JP2015215519A - Process cartridge and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process cartridge capable of suppressing the occurrence of an image failure such as a white dot by suppressing the increase of the surface potential of a cleaning member caused by frictional electrification between an electrifying member and the cleaning member and to provide an image forming apparatus.SOLUTION: In a process cartridge 10 including a photoreceptor 1, a rotatable electrifying member 2, and a cleaning member 9 removing extraneous matter attached to the surface of the electrifying member 2 and including a foaming elastic layer 92 coming into contact with the surface of the electrifying member 2, the cleaning member 9 has an electric resistance higher than that of the electrifying member 2 and when the surface potential of the cleaning member 9 when a voltage is applied to the electrifying member 2, to electrify the photoreceptor 1 is defined as V1, the surface potential of the electrifying member 2 at the time is defined as V2, and a discharge start voltage being the voltage at which discharge is started when a DC voltage is applied to between the cleaning member 9 and the electrifying member 2 is defined as Vth, a relation of |V1-V2|≤|Vth| is satisfied when the voltage is applied to the electrifying member 2, to electrify the photoreceptor 1.

Description

  The present invention relates to a process cartridge and an image forming apparatus including a cleaning member that removes deposits attached to a charging member used in an image forming apparatus using an electrophotographic system or an electrostatic recording system.

  Conventionally, for example, in an electrophotographic image forming apparatus, an electrophotographic photosensitive member (photosensitive member) as an image carrier is used to perform image formation through steps such as charging, exposure, development, transfer, and cleaning. There is a wide variety of process cartridges in which the photosensitive member and at least one of charging means, developing means, and cleaning means as process means acting on the photosensitive member are integrated into a cartridge so that it can be attached to and detached from the main body of the image forming apparatus. It is used.

  In such an image forming apparatus, as a charging unit for charging a photosensitive member as a member to be charged, a charging member disposed in contact with the member to be charged is provided, and a voltage is applied to the member to be charged. A method of charging the is widely used. This method has advantages such that the amount of ozone generated is relatively small and the device can be easily downsized. In particular, a charging roller that is a roller-shaped charging member is often employed.

  However, such a charging roller is in contact with the photoreceptor. Therefore, transfer residual toner, external additives, and the like attached to the photosensitive member are transferred to the charging roller at the contact portion (nip portion) between the photosensitive member and the charging roller, and are attached to the surface of the charging roller. This may affect the image when the charging roller is used for a long time. Therefore, a cleaning member that removes deposits attached to the charging roller may be provided.

  Patent Document 1 proposes a cleaning member in which a contact portion with a cleaning object is made of a melamine resin foam.

  Further, in Patent Document 2, a cleaning member formed in a roller shape with a porous elastic member (sponge material) is brought into contact with the charging roller and is rotated following the rotation of the charging roller, and adheres to the surface of the charging roller. It is disclosed to remove deposits.

JP 2003-66807 A JP-A-5-297690

  However, the cleaning member as described above can be used for the charging roller when compressed at the contact portion with the charging roller or when it is restored to its original state, even when the charging roller rotates following the rotation of the charging roller. Rubbed. Therefore, when the cleaning member is electrically insulating, the surface of the cleaning member is frictionally charged by the friction between the charging roller and the cleaning member, and the potential difference between the surface potential of the charging roller and the surface potential of the cleaning member is discharged. It has been found that the starting voltage may be exceeded. As a result, abnormal discharge is generated from the surface of the cleaning member to the surface of the charging roller, and image defects such as white spots (a phenomenon in which an image appears white) due to a local potential increase on the photosensitive member may occur. is there.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a process cartridge and an image forming apparatus capable of suppressing the occurrence of image defects such as white spots by suppressing an increase in the surface potential of the cleaning member due to frictional charging between the charging member and the cleaning member. Is to provide.

  The above object is achieved by the process cartridge and the image forming apparatus according to the present invention. In summary, the present invention removes a photosensitive member, a rotatable charging member that contacts the photosensitive member and is charged with a voltage to charge the surface of the photosensitive member, and deposits attached to the surface of the charging member. A cleaning member having a foamed elastic layer contacting the surface of the charging member, wherein the cleaning member is detachable from the apparatus main body of the image forming apparatus. The surface potential of the cleaning member when it has an electrical resistance equal to or higher than the resistance and a voltage is applied to the charging member to charge the photosensitive member is V1, and the surface potential of the charging member at that time is When V2 is Vth, and a discharge start voltage that is a voltage at which discharge is started when a DC voltage is applied between the cleaning member and the charging member is Vth, a voltage is applied to the charging member and the photoconductor Obi A process cartridge and satisfying the relationship | when the that is | V1-V2 | ≦ | Vth.

