Image formation apparatus and process cartridge

Abstract

To more effectively removing a toner and external additive adhering to a charging roller by a cleaning roller.SOLUTION: An image formation apparatus 100 includes: an image support 4; a charging roller 5 having a surface 5s contacting the surface of the image support 4 and rotating while contacting the rotating image support 4 to charge the surface 4s of the image support 4; a cleaning roller 15 including a foam elastic layer 15b contacting the surface 5s of the charging roller 5, rotating while contacting the rotating charging roller 5 and for cleaning the surface 5s of the charging roller 5; and development means 2. When defining the storage elastic modulus of the surface 5s of the charging roller 5 measured at a measurement environment of 23°C and 50%RH and a measurement frequency of 10 Hz as E'C and defining the storage elastic modulus of the foam elastic layer 15b of the cleaning roller 15 as E'CC, the storage elastic modulus E'C of the surface 5s of the charging roller 5 and the storage elastic modulus E'CC of the foam elastic layer 15b of the cleaning roller 15 satisfies the relationship of E'C>E'CC.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, that uses an electrophotographic or electrostatic recording system, and to a process cartridge that is detachably mountable to the main body of the image forming apparatus. [Background technology]

[0002] Conventionally, in an image forming apparatus such as a printer using an electrophotographic method, the surface of a photoconductor as an image carrier is uniformly charged by a charging means, and the charged surface of the photoconductor is selectively exposed by an exposure means to form an electrostatic latent image on the photoconductor. Then, a developing means supplies toner as a developer to the electrostatic latent image on the photoconductor to form a toner image on the photoconductor, and the toner image is transferred onto a recording material. After the toner image is transferred from the photoconductor to the recording material, the toner remaining on the photoconductor is removed from the surface of the photoconductor by a cleaning means before the surface of the photoconductor is charged again by the charging means.

[0003] In such image forming apparatuses, there is a process cartridge system in which the photoconductor and the process means acting on the photoconductor are integrated into a cartridge, and this cartridge is detachable from the main body of the image forming apparatus. The process means acting on the photoconductor include a charging member that charges the photoconductor, a cleaning member that removes toner remaining on the photoconductor, and a developing unit (developing device) that develops the electrostatic latent image on the photoconductor with toner. By integrating these process means with the photoconductor into one process cartridge and allowing the user to replace them all at once, usability is improved.

[0004] There is also a process cartridge that employs a contact charging method in which a charging roller, which is a charging member, is brought into contact with a photoconductor to charge the photoconductor. In this case, as the life of the process cartridge increases, toner and fine particles added to the surface of the toner (hereinafter also referred to as "external additives") may accumulate on the surface of the charging roller. This is because the toner and external additives attached to the photoconductor gradually slip through the cleaning member as the process cartridge is used. If the toner and external additives accumulate on the surface of the charging roller in this way and the charging roller becomes dirty, this may cause charging failure of the photoconductor, which may manifest as uneven density in a halftone image. This charging failure is an issue that occurs in the latter half of the life of the process cartridge, and becomes more noticeable the longer the life of the process cartridge.

[0005] In view of this, a configuration has been proposed in which a flexible cleaning sheet is brought into contact with the charging roller to remove toner and external additives (hereinafter also referred to as "adhered matter" or "dirt") adhering to the surface of the charging roller (Patent Document 1). In Patent Document 1, a cleaning blade, which is a cleaning member, is brought into contact with the photoconductor, and any adhering matter that slips between the cleaning blade and the photoconductor and adheres to the charging roller is removed by bringing the cleaning sheet into contact with the charging roller.

[0006] Also, a configuration has been proposed in which a cleaning roller is brought into contact with a charging roller (Patent Document 2). In Patent Document 2, the cleaning roller is rotated so as to have an appropriate peripheral speed difference with respect to the charging roller. This allows all parts of the surface of the cleaning roller to be evenly brought into contact with the charging roller, removing toner and external additive stains adhering to the charging roller. In addition, a sponge material is used for the cleaning roller, and a large amount of foreign matter such as toner transferred from the charging roller to the sponge material due to friction between the cleaning roller and the charging roller is stored in the space of the porous structure. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-61546 A [Patent Document 2] Japanese Patent Application Publication No. 02-272594 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the cleaning sheet described in Patent Document 1 cannot contact the external additives attached to the recesses on the surface of the charging roller, and therefore cannot achieve a significant removal effect. In contrast, even if a brush is used as a cleaning member that is brought into contact with the charging roller, the brush generally has a fiber diameter of several μm. Therefore, although a removal effect can be achieved for toner with a particle size of several μm, a significant removal effect cannot be achieved for external additives with a particle size of several nm to several hundred nm. As a result, streaky image defects may occur on the halftone image in the areas corresponding to the toner and external additives attached to the charging roller.

[0009] In addition, in Patent Document 2, it is said that the charging roller can be cleaned for a long time by storing toner in the space of the sponge material by a configuration in which a cleaning roller made of a sponge material is brought into contact with the charging roller. However, it was found that in the conventional configuration, the cell skeleton of the sponge material causes the external additive to adhere firmly to the surface of the charging roller, which may cause dirt on the surface of the charging roller. In that case, a streak-like image defect may occur on the halftone image in the part corresponding to the external additive adhered to the charging roller. In addition, in the conventional configuration, the space of the porous structure of the sponge material may be clogged with toner. In that case, for example, it may become necessary to replace the cleaning roller with a new one at a predetermined timing, which may make maintenance complicated.

[0010] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to make it possible to more effectively remove toner and external additives adhering to a charging roller by means of a cleaning roller. [Means for solving the problem]

[0011] The above object is achieved by the image forming apparatus and process cartridge according to the present invention. In summary, the present invention is an image forming apparatus comprising a rotatable image carrier, a charging roller having a surface in contact with the surface of the image carrier, rotating in contact with the rotating image carrier and charging the surface of the image carrier, a cleaning roller having a foamed elastic layer in contact with the surface of the charging roller and rotating in contact with the rotating charging roller for cleaning the surface of the charging roller, and a developing means for supplying a developer to the surface of the image carrier to form a developer image, wherein the storage elastic modulus E'C of the surface of the charging roller and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller, measured in a measurement environment of 23°C, 50% RH, and a measurement frequency of 10 Hz, are defined as E'C and E'CC, respectively, and the storage elastic modulus E'C of the surface of the charging roller and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller satisfy the relationship E'C>E'CC.

[0012] According to another aspect of the present invention, there is provided a process cartridge detachable from a main body of an image forming apparatus which supplies a developer to the surface of a rotatable image carrier by a developing means to form a developer image and transfers the developer image to a recording material to form an image on the recording material, the process cartridge comprising: the image carrier; a charging roller which has a surface that contacts the surface of the image carrier, which rotates in contact with the rotating image carrier and charges the surface of the image carrier; and a cleaning roller which has a foamed elastic layer that contacts the surface of the charging roller and rotates in contact with the rotating charging roller for cleaning the surface of the charging roller, the cleaning roller having a foamed elastic layer that contacts the surface of the charging roller and rotates in contact with the rotating charging roller, wherein the storage elastic modulus E'C of the surface of the charging roller and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller are defined as E'C and E'CC, respectively, as measured in a measurement environment of 23° C., 50% RH, and a measurement frequency of 10 Hz, respectively, and are characterized in that the storage elastic modulus E'C of the surface of the charging roller and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller satisfy the relationship E'C>E'CC. Effect of the Invention

[0013] According to the present invention, the toner and external additives adhering to the charging roller can be more effectively removed by the cleaning roller. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the process cartridge. [Diagram 3] FIG. 2 is a schematic cross-sectional view of the drum unit. [Figure 4] FIG. 2 is a schematic diagram showing the adhesion state of an external additive in Example 1. [Diagram 5] 3 is a schematic diagram for explaining a removal mechanism of an external additive in Example 1. FIG. [Figure 6] 3 is a schematic diagram for explaining a removal mechanism of an external additive in Example 1. FIG. [Figure 7] 10 is a schematic diagram for explaining the mechanism of removing an external additive in Example 2. FIG. [Figure 8] 10 is a schematic diagram for explaining the mechanism of removing an external additive in Example 2. FIG. [Figure 9] FIG. 2 is a schematic diagram showing the adhesion state of external additives in Comparative Examples 1 and 2. [Figure 10] FIG. 2 is a schematic diagram for explaining the adhesion mechanism of an external additive in Comparative Examples 1 and 2. [Figure 11] FIG. 2 is a schematic diagram for explaining the adhesion mechanism of an external additive in Comparative Examples 1 and 2. [Figure 12] FIG. 1 is a schematic diagram showing a matrix-domain structure. [Figure 13] FIG. 2 is a schematic cross-sectional view showing the configuration of a charging roller and a cleaning roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0016] [Embodiment 1] <Overall configuration and operation of image forming apparatus> 1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present embodiment is a monochrome laser printer employing a process cartridge system, capable of forming a black monochrome image on a sheet-shaped recording material P by using an electrophotographic system.

[0017] The image forming apparatus 100 has a photosensitive drum 4, which is a rotatable drum-type (cylindrical) photosensitive body (electrophotographic photosensitive body) serving as an image carrier. During image formation, the photosensitive drum 4 is rotated at a predetermined process speed (circumferential speed) in the direction of arrow R1 in the figure (clockwise direction) by a drive motor (not shown) serving as a drive source constituting a drive means provided in the apparatus main body 110. The surface of the rotating photosensitive drum 4 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 5, which is a roller-type charging member serving as a charging means. The charged surface of the photosensitive drum 4 is irradiated with laser light based on image information by an exposure device (laser scanner device) 12 serving as an exposure means (optical means) and is scanned and exposed, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 4. The electrostatic latent image formed on the photosensitive drum 4 is developed (visualized) by a developing device 2 serving as a developing means, which supplies toner T as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 4. In this embodiment, toner T charged with the same polarity as the charge polarity of the photosensitive drum 4 (negative polarity in this embodiment) adheres to an exposed portion (image portion) on the photosensitive drum 4, the absolute value of the potential of which has been reduced by exposure after being uniformly charged (reverse development method). In this embodiment, the regular charge polarity (regular polarity) of the toner T, which is the main charge polarity of the toner T during development, is negative polarity.

[0018] A transfer roller 11, which is a roller-type transfer member serving as a transfer means, is disposed opposite the photosensitive drum 4. The transfer roller 11 is pressed against the photosensitive drum 4 to form a transfer portion (transfer nip) Nt, which is a contact portion between the photosensitive drum 4 and the transfer roller 11. The toner image formed on the photosensitive drum 4 is transferred to a recording material P, which is a transfer target material that is sandwiched and conveyed between the photosensitive drum 4 and the transfer roller 11, at the transfer portion Nt. A transfer power source (high voltage power source) (not shown) is connected to the transfer roller 11 as a transfer voltage application means provided in the device main body 110. During image formation (transfer), a predetermined transfer voltage (transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner T, is applied to the transfer roller 11 by the transfer power source. A recording material (transfer material, recording medium, sheet) P, such as recording paper, an OHP sheet, or a cloth, is fed from a feeding portion 30 toward the transfer portion Nt. The feeding section 30 is configured to include a cassette 31 as a recording material storage section, a pickup roller (feed roller) 32 as a feeding member, and a pressing member (not shown) that presses against the cassette 31. The recording materials P stored in the cassette 31 are separated and fed one by one by the pickup roller 32 and the pressing member. The recording materials P are transported toward the transfer section Nt by a registration roller 41 as a transport member in synchronization with the formation of the toner image on the photosensitive drum 4. The recording material P transported by the registration roller 41 is supplied to the transfer section Nt along a transport guide (not shown).

[0019] The recording material P onto which the toner image has been transferred is conveyed along a conveying guide (not shown) to a fixing device 13 as a fixing means. The fixing device 13 has a pair of fixing rotors, which are composed of a drive roller and a cylindrical sheet that has a built-in heater and is rotatably supported by a support. The pair of fixing rotors applies heat and pressure to the recording material P passing through a fixing section (fixing nip) formed by the drive roller and the cylindrical sheet, thereby fixing (melting, fixing) the unfixed toner image on the recording material P to the recording material P. The recording material P onto which the toner image has been fixed is conveyed by a discharge roller 42 as a conveying member and discharged (output) onto a tray 50 as a discharge section provided outside the apparatus main body 110. When double-sided image formation (automatic double-sided printing) is performed, the recording material P onto which the toner image has been fixed on the first side is conveyed again to the transfer section Nt with the conveying direction and front and back reversed through a reverse conveying path (not shown). Then, the recording material P is discharged to the tray 50 after the toner image is transferred and fixed on the second side.

[0020] On the other hand, toner that is not transferred onto the recording material P during transfer and remains on the photosensitive drum 4 (transfer residual toner, residual toner) is removed from the photosensitive drum 4 and collected by a cleaning device 17 serving as a cleaning means.

