Image forming apparatus

Abstract

To provide an image forming apparatus that can suppress the influence of the printing environment on print quality. [Solution] The image forming apparatus comprises a photoreceptor, a charging roller, and a power supply. The photoreceptor has a relative permittivity of 3.7 to 6.2. The charging roller charges the photoreceptor and has a rotational resistance of 5.2 log Ω to 6.1 log Ω on its surface. The power supply applies a DC voltage to the charging roller.

Description

Technical Field

[0001] This technology relates to an image forming apparatus used for electrophotographic printing.

Background Art

[0002] In an image forming apparatus using an electrophotographic process, a drum-shaped photoreceptor is used as an image carrier. After uniformly charging the surface of the photoreceptor by a charging device, light is irradiated onto the surface of the photoreceptor by an exposure device to form an electrostatic latent image with the charge in the light-irradiated area attenuated. Then, the electrostatic latent image is developed into a toner image by a developing device, and the toner image is directly transferred onto printing paper by applying a transfer voltage of the opposite polarity to the toner to the transfer device, or is first transferred to an intermediate transfer member and then secondarily transferred onto printing paper, and the toner image is thermally fixed to the paper by a fixing device.

[0003] In order to improve the performance of the image forming apparatus, continuous research and development have been carried out on the photoreceptor. For example, Patent Document 1 discloses an electrophotographic photoreceptor that can form a photoreceptive layer well, has excellent charging stability, and can suppress transfer memory.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In image forming apparatuses using electrophotographic processes, print quality can be affected by the printing environment. For example, in low-temperature, low-humidity environments, "fogging" is likely to occur, where toner adheres to the exposed area on the surface of the photoreceptor, while in high-temperature, high-humidity environments, black spots are likely to occur due to localized charge injection in the photoreceptor. The inventors focused on the electrical characteristics of the photoreceptor and the charging roller and found that these electrical characteristics can suppress the influence of the printing environment on print quality.

[0006] In light of the above circumstances, the objective of this technology is to provide an image forming apparatus that can suppress the influence of the printing environment on print quality. [Means for solving the problem]

[0007] To achieve the above objective, an image forming apparatus according to one embodiment of the present invention comprises a photoreceptor, a charging roller, and a power supply. The photoreceptor has a relative permittivity of 3.7 to 6.2. The above-mentioned charging roller charges the photoreceptor, and the rotational resistance of its surface is 5.2 log Ω or more and 6.1 log Ω or less. The power supply applies a DC voltage to the charging roller.

[0008] The above-described image device can prevent "fogging" in low-temperature, low-humidity environments and the formation of black spots in high-temperature, high-humidity environments, thereby suppressing the impact of the printing environment on print quality.

[0009] The charging roller has an elastic layer having conductivity and elasticity, and a surface layer formed on the elastic layer. The surface layer may contain nylon resin, conductive particles, and acrylic particles.

[0010] The photoreceptor may be a single-layer photoreceptor. [Effects of the Invention]

[0011] As described above, the present invention can provide an image forming apparatus that can suppress the influence of the printing environment on print quality. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of the image forming unit included in the image forming apparatus described above. [Figure 3] This is a schematic diagram of the photoreceptor included in the image forming apparatus described above. [Figure 4] This is a schematic diagram of the electrostatic roller included in the image forming apparatus described above. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below.

[0014] [Configuration of the image forming apparatus] An image forming apparatus 100 according to an embodiment of the present invention will now be described. Figure 1 is a schematic diagram showing the configuration of the image forming apparatus 100. The image forming apparatus 100 is, for example, a tandem color printer.

[0015] As shown in Figure 1, the image forming apparatus 100 comprises a control unit 10, an operation unit 20, a paper feeding unit 30, a transport unit 40, a toner supply unit 50, an image forming unit 60, a transfer device 70, a fixing device 80, and a discharge unit 90.

[0016] The control unit 10 controls the operation of each part of the image forming apparatus 100. The control unit 10 includes an arithmetic processing unit and a storage unit (not shown). The arithmetic processing unit is, for example, a CPU (central processing unit), and the storage unit is, for example, semiconductor memory or an HDD (hard disk drive). The arithmetic processing unit controls the operation of the image forming apparatus 100 by executing a control program. The storage unit stores the control program.

[0017] The operation unit 20 receives instructions from the user. When the operation unit 20 receives an instruction from the user, it transmits a signal indicating the instruction from the user to the control unit 10. As a result, the image forming operation by the image forming apparatus 100 is started.

[0018] The paper feeding unit 30 has a paper feed cassette 31 and a paper feed roller group 32. The paper feed cassette 31 can accommodate a plurality of recording media P. The recording media P is, for example, printing paper. The paper feed roller group 32 feeds the recording media P accommodated in the paper feed cassette 31 to the conveying unit 40 one by one.

[0019] The conveying unit 40 includes rollers and guide members. The conveying unit 40 extends from the paper feeding unit 30 to the discharging unit 90. The conveying unit 40 conveys the recording media P from the paper feeding unit 30 to the discharging unit 90 via the image forming unit 60 and the fixing device 80.