  According to another aspect of the present invention, an image carrier, a rotatable charging member that contacts the image carrier and is applied with a DC voltage to charge the image carrier, and adheres to the surface of the charging member. And a cleaning member having a foamed elastic layer contacting the surface of the charging member. The cleaning member has an electrical resistance equal to or higher than that of the charging member. The surface potential of the cleaning member when a DC voltage is applied to the charging member to charge the image carrier is V1, and the surface potential of the charging member at that time is V2. When a discharge start voltage, which is a voltage at which discharge is started when a DC voltage is applied between the charging member and the charging member, is Vth, a DC voltage is applied to the charging member to charge the image carrier. | V -V2 | ≦ | Vth | image forming apparatus characterized by satisfying the relation is provided.

  According to the present invention, an increase in the surface potential of the cleaning member due to frictional charging between the charging member and the cleaning member can be suppressed, and the occurrence of image defects such as white spots can be suppressed.

1 is a schematic cross-sectional view of an image forming apparatus. 2 is a schematic cross-sectional view of an image forming unit of the image forming apparatus. FIG. It is sectional drawing of a charging roller and a cleaning roller. It is a graph which shows the electrical resistance in the environment where a cleaning roller and a charging roller differ. It is a graph which shows the relationship between the electrical resistance of the cleaning roller in 15 degreeC / 10% RH environment, and the surface potential of the cleaning roller at the time of charging operation. It is a schematic diagram of the measuring apparatus of the electrical resistance of a charging roller. It is a schematic diagram of the measuring apparatus of the electrical resistance of a cleaning roller.

  Hereinafter, the process cartridge and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 according to the present exemplary embodiment includes four image forming units PY, PM, PC, and PK as a plurality of image forming units. These image forming portions PY, PM, PC, and PK form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). In this embodiment, the configuration and operation of these image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol indicating an element for any color will be omitted, and the element will be described generally.

  FIG. 2 is a schematic diagram illustrating a longitudinal section of the image forming unit P. The image forming unit P includes a photosensitive drum 1 that is a drum-shaped (cylindrical) electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven at a process speed (peripheral speed) of 100 mm / sec in the direction of arrow R1 in the figure by a driving means (not shown). In the image forming unit P, the following units are arranged around the photosensitive drum 1 in order along the rotation direction. First, a charging roller 2 that is a rotatable roller-shaped charging member as a charging unit is disposed. Next, an exposure device (laser scanner device) 3 as an exposure means (electrostatic latent image forming means) is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-shaped primary transfer member as a primary transfer means is disposed. Next, a drum cleaning device 6 as a photosensitive member cleaning unit is disposed. In the image forming portion P, a cleaning roller 9 that is a roller-shaped cleaning member serving as a charging member cleaning unit is disposed in contact with the charging roller 2. In this embodiment, the charging roller 2 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force, and rotates following the direction of the arrow R2 in the figure as the photosensitive drum 1 rotates. Further, in this embodiment, the cleaning roller 9 is brought into contact with the surface of the charging roller 2 with a predetermined pressing force, and rotates following the direction of the arrow R3 in the figure as the charging roller 2 rotates.

  Further, the image forming apparatus 100 includes an intermediate transfer belt 7 formed of an endless belt member as an intermediate transfer member so as to come into contact with each photosensitive drum 1 of each image forming unit P. The intermediate transfer belt 7 is wound around a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13 as a plurality of support rollers (stretching rollers) with a predetermined tension. The intermediate transfer belt 7 rotates (circulates) in the direction of the arrow R7 in the drawing when the driving roller 11 is rotationally driven in the direction of the arrow R6 in the drawing. The primary transfer roller 5 described above is disposed at a position facing each photosensitive drum 1 on the inner peripheral surface side (back surface side) of the intermediate transfer belt 8. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip portion) N1 where the intermediate transfer belt 7 and the photosensitive drum 1 are in contact with each other. As the intermediate transfer belt 7 rotates, the primary transfer roller 5 is driven to rotate in the direction of the arrow R5 in the figure. Further, a secondary transfer roller 14 that is a roller-like secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 13 on the outer peripheral surface side (front surface side) of the intermediate transfer belt 7. ing. The secondary transfer roller 14 is pressed against the secondary transfer counter roller 13 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip portion) where the intermediate transfer belt 7 and the secondary transfer roller 14 come into contact with each other. ) N2 is formed. A belt cleaning device 17 as an intermediate transfer member cleaning unit is disposed at a position facing the tension roller 12 on the outer peripheral surface side of the intermediate transfer belt 7. The intermediate transfer belt 7 is formed endlessly with a dielectric resin such as polyimide.

