JP2004004334A - Corona discharge device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corona discharge device which uses a needlelike electrode and to realize both reduction of its manufacturing cost and improvement of the durability of the electrode. <P>SOLUTION: The corona discharge device which has a metal electrode having a plurality of needlelike projections arranged linearly at specified intervals (p) and faces an electrostatically charged body to charge it by corona discharge is characterized in that the surface of the metal electrode having the needlelike projections is plated with a conductive material. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona discharge device facing a member to be charged and charging the member to be charged by corona discharge, for example, a charging device or a discharging device used for charging or discharging a predetermined member in an electrophotographic image forming apparatus As a corona discharge device.
[0002]
[Prior art]
2. Description of the Related Art Non-contact corona discharge chargers are used in electrophotographic copying machines, printers, and the like that have been put into practical use. It is known that corona discharge is likely to occur near sharp projections such as needle tips.In some cases, needles are used as discharge electrodes. Met.
[0003]
On the other hand, a corona discharge charger of the wire electrode type as shown in FIG. 5 has a single thin metal wire (tungsten wire) stretched in the air to be a corona discharge electrode, compared with a device using the needle as a discharge electrode. Therefore, the majority of the electrophotographic devices that are actually commercialized use wires as discharge electrodes.
[0004]
However, the corona discharge charger of the wire type has a stable discharge and is easy to obtain the effect, but the wire is apt to be cut, and there is a difficulty in the life and safety measures.
[0005]
In JP-A-5-45999 and JP-A-6-118728, in order to save the trouble of arranging a large number of needles on a substrate, a metal thin plate using copper or SUS material is used as an electrode as described above by etching. For example, as shown in FIG. 4, it is formed into a sawtooth shape by precision press working. According to this method, instead of arranging the needles, it is possible to arrange the sharp-edged electrodes accurately and at low cost to form a corona discharge electrode.
[0006]
[Problems to be solved by the invention]
The reason that needle electrodes have not been used so far is not only because the manufacturing cost is higher than wire electrode type, but also due to the manufacturing conditions, burrs and irregularities occur near the tip of the needle, causing discharge unevenness and Depending on the state, its durability may be a factor. That is, when the discharge continues for a long time, the tip of the needle is oxidized by the discharge and becomes brittle, and the tip of the needle scatters due to the explosion pressure of the discharge, and the tip becomes round, so that there is a problem that the discharge efficiency is reduced. Further, there is a problem that partial discharge unevenness occurs due to a difference in the degree of deterioration of each needle.
[0007]
Similarly, the wire surface may be partially embrittled or deformed even with a wire electrode, but since the wire can be discharged over the entire length, even if any part of the wire no longer discharges, the next part will discharge immediately, causing uneven discharge. Is unlikely to occur.
[0008]
Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a corona discharge device using a needle-shaped electrode, and at the same time, reduce the manufacturing cost and improve the durability of the electrode. It is.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 for achieving the above object has a metal electrode having a plurality of needle-like projections arranged on a straight line at a predetermined interval, and opposes the object to be charged and applies the corona to the object. In a corona discharge device that is charged by discharge, a surface of the metal electrode having the needle-like protrusions is plated with a conductive material.
[0010]
The invention according to claim 2 is characterized in that the metal electrode having the needle-like protrusions is formed by precision-pressing a thin metal plate.
[0011]
The invention according to claim 3 is characterized in that the metal electrode having the needle-like projection is formed by etching a thin metal plate.
[0012]
The invention according to claim 4 is characterized in that a SUS material is used as a material of the metal electrode having the needle-like projections.
[0013]
The invention according to claim 5 is characterized in that the conductive material used for plating the surface of the metal electrode is gold, platinum, copper, nickel, or chromium.
[0014]
The invention according to claim 6, wherein the image carrier, an image forming means for forming a toner image on the image carrier, a transfer means for transferring the toner image to a recording medium, and the toner image transferred to the recording medium And a fixing unit for fixing the corona discharge device according to any one of claims 1 to 5 between the transfer unit and the fixing unit. It is characterized by performing.
