JP2005070311A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain proper image formation over a long term by eliminating an abnormal image, caused by the situation that accumulated toner accumulated near the contact part of an electrifying roller with a photoreceptor adheres to the electrifying roller. <P>SOLUTION: The image forming apparatus is constituted to satisfy ¾Vd¾≥¾Vpre¾+250 (V), if the potential by electrification of an image forming area on the photoreceptor is set as Vd (V) and the potential by electrification before electrification of an image non-forming area on the photoreceptor is set as Vpre (V). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, a facsimile machine, etc. to which an electrophotographic system is applied.

  In the transfer type image forming apparatus, the transfer residual toner remaining on the photoconductor (image carrier) after the transfer is removed from the photoconductor surface by a cleaner (cleaning device) and becomes waste toner. It is desirable not to come out from the aspect. Therefore, there is no special cleaner, and the toner is designed to remove the transfer residual toner on the photoreceptor after transfer from the photoreceptor by performing “development simultaneous cleaning” with the developing device, and collect and reuse it in the developing device. An image forming apparatus using a recycling process (cleanerless system) has also appeared.

  Simultaneous development cleaning means that the toner remaining on the photoconductor after the transfer is developed in the subsequent steps, that is, the photoconductor is continuously charged and exposed to form a latent image, and the latent image is developed. (A fog removal potential difference Vback which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member). According to this method, since the transfer residual toner is collected by the developing device and reused after the next step, waste toner can be eliminated and the running cost of printing can be increased. Further, the cleaner-less has a great space advantage, and the image forming apparatus can be greatly downsized.

  Therefore, in the charging device of Patent Document 1, even when a simple member such as a charging roller or a fur brush is used as the contact charging member in the contact charging, direct injection charging that is more excellent in charging uniformity and stable over a long period of time is performed. As a result, ozone-less direct injection charging with a low applied voltage can be realized with a simple configuration. In this configuration, conductive particles intervene on the contact surface between the contact charging member and the surface to be charged, and there is a difference in the relative speed between the surface of the contact charging member and the surface to be charged. Solved the problem caused by charging failure.

Further, in Patent Document 2 and Patent Document 3, the conductive particles for promoting charging are included in the developer, that is, supplied from the developing device together with the toner. With such an easy process and mechanical configuration, supply of conductive particles for promoting charging and a toner recycling process are realized.
Japanese Patent Laid-Open No. 10-307454 JP-A-10-307455 JP-A-10-307456

  However, in the contact charging method, since the charging member is brought into contact with the member to be charged, the charging member easily picks up the deposit on the member to be charged and becomes dirty. Excessive contamination of the contact charging member causes charging unevenness and the like, thereby reducing charging performance.

  The object to be charged (image carrier) is charged by contact charging, and an electrostatic latent image corresponding to the target image information is formed on the charging surface of the object to be charged. In an image forming apparatus that forms a visible image as a toner image and executes image formation, as the image formation is increased, toner adheres to and is mixed into the contact charging member and accumulates.

  In particular, when the image forming apparatus is a cleanerless system apparatus that does not have a dedicated cleaning device for removing the transfer residual toner from the surface of the charged body after transferring the toner image onto the transfer material, the transfer residual toner on the charged body Is more noticeable because it reaches the contact charging member as it is and adheres to and mixes with the charging member.

  In the case of a cleaner-less system, the transfer residual toner is temporarily attached to the contact charging member. Therefore, the transfer residual toner is removed from the contact charging member by the potential on the photosensitive member before the contact charging member. Sometimes.

  This is because the residual toner that has reached the charging portion is accumulated as it is on the charging roller from the photosensitive drum as the photosensitive member once through the charging roller as a charging member or in the vicinity of the charging nip. The amount of toner accumulated in the vicinity of the charging nip easily accumulates residual toner having the same polarity as that of the charging roller (accumulated toner A) at the upstream side of the photosensitive drum in the charging nip, that is, the portion on the transfer position side. It is. This is because the charging roller is in contact and the charging roller is rotating at the counter with respect to the photosensitive drum in the charging nip portion.

  This toner accumulates during image formation. If discharge control from the charging roller to the photosensitive drum is not performed, the accumulated toner is discharged during image formation. For example, black and half of graphic patterns and the like are discharged. When drawing tones, etc., image defects such as shading that blocks exposure are caused.For example, when drawing white, if the discharged toner cannot be collected by the developing machine, image defects such as fogging will occur. I will wake you up.

  Therefore, it is important to control the movement of the accumulated toner A that causes such harmful effects.

  An object of the present invention is to provide an image forming apparatus in which adhesion of a developer to a charging member is restricted.

  Another object of the present invention is to provide an image forming apparatus in which the movement of the developer accumulated on the upstream side of the contact portion between the charging member and the image carrier is restricted.

  Another object of the present invention is to provide an image forming apparatus that prevents the developer from moving to the charging member when the non-image forming area of the image carrier reaches the position of the charging member.

  Another object of the present invention is to provide an image forming apparatus in which the potential difference between the charging potential of the image forming area of the image carrier and the charging potential before charging of the non-image forming area of the image carrier is reduced. It is.

  Another object of the present invention is to maintain good image formation over a long period of time by eliminating the occurrence of abnormal images due to developer adhesion to the charging member.

  The present invention relates to an image carrier, a charging member that can contact the image carrier, and charges the image carrier, and the electrostatic image formed on the image carrier is developed with a developer at the same time. And a developing unit capable of recovering the developer remaining on the carrier, wherein the charge potential of the image forming region of the image carrier is Vd (V), and the non-image forming region of the image carrier. The image forming apparatus is characterized by satisfying | Vd | ≧ | Vpre | +250 (V), where Vpre (V) is a charging potential before charging.

  The present invention also provides an image carrier, a charging member that is capable of contacting the image carrier, and charging the image carrier, and exposing the image carrier charged by the charging member to expose the electrostatic An exposure means for forming an image; and a developing means capable of developing the electrostatic image formed on the image carrier with a developer and collecting the developer remaining on the image carrier at the same time, In the image forming apparatus in which the image carrier is a photoconductor, the exposure unit exposes at least a non-image forming region of the image carrier.

