been elucidated. The change in the aggregation state as shown in FIG. 2 directly corresponds to the electrical properties and surface uniformity of the final coating film, and the formation of a uniform dispersion in the dispersion and close to the primary particle diameter Reflected. Therefore, the ◆ dispersion method is preferable because an outermost surface layer having excellent durability can be formed as a result.

In the above, preferred examples of unaggregated filler particles have been given. However, an aggregate of filler particles may be used as long as the formula (1) is satisfied. In the case of an aggregate, “filler particles” in a, b, and df in the formula (1) shall be read as “aggregate”. Moreover, although the dispersion process by a paint shaker is performed on the conditions in which an aggregate is formed in the above, it can also be made to disperse | distribute to the state close | similar to a primary particle diameter by changing conditions.
In addition, the dispersion state of the filler particles in the coating liquid can be evaluated using, for example, a light scattering particle size distribution measuring apparatus.

  Various additives may be added to the charge transport layer 13 as necessary. For example, a plasticizer or a leveling agent may be added to the charge transport layer 13 in order to improve the film formability, flexibility, or surface smoothness. Examples of the plasticizer include biphenyl, biphenyl chloride, benzophenone, o-terphenyl, dibasic acid ester (for example, phthalic acid ester), fatty acid ester, phosphate ester, various fluorohydrocarbons, chlorinated paraffin, and epoxy type plasticizer. Etc. Examples of the surface modifier include a silicone leveling agent such as silicone oil, a fluororesin leveling agent, and the like.

  The charge transport layer 13 is formed in the same manner as in the case where the charge generation layer 12 is formed by coating, for example, in a suitable solvent, a charge transport material, a binder resin, filler particles, and, if necessary, the aforementioned additives. Is dissolved or dispersed to prepare a coating solution for a charge transport layer, and the resulting coating solution is applied onto the charge generation layer 12.

Examples of the solvent for the charge transport layer coating solution include aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, tetralin, diphenylmethane, dimethoxybenzene, monochlorobenzene, dichlorobenzene, and halogenated hydrocarbons such as dichloromethane and dichloroethane. Ethers such as tetrahydrofuran, dioxane, dibenzyl ether and dimethoxymethyl ether, ketones such as cyclohexanone, acetophenone and isophorone, esters such as methyl benzoate and ethyl acetate, sulfur-containing solvents such as diphenyl sulfide, hexafluoroisopropanol, etc. And aprotic polar solvents such as N, N-dimethylformamide. One of these solvents may be used alone, or two or more thereof may be mixed and used. In addition, a solvent such as alcohols, acetonitrile or methyl ethyl ketone can be further added to the above-mentioned solvent as necessary. Among these solvents, non-halogen organic solvents are preferably used in consideration of the global environment.

  Examples of the coating method for the charge transport layer coating solution include a spray method, a bar coating method, a roll coating method, a blade method, a ring method, and a dip coating method. Among these coating methods, the dip coating method is particularly excellent in various respects as described above, and is often used when the charge transport layer 13 is formed.

  The film thickness of the charge transport layer 13 is preferably 5 μm or more and 40 μm or less, and more preferably 10 μm or more and 30 μm or less. If the thickness of the charge transport layer 13 is less than 5 μm, the charge retention ability may be lowered, which is not preferable. If the thickness of the charge transport layer 13 exceeds 40 μm, image deterioration may occur, which is not preferable. Further, when a short wavelength laser is used as the exposure light source, it is preferably 5 μm or more and 20 μm or less, more preferably 10 μm or more and 16 μm or less. When the thickness is 5 μm or more and 20 μm or less, absorption and scattering of a short wavelength laser in the charge transport layer can be reduced, sharpness can be improved, residual potential can be reduced, and as a result, image deterioration can be suppressed.

(Photosensitive layer)
Each layer of the photosensitive layer 14 is added with one or more sensitizers such as an electron accepting substance and a dye in order to improve sensitivity and further suppress an increase in residual potential and fatigue due to repeated use. Also good.

  Examples of the electron acceptor include acid anhydrides such as succinic anhydride, maleic anhydride, phthalic anhydride, and 4-chloronaphthalic anhydride, cyano compounds such as tetracyanoethylene and terephthalmalondinitrile, and 4-nitrobenzaldehyde. Aldehydes, anthraquinones, anthraquinones such as 1-nitroanthraquinone, polycyclic or heterocyclic nitro compounds such as 2,4,7-trinitrofluorenone, 2,4,5,7-tetranitrofluorenone, or diphenoquinone compounds An electron withdrawing material or the like can be used. Moreover, what polymerized these electron-withdrawing materials can also be used.