[0020] The toner supply unit 50 supplies toner to the image forming unit 60. The toner supply unit 50 includes a first mounting unit 51Y, a second mounting unit 51C, a third mounting unit 5(1M), and a fourth mounting unit 51K. A first toner container 52Y is mounted on the first mounting unit 51Y. A second toner container 52C is mounted on the second mounting unit 51C, a third toner container 52M is mounted on the third mounting unit 51M, and a fourth toner container 52K is mounted on the fourth mounting unit 51K.

[0021] The first toner container 52Y contains yellow toner, and the second toner container 52C contains cyan toner. The third toner container 52M contains magenta toner, and the fourth toner container 52K contains black toner. Note that the color of each toner is not limited to those shown here, and other colors may be used. The number of colors may be one or more.

[0022] The image forming unit 60 comprises an exposure apparatus 61, a first image forming unit 62Y, a second image forming unit 62C, a third image forming unit 62M, and a fourth image forming unit 62K. Figure 2 is a schematic diagram of the image forming unit 62. The first image forming unit 62Y, the second image forming unit 62C, the third image forming unit 62M, and the fourth image forming unit 62K have the configuration of the image forming unit 62 shown in Figure 2. The image forming unit 62 includes a charging device 63, a developing device 64, a photoreceptor 65, a cleaning device 66, and a static elimination device 67. The charging device 63, the developing device 64, the cleaning device 66, and the static elimination device 67 are arranged along the surface 65a of the photoreceptor 65.

[0023] The exposure apparatus 61 (see Figure 1) irradiates light (dashed line in the figure) onto the surface 65a of the photoreceptor 65 of each image forming unit 62, thereby exposing the surface 65a. Based on the supplied image data, the exposure apparatus 61 irradiates each image forming unit 62 with light for each color, performing exposure. The exposure apparatus 61 can perform exposure using laser light.

[0024] The photoreceptor 65 forms an electrostatic latent image when exposed by the exposure device 61. The surface 65a of the photoreceptor 65 is pre-charged positively or negatively. When this surface 65a is exposed by the exposure device 61, the charge attenuates in the irradiated area, and an electrostatic latent image is formed. The photoreceptor 65 can be made of OPC (Organic Photo Conductor). The detailed configuration of the photoreceptor 65 will be described later. The photoreceptor 65 rotates in the direction indicated by the arrow in Figure 2 (clockwise).

[0025] The charging device 63 positively or negatively charges the surface 65a. The charging device 63 comprises a charging roller 631, a charging voltage power supply 632, and a cleaning brush 633. The charging roller 631 contacts the surface 65a to uniformly charge the surface 65a. The detailed configuration of the charging roller 631 will be described later. The charging voltage power supply 632 applies a charging voltage to the charging roller. A DC voltage is preferred for this charging voltage. The cleaning brush 633 contacts the charging roller 631 to clean it.

[0026] The developing device 64 supplies toner supplied from the toner supply unit 50 to the surface 65a. As shown in Figure 2, the developing device 64 is equipped with a developing roller 641. The toner supplied from the toner container is mixed with a magnetic carrier to form a two-component developer. At this time, the toner becomes charged with the same polarity as the surface 65a due to friction with the carrier.

[0027] The two-component developer is attracted to the developing roller 641 by magnetic force and transported to a position opposite the photoreceptor 65. A voltage is applied between the developing roller 641 and the photoreceptor 65, causing the toner in the two-component developer to adhere to the electrostatic latent image on the surface 65a. This forms a toner image on the surface 65a that matches the electrostatic latent image.

[0028] The developing device 64 of the first image forming unit 62Y is connected to the first toner container 52Y, and yellow toner is supplied. As a result, a yellow toner image is formed on the surface of the photoreceptor 65 of the first image forming unit 62Y. Similarly, the developing device 64 of the second image forming unit 62C is connected to the second toner container 52C, and a cyan toner image is formed on the surface of the photoreceptor 65 of the second image forming unit 62C.

[0029] Furthermore, the developing device 64 of the third image forming unit 62M is connected to the third toner container 52M, and a magenta toner image is formed on the surface of the photoreceptor 65 of the third image forming unit 62M. The developing device 64 of the fourth image forming unit 62K is connected to the fourth toner container 52K, and a black toner image is formed on the surface of the photoreceptor 65 of the fourth image forming unit 62K.

[0030] The cleaning device 66 recovers the toner adhering to the surface 65a after the transfer by the primary transfer roller 71, which will be described later. Specifically, the cleaning device 66 recovers the toner adhering to the surface 65a by pressing the cleaning blade 661 against the surface 65a. The static elimination device 67 removes static electricity from the surface 65a by irradiating it with static elimination light.

