JP4179734B2 - Charging device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device and an image forming apparatus, and more specifically, includes a charger for an electrophotographic recording apparatus that electrostatically transfers onto a recording paper after developing a latent image on a photoreceptor using a developer, and the charger. The present invention relates to an image forming apparatus such as a copy, a printer, and a fax machine.
[0002]
[Prior art]
In an image forming apparatus such as a copy, a printer, a facsimile, or the like, an image carrier is uniformly charged by various methods prior to forming an electrostatic latent image. The mainstream charging method is based on the corona discharge of the charger, but a large amount of ozone is generated during the discharge, and a high voltage power source of about 4 to 10 kV is required. Therefore, in recent years, a contact charging device has been put to practical use as an alternative charging method. This contact charging device is intended for low ozone and low power, and a conductive member such as a conductive roller, a conductive brush, or a conductive elastic blade is brought into contact with the surface of the image carrier, and the conductive member A voltage is applied to charge the image carrier. Several conventional examples of this contact charging device have been proposed. As conventional examples thereof, those disclosed in JP-A-56-144453, JP-A-1-93762, and the like are disclosed. Among these, a roller charging method using a conductive roller as a charging member is particularly preferably used from the viewpoint of charging stability. In the roller charging system, a charged elastic body is charged by pressing a conductive elastic roller against the charged body and applying a voltage thereto.
[0003]
However, recently, a new problem has arisen in the contact charging method such as the roller charging method. As a specific example, it may be caused by NOx adhering to the image carrier, and an image flow phenomenon, a phenomenon that the CTL layer of the image carrier is easily scraped by direct discharge, or the like may occur. Thus, several conventional examples of corona chargers that can solve new problems caused by the contact charging method have been proposed.
[0004]
As one of them, Japanese Patent Laid-Open No. 5-57137 (hereinafter referred to as Conventional Example 1) is provided with a wind control plate for turning the inflow direction of ozone air flowing into the ozone removal filter in an oblique direction. An ozone removing filter that efficiently removes ozone generated by corona discharge of a charging device or a transfer charger is disclosed. Japanese Patent Application Laid-Open No. 5-173659 provides a shutter made of a dielectric that is opened when the decharging charger is operated at an opening facing the surface of the photosensitive member of the decharging charger. There has been proposed an image forming apparatus capable of preventing a product or the like from adhering to the charger wire or the inside of the casing of the pre-cleaning decharging charger and maintaining stable performance. Further, JP-A-8-160717 discloses that the photosensitive member charging current Ip and the grid electrode so that the relationship between the photosensitive member charging current Ip and the grid electrode current Ig satisfies the conditional expression 1.5 ≦ Ig / Ip ≦ 4. The current Ig is set to suppress the generation of ozone and NOx, and even after long-term use of the corona discharge device, there is little discharge unevenness, no image drift occurs, and the surface potential at the start of use of the photoreceptor And a corona discharge device capable of reducing the difference between the surface potential after long-term use has been proposed.
[0005]
[Problems to be solved by the invention]
However, according to the conventional examples 1 to 3, the conventional corona charger generates a large amount of ozone and NOx, and has a structure in which it is removed by a filter before being discharged outside the image forming apparatus in consideration of the influence on the environment. It was. Further, inside the image forming apparatus, it reacts with moisture in the atmosphere and adheres to the photoconductor as an image carrier, causing a problem called image flow. In addition, the durability of the image carrier has been reduced by strongly cleaning the image carrier in order to prevent the occurrence of an image flow or to remove the image flow.
[0006]
The present invention is intended to solve these problems, and an object thereof is to provide a charger and an image forming apparatus capable of reducing generated gas such as ozone and NOx in a corona charger.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the charging device of the present invention has a plurality of charge wires having different wire diameters , and the charge wires are stranded .
[0011]
Furthermore, an image forming apparatus as another invention has the above-described charging device, so that generated gas such as ozone and NOx in the corona charger can be reduced, and maintainability and assemblability can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The charging device of the present invention has a plurality of charge wires having different wire diameters , and the charge wires are stranded.
