JP2009020265A - Corona charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corona charging device designed so that uniform chargeability may be obtained and high speed chargeability may be improved, and to provide an image forming apparatus having the corona charging device. <P>SOLUTION: The corona discharging device 2 includes: a case 53 that is disposed close to a body 1, 11 to be charged, the surface of which is moved, and that has an opening facing the body 1, 11 to be charged; a discharging electrode 52 that is disposed in the case 53 and used to generate equal quantities of positive polarity ion and negative polarity ion by applying a voltage thereto; and a charging potential control means for controlling so that the charging potential of the body 1, 11 to be charged has a prescribed potential. In the corona charging device 2, an upstream discharging electrode 51 is disposed within the case 53 located upstream of the charging electrode 52 in the moving direction of the surface of the body 1, 11 to be charged. The upstream side discharge electrode 51 generates positive polarity ions and negative polarity ions by applying voltage thereto, and generates ions of the same polarity as the polarity used to charge the body 1, 11 to be charged, more than ions of the reverse polarity to the polarity used to charge the body 1, 11 to be charged. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and a corona charging device used therefor.

  As one of corona charging devices, corotron charging devices have been known for a long time. The corotron charging device is composed of a tungsten wire having a diameter of about 50 μm suspended as a corona electrode in a substantially central portion of a metal case made of aluminum or the like formed in a cylindrical or rectangular tube shape having an open portion. In the corotron charging device, a so-called corona discharge is generated between a metal case to which a DC voltage or ground (0 V) is applied and a corona electrode to which a voltage is applied. The surface of the object to be charged can be charged by arranging the object to be charged so as to face the open part of the metal case and supplying ions generated by corona discharge to the object to be charged. Such a corotron charging device has the advantage that the configuration of the device is simple and inexpensive. However, in the case of a DC corotron charging device in which a DC voltage is applied to the corona electrode, potential fluctuations occur due to temperature and humidity changes in the ambient environment. For this reason, it is difficult to uniformly charge the object to be charged to a target potential.

  An AC-type corotron charging device has been known for a long time in order to eliminate the drawbacks of the above-described DC-type corotron charging device. In the AC-type corotron charging device, an AC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage is applied to a corona electrode, thereby suppressing potential fluctuations due to temperature and humidity changes and charging a charged object to a target potential.

  In general, in an AC type corotron charging device, if the absolute value of the AC voltage applied to the corona electrode is the same, the negative discharge current is larger than the positive discharge current. In other words, negative ions are more positive than positive ions. Many are known to occur. For this reason, the balance between the negative discharge current and the positive discharge current is changed by superimposing the DC voltage on the AC voltage, and adjustment is performed so that the charged object has a target charging potential. However, since the ratio at which the negative discharge current is larger than the positive discharge current varies depending on the contamination of the corona electrode with time, there is a problem in that it cannot always be controlled to the same charging potential even under the same voltage condition.

  Therefore, as a corona charging device that uniformly charges the object to be charged, an AC voltage is applied to the corona electrode via a capacitor, and the same potential as the potential to charge the object to be charged to a predetermined charging potential in a metal case surrounding the corona electrode. A corona charging device that applies a direct current voltage is proposed (Patent Document 1 and Patent Document 2). In this corona charging device, by applying an AC voltage to the corona electrode through the capacitor, the amount of current that can flow is limited by the capacitance of the capacitor, so the positive discharge current and the negative discharge current are equivalent. The same amount of positive ions and negative ions can be generated from the corona electrode. Among the positive and negative ions generated from the corona electrode, ions having the opposite polarity to the DC voltage applied to the metal case move to the metal case, and ions having the same polarity as the DC voltage applied to the metal case are charged. Move to the body. When the object to be charged is charged by the ions having the same polarity and the object to be charged and the metal case have the same potential, the equilibrium between the positive ion and the negative ion generated from the corona electrode is apparently stopped. . In this way, the charged body can be charged to a potential equal to the voltage applied to the metal case, so that the charged body can be uniformly charged at a predetermined charging potential.

JP 54-108636 A Japanese Patent Laid-Open No. 55-117162 Japanese Patent No. 2098675 Japanese Patent No. 3646278 Japanese Patent No. 3385008

  However, in the AC type corona charging device, positive ions and negative ions are alternately generated, so that the charging speed is slower than that in the DC type corona charging device. The charging speed is how long it can be charged to the target potential. Thus, when the charging speed is slow, there arises a problem that charging to the target charging potential is impossible when the surface movement speed of the object to be charged is high.

  Here, an image forming apparatus such as a color image copying machine or a printer using an electrophotographic process that employs a corona charging device as a charging means for a photoreceptor will be described. As one of the color image forming apparatuses, a charging device, an exposure unit using an exposure device, a multi-color developing device, a transfer device, and a cleaning device are arranged around the photoconductor to perform charging, exposure, and development processes for each color. By repeating a plurality of times, a toner image of a plurality of colors is formed on the same area of the photosensitive member, and then transferred onto a transfer sheet and fixed to obtain a color image. Various image forming apparatuses are known (for example, Patent Document 3, Patent Document 4, and Patent Document 5). The color superimposing method on the photoconductor is a method that contributes to space saving and resource saving because there is only one photoconductor and no intermediate transfer member is used. Among them, the one disclosed in Patent Document 4 is provided with a charging device, an exposure unit, and a developing device for each color around the photoconductor, and the color on the photoconductor is overlapped without rotating the photoconductor a plurality of times. This is a useful image forming apparatus that enables high-speed image formation without reducing the speed.

  Further, in the color superimposing method on the photoconductor, the toner image already formed on the photoconductor is not disturbed during the developing process of the toner image to be superposed later. A non-contact developing type developing device is used in which the photosensitive member is opposed to the photosensitive member in a non-contact manner. Even if such a non-contact developing device is adopted, the amount of toner to be overlaid from above is reduced due to the influence of the toner image already formed on the photoreceptor, and there is a problem that the amount of overlapped toner is reduced. appear. One possible cause is that the post-exposure potential does not decrease in the same way as the non-toner adhesion region due to the amount of charge of the toner layer already formed on the photoreceptor. . With respect to this problem, the use of a corona charging device having a configuration as described in Patent Document 1 can suppress a decrease in the overlap toner adhesion amount. In other words, the toner image already formed on the photoconductor can be neutralized while the potential of the toner layer and non-toner adhesion area on the photoconductor can be made equal to the DC voltage applied to the metal case. This is because the rear potential can be lowered in the same manner in the toner layer and the non-toner adhesion region. However, as described above, since the AC-type corona charging device has a low charging speed, in the case of performing high-speed image formation like the image forming device described in Patent Document 4, the toner layer and the non-toner adhesion region are aimed. There is a risk that the potential cannot be made.

  The present invention has been made in view of the above problems. The object of the present invention is to provide a corona charging device that has uniform charging properties and improved high-speed charging properties, and an image including the corona charging device. A forming apparatus is provided.

