Image forming apparatus

Abstract

To achieve both uniformity in charging and prevention of failure of charging due to a foreign substance.SOLUTION: An image forming apparatus comprises a rotatable photoreceptor, and a charging brush that is in contact with a surface of the photoreceptor to form a charging part and electrically charges the surface of the photoreceptor. The charging brush has brush fibers including a first type of fibers subjected to crimp processing, and a second type of fibers not subjected to the crimp processing. The ratio of the first type of fibers to the brush fibers in a first portion of the charging brush in a direction of movement of the surface of the photoreceptor in the charging part is higher than the ratio of the first type of fibers to the brush fibers in a second portion of the charging brush located downstream of the first portion in the direction of movement.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus for forming an image on a recording material. [Background technology]

[0002] Patent Document 1 describes charging the surface of a photosensitive drum with a charging brush with conductive fibers implanted therein. Patent Document 2 describes a charging brush that uses crimped yarn as the brush fibers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-56470 A [Patent Document 2] JP 2007-17804 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to charge the photosensitive drum more uniformly using a charging brush, it is desirable to bring the tips of the brush fibers into uniform contact with the surface of the photosensitive drum with a small contact pressure. On the other hand, if a relatively large foreign object such as paper dust gets into the contact area between the charging brush and the photosensitive drum, localized charging defects caused by the foreign object may become apparent as image defects.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an image forming apparatus capable of improving the uniformity of charging while suppressing charging defects caused by foreign matter. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming apparatus comprising: a rotatable photoconductor; and a charging brush that contacts the surface of the photoconductor to form a charging portion and charges the surface of the photoconductor, wherein the charging brush has brush fibers including a first type of fiber that has been subjected to crimping processing and a second type of fiber that has not been subjected to crimping processing, and wherein a ratio of the first type of fiber in the brush fibers in a first portion of the charging brush in a movement direction of the surface of the photoconductor in the charging portion is higher than a ratio of the first type of fiber in the brush fibers in a second portion of the charging brush that is located downstream of the first portion in the movement direction. Effect of the Invention

[0007] According to the present invention, it is possible to provide an image forming apparatus capable of improving the uniformity of charging while suppressing charging defects caused by foreign matter. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a schematic view of a process cartridge according to an embodiment. [Diagram 3] FIG. 2 is a schematic diagram of a charging brush according to an embodiment. [Figure 4] FIG. 2 is a control block diagram according to the embodiment. [Diagram 5] 2A and 2B are diagrams showing a layer structure of a photosensitive drum according to an embodiment. [Figure 6] 3A to 3C are explanatory views of a charging brush according to the first embodiment. [Figure 7] 5A to 5C are explanatory views of a charging brush according to Example 2. [Figure 8] 4A to 4C are explanatory views of a charging brush according to Comparative Example 1. [Figure 9] 6A to 6C are explanatory views of a charging brush according to Comparative Example 2. [Figure 10] 11A to 11C are explanatory views of a charging brush according to Example 3. [Figure 11] 13 is an explanatory diagram of a charging brush according to a modified example. [Figure 12] FIG. 2 is an explanatory diagram of a method for identifying crimped yarn. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] (1. Image forming device) 1 is a schematic diagram showing the configuration of an image forming apparatus 1 according to an embodiment (embodiment 1) of the present invention. The image forming apparatus 1 is a monochrome printer that forms an image on a recording material based on image information input from an external device. The recording material includes various sheet materials of different materials, such as paper such as plain paper and cardboard, plastic film such as sheets for overhead projectors, sheets of special shapes such as envelopes and index paper, and cloth.

[0011] In this embodiment, a monochrome printer is used as an example, but the "image forming device" may be a color printer equipped with multiple cartridges that use toners of different colors as developers. Also, the "image forming device" is not limited to a single-function printer equipped with only an image forming function (printing function), and may be a copier equipped with a copying function, or a multifunction device equipped with multiple functions such as a scanner or facsimile.

[0012] 1, the image forming apparatus 1 has an image forming unit 10 that forms a toner image on a recording material P. The image forming apparatus 1 further has a fixing unit 40 that fixes the toner image formed by the image forming unit 10 to the recording material P. The image forming apparatus 1 performs a series of operations (image forming operation, paper passing operation) in which the image forming unit 10 forms an image on the recording material P while transporting the recording material P one sheet at a time.

[0013] The image forming section 10 has an exposure unit 11 as an exposure means, an electrophotographic process cartridge 20, and a transfer roller 12 as a transfer means that transfers the toner image formed on the photosensitive drum 21 of the process cartridge 20 onto a recording material P.

[0014] The process cartridge 20 is shown in Fig. 2. The process cartridge 20 is a unit in which a photosensitive drum 21 and at least one process means acting on the photosensitive drum 21 to perform each step of the electrophotographic process (charging, exposure, development, transfer, fixing, cleaning, etc.) are integrated. The process cartridge 20 is detachably attached to the apparatus main body 1A of the image forming apparatus 1. Note that the apparatus main body 1A in this embodiment refers to the image forming apparatus 1 without the process cartridge 20.

[0015] The process cartridge 20 in this embodiment has a photosensitive drum 21, a charging brush 22, a charging roller 23, and a developing device 30 including a developing roller 31. The charging brush 22, the charging roller 23, and the developing device 30 are all examples of process means, and are arranged around the photosensitive drum 21. A transfer portion Pa (transfer nip portion) where a toner image is transferred is formed as an area where the photosensitive drum 21 and the transfer roller 12 face each other.

[0016] The photosensitive drum 21 is a photosensitive member formed into a cylindrical shape (drum shape). The photosensitive drum 21 functions as an image carrier that carries a latent image and a toner image. In an image forming operation, the photosensitive drum 21 is rotated by a drive motor 110 (FIG. 4) in a predetermined direction (clockwise direction in FIG. 2) at a predetermined peripheral speed (called a process speed).

[0017] In the image forming apparatus 1 of this embodiment, the printing speed when A4 size recording material P is continuously fed is 30 sheets per minute, and the process speed is 170 mm / sec.

[0018] The charging brush 22 and the charging roller 23 are pressed against the surface of the photosensitive drum 21 with a predetermined pressure. The contact portion between the charging brush 22 and the photosensitive drum 21 is a brush charging portion Pb (first charging portion) where the surface of the photosensitive drum 21 is charged. The contact portion between the charging roller 23 and the photosensitive drum 21 is a charging portion Pc (second charging portion) where the surface of the photosensitive drum 21 is charged. Both the first charging portion and the second charging portion are disposed downstream of the transfer portion in the rotation direction R of the photosensitive drum 21 and upstream of the exposure position Pd where the light from the exposure unit 11 is irradiated on the photosensitive drum 21. The brush charging portion Pb, which is the contact portion between the charging brush 22 and the photosensitive drum 21, is disposed downstream of the transfer portion Pa and upstream of the charging portion Pc of the charging roller 23 in the rotation direction R of the photosensitive drum 21.

[0019] The charging roller 23 (roller member) is an example of a charging means for further charging the surface of the photosensitive drum 21 downstream of the charging brush 22. Instead of the charging roller 23, a corona charger for charging the surface of the photosensitive drum 21 by, for example, corona discharge may be disposed.

[0020] A predetermined charging voltage for charging the surface of the photosensitive drum 21 is applied to the charging brush 22 and the charging roller 23 from a power source of a high-voltage board provided in the image forming apparatus 1. The absolute value of the charging voltage applied to the charging brush 22 is smaller than the absolute value of the charging voltage applied to the charging roller 23.

[0021] 4 shows a control block diagram of the image forming apparatus 1. A brush voltage is applied to the charging brush 22 from a brush power source E4, and a charging roller voltage is applied to the charging roller 23 from a charging power source E1.

[0022] A predetermined voltage is applied to the charging brush 22 and the charging roller 23, so that the surface of the photosensitive drum 21 is uniformly charged to a predetermined potential. In this embodiment, the surface of the photosensitive drum 21 is secondarily charged by the charging brush 22, and then charged by the charging roller 23 to a final potential before exposure (a potential suitable for image formation by exposure and development). In other words, the potential of the surface of the photosensitive drum 21 (drum surface potential) is raised stepwise by charging with the charging brush 22 and the charging roller 23 from the potential immediately after passing through the transfer section. In this embodiment, charging is performed by the charging roller 23 so that the final drum surface potential is -500 V. The charging of the photosensitive drum 21 by the charging brush 22 and the charging roller 23 will be described in more detail in the section "5. Charging Configuration."

[0023] The exposure unit 11 uses a polygon mirror to irradiate the photosensitive drum 21 with a laser beam Lt corresponding to image information input from an external device, thereby scanning and exposing the surface of the photosensitive drum 21. This exposure forms an electrostatic latent image corresponding to the image information on the surface of the photosensitive drum 21. The exposure unit 11 is not limited to a laser scanner device, and may be, for example, an LED exposure device having an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 21. In this embodiment, the laser exposure of the exposure unit 11 reduces the drum surface potential of the solid black portion (exposed portion, printed portion) to -50V (light portion potential).

[0024] Next, the process cartridge 20 will be described. The process cartridge 20 has a developing device 30. The developing device 30 includes a developing roller 31 as a developing member (developer carrier) that carries a developer and supplies it to the photosensitive drum 21, a developing container 32 that forms a frame of the developing device 30, and a supply roller 33 that supplies toner to the developing roller 31. The developing roller 31 and the supply roller 33 are rotatably supported by the developing container 32. The developing roller 31 is disposed at an opening of the developing container 32 so as to face the photosensitive drum 21. The supply roller 33 is in rotatable contact with the developing roller 31, and the toner contained in the developing container 32 is applied to the surface of the developing roller 31 by the supply roller 33.

[0025] The developing device 30 of this embodiment uses a contact development method as a developing method. That is, a toner layer carried by the developing roller 31 comes into contact with the photosensitive drum 21 in a developing section (developing area) where the photosensitive drum 21 and the developing roller 31 face each other. A developing voltage is applied to the developing roller 31 by a developing power source E2 (FIG. 4) which is a developing voltage application section. Under the condition where the developing voltage is applied, the toner carried by the developing roller 31 is transferred from the developing roller 31 to the surface of the photosensitive drum 21 according to the potential distribution on the surface of the photosensitive drum 21, and the electrostatic latent image is developed into a toner image.

[0026] In this embodiment, the development voltage is -300V. In this embodiment, a reversal development method is adopted. That is, after the surface of the photosensitive drum 21 is charged in the charging process, the surface of the photosensitive drum 21 is exposed in the exposure process, and a toner image is formed by adhering to the exposed area, which is the surface of the photosensitive drum 21 where the charge amount has attenuated. The charge applied to the surface of the photosensitive drum 21 in the charging process has the same polarity as the normal polarity of the toner. The development voltage is set so that the potential of the exposed area of ​​the photosensitive drum 21 (light area potential) has a polarity opposite to the normal polarity of the toner with respect to the development voltage, and the potential of the non-exposed area of ​​the photosensitive drum 21 (dark area potential) has a polarity equal to the normal polarity of the toner with respect to the development voltage.