  As the dye, for example, an organic photoconductive compound such as xanthene dye, thiazine dye, triphenylmethane dye, quinoline pigment or copper phthalocyanine can be used. These organic photoconductive compounds function as optical sensitizers.

  Further, an antioxidant or an ultraviolet absorber may be added to each layer of the photosensitive layer 14. In particular, it is preferable to add an antioxidant or an ultraviolet absorber to the charge transport layer 13. Thereby, deterioration with respect to oxidizing gas, such as ozone and nitrogen oxides, can be reduced. Moreover, the stability of the coating liquid when forming each layer by coating can be enhanced.

Moreover, it is preferable to contain antioxidant in the outermost surface layer containing a filler particle. The outermost surface layer containing filler particles is easily oxidized by an active gas during charging of the photoreceptor, such as ozone or NOx, and image blur is likely to occur. Therefore, the presence of an antioxidant can prevent the occurrence of image blur. As the antioxidant, a phenol compound, a hydroquinone compound, a tocopherol compound, an amine compound, or the like is used. Among these, a hindered phenol derivative or a hindered amine derivative, or a mixture thereof is preferably used. The total amount of these antioxidants used is preferably 0.1 to 50 parts by weight per 100 parts by weight of the charge transport material, 0.2 to 1
More preferably, it is 0 part by weight. If the amount of the antioxidant used is less than 0.1 parts by weight, it may not be possible to obtain a sufficient effect for improving the stability of the coating solution and improving the durability of the photoreceptor. On the other hand, if it exceeds 50 parts by weight, the photoreceptor characteristics may be adversely affected.

(Other photoconductor configuration examples)
FIG. 3 is a partial cross-sectional view showing a simplified configuration of the electrophotographic photosensitive member 2 according to the second embodiment of the present invention. The electrophotographic photosensitive member 2 is similar to the electrophotographic photosensitive member 1, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.
What should be noted in the electrophotographic photoreceptor 2 is that an intermediate layer (undercoat layer) 15 is provided between the conductive substrate 11 and the photosensitive layer 14.

  If there is no intermediate layer 15 between the conductive substrate 11 and the photosensitive layer 14, charges may be injected from the conductive substrate 11 into the photosensitive layer 14. This charge lowers the chargeability of the photosensitive layer 14, thereby reducing the surface charge other than the portion to be erased by exposure, and as a result, defects such as fogging may occur in the image. In particular, when an image is formed using a reversal development process, a toner image may be formed by attaching toner to a portion where surface charge is reduced by exposure. For this reason, when the surface charge is reduced due to factors other than exposure, fogging of an image called black spot where toner adheres to a white background and a minute black spot is formed occurs, and as a result, the image quality may be significantly deteriorated. That is, when there is no intermediate layer 15 between the conductive substrate 11 and the photosensitive layer 14, the chargeability in a minute region is reduced due to a defect in the conductive substrate 11 or the photosensitive layer 14. The image may be fogged, resulting in a significant image defect.

  In the electrophotographic photosensitive member 2, since the intermediate layer 15 is provided between the conductive substrate 11 and the photosensitive layer 14 as described above, injection of charges from the conductive substrate 11 to the photosensitive layer 14 is prevented. it can. Accordingly, it is possible to prevent the chargeability of the photosensitive layer 14 from being lowered, to suppress the reduction of surface charges other than the portion to be erased by exposure, and to prevent the occurrence of defects such as fogging on the image.

Further, by providing the intermediate layer 15, the surface of the conductive substrate 11 can be covered and a uniform surface can be obtained, so that the film formability of the photosensitive layer 14 can be improved. In addition, the peeling of the photosensitive layer 14 from the conductive substrate 11 can be suppressed, and the adhesion between the conductive substrate 11 and the photosensitive layer 14 can be improved.
For the intermediate layer 15, a resin layer or an alumite layer made of various resin materials is used.

  The resin material constituting the resin layer includes 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, and polyamide. Examples thereof include resins such as resins, and copolymer resins containing two or more of the repeating units constituting these resins. Moreover, casein, gelatin, polyvinyl alcohol, ethyl cellulose, and the like are also included. 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, so-called copolymer nylon obtained by copolymerizing 6-nylon, 6,6-nylon, 6,10-nylon, 11-nylon, 2-nylon, 12-nylon, and the like, and N Examples thereof include resins obtained by chemically modifying nylon such as -alkoxymethyl-modified nylon and N-alkoxyethyl-modified nylon.

