Electrophotographic photoreceptor and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor and an image forming apparatus that can prevent an image defect.SOLUTION: An electrophotographic photoreceptor has at least a charge generating layer and a charge transport layer formed in this order on a conductive support, and the charge transport layer contains a binder resin, silica particles, and a compound of the general formula (1).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an electrophotographic photoreceptor and an image forming apparatus. [Background technology]

[0002] In recent years, organic photoreceptors (hereinafter, also referred to as "photoreceptor" together with "electrophotographic photoreceptor") have been widely used as electrophotographic photoreceptors.

[0003] Due to the nature of organic materials, organic photoreceptors have a drawback in that the surface is easily worn away by the cleaning blades and other devices used around the photoreceptor. In recent years, this drawback has become more pronounced with the increase in contact charging methods using roller charging. To overcome this drawback, efforts have been made to increase the mechanical strength of the photoreceptor surface and reduce the amount of surface wear.

[0004] For example, Patent Documents 1 and 2 discuss adding silica particles as a filler to the surface layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6369426 [Patent Document 2] Patent No. 6146188 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional prior art, when a photoconductor containing silica in the charge transport layer is left in contact with a charging roller inside a copying machine or printer for several days, a problem occurs in which a streak-like image defect occurs. Furthermore, this streak-like image defect has low recovery properties and may continue to occur for several days, which can be a major problem.

[0007] In view of the above problems, an object of the present disclosure is to provide an electrophotographic photoreceptor and an image forming apparatus capable of preventing image defects. [Means for solving the problem]

[0008] One aspect of the present disclosure is an electrophotographic photoreceptor having at least a charge generating layer and a charge transport layer formed in this order on a conductive support, the charge transport layer containing at least a binder resin, silica particles, and a compound represented by general formula (1).

[0009] In another aspect of the present disclosure, the present invention is characterized by comprising: the electrophotographic photoreceptor; and an image forming section that charges the electrophotographic photoreceptor with a charging roller, and forms an image by exposing, transferring, and fixing the electrophotographic photoreceptor. Effect of the Invention

[0010] As described above, according to the present disclosure, by containing a binder resin, silica particles, and a compound of general formula (1) on a conductive support, it is possible to provide an electrophotographic photoreceptor and an image forming apparatus which have high sensitivity, excellent printing durability, and high mechanical strength, and which are capable of preventing image defects even when left in contact with a charging roller. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic side view showing the configuration of a main part of an image forming apparatus according to the present disclosure. [Diagram 2] FIG. 2 is a schematic side view showing an example of the configuration of a main part of an electrophotographic photoreceptor according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the contents of the present disclosure described in the claims, and all of the configurations described in the embodiments are not necessarily essential as the means for solving the problems of the present disclosure.

[0013] 1. Image forming device 1 is a schematic side view showing a configuration of a main part of an image forming apparatus according to the present disclosure. The image forming apparatus according to the present disclosure includes an electrophotographic photoreceptor 1 according to the present disclosure and an image forming section 50. The image forming apparatus may be, for example, a laser printer.

[0014] The image forming section 50 forms an image by charging the electrophotographic photoreceptor 1 according to the present disclosure with a charging roller 32, exposing, transferring and fixing the image. The image forming section 50 will be described below.

[0015] As shown in FIG. 1, the image forming unit 50 includes a housing 38, a charging unit 32 that charges the electrophotographic photosensitive member 1, an exposure unit 31 that exposes the charged photosensitive member to form an electrostatic latent image, a development unit 33 that develops the electrostatic latent image formed by exposure to form a toner image (makes it visible), a transfer unit 34 that transfers the toner image formed by development onto a recording medium 45, a fixing unit 35 that fixes the transferred toner image on the recording medium 45 to form an image, a cleaning unit 36 ​​that removes and collects toner remaining on the photosensitive member, and a discharge unit (not shown) that discharges surface charge remaining on the photosensitive member.

[0016] The electrophotographic photoreceptor 1 is rotatably supported by the main body of the image forming apparatus 100, and is driven to rotate around a rotation axis 44 in the direction of arrow 41 by a drive unit (not shown). The drive unit includes, for example, an electric motor and a reduction gear, and rotates the electrophotographic photoreceptor 1 at a predetermined peripheral speed by transmitting its driving force to a conductive support constituting a core body of the electrophotographic photoreceptor 1. A charging unit (charger) 32, an exposure unit 31, a developing unit (developer) 33, a transfer unit (transfer charger) 34, and a cleaning unit (cleaner) 36 are provided in this order along the outer circumferential surface of the electrophotographic photoreceptor 1 from the upstream side to the downstream side in the rotation direction of the electrophotographic photoreceptor 1 indicated by arrow 41.

[0017] The charging unit 32 is a roller charger that charges the outer peripheral surface of the electrophotographic photoreceptor 1 uniformly to a predetermined potential. The exposure unit 31 has a semiconductor laser as a light source, and irradiates the surface of the electrophotographic photoreceptor 1 between the charger 32 and the developer 33 with a laser beam light output from the light source, thereby exposing the charged outer peripheral surface of the electrophotographic photoreceptor 1 according to image information. The light is repeatedly scanned in the direction of extension of the rotation axis 44 of the electrophotographic photoreceptor 1, which is the main scanning direction, and these are imaged to sequentially form electrostatic latent images on the surface of the electrophotographic photoreceptor 1. That is, the charge amount of the electrophotographic photoreceptor 1 that is uniformly charged by the charger 32 differs depending on whether it is irradiated with the laser beam or not, and an electrostatic latent image is formed.

[0018] The developing unit 33 is a developing device that develops an electrostatic latent image formed on the surface of the electrophotographic photosensitive member 1 by exposure with a developer (toner), and is provided facing the electrophotographic photosensitive member 1. The developing unit 33 includes a developing roller 33a that supplies toner to the outer peripheral surface of the electrophotographic photosensitive member 1, and a casing 33b that rotatably supports the developing roller 33a about a rotation axis parallel to the rotation axis 44 of the electrophotographic photosensitive member 1 and contains a developer including toner in its internal space.

[0019] The transfer unit 34 is a transfer charger that transfers the toner image, which is a visible image formed on the outer peripheral surface of the electrophotographic photoreceptor 1 by development, onto a transfer paper, which is a recording medium 45, supplied between the electrophotographic photoreceptor 1 and the transfer charger 34 from the direction of the arrow 42 by a transport unit (not shown). The transfer unit 34 is, for example, a contact-type transfer charger that includes the charging unit 32 and transfers the toner image onto the transfer paper by applying a charge of the opposite polarity to that of the toner to the transfer paper.