[0013]
【Example】
FIG. 1 is a schematic configuration diagram of an image forming apparatus having a charging device according to an embodiment of the present invention. Note that the image forming apparatus of this embodiment shown in the figure is a printer or a copier using an electrophotographic process. In the figure, according to the image forming apparatus having the charging device of this embodiment, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device are disposed around an image carrier 1 as a charged body. The devices 6 are sequentially arranged in the clockwise direction. Further, a fixing device 8 for fixing the toner image electrostatically transferred to the transfer material 7 by the transfer device 5 is disposed. The image carrier 1 is a negative-polarity, rotating-drum type electrophotographic OPC photosensitive member having a diameter of 30 mm and a length of 340 mm, and is driven to rotate at a process speed (peripheral speed) of 125 mm / sec in the clockwise direction of the arrow. . The charging device 2 is a corona charger disposed opposite to the image carrier 1, and a charge wire 21 that charges the image carrier 1 by generating a discharge phenomenon by applying a high voltage, and the charge wire 21 and the image carrier. And a grid 22 disposed between the two for performing more uniform charging. A charging bias application power source 23 applies a predetermined charging bias to the charge wire 21 to uniformly charge the peripheral surface of the image carrier 1 to a surface potential, for example, −960 V. Then, the exposure apparatus 3 performs exposure such as laser beam scanning exposure of target image information and slit exposure of a document image on the charging processing surface of the image carrier 1, so that the exposed image information is applied to the surface of the image carrier 1. An electrostatic latent image corresponding to is formed. Next, toner is attached to the electrostatic latent image by the developing device 4 and sequentially visualized as a toner image. The developing device 4 is a two-component contact developing type device, and a developing sleeve 41 that rotates as a developer carrying member is disposed at a distance of, for example, 0.6 mm from the image carrier 1. For example, a developing bias is applied by a DC power source of −600V. Also, minus toner was used as the toner. The configuration of the developing device 4 will be described in detail.
[0014]
On the other hand, the transfer material 7 is nipped from a feeding / conveying device (not shown) to a transfer position which is a contact nip portion between the image carrier 1 and the transfer device 5 at an appropriate timing synchronized with the rotation of the image carrier 1. Be transported. The transfer device 5 includes a rotatable transfer roller, and a predetermined transfer bias having a polarity opposite to that of the toner is applied from the power source 51 to the transfer roller while the transfer material 7 is nipped and conveyed. As a result, the back side of the transfer material 7 is charged with the opposite polarity to the toner, and the toner images on the image carrier 1 are sequentially electrostatically transferred onto the surface of the transfer material 7. In this embodiment, a conductive sponge roller having a resistance of, for example, 5 × 10 ⁷ Ω and a diameter of 16 mm was used as the transfer roller, and transfer was performed by applying a DC voltage by constant current control. The transfer material 7 that has received the transfer of the toner image is separated from the surface of the image carrier 1 and conveyed to the fixing device 8 to be fixed with the toner image, and then discharged to the outside of the apparatus main body or on the back surface. If it is to be formed, it is re-conveyed to the transfer device 5 by re-conveying means (not shown). On the other hand, the transfer residual toner remaining on the image carrier 1 is peeled off from the image carrier 1 by the cleaning device 6 and stored in the cleaning device 6. Thereafter, it is returned to the developing device 4 again.
[0015]
Next, the configuration of the charger in this embodiment will be described. FIG. 2 is a diagram showing a configuration example of a corona charger wire used in the charger of the present embodiment. (A), (b) of the figure is an example in which one end of the charge wire 21 is connected to one connection terminal 25 and the other end is connected to the connection terminal 26 for each charge wire. (C), (d) of the same figure is the example which connected the both ends of the charge wire 21 to the one connection terminal 25,26, and is the figure which made the several charge wire 21 into the strand. As shown in FIG. 2, the maintainability and assemblability of the corona charger can be improved by connecting at least one end of each charge wire of the corona charger to one connection terminal. FIG. 3 is a characteristic diagram showing the relationship between the wire diameter and the ozone generation amount, and FIG. 4 is a characteristic diagram showing the relationship between the wire diameter and the NOx generation amount. Further, FIG. 5 is a characteristic diagram showing the relationship between the current value per unit length of the wire and the ozone concentration when two wires (wire diameter = 50 μm) as shown in FIG. FIG. 6 is a characteristic diagram showing the relationship between the current value per unit length of the wire and the NOx concentration when two wires (wire diameter = 50 μm) as shown in FIG. The vertical axis in FIG. 5 represents the ozone concentration converted per 1 mA of current, and similarly the vertical axis in FIG. 6 represents the NOx concentration. 5 and 6, the horizontal axis indicates the current value obtained by converting the wire length per 1 m unit. From the experimental results shown in FIGS. 3 and 4, it can be seen that the generation amount of ozone and NOx decreases as the wire diameter becomes thinner. In addition, from the experimental results shown in FIGS. 5 and 6, it can be seen that in the current region (1.5 to 2.0 mA / m shown in both figures) used in a normal corona charger, ozone or NOx can be obtained with one or two charge wires. It can be seen that the amount of generation is almost unchanged. That is, if the wire diameter is simply reduced, the amount of ozone and NOx generated decreases, but problems such as difficulty in cleaning from the viewpoint of service maintenance and the like, and the charge wire being easily cut off, occur. However, even if the wire diameter is reduced as shown in FIG. In addition, from the viewpoint of the strength of the charge wire, it is known that the strength of the charge wire is proportional to the cross-sectional area if the cross-sectional shape is the same. Therefore, for example, the diameter of two circular wires having a cross-sectional area equivalent to a charge wire having a circular cross section with a diameter of 60 μm is about 42.4 μm in calculation, and if the charge wire with about 42.4 μm is used, the strength is It can be seen that this is equivalent to a 60 μm charge wire. Similarly, the equivalent of a 50 μm charge wire is about 35.5 μm. However, for example, a 50 μm charge wire is very easy to cut, and the serviceability is markedly reduced compared to 60 μm. Therefore, 35.5 μm or more is desirable even when the number is two.