  According to the present invention, it is possible to prevent the developer accumulated near the contact portion of the charging member from moving to the charging member by appropriately controlling the potential of the non-image forming area of the image carrier. Accordingly, it is possible to prevent the occurrence of abnormal images such as light shielding and fogging, which are harmful effects caused by such a developer falling off from the charging member to the image carrier.

  That is, in this cleanerless process, in order to prevent the developer accumulated in the charged portion from dropping off, the potential contrast between the absolute value of the image carrier before charging and the absolute value of the charging potential is increased. It is important to.

  By increasing the potential contrast in this way, the developer accumulated in the vicinity of the charged portion can be retained, and a good image can be obtained in the cleaner-less process.

  Embodiments of the image forming apparatus of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic structural model diagram of an example of an image recording apparatus according to the present invention.

  The image recording apparatus of this embodiment is a laser printer using a transfer type electrophotographic process, a contact charging system, and a toner recycling system.

(1) Overall Schematic Configuration of Printer 1 is an image carrier. In this embodiment, a φ24 mm rotating drum type negatively charged polarity OPC photosensitive member (negative photosensitive member, hereinafter referred to as a photosensitive drum) is used. The photosensitive drum 1 is rotationally driven in a clockwise direction indicated by an arrow at a constant speed of 85 mm / sec (= process speed PS, printing speed).

  Reference numeral 2 denotes a conductive elastic roller having a diameter of 18 mm (hereinafter referred to as a charging roller) as a contact charging member disposed in contact with the photosensitive drum 1 with a predetermined pressing force. n is a charging nip portion (contact portion) between the photosensitive drum 1 and the charging roller 2. The charging roller 2 holds (supports) conductive charge-promoting particles m (conductive particles for the purpose of charging promotion) on its outer peripheral surface, and a charging nip n between the photosensitive drum 1 and the charging roller 2. The charge promoting particles m are interposed in

  The charging roller 2 is driven to rotate in the reverse direction (counter) to the rotation direction of the photosensitive drum 1 in the charging nip portion n, and is rotated at a speed of about 80% with respect to the surface speed of the photosensitive drum. M is a drive source of the charging roller 2. A predetermined charging bias is applied to the charging roller 2 from the charging bias application power source S1 during image recording by the printer. As a result, the peripheral surface of the rotary photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential by a direct charging (injection charging) method.

  In this embodiment, during image formation by the printer, the switch SW of the charging bias application power source S1 is controlled to be switched to the A contact side, and the DC voltage of about -500 V of the DC power source SDC is applied to the core metal 2a of the charging roller 2. The surface of the rotating photosensitive drum 1 is directly charged to a voltage of about −500 V that is substantially equal to the applied DC voltage (A mode).

  The charging roller 2, the charge accelerating particles m, and direct charging will be described in detail in another section.

  Reference numeral 3 denotes a laser beam scanner (image forming exposure apparatus) as exposure means including a laser diode, a polygon mirror and the like. The laser beam scanner 3 outputs a laser beam whose intensity is modulated in accordance with the time-series electric digital pixel signal of the target image information, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 1 with the laser beam. . By this scanning exposure L, an electrostatic latent image corresponding to target image information is formed on the surface of the rotary photosensitive drum 1. The laser beam scanner 3 is also used to set the pre-charging potential of the photosensitive member to an optimum potential.

  Reference numeral 4 denotes a developing device as developing means. As the developer t, charging promoting particles m are added to the toner t. The electrostatic latent image on the surface of the rotary photosensitive drum 1 is reversely developed as a toner image at the development site a by the developing unit 4. The developing device 4 will be described in detail in another section.

  Reference numeral 5 denotes a medium resistance transfer roller as a contact transfer means, which is brought into pressure contact with the photosensitive drum 1 to form a transfer nip portion b. A transfer material P as a recording medium is fed to the transfer nip b from a paper feed unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias application power source S3. Thus, the toner image on the photosensitive drum 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip b.

  The transfer material P introduced into the transfer nip portion b is nipped and conveyed by the transfer nip portion b, and the toner images formed and supported on the surface of the rotary photosensitive drum 1 on the surface side thereof are successively subjected to electrostatic force and pressing force. Will be transcribed.

  Reference numeral 6 denotes a fixing device such as a heat fixing method. The transfer material P that has been fed to the transfer nip b and has received the transfer of the toner image on the photosensitive drum 1 side is separated from the surface of the rotating photosensitive drum 1 and introduced into the fixing device 6 to receive the fixing of the toner image. It is discharged out of the apparatus as an image formed product (print, copy).

  The printer of this embodiment is a cleaner-less system, and there is no dedicated cleaner (cleaning device) for removing residual transfer residual toner on the surface of the rotating photosensitive drum 1 after transfer of the toner image to the transfer material P. As the photosensitive drum 1 rotates, it reaches the development site a via the charging nip n, and is collected and reused in the development unit 4 by simultaneous development cleaning.

(2) Charging roller 2
The charging roller 2 as a flexible contact charging member in this embodiment is formed by forming a middle resistance layer 2b of rubber or foam on a core metal 2a.

  The middle resistance layer 2b is formulated with a resin (for example, urethane, EPDM), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and is formed in a roller shape on the core metal 2a. Thereafter, the surface was polished as necessary to prepare a charging roller 2 which is a conductive elastic roller having a diameter of about 18 mm and a longitudinal length of about 220 mm.

  The roller resistance of the charging roller 2 of this example was measured and found to be 100 kΩ. As for the roller resistance, 100V is applied between the core metal 2a and the aluminum drum in a state where the charging roller 2 is pressure-bonded to a conductive aluminum drum having a diameter of 24 mm so that the core metal 2a of the charging roller 2 is loaded with a total pressure of 1 kg. And measured.

Here, it is important that the charging roller 2 as a contact charging member functions as an electrode. In other words, it is necessary to provide a sufficient contact state with the member to be charged by providing elasticity, and at the same time to have a sufficiently low resistance to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a low-voltage defect site such as a pinhole is present in the member to be charged. When an electrophotographic photoreceptor is used as the member to be charged, a resistance of 10 ⁴ to 10 ⁷ Ω is desirable in order to obtain sufficient chargeability and leakage resistance.

  The surface of the charging roller 2 desirably has micro unevenness so that the charge promoting particles m can be held, and the surface layer is preferably a foamed layer.