[0031] The transfer device 70 (see Figure 1) transfers the toner image from the photoreceptor 65 to the recording medium P, which is the object to be transferred. Specifically, the transfer device 70 transfers the toner images of each color formed on the surface 65a of the photoreceptor 65 of each image forming unit 62 onto the recording medium P. The transfer device 70 can transfer each toner image onto the recording medium P by a secondary transfer method (intermediate transfer method). For the secondary transfer method, the transfer device 70 has four primary transfer rollers 71, an intermediate transfer belt 72, a drive roller 73, a driven roller 74, and a secondary transfer roller 75.

[0032] The intermediate transfer belt 72 is an endless belt stretched over four primary transfer rollers 71, a drive roller 73, and a driven roller 74. The intermediate transfer belt 72 is driven in accordance with the rotation of the drive roller 73. In Figure 1, the intermediate transfer belt 72 rotates in the direction indicated by the arrow in Figure 1 (counterclockwise). The driven roller 74 is rotationally driven in accordance with the driving of the intermediate transfer belt 72.

[0033] Each image forming unit 62 faces the lower surface of the intermediate transfer belt 72 and is arranged in the order of the first image forming unit 62Y to the fourth image forming unit 62K, from the upstream side to the downstream side in the driving direction of the lower surface of the intermediate transfer belt 72.

[0034] Each primary transfer roller 71 is positioned opposite each photoreceptor 65 via an intermediate transfer belt 72 and is pressed toward each photoreceptor 65. As a result, the toner image formed on the surface 65a of each photoreceptor 65 is sequentially transferred to the intermediate transfer belt 72 by each primary transfer roller 71. In the configuration shown in Figure 1, the yellow toner image, cyan toner image, magenta toner image, and black toner image are transferred to the intermediate transfer belt 72 in this order, but the order of the toner images is not limited to this. Hereinafter, the toner image formed by stacking the yellow toner image, cyan toner image, magenta toner image, and black toner image will be referred to as a "stacked toner image".

[0035] The secondary transfer roller 75 is positioned opposite the drive roller 73 via the intermediate transfer belt 72. The secondary transfer roller 75 is pressed toward the drive roller 73. This forms a transfer nip (contact area) between the secondary transfer roller 75 and the drive roller 73, and as the recording medium P passes through the transfer nip, the secondary transfer roller 75 transfers the layered toner image on the intermediate transfer belt 72 to the recording medium P. The layering order of the layered toner image on the recording medium P is the opposite of the layering order of the layered toner image on the intermediate transfer belt 72. The recording medium P on which the layered toner image has been transferred is transported toward the fuser 80 by the transport unit 40.

[0036] The fuser unit 80 fixes the stacked toner image onto the recording medium P. The fuser unit 80 includes a heating member 81 and a pressurizing member 82. The heating member 81 and the pressurizing member 82 are arranged facing each other to form a fuser nip. The recording medium P, transported from the image forming unit 60, is heated and pressurized at a predetermined fixing temperature as it passes through the fuser nip, and the stacked toner image is fixed onto the recording medium P. The recording medium P is transported from the fuser unit 80 to the discharge unit 90 by the transport unit 40.

[0037] The discharge unit 90 discharges the recording medium P on which the stacked toner image has been fixed. The discharge unit 90 has a pair of discharge rollers 91, a discharge port 92, and a discharge tray 93. The pair of discharge rollers 91 transports the recording medium P to the discharge tray 93 via the discharge port 92.

[0038] The image forming method using the image forming apparatus 100 will now be described. When the control unit 10 acquires image data and the operation unit 20 receives an instruction from the user to start the image forming operation, the photoreceptor 65 in each image forming unit 62 is rotated, and the charging roller 631 uniformly charges the surface 65a.

[0039] Next, the exposure device 61 exposes the surface 65a of each image forming unit 62 according to the image data, forming an electrostatic latent image for each color on the surface 65a. The developing device 64 of each image forming unit supplies toner of each color to the surface 65a, which then electrostatically adheres to the electrostatic latent image for each color. As a result, a toner image of each color is formed on the surface 65a of each photoreceptor 65. If the amount of toner filled in each developing device 64 falls below a specified value due to the formation of the toner image, toner is replenished to each developing device 64 from the first toner container 52Y to the fourth toner container 52K.

[0040] An electric field is applied between the primary transfer roller 71 and the photoreceptor 65 at a predetermined transfer voltage by the primary transfer roller 71. As a result, the toner images of each color on the surface 65a are primary transferred onto the intermediate transfer belt 72. The toner images of each color are stacked, and a stacked toner image is formed on the intermediate transfer belt 72. Subsequently, in preparation for the formation of a new electrostatic latent image, any toner remaining on the surface 65a after the primary transfer is removed by the cleaning device 66.

[0041] As the intermediate transfer belt 72 rotates counterclockwise in conjunction with the rotation of the drive roller 73, the transport unit 40 transports the recording medium P to the transfer nip between the secondary transfer roller 75 and the drive roller 73 at a predetermined timing, and the laminated toner image on the intermediate transfer belt 72 is secondarily transferred onto the recording medium P. The recording medium P on which the laminated toner image has been secondarily transferred is then transported by the transport unit 40 to the fuser 80.