The intermediate layer 15 may contain metal oxide particles. By containing these particles in the intermediate layer 15, the volume resistance value of the intermediate layer 15 can be adjusted, so that the effect of preventing charge injection from the conductive substrate 11 to the photosensitive layer 14 can be enhanced. In addition, the electrical characteristics of the photoreceptor can be maintained under various environments. The particle diameter is preferably in the range of 0.02 to 0.5 μm.
Examples of the metal oxide particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide particles.

  The intermediate layer 15 is formed by, for example, preparing the intermediate layer coating solution by dissolving or dispersing the above-described resin in a suitable solvent, and applying the coating solution to the surface of the conductive substrate 11. When the intermediate layer 15 contains the above-described metal oxide particles or the like, for example, these particles are dispersed in a resin solution obtained by dissolving the above-described resin in an appropriate solvent to form an intermediate layer coating solution. Prepare. Next, the intermediate layer 15 can be formed by applying this coating solution to the surface of the conductive substrate 11.

Water, various organic solvents, or a mixed solvent thereof is used as the solvent for the coating solution for the intermediate layer. For example, a single solvent such as water, methanol, ethanol or butanol, or water and alcohols, two or more alcohols, acetone or dioxolane and alcohols, chlorinated solvents such as dichloroethane, chloroform or trichloroethane and alcohols, etc. A mixed solvent is used. Among these solvents, non-halogen organic solvents are preferably used in consideration of the global environment.
As a method for dispersing the aforementioned particles in the resin solution, a general method using a ball mill, a sand mill, an attritor, a vibration mill, an ultrasonic disperser, a paint shaker, or the like can be used.

  In the intermediate layer coating solution, the ratio C / D between the total weight C of the resin and the metal oxide and the weight D of the solvent used in the intermediate layer coating solution is 1/99 to 40/60. The ratio is preferably 2/98 to 30/70. The ratio E / F between the weight E of the resin and the weight F of the metal oxide is preferably 90/10 to 1/99, more preferably 70/30 to 5/95.

  Examples of the coating method of the intermediate layer coating liquid include a spray method, a bar coating method, a roll coating method, a blade method, a ring method, and a dip coating method. Among these, the dip coating method is relatively simple and excellent in terms of productivity and cost, as described above, and is often used when the intermediate layer 16 is formed.

  The thickness of the intermediate layer 15 is preferably 0.01 μm or more and 20 μm or less, and more preferably 0.05 μm or more and 10 μm or less. When the film thickness of the intermediate layer 16 is smaller than 0.01 μm, it becomes difficult to function as the intermediate layer 15 substantially, and it becomes difficult to cover the defects of the conductive substrate 11 and obtain a uniform surface property. As a result, it is difficult to prevent the injection of charges from the conductive substrate 11 to the photosensitive layer 14, and the chargeability of the photosensitive layer 14 may be deteriorated. When the intermediate layer 15 is formed by dip coating, it is difficult to form the intermediate layer 15 and the photosensitive layer 14 cannot be uniformly formed on the intermediate layer 15. This is not preferable because the sensitivity of the photoreceptor may be lowered.

(Photoconductor manufacturing method)
In the method for producing the photoreceptor, it is preferable that a drying step is included in each formation of the charge generation layer 12, the charge transport layer 13, the intermediate layer 15, and the like. The drying temperature of the photoreceptor is suitably about 50 ° C. to about 140 ° C., and particularly preferably about 80 ° C. to about 130 ° C. When the drying temperature of the photoreceptor is less than about 50 ° C., the drying time is prolonged or the solvent is not sufficiently evaporated and remains in the photosensitive layer, which is not preferable. On the other hand, if the drying temperature exceeds about 140 ° C., the electrical characteristics during repeated use deteriorate, and the image obtained using the photoreceptor may be deteriorated.

(Image forming device)
FIG. 4 is an arrangement side view showing a simplified configuration of the image forming apparatus 30 of the present invention. An image forming apparatus 30 shown in FIG. 4 is a laser printer on which the photoreceptor 1 is mounted. Hereinafter, the configuration of the laser printer 30 and the image forming operation will be described with reference to FIG. The laser printer 30 illustrated in FIG. 4 is merely an example of the image forming apparatus of the present invention, and the image forming apparatus of the present invention is not limited by the following description.