[0020] The cleaning unit 36 ​​is a cleaner that removes and collects toner remaining on the outer peripheral surface of the electrophotographic photosensitive member 1 after the transfer operation by the transfer charger 34, and includes a cleaning blade 36a that separates the toner remaining on the outer peripheral surface of the electrophotographic photosensitive member 1, and a collection casing 36b that contains the toner separated by the cleaning blade 36a. The cleaner 36 is also provided together with a static elimination lamp (not shown).

[0021] The image forming apparatus 100 is also provided with a fixing unit 35 that fixes the transferred image, downstream of the conveyance of the transfer paper 45 that has passed between the electrophotographic photoreceptor 1 and the transfer charger 34. The fixing unit 35 includes a heating roller 35a having a heating portion (not shown), and a pressure roller 35b that is provided opposite the heating roller 35a and is pressed against the heating roller 35a to form a contact portion. Reference numeral 37 denotes a separation portion 37 that separates the transfer paper 45 from the electrophotographic photoreceptor 1, and reference numeral 38 denotes a casing that houses the above-mentioned portions of the image forming apparatus.

[0022] The image forming operation of the image forming apparatus 100 is performed as follows: First, when the electrophotographic photosensitive member 1 is rotationally driven in the direction of the arrow 41 by the drive unit, the surface of the electrophotographic photosensitive member 1 is uniformly charged to a predetermined positive potential by the charger 32 provided upstream of the image forming point of light by the exposure unit 31 in the rotation direction of the electrophotographic photosensitive member 1.

[0023] Next, light according to image information is irradiated from the exposure unit 31 onto the surface of the electrophotographic photoreceptor 1. This exposure removes surface charge from the portions of the electrophotographic photoreceptor 1 irradiated with light, causing a difference in surface potential between the portions irradiated with light and the portions not irradiated with light, forming an electrostatic latent image. Toner is supplied from a developing device 33, which is provided downstream in the rotation direction of the electrophotographic photoreceptor 1 from the image-forming point of light by the exposure unit 31, to the surface of the electrophotographic photoreceptor 1 on which the electrostatic latent image has been formed, developing the electrostatic latent image into a toner image.

[0024] In synchronization with the exposure of the electrophotographic photoreceptor 1, a transfer paper 45 is supplied between the electrophotographic photoreceptor 1 and the transfer charger 34. The transfer charger 34 gives the supplied transfer paper 45 an electric charge of the opposite polarity to the toner, and the toner image formed on the surface of the electrophotographic photoreceptor 1 is transferred onto the transfer paper. The transfer paper 45 with the transferred toner image is transported to the fixing device 35 by the transport unit, and is heated and pressurized when passing through the contact portion between the heating roller 35a and the pressure roller 35b of the fixing device 35, so that the toner image is fixed onto the transfer paper 45 to form a robust image. The transfer paper 45 with the image formed in this way is discharged to the outside of the image forming apparatus 100 by the transport unit.

[0025] Meanwhile, the toner remaining on the surface of the electrophotographic photoreceptor 1 even after the transfer of the toner image by the transfer charger 34 is peeled off from the surface of the electrophotographic photoreceptor 1 and collected by the cleaner 36. The charge on the surface of the electrophotographic photoreceptor 1 from which the toner has been removed in this manner is removed by light from a discharging lamp, and the electrostatic latent image on the surface of the electrophotographic photoreceptor 1 disappears. Thereafter, the electrophotographic photoreceptor 1 is further rotated and a series of operations starting with charging is repeated again to continuously form images.

[0026] The process cartridge is characterized by comprising the electrophotographic photoreceptor 1 of the present disclosure, and at least one selected from a charging unit 32 that charges the electrophotographic photoreceptor 1, a developing unit 33 that develops an electrostatic latent image formed by exposure to light to form a toner image, and a cleaning unit that removes toner remaining on the electrophotographic photoreceptor 1.

[0027] For example, a process cartridge is configured by integrating the electrophotographic photoreceptor 1 of the present disclosure, a charging device, a developing device, and a cleaning device with a support member. When such a process cartridge is incorporated into the image forming apparatus 100, each of the components of the process cartridge is provided in the image forming apparatus 100. Since the process cartridge is detachable from the image forming apparatus 100, it can be easily replaced when worn out.

[0028] 2. Electrophotographic photoreceptor Fig. 2 is a schematic side view showing an example of the configuration of the main part of the electrophotographic photoreceptor 1 according to the present disclosure. As shown in Fig. 2, the electrophotographic photoreceptor 1 according to the present disclosure includes a conductive support 11, an undercoat layer 18, and a photosensitive layer 14 having a charge generating layer 15 and a charge transport layer 16, which are formed in this order. Each component will be described below.

[0029] <Conductive support 11> The conductive support 11 functions as an electrode for the electrophotographic photoreceptor 1 and as a support member, and the material constituting the conductive support 11 is not particularly limited as long as it is a material used in the relevant technical field.

[0030] Specific examples include metal materials such as aluminum, aluminum alloys, copper, zinc, stainless steel, and titanium, as well as polymer materials such as polyethylene terephthalate, nylon, and polystyrene, whose surfaces are laminated with metal foil, subjected to metal vapor deposition, or vapor-deposited or coated with a layer of a conductive compound such as a conductive polymer, tin oxide, or indium oxide, as well as hard paper and glass. Among these, aluminum is preferred from the viewpoint of ease of processing, and aluminum alloys such as JIS 3003, JIS 5000, and JIS 6000 are particularly preferred.

[0031] The shape of the conductive support 11 may be a cylinder (drum), a sheet, a column, an endless belt, etc. Furthermore, the surface of the conductive support 11 may be subjected to anodizing film treatment, surface treatment with chemicals or hot water, coloring treatment, or diffuse reflection treatment such as surface roughening, as necessary, to prevent interference fringes caused by laser light, within a range that does not affect image quality.

[0032] <Undercoat layer (also called "middle layer") 18> The electrophotographic photoreceptor 1 of the present disclosure preferably includes an undercoat layer 18 between the conductive support 11 and the photosensitive layer 14. The undercoat layer 18 generally covers and makes uniform the unevenness of the surface of the conductive support 11, improves the film-forming properties of the charge generating layer 15 containing the charge generating material 12, inhibits the photosensitive layer 14 from peeling off from the conductive support 11, and improves the adhesion between the conductive support 11 and the photosensitive layer 14. Specifically, the undercoat layer 18 prevents the injection of charges from the conductive support 11 into the photosensitive layer 14, prevents a decrease in the chargeability of the photosensitive layer 14, and prevents fogging of the image (so-called black spots).

