JP2010002436A - Charger and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that eliminates the need for changing a voltage applied to a charger to a low value and need for an increase in the size of the image forming apparatus, and prevents the life of an electrostatic latent image carrier from being shortened wastefully. <P>SOLUTION: The charger 2 provided in the image forming apparatus includes shield case 800, electrodes 100 and 200 and a grid electrode 300 accommodated in the shield case 800, and an exhaust fan 800. The grid electrode 300 has a net plate-like shape and both ends of it are connected between mesh holding parts 610 and 620 in a tensioned state. If a drive source for rotating a photoreceptor reversely rotates when the charger 2 is not charging the surface of the photoreceptor, the mesh holding part 620 moves in the direction of arrow F and separates the grid electrode 300 from the surface of the photoreceptor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention forms an electrostatic latent image on the surface of an electrostatic latent image carrier in an image forming apparatus such as a copying machine, a printer, a facsimile machine or a combination machine combining two or more of them, which forms a toner image by electrophotography. The present invention relates to a charger that is charged in advance. The present invention also relates to an image forming apparatus provided with a charger.

  For example, in an image forming apparatus such as an electrophotographic copying machine or a printer, the surface of a photosensitive drum (an example of an electrostatic latent image carrier) is usually charged by a charger, and an original image is transferred from the optical system to the charged area. An electrostatic latent image is formed corresponding to the above, and an electrostatic latent image is formed. The latent image is developed by a developing device to become a visible toner image, which is transferred onto a transfer material by a transfer device and fixed by a fixing device. After the toner image is transferred, the toner remaining on the photoconductor is cleaned by a cleaning device.

  Various types of chargers are known, such as those using corona discharge and those using a contact charging member such as a charging brush or a charging roller that contacts the surface of the photoreceptor. Among these, a charger using corona discharge is usually disposed near the surface of the photoreceptor, and charges the photoreceptor by applying a discharge voltage to a discharge electrode member such as a discharge wire. Some have a grid electrode for controlling charging of the photosensitive member between the discharge electrode member and the surface of the photosensitive member, and this is widely used as a scorotron charger.

  When charging a photoreceptor with such a charger, ozone and nitrogen oxides are usually generated along with discharge, and the nitrogen oxides combine with substances in the air to produce nitrate compounds such as ammonium nitrate. It may occur around the charger and further, such discharge products may adhere to the opposing photoreceptor surface. When the amount of adhesion increases, an oxide film due to the discharge product is formed on the surface of the photoconductor, and the oxide film itself is hydrophilic. Reduce. As a result, a lateral leak occurs on the surface of the photosensitive member, and as a result, an image defect called “image flow” occurs.

  It is believed that the main cause of image drift is due to nitrogen oxides (particularly nitrogen dioxide). When this nitrogen oxide reacts with water, nitric acid is produced, and when it reacts with ammonia in the air, it adheres to the surface of the photoreceptor while having water solubility. After that, it absorbs more moisture under high humidity and lowers the resistance value of the surface of the photoconductor. Since the conductive path is formed at the boundary, the boundary between the image portion and the non-image portion is blurred. As a result, the image is blurred or whitened, and image flow occurs.

  As a measure for preventing such image flow, it is conceivable to remove the discharge products adhering to the photoreceptor. In order to remove the discharge product adhering to the photoconductor, the surface of the photoconductor is scraped off together with the discharge product by a member (for example, a cleaning blade) that is pressed against the photoconductor using a photoconductor whose surface is easily worn. What is necessary is just to comprise.

  Japanese Patent Laid-Open No. 5-323833 (Patent Document 1) discloses an apparatus for polishing the surface of a photoreceptor. This photoconductor polishing apparatus is an electrophotographic apparatus having a cleaning device that steadily removes residual toner from the surface of the photoconductor, and has a polishing blade for polishing the photoconductor, and a drive for operating the polishing blade during non-image formation. Means. According to this photoconductor polishing apparatus, the surface of the photoconductor is polished by the polishing blade to prevent deterioration of the photoconductor due to deposits such as toner filming over a long period of time, and no cleaning failure due to a change with time does not occur.

JP-A-5-323833

  However, the above-described photoreceptor polishing apparatus disclosed in Patent Document 1 only supports defects such as black streaks and black belts due to deterioration of the cleaning capability over time due to wear or chipping of a cleaning blade that removes toner. The discharge products have not been studied. Further, when configured as in Patent Document 1 described above, there is a drawback that the life of the photoconductor is shortened because the surface of the photoconductor is polished. In recent years, such a configuration is not preferable in consideration of the tendency to extend the life by forming a protective layer on the surface of the photoreceptor. Further, when such a polishing processing unit is provided, the manufacturing cost increases, and a space for providing the polishing processing unit around the photosensitive member is required, which causes a problem that the image forming apparatus is increased in size.

  There is also a measure to reduce the voltage applied to the charger in order to suppress the generation amount of the discharge product which is the image flow factor substance. However, when a high-speed image forming operation is required, the charge necessary for charging is not sufficiently supplied onto the photosensitive member, and uneven charging occurs on the image and the necessary surface potential cannot be formed. An image defect called “fogging” to which toner adheres occurs. For this reason, it is not realistic to reduce the amount of discharge products by reducing the voltage applied to the charger.