[0021] In this embodiment, the photosensitive drum 4, the charging roller 5 as process means acting thereon, the developing device 2, the cleaning device 17, etc., integrally constitute a process cartridge C that is detachably mountable to the apparatus main body 110. The process cartridge C is easily mountable to and detachable from the apparatus main body 110 via mounting means 3 such as a mounting guide and a positioning member provided on the apparatus main body 110 and the process cartridge C. The apparatus main body 110 is a component of the image forming apparatus 100 excluding the process cartridge C.

[0022] <Process cartridge> Next, the process cartridge C according to this embodiment will be described with reference to Fig. 2, which is a schematic cross-sectional view of the process cartridge C according to this embodiment.

[0023] As shown in Fig. 2, the process cartridge C is configured to include a drum unit 1 and a developing unit (developing device) 2. In the process cartridge C, the drum unit 1 and the developing unit 2 are connected to each other and are detachably attached to the apparatus main body 110 as a whole. Fig. 3 is a schematic cross-sectional view of the drum unit 1.

[0024] The drum unit 1 has a drum frame 18. The drum frame 18 rotatably supports the photosensitive drum 4, the charging roller 5, and the cleaning roller 15. The charging roller 5 is disposed in contact with the photosensitive drum 4, and the cleaning roller 15 is disposed in contact with the charging roller 5. The drum frame 18 also supports a cleaning blade 6. The cleaning blade 6 is disposed in contact with the photosensitive drum 4. The drum frame 18 also forms a removed toner chamber 18a. The cleaning blade 6 and the removed toner chamber 18a constitute a cleaning device 17.

[0025] In this embodiment, the photosensitive drum 4 has an OPC (organic photoconductor) photosensitive layer and an outer diameter of 24 mm. In this embodiment, during image formation, the photosensitive drum 4 is rotated in the direction of arrow R1 in the figure (clockwise direction) at a peripheral speed of 370 mm / sec.

[0026] In this embodiment, as shown in FIG. 13(a), the charging roller 5 is a conductive member (conductive elastic roller) having a core metal (support, rotating shaft) 5a having a conductive outer peripheral surface (outer surface, outer periphery) and a conductive elastic layer 5b provided on the outer peripheral surface of the core metal 5a. In this embodiment, as an example, the outer diameter of the core metal 5a of the charging roller 5 is 6 mm, and the outer diameter of the elastic layer 5b is 8.5 mm. As shown in FIG. 13(b), the charging roller 5 may further have a surface layer 5c on the outer peripheral surface of the elastic layer 5b. The configuration of the charging roller 5 will be described later. The charging roller 5 is pressed against the photosensitive drum 4 with a predetermined pressing force, and rotates in the direction of the arrow R2 in the figure (counterclockwise direction) in accordance with the rotation of the photosensitive drum 4.

[0027] In this embodiment, the cleaning roller 15, which is a roller-type cleaning member as a cleaning means, is a conductive elastic roller having a core metal (support, rotating shaft) 15a and a foamed elastic layer 15b formed of a foamed elastic body covering the core metal 15a, as shown in Figs. 13(a) and 13(b). In this embodiment, the foamed elastic layer 15b is formed of a urethane sponge as a foamed elastic member (sponge). In this embodiment, the cleaning roller 15 is disposed vertically above the charging roller 5. In this embodiment, as an example, the outer diameter of the core metal 15a of the cleaning roller 15 is 4 mm, and the outer diameter of the foamed elastic layer 15b is 6 mm. The configuration of the cleaning roller 15 will be described later. The cleaning roller 15 is pressed against the charging roller 5 with a predetermined pressing force, and rotates in the direction of the arrow R3 in the figure (clockwise direction) in accordance with the rotation of the charging roller 5.

[0028] The photosensitive drum 4, the charging roller 5, and the cleaning roller 15 are rotatably supported at both ends in the direction of their rotational axes by a drum frame 18. The directions of the rotational axes of the photosensitive drum 4, the charging roller 5, and the cleaning roller 15 are substantially parallel to each other.

[0029] The cleaning blade 6 as a cleaning member is a plate-like member made of rubber as an elastic member, and is supported by a support member and attached to the drum frame 18. The cleaning blade 6 is a plate-like member having a predetermined length and a predetermined thickness in a longitudinal direction disposed approximately parallel to the rotation axis direction of the photosensitive drum 4 and in a lateral direction approximately perpendicular to the longitudinal direction. The cleaning blade 6 is disposed in contact with the surface of the photosensitive drum 4 so as to be in a counter direction to the rotation direction of the photosensitive drum 4 (the tip end in the lateral direction faces the upstream side in the rotation direction of the photosensitive drum 4). The configuration of the cleaning blade 6 will be described in further detail later.

[0030] During image formation (charging), a predetermined charging voltage (charging bias), which is a DC voltage having the same polarity as the charging polarity of the photosensitive drum 4, is applied to the charging roller 5 by a charging power source (high voltage power source) (not shown) as a charging voltage application means provided in the main body 110 of the apparatus. When the charging voltage is applied to the core metal 5a of the charging roller 5 and the potential difference between the surface potential of the photosensitive drum 4 and the potential of the charging roller 5 becomes equal to or greater than the discharge start voltage, discharge is started between the photosensitive drum 4 and the charging roller 5, and the surface of the photosensitive drum 4 is uniformly charged. As a result, a dark potential (VD) is formed on the surface of the photosensitive drum 4. Specifically, in this embodiment, a DC voltage of -1050V is applied to the charging roller 5 as the charging voltage, and the dark potential VD of the surface of the photosensitive drum 4 at this time is set to -500V (VD reference value). A laser beam according to image information is irradiated onto the charged surface of the photosensitive drum 4 from the exposure device 12 provided in the main body 110 of the apparatus through an exposure opening provided in the process cartridge C. Then, a light area potential (VL) is formed on the surface of the photosensitive drum 4 by the disappearance of the surface charge by the carriers from the carrier generating layer. Specifically, in this embodiment, the light area potential at this time is set to -100V. In this manner, an electrostatic latent image is formed on the photosensitive drum 7, which is an image formed by the dark area potential VD and the light area potential VL. This electrostatic latent image is developed (visualized) by the toner T, and a toner image is formed on the photosensitive drum 4.

[0031] The toner remaining on the photosensitive drum 4 after the toner image on the photosensitive drum 4 is transferred to the recording material P (residual toner) is removed from the photosensitive drum 4 by a cleaning blade 6 fixed to the drum frame 18, and is collected in a removed toner chamber 18a. Thereafter, the surface of the photosensitive drum 4 is charged again by the charging roller 5, and the above-mentioned process is repeated.

[0032] On the other hand, the developing unit (developing device) 2 has a developing frame 19. The developing frame 19 forms a developing chamber 19a including the developing sleeve 7 and the regulating blade 9, and a toner storage chamber 19b that stores toner T.

[0033] In this embodiment, the toner T is an insulating one-component magnetic developer (magnetic toner). In this embodiment, the toner T is a negative toner having a volume average particle diameter of about 8.0 μm and a normal charging polarity of negative polarity. An external additive such as silica particles is added to the toner T to ensure the fluidity of the toner T and improve the charging property. As the silica particles, for example, sol-gel silica particles can be used, and the average particle diameter (primary particle diameter) is, for example, 1 nm or more and 200 nm or less. In addition, lubricant particles or the like may be added to the toner T as an external additive. In this embodiment, 400 g of the toner T is stored in the toner storage chamber 19b of the new development unit 2 (process cartridge C).

[0034] In the toner storage chamber 19b, an agitating member 10 is disposed to agitate the toner T and transport it toward the developing chamber 19a. The agitating member 10 has a mounting shaft and a sheet having a fitting hole that fits a dowel provided on the mounting shaft. In this embodiment, the material of the sheet is polyethylene terephthalate. The fitting hole of the sheet is fitted onto the dowel, and the tip of the dowel is enlarged by thermal welding, so that the sheet is fixed onto the mounting shaft. The agitating member 10 is rotatably supported by the developing frame 19 that constitutes the toner storage chamber 19b. During image formation (development), the agitating member 10 is rotated in the direction of the arrow R5 in the figure (clockwise direction) by a driving motor (not shown) that serves as a driving source that constitutes a driving means provided in the main body 110 of the apparatus. As a result, the toner T in the toner storage chamber 19b is agitated and transported to the developing chamber 19a.

[0035] The developing chamber 19a is provided with a developing sleeve 7 as a developer carrier (developing member). The developing sleeve 7 is rotatably supported by a developing frame 19 constituting the developing chamber 19a. In this embodiment, the developing sleeve 7 is formed by coating the surface of a non-magnetic aluminum sleeve with a resin layer containing conductive particles, and has a surface roughness Ra (arithmetic mean roughness, JIS B 0601:1994, JIS B 0031:1994) of 1.0 μm. In this embodiment, the outer diameter of the developing sleeve 7 is 16.0 mm. During image formation (development), the developing sleeve 7 is rotated at a peripheral speed of 350 mm / sec in the direction of the arrow R4 in the figure (counterclockwise direction) by a driving motor (not shown) as a driving source constituting a driving means provided in the apparatus main body 110. As a result, the developing sleeve 7 conveys the toner T to a portion (developing portion) facing the photosensitive drum 4. The developing sleeve 7 has a hollow shape, and a non-rotating magnet roller 8 having a magnetic field generating means with a multi-pole structure is disposed in the hollow portion. The outer diameter of the magnet roller 8 is 14 mm. The magnet roller 8 serves to attract the toner T to the developing sleeve 7 by magnetic force.

[0036] The developing sleeve 7 is rotatably supported at both ends in the direction of its rotation axis by a developing frame 19 that constitutes a developing chamber 19a. The direction of the rotation axis of the developing sleeve 7 and the direction of the rotation axis of the photosensitive drum 4 are substantially parallel to each other.

[0037] In addition, in the developing chamber 19a, a regulating blade 9 is disposed above the developing sleeve 7 as a toner amount regulating member. The regulating blade 9 is fixed to a developing frame 19 constituting the developing chamber 19a. The regulating blade 9 hangs down above the developing sleeve 7 and elastically abuts against the developing sleeve 7 with a predetermined pressure. As a result, the regulating blade 9 regulates the amount of the toner T carried on the developing sleeve 7, applies the toner T in a thin layer on the developing sleeve 7, and imparts an electric charge to the toner T by frictional charging. In this embodiment, the regulating blade 9 is formed of silicone rubber with a rubber hardness of 40° in JIS-A hardness. In this embodiment, the contact pressure Pr of the regulating blade 9 against the developing sleeve 7 is set to about 25 gf / cm. The contact pressure Pr of the regulating blade 9 against the developing sleeve 7 is expressed as a contact load (gf) per unit length (1 cm) in the longitudinal direction of the developing sleeve 7.

[0038] A gap is provided between the developing sleeve 7 and the photosensitive drum 4 by a gap retaining member (not shown). In this embodiment, the gap is set to 200 μm. A developing power source (high voltage power source) (not shown) is connected to the developing sleeve 7 as a developing voltage applying means provided in the apparatus main body 110. During image formation (development), a predetermined developing voltage (developing bias) is applied to the developing sleeve 7 by the developing power source. As a result, a predetermined electric field is formed between the photosensitive drum 4 and the developing sleeve 7 in the developing section, and the electrostatic latent image on the photosensitive drum 4 is reversely developed by the toner T. In this embodiment, an alternating voltage in which a direct current voltage component (developing DC bias) of −350 V and an alternating current voltage component (developing AC bias) having a waveform of 1200 Vpp, a frequency of 1500 Hz, and a square wave are superimposed is applied to the developing sleeve 7 as the developing voltage. By applying such a developing voltage to the developing sleeve 7, it becomes possible for the toner T to fly through the gap between the photosensitive drum 4 and the developing sleeve 7. As a result, the negatively charged toner T is electrically attracted to the image portion of the electrostatic latent image on the photosensitive drum 4, thereby forming a toner image.

[0039] The photosensitive drum 4 and the rotating members of the developing device 2 (the developing sleeve 7 and the stirring member 10) may share a common driving source.

[0040] <Photoreceptor> Next, the photoconductor (photoconductor drum 4) in this embodiment will be further described. In this embodiment, the photoconductor is configured to have a cylindrical conductive metallic support, an undercoat layer formed on the support, and a photosensitive layer (charge generating layer, charge transport layer) formed on the undercoat layer.

[0041] (Support) The support is preferably a conductive support having electrical conductivity. The shape of the support may be a cylinder, a belt, a sheet, or the like. Among these, a cylindrical support is preferable.

[0042] The support material is preferably a metal, a resin, a glass, etc. Among these, an aluminum support using aluminum is preferable.

[0043] (Undercoat layer) An undercoat layer is provided on the support. By providing the undercoat layer, the adhesion function between the support and the layer thereon can be improved, and the photoreceptor can be provided with a charge injection blocking function.

