JP2005070665A - Corona discharge device,and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continue a stable discharge by sufficiently cleaning an electrode without being damaged with a simple configuration. <P>SOLUTION: The corona discharge device 1 is composed of a plate-like electrode 61 having a plurality of pointed projection parts and cleaning members 63a, 63b arranged so as to be moved relatively to the electrode 61 and capable of cleaning the surface of the electrode 61 by scratching the electrode 61 at the time of movement. Each of the cleaning members 63a, 63b has a plate-like shape, consists of a metallic material of which the thickness is 20-40μm and can clean the electrode 61 by being depressed to the electrode 61 at suitable force at the time of movement. Thus, the electrode 61 is sufficiently cleaned, thereby contnuing the stable discharge. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a corona discharge device including an electrode cleaning member.

  In an image forming apparatus for forming an electrophotographic image such as a copying machine, an electrostatic latent image is formed on the surface of an electrophotographic photosensitive member, the electrostatic latent image is visualized by development, and the visualized image is further recorded on a recording paper or the like. The recorded image is obtained by transferring and fixing the toner. The electrophotographic photosensitive member of the image forming apparatus is uniformly charged by a corona discharge device (also called a main charger) before an electrostatic latent image is formed by exposure.

  Conventionally, for example, a tungsten discharge wire having a diameter of 80 to 90 μm has been used as a discharge electrode of a corona discharge device. Since the discharge device using this discharge wire requires a large current to ensure charging uniformity, a large amount of ozone is generated at the time of discharge, and the electrophotographic photosensitive member and corona are used due to the strong oxidizing power of ozone. There was a problem that the discharge device itself deteriorated.

  One of the prior arts for solving such a problem is that a corona discharge device is formed in a needle shape instead of a wire (see Patent Document 1). In the needle-like electrode, the current value for obtaining the same output is reduced to about a quarter, and accordingly, the amount of ozone generated is also reduced to about a quarter. However, when a needle-like electrode is used, a phenomenon occurs in which silicon adheres to the electrode tip as the discharge is repeated. As the amount of silicon adhering to the tip of the electrode increases, the discharge becomes unstable, and if it continues to be used for charging an electrophotographic photosensitive member with an unstable discharge, an image such as streak stains will appear on the formed image The defect that unevenness is formed occurs.

  Further, as a prior art for solving the problem of silicon adhesion in the needle-like electrode as described above, for example, a sponge roller is pressed against the needle-like electrode to remove it (clean it) (see Patent Document 2). Further, a cleaning member composed of a pair of rollers that are rotatably supported sandwiches the needle electrode from both sides, and removes dirt by moving the cleaning member relative to the needle electrode (Patent Document 3). See).

Japanese Unexamined Patent Publication No. 1-312563 Japanese Utility Model Publication No. 2-75658 Japanese Patent No. 3259515

  However, the above-described prior art has the following problems. In the technique disclosed in Patent Document 2, the sponge roller is caught by the tip of the needle-like electrode and is damaged, and the sponge piece torn off at the time of breakage adheres to the tip of the needle-like electrode and destabilizes the discharge. There is a problem that the tip of the needle-like electrode is deformed by the force applied during the rotational movement of the roller. In the technique disclosed in Patent Document 3, the needle electrode is sandwiched and cleaned by a pair of rollers, so that the tip of the needle electrode can be cleaned without the roller sufficiently contacting the tip of the needle electrode. There is a problem that the case does not exist, and there is a problem that the apparatus becomes complicated because a pressing mechanism for sandwiching the needle electrode from both sides is required.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a corona discharge device and an image forming apparatus including the corona discharge device that can be cleaned sufficiently without damaging the electrodes with a simple structure and can continue stable discharge.

The present invention relates to a corona discharge device used for charging an electrophotographic photosensitive member.
A plate-like electrode having a plurality of sharp projections;
A cleaning member provided to be movable relative to the electrode, and cleaning the surface of the electrode by rubbing the electrode during movement,
The cleaning member is a corona discharge device having a plate shape and made of a metal material having a thickness of 20 to 40 μm.

  Moreover, this invention is characterized by the amount of biting of the sharp protrusion part with respect to a cleaning member being 0.2-0.8 mm.

In the present invention, the cleaning member
The width dimension, which is the dimension of the cleaning member in the direction perpendicular to the direction in which the cleaning member moves and in the direction perpendicular to the direction in which the sharp projection extends, is 3.5 mm or more.

In the present invention, the metal material constituting the cleaning member is stainless steel.
According to another aspect of the invention, there is provided an image forming apparatus comprising the corona discharge device according to any one of the above as a charger.