  Accordingly, the present invention provides a charger that charges the surface of an electrostatic latent image carrier that is rotationally driven in an electrophotographic image forming apparatus prior to electrostatic latent image formation, and includes a discharge electrode, a grid electrode, a shield case, The electrostatic latent image bearing member has a long life without setting the voltage applied to the charger so low as to hinder image formation, without increasing the size of the image forming apparatus. It is a first object to provide a charger that can suppress the adhesion of the discharge product to the electrostatic latent image carrier without shortening it.

  The present invention also relates to an image forming apparatus for forming a toner image, in which a surface of a rotating electrostatic latent image carrier is charged by a charger, and an image is formed on a charged area of the electrostatic latent image carrier by the charger. An electrophotographic image forming apparatus having at least one image forming unit that exposes to form an electrostatic latent image and develops the electrostatic latent image to form a visible toner image, the image forming apparatus comprising: In the forming unit, the voltage applied to the charger is not set so low as to hinder image formation, the image forming apparatus is not enlarged, and the life of the electrostatic latent image carrier is not shortened. Therefore, it is a second object to provide an image forming apparatus capable of suppressing the adhesion of the discharge product to the electrostatic latent image carrier and thus forming an image as well.

In order to solve the first problem, the present invention provides the following charger.
A charger that charges the surface of an electrostatic latent image carrier that is rotationally driven in an electrophotographic image forming apparatus prior to electrostatic latent image formation, and includes a discharge electrode, a grid electrode, and a shield case. A vessel,
The shield case is a case fixed at a predetermined position, and has an opening that accommodates the discharge electrode and faces the electrostatic latent image carrier,
The grid electrode is disposed in the opening of the shield case, and has a net-plate shape in which both ends in the direction along the rotation axis of the electrostatic latent image carrier are respectively held and stretched by holding units. Yes,
When the charger is charging the surface of the electrostatic latent image carrier, the mesh plate-like grid electrode is stretched, and when not charged, the mesh plate-like grid electrode is loosened toward the shield case. The charger is provided with an adjusting mechanism for adjusting the tension state of the grid electrode.

  During image formation in the image forming apparatus, image flow hardly occurs. During image formation, the electrostatic latent image carrier surface is charged by the charger to generate discharge products, which are exhausted by the exhaust fan. For this reason, even if it adheres to the surface of the electrostatic latent image carrier, most of the discharge products are exhausted, so that it is only a very small amount of attachment (even if attached, it is removed by polishing with a cleaning blade). The discharge product that causes the image flow to adhere to the electrostatic latent image carrier occurs after the image formation and after the charger and the electrostatic latent image carrier are stopped and left for a while. That is, when a substance that causes image flow accumulates in a specific part of the charger along with an increase in discharge time due to image formation, if the driving of the charger and the electrostatic latent image carrier is stopped, the discharge product is Gradually move to and adhere to the surface of the electrostatic latent image carrier. Since the exhaust fan does not exhaust during this stop, the amount of adhesion on the surface of the electrostatic latent image carrier increases with time, so that it is polished with the cleaning blade during the next image formation or warm-up. However, the discharge product cannot be removed in a short time. As a result of research, the present inventor has clarified that a specific portion where discharge products accumulate is a grid electrode.

  In the charger according to the present invention, the adjustment mechanism causes the grid-plate-like grid electrode to be stretched when the surface of the electrostatic latent image carrier is charged, with a predetermined interval (the grid electrode and the electrostatic latent image carrier). The tensioning state is changed so that the distance between the surface and the surface is maintained and the distance is loosened when not charged. For this reason, when there is no need to charge the electrostatic latent image carrier, the grid electrode in which the discharge product accumulates is separated from the electrostatic latent image carrier, so that the discharge product gradually becomes the surface of the electrostatic latent image carrier. It can suppress that it moves to and adheres to. In this way, the voltage applied to the charger is reduced to such an extent that, for example, image formation is hindered in high-speed image formation or the like, and there is no need to reduce the generation of discharge products itself. There is no defect. Further, the shield case accommodates the discharge electrode and the grid electrode and is fixed at a predetermined position, and the adjustment mechanism only adjusts the tension state of the grid electrode, and electrostatically fixes the grid electrode. Compared with the case where each shield case (discharge electrode and grid electrode) is moved so as to be separated from the surface of the latent image carrier, the size of the charger need not be increased. Further, since it is not necessary to polish the surface of the electrostatic latent image carrier for removing the discharge products, the life of the surface of the electrostatic latent image carrier is not shortened.

  The adjustment mechanism may be configured such that the grid-like grid electrode can be loosened by a drive source that rotationally drives the electrostatic latent image carrier. In this way, it is not necessary to provide a new drive source for adjusting the stretched state of the grid electrode, the charger need not be enlarged, and an increase in manufacturing cost can be suppressed.

