JP2012128081A - Charging member and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging blade 4 capable of collecting stains under the condition of DC voltage application.SOLUTION: A scraping member for scraping the surface of a photoreceptor drum 3 with a tip 43 of a charging blade 4 is provided to facilitate collection of toner and external additives on the photoreceptor drum 3 by the application of bias.

Description

  In the present invention, an uncharged portion is disposed on a counter with respect to an image carrier moving direction on an image carrier (a member to be charged) on which an electrostatic latent image is formed, and moves relative to the image carrier. The present invention relates to a blade-shaped charging member for charging the surface of an image carrier by applying. The present invention also relates to an image forming apparatus using the charging member.

  In the above, representative examples of the image carrier on which the electrostatic latent image is formed include an electrophotographic photosensitive member and an electrostatic recording dielectric. Examples of the image forming apparatus include an electrophotographic type or electrostatic recording type copying machine, a printer, a facsimile, a composite function machine thereof, and an image display display device.

  A transfer type electrophotographic image forming apparatus will be described as an example. This apparatus generally has a charging means for uniformly charging a drum surface to a predetermined polarity and potential with respect to an electrophotographic photosensitive member represented by a rotating drum type (image carrier: hereinafter referred to as a drum). An electrostatic latent image of image information is formed by exposure means that selectively exposes the drum charging surface. Then, the latent image is visualized (developed) as a toner image using a developer (hereinafter referred to as toner) by the developing means. The toner image is transferred onto a recording material (recording medium) by a transfer unit. The toner image on the recording material is fixed as a fixed image by the fixing means, and the recording material is output as an image formed product.

  In recent years, the charging means is a contact type using a rotating charging member such as a belt shape, a roll shape or a brush shape made of semiconductive rubber or resin, or a fixed charging member such as a blade shape or a film shape. Chargers have been attracting attention. Such a contact-type charger usually charges the drum surface to about -500 V by applying a DC voltage of -1.0 to -1.5 kV to charge the drum surface. In addition, since charging may become unstable when only a DC voltage is used, a method of stabilizing charging by superimposing an AC voltage on a DC voltage is used.

  Here, as one of the problems of the contact type charger found in the blade charger, there is contamination of the charger. Normally, the toner remaining on the drum without being transferred is cleaned by the cleaning member and scraped off from the drum. However, not all toner and external additives can be removed sufficiently, and the toner passes through the cleaning member and is conveyed to the charger. Therefore, the cleaning member cannot be cleaned, and the toner and external additive that have passed through are sent to the contact-type charger and adhere to the surface of the charger in contact with the drum.

  Thereafter, when the toner or the external additive adhering to the surface of the charger exceeds a predetermined adhering amount, the uniform discharge is inhibited, and thus non-uniform charging occurs. For this reason, image defects such as vertical stripes due to defective charging are finally generated.

  Because of these problems, it has been required to prevent the surface of the charger from being soiled and to suppress the amount of ozone generated by discharge as much as possible.

  Therefore, a non-contact type charger (apart from the corona charger) that charges the drum surface in a non-contact manner while keeping a gap as small as possible is also considered. In the non-contact type charger that guarantees the narrow gap as described above, the dirt does not always adhere due to the narrow gap. This is considered to be because the toner and external additives remaining without being transferred have a zero or positive charge amount. Therefore, this phenomenon occurs because toner or an external additive having a positive charge under the influence of an electric field is applied to the charging portion to which a negative bias is applied, and then jumps to the charging portion.

  In view of the above, the applicant previously provided a metal member in front of the charging unit to prevent further contamination of the charging unit, and provided a collecting member that collects dirt by applying an electric field to the metal unit. A configuration is proposed (Patent Document 1). According to this configuration, since a large electric field difference can be obtained by charging with a DC voltage and an AC voltage superimposed, it is possible to collect dirt due to the electric field in the metal portion.

JP 7-28305 A

  The present invention relates to a further improvement of the above technique. An object of the present invention is to provide a blade-shaped charging member that can effectively collect dirt even when a DC voltage that does not generate charging noise is applied as an applied voltage, and an image forming apparatus using the charging member. It is in.