  According to the present invention, the cleaning member that is provided so as to be relatively movable with respect to the electrode having the sharp protrusion, and that cleans the surface of the electrode by rubbing the electrode during the movement has a thickness within a suitable range. It is made of a metal material. The cleaning member is sufficiently pressed and elastically deformed when rubbing the electrode, and can sufficiently come into contact with the protrusion of the electrode. Therefore, the cleaning member can sufficiently remove dirt without deforming and damaging the tip of the protrusion of the electrode. Can be excluded. Further, since the cleaning member is made of a metal material having excellent strength, when the electrode is rubbed, the cleaning member is not worn and attached to the tip of the protruding portion of the electrode. By cleaning the electrode using such a cleaning member, the sharp projections of the electrode can be kept clean, so that it is possible to prevent the occurrence of discharge unevenness and the occurrence of image defects due to discharge unevenness. Can be prevented. In this way, the corona discharge device is excellent in discharge stability with a simple configuration in which the cleaning member is formed of a plate-shaped metal material having a thickness in a suitable range, and the cleaning member is moved relative to the electrode and rubbed. Can be realized.

  Further, according to the present invention, the amount of biting of the sharp protrusions with respect to the cleaning member is set within an appropriate range, so that it is possible to efficiently clean without deforming the tips of the protrusions of the electrodes. When the amount of biting is small, cleaning is insufficient, and when the amount of biting is large, the wear life of the cleaning member is shortened. This reliably removes the dirt on the protruding portion of the electrode and further improves the discharge stability.

  Further, according to the present invention, the cleaning member is formed so that the width dimension is 3.5 mm or more, and the value per unit area of the force generated when being deformed by being pressed by the electrode can be reduced. The durability life against repeated deformation can be extended.

  According to the present invention, stainless steel is used for the metal material constituting the cleaning member. Stainless steel has excellent strength and moderate elasticity, and it is difficult to oxidize even in an ozone atmosphere generated by discharge, so that the durability of the apparatus can be improved.

  According to the invention, an image forming apparatus includes the corona discharge device according to any one of the above in a charger. As described above, since the corona discharge device having excellent discharge stability is provided as a charger, there is provided an image forming apparatus capable of stably forming an image with good image quality without streak stains and image unevenness due to discharge unevenness. Is done.

  1 is a perspective view showing a simplified configuration of a corona discharge device 1 according to an embodiment of the present invention, FIG. 2 is a front view of the corona discharge device 1 shown in FIG. 1, and FIG. 4 is a side view of the corona discharge device 1 shown in FIG. 4, and FIG. 4 is a schematic cross-sectional view showing the configuration of the image forming apparatus 2 including the corona discharge device 1 shown in FIG.

  An image forming apparatus 2 shown in FIG. 4 is another embodiment of the present invention, and here, a copying machine 2 which is one of the image forming apparatuses is illustrated. First, the configuration and operation of the copying machine 2 provided with the corona discharge device 1 will be described with reference to FIG. The copying machine 2 includes a document feeding unit 3, an image reading unit 4, a paper feeding unit 5, an image forming unit 6, and a fixing unit 7.

  The document feeder 3 places a double-sided automatic document feeder 8 (abbreviated as RADF: Reversing Automatic Document Feeder) for feeding a document to be copied and a document fed from the RADF 8 at a predetermined position. A document table 9 and a document receiving tray 10 are included. The RADF 8 has a predetermined positional relationship with the document table 9 and is supported in an openable / closable state. The RADF 8 feeds the original so that one side of the original is placed at a predetermined position of the original table 9 and opposed to the image reading unit 4, and the image reading on one side is completed. Then, the document is reversely transferred so that the other surface is placed at a predetermined position on the document table 9 and opposed to the image reading unit 4, and when the image reading on the other surface is completed, the document is removed. The document is discharged to the document receiving tray 10. Such document feeding and front / back reversing operations are controlled in relation to the overall operation of the copying machine 2. When only one side of the original is copied, the reverse transfer of the original is not executed.

The image reading unit 4 is disposed below the document table 9, performs an operation of reading an image of the document fed to the document table 9 by the RADF 8, and reciprocally moves in parallel along the lower surface of the document table 9. Second scanning units 11 and 12, an optical lens 13, and a CCD (photoelectric conversion element)
Charge Coupled Device) line sensor 14.

  The first scanning unit 11 includes an exposure lamp 15 that exposes the surface of a document image to be read and a first mirror 16 that deflects a reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 9. While reciprocating at a predetermined scanning speed. The second scanning unit 12 includes second and third mirrors 17 and 18 that further deflect the reflected light image deflected by the first mirror 16 of the first scanning unit 11 in a predetermined direction. And reciprocally move in parallel along the lower surface of the document table 9 while maintaining a constant speed relationship.

  The optical lens 13 reduces the reflected light image deflected by the third mirror 18 of the second scanning unit 12 and forms an image at a predetermined position of the CCD line sensor 14. The CCD line sensor 14 is a three-line color CCD that can read a black-and-white image or a color image and output line data that is color-separated into red (R), green (G), and blue (B) color components. The reflected light image formed by the optical lens 13 is photoelectrically converted in sequence to output an electrical signal. Document image information output as an electrical signal from the CCD line sensor 14 is input to the image forming unit 6.