[0015]
The invention according to claim 7, wherein the image carrier, an image forming means for forming a toner image on the image carrier, a transfer means for transferring the toner image to a recording medium, and the toner image transferred to the recording medium 6. A corona discharge device according to claim 1, wherein a fixing unit for fixing the toner image is provided to charge or remove a predetermined member in the apparatus main body. It is characterized by.
[0016]
According to the above configuration, the surface of the metal electrode having the needle-like protrusions is plated with a conductive material (preferably, a metal having excellent corrosion resistance), so that the production cost is low, the discharge is stable, and the needle-like electrode has high durability. It is possible to provide an improved corona discharge device. In particular, by applying the corona discharge device having the above configuration to an electrophotographic image forming apparatus, it becomes possible to perform charging and discharging of a recording medium and a predetermined member in the apparatus main body.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments are to be appropriately changed depending on the configuration and various conditions of the apparatus to which the present invention is applied, and It is not intended to limit the scope of the invention to them only, unless specifically stated.
[0018]
[First Embodiment]
FIG. 2 shows a corona discharge charging device having a needle electrode according to a first embodiment to which the present invention is applied. 2, the corona discharge device 30 has a configuration in which a metal electrode having a needle-like protrusion 31a (hereinafter, referred to as a needle-like electrode) and a metal plate as a discharge auxiliary member are provided via an insulating spacer 33. The distance between the electrode 31 and the discharge assisting metal plate 32 is D [mm], and the distance between the tips of the needle-like protrusions 31a of the needle-like electrode 31 is p [mm]. In the present embodiment, the surface of the metal electrode 31 having the needle-like projections 31a is plated with a conductive material 34 such as nickel (preferably a metal having excellent corrosion resistance).
[0019]
With the configuration shown in FIG. 2, an improvement in corrosion resistance can be expected for a needle-like electrode (comparative example: FIG. 4) in which a SUS plate having a thickness of 100 [μm] is manufactured by precision press working (Comparative Example: FIG. 4). Using a needle-shaped electrode (this embodiment: FIG. 1) plated with electroless nickel, the durability of the two was compared.
[0020]
The reason why the SUS material is used as the material of the metal electrode having the needle-like protrusions is that there are advantages such as excellent corrosion resistance, high rigidity, and good workability.
[0021]
The experimental conditions were as follows: D = 4 [mm], p = 8 [mm], and corona discharge when +4000 [V] voltage was continuously applied to each needle electrode from a constant voltage power supply. Changes in the current and the shape of the tip of the needle-like protrusion were observed. The experiment was performed in an environment at a temperature of 23 ° C. and a humidity of 60%.
[0022]
FIG. 6 shows the change with time of the discharge current of both, and FIG. 7 shows the change with time of the shape of the tip R of the needle-like projection. 6 and 7, the time-dependent change of the unplated needle electrode is indicated by a dotted line (REF), and the time-dependent change of the plated needle electrode is indicated by a solid line (KN plating). FIG. 8 shows an example of the result of observing and measuring the shape of the tip of the needle-like projection of the electrode without plating with a microscope.
[0023]
From FIGS. 6 and 7, it can be seen that when a needle-shaped electrode not plated with nickel is used, the discharge current decreases with time, and the R shape of the tip of the needle-shaped protrusion increases. For example, as shown in FIG. 8, after 100 hours, the shape of the tip of the needle-like projection is rounded to R = about 60 μm. On the other hand, by using a nickel-plated SUS needle electrode, embrittlement of the needle electrode due to oxidation is less likely to occur even if corona discharge continues for a long time. Accordingly, it can be seen that a durable corona discharger can be obtained in which the tip of the needle-like projection is hardly rounded and the corona discharge current is hardly reduced.
[0024]
In the case of pressing the SUS plate, precision press processing was used. However, in the comparative example where plating was not performed, discharge unevenness may occur from the beginning due to minute burrs and irregularities generated at the time of pressing. In contrast to the necessity of additional processing, in the present embodiment in which plating is performed, there is an advantage that since the non-uniformity of the surface is improved by plating, it is not necessary to perform additional polishing or the like after pressing. .