[0016]
However, this is not the case when different wire diameters are used. For example, it is conceivable that one is 45 μm and the other is 40 μm. Alternatively, it is conceivable to use 50 μm and 30 μm charge wires. The advantage of using different wire diameters is to increase the distortion of the electric field intensity and suppress the generation of gases such as ozone. Furthermore, it is possible to increase the number of charge wires and match the number of charge wires with a diameter of 10 μm from several tens (for example, 36). Similar to the above, this effect also increases the distortion of the electric field strength and suppresses the generation of gas such as ozone.
[0017]
Next, although the number of times of using the charge wire varies depending on the diameter of the wire, for example, in the case of a 50 μm charge wire, disconnection occurred when the number of times of charging was 5 times or more per 100 mm. In addition, it is known that the number of times increases if the work with the charge wire is performed while heat is applied. In addition, the number of times of contact increases when the wire diameter of the charge wire is reduced. Considering the above circumstances, in order to prevent disconnection in advance in the manufacturing process, the number of times using the charge wire is preferably 20 times or less. Further, in order to increase the distortion of the electric field strength, the generation of gas such as ozone can be suppressed by making the pitch of the stranded wire of the charge wire non-uniform or dense.
[0018]
FIG. 7 shows the simulation result. This figure shows the electric field intensity region where ozone is estimated to be generated by a darkened portion (black), where (a) of FIG. ) Shows the case of two wires. Moreover, FIG. 8 is a figure which shows the relationship of the maximum electric field strength-discharge area | region in the number of wires 1-3. As can be seen from FIG. 8, there is no difference between 1 and 3 up to an electric field strength of 3 × 10 ⁷ (V / m). That is, it can be seen that the number of charge wires is not related to the actual ozone generation amount, and that the wire diameter greatly depends on the ozone generation amount in combination with the experimental results. By the way, when a plurality of charge wires are used to form a stranded wire as described above, the discharge points vary and the charged potential of the photoconductor as the image carrier is not uniform. Therefore, the charging potential can be made uniform by inserting the grid between the charge wire and the photoconductor. In addition, it is not necessary to be concerned with the shape shown in the embodiments, and in addition, tungsten is usually used as the wire material. However, the material is not necessarily limited to tungsten, and another material may be applied to the surface.
[0019]
Here, the configuration of the developing device of FIG. 1 will be described. As shown in FIG. 1, a developing roller 41 as a developer carrying member provided in the developing device 4 is disposed so as to be close to the image carrying member 1, and a developing region is formed in a portion facing both of them. It has come to be. In the developing roller 41, a developing sleeve formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is rotated in an arrow direction, that is, counterclockwise by a rotation driving mechanism (not shown). It is provided as such. Note that the drum diameter of the image carrier 1 is set to 30 mm, and the drum linear velocity is set to 125 mm / sec. The sleeve diameter of the developing sleeve is set to 16 mm, and the sleeve linear velocity is set to 312.5 mm / sec. Therefore, the sleeve linear velocity ratio of the developing sleeve to the drum linear velocity of the image carrier 1 is 2.5. The development gap, which is the distance between the image carrier 1 and the development sleeve, is set to 0.6 mm. The development gap may be set to 30 times or less of the developer particle size. If it is wider than this, the image does not have an image density. If the sleeve linear velocity ratio is 1.1 or more, a sufficient image density can be obtained. In the developing sleeve, a magnet roller body for forming a magnetic field is provided in a fixed state inside the developing sleeve so as to make the developer stand on the surface of the developing sleeve. At this time, the carrier constituting the developer is spiked in a chain shape on the developing sleeve so as to follow the lines of magnetic force emitted from the magnet roller body, and the charged toner with respect to the carrier spiked in the chain shape. Is attached to form a magnetic brush. The magnetic brush is transferred in the same direction as the developing sleeve (counterclockwise direction) as the developing sleeve rotates. The magnet roller body includes a plurality of magnetic poles. Specifically, the development main magnetic pole P1 for causing the developer to rise in the developing area, the magnetic pole P5 for pumping the developer on the developing sleeve, and the developer pumped up on the developing sleeve to the developing area. A magnetic pole P6 to be conveyed and magnetic poles P2 and P3 to convey the developer in the developed region are provided. Each of these magnetic poles P1, P5, P6, P2 and P3 is arranged in the radial direction of the developing sleeve. This magnet roller is composed of 6-pole magnets, but as a magnet roller composed of 8 or more poles, the number of poles is further increased from the P3 pole to the doctor 45 in order to improve the pumping performance and black solid image followability. Also good. Here, a magnet having a magnetic force of 85 mT or more on the developing roller 41 is used. It has also been confirmed that there is no occurrence of abnormal images such as carrier adhesion by having a magnetic force of 60 mT or more. Actually, the magnetic pole contributing to development is developed on the latent image carrier by P1 which is the main magnetic force.