  The paper feeding unit 5 is disposed at the lowermost part of the copier 2 and has a paper tray 19 on which recording paper P as a recording medium is stacked and separated, and a separation roller that separates and feeds the recording paper P in the paper tray 19 one by one. 20 and a paper feed roller 21, and supplies the recording paper P as a recording medium to the image forming unit 6. The recording paper P separated and supplied one by one from the paper supply unit 5 is transported to the front of the image forming unit 6 by transport rollers 22 provided in various transport paths of the recording paper P, and is provided in front of the image forming unit 6. The sheet feeding timing is controlled by the pair of registration rollers 23 and is supplied to the image forming unit 6.

  The image forming unit 6 is disposed between the image reading unit 4 and the paper feeding unit 5, and includes a laser beam scanner unit 24, an image forming station 25, and a transfer conveyance belt mechanism 26. The transfer / conveying belt mechanism 26 is disposed below the image forming unit 6, and has a driving roller 27, a driven roller 28, an endless belt 29 stretched between the driving roller 27 and the driven roller 28, and a surface of the endless belt 29. An adsorption charger 30 for charging and adsorbing the recording paper P and a static eliminator 31 for separating the recording paper P adsorbed on the endless belt 29 are provided.

  The endless belt 29 is driven in the direction of the arrow 32 by rotation around the axis of the drive roller 27. The recording paper P supplied with timing control by the registration roller 23 is electrostatically attracted to the surface-charged endless belt 29 by the suction charger 30 and conveyed in the direction of the arrow 32 described above. An image is transferred to the recording paper P in the process of being conveyed in the direction of the arrow 32 by the endless belt 29, and the recording paper P on which the image has been transferred is peeled off from the endless belt 29 by the static eliminator 31 and is transferred to the fixing unit 7. It is conveyed. Paper feed timing control by the registration roller 23 is detected by a sensor (not shown) provided in the transport path of the recording paper P in the transport direction, and is executed according to the detection output of the sensor.

  Since the copying machine 2 is a color copying machine, four sets of the laser beam scanner unit 24 and the image forming station 25 are provided corresponding to each color of black, cyan, magenta, and yellow. Each of the laser beam scanner units 24 and the image forming station 25 has a pixel signal corresponding to a black component image of the image original information that the color of toner used for development is different from black, cyan, magenta, and yellow. Since the pixel signal corresponding to the cyan color component image, the pixel signal corresponding to the magenta color component image, and the pixel signal corresponding to the yellow color component image are the same, the configuration is the same. The unit 24 and the image forming station 25 will be described as representative examples, and the description of the other will be omitted. When the laser beam scanner unit 24 and the image forming station 25 corresponding to each color are individually shown, alphabetic suffixes: b (black), c (cyan), m (magenta), y (yellow) This is indicated with

  FIG. 5 is an enlarged view showing the configuration of the black image forming laser beam scanner unit 24b and the image forming station 25b. The laser beam scanner unit 24b deflects a laser beam from the semiconductor laser element (not shown) that emits dot light modulated according to image document information input from the image reading unit 4 and a laser beam from the semiconductor laser element in the main scanning direction. A polygon mirror 33b, an fθ lens 34b, 35b for imaging a laser beam deflected by the polygon mirror 33b on the surface of an electrophotographic photoreceptor 40b (hereinafter simply referred to as a photoreceptor), and reflection mirrors 36b, 37b, 38b; Is provided. The laser beam reflected by the reflecting mirror 38b exposes the surface of the photoreceptor 40b of the image forming station 25b, and forms an electrostatic latent image.

  The image forming station 25b is exposed with a photosensitive member 40b that is rotatably supported in the direction of the arrow F around the axis 39b, and the following equipment arranged along the circumferential surface of the photosensitive member 40b, that is, the laser beam described above. The electrostatic latent image formed on the surface of the photosensitive member 40b by developing the charger 41b for uniformly charging the surface of the photosensitive member 40b and the exposure of the laser beam output from the laser beam scanner unit 24b is developed. A developing device 42b for visualizing the image, a transfer discharge device 43b for transferring the developed image, which is provided opposite to the photoreceptor 40b via the endless belt 29, onto the recording paper P on the endless belt 29, and an electrostatic latent image. And a cleaning unit 44b that removes and collects toner remaining on the surface of the photoreceptor 40b after the developing process. The charger 41b, the developing unit 42b, the transfer discharger 43b, and the cleaning unit 44b are provided in this order from the upstream side to the downstream side in the rotation direction indicated by the arrow F.

  The corona discharge device 1 of the present invention is used for the charger 41b. The charger 41b uniformly charges the surface of the photoreceptor 40b by discharging. The surface of the uniformly charged photoreceptor 40b is exposed by the laser beam from the laser beam scanner unit 24b corresponding to the image document information, and the charged amount of the exposed portion and the charged amount of the unexposed portion are changed. Differences occur and an electrostatic latent image is formed.