[0044] The undercoat layer preferably contains a resin. The undercoat layer may further contain an electron transport material, a metal oxide, a metal, a conductive polymer, etc., for the purpose of improving electrical properties. Among these, it is preferable to use an electron transport material or a metal oxide.

[0045] The average thickness of the undercoat layer is preferably from 0.1 μm to 50 μm, more preferably from 0.2 μm to 40 μm, and particularly preferably from 0.3 μm to 30 μm.

[0046] The undercoat layer can be formed by preparing a coating liquid for the undercoat layer containing the above-mentioned materials and a solvent, forming a coating film from this coating liquid, and drying and / or curing the coating film.

[0047] (Charge generation layer) The charge generating layer preferably contains a charge generating material and a resin. The charge generating material is preferably an azo pigment or a phthalocyanine pigment. The resin is more preferably a polyvinyl butyral resin.

[0048] The average thickness of the charge generating layer is preferably from 0.1 μm to 1 μm, and more preferably from 0.15 μm to 0.4 μm.

[0049] The charge generating layer can be formed by preparing a coating liquid for the charge generating layer containing the above-mentioned materials and solvent, forming a coating film from this coating liquid, and drying it.

[0050] (charge transport layer) The charge transport layer preferably contains a charge transport material and a resin. As the charge transport material, a triarylamine compound or a benzidine compound is preferable.

[0051] As the resin, polycarbonate resin and polyester resin are preferable, and as the polyester resin, polyarylate resin is particularly preferable.

[0052] The charge transport layer may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, and abrasion resistance improvers.

[0053] The average thickness of the charge transport layer is preferably 5 μm to 50 μm, more preferably 8 μm to 40 μm, and particularly preferably 10 μm to 30 μm In this embodiment, the average thickness of the charge transport layer is 23 μm.

[0054] The charge transport layer can be formed by preparing a coating liquid for the charge transport layer containing the above-mentioned materials and solvent, forming a coating film from the coating liquid, and drying the coating liquid. The solvent used in the coating liquid is preferably an ether-based solvent or an aromatic hydrocarbon-based solvent.

[0055] In this embodiment, a laminated type photoreceptor having a charge generating layer and a charge transporting layer is used, but a single-layered type photoreceptor containing both a charge generating material and a charge transporting material may be used. The single-layered type photoreceptor can be formed by preparing a coating liquid for a photosensitive layer containing a charge generating material, a charge transporting material, a resin, and a solvent, forming a coating film from this coating liquid, and drying it. The charge generating material, the charge transporting material, and the resin are the same as the examples of materials for the laminated type photoreceptor.

[0056] Also, a protective layer may be formed on the charge transport layer, and this protective layer may be used as the outermost layer of the photoreceptor.

[0057] <Cleaning blade> Next, the cleaning blade 6 in this embodiment will be further described. The cleaning device 17 has the cleaning blade 6 as a cleaning member that comes into contact with the surface of the photosensitive drum 4 to remove the toner and external additives on the photosensitive drum 4.

[0058] In this embodiment, the cleaning blade 6 is made of polyurethane rubber with a JIS-A hardness of 72°, and is held and integrated with the tip of a support member made of sheet metal. In this embodiment, the cleaning blade 6 is in contact with the surface of the photosensitive drum 4 in a counter direction (a direction in which the tip faces upstream in the rotation direction of the photosensitive drum 4) with respect to the rotation direction of the photosensitive drum 4. In this embodiment, the cleaning blade 6 is in contact with the photosensitive drum 4 under the conditions of a contact pressure of 35 N / m, a penetration amount δ of 1.3 mm, and a set angle θ of 22°.

[0059] The desired contact state of the cleaning blade 6 against the photosensitive drum 4 for removing the toner and external additives on the photosensitive drum 4 can be appropriately selected depending on the materials of the photosensitive drum 4 and the cleaning blade 6. It is considered that the desired contact state can be obtained by changing design values ​​other than the hardness, such as the contact pressure, penetration amount, and set angle, which will be described below.

[0060] The penetration amount δ is the penetration length of the tip surface of the cleaning blade 6 when it is assumed that the tip of the cleaning blade 6 does not deform and penetrates into the photosensitive drum 4 as is in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 4. In addition, the set angle θ is the angle between the axis of the cleaning blade 6 and a tangent to the photosensitive drum 4 at the point where the tip surface of the cleaning blade 6 and the photosensitive drum 4 intersect in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 4.

[0061] In order to effectively remove toner and external additives, the penetration amount δ is preferably in the range of 0.5 mm or more and 1.8 mm or less. If the penetration amount δ is smaller than the above range, a phenomenon in which toner slips through the cleaning blade 6 (hereinafter, also referred to as "toner slip-through") may occur, and if it is larger than the above range, the load for rotating the photosensitive drum 4 may become too large. In order to obtain a sufficient contact length (contact distance) between the photosensitive drum 4 and the cleaning blade 6, the penetration amount δ is more preferably in the range of 1.0 mm or more and 1.8 mm or less.

[0062] Furthermore, in order to effectively remove toner and external additives, the set angle θ is preferably in the range of 20 degrees or more and 32 degrees or less. If the set angle θ is smaller than the above range, toner may slip through, and if it is larger than the above range, the cleaning blade 6 may turn over or a slipping noise may occur. Furthermore, in order to achieve both the pressure (contact pressure) at which the photosensitive drum 4 and the cleaning blade 6 come into contact with each other and a margin for the turning over of the cleaning blade 6, the set angle θ is more preferably in the range of 20 degrees or more and 25 degrees or less.

[0063] Furthermore, in order to effectively remove toner and external additives, the contact pressure of the cleaning blade 6 against the photosensitive drum 4 is preferably in the range of 30 N / m to 80 N / m. If the contact pressure is lower than the above range, good cleaning performance may not be obtained, and if it is higher than the above range, the load for rotating the photosensitive drum 4 may become too large. In order to increase the pressure (contact pressure) at which the photosensitive drum 4 and the cleaning blade 6 contact each other, the contact pressure is more preferably in the range of 40 N / m to 80 N / m. The contact pressure of the cleaning blade 6 against the photosensitive drum 4 is expressed as the contact load (N) per unit length (1 m) in the longitudinal direction of the photosensitive drum 4.

[0064] Examples of materials that can be used for the cleaning blade 6 include polyurethane, silicone rubber, fluororubber, chloroprene rubber, and butadiene rubber. Among these, polyurethane is preferred because it has an appropriate strength and flexibility to contact the rotating photosensitive drum 4.

[0065] The cleaning blade 6 may have a JIS-A hardness within the desired range for the entire cleaning blade 6, or may have a hardened layer having a JIS-A hardness within the desired range in the portion that contacts the photosensitive drum 4. By making only the portion of the cleaning blade 6 that contacts the photosensitive drum 4 a hardened layer with a high hardness, it becomes easier to adjust the hardness of the main body of the cleaning blade 6 so that the cleaning blade 6 has flexibility to bend appropriately when it contacts the photosensitive drum 4.

[0066] The hardened layer may be a layer provided on the surface of the cleaning blade 6, but from the viewpoint of enhancing durability, it is preferable that the hardened layer is a layer obtained by processing a part of the main body of the cleaning blade 6.

[0067] When polyurethane is used as the base material of the cleaning blade 6, the hardened layer can be formed as follows. That is, the portion of the cleaning blade 6 that contacts the photosensitive drum 4 is immersed in an isocyanate compound for a certain period of time. Then, the polyurethane contained in the main body of the cleaning blade 6 is reacted with the isocyanate compound, and the reacted portion can be formed as a hardened layer.

[0068] <Charging roller> Next, the charging roller 5 in this embodiment will be further described.

[0069] (Overview of the elastic layer) In this embodiment, the charging roller 5 has an elastic layer. The elastic layer of the charging roller 5 will be described below.

[0070] The elastic layer may be made of one or more types of elastomers such as rubber that have been used in the elastic layer (conductive elastomer layer) of a conventional charging roller. Examples of rubber include the following: 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.

[0071] In addition, the conductivity of the elastic layer can be adjusted to a desired value by appropriately incorporating a conductive agent into the material of the elastic layer. The electrical resistance value of the elastic layer can be adjusted by appropriately selecting the type and amount of the conductive agent used. The preferred range of the electrical resistance value is 10 2 ~10 8 Ω·cm, and a more preferable range is 10 3 ~10 6The electrical resistance is Ω·cm. As a conductive agent for the elastic layer, conductive carbon such as Ketjen Black EC, acetylene black, rubber carbon, color (ink) carbon with oxidation treatment, and pyrolytic carbon can be used. In addition, graphite such as natural graphite and artificial graphite can be used as a conductive agent for the elastic layer. Inorganic or organic fillers and crosslinking agents can be added to the material for the elastic layer.

[0072] (Elastic layer having matrix-domain structure) An elastic layer having a matrix-domain structure can be suitably used as the elastic layer of the charging roller 5. The matrix-domain structure is a structure having a matrix and a plurality of domains dispersed in the matrix.

[0073] -Method of forming matrix domain structure- A method for forming a matrix-domain structure is described.

[0074] 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. Among them, in order to stably exert the function as a conductive member for electrophotography by contacting it with another member, it is preferable to obtain it by the following method. In other words, it is preferable that the elastic layer has a matrix-domain type phase separation structure due to phase separation between a matrix containing a first rubber having insulating properties and a second rubber having conductive properties.

[0075] It is preferable that the elastic layer having a matrix-domain structure in the charging roller 5, which is a conductive member, satisfies the following conditions (i) and (ii). Condition (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. Condition (ii): The volume resistivity of the domain is 1.0×10 1Ω cm or more 1.0×10 4 Must be Ω·cm or less.

[0076] 12 shows a schematic partial cross-sectional view of an elastic layer in a direction perpendicular to the longitudinal direction of a charging roller (conductive roller) 5. An elastic layer 53 (corresponding to elastic layer 5b in FIGS. 13(a) and (b)) has a matrix-domain structure having a matrix 54 and domains 55. The domains 55 contain a conductive agent. Preferably, the domains 55 contain conductive particles 56 that are electronic conductive agents as the conductive agent.

[0077] -Method for measuring volume resistivity of matrix- The volume resistivity of the matrix can be measured by cutting the elastic layer into a thin section and using a microprobe. Examples of the cutting method include a sharp razor, a microtome, and a focused ion beam (FIB) method.

[0078] Regarding the preparation of thin sections, it is necessary to eliminate the effect 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 previously measured with a scanning electron microscope (SEM) or transmission electron microscope (TEM), etc. Therefore, the preferred method of thinning is a method that can prepare very thin samples, such as a microtome.

[0079] The volume resistivity is measured by first grounding one side of the flake, and then identifying the locations of the matrix and domain in the flake. These locations can be identified by a means capable of measuring the volume resistivity or hardness distribution of the matrix and domain, such as a scanning probe microscope (SPM) or an atomic force microscope (AFM). Next, a probe is brought into contact with the matrix, a DC voltage of 50V is applied for 5 seconds, the arithmetic average value of the ground current value for 5 seconds is measured, and the electrical resistance value is calculated by dividing by the voltage. Then, the measured volume resistivity can be obtained by converting the volume resistivity using the film thickness of the flake. At this time, a means capable of measuring the shape of the flake, such as an SPM or an AFM, is preferable because it can measure the film thickness of the flake and therefore the volume resistivity.

[0080] The volume resistivity of the matrix in the elastic layer of the charging roller 5, which is a cylindrical conductive member, can be determined as follows: That is, the elastic layer is divided into four regions in the circumferential direction and five regions in the longitudinal direction, and one thin sample is cut out from each of the regions, and after the above-mentioned measured values ​​are obtained, the arithmetic average value of the volume resistivities of a total of 20 samples is calculated.

[0081] - Domain volume resistivity - The volume resistivity of each domain is smaller than the volume resistivity of the matrix, which is preferable because it makes it easier to limit the charge transport path to a path passing through multiple domains while suppressing unintended charge migration in the matrix.

[0082] Moreover, the volume resistivity of the domain is preferably smaller than the volume resistivity of the matrix by at least five orders of magnitude.

[0083] The volume resistivity of the domain is 1.0×10 1 Ω cm or more 1.0×10 4It is preferable to set the volume resistivity of the domains to Ω·cm or less. By lowering the volume resistivity of the domains, it is possible to suppress the movement 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 this range, the amount of charge that moves within the domains can be dramatically improved, so that the charge transport path can be effectively limited to via the domains.

[0084] 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 of the rubber component 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 of the agent added. 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.

[0085] Examples of the electronic conductive agent to be blended in the domain include oxides such as carbon black, graphite, titanium oxide, and tin oxide; metals such as Cu and Ag; particles that are coated with an oxide or metal to make them conductive, etc. If necessary, two or more of these conductive agents may be blended in appropriate amounts.

[0086] Among the above-mentioned electronic conductive agents, it is preferable to use conductive carbon black, which has a high affinity with rubber and is easy to control the distance between the electronic conductive agents. The type of carbon black to be mixed 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.

