JP2008310080A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device, for preventing image blur resulted from a discharge product by a simple structure without providing a member such as a shielding member. <P>SOLUTION: The device comprises a colored powder carrier area formation means for forming a colored powder carrier area in which a colored powder is carried in a predetermined area of an image carrier surface except in image forming operation, and an image carrier stop position control means for controlling a stop position of the image carrier so that the colored powder carrier area is stopped in a position facing a charging means by reversely rotating the image carrier. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system is a charging device that uniformly charges a surface of an image carrier having a photoconductive material, and exposes the surface of the image carrier to form an electrostatic latent image by the potential difference. An exposure device, a developing device for attaching the colored powder to a surface of an image carrier such as a photoreceptor as a visualized image, a transfer device for transferring the colored powder attached as an image to an image support, and the colored powder as an image support The image forming apparatus includes a fixing device fixed on the surface and a cleaning device that removes the remaining colored powder from the surface of the image carrier.

  Among them, charging of the image carrier is performed by applying a voltage having a high voltage of about 4 to 7 [kV] by direct current or alternating current to a corona charger or a charging roller by a charging device with discharge. In the discharge by these charging devices, discharge products such as ozone, nitrogen oxide, and nitrate are generated, and these discharge products do not disappear even after the charging of the charging device is stopped, and are present in the vicinity of the charging device. When the surface of the image carrier is stopped, the discharge products adhere to the surface of the image carrier and gradually accumulate. Since the accumulated discharge product has a water absorption action, moisture in the air or the like is bonded to the discharge product, and the resistance of the surface of the image carrier is reduced. If a latent image of an image is formed on the surface of the image carrier at this time, a serious failure occurs in which a lettering occurs such that the charged charge of the image carrier flows and consequently the image is blurred. This image blur becomes noticeable particularly under high temperature and high humidity. As a result of the experiment verification, the portion of the image carrier corresponding to the image blur portion was directly under the grid electrode of the corona charger, for example, when left for 8 hours after the image formation pause.

  Looking at the difference in the surface potential of the image carrier when the discharge product is not attached to the surface of the image carrier, if the discharge product is not attached, it is uniform by the charging means. When charged, the potential becomes the charging potential V0, and then the laser beam is irradiated by the exposure means, the potential becomes the exposure potential Vr. On the other hand, when the discharge product adheres to the surface of the image carrier, as a result of exposure, the surface of the image carrier in the exposed region does not change to the exposure potential Vr, but only changes to Vr1 close to the charging potential. This is because the discharge product adhering portion on the surface of the image carrier is reduced in resistance by the discharge product adhering to the surface of the image carrier and absorbing moisture, and the charge generated by exposure exceeds the exposure region around the surface of the image carrier. Because it spreads to. As a result, the potential of the exposed area is not sufficiently lowered, the potential outside the exposed area is somewhat lowered, a shallow latent image is formed, and the toner adhesion amount is reduced during development.

  As means for removing discharge products from the surface of the image carrier, there is one in which a shielding member such as a shutter is provided between the image carrier and charging means. In these proposals, a discharge product generated by charging is prevented from moving to an image carrier by a shielding member, thereby preventing image flow.

JP 7-104564 A Japanese Patent Laid-Open No. 7-104565 JP-A-7-104566

  However, if the shielding member is provided, the configuration and control become complicated and the cost increases.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of preventing image blur caused by discharge products with a simple configuration without providing a member such as a shielding member. That is.

In order to achieve the above object, the first means of the present invention includes an image carrier that carries an electrostatic latent image, a charging means that charges the image carrier, and forms an electrostatic latent image on the image carrier. Latent image forming means, developing means for visualizing the electrostatic latent image with colored powder, transfer means for transferring the visualized image formed by the developing means to a transfer material, and remaining on the image carrier In the image forming apparatus having a cleaning means for collecting the colored powder,
Other than the image forming operation, a colored powder carrying area forming means for forming a colored powder carrying area formed by carrying colored powder on a predetermined area on the surface of the image carrying body, and the coloring by carrying out reverse rotation of the image carrier. Image bearing member stop position control means for controlling the stop position of the image bearing member is provided so that the powder bearing region stops at a position facing the charging unit.

  According to a second means of the present invention, when the image forming operation time of the charging means exceeds a predetermined time in the first means, the visualized image is formed on a predetermined region on the surface of the image carrier other than the image forming operation. Visualized image carrying area forming means for forming a visualized image carrying area formed by carrying the image, and image carrying for controlling the stop position of the image carrying body so that the visualized image carrying area stops at a position facing the charging means. Body stop position control means is provided.

  According to a third means of the present invention, in the first means, the formation of the visualized image carrying area by the visualized image carrying area forming means and the stop of the image carrier based on the control by the image carrying body stop position control means. The image forming operation is stopped when the image forming operation stop time is longer than a predetermined time.