  A laser printer 30 as an image forming apparatus includes a photosensitive member 1, a semiconductor laser 31, a rotary polygon mirror 32, an imaging lens 34, a mirror 35, a corona charger 36 as a charging unit, a developing unit 37 as a developing unit, and transfer paper. It includes a cassette 38, a paper feed roller 39, a registration roller 40, a transfer charger 41 as a transfer means, a separation charger 42, a conveyor belt 43, a fixing device 44, a paper discharge tray 45, and a cleaner 46 as a cleaning means. The The semiconductor laser 31, the rotary polygon mirror 32, the imaging lens 34, and the mirror 35 constitute an exposure unit 49. A light emitting diode may be used in place of the semiconductor laser.

  The photoreceptor 1 is mounted on the laser printer 30 so as to be rotatable in the direction of an arrow 47 by a driving unit (not shown). A laser beam 33 emitted from the semiconductor laser 31 is repeatedly scanned in the longitudinal direction (main scanning direction) with respect to the surface of the photoreceptor 1 by the rotary polygon mirror 32. The imaging lens 34 has f-θ characteristics, and the laser beam 33 is reflected by the mirror 35 to form an image on the surface of the photosensitive member 1 for exposure. By scanning the laser beam 33 and forming an image while rotating the photoconductor 1 as described above, an electrostatic latent image corresponding to image information is formed on the surface of the photoconductor 1.

  The corona charger 36, the developing device 37, the transfer charger 41, the separation charger 42 and the cleaner 46 are provided in this order from the upstream side to the downstream side in the rotation direction of the photosensitive member 1 indicated by an arrow 47. The corona charger 36 is provided upstream of the image forming point of the laser beam 33 in the rotation direction of the photoconductor 1 and uniformly charges the surface of the photoconductor 1. Therefore, the surface of the photosensitive member 1 that is uniformly charged with the laser beam 33 is exposed, and a difference occurs between the charge amount of the part exposed by the laser beam 33 and the charge amount of the part that is not exposed. Electrostatic latent image is formed.

  The developing device 37 is provided on the downstream side in the rotation direction of the photosensitive member 1 with respect to the image forming point of the laser beam 33, supplies toner to the electrostatic latent image formed on the surface of the photosensitive member 1, and converts the electrostatic latent image into toner. Develop as an image. The transfer paper 48 accommodated in the transfer paper cassette 38 is taken out one by one by the paper feed roller 39 and is given to the transfer charger 41 by the registration roller 40 in synchronism with the exposure of the photoreceptor 1. The toner image is transferred onto the transfer paper 48 by the transfer charger 41. A separation charger 42 provided in the vicinity of the transfer charger 41 discharges the transfer paper onto which the toner image has been transferred and separates it from the photoreceptor 1.

The transfer paper 48 separated from the photoreceptor 1 is conveyed to the fixing device 44 by the conveying belt 43, and the toner image is fixed by the fixing device 44. The transfer paper 48 on which the image is formed in this manner is discharged toward the paper discharge tray 45. In addition, after the transfer paper 48 is separated by the separation charger 42, the photoreceptor 1 that continues to rotate further cleans foreign matters such as toner and paper dust remaining on the surface by the cleaner 46. The photoreceptor 1 whose surface has been cleaned by the cleaner 46 is neutralized by a neutralizing lamp (not shown) provided together with the cleaner 46 and then further rotated, and a series of image forming operations starting from the charging of the photoreceptor 1 are repeated. .
In addition, it is possible to employ a configuration in which a plurality of photosensitive members are provided to form a superimposed image using a plurality of different toners. This configuration is called a tandem system.

EXAMPLES Hereinafter, although this invention is demonstrated still in detail using an Example, this invention is not limited to the following description content.
First, a photoconductor prepared by forming a photoconductive layer under various conditions on an aluminum cylindrical support having a diameter of 30 mm and a length of 362 mm will be described as examples and comparative examples. In the following examples and comparative examples, “parts” means parts by weight.

Example 1
Disperse 3 parts of titanium oxide TTO-MI-1 (trademark made by Ishihara Sangyo), 3 parts of alcohol-soluble nylon resin CM-8000 (trademark made by Toray), 60 parts of methanol and 40 parts of 1,3-dioxolane for 10 hours with a paint shaker. By processing, the coating liquid for undercoat layers was prepared. The undercoat layer was formed by depositing the prepared coating solution for the undercoat layer on an aluminum cylindrical support having a diameter of 30 mm and a length of 362 mm so as to have a film thickness of 0.9 μm. .