[0027] In this embodiment, a toner having a particle size of 7 μm and a normal polarity of negative polarity can be used. As an example of the toner, a polymerized toner produced by a polymerization method is used. The toner does not contain a magnetic component, and is a so-called non-magnetic one-component developer in which the toner is supported on the developing roller 31 mainly by intermolecular forces and electrostatic forces (image forces).

[0028] The toner particles may contain a plurality of waxes for adjusting the melting characteristics of the toner during the fixing process and the adhesive strength with the recording medium and fixing member. Fine particles made of silica particles with a particle size of submicron order may be added to the surface of the toner particles for adjusting the fluidity and charging performance of the toner. In this embodiment, the toner particles to which wax and / or fine particles are added as necessary are used as the toner for the developer.

[0029] In this embodiment, an example of using a non-magnetic one-component developer will be described, but a one-component developer containing a magnetic component may be used as the developer. Also, a two-component developer composed of a non-magnetic toner and a magnetic carrier may be used as the developer. When a magnetic developer is used, for example, a cylindrical developing sleeve with a magnet disposed inside is used as the developer carrier.

[0030] An agitating member 34 is provided inside the developing container 32 as an agitating means. The agitating member 34 is driven by a drive motor 110 (FIG. 4) to rotate in a predetermined rotation direction R2, thereby agitating the toner in the developing container 32 and sending the toner toward the developing roller 31 and the supply roller 33. The agitating member 34 also circulates, within the developing container 32, the toner that has not been used for development and has been peeled off from the developing roller 31, and serves to uniformize the toner in the developing container 32.

[0031] A developing blade 35 that regulates the amount of toner carried by the developing roller 31 is disposed at the opening of the developing container 32 in which the developing roller 31 is disposed. The developing blade 35 is formed of, for example, a stainless steel plate. A voltage having an absolute value 200 V higher on the negative polarity side than the developing roller 31 is applied to the developing blade 35 from a blade power source E5 (FIG. 4) that serves as a developing blade application unit. In other words, a voltage 200 V higher on the normal polarity side of the toner is applied to the developing blade 35.

[0032] The toner supplied to the developing roller 31, while being supported on the surface of the developing roller 31, passes through the portion facing the developing blade 35 as the developing roller 31 rotates, and is thereby thinned to a uniform thickness. At the same time, the toner is charged to the normal negative polarity by frictional charging caused by rubbing with the developing blade 35 and direct injection charging caused by the potential difference formed between the developing blade 35 and the developing roller 31.

[0033] A voltage (transfer voltage) having a polarity opposite to the normal polarity of the toner is applied to the transfer roller 12 by a transfer power source E3 (FIG. 4).

[0034] The fixing unit 40 is a thermal fixing type that performs image fixing processing by heating and melting the toner on the recording material. The fixing unit 40 includes a cylindrical fixing film 41, a heater such as a ceramic heater that heats the fixing film 41, a thermistor that measures the temperature of the fixing heater, and a pressure roller 42 that presses against the fixing film 41. The flexible fixing film 41 is an example of a fixing member (heating member), and a rigid fixing roller may be used as the fixing member (heating member). The ceramic heater is an example of a heating means that heats the fixing member (heating member), and a halogen lamp or a coil unit that heats a conductive layer in the fixing member (heating member) by induction heating may be used as the heating means.

[0035] In this embodiment, the photosensitive drum 21, the charging brush 22, and the charging roller 23 are provided in a process cartridge 20 that is detachable from the device main body 1A of the image forming apparatus 1, but the arrangement of the elements is not limited to this. For example, the developing device 30 may be a unit (developing cartridge) that is detachable from the device main body 1A independently of the process cartridge 20 (drum cartridge) that includes the photosensitive drum 21, the charging brush 22, and the charging roller 23. Also, the image forming apparatus 1 may not have a detachable process cartridge 20, and the photosensitive drum 21 and the charging brush 22 may be assembled to the device main body 1A in a manner that does not assume attachment and detachment by the user.

[0036] (2. Control System) 4 is a schematic block diagram showing a control system of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a control unit 150. The control unit 150 has a CPU 151 that performs calculation processing, a memory (storage element) 152 such as a ROM or RAM as a storage means, an input / output unit (not shown) that controls the transmission and reception of signals between various elements connected to the control unit 150, and the like. The RAM stores the detection results of the sensors, calculation results, and the like, and the ROM stores a control program, a data table obtained in advance, and the like. The CPU 151 controls each unit of the image forming apparatus 1 by reading and executing the control program from the memory 152.

[0037] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 1. The control unit 150 executes a predetermined image forming sequence by controlling the transmission and reception of various electrical information signals and the timing of driving. The control unit 150 is connected to each unit of the image forming apparatus 100. For example, in relation to this embodiment, the control unit 150 is connected to a charging power supply E1 that is a second charging power supply, a developing power supply E2, a transfer power supply E3, a brush power supply E4 that is a first charging power supply, a blade power supply E5, an exposure unit 11, a drive motor 110, and the like.

[0038] (3. Image formation operation) Next, the image forming operation of the image forming apparatus 1 will be described with reference to Figs. 1 and 2. When an image formation command is input to the image forming apparatus 1, an image forming process is started by the image forming unit 10 based on image information input from an external computer connected to the image forming apparatus 1. In the image forming process, the photosensitive drum 21 is rotated at a process speed by the drive motor 110. The charging brush 22 and the charging roller 23 uniformly charge the surface of the photosensitive drum 21 in the charging unit. The exposure unit 11 irradiates the photosensitive drum 21 with a laser beam Lt based on the input image information, and forms an electrostatic latent image on the photosensitive drum 21. The developing roller 31 supplies toner to the photosensitive drum 21 in the developing unit, and develops the electrostatic latent image into a toner image.

[0039] In parallel with the image forming process, recording materials P stored in a storage section (feed cassette) provided at the bottom of the apparatus main body 1A are fed one sheet at a time by a feeding member such as a feeding roller. The conveyance of the recording material P is controlled so that the timing at which the recording material P enters the transfer section and the timing at which the toner image formed on the photosensitive drum 21 reaches the transfer section are synchronized. Due to an electric field formed in the transfer section by application of a transfer voltage to the transfer roller 12, the toner image is transferred from the photosensitive drum 21 to the recording material P while the recording material P passes through the transfer section.

[0040] The recording material P that has passed through the transfer section is transported to the fixing section 40, and the toner image is heated and pressurized when passing through a nip section between a fixing film 41 and a pressure roller 42 of the fixing section 40. This causes the toner particles to melt and then adhere, thereby fixing the toner image to the recording material P. The recording material P that has passed through the fixing section 40 is discharged outside the image forming apparatus 1 and stacked.

[0041] (4. Recovery of residual toner after transfer) In this embodiment, a so-called cleanerless configuration (simultaneous cleaning and development) is adopted in which residual toner remaining on the photosensitive drum 21 without being transferred to the recording material P is collected in the developing device 30 and reused for development. The residual toner is developer that remains on the surface of the photosensitive member even after passing through the transfer section. The residual toner is reused through the following process.

[0042] The residual toner includes a mixture of toner charged with a positive polarity, which is the opposite polarity to the normal polarity in this embodiment, and toner charged with a negative polarity but without sufficient charge. A charging voltage that is more negative than the surface of the photosensitive drum 21 is applied to the charging brush 22, which supplementarily charges the surface of the photosensitive drum 21. Hereinafter, the charging process of the photosensitive drum 21 by the charging brush 22 in this embodiment is referred to as supplementary charging.

[0043] Due to the auxiliary charging by the charging brush 22, negative charges are also injected into the transfer residual toner that is positively charged and toner that does not have a sufficient negative charge. As a result, while the transfer residual toner has a sufficient negative charge, the transfer residual toner passes through the contact portion between the charging brush 22 and the photosensitive drum 21 and the contact portion between the charging roller 23 and the photosensitive drum 21 as the photosensitive drum 21 rotates. During the passage, since the transfer residual toner has a sufficient negative charge, the transfer residual toner is unlikely to adhere to the charging brush 22 and the charging roller 23 to which a negative charging voltage is applied. As a result, the charging brush 22 and the charging roller 23 can maintain good charging performance for a long period of time.

[0044] The transfer residual toner adhering to the surface of the photosensitive drum 21 that has passed through the contact area with the charging brush 22 and the charging roller 23 reaches the developing section as the photosensitive drum 21 rotates. The behavior of the transfer residual toner that has reached the developing section will be explained separately for the exposed section and the non-exposed section of the photosensitive drum 21.

[0045] In the non-exposed portion of the photosensitive drum 21, that is, in the region where the drum surface potential is the dark potential Vd, the drum surface potential is negative with respect to the development voltage applied to the development roller 31. Therefore, the transfer residual toner having a sufficient negative charge moves from the photosensitive drum 21 to the development roller 31 by the Coulomb force generated by the electric field formed between the development roller 31 and the photosensitive drum 21, and is collected in the development container 32. The non-exposed portion of the photosensitive drum 21 is not limited to the region that is not irradiated with light at all, and may be the region that is irradiated with weak light as long as the drum surface potential is negative with respect to the development voltage. The toner collected in the development container 32 is agitated and dispersed with the toner previously contained in the development container 32 by the agitation member 34, and is carried by the development roller 31 for use again in the development process.

[0046] On the other hand, in the exposed portion of the photosensitive drum 21, that is, in the region where the drum surface potential is the light portion potential Vl, the drum surface potential becomes positive with respect to the developing voltage applied to the developing roller 31. Therefore, the transfer residual toner having a sufficient negative charge does not move to the developing roller 31 but remains on the photosensitive drum 21, and forms a toner image together with the toner that has moved from the developing roller 31 to the exposed portion. Then, the transfer residual toner in the exposed portion is transferred from the photosensitive drum 21 to the recording material P in the transfer portion as part of the toner image.

[0047] In this embodiment, the dark area potential Vd is −500 V, and the light area potential Vl is −50 V. As described above, since the development voltage is −300 V, the back contrast, which is the potential difference between the dark area potential Vd (the drum surface potential after charging by the charging roller 23) of the photosensitive drum 21 and the development voltage, is Δ200 V. In addition, the development contrast, which is the potential difference between the light area potential Vl of the photosensitive drum 21 and the development voltage, is Δ250 V.

[0048] (5. Charging Configuration) The charging brush 22 and the charging roller 23 in this embodiment will be described in detail.

[0049] As shown in FIG. 2, the charging brush 22 is disposed upstream of the transfer roller 12 and downstream of the charging roller 23 in the rotation direction R of the photosensitive drum 21.