  According to a fourth means of the present invention, in the third means, the predetermined time of the image forming operation pause time is set within 20 minutes.

According to a fifth means of the present invention, in any one of the first to fourth means, the thickness of the toner layer in the visualized image carrying region is 0.2 mg / cm ² or more.

  According to a sixth means of the present invention, in any one of the first to fourth means, when a corona charger is used as the charging means and the image carrier is in a stopped state, the corona charger can be A corona charger is installed so that the opening faces the surface of the image carrier from above in the vertical direction of the surface of the image carrier, and the projection is formed by projecting at least the can opening onto the surface of the image carrier. The visualized image carrying region is formed in a shape that can encompass the figure.

  According to the present invention, it is possible to prevent image blur caused by discharge products adhering to the surface of the image carrier with a simple configuration without providing a member such as a shielding member.

  Hereinafter, an image forming apparatus using the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. 1 is a photosensitive member, 2 is a charger, 21 is a can, 22 is a corona wire, 23 is a grid, 3 is a developing device, 31 is a developing roller, 4 is a recording medium, 5 is a transfer device, 6 is a fixing device, and 7 is a fixing device. A cleaner, 8 is an exposure device, 9 is a toner, and 10 is a carrier.

  The photoreceptor 1 used as an image carrier is rotated in the direction of arrow A in the figure, so that the surface of the photoreceptor 1 is uniformly charged to a negative polarity by a charger 2, and then exposed by an exposure device 8 as a latent image forming unit. Is called. The electrostatic latent image formed on the photoreceptor 1 is reversely developed by the developing device 3 with the toner 9 charged to the negative polarity. The toner 9 image formed on the photosensitive member 1 is transferred from a paper supply unit (not shown) to a recording medium 4 as a transfer material that is fed to a transfer region formed between the photosensitive member 1 and the transfer unit 5. Is done. The recording medium 4 onto which the toner 9 image has been transferred is inserted into a fixing device 6 composed of a heating roller and a pressure roller, and an image is formed by melting and fixing the toner 9 to the recording medium 4.

  The charger 2 includes a can 21 having an opening, a corona wire 22 disposed inside the can 21, a power source (not shown) for applying a predetermined voltage to the corona wire 22, and a grid 23 provided in the opening. It consists of. The charger 2 is disposed in a non-contact manner on the surface of the photoreceptor 1 at a predetermined distance, applies a voltage to the discharge corona wire 22, and charges the photoreceptor 1 to a predetermined polarity and a predetermined potential by corona discharge. In this embodiment, the surface of the photosensitive member 1 is uniformly charged to a negative polarity by a scorotron charger composed of a corona wire 22 and a grid 23.

  Usually, in the transfer process, a positive voltage is applied to the transfer device 5 to transfer the toner on the photoreceptor 1 to the recording medium 4. The recording medium 4 to which the toner image is transferred is separated from the photoreceptor 1 and conveyed to the fixing device 6. The fixing device 6 fixes the toner image on the recording medium 4 by the action of heat and pressure by passing through the nip between the heating roller and the pressure roller. In the image forming apparatus of the present invention, a cleaner 7 for cleaning the transfer residual toner and the carrier on the photosensitive member 1 without being transferred to the recording medium 4 is disposed, and the cleaner 7 employs a cleaning blade.

  By the way, when the photosensitive member 1 is charged using discharge such as corona discharge as in the charger 2 of the present embodiment, ammonia in the air and NOx generated by the discharge react to generate a discharge product such as ammonium nitrate. Will occur. A large amount of such discharge products are generated in the vicinity of the corona wires 22 and the grid 23 of the charger 2, and when the rotation of the photosensitive member 1 is stopped as the image forming operation stops, a part of the surface of the photosensitive member 1 is stopped. The region is in a state facing the charger 2 for a long time. Even when the image forming operation is stopped after the end of the discharge, various discharge products adhere to the region facing the charger 2 on the surface of the photoreceptor 1. As the rotation stop time of the photoconductor 1 is prolonged, the discharge product accumulates in a portion facing the charger 2, so that the developed image is blurred.

  As an example, after applying −800 μA (discharge voltage of about 6 [kV]) to the corona wire 22 and −900 [V] to the grid 23 to uniformly charge the photoreceptor 1 to −900 [V], The surface potential was set to −50 [V] by exposure. The photoconductor 1 was formed by laminating a charge transport layer made of polycarbonate resin on a charge generation layer on an aluminum tube. At this time, the charge generation layer was 0.2 [μm], and the charge transport layer was 25 [μm]. In the above setting, running is performed by repeating charging and exposure continuously for 1 hour under high temperature and high humidity (temperature 28 ° C., humidity 80%), and after leaving the running for 8 hours, a halftone dot image of 600 dpi is obtained. Output.