[0087] If necessary, fillers, processing aids, crosslinking aids, crosslinking accelerators, antiaging agents, crosslinking accelerators, 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 domain within a range that does not impair the effects of the present invention.

[0088] -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 during measurement of the current value is changed to 1 V.

[0089] -Production method- The charging roller 5, which is a conductive member provided with an elastic layer having a matrix-domain structure, 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") comprising a first rubber; Step (iii): 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 core metal (conductive support) directly or via another layer, and curing the layer of rubber composition to form an elastic layer.

[0090] The volume resistivity of each of the matrix and domains can be controlled by, for example, selecting the materials used in each of the above steps and adjusting the manufacturing conditions, as will be described below.

[0091] First, regarding condition (i), the volume resistivity of the matrix is ​​determined by the composition of the MRC.

[0092] As the first rubber used in the MRC, at least one of low-conductivity rubbers 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, and polynorbornene rubber may be used. In addition, on the premise that the volume resistivity of the matrix can be set within the above range, a filler, a processing aid, a crosslinking agent, a crosslinking aid, a crosslinking accelerator, a crosslinking accelerator aid, a crosslinking retarder, an anti-aging agent, a softener, a dispersant, and a colorant may be added to the MRC as necessary. On the other hand, in order to set the volume resistivity of the matrix within the above range, it is preferable that the MRC does not contain an electronic conductive agent such as carbon black.

[0093] Regarding condition (ii), the volume resistivity of the domain can be adjusted by the amount of the electronic conductive agent in the CMB.

[0094] For example, the DBP oil absorption is 40 cm 3 / 100g or more 170cm 3 Take the case of using a conductive carbon black having a porosity of 0.1 to 100 g / mol / g or less as an example. In this case, the condition (ii) can be achieved by preparing the CMB so that the conductive carbon black contains 40% by mass or more and 200% by 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), cycloprene rubber (CR), nitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), silicone rubber, and urethane rubber (U). At least one of these can be used.

[0095] - How to check the matrix domain structure - The presence of a matrix-domain structure in the elastic layer can be confirmed by preparing a thin slice from the elastic layer and closely observing the fracture surface formed in the thin slice.

[0096] Examples of means for cutting the elastic layer into thin slices include a sharp razor, a microtome, FIB, etc. In order to perform more accurate observation of the matrix-domain structure, the thin slices for observation may be subjected to pretreatment such as dyeing or deposition treatment, which can favorably obtain contrast between the domains as a conductive phase and the matrix as an insulating phase.

[0097] The presence of the matrix-domain structure can be confirmed by observing the fracture surface of the formed and, if necessary, pretreated thin section using a laser microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. Observation using a scanning electron microscope (SEM) is preferable as a method that can simply and accurately confirm the matrix-domain structure (island-in-sea structure).

[0098] A slice of the elastic layer is obtained by the above method, and an image is obtained by observing the surface of the slice at 1000 to 10000 times magnification. Then, an image processing means such as ImageProPlus (manufactured by Media Cybernetics) is used to convert the image to 8-bit grayscale and obtain a monochrome image with 256 gradations. Next, the image is inverted to black and white so that the domains in the fracture surface become white, and binarized to obtain an analysis image. The presence or absence of a matrix-domain structure can be determined from the analysis image that has been image-processed to a state in which the domains and matrix are distinguished by binarization.

[0099] When the analysis image includes a structure in which a plurality of domains 55 exist in an isolated state in a matrix 54 as shown in Fig. 12, the presence of a matrix-domain structure in the elastic layer can be confirmed. The isolated state of the domains may be such that each domain is arranged without being connected to other domains, the matrix is ​​connected in the image, and the domains are separated by the matrix. Specifically, when an analysis region is a 50 µm square in the analysis image, the number of domains existing in an isolated state as described above is 80 percent or more of the total number of domains that do not contact the border of the analysis region, and the matrix-domain structure (sea-island structure) is defined as being present.

[0100] The above-mentioned confirmation of the elastic layer of the charging roller 5, which is a cylindrical conductive member, can be performed by dividing the elastic layer equally into 5 equal parts in the longitudinal direction and 4 equal parts in the circumferential direction, randomly selecting one section from each area, for a total of 20 sections, and then carrying out the above-mentioned measurement.

[0101] (Surface layer) The charging roller 5 in this embodiment may have a structure in which a surface layer is laminated on the outside of the elastic layer. This surface layer can be the outermost layer of the charging roller 5. However, as will be described in detail later, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 must satisfy the relationship E'C>E'CC. The surface layer of the charging roller 5 will be described below.

[0102] - Binder resin - The binder used in the surface layer may be a known binder. For example, resin, natural rubber or vulcanized natural rubber, synthetic rubber, etc. may be used. The resin may be a thermosetting resin, a thermoplastic resin, etc. Among them, fluororesin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, etc. are more preferable.

[0103] The surface layer preferably contains a conductive material, such as an ionic conductive material or an electronic conductive material.

[0104] 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, trioctylpropyl ammonium bromide, and modified aliphatic dimethylethyl 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 of two or more.

[0105] 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 fine particles of metals, fibers, and metal oxides have been treated by electrolysis, spray coating, mixing and shaking, etc.; carbon powders such as furnace black, thermal black, acetylene black, ketjen black, PAN (polyacrylonitrile)-based carbon, and pitch-based carbon.

[0106] Examples of furnace black 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 black include FT and MT. These conductive agents can be used alone or in combination of two or more.

[0107] The conductive agent preferably has an average particle size of 0.01 μm or more and 0.9 μm or less, and more preferably 0.01 μm or more and 0.5 μm or less, in which case the volume resistivity can be easily controlled.

[0108] The amount of the conductive agent added to the surface layer is preferably 2 parts by mass or more and 80 parts by mass or less, and more preferably 20 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the binder.

[0109] The conductive agent may be surface-treated. As the surface treatment agent, organic silicon compounds such as alkoxysilane, fluoroalkylsilane, polysiloxane, various coupling agents such as silane, titanate, aluminate, and zirconate, oligomers, or polymer compounds can be used. These may be used alone or in combination of two or more. The surface treatment agent is preferably an organic silicon compound such as alkoxysilane, polysiloxane, various coupling agents such as silane, titanate, aluminate, or zirconate, and more preferably an organic silicon compound.

[0110] The surface layer may be subjected to a surface treatment, such as a surface processing treatment using UV (ultraviolet rays) or an electron beam, or a surface modification treatment in which a compound or the like is attached to and / or impregnated into the surface.

[0111] The average thickness of the surface layer is preferably from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm. By setting the average thickness in this range, it becomes easy to form a surface layer that satisfies the relationship E'C>E'CC described later.

[0112] - Formation of surface layer - The surface layer can be formed by a coating method such as electrostatic spray coating or dipping coating. Alternatively, the surface layer can be formed by adhering or covering a sheet-shaped or tube-shaped layer that has been formed to a predetermined thickness on the lower layer (elastic layer). Alternatively, a method of curing and molding a material into a predetermined shape in a mold can also be used to form the surface layer. Among them, it is preferable to apply a paint by a coating method to form a coating film. When forming a layer by a coating method, the solvent used in the coating liquid may be any solvent that can dissolve the binder resin. Specifically, examples of the solvent 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 resin 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.

[0113] (Configuration of the charging roller) The charging roller 5 in this embodiment can be formed by appropriately using, for example, the above-mentioned materials. However, as will be described in detail later, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 need to satisfy the relationship E'C>E'CC.

[0114] The elastic layer of the charging roller 5 does not need to have a matrix-domain structure. The elastic layer of the charging roller 5 may be, for example, a substantially homogeneous rubber layer having the above-mentioned preferable electrical properties. However, when the elastic layer of the charging roller 5 has a matrix-domain structure, the discharge of the charging roller 5 to the photosensitive drum 4 becomes a microdischarge. As a result, the external additives liberated from the toner, particularly those having a charge of the opposite polarity to the normal charging polarity of the toner (positive charge in this embodiment), are less likely to adhere firmly to the photosensitive drum 4. Therefore, the external additives are easily scraped off by the cleaning blade 6, and the dirt on the charging roller 5 is easily suppressed. For these reasons, it is preferable that the elastic layer of the charging roller 5 has a matrix-domain structure.

[0115] Furthermore, the charging roller 5 is not limited to a single-layer structure of an elastic layer or a two-layer structure of an elastic layer and a surface layer. The elastic layer may be made of multiple layers having different materials or structures, another layer may be provided between the core metal and the elastic layer, or another layer may be provided between the elastic layer and the surface layer.

[0116] (Charging roller surface characteristics) -Overview of the surface characteristics of charging rollers- In this embodiment, the image forming apparatus 100 is configured such that the storage modulus E'C of the surface (outermost surface, outer circumferential surface) of the charging roller 5 and the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 satisfy the relationship E'C>E'CC. The magnitude of the storage modulus (E') correlates with the physical adhesive force, and when the storage modulus (E') is small, the physical adhesive force is stronger than when the storage modulus (E') is large. Therefore, when the relationship E'C>E'CC is satisfied, the adhesive force of the external additive attached to the surface of the charging roller 5 to the cleaning roller 15 is stronger than that to the charging roller 5. In addition, when the charging roller 5 and the cleaning roller 15, which are rotating members, rotate in contact with each other, even if it is aimed to make the moving speeds of the surfaces of both rollers equal, there is usually a certain degree of speed difference between the moving speeds of the surfaces of both rollers. This speed difference is, for example, about ±5%. In particular, when the cleaning roller 15 rotates in accordance with the rotation of the charging roller 5 as in this embodiment, the moving speed of the surface of the cleaning roller 15 is slightly slower than that of the charging roller 5. In a state in which the external additive is more likely to adhere to the cleaning roller 15 than to the charging roller 5 as described above, if there is such a speed difference, the external additive is easily scraped up by the cell skeleton of the foamed elastic layer of the cleaning roller 15 and gathered on the charging roller 5 to form lumps. Furthermore, the deformation of the cell skeleton of the foamed elastic layer of the cleaning roller 15 when it is released from a compressed state due to contact with the charging roller 5 acts to repel the above-mentioned lumps of the external additive and lift them off the surface of the charging roller 5. In this state, when the surface of the charging roller 5 comes into contact with the surface of the photosensitive drum 4, the external additive becomes lumpy and easily adheres to the surface of the photosensitive drum 4, and is therefore easily removed from the surface of the charging roller 5.

[0117] In addition, it is preferable that the Martens hardness of the surface (outermost surface, outer peripheral surface) of the charging roller 5 is 15 N / mm 2 By doing so, the external additives that have become lumps on the surface of the charging roller 5 as described above can be more vigorously repelled and lifted.

[0118] In this manner, in this embodiment, by satisfying the relationship E'C>E'CC, the cleaning roller 15 does not strip the external additive from the charging roller 5, but rather acts to lift the external additive from the surface of the charging roller 5 and return it to the photosensitive drum 4 when it comes into contact with and separates from the charging roller 5. This action also reduces the Martens hardness of the surface of the charging roller 5 to 15 N / mm 2 By adopting the above-mentioned configuration, it is possible to obtain the above-mentioned effects more effectively. With such a configuration, it is possible to maintain the effect of the cleaning roller 15 in removing the external additives from the charging roller 5 for a longer period of time, and to suppress the contamination of the charging roller 5 for a longer period of time. As a result, this is advantageous for extending the life of the process cartridge C.

[0119] Here, the removal of external additives, which become problematic due to accumulation on the surface of the charging roller 5 after long-term use of the process cartridge C, will be described in particular, but toner can also be removed by a similar mechanism. A portion of the toner may be stored in the space in the foamed elastic layer of the cleaning roller 15. Even in that case, according to this embodiment, the toner can be returned from the charging roller 5 to the photosensitive drum 4 by the mechanism described above, so clogging of the space in the foamed elastic layer of the cleaning roller 15 by toner can be suppressed. Therefore, the cleaning roller 15 is likely to maintain good cleaning performance for a long period of time.

[0120] -Storage modulus- The storage modulus (E') is the ability to retain stress stored inside a material such as rubber or resin, and is an index closely correlated with the hardness of the material. The magnitude of the storage modulus (E') correlates with the physical adhesive force. Therefore, by making the storage modulus E'C of the surface of the charging roller 5 and the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 satisfy the relationship E'C>E'CC, the adhesive force of the external additive to the cleaning roller 15 can be made higher than the adhesive force to the charging roller 5. This storage modulus (E') is generally measured using a dynamic mechanical analyzer (DMA).

[0121] In addition, the value of the storage modulus (E') may vary greatly depending on the measurement temperature and measurement frequency. Therefore, in the present invention, the measurement temperature of the storage modulus (E') was set to 23°C and 50% RH (relative humidity), which are the same conditions as those for evaluating the effect of removing dirt from the charging roller 5, as described later. In addition, the excitation frequency of the vibration actually generated when the image forming apparatus 100 is driven varies depending on the rotation speed of the charging roller 5, the difference in peripheral speed between the photosensitive drum 4 and the cleaning roller 15 that contact the charging roller 5, the configuration of the surface of the charging roller 5 (the surface of the elastic layer and the surface layer), and the like. Therefore, in the present invention, the measurement frequency of the storage modulus (E') was set to 10 Hz, which is near the average value of the excitation frequency in the actual machine.