  If the hardness of the charging roller 2 is too low, the shape is not stable, so that the contact with the member to be charged is deteriorated. If the hardness is too high, the charging nip n cannot be secured between the member and the member to be charged. Since the micro contact property to the surface of the member to be charged is deteriorated, the preferred Asker C hardness is 25 to 50 degrees.

  The material of the charging roller 2 is not limited to the elastic foam, and the material of the elastic body may be EPDM, urethane, NBR, silicone rubber, or the like such as carbon black or metal oxide for resistance adjustment to IR or the like. Examples thereof include a rubber material in which a conductive material is dispersed and a foamed material of these materials. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance.

  The charging roller 2 is disposed by being pressed against the photosensitive drum 1 as a member to be charged with a predetermined pressing force against elasticity, and in this embodiment, a charging nip portion n having a nip width of 2 to 3 mm is formed. is there.

(3) Developer 4
In this embodiment, the developing bias voltage was set as follows for each drum surface potential during image formation (image forming area) and between-paper exposure (non-image forming area).

During image formation, the electrostatic latent image on the photosensitive drum 1 side is reversely developed with the toner t while collecting the toner remaining on the drum. The DC voltage of the developing bias voltage is set between the dark part potential and the light part potential of the photosensitive member. At the time of image exposure, image quality is emphasized, and a bias with less image density, gradation, and fog is set. The amount of toner discharged from the charging roller to the drum is reduced by setting the charging bias at the time of image formation to a DC bias. Details of the bias are as follows.
DC voltage: -350V
AC voltage: A peak-to-peak voltage of 900 V, a frequency of 1.8 kHz, and a rectangular wave superimposed voltage.

On the other hand, in the non-image forming area corresponding to the space between the sheets of the photoreceptor, the photoreceptor is uniformly exposed. During this inter-sheet exposure (area), the discharge bias in which AC is superimposed on the charging roller is applied on the drum. A lot of toner is discharged and collected by development. Therefore, the developing bias places importance on the toner recoverability, and the following conditions are set with less fogging on the drum after recovery. Further, the amount of light was adjusted so that the drum potential at the developing position at this time was −150V.
DC voltage: -50V
AC voltage: A peak-to-peak voltage of 1300 V, a frequency of 2.5 kHz, and a rectangular wave superimposed voltage.

  The concept of bias setting at the time of inter-sheet exposure (area) will be described.

  The toner discharged from the charging roller adheres to the drum electrostatically or by other adhesion force. For the recovery of these toners, a force by an electric field is insufficient, and some mechanical oscillation is effective. In the non-contact development, the flying of the toner is greatly involved in the collection of the discharged toner. What can be said in common is that if the amount of toner flying is small, the collectability of the discharged toner is low and the toner contamination of the drum and the charging roller cannot be solved.

  On the other hand, if the toner flies frequently, the toner recoverability can be improved, and the drum and the charging roller can be prevented from being soiled and a good charged state can be obtained. However, when the toner flying becomes excessive, new fog toner is generated, which may result in increased dirt on the drum and the charging roller. Therefore, it is effective that the bias setting at the time of collection increases the toner flying more than the background portion at the time of development. With this in mind, the bias setting for the inter-sheet exposure area will be described in detail.

  Regarding the DC voltage, a back contrast (hereinafter referred to as a recovery voltage) of +150 V is set in the image forming area with respect to the drum potential of −500 V in the background portion (dark portion). A recovery voltage of +100 V was set with respect to the potential after the exposure.

  This is determined in a balanced manner with the development contrast (difference between the image portion and the development DC voltage) in the image forming area from the viewpoint of image quality, whereas in the inter-paper dew area, the drum is used. From the viewpoint of recovering more discharged toner, the recovery voltage is set to + 100V. If the recovery voltage is too large, the toner does not reciprocate between the drum and the sleeve, so that the recovery performance of the toner on the drum is lowered. On the other hand, if it is too large, the toner on the sleeve is also developed. In this example, an appropriate value as the recovery voltage is preferably −50 to +150 V, and more preferably 0 to +100 V.

  Next, although it is the peak-to-peak voltage of the developing bias voltage in the inter-sheet exposure area, if it is small, toner reciprocation does not occur, so that the toner collecting performance on the drum is lowered. On the other hand, the larger the toner is, the more toner flies and the recovery capability is improved. In this example, the peak-to-peak voltage is suitably 900V to 1500V, and further 1100V to 1300V. On the other hand, if the peak-to-peak voltage is too large, not only the fog increases but also a bias leakage phenomenon occurs frequently. Since it is not at the time of image formation, the image defect at the time of the leak does not directly deteriorate the image quality, but the drum or the sleeve is damaged by the leak, and the trace causes the image defect. Also from this point, it is necessary to select an appropriate value for the peak-to-peak voltage.

  Next, as for the frequency, a large tendency is that if it is too small, the recoverability is improved, but new development fog is generated. On the other hand, if it is excessively high, the recoverability is lowered. A suitable range is 1200 to 4000 Hz, and further 1800 to 3000 Hz. However, it was found that this is not the case when optimization is advanced in detail. In this example, the fog on the drum after passing through the development was lower at 2500 Hz between the paper than 1800 Hz in the image, and the recoverability was improved. In particular, when the voltage between peaks was increased, the fog after passing through the development was low and good, so the above settings were performed.

(4) Transfer roller 5
The transfer roller 5 includes a core metal 5a made of SUS, aluminum, and the like, and a volume resistance of about 1 × 10 ⁵ to 1 × 10 ¹² Ω · cm on the outer periphery thereof, for example, EPDM dispersed in carbon black, NBR A medium resistance elastic rubber layer 5b such as a system rubber is coated in a roller shape. The roller resistance is about 1 × 10 ⁸ Ω in a temperature and humidity environment of 23 ° C. and 50%, and the transfer roller 5 is pressure-bonded to a φ24 mm aluminum drum so that a total pressure of about 6N is applied to the core of the transfer roller E. Then, while rotating at a constant peripheral speed of 85 mm / sec (= process speed PS, printing speed), 2 kV was applied between the metal core 5a and the aluminum drum, and measurement was performed.

  The outer diameter is about 15 mm, and the hardness is about 35 degrees when an ASKER-C hardness meter is used and 6N is applied. The bearing is pressed and supported by a spring material with a total load of 7 N so that both ends of the core metal can be rotated by the bearing and the transfer roller 5 is always in contact with the photosensitive drum 1. The transfer roller 5 is driven to rotate.

