Image forming apparatus

Abstract

To prevent the occurrence of a defect due to frictional electrification between a cleaning member and an electrification member.SOLUTION: In an image forming apparatus 100, when a time from a contact of a point on a surface of an electrification member 2 with a cleaning member 8 to the next contact of the point with the cleaning member 8 caused by rotation of the electrification member 2 is defined as a rotation time A [sec], the time constant τ of the electrification member 2 is defined as a value represented by τ=1 / 2πfp [sec] (wherein fp is a frequency at which the absolute value of imaginary number terms, which is obtained from impedance measurement of the electrification member 2, indicates the maximum number), and the time constant τ of the electrification member 2 is defined as an index of attenuation of electric charges on the surface of the electrification member 2, the rotation time A and the time constant τ satisfy the following formula A / τ≥60, and the time constant τ is 1.0×10-5 [sec] or more and 1.2×10-3 [sec] or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile machine that uses an electrophotographic method. [Background technology]

[0002] Conventionally, electrophotographic image forming devices have adopted a process cartridge system in which a photosensitive member and process means acting on the photosensitive member are integrated into a cartridge, and this cartridge is detachable from the main body of the image forming device. The process means acting on the photosensitive member include a charging member that charges the photosensitive member, a cleaning member that removes toner remaining on the photosensitive member, and a developing unit that develops the electrostatic latent image formed on the photosensitive member with toner. By integrating these process means with the photosensitive member into a single cartridge (process cartridge) and allowing users to replace them all at once, usability has been improved.

[0003] There are also cartridges that employ a contact charging system, in which a charging member contacts a photosensitive member to perform charging. A photosensitive drum is often used as the photosensitive member, and a charging roller is often used as the charging member. In cartridges employing a contact charging system, as the cartridge's lifespan increases, toner and fine particles added to the toner surface (hereinafter referred to as "external additives") may accumulate on the surface of the charging roller. As a result, if toner and external additives accumulate on the surface of the charging roller and contaminate the charging roller over time, charging defects may occur, which may manifest as uneven density in halftone images, for example. This charging defect generally occurs toward the latter half of the cartridge's lifespan, and becomes more pronounced as the cartridge's lifespan increases.

[0004] Therefore, a configuration is sometimes used in which a cleaning member is disposed so as to come into contact with the charging roller, thereby removing the toner and external additives (hereinafter also referred to as "adhered matter") that have adhered to the surface of the charging roller.

[0005] Patent Document 1 describes a configuration in which a cleaning roller is in contact with a charging roller, and the cleaning roller has a contact portion that contacts the charging roller and a non-contact portion that does not contact the charging roller. In the configuration described in Patent Document 1, a voltage with a characteristic that cancels out charging of the surface of the charging roller due to friction with the cleaning roller is applied to the charging roller before and after image formation. This is said to be a solution to the following problem: The charging roller is charged by friction between the cleaning roller and the charging roller at the contact portion, while the charging roller is not charged at the non-contact portion, creating a potential difference on the charging roller, and the potential difference between the contact portion and the non-contact portion causes uneven density on the image. This is a solution to this problem. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-145419 Summary of the Invention [Problem to be solved by the invention]

[0007] The surfaces (outer peripheral surface, outer surface) of both the cleaning roller and the charging roller are often made of resin, and frictional charging caused by the two rollers rubbing against each other can be a problem. Due to frictional charging, the charging roller and the cleaning roller carry charges of opposite polarities. This can reduce the absolute value of the surface potential of the charging roller, causing fluctuations in discharge from the charging roller to the photosensitive drum, resulting in "horizontal charging streak images." Horizontal charging streak images are streak-like density unevenness that occurs due to uneven discharge from the charging roller to the photosensitive drum, extending in a direction intersecting (typically approximately perpendicular to) the direction of movement of the surface of the photosensitive drum.

[0008] Discharge from the charging roller occurs in a small gap near the point where the charging roller and the photosensitive drum contact each other. Typically, discharge is completed in the small gap upstream of the contact point between the charging roller and the photosensitive drum. However, as described above, when the absolute value of the surface potential of the charging roller decreases due to frictional charging of the cleaning roller, discharge may not be completed solely by discharge upstream of the contact point between the charging roller and the photosensitive drum, and unstable discharge may occur intermittently in the small gap downstream. Images caused by this intermittent discharge are called "horizontal charging stripe images." As process cartridges and image forming apparatuses continue to have longer lifespans, the charging roller rotates in contact with the cleaning roller for longer periods of time, which can lead to more pronounced horizontal charging stripe images.

[0009] In the configuration described in Patent Document 1, it is necessary to apply a voltage of the opposite polarity to that during image formation to the charging roller before and after image formation, which makes it difficult to implement an operation to cancel out the charge during continuous printing.

[0010] Furthermore, the configuration described in Patent Document 1 is a solution to the problem that occurs during initial driving when the cleaning roller has contact and non-contact portions, and therefore cannot suppress image defects caused by potential changes due to frictional charging of the charging roller during long-term continuous driving.

[0011] SUMMARY OF THE INVENTION An object of the present invention is to prevent problems caused by frictional charging between a cleaning member and a charging member. [Means for solving the problem]

[0012] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus comprising a rotatable photosensitive member, a charging member that contacts the surface of the photosensitive member and charges the surface of the photosensitive member while rotating in a predetermined direction, and a cleaning member that contacts the charging member and cleans the surface of the charging member, wherein when the surface of the photosensitive member is charged by the charging member, the time from when a certain point on the surface of the charging member comes into contact with the cleaning member until the next time the point comes into contact with the cleaning member due to the rotation of the charging member is defined as a rotation time A [sec], and the time constant τ of the charging member is defined as a value expressed by the following equation: τ=1 / 2πfp [sec] (where fp is the frequency at which the absolute value of the imaginary term obtained by measuring the impedance of the charging member takes a maximum value), and the time constant τ of the charging member is defined as an index of attenuation of charge on the surface of the charging member, the rotation time A and the time constant τ satisfy the following equation: A / τ≧60, and the time constant τ is 1.0×10 -5 [sec] or more, 1.2×10 -3 [sec] or less. [Effects of the Invention]

[0013] According to the present invention, it is possible to suppress the occurrence of problems caused by frictional charging between the cleaning member and the charging member. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic diagram illustrating a configuration of a voltage application unit of the image forming apparatus. [Figure 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 4] FIG. 2 is a schematic perspective view of the exterior of a charging roller. [Figure 5] FIG. 2 is a schematic cross-sectional view of an elastic layer of the charging roller. [Figure 6] FIG. 2 is a schematic cross-sectional view of a charging roller. [Figure 7] FIG. 2 is a schematic perspective view of an example of a cleaning roller. [Figure 8] FIG. 10 is a schematic perspective view for explaining a method for measuring the impedance of a charging roller. [Figure 9] FIG. 4 is a schematic cross-sectional view for explaining a method for measuring the impedance of a charging roller. [Figure 10] FIG. 2 is a schematic diagram showing a measurement system for the impedance of a charging roller. [Figure 11] 3 is a schematic cross-sectional view illustrating an example of a shaft support configuration for a charging roller and a driving roller. FIG. [Figure 12] FIG. 10 is a schematic perspective view of another example of a cleaning roller. [Figure 13] FIG. 10 is a schematic cross-sectional view illustrating another example of a shaft support configuration for a charging roller and a driving roller. [Figure 14] FIG. 10 is a schematic cross-sectional view illustrating another example of a shaft support configuration for a charging roller and a driving roller. [Figure 15] FIG. 10 is a schematic graph illustrating a method for calculating the time constant of the charging roller. [Figure 16] 1 is a table showing the configurations of examples and comparative examples. [Figure 17] 10 is a table showing evaluation results. [Figure 18] FIG. 1 is a schematic diagram for explaining an overview of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0016] [First embodiment] 1. Overview of this embodiment The inventors analyzed the phenomenon of horizontal charging streak images and found the following: In other words, in a configuration in which a cleaning roller is in contact with a charging roller, frictional charging occurs between their surfaces, reducing the absolute value of the surface potential of the charging roller. This reduces discharge upstream of the contact point between the charging roller and the photosensitive drum, resulting in horizontal charging streak images. These horizontal charging streak images are caused by a decrease in the absolute value of the surface potential of the charging roller, which reduces the amount of discharge in the minute gap upstream of the contact point between the charging roller and the photosensitive drum, causing intermittent discharge in the minute gap downstream of the contact point.

[0017] As a result of extensive research, the inventors have discovered that the horizontal charging streak images can be suppressed by reducing the time constant, which is an index of the decay of charge on the charging roller, so that frictional charging decays immediately, and by making the interval during which friction occurs between the surface of the charging roller and the cleaning roller sufficiently longer than the time constant.

[0018] To explain further, in a configuration where horizontal charging streak images occur, the inventors measured the surface potential of the charging roller while rotating the cleaning roller in contact with the charging roller, and found that the cause of the horizontal charging streak images is a decrease in the absolute value of the surface potential of the charging roller due to frictional charging as described below.

[0019] 18A and 18B are schematic diagrams for explaining the causes of horizontal charging stripe images, in which Fig. 18A shows a schematic diagram of the surface potential of the charging roller in the configuration of this embodiment, and Fig. 18B shows a schematic diagram of the surface potential of the charging roller in the configuration of a conventional example.

[0020] We measured the frictional charging between the cleaning roller 8 and the charging roller 2. For example, when a voltage of -1000 V was simultaneously applied to the cleaning roller 8 and a voltage of -1000 V to the charging roller 2, it was found that when the charging roller 2 and cleaning roller 8 started to rotate, the surface potential of the cleaning roller 8 changed to about -700 V due to frictional charging. In other words, it can be inferred that a frictional charging potential of +300 V was generated on the surface of the cleaning roller 8.

[0021] Furthermore, when the surface potential of the charging roller 2 was measured at this time, it was found that the absolute value of the surface potential had dropped to about -800 V due to the influence of the +300 V potential of the cleaning roller, even though a voltage of -1000 V was being applied to the charging roller 2. At this time, horizontal charging streak images occurred. It is believed that when the absolute value of the surface potential of the charging roller 2 drops, discharge in the minute gap upstream of the contact point between the charging roller 2 and the photosensitive drum 1 decreases, and intermittent discharge occurs in the minute gap downstream of that contact point, resulting in the horizontal charging streak images.

[0022] Based on these results, the inventors have come to the conclusion that in order to improve the horizontal charging streak images that occur in a configuration in which the cleaning roller 8 is in contact with the charging roller 2, it is necessary to immediately attenuate the frictional charging between the cleaning roller 8 and the charging roller 2.

[0023] Specifically, by setting the time constant of the charging roller 2 to a value in a range that is sufficiently smaller than the time interval during which friction occurs between the surface of the charging roller 2 and the surface of the cleaning roller 8, the charge accumulated on the surface of the charging roller 2 can be attenuated, thereby suppressing the formation of horizontal charging streak images.

[0024] 2. Image forming equipment <Overall Configuration of Image Forming Apparatus> The overall configuration of an image forming apparatus 100 of this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment.

[0025] The image forming apparatus 100 has a process cartridge 10 that is removably mounted in an apparatus main body 110. The apparatus main body 110 of the image forming apparatus 100 is the portion of the image forming apparatus 100 excluding the process cartridge 10. The process cartridge 10 has a rotatable photosensitive drum 1 as an image carrier. The process cartridge 10 also has a charging roller 2, a developing roller 41, a cleaning blade 7, and the like around the photosensitive drum 1. The charging roller 2 charges the surface of the photosensitive drum 1. The developing roller 41 develops the electrostatic latent image formed on the surface of the photosensitive drum 1 with toner 44. That is, the electrostatic latent image formed on the surface of the photosensitive drum 1 is developed into a toner image by the toner charged to the correct polarity (holding the correct charge) carried on the developing roller 41. The cleaning blade 7 also cleans the surface of the photosensitive drum 1. The process cartridge 10 also has a cleaning roller 8 arranged to contact the charging roller 2, a supply roller 42 arranged to contact the developing roller 41, and a developing blade 43. The cleaning roller 8 cleans the surface of the charging roller 2. The supply roller 42 supplies toner to the developing roller 41 and scrapes toner off from the developing roller 41. The developing blade 43 regulates the amount of toner (layer thickness) on the developing roller 41 and applies an electric charge to the toner.