  In order to achieve the above object, a typical configuration of the charging member according to the present invention is such that an uncharged portion is disposed on a counter with respect to the moving direction of the image carrier on the image carrier on which an electrostatic latent image is formed. A blade-shaped charging member for charging the surface of the image carrier by applying a DC voltage by being moved in contact with each other and for discharging the surface of the image carrier. A charging portion and a non-charging portion for preventing discharge on the surface of the image carrier, and the non-charging portion is in contact with the image carrier, and the charging portion and the image carrier It is possible to provide a dischargeable gap with the body, and at least a part of the uncharged portion prevents the discharge from the uncharged portion to the surface of the image carrier. The non-charged portion is a surface of the image carrier. The surface of the image carrier is abutted over the entire width of the image formable area of the image bearing member so that the surface of the image carrier can be slid. In the charging member, the non-charged portion and the image carrier are slid Is a rubbing portion, and a position in the charging portion where discharge occurs with respect to the image carrier is defined as a discharge position, and is present between the rubbing portion and the discharge position, and a discharge position of the charging portion. The concave portion is recessed from the surface of the image carrier, and the concave portion exists on the side facing the image carrier so that an electric field can be formed between the concave portion and the image carrier.

  In the charging member of the present invention, the toner and the external additive are easily separated from the surface of the image carrier by the non-charged portion that abuts the image carrier and rubs the surface of the image carrier. For this reason, it becomes easy to take in toner and external additives at the dirt collecting portion due to the effect of the electric field, and even when a DC voltage that does not generate charging noise is applied as the applied voltage, the dirt is effectively collected and the dirt on the charged portion is removed. Can be prevented.

Schematic diagram of collecting dirt by charging blade according to embodiment 1 Schematic configuration diagram showing an example of an image forming apparatus Schematic of the charging blade according to the first embodiment. (A) is a perspective view of the drum and the charging blade, (b) is a partial perspective view of the drum and the charging blade. Setting schematic diagram of charging blade according to embodiment 1 Explanatory drawing of measuring method of set angle θ and penetration amount δ Schematic diagram of particle (toner) behavior at rubbing part Schematic of the charging blade of the comparative example Schematic of the charging blade according to the second embodiment. FIG. 6 is a schematic perspective view of a roller driving unit of a charging blade according to a second embodiment. Setting schematic diagram of charging blade according to embodiment 2 Schematic diagram of particle (toner) behavior at rubbing part Schematic diagram of collecting dirt by charging blade according to embodiment 2

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

[Example 1]
(1) Overall schematic configuration and image forming operation of an example of an image forming apparatus FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus 1 using a blade-shaped charging member (blade charger) 4 according to the present invention. The apparatus 1 is a process cartridge detachable electrophotographic image forming apparatus (printer) using an electrophotographic process. The apparatus 1 forms an image on a recording material (recording medium, recording medium) P based on an electrical image signal inputted to a control circuit unit (control means: CPU) 100 from a host device 300 such as a personal computer, an image reader, or a facsimile machine. Execute.

  The recording material P is a sheet-like material on which an image can be formed by an electrophotographic process, and examples thereof include paper, a resin sheet, and a label. The control circuit unit 100 exchanges various types of electrical information with the operation unit 200 and the host device 300, and performs overall control according to a predetermined control program and a reference table stored in the storage unit of the image forming operation of the device 1. To control.

  In the apparatus main body of the apparatus 1, a cartridge housing portion 1A is provided. The process cartridge 2 is detachably attached to the cartridge housing portion 1A by a predetermined operation procedure. In this embodiment, the cartridge 2 is an integral process cartridge. That is, the electrophotographic photosensitive drum 3 as a rotating drum type image carrier on which an electrostatic latent image developed by the developer T is formed, and the charging means 4 and the developing means as process means acting on the drum 3 6. The cleaning means 8 is integrally assembled in a common housing.

  In this embodiment, the charging means 4 is a charging blade (blade-shaped charging member). The charging blade 4 will be described later. The developing means 6 is a non-contact developing device using magnetic one-component toner as the developer T. Hereinafter, the developer T is referred to as toner. The toner T used in this embodiment is a magnetic one-component negative toner composed of a base material and a plurality of external additives and having an average particle diameter of 8 μm. The cleaning means 8 is a blade cleaning device using an elastic blade (cleaning blade) 8a as a cleaning member.

  The developing device 6 includes a developing container 6a as a developer containing portion that contains toner T. Further, a developing sleeve 6b as a developer carrying member that develops the electrostatic latent image formed on the drum 3 as a toner image, a non-rotating magnet roller 6c disposed in the sleeve 6b, and toner on the developing sleeve 6b. It has a developing blade 6d for regulating the amount.

  A laser scanner unit (laser optical device) 5 as an image exposure unit is disposed above the cartridge housing portion 1A. The unit 5 outputs a laser beam L modulated in accordance with image information input from the host device 300 to the control circuit unit 100. The laser light L enters the cartridge 2 through the exposure window 2 a on the upper surface side of the cartridge 2. Thereby, laser scanning exposure is performed on the surface of the drum 3.