  In addition, the image forming apparatus 100 includes a feeding / conveying unit for the recording material S such as recording paper, a fixing unit for fixing the toner image on the recording material S, and the like.

  During image formation, the surface of the rotationally driven photosensitive drum 1 is charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by the charging roller 2. In this embodiment, a DC voltage having a predetermined polarity (negative polarity in this embodiment) is applied to the charging roller 2 as a charging voltage (charging bias) from a charging power supply (high voltage power supply) E1 as an application unit. . This DC voltage value is a value equal to or higher than the discharge start voltage between the charging roller 2 and the photosensitive drum 1 (a value larger than the discharge start voltage by the desired charging potential of the photosensitive drum 1 on the charging polarity side of the photosensitive drum 1). Set to The discharge start voltage is a discharge between the charging roller 2 and the photosensitive drum 1 when only the DC voltage is applied to the charging roller 2 and the absolute value of the applied DC voltage is increased. This is the DC voltage value at the point where the DC current flowing through the charging roller 2 suddenly increases. The photosensitive drum 1 is electrically grounded (connected to the ground).

  The surface of the photosensitive drum 1 after the charging process is scanned and exposed by the exposure device 3 in accordance with image information corresponding to each image forming portion P, whereby an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. Is done. The electrostatic latent image formed on the photosensitive drum 1 is developed as a toner image by the developing device 4 using toner as a developer. In this embodiment, the charging polarity (normal charging polarity) of the toner during development is negative (negative polarity). The developing device 4 includes a developing sleeve 41 as a developer carrying member that carries toner and conveys the toner to a portion facing the photosensitive drum 1 (developing position). The developing sleeve 41 is rotationally driven in the direction of arrow R4 in the drawing. At the time of development, a predetermined development voltage (development bias) is applied to the development sleeve 41 from a development power source (high voltage power source) E2 as an application unit. As the development voltage, an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed is used.

  The toner image formed on the surface of the photosensitive drum 1 is transferred (primary transfer) to the surface of the intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion N1. At this time, the primary transfer roller 5 is supplied from a primary transfer power supply (high voltage power supply) E3 as an application means with a primary transfer having a DC voltage having a polarity (positive in this embodiment) opposite to the charging polarity of the toner at the time of development. A voltage (primary transfer bias) is applied. When forming a full-color image, the above-described operations are performed in the image forming units PY, PM, PC, and PK, and the yellow, magenta, cyan, and black toner images formed on the photosensitive drums 1 are sequentially formed. The toner image is transferred onto the intermediate transfer belt 7 so as to overlap.

  The toner image formed on the surface of the intermediate transfer belt 7 is transferred (secondary transfer) to the surface of the recording material S by the action of the secondary transfer roller 14 in the secondary transfer portion N2. The multiple toner images formed by superimposing the four color toners as described above are collectively transferred to the recording material S. The recording material S is nipped and conveyed between the secondary transfer roller 14 and the secondary transfer counter roller 13 together with the intermediate transfer belt 7 in the secondary transfer portion N2. When this recording material S passes through the secondary transfer portion N2, the secondary transfer roller 14 is supplied with a polarity opposite to the charged polarity of the toner from the secondary transfer power source (high voltage power source) E4 as an application means. A secondary transfer voltage (secondary transfer bias) that is a direct current voltage is applied.

  Here, the recording material S used for image formation is stored in a paper feed cassette (not shown). The recording material S is conveyed to the registration roller 15 by a feeding / conveying device (not shown) as a feeding / conveying unit having a feeding roller, a conveyance roller, a conveyance guide and the like. The recording material S is supplied to the secondary transfer portion N2 after the skew is corrected by the registration roller 15.

  The recording material S to which the toner image has been transferred is conveyed along a conveyance guide 18 to a fixing device 22 as a fixing unit. When the recording material S passes through the fixing nip formed by the fixing roller 20 provided with the heating element 19 and the pressure roller 21 in the fixing device 22, the recording material S is heated and pressed by these roller pairs, A toner image is fixed on the surface.