(5) Direct charging a) An appropriate amount of the charge accelerating particles m added to the toner t of the developing device 4 is exposed together with the toner at the developing site a when the developing device 4 develops the toner of the electrostatic latent image on the photosensitive drum 1 side. Shift to the drum 1 side.

  The toner image on the photosensitive drum 1 is attracted and transferred to the transfer material P side by the influence of the transfer bias at the transfer nip portion b. However, the charge accelerating particles m on the photosensitive drum 1 are transferred because they are conductive. It does not move positively to the material P side, but remains substantially adhered and held on the photosensitive drum 1. In addition, the presence of the charge accelerating particles m that are substantially adhered and held on the surface of the photosensitive drum 1 has an effect of improving the transfer efficiency of the toner image from the photosensitive drum 1 side to the transfer material P side. Further, the triboelectric charging polarity (plus) of the electrification promoting particles m is opposite to the triboelectric charging polarity (minus) of the toner so that the electrification promoting particles m are conveyed to the charging nip n without being transferred to the transfer agent P. It is good to do. Further, since the triboelectric charge polarity of the charge accelerating particles m is positive, the charge accelerating particles m are easily held by the charging roller to which a negative voltage is applied.

  In the cleaner-less printer, the residual transfer toner remaining on the surface of the photosensitive drum 1 after transfer and the residual charge promoting particles m are transferred to the charging nip n of the photosensitive drum 1 and the charging roller 2 by the rotation of the photosensitive drum 1. When carried as it is, supply of the charge accelerating particles m to the charging nip n and adhesion / mixing to the charging roller 2 occur.

  Therefore, contact charging of the photosensitive drum 1 is performed in a state where the charge accelerating particles m exist in the charging nip portion n between the photosensitive drum 1 and the charging roller 2.

  b) Since the charge accelerating particles m are present in the charging nip n between the photosensitive drum 1 and the charging roller 2, the frictional effect of the particles m increases the frictional resistance. Even a charging roller that is difficult to hold and contact can be brought into contact with the surface of the photosensitive drum 1 without difficulty and with an effective speed difference. In addition, the charging roller 2 comes into close contact with the surface of the photosensitive drum 1 through the particles m and comes into contact with the surface of the photosensitive drum 1 at a higher frequency.

  By providing a speed difference between the charging roller 2 and the photosensitive drum 1, the chance of the charge accelerating particles m contacting the photosensitive drum 1 at the nip portion between the charging roller 2 and the photosensitive drum 1 is remarkably increased, and high contactability is achieved. The charge accelerating particles m present in the nip portion between the charging roller 2 and the photosensitive drum 1 can rub the surface of the photosensitive drum 1 without any gap so that charges can be directly injected into the photosensitive drum 1. Contact charging of the photosensitive drum 1 by the roller 2 is dominated by direct charging (injection charging) due to the interposition of the charge accelerating particles m.

  As a configuration for providing a speed difference, the charging roller 2 is rotationally driven to provide a speed difference from the photosensitive drum 1. Preferably, in order to temporarily collect and level the transfer residual toner on the photosensitive drum 1 carried to the charging nip n on the charging roller 2, the charging roller 2 is driven to rotate. It is desirable to be configured to rotate in the direction opposite to the direction of movement of the surface. That is, it is possible to preferentially directly charge the toner by temporarily separating the transfer residual toner on the photosensitive drum 1 by reverse rotation.

  Therefore, high charging efficiency that cannot be obtained by conventional roller charging or the like can be obtained, and a charging potential almost equal to the voltage applied to the charging roller 2 can be applied to the photosensitive drum 1. Thus, even when the charging roller 2 is used as the contact charging member, a voltage equivalent to the charging potential required for the photosensitive drum 1 is sufficient as the bias applied to the charging roller 2 and stable and no discharge phenomenon is used. A safe contact charging method or apparatus can be realized.

  Further, since the charging roller 2 is in contact with the photosensitive drum 1 with a speed difference, the transfer residual toner pattern from the transfer nip portion b to the charging nip portion n is disturbed and easily broken. In the toned image, the previous image pattern portion becomes a ghost and hardly appears.

  c) Even if the charge promoting particles m drop off from the charging nip n or the charging roller 2 due to durability, the charge promoting particles contained in the toner t of the developing device 4 as described above are operated by operating the printer. Since m moves to the surface of the photosensitive drum 1 at the development site a and is moved to the charging nip n through the transfer nip b by the movement of the surface of the photosensitive drum 1 and continuously supplied to the charging nip n, the charging nip Good chargeability due to the presence of the charge promoting particles m in the portion n is stably maintained over a long period of time.

  The charge accelerating particles m dropped from the charging nip n and the charging roller 2 are collected by the developing device 4 at the development site a and mixed with the developer t for circulation.

  By carrying the charge accelerating particles m in advance on the surface of the charging roller 2 when the charging device is not used, the above direct charging performance can be exhibited without any problem from the very beginning of the use of the printer.

  d) Since the printer is cleaner-free, the residual toner remaining on the surface of the photosensitive drum 1 after transfer is carried as it is by moving the surface of the photosensitive drum 1 to the charging nip n of the photosensitive drum 1 and the charging roller 2. It adheres to and mixes with the charging roller 2.

  Since the conventional toner is an insulator, the adhesion and mixing of the transfer residual toner to the charging roller 2 is a factor that causes charging failure in charging the photosensitive drum.