[0026] The image forming apparatus 100 also has a transfer roller 5, an exposure device 3, and the like, which are attached to the apparatus main body 110. The transfer roller 5 comes into contact with the photosensitive drum 1 and transfers a toner image from the photosensitive drum 1 to a recording material P. The exposure device 3 also forms an electrostatic latent image corresponding to image data on the surface of the charged photosensitive drum 1.

[0027] FIG. 2 is a schematic diagram showing the power supply configuration of the image forming apparatus 100. As shown in FIG. 2, the image forming apparatus 100 has various power supplies attached to the apparatus main body 110, such as a charging power supply E1, a developing power supply E2, a supply power supply E3, a regulating power supply E4, and a transfer power supply E5. The charging power supply E1, which serves as a charging voltage application unit, applies a predetermined charging voltage (charging bias) to the charging roller 2. In this embodiment, a DC high-voltage power supply is used as the output source of the charging voltage. The developing power supply E2, which serves as a developing voltage application unit, applies a predetermined developing voltage (developing bias) to the developing roller 41. In this embodiment, a DC high-voltage power supply is used as the output source of the developing voltage. The supply power supply E3, which serves as a supply voltage application unit, applies a predetermined supply voltage (supply bias) to the supply roller 42. In this embodiment, a DC high-voltage power supply is used as the output source of the supply voltage. The regulating power supply E4, which serves as a regulating voltage application unit, applies a predetermined regulating voltage (regulating bias) to the developing blade 43. In this embodiment, a DC high voltage power supply is used as the output source of the regulated voltage. A transfer power supply E5 as a transfer voltage application unit applies a predetermined transfer voltage (transfer bias) to the transfer roller 5. In this embodiment, a DC high voltage power supply is used as the output source of the transfer voltage.

[0028] The image forming apparatus 100 also has a fixing device 6 as fixing means attached to the apparatus main body 110. In this embodiment, the fixing device 6 is of a thermal fixing type that heats and melts toner on the recording material P to fix the image on the recording material P. The fixing device 6 has a fixing film, a fixing heater such as a ceramic heater that heats the fixing film, a thermistor that measures the temperature of the fixing heater, and a pressure roller that presses against the fixing film.

[0029] <Configuration of each part of the image forming apparatus> The photosensitive drum 1 is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member). In this embodiment, the photosensitive drum 1 has a photosensitive layer formed of a negatively charged organic photosensitive member on a drum-shaped substrate made of aluminum. The photosensitive drum 1 has an outer diameter of 24 mm and is driven to rotate at a predetermined peripheral speed (surface movement speed) in the direction of arrow R1 in the drawing (clockwise direction) by a driving force transmitted from a drum drive motor D1 (FIG. 3), which is a driving source constituting a driving device as a driving means. The peripheral speed of the photosensitive drum 1 corresponds to the process speed of the image forming apparatus 100. In this embodiment, the photosensitive drum 1 is driven to rotate at a peripheral speed of 260 mm / sec.

[0030] The charging roller 2 is a roller-shaped charging member that serves as charging means. The charging roller 2 is composed of an elastic roller and has a core (support) and a conductive layer (conductive elastic layer) made of conductive rubber that serves as an elastic layer covering the core. In this embodiment, the outer diameter of the core of the charging roller 2 is 6 mm, and the outer diameter of the elastic layer (conductive layer) is 8.5 mm. The charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force, and is rotated in the direction of arrow R2 in the figure (counterclockwise direction) as the photosensitive drum 1 rotates.

[0031] The cleaning roller 8 is a roller-shaped cleaning member serving as cleaning means. The cleaning roller 8 is composed of an elastic roller and has a core (rotating shaft) and a foamed elastic layer (foamed elastic layer) made of urethane sponge as an elastic layer covering the core. In this embodiment, the cleaning roller 8 is disposed vertically above the charging roller 2. In this embodiment, the outer diameter of the core of the cleaning roller 8 is 4 mm, and the outer diameter of the cylindrical elastic layer (foamed elastic layer) is 6 mm. The cleaning roller 8 is pressed against the surface of the charging roller 2 with a predetermined pressing force, and is rotated in the direction of arrow R3 in the figure (clockwise direction) as the charging roller 2 rotates.

[0032] The rotation axis of the charging roller 2 is approximately parallel to the rotation axis of the cleaning roller 8. The charging roller 2 and the cleaning roller 8 are rotatably supported by a cleaning container 9 (described later) via bearing members (not shown).

[0033] In this embodiment, the exposure device 3 serving as exposure means is configured as a laser scanner device (scanner unit, laser exposure unit). The exposure device 3 uses a polygon mirror to irradiate the surface of the photosensitive drum 1 with laser light corresponding to image information input from an external device such as an image reading device or a personal computer, thereby scanning and exposing the surface of the photosensitive drum 1. As a result, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1. Note that the exposure device 3 is not limited to a laser scanner device, and for example, an LED exposure device having an LED array in which multiple LEDs are arranged along the longitudinal direction (rotational axis direction) of the photosensitive drum 1 may be used.

[0034] The image forming apparatus 100 has a charging power supply (high-voltage power supply) E1 that applies a charging voltage to the charging roller 2. When the charging voltage is applied to the core of the charging roller 2, and the potential difference between the surface potential of the photosensitive drum 1 and the potential of the charging roller 2 becomes equal to or greater than the discharge start voltage, discharge begins, and the surface of the photosensitive drum 1 is uniformly charged. As a result, a dark potential VD is formed on the surface of the photosensitive drum 1. Specifically, for example, a DC voltage of −1050 V is applied to the charging roller 2 as the charging voltage, and the dark potential VD of the surface of the photosensitive drum 1 at this time becomes −500 V (VD reference value). A laser beam based on image information is irradiated onto the charged surface of the photosensitive drum 1 from the exposure device 3 through an exposure opening of the process cartridge 10. As a result, charge carriers from the carrier generation layer in the photosensitive layer of the photosensitive drum 1 dissipate the charge on the surface of the photosensitive drum 1, and a light potential VL is formed on the surface of the photosensitive drum 1. At this time, the light area potential VL on the surface of the photosensitive drum 1 is, for example, −100 V. In this way, an electrostatic latent image, which is an image formed by the dark area potential VD and the light area potential VL, is formed on the photosensitive drum 1. This electrostatic latent image is developed (visualized) with toner 44.

[0035] The developing device 4 as a developing means includes a developing roller 41 as a developing member (developer carrier) that carries toner, and a developing container 45 that is the frame of the developing device 4. The developing device 4 also includes a supply roller 42 as a supply member (supply / scraper member) that supplies toner to the developing roller 41 and scrapes the toner from the developing roller 41, and a developing blade 43 as a regulating member that regulates the amount (layer thickness) of toner on the developing roller 41 and applies a charge to the toner on the developing roller 41. The developing roller 41 and the supply roller 42 are rotatably supported by the developing container 45. In this embodiment, the developing roller 41 has an outer diameter of 10 mm. The developing roller 41 is disposed so that a portion of the developing roller 41 is exposed to the outside through a developing opening, which is an opening in the developing container 45 that faces the photosensitive drum 1. The supply roller 42 is disposed so as to abut against the developing roller 41 and applies toner 44, which serves as a developer, contained in the developing container 45, to the surface of the developing roller 41. The supply roller 42 is not necessarily required as long as the toner 44 can be sufficiently supplied to the developing roller 41. The developing blade 43 is disposed so as to contact the surface of the developing roller 41, and is supported by a developing container 45.

[0036] In this embodiment, the developing device 4 uses a contact development method. That is, a toner layer carried on the developing roller 41 comes into contact with the photosensitive drum 1 in a development section (development area) where the photosensitive drum 1 and the developing roller 41 face each other. A development voltage is applied to the developing roller 41 by a development power supply (high-voltage power supply) E2. In this embodiment, for example, a DC voltage of −300 V is applied to the developing roller 41 as the development voltage. When the development voltage is applied to the developing roller 41, the toner carried on the developing roller 41 moves from the developing roller 41 to the surface of the photosensitive drum 1 in accordance with the potential distribution on the surface of the photosensitive drum 1. As a result, the toner adheres to the electrostatic latent image, and a toner image is formed on the surface of the photosensitive drum 1. Note that in this embodiment, the image forming apparatus 100 uses a reversal development method. That is, after being charged in the charging process, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the area (exposed portion) on the surface of the photosensitive drum 1 where the charge amount has been attenuated by exposure in the exposure process, thereby forming a toner image.

[0037] In this embodiment, the toner used has an average particle size of 7 μm and a normal charge polarity (normal polarity) of negative polarity. The normal polarity of the toner is the main charge polarity of the toner during development. In this embodiment, the toner is, for example, a polymerized toner produced by a polymerization method. In this embodiment, the toner does not contain a magnetic component and is a so-called non-magnetic single-component developer that is supported on the developing roller 41 mainly by intermolecular forces and electrostatic forces (image forces). However, a magnetic single-component developer containing a magnetic component may also be used. In addition to toner particles, a single-component developer may contain additives (e.g., wax or silica particles) for adjusting the fluidity and charging performance of the toner. Alternatively, a two-component developer containing toner (non-magnetic toner particles) and carrier (magnetic carrier particles) may also be used. When a magnetic developer is used, a cylindrical developing sleeve with a magnet disposed inside is used as the developing member (developer carrier).

[0038] An agitating member 46 serving as agitation means is disposed inside the developing container 45. The agitating member 46 is driven to rotate in the direction of arrow R6 in the figure (clockwise direction) by a driving force transmitted from a motor, which is a driving source constituting a driving device serving as a driving means. As a result, the toner 44 in the developing container 45 is agitated and transported toward the developing roller 41 and the supply roller 42. The agitating member 46 is driven to rotate at a predetermined rotational speed in conjunction with the rotation of the developing roller 41 and the supply roller 42. Note that the agitating member is not limited to a rotating type. For example, an agitating member having an oscillating type may be employed.

[0039] The developing roller 41 is disposed so as to contact the surface of the photosensitive drum 1 in a developing section where the photosensitive drum 1 and the developing roller 41 face each other. The developing roller 41 is driven to rotate at a predetermined peripheral speed in the direction of arrow R4 in the figure (counterclockwise direction) by a driving force transmitted from a motor, which is a driving source constituting a driving device as a driving means. In this embodiment, when the process cartridge 10 is installed in the image forming apparatus 100, the developing roller 41 is always in contact with the photosensitive drum 1 even when not forming an image. That is, in this embodiment, the image forming apparatus 100 is not provided with a contact / separation mechanism that separates the developing roller 41 from the photosensitive drum 1. In this embodiment, the developing roller 41 is driven to rotate at a peripheral speed that is 1.3 times the peripheral speed of the photosensitive drum 1.

[0040] The supply roller 42 is disposed so as to contact the developing roller 41. The supply roller 42 is driven to rotate at a predetermined peripheral speed in the direction of arrow R5 (counterclockwise) in the figure by a driving force transmitted from a motor, which is a driving source constituting a driving device as a driving means. As the agitating member 46 rotates, the toner 44 in the developing container 45 is agitated and supplied to the supply roller 42. As the supply roller 42 rotates, it supplies the toner 44 onto the developing roller 41 and also scrapes off and removes the toner 44 remaining on the developing roller 41 after passing through the developing unit. The toner 44 removed from the developing roller 41 is mixed with the toner in the developing container 45. A supply voltage is applied to the supply roller 42 by a supply power source (high-voltage power source) E3. In this embodiment, for example, a DC voltage of −400 V is applied to the supply roller 42 as the supply voltage.

[0041] The developing blade 43 is made of a plate-shaped elastic member and is disposed so as to contact the developing roller 41, and is bent by the developing roller 41 against its elasticity. The toner 44 supplied onto the developing roller 41 is regulated by the developing blade 43 to a predetermined amount (layer thickness) and is also charged. The toner layer thus formed on the developing roller 41 is transported to a developing section where the photosensitive drum 1 and the developing roller 41 face each other. A regulated voltage is applied to the developing blade 43 by a regulated power supply (high-voltage power supply) E4. In this embodiment, for example, a DC voltage of −400 V is applied to the developing blade 43 as the regulated voltage.

[0042] In this embodiment, the developing roller 41, the supply roller 42, and the stirring member 46 receive driving force from a motor that is also used as the driving source for the photosensitive drum 1, but at least one of these may be provided with a driving source separate from the driving source for the photosensitive drum 1.