  Thereafter, the recording material S on which the toner image is fixed is discharged outside the apparatus main body of the image forming apparatus 100. Thereby, the image formation on one recording material S is completed.

  Note that toner (residual toner) that is not transferred to the intermediate transfer belt 7 during the primary transfer and remains on the surface of the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the drum cleaning device 6 and collected. The drum cleaning device 6 removes residual toner from the surface of the rotating photosensitive drum 1 by a cleaning blade 61 arranged in contact with the photosensitive drum 1, and removes this toner by a waste toner conveying screw 62 (not shown). To collect). Further, the toner (residual toner) that is not transferred to the recording material S during the secondary transfer and remains on the intermediate transfer belt 7 is removed from the surface of the intermediate transfer belt 7 by the belt cleaning device 17 and collected.

  As described above, the image forming portion P is provided with the cleaning roller 9 as a cleaning member that cleans the surface of the charging roller 2 while rotating in contact with the surface of the charging roller 2. As a result, even if residual toner, external additives, and the like adhere to the charging roller 2 from the photosensitive drum 1, they can be removed from the surface of the charging roller 2 by the cleaning roller 9. As will be described in detail later, the cleaning roller 9 has a foamed elastic layer as a surface layer, and is brought into contact with the surface of the charging roller 2 with a predetermined pressing force so that a nip portion is formed between the cleaning roller 9 and the charging roller 2. Forming. In this embodiment, the charging roller 2 rotates following the rotation of the photosensitive drum 1, and the cleaning roller 9 rotates following the rotation of the charging roller 2. When the cleaning roller 9 comes into contact with the charging roller 2, the foamed elastic layer is compressed, and when separated, the foamed elastic layer attempts to restore the original shape by the elastic restoring force. Thereby, when the cleaning roller 9 comes into contact with the charging roller, the adhering matter adhering to the surface of the charging roller 2 is collected by the pores of the foamed elastic layer. Performs a cleaning action such as wiping. The charging roller 2 and the cleaning roller 9 will be described in detail later.

  In the present embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4, the drum cleaning device 6 and the cleaning roller 9 as process means acting on the photosensitive drum 1 are integrally incorporated in the cartridge container 8 and are integrated as a whole. Thus, the process cartridge 10 is configured. In general, a process cartridge is a cartridge in which a photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit serving as a processing unit that acts on the photosensitive unit are integrated into a cartridge. Detachable. In the present invention, the process cartridge includes a charging member constituting charging means as process means, and a cleaning member for removing deposits attached to the surface of the charging member.

  The operation of the image forming apparatus 100 according to the present exemplary embodiment is comprehensively controlled by a control unit (control apparatus) 50 as a control unit. The control unit 50 includes a CPU that is a central element that performs arithmetic processing, a memory such as a ROM and a RAM that are storage elements, and the like. The RAM stores sensor detection results, calculation results, and the like, and the ROM stores control programs, data tables obtained in advance, and the like. For example, the control unit 50 turns on / off a drive motor (not shown) that drives a rotating body such as the photosensitive drum 1, turns on / off a charging power source E1, a developing power source E2, a primary transfer power source E3, and a secondary transfer power source E4. Controls OFF and output value.

2. Next, the charging roller 2 in this embodiment will be described. FIG. 3A is a schematic cross-sectional view of the charging roller 2.

  In the present embodiment, the charging roller 2 as a charging member has a conductive support (core metal, core material) 21 and one or more coating layers 22 formed around the conductive support 21. The outer peripheral surface is a roller-shaped member that comes into contact with the photosensitive drum 1 as a member to be charged. In particular, in this embodiment, the charging roller 2 has a coating layer 22 having a two-layer structure, and the base layer (elastic layer) 22a and the surface layer (resistance layer, protective layer) 22b of the coating layer 22 are made of different materials. . In other words, at least an elastic layer as the base layer 22a and a resistance layer as the surface layer 22b are provided on the conductive support 21, and an appropriate volume resistance is held in the upper resistance layer, and the object to be charged is held in the lower elastic layer. A moderate elasticity for maintaining the proper contact is maintained. As a result, it is possible to improve the charging uniformity of a charged body such as a photoconductor or to prevent leakage due to pinholes or scratches on the surface of the charged body such as a photoconductor.