  The developing device 42b can freely rotate a developing roller 45b provided to face the photoreceptor 40b, a developer conveying roller 46b that supplies a developer containing toner to the developing roller 45b, a developing roller 45b, and a developer conveying roller 46b. And a casing 47b for accommodating the developer in the internal space. The developer is supplied from the developing roller 45b of the developing device 42b to the surface of the photoreceptor 40b on which the electrostatic latent image is formed, whereby the electrostatic latent image is developed and visualized. The visualized image is transferred to the recording paper P on the endless belt 29 by the transfer discharger 43b as described above.

  Returning to FIG. 4 again, the recording paper P on which the black image is transferred is conveyed in the direction of the arrow 32 while being adsorbed by the endless belt 29, and provided in the following order from the upstream side to the downstream side in the conveyance direction. The cyan, magenta, and yellow laser beam scanner units 24c, 24m, and 24y and the image forming stations 25c, 25m, and 25y are converted into the above-described black image. In the same manner as in, the images are sequentially transferred. In this way, a full color image is formed on the recording paper P. The recording paper P on which the full-color image is formed is peeled off from the endless belt 29 by the static eliminator 31 and fed to the fixing unit 7.

  The fixing unit 7 includes a heating roller 48 that includes a heating unit (not shown), and a pressure roller 49 that is provided to face the heating roller 48 and that is pressed by the heating roller 48 to form a so-called nip portion 50. The recording paper P supplied to the fixing unit 7 is heated and pressurized when passing through the nip part 50, and the developer on the recording paper P is fixed to form a robust image.

  When the recording paper P fixed by the fixing unit 7 forms an image only on one surface, or when the image is formed on the other surface after being reversed after forming the image on one surface, the switching gate 51 operates. The paper is fed upward, and is further discharged to a paper discharge tray 53 by a discharge roller 52. When an image is formed on one surface of the recording paper P and then further on the other surface, the recording paper P is fed downward by the operation of the switching gate 51, and the switchback transport path 54. Then, the image is reversed and then conveyed again to the image forming unit 6. An image is formed on the recording paper P fed to the image forming unit 6 in the same manner as described above.

  Returning to FIGS. 1 to 3, the corona discharge device 1 provided as the charger 41 of the copying machine 2 will be described. The corona discharge device 1 has a plate-like electrode 61 (hereinafter referred to as a needle-like electrode) having a plurality of sharp projections 68, a holding member 62 that holds the needle-like electrode 61, and the needle-like electrode 61. Two cleaning members 63a and 63b which are provided so as to be relatively movable and clean the surface of the needle electrode 61 by rubbing the needle electrode 61 during the movement, and a support member 64 which supports the cleaning members 63a and 63b. And a moving member 65 for moving the cleaning members 63a and 63b and the support member 64, and a shield case 66 for accommodating the needle electrode 61, the holding member 62, the cleaning members 63a and 63b and the support member 64. . The corona discharge device 1 is disposed along the longitudinal direction of the photoconductor 40 in the copying machine 2 while facing the photoconductor 40.

  The acicular electrode 61 is a thin plate member made of stainless steel, for example, and is formed so as to protrude in the short direction from a flat plate portion 67 extending long in one direction and one end surface constituting a side extending in the longitudinal direction of the flat plate portion 67. It is comprised by the sharp-shaped projection part 68 made. Exemplifying the dimensions of the needle electrode 61, the length L2 in the short direction of the flat plate portion 67 is preferably about 10 mm, the length L3 in the protruding direction of the protruding portion 68 is preferably about 2 mm, and the tip of the protruding portion 68 Is preferably about 40 μm, and the pitch TP on which the protrusions 68 are formed is preferably about 2 mm.

  The holding member 62 that holds the needle-like electrode 61 is a member that extends in one direction as in the needle-like electrode 61 and has a reverse T-shaped cross section orthogonal to the longitudinal direction, and is made of, for example, resin. The needle electrode 61 is screwed by a screw member 69 to one side surface of the protruding portion of the holding member 62 in the vicinity of both ends in the longitudinal direction. A voltage of about 5 kV is applied to the needle-like electrode 61 for corona discharge during operation to charge the photoreceptor 40 described above.

  The cleaning members 63a and 63b are made of a metal material having a plate shape, more specifically, a T-shaped planar projection shape, and a thickness t of 20 to 40 μm. As the metal material, phosphor bronze, ordinary steel, stainless steel, or the like can be used. However, since the cleaning members 63a and 63b are used in an ozone atmosphere generated by corona discharge, it is most preferable that the cleaning members 63a and 63b are made of stainless steel from the viewpoint of durability life in consideration of oxidation resistance. Examples of stainless steel include SUS304, which is an austenitic stainless steel defined in Japanese Industrial Standards (JIS) G4305, and SUS430, which is a ferritic stainless steel. Stainless steel may be used.