[0033] The undercoat layer 18 can be formed, for example, by dissolving a binder resin in a suitable solvent to prepare a coating liquid for the undercoat layer, coating this coating liquid on the surface of the conductive support 11, and removing the organic solvent by drying.

[0034] Binder resins for the undercoat layer 18 include binder resins similar to those contained in the photosensitive layer 14 described below, as well as natural polymeric materials such as casein, gelatin, polyvinyl alcohol, and ethyl cellulose, and one or more of these can be used.

[0035] The binder resin of the undercoat layer 18 is required to have properties such as not dissolving or swelling in the solvent used when forming the photosensitive layer 14 on the undercoat layer 18, having excellent adhesion to the conductive support 11, and having flexibility. Therefore, of the above-mentioned binder resins, polyamide resins are preferred, and alcohol-soluble nylon resins are particularly preferred.

[0036] Examples of alcohol-soluble nylon resins include homopolymer or copolymer nylons such as 6-nylon, 66-nylon, 610-nylon, 11-nylon, and 12-nylon, and resins obtained by chemically modifying nylons such as N-alkoxymethyl-modified nylons.

[0037] Examples of solvents for dissolving or dispersing resin materials include water, alcohols such as methanol, ethanol, and butanol, glymes such as methyl carbitol and butyl carbitol, chlorine-based solvents such as dichloroethane, chloroform, and trichloroethane, acetone, dioxolane, mixed solvents of two or more of these solvents, etc. Among these solvents, non-halogenated organic solvents are preferably used in consideration of the global environment.

[0038] The coating solution for the undercoat layer may also contain metal oxide particles, which can easily adjust the volume resistivity of the undercoat layer 18, further suppress the injection of charges into the photosensitive layer 14, and maintain the electrical properties of the photoreceptor under various environments.

[0039] Examples of metal oxide particles include titanium oxide, aluminum oxide, aluminum hydroxide, and tin oxide. In the coating solution for undercoat layer, the ratio (C / D) of the total mass C of the binder resin and the metal oxide particles to the mass D of the solvent is preferably 1 / 99 to 40 / 60, and more preferably 2 / 98 to 30 / 70. The ratio E / F of the mass E of the binder resin to the mass F of the metal oxide particles is preferably 90 / 10 to 1 / 99, and more preferably 70 / 30 to 5 / 95.

[0040] In order to disperse the metal oxide particles in the coating liquid for the undercoat layer, known devices such as ball mills, sand mills, attritors, vibration mills, ultrasonic dispersers, and paint shakers may be used. The coating method for the coating liquid for the undercoat layer may be appropriately selected by taking into consideration the physical properties and productivity of the coating liquid, and may include, for example, spraying, bar coating, roll coating, blade coating, ring coating, and dip coating. Among these, the dip coating method is a method in which a substrate is immersed in a coating tank filled with the coating liquid, and then pulled up at a constant speed or a gradually changing speed to form a layer on the surface of the substrate, which is relatively simple and has excellent productivity and cost, and therefore can be suitably used in the manufacture of photoreceptors. The device used for the dip coating method may be provided with a coating liquid dispersion device, typically an ultrasonic generator, in order to stabilize the dispersibility of the coating liquid.

[0041] The solvent in the coating film may be removed by natural drying, or may be removed by heating. The temperature in such a drying step is not particularly limited as long as it is a temperature at which the solvent used can be removed, but is suitably about 50 to 140°C, and particularly preferably about 80 to 130°C.

[0042] If the drying temperature is less than 50° C., the drying time may be long, and the solvent may not evaporate sufficiently and remain in the photoreceptor layer. If the drying temperature exceeds about 140° C., the electrical characteristics of the photoreceptor may deteriorate during repeated use, resulting in poor quality of the image. Such temperature conditions are common not only to the formation of the undercoat layer 18 but also to the formation of layers such as the photosensitive layer 14 described below and other processes.

[0043] The thickness of the undercoat layer 18 is not particularly limited, but is preferably 0.01 to 20 μm, and more preferably 0.05 to 10 μm. If the thickness of the undercoat layer 18 is less than 0.01 μm, the undercoat layer 18 will not function substantially, and it will not be possible to cover defects in the conductive support 11 to obtain a uniform surface, and it may not be possible to prevent injection of charges from the conductive support 11 into the photosensitive layer 14. On the other hand, if the thickness of the undercoat layer 18 exceeds 20 μm, it is difficult to form a uniform undercoat layer 18, and the sensitivity of the photoreceptor may also decrease. When the conductive support 11 is made of aluminum, a layer containing alumite (alumite layer) may be formed to serve as the undercoat layer 18.

[0044] <Charge generation layer 15> The charge generating layer 15 has the function of generating charges by absorbing irradiated light such as semiconductor laser light in an image forming device or the like, and contains a charge generating material 12 as a main component and, as necessary, a binder resin and additives.

[0045] The charge generating material 12 can be a compound used in the field, specifically, azo pigments such as monoazo pigments, bisazo pigments, and trisazo pigments; indigo pigments such as indigo and thioindigo; perylene pigments such as peryleneimide and perylene acid anhydride; polycyclic quinone pigments such as anthraquinone and pyrenequinone; phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine such as titanyl phthalocyanine; organic photoconductive materials such as squarylium dyes, pyrylium salts, thiopyrylium salts, and triphenylmethane dyes; and inorganic photoconductive materials such as selenium and amorphous silicon, and the like, which have sensitivity in the exposure wavelength range, can be appropriately selected and used. These charge generating materials 12 can be used alone or in combination of two or more.

[0046] Among these charge generating materials 12, it is preferable to use titanyl phthalocyanine represented by the following general formula (A): 1 , X 2 , X3 and X 4 are the same or different and each is a halogen atom, an alkyl group, or an alkoxy group, and r, s, y, and z are the same or different and each is an integer of 0 to 4.

[0047] [ka]

[0048] Titanyl phthalocyanine is a charge generating material 12 that has high charge generation efficiency and charge injection efficiency in the emission wavelength range (near-infrared light) of laser light and LED light that are currently in common use, and generates a large amount of charge by absorbing light, and can efficiently inject the generated charge into charge transport material 13 without accumulating it inside.