[0020]
In FIG. 1, a doctor blade 43 that regulates the height of the developer chain spike, that is, the amount of developer, is installed on the upstream side of the development region in the developer transport direction (counterclockwise direction). . The doctor gap, which is the distance between the doctor blade 43 and the developing sleeve, is set to 0.6 mm. Further, in the rear area of the developing roller 41, a front screw 44 that is pumped up to the developing roller 41 side while stirring the developer in the developing casing is installed. A rear screw 45 is arranged in the developing casing with a partition plate having openings in the longitudinal direction. A toner cartridge storing new toner is detachably attached to the rear end of the developing casing. The toner supplied from the toner cartridge is supplied to the rear screw 45, and is mixed and stirred with the developer while being conveyed to the back side of the drawing by the rotation of the rear screw 45. The developer mixed and stirred on the back side of the drawing is supplied to the front screw 44 from the opening of the partition plate. The developer supplied to the front screw 44 is conveyed to the front side of the drawing by the rotation of the front screw 44. At this time, the developer is supplied to the developing roller 41 by a magnetic field, and the developer on the developing roller 41 is conveyed. The remaining developer is conveyed to the near side, and is supplied to the rear screw 45 through the opening of the partition plate and circulates. The toner must be supplied when the developed developer concentration decreases, but the toner concentration sensor detects the toner concentration in the developing casing and determines that the output value of the toner concentration sensor divides the specified toner concentration value. In this case, the toner is continuously or intermittently supplied from the toner cartridge, and the toner density of the developer in the developing casing is increased to a predetermined value.
[0021]
In such an image forming apparatus, first, exposure writing is performed on the uniformly charged surface of the image carrier 1 to form an electrostatic latent image corresponding to the image. With respect to the electrostatic latent image, toner is selectively supplied from the developing roller 41 of the developing device 4 in the developing area, whereby the electrostatic latent image is developed and a visible image is obtained. Yes. The developer stored in the developing casing is agitated and charged with respect to the developing roller 41, and is then pumped up by the magnetic pole P5. The developer pumped up on the developing sleeve is conveyed to the developing area by the magnetic pole P6, and the developer is spiked in the developing area by the developing main pole P1.
[0022]
In addition, this invention is not limited to the said Example, It cannot be overemphasized that various deformation | transformation and substitution are possible if it is description in a claim.
[0023]
【The invention's effect】
As described above, the charging device of the present invention has a plurality of charge wires having different wire diameters , and the charge wires are stranded. Therefore, gases such as ozone and NOx generated from the charging device can be reduced.
[0027]
Furthermore, an image forming apparatus as another invention has the above-described charging device, so that generated gas such as ozone and NOx in the corona charger can be reduced, and maintainability and assemblability can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus having a charging device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of a charge wire of the charging device according to the present exemplary embodiment.
FIG. 3 is a characteristic diagram showing the relationship between the wire diameter of a charge wire and the amount of ozone generated.
FIG. 4 is a characteristic diagram showing the relationship between the wire diameter of a charge wire and the amount of NOx generated.
FIG. 5 is a characteristic diagram showing the relationship between the current value per unit length of the charge wire and the ozone concentration.
FIG. 6 is a characteristic diagram showing the relationship between the current value per unit length of the charge wire and the NOx concentration.
FIG. 7 is a diagram showing a simulation result.
FIG. 8 is a characteristic diagram showing the relationship between the maximum electric field strength and the discharge region when one to three charge wires are used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1; Image carrier, 2; Charging apparatus, 3; Exposure apparatus, 4; Developing apparatus, 5; Transfer apparatus,
6; Cleaning device, 7; Transfer material, 8; Fixing device,
21; charge wire, 22; grid, 23; charging bias application power source,
24, 25; connection terminal, 41; developing roller, 42, 51; power supply,
43; Doctor blade, 44; Front screw, 45; Rear screw.

Claims (2)

In the charging device for charging said image bearing member to generate ions or electrons by being disposed to face the image bearing member, for applying a voltage,
A charging device comprising a plurality of charge wires having different wire diameters, wherein the charge wires are stranded.   An image forming apparatus comprising the charging device according to claim 1.

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