  Next, 1 part of a polyvinyl butyral resin (ESREC BMS: trademark of Sekisui Chemical Co., Ltd.), a perylene pigment represented by the structural formula (A) (for example, Bulletin of the Chemical Society of Japan, vol. 25 (1952) p411-413) 2 parts and 97 parts of tetrahydrofuran were dispersed with a ball mill for 72 hours to prepare a charge generation layer coating solution. The charge generation layer was formed by depositing the coating solution on the aluminum cylindrical support provided with the undercoat layer so as to have a film thickness of 0.2 μm by a dip coating method.

  Next, 0.18 part of polycarbonate resin (TS2040: made by Teijin Chemicals) and 0.18 part of silica (TS-610: made by Cabot Specialty Chemicals) as filler particles are mixed with 3.24 parts of tetrahydrofuran, and a ball mill is mixed. The primary dispersion coating solution for the charge transport layer was prepared by carrying out a dispersion treatment for 5 hours. At this stage, the filler particles are uniformly dispersed and the dispersion state corresponding to the primary particle diameter (about 17 nm) is maintained. Light scattering particle size distribution analyzer: Microtrac UPA-150 (manufactured by Nikkiso) ) To confirm.

Next, 100 parts of a triarylamine compound (Nippon Distillation Co., Ltd.) represented by the following structural formula (B) as a charge transport material, 138.2 parts of a polycarbonate resin (TS2040), and an antioxidant (Sumilyzer BHT: Sumitomo Chemical) 5 parts) was dissolved in 984 parts of tetrahydrofuran. The primary dispersion coating liquid for charge transport layer was mixed with the obtained solution, and further dispersed for 1 hour with a ball mill to prepare a secondary dispersion coating liquid for charge transport layer. This coating solution was applied onto the above-described charge generation layer by a dip coating method, and the resulting coating film was dried at 130 ° C. for 1 hour to form a charge transport layer having a layer thickness of 28 μm (drying temperature 100). C, drying time 60 minutes).
The photoreceptor of Example 1 was produced through the above process.

(Example 2)
First, 1.25 parts of polycarbonate resin (TS2040) and 1.25 parts of silica (TS-610) are mixed with 22.5 parts of tetrahydrofuran, and then the mixed solution is dispersed in a ball mill for 5 hours. A dispersion coating solution was prepared. Next, 100 parts of a triarylamine compound (Nippon Distillation Co., Ltd.) represented by the structural formula (B) as a charge transport material, 138.75 parts of a polycarbonate resin (TS2040), and 5 parts of an antioxidant (Sumilyzer BHT) Was dissolved in 984 parts of tetrahydrofuran. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

(Example 3)
First, 3.1 parts of polycarbonate resin (TS2040) and 3.1 parts of silica (TS-610) are mixed with 55.8 parts of tetrahydrofuran, and then the mixed solution is dispersed in a ball mill for 5 hours, whereby the primary for the charge transport layer. A dispersion coating solution was prepared. Next, 100 parts of a triarylamine compound (Nippon Distillation Kogyo Co., Ltd.) represented by the structural formula (B) as a charge transport material, 136.9 parts of a polycarbonate resin (TS2040), and 5 parts of an antioxidant (Sumilyzer BHT) Was dissolved in 992 parts of tetrahydrofuran. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

(Example 4)
4.65 parts of polycarbonate resin (TS2040) and 4.65 parts of silica (TS-610) are mixed with 83.7 parts of tetrahydrofuran, and then the mixed solution is subjected to a dispersion treatment for 5 hours by a ball mill, whereby the primary for the charge transport layer. A dispersion coating solution was prepared. Next, 100 parts of a triarylamine compound (Nippon Distillation Kogyo Co., Ltd.) represented by the above structural formula (B) as a charge transport material, 135.35 parts of a polycarbonate resin (TS2040), and 5 parts of an antioxidant (Sumilyzer BHT) Was dissolved in 998 parts of tetrahydrofuran. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

(Example 5)
A photoconductor was prepared in the same manner as in Example 3 except that the filler particles were changed to alumina (Sumicorundum AA-04: manufactured by Sumitomo Chemical Co., Ltd.).

(Example 6)
A photoconductor was prepared in the same manner as in Example 3 except that the filler particles were changed to silica (X-24-9163A: manufactured by Shin-Etsu Chemical Co., Ltd.).