  The adjustment mechanism includes a swing gear that rotates when the electrostatic latent image carrier is driven by the drive source in a direction opposite to the rotation direction during image formation, and the holding unit. The holding unit is configured such that when the charger does not charge the surface of the electrostatic latent image carrier, the driving source rotates the electrostatic latent image carrier in the reverse rotation direction and the swing gear rotates by a predetermined amount. Then, at least one end holding the mesh plate-like grid electrode can be configured to approach the other end. As a result, at least one end of the mesh plate-like grid electrode supported at both ends by the support portion approaches the other end, and the mesh plate-like grid electrode is loosened so that the grid electrode and the electrostatic latent image carrier surface Spacing increases. At this time, when the drive source rotates in the reverse rotation direction and the swing gear rotates by a predetermined amount, one end approaches the other end. For this reason, it is not necessary to provide a new drive source for adjusting the stretched state of the grid electrode, the charger need not be enlarged, and an increase in manufacturing cost can be suppressed.

  The charger may be configured to further include a discharge port for discharging discharge products provided at a position facing the central portion in the rotation axis direction of the electrostatic latent image carrier. Thus, if a discharge port is provided at a position facing the central portion, the discharge product is discharged from the central portion. For this reason, the discharge products generated in the charger are collected in the vicinity of the central portion that is most resistant to image flow, the accumulation of discharge products in the non-central portion is reduced, and the generation is also suppressed in the central portion.

  The charger may be configured to further include a discharge fan provided at a position corresponding to the discharge port. When the discharge port and the discharge fan are provided at the position facing the central portion in this way, the discharge product is discharged more positively from the central portion. For this reason, the discharge products generated in the charger are collected in the vicinity of the central portion that is most resistant to image flow, the accumulation of discharge products in the non-central portion is reduced, and the generation is also suppressed in the central portion.

  In order to solve the second problem, the present invention also charges the surface of the electrostatic latent image carrier that is rotationally driven by a charger, and exposes the image to the charged area of the electrostatic latent image carrier by the charger. Is an electrophotographic image forming apparatus having at least one image forming unit that forms an electrostatic latent image and develops the electrostatic latent image to form a visible toner image, and at least one image forming unit The above-mentioned charger provides an image forming apparatus which is a charger according to the present invention.

  The image forming apparatus according to the present invention includes the charger according to the present invention as a charger, and the charger does not set a voltage applied to the charger so low as to hinder image formation, and Without increasing the size of the image forming apparatus and without significantly shortening the life of the electrostatic latent image carrier, it is possible to suppress the adhesion of discharge products to the electrostatic latent image carrier, and as a result, it is possible to form an image as well. .

  As described above, according to the present invention, there is provided a charger for charging the surface of an electrostatic latent image carrier that is rotationally driven in an electrophotographic image forming apparatus prior to electrostatic latent image formation, including a discharge electrode and a grid. A charger having an electrode and a shield case, without setting the voltage applied to the charger so low as to hinder image formation, without increasing the size of the image forming apparatus, and supporting an electrostatic latent image It is possible to provide a charger that can suppress the adhesion of discharge products to the electrostatic latent image carrier without shortening the life of the body.

  According to the present invention, there is also provided an image forming apparatus for forming a toner image, wherein the surface of the electrostatic latent image carrier to be rotationally driven is charged by a charger, and the electrostatic latent image carrier is charged by the charger. An electrophotographic image forming apparatus having at least one image forming unit that performs image exposure to form an electrostatic latent image and develops the electrostatic latent image to form a visible toner image. In the image forming section, the voltage applied to the charger is not set so low as to hinder image formation, the image forming apparatus is not enlarged, and the life of the electrostatic latent image carrier is shortened. Therefore, it is possible to provide an image forming apparatus capable of suppressing the adhesion of the discharge product to the electrostatic latent image carrier and thus forming an image as well.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[Entire configuration of image forming apparatus]
FIG. 1 shows an example of an image forming apparatus according to the present invention. An image forming apparatus A shown in FIG. 1 (hereinafter sometimes referred to as a printer A) is a tandem type full-color printer. The printer A has an endless intermediate transfer belt 8 wound around a driving roller 81 and a roller 82 facing the driving roller 81. The intermediate transfer belt 8 is rotated counterclockwise in the figure (arrow direction in the figure) α by a driving roller 81 driven by a belt driving unit (not shown).

  A secondary transfer roller 9 faces the drive roller 81 via the intermediate transfer belt 8, and a cleaning device 83 that cleans residual toner and the like faces a roller 82 that faces the drive roller 81. The toner or the like collected by the cleaning device 83 is sent to a waste container by a conveying means (not shown).

  The surface layer portion of the secondary transfer roller 9 is formed of an elastic material, and is pressed against a portion of the intermediate transfer belt 8 supported by the driving roller 81 by a pressing unit (not shown), and a nip is formed between the secondary transfer roller 9 and the intermediate transfer belt 8. And can be rotated following the rotation of the intermediate transfer belt 8 or following the movement of the recording medium S fed into the nip as will be described later. A secondary transfer bias can be applied to the secondary transfer roller 9 at a predetermined timing from a power source (not shown).

  A fixing device FX is disposed above the intermediate transfer belt 8 and the secondary transfer roller 9, a timing roller pair TR is disposed below, and a recording medium S such as recording paper is accommodated below the fixing device FX. The recording medium storage cassette 10 is disposed.