[0043] Cleaning device 11 as cleaning means has cleaning blade 7 as a cleaning member and cleaning container 9 which is the frame of cleaning device 11. Cleaning blade 7 is disposed so as to contact the surface of photosensitive drum 1 and is supported by cleaning container 9. Cleaning blade 7 scrapes toner remaining on the surface of photosensitive drum 1 after the transfer process (transfer residual toner) from the surface of rotating photosensitive drum 1, and stores the toner in recovered toner storage section 12 formed in cleaning container 9.

[0044] The process cartridge 10 is configured by combining a developing container 45 and a cleaning container 9.

[0045] <Image formation operation> Next, the image forming operation of the image forming apparatus 100 will be described. When an image formation command is input to the image forming apparatus 100, the image forming process by the process cartridge 10 is started. The exposure device 3 irradiates the photosensitive drum 1 with laser light based on image information input from an external device such as an image reading device or a personal computer connected to the image forming apparatus 100. At this time, the photosensitive drum 1 has been charged in advance by the charging roller 2, and an electrostatic latent image is formed on the photosensitive drum 1 by the irradiation of the laser light. Thereafter, the electrostatic latent image is developed by the developing roller 41, and a toner image is formed on the photosensitive drum 1.

[0046] A transfer roller 5, which is a roller-type transfer member serving as a transfer means, contacts the photosensitive drum 1 to form a transfer section. The toner image formed on the photosensitive drum 1 is transferred in the transfer section onto a sheet-like recording material (transfer material, recording medium, sheet) P such as paper or a plastic sheet that is sandwiched and conveyed between the photosensitive drum 1 and the transfer roller 5. During transfer, a predetermined transfer voltage, which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner, is applied to the transfer roller 5 by a transfer power supply (high-voltage power supply) E5.

[0047] The recording material P is stored in a cassette 13 serving as a recording material storage unit. The recording material P stored in the cassette 13 is separated one by one by a feed roller 14 serving as a feeding member, sent out of the cassette 13, and conveyed to a pair of registration rollers 15 serving as a conveying member. The pair of registration rollers 15 conveys the recording material P to a transfer unit in synchronization with the toner image on the photosensitive drum 1.

[0048] The recording material P onto which the toner image has been transferred is conveyed to the fixing device 6. The fixing device 6 heats and presses the recording material P as it passes through the nip between the fixing film and the pressure roller. As a result, the toner particles on the recording material P melt and then solidify, thereby fixing the toner image to the recording material P. The recording material P that has passed through the fixing device 6 is discharged (output) to the outside of the apparatus main body 110 (outside the machine) by a pair of discharge rollers (not shown) serving as a discharge means, and is stacked on a discharge tray 16 serving as a stacking unit provided at the top of the apparatus main body 110.

[0049] Furthermore, the untransferred toner remaining on the photosensitive drum 1 after the transfer step is removed from the photosensitive drum 1 by the cleaning device 11 and collected.

[0050] <Control configuration> FIG. 3 is a schematic block diagram showing the control configuration of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 has a control unit 200 that controls each unit of the image forming apparatus 100. The control unit 200 has a CPU 201 as a processing unit, which is a central element that performs calculations. The control unit 200 also has a main body storage unit 210, which serves as a storage unit (storage unit) for storing information and is composed of a ROM, RAM, non-volatile memory, etc. The ROM stores control programs, pre-calculated data tables, etc. The RAM stores information input to the control unit 200, detected information, calculation results, etc., and the non-volatile memory stores various setting information, etc. The CPU 200 and the main body storage unit 210 can transfer and read data to and from each other. The control unit 200 also has an input / output unit (not shown) for exchanging signals between the control unit 200 and each unit.

[0051] The control unit 200 is connected to a driving unit such as a drum drive motor D1. The control unit 200 is also connected to various power sources such as a charging power source E1, a developing power source E2, a supply power source E3, a regulating power source E4, and a transfer power source E5. The control unit 200 is also connected to an exposure device 3, various sensors, and the like. The control unit 200 is also optionally connected to external devices (not shown) such as an image reading device or a personal computer. The control unit 200 can control the operation of each unit of the image forming apparatus 100 to form an image in response to an image signal input from the external device. In this embodiment, the developing roller 41, the supply roller 42, and the agitating member 46 of the developing device 4 are driven by a driving force transmitted from the drum drive motor D1, but at least one of these may be provided with a dedicated driving source.

[0052] 3.Charging roller <Schematic configuration of charging roller> 4 is a schematic perspective view of an example of the charging roller 2. The charging roller 2 has a conductive support (metal core, mandrel) 21 and a conductive layer (elastic layer) 22 formed around the support 21. The conductive layer 22 may have any configuration as long as it satisfies the above-mentioned time constant condition, and specific examples include a configuration having only the conductive elastic layer 22, and a configuration in which a conductive resin layer is further provided on the surface (outer peripheral surface, outer surface) of the conductive elastic layer 22.

[0053] <Conductive support> The support 21 used in the charging roller 2 is conductive and has the function of supporting the elastic layer 22 and other components provided therearound. Examples of materials for the support 21 include metals such as iron, copper, stainless steel, aluminum, and nickel, and alloys thereof. Furthermore, the surface of these materials may be plated or otherwise treated to impart scratch resistance. Furthermore, the support 21 may also be a mandrel in which the surface of a resin base material is coated with a metal or the like to impart electrical conductivity to the surface, or a mandrel made from a conductive resin composition.

[0054] An adhesive layer serving as an adhesive may be provided between the conductive support 21 and the elastic layer 22. In this case, the adhesive is preferably conductive. To achieve conductivity, the adhesive may be appropriately selected from known conductive agents (e.g., ionic conductive agents and electronic conductive agents), and may be used alone or in combination of two or more.

[0055] Examples of binders for adhesives include thermosetting resins and thermoplastic resins, and known resins such as urethane, acrylic, polyester, polyether, and epoxy can be used. Examples of adhesives include Metalock N33 (manufactured by Toyo Kagaku Kenkyusho). Known methods for applying the adhesive include roll coating, sponge coating, and spray coating.

[0056] The adhesive layer between the conductive support 21 and the elastic layer 22 may be provided over the entire surface where the conductive support 21 and the elastic layer 22 contact, or may be provided over a partial area of ​​that surface. For example, in the longitudinal direction (rotational axis direction) of the charging roller 2, an adhesive layer may be provided only in a range of 5 mm to 20 mm in width at both ends of the surface where the conductive support 21 and the elastic layer 22 contact. Note that with respect to a numerical range, the symbol "to" means that the numerical values ​​before and after it are included. The thickness of the adhesive layer is preferably 1 μm to 10 μm from the viewpoint of adhesion between the support (mandrel) 21 and the elastic layer 22.

[0057] <Conductive layer> There are no limitations on the configuration of the conductive layer (elastic layer) 22 as long as the charge transport characteristics of the conductive layer 22 satisfy the above-mentioned time constant condition. The conductive elastic layer 22 can be made of one or more types of elastic materials such as rubber that are used in the elastic layers (conductive elastic layers) of conventional charging rollers. Examples of rubber include: urethane rubber, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, acrylonitrile rubber, epichlorohydrin rubber, and alkyl ether rubber.

[0058] In addition, the conductivity of the elastic layer 22 can be adjusted to a predetermined value by appropriately using a conductive agent. The electrical resistance value of the elastic layer 22 can be adjusted by appropriately selecting the type and amount of the conductive agent. The preferred range of the electrical resistance value is 10 2 ~10 8 Ω·cm, and a more preferable range is 10 3 ~10 6 The electrical resistance is Ω·cm. In addition, conductive carbon such as Ketjenblack EC, acetylene black, rubber carbon, oxidized color (ink) carbon, and pyrolytic carbon can also be used as the conductive agent for the elastic layer 22. In addition, graphite such as natural graphite and artificial graphite can also be used as the conductive agent for the elastic layer 22. Inorganic or organic fillers and cross-linking agents may be added to the elastic layer 22.

[0059] <Elastic layer with matrix domain structure> A conductive roller having an elastic layer 22 with a matrix domain structure is preferably used as the charging roller 2. The matrix domain structure is a structure having a matrix and a plurality of domains dispersed in the matrix.

[0060] <Method for forming matrix domain structure> A specific example of a means for forming the elastic layer 22 having the matrix domain structure of the charging roller 2 will be described.

[0061] A structure having a domain as a conductive phase and a matrix as an insulating phase can be obtained by a method of phase separation or dispersion of a conductive material and an insulating material, as long as the effects of the present invention are not impaired. Among these, an elastic layer (conductive layer) 22 having a matrix-domain phase-separated structure formed by phase separation between a matrix containing a first rubber and a conductive second rubber is preferred. The matrix-domain structure of the conductive layer 22 allows charge to be transported through the conductive domain, making it easier to achieve a time constant within the range of the present invention. It is believed that the charge stops for a certain period of time at the interface between the conductive domain and the insulating matrix, accumulates within the domain, and then conducts between the domains, thereby achieving a state in which an abundant amount of charge is present within the conductive layer 22.

[0062] The elastic layer 22 having a matrix domain structure of the charging roller 2 is preferably a conductive member that satisfies the following components (i) and (ii). Hereinafter, the conductive member will be described using the charging roller 2 as an example, but the conductive member is not limited to the charging roller 2. Component (i): The volume resistivity of the matrix is ​​1.0 × 10 8 Ω·cm or greater than 1.0×10 17 Must be Ω·cm or less. Component (ii): The volume resistivity of the domain is 1.0 × 10 1 Ω cm or more, 1.0×10 4 Must be Ω·cm or less.

[0063] 5 is a schematic partial cross-sectional view of the elastic layer 22 (showing a cross section substantially perpendicular to the rotation axis of the charging roller 2). The elastic layer 22 has a matrix-domain structure having a matrix 22a and domains 22b. The domains 22b contain conductive particles as an electronic conductive agent.

[0064] <Method for measuring volume resistivity of matrix> The volume resistivity of the matrix can be measured with a microprobe by cutting a thin section of the elastic layer 22. Examples of the means for cutting a thin section include a sharp razor, a microtome, and a focused ion beam (FIB) method.

[0065] When preparing thin sections, it is necessary to eliminate the influence of domains and measure the volume resistivity of only the matrix, so it is necessary to prepare thin sections with a thickness smaller than the interdomain distance measured in advance using a scanning electron microscope (SEM) or transmission electron microscope (TEM), etc. Therefore, the preferred method for thinning is a method that can prepare very thin samples, such as a microtome.

[0066] To measure the volume resistivity, first, one side of the flake is grounded, and then the locations of the matrix and domains in the flake are identified. These locations can be identified using a scanning probe microscope (SPM), atomic force microscope (AFM), or other means capable of measuring the volume resistivity or hardness distribution of the matrix and domains. Next, a probe is brought into contact with the matrix, and a DC voltage of 50 V is applied for 5 seconds to measure the arithmetic mean of the ground current for 5 seconds. The electrical resistance is then calculated by dividing the arithmetic mean by the voltage. The flake thickness can then be used to convert the value into volume resistivity. In this case, a means capable of measuring the flake shape, such as an SPM or AFM, is preferred, as it allows the flake thickness and volume resistivity to be measured.

[0067] The volume resistivity of the matrix in the cylindrical conductive member (charging roller 2) can be measured as follows: The elastic layer 22 is divided into four regions in the circumferential direction and into five regions in the longitudinal direction (direction of the rotation axis of the charging roller 2), and one thin sample is cut out from each of these regions. After obtaining the above-mentioned measurements, the arithmetic mean value of the volume resistivities of a total of 20 samples is calculated.

[0068] <Volume resistivity of domain> The volume resistivity of each domain is smaller than that of the matrix. This is preferable because it makes it easier to limit the charge transport path to a path that passes through multiple domains while suppressing the movement of unintended charges in the matrix. In addition, the volume resistivity of the domain is preferably at least five orders of magnitude larger than that of the matrix. The volume resistivity of the domain is 1.0 × 10 1 Ω cm or more, 1.0×10 4 It is preferable to keep the volume resistivity of the domains at Ω·cm or less. By lowering the volume resistivity of the domains, it is possible to suppress the migration of unintended charges in the matrix, while more effectively limiting the charge transport path to a path that passes through multiple domains. By lowering the volume resistivity of the domains to the above range, the amount of charge that moves within the domains can be dramatically improved, effectively limiting the charge transport path to a path that passes through the domains.

