Image forming apparatus

Abstract

The first and second charged members are thoroughly cleaned. [Solution] The system comprises a photoreceptor, a first charged member, a second charged member, a developing unit, a transfer unit, and a control unit capable of executing a cleaning mode in which a first cleaning operation is performed to clean the first charged member, followed by a second cleaning operation to clean the second charged member. The control unit ensures that in the first cleaning operation, Vp ≤ Vd2

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet.

Background Art

[0002] According to Patent Document 1, an image forming apparatus of an injection charging method is disclosed in which a charging brush is brought into contact with a photosensitive drum, and charges are injected from the charging brush into a charge injection layer of the photosensitive drum to charge the photosensitive drum. This image forming apparatus has a cleaning device that removes transfer residual toner remaining on the photosensitive drum after transferring the toner image to the transfer material.

[0003] The charging brush described in Patent Document 1 can charge only the place where it is in direct contact with the photosensitive drum, but there is a possibility that uneven charging potential of the photosensitive drum may occur due to uneven contact of the charging brush. When uneven charging potential of the photosensitive drum occurs, image defects occur in the toner image developed on the photosensitive drum.

[0004] According to Patent Document 2, an image forming apparatus that charges a photosensitive drum by an injection charging method using a first charging brush and non-contact discharge by a second charging brush is disclosed. After performing injection charging on the photosensitive drum by the first charging brush in this way, the photosensitive drum is charged by discharge with the second charging brush, so that uneven charging potential of the photosensitive drum can be suppressed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, in general, there are known cleanerless image forming apparatuses that omit the cleaning device for removing transfer residue toner and instead recover the transfer residue toner in the developing unit. If the transfer residue toner has the correct charge, which is the same polarity as the voltage applied to the charging brush, the transfer residue toner can easily pass through the charging brush. However, actual transfer residue toner includes toner with the opposite polarity to the correct polarity or toner with almost no charge. For this reason, in injection charging type and cleanerless type image forming apparatuses, the transfer residue toner may not be able to pass through the charging brush and may adhere to the charging brush.

[0007] In the above-mentioned Patent Document 2, if the potential of the first and second charging brushes is weakened, for example, in order to remove deposits from the first and second charging brushes, the surface potential of the photosensitive drum that has passed through the first charging brush will depend on the potential of the first charging brush. In that case, there is a risk that the potential contrast between the second charging brush and the photosensitive drum will be insufficient, and deposits on the second charging brush will not be removed.

[0008] Therefore, the present invention aims to provide an image forming apparatus capable of effectively cleaning the first charged member and the second charged member. [Means for solving the problem]

[0009] According to one aspect of the present invention, an image forming apparatus includes a photoreceptor having a charge injection layer containing conductive particles and configured to be rotatable in a predetermined rotation direction, a first charging member that contacts the surface of the photoreceptor to charge the surface, a developing unit that is disposed downstream of the first charging member in the rotation direction and develops an electrostatic latent image formed on the surface into a toner image, a second charging member that is disposed between the first charging member and the developing unit in the rotation direction and contacts the surface of the photoreceptor to charge the surface, a transfer unit that transfers the toner image to a transfer member, and a control unit that controls voltages applied to the first charging member and the second charging member respectively. The control unit is capable of executing an image forming mode in which the toner image is transferred to the transfer member and a cleaning mode that is executed at a timing different from the image forming mode. In the cleaning mode, a second cleaning operation for cleaning the second charging member is executed after a first cleaning operation for cleaning the first charging member. The control unit controls the voltages applied to the first charging member and the second charging member such that the absolute value of the potential of the first charging member is Vp, the absolute value of the potential of the second charging member is Vs, the absolute value of the surface potential of the photoreceptor before passing through the first charging member is Vd1, and the absolute value of the surface potential of the photoreceptor after passing through the first charging member and before passing through the second charging member is Vd2, and Vp ≦ Vd2 < Vd1 is satisfied in the first cleaning operation and Vs < Vd2 is satisfied in the second cleaning operation.

Advantages of the Invention

[0010] According to the present invention, the first charging member and the second charging member can be cleaned well.

Brief Description of the Drawings

[0011] [Figure 1] An overall schematic view showing an image forming apparatus according to the present embodiment. [Figure 2] A cross-sectional view showing the layer structure of a photosensitive drum. [Figure 3] A schematic view showing a comb-shaped electrode. [Figure 4] This diagram shows the potentials of the charging brush, charging roller, and developing roller, as well as the designations of the drum potential before and after each component passes through. [Figure 5] A timing chart showing the state of each component in image formation mode and charged component cleaning mode. [Figure 6] A block diagram showing the control block of an image forming apparatus. [Modes for carrying out the invention]

[0012] (1. Image forming apparatus configuration) Figure 1 is a schematic diagram of the image forming apparatus 100 equipped with process cartridges PY to PK according to this embodiment. In this embodiment, the image forming apparatus 100 is an electrophotographic laser beam printer compatible with Legal size paper, capable of forming images at a process speed of 210 mm / s and 600 dpi.

[0013] The image forming apparatus 100 shown in Figure 1 includes an image forming unit 40 for forming an image on a sheet K, a sheet feeding unit 50, and a fixing device 17. The sheet K includes paper such as paper and envelopes, plastic films such as overhead projector sheets (OHP), and cloth. Furthermore, the term "image forming apparatus" includes printers, copiers, facsimile machines, and multifunction devices, and refers to a device that forms an image on a sheet used as a recording medium based on image information input from an external PC or image information read from a document. In addition to the main unit with image forming function, an image forming apparatus may also include auxiliary equipment such as optional feeders, image readers, and sheet processing devices, and the entire system with such auxiliary equipment connected is also a type of image forming apparatus.

[0014] The image forming unit 40 includes four process cartridges PY, PM, PC, and PK, which each form toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K), and a laser scanner 7.

[0015] Note that the four process cartridges PY, PM, PC, and PK have the same configuration except for the colors of the images they form. Therefore, only the configuration of the process cartridge PY and the image forming process will be described, and the descriptions of the process cartridges PM, PM, and PK will be omitted.

[0016] The process cartridge PY includes a photosensitive drum 1, a charging brush 2, a developing roller 3, a toner container 23 that houses the developing roller 3, a charging roller 4, and a pre-exposure device 5. The photosensitive drum 1 is a cylindrical body having a plurality of functional layers with a charge injection function on its outermost layer and a diameter of 24 [mm]. The photosensitive drum 1 is configured to be rotatable in a predetermined rotational direction, which is the direction of the arrow shown in FIG. 1. The configuration of the photosensitive drum 1 will be described in detail later.

[0017] The charging brush 2 as the first charging member is pressed against the photosensitive drum 1 with a predetermined pressing force to form a first charging nip. The charging roller 4 as the second charging member is disposed between the charging brush 2 and the developing roller 3 in the rotational direction of the photosensitive drum 1. The charging roller 4 is a rubber roller with a diameter of 8 [mm] formed by molding conductive rubber on a metal shaft. The charging roller 4 is pressed against the photosensitive drum 1 with a predetermined pressing force to form a second charging nip. Also, the charging roller 4 is configured to rotate idly following the photosensitive drum 1. The charging brush 2 and the charging roller 4 are configured such that charging voltages are independently applied thereto by a first charging voltage applying unit and a second charging voltage applying unit (not shown). The charging configuration for charging the photosensitive drum 1 will be described in detail later.

[0018] The developing roller 3 as a developing unit is a rubber roller formed by molding conductive rubber on a metal shaft, and is pressed against the photosensitive drum 1 with a predetermined pressing force to form a developing nip. The developing roller 3 is arranged downstream of the charging brush 2 and the charging roller 4 in the rotation direction of the photosensitive drum 1. The developing roller 3 is driven by a driving means (not shown) so as to be rotatable at a speed higher than that of the photosensitive drum. Further, the developing roller 3 is configured to be able to transition between a contact state in which it contacts the photosensitive drum 1 and a separation state in which it is separated from the photosensitive drum 1.

[0019] The laser scanner 7 irradiates the photosensitive drum 1 with a laser based on an image signal to expose the photosensitive drum 1. In the present embodiment, the laser scanner 7 is provided one by one for the photosensitive drums 1 of each process cartridge, but one laser scanner may have four light emitting portions.

[0020] The photosensitive drum 1 is charged to a dark part potential of a predetermined negative polarity by applying a voltage of a predetermined negative polarity to the charging brush 2 and the charging roller 4. In the part of the photosensitive drum 1 exposed by the laser irradiated from the laser scanner 7, the potential decreases, and an electrostatic latent image of a predetermined bright part potential is formed. Hereinafter, the part charged to the dark part potential (Vd) is referred to as the dark part Vd, and the part charged to the bright part potential (Vl) is referred to as the bright part Vl.

[0021] By applying a predetermined negative voltage (Vdc) to the developing roller 3 and creating an appropriate potential difference between the dark area Vd and the bright area Vl, the toner on the developing roller 3 is transferred only to the bright area Vl as the electrostatic latent image passes through the developing nip, thereby revealing the electrostatic latent image. The difference between the voltage (Vdc) applied to the developing roller 3 and the bright area potential (Vl) of the photosensitive drum 1 is called the development contrast, and this potential difference allows for the control of the amount of toner developed from the developing roller 3 to the photosensitive drum 1. Furthermore, the difference between the bright area potential (Vd) of the photosensitive drum 1 and the voltage (Vdc) applied to the developing roller is called the back contrast, and this potential difference suppresses the occurrence of fogging, where unwanted toner is developed in the unexposed area, i.e., the dark area Vd, of the photosensitive drum 1. In this embodiment, settings were adopted where Vd=-520[V], Vl=-120[V], and Vdc=-320[V] result in a development contrast and background contrast of 200[V].

[0022] The toner used in this embodiment is composed of toner particles with an average particle size of 6.4 [μm], to which silica fine particles with an average particle size of 20 [nm] are added externally, and which are negatively charged. The average particle size refers to the average particle diameter determined from the particle volume, which can be measured, for example, by the Coulter method.

[0023] Furthermore, the image forming unit 40 is provided with an intermediate transfer belt 8 wrapped around a drive roller 9, a tension roller 10, and an opposing roller 28, and primary transfer rollers 6Y, 6M, 6C, and 6K are provided inside the intermediate transfer belt 8. The primary transfer rollers 6Y, 6M, 6C, and 6K, which act as the transfer unit, are each positioned to face the photosensitive drum 1 of each process cartridge. The intermediate transfer belt 8, which acts as the material to be transferred, is an endless belt made of two layers of resin material, with a resin surface layer of 2 [μm] thickness coated on a base layer of 60 [μm] thickness, and is rotated in the direction of arrow Z by the drive roller 9.

[0024] The fixing device 17 includes a fixing film 18 heated by a heater (not shown) and a pressure roller 19 that presses against the fixing film 18. The sheet feeding unit 50 is located at the bottom of the image forming apparatus 100 and includes a cassette 13 that supports the sheet, a feeding roller 14 for feeding the sheet, and a pair of transport rollers 15. The feeding roller 14 and the pair of transport rollers 15 constitute the feeding and transport device 12.

[0025] Next, the image forming operation of the image forming apparatus 100 configured in this way will be described. When an image signal is input to the laser scanner 7 from a personal computer (not shown), the laser scanner 7 irradiates a laser corresponding to the image signal onto the photosensitive drum 1 of the process cartridge PY.