[0049] Titanyl phthalocyanine represented by general formula (A) can be produced by known production methods such as the method described in Phthalocyanine Compounds by Moser, Frank H and Arthur L. Thomas, Reinhold Publishing Corp., New York, 1963. For example, in the case of unsubstituted titanyl phthalocyanine in which r, s, y and z are 0 among the titanyl phthalocyanine compounds represented by general formula (A), phthalonitrile and titanium tetrachloride are melted by heating or reacted by heating in a suitable solvent such as α-chloronaphthalene to synthesize dichlorotitanyl phthalocyanine, and then hydrolyzed with a base or water. In addition, a titanyl phthalocyanine composition can also be produced by reacting isoindoline with titanium tetraalkoxide such as tetrabutoxytitanium in a suitable solvent such as N-methylpyrrolidone by heating.

[0050] Methods for forming the charge generation layer 15 include a method of vacuum-depositing the charge generation material 12 on the conductive support 11, and a method of dispersing the charge generation material 12 in a solvent and applying a coating liquid for the charge generation layer onto the conductive support 11. Among these, a method of dispersing the charge generation material 12 in a binder resin solution obtained by mixing a binder resin in a solvent by a conventionally known method and applying the coating liquid for the charge generation layer onto the conductive support 11 is preferred. This method will be described below.

[0051] The binder resin is not particularly limited, and any resin known in the art can be used. Examples of the binder resin include polyester, polystyrene, polyurethane, phenolic resin, alkyd resin, melamine resin, epoxy resin, silicone resin, acrylic resin, methacrylic resin, polycarbonate, polyarylate, polyphenoxy, polyvinyl butyral, and polyvinyl formal resins, as well as copolymer resins containing two or more of the repeating units constituting these resins.

[0052] 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. These resins can be used alone or in combination of two or more.

[0053] Examples of the solvent include halogenated hydrocarbons such as dichloromethane and dichloroethane, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran (THF) and dioxane, alkyl ethers of ethylene glycol such as 1,2-dimethoxyethane, aromatic hydrocarbons such as benzene, toluene and xylene, and aprotic polar solvents such as N,N-dimethylformamide and N,N-dimethylacetamide. These solvents can be used alone or in combination of two or more.

[0054] The compounding ratio of the charge generating substance 12 to the binder resin is preferably such that the proportion of the charge generating substance 12 is in the range of 10 to 99% by mass. If the proportion of the charge generating substance 12 is less than 10% by mass, the sensitivity may decrease. On the other hand, if the proportion of the charge generating substance 12 exceeds 99% by mass, not only the film strength of the charge generating layer 15 decreases, but also the dispersibility of the charge generating substance 12 decreases and coarse particles increase, and the surface charge decreases in areas other than those that should be erased by exposure, which may cause image defects, particularly image fogging called black spots, in which toner adheres to a white background and tiny black spots are formed.

[0055] Before dispersing the charge generating material 12 in the binder resin solution, the charge generating material 12 may be pulverized in advance using a pulverizer. Examples of the pulverizer that can be used for the pulverization include a ball mill, a sand mill, an attritor, a vibration mill, and an ultrasonic disperser.

[0056] Examples of dispersing machines used for dispersing the charge generating material 12 in the binder resin solution include a paint shaker, a ball mill, a sand mill, etc. Appropriate dispersion conditions should be selected so as to prevent the incorporation of impurities due to wear of the container and members constituting the dispersing machine.

[0057] The coating liquid for the charge generating layer may be applied by the same method as the coating liquid for the undercoat layer, and a dip coating method is particularly preferred.

[0058] The thickness of the charge generating layer 15 is not particularly limited, but is preferably 0.05 to 5 μm, and more preferably 0.1 to 1 μm. If the thickness of the charge generating layer 15 is less than 0.05 μm, the efficiency of light absorption may decrease, and the sensitivity of the photoconductor may decrease. On the other hand, if the thickness of the charge generating layer 15 exceeds 5 μm, the charge transfer inside the charge generating layer 15 becomes the rate-limiting step in the process of erasing the charge on the surface of the photosensitive layer 14, and the sensitivity of the photoconductor may decrease.

[0059] <Charge transport layer 16> The charge transport layer 16 is obtained by incorporating a charge transport material 13 capable of receiving and transporting charges generated by a charge generating material 12 into a binder resin 17. The charge transport layer 16 is characterized by containing at least a binder resin 17, silica particles 20, and a compound 19 of general formula (1).

[0060] [ka]

[0061] In the above general formula (1), the substituents R1 to R5 are any one type of substituent selected from the group consisting of a hydrogen atom, a cyano group, a nitro group, a halogen atom, a hydroxyl group, an alkyl group, an aryl group, a heterocyclic group, an ester group, an alkoxy group, an aralkyl group, an allyl group, an amide group, an amino group, an acyl group, an alkenyl group, an alkynyl group, a carboxyl group, a carbonyl group, and a carboxylic acid group.

[0062] The following mechanism is thought to be the cause of streak-like image defects that occur when a photoconductor containing silica in the charge transport layer 16 is left in contact with a charging roller inside a copier or printer for several days. When a charging roller is brought into contact with an electrophotographic photoconductor 1, the charging roller deforms, and this deformation generates a small amount of charge due to the piezoelectric effect of the ionic conductive material used in the surface layer of the charging roller. It is thought that this charge penetrates into the charge transport layer 16 and is adsorbed to the silica particles 20, which then have an internal charge and cause streaks. It is thought that the compound 19 of general formula (1) can adsorb a charge to the compound 19 of general formula (1), and the charge adsorbed to the silica particles 20 can be easily released, thereby suppressing the occurrence of streaks and making it easier to recover.

[0063] Specific examples of the compound 19 of the general formula (1) include the following compounds (2) and (4) to (9).

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[0071] Among these compounds, compound (2) is preferred in terms of initial sensitivity.

[0072] The content of the compound of general formula (1) in the charge transport layer 16 is preferably 15 to 50 wt %, more preferably 25 to 40 wt %, based on the content of the silica particles 20 in the charge transport layer 16 .

[0073] If the content of compound 19 of general formula (1) is less than 15 wt %, the effect of suppressing the occurrence of streaks caused by contact with the charging roller and the effect of improving recovery are insufficient, and if it exceeds 50 wt %, the initial sensitivity may deteriorate.

[0074] In this disclosure, "silica" means silicon dioxide (SiO2). Examples of silica particles 20 used in the present invention include particles synthesized by a dry method and a wet method. Examples of dry method silica include fumed silica obtained by burning silicon tetrachloride, and arc method silica in which silica is microparticulated in a gas phase by high energy such as plasma. Examples of wet method silica include precipitation method silica particles synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material, and gel method silica particles synthesized under acidic conditions. In addition, there are colloidal silica particles obtained by making acidic silicic acid alkaline and polymerizing it, and sol-gel method silica particles obtained by hydrolysis of an organic silane compound.