  In this embodiment, when the photosensitive drum 1 is charged by the charging roller 2, the charging roller 2 receives a charging voltage of −1200 V which is a negative DC voltage from the charging power source E <b> 1 through the conductive support 21. Charging bias) is applied.

  As a material for the surface layer (resistive layer) 22b of the charging roller 2, acrylic resin, polyamide resin, polyurethane resin, fluororesin, a mixture thereof, or conductive particles such as carbon black and metal oxide are dispersed in these materials. Things can be used. In the present embodiment, the surface layer 22b of the charging roller 2 is configured using acrylic resin as a main component. These materials can bring high negative chargeability to the charging roller 2 due to the electron attractive effect. The surface layer 22b of the charging roller 2 can be formed by, for example, dip coating, spray coating, roller coating, or the like.

  The material of the base layer (elastic layer) 22a of the charging roller 2 includes ethylene propylene rubber (EPDM), styrene butadiene rubber (SBR), chloroprene rubber (CR), nitrile butadiene rubber (NBR), butyl rubber (BR), isoprene. Synthetic rubber such as rubber (IR), epichlorohydric rubber (CO, ECO), urethane rubber (U) and silicone rubber, natural rubber (NR), styrene butadiene styrene (SRS), polyolefin-based and polyurethane-based thermoplastic elastomer, or these A mixture of the above can be used. In this embodiment, the base layer 22a of the charging roller 2 is mainly composed of a medium resistance material having an ionic conduction mechanism using epichlorohydrin rubber (ECO, CO) as a main component. A synthetic rubber material is preferably used as the material of the elastic layer in order to stably contact the charged body such as a photoreceptor and the charging roller 2. The charging roller 2 may have a layer in which conductive powder such as carbon black, graphite, metal powder and metal oxide is dispersed in an elastic material in order to impart conductivity. In addition, a relatively large amount of conductive fine powder may be blended in the elastic material to reduce the required resistance. When a large amount of conductive fine powder is blended, the hardness of the elastic material may increase, but a relatively large amount of softening oil or plasticizer may be blended in order to reduce the hardness to a required level. The base layer 22a of the charging roller 2 can be formed by molding or the like.

The electric resistance (volume resistance value) of the charging roller 2 is preferably 10 ⁶ Ω or less and more preferably 10 ⁵ Ω or less in a normal temperature and normal humidity environment (NN environment) (25 ° C./50% RH). If the electric resistance of the charging roller 2 is higher than this, a voltage drop at the charging roller 2 may occur when a charging voltage is applied, and the potential that can be formed on the surface of the photosensitive drum 1 may decrease. The electrical resistance of the charging roller 2 may be as small as possible, but is usually about 10 ² Ω or more for reasons of manufacturing. As shown in FIG. 4, the electrical resistance of the charging roller 2 (indicated as “log · Ω” in FIG. 4) varies depending on the environment. In this embodiment, the electric resistance of the charging roller 2 is 10 ⁵ Ω or less throughout the entire life of the charging roller 2 and regardless of the environment.

  Note that the life of the charging roller 2 may be a period in which a desired performance set in advance can be achieved. As the environment, an environment in which the image forming apparatus 100 can be used may be considered. Here, a low temperature and low humidity environment (LL environment) (15 ° C./10% RH), a normal temperature and normal humidity environment (NN environment) (25 ° C. / 50% RH), high temperature and high humidity environment (HH environment) (30 ° C./80% RH)). The same applies to the electrical resistance of the cleaning roller 9 described later.

  Here, a method for measuring the electrical resistance of the charging roller 2 will be described. In this embodiment, the electrical resistance of the charging roller 2 was measured by a dynamic resistance measuring method in which a charging member is brought into contact with a conductive base and driven to rotate by using a measurement system as shown in FIG. . That is, the conductive support 21 of the charging roller 2 is brought into contact with an aluminum cylinder 201 as a conductive substrate for rotational driving. In this state, a DC voltage of 500 V is applied from the power source 202 to the conductive support 21 of the charging roller 2 while the charging roller 2 is driven and rotated by rotating the cylinder 201 by a motor (not shown). At this time, the current flowing through the reference resistance (1 KΩ) 203 is measured by the tester 204, and the electric resistance of the charging roller 2 is calculated. Here, the load applied to both ends of the conductive support 21 of the charging roller 2 was 500 g. The diameter of the cylinder 201 was 30 mm. The peripheral speed of the cylinder 201 was 23.56 mm / sec.