[0042] The recording medium P, transported to the fixing device 80, is heated and pressurized by the heating element 81 and the pressurizing element 82, causing the laminated toner image to fix to the surface of the recording medium P, and a color image is formed on the recording medium P. The recording medium P on which the color image has been formed is discharged to the discharge tray 93 in the discharge unit 90.

[0043] The image forming apparatus 100 has the configuration described above. The configuration of the image forming apparatus according to the present invention is not limited to that described above, and may include a photoreceptor 65 and a charging roller 631 having the configuration described later. For example, although the image forming apparatus 100 is an image forming apparatus capable of forming color images, the image forming apparatus according to the present invention may be an image forming apparatus capable of forming monochrome images. In this case, the image forming apparatus may include only one image forming unit.

[0044] Furthermore, although the image forming apparatus 100 is a tandem type image forming apparatus, the image forming apparatus according to the present invention may be a rotary type image forming apparatus. In addition, although the image forming apparatus 100 is a touchdown development type image forming apparatus, the image forming apparatus according to the present invention may be an image forming apparatus with a development method other than the touchdown development method.

[0045] Furthermore, although the image forming apparatus 100 is an intermediate transfer type image forming apparatus, the image forming apparatus according to the present invention may be a direct transfer type image forming apparatus. In this case, the toner image is directly transferred from the photoreceptor 65 to the recording medium P while the photoreceptor 65 is in contact with the recording medium P. In addition, although each image forming unit 62 is equipped with a static elimination device 67, each image forming unit 62 may not be equipped with a static elimination device 67.

[0046] [Composition of the photoreceptor] The structure of the photoreceptor 65 described above will now be explained. Figure 3 is a cross-sectional view of the surface of the photoreceptor 65. As shown in the figure, the photoreceptor 65 comprises a conductive substrate 651 and a photosensitive layer 652. The conductive substrate 651 is made of a conductive material such as aluminum and has a cylindrical shape. The photosensitive layer 652 is made of an organic photosensitive material and is formed as a thin film on the conductive substrate 651. Generally, there are "single-layer photoreceptors" in which the photosensitive layer is a single layer and "multilayer photoreceptors" in which the photosensitive layer is a multiple layer, but a single-layer photoreceptor is preferred for the photoreceptor 65. An undercoat layer may be provided between the conductive substrate 651 and the photosensitive layer 652.

[0047] The photosensitive layer 652 consists of an organic photosensitive material as described above, and specifically contains a charge generating material, a hole transport material, an electron transport material, and a binder resin.

[0048] Examples of charge-generating materials include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free sodium compounds, metallic sodium compounds, squaline pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (e.g., selenium, selenium-tellurium, selenium-arsenide, cadmium sulfide, and amorphous silicon), pyryllium pigments, anthenslon pigments, triphenylmethane pigments, surene pigments, toluidine pigments, pyrazoline pigments, and quinacridone pigments. The photosensitive layer 652 may contain only one type of charge-generating material, or it may contain two or more types of charge-generating materials.

[0049] Specifically, Y-type titanylphthalocyanine, a phthalocyanine pigment, can be used as the charge generating material. Y-type titanylphthalocyanine is shown below in (Equation 1).

[0050] [ka]

[0051] Examples of hole transport materials include triphenylamine derivatives, diamine derivatives (e.g., N,N,N',N'-tetraphenylbenzine derivatives, N,N,N',N'-tetraphenylphenylenediamine derivatives, N,N,N',N'-tetraphenylnaphthylenediamine derivatives, N,N,N',N'-tetraphenylphenantolylenediamine derivatives, and di(aminophenylethenyl)benzene derivatives), oxadiazole compounds (e.g., 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole) Examples include ), styryl compounds (e.g., 9-(4-diethylaminostyryl)anthracene), carbazole compounds (e.g., polyvinylcarbazole), organic polysilane compounds, pyrazoline compounds (e.g., 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds. The photosensitive layer 652 may contain only one type of hole transport material, or it may contain two or more types of hole transport materials.

[0052] Specifically, the substance shown in (Equation 2) below can be used as the hole transport material.

[0053] [ka]

[0054] Examples of electron transport materials include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds. The photosensitive layer 652 may contain only one electron transport material or two or more electron transport materials.

[0055] Specifically, the substance shown in (Equation 3) below can be used as the electron transport material.

[0056] [ka]

[0057] Examples of binder resins include polyarylate resins, polycarbonate resins, styrene-based resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, styrene-acrylic acid copolymers, acrylic copolymers, polyethylene resins, ethylene-vinyl acetate copolymers, chlorinated polyethylene resins, polyvinyl chloride resins, polypropylene resins, ionomers, vinyl chloride-vinyl acetate copolymers, polyester resins, alkyd resins, polyamide resins, polyurethane resins, polysulfone resins, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyvinyl acetal resins, and polyether resins, silicone resins, epoxy resins, phenolic resins, urea resins, melamine resins, epoxy-acrylic acid resins, and urethane-acrylic acid copolymers. The photosensitive layer 652 may contain only one type of binder resin, or it may contain two or more types of binder resins.