  However, even in this case, since the charge accelerating particles m are present in the charging nip n between the photosensitive drum 1 and the charging roller 2, it is possible to maintain the close contact property and contact resistance of the charging roller 2 to the photosensitive drum 1. Regardless of contamination of the transfer roller 2 by the transfer residual toner, ozone-less direct charging can be stably maintained for a long time with a low applied voltage, and uniform chargeability can be provided.

  e) The transfer residual toner adhering to and mixed in the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 1 to reach the developing portion a along with the movement of the surface of the photosensitive drum 1. (Toner recycling). As described above, the simultaneous development cleaning is performed in the image forming process in which the toner remaining on the photoreceptor 1 after the transfer is continued, that is, the photoreceptor is continuously charged and exposed to form a latent image, and the latent image is developed. At this time, the image is recovered by the fog removal bias of the developing device, that is, the fog removal potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member. In the case of reversal development as in the printer in this embodiment, this simultaneous development cleaning is performed by attaching toner from the dark portion potential of the photosensitive member to the developing sleeve and from the developing sleeve to the bright portion potential of the photosensitive member. This is done by the action of an electric field.

  f) If the amount of the charge accelerating particles in the charging nip n between the photosensitive drum 1 as the image carrier and the charging roller 2 as the contact charging member is too small, the lubricating effect by the particles cannot be obtained sufficiently. Since the friction between the charging roller 2 and the photosensitive drum 1 is large, it is difficult to drive the charging roller 2 to the photosensitive drum 1 with a speed difference. That is, the driving torque becomes excessive, and if the surface is rotated forcibly, the surfaces of the charging roller 2 and the photosensitive drum 1 are scraped.

Furthermore, the effect of increasing the contact opportunity by the particles may not be obtained, and sufficient charging performance cannot be obtained. On the other hand, when the amount of the inclusion is too large, dropping of the charge accelerating particles from the charging roller 2 is remarkably increased, which adversely affects image formation. According to experiments, the amount of intervening is desirably 10 ³ pieces / mm ² or more. If it is lower than 10 ³ pieces / mm ² , a sufficient lubricating effect and an effect of increasing the contact opportunity cannot be obtained, resulting in a decrease in charging performance.

More desirably, the intervening amount is 10 ^{3 to} 5 × 10 ⁵ pieces / mm ² . If it exceeds 5 × 10 ⁵ particles / mm ² , the dropout of the particles to the photoconductor 1 is remarkably increased, resulting in insufficient exposure of the photosensitive drum 1 regardless of the light transmittance of the particles themselves. If it is 5 × 10 ⁵ particles / mm ² or less, the amount of particles falling off can be kept low and the adverse effect can be improved. When the abundance of particles dropped on the photosensitive drum 1 in the intervening amount range was measured, it was 10 ² to 10 ⁵ particles / mm ² , so that the abundance that is not harmful in image formation is 10 ⁵ particles / mm. ² or less is desired.

  A method for measuring the intervening amount and the existing amount on the photosensitive drum 1 will be described. It is desirable that the amount of intervening is directly measured at the charging nip n between the charging roller 2 and the photosensitive drum 1, but most of the particles present on the photosensitive drum 1 before contacting the charging roller 2 move in the opposite direction while contacting. In this example, the amount of particles on the surface of the charging roller 2 immediately before reaching the charging nip n is used as the intervening amount.

  Specifically, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped in a state where no charging bias is applied, and the surfaces of the photosensitive drum 1 and the charging roller 2 are video microscope (OLYMPUS OVM1000N) and digital still recorder (DELTIS manufactured). SR-3100). The charging roller 2 is in contact with the slide glass under the same conditions as the case where the charging roller 2 is in contact with the photosensitive drum 1, and the contact surface of the charging roller 2 is 10 or more with a 1000 × objective lens from the back surface of the slide glass. I took a picture. In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where particles were present was measured using desired image processing software.

  Further, the abundance on the photosensitive drum 1 was also measured by photographing the same on the photosensitive drum 1 with a similar video microscope. The amount of the intervening was adjusted by setting the blending amount of the charge accelerating particles m in the developer t of the developing device 4. Generally, the charge accelerating particles m are blended in an amount of 0.01 to 20 parts by weight with respect to 100 parts by weight of developer (toner).

(6) Charging roller cleaning mode In this embodiment, the transfer residual toner adhering to and mixed in the charging roller 2 as a contact charging member, which is a charging inhibiting factor, is transferred to the non-image of the image forming apparatus, for example, between sheets. A roller cleaning mode (contact charging member cleaning mode) that efficiently removes the toner from the charging roller 2 at the time of formation is provided, whereby the contamination level due to the transfer residual toner of the charging roller 2 is always kept low, and good chargeability, Maintain stable image recording over a long period of time.

  That is, as a voltage application mode for the charging roller 2 as a contact charging member, an A mode (non-roller cleaning) in which a DC voltage is applied to uniformly charge the photosensitive drum 1 as an image carrier in an image forming area. Mode) and a B mode (roller cleaning mode) in which a voltage obtained by superimposing a DC voltage and an AC voltage (cleaning bias) is applied in a non-image forming area, and the frequency of the AC voltage in the B mode is about 5 ˜500 Hz.

a) A Mode In this embodiment, when an image is formed by the printer, the switch SW of the charging bias application power source S1 is controlled to be switched to the A contact side by a sequence control circuit (not shown), and the core metal 2a of the charging roller 2 is DC-controlled. When the DC voltage of the power source SDC = −500 V is applied, the surface of the rotary photosensitive drum 1 is directly charged to a voltage of approximately −500 V, which is substantially equal to the applied DC voltage, and image formation is executed. That is, a DC voltage is applied to the charging roller 2 with respect to an area that becomes an image forming area of the photoconductor.

b) B mode In this embodiment, the switch SW of the charging bias application power source S1 is controlled to be switched to the B contact side by a sequence control circuit (not shown) at the time of paper non-image formation. By connecting the AC power source SAC to the SDC in series, the DC voltage: −550 V is applied to the core metal 2 a of the charging roller 2.
AC voltage: A peak-to-peak voltage of 100 V, a frequency of, for example, 200 Hz, and a rectangular wave superimposed voltage are applied. That is, a superimposed voltage of the AC voltage and the DC voltage is applied to the charging roller 2 with respect to an area that becomes a non-image forming area of the photoconductor.

  By maintaining this bias relationship, the toner accumulated on the charging roller 2 is developed into a non-image forming area on the photosensitive drum 1 (discharge of the toner on the charging roller 2 to the photosensitive drum 1 side). Further, the toner can be collected in the developing device by the back contrast of the developing device 4.

  That is, the charging roller adhering toner, which becomes a charging inhibiting factor, is efficiently removed to the non-image forming area of the photoconductor to maintain the charging property by the charging roller for the next image forming area. Can do.