In order to achieve the above object, the invention of claim 1 is provided in a case that is close to a charged body that moves on the surface and that has an opening on the side facing the charged body, and is disposed inside the case. Corona charging provided with a discharge electrode that generates equal amounts of positive and negative ions by applying a voltage, and charging potential control means for controlling the charged potential of the charged body to a predetermined potential In the apparatus, a polarity is applied to the case where the charged object surface moves upstream of the discharge electrode to generate positive and negative ions by applying a voltage, and to charge the charged object. And an upstream discharge electrode for generating more ions having the same polarity as ions having the opposite polarity to the polarity to be charged.
Further, the invention of claim 2 is the corona charging device according to claim 1, wherein the discharge voltage is applied to the discharge electrode via a capacitor, and the upstream discharge electrode is connected to the AC voltage or DC voltage. And a second voltage applying means for applying an alternating voltage on which is superimposed.
Further, the invention of claim 3 is the corona charging device of claim 1, further comprising voltage applying means for applying an alternating voltage or an alternating voltage superimposed with a direct voltage to the discharge electrode and the upstream discharge electrode. The voltage applying means applies voltage to the discharge electrode via a capacitor and applies voltage directly to the upstream discharge electrode.
According to a fourth aspect of the present invention, in the corona charging device according to the first, second, or third aspect, the charging potential control means is a grid electrode, and the grid electrode is provided between the discharge electrode and the body to be charged. It is characterized by this.
According to a fifth aspect of the present invention, the image carrier, one or more charging means for charging the image carrier, and the image carrier charged by the charging means are exposed to expose the latent image for each color. A latent image forming means for forming an image; and a plurality of developing means for visualizing the latent image formed on the image carrier with toners of different colors. A latent image is formed on the image carrier by exposing the image carrier to the latent image, and the developing unit develops the latent image on the single image carrier. In the image forming apparatus for sequentially forming toner images of respective colors to form color toner images, the corona charging device according to claim 1, 2, 3 or 4 is used as the charging means.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the latent image forming means exposes a non-image portion on the image carrier charged by the charging means to expose a latent image for each color. The plurality of developing means develops a latent image of a corresponding color with toner having a polarity opposite to the charging polarity with which the charging means charges the image carrier. It is what.
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the developing means is a toner carrying the toner, which is disposed so as to face the image carrier in a non-contact manner in the development area. And a plurality of electrodes provided on the toner carrier so as to be along the surface of the toner carrier and insulated from each other, the plurality of electrodes each having a relative polarity direction of an applied voltage. Are different from each other in the plurality of adjacent electrodes, and have a hopping electric field generating means for hopping the toner.
The invention according to claim 8 is the image forming apparatus according to claim 7, wherein the toner carrier moves the toner carried on the surface of the toner carrier by moving the surface of the toner carrier. It is a surface moving member conveyed to a development area.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the hopping electric field generating means conveys the toner to the development area while hopping the toner carried on the surface of the toner carrying member. A traveling wave electric field for generating the electric field is generated on the surface of the toner carrier.

  In the present invention, first, the charged body is charged to the above-mentioned polarity by ions having the same polarity as the charged polarity generated from the upstream discharge electrode. Then, the charged potential of the charged body is controlled by the charging potential control means while supplying ions to the charged body from the discharge electrode located downstream of the upstream discharge electrode in the moving direction of the charged body surface. The body is uniformly charged to a predetermined charging potential. In other words, the ions generated from the discharge electrode are supplied to the charged body charged in advance with the polarity generated by the ions generated from the upstream discharge electrode to charge the charged body to a predetermined charging potential. As a result, supply of ions generated from the discharge electrode necessary for setting the charged body to a predetermined charging potential to the charged body is possible, compared to the case where the charged body is not charged in advance to the polarity to be charged. The amount is small. Therefore, the charged object can be uniformly charged to a predetermined charging potential in a shorter time than the configuration in which the upstream discharge electrode is not provided.

  As described above, according to the present invention, there are excellent effects that uniform chargeability can be obtained and high-speed chargeability can be improved.

[Embodiment 1]
Hereinafter, an embodiment in which the present invention is applied to a printer as an image forming apparatus will be described. First, the configuration and operation of the printer according to this embodiment will be described.
FIG. 2 is a schematic configuration diagram of the entire printer according to the present embodiment. An image forming unit is provided at the center of the main body of the image forming apparatus, and the image forming unit includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, there are a corona charging device 2 and a developing device 4 for forming toner images of yellow (Y), magenta (M), cyan (C), and black (Bk) colors. Four sets are arranged counterclockwise. Further, an exposure device 5 for irradiating the photosensitive drum 1 with the laser light L is provided on the right side of the device, and a latent image for each color is formed in an exposure portion between each corona charging device 2 and each developing device 4. The laser beam L is irradiated. That is, corona charging device 2Y for yellow (Y), exposure unit 3Y, developing device 4Y, corona charging device 2M for magenta (M), exposure unit 3M, developing device 4M, corona charging device 2C for cyan (C). The exposure unit 3C, the developing device 4C, the black (Bk) corona charging device 2Bk, the exposure unit 3Bk, and the developing device 4Bk are arranged in this order. In addition, a transfer belt device 9 and a cleaning device 14 are provided around the downstream photosensitive drum 1. Note that the image forming unit of the present embodiment is a process cartridge that is integrated with the photoconductor 1, the corona charging device 2, the developing device 4, and the cleaning device 14, and is detachable from the apparatus main body. The configuration as the process cartridge is not limited to the configuration as in the present embodiment, and the image forming unit may not be a process cartridge.

  For the corona charging devices 2Y, 2M, 2C, and 2Bk, the exposure units 3Y, 3M, 3C, and 3Bk, and the developing devices 4Y, 4M, 4C, and 4Bk, the parts with the same configuration and operation are subscripts Y, M, and C. , Bk is omitted for explanation.

  The exposure device 5 has an integrated unit configuration that radiates laser light L to the photosensitive drum 1 in four radial positions. The exposure device 5 irradiates the exposure unit 3 on the uniformly charged photosensitive drum 1 with laser light L based on the image data of each color, thereby forming a latent image of each color. In addition, the exposure apparatus 5 may be comprised from the four bodies unitized for every color, or may be comprised from each LED array.

  The developing device 4 includes a toner carrying roller 61 that is provided at a position facing the photoconductive drum 1 and electrostatically carries the toner and conveys the toner to the developing area of the photoconductive drum 1.

The transfer belt device 9 includes a transfer belt 13, a driving roller 10 that stretches the transfer belt 13, a driven roller 8, and a transfer roller 12. A transfer roller 12 is disposed inside the transfer belt 13 in a region where the transfer belt 13 is in contact with the circumferential surface of the photosensitive drum 1, and a transfer area in which the toner image on the photosensitive drum 1 is transferred onto a recording sheet carried by the transfer belt 13. Form. The transfer belt 13 is an endless belt. This belt has a volume resistance of 10 ⁸ to 10 ¹² [Ω · cm] and a thickness of 0.5 to 2.0 [mm] made of silicon rubber or urethane rubber, and for preventing toner filming. It is a rubber belt having a two-layer structure of a semiconductive surface layer of fluorine coating having a thickness of 5 to 50 [μm]. Instead of the rubber-like substrate, a semiconductive polyester having a thickness of 0.1 to 0.5 [mm], polystyrene, polyethylene, polyethylene terephthalate, or the like can also be used. The transfer belt 13 is provided with a belt cleaning device (not shown) for cleaning the belt surface.

  The cleaning device 14 includes a cleaning blade 15 and a fur brush 16. Note that the cleaning blade 15 alone may be used.

  A fixing device 18 is disposed downstream of the transfer belt device 9 with respect to the conveyance direction of the recording paper. The fixing device 18 includes an endless fixing belt 19, two rollers that support the fixing belt 19, a tension roller 20, and a pressure roller that is in pressure contact with the fixing belt 19.

  In addition, a paper feed cassette 31 that stores recording paper as a transfer material, and a paper feed roller 32 that feeds the recording paper from the paper feed cassette 31 and a feed roller 33 are disposed at the lower part of the image forming apparatus main body. A conveyance roller pair 34 and a registration roller pair 35 are provided on the recording paper conveyance path to the transfer belt 13. A paper discharge roller 27 that discharges to a recording paper stack provided on the main body in the recording paper conveyance path after the fixing device 18, a reverse roller 28 in the double-sided printing path, and a reverse path to the registration roller pair 35. Is provided with three pairs of conveying rollers. Further, a manual paper feed unit is provided on the left side of the main body, and a pickup roller 29 and a feed roller for feeding and transporting recording paper are disposed.

Next, the operation of the image forming apparatus having the above configuration will be described.
The original image is temporarily stored as an image signal for each color of Y, M, C, and Bk by reading an image read by an image sensor of an image reading device (not shown) separate from the present device or an image edited by a computer. Is stored and stored. At the start of image recording, the photosensitive drum drive motor (not shown) is started to rotate the photosensitive drum 1 counterclockwise, and at the same time, application of potential is started by the charging action of the Y corona charging device 2Y. After the photosensitive drum 1 is granted the potential, the first color signal or yellow by the laser beam L _Y emitted from the exposure device 5 exposure based on the electrical signal corresponding to the image signal is started in the drum (Y) A latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface by rotational scanning. The latent image for Y is developed in a non-contact manner by the toner conveyed to the portion facing the photosensitive drum 1 by the toner carrying roller 61 of the developing device 4Y, and a yellow (Y) toner image is formed on the photosensitive drum 1. Is formed.