[0058] Specifically, as the binder resin, a polyalate resin having the repeating units shown in (Equation 4) to (Equation 7) below can be used. For example, each repeating unit is 40 parts by mass of (Equation 4), 10 parts by mass of (Equation 5), 25 parts by mass of (Equation 6), and 25 parts by mass of (Equation 7).

[0059] [ka]

[0060] [ka]

[0061] [ka]

[0062] [ka]

[0063] The photosensitive layer 652 has the above-described structure. In addition to the materials described above, the photosensitive layer 652 may also contain additives. Examples of additives include ultraviolet absorbers, antioxidants, radical scavengers, singlet quenchers, softeners, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, waxes, donors, surfactants, plasticizers, sensitizers, and leveling agents. The photosensitive layer 652 may contain one or more of these additives.

[0064] The relative permittivity of the photoreceptor 65 is preferably 3.7 to 6.2. The relative permittivity of the photoreceptor 65 can be adjusted by the content of the charge generating material in the photosensitive layer 652. Specifically, when using the Y-type titanyl phthalocyanine shown in (Formula 1) above as the charge generating material, the relative permittivity of the photoreceptor 65 can be set to 3.7 to 6.2 by setting the content of Y-type titanyl phthalocyanine to 2 phr to 7 phr. Note that "phr" represents parts by mass of Y-type titanyl phthalocyanine per 100 parts by mass of binder resin.

[0065] [Method for manufacturing photoreceptors] A method for manufacturing the photoreceptor 65 will now be described. The photoreceptor 65 can be manufactured by forming a photosensitive layer 652 on a conductive substrate 651. The photosensitive layer 652 can be formed on the conductive substrate 651 by preparing a coating solution by mixing a solvent with the above-mentioned charge generating material, hole transport material, electron transport material, and binder resin, applying this coating solution to the conductive substrate 651, and removing the solvent. The materials can be mixed using a bead mill, roll mill, ball mill, attritor, paint shaker, rod-shaped ultrasonic oscillator, or ultrasonic disperser.

[0066] The solvent can be any solvent capable of dissolving the binder resin, and examples include alcohols (specifically methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (specifically n-hexane, octane, and cyclohexane), aromatic hydrocarbons (specifically benzene, toluene, and xylene), halogenated hydrocarbons (specifically dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene), ethers (specifically dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether), ketones (specifically acetone, methyl ethyl ketone, and cyclohexanone), esters (specifically ethyl acetate and methyl acetate), dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide.

[0067] The coating solution can be applied using a method that allows for uniform application, and one of the following methods can be used: dip coating, spray coating, spin coating, bar coating, or blade coating. The solvent can be removed by heating, reduced pressure, or a combination of heating and reduced pressure, specifically using a high-temperature dryer or a vacuum dryer.

[0068] [Structure of the electrostatic roller] The configuration of the electrostatic roller 631 described above will now be explained. Figure 4 is a cross-sectional view of the electrostatic roller 631. As shown in the figure, the electrostatic roller 631 comprises a conductive shaft 634, an elastic layer 635, and a surface layer 636.

[0069] The conductive shaft 634 is a rod-shaped component made of a conductive material. Examples of conductive materials include metals such as iron, aluminum, titanium, copper, and nickel, alloys such as stainless steel, duralumin, brass, and bronze, and composite materials made by solidifying carbon black or carbon fibers with plastic. The conductive shaft 634 may be cylindrical or cylindrical in shape.

[0070] The elastic layer 635 is conductive and elastic and is provided around the conductive shaft 634. As the material for the elastic layer 635, a mixture of an elastic material and a conductive material can be used. Examples of elastic materials include hydrin rubber, polyurethane elastomer, hydrin rubber, styrene-butadiene rubber (SBR), polynorbornene rubber, ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), butadiene rubber (BR), isoprene rubber (IR), natural rubber (NR), and silicone rubber. Hydrin rubber is more preferred as the elastic material, and specifically epichlorohydrin rubber is preferred.

[0071] The conductive material mixed with the above-mentioned elastic material is at least one of an electronic conductive material and an ionic conductive material. Examples of electronic conductive materials include carbon black, graphite, potassium titanate, iron oxide, titanium oxide, zinc oxide, and tin oxide. Tin oxide and carbon black are more preferred as electronic conductive materials. The content ratio of the electronic conductive material in the elastic layer 635 is preferably 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the elastic material.

[0072] Examples of ionic conductive materials include organic salts (e.g., sodium trifluoroacetate), inorganic salts (e.g., quaternary ammonium salts), metal complexes, and ionic liquids. Sodium trifluoroacetate is more preferred as the ionic conductive material. The preferred content of the ionic conductive material in the elastic layer 635 is 0.1 parts by mass to 2 parts by mass per 100 parts by mass of elastic material.