  In this case, by supplying the charge accelerating particles m to the charging roller 2, the toner releasability from the top of the charging roller 2 is improved, that is, the releasability is increased. The discharge of the toner to the photosensitive drum 1 side is promoted, the charging roller 2 contaminated with the toner is efficiently cleaned, and the ozone-less direct charging and the toner recycling system can be executed without any problem with a low applied voltage, thereby obtaining a high-quality image. It is possible to maintain the formation over a long period of time and to maintain a high-quality image formation over a long period of time even after outputting an image with a high image ratio.

  In the B mode, the cleaning bias applied to the charging roller 2 is desirably set so that the difference between the photosensitive drum potential and the charging roller potential on the downstream side of the charging nip n in the photosensitive drum moving direction is large. It is better to set it.

  In the charging method using direct charging as in this embodiment, a potential approximately equal to the potential applied to the charging roller 2 that is a contact charging member is applied to the surface of the photosensitive drum 1 that is a member to be charged. A potential difference is unlikely to occur between the drums 1.

  Naturally, it is necessary to uniformly charge the surface of the photosensitive drum during image recording, but it is necessary to apply an AC bias (cleaning bias) to generate a potential difference in a roller cleaning mode including non-image recording. Accordingly, it is desirable to select a cleaning bias so that a potential difference is generated between the inside of the charging nip n and the downstream side in the photosensitive drum moving direction.

(7) Image forming exposure apparatus 3
The image forming exposure apparatus 3 is a laser scanner as described above. In this method, a light beam such as a laser beam is reflected by a rotating polygon mirror that rotates at high speed, deflected and scanned, and the obtained scanning light is imaged on a photoconductor on a rotating drum to form an electrostatic latent image. . Based on the image information, the lighting of the laser is controlled. The laser control used in this embodiment is laser ON / OFF control based on binarized data.

(8) Optimization of potential before charging FIG. 2 is a schematic diagram of image damage due to light shielding and fogging caused by a cleanerless process. This is mainly an image defect that occurs in a belt shape after the second sheet during continuous paper feeding. The generation mechanism will be described below.

  FIG. 3 is a schematic diagram for explaining the mechanism of image defect occurrence. Since this is a cleanerless process, the untransferred toner remaining on the photosensitive drum after transfer reaches the charging roller 2 and is transferred and accumulated on the charging roller rotating in the direction opposite to the photosensitive drum rotation direction. . For example, when a pattern with a high printing rate (for example, solid black (entire black), 1d / 1s, etc.) is used, the amount of toner remaining after transfer increases and toner that cannot be transferred onto the charging roller is transferred from the photosensitive drum to the charging roller. Is accumulated in the area A near the nip exit in the rotation direction of the charging roller. The accumulated toner is the accumulated toner A described above, and is held on the surface of the photosensitive drum by the force F by the electric field E generated by the electric potential relationship between the photosensitive drum and the charging roller. As a result, the accumulated amount increases or is discharged onto the charging roller.

  For example, when there is a potential step that makes the electric field weaker than the previous potential history, the accumulated residual toner A is discharged to the photosensitive drum via the charging roller by moving to the charging roller. If the discharged toner is an area that becomes an image exposure area, exposure by a laser or the like is prevented, and a latent image to be formed cannot be formed, and white spots called light shielding occur. If it is a solid white (entire white) portion outside the image exposure area, the exposure is not hindered, but the portion that cannot be recovered by development reaches the transfer nip and appears as a fog on the image. The image defects as described above are the causes of the image defects that occur in the band shape shown in FIG.

  Next, a description will be given of the occurrence position of an image defect that occurs in a belt-like manner, involving paper passing history such as charging, exposure, development, and transfer during continuous paper passing. The surface potential of the photosensitive drum will be described below. The surface potential on the photosensitive drum described below was measured using a MODEL 344 surface potential meter manufactured by TREK.

  FIG. 4 shows a comparative example of this configuration, in which a horizontal line of 1d (dots) / 1S (space) is repeatedly drawn at 600 dpi (a line for one dot is turned on and off alternately by a laser scanner) and continuously drawn. It represents the potential on the photosensitive drum after transfer when the paper is passed. As shown in the figure, during image formation (image forming area of the photoreceptor) becomes higher than the charged potential (−500 V) (the absolute value of the potential is lowered) due to the effects of charging, exposure, and transfer. In the case of this image, it was about −150 V during image formation (potential contrast with charged potential was 350 V). Although not shown, when black, the voltage is about −100 V (potential contrast with the charged potential 400 V), and when solid white, the voltage is about −450 V (potential contrast with the charged potential is 50 V).

  In the non-image forming area, the image exposure is turned off to lower the photosensitive drum potential (the absolute value increases), and the transfer bias is weakened to prevent memory from being transferred to the photosensitive drum. The charging potential was about −500 V (potential contrast with charging potential 0 V), or about −550 V (potential contrast with charging potential −50 V) when cleaning the charging roller.

  That is, normally, the portion where the potential contrast with the charged potential is the smallest in the sheet passing history is the non-image forming region portion. When this portion reaches the charging portion, the potential contrast becomes extremely small, and the accumulated toner A is transferred onto the charging roller, and after approximately one round of the charging roller, it is discharged onto the photosensitive drum. Therefore, the influence of the accumulated toner A occurs on the second and subsequent sheets during continuous paper feeding as shown in FIG. 2, and the position is also one round of the photosensitive drum + one round of the charging roller (drum from the region where the potential contrast is low. Occurs after (up conversion distance). When the potential contrast is large, an electric field F that prevents toner from moving from the photosensitive drum to the charging roller is formed with respect to the accumulated toner A as shown in FIG. Does not move to the roller.

  The circumference of the photosensitive drum in this configuration is about 75 mm because the diameter of the photosensitive drum is φ24, and the circumference of the charging roller (φ18) is about 80% with respect to the photosensitive drum. When converted to the distance traveled by the drum while the charging roller makes one round, the distance is about 70 mm. For this reason, one rotation of the photosensitive drum + one rotation of the charging roller (equivalent distance on the drum) is about 145 mm.

  Therefore, in this embodiment, in order to take measures against light shielding and fogging, the image forming exposure apparatus 3 is turned on even in the region that becomes the non-image forming region, and the non-image forming region of the photosensitive drum is uniformly discharged. The image forming area is controlled so as to increase the potential contrast between the charging potential (voltage applied to the charging member) in the area to be the image forming area and the potential in the non-image forming area of the photosensitive drum, thereby preventing light shielding and fogging. It is characterized by that.