Then, on the photosensitive drum 1 the toner image of the yellow (Y), is assigned the potential by the charging action of the M corona charging device 2M, the second color by the laser beam L _M emitted from the exposure device 5 An exposure is performed with an electric signal corresponding to the signal, that is, the magenta (M) image signal, and a latent image corresponding to the magenta (M) image of the original image is formed. The latent image for M is developed in a non-contact manner by the toner conveyed to the portion facing the photosensitive drum 1 by the toner carrying roller 61 of the developing device 4M, and magenta on the yellow (Y) toner image. The toner images (M) are sequentially superimposed and formed. C corona charging device 2C by a similar process, the toner image of cyan (C) corresponding to the third color signal by exposure and development apparatus 4C according to the laser light L _C from the exposure device 5 is also a corona charging device 2Bk A black (Bk) toner image corresponding to the fourth color signal is sequentially superimposed and formed by the exposure and developing device 4Bk from the exposure device 5 with the laser beam _LBk , and within one rotation of the photosensitive drum 1. A color toner image is formed on the peripheral surface.

  On the other hand, the recording paper is carried out from the paper feed cassette 31 by the operation of the paper feed roller 32, the feed roller 33, and the transport roller pair 34 and transported to the resist roller pair 35, and is synchronized with the transport of the color toner image on the photosensitive drum 1. Then, the sheet is fed to the transfer area of the transfer belt 13. In the transferred recording sheet, a color toner image is sequentially transferred onto the recording sheet by applying a bias voltage having a polarity opposite to that of the toner by the transfer roller 12 in the transfer area.

  After the transfer, the transfer residual toner on the photosensitive drum 1 is cleaned by the cleaning device 14. For cleaning, first, the residual toner is peeled off from the photosensitive drum 1 by the fur brush 16, and then completely scraped off by the cleaning blade 15 downstream thereof. The cleaned toner is sent by a cleaning screw 17 to a waste toner bottle (not shown).

  Further, when the recording sheet that has received the transfer of the color toner image is electrostatically attached to the transfer belt 13 and conveyed to the drive roller 10, the leading end of the recording sheet is separated from the transfer belt 13 by the curvature and is transferred to the fixing device 18. The sheet is conveyed, nipped and conveyed between the fixing belt 19 and the pressure roller, heated, fused with toner, and then discharged to the apparatus stack unit 26 via the sheet discharge roller 28.

  In the case of duplex printing, the recording paper is conveyed to the reverse roller 28 side and is sent again to the registration roller 25 by the reverse rotation of the reverse roller 28. Then, in synchronization with the color toner image formed on the photosensitive drum 1, it is sent to the nip portion of the transfer belt 13, transferred to the back surface of the recording paper, passes through the fixing device 18 again, and is discharged to the stack portion 26. Is done.

[Example 1]
FIG. 1 is a schematic configuration diagram of a corona charging device 2 employed in the full-color image forming apparatus according to the present embodiment. The corona charging device 2 of the present embodiment includes two corona electrodes, a shield 53 (metal case), a capacitor 54, and two high-voltage power supplies.

  The two corona electrodes are 60 [μm] diameter wires made of tungsten. An AC voltage or an AC voltage superimposed with a DC voltage is applied to the corona electrode from a high voltage power supply 55. The shield 53 is made by processing a stainless steel plate having a thickness of 1 mm, and is disposed so as to surround the corona electrode. The side of the shield 53 facing the photosensitive drum 1 is open. The material constituting the shield 53 may be any material as long as it has conductivity, but stainless steel is adopted from the viewpoint of ozone resistance. In FIG. 1, the two corona electrodes are partitioned by the shield 53, but in some cases, the two corona electrodes may be opened as shown in FIG. 3. A DC voltage is applied to the shield 53 from a high voltage power source 56.

  FIG. 4 shows the dimensions of the corona charging device 2 of this embodiment. The distance between the corona electrode and the shield 53 is [4 mm]. The distance from the corona electrode to the opening of the shield 53 is 3 [mm], and the distance from the opening of the shield 53 to the surface of the photosensitive drum is 2 [mm], that is, the distance from the corona electrode to the surface of the photosensitive drum is 5 [mm]. ]. Further, the length of the corona electrode and the shield 53 surrounding it in the direction not shown in FIG. 4 is 330 [mm].

  The corona charging device 2 of this embodiment has a high charging speed and excellent charge potential controllability. The principle will be described below.

  When an alternating voltage is applied to the corona electrode, both negative and positive ions are generated by the discharge. However, as described in the literature (electrophotographic process technology p. 54, supervised by Masahiko Itaya, Trikeps, 1992), since negative discharge is stronger when negative and positive are the same voltage, the corona electrode When an AC voltage is applied to the photosensitive drum 1 to charge the photosensitive drum 1, the photosensitive drum 1 is negatively charged.

  Therefore, by superimposing the DC voltage on the AC voltage, the balance between the negative discharge and the positive discharge can be changed to adjust the photosensitive drum 1 to the target charging potential. However, since the ratio of negative discharge is higher depending on various conditions such as temperature and humidity and the contamination of the corona electrode over time, there is a problem that the same charging potential cannot always be controlled even under the same voltage condition. .

  Further, in the case of applying a DC voltage to the corona electrode via the capacitor 54 and applying a DC voltage to the shield 53, the charged object can be charged to a potential substantially equal to the bias applied to the shield 53. . Since a direct current does not flow to the corona electrode because it is connected to the capacitor 54, the same amount of positive and negative ions is always generated without depending on various conditions such as temperature and humidity and the contamination of the corona electrode over time. I will let you. Ions having the opposite polarity to the DC voltage applied to the shield 53 arrived, ions having the same polarity as the DC voltage applied to the shield 53 reached the object to be charged, and the object to be charged and the shield 53 became the same potential. Sometimes the movement of positive and negative ions stops. Because of this principle, the charging potential can always be controlled to a target value. However, this method has the disadvantage that the charging speed is slow because only equal amounts of positive and negative ions are generated alternately. The charging speed is how long it can be charged to the target potential. Therefore, when the moving speed of the photosensitive drum 1 is high or when the film thickness of the photosensitive drum 1 becomes thin, there is a problem that it becomes impossible to charge to a target charging potential.

  In this embodiment, an AC voltage or an AC voltage superimposed with a DC voltage is output from the high voltage 1. Since a voltage is directly applied to the upstream corona electrode 51 in the rotation direction of the photosensitive drum, charging can be performed at a high speed by generating a large number of ions having a polarity on the charging side of the photosensitive drum 1. When the photosensitive drum 1 is charged negatively, the negative discharge is originally stronger, so that the DC voltage may not be superimposed depending on the case. When the photosensitive drum 1 is charged positively, a large DC voltage must be superimposed to compensate that the positive discharge is weaker than the negative discharge.

  The surface potential of the photosensitive drum after passing through the corona electrode 51 is charged to be larger than the target charging potential because the polarity ion generation amount on the side to charge the photosensitive drum 1 is increased to increase the charging speed. Sometimes.

  For this reason, in this embodiment, the charging potential is controlled by the corona electrode 52. Specifically, an AC voltage or a DC voltage superimposed with a DC voltage is applied to the corona electrode 52 from a high-voltage power supply 55 via a capacitor 54. Since the DC voltage is cut by the capacitor 54, positive and negative ions are applied. As described above, the charged potential on the surface of the photosensitive drum can be converged to a potential equal to the DC voltage applied to the shield 53 from the high-voltage power source 56.

  Therefore, if the surface potential of the photosensitive drum after passing through the corona electrode 51 is larger than the target charging potential, the photosensitive drum 1 can be neutralized to obtain the target charging potential. If the surface potential of the photosensitive drum after passing through the corona electrode 51 is smaller than the target charging potential, the photosensitive drum 1 can be further charged to obtain the target charging potential. In this way, the charging potential of the photosensitive drum 1 can always be controlled to the DC voltage applied to the shield 53.

  Based on the above principle, the present invention is a system having a large charging speed and excellent controllability of the charging potential. Furthermore, only two high-voltage power supplies are required as in the past, such as the high-voltage power supply 55 applied to the corona electrode 51 and the corona electrode 52 and the high-voltage power supply 56 applied to the shield 53, while having such a capability. is there. Naturally, as shown in FIG. 5, a high voltage power source 59 that applies an AC voltage or an AC voltage on which a DC voltage is superimposed on the corona electrode 51, a high voltage power source 58 that applies an AC voltage to the corona electrode 52 via a capacitor, Even when three high-voltage power sources are used, such as the high-voltage power source 56 that applies a DC voltage to the shield 53, the same effect as described above can be obtained.