  Regardless of which stainless steel is used as the cleaning members 63a and 63b, the hardness of the stainless steel should be 115 or more on the Rockwell hardness M scale defined in the American Society for Testing and Materials (ASTM) standard D785. desirable. This is because if the Rockwell hardness is less than 115, the hardness is too soft, so that when the contact is made against the needle-like electrode 61 and rubbed, the cleaning member is undesirably deformed and a cleaning effect cannot be obtained. Even though the hardness of the cleaning members 63a and 63b is high, there is no particular functional problem, so there is no need to set an upper limit, but the upper limit value of Rockwell hardness M scale defined in ASTM standard D785 is 130. Therefore, if an upper limit is provided, it will be 130.

  Next, the reason for limiting the range of the thickness t of the cleaning members 63a and 63b will be described. When the thickness t is less than 20 μm, the deformation when contacting the needle electrode 61 is easy, but the pressing force against the needle electrode 61 obtained as a reaction force accompanying the deformation becomes weak. The adhered dirt cannot be removed sufficiently. If the thickness t exceeds 40 μm, the dirt adhering to the needle electrode 61 can be sufficiently removed, but the rigidity increases and the pressing force against the needle electrode 61 becomes too strong. There is a risk that the tip of the portion 68 may be deformed and damaged. As a result, if the thickness t is out of the proper range, image unevenness due to defective charging may occur, which is not preferable.

  Further, the width dimension w of the cleaning members 63a and 63b in the T-shaped vertical bar portion that is in contact with the needle electrode 61, that is, the direction perpendicular to the direction in which the cleaning members 63a and 63b move and the direction in which the protrusion 68 extends. In contrast, the dimension w of the cleaning members 63a and 63b in the vertical direction is 3.5 mm or more.

  If the width dimension w is less than 3.5 mm, the value per unit area of the force generated when the needle-like electrode 61 is pressed and deformed increases, so that fatigue failure due to repeated deformation is likely to occur, and the durability life is reduced. . By setting the width dimension w to 3.5 mm or more, the value per unit area of the force described above can be reduced and the durability life against repeated deformation can be increased. However, if the width is excessively wide, the rigidity becomes too strong. In order to increase the size of the apparatus, the upper limit is preferably set to about 10 mm.

  Further, the relative arrangement of the cleaning members 63a and 63b and the needle electrode 61 will be described. The cleaning members 63a and 63b and the needle-like electrode 61 are preferably arranged so that the amount of biting d of the protrusion 68 of the needle-like electrode 61 with respect to the cleaning members 63a and 63b is 0.2 to 0.8 mm. . Here, the biting amount d is a state in which the cleaning members 63a and 63b and the protrusion 68 are projected on a virtual plane perpendicular to the direction in which the cleaning members 63a and 63b move relative to the needle electrode 61. The amount of the cleaning members 63a, 63b and the protruding portion 68 is defined as the length overlapping in the extending direction of the protruding portion 68.

  When the biting amount d is less than 0.2 mm, the pressing force against the needle electrode 61 obtained as a reaction force accompanying the deformation of the cleaning members 63a and 63b becomes weak, so that the dirt adhering to the needle electrode 61 is sufficiently removed. I can't. When the biting amount d exceeds 0.8 mm, the dirt adhering to the needle electrode 61 can be sufficiently removed, but the pressing force against the needle electrode 61 obtained as a reaction force accompanying the deformation of the cleaning members 63a and 63b. Is too strong, there is a risk that the tip of the protrusion 68 of the needle electrode 61 may be deformed and damaged. As a result, if the biting amount d is out of the proper range, image unevenness due to defective charging may occur, which is not preferable.

  The support member 64 that supports the cleaning members 63a and 63b is a member having an inverted L shape. The arm portions of the cleaning members 63 a and 63 b having a T shape are attached to the beam-shaped portion of the support member 64. The two cleaning members 63 a and 63 b are provided so as to have a predetermined interval L <b> 1 with respect to the direction of movement relative to the needle electrode 61. The interval L1 is selected such that when one cleaning member 63a contacts the needle electrode 61 and is deformed, the other cleaning member 63b does not hit the deformed cleaning member 63a. It can adjust with the thickness of the beam-shaped part of the supporting member 64 with which it mounts | wears.

  The preferable value of the distance L1 is preferably determined by testing in advance the deformation state of the material used as the cleaning member because the deformation state is different if the material used for the cleaning member is different. When the cleaning members 63a and 63b are made of stainless steel having a thickness t of 30 μm, for example, the interval L1 is selected to be 2 mm. By providing the above-described distance L1 between the two cleaning members 63a and 63b, the deformation of one cleaning member 63a is inhibited by the other cleaning member 63b while rubbing the needle electrode 61. Since the pressing force within a preferable range can be maintained, the tip of the needle electrode 61 can be sufficiently cleaned without being deformed and damaged.

