JP2004004335A - Charging device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device which attains stable discharging performance with simple constitution and an image forming device equipped with the same. <P>SOLUTION: A device meets conditions of D≥3 and P≥D≥V, where P is the separation distance between needle tips 23a of a plurality of needlelike electrodes 23 of the charging device 22 in terms of mm, V is a voltage applied between a needlelike electrode 23 and a discharge auxiliary metal plate 24 in terms of kV, and D is the distance between the needle tip 23a of the needlelike electrode 23 and the discharge auxiliary metal plate 24 in terms of mm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device and an image forming apparatus provided with the same, and more particularly to a charging device suitable for charging or discharging a recording medium onto which a toner image has been transferred by an electrophotographic image forming device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, an image forming apparatus such as a printer or a facsimile used as an output device of a computer or a copying machine for forming an image of image data read from an image scanner has been widely used.
[0003]
Further, many types of image forming means, such as, for example, a hot-melt type, a thermal sublimation type, a thermal transfer type, an ink jet type, and an electrophotographic type, have been developed according to applications. Among these, as shown in FIG. 8, four process stations 1a, 1b, 1c, and 1d, which are image forming units of different colors, are arranged side by side, and full-color using four colors of cyan, yellow, magenta, and black. 2. Description of the Related Art An electrophotographic image forming apparatus has been proposed as a high-speed color image forming method (a so-called in-line method).
[0004]
In FIG. 8, process stations 1a to 1d have photosensitive drums 2a to 2d as image carriers, and the surfaces of the photosensitive drums 2a to 2d are uniformly charged by primary chargers 3a to 3d. After that, for example, an exposure device 4a to 4d such as an LED (light emitting diode) or a laser receives exposure based on image information to form an electrostatic latent image. This electrostatic latent image is developed with toner of each color by developing devices 5a to 5d.
[0005]
Each of the process stations 1a to 1d is detachable from the image forming apparatus main body as a process cartridge. Each process cartridge has a configuration in which each of the photosensitive drums 2a to 2d, the primary chargers 3a to 3d, the developing devices 5a to 5d, and the cleaning means 6a to 6d are integrated.
[0006]
On the other hand, the transfer material S serving as a recording medium accommodated in the feeding cassette 15 is fed into the image forming apparatus main body by the feeding roller 16, is conveyed by the registration roller pair 17, and then is supplied by the suction bias power supply 13 to the positive polarity. A transfer roller 7 serving as a transfer material carrier is electrostatically attracted to and carried by a suction roller 12 to which a suction bias voltage is applied.
[0007]
The transfer / conveyance belt 7 is stretched by four rollers: a driving roller 8, a suction-opposed roller 9, and tension rollers 10 and 11. The process stations 1a, 1b, 1c, 1d of the respective colors of cyan, yellow, magenta, and black are arranged on the surface of the transfer conveyance belt 7 in order from the upstream side along the moving direction of the transfer conveyance belt 7 (the direction of arrow a in FIG. 8). Are arranged substantially perpendicularly to.
[0008]
The transfer material S adsorbed on the transfer / conveying belt 7 sequentially passes through the process stations 1a to 1d for the respective colors, and the toner images of the respective colors carried on the photosensitive drums 2a to 2d are sequentially transferred electrostatically. After that, these toner images are heated and pressed in the fixing device 18 to be fixed on the transfer material S to form a permanent image.
[0009]
[Problems to be solved by the invention]
However, in the above-described conventional example, the transfer material S such as a paper or a synthetic resin, which is a dielectric, passes through the four process stations 1a to 1d and, therefore, carries a large amount of charge because it undergoes four transfer steps.
[0010]
For this reason, a peeling discharge phenomenon occurs at a peeling / separating portion from the transfer / conveyance belt 7 provided on the peripheral surface of the driving roller 8, and a phenomenon that the toner image transferred onto the transfer material S is disturbed along the discharge pattern. appear.