[Modification]
Further, as shown in FIG. 6, a grid 57 electrode may be provided between the corona electrode 52 and the surface of the photosensitive drum. The grid 57 electrode is a metal electrode that is meshed. For example, a stainless steel plate having a thickness of 0.1 [mm] meshed at a pitch of 1 [mm] by edging is used. The grid 57 electrode is electrically connected to the shield 53 electrode, and a DC voltage is also applied from the high voltage power source 56. Note that a DC voltage may be applied to the grid 57 electrode from another high-voltage power supply.

  When the grid 57 electrode is provided, the charging potential can be accurately controlled by a target value. Therefore, if there is a problem in the uniformity of the charged potential, this can be solved.

[Comparative Experiment 1]
[Comparative Example 1]
A corona charging device 2 of Comparative Example 1 is shown in FIG. The distance between the corona electrode and the shield 53 is 8 [mm]. The distance from the corona electrode to the opening of the shield 53 is 5 [mm], and the distance from the opening of the shield 53 to the surface of the photosensitive drum is 2 [mm], that is, the distance from the corona electrode to the surface of the photosensitive drum is 7 [mm]. ]. An AC voltage is applied to the corona electrode from a high voltage power supply 55 via a capacitor 54, and a DC voltage is applied to the shield 53 from a high voltage power supply 56.

<Negative charging>
The charging speed can be evaluated by the characteristic of how far the photosensitive drum 1 can be charged to the target charging potential as the moving speed increases.

  The corona charging device 2 of Example 1 or Comparative Example 1 is arranged around the photosensitive drum 1 (photosensitive member film thickness = 25 [μm]), and the surface of the photosensitive drum 1 is charged. Then, a surface potential meter (surface potential meter Model 344 manufactured by Trek) is disposed at a position of 30 [mm] on the downstream side in the rotation direction of the photosensitive drum, and the charged potential of the photosensitive drum 1 is measured. Then, the photosensitive drum moving speed is changed from 50 [mm / sec] to 400 [mm / sec]. The result is shown in FIG.

  The condition of Comparative Example 1 is that the high voltage power supply 55 outputs an AC voltage with a peak-to-peak voltage of 12 [kV] and a frequency of 2 [kHz], and the high voltage power supply 56 outputs a DC voltage of −500 [V]. The capacitor 54 is 1000 [pF].

  The conditions of the first embodiment are as follows: a high voltage power supply 55 outputs a DC voltage of −500 [V] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]; Output a DC voltage of −500 [V], and a capacitor 54 of 1000 [pF] was used.

  From FIG. 8, in the case of the comparative example 1, as the photosensitive drum moving speed increases, the target charging potential of −500 [V] cannot be charged. On the other hand, in the case of Example 1, it can be seen that even if the photosensitive drum moving speed is increased, it does not deviate much from the target charged potential of −500 [V]. That is, it can be seen that the charging speed is high.

<For positive charging>
FIG. 9 shows the result when the photosensitive drum 1 is positively charged in an experiment similar to that of the negative charging.

  The conditions of Comparative Example 1 are that the high voltage power supply 55 outputs an AC voltage with a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz], and the high voltage power supply 56 outputs a DC voltage of 500 [V], The capacitor 54 is 1000 [pF].

  The condition of the first embodiment is that the high-voltage power supply 55 outputs a DC voltage of 1.5 [kV] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]. Output a DC voltage of 500 [V], and a capacitor 54 of 1000 [pF] was used.

  From FIG. 9, in the case of the comparative example 1, as the photosensitive drum moving speed increases, the target charging potential of 500 [V] cannot be charged. On the other hand, in the case of Example 1, it can be seen that even if the photosensitive drum moving speed increases, it does not deviate much from the target charged potential of 500 [V]. That is, it can be seen that the charging speed is high.

[Comparative Experiment 2]
Next, an experiment is carried out on charging uniformly by erasing the history of potential distribution in the previous stage by one charge, which is one of the problems of the color superposition method on the photosensitive drum. In order to realize this, a large charging speed is required. This is because when a charged part and an uncharged part are charged simultaneously, only the uncharged part must be greatly charged without further charging the charged part. That is, the charged potential must be quickly converged, which means that the charging speed is high.

  In this embodiment, the difference in charging speed between Example 1 and Comparative Example 1 described above was confirmed by the following experiment. The contents of the experiment will be described with reference to FIG.

  First, the photosensitive drum 1 is charged to a target charging potential of −500 [V] by the corona charging device 2 of Example 1 or Comparative Example 1. The maximum output is written to this, and the potential is lowered to the post-exposure potential (which was -50 [V] in this comparative experiment). Then, an uneven potential distribution can be obtained. Thereafter, recharging is performed by the same corona charging device 2. At this time, the post-exposure potential is charged to substantially the same potential at the first time, but the potential charged at the first time is charged to be larger than that. This occurs because the potential has not converged at the first charge. If the potential converges at a large charging speed in the first charging, the potential should hardly change even in the second recharging.

The results of this comparative experiment are shown in Table 1. The photosensitive drum linear velocity was 150 [mm / s], and the photosensitive drum film thickness was 25 [μm].

  The conditions of Comparative Example 1 are that the high-voltage power supply 55 outputs an AC voltage with a peak-to-peak voltage of 12 [kV] and a frequency of 2 [kHz], and the high-voltage power supply 56 outputs a DC voltage of −500 [V]. The capacitor 54 is 1000 [pF].

  The conditions of the first embodiment are as follows: a high voltage power supply 55 outputs a DC voltage of −500 [V] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]; Output a DC voltage of −500 [V], and a capacitor 54 of 1000 [pF] was used.

  From Table 1, although the potential difference after recharging (after the second charging) in Comparative Example 1 (the potential difference between the charging potential of the first non-exposed portion and the charging potential of the first exposed portion) is 45 [V]. On the other hand, the potential difference after recharging (after the second charging) in Example 1 (the potential difference between the charging potential of the first non-exposed portion and the charging potential of the first exposed portion) is 10 [V]. It can be said that 1 was more uniformly charged. This is because the corona charging device 2 of Example 1 has a high charging speed as shown in the comparative experiment 1, and thus, the charge distribution is erased uniformly by charging one time in this way. It is thought that was made.

[Comparative Experiment 3]
[Comparative Example 2]
A corona charging device 2 of Comparative Example 2 is shown in FIG. This is a normal scorotron charging device in which a grid 57 is installed at the opening of the shield 53. The distance between the corona electrode and the shield 53 is 8 [mm]. The distance from the corona electrode to the grid 57 is 5 [mm], the distance from the grid 57 to the surface of the photosensitive drum is 2 [mm], that is, the distance from the corona electrode to the surface of the photosensitive drum is 7 [mm]. A DC voltage is applied to the corona electrode from a high voltage power supply 55, and a DC voltage is applied to the shield 53 from a high voltage power supply 56.

  In this comparative experiment, the corona charging device 2 of Example 1 and Comparative Example 1 and Comparative Example 2 described above were compared with respect to the toner layer potential problem, which is one of the problems of the color superposition method on the photosensitive drum. Do.

  The problem of the toner layer potential in the color superimposing method on the photosensitive drum is that the toner after exposure related to the formation of the toner image of the next color depends on the charge amount of the toner layer already formed on the photosensitive drum 1. The potential of the layer and the non-toner adhesion area does not decrease in the same manner, and the adhesion amount of the next color toner to be superimposed on the toner image already formed on the photosensitive drum 1 is reduced. is there.

As an experiment, the photosensitive drum 1 is charged to about −500 [V], and then the entire surface is exposed to develop a solid image. The toner adhesion amount is adjusted to approximately 0.45 [mg / cm ² ]. When light is sufficiently applied to the photosensitive drum 1 to which the toner layer is adhered, only the toner layer potential remains as the surface potential, so the toner layer potential after development is measured with a surface potential meter.