[0073] The elastic layer 635 may further contain one or more additives such as plasticizers, fillers, vulcanizing agents, vulcanization accelerators, antioxidants, scorch inhibitors, dispersants, and release agents.

[0074] The surface layer 636 contains a binder resin, conductive particles, and resin fine particles. A polyamide resin can be used as the binder resin, with nylon resin being more preferable. Specifically, the copolymer nylon resin "PA100-AS" (manufactured by T&K TOKA Co., Ltd.) can be used as the nylon resin. The binder resin content in the surface layer 636 is preferably 25% by mass or more and 60% by mass or less, and more preferably 35% by mass or more and 45% by mass or less. By setting the content to 25% by mass or more, sufficient strength of the surface layer 636 can be ensured, and by setting it to 60% by mass or less, it becomes easier to ensure the amount of resin particles and conductive particles in the surface layer 636.

[0075] Conductive particles impart appropriate conductivity to the surface layer. Examples of conductive particles include carbon black, graphite, and metal oxide particles. Examples of metal oxides include potassium titanate, iron oxide, titanium oxide, zinc oxide, tin oxide, antimond-doped tin oxide, and phosphorus-doped tin oxide. Carbon black is more preferable as the conductive particle.

[0076] The resin particles impart an appropriate surface roughness to the surface layer 636. Examples of resins that form the resin particles include (meth)acrylic resin, urethane resin, silicone resin, polyester resin, polystyrene resin, styrene-(meth)acrylic resin, and polyolefin resin. Acrylic resin is more preferable as the resin, and specifically, "MZ-5HN" (crosslinked acrylic dispersed particles, manufactured by Soken Chemical Co., Ltd.), which consists of crosslinked polymethyl methacrylate, can be used.

[0077] The electrostatic roller 631 is preferably one in which the rotational resistance of the surface, i.e., the surface of the surface layer 636, is between 5.2 log Ω and 6.1 log Ω. This rotational resistance can be adjusted by the content of conductive particles in the surface layer 636. Specifically, when carbon black and tin oxide particles are used as conductive particles, the rotational resistance can be set to 5.2 log Ω and 6.1 log Ω by setting the carbon black content to 5 phr and the tin oxide particle content to 8 phr and 40 phr or less. Note that "phr" represents the parts by mass of carbon black or tin oxide particles per 100 parts by mass of elastic material.

[0078] [Method for manufacturing an electrostatic roller] A method for manufacturing the electrostatic roller 631 will now be described. The electrostatic roller 631 can be manufactured by forming an elastic layer 635 on a conductive shaft 634 and then forming a surface layer 636 on the elastic layer 635. The elastic layer 635 can be formed by preparing a composition by mixing the elastic material and conductive material described above, heating this composition and injecting it into a mold in which the conductive shaft 634 is set, and then demolding after cooling. The mixing of the elastic material and conductive material can be done using a stirrer.

[0079] The surface layer 636 can be formed on the elastic layer 635 by preparing a coating solution by mixing a solvent with the aforementioned binder resin, conductive particles, and resin particles, applying this coating solution to the elastic layer 635, and then removing the solvent. The materials can be mixed using a wet disperser such as a ball mill, bead mill, or roll mill.

[0080] The coating solution can be applied using a method that allows for uniform application, and one of the following methods can be used: dip coating, spray coating, spin coating, bar coating, or blade coating. The solvent can be removed by heating, reduced pressure, or a combination of heating and reduced pressure, specifically using a high-temperature dryer or a vacuum dryer.

[0081] [Effects of image forming apparatus] As described above, the image forming apparatus 100 includes a photoreceptor 65 having a relative permittivity of 3.7 to 6.2 and a charging roller 631 having a surface rotational resistance of 5.2 log Ω to 6.1 log Ω. This allows the surface potential of the photoreceptor 65 to be lowered to 160 V or less. When the surface potential of the photoreceptor 65 is high, "white area carrier development," in which carriers move to the surface of the photoreceptor 65, is more likely to occur, but by lowering the surface potential of the photoreceptor 65, the occurrence of this phenomenon can be suppressed.

[0082] Furthermore, in general, image forming apparatuses experience "fogging," where toner adheres to the exposed area of ​​the surface 65a in low-temperature, low-humidity (LL) environments. However, in the image forming apparatus 100, the occurrence of fogging can be suppressed by configuring the photoreceptor 65 and the charging roller 631 as described above. In addition, in general, image forming apparatuses experience black spots on the recording medium due to localized charge injection into the photosensitive layer 652 in high-temperature, high-humidity (HH) environments. However, in the image forming apparatus 100, the occurrence of black spots can be suppressed by configuring the photoreceptor 65 and the charging roller 631 as described above. As described above, the image forming apparatus 100 can suppress the influence of the printing environment on print quality. [Examples]

[0083] Photoreceptors and charging rollers according to the embodiments and comparative examples of the present invention were fabricated, and various physical properties were measured. Furthermore, the printing performance of an image forming apparatus equipped with the fabricated photoreceptors and charging rollers was evaluated.