[0026] At this time, the surface of the photosensitive drum 1 is uniformly charged to a negative potential by the charging brush 2 and the charging roller 4, and an electrostatic latent image is formed on the surface when a laser is shone from the laser scanner 7. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing roller 3, and a yellow (Y) toner image is formed on the photosensitive drum 1.

[0027] Similarly, laser light from the laser scanner is shone onto each photosensitive drum of process cartridges PM, PC, and PK, forming magenta (M), cyan (C), and black (K) toner images on each drum. The toner images of each color formed on each drum are transferred to the intermediate transfer belt 8 by primary transfer rollers 6Y, 6M, 6C, and 6K to which a positive voltage is applied, and then transported by the intermediate transfer belt 8 to the secondary transfer roller 11. The image formation process for each color is performed at a timing that overlaps with the upstream toner image that has been primary transferred onto the intermediate transfer belt 8.

[0028] After the toner image is first transferred from the photosensitive drum 1 to the intermediate transfer belt 8, the surface potential of the photosensitive drum 1 is discharged to approximately 0[V] by the pre-exposure device 5. This is done to equalize the potential unevenness on the surface of the photosensitive drum 1, which is caused by exposure by the laser scanner 7 and discharge by the primary transfer roller, and to obtain a uniform dark area potential (Vd).

[0029] In parallel with this image formation process, the sheet K housed in the cassette 13 of the sheet feeding unit 50 is transported to the registration roller pair 16 by the feeding and transport device 12. The sheet K's skew is corrected when its leading edge strikes the nip of the registration roller pair 16, which is in a stationary state. The sheet K, whose skew has been corrected by the registration roller pair 16, is transported at a predetermined transport timing. Then, the full-color toner image on the intermediate transfer belt 8 is transferred to the sheet K by a positive polarity secondary transfer bias applied to the secondary transfer roller 11, which acts as a secondary transfer unit.

[0030] The sheet K onto which the toner image has been transferred is subjected to predetermined heat and pressure by the fixing film 18 and pressure roller 19 of the fixing device 17, causing the toner to melt and solidify (fix) to the sheet. The sheet K that has passed through the fixing device 17 is discharged into the discharge tray 29 by the discharge roller pair 20.

[0031] The image forming apparatus 100 of this embodiment employs a cleanerless system using a development-simultaneous cleaning method. That is, after the toner image is first transferred from the photosensitive drum 1 to the intermediate transfer belt 8, the toner remaining on the surface of the photosensitive drum 1, which is the primary transfer residue toner, is electrostatically collected at the development nip. The primary transfer residue toner includes toner with negative polarity, which is the normal charging polarity, and toner with positive polarity, which is the opposite polarity.

[0032] The negatively polarized primary transfer residue toner on the surface of the photosensitive drum 1 remains on the surface of the photosensitive drum 1 when passing through the first and second charged nips. This is because the surface potentials of the charged brush 2 and charged roller 4 have a negatively higher potential than the surface potential of the photosensitive drum 1 (hereinafter referred to as the drum surface potential). At this time, the drum surface potential is 0 [V]. Subsequently, the primary transfer residue toner is transferred from the photosensitive drum 1 to the developing roller 3 and recovered at the developing nip. This is because the potential of the developing roller 3, to which a voltage of positive polarity (Vdc) is applied, is lower than the dark area potential (Vd) of the photosensitive drum 1.

[0033] On the other hand, positively polarized primary transfer residue toner is transferred to the charging brush 2 and charging roller 4, which have a negative potential higher than the drum surface potential, as they pass through the first and second charging nip, and adheres to the charging brush 2 and charging roller 4. If this toner continues to accumulate on the charging brush 2 and charging roller 4, it may hinder the injection of charge from the charging brush 2 and charging roller 4 to the surface of the photosensitive drum 1. For this reason, in the image forming apparatus 100 with this configuration, a charging member cleaning mode is performed after the image forming operation on the sheet K to electrostatically remove toner and other deposits on the charging brush 2 and charging roller 4. The charging member cleaning mode will be described in detail later.

[0034] Furthermore, after the toner image is secondarily transferred from the intermediate transfer belt 8 to the sheet K, the toner remaining on the surface of the intermediate transfer belt 8, known as secondary transfer residue toner, is mechanically scraped off by the cleaning blade 21, which acts as a cleaning component. The secondary transfer residue scraped off by the cleaning blade 21 is then collected in the waste toner collection container 22.

[0035] Furthermore, the image forming apparatus 100 has a control board 25 on which electrical circuits for controlling the image forming apparatus 100 are mounted. Figure 6 is a block diagram showing the control block of the image forming apparatus 100. As shown in Figure 6, the control board 25 is equipped with a CPU (Central Processing Unit) 26 as a control unit, a ROM (Read Only Memory) 71, and a RAM (Random Access Memory) 72. Various programs are stored in the ROM 71, and the CPU 26 reads and executes the programs stored in the ROM 71. The RAM 73 is used as a workspace for the CPU 26.

[0036] The CPU 26 is responsible for controlling the intermediate transfer belt drive motor 73, the transport drive motor 74, and the drum motor 75, as well as controlling various image signals related to image formation. The intermediate transfer belt drive motor 73 is a motor for driving the intermediate transfer belt 8. The transport drive motor 74 is a motor for driving the feed transport device 12, the registration roller pair 16, and the fixing device 17. The drum motor 75 is the drive source for the process cartridge. The CPU 26 controls the voltage applied to the charging brush 2 and charging roller 4, the developing roller 3, and each transfer roller, etc., by controlling the charging power supply 61, the developing power supply 62, and the transfer power supply 63. Alternatively, the CPU 26 may not control the voltage applied to the charging brush 2 and the charging roller 4 with a single charging power supply 61, but may control the voltage applied to the charging brush 2 and the charging roller 4 with separate charging power supplies. The transfer power supply 63 may be divided into multiple primary transfer power supplies that control the voltage applied to the primary transfer rollers 6Y, 6M, 6C, and 6K, and a secondary transfer power supply that controls the voltage applied to the secondary transfer roller 11. Furthermore, a separate CPU may be provided for controlling the various motors mentioned above and a separate CPU for controlling the various power supplies mentioned above.

[0037] (2. Photosensitive drum) Next, the layer structure of the photosensitive drum 1 will be described with reference to Figure 2. Figure 2 is a cross-sectional view showing the layer structure of the photosensitive drum 1. The photosensitive drum 1 has a layer structure from bottom to top consisting of a support 101, a conductive layer 102, an undercoat layer 103, a photosensitive layer 104, and a charge injection layer 105. The photosensitive layer 104 has a charge generation layer 104p and a charge transport layer 104c, and the charge injection layer 105 contains conductive particles 105p. The photosensitive drum 1, as a photoreceptor, is formed by providing multiple layers on a cylindrical support 101, but a belt-shaped or sheet-shaped photosensitive member may be used instead of the photosensitive drum 1.

[0038] One method for manufacturing the photosensitive drum 1 is to prepare coating solutions for each layer, apply them in the desired order, and then dry them. Methods for applying the coating solutions include immersion coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, and ring coating. Among these, immersion coating is preferred from the viewpoint of efficiency and productivity. The layers of the photosensitive drum 1 will now be described.

[0039] (2-1.Support) The support 101 of the photosensitive drum 1 is preferably a conductive support. The shape of the support 101 can be cylindrical, belt-shaped, or sheet-shaped, but cylindrical is preferred. The surface of the support 101 may also be subjected to electrochemical treatments such as anodizing, blasting, or cutting. The material of the support 101 is preferably metal, resin, or glass. Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among these, the support 101 is preferably made of aluminum. Furthermore, resins and glass may be imparted with conductivity by mixing or coating them with a conductive material.

[0040] (2-2. Conductive layer) In the photosensitive drum 1, a conductive layer 102 can be provided on the support 101. By providing the conductive layer 102, scratches and irregularities on the surface of the support 101 can be concealed, and the reflection of light on the surface of the support 101 can be controlled. Preferably, the conductive layer 102 contains conductive particles and a resin. Examples of materials for the conductive particles include metal oxides, metals, and carbon black.

[0041] Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, and bismuth oxide. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, and silver.

[0042] The average thickness of the conductive layer 102 is preferably 1 μm or more and 50 μm or less, and particularly preferably 3 μm or more and 40 μm or less. The conductive layer 102 can be formed by preparing a coating solution for the conductive layer containing the above-mentioned materials and solvents, forming this coating film, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Methods for dispersing conductive particles in the coating solution for the conductive layer include using a paint shaker, sand mill, ball mill, or liquid impaction type high-speed disperser.

[0043] (2-3. Lower layer) The photosensitive drum 1 may have an undercoat 103 provided on the support 101 or the conductive layer 102. The average thickness of the undercoat 103 is preferably 0.1 [μm] or more and 50 [μm] or less, more preferably 0.2 [μm] or more and 40 [μm] or less, and particularly preferably 0.3 [μm] or more and 30 [μm] or less.

[0044] Examples of resins for the undercoat layer 103 include polyacrylic acid resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyethylene oxide resin, polypropylene oxide resin, ethylcellulose resin, methylcellulose resin, polyamide resin, polyamic acid resin, polyurethane resin, polyimide resin, polyamide-imide resin, polyvinylphenol resin, melamine resin, phenol resin, epoxy resin, and alkyd resin. In addition, the undercoat layer 103 may contain inorganic compounds or organic compounds other than resin.

[0045] Examples of inorganic compounds include gold, silver, aluminum, zinc oxide, lead white, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, indium oxide, tin oxide, zirconium oxide, barium sulfate, and strontium titanate.

[0046] Examples of organic compounds include electron transport compounds and conductive polymers. Examples of conductive polymers include polythiophene, polyaniline, polyacetylene, polyphenylene, and polyethylenedioxythiophene. Examples of electron transport materials include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halides, silole compounds, and boron-containing compounds.

[0047] The undercoat layer 103 is obtained by preparing an undercoat coating solution containing the above-mentioned materials, applying it to the support 101 or the conductive layer 102, and then drying or curing the coating film. Examples of solvents used when preparing the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, or aromatic hydrocarbon-based solvents. Dispersion methods for dispersing particles in the coating solution include using a paint shaker, sand mill, ball mill, or liquid impaction type high-speed disperser.

[0048] (2-4. Photosensitive layer) The photosensitive layer 104 comprises a charge generation layer 104p and a charge transport layer 104c. The charge generation layer 104p preferably contains a charge generation substance and a resin. Examples of charge generation substances include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred. The content of the charge generation substance in the charge generation layer 104p is preferably 40% to 85% by mass, and more preferably 60% to 80% by mass, based on the total mass of the charge generation layer 104p.

[0049] Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenolic resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, and polyvinyl chloride resin. Among these, polyvinyl butyral resin is more preferred.

[0050] Furthermore, the charge generation layer 104p may further contain additives such as antioxidants and ultraviolet absorbers. Specifically, examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, and the like.

[0051] The charge generation layer 104p can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned materials and solvents, forming this coating film on the undercoat layer 103, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. The film thickness of the charge generation layer 104p is preferably 0.1 [μm] to 1.5 [μm], and more preferably 0.15 [μm] to 1.0 [μm].

[0052] The charge transport layer 104c preferably contains a charge transport material and a resin. Examples of charge transport materials include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these materials. Among these, triarylamine compounds and benzidine compounds are preferred.