[0122] Furthermore, the value of the storage elastic modulus (E') may vary depending on the depth from the surface (outermost surface, outer peripheral surface) of the charging roller 5. Therefore, in the present invention, the storage elastic modulus E'C of the surface of the charging roller 5 is a value measured at a depth of 10 μm or less from the surface of the charging roller 5. Here, when the surface (outermost surface, outer peripheral surface) of the charging roller 5 is composed of an elastic layer, the value of the storage elastic modulus (E') of the surface of the charging roller 5 is a value measured at a depth of 10 μm or less from the surface of the elastic layer. Also, when the surface (outermost surface, outer peripheral surface) of the charging roller 5 is formed of a surface layer formed on the elastic layer, the value of the storage elastic modulus (E') of the surface of the charging roller 5 is a value measured at a depth of 10 μm or less from the surface of the surface layer. This is because it has been found that the storage elastic modulus (E') at a depth of about 10 μm or less from the surface of the charging roller 5 correlates with the adhesion of external additives. The method of measuring the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 will be described later in more detail.

[0123] More specifically, in order to check the rubber hardness of the surface of the charging roller 5, the storage modulus E'C of the surface of the charging roller 5 was measured as follows. The measurement of the storage modulus E'C of the surface of the charging roller 5 was performed using a dynamic viscoelasticity measuring device (product name: EPLEXOR-500N, manufactured by GABO). As described above, the measurement sample was taken with a microtome from the surface of the charging roller 5 to a depth of about 10 μm. The measurement of the storage modulus (E') was performed under the following conditions.

[0124] [Measurement conditions] Measurement mode: Tensile test mode ·Measurement frequency: 10Hz ·Measurement temperature: 23℃ ·Measurement humidity: 50%RH Transducer: 25N Dynamic Distortion: 1.0% Static distortion: 2.0% Measurement sample shape: Width 5.0mm x Length 20mm

[0125] -Martens hardness- Martens hardness is a physical property that is determined by pressing an indenter into a test object while applying a load, and is expressed as (test load) / (surface area of ​​the indenter under the test load) (N / mm 2 ) The Martens hardness includes both plastic and elastic deformation components.

[0126] The Martens hardness of the surface (outermost surface, outer circumferential surface) of the charging roller 5 is set to 15 N / mm from the viewpoint of efficiently lifting and moving the external additives attached to the surface of the charging roller 5. 2 In other words, it is preferable that the Martens hardness of the surface of the charging roller 5 is 15 N / mm 2 By doing so, the cell skeleton of the foamed elastic body of the cleaning roller 15 can more vigorously repel the lumps of external additives formed on the surface of the charging roller 5, causing them to float from the surface of the charging roller 5. This is thought to be because, due to the hardness of the surface of the charging roller 5, the temporal transition from compression to release of the cell skeleton of the cleaning roller 15 is accelerated at the moment when the charging roller 5 is released from the contact portion between the charging roller 5 and the cleaning roller 15, as will be described later. From this point of view, the Martens hardness of the surface of the charging roller 5 is 15 N / mm 2 It is preferable to set the resistance to 25N / mm or more. 2 However, from the viewpoint of the limitations of the resin materials that can be used to form the charging roller 5 using thermosetting resin and thermoplastic resin, the Martens hardness of the surface of the charging roller 5 is preferably 40 N / mm 2In order to prevent the surface of the charging roller 5 from being contaminated by the charging roller 5 crushing the toner and external additives that have passed through the cleaning blade 6, the Martens hardness of the surface of the charging roller 5 is set to 35 N / mm 2 More preferably, it should be 30N / mm 2 It is even more preferable that:

[0127] The Martens hardness of the surface of the charging roller 5 was measured using a microhardness tester (product name: Picodentor HM500, manufactured by Helmut Fischer) which is a surface coating property tester. In addition, the software used was "WIN-HCU" (product name) which is an accessory of the surface coating property tester.

[0128] An indenter such as a pyramid is pressed into the object under test while applying a relatively small predetermined test load, and the surface area in contact with the indenter is calculated from the indentation depth at the time when the indenter reaches a predetermined indentation depth, and the Martens hardness (universal hardness) is calculated from the following formula. In the present invention, the hardness when indented with a load of 1 mN is used.

[0129] More specifically, the Martens hardness of the surface of the charging roller 5 was measured as follows. Based on ISO 14577, the measurement was performed using a surface coating physical property tester (product name: Picodentor HM500, manufactured by Helmut Fischer). The Martens hardness was measured at 10 measurement points arbitrarily selected in the center of the longitudinal direction of the elastic layer of the charging roller 5. The arithmetic mean value of the values ​​obtained by the measurement was taken as the measured value of the Martens hardness of the surface of the charging roller 5. The measurement conditions are shown below.

[0130] [Measurement conditions] Measurement indenter: Square pyramid indenter (angle 136°, Berkovich type) Indenter material: Diamond ·Measurement environment: Temperature 23℃, 50%RH Loading and unloading speed: 1mN / 50sec Maximum pressing force: 1mN

[0131] A load was applied at the speed described above under the above conditions to measure the load-hardness curve, and the Martens hardness at the point when the indentation depth reached 0.1 μm was calculated using the following formula. Martens hardness HM (N / mm 2 ) = F (N) / surface area of ​​indenter under test load (mm 2 ) In the above formula, F represents force.

[0132] -Surface roughness- The material (material of the elastic layer and surface layer) forming the surface (outermost surface, outer peripheral surface) of the charging roller 5 may contain spherical fine particles that form an uneven shape on the surface in order to impart an appropriate surface roughness to the surface of the charging roller. When the material forming the surface of the charging roller 5 contains spherical fine particles, it becomes easy to make the surface roughness of the surface of the charging roller 5 uniform, and even if the surface is worn, it becomes easy to reduce the fluctuation in the surface roughness and maintain a constant surface condition.

[0133] The volume average particle diameter of the spherical particles is preferably 5 μm or more and 30 μm or less. A laser diffraction particle size distribution measuring device (product name: LS-230 type; manufactured by Coulter) equipped with a liquid module can be used to measure the volume average particle diameter of the particles. The measurement is performed by adding a small amount of surfactant to about 10 cc of water, adding about 10 mg of particles to the water, dispersing the particles for 10 minutes using an ultrasonic disperser, and then performing the measurement under the conditions of a measurement time of 90 seconds and a measurement count of 1 time. The value measured by the above measurement method can be used as the value of the volume average particle diameter.

[0134] The content of the spherical fine particles is preferably 1 part by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the resin (for example, polyester resin, polyurethane resin component) forming the surface of the charging roller 5.

[0135] Examples of materials for the spherical fine particles include urethane resin, polyester resin, polyether resin, acrylic resin, polycarbonate resin, polyethylene resin, and nylon resin. These spherical fine particles can be produced, for example, by suspension polymerization or dispersion polymerization.

[0136] From the viewpoint of suppressing adhesion of toner and external additives to the surface of the charging roller 5, and from the viewpoint of controlling the potential of the photosensitive drum 4, the surface roughness Rz (ten-point average roughness, JIS B 0601:1994, JIS B 0031:1994) of the surface of the charging roller 5 is preferably 0.1 μm or more and 25 μm or less, and more preferably 1.0 μm or more and 20 μm or less.

[0137] <Cleaning roller> Next, the cleaning roller 15 in this embodiment will be further described.

[0138] (Cleaning roller configuration) The cleaning roller 15 is a cleaning member that comes into contact with the charging roller 5 to clean the charging roller 5. The cleaning roller 15 has an elastic layer that comes into contact with the charging roller 5, and this elastic layer is a foamed elastic layer made of a foamed elastic body. The foamed elastic layer forms the surface (outermost surface, outer peripheral surface) of the cleaning roller 15.

[0139] Examples of materials for the foamed elastic layer include foamable resins (polyurethane, polyethylene, polyamide, polypropylene, etc.), rubber materials (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, butyl rubber, etc.), and materials made by blending two or more kinds of them. In addition, these may contain auxiliary agents such as foaming assistants, foam stabilizers, catalysts, curing agents, plasticizers, and vulcanization accelerators, as necessary.

[0140] The material of the foamed elastic layer is preferably a foamed polyurethane that is strong against tension, from the viewpoint of preventing scratches on the surface of the object to be cleaned (the charging roller 5) due to friction and preventing tearing or breakage over a long period of time. Examples of polyurethane include reaction products of polyols (e.g., polyester polyols, polyether polyols, polyesters, acrylic polyols, etc.) and isocyanates (e.g., 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, tolylene diisocyanate, 1,6-hexamethylene diisocyanate, etc.), and may contain a chain extender (1,4-butanediol, trimethylolpropane).

[0141] The foaming of polyurethane is generally carried out using a foaming agent such as water or an azo compound (e.g., azodicarbonamide, azobisisobutyronitrile, etc.) If necessary, assistants such as a foaming assistant, a foam stabilizer, and a catalyst may be added to the foamed polyurethane.

[0142] Here, the contact pressure of the cleaning roller 15 against the charging roller 5 is preferably 40 mN / mm or less. In other words, if the cleaning roller 15 is brought into contact with the charging roller 5 with a contact pressure exceeding 40 mN / mm, the charging roller 5 is braked by the contact pressure from the cleaning roller 15. As a result, the charging roller 5 does not rotate, and there is a possibility that the charging of the photosensitive drum 4 may be impaired. From this viewpoint, the contact pressure of the cleaning roller 15 against the charging roller 5 is preferably 40 mN / mm or less, and more preferably 20 mN / mm or less. On the other hand, in order to remove dirt from the charging roller 5, the contact pressure of the cleaning roller 15 against the charging roller 5 is preferably 0.5 mN / mm or more. In other words, if the contact pressure of the cleaning roller 15 against the charging roller 5 is smaller than the above value, there is a possibility that the cleaning roller 15 may not be able to sufficiently remove dirt from the charging roller 5. From this viewpoint, the contact pressure of the cleaning roller 15 against the charging roller 5 is preferably 0.5 mN / mm or more, and more preferably 1.0 mN / mm or more. In this embodiment, the cleaning roller 15 is brought into contact with the charging roller 5 at a contact pressure of 20 mN / mm, and is rotated in accordance with the rotation of the charging roller 5. The contact pressure of the cleaning roller 15 with respect to the charging roller 5 is expressed as a contact load (mN) per unit length (1 mm) of the charging roller 5 in the longitudinal direction.

[0143] (Storage modulus) As described above, in this embodiment, the image forming apparatus 100 is configured such that the storage modulus E'C of the surface (outermost surface, outer circumferential surface) of the charging roller 5 and the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 satisfy the relationship E'C>E'CC. As a result, the cleaning roller 15 collects the external additives adhering to the surface of the charging roller 5 in clumps, floats the external additives from the surface of the charging roller 5, and returns them to the photosensitive drum 4, thereby making it possible to effectively clean the external additives from the surface of the charging roller 5.

[0144] In this embodiment, the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 was measured in order to examine the hardness of the base material (matrix material) constituting the foamed elastic body of the foamed elastic layer of the cleaning roller 15. In this embodiment, the following method was used to measure the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15.

[0145] The foamed elastic layer portion (urethane sponge) of the cleaning roller 15 was frozen with liquid nitrogen and crushed into powder, and this powder was compressed under a load of approximately 5.0 N into a pellet shape with a diameter of 10 mm and a thickness of 5 mm to prepare a sample. The storage elastic modulus (E') of this sample was then measured. The measurement of the storage elastic modulus (E') was performed using the same device and under substantially the same conditions as those used in the measurement of the storage elastic modulus E'C of the surface of the charging roller 5.

[0146] The storage modulus E'C of the surface of the charging roller 5 described above is a parameter representing the "hardness of rubber." Meanwhile, the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 is a parameter representing the "hardness of the matrix material constituting the foam." By using the storage modulus (E') in this way, it is possible to compare the surface of the charging roller 5 and the foamed elastic layer of the cleaning roller 15 in terms of physical adhesive force.

[0147] (Manufacturing method of cleaning roller) Next, an example of a method for manufacturing the cleaning roller 15 in this embodiment will be described.

[0148] First, a polyurethane foam is produced. For example, a polyether polyol is used as a polyol, and water as a blowing agent, triethylenediamine and tin octanoate 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 polyurethane foam obtained is cut into a plate shape, and a hole is made for inserting the core metal (rotating shaft) 15a of the cleaning roller 15. The core metal 15a of the cleaning roller 15 is inserted and fixed into the hole, and the outer circumferential surface is polished to produce the cleaning roller 15.