[0025]
Further, in the present embodiment, the case where nickel is used as the conductive material used for plating the metal electrode having the needle-like projections is exemplified.However, the present invention is not limited to this. It has been confirmed that the same effect can be obtained by using platinum, copper, chromium and the like.
[0026]
In addition, the metal electrode having the needle-shaped protrusion according to the present embodiment may be formed into a needle-like shape by etching a thin metal plate other than the above-described press working. In this case, the same effect can be obtained. did it. In addition to the SUS material, a material such as phosphor bronze having excellent corrosion resistance and high rigidity can be used as the thin metal plate.
[0027]
[Second embodiment]
FIG. 3 shows an electrophotographic image forming apparatus provided with a corona discharge device having the plated needle electrodes. In the present embodiment, an image forming apparatus (printer) using a so-called four-color full-color electrophotographic system in which four process stations 1a, 1b, 1c, and 1d as image forming units of different colors are arranged and arranged. It will be described using FIG.
[0028]
The 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 as charging means. Thereafter, an exposure is performed based on image information by the exposure devices 4a to 4d such as LEDs and lasers, and an electrostatic latent image is formed. This electrostatic latent image is developed with a toner of each color by developing devices 5a to 5d as developing means. The toner remaining on the surfaces of the photosensitive drums 2a to 2d after the transfer is removed by cleaning devices 6a to 6d as cleaning means.
[0029]
Each of the process stations 1a to 1d is detachable from a main body (not shown) of the image forming apparatus as a process cartridge. Each process cartridge has a configuration in which the photosensitive drum 2, the primary charger 3, the developing device 5, and the cleaning device 6 are integrated.
[0030]
In the case of the image forming apparatus, the transfer material S is sent out from the feeding cassette 15 into the image forming apparatus by the feeding roller 16 and is conveyed to the registration roller 17. Then, a positive suction bias is applied from the suction bias power supply 13. The transfer roller 7 serving as a transfer material carrier is electrostatically attracted to and carried by the suction roller 12 to be carried.
[0031]
In the image forming apparatus, the transfer / conveying belt 7 is wound around four rollers: a driving roller 8, a suction opposing roller 9, and tension rollers 10 and 11.
[0032]
The process stations 1a, 1b, 1c, 1d of the respective colors of cyan, yellow, magenta, and black are arranged substantially vertically from the upstream along the moving direction (arrow direction) of the transfer conveyance belt 7.
[0033]
The transfer material S adsorbed on the transfer conveyance belt 7 sequentially passes through the process stations 1a to 1d of the respective colors, and the toner images of the respective colors on the photosensitive drums 2a to 2d are electrostatically transferred by transfer rollers 14a to 14d as transfer means. Are sequentially transferred. After that, these toner images are heated and pressed by a fixing device 18 as a fixing unit to be fixed on the transfer material S to form a permanent image. The transfer material S on which the image has been fixed is discharged onto a discharge tray 19.
[0034]
When double-sided printing is performed on the transfer material S, the transfer material S on which an image is formed on one surface as described above is re-used by using the re-feed path 20 and the re-feed roller 21. And an image is formed on the other surface in the same manner.
[0035]
In the image forming apparatus shown in FIG. 3, a corona discharge device 22 as a corona discharge device having plated needle electrodes is disposed on the image surface side of a transfer portion between the transfer conveyance belt 7 and the fixing device 18. In this case, the interval between the corona discharger 22 and the transfer material S, which is a member to be charged, is set to, for example, 10 to 50 [mm]. At this time, when the transfer material S passes through the four process stations, it undergoes four transfer steps, and thus receives a large amount of electric charge and maintains a high potential such as -3000 [V]. For this reason, a peeling discharge phenomenon occurs at the separation portion of the transfer conveyance belt, and a phenomenon that the toner image transferred onto the transfer material S is disturbed along the discharge pattern occurs. In particular, it occurs remarkably in a low-temperature and low-humidity environment in which the transfer material has high resistance and is easily charged, or in the second-side printing in a dry state after passing through a fixing step once in double-sided printing.