  Thereafter, the surface of the photosensitive drum (including the toner layer) is recharged to −500 [V] again using the corona charging device 2 of Example 1, Comparative Example 1 or Comparative Example 2. Thereafter, when the photosensitive drum 1 having the toner layer adhered thereto is sufficiently exposed to light, only the toner layer potential remains as the surface potential. Therefore, the toner layer potential after recharging is measured with a surface potential meter.

  The condition of Comparative Example 1 is that the high voltage power supply 55 outputs an AC voltage with a peak-to-peak voltage of 12 [kV] and a frequency of 2 [kHz], and the high voltage power supply 56 outputs a DC voltage of −550 [V]. The capacitor 54 is 1000 [pF].

  The condition of Comparative Example 2 is that a DC voltage of −5 [kV] is output from the high-voltage power supply 55, a DC voltage of −550 [V] is output from the high-voltage power supply 56, and the capacitor 54 is 1000 [pF]. The thing of was used.

  The conditions of the first embodiment are as follows: a high voltage power supply 55 outputs a DC voltage of −500 [V] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]; Output a DC voltage of −500 [V], and a capacitor 54 of 1000 [pF] was used.

The results of this comparative experiment are shown in Table 2. In the case of Comparative Example 1 and Comparative Example 2, the toner layer potential increases after development due to recharging, but in the case of Example 1, the toner layer potential can be reduced to nearly zero.

  As described above, the reason why the toner layer potential after recharging can be reduced to nearly 0 in Example 1 is considered to be described below. That is, in the corona charging device 2 according to the first embodiment, sufficient ions are supplied to charge the photosensitive drum 1 to −500 [V] as described above under the voltage condition applied to the corona electrode 51. After passing through the electrode 51, the surface of the photosensitive drum is temporarily charged to −500 [V] or more. Thereafter, the surface potential of the photosensitive drum is returned to −500 [V] for the reason described above when passing through the corona electrode 52. As described above, once the potential is raised and then lowered, the charge of the toner can be removed when the toner layer is formed on the photosensitive drum 1.

[Embodiment 2]
[Example 2]
A second embodiment in which the present invention is applied to a laser printer (hereinafter simply referred to as a printer 100) that is an electrophotographic image forming apparatus will be described below.
FIG. 12 is a schematic configuration diagram of the printer 100 according to the second embodiment. A printer 100 shown in FIG. 12 includes a photoconductor belt 11 in which an organic photoconductor is formed in a belt shape, and is rotated in the direction of arrow E in the drawing by a rotation driving mechanism (not shown).

  Developing devices 4K, 4M, 4C, and 4Y, which are developing cartridges, and a corona charging device 2 to be described later are opposed to the photosensitive belt 11 for each color, and toner images are sequentially transferred to the photosensitive belt 11 as the photosensitive belt 11 moves. 11 are configured to be stacked on top of each other. This is a configuration called a one-pass color. Further, the developing device 4 as a developing cartridge can be detached from the space opened by the retraction of the photosensitive belt 11 and can be replaced by the user.

  The optical writing devices 4K, 4M, 4C, and 4Y are devices for writing latent images corresponding to black, magenta, cyan, and yellow, respectively, on the charged photosensitive belt 11 according to image information. Various devices such as an optical scanning device using a polygon and an LED array can be used.

  Below the photosensitive belt 11, there is provided a paper feeding device 5 for storing a transfer material such as the transfer paper P and for starting transfer of the transfer paper P during image formation. A fixing device 3 including a heating roller 18 a and a pressure roller 18 b facing the heating roller 18 a for fixing an unfixed toner image formed on the transfer paper P is provided above the photosensitive belt 11. It is.

  At the time of image formation, the transfer paper P sent from the paper feeding device 5 is conveyed to a contact portion between the photoconductor belt 11 and the transfer device 32, and a full color image formed on the photoconductor belt 11 is transferred at this contact portion. The image is transferred onto the transfer paper P by the voltage applied to the device 32. Thereafter, when the transfer paper P reaches the fixing device 3, the toner image on the transfer paper P is heated while being sandwiched between the heating roller 18a and the pressure roller 18b to be fixed on the transfer paper P. A visible image is formed.

  Toner that remains on the photosensitive belt 11 without being transferred (transfer residual toner) is cleaned by the cleaning device 38, and the surface of the photosensitive belt 11 after cleaning is used for the next image formation.

  FIG. 13 is an enlarged schematic configuration diagram in the vicinity of the photosensitive belt 11. In FIG. 13, the photosensitive belt 11 is arranged in the center, and on the circumference thereof, four color corona charging devices 2Y, 2M, 2C, 2K, an exposure device (not shown), and four color developing devices 4Y, 4M, 4C and 4K, a transfer device 32, and a cleaning device 38 are arranged. Although the photosensitive belt 11 is used here, there is no problem even if the photosensitive drum 1 is used.

  In this embodiment, four color toner images of yellow, magenta, cyan, and black are superimposed on the photosensitive belt 11 to form a color image. This mechanism will be described. In FIG. 13, the corona charging device 2 and the developing device for four colors are arranged in the order of YMCK from the upstream side to the downstream side in the circumferential direction (arrow direction) of the photosensitive belt 11, and the toner images are superimposed in the order of YMCK. . Note that the superposition order is not limited to this.

  The photosensitive belt 11 is rotated at a linear speed of 150 [mm / sec]. In the corona charging device 2Y, the photosensitive belt 11 is uniformly charged at −500 [V], and the yellow image portion is exposed by the writing light 13Y output from the exposure device 3Y to form an electrostatic latent image. The negatively charged yellow toner is developed by the developing device 4Y having a developing bias of −300 V, and this electrostatic latent image is formed on the photoreceptor belt 11 as a yellow toner image. Here, the negatively charged toner is developed by negatively charging the photosensitive belt 11, but the positively charged toner may be developed by positively charging the photosensitive belt 11.

  Next, the magenta toner image is superimposed on the photosensitive belt 11 on which the yellow toner image is formed by the same charging, exposure, and development processes as those for the yellow color. The same applies to cyan and black colors. In this manner, four color toner images of yellow, magenta, cyan, and black are superimposed on the photosensitive belt 11.

  Then, the four color toner images are collectively transferred to the recording paper conveyed by the paper conveyance path 15 by the transfer device 32. Finally, the toner image is fixed on the recording paper by the fixing device 18 and an image is output.

  An exposure apparatus (not shown) that outputs the writing light 13Y, 13M, 13C, and 13K uses a laser diode element having a wavelength of 780 nm. However, the present invention is not limited to this.

  In this embodiment, the corona charging devices 2Y, 2M, 2C, and 2K use the corona charging device 2 described in the first embodiment. However, the charging device 2Y for the first color does not cause a problem specific to IOI (Image On Image), so any charging device may be used. In some cases, the corona charging device 2 described in the first embodiment is used for only one of the second color corona charging device 2M, the third color corona charging device 2C, and the fourth color corona charging device 2K. Also good.

  The condition of the corona charging device 2 is that the high voltage power supply 55 outputs a DC voltage of −500 [V] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]. Outputs a DC voltage of −500 [V], and the capacitor 54 is 1000 [pF].

  As shown in Comparative Experiment 3, by using the corona charging device 2 of Example 1, the toner layer potential can be made substantially 0V while charging the surface of the photoreceptor belt 11. That is, as described above, the voltage condition applied to the corona electrode 51 supplies sufficient ions to charge the photosensitive belt 11 to −500 [V], so that after passing through the corona electrode 51, the photosensitive belt. 11 The surface is temporarily charged to −500 [V] or more. Thereafter, when passing through the corona electrode 52, the surface potential of the photoreceptor belt is returned to -500 [V].

  As described above, once the potential is raised and then lowered, the charge of the toner can be removed when the toner layer is formed on the photosensitive belt 11. Furthermore, since both the positive ions and the negative ions are generated to eliminate the charge, the reversely charged toner is not generated, the charge amount of the toner becomes almost zero, and the toner layer potential can be made almost 0V. Therefore, since an appropriate development potential can be created, a high-quality image forming apparatus can be realized.

  Next, the developing devices 4Y, 4M, 4C, and 4K used in the present embodiment will be described. In the present embodiment, since the next color toner image is developed from the previous color toner image, a non-contact developing device is used so as not to disturb the previous color toner image.

  A developing device 4Y of this embodiment is shown in FIG. Since the other developing devices 4M, 4C, and 4K are the same, here, the developing device 4Y will be representatively described.