  The shield case 66 is made of, for example, stainless steel, and is a container-like member having an external shape of a rectangular parallelepiped and having an internal space and having an opening on one surface facing the above-described photoreceptor 40. The shield case 66 extends long in the same direction as the needle electrode 61 and has a substantially U-shaped cross section in a direction orthogonal to the longitudinal direction. The holding member 62 described above is attached to the bottom surface 71 of the shield case 66. The end of the columnar portion of the support member 64 is slidably inserted into a groove 73 formed by the inner surface 72 of the shield case 66 and the holding member 62.

  A through hole 74 is formed in the columnar portion of the support member 64 in parallel with the direction in which the needle electrode 61 extends, and a moving member 65 is provided through the through hole 74. Since the moving member 65 is fixed to the support member 64 at a portion inserted through the through hole 74, the support member 64 is pulled into the groove 73 by pulling the moving member 65 in the extending direction of the needle electrode 61. Can be moved in the direction in which the needle electrode 61 extends by being guided by the groove 73. That is, since the cleaning members 63a and 63b supported by the support member 64 move in the extending direction of the needle electrode 61, the cleaning members 63a and 63b are brought into contact with the needle electrode 61 and rubbed as described above. Can do.

  The moving member 65 is a thread-like or wire-like member, extends outward from the shield case 66 through a hole or gap formed in the shield case 66, and is a pulley provided on the outer surface of the shield case 66 or the machine body of the copying machine 2. The end is suspended via 75a and 75b. The ends of the pulleys 75a and 75b and the moving member 65 are omitted in FIGS. The end of the moving member 65 is extended to the outside of the copying machine 2 so that the needle electrode 61 can be cleaned without removing the corona discharge device 1 from the copying machine 2 and without opening the copying machine 2. It is preferable to be able to do so.

  When the cleaning member 63a, 63b is brought into contact with the needle-like electrode 61 by pulling the moving member 65 for cleaning, the pressing force of the cleaning member 63a, 63b against the needle-like electrode 61 becomes 10 gf or more and 30 gf or less. To be adjusted. This adjustment of the pressing force can be performed as follows, for example.

  With weights of various weights prepared, with a weight of each weight suspended from one end of the moving member 65, a spring balance or the like is connected to the cleaning member 63a or 63b, and the cleaning member 63a or 63b is connected. Measure the applied force. A weight having this force in the range of 10 gf to 30 gf is selected in advance, and when the needle electrode 61 is cleaned, the weight selected in advance is suspended from the end of the moving member 65 to obtain a desired weight. It can be cleaned with a pressing force. Further, an electric motor whose rotational torque has been adjusted in advance may be connected to the end of the moving member 65 to obtain a desired pressing force.

  The reason why the pressing force is limited to 10 gf or more and 30 gf or less is as follows. If the pressing force is less than 10 gf, the deposits on the needle electrode 61 cannot be sufficiently removed. If the pressing force exceeds 30 gf, the tip of the protrusion 68 of the needle electrode 61 is deformed and damaged.

  FIG. 6 is a perspective view showing a simplified configuration of a corona discharge device 81 which is a modification of the embodiment of the present invention. The corona discharge device 81 is similar to the corona discharge device 1 of the above-described embodiment, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted in the corona discharge device 81 that the needle electrode 61 is formed so as to be shorter than the length of the holding member 62 in the longitudinal direction. That is, a portion 82 (hereinafter referred to as a retracting portion 82) where the needle-like electrode 61 is not provided is formed.

  In the retracting portion 82, cleaning members 63a and 63b are disposed and accommodated when the needle-like electrode 61 is not used for cleaning, that is, when the corona discharge device 81 is in operation to charge the photoreceptor 40. As described above, the cleaning members 63a and 63b that are not used for cleaning the needle-like electrode 61 are disposed and accommodated in the above-described retracting portion 82 (hereinafter, the disposed and accommodated state is referred to as a retracted state). The complexity of attaching and detaching the cleaning members 63a and 63b to and from the apparatus is eliminated when cleaning is performed and when cleaning is not performed.

  Further, when the cleaning members 63a and 63b are formed of a conductive material such as stainless steel, the discharge from the needle-like electrode 61 to the cleaning members 63a and 63b during corona discharge and the two from the cleaning members 63a and 63b are performed. In order to prevent damage to the photoreceptor 40 or the copying machine 2 and generation of electromagnetic waves due to the subsequent discharge, it is preferable that the separation distance between the cleaning members 63a and 63b in the retracted state and the needle electrode 61 is 5 mm or more.

  7 is a perspective view showing a simplified configuration of a corona discharge device 85, which is another modification of the embodiment of the present invention, and FIG. 8 is a front view of the corona discharge device 85 shown in FIG. The corona discharge device 85 according to the present embodiment is similar to the corona discharge device 81 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

  In the corona discharge device 85, a grid 86 for improving the charging uniformity of the photosensitive member 40 is provided between the needle-like electrode 61 and the photosensitive member 40, and a predetermined voltage is applied to the grid 86. The uniformity of charging to the photoreceptor 40 is improved.