[0075] Examples of dry silica particles include combustion silica (fumed silica) obtained by burning a silane compound, and deflagration silica obtained by explosively burning metallic silicon powder.

[0076] Examples of wet silica particles include wet silica particles obtained by a neutralization reaction between sodium silicate and a mineral acid (precipitation method silica synthesized and agglomerated under alkaline conditions, gel method silica particles synthesized and agglomerated under acidic conditions), colloidal silica particles (silica sol particles) obtained by making acidic silicic acid alkaline and polymerizing it, and sol-gel method silica particles obtained by hydrolysis of an organic silane compound (e.g., alkoxysilane).

[0077] Among these, from the viewpoint of suppressing image defects due to the generation of residual potential and other deterioration of electrical properties (suppressing deterioration of fine line reproducibility), it is desirable to use combustion method silica particles having a low silanol group content on the surface and a low void structure as the silica particles 20.

[0078] The content of the silica particles 20 of the present disclosure is preferably 5 to 15 wt %, and more preferably 7 to 12 wt %, based on the total solid content in the charge transport layer 16. If the content of the silica particles 20 is less than 5 wt %, the effect on the abrasion resistance of the photoreceptor is insufficient, while if it is 15 wt % or more, the aggregates of the silica particles 20 are likely to cause a state in which part of the edge portion of the cleaning blade is chipped, making it impossible to sufficiently clean the remaining toner, which may cause streak-like defects in the printed image.

[0079] The number average primary particle diameter of the silica particles 20 of the present disclosure is preferably 12 to 30 nm, and more preferably 16 to 20 nm. If the particle diameter of the silica particles 20 is less than 12 nm, the effect on the abrasion resistance of the photoreceptor is insufficient, and if it is more than 30 nm, a state in which part of the edge part of the cleaning blade is easily chipped off, making it impossible to sufficiently clean the remaining toner, and may cause streak-like defects in the printed image.

[0080] The number average primary particle diameter referred to here is the measurement value of the Feret's direction average diameter when the microparticles are magnified 10,000 times using a TEM (transmission electron microscope), 100 particles are randomly observed as primary particles, and image analysis is performed.

[0081] The charge transport layer binder resin 17 used in the present disclosure is a polycarbonate resin or polyarylate resin well known in the art, which has excellent compatibility with the charge transport material 13 and is also excellent in electrical insulation, transparency, electrical properties, film properties, abrasion resistance, etc. Among them, a copolymer polycarbonate having a structure of the following general formula (3) is preferable because it has good dispersibility and abrasion resistance of the silica particles 20. In the formula (3), R6 and R7 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a fluoroalkyl group having 1 to 10 carbon atoms, n and m satisfy 0.4≦n / (m+n)≦0.6, and the chain end group is a monovalent aromatic group or a monovalent fluorine-containing aliphatic group.

[0082] [ka]

[0083] Specific examples of the compound of general formula (3) include the following copolymer polycarbonates (10) to (13). In formulas (10) to (13), n and m preferably satisfy 0.4≦n / (m+n)≦0.6, and the chain end group is a monovalent aromatic group or a monovalent fluorine-containing aliphatic group. If it is less than 0.4, the abrasion resistance is significantly deteriorated, and if it is more than 0.6, the solubility may be deteriorated or gelation may occur when dissolved.

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[0088] Such copolymeric polycarbonates can be synthesized by known methods.

[0089] The content of the binder resin 17 and the content of the silica particles 20 in the present disclosure preferably satisfy the following formula. (Amount of binder resin 17 in charge transport layer 16 / Total solid content of charge transport layer 16)+(Amount of silica particles 20 in charge transport layer 16 / Total solid content of charge transport layer 16)×5<1.25

[0090] When the compound 19 of the general formula (1) and the silica particles 20 are contained in the charge transport layer 16, the sensitivity may be significantly deteriorated when the layer is used repeatedly. This is because the silica particles 20 cause unevenness at the interface between the charge generation layer 15 and the charge transport layer 16, and the binder resin 17 in the charge transport layer 16 penetrates into the charge generation layer 15, resulting in a state in which the material of the charge generation layer 15 and the material of the charge transport layer 16 are mixed together. This is thought to be because the action between the compound of the general formula (1) and the charge generation material becomes too large, resulting in excessive trapping of charges. Therefore, when the amount of the silica particles 20 increases, it is necessary to reduce the amount of the binder resin 17. As a result of intensive studies based on these ideas, it was found that by satisfying the above formula, the deterioration of sensitivity can be suppressed even when the layer is used repeatedly. As a more preferable range, the value of the above formula is preferably 0.75 or more. If it is less than 0.75, the amount of the silica particles 20 and the amount of the binder resin 17 decrease, and the abrasion resistance may deteriorate.

[0091] The charge transport material 13 used in the present disclosure may be any compound capable of transporting charges generated in the charge generating layer 15. Examples of the charge transport material 13 include various known compounds as listed below. Examples include carbazole 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, and aromatic amine derivatives. Also included are polymers having groups derived from these compounds in the main chain or side chain, such as poly-N-vinylcarbazole, poly-1-vinylpyrene, and poly-9-vinylanthracene. These may be used alone or in combination of two or more.

[0092] Among these, the stilbene derivative (14) having the following structure is preferred in terms of electrical properties. In formula (14), R1, R2, R5, and R6 may be the same or different and each represents an alkyl group, an alkoxy group, an aryl group, or an aralkyl group. m, n, p, and q may be the same or different and each represents an integer of 0 to 3. R3 and R4 may be the same or different and each represents a hydrogen atom or an alkyl group.

[0093] [ka]

[0094] Such a stilbene compound can be synthesized by a known method.

[0095] Suitable structures of the stilbene derivative (14) of the charge transport material 13 include the following compounds (15), (16), and (17).

[0096] [ka]

[0097] [ka]

[0098] [ka]

[0099] The thickness of the charge transport layer 16 is preferably 18 μm to 42 μm, and more preferably 25 to 37 μm. If the thickness is less than 18 μm, the durability is insufficient, and if it exceeds 42 μm, the electrical characteristics may deteriorate.

[0100] Moreover, the charge transport layer 16 is preferably formed as the outermost layer. EXAMPLES

[0101] Hereinafter, the electrophotographic photoreceptor 1 and the image forming apparatus according to the present disclosure will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the examples described here.

[0102] Example 1 Three parts by weight of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: Tiebaque TTO-D-1) and two parts by weight of copolymer polyamide (nylon) (manufactured by Toray Industries, Inc., product name: Amilan CM8000) were added to 25 parts by weight of methyl alcohol, and the mixture was dispersed for eight hours using a paint shaker to prepare 3 liters of a coating solution for the undercoat layer.