  A transfer roller 7 abuts on the lower surface of the drum 3 of the cartridge 2 to form a transfer nip portion N. The cartridge 2 accommodated in the cartridge accommodating portion 1A is pressed and fixed to a positioning portion (not shown) on the apparatus main body side by a pressing means (not shown). A drive output unit (not shown) on the apparatus main body side is coupled to a drive input unit (not shown) of the cartridge 2. Further, various electrical contacts (not shown) on the apparatus main body side are electrically connected to various electrical contacts (not shown) of the cartridge 2.

  The image forming operation is as follows. The drum 3 is rotationally driven in a clockwise direction indicated by an arrow A at a predetermined process speed, in this embodiment, 100 mm / sec. Unit 5 is also driven. In synchronization with this drive, a predetermined charging bias is applied from the charging bias application power source E to the charging blade 4 at a predetermined control timing, and the surface of the drum 3 is brought into a predetermined polarity and potential by the charging blade 4 in a non-contact manner. It is charged uniformly. The unit 5 scans and exposes the surface of the drum 3 with a laser beam L modulated in accordance with an image signal. As a result, an electrostatic latent image corresponding to the image signal is formed on the surface of the drum 3.

  The formed electrostatic latent image is supplied with toner by a developing sleeve 6b of the developing device 6 and developed as a toner image. The developing sleeve 6b is driven to rotate at a predetermined speed in the counterclockwise direction indicated by the arrow. A predetermined developing bias is applied to the developing sleeve 6b at a predetermined control timing from a developing bias applying power source (not shown).

  On the other hand, the sheet feeding roller 14 of the sheet feeding mechanism unit 13 is driven, and the recording material (recording medium) P is separated and fed. The recording material P passes through a sheet path 15 including registration means (not shown), is introduced into the transfer nip portion N at a predetermined control timing, and is nipped and conveyed through the nip portion N. While the recording material P passes through the nip portion N, a predetermined transfer bias is applied to the transfer roller 7 from a transfer bias application power supply unit (not shown). As a result, the toner image on the drum 3 side is sequentially transferred onto the surface of the recording material P.

  The recording material P that has exited the nip portion N is separated from the surface of the drum 3 and introduced into the fixing device 10. In this embodiment, the fixing device 10 is a heat roller fixing device, and the recording material P is nipped and conveyed at the fixing nip portion and receives heat and pressure. As a result, the unfixed toner image on the recording material P is fixed by heat and pressure as a fixed image. Then, the recording material P exiting the fixing device 10 passes through the sheet path 16 and is sent to the paper discharge tray 12 on the upper surface of the apparatus 1 as an image formed product.

  Further, the transfer residual toner remaining on the drum 3 without being transferred to the recording material P in the transfer nip N is scraped off by the cleaning blade 8a of the cleaning device 8 and stored in the waste toner container 8b. The cleaned drum 3 is repeatedly used for image formation.

(2) Configuration of Charging Blade 4 FIG. 3A is a diagram illustrating the configuration of the charging blade 4 in this embodiment. 4A is a perspective view of the drum 3 and the charging blade 4, and FIG. 4B is a partial perspective view of the drum 3 and the charging blade 4. FIG. 5 is a diagram for explaining the setting of the charging blade 4 with respect to the drum 3.

  The charging blade 4 is configured such that a non-charged portion 43 is disposed on a counter with respect to a drum moving direction (image carrier moving direction) A and moves relatively in contact with the drum 3 to apply a DC voltage. This is a blade-shaped charging member for charging the surface of the drum 3.

  The charging blade 4 has a charging unit 44 for discharging the surface of the drum 3 and a non-charging unit 43 for not discharging the surface of the drum 3. The charging unit 44 and the non-charging unit 43 are supported by the support unit 42. The non-charging portion 43 can be in contact with the drum 3 to provide a dischargeable gap H (FIG. 5B) between the charging portion 44 and the drum 3.

  The non-charging portion 43 is made of a material having a higher resistance than the charging portion 44 so that the non-charging portion 43 does not discharge the surface of the drum 3 from the non-charging portion 43. The non-charging portion 43 is provided so as to be slidable on the surface of the drum 3 by contacting over the entire width of the image formable region width G on the surface of the drum 3.

  This will be described more specifically. The support portion 42 is a conductive elastic support member that also serves as an electrode plate (electrode portion). In this embodiment, the support portion 42 is a phosphor bronze plate (metal member) having a thickness of 100 μm. The support part 42 is long in the generatrix direction (drum axis direction) of the drum 3 and has a length corresponding to the entire image forming area width G of the drum 3. The base side of the support part 42 (one end part side in the short direction of the support part 42) is held by the holder 41.

  In this embodiment, the holder 41 is a rigid metal plate and is electrically connected to the support portion 42. A non-charging portion 43 as a charging blade tip portion is disposed on the tip side of the support portion 42 (the side opposite to the holder 62 side). In this embodiment, the non-charging portion 43 is urethane rubber (insulating member).