Examples of the present invention will be described below.
A copying machine 2 including the corona discharge device 1 according to the embodiment of the present invention was prepared, and a cleaning test was performed. However, four types of corona discharge devices 1 to which cleaning members made of different materials were attached were prepared. There are four types of materials for the cleaning member used in the corona discharge device 1: polysulfone, polyimide A, polyimide B, and stainless steel (SUS304: abbreviated SUS). Table 1 shows the Rockwell hardness of the four types of materials.

  The cleaning test was conducted as follows. A voltage was applied to the needle-like electrode 61 of the corona discharge device 1, and silicon or the like was attached to the needle-like electrode 61 by aging for 120 hours continuously while controlling the constant current so that the current value was minus (−) 600 μA. Here, aging for 120 hours is copying an image on 200,000 sheets of A4 size recording paper, which is a paper size defined in JIS-P0138.

After aging for 120 hours, in the corona discharge device 1 equipped with cleaning members made of four kinds of materials, the cleaning member was reciprocated once in the extending direction of the needle-like electrode for cleaning. After cleaning, a voltage was applied to the needle electrode, the current value was −600 μA, and the sample image was copied onto one sheet of recording paper. The copied sample image was visually observed to evaluate the noise rank of the image. Further, by visually observing the needle-shaped electrode before and after cleaning, the adhesion of the scraped material to the needle tip, the bending of the needle tip, and the cleaning property of the deposit were evaluated. The evaluation index will be described below.
(A) Noise rank: an index for evaluating the degree of noise appearing in an image. Sample images were visually observed, and those with no image unevenness were evaluated as good (◯), and those with image unevenness were evaluated as defective (×).
(B) Adhering of the scraped material to the needle tip: When the cleaning member is abutted against the needle electrode and rubbed, the cleaning member is shaved and applied to the tip of the protrusion of the needle electrode (referred to as the needle tip). Whether or not it was adhered was determined by visually observing the needle-like electrode before and after cleaning with an magnifying projector. The case where the scraped material did not adhere to the needle tip was evaluated as good (◯), and the case where the scrap was attached to the needle tip was evaluated as poor (×).
(C) Needle tip bend: A cleaning member is brought into contact with the needle-like electrode and rubbed to clean whether or not the needle tip that is the tip of the needle-like electrode protrusion has been deformed by an enlargement projector. Judgment was made by visual observation of the front and rear needle electrodes. The case where the needle tip was not bent was evaluated as good (◯), and the case where the needle tip was bent was evaluated as defective (×).
(D) Adherent cleaning property: After cleaning the needle electrode with a cleaning member, it is determined by visually observing the needle electrode before and after cleaning with an magnifying projector whether or not the needle electrode deposit has been removed. did. The case where the deposits were removed was evaluated as good (◯), and the case where the deposits were not sufficiently removed was evaluated as bad (x).

(Example 1)
In Example 1, the thickness t of the cleaning member is 30 μm, the width dimension w is 5 mm, the biting amount d of the protrusion of the needle electrode into the cleaning member is 0.5 mm, and the needle for reciprocating the cleaning member once A cleaning test was conducted by changing the pressing force on the electrode to 10 and 30 gf.

  The evaluation results by the cleaning test are shown in Table 1. As shown in Table 1, the cleaning member made of SUS, which is a metal material, satisfies the evaluation good (◯) in all the evaluation indexes regardless of whether the pressing force is 10 or 30 gf. This is the case where they abut. The cleaning member made of polyimide B, which is a non-metallic material, also satisfies the evaluation good (◯) in all the evaluation indexes. This is because polyimide B has a Rockwell hardness 115 similar to that of a metallic material. Is.

(Example 2)
Example 2 is the same as Example 1 except that a cleaning member made of phosphor bronze having a thickness of t: 30 μm was added as a test object, and the cleaning member was repeatedly reciprocated in the extending direction of the needle electrode. A cleaning test was conducted. Each time the cleaning member was reciprocated once, the presence or absence of bending of the needle tip and the presence or absence of damage to the cleaning member were visually observed. Either or both of the needle tip bending and the cleaning member breakage occurred, and the number of possible cleanings, which was the number of reciprocations when it was determined that the needle electrode could no longer be cleaned, was determined for each cleaning member. It was evaluated that the greater the number of possible cleanings, the better the durability.

  The evaluation results are shown in Table 2. There is a difference in durability between the metal material and the polymer material, and the metal material SUS and phosphor bronze are more durable than the polymer material polyimide. In addition, among metal materials, it can be seen that SUS is superior in durability to phosphor bronze.