  The fixing device FX includes a fixing heating roller incorporating a heat source such as a halogen lamp heater and a pressure roller pressed against the fixing heating roller. The recording medium S accommodated in the recording medium accommodating cassette 10 can be pulled out one by one by the medium supply roller 11 and supplied to the timing roller pair TR.

  Between the driving roller 81 and the roller 82 around which the intermediate transfer belt 8 is wound, the yellow image forming unit Y, the magenta image forming unit M, and the like along the intermediate transfer belt 8 from the roller 82 to the driving roller 81. The cyan image forming unit C and the black image forming unit K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photosensitive member 1 as an electrostatic latent image carrier, and a charger 2, an exposure device 3, a developing unit 4, and the like around the photosensitive member. The primary transfer roller 5 and the cleaning device 6 are arranged in this order.

  In each image forming unit, a process cartridge including a photoreceptor 1, a charger 2, a developing device 4, and a cleaning device 6 is formed. That is, the yellow process cartridge YC for forming the yellow image forming portion Y, the magenta process cartridge MC for forming the magenta image forming portion M, the cyan process cartridge CC for forming the cyan image forming portion C, and the black image forming This is a black process cartridge KC for forming the portion K. Each process cartridge is detachable from the main body of the image forming apparatus.

  The primary transfer roller 5 is opposed to the photoreceptor 1 with the intermediate transfer belt 8 therebetween, and rotates as the belt travels. A primary transfer bias for primary transfer of a toner image formed on the photoreceptor 1 to the intermediate transfer belt 8 can be applied to the primary transfer roller 5 from a power supply (not shown) at a predetermined timing. The exposure apparatus 3 can perform image exposure by dot (point) exposure on the photosensitive member 1 by blinking of a laser beam in accordance with image information provided from a personal computer (not shown) or the like.

  The photoconductor 1 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown). The charger 2 in each image forming unit is not limited thereto, but is a scorotron charger in this example, and a charging voltage is applied from a power source at a predetermined timing.

  The developing device 4 in each image forming unit is a one-component developing device using a so-called one-component developer mainly composed of toner. Although not limited thereto, the developing device 4 is formed on the photoreceptor 1 using a developer (so-called one-component developer) mainly composed of non-magnetic toner (here, negatively charged non-magnetic toner). The electrostatic latent image can be reversely developed by the developing roller 41 to which a developing bias is applied from a power supply (not shown).

  According to this printer A, an image is formed using one or more of Y, M, C, and K image forming units under the instruction and control of a control unit (not shown) that controls the operation of the image forming apparatus. can do. Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is applied to the intermediate transfer belt 8 by 1. Next transfer.

  That is, in the yellow image forming portion Y, the photosensitive member 1 is rotated in the clockwise direction in the drawing, and the surface is uniformly charged to a predetermined potential by the charger 2, and the yellow region for the yellow image is transferred from the exposure device 3 to the charged area. Image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 1. The electrostatic latent image is developed by a developing roller 41 to which a developing bias of a developing unit 4 having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto an intermediate transfer belt 8 by a primary transfer roller 5. Primary transfer. At this time, a primary transfer bias is applied to the primary transfer roller 5 from a power supply (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the intermediate transfer belt 8, and a cyan toner image is formed and transferred to the intermediate transfer belt 8 in the cyan image forming unit C. A black toner image is formed at K and transferred to the intermediate transfer belt 8.

  Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 8. Thus, the multiple toner image formed on the intermediate transfer belt 8 moves toward the secondary transfer roller 9 by the rotation of the intermediate transfer belt 8.

  On the other hand, the recording medium S is pulled out from the recording medium accommodating cassette 10 by the medium supply roller 11, supplied to the timing roller pair TR, and is on standby.

  Thus, the recording medium S waiting at the timing roller pair TR is supplied to the nip portion between the intermediate transfer belt 8 and the secondary transfer roller 9 in accordance with the multiple toner images sent by the intermediate transfer belt 8. The multiple toner images are secondarily transferred onto the recording medium S by a secondary transfer roller 9 to which a secondary transfer bias is applied from a power supply (not shown). Thereafter, the recording medium S is passed through the fixing device FX, where the multiple toner images are fixed on the recording medium S under heat and pressure. The recording medium S is continuously discharged to the discharge tray T by the discharge roller pair DR.

  Transfer residual toner or the like remaining on the photoreceptor 1 in the primary transfer of the toner image to the intermediate transfer belt 8 is cleaned by the cleaning device 6, and secondary transfer residual toner or the like remaining on the intermediate transfer belt 8 by the secondary transfer. Is cleaned by a cleaning device 83. Each of these cleaned and removed toners is sent to a waste container by a conveying means (not shown).

  Note that the image forming apparatus according to the present invention is not limited to such a tandem type full-color image forming apparatus. Even a cycle type full-color image forming apparatus can be applied as the image forming apparatus according to the present embodiment. Further, it may be a monochrome image forming apparatus. In other words, an image forming unit equipped with a transfer unit for transferring a toner image held by the electrostatic latent image carrier to a recording medium and equipped with a charger for uniformly charging the electrostatic latent image carrier before forming the electrostatic latent image. Any device may be used.