3. Next, the cleaning roller 9 in this embodiment will be described. FIG. 3B is a schematic cross-sectional view of the cleaning roller 9.

  In this embodiment, the cleaning roller 9 as a cleaning member has a rod-like support portion (core metal, core material) 91 and an elastic layer 92 formed around the support portion 91, and the outer peripheral surface thereof. Is a roller-shaped member that contacts the charging roller 2. The elastic layer 92 includes a foamed elastic layer as an outermost layer (contact portion) that contacts the surface (outer peripheral surface) of the charging roller 2. In particular, in the present embodiment, the cleaning roller 9 includes a support portion 91 and a foamed elastic layer 92 that contacts the charging roller 2 formed on the outer peripheral surface of the support portion 91. As long as the elastic layer 92 has a foamed elastic layer as the outermost layer, it may have one or more other elastic layers as the inner layer. An example of the structure of the foamed elastic body (porous elastic member) constituting the foamed elastic body layer 92 is an open cell structure. In this embodiment, the cleaning roller 9 is electrically floating (float).

  The support portion 91 of the cleaning roller 9 is preferably a columnar bar-shaped member. The material in particular of the support part 91 is not restrict | limited, For example, materials, such as a metal or a synthetic resin, can be used. In addition, when the support part 91 is comprised with a synthetic resin, it is preferable to contain an electroconductive substance and to provide electroconductivity. Examples of the support portion 91 include a metal columnar shaft and a resin columnar shaft.

  The foamed elastic layer (contact portion) 92 of the cleaning roller 9 is formed on the outer peripheral surface of the support portion 91 with a substantially uniform thickness, and its outer shape is cylindrical. The foamed elastic layer 92 of the cleaning roller 9 is configured by adding a charge control agent (conductive agent) having a lower frictional charging property to the foamed resin material to the material constituting the surface of the charging roller 2 than the foamed resin material. It is preferable that Thereby, as will be described in detail later, the electrical resistance of the cleaning roller 9 can be appropriately controlled. The thickness of the foamed elastic layer 92 of the cleaning roller 9 can be selected as appropriate, but is preferably 1 to 50 mm, and more preferably 1 to 15 mm. Further, the overall radius of the cleaning roller 9 is preferably 2 to 100 mm, and more preferably 2 to 40 mm.

  Typical foamed resins are those in which a gas is dispersed and expanded in a molten or flowing synthetic resin, the resin is solidified, and molded as a resin having bubbles (translated by Tatsuta Mita, Polymer Dictionary, Maruzen). 1994, "Foam"). Examples of suitable synthetic resins include thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, viscose, ionomer, or polyurethane, epoxy resin, phenol / urea resin, melamine resin, urea / formaldehyde resin. And thermosetting resins such as pyranyl resin, silicone resin, and acrylic resin. As the foaming agent, a physical foaming agent that generates gas by physical change can be used, but a chemical foaming agent that generates gas by heating is preferable. As the resin used as a raw material, a thermosetting resin can also be used in terms of its hardness and durability. Examples of such thermosetting resins include urethane resins and melamine resins, and urethane resins are preferred.

  Examples of the conductive agent include carbon black and metal particles as an electronic conductive agent, and a monomer capable of imparting ionic conductivity as an ionic conductive agent. By kneading these in the foamed resin, the charge of the cleaning roller 9 can be neutralized and the charge can be eliminated. In the present embodiment, it is preferable to use an ionic conductive agent in order to reduce rubbing scratches caused by the conductive agent of carbon black or metal particles on the surface of the charging roller 2.

  Here, the cleaning roller 9 is configured to satisfy the relationship of Ω1 ≧ Ω2 when the electrical resistance of the cleaning roller 9 is Ω1 and the electrical resistance of the charging roller 2 is Ω2. That is, the cleaning roller 9 is configured to have an electrical resistance that is greater than or equal to that of the charging roller 2. If the electrical resistance of the cleaning roller 9 is lower than the electrical resistance of the charging roller 2, the charging voltage applied to the charging roller 2 is affected even if no discharge occurs between the charging roller 2 and the cleaning roller 9. May end up. On the other hand, the upper limit of the electrical resistance of the cleaning roller 9 is set as follows. That is, the surface potential of the cleaning roller 9 when the voltage is applied to the charging roller 2 to charge the photosensitive drum 1 is V1, and the surface potential of the charging roller 2 at that time is V2. Further, a discharge start voltage that is a voltage at which discharge is started when a DC voltage is applied between the cleaning roller 9 and the charging roller 2 is defined as Vth. At this time, the voltage is set so as to satisfy the relationship of | V1-V2 | ≦ | Vth | when a voltage is applied to the charging roller 2 to charge the photosensitive drum 1. That is, during the charging operation, the potential difference between the surface potential of the charging roller 2 and the surface potential of the cleaning roller 9 is maintained below the discharge start voltage. The discharge start voltage is a discharge generated between the charging roller 2 and the cleaning roller 9 when only the DC voltage is applied to the charging roller 2 and the absolute value of the applied DC voltage is increased. This is the DC voltage value at the point where the DC current flowing through the charging roller 2 suddenly increases.