[0011]
In particular, when forming an image in a low-temperature and low-humidity environment in which the transfer material S has high resistance and is easily charged, or when forming a double-sided image, the second surface of the transfer material S that has been dried after passing through the fixing process in the image formation on the first surface once. Notably occurs during image formation.
[0012]
For this reason, a wire type corona charger 51 as shown in FIG. 9 is arranged between the transfer conveyance belt 7 and the fixing device 18 as shown in FIG. In general, the transfer material S is neutralized by the corona charger 51, and a method of eliminating image defects by preventing peeling discharge is generally adopted.
[0013]
Although there are various types of corona charging methods, a corona charger 51 as shown in FIG. 9 is usually employed to obtain a stable discharge. In the corona charger 51 shown in FIG. 9, a tungsten wire 52 having an outer diameter of 60 μm is shielded by a shield plate 53 having a U-shaped cross section, and a DC high-voltage power supply 54 is connected between the shield plate 53 and the tungsten wire 52. Have been.
[0014]
Such a wire type corona charger 51 has a feature that the discharge is stable and a static elimination effect is easily obtained, but it is suitable for cleaning such as when the tungsten wire 52 is contaminated and for jamming the transfer material S. The cutting of the tungsten wire 52 is apt to occur, and there are difficulties in life, safety measures, and the like.
[0015]
On the other hand, in a charger having a needle-shaped electrode, there is no fear of wire cutting or the like as in the corona charger 51, but since the current rises sharply near the discharge threshold and the discharge is unstable, the static elimination effect is difficult to stabilize. A complicated configuration is required to stabilize corona discharge current, such as using a grid in the opening of the charger, or electrically separating a plurality of needle electrodes from each other, and providing an independent resistor. There were drawbacks. Therefore, a charging device having a simple configuration and having a needle-shaped electrode having stable discharge performance has been desired.
[0016]
An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a charging device capable of achieving stable discharge performance with a simple configuration and an image forming apparatus including the same. is there.
[0017]
[Means for Solving the Problems]
The charging device according to the present invention for achieving the above object has a plurality of needle electrodes arranged on a straight line at a predetermined interval, a discharge auxiliary member disposed near a needle tip of the needle electrode, Voltage applying means for applying a voltage between the needle-shaped electrode and the discharge assisting member, and applying a voltage between the needle-shaped electrode and the discharge assisting member by the voltage applying means to produce the needle-shaped In a charging device that discharges between an electrode and the discharge assisting member and charges an object to be charged located in the vicinity of the needle-like electrode, a unit of a separation distance between needle tips of the plurality of needle-like electrodes is mm. The numerical value when expressed is P, the numerical value when the unit of the voltage applied between the needle electrode and the discharge auxiliary member is expressed in kV is V, the needle tip of the needle electrode and the discharge auxiliary member, Where D is the numerical value when the unit of the separation distance is expressed in mm, 3, and it is characterized by being configured so as to satisfy the condition of P ≧ D ≧ V.
[0018]
Since the present invention is configured as described above, the distance P (mm) between the needle tips of the plurality of needle electrodes, the distance D (mm) between the needle tips of the needle electrodes and the discharge auxiliary member, By appropriately setting the relationship between the voltage V (kV) applied between the electrode and the discharge assisting member, the discharge characteristics can be stabilized, and thereby stable discharge performance can be obtained. Further, a charging device with higher safety can be provided.
[0019]
Further, the image forming apparatus according to the present invention includes an image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image to a recording medium, An image forming apparatus including a fixing unit disposed downstream of the recording medium conveyance direction and fixing a toner image transferred to the recording medium, wherein the transfer unit and the fixing unit are connected to the charging device on a recording medium conveyance path. And the recording medium is charged or neutralized by the charging device.
[0020]
According to the above configuration, the charging device is disposed between the transfer unit and the fixing unit on the recording medium conveyance path, and the recording device is charged or discharged by the charging device, so that a large amount of electric charge is obtained through the transfer process. This prevents the occurrence of a discharge phenomenon when the recording medium is removed from the transfer conveyance belt by removing the charge of the recording medium, thereby preventing a phenomenon in which the toner image transferred onto the recording medium is disturbed along the discharge pattern. Image defects can be prevented.