[Charger configuration]
FIG. 2 is a perspective view showing the charger 2 in the image forming apparatus of FIG. FIG. 2 is shown in an exploded state with the grid electrode 300 facing upward. The charger 2 includes a first corona discharge wire 100 and a second corona discharge wire 200 (both discharge electrodes) which are parallel to each other, and these discharge wires (the first corona discharge wire 100 and the second corona discharge wire). 200) and the photoreceptor 1 are provided with a grid-like (mesh) grid electrode 300. Further, a stabilizing plate 400 facing the first corona discharge wire 100 and the second corona discharge wire 200 on the side opposite to the grid electrode 300 is provided. Note that the entire charger 2 is housed in a shield case 800. An exhaust fan 820 is provided below the shield case 800.

  The discharge product generated by the corona discharge in the charger 2 passes through the discharge port 401 of the stabilizing plate 400 and the discharge port 810 of the shield case 800 in the direction of arrow C, and in the direction of arrow D (that is, in the charger 2). To the outside) and exhausted by the exhaust fan 820. The exhaust fan 820 is basically operated while the image forming apparatus A is in operation. As will be described in detail later, in addition to being operated during charging as in the prior art, even when charging is stopped, the grid electrode 300 is separated from the photoreceptor 1 as in the present embodiment, and the exhaust is performed. The fan 820 is operated to discharge the discharge product to the outside of the charger 2 (outside of the image forming apparatus A).

  The first corona discharge wire 100 and the second corona discharge wire 200 are obtained by performing gold plating on a tungsten wire (diameter of about 50 μm). The grid electrode 300 is a mesh type electrode formed by punching a stainless steel plate into a mesh plate shape. The stabilizing plate 400 is provided with a discharge port 401 so as to discharge a discharge product such as ozone generated during discharge by generating an ion flow not directed to the photoreceptor 1 to the outside of the charger 2.

  As shown in FIG. 2, the charger 2 includes a holder 510 and a holder 520 on both sides, and both end portions of the stabilizer 400 are fitted into a notch step portion 513 and a notch step portion 523 of the holder. Do not use screws or other suitable means. The holder 510 has a pin 511 for hooking the first corona discharge wire 100 and a pin 512 for hooking the second corona discharge wire 200. The holder 520 includes a conductive locking portion 521 that hangs the first corona discharge wire 100 and a conductive locking portion 522 that hangs the second corona discharge wire 200.

  The first corona discharge wire 100 has a spring-like hook portion 101 at one end hooked on the pin 511 and a hook portion 102 at the other end hooked on the conductive locking portion 521. The second corona discharge wire 200 has a spring-like hook portion 201 at one end hooked on the pin 512 and a hook portion 202 at the other end hooked on the conductive locking portion 522. In this way, the first corona discharge wire 100 and the second corona discharge wire 200 are stretched at predetermined positions. The first corona discharge wire 100 and the second corona discharge wire 200 stretched in this way are, for example, equidistant from the photoconductor 1 and parallel to the photoconductor 1.

  Further, a mesh holding unit 610 is provided in the vicinity of the holder 510, and a mesh holding unit 620 is provided in the vicinity of the holder 520. The mesh holding portion 610 is fitted with an engaging member 611 so as to be slidable in a direction parallel to the wire, and is elastically supported by a leaf spring or the like (that is, the grid electrode 300 is attached). (It is pulling in the left direction in FIG. 2). Further, an engagement member 621 is fixed to the mesh holding part 620. The mesh holding unit 620 can swing in the arrow E direction and the arrow F direction. When the mesh holding unit 620 is in the arrow E direction, the mesh electrode 300 is stretched, and when the mesh holding unit 620 is in the arrow F direction, the grid electrode 300 is loosened. Note that the mesh holding unit 610 may have the same configuration as the mesh holding unit 620. Details of the mesh holding unit 620 will be described later.

  The grid electrode 300 has a hole 301 at one end thereof in the engaging member 611 of the mesh holding portion 610 (in the direction of arrow A) and a hole 302 in the other end thereof in the engaging member 621 of the mesh holding portion 620 (indicated by arrow B). The first corona discharge wire 100 and the second corona discharge wire 200 and the photoreceptor 1. The grid electrode 300 stretched in this way is parallel to a plane including the first corona discharge wire 100 and the second corona discharge wire 200, for example.

  A voltage is applied to the first corona discharge wire 100 and the second corona discharge wire 200 via the conductive locking portion 521 and the conductive locking portion 522 in the holder 520. The grid electrode 300 is grounded via the varistor 700. Furthermore, the stabilizer 400 is also grounded.

  In the charger 2 in FIG. 2, a high voltage of several kV is applied to the first corona discharge wire 100 and the second corona discharge wire 200 to generate corona discharge. The generated charges move onto the photosensitive member 1 to charge the surface of the photosensitive member 1, and at this time, a voltage is also applied to the grid electrode 300 in order to obtain a desired potential. When the potential on the grid electrode 300 and the potential on the photoconductor 1 become equal, the movement of the charge on the photoconductor 1 stops, and the charge generated from the first corona discharge wire 100 and the second corona discharge wire 200. Flows into the shield case 800. The shield case 800 may be grounded at the same potential as the grid electrode 300.