[0149] In this embodiment, a polyether polyol (product name: CARADOL56-16, manufactured by SHELL) having an average molecular weight of 3000 obtained by addition polymerization of propylene oxide to glycerin was used as the polyol. 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 to 10 μm) were added to 100 g of this polyether polyol, and the mixture was stirred for 5 minutes with a mixer, and 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 liquid. TDI-80 is a mixture of 80 mass % of 2,4-tolylene diisocyanate and 20 mass % of 2,6-tolylene diisocyanate. The isocyanate index was set to 108.

[0150] 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 content of melamine powder in the polyurethane foam was 16.5 mass% (={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.

[0151] After foaming, the polyethylene bag was removed and the foam was cut into a plate having a thickness of 18 mm. Next, a hole having a diameter of 4 mm was drilled to insert the core metal 15a of the cleaning roller 15. Meanwhile, a steel core metal 15a having been electroless nickel plated was prepared, and an ethylene-vinyl acetate hot melt adhesive was applied to the surface of the core metal 15a to a thickness of about 100 μm. The core metal 15a was inserted into the hole of the polyurethane foam, and after induction heating, the core metal 15a was cooled to fix the core metal 15a in the polyurethane foam. Then, the outer peripheral surface of the polyurethane foam was polished to prepare a cleaning roller 15 having an outer diameter of 6 mm.

[0152] <Examples / Comparative Examples> Next, the effects of this embodiment will be further described using examples (Examples 1 to 4) according to this embodiment and comparative examples (Comparative Examples 1 and 2) for comparison with the examples. In the comparative examples, elements having functions and configurations equivalent to those of this embodiment are also given the same reference numerals.

[0153] Example 1 - Manufacturing the charging roller - A method for producing the charging roller 5 of the first embodiment will be described.

[0154] The materials shown in Table 1 in their types and amounts were mixed in a pressure kneader to obtain an unvulcanized domain composition (1).

[0155] [Table 1]

[0156] Moreover, the materials shown in Table 2 in their types and amounts were mixed in a pressure kneader to obtain an unvulcanized rubber composition (1).

[0157] [Table 2]

[0158] Moreover, 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 an elastic layer.

[0159] [Table 3]

[0160] 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 plating was applied. Next, an adhesive, Metalock U-20 (product 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, using a roll coater. The round bar coated with the adhesive was used as the core metal (conductive support) 5a of the charging roller 5.

[0161] 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 core metal 5a and a mechanism for discharging the unvulcanized rubber roller, and the temperature of the extruder and the crosshead was adjusted to 80° C., and the conveying speed of the conductive mandrel was adjusted to 60 mm / sec. Under these conditions, the rubber composition (1) for molding the elastic layer containing the unvulcanized rubber composition (1) was fed from the extruder, and the outer peripheral surface of the core metal 5a was covered with the rubber composition (1) for molding the elastic layer in the crosshead, thereby obtaining an unvulcanized rubber roller (1).

[0162] 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) of the rubber composition (1) for molding the elastic layer, thereby obtaining a roller with an elastic layer formed on the outer circumferential surface of the core metal 5a. After that, 10 mm of each end of the elastic layer was cut off, making the length of the elastic layer in the longitudinal direction 231 mm.

[0163] Finally, the surface of the elastic layer was ground with a grindstone to obtain an elastic layer roller (1) having a crown of 80 μm, with a diameter of 8.42 mm at positions 90 mm from the center to both ends in the longitudinal direction, and a diameter of 8.5 mm at the center in the longitudinal direction.

[0164] After that, ultraviolet light with a wavelength of 254 nm was applied at an integrated dose of 9000 mJ / cm 2The surface of the elastic layer roller (1) was irradiated with ultraviolet light so as to be treated. A low pressure mercury lamp (manufactured by Toshiba Lighting & Technology Corporation) was used as a source of ultraviolet light. In this way, the charging roller (1) of Example 1 was produced.

[0165] -Creating a cleaning roller- The method for producing the cleaning roller 15 of Example 1 is the same as the method described above as one example of the method for producing the cleaning roller 15 of this embodiment.

[0166] Example 2 - Manufacturing the charging roller - A method for producing the charging roller 5 of the second embodiment will be described.

[0167] The charging roller (2) of Example 2 was produced by forming the surface layer (1) on the elastic layer roller (1) in the following manner.

[0168] A surface layer coating liquid (1) for forming the surface layer (1) was prepared as follows.

[0169] 100.0 parts by mass of acrylic polyol (trade name: DC2016, manufactured by Daicel Chemical Industries, Ltd.), 14 parts by mass of isocyanate A (trade name: Bestanate B1370, manufactured by Degussa Co., Ltd.), 80 parts by mass of isocyanate B (trade name: Duranate TPA-880E, manufactured by Asahi Kasei Chemicals Co., Ltd.), 35 parts by mass of carbon black (trade name: MA230, manufactured by Mitsubishi Chemical Co., Ltd., number average particle size 30 nm), and 0.25 parts by mass 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 solid content of 25% by mass to prepare a mixed solution (1). 270 g of the above mixed solution (1) and 200 g of glass beads with an average particle size of 0.8 mm were placed in a glass bottle with a capacity of 450 mL, and dispersed for 24 hours using a paint shaker disperser.

[0170] After dispersion as described above, 30 parts by mass of acrylic particles having an average particle size of 10.0 μm (product name: Ganzpearl GM-1001, manufactured by Aica Kogyo Co., Ltd.) was added. Then, the mixture was further dispersed for 25 minutes, and the glass beads were removed to obtain a surface layer coating solution (1).

[0171] The elastic roller (1) was dipped (dipped) in the surface layer coating liquid (1) with its longitudinal direction in the vertical direction and its upper end portion held, and then pulled up. The dipping time for the above dip coating was 9 seconds, and the roller pulling speed was adjusted so that the initial speed was 20 mm / sec and the final speed was 12 mm / sec, and the speed was changed linearly with respect to time between 20 mm / sec and 12 mm / sec. After coating, the roller was air-dried for 30 minutes at a temperature of 23°C. Next, the roller was dried in a hot air circulation dryer at a temperature of 80°C for 1 hour and at a temperature of 160°C for 1 hour to form a dry film of the coating film of the surface layer coating liquid (1) on the elastic layer roller (1), thereby producing the charging roller (2) of Example 2. The average film thickness of the surface layer was 25 μm.

[0172] -Creating a cleaning roller- The method for producing the cleaning roller 15 of Example 2 is the same as the method described above as one example of the method for producing the cleaning roller 15 of this embodiment.

[0173] (Examples 3 and 4) - Manufacturing the charging roller - A method for producing the charging roller 5 of the third and fourth embodiments will be described.

[0174] In Example 3, when preparing the surface layer coating liquid (1) shown in the method for producing the charging roller 5 in Example 2, the amount of carbon black (product name: MA230, manufactured by Mitsubishi Chemical Corporation, number average particle diameter: 30 nm) added (added amount) was reduced from 35 parts by mass in Example 2, so that the Martens hardness of the surface of the charging roller 5 was reduced to 15.0 N / mm 2In Example 4, similarly, when preparing the surface layer coating solution (1), the amount of carbon black (product name: MA230, manufactured by Mitsubishi Chemical Corporation, number average particle size: 30 nm) added (added amount) was reduced from 35 parts by mass in Example 2, so that the Martens hardness of the surface of the charging roller 5 was adjusted to 10.0 N / mm 2 The other points of the method for producing the charging roller 5 of Examples 3 and 4 are the same as the method for producing the charging roller 5 of Example 2.

[0175] -Creating a cleaning roller- The method for producing the cleaning roller 15 of Examples 3 and 4 is the same as the method described above as one example of the method for producing the cleaning roller 15 of this embodiment.

[0176] (Comparative Example) - Manufacturing the charging roller - A method for producing the charging rollers 5 of Comparative Examples 1 and 2 will be described.

[0177] The charging rollers (3) of Comparative Examples 1 and 2 were produced in the same manner as the charging roller (1), except that the unvulcanized rubber composition (1) was changed to the unvulcanized rubber composition (2) shown below.

[0178] The materials shown in Table 4 in their types and amounts were mixed in a pressure kneader to obtain an unvulcanized rubber composition (2).

[0179] [Table 4]

[0180] -Creating a cleaning roller- The preparation of the cleaning roller 15 of Comparative Example 1 and Comparative Example 2 will be described.

[0181] In Comparative Example 1, the amount of tolylene diisocyanate added per 100 g of polyether polyol described above was increased to 51.3 g in Examples 1 to 4, and a polyurethane foam was prepared so that the storage modulus of the foamed elastic layer was 30 MPa. In Comparative Example 2, the amount of tolylene diisocyanate added per 100 g of polyether polyol was increased to 51.3 g in Examples 1 to 4, and a polyurethane foam was prepared so that the storage modulus of the foamed elastic layer was 20 MPa. Other points of the method for producing the cleaning roller 15 in Comparative Example 1 and Comparative Example 2 are the same as those described above as an example of the method for producing the cleaning roller 15 in this embodiment.

[0182] (Effectiveness check) For the examples (Examples 1 to 4) and the comparative examples (Comparative Examples 1 and 2), evaluation experiments were conducted to confirm the effect of the cleaning roller 15 in removing dirt from the charging roller 5. The evaluation experiments were conducted using a laser beam printer (HP LaserJet Enterprise M612dn 71 ppm (A4)) manufactured by Hewlett Packard. The contents of the evaluation experiments are described below.

[0183] First, a new process cartridge C incorporating the charging roller 5 and cleaning roller 15 of each of the examples (Examples 1 to 4) and the comparative examples (Comparative Examples 1 and 2) is mounted on the image forming apparatus 100, and 10,000 sheets of horizontal line images (straight lines substantially perpendicular to the conveying direction of the recording material P) with a print rate of about 2% are printed. Then, one uniform halftone image with a print rate of about 30% is printed as a sample image. If streaks occur in the image conveying direction in the halftone image, the charging roller 5 is observed as described below. If there is no problem with the image, another 10,000 sheets are printed, and the process is repeated until the total number of printed sheets reaches 60,000. The paper passing test (printing of horizontal line images and printing of sample images) as described above was performed in an environment of 23°C and 50% RH. The characteristics of the charging roller 5 and cleaning roller 15 in the examples (Examples 1 to 4) and the comparative examples (Comparative Examples 1 and 2) are as shown in Table 5.

[0184] [Table 5]

[0185] The evaluation criteria were as follows: When the surface of the charging roller 5 after the paper feed test was observed, the adhesion of external additives was observed in the area where the streaks occurred on the surface of the charging roller 5 in the configuration where the streaks occurred on the image. The evaluation result for such a configuration was "× (bad)".

[0186] Furthermore, even in configurations where no streaks occurred on the image, when the surface of the charging roller 5 was observed after the paper feed test, the amount of external additive adhered in streaks was observed on the surface of the charging roller 5, although the amount was less than in the configurations where streaks occurred on the image. For such configurations, the evaluation result was rated as "△ (slightly poor)".

[0187] In addition, for configurations in which no streaks occurred on the image and no external additives were found to adhere to the surface of the charging roller 5 when the surface of the charging roller 5 was observed after the paper feed test, the evaluation result was rated as "○ (good)".

[0188] Here, the configuration in which no dirt occurs on the charging roller 5 or the level of dirt occurrence is kept to a "△" level up to 50,000 sheets is defined as a configuration in which the effect of removing dirt from the charging roller 5 by the cleaning roller 15 is maintained for a longer period of time, thereby achieving a longer life.

[0189] The evaluation results are shown in Table 6.

[0190] [Table 6]

[0191] As shown in Table 6, in Comparative Example 1, no contamination of the charging roller 5 occurred up to 20,000 sheets (level "good"), but contamination of the charging roller 5 occurred at a level of "poor" at 30,000 sheets. Also, in Comparative Example 2, no contamination of the charging roller 5 occurred up to 30,000 sheets (level "good"), but contamination of the charging roller 5 occurred at a level of "poor" at 40,000 sheets.

[0192] In contrast, in Example 1, no dirt on the charging roller 5 occurred up to 40,000 sheets (level "good"). However, in Example 1, dirt on the charging roller 5 occurred at a "△" level at 50,000 sheets, and dirt on the charging roller 5 occurred at an "X" level at 60,000 sheets. In Example 2, dirt on the charging roller 5 did not occur throughout the experiment (level "good"). In Example 3, dirt on the charging roller 5 did not occur up to 50,000 sheets (level "good"), but dirt on the charging roller 5 occurred at a "△" level at 60,000 sheets. Furthermore, in Example 4, dirt on the charging roller 5 did not occur up to 40,000 sheets (level "good"), but dirt on the charging roller 5 occurred at a "△" level at 50,000 sheets, and dirt on the charging roller 5 occurred at an "X" level at 60,000 sheets.

[0193] Hereinafter, the mechanism by which the stains on the charging roller 5 occur and the mechanism by which the stains on the charging roller 5 are removed will be further described by comparing comparative examples (Comparative Examples 1 and 2) with examples (Examples 1 to 4).