  The developing device 4Y includes a case that accommodates a toner carrying roller 61, a mag roller 62, a two-component developer, and stirring screws 63 and 64. Except for the toner carrying roller 61, it is the same as the normal two-component developing system. The two-component developer is obtained by mixing toner in magnetic carrier powder so that the weight ratio is about 6 [wt%]. The two-component developer is conveyed to the toner carrying member by a mag roller 62 enclosing a permanent magnet, and a part of the toner is transferred to the toner carrying roller by a bias potential applied thereto. The toner transferred to the toner carrying roller 61 forms a cloud state (a state in which the toner is floating) according to the principle described below, and the developing portion (a portion facing the image carrier) is rotated by the rotation of the toner carrying roller 61. Carried to.

  A toner image is formed by the difference between the average potential on the surface of the toner carrying roller 61 and the potential of the image carrier, and unnecessary toner that has not contributed to development returns to the mag roller 62 again. Since the cloud is formed, the adhesion force of the toner is very low, and the toner returned from the developing portion by the toner carrying roller 61 is easily scraped off by the spikes of the two-component developer following the rotation of the mag roller 62. It is averaged. By repeating this, a substantially constant amount of toner is always carried on the toner carrying roller 61 in a cloud state. Although the two-component developing method is adopted as a method for supplying toner to the toner carrying roller 61, the configuration of the developing device is not limited to this.

  The toner carrying roller 61 will be described. FIG. 15 shows an enlarged surface of the toner carrying roller 61. A spatially periodic aluminum vapor deposition electrode 76 is disposed on the support base 75, and the surface is covered with a resin coat 77.

  As shown in FIG. 16, voltages Va and Vb having different waveforms are applied alternately to the periodic electrodes. As shown in FIG. 17, Va and Vb are opposite in time (phase is shifted by 180 degrees). Then, an oscillating electric field is formed between the electrode to which Va is applied and the electrode to which Vb is applied. Therefore, the toner hops between the electrode to which Va is applied and the electrode to which Vb is applied to form a cloud state (a state where the toner is floating). In this way, the toner can be carried in a cloud state on the toner carrier. In FIG. 17, Va and Vb are shown as rectangular waves, but normal AC voltages formed by sine waves may be used. Here, the periodic electrodes are divided into two and voltages having different waveforms are applied alternately. However, if the conditions are such that a vibrating electric field is formed and the toner hops to form a cloud state, the periodic electrodes are divided into three or more. You may comprise so that the voltage of a different waveform may be applied to each.

  Here, a voltage in which an AC component is a rectangular wave having a peak-to-peak voltage of 600 [V] and a frequency of 1 [kHz] and a DC component of −300 [V] is superimposed is applied to Va and Vb. The development bias that triggers the development of the latent image with toner in the development region is the time average value of this voltage. That is, the developing bias is −300 [V].

  Since this developing method forms and develops a cloud state, it is possible to reduce the influence of the adhesive force between the toner carrier and the toner. Therefore, the toner can respond to a small development electric field in the development region, and a sufficient toner adhesion amount can be obtained even with such a small development bias.

  Furthermore, if the amount of adhesion between the toner and the toner carrier is very small, development can be performed faithfully with respect to the latent image potential, so that an image with high dot reproducibility and excellent quality can be obtained.

[Example 3]
The overall configuration of the image forming apparatus of the third embodiment is the same as that of the second embodiment and is shown in FIG. The operation is the same as in the second embodiment.

  The corona charging device 2 uses the corona charging device 2 of the first embodiment shown in FIG. As in the second embodiment, the reversely charged toner is not generated, the charge amount of the toner becomes almost zero, and the toner layer potential can be made almost 0 [V]. Therefore, since an appropriate development potential can be created, a high-quality image forming apparatus can be realized.

  The third embodiment is different from the second embodiment in the developing devices 4Y, 4M, 4C, and 4K. Since all the developing devices are the same, the developing device 4Y will be representatively described.

  The developing device of Example 3 has substantially the same shape as the developing device of Example 2, and is shown in FIG. The difference is the toner carrying roller 61. FIG. 18 shows an enlarged surface of the toner carrying roller 61 of the third embodiment. A spatially periodic aluminum vapor deposition electrode 76 is disposed on the support base 75, and the surface is covered with a resin coat 77.

  In the third embodiment, the periodic electrodes are divided into three as shown in FIG. 18 (here, three or more may be used), and voltages Va and Vb having different waveforms are applied to the respective electrodes as shown in FIG. , Vc is applied. Then, as in Example 2, the toner hops between the electrode to which Va is applied, the electrode to which Vb is applied, and the electrode to which Vc is applied to form a cloud state (a state where the toner is floating). .

  Further, as shown in FIG. 20, a traveling wave electric field for conveying toner is generated by appropriately shifting the phases of Va, Vb, and Vc. As a result, the toner can be conveyed. Therefore, the toner in the cloud state can be conveyed to the developing portion (the portion facing the image carrier) without mechanically rotating the toner carrying roller 61 itself.

  Here, to Va, Vb, and Vc, a voltage in which an AC component is a rectangular wave having a peak-to-peak voltage of 600 [V] and a frequency of 1 [kHz] and a DC component of −300 [V] is superimposed is applied. The development bias that triggers the development of the latent image with toner in the development region is the time average value of this voltage. That is, the developing bias is −300 [V].

  In this developing method, a cloud state is formed and developed, so that the amount of adhesion between the toner and the toner carrier is very small. Therefore, under the condition that the toner is sufficiently conveyed to the development area, the development is completed when the photosensitive belt potential with the toner attached on the photosensitive belt 11 becomes equal to the development bias. That is, a sufficient toner adhesion amount can be obtained even with a small development potential.

  Furthermore, if the amount of adhesion between the toner and the toner carrier is very small, development that is faithful to the latent image potential can be performed, so that an image with high dot reproducibility and excellent quality can be obtained.

[Example 4]
The basic configuration of the image forming apparatus of the fourth embodiment is the same as that of the second and third embodiments, and is shown in FIG.

  As shown in FIG. 13, the photosensitive belt 11 is arranged at the center, and on the circumference thereof, four-color corona charging devices 2Y, 2M, 2C, and 2K, an unshown exposure device, and a four-color developing device 4Y. 4M, 4C, and 4K, a transfer device 32, and a cleaning device 38 are disposed. Although the photosensitive belt 11 is used here, there is no problem even if the photosensitive drum 1 is used.

  In this embodiment, four color toner images of yellow, magenta, cyan, and black are superimposed on the photosensitive belt 11 to form a color image. This mechanism will be described. In FIG. 13, the corona charging device 2 and the developing device 4 of four colors are arranged in the order of YMCK from the upstream side to the downstream side in the circumferential direction (arrow direction) of the photosensitive belt 11, and the toner images are superimposed in the order of YMCK. Match. Note that the superposition order is not limited to this.

  The photosensitive belt 11 is rotated at a linear speed of 150 [mm / sec]. In the corona charging device 2Y, the photosensitive belt 11 is uniformly charged at 500 [V], and a yellow non-image portion is exposed by writing light 13Y output from an exposure device (not shown) to form an electrostatic latent image. The negatively charged yellow toner is developed by the developing device 4Y having a developing bias of 300 [V], and this electrostatic latent image is formed on the photoreceptor belt 11 as a yellow toner image. Here, the negatively charged toner is developed by positively charging the photosensitive belt 11, but the positively charged toner may be developed by negatively charging the photosensitive belt 11.

  Next, the magenta toner image is superimposed on the photosensitive belt 11 on which the yellow toner image is formed by the same charging, exposure, and development processes as those for the yellow color. The same applies to cyan and black colors. In this manner, four color toner images of yellow, magenta, cyan, and black are superimposed on the photosensitive belt 11.

  Then, the four color toner images are collectively transferred to the recording paper conveyed by the paper conveyance path 15 by the transfer device 32. Finally, the toner image is fixed on the recording paper by the fixing device 18 and an image is output.

  An exposure apparatus that outputs writing light 13Y, 13M, 13C, and 13K uses a laser diode element having a wavelength of 780 [nm]. However, the present invention is not limited to this.