[Grid electrode retraction mechanism]
In the charger 2 of the image forming apparatus A according to the present embodiment, a site that is a contamination source of the image flow factor substance is identified and a countermeasure mechanism is provided for the site so that the image flow phenomenon can be reliably suppressed. By providing, it is possible to prevent accumulation of an image flow factor substance on the surface of the photoreceptor 1.

  Little image flow occurs during image formation. This is because, during image formation, a large amount of discharge products such as ozone and nitrogen oxide (NOx) are generated by charging, and these substances are exhausted by an exhaust fan 820 as shown in FIG. Even if it adheres to one surface, since it is exhausted by the exhaust fan 820, it is a very small amount. For this reason, it can be adequately handled by polishing the cleaning blade performed during warm-up.

  The image flow occurs after the image formation, after the charging device 2 and the photosensitive member 1 are stopped and left for a while. That is, when the discharge time due to the image formation on the recording medium S increases and a substance that causes image flow accumulates in a specific portion in the charger 2, if the driving of the charger 2 and the photoreceptor 1 is stopped, the discharge is performed. The product gradually moves to and adheres to the surface of the photoreceptor 1. During this stop, exhaust by the exhaust fan 820 and polishing by the cleaning blade are not performed, so that the amount of adhesion on the surface of the photoreceptor 1 increases with time. Therefore, even when the photosensitive member 1 is driven and polished with the cleaning blade during the next image formation or warming up, the discharge product is not removed in a short time. In addition, it is conceivable to extend the exhaust processing by the exhaust fan 820 after the image formation at the time of stoppage, but this cannot be coped with when the main power supply of the image forming apparatus A is cut off.

  For this reason, in this embodiment, the portion of the charger 2 in which the image flow factor substance is accumulated is specified, and a countermeasure mechanism is provided to prevent image flow. As a result of searching for the range in which the substance that causes image flow is accumulated, the grid electrode 300 is replaced with a new one from a durable product and left to stand overnight. It turned out to be a source of contamination that accumulates substances. Therefore, the charger 2 in the image forming apparatus A according to the present embodiment is provided with a mechanism (hereinafter referred to as a retracting mechanism) for moving the grid electrode 300 away from the photosensitive member 1 after charging is completed to suppress image flow. .

[Configuration of grid electrode retracting mechanism]
The structure of the retracting mechanism of the grid electrode 300 is shown in FIGS. 3, 4, and 5 are a perspective view, a side view, and a front view showing the grid electrode 300 in a normal stretched state (a charged state that is not retracted), and FIGS. 6, 7, and 8. These are a perspective view, a side view, and a front view showing the grid electrode 300 in a retracted state (uncharged state). With reference to these drawings, the configuration of the retracting mechanism of the grid electrode 300 will be described below.

  The retracting mechanism of the grid electrode 300 gives a predetermined urging force in order to keep the distance between the swing electrode 120 meshed with the drive gear 110 that drives the photosensitive member 1 and the grid electrode 300 and the photosensitive member 1 constant. The mesh holding unit 620 that holds the grid electrode 300, the cam 140 that pushes the locking unit 640 that is a part of the mesh holding unit 620 downward, and the idle gear 130 that connects the cam 140 and the swing gear 120. Is done.

  When the mesh holding portion 620 is pressed by the shaft 630 and the engaging portion 640 of the mesh holding portion 620 is pushed downward by the projection 142 of the cam 140, as shown in FIGS. Lean to. Mesh holding portion 620 engages hole 302 at the other end of grid electrode 300 with engaging member 621 (in the direction of arrow B). For this reason, when the mesh holding part 620 is tilted in the direction indicated by the arrow F, the grid electrode 300 is loosened, and the distance between the photoreceptor 1 and the grid electrode 300 is increased.

  On the other hand, when the mesh holding portion 620 is pressed by the shaft 630 and the engaging portion 640 of the mesh holding portion 620 is not pushed downward by the protrusion 142 of the cam 140, the mesh holding portion 620 is shown in FIGS. In this way, it is inclined in the direction of arrow E by a return member (not shown) (for example, an elastic member such as a spring or a plate spring that slides the engaging member 611 in the mesh holding portion 610 described above). For this reason, when the mesh holding unit 620 is tilted in the direction of arrow E, the grid electrode 300 is stretched to hold the distance between the photoreceptor 1 and the grid electrode 300 at a predetermined distance (for example, 1 mm).

  During image formation, the photoreceptor 1 rotates in the direction of the arrow shown in FIG. Meanwhile, the rotating shaft 122 of the rocking gear 120 is pushed upward obliquely by the drive gear 110 as shown by the white arrow in FIGS. For this reason, the oscillating gear 120 is separated from the idle gear 130 without meshing, that is, the oscillating gear 120 is only rotated (idly rotated) by the drive gear 110. Therefore, during image formation (that is, during charging), the mesh holding unit 620 is held by an elastic material or the like in the direction of arrow E as shown in FIGS. As a result, the grid electrode 300 maintains a predetermined distance from the photoreceptor 1.