[0103] An aluminum drum-shaped conductive support having a diameter of 30 mm and a length of 372 mm was immersed in the obtained coating liquid for the undercoat layer and then pulled out. The obtained coating film was allowed to dry naturally to form an undercoat layer with a thickness of 1 μm on the conductive support.

[0104] An oxo-titanyl phthalocyanine represented by the following structural formula (18) to be used as a charge generating material was previously obtained as follows.

[0105] [ka]

[0106] 29.2 g of diiminoisoindoline and 200 ml of sulfolane were mixed, and 17.0 g of titanium tetraisopropoxide was added and reacted under a nitrogen atmosphere at 140° C. for 2 hours. The resulting reaction mixture was allowed to cool, and the precipitate was collected by filtration, washed successively with chloroform and a 2% aqueous hydrochloric acid solution, further washed successively with water and methanol, and dried to obtain 25.5 g of blue-purple crystals.

[0107] As a result of chemical analysis of the obtained compound, it was confirmed that it was oxo-titanyl phthalocyanine represented by the above structural formula (18) (yield 88.5%).

[0108] 1 part by weight of the obtained titanyl phthalocyanine and 1 part by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name: BM-2) were added to 98 parts by weight of methyl ethyl ketone, and the mixture was dispersed for 2 hours using a paint shaker to prepare 3 liters of a coating solution for the charge generating layer.

[0109] The obtained coating liquid for the charge generating layer was applied onto the undercoat layer by the same dipping method as in the formation of the undercoat layer, and the obtained coating film was allowed to dry naturally to form a charge generating layer having a thickness of 0.3 μm.

[0110] Next, 230g of compound (15) as a charge transport material, 414g of a binder resin having the structure of compound (12) as a polycarbonate resin, n / (m+n)=0.4, an end group having the following structure (formula (19)), and a mass average molecular weight of 55000, 23.0g of compound (2), 68.7g of silica particles (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm), 11.5g of an antioxidant (manufactured by BASF: Irganox1076), and 2810g of tetrahydrofuran were added and mixed, and the mixture was stirred for 15 hours in a ball mill. The resulting mixture was subjected to 5-pass dispersion processing using a particle dispersion device (manufactured by Microfluidics, model: M-110P) to prepare a coating solution for a charge transport layer. The mixture obtained was applied onto the charge generating layer by the same immersion method as in the formation of the undercoat layer, and the resulting coating was dried at 130° C. for 1 hour to form a charge transport layer with a thickness of 34 μm, thereby obtaining an electrophotographic photoreceptor as shown in FIG. 1.

[0111] [ka]

[0112] Example 2 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 9.20 g, and 2810 g of tetrahydrofuran was changed to 2750 g.

[0113] Example 3 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 11.5 g, and 2810 g of tetrahydrofuran was changed to 2760 g.

[0114] Example 4 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 17.3 g, and 2810 g of tetrahydrofuran was changed to 2790 g.

[0115] Example 5 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 27.6 g, and 2830 g of tetrahydrofuran was changed to 2750 g.

[0116] Example 6 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 32.2 g, and 2850 g of tetrahydrofuran was changed to 2750 g.

[0117] Example 7 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 36.8 g, and 2810 g of tetrahydrofuran was changed to 2870 g.

[0118] Example 8 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 10.6 g, 68.7 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) was changed to 32.1 g, and 2810 g of tetrahydrofuran was changed to 2630 g.

[0119] Example 9 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 12.9 g, 68.7 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) was changed to 38.9 g, and 2810 g of tetrahydrofuran was changed to 2660 g.

[0120] Example 10 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 16.6 g, 68.7 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) was changed to 50.6 g, and 2810 g of tetrahydrofuran was changed to 2720 g.

[0121] Example 11 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 31.1 g, 68.7 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) was changed to 93.6 g, and 2810 g of tetrahydrofuran was changed to 2930 g.

[0122] Example 12 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, 23.0 g of compound (2) was changed to 39.1 g, 68.7 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) was changed to 117 g, and 2810 g of tetrahydrofuran was changed to 3050 g.

[0123] (Example 13) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, the binder resin of compound (12) was changed from 414 g to 276 g, the compound (2) was changed from 23.0 g to 34.5 g, the silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were changed from 68.7 g to 104 g, and tetrahydrofuran was changed from 2810 g to 2470 g.

[0124] Example 14 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, the binder resin of compound (12) was changed from 414 g to 322 g, the compound (2) was changed from 23.0 g to 34.5 g, the silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were changed from 68.7 g to 104 g, and tetrahydrofuran was changed from 2810 g to 2640 g.

[0125] Example 15 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, the binder resin of compound (12) was changed from 414 g to 460 g, the compound (2) was changed from 23.0 g to 41.4 g, the silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were changed from 68.7 g to 129 g, and tetrahydrofuran was changed from 2810 g to 3280 g.

[0126] (Example 16) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating solution for the charge transport layer, the binder resin of compound (12) was changed from 414 g to 575 g, the compound (2) was changed from 23.0 g to 48.3 g, the silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were changed from 68.7 g to 149 g, and tetrahydrofuran was changed from 2810 g to 3810 g.

[0127] (Example 17) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were replaced with silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL RX300 (registered trademark), number average primary particle diameter 7 nm).

[0128] (Example 18) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were replaced with silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL RX200 (registered trademark), number average primary particle diameter 12 nm).

[0129] (Example 19) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were replaced with silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NAX50 (registered trademark), number average primary particle diameter 30 nm).

[0130] (Example 20) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) were replaced with silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL RX50 (registered trademark), number average primary particle diameter 40 nm).

[0131] Example 21 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, compound (5) was used instead of compound (2).

[0132] Example 22 An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, compound (9) was used instead of compound (2).

[0133] (Example 23) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, the binder resin of compound (12) was changed to a polycarbonate resin having the following structure (formula (20)) (manufactured by Teijin Chemical Co., Ltd., product name: TS2050, mass average molecular weight 50,000).

[0134] [ka]

[0135] (Example 24) An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that in the preparation of the coating liquid for the charge transport layer, the binder resin of compound (12) was changed to a binder resin having the structure of compound (10) with n / (m+n)=0.30.

[0136] Comparative Example 1 A photoreceptor was prepared in the same manner as in Example 1, except that the compound (2) was not contained (that is, the compound of general formula (1) was not contained) in the preparation of the coating liquid for the charge transport layer.