  The fourth embodiment differs from the second and third embodiments in the manner of operation in the following points. In the second and third embodiments, the photosensitive belt 11 is charged, the image portion is exposed, and toner having the same polarity as the charged polarity of the photosensitive belt 11 is reversely developed on the image portion. A so-called negative / positive system is employed. On the other hand, in the fourth embodiment, the photosensitive belt 11 is charged, a non-image portion is exposed, and the image portion is developed with toner having a charge opposite to the charged polarity of the photosensitive belt 11. A positive / positive system is adopted.

  When the positive / positive method is used in the color superposition method on the photosensitive belt 11, the charging polarity of the toner and the charging polarity of the photosensitive belt 11 are opposite. Therefore, when the photosensitive belt 11 is charged, the previous toner layer is removed. There is an advantage that the toner layer potential can be reduced to almost zero by eliminating the charge. Therefore, since the toner layer potential does not become a problem until two colors are superimposed, a general corona charging device 2 can be used. However, if an attempt is made to superimpose three or more colors, the toner layer potential still becomes a problem. However, in this case, the photosensitive belt 11 is not charged while discharging the charge held by the toner layer as in the negative / positive method, but the charge already held by the toner layer is almost zero. Therefore, the function of the corona charging device 2 required for the positive / positive system may be smaller.

  In this embodiment, the corona charging devices 2Y, 2M, 2C, and 2K use the corona charging device 2 described in the first embodiment. However, as described above, the general corona charging device 2 may be used when charging the first color and the second color. Particularly, when the corona charging device 2 described in the first embodiment is used, the corona charging device 2C for the third color and the corona charging device 2K for the fourth color are effective.

  The condition of the corona charging device 2 is that a high voltage power supply 55 outputs a DC voltage of −300 [V] superimposed on an AC voltage having a peak-to-peak voltage of 10 [kV] and a frequency of 2 [kHz]. A DC voltage of −500 [V] is output, and the capacitor 54 is 1000 [pF].

  As shown in Comparative Experiment 3, when the corona charging device 2 of Example 1 is used, the toner layer potential can be made substantially 0 [V] while charging the surface of the photoreceptor belt. In the corona charging device 2 of the first embodiment, both positive ions and negative ions are generated, so that the charge held by the toner layer can be converged with zero. That is, if the toner layer has a charge, the charge is eliminated, and if the toner layer has a charge of 0, it is kept at 0.

  Therefore, the toner layer potential can always be almost 0 [V], and an appropriate development potential can be created, so that a high-quality image forming apparatus can be realized. Further, the problem of reversely charged toner does not occur.

  The developing devices 4Y, 4M, 4C, and 4K can achieve the same effect by using the developing device described in the second embodiment. Further, the developing device described in Embodiment 3 may be used.

As described above, according to each embodiment, in the case where the photosensitive drum 1 to the photosensitive belt 11 that are the objects to be charged that move on the surface are close to each other and the opening is provided on the side facing the photosensitive drum 1 to the photosensitive belt 11. A certain shield 53, a corona electrode 52 which is disposed inside the shield 53 and generates an equal amount of positive and negative ions by applying a voltage, and the photosensitive drum 1 to the photosensitive belt. In the corona charging device 2 provided with a high voltage power source 56 and a shield 53 or a grid 57 constituting charging potential control means for controlling the charging potential of the eleventh electrode to a predetermined potential, the surface of the photosensitive drum is moved more than the corona electrode 52. The positive and negative ions are generated by applying a voltage in the shield 53 on the upstream side in the direction to the upstream side in the movement direction of the photoreceptor belt, The drum 1 to the polarity and the same polarity ions for charging the photoreceptor belt 11 and the polarity to the charging are disposed a corona electrode 51 on the upstream side discharge electrode often cause than opposite polarity ions. First, the photosensitive drum 1 to the photosensitive belt 11 are charged to the charging polarity by ions having the same polarity as the charging polarity generated from the corona electrode 51. Then, while supplying ions from the corona electrode 52 to the photosensitive drum 1 to the photosensitive belt 11, the photosensitive drum 1 to the photosensitive belt are charged by the charging potential control means including the high voltage power source 56 and the shield 53 or the grid 57. 11, the photosensitive drum 1 to the photosensitive belt 11 are uniformly charged to a predetermined charging potential. That is, the ions generated from the corona electrode 52 are supplied to the photosensitive drum 1 to the photosensitive belt 11 charged in advance with the polarity charged by the ions generated from the corona electrode 51 to supply the photosensitive drum 1 to the photosensitive belt. 11 is charged to a predetermined charging potential. As a result, the corona electrode 52 required for setting the photosensitive drum 1 to the photosensitive belt 11 to a predetermined charging potential is used as compared with the case where the photosensitive drum 1 to the photosensitive belt 11 are not charged in advance to the polarity to be charged. The amount of ions generated from the toner to the photosensitive drum 1 to the photosensitive belt 11 can be reduced. Therefore, the photosensitive drum 1 to the photosensitive belt 11 can be uniformly charged to a predetermined charging potential in a shorter time than the configuration in which the corona electrode 51 is not provided. Therefore, uniform chargeability can be obtained and high-speed chargeability can be improved.
Moreover, according to each embodiment, the high voltage power supply 58 which is the 1st voltage application means which applies an alternating voltage to the corona electrode 52 via the capacitor | condenser 54, and the alternating current voltage which superimposed the alternating voltage or direct current voltage on the corona electrode 51 And a high-voltage power supply 59 which is a second voltage applying means for applying. As a result, it is possible to suppress the potential fluctuation caused by the temperature and humidity change as in the DC corona charging device, and to charge the photosensitive drum 1 to the photosensitive belt 11 to a target potential. Further, since an AC voltage is applied to the corona electrode 52 via the capacitor 54, the same amount of positive ions and negative ions can be generated, and as described above, the control of the charging potential without generating the reversely charged toner. Can increase the sex.
Moreover, according to each embodiment, it has the high voltage power supply 55 which is a voltage application means which applies the alternating voltage or the alternating voltage which superimposed the direct current voltage to the corona electrode 51 and the corona electrode 52, and the high voltage power supply 55 is the corona A voltage is applied to the electrode 52 via the capacitor 54, and a voltage is directly applied to the corona electrode 51. As a result, it is possible to suppress the potential fluctuation caused by the temperature and humidity change as in the DC corona charging device, and to charge the photosensitive drum 1 to the photosensitive belt 11 to a target potential. Further, since an AC voltage is applied to the corona electrode 52 via the capacitor 54, the same amount of positive ions and negative ions can be generated, and as described above, the control of the charging potential without generating the reversely charged toner. Can increase the sex. Furthermore, since a voltage can be applied to the corona electrode 51 and the corona electrode 52 with a single power source, it is possible to reduce costs and save space.
Further, according to each embodiment, the grid 57 electrode is used for the charging potential control means, and the grid 57 electrode is provided between the corona electrode 52 and the photosensitive drum 1 to the photosensitive belt 11, so that the grid 57 electrode is used. Since the charging potential can be controlled, the controllability of the charging potential is further improved and the charging uniformity is also improved.
Further, according to each embodiment, the photosensitive drum 1 to the photosensitive belt 11 as an image carrier, one or more charging means for charging the photosensitive drum 1 to the photosensitive belt 11, and the charging means. An exposure device that is a latent image forming unit that exposes the charged photosensitive drum 1 to the photosensitive belt 11 to form a latent image for each color, and is formed on the photosensitive drum 1 to the photosensitive belt 11. A developing device that is a plurality of developing means for visualizing the latent image with toners of different colors, and for each color, the photosensitive drum 1 to the photosensitive belt 11 are charged by a charging means. The exposure device exposes the photosensitive drum 1 to the photosensitive belt 11 to form a latent image, and the developing device develops the latent image, whereby the single photosensitive drum 1 to the photosensitive belt 11 is developed. To each In the printer which is an image forming apparatus that sequentially forms the toner images to form a color toner image, the corona charging device 2 of the present invention is used as the charging means, so that the potential corresponding to the preceding toner image can be obtained at a high charging speed. The history of distribution can be erased, the charge held by the toner can be eliminated without generating a reversely charged toner, and the toner layer potential can be made very small. Therefore, an image forming apparatus such as a printer that can form a high-quality image with a small size and low cost can be obtained.
Further, according to the second embodiment, the exposure device exposes a non-image portion of the photosensitive belt charged by the corona charging device 2 to form a latent image for each color. The corona charging device 2 develops a latent image of a corresponding color with toner having a polarity opposite to the charging polarity for charging the photosensitive belt 11. As a result, since the polarity for charging the photosensitive belt 11 and the polarity of the charge held by the toner to be developed are reversed, the toner layer can be discharged more efficiently during charging, and the potential of the toner layer can be reduced to almost zero. it can. Therefore, it is possible to obtain an image forming apparatus such as a printer that can form a higher quality image with a small size and at a low cost.
Further, according to the second embodiment, the developing device 4 includes a developing roller that is a toner carrier that carries toner and is disposed so as to face the photosensitive belt 11 in a non-contact manner in the development region, and a toner carrying roller 61. And a plurality of electrodes provided on the toner carrying roller 61 so as to be insulated from each other, the plurality of electrodes being connected to the plurality of electrodes adjacent to each other in the direction of relative polarity of the applied voltage. And hopping electric field generating means for hopping the toner. Accordingly, since the toner on the toner carrying roller 61 is in a floating state (referred to as toner cloud), the amount of adhesion between the toner and the toner carrying roller 61 is very small. Therefore, even with a small development potential (difference between the photoreceptor belt potential and the development potential in the image area), sufficient development can be performed without contact. If the development potential is small, the potential difference between the development bias and the non-image portion can be increased without changing the charging potential of the photosensitive belt 11, so that the occurrence of background stains can be suppressed. Furthermore, if the amount of adhesion between the toner and the toner carrying roller 61 is very small, development can be performed faithfully with respect to the latent image potential, so that an image with high dot reproducibility and excellent quality can be obtained.
Further, according to the second embodiment, the toner carrying roller 61 is a surface moving member that conveys the toner carried on the surface of the toner carrying roller 61 to the development area by moving the surface of the toner carrying roller 61. is there. Thus, the toner carried on the surface of the toner carrying roller 61 can be easily conveyed to the development area.
According to the second embodiment, the hopping electric field generating means generates a traveling wave electric field for conveying the toner to the development area while hopping the toner carried on the surface of the toner carrying roller 61. It is generated on the surface of the carrying roller 61. Accordingly, since the toner carried on the toner carrying roller 61 can be conveyed to the developing region by the traveling wave electric field without rotating the toner carrying roller 61, a driving unit for driving the toner carrying roller 61 is not necessary. In addition, the apparatus body can be further downsized.