[0021]
Another image forming apparatus according to the present invention includes an image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image to a recording medium, and a recording medium. In an image forming apparatus having a fixing unit for fixing a transferred toner image, a predetermined member in the image forming apparatus is charged or discharged by the charging device.
[0022]
According to the above configuration, it is possible to charge or discharge a predetermined member inside the image forming apparatus main body with a simple configuration.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to the drawings, an embodiment of an image forming apparatus using a full-color electrophotographic method as an example of a charging device according to the present invention and an image forming apparatus including the charging device will be specifically described. FIG. 1 is a cross-sectional explanatory view showing a schematic configuration of an image forming apparatus according to the present invention, FIG. 2 is a partially enlarged view showing an arrangement configuration of a charging device according to the present invention, and FIG. 3 is a first embodiment of a charging device according to the present invention. FIG. 4 is a perspective explanatory view showing a configuration of a charging device according to a second embodiment of the present invention, FIG. 5 is a diagram showing a discharge starting voltage in the charging device of the first embodiment, FIG. 6 shows the distance P between the needle tips of a plurality of needle electrodes when the distance D between the needle tips of the needle electrodes and the discharge auxiliary member is set to 4 (mm) in the charging device of the first embodiment. Is a diagram showing the relationship between each applied voltage and discharge current at 2 (mm), 3 (mm), 4 (mm), 6 (mm), 8 (mm), 10 (mm), and 12 (mm). FIG. 7 is a diagram showing a temporal change in the amount of current when a sheet as a recording medium is passed through a charging device.
[0024]
First, the configuration of an image forming apparatus including the charging device according to the present invention will be described with reference to FIG. The image forming apparatus shown in FIG. 1 includes four process stations 1a, 1b, 1c, and 1d serving as image forming means of four different colors of cyan, yellow, magenta, and black, which are arranged side by side. It is configured as an image forming apparatus used.
[0025]
The process stations 1a to 1d have photosensitive drums 2a, 2b, 2c and 2d serving as image carriers, and the surfaces of the photosensitive drums 2a to 2d are arranged around the respective photosensitive drums 2a to 2d. After being uniformly charged by the charged primary chargers 3a, 3b, 3c, 3d, the primary chargers 3a, 3b, 3c, 3d receive exposure based on image information by exposure devices 4a, 4b, 4c, 4d such as LEDs (light emitting diodes), lasers, and the like. Thus, an electrostatic latent image is formed. This electrostatic latent image is developed with a toner of each color by a developing device 5a, 5b, 5c, 5d.
[0026]
Each of the process stations 1a to 1d is detachable from the image forming apparatus main body as a process cartridge. Each process cartridge has a configuration in which each of the photosensitive drums 2a to 2d, the primary chargers 3a to 3d, the developing devices 5a to 5d, and the cleaning means 6a, 6b, 6c, 6d are integrally integrated.
[0027]
On the other hand, the transfer material S serving as a recording medium accommodated in the feeding cassette 15 is fed into the image forming apparatus main body by the feeding roller 16, is conveyed by the registration roller pair 17, and then is supplied by the suction bias power supply 13 to the positive polarity A transfer roller 7 serving as a transfer material carrier is electrostatically attracted to and carried by a suction roller 12 to which a suction bias voltage is applied.
[0028]
The transfer / conveyance belt 7 is stretched by four rollers: a driving roller 8, a suction-opposed roller 9, and tension rollers 10 and 11. The process stations 1a, 1b, 1c, 1d of the respective colors of cyan, yellow, magenta, and black are arranged on the surface of the transfer conveyance belt 7 in order from the upstream side along the moving direction of the transfer conveyance belt 7 (the direction of arrow a in FIG. 8). Are arranged substantially perpendicularly to.