[0069] The volume resistivity of the domain can be adjusted by using a conductive agent in the rubber component of the domain to set the conductivity to a predetermined value. The volume resistivity of the domain can be adjusted by appropriately selecting the type of electronic conductive agent and the amount added. When the volume resistivity of the domain is 1.0 × 10 1 Ω cm or more, 1.0×10 4 The conductive agent used to control the resistivity to Ω·cm or less is preferably an electronic conductive agent that can greatly change the volume resistivity from high to low depending on the amount dispersed.

[0070] Examples of the electronic conductive agent to be blended into the domain include oxides such as carbon black, graphite, titanium oxide, and tin oxide; metals such as Cu and Ag; and particles coated with an oxide or metal to make them conductive. If necessary, two or more of these conductive agents may be blended in appropriate amounts.

[0071] Among the above-mentioned electronic conductive agents, it is preferable to use conductive carbon black, which has a high affinity with rubber and allows easy control of the distance between the electronic conductive agents. The type of carbon black to be compounded into the domain is not particularly limited. Specific examples include gas furnace black, oil furnace black, thermal black, lamp black, acetylene black, and ketjen black.

[0072] If necessary, fillers, processing aids, crosslinking aids, crosslinking accelerators, antioxidants, crosslinking accelerator aids, crosslinking retarders, softeners, dispersants, colorants, and the like, which are generally used as compounding agents for rubber, may be added to the rubber composition for the domains within a range that does not impair the effects of the present invention.

[0073] <Method for measuring volume resistivity of domain> The volume resistivity of the domain may be measured in the same manner as in the above-described method for measuring the volume resistivity of the matrix, except that the measurement location is changed to a location corresponding to the domain and the applied voltage when measuring the current value is changed to 1 V.

[0074] <Method of manufacturing the charging roller> The conductive member (charging roller 2) can be formed, for example, by a method including the following steps (i) to (iv). Step (i): preparing a domain-forming rubber mixture (hereinafter also referred to as "CMB") containing carbon black and a second rubber; Step (ii): preparing a matrix-forming rubber mixture (hereinafter also referred to as "MRC") containing a first rubber; Step (iii): A step of kneading the CMB and the MRC to prepare a rubber mixture having a matrix-domain structure. Step (iv): A step of forming a layer of the rubber mixture prepared in step (iii) on a conductive support 21 directly or via another layer, and curing the layer of rubber composition to form an elastic layer 22.

[0075] The components (i) and (ii) can be controlled by, for example, selecting the materials used in each of the above steps and adjusting the manufacturing conditions, as will be explained below.

[0076] First, regarding component (i), the volume resistivity of the matrix is ​​determined by the composition of the MRC. The first rubber used in the MRC may be at least one low-conductivity rubber, such as natural rubber, butadiene rubber, butyl rubber, acrylonitrile butadiene rubber, urethane rubber, silicone rubber, fluororubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, or polynorbornene rubber. Furthermore, as long as the volume resistivity of the matrix can be kept within the above-mentioned range, fillers, processing aids, crosslinking agents, crosslinking aids, crosslinking accelerators, crosslinking accelerator aids, crosslinking retarders, antioxidants, softeners, dispersants, and colorants may be added to the MRC as needed. On the other hand, in order to keep the volume resistivity of the matrix within the above-mentioned range, it is preferable not to include an electronic conductive agent such as carbon black in the MRC.

[0077] Regarding the component (ii), the volume resistivity of the domain can be adjusted by the amount of the electronic conductive agent in the CMB. For example, when the DBP oil absorption is 40 cm 3 / 100g or more, 170cm 3 Take the case of using conductive carbon black with a conductivity of 100 g or less. In this case, component (ii) can be achieved by preparing the CMB so that the conductive carbon black is contained in an amount of 40 mass % or more and 200 mass % or less, based on the total mass of the CMB. Specific examples of the second rubber that can be used in the CMB include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), ethylene-propylene rubber (EPM, EPDM), chloroprene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U). At least one of these can be used.

[0078] <How to check the matrix domain structure> The presence of the matrix domain structure in the elastic layer 22 can be confirmed by preparing a thin section from the elastic layer 22 and closely observing the fracture surface formed on the thin section.

[0079] Examples of the means for thinning include a sharp razor, a microtome, an FIB, etc. In order to observe the matrix domain structure more accurately, the thin section for observation may be subjected to pretreatment such as staining or vapor deposition, which favorably enhances the contrast between the domains as the conductive phase and the matrix as the insulating phase.

[0080] The presence of a matrix domain structure can be confirmed by observing the fracture surface of a thin section that has been formed and pretreated as necessary using a laser microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), etc. Observation using a scanning electron microscope (SEM) is preferred as it allows for a simple and accurate confirmation of the sea-island structure (matrix-domain structure).

[0081] A thin section of the elastic layer 22 is obtained using the above-described method, and the surface of the thin section is observed at 1000x to 10000x magnification to obtain an image. Then, using image processing software such as ImageProPlus (manufactured by Media Cybernetics), an 8-bit grayscale image is obtained, resulting in a monochrome image with 256 gradations. The image is then inverted and binarized so that the domains within the fracture surface appear white, and an analysis image is obtained. The presence or absence of a matrix-domain structure can be determined from the analysis image, which has been image-processed to distinguish the domains and matrix through binarization.

[0082] 5, when the analysis image includes a structure in which a plurality of domains 22b exist in an isolated state in a matrix 22a, it is possible to confirm the presence of a matrix domain structure in the elastic layer 22. The isolated state of the domains may be such that each domain is arranged in a state in which it is not connected to other domains, the matrix is ​​connected in the image, and the domains are separated by the matrix.

[0083] <Conductive surface layer> The charging roller 2 preferably has a conductive surface layer 23 on the surface of the conductive elastic layer 22 as described above. Figure 6 is a schematic cross-sectional view of the charging roller 2 provided with the surface layer 23 (showing a cross section substantially perpendicular to the rotation axis of the charging roller 2). By providing the conductive surface layer 23, charge migration in the surface direction on the outermost surface becomes more efficient, thereby making it possible to further reduce the time constant. The conductive surface layer 23 may be formed by adding a conductive material to a binder.

[0084] The preferred volume resistivity of the conductive surface layer 23 is in a range that satisfies the above-mentioned time constant condition, and specifically, is 1.0×10 5 Ω cm or more, 1.0×10 9 It is preferable that the resistivity is Ω·cm or less.

[0085] <Binder> Known binders can be used for the surface layer 23. Examples include resin, natural rubber, vulcanized natural rubber, and synthetic rubber. Resins such as thermosetting resins and thermoplastic resins can be used. Among these, fluororesins, polyamide resins, acrylic resins, polyurethane resins, silicone resins, and butyral resins are more preferred.

[0086] The surface layer 23 preferably contains a conductive material. Examples of conductive materials that can be used include ionic conductive agents and electronic conductive agents. Examples of ionic conductive agents include inorganic ionic substances such as lithium perchlorate, sodium perchlorate, and calcium perchlorate; cationic surfactants such as lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, trioctyl propyl ammonium bromide, and modified aliphatic dimethyl ethyl ammonium ethosulfate; zwitterionic surfactants such as lauryl betaine, stearyl betaine, and dimethyl alkyl lauryl betaine; quaternary ammonium salts such as tetraethyl ammonium perchlorate, tetrabutyl ammonium perchlorate, and trimethyl octadecyl ammonium perchlorate; and organic acid lithium salts such as lithium trifluoromethanesulfonate. These can be used alone or in combination.

[0087] Examples of electronic conductive agents include: fine particles and fibers of metals such as aluminum, palladium, iron, copper, and silver, and metal oxides such as titanium oxide, tin oxide, and zinc oxide that have been treated to be conductive; composite particles in which the surfaces of the above-mentioned metal fine particles, fibers, and metal oxides have been treated by electrolysis, spray coating, or mixing and shaking; and carbon powders such as furnace black, thermal black, acetylene black, ketjen black, PAN (polyacrylonitrile)-based carbon, and pitch-based carbon.

[0088] Examples of furnace blacks include SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, I-ISAF-HS, HAF-HS, HAF, HAF-LS, T-HS, T-NS, MAF, FEF, GPF, SRF-HS-HM, SRF-LM, ECF, and FEF-HS. Examples of thermal blacks include FT and MT. These conductive agents can be used alone or in combination.

[0089] The conductive agent preferably has an average particle size of 0.01 μm to 0.9 μm, and more preferably 0.01 μm to 0.5 μm. This range makes it easier to control the volume resistivity of the matrix. The amount of conductive agent added to the surface layer 23 is preferably 2 parts by mass to 80 parts by mass, and more preferably 20 parts by mass to 60 parts by mass, per 100 parts by mass of the binder.

[0090] The surface of the conductive agent may be surface-treated. Usable surface treatment agents include organosilicon compounds such as alkoxysilanes, fluoroalkylsilanes, and polysiloxanes; various silane-, titanate-, aluminate-, and zirconate-based coupling agents; and oligomers or polymer compounds. These may be used alone or in combination of two or more. Preferred are organosilicon compounds such as alkoxysilanes and polysiloxanes; various silane-, titanate-, aluminate-, or zirconate-based coupling agents; and more preferred are organosilicon compounds.

[0091] The surface layer 23 may be subjected to a surface treatment. Examples of the surface treatment include a surface processing treatment using UV or electron beams, and a surface modification treatment in which a compound or the like is attached to or impregnated into the surface. The surface layer 23 preferably has a thickness of 0.1 μm or more and 100 μm or less. The thickness of the surface layer 23 is more preferably 1 μm or more and 50 μm or less.

[0092] <Method for forming the surface layer> The surface layer 23 can be formed by a coating method such as electrostatic spray coating or dipping coating. Alternatively, the surface layer 23 can be formed by adhering or covering a sheet-shaped or tube-shaped layer that has been previously formed to a predetermined thickness. Alternatively, the surface layer 23 can be formed by curing and molding a material into a predetermined shape in a mold. Among these, the coating method is preferred, in which a coating is applied to form a coating film. When forming a layer by a coating method, the solvent used in the coating solution may be any solvent that can dissolve the binder. Specific examples include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide; ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; and aromatic compounds such as xylene, ligroin, chlorobenzene, and dichlorobenzene. These solvents are appropriately selected depending on the binder used. As a method for dispersing the binder, particles, etc. in the coating liquid, known solution dispersion means such as a ball mill, a sand mill, a paint shaker, a dyno mill, or a pearl mill can be used.

[0093] 4. Cleaning roller <Cleaning roller configuration> 7 is a schematic perspective view of an example of the cleaning roller 8. The cleaning roller 8 is a cleaning member that comes into contact with the charging roller 2 to clean the charging roller 2. The cleaning roller 8 has a rotating shaft (core metal, mandrel) 81 and an elastic layer 82 that is formed around the rotating shaft 81 and comes into contact with the charging roller 2, and the elastic layer 82 is made of a foam (foamed elastic layer).

[0094] Examples of materials for the foamed elastic layer 82 include foamable resins (such as polyurethane, polyethylene, polyamide, or polypropylene), rubber materials (such as silicone rubber, fluororubber, urethane rubber, EPDM (ethylene-propylene-diene rubber), NBR (acrylonitrile-butadiene copolymer rubber), CR (chloroprene rubber), chlorinated polyisoprene, isoprene, acrylonitrile-butadiene rubber, styrene-butadiene rubber, hydrogenated polybutadiene, and butyl rubber), or blends of two or more of these. If necessary, these materials may contain additives such as foaming aids, foam stabilizers, catalysts, curing agents, plasticizers, or vulcanization accelerators.

[0095] The foamed elastic layer 82 is preferably made of a tensile-resistant foamed polyurethane, particularly from the viewpoint of preventing scratches on the surface of the object to be cleaned (the charging roller 2) due to friction and preventing tearing or breakage over the long term. Examples of polyurethane include reaction products of polyols (such as polyester polyols, polyether polyols, polyesters, and acrylic polyols) with isocyanates (such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, tolylene diisocyanate, and 1,6-hexamethylene diisocyanate), and may also contain a chain extender (1,4-butanediol, trimethylolpropane).