<Non-charging part 43>
The non-charging portion 43 is intended to be positioned at the same time so as to have a gap H that allows the charging portion 44 to be discharged in contact with the drum 3 and to make it easy to leave the drum 3 by rolling the toner on the drum. Further, the non-charging portion 43 rubs the surface of the drum so that the toner and the external additive can be easily peeled off from the surface of the drum, so that the entire image formable region width G can be rubbed. It is arranged over.

  Further, by making the non-charged portion 43 that is a sliding portion insulating, it is possible to obtain good charge by preventing discharge at a portion different from the charged portion 44. However, since it suffices to suppress the discharge from the non-charged portion 43 to the surface of the drum 3, it is only necessary to insulate the support portion 42 which is an electrode plate. The tip of the non-charged portion 43 is shown in FIG. As shown, the conductive rubber 47 may be used. Since the non-charging portion 43 is in contact with the surface of the drum 3, the elastic material is used to prevent the surface of the drum 3 from being damaged.

<Charging unit 44>
A charging portion 44 is attached to the surface of the support portion 42 facing the drum 3 along the length of the support portion 42 in order to charge the drum surface using discharge. In this embodiment, the charging portion 44 is a medium resistance conductive rubber, and is joined to the support portion 42 by a conductive adhesive. Accordingly, the charging unit 44 is electrically connected to the support unit 42. The support portion 42 is electrically connected to the holder 41.

  The resistance of the conductive rubber of the charging unit 44 is about 10 ^ 8 Ωcm. The charging unit 44 is an elastic body because it uses conductive rubber. In order to reduce the charging voltage, it is necessary to make the gap H as narrow as possible. Therefore, the elastic body is used to prevent scratches at the time of contact with the drum 3 such as when dropped.

  The non-charging part 43 and the charging part 44 are attached to the same support part 42. This is because the non-charging portion 43 and the charging portion 44 are attached to the same member 42, so that the positioning can be performed at the portion where the charging blade 4 abuts against the drum 3, so that the positional accuracy is improved. In addition, the charging unit 44 is attached so as not to contact the non-charging unit 43, and as a dirt collecting unit only between the non-charging unit 43 and the charging unit 44 is a support unit 42 which is an electrode plate. There is a recess 45.

  At this time, the width M between the non-charging portion 43 and the charging portion 44 is 5 mm in this embodiment. A line segment K extending from the point 0 where the non-charging portion 43 contacts the drum 3 to the downstream side in the drum rotation direction (image carrier moving direction) A is arranged so that the toner and the external additive can easily face the recess 45. I have 46. The angle α at this time is an angle formed from a perpendicular line U extending from the point O in contact with the drum 3 on the extended line of the holding portion 42, and in this embodiment, α = 45 °.

  As the range of α, since the dirt cannot be collected unless the guide portion 46 is directed to the dirt collecting portion 45, 0 ° ≦ α <point O (a point in contact with the photosensitive drum) and point P (the charging portion and the dirt collecting portion). The angle β (65 ° in this embodiment) formed by the line segment L connecting the intersections) may be used.

  That is, in the charging blade 4, the portion where the non-charged portion 43 and the drum 3 are rubbed is the rubbing portion D, and the position in the charging portion 44 where discharge is generated with respect to the drum 3 is the discharge position 44 a. A concave portion 45 as a dirt collecting portion is provided between the rubbing portion D and the discharge position 44a. The recess 45 is a recess that is recessed from the surface of the discharge position 44 a of the charging unit 44. The concave portion 45 exists on the side facing the drum 3 so that an electric field can be formed between the concave portion 45 and the drum 3.

<Charging blade settings>
The charging blade 4 is arranged with respect to the drum 3 with the longitudinal direction parallel to the generatrix direction of the drum 3. The charging blade 4 is arranged in a counter direction with respect to the rotation direction A of the drum 3. Then, the non-charging portion 43 is brought into contact with the drum 3, the holder 41 is fixed to the housing of the cartridge 2, and the non-charging portion 43 is brought into contact with the drum 3 with a predetermined pressing force by the bending reaction force of the support portion 42. It will be in the state. In this contact state, the charging unit 44 is disposed so as to face the non-contact with the drum 1. The discharge position 44 a of the charging unit 44 is disposed in a non-contact manner with a dischargeable gap H between the charging unit 44 and the drum 1.