[0053] The content of the charge transport material in the charge transport layer 104c is preferably 25% by mass or more and 70% by mass or less, and more preferably 30% by mass or more and 55% by mass or less, based on the total mass of the charge transport layer 104c.

[0054] Examples of resins include polyester resin, polycarbonate resin, acrylic resin, and polystyrene resin. Among these, polycarbonate resin and polyester resin are preferred. Polyarylate resin is particularly preferred among polyester resins. The content ratio (mass ratio) of charge transport material to resin is preferably 4:10 to 20:10, and more preferably 5:10 to 12:10.

[0055] Furthermore, the charge transport layer 104c may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, lubrication agents, and wear resistance improvers. Specifically, examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0056] The charge transport layer 104c can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvents, forming this coating film on the charge generating layer 104p, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents or aromatic hydrocarbon-based solvents are preferred.

[0057] The thickness of the charge transport layer 104c is preferably 3 [μm] or more and 50 [μm] or less, more preferably 5 [μm] or more and 40 [μm] or less, and particularly preferably 10 [μm] or more and 30 [μm] or less.

[0058] (2-5. Charge injection layer) The photosensitive drum 1 used in this embodiment is characterized by having a charge implantation layer 105 containing conductive particles 105p on its outermost surface. That is, the charge implantation layer 105 includes the surface of the photosensitive drum 1. The charge implantation layer 105 may contain polymers and resins of compounds having polymerizable functional groups. Examples of polymerizable functional groups include isocyanate groups, blocked isocyanate groups, methylol groups, alkylated methylol groups, epoxy groups, metal alkoxide groups, hydroxyl groups, amino groups, carboxyl groups, thiol groups, carboxylic acid anhydride groups, carbon-carbon double bond groups, alkoxysilyl groups, and silanol groups. Monomers having charge transport ability may be used as compounds having polymerizable functional groups. Examples of resins include polyester resins, acrylic resins, phenoxy resins, polycarbonate resins, polystyrene resins, phenolic resins, melamine resins, and epoxy resins. Among these, acrylic resins are preferred.

[0059] The conductive particles 105p contained in the charge injection layer 105 include metal oxide particles such as titanium oxide, zinc oxide, tin oxide, and indium oxide. When metal oxides are used as conductive particles 105p, the metal oxides may also contain elements such as niobium, phosphorus, and aluminum, or their oxides. The conductive particles 105p may also have a laminated structure having core material particles and a coating layer covering the particles. Examples of core material particles include titanium oxide, barium sulfate, and zinc oxide. Examples of coating layers include metal oxides such as titanium oxide and tin oxide.

[0060] The conductive particles 105p are preferably titanium oxide particles containing niobium. In other words, the conductive particles 105p are preferably metal oxides containing titanium atoms and niobium atoms. As niobium-containing titanium oxide particles, various shapes can be used, such as spherical, polyhedral, ellipsoidal, flaky, and needle-shaped. Among these, spherical, polyhedral, and ellipsoidal shapes are preferred from the viewpoint of reducing image defects such as black spots. In this embodiment, it is even more preferable that the niobium-containing titanium oxide particles are spherical or polyhedral in shape close to a sphere. The niobium-containing titanium oxide particles are preferably anatase-type or rutile-type titanium oxide particles, and it is even more preferable that they are anatase-type titanium oxide particles. Using anatase-type titanium oxide results in good implantation charging properties.

[0061] In this embodiment, it is particularly preferable that the conductive particles 105p are particles having anatase-type titanium oxide particles as a core material and titanium oxide that coats the surface of the core material and contains niobium. When the conductive particles 105p have niobium-containing titanium oxide particles, the niobium content in the conductive particles 105p is preferably 0.5% by mass or more and 15.0% by mass or less, and more preferably 2.6% by mass or more and 10.0% by mass or less. If the niobium content in the conductive particles 105p is 0.5% by mass or more, a high effect of suppressing image flow can be obtained, and if it is 15.0% by mass or less, the volume resistivity of the charge injection layer 105 does not become too large.

[0062] When using a metal oxide as the conductive particle 105p, it is preferable to treat the surface of the metal oxide particles with a silane coupling agent or the like from the viewpoint of dispersibility and liquid stability. Furthermore, when using a metal oxide as the conductive particle 105p, its volume average particle size is preferably 1 nm or more and 500 nm or less, more preferably 3 nm or more and 300 nm or less, and even more preferably 5 nm or more and 100 nm or less.

[0063] The charge injection layer 105 may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, lubricity enhancers, and wear resistance improvers. Specific examples of additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0064] The charge implantation layer 105 can be formed by preparing a coating solution for the charge implantation layer containing the above-mentioned materials and solvents, forming this coating film on the photosensitive layer 104, and drying and / or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. The film thickness of the charge implantation layer 105 is preferably 0.2 [μm] to 5 [μm], and more preferably 0.5 [μm] to 3 [μm].

[0065] (2-6. Method for measuring the volume resistivity of the charge injection layer) The volume resistivity of the charge injection layer 105 can be measured using a pA (picoampere) meter. The method for measuring the volume resistivity of the charge injection layer 105 will be explained with reference to Figure 3. Figure 3 is a schematic diagram showing a comb-shaped electrode 105a that can be used when measuring the volume resistivity of the charge injection layer 105. A comb-shaped electrode 105a as shown in Figure 3, with an inter-electrode distance (D) = 180 [μm] and a length (L) = 59 [mm], is fabricated on a PET film by vapor deposition, and a charge injection layer 105 with a thickness (T1) of 2 [μm] is placed on top of it. The comb-shaped electrode 105a consists of two comb-shaped electrodes that are insulated from each other. Under conditions of 23°C / 50%RH, the DC voltage (I) when a DC voltage (V) of 100 [V] is applied between the comb-shaped electrodes 105a is measured, and the volume resistivity ρv (Ω·cm) is obtained by the following formula (1). Volume resistivity ρv(Ω cm)=V(V)×T1(cm)×L(cm) / {I(A)×D(cm)}···(1)

[0066] When measuring the volume resistivity of the charge injection layer 105, which exists as a surface layer of the photosensitive drum 1 rather than the charge injection layer 105 alone, the surface resistivity of the charge injection layer 105 is measured, and the obtained value is converted to volume resistivity. A comb-shaped electrode 105a with an electrode distance (D) = 180 [μm] and a length (L) = 59 [mm] as shown in Figure 3 is fabricated on the surface of the charge injection layer 105 of the photosensitive drum 1 by gold deposition. The DC voltage (I) is measured when a DC voltage (V) of 1000 [V] is applied between the comb-shaped electrodes 105a in an environment of 23°C / 50%RH, and the surface resistivity ρs of the charge injection layer is calculated from DC voltage (V) / DC voltage (I). Using the obtained surface resistivity ρs and the film thickness t (cm) of the charge injection layer 105, the volume resistivity ρv (Ω·cm) can be obtained by the following equation (2). ρv = ρs × t ···(2) (ρv: volume resistivity, ρs: surface resistivity, t: thickness of the charge injection layer)

[0067] In this measurement, since a minute amount of current is to be measured, it is preferable to use a resistance measuring device capable of measuring minute currents. For example, the Hewlett-Packard picoammeter 4140B is one such device. The comb-type electrodes used and the applied voltage should be selected to obtain an appropriate signal-to-noise ratio based on the material and resistance value of the charge injection layer.

[0068] <Examples> The following describes an example of this embodiment.

[0069] (3. Method for manufacturing a photosensitive drum) (3-1.Support) As shown in Figure 2, the support 101 of the photosensitive drum 1 is made up of an aluminum cylinder with a diameter of 24 mm and a length of 257.5 mm.

[0070] (3-2. Conductive layer) The conductive layer 102 of the photosensitive drum 1 is manufactured as follows: A dispersion consisting of titanium oxide (TiO2) particles coated with oxygen-deficient tin oxide (SnO2) as metal oxide particles, a phenolic resin as a binder, 1-methoxy-2-propanol as a solvent, silicone resin particles as a surface roughening agent, and silicone oil as a leveling agent is immersed and coated onto the support 101, and heated at 140°C for 1 hour to form a conductive layer 102 with a thickness of 30 [μm] on the support 101.

[0071] (3-3. Lower layer) An electron transport material represented by the following formula (E-1), a blocked isocyanate, a styrene-acrylic resin, and a silica slurry were dissolved in a mixed solvent of 1-butanol and acetone, and this mixture was immersed and coated onto the conductive layer 102. This mixture was then heated at 170°C for 30 minutes to form an undercoat layer 103 with a thickness of 0.7 [μm].

[0072] [ka]

[0073] (3-4. Photosensitive layer) As described above, the photosensitive layer 104 has a charge generation layer 104p and a charge transport layer 104c. A coating solution prepared by diluting crystalline hydroxygallium phthalocyanine and polyvinyl butyral resin with cyclohexanone and ethyl acetate was immersed and coated onto the undercoat layer 103, and dried at 95°C for 10 minutes to form a charge generation layer 104p with a film thickness of 0.20 [μm].

[0074] A coating solution was prepared by dissolving a charge transport material represented by formula (C-1), a charge transport material represented by formula (C-2), a charge transport material represented by formula (C-3), polycarbonate, and a polycarbonate resin having copolymer units of formulas (C-4) and (C-5) in a mixed solvent of orthoxylene, methyl benzoate, and dimethoxymethane. This coating solution was then applied to the charge generating layer 104p by immersion to form a coating film, and the coating film was dried at 120°C for 30 minutes to form a charge transport layer 104c with a thickness of 12 [μm]. [ka] [ka] [ka] [ka] [ka]

[0075] (3-5. Charge injection layer) A coating solution was prepared by mixing a compound represented by the following structural formula (O-1) as a binder resin and niobium-containing titanium oxide particles as conductive particles in a mixed solvent of 1-propanol and cyclohexane. This solution was then immersed and coated onto the charge transport layer 104c to form a coating film, which was dried at 50°C for 6 minutes. Subsequently, the coating film was irradiated with an electron beam under a nitrogen atmosphere, and then the temperature of the coating film was raised to 117°C under a nitrogen atmosphere. Next, the coating film was allowed to cool naturally in air until its temperature reached 25°C, and then heat-treated for 1 hour under conditions that brought the temperature of the coating film to 120°C to form a charge implantation layer 105 with a thickness of 2 [μm]. [ka]

[0076] In this embodiment, the coating solution was mixed in the following proportions to be immersed and applied onto the charge transport layer 104c, and the volume resistivity of the coating film formed by the coating solution was approximately 1.0 × 10^13 [Ω·cm]. Compounds represented by structural formula (O-1) (79 parts) 76 parts of niobium-containing titanium dioxide particles 1-Propanol 100 units Cyclohexane 100 copies

[0077] (4. Injection and charging configuration) The charging configuration in this embodiment is characterized by charging the charge injection layer 105, which is the outermost layer of the photosensitive drum 1, by combining direct charge injection from the charging brush 2 and spark discharge by the charging roller 4.

[0078] The electrostatic brush 2 is a bar brush made by attaching a 5 mm wide fabric, which is made of conductive nylon fibers processed into a pile fabric using carbon as a conductive agent, to a 1 mm thick plated steel sheet. In other words, the electrostatic brush 2 has a support member made of sheet metal and a brush portion made of conductive fibers that is attached to the support member and rubs against the photosensitive drum 1.