[0036]
As shown in FIG. 3, a corona discharger (hereinafter, referred to as a needle-like charger) 22 having needle-like electrodes is disposed between the transfer conveyance belt 7 and the fixing device 18 in order to prevent image disorder due to the peeling discharge phenomenon. Then, at a point where the transfer material S is separated from the transfer / conveyance belt 7, as an example, a voltage of +3800 [V] is applied to the needle electrode of the needle charger of P = 8 [mm] and D = 4 [mm]. To generate corona discharge.
[0037]
When the transfer material S does not exist, almost all of the current of, for example, 60 [μA] due to the corona discharge of the needle charger (needle electrode) flows into the discharge auxiliary metal plate. When a transfer material S of, for example, -3000 [V]) passes as an opposing charged object at a speed of, for example, 100 [mm / s], the corona discharge current is increased to 60 [μA] due to a change in the electric field near the needle electrode. To, for example, 70 [μA], and a part of the current flows as ionic wind to the transfer material S, thereby removing the charge of the transfer material S, thereby preventing an image defect due to peeling discharge. In this case, the amount of current flowing into the transfer material S as ion wind is at most 3 [μA] or less.
[0038]
In the above-described configuration, a continuous paper passing durability test was performed in a low-temperature and low-humidity environment where peel discharge is likely to occur, in this case, an environment of a temperature of 15 ° C. and a humidity of 10%, and nickel plating was performed as in the first embodiment. The effect of a corona discharger having a SUS material needle electrode provided with a SUS material and a corona discharger having a SUS material needle electrode not subjected to nickel plating were confirmed. The result is shown in FIG. The needle-shaped electrode was cleaned every 20K (K = 1000) sheets, and the evaluation was performed so that dirt and the like did not affect the discharge amount.
[0039]
In a corona discharger using an unplated SUS needle-like electrode, the discharge amount decreases with continuous paper passing, and the discharge amount of each needle-like protrusion varies. As a result, discharge unevenness appears in the image from about 100K sheets of continuous paper passing. On the other hand, by using the nickel-plated needle-shaped electrode, a corona discharger with a stable discharge amount could be obtained even when 300K sheets were continuously fed.
[0040]
As described above, in the case of the above-described configuration, the charge of the transfer material S is removed by corona discharge by the needle-shaped charger 22 when the transfer material S is peeled from the transfer conveyance belt 7, and the peel discharge can be stably prevented over a long period of time. Therefore, unlike the corona wire method, there is no need to worry about wire breakage, and there is no need to take safety measures such as leaks. It is possible to provide a corona discharger that does not require replacement, has low manufacturing costs, has a long life, and has stable performance.
[0041]
In the present embodiment, an example is shown in which the corona discharge device exemplified in the first embodiment is used for removing the charge of the transfer material S in the above-described in-line type image forming apparatus. The present invention is not limited to this, and it is also effective to apply the above-described corona discharge device to charge or remove a predetermined member such as a photosensitive drum, a transfer / transport belt, and a fixing device.
[0042]
[Other embodiments]
In the above-described second embodiment, four image forming units of different colors are used for color image formation. However, the number of used units is not limited, and may be appropriately set as needed.
[0043]
In the above-described second embodiment, as a process cartridge (process station) detachable from the apparatus main body, a photosensitive drum, and a charging unit, a developing unit, and a cleaning unit as process units acting on the photosensitive drum are provided. Although the process cartridge has been illustrated as an example, the present invention is not limited to this, and is a process cartridge that integrally includes any one of a charging unit, a developing unit, and a cleaning unit in addition to the photosensitive drum. Is also good.
[0044]
Further, in the above-described second embodiment, the configuration in which the process cartridge including the photosensitive drum is detachable from the apparatus main body is exemplified. However, the present invention is not limited to this. For example, each constituent member is incorporated in the apparatus main body. The configuration may be such that each component is detachable from the apparatus body.