[0096] Polyurethane foaming is generally carried out using a foaming agent such as water or an azo compound (e.g., azodicarbonamide, azobisisobutyronitrile, etc.) If necessary, foaming aids such as a foaming assistant, a foam stabilizer, and a catalyst may be added to the foamed polyurethane.

[0097] Here, in order to remove deposits (contamination such as toner and external additives) on the surface of the charging roller 2, it is desirable that the contact pressure (contact state) of the cleaning roller 8 against the charging roller 2 be 40 mN / mm or less. This contact pressure may be approximately 0 mN / mm (simple contact state). If the cleaning roller 8 is brought into contact with the charging roller 2 with a contact pressure exceeding 40 mN / mm, the charging roller 2 will be braked by the contact pressure from the cleaning roller 8, preventing the charging roller 2 from rotating properly and potentially resulting in poor image quality due to insufficient charging.

[0098] The cleaning roller 8 rotates in contact with the surface of the charging roller 2, thereby removing at least some of the deposits from the surface of the charging roller 2. If the surface layer of the cleaning roller 8 is made of a foam, the deposits can be stored in the cells, allowing the surface of the charging roller 2 to be cleaned for a longer period of time.

[0099] <Cleaning Roller Manufacturing Method> Next, a method for manufacturing the cleaning roller 8 will be described.

[0100] First, a polyurethane foam is produced. For example, a polyether polyol is used as the polyol. Water as a blowing agent, triethylenediamine and tin octoate as catalysts, and melamine powder are added and mixed, and then tolylene diisocyanate as a polyisocyanate is added and foamed to prepare a polyurethane foam. The resulting polyurethane foam is cut into a plate, and a hole is made in it for inserting the rotating shaft 81 of the cleaning roller 8. The rotating shaft 81 of the cleaning roller 8 is then inserted into the hole and fixed, and the surface (periphery, outer surface) is polished to produce the cleaning roller 8.

[0101] 5.Measuring method for the time constant of a charging roller The time constant according to the present invention is obtained by the following impedance measurement.

[0102] Impedance can be measured by the following method. To eliminate the influence of contact resistance between the conductive member (charge roller 2) and the measurement electrode during impedance measurement, the following procedure is used: A low-resistance thin film is deposited on the surface of the conductive member, and the thin film is used as an electrode. The conductive support 21 is used as a ground electrode, and the impedance is measured via two terminals. Examples of methods for forming the thin film include metal deposition, sputtering, applying a metal paste, and attaching a metal tape. Among these, a method of forming a thin metal film, such as platinum or palladium, as an electrode by deposition is preferred from the perspective of reducing contact resistance with the conductive member. When forming a thin metal film on the surface of a conductive member, considering the simplicity and uniformity of the thin film, it is preferable to use a vacuum deposition apparatus equipped with a mechanism for gripping the conductive member (charge roller 2) and, for conductive members with a cylindrical cross section, an additional rotation mechanism.

[0103] For conductive members with a curved cross section, such as a circular one, it is difficult to connect the above-mentioned metal thin film as the measurement electrode to the impedance measurement device, so the following method is preferably used. Specifically, a metal thin film electrode with a width of approximately 10 mm to 20 mm is formed in the longitudinal direction of the conductive member, and then a metal sheet is tightly wrapped around it. The metal sheet is then connected to the measurement electrode extending from the measurement device for measurement. This allows the measurement device to conveniently acquire electrical signals from the conductive layer (elastic layer) 22 of the conductive member, enabling impedance measurement. The metal sheet may be any metal sheet with an electrical resistance equivalent to that of the metal part of the connection cable of the measurement device when measuring impedance; for example, aluminum foil or metal tape can be used. The impedance measurement device can be an impedance analyzer, network analyzer, spectrum analyzer, or other device with a resistance of 1.0 x 10 7 Any device capable of measuring impedance in a frequency range up to 100 Hz may be used. Among these, it is preferable to perform measurement using an impedance analyzer, taking into account the electrical resistance range of the conductive member.

[0104] The impedance measurement conditions are as follows: An impedance measuring device was used, and the impedance was measured at 1.0 x 10 -2 Hz~1.0×10 7 Impedance is measured in the Hz frequency range. Measurements are performed under an environment with a temperature of 23°C and a humidity of 50% RH (relative humidity). To reduce measurement variability, it is preferable to set five or more measurement points per digit of frequency. The amplitude of the AC voltage is 1 V. Regarding the measurement voltage, measurements may be performed while applying a DC voltage, taking into account the voltage share applied to the conductive member (charging roller 2) in the image forming apparatus 100. Specifically, measurements may be performed while applying a DC voltage of 10 V or less superimposed on an oscillating voltage. This is suitable for quantifying the characteristics of charge transport and accumulation.

[0105] Next, a method for calculating the time constant will be described. The measurement results obtained under the above conditions are analyzed using, for example, spreadsheet software (for example, "Windows Excel" (trade name, manufactured by Microsoft Corporation) as follows: The absolute value of the imaginary term obtained by impedance measurement is plotted on a double logarithmic graph against the measurement frequency. The frequency fp [Hz] at which this imaginary term shows a maximum value is calculated, and the time constant τ = 1 / 2πfp (= 1 / (2π × fp)) [sec] is calculated, thereby obtaining the time constant according to the present invention.

[0106] When measuring the time constant of a cylindrical conductive member (charge roller 2), the longitudinal direction (the direction of the rotation axis of the charge roller 2) is divided into five equal parts, and measurements are taken at five arbitrary locations within each of these areas, and the arithmetic average of the measured time constants at the five locations is calculated.

[0107] 6. Examples and Comparative Examples The charging roller, the process cartridge, and the image forming apparatus will be described in detail below with reference to specific examples, but the technical scope of the present invention is not limited to these.

[0108] First, a method for manufacturing the charging roller 2 in the examples and comparative examples will be specifically illustrated and explained.

[0109] The table in FIG. 16 shows an outline of the configuration of each charging roller in Examples 1 to 5 and Comparative Examples 1 to 4 described below.

[0110] 6-1. Example 1 6-1-1. Manufacture of charging roller (1) <Preparation of Unvulcanized Domain Composition> The materials shown in Table 1 in their types and amounts were mixed in a pressure kneader to obtain an unvulcanized domain composition (1).

[0111] [Table 1]

[0112] <Preparation of Unvulcanized Rubber Composition> The materials shown in Table 2 in their types and amounts were mixed in a pressure kneader to obtain an unvulcanized rubber composition (1).

[0113] [Table 2]

[0114] <Preparation of Rubber Composition for Forming Elastic Layer> The materials shown in Table 3 in their types and amounts were mixed in an open roll to prepare a rubber composition (1) for molding the elastic layer.

[0115] [Table 3]

[0116] <Forming of elastic layer> A round bar with a total length of 252 mm and an outer diameter of 6 mm was prepared, the surface of which was made of free-cutting steel and electroless nickel-plated. Next, using a roll coater, an adhesive, Metalock U-20 (trade name, manufactured by Toyo Kagaku Kenkyusho Co., Ltd.), was applied to the entire circumference of the round bar over a range of 230 mm, excluding 11 mm at each end. In Example 1, the round bar coated with the adhesive was used as the conductive support 21.

[0117] Next, a die with an inner diameter of 12.5 mm was attached to the tip of a crosshead extruder having a mechanism for feeding the conductive support 21 and a mechanism for discharging the unvulcanized rubber roller. The temperatures of the extruder and the crosshead were adjusted to 80°C, and the conveying speed of the conductive support (mandrel) 21 was adjusted to 60 mm / sec. Under these conditions, the unvulcanized rubber composition (1) was fed from the extruder, and the conductive support 21 was coated with the unvulcanized rubber composition in the crosshead, thereby obtaining an unvulcanized rubber roller (1).

[0118] Next, the unvulcanized rubber roller (1) was placed in a hot air vulcanizing furnace at 170°C and heated for 60 minutes to vulcanize the unvulcanized rubber composition (1), thereby obtaining a roller having an elastic layer formed around the conductive support 21. Thereafter, 10 mm of each end of the elastic layer 22 was cut off, so that the longitudinal length of the portion where the elastic layer 22 was provided was 232 mm.

[0119] Finally, the surface of the elastic layer 22 was polished with a grindstone, thereby obtaining an elastic layer roller (1) having a diameter of 8.5 mm at the longitudinal center and 8.42 mm at positions 90 mm from the longitudinal center to both ends.

[0120] The charging roller (1) of Example 1 was produced by forming a surface layer (1) on an elastic layer roller (1) in the following procedure.

[0121] <Preparation of coating liquid for surface layer> A surface layer coating liquid (1) for forming the surface layer (1) was prepared as follows.

[0122] Under a nitrogen atmosphere, 27 parts by mass of polymeric MDI (trade name: Millionate MR200, manufactured by Nippon Polyurethane Industry Co., Ltd.) and 100 parts by mass of polycarbonate polyol (trade name: T5652, manufactured by Asahi Kasei Chemicals Corporation) were slowly added dropwise to the reaction vessel while maintaining the temperature inside the reaction vessel at 65°C. After the addition was completed, the mixture was allowed to react at 65°C for 2 hours. The resulting reaction mixture was cooled to room temperature to obtain an isocyanate-terminated prepolymer P-1 having an isocyanate group content of 4.3%.

[0123] 54.9 parts by mass of isocyanate-terminated prepolymer P-1, 41.52 parts by mass of polycarbonate polyol (trade name: T5652, manufactured by Asahi Kasei Chemicals Corporation), and 28 parts by mass of carbon black (trade name: MA230, manufactured by Mitsubishi Chemical Corporation, number-average particle diameter: 30 nm) were dissolved in methyl ethyl ketone (MEK) to adjust the solids content to 27% by mass. In this manner, mixed solution (1) was prepared. 270 g of mixed solution (1) and 200 g of glass beads with an average particle size of 0.8 mm were placed in a 450 mL glass bottle and dispersed for 12 hours using a paint shaker disperser. After dispersion, 15 parts by mass of urethane particles with an average particle size of 7.0 μm (trade name: Dimic Beads UCN-5070D, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) were added. The mixture was then dispersed for an additional 15 minutes, and the glass beads were removed to obtain surface layer coating solution (1).

[0124] <Formation of a conductive surface layer> The elastic layer roller (1) was oriented with its longitudinal direction in the vertical direction, and its upper end was gripped and immersed (dipped) in the surface layer coating liquid (1) and then pulled up. In this dip coating, the immersion time was 9 seconds, and the roller pull-up speed was adjusted so that the initial speed was 22 mm / sec and the final speed was 8 mm / sec, with the speed varying linearly with time between 22 mm / sec and 8 mm / sec. After coating, the roller was air-dried at 23°C for 30 minutes. The roller was then dried in a hot air circulation dryer at 80°C for 1 hour and then at 160°C for 1 hour, forming a dried coating film of the surface layer coating liquid (1) on the elastic layer roller (1).

[0125] Furthermore, the cumulative amount of ultraviolet light with a wavelength of 254 nm is 9000 mJ / cm 2 The surface of the dried film was irradiated with ultraviolet light so that the outermost skin layer of the dried film was removed, and a surface layer 23 was formed in which the conductive particles (conductive carbon black) in the dried film were exposed to the surface. A low-pressure mercury lamp (manufactured by Toshiba Lighting & Technology Corporation) was used as the ultraviolet light source. In this way, the charging roller (1) of Example 1 was produced.

[0126] <Measurement of time constant> As a pretreatment, platinum was vapor-deposited onto the surface of the rotating charging roller to create a measurement electrode. At this time, masking tape was used to create an electrode 1.5 cm wide and uniform in the circumferential direction. By forming this electrode, it is possible to minimize the contribution of differences in the contact area between the measurement electrode and the conductive member (charging roller) due to the surface roughness of the charging roller.

[0127] Next, an aluminum sheet was tightly wrapped around the electrode, and the electrode was connected to the measurement electrode of an impedance measuring device (trade names: Solartron 1260 and Solartron 1296; manufactured by Solartron Corporation) via the aluminum sheet.

[0128] Fig. 8 is a schematic perspective view of the charging roller with the measurement electrode formed thereon. Fig. 9 is a schematic cross-sectional view of the charging roller 2 with the measurement electrode formed thereon (showing a cross-section substantially perpendicular to the rotation axis of the charging roller 2). Fig. 10 is a schematic diagram of this measurement system.