(Example 7)
A photoconductor was prepared in the same manner as in Example 3 except that the filler particles were changed to silica (SO-E5: manufactured by Admatex).

(Example 8)
A photoconductor was prepared in the same manner as in Example 3 except that the antioxidant (Sumilyzer BHT: manufactured by Sumitomo Chemical) was not added to the primary dispersion coating solution for the charge transport layer.

(Comparative Example 1)
For charge transport layer, 3.1 parts of polycarbonate resin (TS2040) and 3.1 parts of silica (TS-610) are mixed with 55.8 parts of tetrahydrofuran, and then the mixture is dispersed in a paint shaker for 5 hours. A primary dispersion coating solution was prepared. When the particle size distribution of the filler particles in the coating solution was measured, it was confirmed that a coarse aggregate (particle size 1 μm) that was clearly larger than the primary particle size was formed. A photoconductor was prepared in the same manner as in Example 3 except that the obtained coating solution was used.

(Comparative Example 2)
Primary charge transport layer layer is prepared by mixing 0.12 part of polycarbonate resin (TS2040) and 0.12 part of silica (TS-610) with 2.16 parts of tetrahydrofuran, and then dispersing the mixture in a ball mill for 5 hours. A dispersion coating solution was prepared. Next, 100 parts of a triarylamine compound (Nippon Distillation Kogyo Co., Ltd.) represented by the structural formula (B) as a charge transport material, 139.8 parts of a polycarbonate resin (TS2040), and 5 parts of an antioxidant (Sumilyzer BHT) Was dissolved in 980 parts of tetrahydrofuran. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

(Comparative Example 3)
A primary dispersion coating solution for a charge transport layer is prepared by mixing 5.0 parts of a polycarbonate resin (TS2040) and 5.0 parts of silica (TS-610) with 90 parts of tetrahydrofuran, and dispersing the mixture in a ball mill for 5 hours. Was prepared. Next, 100 parts of a triarylamine compound (Nippon Distillation Kogyo Co., Ltd.) represented by the above structural formula (B) as a charge transport material, 135.0 parts of a polycarbonate resin (TS2040), and 5 parts of an antioxidant (Sumilyzer BHT) Was dissolved in 1005.6 parts of tetrahydrofuran. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

(Comparative Example 4)
100 parts of a triarylamine compound represented by the above structural formula (2) (manufactured by Nippon Distillation Co., Ltd.), 140 parts of a polycarbonate resin (TS2040) and 5 parts of an antioxidant (Sumilyzer BHT) are added to 980 parts of tetrahydrofuran as a charge transport material. Mix and dissolve. A photoconductor was prepared in the same manner as in Example 1 except that the obtained solution was used for the secondary dispersion coating solution for the charge transport layer.

The types, compositions, average filler particle distance a (nm), filler particle diameter b (nm), filler particle density df (g / cm ³ ) of Examples 1-8 and Comparative Examples 1-4, Table 1 shows the average density dm (g / cm ³ ), the Rf value (df × b ³ ) / (dm × a ³ ), and the content (% by weight) in the charge transport layer of the surface layer. In addition, the measuring method of a, b, df, and dm is described below. Table 1 shows the type of charge transport material (CTM), the type of resin for the charge transport layer, and the type of antioxidant. Furthermore, the dispersion state of the filler particles in the secondary dispersion coating liquid for charge transport layer evaluated as follows is shown in Table 1.

[Dispersed state of filler particles]
About the superiority or inferiority of the dispersed state of the filler particles, the particle size distribution was measured with a particle size distribution measuring device (UPA-150 (manufactured by Nikkiso)). The state in which the filler particles are stably dispersed to a state close to the primary particle diameter (when the distribution is shown) is ◯, and the state where the aggregate of micron order is formed (when the distribution is shown) X.

[Measuring method of a, b, df and dm]
Further, a was obtained as a calculated value from the amount of filler particles added and the volume of the coating film as a medium because a uniform dispersion state could be confirmed in this example.
Since b is a commercially available filler particle, it quoted from the catalog value.
Since df is a commercially available filler particle, the catalog value was quoted.
The dm was obtained by measuring and measuring the volume and weight of the coating film.

A color tandem digital multifunction peripheral AR-C260 (made by Sharp Corporation: SONY as an exposure light source) in which each of the photoreceptors of Examples 1 to 8 and Comparative Examples 1 to 4 was modified for testing so that the developing device and the surface potential measuring device could be replaced. A semiconductor laser manufactured by 489.9 nm was used. Next, 100,000 images of the following character test chart were formed using this multi-function machine, and the sensitivity, printing durability, and image were evaluated by the following methods (monochrome printing during sample image output and image formation).