  For the portion where the image forming exposure apparatus 3 cannot be turned on, it is preferable to control the charging potential by charging the drum by applying a bias (plus bias) to the transfer member (transfer roller). That is, even if the non-image forming area of the photosensitive member is negatively charged by the charging roller, the absolute value of the charging potential may be lowered by applying a voltage having a polarity opposite to the charging potential to the transfer roller.

  FIG. 5 shows a simple description of each process sequence of this configuration (Example 1), the drum potential before charging, and the state on the drum after charging. The potential before charging is affected by the previous charging by the charging roller, the charge removal by the laser of the exposure device 3, and the charging by transfer. During paper passing, that is, in the image forming area of the photosensitive member, the potential becomes about −100 V due to charging by the charging roller, discharging by the laser, and charging by transfer (during solid black printing). When the laser is turned off at the rear end of the paper, it becomes about −150 V due to charging by transfer, and thereafter, it becomes about −150 V by turning on and off the laser exposure in the gap between papers, that is, in the non-image forming area of the photoreceptor. .

  In transfer, it is preferable to reduce the transfer bias as much as possible in order to eliminate the image defect due to the occurrence of the plus memory because the drum potential between the sheets becomes positive. Therefore, the current supplied to the transfer member is controlled at 0 μA between the sheets. While the area corresponding to the leading edge position of the next paper reaches the transfer position, the transfer bias applied to the transfer member is applied in advance, while the area corresponding to the leading edge position of the paper reaches the laser exposure position. Then, laser neutralization is turned off and the process proceeds to a normal image forming process. The timing of each control was performed based on the output of the paper timing detection means and the like.

  As described above, by controlling the image forming exposure apparatus (laser scanner) 3 and transferring control, the pre-charging drum potential in the non-image forming area (area corresponding to the gap between the sheets) of the photoconductor is more than a certain value (the absolute value of the potential is constant). The potential can be controlled to the following). Accordingly, the potential difference between the pre-charging potential of the image forming area and the non-image forming area of the photosensitive member and the potential applied to the charging member can be kept to some extent (250 V or more described later). Can be prevented.

  Table 1 shows the results of the electric potential during the non-image formation and the occurrence of light shielding and fogging at this time.

  At this time, an experiment was performed by adjusting the laser intensity of the laser scanner 3 in the non-image forming area independently of the image forming. The evaluation of the occurrence of light shielding and fogging was performed by a two-step evaluation of “NG” when 100 sheets of NG were produced due to light shielding fogging when 100 sheets were continuously passed, and “◯” when not.

  From this result, when the drum potential before charging the non-image forming area is set to −250 V or more, the light shielding and fogging as described above do not occur. Here, since the charging potential of the region serving as the image forming region (the potential applied to the charging member with respect to the region serving as the image forming region) is −500 V, the absolute value of the charging potential of the region serving as the image forming region is The difference from the absolute value of the drum potential before charging in the non-image forming area is preferably 250 V or more.

That is, assuming that the charging potential of the region that becomes the image forming region of the photoconductor is Vd (V), and the pre-charging potential Vpre (V) of the non-image forming region of the photoconductor,
It is preferable to satisfy | Vd | ≧ | Vpre | + 250V.

  By setting in this way, the accumulated toner A is stably held upstream of the contact portion between the photoconductor and the charging roller, and the state on the drum after charging is only discharged by the cleaning bias for non-image formation, and the image Spitting during formation can be prevented. As a result, it is possible to prevent light shielding and fogging, which are adverse effects related to the residual toner attached to the charging roller.

  In this embodiment, in order to simplify the configuration, the laser light quantity control is performed in binary, so that the potential between the papers is at least −150 V. This configuration is more preferable because it allows a large margin. However, the same effect can be obtained particularly when the pre-charging potential in the non-image forming area is −250 V or more (the absolute value of the pre-charging potential in the non-image forming area is 250 V or less). Even if laser control is performed with multi-value control, the same effect can be obtained as long as it is −250 V or higher.

  By performing the control as described above, the potential contrast between the charging roller and the photosensitive drum increases (becomes 250 V or more), and the accumulated toner A can be held in the area A. Therefore, the light shielding as described in the first embodiment is performed. It can prevent fogging.

  The second embodiment is almost the same as the configuration of the first embodiment, except that the image exposure apparatus (laser scanner) 3 is not used as the potential control means of the non-image forming region of the photoreceptor. Control is performed by a charging application voltage applied to the charging member 2.

The charging control different from that in the first embodiment will be described below.
Charging roller cleaning mode B mode:
In this embodiment, the switch SW of the charging bias application power source S1 is controlled to be switched to the B contact side by a sequence control circuit (not shown) in an area corresponding to the space between the sheets, which is a non-image forming area of the photoconductor. Then, the AC power supply SAC is connected in series with the DC power supply SDC, so that the DC voltage: −150 V is applied to the core metal 2a of the charging roller 2.
AC voltage: A peak-to-peak voltage of 100 V, a frequency of, for example, 200 Hz, and a rectangular wave superimposed voltage are applied.

  As described above, according to the present embodiment, the charging bias is V1 = −500 V with respect to the region serving as the image forming region of the photoconductor (A mode), and (B Mode), and the charging bias is V2 = −150V. That is, | V1 |> | V2 |.

  By maintaining this bias relationship, the toner accumulated on the charging roller 2 is developed on the photosensitive drum 1 (the toner on the charging roller 2 is discharged to the photosensitive drum 1 side), and the toner is further transferred to the developing device 4. It can be recovered with back contrast.

  In other words, the charging property can be maintained by efficiently removing the toner adhering to the charging roller, which becomes a charging inhibiting factor, to the region that becomes the non-image forming region of the photosensitive member.

  In this case, by supplying the charge accelerating particles m to the charging roller 2, the toner releasability from the top of the charging roller 2 is improved, that is, the releasability is increased. The discharge of toner to the photosensitive drum 1 side is promoted, the charging roller 2 contaminated with the toner is efficiently cleaned, and ozone-less direct charging and a toner recycling system can be executed without any problem with a low applied voltage, and a high-quality image is obtained. It is possible to maintain the formation over a long period of time and to maintain a high-quality image formation over a long period of time even after outputting an image with a high image ratio.