  In the present embodiment, as described above, the foamed elastic layer 92 of the cleaning roller 9 has a charge control in which the foamed resin material is less triboelectrically charged with the material constituting the surface of the charging roller 2 than the foamed resin material. An agent (conductive agent) is added to the structure. The electrical resistance of the cleaning roller is controlled by the potential difference between the surface potential of the charging roller and the surface potential of the cleaning roller when a voltage is applied to the charging roller to charge the photosensitive drum. It is controlled to be smaller than when no agent is added. Here, the electrical resistance of the cleaning roller 9 is equal to the surface potential of the charging roller 2 when the voltage is applied to charge the photosensitive drum 1 and the surface potential of the cleaning roller 9 at that time is the same. Or it is preferable to control in the direction which becomes high at the same polarity side. As a result, it is possible to more efficiently collect on the cleaning roller 9 adhering matter having a polarity opposite to the charging voltage attached to the charging roller 2 from the surface of the photosensitive drum 1 due to the surface potential of the charging roller 2. However, as described above, the potential difference between the surface potential of the charging roller 2 and the surface potential of the cleaning roller 9 is set to be equal to or less than the discharge start voltage.

More specifically, as shown in FIG. 4, the electrical resistance value of the cleaning roller 9 is set to a value equal to or higher than the electrical resistance value of the charging roller 2, more preferably higher than the electrical resistance value of the charging roller 2. On the other hand, the electrical resistance value of the cleaning roller 9 is preferably 10 ¹¹ Ω or less.

FIG. 5 shows the cleaning roller 9 with respect to the electrical resistance (indicated as “log · Ω” in FIG. 5) of the cleaning roller 9 in a low temperature and low humidity environment (LL environment) where the electrical resistance is the highest among the environments shown in FIG. The relationship of surface potential is shown. As can be seen from FIG. 5, when the electrical resistance of the cleaning roller 9 exceeds 10 ¹¹ Ω, the surface potential of the cleaning roller 9 has the same polarity as the polarity of the charging voltage rather than the potential of the charging voltage applied to the charging roller 2. It tends to increase rapidly to the side (minus side in this embodiment). Therefore, the potential difference between the surface potential of the charging roller 2 and the surface potential of the cleaning roller 9 may be equal to or higher than the discharge start voltage. Thus, in this embodiment, the upper limit value of the electrical resistance of the cleaning roller 9 is preferably 10 ¹¹ Ω. As long as the electrical resistance of the cleaning roller 9 is equal to or higher than the electrical resistance of the charging roller 2, it can be set to any value below the upper limit. RH) is preferably 10 ⁹ Ω or less, and more preferably 10 ⁸ Ω or less. It can be said that the cleaning roller 9 having such electric resistance has conductivity. In this embodiment, the electrical resistance of the cleaning roller 9 is 10 ⁸ Ω or less throughout the lifetime of the cleaning roller 9 and regardless of the environment.

  Here, a method for measuring the electrical resistance of the cleaning roller 2 will be described. In this example, the electrical resistance of the cleaning roller 9 was measured using a measurement system as shown in FIG. That is, the cleaning roller 9 is brought into contact with a stainless steel flat plate 301 as a conductive substrate. In this state, the measuring instrument 302 applies a DC voltage of 100 V to the support portion 91 of the cleaning roller 9 to measure the electrical resistance. As the measuring instrument 302, ULTRA HIGH RESISTANCE METER manufactured by ADVANTEST was used. The load applied to both ends of the support portion 91 of the cleaning roller 9 was 100 g.