[0079] The conductive nylon fibers have a fineness of 2 denier and a flocking density of 240 fibers / mm². 2 The pile length is 6 mm, and the brush is in contact with the photosensitive drum 1 such that the amount of penetration from the tip of the brush is 0.5 mm. The direct electrostatic charge injection by the electrostatic brush 2 improves as the contact area between the electrostatic brush 2 and the photosensitive drum 1 increases. Therefore, the greater the amount of penetration of the electrostatic brush 2 into the photosensitive drum 1, the greater the contact area and the better the electrostatic charge injection.

[0080] On the other hand, if the amount of charging brush 2 that penetrates the photosensitive drum 1 exceeds a predetermined amount, the contact pressure between the charging brush 2 and the photosensitive drum 1 increases, which may cause scratches on the photosensitive drum 1 caused by the charging brush 2. Also, in the cleanerless image forming apparatus 100, if the amount of charging brush 2 that penetrates is too high, the charging brush 2 may block the residual toner remaining on the surface of the photosensitive drum 1, which may reduce the charging ability of the charging brush 2. Therefore, the design values ​​of the charging brush 2, such as the bristle density, fineness, pile length, and penetration amount, need to be set in a way that balances the above considerations with the charging ability.

[0081] In this embodiment, a charging brush 2 with a resistance of 1 × 10^5 [Ω] was used. The resistance of the charging brush 2 was calculated from the current flowing when the charging brush 2 was brought into contact with a metal cylinder of the same diameter as the photosensitive drum 1 under the same conditions and a voltage of -100 [V] was applied. The resistance of the charging brush 2 can be controlled by changing the material of the conductive fibers of the charging brush 2, but a lower resistance of the charging brush 2 improves the charging ability of the charging brush 2.

[0082] Furthermore, the charging roller 4 is an 8mm diameter rubber roller formed by molding conductive rubber on a metal shaft. Since the purpose of the charging roller 4 is to equalize the potential unevenness in the first charging nip between the charging brush 2 and the photosensitive drum 1, it is desirable that the configuration be such that the injected charging performance is low and stable spark discharge performance can be obtained. In order to suppress the injected charging from the charging roller 4, a configuration in which the surface of the charging roller 4 has high resistance and a configuration in which the contact area with the photosensitive drum 1 is small is effective.Therefore, in this embodiment, a two-layer charging roller 4 having a high-resistance surface layer was adopted, in which a coating liquid mixed with particles of approximately 20 [μm] in a urethane-based resin material was spray-coated onto the surface of conductive hydrin rubber obtained by extrusion processing. The volume resistivity of the high-resistance surface layer is approximately 1 × 10^14 [Ω·cm].In addition, the arithmetic mean roughness Ra, which is a numerical representation of the surface roughness of the high-resistance surface layer, is approximately 2.0 [μm]. From the standpoint of suppressing injection charging, it is desirable that the volume resistivity of the high-resistivity surface layer be 1 × 10^12 [Ω·cm] or higher, and that the arithmetic mean roughness Ra of the high-resistivity surface layer be 0.5 to 3.0 [μm].

[0083] Next, the details of the charged component potentials and the surface potential of the photosensitive drum 1 (hereinafter also referred to as the drum potential) during image formation, when an image (toner image) is formed on the sheet K, will be described using Figure 4 and Table 1 below. Figure 4 shows the potentials of the charged brush 2, charged roller 4, and developing roller 3, and the designations of the drum potential before and after passing through each component, while Table 1 shows the respective potentials.

[0084] In Figure 4 and Table 1, the potential of the charging brush 2 is defined as the brush potential Vp, the potential of the charging roller 4 as the roller potential Vs, the potential of the developing roller 3 as the developing potential Vdc, and the drum potential before passing through the charging brush 2 as the first drum potential Vd1. Furthermore, the drum potential after passing through the charging brush 2 and before passing through the charging roller 4 is defined as the second drum potential Vd2, and the drum potential after passing through the charging roller 4 is defined as the third drum potential Vd3. It should be noted that the third drum potential Vd3 is the dark area potential (Vd) of the photosensitive drum 1 from the second rotation onward.

[0085] The potentials Vd1 for the first drum, Vd2 for the second drum, and Vd3 for the third drum were measured by modifying the black process cartridge PK of the image forming apparatus 100. Potential measuring probes (model 3800-S2: manufactured by Trek Japan Co., Ltd.) were placed at each measurement position at a distance of 0.5 mm from the drum surface and in the center in the width direction. The positioned potential measuring probes were connected to a surface potential meter (model 370: manufactured by Trek Japan Co., Ltd.) to measure the surface potential of the photosensitive drum 1.

[0086] The first drum potential Vd1, brush potential Vp, second drum potential Vd2, roller potential Vs, third drum potential Vd3, bright area potential (Vl), and development potential Vdc during image formation are as shown in Table 1 below. [Table 1]

[0087] The first drum potential Vd1 is approximately 0[V] because the surface of the photosensitive drum 1 is discharged by the pre-exposure device 5. The brush potential Vp is -500[V], which is below the discharge threshold relative to the first drum potential Vd1. It has been confirmed that discharge current begins to flow in the first charging nip, the second charging nip, and the primary transfer nip when the potential difference is 550[V] or higher. That is, the discharge threshold is 550[V]. The second drum potential Vd2 is -430[V], and in this embodiment, the photosensitive drum 1 is configured to be charged by injection charging to a desired dark area potential (Vd) of -520[V] by more than 80%. The roller potential Vs is -1070[V], which is negatively higher in polarity by 550[V] relative to the desired dark area potential (Vd) of -520V, which is the discharge threshold. The potential Vd3 of the third drum was -520[V], confirming that the desired dark area potential (Vd) value was obtained.

[0088] (5. Image formation mode and charged component cleaning mode) As described above, in the image forming apparatus 100 according to this embodiment, a charging member cleaning mode is performed after the image forming operation on the sheet K in order to electrostatically remove deposits such as toner that have adhered to the charging brush 2 and the charging roller 4. The details of the image forming mode and charging member cleaning mode that the CPU 26 of the image forming apparatus 100 can execute will be described below with reference to section 5.

[0089] Figure 5 is a timing chart showing the rotation state of the photosensitive drum 1 and intermediate transfer belt 8, the state of the applied voltage to the charging brush 2, charging roller 4, developing roller 3 and primary transfer roller 6, the exposure state of the laser scanner 7, the contact state of the developing roller 3, and the illumination state of the pre-exposure device 5 in each mode when the image forming apparatus 100 receives a print signal, as well as the image forming mode and the charged component cleaning mode. When the image forming apparatus 100 receives a print signal from an external computer or the like, the CPU 26 executes the image forming mode.

[0090] In image formation mode, the photosensitive drum 1 and the intermediate transfer belt 8 begin to rotate, respectively, due to a drum motor and an intermediate transfer belt drive motor (not shown). Subsequently, a charging voltage is applied to the charging brush 2 by a charging voltage application unit (not shown) so that the brush potential Vp in image formation mode becomes -500[V]. Next, a charging voltage is applied to the charging roller 4 by a charging voltage application unit (not shown) so that the roller potential Vs in image formation mode becomes -1070[V].

[0091] Next, the developing roller 3 is moved from a separated state to a contact state, and at the same time, a voltage is applied to the developing roller 3 so that the developing potential Vdc becomes -350[V]. Then, a voltage of +800[V] is applied to the primary transfer roller 6. Furthermore, the pre-exposure device 5 is turned on, and the laser scanner 7 becomes ready to form an image. When the image formation on the photosensitive drum 1 by the laser scanner 7 is completed, the pre-exposure device 5 is turned off, and the image formation mode ends. Following the image formation mode, the CPU 26 starts a charged member cleaning mode as a cleaning mode.

[0092] Furthermore, the pre-exposure device 5 is switched off earlier by a time equal to the distance from the pre-exposure device 5 to the charging brush 2 divided by the process speed of the photosensitive drum 1, based on the timing of transitioning to the charged component cleaning mode. This makes it possible to make the first drum potential Vd1 in the charged component cleaning mode equal to the dark area potential (Vd) of -520[V], making it easier to secure the potential difference (potential contrast) necessary for cleaning the charging brush 2.

[0093] In the charged component cleaning mode, a first deposit removal process is performed to primarily remove deposits attached to the charged brush 2, followed by a second deposit removal process to primarily remove deposits attached to the charged roller 4. Hereinafter, the brush potential Vp in the first and second deposit removal processes will be referred to as the first brush cleaning potential and the second brush cleaning potential, respectively. Similarly, the roller potential Vs in the first and second deposit removal processes will be referred to as the first roller cleaning potential and the second roller cleaning potential, respectively.

[0094] When the first deposit removal process begins, the CPU 26 applies a charging voltage to the charged brush 2 so that the brush potential Vp becomes the first brush cleaning potential, and simultaneously transitions the developing roller 3 from a contact state to a separated state. Next, the CPU 26 applies a charging voltage to the charged roller 4 so that the roller potential Vs becomes the first roller cleaning potential, and simultaneously turns off the voltage applied to the developing roller 3. The timing for turning off the voltage applied to the developing roller 3 can be any timing during the charged material cleaning mode, as long as the developing roller 3 is in the separated state and its rotation has stopped. The roller potential Vs is switched with a delay of a time equal to the distance from the charged brush 2 to the charged roller 4 divided by the process speed of the photosensitive drum 1, relative to the timing of switching the brush potential Vp. In this embodiment, deposit removal from the charged brush 2 and deposit removal from the charged roller 4 are performed at the same location on the drum surface.

[0095] In the first deposit removal process, deposits such as toner accumulated on the charging brush 2 are removed from the charging brush 2 and then divided into those that reattach to the charging roller 4 and those that pass through the charging roller 4. These deposits mainly have a positive charge. The deposits that pass through the charging roller 4 then pass through the developing roller 3, which is in a separated state. As the deposits pass through the primary transfer nip formed between the photosensitive drum 1 and the primary transfer roller, they are transferred to the intermediate transfer belt 8, which has a negatively higher potential than the surface potential of the photosensitive drum 1, and are then collected by the cleaning blade 21. The first deposit removal process is performed for a first execution time t1, and then the second deposit removal operation is performed for a second execution time t2.

[0096] After the first deposit removal process, the CPU 26 controls the system to initiate the second deposit removal process by applying a charging voltage to the charged brush 2 so that the brush potential Vp becomes the second brush cleaning potential. Next, the CPU 26 applies a charging voltage to the charged roller 4 so that the roller potential Vs becomes the second roller cleaning potential. The roller potential Vs is switched with a delay of a time equal to the distance from the charged brush 2 to the charged roller 4 divided by the process speed of the photosensitive drum 1, based on the timing of switching the brush potential Vp. In this embodiment, deposit removal from the charged brush 2 and deposit removal from the charged roller 4 are performed at the same location on the drum surface.

[0097] In the second deposit removal process, the deposits accumulated on the charging roller 4 pass through the developing roller 3, which is in a separated state. The deposits then pass through the primary transfer nip formed between the photosensitive drum 1 and the primary transfer roller, where they are transferred to the intermediate transfer belt 8, which has a potential higher than the surface potential of the photosensitive drum 1, and are subsequently collected by the cleaning blade 21. The second deposit removal operation ends when the voltage applied to the charging brush 2, the voltage applied to the charging roller 4, and the voltage applied to the primary transfer roller are turned OFF, stopping the driving of the photosensitive drum 1 and the intermediate transfer belt 8.