[0045]
In the above-described second embodiment, a printer is exemplified as an image forming apparatus. However, the present invention is not limited to this. For example, another image forming apparatus such as a copying machine or a facsimile apparatus, or a function thereof. Other image forming apparatuses such as a multi-function machine that combines the above, or using a drum instead of the above-mentioned belt as a transfer material carrier, and transferring toner images of each color sequentially on a transfer material carried on the transfer material carrier And an intermediate transfer member such as a belt or a drum, and successively superimpose and transfer the toner images of each color onto the intermediate transfer member, and collectively transfer the toner images carried on the intermediate transfer member onto a transfer material. The same effect can be obtained by appropriately applying the above-described corona discharge device according to the present invention to the image forming apparatus.
[0046]
【The invention's effect】
As described above, according to the present invention, the metal electrode having the needle-like projections is plated with a conductive material (preferably, a metal having excellent corrosion resistance), so that the production cost is low and the discharge has stable durability. It is possible to provide a corona discharge device using a high needle electrode. In particular, by applying the corona discharge device having the above configuration to an electrophotographic image forming apparatus, it becomes possible to perform charging and discharging of a recording medium and a predetermined member in the apparatus main body.
[Brief description of the drawings]
FIG. 1 is a front view of a needle electrode according to an embodiment of the present invention.
FIG. 2 is a perspective view illustrating a state of a corona discharger having a needle electrode.
FIG. 3 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 4 is a front view of a needle electrode according to a conventional example.
FIG. 5 is a perspective view illustrating a state of a wire type charger.
FIG. 6 is a diagram illustrating a change with time of a discharge current when corona discharge is continued.
FIG. 7 is a diagram illustrating a temporal change in the shape of the tip of a needle-like protrusion when corona discharge is continued.
FIG. 8 is a diagram showing an example of an observation result of the shape of the tip of a needle-like projection when corona discharge is continued.
FIG. 9 is a diagram illustrating an example of an observation result of discharge unevenness appearing on an image at the time of a continuous paper passing durability test.
[Explanation of symbols]
S: transfer materials 1a, 1b, 1c, 1d: process stations 2a, 2b, 2c, 2d: photoconductor drums 3a, 3b, 3c, 3d: primary chargers 4a, 4b, 4c, 4d: exposure devices 5a, 5b, 5c, 5d Developing devices 6a, 6b, 6c, 6d Cleaning device 7 Transfer / conveying belt 8 Drive roller 9 Suction opposing rollers 10, 11 Tension roller 12 Suction roller 13 Suction bias power supplies 14a to 14d Transfer Roller 15 Feeding cassette 16 Feeding roller 17 Registration roller 18 Fixing device 19 Discharge tray 20 Refeeding path 21 Refeeding roller 22 Needle charger (corona discharger)
Reference Signs List 30 Corona discharge device 31 Needle electrode 31a Needle protrusion 32 Discharge auxiliary metal plate 33 Insulating spacer 34 Conductive material

Claims (7)

In a corona discharge device having a metal electrode having a plurality of needle-shaped protrusions arranged on a straight line at predetermined intervals, and facing the member to be charged, and charging the member to be charged by corona discharge,
A corona discharge device wherein a surface of the metal electrode having the needle-like projections is plated with a conductive material. 2. The corona discharge device according to claim 1, wherein the metal electrode having the needle-like protrusions is formed by precision-pressing a thin metal plate. 3. 2. The corona discharge device according to claim 1, wherein the metal electrode having the needle-like projections is formed by etching a thin metal plate. 3. The corona discharge device according to any one of claims 1 to 3, wherein a SUS material is used as a material of the metal electrode having the needle-like protrusions. The corona discharge device according to any one of claims 1 to 4, wherein the conductive material used for plating the surface of the metal electrode is gold, platinum, copper, nickel, or chromium. Image carrier, image forming means for forming a toner image on the image carrier, transfer means for transferring the toner image to a recording medium, fixing means for fixing the toner image transferred to the recording medium, In the image forming apparatus having
An image forming apparatus, wherein the corona discharge device according to any one of claims 1 to 5 is installed between the transfer unit and the fixing unit, and performs charge elimination of a recording medium. 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. An image forming apparatus having
An image forming apparatus comprising the corona discharge device according to any one of claims 1 to 5 for charging or discharging a predetermined member in the apparatus main body.

Images