[0129] As shown in Figures 8 and 9, a platinum vapor-deposited layer 73 was formed on a charging roller 2 having a conductive support 21 and a conductive layer (elastic layer) 22 with a matrix domain structure, and an aluminum sheet 74 was wrapped around this. As shown in Figure 9, it is important that the conductive layer 22 with a matrix domain structure is sandwiched between the conductive support 21 and the platinum vapor-deposited layer (measurement electrode) 73. Then, as shown in Figure 10, the aluminum sheet 74 was connected to the measurement electrode on the side of an impedance measurement device 70 (Solatron 1260 and Solartron 1296, manufactured by Solartron Corporation). Impedance measurements were performed using the conductive support 21 and the aluminum sheet 74 as the two electrodes for measurement.

[0130] Impedance measurements were performed in an environment with a temperature of 23°C and a relative humidity of 50%, with an AC voltage of 1Vpp and a frequency of 1.0 x 10 -2 Hz~1.0×10 7The measurement was performed at 100 Hz (measurements were taken at five points each time the frequency changed by one digit), and the impedance measurement results were obtained. Next, as shown in FIG. 15, the measurement results were used to plot the absolute value |Z″| of the imaginary term obtained by the impedance measurement on a double logarithmic graph against the measurement frequency f. The frequency fp [Hz] at which this imaginary term takes its maximum value was calculated, and the time constant τ=1 / 2πfp [sec] was calculated, thereby obtaining the time constant according to the present invention.

[0131] In Example 1, the time constant τ of the charging roller (1) was 1.20E-3 [sec]. For convenience, it is assumed that the time constant τ is 1.20×10 -3 is sometimes written as "1.20E-3". The same applies to other values ​​for the time constant τ and the rotation time A described below.

[0132] 6-1-2. Manufacturing of cleaning rollers The polyol used was a polyether polyol (product name: CARADOL56-16, manufactured by SHELL) with an average molecular weight of 3,000, obtained by addition polymerization of propylene oxide to glycerin. 100 g of this polyether polyol was mixed with 4.0 g of water as a blowing agent, 0.1 g of triethylenediamine and 0.23 g of stannous octoate (stannous octoate) as catalysts, and 30 g of melamine powder (manufactured by Mitsui Chemicals, Inc., average particle size 1-10 μm) and stirred for 5 minutes in a mixer. Then, 51.3 g of tolylene diisocyanate (product name: TDI-80, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added and stirred for 7 seconds to obtain a mixed solution. TDI-80 is a mixture of 80% by mass of 2,4-tolylene diisocyanate and 20% by mass of 2,6-tolylene diisocyanate. The isocyanate index was set to 108.

[0133] The mixture was then quickly poured into a polyethylene bag measuring 30 cm in length and 30 cm in width and foamed to obtain a polyurethane foam. The melamine powder content in the polyurethane foam was 16.5% [[30 / (100+51.3+30)]×100]. The average cell diameter of the obtained polyurethane foam according to JIS K6400 was 400-600 μm and the density was 50 kg / m. 3 It was.

[0134] After foaming, the polyethylene bag was removed and the foam was cut into a plate with a thickness of 18 mm. Next, a hole with a diameter of 4 mm was drilled to insert the rotating shaft 81 of the cleaning roller 8. Separately, a rotating shaft 81 made of steel with electroless nickel plating was prepared, and an ethylene-vinyl acetate hot melt adhesive was applied to its surface to a thickness of approximately 100 μm. This rotating shaft 81 was inserted into the hole in the polyurethane foam, induction heated, and then cooled, thereby fixing the rotating shaft 81 within the polyurethane foam. The surface of the polyurethane foam was then polished to produce a cleaning roller 8 with an outer diameter of 6 mm.

[0135] In Example 1, the cleaning roller 8 was configured to be in contact with the charging roller 2 (the charging roller (1)) with a contact pressure of 20 mN / mm and to rotate following the rotation of the charging roller 2 (the charging roller (1)).

[0136] 6-1-3. Shaft support structure of cleaning roller and charging roller 11 is a schematic cross-sectional view showing the shaft support structure of the charging roller 2 and cleaning roller 8 in Example 1 (showing a cross section substantially perpendicular to the rotation axis of the charging roller 2). Note that while Fig. 11 shows the structure of one end side in the rotation axis direction of the charging roller 2, the structure of the other end side is similar (substantially symmetrical with respect to a plane passing through the center of the rotation axis direction of the charging roller 2).

[0137] In the first embodiment, as shown in FIG. 11 , the rotation shaft of the charging roller 2 (both ends of the support 21) and the rotation shaft of the cleaning roller 8 (both ends of the rotation shaft 81) are rotatably supported by bearing members 51 at fixed positions so that the distance between the two rotation shafts is constant. The bearing members 51 are slidably supported by the cleaning container 9. A pressure spring 61, which is a biasing member serving as a biasing means, is provided between the bearing member 51 and the cleaning container 9. The pressure spring 61 biases the bearing member 51 in a direction toward the rotation center of the photosensitive drum 1, i.e., along a straight line L1 (substantially parallel in this example). Therefore, the charging roller 2 is pressed against the photosensitive drum 1 and comes into contact with it.

[0138] 6-1-4. Contact position of cleaning roller and charging roller 11, the contact position between the cleaning roller 8 and the charging roller 2 was located on a line L1 passing through the rotation center of the photosensitive drum 1 and the rotation center of the charging roller 2. The contact position between the cleaning roller 8 and the charging roller 2 is represented by a midpoint in the direction of movement of the surface of the charging roller 2.

[0139] 6-1-5.Measuring method for charging roller rotation time The time it takes for the charging roller 2 to rotate from when a point on the surface of the charging roller 2 comes into contact with the cleaning roller 8 until it comes into contact with the cleaning roller 8 again is defined as the rotation time A [sec].

[0140] The rotation time A was calculated using the following method. First, a marking was made with an oil-based pen on the surface of the charging roller 2 at the contact point between the cleaning roller 8 and the charging roller 2. Next, the photosensitive drum 1 was rotated by hand, causing the charging roller 2 to rotate in a driven manner until the marked portion of the charging roller 2 came into contact with the cleaning roller 8 again. The rotation time A [sec] was then calculated based on the number of rotations of the charging roller 2 (how many rotations it makes) until the marked portion came into contact with the cleaning roller 8 again, the diameter (outer diameter) of the charging roller 2, and the process speed (the speed at which the surface of the charging roller 2 moves during charging).

[0141] In Example 1, the rotation time A was 0.116 [sec].

[0142] For Example 1, image evaluation 1 and image evaluation 2, which will be described later, were performed.

[0143] 6-2. Comparative Example 1 The charging roller 2 used was a charging roller (3) manufactured by the following manufacturing method. Other than that, the same as in Example 1.

[0144] For Comparative Example 1, similarly to Example 1, image evaluation 1 and image evaluation 2, which will be described later, were carried out.

[0145] As will be described later, in Comparative Example 1, the time constant of the charging roller 2 was large and the absolute value of the surface potential of the charging roller 2 dropped significantly, resulting in the occurrence of horizontal charging stripe images.

[0146] The charging roller (3) of Comparative Example 1 was produced by changing the unvulcanized rubber composition (1) and the rubber composition for molding elastic layer (1) of the charging roller (1) of Example 1 to the following unvulcanized rubber composition (3) and the rubber composition for molding elastic layer (3), respectively, and by carrying out ultraviolet treatment without forming the surface layer 23. Otherwise, the charging roller (3) was produced under the same conditions as the charging roller (1) of Example 1.

[0147] [Table 4]

[0148] [Table 5]

[0149] 6-3. Comparative Example 2 The charging roller 2 used was a charging roller (4) manufactured by the following manufacturing method. Other than that, the same as in Example 1.

[0150] For Comparative Example 2, similarly to Example 1, image evaluation 1 and image evaluation 2, which will be described later, were carried out.

[0151] As will be described later, in Comparative Example 2, the time constant of the charging roller 2 was smaller than that of Comparative Example 1, but larger than that of Example 1, and horizontal charging stripe images occurred in Image Evaluation 2.

[0152] The charging roller (4) of Comparative Example 2 was produced by changing the unvulcanized rubber composition (2) and the rubber composition for molding the elastic layer (2) of the charging roller (2) of Example 2 described later to the unvulcanized rubber composition (4) and the rubber composition for molding the elastic layer (4) described below, respectively. Otherwise, the charging roller (4) was produced under the same conditions as the charging roller (2) of Example 2. In Comparative Example 2, the surface layer 23 was produced using the surface layer coating liquid (2) in the same manner as in Example 2.

[0153] [Table 6]

[0154] [Table 7]

[0155] 6-4. Comparative Example 3 The charging roller 2 used was a charging roller (5) manufactured by the following manufacturing method. Other than that, the same as in Example 1.

[0156] For Comparative Example 3, similarly to Example 1, image evaluation 1 and image evaluation 2, which will be described later, were carried out.

[0157] In Comparative Example 3, when producing the charging roller (5), a surface layer coating liquid (3) was used in which the parts by mass of carbon black (product name: MA230, manufactured by Mitsubishi Chemical Corporation, number average particle size 30 nm) added was changed to 50 parts by mass in the surface layer coating liquid (2) of Comparative Example 2. Otherwise, production was carried out under the same conditions as for the charging roller (4).

[0158] 6-5. Comparative Example 4 Comparative Example 4 is the same as Comparative Example 2 except for the following configuration.

[0159] For Comparative Example 4, similarly to Example 1, image evaluation 1 and image evaluation 2, which will be described later, were carried out.

[0160] In Comparative Example 4, gears were attached to the charging roller 2 and the photosensitive drum 1, and the gear of the charging roller 2 received force from the gear of the photosensitive drum 1, thereby driving the charging roller 2 to rotate at a desired peripheral speed.

[0161] In Comparative Example 4, the peripheral speed of the charging roller 2 is set slower than the peripheral speed of the photosensitive drum 1 so that A / τ≧60.

[0162] In Comparative Example 4, the rotation time A was 0.160 [sec].

[0163] 6-6. Example 2 The charging roller 2 used was a charging roller (2) manufactured by the following manufacturing method. Other than that, the same as in Example 1.

[0164] In Example 2, in addition to performing image evaluation 1 and image evaluation 2, which will be described later, as in Example 1, image evaluation 3, which will be described later, was also performed.

[0165] The charge roller (2) of Example 2 was produced by changing the unvulcanized domain composition (1), unvulcanized rubber composition (1), and elastic layer molding rubber composition (1) of the charge roller (1) of Example 1 to the unvulcanized domain composition (2), unvulcanized rubber composition (2), and elastic layer molding rubber composition (2) described below, respectively, and further changing the surface layer coating liquid (1) of the charge roller (1) of Example 1 to the surface layer coating liquid (2), according to the procedure described below. Otherwise, the charge roller (2) was produced under the same conditions as the charge roller (1) of Example 1.

[0166] [Table 8]

[0167] [Table 9]

[0168] [Table 10]

[0169] A surface layer coating liquid (2) for forming the surface layer (2) was prepared as follows.

[0170] 100.0 parts by weight of acrylic polyol (trade name: DC2016, manufactured by Daicel Chemical Industries, Ltd.), 14 parts by weight of isocyanate A (trade name: Bestanate B1370, manufactured by Degussa Corporation), 80 parts by weight of isocyanate B (trade name: Duranate TPA-880E, manufactured by Asahi Kasei Chemicals Corporation), 35 parts by weight of carbon black (trade name: MA230, manufactured by Mitsubishi Chemical Corporation, number average particle diameter 30 nm), and 0.25 parts by weight of ether-modified dimethyl silicone oil (trade name: SH-28PA, manufactured by Toray Dow Corning Silicone Co., Ltd.) were dissolved in methyl ethyl ketone (MEK) and adjusted to a solids content of 25% by weight. Mixed solution (2) was prepared in this manner. 270 g of the mixed solution (2) and 200 g of glass beads with an average particle size of 0.8 mm were placed in a 450 mL glass bottle and dispersed for 24 hours using a paint shaker disperser. After dispersion, 30 parts by mass of acrylic particles having an average particle size of 10.0 μm (trade name: Ganzpearl GM-1001, manufactured by Aica Kogyo Co., Ltd.) were added, followed by further dispersion for 25 minutes, and the glass beads were removed to obtain a surface layer coating solution (2).