[0029]
Transfer rollers 14a, 14b, 14c, and 14d serving as transfer means are disposed inside the transfer conveyance belt 7 so as to face the respective photosensitive drums 2a to 2d, and the transfer material S adsorbed on the transfer conveyance belt 7 is disposed. When sequentially passing through the process stations 1a to 1d of the respective colors, the toner images of the respective colors carried on the respective photosensitive drums 2a to 2d are electrostatically successively transferred onto the surface of the transfer material S by the operation of the transfer rollers 14a to 14d. Transcribed.
[0030]
A fixing device 18 serving as a fixing unit is disposed downstream of the transfer roller 14d, which is the transfer unit, at the most downstream side in the recording medium transport direction. A charging device 22 that charges or removes the transfer material S that is a recording medium is provided between the roller 14d and the fixing device 18 that serves as a fixing unit.
[0031]
The transfer material S on which the toner images have been transferred from the photosensitive drums 2a to 2d by the transfer rollers 14a to 14d is peeled off from the peripheral surface of the driving roller 8 and is discharged by the charging device 22 to be conveyed to the fixing device 18 where the fixing is performed. After the toner image is fixed on the transfer material S by being heated and pressed in the device 18 to form a permanent image, the toner image is discharged onto a discharge tray 19 provided outside the apparatus.
[0032]
The residual toner remaining on each of the photosensitive drums 2a to 2d is collected by each of the cleaning means 6a to 6d, and the surfaces of the photosensitive drums 2a to 2d are cleaned.
[0033]
When an image is formed on both sides of the transfer material S, the transfer material S discharged onto the discharge tray 19 is re-fed and reversed by the re-feed guide 20 and the re-feed roller 21 and the like. After the toner image is formed on the second surface by the action of the process stations 1a, 1b, 1c, 1d and the transfer rollers 14a to 14d, the toner image is formed on the peripheral surface of the drive roller 8 The toner image is removed by the charging device 22, the toner image is fixed on the transfer material S in the fixing device 18, and then discharged onto a discharge tray 19 provided outside the apparatus.
[0034]
As shown in FIGS. 2 and 3, the charging device 22 includes a plurality of needle electrodes 23 linearly arranged at predetermined intervals, and a discharge assisting electrode 23 disposed near a needle tip 23 a of the needle electrode 23. A discharge auxiliary metal plate 24 serving as a member is provided electrically insulated with an insulating spacer 25 interposed therebetween. The discharge auxiliary metal plate 24 is grounded, and the positive electrode side of a high-voltage DC power supply 26 serving as a voltage applying unit is connected to the positive electrode side. It is electrically connected to the needle electrode 23.
[0035]
Then, a DC voltage is applied between the needle electrode 23 and the auxiliary discharge metal plate 24 by the high-voltage DC power supply 26 to cause a discharge between the needle electrode 23 and the auxiliary discharge metal plate 24, and the vicinity of the needle electrode 23. The transfer material S made of paper, synthetic resin, or the like serving as a member to be charged, which is located in the area, can be charged or discharged.
[0036]
Here, the value when the unit of the distance between the needle tips 23a of the plurality of needle electrodes 23 (hereinafter, referred to as “pitch”) is expressed in mm is P, the needle tips 23a of the needle electrodes 23 and the discharge auxiliary metal D is a numerical value when the unit of the separation distance from the plate 24 is expressed in mm, and V is a numerical value when the unit of the voltage applied between the needle electrode 23 and the discharge auxiliary metal plate 24 is kV. FIG. 5 shows the firing voltage Vs (kV) at each separation distance D (mm), and FIG. 6 shows the pitch P (mm) when the separation distance D (mm) is set to 4 (mm). It is a figure which shows the relationship between each applied voltage and discharge current in 2 (mm), 3 (mm), 4 (mm), 6 (mm), 8 (mm), 10 (mm), and 12 (mm).
[0037]
Generally, when a high voltage is applied to a conductive member, a unit when the unit of the separation distance between the two conductive members is expressed in mm is D ₁ and a unit of the potential difference is from the viewpoint of preventing leakage from other conductive members. Is represented by kV, and it is necessary to satisfy D ₁ ≧ V _{1 where} V ₁ is a numerical value.