[0084] [Fabrication of the photoreceptor] The photoreceptor was prepared as follows. First, a coating solution was prepared by dispersing the following materials in a solvent using a rod-shaped acoustic oscillator. The dispersion time was 10 minutes. The materials were: Y-type titanyl phthalocyanine as shown in (Formula 1) above as a charge generating material, 60 parts by mass of the substance shown in (Formula 2) above as a hole transport material, 50 parts by mass of the substance shown in (Formula 3) above as an electron transport material, and 100 parts by mass of polyalate resin as shown in (Formula 4) above as a binder resin. The content of Y-type titanyl phthalocyanine differed between the examples and comparative examples. The polyalate resin contained 40 parts by mass of repeating units shown in (Formula 4), 10 parts by mass of repeating units shown in (Formula 5), ​​25 parts by mass of repeating terminals shown in (Formula 6), and 25 parts by mass of repeating units shown in (Formula 7). The solvent was 500 parts by mass of tetrahydrofuran.

[0085] Next, the prepared coating solution was filtered through a 5 μm mesh filter. The coating solution was then applied to the surface of the conductive substrate using a dip-coating method to form a coating film. The coating film was dried at 120°C for 50 minutes to remove the solvent and form a photosensitive layer. The thickness of the photosensitive layer was approximately 35 μm. The photoreceptor was prepared in the manner described above.

[0086] [Manufacturing of an electrostatic roller] The electrostatic roller was manufactured as follows. First, the following materials were stirred and mixed using a stirrer to prepare the composition. The materials were: 100 parts by mass of epichlorohydrin rubber ("Epichromer CG-102" (manufactured by Osaka Soda Co., Ltd.)), 5 parts by mass of vulcanization aid (zinc oxide, "Zinc Oxide Type 2" (manufactured by Mitsui Mining & Smelting Co., Ltd.)), 1.5 parts by mass of vulcanization accelerator (MBT (2-Mercaptobenzothiazole), "Noxellar MP" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)), 1 part by mass of sulfur ("Sulfax PS" (manufactured by Tsurumi Chemical Industry Co., Ltd.)), 50 parts by mass of filler (calcium carbonate, "Hakuenka CC" (manufactured by Shiraishi Kogyo Co., Ltd.)), 20 parts by mass of electronically conductive material (carbon black, "Asahi #50" (manufactured by Asahi Carbon Co., Ltd.)), and 0.5 parts by mass of ionic conductive material (sodium trifluoroacetate).

[0087] A conductive shaft (6 mm in diameter) was placed in a mold, the above composition was poured into the mold, heated at 160°C for 20 minutes, then cooled and demolded to form an elastic layer with a thickness of 1.8 mm on the outer circumference of the conductive shaft.

[0088] Next, a coating solution was prepared by dispersing the following materials in a solvent using a ball mill. The materials consisted of 100 parts by mass of copolymerized nylon resin ("PA100-AS" (manufactured by T&K TOKA)) as a binder resin, 50 parts by mass of crosslinked acrylic dispersed particles ("MZ-5HN" (manufactured by Soken Chemical Co., Ltd.)) as resin particles, and 5 parts by mass of tin oxide particles ("SP2" (manufactured by Mitsubishi Materials Corporation)) and carbon black (manufactured by Tokai Carbon Co., Ltd.) as conductive particles. The content of tin oxide particles differed between the examples and comparative examples. 1-butanol was used as the solvent.

[0089] Next, the prepared coating solution was applied to the outer circumference of the elastic layer described above to a thickness of 10 μm by blade coating to form a coating film. Furthermore, the coating film was dried in an electric furnace at 120°C for 40 minutes to remove the solvent and form a surface layer. The electrostatic roller was manufactured in this manner.

[0090] [measurement] The photoreceptor, charging roller, and image forming apparatus equipped with these components, which were fabricated as described above, underwent various measurements as follows.

[0091] (Measurement of photoreceptor current flow) Using the "TASKalfa MA4500ci" image forming apparatus evaluation unit (manufactured by Kyocera Document Solutions), the current flowing into the photoreceptor was measured when the photoreceptor was charged to V0 (initial surface potential): 470V. The current was measured using a microampere meter "MA-100N" (manufactured by Narika).

[0092] (Measurement of rotational resistance of charged roller) The fabricated conductive roller was rotated under a load of 10N, and the resistance was measured when a voltage of 500V was applied for 5 seconds between the iron roller in contact with the surface and the conductive shaft. An "R8340 ULTRAHIGH RESISTANCE METER" (manufactured by ADVANTEST) was used to measure the resistance.

[0093] (Durability test) Printing was performed using the "TASKalfa MA4500ci" image forming apparatus evaluation unit (manufactured by Kyocera Document Solutions Corporation). The print pattern was a 5% density character image, the printing method was continuous printing, the number of printed sheets was 100,000, and the evaluation paper was "Askul Multipaper Super Economy+". The charging polarity of the charging roller was positive, the applied voltage to the charging roller was DC voltage, and the transfer method was intermediate transfer method.