[0050] The charging brush 22 is held by a brush holding sheet 22a. The brush holding sheet 22a is attached to a frame 22b of the process cartridge 20. In addition, a blow-out prevention sheet 22c is attached to the frame 22b. The charging brush 22, the brush holding sheet 22a, the frame 22b, and the blow-out prevention sheet 22c form one unit (charging brush unit) that acts on the photosensitive drum 21.

[0051] The brush holding sheet 22a is a flexible sheet member made of, for example, PET (polyethylene terephthalate). The brush holding sheet 22a is attached to the frame 22b with adhesive, double-sided tape, or the like. The charging brush 22 is fixed on the brush holding sheet 22a with, for example, double-sided tape. The charging brush 22 is brought into contact with the surface of the photosensitive drum 21 at a predetermined contact pressure by the bending of the brush holding sheet 22a. The brush holding sheet 22a in this embodiment is made of PET with a thickness of 50 μm, but other sheet members such as a stainless steel sheet (SUS thin plate) may also be used. It is preferable that the holding member for holding the charging brush 22 has appropriate flexibility and can bring the charging brush 22 into contact with the surface of the photosensitive drum 21 at an appropriate contact pressure by bending. The holding member for holding the charging brush 22 may be conductive.

[0052] The blowout prevention sheet 22c is, for example, a resin sheet having a thickness of 30 μm. The blowout prevention sheet 22c is attached to the frame body 22b with an adhesive or the like, and is in contact with the surface of the photosensitive drum 21 at a position different from the charging brush 22 in the rotation direction R of the photosensitive drum 21. The blowout prevention sheet 22c is in contact with the surface of the photosensitive drum 21 (belly contact) at a predetermined intrusion amount into the surface of the photosensitive drum 21 and in an area other than the tip of the blowout prevention sheet 22c. The intrusion amount is a size of the blowout prevention sheet 22c intruding into the inside of a virtual cylindrical surface corresponding to the surface of the photosensitive drum 21 when it is assumed that the photosensitive drum 21 does not exist.

[0053] When viewed in the direction of the rotation axis of the photosensitive drum 21, the charging brush 22, the brush holding sheet 22a, the frame 22b, and the blow-out prevention sheet 22c form a closed space below the charging brush 22 in the direction of gravity (downward in the figure). Foreign matter such as paper dust blocked by the charging brush 22 is contained in this closed space, thereby preventing the foreign matter from scattering inside the image forming apparatus 1. In other words, the brush holding sheet 22a, the frame 22b, and the blow-out prevention sheet 22c form a storage section that stores foreign matter collected from the photosensitive drum 21 by the charging brush 22, upstream of the charging brush 22 in the rotation direction R of the photosensitive drum 21. The storage section may be formed, for example, by only the frame 22b.

[0054] In this embodiment, the charging brush unit has a storage section for storing foreign objects, and the storage section is provided with the blow-out prevention sheet 22c. However, the storage section may not have the blow-out prevention sheet 22c, and the charging brush unit may not have a storage section. For example, as shown in FIG. 11, the space upstream of the charging brush 22 in the rotation direction R of the photosensitive drum 21 may be an open space. In the modified example of FIG. 11, the foreign object D that has reached the charging brush 22 is held by the charging brush 22 in a state where it is entangled by a part of the charging brush 22 (for example, a crimped brush part 22G made of crimped yarn 22g, which will be described later). In cases where the life of the process cartridge 20 is relatively short and the charging brush 22 can hold the foreign object D throughout its life, and in other cases where the foreign object D is unlikely to scatter, the charging brush unit may not have a storage section.

[0055] As shown in Fig. 3, the charged brush 22 includes a brush body 220 and a base metal plate 22d as a support for supporting the brush body 220. The brush body 220 includes a base cloth 22e and a large number of brush fibers (22f, 22g) implanted in the base cloth 22e. The base metal plate 22d is, for example, a stainless steel plate having a thickness of 1 mm. The base cloth 22e is a woven fabric including warp and weft threads, and is attached to the base metal plate 22d. In this embodiment, two types of pile yarns (22f, 22g) are used as the brush fibers. The pile yarns (22f, 22g) are woven into the base cloth 22e by pile weaving, and are raised in a direction perpendicular to the base cloth 22e.

[0056] Hereinafter, the direction perpendicular to the base fabric 22e and in which the pile yarns (22f, 22g) are raised is referred to as the Z direction or brush height direction. The direction perpendicular to the Z direction and in which the base fabric 22e extends in an elongated manner is referred to as the X direction or the longitudinal direction of the charging brush 22. The direction perpendicular to both the X direction and the Z direction is referred to as the Y direction or the transverse direction of the charging brush 22. The X direction (longitudinal direction) is substantially the same as the direction of the rotation axis of the photosensitive drum 21 when the charging brush 22 is attached to the image forming apparatus 1. The Y direction (transverse direction) is the direction along the movement direction of the surface of the photosensitive drum 21 at the contact portion between the charging brush 22 and the photosensitive drum 21, and is the direction facing downstream in the rotation direction R of the photosensitive drum 21. In the following description, the arrangement of elements based on the rotation direction R of the photosensitive drum 21 can be restated as based on the Y direction (transverse direction) of the charging brush 22.

[0057] The charged brush 22 of this embodiment includes two types of pile yarns as brush fibers (brush bristles): straight yarns 22f and crimped yarns 22g. In other words, the charged brush 22 has brush fibers that include a first type of fiber (crinkled yarns 22g) that has been subjected to a crimping process, and a second type of fiber (straight yarns 22f) that has not been subjected to a crimping process. In this embodiment, pile weaving is used as a method for implanting the brush fibers in the base fabric 22e, but other implantation methods, such as electrostatic implantation, may also be used.

[0058] The length of the charging brush 22 in the X direction (longitudinal direction) is, for example, 235 mm. The length of the charging brush 22 can be changed according to, for example, the longitudinal range (maximum paper passing area) through which a sheet S of the maximum width on which the image forming apparatus 1 can form an image passes. Because paper dust is mainly generated at the contact area between the photosensitive drum 21 and the recording material P, it is preferable that the length of the charging brush 22 is equal to or greater than the width of the maximum paper passing area.

[0059] The straight yarn 22f is a fiber having electrical conductivity. The straight yarn 22f is, for example, a pile yarn in which carbon, which is an electrically conductive particle, is dispersed in 6-nylon. The pile yarn may be made of synthetic resin such as polyester or acrylic, in addition to 6-nylon. The electrically conductive particles may be made of nickel, tin oxide, or the like, in addition to carbon.

[0060] The fiber diameter of the straight yarn 22f is preferably 5 μm to 80 μm, and more preferably 10 μm to 20 μm. In this embodiment, the fiber diameter of the straight yarn 22f is 15 μm, and the fineness is 2 denier. The fiber density of the straight yarn 22f is 50 to 400 KF (kilo filaments) / inch. 2 is preferable, and more preferably 100 to 300KF / inch 2 In this embodiment, the fiber density of the straight yarn 22f is 240 KF / inch 2 In the case of pile weaving, the fiber density of the brush fibers indicates the number of brush fibers planted per unit area of ​​the base fabric 22e at the base of the brush fiber stalks, and is different from the apparent fiber density at the contact portion between the charging brush 22 and the photosensitive drum 21.

[0061] In the above, the unit of fiber density of the brush fibers is KF / inch. 2 (number of fibers per square inch. 1KF is 1000 brush fibers) was used, but 1inch 2 is about 645mm 2 Therefore, 645KF / inch 2 =1KF / mm 2 The unit of fiber density can be converted as follows:

[0062] After the straight yarn 22f is woven into the base cloth 22e, it is subjected to processes such as raising and shearing, and then cut to a preset brush height. The brush height is preferably 3 mm to 9 mm, and more preferably 4 mm to 7 mm. In this embodiment, the brush height including the base metal plate 22d, the base cloth 22e, and the pile yarns (22f, 22g) is 6 mm. Since the thickness of the base metal plate 22d is 1 mm and the thickness of the base cloth 22e is 0.5 mm, the fiber length of the raised straight yarn 22f is about 4.5 mm.

[0063] The crimped yarn 22g may be the same as the straight yarn 22f in terms of pile yarn material, fiber diameter, fiber density, and brush height. The difference from the straight yarn 22f is that the pile yarn is made into a crimped yarn (false twisted yarn) by crimping the yarn after spinning. The straight yarn 22f is a fiber that is not crimped after spinning. The crimped yarn 22g is made by weaving the pile yarn after spinning into a base fabric, and then performing processes such as raising and shearing, and then cutting the crimped yarn 22g at a preset brush height. Therefore, the Z-direction end face of the charged brush 22 formed by the crimped yarn 22g and the Z-direction end face of the charged brush 22 formed by the straight yarn 22f are aligned in height in the Z direction.

[0064] The pile yarn can be crimped by a conventional method. For example, a method of applying strain to the yarn and heat setting it is common. The crimp strength of the crimped yarn 22g is preferably such that adjacent crimped yarns 22g are entangled with each other when woven into the base fabric 22e.

[0065] When it is unclear at a glance whether the brush fibers of the charged brush 22 are crimped yarns 22g or straight yarns 22f, they may be determined as follows. As shown in FIG. 12, the brush fibers of the charged brush 22 are cut from the root and collected, and each brush fiber is placed on a horizontal surface and observed from directly above (i.e., a vertical projection parallel to the light in the direction of gravity is observed). The straight line connecting the root and tip of the brush fiber is defined as line L, and the curve that follows the brush fiber from the root to the tip is defined as curve C. The length along curve C from one end point of curve C (the root of the brush fiber) to an arbitrary point p on curve C is defined as variable x, and the distance from point p to line L is defined as function f(x) of x. If the graph of y=f(x) has an inflection point, the brush fiber is determined to be crimped yarn 22g, and if not, the brush fiber is determined to be straight yarn 22f (non-crimped yarn). In FIG. 12, the brush fibers shown in the "actual object" and the brush fibers shown in the "schematic diagram (parallel projection)" to the right of it are not the same fibers.

[0066] In this embodiment, the crimped yarn 22g is woven into a first region A1 of the base fabric 22e in the Y direction (short side direction). The straight yarn 22f is woven into a second region A2 of the base fabric 22e in the Y direction (short side direction). The first region A1 has a width of 2 mm, and the second region A2 has a width of 3 mm. The second region A2 into which the straight yarn 22f is woven is provided downstream, in the rotation direction R of the photosensitive drum 21, of the first region A1 into which the crimped yarn 22g is woven.

[0067] The crimped yarns 22g woven into the first region A1 of the base fabric 22e form a crimped brush portion 22G as a first portion of the charged brush 22. The straight yarns 22f woven into the second region A2 of the base fabric 22e form a straight bristle brush portion 22F as a second portion of the charged brush 22 located downstream of the first portion in the moving direction of the surface of the photosensitive drum 21 at the contact portion between the charged brush 22 and the photosensitive drum 21. The first portion (crinkled brush portion 22G) of the charged brush 22 is an assembly of brush fibers supported in the first region A1 of the base fabric 22e. The second portion (straight bristle brush portion 22F) of the charged brush 22 is an assembly of brush fibers supported in the second region A2 of the base fabric 22e.