  As described above, according to the present embodiment, an ion conductive sponge roller is used as the cleaning roller 2, and its electric resistance is equal to or higher than that of the charging roller 2, and between the charging roller 2 and the cleaning roller 9 during the charging operation. It is set so that the potential difference is kept below the discharge start voltage. Preferably, the electrical resistance of the cleaning roller 2 is set regardless of the environment and throughout the lifetime of the charging roller 2 and the cleaning roller 9. As a result, an increase in the surface potential of the cleaning roller 9 due to frictional charging between the charging roller 2 and the cleaning roller 9 can be suppressed, and the occurrence of image defects such as white spotted images can be suppressed.

Others While the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the charging voltage applied to the charging member is a DC voltage, but is not limited thereto. The charging voltage applied to the charging member may be an oscillating voltage obtained by superimposing a DC voltage (DC component) on an AC voltage (AC component). In this case, the peak-to-peak voltage Vpp of the AC voltage applied to the charging member is at least twice the discharge start voltage when a DC voltage is applied to the charging member. As a result, AC discharge occurs, and the surface potential of the member to be charged converges to a (substantially identical) charging potential corresponding to the DC voltage applied to the charging member.

  In the above-described embodiments, the case where the charging member is a charging roller that is a rotating body has been described. However, the rotating body as the charging member is not limited to a roller shape, and may be a belt shape or the like. . For example, the belt-shaped charging member can be composed of an endless belt that is stretched around a plurality of support rollers. For example, one of the support rollers contacts the photoconductor via the belt, and the other of the support rollers. One can abut against the cleaning member via the belt.

  In the above-described embodiment, the case where the cleaning member is a rotating body that rotates following the rotation of the charging member has been described. It is preferable for the cleaning member to be such a rotating body that rotates in a driven manner because the charging roller can be cleaned well while suppressing the occurrence of scratches on the surface of the charging member. However, if desired, the cleaning member may be fixedly disposed on the surface of the charging member. For example, a pad shape, a sheet shape, or a blade shape that rubs the surface of the charging member as the surface of the charging member moves is used. Further, the cleaning member may be a rotating body that is rotationally driven, such as rotating with a circumferential speed difference from the charging member.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 9 Cleaning roller 91 Support part 92 Foam elastic body layer

Claims (6)

A photoreceptor,
A rotatable charging member that contacts the photoconductor and is charged with a voltage to charge the surface of the photoconductor;
A cleaning member having a foamed elastic body layer in contact with the surface of the charging member for removing deposits attached to the surface of the charging member;
A process cartridge that can be attached to and detached from the main body of the image forming apparatus.
The cleaning member has an electric resistance equal to or higher than that of the charging member, and a surface potential of the cleaning member when a voltage is applied to the charging member to charge the photoconductor is V1, When the surface potential of the charging member at that time is V2, and the discharge start voltage, which is the voltage at which discharge starts when a DC voltage is applied between the cleaning member and the charging member, is Vth, A process cartridge satisfying a relationship of | V1-V2 | ≦ | Vth | when a voltage is applied to a member to charge the photosensitive member.   The foamed elastic layer is formed by adding a charge control agent having a lower frictional charging property to the foamed resin material and a material constituting the surface of the charging member than the foamed resin material. The process cartridge according to claim 1.   The process cartridge according to claim 2, wherein the charge control agent is an ion conductive agent.   The cleaning member includes a support portion, and an elastic layer that is formed around the support portion and includes the foamed elastic body layer in contact with the charging member at an outermost layer, and an outer peripheral surface of the elastic layer is the charging surface. The process cartridge according to any one of claims 1 to 3, wherein the process cartridge is a roller-shaped member that contacts the member and is rotated following the rotation of the charging member.   The charging member is a roller-shaped member having a conductive support and one or more coating layers formed around the conductive support, the outer peripheral surface of which is in contact with the photoconductor. The process cartridge according to any one of claims 1 to 4, wherein: An image carrier;
A rotatable charging member that contacts the image carrier and is charged with the direct current voltage to charge the image carrier;
A cleaning member having a foamed elastic body layer in contact with the surface of the charging member for removing deposits attached to the surface of the charging member;
In an image forming apparatus having
The cleaning member has an electric resistance equal to or higher than the electric resistance of the charging member, and the surface potential of the cleaning member when a DC voltage is applied to the charging member to charge the image carrier is V1. When the surface potential of the charging member at that time is V2, and the discharge start voltage, which is the voltage at which discharge starts when a DC voltage is applied between the cleaning member and the charging member, is Vth, An image forming apparatus satisfying a relationship of | V1-V2 | ≦ | Vth | when a DC voltage is applied to the charging member to charge the image carrier.

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