  After the end of charging, the photosensitive member 1 rotates backward by a predetermined amount in the direction of the arrow shown in FIG. At that time, the rotation shaft 122 of the swing gear 120 is pushed down obliquely downward by the drive gear 110 as shown by the white arrow in FIGS. For this reason, the rocking gear 120 meshes with the idle gear 130. The meshed idle gear 130 transmits the rotational force of the drive gear 110 to the cam 140. That is, the rocking gear 120 is rotated by a predetermined rotation of the drive gear 110 (this predetermined rotation is a rotation that at least the projection 142 pushes down the locking portion 640 as shown in FIG. 6), and the idle gear is rotated. In this state, the cam 140 is rotated via 130. For this reason, after charging is completed, the mesh holding unit 620 is moved in the direction indicated by the arrow F as shown in FIGS.

  As a result, the grid electrode 300 is loosened and cannot maintain a predetermined distance (distance during charging) from the photosensitive member 1, and the distance increases. That is, when charging in image formation is completed, the photosensitive member 1 rotates by a predetermined amount in a direction opposite to that during image formation. As a result, the oscillating gear 120 meshes with the idle gear 130, and the cam 140 is moved by a predetermined displacement amount by the idle gear 130. When the mesh holding unit 620 moves in the direction of arrow F in FIG. 6, the tension of the grid electrode 300 is weakened and the grid electrode 300 is loosened, so that the grid electrode 300 can be moved away from the photoreceptor 1.

  In the present embodiment, as described above, a retracting mechanism for retracting the grid electrode 300 is provided, but this retracting mechanism moves the position of the shield case 800 (the shield case 800 is fixed and does not move). It is also a feature that only the grid electrode 300 is retracted from the photoreceptor 1. After the charging is completed, the shield case 800 is not moved, and the grid electrode 300 is moved away from the photosensitive member 1 to prevent the image flow. In order to obtain such an effect, the charger 2 itself or the grid electrode 300 including the shield case 800 is not moved, but only the grid electrode 300 is retreated, so that a new large retreat space is not required. Also, a large drive source for moving the shield case 800 is not required.

[Operation of Image Forming Apparatus]
The operation of the image forming apparatus A including the charger 2 having the above structure will be described.

  When an image is being formed and the charger 2 is continuously charged, a drive gear 110 that rotates the photoreceptor 1 is driven by a motor (not shown) provided on the rotating shaft 112 as shown in FIGS. 5 is rotated in the direction indicated by 5 (clockwise in FIG. 4). By the rotation of the drive gear 110, the swing gear 120 is pushed upward obliquely (in the direction of the white arrow in FIGS. 3 and 4), and the swing gear 120 and the idle gear 130 are separated from each other. The cam 140 does not rotate.

  Since the cam 140 does not rotate, the mesh holding unit 620 that stretches the grid electrode 300 is in an upright state (a state in the direction of arrow E shown in FIGS. 2, 3, and 5), and the grid electrode 300 is photosensitive A predetermined distance from the body 1 is maintained. For this reason, the surface of the photoreceptor 1 is charged to a desired potential by the charger 2.

  When charging by the charger 2 is completed, the drive gear 110 for rotating the photosensitive member 1 is moved in the direction shown in FIGS. 6 to 8 (in FIG. 7) by a motor (not shown) provided on the rotating shaft 112. Counterclockwise) by a predetermined amount. The rotation of the drive gear 110 causes the swing gear 120 to be pushed down obliquely downward (pressed down in the direction of the white arrow in FIGS. 6 and 7), and the swing gear 120 and the idle gear 130 mesh with each other. The cam 140 rotates via the idle gear 130.

  When the cam 140 rotates, the mesh holding unit 620 that stretches the grid electrode 300 is in an inclined state (in the direction indicated by the arrow F shown in FIGS. 2, 6, and 8), and the grid electrode 300 is being charged. A distance longer than a predetermined distance (distance between the photoreceptor 1 and the grid electrode 300) is maintained. For this reason, it is possible to suppress discharge products from adhering to the photoreceptor 1 and to suppress image defects such as image flow.

[Relationship between distance from grid electrode to photoconductor and image flow]
The relationship between the distance from the grid electrode 300 to the photoreceptor 1 and the image flow when the image forming apparatus A is operated in this way will be described.

  Table 1 shows the result of confirming the image flow when the distance between the grid electrode 300 and the photosensitive member 1 is changed. In Table 1, “◯” indicates no image flow, “Δ” indicates a level where image flow occurs in a halftone image but the image flow is not noticeable in a character pattern, etc., and “×” indicates image flow even in a character pattern. It is a level that occurs. As can be seen from Table 1, it was confirmed that the image flow improved when the distance between the grid electrode 300 and the photosensitive member 1 was increased. Note that the distance when the grid electrode 300 is not retracted is 1 mm.

  Further, in the charger 2 described above, the grid electrode 300 is farthest from the photoconductor 1 at a position facing the central portion of the rotating shaft of the photoconductor 1 (near the center). For this reason, as shown in FIG. 9, if the discharge port 810 is provided in the vicinity of the central portion, the discharge products generated in the charger 2 by the exhaust fan 820 are collected in the vicinity of the central portion having the most resistance to image flow. It is done. For this reason, while accumulation of the discharge product in a non-central part reduces, the generation | occurrence | production can also be suppressed also in a central part. Note that the exhaust fan 820 may be shared with a fan having other functions. In this case, the charger 2 includes up to the discharge port 810 provided in the shield case 800.