  A predetermined charging bias is applied to the conductive holder 41 from the charging bias application power source E (FIG. 2), and the bias is applied to the charging unit 44 via the holder 41 and the support unit 42. As a result, the surface of the drum 3 is uniformly charged to a predetermined polarity and potential by discharging to the surface of the drum 3 in the minute gap H between the discharge position 44a of the charging unit 44 and the drum 3. The

  In this embodiment, a DC voltage of −1.0 kV is applied to the charging unit 44 by the power source E, and the drum surface is charged to about −500V. Therefore, a negative voltage necessary for charging is applied to the support portion (phosphor bronze portion) 42 of the recess 45, which is a dirt collecting portion, at the same time as the charging voltage is applied, and a DC voltage of -1.0 kV is applied.

  The setting of the charging blade 4 for the drum 3 with respect to the drum 3 will be described with reference to FIGS. The non-charging portion 43 of the charging blade 4 is disposed in contact with the drum 3. The charging blade 4 is arranged in the counter direction with respect to the rotation direction A of the drum 3. Further, the charging unit 44 is separated from the surface of the drum 3 with a dischargeable gap H in order to charge the drum surface to a predetermined voltage. The charging blade 4 in this embodiment is in edge contact with a set angle θ = 24 ° and an intrusion amount δ = 0.5 mm.

  The intrusion amount δ is a virtual amount that has entered the drum 3 as it is without deformation of the blade tip, and the set angle θ is an angle formed by a tangent at the point where the blade tip and the drum intersect with the blade. . A method for obtaining the actual set angle θ and the penetration amount δ will be described with reference to FIG. The setting angle θ and the penetration amount δ are measured in a state where the drum 3 is removed from the arrangement state of the charging blade 4 and the drum 3 at the time of image formation.

  In FIG. 6A, a position where the drum 3 is arranged at the time of image formation is defined as a virtual drum 3. An axis that passes through the center of the virtual drum 3 and includes an edge portion at the tip of the charging blade 4 (the tip is described in the example of the non-charging portion 43 in FIG. Axis. An axis that passes through the center of the virtual drum 1 and is perpendicular to the X axis is defined as a Y axis. As shown in the figure, the coordinates of the charging blade 4 from the virtual drum center 0 are measured. The set angle θ and the intrusion amount δ can be obtained from the coordinate x in the x direction from the center of the drum, the coordinate y in the y direction, and the radius r of the drum 1 using the equations (1) and (2).

δ = √ (r ^ 2-x ^ 2) -y (1)
θ = sin−1 (x / r) (2)
Next, the case where the object that comes into contact with the charging blade is a flat surface 3 ′ such as a photosensitive belt will be described with reference to FIG. Unlike FIG. 6A, the setting angle θ does not change even if the contact position of the charging blade changes. Therefore, the setting angle θ, which is the angle formed with the virtual belt, can be easily known by measuring the attachment angle of the blade with respect to the virtual belt plane 3 ′. Further, the intrusion amount δ can be obtained from the distance g from the virtual belt to the blade edge and the set angle θ using Equation (3).

δ = g / cos θ (3)
The set angle θ and the penetration amount δ of the charging blade 4 can be obtained from the above equations (1) to (3).

  The charging unit 44 can always maintain 7.5 to 150 μm capable of discharging the gap α with the drum 3. In addition, the larger the area that can be discharged as much as possible, the more stable the charging is, so the contact angle and the penetration amount are determined. By setting as described above, the toner and the external additive that have passed through the non-charging portion 43 are attracted to the dirt collecting portion 45 together with the application of the charging bias by the effect of the electric field. Nothing will happen.

<Transfer residual toner and external additive>
In this embodiment, a negatively charged toner is used. Normally, the toner is negatively charged by frictional charging and sent to the transfer portion N. Then, a positive voltage (+1.0 kV in the present embodiment) is applied at the transfer portion N and transferred onto the recording material P. However, not only the toner is negatively charged by frictional charging, but also there are some toners and external additives that are positively charged. For this reason, the positively charged toner and the external additive are not transferred at the transfer portion N, but are sent to the cleaning portion as a transfer residue.

  It is only necessary that the cleaning unit can remove all the particles from the drum for cleaning. However, external additives and toner fine powder cannot be cleaned because they have a small particle size, and finally the charging unit 44 of the charging blade 4 can be cleaned. Will be sent to. For this reason, the positively charged toner or the external additive is attracted to the charging unit 44 to which a negative bias is applied, causing the charging unit 44 to become dirty.

<Rubbing at rubbing part D>
The role of the non-charging portion 43 in the charging blade 4 that forms the rubbing portion D in contact with the drum 3 will be described with reference to FIG. When the untransferred toner Ta remaining on the drum 3 without being transferred is sent to the rubbing portion D, the external additive and toner are rubbed in the rubbing portion D. At this time, the external additive and toner change the adhesion surface adhering to the drum 3 by the rubbing portion D, and roll between the drum 3 and the non-charging portion 43. At that time, the external additive and the toner are rubbed by the rubbing portion D, so that the moving speed is slow with respect to the drum 3.