[0098] (6. Potential control pattern during charging component cleaning mode) In the charged component cleaning mode, the voltage applied to the charged brush 2 and charged roller 4 is switched as shown in Table 2 below. Table 2 shows the combinations of the first execution time t1, second execution time t2, first drum potential Vd1, brush potential Vp, second drum potential Vd2, roller potential Vs, and third drum potential Vd3 in the charged component cleaning mode. In Table 2, the first drum potential Vd1, brush potential Vp, second drum potential Vd2, roller potential Vs, and third drum potential Vd3 are shown for both the first deposit removal process and the second deposit removal operation. [Table 2]

[0099] Examples 1 to 3 perform a first deposit removal operation by ensuring the necessary potential contrast to remove deposits from the charged brush 2, and then perform a second deposit removal operation by ensuring the necessary potential contrast to remove deposits from the charged roller 4. In other words, Examples 1 to 3 are control patterns that aim to obtain good deposit removal performance by performing a first deposit removal operation as a first cleaning operation to clean the charged brush 2, and a second deposit removal operation as a second cleaning operation to clean the charged roller 4.

[0100] Comparative Example 1 is a control pattern in which the voltage application to the charged brush 2 and charged roller 4 is kept OFF so that the brush potential Vp and roller potential Vs are 0 [V] during both the first deposit removal process and the second deposit removal operation. Comparative Example 2 is a control pattern aimed at removing deposits attached to the charged roller 4 in the first deposit removal process and removing deposits attached to the charged brush 2 in the second deposit removal operation. In each example shown in Table 1, for the sake of simplifying the control, the first execution time t1 and the second execution time t2 were set to be multiples of the rotation period of the photosensitive drum 1, which is approximately 359 [msec].

[0101] (Details of Each Pattern in the First Deposit Removal Process) In the following, when representing the magnitude relationship of potentials using inequality signs, it is shown by inequalities that hold for the absolute values of those potentials. That is, the numerical values of the first drum potential Vd1, brush potential Vp, second drum potential Vd2, roller potential Vs, and third drum potential Vd3 may be read as their absolute values respectively.

[0102] In Examples 1 to 3 and Comparative Example 1, in the first deposit removal process, by controlling the applied voltage of the charging brush 2 so as to satisfy the relationship Vp < Vd1, it is a control pattern for removing deposits mainly having positive charges accumulated on the charging brush 2. On the other hand, in Comparative Example 2, in the first deposit process, by controlling the applied voltage of the charging roller 4 so as to satisfy the relationship Vs < Vd2, it is a control pattern for removing deposits mainly having positive charges accumulated on the charging roller 4.

[0103] The first drum potential Vd1 can be controlled by charging by the charging brush 2 and the charging roller 4 in the drum rotation before passing through the charging brush 2, discharging by the laser scanner 7, discharging at the primary transfer nip, discharging by the pre-exposure device 5, etc. In each example in Table 1, during the execution of the charging member cleaning mode, the first drum potential Vd1 is maintained high by not performing discharging by the laser scanner 7 and the pre-exposure device 5. Thereby, a wide potential contrast, which is the difference between the first drum potential Vd1 for cleaning the charging brush 2 and the brush potential Vp, can be obtained.

[0104] In Example 1, the voltage applied to the charged brush 2 is turned OFF so that the brush potential Vp is 0[V]. This ensures a potential contrast of 520[V] for cleaning the charged brush 2, allowing for effective removal of deposits attached to the charged brush 2. On the other hand, since the charged brush 2 uses an injection charging method, the second drum potential Vd2, which is the drum potential after passing through the charged brush 2, is lower than the first drum potential Vd1. Therefore, the second drum potential Vd2 in Example 1 is -50[V]. In addition, the voltage applied to the charged roller 4 is turned OFF so that the roller potential Vs is 0[V]. As a result, in the first deposit removal operation, the potential contrast, which is the difference between the second drum potential Vd2 and the roller potential Vs for cleaning the charged roller 4, is 50[V].

[0105] In Example 2, the voltage applied to the charged brush 2 is controlled so that the brush potential Vp is -260[V]. This ensures a potential contrast of 260[V] for cleaning the charged brush 2, allowing for the removal of deposits adhering to the charged brush 2. On the other hand, because the brush potential Vp is -260[V], the second drum potential Vd2 becomes -300[V]. And since the roller potential Vs is 0[V], a potential contrast of 300[V], which is the difference between the second drum potential Vd2 and the roller potential Vs, can be ensured for cleaning the charged roller 4.

[0106] In Example 3, the potential contrast for cleaning the charged brush 2 is 520[V], similar to Example 1, but the first execution time t1 is changed to 718[ms]. That is, in the first deposit removal operation, the photosensitive drum 1 is rotated twice to further improve the deposit removal performance of the charged brush 2.

[0107] On the other hand, in Example 3, similar to Example 1, the second drum potential Vd2, which is the drum potential after passing through the charging brush 2, drops to -50 [V]. Therefore, in order to ensure the same potential contrast for cleaning in the second round as in the first round of the photosensitive drum 1, it is necessary to increase the absolute value of the drum potential between after passing through the charging brush 2 in the first round and before passing through the charging brush 2 in the second round. In Example 3, by setting the roller potential Vs to -1070 [V], the potential difference between the second drum potential Vd2 and the roller potential Vs is set to be not less than the discharge threshold value, and the third drum potential Vd3, that is, the first drum potential Vd1 in the second round, can be maintained at -520 [V]. In Example 3, in the first deposit removal operation, the absolute value of the roller potential Vs is higher than the absolute value of the second drum potential Vd2, resulting in a potential contrast that makes it difficult to clean the charging roller 4.

[0108] Comparative Example 1 has the same control pattern as Example 1 for the first deposit removal operation. In Comparative Example 2, by setting the brush potential Vp to -500 [V], the second drum potential Vd2 is maintained as high as -510 [V], and the roller potential Vs is set to 0 [V]. As a result, in the first deposit removal operation, a potential contrast of 510 [V] for cleaning the charging roller 4 is ensured. On the other hand, the potential contrast for cleaning the charging brush 2 remains at 20 [V].

[0109] (6-2. Details of Each Pattern in the Second Deposit Removal Process) In Examples 1 to 3, in the second deposit removal process, by controlling the applied voltages of the charging brush 2 and the charging roller 4 so as to satisfy the relationship Vs < Vd2, it is a control pattern for removing deposits mainly having positive charges accumulated on the charging roller 4. In Comparative Example 1, in the second deposit removal operation as well as in the first deposit removal operation, the applied voltages to the charging brush 2 and the charging roller 4 are turned off. On the other hand, in Comparative Example 2, in the second deposit removal process, by controlling the applied voltage of the charging brush 2 so as to satisfy the relationship Vp < Vd1, it is a control pattern for removing deposits mainly having positive charges accumulated on the charging brush 2.

[0110] The second drum potential Vd2 can be controlled by setting the brush potential Vp with respect to the first drum potential Vd1. Also, similar to the first deposit removal operation, the first drum potential Vd1 can be controlled by charging by the charging brush 2 and the charging roller 4 in the drum rotation before passing through the charging brush 2, discharging by the laser scanner 7, discharging at the primary transfer nip, discharging by the pre-exposure device 5, etc.

[0111] In each of the examples in Table 2, in order to shorten the required time of the charging member cleaning mode, the second deposit removal operation is started immediately after the first deposit removal operation is completed. Therefore, the first drum potential Vd1 in the second deposit removal operation is equal to the third drum potential Vd3 in the first deposit removal operation. Thus, in the second deposit removal operation, when the absolute value of the first drum potential Vd1 is low, it is desirable to set the brush potential Vp so as to satisfy Vd1 < Vp in order to widen the potential contrast for cleaning the charging roller 4. Thereby, the absolute value of the second drum potential Vd2 can be made higher than the absolute value of the first drum potential Vd1.

[0112] In Example 1, the applied voltage to the charging brush 2 is controlled so that the brush potential Vp becomes -500 [V]. Thereby, Vd2 > Vd1 can be achieved. Also, by setting the roller potential Vs to 0 [V], a potential contrast of 430 [V] for cleaning the charging roller 4 is ensured. On the other hand, since Vp > Vd1, the charging brush 2 is not cleaned.

[0113] In Example 2, a potential contrast of 430 [V] for cleaning the charging roller 4 is ensured in the same manner as in Example 1. Also, since Vp > Vd1, the charging brush 2 is not cleaned. When the first drum potential Vd1 is at a low potential as in Examples 1 and 2, by setting the brush potential Vp such that Vd1 < Vp, the second drum potential Vd2 can be controlled to be higher than the first drum potential Vd1. Thereby, a wide potential contrast for cleaning the charging roller 4 can be obtained.

[0114] In Example 3, the roller potential Vs is set to -1070[V] during the first deposit removal operation, resulting in a first drum potential Vd1 of -520[V]. The voltage applied to the charged brush 2 is then controlled so that the brush potential Vp is -500[V]. This allows the second drum potential Vd2 to be set to -510[V]. Furthermore, by setting the roller potential Vs to 0[V], a potential contrast of 510[V] is secured for cleaning the charged roller 4. On the other hand, the potential contrast for cleaning the charged brush 2 is 10[V], and therefore the charged brush 2 is not cleaned.

[0115] In Comparative Example 1, during the second deposit removal operation, the potential contrast for cleaning the charged roller 4 was 10[V], and cleaning of the charged roller 4 was not performed. On the other hand, the potential contrast for cleaning the charged brush 2 was 50[V].

[0116] In Comparative Example 2, during the second deposit removal operation, the voltage applied to the charged brush 2 is turned OFF so that the brush potential Vp becomes 0[V]. This ensures a potential contrast of 510[V] for cleaning the charged brush 2. On the other hand, the second drum potential Vd2 becomes -10[V], and the roller potential Vs is set to 0[V], resulting in a potential contrast of 40[V] for cleaning the charged roller 4.

[0117] (7. Evaluation Methods) In the image forming apparatus 100 shown in Figure 1, the external appearance of the charging brush 2 and charging roller 4 after performing the image forming mode and the charging member cleaning mode was checked using the control patterns shown in Table 2 for each example. By checking the external appearance of the charging brush 2 and charging roller 4, the ability to remove deposits from the charging brush 2 and charging roller 4 can be evaluated. Although deposits that adhere to and accumulate on the charging brush 2 and charging roller 4 include not only toner but also external additives and substances derived from the recording material, long-term durability evaluation is required, so only the removal performance for toner, which can be evaluated in a short time, was checked. The effectiveness was confirmed under the conditions shown below.

[0118] The evaluation was conducted under conditions of 23°C and 50% humidity, using process cartridges PY to PK for each color, to continuously form 30 pages of full black images with 100% print coverage. The electrostatic component cleaning mode was activated after the image formation mode. The recording material used was A4 size GF-C081 (manufactured by Canon).

[0119] To visually inspect the charging brush 2 and charging roller 4, the photosensitive drum 1 was removed from the process cartridge, and the amount of toner accumulated on the charging brush 2 and charging roller 4 was observed under magnification. In Table 3, for each of the charging brush 2 and charging roller 4, configurations with a large amount of toner attached and poor toner removal performance were marked with ×, and configurations with a small amount of attached toner and good toner removal performance were marked with ○. At the same time, the amount of toner within the magnified field of view was counted to rank the toner removal performance.