[0068] In the present embodiment, the charged brush 22 is integrated with the crimped brush portion 22G and the straight bristle brush portion 22F as a single brush member, but as in embodiments 2 and 3 described below, the crimped brush portion 22G and the straight bristle brush portion 22F may be disposed separately. The charged brush 22 may be a brush unit including two or more brushes that are independent of each other. In other words, the crimped brush portion 22G (first portion of the charged brush 22) may be a first brush, and the straight bristle brush portion 22F (second portion of the charged brush 22) may be a second brush that is disposed away from the crimped brush portion 22G on the downstream side in the rotation direction R of the photosensitive drum 21.

[0069] The ratio of the crimped yarns 22g (first type of fiber) in the brush fibers in the first portion of the charged brush 22 is at least higher than the ratio of the crimped yarns 22g in the brush fibers in the second portion of the charged brush 22. The "ratio" here refers to the ratio of the number of crimped yarns 22g included in the first portion or the second portion to the number of brush fibers constituting the first portion or the second portion (the total number of crimped yarns 22g and the number of straight yarns 22f). This makes it possible to achieve both uniform charging and suppression of charging failures caused by foreign matter, as described later. In this embodiment, the ratio of the crimped yarns 22g in the brush fibers in the first portion (crimped brush part 22G) of the charged brush 22 is 100%, and the ratio of the crimped yarns 22g in the brush fibers in the second portion (straight brush part 22F) of the charged brush 22 is 0%.

[0070] In this embodiment, the first area A1 and the second area A2 are arranged with a gap of 0.3 mm in the Y direction (short direction). This gap is set so that the crimped brush portion 22G made of the crimped yarn 22g woven in the first area A1 and the straight hair brush portion 22F made of the straight hair yarn 22f woven in the second area A2 come into contact with each other. That is, in the rotation direction R of the photosensitive drum 21, the downstream end of the crimped brush portion 22G and the upstream end of the straight hair brush portion 22F come into contact with each other. The gap between the first area A1 and the second area A2 may be 0.3 mm or less. In addition, when the degree of crimping of the crimped yarn 22g is high, the crimped brush portion 22G and the straight hair brush portion 22F can come into contact with each other even if the gap between the first area A1 and the second area A2 is greater than 0.3 mm.

[0071] By configuring the crimped brush portion 22G and the straight bristle brush portion 22F to come into contact with each other, as described below, the straight bristle brush portion 22F can support the crimped brush portion 22G from the downstream side in the rotation direction R of the photosensitive drum 21, thereby suppressing bristles from falling over of the crimped yarns 22g. In order to suppress bristles from falling over by contacting the crimped brush portion 22G with the straight bristle brush portion 22F, the distance between the first region A1 and the second region A2 is preferably 2 mm or less.

[0072] In this embodiment, two types of pile yarns (22f, 22g) are woven into a common base fabric 22e, but the two types of pile yarns (22f, 22g) may be woven into separate base fabrics, and the two base fabrics may be attached to a common base metal sheet 22d.

[0073] The straight yarn 22f and the crimped yarn 22g are electrically connected to the base metal plate 22d together with the base cloth 22e via a conductive paste (not shown). The base metal plate 22d is electrically connected to the brush power supply E4 so that a voltage can be applied from the brush power supply E4. In other words, the straight yarn 22f and the crimped yarn 22g are provided so that the voltage can be controlled by the brush power supply E4. In other words, the control unit 150 can control the voltage applied to the brush fibers of the charging brush 22.

[0074] The resistance value of the charged brush 22 is measured by pressing a stainless steel sheet metal vertically from above the charged brush 22 (Z direction) to a penetration depth of 1 mm, and applying a voltage between the base sheet metal 22d. The penetration depth is the difference between the bristle height of the brush fibers before the stainless steel sheet metal comes into contact and the bristle height of the brush fibers when the stainless steel sheet metal is pressed against it. The applied voltage is +250V, and the resistance value 5 seconds after the voltage is applied is taken as the brush resistance. A HIOKI ST5520 was used to measure the resistance.

[0075] In this embodiment, the brush resistance is 1.0×10 4 Ω~1.0×10 6 The brush resistance is in the range of Ω. The brush resistance can be controlled to a desired value by changing the material of the conductive particles dispersed in the conductive pile yarn or the content of the conductive particles in the raw resin of the pile yarn.

[0076] If the brush resistance is too large, it becomes difficult for current to flow through the brush fibers, and there is a possibility that the surface of the photosensitive drum 21 cannot be appropriately charged. Also, if the brush resistance is too small, a large current flows locally from the charging brush 22 to the photosensitive drum 21, and a phenomenon (so-called pinhole leak) in which the photosensitive layer of the photosensitive drum 21 is broken down is likely to occur. In view of the above, the brush resistance is set to 1.0×102 Ω~1.0×10 8 It is preferable to set the range to 1.0×10 4 Ω~1.0×10 6 More preferably, it is in the range of Ω.

[0077] The brush fibers (22f, 22g) of the charging brush 22 contact the photosensitive drum 21 at a predetermined contact pressure due to the elasticity of the brush holding sheet 22a, which is a flexible sheet member. In this embodiment, the charging brush 22 has a length of 235 mm in the longitudinal direction and a width of approximately 5 mm in the lateral direction. The charging brush 22 contacts the photosensitive drum 21 with a total pressure of 60 gf.

[0078] If the contact pressure of the brush is too high, the charging brush 22 may scratch the photosensitive drum 21.

[0079] In addition, this embodiment employs a cleanerless configuration that does not include a cleaning member for removing residual toner after transfer. In the cleanerless configuration, if the contact pressure between the charging brush 22 and the photosensitive drum 21 is high, the residual toner after transfer is blocked by the charging brush 22, which may cause contamination of the brush and a decrease in charging performance.

[0080] Furthermore, if the contact pressure of the charging brush 22 is too low, the charging brush 22 may not contact the surface of the photosensitive drum 21 with a uniform contact pressure, or the brush may tilt or move due to the rotation of the photosensitive drum 21.

[0081] In view of the above, it is desirable that the contact pressure (total pressure, total load) of the charging brush 22 with respect to the photosensitive drum 21 be in the range of 40 gf to 200 gf.

[0082] Incidentally, instead of the configuration in which the charging brush 22 is brought into contact with the photosensitive drum 21 by the elasticity of the brush holding sheet 22a, both longitudinal ends of the support of the charging brush 22 may be urged by urging means such as a spring or rubber. In other words, the brush fibers of the charging brush 22 may be brought into contact with the surface of the photosensitive drum 21 by the urging force of the urging means that urges the support.

[0083] Also, a configuration in which the support of the charging brush 22 is fixed to the frame body 22b and brought into contact with the photosensitive drum 21 with a predetermined penetration amount may be used. In other words, the image forming apparatus 1 may include a support that supports the charging brush 22 and whose position relative to the rotation axis of the photosensitive drum 21 is fixed. In this case, the distance between the support and the surface of the photosensitive drum 21 is made shorter than the dimension of the charging brush 22 in the bristle height direction (Z direction) of the brush fibers before the charging brush 22 is attached to the support. This allows the brush fibers of the charging brush 22 to contact the photosensitive drum 21 with a predetermined penetration amount.

[0084] The charging brush 22 is preferably arranged so that the center of the charging brush 22 in the Y direction (short direction) is located between 30° and 150° in the rotation direction R of the photosensitive drum 21 (clockwise in FIG. 1), with the downward direction of the photosensitive drum 21 in the gravity direction (downward direction in FIG. 1) being 0°. In this embodiment, the charging brush 22 is arranged at a position where the angle θ (FIG. 1) is 100°. Also, as shown in FIG. 1, the charging brush 22 is arranged so that a vertical line 22h that passes through the center of the charging brush 22 and is perpendicular to the base fabric 22e passes through the rotation axis A21 of the photosensitive drum 21. In other words, when viewed in the direction of the rotation axis of the photosensitive drum 21, the center position of the contact portion between the charging brush 22 and the photosensitive drum 21 in the rotation direction of the photosensitive drum 21 is preferably located within a range of 30° to 150° in terms of the angle θ measured in the rotation direction of the photosensitive drum 21 based on a half line drawn from the rotation axis in the gravity direction.

[0085] Incidentally, the charging brush 22 may be disposed such that the base fabric 22e is inclined with respect to the surface of the photosensitive drum 21. In other words, when viewed in the direction of the rotation axis A21 of the photosensitive drum 21, the charging brush 22 may be disposed such that the short side direction (Y direction) of the charging brush 22 obliquely intersects with the tangent direction of the photosensitive drum 21 at the contact portion between the charging brush 22 and the photosensitive drum 21. The inclination direction may be a direction in which the base fabric 22e approaches the surface of the photosensitive drum 21 the further upstream in the rotation direction R of the photosensitive drum 21.

[0086] The charging brush 22 charges the surface of the photosensitive drum 21 that has passed through the transfer section (the surface of the photosensitive drum 21 after the transfer process). On the surface of the photosensitive drum after the transfer process, a relatively large potential unevenness (unevenness in the drum surface potential) occurs due to discharge of the transfer roller 12. In this embodiment, a transfer voltage of +1000V is applied to the transfer roller 12.

[0087] On the surface of the photosensitive drum 21, the area where a toner image was formed before the transfer process (exposed area before the development process) is the printed area, and the area where a toner image was not formed before the transfer process (unexposed area before the development process) is the non-printed area. The drum surface potential of the non-printed area before the transfer process is a dark area potential Vd (-500V in this embodiment), and the drum surface potential of the printed area is a light area potential Vl (-50V in this embodiment). Due to the transfer process, the drum surface potential of the non-printed area changes from -500V to -250V, and the drum surface potential of the printed area changes from -50V to +50V.

[0088] It should be noted that the drum surface potential after the above-mentioned transfer process is merely an average value, and there are some localized locations where the potential is significantly different from the average value.

[0089] The charging brush 22 charges the surface of the photosensitive drum 21 after the transfer process, and also equalizes the drum surface potential after the transfer process (reducing potential unevenness). In this embodiment, a charging voltage of -500V is applied to the charging brush 22. In this embodiment, after charging by the charging brush 22, the drum surface potential is further raised uniformly to the dark potential Vd by the discharge of the charging roller 23. In this embodiment, a charging voltage of -1000V is applied to the charging roller 23.

[0090] In the cleaner-less configuration employed in this embodiment, at least a portion of the transfer residual toner reaches the contact portion between the charging brush 22 and the photosensitive drum 21 and the contact portion between the charging roller 23 and the photosensitive drum 21 .