  Thereafter, immediately after the external additive or toner passes through the rubbing portion D, the influence of the rubbing portion D is eliminated, so that the drum 3 must move at the rotational speed. For this reason, the toner and the external additive are subjected to a sudden change in the moving speed immediately after passing through the rubbing portion D, so that the toner and the external additive are liable to float from the surface of the drum 3no by rolling or jumping. Therefore, the toner and external additive can be moved away from the drum 3 by the rubbing portion D, thereby causing the toner and the external additive to leave the drum. For this reason, toner and external additives that are positively charged by applying a negative bias are easily moved from the drum 3 toward the dirt collecting portion 45.

<Dirt collection mechanism (mechanism)>
Next, the dirt collecting mechanism in the recess 45 will be described with reference to FIG. The toner and the external additive Ta that are easily peeled off from the drum 3 by the rubbing portion D are then sent to the concave portion 45 that is a dirt collecting portion. Therefore, since a voltage of −1.0 kV, which is a charging voltage, is applied to the metal portion in the concave portion 45, the positively charged toner and external additive that are easily peeled off from the drum 3 by the rubbing portion D are applied to the electric field E. It will be attracted to the recess 45 under the force. Therefore, toner and external additives attracted by the charging unit 44 are reduced, and good charging can be maintained without causing charging failure.

  That is, in the case of a system in which charging is performed by applying a charging voltage in which a DC voltage and an AC voltage are superimposed on the charging blade 4, a large electric field difference can be obtained. Is possible. However, in a superimposed electric field of direct current voltage and alternating current voltage, a plate-like structure causes large vibrations and large charge noise. For this reason, there has been a restriction that only a DC voltage with a small charging sound can be applied due to the recent trend of noise reduction. For this reason, when only a DC voltage is applied, the strength of the electric field is weaker than the superimposed voltage of the DC voltage and the AC voltage, and it has become difficult to reliably collect dirt at the metal portion.

  In the first exemplary embodiment, the toner and the external additive are easily separated from the surface of the drum 3 by the non-charging portion 43 that contacts the drum 3 and rubs the surface of the drum 3. Therefore, it becomes easy for toner and external additives to be taken in by the dirt collecting unit 45 due to the effect of the electric field, and even when a DC voltage that does not generate charging noise is applied as the applied voltage, the dirt is effectively collected and charged by the charging unit 44. Dirt can be prevented.

(3) Verification Experiment Here, a verification experiment was conducted to determine whether the charging failure was improved by collecting dirt in this example. The experiment was conducted in an environment with a temperature of 23 ° C. and a humidity of 50%. A DC voltage of charging voltage -1.0 kV is applied, and it is confirmed whether or not charging failure due to adhesion of an external additive or toner is improved by the presence of the rubbing portion D.

  As a confirmation method, a halftone image is printed periodically while printing a horizontal line with a printing rate of 2% by continuous paper feeding, and it is confirmed how much printing can be performed without causing a charging failure. Compare the occurrence of vertical stripes on halftone images as a measure of charging failure. As the charging blade having the rubbing portion D, the charging blade 4 of Example 1 was used. For comparison, a charging blade 4A as shown in FIG. 8 is used as a charging blade having no rubbing portion.

  The charging blade 4A of the comparative example is disposed on the drum 3, and a phosphor bronze plate having a thickness of 100 μm is used as the support portion 71. Further, a gap 73 is defined using a spacer 73 at the outer edge of the image area so that a predetermined discharge gap can be maintained between the charging portion 72 and the drum 3. The phosphor bronze plate, which is the support portion 71, is exposed at the tip portion, and this becomes the dirt collecting portion 74. At this time, since the charging voltage −1.0 kV is applied to the support portion 71, a DC voltage of −1.0 kV is applied to the tip portion, that is, the dirt collecting portion 74.

  Table 1 shows the state of occurrence of vertical stripes when the above two charging blades 4 and 4A are used. At this time, it is set as no generation | occurrence | production (circle), slight generation | occurrence | production (triangle | delta), and generation | occurrence | production x.

From the above, in the first embodiment, in the charging blade 4 to which the DC voltage is applied, the toner and the external additive are rubbed and rolled by the rubbing portion D by the rubbing portion D, whereby the toner and the external additive are applied by the electric field force. The dirt collecting part 45 makes it easy to draw. As a result, the charging portion 44 can be prevented from being soiled and charging failure can be prevented.

[Example 2]
In the first embodiment, the non-charging portion 43 which is the blade tip is a fixed system as a rubbing member. However, the non-charging portion 43 is rotatable by a roller in this embodiment.