[0120] Furthermore, in order to individually verify the adhesion removal performance of the first adhesion removal operation and the second adhesion removal operation, the appearance of the charging brush 2 and the charging roller 4 was checked in two states: when the image forming apparatus 100 was stopped at the end of the first adhesion removal operation, and when the second adhesion removal operation was completed.

[0121] (8. Evaluation Results) The evaluation results for each control pattern in Table 2 are shown in Table 3 below. Based on the evaluation of the appearance of the charged brush 2 and charged roller 4 after the completion of the second deposit removal operation, Examples 1 to 3 showed good deposit removal performance for both the charged brush 2 and the charged roller 4. On the other hand, in Comparative Examples 1 and 2, deposits were removed from the charged brush 2, but not from the charged roller 4. [Table 3]

[0122] (8-1. Difference in the amount of deposits after the first deposit removal operation) The appearance of the charging brush 2 after the first deposit removal operation was best in Example 3, followed by Example 1 and Comparative Example 1, and then Example 2. Comparative Example 2 failed to remove almost all of the deposits from the charging brush 2. On the other hand, the appearance of the charging roller 4 was best in Comparative Example 2, followed by Example 2. Furthermore, Example 1 and Comparative Example 1 had a large amount of deposits on the charging brush 2, while Example 3 had the largest amount of deposits on the charging brush 2.

[0123] In Example 1, a potential contrast of 520[V] was secured for cleaning the charging brush 2, which is thought to have resulted in good adhesion removal performance of the charging brush 2. On the other hand, in the first adhesion removal operation, the potential contrast for cleaning the charging roller 4 was only 50[V], so an electrostatic force was not obtained to transfer the adhesion on the charging roller 4 to the photosensitive drum 1, and it is thought that almost no adhesion was removed from the charging roller 4. In addition, because the potential contrast for cleaning the charging roller 4 was small, some of the adhesion removed from the charging brush 2 reattached to the charging roller 4 due to physical adhesion, and it is thought that there was more adhesion on the charging roller 4 than before the first adhesion removal operation was performed.

[0124] In Example 2, a potential contrast of 260[V] was secured for cleaning the charged brush 2, which is considered to have resulted in relatively good deposit removal performance for the charged brush 2. Furthermore, a potential contrast of 300[V] was secured for cleaning the charged roller 4, which is considered to have resulted in good deposit removal performance for the charged roller 4.

[0125] In Example 3, a potential contrast of 520[V] was secured for cleaning the charged brush 2, and the first deposit removal operation was performed continuously for two rotations of the photosensitive drum 1, so it is thought that the best deposit removal performance of the charged brush 2 was obtained. On the other hand, the absolute value of the roller potential Vs was higher than the absolute value of the second drum potential Vd2, and the potential relationship was such that positively charged deposits were electrically attracted to the charged roller 4. Therefore, in addition to the deposits that were originally accumulated on the charged roller 4 not being removed, deposits that had been transferred from the charged brush 2 to the photosensitive drum 1 were transferred back to the charged roller 4, so it is thought that there were more deposits on the charged roller 4 than before the first deposit removal operation was performed.

[0126] Comparative Example 1 uses the same control pattern as Example 1 for the first deposit removal operation, and therefore the deposit removal performance of the charged brush 2 is the same as in Example 1. Comparative Example 2 is, Because the potential contrast for cleaning the charged brush 2 was only 20[V], it is thought that the electrostatic force required to transfer the deposits on the charged brush 2 to the photosensitive drum 1 was insufficient, and therefore almost no deposits were removed from the charged brush 2. On the other hand, because a potential contrast of 510[V] was secured for cleaning the charged roller 4, it is thought that good deposit removal performance was obtained from the charged roller 4.

[0127] (8-2. Difference in the amount of deposits after the second deposit removal operation) After the second deposit removal operation, the charged brush 2 in all of Examples 1-3 and Comparative Examples 1-2 had successfully removed the deposits. The appearance of the charged brush 2 was best in Example 3, followed by Example 1 and Comparative Examples 1 and 2, and then Example 2. On the other hand, the appearance of the charged roller 4 was best in Example 2, followed by Examples 1 and 3. Comparative Examples 1 and 2 were hardly able to remove the deposits from the charged brush 2.

[0128] In Example 1, a potential contrast of 430[V] was secured for cleaning the charged roller 4, which is considered to have resulted in good adhesion removal performance of the charged roller 4. On the other hand, On the other hand, the absolute value of the brush potential Vp is higher than the absolute value of the first drum potential Vd1, and the potential relationship is such that positively charged deposits are electrically attracted to the charged brush 2. However, the deposits removed from the charged roller 4 are transferred to the intermediate transfer belt 8 and then mechanically scraped off by the cleaning blade 21, so they do not reach the charged brush 2. For this reason, it is thought that the state of the charged brush 2 immediately after the completion of the first deposit removal operation was maintained.

[0129] In Example 2, a potential contrast of 430[V] was secured for cleaning the charging roller 4, and cleaning of the charging roller 4 was also possible during the first deposit removal operation. Therefore, it is considered that the best deposit removal performance of the charging roller 4 was obtained. On the other hand, similar to Example 1, the absolute value of the brush potential Vp was higher than the absolute value of the first drum potential Vd1, but it is considered that the state of the charging brush 2 immediately after the completion of the first deposit removal operation was maintained.

[0130] In Example 3, a potential contrast of 510[V] was secured for cleaning the charging roller 4, which is considered to have resulted in good adhesion removal performance of the charging roller 4. Although Example 3 had the largest potential contrast for cleaning the charging roller 4 among Examples 1 to 3, a large amount of adhesion transferred from the charging brush 2 to the photosensitive drum 1 during the first adhesion removal operation and then re-transferred to the charging roller 4. For this reason, the appearance of the charging roller 4 was considered to be about the same as in Example 1. On the other hand, the potential contrast for cleaning the charging brush 2 was 10[V], and almost no adhesion could be removed from the charging brush 2, which is considered to have maintained the condition of the charging brush 2 immediately after the completion of the first adhesion removal operation.

[0131] In Comparative Example 1, since the potential contrast for cleaning the charging roller 4 was only 10[V], it is thought that almost no deposits were removed from the charging roller 4 during the second deposit removal operation, similar to the first deposit removal operation. On the other hand, since the potential contrast for cleaning the charging brush 2 was only 50[V], almost no deposits were removed from the charging brush 2, and it is thought that the state of the charging brush 2 was maintained as it was immediately after the first deposit removal operation was completed. From the evaluation results of Comparative Example 1, it was confirmed that even when a control to turn OFF the voltage applied to the charging brush is applied to a charging roller separately from the charging brush in order to clean an injection-charging type charging brush, it is difficult to remove deposits from the charging roller.

[0132] In Comparative Example 2, a potential contrast of 510[V] was secured for cleaning the charged brush 2 during the second deposit removal operation, resulting in good deposit removal performance for the charged brush 2. On the other hand, the potential contrast for cleaning the charged roller 4 was only 40[V], so it is thought that almost no deposits were removed from the charged roller 4. Furthermore, because the potential contrast for cleaning the charged roller 4 was small, some of the deposits removed from the charged brush 2 reattached to the charged roller 4 due to physical adhesion, resulting in more deposits on the charged roller 4 than before the first deposit removal operation was performed.

[0133] From the evaluation results of Comparative Examples 1 and 2 and Examples 1 to 3, in the image forming apparatus 100 using the charging brush 2 as the first charging member, after performing the first deposit removing operation for removing deposits on the charging brush 2, it was confirmed that performing the second deposit removing operation for removing deposits on the charging roller 4 as the second charging member is effective for satisfactorily removing the deposits adhering to the charging brush 2 and the charging roller 4.

[0134] (9. Summary) As described above, in each of the examples shown in Table 2, the cleanerless image forming apparatus 100 using the simultaneous development cleaning method is used, in which the photosensitive drum 1 is charged in the image forming mode by the charging brush 2 of the injection charging method and the charging roller 4 that generates a spark discharge. In this example, the discharge threshold is 550 [V]. As can be seen from Table 1 described above, in the image forming mode, (Vp - Vd1) is less than the discharge threshold, and (Vs - Vd2) is not less than the discharge threshold. Thereby, in the image forming mode, no discharge occurs in the charging brush 2, and discharge occurs in the charging roller 4, so that uneven potential of the photosensitive drum 1 can be suppressed. Then, after the image forming mode ends, the CPU 26 of the image forming apparatus 100 executes a charging member cleaning mode including the first deposit removing operation and the second deposit removing operation.

[0135] In the first deposit removing operation, the CPU 26 controls the voltage applied to the charging brush 2 so as to satisfy Vp < Vd1 in order to ensure the potential contrast for cleaning the charging brush 2. By satisfying Vp < Vd1, the relationship between the charging brush 2 of the injection charging method and the drum potential satisfies Vp ≦ Vd2 < Vd1. Thereby, deposits adhering to the charging brush 2 can be satisfactorily removed. That is, the charging brush 2 can be satisfactorily cleaned.

[0136] In Example 3 shown in Tables 2 and 3, during the execution of the first deposit removal operation, the photosensitive drum 1 was rotated a plurality of times (twice in Example 3), and the voltage applied to the charging roller 4 was controlled so that Vd2 < Vs was satisfied and (Vd2 - Vs) was equal to or greater than the discharge threshold. As a result, even after the second rotation of the photosensitive drum 1 that rotates a plurality of times, Vd2 < Vd1 is satisfied, and the first drum potential Vd1 (= the third drum potential Vd3) can be maintained at a high level, improving the deposit removal performance of the charging brush 2.

[0137] In Examples 1 to 3, the CPU 26 controls the voltages applied to the charging brush 2 and the charging roller 4 so that Vs < Vd2 and Vs < Vp are satisfied in the second deposit removal operation.

[0138] In Examples 1 and 2, the CPU 26 controls the voltage applied to the charging brush 2 so that Vd1 < Vd2 ≤ Vp is satisfied in the second deposit removal operation. In Examples 1 and 2, the voltage applied to the charging roller 4 is controlled so that the roller potential Vs becomes 0 [V] in the first deposit removal operation and the second deposit removal operation. As a result, a wide potential contrast for cleaning the charging roller 4 can be obtained. In Example 3, as described above, by setting the roller potential Vs high in the first deposit removal operation, the potential contrast for cleaning the charging roller 4 in the second deposit removal operation that is continuously performed after the first deposit removal operation is configured to be wide.

[0139] Preferably, the CPU 26 controls the voltages applied to the charging brush 2 and the charging roller 4 so that (Vd1 - Vp) is 250 [V] or more in the first deposit removal operation and (Vd2 - Vs) is 250 [V] or more in the second deposit removal operation. By ensuring such potential contrasts in the first charging nip and the second charging nip, deposits adhering to the charging brush 2 and the charging roller 4 can be removed well. That is, the charging brush 2 and the charging roller 4 can be cleaned well.

[0140] In addition, in Examples 1 and 3, in the first deposit removal operation, the brush potential Vp is set to 0 [V]. This allows for a wide potential contrast for cleaning the charged brush 2 and enables energy savings.