[0091] The transfer residual toner includes not only toner of the original negative polarity, but also toner that has been charged to the opposite polarity, positive polarity, by the transfer process, and toner that has almost no charge. Because a voltage that is more negative than the photosensitive drum 21 is applied to the charging brush 22, the transfer residual toner is recharged to negative polarity by the charging brush 22 when passing through the contact portion between the charging brush 22 and the photosensitive drum 21. Because a voltage that is more negative than the photosensitive drum 21 is also applied to the charging roller 23, the transfer residual toner that has been charged to negative polarity reaches the contact portion of the developing unit as the photosensitive drum 21 rotates without adhering to the charging roller 23, and is collected in the developing container 32.

[0092] The charging roller 23 is in contact with the photosensitive drum 21 with a predetermined pressure force. In this embodiment, the charging roller 23 is in contact with the photosensitive drum 21 with a load of 500 gf.

[0093] The charging roller 23 of this embodiment has a multi-layer structure in which a stainless steel core having a diameter of 6 mm is used as a support, and the periphery of the core is covered with multiple flexible resin layers. In this embodiment, the multiple resin layers are a two-layer structure including a base layer which is a first resin layer covering the core, and a surface layer which is a second resin layer covering the base layer. The resin material of the base layer is conductive hydrin rubber in which conductive carbon is dispersed. The base layer of conductive hydrin rubber is formed on the core by extrusion molding, and has a film thickness of about 2 mm. In this embodiment, conductive hydrin rubber is used as the base layer, but it is not limited to this as long as it is a flexible and conductive resin material.

[0094] As shown in FIG. 5(a), the photosensitive drum 21 in this embodiment has a conductive support 21a made of an aluminum cylinder, a conductive layer 21b, an undercoat layer 21c, and a photosensitive layer consisting of two layers, a charge generating layer 21d and a charge transport layer 21e.

[0095] In order to suppress scraping of the surface of the photosensitive drum 21 and to adjust the friction coefficient, the photosensitive drum 21 may be provided with an additional layer (surface layer, release layer) coated on the charge transport layer 21e.

[0096] Furthermore, as shown in FIG. 5(b), a charge injection layer 21f may be provided on the charge transport layer 21e in order to reduce the resistance value of the surface of the photosensitive drum 21 to a predetermined value.

[0097] The charging brush 22 can easily secure a large contact area with the photosensitive drum 21 and has excellent charge injection performance, so by combining it with the photosensitive drum 21 provided with the charge injection layer 21f, the charging performance can be further improved.

[0098] As described in the above-mentioned Patent Document 1, the charge injection layer 21f contains an appropriate amount of conductive particles 21g, so that the resistance value can be adjusted. From the viewpoint of the electrostatic latent image maintenance performance and the charging performance of the charge injection layer 21f, the volume resistance value of the charge injection layer 21f is set to 1.0×10 11 Ω cm or more 1.0×10 14 It is desirable to keep it at Ω·cm or less.

[0099] As described above, in this embodiment, a two-stage charging process is performed in which auxiliary charging is performed by the charging brush 22, and then recharging is performed by the charging roller 23. However, the surface of the photosensitive drum 21 may be uniformly charged to a desired drum surface potential (a potential at which an appropriate toner image can be created by the exposure process and development process) by charging only by the charging brush 22.

[0100] (6. Electrostatic obstruction due to foreign matter) When foreign matter such as paper powder passes through the contact area between the charging brush 22 and the photosensitive drum 21, and the contact area between the charging roller 23 and the photosensitive drum 21, the foreign matter may hinder charging of the surface of the photosensitive drum 21 by the charging brush 22 and the charging roller 23, resulting in localized charging defects. In particular, when the size of the foreign matter is relatively large, image defects due to charging defects caused by the foreign matter may become apparent in the image (referred to as a printed image) formed on the recording material P in the subsequent image forming process.

[0101] While image defects caused by foreign matter can occur even in image forming devices equipped with a cleaning member that collects residual toner after transfer, the problem is more pronounced in a cleanerless configuration such as that of this embodiment, as will be explained below.

[0102] First, in the cleaner-less configuration, the transfer residual toner is transported to the developing unit. When the transfer residual toner passes through the contact portion between the charging brush 22 and the photosensitive drum 21 and the contact portion between the charging roller 23 and the photosensitive drum 21, the transfer residual toner itself may hinder the charging of the photosensitive drum 21 by the charging brush 22 and the charging roller 23, which may cause localized charging defects. However, since the particle size of the transfer residual toner is small (7 μm in this embodiment), there is a low possibility that a visually noticeable image defect will occur in the printed image on the recording material P, and this does not pose a problem in practical use.

[0103] According to the inventor's study, in the configuration of this embodiment, if the size of the area where charging failure occurs on the surface of the photosensitive drum 21 is approximately 0.3 mm in diameter or less, no image failure easily visible to a general user occurs in the printed image on the recording material P. In addition, in order to reduce the possibility of an image failure that is visible to a general user being visualized, it is desirable that the area where charging failure occurs is 0.1 mm in diameter or less. Therefore, in this embodiment, there is no practical problem with the transfer residual toner passing through the charging brush 22.

[0104] However, in the cleanerless configuration, in addition to the residual toner after transfer, foreign matter from outside the image forming apparatus 1 may enter the contact portion between the charging brush 22 and the photosensitive drum 21 and the contact portion between the charging roller 23 and the photosensitive drum 21. Examples of foreign matter include paper dust generated from the paper used as the recording material P and dust and other particles contained in the air taken into the image forming apparatus 1 from the outside. Foreign matter may be transported together with the recording material P and adhere to the photosensitive drum 21 at the transfer portion, or foreign matter floating in the air may adhere to the photosensitive drum 21.

[0105] These foreign objects may be 0.1 mm to several mm in size. Hereinafter, foreign objects with a major axis diameter of 0.1 mm or more will be referred to as "large-sized foreign objects." If a large-sized foreign object adheres to the photosensitive drum 21 and passes through the contact portion between the charging brush 22 and the photosensitive drum 21, and the contact portion between the charging roller 23 and the photosensitive drum 21, a charging failure will occur in an area on the surface of the photosensitive drum 21 according to the size of the foreign object. In other words, the area where charging failure occurs due to a large-sized foreign object may have a diameter of 0.1 mm or more.

[0106] When charging failure occurs in an area with a diameter of approximately 0.1 mm or more, there is a possibility that image failure visible to a general user will occur in the print image formed on the recording material P in the subsequent image forming process. Examples of image failures include black dots in an area that is originally white (solid white area) and roughness in halftone images.

[0107] Here, the charging brush 22 of this embodiment has a crimped brush portion 22G formed of crimped yarns 22g in a first area A1, which is an area on the upstream side in the rotation direction R of the photosensitive drum 21 (FIG. 3). The charging brush 22 can entangle and collect foreign matter such as paper powder adhering to the photosensitive drum 21 with the crimped yarns 22g.

[0108] That is, the crimped yarn 22g is a brush fiber that has been shrunk by the crimping process, so the apparent density of the brush fibers in the crimped brush portion 22G is high. In the crimped yarn 22g used in this embodiment, pile yarns of about twice the length are used to achieve the same brush height compared to the straight hair yarn 22f woven at the same number density. In other words, the pile yarns are shrunk by the crimping process, so that the brush fibers are present at a spatial density about twice as large in the crimped brush portion 22G as compared to the straight hair brush portion 22F. The spatial density is the ratio of the volume that the brush fibers occupy to the rectangular parallelepiped space defined by the longitudinal and lateral lengths of the charged brush 22 and the bristle height of the brush fibers relative to the base fabric 22e.

[0109] In addition, the crimping process causes no regularity in the crimping, and the crimped yarns 22g are raised in random directions, so that the crimped yarns 22g are entangled with each other at a high density.

[0110] Therefore, large foreign matter that reaches the contact portion between the charging brush 22 and the photosensitive drum 21 cannot pass through the crimped yarns 22g (crinkled brush portion 22G) that are entangled at a high density, and is entangled by the crimped yarns 22g (crinkled brush portion 22G). As a result, it is possible to prevent large foreign matter from entering the contact portion between the photosensitive drum 21 and the straight bristle brush portion 22F downstream of the crimped brush portion 22G.

[0111] When the large foreign matter entangled in the crimped brush portion 22G becomes a certain amount of mass, it breaks down and falls in the direction of gravity due to vibrations of the image forming apparatus 1 during image formation or when the feed cassette is attached, and is stored in the closed space described above. In this embodiment, the foreign matter that has fallen from the charging brush 22 is stored in the closed space throughout the life of the process cartridge 20.

[0112] In this embodiment, the fiber diameter of the crimped yarn 22g is 15 μm. Therefore, foreign matter or transfer residual toner smaller than 15 μm in size passes through the charging brush 22 without being entangled at the contact portion between the crimped brush portion 22G and the photosensitive drum 21. However, as described above, even if charging failure occurs due to foreign matter or transfer residual toner of this size, there is a low possibility that a print image on the recording material P will have a level of image failure that is visible to a general user, so there is no practical problem. Note that foreign matter or transfer residual toner smaller than 15 μm in size has a large electrostatic adhesion force and non-electrostatic adhesion force with the photosensitive drum 21, so it can pass through the contact portion between the charging brush 22 and the photosensitive drum 21 without being scraped off by the contact pressure of the charging brush 22 in this embodiment.

[0113] Incidentally, the crimped yarn 22g is a brush fiber that has been subjected to a crimping process to give it irregular curls, and therefore, compared to the straight yarn 22f that is raised perpendicularly to the base fabric 22e, the brush fiber is weak (has low bending rigidity) and tends to collapse easily. Therefore, compared to the straight yarn 22f, the crimped yarn 22g is more likely to collapse downstream in the rotation direction R of the photosensitive drum 21 by being dragged by the surface of the rotating photosensitive drum 21 or pushed by a foreign object conveyed by the photosensitive drum 21. Hereinafter, the collapse of the brush fiber downstream in the rotation direction R of the photosensitive drum 21 is referred to as "hair collapse." When the crimped yarn 22g collapses, there is a possibility that a foreign object once entangled in the crimped yarn 22g is spit out onto the photosensitive drum 21, or that the crimped yarn 22g is unable to entangle a foreign object that newly enters the charging brush 22.

[0114] In this embodiment, the crimped brush portion 22G and the straight hair brush portion 22F are arranged so that the straight hair brush portion 22F formed from the straight hair yarn 22f contacts the crimped brush portion 22G formed from the crimped yarn 22g from the downstream side in the rotation direction R of the photosensitive drum 21. The straight hair yarn 22f is raised perpendicularly to the base fabric 22e, and is stiffer (has higher bending rigidity) than the crimped yarn 22g that has been subjected to a crimping process.