<Configuration of charging blade>
FIG. 9 is a configuration diagram of the charging blade 4 of this embodiment. The charging blade 4 of this embodiment is different from the charging blade 4 (FIG. 3) of the first embodiment in that the non-charging portion 43 is a rotatable roller. The other configuration of the charging blade is the same as that of the charging blade 4 of the first embodiment. The roller 43 as a non-charging part covers a φ3 cored bar 85 with an insulating elastic rubber 86 to form a φ4.2 roller.

  The roller 43 abuts against the drum 1. In the present embodiment, as shown in FIGS. 10 and 11, the roller 43 is driven with respect to the rotation direction A of the drum 3 at the contact portion with the drum 3 by the drive gear 93 and the gear trains 94 and 95 from the three drums. It is rotationally driven in the counter direction B. A contact portion between the roller 43 and the drum 3 is a rubbing portion D.

  The roller 43 slidably rubs the entire surface of the image-formable region G (FIG. 4A) of the drum 3 so that the toner and external additives can be easily peeled off from the surface of the drum 3 by rubbing the surface of the drum 3. The entire region G is disposed so that it can be rubbed. The roller 43 is pressed and supported by a spring 92 on the bearing 91 at the end of the cored bar. Further, the roller 43 rotates in the counter direction with respect to the drum 3 through the gears 93, 94, and 95.

<Charging blade settings>
As shown in FIG. 11, the roller 43 at the tip of the charging blade 4 is disposed in contact with the drum 3 and rotates in the counter direction B with the drum 3. The charging blade 4 is arranged in the counter direction with respect to the rotation direction A of the drum 3. Further, the charging unit 44 is separated from the surface of the drum 3 with a dischargeable gap H in order to charge the surface of the drum 3 to a predetermined voltage. The setting angle in this embodiment is θ = 24 °.

  At this time, the phosphor bronze plate as the support portion 42 is disposed on the roller 43 with a predetermined pressure. This allows the charging unit 44 to always maintain 7.5 to 150 μm capable of discharging the gap H with the drum 3. The pressing force in this example is 30 gf / cm. In addition, since the charging is stabilized as the area that can be discharged as wide as possible, the pressing and setting angles of the support portion 42 are determined according to each case.

<Rubbing mechanism in roller 43>
Next, the rubbing mechanism in the front roller 43 will be described with reference to FIG. As the roller 43 counter-rotates with respect to the drum 3, the transfer residual toner and the external additive Ta are rubbed. At this time, the toner and the external additive are rotated by the roller 43, and the moving speed of moving on the drum 3 is slowed down. Compared with the stationary non-charging portion 43 of the first embodiment, the rotatable roller as the non-charging portion 43 in the present embodiment rotates in the counter direction with respect to the drum 3, so that the moving speed is further delayed. Become.

  Therefore, as shown in FIG. 12, the transfer residual toner and the external additive can change the adhesion surface adhering to the drum 3 and easily peel off from the drum 3. Further, immediately after passing through the roller 43, the toner and the external additive must move at the same speed as that of the drum 3, and receive a force of a rapid speed change.

  Therefore, the toner and the external additive are easily separated from the drum 3 by rolling or jumping on the drum 3 due to a sudden change in the moving speed. In addition, since the roller 43 counter-rotates with respect to the drum 3, toner and external additives can adhere to the roller 3, so that dirt can be further collected by the roller 43. There is also an advantage that the additive becomes difficult.

<Dirt collection mechanism>
Next, explanation of the dirt collecting mechanism will be given with reference to FIG. The toner and external additives that are easily peeled off from the drum 3 by the roller 43 are then sent to a dirt collecting portion (concave portion) 45. Therefore, in the dirt collecting unit 45, a voltage of −1.0 kV, which is a charging voltage, is applied to the metal part (holding unit 42), so that the toner and external additives that are easily peeled off from the drum 3 by the roller 43 are applied to the electric field. Is attracted to the dirt collecting part 45. Therefore, toner and external additives attracted by the charging unit 44 are reduced, and good charging can be maintained without causing charging failure.

<Verification experiment>
Here, a verification experiment was conducted to determine whether the charging failure is improved by collecting dirt in this example. The experiment was conducted in an environment with a temperature of 23 ° C. and a humidity of 50%. A DC voltage of a charging voltage of −1.0 kV is applied, and it is confirmed whether the charging failure is improved by the dirt collecting unit 45. As a confirmation method, a halftone image is printed periodically while printing a horizontal line with a printing rate of 2% by continuous paper passing to check how much printing can be performed without causing a charging failure. Compare the occurrence of vertical stripes on halftone images as a measure of charging failure.

  The charging blade 4 of the second embodiment is used as a charging blade having a rubbing member at the tip, and a charging blade 4A as shown in FIG. 8 is used as a charging blade having no rubbing member. Table 2 shows the state of occurrence of vertical stripes at this time. At this time, it is set as no generation | occurrence | production (circle), slight generation | occurrence | production (triangle | delta), and generation | occurrence | production x.