  In the B mode, the cleaning bias applied to the charging roller 2 is desirably set so that the difference between the photosensitive drum potential and the charging roller potential on the downstream side of the charging nip n in the photosensitive drum moving direction is large. It is better to set it.

  In the charging method using direct charging as in this embodiment, a potential approximately equal to the potential applied to the charging roller 2 that is a contact charging member is applied to the surface of the photosensitive drum 1 that is a member to be charged. A potential difference is unlikely to occur between the drums 1.

  Naturally, it is necessary to uniformly charge the surface of the photosensitive drum during image recording, but it is necessary to apply an AC bias (cleaning bias) to generate a potential difference in a roller cleaning mode including non-image recording. Accordingly, it is desirable to select a cleaning bias so that a potential difference is generated between the inside of the charging nip n and the downstream side in the photosensitive drum moving direction.

  FIG. 6 shows the sequence control of the second embodiment.

  The drum potential before charging is affected by charging by a charging roller, discharging by a laser, and charging by transfer. During the sheet passing, that is, the area to be the image forming area, the potential becomes about −100 V due to charging by the charging roller, charge removal by the laser, and charging by transfer (during solid black printing). For the region corresponding to the trailing edge of the paper, when the laser is turned off, it becomes about −150 V due to charging by transfer. The subsequent area becomes about −150 V by lowering the transfer bias and increasing the charge.

  The transfer is preferably performed by reducing the transfer bias as much as possible in order to eliminate image defects due to the plus memory of the drum between the sheets. Therefore, the current applied to the transfer member is controlled between the sheets by 0 μA. In a region corresponding to the position of the leading edge of the next paper, a transfer bias is applied in advance, the charging bias is returned to -500 V, and the process proceeds to a normal image forming process.

  By performing such control, the potential contrast between the charging roller and the photosensitive drum is increased, and the accumulated toner A can be held in the area A. Therefore, light shielding and fogging as described in the first embodiment can be prevented. Can do. Moreover, since the same effect is acquired even if Example 1 and Example 2 are used simultaneously, you may use it simultaneously.

It is a figure showing the structure of the electrophotographic process of this invention. It is a schematic diagram showing the problem which this invention solves. It is a schematic diagram explaining the problem which this invention solves. FIG. 6 is a diagram illustrating a potential on a photosensitive drum after transfer. It is a figure showing the electric potential on the photosensitive drum before charging. It is a figure showing the electric potential on the photosensitive drum before charging.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Laser beam scanner 4 Developing device 4a Developing sleeve t Developer (toner)
m Charge accelerating particles 5 Transfer roller 6 Fixing device P Transfer material

Claims (21)

An image bearing member, a charging member that can contact the image bearing member, and that charges the image bearing member; and an electrostatic image formed on the image bearing member is developed with a developer, and at the same time remains on the image bearing member. An image forming apparatus having a developing unit capable of recovering the developing developer,
If the charge potential in the image forming area of the image carrier is Vd (V) and the pre-charging potential in the non-image formation area of the image carrier is Vpre (V), then | Vd | ≧ | Vpre | An image forming apparatus satisfying +250 (V).   The image carrier is a photoconductor, and the apparatus includes an exposure unit that exposes the image carrier charged by the charging member to form the electrostatic image, and the exposure unit includes at least the exposure unit. The image forming apparatus according to claim 1, wherein a non-image forming area is exposed.   If the applied voltage applied to the charging member for the region to be the image forming region is V1, and the applied voltage applied to the charging member for the region to be the non-image forming region is V2, | V1 | 3. The image forming apparatus according to claim 1, wherein: | V 2 | is satisfied.   The image forming apparatus according to claim 1, wherein the charging member is moved in a direction opposite to the image carrier at a contact portion between the charging member and the image carrier.   The image forming apparatus according to claim 1, wherein the charging member is a flexible and rotatable roller.   6. The image forming apparatus according to claim 1, wherein conductive particles exist at least in a nip portion between the charging member and the image carrier. The image forming apparatus according to claim 6, wherein a volume resistance value of the conductive particles is 10 ¹² Ω · cm or less. The image forming apparatus according to claim 6, wherein a volume resistance value of the conductive particles is 10 ¹⁰ Ω · cm or less.   9. The developer according to claim 6, wherein the developer includes toner and the conductive particles, and the conductive particles are supplied to the image carrier by the developing unit and supplied to the nip portion. Image forming apparatus.   10. The image forming apparatus according to claim 1, wherein an electric field for moving a developer from the charging member to the image carrier is formed in a region to be the non-image forming region.   11. The image forming apparatus according to claim 1, further comprising a transfer unit that transfers an image of the developer formed on the image carrier to a transfer material. An image carrier, a charging member that can contact the image carrier, and charges the image carrier, and an exposure unit that exposes the image carrier charged by the charging member to form the electrostatic image And developing means capable of developing the electrostatic image formed on the image carrier with a developer and collecting the developer remaining on the image carrier at the same time, the image carrier being a photoconductor In the image forming apparatus,
The image forming apparatus, wherein the exposure unit exposes at least a non-image forming area of the image carrier.   When the applied voltage applied to the charging member with respect to the image forming area of the image carrier is V1, and the applied voltage applied to the charging member with respect to the non-image forming area is V2, | V1 |> | The image forming apparatus according to claim 12, wherein V2 | is satisfied.   The image forming apparatus according to claim 12, wherein the charging member is moved in a direction opposite to the image carrier at a contact portion between the charging member and the image carrier.   15. The image forming apparatus according to claim 12, wherein the charging member is a flexible and rotatable roller.   The image forming apparatus according to claim 12, wherein conductive particles are present at least in a nip portion between the charging member and the image carrier. The image forming apparatus according to claim 16, wherein a volume resistance value of the conductive particles is 10 ¹² Ω · cm or less. The image forming apparatus according to claim 16, wherein a volume resistance value of the conductive particles is 10 ¹⁰ Ω · cm or less.   19. The developer according to claim 16, wherein the developer includes toner and the conductive particles, and the conductive particles are supplied to the image carrier by the developing unit and supplied to the nip portion. Image forming apparatus.   20. The image forming apparatus according to claim 12, wherein an electric field for moving a developer from the charging member to the image carrier is formed in a region to be the non-image forming region.   21. The image forming apparatus according to claim 12, further comprising a transfer unit that transfers the developer image formed on the image carrier to a transfer material.

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