[0115] Therefore, the crimped yarns 22g of the crimped brush portion 22G are supported by the straight hair yarns 22f of the straight hair brush portion 22F, so that the crimped yarns 22g can be prevented from falling down.

[0116] Incidentally, as shown in Fig. 3, the fibers of the crimped yarn 22g are irregularly crimped by the crimping process, so that the tip positions (hair heights) of the brush fibers in the Z direction tend to be non-uniform. Therefore, it is difficult to bring the tips of the crimped yarns 22g of the crimped brush portion 22G into contact with the surface of the photosensitive drum 21 with uniform contact pressure. In charging with the charging brush 22, it is desirable to bring the charging brush 22 into uniform contact with the photosensitive drum 21 with as small a pressure as possible in order to obtain good charging performance. However, if the tips of the brush fibers do not come into contact with the surface of the photosensitive drum 21 with uniform contact pressure, it is difficult to uniformly charge the surface of the photosensitive drum 21 via the brush fibers.

[0117] If the surface of the photosensitive drum 21 is not uniformly charged by the charging brush 22, there is a possibility that potential unevenness will remain in the drum surface potential after charging by the charging roller 23. Specifically, if the brush fibers of the charging brush 22 are not in contact with the surface of the photosensitive drum 21 partially due to the position in the longitudinal direction of the charging brush 22, stripe-like potential unevenness extending in the sub-scanning direction of the photosensitive drum 21 may occur. If the potential unevenness after charging by the charging brush 22 is large, the potential unevenness will remain even after charging by the charging roller 23, and the non-uniformity of charging by the charging brush 22 may become apparent as stripe-like density unevenness in the printed image.

[0118] In contrast, the straight hair yarns 22f that have not been subjected to crimping can easily align the tip positions (hair height) of the brush fibers in the Z direction. Therefore, it is possible to bring the tips of the straight hair yarns 22f of the straight hair brush portion 22F into contact with the surface of the photosensitive drum 21 with uniform contact pressure. In this way, when the tips of the brush fibers come into contact with the surface of the photosensitive drum 21 with uniform contact pressure, the surface of the photosensitive drum 21 can be uniformly charged via the brush fibers.

[0119] As described above, in this embodiment, the crimped brush portion 22G formed from the crimped yarn 22g is positioned upstream in the rotation direction R of the photosensitive drum 21, and the straight hair brush portion 22F formed from the straight hair yarn 22f is positioned downstream in the rotation direction R of the photosensitive drum 21.

[0120] This makes it possible to trap large foreign matter in the upstream crimped brush portion 22G and prevent the large foreign matter from entering the contact portion between the downstream straight bristle brush portion 22F and the photosensitive drum 21. This makes it possible to reduce the occurrence of image defects caused by large foreign matter.

[0121] In addition, by charging the surface of the photosensitive drum 21 with the straight bristle brush portion 22F having uniform bristle height, the surface of the photosensitive drum 21 can be charged more uniformly.

[0122] Furthermore, in this embodiment, the upstream crimped brush portion 22G and the downstream straight brush portion 22F are arranged so as to come into contact with each other. This allows the crimped yarns 22g of the crimped brush portion 22G to be supported by the straight yarns 22f of the straight brush portion 22F, and prevents the crimped yarns 22g from falling downstream in the rotation direction R of the photosensitive drum 21. In other words, the functions of the crimped brush portion 22G and the straight brush portion 22F can be maintained for a longer period of time. In addition, as described in the third embodiment below, the space required for arranging the charging brush 22 is smaller than when the width of the crimped brush portion 22G in the short side direction is increased to reduce the effect of bristles falling, which is advantageous for miniaturizing the image forming apparatus 1.

[0123] The crimped yarn 22g may fall over when the charging brush 22 is assembled to the process cartridge 20. In this embodiment, the upstream crimped brush portion 22G and the downstream straight brush portion 22F are arranged to be in contact with each other, so that the crimped yarn 22g may not fall over when assembled.

[0124] In addition, both the crimped brush portion 22G and the straight bristle brush portion 22F are configured to allow the transfer residual toner to pass through. Specifically, the density of the crimped yarns 22g and the straight bristle brush portion 22F in the crimped brush portion 22G and the straight bristle brush portion 22F, the contact pressure with the photosensitive drum 21, the fiber diameter of the crimped yarns 22g and the straight bristle brush portion 22F, etc. are set so as to allow the transfer residual toner to pass through. Therefore, the transfer residual toner can be efficiently collected in the developing portion.

[0125] (7. Charging Performance of Examples and Comparative Examples) The results of an experiment comparing the charging performance, etc., of the charging brush 22 according to the embodiment and the charging brush 22 according to the comparative example will be described.

[0126] Example 1 6(a) to (c) are explanatory diagrams of the charging brush 22 of Example 1. Fig. 6(a) is a cross-sectional view showing a cross section along the Y direction (short side direction) of the charging brush 22. Fig. 6(b) is a schematic diagram showing a state in which the charging brush unit is assembled to the photosensitive drum 21. Fig. 6(c) is a schematic diagram showing the charging brush unit after a paper passing operation.

[0127] Example 2 7(a) to (c) are explanatory diagrams of the charging brush 22 of Example 2. Fig. 7(a) is a cross-sectional view showing a cross section along the Y direction (short side direction) of the charging brush 22. Fig. 7(b) is a schematic diagram showing a state in which the charging brush unit is assembled to the photosensitive drum 21. Fig. 7(c) is a schematic diagram showing the charging brush unit after a paper passing operation.

[0128] 7(a) and (b), in the charged brush 22 of Example 2, the first region A1 in which the crimped yarns 22g are woven and the second region A2 in which the straight yarns 22f are woven are separated from each other in the base fabric 22e, and the crimped brush portion 22G and the straight brush portion 22F are not in contact with each other. The other configurations of the charged brush 22 of Example 2 are the same as those of the charged brush 22 of Example 1.

[0129] Comparative Example 1 Figures 8(a) to (c) are explanatory diagrams of the charging brush 22 of Comparative Example 1. Figure 8(a) is a cross-sectional view showing a cross section along the Y direction (short side direction) of the charging brush 22. Figure 8(b) is a schematic diagram showing a state in which the charging brush unit is assembled to the photosensitive drum 21. Figure 8(c) is a schematic diagram showing the charging brush unit after a paper passing operation.

[0130] 8(a) and 8(b), the charged brush 22 of Comparative Example 1 includes only crimped yarns 22g as brush fibers, and does not include straight yarns 22f. The rest of the configuration of the charged brush 22 of Comparative Example 1 is similar to that of the charged brush 22 of Example 1.

[0131] Comparative Example 2 9(a) to (c) are explanatory diagrams of the charging brush 22 of Comparative Example 2. Fig. 9(a) is a cross-sectional view showing a cross section along the Y direction (short side direction) of the charging brush 22. Fig. 9(b) is a schematic diagram showing a state in which the charging brush unit is assembled to the photosensitive drum 21. Fig. 9(c) is a schematic diagram showing the charging brush unit after a paper passing operation.

[0132] 9(a) and 9(b), the charged brush 22 of Comparative Example 2 includes only straight yarns 22f as brush fibers, and does not include crimped yarns 22g. The rest of the configuration of the charged brush 22 of Comparative Example 2 is similar to that of the charged brush 22 of Example 1.

[0133] Example 3 Figures 10(a) to (c) are explanatory diagrams of the charging brush 22 of Example 3. Figure 10(a) is a cross-sectional view showing a cross section along the Y direction (short direction) of the charging brush 22. Figure 10(b) is a schematic diagram showing a state in which the charging brush unit is assembled to the photosensitive drum 21. Figure 10(c) is a schematic diagram showing the charging brush unit after a paper passing operation.

[0134] 10(a) and 10(b), the charged brush 22 of Example 3 is configured such that the width of the crimped brush portion 22G in the Y direction (short direction) is longer than that of Example 2. That is, in the charged brush 22 of Example 3, the first region A1 in which the crimped yarns 22g are woven and the second region A2 in which the straight yarns 22f are woven are separated from each other in the base fabric 22e, and the crimped brush portion 22G and the straight hair brush portion 22F are not in contact with each other. The other configurations of the charged brush 22 of Example 3 are the same as those of the charged brush 22 of Example 1.

[0135] The width of crimped brush part 22G in the Y direction (short side direction) is, for example, 5 mm, and the width of straight bristle brush part 22F in the Y direction (short side direction) is, for example, 3 mm. In Example 3, the width of crimped brush part 22G is wider than the width of straight bristle brush part 22F. In order to more reliably suppress bristles from falling over in crimped brush part 22G, it is preferable that the width of crimped brush part 22G in the Y direction (short side direction) is 5 mm or more.

[0136] Evaluation method and results Table 1 shows the results of evaluation of the configurations of Examples 1 to 3 and Comparative Examples 1 and 2 with respect to initial charging performance, performance in suppressing the effect of foreign matter on charging, and space saving.

[0137] The initial charging performance was evaluated as follows: the surface potential of the photosensitive drum 21 was measured after it had passed the charging brush 22 and before it reached the charging roller 23. If a potential difference (potential unevenness) of a predetermined threshold or more was not observed in the measurement results with respect to the target potential of charging by the charging brush 22, the initial charging performance was judged to be good (◯), and if such a potential difference was observed, the initial charging performance was judged to be poor (×).

[0138] The influence of foreign matter on charging was evaluated as follows. A paper feed operation was performed on the image forming apparatus 1 equipped with the charging brush 22 of the embodiment or the comparative example to output a predetermined test image. The test image is a horizontal line pattern in which thin lines are arranged at regular intervals in the sheet width direction (main scanning direction of the photosensitive drum 21) with a print rate of 2% (coverage rate of the image with respect to the effective printing area on the recording material P). In addition, a paper feed operation was continuously performed on a number of recording materials P (200 sheets in this example) that were such that foreign matter such as paper powder began to accumulate at the contact portion between the charging brush 22 and the photosensitive drum 21. If no black dot images with a diameter of 0.3 mm or more were observed on the output recording material P during the continuous paper feed operation, the performance of suppressing the influence of foreign matter on charging was judged to be good (◎). If black dot images were observed but were of no practical problem, the performance was judged to be acceptable (○), and if black dot images of practical concern were observed, the performance of suppressing the influence of foreign matter on charging was judged to be poor (×).

[0139] The space saving was evaluated relatively based on the differences in the configuration of the charging brush 22 itself and the charging brush unit.

[0140] [Table 1]

[0141] 6(c), in Example 1, in the straight hair brush portion 22F located downstream of the crimped brush portion 22G in the rotation direction R of the photosensitive drum 21, the tip of the straight hair yarn 22f contacts the surface of the photosensitive drum 21 with a uniform contact pressure. Therefore, the charging brush 22 of Example 1 can uniformly charge the surface of the photosensitive drum 21. Therefore, the initial charging performance of the charging brush 22 of Example 1 was good.