[0137] Comparative Example 2 A photoreceptor was prepared in the same manner as in Example 1, except that the coating solution for the charge transport layer did not contain silica particles (manufactured by Nippon Aerosil Co., Ltd., product name: AEROSIL NX130 (registered trademark), number average primary particle diameter 16 nm) and was not subjected to dispersion treatment using a particle dispersion device (manufactured by Microfluidics, model: M-110P).

[0138] The conditions for the above examples and comparative examples are shown in Table 1.

[0139] [Table 1]

[0140] [evaluation] The photoreceptors prepared in Examples 1 to 24 and Comparative Examples 1 and 2 were mounted in a unit of a digital copier (Model: BP-50C65, manufactured by Sharp Corporation) modified for testing, and electrical characteristics, printing durability tests, and image evaluations were performed.

[0141] [Initial characteristics] The developing unit was removed from the copier, and a surface potential meter (Trek Japan: Model 344) was installed instead at the developing section, and the surface potential of the photoconductor without exposure was adjusted to -600 V in an environment of 25°C and 50% relative humidity, and the surface potential VL of the black background was measured in that state. The sensitivity was evaluated based on the obtained VL according to the following criteria.

[0142] <Judgment criteria> VG:VL(-V)< 130 It can also be used without problems in high-speed multifunction machines or printers that require high sensitivity. G: 130 ≦ VL(-V)< 160 It can be used without problems on medium to low speed multifunction devices or printers. NB:160≦VL(-V)< 200 If you have a slow, inexpensive multifunction device or printer, the density will be a little low, but you can use it without any problems. B: VL(-V)≧ 200 Due to poor sensitivity, the concentration is low, which is problematic in practical use.

[0143] [Fatigue properties] After the above sensitivity measurement, the developing unit was attached, and the pressure with which the cleaning blade of the cleaning unit contacted the photoconductor, the so-called cleaning blade pressure, was set to 21 gf / cm (2.06 × 10 -1 The linear pressure was adjusted to N / cm (initial linear pressure). A character test chart (ISO19752) was printed on 300,000 sheets of recording paper in a 25°C / 50% environment to perform fatigue and print endurance tests. After the test, the surface potential VL was measured using the same procedure as above. The difference between the VL after the test and the initial VL was taken as ΔVL, and the fatigue characteristics were evaluated according to the following criteria.

[0144] <Judgment criteria> VG:ΔVL< 40 It can also be used without problems in multifunction machines or printers that require high image quality without changes in density or color. G:40 ≦ ΔVL< 60 It can be used at a level where the change in density and color is barely noticeable. NB:70 ≦ ΔVL< 100 Although there is some change in density and color, it can be used without problems in inexpensive multifunction devices and printers. B: ΔVL≧ 100 The density and color tone change significantly every time printing is performed, which is problematic in practical use.

[0145] [Print durability] The thickness of the photosensitive layer at the start of the printing durability test and after 300,000 images were formed was measured using a film thickness measuring device (Filmetrics, Model: F-20-EXR).

[0146] The amount of scraping per 100,000 rotations of the photoconductor drum was calculated from the difference between the thickness at the start of the printing test and the thickness after 300,000 images were formed, and the printing durability was evaluated based on the amount of scraping obtained according to the following criteria. Note that the greater the amount of scraping, the worse the printing durability was evaluated to be.

[0147] <Judgment criteria> VG: Amount of wear < 1.00μm / 100,000 revolutions It can also be used without problems in multifunction devices or printers that require a long life. G: 1.00μm / 100,000 revolutions ≦ Cutting amount < 1.50μm / 100,000 revolutions Although the amount of wear is somewhat large, it can be used without problems except in multifunction devices or printers where a long life is required. NB: 1.50μm / 100,000 revolutions ≦ Cutting amount < 2.00μm / 100,000 revolutions Although there is a large amount of wear, it can be used without problems if it is an inexpensive multifunction device or printer. B: Amount of scraping ≧ 2.00μm / 100,000 revolutions The amount of chipping is large, which is problematic in terms of practical use.

[0148] <Cleaning ability> In order to confirm the level of cleaning defects of the photoreceptor after the printing durability test, the photoreceptor after 300,000 images were formed was set in the above-mentioned copier, and one 100% density untransferred image was output on an A4 sheet of paper. Immediately after that, the image forming device was forcibly stopped, and the surface of the photoreceptor was visually observed, and the degree of cleaning defects was evaluated based on the following evaluation criteria.

[0149] <Judgment criteria> VG: No occurrence. G: It can be used without problems in any machine other than a multifunction machine or printer that requires high image quality, where one or two cleaning defects are observed. NB: 3 to 5 cleaning defects were observed, but if it is an inexpensive multifunction device or printer, it can be used without problems. B: Numerous cleaning defects were observed, and problems existed in practical use.

[0150] <Charging roller contact stripe> To check the level of streaks caused by the contact of the charging roller, the initial photoconductor was set in the copier and left for two weeks in a 30°C / 85% RH environment. Immediately after leaving it, and after 3 minutes, 10 minutes, 1 hour, and 1 day, one halftone image was printed out and visually observed, and the degree of streaks was evaluated based on the following evaluation criteria.

[0151] <Judgment criteria> VG: No streaks appear even immediately after leaving the image. Or, streaks appear immediately after leaving the image, but disappear after 3 minutes. G: Although streaks still appear after 3 minutes, after 10 minutes the streaks have disappeared from the image. NB: Although streaks still appear after 10 minutes, after 1 hour the streaks have disappeared from the image. B: Streaks also appeared on the image after one day, which was problematic in practical use.

[0152] The results of the above evaluation are shown in Table 2.

[0153] [Table 2]

[0154] The results in Table 2 reveal the following:

[0155] In electrophotographic photoreceptors having a charge transport layer, photoreceptors (Examples 1 to 24) containing at least a binder resin, silica particles, and a compound of general formula (2) in the charge transport layer have excellent wear resistance due to the inclusion of silica particles, and it was confirmed that there are no problems with images even when left in contact with a charging roller, and there are no problems in practical use in terms of electrical characteristics, wear resistance, and cleanability at the initial stage and after fatigue. A photoreceptor (Comparative Example 1) that does not contain a compound of general formula (2) (also does not contain a compound of general formula (1)) generates streaks when left in contact with a charging roller for one day, which is problematic in practical use. It can be seen that a photoreceptor (Comparative Example 2) that does not contain silica particles has significantly inferior wear resistance.