  As a result, partially blurred image blur occurred. The portion where the image is whitened out is the portion immediately below the grid 23 of the charger 2. This is because the discharge product adhering to the surface of the photosensitive member 1 absorbs water, the resistance of the surface of the photosensitive member 1 becomes low, and even when the laser beam from the charger 2 is irradiated, the charge is more than the exposed region. This is because a flow of charged charges that does not sufficiently lower the surface potential of the exposed region occurs. Due to this influence, a latent image cannot be formed, and the potential drops only insufficiently, resulting in a blurred image blur. Therefore, in this embodiment, a toner layer can be formed on the surface of the photosensitive member 1 by the developing machine 3 even at times other than the developing operation.

  FIG. 2 is a flowchart illustrating control for preventing image blur of the image forming apparatus according to the present exemplary embodiment. First, when the image forming operation is completed (S1), the photosensitive member 1 is rotated again to operate the charger 2, the exposure device 8, and the developing device 3 to apply a predetermined developing bias to the developing roller 31 of the developing device 3. Then, a solid image is formed on the photoreceptor 1 (S2). As a result, a toner carrying area is formed on the surface as a predetermined area on the surface of the photoreceptor 1. At this time, a toner carrying region is formed from the developing device 3 to the position of the cleaner 7 on the image carrier. Here, the image carrier is rotated in the reverse direction, and the rotation is controlled so that the toner carrying region is directly below the charger 2.

  Here, the toner adhesion amount of the nine layers of toner was variously changed by bias control, and only the discharge was performed in a state where the photosensitive member 1 was stopped at each adhesion amount, and the image blur was evaluated. Also, the discharge time was changed to four types of 8, 16, 24, and 48 hours. Also, evaluation of image blur is performed after leaving the image forming operation pause time for 24 hours in a high-temperature and high-humidity environment where temperature is 28 [° C.] and humidity is 80 [%]. , And output a 600 dpi halftone image. The evaluation criteria were ◯ when no image blur occurred, Δ when a little image blur occurred, and x when an image blur occurred completely. The results are shown in Table 1 below.

From the results of Table 1, image blurring is more likely to occur as the toner adhesion amount of the toner 9 layer between the photosensitive member 1 and the charger 2 decreases, and the image blurring decreases as the toner adhesion amount increases. I understood that. Further, it was found that if the toner adhesion amount is 0.2 mg / cm ² or more, image blur does not occur regardless of whether the discharge time is 1 hour or 3 hours. Therefore, it can be said that if the toner adhesion amount is 0.2 mg / cm ² or more, it is possible to reliably prevent the product due to discharge from adhering to the surface of the photoreceptor 1 and to prevent the occurrence of image blur.

Therefore, also in this embodiment, the toner adhesion amount on the surface of the photoreceptor 1 was controlled to be uniformly adhered to 0.2 mg / cm ² or more by the developing bias. Further, the time required for the toner carrying region to reach the position facing the grid 23 of the charger 2 is calculated from the development time for forming the toner carrying region and the rotation speed of the photosensitive member 1 in advance, and a memory (not shown) is calculated. To remember). The memory and the driving means for controlling the driving of the photosensitive member 1 at the timing stored in the memory have a photosensitive member driving control means as an image carrier stop position controlling means. Then, rotational driving in the opposite direction to the image formation of the photosensitive member 1 is performed (S3). If the predetermined rotation time has not been reached (N in S4), the rotational driving rotational driving in the reverse direction to the image formation of the photosensitive member 1 is continued. When the predetermined rotation time has elapsed (Y in S4), the rotation of the photosensitive member 1 is stopped (S5), and the apparatus is stopped. As a result, the rotation of the photosensitive member 1 can be stopped in a state where the toner carrying region comes to a position facing the grid 23 of the charger 2.

  In this way, the toner 9 is adhered to the surface of the photosensitive member 1 to form a toner carrying region during a time other than the image forming operation, the photosensitive member 1 is reversed, and the rotation between the charger 2 and the photosensitive member 1 is stopped. By interposing the toner 9 layer on the surface, it is possible to reliably prevent discharge products existing between the charger 2 and the surface of the photoreceptor 1 from directly attaching to the surface of the photoreceptor 1. Thereby, it is possible to prevent the occurrence of image blur due to the adhesion of the discharge product.

  As in the first embodiment, a toner carrying area is not necessarily formed on the surface of the photoreceptor 1 after the image forming operation is finished, but a certain time has passed after the image forming operation is finished until the next image forming operation is performed. Only when the toner carrying area is formed on the surface of the photoreceptor 1. Since portions other than the following description are the same as those in the first embodiment, the description is omitted.