[0142] Large-sized foreign matter D such as paper powder is entangled by the crimped yarn 22g (crinkled brush portion 22G), and the foreign matter D is prevented from entering the contact portion between the straight yarn 22f (straight bristle brush portion 22F) and the photosensitive drum 21 or the contact portion between the charging roller 23 and the photosensitive drum 21. When the foreign matter D becomes a certain amount of mass, it breaks down due to vibration of the device, etc., as described above, and falls in the direction of gravity, and is accumulated in the closed space within the charging brush unit. Therefore, the deterioration of charging performance due to the foreign matter D entering the contact portion between the straight bristle brush portion 22F and the photosensitive drum 21 or the contact portion between the charging roller 23 and the photosensitive drum 21 is suppressed. In other words, the charging brush 22 of Example 1 had good performance in suppressing the influence of foreign matter on charging.

[0143] 7B, in the initial state, the surface of the photosensitive drum 21 can be uniformly charged by the straight bristle brush portion 22F. Therefore, the initial charging performance of the charging brush 22 in Example 2 was good.

[0144] In addition, in Example 2, large-sized foreign matter D such as paper powder can be entangled by the crimped yarn 22g (crinkled brush portion 22G). Therefore, the charging brush 22 of Example 2 was able to suppress the effect of the charging of foreign matter to a level that does not pose a practical problem.

[0145] However, in Example 2, since the crimped brush portion 22G and the straight bristle brush portion 22F are separated, the bristles of the crimped yarn 22g may fall down during the paper passing operation. As a result, as shown in Fig. 7(c), a large-sized foreign object D may enter the contact portion between the straight bristle brush portion 22F and the photosensitive drum 21 or the contact portion between the charging roller 23 and the photosensitive drum 21, causing charging failure due to the foreign object D. For this reason, the charging brush 22 of Example 1 was able to more stably suppress the influence of the foreign object on the charging compared to the charging brush 22 of Example 2.

[0146] In Comparative Example 1, as shown in Fig. 8(a), the entire charged brush 22 is formed of crimped yarn 22g, and the width of the crimped brush portion 22G in the Y direction (short direction) is wider than that of Example 2. For this reason, as shown in Fig. 8(c), the crimped yarn 22g is less likely to collapse, and the performance of capturing foreign matter D is less likely to decrease. For this reason, the charged brush 22 of Comparative Example 1 had good performance in suppressing the effect of foreign matter on charging.

[0147] However, in Comparative Example 1, since the entire charging brush 22 is formed of crimped yarn 22g, it is difficult to align the height of the end faces of the tips of the brush fibers as shown in Fig. 8(a). Therefore, in the initial state shown in Fig. 8(b), the tips of the crimped yarn 22g do not contact the surface of the photosensitive drum 21 with uniform contact pressure, making it difficult for the charging brush 22 to uniformly charge the surface of the photosensitive drum 21. For this reason, the initial charging performance of the charging brush 22 in Comparative Example 1 was inferior to that of Example 1.

[0148] In Comparative Example 2, as shown in Fig. 9(a), the entire charging brush 22 is made of straight hair yarn 22f, and the height of the end face of the tip of the brush fiber is uniform. As shown in Fig. 9(b), in Comparative Example 2, in the initial state, the surface of the photosensitive drum 21 can be uniformly charged by the straight hair brush portion 22F. Therefore, the initial charging performance of the charging brush 22 in Comparative Example 2 was good.

[0149] However, in Comparative Example 2, since the entire charging brush 22 is formed of straight hair yarns 22f, it is difficult to capture large-sized foreign matter D, as shown in Fig. 9(c). As a result, large-sized foreign matter D enters the contact portion between the straight hair brush portion 22F and the photosensitive drum 21 or the contact portion between the charging roller 23 and the photosensitive drum 21, causing charging failure due to the foreign matter D. For this reason, the charging brush 22 in Comparative Example 2 was inferior to Example 1 in terms of performance in suppressing the effect of foreign matter on charging.

[0150] In Example 3, as shown in Fig. 10(a), the crimped brush portion 22G and the straight brush portion 22F are separated from each other, but the width of the crimped brush portion 22G in the Y direction (short direction) is wider than that of Example 2. For this reason, as in Comparative Example 1, the crimped yarn 22g is less likely to collapse as shown in Fig. 10(c), and the performance of capturing foreign matter D is less likely to decrease. For this reason, the charged brush 22 of Example 3 had good performance in suppressing the effect of foreign matter on charging.

[0151] 10B, in the initial state, the surface of the photosensitive drum 21 can be uniformly charged by the straight bristle brush portion 22F. Therefore, the initial charging performance of the charging brush 22 in Example 2 was good.

[0152] However, in Example 3, the crimped brush portion 22G and the straight brush portion 22F are disposed apart from each other, and the width of the crimped brush portion 22G in the Y direction (short side direction) is larger than that in Example 2. For this reason, in Example 3, the size of the charged brush 22 itself is larger than that in Examples 1 and 2 and Comparative Examples 1 and 2.

[0153] In contrast, in the charged brush 22 of Example 1, the crimped brush portion 22G and the straight bristle brush portion 22F are arranged so as to be in contact with each other, and the width of the crimped brush portion 22G in the Y direction (short side direction) is smaller than that of Example 3. In Example 1, the straight bristle brush portion 22F supports the crimped brush portion 22G, so that bristles are less likely to fall over even if the width of the crimped brush portion 22G is short. Therefore, the charged brush 22 of Example 1 is excellent in terms of space saving.

[0154] If the charging brush 22 itself is small as in the first embodiment, the charging brush 22 and the charging brush unit can be made smaller, which makes it possible to reduce material costs, etc. Also, if the charging brush 22 itself is small, the volume of the closed space (storage section for storing foreign matter) below the charging brush 22 can be increased, which is advantageous in extending the life of the process cartridge 20 because it increases the amount of foreign matter D that can be stored. Also, since the external shape of the closed space (storage section) can be small, this is also advantageous in terms of making the process cartridge 20 and image forming apparatus 1 smaller.

[0155] As described above, by using the charging brush 22 exemplified in the first to third embodiments, it is possible to provide an image forming apparatus capable of improving the uniformity of charging while suppressing charging defects caused by foreign matter.

[0156] Furthermore, by using the configuration of the charging brush 22 exemplified in Examples 1 to 3, it is possible to provide a charging brush for use in an image forming apparatus that can simultaneously improve the uniformity of charging and suppress poor charging caused by foreign matter.

[0157] Furthermore, by using a cartridge (process cartridge or drum cartridge) equipped with the charging brush 22 exemplified in Examples 1 to 3, it is possible to provide a cartridge that can achieve both uniform charging and suppression of charging defects caused by foreign matter.

[0158] (8. Modifications regarding the ratio of crimped yarn and straight yarn) In the first to third embodiments, conductive pile yarns (22f, 22f) are used as the brush fibers (brush bristles) of the charging brush 22. In the first to third embodiments, the straight yarns 22f (second type of fiber) are desirably conductive fibers having a resistance value in an appropriate range to appropriately charge the surface of the photosensitive drum 21. On the other hand, in the first to third embodiments, the crimped yarns 22g have a main role of entangling foreign matter, and do not necessarily have to be conductive. In other words, the crimped yarns 22g (first type of fiber) may be non-conductive fibers formed of an insulating material that does not contain conductive particles.

[0159] In addition, in the first to third embodiments, all of the brush fibers woven into the base fabric 22e in the first region A1 (FIG. 3) on the upstream side in the rotation direction R of the photosensitive drum 21 are crimped yarns 22g. However, the present invention is not limited to this, and only a part of the brush fibers woven into the first region A1 may be crimped yarns 22g. In other words, the brush fibers woven into the first region A1 may include straight yarns 22f. Even when only a part of the brush fibers woven into the first region A1 are crimped yarns 22g, the brush fibers including the crimped yarns 22g are entangled with each other to entangle large foreign objects, thereby obtaining the same function as the charging brush 22 of the first to third embodiments. In other words, the brush fibers woven into the first region A1 are entangled with each other to increase the spatial density, and entangle foreign objects larger than 15 μm in size, for example.

[0160] From the viewpoint of more densely intertwining the brush fibers woven in the first region A1, it is desirable that 50% or more (more preferably, 75% or more) of the brush fibers woven in the first region A1 are crimped yarns 22g. In other words, it is desirable that the ratio of the first type of fiber (crimped yarns 22g) in the brush fibers in the first portion of the charged brush 22 is 50% or more (more preferably, 75% or more).

[0161] In addition, in the first to third embodiments, all of the brush fibers woven into the base fabric 22e in the second region A2 (FIG. 3) downstream in the rotation direction R of the photosensitive drum 21 are straight hair yarns 22f. However, only a part of the brush fibers woven into the second region A2 may be straight hair yarns 22f. In other words, the brush fibers woven into the second region A2 may include crimped hair yarns 22g. Even when only a part of the brush fibers woven into the second region A2 are straight hair yarns 22f, the surface of the photosensitive drum 21 is appropriately charged by the brush fibers whose tips are uniform in height, and thus the same function as the charging brush 22 in the first to third embodiments can be obtained. In addition, if the brush part of the second region A2 including the straight hair yarns 22f, which are stiffer than the crimped hair yarns 22g, is in a positional relationship capable of supporting the brush part of the first region A1 including the crimped hair yarns 22g, the crimped hair yarns 22g can be prevented from falling down.

[0162] From the viewpoint of allowing the brush fibers woven into the second region A2 to more appropriately charge the surface of the photosensitive drum 21, it is desirable that 80% or more (more preferably, 90% or more) of the brush fibers woven into the second region A2 are straight hair yarns 22f. In other words, it is desirable that the ratio of the second type of fiber (straight hair yarns 22f) in the brush fibers in the second portion of the charging brush 22 is 80% or more (more preferably, 90% or more). In addition, if 80% or more (more preferably, 90% or more) of the brush fibers woven into the second region A2 are straight hair yarns 22f, the brush portion of the first region A1 including the crimped yarns 22g can be supported and hair collapse can be suppressed.

[0163] Moreover, the charged brush 22 in Examples 1 to 3 was composed of two parts (crimped brush part 22G and straight brush part 22F) with different ratios of crimped yarn 22g in the brush fibers. However, the charged brush 22 may have three or more parts with different ratios of crimped yarn 22g in the brush fibers. In this case, the "first part" of the charged brush 22 refers to the most upstream part in the rotation direction R of the photosensitive drum 21 among the three or more parts with different ratios of crimped yarn 22g in the brush fibers. Moreover, the "second part" of the charged brush 22 refers to the most downstream part in the rotation direction R of the photosensitive drum 21 among the three or more parts with different ratios of crimped yarn 22g in the brush fibers.