[0156] The photoconductors of Examples 1 to 7 were used to confirm the dependency of the amount of the compound of general formula (2) added to the charge transport layer. From Examples 2 and 3, it was found that when the content of the compound of general formula (2) relative to the silica particles was 17%, the effect on the streaks that occur when the charging roller was in contact with the silica particles was reduced, and when it was 13%, the effect was even less. From Examples 6 and 7, it was found that when the content of the compound of general formula (2) relative to the silica particles was 47%, the initial sensitivity was slightly deteriorated, and when it was 53%, the initial sensitivity was greatly deteriorated. From this, it was found that the content of the compound of general formula (2) relative to the silica particles was preferably 15 to 50%. From Examples 4 and 5, it was found that 25 to 40% was even more preferable.

[0157] The content dependency of silica particles in the charge transport layer was confirmed for the photoreceptors of Examples 8 to 13. From Examples 8 and 9, it was found that when the silica content of the charge transport layer is 5.5% relative to the total solid content, the effect on wear resistance is reduced, and when it is less than 4.6%, the effect is even less. From Examples 12 and 13, it was found that when the silica content of the charge transport layer is 14.4% relative to the total solid content, the cleaning property tends to deteriorate, and when it is 15.8%, the cleaning property deteriorates further. From this, it was found that the silica content of the charge transport layer is preferably 5 to 15% relative to the total solid content. From Examples 10 and 11, it was found that 7 to 12% is even more preferable.

[0158] From the photoreceptors of Examples 14 to 16, it can be seen that in Example 15, where the value of the following formula is 1.27, the deterioration of sensitivity after fatigue tends to be large, and in Example 16, where the value is 1.30, the deterioration is even greater. From this, it can be seen that it is preferable for the value of the formula to be less than 1.25. (Amount of binder resin in charge transport layer / total solid content in charge transport layer) + (Amount of silica particles in charge transport layer / total solid content in charge transport layer) x 5

[0159] The particle size dependency of silica particles was confirmed for the photoreceptors of Examples 17 to 20. Example 17 shows that when the number average primary particle size of silica particles is 7 nm, the effect on abrasion resistance is small. Example 20 shows that when the number average primary particle size of silica particles is 40 nm, cleaning properties tend to deteriorate. Examples 18 and 19 show that a size of 12 to 30 nm is more preferable.

[0160] Various compounds of general formula (2) were confirmed in the photoreceptors of Examples 1, 21, and 22. All of the compounds were effective against streaks that occur when the photoreceptor is in contact with a charging roller. From the results of the initial sensitivity, it can be seen that compound (2) is suitable.

[0161] Various binder resins were confirmed for the photoreceptors of Examples 1, 23, and 24. The polycarbonate of Example 23 had slightly inferior abrasion resistance compared to the copolymer polycarbonates of Examples 1 and 24. Furthermore, when Examples 1 and 24 are compared, it is found that the binder resin of general formula (12) is preferable based on the abrasion resistance results.

[0162] As described above, according to the present disclosure, by containing a binder resin, silica particles, and a compound of general formula (1) on a conductive support, the toner has high sensitivity, excellent printing durability, and high mechanical strength, and can prevent image defects even when left in contact with a charging roller.

[0163] Although each embodiment and each example of the present disclosure have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure.

[0164] For example, a term described at least once in the specification or drawings together with a different term having a broader meaning or the same meaning may be replaced with the different term anywhere in the specification or drawings. In addition, the configurations and operations of the electrophotographic photoreceptor and the image forming apparatus are not limited to those described in the embodiments and examples of the present disclosure, and various modifications are possible. [Explanation of symbols]

[0165] 1 electrophotographic photoreceptor, 11 conductive support, 12 charge generating material, 13 charge transport material, 14 photosensitive layer (laminated photosensitive layer), 15 charge generating layer, 16 charge transport layer, 17 binder resin, 18 undercoat layer, 19 compound of general formula (1), 20 silica particles, 31 exposure unit (semiconductor laser), 32 charging unit (charging roller), 33 developing unit (developer), 33a developing roller, 33b casing, 34 transfer unit (transfer charger), 35 fixing unit (fixer), 35a heating roller, 35b pressure roller, 36 cleaning unit (cleaner), 36a cleaning blade, 36b recovery casing, 37 separation unit, 38 housing, 41, 42 arrow, 44 rotation axis, 45 recording medium (recording paper or transfer paper), 100 Image forming device

Claims

1. An electrophotographic photoreceptor having at least a charge generating layer and a charge transport layer formed in this order on a conductive support, The electrophotographic photoreceptor, wherein the charge transport layer contains a binder resin, silica particles, and a compound represented by general formula (1). 【Chemistry 1】 (In the general formula (1), the substituents R1 to R5 are any one type of substituent selected from the group consisting of a hydrogen atom, a cyano group, a nitro group, a halogen atom, a hydroxyl group, an alkyl group, an aryl group, a heterocyclic group, an ester group, an alkoxy group, an aralkyl group, an allyl group, an amide group, an amino group, an acyl group, an alkenyl group, an alkynyl group, a carboxyl group, a carbonyl group, and a carboxylic acid group.)

2. 2. The electrophotographic photoreceptor according to claim 1, wherein the compound of the general formula (1) is contained in an amount of 15 to 50 wt % based on the content of the silica particles.

3. 2. The electrophotographic photoreceptor according to claim 1, wherein the silica particles are contained in an amount of 5 to 15 wt % based on the total solid content in the charge transport layer.

4. (amount of the binder resin in the charge transport layer / total solid content of the charge transport layer)+(amount of the silica particles in the charge transport layer / total solid content of the charge transport layer)×5<1.25 4. The electrophotographic photoreceptor according to claim 3, which satisfies the above.

5. 2. The electrophotographic photoreceptor according to claim 1, wherein the compound represented by the general formula (1) is represented by the general formula (2). 【Chemistry 2】

6. 2. The electrophotographic photoreceptor according to claim 1, wherein the number average primary particle diameter of the silica particles is 12 to 30 nm.

7. The electrophotographic photoreceptor according to claim 1 , wherein the binder resin has a structure represented by general formula (3). 【Chemistry 3】 (In formula (3), R 6 , R 7 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a fluoroalkyl group having 1 to 10 carbon atoms, n and m satisfy 0.4≦n / (m+n)≦0.6, and the chain end group is a monovalent aromatic group or a monovalent fluorine-containing aliphatic group.

8. 2. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer is formed as a surface layer.

9. The electrophotographic photoreceptor according to any one of claims 1 to 8, an image forming section which charges the electrophotographic photoreceptor with a charging roller, and then exposes, transfers, and fixes the image to form an image; An image forming apparatus comprising:

Images