[0141] <Other Embodiments> In the first deposit removal operation of Example 3, the same potential control pattern was used for the first and second rotations of the photosensitive drum 1. However, it is also possible to set the potential to change for each rotation. Specifically, the potential control pattern for the second rotation may be changed as in Examples 1 and 2. In Example 3, since the first deposit removal operation ends after rotating the photosensitive drum 1 twice and transitions to the second deposit removal operation, it is not necessary to increase the third drum potential Vd3 at the end of the first deposit removal operation, and it is not essential to set the roller potential Vs high. For example, the CPU 26 may control the voltage applied to the charging roller 4 such that Vd2 < Vs and (Vs - Vd2) is equal to or greater than the discharge threshold when the photosensitive drum 1 makes its first rotation in the first deposit removal operation. Then, the CPU 26 may control the voltage applied to the charging roller 4 such that Vs ≤ Vd2 when the photosensitive drum 1 makes its second rotation in the first deposit removal operation. Thereby, the third drum potential Vd3 ( = the first drum potential Vd1 at the start of the second deposit removal operation) at the end of the first deposit removal operation can be made equal to or less than the second drum potential Vd2. By lowering the roller potential Vs when the photosensitive drum 1 makes its second rotation in the first deposit removal operation, the amount of deposits removed from the charged brush 2 that is collected by the charging roller 4 can be reduced, and the deposit removal performance of the charging roller 4 can be improved.

[0142] Furthermore, in Example 3, the photosensitive drum 1 is rotated twice during the first deposit removal operation, and then the process moves to the second deposit removal operation. However, the photosensitive drum 1 may be rotated more than two times during the first deposit removal operation. In that case, as described above, it is not essential to increase the third drum potential Vd3 at the end of the first deposit removal operation. On the other hand, except for the final rotation of the photosensitive drum 1, it is desirable to maintain a high roller potential Vs in order to ensure cleaning performance from the charged brush 2.

[0143] Furthermore, in Example 3, the roller potential Vs was set to -1070[V] during the first deposit removal operation to maintain a high first drum potential Vd1 during the second rotation of the photosensitive drum 1, but the method is not limited to this. For example, a potential difference of 550[V] or more, which is the discharge threshold, may be set at the primary transfer nip to raise the first drum potential Vd1 during the second rotation of the photosensitive drum 1. Specifically, as in Example 1, by applying -1070[V] to the primary transfer roller against a potential of Vs=0V and Vd3=-50V, the first drum potential Vd1 can be set to a potential close to -520[V].

[0144] Furthermore, in Examples 1 to 3, the brush potential Vp was set to a constant value during the first deposit removal operation, but this can be changed. Specifically, this can include configurations in which the brush potential Vp is changed in steps, configurations in which it is periodically switched with an amplitude, or configurations in which the amplitude is varied. The pattern of the brush potential Vp should preferably be selected according to the charge distribution of the deposits accumulated on the charged brush 2. In configurations in which a large amount of deposits with zero or negative charge accumulate, a pattern in which the brush potential Vp is periodically switched with an amplitude makes it easier to remove deposits of both polarity.

[0145] In addition, in each of the above-described embodiments, a drum cleanerless method without a cleaning means for the primary transfer residual toner on the photosensitive drum 1 is used, but a cleaning means for the primary transfer residual toner may be provided. For example, even in a so-called blade cleaning method in which a rubber blade is brought into contact with the photosensitive drum 1 to collect the primary transfer residual toner, the charging brush 2 or the charging roller 4 may be contaminated due to the adhesion of fine particles such as external additives and toner matrix resins that have passed through the rubber blade. Similar to the cleanerless configuration, substances adhering to the charging brush 2 or the charging roller 4 tend to have a positive charge. Therefore, by executing the above-described charging member cleaning mode, the charging brush 2 and the charging roller 4 having good adhesion removal performance can be obtained.

[0146] Also, in each of the above-described embodiments, in the charging member cleaning mode, a configuration is used in which the developing roller 3 is separated from the photosensitive drum 1 and the voltage applied to the developing roller 3 is turned off. However, the developing roller 3 may be kept in contact with the photosensitive drum 1 and the voltage may be continuously applied. In this configuration, in order for the deposits having a positive charge removed from the charging brush 2 and the charging roller 4 to stay on the photosensitive drum 1 when passing through the developing nip, it is necessary to satisfy Vdc < Vd3. That is, when Vdc = 320 [V], the voltage applied to the charging brush 2 and the charging roller 4 is controlled so that the third drum potential Vd3 becomes larger than 320 [V]. For example, by setting the roller potential Vs high as in the first deposit removal operation of Example 3, Vdc < Vd3 can be satisfied. Also, in the second deposit removal operation, by controlling the brush potential Vp so that Vd2 > Vdc, Vdc < Vd3 can be satisfied. The deposits that have passed through the developing nip are transferred to the intermediate transfer belt 8 having a potential higher than negative and higher than the surface potential of the photosensitive drum 1 at the time of passing through the primary transfer nip, and then are collected by the cleaning blade 21.

[0147] Furthermore, in the embodiments described above, a full-color image forming apparatus 100 was used, which performs image formation using four process cartridges containing four toners. However, a so-called monocolor image forming apparatus that uses only one process cartridge may also be used. In monocolor image forming apparatuses, a direct transfer method is often used, in which there is no intermediate transfer belt, and the photosensitive drum and transfer roller perform direct transfer via the recording material. In the direct transfer method, since the recording material is in direct contact with the surface of the photosensitive drum, fibers and fillers contained in the recording material tend to adhere to the surface of the photosensitive drum after transfer, and fibers and fillers derived from the recording material also tend to adhere to and accumulate on the charging brush. In the direct transfer method as well, the paper components adhering to the charging brush tend to have a positive charge. Therefore, by performing the charging member cleaning mode of each embodiment described above, similar to the embodiments described above, a charging brush 2 and a charging roller 4 with good adhesion removal performance can be obtained.

[0148] Furthermore, in the embodiments described above, a volume resistivity of 1.0 × 10^13 [Ω·cm] was used for the charge injection layer 105 of the photosensitive drum 1, but similar effects can be obtained even with a different volume resistivity configuration. When the volume resistivity is less than 1.0 × 10^13 [Ω·cm], the injection charging by the charging brush 2 is high, and the second drum potential Vd2 becomes almost equal to the brush potential Vp. This makes it easy to control the second drum potential Vd2, but the deposit removal performance of the charging roller 4 during the first deposit removal operation tends to decrease. Specifically, in Embodiment 1, the second drum potential Vd2 becomes almost 0 [V], so the potential contrast between the second drum potential Vd2 and the roller potential Vs becomes 0. Therefore, it is desirable to ensure the cleaning performance of the charging brush 2 and the charging roller 4 by setting the potentials of the brush potential Vp and the roller potential Vs. Furthermore, when the volume resistivity exceeds 1.0 × 10^13 [Ω·cm], the injection charging effect by the charging brush 2 is low, and the second drum potential Vd2 is maintained higher than the brush potential Vp, making it easier to remove deposits from the charging roller 4 during the first deposit removal operation.

[0149] Furthermore, from the viewpoint of charge retention, below 1.0 × 10^9 [Ω·cm], it becomes difficult to maintain the latent image, raising concerns about a decrease in the print quality of fine lines. Also, from the viewpoint of injection charging, above 1.0 × 10^14 [Ω·cm], the injection charging is low, requiring the application of a charging voltage exceeding the discharge threshold to obtain the desired dark area potential (Vd) of the photosensitive drum 1, thus negating the advantages of the injection charging configuration. From the viewpoints of removal of charged brush deposits and injection charging, it is desirable that the volume resistivity of the photosensitive drum 1 be between 1.0 × 10^9 [Ω·cm] and 1.0 × 10^14 [Ω·cm].

[0150] Furthermore, in the embodiments described above, a charging brush 2 consisting of a bar brush with a resistance of 1 × 10^5 [Ω] was used as the injection member, but similar effects can be obtained even with configurations with different resistance values. When the resistance value is below 1.0 × 10^5 [Ω], the injection charging performance by the charging brush 2 increases, making it easier to control the second drum potential Vd2, but the cleaning performance of the charging roller 4 during the first deposit removal operation tends to decrease. On the other hand, when the resistance value of the charging brush 2 exceeds 1.0 × 10^5 [Ω], the injection charging performance by the charging brush is low, and the second drum potential Vd2 is maintained higher than the brush potential Vp, making it easier to remove deposits from the charging roller 4 during the first deposit removal operation. Also, from the viewpoint of injection charging performance, when it exceeds 1.0 × 10^9 [Ω], the injection charging performance is low, and it becomes necessary to apply a charging voltage exceeding the discharge threshold in order to obtain the desired dark area potential (Vd) of the photosensitive drum 1, thus losing the advantages of the injection charging configuration. From the viewpoint of the ability to remove deposits and the ability to inject charge, it is desirable that the resistance of the charging brush 2 be 1.0 × 10^9 [Ω] or less.

[0151] Furthermore, in the embodiments described above, a charging brush 2 consisting of a bar brush was used as the injection member (first charging member), but similar effects can be obtained with other injection members. Specifically, a brush roller in which conductive nylon fibers are wound around a roller-shaped core, or a conductive rubber roller can be used as the injection member. The brush roller is made of conductive fibers and rotates in accordance with the photosensitive drum 1. The rubber roller is made of conductive, low-resistance rubber and rotates in accordance with the photosensitive drum 1. When the above rubber roller is used as the injection member, although the charge injection capability is reduced compared to the bar brush, it has been confirmed that charge injection is possible with a resistance value of about 1 × 10^5 [Ω].

[0152] Furthermore, while the above-described embodiments used a configuration in which the charged component cleaning mode was performed after image formation, the charged component cleaning mode may be performed at other times. Specifically, it can be performed when the power to the image forming apparatus is turned on, when it wakes up from sleep mode, before the image forming operation, or between images (between sheets of paper) during the image forming operation. In other words, the charged component cleaning mode can be performed at a different time from the image forming mode.

[0153] Furthermore, in the embodiments described above, a configuration was used in which a negatively charged toner was used and a negative charging voltage was applied. However, a configuration in which a positively charged toner was used and a positive charging voltage was applied may also be used. In that case, the primary transfer residue toner mainly has a negative charge and accumulates on the charging brush 2 and charging roller 4 to which a positive charging voltage is applied. However, by reversing the polarity of the voltage applied to each component as shown in the embodiments above, a charging brush 2 and charging roller 4 with good deposit removal performance can be obtained in a similar manner.