(Example 3)
In Example 3, only SUS is used as the cleaning member, cleaning members made of SUS having various thicknesses are prepared, the width dimension is w: 5 mm, the biting amount is d: 0.5 mm, and the needle electrode of the cleaning member is used. A cleaning test was conducted in the same manner as in Example 2 except that the pressing force was 20 gf. About the cleaning member which consists of SUS of each thickness, the frequency | count of cleaning was calculated | required and durability was evaluated. The results are shown in Table 3. As the thickness of the cleaning member decreases, the cleaning member is more likely to be damaged, and the number of possible cleanings is reduced. On the other hand, if the thickness is too thick, the elasticity is lowered and the rigidity is increased, so that the needle tip is likely to be bent, and the number of possible cleanings is reduced. With the SUS cleaning member having a thickness set in the range of 20 to 40 μm, the number of possible cleanings of 50 times or more was achieved.

Example 4
In Example 4, SUS having a thickness t of 30 μm and a width dimension w of 5 mm was used as the cleaning member, and the same as in Example 3 except that the biting amount d was changed to 0.1 to 0.9 mm. A cleaning test was conducted. For the set value of each biting amount d, the number of cleanings was determined and the durability was evaluated. The results are shown in Table 4. The amount of biting d is optimally 0.5 mm, and as it becomes smaller, the cleaning property decreases, and as it becomes larger, the tip of the needle tends to be bent. When the amount of biting d was set in the range of 0.2 to 0.8 mm, the number of possible cleanings of 30 times or more was achieved.

(Example 5)
In Example 5, a cleaning test was performed in the same manner as in Example 3 except that SUS having a thickness t of 30 μm was used as the cleaning member and the width dimension w was changed to 2.5 to 5.0 mm. About each width dimension w, the frequency | count of cleaning was calculated | required and durability was evaluated.

  The results are shown in Table 5. If the width dimension w of the cleaning member is less than 3.5 mm, the number of cleanable times until cleaning becomes impossible due to damage to the cleaning member is small, and the durability is poor. When the thickness is 3.5 mm or more, the cleaning member is still damaged, but the number of cleanings is 50 times or more, and excellent durability is exhibited. By setting the width w of the cleaning member to 3.5 mm or more, the value per unit area of the force generated when the needle-shaped electrode is deformed by being pressed can be reduced, so that the fatigue life against repeated bending deformation can be reduced. It seems to be longer and improve durability.

  As described above, in the present embodiment, the image forming apparatus is the copying machine 2, but is not limited to this, and is a laser printer that forms an image according to image information given from a computer or the like. May be. The laser beam scanner unit 24 scans the laser beam to expose the photoconductor 40 and optically writes image information on the photoconductor 40. However, the present invention is not limited to this, and instead of the laser beam scanner unit 24, An LED head composed of a light emitting diode (LED) array and an imaging lens may be used as the writing optical system. The LED head is smaller in size than the laser beam scanner unit, and has no moving parts and is silent. Therefore, the LED head is suitably used for an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units. be able to.

It is a perspective view which simplifies and shows the structure of the corona discharge apparatus 1 which is one Embodiment of this invention. It is a front view of the corona discharge apparatus 1 shown in FIG. It is a side view of the corona discharge apparatus 1 shown in FIG. It is a schematic sectional drawing which shows the structure of the image forming apparatus 2 provided with the corona discharge apparatus 1 shown in FIG. FIG. 3 is an enlarged view showing configurations of a black image forming laser beam scanner unit 24b and an image forming station 25b. It is a perspective view which simplifies and shows the structure of the corona discharge apparatus 81 which is a modification of embodiment of this invention. It is a perspective view which simplifies and shows the structure of the corona discharge apparatus 85 which is another modification of embodiment of this invention. It is a front view of the corona discharge apparatus 85 shown in FIG.

Explanation of symbols

1, 81, 85 Corona discharge device 2 Copying machine 3 Document feeding unit 4 Image reading unit 5 Paper feeding unit 6 Image forming unit 7 Fixing unit 61 Needle electrode 62 Holding member 63 Cleaning member 64 Supporting member 65 Moving member 66 Shield Case 82 Retractor 86 Grid

Claims (5)

In a corona discharge device used for charging an electrophotographic photosensitive member,
A plate-like electrode having a plurality of sharp projections;
A cleaning member provided to be movable relative to the electrode, and cleaning the surface of the electrode by rubbing the electrode during movement,
Cleaning member
A corona discharge device having a plate shape and made of a metal material having a thickness of 20 to 40 μm. The amount of biting of the sharp protrusion on the cleaning member is
The corona discharge device according to claim 1, wherein the corona discharge device is 0.2 to 0.8 mm. Cleaning member
The width dimension, which is the dimension of the cleaning member in the direction perpendicular to the direction in which the cleaning member moves and in the direction perpendicular to the direction in which the sharp protrusion extends, is 3.5 mm or more. 2. The corona discharge device according to 2.   The corona discharge device according to claim 1, wherein the metal material forming the cleaning member is stainless steel.   An image forming apparatus comprising the corona discharge device according to claim 1 as a charger.

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