  Table 2 shows the result of confirming the image flow when the distance between the grid electrode 300 and the photosensitive member 1 is changed and the position of the exhaust port is changed. As shown in Table 2, it can be seen that the image flow level is improved when the exhaust port is provided in the vicinity of the central portion, rather than when the exhaust port is provided at the end.

  As described above, according to the image forming apparatus A including the charger 2 according to the present embodiment, the voltage applied to the charger 2 is not set so low as to hinder image formation, and image formation is performed. To provide an image forming apparatus capable of suppressing the adhesion of discharge products to the photosensitive member 1 without increasing the size of the device A and without shortening the life of the photosensitive member 1 and thus forming an image as well. Can do.

  In the above-described embodiment, the rotational force transmitted from the driving gear of the photosensitive member 1 to drive the mesh holding unit 620, which is a mechanism that loosens the grid electrode 300 and widens the distance between the grid electrode 300 and the photosensitive member 1. However, the present invention is not limited to this. Other drive sources may be used.

  The embodiment disclosed this time is merely an example, and the present invention is not limited to the embodiment described above. The scope of the present invention is indicated by each claim in the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are intended. Including.

1 is a diagram illustrating an outline of a configuration of a full-color printer which is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the charger in FIG. 1. It is a perspective view (the 1) of the retracting mechanism of the grid electrode in a charger. It is a side view (the 1) of the retracting mechanism of the grid electrode in a charger. It is a front view (the 1) of the retraction mechanism of the grid electrode in a charger. It is a perspective view (the 2) of the retracting mechanism of the grid electrode in a charger. It is a side view (the 2) of the retracting mechanism of the grid electrode in a charger. It is a front view (the 2) of the retracting mechanism of the grid electrode in a charger. FIG. 3 is a front view of the vicinity of a charger including an exhaust fan.

Explanation of symbols

A Printer Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit YC, MC, CC, KC Process cartridge 1 Photoconductor 2 Charger 3 Exposure device 4 Developer 5 Primary transfer roller 6 Cleaning Device 8 Intermediate transfer belt 9 Secondary transfer roller 10 Recording medium storage cassette 11 Medium supply roller 41 Developing roller 81 Drive roller 82 Roller 83 Cleaning device 100, 200 Corona discharge wire 101, 201 Spring-like hook portion 102, 202 Hook portion 110 Drive Gear 112 Rotating shaft 120 Oscillating gear 130 Idle gear 140 Cam 142 Projection part 300 Grid electrode 400 Stabilizing plate 401 Discharge port 510, 520 Holder 511, 512 Pin 521, 522 Conductive locking part 610, 620 Mesh Sandwiching member 611 engages member 630 shaft 640 locking portion 700 varistor 800 shield case 810 outlet 820 exhaust fan

Claims (6)

A charger that charges the surface of an electrostatic latent image carrier that is rotationally driven in an electrophotographic image forming apparatus prior to electrostatic latent image formation, and includes a discharge electrode, a grid electrode, and a shield case. A vessel,
The shield case is a case fixed at a predetermined position, and has an opening that accommodates the discharge electrode and faces the electrostatic latent image carrier,
The grid electrode is disposed in the opening of the shield case, and has a net-plate shape in which both ends in the direction along the rotation axis of the electrostatic latent image carrier are respectively held and stretched by holding units. Yes,
When the charger is charging the surface of the electrostatic latent image carrier, the mesh plate-like grid electrode is stretched, and when not charged, the mesh plate-like grid electrode is loosened toward the shield case. The charger is provided with an adjusting mechanism for adjusting the tension state of the grid electrode.   2. The charger according to claim 1, wherein the adjustment mechanism is configured so that the grid-like grid electrode can be loosened by a driving source that rotationally drives the electrostatic latent image carrier. 3. The adjustment mechanism is
A swing gear that rotates when the electrostatic latent image carrier is driven by the drive source in a direction opposite to the rotation direction during image formation; and the holding unit.
The holding unit is configured such that when the charger does not charge the surface of the electrostatic latent image carrier, the drive source rotates the electrostatic latent image carrier in the reverse rotation direction so that the swing gear is a predetermined amount. 3. The charger according to claim 2, wherein at least one end holding the mesh plate-like grid electrode is configured to approach the other end when rotated.   4. The charging device according to claim 1, further comprising a discharge port that discharges a discharge product provided at a position facing a central portion in a rotation axis direction of the electrostatic latent image carrier. 5. The charger as described.   The charger according to claim 4, further comprising a discharge fan provided at a position corresponding to the discharge port.   The surface of the electrostatic latent image carrier to be rotationally driven is charged by a charger, and the electrostatic latent image carrier charged by the charger is subjected to image exposure to form an electrostatic latent image. An electrophotographic image forming apparatus having at least one image forming unit that develops an image to form a visible toner image, wherein the charger in at least one image forming unit is any one of claims 1 to 5. An image forming apparatus comprising the charger according to claim 1.

Images