[0171] The elastic layer roller for the charging roller (2) was oriented with its longitudinal direction in the vertical direction, and its upper end was gripped and immersed (dipped) in the surface layer coating liquid (2) and then pulled up. In this dip coating, the immersion time was 9 seconds, and the roller pull-up speed was adjusted so that the initial speed was 20 mm / sec and the final speed was 12 mm / sec. The speed was changed linearly with time between 20 mm / sec and 12 mm / sec. After coating, the roller was air-dried at 23°C for 30 minutes. The roller was then dried in a hot air circulation dryer at 80°C for 1 hour and then at 160°C for 1 hour to form a dried coating film of the surface layer coating liquid (2) on the elastic layer roller for the charging roller (2), thereby producing the charging roller (2) of Example 2.

[0172] 6-7. Example 3 In Example 3, a roller formed by winding a sponge sheet spirally around a metal rotating shaft (herein also referred to as a "spiral roller") was used as the cleaning roller 8. Other than that, the example was the same as Example 2.

[0173] For Example 3, similarly to Example 2, image evaluation 1, image evaluation 2, and image evaluation 3, which will be described later, were performed.

[0174] FIG. 12 is a schematic side view of the cleaning roller 8 used in Example 3. As shown in FIG. 12, the cleaning roller 8 has a metal rotating shaft (core) 84 and a foamed elastic layer formed of a sponge sheet 85 spirally wound around the rotating shaft 84. The cleaning roller 8 has the sponge sheet 85 as a cleaning portion that contacts the roller portion (elastic layer 22) of the charging roller 2, and the rotating shaft 84 as a non-cleaning portion that has a smaller diameter than the cleaning portion and does not contact the roller portion of the charging roller 2. In other words, the cleaning roller 8 is formed by winding the cleaning portion spirally around the non-cleaning portion. The cleaning roller 8 is configured so that the cleaning portion and the non-cleaning portion alternately face each other with respect to a certain point on the surface of the charging roller 2 in the direction of the rotation axis of the charging roller 2.

[0175] In Example 3, the rotation time A was 0.232 [sec].

[0176] 6-8. Example 4 In the fourth embodiment, the contact position between the cleaning roller 8 and the charging roller 2 is different from that in the third embodiment.

[0177] 13 is a schematic cross-sectional view showing the shaft support configuration of the charging roller 2 and cleaning roller 8 in Example 4 (showing a cross section substantially perpendicular to the rotation axis of the charging roller 2). Note that while FIG. 13 shows the configuration of one end side in the rotation axis direction of the charging roller 2, the configuration of the other end side is similar (substantially symmetrical with respect to a plane passing through the center of the rotation axis direction of the charging roller 2).

[0178] In the fourth embodiment, as shown in FIG. 13 , the rotation shaft of the charging roller 2 (both ends of the support 21) and the rotation shaft of the cleaning roller 8 (both ends of the rotation shaft 84) are rotatably supported by bearing members 51 at fixed positions so that the distance between the two rotation shafts is constant. The bearing members 51 are slidably supported by the cleaning container 9. A pressure spring 61, which is a biasing member serving as a biasing means, is provided between the bearing member 51 and the cleaning container 9. The pressure spring 61 biases the bearing member 51 in a direction toward the rotation center of the photosensitive drum 1, i.e., along a straight line L1 (in this example, substantially parallel to the straight line L1). Therefore, the charging roller 2 is pressed against the photosensitive drum 1 and comes into contact with it.

[0179] 13 , a line passing through the rotation center of the photosensitive drum 1 and the rotation center of the charging roller 2 is defined as line L1, and a line passing through the rotation center of the charging roller 2 and the rotation center of the cleaning roller 8 is defined as line L2. In Example 4, the cleaning roller 8 was arranged so that line L2 was inclined at an angle of 21° (angle θ) with respect to line L1 in the direction opposite to the rotation direction of the charging roller 2. The contact position between the cleaning roller 8 and the charging roller 2 was located on line L2. In this way, in Example 4, the cleaning roller 8 was arranged so that line L2 was located upstream of line L1 in the rotation direction of the charging roller 2 and downstream of the contact position between the charging roller 2 and the photosensitive drum 1, with respect to the rotation center of the charging roller 2 as the reference.

[0180] For Example 4, similarly to Example 3, image evaluation 1, image evaluation 2, and image evaluation 3, which will be described later, were carried out.

[0181] 6-9. Example 5 In the fifth embodiment, the method of urging the cleaning roller 8 against the charging roller 2 is different from that in the fourth embodiment. Other than that, the fifth embodiment is the same as the fourth embodiment.

[0182] 14 is a schematic cross-sectional view showing the shaft support configuration of the charging roller 2 and cleaning roller 8 in Example 5 (showing a cross section substantially perpendicular to the rotation axis of the charging roller 2). Note that while Fig. 14 shows the configuration of one end side in the rotation axis direction of the charging roller 2, the configuration of the other end side is similar (substantially symmetrical with respect to a plane passing through the center of the rotation axis direction of the charging roller 2).

[0183] In the fifth embodiment, as shown in Fig. 14, the rotation shaft of the charge roller 2 (both ends of the support 21) is rotatably supported by charge roller bearing members (first bearing members) 52. The charge roller bearing member 52 is slidably supported by the cleaning container 9, and a charge roller pressure spring 62, which is a first biasing member serving as a biasing means, is provided between the charge roller bearing member 52 and the cleaning container 9. The charge roller pressure spring 62 biases the charge roller bearing member 52 in a direction toward the rotation center of the photosensitive drum 1, that is, along a straight line L1 (substantially parallel in this example). As a result, the charge roller 2 is pressed against the photosensitive drum 1 and comes into contact with it.

[0184] On the other hand, in Example 5, as shown in FIG. 14 , the cleaning roller 5 is brought into contact with the surface of the charge roller 2 with a predetermined pressing force by a cleaning roller pressure spring 63, and is rotated in accordance with the rotation of the charge roller 2. That is, the rotation shaft of the cleaning roller 8 (both ends of the rotation shaft 84) is rotatably supported by cleaning roller bearing members (second bearing members) 53. The cleaning roller bearing members 53 are slidably supported by the charge roller bearing member 52. A cleaning roller pressure spring 63, which is a second biasing member serving as a biasing means, is provided between the cleaning roller bearing member 53 and the charge roller bearing member 52. The cleaning roller bearing member 53 is movably supported by the charge roller bearing member 52 via the cleaning roller pressure spring 63. The cleaning roller pressure spring 63 biases the cleaning roller bearing member 53 in a direction toward the rotation center of the charge roller 2, i.e., along the straight line L2 (approximately parallel in this example). Therefore, the cleaning roller 8 is pressed against and contacts the charge roller 2.

[0185] In this way, by biasing the cleaning roller 8 against the charging roller 2 by the cleaning roller pressure spring 63, the pressure of the cleaning roller 8 against the charging roller 2 tends to be stable. Therefore, for example, even if the hardness of the sponge portion of the cleaning roller 8 increases as the sponge portion continues to collect toner, the pressure of the cleaning roller 8 against the charging roller 2 is relatively unlikely to increase.

[0186] Furthermore, the cleaning roller pressure spring 63 and the charging roller pressure spring 62 are disposed at an angle (the angle between the straight line L1 and the straight line L2). This is because, even if the contact position of the cleaning roller 8 is shifted from the straight line L1, the urging direction of the cleaning roller 8 and the urging direction of the charging roller 2 can be set independently to predetermined directions.

[0187] In this embodiment, in a cross section approximately perpendicular to the rotation axis of the charging roller 2, the force direction of the cleaning roller 8 is toward the center of rotation of the charging roller 2, and the force direction of the charging roller 2 is toward the center of rotation of the photosensitive drum 1.

[0188] 7. Evaluation Method To evaluate the horizontal charging streak images, the following evaluation test was carried out, and the evaluation results are shown in the table of FIG.

[0189] <Test equipment> An electrophotographic laser printer (trade name: LaserJet Pro 4003dw, manufactured by HP) according to this embodiment was prepared as an electrophotographic image forming apparatus. To evaluate high-speed processes, the laser printer was modified so that the number of sheets output per minute was 47 sheets per minute on A4-sized paper, which was higher than the original output number. The recording material output speed was set to 230 mm / sec. To evaluate each example and comparative example, the device body and process cartridge of the laser printer were modified as needed. Each charging roller of Examples 1 to 5 and Comparative Examples 1 to 4 was attached to a process cartridge, and the following image evaluations were performed.

[0190] <Image evaluation 1> As image evaluation 1, the following evaluation test was carried out.

[0191] The charging roller, laser printer, and process cartridge were left in an environment of 32.5° C. / 80% RH for 48 hours in order to acclimate them to the evaluation environment.

[0192] The charging roller that had been left in the above environment was set as the charging roller of a process cartridge that had also been left in the above environment, and was then installed in a laser printer that had also been left in the above environment. Thereafter, a total of 12,000 images were output continuously under the same environment.

[0193] The image to be output was a 4-point letter "E" printed on A4 paper with a print rate of 1.0%. The charging bias was -1040V, the dark potential VD was -530V (VD reference value), and the light potential was -100V.

[0194] Thereafter, a halftone image (an image in which horizontal lines with a width of 1 dot and an interval of 2 dots are drawn in a direction substantially perpendicular to the moving direction of the surface of the photosensitive drum) was output. This halftone image was visually observed, and the horizontal charging streak image was evaluated according to the following criteria.

[0195] Evaluation of horizontal static streaks on halftone images Rank A: No horizontal charging streak images are observed on the halftone image even when observed under a microscope. Rank B: No horizontal charging streaks are visible on the halftone image when observed visually, but dot irregularities are observed when observed under a microscope. Rank C: Horizontal charging streaks are visually observed on part of the halftone image. Rank D: Horizontal charging streaks are visually observed over the entire surface of the halftone image.

[0196] <Image evaluation 2> In Image Evaluation 2, the laser printer was modified so that the number of sheets output per minute was 75 sheets / minute on A4 size paper, in contrast to Image Evaluation 1 above. The output speed of the recording material was set to 370 mm / sec. Otherwise, the evaluation was performed in the same manner as in Image Evaluation 1 above.

[0197] <Image rating 3> In image evaluation 3, the following operations were performed immediately after image evaluation 2.

[0198] Under the same environment, a total of 30,000 images were output continuously.

[0199] The image to be output was a 4-point alphabet letter "E" printed on an A4 size sheet of paper with a print rate of 1.0%.

[0200] Thereafter, a halftone image (an image in which horizontal lines with a width of 1 dot and an interval of 2 dots are drawn in a direction substantially perpendicular to the moving direction of the surface of the photosensitive drum) was output. This halftone image was visually observed, and the horizontal charging streak image was evaluated according to the following criteria.

[0201] Evaluation of horizontal static streaks on halftone images Rank A: No horizontal charging streak images are observed on the halftone image even when observed under a microscope. Rank B: No horizontal charging streaks are visible on the halftone image when observed visually, but dot irregularities are observed in part of the image when observed under a microscope. Rank C: No horizontal charging streaks are visible on the halftone image when observed visually, but dot irregularities are visible across the entire image when observed under a microscope. Rank D: Horizontal charging streaks are visually observed on part of the halftone image.

[0202] 8. Evaluation Results As described above, when the surface of the photosensitive member 1 is charged by the charging member 2, the time from when a certain point on the surface of the charging member 2 comes into contact with the cleaning member 8 until the next time the charging member 2 comes into contact with the cleaning member 8 due to the rotation of the charging member 2 is defined as the rotation time A [sec].

[0203] The time constant τ of the charging member 2 is expressed by the following formula: τ=1 / 2πfp[sec] (wherein fp is the frequency at which the absolute value of the imaginary term obtained by measuring the impedance of the charged member 2 is at a maximum) The time constant τ of the charging member 2 is defined as an index of the decay of the charge on the surface of the charging member 2.

[0204] At this time, based on the evaluation results of the examples and comparative examples, the image forming apparatus 100 determines whether the rotation time A and the time constant τ satisfy the following formula: A / τ≧60 Fulfilling The time constant τ is 1.0×10 -5 [sec] or more, 1.2×10 -3 The configuration is set to be less than [sec].