[0194] (Contamination of the charging roller in Comparative Examples 1 and 2) First, the mechanism by which stains occur on the charging roller 5 in Comparative Examples 1 and 2 will be described with reference to Figs. 9 to 11. In particular, the mechanism by which external additives become difficult to remove will be described in Comparative Examples 1 and 2. Toner can also become difficult to remove due to a similar mechanism.

[0195] 9(a) is a schematic diagram showing the positional relationship between the cleaning roller 15 and the charging roller 5 in Comparative Example 1, and Fig. 9(b) is a schematic diagram for explaining the adhesion state of the external additive on the surface of the charging roller 5. In Comparative Example 1, the external additive 16 adhered to the surface 5s of the charging roller 5 did not show any significant change after passing through the contact portion (cleaning nip) Nc between the cleaning roller 15 and the charging roller 5, and became difficult to remove.

[0196] Figures 10 and 11 are schematic diagrams for explaining the mechanism by which the cleaning roller 15 makes it difficult to remove the external additive on the surface 5s of the charging roller 5 in Comparative Example 1. Note that Figures 10 and 11 schematically show a cross-section substantially orthogonal to the rotation axis direction of the charging roller 5 in the vicinity of the surface of the charging roller 5. For the sake of convenience in representing the above mechanism, the external additive attached to the surface of the charging roller 5 or the photosensitive drum 4 may be shown inside the surface.

[0197] The external additive 16 that has passed through the cleaning blade 6 adheres electrostatically or non-electrostatically to the surface 5s of the charging roller 5 at the contact portion between the charging roller 5 and the photosensitive drum 4 (state of Fig. 10(a)).

[0198] The external additive 16 attached to the surface 5s of the charging roller 5 is carried to the contact portion Nc between the cleaning roller 15 (more specifically, the cell skeleton 15s of the foamed elastic layer 15b made of urethane sponge) and the surface 5s of the charging roller 5. At the contact portion Nc between the surface 5s of the charging roller 5 and the cleaning roller 15, the adhesion force of the external additive 16 to the charging roller 5 is higher than that to the cleaning roller 15. This is because in Comparative Example 1, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 have the relationship of E'C < E'CC. As a result, a force in the direction of arrow F in Fig. 10(b) (the direction from the cleaning roller 15 to the charging roller 5) acts on the external additive 16. This is because a state with a low storage elastic modulus (E') has a high physical adhesion force, and a state with a high storage elastic modulus (E') has a low physical adhesion force. That is, when the charging roller 5 and the cleaning roller 15 with different storage elastic moduli (E') come into contact with the external additive 16, the charging roller 5 with a lower storage elastic modulus (E') has a higher adhesion force of the external additive 16. Therefore, it becomes difficult for the external additive 16 to transfer from the charging roller 5 to the cleaning roller 15 (state of Fig. 10(b)).

[0199] The cleaning roller 15 rotates passively as the charging roller 5 rotates. Therefore, the cleaning roller 15 rotates slightly behind the charging roller 5 (state of Fig. 10(c)).

[0200] When the charging roller 5 further rotates, the cleaning roller 15 also rotates accordingly, with a slight delay as described above. As a result, some of the external additives 16 attached to the surface 5s of the charging roller 5 are moved as if being scraped up by the cell skeleton 15s of the cleaning roller 15, and a small amount of lumps 16s of the external additives 16 is formed. On the other hand, most of the external additives 16 attached to the surface 5s of the charging roller 5 slips under the cell skeleton 15s of the cleaning roller 15 due to contact with the cell skeleton 15s of the cleaning roller 15, and firmly adheres to the surface 5s of the charging roller 5 (the state shown in FIG. 10(d)).

[0201] Next, the surface 5s of the charging roller 5 leaves the contact portion Nc with the cleaning roller 15, and the contact pressure from the cleaning roller 15 disappears, and the shape returns to the original state. At this time, a small amount of lumps 16s of the external additive 16 formed by the cell skeleton 15s of the cleaning roller 15 remains on the surface 5s of the charging roller 5 (the state in FIG. 11(e)).

[0202] Thereafter, the lump 16s of the external additive 16 on the charging roller 5 is carried to the contact portion between the charging roller 5 and the photosensitive drum 4 while remaining attached to the surface of the charging roller 5 (the state of FIG. 11(f)).

[0203] Then, some of the lumps 16s of the external additive 16 on the charging roller 5 move from the surface 5s of the charging roller 5 to and adhere to the surface 4s of the photosensitive drum 4. On the other hand, most of the external additive 16 adheres firmly to the surface 5s of the charging roller 5 and does not move to the surface 4s of the photosensitive drum 4 (the state in FIG. 11(g)).

[0204] As described above, in Comparative Example 1, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 have a relationship of E'C < E'CC. As a result, the external additive 16 attached to the surface 5s of the charging roller 5 has a higher adhesion force to the charging roller 5 than to the cleaning roller 15. Therefore, it becomes difficult to remove the external additive 16 attached to the surface 5s of the charging roller 5 by the cleaning roller 15. In this case, with the long-term use of the process cartridge C, the external additive accumulates on the surface of the charging roller 5, which may cause a charging failure of the photosensitive drum 4 due to the contamination of the charging roller 5. That is, it can be a factor that hinders the extension of the service life of the process cartridge C.

[0205] In Comparative Example 2, as in Comparative Example 1, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 have a relationship of E'C < E'CC. However, in Comparative Example 2, the difference between E'C and E'CC is smaller than that in Comparative Example 1. As a result, in Comparative Example 2, the action of forming the mass 16s of the external additive 16 on the surface 5s of the charging roller 5 and the action of vigorously bouncing and floating this mass 16s work more than in Comparative Example 1. As a result, in Comparative Example 2, it is considered that the effect of removing the contamination of the charging roller 5 by the cleaning roller 15 is slightly improved compared to Comparative Example 1.

[0206] (Removal of contamination of the charging roller in Examples 1 to 4) Next, with reference to FIGS. 4 to 8, the mechanism for removing the contamination of the charging roller 5 in Examples 1 to 4 will be described. Here, in particular, the mechanism by which the external additive becomes easier to remove in Examples 1 to 4 will be described. The toner can also be made easier to remove by the same mechanism.

[0207] Fig. 4(a) is a schematic diagram showing the positional relationship between the cleaning roller 15 and the charging roller 5 in Example 1, and Fig. 4(b) is a schematic diagram for explaining the adhesion state of the external additive on the surface of the charging roller 5. In Example 1, the external additive 16 adhered to the surface 5s of the charging roller 5 was collected in clumps at the contact portion (cleaning nip) Nc between the cleaning roller 15 and the charging roller 5, and was in a state that was easy to remove.

[0208] 5 and 6 are schematic diagrams for explaining the mechanism by which the cleaning roller 15 easily removes the external additive 16 from the surface 5s of the charging roller 5 in Example 1. Note that Fig. 5 and Fig. 6 are schematic views showing a cross section approximately perpendicular to the rotation axis direction of the charging roller 5 in the vicinity of the surface of the charging roller 5, and for convenience of illustrating the above mechanism, the external additive adhering to the surface of the charging roller 5 or the photosensitive drum 4 may be shown inside the surface.

[0209] The external additive 16 that has slipped through the cleaning blade 6 adheres electrostatically or non-electrostatically to the surface 5s of the charging roller 5 at the contact portion between the charging roller 5 and the photosensitive drum 4 (the state in FIG. 5(a)).

[0210] The external additive 16 attached to the surface 5s of the charging roller 5 is carried to the contact portion Nc between the cleaning roller 15 (more specifically, the cell skeleton 15s of the foamed elastic layer 15b made of urethane sponge) and the surface 5s of the charging roller 5. At the contact portion Nc between the surface 5s of the charging roller 5 and the cleaning roller 15, the external additive 16 has a stronger adhesion force to the cleaning roller 15 than to the charging roller 5. This is because, in the first embodiment, the storage modulus E'C of the surface of the charging roller 5 and the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 have a relationship of E'C>E'CC. As a result, a force acts on the external additive 16 in the direction of the arrow F in FIG. 5(b) (the direction from the charging roller 5 to the cleaning roller 15). This is because a state in which the storage modulus (E') is low results in a high physical adhesion force, and a state in which the storage modulus (E') is high results in a low physical adhesion force. In other words, when the charging roller 5 and the cleaning roller 15, which have different storage moduli (E') with respect to the external additive 16, come into contact with each other, the cleaning roller 15, which has a lower storage modulus (E'), has a higher adhesive force of the external additive 16. Therefore, the external additive 16 is more likely to transfer from the charging roller 5 to the cleaning roller 15 (state in FIG. 5(b)).

[0211] The cleaning roller 15 is rotated following the rotation of the charging roller 5. Therefore, the cleaning roller 15 rotates slightly later than the charging roller 5. As a result, the cell skeleton 15s of the cleaning roller 15 receives a compressive force in the rotation direction of the charging roller 5 while moving relatively in the opposite direction to the rotation direction of the charging roller 5 (state of FIG. 5(c)).

[0212] When the charging roller 5 further rotates, the cleaning roller 15 also rotates accordingly, with a slight delay as described above. At this time, the external additive 16 is only lightly attached to the surface 5s of the charging roller 5, and can be easily moved by contact with the cell skeleton 15s of the cleaning roller 15. As a result, the external additive 16 attached to the surface 5s of the charging roller 5 is moved as if scraped up by the cell skeleton 15s of the cleaning roller 15, and a mass 16s of the external additive 16 is formed (the state shown in FIG. 5(d)).

[0213] Next, the moment arrives when the surface 5s of the charging roller 5 leaves the contact portion Nc with the cleaning roller 15. At the moment when the surface layer 5s of the charging roller 5 leaves the cleaning roller 15, the compressive force that has been stored in the cell skeleton 15s of the cleaning roller 15 is suddenly released. At this time, the cell skeleton 15s of the cleaning roller 15 vigorously repels the lumps 16s of the external additive 16 that have formed on the surface 5s of the charging roller 5 up until that point, and lifts them off the surface of the charging roller 5 (the state of FIG. 6(e)).

[0214] Thereafter, the lump 16s of the external additive 16 on the charging roller 5 is carried to the contact portion between the charging roller 5 and the photosensitive drum 4 while remaining attached to the surface of the charging roller 5 (the state of FIG. 6(f)).

[0215] Then, the lump 16s of the external additive 16 on the charging roller 5 moves from the surface 5s of the charging roller 5 onto the surface 4s of the photosensitive drum 4 and adheres thereto (the state of FIG. 6(g)).

[0216] The external additive 16 adhered to the surface 4s of the photosensitive drum 4 is then collected into the developing device 2 by the developing sleeve 7 at the developing section, transferred onto the recording material P at the transfer section, or collected into the cleaning device 17 by the cleaning blade 6.

[0217] As described above, in the first embodiment, the storage modulus E'C of the surface of the charging roller 5 and the storage modulus E'CC of the foamed elastic layer of the cleaning roller 15 have a relationship of E'C>E'CC. As a result, the external additive 16 attached to the surface 5s of the charging roller 5 has a stronger adhesion to the cleaning roller 15 than to the charging roller 5. Therefore, the external additive 16 attached to the surface 5s of the charging roller 5 can be easily moved by the cell skeleton 15s of the cleaning roller 15. That is, in the first embodiment, the cleaning roller 15 has a function of collecting the external additive 16 attached to the surface 5s of the charging roller 5 in a lump and simply moving it without rubbing it. With this function, the external additive 16 can be lifted from the surface 5s of the charging roller 5, and the function of cleaning the external additive 16 on the surface 5s of the charging roller 5 is realized by returning it to the photosensitive drum 4. In other words, the cleaning roller 15 does not scrape off the external additive 16, but rather acts to lift the external additive 16 from the surface 5s of the charging roller 5 and return it to the photosensitive drum 4 when it comes into contact with and separates from the charging roller 5. Therefore, the external additive is less likely to accumulate on the surface of the charging roller 5 and on the cleaning roller 15. Therefore, the effect of the cleaning roller 15 in removing the external additive from the charging roller 5 can be maintained for a longer period of time, and contamination of the charging roller 5 can be suppressed for a longer period of time. As a result, this is advantageous for extending the life of the process cartridge C.

[0218] 7 and 8 are schematic diagrams for explaining the mechanism by which the cleaning roller 15 easily removes the external additive 16 from the surface 5s of the charging roller 5 in the second embodiment. The above-mentioned mechanism in the second embodiment shown in FIGS. 7 and 8 is the same as the above-mentioned mechanism in the first embodiment shown in FIGS. 5 and 6. That is, in the second embodiment, the external additive 16 on the surface of the charging roller 5 is removed through the states shown in FIGS. 7(a) to (d) and 8(e) to (g), which are the same as the states shown in FIGS. 5(a) to (d) and 6(e) to (g) in the first embodiment. However, in the second embodiment, as shown in FIGS. 7 and 8, the charging roller 5 has a surface layer 5c on the elastic layer 5b, and this surface layer 5c forms the surface 5s of the charging roller 5.