[0164] Furthermore, the charging brush 22 may be configured so that the ratio of the crimped yarns 22g in the brush fibers changes continuously along the rotation direction R of the photosensitive drum 21. In this case, the "first portion" of the charging brush 22 refers to the most upstream portion of the charging brush 22 in the rotation direction R of the photosensitive drum 21. Furthermore, the "second portion" of the charging brush 22 refers to the most downstream portion of the charging brush 22 in the rotation direction R of the photosensitive drum 21.

[0165] (Other embodiments) In the above-described embodiment, a direct transfer type configuration in which a toner image (developer image) is directly transferred from the photosensitive drum 21 to a recording material P as a transfer target has been exemplified, but the image forming apparatus may be of an intermediate transfer type equipped with an intermediate transfer body. In the intermediate transfer type, the toner image is primarily transferred from the photosensitive drum 21 to an intermediate transfer body such as an intermediate transfer belt, and then the toner image is secondarily transferred from the intermediate transfer body to the recording material P, thereby forming an image on the recording material P.

[0166] Summary of the Disclosure The present disclosure includes at least the following: (Configuration 1) A rotatable photoreceptor; a charging brush that contacts the surface of the photoconductor to form a charging portion and charges the surface of the photoconductor; Equipped with the charging brush has brush fibers including a first type of fiber that has been subjected to a crimping process and a second type of fiber that has not been subjected to a crimping process; a ratio of the first type of fibers in the brush fibers in a first portion of the charging brush in a moving direction of the surface of the photoconductor in the charging unit is higher than a ratio of the first type of fibers in the brush fibers in a second portion of the charging brush located downstream of the first portion in the moving direction; 1. An image forming apparatus comprising: (Configuration 2) The ratio of the first type of fibers in the brush fibers in the first portion is 50% or more; The ratio of the second type of fibers in the brush fibers in the second portion is 80% or more. 2. The image forming apparatus according to claim 1, (Configuration 3) a downstream end of the first portion and an upstream end of the second portion in a rotation direction of the photoconductor are in contact with each other; 3. The image forming apparatus according to claim 1, wherein the first and second components are arranged in a same plane. (Configuration 4) the first portion is a first brush; The second portion is a second brush disposed downstream from the first brush in the rotation direction of the photoconductor. 3. The image forming apparatus according to claim 1, wherein the first and second components are arranged in a same plane. (Configuration 5) The charging brush has a base fabric, The first type of fiber and the second type of fiber are pile woven into the base fabric. 5. The image forming apparatus according to any one of configurations 1 to 4. (Configuration 6) In a rotation direction of the photoconductor, a distance between a first region of the base fabric into which the brush fibers of the first portion are woven and a second region of the base fabric into which the brush fibers of the second portion are woven is 2 mm or less. 6. The image forming apparatus according to configuration 5. (Configuration 7) The second type of fiber is electrically conductive. 7. The image forming apparatus according to any one of configurations 1 to 6. (Configuration 8) The first type of fiber is not electrically conductive. 8. The image forming apparatus according to claim 7, (Configuration 9) The resistance of the charging brush is 1.0×10 2 Ω~1.0×10 8 Ω, 9. The image forming apparatus according to any one of configurations 1 to 8. (Configuration 10) a flexible sheet member for supporting the charging brush; The elasticity of the sheet member causes the brush fibers to contact the surface of the photoreceptor. 10. The image forming apparatus according to any one of configurations 1 to 9, (Configuration 11) A support for supporting the charging brush; a biasing means for biasing the support member in a direction approaching the photosensitive member; Further comprising: the brush fibers are in contact with the surface of the photoreceptor by the biasing force of the biasing means; 10. The image forming apparatus according to any one of configurations 1 to 9, (Configuration 12) a support member for supporting the charging brush and fixed in position relative to the rotation axis of the photoreceptor; a distance between the support and the surface of the photoconductor is shorter than a dimension of the charging brush in a bristle height direction of the brush fibers before the charging brush is attached to the support; 10. The image forming apparatus according to any one of configurations 1 to 9, (Configuration 13) When viewed in the direction of the rotation axis of the photoconductor, the center position of the contact portion between the charging brush and the photoconductor in the rotation direction of the photoconductor is disposed within a range of 30° to 150° as an angle measured in the rotation direction of the photoconductor with respect to a half line drawn from the rotation axis in the direction of gravity. 13. The image forming apparatus according to any one of configurations 1 to 12. (Configuration 14) a storage unit provided upstream of the charging brush in the rotation direction of the photoconductor and configured to store foreign matter collected from the photoconductor by the charging brush; 2. The image forming apparatus according to claim 1, (Configuration 15) an exposure means for exposing the photoreceptor; a transfer means for forming a transfer portion facing the photoreceptor and transferring a developer image formed on the photoreceptor to a transfer target; Further comprising: In a rotation direction of the photoconductor, the charging unit is disposed downstream of the transfer unit and upstream of an exposure position where the light from the exposure unit is irradiated. 15. The image forming apparatus according to any one of configurations 1 to 14. (Configuration 16) a developer container for accommodating the developer; a developing member that faces the photoconductor to form a developing portion and supplies a developer to the photoconductor; the image forming apparatus recovers the developer remaining on the surface of the photoconductor after passing through the transfer unit into the developing container by the developing member; the charging brush allows the developer to pass through a contact portion between the charging brush and the photoreceptor; 16. The image forming apparatus according to claim 15, (Configuration 17) a charging unit that is provided downstream of the charging unit and upstream of the exposure position in the rotation direction of the photoconductor and charges a surface of the photoconductor; 17. The image forming apparatus according to claim 15 or 16, (Configuration 18) the absolute value of the voltage applied to the charging brush is smaller than the absolute value of the voltage applied to the charging means; 18. The image forming apparatus according to claim 17, (Configuration 19) The charging means is a roller member. 19. The image forming apparatus according to configuration 17 or 18. (Configuration 20) The transfer medium is a recording material for recording an image. 20. The image forming apparatus according to any one of configurations 15 to 19. (Configuration 21) the transfer medium is an intermediate transfer medium for performing a second transfer of the developer image onto a recording material after the developer image has been primarily transferred from the photosensitive member; 20. The image forming apparatus according to any one of configurations 15 to 19. [Explanation of symbols]

[0167] 21...Photosensitive body (photosensitive drum) / 22...Charging brush / 22f...Brush fiber, second type of fiber (straight yarn) / 22g...Brush fiber, first type of fiber (curly yarn)

Claims

1. A rotatable photoreceptor; a charging brush that contacts the surface of the photoconductor to form a charging portion and charges the surface of the photoconductor; Equipped with the charging brush has brush fibers including a first type of fiber that has been subjected to a crimping process and a second type of fiber that has not been subjected to a crimping process; a ratio of the first type of fibers in the brush fibers in a first portion of the charging brush in a moving direction of the surface of the photoconductor in the charging unit is higher than a ratio of the first type of fibers in the brush fibers in a second portion of the charging brush located downstream of the first portion in the moving direction; 1. An image forming apparatus comprising:

2. A ratio of the first type of fibers in the brush fibers in the first portion is 50% or more; The ratio of the second type of fibers in the brush fibers in the second portion is 80% or more.

2. The image forming apparatus according to claim 1,

3. a downstream end of the first portion and an upstream end of the second portion in a rotation direction of the photoconductor are in contact with each other; 2. The image forming apparatus according to claim 1,

4. the first portion is a first brush; the second portion is a second brush disposed downstream from the first brush in a rotation direction of the photoconductor, 2. The image forming apparatus according to claim 1,

5. The charging brush has a base fabric, The first type of fiber and the second type of fiber are pile woven into the base fabric.

2. The image forming apparatus according to claim 1,

6. In a rotation direction of the photoconductor, a distance between a first region of the base fabric into which the brush fibers of the first portion are woven and a second region of the base fabric into which the brush fibers of the second portion are woven is 2 mm or less.

6. The image forming apparatus according to claim 5,

7. The second type of fiber is electrically conductive.

2. The image forming apparatus according to claim 1,

8. The first type of fiber is not electrically conductive.

8. The image forming apparatus according to claim 7,

9. The resistance value of the charging brush is 1.0×10 ２ Ω~1.0×10 ８ Ω, 2. The image forming apparatus according to claim 1,

10. a flexible sheet member for supporting the charging brush; The elasticity of the sheet member causes the brush fibers to contact the surface of the photoreceptor.

2. The image forming apparatus according to claim 1,

11. A support for supporting the charging brush; a biasing means for biasing the support member in a direction approaching the photosensitive member; Further comprising: the brush fibers are in contact with the surface of the photoreceptor by the biasing force of the biasing means; 2. The image forming apparatus according to claim 1,

12. a support member for supporting the charging brush and fixed in position relative to the rotation axis of the photoreceptor; a distance between the support and the surface of the photoconductor is shorter than a dimension of the charging brush in a bristle height direction of the brush fibers before the charging brush is attached to the support; 2. The image forming apparatus according to claim 1,

13. When viewed in the direction of the rotation axis of the photoconductor, the center position of the contact portion between the charging brush and the photoconductor in the rotation direction of the photoconductor is disposed within a range of 30° to 150° as an angle measured in the rotation direction of the photoconductor with respect to a half line drawn from the rotation axis in the direction of gravity.

2. The image forming apparatus according to claim 1,

14. a storage unit provided upstream of the charging brush in the rotation direction of the photoconductor and configured to store foreign matter collected from the photoconductor by the charging brush; 2. The image forming apparatus according to claim 1,

15. an exposure means for exposing the photoreceptor; a transfer means for forming a transfer portion facing the photoreceptor and transferring a developer image formed on the photoreceptor to a transfer target; Further comprising: In a rotation direction of the photoconductor, the charging unit is disposed downstream of the transfer unit and upstream of an exposure position where the light from the exposure unit is irradiated.

15. The image forming apparatus according to claim 1,

16. a developer container for accommodating the developer; a developing member that faces the photoconductor to form a developing portion and supplies a developer to the photoconductor; the image forming apparatus recovers the developer remaining on the surface of the photoconductor after passing through the transfer unit into the developing container by the developing member; the charging brush allows the developer to pass through a contact portion between the charging brush and the photoreceptor; 16. The image forming apparatus according to claim 15.

17. a charging unit that is provided downstream of the charging unit and upstream of the exposure position in the rotation direction of the photoconductor and charges a surface of the photoconductor; 16. The image forming apparatus according to claim 15.

18. the absolute value of the voltage applied to the charging brush is smaller than the absolute value of the voltage applied to the charging means; 18. The image forming apparatus according to claim 17.

19. The charging means is a roller member.

18. The image forming apparatus according to claim 17.

20. The transfer medium is a recording material for recording an image.

16. The image forming apparatus according to claim 15.

21. the transfer medium is an intermediate transfer medium for performing a second transfer of the developer image onto a recording material after the developer image has been primarily transferred from the photosensitive member; 16. The image forming apparatus according to claim 15.

Images