[0205] More preferably, the time constant τ of the charging roller 2 is 1.0×10 -5 [sec] or more, 1.0×10 -4 The configuration is set to be less than [sec].

[0206] Note that, as long as both the above-mentioned requirements for A / τ and the requirements for the range of the time constant τ are satisfied, no particular upper limit for A / τ is set. However, based on the evaluation results of the examples and comparative examples, it can be shown that A / τ≦8000, preferably A / τ≦2320, is satisfied.

[0207] Hereinafter, the present invention will be described in more detail based on the evaluation results of Examples and Comparative Examples.

[0208] <Superiority of Examples over Comparative Examples> The advantages of the Example over Comparative Examples 1 and 2 will be explained.

[0209] First, in Comparative Example 1, the time constant of the charging roller 2 was large, and therefore A / τ≧60 was not satisfied in Image Evaluation 1 and Image Evaluation 2. As a result, the rubbing interval on the surface of the charging roller 2, which generates frictional charging between the charging roller 2 and the cleaning roller 8, was faster than the charge decay of the charging roller 2, and charge accumulation occurred on the charging roller 2. As a result, when continuous image output was performed, the absolute value of the surface potential of the charging roller 2 decreased. As a result, visually observable horizontal charging streak images occurred on part of the image in Image Evaluation 1, and on the entire image in Image Evaluation 2.

[0210] Furthermore, in Comparative Example 2, the time constant of the charging roller 2 is smaller than that of Comparative Example 1 but larger than that of the Example, and therefore A / τ≧60 is satisfied in Image Evaluation 1, but A / τ≧60 is not satisfied in Image Evaluation 2, which is set at a high printing speed. As a result, no visually observable horizontal charging streak images occurred in Image Evaluation 1, but visually observable horizontal charging streak images occurred in part of the image in Image Evaluation 2.

[0211] Next, the advantages of the embodiment will be described.

[0212] In Example 1, the time constant was smaller than in Comparative Example 1, and therefore A / τ≧60 was satisfied in Image Evaluation 1 and Image Evaluation 2. Therefore, for the reasons described above, the absolute value of the surface potential of the charging roller 2 did not decrease, and a good image was confirmed in Image Evaluation 1. On the other hand, in Image Evaluation 2, which had a faster printing speed, the A / τ value was smaller than in Image Evaluation 1, and although no visually observable horizontal charging streak images occurred, image dot disturbances were confirmed under a microscope. This is thought to be because the time from when the charging roller 2 experiences charge accumulation due to friction until it is subjected to friction again is approximately the same as the time until the charge decay is complete, and therefore horizontal charging streak images that are not visually observable occurred.

[0213] Next, Comparative Examples 3 and 4 will be described, which satisfy A / τ≧60 but have other drawbacks.

[0214] In Comparative Example 3, the time constant of the charging roller 2 was very small, and the electrical resistance was also small. Horizontal black stripes appeared on the image in Image Evaluation 1. This is thought to be because the time constant was so small that the electric field concentrated on a part of the surface of the charging roller 2, causing a current to flow to the photosensitive drum 1, resulting in poor charging.

[0215] In addition, in Comparative Example 4, the same charging roller (4) as in Comparative Example 2 is used, but the peripheral speed of the charging roller 2 is slower than the peripheral speed of the photosensitive drum 1 so that A / τ≧60 in Image Evaluation 1 and Image Evaluation 2. Frictional resistance occurs between the charging roller 2 and the photosensitive drum 1 due to the difference in peripheral speed, and the contact state between the charging roller 2 and the photosensitive drum 1 becomes unstable, causing blurring. This is thought to be the reason for the lateral density fluctuation in the image in Evaluation 1.

[0216] <Other more effective examples> Next, another embodiment that is even more effective than the first embodiment will be described.

[0217] In Example 2, the time constant of the charging roller 2 is smaller than in Example 1. As a result, the value of A / τ is sufficiently larger than 60, and the charge decay is sufficiently faster than the charge accumulation on the charging roller 2, so good images were obtained in Image Evaluation 1 and Image Evaluation 2.

[0218] On the other hand, in Example 2, horizontal charging streak images occurred on a portion of the image in Image Evaluation 3. This is thought to be due to the following reason: As toner collected on the sponge-like cleaning roller 8 accumulates over a long period of printing, the surface of the cleaning roller 8 hardens, and the contact pressure between the cleaning roller 8 and the charging roller 2 increases. This intensifies the effect of frictional charging on the charging roller 2. In such a case, the effect of charging due to friction between the cleaning roller 8 and the charging roller 2 appears as poor charging when the charging roller 2 immediately passes through the contact point between the charging roller 2 and the photosensitive drum 1. This is because the effect of frictional charging due to a single friction stroke is so great that the charge does not decay in time before the charging roller 2 reaches the contact point with the photosensitive drum 1. This is thought to be why horizontal charging streak images occurred on a portion of the image in Image Evaluation 3.

[0219] Example 3 differs from Example 2 in that the cleaning roller 8 is made by spirally winding a sponge sheet 85 around a rotation shaft 84. By adjusting the interval (pitch) of the spirally wound sponge sheet 85, it is possible to reduce the chance of friction between the charging roller 2 and the cleaning roller 8 (surface of the sponge sheet 85). In Example 3, by adjusting the winding method of the sponge sheet 85 so that the chance of friction between the charging roller 2 and the cleaning roller 8 is half that of Example 2, the result of image evaluation 3 was one rank better than Example 2.

[0220] Example 4 differs from Example 3 in that the contact position between the cleaning roller 8 and the charging roller 2 is changed. In Example 4, the contact position between the cleaning roller 8 and the charging roller 2 is shifted upstream in the rotation direction of the charging roller 2 compared to the position in Example 3. This allows the charge of the charging roller 2 to more easily decay due to friction between the surface of the charging roller 2 and the photosensitive drum 1 after friction with the cleaning roller 8. As a result, Example 4 achieved a result in image evaluation 3 that was one rank better than Example 3. In the configuration of Example 4, the inclination (angle θ) of the line L2 with respect to the line L1 was set to 21°, but this is not limited to this. This angle θ can be appropriately set so as to obtain desirable results similar to Example 4. This angle θ is preferably approximately 5° or more and 90° or less, and typically 10° or more and 45° or less.

[0221] Example 5 differs from Example 4 in the method of biasing the cleaning roller 8 against the charging roller 2. In Example 5, the cleaning roller bearing member 53 and the cleaning roller pressure spring 63 are supported by the charging roller bearing member 52. The cleaning roller pressure spring 63 presses the cleaning roller 8 against the charging roller 2 to bring it into contact with it. Therefore, even if the surface of the cleaning roller 8 hardens due to the accumulation of toner trapped in the sponge portion of the cleaning roller 8, it is possible to suppress an increase in the contact pressure between the cleaning roller 8 and the charging roller 2. This makes it possible to reduce the effect of frictional charging on the charging roller 2 more than in Example 4, and the result of image evaluation 3 was one rank better than in Example 4.

[0222] As described above, according to this embodiment, the residual charge on the charging roller 2 decays faster than the charging roller 2 repeatedly rubs against the cleaning roller 8. This reduces the charge accumulation on the charging roller 2, suppresses the occurrence of uneven discharge from the charging roller 2 to the photosensitive drum 2, and suppresses the occurrence of image defects due to insufficient charging of the photosensitive drum 1. Therefore, according to this embodiment, even during long periods of continuous driving, it is possible to suppress charging of the charging roller 2 by the cleaning roller 8 and suppress the occurrence of image defects due to insufficient charging of the photosensitive drum by the charging roller 2.

[0223] [Other embodiments] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0224] In the above embodiment, the cleaning member is a cleaning roller, but the present invention is not limited to this. The cleaning member may be a brush-like member, a blade-like member, a sheet-like member, or the like.

[0225] In the above embodiment, the image forming apparatus is of a process cartridge type, but the present invention is not limited to this. The present invention can also be applied to an image forming apparatus in which the process means is not easily detachable from the main body of the apparatus, and similar effects can be obtained.

[0226] In the above-described embodiment, a spiral roller is used as an example of a cleaning member having cleaning portions and non-cleaning portions, but this is not limiting. For example, a cleaning member having a rotating shaft and multiple cleaning portions spaced apart along the axial direction of the rotating shaft may be configured to move in the axial direction of the rotating shaft. This also allows the cleaning portions and non-cleaning portions to alternately face a certain point on the surface of the charging member. Alternatively, a cleaning member having multiple cleaning portions arranged radially around the rotating shaft may be configured to rotate.

[0227] The present invention can be applied not only to monochrome image forming apparatuses with one image forming unit, but also to color image forming apparatuses with multiple image forming units, for example, a color image forming apparatus that transfers a toner image to a recording material via an intermediate transfer body. In this case, the present invention can be applied to at least one of the multiple image forming units, and the same effects can be obtained. Also, in this case, the process means in at least one of the multiple image forming units may be detachably mounted on the apparatus main body as a process cartridge. [Explanation of symbols]

[0228] 1 Photosensitive drum 2 Charging roller 8 Cleaning roller 10 Process cartridge 100 Image forming device P recording material

Claims

1. a rotatable photoreceptor; a charging member that contacts the surface of the photoreceptor and charges the surface of the photoreceptor while rotating in a predetermined direction; a cleaning member that comes into contact with the charging member and cleans the surface of the charging member; and When the surface of the photosensitive member is charged by the charging member, the time from when a certain point on the surface of the charging member comes into contact with the cleaning member until the next time the charging member comes into contact with the cleaning member due to rotation of the charging member is defined as a rotation time A [sec], The time constant τ of the charging member is calculated by the following formula: τ=1 / 2πfp [sec] (wherein fp is the frequency at which the absolute value of the imaginary term obtained by measuring the impedance of the charging member is at a maximum) and the time constant τ of the charging member is defined as an index of decay of the charge on the surface of the charging member, The rotation time A and the time constant τ are expressed by the following equation: A / τ≧60 Fulfilling The time constant τ is 1.0×10 －５ [sec] or more, 1.2×10 －３ [sec] or less.

2. The time constant τ is 1.0×10 －５ [sec] or more, 1.0×10 －４ 2. The image forming apparatus according to claim 1, wherein the time is 100 [sec] or less.

3. 2. The image forming apparatus according to claim 1, wherein the charging member is configured to rotate in accordance with the rotation of the photosensitive member.

4. 2. The image forming apparatus according to claim 1, wherein the cleaning member is rotatable.

5. 5. The image forming apparatus according to claim 4, wherein the cleaning member is a roller having a rotation shaft and an elastic layer formed in a cylindrical shape around the rotation shaft.

6. 5. The image forming apparatus according to claim 4, wherein the cleaning member comprises a cleaning portion that contacts the surface of the charging member to clean the surface of the charging member, and a non-cleaning portion that is smaller in diameter than the cleaning portion and does not contact the surface of the charging member, and the cleaning portion and the non-cleaning portion are configured to alternately face a certain point on the surface of the charging member in the direction of the rotation axis of the charging member.

7. 5. The image forming apparatus according to claim 4, wherein the cleaning member is a roller having a rotation shaft and an elastic layer spirally formed around the rotation shaft.

8. 5. The image forming apparatus according to claim 4, wherein the cleaning member is configured to rotate in accordance with the rotation of the charging member.

9. 2. The image forming apparatus according to claim 1, wherein, in a cross section substantially perpendicular to the rotation axis of the charging member, when a line L1 is defined as a line passing through the rotation center of the photosensitive body and the rotation center of the charging member, and a line L2 is defined as a line passing through the rotation center of the cleaning member and the rotation center of the charging member, the cleaning member is disposed so that, with respect to the rotation center of the charging member as a reference, the line L2 is located upstream of the line L1 in the rotation direction of the charging member and downstream of a contact position between the charging member and the photosensitive body.

10. a movable first bearing member that rotatably supports the charging member; a second bearing member that rotatably supports the cleaning member, the second bearing member being movably supported by the first bearing member; a first biasing member that biases the first bearing member toward the image carrier; a second biasing member that biases the second bearing member toward the charging member, the second biasing member being supported by the first bearing member; 2. The image forming apparatus according to claim 1, further comprising:

11. 11. The image forming apparatus according to claim 1, wherein a cartridge including the photosensitive member, the charging member, and the cleaning member is configured to be removable.

Images