[0094] (Overlap evaluation) The above durability test was conducted in an environment of 23°C and 50% humidity. Blank paper was printed in an LL environment (10°C and 10% humidity) to obtain an image for fogging evaluation. The fogging density was defined as the average value of the image densities at three points in the blank paper image minus the image densities of the base paper. The fogging density was evaluated as follows: "Evaluation A": 0.010 or less, "Evaluation B": greater than 0.010 and 0.020 or less, and "Evaluation C": greater than 0.020.

[0095] (Sensitivity measurement) The above durability test was conducted in an environment of 23°C and 50% humidity, and the surface potential of the photoreceptor was measured. The charging potential of the charging roller was 470±30V, the exposure intensity was 1.16μJ / m², with a wavelength of 780nm, a full width at half maximum of 20nm, and a light intensity of 1.16μJ / m². 2 The surface potential was measured using a surface potential meter "MODEL 344" (manufactured by TREK) and a potential measurement probe (manufactured by TREK).

[0096] (Sunspot evaluation) The above durability test was conducted in an environment of 23°C and 50% humidity. Then, blank paper was printed in an HH environment (32.5°C and 80% humidity), and the presence or absence of black spots was checked. If no black spots occurred, it was classified as "no occurrence," and if one or more black spots occurred, it was classified as "occurred."

[0097] Table 1 below shows the configuration of the photoreceptor and charging roller and the evaluation results for each embodiment.

[0098] [Table 1]

[0099] As shown in Table 1, in Examples 1 to 14, the amount of charge generating material ("CGM" in the photosensitive layer of the photoreceptor) is 3 phr or more and 7 phr or less, and the relative permittivity of the photoreceptor ("εr" in the table) is 3.7 or more and 6.2 or less. As described above, the charge generating material is Y-type titanyl phthalocyanine, and "phr" represents the parts by mass of Y-type titanyl phthalocyanine per 100 parts by mass of binder resin.

[0100] Furthermore, in Examples 1 to 14, the amount of tin oxide particles ("tin oxide" in the table) in the elastic layer of the charging roller was 8 phr or more and 40 phr or less, and the rotational resistance was 5.2 log Ω or more and 6.1 log Ω or less. "phr" represents the parts by mass of tin oxide particles per 100 parts by mass of elastic material.

[0101] The evaluation results for Examples 1 to 14 all showed a sensitivity (surface potential) of 160V or less, a fogging evaluation of "A", and a sunspot evaluation of "A", indicating a good judgment (indicated by "〇" in the table).

[0102] On the other hand, in Comparative Examples 1 to 4, although the relative permittivity of the photoreceptor (εr in the table) was between 3.7 and 6.2, the rotational resistance of the charging roller was not between 5.2 log Ω and 6.1 log Ω. The evaluation results showed that either the fogging evaluation or the black spot evaluation was not good, resulting in a poor judgment (× in the table).

[0103] Furthermore, in Comparative Examples 5 and 6, although the rotational resistance of the charging roller was between 5.2 log Ω and 6.1 log Ω, the relative permittivity of the photoreceptor (εr in the table) was not between 3.7 and 6.2. The evaluation results showed that either the sensitivity (surface potential) or the fogging evaluation was not good, resulting in a poor judgment (× in the table).

[0104] Furthermore, in Comparative Examples 7 to 10, the relative permittivity of the photoreceptor (εr in the table) was not between 3.7 and 6.2, and the rotational resistance of the charging roller was not between 5.2 log Ω and 6.1 log Ω. The evaluation results showed that one or two of the sensitivity (surface potential), fogging evaluation, and black spot evaluation were not satisfactory, resulting in a judgment of (× in the table).

[0105] As shown above, by setting the relative permittivity of the photoreceptor to 3.7 or more and 6.2 or less, and the rotational resistance of the charging roller surface to 5.2 log Ω or more and 6.1 log Ω or less, as in Examples 1 to 14, it is possible to achieve good sensitivity, fogging evaluation, and black spot evaluation. [Explanation of Symbols]

[0106] 100…Image forming apparatus 65...Photoreceptor 631... Electrostatic roller 635...Elastic layer 636…Surface layer

Claims

1. A photoreceptor having a relative permittivity of 3.7 to 6.2, A charging roller is used to charge the photoreceptor, and the surface rotational resistance is 5.2 log Ω or more and 6.1 log Ω or less. A power supply that applies a DC voltage to the charging roller and An image forming apparatus comprising the following:

2. An image forming apparatus according to claim 1, The charging roller has an elastic layer having conductivity and elasticity, and a surface layer formed on the elastic layer. The surface layer contains nylon resin, conductive particles, and acrylic particles. Image forming apparatus.

3. An image forming apparatus according to claim 1 or 2, The aforementioned photoreceptor is a single-layer photoreceptor. Image forming apparatus.

Images