[Sensitivity (electric property) evaluation]
Remove the developer from the copier, and replace it with a surface potential meter (Trek Japan: model)
344) was attached. Using this copying machine, the surface potential of the photoconductor when it was not exposed to laser light in a normal temperature / normal humidity (N / N) environment at a temperature of 25 ° C. and a relative humidity of 50% was measured. Adjusted to -600V. In this state, exposure is performed with laser light (0.4 μJ / cm ² ), the initial surface potential of the photosensitive member is set to exposure potential VL1 (−V), and a character test chart is printed on 100,000 sheets of recording paper. The surface potential after the printing test was measured as the exposure potential VL2 (−V). The sensitivity was evaluated from the obtained VL according to the following criteria. Note that the smaller the absolute value of the exposure potential VL, the higher the sensitivity of the photoconductor.
<Criteria>
○: | VL | <80 (V)
Δ: 80 (V) ≦ | VL | <110 (V)
×: 110 (V) ≦ | VL |

[Evaluation of printing durability]
The cleaning blade of the cleaning device provided in the remodeled AR-C260 was adjusted so that the pressure at which the cleaning blade was in contact with the photosensitive member, so-called cleaning blade pressure, was 21 gf / cm (2.06 × 10 ⁻¹ N / cm: initial linear pressure). A printing test was performed by printing a character test chart on 100,000 sheets of recording paper for each photoconductor in an N / N environment.
The test chart specified by ISO19752 was used as the character test chart.
The thickness of the photosensitive layer at the start of the printing durability test and after the 100,000 sheets of images were formed was measured using a film thickness measuring device (trade name: F-20-EXR, manufactured by Filmetrics). From the difference between the film thickness at the start of the printing durability test and the film thickness after 100,000 sheets of images were formed, the amount of abrasion per 100,000 revolutions of the photosensitive drum was determined. The printing durability was evaluated from the obtained amount of scraping according to the following criteria. In addition, it means that printing durability is so bad that there is much scraping amount.
<Criteria>
◯: scraping amount d <0.8 μm / 100 k rotation Δ: 0.8 μm / 100 k rotation ≦ scraping amount d <1.0 μm / 100 k rotation ×: 1.0 μm / 100 k rotation ≦ scraping amount d

[Image evaluation]
1) Image determination (dot / character reproducibility <sharpness>)
Using a test copying machine, a 1-dot 1-space image equivalent to 1200 dpi and a 5-point character image were output in the N / N environment before the printing test. From these images, image evaluation (character / dot reproducibility) was performed according to the following criteria.
○: A clear image with no abnormality on the image by visual inspection.
Δ: A level in which a slight dot / character disorder is visually observed on the image, but there is no problem in actual use.
X: An image that is visually blurred due to disturbance of dots and characters on the image.

2) Image determination (density unevenness)
By outputting a halftone image of the image quality degradation level after the printing durability test, density unevenness was evaluated according to the following criteria.
○: There is no density unevenness in the image visually. Good picture.
Δ: Density unevenness in image visually. There is no problem in actual use.
X: Density unevenness in image visually. A level that causes problems in actual use.

3) Image determination (image blur)
By outputting a 1-dot 1-space image equivalent to 1200 dpi and a 5-point character image as the image quality degradation level after the printing durability test, image blur was evaluated according to the following criteria.
○: There is no image blur on the image visually. Good picture.
(Triangle | delta): Although the partial image blur generate | occur | produced on the image visually, it is a level which does not have a problem in actual use.
X: One or more image blurs occur on several parts of the image or in a wide range by visual inspection.

[Comprehensive evaluation / (Electrical characteristics, printing durability, image evaluation)]
Based on the determination results of the above five items, the determination is made as follows.
◎: All 5 items ○
○: One or more items with only ○ or △ out of 5 items △
×: At least one or more ×
The evaluation results are shown in Table 2.