[0038]
Here, in the case of the charging device 22 having a configuration as shown in FIG. 3, D represents a numerical value when the unit of the separation distance between the needle tip 23 a of the needle electrode 23 and the discharge auxiliary metal plate 24 is mm, and Assuming that Vs is a numerical value when the unit of the voltage at which discharge is started with respect to the separation distance D (mm) is kV, the separation distance D (mm) satisfying the condition of D ≧ Vs is D ≧ It becomes 3.
[0039]
Next, FIG. 6 shows the needles of a plurality of needle electrodes 23 at a numerical value D = 4 (mm) when the unit of the separation distance between the needle tip 23a of the needle electrodes 23 and the discharge auxiliary metal plate 24 is expressed in mm. When the unit of the distance (pitch) between the tips 23a is expressed in mm, the numerical value P (mm) is 2 (mm), 3 (mm), 4 (mm), 6 (mm), 8 (mm), 10 The relationship between each applied voltage and the discharge current at (mm) and 12 (mm) is shown.
[0040]
From this table, it can be seen that when the pitch P (mm) = 2 (mm), the discharge starting voltage Vs is high, and the discharge current changes rapidly as the voltage V increases, making it difficult to obtain a stable discharge phenomenon. As shown in FIG. 6, as the pitch P (mm) is increased (the pitch is increased), the discharge starting voltage Vs decreases, and the relationship between the applied voltage and the discharge current changes almost linearly. , The discharge phenomenon becomes stable.
[0041]
This is because, by increasing the pitch P (mm) (widening the pitch), the potential interference between the needle tips 23a adjacent to the needle electrodes 23 is prevented, and the efficiency of each needle of the needle electrodes 23 is reduced. This is because good electric field concentration is performed.
[0042]
Practically, it can be used with P ≧ D (the pitch P (= 4 mm or more) ≧ separation distance D (= 4 mm) in FIG. 6) at which the discharge starts to be stable, and more preferably, a region satisfying P ≧ 2D. If the pitch P (mm) is too wide, charging unevenness may occur on the transfer material S serving as a member to be charged. If it is necessary to prevent this, it is preferable to set 5D ≧ P.
[0043]
From the above, if the relationship among D, P, and V is configured so as to satisfy the condition of {D ≧ 3, and P ≧ D, D ≧ V, P ≧ D ≧ V... preferable.
[0044]
FIG. 4 shows the configuration of a second embodiment of the charging device according to the present invention. The discharge auxiliary metal plates 24a and 24b are provided on both sides of the needle electrode 23 with insulating spacers 25a and 25b interposed therebetween. The discharge auxiliary metal plates 24a and 24b are grounded, and the positive electrode side of the high voltage DC power supply 26 is electrically connected to the needle electrode 23.
[0045]
In the charging device 22 having the configuration shown in FIG. 4, the discharge current amount per needle of the needle electrode 23 is increased, so that more stable discharge performance can be obtained, and the transfer material S can be stably charged or neutralized. You can do it.
[0046]
In this case, when the unit of the distance between the needle tip 23a of the needle electrode 23 and each of the discharge assisting metal plates 24a and 24b is expressed in mm, the numerical values are represented by Da and Db, respectively. Then, the numerical value Da when the unit of the separation distance between the needle tip 23a of the needle electrode 23 and the discharge auxiliary metal plate 24a having a smaller (closer) separation distance satisfies the above equation (1). Is required.
[0047]
As described above, the separation distance D (mm) between the needle tip 23a of the needle electrode 23 of the charging device 22 and the discharge auxiliary metal plate 24 (24a, 24b) is set to an appropriate distance so as to satisfy the above formula (1). By further optimizing the distance (pitch) P (mm) between the needle tips 23a of the needle electrodes 23, the discharge starting voltage Vs is reduced, potential interference between the needle tips 23a is prevented, and efficiency is improved. By achieving a good electric field concentration, stable charging or static elimination performance can be obtained with a simple configuration.