From the above, in the second embodiment, the toner and the external additive can be easily separated from the drum 3 by the roller 43 in the charging blade to which the DC voltage is applied. Therefore, it is possible to prevent the charging unit 44 from being stained by preventing the charging unit 44 from becoming dirty by making the toner and the external additive easily attracted by the stain collecting unit 45 by the force of the electric field.

[Other matters]
1) The image carrier on which the electrostatic latent image is formed in the present invention is not limited to the electrophotographic photosensitive member in the electrophotographic system of the embodiment. It may be an electrostatic recording dielectric in an electrostatic recording system. The image carrier is not limited to the drum type. It may be in the form of an endless rotating belt or a traveling end belt. Further, the image carrier may be in the form of a sheet-like member (electrofax paper, electrostatic recording paper) conveyed by the conveying means.

  2) The relative movement of the image carrier and the charging member is not limited to the form in which the image carrier moves relative to the fixed charging member as in the embodiment, and the charging member moves to the fixed image carrier. A form in which both the charging member and the image carrier move is also included.

  3) In the present invention, charging on the surface of the image carrier by the charging member includes charging for neutralizing the surface of the image carrier. The blade-shaped charging member of the present invention can also be used as a cleaning and charging blade for the image carrier 1.

  3 .. Image carrier 4.. Blade-shaped charging member 44.. Charging part 43.. Uncharged part H.. Dischargeable gap G.. Image forming area width 42. Part, D ... Rubbing part, 44a ... Discharge position, 45 ... Concave part (dirt collecting part)

Claims (6)

The non-charged portion is disposed on the counter with respect to the moving direction of the image carrier and moves relative to the image carrier on which the electrostatic latent image is formed, and moves relative to the image carrier to apply a DC voltage. A blade-shaped charging member for charging the surface of
A charging unit for discharging the surface of the image carrier;
An uncharged portion for not discharging the surface of the image carrier,
The uncharged portion is in contact with the image carrier, and it is possible to provide a dischargeable gap between the charged portion and the image carrier.
The non-charging part is made of a substance having a higher resistance than the charging part so as not to discharge from the non-charging part to the surface of the image carrier.
The non-charging portion is provided so as to be slidable on the surface of the image carrier by contacting over the entire width of the image formable region width of the surface of the image carrier.
In the charging member, a portion where the non-charged portion and the image carrier are rubbed with each other is a rubbing portion, and a position in the charging portion that causes discharge with respect to the image carrier is a discharge position.
A concave portion that exists between the rubbing portion and the discharge position and that is recessed from the surface of the discharge portion of the charging portion is provided so that an electric field can be formed between the concave portion and the image carrier. A charging member, which is present on a side facing the image carrier.   2. The electrode unit for supporting the charging unit and the non-charging unit and applying a voltage to the charging unit, wherein a part of the electrode unit forms the recess. Charging member.   It has a dirt guide part which goes from the contact position of the non-charging part and the image carrier to the concave part, and an extension line of a line along the dirt guide part from the contact position intersects the concave part. The charging member according to any one of claims 1 and 2. A charging member that charges the surface of the image carrier by applying a DC voltage to the image carrier on which an electrostatic latent image is formed with an uncharged portion in contact with the moving direction of the image carrier;
A charging unit for discharging the surface of the image carrier;
An uncharged portion for not discharging the surface of the image carrier,
The uncharged portion is in contact with the image carrier, and it is possible to provide a dischargeable gap between the charged portion and the image carrier.
The non-charging part is made of a substance having a higher resistance than the charging part so as not to discharge from the non-charging part to the surface of the image carrier.
The non-charging portion is provided so as to be slidable on the surface of the image carrier by contacting over the entire width of the image formable region width of the surface of the image carrier.
The non-charging part is a rotatable roller,
In the charging member, a portion where the non-charged portion and the image carrier are rubbed with each other is a rubbing portion, and a position in the charging portion that causes discharge with respect to the image carrier is a discharge position.
A concave portion that exists between the rubbing portion and the discharge position and that is recessed from the surface of the discharge portion of the charging portion is provided so that an electric field can be formed between the concave portion and the image carrier. A charging member, which is present on a side facing the image carrier.   The charging member according to claim 4, wherein the roller is rotated in a counter direction with respect to a moving direction of the image carrier at a rubbing portion with the image carrier.   An image forming apparatus comprising: a blade-shaped charging member for charging a surface of an image carrier on which an electrostatic latent image is formed; and a power source for applying a voltage to the charging member. An image forming apparatus comprising the charging member according to claim 1.