[0154] The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0155] Summary of this disclosure This disclosure includes at least the following: (Composition 1) A photoreceptor having a charge injection layer containing conductive particles and configured to be rotatable in a predetermined rotational direction, A first charging member that charges the surface of the photoreceptor by contacting it, A developing unit is positioned downstream of the first charged member in the rotational direction and develops the electrostatic latent image formed on the surface as a toner image, A second charging member is positioned between the first charging member and the developing unit in the aforementioned rotational direction, and charges the surface of the photoreceptor by contacting it, A transfer unit that transfers the toner image to the material to be transferred, A control unit that controls the voltage applied to the first charged member and the second charged member, respectively, and is capable of executing an image forming mode for transferring the toner image to the member to be transferred, and a cleaning mode which is executed at a timing different from the image forming mode, wherein a second cleaning operation is performed to clean the second charged member after a first cleaning operation is performed to clean the first charged member, When the absolute value of the potential of the first charged member is Vp, the absolute value of the potential of the second charged member is Vs, the absolute value of the surface potential of the photoreceptor before passing through the first charged member is Vd1, and the absolute value of the surface potential of the photoreceptor after passing through the first charged member and before passing through the second charged member is Vd2, The control unit controls the voltages applied to the first charging member and the second charging member so that Vp ≦ Vd2 < Vd1 is satisfied in the first cleaning operation and Vs < Vd2 is satisfied in the second cleaning operation. An image forming apparatus characterized by the above. (Configuration 2) In the image forming mode, the control unit controls the voltages applied to the first charging member and the second charging member so that (Vp - Vd1) is less than the discharge threshold value and (Vs - Vd2) is greater than or equal to the discharge threshold value. The image forming apparatus according to Configuration 1, characterized by the above. (Configuration 3) Examples 1 to 3 The control unit controls the voltages applied to the first charging member and the second charging member so that (Vd1 - Vp) is 250 [V] or more in the first cleaning operation and (Vd2 - Vs) is 250 [V] or more in the second cleaning operation. The image forming apparatus according to Configuration 1 or 2, characterized by the above. (Configuration 4) Examples 1 to 2 The control unit controls the voltage applied to the first charging member so that Vd1 < Vd2 ≦ Vp is satisfied in the second cleaning operation. The image forming apparatus according to any one of Configurations 1 to 3, characterized by the above. (Configuration 5) Examples 1 to 2 The control unit controls the voltage applied to the second charging member so that Vs = 0 [V] in the first cleaning operation and the second cleaning operation. The image forming apparatus according to Configuration 4, characterized by the above. (Configuration 6) Example 1 The control unit controls the voltage applied to the first charging member so that Vp = 0 [V] in the first cleaning operation. The image forming apparatus according to Configuration 5, characterized by the above. (Configuration 7) The control unit controls the voltage applied to the second charging member such that Vd2 < Vs is satisfied in the first cleaning operation and (Vs - Vd2) is equal to or greater than the discharge threshold value. The image forming apparatus according to Configuration 1 or 2, characterized by this. (Configuration 8) Example 3 The control unit rotates the photoreceptor a plurality of times during the execution of the first cleaning operation. In the first cleaning operation, when the photoreceptor rotates for the second time, Vd2 < Vd1 is satisfied. The image forming apparatus according to Configuration 7, characterized by this. (Configuration 9) The control unit rotates the photoreceptor a plurality of times during the execution of the first cleaning operation. (i) In the first cleaning operation, when the photoreceptor rotates for the first time, the control unit controls the voltage applied to the second charging member such that Vd2 < Vs is satisfied and (Vs - Vd2) is equal to or greater than the discharge threshold value. (ii) In the first cleaning operation, when the photoreceptor rotates for the second time, the control unit controls the voltage applied to the second charging member such that Vs ≤ Vd2 is satisfied. The image forming apparatus according to Configuration 1 or 2, characterized by this. (Configuration 10) The control unit controls the voltages applied to the first charging member and the second charging member respectively such that Vs < Vp is satisfied in the second cleaning operation. The image forming apparatus according to any one of Configurations 1 to 9, characterized by this. (Configuration 11) The control unit periodically switches Vp in the first cleaning operation. The image forming apparatus according to any one of Configurations 1 to 10, characterized by this. (Configuration 12) The developing unit is separated from the photoreceptor in the cleaning mode. The image forming apparatus according to any one of Configurations 1 to 11, characterized by this. (Configuration 13) The developing unit is in contact with the photoreceptor in the first cleaning operation. When the absolute value of the potential of the developing unit is Vdc and the absolute value of the surface potential of the photoreceptor after passing through the second charging member is Vd3, the control unit controls the voltages applied to the first charging member and the second charging member so that Vdc < Vd3 is satisfied in the first cleaning operation. The image forming apparatus according to any one of Configurations 1 to 11, characterized in that. (Configuration 14) The volume resistivity of the charge injection layer is 1.0×10^9 [Ω·cm] or more and 1.0×10^14 [Ω·cm] or less. The image forming apparatus according to any one of Configurations 1 to 13, characterized in that. (Configuration 15) The conductive particles include a metal oxide containing titanium atoms and niobium atoms. The image forming apparatus according to any one of Configurations 1 to 14, characterized in that. (Configuration 16) The first charging member has a support member, a brush portion that is attached to the support member and made of conductive fibers, and rubs against the photoreceptor. The image forming apparatus according to any one of Configurations 1 to 15, characterized in that. (Configuration 17) The resistance value of the first charging member is 1.0×10^9 [Ω] or less. The image forming apparatus according to Configuration 16, characterized in that. (Configuration 18) The second charging member is composed of conductive rubber and includes a roller that rotates idly with respect to the photoreceptor. The image forming apparatus according to any one of Configurations 1 to 17, characterized in that. (Configuration 19) The second charging member has a high-resistance surface layer having a volume resistivity of 1.0×10^12 [Ω·cm] or more, and the surface is charged by spark discharge. The image forming apparatus according to Configuration 18, characterized in that. (Composition 20) The developing unit electrostatically recovers the toner remaining on the photoreceptor after the toner image has been transferred to the transfer target by the transfer unit. An image forming apparatus according to any one of configurations 1 to 19, characterized by the features described herein. (Composition 21) The system further includes a secondary transfer unit that transfers the toner image transferred to the transfer target member to a sheet. An image forming apparatus according to any one of configurations 1 to 20, characterized by the above. (Composition 22) In the cleaning mode, the deposits adhering to the first charged member and the second charged member are electrostatically moved to the transfer member via the photoreceptor. The system further includes a cleaning member for removing the deposits on the transfer member. The image forming apparatus according to configuration 21, characterized by the features described above. [Explanation of Symbols]

[0156] 1: Photoreceptor (photosensitive drum) / 2: First charging component (charging brush) / 3: Developing unit (developing roller) / 4: Second charging component (charging roller) / 6Y: Transfer unit (primary transfer roller) / 8: Transferred component (intermediate transfer belt) / 11: Secondary transfer unit (secondary transfer roller) / 21: Cleaning component (cleaning blade) / 26: Control unit (CPU) / 100: Image forming apparatus / 105: Charge injection layer / 105p: Conductive particles

Claims

1. A photoreceptor having a charge injection layer containing conductive particles and configured to be rotatable in a predetermined rotational direction, A first charging member that charges the surface of the photoreceptor by contacting it, A developing unit is positioned downstream of the first charged member in the rotational direction and develops the electrostatic latent image formed on the surface as a toner image, A second charging member is positioned between the first charging member and the developing unit in the rotational direction, and charges the surface of the photoreceptor by contacting it, A transfer unit that transfers the toner image to the material to be transferred, A control unit that controls the voltage applied to the first charged member and the second charged member, respectively, and is capable of executing an image forming mode for transferring the toner image to the member to be transferred, and a cleaning mode which is executed at a timing different from the image forming mode, wherein a second cleaning operation is performed to clean the second charged member after a first cleaning operation is performed to clean the first charged member, When the absolute value of the potential of the first charged member is Vp, the absolute value of the potential of the second charged member is Vs, the absolute value of the surface potential of the photoreceptor before passing through the first charged member is Vd1, and the absolute value of the surface potential of the photoreceptor after passing through the first charged member and before passing through the second charged member is Vd2, The control unit controls the voltages applied to the first and second charging members, respectively, such that Vp ≤ Vd2 < Vd1 is satisfied in the first cleaning operation and Vs < Vd2 is satisfied in the second cleaning operation. An image forming apparatus characterized by the following features.

2. The control unit controls the voltages applied to the first and second charged members, respectively, in the image forming mode, such that (Vp - Vd1) is less than the discharge threshold and (Vs - Vd2) is greater than or equal to the discharge threshold. The image forming apparatus according to feature 1.

3. The control unit controls the voltages applied to the first and second charging members, respectively, such that (Vd1 - Vp) is 250 [V] or more during the first cleaning operation and (Vd2 - Vs) is 250 [V] or more during the second cleaning operation. The image forming apparatus according to feature 1.

4. The control unit controls the voltage applied to the first charged member such that Vd1 < Vd2 ≤ Vp is satisfied during the second cleaning operation. The image forming apparatus according to feature 1.

5. The control unit controls the voltage applied to the second charged member such that Vs = 0 [V] during the first cleaning operation and the second cleaning operation. The image forming apparatus according to feature 4.

6. The control unit controls the voltage applied to the first charged member so that Vp = 0 [V] during the first cleaning operation. The image forming apparatus according to feature 5.

7. The control unit controls the voltage applied to the second charged member such that Vd2 < Vs and (Vs - Vd2) is equal to or greater than the discharge threshold during the first cleaning operation. The image forming apparatus according to feature 1.

8. The control unit rotates the photoreceptor multiple times while performing the first cleaning operation. In the first cleaning operation described above, when the photoreceptor is in its second rotation, Vd2 < Vd1 is satisfied. The image forming apparatus according to feature 7.

9. The control unit rotates the photoreceptor multiple times while performing the first cleaning operation. (i) In the first cleaning operation, the voltage applied to the second charging member is controlled such that when the photoreceptor is in its first rotation, Vd2 < Vs and (Vs - Vd2) is equal to or greater than the discharge threshold. (ii) In the first cleaning operation, the voltage applied to the second charging member is controlled such that Vs ≤ Vd2 is satisfied when the photoreceptor is in its second rotation. The image forming apparatus according to feature 1.

10. The control unit controls the voltages applied to the first and second charged members, respectively, so that Vs < Vp is satisfied during the second cleaning operation. The image forming apparatus according to feature 1.

11. The control unit periodically switches Vp during the first cleaning operation. The image forming apparatus according to feature 1.

12. The developing unit is spaced apart from the photoreceptor in the cleaning mode. The image forming apparatus according to feature 1.

13. The developing unit is in contact with the photoreceptor during the first cleaning operation. The control unit controls the voltages applied to the first and second charging members, respectively, such that Vdc < Vd3 is satisfied during the first cleaning operation, when Vdc is the absolute value of the potential of the developing unit and Vd3 is the absolute value of the surface potential of the photoreceptor after passing through the second charging member. The image forming apparatus according to feature 1.

14. The volume resistivity of the charge injection layer is 1.0 × 10⁹ [Ω·cm] or greater and 1.0 × 10¹⁴ [Ω·cm] or less. The image forming apparatus according to feature 1.

15. The conductive particles include a metal oxide containing titanium atoms and niobium atoms. The image forming apparatus according to feature 1.

16. The first charging member comprises a support member and a brush portion attached to the support member and made of conductive fibers, which rubs against the photoreceptor. The image forming apparatus according to feature 1.

17. The resistance of the first charged member is 1.0 × 10⁹ [Ω] or less. The image forming apparatus according to feature 16.

18. The second charging member is made of conductive rubber and includes a roller that rotates in accordance with the photoreceptor. The image forming apparatus according to feature 1.

19. The second charging member has a high-resistivity surface layer with a volume resistivity of 1.0 × 10¹² [Ω·cm] or more, and the surface is charged by spark discharge. The image forming apparatus according to feature 18.

20. The developing unit electrostatically recovers the toner remaining on the photoreceptor after the toner image has been transferred to the transfer target by the transfer unit. The image forming apparatus according to any one of claims 1 to 19.

21. The system further includes a secondary transfer unit that transfers the toner image transferred to the transfer target member to a sheet. The image forming apparatus according to any one of claims 1 to 19.

22. In the cleaning mode, the deposits adhering to the first charged member and the second charged member are electrostatically moved to the transfer member via the photoreceptor. The system further includes a cleaning member for removing the deposits on the transfer member. The image forming apparatus according to feature 21.

Images