[0048]
In the image forming apparatus shown in FIG. 1, instead of the wire type corona charger 51 of the conventional example shown in FIGS. 8 and 9 described above, a charging device 22 shown in FIGS. The transfer material S is disposed on the toner image surface side of the transfer material S at a portion where the transfer material S is transferred to the device 18. Is set to, for example, 10 mm to 50 mm.
[0049]
When the transfer material S passes through the four process stations 1a to 1d, it receives a large amount of charge because it undergoes four transfer steps by each of the transfer rollers 14a to 14d. For example, a high potential of about -3000V is applied and the transfer material S is charged. Hold.
[0050]
Therefore, a separation discharge phenomenon occurs at a separation portion formed by the peripheral surface of the drive roller 8 of the transfer conveyance belt 7, and a phenomenon that the toner image transferred onto the transfer material S is disturbed along the discharge pattern occurs. In particular, when forming an image in a low-temperature and low-humidity environment in which the transfer material S has high resistance and is easily charged, or when forming a double-sided image, the second surface of the transfer material S that has been dried after passing through the fixing process in the image formation on the first surface once. Notably occurs during image formation.
[0051]
In order to prevent the image disturbance due to the peeling discharge phenomenon, as shown in FIG. 1, a charging device 22 is disposed between the transfer conveyance belt 7 and the fixing device 18 on the recording medium conveyance path. For example, on the peripheral surface of the driving roller 8 from which the transfer material S is separated, the distance between the needle tips 23a of the needle electrodes 23 of the charging device 22 (pitch) P (mm) = 8 (mm). The distance D (mm) between the needle tip 23a of the needle electrode 23 and the auxiliary discharge metal plate 24 (24a, 24b) is 4 (mm), and the voltage is applied between the needle electrode 23 and the auxiliary discharge metal plate 24. A corona discharge is generated using the charging device 22 under the condition that the voltage V (kV) is set to 3.8 (kV).
[0052]
When the transfer material S is not present, substantially all of the discharge current of, for example, 60 μA flows into the discharge auxiliary metal plate 24 (24a, 24b) due to the corona discharge of the charging device 22. For example, when the transfer material S to which (−3000 V) is applied passes as an object to be charged facing the charging device 22 at a speed of, for example, 100 mm / sec, the corona discharge current is reduced due to a change in the electric field near the needle electrode 23 as described above. From 60 μA to, for example, 70 μA, and furthermore, as shown in FIG. 2, as shown in FIG. 2, the charge of the transfer material S is removed by flowing as ion wind to the transfer material S, thereby preventing image defects due to peeling discharge. Can be done.
[0053]
In this case, the amount of current flowing into the transfer material S as ion wind is at most 3 μA or less. FIG. 7 is a schematic diagram showing an example of the relationship between the input current to the needle electrode 23 and the current flowing into the discharge auxiliary metal plate 24 (24a, 24b).
[0054]
According to the above configuration, when the transfer material S is peeled from the transfer conveyance belt 7, the charge of the transfer material S is removed by corona discharge of the charging device 22, and peeling discharge can be prevented.
[0055]
Therefore, unlike the corona charger 51 using the tungsten wire 52 shown in FIG. 8 and FIG. The charging device 22 that can exhibit performance can be provided.
[0056]
Note that, in the above-described embodiment, an example in which the charge removal of the in-line transfer material S is performed using the charging device 22 has been described. However, the present invention is not limited to this. The present invention is also applicable to the case where charging or static elimination of the photosensitive drums 2a to 2d, the transfer / conveyance belt 7, the fixing device 18 and the like, which are predetermined members in the above, is performed.
[0057]
【The invention's effect】
Since the present invention has the above-described configuration and operation, the separation distance (pitch) between the needle tips of the needle electrodes of the charging device and the separation distance between the needle tips of the needle electrodes and the discharge assisting member are determined. By appropriately setting, a charging device with stable discharge performance and high safety can be provided.