  Note that if the image forming operation pause time is within 20 minutes, no image blur will occur. If the image forming operation pause time is 40 minutes to 50 minutes, a slight image blur will occur (.DELTA.). (×). As a result, there is a correlation between the image forming operation pause time and the image blur occurrence state. If the image forming operation pause time is within 20 minutes, no image blur occurs. It has been found that the discharge product adheres to the surface portion of the photoreceptor 1 stopped at a position opposite to the above, and the above-mentioned problem occurs.

  Therefore, in this embodiment, the predetermined time of the image forming operation pause time is set to 20 minutes, which is considered to cause a large risk of image blur when this time has passed, so that image blur can be efficiently prevented. Since the solid image forming operation for preventing the image blur is performed only when there is a possibility that the image blur occurs when the pause time of the image forming operation exceeds 20 minutes, the image blur can be effectively prevented and the image blur can be prevented. Practical.

  Instead of attaching the toner 9 to the entire surface of the photoreceptor 1 as in the first and second embodiments, the toner 9 is attached only to a predetermined region on the surface of the photoreceptor 1. Since portions other than the following description are the same as those in the first embodiment, the description is omitted. In this embodiment, the scorotron charger is used as the charging device, but the present invention is not limited to this. When the photosensitive drum is in a stopped state, the charging device can be applied to other charging devices as long as the casing opening of the charging device is provided so as to face the surface of the photosensitive drum from above the photosensitive drum surface in the vertical direction. it can. For example, corotron is also applicable.

  Further, in the configurations of the first to third embodiments, in order to form a toner carrying area on the surface of the photosensitive member 1, the charger 2 and the exposure device 8 are not used, and the developing device 3 is driven and the developing roller 31 is applied. A toner carrying region can be formed on the image carrier only by applying a developing bias. In this embodiment, a scorotron is used as the charger 2, but a charging roller may be used as long as it is not in contact with the photoreceptor 1. Further, the photoreceptor 1 may be other than OPC, for example, an inorganic photoreceptor or an amorphous silicon photoreceptor.

  According to the image forming apparatus of the present invention, since the discharge product can be prevented from directly adhering to the surface of the image carrier while the image carrier is stopped, only when it is necessary to prevent the image blur caused by the discharge product. There is an effect that it can be efficiently performed.

  Further, according to the image forming apparatus of the present invention, it is not necessary to provide a new member or equipment as the toner carrying region forming means, so that it is possible to easily prevent the image blur caused by the discharge product without providing a special equipment. There is an effect that can be realized with a simple configuration. Furthermore, it can be applied to an image forming apparatus using a discharge phenomenon.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating control for preventing image blur of the image forming apparatus in the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charger, 21 ... Can, 22 ... Corona wire, 23 ... Grid, 3 ... Developing machine, 31 ... Developing roller, 4 ... Recording medium, 5 ... Transfer device, 6 ... Fixing machine, 7 ... Cleaner, 8 ... exposure device, 9 ... toner, 10 ... carrier.

Claims (6)

An image carrier that carries an electrostatic latent image; a charging unit that charges the image carrier; a latent image forming unit that forms an electrostatic latent image on the image carrier; An image forming apparatus comprising: a developing unit that visualizes an image with a body; a transfer unit that transfers a visualized image formed by the developing unit to a transfer material; and a cleaning unit that collects the colored powder remaining on the image carrier. In
Other than the image forming operation, a colored powder carrying area forming means for forming a colored powder carrying area formed by carrying colored powder on a predetermined area on the surface of the image carrying body, and the coloring by carrying out reverse rotation of the image carrier. An image forming apparatus comprising: an image carrier stop position control unit configured to control a stop position of the image carrier so that a powder carrying region stops at a position facing the charging unit.   The image forming apparatus according to claim 1, wherein when the image forming operation time of the charging unit exceeds a predetermined time, a visualized image is carried on a predetermined region on the surface of the image carrier other than the image forming operation. Visualized image carrying region forming means for forming a visualized image carrying region, and image carrier stop position control for controlling the stop position of the image carrier so that the visualized image carrying region stops at a position facing the charging unit. And an image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the formation of the visualized image carrying region by the visualized image carrying region forming unit and the stop of the image carrier based on the control by the image carrier stopping position control unit are performed as an image forming operation. An image forming apparatus that operates when a pause time of an image forming operation that has been paused exceeds a predetermined time.   4. The image forming apparatus according to claim 3, wherein the predetermined time of the image forming operation pause time is set to 20 minutes or less. 5. The image forming apparatus according to claim 1, wherein a toner layer thickness in the visualized image carrying region is 0.2 mg / cm ² or more.   5. The image forming apparatus according to claim 1, wherein when the corona charger is used as the charging unit and the image carrier is in a stopped state, the can opening portion of the corona charger is A corona charger is installed so as to face the image carrier surface from above in the vertical direction of the image carrier surface, and includes at least a projection view formed by vertically projecting a can opening on the image carrier surface. An image forming apparatus, wherein the visualized image carrying region is formed in a shape that can be formed.

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