[0219] Here, in Example 2, similarly to Example 1, the storage elastic modulus E'C of the surface of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 have a relationship of E'C>E'CC. However, in Example 2, the difference between E'C and E'CC is larger than in Example 1. Also, in Example 2, the Martens hardness is 25 N / mm 2 In the second embodiment, this is achieved by providing a surface layer 5c on the outer side of the elastic layer 5b of the charging roller 5.

[0220] In Example 2, the difference between E'C and E'CC is larger than that in Example 1, so that the action of forming a mass 16s of the external additive 16 on the surface 5s of the charging roller 5 and the action of flicking and lifting this mass are more effective than in Example 1. Also, in Example 2, the Martens hardness is 25 N / mm, which is larger than that in Example 1. 2 This more effectively acts to vigorously repel and lift up the lumps 16s of the external additive 16 formed on the surface 5s of the charging roller 5. From the results of Examples 1 to 4, this effect is observed when the Martens hardness is 15 N / mm 2 As a result, it is possible to remove the external additive 16 more efficiently in Example 2 (and Example 3) than in Example 1.

[0221] From the results of Examples 1 and 2, it can be seen that the effect of the present embodiment described above can be obtained even if the difference between E'C and E'CC is about 10 MPa, or in other words, even if E'C is about twice as large as E'CC. As a result of further investigation by the present inventors, in order to make the effect of the present embodiment described above more significant, the difference between E'C and E'CC is preferably 1 MPa or more, more preferably 10 MPa or more, and even more preferably 100 MPa or more. In other words, E'C is preferably twice as large as E'CC or more, more preferably 10 times as large as E'CC or more, and even more preferably 100 times as large as E'CC or more.

[0222] However, the storage elastic modulus E'C of the surface of the charging roller 5 is preferably 5 MPa or more and 3000 MPa or less. In other words, if it is greater than this range, the charging roller 5 may be contaminated by the toner crushed by the charging roller 5, and vertical stripe images may be easily generated. Also, if it is less than this range, the tackiness of the surface of the charging roller 5 may become strong, and toner adhesion to the surface of the charging roller 5 may be easily generated. From this viewpoint, E'C is preferably 5 MPa or more and 3000 MPa or less, and more preferably 10 MPa or more and 2000 MPa or less.

[0223] The storage elastic modulus E'CC of the foamed elastic layer of the cleaning roller 15 is preferably 1 MPa or more and 500 MPa or less. In other words, if it is greater than this range, the cleaning roller 15 may harden and may not be able to follow the rotation of the charging roller 5. If it is less than this range, the toner T and the external additive 16 may easily adhere to the cleaning roller 15. From this viewpoint, E'CC is preferably 1 MPa or more and 500 MPa or less, and more preferably 5 MPa or more and 100 MPa or less.

[0224] Thus, in this embodiment, the image forming apparatus 100 includes a rotatable image carrier (photosensitive drum) 4, a charging roller 5 having a surface 5s in contact with the surface of the image carrier 4, which rotates in contact with the rotating image carrier 4 and charges the surface 4s of the image carrier 4, a cleaning roller 15 having a foamed elastic layer 15b in contact with the surface 5s of the charging roller 5 and which rotates in contact with the rotating charging roller 5 for cleaning the surface 5s of the charging roller 5, and a developing means (developing device) 2 that supplies developer to the surface 4s of the image carrier 4 to form a developer image, and the storage elastic modulus E'C of the surface 5s of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer 15b of the cleaning roller 15, measured in a measurement environment of 23°C, 50% RH, and a measurement frequency of 10 Hz, are defined as follows: the storage elastic modulus E'C of the surface 5s of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer 15b of the cleaning roller 15 satisfy the relationship E'C>E'CC. The charging roller 5 may be configured to have an elastic layer 5b that forms the surface 5s of the charging roller 5. The charging roller 5 may also be configured to have an elastic layer 5b and a surface layer 5c that forms the surface 5s of the charging roller 5. In addition, the Martens hardness of the surface 5s of the charging roller 5 may be 15 N / mm 2 More than 40N / mm 2 or less. In this embodiment, the cleaning roller 15 is rotated following the rotation of the charging roller 5. In this embodiment, the elastic layer 5b of the charging roller 5 has a matrix containing a first rubber and a plurality of domains dispersed in the matrix, and the domains contain a second rubber and an electronic conductive agent. Here, the volume resistivity of the matrix is ​​preferably 1.0×10 8 Ω cm or greater than 1.0×10 17 The volume resistivity of the domain is preferably 1.0×10 1 Ω cm or more, 1.0×10 4It is preferable that the resistivity is Ω·cm or less. In the present embodiment, a process cartridge C is provided that is detachable from an apparatus main body 110 of an image forming apparatus 100 that supplies a developer to a surface 4s of a rotatable image carrier 4 by a developing means 2 to form a developer image, and transfers the developer image to a recording material P to form an image on the recording material P. This process cartridge C has the image carrier 4, the charging roller 5, and the cleaning roller 5, and is configured such that the storage elastic modulus E'C of the surface 5s of the charging roller 5 and the storage elastic modulus E'CC of the foamed elastic layer 15b of the cleaning roller 15 satisfy the relationship E'C>E'CC in a measurement environment of 23° C., 50% RH, and a measurement frequency of 10 Hz.

[0225] As described above, according to this embodiment, the toner and external additives adhering to the charging roller 5 can be more effectively removed by the cleaning roller 15. This allows the effect of the cleaning roller 15 in removing the toner and external additives from the charging roller 5 to be maintained for a longer period of time, and the contamination of the charging roller 5 can be suppressed for a longer period of time. As a result, this is advantageous for extending the life of the process cartridge C.

[0226] [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.

[0227] The image forming apparatus to which the present invention can be applied is not limited to the image forming apparatus having the basic configuration shown in the above embodiment. For example, the present invention can be applied to an image forming apparatus that has a plurality of detachable process cartridges and can transfer a plurality of color toner images to a recording material using an intermediate transfer body such as an intermediate transfer belt to form a full-color image. In the above embodiment, the image forming apparatus is configured so that the process cartridge is detachable. However, the present invention is not limited to such an aspect, and the present invention can be applied to an image forming apparatus in which a process unit similar to that constituting the process cartridge in the above embodiment is provided in the device body. In addition, for example, the drum unit in the above embodiment may be substantially detachable from the device body by itself. The process cartridge may have a photosensitive body, a charging roller, and a cleaning roller. Examples of the image forming apparatus include a copying machine, a printer (laser beam printer, LED printer, etc.), a facsimile machine, a word processor, and a multifunction machine (multifunction printer) thereof.

[0228] In addition, in the above-mentioned embodiment, the developing device uses a non-contact developing method in which the image carrier and the developer carrier are arranged facing each other with a predetermined gap, but is not limited to this. The developing device may use a two-component developing method using a two-component developer, or a contact developing method in which the image carrier and the developer carrier are arranged in contact with each other. In other words, the developer is not limited to the magnetic one-component developer in the above-mentioned embodiment, but may be a two-component developer or a non-magnetic one-component developer.

[0229] In addition, in the configuration in which the cleaning roller rotates following the rotation of the charging roller as in the above embodiment, a peripheral speed difference can be provided so that the cleaning roller rotates slightly behind the rotation of the charging roller with a simple configuration without requiring a special configuration or control. In the above embodiment, the charging roller is also configured to rotate following the rotation of the photosensitive drum. However, at least one of the charging roller and the cleaning roller may be driven to rotate. As described above, for example, in a configuration in which the charging roller and the cleaning roller are driven to rotate, even if it is aimed to make the peripheral speeds of both rollers equal, it is generally difficult to make them completely equal, and a slight peripheral speed difference (for example, about ±5%) occurs. Therefore, even in such a configuration, it is possible to obtain the effect of removing external additives and toner on the charging roller by the cleaning roller as described in the above embodiment. At least one of the charging roller and the cleaning roller may be driven to rotate so as to provide a predetermined peripheral speed difference (for example, about ±5%) in advance. In this case, the peripheral speed of the cleaning roller may be faster than the peripheral speed of the charging roller, and in this case too, the effect of scraping up the external additives and repelling and floating them can be obtained, which corresponds to the above-described embodiment.

[0230] The present invention can also be applied to a so-called cleaner-less image forming apparatus (process cartridge) that does not have a special cleaning device for cleaning the image carrier, and that collects toner such as residual toner after transfer in a developing device. [Explanation of symbols]

[0231] 4 Photosensitive drum 5. Charging roller 5s Surface of the charging roller 6 Cleaning blade 15 Cleaning roller 15s Cellular skeleton of foamed elastic layer of cleaning roller 100 Image forming device T Toner P Recording material

Claims

1. A rotatable image carrier; a charging roller having a surface that contacts the surface of the image carrier, the charging roller rotating in contact with the rotating image carrier, and charging the surface of the image carrier; a cleaning roller for cleaning the surface of the charging roller, the cleaning roller including a foamed elastic layer in contact with the surface of the charging roller and rotating in contact with the rotating charging roller; a developing unit that supplies a developer to the surface of the image carrier to form a developer image, When the storage elastic modulus of the surface of the charging roller is defined as E'C and the storage elastic modulus of the foamed elastic layer of the cleaning roller is defined as E'CC, the storage elastic modulus of the surface of the charging roller and the storage elastic modulus of the foamed elastic layer of the cleaning roller are defined as E'CC, as measured in a measurement environment of 23°C, 50% RH, and a measurement frequency of 10 Hz. E'C>E'CC The image forming apparatus is characterized in that the above relationship is satisfied.

2. 2. The image forming apparatus according to claim 1, wherein the charging roller has an elastic layer that forms the surface of the charging roller.

3. 2. The image forming apparatus according to claim 1, wherein the charging roller has an elastic layer and a surface layer that forms the surface of the charging roller.

4. The Martens hardness of the surface of the charging roller is 15 N / mm ２ Above, 40N / mm ２ 4. The image forming apparatus according to claim 1, wherein:

5. 4. The image forming apparatus according to claim 1, wherein the cleaning roller is rotated in accordance with the rotation of the charging roller.

6. 4. The image forming apparatus according to claim 2, wherein the elastic layer of the charging roller has a matrix containing a first rubber and a plurality of domains dispersed in the matrix, the domains containing a second rubber and an electronic conductive agent.

7. The volume resistivity of the matrix is ​​1.0×10 ８ Ω cm or more, 1.0×10 １７ 7. The image forming apparatus according to claim 6, wherein the resistance is Ω·cm or less.

8. The volume resistivity of the domain is 1.0×10 １ Ω・cm or more, 1.0×10 ４ 7. The image forming apparatus according to claim 6, wherein the resistance is Ω·cm or less.

9. A process cartridge detachably mountable to a main body of an image forming apparatus which supplies a developer to a surface of a rotatable image carrier by a developing means to form a developer image, and transfers the developer image onto a recording material to form an image on the recording material, The image carrier; a charging roller having a surface that contacts the surface of the image carrier, the charging roller rotating in contact with the rotating image carrier, and charging the surface of the image carrier; a cleaning roller for cleaning the surface of the charging roller, the cleaning roller including a foamed elastic layer in contact with the surface of the charging roller and rotating in contact with the charging roller; When the storage elastic modulus of the surface of the charging roller is defined as E'C and the storage elastic modulus of the foamed elastic layer of the cleaning roller is defined as E'CC, the storage elastic modulus of the surface of the charging roller and the storage elastic modulus of the foamed elastic layer of the cleaning roller are defined as E'CC, as measured in a measurement environment of 23°C, 50% RH, and a measurement frequency of 10 Hz. E'C>E'CC A process cartridge characterized in that the above relationship is satisfied.

10. 10. A process cartridge according to claim 9, wherein said charging roller has an elastic layer forming said surface of said charging roller.

11. 10. A process cartridge according to claim 9, wherein said charging roller has an elastic layer and a surface layer which forms said surface of said charging roller.

12. The Martens hardness of the surface of the charging roller is 15 N / mm ２ Above, 40N / mm ２ 12. The process cartridge according to claim 9, wherein the following is true:

13. 12. The process cartridge according to claim 9, wherein the cleaning roller is rotated in accordance with the rotation of the charging roller.

14. 12. The process cartridge according to claim 10, wherein the elastic layer of the charging roller has a matrix containing a first rubber and a plurality of domains dispersed in the matrix, the domains containing a second rubber and an electronic conductive agent.

15. The volume resistivity of the matrix is ​​1.0×10 ８ Ω cm or more, 1.0×10 １７ 15. The process cartridge according to claim 14, wherein the resistance is Ω·cm or less.

16. The volume resistivity of the domain is 1.0×10 １ Ω・cm or more, 1.0×10 ４ 15. The process cartridge according to claim 14, wherein the resistance is Ω·cm or less.

Images