  In each embodiment, the corona charging device 2 of each example is provided with two corona electrodes. However, if the number of corona electrodes provided is two or more, a large charging speed as described above can be obtained. it can. In each embodiment, the corona charging device 2 of each embodiment is used as a charging device of a printer that forms a color image by superimposing toner images on the photosensitive drum 1 to the photosensitive belt 11. Of course, it can be used for an image forming apparatus such as a printer other than the above-described system. In other words, by using the corona charging device 2 of each embodiment, the charged object such as the photosensitive drum 1 can be charged at a high charging speed, so that the image forming speed can be increased.

1 is a schematic configuration diagram of a corona charging device in Embodiment 1. FIG. 1 is a schematic configuration diagram of a printer according to Embodiment 1. FIG. The schematic block diagram of the corona charging device with which between two corona electrodes was open | released. FIG. 3 is a schematic configuration diagram illustrating dimensions of the corona charging device according to the first embodiment. The schematic block diagram of the corona charging device which provided three high voltage power supplies. The schematic block diagram of the corona charging device in a modification. 1 is a schematic configuration diagram of a corona charging device in Comparative Example 1. FIG. 6 is a graph showing the relationship between the photosensitive drum linear velocity and the charging potential in Example 1 and Comparative Example 1 in the case of negative charging. 6 is a graph showing the relationship between the photosensitive drum linear velocity and the charging potential in Example 1 and Comparative Example 1 in the case of positive charging. The schematic diagram which showed the experiment content of the comparative experiment 2. FIG. The schematic block diagram of the corona charging device in the comparative example 2. FIG. FIG. 3 is a schematic configuration diagram of a printer according to a second embodiment. FIG. 2 is an enlarged schematic configuration diagram in the vicinity of a photosensitive belt. FIG. 6 is a schematic configuration diagram of a developing device in Embodiment 2. FIG. 6 is an enlarged view of a surface portion of a toner carrying roller in Embodiment 2. The figure which showed the toner cloud state at the time of applying the voltage of the waveform from which an electrode which is periodically arranged alternately differs. The wave form diagram of the voltage applied to the electrode arranged periodically. FIG. 6 is an enlarged view of a surface portion of a toner carrying roller in Embodiment 3. The figure which showed the toner cloud state at the time of applying the voltage of the waveform from which an electrode which is periodically arranged alternately differs. The wave form diagram of the voltage applied to the electrode arranged periodically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Corona charging device 4 Developing device 11 Photoconductor belt 51 Corona electrode 52 Corona electrode 53 Shield 54 Capacitor 55 High voltage power source 56 High voltage power source 57 Grid 58 High voltage power source 61 Toner carrying roller 62 Mag roller 63 Stir screw 64 Stir screw 75 Support Base 76 Aluminum evaporated electrode 77 Resin coating

Claims (9)

A case that has an opening on a side that is close to the charged body that moves on the surface and faces the charged body;
A discharge electrode disposed inside the case and generating an equal amount of positive and negative ions by applying a voltage;
In a corona charging device comprising charging potential control means for controlling the charging potential of the member to be charged to a predetermined potential,
The same polarity as the polarity for generating positive and negative ions by applying a voltage in the case on the upstream side in the moving direction of the surface of the member to be charged with respect to the discharge electrode, and charging the member to be charged A corona charging device is provided with an upstream discharge electrode for generating a larger amount of ions than those having a polarity opposite to the polarity to be charged. The corona charging device of claim 1.
First voltage applying means for applying an AC voltage to the discharge electrode via a capacitor;
And a second voltage applying means for applying an AC voltage or an AC voltage superimposed with a DC voltage to the upstream discharge electrode. The corona charging device of claim 1.
A voltage applying means for applying an alternating voltage or an alternating voltage superimposed with a direct voltage to the discharge electrode and the upstream discharge electrode;
The corona charging device, wherein the voltage applying means applies a voltage to the discharge electrode via a capacitor and directly applies a voltage to the upstream discharge electrode. The corona charging device according to claim 1, 2 or 3,
The charging potential control means is a grid electrode,
A corona charging device, wherein the grid electrode is provided between the discharge electrode and the member to be charged. An image carrier;
One or more charging means for charging the image carrier;
Latent image forming means for forming a latent image for each color by exposing the image carrier charged by the charging means;
A plurality of developing means for visualizing the latent images formed on the image carrier with different color toners,
For each color, the image carrier is charged by the charging unit, the latent image forming unit is exposed on the image carrier to form a latent image, and the latent image is developed by the developing unit. In an image forming apparatus for forming a color toner image by sequentially forming toner images of respective colors on a single image carrier,
An image forming apparatus using the corona charging device according to claim 1, 2, 3, or 4 as the charging means. The image forming apparatus according to claim 5.
The latent image forming means exposes a non-image portion on the image carrier charged by the charging means to form a latent image for each color, and the plurality of developing means include the charging means An image forming apparatus, wherein a latent image of a corresponding color is developed with a toner having a polarity opposite to a charging polarity for charging the image carrier. The image forming apparatus according to claim 5 or 6,
The developing means is disposed so as to face the image carrier in a non-contact manner in a development region, and a toner carrier that carries the toner;
A plurality of electrodes provided on the toner carrier and insulated from each other along the surface of the toner carrier, and the plurality of electrodes are adjacent to each other in the direction of relative polarity of the applied voltage. An image forming apparatus comprising: a hopping electric field generating means for hopping toner by being different from each other by a plurality of electrodes. The image forming apparatus according to claim 7.
The toner carrier is a surface moving member that conveys the toner carried on the surface of the toner carrier to the development area by moving the surface of the toner carrier. . The image forming apparatus according to claim 8.
The hopping electric field generating means generates a traveling wave electric field on the surface of the toner carrying member for hopping the toner carried on the surface of the toner carrying member and conveying the toner to the developing region. What is claimed is: 1. An image forming apparatus comprising:

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