[0058]
In addition, by applying this charging device to an electrophotographic image forming apparatus, it is possible to prevent an image defect due to a discharge phenomenon, and to charge or discharge a predetermined member.
[Brief description of the drawings]
FIG. 1 is an explanatory sectional view showing a schematic configuration of an image forming apparatus according to the present invention.
FIG. 2 is a partially enlarged view showing an arrangement configuration of a charging device according to the present invention.
FIG. 3 is a perspective explanatory view showing a configuration of a first embodiment of a charging device according to the present invention.
FIG. 4 is a perspective explanatory view showing a configuration of a second embodiment of the charging device according to the present invention.
FIG. 5 is a diagram showing a discharge starting voltage in the charging device of the first embodiment.
FIG. 6 shows the charging device of the first embodiment, in which the distance between the needle tips of the plurality of needle electrodes is set to 4 (mm) when the distance D (mm) between the needle tips of the needle electrodes and the discharge auxiliary member is set to 4 (mm). And the applied voltage at the separation distance (pitch) P (mm) of 2 (mm), 3 (mm), 4 (mm), 6 (mm), 8 (mm), 10 (mm), and 12 (mm) FIG. 4 is a diagram illustrating a relationship with a discharge current.
FIG. 7 is a diagram illustrating a temporal change in the amount of current when a sheet as a recording medium is passed through a charging device.
FIG. 8 is a diagram illustrating a configuration of a conventional image forming apparatus.
FIG. 9 is a diagram showing a configuration of a wire type corona charger.
[Explanation of symbols]
1a to 1d process station, 2a to 2d photoconductor drum, 3a to 3d primary charger, 4a to 4d exposure device, 5a to 5d developing device, 6a to 6d cleaning means, 7 transfer transfer belt , 8: drive roller, 9: suction opposing roller, 10, 11: tension roller, 12: suction roller, 13: suction bias power supply, 14a to 14d: transfer roller, 15: feeding cassette, 16: feeding roller, 17 .., Registration roller pair, 18, fixing device, 19, discharge tray, 20, re-feed guide, 21, re-feed roller, 22, charging device, 23, needle electrode, 23 a, needle tip, 24, 24 a, 24 b ... discharge auxiliary metal plate, 25, 25a, 25b ... insulating spacer, 26 ... high voltage DC power supply, S ... transfer material

Claims (3)

A plurality of needle-like electrodes arranged on a straight line at predetermined intervals, a discharge auxiliary member arranged near a needle tip of the needle-like electrode, and applying a voltage between the needle-like electrode and the discharge auxiliary member. A voltage applying means for applying a voltage between the needle electrode and the discharge assisting member by the voltage applying means to cause a discharge between the needle electrode and the discharge assisting member. In a charging device for charging an object to be charged located in the vicinity of the shape electrode,
When the unit of the distance between the needle tips of the plurality of needle electrodes in mm is represented by mm, and the unit of the voltage applied between the needle electrodes and the discharge assisting member is kV is represented by kV. Where V is the numerical value of D, and D is the numerical value when the unit of the separation distance between the needle tip of the needle electrode and the discharge assisting member is mm.
A charging device characterized by satisfying a condition of D ≧ 3 and P ≧ D ≧ V. An image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image to a recording medium, and a transfer unit that is disposed downstream of the transfer unit in the recording medium conveyance direction, and Fixing means for fixing the toner image transferred to the recording medium,
An image forming apparatus, comprising: the charging device according to claim 1 disposed between the transfer unit and the fixing unit on a recording medium transport path, and charging or discharging the recording medium by the charging device. An image carrier, an image forming unit for forming a toner image on the image carrier, a transfer unit for transferring the toner image to a recording medium, and a fixing unit for fixing the toner image transferred to the recording medium In the image forming apparatus,
An image forming apparatus, wherein a predetermined member in the image forming apparatus is charged or neutralized by the charging device according to claim 1.

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