The photoconductors of Examples 1 to 8 using filler particles satisfying 1.0 × 10 ⁻³ ≦ (df × b ³ ) / (dm × a ³ ) ≦ 2.5 × 10 ⁻² are average shaved during 100,000 actual shots. The amount (drum film slip amount) was 1 μm or less, indicating good printing durability. Further, as compared with Examples 3, 6, and 7, the photoconductor using the filler particles having a small particle diameter has more stable electric characteristics and higher sharpness (character dot reproducibility is better). I understood. Furthermore, from the comparison of the exposure potentials of Examples 3, 6, 7 and Example 5, it was confirmed that silica tends to be slightly superior in electrical stability to alumina. In addition, comparison between Example 3 and Example 8 revealed that the introduction of an antioxidant improved the resistance to gases such as O _{3 and} NOx generated near the charger during actual shooting.

In the photoreceptor of the comparative example using filler particles outside the range of 1.0 × 10 ⁻³ ≦ (df × b ³ ) / (dm × a ³ ) ≦ 2.5 × 10 ⁻² ,
-Significant deterioration of electrical stability due to non-uniform dispersion, and generation of abnormal images such as sharpness and image blur (Comparative Example 1),
-Significant deterioration of printing durability (Comparative Examples 2 and 4),
・ Images generated because the outermost surface layer was not refaced due to significant deterioration of electrical stability, sharpness reduction and improved wear resistance due to the large amount of filler particles added, making it more susceptible to acid gas Occurrence of abnormal images such as blurring and image unevenness (Comparative Example 3)
Was confirmed.

(Comparative Example 5)
The sensitivity, printing durability, and image were evaluated in the same manner as described above except that the photoconductor of Example 1 was used and the transmission wavelength of the semiconductor laser of the exposure device was changed to 780 nm. The results are shown in Table 3 below.

From Example 3 and Comparative Examples 4 and 5, by using a short wavelength laser, the dot / character reproducibility (sharpness) becomes high,
-Even when filler particles were added, the effect of scattering by laser light was suppressed, and as a result, it was confirmed that abnormal images such as density unevenness and image blurring did not occur even after repeated fatigue.

1 is a schematic partial cross-sectional view of an electrophotographic photosensitive member of the present invention. It is a graph which shows the difference of the aggregated particle diameter by the dispersion conditions of a filler particle. 1 is a schematic partial cross-sectional view of an electrophotographic photosensitive member of the present invention. 1 is a schematic side view of an image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Electrophotographic photoreceptor 11 Conductive substrate 12 Charge generation layer 13 Charge transport layer 14 Photosensitive layer 15 Intermediate layer 30 Laser printer (image forming apparatus)
DESCRIPTION OF SYMBOLS 31 Semiconductor laser 32 Rotating polygon mirror 34 Imaging lens 35 Mirror 36 Corona charger 37 Developing device 38 Transfer paper cassette 39 Paper feed roller 40 Registration roller 41 Transfer charger 42 Separation charger 43 Conveyor belt 44 Fixing device 45 Paper discharge tray 46 Cleaner 47 Arrow 48 Transfer paper 49 Exposure means

Claims (6)

An electrophotographic photoreceptor having at least a charge generation layer and a charge transport layer in this order on a conductive substrate,
The charge transport layer that is the outermost surface layer of the electrophotographic photoreceptor contains filler particles,
Filler particles in the outermost surface layer are represented by the following formula (1).
1.0 × 10 ⁻³ ≦ (df × b ³ ) / (dm × a ³ ) ≦ 2.5 × 10 ^-2 (1)
(In the formula, a means the average distance between filler particles (nm), b means the average filler particle diameter (nm), df means the density of filler particles (g / cm ³ ), and dm is the maximum. It is a uniform dispersion state satisfying the average density (g / cm ³ ) of the solid content of the surface layer,
The electrophotographic photosensitive member, wherein the charge generation layer includes a material capable of generating charge by exposure light having an oscillation wavelength of 350 to 500 nm. The electrophotographic photosensitive member according to claim 1, wherein the filler particles are made of silicon oxide. The electrophotographic photosensitive member according to claim 1, wherein the filler particles have a particle diameter of 5 to 100 nm . The electrophotographic photosensitive member according to claim 1 , wherein the charge transport layer further contains an antioxidant.   An image forming apparatus comprising a photoconductor, a charging unit, an exposure unit, a developing unit, and a transfer unit, wherein the photoconductor includes the electrophotographic photoconductor according to claim 1.   A photosensitive member, a charging unit, an exposure unit, a developing unit, and a transfer unit, the plurality of the photosensitive members are provided in order to form a superimposed image, and the plurality of photosensitive members are arranged in a tandem manner; An image forming apparatus, wherein the means includes a plurality of toners, and the plurality of photoconductors includes the electrophotographic photoconductor according to claim 1.

Images